Towards Predicting a Microstructure's Susceptibility to Spall: Non-equilibrium Molecular Dynamics Simulations of Tantalum

Eric N. Hahn, Saryu J. Fensin, Timothy C. Germann

Los Alamos National Laboratory

We employ non-equilibrium molecular dynamics simulations to investigate the dynamic tensile response of tantalum. The physics of spallation depends on the complex interplay of material strength, strain rate, shock strength, and potential void nucleation sites determined by microstructure and deformation history. Using single-, bi-, and poly-crystalline samples we target specific spall responses. Simulations of single crystals allow for an evaluation of intragranular failure while bi-crystalline simulations allow us to pinpoint specific grain boundaries that have been identified experimentally as weak points. Poly-crystalline simulations, using experimentally informed microstructures from wrought and additively manufactured samples, reproduce collective grain behavior and are used to evaluate the role of grain boundary inclination with respect to the shock direction in addition to differences in plasticity across neighboring grains. We find that boundaries perpendicular to the loading direction show a higher propensity to fail, however, local plasticity and crystalline orientation conspire such that some grain boundaries fail preferentially to one another. When the spall plane aligns with a grain boundary we observe the rapid separation of the boundary as multiple growing voids quickly coalesce with one another.