Impulse transfer during granular matter impact with inclined sliding surfaces

Abstract

The collision of hard particles with inclined surfaces transfers an impulse that increases with impact angle and coefficient of friction between the particles and surface. A high friction coefficient therefore substantially reduces the impulse reduction benefit achieved by inclination. A recent study has shown that the attachment of a light sliding plate placed to a lubricated (low friction) inclined surface significantly reduced the transferred momentum from high velocity sand particle impact compared to that transferred with no sliding plate. However, the transferred impulse still exceeded frictionless limit predictions. Particle-based simulations indicated that the light plate was accelerated too rapidly, quickly escaping the surface, and failing to intercept later arriving sand and (air and detonation product) gas particles. A momentum transfer model has been used to explore the regimes of sliding plate interaction with particle slugs, and to identify conditions where the frictionless limit for solid particle impacts is reached. Experiments with particles accelerated by a buried explosion confirm predictions that raising the ratio of the sliding plate mass to that of the sand particles decreases the transferred impulse to the frictionless limit. Interestingly, heavy sliding plates that remained near the most intensely loaded apex of the targets also reduced the late arriving impulse carried by gas particles. However, this approach required the plate mass to rise with incident impulse. Particle-based simulations of the experimental set-up reveal that the sequential sliding of multiple stacked sliding plates successfully avoided any exposure of the underlying target to direct sand particle impact, and provided a lightweight approach for impulse mitigation over a wide range of incident impulse levels.