Postbuckling and Growth Behavior of Face-Sheet Delaminations in Sandwich Composites

Abstract

A bending load on a sandwich beam consisting of two fiber-reinforced sheets (skins) separated by a low stiffness core is equivalent to a compressive force on one face and a tensile force on the other. Should an interface crack between the layers of the composite face-sheet or between the core and the composite face-sheet exists on the compressively loaded face, local buckling and subsequently growth of this interface crack (delamination) may occur. This may also naturally occur under pure compression. In this study, the buckling, postbuckling and delamination growth behavior is studied through a procedure that is based on the large deflections of the delaminated layer. First, the solution is derived for the postbuckled states by using the elastica theory to model the large deflections of the thin delaminated layer and the sandwich beam theory (for unsymmetric sections) that includes transverse shear, to model the (relatively modest) deflections of the rest of the structure. This postbuckling solution is subsequently used to study the growth of the mixed mode interface crack through an energy release rate approach. The consequences of the elastic mismatch between core and face sheet are discussed and illustrative results are presented for several sandwich construction configurations.