Mechanisms of Shock Dissipation in Semicrystalline Polyethylene*

This work analyzes various mechanisms for the dissipation of shock wave energy in a realistic, atomically detailed model of semicrystalline polyethylene (SCPE), for the purpose of understanding how this material can be applied in protective armor for people and equipment. The mechanisms considered for shocks 10 GPa and less are structural and vibrational in manner. Systems are studied using equilibrium molecular dynamics with a Hugoniostat to simulate application of the shock wave. To determine the extent of structural dissipation, order parameters and configuration time series are collected during the course of the shock simulations at different pressures and crystallinity fractions. Vibrational data are analyzed by computing density of states spectra pre- and post-shock. We conclude that the major mechanisms responsible for the shock energy dissipation of SCPE are plastic deformation and amorphization of the systems, manifested as changes in material gradients and order parameters, as well as changes to the crystalline structure via chain slip and reshaping of the unit cell.