Nonlinear behavior of composite sandwich beams in three-point bending

The load-deflection behavior of a composite sandwich beam made of unidirectional carbon/epoxy facings and a PVC closed-cell foam core in three-point bending was investigated both experimentally and theoretically. A nonlinear mechanics of materials analysis that accounts for the combined effect of the nonlinear behavior of the facings and core materials (material nonlinearity) and the large deflections of the beam (geometric nonlinearity) was developed. The theory favorably predicted the experimental results. It was found that the effect of material nonlinearity on the deflection of the beam is more pronounced for shear dominated core failures and takes place for small beam lengths. For large beam lengths the observed nonlinearity is small and is attributed to the combined effect of the nonlinear stress-strain behavior of the facings and to the large deflections of the beam.