Failure modes and optimization of sandwich structures for load resistance

Sandwich construction using foam cores is used in applications, and an understanding of failure loads is an important part of the design process. Tests on sandwich beam specimens with embedded strain gages show that the simpler analysis procedures can be in error by large factors, while an elasticity solution from the literature gives good agreement with the experiments. Comparisons with laboratory tests on sandwich bend specimens with carbon-epoxy faces and polyurethane foam cores of several densities show that the elasticity solution, in conjunction with criteria for failure of the faces and yield of the core give good agreement with the data, and show that the mode of failure and the load at failure could be predicted. Optimization of sandwich structures for strength/weight is considered, and it is shown that the laboratory strength data support the theoretical optimization results.