Abstract: The densification of heterogeneous porous polymer-bonded explosive (PBX) entails highly complex interactions between mesoscale deformation and microscale multiphase evolution, posing major challenges to predictive cross-scale design and performance tailoring. To address this issue, a novel three-dimensional multiscale discrete element method (DEM) modelling framework is proposed to elucidate the cross-scale structural responses and underlying mechanisms governing densification. The framework employs an innovative segmentation-embedding and scale-filling strategy to realistically reconstruct the heterogeneous multiphase microstructure, comprising brittle crystalline skeletons, thin-layer binders, and irregular pore networks. The study captured a significant anisotropic mesoscale deformation pattern dominated by polar contact zones and strong force chains, while revealing a distinct “dense shell-sparse core” density gradient driven by spatially heterogeneous crystal fragmentation and induced structural rearrangement at the microscale. Based on these findings, a multiscale densification mechanism of PBX characterized by “macroscale load-driven, mesoscale deformation response, and microscale multiphase co-evolution” was proposed, revealing the synergistic densification effect of crystal fragmentation and binder migration in the dynamic game of “damage-repair”. This work not only advances understanding of deformation and damage in multiphase composites but also provides guidance for manufacturing process optimization and structural design to achieve tailored performance.

Key words: Polymer-bonded explosive, Anisotropic deformation, Multiscale discrete element method modelling, Densification mechanism