Examination of the failure of sandwich beams with core junctions subjected to transverse shear loading

The article concerns failure and fatigue phenomena associated with local effects occurring in the vicinity of junctions between different core materials in sandwich beams subjected to transverse shear loading. It is known from analytical and numerical modeling that these effects lead to stress concentrations at such junctions. However, their influence on the failure behavior is not fully understood, and there are indications that the available models overestimate the importance of the local effects. In the present article, typical sandwich beam configurations with glass fiber-reinforced plastic face sheets and core junctions between polymer foams of different densities and rigid aluminium were tested under quasi-static and fatigue loading conditions. The failure behavior was compared with results from finite element analyses using various failure criteria. It was found that for the transverse shear load case the inherent core shear stresses overrule the local effects in terms of being most critical with respect to causing failure for the most common sandwich configurations using low density semi-brittle polymer foam cores. A simple maximum shear stress criterion is appropriate for failure prediction (core shear failure) in those cases. However, if very strong core materials and thin face sheets are used, the stress concentrations induced by local effects can cause failure in the faces. Accordingly, the local face stresses can be of importance and should be taken into account for failure prediction.