The effect of friction and fracture on weak shock propagation in granular salt

This study performed computational modeling of weak shock compaction in granular salt over various impact velocities ranging from 95 m/s to 245 m/s to investigate the role of friction and fracture on shock dynamics. Explicit grain-resolving hydrodynamics simulations were executed and compared to previously reported experimental data. A new algorithm for integrating both inter-granular and intra-granular frictional forces was implemented and found to affect both the measured particle and shock speed throughout the specimen. An explicit fracture plane was added to each salt grain, which was found to drastically affect shock propagation in systems with friction, but not in systems without friction. We found that the simulation resolving both friction and explicit grain fracture was closest to matching the measured experimental data at high impact velocities, and the simulation with only friction matched the best at low impact velocities, thereby illustrating the importance of these physics in the weak shock regime. Notably, our results indicate that neither friction nor grain fracture significantly affects the slope of the shock velocity-particle velocity Hugoniot – an important material property – in the range of impacts studied. Moreover, our results indicate that the Rankine-Hugoniot jump conditions may underestimate the pressure experienced by the bulk material in granular assemblies with high friction and confinement.