Virtual melting and microstructure effects in spall failure in single crystal niobium: a molecular dynamics study

Spall refers to a material failure caused by tensile stress waves, a phenomenon with critical implications in materials subjected to extreme conditions, such as ballistic impact and explosive loading. During the shock loading of single crystals, an amorphization of the atomic structure occurs at the shock front, a process known as virtual melting or premelting. However, the subsequent recrystallization and its impacts on spall strength are not fully understood. Using large-scale non-equilibrium molecular dynamics simulations, we investigate this stress relaxation mechanism with atomistic resolution. State-of-the-art analysis of the MD trajectories provides detailed information into the stress state and the microstructure evolution before, during and after virtual melting. Our findings highlight how variations in the shock strength influence the degree of virtual melting and the resulting dislocation density, as well as the eventual material failure.