CONTEXT: The formation of hot spots and chemical decomposition of explosives under shock loading are crucial for understanding the initiation of heterogeneous explosives. In this study, molecular dynamics simulations were employed to investigate the collapse of nanovoids, hotspot formation, and decomposition reactions of HMX under four typical stress wave loadings: long-pulse, short-pulse, triangular wave, and ramp wave. Different loading modes lead to varying critical transition velocities at which void collapse shifts from uniform to jetting collapse. For long-pulse loading, short-pulse and ramp wave loadings, and triangular wave loading were about 1.75 km/s, 2.25 km/s, 2 km/s and 2.5 km/s, respectively. Furthermore, it was found that under the uniform collapse mode, the hot spot temperature remains below 2000 K, and the initial decomposition pathway of HMX primarily involved the breaking of the N-NO��� bond. In the jetting collapse mode, hydrogen transfer and the formation of HONO were observed. These findings contribute to a better understanding of the relationship between shock loading modes and void collapse patterns in explosives, revealing the initial reaction pathways of HMX under different collapse modes, and providing theoretical guidance for experimental investigations, to provide a theoretical basis for developing a new ignition model.
METHODS: Based on the ReaxFF-MD method, Lammps software was used to simulate the shock process of the HMX system with circular holes, and the reaction force field files containing C, H, O, and N elements were used. The post-processing of the results was implemented using OVITO and self-programmed Python scripts.
