Thermal mechanical anisotropic constitutive model and numerical simulations for shocked β-HMX single crystals

The present study develops a crystal plasticity model for low-symmetric β-HMX octahydro-l,3,5,7-tetranitro-l,3,5,7-tetrazocine single crystals with only limited operative slip systems, accounting for nonlinear elasticity, volumetric coupled with deviatoric behavior, as well as thermo-dynamical consistency. Based on the decomposition of the stress tensor, the modified equation of state for anisotropic materials is adopted. Simulation results of the planar impact on β-HMX single crystals show good agreement with existing experimental data by Dick et al. (2004a). In addition to providing new perspective to a range of orientation-dependent shock behaviors of β-HMX single crystal, the present work also discusses dislocation density, shear stress, strain localization, and anisotropic temperature increase in shocked β-HMX single crystals under shock loading. The proposed formulation and algorithms can also be applied to other low-symmetric crystals under impact or shock loading which gives irrecoverable deformation by crystallographic slip. Temperature calculations with various characteristic features for different orientations based on numerical simulations are explained, but no comparison with available experimental data is possible to our knowledge. Future studies should also examine phase change and twining as they also often occur in β-HMX single crystals.