Assessment of the delamination hazard of the core face sheet bond in structural sandwich panels

Delamination of the adhesive bond between face sheets and cellular core of structural sandwich panels is a major problem in sandwich construction. Due to incompatibilities in the modes of deformation associated with the face sheets and the cellular core, stress concentrations and singularities can occur even in absence of cracks. These stress concentrations are assumed to govern the onset of delamination. In the present study, a mesoscale concept for a first-order assessment of the delamination hazard induced by the incompatibility in the modes of deformation at the interface between core and face sheets is presented. The approach is based an a fourth order tensor which can easily be derived from the effective elasticity tensor for the cellular core. Due to the general formulation, the concept is applicable to all types of two dimensional cellular sandwich cores irrespectively of cell geometry and loading conditions. The approach is illustrated by an analysis of three examples concerning commercial sandwich core geometries as well as a more general non-orthotropic cellular structure.