Discrete particle simulation of shock wave propagation in a binary Ni plus Al powder mixture

Numerical simulations of shock wave propagation through discretely represented powder mixtures were performed to investigate the characteristics of deformation and mixing in the Ni+Al system. The initial particle arrangements and morphologies were imported from experimentally obtained micrographs of powder mixtures pressed at densities in the range of 45%-80% of the theoretical maximum density (TMD). Simulations were performed using these imported micrographs for each density compact subjected to driver velocities (U-p) of 0.5, 0.75, and 1 km/s, and the resulting shock velocity (U-s) was used to construct the U-s-U-p equation of state. The simulated equation of state for the 60% TMD mixture was validated by matching results obtained from previous gas-gun experiments. The details of shock wave propagation through the Ni+Al powder mixtures were explored on several scales. It is shown that the shock compression of mixtures of powders of dissimilar densities and strength is associated with heterogeneous deformation processes leading to focused flow, particulation, and vortex formation, resulting in local fluctuations in pressure and temperature, which collectively are responsible for highly irregular shock fronts and unstable high-pressure states in granular media.