Publications Details
Coarse-Grained Reactive Molecular Dynamics Simulations of Heterogeneities in Shocked Energetic Materials (LDRD Final Report)
This report summarizes the result of LDRD project 16-0161, titled "Coarse-Grained Re- active Molecular Dynamics Simulations of Heterogeneities in Shocked Energetic Materials." The purpose of the project was to develop a coarse-grained reactive molecular dynamics capability in LAMMPS enabling simulations of initiation in energetic materials comparable in accuracy to what is currently possible using large-scale reactive molecular dynamics, but with greatly reduced computational cost. The starting point for this work was the reactive dissipative particle dynamics (DPD) approach, which has been implemented as the new USER-DPD package in LAMMPS by researchers at Army Research Laboratory. Using modified versions of the examples provided with the new package, we examined the computational efficiency of the method, as well as its ability to model energy release in energetic materials. We observed that the Shardlow splitting method provides a great speed and accuracy advantage over conventional velocity Verlet time integration. We observed that the generic model of an energetic material provided with the USER-DPD package exhibited incomplete reaction under constant volume conditions. This was caused by quenching of the internal temperature of the molecules due to a rapid build-up of repulsive interactions between product gas components under constant volume conditions. Under constant pressure conditions, complete reaction was observed, as volume expansion prevented the buildup of strong repulsive interactions. Finally, a more realistic model calibrated to reproduce the equation of state of the RDX molecular crystal was examined. This model exhibited much less quenching of the internal temperature under constant volume conditions and reacted very rapidly under constant pressure conditions.