The low velocity impact response of foam-based sandwich structures

Abstract

The low velocity impact response of a range of foam-based sandwich structures has been investigated using an instrumented falling-weight impact tower. Initially, the rate-sensitivity of the skin and core materials was investigated through a series of flexure and indentation tests. Here, it was shown that the flexural modulus of the skins and all 11 foam materials did not exhibit any sensitivity to crosshead displacement rate over the conditions studied here. In addition, it was shown that the indentation response of the sandwich structures could be modelled using a simple indentation law, the parameters of which did not exhibit any sensitivity to loading rate. Low velocity impact tests on the sandwich structures resulted in a number of different failure modes. Here, shear fracture was found to occur in the PVC/PUR systems based on brittle core materials. In contrast, buckling failures in the uppermost composite skin were observed in the intermediate modulus systems, whereas initial damage in the higher modulus PVC/PUR systems took the form of delamination within the top surface skin. It has been shown that a simple energy-balance model based on the dissipation of energy during the impact event can be used to successfully model the elastic response of foam-based sandwich structures. The energy-balance model is particularly useful since it can be used to establish the partition of energy during the impact process.