Role of Inelastic Transverse Compressive Behavior on Kevlar KM2 Single Fiber Transverse Impact

Abstract

Kevlar® KM2 fibers used in high velocity impact applications exhibits a nonlinear inelastic behavior in transverse compression with an elastic limit less than 1.5% strain. The effect of this transverse behavior on a single KM2 fiber subjected to a cylindrical and a fragment-simulating projectile (FSP) transverse impact is studied with a 3D finite element model. The inelastic behavior results in a significant reduction of fiber bounce velocity and projectile-fiber contact forces by 40% compared to an elastic behavior. The inelastic dissipation and reduced bounce leads to an inelastic collision rather an elastic collision. The fiber experiences multi-axial stress states during impact including transverse compression, axial tension, axial compression and interlaminar shear at the location of failure. In addition, for a FSP impact, significant multi-axial strain concentrations are predicted. Thus, the experimentally measured yarn breaking speeds are lower than classical Smith theory and may be attributed to the multi-axial loading stress concentration and property degradation mechanisms.