Molecular dynamics analysis of shock passage through (010)-oriented β-HMX containing fields of pre-existing dislocations

We report all-atom simulations of shock propagation in quasi-2D samples of (010)-oriented β-HMX (P2₁/n) containing fields of pre-existing dislocations. The goal is to understand the mechanical evolution as functions of dislocation density ρ and impact speed u_p. Dislocation fields were generated by inserting N = 44, 22, or 12 dislocations with mixed edge  {(010)[001], (001)[010]} and screw  {(010)[100]} character randomly into the sample, which was 5 nm × 150 nm × 150 nm in size. The corresponding ρ values are 2 × 10¹⁵, 1 × 10¹⁵, and 0.5 × 10¹⁵ m^-2. Above a threshold shock intensity, the dislocations split into <111> partials. Impacts with u_p = 1.00 km s^-1 were studied for all three ρ, along with 0.75 and 0.50 km s^-1 for the largest ρ. Effective plastic strain rates (PSRs) were obtained from stress profiles, whence average dislocation velocities <v> were obtained using the Orowan equation. For ρ = 2 × 10¹⁵ m^-2, the PSR and <v> increase with increasing u_p. For u_p = 1.00 km s^-1, increasing ρ leads to an increase in PSR but a decrease in <v>. Resolved shear stress (RSS) profiles for the partials show that dislocation motion ceases when the RSS falls below a threshold that is consistent with published critical RSS values for the same slip systems under non-shock conditions.