Experimental evaluation and statistical characterization of the strength and strain energy density distribution of Kevlar KM2 yarns: exploring length-scale and weaving effects

Abstract

This article experimentally investigates the tensile strength distributions of 600 den Kevlar KM2 yarns under quasi-static tensile loading. The strength distributions were best characterized using the 3-parameter Weibull and generalized Gamma distributions. In order to assess the effects of weaving on the strength distributions, Kevlar yarns were tested from a spool and then compared to yarns extracted from greige and scoured Kevlar fabrics. The weaving process and treatments caused various levels of strength degradation which shifted the strength distributions toward lower strengths. The warp yarns were degraded to a greater extent than the fill yarns. The scouring process induced further strength degradations in the woven fabric. Length-scale effects were studied by using gage lengths varying between 25.4 and 381.0 mm. The strength distributions were observed to shift toward lower strengths with increasing gage lengths. A new distribution function based on a modification to the 3-parameter Weibull distribution is proposed to account for length-scale effects. In addition to the strength distributions, the experimental load—extension plots are used to compute the strain energy density or work-to-break values normalized by the yarn volume, which are then statistically characterized and analyzed in a similar manner.