Simulations of High-Pressure Phases in RDX

Abstract

Using a fully flexible molecular potential in equilibrium molecular dynamics simulations, we study the α- and γ-polymorphs of the energetic molecular crystal hexahydro-1,3,5-trinitro-s-triazine (RDX), their respective properties, and the conditions that contribute to the stress-induced γ → α solid-solid phase transition mechanisms. We find the pressure-dependent atomic structure, mechanical properties, and transition behavior to be described reasonably well. Uniaxial deformation of α-RDX along the crystal axes is shown to result in three different crystal responses where compression of the c-axis results in the α → γ transition, compression of the b-axis causes a transition with resulting structure similar to stacking faults observed by Cawkwell et al. [ J. Appl. Phys. 2010, 107, 063512], and no transitions are observed for compression of the a-axis.

Multiscale modeling of energetic materials: Easy to say, harder to do

“…MD studies using the quantum-based RDX model have produced results that are in good agreement with experimental measurements under a wide variety of experimental conditions, including shock [3,4].…”

“…[3,4]; however, these simulations cannot properly depict the effects of microstructural heterogeneities inherent in composite EMs, due to limitations on Figure 2. Snapshots of the PETN system at t=0 (topmost frame) and 567 fs (second frame).…”

Molecular Dynamics Simulations of the Collapse of a Cylindrical Pore in the Energetic Material α-RDX

“…1a) has been widely studied both experimentally [38][39][40][41][42][43][44][45] and theoretically [35,[46][47][48][49][50][51][52]. There are four known polymorphs of RDX, denoted a [53], b [54], e [55], and c [56].…”

Investigation of Fundamental Processes and Crystal-Level Defect Structures in Metal-Loaded High-Explosive Materials under Dynamic Thermo-Mechanical Loads and their Relationships to Impact Survivability of Munitions (Thrust 4, Topic J)

“…Dislocation-mediated plasticity (homogeneously nucleated metastable stacking faults) has been predicted for weak shocks (1.3 GPa < P s < 2.0 GPa) on (111) 11 and (021) 12 planes in α-RDX; for that same material, nanoscale shear bands were predicted for shocks (P s ~ 10.0 GPa) propagating along [100] 13,14 and the polymorphic α-γ solid-solid phase transition was reported for shocks propagating along [001]. [14][15][16] These kinds of well-defined plastic deformation processes observed for PETN, α-HMX, and α-RDX are less pronounced in shocked crystalline nitromethane. The MD simulation results of Siavosh-Haghighi et al 17 show that shocks along [100] with P s > 17.0 GPa induce melting within 4 ps in nitromethane.…”