No title

IJCST 9,1

10 Received September 1995 Revised and accepted May 1996

Water vapour transfer in waterproof breathable fabrics Part 1: under steady-state conditions J.E. Ruckman Department of Clothing Design and Technology, The Manchester Metropolitan University, UK Introduction The requirement to study water vapour transfer through clothing fabrics arises from the phenomenon of the human body continually losing water, mostly by evaporation from the skin[1,2]. The loss of water vapour through clothing is fundamental for heat balance of the body and for comfort. If a fabric provides too great a barrier to its passage, liquid moisture is formed by condensation of water vapour and the sensation of discomfort is increased, partly from a feeling of clamminess and partly because the wet clothing clings[3,4]. A considerable amount of work has been done on mechanisms of water vapour transfer through fibres[5-7], textile fabrics[8-12], layered fabrics[13-15], textile systems[16,17], and clothing assemblies[18-20]. However, for the most part investigations were carried out only under steady state conditions, and little work has been done with waterproof fabrics. Water vapour transfer is regarded as being a particularly important factor in the manufacture of waterproof breathable fabrics. These fabrics are used in clothing for outdoor occupations (e.g. farming and construction industries) and clothing for arduous pursuits (e.g. cycling and mountaineering). Such fabrics are also used in the offshore oil and fishing industries and uniforms for the armed services. This protective clothing is in general exposed to low temperatures, to wind, to rain, and occasionally to severe conditions of wind-driven rain.

International Journal of Clothing Science and Technology, Vol. 9 No. 1, 1997, pp. 10-22. © MCB University Press, 0955-6222

Experimental Twenty-nine waterproof breathable fabrics which are used to construct sportswear and foul weather garments were randomly chosen to be tested under various environmental conditions. The fabrics were grouped together by reference to manufacturing methods irrespective of their brand names; five polyurethane coated fabrics, six cotton ventiles, five microfibre fabrics, four PTFE-laminated fabrics, four poromeric polyurethane-laminated fabrics, and five hydrophilic-laminated fabrics. The specifications for these samples are given in Table I. To measure the water vapour transfer without a temperature gradient, a glass dish method was used at various air temperatures with various air gaps. A circular sample was placed on a dish of diameter 67mm and height 95mm

Sample fabric

Production type

A3 A33 A7 A77 A9 L1 L11 L2 L22 L3 L33 Dsa Es2 Es4 C20 C24 PL2 PL3 WJa WJb CT2 CC2 SK2 SB2 M1 P1 S1 C1 W1

Polyurethane coated Polyurethane coated Polyurethane coated Polyurethane coated Polyurethane coated Cotton ventile Cotton ventile Cotton ventile Cotton ventile Cotton ventile Cotton ventile Microfibre fabrics Microfibre fabrics Microfibre fabrics Microfibre fabrics Microfibre fabrics PTFE-laminated PTFE-laminated PTFE-laminated PTFE-laminated Poromeric polyurethane Poromeric polyurethane Poromeric polyurethane Poromeric polyurethane Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated

Weight (g/m2)

Thickness (mm)

108.7 164.8 141.6 139.2 110.0 198.4 188.4 208.0 209.5 219.6 172.5 95.4 84.5 85.5 94.0 78.1 186.0 184.8 187.1 182.0 108.8 96.0 84.1 85.5 94.2 95.8 77.8 90.0 147.0

0.08 0.11 0.10 0.11 0.10 0.15 0.15 0.13 0.13 0.15 0.12 0.06 0.05 0.06 0.06 0.07 0.20 0.20 0.16 0.18 0.08 0.07 0.05 0.06 0.07 0.08 0.12 0.12 0.10

which was filled with water to a level of 2mm below the sample fabric to simulate no or minimal air gap. To assess the effect of an air gap, various air gaps between the water surface and the sample were set accurately at 5, 10, 15, and 20mm. A sample was placed on the dish, held tightly down over the side of the dish, and fastened there by means of a copper wire band. Thick grease was also used to prevent the escape of water vapour from the side. To measure the water vapour transfer in the presence of a temperature gradient, the water-filled dishes were placed on a hot plate before fitting the fabric samples in order to condition the temperature. The hot plate used was thermostatically controlled to keep the water temperature at 33ºC (human body temperature[21]) inside the dishes. A magnetic stirrer was put in the dish in order to ensure a consistent temperature throughout the dish. Once the samples were placed on the glass dish, it was usual to allow a conditioning period of about two hours. The dish was then weighed and the test carried out for a further period of several hours, at the end of which the dish

Water vapour transfer – Part 1

11

Table I. Specifications of the samples

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12

was weighed again to determine the amount of water vapour which had evaporated through the sample. All preparations and experiments were carried out in a climatic chamber in which temperatures can be controlled from –30°C to 40°C. The loss in weight of water is used to calculate the water vapour transfer of the fabric by Fick’s equation[22] derived as follows; Q U= tA where U = water vapour transmission, Q = mass of water vapour, t = time and A = area. Results and discussion Water vapour transfer without a temperature gradient The water vapour transfer rates at an air temperature of 20ºC are plotted in Figure 1. Mean values for groups of samples classified according to the type of product were taken to plot the graphs. The range of variations within each group of samples as a percentage of the mean was between 1.68 per cent and 5.21 per cent, except for the polyurethane-coated fabrics, which demonstrated a variation of 17.5 per cent. It is apparent from Figure 1 that the rate of water vapour transfer initially falls in a roughly exponential manner for the first six hours, the fall becoming linear after that time. The rates of water vapour transfer are ranked as follows: microfibre fabrics (MF), cotton ventiles (CV), PTFE-laminated fabrics (PTFE), poromeric polyurethane-laminated fabrics (PP), hydrophiliclaminated fabrics (HP), polyurethane coated fabrics (PU). This ranking

Figure 1. Water vapour transfer for various fabrics at an air temperature of 20°C

demonstrates that water-repellent finishing on tightly woven fabrics allows the Water vapour greatest water vapour transfer followed by laminating and coating. transfer – Part 1 Water vapour may diffuse through the inter-yarn spaces, through the interfibre spaces, through the fibre substance itself, and through the free air spaces[8,9,19]. At the same time, it may also be affected by many factors such as thickness of the fabric and air permeability[10]. In analysing the results of 13 these experiments, however, it is noticeable that the waterproof breathable fabrics are ordered into groups determined by the type of product rather than being ordered according to other factors. It is therefore apparent that the type of product, which contributes to the existing diffusion theory owing to its membrane characteristics, also has an effect on the water vapour transfer rate. The water vapour transfer rates at various air temperatures are shown in Figure 2, from which several points of interest emerge. First, the water vapour transfer rate of various waterproof breathable fabrics at the air temperatures of 10ºC and 0ºC shows the same sequence as that at the air temperature of 20ºC. The difference between the rates for various fabrics becomes closer as the temperature falls, and eventually there is not much difference between water vapour transfer rates. Second, the results reveal that the water vapour transfer rates at the lower air temperatures are somewhat lower than they could be. This is presumed to be due to the vapour pressure difference between the inside of the dish and the ambient air. At 20ºC, maximum vapour pressure is 2.333kPa inside the dish[23]. The relative humidity in the ambient air when the experiments were being carried out was measured as 65 per cent RH, and hence

Figure 2. Water vapour transfer at various air temperatures

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Table II. Vapour pressure differences across the fabric under steady state conditions without a temperature gradient

actual vapour pressure in the ambient air was 1.520kPa. This results in a difference in vapour pressure across the fabric of 0.813kPa. Having compared the vapour pressure differences across the fabric at air temperatures of 10ºC and 0ºC (as given in Table II) with Figure 2, it can be seen that the water vapour transfer rates are approximately proportional to the vapour pressure difference across the fabric. This result therefore supports the view that water vapour transfer is not governed directly by air temperature but by water vapour pressure, especially vapour pressure difference. Air temperature (ºC)

Relative humidity (per cent)

Vapour pressure (kPa)

Pressure difference (kPa)

0 10 20

45 55 65

0.610 1.228 2.339

0.333 0.547 0.813

The effect of the air gap on water vapour transfer The water vapour transfer rates through the fabrics and through the air gaps at an air temperature of 20ºC are shown in Figure 3. It is immediately apparent from these results that the water vapour transfer decreases as the air gap increases. As has been identified previously by many commentators[10,11,24,25], it has long been considered that the water vapour transfer from the dish is governed by the total resistance to diffusion offered by the air layer inside the dish, the fabric covering the mouth of the dish, and a second air layer through which a water vapour pressure gradient extends some distance outward from the external face of the fabric. According to Whelan et al.[10], the rate of water vapour transfer per unit area bears a linear relationship to the vapour pressure differences and to the inverse of the total resistance. For constant vapour pressure difference, therefore, the inverse of the rate is proportional to the total resistance. When it is considered that there is no external air layer because of natural convection on the external face of the fabric, the rate is inversely proportional to the combined resistance of the air layer inside the dish and the resistance of the fabric. It would be expected, then, that if a series of tests were carried out in which the distance between the underside of the fabric and the surface of the water were varied, the inverse of the water vapour transfer rate would bear a linear relationship to this distance. However, actual experimental results revealed that there might be certain exceptions. According to Figure 3, it can be said that the results for each type of fabric lie on approximately linear lines, but the different types have different slopes. In the case of cotton ventiles (CV) and microfibre fabrics (MF), however, this linear relationship is not shown clearly between 15mm and 25mm air gaps. Even for the linear relationship between water vapour transfer and air gap in the other fabrics, the water vapour transfer rate does not decrease in a precisely linear fashion with an increase in the thickness of the air gap. As Figures 4 and 5

Water vapour transfer – Part 1

15

Figure 3. Relationship between air gap and water vapour transfer

show, the difference in water vapour transfer rate between air gaps of 5mm and 10mm differs from that between 10mm and 15mm and so on. Comparison of transfer rates for various air gaps shows that for larger air gaps the total water vapour transfer does not decrease in proportion to the extra amount of air gap; in fact, it decreases only slowly with increasing air gaps. For air gaps over

Figure 4. Effect of the size of air gap on cotton ventile

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Figure 5. Effect of the size of air gap on PTFE laminated fabrics

20mm in particular, the water vapour transfer rate does not show proportionality but becomes almost constant. This peculiarity is to be attributed to disturbance of the air gap by convection. Convection arises because of the difference between the density of the air at the top and bottom of the gap[20], and is therefore partly due to the difference in temperature and partly due to the difference in the water vapour pressure. A similar phenomenon is to be observed in the thermal insulation of an air layer and its thickness. As noted by some observers on thermal conductivity, the contribution of an air space to the total thermal resistance levels off, under ordinary conditions of experiments, at about 20-25mm[11,26]. Some other observers have found that the thermal resistance of air gaps increases at first with increasing thickness of the air gap, but for gaps greater than about 10-15mm[10,20] the thermal resistance of the gap is independent of the size of the gap. Although the effect of convection on water vapour transfer through air gaps is not as significant in these experiments as it is for thermal insulation, the results imply that there is the possibility of a significant effect if the size of air gap exceeds 15mm, as the results for cotton ventiles and microfibre fabrics have indicated. Water vapour transfer with a temperature gradient The results obtained for water vapour transfer in the presence of a temperature gradient revealed that the water vapour transfer rate in the presence of a temperature gradient is widely different from that in the absence of a temperature gradient. This is because the water vapour pressure at 33ºC is much higher than at given air temperatures for the experiments.

Considering that actual measurement of temperatures near the inner surface Water vapour of the fabric did not remain at the water temperature of 33ºC at any ambient air transfer – Part 1 temperature but varied greatly, in some cases recording 27ºC when the dish was exposed to air temperatures below 0ºC, the results were calculated as below, incorporating actual water vapour pressure differences. This is due to the fact that the vapour pressure which governs the rate of water vapour transfer is not 17 that on the human skin but that near the inner surface of the fabric Q U= tA ∆p where U = water vapour transmission, Q = mass of water vapour, t = time, A = area and ∆p = vapour pressure difference. Figure 6 shows the water vapour transfer rates of various waterproof breathable fabrics under different air temperatures. The rates are ranked; microfibre fabrics (MF), PTFE-laminated fabrics (PTFE), cotton ventiles (CV), hydrophilic-laminated fabrics (HP), poromeric polyurethane-laminated fabrics (PP), polyurethane coated fabrics (PU). This result demonstrates that the type of product has no effect on water vapour transfer in contrast to the rates obtained in absence of a temperature gradient. The plots presenting different types of coating method show a totally different figure from the expected one. If the water vapour transfer is governed only by pressure differences, the plots should show either linearity, or, as is more likely, exponentiality. A higher value at –20ºC and lower value at 20ºC should be observed resulting from the greater the pressure difference and therefore greater water vapour transfer. In fact, this

Figure 6. Water vapour transfer at various air temperatures

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Plate 1. Filmwise condensation formed on a hydrophilic laminated fabric

trend has been shown in all cases where the air temperature is above 0ºC. The unexpected changes below 0ºC imply a certain disturbance. A possible explanation for this is that condensation occurred on the inner surface of the fabric during experimentation. Condensation occurs within the fabric whenever the local vapour pressure rises to the saturation vapour pressure at the local temperature[27], and therefore occurs when it is easier for water vapour to diffuse into that part of the fabric from the skin than it is for it to diffuse away to the environment. Since diffusion is driven by the vapour pressure gradient, although the water vapour transfer rate is high, more water may diffuse in than out. This situation is almost certain to occur when the ambient air temperature is low. When the dish is placed on the hot plate for experiment, the vapour pressure at the surface of the water rises to the saturation vapour pressure at 33ºC. The vapour pressure at the inner surface of the fabric can be no more than the saturation vapour pressure at the fabric temperature, which is lower than 33ºC. A vapour pressure gradient exists, so water evaporates from the surface of the water and diffuses to the fabric where it condenses. From the observation of condensation during experiments, it was shown that polyurethane-coated fabrics and poromeric polyurethane-laminated fabrics formed thick filmwise condensation[28], and hydrophilic-laminated fabrics formed thin filmwise condensation (Plate 1) while microfibre fabrics and cotton ventiles showed mixed condensation (Plate 2) and drop-wise condensation (Plate 3) respectively. Surprisingly, PTFE-laminated fabrics formed no

Water vapour transfer – Part 1

19

Plate 2. Mixed condensation formed on a microfibre fabric

Plate 3. Dropwise condensation formed on a cotton ventile

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condensation, but just showed marginal wetness on the inner surface of the fabric. Owing to these different types of condensation, which imply different quantities of condensed water, the sequences in the rate of water vapour transfer changed slightly. PTFE-laminated fabrics show a higher rate than cotton ventiles, unlike the results shown in Figure 2. This also happened in the case of hydrophilic-laminated fabrics and poromeric polyurethane-laminated fabrics. In the case of polyurethane-coated fabrics, the water vapour transfer rate reduced dramatically compared with that obtained from the experiment without a temperature gradient. In addition to the changes of rank in the water vapour transfer rate, the gap between the plot for water vapour transfer at an air temperature of 0ºC and that at an air temperature of 20ºC was narrowed, compared with the results obtained from the experiments without temperature gradient, as a result of condensation. Conclusions A range of waterproof breathable fabrics which are used to construct sportswear and foul weather garments was selected and subjected to various experiments. The purpose of these experiments was to clarify and to investigate basic principles and mechanisms of water vapour transfer which should be considered in the design and manufacture of sportswear and foul weather garments. In the absence of a temperature gradient, the following conclusions were drawn: (1) The types of product and the characteristics of membranes have an effect on water vapour transfer at various air temperatures. The rates of water vapour transfer are ranked as follows, indicating that water-repellent finishing on tightly woven fabrics has the greatest water vapour transfer followed by laminating and coating; microfibre fabrics; cotton ventiles, PTFE-laminated fabrics; poromeric polyurethane-laminated fabrics, hydrophilic-laminated fabrics; and polyurethane-coated fabrics. (2) Water vapour transfer is not governed directly by air temperature but by water vapour pressure, especially vapour pressure difference; the greater the vapour pressure difference, the greater the water vapour transfer rate. (3) The water vapour transfer rate decreases as the air gap increases, but for air gaps greater than about 15mm this trend does not exist. In the presence of a temperature gradient, the following conclusions were found: (4) Condensation is found to be a major factor affecting water vapour transfer, especially for air temperatures below 0ºC. Condensation occurred the least on the inner surface of PTFE-laminated fabrics; followed by cotton ventiles; microfibre fabrics; hydrophilic-laminated

fabrics; and poromeric polyurethane-laminated fabrics; polyurethaneWater vapour coated fabrics. transfer – Part 1 (5) The rates of water vapour transfer in the presence of a temperature gradient are ranked differently from the rates obtained in the absence of a temperature gradient due to the greater vapour pressure differences and condensation. The fabrics were ranked as follows; microfibre fabrics, 21 PTFE-laminated fabrics, cotton ventiles, hydrophilic-laminated fabrics, poromeric polyurethane-laminated fabrics, polyurethane-coated fabrics. The above findings, although dealing only with steady state conditions in this part of the paper, suggest that careful consideration should be given when choosing appropriate waterproof breathable fabrics for manufacturing sportswear and foul weather garments. Such garments will be worn on a human body which produces a different range of temperatures according to activity and which is constantly moving, creating air gaps between inner and outer garments. The garments will be exposed to various environments, some of which could cause condensation inside the garment. The end use envisaged for the garment and the environment it will be used in, therefore, should always be taken into account. References 1. Weiner, J.S. and Edholm, O.G., “Thermal physiology”, in Edholm, O.G. and Weiner, J.S. (Eds), The Principles and Practice of Human Physiology, Academic Press, London, 1981. 2. Fanger, P.O., Thermal Comfort: Analysis and Applications in Environmental Engineering, McGraw-Hill, New York, NY, 1972. 3. Rees, W.H., “Comfort and the water vapour permeability of textiles”, WIRA Report 80, January 1970. 4. Rees, W.H., “Physical factors determining the comfort performance of textiles”, Shirly Institute 3rd Seminar: Textiles in Comfort, 1971. 5. Fourt L., Craig, R.A. and Rutherford, B., “Cotton fibres as means of transmitting water vapour”, Textile Research Journal, Vol. 27 No. 5, 1957, pp. 362-8. 6. Hong, K., Hollies, N.R.S. and Spivak, S.M., “Dynamic moisture vapor transfer through textiles: part 1: clothing hygrometry and the influence of fibre type”, Textile Research Journal, Vol. 58 No. 12, 1988, pp. 697-706. 7. Ito, H. and Muraoka, Y., “Water transport along textile fibres as measured by an electrical capacitance technique”, Textile Research Journal, Vol. 63 No. 7, 1993, pp. 414-20. 8. Weiner, L.I., “The relationship of moisture vapour transmission to the structure of textile fabrics”, Textile Chemists and Colourists, Vol. 2 No. 22, 1970, pp. 378-85. 9. Weiner L.I., “Moisture Vapour Transmission in Textile Fabrics”, Shirly Institute 3rd Seminar: Textiles in Comfort, 1971. 10. Whelan, M.E., MacHattie, L.E., Coodings, A.C. and Turl, L.H., “The diffusion of water vapour through laminae with particular reference to textile fabrics”, Textile Research Journal, Vol. 25 No. 3, 1955, pp. 197-222 11. Fourt, L. and Harris, M., “Diffusion of water vapour through textiles”, Textile Research Journal, Vol. 17 No. 5, 1947, pp. 256-63. 12. Peirce, F.T., Rees, W.H. and Ogden, L.W., “Measurement of the water vapour permeability of textile fabrics”, Journal of Textile Institute, Vol. 36, 1945, pp. T169-T176.

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13. Wang, J.H. and Yasuda, H., “Dynamic water vapor and heat transfer through layered fabrics: part 1: effect of surface modification”, Textile Research Journal, Vol. 61 No. 1, 1991, pp. 10-20. 14. Yasuda, H. and Miyama, M., “Dynamic water vapor and heat transfer through layered fabrics: part 2: effect of chemical nature of fibres”, Textile Research Journal, Vol. 62 No. 4, 1992, pp. 227-35. 15. Gibson, P.W., “Factors influencing steady-state heat and water vapour transfer measurements for clothing materials”, Textile Research Journal, Vol. 63 No. 12, 1993, pp. 749-64. 16. Woodcock, A.H., “Moisture transfer in textile systems, part 1”, Textile Research Journal, Vol. 32 No. 8, 1962, pp. 628-33. 17. Woodcock, A.H., “Moisture transfer in textile systems, part 2”, Textile Research Journal, Vol. 32 No. 9, 1962, pp. 719-23 18. Adler, M.M. and Walsh, W.K., “Mechanisms of transient moisture transport between fabrics”, Textile Research Journal, Vol. 54 No. 5, 1984. 19. Mecheels, J., “Concomitant heat and moisture transmission properties of clothing”, Shirly Institute 3rd Seminar: Textiles in Comfort, 1971. 20. Spencer-Smith, J.L., “The physical basis of clothing comfort, part 3 – water vapour transfer through dry clothing assemblies”, Clothing Research Journal, Vol. 5 No. 3, 1977, pp. 82-100. 21. Hardy, J.D., “Heat Transfer”, in Newburgh L.H. (Ed.), Physiology of Heat Regulation and the Science of Clothing, Hafner, London, 1968. 22. Crank, J., The Mathematics of Diffusion, Clarendon Press, Oxford, 1975. 23. Handbook of Chemistry and Physics, 68th edition, CRC Press, Cleveland, OH, 1980. 24. Water Vapour Transmission of Materials in Sheet Form, ASTM E96-66, 1981. 25. Method of Test for Resistance of Materials to Water Vapour Diffusion, Canadian Standard; CAN 2-4, 2-M77, Method 49, 1977. 26. Ea, J.Y. and Song, T.O., “A study on the thermal insulation value of air layers between fabrics”, J. Korean Society of Tex. Eng. and Chem., Vol. 8 No. 2, 1981, pp. 21-8. 27. Collier, J.G., Convective Boiling and Condensation, McGraw-Hill, New York, NY, 1972. 28. Jerger, E.W. and Coonan, F.L., “An experimental study of the effect of surface condensation on the performance of compact heat exchangers”, in Wexler, A. (Ed.), Humidity and Moisture: Measurement and Control in Science and Industries: Vol. 2, Reinhold, New York, NY, 1965.

Water vapour transfer in waterproof breathable fabrics Part 2: under windy conditions J.E. Ruckman Department of Clothing Design and Technology, The Manchester Metropolitan University, UK

Water vapour transfer – Part 2

23 Received September 1995 Revised May 1996

Introduction It is clear from Part 1 of this paper that the water vapour transfer rate from the internal side of a fabric to the external environment is directly proportional to the vapour pressure difference between the inner surface of the fabric and the ambient air. This observation was also made in many previous studies[1-4]. This relationship, however, may not be strictly true when forced convection takes place at the outer surface of the fabric. Heat transfer by forced convection occurs when the fluid motion is artificially induced with a pump or a fan which forces the fluid to flow over the surface. Water vapour transfer from the outer surface of the clothing fabric to the surrounding atmosphere in forced convection behaves in precisely the same way as convective heat transfer in these conditions[5-7]. In real life conditions, forced convection occurs when air movement develops either laminar or turbulent boundary layers over a surface. Laminar layers cause continuous stream-line wind and turbulent boundary layers cause a superimposed turbulent wind which tends to break down into a series of eddies[8]. Under these windy conditions, there is not only diffusion of water vapour through the fabrics, but also mass movement of air through and over them, which evacuates the water vapour. Therefore, it is necessary to observe water vapour transfer under windy conditions, as most sportswear and foul weather garments made of waterproof breathable fabrics will be exposed to wind and various severe environmental conditions. Theoretical solution of forced convection The effect of wind speed on water vapour transfer rate has been studied by many[9,10], some using air tunnels which create stream-line wind[11-13]. These studies have concentrated on stream-line wind because it penetrates the fabric more easily than turbulent air at the same speed. Stream-line wind rarely occurs in nature, however, and hence the laboratory technique tends to exaggerate the water vapour transfer rate. Clark and Edholm[14] have observed that the turbulent air movement created by helicopter rotors causes extremely high rates of body heat loss. However, both stream-line wind or 25m/s strong turbulent wind occur very rarely in real life situations, and therefore it is more useful to analyse water vapour transfer by forced convection using a more realistic range

International Journal of Clothing Science and Technology, Vol. 9 No. 1, 1997, pp. 23-33. © MCB University Press, 0955-6222

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of air velocities. The following theoretical consideration, therefore, is presented on the basis of typical weather conditions, randomly chosen within the UK, with an average monthly wind velocity ranging from 2 m/s to 7 m/s[15]. Water vapour transfer from the surface of the human skin to the external environment under windy conditions is governed by three parts in clothing assembly. These are the air gap between the surface of the skin and inner side of the fabric, the structure of the fabric, and the existence of a boundary layer caused by forced convection. Although some[3,4] have tried to analyse the water vapour transfer through these three parts of the clothing assembly, because of the complexity of the structure of these parts and the difficulty in separating them to consider each part’s effects in isolation, there still is no well developed theoretical model in existence. To determine the effect on water vapour transfer of various waterproof breathable fabrics under windy conditions it is therefore necessary to make two assumptions as follows: (1) The theoretical calculation of the convective heat transfer assumes that the human skin is in contact with the external environment with no clothing in place[6,16,17]. (2) The experimental results quantify the rate of water vapour transfer from the human skin (simulated by the surface of water at a constant temperature of 33ºC[17] within a dish) to the external environment through an air gap and a fabric. The 2mm air gap between the surface of the water and the inner surface of the fabric is the maximum air gap recognized by researchers as being negligible[3,4,18]. The calculation of a rate of heat loss by convection requires the estimation of Nusselt number, Nu, which expresses the ratio of the actual heat transfer coefficient for convection. The forced convection Nusselt number is given by[16]: Nu = C Rem Prn (1) where C = constant which depends on the smoothness of the surface; Re = Reynolds number; = vd/µ (v: air velocity, d: length of surface, µ: dynamic viscosity); Pr = Prandtl number; = µCp/k (Cp: specific heat, k: thermal conductivity); m and n = constants which depend on the degree of turbulence. According to Monteith[7] and Clark and Edholm[19], the Nusselt number is defined as follows in the case of real life in which the boundary layer is usually turbulent: Nu = 0.026 Re0.81 Pr0.33. (2) All properties used for calculation are given in Table I. These are for the relevant air temperatures which were maintained during the experiments for the present work. The calculated Prandtl numbers are also given in the same

Table because they can be regarded as a property of air which varies according Water vapour to the air temperatures. The calculated Reynolds number and Nusselt number transfer – Part 2 for various wind speeds at various air temperatures are also given in Table II. Having obtained relevant numbers, convective heat loss can be calculated as follows[6,7,19]; Hc = Nu k (Ts – Ta)/d (3) 25 where Ts = skin temperature; Ta = air temperature. Air temperature ρ (ºC) (kg/m3) 0 10 20 Source:[8,22]

1,276 1,270 1,264

Air temperature (ºC) Re 0 10 20

400.43 387.13 372.52

µ (kg/m s)

Cp (KJ/kgK)

k (W/mK)

Pr

5.619 × 10-4 5.812 × 10-4 6.040 × 10-4

2.261 2.320 2.387

0.282 0.284 0.286

4.505 × 10-3 4.748 × 10-3 5.041 × 10-3

2.5 m/s

5.0 m/s

Table I. Properties of air

10.0 m/s

Nu

Re

Nu

Re

Nu

0.561 0.555 0.549

800.85 774.26 745.03

0.983 0.973 0.962

1,601.71 1,548.52 1,490.06

1.724 1.706 1.687

It is obvious from the equation that the convective heat loss is proportional to the Nusselt number when the given environmental conditions are the same. Therefore, assuming water vapour transfer by forced convection behaves in precisely the same way as convective heat transfer, it can be concluded that water vapour transfer is also proportional to Re0.81 number. This is because the Prandtl number is a property of air and hence the Nusselt number is proportional to Re0.81 according to equation (2). Calculated values for Hc based on the theoretical solution are shown in Figure 1, implying a linear relationship between water vapour transfer rate and Re0.81. Experimental Twenty-four waterproof breathable fabrics which are used to construct sportswear and foul weather garments were randomly chosen to be tested under various environmental conditions. The fabrics were grouped together by reference to manufacturing methods irrespective of their brand names; six cotton ventiles, five microfibre fabrics, four PTFE-laminated fabrics, four poromeric polyurethane-laminated fabrics, and five hydrophilic-laminated fabrics. The specifications for these samples are given in Table III.

Table II. Calculated values of Reynolds numbers and Nusselt numbers for various wind speeds

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Figure 1. Water vapour transfer due to forced convention

To measure water vapour transfer under windy conditions, a glass dish on a hot plate and a fan providing various wind speeds from 0m/s to 10.0m/s were used in various air temperatures. The fan used was 480mm in diameter, spinning at a maximum of 1,440 revolutions per minute. The hot plate used was thermostatically controlled to keep the water temperature inside the dish at 33ºC (human body temperature[17]). A magnetic stirrer was put in the dish to ensure a consistent temperature throughout the water in the dish. A circular sample was placed on a dish of diameter 90mm and height 200mm which was filled with water at 33ºC to a level of 2mm below the sample fabric to simulate no or minimal air gap. The sample was then held tightly down over the sides of the dish, and fastened there by means of a copper wire band and a rubber band. Thick grease was also used to prevent the escape of the water vapour from the side. Experiments were carried out in the relatively still air of the climatic chamber and in front of the fan with the air passing in a direction parallel to the surface of the fabric. The air from the fan was blown through a grid of wire mesh to equalize the flow and minimize turbulence. The desired speeds of 2.5m/s, 5.0m/s and 10.0m/s were achieved using the speed controller and altering the distance between the fan and the experimental area. The air velocity was monitored constantly by a thermistor-type hot wire anemometer. It was important to observe the condensation which might have formed on the inner surface of the sample fabric, and to measure the temperature near the inner surface of the fabric to determine the vapour pressure difference for calculation. Both

Sample fabric

Production type

L1 L11 L2 L22 L3 L33 Dsa Es2 Es4 C20 C24 PL2 PL3 WJa WJb CT2 CC2 SK2 SB2 M1 P1 S1 C1 W1

Cotton ventile Cotton ventile Cotton ventile Cotton ventile Cotton ventile Cotton ventile Microfibre fabrics Microfibre fabrics Microfibre fabrics Microfibre fabrics Microfibre fabrics PTFE laminated PTFE laminated PTFE laminated PTFE laminated Poromeric polyurethane Poromeric polyurethane Poromeric polyurethane Poromeric polyurethane Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated

Weight (g/m2)

Thickness (mm)

198.4 188.4 208.0 209.5 219.6 172.5 95.4 84.5 85.5 94.0 78.1 186.0 184.8 187.1 182.0 108.8 96.0 84.1 85.5 94.2 95.8 77.8 90.0 147.0

0.15 0.15 0.13 0.13 0.15 0.12 0.06 0.05 0.06 0.06 0.07 0.20 0.20 0.16 0.18 0.08 0.07 0.05 0.06 0.07 0.08 0.12 0.12 0.10

observation and measurement were made after weighing 24 hours later. The loss in weight of water was used to calculate the water vapour transfer of the fabric using Fick’s equation[20] as follows: Q U= tA ∆p where U = water vapour transmission, Q = mass of water vapour, t = time, A = area and ∆p = vapour pressure difference. Experimental results and discussion Several points of interest emerge from a comparison of the results shown in Figures 2, 3 and 4, which were plotted for various air temperatures. First, water vapour transfer increases as air temperature falls, regardless of the wind speed. This phenomenon has already been shown by the experiment under steady state conditions in Part 1 of this paper, and it is obvious that the greater the vapour pressure difference across the fabric, the greater the water vapour transfer. Second, the water vapour transfer rate increases as the wind speed increases. Since the air is in motion above the sample fabric all the time, air pressure above the fabric is reduced. This reduces the vapour pressure above the fabric and

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27

Table III. Specifications of samples

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Figure 2. Effect of wind velocity on water vapour transfer at an air temperature of 20ºC

hence increases the difference in vapour pressure between the air above and below the fabric, increasing water vapour transfer. Third, the sequence of the rates of water vapour transfer is shown to be microfibre fabrics (MF), cotton ventiles (CV), PTFE-laminated fabrics (PTFE), hydrophilic-laminated fabrics (HP) and poromeric polyurethane-laminated fabrics (PP) from highest to lowest values at over 2.5m/s of wind speed. The range

Figure 3. Effect of wind velocity on water vapour transfer at an air temperature of 10ºC

Water vapour transfer – Part 2

29

Figure 4. Effect of wind velocity on water vapour transfer at an air temperature of 0ºC

of variations within each group of samples as a percentage of the mean was not more than 3.5 per cent. The sequence is slightly changed from that under steady state conditions which was ranked; MF > PTFE > CV > HP > PP. This change can be explained by condensation. As shown in Table IV, it was observed that microfibre fabrics and cotton ventiles formed condensation when the wind speed was 0m/s whereas such condensation was not evident under windy conditions. Therefore, the water vapour transfer rate of cotton ventiles at 0m/s of wind speed inevitably fell, and resulted in a value less than that for PTFE-laminated fabrics. Comparison of theoretical solution and experimental results From the theoretical solution, it was suggested that water vapour transfer and Re0.81 have a linear relationship, and hence water vapour transfer is proportional

0ºC Fabric 0.0 samples (m/s)

2.5

5.0

10.0

Air temperature 10ºC 0.0 2.5 5.0 10.0

0.0

20ºC 2.5 5.0

10.0

CV O X X X O X X X O X X X MF O X X X O X X X O X X X PTFE W W X X X X X X X X X X PP O O O O O O O O O O O X HP W W W W W W W W W W W W Key: CV: cotton ventiles; MF: microfibre fabrics; PTFE: PTFE-laminated fabrics; PP: polyurethane-laminated fabrics; HP: hydrophilic-laminated fabrics; O: Condensation formed; W: Slightly wet; X: Condensation did not form; m/s: metres per second (wind speed)

Table IV. Condensation observed after 24 hours

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to V0.81, since this is the form in which wind speed is expressed in the Reynolds number for forced convection. Figure 5 illustrates the comparison between the theoretical solution and experimental results for water vapour transfer under windy conditions by showing the results of the corresponding theoretical calculation together with the experimental results. Although the plot according to the theoretical calculation shows linearity, the typical experimental results of the water vapour transfer rate for PTFE-laminated fabrics at various air temperatures do not show a linear relationship with V0.81. When the experimental results are plotted against V0.5, as shown in Figure 6, it can be seen that water vapour transfer is proportional to V0.5. Thus, by inserting a layer of waterproof breathable fabric between the surface of the water (simulating human skin) and the external windy environment, the rate of water vapour transfer decreases such that it is proportional to V0.5 and not V0.81.

Figure 5. Comparison of plots for predicted results and for PTFE-laminated fabrics

Waterproof breathable fabrics in general have relatively low permeability among fabrics used to construct outdoor garments. It is evident, therefore, that for the relatively permeable fabrics the water vapour transfer rate is proportional to V x, where x is between 0.5 and 0.81. Fan and Keighley[21] observed a similar phenomenon with respect to convective heat transfer. It is also apparent from a comparison of the exponential slopes of V0.81 and V0.5 that the greater the wind speed the greater the difference between water vapour transfer with no fabric and with fabric in place. Having compared the test results with forced convection theory, and bearing in mind that the contribution of waterproof breathable fabrics to water vapour transfer is even more significant in high winds, the same procedure was followed for a comparison between free convection theory and the experimental results, using the equation derived by Monteith[7] as follows:

Nu = 0.63 (Gr × Pr)0.25 (4) Water vapour transfer – Part 2 where Gr = Grashof number = d3 ρ2 g (Ps – Pa)µ2 (d: length of surface, ρ : density of air, g: gravity, Ps: vapour pressure at skin, Pa: vapour pressure in air) 31 Pr = Prandtl number In air, for Pr = 0.71[8,22], the above equation simplifies to (5) Nu = 0.58 Gr0.25.

Figure 6. Comparison of adjusted slopes for predicted results and for PTFElaminated fabrics

From Figure 7, in which the corresponding values of water vapour transfer are plotted against the calculated Grashof number, it is obvious that the water vapour transfer rate increases as the Grashof number increases. This indicates that the water vapour transfer rate increases as air temperature decreases. This result therefore supports the findings of Part 1 of this paper that the water vapour transfer rate at various air temperatures is somewhat lower than expected, as it is vapour pressure difference which governs the water vapour transfer rate and not air temperature. Conclusions A range of waterproof breathable fabrics which are used to construct sportswear and foul weather garments was selected and subjected to various experiments. The purpose of these experiments was to investigate the basic principles and mechanisms of water vapour transfer under windy conditions which should be considered in the design and manufacture of sportswear and foul weather

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Figure 7. Water vapour transfer due to free convection

garments. Together with the empirical results, a theoretical solution of forced convection was considered, and the following conclusions were drawn: (1) The water vapour transfer rate increases as air temperature falls regardless of the wind speed. (2) The greater the wind speed, and hence the greater the difference in vapour pressure across the fabric, the greater the water vapour transfer. (3) The rates of water vapour transfer are ranked under windy conditions as follows, demonstrating that the fabrics exhibiting condensation allow the least water vapour transfer; microfibre fabrics, cotton ventiles, PTFE-laminated fabrics, hydrophilic-laminated fabrics, and poromeric polyurethane-laminated fabrics. (4) The theoretical model of forced convection between the human skin and the external environment is found to be proportional to V 0.81. The experimental results of water vapour transfer which include a layer of fabric is proportional to V 0.5 . This suggests that as wind velocity increases the effect of a layer of fabric on water vapour transfer increases in significance. The above findings suggest that careful consideration should be given to suitability for intended end use when selecting waterproof breathable fabrics for the manufacture of sportswear and foul weather garments, especially garments to be used under windy conditions. In particular it should be taken into account that different types of product behave differently under windy

conditions in terms of the formation of condensation. Further research is Water vapour recommended into the effect of the direction of wind relative to the surface of the transfer – Part 2 fabric on water vapour transfer including more severe wind conditions than the average UK wind velocity of 2-10m/s. References 1. Weiner, L.I., “The relationship of moisture vapour transmission to the structure of textile fabrics”, Textile Chemists and Colourists, Vol. 2 No. 22, 1970, pp. 378-85. 2. Weiner, L.I., “Moisture vapour transmission in textile fabrics”, Shirly Institute 3rd Seminar: Textiles in Comfort, 1971. 3. Whelan, M.E., MacHattie, L.E., Coodings, A.C. and Turl, L.H., “The diffusion of water vapour through laminate with particular reference to textile fabrics”, Textile Research Journal, Vol. 25 No. 3, 1955, pp. 197-222. 4. Fourt, L. and Harris, M., “Diffusion of water vapour through textiles”, Textile Research Journal, Vol. 17 No. 5, 1947, pp. 256-63. 5.. Eckert, E.R.G. and Drake, R.M. Jr, Analysis of Heat and Mass Transfer, McGraw-Hill, New York, NY, 1972. 6. Mitchell, D., “Convective heat transfer from man and other animals”, in Monteith, J.L. and Mount, L.E. (Eds), Heat Loss from Animals and Man, Butterworth, London, 1974. 7. Monteith, J.L., Principles of Environmental Physics, Edward Arnold, London, 1973. 8. Schlichting, H., Boundary-Layer Theory, Pergamon Press, London, 1968. 9. Lamb, G., “Heat and water vapour transport in fabrics under ventilated conditions”, Textile Research Journal, Vol. 62 No. 7, 1992, pp. 387-92. 10. Kim, J.O. and Spivak, S.M., “Dynamic moisture vapor transfer: part 2: further techniques for microclimate moisture and temperature measurement”, Textile Research Journal, Vol. 64 No. 2, 1994, pp. 112-21. 11. Cena, K. and Clark, J.A., “Transfer of heat through animal coats and clothing”, in Robertshaw D. (Ed.), Environmental Physiology III, University Park Press, Baltimore, 1979. 12. Spencer-Smith, J.L., “The physical basis of clothing comfort, part 3 – water vapour transfer through dry clothing assemblies”, Clothing Research Journal, Vol. 5 No. 3, 1977, pp. 82-100. 13. Peirce, F.T, Rees, W.H. and Ogden, L.W., “Measurement of the water vapour permeability of textile fabrics”, Journal of Textile Institute, Vol. 36, 1945, pp. T169-T176. 14. Clark, R.P. and Edholm, O.G., Man and his Thermal Environment, Edward Arnold, London, 1985. 15. Monthly Weather Report, The Meteorological Office, 1981-1990. 16. Bird, R.B., Transport Phenomena, Wiley, New York, NY, 1960. 17. Hardy, J.D., “Heat transfer”, in Newburgh L.H. (Ed.), Physiology of Heat Regulation and the Science of Clothing, Hafner, New York, NY, 1968. 18. Ea, J.Y. and Song, T.O., “A study on the thermal insulation value of air layers between fabrics”, Journal of Korean Society of Textile Engineers and Chemists, Vol. 18 No. 2, 1981, pp. 21-8. 19. Clark J.A., Owen, J.M. and Turner, A.B., “The physics of the microclimate”, in Cena, K. and Clark, J.A. (Eds), Bioengineering Thermal Physiology and Comfort, Elsevier Scientific, Oxford, 1981. 20. Crank, J., The Mathematics of Diffusion, Clarendon Press, Oxford, 1975. 21. Fan, J. and Keighley, J.H., “A theoretical and experimental study of the thermal insulation of clothing in windy conditions”, International Journal of Clothing Science and Technology, Vol. 1 No. 1, 1989, pp. 21-9. 22. Baylay, F.J. et al., Heat Transfer, Nelson, London, 1972.

33

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34 Received May 1996 Revised August 1996

Modelling job complexity in garment manufacture by inductive learning Patrick C.L. Hui Institute of Textiles and Clothing, The Hong Kong Polytechnic University

K.C.K. Chan Department of Computing, The Hong Kong Polytechnic University, and

K.W. Yeung Institute of Textiles and Clothing, The Hong Kong Polytechnic University

International Journal of Clothing Science and Technology, Vol. 9 No. 1, 1997, pp. 34-44. © MCB University Press, 0955-6222

Introduction and background In the past, a large number of garment manufacturing models[1-5] have been developed to model garment production behaviour for improving productivity, reducing costs and improving quality. These models range from full deterministic to full stochastic models. Representation of uncertainty in these models is often necessary because, in the garment industry, uncertainty arises not only in the marketplace but also during the production cycle. It is especially true when predicting the complexity of production orders. The complexity of production orders, when properly measured, can reflect the degree of difficulty in handling an order. Knowing how difficult it is to handle an order allows us to predict accurately the requirement for resources (such as operators, equipment and materials) and to prepare for an effective order scheduling. Under normal circumstances, an order could be divided into three main operations – cutting, assembling, and finishing (Figure 1). Within each operation, a series of jobs such as cuff making, placket making and sleeve making could be determined by customer requirements. When a complicated production job is encountered, the apparel manufacturer should plan to allocate the appropriate resources very carefully prior to carrying out real production in order to be able to deliver on time, minimize cost and achieve good quality. A field expert is normally required to produce the capacity plan based on his or her experience and expertise. The capacity plan includes a production schedule, manpower allocation, machinery utilization and materials requirements. If the degree of complexity of a production job is high, it will put a lot of effort on some operations during the production. For instance, the fashioned style men’s shirts may require a lot of effort on colour/pattern matching during assembling resulting in it becoming the bottleneck for the production job.

Therefore, it is important that a garment manufacturer be able to estimate the complexity of a production job at an early stage of the production cycle since such knowledge often leads to the discovery of the production bottleneck. The sooner such a discovery is made before production, the better one can plan accordingly so as to reduce the manufacturing cost and increase productivity. Appropriate methodology for modelling job complexity in garment manufacture is, therefore, required to meet the need for quick response in the local market.

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Figure 1. Input/process/output model of garment manufacturing

Despite its importance, there is no formal methodology, neither mathematical nor statistical, for the modelling and prediction of the complexity of various jobs in a typical garment factory. The measurement of the complexity of a job is often subjectively estimated. The experience of garment individuals is normally relied on for such a task. For consistency and reliability, the expertise of these individuals can be captured in an expert system. However, while this could provide a solution to the job-complexity-estimation problem, the construction of these expert systems is rather difficult and time-consuming. Very often, system analysts are required to conduct interviews with domain experts to extract relevant knowledge from them. Other than communication problems, knowledge engineers may find domain experts unable to describe how they can do what they do when it comes to judgement, experience and intuition. Not being experts themselves, system analysts may have difficulties in interpreting and integrating experts’ answers. To overcome the problems associated with the knowledge acquisition process, Chan and Wong[6] suggested the use of a technique called automatic pattern analysis and classification system (APACS) that is implemented by the inductive learning algorithm. The technique is able to uncover the hidden knowledge in a set of data automatically to construct the knowledge base of expert systems. It is able to do so even when the data contain erroneous, missing and redundant values.

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In this paper, we describe how the APACS technique can be used automatically to generate an expert system. For performance evaluation, we used a set of real data. We compared the accuracy of the resulting system with that achieved by human experts. The data we used involve six factors of garment production: operation type, bundle size and type, standard allowable minutes for a particular style being produced, machinery type, and degree of labour skills required for manufacturing. In the next section, the problem definitions in garment production planning are addressed; in the third section, modelling of garment production systems especially in job complexity. In the fourth section, the inductive-learning technique used in our test is discussed. Following this discussion, the experimental design is established and the results are compared with real data. The recommendations and conclusions of this study are drawn in the last section. Problems associated with job complexity and production planners in apparel manufacturing Chuter[7] indicated that there are key factors in scheduling and controlling garment production: • Throughput time per unit: standard allowable minutes (SAM) for style being produced in each operation. • Work in process delays: this is used to buffer in a number of processes against fluctuations in output. However, it will cause an extension in throughput time. • Critical paths: some processes may be arranged either in parallel or in serial. This will affect the time taken for the whole production. • Bottleneck operations: this is essential to identify the processes for which limited capacity restricts output. • Plant utilization: this estimates the available time in the plant to be used effectively. • Minimum order size: this relates to the expected contribution per unit of the order. • Effects of changeover: this estimates the expected loss of output and materials when one style or type of product is replaced by another. • Waste percentage: this predicts the cloth utilization in cutting, the loss of produced garments in rejects, and cloth in recuts. In order to schedule works more properly, Chuter[7] commented that the most critical factors are bottleneck operation, critical path, effect of changeover and plant utilization. These items are related to the complexity of order in apparel manufacturing. Although some sources[8-11] have made progress in the modelling of garment manufacture in the area of sewing-machine setting, seam pucking and production management, there is no appropriate model in order

complexity. An order can be divided into some jobs that perform a particular task such as cutting, assembling, and finishing for producing a particular style of garment. Job complexity is one basic element for production management in apparel manufacture which assists the production planner in identifying a bottleneck operation, critical production process path and effect of changeover. However, the term job complexity has many definitions which are still subjective. Currently, there is no appropriate methodology to model the degree of job complexity in garment production. It only relies on the experience of garment experts to identify the degree of job complexity for each order. In the real situation, there is no good planning system to prevent the operational problems occurring in garment manufacture, such as the bottleneck operation. Therefore, an appropriate solution is needed to tackle the above problems. Modelling of job complexity in clothing production systems Through the literature reviews[2,8-11], in relation to the modelling of job complexity, it is clear that there is no model for job complexity estimation. In modelling the job complexity in garment production, the criteria for measurement of job complexity should be identified first. After studying in a men’s shirt factory under bundle progressive method as well as the advice of field experts, the model of measuring job complexity is established as illustrated in Figure 2, and the criteria used are listed as follows: • Is the bundle required a special operational skill such as matching a pattern and bundle number prior to assembling together? (It is measured by the attribute of operation number – X1) • Is the bundle size smaller than eight pieces for fashioned style or smaller than 15 pieces for non-fashioned style? (It is measured by the attribute of bundle size – X2) • Is the ratio of standard allowable minutes (SAM) for style being produced to SAM for basic style produced for the operation greater than 1.5? (It is measured by the attribute of SAM for the style being produced – X3 and the attribute of standard allowable minutes for the basic style produced – X4) • Is the bundle running on the special machine only? (It is measured by the attribute of operation number – X1) • Is the bundle performed by fully skilled labour? (It is measured by the attribute of worker number with standard allowable minutes percentage – X 5) • Is the type of bundle off-standard? (It is measured by the attribute of bundle type – X6) The above-mentioned criteria are used to classify each individual bundle as either “good” or “bad”. The classification of bundle is used to measure the degree of job complexity for a production order. If the production job cannot

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Figure 2. Model of measuring job complexity in garment manufacture

meet one of these criteria, the job is classified as “bad”. Otherwise, it is classified as “good”. The total numbers of “good” and “bad” bundles are counted respectively. If the portion of “bad” bundles in entire order is higher than the management’s expectation, it means that the production planner should pay more attention to a particular area such as bundle size, machinery, and labour in the capacity planning. Development of a model in job complexity is worthwhile for garment production planning.

Methodologies To solve the classification problem of each individual bundle that is encountered by the apparel manufacturer, a three-phase inductive learning algorithm developed by Chan and Wong[6] is proposed: the detection of underlying patterns in a database of preclassified records; the construction of classification rules based on the detected patterns; the use of these rules to predict the class membership of an object not originally in the database. (1) Detecting underlying patterns in a database of preclassified records A set of effective classification rules should be constructed based only on the hidden patterns underlying the noisy data in a given database of preclassified records. These patterns may be revealed by identifying attributes that provide relevant information for the classification task. The identification of such attributes could be very easy if the learning environment is deterministic, but much more difficult if the environment is probabilistic. In the presence of uncertainty, many systems consider an attribute as useful for classification if it is statistically dependent on the classes according to the chi-square test[12-19]. As illustrated by Chan and Wong[6], they constructed a twodimensional contingency table (Table I) with P rows and K columns, P being the total number of classes and K the total number of different values that Attrj can take on. Let Opk be the total number of objects in Cp characterized by Vjk and epk be the total number of objects expected to have the characteristic Vjk. Then, epk = ( ∑ o∏ ∑oik / M)

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(1)

where M = ∑ opk and, owing to the possibility of having missing values in the data, M ≤ N.

Attrj Vjk

Class

Vj1

C1

O11 .......................... O1k ............................ O1K (e11) ......................... (e1k) ............................ (e1K)

O1+

Op1.......................... Opk ............................ OpK (ep1) ......................... (epk) ............................ (epK)

Op+

OP1 ......................... OPk ............................ OPK (eP1) ........................ (ePk)............................ (ePK)

OP+

O+1......................... O+k ........................... O+K

M

. . Cp . . CP Totals

VjK

Totals

Table I. A two-dimensional contingency table with P rows and K columns

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A chi-square statistic can be defined as X 2 = ∑ ∑ (opk – epk)2 / epk = ∑ ∑ (o2pk / epk ) – M. (2) 2 According to the chi-square test, if X d,∝ is greater than the critical value X 2 d,∝ where d = (P–1)(K–1) is the degree of freedom and ∝ is the confidence level, then Attrj is statistically dependent on the classes and is therefore relevant in determining the class membership of the objects. If, however, X2 ≤ χ2d,∝, then there is not enough evidence to support such a conclusion. Chan and Wong[6] proposed using the adjusted difference to find relevant feature for Cp instead of using the chi-square test. An adjusted difference is defined as dpk = zpk / Vpk1/2 (3) where Vpk is the maximum likelihood estimate of the variance of zpk and is given by Vpk = (1 – op+/M) (1 – o+k/M) (4) where op+ is the total number of objects in the data set that are in Cp; and o+k is the total number of training objects that have the characteristic Vjk [20]. A dpk > +1.96 indicates that the presence of Vjk is a relevant feature for Cp. In other words, given that an object is characterized by Vjk, it is more likely for it to be a member of Cp than other classes. If dpk ≤ –1.96, it indicates that the absence of Vjk is a relevant feature for Cp. Values of Attrj show no correlation with any class and yield no information on how an object should be classified. Such values are irrelevant for the learning process. Their presence may cause overfitting[21] and the generation of misleading classification rules, and hence they are discarded from further analysis. In garment manufacture, the vector of relative features (C b ) for classification of the bundle either in “good” or “bad” is formulated as follows: Cb = {X1, X2, X3, X4, X5, X6} Notation of each feature (X1, …, X6) is described in the previous section. (2) Rule generation based on detected pattern To ensure that the relevant features for each class are used in the construction of classification rules, they are explicitly represented by rules of the following form: If then with weight of evidence W = log[Pr(vjk | Class = cp) / Pr(vjk | Class ≠ cp)] where the condition part specifies the attribute values that an object should possess if it is to belong to the class predicted by the conclusion part. W is the weight of evidence associated with the rules.

As an illustration, suppose that X1 is a relevant feature for Cb. An object characterized by X1 is, therefore, more likely to belong to Cb than to other classes. This information can be represented in the form of a rule: If value of attribute X1 of an object is Ai , (and/or value of attribute X2 of an object is Aj, … ,and/or value of attribute Xn of an object is An) then that an object belongs to Cb is with weight of evidence W where W measures the amount of positive or negative evidence that is provided by X1 supporting or refuting an object that it characterizes to be classified into Cb. (3) Prediction of class membership Given a set of classification rules, an object may be classified by matching its description against each rule in turn. In the case of a perfect environment, the object may simply be assigned to the class predicted by the conclusion part of a rule if its attribute values satisfy the condition part exactly. In an uncertain environment, the object description is often found only partially to match that of a class description. Suppose that a given object (Oj) is being classified. An object (Oj) is described by n characteristics (val1, val2, val3, …, valn). To seek those classes whose descriptions are partially matched by that of Oj, a full set of classification rules (constructed by step 2) is searched through to see which of them are matched. If an attribute value, say valn of Oj, satisfies the condition part of a rule which predicts, we can conclude that the description of Oj matches partially that of Coj. To decide which specific class an object Oj should be classified into when its description matches that of more than one class, it must be noted that each of the attribute values of O j that matches the classification rules can be considered as providing some evidence for or against the assignment of Oj to those classes predicted by the rules. For this reason, the decision regarding to which class Oj should be assigned can be made based on the various pieces of evidence provided by the attribute values. It means that, among all the possible classes, Oj is assigned to the class with the maximum weight as the classification result. It is necessary to estimate and combine quantitatively this evidence. It should have the property that its value increases with the number and the strength of the positive evidence supporting a specific class assignment and decreases with the number and the strength of the negative evidence refuting such an assignment. Results and discussion To illustrate how the induced rules can be employed for the classification task, let us suppose that the data used in our experiment are concerned with the operation transaction records collected from an apparel-manufacturing factory. Each transaction record consists of the following attributes and its nature: Worker(0) – Worker number, discrete nature into five digits intervals;

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Group(1) – Group number, discrete nature in 11 possible values; OPN(2) – Operation number, discrete nature in 68 possible values; Bundle(3) – Bundle number, discrete nature into six digits intervals; Type(4) – Type of bundle, discrete nature in two possible values; Qty(5) – Quantity of bundle, continuous nature into five digits intervals; Job(6) – Job number, discrete nature in two possible values; SAM(7) – Standard allowable minutes for the operation, continuous nature into five digits intervals; Good_Bad(8) – Classification status, discrete nature in three possible values. By the experts’ experience and their judgement, each record may belong to the class of (1) good; (2) bad; and (3) unknown that indicates the Good_Bad field. A training set of data consisting of 566 records is randomly selected for learning and the rest of the data (834 records) were used for testing the algorithm. The rules for classification are induced from the following initial conditions: (1) If value of Qty(5) lies between 1.00 and 7.00, value of Worker(0) lies between 1.00 and 21.00, and value of SAM(7) lies between 37.26 and 64.15, the record is classified as Bad with weight = 0.5. (2) If value of OPN(2) is 52.00, value of Bundle(3) lies between 1.00 and 90.00, and value of Type(4) is 1.00, the record is classified as Bad with weight = 0.5. (3) If value of Bundle(3) lies between 168.00 and 294.00, value of Group(1) is 2.00, and value of SAM(7) lies between 37.26 and 64.15, the record is classified as Bad with weight = 0.5. (4) If value of Group(1) is 4.0, value of SAM(7) lies between 23.31 and 37.26, and value of Bundle(3) lies between 168.00 and 294.00, the record is classified as Good with weight = 0.5. (5) If value of Type(4) is 1.0, value of OPN(2) is 27.00, and value of Qty(5) lies between 23.00 and 78.00, the record is classified as Good, with weight = 0.5. (6) If value of Bundle(3) lies between 294.00 and 439.00, value of Type(4) is 2.00, and value of Worker(0) lies between 21.00 and 39.00, the record is classified as Unknown with weight = 0.5. (7) If value of OPN(2) is 40.00, value of Bundle(3) lies between 90.00 and 168.00, and value of Type(4) is 1.00, the record is classified as Bad with weight = 0.5. (8) If value of OPN(2) is 53.00, value of Type(4) is 1.00, and value of Qty(5) lies between 7.00 and 15.00, the record is classified as Good with weight = 0.5. After several instances of rules induction learned from training data, the above initial rules with weight are changed. For instance, (1) If value of Type(4) is 1.00, and value of Qty(5) lies between 7.00 and 15.00, the record is classified as Bad with weight = –0.45. (2) If value of Type(4) is 1.00, and value of Worker(0) lies between 77.00 and 87.00, the record is classified as Unknown with weight = 0.43.

(3) If value of Bundle(3) lies between 168.00 and 294.00, and value of Group(1) is 11.00, the record is classified as Good with weight = 0.42.

Modelling job complexity

(4) If value of Type(4) is 1.00, and value of SAM(7) lies between 6.69 and 14.27, the record is classified as Bad with weight = –0.41. (5) If value of Group(1) is 3.00, and value of Type(4) is 1.00, the record is classified as Good with weight = 0.37. (6) If value of Type(4) is 1.00, and value of Qty(5) lies between 20.00 and 23.00, the record is classified as Unknown with weight = –0.34. (7) If value of Bundle(3) lies between 294.00 and 439.00, and value of Type(4) is 1.00, the record is classified as Unknown with weight = 0.27. (8) If value of Group(1) is 3.00, and value of Type(4) is 1.00, the record is classified as Unknown with weight = –0.23. After running and being verified with the remaining data, the results of this experiment indicate that the APACS has a greater classification accuracy (about 95 per cent). It means that the decisions made by APACS are in close agreement with those of human judgement. Conclusion – future work We have presented a new methodology – rule induction for handling job complexity in apparel manufacturing based on formulating it as the classification problem (Good/Bad/Unknown). Its effectiveness in classification tasks has been evaluated by experiments using real life data, and the results are very encouraging. The proposed learning algorithm used in our experiment is automatic pattern analysis and classification system (APACS). The main characteristics of this algorithm include: (1) its ability to identify the values of an attribute that provide important information for the characterization of a class of instances; (2) its ability to accommodate the uncertain and non-homogeneous nature of human concepts through the use of the weight of evidence; (3) its ability to avoid the construction of rules that are too specific for overcoming the overfitting problem; and (4) its ability to acquire accurate decision rules without the need for much domain knowledge, which, if available, can also be readily included in the learning process to improve further the efficiency of the classification tasks. The performance of APACS is quite good as it attains a higher classification accuracy. We believe that APACS is superior to many existing approaches even though detailed comparison with these approaches is as yet unavailable. In the future, we will apply this algorithm to solve the problems of apparel manufacturing in qualitative measure such as the supervisory control strategy – line balancing.

43

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References 1. Yiu, H.C., “Object-oriented computer simulation for clothing manufacture”, BACS final year project, Institute of Textiles & Clothing, Hong Kong Polytechnic, 1994. 2. Fozzard, G.J.W., “Simulation of clothing manufacture”, PhD Thesis, Manchester Polytechnic, 1989. 3. Ma, C., “Simulation model of clothing manufacture”, MPhil Thesis, Hong Kong Polytechnic, 1991. 4. Fishwick, P.A., “Computer simulation: growth through extension”, Technical Report, University of Florida, April 1994. 5. Harlock, S.C. and Yu, C.P. “Computer simulation of woollen knitwear production”, Textile Asia, June 1994, pp. 53-6. 6. Chan, C.C.K. and Wong, K.C.A., “APACS: a system for the automatic analysis and classification of conceptual patterns”, Computing Intelligence, Vol. 6, 1990, pp. 119-31. 7. Chuter, A.J., Introduction to clothing production management, 2nd edition, Blackwell Science, 1995. 8. Chang, K.P., Dae, H.L. and Tae, J.K., “Knowledge-based construction for an expert system in garment manufacture”, Proceedings of the 3rd Asian Textile Conference, Vol. II, 1995, pp. 755-62. 9. Whitaker, D., “An analysis of sewing machine breakdowns – queuing theory versus simulation”, Clothing Research Journal, Vol. 5 No. 1, 1977, pp. 18-27. 10. Stylios, G. and Sotomi, J.O., “A neuro-fuzzy control system for intelligent overlock sewing machines”, International Journal of Clothing Science and Technology, Vol. 7 No. 2/3, 1995, pp. 49-55. 11. Stylios, G. and Parsons-Moore, R., “Seam pucker prediction using neural computing”, International Journal of Clothing Science and Technology, Vol. 5 No. 5, 1993, pp. 24-7. 12. Quinlan, J.R., “Discovering rules by inductive from large collections of examples”, in Michne, D. (Ed.), Expert Systems in the Micro-electronic Age, Edinburgh University Press, Edinburgh, UK, 1979. 13. Quinlan, J.R., “Learning from noisy data”, in Michelski, R.S., Carbonell, J.G. and Mitchell, T.M. (Eds), Machine Learning: An Artificial Intelligence Approach Vol. 2, Tioga Publishing Co., Palo Alto, CA, 1986. 14. Quinlan, J.R., “Induction of decision trees”, Machine Learning, Vol. 1 No. 1, 1986, pp. 81-106. 15. Hart, A.E., “Experience in the use of an inductive system in knowledge engineering”, in Bramer, M.A. (Ed.), Research and Development in Expert Systems, Cambridge University Press, Cambridge, UK, 1985, pp. 117-26. 16. Bratko, I. and Kononenko, I., “Learning diagnostic rules from incomplete and noisy data”, in Phelps, B. (Ed.), Interactions in Artificial Intelligence and Statistical Methods, Technical, Aldershot, 1987. 17. Cestnik, B., Kononenko, I. and Bratko, I., “ASSISTANT 86: a knowledge-elicitation tool for sophisticated users”, in Bratko, I. and Larvac, N. (Eds), Progress in Machine Learning. Proceedings of EWSL 87, Second European Working Session on Learning, Bled, Yugoslavia, 1987, pp. 31-45. 18. Kononenko, I., Bratko, I. and Roskar, E., Experiments in Automatic Learning of Medical Diagnostic Rules, Technical Report, Jozef-Stefan Institute, Ljublijana, Yugoslavia, 1984. 19. James, M., Classification Algorithms, Collins, London, 1985. 20. Haberman, S.J., “The analysis of residuals in cross-classified tables”, Biometrics, Vol. 29, pp. 205-20, 1973. 21. Watkins, C.J.C.H., “Combining cross-validation and search”, in Bratko, I. and Larvac, N. (Eds), Progress in Machine Learning.. Proceedings of EWSL 87, Second European Working Session on Learning, Bled, Yugoslavia, 1987, pp. 79-87.

Protective overalls: evaluation of garment design and fit

Protective overalls

Janice Huck, Oprah Maganga and Younghee Kim Department of Clothing, Textiles & Interior Design, Kansas State University, Manhattan, USA Introduction Ideally, clothing which is worn in a work environment must have sufficient ease to allow the worker to move uninhibited, as well as being perceived as comfortable by the wearer. If a garment binds or restricts the wearer or, conversely, is too large, wearer mobility and the level of protection the clothing provides can be adversely affected. For example, a crotch length that is too long may prevent a worker from moving quickly or may tear and leave him vulnerable to hazardous materials[1]. Also, a worker who finds his or her clothing uncomfortable may be tempted not to wear the protective clothing at all. The need to provide better wearer mobility is a common theme for protective apparel designers[1]. One method used to evaluate the restriction to movement caused by protective clothing is by movement analysis. The study of movement can either be generalized to investigate a wide range of movements or specifically to the tasks being performed by the wearer[2]. Movement analysis may involve measurement of range-of-motion (ROM) for various body joints using goniometers or other similar instrumentation[3,4]. The strain exerted on a garment owing to wearer movement can be evaluated using seamstress analysis[5] or garment slash analysis[2,6]. Also, visual analysis by trained observers can be used to provide additional insight into the problems associated with movement while wearing protective clothing[7]. Finally, the wearer’s subjective preferences can be ascertained[4,8]. Proper fit of apparel depends on the relationship of the size of the garment compared with the size of the wearer. Garment ease is defined as the difference between the size of the garment and the size of the wearer. Research has shown that a significant problem area for fit in protective clothing is in the crotch area. For example, in a study done on overalls worn for asbestos abatement work, 80 per cent of the subjects indicated the crotch area was prone to ripping[9]. Addition of fabric to provide garment ease in the crotch area could possibly help eliminate the ripping of the garment, but too much ease may restrict certain leg movements (e.g. extension). While substantial research has been done to evaluate the fit and mobility aspects of protective clothing, no research was found that has attempted to determine the specific effects of differing amounts of garment ease in protective garments or how the fit in one area of a garment may impact on the fit in other

45 Received May 1996 Revised August 1996

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areas of the garment. The purpose of this study was first to look at alternative overall designs which added crotch ease in different garment areas and second to explore a research methodology that could isolate the effects of garment ease in one specific area of the garment, while ease in all other garment areas was controlled. This methodology may provide information to designers and manufacturers on the amounts of garment ease that should be incorporated into protective apparel to provide for maximum wearer comfort and mobility, and provide a means to evaluate the dynamic aspects of garment fit, i.e. how manipulation of ease in one area of the garment may affect the fit of other areas of the garment. Experiment The experimental design for this research was a factorial design with a control. A randomized complete block design was used, with each subject as a block. The design was a repeated measures design; i.e. each subject served as his own control. While each subject wore an overall made to his measurements and with minimum crotch length ease, a garment stress analysis procedure was used to determine the amount of ease that would be optimal in the crotch area of the overall. Then two more custom-fit overalls were developed for each subject, each with a unique method of adding the amount of crotch ease that was determined from the garment stress analysis procedure. The independent variable for this study was the location of added crotch ease in protective overalls. There were two levels of the independent variable: (1) the total needed crotch ease was added to the back torso of the overall only (Garment 2); and (2) half of the total needed crotch ease was added to the front torso of the overall and the other half of the total needed crotch ease was added to the back torso of the overall (Garment 3). The overall with the minimum amount of crotch ease (Garment 1) was used to compare the added ease conditions with this minimum ease condition. The dependent variables for this study were: (1) physical measurements of range-ofmotion for five body movements using a Leighton Flexometer[10,11] and (2) the score on a subjective evaluation scale each subject filled out after completing an exercise protocol while wearing the protective overalls. The range-of-motion movements measured were: (1) shoulder flexion/extension, (2) shoulder adduction/abduction, (3) knee flexion/extension, (4) hip extension/flexion, and (5) trunk extension/flexion[10]. A scale to evaluate subjects’ perceptions as to garment comfort and fit was developed specifically for this experiment using a semantic differential format[12]. Five male subjects were used in this study. Since crotch ease in protective overalls was the main focus of this study, subjects were chosen on the basis of vertical trunk circumference (see Figure 1). All subjects were deemed to be

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Figure 1. Vertical trunk circumference

within one standard deviation of the mean value of American males for vertical trunk circumference[13]. Development of control overalls During the sign-up session for subjects, each potential subject was informed as to the nature of the research project and the extent of his participation as a subject. Also, the potential subject was measured for vertical trunk circumference to determine if his measurement fell within one standard deviation of the mean value of American males. Those chosen to participate in the study were instructed to return at a specified time to allow researchers to take body measurements that would be used as a basis for pattern development of custom-fitted overalls (Figure 2 and Table I). For the first testing session, the subject was asked to wear underwear, socks, a T-shirt and blue jeans. Body measurements were taken over these garments. (Subjects were asked to wear the same clothing ensemble for all subsequent testing.) These body measurements were used to draft an overall pattern for the subject, using a computer program written specifically for this purpose. Since each overall was drafted according to specific individual measurements, ease (the amount that the overall was bigger than the wearer) was controlled, allowing a consistent fit for each subject. For the control overall pattern, a minimum amount of crotch ease was provided; garment patterns had vertical

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Figure 2. Body measurement used for garment development

trunk measurement ease of 10.7cm (4.0in) greater than the body vertical trunk circumference measured on the subject. Using consistent construction techniques, an overall that would serve as the control garment (Garment 1) was constructed for each subject out of a polyester/cotton blend fabric (Table II).

Measurement Height Chest circumference Back waist length Back shoulder length Waist circumference Hip circumference Vertical trunk circumference Crotch depth Full pants length Sleeve length Total body length

Weight

Mean cm (in)

SD cm (in)

Minimum cm (in)

Maximum cm (in)

173.3 (69.0) 95.3 (37.5) 46.2 (18.2) 15.0 (5.9) 85.1 (33.5) 96.8 (38.1) 168.1 (66.2) 23.6 (9.3) 99.1 (39.0) 63.2 (24.9) 160.5 (62.3)

3.6 (1.4) 7.4 (2.9) 3.0 (1.2) 1.3 (0.5) 9.4 (3.7) 4.6 (1.8) 4.3 (1.7) 0.5 (0.2) 5.3 (2.1) 6.4 (2.5) 6.6 (2.6)

172.7 (68.0) 88.9 (35.0) 41.7 (16.2) 14.0 (5.5) 77.0 (30.3) 93.0 (36.6) 163.8 (64.5) 22.9 (9.0) 91.4 (36.0) 53.3 (21.0) 148.8 (58.6)

180.3 (71.0) 104.6 (41.2) 148.5 (19.1) 17.0 (6.7) 99.1 (39.0) 103.6 (40.8) 174.0 (68.5) 24.1 (9.5) 106.2 (41.8) 68.6 (27.0) 165.9 (65.3)

km (lb) 71.8 (158.0)

km (lb) 7.6 (15.7)

km (lb) 65.9 (145.0)

km (lb) 81.8 (180.0)

Fibre content Fabric construction Fabric count: ASTM Test Method D3775-85 (ASTM, 1989) (warp/cm × filling/cm) (warp/in × filling/in) Fabric weight: ASTM Test Method D3776-85 (ASTM, 1989) (g/m2) (oz/yd2) Fabric thickness (ASTM Test Method D-1777-64 (ASTM, 1989) (cm) (in)

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Table I. Body measurement of subjects

50% polyester/50% cotton Plain weave 42 × 20 107 × 51 148.03 4.37 0.03 0.01

Table II. Fabric characteristics

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Range of motion measurements for the control overall When the control overall was completed, each subject was asked to return for the next testing session. The subject was asked to don his control overall (Garment 1) over socks, underwear, T-shirt and jeans (the same clothing ensemble used when body measurements were taken). For each joint movement measured, a Leighton Flexometer was strapped on the subject at the appropriate body location[11]. The subject was instructed to take the appropriate body position (solid line portions on Figure 3). If the subject was required to move to attain this position, he was told to move to the fullest extent possible without straining. The weighted dial of the Flexometer was then locked in the zero position. The subject was then instructed to move to the second position (dotted line portions on Figure 3). Again, the subject was told to move to the extent possible without straining. While in this position, the weighted pointer of the Flexometer was locked. The subject was then allowed to relax and a reading (representing range of motion of the body segment in degrees) was taken. To minimize error of measurement, this procedure was repeated twice more (for a total of three measurements). The same procedure was used to obtain data for all joint movements. The order of presentation of the joint movements was randomized between subjects. Exercise protocol for the control overall After the subject had completed the range of motion movements, he was asked to complete an exercise protocol. The exercise protocol was based on the procedure outlined in ASTM F1154-88[14] for evaluating the comfort, fit and function of chemical protective suits. Basically, this exercise protocol consisted of a series of movements that represented the physical movement that might be required in a work environment where overalls are worn and which incorporated body movements that would be expected to strain the overalls (Table III). Prior to having the subject complete the exercise routine, the researchers demonstrated each of the movements to be completed. A pre-recorded audiotape directed the subject through the various movements during the exercise protocol. Also the researchers recorded their visual observations of subjects as each subject completed the exercise protocol. Finally, each subject was asked to complete a wearer acceptability scale after completing the exercise protocol (Table IV). This wearer acceptability scale consisted of a series of descriptive adjective sets to determine how subjects felt and also how they perceived the fit and comfort of their clothing. Determination of needed crotch ease After completing the exercise protocol and filling out the wearer acceptability scale as described above and with the subject still wearing Garment 1, the researcher used scissors to make a horizontal slit in the overall from side seam to side seam at waist level in the back of the overall. The subject was asked to

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Figure 3. Range of motion measurements

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Exercise order 1 2 3 4 5 6

Table III. Exercise protocol

Procedure Kneel on left knee, kneel on both knees, kneel on right knee, stand Duck squat, raise arms Stand erect. With arms at sides, bend body to left and return, bend body forward and return, bend body to right, and return Stand erect. Extend arms overhead, then bend elbows Stand erect. Extend arms perpendicular to sides of torso. Twist torso left and return, twist torso right and return Stand erect. Reach arms across chest completely to opposite sides. Repeat exercise a total of three times

7

Walk along tapea

8

Crawl on hands and knees along tapea

Source: ASTM F1154-88 Note: a A strip of masking tape was placed on the floor as a guide

Place a check between each pair of adjectives at the location that best describes how you feel: 1. Comfortable 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1* Uncomfortable 2. Acceptable 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Unacceptable 3. Tired 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 Rested Place a check between each pair of adjectives at the location that best describes the clothing you are wearing: 4. Flexible 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Stiff 5. Easy to put on 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Hard to put on 6. Freedom of moveRestricted movement ment of arms 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 of arms 7. Easy to move in 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Hard to move in 8. Satisfactory fit 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Unsatisfactory fit 9. Freedom of moveRestricted movement ment of legs 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 of legs 10. Freedom of moveRestricted movement ment of torso 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 of torso 11. Dislike 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 Like 12. Loose 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Tight 13. Crotch of overall right Crotch of overall too distance from body close or too far from 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 body Table IV. Wearer acceptability scale

* Number added for reader reference only

assume a crouching position with arms extended in front of the body (Figure 4). With the subject in this position, in which the overall was strained maximally in the crotch area, the researcher measured the vertical gap formed by the slit at the garment centre-back. The subject was allowed to stand and relax. This measurement was repeated three times.

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Figure 4. Determination of needed crotch ease

The mean value of the three measurements was considered to be the amount of ease needed in the vertical trunk circumference measurement of the overall that would provide enough ease to allow the wearer to move with minimum garment restriction, while not adding so much ease to the garment that movement might be compromised. This vertical trunk circumference ease measurement, along with the same other body measurements used in the control overall pattern, was used for further pattern development (Table V). (Therefore, the only difference

Measurement Added crotch (vertical circumference) ease

Mean cm (in)

SD cm (in)

17.0 (6.7)

1.0 (0.4)

Minimum cm (in) 15.2 (6.0)

Maximum cm (in) 17.8 (7.0)

Table V. Added amounts of crotch (vertical circumference) ease

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in garments between the control overalls and the two experimental overalls for each subject was the vertical trunk circumference ease measurement.)

54

Development of experimental overalls Using the vertical trunk circumference measurement of each subject plus the needed ease as determined by measurement of the garment slit opening, two more overall patterns were drafted for each subject. For one experimental overall pattern (Garment 2), the needed ease for the vertical trunk circumference was used to lengthen the back pattern of the overall only (Figure 5) in a manner used by previous researchers[2].

Figure 5. Overall pattern with crotch ease added to back only

A casing with elastic was added to the centre-back torso area of the overall to control the added fullness. For the second experimental overall pattern, the vertical trunk circumference was used to lengthen the front and back patterns of the overall (both front and back were lengthened one-half of the total crotch ease amount required) (Figure 6). Two overalls per subject with appropriate vertical trunk circumference measurements were constructed from the same polyester/ cotton fabric used for the control overall, using identical construction techniques. Range of motion measurements and exercise protocol in experimental overalls When the two experimental overalls for each subject were completed, the subject was asked to return for testing. Again, the subject was asked to don the appropriate experimental overall over socks, underwear, T-shirt and jeans. Range of motion measurements were taken for each subject in each experimental overall using the Leighton Flexometer and the protocol described previously. After the subject had completed the range of motion movements, he was asked to complete the same exercise protocol as he did in the control overall. Each subject was asked to complete the wearer acceptability scale as described previously. The order of presentation of the two experimental overalls was randomized between subjects. Results and discussion Subject characteristics Body measurements for the five participating subjects are shown in Table I. The mean vertical trunk circumference for the subjects in this study was 168.1 cm (66.2 in) and corresponds to a measurement within one standard deviation of that reported for American males[13]. The mean total amount of ease added to the vertical trunk circumference of the experimental overalls (determined by measuring the gap formed when the control overall was slit at the centre-back) was 17.0cm (6.7in) (Table V). It is interesting to note the small standard deviation for this measurement, 1.0cm (0.4in). This finding may suggest the possibility that a specific amount of ease could be used to provide good fit and mobility in the crotch area for a large number of overall wearers. Certainly, this finding warrants further study with larger and more diverse sample populations. Range of motion measurements The measurements for range of motion for each of the five body movements are presented in Table VI. Also, the per cent of difference in range of motion of the experimental garments over the control garment was calculated to indicate any improvement or decrement to wearer movement. Since the main focus of this study was the vertical trunk circumference ease in the garment, the trunk flexion range of motion measurements was of primary interest. As can be seen from Table VI, Garment 2 allowed for greater trunk flexion than did Garment 1 (the control overall) for all subjects, ranging from a 3.8 to 11.5 per cent increase in ROM. Overall, the mean increase in trunk

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Figure 6. Overall pattern with crotch ease added to front and back

Subject Trunk flexion 1 2 3 4 5 Mean Shoulder adduction 1 2 3 4 5 Mean Shoulder flexion 1 2 3 4 5 Mean Knee flexion 1 2 3 4 5 Mean

Garment 1 ROM

Garment 2 ROM Change

Garment 3 ROM Change

113.3 150.3 139.0 112.0 140.0

124.6 165.0 155.0 116.3 150.6

+10.0 +9.8 +11.5 +3.8 +7.6 +8.5

115.3 155.0 132.3 102.3 141.3

+1.8 +3.1 –4.8 –8.7 0.9 –1.5

119.0 115.3 146.7 121.0 128.0

117.7 126.7 131.0 124.3 129.0

–1.1 +9.9 –10.7 2.7 0.8 +0.3

132.0 120.3 150.0 121.7 125.0

+10.9 +4.3 +2.2 +0.6 +2.3 +4.1

181.3 183.3 182.7 184.0 150.3

182.3 161.3 159.3 157.3 170.0

+0.6 –12.0 –12.8 –14.5 13.1 –5.1

162.7 172.0 154.0 152.7 160.0

–10.3 –6.2 –15.7 –17.0 –6.5 –11.1

120.0 122.7 119.0 133.0 133.7

125.3 118.7 121.3 122.3 127.0

+4.4 –3.3 +1.9 –8.0 –5.0 –2.0

127.3 127.0 120.7 118.0 128.7

+6.1 +3.5 +1.4 –11.3 +3.7 +0.7

ROM for Garment 3 over Garment 1 was 8.5 per cent. Garment 3 did allow greater trunk flexion for only two of the subjects (1.8 per cent and 3.1 per cent respectively). For the other three subjects, trunk flexion ROM was decreased in Garment 3 when compared with Garment 1. These findings appear to show that the design of Garment 2 (which added all the crotch ease to the back of the garment) would be a preferable design feature to maximize wearer mobility. Adding crotch ease to both the front and back of the overall did not increase trunk flexion over the control garment. For the other four range of motion measurements, the results indicate the dynamic nature of the fit of a garment (Table VI). While trunk flexion was significantly increased in Garment 3 over Garment 1, shoulder abduction was increased less than 1.0 per cent. While this amount is probably not significant in actual wearing and use conditions, the decrease in knee flexion and shoulder flexion (i.e. –2.0 per cent and –5.1 per cent, respectively), indicate that vertical

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Table VI. Range of motion (ROM) by design

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trunk circumference ease may decrease wearer mobility in other body areas. It is hypothesized that the decrease in knee flexion was probably due to the fact that no additional circumference ease was added to the front of the garment, and therefore knee flexion would not be increased; the decrease may possibly be due to additional constriction at the waist area in the garment due to the elastic across the back of the garment. Controlling the crotch ease in the back of the garment may have also caused the decrease in shoulder flexion, since the subject would have to exert additional effort to raise the arm and stretch the elastic to complete the movement. In certain work environments where movement of body areas other than the trunk flexion must be maximized for worker safety, this finding needs to be considered when evaluating a potential overall design. As can be seen from Table VI, Garment 2 was less restrictive to movement for shoulder adduction, shoulder flexion and knee flexion than was Garment 3. This finding indicates that the method of adding crotch ease to the back of the garment only is preferable to adding the ease to both the front and back of the garment. The substantial increase in trunk flexion for Garment 2 over Garments 1 and 3 would indicate that the amount and location of ease in Garment 2 are a desirable design alternative. Subjective preferences of subjects While objective measures, such as range of motion, can be used to evaluate the design of protective clothing, it is also important to determine wearers’ perceptions of the clothing. If the clothing is perceived to be unacceptable to the wearer, he or she may not wear the clothing and thus be exposed to the very hazards from which the clothing is designed to protect him or her. Several adjective sets which could describe the fit of the clothing and how the clothing was perceived by the wearer were used in the wearer acceptability scale. The scale was filled out after each subject completed an exercise protocol that included a number of physical movements that might be required in a work situation. The mean scores for each adjective set and the total score (all adjective set scores summed) are shown in Table VII. In general, subjects preferred the two experimental garments over the control garment. In a few instances, however, the control garment was perceived more favourably than the experimental garment. For example, the control garment, with its minimum crotch ease, was perceived as more acceptable than Garment 3. Additionally, Garment 1 was perceived as providing more freedom of movement of the leg than was Garment 3. Interestingly, subjects rated Garment 2 lowest on the adjective set of like/dislike. It is hypothesized that this result may have occurred because of the unconventional look of this overall owing to the elastic and bunched fabric at the centre-back waist area of the garment.

Garment 1a

Adjective

Comfortable/uncomfortable Acceptable/unacceptable Tired/rested Flexible/stiff Easy to put on/hard to put on Freedom of movement of arms/restricted movement of arms Easy to move in/hard to move in Satisfactory fit/unsatisfactory fit Freedom of movement of legs/restricted movement of legs Freedom of movement of torso/restricted movement of torso Dislike/like Loose/tight Crotch too far from body/crotch too close to body Notes:

Garment 2a

Garment 3a

4.8 5.4 3.4 5.0 5.4

6.2 6.0 2.6 6.8 6.2

4.8 4.8 3.2 6.0 7.0

5.6 4.8 4.2

5.6 6.2 6.0

5.8 4.8 4.6

6.4

6.6

4.8

6.0 5.2 3.8

7.6 4.4 5.6

6.6 5.4 4.0

2.6

6.0

2.0

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aGarment

1 = control overall (with minimum ease) Garment 2 = overall with all ease added to back Garment 3 = overall with half ease added on back and half added on front

9 = value closest to first item on descriptor set; 1 = item closest to second item on descriptor set

Researchers’ observations In addition to the above results, the researchers also observed that, during the exercise protocol, Garment 1 was very tight in the crotch area and not only restricted movement of the torso, but also restricted movement of the arms when the subjects were crawling or bending forward. Also, when the wearer assumed a crouching position, it was not easy for him to raise his arms above his head. The crotch of Garment 2 was also close to the body when the elastic controlling the back fullness was not stressed. However, when the wearer was crawling or assumed a crouching position, the garment stretched at the back allowing more mobility in the torso than did Garment 1 and subjects could raise their arms more easily than they could in Garment 1. Garment 3 restricted movement of legs during walking and crawling and kneeling, but allowed more mobility of the torso during crawling and bending than Garment 1. It was, however, difficult for subjects to assume a crouching position in this overall since the crotch was lowered. One of the overalls that had added ease both in

Table VII. Mean scores for adjective descriptor sets on the wearer acceptability scale

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front and back was torn at the crotch; this is similar to Ashdown’s findings[9] in a similar overall design for asbestos abatement. Conclusions Protective clothing should provide maximum protection and comfort. It is important that the protective clothing fits properly so that wearer movement is not inhibited. This study explored a methodology that can be used to evaluate design features and fit of protective overalls, as well as wearer acceptance. The results of this study indicate a design feature of adding a specific amount of crotch ease to the back of protective overalls may be desirable over the more traditional method of dividing this added ease evenly between the front and the back of the overall. It also evaluated the dynamic nature of fit; looking at how design changes may affect different aspects of wearer mobility. The methodology used in this study can be used in evaluation of other types of protective clothing, giving researchers a way to evaluate objectively the fit and design features of garments, as well as the effect such design features will have on wearer mobility. References 1. Keeble, V.B., Prevatt, M.B. and Mellian, S.A., “An evaluation of fit of protective overalls manufactured to a proposed revision of ANSI/ISEA 101”, in McBriarty, J.P. and Henry, N.W. (Eds), Performance of Protective Clothing: Fourth Volume, ASTM STP 1133, American Society for Testing and Materials, Philadelphia, PA, 1992, pp. 675-97. 2. Ashdown, S.P. and Watkins, S.M., “Movement analysis as the basis for the development and evaluation of a protective overall design for asbestos abatement”, in McBriarty, J.P. and Henry, N.W. (Eds), Performance of Protective Clothing: Fourth Volume, ASTM STP 1133, American Society for Testing and Materials, Philadelphia, PA, 1992, pp. 660-74. 3. Adams, P.S., Slocum, A.C. and Herring, G., “An approach for predicting garment effects on range of motion based on measurement of garment ease”, Proceedings of the Second International Symposium on Consumer Environmental Issues: Safety, Health, Chemicals, and Textiles in the Near Environment, 1992, pp. 216-29. 4. Huck, J., “Restriction to movement in fire-fighter protective clothing: evaluation of alternative sleeves and liners”, Applied Ergonomics, Vol. 22 No. 2, 1991, pp. 91-100. 5. Worthing, A.P., “Stress in seams”, Shirly Institute Bulletin, No. 5, 1974, pp. 131-6. 6. Crow, R.M. and Dewar, M.M., “Stress in clothing as related to seam strength”, Textile Research Journal, Vol. 56, 1986, pp. 467-73. 7. Watkins, S.M., “The design of protective equipment for ice hockey”, Home Economics Research Journal, Vol. 5 No. 3, 1977, pp. 164-8. 8. Huck, J. and McCullough, E.A., “Firefighter turnout clothing physiological/subjective evaluation”, in Mansdorf, S.Z., Sager, R. and Nielsen, A.P. (Eds), Performance of Protective Clothing: Second Symposium, ASTM STP 989, American Society for Testing and Materials, Philadelphia, 1988. 9. Ashdown, S.P., “Analysis of task-related movement of asbestos abatement crews as a basis of design of protective overalls”, unpublished Master’s thesis, Cornell University, 1989. 10. Leighton, J.R., “An instrument and technique for the measurement of range of joint motion”, Archives of Physical Medicine and Rehabilitation, 1955, pp. 571-8.

11. Leighton, J.R., “The Leighton Flexometer and flexibility test”, Journal of the Association of Physical and Mental Rehabilitation, Vol. 20, 1966, pp. 86-93. 12. Rohles, F.H., Konz, S.A., McCullough, E.A. and Milliken, G.A., “A scaling procedure for evaluating the comfort characteristics of protective clothing”, Proceedings of the 1983 International Conference on Protective Clothing Systems, Stockholm, Sweden, 1983. 13. McConville, J.T. and Laubach, L.L. “Anthropometry”, in Webb Associates (Eds), Anthropometry Source Book, Volume 1: Anthropometry for Designers, National Aeronautics Space Administration, Yellow Springs, OH, 1978, pp. III-1 - III-106. 14. American Society for Testing and Materials, “Standard practices for qualitatively evaluating the comfort, fit, function and integrity of chemical-protective suit ensembles”, ASTM F1154-88, 1988.

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62 Received April 1996 Revised and accepted August 1996

Aspects of a product model supporting apparel virtual enterprises Peter Denno National Institute of Standards and Technology, Gaithersburg, Maryland, USA Introduction The American Apparel Manufacturers Association (AAMA) has defined a standard for the exchange of apparel pattern piece data (AAMA, 1993). This standard has enabled software products from various vendors to interoperate. However, emerging apparel product development systems require more extensive design and product specification information than the current AAMA exchange form provides. These systems would be better served by a standards-based exchange form that allows the systems to communicate the breadth of garment product information that they contain. This new exchange format could also enhance the operation of apparel virtual enterprises, an entrepreneurial-spirited mode of business that is becoming possible as businesses increasingly use computer and Internet technology in the product development cycle. This paper considers what a new pattern data exchange form, called here the virtual garment prototype (VGP), should contain in order to support emerging apparel product development design software and apparel virtual enterprises. The first section of the paper discusses the old and new information requirements of apparel design systems. The second section outlines the content of the VGP. The third section considers how the apparel industry might find competitive advantage by operating as virtual enterprises; and how the VGP would help in this area. The final section discusses how the technology, methodology and standards developed by ISO STEP (International Organization for Standards, Standard for the Exchange of Product Model Data) can be employed as a foundation for the development of the VGP. New information requirements Design development in apparel includes market forecasting, design, pattern making, grading, piece goods and trim sourcing, and prototype creation (Figure 1). Two sorts of software have assisted in these areas: pattern-making systems and product data management (PDM or “specification”) systems. Until recently,

International Journal of Clothing Science and Technology, Vol. 9 No. 1, 1997, pp. 62-74. © MCB University Press, 0955-6222

This paper would not be possible without the help of KaMing Tam and the many discussions I enjoyed with her and her colleagues at London Fog and elsewhere. Thanks are due also to Mary Mitchell and the apparel project people at NIST (Tina Lee, Howard Moncarz and Jeane Ford).

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63 Figure 1. Production activities showing cycles of refinement in specification and costing

pattern-making systems have played only a minor role in this effort, providing the storage and manipulation of individual pieces as it relates to the larger design process occurring outside the system. Also, PDM systems were not widely used. Both of these situations have changed recently: newer computeraided pattern-making systems are more than geometry editors, and the use of PDM is now commonplace. Pattern-making and PDM systems have often been derivative products for vendors whose principal products are marker-making systems and cutters. The immediate advantage of computer-aided pattern making is the elimination of the digitizing needed for computerized marker making. The disadvantage of the computer-aided approach is the loss of the “hands-on feel” of manual pattern making (e.g. tactile smoothness of design lines, sense of life-size proportions of pieces, etc.). Since pattern-making software often originated from the marker-making systems, the design systems information model originally lacked designspecific information. The pattern information required for marker making is little more than the grain line and cut line of individual pieces. Design development, of course, encompasses many more activities and information requirements than does marker making. Progress in apparel pattern-making systems is evident in commercially available systems, advanced research (Hunter, 1990; McCartney and Hinds, 1992; Okabe et al., 1992) and emerging standards for apparel information systems (AAMA, 1993; MONCARZ). The advances in pattern-making systems are following the trend in geometric design systems in general by providing higher level design abstractions and domain-specific functionality (e.g. manipulation, in concert, of all the pieces composing a seam, generation of linings from rough specifications, automated grading). The pattern-making system is evolving from an individual piece geometry editor to a system that manipulates assemblies of pieces, thus more closely reflecting the knowledge-

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intensive work performed by pattern makers, graders and sewers. Instead of requiring that the pattern maker individually modifies the geometry of every piece affected by a change, as was previously necessary (for example, to improve fit) the newer systems provide tools to move seams and automatically update every piece associated with the modification. To make this new functionality possible it is necessary to represent and encode more encompassing information regarding not just the pieces, but also the relationship between pieces, and the relationship between the garment and the body. It is necessary to compose seams from pieces, describe linings in relation to complete garments, position fusible under self or shell fabric, and associate fabrics and trims with the garment model. Finally, information such as seam types, construction details, fabric and trim specification decreases the ambiguity in what real configuration of the garment the data model describing it actually represents. If enough information is specified, it should be possible for two manufacturers, using nothing but the model, to produce garments that are indistinguishable[1]. Defining the virtual garment prototype Defining a product model is a difficult task. ISO STEP describes useful guidelines to aid in the development of product models such as the VGP (Fowler, 1995). Before discussing the STEP method, however, it is useful to consider informally what the model should contain. Therefore, potential VGP modelling features are presented here. In this investigation, two paths to identifying this information have proved useful. One path stems from an analysis of the product development activities. (e.g. market forecasting, conceptual design, pattern making, prototype creation, grading)[2]. This path leads to some obvious and important information requirements, discussed in the following section. A second approach is to consider what work is being performed, or can be performed, by pattern-engineering systems. This path can lead to some requirements that are usually left unstated in interactions between people. Information requirements leading from activity analysis The activities of market forecasting, design conceptualization, pattern development, prototype creation and sourcing are typically performed in cycles of refinement. Table I describes some information sources and usage in these activities. In this Table information that is recycled for refinement of the product definition is enclosed in square brackets in the “activities consuming” column. In a complete analysis of this type each of the activities would be further decomposed to subactivities, and the information content conveyed between activities would be elaborated on. The level of information required in one area, construction features, is illustrated in a suit jacket example and seam data model in later sections of the paper.

Activity producing Market forecasting Design Pattern making

Grading

Information produced

Activities consuming

Market trend Style concept Cost constraints Style development Selection of trims Pieces Piece geometry (e.g. cut lines, sew lines) Construction features (e.g. seams) Style features (e.g. folds, fullness features) Graded pieces

Design, sourcing Design Sourcing Pattern making (market forecasting) Sourcing Prototypes (market forecasting, design) Grading, sewing Grading, sewing Grading, sewing Marker making

Information requirements of pattern engineering systems In this paper the term pattern-engineering system refers collectively to product data management (PDM), and pattern-development systems. Grouping these systems together is justified from the standpoint of fulfilling their similar information requirements. Commercial products that are clearly focused on either pattern development or garment specification are better served by a single data exchange specification that addresses both than by an exchange specification that addresses only one of these systems. This is because there is significant interaction possible between the data from each system: specification can affect pattern pieces (e.g. seam type can affect seam allowance); and pattern piece can affect specification (e.g. piece size can determine garment measurements). A goal of the virtual garment prototype is to provide an exchange form for pattern-engineering systems. It is possible to identify some of the content of the VGP by considering how software would employ it. This approach has the advantage of not assuming too much; where people often see obvious relationships (e.g. sleeve cap and armhole go together) computers need a formal relationship defined. The list below enumerates some of the higher-level abstractions that are absent from existing apparel pattern exchange standards. The problem facing pattern engineering systems in using these exchange forms is the need to re-establish these higher-level abstractions and relationships after receiving the exchanged data[3]: • Automated grading: requires knowledge of seams, fullness, assembly, orientation and placement cues between body and garment, target garment dimensions and dimensioning on assemblies. • Pattern development tools: requires piece relationships across multiple pieces that react to modifications in concert. This, in turn, requires knowledge of seams, assembly, fullness features, orientation and placement cues, and pattern-making techniques.

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65 Table I. Information producers and consumers in product development activities

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66

•

•

•

Generation of cut l ine from sew line: requires knowledge of seam properties, stitch properties and fabric properties. Generation of linings and fusibles: requires design specifications, knowledge of shell assembly, as well as the requirements of pattern development tools above. Draping visualization: requires knowledge of assembly, and material properties for shell, fusibles and lining, orientation and placement cues between the body and garment. Pattern adjustments for alternative fabrics: requires knowledge of assembly and material properties for original and alternative fabrics, pattern-making techniques. Costing (estimating marker utilization and other downstream considerations): requires reference to vendor data for fabrics, trims and assembly information.

An example: a suit jacket sleeve and front panel In the previous section, potentially complicated constructs were referred to with terms such as “properties of” or “knowledge of”. This section develops a few of these constructs further. To illustrate how some of the suggested features of the VGP are integrated and employed, an example is provided. Figure 2 shows the partial detail of information describing a suit jacket sleeve and front panel. The figure shows essential construction, dimensioning annotation and body landmarks for use in pattern making, draping simulation and grading. The example does not detail the collar, pockets, sew line, notches or sewing. By identifying both common seams and coincident points as shown in Figure 2, the seam ease inherent in the seam is represented. Body landmarks on the pieces help to identify the relationship between the garment and the body for use in grading and draping. Although the construction details of this jacket are mostly typical, the detail shown is not sufficient for computerized reconstruction of the garment. For example, it is not clear at this level of detail whether the pieces overlay or abut at the seams. There are many examples (e.g. pockets commonly employed in outerwear), where only the responsible pattern maker would understand the construction from individual, unannotated pattern pieces. In these cases either a real prototype or VGP is essential. Figure 3 is a graphical representation of a data model defining a seam. This figure is an elaboration of the information describing seams found in Figure 2. The common seams and coincident points of Figure 2 are represented here by sewn seam and mating end Pt data entities respectively. The figure illustrates the complexity of information necessary to describe a seam unambiguously. The representation is intended to allow description of seam ease, and different stitch types across multiple pieces. Similar levels of complexity are required to describe body landmarks, vendors, grading

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Figure 2. Construction details of a suit jacket sleeve and front panel

dimensions, and fullness features, etc. This figure uses a graphical representation of the data specification language used in STEP product data modelling. Such data specifications are an end product of the collaborative efforts between apparel and STEP data-modelling experts. With these representations in hand, software tools can be applied to produce automatically software to exchange the product data. This software can be included in pattern-engineering and product data-modelling software products, making it possible for them to interoperate with each other. The virtual garment prototype in apparel virtual enterprises Industrial virtual enterprises Having suggested the content of the VGP, this section discusses the purposes it would serve among apparel virtual enterprises, an entrepreneurial-spirited mode of business that could change the way the industry operates. Virtual enterprises (VEs) are currently the focus of much attention and research both in apparel (AMTEX) and more generally (Davidow and Malone, 1992; NIIIP, 1995). The National Industrial Information Infrastructure Protocols (NIIIP) is a 30-month, $30 million technology reinvestment project developing infrastructure and standards to enable virtual enterprises. NIIIP defines a virtual enterprise as a temporary consortium of individuals, often crossing

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Figure 3. An EXPRESS-G model of a seam

company boundaries, who come together quickly with the goal of exploiting fast-changing opportunities. Within the virtual enterprise members share costs and skills, each contributing their core competences. VEs are formed without regard to size, organizational, or technical boundaries in order to provide timely and competitive products and services (NIIIP, 1995). The Internet has, more than any other technology, enabled the emergence of virtual enterprises. However, a virtual enterprise is more than just business use of the Internet. Virtual enterprise technology provides the VE temporary consortium with the following services: •

Work flow management: participants in a VE rely on VE software to coordinate schedules, present work tasks to individuals at the proper time and co-ordinate data access.

•

Creation/dissolution: VE software provides the ability to select participating companies, define roles and schedules and clean up after the work is complete.

•

Security: VE software protects intellectual assets from malicious outsiders and industrial espionage. Protection might even include

insulating members from one another’s aspects of business which are not part of the collaboration. • Access to product data: particularly in an industrial virtual enterprise, where the goal is to produce a manufactured product, the members must be able to communicate and share product data. The above services are essential qualities of collaborative manufacturing of any sort. In particular, VEs could provide the apparel industry with some significant advantages[4]: • The virtual enterprise can provide the manufacturer with flexibility in identifying contractors, suppliers and facilities for the production of its products (commonly referred to as an agile supply chain). • Conversely, a manufacturer with excess capacity may use the VE infrastructure to become a contractor. For example, a manufacturer with a predictable slump between seasons in its cutting and sewing facility might offer cutting and sewing to other enterprises[5]. • The virtual enterprise provides the small business and those possessing sought-after skills with a market for their services. This is particularly useful to apparel manufacturers in the USA, where pattern makers are in high demand. To serve these purposes the VGP (and product models in general) should possess the following qualities: (1) the information must interoperate in an environment characterized by heterogeneous computer systems and various software applications (the VE environment); (2) the product model should strive to eliminate ambiguity pertaining to the product’s actual characteristics; (3) the product model should strive to eliminate the reconstruction of work performed previously in the development process. These ideas are discussed below. Barriers to work distribution Today, in large apparel-producing cities, there are companies that specialize in garment grading for a diverse group of local customers. Apparel virtual enterprises would make it possible to extend this distribution of work into more tasks of the design cycle and to provide a global market for customers and suppliers of the work. To achieve this, the essential product information must be interoperable, distributed geographically, and shared temporally, as the design process proceeds. Distributing the design of apparel is a difficult task because apparel design typically requires close co-operation between the various contributors over a very short schedule. As illustrated in Figure 1, product development tasks are

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interleaved with costing and sourcing activities. The process of determining a production design is one of iterative refinement, where the principal design tasks are influenced by current market and cost information. The design process requires the co-operation of a team with very diverse skills: merchandisers forecast the market for an idea; designers develop conceptual designs; pattern makers make patterns from conceptual sketches, graders reproduce patterns in various sizes, and sourcing buyers find suppliers for the product’s piece goods and trims. Although the diversity of skills required argues for distribution into guilds (i.e. pattern making, grading or sourcing are outsourced to firms with expert ability), the problem of communicating information into each task is a barrier against this happening. For example, when a team consisting of merchandiser/designer and pattern maker decide that the sleeve of a garment has too much fullness at the armhole, the pattern maker must modify the design. If the exchange form only encodes individual piece geometry, integral characteristics of the garment construction must be recovered. In order to make the modification, the pattern maker must first mentally reconstruct the sleeve, front, back, lining, fusible and perhaps shoulder pad placement and consider the fabric properties involved before judging how to modify the garment. To do this mental reconstruction with ease the pattern maker must have either recently worked on the pattern (arguing against flexibility in who does the work) or have a prototype in hand (arguing against operation as a virtual enterprise). Mental reconstruction, which also occurs in grading, is a consequence of the necessary information being absent from the exchange form. In summary, storing the relationships of an information-rich garment product model will enhance the ability of people to grasp quickly the significant structure of the problem and will eliminate the introduction of errors that would occur were it necessary to reconstruct and make assumptions about the product configuration. These attributes are essential to operation in a virtual enterprise environment. Methodology for development of the product model The complexity of the VGP product model calls for its development by a crosstrained team of industry and information modelling experts. A methodology for the development of product models has been defined by the Standard for the Exchange of Product Model Data (STEP) (Fowler, 1995). This section introduces STEP and the STEP architecture. ISO (International Organization for Standards) TC184/SC4 is a technical committee that is developing an international standard, ISO-10303 (commonly called STEP) for representing product model data and their exchange. The STEP community comprises 26 national member bodies. STEP development is industry-driven, rather than driven by software vendors. The initial release of STEP (December 1994) includes the definition of an information modelling language, information resources which are general enough to support multiple

industries, and specific application protocols for three-dimensional design and drafting. Many other STEP application protocols are approaching international standards status, including such diverse areas as ship construction and NC cutpath planning. STEP architecture In STEP terminology, a virtual garment prototype product model would be described by an application protocol (AP). An AP is a computer and human readable specification document written using the EXPRESS information modelling language (Schenck and Wilson, 1994). The application protocol defines concepts or entities containing typed attributes[6]. The AP also contains rules and relationships governing types and values of attributes, the cardinality of sets of entities, etc. These rules reflect the semantics of the realworld artefact being modelled. For example, a rule might require that seam entities reference sew-line entities, not cut-line entities. These rules are defined to ensure the fidelity of the model to the intentions of the industry experts involved in its definition and the application programs that exchange data by it. (For example, applications that exchange information in the form of the AP promise to describe seams by reference to sew lines, not cut lines.) Such rules are the basis of software interoperability. The application protocol, even in an entirely new industrial area for STEP application, relies on pre-defined basic building-block entities called integrated resources which have been established as commonly useful to the description of artefacts (e.g. bezier curves, release approvals, etc.) (Barnard et al., in press). Domain-specific concepts, such as the sew line, can be produced by specializing a similar concept in the integrated resources. Hence, owing to integrated resources, it is not necessary for VGP developers to define by themselves the substantial foundation of concepts that would be necessary without integrated generic resources. To date these integrated resources have been rich enough to support, with only minor extension, a diverse set of applications. Similarly, STEP defines application interpreted constructs for the consistent representation of commonly used concepts across domains. Application interpreted constructs can be thought of as a library containing a set of concepts that satisfy a specific purpose. Because the same application interpreted construct can be found in applications across disciplines (e.g. a pattern development system and a production-scheduling system might share a construct that indicates that a pattern is approved for marker making) they provide a degree of interoperability between these systems. Application interpreted constructs are a means for various systems to communicate common concepts. Virtual enterprises and manufacturing execution Virtual enterprise technology provides the ability to distribute work and provide flexibility in terms of where, when and by whom the work is performed.

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Thus virtual enterprises provide a form of manufacturing agility that most clearly benefits activities of the design cycle (market forecasting to marker making of Figure 1) but may find application to a lesser degree in the manufacturing execution cycle (marker making to marketplace in Figure 1). More than most industries, apparel production is made difficult by variation in properties of raw materials and “part mix” (specifically, variations of garment size and fabric properties). For example, variations in fabric properties from one dye lot to another make automation of sewing difficult, (as does the lack of rigidity of fabric itself). Variation in fabric width forces re-work of markers, change of size combination in cut planning, etc. Solutions to these problems require agility in manufacturing execution (e.g. shopfloor control). The application of virtual enterprise technology to manufacturing execution is a new area of research (ATP, 1995). Currently, one may only speculate as to how virtual enterprise technology might benefit. For example, the workflow management component of a virtual enterprise may generate a task to re-work the marker off-site when the actual fabric spread is narrower than the planned marker. Conclusion The garment industry is perhaps the industry that could most benefit by operating as virtual enterprises. The majority of this benefit can be realized in the design cycle activities and in communication to suppliers and contractors. Unlike the aerospace and automotive industries, the garment industry does not rely on sophisticated, proprietary manufacturing processes that tend to keep finished product manufacturing concentrated in a few companies. Manual sewing is largely a commodity, and sewing requirements are easily communicated. The garment industry relies on many globally distributed contractors for production. Apparel virtual enterprises can provide agility in the distribution of work among this large pool of contractors. Further, apparel product development requires the co-operation of individuals with a very diverse skill set. Some of these skills, particularly pattern making and grading are continually in short supply in the USA. Some of this shortage will be met by better pattern-engineering systems; some shortage could be relieved, were the people with these skills able to reach a global market for their work, that is, were apparel virtual enterprises common. As a means to enable more agile production, the advantage of apparel virtual enterprises is even more obvious. Some segments of the industry experience huge fluctuations in product development effort, tracking the transition from one fashion season to the next. By operating in virtual enterprises, other segments of the industry could more easily utilize the product development capacity of this segment during its slow period. Finally, there is the largely unexplored domestic market for custom clothing. The efficient manufacture of custom clothing requires agility in manufacturing and intelligence in product models. Automated grading for custom fit, for

example, is possible only when body measurements can be related back to garment dimensions, to piece constructions and, finally, to individual pieces. This requires an information model that contains the high-level abstractions such as garment dimensions and the relationships that bridge levels of abstractions down to primitive geometry. Both apparel virtual enterprises and pattern-engineering systems require a standards-based product model that is information-rich in the high level abstractions of the product development process. The product model must communicate the design unambiguously. It must not require that product developers re-establish these high level abstractions and relationships when receiving the model. The information must be encoded in the exchange form. This paper suggests what an information-rich garment product model should contain. Further it proposes to leverage STEP technology and methodology which is well suited for its development. The ready-to-wear pattern-making STEP AP (Lee, 1995), may serve as a starting point for the development of the VGP. Notes 1. Models of this level of detail are possible. Discrete part manufacturing has benefited from working to this goal since the early 1970s. This ability is the essence of the model being free of ambiguity. 2. A scoping of apparel enterprise activities is provided by Moncarz and Lee (1993). 3. The pattern information of the virtual garment prototype can be encoded as a flat-pattern model (as is the AAMA model). Although some usages, such as draping simulation, are three-dimensional, the creation of the three-dimensional shape from flat-pattern pieces is possible using construction information that describes seams, fullness and design features, etc. Construction information reduces ambiguity in the model. 4. Some of these ideas are already being tested in the AMTEX Demand Activated Manufacturing Architecture (AMREX). 5. Of course, this is not a new idea, but by possessing interoperable, information-rich descriptions of products, buyers and suppliers can more easily assess the feasibility of collaboration. 6. Entities can be thought of as corresponding to objects in programming languages. Entities are identified by rectangles in the EXPRESS-G diagram of Figure 3. References “Advanced Technology Program (ATP): technologies for the integration of manufacturing applications” (1995), Commerce Business Daily, US Government Publication, Washington, DC, 17 May. American National Standard for Pattern Data Interchange – Data Format (AAMA) (1993), ANSI/AAMA-292, American National Standards Institute, Inc., 3 September. The American Textile Partnership (AMTEX) (1996), DAMA Homepage, http://dama.tis.llnl.gov/, 11 October. Barnard, F., Allison, G.M. and Yang, Y., Guidelines for AIM Development, ISO TC184/SC4 N304 (in press). Davidow, W.H. and Malone, M.S. (1992), The Virtual Corporation: Structuring and Revitalizing the Corporation for the 21st Century, HarperBusiness, New York, NY.

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Fowler, J. (1995), STEP for Data Management, Exchange and Sharing, Technology Appraisals Ltd, Twickenham. Hunter, A. (1990), Quick Response in Apparel Manufacturing: A Survey of the American Scene, The Textile Institute, UK, Chapter 12, “Technology”. Lee, Y.T. (1995), Extensions of the Prototype Application Protocol for Ready-to-Wear Apparel Pattern-Making, National Institute of Standards and Technology, NISTIR 5727, October5. McCartney, J. and Hinds, B.K. (1992), “Computer-aided design of garments using digitized threedimensional surfaces”, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, v. 206 n B 3, pp. 199-206. Moncarz, H.T. and Lee, Y.T. (1993), “Report on scoping the apparel manufacturing enterprise”, International Journal of Clothing Science and Technology, Vol. 5 Nos 4/5. The NIIIP Reference Architecture (1995), The National Industrial Information Infrastructure Protocols Consortium, December. See also: NIIIP Homepage, http://www.niiip.org/ Okabe, H., Imaok, H., Tomiha, T. and Niwayaa, H. (1992), “Three dimensional apparel CAD system”, 19th Annual ACM Conference on Computer Graphics and Interactive Techniques, SIGGRAPH ’92, Chicago, IL, 26-31 July. Schenck, D. and Wilson, P. (1994), Information Modelling: The EXPRESS Way, Oxford University Press, New York, NY, STEP.

Communications

Communications

Assembling textile structures: wear simulation J.P. Domingues Universidade da Beira Interior, Covihá, Portugal

A.M. Manich, R.M. Sauri

75 Received June 1995 Revised April 1996

Spanish Council for Scientific Research, Research & Development Center of Barcelona, Barcelona, Spain, and

A. Barella Real Academia de Ciencias y Artes, Barcelona, Spain Introduction Tests of fatigue simulation concerning seams, within the mechanics of assembling textile structures, have not often been carried out. On the contrary, this sort of study is more current in other technological fields[1] and in textiles concerning fibre yarn and fabrics (see, for instance, [2]). Maybe the most relevant antecedents concern determined aspects of compound textile structures, named garments, in which simulation techniques to predict the wear performance were applied[3-5]. The goal of the present work is the study of the wear simulation by starting from a different basis: standardized seams were performed on a total of 40 fabrics[6] which were submitted to a series of fatigue-simulation cycles including: washing, drying, submission to a static mechanical load under determined characteristics and steam ironing. Parameters analysed after successive cycles were: the fabric strength and elongation to break; the seam’s strength and slippage; the seam’s efficiency; the seam’s opening limit and the modulus at both 1mm and at break. The experiment As previously stated, 40 fabrics made from wool or blends containing wool (except two cases), the characteristics of which are indicated in Table I, were used in the experiments. Seams type 1.01.01 by using the 301 stitch and with a density of four stitches/cm were performed in each fabric. Samples consisted of three specimen tests sewn in the warp direction and other three sewn in the weft direction. Sewing thread characteristics are indicated in Table II. This article was presented as a paper at the IWTO Technical Committee Meeting held in December 1994 in Nice. The authors would like to thank the Portuguese and Spanish governments for their financial support through the JNICT (Ciencia Programme), DGICYT (PB 90-0097) and JNICT/CSIC Project “Estudios de fiabilidad de la unión de estructuras textiles compuestas”.

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Table I. Some fabric characteristics

Warp yarns Threads Twist Linear in fabric level density (ends/cm) (tpm) (tex)

Reference no. Composition

Weave

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Twill 12 Twill 4 Twill 3 Twill 3 Twill 8 Plain Twill 4 Twill 4 Twill 4 Twill 12 Twill 4 Twill 4 Twill 3 Sateen 5 Twill 3 Plain Twill 4 Twill 4 Twill 4 Twill 4 Twill 4 Twill 4 Plain Twill 12 Twill 4 Plain Crêpe Twill 3 Plain Plain Twill 4 Twill 3 Crêpe Twill 6 Twill 4 Com. twill Twill 4 Plain Crêpe Plain

WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO 100 per cent WO/PES 60/40 per cent WO/PES 60/40 per cent WO/PES 60/40 per cent WO/VISC 30/70 per cent WO/VISC 30/70 per cent WO/VISC 30/70 per cent 50%VI/19PE/16WO/5LI 47VI/22PE/19WO/12LI 47VI/22PE/19WO/12LI 47VI/22PE/19WO/12LI 47VI/22PE/19WO/12LI 35VI/30PE/25WO/10LI WO/PES 35/65 per cent WO/PES 50/50 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent WO/PES 55/45 per cent VISC/LIN 80/20 per cent VISC/LIN 80/20 per cent

20 18 22 36 10 19 14 7 7 20 20 24 30 32 30 19 20 20 20 20 20 20 20 22 20 22 26 32 22 19 26 33 18 24 24 38 33 19 18 20

632 50.00 800 25.00 610 40.00 670 33.33 260 111.1 610 40.00 445 83.33 321 142.9 218 166.7 632 50.00 465 55.00 610 40.00 610 40.00 610 40.00 610 40.00 610 40.00 572 95.24 572 95.24 572 95.24 533 55.56 572 95.24 572 95.24 610 40.00 610 40.00 610 40.00 670 33.33 610 40.00 610 40.00 670 33.33 610 40.00 610 40.00 720 28.57 800 25.00 610 40.00 610 40.00 610 40.00 670 33.33 610 40.00 533 55.56 533 55.56

Weft yarns Threads Twist Linear in fabric level density (picks/cm) (tpm) (tex) 20 27 22 21 7 19 12 7 7 20 19 24 18 26 23 20 17 20 19 19 19 19 20 23 20 20 23 19 22 18 24 24 28 21 24 22 20 19 18 17

632 800 610 670 321 610 445 321 218 632 465 610 610 800 800 610 572 572 572 610 572 572 520 610 610 670 520 520 558 610 610 720 800 610 610 610 1050 1050 533 533

50.00 25.00 40.00 33.33 142.9 40.00 83.33 142.9 166.7 50.00 55.56 40.00 40.00 25.00 25.00 40.00 95.24 95.24 95.24 40.00 95.24 95.24 41.67 40.00 40.00 33.33 41.67 41.67 64.52 40.00 40.00 28.57 25.00 40.00 40.00 40.00 37.04 37.04 55.56 55.56

Characteristics Linear density (tex) Retwist (t/m) Breaking load (cN) Breaking elongation (per cent) Breaking work (cN.cm) Tenacity (cN/tex) Breaking time (s) Modulus (0-5 per cent) (cN/tex) Thick points (µm) Thin points (µm) Neps (µm) Unevenness (CV per cent)

Values 27.77 972 Z 1,034.61 19.76 5,073.13 37.25 21.19 189.60 2 0 8 6.33

The systematic pursuit of the process consisted in testing the specimens after each of the cycles indicated as follows: 0-1-2-3-4-5-10-15-20. This means the total test of 2,160 specimens and the calculation of 720 mean values for each analysed parameter. It is useless to list all the results here. If necessary, they are stated in reference [6]. In Figure 1, we have represented schematically the fatigue cycle’s process. Following this scheme, a summarized description of each phase of the cycle will be given. Washing Washing was carried out by means of a home washing machine by selecting a programme with a reduced mechanical action, especially for woollen fabrics[7]. Conditions were: •

Washing. Horizontal axis and front loading drum. First level filling time: 118 seconds. Second level filling time: 71 seconds. Clockwise movement time: 5 seconds. Anticlockwise movement time: 5 seconds. Stop time between movement inversion senses: 20 seconds. Water emptying time: 114 seconds. Overall washing time: 956 seconds. Temperature: 30˚C.

•

Rinsing. Three rinses were carried out. First level filling time: 168 seconds. Second level filling time: 100 seconds. Clockwise and anticlockwise movement time and stop time: as in the washing stage. Water emptying time: 200 seconds. During the third rinsing there is no emptying. Overall rinsing time 480 + 480 + 240 seconds.

•

Centrifugation. With simultaneous third rinse water. Direct and inverse movement times: 5 seconds. Stop time: 20 seconds. Overall centrifugation time: 202 seconds. Stop and emptying time: 200 seconds.

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Table II. Sewing thread (core spun polyester/cotton yarn) characteristics

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Start Washing Drying

78

Mechanical fatigue Ironing No

Fatigue cycles reached? Yes Mechanical testing

Seam slippage simulation

Figure 1. Scheme of the fatigue cycle process

End

•

• •

•

Detergent. The applied detergent was the same for each wash. Concentration was varied according to the specimen mass. The detergent type was the one recommended by the IWS (with a percentage of a non-ionic surfactant lower than 5 per cent and a percentage of an anionic surfactant between 15 and 30 per cent). Drying. Specimens were hung vertically without tensions after washing and rinsing for 24 hours at a temperature of 30˚C. Mechanical fatigue. After drying, specimens were submitted to a 2.5daN/cm static mechanical load for 30 minutes, by means of an expressly designed device. Ironing. A steam iron device was used, working on a table with air suction, Temperature: 110˚C. Time: 3 seconds.

Determination of the specimen test dimensional variations The applied standard corresponds to reference [7]. This operation aims to determine the dimensional variations suffered by the specimens tested during the fatigue process, and especially those due to the mechanical and chemical action of the successive washings.

Specimens were marked on the opposite side to the seam and two parallel Communications lines 100mm apart were drawn. Three values in the warp direction and three values in the weft direction were determined for each fabric. Measurements were carried out at the end of each of the cycles involving a strength test (namely first, second, third, fourth, fifth, tenth, fifteenth and twentieth) and before this test. Values obtained were used for an ulterior correction of the 79 specimen’s dimensions during the calculation of the responses to compensate for the elongation and shrinking effects suffered by the fabrics which could affect the fabric and/or seam strength and elongation or slippage. Determination of the fabric strength and breaking elongation and seam strength and slippage Strength tests were carried out according to a modus operandi [6,8] which is a variant of the ISO standard. This test applies the “grab” technique and was carried out by means of a computerized “Instron” strength tester. The same instrument was used for the simulation of the loads that are supported by seams and produce these successive openings (from 1mm to 6mm in 1mm steps). The values for the obtained loads for the successive openings were corrected by means of a compensatory value for the initial load of 0.5daN as stated in the applied standard. In all cases the jaw’s displacement was 300mm per minute. The specimen’s length was 75mm and the specimen’s surface 100mm × 150mm. All tests were carried out in a standardized atmosphere (65 ± 2 per cent RH and 20 ± 2˚C). Specimens were maintained in such atmosphere for at least 48 hours. Definitions of elastic parameters in relation to seams •

Seam breaking strength: value of the load supported by the seam corresponding to the break, expressed in daN. When this value is given by warp this means that the seam follows the weft direction and vice versa.

•

Seam breaking slippage: value of the slippage attained by the seam zone in the fabric yarns, in the seam or in both places at the breaking point. When this value expressed in mm is given by warp, this means that the seam follows the weft direction and vice versa.

•

Seam slippage: slippage due to the fabric warp yarns sliding, to the seam sliding or both simultaneously expressed in mm. When this value is given by warp this means that the seam follows the weft direction and vice versa.

•

Seam efficiency: ratio between the seam-breaking load and the fabricbreaking load expressed as a percentage. This parameter allows evaluation of the fabric strength variations due to the seam introduction.

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•

Opening limit: seam opening in mm which corresponds to the maximum load supported by the seam before breaking, obtained by computer simulation. The load simulation is corrected by means of a compensation factor for the fabric. The produced opening can vary between 0 and 6mm in 1mm steps.

80

•

1mm modulus. This value is indicated by the A × B parameter and gives the tangent value to the curve defined by the Y = A.X B function that represents the seam’s load-elongation relationships. This parameter is obtained when X corresponds to a 1mm seam opening.

•

Seam-breaking modulus: ratio between the seam-breaking load and the seam slippage in the breaking point expressed in cN/mm.

Experiment results and discussion It has been stated earlier that it would be useless to reproduce the large number of experimental values. It has been considered preferable to go directly to the results of their statistical analysis. Eight ANOVAS were carried out, one for each considered parameter: fabric strength and break elongation; seam strength and slippage; seam efficiency; seam opening limit and both 1mm and breaking modulus. In addition, some of the results will appear in a graphical form during the discussions. The ANOVAS have separated the: •

main effects: seam direction (with 1 degree of freedom (df)) and cycles (with 8df);

•

interaction sense × cycles (with 8df);

•

residual variance (with 702df but occasionally a few anomalous values were discarded).

For the sake of brevity, only a summary of the ANOVAS in terms of significance is included in Table III. Fabric strength Table III shows the existence of highly significant differences (at 1 per cent level) between the warp and weft directions, whereas the number of cycles does not affect the parameter significantly. There are no significant interactions. The mean strength in warp direction was 46.57 ± 1.61daN, whereas weft direction figures were 37.03 ± 1.61daN at (95 per cent confidence intervals for the mean values). Figure 2 shows the evolution of the strength both for warp and weft directions, during all the experiment (20 fatigue cycles). It can be observed that, in relative terms, the strength in the warp direction shows a loss more marked than in the weft direction. The loss of strength in 20 fatigue cycles represents more than 5 per cent (almost 6 per cent) on average (near 8.7 per cent in the warp direction and 1.3 per cent in weft direction).

Main effects Parameters Fabric strength Fabric-breaking elongation Seam strength Seam slippage Seam efficiency Opening limit 1mm modulus Breaking modulus

Seam sense Significance (%)

F

Interaction Cycles Significance (%)

F

F

Significance (%)

64.73

1

0.19

None

0.15

None

15.32 13.51 2.80 18.52 4.54 14.59 8.36

1 1 10 1 5 1 1

15.13 5.04 2.96 0.75 6.71 12.18 2.67

1 1 1 None 1 1 1

0.22 0.22 0.12 0.04 0.46 0.40 0.56

None None None None None None None

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Table III. Summary of the ANOVAS

Fabric strength (daN) 50 48 46 44 42 Key

40

Warp Weft

38 36 0 1 2 3 4 Fatigue cycles

5 10 15 20

Fabric-breaking elongation Here, highly significant effects (at the 1 per cent level) are verified for both direction and cycles. Interaction is not significant. Figure 3 shows the elongation evolution in the function of the number fatigue cycles. Initially the fabric-breaking elongation was, on average, 28.32 ± 0.80mm in the warp direction and 26.08 ± 0.80mm in the weft direction. In the figure, a decreasing trend can be observed up to four or five cycles (warp direction or weft direction). At this point, the tendency suddenly changes and for ten or more fatigue cycles an increase of the elongation is observed up to the end of the experiment. The first trend could be due to a dimensional change of the specimen, maybe by wool felting. The second trend seems to be explained by the loss of consistency

Figure 2. Influence of the fatigue cycle on fabric strength

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Fabric-breaking elongation (mm) 37 Key Warp 35 Weft 33

82

31 29 27

Figure 3. Influence of the fatigue cycles on fabricbreaking elongation

25 23 0 1 2 3 4 Fatigue cycles

5 10 15 20

due to the structural modifications suffered by the fabric and yarns. In the first phase, the elongation loss in the weft direction is greater than in the warp direction, due possibly to the lesser fabric weft count with a greater probability of entanglements and weft felting that oppose the elongation. The final elongation increase for the 20 fatigue cycles is of the order of 34 per cent in the warp direction and 25 per cent in the weft direction. Seam strength The seam direction (warp or weft) produces highly significant (at the 1 per cent level) differences but the number of fatigue cycles gives differences only significant at the 5 per cent level. Interaction is not significant. Average values for the warp and weft directions are, respectively, 14.35 ± 0.27daN and 13.64 ± 0.27 daN (always with 95 per cent confidence limits). Figure 4 shows the parameter evolution during the 20 fatigue cycles. Here the trend is characterized by a strength increase and this is more accentuated for the weft direction than for the warp direction. This trend could be justified by the fabric dimensional variations and the entanglement between fabric yarns and sewing thread. Increases suffered during the experiment were 11.5 per cent and 14.93 per cent in the warp and weft directions, respectively. Seam slippage Both the main effects are significant: at the 10 per cent level for the seam direction and at the 1 per cent level for the cycles, without significant interaction. The experiment mean values were 16.02 ± 0.80mm in warp direction and 17.10 ± 0.80mm in weft direction (95 per cent confidence limits), respectively. Figure 5 shows the observed trends during 20 washing cycles. A phenomenon similar to the one observed for the fabric-breaking elongation has been found here: a decrease up to the fourth or fifth cycle and then an increase

until the end of the experiment, very marked after the tenth cycle. The final Communications values are very near to the original ones for weft direction seams but greater for warp direction seams. Respective differences were: 10.72 per cent and 25.76 per cent. In this instance, it is found that slippage is higher for the weft direction seams, in which there is a higher fabric contraction that favours the fabric yarns felting and the entanglement between fabric yarns and sewing thread; thus the 83 forces that oppose slippage diminish it when the seams are in the warp direction. On the other hand, the tendency – first to decrease and then increase – can be attributed to dimensional variations (such as contraction) in the first case and to structural fabric modification (higher felting and yarn disorder) in the second. Seam strength (daN) 16

15

14

13

Key Warp Weft

12 0 1 2 3 4 Fatigue cycles

5 10 15 20

Figure 4. Influence of the fatigue cycles on seam strength

Seam slippage (mm) 20 19 18 17 16 Key

15

Warp Weft

14 0 1 2 3 4 Fatigue cycles

5 10 15 20

Figure 5. Influence of the fatigue cycles on seam slippage

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Seam efficiency Only significant differences are shown (at the 1 per cent level) for the seam direction. Neither cycle or interaction is significant. Mean experimental values are 36.79 ± 2.33 per cent for the warp direction and 44.01 ± 2.33 per cent for the weft direction seams (95 per cent confidence limits). Figure 6 shows the observed trends that are growing for both warp and weft direction seams. Efficiency level is higher for the weft direction seams. Differences between the start and the end of the experiment are +23.58 per cent and +14.38 per cent respectively for warp and weft direction seams. The explanation for this evolution is involved in the parameter definition and, thus, determined by both the seam and fabric strengths. Seam opening limit Both the seam direction and the cycles are highly significant at the 5 per cent level. Interaction is not significant. Mean values were, respectively, 3.29 ± 0.4mm for warp direction seams and 3.51 ± 0.14mm for weft direction seams. It can be seen that this parameter is slightly higher in the weft direction seams. Figure 7 shows that the trend is markedly downward when the number of fatigue cycles increases. The final value was –23 per cent for warp direction seams and –32.9 per cent for weft direction seams. These values are practically equal. The explanation is similar to the one given for seams slippage in relation to weft direction values concerning the higher values found in this instance versus warp direction values. The decrease of the parameter in function to the cycle number is related to structural fabric changes that are added progressively and which make it difficult for the seams to open. 1mm modulus (A × B) The two main effects are highly significant (at the 1 per cent level) but the interaction is not significant. Mean values for the experiment were 3.22 ± Seam efficiency (per cent) 48

44

40

36 Figure 6. Influence of the fatigue cycles on seam efficiency

Key Warp Weft

32 0 1 2 3 4 Fatigue cycles

5 10 15 20

0.12daN in the warp direction and 2.90 ± 0.12 daN in the weft direction. In this Communications case the first value is higher. Figure 8 shows the evolution in function of the fatigue cycles. The trend is ascendant and the increase is +52.7 per cent in the warp direction and +56.6 per cent in the weft direction, respectively. These results are in concordance with those corresponding to the seam strength and they are attributable to an increase in fabric felting, mainly in the seam area. 85 Breaking modulus The main effects are highly significant (at the 1 per cent level), whereas interaction is not significant. Mean values are 0.97 ± 0.03daN/mm for warp direction seams and 0.91 ± 0.03daN/mm for weft direction seams. The first value is slightly higher than the second one. Seam opening limit (mm) 4.3 4 3.7 3.4 3.1

Key Warp Weft

2.8 0 1 2 3 4 Fatigue cycles

5 10 15 20

Figure 7. Influence of the fatigue cycles on seam opening limit

1mm modulus 3.8

3.4

3

2.6

Key Warp Weft

2.2 0 1 2 3 4 Fatigue cycles

5 10 15 20

Figure 8. Influence of the fatigue cycles on seam modulus at 1mm

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Figure 9 shows the evolution of this modulus during the experiment. There is a maximum value for the fourth cycle for both warp and weft directions. Final values are lower than initial ones for warp direction seams (–7 per cent). For weft direction seams the maximum value position is less defined (two “peaks” have emerged for four and ten cycles). Notwithstanding, in this instance the final modulus is higher than the initial one (+9.7 per cent). The explanation of these facts can be based on same arguments put forward for seam slippage. The relaxation of both the fabrics and seams during the intermediate cycles allows greater seam slippage, but then the new structural changes produced in the fabric during the final cycles tend to reverse the trend. Seam rupture modulus 1.05 1 0.95 0.9 Key

0.85 Figure 9. Influence of the fatigue cycles on seam rupture modulus

Warp Weft 0.8 0 1 2 3 4 Fatigue cycles

5 10 15 20

Conclusions Six conclusions can be drawn from this study: (1) The fabric strength and the seam opening limit are greater when the seams follow the warp direction than for seams following the weft direction. In both instances the values decrease from the start to the end of the experiment. (2) The seam strength and the 1mm modulus are greater for seams following the warp direction than for those following the weft direction. Values increase from the start to the end of the experiment. (3) The fabric-breaking elongation is higher for seams performed in the warp direction than for seams following the weft direction. When the number of fatigue cycles increases, the elongation decreases to a minimum value and then rises to the end of the experiment and, at that point, it exceeds the initial values. (4) The seam slippage is higher for the weft direction seams than for the warp direction seams. When the number of fatigue cycles increases the

slippage decreases down to a minimum and then rises up to the end of Communications the experiment, surpassing the initial values. (5) The seam efficiency is greater for the weft direction seams than for the warp direction seams. When the number of fatigue cycles increases, the seam efficiency follows the same trend. (6) The breaking modulus is higher for the warp direction seams than for 87 the weft direction seams. When the fatigue cycles grow, an increase of the modulus is produced up to a maximum value and then it decreases. Final values are higher than initial ones for the warp direction seams. These results have a suitable technological explanation that has been analysed in this paper. References 1. Johnson, L.G., The Statistical Treatment of Fatigue Experiments, Elsevier, Amsterdam, 1974. 2. Barella, A., Memorias de la Real Academia de Ciencias y Artes de Barcelona, Vol. 63 No. 2, 1972, p. 776. 3. Saurí, R.M., Manich, A.M., Llória, J. and Barella, A., “A factorial study of seam resistance: woven and knitted fabrics”, Indian Journal of Textile Research, Vol. 12, 1987, p. 188. 4. Barella, A., Saurí, R.M. and Manich, A.M., “Contribution à l’étude du comportement à l’usage des vêtements et sous-vêtements. 1ère partie: simulation du comportement dynamique”, Bulletin Scientifique de l’Industrie Textile de France, Vol. 13 No. 51, 1984, p. 31. 5. Barella, A., Saurí, R.M., Llória, J. and Manich, A.M., “Contribution à l’étude du comportement à l’usage des vêtements et sous-vêtements. 2eme partie: essai statique et généralisation de la méthode”, Bulletin Scientifique de l’Industrie Textile de France, Vol. 13 No. 52, 1984, p. 43. 6. Domingues, J.P., “Mecânica da uniâo de estructuras têxteis”, PhD thesis, Universidade da Beira Interior, Portugal, 1992. 7. Norma Portuguesa NP 3162, “Têxteis. Determinaçao das variacioes dimensionais, lavagen e secagem domésticas”, 1986. 8. Manich, A.M., Domingues, J.P. and Saurí, R.M., “Comparison between standards for seam woven fabrics’ properties determination”, International Journal of Clothing Science and Technology, Vol. 5, November 1994.

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98 Received August 1995 Revised and accepted October 1996

Two-component multilayered woven fabrics: weaves, properties and computer simulation S.V. Lomov, B.M. Primachenko and N.N. Truevtzev St Petersburg State University of Technology and Design, Russia Introduction Two-component multilayered woven fabrics provide many possibilities for a designer to vary the appearance of garments; introduce features such as bulk, strength and abrasion resistance; produce liningless garments with good hygienic properties; and combine special garment functions (e.g. protective properties) with ergonomic factors. This paper gives examples of such fabrics, reports results of investigations of their properties and briefly presents a computer system for their design. Structure of two-component multilayered fabrics Two-component multilayered fabrics (TCMF) are woven using two interlaced weaves: main and lining. The main weave, which forms the outer surface, gives the desired appearance of the fabric and provides its strength and abrasive resistance. When yarns with special properties are used in this weave, they can give the fabric a protective ability (for example, antiflammable garments or gloves for metallurgists). The lining weave forms the inner fabric surface and provides hygienic properties for the garment. In some cases the situation can be reversed: the lining is made from strong yarns and gives strength to a fabric, and the main layer is woven with bulky yarns and forms a “warm” outer surface.

International Journal of Clothing Science and Technology, Vol. 9 No. 2, 1997, pp. 98-112. © MCB University Press, 0955-6222

Examples of TCMF weaves Design of TCMF weaves can be based on traditional weaves: plain, twill or sateen, stripe and check or Jacquard. Additional effects can be added to the main weave, which forms a face of the fabric, using coloured yarns. Two examples are shown in Figure 1 (cross-section perpendicular to the weft direction). The fabric in Figure 1a has a plain weave as a base. The main weave consists of one, three, four and six warp yarns intersecting with four weft layers; the lining weave consists of two and five warp yarns (two weft layers). Two weaves are connected by the fourth weft layer. The fabric in Figure 1b is based on rib weave. The main weave consists of one, three, four and six warp yarns (three weft layers); the lining weave consists of two and five warp yarns (one weft layer). Two weaves are connected by only one weft yarn in a weave repeat (first weft yarn in fourth layer).

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Figure 1. Examples of plain and rib weaves

Coding of TCMF weaves In Figure 2 the traditional weave patterns for weaves from Figure 1 are shown. These patterns represent the order of weave formation on a loom, but do not give a clear picture of the spatial disposition of yarns in multilayered fabric, which can be provided by a representation of weave similar to Figure 1. Then the method of coding of TCMF weaves is based on its cross-section along warp direction[1,2]. For each warp yarn i a succession of so-called “crossing codes”, w ij , is formed. Here i = 1 … I and j = 1 … J, where I is the number of warps in the weave repeat, and J is the number of weft rows in the weave repeat. If L is the number of weft layers, then the number of weft yarns in a repeat is LJ. In Figure 1a I = 6, J = 4, L = 5, LJ = 20; in Figure 1b I = 6, J = 4, L = 4, LJ = 16. Crossing codes are defined as follows: wij = 0, if warp yarn i crosses the weft row j on the face surface of a fabric; and wij = n, if warp yarn i crosses the weft row j under the weft layer n.

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Figure 2. Traditional weave patterns for weaves from Figure 1

Sets of crossing codes for all warp yarns form weave code matrix W = ||wij||. For example, the code matrices for weaves from Figure 1 are shown in Table I. Note that for traditional one-layer weaves, the code matrix and weave pattern are essentially the same. Properties of two-component multilayered fabrics As examples of TCMF let us consider fabrics with weaves shown in Figure 1 and with different yarns: (1) Main weave – flax; lining weave – cotton (2) Main weave – rayon; lining weave – cotton. Yarn properties are shown in Table II, and properties of the fabrics in Table III. Fabric properties were measured with Russian standard techniques (GOST 3811-72, GOST 12023-66, GOST 3813-72, GOST 18976-73). The remarkable feature of the data shown in Table III is the good tenacity of yarns in the fabrics in spite of a high thickness and high crimp of yarns (crimp of warp yarns is about 15 per cent). The fabric combines good bulk (average density is about 0.3 g/cm3) with a high strength coefficient and high abrasive resistance. Inherent flax and rayon mechanical properties are well preserved in

Figure 1a 0 3 3 2 5 2

2 5 1 0 3 4

0 3 3 2 5 2

2 5 1 0 3 4

Figure 2a 0 4 1 2 3 4

0 4 1 1 3 3

2 3 3 0 4 2

1 3 2 0 4 2

Linear density, tex Twist, tpm Strength, cN Bending rigidity, cN mm2

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Table I. Code matrices for weaves from Figure 1

Flax dyed yarn

Rayon dyed yarn

Cotton raw yarn

64.0 487 1093 9.0

31.0 × 2 500 930 3.1

29.4 × 3 444 947 2.2

the woven structure. High initial crimp is diminished in the process of fabric deformation in tension. Computer aided design of multilayered fabrics Starting with the classical paper by Peirce[3], much work was done in the following decades to create a basis for the development of mechanical models of the internal structure and deformation behaviour of woven fabrics. The principle of energy minimization was introduced by Hearle and Shanahan[4] and de Jong and Postle[5], which provides an efficient tool to solve this problem. The complex description of the interaction of bent yarns in a fabric was incorporated into the software reported by Konopasek[6]. The general features of the simulation of fabric tension, shear and bending were described by Kawabata et al.[7]; Reumann[8] used them in the model of the tension of fabrics with various weaves. The general equations for woven flexible shells as an orthotropic material were written by Cristoffersen[9], Kilby[10], Ridel and Gulin[11] and others. There are also many works dealing with minor particular problems. Research into the mathematical modelling of the structure and properties of fabric structure has been in progress at the St Petersburg State University of Technology and Design over the past few years; results were published

Table II. Properties of yarns

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Table III. Fabric propertiesa

5-layers weave (Figure 1a) Yarns Ends per cm Picks per cm Arcal density, g/m2

Flax + cotton Rayon + cotton 37.1 48.1 43.6 46.4 593 661 (592) (655) Thickness, mm 1.9 1.7 (1.82) (1.66) Strength, N (strip 50 mm 1660 1928 width), warp/weft (1550) (1780) 2151 1941 (2132) (1870) Strength coefficientb, 0.86 0.86 warp/weft 0.90 0.90 Elongation at break, %, 19.5 32.3 warp/weft (18.3) (30.0) 6.3 17.7 (7.1) (18.5) Abrasive resistance, cycles more than 20,000 16426 Note: a Computed properties shown in parentheses b Fabric strength per yarn/yarn strength

4-layers weave (Figure 1b) Flax + cotton Rayon + cotton 36.7 47.9 54.9 53.0 575 691 (650) (680) 2.1 2.1 (1.90) (1.89) 1970 1913 (1830) (1780) 2538 2259 (2510) (2190) 1.0 0.78 0.85 0.91 19.6 24.0 (18.7) (22.7) 7.3 14.2 (7.9) (15.8) more than 20,000 11358

elsewhere[12-16]. Here we will present an outline of the mathematical models used and provide an example of the simulation of TCMF. Objectives The mathematical models which have been developed simulate woven materials with complex 3D structures and enable the user to predict: • geometric properties of the fabric – areal density, thickness, porosity, surface smoothness, etc.; • the view of the fabric cross-sections along warp or weft direction; • permeability properties governed by porosity; • ultimate strength parameters in tension (force and deformation); • tension, shear and bending diagrams; and • geometric properties in the deformed state. The diagrams for three deformation modes (tension, shear and bending) yield the complete description of the mechanical behaviour of a fabric as an orthotropic shell to use in the models of woven structures under complex loading[10,11].

Structure of the model The interlinks in the system of mathematical models and computational methods are shown in Figure 3. The core of this system consists of the method of multilayered woven structure coding (described above) and the model of yarn bending in the elementary interval between two crossings of warp and weft. Combined via the principle of minimum energy into the geometric model of yarns in the fabric, these two models produce methods for computation of the geometric properties of the fabric and form the basis for the description of the mechanical behaviour. We will now briefly describe the components of the structure shown in Figure 3.

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Bent elements of yarns Let us consider the bending of the warp (Figure 4). The cross-sections of weft yarns at its ends are deformed; the coefficients of compression of yarns in woven fabric are well-known[15] and are considered constant. This is the case when we consider the yarns with a significant twist used in TCMF.

Figure 3. Links between models and computational methods

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104

Figure 4. Bending the warp

The problem of determination of yarn shapes within the fabric is divided into two steps. First, yarn crimp height h is considered known and the shape of the bent element of warp between intersections with weft z(x), 0 ≤ x ≤ p, where p is the weft spacing, is computed. The function z(x) must satisfy boundary conditions: z(0) = h/2, z(p) = –h/2, z'(0) = z'(p) = 0 z(x) is approximated by spline of the third order (the solution of the linear energy minimization problem) with the polynomial correction with the unknown factor A: z( x ) = h [1 / 2 – 3( x / p)2 + 4( x / p)3 + A( x / p)2 (( x / p) – 1)2 (( x / p) – 1 / 2 )]

(1)

Factor A in (1) is found from the minimization of the non-linear energy integral: p

∫

0

( z")2  1 + ( z' )2   

5 /2

dx → min

This one-dimensional minimization problem is solved numerically for a set of values h/p; the table of A vs. h/p is then constructed and used in the subsequent calculations. When function (1) is determined, we can compute the characteristic functions of the bent element: average curvature, energy, slope θ, length, etc. as functions of the parameter (h/p). For example, the energy of a bent element will be: p

w = 1 B∫ 2

0

( z")2  1 + ( z' )2   

5 /2

dx =

B

F ( h / p)

(2 )

p

where B is the bending rigidity of a yarn, and F is the dimensionless function tabulated via numerical integration; the transverse force acting on weft yarn in the intersection and due to warp bending Qb can be evaluated as:

Qb≈2w/h

(3)

assuming that the work done by this force Qbh/2 in yarn bending is equal to the energy change w; the length of a bent element is: p

l = ∫  1 + ( z' ) 2   

1/ 2

dx = p (1 + c ( h / p ))

( 4)

0

where the dimensionless function c(h/p) is also tabulated after numerical integration. Geometry of yarns in a fabric We can now sum up all energy functions of all bent elements of all yarns in the weave repeat and compute the total bending energy: WΣ = ∑ ∑ wαWkα + ∑ ∑ wαWe k α k

α k

where α designates any (warp or weft) yarn, and k the bent element on it; the upper indices refer to warp and weft, and energies of the bent elements are computed with equation (2): wαk =

Bα F ( hα / Pαk ) Pαk

Crimp heights h for warp and weft yarns are related; the generalization of Peirce’s equation[3] yields: hWα = ∆Z + (d Wα + d We ) – ( h1We + hWe 2 )/2

(5 )

W α,We

are the vertical dimensions of warp and weft yarns, hWe1,2 are where d crimp heights of weft yarn intersecting with the given warp yarn in the given bent element, ∆Z is the vertical displacement of weft layers for these yarns (∆Z = 0 if these weft yarns belong to the same layer). The minimum energy condition will then be:

∂w ∂WΣ = ∑ ∑ αk = 0 ∂hβ α k ∂hβ

(6 )

for any weft yarn β. From (2), for any bent element:

∂w B = G ( h / p) ∂h p2

(7 )

where the dimensionless function G is tabulated after numerical differentiating F(h/p). Now from (5-7) the equations determining the minimum energy configuration become:

Multilayered woven fabrics

105

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106

–

1 2

∑∑ i

k

α BW i

( ) PikWα

 hWe   hWα  BWe j j i G We  = 0 G + 2  Wα  ∑ ∑ 2     Pik  i k P We  Pjk  jk

( )

(8 )

j = 1…LJ where k is the index for the bent element. The sum for warp includes only bent elements of warp yarn i which has contact with weft yarn j; 1/2 before this sum appears because each weft crimp height hjWe enters the energy expression for the warp twice (see (5)). Equations (5) and (8) constitute a system of I+LJ equations for I+LJ unknown crimp heights h a of warp and weft yarns. From these algebraic equations ha are determined with the iterations method; combined with (1) and the weave coding, the values of ha give the complete description of yarn shapes in the fabric. This description allows us to compute all geometric properties and produce the pictures of cross-sections of fabric along the warp and weft direction, fabric porosity and surface smoothness. Mechanical properties of the fabric Here an algorithm for simulation of the fabric biaxial tension will be discussed. We suppose that mechanical properties of yarns in tension are given in the form T = fα(e), where T is the tension of yarn, e its elongation, and f(e) the tensile diagram, linear or not. Tensile diagrams are stored in the form of spline approximation for all different types of warp and weft yarns in the fabric. To compute the tensile diagram of a fabric, successive deformation steps are considered. For given deformations ewa, ewe of a fabric (along warp and weft) the tension force per unit width of it is computed as follows. Assuming that the deformation is distributed uniformly within the element of a fabric, equations (1-2) for the deformed fabric element are rewritten in the “deformed” Lagrangian co-ordinate system x′y′z′ with the deformation values as the parameters in the transformation: (x,y,z)→(x′y′z′ ) For the tensile deformation in x and y directions this leads to the simple transformation (dashed symbols denote the deformed state): x'=x(1+ewa), y'=y(1+ewe), z'=z The description of all bent elements of warp and weft yarns in a weave repeat are then built up with new spacing between yarns: p’wa= pwa(1+ewa), p'we= pwe(1+ewe) Lengths of bent elements of warp and weft yarns l′ak are then computed with (4). With deformed lengths of yarns computed, we can evaluate their deformations ea as ' ea = ∑ lak / ∑ lak – 1 k

k

(9)

and compute tension in yarns Ta=fa (ea) from the given tension curves fa (e). To compute crimp heights of weft in the deformed state (warp crimp is determined by weft via (5)) let us consider the energy equation, which expresses the equality of the work done by transverse forces on displacements of intersection points and change of bending energy of yarns for all weft yarns:  

 

wa ∑  –  Q jkwe1 + Q jkwe2  + 2Q(wajk ) δh j = δw we j – ∑ δw( jk ) j = 1… Lj k

(10 )

k

In this equation subscript k is the number of weft bent elements, subscripts 1 and 2 designate two ends of element k, and (jk) designates an element of warp yarn which intersects element k of weft yarn j at the end 1. Qa (a stands for any yarn, warp and weft) are transverse forces, evaluated from Ta and yarn slope θa: (11) Qa = Qab + 2Tasinθa , where the first term designates transverse forces due to bending and computed by (3), and the second forces caused by yarn tension; δha and δwak are changes in crimp height and in bending energy for yarn a and element k; δ w ak is computed as the difference of yarn energy for the undeformed and deformed states with crimp heights ha and ha+δha respectively, determined by (2). Note that forces and energy changes in (10) depend on δ h a because they are determined by the yarn’s crimp in the deformed state, so equation (10) is nonlinear with the complex dependence on δ h a defined by system (8) for the deformed and undeformed state of a fabric. This approach yields the iterative algorithm for “adjusting” crimp heights in the deformed state and transverse forces similar to those used in [7]: (1) Compute yarn spacing in the deformed state. (2) Let δha=0. (3) Compute yarn shapes with crimp heights ha+δha. (4) Compute the deformations of yarns ea with (9) and tensions Ta=fa (ea). (5) Compute new value of δha from (8) with values of transverse forces and bending energies computed with the current δha. (6) Check the convergence of δha; if it is not reached, go to step 3. (7) Compute forces applied to the fabric summing up all tensions in yarns in the fabric repeat. Simulated features of two-component multilayered fabrics Geometry of yarns In Figures 5 and 6 and Table III the results of computer simulation of the described fabrics are shown. There is good agreement between computed and measured parameters of fabrics. Computer simulation allows a technologist not only to predict fabric properties, but also to look “inside” the fabric he designs. TCMF has the following features:

Multilayered woven fabrics

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Figure 5. Computer simulations

(1) Weft rows are not strictly vertical (as they appear in weave representation, see Figure 1). This is due to the fabric motion in the process of weaving and to the natural rigidity of yarns, which follow their paths assuring an equilibrium between warp and weft interaction forces. This displacement of weft yarns and warp and weft crimp results in a fabric which is denser than it appears to be from the weave structure. (2) When a fabric is stretched along the warp, the crimp of warp yarns is considerably diminished (compare Figures 5a and 5b, 6a and 6b). For warp yarns it changes from 14-15 per cent to 7-8 per cent for flax yarns (bright sections on Figures 5 and 6) and from 8-9 per cent to 5-6 per cent for cotton yarns (dark sections). This accounts for a high value of the strength coefficient. At the same time the weft crimp increases; this results in a diminished thickness of fabric when strengthened (by about 20 per cent). (3) Yarns are considerably compressed in a fabric. This high rate of compression is a result of a high yarn crimp in a thick multilayered fabric and therefore of large warp/weft interaction forces in the process of fabric formation on a loom.

Multilayered woven fabrics

109

Figure 6. Computer simulations

(4) The complex woven structure of a fabric can result in unexpected surface patterns (Figures 5c and 6c). To compute these patterns, the section of fabric parallel to its surface at a distance of 0.2 mm from it was analysed and regions of warp and weft yarn above this plane were computed using the geometric model of yarns within the fabric. These dark regions are shown in Figures 5c and 6c. This computation is similar to the “ink test”: ink-covered fabric surface is pressed to a smooth table and the print shows the structure of this surface. The pronounced elongated spots of warp yarns in Figure 6c are clearly suggested by a weave structure, but long weft “arrows” in Figure 5c are difficult to predict without the computation. They are caused by long weft floats: for

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Figure 7. Geometric model of yarns and results of computer simulation of pores

example, weft yarn 1,1 (see Figure 1a) is supported by warp only on boundaries of the weave repeat and therefore lies almost parallel to the fabric surface; its crimp and change of thickness allow it to form a relief above the surface. Porosity of multilayered fabrics As can be expected from the complex weave structure of TCMF, pores formed between yarns in a fabric have a very curved form. Warp spacing for fabrics described in Tables II and III is so small, and warp yarns are placed so close one to another, that there are no pores if one looks at the fabric along the direction

Multilayered woven fabrics

111

Figure 8. Computer simulation of pores

normal to its surface. Nevertheless the fabric has a significant porosity, which manifests itself if the direction of view is inclined. Let us consider for example the first of the fabrics in Table III. A geometric model of yarns in a fabric allows us to produce a picture of pores in a fabric when it is viewed from the direction defined by angles α and β (Figure 7a). The maximum porosity will appear when angle α gives a direction parallel to inclined weft rows; from Figure 5 this angle can be estimated as α = 30°. Results of computer simulation of pores for different β is shown in Figures 7b, 7c and 8. Porosity P and mean pore diameter d were computed by the digital analysis of pore images (Figure 8). The porosity is the ratio of the area S of “white”pores to the total area of the image; mean pore diameter is computed as d = 4S/Π, where Π is the total pore perimeter. This example shows that TCMF can combine high cover level with a considerable porosity and, consequently, good air permeability, providing properties necessary for usage in clothing. Conclusion Two-component multilayered fabrics have a combination of properties which is difficult to achieve in traditional fabrics (bulk combined with good tenacity,

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high cover level with porosity); they can be used in liningless garments and can also cope with ergonomic restrictions when using fibres with special protective properties. The CAD system can be used to help a technologist to choose yarns for warp and weft, fabric weave and picks/ends count to meet demands specified by a particular fabric usage. There are other possible structures of TCMF. When a fabric must be produced with maximum rigidness and density, so-called “compact packed” weaves can be used. In these weaves warp and weft yarns are very close to each other, and are extremely bent and compressed; it is possible to produce fabrics with an average density 0.45 g/cm3 and thickness up to 2 mm. Compact packed fabrics will be a subject of future publications. References 1. Lomov, S.V. and Gusakov, A.V., “The coding of the layered-carcassed weaves”, Textile Technology, No. 4, 1993, pp. 43-50 (in Russian). 2. Lomov, S.V. and Gusakov, A.V., “Modellirung von drei-dimensionallen gewebe strukturen”, Technische-Textillien, Bd. 38, March 1995, pp. 20-1. 3. Peirce, F.T., “The geometry of cloth structure”, Journal of the Textile Institute, Vol. 28 No. 3, 1937, pp. T45-T96. 4. Hearle, J.W.S. and Shanahan, W.J., “An energy method for calculation in fabric mechanics”, Journal of the Textile Institute, Vol. 69 No. 4, 1978, pp. 81-110. 5. de Jong, S. and Postle, R., “Energy optimization method for fabric mechanics”, Mechanics of Flexible Fibre Assemblies, Amsterdam, 1980, pp. 227-41. 6. Konopasek, M., “Textile application of slender body mechanics”, Mechanics of Flexible Fibre Assemblies, Amsterdam, 1980, pp. 293-310. 7. Kawabata, S., Niwa, M. and Kawai, H., “The finite deformation theory of plain weave fabrics”, Journal of the Textile Institute, Vol. 64 No. 1, 1973, pp.47-85. 8. Reumann, R.-D., “Neuartiges Berechnungsverfahren fur das flachenstruktur-abhängige Kraft-Dehnungs-Verhalten textiler Flachengebilde”, Wissenschaftliche Zeitung Technische University of Dresden, Vol. 37 No. 6, 1988, pp.163-9. 9. Cristoffersen, J., “Fabrics: orthotropic materials with a stress-free shear mode”, Journal of Applied Mechanics, Vol. 47 No. 1, 1980, pp.71-4. 10. Kilby, W.F., “Planar stress-strain relationships in woven fabrics”, Journal of the Textile Institute, Vol. 54 No. 1, 1963, pp. T9-T27. 11. Ridel, V.V. and Gulin, B.V., Dynamics of Soft Shells, Nauka, Moscow, 1990 (in Russian). 12. Lomov, S.V., “Description of yarn shape in a woven with splines”, Textile Technology, No. 5, 1990, pp. 49-52 (in Russian). 13. Lomov, S.V. and Mokeev, M.N., “Computing the strength of a bent woven tube under pressure”, Textile Technology, No. 4, 1991, pp. 47-52 (in Russian). 14. Lomov, S.V. and Primachenko, B.M., “Mathematical modelling of tension of a two-layered fabric with a non-linear yarn deformation”, Textile Technology, No. 1, 1992, pp. 49-53 (in Russian). 15. Lomov, S.V., “Computer aided design of multilayered woven structures”, Textile Technology, No. 1, 1993, pp. 40-5; No. 2, 1993, pp. 47-50; No. 3, 1993, pp. 46-9 (in Russian). 16. Lomov, S.V. and Truevtzev, N.N., “A software package for the prediction of woven fabrics’ geometric and mechanical properties”, Fibres & Textiles in Eastern Europe, Vol. 3 No. 2, 1995, pp. 49-52.

Investigation of pressure fields on clothing presses

Pressures on clothing presses

Zbigniew Poli nski ´ and Wlodzimierz Wiec zlak ´ Technical University of Lód z´, Institute of Metrology, Clothing Technology and Non-wovens, Poland Introduction Development of methods for the thermal treatment of clothing products creates new possibilities for use and automation of this technology. The technology of cementing, which permits a decrease in labour consumption and an increase in the treatment quality, is an example. In all these solutions, presses are used. Generally, thermal treatment has the following basic parameters: the temperature and its distribution on the press plates, the pressure with a pressure field, and the time of treatment. In the case of forming processes, the charge dampness is additionally regulated. During treatment these parameters are subject to inspection and control. However, the control methods used are inaccurate, hence the final effects of the treatment can be qualitatively different. There is thus insufficient knowledge of physical processes conditioning the technology of thermal treatment. One of the basic parameters of thermal treatment is the character of a pressure field acting on the charge being treated. It depends on: the construction and structure of the press; the stucture of pressing surfaces, which in most cases have elastic properties, due to the use of appropriate linings; and the elastic properties of the material being pressed. Inspection of the pressure field aims to detect errors caused by the incorrect construction of pressing plates (e.g. bending of the plates while closing), and to confirm compliance of treatment conditions with the specifications. These are, for example, specifications of uniformity of the pressure field or the concentration of pressures on some areas of the charge surface under treatment. Analysis of the literature shows that there is a gap concerning the methods of investigation of the pressure field on clothing presses. The present work aims to fill this gap. The investigations presented here were intended to check to what degree it is possible to control the pressure field of closed-type presses and the role of the lining in shaping the pressure field. To this end a method of investigation of the pressure field has been developed and the effect of physical properties of the most common linings on the formation of the pressure in selected press types has been assessed. Initial considerations Every clothing press is equipped with an elastic lining to ensure the proper pressure of the plates over the whole surface of the press working field. The effect

113 Received June 1995 Revised and accepted October 1996

International Journal of Clothing Science and Technology, Vol. 9 No. 2, 1997, pp. 113-127. © MCB University Press, 0955-6222

IJCST 9,2

114

of their properties on the character of the pressure field has not yet been studied. The theoretical analysis of the present work has been based, in the first approximation, on the assumption that, depending on the press type, the behaviour of the lining can be described by Maxwell equations or Kelvin-Voigt equations. These models can be used for analysing the pressure field in presses of so-called closed and open structure (in closed presses the plates are pressed to each other with a constant force, independent of time; in open presses the distance between the plates is constant, independent of time). Mechanical properties of the elastic lining were described by two characteristics. One was the function: ε = ε (t) at (p = constant) in which:

ε=

∆H H

where: ∆H = the change in the lining thickness (m); H = the initial thickness of the lining H (m); ε = the relative deformation (-); and t = the time (s). The second property of the lining was described as a change in the pressure as a function of time at a fixed initial strain (ε = constant): p = p ( t ) p [ Pa ]; It must be taken into consideration that the press plate surfaces (upper and lower) may not be parallel. With the lining compressed, this out-of-parallelism causes a non-uniform field of pressures of the press. In the loaded press (i.e. with the clothing element under treatment) the thickness of the clothing element being treated varies in different places. In addition, the clothing element does not generally cover the whole working field of the press. Another assumption is that the plates are ideally rigid; the clothing element does not deflect, and deformations are taken over by the lining. Furthermore, phenomena occurring during the closing of the press have been neglected in the considerations, since it is a momentary process compared with the duration of the whole technological cycle. The time of closing of the press should be counted from the moment of contact of the upper plate with the lower plate in any point, to the moment when the surface of contact of the plates does not change in time. For the analysis, model characteristics of relaxation and creep of the elastic lining have been assumed: E p = p0 exp(– t ) (1) η p E (2 ) ε = 0 [1 – exp(– t )] E η

according to the model of a real body, of Maxwell and Kelvin-Voigt, respectively, where: E = the modulus of elasticity; η = the coefficient of viscosity; and p0 = the initial pressure.

Pressures on clothing presses

Analysis of the pressure field during the technological cycle For a description of changes in the linings of “open” presses, the phenomenon of relaxation of stresses can be used. In this case, the condition of the constant distance between the plates in any point of the working field must be fulfilled, i.e. the mean relative deflection of the lining does not depend on time: ε–w = constant (3)

115

–

while the mean pressure p varies. The pressure in any point of the working field of the press can be described by function (1): E p = p0 exp[– (t – t0 )] (4 ) η where: p0 = is the function of the pressure distribution on the working field of the press at the moment t = t0; and t0 = the moment of closing of the press. From formula (4), therefore, the pressure in the open-type press approaches zero at any point with the lapse of time. For a description of the relationship between the deformation and pressures in the lining in “closed” presses, the phenomenon of creep, defined by formula (2) has been employed: p E ε = [1 – exp(– t )]. (5 ) E η Following differentiation, one obtains: ∂ε ∂ε dε = dp + dt . (6 ) ∂p ∂t But: dε dt

vw

is the relative rate of deflection of the lining; thus in general: ∂ε dp ∂ε vw = + . ∂p dt ∂t Taking (5) into account one obtains:

(7 )

IJCST 9,2

1

vw =

[1 – exp(–

E

E

η

dp

t )]

dt

+

p

η

exp(–

E

η

t ).

(8 )

From (8) the rate of change in the pressure in a given point of the press working field can be determined:

116

dp dt

vw – =

1

p

η

E

exp(–

t)

η E

[1 – exp(–

η

E

.

(9 )

t )]

For closed presses general relationships can be formulated: • The sum of rates of changes in the pressure on the pressure field at a given moment in time equals zero: dp (10 ) ∫ ∫ ( ) ds = 0. dt s •

The pressure force of the press plates does not depend on time and is constant: (11) N = ∫ ∫ p ds = constant . s

•

The relative rate of deflection of the lining depends only on time; it does not depend on the position: vw= vw(t). (12)

•

There is a definite distribution of pressure at the moment of closing of the press: (13) ps= p(s,t0). For the pressure distribution given in a discrete manner, and applying dependences (10) and (11) one obtains: n

∑

i =1

vw – 1

pi

η

exp(–

[1 – exp(–

E

E

η

E

η

t) ∆si = 0

(14 )

t )]

n

N = ∑ ∆si pi = N i =1

where: ∆si = the surface of the i-th element of the press working field; pi = the mean pressure on the i-th element; and i = 1, 2, ..., n = the number of elements of the working field surface.

(15 )

Pressures on clothing presses

From (14) the relative rate of deflection of the lining can be determined: n

∑ pi

vw

∆si

i =1

n

η ∑ ∆si

exp(–

E

η

t ).

Substituting (15) into (16) one obtains: E N exp(– t ) η vw = sp η

(16 )

117

(17 )

where: n

s p = ∑ si i =1

is the surface of the press working field. Elementary changes in the pressure in any points of the working field of the press can now be determined from formula (9): E ( p – pi ) η dpi = dt (18 ) E exp( t ) – 1 η where: p=

N

.

sp

–p = constant for the closed-type press. Differential equation (18) can be solved and the fol1owing is obtained: E E ( ps – p )[exp( t0 ) – 1] exp( t ) η η p= p+ (19 ) E E exp( t0 ) [exp( t ) – 1] η η for t >= t0 . Analysing relationships (18) and (19), one can state that: • the elementary changes in the pressure are proportional to the pressure in a given point and the mean pressure; • the elementary changes in the pressure decrease with time; and • for t >> t0 no uniform pressure field is obtained.

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118

In the range to ⇒ 0, the pressure on the working field of the press approaches the mean pressure: E ( ps – p ) [exp( t0 ) – 1] η p= p+ . E exp( t0 ) η It can be proved that in the case of both “open” and “closed “ presses the elastic lining has properties which equalize the pressure during the technological cycle. Assuming that there are two points in which minimum and maximum pressures occur initially, the range of pressures ∆p in time has been investigated. For “closed” presses one has: ∆p = pmax – pmin , (20 )

[exp( ∆p(t ) = ∆p exp(

E

η E

η

t0 ) – 1] exp( t0 ) [exp(

E

η

E

η

t) (21)

t ) – 1]

for t > = t0. From the above therefore, the pressure ranges in time decrease in both cases. Figure 1, for comparison, shows how the relative pressure range for both types of presses for t >= t0 varies. It can be seen that it depends on the η–E ratio of the lining. This effect is considerable for the open-type presses (for real linings η–E amounts to approx. 4 × 10–2 × s–1 i.e. τ = Eη– = 25 sec). After a relatively short time (maximum 1 sec) the pressure field on the closedtype press becomes practically stationary. This property is significant from the point of view of the new method for the measurement of pressure on presses by means of a friction strap. This method requires that the pressure field under investigation should be stationary. Effect of the elastic lining thickness on the pressure field of presses The character of the pressure field of presses is also affected by other parameters of the elastic lining. One of the basic parameters is the lining thickness. To establish the effect of the lining thickness it has been assumed that for the moment t = t0 one has the following data: • the pressure distribution on the press working field p(x, y); and • the characteristics of the lining ε = ε (p). With these assumptions the mean pressure can be determined for a given pressure field:

Pressures on clothing presses

119

Figure 1. Relative losses of pressure as a function of time for presses of “closed” type (a) and “open” type (b)

p=

1 S

∫ ∫ p( x , y )

dx dy

(22 )

s

The distribution of changes in the lining thickness can also be determined: (23) ∆H(x,y) = H ε [p(x,y,)] as well as the mean change in the lining thickness: — –) ∆ H = H ε (p

(24)

The difference in changes in the lining thickness (a common defect in real press linings is out-of-parallelism of the plates, which has been taken into account in the considerations): — ∆H(x,y)–∆ H is a function of the out-of-parallelism of the press plates in relation to the mean change in the elastic lining thickness of the press. For a given press it does not change in time. Thus:

IJCST 9,2

— ∆H(x,y) – ∆ H = H{ε[p(x,y)] – ε( –p )}.

(25)

For small differences in pressures for a given lining, the following can be assumed: k=

120

p( x , y ) – p

ε [ p( x , y )] – ε ( p )

= constant

( 26 )

where k = the coefficient of proportionality. From equations (25) and (26) the following results: p( x , y ) =

k [ ∆H ( x , y ) – ∆H ] H

+ p.

(27 )

From formula (27), it results that, for a fixed function of the out-of-parallelism of the press plates, the pressure distribution approaches the mean pressure with an increase in the lining thickness. The model results obtained show a significant effect of the lining thickness on the character of the press pressure field. By appropriately selecting parameters of the lining the pressure field of the press can be shaped to an extent. It has been proved that the dispersion of pressures on the pressure field decreases with time, that is to say, the greatest occur just after the closing of the press. This is of essential importance in practice, since the thickness and the characteristics ε = ε (p) of the lining are decisive of the character of the pressure field. An appropriately selected elastic lining can lessen the effects of some mechanical defects of the presses themselves, such as some out-of-parallelism at the press plates, or their too low rigidity, which causes the plates to become out-of-parallel only when they are pressed against each other. By theoretically selecting the lining thickness with its given characteristics ε = ε (p), an arbitrarily small, assumed magnitude of the pressure range on the press can be obtained, particularly on the clothing product under treatment. Using linings of different parameters the pressure field can be knowingly shaped, depending on the type of technological operation performed on the press. For example, the operation of the final ironing or the forming of clothes does not necessarily require a uniform pressure distribution. In this work an attempt has been made to solve the problem of cementing clothing elements on the presses of flat working surfaces, by way of example. In this case, a uniform pressure field is advantageous, hence special attention has been paid to the solution to the problem thus stated. To conclude, it should be stated that the following data should be provided in order to characterize the pressure field of a specific press (e.g. for certification of conformity): •

the values of parameters characterizing the pressure field, e.g. the mean pressure, the indices characterizing the pressure dispersion;

•

the elastic lining thickness; and

•

the lining characteristics ε = ε (p).

Results of the measurement of the press pressure field The new measurement method has been used to make a chart of the press working field pressures. The results presented have been obtained from the measurements made on a “closed” press of flat plates, of the LW-45 type of “Protomet” make. The results of the effect of the elastic lining thickness on the character of the press pressure field have been presented. Measurements have been carried out on the press both with and without a clothing element being treated (see Figures 2-4; the position of the elements has been marked with a broken line in Figure 4). In the investigations, linings of foam silicon rubber of the Rorhau make were used. The method permits measurements of pressure to be made at a temperature of the press operation when materials resistant to elevated temperatures (the strap) are used. The following have been assumed as the indices of the pressure field:

Pressures on clothing presses

121

–

•

the mean pressure p ;

•

the pressure range on the press working field R; and

•

the coefficient of pressure variation V.

The results have been presented in Table I. It can be stated that the effect of the lining thickness on the character of the pressure field is considerably greater in

Figure 2. The pressure field of a press of the lateral suspension of the upper plate

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122

Figure 3. The pressure field of a press of the central suspension of the upper plate

Figure 4. The pressure field of a press with glued fabric samples and of the central suspension of the upper plate

a

the case of the press with the clothing element treated. An increase in the lining thickness generally results in a decrease in the pressure range, a decrease in the maximum pressure, an increase in the minimum pressure and a decrease in the coefficient of pressure variation.

No. 1 2 3 4

Lining H ω (mm) (mm/mPa) 6 12 6 12

33.7 67.4 33.7 67.4

Pressure field on the press lining p– R pmax pmin V (kPa) (kPa) (kPa) (kPa) (%) 12.62 12.34 11.02 11.44

19.54 17.91 30.95 26.06

22.80 21.17 30.95 27.69

3.25 3.25 0.00 1.62

32.01 31.29 73.18 52.29

Pressure field on the product p– R pmax pmin V (kPa) (kPa) (kPa) (kPa) (%)

– – – – – – – – – – 17.71 27.60 32.90 5.40 33.50 16.73 14.40 27.50 13.10 23.60

Pressures on clothing presses

123

Table I. The effect of the lining thickness on the pressure field

Appendix: The method of measurement of pressures and investigation of pressure distribution between the clothing press plates Plates are working elements of presses used in the clothing treatment of the cyclic character. The suspension of the lower plate is of the elastic character, while the upper plate is connected rigidly with the closing mechanism. Generally, at least one of the plates is covered with an elastic lining. In the technological process the press plates are heated to a temperature of about 250°C. A schematic diagram of the press is shown in Figure A1.

1

N

2

a

3

∆

Key 1 – The upper plate 2 – The charge 3 – The lining 4 – The lower plate

4

N – The pressure of the plates ∆ – The distance between the upper and lower plate

N = const – the “closed” press

∆ = const – the “open” press

Figure A1. The schematic diagram of the press

IJCST 9,2

The object of the investigation is the pressure field of clothing presses created by the system: •

the upper plate of the press; and

•

the lower plate of the press being at a constant temperature.

When developing the method of measurement of pressure and pressure distribution on clothing presses, the following have been taken into consideration:

124

•

the method of measurement should not greatly affect the character of the press pressure field;

•

it must ensure high reproducibility of results; and

•

it should allow the measurement of pressure and pressure distribution in the idle cycle (without a charge) or the operating cycle.

It can be seen that these requirements are strict, yet only a method which fulfils these conditions can find a use in the investigation of the pressure field of presses. The methods developed previously do not completely meet the above conditions. The method of pressure distribution measurement presented is an indirect method, in which the phenomenon of frictional forces has been used in the following manner. A thin, limp, inextensible band of constant width (over its whole length) is pulled out from the compressed plates of the machine. Figure A2 presents an exemplary measurement field of the machine in the vertical projection, with a friction band. For presses of flat plates, when the dependence of the frictional force of a given pair of bodies can be approximated with a small error by means of Amontons’ law, the following relationship occurs: dF ds

= –2 aµp( s)

(A1)

where: F = the force of pulling of the band (N); s = the distance covered by the band end (m); a = the band width (m); m = the coefficient of kinetic friction; and p (s) = the pressure as a function of the band end position (Pa). One therefore obtains: p( s) = –

1 dF 2 aµ ds

.

(A2)

Formula (A2) can be used in practice after its transformation into the form: p( s) = –

v z kF dl F 2 aµv dl z

.

(A3)

where: vz = the registration rate (m/sec); kF = the force scale (N/m); 1F = the magnitude of swing during the registration of the strap pulling force (m); v = the strap pulling rate (m/sec); and 1z = the registration path (m). To be able to determine the place in which the pressure defined by formula (A3) occurs, the position of the band end must be determined:

a B–B

Pressures on clothing presses

1

2

F

a 3

125

4

y

A

5 6 7

l

a

v

F

B

B

x

O

S

L

Key 1 – The upper plate 5 – The charge 2 – The upper cover 6 – The linning 3 – The measuring strap 7 – The lower plate 4 – The lower cover

s=

v

vz

l z.

Figure A2. The idea of the pressure measurement method

(A4)

It should be noted that the band width affects the accuracy of measurements. The pressure determined by the above method is a linear-mean pressure in relation to the band width. The narrower the band, the greater the accuracy. However, a decrease in the magnitude of the strap pulling force and a limited possibility of the instruments amplifying and processing this decreased signal of the force from the extensometer transducer should then be taken into consideration. It has been assumed that the band width of 10 mm, compared with the dimensions of the investigated press plates, ensures the measurement of pressure with a technologically useful accuracy. To obtain the image of pressure distribution over the whole surface of the plate, the number of measurements must be suited to the plate dimensions (Figure A3). These measurements can be carried out successively.

IJCST 9,2

n

.

126

.

A

. .

a

3

Figure A3. The plan of measurements on the press

2

1

L

The effect of the order of closing and opening cycles of the press will be minimal when the conditions of temperature and pressures stabilize, and the lining has worked for an appropriately long period of time. The number of measurements on the surface investigated depends on the aim of the investigations. For inspection purposes, it is sufficient to make the next measurement at a distance of 0.15-0.2 m from the previous one. For technological and scientific investigations the measurement frequency can be greater, depending on the accuracy assumed. Of course, a system of many measurement paths can be considered and a set of straps covering the whole surface can be pulled out simultaneously. However, this would be rather a complicated manner of measurement and, what is more important, very expensive. The real value of the pressure between the plates of the press can be slightly lower than that obtained by means of the method presented. This is due to the fact that the strap has a definite thickness and it dips into the elastic lining of the press. However, this difference is slight. For example, for a lining of thickness H = 5 × 10 –3m, strap thickness 5 × 10 –5m, and with an assumption that the lining deforms linearly, at maximum pressure for the thickness H = 25 × 10–4m, the estimated error should be less than 2 per cent. This error measurement method can be counted among the systematic errors. The technological process of clothing treatment takes place at definite pressure ranges. Cementing, for example, occurs at about 15-40 kPa. Thus, it is sufficient for the dependence of the friction force on the pressure – measurement strap and the covers – to be tested within a range of 10-70 kPa. As it results from investigations of the friction coefficient, the dependence for the assumed pair of bodies is practically linear within this pressure range and the non-linearity error does not exceed 3 per cent.

It has been estimated that the maximum systematic error of the pressure measurement should not exceed 10 per cent when this method is used. The deviation from Amontons’ law, the measuring path non-linearity error and the effect of the measuring strap thickness have been taken into consideration. It should also be stated that this method is useful for the investigation of the stationary pressure field, i.e. a field that does not depend on time. A schematic diagram of the device is given in Figure A4. The measuring system path is composed of the following elements: •

the extensometer sensor of the force;

•

the extensometer amplifier; and

•

the microcomputer and the recorder connected to it in parallel, for inspection purposes.

7

6

3

Pressures on clothing presses

127

1 2 4

X-Y

>

5

MC

Key 1 – The measuring strap 2 – The plates of the press under investigation 3 – The extensometer sensor 4 – The drawing screw 5 – The drawing screw drive 6 – The extensometer amplifier 7 – The microcomputer and the recorder

The whole path has been calibrated and it has been found that the non-linearity error does not exceed 5 per cent. To obtain successive values of pressures, formula (A3) should be used. It is convenient to process the successive courses of the strap pulling force and then to analyse them. Such an analysis can be carried out by means of an appropriate computer program.

Figure A4. The schematic diagram of the device

IJCST 9,2

Sewability of denim B.K. Behera, S. Chand Indian Institute of Technology, New Delhi, India

128

T.G. Singh and P. Rathee Institute of Home Economics, University of Delhi, New Delhi, India

Received August 1995 Revised and accepted December 1996

International Journal of Clothing Science and Technology, Vol. 9 No. 2, 1997, pp. 128-140. © MCB University Press, 0955-6222

Introduction Fabric quality alone does not fulfil all the criteria for production of high quality garments. The conversion of a two-dimensional fabric into a three-dimensional garment involves many other interactions[1] such as selection of a suitable sewing thread, optimization of sewing parameters, ease of conversion of fabric to garment and actual performance of a sewn fabric during wear of the garment. The selection of sewing thread for a fabric depends on the dimensional and mechanical properties of the fabric and the sewing thread, their compatibility, the sewing process and the end use of the garment[2-11]. Similarly the quality and performance of a sewn garment depends on various factors such as seam strength, slippage, puckering, appearance and yarn severance[4,12]. All these factors combined together contribute to sewability of the fabric which is considered to be one of the most important aspects of clothing science. The study of sewability in clothing manufacture in general and its importance, particularly in denim based clothing, has considerable relevance in today’s advanced garment manufacturing processes. Modern garment manufacturing processes use motorized high-speed sewing machines, which exert very high tensions in the thread and also high forces of penetration of needles in the fabric[10,13]. As a result, both the sewing thread and the yarns in the fabric get abraded/severed during the seaming process. The extent of damage becomes more critical if the fabric being used is of a dense, thick and heavy construction such as denim. At the same time, if the sewing thread is not properly selected with respect to the construction of the fabric and nature of treatment the thread will get during sewing, the seam performance will deteriorate in the final garment. In the context of denim based garments, particularly trousers and jackets, sewing thread is not only used for joining the fabric but also for decorative purposes along the seam line. The thread poses a linear projection on the surface of the garments and is subjected to more abrasion than the garment. Therefore, unless the sewing thread chosen for a denim garment is stronger, it may break before the fabric does. This study evaluated the sewability of denim in relation to the dimensional and mechanical properties of the fabric and sewing threads.

Materials and methods Materials Denim fabrics. Commercially available blue denim, produced by the pioneer denim manufacturers of India, covering a wide range of weights (6.5, 10.0, 12.5, 14.5 and 15.5 oz/yd), and commonly used for clothing, was selected for the study. Sewing threads. Threads of three different compositions and commercially available ticket numbers were selected for sewing of denim fabrics. The details of the selected threads with their codes are given in Table I.

Thread code

Composition

C/10 C/24 C/30 C/50 P/20 P/25 P/30 P/50 P/80 CS/35 CS/50 CS/75

Cotton Cotton Cotton Cotton Spun polyester Spun polyester Spun polyester Spun polyester Spub polyester Core spun Core spun Core spun

Ticket number

Ply

10 24 30 50 20 25 30 50 80 35 50 75

6 6 3 3 4 4 3 3 3 3 2 2

Methods Fabric constructional parameters The fabric thickness was measured according to the ASTM DI777 test method, on the Prolific thickness tester (ESSDIEL). Fabric weight was measured with an electronic weighing balance. End and pick density were measured using the fabric dissection[14] method. Crimp in warp and weft was measured according to ASTM D 3883 test methods, on the Shirley crimp tester. Yarn count was measured using Beesley’s balance. Fabric mechanical properties. The tensile test for measurement of breaking load and breaking elongation was conducted according to the ASTM DI682 test method, on the Instron Tensile Tester. Compressibility was also measured on the Instron Tensile Tester. Flexural rigidity of the fabrics was measured on the Shirley Cyclic Bending Tester. In this experiment, fabric specimens of 25 × 12.5 mm size were tested for determining the curvature scale reading corresponding to various couple scales. The pendulums of different weights were selected for testing different samples. The specimen was bent up to a maximum curvature of 3 cm–1. Five tests were performed for each sample and the average value for elastic flexural rigidity and coercive couple of frictional stiffness (Go, dyne cm2/cm) were calculated using the following formulae:

Sewability of denim

129

Table I. Sewing thread details

IJCST 9,2

Go =

F ( As – AR – AQ )

.

2

Coercive couple of frictional stiffness Co dyne cm/cm

130

Co =

F ( AR – Ap ) 2

where: F = pendulum factor; F = 200 dyne cm/cm for 6.5 oz/yd2 = 5000 dyne cm/cm for 10, 12.5, 14.5, 15.5 oz/yd2; AP, AQ, AR, AS = couple scale readings corresponding to zero curvature after first reversal, –1.0 cm–1 curvature, zero curvature after second reversal, and +10 cm–1 curvature, respectively. Sewing thread properties. All tests for the analysis of sewing thread properties such as diameter, shrinkage, strength and elongation were carried out according to ASTM D 204 test method for testing of sewing threads. Diameter was measured on the Prolific Thickness Tester (ESSDIEL). Breaking load and elongation were measured on the CRE tensile testing machine. Sewing. Sewing was done on the Singer (industrial) sewing machine 191 D x 258 A. The standard sewing conditions maintained for the test sample were as follows: • Machine speed: 2,500 stitches/min. • Seam geometry: plain lock stitch seam. • Linear stitch density: eight stitches/inch. • Needle size: three different needle sizes were used according to the fabric thickness and weight. Needle no. 16 was used for light weight (6.5 oz/yd2) fabric. For medium weight (10 and 12.5 oz/yd2) and heavy weight (14.5, 15.5 oz/yd2) fabrics needle nos 18 and 20 were used respectively. The tension screw on the bobbin case was adjusted until the bobbin and its case just moved down the thread, i.e. the thread tension was very nearly equal to the weight of the bobbin and its case[15]. The upper thread tension was then set to give a balanced stitch. A seam allowance of 1 inch was given for all the samples. Dimensional stability of sewn samples. Half of the six sewn samples were laundered to determine the effect of laundering on the seam appearance and performance characteristics. Laundering was carried out with the following specifications: • water: 20 times the weight of the fabric; • soap: 5 g/l water; • temperature: 40°C; and • time: 30 min.

Seam quality analysis. Analysis of the seam quality[16,2] was done by studying seam strength, pucker, slippage, yarn severance and seam appearance. Seam strength was measured according to the ASTM-DI683 test method for failure in sewn seams of woven fabrics, on the Instron tensile tester. Seam efficiency was calculated using the following formula: Seam Tensile Strength Seam efficiency(%) = × 100. Fabric Tensile Strength The seam slippage test was carried conducted according to ASTM DI683. Seam slippage was obtained by calculating the difference in elongation of the fabric from that of a fabric with a seam in it on the Instron tensile tester. Seam pucker was determined by measuring the difference in fabric and seam thickness under a constant compressive load[17] on the Instron tester. The seam thickness strain was calculated using the formula: t – 2t Thickness Strain (%) = s × 100 2t where ts is seam thickness, and t is fabric thickness. The seam damage test was conducted according to the ASTM-DI908 test method for needle related damage due to sewing in woven fabrics, on the Hiscope 3D measuring system with a magnification of 100 in reflection mode. For each sample, needle cutting index was determined using the following formula: No. of yarns cut/inch Needle Cutting Index (%) = × 100. No of yarns in fabric/inch Results and discussion The fabric performance for the engineering of clothing manufacture is known as tailorability which is usually characterized by formability and sewability[11]. Formability is related to the minimum compression sustainable by a fabric before the onset of buckling[16,18,19] whereas sewability is the ease of formation of shell structures and style and absence of fabric distortion and damage. Since the fabric undergoes deformation due to applications of stress in the making up process, mechanical properties of the fabric play an important role in the study of sewability. As sewing thread is a vital component of sewn fabric, the properties of sewing threads must be analysed in a study of sewability. Fabric dimensional properties The dimensional parameters of the fabrics are given in Table II. It can be seen that, with the exception of light weight denim (6.5 oz/yd2), all fabrics fall within a close range of fabric thread density. Increase in mass has been obtained by incorporating coarser yarn and interlacement with longer floats. The results also show that the fabric thickness and cover factor increase with increase in the areal density of the fabric.

Sewability of denim

131

IJCST 9,2

Areal density Fabricsett (Ne) Yarn count Thickness Crimp (%) Cover factor (oz/yd2) Nominal Actual EPI PPI Warp Weft Weave (mm) Warp Weft Warp Weft Cloth 6.5

6.5

86

49

14

10

11.9

70

43

6

8

12.5

13.1

69

40

6

10

Table II. Dimensional parameters 14.5 15.5 of the fabrics

16.9

73

44

5.1

7

Twill 3/1

0.979

18.5

8.7

14.3

6.2

17.0

71

48

5

6

Twill 3/1

0.935

18.3

5.6

14.2

8

132

16.3 Twill 2/1

0.491

11.3

8.1

6.1

3

8.5

Twill 2/1

0.755

14.9

5.6

11.6

5.3 14.8

Twill 3/1

0.913

9.1

6

11.5

4

13.8 7.4 18.1

Fabric mechanical properties Fabric mechanical properties such as bending stiffness, compressibility and tensile properties are given in Table III. The results show that the breaking strength and breaking elongation of the fabrics increase with the increase of fabric areal density, in the warp direction. The flexural rigidity and coercive couple of heavy denim fabrics are substantially higher than the low weight denim fabrics; however no clear-cut trend with the increase of fabric areal density has been found. The decrease in compressibility of the fabrics with the increase in fabric areal density could be due to the increasing cover factor of the fabric which hinders the yarn mobility within the fabric structure due to jamming. Dimensional properties of sewing thread The dimensional properties of sewing threads of various compositions and ticket numbers are given in Table IV. It may be seen that the diameter of the thread for similar ticket numbers in all compositions is highest for corespun threads, followed by spun polyester and cotton threads. This is due to the fact that polyester fibres have more specific volume compared to cotton fibre. The highest diameter of corespun thread is due to its composite structure, in which cotton sheath is loosely wrapped around the filament, resulting in a bulkier structure. Since the threads taken for the study are finished threads, they have undergone all probable dimensional changes during their processing and

Fabric wt. (oz/yd2)

Table III. Fabric mechnical properties

6.5 10 12.5 14.5 15.5

Breaking strength (KN) 0.267 0.353 0.384 0.528 0.689

Tensile properties Breaking Work of extension (%) rupture (J) 13.5 13.3 13.4 15.5 15.6

1.80 2.35 2.57 4.1 5.37

Bending stiffness Go*

Co*

Compressibility(%)

33 410 575 405 470

34 650 600 925 610

20.79 15.06 15.17 12.17 11.42

Thread type C/10 C/24 C/30 C/50 P/20 P/25 P/30 P/50 P/80 CS/35 CS/50 CS/75

Ply

Diameter (mm)

6 6 3 3 4 4 3 3 3 3 2 2

0.38 0.29 0.25 0.20 0.44 0.37 0.29 0.22 0.19 0.38 0.29 0.22

Shrinkage (%) 0.3 2.2 0.4 0.3 0 0 0 0.1 0 0 0 0

therefore do not show any further perceptible change for polyester and corespun threads. However, 100 per cent cotton thread, being a cellulosic material, exhibits some amount of shrinkage after washing. Mechanical properties of sewing threads Table V shows the breaking strength, breaking extension, and work of rupture of the sewing threads tested in the single strand and loop method. It can be seen that among the three different compositions, corespun threads show the highest values of breaking strength and extension, compared to polyester and cotton threads. Cotton threads have the lowest value of breaking strength and extension. The high strength of corespun and polyester threads is attributed to the presence of stronger filaments in the core and stronger polyester fibres, respectively[5]. Sewability Sewability is defined as the ability and ease with which fabric components can be qualitatively and quantitatively seamed together, to convert a garment[4]. The characteristics of a high-quality seam are strength, elasticity, durability, stability and appearance[4,5]. These qualities can be measured by seam parameters such as seam efficiency, pucker, slippage, damage and appearance. Seam efficiency. The results for seam efficiency of five different denim fabrics sewn with a wide range of threads with respect to composition and linear density (ticket number) are shown in Table VI. It can be seen that the seam efficiency of the lightest fabric invariably increases with the increase in ticket number (i.e. decrease of linear density) of the sewing threads irrespective of their composition. Contrary to this, the seam efficiency of the heaviest denims (14.5 and 15.5 oz/yd2) significantly decreases with the increase in ticket number for all three compositions of the threads. The seam efficiency of the remaining medium weight denims shows a mixed trend under the identical sewing conditions as with light and heavy denims.

Sewability of denim

133

Table IV. Sewing thread dimensional properties

IJCST 9,2 Sewing thread code

134

C/10 C/24 C/30 C/50 P/20 P/25 P/30 P/50 P/80 CS/35 CS/50 CS/75

Table V. Tensile properties of sewing threads

Breaking strength (kg)

Single strand Breaking extension (%)

2.28 (3.6)a 1.88 (4.3) 1.28 (6.2) 0.89 (11.5) 5.29 (7.2) 5.07 (3.5) 3.69 (5.6) 1.04 (7.1) 1.32 (5.3) 4.49 (2.2) 3.29 (4.2) 1.83 (1.4)

8.22 (9) 6.22 (3.9) 6.64 (5.4) 5.27 (10.1) 20.32 (4.4) 18.77 (2.9) 17.18 (3.2) 16.80 (3.8) 19.38 (4.4) 24.40 (2.9) 24.20 (4.8) 19.30 (2.9)

Work of rupture (kgfmm)

Breaking strength (kg)

Loop Breaking extension (%)

5.2

3.90 (6.2) 2.26 (7.1) 3.22 (6.5) 1.49 (15.1) 7.71 (8.6) 5.59 (7.9) 5.74 (8.6) 1.79 (8.3) 2.06 (8.1) 6.40 (4.9) 4.34 (4.8) 2.21 (5.5)

6.37 (7.7) 5.18 (6.2) 5.11 (6) 3.56 (13.1) 16.18 (4.8) 13.85 (4.3) 14.16 (4.9) 15.30 (5.2) 15.36 (4.9) 18.50 (3.5) 16.30 (2.7) 11.60 (6.3)

5.8 4.2 2.3 53.7 47.6 31.7 8.7 12.8 54.7 39.8 17.6

Work of rupture (kgfmm) 12.4 5.8 5.7 2.7 62.4 38.7 40.6 13.7 15.8 58.0 35.3 12.8

Note: All figures in brackets indicate the CV%

a

Seam efficiency largely depends on tensile behaviour of fabric and thread, the combination of fabric and thread, the dimensional and surface characteristics of sewing thread and other machine and process parameters, which are kept constant in this study for all combinations of fabric weight and thread types. Since the breaking strength and extension of finer sewing threads are lower than the coarser threads, the former gives higher seam efficiency when sewn with lower weight denim fabric due to better compatibility of tensile properties. Similarly, the heavier denim fabrics, being more elastic in nature, when sewn with coarse sewing threads, provide higher seam efficiency. If the strength and durability of seams is the major requirement in the final garment, a suitable combination of thread and fabric could be made from their tensile properties in order to achieve an acceptable seam efficiency within a range of 80 per cent or more[4]. In the light of this fact, the results clearly suggest that:

Sewability of denim

Sewing thread – ticket numbers Fabric wt (oz/yd2)

C/10

C/24

C/30

C/50

P/25

P/30

P/50

P/80 CS/35

CS/50

CS/75

6.5 10.0 12.5 14.5 15.5

30.7 93.6 90.1 72.1 65.1

66.0 95.2 85.0 44.4 42.6

90.0 80.1 67.8 39.9 35.0

76.3 50.4 44.0 36.4 28.9

20.2 49.4 47.1 98.5 98.6

37.2 56.6 42.7 94.7 97.2

98.1 73.7 62.9 23.2 23.2

97.5 72.2 73.2 57.2 39.4

26.3 65.0 87.5 85.3 86.0

74.8 69.9 77.0 46.9 45.9

9.9 16.0 18.1 99.8 99.8

135 Table VI. Seam efficiency (%)

•

Light weight denim fabric should be sewn with either fine polyester thread or coarser cotton threads. • Heavy weight denim fabric should be preferably sewn either with coarse corespun threads or coarse polyester threads. • Cotton threads are not suitable for heavy weight denim. • Fine corespun threads are not suitable for denim fabric. Seam pucker. This is a distortion in the surface of a sewn fabric and appears as a swollen effect along the line of the seam[3,11,20]. It is determined by measuring the percentage increase in the thickness of the seamed fabric over the original fabric under a constant load[17,18]. The results for seam pucker before and after wash are given in Tables VII and VIII respectively. It can be seen that puckering Sewing thread – ticket numbers Fabric wt (oz/yd2)

C/10

C/24

C/30

C/50

P/25

P/30

P/50

P/80 CS/35

CS/50

CS/75

6.5 10.0 12.5 14.5 15.5

8.6 13.7 24.6 27.6 29.4

14.4 22.5 36.1 40.0 46.6

8.5 26.5 24.2 30.9 34

3.1 27.9 36.3 38.1 29

15.8 24.5 36.3 45.5 65.7

8.2 33.5 35.5 38.7 35.6

3.7 8.4 13.3 9.1 6.6

0.54 8.6 25.4 45 31.4

8.1 17.2 36.8 28 28.8

3.2 3.6 16 28.7 30.1

CS/50

CS/75

10.2 30.0 24.4 25.2 12.0

4.8 6.6 6.2 17.8 18.0

4.3 41.5 31.2 57.6 50

Table VII. Seam pucker – before wash (%)

Sewing thread – ticket numbers Fabric wt (oz/yd2)

C/10

C/24

C/30

C/50

P/25

P/30

P/50

6.5 10.0 12.5 14.5 15.5

10.2 10.4 28.0 21.0 25.0

8.71 13.3 28.0 30.0 41.0

15.4 20.0 20.7 21.6 28.0

10.2 24.6 15.7 13.6 5.0

10.2 23.3 28.0 10.5 25.0

8.7 12.0 13.6 21.0 21.0

5.1 11.3 8.6 7.8 5.0

P/80 CS/35 2.8 6.0 7.2 5.2 0

6.7 33.3 30.2 12.6 12.0

Table VIII. Seam pucker – after wash (%)

IJCST 9,2

136

consistently increases with the increase in fabric weight irrespective of thread composition and ticket number. The extent of seam pucker is highest for polyester, followed by corespun and cotton thread. Except for cotton thread, heavy weight fabric sewn with coarse threads exhibits very high pucker. It is well-known that seam pucker takes place mainly due to the contractive forces introduced in the seam during sewing[21]. When the contractive force exceeds the buckling resistance of fabric inside a stitch, the fabric starts puckering along the seam line. When the sewing thread penetrates into a heavy weight fabric, it introduces very high contractive force. Therefore, high puckering has been seen in heavy weight fabrics. The results given in Table VIII show that seam pucker after wash for all the fabrics decreases except in the case of 6.5 oz/yd2. This decrease in pucker may be due to the fact that the original seam pucker of the fabric is due to the mechanical restraint in the seam caused by the high cover factor of these fabrics. The pucker developed is basically the deformation of fabric yarns caused by the penetration of the thread and the needle during the sewing operation. After washing the mechanical restraint reduces by relaxation process and the variation in the thickness along the seam line is reduced, resulting in less pucker. The shrinkage in the fabrics with 10, 12.5, 14.5 and 15.5 oz/yd2 is lower compared to 6.5 oz/yd2. Thus the washing process, instead of causing high pucker due to differential shrinkage of fabric and sewing thread, resulted in relaxation of the yarns in the fabric, which accommodated the fabric yarns and the sewing thread inside the fabric structure and reduced the disruption along the seam line. The increase in pucker after wash in the fabric with 6.5 oz/yd2 could be accounted for by the poor dimensional stability of the fabric. As reported[5], even a 2 per cent shrinkage is enough to cause pucker in a fabric. The shrinkage in sewing threads is almost negligible for all the threads except cotton ticket number 24, and this resulted in the differential shrinkage between the fabric and the thread and caused pucker. Seam slippage. A partial or complete loss of seam integrity manifested by yarn slippage parallel to the stitch line is considered as seam slippage. It is caused by pulling out of the yarns in the fabric from the seam under strain and is determined by calculating the difference in the extensibility of the fabric and the seamed fabric. Results for seam slippage are given in Table IX. The combination of low weight fabrics and coarse ticket number threads usually gives high slippage. The effect is more pronounced in corespun threads followed by polyester and cotton threads. In general, with the decrease in the linear density of the thread the seam slippage decreases for 100 per cent polyester threads and corespun threads sewn with low weight fabrics. With heavy weight fabrics the trend is reversed. The highest seam slippage for fabrics sewn with corespun thread may be attributed to incompatible tensile properties of the thread and fabric. High extensibility of corespun threads compared to fabrics resulted in more seam slippage. Fabric sewn with cotton thread gives comparatively lower slippage due to minimum difference of extensibility between the fabrics and the threads.

It may be inferred that the selection of highly extensible polyester based threads should be made more judiciously in order to avoid undesirable seam slippage. Results for seam slippage after wash are given in Table X. The results clearly show an overall decrease in the percentage seam slippage of the sewn fabric after wash for all fabric-thread combinations. This is due to the relaxation taking place during washing, which results in stronger gripping of threads by the fabric providing high frictional resistance during the tensile loading of the seam and hence less slippage. Needle cutting index. The fourth key parameter to evaluate the sewability of fabrics is needle cutting index. It indicates the number of damages of cross threads during sewing operation. Yarns having damage of more than 50 per cent were considered only as a damage. Penetration of needle between two fabric yarns, and mere sliding were not considered as a damage. The results for needle cutting index (damage of the weft yarns) are shown in Table XI. The

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137

Sewing thread – ticket numbers Fabric wt (oz/yd2)

C/10

C/24

C/30

C/50

P/25

P/30

P/50

P/80 CS/35

CS/50

CS/75

6.5 10.0 12.5 14.5 15.5

10.3 0.7 6.4 –1.1 –1.6

5.7 –0.4 –0.3 –4.0 –4.3

–1.8 –1.1 –2.2 –6.1 –6.7

–1.6 –3.2 –4.6 –6.6 –8.3

15 10.9 14.1 4.5 3.0

13.5 9.9 9.2 0.3 0.1

0.5 2.6 –2.7 –7.3 –7.4

1.3 1.9 –2.8 –4.7 –6.7

22.9 3.6 8.7 –0.3 –3.0

–0.8 0 –0.6 –3.5 –5.5

20.3 18.7 15.2 5.7 2.8

Table IX. Seam slippage – before wash (%)

Sewing thread – ticket numbers Fabric wt (oz/yd2)

C/10

C/24

C/30

C/50

P/25

P/30

P/50

P/80 CS/35

CS/50

CS/75

6.5 10.0 12.5 14.5 15.5

4.9 0.7 4.2 –1.6 –1.9

5.0 0.2 0.3 –1.7 –1.7

0 –0.5 –0.5 –2.9 –5.1

–4.3 –3.5 –3.3 –4.2 –5.8

13.4 6.2 6.7 4.0 2.0

3.2 6.4 5.2 1.1 2.9

–0.4 –0.6 –0.9 –3.9 –5.1

–0.7 0.2 –1.3 –3.5 –4.3

5.8 3.0 4.9 0 –0.7

0.1 0.5 0.6 –3.8 –5.0

6.0 8.2 6.8 4.1 1.6

Fabric wt (oz/yd2)

C/10

C/24

C/30

Sewing thread – ticket numbers C/50 P/25 P/30 P/50 P/80 CS/35 CS/50

CS/75

6.5 10 12.5 14.5 15.5

14.8 15.7 15.6 16.5 17.7

4.5 7.5 13.7 14.4 14.5

9.1 11.6 12.2 13.6 16.1

6.6 11.8 9.5 12.5 12.5

7.6 11.6 10.6 13.6 13.5

10.7 13.7 11.0 14.7 15.6

10.2 7.6 12.7 11.2 11.9 9.8 14.2 12.8 14.6 13.0

7.1 10.5 10.0 11.4 11.4

15.3 15.7 15.6 17.0 18.2

8.1 12.5 11.6 13.5 15.3

Table X. Seam slippage – after wash (%)

Table XI. Needle cutting index (%)

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damage is comparatively higher with cotton and corespun threads than 100 per cent polyester threads. It may be observed that the damage invariably decreases with the increase in ticket number. Also the damage increases with the increase of the fabric weight for all thread compositions and ticket numbers. The extent of yarn damage during sewing mainly depends on fabric sett, cover factor, weave, stitch density, thread diameter and surface properties of the sewing thread. The maximum damage in the case of corespun threads is due to higher thread diameter and more surface friction of corespun yarns. The reason for the decrease in damage with the increase in ticket number is attributed to the lower diameter of the thread. The increase in cover factor along with the decrease of compressibility of the fabric with the increase in fabric weight results in a higher value of the needle cutting index. It may be observed from the results that the cover factor is more sensitive to the needle cutting index than fabric weight. The reason for the lower value of the needle cutting index in 12.5 oz/yd2 fabric as compared to 10 oz/yd2 fabric could also be accounted for by the weave structure of the two. The longer float length or lesser number of interlacements in 12.5 oz/yd2 fabric, would permit more mobility of yarns, thus reducing the yarn severance. Seam appearance. Although sewability of the fabric has been quantitatively assessed by seam efficiency, pucker, slippage, and needle cutting index, the appearance of the seam is the ultimate indicator from the aesthetic point of view of the garment. The main findings during microscopic observations of the seam line are as follows: • The sewing combination of light weight fabric with finer threads and heavyweight fabrics with coarser threads gives a better appearance. • Lightweight fabrics when sewn with coarse threads exhibit more yarn sliding. • On average some combinations of corespun threads with denim give a more uniform and smooth appearance compared to cotton and polyester sewn seams. Correlation between fabric and thread properties with sewability parameters A linear correlation has been determined between various performance indices of sewability and the fabric/thread properties and the results are shown in Table XII. It can be seen from the table that seam efficiency has a high correlation with fabric strength, fabric extension, single strand and loop strength of the sewing thread. The correlation between seam efficiency and cover factor is good, whereas the correlation of loop extensibility and single strand thread extensibility with seam efficiency is moderate. The dependence of seam pucker is highest on cloth cover factor followed by the extensibility of the fabric and crimp in the warp yarn. Seam slippage gives a negative correlation with fabric strength extension and cover factor which supports our findings, explained earlier. Breaking extension of the single strand and loop of the sewing thread give moderate dependence with a correlation coefficient of the order of 0.5.

SN

Sewability indices

Thread/fabric properties

1

Seam efficiency

Fabric strength Fabric extension Cloth cover factor Single strand thread breaking strength Single strand thread breaking extension Looped thread breaking strength Looped thread breaking extension Cloth cover factor Fabric extension Warp crimp Cloth cover factor Fabric strength Fabric extension Single strand thread breaking extension Looped thread breaking extension Cloth cover factor Weft cover factor Fabric compressibility Thread diameter

2

Seam pucker

3

Seam slippage

4

Seam damage

Correlation coefficient (r) 0.92 0.99 0.81 0.94 0.57 0.93 0.53 0.98 0.70 0.78 –0.85 –0.97 –0.96 0.57 0.53 0.82 0.95 –0.82 0.92

As expected the needle cutting index gives excellent correlation (0.95) with weft cover factor because the sewing was done parallel to warp yarns. The sewing thread diameter also gives a very good correlation with needle cutting index (0.92). Fabric compressibility gives a negative correlation with needle cutting index due to the fact that the yarns in the fabric have access to sliding. Conclusions Sewability of denim fabrics is assessed by seam efficiency, seam pucker, seam slippage, needle cutting index, and seam appearance. For lightweight fabrics, seam efficiency increases with the decrease in linear density of thread; for heavyweight denim, seam efficiency decreases with the increase in thread linear density. Lightweight denim fabrics should be sewn with either finer polyester threads or coarser cotton threads. Heavyweight denim fabrics should be sewn with either coarse corespun threads or coarse polyester threads to achieve satisfactory seam efficiency. Cotton threads are not suitable for heavyweight denim fabrics. It is advisable not to use fine corespun threads for denim fabric from a seam efficiency point of view. The tensile properties of fabric and threads are the most important factors for sewability. Cotton threads are the best for sewing denim fabric from a seam puckering point of view and polyester threads are more prone to develop pucker. Corespun threads are comparatively less susceptible to the development of pucker than polyester threads. Sewing of lightweight denim with coarse threads result in high seam slippage. The extent of slippage in less compatible thread-fabric combinations is more with corespun threads, followed by polyester and cotton threads. Seam slippage reduces after

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Table XII. Correlation coefficients

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washing in almost all cases of sewing of denim fabrics. Needle cutting index decreases with decrease in the linear density of sewing threads for all the fabrics and the damage increases with the increase in fabric weights for a given ticket number. Corespun threads give maximum yarn damage compared to cotton and polyester threads. Needle cutting index is affected by fabric cover factor and weave.

140 References 1. Dureja, S., “Three dimensional engineering technique”, Clothline, 1992. 2. Chamberlain, N.H., Seam Pucker, its Causes and Prevention, Technological Report No. 10, Clothing Institute. 3. Stylios, G. and Lloyd, D.W., “A technique for identification of seam pucker due to fabric structural jamming”, International Journal of Clothing Science and Technology, Vol. 1 No. 2, 1989. 4. Mehta, P.V., An Introduction to Quality Control for Apparel Industry, JSN International, Japan, 1985. 5. Salhotra, K.R., Hari, P.K. and Sundareshan, G., “Sewing thread properties”, Textile Asia, September 1994, pp. 46-7. 6. Mori, M. and Niwa, M., “Investigation of performance of sewing thread”, International Journal of Clothing Science and Technology, Vol. 6 Nos 2/3, 1994. 7. Rathee, P., “Sewability and comfort behaviour of denim”, MSc Thesis, Department of Textiles and Clothing, Institute of Home Economics, University of Delhi, 1995. 8. Shishoo, R.L., “Evaluation of fabric”, Textile Asia, August 1991. 9. Kawabata, S. et al., Application of Objective Measurement to Clothing Manufacture, Textile Objective Measurement and Automation in Garment Manufacture, Kyoto, 1991, p. 18. 10. Shishoo, R.L., “Fabric properties and making up processes”, Textile Asia, February 1989, p. 66. 11. Kawabata, S. and Niwa, M., “Fabric performance in clothing and clothing manufacture”, Journal of the Textile Institute, Vol. 80 No. 1, 1989. 12. Choudhry, K., “Sewability of suiting fabrics”, MSc Thesis, University of Delhi, 1995. 13. Venkatapathy, D., “Importance of thread and needle”, Clothline, March 1992. 14. Booth, J.E., Principles of Textile Testing, Newness, Butterworths, Boston, MA, 1976. 15. Chamberlain, N.H. and Crow, R.M., Performance of Sewing Thread on Industrial Sewing Machines, Report No. 21, Clothing Institute. 16. Lindberg, J. et al., Journal of the Textile Institute, Vol. 51 No. 3, 1960. 17. Amirbayat, J. and Miller, J.M., International Journal of Clothing Science and Technology, Vol. 3 No. 3, 1972. 18. Hari, P.K. et al., Contribution to Garment Manufacturing: Mechanism of Sewing Thread Breakage and Seam Pucker, Department of Textile Technology, Indian Institute of Technology, Delhi, 1993. 19. Ramalingam, S., “Seam puckering – its causes and remedies”, Clothline, June 1989, pp. 76-82. 20. Taylor, J. and Clarke, F.J., “Physics of seam pucker”, Textile Industries, Vol. 131 No. 4, 1967. 21. Stylios, G. and Lloyds, D.W., “Prediction of seam pucker in garments by measuring fabric mechanical properties and geometric relationship”, International Journal of Clothing Science and Technology, Vol. 2 No. 1, 1990, pp. 6-15.

Water vapour transfer in waterproof breathable fabrics Part 3: under rainy and windy conditions J.E. Ruckman Department of Clothing Design and Technology, The Manchester Metropolitan University, Manchester, UK

Water vapour transfer – Part 3

141 Received September 1995 Revised and accepted May 1996

Introduction Parts 1 and 2 of this paper confirmed that the water vapour transfer rate from the human body to the environment is directly proportional to the vapour pressure difference between the inner side and the outer side of the fabric. This phenomenon was noted under both steady state and windy conditions although some disturbance was observed when condensation formed on the inner surface of the fabric. Considering the circumstances under which waterproof breathable fabrics are used, however, it is important to investigate whether the above findings for experiments under dry conditions are also applicable under rainy conditions. Many researchers[1-3] have tried to resolve the argument as to whether the water vapour transfer from the local environment of the human body at a relative humidity less than 100 per cent to a rainy environment of a relative humidity of almost 100 per cent is possible. This question, nevertheless, has remained unsolved or partially solved with restrictions. This is mainly because the rain simulators or the rain testers which have been constructed so far are made to be used in a small area[4,5], so that it is impossible to simulate severe wind-driven rainy conditions. In addition, although it is generally understood that most waterproof breathable fabrics may breathe even when it is rainy, it is not clear whether they also breathe under a prolonged severe rainy situation. Waterproof breathable fabrics are mostly used under such severe conditions, and good performance outdoors for a considerable time is regarded as being of primary importance for outdoor clothing. It is therefore necessary to assess their performance under rainy conditions, primarily to determine their breathability effectiveness when subjected to 100 per cent relative humidity, and to assess their performance further under wind-driven rainy and prolonged severe rainy conditions. Preliminary experiments To consider the question of whether water vapour transfer from the local environment of relative humidity less than 100 per cent to a rainy environment of relative humidity of almost 100 per cent is possible, basic measurements

International Journal of Clothing Science and Technology, Vol. 9 No. 2, 1997, pp. 141-153 © MCB University Press, 0955-6222

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were first made under a rain simulator. The simulator, as described by Keighley[1], covers a circle of 30 cm diameter and produces water droplets of 3.4 mm in diameter with velocity of 4.43 m/s. Twenty-four waterproof breathable fabrics which are used to construct sportswear and foul weather garments were randomly chosen from the market to be tested under a rain simulator. The fabrics were grouped together according to their manufacturing methods irrespective of their brandnames: six cotton ventiles, five microfibre fabrics, four PTFE laminated fabrics, four poromeric polyurethane laminated fabrics, and five hydrophilic laminated fabrics. The specifications for these samples are given in Table I. To measure water vapour transfer under rainy conditions, a glass dish method was used at various air temperatures. A dish (of diameter 67 mm and height 95 mm) was designed to have a sloping top end so that the rainwater from the rain simulator did not collect on the sample fabric covering the top. The lower part of the dish had a tilted wing, large enough to cover the hot plate, around it to prevent the temperature of the hot plate falling due to water falling on to it. A circular sample was placed on a dish which was filled with water to a level of 2mm below the sample fabric near the lower edge of the dish. A magnetic stirrer was put in the dish in order to maintain a water temperature of

Sample fabric L1 L11 L2 L22 L3 L33 Dsa Es2 Es4 C20 C24 PL2 PL3 WJa WJb CT2 CC2 SK2 SB2 M1 P1 S1 Table I. C1 Specifications of samples W1

Production type Cotton ventile Cotton ventile Cotton ventile Cotton ventile Cotton ventile Cotton ventile Microfibre fabrics Microfibre fabrics Microfibre fabrics Microfibre fabrics Microfibre fabrics PTFE laminated PTFE laminated PTFE laminated PTFE laminated Poromeric polyurethane Poromeric polyurethane Poromeric polyurethane Poromeric polyurethane Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated Hydrophilic laminated

Weight (g/m2)

Thickness (mm)

198.4 188.4 208.0 209.5 219.6 172.5 95.4 84.5 85.5 94.0 78.1 186.0 184.8 187.1 182.0 108.8 96.0 84.1 85.5 94.2 95.8 77.8 90.0 147.0

0.15 0.15 0.13 0.13 0.15 0.12 0.06 0.05 0.06 0.06 0.07 0.20 0.20 0.16 0.18 0.08 0.07 0.05 0.06 0.07 0.08 0.12 0.12 0.10

33°C[6] throughout the beaker. A sample was then held tightly down over the Water vapour side of the dish, and fastened there by means of a copper wire band. Thick transfer – Part 3 grease was also used to prevent the escape of water vapour from the side. Experiments were carried out in the relatively still air of the climatic chamber. For the experiment under wind-driven rainy conditions, the rain simulator was located in front of a fan producing a wind of velocity 2.5 m/s 143 passing across the surface of the sample fabric. After a conditioning period of two hours, the dish was weighed and the test carried out for a further 24 hours, at the end of which time the dish was weighed again to determine the amount of water vapour which had evaporated through the sample. To make accurate measurements of water vapour transfer, fabrics were weighed separately before and after experiments to determine the amount of water taken up by the fabrics. Excessive water from the outer surface of the fabrics was wiped off with absorbent papers after testing in order to weigh the water taken up more accurately. The loss in weight of water is used to calculate the water vapour transfer rate of the fabric using Fick’s equation[7] as follows: Q – Fu U= tA where: U = water vapour transmission; Q = mass of water vapour; t = time; A = area; and Fu = amount of water taken up by the fabric. Water vapour transfer under rainy conditions The water vapour transfer rates under rainy conditions at various rain temperatures are plotted in Figure 1. Mean values for groups of samples classified according to the type of product were taken to plot the graphs. The range of variations within each group of samples as a percentage of the mean was between 1.5 and 4.7 per cent, both under rainy and wind-driven rainy conditions. It is clear from Figure 1 that the waterproof breathable fabrics breathe even in rainy conditions at any rain temperatures except for microfibre fabrics. Microfibre fabrics cease breathing well before 24 hours and have therefore not been included in the discussion section. It is also evident that water vapour transfer in waterproof breathable fabrics decreases as rain temperature increases. The rates of water vapour transfer are ranked as follows: PTFE laminated fabrics, cotton ventiles, poromeric polyurethane laminated fabrics, hydrophilic laminated fabrics, polyurethane coated fabrics. The breathability of the fabrics under rainy conditions may be explained by reference to the concept of the absolute moisture content of air. The direction of water vapour transfer by diffusion depends on the absolute difference in water vapour concentration. The data in Table II therefore suggest that it is possible for diffusion to occur from an area with less than 100 per cent relative humidity

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Figure 1. Water vapour transfer at various rain temperatures

Temperature (°C) 0 0 0 0 10 10 10 10 20 20 20 20 33 Table II. 33 The relation of 33 temperature and relative humidity to the absolute 33 Source: [8] moisture content

Relative humidity (%)

Absolute moisture content (%)

100 90 70 50 100 90 70 50 100 90 70 50 100 90 70 50

0.6 0.5 0.4 0.3 1.2 1.1 0.8 0.6 2.4 2.2 1.7 1.2 4.7 4.2 3.3 2.4

to an area with 100 per cent relative humidity if the concentration gradient is Water vapour favourable. For example, when the water temperature inside the dish is 33°C, transfer – Part 3 and the relative humidity of the air between water level and the inner surface of the fabric is 90 per cent, absolute moisture content is 4.2 per cent. However, at any given air temperature for rainy conditions, the absolute moisture content does not exceed that of 33°C, 90 per cent RH. Consequently, water vapour will 145 diffuse from the air at higher temperature and lower relative humidity to the air at lower temperature and higher relative humidity. In the clothing system, the temperature of the air between human body and clothing is usually higher than that of outside air and, because of the insensible perspiration emitted by the body, the inside air has a higher moisture content than the outer side, although it has a lower relative humidity than the latter. Therefore, under conditions of stable water vapour transfer in water vapour breathable fabrics, these fabrics worn by a warm and moist human body breathe in rainy conditions. As was noticed in Part 1 of this paper, when the warm and moist air from the body meets the waterproof breathable fabric which acts as a cold wall, condensation occurs. Whether or not the water vapour will accumulate depends on the breathability of the fabric. The process of condensation causes a temperature rise in the fabric, and thus the vapour gradient over the fabric changes. This situation becomes more complex when rain falls on the outside of the fabric. The rain constantly cools the fabric, while the condensation of water on the inside constantly heats it. Therefore it is clear that breathability of the fabric is much more important under rainy conditions. According to the observation of condensation inside the fabric after 24 hours, it was discovered that most of the samples formed more condensation than they formed under dry conditions. However, PTFE laminated fabrics did not show much condensation but very slight wetness as shown under dry conditions. As a result, the PTFE laminated fabrics show a good performance even under rainy conditions while the others show less breathability. Water vapour transfer under wind-driven rainy conditions From the results obtained, as shown in Figure 2, it is clear that water vapour transfer under wind-driven rainy conditions decreases as rain temperature increases. In comparison with Figure 1, however, the overall water vapour transfer rate under wind-driven rainy conditions is slightly less than that under rainy conditions. This phenomenon does not confirm the findings of Part 2 of this paper, namely that the greater the wind speed and hence the greater the difference in vapour pressure across the fabric, the greater the water vapour transfer. As shown in Part 2 of this paper, the difference in water vapour transfer rate in waterproof breathable fabrics under steady state conditions and windy conditions of 2.5 m/s of wind velocity is marginal. The difference, however, became wider as the wind velocities increased to 5.0 m/s and 10.0 m/s. In a similar way, a wind velocity of 2.5 m/s under rainy conditions did not contribute much to an increase in vapour pressure difference. Any positive contribution was possibly masked by the disturbance of rain falling on to the fabric surface

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Figure 2. Water vapour transfer under wind-driven rainy conditions

and consequently increasing condensation on the inner surface of the fabric, thereby decreasing the rate of water vapour transfer compared to that under rainy conditions with no wind. Figure 2 shows the comparable water vapour transfer rates for fabrics, and it is clear that PTFE laminated fabrics sustain a relatively high breathability compared to the other fabrics. The marked difference between PTFE laminated fabrics and the others may be explained by the much better resistance of PTFE laminated fabrics to condensation, especially under windy conditions. Because the other fabrics more readily allow condensation, this creates a barrier impeding water vapour transfer. Secondary experiments The precipitation simulator was designed to produce severe rain over a large area. It has two major components, shower heads and a water supply system. A diagram of the apparatus is given in Figure 3. A frame was constructed from 50 mm × 50 mm soft wood, which was held together with brass plates, and was fixed on to the walls at a height of 2.4 metres using mild steel brackets. The height was chosen to satisfy the requirement of the AATCC raintester specification[9]. Pipework was made from 15mm copper tubing using capillary fittings and the shower heads with 365 0.5mm holes were fixed to the tubing using 15mm push-pull hose connectors. The pipework was then fixed to the underside of the framework using pipe clips. Connection to the water supply was made via a tap connector fitting to a hose using a pipe

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147

Figure 3. Precipitation simulator unit

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connector. The hose pipe was then fixed to the flow meter using a pipe connector. The flow meter was connected in a similar way to a 15mm tap connector. The water supply was taken directly from the mains water using a 15mm capillary fitting. The pipework was taken up to a second fitting, one side going to the flow meter, the other side going to the pressure meter via a valve and a screw fitting. The pressure meter was screwed directly into the fitting. The flow meter used is a variable area flowmeter, which consists of an accurately tapered tube with the narrow end at the bottom and a free piston. The tube is vertical with an upward flow of water when the piston position is read directly. This flowmeter always maintained around 3 per cent accuracy when the precipitation simulator was working. The pressure meter is a direct measurement transducer indicator which was calibrated with a pressure of 1,000 psi. Throughout the experiments under atmospheric conditions, water flow was kept at 1,200 ± 30 l/h, and water pressure kept at 40 ± 0.5 psi. The simulation of rain was achieved by the apparatus with four shower heads. These four shower heads covered a circle of diameter 127 cm with some overlap area. The drop size was determined using two methods: a direct method using photographs of water droplets taken along with a scale; and an indirect method involving a simple calculation performed to determine the mass of a single water drop using rate of flow, the time for a drop to fall from the shower head to the surface, which was measured by videotape, and the number of holes in the shower head. The two results from both the direct method and indirect method give a drop size of 1.3 mm diameter. The severity of rain is determined not only by drop size but also by its duration, mass precipitation rate, velocities, and the area over which it falls. The theoretical velocity of a spray leaving the orifice of a nozzle is proportional to the square root of the pressure supplied at the nozzle[10], therefore the calculated velocity of the rain is 6.32 m/s. This results in the simulation of a rain form, classed as heavy to excessive. A comparison of the rain simulated in this paper with other types of rain is shown in Table III.

Type of raindrop

Diameter (mm)

Velocity (m/s)

Kinetic energy (J)

0.2 0.5 1.0 1.5 2.1 3.0 6.4 1.3

0.75 2.00 4.00 5.00 6.00 7.00 5.40 6.32

0.012 × 10–7 0.92 × 10–7 42 × 10–7 220 × 10–7 870 × 10–7 3460 × 10–7 20000 × 10–7 152 × 10–7

Drizzlea Light raina Moderate raina Heavy raina Excessive raina Cloudbursta Bundesmann testb Precipitation simulator Table III. Drop sizes of various types of rain

Notes: a Data from Shishoo[4] b Data from Bundesmann[3,5]

To investigate the effect of prolonged rain on water vapour transfer, a further Water vapour set of experiments was carried out using the precipitation simulator. For each transfer – Part 3 experiment, the same procedure was used as before for the preparation of fabrics on the glass dish with a sloping top. In addition to the 24 waterproof breathable fabrics used for the preliminary experiments, five polyurethane coated fabrics were also chosen to be tested. The specifications for these 149 samples are given in Table IV. The experiment was carried out in the relatively still air of less than 1.0 m/s wind speed outdoors. Rain temperatures were checked every day by measuring the temperature of rainwater collected in the container, and the average rain temperature obtained during the experiments was 12.6°C. Sample fabric

Production type

A3 A33 A7 A77 A9

Polyurethane coated Polyurethane coated Polyurethane coated Polyurethane coated Polyurethane coated

Weight (g/m2)

Thickness (mm)

108.7 164.8 141.6 139.2 110.0

0.08 0.11 0.10 0.11 0.10

Water vapour transfer under prolonged rainy conditions The results obtained are shown in Table V, in which a typical fabric for each manufacturing method group was chosen for testing. The water vapour transfer rates are lower than those obtained under the rain simulator. This is due to the severity of the simulated rain produced by the precipitator simulator. The marks x in the Table indicate the day when the fabric stopped breathing. The results show that waterproof breathable fabrics stop breathing after a certain period. Although the durabilities in performance of breathability are ranked – hydrophilic laminated fabrics, polyurethane coated fabrics, PTFE laminated fabrics, poromeric polyurethane laminated fabrics, cotton ventiles, microfibre fabrics – from higher to lower value, in many fabrics breathing stopped at quite an early stage. In fact, it has been shown that the glass dish actually gains water when they stop breathing, which suggests that rainwater penetrated the fabric. This happened to all the fabrics except hydrophilic laminated fabrics. The gain in weight may be explained by the phenomenon of penetration of raindrops. According to observations during the experiment, for several hours after starting the test, water droplets formed mercury shapes and rolled down along the fabric surfaces. As Cassie and Baxter[11,12] have already noticed, there is no wetting of a porous surface until the formation of mercury shape ceases. However, when the fabrics are exposed to prolonged severe rain, if a number of water drops fall successively into the same pore, a water film will form between the fibres. As a result, the contact angle decreases and water will

Table IV. Specifications of the samples

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Table V. Water vapour transfer rate under prolonged rainy conditions (g/m2/24h)

Day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

PU

CV

MF

PTFE

PP

HP

194.2 177.7 167.0 161.4 163.5 158.4 157.9 154.6 153.8 151.5 152.5 157.6 154.5 143.5 x

470.1 429.3 x

x

594.3 537.8 497.4 398.1 388.4 360.1 x

129.7 128.9 128.3 118.7 122.6 x

564.9 534.1 528.3 513.1 510.7 503.2 503.1 502.5 501.7 502.6 508.9 505.3 509.1 507.5 501.9 503.1 504.1 503.8 502.2 498.4 493.3 493.2 499.5 496.8 491.7 490.4 497.5 494.7 490.8 489.1

Notes: PU, polyurethane coated fabric; CV, cotton ventile; MF, Microfibre fabric; PTFE, PTFE laminated fabric; PP, poromeric polyurethance laminated fabric; HP, hydrophilic laminated fabric; x indicates the day the fabric stopped breathing

not be withdrawn completely from the pore. Succeeding drops falling into the pore will then force the water surface into it and the water will withdraw to a lesser extent because the contact angle has decreased. This process of penetration of the fabric by rain will continue until the kinetic energy of falling drops is not sufficient to force the water column deeper into the pore.

Figure 4 shows a comparison of the water vapour transfer rates for the Water vapour polyurethane coated fabric, the PTFE laminated fabric and the hydrophilic transfer – Part 3 laminated fabric. These are regarded respectively as being the original waterproof breathable fabric, the most common waterproof breathable fabric, and the latest waterproof breathable fabric. These three different types of breathable fabrics are basically from different types of production processes. 151 Figure 4 demonstrates that the three different types of waterproof breathable fabrics behave differently under prolonged rainy conditions. The lowest water vapour transfer rate is shown in the case of polyurethane coated fabrics. This is not surprising, as the polyurethane coating process results in a continuous polymer coating, which acts as a barrier. Although the fabric showed very low breathability, the fabric may be said to be good for waterproof clothing, as the fabric actually showed durable performance in waterproofing by breathing for 15 days. In the case of PTFE laminated fabric, the performance in breathability decreased dramatically as days went by, in contrast to the excellent performance shown in dry, windy, and even in moderate rainy conditions. This excellent performance was due to the fact that very little condensation formed on the inner surface of this fabric. Figure 4 shows, however, that they still performed the best for two days, but then started to lose their breathability. This phenomenon may be explained by two factors. First, when the fabric is exposed to severe rain, the rainwater may remain as liquid water on the outer surface of the fabric. Therefore, the small pores swell on contact with liquid water, which causes a decrease in the breathability of the pores. Second, some of the pores may be

Figure 4. Water vapour transfer under prolonged rainy conditions

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enlarged by the impact of the falling rain which has a relatively high velocity and hence kinetic energy as explained above, so that the cool rainwater may penetrate through some of the enlarged outer pores of the fabric. The hydrophilic laminated fabric is shown to perform comparatively well under prolonged rainy conditions. Although it demonstrated poor breathability under dry and windy conditions, it shows consistent breathability throughout the experimental period and it seems to hold its performance ability for a long time. This may be due to the characteristic of the non-porous hydrophilic membrane, which provides a sufficient number of chemical groups to act as stepping stones for water vapour transfer. The water molecules can therefore pass between tightly packed chains to regions where gaps exist between the chains. Consequently, despite the hydrophilic layers being saturated by the constant supply of cool rainwater, warm and moist water vapour from the body can evaporate continuously irrespective of the severe prolonged rainy conditions. Conclusions A range of waterproof breathable fabrics which are used to construct sportswear and foulweather garments was selected and subjected to various experiments. The purpose of these experiments was to investigate whether the water vapour transfer from the local environment of relative humidity less than 100 per cent to a rainy environment of relative humidity of almost 100 per cent is possible, and if so, whether it is also applicable under wind-driven rainy conditions and under prolonged rainy conditions. It was technically difficult to reproduce the exact data for water vapour transfer under prolonged rain due to the fact that the precipitation simulator was placed outside. Similar results were obtained, however, when the experiments were repeated under comparable weather conditions. The actual values of water vapour transfer rate varied by no more than 6 per cent from the original results, and the ratings of performance for the fabrics were identical. From the experiments, the following results were obtained: (1) Water vapour transfer in waterproof breathable fabrics decreased as rain temperature increased. (2) Waterproof breathable fabrics did breathe under rainy conditions; however, the breathability of most of them ultimately ceased after long exposure to prolonged severe rainy conditions. (3) More condensation was observed on all fabrics under rainy conditions than under dry conditions except for PTFE laminated fabrics which formed the least condensation. (4) The water vapour transfer rate was reduced under wind-driven rainy conditions compared to that under rainy conditions for all fabrics due to the disturbance of both rain and condensation. It is now clear from Parts 1, 2 and 3 of this paper that water vapour transfer depends very much on the atmospheric conditions. It can generally be

concluded that wind increases and rain decreases the water vapour transfer Water vapour rate of a fabric, giving in descending order of water vapour transfer transfer – Part 3 performance: windy, dry, wind-driven rainy, rainy. These findings suggest that careful consideration should be given when choosing the appropriate waterproof breathable fabrics for manufacturing sportswear and foul weather garments. The end use envisaged for the garment and the environment it will be 153 used in should always be taken into account. These protective garments are in general exposed to low temperatures, to wind, to rain, and to occasional severe conditions of wind-driven rain. References 1. Keighley, J.H., “Breathable fabrics and comfort in clothing”, Journal of Coated Fabrics, Vol. 15, October 1985, pp. 89-104. 2. Polfus, W.F., “Treatment of outwear for rain protection”, Journal of Coated Fabrics, Vol. 7, January 1978, pp. 218-22. 3. Tentative textile standard, “Method of testing water repellency of cotton fabrics permeable to air using Bundesmann type apparatus”, Journal of the Textile Industry, Vol. 38, 1947, p. S4. 4. Shishoo, R.L., “Recent developments in breathable high functional fabrics”, Nonwoven World, February 1987. 5. Bundesmann, “Eine neue Apparatur Zur Gebrauchswertprüfung Wasserabstopend imprägnierter Textilien”, Melliand Textilberichte, Vol. 16, 1935, pp. 128-31. 6. Hardy, J.D., “Heat transfer”, in Newburgh, L.H. (Ed.), Physiology of Heat Regulation and the Science of Clothing, Hafner, London, 1968. 7. Crank, J., The Mathematics of Diffusion, Clarendon Press, Oxford, 1975. 8. Tanner, J.C., “Breathability, comfort and Goretex laminates”, Journal of Coated Fabrics, Vol. 8, April 1979, pp. 312-22. 9. Water Resistance; Rain Test, AATCC 35, 1985. 10. Engineering Data, BETE Fog Nozzle Inc., 1987. 11. Cassie, A.B.D. and Baxter, S., “Wettability of porous surface”, Transactions of the Faraday Society, Vol. 40, 1944. 12. Baxter, S. and Cassie, A.B.D., “The water repellency of fabrics and a new water repellency test”, Journal of the Textile Industry, Vol. 46, 1945, p. T67.

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Communications Marker making in small clothing companies – Part 2

166

Cathy Hands Milliken & Company, Spartanburg, South Carolina, USA

Helmut H.A. Hergeth and Peyton Hudson North Carolina State University, Raleigh, North Carolina, USA Introduction This article is the second in a two-part series that looks at small clothing companies in the USA, examining their current manufacturing situation, and looking at their investment in CAD/CAM systems for grading and marker making. This part will discuss environmental issues and the importance of cutting fabric cost, and will present a case study and recommendations for the small clothing company. Summary of Part 1 Part 1 discussed the history and benefits of CAD systems. A survey of small clothing companies in the states of North and South Carolina was taken, and the responses regarding type of company, fabrics used, cost of operating, and usage of CAD/CAM equipment was given. Case study A, a tie manufacturer, was examined regarding feasibility of investment in a CAD/CAM system based on fabric savings, labour costs and waste disposal.

International Journal of Clothing Science and Technology, Vol. 9 No. 2, 1997, pp. 166-176. © MCB University Press, 0955-6222

Environmental aspects of waste reduction in the clothing industry Cheremisinoff and Ferrante[1] discuss the increasingly stringent environmental regulations on waste disposal. They emphasize the importance of reducing the amount of waste produced, thereby reducing the cost of disposal. Waste reduction not only reduces disposal costs, but ultimately reduces environmental costs. When a company initiates a waste reduction programme, plant modernization is often the first step. The resulting increase in competitiveness and profitability, accompanied by waste reduction improves the image of the company. Modernization usually includes both technological and process modifications, accompanied by changes in equipment, operational settings, and even in degree of automation. How does this apply to the clothing industry? Tuggle[2] discussed how AAMA members have increased spending in environmental areas, as well as giving the environmental issues a high priority in the company. He quotes the results of the 1993 TAC Environmental Survey’s list of cutting waste of 176 million pounds per year. Of particular interest was the increase in landfill costs

for Russell Corporation. Disposal costs for them jumped over 86 per cent in the Communications: past two years, mostly because the close of the nearby landfill forced them to marker making – transport waste to a more distant landfill. Efforts that Russell is making to Part 2 reduce waste, according to Tuggle are the following: (1) Maintain consistent waste handling procedures. (2) “Fine-tune” target waste levels for all processes. 167 (3) Report all waste and identify it properly. (4) Bring all seam-off waste to one location for distribution to vendors. (5) Set up random visits to check each clothing plant. (6) Randomly check the textile operations and reports. Research is also under way to recover the fabric waste and channel it back into fabric, or make other uses for it. This research includes identifying the feasibility of different alternatives, determining the amount of waste, the location of the waste, and discovering processes that will accept both cotton and polyester. The importance of fabric cost in marker making Fabric is the single largest factor in the cost of a garment, and fabric prices are continuously increasing. In 1987, direct materials (fabric, thread, buttons, etc.) accounted for 50.76 per cent of the total manufactured cost[2]. Powell[3] estimated fabric costs alone to be 35-40 per cent of the selling price of a garment. A 2.5 per cent reduction in fabric could save a company 1 per cent in cost. Gustas[4] calculated how a 1 per cent reduction in cost would affect the bottom line. For his example, he used a fabric cost of 45 per cent of sales. As shown in Table I, this reduction in material costs caused profit to increase by 10 per cent.

Sales Fabric cost of sales Other Profit before tax

Before ($)

After 1% improvement ($)

100.00 45.00 50.50 4.50

100.00 44.55 50.50 4.95

A fabric cost estimate of 45 per cent of sales could even be low for some companies. In a study done by the Clothing Industry Productivity Association and National Productivity Institute of South Africa[5], they used fabric costs of 46.5 per cent in all calculations. Case B: a dress manufacturer Company B is a manufacturer of dresses and uniforms. This company employs 55 people to produce garment designs, pattern designs, graded patterns,

Table I. Effect of reducing fabric cost as percentage of sales

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markers, and cut and sew. Garments are made in a wide range of both misses and half sizes, some by contract. The fabrics used range from warp knits to wovens, and include prints, stripes, and plaids. Common widths include 44/45, 58/60 and 62/64 inches. The fabric price range is small, from $1.00 to $1.75 per yard. The estimated amount of fabric used per year is 250,000 yards, resulting in a fabric cost of $250,000437,500 per year. Estimated costs per garment were attributed as follows: 30 per cent to fabric, 30 per cent to direct labour, 37 per cent to overheads, and 3 per cent to other materials. The company changes styles only infrequently throughout a given year. Basic styles are their consistent product week after week. The garment and pattern design, as well as grading, is undertaken to correct fitting problems and for the contract work for the most part. This is estimated to be around three to five times per year. Grading takes approximately two days of six or seven hours each. An option is to subcontract grading to a company with a CAD system, but at a cost of $110 for six sizes, in-house completion is cost-effective. Marker making is done on an as-needed basis. With standard styles and standard widths, the company judiciously keeps copies of the markers for each style, each ratio of sizes, and each width. A large storeroom for the markers is required. If a fabric is received wider than that ordered in standard width (about 5 per cent of the fabric used), a decision to relay the marker or cut it as is has to be made. If matching is required, as in the case of plaids and stripes, the marker is often relaid to take advantage of the fabric savings afforded by the wider width. (The marker maker is paid $5.50 per hour, and one marker takes approximately two hours.) New markers are affordable and often advisable. Markers are taken from storage and copied with a Sepia-master Blueline copy system. An image of the pattern pieces on the paper is created, almost like rubbing carbon paper. Use of the system can also cause an odour. There are two alternatives for the waste fabric. Cotton/polyester blends are cut up and sold as quilt squares for $1.80 per pound. Scraps that are too small for squares are sold for $0.20 per pound. Polyester, which represents 50 per cent of fabric used, is thrown away. Disposal costs are fixed at $99 per month. Testing and results The markers furnished were for a raglan-style, short sleeve dress with a front button placket, and a collar in sizes ranging from 14 1/2 to 24 1/2. Because of the usual assortment cut for this style (4, 5, 6, 6, 5, 4), and the small number of the orders, the sizes were distributed into two markers: one containing the 16 1/2, 18 1/2, and 20 1/2 sizes, and the other the 14 1/2, 22 1/2, and 24 1/2 sizes. The markers were designed for 58-inch wide fabric, with half an inch selvage allowance on each side, making 57 inches of cuttable width. The fabric did not require matching. The pattern pieces were digitized from the furnished marker into the computer, taking approximately 35 minutes. The pieces were used for creating a

garment file from which marker files were developed, a process which took five Communications: minutes. marker making – The markers were created in two ways. One marker of each size assortment Part 2 allowed a quarter-inch gap between pieces, as required by the manufacturer. A second allowed only an eighth-inch gap, in an effort to maximize marker efficiency. A total of 20 markers was produced by laying each marker five times, 169 with the time required, the length of fabric consumed, and the resulting efficiency recorded for each one. These are given in Tables II-V. Time (min)

Yardage

Efficiency (%)

20 25 15 15 20

6yd, 8.38” 6yd, 6.93” 6yd, 4.25” 6yd, 4.50” 6yd, 4.13”

85.71 85.95 87.31 87.20 87.35

Time (min)

Yardage

Efficiency (%)

30 15 25 20 20

6yd, 6.69” 6yd, 6.22” 6yd, 5.97” 6yd, 7.88” 6yd, 3.94”

86.03 86.54 86.63 85.47 87.42

Time (min)

Yardage

Efficiency (%)

6yd, 6.75” 6yd, 4.16” 6yd, 0.13” 5yd, 34.09” 5yd, 33.41”

86.32 84.40 85.98 86.79 87.07

Yardage

Efficiency (%)

6yd, 2.16” 5yd, 35.09” 6yd, 7.59” 5yd, 33.69” 5yd, 33.16”

85.17 86.40 83.10 86.95 87.18

30 15 15 20 15

Time (min) 25 20 30 15 15

Table II. Sizes 14H, 22H and 24H, quarter-inch gap

Table III. Sizes 14H, 20H and 24H, eighth-inch gap

Table IV. Sizes 16H, 18H and 20H, quarter-inch gap

Table V. Sizes 16H, 18H and 20H, eighth-inch gap

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Figure 1. Sizes 14H, 22H and 24H marker

The best of the 14H markers is shown in Figure 1. For the 16H markers, a direct comparison of the efficiencies obtained from the quarter-inch gap versus the eighth-inch gap is shown in the markers depicted in Figures 2 and 3. These have the same lay plan, but the efficiencies obtained due to the gap are different by 0.11 per cent. The yardage required is only a quarter of an inch greater by using a quarter-inch instead of an eighth-inch gap. Use of only an eighth-inch gap, instead of the quarter-inch gap, could save 275 yards per year, or $275-481 per year.

Communications: marker making – Part 2 171

Figure 2. Sizes 16H, 18H and 22H marker, quarter-inch gap

In comparing the computer-obtained efficiencies with the hand laid efficiencies, the CAD system demonstrated a significant increase in efficiency with a decrease in time. The best efficiency and the time to achieve it are shown in Tables VI and VII. The CAD system not only saved 1.66 hours for the 14H marker, but also 1.75 hours for the 16H marker. The increase in efficiency is from 2 to 4 per cent. On average, this could save 1.71 hours and 2.92 per cent of fabric per marker. This

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Figure 3. Sizes 16H, 18H and 22H marker, eighth-inch gap

Table VI. Times and efficiencies for markers – 14H, 22H and 24H

Table VII. Times and efficiencies for markers – 16H, 18H and 20H

Hand-laid Computer

Hand-laid Computer

Time

Efficiency

2 hours 20 minutes

85.45% 87.42%

Time

Efficiency

2 hours 15 minutes

83.31% 87.18%

calculates to a fabric savings of 7,300 yards per year, or $7,300-12,775 reduction Communications: per year in fabric costs alone. Labour savings for the marker maker would be marker making – $9.63 per marker. Part 2 To analyse the effect that creating markers more suited to the ratios would have, new markers were developed to reflect the ratio actually needed. Three markers were developed, each consisting of two sizes. The combinations were 14 173 1/2 with 24 1/2, 16 1/2 with 22 1/2, and 18 1/2 with 20 1/2. An eighth-inch gap was used, as it had been determined to have the best yield. These markers were laid. The results obtained from laying these markers are shown in Tables VIII-X. By adding the best of these and comparing that total to the total amount required by the original two markers of three sizes each, it can be seen that this method requires 5.88 inches more fabric and is less efficient by 1.16 per cent. The indication is that more sizes per marker afford a higher yield, as suggested

Time (min)

Yardage

Efficiency (%)

10 15 10 12 15

4yd, 2.72” 4yd, 2.38” 4yd, 3.56” 4yd, 3.66” 4yd, 7.81”

85.84 86.05 85.35 85.29 82.96

Time (min)

Yardage

Efficiency (%)

5 7 10 10 15

4yd, 6.13” 4yd, 4.06” 4yd, 3.56” 4yd, 4.22” 4yd, 3.47”

84.10 85.27 85.56 85.18 85.61

Time (min)

Yardage

Efficiency (%)

12 7 15 10 10

4yd, 2.16” 4yd, 1.13” 4yd, 4.84” 4yd, 3.78” 4yd, 3.91”

86.15 86.76 84.59 85.19 85.13

Table VIII. Sizes 14H, 24H, two-size marker

Table IX. Sizes 16H, 22H, two-size marker

Table X. Sizes 18H, 20H, two-size marker

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in the paper from the Clothing Industry Productivity Association and the National Productivity Institute of South Africa, Part II[6]. Analysis and conclusions There is great potential for fabric and labour savings for this company by using a CAD system. But is it worth the investment? Grading is only performed three to five times per year, for a period of 12-14 hours each time. At 36-70 hours per year, the labour cost ranges from $198 to $385. Using a CAD system, the garment furnished would take 90 minutes, if the standard grade rules were not already in the system. This labour cost, at the same rate, would be $8.25 per garment, or $25-41 per year, for a realized savings of $173-344 per year. The patterns would be stored on the computer, eliminating the requirement for the present amount of space needed for storage. The patterns would be more precise and sizes would be more consistent. In marker making, the company has two options: (1) Maximize the efficiencies of their current markers, and develop new markers of maximum efficiencies throughout the year. This would not require investment in a CAD system; all of the existing markers could be reworked by hand or a company with CAD could be contracted to do this. The company could continue to use the same method of storing large numbers of markers and copying them for each use. In this way, it could take advantage of the savings without a long-term investment. (2) Invest in a CAD system. This would allow the company to have the resource on hand at all times. Storage space would be reduced. The labour savings for marker making would be 5-8.5 hours per year, amounting to a total saving of $28-47 per year. Since new markers are made on fewer than 5 per cent of the orders each year, the system would be applied to only 12,500 yards of fabric per year. This could save 365 yards of fabric per year or $365-639 per year. Markers would be stored on the system, plotted as needed, eliminating storage space. Cutting lines would be clearer and more consistent, making it easier for the cutter to be accurate. Reducing the amount of waste does not save any additional money due to the fixed disposal costs. Increasing marker efficiency and ordering less fabric will reduce the number of scraps and squares, eliminating the opportunity to recoup some of the fabric costs in resales. The other alternative would be to continue to purchase the same amount of fabric, once it is determined that the resale value of the scraps is greater than the cost of purchasing and cutting up the fabric. With CAD/CAM grading and marking systems priced for as little as $10,000, the fabric savings for the first year on reworking the markers alone ($7,30012,775) could justify investment in a system. When labour savings for grading ($173-344) and marking ($28-47), and fabric savings ($365-639) resulting from reworked patterns, markers and contracts are added, the saving is $7,86613,805 for the initial year, with each additional year’s savings amounting to

$566-1,030. In the best case scenario, the system would pay for itself in one year. Communications: Using the low end figures, the payback period would be five years. A ten-year marker making – investment at an interest rate of 10 per cent has a present value of $10,114. Part 2 This company should consider looking further into investment into a CAD system. As fabric prices increase and the cost of systems decrease, such an investment becomes more and more advisable. With a strong potential to save 175 money, this company could become more competitive. Recommendations for small clothing manufacturers Is investment in a CAD/CAM system right for you? Calculate it: if the cost of the equipment is Ko, and the variable cost (labour, energy, material, etc.) is C, then the cost saving per marker is (B-C) with B being the cost per marker made manually or contracted out. Whether or not it is economical to invest in an automatic marker making system depends on how many markers a company makes per year or per season. The minimum number calculated on an annual basis is: Na =

K0 (q − 1)q n ( B − C )(q n − 1)

where: Na = number of markers per year; q = (1 + p/100), with p = percentage interest; and n = number of years payoff. Calculated seasonally, compounding the interest seasonally over the payoff period, the minimum number of markers per season is: K0 (q − 1)q nm Ns = ( B − C )(q nm − 1) where: Ns = number of markers per season; q = 1 + (p/(m × 100)); p = percentage interest; m = number of seasons per year; and n = number of years until payoff. Example: Assuming 10 per cent interest (p = 10), two seasons per year (m = 2), and a payoff time of two years (n = 2), an investment cost of $10,000 (K0 = 10,000), and variable cost of making the marker with the equipment being C = $20 and without the equipment being B = $150, the minimum number of markers per season would be: Ns =

10 , 000(1 + ( 0.10 / 2000 ) – 1)(1 + ( 0.10 / 200 ))2⋅2 (150 – 20 )((1 + ( 0.10 / 200 ))2⋅2 – 1)

.

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Ns = 21.69; so in this case, the minimum number of markers per season that makes this economical is 22. With this guideline, companies can determine for themselves whether investment in their own CAD/CAM system is economical. With research into the choices available, and a decision based on their own business needs, companies can stay competitive in today’s changing market. References 1. Cheremisinoff, P.N. and Ferrante, L.M., Waste Reduction for Pollution Prevention, Pudvan, Northbrook, IL, 1989. 2. Tuggle, L., “Environmental overview and outlook”, Apparel Research Conference Proceedings, 1994. 3. Powell, L.Q., “More efficient marking”, Femme-Lines, November-December 1977, pp. 13-15. 4. Gustas, L.F., “Improved profitability from better material utilization”, Femme-Lines, November-December 1977, p. 12. 5. Clothing Industry Productivity Association and National Productivity Institute, “A comprehensive material utilization study, Part I”, Clothing Manufacturer, May 1989, pp. 34-43. 6. Clothing Industry Productivity Association and National Productivity Institute, “A comprehensive material utilization study, Part II”, Clothing Manufacturer.

IJCST 9,2

Communications Marker making in small clothing companies – Part 1

154

Cathy Hands Milliken & Company, Spartanburg, South Carolina, USA

Helmut H.A. Hergeth and Peyton Hudson North Carolina State University, Raleigh, North Carolina, USA Introduction This article is the first in a two-part series that looks at the small clothing company in the USA, examining its current manufacturing situation, and looking at the investment in CAD/CAM systems for grading and marker making. Part 1 discusses the history and benefits of CAD systems, then explores the distribution of clothing companies in the USA. The results of the small clothing company survey are discussed and one case study is presented.

International Journal of Clothing Science and Technology, Vol. 9 No. 2, 1997, pp. 154-165. © MCB University Press, 0955-6222

History of CAD/CAM systems for grading and marker making Computer aided design and computer aided manufacturing systems for clothing were first developed in the early 1970s[1]. These systems could initially be used only for pattern grading and computer assisted marker making. Each system functioned as an isolated island, incompatible with any other computer systems. By 1982, only two companies were producing the 400 systems in use worldwide[2]. These systems, while they enabled an operator to produce markers five times faster then before, were priced in the range $100,000$300,000, depending on their speed and scope. The price alone kept many manufacturers out of the market. By 1988-89, almost 20 companies were offering computer assisted grading and marking equipment; many of the packages could be obtained as software only[3]. The increased competition, as well as a decreased cost of technology, helped make systems affordable to greater numbers of manufacturers. Automatic marker making was becoming available, though limited in capability. Many advantages in having PC-based CAD systems are recognized[4]. The programs may be run through application management systems, making them easier to use, allowing multi-tasking, and opening the door to more integrated systems, making data transfer from one station to another easier. Companies are no longer necessarily tied to one vendor for their hardware and software needs. By 1993, the problem of the isolated islands was being investigated at the Apparel-CIM Center at the University of Southwestern Louisiana[5], as a joint project between the A-CIM Center and the American Apparel Manufacturers Association. The goal was to develop a set of standards that would allow

patterns to be exchanged between computer systems, regardless of vendor. Communications: This compatibility would allow design centres to send pattern and marker marker making – information to manufacturers, irrespective of their system, thereby speeding up Part 1 the manufacturing process. By the end of 1993, many of the CAD/CAM vendors had automatic marker making capability. Much work remains to be done, however, due to the heuristic 155 nature of the process. The technique is being employed for costing purposes only, with the interactive method being the choice for production markers[6]. Li[7] developed a program that enables an automatic marking system to compact (place the pattern pieces as closely together as possible) in only 30-45 seconds. He proved that this method takes less time and is as efficient as, if not more efficient, than a human operator compacting the marker. CAD/CAM systems are becoming more affordable all the time[8]. The first CAD/CAM systems were so expensive, that only the largest companies could justify purchasing them. Today’s third generation systems offer even more advantages than their predecessors, at less than one-tenth the price. For the first time, small companies may be able to justify their purchase. The decision to invest now, or to wait for the potential advancements and lower prices of the future, can be aided by answering two questions: (1) Is there a risk that by not investing – benefits could be lost while the business stagnates? (2) Can the investment be justified now, with the current costs and performance? If both answers are “yes”, investment in an initial system now is a sound idea, with further investments in advancements once the system has paid for itself. Benefits to computer assisted grading and marker making A study done by the Clothing Industry Productivity Association and National Productivity Institute of South Africa revealed marker utilization as one of the six key ways to improve material utilization. Marker efficiency can be improved through various methods. Cutting multiple size, rather than single size markers is one of the most effective ways. The efficiencies can be checked and monitored by checking the area of the pattern versus the area of the marker. Reengineering the patterns often helps to improve efficiency. Corners of patterns can often be reduced without affecting the sewability or wearability of the garment. It may also be possible to tilt the pattern slightly or to eliminate or to add seams. While adding seams may increase the sewing cost, significant fabric savings may be the result. The use of computers to aid in the development of markers has led to these more efficient markers being generated very quickly. The most significant potential for savings is in women’s clothing, where the styles change frequently. No significant savings can be expected from classic menswear as most of these companies have maximized their efficiencies. According to Rechtman[9], in 1978 there were three options a company had to control material utilization. The first, and most risky method, was to estimate

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fabric requirements “by the seat of your pants”. This method, if wrong, could cost you your company. The second method involved the use of an area integrator, which calculates the total square inches in each pattern piece. When the total area of the pattern pieces to be laid was divided by the width of the fabric, the optimal fabric length needed for the marker was obtained. When the integrator was used with a pantograph, it cut pattern pieces on a one-fifth scale for use on a one-fifth scale planning board for accurate, efficient means of planning the marker. The third method was by using a computer, which was faster and more accurate. The computer stored the number of pieces needed, so none is forgotten, and assisted the operator in getting the pieces as close together as possible. It also gave a running update of the marker’s efficiency, so the operator knew how he/she was doing. This method was very costly and only the large companies could afford it. Recommendations for improving marker efficiency for various sized companies were made by the Clothing Industry Productivity Association and National Productivity Institute of South Africa in Part III[10] of their study. For a small manufacturer (fewer than 100 employees) it was recommended that the areas of the patterns be calculated by hand. The medium-sized company (101500 employees) was assumed to have more resources at its disposal. The use of miniaturized marker making equipment was recommended. Miniaturized marker making equipment or the use of a computer was recommended for large companies (greater than 500 employees). Pattern quality is a primary concern in improving material utilization in the marker, according to Kosh[11]. She stresses the importance of making sure the pattern pieces are balanced, the seams match in length, notches match and are in the appropriate location, reference lines are included, and the pattern, when sewn up, meets garment specifications. Having the patterns graded correctly is also important, as an incorrectly graded point (she uses the shoulder seam for an example), can change the way the pieces lay into the marker, reducing the efficiency, and creating poorer fitting, lower quality garments. By keeping the shoulder seams of the garment parallel, the pieces fit together more readily in the marker, and there is a more consistent fit throughout all of the garment sizes. She explains how easy it is to have the specific grade rules for each change in angle of the shoulder line already entered into a computer grading system. This method not only keeps these grades more consistent, but it also makes it much easier for the grader, saving valuable time. The traditional method of grading garment patterns involves tedious measuring and extreme care. It can also be very time consuming. Finkel[12] discusses how this time can be dramatically reduced, with very accurate results. He claims that use of a computer grading system reduces grading time to onethird to one-fifth of the time required to grade manually. Also, the pattern pieces do not need to be cut in instances where a computer marking system is available, thereby saving on paper costs. The patterns are also more consistent, as the computer draws the pieces exactly the same each time, to within 0.015 mm.

There are many benefits of computer assisted marker making. Material Communications: utilization can improve from 1 to 3 per cent over that of a miniature marker marker making – maker. One operator can make five markers by computer in the time it takes to Part 1 produce one manual marker in full scale. Reduced labour costs and faster production are the benefits. Records of the markers are stored on the computer or on disk, protected from damage and easily retrieved for reference or reuse. 157 The markers are of higher quality, as pieces cannot slip, so cutting lines are more consistent. Plaids and stripes are more easily matched. Pieces cannot be forgotten and accidentally left out. The current systems can also be integrated with computerized numeric cutters for automatic cutting of the garments. Vendors today are also offering systems that can plan the marker to permit a faster, more accurate estimate of fabric cost. The use of standardized patterns will enhance and accelerate the transfer of pattern data between locations, making such systems beneficial for even the contractors. Distribution of US clothing companies by size and type The preliminary report of the Department of Commerce 1992 survey of manufacturers[13] revealed that the US clothing industry consists of 13,900 companies, employing 7,746,600 people. This may seem significant, but it is a decrease of 13.10 per cent in total companies, and a 12.51 per cent decrease in total employees from 1987. According to the 1987 Department of Commerce survey, approximately 95 per cent of the over 15,000 clothing companies in the USA employed an average of fewer than 100 people[14] (see Figure 1). Looking at the types of companies in the USA, more than 50 per cent of the companies are manufacturers (see Figure 2). This distribution includes, in addition to companies producing clothing outerwear, activewear, tailored clothing, and lingerie, the companies that produce men’s and boys’ underwear and neckwear, brassières and girdles, millinery, leather and sheep-lined clothing, belts, and accessories as manufacturers such as these were not 500-999 employees 1 per cent

1,000-2,499 employees 0 per cent

250-499 employees 4 per cent 100-249 employees 10 per cent 50-99 employees 12 per cent

20-49 employees 21 per cent

1-4 employees 25 per cent

5-9 employees 12 per cent

10-19 employees 15 per cent

Figure 1. Distribution of clothing companies by size

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Figure 2. Distribution of clothing companies by type

Multi-plant company contractors 2 per cent

Manufacturers 52 per cent

Independent contractors 40 per cent

Jobbers 6 per cent

otherwise classified. This distribution remains consistent when looking at the small companies (see Figure 3). Multi-plant company contractors 1 per cent

Manufacturers 51 per cent

Independent contractors 42 per cent Figure 3. Distibution of small clothing companies (fewer than 100 employees) by type

Jobbers 6 per cent

Survey of small clothing companies In an attempt to determine the number of companies already using CAD/CAM systems, and the methods currently employed by non-CAD companies to make markers, surveys were sent to 230 small clothing companies in both North and South Carolina. This geographic area was selected not only for its proximity to North Carolina State University, but also because a large number of clothing companies are located in the Carolinas. The companies and their addresses were obtained from the 1992 North Carolina Directory of Manufacturers and the 1994 South Carolina Industry Directory. An example of the survey is given in the Appendix. Survey results Forty of the original 230 surveys were returned because the companies were out of business. Two companies knit full-fashioned garments, which required no

sewing, while two other companies had switched to only screen printing Communications: endeavours. Twenty-nine completed surveys were returned, with information marker making – about the respective company’s operations. Eighteen companies were Part 1 contractors, ten produced branded clothing, and one was a subsidiary location. This is a far different distribution from the total US distribution where manufacturers comprise over 50 per cent of the total. 159 Of the contractors, seven were sew-only locations, furnished with already cut parts requiring only assembly. Seven were cut and sew operations. Only four of the contractors even made their own markers. One company has a CAD system solely used for plotting out markers sent on disk by the contracting company. Of the ten manufacturers, six produce their own garment designs, eight generate their own patterns, and all plan and lay their own markers, as well as cut and assemble the clothing products. Of these companies, four have their own CAD systems. The one plant which is a subsidiary location has its own computer system, for ease in communicating designs, patterns, and markers to the other locations. Computer systems were found in six of the 29 companies. Among the remaining 23, the seven sew-only companies have no need for a grading and marking system. All of the other companies could potentially benefit from investment in a system, if only for marker plotting. As the findings of this survey show, 55 per cent of the small clothing companies can potentially benefit from a CAD system, through improved communications, and savings in fabric, time, labour and waste (see Figure 4). Whether the savings realized can justify the investment is a determination that each individual company must make for itself. The methods employed for marker making by the companies reporting included computer methods, tracing of patterns directly on to the fabric (eight companies), and creation of a stencil on paper (eight companies). The average time to lay a marker was 1.9 hours.

Have computer 21 per cent

Manufacturer (computer) 21 per cent

Make markers 14 per cent

Sew-only (no need) 23 per cent

Cut and sew (communication) 21 per cent

Figure 4. Potential for computer investment by reported companies

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The report of annual fabric usage ranged from 9,000 to 6,000,000 yards. Fabric prices ranged from $0.50 to $40 per yard. A fabric cost of $1,600 per garment was reported by a speciality manufacturer. Fabric costs are the most significant factor in overall garment costs. Only three companies failed to acknowledge fabric costs as the number one cost. Of these, two ranked direct labour costs higher, and one ranked cost of other materials first. The average for all of the companies is shown in Figure 5. Very few companies reported the use of a single type of fabric. The majority of companies worked with both knit and woven fabric structures (see Figure 6). Solids were very popular (76 per cent of companies), but a surprising number of companies (approximately 30 per cent), make clothing from stripes and plaids, some exclusively. Prints were also used by 36 per cent of those who reported. Other 11 per cent

Fabric 40 per cent

Overhead 20 per cent Figure 5. Average costs per garment

Direct labour 29 per cent

Figure 6. Fabrics used by companies

Case study analysis Two companies, operating without CAD systems, expressed an interest in providing examples of a typical production marker, as well as further information on their company. One of these companies will be discussed in this article, and the other in Part 2.

Once the markers were received at the research location, the garment pattern Communications: pieces were digitized from the marker into the available CAD system. The marker making – system used was a Lectra 3.0. After digitizing, the pieces were checked for any Part 1 digitizing errors, garment files were made, and markers were laid. A record of the time devoted to each task was kept. Markers of the same width as those furnished were created. Five versions of each marker were laid, with the time 161 required and the efficiency obtained recorded for each. The efficiencies of the original markers were calculated by using the square inch areas of the garment pieces generated by the computer, divided by the total square inch area of the marker (the product of the length times the width). Grading times were based on averages of students who graded a pair of pants using the computer. Entering the grade rules consumed 15 minutes of the students’ time. Case A: a tie manufacturer The company Company A is a tie manufacturer employing 27 people. It does its own garment design, pattern design, marker making, cutting and sewing. Currently, with little change in men’s tie styles, new patterns have not been developed in over three years, compared to the 1970s era when tie widths changed every three to four months. The fabric used is specially printed and woven silk tie fabric. Much of the fabric is printed in engineered blocks, with definite places to put the wide end and narrow end of the tie. There are two blocks across the width of the fabric. The fabric widths include 40, 45, 50, 55 and 60 inches. The fabric costs range from $12.50 to $25.00 per yard, with a usage of 10,000-12,000 yards per year. There are 250-300 fabric designs in three to four colour ways per year. The markers are created by hand. The marker is made on paper, the paper perforated, laid on fabric that is face down, and dusted to leave the cutting lines on the fabric. This takes one-and-a-half to two hours. The actual time to draw up the marker is five minutes. The marker maker is paid $11.88 per hour. As a percentage of garment costs, fabric is 30 per cent of the total. Direct labour and overheads account for 30 per cent each and other materials are 10 per cent. Waste material is disposed of at a fixed cost of $108 per month. There have been no changes in price in the past few years. Scraps have sometimes been sold, but they are usually so small, that there is little demand. Testing and results The furnished marker was for two ties that made up to a finished length of 55 inches. Marker width was 25 inches. Because of the way ties are tied, the fabric must be cut on the bias, or at a 45-degree angle to the grainline, for the fabric to bend and fold smoothly. Most ties have one seam in the centre of the length where piecing occurs. This pattern had two seams, which helped improve fabric efficiency by filling up the corners of the block (see Figure 7).

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Figure 7. Tie marker

Assuming that the placement of the tie parts was not dictated by the fabric print, an attempt was made to improve marker efficiency. The results are shown in Table I, with the original arrangement listed first. Due to the nature of the pieces, there is little to no opportunity for improvement in the marker. If the printed pattern dictates a particular layout, then there is no possibility for improvement. Analysis This company does not perform grading, as ties are one size. Most of their cutting is dictated by a printed fabric pattern, with some variation between

blocks, even of the same pattern. There is little or no opportunity for fabric Communications: savings or disposal savings. The only potential saving is in labour reduction for marker making – marker making; transferring the marker onto the fabric. Perforating the paper Part 1 marker takes a long time. This could be accelerated through the use of a special plotter to perforate the paper. A saving of one hour per marker for 250 markers per year would realize $2,970 savings in labour costs per year, assuming the 163 marker maker would work fewer hours. This amounts to a four-year payback period for an estimated $11,000 system. At 10 per cent interest over five years, the present value of the investment would be $11,259.

Time (min) 3 4 3 4 5

Yardage (inches)

Efficiency (%)

27.78 33.09 30.47 34.16 31.91

83.46 70.09 76.10 67.93 72.71

This company should look into the possible options for perforating the markers. With the high labour cost, investment in a new method is advisable. Conclusions Clothing manufacturing is becoming more and more competitive. Computer aided marker making appears to be suitable for an increasing number of manufacturers. Part 2 will discuss the importance of fabric cost in manufacturing, as well as the significance of waste reduction. A second case study, a dress manufacturer, will be presented. A possible method to determine the feasibility of CAD investment is included. References 1. “An introduction to the CIMple solution”, Clothing International, February 1989, p. 32. 2. Cole, W.R. Jr, “Computer grading and marking”, Clothing Industry Magazine, April 1982, pp. 36-42. 3. Eberly, N., “Cutting room update, Part 2”, Clothing Manufacturer, July 1990, pp. 30-7. 4. Major, C., “CAD/CAM: developments toward integration”, Textiles, 1993, pp. 12-13. 5. DeWitt, J.W., “New CAD standard creates level playing field”, Clothing Industry Magazine, May 1993, pp. 18-22. 6. Fozzard, G. and Hardaker, C., “CAD at IMB”, World Clothing Manufacturer, December 1993, pp. 33-9. 7. Li, Z., Compaction Algorithms for Non-convex Polygons and their Applications, Harvard University, Cambridge, MA, 1994. 8. Knox, A., “CAD/CAM in the clothing industry”, World Clothing Manufacturer, October 1994, pp. 20-2. 9. Rechtman, M., “A typical tragedy in three acts”, Bobbin, October 1978, pp. 166-70.

Table I. Tie markers

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10. Clothing Industry Productivity Association and National Productivity Institute, “A comprehensive material utilization study, Part III”, Clothing Manufacturer, November 1989, pp. 40-8. 11. Kosh, K., “Pattern quality, MU and CAD/CAM systems”, Clothing Manufacturer, August 1990. pp. 11-16. 12. Finkel, J.M., “Systems drastically reduce time and labor cost”, Clothing Industry Magazine, April 1984, pp. 50-1. 13. US Department of Commerce, Bureau of Census, 1992 Census of Manufacturers, Preliminary Report, SIC Codes 2311, 2321, 2322, 2323, 2325, 2326, 2329, 2331, 2335, 2337, 2339, 2341, 2342, 2361, 2369, 2371, 2381, 2384, 2385, 2386, 2387, 2389. 14. US Department of Commerce, Bureau of Census, 1987 Census of Manufacturers, Industry Series, SIC Codes 2311, 2321, 2322, 2323, 2325, 2326, 2329, 2331, 2335, 2337, 2339, 2341, 2342, 2361, 2369, 2371, 2381, 2384, 2385, 2386, 2387, 2389. Appendix. Clothing company questionnaire Number of employees___________________________________________________________ Which of the following does your company/location do (check all that apply): ________ Garment design

________ Pattern making/design

________ Marker making

________ cutting?

Are you a:

________ Contractor ________ Manufacturer of branded apparel ________ Subsidiary?

Type of product produced (check all that apply): ________ Men’s and boys’ suits, coats, overcoats ________ Men’s and boys’ trousers and slacks ________ Men’s and boys’ work clothing ________ Men’s and boys’ sportswear ________ Men’s and boys’ shirts ________ Women’s blouses and skirts ________ Women’s suits, skirts, and coats ________ Underwear and nightwear ________ Children’s blouses, skirts, and shirts ________ Children’s outerwear ________ Robes and dressing gowns ________ Accessories (gloves, hats, belts, etc.)

Structure of fabric used (check all that apply): ________ Warp knit (tricots, etc.)

________ Woven

________ Circular weft knit (jersey, etc.)

________ Non-woven

Communications: marker making – Part 1

________ Tubular weft knit (jersey, etc.) Do you primarily use:

________ Solids ________ Prints ________ Stripes/plaids?

Price range of fabric per yard ____________________________________________________ Widths of fabrics used __________________________________________________________ Amount of fabric used per year, in yards ___________________________________________ Approximate percentage of the following in garment costs: ________ Fabric

________ Other materials

________ Direct labour

________ Overheads

To make/generate markers, do you use a computer system, stencil on to paper, or trace directly on to fabric? ____________________________________________________________________________ Average number of man hours to make a marker_____________________________________

165

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The effect of selected mechanical properties acquired by the KES-F instruments on the level of puckering of cotton fabrics after washing Lubos Hes, Fatima M. Pinheiro, Miranda M.C. Goncalves and Arthur Cavaco-Paulo Universidade do Minho, Guimaraes, Portugal Introduction Within the wide range of woven fabrics made of synthetic yarns and their blends with cotton, the 100 per cent cotton products still offer the best handle and excellent physiological properties, but their nature leads to the creation of wrinkles and puckers, which have to be avoided in the final product (garment). Therefore, the finishing of these products commonly includes the permanent press treatment, based on the application of the crosslinked (polymerized) resins preferably not containing the free formaldehyde. Moreover, the finishing process also should reduce the shrinking (due to the mercerization), and the handle might be even improved though softeners. Such a long series of individual processes sometimes results in the occurrence of final effects which (owing to some cross-effects) differ from those expected. Since it happened in one Portuguese factory, the people responsible have decided to determine all the mechanical properties of the successful products and the fabrics exhibiting the puckering effects, with the objective of storing the mechanical properties of the quality products and avoiding the wrong finishing approaches. Thus, the quality of the goods is verified not only subjectively, but also by laboratory tests. As well as the measured mechanical properties, the levels of formability and sewability were also calculated and related to the puckering level determined subjectively[1]. As regards the formability F, the concept of Lindberg was used, but based on the direct applications of the results determined by the KES-F instruments, according to the relation F = B ε / 49 , 5. (1)

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 188-192. © MCB University Press, 0955-6222

The other parameter, the sewability SK (according to Kawabata) was calculated by the equation

S K = 500 ⋅ G ⋅ LT/2HG5 ⋅ W ⋅ EMT.

(2)

Meanings and units of all the parameters mentioned are identical with those published in [2]. Simultaneously with the objective measurement of the mechanical properties of cotton fabrics, the level of puckering of the samples was determined subjectively by a group of factory experts. The results were treated statistically and represented graphically. Besides the mechanical properties, the thermal-contact feeling of the fabrics was also determined, with special emphasis on the level of the coefficient of variation CV [per cent] of thermal absorptivity b of the tested fabrics. The principal idea of this study depends on the assumption that the puckering fabric should exhibit higher values of CV, since the thermal contact area is poorly defined in this case. The thermal absorptivity b [Ws1/2/m2] measured, e.g. by means of the alambeta instrument[3] expresses the level of warm-cool feeling – see [4].

Selected mechanical properties 189

Experimental Samples preparation All the samples of 100 per cent cotton twill were subjected to various kinds of finishing treatment, ranging from desizing and singeing (for all samples) to mercerization, sanforization and softening. For every treatment group, three samples were prepared. Some of these samples were not washed before being measured by means of the KES-F instruments, other samples (each having three pieces) were washed and pressed. Other groups of samples were subjected to the permanent press treatment, where the temperatures of polymerization were set to 150˚C, 160˚C and 170˚C – see the points PI, P2 and P3 in Figure 1. After the measurement, these samples were washed and measured again.

Figure 1. Vector map of changes of mechanical and thermal properties of cotton fabrics due to resin crosslinking (polymerization) P and washing W

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Statistical treatment of results All the mentioned results were demonstrated either by simple diagrams, or by the vector diagrams, applying the multivariate analysis method according to Bishop and Cox[5]. Data for the vectors map were obtained by principal components analysis. The co-ordinates of the vectors are “the factor scores coefficients” for each parameter and “the factor scores” are given by the position of each fabric sample on the maps. A high correlation between data of two different parameters is evaluated by the projection of one vector on to the other. The values of the mechanical parameters of the fabrics are obtained from their projections on to the respective parameter vectors. It has to be mentioned, that in this study the values of mechanical parameters for weft and warp direction were not treated separately, but medium values were used for simplicity. Results evaluation Figure 2, characterizing one of the samples, should serve as a proof that washing reduces sewability and formability of the tested fabrics and some of the selected parameters as well, which results in lower resistance against puckering. The final pressing recovers this lack just partially. According to Figure 1, the unwashed samples containing the resin crosslinked at various temperatures P1, P2, P3 are always very resistant to puckering, but washing (W) partially reduces this advantage. It has to be noted, that there were also some other samples treated in different way, or samples with slightly increased yarn density (both in weft and warp direction), which had shown good resistance to puckering after washing. From the comparison of the KES-F mechanical properties of tested fabrics with their resistance to puckering, it may be concluded that the best resistance

Figure 2. Vector map of changes of mechanical and thermal properties of cotton fabrics due to washing and pressing

is shown by samples exhibiting high values of 2HB, 2HG and 2HG5 and sewability as well. To some extent also higher levels of B, G and formability help to keep the samples smooth – see Figures 3-7. Note that the values for weft and warp direction may be different.

Selected mechanical properties 191 Figure 3. Graphic correlation between warp and weft for values of (G)

Figure 4. Graphic correlation between warp and weft for values of (2HG)

Figure 5. Graphic correlation between warp and weft for values of (2HG5)

Figure 6. Graphic correlation between warp and weft for values of (B)

Figure 7. Graphic correlation between warp and weft for values of (2HB)

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In the study, the idea of correlating the occurrence of fabric puckering with the level of the variation coefficient of thermal absorptivity of the tested samples was also investigated, since the uneven surface of puckered fabric, when being measured by means of the the alambeta instrument, should theoretically exhibit higher dispersion of such a surface characteristic as the mentioned thermal absorptivity or qmax (when evaluating the warm-cool feeling of fabrics by means of the thermolabo instrument). Unfortunately, the results did not verify the validity of this assumption for all the fabrics tested within the mentioned project. References 1. Pinheiro, M.F., “Investigation of changes of mechanical and thermal properties of cotton fabrics due to finishing”, Industrial Project, in Portuguese, co-adviser M. Granja, MSc, Universidade do Minho, 1995. 2. Kawabata, S., The Standardization and Analysis of Hand Evaluation (2nd ed.), Textile Machinery Society of Japan, Osaka, 1980. 3. Instruction manuals of the alambeta and permetest instruments, SENSORA Liberec Registered Company, Czech Republic, 1990. 4. Hes, L., “Thermal properties of non-wovens and some new methods of their evaluation”, in Proceedings of the INDEX 97 Congress, Genf, 1997. 5. Bishop, D. and Cox, D., “Application of a multivariate analysis method to a comparative study of fabric characteristics”, Journal of the Textile Institute, Vol. 85 No. 78.

Influence of washing/ironing cycles on selected properties of cotton type weaves Ji˘rí Militk´y and Vladimír Bajzík

Influence of washing/ironing cycles 193

Department of Textile Materials, Textile Faculty, Technical University, Liberec, Czech Republic Introduction It is well known that the properties of worn materials are often quite different from fresh ones. During the wearing cycle the fabrics are subjected to combined action of abrasion, washing and ironing. The main aim of this contribution is a description of the influence of washing/ironing cycles on the hand, shrinkage and surface roughness of selected weaves for men’s shirts. The samples were chosen from standard industrial production with two different finishings (sanforization or soft finishing). The subjective hand was evaluated by a group of consumers. The shrinkage has been measured by the direct measurement of the dimensional changes. The surface roughness has been estimated from the peaks on the load-displacement curve for the metal disc moved along the fabrics surface which is fixed vertically on the metal desk. For quantification of the influence on the washing/ironing cycle on the abovementioned characteristics the ANOVA methods and simple t-tests are used. Experimental part Three types of cotton weaves determined for men’s shirts were used for investigation. These samples were obtained from industrial production. The fabrics were mechanically stabilized by sanforization (abbreviation S). One part was then chemically finished by a softening agent (abbreviation F). Basic parameters of fabrics are given in Table I. The differences in the fabrics construction are at first sight not so high. Based on preliminary knowledge the consumer’s response to utilization of these weaves is not the same. The cover factor was computed from the sett and fineness data only. The washing/ironing cycle was realized by three successive operations: (1) washing in home type washing machine at 60˚C under standard conditions; (2) drying in free state at climatized conditions; (3) ironing at 200˚C.

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 193-199. © MCB University Press, 0955-6222

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Units

Caprino

194

Abbreviation Sett warp Sett weft Fineness warp Fineness weft Area weight* Area weight** Thickness Cover factor

– [m–1] [m–1] [tex] [tex] [g.m–3] [g.m–3] [mm] [%]

C 540 280 11.0 11.0 103.0 96.3 0.27 64.79

Table I. Fabrics’ properties

*Softened (F) **Sanforized (S)

Bugati B 420 290 14.5 16.5 110.6 116.6 0.3 64.59

Sarego S 420 270 12.5 11.5 102.4 97.1 0.3 58.07

The subjective hand and surface roughness were investigated before (abbreviation B) and after ten times repeating of washing/ironing cycle (abbreviation A10). The shrinkage was measured after the cycle was performed once (abbreviation A1), and again after the cycle had been repeated ten times. Subjective hand Subjective evaluation of hand was realized by the judges of 40 trained respondents. The individual samples were ranked according to their hand. Rank 6 corresponds to worst hand and 1 to the best hand of six investigated samples. From the results the sample rating median Xme, of subjective hand was computed by the following procedure[1]: (1) From absolute frequencies ni i = 1, … 6 corresponding to number of respondents giving the subjective hand of one investigated textile to i-th rank the relative frequencies n fi = i (1) n and cumulative relative frequencies j

fi = ∑ fi j = 1 , … 6

(2 )

i =1

were computed. The sample size is equal to 6

n = ∑ ni = 40.

(3 )

i =1

(2) The median category Me is specified from inequality FMe – 1 < 0.5 , FMe ≥ 0.5.

(4 )

(3) The sample rating median of subjective hand is computed from relation

X Me = Me + 0.5 –

FMe – 0.5

.

(5 )

fMe

Characteristic X me is estimator of population rating median Med. For description of estimator X me quality the confidence interval of 95 per cent containing population value Med has to be created. The following procedure adapted from Quenouille[2] is suitable: (1) Computation of cumulative frequencies 0.5 ± 0.98 ( FD* , FH* ) = . n

Influence of washing/ironing cycles 195

(2) Selection of categories D and H, in which the FD* and FH* are placed (3) Computation of coefficients d=

FD* – FD – 1 fD

,h =

FH* – FH – 1

.

fH

(4) Construction of rating median confidence interval of 95 per cent D – 0.5 + D ≤ Med ≤ H – 0.5 + h . These confidence intervals can be used for testing purposes. If for two fabrics the rating median confidence intervals intersect the handle grades are from a statistical point of view the same (on the significance level 5 per cent). Sample rating medians and corresponding confidence intervals of 95 per cent are given in Table II. Dimensional changes after washing The dimensional changes (most often shrinkage) in weft (abbreviation U) and warp (abbreviation O) directions were measured by the standard procedure. Then repeated measurements are realized. The mean shrinkages and corresponding confidence intervals for warp direction are given in Table III and for weft direction in Table IV. In cases where stretching occurred the values are indexed by an asterisk.

Treatment abbreviation

Xme

CS CF BS BF SS SF

5.8 5.2 2.1 1.2 3.5 3.2

No washing (B) Interval 5.4-6.0 4.8-5.6 1.7-2.7 1.0-1.6 2.8-4.0 2.7-3.7

Washing/ironing (A) Xme Interval 5.6 5.0 4.1 1.4 2.0 2.8

4.8-6.0 4.4-5.6 3.4-4.6 1.0-2.8 1.0-2.6 2.2-3.6

Table II. Sample rating medians and confidence intervals

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Surface roughness The simple method for assessment of the fabric’s roughness and friction resistance by using a special adaptor to the Instron tensile tester was selected. The principle is to register the force course S [mN] needed to move the metal disk along the fabric’s surface which is fixed vertically on the metal desk. This force course presents N L local minima S Li and N U local maxima S Ui . The average friction resistance U is defined as ∑ SUi + ∑ S Li U = KF

(i)

(i)

(6 ) N L + NU where K F is proportionality coefficient (recount to the force unit). The corresponding variation of all peaks is defined as  ( S – U )2 ∑ ( S Li – U )2   ∑ Ui (i) . R = 0.5 K R  ( i ) (7 ) +   NU NL     Here KR has the same meaning as constant KF in the equation (6). The surface roughness can be then expressed as the variation coefficient

Treatment abbreviation

Table III. Shrinkage in [per cent] warp direction

CS CF BS BF SS SF

3.0 0.9 1.2 0.6 0.5 0.7

Treatment abbreviation

Table IV. Shrinkage in [per cent] weft direction

CS CF BS BF SS SF *Stretch

1 × washing/ironing (A1) Mean Confidence interval

1 × washing/ironing (A1) Mean Confidence interval 2.3 1.4 1.8* 1.1 0.5 2.2*

occurs

2.2-3.8 0.4-1.4 0.4-2.0 0.2-1.0 0.4-0.6 0.6-0.8

1.8-2.8 1.0-1.8 2.6*-1.0* 0.2-2 3.0*-0.4 5.1*-0.7

10 × washing/ironing (A10) Mean Confidence interval 5.2 2.8 2.8 1.8 2.2 2.0

4.8-5.6 2.4-3.2 2.1-3.5 1.1-2.5 1.8-2.6 1.6-2.4

10 × washing/ironing (A10) Mean Confidence interval 1.8 1.0 1.7* 0.3* 0.7 4.5*

0.7-2.9 0.1*-2.1 3.3*-0.1* 2.3*-1.7 2.4*-3.8 8.0*-1.0

SR =

100.U

.

(8 )

R The average values of SR for individual fabrics are presented in Table V. Treatment abbreviations

No washing (B) Weft Warp

Washing/ironing (A) Weft Warp

CS CF BS BF SS SF

9.2 13.3 17.1 14.5 13.9 14.0

11.6 13.7 15.6 13.3 16.8 14.4

19.7 17.9 21.2 20.2 22.5 21.8

18.5 17.3 20.4 17.6 21.3 18.8

Influence of washing/ironing cycles 197

Table V. Surface roughness [per cent]

ANOVA analysis For investigation of the effect of weave type (factor A), softening (factor B) and washing/ironing cycles (factor C) on the hand, maximum shrinkage (warp direction) and maximum roughness (warp direction) the Analysis of Variance (ANOVA) technique has been used. In the first step the model with interaction has been selected. In cases when interactions were insignificant the reduced model containing the main effects only has been applied. The influence of levels of individual factors on differences between investigated properties were quantified by the contrasts analysis. The Scheffé type contrasts were constructed. For explaining the hand grade variation due to presence of factors A,B,C the reduced model without interactions is sufficient. The ANOVA results are given in Table VI. Based on the contrasts analysis the statistically significant differences between Caprino-Bugati and Caprino-Sarego were found. For description of maximum shrinkage variation due to factors A,B,C the ANOVA model with interactions must be used. The ANOVA results are in Table VII. Practically all contrasts are significant for this case. Maximum roughness variation due to presence of factors A,B,C is described by the reduced model without interactions. These results are given in Table VIII. Based on the contrasts analysis the statistically significant differences Source Main effects A:weave type B:finish C:washing/ironing Residual Total (corrected)

Sum of squares

d.f.

F-ratio

Significance level

22.762 1.5408 0.000833 5.3858 29.689

2 1 1 7 11

14.792 2.003 0.001

0.0031 0.1999 0.975 Table VI. ANOVA for hand grade

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198 Table VII. ANOVA for shrinkage (warp direction)

Source Main effects A: weave type B: finish C: washing/ironing Interactions AB AC BC Residual Total (corrected)

Source

Table VIII. ANOVA for roughness (warp direction)

Main effects A: weave type B: finish C: washing/ironing Residual Total (corrected)

Sum of squares

d.f.

F-ratio

Significance level

2 1 1

3675 3721 9801

0.0003 0.0003 0.0001

2.602 0.245 0.101 0.001667 20.342

2 2 1 2 11

15610 147 121

0.0006 0.0068 0.0082

Sum of squares

d.f.

F-ratio

Significance level

2 1 1 7 11

20.87 22.94 20.26

0.0011 0.0020 0.0028

6.125 3.101 8.167

15.167 8.333 7.363 2.543 33.407

between Caprino-Bugati and Caprino-Sarego were found. Statistically significant differences due to softening and due to washing/ironing cycles were found as well. Discussion From the point of view of hand the best weaves are Bugati and the worst Caprino. Caprino is the worst one but differences between Bugati and Sarego are statistically insignificant. The softening leads to the better hand but the significant influence are chosen for the Bugati weaves only. The washing/ironing cycles improve the hand and the differences between various weaves are smaller. Maximal differences due to washing/ironing cycles are found for sanforized fabrics (softening due to washing occurs). From the point of view of statistical significance only the influence of fabric type (factor A) is important. The differences due to softening and washing/ironing are statistically not substantial. The dimensional changes are higher for sanforized fabrics. Softening leads to better stabilization. Maximal shrinkage is found for Caprino weave. Bugati (F) are dimensionally stable after washing/ironing ten times. Shrinkage is influenced by the presence of all factors and interactions. Surface roughness is smaller for Caprino weave. Due to washing/ironing the surface roughnesses are changed probably mainly due to dimensional changes.

Based on the ANOVA model the roughness is significantly influenced by all the Influence of investigated factors but not by the interactions. washing/ironing From the statistical point of view the significant differences in roughness cycles exists for Caprino-Bugati and Caprino-Sarego only. Conclusion The results which have been presented clearly show that the influence of washing/ironing cycles on the properties of cotton weaves is very complex. The stabilization of dimensions occurs but the hand is not varied systematically. The spread of hand rating in washed/ironed samples is higher, probably owing to changes of bulkiness and deformability. Apart from this, the hand, shrinkage and surface roughness is dependent mainly on the type of fabric. References 1. Plackett, R.L., The Analysis of Categorical Data, Griffin, London, 1974. 2. Quenouille, M.H., Rapid Statistical Calculations, Griffin, London, 1976.

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Problems in recently manufactured worsted men’s suiting from the point of view of suit quality Kitoshi Ito Osaka Apparel Manufacturing Modernization Association, Osaka, Japan

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 200-202. © MCB University Press, 0955-6222

In the line production system, one of the most difficult problems for the apparel manufacturer is the problem caused by the unstable behaviour of the fabric in dimensional and mechanical terms. On the manufacturing line, steam pressing is used several times during the tailoring process. Even when the steaming process is adjusted to mild temperatures, the properties of the fabric are changed. This causes damage in the appearance of the finished suit. Because it is partly custom-made, repairing of the finished suit is necessary and takes a lot of time. The troubles caused by instability of fabrics are increasing now in spite of there being less difference between modes and former tailoring processes. One reason of this trend perhaps is the properties of recent fabrics, such as: • Modern “high tech” finishing uses various techniques to improve fabric hand such as new chemical treatments, without consideration for the fabric’s unstable behaviour in the tailoring process. • Following consumers’ demands relating to fashion or commercialism in marketing, various fabrics having different structures and woven with different combinations of various types of fibres are produced and transferred to apparel manufacturers without sufficient data about the fabric. These fabrics are processed online at the same time, because of the semi-custom-made system. • Single yarn weaves are becoming popular for summer suiting, replacing conventional two- or threefold yarns, and control of the property woven from the single yarn fabric is difficult compared with the conventional yarn weaves. In order to control the property, various techniques of finishing are frequently applied, making fabric property very complex. Figure 1 shows a typical example (sample no. 13) of the change in the tensile and shear properties of a suiting before and after the tailoring process. The original fabric property marked with - -l- - moves to the property marked with –l – after the processing. This change must be predicted and considered at processing, to prevent pucker or buckled surface ,which is called “bubbling”, appearing on the finished suit. These unusual types of changes in fabric

Problems in worsted men’s suiting 201

Figure 1. The changes in the mechanical properties resulting from the tailoring process. A typical complex fabric made from single yarn. N, C1, … W are symbols of the fabrics with different condition of tailoring process

property during the tailoring process are now becoming not unusual even for higher grade suiting; and rather, they are increasing in general. Figure 2 shows an example of the typical conventional suiting (sample no. 27) made around 1982. Although EM1 (extensibility in warp direction) is out of the good zone (marked by shadow), the changes of properties are very small compared with the example shown in Figure 1. To meet such a situation, the only counter measure we can do from the apparel side is to apply a careful sponging of the fabric before tailoring. In Figures 1 and 2, several filled marks

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Figure 2. The changes in the mechanical properties by tailoring process. A typical traditional fabric made from threefold yarn. The property of this fabric is not necessarily good, because of too large EM (tensile elongation along warp direction); however the property is less changed before and after tailoring

show the properties after the sponging. The fabric properties are becoming close to those properties appearing after tailoring. The sponging process is now becoming necessary because of the increasing difficulty in fabrics; however, we require first that textile engineers must study the tailoring process and fabric behaviour in relation to the process. Reference 1. Kawabata, S. and Niwa, M., “Fabric performance in clothing and clothing manufacture”, Journal of the Textile Institute, Vol. 80, 1989, p. 30.

An experiment on human sensory measurement and its objective measurement Case of the measurement of seam pucker level

Human sensory measurement

203

Sueo Kawabata University of Shiga Prefecture, Hikone, Japan

Miyuki Mori and Masako Niwa Nara Women’s University, Nara, Japan Sensory value and geometrical quantity of seam pucker In subjective evaluation, seam pucker is usually evaluated by means of visual observation of the seam line while comparing the pucker with a standard set of pucker levels, such as an American Association of Textile Chemists and Colorists (AATCC) standard set of photographs of pucker[1]. Also the pucker level is expressed numerically by numbers from 5 to 1 in order of the smoothness of the seam line; this is called “seam smoothness” and is a standardized sensory value. We have applied this standard for our subjective measurement. The evaluated scores from eight judges, female graduate students, were averaged to determine the subjective value. The geometrical shape of a pucker was measured by a scanning laser beam while measuring the pucker height. The height signal passes through a secondorder high cut filter with a cut frequency of 1 Hz (sweep velocity is 4 cm/s; therefore, 1 Hz is equivalent to 4 cm of wave length) to eliminate the influence of longer wave on the pucker evaluation. This processing of the pucker signal is based on the same principle as applied in surface roughness measurement with a KESF surface tester. The processed signal is averaged for an area, 10 cm in length along the seam line and 4 cm in width (2 cm from both sides of the seam line). The laser beam scans in the direction parallel to the seam line at 2 mm intervals, that is, 21 scans in the direction parallel to the seam line to detect the pucker wave. The scanning path is shown in Figure 1 and a reproduced pucker wave on a computer in Figure 2. The pucker height is processed by the filter and averaged with an integral circuit as follows: F=

1 A

∫

f ( x , y ) – f ( x , y ) dxdy

(1)

S

where, F, mm; average pucker amplitude,

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 203-206. © MCB University Press, 0955-6222

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x; y, mm; distance on the projection of the pucker surface on the table along the seam line and transverse to the seam line, respectively, f(x, y), mm; height of the pucker surface from the base table, f (x, y) ,mm; average off(x, y), and S, mm2; area scanned.

Figure 1. Laser scanning

Figure 2. Reproduced pucker wave with computer data processing

An analysis of the sensory evaluation of seam pucker We have no precise interpretation of the scale of sensory pucker measurement, even in the standardized pucker scale by AATCC. When the values for a physical quantity increase, human sensation can detect this. According to the Weber-Fechner law (1860), the threshold value is proportional to the quantity. This law leads a relation that the sensory value is proportional to the logarithm of the quantity of the physical stimulation. This relation may be derived also from the assumption that we feel that the sensory value becomes one rank higher when the stimulation becomes twice the present value, or more generally, n times the present value. This scaling is perhaps based on the situation that we have originally no reference for the sensory measurement, the only standard may be a scale of so many times of the present value. The usual scale is twice the present value (n = 2). This is a floating scale and enables us to

measure a wide range of quantities, for example, from a few grams to several kilograms in weight measurement. If the sensory value S is expressed by number such as 5, 4, 3, 2, 1, then S is related to the physical quantity Z based on the floating scale as follows. dS = (n – 1)

dZ

. (2 ) Z Solving (2) for S, S = ln Z/(n – 1) + c is derived, where c is a constant value. If Z0 is a value of Z corresponding to a referred sensory value S0, S – S0 =

2.303

(

)

log Z – log Z 0 . (3 ) n –1 When the “double” rule in the sensory measurement is applied, n = 2 and the coefficient of log Z becomes 2.303. Experiment AATCC defined seam smoothness, SS, based on their standard photograph of pucker appearance such as 5 = a very little pucker, 4 = a little pucker …1 = large degree of pucker. If pucker value, (PV), is defined so that 5 = large degree of pucker, … 1 = a very little pucker, SS and PV are the same measurement system, with opposite order such that, PV = 6 – SS . (4 ) Replacing Z in (3) by F and S by PV, and from (4), SS is predicted by the objective measure F as follows: SS = 5 –

Human sensory measurement

2.303 n –1

(log F – log F ) 0

(5 )

where basic SS is 5. Figure 3 shows a plot of subjective SS against log F for three fabrics: a lady’s thin dress fabric, men’s summer suiting, and men’s winter suiting. A linear relation between SS and log F was obtained for these three fabrics. The slope is 1.8 and F 0 is 0.0727 mm. From this slope, n = 2.3 is obtained. The “double” rule is roughly applicable. The scaling of SS is also influenced by the setting of the boundary value of SS and this influences the value of n. Discussion and conclusion The objective measurement presented here can predict with a high degree of accuracy the degree of seam pucker. It shows that AATCC standard needs an additional degree of SS = 6, that is, a level of no pucker at all. This lack of degree disturbs the linear relation between SS and log F. As mentioned before, the sensory evaluation of pucker is relatively simple compared with fabric hand evaluation, even though it is a visual evaluation of a complex geometry. Therefore, the objective evaluation is very precise and much

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Figure 3. Predicted SS based on F Note: Scale was extended to 6 (no pucker at all) and 0 and negative value (for terrible pucker produced in laboratory experiment). Solid line is the prediction line and its measurement slope is 1.8.

better than the subjective method, which must be replaced with an objective method. This method presented here is already in practical use in laboratory and proving its accuracy and usefulness. Reference 1. AATCC TEST Method 88B-1992, AATCC Technical Manual, AATCC, 1993.

Objective hand evaluation of non-wovens used for nappies Hiroko Yokura

Objective hand evaluation of non-wovens 207

Faculty of Education, Shiga University, Japan and

Masako Niwa Department of Textile Apparel Science, Nara Women’s University, Nara, Japan Introduction Disposable nappies are improving rapidly in the personal care market. Nappies come in contact with the skin. Non-wovens are used for nappies and consumers are concerned as to whether these cause dermatitis. The water transport properties and hand (softness and smoothness) of nappies are considered to be concerned with nappy dermatitis. A method for the objective measurement of the fabric hand of men’s suiting has been developed[1]. This objective hand evaluation system has been applied to the objective evaluation of a group of non-wovens which are used for materials near human skin[2,3]. In this study, we extend our investigations to the objective hand evaluation of non-wovens used for disposable nappies, which included the top sheet, absorber and waterproof layer. Experiment Test nappies: 29 samples of commercially produced nappies were selected in September 1995. The items were 18 baby’s nappies, eight adult incontinence briefs and three adult incontinence pads. Subjective evaluation of nappies’ hand Twenty-six samples were tested. The hand of the nappies was assessed by young mothers and female students under both dry and wet conditions. They were asked only to judge whether the hand was good or poor, based on the sensation from contact with the nappy. They evaluated sample quality in random order using a scale of 1 (poor) to 5 (excellent). The dry or wet nappies were tested individually by two groups: the dry nappy group (31 mothers) and the wet nappy group (four mothers and 16 female students). The preliminary investigation showed a good correlation between the judgement of mothers and that of female students. In the sensory and mechanical tests of wet nappies, a sample was cut from the nappy’s centre, and put into a 7.5 × 10.5 mm2 cell. Then, the segment was moistened with 30g of a 0.9 per cent NaC1 solution (0.4g/cm2) by using the injector (constant pressure: 500gf). The temperature of

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 207-213. © MCB University Press, 0955-6222

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the solution was 32˚C. The wet segments were set into the conditioning box of 32˚C, 98 per cent relative humidity (RH) during the sensory test. The judges reached into the box and evaluated the nappy’s hand. Compression and surface properties The compression and surface parameters of the nappies, which could be related to the soft and smooth feeling of nappies, were measured by the KES system. Table I shows the surface and compression parameters. In this study, we investigated both the sensor for surface friction and the indenter for compression. In the case of the top sheet non-woven fabrics, a single wire sensor for surface friction was used[2]. In this case, a single wire sensor and 20 wires/cm2 sensor were tested. For the compression test, two indenters were tested, 2cm2 standard disk and 3.1 cm diameter rubber ball.

Parameters

Description

Measuring conditions

Surface MIU MMD

Coefficient of friction Mean deviation of MIU

Sensor (contact force) (1) a single U-shape wire (5 gf) (2) 20 U-shape wires/cm2 (30gf/cm2)

SMD

Geometric roughness

Compression LC Linearity of compression/thickness curve WC RC

Indenter (maximum pressure) (1) 2 cm2 standard disk (10gf/cm2) (2) 3.1 cm diameter rubber ball (20 gf)

Compressional energy Compressional resilience

Construction Table I. T Thickness Surface and compression W Weight/unit area parameters

Water retention property A sample was cut from the nappy’s centre, and put into a 7.5 × 10.5 mm2 cell. The segment was moistened with 30g of a 0.9 per cent NaCl solution (0.4g/cm2) by using the injector (constant pressure: 500 gf). After immersion in the solution for five minutes, the filter paper was placed on the segment, and pressed for 30 seconds under pressure of 45gf/cm2 (corresponding to the body pressure during use of the nappy). The weight of the solution absorbed into the filter paper was measured and defined as “Rewet”. Results and discussion Objective hand evaluation of dry nappies The mean score of the subjective hand assessments was used as the total hand value (THVsub) of the nappy. The mean values of the correlation coefficients

between individuals and the mean scores within each group were 0.544 for dry nappies and 0.743 for wet nappies. The agreement by the individual judges was low for the dry nappy compared with the wet nappy and other non-wovens. Table II shows the correlation coefficients between the THVsub of dry nappies and the compression and surface parameters. In the case of non-woven fabrics, it was concluded that the surface parameters correlated with the THV more highly in the transverse direction[2]. We applied both the average of the values in machine and transverse directions and the transverse direction for the surface parameters. The THVsub of dry nappy was correlated with their surface properties obtained using the single wire sensor. The nappies with good hand showed small values of MMD and SMD. For the compression properties, using the rubber ball indenter is better than the standard disk indenter. Using these parameters, we applied the suiting THV equation to nappies’ THV calculation. The objective system of evaluation of non-wovens had already been presented[2,3]. In the case of nappies, only their surface and compression properties were applied to the primary hand value calculations. Table III shows the correlation coefficients between the THVsub of dry nappies and the primary hand and total hand values. The THVsub of dry nappy was correlated with NUMERI (Smoothness) and THV. The KN-301W equation has the ability to evaluate the hand quality of top sheet non-wovens[2]. It was also confirmed that the KN-301W equation has the ability to evaluate the hand quality of dry nappies using only the surface and compression properties. The THVsub of dry nappies was correlated with the THV of their top sheet fabrics (correlation coefficients: r = 0.527), which was calculated by the Parameters

209

Correlation coefficients (r)

Surface (average) MIU MMD SMD

Single wire –0.390 –0.636* –0.661*

20 wires/cm2 –0.409 –0.583*

Surface (transverse) MIU-2 MMD-2 SMD-2

Single wire –0.371 –0.548* –0.471

20 wires/cm2 –0.337 –0.464

Compression LC WC RC

Standard disk –0.051 0.071 0.296

Rubber ball –0.357 0.050 0.483

Thickness, T Weight, W

–0.250 –0.139

–0.406

Note: *: 1 per cent significance level, r > 0.496

Objective hand evaluation of non-wovens

Table II. Correlation coefficients between the THVsub of dry nappy and each of the compression and surface properties

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210 Table III. Correlation coefficients between the THVsub of dry nappies and each of the primary hand and total hand values

Parameters Primary hand value KOSHI NUMERI FUKURAMI Total hand value THV

Correlation coefficients (r) Condition I 0.133 0.659* 0.513* 0.643*

Condition II 0.156 0.575* 0.462 0.563*

Notes: *: 1 per cent significance level, r > 0.496 Condition I: use the average of the values in machine and transverse directions as the surface properties Condition II: use the values in transverse directions as the surface properties

objective hand evaluation system for non-wovens[3]. We found that the THV of the top sheet of nappies contribute to the THV of nappies. Objective hand evaluation of wet nappies The relationship between the THVsub of dry and wet nappies is shown in Figure 1. The value of correlation coefficients is 0.486, the quality criteria of wet nappies differ from that of dry nappies. However, within each-end use group, the THVsub of dry nappies was correlated with the THV sub of wet nappies. The values of the correlation coefficients were 0.593 for baby nappies and 0.767 for adult incontinence wear. The THVsub of adult incontinence wear, compared with babies’ nappies, was noticeably reduced when they were wet.

Figure 1. Relationship between the THVsub of dry and wet nappies

Table IV shows the correlation coefficients between the THVsub of wet nappies and the compression and surface parameters. The THVsub of wet nappy was correlated with their compression properties. The nappies with good hand showed small value of LC and large value of RC. Using these parameters, we calculated the hand values of wet nappies in the same manner as with dry ones. However, we cannot observe any correlation. For the next investigation, we measured the water retention property of wet nappies. The relationship between the THVsub of wet nappies and the value of rewet is shown in Figure 2. The correlation coefficient is –0.751. Parameters Surface (average) MIU MMD SMD Surface (transverse) MIU-2 MMD-2 SMD-2 Compression LC WC RC Thickness, T Weight, W Note: *: 1 per cent significance level, r > 0.496

Objective hand evaluation of non-wovens 211

Correlation coefficients (r) Single wire –0.071 –0.061 –0.297 –0.336 –0.167 –0.390 Rubber ball –0.623* –0.281 0.645* 0.472 0.509*

Table IV. Correlation coefficients between the THVsub of wet nappies and each of the compression and surface properties

Figure 2. Relationship between the THVsub of wet nappies and the value of rewet

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We applied the stepwise regression analysis[1] to derive the equation which connects the rewet, compression and surface properties directly to the THVsub of wet nappy as follows: THVcal = C 0 +

212

9

∑

Zk

(1)

k =1

where Zk represents the contribution of these properties to THV, and can be calculated by equation (2): Z k = C k1 (Yk – M k1 ) / σ k1 + C k2 (Yk2 – M k2 ) / σ k2

(2 )

where C0, Ck1, Ck2 = constant coefficients, Yk = value of kth property, Mk1 = population mean value of kth property Y k for nappies, σ k1 = population standard deviation of k property Yk, Mk2 = population mean value of the square of kth property Y k, σk2 population standard deviation of the square of kth property Yk. The contribution Zk of each parameter to the THV of wet nappies is given in Figure 3. The first step was the rewet; a lower value of rewet increases THV. The second step was the compression parameters. Lower values of LC and logWC, and higher value of RC increase THV. The third step was the surface parameters. Lower values of MIU and logSMD increase THV. There is an optimum zone for logMMD. The fourth step was construction, but the

Figure 3. The contribution Zk of each parameter to the THV of wet nappies

Objective hand evaluation of non-wovens 213

Figure 4. Relationship between the THVcal and THVsub of wet nappies

contribution is small. The relationship between the THVcal and THVsub of wet nappies is shown in Figure 4. The correlation coefficient is 0.922. Conclusions The following four conclusions can be reached from this study: (1) The THVsub of dry nappy was correlated with their surface properties which were obtained using the single wire U-shape sensor. (2) The KN-301W equation has the ability to evaluate the hand quality of dry nappies, using only the surface and compression properties. (3) The THVsub of wet nappy was correlated with both their water retention property (rewet) and their compression properties which were obtained using the rubber ball indenter. (4) We found the equation connects the rewet, compression and surface properties directly to the THVsub of wet nappy using the stepwise block regression method. References 1. Kawabata, S., The Standardization and Analysis of Hand Evaluation, (2nd ed.), HESC, the Textile Machinery Society of Japan, 1980. 2. Kawabata, S., Niwa, M. and Wang, F., Text. Res. J., Vol. 64 No.10, 1994, pp. 597-610. 3. Niwa, M., Wang, F. and Kawabata, S., Proceedings of the 23rd Textile Research Symposium at Mt Fuji, 1994, pp. 143-51.

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Analysis of “wet” sensation for lingerie fabrics Sachiko Sukigara

214

Faculty of Education, Niigata University, Niigata, Japan and

Masako Niwa Faculty of Human Life and Environment, Nara Women’s University, Nara, Japan Introduction The feeling of “moist” discomfort and the sensation of dampness during wear is influenced by clothing as well as by other physiological factors. In the case of lingerie, the fabric directly contacts the skin during wear, so the fabric properties play an important role in the sensation of dampness. As the body perspires, the lingerie worn sometimes produces a very uncomfortable sensation. Water movement through the lingerie fabric to the air is one of the key parameters in such circumstances. Water evaporation produces a drop in the temperature between the skin and fabric. The speed of water movement through the fabric might be related to thermal sensation. The microclimate between the skin and fabric also influences both thermal and tactile sensation. The presence of water between the skin and fabric also changes the frictional property between them. In this study, we attempt to clarify the effect of moisture in various fibre materials on the sensation of dampness by means of both subjective and objective trials. Samples Four lingerie fabrics made from different fibre types were chosen, as shown in Table I. These samples had already been evaluated for their tactile characteristics in lingerie by 86 women. Sample P2 scored highest in overall comfort and P1 showed the lowest score[l].

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 214-219. © MCB University Press, 0955-6222

Subjective trials Wet samples against normal skin It has been reported that a wet sensation is influenced by the temperature and water content of a sample as well as the ambient temperature and relative humidity[2,3]. When filter papers with a water content of 160 to 180 per cent were placed on the skin, a small degree of wetness was detected at 20˚C, 65 per cent relative humidity (RH)[2]. The differences in dampness perception became smaller as the ambient humidity increased from 25 to 75 per cent RH[3]. Based on a literature survey, we chose an experimental condition which would be as sensitive as possible to assess the wet sensation, as follows:

• Ambient temperature and humidity: 20˚C, 50 per cent RH; • Temperature of water: 3˚C lower than skin temperature; • Water content of a fabric: 150 to 250 per cent. A sample (7 × 10cm) was put in water at a temperature of 3˚C lower than skin temperature. Excess water was removed to obtain a water content of 150 to 250 per cent, then the sample was placed on the back of the subject’s neck. The subject felt a wet sensation but could not detect a difference in wetness among samples of the same water content. The subject strongly felt the wetness when the sample was removed. In this case, the subject felt coolness or a chilling sensation rather than wetness. For samples with high water content, the stickiness to the skin might be one of the parameters to be evaluated.

P1 P2 S1 C1

Fibre

Structure

Polyester Polyester Silk Cotton

Tricot jersey Tricot jersey Plain knit Tricot jersey

Yarn count

Wales cm–1

Course cm–1

Weight mg/cm2

Thickness mm

50d-36fil 50d-36fil 126d-28fil 100d/2

21 21 16 15

25 24 19 27

14.76 9.71 7.74 13.28

0.404 0.339 0.321 0.792

Conditioned sample against wet skin A test sample conditioned at 20˚C, 65 per cent RH was placed on the subject’s forearm and moved for about five seconds. Thirty female subjects were asked to assess tactile sensations such as smooth/rough, cool/warm, clammy/absorbent according to the Scheffé’s paired comparison method for three samples (P2, SI, CI). An experiment was also carried out for slightly wet skin which was obtained using a wet towel to wipe the skin. Figure 1 shows the yardstick for the clammy, cool and smooth feeling. Sample P2 shows less clamminess compared to the other two samples for both normal and wet skin conditions. From observations of the above two subjective trials, we designed simulation tests to investigate the mechanism of the wet sensation. Simulation tests Simulating the presence of perspiration on skin Both the heat and moisture transfer of a fabric can be related to the wet or damp sensation. First, the thermal properties of fabrics were measured. A KES thermolabo II was used to measured the following characteristics. • Qdc: the heat loss from a heat plate to the air environment through a specimen (W.m–2); • Qwc: the heat loss from a wet heat plate to the air environment through a specimen (W.m–2) (see Figure 2); • λ: the effective thermal conductivity of a fabric (Wm–1K–1);

Analysis of “wet” sensation for lingerie 215

Table I. Samples

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Figure 1. Difference in “clammy”, “cool” and “smooth” feeling for three samples for both normal and wet skin

•

Co: the transient heat flow using a finger robot[4] which correspond to the warmth or coolness of a fabric surface (sec–1);

•

m: the rate of water transfer through specimen is estimated as follows m = (Qwc – Qdc)/ (gm–2 s–1) where E = 2422J/g: heat of vaporization at 30˚C. The experiment was carried out in a room conditioned at 20˚C, 65 per cent RH. The values obtained are listed in Table II. It can be seen in Figure 1 that sample P2, which has the largest value for m, showed significantly less of a clammy feeling than the other samples.

Analysis of “wet” sensation for lingerie 217

To simulate an actual wearing condition The vapour concentrations in a skin-clothing microclimate might be related to the wet sensation. We designed an experimental condition in which a lady wears lingerie with a thin dress (cotton and polyester sample) on top, as shown in Figure 2b. The humidity in the space is measured. Polyester film was also used as a top material for comparison purposes. The details of the polyester film and two thin dress fabrics are shown in Table III.

Figure 2. Simulation tests design

P1 P2 S1

Qdc Wm–2 K–1

Qwc Wm–2 K–1

m gm–2sec–1

λ Wm–1 K–1

(× 10) 9.9 10.4 9.4

(× 10) 38.5 42.2 39.3

(× 10–1) 1.18 1.32 1.23

(× 10–2) 5.43 4.61 3.5

Structure Polyester film Cotton Polyester

Plain weave Plain weave

Co Air resistance THV-s sec–1 Pa.s/m (KN304) (× 10–2) 3.46 3.17 3.33

83.2 19.2 17.4

1.86 2.85 2.99

Weight (g/m2)

Thickness (mm)

Air flow resistance (Pa.s/m)

35 86 86

0.203 0.355 0.361

19.8 13.4

Table II. Thermal properties of fabrics

Table III. Ladies’ thin dress fabrics

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Table IV shows the temperature and humidity in the microclimate for various samples. This ambient condition was set for a hot summer day of 32.4˚C, 55.8 per cent RH. When cotton or polyester thin dress fabrics were used for the top fabrics, the relative humidity in the microclimate was in the range of 66.0 to 70.6 per cent, which is assumed to be very uncomfortable. However, the differences in the relative humidities of the lingerie materials are marginal. Simulating the stickiness between lingerie and skin The frictional property between lingerie fabrics with a water content of 100 to 250 per cent and artificial skin were measured to investigate the degree of stickiness to the skin. Samples with a water content of 100 to 250 per cent are placed on the artificial skin. which is on the plate of KES-SE surface tester, as shown in Figure 3. The contactor, which has an area of 2.9 × 3.4cm2 covered by an artificial skin, was moved at a rate of 1 mm/sec under a pressure of 0.31N. The obtained coefficient of frictions between the lingerie and artificial skin (µ) is plotted against the water content (Figure 4). The coefficient of friction increased in the increase of water content. It is considered that the space between yarns fills with water, and this water sticks to the artificial skin and stops the movement of fabric. In this experiment, the cotton and silk sample

Micro climate

Table IV. Temperature and humidity in the microclimate

Figure 3. The apparatus used to measure the friction between lingerie fabric and artificial skin

Thin dress

Lingerie

Temp (˚C)

Hum. (% RH)

Film

P1 P2 S1 C1

33.9 33.9 33.9 33.9

100 100 100 100

Cotton

P1 P2 S1 C1

32.6 32.6 32.6 32.5

67.8 67.6 66.0 66.8

Polyester

P1 P2 S1 C1

32.8 32.8 32.8 32.7

70.6 68.5 68.0 67.7

Analysis of “wet” sensation for lingerie 219

Figure 4. The plot of µ against the water content of four samples

shows larger values for the coefficient of friction than polyester samples for throughout the entire water content range. Conclusions The sensations of dampness and wetness are influenced by tactile sensation, thermal sensation and water vapour sensation. When the fabric is covered with water, that is, the fabric water content is in the range of 150 to 250 per cent, wetness, stickiness and coolness are strongly detected by the subject. When the fabric water content is less than 10 per cent, the subject can detect the dampness, smoothness and coolness. It was found that subjective sensation is related to the speed of moisture transmission measured by the simulation test. References 1. Sukigara, S., Fujimoto, T. and Niwa, M., Sen’i gakkaishi, Vol. 49, 1993, pp. 294-305. 2. Koshiba, T. and Tamura, T., J. Japan Res. Assoc. for Text. End-use, Vol. 36, 1995, pp. 119-31. 3. Plante, A.M., Holcombe, B.V. and Stephene, L.G., Textile Res. J., Vol. 65, 1995, pp. 293-8. 4. Kawabata, S., Nakanishi, M. and Niwa, M., Sen’i Gakkai Symposia Preprints,1990B, Seni Gakkai, B17, 1990.

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Effect of seams on fabric drape Jinlian Hu, Siuping Chung and Ming-tak Lo

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International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 220-227. © MCB University Press, 0955-6222

The Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Introduction “Drape” in textiles is a term which describes the unique characteristics of a fabric under its own weight when supported in some areas, but not in other places. Smooth three-dimensional folds of the fabric formed under the aforesaid conditions are the main feature. To some extent, it is used to represent the gracefulness of a fabric in appearance and its comfortableness in touch. This does not apply to other sheet materials such as papers. During recent years, the investigation of fabric drape has attracted the attention of many researchers because of the attempts to realize the clothing CAD system by introducing the fabric properties, in which fabric drape is the key element. It is obvious that fabrics have to be sewn together for a garment to be formed. The seams of a garment affect the fabric drape greatly. It is unrealistic to realize the appearance of a garment system without the consideration of seams and the methods of assembling of fabrics into garments. Suda and Nagasaka[1] investigated the effect of seam on fabric bending rigidity tested in the KES system by varying seam allowances, the number of seams on the same specimen, the type of stitches, seam and sewing thread. They concluded that a seam has distinctive effects on the bending property of a fabric. In another paper[2], they studied the effect of seam and hem of a flared skin on the drape profile, by bonding narrow strips of non-woven fabrics at the edge or along the radial direction of circular fabrics. They observed that the bending rigidity of the bonded part increased with the width and/or the number of bonded layers of the non-woven fabric. In the samples with only their edge bonded, the drape coefficient increased, and there was a negative correlation between the number of nodes formed and the rigidity of the bonded layers. In the case of samples with bonded strips in radial directions, the fourth layer of non-woven fabric seemed to have distinctive influence on node formation. Dhingra and Postle[3] investigated bending properties of fabrics with seam. They used wool woven fabric with 2/2 twill structure. It was found that seam has little effect on fabric shear rigidity and hysteresis, but has a significant effect on bending rigidity under some circumstances. When a seam is perpendicular to the axis of bending with 1 mm seam allowance (SA), bending rigidity is three to four times greater than the bending rigidity with no seam. When a seam is parallel to the axis of bending with SA of 1 mm, there is little effect on bending rigidity. When seam allowance is greater than 2.5mm,

bending resistance increases, but the effect is not as significant as in the perpendicular direction, which is because more freedom area of unsewn part is found in the former. Bending hysteresis or bending moment B0 is strongly affected by seam allowance. For 1mm SA, B0 with no seam: B0 with seam = 1:911 and for 10mm SA B0 with no seam = 1:2633. Apart from the above study, it seems that the existing theoretical and experimental work in fabric drape has been mainly restricted to fabric without seam. Even from these three papers, the research into seam properties is mainly concentrated on bending rigidity on pure bending tests. The drape of fabric with seam was simulated as sticking strips of non-woven fabrics. This will probably not reflect the drape of a fabric with a real seam. This paper presents part of the results from a project entitled “The effect of seams as assembling methods of a garment on fabric drape”. The effect of real seams on drape coefficient, bending length and draped profile, e.g. node positions of fabrics, are the main concern in this paper.

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Experiment In the present study, the Cusick Drapemeter was used for the evaluation of fabric drape in terms of drape coefficient and appearance. The FAST-2 bending tester and Peirce’s Flexometer were employed to measure bending length. Brother Exedra (DB2-B737-403) lockstitch sewing machine, sewing needle number 11, polyester spun thread B754, C9700 with yarn count 120 were chosen for sewing. All sewn fabrics had stitch density of 4 stitches/cm. Stitch tension was maintained constant on the both sides of the fabric. All specimens were placed in the standard testing atmosphere for 24 hours before test. Materials used are woven fabrics. Bending length When a seam is parallel to the hanging edge of the cantilever (bending axis), it is called a horizontal seam in this context, while that which is perpendicular to the hanging edge is called a vertical seam. Vertical seams are always arranged in the middle of the specimens, while the positions of the horizontal seams vary in the test specimen (see Figure 1).

Figure 1. Vertical and horizontal seams for bending length test

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Three specimens, from warp and weft respectively, were made with finished size 5cm × 20cm for which 2.5cm were cut off from all sewn fabrics at both ends to reduce the uneven stitch tension for centre-cut vertical seam specimens. The FAST-2 tester was used for the vertical seam. These seams were made with seam allowance: 0 (no seam), 1mm, 2.5mm, 5mm, 10mm, 15mm, 20mm and 25mm. Peirce’s Flexometer was used in the bending test for testing the fabric with a horizontal seam. Five cm from the free end of fabric is chosen for the bending point to determine the bending length of a fixed seam position. Three 3cm × 20cm specimens were cut from the warp and the weft of the sewn fabric respectively. The horizontal seam was sewn at 5cm, 2.5cm, 0.5cm respectively from the bending edge. Seam allowances of the sewn fabric vary according to the seam positions. They are as follows: Seam allowances of 0 (no seam), 1mm, 2.5mm, 5mm, 10mm, 15mm, 20mm, 25mm, 30mm, were made when seam position is located at 5cm from the free end. Seam allowances of 1mm, 2.5mm, 5mm, 10mm, 15mm, 20mm, 25mm, are made when seam position is located at 2.5cm from the free end. Seam allowances of 1mm, 2.5mm, 5mm were made when seam position is located at 0.5cm from the free end. Drape test There are many ways to have seams made on the drape test specimens. One is straight along a radial direction, the other has circular shape at a distance from the specimen centre. Furthermore, straight seams can be single on warp or weft direction or along any radial direction, or double-crossed along the warp and weft directions. In the present study, single and double-crossed radial seams along warp or/and weft directions were made for the tests. The largest template with 36cm in diameter is chosen for the present research, because the fabric weight is large in the first place. Drape coefficient will be compared on various seam allowances of 1mm, 5mm, 10mm, 15mm and 20mm. Projected drape profiles of fabrics were observed during the some drape tests. Results analysis The results from the study can be summarized as the following. Bending length The results from bending length tests are represented by Figure 2. From this figure, for a vertical seam, it was observed that the bending length of a specimen increases with seam allowance (SA) rapidly in the initial region (from 0-1mm), and then remains almost constant when seam allowance increases. For a horizontal seam, the bending length may decrease at very small SA, but increases with larger SA and the increase magnitude even at the later stage is not as significant as the vertical seam. Furthermore, the position of the seam to the bending edge has the effect on bending length. The further the seam positioned, the smaller the bending length for a horizontal seam.

From Table I and Figure 2, a specimen without a seam has the lowest value compared with a vertical seam, but this is not true for the horizontal seam in terms of bending length. Bending length of a specimen with a vertical seam is always larger than that of the horizontal seams. According to Peirce, bending length is a measure of fabric bending stiffness. Therefore, it needs to be noted that the results obtained here is different from increasing the width of sticking a narrow piece of fabric on the specimen (similar to the increase of SA). In the case of sticking a strip of fabric, the conclusion will be true that the stiffness of the specimen will be increased with the increase of SA (the width of the stuck fabric), and then the bending length of the fabric will increase continuously with SA. The bending length test is also different from pure bending test. According to Dhingra and Postle[3], the bending stiffness will increase with the increase of SA, but, bending length test reveals that the bending length can only be increased to a certain extent, and then remain constant when SA increases for vertical seams. For horizontal seams, the increase of SA may lead to a lower bending length than without a seam. Generally speaking, it seems that seams probably stiffen the fabric locally in certain directions, but drape property of a specimen or a structure is different from the increase of the local stiffness.

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Drape coefficient Suda et al.[1] described their attempt to bond strips of non-woven fabric on a specimen to simulate seams on a garment where increased SA caused Seam allowance in mm/ bending length in mm Vertical seam Horizontal seam positioned 5cm from the free end Horizontal seam positioned 2.5cm from the free end Horizontal seam positioned 0.5cm from the free end

0 20.5

1 32

2.5 33.8

5 33.4

10 36

15 36.5

20 37.6

25 –

30 –

20.5

20

21.2

22.4

23

25.6

25

24

24

20.5

17.8

18.5

18.8

17

16

15.7

20

–

20.5

17.6

17

16.6

–

–

–

–

–

Table I. Bending length of vertical and horizontal seams with various seam allowances

Figure 2. Bending length of fabrics with horizontal seam (various seam positions but bending point at 5cm from the free end), and vertical seam (sewn at centre)

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continuous increase in drapeability. Unlike their conclusion, it has been found by the present authors that the increase of seam allowance does not continuously increase the drapeability of a fabric. Instead, drape coefficient increases with seam allowance first, and then decreases with the increase of seam allowance, as can be seen in Figure 3. It needs to be noted that the drape test is also different from bending length test. If this is simulated to the situation of vertical seams in the cantilever test, the increase rate of drape coefficient is much lower than bending length and the maximum drape coefficient is at SA close to 10mm (2mm or so for bending length).

Figure 3. Drape coefficient of cotton fabric against various seam allowances for double cross plain seams sewn at warp and weft directions

Projected drape profile of fabric with seams When the seams are on the warp and/or weft directions of a circular specimen, the folds of the drape profile were observed to be formed usually on the seam directions. This is partly because the beading stiffness of the seam is usually higher than other places and partly because the seam has a supportive function to the drape of the local fabric. Thus on a circular cross-sewn double seam specimen, there are four nodes dominating the projected drape profile. For a straight single seam specimen on the warp or weft direction, there are usually two folds dominating the profile but the fold on the two sides of the seam is very diversified as shown in Figure 4. Projected drape profile of fabrics without seams From the results obtained in the above section, some general conclusions can be drawn and more tests were done for unsewn fabrics from the present study with orthotropical and isotropical properties. Orthotropic structure. Woven fabrics are usually considered as orthotropic structure, and the bending stiffness on the warp direction is usually larger than that of the weft. In this case, there are usually two folds on the warp direction along the two opposite radial directions of the circular specimen supported in the middle by a smaller pedestal. This feature of drape profile seems to be stable when tested at different times, particularly for thick fabrics. The larger the difference between warp and weft bending stiffness, the more obvious the orientation of the draped folds, as shown in Figure 5.

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Figure 4. Nodes formed at seam positions at warp or/and weft (Nodes are more concentrated at the seamed area as seam allowances increases)

Figure 5. Orthotropic structure – nodes form at the warp direction as bending stiffness is greater than that in weft direction

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Isotropic structure. If bending stiffness of the fabric in the warp and weft directions are similar or the same, the fabric can be considered as an isotropic structure. Under these circumstances, the draped profile observed in the present study seams not to be stable when tested at different times under the same conditions. Moreover, the orientation of the nodes is not clear. This means that the drape behaviour is more complicated when the fabric is isotropic in nature, as shown in Figure 6.

Figure 6. Isotropic structure – bending stiffness is similar in warp and weft, there is no specific node orientation

Conclusions In this paper, the relationships between fabric drapeability and seam allowance, seam positions and seam directions have been studied in terms of drape coefficient, bending length and drape profile. A specimen without a seam has the lowest value compared with a vertical seam on a cantilever test, but this is not true for the horizontal seam in terms of bending length. The bending length of a specimen with a vertical seam is always larger than that of the horizontal seams. For a vertical seam, the bending length increases with SA very rapidly at the initial stage, but remains almost constant later when SA increases. The node orientation of draped profile of a circular specimen was found to coincide with seam directions. By applying this finding to fabric specimens without seams, a relationship between the nodes of draped specimen and fabric directionality has been found. Or from the results obtained from sewn specimens, the draping profile of a fabric without a seam can be predicted and has been proved by extended experimental work. That is, for an orthotropical fabric, the nodes are oriented to the fabric direction with larger bending stiffness such as warp direction if warp bending stiffness is larger. By contrast, the node orientation for an isotropic fabric is not clear, and node positions are not always stable when tested again and again.

From the present study, it is clear that the drape coefficient increases with seam allowance first, and then decreases with the increase of seam allowance. So the change trends seem to be different from that on cantilever test. Therefore, it is believed that the cantilever test for bending length is different from drape test as well as pure bending test. The drape behaviour of a fabric with seams seem to be much more complicated than that of simple fabrics. Seam positions, seam types, seam structure, seam directions and testing methods all affect the results. It is hoped that the knowledge gained from the present research on fabric drape will be useful in the determination of the drape profile on garment in practical use. Moreover, it has significant value in paving the way for establishing clothing CAD systems, which will enable customers or manufacturers to observe that fabrics with different properties will produce different garment profiles for a certain style. In addition, it sheds light on fundamental mechanisms operating in fabric drape behaviour. However, the research work in this area seems to be enormous. A comprehensive and practical pool of knowledge needs wide attention and concerted effort from many researchers and long-term accumulation of results. References 1. Suda, N. and Nagasaka, T., “Influence of the partial change of bending property on the formation of nodes”, Report of Polymeric Materials Research Institute, No. 142, 1984, pp. 47-55. 2. Suda, N. and Nagasaka, T., “Dependency of various sewing conditions on the bending property of seams”, Report of Polymeric Materials Research Institute, No. 142, 1984, pp. 39-45. 3. Dhingra and Postle, “Some aspects of the tailorability of woven and knitted outwear fabric”, Clothing Research Journal, No. 8, 1980, pp. 59-76.

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The causes and prevention of rippling or localized delamination in fused garment parts J. Fan and W. Leeuwner CSIR Division of Textile Technology, Port Elizabeth, South Africa Introduction Nowadays, most garments are fused in certain areas. Rippling, sometimes referred to as localized delamination or surface distortion in fused garment parts, is a very common and serious problem. This problem could arise from improper fusing press settings, malfunction of the fusing press, incompatibility of outer fabric and fusible interlining, surface finish of outer fabrics, defects of interlinings and excessively severe garment treatments (e.g. incorrect dry cleaning conditions), etc.[1]. Scardino[2] suggested that differential shrinkage and compliance between the outer fabric and fusible interlinings are the major causes of rippling. From practical experience, it is believed that that poor bond strength between the outer fabric and fusible interlining and excessively severe garment treatments (e.g. dry-cleaning) after the garment is made can also cause rippling. The present work is undertaken with a view to understanding the causes of the problem better and to establish guidelines which can be implemented practically to prevent the occurrence of rippling in fused garment parts. Theory Consider a composite produced by fusing a relatively low shrinkage component A to a relatively high shrinkage component B as shown in Figure 1. After the composite has gone through a shrinking process (e.g. dry-cleaning) the low shrinkage component A is in-plane compressed from its shrunk state and the relatively high shrinkage component B is extended from its shrunk state. Assuming the shrinkage of component A is Sa (per cent), that of component B is Sb(per cent) and the in-plane compression of component A is Da (per cent). the extension of component B (Db) would be Db = (1 – Sa ) – (1 – Sb ) – Da .

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 228-235. © MCB University Press, 0955-6222

Since the compression force and extension force should be equal in the composite, we have Da / Ca = {(1 – Sa ) – (1 – Sb) – Da }/ Eb

(1)

The causes and prevention of rippling 229

Figure 1. Dimensions of fusing components and fused composites before and after shrinkage

where Ca is the in-plane compressibility of component A and Eb is the extensibility of component B. From Equation (1) we get Da = ( Sb – Sa ) /(1 + Eb / Ca ).

(2 )

If the compression formability as defined by Lindberg et al.[3] of component A is F, the potential of component A to buckle would be Sb – Sa F (1 + Eb / Ca )

.

The differential shrinkage also induces shearing forces on the points of fusing, which can separate the bond if the bond strength is not high enough, and, once the bond is separated, the potential to buckle would be higher since the relatively low shrinkage component would buckle over a longer distance. The bond strength is therefore very important in terms of the non-occurrence and severity of rippling. The higher the bond strength, the lower the potential to buckle or ripple. Therefore, the rippling potential of the fused composites should be proportional to: Sb – Sa F P (1 + Eb / Ca ) where P is bond strength. Since fabrics normally shrink less than fusible interlinings for fused garment parts which are dry-cleaned, we define the rippling potential (R) as

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R=

Si – Sf F P (1 + Ci / Cf )

(4 )

where Si and Sf are the shrinkages (in per cent) of the fusible interlining and the fabric, respectively, after dry cleaning; F is the formability of the outer fabric; P is the bond strength in cN; Cf is the compressibility of the fabric (in per cent) at low stress, which can be estimated from the low stress extensibility of the fabric (e.g. E20-E5 from the FAST system); Ci is the low stress extensibility of the fusible interlining. Experimental In order to validate whether the defined concept of rippling potential has actually combined the effects of most relevant factors related to the occurrence and severity of rippling, an experiment was carried out. Since rippling often occurs in double fused areas in practice, this experiment was designed to investigate the rippling of double fused composites. Sample preparation Thirty-two wool or wool blend fabrics. ranging from lightweight to heavyweight, and six different fusible interlinings were selected for the experiment. The 32 fabrics were divided into six groups, with each group having five or six fabrics and having a similar fabric mass distribution (viz. from lightweight to heavyweight). The outer fabrics in each group were prepared to be fused with one of the six fusible interlinings. From each fabric, six 300mm × 300 mm samples were cut. Three fabric samples were marked with dots 250mm apart for three measurements in the warp and three in the weft direction for determining the fabric shrinkage after each experimental procedure (i.e. fusing, dry-cleaning and air-conditioning). The remaining three fabric samples were marked with dots 200mm apart towards the corners of the samples since these fabric samples were prepared to be fused to the fusible interlinings and parts of the fused composites were to be cut off for testing the bond strength. From each fusible interlining, 18 samples of 300mm × 300mm were cut. Out of these 18 samples, eight were marked with dots 250mm apart for determining shrinkage after each experimental procedure. The remaining samples were prepared for being fused with the marked fabric samples or fusible interlining samples. Experimental procedures Experiments were carried out in a process consisting of the following eight steps: (1) After the samples were cut, all of them were conditioned for 24 hours in the standard atmosphere (20˚C and 65 per cent RH). The dimensions (i.e. distance between the marked dots in the warp and weft directions) of each sample were measured after conditioning.

(2) After the samples were conditioned, they were fused using a flat-bed fusing machine. The temperature of the fusing machine was set at 150˚C to give acceptable glueline temperature (between 126 and 130˚C). The pressure was set at 300 gf/cm2. Fusing time was set at 22, 25 and 27 seconds for the light, medium and heavyweight fabrics, respectively. Fabrics in each of the six groups (three samples for each fabric marked with dots 200mm × 200mm apart) were fused to double layers of one of the six fusible interlinings. Three remaining fabric samples, which were marked with dots 250mm × 250mm apart, were not fused, but went through the same fusing process as if they were fused to take into account the shrinkage of fabric due to fusing. Four marked samples of each fusible interlining were fused to silicone paper. The remaining four marked single layer samples and four unmarked single layer samples of each fusible interlining were fused together on to silicone paper. (3) After fusing, all samples were again conditioned in the standard atmosphere for 24 hours. The silicone paper was then peeled off from the single-layer and double-layer fusible interlining samples. After that, the dimensions of the samples were remeasured and recorded. (4) One specimen (25.4mm wide and 152mm) in each direction was cut from each fused composite sample. The tests ware carried out in accordance with AATCC Test Method 136-1985 using the average peak load. (5) To prepare for dry-cleaning, all fabric, fusible interlining and fused composite samples were overlocked at their edges. The adhesive side of the fusible interlining samples was also covered with a lightweight, open structure fabric to prevent the adhesive coming into direct contact with other samples during dry-cleaning. (6) The samples were dry-cleaned in a Bowe 314c machine with cage diameter 817mm, depth 440mm, volume 0.23 cubic metre, G-factor cleaning 0.62 and G-factor extraction 80.7. The dry-cleaning load consisted of approximately 5 kg samples and 5 kg cotton fabrics to bring the total load to about 10 kg. Samples were dry-cleaned for five cycles, each cycle consisted of a 15-minute wash with 800ml Finesse emulsion added, followed by a five-minute rinse. (7) After dry-cleaning, the samples were again conditioned for 24 hours in the standard atmosphere, after which the dimensions of the samples were remeasured and recorded. (8) Three people were invited to rate the appearance of the fused composites in terms of the degree of rippling, 1 being severe rippling, 2 rippling, 3 slight rippling, 4 no apparent rippling, 5 absolutely no rippling. The direction of rippling was also noted. Physical and mechanical properties of outer fabrics and fusible interlining The 32 outer fabrics, six single-layer fusible interlinings and six double-layer fusible interlinings were also tested using the FAST system[4] to measure the dimensional stability, low stress extensibility, formability, etc.

The causes and prevention of rippling 231

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Results and discussion Results Table I lists the actual degree of rippling, direction of rippling, rippling potential and bond strength of the fused composites as well as the shrinkages and other relevant properties of the outer fabrics and fusible interlinings. In this table, the actual degree of rippling is the average of the ratings of three judges and three samples. The rippling potential was calculated using equation (4) defined in the second section of this paper. The shrinkages of the samples after fusing and conditioning and after dry-cleaning and conditioning were calculated using the following formula: S=

Do – Da

* 100 (5 ) Do where S is shrinkage in percent, Do is the dimension before fusing, Da is the dimension after fusing and conditioning or the dimension after dry-cleaning and conditioning. As can be seen from the results in Table I, in most cases rippling occurred along the weft direction, owing to the differential shrinkage of the warp. The shrinkage of the fabric after dry-cleaning and conditioning was normally less than that of fusible interlinings, except for one fused composite, in which the outer fabric was a thick woollen one. Causes of rippling The actual degree of rippling of the fused composites after dry-cleaning and conditioning is plotted against the calculated rippling potential (R) in the corresponding direction in Figure 2. As can be seen, the degree of rippling was largely determined by the rippling potential (since R square was very high), which is the combination of differential shrinkage, fabric formability, extensibility or compressibility of outer fabric and fusible interlining and bond strength. Prevention of rippling Based on the improved understanding of the causes of rippling, in order to prevent rippling, the outer fabric and fusible interlining must be compatible in terms of shrinkage and compliance. In order to prevent a degree of rippling which cannot be pressed away with light pressing, one should ensure that the rippling potential is less than a pre-determined tolerance limit (such as 5.2 as shown in Figure 2) during the selection of fusible interlinings. Practically speaking, for lightweight and low shrinkage fabrics, such as microfibre fabrics, the required fusible interlinings should have minimum shrinkage during drycleaning and maximum extensibility. Furthermore, the required minimum bond strength must be ensured during fusing. This requires consistent fusing conditions and strict quality control procedure. The required minimum bond strength for different types of fabrics are generally as follows: • 800 cN/5cm for light weight ladies’ fabrics;

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F27 F28 F29 F30 F31 F32

F D A B F D F A C C B E A C F D A D E B A E F E B C B B D E D C

Fabric Fusible ID interlining

283 352 359 256 173 177 201 182 180 153 391 233 220 244 159 140 167 176 175 171 153 142 234 178 180 151 183 202 235 378 118 182

Fabric mass (g/m2) 0.1 0.7 1.9 0.6 0.6 0.3 0.4 0.8 0.7 0.8 0.8 0.5 0.5 1.1 0.7 0.6 1.1 0.8 0.9 0.9 0.6 0.5 0.7 0.8 1.1 0.5 1.1 0.5 1.0 2.3 0.4 0.5

0.2 0.6 0.5 0.2 0.3 0.6 0.6 1.0 0.7 1.8 2.5 0.4 0.8 0.9 0.5 0.4 1.3 2.2 3.1 1.2 1.3 0.9 1.7 1.3 1.8 0.7 2.3 1.8 1.7 3.2 0.7 0.9

Fabric (%) Warp Weft 0.3 0.4 0.6 0.5 0.3 0.4 0.3 0.6 0.5 0.5 0.5 0.3 0.6 0.5 0.3 0.4 0.6 0.4 0.3 0.5 0.6 0.3 0.3 0.3 0.5 0.5 0.5 0.5 0.4 0.3 0.4 0.5

0.5 1.8 0.8 0.5 0.5 1.8 0.5 0.8 3.0 3.0 0.5 0.4 0.8 3.0 0.5 1.8 0.8 1.8 0.4 0.5 0.8 0.4 0.5 0.4 0.5 3.0 0.5 0.5 1.8 0.4 1.8 3.0

Extensibility Single fusible (%) Warp Weft 0.2 0.2 0.5 0.2 0.2 0.2 0.2 0.5 0.4 0.4 0.2 0.2 0.5 0.4 0.2 0.2 0.5 0.2 0.2 0.2 0.5 0.2 0.2 0.2 0.2 0.4 0.2 0.2 0.2 0.2 0.2 0.4

0.2 1.0 0.5 0.1 0.2 1.0 0.2 0.5 1.5 1.5 0.1 0.1 0.5 1.5 0.2 1.0 0.5 1.0 0.1 0.1 0.5 0.1 0.2 0.1 0.1 1.5 0.1 0.1 1.0 0.1 1.0 1.5

Double fusible (%) Warp Weft 0.60 0.18 0.51 –0.07 0.89 0.36 0.53 0.08 0.97 –0.14 0.27 0.23 0.16 0.25 –0.05 –0.05 0.08 –0.05 –0.02 0.17 0.24 0.09 0.17 0.23 0.02 –0.05 0.08 0.07 –0.14 0.46 –0.21 0.13

0.13 0.08 0.09 –0.07 0.18 0.34 0.50 0.11 0.34 0.00 0.02 0.18 –0.00 0.18 0.24 0.12 –0.08 –0.12 –0.17 0.16 0.29 0.08 –0.12 0.03 –0.12 –0.02 –0.09 0.12 0.43 –0.13 –0.53 –0.16

Fabric (%) Warp Weft 0.51 0.51 0.17 0.19 0.51 0.51 0.51 0.17 0.28 0.28 0.19 0.51 0.17 0.28 0.51 0.51 0.17 0.51 0.51 0.19 0.17 0.51 0.51 0.51 0.19 0.28 0.19 0.19 0.51 0.51 0.51 0.28

–0.10 0.30 –0.27 0.21 –0.10 0.30 –0.10 –0.27 0.20 0.20 0.21 –0.04 –0.27 0.20 –0.10 0.30 –0.27 0.30 –0.04 0.21 –0.27 –0.04 –0.10 –0.04 0.21 0.20 0.21 0.21 0.30 –0.04 0.30 0.20

0.46 0.41 0.19 0.21 0.46 0.41 0.46 0.19 0.21 0.21 0.21 0.39 0.19 0.21 0.46 0.41 0.19 0.41 0.39 0.21 0.19 0.39 0.46 0.39 0.21 0.21 0.21 0.21 0.41 0.39 0.41 0.21

–0.04 0.26 –0.02 0.13 –0.04 0.26 –0.04 –0.02 0.14 0.14 0.13 0.16 –0.02 0.14 –0.04 0.26 –0.02 0.25 0.16 0.13 –0.02 0.16 –0.04 0.16 0.13 0.14 0.13 0.13 0.26 0.16 0.26 0.14

Shrinkage after fusing Single fusible Double fusible (%) (%) Warp Weft Warp Weft

The causes and prevention of rippling 233

Table I. Actual degree of rippling, rippling direction, rippling potential and bond strength of fused composite as well as the shrinkages and other relevant properties of outer fabrics and fusible interlinings

Table I. (continued )

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F27 F28 F29 F30 F31 F32

F D A B F D F A C C B E A C F D A D E B A E F E B C B B D E D C

0.14 1.39 2.40 0.63 0.38 0.22 0.34 0.48 0.50 0.30 2.20 0.49 0.45 0.74 0.21 0.17 0.37 0.32 0.36 0.32 0.21 0.20 0.68 0.34 0.42 0.18 0.51 0.49 1.07 5.04 0.22 0.40

0.41 0.64 0.59 0.17 0.26 0.34 0.35 0.46 0.45 0.48 4.41 0.26 0.45 0.68 0.13 0.10 0.34 0.52 0.85 0.35 0.41 0.23 1.25 0.47 0.59 0.23 0.89 0.74 0.96 5.11 0.34 0.53

1.26 0.65 1.23 0.74 1.44 0.80 1.05 0.42 1.37 0.03 2.29 1.13 0.87 0.73 0.43 0.36 0.23 0.26 0.19 0.58 0.64 0.47 0.91 0.47 0.38 0.40 0.40 0.36 –0.03 2.02 0.17 0.74

0.69 0.30 0.10 0.12 0.38 0.67 0.94 0.24 0.59 0.20 0.56 0.92 0.29 0.57 0.54 0.44 –0.03 –0.07 –0.40 0.54 0.65 0.32 0.59 0.24 –0.01 0.46 –0.14 0.61 0.71 0.41 –0.20 –0.02

3.26 3.10 1.72 2.53 3.26 3.10 3.26 1.72 2.01 2.01 2.53 2.66 1.72 2.01 3.26 3.10 1.72 3.10 2.86 2.53 1.72 2.66 3.26 2.66 2.53 2.01 2.53 2.53 3.10 2.66 3.10 2.01

0.41 1.40 0.34 0.76 0.41 1.40 0.41 0.34 1.61 1.81 0.76 0.60 0.34 1.81 0.41 1.40 0.34 1.40 0.60 0.76 0.34 0.60 0.41 0.60 0.76 1.61 0.76 0.76 1.40 0.60 1.40 1.61

2.72 3.72 1.71 2.75 2.72 3.72 2.72 1.71 2.43 2.43 2.75 2.86 1.71 2.43 2.72 3.72 1.71 3.72 2.86 2.75 1.71 2.86 2.72 2.85 2.75 2.43 2.75 2.75 3.72 2.86 3.72 2.43

0.97 1.06 1.03 0.96 0.97 1.06 0.97 1.03 1.15 1.15 0.96 1.07 1.03 1.15 0.97 1.06 1.03 1.06 1.07 0.96 1.03 1.07 0.97 1.07 0.96 1.15 0.96 0.96 1.06 1.07 1.08 1.15

620 555 685 875 597 707 976 712 481 239 1461 1417 743 561 412 235 651 315 1097 725 698 555 1079 868 732 279 778 824 403 1730 193 213

480 647 782 834 591 701 951 645 471 12 1490 1290 731 834 401 251 550 304 746 654 641 507 1059 692 517 282 784 770 388 2060 160 230

Shrinkage after dry cleaning Bond Fabric Single fusible Double fusible strength (%) (%) (%) (N) Warp Weft Warp Weft Warp Weft Warp Weft 5.6 3.1 0.2 2.7 4.2 11.3 3.4 2.3 2.8 26.0 0.1 1.9 1.6 3.0 20.6 83.1 4.2 27.5 5.8 7.6 4.0 17.2 1.9 8.8 6.5 22.5 5.0 4.2 7.3 0.1 55.9 11.0

0.7 0.7 1.0 4.0 2.3 0.6 0.1 1.8 0.8 4.4 0.1 0.3 1.2 0.5 5.9 7.1 4.1 4.1 2.2 1.7 1.0 5.7 0.3 2.4 3.0 3.4 1.5 0.6 0.6 0.1 9.6 3.6

Rippling potential Warp Weft 4.4 4.0 4.0 4.0 3.2 2.0 4.3 4.0 4.7 2.0 5.0 4.4 3.1 4.9 2.3 1.0 3.0 2.0 3.0 4.3 3.0 2.8 5.0 3.1 4.0 2.0 4.2 4.3 3.2 4.8 1.0 2.8

Average rippling rating

234

Fabric Fusible ID interlining

Fabric formability (mm2) Warp Weft

Weft Both

Weft

Weft

Weft

Both Weft Both Weft Weft Weft Weft Weft

Weft/both

Weft

Warp Weft

Rippling direction

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The causes and prevention of rippling 235

Figure 2. Rippling potential versus the actual degree of rippling (expressed as a rating)

• 1200 cN/5cm for medium weight ladies’ and men’s suiting; • 1400 cN/5cm for heavy weight ladies’ and men’s suiting. Although not investigated in this work, the conditions during garment treatments (i.e. dry-cleaning or washing) must be carefully controlled. Excessive steam, temperature and mechanical action during garment treatment can cause excessive shrinkage of fabrics or fusible interlinings and the weakening of bond strength, and as a result, rippling. Conclusions As a result of this investigation, the causes of rippling (localized delamination or surface distortion) are better understood. Some guidelines for the prevention of rippling or localized delamination are suggested. References 1. Ajemain, R., “Tailoring the right approach to interlinings”, Bobbin, February 1994, pp. 88-92. 2. Scardino, F., “Mechanism and source of surface distortion in garments containing interfacings”, in Kawabata, S. et al. (Eds), Proceedings of the Third Japan-Australia Joint Symposium on Objective Measurement: Applications to Product Design and Process Control, 1985, pp. 183-91. 3. Lindberg, L., Waesterberg, L. and Svenson, R., “Wool fabrics as garment construction materials”, Journal of the Textile Institute, Vol. 51, 1960, pp. T1475-92. 4. FAST (Fabric Assurance by Simple Tests) Manual, CSIRO Division of Wool Technology, Australia, 1989.

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236

Evaluation of rheological properties of a thread using numerical methods Jelka Ger˘sak University of Maribor, Faculty of Mechanical Engineering, Institute of Textile and Garment Manufacture Processes, Maribor, Slovenia Introduction Sewing thread as a joining element of textile surfaces does not have a clearly defined structure in a produced seam. This structure depends on type and quality of fibres, raw material, construction parameters, twist, linear density and surface treatment. Furthermore, it depends also on technologically conditioned forces that act on a thread in sewing process[1,2]. On the basis of knowledge of mechanical properties of fibres and threads it can be assumed that these structures are visco-elastic. They have the elasticity of hard substances and the viscosity of fluids. Visco-elastic behaviour of threads is not coincidental. It is conditioned by a complex anisotropy arrangement of molecules, on which acts the macroscopic deformation[3,4]. Visco-elastic behaviour of a thread, which includes the fractal geometry of linear formed yarns and fibres, can be traced by static and dynamic-mechanical tests. Using the static tests the influence of acting force and deformation during a longer time period can be observed. Dynamic tests obtain information on thread behaviour in very short time intervals[3,5]. Considering the complexity of a problem of thread’s rheological properties evaluation, the evaluation of visco-elastic properties of a thread on the basis of static tests using the numerical methods will be shown within this contribution.

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 236-240. © MCB University Press, 0955-6222

Visco-elastic properties of a thread The tension-deformation σ (ε) curve served as a starting point for evaluation of visco-elastic properties of threads. Here, the following parameters, gained on the basis of the tension σ – deformation ε curve are significant[2,3]: • module of elasticity E; • extreme value of module of elasticity change; • loading σy and extension εy in the flow point; and • work until the break Ap, a part of elastic work Ae1 and work till the flow point Ay. The module of elasticity E, which is gained from the first derivative of the curve σ (ε), represents the resistance against further deformation which appears in a thread. The modules of elasticity E0, E1 and E2 can be defined from the course of the elasticity curve E (see Figure 1).

Evaluation of rheological properties 237

Figure 1. Course of the viscoelastic properties of a thread, gained on the basis of the tension σ – deformation (ε) curve

Starting module of elasticity E0 and adequate extension ε0 are defined in the first gradation point of the curve E. Modules E1 and E2 as well as adequate extensions ε1 and ε2 are defined in the second point. The third gradation point, with the second derivative σ ′′ = 0, which runs from minimum to maximum. The starting module of elasticity E 0 appears at the start of loading. The deformation is at this point in proportion to loading since it is in the area of elastic deformation, where Hook’s law is valid. The elasticity threshold is followed by the plastic threshold, i.e. the threshold of flowing σy, which gives the force that is responsible for the first irreversible change or deformation. The flowing threshold is of practical importance. The definition of the force which causes the first irreversible deformation is namely a basis for the definition of the allowed loading of a thread in the sewing process. Furthermore, it also presents a basis for determination of maximal dynamic loading during use of a garment. The flow threshold, i.e. the tension σy and extension in the flow point εy, are numerically determined on the σ (ε) curve in a point, where the third derivative σ′′′= 0. The evaluation of the tension σ – deformation ε curve could be practically explained in this way: some “loose” fibres are being stretched in a longitudinal direction when a thread is exposed to stretching load. Hereby a movement of the fibres, spun into thread, does not appear. After that stage greater force is needed for stretching of a thread. This reflects in maximum of the module of elasticity E (value E0). This value of module of elasticity is rapidly reduced since the acting stretching load causes first slips of fibres. The stretch loading remains unchanged from that moment, which is reflected in a reduction of the module of elasticity. It reduces to value E1. At this point, the slipping and deformation of fibres, spun into thread, are the largest. From that

IJCST 9,3

moment the stretch loading causes bigger and bigger strains on the fibres. Since the fibres are very stretched, they cause pressure in the direction transversal to the acting load. This leads to increase of a tension. At the same time the module of elasticity is also increasing. A break of a thread will occur when fibres, spun into thread, do not hold further loading (value E2).

238

Evaluation of visco-elastic properties of sewing threads The evaluation of visco-elastic properties of a sewing thread is based on evaluation of the tension σ – deformation ε curve, gained from the course of a function load Fs – extension ε. The thread tension σs is expressed as:

σs =

Fs

(1)

Tt

where Tt is linear density of a thread, in tex (the basic unit). The B-spline approximation using the least squares method was chosen as an appropriate and suitably smooth curve for construction of the average σ (ε) curve. The average curve, which arises from the B-spline approximation – by gluing the small parts of cubic parabolas – is expressed in the form: f ( x ) = c1 N1 ( x ) + c2 N 2 ( x ) + … + c p N p ( x )

(2 )

Ni(x); i = 1, 2, …, p is normalized B-spline and ci(x); i = 1, 2 …, p are coefficients. Parts of cubic parabolas are smoothly glued in points, which abscissae represent the nodes. A suitable computer program VILSUK has been designed and programmed for that purpose. This software calculates the parameters needed for evaluation of visco-elastic properties of a thread on the basis of numerical values of the tension-deformation σ (ε) curve. An appropriate program from the NAG program library was used for calculation of the above-mentioned approximation function and its derivatives, i.e. σ (ε)′, σ (ε)′′ in σ (ε)′′′. Data, describing the position of inner nodes on the whole interval [a, b] were given in the input file for calculation of derivatives. Data about the outer nodes, being equal to left terminative point a or right terminative point b of this interval, were input during the program run. Furthermore, the integral of approximation function was calculated numerically using the trapezoid method. It is expressed as: b

∫a f ( x )dx =

h

( y0 + 2 y1 + 2 y2 + … + 2 yn – 1 + yn ) + Rn (3 ) 2 where R n, is the relative error and h the length of the sub-interval on the integration interval [a, b]. If the function is at least two times continuously derivative on the interval [a, b], the error Rn can be calculated as follows: Rn ≤

(b – a ) 3 2

max f ′′( x ) .

a≤ x ≤b

12n The error Rn decreases rapidly with increased number of sub-intervals n.

(4 )

Results of the evaluation of visco-elastic properties of a sewing thread By inputting the required data into the input file of VILSUK program, such as: number of intervals m on the abscisse, real linear density of a thread Tt, number of intervals ncap on a curve, values on the abscisse, where the nodes are determined, and values of the load-elongation F(ε) curve, given as xr and yr, r = 0, 1, …, m, the program calculates the approximation function σ ( ε ), its derivatives, i.e. σ (ε)′, σ (ε)′′ in σ (ε)′′′, as well as the integral under the curve. The results of numerically gained values can be presented graphically using MS Excel® or a similar program. Achieved results of evaluation of visco-elastic properties of a thread using the VILSUK program are shown in Figure 2. Evaluation of visco-elastic properties of the same thread using the existing program DINARA[6] was carried out for comparative purposes. This program calculates the average curve σ (ε) on the basis of interpolation (Figure 3).

Evaluation of rheological properties 239

Discussion and conclusions Analysis of the results of numerical evaluation of thread’s visco-elastic properties using the VILSUK program confirmed the suitability of B-spline approximation using the least squares method. This was also confirmed by the derivatives of a curve σ (ε) (Figure 2). It can be seen that the first derivative is continuous. In second derivative the non-continuous nature can be hardly seen, and in the third derivative it is present only in a minor form. Furthermore, on the basis of comparison of the average curve σ (ε), gained by the existing program DINARA, which uses the Lagrange’s interpolation expression, and proposed program VILSUK, it can be seen that the

Figure 2. Graphical view of a tension-elongation σ (ε) curve, derivatives σ (ε)′, σ (ε)′′ in σ (ε)′′′ and integral for PES thread, calculated by VILSUK program

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240

Figure 3. Graphical view of a tension-elongation σ (ε) curve, derivatives σ (ε)′, σ (ε)′′ in σ (ε)′′′ and integral for PES thread, calculated by DINARA program

interpolation method is not suitable. This is reflected in the non-continuous nature of curves of all three derivatives (Figure 3). On the basis of achieved results of evaluation of visco-elastic properties of a thread and the above-mentioned comparison, it is evident that the proposed program VILSUK, from the mathematical point of view, ensures the construction of a real average curve σ (ε), which fits the actually measured values as a suitably smooth approximation curve. References 1. Gers˘ak, J., “Dynamic loading of a thread as a consequence of technologically conditional forces in stitch formation process” (in Croatian), Tekstil, Vol. 40 No. 5, 1991, pp. 213-22. 2. Gers˘ak, J. and Knez, B., “Thread’s technical-technological parameters and their influence on scan strength” (in Croatian), Tekstil, Vol. 41 No. 5, 1992, pp. 211-18. 3. Gers˘ak, J., “Rheological properties of threads: their influence on dynamic loads in the sewing process”, International Journal of Clothing Science and Technology, Vol. 7 No. 2/3, 1995, pp. 71-80. 4. Gruber, E., Polymer Chemistry, Dietrich Steinkopff Verlag, Darmstadt, 1980 (in German). 5. Bobeth, W., Berger, W., Faulstich, H., Fischer, P., Heger, A., Jacobasch, H.-J., Mally, A. and Mikut, I., Textile Fibres: Quality and Properties, Springer-Verlag, Berlin Heidelberg, New York, NY, 1993 (in German). 6. Bukos˘ek, V, “Computer-aided evaluation of visco-elastic properties of fibres”, Tekstilec, Vol. 26 No. 12, 1986, pp. 24-9 (in Slovene).

Sewing needle penetration force study

Sewing needle penetration force study

Karl Gotlih University of Maribor, Faculty of Mechanical Engineering, Institute for Textile and Garment Manufacture Processes, Maribor, Slovenia

241

Introduction The penetration force of the sewing needle is the quantitative measure of the damage which appears in the garment as the result of the sewing process[1-3]. To get a better look at this process, knowledge of the fabric, the used thread, the sewing needle and the sewing machine mechanisms is important. In this work a mathematical model for the determination of the sewing needle penetration force is developed and the results are compared with measured values[4] for the chosen fabric, sewing needle and sewing machine. The fabric model The fabric was modelled as a plain weave fabric. It is a simple combination of parallel warp and parallel weft threads with no friction in the crossings of the threads. For this fabric model we need the thickness of each thread and the distance increment in the warp direction and in the weft direction of the threads. These data are easy to obtain from the fabric with a stereo microscope. The image of such plain weave fabric with one perforation of a sewing needle is shown in Figures 1 and 2. To find the mechanical behaviour of each thread in the fabric a standard tear experiment of the thread was done. The first derivative of the stress-deformation function of the thread measured at the tear experiment gives the Young’s module of the thread. For simplification reasons we assume that the material of the thread is just elastic deformed. This means that the thread can be modelled as an ideal Hook’s material. The first derivative of the stress-deformation function, for the thread from the plain weave fabric shown in Figure 1 and 2, is shown in Figure 3. The sewing needle model The sewing needle tip is modelled as a cone. The geometric data are identical with a normal sewing needle with the number 80. For modelling reasons the sewing needle is simplified. In the study we are looking for the maximum sewing needle penetration force. This force appears when the needle has its eye in the fabric. The cone was geometrically modelled with the correct dimensions from the tip of the sewing needle to the eye. The model of the mechanism for the sewing needle movement For the mechanism simulation, for the motor torque transformation into the sewing needle penetration force, a model of a slider-crank transformation

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 241-248. © MCB University Press, 0955-6222

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242 Figure 1. The plain weave fabric stereo microscope picture with a sewing needle perforation in the warp direction

Figure 2. The plain weave fabric stereo microscope picture with a sewing needle perforation in the weft direction

Figure 3. The Young’s module of the thread from the fabric from Figures 1 and 2

mechanism[5] which is built into the sewing machine, is developed (Figure 4). Sewing needle The equations which describes the transformation of the motor torque into the penetration force sewing needle penetration force are: study  F    –1  M  x   = [ J]    Fy   0 

 cos ϕ 3   r .sin(ϕ 3 – ϕ 2 ) [ J ] –1 =  2  – cos ϕ 2   r2 .sin(ϕ 3 – ϕ 2 )

(1)

243  sin ϕ 3  r3 .sin(ϕ 3 – ϕ 2 )  . – sin ϕ 2   r3 .sin(ϕ 3 – ϕ 2 ) 

(2 )

In the equations (1) and (2) Fx is the needle penetration force and Fy is the perpendicular force which acts on the guides, [ J ]–1 is the inverse Jacobian matrix (the transformation matrix between the motor torque M and the needle penetration force Fx). r2, r3, ϕ2, ϕ3 are the geometric and kinematic data of the slider-crank mechanism in Figure 4.

Figure 4. The slider-crank mechanism

The sewing needle penetration force study For the model being developed, the fabric penetration of the fabric with the sewing needle, some restrictions must be done. As mentioned earlier the fabric is a combination of parallel warp and weft threads with no friction in the connections. The sewing needle is a simple geometric cone which penetrates into the fabric in such a way that the threads are not damaged but just elastic deformed Figure 5. The threads are treated as pure Hook’s material. This means that just elastic deformations in the thread, when it is deformed, appear. The elastic deformation in each thread causes a force which then causes the normal force between the deformed thread and the sewing needle. This normal force produces the friction force of one thread because of the friction between the thread and the sewing needle.

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244 Figure 5. The sewing needle penetration model

The force in the thread when it is deformed is: 1 2.( R .aˆ + ( )2 – h 2 – R 2 ) – l 2 F = A.ε . E = A. E . . (3 ) l The normal force produced in the thread (Figure 6) is: F .l FN = . (4 ) 1 ∆l + 2 2 If more threads in the penetration process are deformed, the total normal force is: FN =

NR

∑

FNi .

(5 )

i =1

The total sewing needle penetration force as a function of the friction coefficient is: (6 ) FT = FN .µ . The coefficient of friction was measured with the friction meter for the combination threadsteel (sewing needle material).

Figure 6. The force system and the normal force FN on the elastic deformed thread

In the equations (3) to (6) are: ε is the specific deformation of the thread, A is the Sewing needle cross area of the thread, E is the Young’s module of the thread, R is the actual penetration force sewing needle radius, h is the distance increment between the parallel warp study threads and parallel weft threads, l is the length of the thread which is in the penetration process deformed, FN is the normal force of the deformed thread and µ is the friction coefficient.

245

Example As mentioned earlier the fabric is a plain weave fabric with 295 warp threads per 10cm and 270 weft threads per 10cm. The thread (warp and weft threads) are spun from 100 per cent cotton. The Youngs module for the mentioned thread as a function of the specific deformation is shown in Figure 3. The friction coefficient is measured on the friction meter. The value of this coefficient, for very slow movements of the thread around the guides, is

µ = 0.12.

(7 )

The penetration force, the friction force between the sewing needle and the fabric is as the function of the needle penetration shown in the Table I and in Figure 7. Sewing needle penetration force measuring The sewing needle penetration force was measured on the Brother EXEDRA DB2-B737-913 Mark II sewing machine. The measuring device, with strain gauges, is our own construction. The results are shown as a print from the HP

Sewing needle penetration (mm) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

Actual sewing needle radius (mm)

Number of elastic deformed threads

Total frictional force between the needle and the fabric (cN)

0.000 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200 0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450

0 0 0 0 0 4 4 4 4 4 4 4 4 4 4 8 8 8 8

0.000000 0.000000 0.000000 0.000000 0.000000 0.002627 0.010948 0.025282 0.065920 0.107460 0.187298 0.274123 0.357381 0.456901 0.574037 0.713514 0.908502 1.111404 1.409497

Table I. The sewing needle penetration force (the total frictional force between the sewing needle and the fabric) as a function of the needle penetration into the fabric

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246

Figure 7. The sewing needle penetration force with respect to the sewing needle penetration into the fabric

54501A digital oscilloscope with the printer HP 2225. The measuring was done with the sewing machine shaft speed ω = 47.59 rd/s. The print of the measured sewing needle penetration force as the function of time (the rotation of the sewing machine shaft) is shown in Figures 8 and 9. Conclusion The mathematical model for the calculation of the sewing needle penetration force is an experiment which could show how it is possible to get better mathematical models of the fabric through simple experiments and 1. 200 mV/div offset: 0.000 V 1.000: 1 dc

1N = 100mV

0

Figure 8. The measured sewing needle penetration force for the seam in the warp direction

0.00000 s Vmarker2(1) Vmarker1(1) Delta V(1)

1

2 3

4

4. 400 mV/div offset: 0.00 V 1.000: 1 dc

100.000 ms 200.000 ms 20.0 ms/div 143.750mV Stop market: 131.600ms 0.00000 V Start market: 124.000ms 4. 100.0 mV 143.750mV Delta t: 6.80000ms 1/Delta T: 147.059m

1. 200 mV/div offset: 0.000 V 1.000: 1 dc

Sewing needle penetration force study

1N = 100mV

247 0

0.00000 s Vmarker2(1) Vmarker1(1) Delta V(1)

1

2

3

4

4. 400 mV/div offset: 0.000 V 1.000: 1 dc

100.000 ms 200.000 ms 20.0 ms/div 118.750mV Stop market: 131.600ms 0.00000 V Start market: 124.000ms 4. 100.0 mV 118.750mV Delta t: 7.59999ms 1/Delta T: 131.579Nz

mathematical background. The penetration force of the sewing needle could also be measured and this fact gives us the answer as to how far or how near to the correct material model of the fabric the hypotheses presented in this work are. The comparison of the measured and calculated values shows that the values are very different. Thus means that the mathematical model must be further developed in the following directions: • Better knowledge of the fabric and the threads in the fabric is needed. • Better knowledge is required of the mechanical properties of the thread in the fabric and the interaction of the threads of the fabric. Figures 1 and 2 show different perforations dependent on whether the seam is in the warp or weft direction. The presented model deals with constant mechanical properties of the thread. Figure 3 shows that the rheological behaviour of the thread changes with the growth of deformation. • A better geometrical model of the sewing needle is needed. • The coefficient of friction is the function of the sewing needle penetration speed. So the coefficient must be determined as the function of this speed. • The process of fabric penetration presented in this work is the simplest possible. It is also possible that the thread is damaged by the sewing needle damages the thread or a knot in the fabric. The real penetration force is then a statistical combination of these different possible modes (the deformation of the threads, the damage of one or more threads and the damage of a knot in the fabric).

Figure 9. The measured sewing needle penetration force for the seam in the weft direction

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References 1. Braun, M. and Ruing, E., “The influence of thread softening on sewing needle penetration force, needle temperature and interlocking point damage in sewing jersey”, Wirkerei- und Strickerei-Technik, Vol. 12, Coburg, December 1974. 2. Poppenwimmer, K. “Sewing damage and its prevention”, Sonderdruck aus Melliand Textilberichte, Vol. 70, 1989, pp. 670-1. 3. Gers˘ak, J. and Knez, B., “Determination of the penetration forces of the sewing needle in the sewing process”, Tekstil, Vol. 34 No. 10, 1985, pp.759-68 (in Croatian). 4. Gotlih, K. and S˘paner, M., “Development of a measuring system on a sewing machine”, Workshop on garment engineering, ’94, Tehnis˘ka fakulteta Maribor, ITKP, 1994, pp. 74-81 (in Slovene). 5. Sandor, G.N. and Erdman, A.G., Advanced Mechanism Design, Analysis and Synthesis, Prentice-Hall, Englewood Cliffs, NJ, 1984.

Integrated 3D sewing technology and the importance of the physical and mechanical properties of fabrics

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Philipp Moll Moll Automatische Nähsysteme GmbH, Alsdorf, Germany Introduction The sewing process has remained largely unchanged for 150 years. As an operator shapes the parts and guides the materials by hand, he or she is also able to take account of material properties when working, because of the extremely highly developed sensory and mechanical systems with which human beings are equipped. Nonetheless, the increasing importance of technical textiles has meant that even these highly developed systems are unable to cope with some problems, for example, the sewing together of airbag fabrics is problematic, owing to the low friction between the surfaces. At the same time it is necessary to recognize that this manual sewing process defines both the costs and the quality of production, while it also limits the design possibilities owing to restrictions in handling. A new three-dimensional sewing system has been developed which, by changing the basis on which fabric parts are sewn together allows the automatic manufacture of parts without highly skilled labour, in three dimensions and with a high output. In order to understand the exciting possibilities offered by the new technology, and to understand the changed demands placed on the materials to be sewn together, it is first necessary to understand the differences between traditional and automatic sewing. This process is limited by a number of factors: (1) The textile parts have a poor form stability, that is to say they are highly flexible. It is thus extremely difficult to recognize the shape and the dimensions of these parts automatically which is a precondition for any further automation. (2) As current cutters do not cut single layers at a high enough speed, it is necessary to stack the layers of fabric one upon another, and to cut these at reasonable speed. Unfortunately, these stacks of fabric must then be separated by hand for sewing, as only single layers of fabric are joined together.

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 249-251. © MCB University Press, 0955-6222

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(3) Although it is possible to separate one layer of fabric from another, it is not possible to separate the cut pieces reliably from one another so that automatic unstacking of fabric parts becomes impossible. This means that human fingers are irreplaceable for this operation. (4) Sewing machines in the current form have changed little for 150 years. They have been designed to be operated by human beings and to join fabrics together by simultaneously knotting the threads and transporting the fabrics – and this at high speed. (5) The wide range of fabrics to be sewn with different fibres, production processes, surface characteristics, stretch behaviour, thickness, etc. means that with conventional sewing machines there is displacement of the two layers of fabric and seam puckering as a result of the transport mechanism. These irregularities must be adjusted manually by the operator on the sewing machine. Automatic distribution of fullness is impossible in 2D sewing. (6) Traditional sewing relies on the edge of the fabric to provide a reference for all further operations. This reference point is flawed, however, because of a number of factors which cannot be influenced by hand: • the accuracy of the cut parts, generally ± 2mm; • the accuracy of sewing, generally ± 1mm; • relaxation shrinkage after cutting; • hygral expansion or shrinkage due to atmospheric changes. These factors produce variations of up to ± 6mm in objects being sewn together. Additionally, they are bound to produce errors in the shape and volume of objects being sewn together as a two-dimensional reference system is being used to define three-dimensional parts. It is important to notice that all comments regarding the accuracy of sewing relate to the distance between the seams. This is what the customer tries on; whether a jacket fits properly or not is a function of the distance between the seams, however much value we may put on constant seam selvages. In effect, the current sewing practice is similar to the work of an artist, the individual mastery of the craft of sewing produces objects which each time are a little different – rather like a good work of art. The basis of automatic sewing is the separation of the work process into individual processes. At the same time the conception of the process ensures high outputs and low wage costs, thus ensuring that sewing operations can be sited close to the markets they are supplying. The flexibility and quick response required of modern suppliers is thus much easier to provide, with far less emphasis on logistics and the accompanying risks. The basis of 3D sewing relies on the following principles: • Moulds are used to give flexible fabric parts stability. • Lightweight sewing machines must only knot the threads together, no longer carrying out transport operations as well.

•

Industrial robots guide the sewing machines, thus providing a transport mechanism. • The shape of the parts to be sewn is defined by the three-dimensional moulds. • Parallel processing of loading, joining, sewing and unloading reduces cycle time significantly. • Non-skilled labour is used. • Since fabric parts are sewn while mounted on the dummy, the fullness of the fabric is distributed correctly before sewing. As with all automation processes, the process requires some modification of the products to be made and of the materials being used. As a comparison, 100 years ago, cars were made as individual works of art, each body panel being beaten by hand to the shape required. Today nobody would imagine making steel body work without using automatic pressing systems. The shape of the parts and indeed the material being used have been adapted to take best advantage of the automatic process being used. Automatic sewing places similar demands on the goods to be produced. It thus requires a different discipline from that of designers. In particular, it offers the chance to make exciting shapes without worrying about whether they can be sewn by hand. That, however, is the subject of another paper. It is important to note that the properties of fabrics being sewn together become important. This does not necessarly mean that all properties must be changed. Rather, it means the properties must be monitored and produced within closer tolerances. The automatic handling of the fabric parts requires us to understand the stiffness and the bending behaviour of fabrics in more detail. We also need to establish the behaviour under different climatic conditions. When we combine these factors with the small design changes required for automatic sewing we are able to improve the outputs greatly, compared with traditional production. Summary A three-dimensional sewing system has been developed which enables fabric parts to be sewn together extremely quickly and with a high accuracy. The system places demands on the materials being used, like all automation processes. The fabrics must not necessarly be changed, but it is necessary to understand their performance. The company is carrying out a continual development process to ensure that the fabric properties and the fabric required by the customers are always able to be sewn by automatic systems.

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A new evaluation of seam pucker and its applications Chang Kyu Park and Dae Hoon Lee Textile Technology Center, Korea Academy of Industrial Technology, Suwon, Korea and

Tae Jin Kang Department of Fiber & Polymer Science, Seoul National University, Seoul, Korea Introduction Seam pucker is regarded as a matter of primary concern in garment manufacture. Until now the subjective evaluation method by the American Association of Textile Chemists and Colorists (AATCC) has been used[1]. The sample is graded according to five photographs of standards. However, AATCC grades do not give sufficient information for analysing and solving the seam pucker problems. The shortcomings of this subjective method include emotional and unsteady procedure, need for time-consuming training, and slow response. For several decades, many methods for evaluation of seam pucker have been reported using new technology[2-4]. Most of them resulted in good correlations in comparison with the subjective AATCC rating. However, they were developed to provide substitute devices for the human eye by the AATCC method, not to redefine the evaluation of seam pucker. The objective of this study is to develop the measurement system, to redefine the seam pucker with the shape parameters, and to evaluate it using artificial intelligence.

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 252-255. © MCB University Press, 0955-6222

Measurement system For the sample preparation the lockstitch sewing machine was modified by additional attachments such as guide rail, fabric tension controller, long plate, machine control panel, etc. By using this machine the samples can be automatically sewn without human operation. New devices using laser technology were developed, consisting of four components: laser scanner with XY position controller, amplifier, A/D converter, and IBM-compatible PC. All the software and user interface are performed under MS Windows95, which was coded by MSVC++4.0 and MSVBasic 4.0. The measured area of the fabric is width (80mm) × length (254mm). The 17 lines with 5mm intervals were selected in a parallel direction

with the seam line of the fabric. The 128 points with 2mm intervals along each line were measured. Seam pucker with shape parameters The shape of seam pucker can be defined as three-dimensional waves which are often superimposed and enlarged, and which also disappear. Sine curve with a cycle was assumed as the wave of the puckered surface. Also, in Figure 1 the new standards of seam pucker are defined using five shape parameters such as the number of random points related to wave generation, the wave amplitude and frequency at seam line, and the wave amplitude and frequency at edge line. In particular, the number of points takes into consideration the irregularity of the materials and processing conditions. The new standards with the shape parameters are different from the discrete AATCC standards, and can represent the infinite shapes. With the new standards, the material properties which cause seam pucker, as well as sewing parameters, can be examined in detail.

Start amplitude

1 2

Start wave length

3

End wave length

4

253

zy Seam line

x End amplitude

A new evaluation of seam pucker

3

1 2

4 5

No. of random point 5

Simulator of seam pucker A simulator was developed to construct the artificially intelligent machine for evaluating seam pucker, and also to show its new standards graphically. For simplifying and simulating seam pucker, one of the most important assumptions is that the fabric is regarded as a two-dimensional plate without thickness. Also, the seam line was assumed to be a straight line on the puckered surface. The waves are generated on the seam line, and propagated to the edge line in the direction perpendicular to the seam line. The positions of the wavegenerating points are randomly generated. When the superposition between the waves occurs, the amplitude and wave length are changed by the new defined modes and state algorithm. The shape with five shape parameters can

Figure 1. Five shape parameters of seam pucker

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be stochastically simulated for considering the irregularity of the materials and processing conditions. Figure 1 also shows the simulated seam pucker with five shape parameters. New evaluation method using artificial intelligence The puckered shape is converted into numerical data on a three-dimensional co-ordinate by the developed laser measurement system. The data along the seam line are transformed into power spectra at frequency domain using FFT. For an objective evaluation of the seam pucker using AATCC standards, two neural networks were constructed using the error back propagation model. The power spectra create the specified patterns for neural networks, which evaluate the seam pucker by simulating the AATCC rating of well-trained human experts. For evaluating seam pucker using the new standards, the neurofuzzy engine was constructed by pattern recognizing and learning. The designed engine can evaluate the analogue shape parameters of measured seam pucker. The power spectra of sewn fabrics using FFT create the specified fuzzy patterns through a fuzzification process such as fuzzy projection and fuzzy scalar product. Thus the five shape parameters can be obtained by the pattern recognition of neurofuzzy engine and defuzzification process. Results The 100 puckered samples were evaluated subjectively by five human experts and objectively by the developed system for comparing the AATCC grades. The

Figure 2. Users and non-users of DFM

result showed a good correlation, of which the coefficient between subjective and objective evaluation is 0.8468. Five shape parameters of each sample were obtained using the new standards. All the types of the seam pucker can be simulated. It was shown that the fabrics with the same grade of pucker had the different shape parameters. Figure 2 shows an example of results. Conclusions The new standards of seam pucker with the five shape parameters was suggested and the evaluation method was developed using FFT and artificial intelligence. It has been shown that prediction and optimization of seam pucker are possible using the approaches developed in this study with material properties and processing parameters. The developed system for seam pucker is already in use at a men’s suit company and at a textile manufacturing factory in Korea. They have used the systems to improve the quality of products. References 1. AATCC Technical Manual, Vol. 69, 1994, p. 115. 2. Watanabe, S., “Tailorability”, Journal of Japan Res. Associates for Text. End-users, Vol. 23 No. 12, 1982, p. 499. 3. Inui, S. and Shibuya, A., “Objective evaluation of seam pucker”, International Journal of Clothing Science and Technology, Vol. 4 No. 5, 1992, p. 24. 4. Stylios, G. and Sotomi, J.O., “Investigation of seam pucker in lightweight synthetic fabrics as aesthetic properties (Parts I, II)”, Journal of Textile Institute, Vol. 84 No. 4, 1993, pp. 593, 610.

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Dynamic clothing simulation based on skeletal motion of the human body Takatoshi Saeki, Takao Furukawa and Yoshio Shimizu Faculty of Textile Science and Technology, Shinshu University, Nagano, Japan

International Journal of Clothing Science and Technology, Vol. 9 No. 3, 1997, pp. 256-263. © MCB University Press, 0955-6222

Introduction Ideally, computer-aided apparel design systems should reflect end-users’ tastes. We describe the construction of an interactive apparel design system using the World Wide Web. Clothing simulation is a principal component of an interactive apparel design system. Simulations based on mechanical models of cloth have been proposed[1-4] for the purpose of constructing three-dimensional apparel computer-aided design (CAD) systems. In apparel CAD systems, materials are flexible and many design factors are considered. The clothing simulations based on the mechanical models require huge computational expenses in order to predict the precise shapes of the cloth. Cloth that shows anisotropy and non-linear mechanical properties can be written by a non-linear partial differential equation with boundary and initial conditions. Even if we use numerical analysis on high performance computers, it is difficult to solve the non-linear partial differential equation describing the dynamic cloth deformation. Moreover, collision detection between the clothes and the human body incurs a high computational cost. The clothing deformation with human body motion affects aesthetic appreciation, so that dealing with the dynamic cloth deformation is necessary for the simulation of clothing. Representation of human bodies in computer graphics has been an important research subject. In the apparel fields, spline surfaces and blobs[5] have been applied for this purpose. At the present time, motion capture systems and motion generation based on mathematical models[6] are proposed. Muscles and skeletons in a human body work as active and passive organs, respectively. In other words, muscle contraction moves the skeleton that restricts human body posture. This paper incorporates these motions, as well as the resulting dynamic clothes deformation, in its proposal for clothing simulation. In order to do so, we first express the construction of an interactive apparel design system. Next, the functions of each of the system’s modules are described. Finally, we explain the potential applications of the interactive apparel design system, and give details of a single example.

System construction To reflect end-users’ tastes, we propose a system that performs clothing simulation in the virtual world, as shown in Figure 1. The system consists of the human body, clothes and environmental modules. The human body module describes the skeleton, physique and motion models of the human body. The clothes module consists of shape, material and colour models. The environmental module incorporates the models of illumination and of scene elements. The module that performs the simulation for clothing based on skeletal motion assembles outputs from the human body and clothes modules. Thus the simulation of clothing in the virtual world is executed by integration of the outputs from each module.

Dynamic clothing simulation 257

Figure 1. Outline of clothing simulation in a virtual world

Human body model Skeletal model Twenty individual bones are used to construct the human body model for the simulation of clothing, allowing for a body motion of high verisimilitude. The body motion is restricted by joints, which are assigned to connect the various bones as follows: one joint for the connection between head and neck, two joints for the tripartite torso, two for each of the tripartite upper and lower limbs, and one joint, the pelvis, connecting the vertebrae and legs. A real human body has 17 pieces of bones as vertebrae; we simplify this model and describe the vertebrae with three bone pieces. Skeletal motion The muscles contract as an active organ to determine human body motion, while the skeleton works as a passive organ to restrict motion. Because it is the rotation of joints which constructs the complex motion patterns of the human

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body, we describe body motion by bone length and the joint angles between bones. Each bone length is a constant, but the joint angles change with the skeletal motion. Thus, the joint angles constitute time series data. Physical model The physical model of the human body employs Bézier surfaces to describe the shapes. The shapes of the Bézier surfaces are determined by the co-ordinates of control points and written using a piecewise polynomial. Figure 2(a) illustrates a cylindrical surface constructed of two bi-cubic Bézier patches. Control points that determine the shape of the patches are shown in Figure 2(b). A bi-cubic Bézier patch f(u, v) is defined as f (u , v ) =

3

3

∑ ∑

Bi , 3 (u ) B j , 3 ( v ) bij .

i=0 j =0

(1)

( 0 ≤ u ≤ 1, 0 ≤ v ≤ 1) where Bi,3 are Bernstein functions and bij are considered control points of Bézier surfaces:  3 Bi , 3 (u ) =   (1 – u )3 – i u i i

(2 )

Shapes of a bi-cubic Bézier patch are described by 16 control points. The skin of the upper and lower limbs can be represented by a few Bézier patches. Bézier surfaces corresponding to skin are defined in local co-ordinates that describe each bone. The diameter of the torso, arms and legs can be expressed as the distance between principal axes of the bone and the control points of Bézier patches representing the skin. Thus fat and thin bodies can be generated by changing the diameter of the standard body. Facial model Generally, when we look at a person, our eyes are oriented to the person’s face. It is difficult to represent the face by three-dimensional computer graphics, because the face consists of complex parts – hair, eyes, mouth, etc. In order to

Figure 2. Bi-cubic Bézier patches and its control points

create precise facial models using traditional, three-dimensional computer graphics, a prohibitive number of polygons is needed. Even so, these generated faces lack realism. On the other hand, two-dimensional facial images, like those from photographs, appear natural even at low image resolutions. We therefore adopt the two-dimensional facial image as our facial model, mapping it across a plane region placed at the head of the human body model. Facial images taken from various viewpoints allow for the motion of models and the shifting viewpoints of observers.

Dynamic clothing simulation 259

Clothes model In order to estimate clothes deformation according to human body motion in real time, we employ a simple geometric model as a clothes model. Complex clothes shapes can then be represented by approximate assemblage of bi-cubic Bézier surfaces. Clothes shape model based on skeletal motion We define the relation between the skeletal model and the control points of the Bézier surfaces describing the clothes model such that the control points in three-dimensional space are moved by the skeletal motion. In this way, the clothes deformation by the human body motion can be represented. For example, consider the procedure for defining the relation between the skeletal model and the control points representing a skirt. First, we determine the waist and hip positions on the skeletal model. Human body sections at the waist and the hip are approximated by two semi-ellipses that have different ellipticities, as shown in Figure 3. The two semi-ellipses share in common a line of apsides, but the lengths of their minor axes are different. The flat and round semi-ellipses are placed at the front and back of the human body, respectively. The lengths of the ellipse axes are determined by the waist and hip sizes. Since the perimeter of the semiellipse is calculated by elliptic integral, an allotment of the waist and hip sizes to the front and back part of the semi-ellipses determines the length of the axes. Next, two ovals are placed at the thighs and knees of the body model to determine the shape of a knee-length skirt. The ovals represent the shape of the

Figure 3. The relation between skeletal motion and a skirt shape

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skirt and are defined by the posture of the legs. An oval is determined by the following procedure. We define a circle the radius of which is greater than or equal to the diameter of the thigh or knee. The circle is defined on the plane perpendicular to the thigh bone. In this way, two circles are placed at the right and left of the thigh or knee. Moreover, we determine two tangent lines that contact the circumference of the two circles. Four tangent lines are determined by two circles; however, we choose two tangent lines that do not cross each other. These circles and tangent lines define the oval at the thigh or knee. Such ovals are extensible to define generalized cones that represent the skirt shape. We approximate these generalized cones by Bézier surfaces, so that the positions of the control points are determined. Material and colour models Material model It is difficult to render the texture of cloth using the current technology of computer graphics. Although we could make a geometric model of each type of yarn used in a particular cloth, the resulting model, though technically precise, would not be useful at low image resolution. We thus need to apply certain enhancements to the rendering of clothes at low image resolution. In this paper, the material model allows for detailed structuring in clothes: in the case of a skirt, flares and pleats. A normal on a plane is defined as a unique vector; however, Gouraud or Phong shading models scatter the direction of the normal on a plane. Brightness at a point on the plane is fundamentally calculated by the inner product of the surface normal and light vectors. Despite the geometrical model being represented as a plane, the brightness distribution on the plane can be changed by this method. Where the flare of a skirt is represented as a geometric surface model, complex functions or many piecewise polynomial patches, such as the Bézier patch, are required. Since complex geometric models of the clothes are not useful in low-image resolution displays, we employ a few Bézier patches to represent the shape of the clothes. In order to represent such fine structures as the flare of a skirt, we control the normal vectors on the Bézier patches. The skirt flare then represented by circular variation of the normal vectors on Bézier patches. Colour model We deal mainly with optical properties of the material colour, such as the specular and diffuse components of the reflection on the surface. The module of the colour model relates the material texture and the optical properties. When end-users choose textiles for their clothes, the colour model module produces the optical properties of the material and sends these data to the subsequent module. For example, silk is a lustrous material, so its specular component is enhanced by comparison to materials like cotton.

Environmental model Because end-users will be interested in the appearance of their clothes in the actual intended environments, the simulation of virtual environments is critical to the interactive apparel CAD system. The environmental model consists of scene components and illumination. Illumination components determine the optical properties of the light, such as daylight or lamplight. Because the frequency distributions of daylight and lamplight are different, the colour of clothes under these illuminations seems also to differ. Scene components are contained in a scenery database. It is much less difficult to construct a three-dimensional model of a restricted space, such as a room, than it would be to represent the complexity of settings like the sea, mountains, or forests. In this paper, we employ image data of sights to create a scene model within a restricted space. Thus, the human body model wearing the clothes is assembled with the appropriate visual imagery. This environmental model permits the simulation of clothing in a virtual environment.

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Simulation In our simulation of clothing, we employ the motion data of a walking fashion model input with the motion editor. End-users can choose factors of the skirt, such as the shape and materials, by using the WWW browser. When an enduser chooses a knee-length skirt made of silk, computer animation emphasizing the cloth’s lustre is created, as seen in Figure 4. Figure 4 shows front views of a walking woman wearing a knee-length silk skirt. The animation goes from left to right and downwards. The skirt deformation by the locomotion is generated by the clothes shape model based on the skeletal motion. Two pieces of Bézier patches are used to construct the skirt. It is confirmed that the skirt’s shape changes with the model’s leg motions. A computer animation created from another viewpoint is shown in Figure 5. Here, the facial image is altered from that in Figure 4. Despite the use of simple human body and clothes models, a natural simulation for clothing is created. Figure 6 shows the result of a gathered skirt. The geometric model of the skirt is the same here as in Figure 5. Scattered normal vectors on the Bézier surface allow us to depict these gathers without altering the geometrical model. Figure 7 shows similar results for a long skirt. Since the lowest Bézier control points are placed at the shin, the skirt bends at the knee. Moreover, the skirt shapes change naturally with the skeletal motion of the lower limbs.

Figure 4. Front view of the walking model wears knee-length skirt

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262 Figure 5. Walking model wears knee-length skirt

Figure 6. Walking model wears knee-length gathered skirt

Figure 7. Walking model wears long gathered skirt

Figure 8. Clothing simulation in a virtual environment

This interactive apparel CAD system permits end-users to choose the shape and material of clothing. Figure 8 shows the simulation of clothing in a virtual world. The left side of Figure 8 shows possible scenes that an end-user may want to visit. The end-user chooses a scene, then watches while the animation of a human model wearing the clothing is displayed.

Conclusion This paper describes the construction of an interactive apparel CAD system using WWW. In order to implement this simulation for clothing, the proposed system must include several modules. These are the human body, the clothes and the environmental models. The outputs from each module are unified to the module that performs the simulation of clothing in the virtual environment. By allowing end-users to choose the shape and material of clothing in a setting of their choice, this system permits the unique design of clothes according to individual tastes. References 1. Okabe, H., Imaoka, H., Tomiha, T. and Niwaya, H., “Three dimensional apparel CAD system”, ACM Computer Graphics (Proceedings of SIGGRAPH ’92), Vol. 26, 1992, pp. 10510. 2. Sakaguchi, Y., Minoh, M. and Ikeda, K., “PARTY: a numerical calculation method for a dynamically deformable cloth model”, Transactions of IEICE(D-II), Vol. J77-D-II No. 5, 1994, pp. 912-21 (in Japanese). 3. Sakaguchi, Y., Minoh, M. and Ikeda, K., “PARTY: dress shape calculations method with collision effect between dress and human body”, Transactions of IEICE(D-II), Vol. J78-D-II No. 3, 1995, pp. 481-91 (in Japanese). 4. Volino, P., Courchesne, M. and Thalmann, N.M., “Versatile and efficient techniques for simulating cloth and other deformable objects”, Proceedings of SIGGRAPH ’95, 1995, pp. 137-44. 5. Matsuda, R. and Imaoka, H., “Modelling of human body by density balls for garment design”, Sen’i gakkaishi, Vol. 50 No. 5, 1994, pp. 221-8 (in Japanese). 6. Tsutsuguchi, K., Sakaino, H. and Watanabe, Y., “Terrain adaptive human walking animation”, Transactions of IEICE(D-II), Vol. J-77-D-II No. 8, 1994, pp. 1663-70 (in Japanese). Further reading Breen, D.E., House, D.H. and Wozny, M.J., “Predicting the drape of woven cloth using interacting particles”, Proceedings of SIGGRAPH ’94, 1994, pp. 365-72. Bruderlin, A. and Calvert, T.W., “Goal-directed, dynamic animation of human walking”, ACM Computer Graphics, Vol. 23 No. 3, 1989, pp. 233-42. Chen, D.T. and Zeltzer, D., “Pump it up: computer animation of a biochemically based model of muscle using the finite element method”, Computer Graphics, Vol. 26 No. 2, 1992, pp. 89-98. Matsuda, R. and Imaoka, H., “A graphics method to simulate garment fitting on a human model in various postures”, Sen’i gakkaishi, Vol. 51, 1995, pp. 225-33 (in Japanese). Singh, K., Ohta, J. and Kishino, F., “Realistic modelling and animation of a muscle and skin layer for human figures using implicit function techniques”, Technical Report of IPSJ, No. 94-CG-59, 1994, pp. 49-56.

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Grain alignment: effects on fabric and garment drape Belinda T. Orzada

272

Department of Consumer Studies, University of Delaware, Newark, Delaware, USA

Mary Ann Moore College of Human Sciences, Florida State University, Tallahassee, Florida, USA, and

Billie J. Collier School of Human Ecology, Louisiana State University, Baton Rouge, Louisiana, USA

International Journal of Clothing Science and Technology, Vol. 9 No. 4, 1997, pp. 272-284. © MCB University Press, 0955-6222

Introduction Fabric grainline position in relation to its placement in each piece of a completed garment is a critical element in apparel construction and, ultimately, garment appearance and quality. “Tilt” is a term used in apparel manufacturing to refer to the degree to which a pattern piece can be adjusted within the marker to maximize fabric efficiency. A recent survey of US apparel industry marker making standards relative to pattern grain alignment found tilting patterns offgrain within markers to be a current apparel industry practice (Orzada and Moore, 1997). Although apparel production textbooks warn against laying patterns off-grain because to do so will affect the drape and fit of a garment, manufacturers occasionally do this to increase fabric utilization (Hudson, 1988). Apparel manufacturers are constantly seeking ways to reduce production costs. One way to reduce these costs is to increase fabric utilization. Computer marking systems offer this possibility. Current research in computer marking capabilities is exploring rotational compaction (tilting) during automatic marker generation as a method of optimizing pattern layouts (Li and Milenkovic, 1995; Shanley et al., 1995). However, this research concentrates on development of computer programs necessary to make automatically generated markers more efficient, and does not address the effect of tilted patterns on garment drape or quality. Fabric drape is an important element in a garment’s overall aesthetic appearance and is one of the most important properties of interest to fabric and apparel buyers. Drape is defined as the arrangement of a fabric in graceful folds as a result of gravity (Mehta, 1985) and is dependent on a fabric’s structural and mechanical properties (Collier, 1991). Undesirable garment drape occurs when garment seams twist towards the back or front or when nodes (folds) form different shapes on each side of the garment. Pattern pieces positioned

incorrectly (off-grain) in the marker may precipitate undesirable garment drape Grain alignment: (Moore, 1992). effects on fabric Researchers have been concerned with assessing the behaviour of draped and drape fabrics for a number of years. Previous drape research has concentrated on the development of quantitative drape evaluation methods (Chu et al., 1950), the correlation of these drape values with fabric mechanical properties thought to 273 influence drape (Collier, 1991; Collier et al., 1989; Cusick, 1965, 1968; Skelton, 1976), and with subjective drape evaluations (Collier, 1991; Sudnik, 1972). Recent research in fabric mechanical and physical processes in relation to apparel manufacturing processes has concentrated primarily on predicting and improving fabric tailorability (Majar et al., 1989; Shishoo, 1990, 1995) and has omitted one very important influence on fabric drape: grain alignment. Very few studies examining elements of fabric grain were found through a review of the literature. Dhingra and Postle (1990) examined fabric compressibility and bending behaviour in the lengthwise and bias directions. In woven fabrics, compressibility along the bias direction was higher while bending stiffness was lower. Gardner et al., (1978) found that the angle of fabric bias has a significant effect on breaking strength of seamed and unseamed fabric samples. In objective tests of fabric skewness effects on the drape of four gore skirts, Moore et al. (1995) examined five skewness levels and determined differences were excessive for distance between adjacent nodes, and that asymmetry was significant at 4.4 per cent skewness. Fabric grain, along with thickness and fibre type, was found useful in predicting the behaviour of fabric within enclosed seams. Recognizing the limited research related to either the influence of lengthwise grain alignment on drape characteristics or fabric mechanical properties, or the importance of grain alignment in apparel manufacturing, this study was designed to examine the relationship between fabric drape and grain alignment. Both subjective and objective analyses were conducted, since correlation of subjective assessments and instrumental evaluation of fabric physical and mechanical characteristics has proven a reliable method for the scientific expression of aesthetic fabric properties (Collier, 1991). Five experimental fabrics composed of 100 per cent cotton with 3/1 twill weave construction were selected for analysis. Physical fabric property measurements shown in Table I were determined according to ASTM (American Society for Testing and Materials, 1985) methods. Although all fabrics were selected as representative of bottom weight fabrics, a range of fabric weights, thicknesses and counts were included in the analysis. Fabrics A and B were gabardines; Fabrics C and D were both heavy denims; and Fabric E was a lightweight denim. Furthermore, these fabrics were considered representative of fabrics appropriate for the straight skirt style used in the subjective evaluation portion of this study.

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Fabric

Weight (g/m2)

Thickness (mm)

Count (yarns/25mm)

A

274

0.575

116 × 56

B

288

0.543

114 × 56

C

413

0.785

66 × 38

D

433

0.853

57 × 38

E

316

0.620

105 × 52

Quantitative drape evaluation Methodology Our first research objective was to measure fabric drape and shearing behaviour and to relate these properties to grain alignment (tilt angle). To meet this objective, the following methodology was followed. A computer-aided pattern design and marking system was utilized to draft patterns for fabric specimens, and to tilt accurately the half-circle drape patterns and the shear tilt patterns at specific angles. Data obtained from a survey of apparel industry marker-making standards relative to pattern grain alignment revealed that tilting patterns off-grain within markers is a current industry practice (Orzada and Moore, 1997). Therefore, tilt amounts reported in survey responses were used as a basis for selecting the variations of tilt in which to examine the effect of grain alignment on fabric drape and shearing behaviour. As is presented in Table II, 12 different tilt variations were examined for influences on drape. Base tilt angles of 0, 3, 6 and 9 were used. For four tilt variations, the base tilt amount was used for both halves of the circle. For the other fabric specimens, the base tilt amount was utilized for one half, while the second half was tilted an amount equal to the base tilt plus 2 (the minimum tilt difference) or 4 (the maximum tilt difference). Patterns for the fabric specimens were drafted according to the following dimensions: (1) for the drape analysis, a 10-inch diameter circle (Chu et al., 1950) and a half-circle pattern with a five-inch radius; and Base tilt angles (degrees) Table II. Factorial design of tilt variation fabric and garment drape samples

0 3 6 9

Difference between tilt angles (degrees) +0°(x) +min(2) +max (4) 0/0 3/3 6/6 9/9

0/2 3/5 6/8 9/11

0/4 3/7 6/10 9/13

(2) for the shear and bending analyses, a 20 × 20cm pattern (Kawabata, Grain alignment: 1980). effects on fabric A one-fourth inch seam allowance was added to the straight edge of the halfcircle pattern. Separate markers were made for the drape specimens and the shear and bending specimens. Patterns were positioned in the marker according to ASTM guidelines (American Society for Testing and Materials, 1985). Half-circle fabric specimens were sewn together in the appropriate tilt combinations with centre seamlines pressed open. To assess the influence of the seam on fabric drape, one of the tilt variations included was cut on correct grain alignment (0/0 tilt). Unseamed drape specimens from each fabric served as controls. Drape values were measured on a five-inch diameter pedestal utilizing a drape tester developed by Collier et al. (1988) and further validated by Collier (1991) and Collier et al. (1989). The drape tester consists of a box with photovoltaic cells in the base and a light source on the lid which is above the specimen when the lid is closed. The amount of light blocked when the fabric specimen is draped over the plate is determined by its draping conformation and is normalized on a scale of 0-100 per cent. A high degree of drape results in a high voltage rating (Collier, 1991). Specimens were draped over the pedestal face up with the centre seam (tilt variation) or the lengthwise grain (control) parallel to the sides of the drape tester box. Drape values are traditionally obtained by draping fabric specimens face up then reverse side up, with duplicate measurements taken for each fabric specimen (Collier, 1991). However, because garment seams are located inside the garment, drape values for the tilt specimens were taken with the fabric face up only. Three specimens of each tilt variation were tested with three measurements taken of each. To measure fabric mechanical properties related to drape, two instruments from the Kawabata Evaluation System for Fabrics (KES-F) were utilized. The pure bending tester was used to measure fabric bending resistance to obtain bending modulus and bending hysteresis values of control specimens (0 tilt). The shear tester was used to obtain shear stiffness, shear hysteresis at 0.25 and shear hysteresis at 2.5 values for both control and tilt variation specimens. Duplicate measurements in warp and weft directions on three specimens of each fabric were made using the Kawabata instruments. Two variations to traditional shear testing on KES-F were instigated. First, to investigate the effect of grain alignment on fabric shear properties, fabric specimens for shear measurements, which are traditionally cut on straight grain (Kawabata, 1980), were cut in 12 different tilt variations. Shear measurements were taken from fabric specimens cut at the same tilt angles used for the drape tests (0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 13). Shear specimens were not sewn together in tilt combinations as the drape specimens were, since the Kawabata Shear Tester could not accommodate this variation.

and drape 275

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The second method variation was required due to the fabrics utilized in the present study. Kawabata (1980) set standards for shear testing of suiting fabrics at 8 of shear deformation; however, the stiffness of the bottom weight fabrics examined in this study required that maximum shear deformation be reduced to 4 to prevent excessive fabric buckling. Therefore, shear hysteresis values were measured at 0.25 and 2.5, rather than 0.5 and 5.0. Results and discussion Drape values. Fabric drape specimens exhibited a small range of drape values (29-41 per cent). However, the drape tester was able to distinguish among them (Table III). When examining the tilt variation drape values, no consistent relationship between tilt angle and drape value was revealed. Fabric E exhibited the most consistent drape values of the five fabrics, a difference of only 2.4 per cent separated the most drapable tilt variation specimen (3°/3°) at 29.9 per cent from the least drapable (0°/2°) at 27.5 per cent. Drape values obtained for the other four fabrics showed less consistency between tilt variations. Fabric B’s drape values were the least consistent, with a difference of 6.7 per cent between the least and most drapable specimens, 36.0 per cent (9°/9°) and 42.7 (9°/11°). No significant differences in draping behaviour were found between control drape specimens and those with tilt variations. Fabric mechanical properties. Means of fabric mechanical properties and drape values are presented in Table III. No clear pattern of relationships emerges from the data. This may be due to the physical characteristics of the fabric specimens. For example, the lower drapability of Fabric E, despite its lighter weight, may be due to its higher fabric count. Relationships between drape values and fabric physical and mechanical properties were further examined through Pearson correlation coefficients. Correlations with drape were negative for the three shear properties, the two bending properties, weight and thickness, and were positive for fabric count. Although none of the correlations were significant, results tend to confirm Collier et al.’s (1989) findings which revealed negative correlations between drape and shear stiffness.

Drape values Fabric (per cent)

Table III. Means of fabric mechanical properties

A B C D E

32.9 37.3 40.8 29.1 29.1

Shear stiffness (gf/cm.deg)

Shear hysteresis at 0.25° (gf/cm)

Shear hysteresis at 2.5° (gf/cm)

3.15 2.60 10.50 12.25 5.94

6.87 7.00 20.75 22.00 21.21

8.15 8.33 22.92 23.75 17.10

Bending Bending modules hysteresis (gf.cm2/cm) (gf.cm/cm) 0.1815 0.2282 0.7857 1.0167 0.5940

0.2512 0.3208 1.2103 1.3198 0.8543

With one exception, Pearson correlations revealed significant positive Grain alignment: relationships among the physical and mechanical properties; fabric count effects on fabric exhibited negative correlations with each of the other properties. The large and drape number of significant correlations among fabric physical and mechanical properties contrasts with a study by Collier (1991) in which only two significant correlations, shear stiffness with shear hysteresis at 5 and with bending 277 modulus, were revealed. Use of fabrics which did not vary widely in their weight, thickness and count properties, and were identical in their fibre type and weave structures, may have facilitated obtaining these strong correlations. Collier used a wide variety of fabrics to validate the drape tester. Shear tilt variations. Figure 1 demonstrates the visual differences observed between the shapes of the shear hysteresis diagram when the control (0 tilt) is compared to a specimen cut at 13 tilt. Shapes of the shear diagrams are similar for the forward (right) portion of the curve. However, for the left side of the diagram, the 13 tilt specimen has a higher slope and a deeper hysteresis width. For all five fabrics, as tilt amount increases, asymmetry of shear curves becomes more pronounced. This means that when a pattern piece is cut offgrain in a garment, the fabric will shear differently in each direction. Consequently, this asymmetric shearing will ultimately affect the folds which form as the garment drapes around the body. As may be observed from Figures 2, 3 and 4, generally, there was an increase in all three shear values (shear stiffness, shear hysteresis at 0.25 and shear hysteresis at 2.5) as tilt angles increased across all five fabrics. The most consistent increases in shear values were found for Fabric A. For Fabrics A, B

FS gf/cm

15

10

5

–8

–6

–4

–2

0

2

4 6 Ø degree

8

–5

–10 Key

0˚ tilt 13˚ tilt

–15

Figure 1. Comparison of shear curves at 0° and 13° tilt angles

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278

6 4 2 0

Figure 2. Effect of tilt amount on shear stiffness

0 1 2 3 4 5 Tilt angle (degrees)

6

7

8

9

10 11 12 13

Key A

B

C

D

E

Shear hysteresis at 0.25˚ (gf/cm) 32 28 24 20 16 12 8 4

Figure 3. Effect of tilt amount on shear hysteresis at 0.25°

0 0 1 2 3 4 5 Tilt angle (degrees)

6

7

8

9

10 11 12 13

Key A

B

C

D

E

Shear hysteresis at 0.25˚ (gf/cm) 32 28 24 20 16 12 8 4 0

Figure 4. Effect of tilt amount on shear hysteresis at 2.5°

0 1 2 3 4 5 Tilt angle (degrees)

6

7

8

9

10 11 12 13

Key A

B

C

D

E

and D, all three shear measurements were significantly different from the Grain alignment: control (0 tilt) by at least two standard deviations for the majority of tilt angles. effects on fabric For each of Fabric C’s shear measurements, as well as the shear stiffness values and drape of Fabric E, those tilt angles 7 and above were generally significantly different from the control values by at least two standard deviations. Significant differences from the control for Fabric E’s shear hysteresis at 0.25 and 2.5 279 values, however, may be observed at tilt angles of 10 and 9 and above, respectively. The influence of this general increase was revealed in Pearson correlations of tilt with shear properties. For each of the five fabrics and three shear properties, increases in tilt amounts were positively and significantly correlated (p > 0.05 or stronger) with increased shear values. The ability to accept shear deformation is essential for shaping a fabric into a three-dimensional garment. Fabrics with lower shear stiffness values conform to three-dimensional curvatures most readily (Majar et al., 1989). In this study, specimens with larger tilt angles had increased resistance to shear that resulted in higher shear values. This increase in hysteresis with tilt angle indicates less recovery of energy which could affect draping and asymmetry. Therefore, when a garment is constructed with tilted pieces, those tilted pieces will resist shear deformation and will buckle rather than lie straight. Subjective drape evaluation Objectives Our second research objective was to evaluate subjectively drape preference and amount and relate these evaluations to grain alignment. Specifically, the research objectives were to: (1) ascertain whether subjective evaluations of fabric drape amount and drape preference may be correlated with the drape values; (2) determine the effects of tilting pattern pieces off-grain during marker making on apparel design students’ subjective evaluations of garment drape; and (3) examine whether differences in level of apparel design experience affect subjective evaluations of fabric and garment drape. Methodology A convenience sample of 21 students at two levels in a university apparel design programme subjectively evaluated the drape of the five experimental fabrics and 12 skirts constructed from each fabric. For the purposes of this study, beginning apparel design students who had completed one apparel construction course (n = 13) are identified as Group 1, while Group 2 includes the more advanced students who were junior and senior level apparel design majors (n = 8). To orient the judges, drape was defined and sample fabrics of both high and low drapability were draped over the pedestal by the researcher as examples prior to subjective evaluation of the experimental fabrics. One drape specimen

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from each of the five experimental fabrics was subjectively evaluated. Circular fabric specimens were draped one at a time over a wooden pedestal to duplicate the conformation occurring during objective drape measurement on the drape tester. Student judges individually evaluated fabric drape amount and their preference for the aesthetic draping qualities of each experimental fabric on a 7point Likert-type scale (7 = highly drapable or highly preferred). Subjective garment evaluation was conducted using 12 skirts constructed from each of the five experimental fabrics. The skirt is the garment traditionally utilized for subjective drape evaluation because of the inherent drapability of the garment. Additionally, in our examination of grain alignment and drape, it is appropriate to note that skirts are among the garments tilted off-grain by the apparel industry. Forty-three per cent of those manufacturers which tilted garments reported tilting skirts off-grain (Orzada and Moore, 1997). Tilt amounts reported by Orzada and Moore were used as a basis for selecting the variations of tilt in which to construct the skirts. The 12 tilt combinations defined in Table II were again utilized in skirt construction with skirt fronts being tilted according to the first tilt angle and skirt backs tilted according to the second tilt angle. Skirts were randomly positioned on 12 dress forms for subjective evaluation, one fabric at a time. Each judge evaluated the drape of skirt grain variations on a 7-point scale. The skirts were evaluated on four items: (1) the actual amount of fabric drape rated by visual observation only (7 = highly drapable); (2) the accuracy of pattern layout rated by visual observation only (7 = accurate layout); (3) the accuracy of pattern layout from a close-up inspection (7 = accurate layout); and (4) the preferred garment for purchase (7 = highly preferred). Visual observations were made from a distance of three to four feet. For closeup observations, students were allowed to examine the skirts closely, touching them if necessary. Results and discussion Fabric drape. Significant positive correlations between subjective evaluations of fabric drape amount and drape preference for four of the experimental fabrics were identified: Fabric A (r = 0.63, p < 0.001), Fabric B (r = 0.62, p < 0.01), Fabric D (r = 0.39, p < 0.05), and Fabric E (r = 0.66, p < 0.001). A weak positive correlation was revealed for Fabric C; however, the correlation did not reach significance. Collier (1991) also found drape amount and drape preference to be correlated, indicating that the more drapable fabrics were those with draping behaviours preferred by the judges. Differences discovered between the beginning and advanced students’ subjective evaluations of fabric drape may be examined in Table IV. The

Fabric A Drape amount Combined sample Group 1 Group 2 Drape preference Combined sample Group 1 Group 2

Fabric B

Variable Fabric C

Fabric D

Fabric E

Mean SD Mean SD Mean SD

3.14 1.49 3.85 1.28 2.00 1.07

3.29 1.31 3.62 1.26 2.75 1.28

1.95 1.12 2.00 1.08 1.87 1.25

1.19 0.81 1.08 0.76 1.37 0.92

1.95 0.97 2.15 0.69 1.62 1.30

Mean SD Mean SD Mean SD

3.71 1.38 3.92 1.12 2.25 1.17

3.80 1.32 3.33 1.56 3.00 0.93

4.10 1.34 3.38 1.26 2.13 1.13

4.71 1.38 2.62 1.61 1.75 0.71

3.67 1.43 3.92 1.32 2.37 1.06

advanced apparel design students, Group 2, rated all five fabrics lower (more strictly) on both drape amount and drape preference than did the beginning students, Group 1. Additionally, Group 2 students were more consistent in their drape preference ratings of the specimens as is evident in their lower standard deviations. ANOVA revealed significant differences between the two groups’ evaluations of drape preference for Fabrics A (F = 10.78, p < 0.01), C (F = 5.34, p < 0.05), and E (F = 7.8, p < 0.01). Drape amount was evaluated more similarly by the two groups across the five fabrics. Fabric A’s evaluations were the only drape amount evaluations found to be significantly different between the two groups (F = 11.58, p < 0.01). When relationships between subjective and objective drape evaluations were examined, the student evaluators’ assessments of fabric drape were highly correlated with drape values. Group 2’s subjective evaluations of fabric drape amount were significantly correlated with drape values (r = 0.95, p < 0.05). Pearson correlation coefficients for Group 1 (r = 0.71) and the combined sample (r = 0.79) were high as well, although neither reached significance. Of the drape preference evaluations, only Group 2’s evaluations revealed a strong correlation with drape values; a Pearson correlation of 0.77 was found, but was not significant. Each of the eight fabric properties examined exhibited significant Pearson correlations with subjective drape evaluations. Both drape preference and drape amount were negatively correlated with each of the fabric properties. Additionally, correlations between drape amount and the eight fabric properties were stronger than those of drape preference evaluations. Garment drape. For each fabric, the 12 skirts were ranked by the researcher based on tilt variation amount. Each skirt with the least tilt (0 front/0 back) was

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Table IV. Means of subjective evaluation of fabric drape

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ranked 1, followed by the skirt with 0 front/2 back tilt (ranked 2), etc. The skirts tilted off-grain the most were ranked 12 (9 front/13 back). The judges’ four subjective evaluation scores (drape amount, accurate layout – visual, accurate layout – close-up, and preferred garment for purchase) were combined to obtain subjective evaluation means for each skirt. Mean scores were converted to ranks and compared to the researchers’ skirt ranks which were based on the amount of tilt variation used. The more advanced students exhibited higher sensitivity to small differences in drapabilty as demonstrated by their evaluations of garment drape. Group 2’s evaluations were in agreement with the researcher’s skirt ranks for 62 per cent of the skirts, while Group 1 agreed with the skirt ranks for only 47 per cent of skirts. Spearman analysis (Table V) revealed strong positive correlations between skirt rank and Group 2’s subjective evaluations for Fabrics C (r = 0.82, p < 0.001), D (r = 0.83, p < 0.001), and E (r = 0.61, p < 0.05). Group 1’s evaluations were significantly correlated with the skirt ranks for Fabric C only (r = 0.66, p < 0.01). In previous studies exploring subjective assessments of aesthetic fabric properties, only Yick et al. (1995) have reported data based on levels of experience of the judges. Although a direct comparison cannot be made because

Fabric

Combined sample

Group 1

Group 2

A

r r2 p

0.1469 0.0126 0.33

–0.0699 0.0049 0.42

0.1684 0.0284 0.30

B

r r2 p

0.2727 0.0744 0.20

0.1086 0.0118 0.37

0.2797 0.0782 0.19

C

r r2 p

0.7636 0.5831 0.002**

0.6620 0.4382 0.01**

0.8182 0.6695 0.001***

D

r r2 p

0.5035 0.2535 0.05*

–0.0070 0.0001 0.49

0.8252 0.6810 0.001***

Table V. E r 0.1786 Spearman rank-order r2 0.0319 correlation coefficients p 0.29 of skirt rank and subject evaluation groups by fabric Key *p < 0.05, **p < 0.01, ***p < 0.001

–0.0105 0.0001 0.49

0.6060 0.3672 0.02*

Yick et al.’s study examined fabric hand rather than drape, it is interesting to Grain alignment: note that this research yielded no differences between assessments of students effects on fabric and apparel industry professionals. and drape Conclusions and recommendations Apparel manufacturers are constantly looking for ways to reduce production costs; however, this should not occur at the cost of garment quality. In this study, we examined the effects of a common apparel industry practice, tilting patterns off-grain on fabric and garment drape evaluations. Degree of tilt significantly increased shear stiffness and hysteresis for the twill fabrics examined in this study. In addition, off-grain fabric specimens exhibited more asymmetrical shear curves. However, since there was no consistent relationship between tilt angle and drape value, an objective measure of amount of drape, the most significant effect of tilting may be on drape symmetry and appearance. Although limited by the small sample size, results of subjective garment drape evaluation suggest that those persons with more design experience are more capable of identifying variations in grain alignment than those with little experience. Advanced students have more experience with apparel fabrics and greater knowledge of their properties and what combination of properties make a fabric acceptable for a particular design. As graduates of an apparel design programme, students should be aware of the effect that grain has on garment drape and apply this knowledge in the workplace. References American Society for Testing and Materials (1985), Annual Book of ASTM Standards, Vol. 7.01. Chu, C., Cummings, C. and Teixeira, N. (1950), “Mechanics of elastic performance of textile materials, part V: a study of the factors affecting the drape of fabrics – the development of a drape meter”, Textile Research Journal, Vol. 20 No. 8, pp. 539-48. Collier, B. (1991), “Measurement of fabric drape and its relation to fabric mechanical properties and subjective evaluation”, Clothing and Textiles Research Journal, Vol. 10 No. 1, pp. 46-52. Collier, B., Paulins, V. and Collier, J. (1989), “Effects of interfacing type on shear and drape behavior of apparel fabrics”, Clothing and Textiles Research Journal, Vol. 7 No. 3, pp. 51-6. Collier, B., Collier, J., Scarberry, H. and Swearingen, A. (1988), “Development of a digital drape tester”, ACPTC Combined Proceedings, p. 35. Cusick, G. (1965), “The dependence of fabric drape on bending and shear stiffness”, Journal of the Textile Institute, Vol. 56, pp.T596-T606. Cusick, G. (1968), “The measurement of fabric drape”, Journal of the Textile Institute, Vol. 59 No. 6, pp. 253-60. Dhingra, R. and Postle, R. (1990), “Some aspects of the tailorability of woven and knitted outerwear fabrics”, Clothing Research Journal, Vol. 8, pp. 59-76. Gardner, F., Burtonwood, B. and Munden, D. (1978), “The effect of angle of bias and other related parameters on seam strength of woven fabrics”, Clothing Research Journal, Vol. 6 No. 3, pp. 130-40. Hudson, P. (1988), Guide to Apparel Manufacturing, MEDIApparel, Inc., Greensboro, NC. Kawabata, S. (1980), The Standardization and Analysis of Hand Evaluation, 2nd ed., The Textile Machinery Society of Japan.

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Li, Z. and Milenkovic, V. (1995), “Compaction and separation algorithms for non-convex polygons and their applications”, European Journal of Operational Research, Vol. 84, pp. 539-61. Majar, T., Ajiki, I. and Postle, R. (1989), “Fabric mechanical and physical properties relevant to clothing manufacture – part 2: structural balance, breaking elongation and curvature of seams”, International Journal of Clothing Science and Technology, Vol. 1 No. 2, pp. 5-10. Majar, T., Ajiki, I., Dhingra, R. and Postle, R. (1989), “Fabric mechanical and physical properties relevant to clothing manufacture – part 3: shape formation in tailoring”, International Journal of Clothing Science and Technology, Vol. 1 No. 3, pp. 6-13. Mehta, P. (1985), An Introduction to Quality Control for the Apparel Industry, J.S.N. International, Inc. Moore, C. (1992), “Factors that affect undesirable garment drape”, Journal of Home Economics, Vol. 84 No. 3, pp. 31-4. Moore, C., Gurel, L. and Lentner, M. (1995), “Effects of fabric skewness on the drape of four-gore skirts”, Clothing and Textiles Research Journal, Vol. 13 No. 2, pp. 131-8. Orzada, B. and Moore, M. (1997), “Learn to avoid marker mishaps”, Bobbin, Vol. 38 No. 7, pp. 84-6. Shanley, L., Anderson, L. and Milenkovic, V. (1995), “Part layout and optimization of part shape for layout in apparel manufacturing”, National Textile Center Research Briefs, May, p. 29. Shishoo, R. (1990), “Relation between fabric mechanical properties and garment design and tailorability”, International Journal of Clothing Science and Technology, Vol. 2 No. 3/4, pp. 40-7. Shishoo, R. (1995), “Importance of mechanical and physical; properties of fabrics in the clothing manufacturing process”, International Journal of Clothing Science and Technology, Vol. 7 No. 2/3, pp. 35-42. Skelton, J. (1976), “Fundamentals of fabric shear”, Textile Research Journal, Vol. 46, pp. 862-9. Sudnik, Z. (1972), “Objective measurement of fabric drape: practical experience in the laboratory”, Textile Institute and Industry, Vol. 10 No. 1, pp. 14-18. Yick, K., Cheng, K. and How, Y. (1995), “Subjective and objective evaluation of men’s shirting fabrics”, International Journal of Clothing Science and Technology, Vol. 7 No. 4, pp. 17-29.

Ergonomic equipment investments: benefits to apparel manufacturers Betty G. Dillard Textile and Apparel Management, University of Missouri, Columbia, Missouri, USA and

Tina Frazier Schwager

Ergonomic equipment

285 Received November 1995 Revised and accepted February 1997

Consumer Division, Freudenberg Nonwovens, Durham, North Carolina, USA Mass production of apparel has traditionally been a labour-intensive process, with production workers performing single operations using the same repetitive motions throughout an eight-hour day. This not only leads to boredom with the job, but it also increases the risk of health problems occurring. The number of lost working days, a commonly used health and safety measurement, almost quadrupled in the textile and apparel industry over the last decade from 37 in 1984 to 141 in 1993 per 100 FTE[1]. The increase in work-related injuries and illnesses over the last five years in the USA has caused many manufacturers to consider making changes in the workplace to reduce stress on the body[2]. Many of these changes are based on principles of ergonomics, the science that studies the relationship between workers and their working environment. An important principle of ergonomics is that once a job or task goes beyond the worker’s physical limitations, injuries will result[3]. Such injuries, often referred to as repetitive motion injuries or cumulative trauma disorders (CTDs), have a cumulative effect on the body; therefore, the tendency towards injury increases with age. Using ergonomics principles means addressing the physical demands placed on the worker, both understanding how these demands stress the body and finding solutions that will reduce the demands or stressors to a minimal level. Prevention is very important in this manufacturing segment where the labour resource is valued, and manufacturers cannot afford to lose trained workers. Prevention strategies include education and training for workers, redesigning workstations, changing methods for operations where the incidence of workrelated injuries and illnesses is high, using modular or team production systems to encourage operators to change tasks throughout the day and investing in ergonomic equipment and work aids[4]. Some of these strategies require very little investment in time and money resources while others require huge investments of these resources. Investing in ergonomic equipment is a major investment for most companies because of the high initial cost of the equipment. Ergonomic equipment is

International Journal of Clothing Science and Technology, Vol. 9 No. 4, 1997, pp. 285-300. © MCB University Press, 0955-6222

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defined as any type of equipment that is designed specifically to reduce the risk of injury or illness to workers. Using this definition, it includes a variety of equipment such as ergonomic chairs, automated sewing equipment and adjustable tilt tables. Research is needed to determine the extent to which apparel companies are investing in ergonomic equipment and whether positive results have occurred when such investments are made. Maintaining a healthy workforce not only benefits the workers, but it can enable manufacturers to be more competitive in the global market. Benefits through cost savings can be more readily documented with some investments, such as automated sewing equipment, because of increased productivity and improved quality of products. However, other investments such as ergonomic chairs and adjustable tilt tables may show less immediate benefit to the company, but often lead to cost reduction over time in lower workers’ compensation costs and lower turnover rate for production workers because of improved employee morale. The purpose of this study was to determine the extent to which manufacturers were investing in ergonomic equipment, what specific types of equipment investments had been made and whether companies which made such investments experienced positive results in lowered workers’ compensation costs, increased productivity, improved quality and improved employee morale. Historical background in ergonomics Understanding the effects of physical labour and the stress invoked on the human body is not a concept of the twentieth century. In the 1700s Ramazzini described this relationship when he wrote, “Manifold is the harvest of diseases reaped by craftsmen … As the … cause I assign certain violent and irregular motions and unnatural postures by which … the natural structure of the living machine is so impaired that serious diseases gradually develop”[5]. Regardless of the insight and knowledge of Ramazzini’s words, further progress was not made until the late nineteenth century. In the late 1800s, Frederick Winslow Taylor proposed the principles of scientific management[6]. He was able to improve production and reduce work fatigue through the development of methods and hand tools in a Philadelphia Steel Company. He advocated designing the machine to match the operator’s abilities to achieve maximum safety, comfort and efficiency. Further progress was made by Frank and Lillian Gilbreth in the 1920s and 1930s. Much of the Gilbreths’ work provided the foundation for further research into the science of ergonomics, in addition to providing the foundation for industrial engineering[7]. Following the Gilbreths’ work, it was not until the 1940s that the relationship between job and man was again addressed when Second World War pilots were given the responsibility of operating complex aircraft which lacked engineering for human factors. The discipline of ergonomics emerged in Great Britain in July 1949 with interested individuals meeting at the Admiralty in London[8], and ergonomics was first formally established in the USA in 1957 through the Human Factors Society[9]. In the 1960s and 1970s ergonomics became a familiar study to the field of industrial engineering, and by the late 1970s ergonomics was

recognized as a multidisciplinary field at the University of Michigan School of Engineering. Well-known researchers at the Center for Ergonomics at Ann Arbor represented the specific fields of industrial hygiene, occupational medicine, and occupational safety. Research conducted at the University of Michigan determined factors which caused carpal tunnel syndrome, the chronic condition associated with inflammation and tissue congestion in the carpal tunnel of the wrist[10,11]. This led to evaluating jobs regarding potential risk relating to ergonomic issues as well as establishing a basis for developing ergonomic standards. The Occupational Safety and Health Administration (OSHA) is the government agency in the USA with responsibility for establishing regulations governing the health and safety of workers. According to the 1970 Occupational Safety and Health Act, “the general duty of all employers is to provide their employees with a workplace free from recognized serious hazards”[12]. This is a very broad statement which applies to all work-related illnesses and injuries as defined by the US Department of Labor[13]. Occupational illness is defined as any abnormal condition or disorder, other than one resulting from an occupational injury, caused by exposure to factors associated with employment. Included are acute and chronic illnesses or diseases which may be caused by inhalation, absorption, ingestion or direct contact. An occupational injury is defined as one which results from a work-related event or from a single instantaneous exposure in the work environment. The meat packing industry was the first industry in the USA in which ergonomics in the manufacturing setting was seriously addressed by OSHA, in part because of the extremely high incidence of work-related health problems in that industry. The Ergonomics Program Management Guidelines for Meat Packing Plant[12] was the basis for the Federal Ergonomic Standard drafted in 1994 which will apply to all industries, and is projected to have an estimated $11 billion compliance cost[14]. Compliance costs include the necessary record keeping system, workers’ compensation insurance premiums and claim settlement, as well as OSHA fines for non-compliance with a single violation being as much as $10,000 or more[15,16]. Therefore, companies are motivated today more than ever before to develop preventive strategies both to control costs and to ensure a healthy, productive workforce so important to this industry. Review of related research Research that relates specifically to the apparel manufacturing industry has been conducted primarily in the last decade. Much of the impetus for the research came from events described in the earlier section. Because it is a multidisciplinary science, research has been conducted in the medical sciences and engineering as well as the social sciences. Underlying theory for the study of preventive strategies used for the study is that proposed by Baggerman[17]. This model uses a holistic macro-ergonomics approach consisting of two subsystems:

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(1) the technical sub-system involving equipment, workplace design, environment; and (2) the social sub-system consisting of job design, training, culture and management style. Although it is important to view preventive strategies using a holistic approach, the technical sub-system is the portion that relates to this study. Therefore, the review of related research is limited to studies that have examined equipment used by sewing operators to assemble garments. The use of preventive strategies in the technical subsystem means redesigning equipment and workstation so that it can be adjusted to meet the needs of the worker, thereby enabling the worker to be highly productive without stressing the body. In order to develop preventive strategies, one must first look to medical science to determine what specific musculoskeletal disorders occur in apparel production workers, what causes these disorders, and how they can be prevented. Injuries to the musculoskeletal system are not new as an area of research; however, they have recently become widely studied with regard to the work environment. Musculoskeletal injuries occur in the muscles or joints, resulting in tears to the muscle, inflammation of the tendons in the joint area or damage to nerves. As they relate to the upper body, they may be classified into three types: tendon disorders, nerve disorders and neurovascular disorders[18]. During the working years (ages 18 to 64) more people are disabled from musculoskeletal problems than from any other category of disorder[19,20]. According to medical scientists, the majority of these musculoskeletal injuries are not the result of accidents or sudden injuries, but rather develop gradually as a result of repeated microtrauma[18]. No uniform label has been adopted; however, they are most commonly referred to as repetitive strain injuries, repetitive motion injuries or cumulative trauma disorders (CTDs). The latter term is perhaps the most descriptive and indicates the cumulative nature of such illnesses as they develop gradually over a period of weeks, months or even years. Trauma refers to the bodily injury from mechanical stresses, and often is only a microtrauma initially. Although the body has the ability to recover from minor stress, research indicates that when recovery time is insufficient, when work is highly repetitive with forceful or awkward postures, the worker is at risk of developing CTD[21,22]. Research in apparel manufacturing conducted on musculoskeletal injuries by Vihma et al.[23] concluded that sewing machine operators experienced significant job-related musculoskeletal pain. Operators’ complaints were specific to the neck, shoulders and lower limbs. According to their research, musculoskeletal complaints were attributed to the working posture of the sewing operator. Specific illnesses identified were tendonitis, carpal tunnel disorders and neurovascular complications. In a more recent study, factors which have been linked to sewing operators’ poor postures were visual demands of the work, the workstation design and inadequate seating[24]. These researchers found that insufficient lighting of the

work area required the operators to lean in towards their work area resulting in a hunched posture. The workstation design was such that the workers had to adapt to it, rather than having the workstation designed for the worker. Work tables did not allow enough surface area for workers to rest their upper limbs, and workstation height led to awkward postures. Because sewing has traditionally been done in a seated position, the design and benefits of ergonomically designed chairs have been studied by a number of researchers[25-29]. Although using a chair for industrial sewing operations reduces body fatigue, it may also introduce excessive musculoskeletal stresses if the sitting posture is supported improperly[26-28]. Musculoskeletal stresses can be lessened if a larger trunk-thigh angle is maintained at 135 degrees with the lumbar spine in neutral position[29]. Early studies evaluated a single variable while other variables were fixed. However, in the study conducted by Yu et al.[28] the following features were evaluated at the same time: seat height, seat angle, seat rocking, seat swivel, back-rest distance, backrest height and back-rest angle. Results of the study using two females who represented 90 per cent of the population according to body measurements, were that seat height should be adjustable between 51 and 61cm, the back-rest distance should be adjustable between 10 and 15cm, the back-rest height should be fixed at 25cm, and the seat pan should be allowed to swivel freely. They concluded that to provide the best results in adaptability, the chair should allow for adjustments in seat height, back-rest, back-rest height and a swivelling seat pan. Ergonomic chairs are produced commercially by a number of different companies. Engineers and consultants to the industry promote the use of ergonomic chairs to support the torso in a balanced work posture and to minimize fatigue[3,30]. With the improved support and lowered fatigue, researchers were interested in examining changes in productivity levels with ergonomic chairs. Because the cost of chairs represents a major expenditure by most companies, positive results from research studies could motivate upper level managers to invest in new chairs. In a study conducted by Clemson Apparel Research, productivity data were collected before and after Adjusto ergonomic chairs were installed in two sewing companies[31]. One company showed statistically significant improvement in productivity while the other showed a slight decrease in productivity (not significant). Subjective data collected from interviews with employees showed that employees using ergonomically designed chairs appeared to experience considerably less physical discomfort during the day at both companies. Researchers at Georgia Institute of Technology, using 12 female sewing operators in a medium-sized apparel company as subjects, conducted a study in which a traditional chair design was compared to the adjustable ergonomic chair[32]. Results indicated that the experimental group reported less discomfort in the lower and middle back with the ergonomic chair. They also reported lower levels of lower extremity discomfort, although the ergonomically designed

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chairs were not credited with improvements in productivity. Researchers also cautioned that discomfort is a highly subjective and complex phenomenon. Limited research has been conducted in comparing the seated posture to the standing posture when performing sewing operations. Historically, sewing has been done predominantly by women in a seated position, in part because work that requires fine muscle co-ordination and extensive hand manipulations can be more easily accomplished in the seated position. In addition, the feet were free to use foot controls on the machine. However, the body has a more limited range of motion in the seated position and it reduces the mechanical advantage of the body, thus causing greater fatigue when power is exerted. Textile and Clothing Technology Corporation (TC)[2] has conducted research using stand-up operators working in modular teams. According to their research[3], working in a standing posture has several advantages: the principles of motion economy are more easily applied to work methods; the worker exercises greater control over the task area; the work method can more easily incorporate most of the characteristics of easy movement; and the worker develops a rhythm through establishing ballistic motion, using natural reaches and motions in sewing and handling materials. A worker can achieve even better use of the ballistic motion patterns of the body by tilting the work surface[3]. Therefore, adjustable tilt tables were developed as a means of adding additional flexibility to the workstation. They can easily be lowered or lifted to accommodate either a sitting or standing posture. In addition, they can be tilted at a different angle from that of the traditional work table. This allows the operator to achieve better posture and to see the work area better. In addition to research and development in the area of ergonomic chairs and tilt tables, a third area that has been studied in terms of preventing workplace injuries and illnesses is that of using automatic sewing equipment. Automatic sewing equipment is defined as machinery which requires minimal operator involvement[33]. It ranges from fully automated/computerized equipment requiring the operator only to load the piece or pieces at the machine, to only a degree of automation requiring some manual operation to be performed by the operator. Automated equipment is expensive, but often can be justified because the production rates may be two to four times the speed of manual machines[34]. In addition to increased productivity, other benefits from automatic sewing equipment are providing improved quality through greater consistency and reducing operator fatigue, thus a prevention strategy for decreasing workplace injuries and illnesses[34]. This has been especially important in the jeans industry where the fabric is heavy and stiff, and operators often use awkward postures and a great deal of force to assemble the product. OSHA’s proposed guidelines for ergonomic programmes specifically advised companies to identify high-risk jobs based on records during the past two years, the number of repetitive motions in a given time period, awkward work postures for more than two hours’ total, use of vibrating tools or equipment for more than two hours’ total, and handling objects weighing more than 25 pounds more than

once in each workshift[14]. The use of ergonomic chairs, tilt tables and automated equipment could assist in lowering risk in certain operations; however, the reality is that they are expensive investments, particularly to small or medium-sized companies. Based on the review of research related to ergonomic equipment and the need by managers to justify expenditures on new equipment, the specific objectives of the study were: (1) to determine the extent to which apparel manufacturers were investing in specific kinds of ergonomic equipment: ergonomic chairs, adjustable tilt tables, and automated sewing equipment; (2) to examine the results achieved in making such investments in four specific areas: lowered workers’ compensation costs, increased productivity, increased quality, and improved employee morale; and (3) to determine whether a relationship existed between investments made in each of the three specific types of equipment and each of the positive results. Method Data used in the study were generated from responses to a mailed questionnaire by apparel and sewn products manufacturers in the USA. The data were collected from May to July 1993. Procedure The questionnaire was developed during February 1993 according to guidelines recommended by Dillman[35]. It was piloted with University of (state) researchers and upper level managers in ten apparel companies which had been part of a preliminary study. The questionnaire was revised based on input from the pilot study, and mailed in Spring 1993 to 500 apparel and sewn products manufacturers in the USA which indicated they had five or more employees. Those with fewer than five employees were excluded because health and safety issues involving workers’ compensation in (state) do not apply to firms which have fewer than five employees. The 12-page questionnaire was developed based on a review of the literature and data from in-depth interviews conducted with ten upper level managers who had major responsibility for worker health and safety in their companies. The questionnaire was comprehensive and included the following sections: (1) broad concerns regarding worker health and safety; (2) preventive strategies used to improve worker health and safety; (3) medical diagnosis and treatment for workers; (4) workers’ compensation; (5) health insurance for employees and their families;

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(6) regulations by the Occupational Safety and Health Administration (OSHA); (7) equipment and workstation design; (8) ergonomics and safety programmes; and (9) demographic information. Because of the specific interest in (state) manufacturers, and financial support provided by the University of (state) Agricultural Experiment Station, the questionnaire was sent to the entire population of (state) apparel and sewn products manufacturers (190 companies), which were listed in the (state) Textile and Apparel Center Directory[36] and which had five or more employees. The other 310 companies in the sample were companies listed in the 1992 Membership Directory of the American Apparel Manufacturers Association[37] whose home offices were located outside (state), but in the USA. A cover letter was addressed to the director of human resources explaining the purpose of the study and encouraging response. A postage paid, selfaddressed envelope was enclosed with the questionnaire. A postcard was mailed approximately two weeks later to the entire sample to thank those who had responded and to urge response from those who had not yet completed the survey. One month later a second questionnaire was mailed to those who had not yet responded with a letter stressing the importance of each company’s response to the study. One hundred and forty-nine questionnaires were returned which represented a response rate of 30 per cent. Fifteen were not usable because the company no longer had production in this country or the questionnaire was incomplete. Two other respondents did not answer the question that applied to equipment investments made in the last three years. Therefore, the number of responses used for this portion of the study was 132. Description of the sample Approximately 60 per cent of the respondents were CEOs, presidents, owners, directors of human resources or vice presidents of manufacturing. The remaining 40 per cent were other upper level managers who had primary responsibility for worker health and safety. Almost 37 per cent of the 132 companies had fewer than 100 employees, another 40 per cent had 100 to 499 employees and the remaining 23 per cent had 500 or more employees. Almost half of the companies (46 per cent) reported having only one manufacturing facility, and only 17 per cent had more than four facilities. Approximately half had one or more production facilities in (state) and half had production facilities located in other states. Product type ranged from outerwear and sportswear to very specialized garments such as swimwear and leotards. Specification of variables Section VI of the questionnaire consisted of questions related to equipment and workstation design. Specific categories for the variables were based on both the

review of the literature and data from in-depth interviews conducted in an earlier phase of the research project. The first objective of the study was addressed by examining frequencies of variables in Question 1 of that section. Respondents were asked whether their companies had invested in new equipment in the last three years to improve the health and safety of workers. If they answered “yes”, they were asked to check any of the following that were purchased: ergonomic chairs, back braces/supports, wrist/arm braces, tilt tables, automated sewing equipment, fork lifts, and other. The study examined only the three specific types of equipment important in the sewing process: ergonomic chairs, tilt tables, and automated sewing equipment. The second objective was addressed by responses to a question asking whether they had seen positive changes resulting from new equipment investments. They were asked to check as many as applied from a list of four: lowered workers’ compensation costs, increased productivity, increased quality, improved employee morale. The third objective examined the relationship between each of the three equipment variables in the first objective, and each of the resulting change variables described above. Statistical analysis Data entry and analysis was done using the SAS Version 6.10[38,39]. Descriptive statistics were used to compare frequencies for each equipment variable as well as to determine how many invested in more than one type of equipment. Descriptive statistics were used in the same manner to examine the frequencies of each resulting positive change variable as well as the number that experienced more than one positive change. Chi-square analysis was used to test the significance of the relationship between each of the types of equipment investments and each of the resulting changes. The response categories for each were “yes” if the variable was checked and “no” if it was not checked, resulting in a 2 × 2 contingency table for each set of variables. Statistical results were evaluated at the 0.05 level of significance. Fisher’s exact test was used in the event that variables tested produced cells with expected counts less than five. The Yates’ correction was used to correct for continuity recommended when the chi-square tables have 1 df and the expected value of any cell is less than 5[40]. Results and discussion Investments in ergonomic equipment Of the 132 apparel manufacturers responding to that question, 109 (82.6 per cent) indicated that they had made new equipment purchases in the last three years for worker health and safety reasons. Frequencies from those 109 respondents are presented in Table I. As shown in Table I, investments in automatic sewing equipment had the greatest number with more than two-thirds of the companies making this investment in the last three years. Frequencies in Table I show that more than half invested in ergonomic chairs, while less than one-third invested in tilt tables. Further analysis of frequencies showed that 43 of the respondents

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indicated they invested in two of the three types of equipment while only 17 indicated they invested in all three types of equipment. Although automated sewing equipment is a huge expenditure for companies, it is often easier to justify based on cost accounting systems used. The gains in both productivity and quality are easy to document, thus payback on the investment is often relatively short, particularly in larger companies. On the other hand, investing in ergonomic chairs would be much lower in cost per chair than automated sewing equipment or tilt tables. However, companies which invest in ergonomic chairs for all production workers will also have a significant dollar investment, and it may be more difficult to sell upper level management on expenditures for chairs because the immediate results are less tangible. It was not surprising that as many as 60 per cent had invested in ergonomic chairs because of the reported benefits in reducing fatigue and increasing comfort of the worker. Manufacturers should be cautioned that some chairs that are marketed as “ergonomic chairs” do not have the adjustable features that are needed in order really to fit the individual operator’s needs. Those with fewer features will generally cost less, but if preventing illness and injury is the goal of the company, selecting a chair of high quality and maximum adjustability is important. The number of companies which invested in tilt tables was lower than for the other two types of equipment; however, 30 per cent indicated that they made this investment. Investments in adjustable tilt tables often means that the company is using or considering the use of stand-up sewing, often associated with the modular production system. Tilt tables are more expensive than ergonomic chairs for the initial purchase; however, their cost would be far less than investing in fully automated sewing equipment. It is also important to keep in mind that companies who are shifting to stand-up sewing will probably not be investing in ergonomic chairs. Positive changes resulting from new equipment investments Respondents were asked whether they had experienced positive changes as a result of new equipment investments. Frequencies reported in Table II indicated Variable

Table I. New equipment investments made to improve worker health and safety

Frequency

Per cent

Type of equipment investment made in the last three years Automated sewing equipment Ergonomic chairs Tilt tables

75 64 33

68.8 58.7 30.3

Investments made in at least two types of equipment

43

39.4

Investments made in all three types of equipment Note: n = 109

17

15.6

that 99 of the 109 respondents (75 per cent) who made equipment investments reported they had experienced positive results. They were asked to check as many as applied from the list provided. Increased productivity was experienced by the greatest number, more than 80 per cent of the companies; however, over three-fourths experienced improved employee morale and more than half experienced improved quality. Lowered workers’ compensation costs was the category checked least often (34 per cent of respondents). This may be due to the lag time experienced between implementing preventive strategies such as equipment investments and redesigned workstations, to the point at which workers’ compensation costs are lowered. According to interview data from an earlier phase of the study, if claims and insurance premiums are high because of the number and severity of problems, it takes three to five years for costs to go down even with reduction in number of cases. It is also interesting to note that 83.8 per cent experienced positive results in at least two areas, 56.5 per cent experienced positive results in at least three of the four areas, and 22.2 per cent experienced positive changes in all four areas. These results provide further support for manufacturers to invest in ergonomic equipment. They not only help improve the health and safety of workers as documented by previous research, but they also provide additional benefits to the company. Results of the chi-square analysis, presented in Table III, provide a basis for examining more specifically the relationships between each of the three types of equipment investments, and each of the positive change variables. Results are based on the number of respondents who experienced positive changes discussed above. Although 99 respondents indicated they had experienced positive results, only 95 respondents completed both the positive changes question and the specific equipment purchases made. Therefore the number

Variable Positive changes resulting from equipment investments Increased productivity Improved employee morale Increased quality Lowered workers’ compensation costs Number who experienced two of the positive changes listed above Number who experienced three of the positive changes listed above Number who experienced all four of the positive changes listed above Note: n = 99

Frequency

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295

Per cent

83 76 63 34

83.8 76.8 63.6 34.3

27

27.3

34

34.3

22

22.2

Table II. Positive changes resulting from new equipment investments

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used for chi-square analysis was 95. The chi-square results reported in Table III are those using the application of Yate’s correction for continuity. Fisher’s exact test was used for two sets of variables, each having one cell count with fewer than five: tilt tables and increased productivity, and tilt tables with improved employee morale. As Table III indicates, a significant difference was found between investments in automatic sewing equipment and both increased productivity and improved quality. The relationship between automatic sewing equipment and productivity has been documented by at least one previous study[31]. Increased productivity results from several factors, including the speed at which the garment pieces are prepared for the sewing process, the speed at which the sewing occurs and the speed at which the finished work is disposed from the machine. One engineer who was interviewed in the previous phase of the research project cautioned that the use of automated sewing equipment does not eliminate all repetitive motions but it does minimize them. The repetitive motions can still be a problem because of the speed at which operators are required to load pieces into the automated sewing equipment. The significant relationship between automated sewing equipment and increased quality results from minimizing inconsistencies that result from human error, particularly when the body is fatigued. The use of automated

Variable

Table III. Relationship between equipment investments and positive changes

DF

Continuity adjusted χ2 p-value

Automatic sewing equipment Increased productivity Lowered workers’ compensation costs Increased quality Improved employee morale

1 1 1 1

5.18 0.05 5.85 0.11

0.02* 0.82 0.02* 0.74

Adjustable tilt tables Increased productivity Lowered workers’ compensation costs Increased quality Improved employee morale

1 1 1 1

1.78 0.48 3.17 3.51

0.18 0.49 0.08 0.06

Ergonomic chairs Increased productivity Lowered workers’ compensation costs Increased quality Improved employee morale

1 1 1 1

0.00 0.13 0.11 2.46

1.00 0.72 0.74 0.12

Note: n = 95, * = significant at the 0.05 level

sewing equipment is a means of deskilling specific sewing operations, that is to decrease the variability that results from positioning and guiding the garment pieces in the sewing process. By providing greater consistency, the quality is improved, and the number of garments sold at first quality prices is increased. It also reduces the many hidden costs of poor quality, such as customer returns and dissatisfied retailers and consumers who find new sources in competitors’ products. A significant relationship was not found between tilt tables and any of the positive change variables using the adjusted chi-square. However, the relationship with improved employee morale was approaching significance at the 0.05 level, and the Fisher Exact test was significant. This relationship needs to be examined in greater detail because it may reflect greater satisfaction by workers that results from the increased adjustability of the workstation to meet their specific needs. Often the use of tilt tables involves a more complex change in the workplace which consists of stand-up sewing, production in modular teams and employee empowerment. Although not all work-related health problems will improve using stand-up sewing because of stress to the back and legs, the adjustable tilt tables offer the opportunity for operators to stand part of the day and sit part of the day. Improved employee morale can be tracked by managers not only in getting feedback from employees, but also by examining absenteeism and turnover rates. When these are lower, it often reflects greater job satisfaction by employees. A significant difference was not found between investments in ergonomic chairs and any of the four positive change variables. This finding may reflect the lack of any precise description of an “ergonomic chair”; some of these companies may have invested in chairs that truly were not in the best interest of the employees in terms of comfort and adjustability. One might expect that there would be a significant relationship with improved morale because of the message that would be conveyed by company managers that they are trying to improve the workplace and make it a more comfortable place to work. The selection of chairs is a more complicated process with the many adjustability factors, and the ease with which adjustments can be made. Selecting an appropriate chair reflects the need for a subjective assessment by operators more than the other two types of equipment and it may take longer for positive results to occur. A significant difference was not found for any equipment investments and lowered workers’ compensation costs. As discussed earlier, only 34 per cent experienced lowered workers’ compensation costs because of the lag time that often occurs. Follow-up studies will be important to provide justification as to the importance of ergonomic equipment investments to lowered workers’ compensation costs. Summary and implications Results of the study confirmed that US companies are investing in ergonomic equipment as a preventive strategy to improve worker health and safety, with

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83.8 per cent of the respondents indicating they had made such investments in the last three years. The greatest number, more than two-thirds, invested in automated sewing equipment, more than half invested in ergonomic chairs, and approximately 30 per cent invested in adjustable tilt tables. Companies generally need to be able to justify such investments in tangible benefits that will show increased profitability. Positive changes were experienced by 75 per cent of the companies. The change experienced by the greatest number was increased productivity (more than 80 per cent) followed by improved employee morale, improved quality and lowered workers’ compensation costs. Only 34 per cent of the respondents indicated their workers’ compensation costs were lower; however, the lag time before cost reduction would occur based on reduced workplace injuries and illnesses is usually at least three years. Chi-square analysis showed a significant difference between investments in automatic sewing equipment and both increased productivity and increased quality. These findings are consistent with earlier studies. Both of these provide justification for investing in automated sewing equipment even though the cost is high. Benefits can be documented by increase in number of units produced and the increase in percentage of first-quality goods produced. Although the continuity-adjusted chi-square was not significant for improved employee morale and any of the three types of ergonomic equipment, it was approaching significance with tilt tables. Investing in ergonomic equipment to improve employee morale is less tangible and may be more difficult to measure. Improved employee morale can often be seen in lower turnover rates and lower absenteeism. Both of these can benefit a company through lower training costs and increased productivity. No significant differences were found between investments in ergonomic chairs and any of the positive change variables. This may reflect the mixed response to ergonomic chairs by both management and workers. Investing in the chair that best meets the worker’s needs in terms of comfort and adjustability may be the key in documenting positive changes. Many companies have invested in chairs because it appears that they believe it is the right thing to do. Opportunities for future research in this area are numerous. In-depth cost/benefit analysis will provide more precise measures of the positive effects of investing in ergonomic equipment. Data for doing this will be more reliable if collected in three to five year intervals following equipment investments. Studies that involve both subjective assessment by workers as well as the objective assessment by managers of these companies will increase the accuracy of the results and provide greater insights about whether investing in ergonomic equipment improves employee morale or increases employees’ level of satisfaction with their jobs. This would be particularly true with ergonomic chairs; additional research could shed more light on why this may or may not be a good investment for employees. Research is needed that focuses on the education and training needs of workers fully to understand and use the adjustability features of workstations including chairs, tables and automated equipment. Qualitative data in the form of interviews with workers as well as

observations in manufacturing facilities will provide more comprehensive findings to enable researchers to draw more accurate conclusions in this complex area. References 1. American Apparel Manufacturers Association (AAMA), Managing Safety in Apparel, Report of the Technical Advisory Committee, AAMA, Arlington, VA, 1995. 2. Dillard, B.G., “Education and training as a strategy for improving worker health and safety: a survey of US apparel companies”, Journal of Consumer Studies and Home Economics (in press). 3. Vasbinder, D.M., “Making the perfect match”, Bobbin, September 1993, pp. 126-36. 4. Roughton, J., “Implementing an ergonomic program: developing procedures”, Industrial Engineering, Vol. 25 No. 9, 1993, pp. 44-9. 5. Tichauer, E.R., The Biomechanical Basis of Ergonomics, Wiley-Interscience Publications, New York, NY, 1978. 6. Thompson, C.B., The Taylor System of Scientific Management, A.W. Shaw Company, New York, NY, 1917. 7. Tillman, P. and Tillman, B., Human Factors Essentials, McGraw-Hill, New York, NY, 1991. 8. Oborne, D.J., Branton, R., Leal, F., Shipley, P. and Stewart, T., Person-centred Ergonomics, Taylor and Francis Ltd, London, 1993. 9. Lloyd, B., “OSHA traumatizes apparel makers”, Women’s Wear Daily, Vol. 160 No. 97, 1990, p. A14.. 10. Silverstein, B.A., Fine, L.J. and Armstrong, T.J., “Occupational factors and carpal tunnel syndrome”, American Journal of Industrial Medicine, Vol. 11, 1987, pp. 343-8. 11. Industrial Biomechanics, Inc., A Management Guide. Ergonomics in the Apparel and Textile Industries, American Apparel Manufacturers Association, Arlington, VA, 1990. 12. Occupational Safety and Health Administration, Ergonomics Program Management Guidelines for Meat Packing Plants (Publication No. OSHA 3123), US Government Printing Office, Washington, DC, 1991. 13. US Bureau of Labor Statistics, Occupational Injuries and Illnesses in the United States by Industry, US Department of Labor, Washington, DC, 1988-1993. 14. Occupational Safety and Health Administration, “Ergonomic protection standard”, unpublished draft document, 1995. 15. Carter, G.H., “A practical guide to work site analysis”, Bobbin, December 1994, pp. 57-61. 16. Alexander, D.C. and Seay, M.R., “OSHA and ergonomics”, Bobbin, March 1991, pp. 96, 98, 100, 102. 17. Baggerman, M., “Macro-ergonomics aid in meeting OSHA standards”, Apparel Industry Magazine, August 1993, pp. 56-62. 18. National Institute for Occupational Safety and Health, “Description of common cumulative trauma disorders”, in Putz-Anderson, V. (Ed.), Cumulative Trauma Disorders: A Manual for Musculoskeletal Disease of the Upper Limbs, Taylor and Francis, New York, NY, 1990. 19. Haber, L.D., “Disabling effects of chronic disease and impairment”, Journal of Chronic Diseases, Vol. 24, 1971, pp. 469-87. 20. Kelsey, J.L., Epidemiology of Musculoskeletal Disorders, Oxford Press, New York, NY, 1982. 21. Keyserling, W.M., Stetson, D.S., Silverstein, B.A. and Brouwer, M.L., “A checklist for evaluating ergonomic risk factors associated with upper extremity cumulative trauma disorders”, Ergonomics, Vol. 36 No. 7, 1993, pp. 807-31. 22. Feldman, R.G., Goldman, R. and Keyserling, W.M., “Peripheral nerve entrapment syndromes and ergonomic factors”, American Journal of Industrial Medicine, Vol. 4, 1983, pp. 661-81.

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23. Vihma, T., Nurminen, M. and Mutanen, P., “Sewing machine operators’ work and musculoskeletal complaints”, Ergonomics, Vol. 25 No. 4, 1982, pp. 295-8. 24. Kelly, M.J., Ortiz, D.J., Folds, D.J. and Courtney, T.K., “Ergonomic challenges in conventional and advanced apparel manufacturing”, International Journal of Human Factors in Manufacturing, Vol. 2 No. 1, 1992, pp. 39-54. 25. Drury, C.G. and Coury, B.G., “A methodology for chair evaluation”, Applied Ergonomics, Vol. 13, 1982, pp. 195-202. 26. Mandal, A.C., “The seated man (homo sedens), the seated work position: theory and practice”, Applied Ergonomics, Vol. 12, 1976, pp. 19-26. 27. Corlett, E.N. and Eklund, J.A.E., “How does a backrest work?”, Applied Ergonomics, Vol. 15, 1984, pp. 111-14. 28. Yu, C.Y., Keyserling, W.M. and Chaffin, D.B., “Development of a work seat for industrial sewing operations: results of a laboratory study”, Ergonomics, Vol. 31 No. 12, 1988, pp. 1765-86. 29. Yu, C.Y. and Keyserling, W.M., “Evaluation of a new work seat for industrial sewing operations”, Applied Ergonomics, Vol. 20 No. 1, 1989, pp. 17-25. 30. Hunter, C., “The science of seating”, Apparel Industry Magazine, April 1991, pp. 42-8. 31. Peck, J.C., “Cheers for chairs”, Apparel Industry Magazine, September 1990, pp. 114-17. 32. Ortiz, D.J., Kelly, M.J., Courtney, T.K. and Folds, D.J., “The impact of a chair as an ergonomic intervention in conventional trouser manufacturing”, Georgia Tech Research Institute Report, Georgia Institute of Technology, Atlanta, GA, 1990. 33. Solinger, J., Apparel Manufacturing Handbook. Analysis Principles, and Practice, Bobbin Media Corp., Columbia, SC, 1988. 34. Schroer, B.J. and Ziemke, M.C,. “Human resource issues affecting the survival of US apparel manufacturing”, The International Journal of Human Factors in Manufacturing, Vol. 4 No. 1, 1994, pp. 55-64. 35. Dillman, D.A., Mail and Telephone Surveys, the Total Design Method, John Wiley & Sons, New York, NY, 1978. 36. (State) Textile and Apparel Center, Directory of Apparel and Sewn Products Manufacturers, 1992. 37. American Apparel Manufacturers Association, Directory of Members and Associate Members of the American Apparel Manufacturers Association, 1992. 38. SAS Institute, Inc., SAS User’s Guide: Basics, 5th ed., Cary, NC, 1985. 39. SAS Institute, Inc., SAS/STAT User’s Guide (Version 6, 4th ed.) Cary, NC, 1990. 40. Cody, R.P. and Smith, J.K., Applied Statistics and the SAS Programming Language, PrenticeHall, Englewood Cliffs, NJ, 1991.

Instrumental design for capturing three-dimensional moiré images W.M. Yu

Threedimensional moiré images 301

Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong

S.C. Harlock and G.A.V. Leaf Department of Textile Industries, The University of Leeds, Leeds, UK, and

K.W. Yeung Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong Introduction For the measurement of unstable soft materials such as apparel products, contact methods are not applicable because the subjects deform easily. Moiré topography has proved to be a very effective non-contact method to measure both convex and concave surface profiles of a three-dimensional form. A shadow moiré technique was developed in our earlier research work (Yu et al., 1995) for monitoring the variations of moulded cups as a means for assessing their shape conformities. However, there are several limitations in ensuring the quality of the moiré image, which is most essential to safeguard an accurate analysis of shape. This paper describes the methods of setting up the moiré system and the tolerance of the instrumental error. Moiré theory Based on the geometrical approach (Pirodda, 1982), a theoretical interpretation of the moiré phenomenon is presented as follows. A small area of grating around Q is projected around P on the cup surface U. The shadow observed from the camera, C, through the grating around R is the moiré result of the grating around Q with a different direction and spacing from the original. On the image plane I, the grating and its shadow on the object surface U are imaged according to two sets of lines k and h. A point such as P1 on I lies on a moiré fringe since it is the image of a point P on the object surface U where the line k of light projection and line h of sight observation intersect. In our experimental set-up, the light source and the camera are arranged at the same height L = Ls = Lc from the grid. A series of points like P, which are intersections of k and h lines, form a plane surface (Figure 1). Other plane surfaces are generated in the same way by the k and h lines crossing pairs of

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l

P′

S

d

O

Lc Y

Ls = Lc = L

X

k

h

Z O Figure 1. Schematic arrangement of the shadow moiré system set-up

g

R

Q z1 z2 P

n=1 n=

U

grid lines spaced by 2g, 3g, etc. These surfaces intersect the object surface U and show up as moiré fringes. Line n = 1 is the family of intersection of rays from S and C which pass through the adjacent grid slits (k – h = 1, where k and h notate the slits as illuminated by rays originating respectively from S and C). For example at point P, the rays passing through grid slits two spaces apart, line n will be equal to 2, which corresponds to the case k – h = 2. An elementary geometric analysis reveals that triangles ORC and QRP are similar. For Ls = Lc = L, the distance, d, connecting S and C, is parallel to the grid plane,

(1) where zn corresponds to a fringe elevation of the object surface measured from the grid plane, and the absolute fringe number n = 0, 1, 2, … for bright fringes or n = –12, –32, –25, …, for dark fringes. If the fringe number n is known, a series of distances zn can be computed from Equation 1 and tabulated in Table I, where, in the present study, the grid line spacing, g = 2, the distance from the light source and the camera to the object, L = 449 and the distance apart, d = 164. It is evident that the depth of the fringes zn depends on n, g, L and d. It is also obvious that the interval of moiré fringes ∆z is not constant but increasing with the distance to the grid.

Fringe number 1 2 3 4 5 6 7 8 9 10

zn

∆z

5.54 11.23 17.05 23.03 29.16 35.45 41.91 48.54 55.36 62.36

5.54 5.68 5.83 5.98 6.13 6.29 6.46 6.63 6.82 7.00

Experimental set-up In the measurement of a bra cup, the visibility of the fringes (Yu, 1996) produced by objects of such a great depth was a function of the line spacing of the grating, the diffusion of light at the cup’s surface, the resulting fringe interval and the camera settings. For accurate moiré photographs, the system had to have: (1) a constant angle of light illumination; (2) an accurate control of the positions of and the distances between the camera and light sources; and (3) parallelism of the grid plane, object plane and the plane passing through the nodal points of the camera and light sources. Based on such considerations, an integrated system was designed with a rigid support for the four basic elements in the moiré system that consisted of a camera, a light source, a translatable grid plane and a specimen supported naturally with minimum contact. Camera A 28-70mm focal length, 35mm single-lens reflex roll film camera was used. To produce a good resolution of fringes, it was necessary to arrange the camera at some distance from the grid so as to produce a bigger L and wider fringe interval. Therefore, the camera height needed to be greater than 440mm in order to photograph the whole area of the brassière cup. The actual distance was chosen to be 449mm for convenience of fixtures on the frame and the alignment with the lamp. The next parameter to be fixed was the position of the camera in the x-y plane (Figure 2). The camera’s optical axis was aligned with the z-axis, the centre of the camera lens was adjusted by moving sideways in the x-direction until the observation centre coincided with the origin of the system and the centre of the specimen plane.

Threedimensional moiré images 303

Table I. Fringe order table

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Shutter firing

Z Y

304

Metal bar 1 Grid plane releasing button

X Camera

Bolt

Halogen lamp Figure 2. Camera and lamp mountings on the frame top

Steel board

Slot Metal bar 2

Light source Having established the above settings, the distance between the camera and the light sources had to be decided. If this distance was small, then the grid pitch should be small to give a reasonable interval between contour lines. But, when the distance was large, unacceptable shadowing of the cup surface would result. A good compromise was found by setting d = 164mm. It has been reported (Patorski, 1993) that the smaller the light source size in the direction perpendicular to grid lines, the sharper is the shadow cast and the greater is the depth of field over which it is sharp. Therefore, to provide sufficient illumination of the grid, long narrow light sources should be placed symmetrically with respect to the observation direction (Cabaj et al., 1974). Several types of light sources were tried. Among them a 150 watt tungsten halogen lamp proved to be the best choice for this application. Grids The grid design was critical. Many authors have laboured over suitable methods of producing a suitable grid construction. These were mainly fabricated in two ways, “strung” and “printed”. String grids were made by stretching nylon fishing line using two long screws as pitch guides. This is a common method of making grids for use in the moiré measurement of the human body, but the termination and tensioning of many hundreds of strings cannot always guarantee the accurate parallelism of the grid lines. Printed grids consist of a transparent substance such as a sheet of glass or plastic, on which grid lines are printed with pitches corresponding to a few lines per millimetre. Although there are no strings to space, tension or repair, there are drawbacks. Flexible substances are difficult to keep flat, hence compromising the accuracy of the fringe geometry. The materials are not perfectly transparent and therefore significantly reduce fringe brightness. An additional problem is the high likelihood of damage to the grid with repairs difficult to undertake, and

scratches, dust and fingerprints seriously degrade its performance. If the transparency was placed on or sandwiched between glass, there is no real advantage because of the light reflection from the glass surface. Both methods were therefore found inaccurate and inconvenient for the present work. The technique of photo-chemical machining (PCM) was employed to construct the grids. The procedure employed photographic techniques and therefore eliminated mechanical distortion and ensured a rigid and flat plane of parallel grids. The process was conducted by transferring a chemicallyresistant photographic image on to a sheet of metal and subjecting the developed sheet to chemical etching which dissolved away the unwanted metal and left the desired grid pattern (Leung, 1994). Pitch size of the grids The pitch size of the grids applied in typical human torso studies ranges from 1mm to 2mm. Therefore, two grating planes were made with pitch sizes 1mm and 2mm respectively. The latter provided reasonably visible fringes, but the former gave more detailed information of the cup shape. The best overall results achieved by a renowned researcher (Takasaki, 1982) are achieved with solid strings whose diameter was exactly half the grid pitch. Therefore, parallel strips of 1mm width and with 1mm spacing were used to make a grating with 2mm pitch size. Too fine a grating was not used because the fringe interval became too narrow to provide the necessary depth of field to accommodate the surface to be analysed. It caused diffraction of light which blurred the shadow. Also fine grids made of rectilinear metal lines that horizontally hang free in the air tended to sag due to gravity. Considerations of fringe visibility In order to enhance the fringe visibility, further considerations in designing the system were taken, as follows. Fringe localization In general, topographic moiré fringes are not located on the surface of the object under test, but formed some distance in front of or behind the surface. It was suggested that particular attention should be paid to the dependence of fringe location on the surface angle of the object and the setting distance from the grating (Yoshizawa et al., 1982). Moiré fringe patterns that appeared sharp to the eye were sometimes quite fuzzy on the photographs of the cup surface. The eyes of the observer dynamically focus on the fringes, tracking the optimal focal length as the spatial localization varies over the encoded scene, but the camera lens could not do this. Hence when making photographic records of shadow moiré fringes of objects like the bra cup with large local changes of curvature, it was concluded that the cup should be placed as close to the shadow grid as possible, and that the lens apertures be kept as small as possible to maximize the depth of field.

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306

Surface reflectance A property of a foam plastic cup that militated against obtaining high fringe contrast was the roughness of its surface. Light penetrated into the foam cells and was not reflected from the cup surface layer. Back-scattered light from the dimples beneath the surface plane would be re-emitted from an intended shadow. Hence the shadow of the grating could be blurred by the light diffusion in the little holes in the surface. A similar problem of forming a sharp shadow also arises with human skin because of its translucency. The application of liquid pigment with a good covering power on to the skin to improve the fringe contrast (Takasaki, 1970) was suggested. This, however, was not suitable for foamed materials because the liquids would deform the cup shape. It was found that the best moiré fringe contrast was obtained when the surface under test was coated with white talcum powder. To prepare an even coating on the surface, a foam cup was shaken for about ten seconds in a large plastic bag containing the powder. Excess powder was removed by gently tapping the cup in the bag. To avoid unwanted light reflecting from the apparatus, matt black paint was applied to all the reflective surfaces. The whole instrument was also covered with a large black cloth during photographing in the dark room. Photographic parameters The depth of field should be made large enough to include both the grid and its shadow. Increasing the focal depth of the optical imaging system meant limiting its aperture and using a longer exposure time. Moiré fringes of appreciable contrast could then be recorded, together with a sharp image of the object (Janssens et al., 1985; Kafri and Keren, 1981). After much experimentation, it was found that the use of high-speed film with under exposure and extended development was essential to obtain a sharp image of the moiré fringes. Therefore, the cup underneath the grids was photographed onto Ilford HP5 film, rated at 400ASA, at an exposure of half a second and an aperture of f/16. Grid translation The moiré image became “noisy” and difficult to assess when there were large curvatures. In this case it was also necessary to take into account the additional sources of noise. It was noted that the grid lines, shadow lines and the noise fringes moved together when the grid was displaced laterally, whereas the contour moiré fringes remained stationary (Allen and Meadows, 1971). Thus, by translating the grid, accompanied by appropriate exposure time, the noise terms were averaged and became indistinguishable in the picture. Simultaneously, errors of periodicity in the grid were averaged out. The improvement in the quality of the fringe pattern influenced directly the accuracy of measurement. Figure 3 illustrates the improvement that can be gained by the grid translation method.

Translation of the grid would eliminate the alias pattern, especially for objects with large inclinations. In the experimental set-up, the grid plate and specimen were carefully placed on two perspex plates parallel to the plane of the camera and lamp. The grid plate was placed on the uppermost level of the cabinet on which a pneumatic translation device was installed to control movement perpendicular to the grid lines.

(a)

(b)

The grid translation system consisted of a pneumatic cylinder controlled by a three-way valve. One branch was attached to the cylinder which activated the movement of the grid plane, another branch connected to a foot pump which acted as an air compressor, and the third branch was controlled by a press button which released the air and moved back the grid plane to the original position. The releasing action was synchronized, with the camera shutter firing during photographic recording. The translation speed could be regulated by turning the pressure screw and adjusting the air supply to the pneumatic cylinder. Several authors described the advantages of translation of the grating, but only Takasaki has mentioned specifically that the movement of the grating by not more than ten pitches effectively averaged the spurious fringes (Takasaki, 1982). This was verified in our system. Slow movement resulted in an unsatisfactory elimination of the unwanted grid shadows. The most suitable translation speed was found to be 35mm/sec, and the exposure time was 0.5 sec, which meant that a distance of 17.5mm was moved during exposure. With a pitch of 2mm, the translation was thus less than ten pitches. Validation of the moiré system To summarize, the moiré instrument consists mainly of a regularly spaced grating, a light source and a camera. The appropriate dimensions of the completed components finally chosen in the experimental set up were: L = distance from the camera and light source to the grid = 449mm; d = distance between the camera and the light source = 164mm; g = pitch size of the grating = 2mm. The instrumental error can be evaluated when the functional relationship connecting the final result with the variable components, as well as the error

Threedimensional moiré images 307

Figure 3. Moiré pattern on a mould (a) with a stationary grid and (b) with grid translation during exposure

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structure for these components, are known. The effect of variation in the system components such as L, d, and g can be estimated by differentiation of equation 1 and applying the law of error propagation. If zn = f (L, d, g), where L, d, g are independent variables, then

308

(2) Since zn = ngL/d – ng, the following expression is obtained for the rms (root mean square) error σ2zn of the distance of the nth fringe to the grating in terms of rms error σ 2L, σ 2d, and σ2g in the distances L, d and the grid spacing g respectively.

In terms of coefficients of variation V,

Hence

(3) Suppose that VL2 = Vd2 = Vg2, then

(4) The coefficient of variation Vzn increases with the distance to the grating, i.e. with an increasing fringe sequential number n. In this work, the maximum fringe orders on most of the foam samples were between 6 and 7. According to Table I, at a distance of 35.45mm (n = 6) from the grating, the fringe interval was 6.29mm. It was considered that a value for σzn equal to a quarter of this was reasonable; hence it was required that σzn ≤ 1.5725mm or Vzn ≤ 1.5725/ 35.45 = 0.04436.

Since d = 164, g = 2, Equation 4 gives

VL = Vd = Vg ≤ 0.0243 (or 2.43 per cent) will be allowed for the sixth fringe. In the case of n = 7, zn = 41.91, and ∆zn = 6.46, if it is required that σzn ≤ a quarter of ∆zn = 1.61, i.e. Vzn ≤ 1.61/ 41.91 = 0.0384, Equation 4 will give

VL = Vd = Vg ≤ 0.0210 (or 2.10 per cent) will be tolerated for the seventh fringe. To summarize, the instrumental set-up is reliable for n = 6, if the dimensions can be set to within 2.43 per cent coefficient of variation of the set-up including the length L, distance d and the grid size g. However, this tolerance will be 2.10 per cent for the larger distance from the fringe (n = 7) to the grating. This suggests that the system gives reliable data for the area near the cup apex, but careful setting is necessary for a better accuracy of measurements around the cup rim. Conclusion This paper describes the development of an experimental non-contact shadow moiré system based on the theory of moiré topography. This system proved to be an effective method for the topographical measurement of both the convex and concave three-dimensional contour profiles of foam-moulded bra cups. The importance of controlling the image contrast and visibility was emphasized. A photographic frame with appropriate design for controlling the position of the light source, the camera, the grid and the cup sample was constructed, followed by the photo-chemically machined grid plate and the pneumatic grid translation device needed to produce a high contrast moiré picture. Moreover, the covering of the cup surface and the alignment of the cup sample was carefully done. Photographic parameters were found to be optimal at an exposure of half a second with an aperture of f/16 on HP5 film. To conclude, a simple method has been developed for the characterization of the three-dimensional shape of moulded brassière cups, and such characterization can be used as a form of communication in the industry. The tolerance of the instrumental error was derived and the confidence with the moiré set-up was assured. This indicates the suitability of shadow moiré topography for shape measurements on moulded brassière cups.

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References Allen, J.B. and Meadows, D.M. (1971), “Removal of unwanted patterns from moiré contours maps by grid translation techniques”, Applied Optics, Vol. 10 No. 1, pp. 210-12. Cabaj, A., Ranninger, G. and Windischbauer, G. (1974), “Shadowless moiré topography using a single source of light”, Applied Optics, Vol. 13 No. 4, pp. 722-3. Janssens, J.L., Decraemer, W.F. and Vanhuyse, V.J. (1985), “Visibility depth of shadow moiré fringes in function of extended light source and aperture of recording system”, Optik, Vol. 71, pp. 45-51. Kafri, O. and Keren, E. (1981), “Fringe observation and depth of field in moiré analysis”, Applied Optics, Vol. 20, pp. 2885-6. Leung, H.M. (1994), PCM Technology, Industrial Centre, The Hong Kong Polytechnic University. Patorski, K. (1993), Handbook of the Moiré Fringe Technique, pp. 220-53. Pirodda, L. (1982), “Shadow and projection moiré techniques for absolute or relative mapping of surface shapes”, Optical Engineering, Vol. 21, pp. 640-9. Takasaki, H. (1970), “Moiré topography”, Applied Optics, Vol. 9 No.6, Optical Society of America, p. 1469. Takasaki, H. (1982), “Moiré topography from its birth to practical application”, Optics and Laser in Engineering, Vol. 3 No. 1, p. 9. Yoshizawa, T. and Tashiro, H. (1982), “Localisation of fringes in moiré topography”, Optics and Laser in Engineering, Vol. 3, pp. 29-44. Yu, W.M. (1996), “The effects of polyurethane foam properties and moulding conditions on the shape characteristics of brassière cups”, PhD thesis, The University of Leeds, p. 98. Yu, W.M., Harlock, S.C. and Yeung, K.W. (1995), “Contour measurement of moulded brassière cups using a shadow moiré technique”, Proceedings of The Third Asian Textile Conference, Hong Kong, pp. 300-8.

Communications The bra design process – a study of professional practice C. H. M. Hardaker and G.J.W. Fozzard

Communications: the bra design process 311

Department of Textiles and Fashion, School of Design and Manufacture, De Montfort University, Leicester, UK Introduction This paper examines the working methods of the professional bra designer. In contrast to the wealth of literature describing the history of the bra[1-6], there is a lack of published material devoted to its design and manufacture. Therefore, to ascertain the details of the commercial bra design process, a study of professional design methods was performed. The bra is one of the most close fitting garments worn by women today. Designed to support and mould the soft tissues of the upper female form, the garment is shaped to fit exactly the contours of the body. Further to these requirements the garment must also be comfortable to wear and aesthetically pleasing. Moreover, to cater for the variation that exists in the size and shape of the female population, the commercial product has to meet these exacting criteria in a wide range of sizes. After informal discussions with professional designers and colleagues at De Montfort University, it was apparent that the design process relies heavily on the expertise of the designers and involves a high level of heuristics knowledge. Several important aspects of the process were identified: fabric selection, pattern development and grading. These and further topics formed the basis of a survey of professional designers. Overview of the design process Bra design is a lengthy process requiring a combination of design creativity, precision pattern making skills and a detailed knowledge of fabric performance. Most bras are constructed from flat panels of stretch fabric, which are accurately shaped to the nearest millimetre. These pieces are assembled into a three-dimensional garment and fitted to a life model. Here the designer can check that the garment supports the human shape without any adverse distortion of the garment or discomfort to the wearer, making any adjustments that are necessary. This is the start of the prototyping loop, which can involve many iterations of fit and pattern amendment to achieve a well-fitting bra. When the designer is satisfied with the fit of the sample garment, the pattern pieces are graded across the intended size range. These graded patterns are also fitted to life models and adjusted as necessary. This instigates many more instances of the “fit and amend” loops which will be carried out in parallel and

International Journal of Clothing Science and Technology, Vol. 9 No. 4, 1997, pp. 311-325. © MCB University Press, 0955-6222

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in series. Some indication of this proliferation is shown in Figure 1, where three sizes are graded in parallel. Finally, when the graded patterns have been perfected, the style and appropriate manufacturing instructions are sent through to production. Inspiration and moodboard

312

Fabric selection

Fabric testing

Concept development

Fashion sketch

First pattern in sample size

(First) sample garment

Fit to life model

Pattern development

Assess fit

Adjust sample and amend pattern

No

Yes

Grade sample pattern over a range of sizes

Graded sample size a

Graded sample size b

Graded sample size c

Fit to life model

Fit to life model

Fit to life model

Assess fit

Yes

No

Adjust sample and amend pattern

Assess fit

Yes

Set of graded patterns

Figure 1. The bra design process

Production

No

Adjust sample and amend pattern

Assess fit

Yes

No

Grading

Adjust sample and amend pattern

Over recent years computer-aided design systems have been used for pattern amendment and grading. These systems store pattern shapes as vector outlines, which enable accurate and speedy adjustment of shape. When used in grading, sample size patterns can be resized by specifying the required amount of growth at grade points around the piece. These increments are specified as Cartesian co-ordinates and known as a grade rules. The graded pieces are displayed on screen superimposed on the sample size as a nest. They can then be plotted out on to paper either in a nest format or as separate sizes. If any alterations are required the pieces can be regraded quickly by altering the appropriate grade rule. The design process is unique for each bra. The pattern shapes for each garment are dependent on the characteristics of the fabric used and the design attributes of the style. This relationship means that it is the usual practice to design each new style of bra from first principles. It is rare that pattern pieces from an existing style can be adapted and reused as is the case in other areas of clothing design. To indicate the degree of complexity involved, a full set of bra patterns consists of a minimum of five pieces, but typically styles will often have ten pieces or more. Some styles can have as many as 22 separate pieces. The style will be produced in typically 20 sizes, with some styles graded over as many as 56 sizes. The survey A survey was designed to obtain an insight into the working methods of professional bra designers. Two methods were used: a postal questionnaire and interviews with designers during visits to bra manufacturers. The questionnaire An informal questionnaire was designed to provide designers with the opportunity to discuss current practice within the design role. The questionnaire was in two parts. The first part was concerned with basic company details and the types of bra designed. The second part was designed to elicit comments and opinions on aspects of the design process. The following topics were used for discussion; sizing, fabric selection, pattern development specifically fitting and grading, the use of computer-aided design (CAD), wear trials, design expertise and experience. The format of the questionnaire was deliberately open to ensure that respondents could express personal opinions. Each topic was listed separately along with several prompts to provide a possible framework for the reply. For example the section on fitting, provided the following prompts: When are life models used in fitting? Are they professional models or do you use your own staff? Do you use the stand? How does the fitting process vary with different types of bra?

The respondents were thus free to comment on those aspects of fitting and any other relevant features of the fitting process.

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314

A pilot version of the questionnaire was completed by colleagues in the Department of Fashion and Textiles at De Montfort University and modified accordingly before despatch. The survey was sent to 45 UK-based foundation wear and courtesy manufacturers, addressed to the Head of Design. Company names and addresses were obtained from the 1995 edition of the Fame database[7]. Company visits Interviews following a similar format to the postal questionnaire took place on site at two bra manufacturers. On both occasions interviews were with designers and graders. Results A total of ten companies were successfully evaluated: eight replies were received from the postal questionnaire and two replies were obtained from company visits. The results from the survey have been collated and summarized in Tables I-VI, with each Table providing the response to one of the questionnaire topics. In general the answers obtained were highly detailed, in some cases going beyond the scope of the original question. To preserve confidentiality company names and addresses have not been included. Discussion The survey showed that the working methods of the professional bra designer are heavily reliant on heuristics, confirming the results of the authors’ earlier informal discussions. It was apparent that elements of standard practice do exist; however, it was also evident that each company had developed its own individual working method. The survey showed that several issues in particular demonstrated this individuality. Of particular note were the use of proprietary sizing constraints and the approach to fitting and grading. Sizing The survey exposed some disparity in sizing. Although all companies used the same size notation to classify sizes, they all used their own size chart to size garments (see Table I). (The size notation was developed by the US company Warners in the 1930s. It combines the bust measurement in inches with an annotated cup size: AA, B, C, D, DD, E, etc.) This lack of a standard set of measurements has led to a high level of non-uniformity in the marketplace. Garments can be labelled the same size but if produced by different manufacturers using proprietary sizing constraints then consistency in true measurements will be limited. Fabric selection There was total agreement on the importance of fabric behaviour and fabric aesthetics in the design process (see Table II). Assessing fabric properties was

J

I

H

G

F

E

D

C

B

A

Company

Metric Metric and imperial Metric Metric and imperial

Metric and imperial

Metric Metric and imperial Metric

Own size chart

Own size chart

Own size chart

Own size chart

Own size chart

Own size chart

Own size chart

Own size chart

Brand a – 34B or 34D Brand b – 36D

34B

34B

Brand a – 34B Brand b – 34C or 36DD

34B

Usually 34B, larger sizes 42C

34B or medium

34B, larger sizes 38B

Usually 34B, larger sizes 34D

Metric

Own size chart

Sample size(s) 34B, different for petite or outsize

Metric or imperial

New chart for each product Metric

Size chart

Minimum number of sizes 15 Maximim number of sizes 35

Not disclosed

Not disclosed

Not disclosed

Base range 32B-42B, cup sizes not disclosed

Not disclosed

Not disclosed

20+

Not disclosed

Minimum number of sizes 10 Maximim number of sizes 56

Typical size range

Communications: the bra design process 315

Table I. Sizing and size ranges

Constantly looking out for new Used where possible fabrics with surface effects

Used for innovative ideas

Used for innovative ideas

Experiment with new fabrics

Constantly looking for new fabrics for fashion ranges

Choose new fabrics for specific Small repertoire of Required to determine fabrics’ suitability performance features and familiar fabrics which are for purpose aesthetic qualities used for basic functions

Used all the time. Fashion bras demand the use of new fabrics

C

D

E

F

G

H

I

J

Limited use

Used where possible

Used where possible

Used where possible

Used where possible

Constantly looking out for new Used where possible fabrics for fashion ranges

A

B

Needed for innovative ideas. Used where possible Not used for the whole garment Used to update ranges Used where possible

Table II. Fabric selection Utmost importance. Necessary to test as fabric does not always agree with manufacturer’s specification

Utmost importance for continuity of quality and suitability of purpose

Not disclosed

Utmost importance for continuity of quality and suitability of purpose

Not disclosed

Utmost importance

Guide for fabric’s performance

Not disclosed

Not disclosed

Laboratory tests done on site

Not disclosed

Not disclosed

Laboratory tests done on site

All fabrics are tested on site

Laboratory tests done on site

Utmost importance in design and production. Not disclosed Need consistency in production Not disclosed Not disclosed

Testing facilities

Use of new fabrics

Use of established fabrics Reliance on technical specifications

316

Company

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seen as an intrinsic part of the design role and essential for rapid development of patterns. Fabric properties are so critical in determining the shape of a pattern, that a new set of patterns has to be developed if the intended fabric for an existing style is changed. Consequently, existing patterns are rarely amended, although “tried and trusted” fabrics are used where possible for basic panels such as the wings and straps. The majority of fabrics used in bra design are stretch fabrics. Their construction is varied: woven, knitted and lace fabrics are all used. However, most fabrics will contain a small percentage of an elastomeric fibre. When selecting a new fabric a designer will base an initial judgement on its visual appearance, tactile qualities and stretch properties. Knowing what has worked in the past is a key part of the selection process as is the fabric technical specification. This is supplied with the fabric and provides details on the fabric composition, construction, physical attributes and selected mechanical properties. A typical technical specification for a warp knitted stretch fabric is shown in Table III. The tensile strength of a stretch fabric is indicated by the warp and weft moduli. This is specified for wing fabrics and other stretch fabrics including lace and gives the designer an indication of the control or support that a fabric will offer. The higher the modulus, the more control provided. A further parameter is specified for lace. Its open type structure tends to be dimensionally unstable in tension and so its bursting strength is used as a measure of its ability to withstand normal pressure. The fabric extension or

Material description

Material components split according to fibre, dtex, Nm or Nec. Warp, weft and any inner or outer covering threads described

Specification of finished fabric

Knitting construction, machine type, number of ground and pattern bars. Total width and working width. Weight per running metre and weight/square metre

Mechanical properties

Extension warp (per cent), extension weft (per cent) at a given load Modulus for a given extension

Material composition

Polyamide, polyester, cotton, viscose, elastane, etc.

Fastness

Washing, perspiration, rubbing dry, light, water, sea water, etc.

Shrinkage

Per cent shrinkage at various temperatures and after tumble drying

Finishing specification

Formalin free, chlorine free

Recommended wash care symbols

Communications: the bra design process 317

Table III. Technical specifications for a warp knitted fabric

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stretch percentage is also an important parameter used to assess the suitability of elastic bindings and shoulder straps. Bra manufacturers do not rely on the technical data sheets supplied with fabric. It is usual for a company to have its own on-site testing laboratory to check and augment the supplier’s information. The range of tests carried out is extensive and follows standard procedures as defined by the British Standards Institute or equivalent. A selection of mechanical tests can be seen in Table IV. Other tests will also be performed to check the fabric’s composition, physical dimensions, shrinkage, fastness and also to assess stability, sewability and durability. Once the garment goes through to production fabric technical specifications are used to measure consistency. Bulk supplies of fabric are selectively tested to check for any deviations from the original specification used in design. Pattern development “Trial and error” is a predominant feature of the pattern development process. It is extremely unlikely that the first pattern cut for a new style will be right first time. The final pattern pieces are only developed after a succession of sample garments have been fitted and adjusted. It was the accepted practice to assess the fit of a garment on a life models; all companies felt that this was the only way to achieve a well-fitting garment (see Table V). The life models used in most cases were company employees, although professional models and local consumers were also used for some fittings. Two companies did use the stand for trial fittings of first designs, with one company going as far as a “life-like fibreglass dummy”. The dress stand was also used occasionally to mark out new design ideas. Fitting sample garments is extremely important in both the pattern development and grading processes. It is apparent that there is a strong reliance on life models during fitting, which poses some problems in maintaining size consistency and in availability. Grading Grading methods varied between companies. While most companies used the traditional approach and graded all pattern shapes for each size, there was some use of the cross-grading method. (The cross-grading method assumes that adjacent cup sizes across base size ranges are equivalent, e.g. the 34B cup is equivalent to the 36A and 32C, etc. This dual use of certain pattern shapes can save considerable time spent grading.) Three companies used this method regularly with five others occasionally cross-grading. Again, great emphasis is placed on checking the fit of the graded garments, with seven companies fitting all graded sizes to life models. Inevitably this is a lengthy process; typical times to grade and fit all sizes were quoted to vary from a minimum of two months to a maximum of eight months.

Key

Burst tests

Elastic fabrics

Test for: Narrow and wide elastic fabrics. Applicable for weft and warp knitted fabrics

Knitted and lace fabrics

BS 4952*

BS 4768**

Fabric specimens are cut to determine machine direction extension or cross-direction extension. Using a tensile testing machine the force extension curve is determined for at least five specimens for a specified force. The rate of extension and retraction is set to 500mm/min. Specimens are cycled between zero extension and maximum force with results taken from second cycle. The mean percentage extension at the specified force is calculated Fabric specimens are prepared to determine either the crossdirection modulus or machine direction modulus. Using the above results, the modulus or force at each value of extension or retraction is recorded. The mean value is taken The force extension determined again. On the second cycle maximum force is held for ten seconds and the applied force is reduced to zero in a further 7.5 seconds. When unloaded the specimen is allowed to relax for one minute. The residual extension is calculated by comparing the original specimen length with the results from the test A hydraulic bursting tester is used. A circular specimen of fabric is subjected to hydraulic pressure until it bursts. The pressure when this occurs is recorded. The bursting distension is the height of the bulge measured immediately prior to the rupture

Modulus (N). The force needed to produce a specified extension

Residual extension (per cent)

Bursting strength (kN/m2) Bursting distension (mm)

Method used

Extension at a specified force (per cent)

Parameter measured

*BS 4952: methods of test for elastic fabrics[8] **BS 4768: method for the determination of the bursting strength and bursting distension of fabrics[9]

Suitable for

BS test

Communications: the bra design process 319

Table IV. Testing the mechanical properties of stretch fabrics

Table V. Pattern development, fitting and grading

Never used in fitting

Local consumers, staff and professional models First designs are fitted on After fitting to the dummy, designs are a life-like fibre glass then fitted to staff of the correct size. dummy Customer provides own professional models Sometimes used to mark Staff and local consumers are used for out design lines when fitting. Professional models are used for working on a new garment. shows Never used in fitting Never used in fitting Staff used for fittings. Professional models used for shows and presentations Never used in fitting Fit to staff, professional models and local consumers

Never used in fitting

I

J

H

G

F

E

Professional models used as well as staff. Models are frequently measured to ensure consistency Used for trial fittings, Staff and local consumers used. modifications only made Professional models not used as it is felt after fitting to a life model that they do not represent the average customer

34B-38B, 34C-40C 34D-40D, 36E-38E 42F-42G

All

As many as possible

All

All

As many as possible

All cup sizes for 34 and 38 base sizes All

D

Staff and professional models used

Never used in fitting

C

B

Only used to mark a new Mainly local models, professional models All idea. Never used in fitting rarely used Never used in fitting Staff and professional models used As many as possible

A

Use of life models

Not used, not practical for a large size range Not used

Sometimes used

Sometimes used

Cross-grading used for smaller cup sizes

Sometimes, if the style is suitable

Rarely

Not on brand name lines. Sometimes for contact lines Yes, if appropriate

Yes, if appropriate

Using the crossgrading method

Min. number of sizes 15. Max. number of sizes 35

Not disclosed

Min. 3 months Max. 6 months Not disclosed

6-7 months, inclusive of wear trials

Weeks

Not disclosed

Min. 2 months

Min. 2 months Max. 6 months Not disclosed

Typical time to grade and fit all sizes in range

320

Company Use of the dress stand

Sizes fitted on life models

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The use of CAD A high proportion of the surveyed companies were using CAD systems for grading and lay planning; some companies also had computer-controlled cutting facilities. Their responses clearly indicated their appreciation of the speed, accuracy and flexibility that the CAD method can offer (see Table VI). In addition to grading a small proportion of the companies with CAD were using their systems for pattern drafting. In all cases this was to adapt existing styles stored on the system. CAD was not used to design the first pattern for a garment; this was still done by hand. It was interesting to note that only one CAD user provided some indication of the time taken to grade a style. This was still in the region of three to eight months. This indicates that, even though the CAD method can reduce the time spent on the mechanics of grading, there is still a substantial amount of time to be spent fitting and adjusting the graded patterns. A system that incorporated three-dimensional working methods and addressed the idiosyncrasies of the bra fitting process was regarded as an important requirement for future CAD systems. Three-dimensional CAD systems are used widely in other areas of design, but because of the nature of clothing design and the difficulties associated with modelling fabric accurately, few 3D CAD systems exist. Wearer trials Fit is further assessed through wearer trials. All companies perform some type of trial to evaluate the performance of a garment over a set period of time (see Table VII). These trials are usually performed in the development stage, but in some cases trials are performed well into production. Here, panels of testers, usually a mixture of company employees and local consumers, will rate the garment in terms of fit, comfort and durability, on an ordinal scale. Design expertise and experience It was apparent that companies felt that successful design came only with experience and no clear rules could be distilled for success. This heuristic knowledge was considered to be essential to develop well-fitting garments within commercial time constraints (see Table VIII). Further to the heuristics of fabric performance and pattern development, the ability to visualize a flat pattern in three-dimensional terms was also considered a vital part of the designer’s skills base. Such expertise is learned over a number of years with senior designers training junior staff. One company quoted that it took five years after graduating to become a bra designer. Conclusions The survey confirmed that the bra design process is unique for each bra, dependent on its design attributes and fabric characteristics. The working methods of the bra designers surveyed appeared to adhere to a standard framework, although there were some variations noted. Typical stages in the

Communications: the bra design process 321

Table VI. Use of computer-aided design techniques

No

Yes

Yes

Yes

Yes

Yes

Yes

J

I

Yes

Yes. Two No. Designer drafts stations, no all patterns by hand link to CAM Yes. Nine Yes stations, links to CAM

H

D E F G

C

B

Yes. One No. Original patterns Yes. CAD used to Yes station, links are produced grade all garments. to CAM manually Used to modify grades to improve fit Yes. Two Used for modifying Yes. CAD used to Yes stations, existing patterns grade all styles and links to CAM to measure the resultant grades Yes. One No. Original patterns Yes. CAD used to Yes station, links are produced grade all garments to CAM manually Used to modify grades to improve fit None – – – Yes No Yes Yes Not disclosed – – – Yes. Three No. Designer drafts Yes. CAD used to Yes, for stations, no the patterns by hand grade cup and back costings and link to CAM sizes production

A

Used for grading

Used for lay planning

Any improvements to the systems are welcomed

Not disclosed

Potential improvements

Grading: time savings and accuracy

Pattern development and grading: speed, accuracy, flexibility

The use of 3D body scans for pattern development. Improved automatic marker making and more accurate cutting Not disclosed

Grading: speed at which A system that specificgraded patterns can be altered ally addresses the during fitting process idiosyncrasies of bra fitting – – Not disclosed Not disclosed – – Grading: quicker and reduces Cannot foresee a substitute lead times for development for the fitting on to the human form, especially the larger cup sizes Grading: time savings and Not disclosed accuracy

Grading. Time savings and accuracy

Grading. Time savings and accuracy

Which process is best suited to CAD? Perceived benefits

322

Company Use of CAD

Used for pattern making

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J

I

H

G

F

E

D

C

B

A

Company employees and professional models for some sizes Company employees and consumers

During development During grading through to final production Not specified During grading

Not disclosed Throughout development and into production Throughout development and on finished stock

Not disclosed

To evaluate comfort and durability

Not disclosed

To iron out as many problems as possible before the garment goes into production

Necessity

To test comfort, fit and durability

To test durability, comfort, support, appearance and fit

To select optimal fabrics From prototype stage and for garment and to at every stage in the improve garment fit development process

Company employees and local consumers

30-40 company employees and local consumers

Company employees, local consumers

Company employees

Not disclosed

Company employees

Company employees

Not disclosed

To evaluate fit, fabric performance, comfort, colour fastness and other attributes

How many sizes are wear tested?

Not disclosed

All sizes tested

As many as possible

As many as possible

Every size by at least one person, more if possible

Not disclosed

Several garments per size

As many as possible

As many garments are tested as time allows

Panel of testers, most of whom Not disclosed are company employees

Who participates in wearer trials?

During grading

When is wear testing performed?

Not disclosed

Why are wear tests Company performed?

Not disclosed

Not disclosed

Not disclosed

Not disclosed

Not disclosed

Not disclosed

Six months

Not disclosed

Not disclosed, but will test as many garments as possible

Not disclosed

How long is a typical trial?

Communications: the bra design process 323

Table VII. Wear tests

Expected

Expected, even with the most experienced designers there will be some “trial and error” in fitting some styles

Expected

Expected. When fitting a garment there is always a calculated reason for making an alteration to a pattern

There is always some degree of “trial and error”

There is always some degree of “trial and error”

Rarely right first time. On average the design is right on the third development loop

Even with very experienced staff there is a great deal of “trial and error”

D

E

F

G

H

I

J

Designer experience can ensure that new styles are fitted quicker. The ability to pass this expertise on to trainee designers is important The ability to see a flat pattern in 3D is important. This comes easily to some designers while others have to learn through experience. Achieving a good fit is learned through experience and cannot be specified in a series of rules Essential, an experienced designer and grader will be able to achieve results much quicker Essential, an experienced designer and grader will be able to achieve results much quicker Designer’s expertise is vital for styling and fabric choice. Experience of fit is extremely important in meeting deadlines Rely on designer’s experience

Not disclosed

Knowing which styles will fit well and grade easily is important. Fashion ranges are more challenging and development time is longer. Expertise is vital Not disclosed

Not disclosed

Not disclosed. Respondent has ten years’ design experience Not disclosed

Not disclosed

Not disclosed

Not disclosed. Respondent had a BA degree in Contour Fashion and five years’ experience It takes five years’ training after graduation to become a bra designer. After five years final grades are still checked by a senior designer Not disclosed. Respondent had 23 years’ design experience

Not disclosed

C

B

Many years to become proficient

Not disclosed

Expected, products are rarely right first time, unless style is simple and based on an existing successful pattern Expected, it is only through “trial and error” that a designer builds up the experience necessary for bra design

A

Table VIII. Comments on design expertise and experience Training time

324

Company The role of “trial and error” in design development The need for design experience and expertise

IJCST 9,4

design include: the initial design and fabric selection, pattern development, grading and evaluative wear trials. Specifically it can be concluded that: (1) While all manufacturers surveyed use the same size notation, there appears to be no industry-wide size chart. (2) Fabric technical specifications are used to judge a fabric’s suitability for purpose and also as a way of measuring consistency throughout production. (3) A great deal of attention is paid to the fit of the garment at the pattern development and grading stages, with a succession of prototypes fitted to life models before arriving at the final product. Grading in particular is a lengthy process, taking a minimum of two months and in some cases as long as eight months to grade a style. (4) CAD methods were used by some companies, particularly for grading and lay planning. (5) “Trial and error” is an accepted part of the design process ameliorated only by a designer’s heuristic knowledge. (6) Garment fit is further assessed through wearer trials where the performance of a garment is evaluated over a set period of time. Note and references 1. Carter, A., Underwear, the Fashion History, Batsford, London, 1992. 2. Colmer, M., Whalebone to See-through, a History of Body Packaging, Johnston and Bacon, London, 1979. 3. Cunnington, P. and Willett, C., The History of Underclothes, Faber, London, 1981. 4. Ewing, E., Fashion in Underwear, Batsford, London, 1971. 5. Ewing, E., Dress and Undress, a History of Women’s Underwear, Batsford, London, 1978. 6. Saint Laurent, C., A History of Ladies’ Underwear, Joseph, London, 1968. 7. Published by Jordans and Sons, London, 1994, The Fame database is published 12 times per year and provides detailed financial information on 108,000 UK companies. Companies with a turnover of over £700,000 are listed. 8. BS 4952: Methods for Test of Elastic Fabrics, British Standards Institution, London, 1992. 9. BS 4768: Method for the Determination of the Bursting Strength and Bursting Distension of Fabrics, British Standards Institution, London, 1972.

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Strength reduction of sewing threads during high speed sewing in an industrial lockstitch machine Part I – mechanism of thread strength reduction G. Sundaresan, P.K. Hari and K.R. Salhotra Department of Textile Technology, IIT, New Delhi, India Introduction During high speed sewing, the sewing thread, especially the needle thread, is subjected to stresses that adversely influence both its processing and functional performance. The level of the stresses depends on the tensile and other properties of the needle thread and its interaction with machine elements, the fabric and the bobbin thread. A good sewing thread should give negligible breaks and acceptable seam appearance, i.e. proper stitch geometry and tight, uniform and unpuckered seam. The sewing performance of threads is generally assessed by studying the thread dynamic tension and/or strength reduction[1]. Studies based on the former have been less common owing to the limitations of measurement systems. Therefore, earlier studies were mainly related to the strength reduction of sewing threads. The effect of certain thread properties and machine parameters on the strength reduction was studied by many researchers including Crow and Chamberlain[2], Gersak[3] and Gersak and Knez[4]. However, the mechanism of thread strength reduction is still not very clear. The extent of strength reduction is a function of the magnitude of the stresses acting on the threads and their ability to withstand the degrading effect of the stresses. The reduction in thread strength can be due to the changes in the mechanical properties of the fibre due to dynamic loading and/or due to the changes in the thread structure. Therefore, the objective of the present work is to investigate and segregate the causes for the thread strength reduction. An understanding of this aspect will be extremely useful to the sewing thread manufacturer in engineering the thread with specific properties and hence optimize the cost and improve sewing quality.

International Journal of Clothing Science and Technology, Vol. 9 No. 5, 1997, pp. 334-345. MCB University Press, 0955-6222

Theoretical background The mechanical behaviour of spun yarns depends on the properties of constituent fibres and their arrangement[5-9]. During tensile loading, the

tension generated by the applied strain is transferred to the fibres through the interfacial shear stress which depends on the transverse force and the property of the interface. The tensile stress in a fibre at any point and hence the modulus of the yarn at that point will, therefore, be determined by these two factors in addition to the fibre modulus. While the transverse force, developed owing to the radial compression of the yarn depends on the structural properties of the thread like packing coefficient, inter-ply pressure, twist and migration[5,6,8], the interfacial shear stress depends on factors like fibre friction and geometry of the contact surface. Therefore, any change in the tensile property of sewn threads can be attributed to the changes in: •

the property of the constituent fibres;

•

the fibre frictional properties; and/or

•

the transverse force buildup.

Among last two factors, the frictional property of the fibres is not expected to change as a result of sewing. So any change in the tensile behaviour of the sewn thread without corresponding reduction in fibre strength can be attributed to changes in the transverse force buildup which in turn can be related to the changes in the structure of the parent thread. The changes in the modulus of the sewn thread is one of the most important and useful tools to examine such mechanisms. Further, the cross-sectional and scanning electron microscopic (SEM) studies of the thread can shed light on the structural damages like changes in thread packing. The cross-sectional study can, especially, provide interesting information as the cross-sectional size and shape of the thread are known to have important bearing on its mechanical properties. As the tensile strain in the yarn progressively increases, both the tension on the fibres tending to cause slippage and the transverse force, which creates the frictional resistance to slippage, increase. However, the rate and the extent of tension build-up is limited by the extent of self-locking structure achieved due to the transverse forces. In a structurally damaged thread, this will depend on the severity of the damages and also on certain structural parameters of the thread like fibre length, twist and number of plies. This is due to the fact that lower initial tension in a yarn reduces the build-up of transverse force which is proportional to the first power of yarn tension. This will reduce frictional gripping which in turn will further reduce yarn tensile stress. Thread tensile failure The relation between the stress required to overcome the frictional resistance and the tensile strength of the fibre determines the fracture mechanism of a thread[5-7,9]. If the interfibre frictional force is higher than the fibre strength, the yarn breakage will be predominantly caused by fibre breakage. Conversely, if it is lower than the fibre strength, the failure will be dominated by fibre

Strength reduction of sewing threads 335

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336

slippage. This also determines the breaking elongation and hence the toughness of the thread. The fracture mechanism of composites with finite fibre length depends on the mean fibre length and its distribution and the frequency and the severity of faults in the fibres[10]. Similar mechanism will also exist in the breakage of the threads. If the fibre length is less, slippage will be comparatively easier. However, the damage inflicted on the fibre during the sewing process will reduce its strength. In this case, the tendency of failure at weak points is determined by their frequency and degree of weakness so that these two parameters will have a direct influence on the slippage of the fibre during breakage and hence on thread toughness. Materials and methods Three commercial cotton and polyester spun sewing threads with details as given in Table I were selected for the present study. In order to assess the degrading effect of fabric constructional parameters one paper and two fabrics with details as given in Table II were used. The use of paper is expected to eliminate the effect of fabric completely. A Singer industrial lockstitch machine (model 191D 200AA) was used for these trials. It was run at 4000 spm. with Singer needle 16 and stitch dial number 2.5. The seams were made with two layers of fabric/paper in superimposed position. The static tension was adjusted to get a balanced stitch and the seam balance ratio was measured in all the cases. The needle thread

Thread code Table I. Properties of sewing threads

Table II. Fabric particulars

PC120 PC80 CN50

Fineness tex 13.9 × 2 12.3 × 3 12.3 × 3

Initial Twist Tenacity Elongation modulus Toughness ply/single Mean CV Mean CV Mean CV Mean CV m–1 Direction cNtex–1 (%) (%) (%) cNtex–1 (%) cNtex–1 (%) 1067/929 882/929 776/1083

Z/S Z/S Z/S

34.7 33.8 23.7

8.3 7.3 6.1

12.4 15.2 5.4

6.3 3.7 8.6

341.0 10.8 248.0 5.9 413.0 12.8

1.94 2.09 0.62

12.3 9.7 12.0

Fabric weave

Warpa

Tex

Weftb ends (cm–1)

Tex

Picks (cm–1)

FA FB

Plain Plain

10.7 10.7

41 41

17.2 17.2

29 17

Notes: a FA and FB: polyester twisted filament b FA and FB: polyester textured filament

tension was 80 cN for the polyester spun threads and 85 cN for the cotton thread. The bobbin thread tension was 25 cN for all threads. In order to assess the change in the tensile properties of the sewn threads, the needle thread was carefully taken out of the seam by first removing the bobbin thread and then tested on the Instron tensile tester interfaced with a computer. The tensile strength of the fibres extracted from the parent and the sewn thread was also measured for PC80 and PC120 threads to assess the strength reduction of the fibres. In all the cases, 100 tests were carried out and the test conditions were maintained as per ASTM standard. The initial tensile modulus of the threads and fibres was estimated using the secant modulus calculated between 0 and 2 per cent strain. All the tensile properties, namely, tenacity, elongation percentage, initial modulus and toughness were calculated using the Series IXR software of the Instron Corporation. The change in these tensile properties of the sewn threads and fibres was then calculated using the following expression: Reduction% =

TPp – TPs TPp

× 100

(1)

Where,TPp is the mean value of the tensile property of the parent thread and TPs is the mean value of the corresponding tensile property of the sewn thread. A negative sign in some of the calculated values indicates increase in that particular property. The linear density of polyester fibres was estimated using the average fibre diameter values measured using the Projectina optical microscope. The specific gravity was taken as 1.38gcm–3. The structural and physical damage of the threads and constituent fibres were also observed using the scanning electron microscope. The thread crosssections of parent and sewn threads were also studied in order to obtain a greater insight into the structural damages of the sewn threads. For this, the threads were embedded in PVA, then moulded into blocks using paraffin wax for sectioning using a microtome. The images were then recorded on to a video cassette using a Cryo CCD camera attached to the Karlzeiss Axioscope light compound microscope for further processing. The cross-sectional photographs were obtained from the recorded images using a video matrix imager. Results and discussion Reduction in thread strength and initial modulus The reduction in the various tensile properties of the sewn thread calculated using equation (1) is given in Table III along with their CV percentage. The CV percentage of the tensile properties of the sewn thread was, generally, found higher than that of their respective parent thread suggesting the existence of wide variations in the severity of damage along the thread. This could be attributed to the larger variations in the peak tensions between sewing cycles observed by the present authors and other researchers[11] during the studies on dynamic needle thread tension.

Strength reduction of sewing threads 337

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The percentage reduction in the tenacity of the sewn threads ranges from a maximum of 30.6 in the case of CN50 sewn with fabric FA to a minimum of 14.0 for PC120 with paper. The stress-strain curves for the parent and the sewn PC80 thread is given in Figure 1. It can be seen from the figure that the reduction in the tenacity of the sewn threads is accompanied with a significant change in its stress-strain behaviour, especially in its initial region. The reduction in the initial modulus of the sewn threads is given in Table III. This may be slightly overestimated due to some permanent crimp set in the sewn threads. The CV percentage of the initial modulus of the sewn threads was also found to be high due to the variations in the stress-strain behaviour of the sewn threads in this region. Tenacity (cN/tex)

Key Parent Sewn with paper Sewn on paper without bobbin thread Sewn with fabric FA Sewn with fabric FB

30.0

20.0

10.0

Figure 1. Stress-strain curves for PC80 threads

0 0 4.0 Strain (per cent)

8.0

12.0

16.0

20.0

In view of the significant difference in the initial region, this portion of the loadelongation curve was zoomed in order to gain further insight into the difference in the tensile behaviour of parent and sewn threads. The curves, given in Figure 2, indicate the presence of fibre slippage in the case of sewn threads while it is absent in parent threads. The slope of the initial stress-strain curve for the parent thread is steep with little fibre slippage thus indicating well-developed

Breaking elongationa Red. CV (%) (%)

Toughness Red. CV (%) (%)

Initial modulus Red. CV (%) (%)

6.9 6.2 6.6

27.3 28.7 16.1

12.7 11.5 12.8

14.2 48.1 66.5

11.4 16.8 18.8

9.0 12.1 0.0

6.9 5.9 12.9

29.9 30.1 45.2

13.1 9.7 19.2

49.5 58.7 61.3

23.3 31.4 36.6

0.0 0.0 –22.1

8.5 5.2 12.9

28.4 24.4 37.1

14.1 8.7 12.8

71.0 65.3 82.4

45.0 32.9 43.3

Thread code

Tenacity Red. CV (%) (%)

Sewn on paper PC120 PC80 CN50

14.0 20.5 21.7

8.3 8.1 7.7

15.7 7.4 –28.0

17.6 18.9 30.6

9.2 7.3 12.7

20.3 20.7 28.5

9.5 7.0 8.2

Sewn on fabrics Fabrics FA PC120 PC80 CN50 Fabric FB PC120 PC80 CN50

Sewn on paper without bobbin thread PC80 10.2 7.3

19.0

5.8

22.5

10.2

6.2

Note: a Minus sign indicates increase in elongation-at-break

11.4

Strength reduction of sewing threads 339

Table III. CV percentage of and percentage change in tensile properties of the thread

Tenacity (cN/tex) 1.5

1.0

Key Parent Sewn with paper Sewn on paper without bobbin thread Sewn with fabric FA

0.5

0 0 0.2 0.4 Strain (per cent)

0.6

0.8

1.0

1.2

Figure 2. Initial region of the stress-strain curves for PC80 threads

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Plate 1. SEM photograph of PC80 thread sewn with paper

Plate 2. Cross-section of PC80 thread: (a) parent thread; (b, c) sewn with fabric FB

transverse force. Conversely, the initial slope of the stress-strain curve for the sewn threads is inclined towards the strain axis exhibiting significant fibre slippage during loading. This indicates significant reduction in the build-up of transverse force due to some structural disintegration. Thread structural studies Cross-sectional and scanning electron microscopic studies of the sewn thread, Plate 1 and Plate 2(b,c), confirm the structural damage in the thread due to sewing. The figures reveal the following:

•

•

The displacement of the plies has taken place only at specific locations, Plate 1 and Plate 2(c). The damages are mostly concentrated at the interlocking portion of the needle thread in the stitch, where maximum tension, bending and thread-thread abrasion is taking place, Plate 1. The thread twist has also been altered considerably at this point, the surface fibres also being pulled out of the structure. The individual plies have also been slightly displaced. The cross-sectional shape of the sewn threads, Plate 2(b,c) is also found considerably altered as compared to that of the parent thread, Plate 2(a).

Sewing without bobbin thread In order to further confirm the fact that the damage at the interlocking portion of the thread is mainly responsible for its strength reduction, sewing was carried out on paper using PC80 without the presence of bobbin thread and the strength reduction was assessed. The strength loss was only 10 per cent as against 20 per cent for the same thread when sewn with bobbin thread. There is lower loss in initial modulus with little fibre slippage, as shown in Figures 1 and 2. Therefore, the reduction in the initial modulus of the thread is mainly due to the displacement of the individual plies at certain points of the sewn thread and due to non-contribution partly by the surface fibres to the thread tension. As the tension builds up though the frequency and the extent of fibre stickslip in sewn threads reduces, the tension developed at any strain is generally lower than that in the parent thread. While this difference is very large in the case of cotton threads, it is less in polyester threads. In the case of cotton thread namely CN50, where the loss in the initial modulus is higher (Figure 3), there is considerable loss in both the tension generated and the rate of tension build-up as compared to the polyester thread. The initial portion of the stress-strain curve (Figure 4), shows severe fibre slippage with greater frequency and extent of stick-slip. The occurrence of complete slippage of certain fibre ends must be due to the presence of shorter fibres and pull-out of longer length of fibres. The severity of structural damage is confirmed by the SEM micrograph of the sewn thread, Plate 3. This can be attributed to the poor abrasion resistance of cotton sewing threads. Break propagation and thread breakage in sewn threads The break propagation of sewn threads is cascading as opposed to the catastrophic failure of the parent threads. Once the break has been initiated in the sewn thread, the failure was generally observed to be propagating slower. The plies break individually, the failure being initiated by the breakage of the weaker component. However, sometimes near-catastrophic breaks were also observed. This suggests the existence of variations in the relative strength of fibres and hence the plies. The failure of sewn threads is predominant with fibre slippage as seen in Plate 4(a). The broken ends exhibit gradual reduction in the number of fibres

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Tenacity (cN/tex) 25

Key

342

20

Parent Sewn with paper Sewn with fabric FA Sewn with fabric FB

15

10

5

Figure 3. Stress-strain curves for CN50 thread

0 0 2.0 Strain (per cent)

4.0

6.0

8.0

10.0

with complete fibre pull-out at the end and a longer break zone. Conversely, the fracture zone of the parent thread is smaller with the breakage of most of the fibres as seen in Plate 4(b) indicating cumulative build-up of self-locking structure where slip is adequately prevented. Reduction in fibre strength and fibre damages A comparison of the tenacity of fibres extracted from the parent and sewn threads shows a strength reduction of 8.9 per cent in the case of PC120 and 4.8 per cent in the case of PC80 (Table IV). There is also significant reduction in the percentage elongation of the fibres extracted from the sewn threads. Higher strength reduction in PC120 can be attributed to higher specific tensile loading because of its fineness. This is confirmed by significant increase in the modulus of the fibre. Nevertheless, the fibre strength reduction is much less as compared to the thread strength reduction in both the cases. Reduction in thread toughness The reduction in the toughness of the thread is owing to the cumulative effect of the reduction in its modulus and elongation. In general, polyester threads

Strength reduction of sewing threads

Tenacity (cN/tex) 1.5

343 1.0

0.5 Key Parent Sewn with paper Sewn with fabric FA Sewn with fabric FB 0 0 0.2 0.4 Strain (per cent)

0.6

0.8

1.0

1.2

Figure 4. Initial region of the stress-strain curves for CN50 threads

Plate 3. SEM photograph of CN50 thread sewn with paper

exhibit lower reduction than cotton threads in all the cases. This is mainly owing to higher loss in modulus in cotton threads. Nevertheless, the loss in CN50 thread the sewn with paper is much less in spite of the significant loss in its modulus. Analysis of the stress-strain curve, Figure 4, indicates that the elongation-at-break of the thread is much higher than the parent thread itself. This must be due to the contribution of fibre slippage to the work of rupture of the thread. The presence of relatively shorter

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344

Plate 4. (a), and (b) SEM photograph of the broken ends of PC80 thread

Tenacity Thread code Table IV. CV percentage of and percentage change in fibre tensile properties

PC80 (1.7 dtex) PC120 (1.1 dtex)

Red. (%)

CV (%)

Red. (%)

4.8 8.9

14.3 13.5

13.8 17.6

Strain initial modulusa CV Red. (%) (%) 14.7 18.4

–1.0 –11.4

CV (%) 18.0 16.9

Note: a Minus sign indicates increase in modulus

fibres in the cotton thread should result in the easier pullout of the ends of such fibres near the surface. This allows greater freedom to these fibres to undergo slight slip and thus rearrange themselves to sustain the applied load thus significantly contributing to the elongation of the thread. On the other hand, the presence of longer and uniform fibre in polyester threads prevents large slippage of fibre ends during tension build-up. The difference in the extent of fibre pull-out can be noticed from Figure 2 and Plate 3. However, the elongation and the toughness of the thread reduces considerably when sewn with fabrics. This can be attributed to the higher loss in the strength of cotton fibres when sewn with fabrics. The occurrence of isolated fibre breaks near the failure point of the thread (Figure 4), confirms this. Conclusions The mechanism of strength reduction of sewing threads has been discussed. The thread strength reduction is found to be the cumulative effect of structural disintegration and loss in fibre strength.

However, the structural openness of the thread, namely, the pull-out of fibres and the displacement of the plies at the thread interlacing point in the stitch have been found to be the dominant factor influencing its strength reduction. This is indicated by the significant reduction in thread modulus and the slippage of fibres in the initial region of the stress-strain curve. The fibre strength reduction has been found to be only marginal as compared to the thread strength reduction. Cotton threads exhibit higher strength loss than polyester threads. Additionally, the study using the computer integrated acquisition of tensile data proves to be a very useful tool to examine fibre slippage during tensile loading and hence to understand the mechanism of tension build-up. It is expected that the above technique will provide greater understanding on the tensile behaviour of plied and cabled structures. References 1. Hari, P.K., Salhotra, K.R., Sundaresan, G. and Chopra, K., “Contribution to garment manufacture: mechanism of sewing thread breakage and seam pucker”, World Textile Conference, University of Huddersfield, Huddersfield, June, 1994. 2. Crow, R.H. and Chamberlain, N.H., The Performance of Sewing Threads in Industrial Sewing Machines, Clothing Institute Technological Report, No. 21, The Clothing Institute, 1969, London. 3. Gersak, J., “Rheological properties of thread: their influence on dynamic loads in the sewing process”, International Journal of Clothing Science and Technology, Vol. 7 No. 2/3, 1995, pp. 71-80. 4. Gersak, J. and Knez, B., “Reduction in thread strength as a cause of loading in sewing process”, International Journal of Clothing Science and Technology, Vol. 3 No. 4, 1991, pp. 6-12. 5. Barella, A., “Law of critical yarn diameter and twist. Influence on yarn characteristics”, Textile Research Journal, Vol. 20 No. 4, 1950, pp. 249-58. 6. Hearle J.W.S., “ Theory of the mechanics of staple fibre yarns”, in Hearle, J.W.S., Grosberg, P. and Backer, S. (Eds), Structural Mechanics of Fibres, Yarns and Fabrics, WileyInterscience, New York, NY, 1969. 7. Hearle J.W.S., “Observed extension and breakage of spun yarns”, in Hearle,J.W.S., Grosberg, P. and Backer, S. (Eds), Structural Mechanics of Fibres, Yarns and Fabrics, WileyInterscience, New York, NY, 1969. 8. Backer, S. and Hsu, P., “Structural mechanics of plied twisted structure with partial frictional constraints”, in Kawabatta, S., Postle, R. and Niwa, M. (Eds), Proceedings of the Third Japan/Australia Joint symposium on Objective Measurement: Applications to Product Design and Process Control, Textile Machinery Society of Japan, Osaka, Japan, 1985, pp. 101-8. 9. Broughton, M., Roy, Jr, Yehia El Mogahzy and Hall, D.M., “Mechanism of yarn failure”, Textile Research Journal, Vol. 62 No. 3, 1992, pp. 131-4. 10. Cooper, G.A., “The fracture toughness of composites reinforced with weakened fibres”, Journal of Material Science, Vol. 5, 1970, pp. 645-54. 11. Kamata, Y., Kinoshita, R., Ishikawa, S. and Fujisaki, K., “Disengagement of needle thread from rotating hook, effects of its timing on tightening tension, industrial single needle lockstitch machine”, Journal of Textile Machinery Society of Japan, Vol. 30, 1984, pp. 40-9.

Strength reduction of sewing threads 345

IJCST 9,5

Coveralls for grass fire fighting Janice Huck and Younghee Kim

346 Received November 1996 Revised July 1997 Accepted August 1997

International Journal of Clothing Science and Technology, Vol. 9 No. 5, 1997, pp. 346-359. MCB University Press, 0955-6222

Department of Clothing, Textiles and Interior Design, Kansas State University, Manhattan, Kansas, USA Introduction In recent years, the public is becoming more aware of the dangers associated with fighting wildland fires, e.g. forest and grass fires. The number of these types of fires in the USA is increasing due to drought conditions, increasing urbanization, and the policies of governmental agencies to suppress wild fires rather than letting them burn. The hazardous nature of wild fire fighting is exemplified by the death of 14 fire fighters who died fighting a wild fire in Colorado in 1994 (Adler et al., 1994). Also, in some rural areas, ranchers and farmers deliberately set fires in the spring of the year to clear the ground of unwanted vegetation and to encourage the development of new vegetation. Too often, these fires get out of control and require the response of fire personnel to contain and extinguish them. Many rural communities depend on the services of a volunteer fire department to respond to both structural and wild fires. The hazards faced by volunteers are shown by the statistics that, of the 88 fire fighter fatalities in the USA in 1995, 50 were volunteers (National Fire Protection Association, 1996). Wildland and grass fire fighting requires specialized clothing and equipment to protect the fire fighter and allow him or her to do the job. The fire fighter may be required to wear flame resistant clothing, carry tools, communication equipment, and perhaps a backpack water container. Many fire fighters in volunteer fire departments who respond to grass fires choose not to wear full turnout gear, but rather flame-resistant coveralls. These coveralls provide a degree of protection from flame and heat, but are less restrictive to movement and less thermally stressful than full turnout gear. These coveralls may be obtained from a variety of sources, from those specifically designed for fire fighting by protective clothing manufacturers to military surplus flight coveralls. The National Fire Protection Agency has recognized the need for standards for protective clothing for wild fire fire fighting, and has developed NFPA 1977, Protective Clothing and Equipment for Wildland Firefighting (National Fire Protection Association, 1977). This standard primarily deals with textile properties, flammability requirements of the fabrics and materials, as well as design and sizing specifications. Although some research has explored the use of alternative fabrics for fire fighter coveralls (Bellingar et al., 1995) and the restriction to mobility that can

occur when protective coveralls are worn (Adams and Keyserling, 1995), no specific research could be found which specifically examined coverall design and fit features. The purpose of this research, therefore, was to use a functional design process approach to develop a coverall for wildland and/or grass fire fighting, with a special emphasis on sizing and proper fit to maximize wearer comfort and mobility, as well as incorporation of design features which would improve the functionality of the garment. Methodology The design process DeJonge (1984) advocated the use of an objective, structured approach for the development of functional apparel to optimize the design solution. An outline of the functional design process that was applied to this study is shown in Figure 1. The general objective of this project was to design and evaluate clothing for grass fire fire fighting that would optimize fire fighter mobility and comfort. The specific tasks associated with grass fire fighting were ascertained, using input from fire fighters familiar with this type of fire fighting and through researcher observation. The literature was reviewed for information regarding anthropometric data for males, thermal regulation of body temperature and clothing interaction variables that affect thermal regulation, and sizing and fit of protective apparel. Appropriate National Fire Protection Association standards were also reviewed. Fire protective clothing currently available on the market was examined, as well as other types of protective coveralls. Based on the problem structure outline, the following design specifications were identified: safety; comfort; wearer acceptance; and production: (1) Safety: The clothing should be designed with wearer safety as a priority. The worker should be safe from exposure to flame and heat and should be able to move in an unrestricted manner. The National Fire Protection Association has set specific fabric and design parameters to minimize exposure to flame and heat; therefore, this research focused on sizing and fit of coveralls to enhance wearer safety and mobility. (2) Comfort: The worker will be most likely to wear protective clothing if it is comfortable. If the clothing is uncomfortable, the wearer may opt not to wear it, particularly in volunteer fire fighting situations where it may be an individual’s prerogative to determine what protective clothing is used. (3) Wearer acceptance: If the clothing meets the psychological needs of the wearer, he or she will be more likely to wear the clothing. These psychological needs include aspects of comfort, appearance, etc. (4) Production: The design should be able to be produced at a cost that can be competitive in the marketplace. Ease of production will influence the cost of producing the garment, and therefore needs to be considered in determining design features. Finally, NFPA standards need to be considered (e.g. seaming techniques, materials requirements, etc.).

Coveralls for grass fire fighting 347

IJCST 9,5

General request Clothing for grass fire fire fighting

Exploration of the design situation General objective

348

●

Review of literature

Design and evaluate clothing for grass fire fire fighting

Problem definition

The design process Grass fire fighting task requirements Fire fighter safety and comfort

● ● ●

● ●

Input from fire fighters Observation

Problem structure perceived Literature search ● ● ●

Anthropometric data Thermal regulation Sizing and fit of protective clothing

User input ●

●

Interviews with volunteer fire fighters Survey of volunteer fire fighters’ clothing needs and usage

Market analysis

Materials analysis ●

Compliance with NFPA 1977

●

Analysis of similar garments on market

Design specifications Safety ● ●

Sizing/fit Mobility

Comfort ● ●

Fit Mobility

Production

Psychological ●

Acceptance

● ● ●

Cost Ease of production Compliance with NFPA 197

Interaction of design criteria established

Prototype development

Figure 1. Functional design process for coveralls for grass fire fighting

Design development Objective analysis ● ●

Range of motion measurement Video analysis

Subjective analysis ●

Semantic differential scale

The design interaction matrix Using the design specifications established for the coveralls, DeJonge’s (1984) technique was used to construct an interaction matrix (Figure 2). This interaction matrix allowed the designers to determine which design specifications were compatible with one another, in conflict with one another, or would require some accommodation to be compatible with each other. As can be seen from this matrix, the thermal comfort of the wearer is in conflict with

1

2

3

4

5

6

7

8

9

2

2

1

0

1

1

1

1

2

2

2

1

2

1

1

1

0

1

0

0

2

Safety 1.

Fabric and notions

2.

Seaming strategies

3.

Body coverage

Size of garment

5.

Thermal comfort

6.

Design features

= 0 = Conflict = 1 =Accommodation = 2 = No conflict

Wearer acceptance 4.

Key

1

2

1

0

2

1

2

2

2

1

1

0

1

Coveralls for grass fire fighting 349

Ease of movement 7.

Range of motion

Production 8.

Cost of production

9.

Ease of production

1

safety; this is unavoidable if the clothing is to meet NFPA standards, as the fabrics and the body coverage of the garment will decrease the wearer’s ability to dissipate body heat. Also, the total body coverage that is desired may negatively affect wearer movement. This conflict can be minimized by proper fit and design features of the garment, and therefore fit and minimization of restriction of mobility were major objectives of the design development process used in this study. Experimental design The research design for this study was a repeated measures design (design X subject). The independent variable was two different designs of coveralls, i.e. the coveralls currently worn by the fire fighter subject; and the redesigned prototype coveralls. The dependent variables were: (1) an objective measurement of range of motion for selected body movements; and (2) wearers’ subjective evaluations of the current and prototype coveralls after completing an exercise protocol that involved various physical movements used in fighting grass fires. Subjects Ten male fire fighters from local area volunteer fire departments participated in the study. All had experience fighting grass fires, and all used coveralls for this type of fire fighting. Their physical characteristics and years of fire service experience are shown in Table I. User input into the design process During an initial visit, each of the ten participating fire fighters was interviewed. The subject was asked to provide input on his level of satisfaction

Figure 2. Interaction matrix for design criteria

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Age (years)

Height cm (in)

Weight kg (lb)

1

54

2

42

3

45

4

29

5

35

6

33

7

41

8

44

9

41

10

29

180.3 (71.0) 180.3 (71.0) 172.7 (68.0) 172.7 (68.0) 177.8 (70.0) 172.7 (68.0) 175.3 (69.0) 167.6 (66.0) 182.9 (72.0) 177.8 (70.0) 176.0 (69.3) 4.7 (1.8)

77.2 (170.0) 85.0 (187.0) 86.6 (190.5) 77.2 (170.0) 113.6 (250.0) 84.1 (185.0) 72.2 (160.0) 75.0 (165.0) 113.6 (250.0) 93.2 (205.0) 87.8 (193.3) 14.9 (32.8)

Subject

350

Table I. Fire fighters’ physical characteristics and fire service experience

Mean

39.3

Std dev.

7.8

Fire service experience (years) 14 11 6 7 9 7 5 1 10 6 7.6 3.6

with his current coveralls, design features he would like to see incorporated into the coveralls, and the types of movements that he perceived as being restricted by his coveralls. Each interview was taped using an audio recorder and transcribed for later review. Each subject was measured for body dimensions that would be needed to develop a coverall pattern. The subject’s body conformation was visually documented by taking front, side and back full-length pictures using a digital camera, with the images transferred to a computer. Also, the current coveralls worn by the fire fighter were examined for design, fabric, and styling features. The subject was asked to don his current fire fighter coveralls over a pair of appropriately sized jeans and T-shirt. He was asked to demonstrate the type of activities he would perform in a grass fire fighting situation. These movements were recorded using a video camera for later review, and served as the basis for development of the exercise protocol used later in the study, as well as giving the designers visual documentation of the restriction to mobility and other design problems with the fire fighter’s coveralls. Design development Using the information derived from initial interviews with fire fighters, the literature review, and examination of similar products on the market, a new

coverall was designed. Since restriction to movement can be largely attributed to improper fit of the garment, each coverall was made specifically to the individual fire fighter’s measurements. Although this is impractical in the current marketplace, it is highly likely that with advancing technology, individually sized garments can some day be cost-effective in the marketplace. Since movement in the crotch area was most often listed as a source of improper fit and restricting mobility, the ease in the crotch area was based on a previous study that determined an optimum amount of ease for the body length of coveralls (Huck et al., forthcoming). The final design is illustrated in Figures 3 and 4. The design features of the prototype coveralls included: • Features to facilitate comfort, mobility and utility: the inclusion of stretch panels in the upper back, the back waist area, and in the leg crotch area to facilitate movement of the trunk, hip and legs; consistent fit of the garment over body measurements (by drafting each pattern to individual measurements); a panel of fabric over the stretch fabric in the upper back, designed to protect the stretch fabric and provide a cushion of fabric for the wearer using a backpack water container; a generously-

Coveralls for grass fire fighting 351

Hook and loop tape Radio pocket

Zipper

Adjustable waist tabs

Inseam pocket Stretch panel

Hook and loop tape

Zipper Hook and loop tape

Figure 3. Prototype coverall (front view)

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Back with overpanel

Back with overpanel not shown

352 Stretch panels

Elastic band

Figure 4. Prototype coverall (back view)

sized inseam hip pocket, with a side seam opening in the coveralls to allow the wearer to access his jeans pockets; a pocket to carry a two-way radio. • Fastening systems: a centre front opening consisting of a zipper and overflap of velcro hook and loop tape; a band collar with velcro hook and loop tape; cuffs with velcro hook and loop tape; lower leg openings with zipper and overflap of velcro hook and loop tape. • Adjustability features: collar size, lower leg, and lower arm size (due to adjustability of velcro closure system); waist adjustability (waist elastic with tabs that could be adjusted to wearer’s preference). Because of the prohibitive cost of using flame resistant materials for the prototype coveralls, a fabric of similar weight and hand to fabrics that would meet NFPA Standard 1977 was used. This fabric was a 50/50 polyester and cotton blend, with a weight of 149.2g/m 2 (4.4oz/yd 2 ). Typically, fabrics commercially used in this type of coverall would be an aramid plain weave fabric with an approximate weight of 203.4-237.4g/m2 (6-7oz/yd2). For certain body measurements, an appropriate amount of garment ease was allowed at specific locations in the coverall (Table II and Figure 5) (Huck et al., forthcoming). The amount of garment ease provided at each location was based on previous research (Huck et al., forthcoming) and researcher experience with garment construction and pattern drafting. The designers’ objective was to

Body measurement

Ease cm (in)

NFPAa cm (in)

Chest circumference

10.2 (4.00) 5.1 (2.00) Variableb Variableb 5.1 (2.00) 15.2 (6.00)

–

Back waist length Waist circumference Hip circumference Crotch depth Vertical trunk circumference

Coveralls for grass fire fighting

– – – –

353

25.4 (10.00)

Notes: a NFPA standard 1977; recommended minimum ease for one-piece custom made garments b The ease at this body location was variable since the side seam of the garment was a straight line drawn from the underarm/sideseam intersection to the waist and then with a slight angle from the waist to the hem; the amount of ease was therefore controlled by the subject’s chest circumference measurement

provide a coverall sized for maximum wearer comfort and mobility, and yet not have the coveralls so oversized as to decrease comfort and/or mobility. Using a combination of computer-aided and hand drafting, a pattern for the prototype coveralls was developed for each subject. All coveralls were sewn using consistent and appropriate construction techniques. Prototype evaluation Wearing jeans and T-shirt, the subject donned his current coveralls. Using a digital camera and computer software, several range-of-motion movements were recorded (see Figure 6). A “picture” was taken with the subject in the initial position. The subject was then asked to move to the second position (which was the range of motion possible). A “picture” of this second position was then taken. Each range of motion movement was repeated and photographed three times. This protocol was repeated with the subject wearing the prototype coveralls over jeans and T-shirt. The subject was then asked to complete an exercise protocol twice, once wearing his current coveralls and once wearing the prototype coveralls over jeans and T-shirt (order was randomized between subjects). The exercise protocol included representative tasks which had been identified and selected from the initial interviews. After completing each exercise protocol, the subject was asked to fill out a subjective evaluation scale to determine his perception of fit and mobility while wearing the coveralls (Table III). Results and discussion Range of motion (ROM) The digital photographs of each subject in the beginning and ending positions for each ROM movement were stored in the computer. Using Hijaak computer

Table II. Amount of garment ease for selected body measurements

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Chest circumference

354 Chest level Back waist length Vertical trunk circumference (back)

Waist level

Crotch depth

Vertical trunk circumference (front)

Hip level Crotch level

Back pattern

Front pattern

Figure 5. Prototype coverall pattern

software and an angle measuring function included in the software, the difference between the first and second positions (in degrees) was calculated. Table IV shows the mean range-of-motion (in degrees) for the ten movements. The prototype coveralls allowed greater freedom of movement for all movements, ranging from +3.8 to +28.7 per cent. The increase in range of motion for the wearer associated with the prototype coveralls was due to a combination of two factors: design features which enhanced wearer mobility (e.g. stretch panels); and appropriate ease in the garment due to customization of fit. The greatest increases in range of motion for the prototype coveralls were for the sitting trunk flexion (+28.7 per cent), hip flexion/extension (knee, +10.8 per

Coveralls for grass fire fighting 355 a

b

f

c

g

j

d

e

h

i

Range of motion measurements (solid lines indicate initial position; dotted lines indicate second position) a. shoulder abduction/adduction b. shoulder flexion/extension c. trunk flexion (standing) d. trunk flexion (sitting) e. trunk lateral flexion f. hip flexion/extension (knee) g. hip flexion/extension (trunk) h. hip adduction i. upper leg adduction j. upper leg flexion

cent) and hip flexion/extension (trunk, +10.1 per cent). It is assumed that the stretch panels in the back of the coveralls were largely responsible for the increases in range of motion, as these panels can stretch to allow the wearer to move freely. Also, proper fit will enhance wearer movement. The increase in hip adduction, upper leg flexion, and upper leg adduction in the prototype coveralls is also probably due, in part, to the inclusion of stretch panels in the crotch area of the legs. Based on previous research, these increases in ROM are also probably partially attributable to a good fit in the torso length of the prototype coveralls to the wearer (Huck et al., forthcoming). In grass fire fighting situations, where climbing over fences and other obstacles, walking, and bending are key movements the fire fighter has to accomplish, the less restriction to mobility provided by the prototype coveralls is highly desirable. The stretch panels in the upper back also allowed for some increases in range of shoulder movement (i.e. shoulder abduction/adduction, 3.9 per cent, shoulder flexion/extension, +0.9 per cent). These slight increases might not translate into

Figure 6. Range of motion measurements

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356

Place a tick in the blank at the location that best describes how you feel: Comfortable 9 a 8 7 6 | 5 | 4 3 2 1 Uncomfortable Acceptable 9 8 7 6 | 5 | 4 3 2 1 Unacceptable Tired 9 8 7 6 | 5 | 4 3 2 1 Rested Place a tick in the blank at the location that best describes the clothing you are wearing: 9 8 7 6 | 5 | 4 3 2 1 Stiff Flexible Easy to put on 9 8 7 6 | 5 | 4 3 2 1 Hard to put on Freedom of movement of arms 9 8 7 6 | 5 | 4 3 2 1 Restricted movement of arms Easy to move in 9 8 7 6 | 5 | 4 3 2 1 Hard to move in Satisfactory fit 9 8 7 6 | 5 | 4 3 2 1 Unsatisfactory fit Freedom of movement of legs 9 8 7 6 | 5 | 4 3 2 1 Restricted movement of legs Freedom of movement of torso 9 8 7 6 | 5 | 4 3 2 1 Restricted movement of torso Like 9 8 7 6 | 5 | 4 3 2 1 Dislike Loose 9 8 7 6 | 5 | 4 3 2 1 Tight Place a tick in the blank at the location that best describes how you can move in the coveralls: Walking 9 8 7 6 | 5 | 4 3 2 1 Hard to do Easy to do Stepping on to a table Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Jumping off a table Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Pumping motion Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Bending torso back and forth Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Spreading arms out Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Sweeping motion Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Squatting Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Raking motion Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Toe touches Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do Crawling Easy to do 9 8 7 6 | 5 | 4 3 2 1 Hard to do

Table III. Wearer acceptability scale

Note: *Numbers added for reader reference only; a “9” indicates the best possible rating; a “1” indicates the poorest possible rating

much improvement, however, over the current coveralls in actual wearing situations. The water backpack that fire fighters often wear in grass fire fighting situations will also restrict arm movement, no matter what the coverall design. Therefore, the slight increases in ROM provided by the prototype coveralls may not be as important as those involving leg and torso movement.

Range of motion measurement Shoulder abduction/adduction Shoulder flexion/extension Trunk flexion/extension (standing) Trunk flexion (sitting) Trunk lateral flexion Hip flexion/extension (knee) Hip flexion/extension (trunk) Hip adduction Upper leg adduction Upper leg flexion Mean

Mean Mean value value prototype current coveralls coveralls (degrees) (degrees) 131.6 190.6 131.3 30.6 68.0 70.1 81.0 52.9 47.1 83.2

136.7 192.4 143.9 39.4 70.9 77.7 89.2 58.1 49.7 86.4

Change prototype coveralls from current coveralls (per cent) 3.9 0.9 9.6 28.8 4.3 10.8 10.1 9.8 5.5 3.8 9.2

Overall, the range of motion in the prototype coveralls was increased an average of about 9 per cent over the coveralls currently worn by the fire fighters. Wearer acceptability After completing the exercise protocol in both the current and prototype coveralls, the subjects were asked to complete a Wearer Acceptability Scale (Table III). The mean values of the scores (ranging from a possible “1” to “9”) were tabulated. The results are presented in Table V. For all adjective sets, the prototype coveralls were preferred to the current coveralls. The most significant differences were for adjective sets of “flexible/stiff”( +32.8 per cent), toe touches (“easy to do/hard to do”) (+31.7 per cent), “loose/tight” (+30.9 per cent), and squatting (“easy to do/hard to do”) (+29.7 per cent). As can be seen from Table V, it is apparent that the prototype coveralls were preferred to the current coveralls, and the magnitude of the preference for the prototype coverall is probably greater than can be attributed to the novelty effect. Based on these results, it is probable that fire fighters would find the prototype coveralls more comfortable and acceptable to wear than their current coveralls in actual wearing conditions. The design features incorporated into the prototype coveralls would probably increase production costs, since additional materials (e.g. stretch fabrics) and additional production time (e.g. sewing in the leg gussets and addition of a radio pocket). The increased production costs would result in a garment that is probably more expensive to purchase than current coveralls on the market; however, the large increases in wearer satisfaction would perhaps indicate that fire fighters would be willing to pay the additional costs. Also, the customization of sizing is an issue that must be addressed for production to be feasible of this prototype coverall. With the aid of a computer program that partially drafted the coverall pattern to specific measurements,

Coveralls for grass fire fighting 357

Table IV. Range of motion measurements

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358

Table V. Wearer acceptability scale results

Flexible/stiff Toe touches (easy to do/hard to do) Loose/tight Squatting (easy to do/hard to do) Stepping on to table (easy to do/hard to do) Freedom of movement of legs/restricted movement of legs Satisfactory fit/unsatisfactory fit Bending torso (easy to do/hard to do) Easy to move in/hard to move in Spreading arms (easy to do/hard to do) Freedom of movement of torso/restricted movement of torso Jumping off table (easy to do/hard to do) Crawling (easy to do/hard to do) Freedom of movement of arms/restricted movement of arms Easy to put on/hard to put on Tired/rested Comfortable/uncomfortable Raking motion (easy to do/hard to do) Pumping motion (easy to do/hard to do) Sweeping (easy to do/hard to do) Like/dislike Walking (easy to do/hard to do) Acceptable/unacceptable Total

Mean value current coverallsa

Mean value prototype coverall

Change prototype coveralls from current coveralls (per cent)

6.4 6.3 5.5 6.4 6.7

8.5 8.3 7.2 8.3 8.5

32.8 31.7 30.9 29.7 26.9

6.6 6.3 6.9 6.8 7.2

8.3 7.8 8.5 8.3 8.7

25.8 23.8 23.2 22.1 20.8

7.0 7.4 7.3

8.4 8.8 8.4

20.0 18.9 15.1

7.1 6.0 6.8 6.8 7.8 8.0 8.0 7.2 8.2 7.8 160.5

8.1 6.8 7.6 7.6 8.7 0.8 8.6 7.7 8.7 7.9 188.5

14.1 13.3 11.8 11.8 11.5 –90.0 7.5 6.9 6.1 1.3 17.4

Note: A “9” was the best possible rating; a “1” was the poorest possible rating

a

the pattern was not time-consuming to produce. Many other types of garments (e.g. men’s suits) are more or less custom fit to body measurements and, with current technology, single layers of fabric can be cut using computer-generated cutters efficiently. With increasing technology, it may soon be feasible to be able to custom fit protective garments to the wearer. Even if garments cannot be precisely controlled for fit as they were in this research, it is important that coveralls with limited sizing be carefully fit to maximize wearer comfort and mobility. The amounts of ease incorporated into the prototype coveralls may provide information to those purchasing and wearing coveralls, as they compare their body measurements to garment measurements of coveralls to maximize fit. Also, the incorporation of design features, such as the stretch panels, may allow a coverall to more adequately fit a variety of body types, even though the garment may not be custom fit to the wearer.

Conclusions The purpose of this research was to design a coverall for fire fighting, with a special emphasis on sizing and proper fit to maximize wearer comfort and mobility as well as incorporate design features which would improve the functionality of the garment. Using a structured design approach, a prototype coverall was developed. The prototype coverall was evaluated using objective measurements of range of motion for ten selected body movements and subjectively by having wearers fill out a wearer acceptability scale to determine their perceptions of fit and comfort in both their current and prototype coveralls. For all measurements, the prototype coveralls were preferable to the current coveralls worn, indicating the potential for further development of this design. It should be noted that, since the fabrics used in this study were lighter in weight and slightly different in hand and stiffness from fabrics used in actual coveralls, some results may be due to fabric, rather than design. Further research is needed, particularly in a field situation. The prototype coverall needs to be evaluated in actual wearing conditions, i.e. grass fire fighting situations. Based on such field study and evaluation, it is anticipated that some design and fit features might need to be modified to maximize the design. References Adams, P.S. and Keyserling, W. (1995), “The effect of size and fabric weight of protective coveralls on range of gross body movements”, American Industrial Hygiene Association Journal, Vol. 56, April, pp. 333-40. Adler, J., Springen, K., Keene-Osborne, S., King, P. and Woodruff, D. (1994), “Blowup”, Newsweek, 18 July, pp. 28-31. Bellingar, T., Shanley, L.A., Slaten, B. and Brady, P. (1995), “Use of carbonaceous fiber in wildland firefighter protective clothing”, Safety and Protective Fabrics, Vol. 4 No. 2, March-April, pp. 20-4. DeJonge, J.O. (1984), “Forward: the design process”, in Watkins, S.M. (Ed.), Clothing: The Portable Environment, Iowa State University Press, Ames, IA, pp. vii-xi. Huck, J., Maganga, O. and Kim, Y., “Protective coveralls: evaluation of garment design and fit”, (forthcoming), International Journal of Clothing Science and Technology. National Fire Protection Association (1993), NFPA 1977, Standard on Protective Clothing and Equipment for Wildland Fire Fighting, ANSI/NFPA 1977, 20 August. National Fire Protection Association (1996), “Less than 100 firefighter fatalities in 1995; third decline in last four years”, http://www.wpi.edu/Acade.../NFPA/newsrelease.html#2, pp. 2-3.

Coveralls for grass fire fighting 359

IJCST 9,5

Mechanical stability of fused textile systems M. Gutauskas and V. Masteikaite

360 Received May 1996 Revised and accepted July 1997

International Journal of Clothing Science and Technology, Vol. 9 No. 5, 1997, pp. 360-366. © MCB University Press, 0955-6222

Kaunas University of Technology, Kaunas, Lithuania Introduction Fusing technology such as a thermoplastic adhesive bond between face fabric and interlining is well known in clothing industry. Many adhesive compositions are used in the fusing process. Polyamide and polyethylene covering dots or coating the surface of the interlining are most suitable for this purpose. Heat and pressure used in the fusing process leads to the flow of thermoplastic material into the cross-section of face fabric and interlining. Thus, the stiffness of the fused textile system is always considerably greater than the sum of the individual fabric’s stiffness. So, it is to be expected that this textile system is more breakable, brittle and unstable. Numerous factors have an effect on the stability of the fusing system while a garment is being worn. One of these is mechanical action. Any loss in bond strength in the fusing system during wear will influence a garment’s quality. Object and method of investigation The aim was to study the feasibility of the application of two original instruments – ERDT-3[1] and ARRV[2,3] – for the evaluation of the mechanical stability of the adhesive layer between two panels of fabric. The schematic presentations of these instruments are shown in Figures 1 and 2. The tests were based on the dynamic fatigue of fused textile systems. It is possible to obtain biaxial tension of the specimen in two ways using the pneumatic pulser ERDT-3. They are one-sided loading and double-sided loading (Figure 1). The circular specimen (1) with working surface area 100cm2 was fixed in the vertical position around its perimeter between two hermetic chambers (2) and (3) which are connected with block of control distribution (5) and compressor by the tubes (4). The pulser ERDT-3 is worked under constant amplitude of pressure. The limits of pressure amplitude (p = 0.06-0.005MPa) are controlled by special sensing elements. The velocity and character of the loading and unloading area are regulated by constriction. In one-sided loading, the specimen pulsated only in one chamber and the size of its formed membrane changed. In the case of the double-sided loading specimen both chambers fill out in succession. At the moment of removing from one chamber to another the specimen shrinks and a popping sound is heard. In every loading cycle the bend of the specimen increases according to the exponential curve in condition when pmax = const, pmin = const. Besides the repeated uniaxial loading the specimen also experiences surface abrasion in the rotary-rolls instrument ARRV (Figure 2). Two rectangular

2

3

Mechanical stability of fused textile systems

1

361 4 Compressed air supply

Figure 1. Schematic view of pneumatic pulser ERDT-3

5

1

2

4

3

7

5

6

8

specimens (7) (150 × 60mm) were fixed vertically in the frames (8) by the upper and lower ends without tension. During the test they were repeatedly acted by two rolls (4) (∅ 40mm), which receive rotation frequency 2.0Hz from the rotor (1) (∅ 105.8mm). The movement of the polished steel rolls (4) on the specimens (7) is determined by the position of tooth-wheels (5, 6) (I = 3.5) and fastening bolts (3). This movement can be carried out in three ways:

Figure 2. Working zone of rotaryrolls instrument ARRV

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(1) rolls free rotation about axle (2) (rolls are rolled across the surface of the specimen); (2) rolls are reinforced with axle (2) (rolls are slipped across the surface of the specimen with the velocity ν = 0.9m/s); (3) rolls have additional rotations to the direction of rotary (1) movement (the surface of the specimen is “scraped” by the rolls with the velocity ν = 1.8m/s)[3,4]. The distance used between specimens was 110mm. In this case the degree of relative deformation was obtained 2.7 per cent. It is possible to change the distance between specimens within the limits of 60-140mm. The instrument ARRV allows provision for unequal loading along the upper and lower parts of the specimen (Figure 2). It was expected that after the fatigue process the structure of the adhesive layer will change and the bond strength between the face fabric and interlining will decrease gradually. In addition, these findings should depend on the conditions of fatigue and deformation of the textile systems. The experiment was carried out with fabrics for suits with a weight range 205-272g/m2: A, C (warp-knitted, 100 per cent PE), P (2/2 twill, 45 per cent wool, 55 per cent PE), W (plain woven, 55 per cent wool, 45 per cent PE); fabrics for overcoats with weight range 303-486g/m2: B (2/2 twill weave, 50 per cent wool, 13 per cent PA, 37 per cent viscose), M (2/2 twill weave, 42 per cent wool, 58 per cent acrylic), D (plain woven, 72 per cent wool, 28 per cent acrylic), E (sateen wave, 50 per cent wool, 50 per cent viscose); shirting fabric R with weight 125g/m2 (plain woven, 100 per cent cotton) and interlinings L (weight 160g/m2, plain woven, 100 per cent cotton, polyethylene coating), K (weight 120g/m 2, plain woven, 100 per cent viscose, polyamide dots). The interlinings were fused with face fabrics (warp to warp) on a flatbed press machine. The fusing parameters were: temperature T = 150°C, time τ = 20-40s, pressure p = 0.1-0.02MPa. Results and discussions It is known that the bond strength of fused systems is one of the most important parameters which greatly influence the quality of a garment. During the fusing process the adhesive dots change their geometrical shape. It was determined[5] that after the fusing process the polyamide dots have changed their crosssection in 46 per cent of cases when the pressure was 0.02MPa and in 96 per cent, when p = 0.1MPa. The cross-section of the adhesive point was determined by biological microscope with micrometer. For this test one layer of thermal resistant transparent film fused with other layer of fabric covered with adhesive dots was used. As the dots have an irregular circle shape the cross-section of every dot was measured in four directions by turning the micrometer every 45°. For a different kind of specimen (unfused and fused under p = 0.02MPa and p = 0.1MPa) the 80 measurement values were average. Evidently, degree of changes in geometry of adhesive dots depends not only on fusing conditions but also on

the properties of the fused fabrics. If the substrate is soft and spongy, the Mechanical starting shape of the dots will be changed noticeably than in the case of the flat stability of fused and close substrate. In this second case the adhesives are more brittle and less textile systems stable under the mechanical effect. The following conclusion was based on the bond strength decrease in textile systems after their fatigue (Tables I and II). The bond strength of the textile systems was determined by dynamometer 363 using a specimen sized 100 × 20mm. The velocity of separation of the interlinings from the face fabric was 100mm/min. The 70 measuring values were averaged for every type of system. The textile systems presented in Table I had the impermeable adhesive coating. Evidently under OI fatigue the decreases in bond strength of the textile systems are 3-3.5 times less than under OF fatigue. This is because in the OF fatigue air flow penetrates through the face fabric, reaches the adhesive layer and bends it. The interlining is torn out of the face fabric under the air flow. The tension appears in the adhesive layer and the repeated pulsating process leads to the gradual failure of bond strength. On the contrary, the interlining itself has System and initial bond strength, N/cm A+L 3.96 B+L 6.34

Type of fatigue

Decrease in bond strength (%)

Relative error (%)

OI OF TS OI OF TS

22.8 72.8 63.0 23.6 67.0 48.3

4.4 3.8 5.4 3.2 7.4 8.4

Notes: OI = one-sided loading when the interlining is affected with air flow. OF = one-sided loading when the face fabric is affected with air flow. TS = double-sided loading. Testing conditions of fatigue: frequency 1.0Hz, duration 16.67min (OI and OF = 1,000 cycles, TS = 500 cycles), air flow pressure p = 0.06-0.005MPa

Fusing pressure, MPa 0.02 0.06 0.10

Textile system

Initial bond strength N/cm

Bond strength decrease (%)

M+K Z+K M+K Z+K M+K Z+K

3.84 3.68 4.88 3.70 5.84 4.64

29.2 23.9 0 33.7 9.6 34.5

Notes: Double-sided fatigue was used with instrument ERDT-3. Testing conditions: p = 0.06-0.005MPa, n = 1,000 cycles, frequency = 1.0Hz

Table I. Changes in the separation force of fused systems after fatigue

Table II. Dependency between systems bond strength and fusing pressure

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contact with the air flow during OI fatigue. So, it bends and pushes out the other component of the system (face fabric) and at the same time the tangential tension in the system appears. In this case, mechanical destruction is less evident. During the double-sided fatigue test (TS) the decrease in bond strength of the textile systems is intermediate. In addition, it was obtained that 1/2 (OI + OF) ≅ TS. It should be noted that in the double-sided fatigue process the specimen undergoes instantaneous relaxation. So, it was expected that such type of fatigue causes less cycle deformation than OF fatigue. Table II represents the instability results of those textile systems (covering of polyamide dots) where tensile modules of layers varied in ratio M:K ≅ 1:4 and Z:K ≅ 1:1. It is clear from Table II that higher pressure allows to obtain greater bond strength of textile systems. It was found, that the repeated cycle of pressing also leads to an increase of bond strength in specimens (Figure 3). The increase in bond strength between layers means that every additional pressing cycle changes the degree of penetration of the adhesive dots into the structure of the material. Thus a deeper and bigger contact area was obtained. It can be noted that less decrease in bond strength is observed under a medium pressure (0.06MPa) for a textile system having a ratio of layers tensile module 1:4 (M + K) and for a system with equal layers tensile module (Z + K) under light pressure (0.02MPa). These results show that textile systems with similar stiffness layers are more sensitive to fatigue. Since the stability of a textile system depends not only on its initial bond strength it is also necessary to appreciate its tensile modules. The influence of the different testing conditions using instrument ARRV on the stability of textile systems is presented in Table III. It is clearly seen that in conditions I the decrease in the bond strength of the textile systems is less than in conditions III. Further it should be noted that the abrading interlining surface leads more rapidly to the decrease of bond strength (67.0 per cent) than in the process of thick soft face fabric abrasion (31.8 per cent). The reason for the additional bond strength decrease during test conditions II and III was the appearance of shear phenomenon between layers.

P, N/cm 15 10 5 Figure 3. Dependence of pressing cycles on bond strength of textile system W + K

0 0 n

1

2

3

4

5

6

The analysis of the fabric’s surface texture made after abrading shows the same Mechanical correlation between conditions using instrument ARRV and amount of shake- stability of fused down of the surface fibres[4]. textile systems It was observed experimentally that for the same interlining and in the same fusing conditions the decrease of bond strength depends on the duration of fatigue, thickness and tensile modules of the face fabric (Table IV).

365

Testing conditions I II III

Abrading surface of system

Bond strength after fatigue, N/cm

Bond strength decrease (%)

Face fabric Interlining Face fabric Interlining Face fabric Interlining

5.5 6.4 5.1 5.8 4.9 2.4

24.1 ± 6.3 11.7 ± 1.6 30.3 ± 4.9 20.7 ± 6.1 31.8 ± 4.6 67.0 ± 6.2a

Notes: The initial bond strength = 7.3N/cm. aThe interlining in the centre of the specimen was rubbed off

Face fabric

System layers

For suit For overcoat aFor overcoat

C+L D+K D+K

For overcoat For suit aFor suit

E+K P+K P+K

For shirt

R+K

Fatigue duration h 1.0 1.0 0.25 0.5 1.0 1.5 3.0 0.5 0.5 0.25 0.5 1.0 1.5 3.0 0.5

Layers Layers tensile thickness modules mm N/mm2

Table III. Changes in bond strength of textile system M + K after fatigue process using instrument ARRV

Bond strength Lost after Initial effect on face N/cm fabric (%)

0.9 + 0.27 1.9 + 0.45 1.9 + 0.45

0.20 + 4.0 0.36 + 6.54 0.36 + 6.54

2.80 5.44 9.28

2.0 + 0.45 0.5 + 0.45 0.5 + 0.45

0.26 + 6.54 9.7 + 6.54 9.7 + 6.54

7.36 2.00 2.36

0.35 + 0.45

3.1 + 6.45

2.72

77.0 67.3 20.0 28.8 46.5 62.9 85.0 45.5 68.1 0.0 12.8 23.8 47.5 60.1 87.3

Notes: Tensile modulus, in force per unit area, was determined from load/extension curves, when Table IV. extensibility ε = 6.2 5%. This rate of deformation corresponds to the degree of specimen Decrease of bond deformation during its fatigue. The thickness and tensile modulus were determined from initial strength after fatigue unfused fabric state. Fabric thickness was measured at 5gf/cm2 pressure force with 0.01mm process using resolution. The specimen size for tensile tests was 50mm wide instrument ARRV aFusing conditions of these systems were more severe (duration of pressing was increased two (testing conditions, times τ = 20s and τ = 40s). The specimen’s warp direction was oriented vertical representative quantities)

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It was found that changes of bond strength for systems* and duration of fatigue process approximately exhibits an exponential relationship. The characters of these curves can be expressed in the following form: PD+K(t)* = 28.7exp 0.42 ⋅ t; PP+K(t)* = 13.0exp 0.61 ⋅ t. where t is duration of fatigue, h, (correlation 0.93 and 0.90, respectively). It should be ascertained that in the first 15 minutes of the fatigue process the decrease of bond strength in stiffener systems (with suit face fabric) is not so noticeable as in the case of the soft system (with overcoat face fabric). The presented data was calculated by a computer program applying the Augo method and Kolrausch equation. Conclusions The following three conclusions can be derived: (1) The original models of instruments which enables simulation of some clothes wearing conditions were found and may be easily adopted to estimate the mechanical stability of fused materials. (2) The relations between fusing conditions, fabrics properties, adhesive line texture and instability of textile systems in mechanical treatment were determined. (3) It was shown that an increase in pressure or amount of pressure cycles leads to the formation of comparatively strong initial bond strength in textile systems but these become unstable after mechanical treatment. References 1. Gutauskas, M., Kudakaite, P. and Sakalauskaite, D., “Rasshirenye Funktsionalnikh Vozmozhnostey Priborov dlya Ispytanya Ploskykh Materialov Dvukhosnym Nagruzhenyem, Tekhnologya Tekstilnovo I Kozhevenovo Proyzvodstva” (Expansion the Functional Possibility of Instruments for Testing Flat Fabrics under Bi-axial Loading), Technology of Textile and Leather Production, X, Vilnius, 1981, pp. 38-41. 2. Henno, I. and Jouhet, R., “Appareil destine a la mesure du pochage des tissus elasstiques”, Bull. ITF, Sa, Vol. 22 No. 135, pp. 281-4. 3. Patent of USSR No 1104386, “Ustroystvo dlya Tsiklicheskovo Nagruzhenya Ispytuyemovo obraztsa” (The Apparatus for Cyclic Loading of Test Specimen), Int.Cl. G01N 3/34; G01N 3/56, 1983. 4. Panasiuk, L. and Gutauskas, M., “Otsenka Izmenenyj Prochnosti Klejevovo Soyedinenya Dublirovanoy Systemy pri Mekhanicheskom Utomlenii, Izvestya Vuzov, Tekhnologya Lekhkoy Promyshlennosty” (The Estimation of Bond Strength Change in Fusing Systems after Mechanical Fatigue), Technology of Light Industry, Kyev, No. 4, 1984, pp. 18-21. 5. Gutauskas, M., Masteikaite, B. and Petrauskas, A., “O Vybore Rezhima Dublirovanya Tkaney Verkha Prokladochnymi Klejevymi Materialami, Shveynaya Promyshlennost” (The Choice of Fusing Conditions for Face Fabrics and Interlinings), Clothing Industry, Moscow, No. 1, 1981, pp. 27-8.

Communications

Communications

An object-oriented model of apparel pattern making Thong-Hwee Koh and Eng-Wah Lee Gintic Institute of Manufacturing Technology, Singapore and

Yong-Tsui Lee

367 Received July 1995 Accepted May 1996

School of Mechanical and Production Engineering, Nanyang Technological University, Singapore Introduction Apparel pattern making is the process of transforming three-dimensional (3D) fashion designs into their two-dimensional (2D) constituent pattern pieces. Pattern pieces are flat irregular shapes that represent a piece of garment in sections. They contain information like seam and hem allowances, grainline, size, balance marks, placement for buttons, buttonholes, pockets, etc. (Kopp et al., 1982) To realize a working garment, the pattern-making process needs to be constantly iterated through three steps: fashion analysis, pattern design and pattern drafting. These iterations result in changes to the basic blocks or secondary pattern pieces before arriving at the final pattern pieces (Koh, 1994). Basic blocks are the plain, flat, outlined shapes that closely represent the respective parts of the human figure, while secondary pattern pieces are those basic blocks that have been refined to produce specific shapes but yet are adaptable for further designing through the addition of more fashion details. The ultimate objective of this work is the design and development of a computer-aided apparel pattern-making system (Koh, 1994). In order to do that, it is necessary to analyse and model the different aspects of the pattern-making process. This paper presents the results of this analysis and proposes an object oriented (OO) model. The model is defined as a requirement specification and is described in terms of: its required behaviour, the objects present in it and how they are organized, the primary behaviour and the life cycle of each object, and the sequence of activities in the model (Gibson, 1990). It is thus a sequence of interactions of active objects that provides the required behaviour of the overall process. This pattern-making model is an initial model as the work focused on specifying the major aspects of the process. However it will provide the basis for further studies and evaluations on the other aspects of apparel patternWe wish to thank Professor Ding-Yuan Liu and Professor Jia-Ye Wang of Gintic Institute of Manufacturing Technology and Mr Masjuri bin Maswan of the Institute of Technical Education, Singapore, for their input to the work reported in this paper.

International Journal of Clothing Science and Technology, Vol. 9 No. 5, 1997, pp. 367-379. © MCB University Press, 0955-6222

IJCST 9,5

making, so that a complete understanding of it can eventually be achieved. Section 2 of this paper presents the behaviour of the pattern-making model. Section 3 examines the objects present in it and how they are organized. Sections 4 and 5 provide examples on the primary behaviour and the life cycle of the objects respectively. Section 6 studies the sequence of activities present in it.

368

Object behaviour analysis The object behaviour analysis (OBA) method (Gibson, 1990) develops a conceptual model of the process as performed in apparel mass manufacturing. It creates a hierarchy of objects, each with its own unique behaviour that is an abstraction of the corresponding object in the real world. An object, for the purpose of computer-aided design (CAD), is a collection of attributes that describe some physical or abstract entity that can be computationally represented and operated on. These attributes include the shape of the object and the pertinent non-shape information that is used by applications that require the model, such as material, cost and function (Kalay, 1989). The behaviour of each object specifies its responsibilities, i.e. what it is supposed to do. Through these objects, their relationships and interactions with each other are modelled, and similarly the behaviour of the whole system. The model obtained through OBA uses the existing heuristic rules of pattern making that are the design rules for developing coherent pattern pieces given a particular set of fashion design requirements. This is in contrast to the current investigations on the bijective map approach where the mathematical functions for the transformation of a 3D garment to 2D pattern pieces are being researched (Hinds et al., 1992; Okabe et al., 1992; Ng et al., 1993). The significance of this OO model is also enhanced as it is independent of the implementation platform. Behaviour of the pattern-making model The required behaviour of the pattern-making model can be viewed in terms of the subprocesses of fashion analysis, pattern design and pattern drafting. Behaviour of fashion analysis The initial process of fashion analysis seeks to classify appropriately any new fashion illustration into the correct type of garment and its fashion features (Figure 1). In so doing, the set of pattern-making rules for that particular garment type is used to determine a close intermediate style (Koh, 1994). This intermediate style is subsequently divided into garment sections whose secondary pattern pieces are known. The exact nature and locations of those new fashion features are then determined with respect to these garment sections. Hence pattern making consists of identifying the type of garment, the fashion features for the new design and the locations of these features on the garment. Furthermore, this fashion design specification is accompanied by the size specification, which lists the key physical dimensions for that garment. This size specification comes from either the apparel buyer or the mass manufacturer.

New fashion design

Close immediate style

+

Fashion features

Garment section

Secondary pattern-pieces

herefore

New fashion design

Secondary pattern-pieces

+

Fashion features

= Modified patternpieces

  

Communications

Fashion analysis

369

Pattern design

Pattern drafting

Figure 1. The apparel patternmaking process

There is an inherent structure behind these input specifications as seen in Figure 2. It also shows an example for a cross pocket opening fashion feature on a pair of jeans. The aim of this initial stage is thus to elicit inputs to this specification. Behaviour of pattern design Identifying a suitable garment type for the new fashion illustration enables its subdivision into garment sections that determine the appropriate secondary pattern pieces (or even the basic blocks) to be used as the starting-point in pattern design (Figure 3). The nature of the fashion features on the illustration then describes the final shapes of these pattern pieces and specifies any additional (or attachment) pattern piece needed (Koh, 1994). Moreover, the locations and sizes of these features determine exactly how the secondary pattern pieces are to be modified into the final pattern pieces. Figure 4 shows an example that is a continuation from the cross pocket opening feature shown in Figure 2. Many levels possible Physical dimensions Garment category

Garment type

Garment subtype

Garment section

Fashion feature type

Fashion feature subtype

Fashion feature

Example: Size specs Men’s wear

Pants

Jeans

Front panel

Pocket

Pocket opening

Cross pocket opening

Figure 2. Structure of the patternmaking input specification

Many levels possible

IJCST 9,5

Physical dimensions Garment category

Garment type

Garment subtype

Fashion feature type

Garment section

Fashion feature subtype

Fashion feature

370 Secondary pattern piece

Figure 3. Determination of secondary pattern pieces and attachment pattern pieces

Determine secondary pattern piece to use

Secondary pattern piece modifications + Attachment pattern pieces

Determine fashion features required

Specifically for each garment section identified, a corresponding set of patternmaking rules is used to determine its main pattern piece according to both its secondary pattern piece and its physical dimensions given in the size specification (Figure 5). This type of rules, named pattern drafting rules, uses all the basic blocks and the secondary pattern pieces as design templates. Cut

Fashion feature

Front panel basic block Pocket facing pattern

Pocket edge facing pattern

Pocket bag pattern

Additional pattern pieces Example: Size specs Men’s wear

Figure 4. Jeans’ cross pocket opening fashion feature and its resultant pattern pieces

Pants

Jeans

Front panel

Front panel pattern piece

Pocket

Pocket opening

Cross pocket opening

Cross pocket opening on front panel pattern piece + Pocket facing pattern piece Pocket edge facing pattern piece Pocket bag pattern piece

However, the garment section also contains fashion features which give rise to Communications two other types of pattern-making rules needed for implementing them. One type, named pattern modification rules, is used to modify further the shape and size of its main pattern piece (Figure 6).

Size specification

Secondary pattern piece Get

Garment section

Invoke

Get

Pattern making rule

Garment section

Contain

Design

Final pattern piece

Modify

Figure 5. Pattern drafting rule initially determines the pattern piece

Fashion feature Invoke

Final pattern piece

371

Patternmaking rule

Figure 6. Pattern modification rule modifies the pattern piece for fashion feature

The other type, named pattern compatibility rules, is used to design any attachment pattern piece required with the necessary shape and size information from that main pattern piece – to ensure physical compatibility between them (Figure 7). Therefore, there are three types of pattern-making rules. An example is seen in Figure 4 where a pattern drafting rule initially determines the front panel pattern piece. A pattern modification rule then cuts a pocket opening from it,

Garment section

Contain

Fashion feature Invoke

Final pattern piece

Get attachment info

Patternmaking rule Design

Final attachment pattern piece

Figure 7. Pattern compatability rule designs the attachment pattern piece for fashion feature

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while three separate pattern compatibility rules design the three attachment pattern pieces.

372

Behaviour of pattern drafting When all the pattern pieces have been designed for a whole garment, the last stage of pattern making is their drafting as a set of finalized pattern pieces (Figure 8). Final pattern piece

Draft

Drawing

Figure 8. Drafting the final pattern pieces

Final attachment pattern piece

Draft

Organization of the pattern-making objects In building the system model of the apparel pattern-making process, the various types of objects found in the real world need to be identified. For example, as depicted in Figure 9, “Fashion design” type object is made up of “Illustration” type, “Size spec” type and “Final pattern piece” type objects. A new fashion design is created in the manufacturer’s database when a buyer comes with a fashion illustration. A size specification is then defined for it either by the buyer or the manufacturer himself. It is from both these specifications that the results of the pattern-making process are obtained, which are the final pattern pieces of that fashion design. In accordance with Figure 2, the various front end objects under the “Illustration” type object can be organized as shown in Figure 10. Examples of the real world objects for “Garment type” type, “Size spec” type, “Garment section” type, “Fashion feature type” type and “Fashion feature” type objects are provided in Figure 11, which uses men’s jeans for illustration.

Overall view

Illustration

Figure 9. Overall view of the apparel pattern-making objects

Key “a part of” relationship “partner” relationship

Fashion design

Size spec

Final pattern piece

Communications

Garment type

Garment section

373 Fashion feature type

Fashion feature

Key “a part of” relationship “a kind of” relationship

As mentioned, all pattern-making earlier rules can be viewed as in Figure 12. The “Secondary pattern piece” type object refers to that pattern piece that can be used for further designing through additional refinements, while the “Final pattern piece” type object refers to that pattern piece that is already completed for a particular fashion design. Consequently, the relationships of the various types of pattern pieces are shown in Figure 13. In addition, this “Pattern piece” type object is made up of the “Shape” type object which represents a flat geometrical shape. These shapes can be complex, as seen in Figure 4 where they are likely to consist of many curves and straight lines. There are also simpler shapes. For example, the patch pocket on a men's shirt is simply a rectangle. Furthermore, the nature of the female body requires the circle in the construction of the pattern pieces over the breast areas. Consequently, the “Shape” type object consists of the “Line” type, the “Curve” type and the “Ellipse” type objects – with circle being a special case under the “Ellipse” type (Figure 14). In summary, these are the major classes of objects found in apparel pattern making. The classifications show the “a part of” and “a kind of” relationships between them. These two relationships essentially provide two orthogonal perspectives of any complex system (Booch, 1991). Primary behaviour of the pattern-making objects The primary behaviours of the various pattern-making objects are viewed with respect to the system behaviours, the relationships of the objects in Sections 2 and 3 respectively. Every object belongs to a class (i.e. object type) that specifically defines its responsibilities (i.e. how the object is expected to behave) and its collaborations with the other objects (i.e. what does it affect and what is it affected by). Examples of these classes of object and their respective behaviours are given in Figures 15 and 16. The complete set is given in (Koh, 1994).

Figure 10. Objects found within the “illustration” type object

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Men’s jeans Fullness

None Pin tucks Pleats

Pocket

374

Box Inverted Knife

Cross Side (straight) Slant Banana

Pocket opening

Square base

Patch pocket

Front panel

Round base Fly opening

Zipper

Visible

Button

Leg finishing

Fullness

Mitred corner

Concealed

Pointed base

Plain Cuff (PTU) Box Inverted Knife

Pleats Darts Gathers Tucks

Jetted Back panel

Pocket

No flap Flap No flap Flap

Pocket opening

Welt

Patch pocket

Square base Round base

Yoke

Waistband

Figure 11. Example of “garment type” type, “size spec” type, “garment section” type, “fashion feature type” type and “fashion feature” type objects

Plain Buckle and strap

Plain Plain and gathers Buckle and strap Gathers Belt loops

Size specifications

Mitred corner Pointed base

Side seam Leg seam Front crotch Back crotch Waist Hip Thigh Knee Leg bottom

Key “a part of” relationship “a kind of” relationship

States and life cycles of the pattern-making objects The dynamic behaviour of a pattern-making object is seen from its state spaces and in the events that cause its transitions between these states (Booch, 1991). A state transition diagram depicts this behaviour and thus shows its life cycle.

An example of a life cycle for the “Fashion design” type object is shown in Communications Figure 17. When a fashion design is created, it starts with specifying the desired design and this also includes working out its pattern pieces. When these are done, the fashion design is deemed completed and kept by filing it away. A fashion design can be retrieved from storage and reused by making modifications to it. Again, when completed, it is filed away for keeping. If a

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Pattern drafting rule

Secondary pattern piece

Patternmaking rule

Key “a kind of” relationship

Pattern modification rule

Pattern compatibility rule

Pattern piece

Key “a kind of” relationship

Final pattern piece

Final attachment pattern piece

Figure 12. “Pattern-making rule” type objects

Figure 13. “Pattern piece” type objects

Pattern piece

Shape

Ellipse

Key “a part of” relationship

Curve

Line

Figure 14. Further classification for the “pattern piece” type object

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fashion design is no longer wanted, it can be discarded. This can happen when it is initially created, during subsequent modifications or even after it has been filed away. When a fashion design has been discarded, the next fashion design has to be created through a new session. For a complete set of life cycles for the other objects, see Koh (1994).

376 Class Name:

Responsibility: 1, Determines a new fashion design 2, Holds the fashion illustration of this new design 3, Holds the size specification for this new design 4, Holds the final pattern pieces of this new design

Figure 15. Example of the primary behaviour of “fashion design” type object

Collaborator: Fahion illustration, size spec, final pattern piece

Class Name:

Figure 16. Example of the primary behaviour of “fashion illustration” type object

Fashion Design

Fashion Illustration

Responsibility: 1, Shows a fashion illustration (or sample garment) for every new fashion design 2, Is accompanied by the corresponding size specification at all times 3, Holds the garment type of this new design Collaborator: Fahion design, size spec, garment type

Activities in the pattern-making model The whole sequence of activities in apparel pattern making arises from the behaviours of all the pattern-making objects and their interactions with one another. These activities are similarly seen in terms of fashion analysis, pattern design and pattern drafting. Activities in fashion analysis Fashion analysis begins with the identification of the various fashion inputs from the fashion illustration. These inputs are systematically classified through the order: type of garment, garment sections in that type of garment, types of fashion features found on each garment section, and the specific fashion feature itself under each fashion feature type (Figure 18). At the same time, the input of corresponding physical dimensions for this fashion design is also needed and is provided by its size specification.

Communications Specify design

Keep

File design Keep

Design Retrieve

Reject Reject

Discard design

Reject

Modify design

377 Figure 17. Example of the life cycle of “fashion design” type object

Activities in pattern design The activities present in this pattern design process are shown in Figure 19. The garment section determines its corresponding secondary pattern piece, from which its final pattern piece is derived with the correct physical dimensions from the size specification. Its fashion features determine the geometrical changes needed to be incorporated into this final pattern piece, and also any final attachment pattern piece required to complete the effects of the features. These final attachment pattern pieces are set to the correct shapes and Fashion design Illustration

Garment type

Size spec

Garment section

Fahion feature type

Fashion feature

Figure 18. Events in the fashionanalysis process

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Part library

Fashion design

Secondary pattern piece

Illustration

Size spec

Garment type

378 Final pattern piece

Pattern-making rule

Garment section Pattern drafting rule Fahion feature type

Pattern modification rule

Part library

Fashion design Illustration

Garment type

Final attachment pattern piece

Pattern compatibility rule

Fashion feature

Figure 19. Events in the patterndesign process

Final pattern piece

Size spec

Pattern making rule

Secondary pattern piece

Final pattern piece

Garment section Draft pattern rule Fahion feature type

Final pattern piece

Drawing Modify pattern rule Final attachment pattern piece

Figure 20. Events in the patterndrafting process

Fashion feature

Compatible pattern rule

sizes by using the information of the final pattern piece to ensure physical Communications compatibility with one another. Activities in pattern drafting In pattern drafting, the final pattern pieces and the final attachment pattern pieces are drafted on to a drawing in full size. Figure 20 shows the activities of this stage. Summary An OO apparel pattern-making model has been created as a system requirements specification. This specification spells out an initial understanding of the process in terms of its behaviours, the components of the process that exhibit those behaviours, and their relationships and interactions with each other. The model has been subsequently used to develop a knowledge based system for apparel pattern making (Koh, 1994). References Booch, G. (1991), Object Oriented Design: With Applications, The Benjamin Cummings Publishing Company, Inc., Redwood City, CA. Gibson, E. (1990), “Objects – born and bred”, BYTE, October, pp. 245-54. Hinds, B.K., McCartney, J., Hadden, C. and Diamond, J. (1992), “3D CAD for garment design”, International Journal of Clothing Science and Technology, Vol. 4 No. 4, pp. 6-14. Kalay, Y.E. (1989), Modeling Objects and Environments, John Wiley & Sons, New York, NY. Koh, T.H. (1994), “Computer aided apparel pattern-making application”, MEng Thesis, Nanyang Technological University. Kopp, E., Rolfo, V., Zelin, B. and Gross, L. (1982), Designing Apparel through the Flat Pattern, Fairchild Publications, New York, NY. Ng, R., Chan, C.K., Au, R. and Pong, T.Y. (1993), “Computational technique for 3-D pattern design”, Textile Asia, September, pp. 62-4. Okabe, H., Imaoka, H., Tomiha, T. and Niwaya, H. (1992), "Three dimensional apparel CAD system”, Computer Graphics, Vol. 26 No. 2, July, pp. 105-10.

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