Shock response of cyclotetramethylene tetranitramine (HMX) single crystal at elevated temperatures

To investigate the shock response of cyclotetramethylene tetranitramine (HMX) single crystals at elevated temperatures (below the phase transition point), plate impact experiments at elevated temperatures were designed and conducted. The HMX/window interface particle velocities at temperatures of 300 K, 373 K, and 423 K were measured by the velocity interferometry system for any reflector (VISAR) technique. To further analyze the related mesoscale deformation mechanisms, a nonlinear thermoelastic-viscoplastic model was developed, which considers thermal activation and phonon drag dislocation slip mechanisms. The proposed model could well reproduce the measured thermal hardening behavior of Hugoniot elastic limit (HEL) of HMX single crystals. At elevated temperatures, the reduced dislocation mobility was observed, which stems from both phonon scattering and radiative damping effects. Comparatively speaking, radiative damping contributes less than phonon scattering to thermal hardening behavior. The calibrated model was further used to predict shock response of HMX single crystals with different thicknesses at different initial temperatures. Both the stress relaxation and elastic precursor decrease with thickness are mainly due to the rapid dislocation generation. These insights shed light on the interplay between dislocation motion and dislocation generation in thermal hardening behavior, stress relaxation, and elastic precursor decay, which serves to reveal the mesoscale deformation mechanisms at elevated temperatures.