Shock interactions with heterogeneous energetic materials
The complex physical phenomenon of shock wave interaction with material heterogeneities has significant importance and nevertheless remains little understood. In many materials, the observed macroscale response to shock loading is governed by characteristics of the microstructure. Yet the majority of computational studies aimed at predicting phenomena affected by these processes, such as initiation and propagation of detonation waves in explosives, or shock propagation in geological materials, employ continuum material and reactive burn model treatment. In an effort to highlight the grain-scale processes that underlie the observable effects in an energetic system, a grain-scale model for hexanitrostilbene (HNS) has been developed. Measured microstructures were used to produce synthetic computational representations of the pore structure, and a density functional theory molecular dynamics (DFT-MD) derived equation of state (EOS) was used for the fully dense HNS matrix. The explicit inclusion of microstructure along with a fully-dense EOS resulted in close agreement with historical shock compression experiments. More recent experiments on dynamic reaction threshold were also reproduced by inclusion of a global kinetics model. The complete model was shown to reproduce accurately the expected response of this heterogeneous material to shock loading. Mesoscale simulations were shown to provide clear insight into the nature of threshold behavior, and are a way to understand complex physical phenomena.