Mechanics analysis of staple yarns provides an understanding of the yarn deformation and failure mechanisms. Work to date on the subject has mostly focused on modulus and strength rather than the progressive deformation mechanisms when a low-twist staple yarn is subjected to tensile loading. This thesis presents a theoretical model to predict the entire load-extension response of low-twist staple yarns. The model is also used to study the response of such yarns when subjected to cyclic tensile loading. The work involves: (a) analyzing fiber end slippage effect due to fiber length discontinuities in a staple yarn and studying the stress distribution along the fiber under both tensile loading and unloading conditions; (b) deriving a theoretical expression for the transverse pressure across the yarn considering the variation of the fiber packing density across the yarn section and the consolidation of the yarn under tensile deformation; and (c) predicting the entire load-extension curve of the yarn and the yarn response under cyclic tensile loading conditions. To verify the theoretical model, experiments were carried out including monotonic and cyclic tensile tests. Several yarn parameters are varied to study their effect on the yarn behavior. Comparison between experimental data and theoretical predictions shows that the predicted yarn behavior (monotonic and cyclic tensile behavior) is in reasonable agreement with the experiment results. A parametric study was conducted to explore the effect of fiber properties and yarn structural parameters on the yarn mechanical behavior.
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