Explosive fragmentation of brittle granular materials

This study experimentally investigates the dynamic fragmentation behaviors of brittle granular materials subjected to explosive loadings, employing a concentric shell configuration. The setup consisted of a high-explosive sphere surrounded by a densely packed shell of dry glass spheres. To minimize reflection enhancement, the particle shells were confined within thin-walled glass casings, effectively simulating air-exposed conditions. This configuration allowed rarefaction waves reflected from the outer surface of the particle shell to significantly influence particle fragmentation, particularly in thinner shells. A specialized fragment-collecting apparatus was designed to prevent collision-induced damage to particle fragments, enabling the recovery of most fragments with preserved post-test morphologies following the explosion tests. A comprehensive analysis was conducted on the breakage extent and pulverization degree of the fragmented brittle particles, utilizing metrics such as breakage index, fragmentation volume fraction, and fractal dimension. These parameters exhibited significant variations as the particle shell thickness increased from a dimension comparable to the explosive radius to several times that radius. Notably, the thinnest particle shell underwent near-total particle crushing, evidenced by a fractal dimension of up to 3.2, indicating intense fractal crushing. When the shell thickness increased to 3.75 times the explosive radius, the fragmentation volume fraction was nearly halved, and the fractal dimension decreased significantly. These variations in fragmentation behaviors highlight the impact of divergent blast waves, which impart transient explosive loadings with rapidly decaying overpressures on the particles. The experimental results elucidate the relationship between explosive fragmentation and transient explosive loadings, providing estimations for the radii of pulverized and fractured spherical zones. Particles fragmented by explosive loadings exhibit a markedly higher fractal dimension compared to those fractured by quasi-static loadings, even when fragmentation volume fractions are similar. This suggests distinct breakage mechanisms between the two loading conditions.