Abstract
Owing to their high strength and stiffness to mass ratio, composite sandwich structures have increasing been used for various engineering applications especially where mass has a direct influence on operating cost and performance. In sandwich structures, the core has an important role of separating and stabilising the skins as well as transferring shear and compressive stresses between the skins. Therefore, the core properties have a strong influence on the strength and perforation resistance of sandwich structures. In this study, the aim is to investigate the effect of grading the core on the structural as well as impact performance of sandwich panels made of GFRP skins and PVC foam core. Both low and high velocity impacts are considered. High speed 3D digital image correlation is employed to extract full-field displacement and strain contours during impact. Grading the core is found to result in a more stable failure process under quasi-static loading which can sustain larger deflections before final failure. Under impact loading, grading the core can improve the perforation resistance if a lower density core layer is immediately behind the impacted skin. The efficiency of grading, however, is influenced by the deformability of the impactor.