Spall damage of copper under supported and decaying shock loading

Abstract

We investigate spall damage of single crystal Cu under supported (square) and decaying (Taylor wave) shock wave loading with molecular dynamics simulations. Varying the target-to-flyer plate thickness ratio R (with target thickness fixed) as well as the impact velocity induces square and Taylor waves with different pulse shapes, durations and strengths, which are well correlated with prespall damage, spall strength, and spall damage. Taylor wave loading results in higher spall strength than the supported shock loading at the same impact velocities, and the spall strength can be similar for both loadings with the same peak free surface velocities, while Taylor wave loading induces less spall damage than square wave loading. Void nucleation is preceded by plasticity and solid-state disordering. Multiple spall events appear to be independent of each other at the early stage of spallation. In applying the acoustic method for deducing the spall strength from the free surface velocity histories, one should consider the proper sound speed and R. The method works better for large R (Taylor waves) than for small R (square waves). However, this method may significantly underestimate strain rate for both types of loading.