Sandwich modeling with an application to the residual strength analysis of a damaged compression panel

Finite element models of sandwich structures are often based on classical sandwich theory which reduces the essentially three-dimensional composite — a combination of two high strength faces separated by a light weight core — to a two-dimensional, deformable reference surface to which certain appropriate stiffness properties against stretch, bending and transverse shear are attached.The simplification introduced in this way is well established, but it suffers from a number of drawbacks that restricts its range of applicability rather severely. The drawbacks concern among others, the kinematic and dynamic boundary conditions that prohibit a realistic application of the loading along the edges. They also concern the inability of this model to study local effects such as buckling of the faces.In the present paper, we demonstrate how, with a relatively simple means, a sandwich model can be introduced that does not suffer from the deficiencies mentioned above. Moreover, this improved model provides the possibility to study the detrimental effect of delamination of the faces, and/or, decohesion zones between the core and faces, on the buckling strength of sandwich compression panels.The modification proposed here makes use of existing shell finite elements that are standard in many finite element codes. These shell elements are used to model the deformation of the faces of the sandwich, while the coupling between the two shell components is carried out by applying an appropriate penalty function that represents the deformation of the core.In this paper, we describe this model in some detail and solve an example problem involving the buckling of a sandwich plate with a partially debonded face plate.