The effect of a slow impact on sandwich plates

The purpose of this paper is to study the relation between the impact force and the corresponding elastic indentation produced by a rigid sphere falling on a sandwich plate. The analysis of the problem is articulated in three steps. Firstly, an explicit elastic solution for a sandwich panel, statically loaded by a distribution of surface pressures, reproducing Hertz's contact law of a rigid sphere on an elastic half-space, is derived. Then, a certain number of quasi-static impact tests made on sandwich specimens constituted by two layers of graphite epoxy and a core of cellular foam are collected and discussed. Finally, the results are compared with those obtained from a finite element analysis having considered the plate as a three-dimensional elastic body. The conclusion is that the Hertzian contact pressure distribution is appropriate to describe the response of sandwich panels with a high-density core, but the assumption is not appropriate when the core has low-density.