Explosively driven dynamic compaction of granular media

This paper reports experimental investigations into the dynamic compaction of particle rings subjected to moderate explosions confined in a radial Hele-Shaw cell. The findings reveal marked transitions in the flow regimes corresponding to the evolution of the transient pressure fields inside the granular medium induced by unsteady gas infiltration. As the pressure fields evolve from being localized to diffusive with a substantial reduction in intensity, three sequent flow regimes with distinct rheologies are identified. Specifically, these flow regimes are found to be governed by the localized strong pressure field, then the competition between the diffusive pressure field and wall friction, and finally, solid stresses in the presence of rarefaction waves. A Bingham-type rheology can adequately describe the granular compaction when the pressure gradients remain the dominant driving forces, whereas the frictional nature of the granular flows becomes increasingly significant as the solid stresses set in. As the pressure gradients phase out, rarefaction decompaction commences. However, this only manages to relax the innermost layers of the compacted particles due to a distinctive compressive deformation pattern, giving rise to a discontinuous flow field. These findings shed light on the rheology of dense granular flows subjected to unsteady pressure loadings involving diverse flow-particle and particle-particle interactions.