The effect of confinement and material heterogeneities on the dynamics of a granular medium subjected to impact loading

Abstract

Compared with the mechanics of continua that has been established well, the mechanical characteristics of granular particles, in particular, the dynamic ones, have not been thoroughly clarified yet. Therefore, in our previous preliminary study, dynamic stress transfer as well as wave and fracture development in granular media has been recorded using the experimental technique of dynamic photoelasticity in conjunction with high-speed cinematography. Penny-shaped particles have been prepared by a digital laser cutter and piled on a rigid horizontal plane to form a model slope with some inclination angle. The two-dimensional slope has been subjected to dynamic impact on its top free surface. From the experimentally recorded particle motion and transient stress evolution, two dissimilar failure patterns have been identified. One is the complete collapse of the slope or mass flow due to unidirectional force-chain-like stress transfer, and the other one is the toppling-type separation of the slope face caused by broadly expanding two-dimensional waves. Whichever occurs seems to be governed by the temporal profile of the energy given by the impact. Here, in order to investigate the effect of confinement and possibly material heterogeneities on granular dynamics, first, experimentally, solid plates are additionally placed on some boundaries of the model slopes. It is found that stress transfer and dynamic motion in the confined granular medium is largely controlled by the additional solid boundaries. Then, in order to numerically confirm the above experimental observations, the open source code ESyS-Particle is employed. The numerical results compare well with the experimental ones if the parameters required for the numerics are carefully and properly selected.