A unified model of anisotropy, thermoelasticity, inelasticity, phase transition and reaction for high-pressure ramp-loaded RDX single crystal

A unified thermomechanical consistent model integrating multiple mechanisms, including material anisotropy, nonlinear thermoelasticity, inelasticity, phase transition, and chemical reaction, is developed for cyclotrimethylene trinitramine (RDX) crystal under high-pressure ramp-loading. (i) The nonlinear thermoelasticity of material is described by pressure-temperature-dependent elasticity tensor and a free-energy based complete equation of state. (ii) The cracking-mediated brittle damage on eleven cleavage planes and dislocation-mediated ductile plasticity on thirteen slip systems are considered in inelastic deformation. (iii) The phase transition kinetics is dependent on a thermodynamic consistent driving force. (iv) The chemical reaction is described by a reactive flow model integrating equations of state for solid reactants and gaseous products, Arrhenius-type reaction rate model and mixed rule. The proposed model is utilized to simulate the mechanical-thermal-chemical responses of (100) and (010) oriented ramp-loaded RDX crystals at pressure up to ~33GPa. The simulated results are well in agreement with the experimental data and reveal a four-wave structure (elastic-inelastic-phase transition-reaction wave) hidden behind the pressure wave profiles. Crack and dislocation activities on (110) and (1-10) crystal planes play a dominant role in macroscopic inelasticity of (100) oriented RDX. Compared to (100) oriented RDX, the (010) oriented RDX exhibits a higher α→γ phase transition criterion and a faster chemical reaction, which is associated with the different overall heating rate and thermomechanical state.