Sub-surface fracture of a thin metallic foil under impact loading

We examine here sub-surface fracture of a thin metallic foil sandwiched between two elastomeric layers under impact. In particular we generate a vertical stack consisting of alternate layers of soft elastomers and thin aluminum foils and place it on a rigid substrate; we then allow a rigid sphere to impact the stack from a small vertical height. We show that under impact the foil at the top of the stack undergoes buckling deformation; however the foil sandwiched between the two elastic layers undergoes both deformation and fracture. We show that because of friction at the contacting interfaces with the elastomer, the sandwiched foil is subjected to in-plane stretching which when exceeds a threshold limit causes fracture. Experiments show that this threshold condition is reached within a range of critical thicknesses of the top and bottom elastomeric layers, for a given height of impact of the rigid spherical indenter. We present a theoretical analysis to predict the critical thickness of the stack below which the foil is expected to undergo fracture and also the critical heights within this stack at which the foil would fracture.