Two-dimensional mesoscale simulations of shock response of dry sand

Simulations were done to gain insight whether the shock response of dry sand at low stresses would vary with porosity and whether the effects of friction between grains under confinement could be extracted from the planar plate impact experimental data. The sand sample was modeled as grains separated by voids representing porosity. The simulation procedure coupled grain deformations with frictional sliding at grain boundaries. The shock response of dry sand varied considerably with porosity. The sample compacted through pore closure followed by inelastic pore collapse mechanisms affecting the inhomogeneous response and shock rise time. The sample attained final compaction in the shock state long after attaining peak longitudinal velocity/stress. The calculated shock Hugoniot for a sample of high (40%) porosity was in agreement with experimental data. The U-s - U-p slopes for sand of 10% and 20% porosity were found to be negative. The calculated sigma H - rho(H) Hugoniot suggested that the two slopes would become positive at higher stresses in order to approach the solid Z-cut quartz Hugoniot at full compaction. High porosity sand may never exhibit negative slopes. It is concluded that the effects of friction between grains can be successfully extracted from a coupled experimental-computational approach. This requires measuring the velocity profile in the back buffer, elastic buffer material, and code capable of simulating frictional sliding between grains. The dispersion effect increased the slope of the velocity profile with propagation distance but did not result in a wave speed reduction or shock attenuation. This may be due to the small grain size and sample thickness as well as the absence of grain fragmentation in the present simulations. (C) 2015 AIP Publishing LLC.