Thermoelastic stress analysis of sandwich structures with core junctions

The paper concerns local effects occurring in the vicinity of junctions between different cores in sandwich beams subjected to cyclic tensile in-plane or transverse bending loading. It is known from analytical and numerical modelling that these effects display themselves by an increase of the bending stresses in the faces as well as the core shear and transverse normal stresses at the junction. In the present paper the local effects have been studied experimentally by means of thermoelastic stress analysis (TSA) for two types of sandwich beams with aluminium and glass-fibre reinforced plastic (GFRP) face sheets and core junctions with polymer foams of different densities and aluminium edge stiffeners. Calibration tests on the constituent materials have been used to obtain the calibration constants necessary for calculating stress data from the thermal data. Reference data obtained from finite element modelling (FEM) were used for comparison with the experimentally obtained results. In tests examining the sandwich face surface stresses looking on the top or bottom side of the sandwich beam, the TSA was able to predict confidently the overall nominal surface stresses in the regions that were undisturbed by the discontinuities. A local variation of face surface stresses in the vicinity of the core junctions was qualitatively captured by the TSA, but of different magnitudes than predicted by the FEM. In tests examining the stresses at the sandwich?s longitudinal edge, the quality of the data was significantly affected by motion effects in the bending tests, even when employing motion compensation software. For the tensile in-plane loading case, the effects of motion were less pronounced and stress data could be obtained without the motion compensation. The local variation of face stresses was not resolved properly by the TSA, whereas in the aluminium core the local stress patterns from TSA were similar to the ones predicted by the FEM. In the foam core materials, no reliable stress data were obtained.