Mechanism of quasi-static fatigue of wool yarn in warp-knitting processing from finite-element simulation

In this study, the quasi-static fatigue of compact wool blended siro-spun, ring-spun, and ring-spun plied yarn passing through a tricot machine was characterized and analyzed by finite-element simulation. The influence of yarn guide elements on yarn strength and hairiness, and the kurtosis and skewness of the knitting tension, indicating the relationship between the yarn tension and the machine speed during the let-off movement, were studied. An equivalent finite-element model of wool yarn was established to simulate the force and damage of wool yarn during the let-off motion. The results show that the strength of the three types of wool yarn decreased by 14%, 11.1%, and 40.5%; at the same time, the fraction of yarn with a hairiness of 3 mm and above clearly increased after the yarn passed through the heck, increasing by 120.8%, 124.7%, and 151.8%, respectively. The tension kurtosis of the compact, 14.7 tex, 50% wool–50% polyester, siro-spun yarn was 0.84, and the tension skewness was −0.828 at 900 r/min, which was stable for high-speed warp-knitting. The mechanism of the quasi-static fatigue of wool yarn was obtained; this provides an experimental and theoretical basis for the further study of the warp-knitting of wool yarn.