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P. Radhakrishnaiah and Gan Huang
Georgia Institute of Technology
School of Textile & Fiber Engineering
Atlanta, GA 30332-0295 |
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ABSTRACT
Cotton yarns representing ring, rotor and friction spinning technologies and cotton/polyester yarns representing ring, rotor and air-jet spinning technologies were tensile tested at a range of traverse rates (15-2,000 mm/min) to assess the influence of rate of traverse on the tensile behavior of the individual yarns. The yarns were also tested at normal (500mm) and short (45mm) gauge lengths to compare the stress/strain responses and the failure modes obtained at these gauge lengths.
Results showed that many stress-strain parameters and the rupture behavior of the yarns are typically characteristic of the spinning system used to produce the yarn. Results also showed that the breaking strength of the yarns representing the modern spinning technologies has a stronger association with traverse rate, compared to the breaking strength of the ring spun yarns.
Introduction
The tensile behavior of spun yarns is a function not only of the fiber characteristics such as length, fineness and strength but also of the nature of fiber arrangement in the yarn. Thus yarn structural parameters in addition to fiber physical properties play a significant role in determining the tensile behavior, namely, strength, modulus, elasticity, yield stress, work of rupture and elongation properties of spun yarns. While the ring spinning process is known to give a yarn in which the fibers are believed to be more effectively interlocked, some of the new spinning technologies (rotor, air-jet and friction) are known to deliver structures with less than optimum fiber entanglement. In recent years, many research workers (1-11) have reported on the properties and performance aspects of yarns and fabrics that represent the new spinning systems. Most of this evaluation and comparison, however, was confined to standard test methods and the results thus obtained may not correctly reflect the behavior of the different yarns and fabrics under nonstandard loading conditions. Even in the traditional apparel end use, yarns and fabrics undergo stresses and strains that are significantly different from those applied in the standard yarn and fabric tensile tests. Thus the tensile behavior of yarns evaluated under standard test procedures cannot always be expected to fully reflect the performance of their end products. More recently, researchers have shown that yarn strength evaluated at shorter gauge lengths is a better predictor of fabric strength as opposed to the strength evaluated at the standard (254 mm) gauge length (19). The importance of understanding the stress/strain response of yarns and fabrics under nonstandard loading conditions can be further appreciated if one considers the ever expanding range of their non-traditional applications--aircraft, space vehicles, automobiles, reinforced composites and a host of other industrial uses.
Background
The effect of rate of loading on the tensile properties of spun yarns was first investigated by Midgeley and Pierce (12) in 1926. Working on a 16.4 tex cotton yarn, the authors observed that the yarn breaking strength bears an inverse logarithmic relationship with the time to break, expressed in seconds. In other words, the work of Midgeley and Pierce revealed for the first time that the breaking load of a medium count ring spun cotton yarn drops by 10% for every ten-fold increase in the breaking time. Working on the same subject at a later date, Meredith (13) observed that the breaking strength of ring spun cotton yarn drops by 9% for every ten-fold increase in the breaking time, within the breaking time range of 10 sec - 3 hrs. Meredith also showed that low twist yarn gives a larger percentage drop in strength compared to normal twist yarn and that maximum breaking extension for normal twist yarn occurs within the breaking time range of 1-10 sec. Compliance Ratio, which Meredith defined as extension per unit load, was shown to decrease linearly with the logarithm of the rate of extension. A drop in compliance ratio of 7.8% was observed with a ten-fold increase in the rate of extension.
During the time of Midgeley and Pierce and also that of Meredith, the three high production spinning technologies considered in this work (rotor, air-jet and friction spinning) were not available. As a consequence, the works of these authors were confined to ring spun yarns. In recent years, Balasubramanian and Salhotra (14), and also Kaushik and his coworkers (15) investigated the influence of rate of loading on the tensile behavior of rotor spun yarns. Working on 100% cotton ring and rotor spun yarns made from three different cottons, Balasubramanian and Salhotra failed to observe a steady increase in tenacity with increasing strain rate. It was shown that the tenacity reaches a peak value around a strain rate of 20 cms/min and thereafter declines gradually. This behavior was found to be true for both ring and rotor yarns, for three different cotton varieties, and for three yarn twist levels. The authors thus concluded that maximum tenacity occurs not at the maximum strain rate as observed by Midgeley and Pierce but at an optimum rate of strain. It was explained that even though more fibers tend to break rather than slip at higher strain rates (16), the insufficient time available for fiber realignment at very high strain rates, may in fact result in a net strength reduction.
Kaushik et al (15) studied the influence of extension rate and specimen length on the tensile behavior of rotor spun acrylic/viscose rayon yarns. They observed that maximum yarn tenacity occurs at a strain rate of 20 cm/min for a gauge length of 10 cm and at a strain rate of 100 cm/min for a gauge length of 50 cm. Breaking extension on the other hand, was shown to increase with increasing extension rate for viscose and acrylic yarns and their blends. Hearle and Thakur (17) studied the effects of rate of extension and gauge length on the load-extension behavior of twisted multifilament yarns. They observed sharp (catastrophic) yarn breaks at a specimen length of 10 cm but the breaks were partial and nonsimultaneous at shorter gauge lengths (2.5 cm and 1.0 cm). Rate of extension, in addition to gauge length, was found to influence the breakage mode. Thus partial breaks were observed even at a 10 cm gauge length when the rate of extension was sufficiently low. The authors explained that the elastic energy stored in a yarn that is under increasing axial tension will be a function of the gauge length and that the energy stored in short gauge length tests may not be adequate to cause sharp and instantaneous breaks.
Hussain et al (18) studied the influence of gauge length on the tensile properties of ring and rotor spun cotton yarns. They observed a decrease in tenacity, breaking strain, and specific work of rupture as the gauge length was increased from 1 to 70 cm. The decrease, as can be expected, was found to be more pronounced for ring spun yarns than for rotor yarns.
In their recent work, Realff et al (19) dealt with the influence of gauge length on yarn properties. Yarns produced on ring, air-jet, and rotor spinning systems were tensile tested at a range of gauge lengths above and below the mean staple length. At longer gauge lengths, yarn failure was found to be the result of combined slippage and breakage. At shorter gauge length, yarn failure was shown to result from a greater extent of fiber breakage and less slippage. The balance between slippage and breakage was shown to vary with yarn structure. Thus slippage was found to be more predominant in the failure of air-jet yarn, especially at longer gauge lengths. The strength obtained at very short gauge lengths was shown to differ considerably from that predicted based on the weakest link theory and the authors argued that this deviation from predicted value serves as proof of a change in failure mechanism at very short gauge lengths.
The overall objective of the present work is to understand the stress-strain responses and failure modes of structurally different yarns so that more appropriate yarn and fabric engineering for a range of apparel and non-apparel end-uses can be practiced in the future. Some specific goals are to:
- Study the influence of rate of loading on the stress-strain response of cotton and cotton/polyester yarns corresponding to ring, rotor, air-jet and friction spinning technologies.
- Compare the results of rate of loading experiments with those obtained by earlier workers.
- Examine the stress-strain responses of individual yarns at normal (500 mm) and short ( 45 mm) gauge lengths, and
- Compare the failure modes of individual yarns at normal and short gauge lengths.
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Materials and Methods
Production of yarn samples - The 100% cotton yarns representing ring, rotor and friction spinning systems were made from a single cotton mixing that was suitable for producing a 30tex (20s Ne) ring yarn. A Whitin Roberts ring frame which had an ultradraft top arm drafting system was used to produce the ring yarn. The rotor yarn was made on a Schubert & Salzer RU11 machine and the friction yarn was made on a Platt-Saco-Lowell Masterspinner. The spinning speeds and twist multiples employed for the three cotton yarns were those that are considered appropriate by commercial spinners, based on their experience with each of the spinning systems. The nominal count of all the three yarns was 18s (Ne).
The cotton/polyester yarns (50:50 blend) were made on ring, rotor and air-jet spinning systems. The Platt's Master Spinner (friction spinning unit) was not used for the production of cotton/polyester yarn because the manufacturers of the machine do not recommend its use for blended yarns. The cotton/polyester yarns corresponding to ring and rotor spinning systems were made on the same machines that were used for the production of 100% cotton yarns and the air-jet yarn was made on a Murata jet spinner (model MJS 802). The nominal count again was 18s (Ne) for all the three cotton/polyester yarns. As in the case of 100% cotton yarns, the selection of raw materials and manufacturing conditions for the cotton/polyester yarns was guided by industry norms. The industry norms were chosen so that the work would be relevant to a large volume of yarns produced by commercial spinners.
Testing of yarns -- To study the influence of rate of loading on yarn tensile properties, the yarns were tested on Statimat-M strength tester, choosing a range of extension rates (15,50,100, 150,180,200,250,300,350,400,450,750,1200 and 2000 mm/min) and a gauge length of 500 mm. The yarns were also tested at a gauge length of 45 mm in order to compare the stress/strain response and failure modes obtained at this gauge length with that obtained at the normal (500 mm) gauge length. The average breaking load and breaking extension were computed on the basis of 100 strength tests for the normal gauge (500 mm) strength test and on the basis of 50 tests for the short gauge (45 mm) strength test.
Top Results and Discussion
Figures 1-6 show the stress-strain responses of the experimental yarns corresponding to the two gauge lengths and also that corresponding to different traverse rates. Figures 7-12 show the nonlinear regression plots of traverse rate versus breaking load and also the corresponding prediction equations for breaking load.
Following are some of the obvious conclusions that can be drawn from the stress-strain curves and the regression plots:
- There are major differences in the stress-strain behavior of the cotton yarns representing the three spinning technologies
- The average stress-strain curves of the cotton/polyester yarns representing the three spinning systems are somewhat similar up to the yield point but they differ substantially above the yield point
- Traverse rate appears to have a very similar effect on the stress-strain response of the three cotton yarns
- The polyester/cotton yarns representing the three different spinning systems, however, fail to show a similar change in stress-strain response with the change in traverse rate
- All the six experimental yarns show catastrophic failure at 500 mm gauge length. At 45 mm gauge length, the ring spun yarns show mostly catastrophic failure while the rotor, air-et and friction spun yarns show mostly non-catastrophic failure
- The breaking strength of the experimental yarns corresponding to rotor, air-jet and friction spinning technologies shows a stronger association with traverse rate compared to the breaking strength of the ring spun yarn. Thus knowing the breaking strength of these yarns at a particular traverse rate, their strength at other traverse rates can be more accurately predicted than that of the ring spun yarns.
Top LITERATURE CITED
- Chasmawala, J. Rasesh, Hansen M. Steven, and Jayaraman Sundaresan, Structure and properties of Air-jet spun yarns, Text. Res. J. 60 (2), 61-68 (1990).
- Trilett, A. Barbara, Evaluation of Fiber and yarn from Three Cotton Fiber Mutant Lines, Text. Res. J. 60 (3), 143-148 (1990).
- Kimmel, B. Linda and Sawhney A.P.S., Comparison of DREF-3 cotton Yarns produced by Varying Core Ratios and Feed Rates, Text. Res. J. 60 (12), 714-718 (1990).
- Paek, L. Soae, Pilling, Abrasion and Tensile properties of fabrics from Open-End and Ring Spun Yarns, Text. Res. J. 59 (10), 577-583 (1989).
- Lord, P.R., and Radhakrishnaiah, P., A comparison of Various Woven Fabrics Containing Friction, Rotor and Ring Spun Cotton Yarn Fillings, Text. Res. J. 58 (6), 354-362 (1988).
- Lord, P.R., and Radhakrishnaiah, P., Tenacities of Plied Friction-spun, Rotor-spun and Ring-spun yarns, J. Text. Inst. 78(2), 140-142 (1987).
- Lord, P.R., and Radhakrishnaiah, P., Assessment of the Tactile Properties of Woven Fabrics Made From Various Types of Staple Fibre yarn, J. Text. Inst. 79 (1), 32 -52 (1989).
- Louis, G.L., Salaun, H.L., and Kimmel B. Linda, Comparison of Properties of Cotton Yarns produced by the DREF-3, Ring and Open-End Spinning Methods, Text. Res. J. 55 (6), 344-351 (1985).
- Barella, A., Manich, A.M., Friction Spun Yarns Versus Ring and Rotor Spun Yarns: Resistance to Abrasion and Repeated Extensions, Text. Res. J. 59 (12), 767-769 (1988).
- Salhotra, K.R., and Balasubramanian, P., Fiber Rupture During Tensile Failure of Ring and Rotor Yarns, Indian J. Text. Res. 9(3), 4-7, (1984).
- Mohamed, M.H., and Lord, P.R., Comparison of Physical Properties of Fabrics Woven from Open-End and Ring Spun Yarns, Text. Res. J. 43, 154-166 (1973).
- Midgeley, E., and Pierce, F.T., Tensile Tests for Cotton Yarns, the Rate of Loading, J. Text. Inst. 17, T330-T341 (1926).
- Meredith, R., The Effect of Rate of Extension on the strength and Extension of Cotton Yarn, J. Text. Inst. 41, T199-T224 (1950).
- Balasubramanian, P., and Salhotra, K.R., Effect of Strain Rate on Yarn Tenacity, Text. Res. J. 55(1), 74-75 (1985).
- Kaushik, R.C.D., Salhotra, K.R., and Tyagi, G.K., Influence of Extension Rate and Specimen Length on Tenacity and Breaking Extension of Acrylic/Viscose Rayon Rotor Spun Yarns, Text. Res. J. 59(2), 97-100 (1989).
- Singh, V.P., and Sengupta, A.K., A New Method of Estimating the Contribution of Fiber Rupture to Yarn Strength, and its Application, Text. Res. J. 47(3), 186-188 (1977).
- Hearle, J.W.S., and Thakur, V.M., The Breakage of Twisted Yarns, J. Text. Inst. 52, T149-T163 (1961).
- Hussain, G.F.S., Nachane, R.P., Krishna Iyer, K.R., and Srinathan, B., Weak-Link Effect on Tensile Properties of Cotton Yarns, Text. Res. J. 60(1), 69-77(1990).
- Realff, M.L., Seo, M., Boyce, M.C., Schwartz, P., and Backer, S., Mechanical Properties of Fabrics Woven from Yarns Produced by Different Spinning Technologies: Yarn Failure as a Function of Gauge Length, Text. Res. J. 61(9), 517-530 (1991).
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Figure 1: Stress-Strain Behavior of Cotton Yarns
Top Figure 2: Average Stress-Strain Curves for Cotton Yarns
Top Figure 3: Stress-Strain Behavior of Poly/Cotton Yarns
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Figure 4: Average Stess-Strain Curves for Poly/Cotton Yarns
Top Figure 5: Average Stress-Strain Curves of Cotton Yarns at Different Traverse Rates
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Figure 6: Average Stress-Strain Curves of Poly/Cotton Yarns at Different Traverse Rates
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Figure 7: Regression Plot of Breaking Force vs. Speed for Ring Spun 18s Cotton Yarn
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Figure 8: Regression Plot of Breaking Force vs. Speed for 18s Rotor Spun Cotton Yarn
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Figure 9: Regression Plot of Breaking Force vs. Speed for 18s Friction Spun Cotton Yarn
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Figure 10: Regression Plot of Breaking Force vs. Speed for 18s Ring Spun Cotton/Polyster Yarns
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Figure 11: Regression Plot of Breaking Force vs. Speed for 18s Rotor Spun Cotton/Polyster Yarn
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Figure 12: Regression Plot of Breaking Force vs. Speed for 18s Airjet Spun Cotton/Polyester Yarn
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