Apparent Violations of the Rankine-Hugoniot Equation in Very Porous Materials

The Rankine-Hugoniot Equation is a tenet of shock physics, predicting the existence of a relationship between initial and final states within a shock wave based only on simple conservation laws and a steady-state assumption. Experiments in highly porous materials appear inconsistent with Rankine-Hugoniot predictions derived from first-principle calculations. Resolving these inconsistencies is challenging due to the inherent variability in porous target fabrication, that often leads to large experimental uncertainties. Here, we use molecular dynamics to explore the conditions in which highly porous materials (silica glass, copper, and a Lennard-Jones model system) stray from the Rankine-Hugoniot predictions. Indications are that open pores allow for effective pre-heating of the porous material ahead of the shock front, and an empirical pre-heating model can be formulated to correct for the effect in hydrocodes.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy National Nuclear Security Administration under contract DE-NA0003525. The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or the United States Government.