The purpose of this investigation is to report the fatigue behavior of cotton and cotton—polyester blended yarn. A mechanism of fatigue behavior of staple yarn is suggested. The expressed mechanism of staple yarn fatigue is based on three stages: yarn decrimping, fiber slippage arising from inter fiber friction, and fiber elongation. The yarn decrimp mechanism occurs just at the initial stage of fatigue. The region of the sharp variations of the yarn viscoelastic properties up to nearly 1000 cycles of loading is attributed to the ability of the fiber to reorganize inside the yarn structure. Finally, the region of the steady variations of the viscoelastic properties of yarn seems to be due to fiber elongation. In this research, cotton and cotton—polyester blended yarn has been produced by rotor spinning. The general yarn characterization analysis has been performed, and then the viscoelastic properties of yarn have been analyzed by the Dynamic Mechanical Analyzer DMA 2980. The fatigue results reveal that the polyester fiber component has an important role in improving the fatigue resistance of the yarn to tensile cyclic loading. It has also been demonstrated that greater variations of yarn viscoelasticity are obtained with higher strain percent, so that at 1% strain the 100% cotton yarn reveals immediate failure. These results are interesting in view of the weaving process.
In this investigation, the relationships between the warp knitted fabric fatigue behaviour and its structural parameters are examined as these are important factors influencing the mechanical properties of the fabric. For the experimental work, a uniaxial tensile fatigue tester with a single station has been designed and constructed. Cycling was continuously variable to a maximum of 115 cycles min 21 , and the maximum stroke was adjustable up to 10 cm. A series of experiments was conducted to study the effect of stroke on the performance of various warp knitted structures with a view to changing the underlap length of the front guide bar or back guide bar (Tricot, Locknit, Reverse Locknit, Satin and Sharkskin) under cyclic tension. During fatiguing at different cycles and for various strokes, it was found that only insignificant differences were produced in the breaking tenacity of the polyester yarns and fabric samples, whereas their deformation and tensile modulus values increased and breaking extension decreased. The increase in front guide bar underlap, and simultaneously the increase in the underlap angle to the tensile direction, cause an increase in fabric deformation. In most samples, with the increase in underlap length in the front guide bar or back guide bar, the percentage of tensile modulus and the breaking extension % variations are greater than in Tricot fabric, but this change is more pronounced for samples with a longer front guide bar. These variations were attributed to the existence of space for yarn movement inside the fabric structure as the main fabric structural parameter, and also to the underlap length as the other parameter.
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