A fully coupled thermomechanical dislocation model for explosive crystal (β-HMX) subjected to isentropic compression loading

A fully coupled thermomechanical dislocation model is developed to analyze the thermomechanical responses of explosive crystal β-cyclotetramethylene tetranitramine (β-HMX) subjected to isentropic compression loading. The volumetric thermoelastic deformation is considered by a complete equation of state (logarithmic EoS) and the dislocation-based plasticity includes the automatic transition from the low-rate thermally activated to the high-rate drag limited regime. The proposed model is applied for the first time to simulate isentropic compression experiments (ICE) on oriented HMX single crystals. The calculated results can well capture the isentropic elastic limit, stress relaxation and steeper plastic wave speed of the ICE wave profiles. Nonlinear thermoelasticity by both pressure-dependent elasticity tensor and the complete EoS is shown to be responsible for the obvious steepness in wave profiles. The anisotropic elastoviscoplastic response can be distinctly reflected by detailed dislocation activities on seven slip systems instead of phenomenological model just through empirical determination. Pure isentrope is decoupled from quasi-isentrope by subtracting the contribution from deviatoric strain and thermal effect, providing thermodynamically consistent data for complete EoS. Contributions of anisotropic temperature rises by pressure volume work and dislocation-based plasticity work are influenced by loading history. Results provide insights into understanding the transition from isentropic wave to shock wave and ignition behavior of explosives at the mesoscale under complex thermodynamic scenarios.