Spall strength of aluminium single crystals under high strain rates: Molecular dynamics study

The spall process of single crystal aluminium under triangular waves loading has been performed with molecular dynamics simulations. The variation of spall stress with shock strength is directly calculated using the virial formula. Our simulations show that the spall strength keeps a linear reduction with the spall temperature before melting, whose occurrence will weaken this reduction tendency. This result is qualitatively different from the acoustic approximation, for the latter is out of work under such strong shock loading. We observe the increase of plastically deformed zones with impacting velocity before release melting and also the transition from plastic deformation to disordered state after melting. The microscopic views of voids nucleation and growth are also presented. The void nucleation is found primely along the close-packed plane {111}, and with increasing impacting velocity the void shape tends to spherical. After melting, the voids nucleate in complete disordered state, and the void number increases apparently, where the temperature effect is no more remarkable as in solid state.