Dynamic modeling of Kevlar KM2 single fiber subjected to transverse impact

Abstract

In this paper, the transverse impact onto a Kevlar KM2 single fiber is studied using analytical and numerical models. The impact response of fibers with reduced longitudinal shear moduli (‘string’ model) is studied with a 3D finite element model and the wave propagation results converge to the classic 1D analytic solution that supports only axial loads. A dispersive flexural wave mode is predicted numerically for the single fiber during transverse impact due to its finite longitudinal shear modulus. The numerical results are confirmed with an analytical solution derived for the response of an infinitely long Euler–Bernoulli beam subjected to a constant velocity impact. Fiber bounce is predicted for impact with a cylindrical projectile with fiber velocity exceeding impact velocity by 60–80%. At short time scales significant transverse compressive stresses and strains develop in the fiber and the magnitude depends on the impact velocity. The breaking speed predicted by the 3D model based on maximum principal stress criterion for a single fiber is between 26% (membrane failure) and 76% (combined membrane and flexure failure) less than the 1D analytical solution. The flexural wave and projectile fiber interactions induce curvatures in the fiber significant enough to induce compressive fiber failure and fibrillation.