Study on the anisotropic response of condensed-phase RDX under repeated stress wave loading via ReaxFF molecular dynamics simulation.

Anisotropic mechanical response and chemical reaction process of cyclotrimethylene trinitramine (RDX) along crystal orientations were studied with molecular dynamics simulations using ReaxFF potential under repeated stress wave loading. In the simulations, shocks were propagated along the [010], [001], [210], [100], [111], and [102] orientations of crystal RDX at initial particle velocity Up in the range of 1∼4 km/s. For shocks at Up ≤ 2 km/s, local stacking fault and molecular conformational change can only cause marginal temperature and pressure increase without molecular decomposition. As shocks increase to Up ≥ 2.5 km/s, rupture of N-NO2 bond accompanied by partial HONO elimination dominates the main chemical reactions at the initial stage. The ordering of the follow-up consumption of NO2 and ring-breaking rate is directly consistent with that of increasing rate in temperature and pressure. The (210) and (100) planes are more sensitive to shocks in temperature and pressure profiles than the (111) plane, which agrees well with experimental observations and theoretical results in the literature. Therefore, the repeated dynamic loading model in conjunction with MD simulation using ReaxFF potential for crystal RDX indicates that these methods can be applied to study the mechanical response and chemical reaction process of polymer bonded explosives that are commonly subjected to compressive and tensile stress waves observed in practice.