Tensile Fatigue Behavior of Staple Yarns

Abstract

The failure of warp yarns on a loom is often caused by repeated cyclical elongation at small stresses well below the breaking point applied under static load. The phenom enon, commonly known as fatigue, is caused by the gradually diminishing resistance of the material, attributable to cumulative damage. Generally, there is no prior indi cation of impending failure due to fatigue. In this work, we have studied the fatigue behavior of warp yarn under cyclical elongation accompanied by abrasion action as measured on a Sulzer-Ruti Webtester on the basis of three criteria—failure, damage rate, and visual appearance. Fatigue behavior expressed in terms of cycles at failure exhibits a wide scatter, displaying a pattern that deviates from normal distribution. A three-parameter Weibull distribution fitted to experimental results consistently displays a unimodal pattern. The rate of fatigue damage expressed in terms of loss in tensile property indicators has proven useful in assessing the fatigue-sustaining capacity of yarn and thereby predicting impending failure. SEM photographs display the abrasion fatigue damage inflicted on the fine structure of yarns and fibers. We have systematically studied, the effect of fatigue parameters that characterize the intensity of fatigue action, such as base tension, speed of fatiguing, abrasion pin position, and strain amplitude. Increasing intensity of fatigue action results in rapid yarn deterioration. Base tension and abrasion pin deflection have profound effects on fatigue. Fatiguing speed and strain amplitude tend to accelerate yarn deterioration, though the experimental results show a slower rate but greater variability. Representing fatigue data based on failure criterion in terms only of characteristic lifetime, which is one of the three parameters of the Weibull distribution, is not enough. A representation in terms of complete distribution yields more useful information about the extent of dispersion and the extreme value in the experimental results.