Characterization of local effects at core junctions in sandwich structures using thermoelastic stress anaylsis

Local effects at core junctions in sandwich structures are studied using thermoelastic stress analysis (TSA). At the core junctions, large stress gradients occur owing to local bending of the face sheets and tension and compression of the adjacent cores. In the neighbourhood of large stress gradients it is known that non-adiabatic behaviour occurs which causes significant departures from the isentropic assumption that underpins TSA. Analytical estimates of the boundaries of adiabatic behaviour are made which show that TSA cannot capture the local effects using practical loading frequencies with thin aluminium face sheets, and this is confirmed experimentally. An experimental model of the sandwich beam is designed that shows that the local effects can be captured using TSA. It is also demonstrated that TSA can be used to assess local effects in sandwich constructions with glass-fibre-reinforced plastic face sheets. Reference data obtained from independently validated finite element analyses were used for comparison with the TSA results. A discussion on the effect of surface pattern and the introduction of noise due to motion is included in the paper. The data are presented in terms of stress and calibration tests on the constituent materials are carried out and reported in the paper.