Modeling and numerical investigation of mechanical twinning in β-HMX crystals subjected to shock loading

Abstract

This manuscript establishes a crystal plasticity finite element (CPFE) model with large volumetric deformation for β-HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) energetic crystals with emphasis on the deformation twinning behavior under shock loading conditions. The CPFE model captures the nonlinear response of the monoclinic crystal through the application of large volumetric change under shock condition, dislocation slip at low and high moving speeds and mechanical twinning idealized by the twin volume fraction evolution. The twinning behavior is distinguished from dislocation slip through the decomposition of the plastic velocity gradient in which dislocation slip, twinning and slip in the twinned region are separately considered. Third-order Birch Murnaghan EOS is incorporated in the CPFE framework to describe the volumetric deformation under extreme pressure induced by explosion or impact. The results of the numerical investigations show that the twinning behavior exhibits strong orientation dependency, which becomes more evident at higher loading regime. Particle shape significantly affects the twin concentration. Peak twin volume fraction in HMX polycrystalline with regularized particle shapes is lower compared with mesostructure with realistic particle morphologies.