The initial reaction mechanism of energetic materials under impact loading and the role of crystal properties in impact initiation and sensitivity are still unclear. In this paper, we report reactive molecular dynamics simulations of shock initiation of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) crystals containing a cube void. Shock-induced void collapse, hot spots formation and growth, as well as spalling are revealed to be dependent on the shock velocity. The void collapse times are 1.5 and 0.7 ps, for the shock velocity of 2 and 4 km·s–1, respectively. Results indicate that the initial hot spot formation consists of two steps: one is the temperature rise caused by local plastic deformation and the other is the temperature increase resulting from the collision of upstream and downstream particles during the void collapse. Whether hot spots will continue to grow or quench depends on sensitive balance between energy release caused by local physical and chemical reactions and various heat dissipation mechanisms. In our simulations, hot spot would grow for Up = 4 km·s–1; hot spot is weak to some extent for Up = 2 km·s–1. The tensile wave reflected by the shock wave after reaching thefree surface causes the spalling, which depends on the initial shockvelocity. Typical spalling occurs for the shock velocity 2 km·s–1, while the tensile wave induces the microsplit regionin RDX crystals in the case of Up = 4km·s–1. Chemical reactions are studied forRankine–Hugoniot shock pressures Ps = 14.4, 57.8 GPa. For the weak shock, there is almost no decompositionreaction of the RDX molecules near the spalling region. On the contrary,there are large number of small molecule products, such as H2O, CO2, NO2, and so forth, around the microsplitregions for the strong shock. The ruptures of N–NO2 bond are the main initial reaction mechanisms for the shocked RDXcrystal and are not affected by shock strength, while the microsplitslows down the decomposition rate of RDX. The work in this paper canshed light on a thorough understanding of thermal ignition, hot spotgrowth, and other physical and chemical phenomena of energetic materialscontaining voids under impact loading.
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