Effects of Heating-Induced Phase Transition on Damage for HMX Crystal

At high temperature loading, the thermal expansion and solid-solid phase transition firstly occur in HMX-based PBXs prior to the melting and decomposition of HMX crystal, thereby inducing the abrupt change of mechanical and safety properties. A constitutive model integrating with several deformation mechanisms, including thermal expansion, and phase transition was developed to investigate the effects of heating-induced phase transition on damage evolution. The influence mechanisms of phase transition in binder-bonded HMX single crystal on the volumetric deformation, stress states and crack nucleation and growth were revealed from the viewpoint of mechanics. The effects of heating rate on phase transition and crack related damage evolution were quantitatively analyzed. The calculated results show that, as the increase of loading temperature, tension stress formed due to the thermal expansion and $\,\beta $→$\delta $ phase transition in unilateral-restrained HMX crystal and local shear stress formed due to mutually compression between crystal and binder, contribute to the nucleation and growth of HMX crystal. The number density of cracks exhibits a remarkable growth near the phase transition temperature, thereby inducing the irreversible damage. The heating rate has a significant influence on the nucleation and growth of cracks. Large heating rate will increase the crack related damage level of crystal, thereby increasing the number density of potential hotspots and risks of inadvertent ignition.