Dispersal behavior of granular materials under explosive loading

Unlike a solid ring that expands with a single Gurney velocity, a granular ring develops a radially varying velocity field, leading to a concentration distribution across the cloud. Using laboratory-scale quasi-two-dimensional experiments and coupled FEM-DEM simulations, we investigate the expansion dynamics of granular rings, quantifying the trajectories of the inner, peak-concentration, and outer radii. These trajectories exhibit two distinct stages: an inertia-driven phase followed by drag-dominated deceleration. For the inertia-driven stage, we propose semi-linear scaling laws, based on a modified Gurney velocity, that collapse the trajectories of all three radii across varying shell thickness, particle size, and density. Morphologically, the granular cloud displays a systematic transition from jetting to non-jetting patterns as thickness or density increases, with spike-like jets evolving into irregular corrugations. Simulations reveal that the inertia-driven expansion originates from a radially varying velocity field governed by the interplay of primary compaction, reflected rarefaction, and secondary compaction waves. Furthermore, jetting is traced to heterogeneous momentum transfer during primary compaction, where high-velocity clusters form and are subsequently augmented during the rarefaction phase.