Low velocity impact and flexural performance of sandwich structures with cork and polymer foam cores

The core material plays an important role in the static behavior of sandwich structures, but particularly in their dynamic behavior. Cork with its unique flexibility, elasticity and compressibility properties is an excellent natural energy absorber and motivates the study of its incorporation in sandwich construction. In this work, flexural and impact behaviors of sandwich structures with fiberglass/epoxy face sheets, different cork based core materials, and PMI, PU and PVC foam cores are experimentally studied by four-point bending and low velocity impact, and compared. Flexural properties of cork based structures are lower than those of structural polymer foams for the geometries explored in this work. Core indentation was the single collapse mode observed in this study; therefore, further studies including other specimen geometries for four and three-point bending are required to evaluate other collapse modes and understand the full behavior of cork under flexural loading. Damage tolerance exhibited by cork core structures subject to low velocity impact make cork an improved core material, particularly for sandwich structures likely to regularly suffer low velocity impact events. Ongoing work on cork based core materials modified with a nanoporous gel, and with a dispersion of carbon nanotubes in the bonding layer, is briefly mentioned.