Effect of Migration Structure on Tensile Strength of a Natural Fiber Twisted Yarn and Markov Chain Simulation

Natural fibers are often used as a continuous twisted yarn, which are suitable for reinforcement of fibrous composites. In the twisted yarn, we often encounter phenomenon called 'migration', which means, single yarns (spun yarns) shift from outer layer to inner and vice versa. In this study, we first observed migration structure of ramie twisted yarns through an X-ray CT scanner. Results showed that migration occurred irregularly in the yarn, from which we found three kinds of single yarns' array patterns, i. e. Regular array (RA), Inside superior array (IS), Outside superior array (OS). RA means that a cross-section is composed of seven and twelve single yarns in the inside and outside layers, respectively. IS means that the number of single yarns in the inside is more than RA, and OS means that the number of the outside is more. These patterns were found to have a correlation with the number of single yarns involving migration. This phenomenon was also simulated by Markov chain model. Finally, the effect of migration on tensile properties was clarified such that, when the number of IS occupies more in a specimen, this yarn structure leads to higher tensile strength.