Anisotropic mechanical-thermal-phase transformation response of cyclotetramethylene tetranitramine (HMX) single crystal under ramp loading

A thermomechanical consistent model for cyclotetramethylene tetranitramine (HMX) is developed, which considers material anisotropy, nonlinear thermoelasticity, dislocation-based plasticity, shear cracking induced damage and physical-based phase transformation. The proposed model is employed to investigate the mechanical-thermal-phase transformation response of oriented HMX single crystals under isentropic compression ramp loading at pressures up to ~50GPa for the first time. The proposed model could well reproduce the anisotropic three-wave structure profiles for loading on (0 1 0) and (0 1 1) orientations, including the isentropic elastic limit and stress relaxation after phase transformation. The incorporated inelastic deformation mechanism (plasticity, damage) and phase transformation are responsible for the calculated anisotropic thermomechanical response. Specifically, damage outstands for loads on (0 1 0) orientation while plasticity is more prominent for loads on (0 1 1) orientation. Pressure-temperature-relative volume relation is directly obtained, which agrees well with experimental result from Hooks et al. (2006). Phase transformation response and its effect on thermomechanical behavior are quantified.