Multiple mesoscopic hotspot mechanisms model and its applications in drop impact hazard simulations

Due to the complex stress state (shearing, compression, friction, etc.) of the charged polymer-bonded explosives (PBXs) under accidental drop impact loading, a physical model is needed to describe the hotspot formation and ignition responses to predict the safety of PBXs. A mechanical-thermal-chemical-coupled model incorporating microcrack and microvoid-related damage followed by ignition, which is predicted based on an innovative defect-related ignition criterion of effective inelastic work, is developed to evaluate PBX charge hazards under drop impact loading. The results show that (i) microcrack hotspots play a critical role in the total temperature under low-velocity (<175 m/s) drop impact loading. Under high-velocity (>175 m/s) drop impact loading, microvoid hotspots become the dominant position owing to the timescale of the microvoid hotspot formation being shorter (~10 μs), (ii) the bulk temperature rise can be ignored for its insignificant contribution to the calculation of total temperature, and (iii) a defect-related criterion model is established which is suitable for determining threshold velocity for dropped PBX charge ignition occurrence. The simulated pressure and defect-related ignition response of PBXs are in good agreement with the tests performed by China Academy of Engineering Physics.