Mesoscale Simulations on the Effects of Rate-Dependent Strength and the Shock-to-Detonation Behavior of Explosive Materials*

We have developed mesoscale shock-initiation models for an explosive material that explicitly simulate the formation and growth of hotspots, and the subsequent transition to detonation. These models use high-resolution scanning electron microscope (SEM) images of pellet cross-sections as an input. Arrhenius reaction kinetics, based on the local temperature of the solid as it is deformed and heated by the shock wave, were calibrated against threshold flyer-velocity data from shock-initiation experiments. Critical to these hydrodynamic models is the strain rate-dependent yield and failure of single grains during compression. Unfortunately, experimental data for the high-strain rate response of explosive materials at micron length-scales is difficult to obtain. Therefore, we used molecular dynamics (MD) simulations of pore collapse for shock pressures spanning the viscoplastic to hydrodynamic regimes to calibrate the Steinberg-Guinan-Lund (SGL) strength model. This SGL model was implemented into our shock-initiation model and shown to markedly influence hotspot ignition at the microscale and growth-to-detonation at the macroscale. By comparison, a similarly trained elastic perfectly plastic model did not capture the length-scale dependence of pore collapse, which is known to be captured by MD and the SGL model. These efforts demonstrate the utility and success in upscaling MD results into complex hydrodynamic models to improve the predicted correlations between heterogenous microstructures and their performance.