Indentation failure of foam cored sandwich structures subjected to elevated temperatures

This research explores the detrimental effect of elevated temperatures on local indentation failure of polymer foam cored sandwich structures with laminated glass fibre reinforced epoxy face sheets. A simple analytical model to predict the critical indentation failure load at elevated temperatures is presented and validated against experimental observations. For this purpose, a sandwich beam loaded in three-point bending with an induced through-thickness elevated temperature profile was studied experimentally and by means of analytical and finite element models. In the experiment, the through-thickness temperature gradient was induced with an infrared lamp pointing on the top face sheet, while the local displacement and strain fields near the applied point load were recorded by digital image correlation. The analytical model proposed, which accounts for temperature degraded/reduced foam core properties, superimposes the local response, approximated by the classical Winkler foundation model, and the global response obtained by sandwich beam theory. The comparative study has shown that the critical load causing core crushing failure reduces significantly with elevated temperatures by as much as 50% at an elevated temperature of 90celcius. It is shown that the simple analytical model can predict the local deflections and core stresses of foam cored composite sandwich structures subjected to simultaneous localized mechanical loading and elevated temperatures. Thus, the analytical model can be used as a preliminary design tool to determine the critical core crushing load at elevated temperatures.