Simulations of Deflagration Waves in HMX

Large-scale 1D simulations (≥1M atoms) of deflagration waves in the energetic material HMX were performed using ReaxFF-lg. These were ignited either by thermal hot spots or shock-induced collapse of voids (i.e. gaps). For ignition temperatures >1200K, the deflagration waves reached steady-state fairly rapidly, with deflagration velocities ≥ 50 m/s and quite thin reaction fronts of ~10 nm. The propagation velocities were highly dependent on the state of the material in front of the wave. In the void collapse simulations, very rapid (~2,000 m/s) deflagration waves were observed propagating backwards (compared to the shock direction) into the doubly-shocked material that filled the void space, and which was at ~1500K. The reaction chemistry could be mapped cleanly onto a six-component reduced chemistry model that had been formulated from smaller scale NVT simulations using the Non-negative Matrix Factorization technique. This model includes pressure dependent Arrhenius rates and gamma-law EOS forms for the intermediates. This demonstrates a clean connection between thermal and shock-induced chemistry and enables the formulation of a deflagration model for this material.