On the transition from weak to strong shock response

Abstract

Many materials show differing responses to weak than to strong shock waves. This study looks at the threshold in behavior that occurs between these two regimes and offers a hypothesis to define it that is supported by available data. It appears that weak shock behavior is characterized by the local collapse of material microstructure to place solids at less than the maximum density, while strong shock compression induces a homogeneous, hydrodynamic state and reduces bandgaps under extreme high pressures and temperatures. The transition from one to the other occurs by the collapse of mesoscale volume defects, activating a suite of mechanisms to achieve theoretical maximum density. This threshold is hypothesized to be the stress corresponding to the theoretical strength of the element—the weak shock limit. This is tested here for solid elements across the periodic table. Above this limit, shock velocity is found to have linear dependence with particle velocity behind the front for elements in the strong shock regime, and values for the constants characterizing this response are determined. The variation of these with atomic number highlights the dependence on the electronic state under compression and reflects some of the observed electromagnetic properties of elements beyond this limit.