Modeling Dynamic High-Pressure Plasticity in Platinum

High-energy lasers enable determination of dynamic metal strength at very high pressures by driving plastic flow in compression. Experiments at the National Ignition Facility have induced Rayleigh-Taylor instability and inferred high-pressure dynamic strength from the resulting ripple growth in accelerated platinum (Pt) samples. Here we use molecular dynamics (MD) to simulate Pt plasticity during ramp compression to a peak pressure of 430 GPa. Two kinds of MD simulations have proven useful: (1) model ramp compression simulations at fixed strain rates and (2) simulations of the actual non-monotonic experimental loading that capture the times and length scales relevant to the flow. The MD flow stress is found to agree well with that inferred from experiment. Analysis of the simulations provides additional information about deformation mechanisms valuable for model building but unavailable from the experimental diagnostics. We comment on the rate and size dependence of the deformation mechanisms.