Study on the Hole Collapse and High-Temperature Zone Formation of Explosive with Cavity Under Impact

The formation of hotspots and ignition phenomena within a cavity-containing explosive particle cloud under impact has garnered significant attention. However, research at the mesoscopic scale remains limited, with most studies primarily focusing on drop hammer and free-fall testing methods. Therefore, there is an urgent need for investigations into the deformation, temperature rise patterns, dissipative mechanisms and heat transfer mechanisms of mesoscopic explosive particle clouds under impact. This study established a mathematical and physical model suitable for analyzing explosive deformation and temperature rise under both fall and shock wave impacts, accurately capturing the dynamics and thermodynamics of particles and fluids. Utilizing the discrete element method, the model accounted for the elastoplastic contact processes between particles, systematically considering their elastoplastic collisions and shear history, thereby accurately resolving particle motion and collision behavior. The momentum equation incorporated bidirectional coupling of drag forces between particles and the gas phase, while the energy equation addressed sliding friction dissipation, rolling resistance dissipation, plastic dissipation, heat transfer between particles, and thermal interactions between particles and the fluid. This study examined the influence of particle size on the fall process of explosive particle cloud. It is observed that smaller particle sizes result in a larger area of the trapezoidal temperature rise zone and a larger area of the symmetrical high-temperature region during the fall process, leading to a higher final average temperature. Variations in particle size result in different particle counts within the cloud, which in turn alters collision dissipation behaviors among particles, contributing to temperature discrepancies. Furthermore, the differences in the evolution of sliding friction and rolling resistance dissipation are apparent at an early stage during the fall, whereas the differences in plastic dissipation are only apparent at a later stage of the fall. Additionally, a comparative analysis of the key dissipative source terms—specifically the evolution of plastic dissipation—under both drop and shock wave conditions was presented. During the drop process, the evolution of plastic work primarily occurs during the formation of the high-temperature zone and the collapse of holes, both of which involve significant plastic collisions between particles. In contrast, during shock wave impact, plastic dissipation is predominantly focused on the early stages of hole deformation within the particle cloud, after which the temperature of the explosive particles increases mainly through two-phase heat transfer.