Numerical investigation of explosive fragmentation of brittle granular media

This study investigates the fragmentation behavior of brittle granular media under explosive loading using a coupled finite element-discrete element method (FEM-DEM) framework. The results reveal that conventional crushing criteria based on instantaneous principal stresses systematically overestimate the experimentally derived volume fraction of crushed particles, as they neglect the critical timescale competition between transient blast impulses and intra-particle fracture propagation. To address this limitation, we develop a time-dependent crushing criterion that integrates time-averaged oscillating shear stress with Weibull statistics of particle strength to account for premature unloading effects during ultra-short loading events. Simulations implementing this approach achieve significantly improved agreement with experimental measurements across varying mass ratios between particles and explosive. Furthermore a consistent three-zone fragmentation pattern emerges, including a fully pulverized inner region adjacent to the charge, a partially fractured intermediate zone in which fragmented and intact particles mix together, and a largely intact outer region with minimum fragmentation. Analysis demonstrates that this spatial distribution results from the interplay between blast wave attenuation characteristics and particle strength heterogeneity. Based on these findings, we develop a semi-empirical model that predicts crushed volume fractions as a function of scaled distance, providing a practical tool for assessing blast-induced fragmentation in granular systems. This work establishes a physics-based framework that captures essential dynamic fracture processes previously unaccounted for in granular media under explosive loading.