Pore size effect on hotspot formation in shocked explosive crystal

Multiscale modeling of pore collapse and hotspot formation is essential for understanding shock sensitivity and initiation in high explosives, yet the mechanisms governing size-dependent behavior across scales remain insufficiently elucidated. To this end, an atomistically informed dislocation plasticity model incorporating size effect is developed for cyclotetramethylene tetranitramine (HMX), which includes nonlinear thermoelasticity, size-dependent dislocation motion and homogeneous dislocation nucleation, as well as melting criteria. Multiscale pore collapse simulations based on the proposed model could well reproduce the size effect and input pressure dependence on the pore collapse rate observed in molecular dynamics results and experiments. By comparing the temperature fields of pore collapse at different pore sizes and loading velocities, five distinct pore collapse modes, classified as overall bulk collapse, equatorial shear band, 45° shear band, twin jets, and single jet, are identified. The size effects of dislocation mechanisms are further decoupled and evaluated. The results reveal that as the pore size increases, the dominant size effect mechanism transitions from that of the critical shear stress for dislocation generation to that of the homogeneous nucleation coefficient. In addition, based on the hotspot temperature extracted, a size-dependent transition from shear-induced to hydrodynamics-induced hotspot formation is revealed, providing new insights into the evolution of energy localization across scales. The present work bridges pore collapse information across multiple scales and promotes multiscale modeling of pore collapse dynamics and hotspot temperatures for the initiation of high explosives.