Shock-induced spall in solid and liquid Cu at extreme strain rates

We investigate spallation in solid and liquid Cu at high strain rates induced by planar shock loading with classical molecular dynamics. Shock simulations are performed at different initial temperatures and shock stresses but similar strain rates (epsilon center dot similar to 10(10)-10(11) s(-1)). The anisotropy in spall strength (sigma(sp)) is explored for five crystallographic orientations, << 100 >>, << 110 >>, << 111 >>, << 114 >>, and << 123 >>. For liquid, we examine shock- and release-induced melts as well as premelted Cu. The acoustic method for deducing sigma(sp) and epsilon center dot is a reasonable first-order approximation. The anisotropy in sigma(sp) is pronounced for weak shocks and decreases for stronger shocks. Voids are nucleated at defective sites in a solid. For weak solid shocks, spallation occurs without tensile melting; for stronger shocks or if the temperature right before spallation (T-sp) is sufficiently high, spallation may be accompanied or preceded by partial melting. T-sp appears to have a dominant effect on spallation for the narrow range of epsilon center dot studied here. sigma(sp) decreases with increasing T-sp for both solids and liquids, and sigma(sp)(T-sp) follows an inverse power law for liquids. The simulated sigma(sp) for solid Cu at low T-sp is consistent with the prediction of the power-law relation sigma(sp)(epsilon center dot) based on low strain rate experiments.