Failure initiation and progression of sandwich beams under cyclic bending tests

This study presents experimental results and analysis of failure of sandwich beams with steel face sheets and polyurethane core tested in three-point bending. Firstly, a series of experiences are conducted in order to obtain the mechanical properties of the metallic face sheets and the foam core. To model the foam behavior, quasi-cyclic tests were performed by increasing the punch stroke. An exponential model is proposed describing the variation of the elastic modulus as a function of the strain. Secondly, the quasi-static and quasi-cyclic bending tests are carried out leading to failure of the sandwich beam. The results of the quasi-cyclic bending show that the behavior of the sandwich beam is similar to the foam behavior in quasi-cyclic compression. Thirdly, a Finite Element Analysis (FEA) is performed in order to predict the observed foam fracture in bending test using a shear damage criterion for the foam core. The comparisons show a satisfactory agreement between the experimental results and the FEA predictions.