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A thorough investigation of failure behavior of composite sandwich beams under three-and four-point bending was undertaken. The beams were made of unidirectional carbon/epoxy facings and a PVC closedcell foam core. The constituent materials were fully characterized and in the case of the foam core, failure envelopes were developed for general two-dimensional states of stress. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. The initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions.

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In sandwich structures with soft foam core materials, the relationship between load and deflection under the load, also called contact law or indentation, plays a very important role. This work presents a combined experimental and analytical study of the contact behavior of sandwich beams with polyvinyl chloride (PVC) foam cores. The mechanical properties of the sandwich constituents were fully determined and sandwich beams, facesheet-foam and foam blocks were tested under quasi-static loading. These experimental results were used to model the load-deflection curve that includes a linear range followed by a nonlinear portion. The linear model was derived from the Winkler foundation theory and the nonlinear one was obtained by fitting experiments.