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 (similar to 10 mu s), (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.

Automated summary

In order to predict the safety of polymer-bonded explosives (PBXs) under accidental drop impact loading, a physical model is developed to describe the hotspot formation and ignition responses. The model incorporates microcrack and microvoid-related damage followed by ignition, which is predicted based on an innovative defect-related ignition criterion. The results show that microcrack hotspots and microvoid hotspots play critical roles under different impact velocities, and a defect-related criterion model is established for determining the threshold velocity for ignition occurrence.