Crack nucleation and propagation in β-HMX induced by structural phase transitions

Abstract

Exploring the micro-mechanisms of crack nucleation and propagation in β-HMX, a high-energy molecular crystal, is crucial for predicting the explosive lifetime. In this study, molecular dynamics simulations were employed to simulate the fracture of β-HMX under tensile loading. Our results show that β-HMX single crystals undergo fracture via molecular phase transitions and aggregation. Crack nucleation and propagation are closely linked to these transitions. During plastic deformation, stress-induced local temperature elevations trigger the β to α and β to δ transitions. Once the phase-transformed clusters reach a critical size, cracks begin to nucleate. During the subsequent crack propagation, the proportions of the α and δ phases increase, and the cracks propagate predominantly along the phase transition regions. Crack tips exhibit twinning zones where β to α transitions occur, enabling crack penetration and connectivity. This atomic-level insight elucidates the pivotal role of the phase transitions in the nucleation and propagation of cracks.