Hotspot formation in amorphous energetic materials due to shock-induced void collapse

High energy explosives are typically used in their common crystalline form. Most studies have been focused on crystalline phases. Molecular crystals tend to exhibit polymorphism and can often be engineered to form amorphous solids, lacking long-range order. Amorphous high-energy density materials open interesting opportunities in terms of processing and properties not accessible to crystals. While amorphous formulations lack defects typical of crystals such as dislocations and grain boundaries, and their processing can minimize cracking and sharp surface angles, porosity is a common defect. The collapse of porosity is known to play a central role in the initiation of detonation and this contribution uses molecular dynamics simulations to characterize this process. We find that, just as in crystals, the collapse of cylindrical voids exhibits a transition from viscoelastic to a hydrodynamic with increasing shock strength. Interestingly, in the viscoelastic regime the collapse of pores in the amorphous HMX results in higher temperatures as compared the crystalline case. In contrast, the hotspot temperature is lower in the amorphous phase than in the crystal for strong shocks, in the hydrodynamic regime. The simulations reveal the molecular level mechanisms behind these observations.