An Analytical Method for Tensile-Test Curves of Slacked Multifilament Yarn

In conventional tensile tests for textile materials, a pretension is applied to the specimens to obtain a credible sample length. However, when we wear a comfortable garment, many yarns in it are not stretched. So, we consider that the transition behavior of textile materials from relaxed to low-stress conditions is important in evaluating the comfort of a garment. As a preliminary study, we developed an analytical method for tensile-test results of slacked yarn, where we applied the Savitzky-Golay approach to compute the second derivative-graphs of the original curves and fitted them with two beta distribution probability density functions using the least-squares method. In the experiment, we measured the tensile-test curves of an untwisted polyester multifilament yarn with intentional slack. Our results show that the second-derivative graph is well summarized by our model using the least-squares method. As well, the overall load-extension properties, including slack length of each specimen, also can be analyzed objectively in our method.