DIRECT SIMULATION OF SHOCK AND RELEASE PROCESSES IN GEOLOGICAL MATERIALS (Invited Presentation)

The dynamic response of geological materials subjected to impact and shock can be difficult to characterize. Numerous material models and equations of state, which have been empirically or semi-analytically derived, have been proposed. Typically these models treat soils as a bulk material where the anisotropic nature of the materials is lost. In this work, the bulk dynamic response of sand is constructed by simultaneously modeling each constituent and then averaging over a representative volume element in order to derive the bulk response. The bulk shock Hugoniot and release isentropic for loose dry sand, which has demonstrated a wide range of behaviors when subjected to shock and impact loading, is constructed. The formation of force chains, pore collapse and grain fracture are some of the phenomenological behaviors which govern the sand response at the small scale, complicate the dynamic interactions moving up in scale, and are suspected to contribute to differing degrees of accuracy of bulk models at the largest scales. The computational simulations can bridge the gap between the various scales and can be used to construct bulk material models. This approach is termed meso-scale modeling. The mesoscale results compare favorably to data gathered from a one-dimensional plane-strain impact experiments.