Collision process of a bead on a two-dimensional bead packing: Importance of the inter-granular contacts

The collision of an impacting bead on a 2D bead packing is experimentally investigated. It is found that the energy dissipated in the collision is strongly dependent on the density of inter-granular contacts in the packing. We show indeed that the energy released by the packing after the impact is increased when the density of inter-grain contacts is lowered. This increase manifests itself by means of an important augmentation of the number of grains ejected from the packing. In addition, we propose a phenomenological description of the propagation of the shock wave (induced by the impacting bead) through the packing. This description is inspired from percolation models and provides a plausible explanation for the increase of the energy released by a packing with a low density of inter-grain contacts.