Scaling effects in the low velocity impact response of sandwich structures

Abstract

Scaling effects in the impact behaviour of foam-based sandwich structures have been investigated using an instrumented drop-weight impact tower. Four scaled sizes of sandwich panel, manufactured by bonding a woven carbon fibre reinforced epoxy composite to a PMI (polymethacrylimide) foam core, were investigated. Low velocity impact tests on the sandwich structures resulted in a localised mode of fracture in all scale sizes at all energies. The resulting load–displacement traces were normalised by their appropriate scaling factors to highlight potential size effects in the impact response of the structures. Additional indentation tests were conducted at quasi-static and dynamic rates of loading to investigate scaling effects in the contact response of the sandwich panels.Size effects were observed in the load–displacement traces of the smaller samples following indentation tests at both quasi-static and dynamic rates of loading, most likely due to the relative size of the radius of the impactor and the weave dimensions of the composite skins. However, for all scale sizes, both the level and type of damage were similar in polished cross-sections removed from the indented panels. Under low velocity impact loading, for a given scaled impact condition, the energy absorbed by the sandwich panels was similar across all four scale sizes, suggesting that the impact response of these sandwich structures obeys a simple scaling law. An examination of the cross-sections of the impact-damaged sandwich structures also suggested that damage was similar in all of the samples for a given scaled impact energy. This evidence suggests that, providing microstructural effects do not play a significant role, simple scaling laws can be used to predict the low velocity impact response of sandwich panels of this type.