Compressive Behavior of Multiply Delaminated Composite Laminates Part 1: Experiment and Analytical Development

Abstract

The basic mechanics and mechanism concerning compressive stability of composite laminates with multiple circular delaminations is studied analytically and experimentally. An experimental program, employing two types of quasi-isotropic laminates with a conventional and toughened epoxy resin, is used to evaluate the validity of the mechanistic model and further demonstrate the accuracy of finite element analysis conducted in the associated paper. Embedded delaminations are introduced at regular intervals in the thickness direction. The loading edges are fixed, and the side edges are simply supported. Although the buckling load does not depend on the matrix resin toughness, the strength is affected by the toughness. In the analysis, a buckling equation is derived using the Rayleigh-Ritz method, based on classical plate theory and solved as an eigenvalue problem. This method is chosen due to its efficiency. As the buckling mode of the lowest buckling load becomes physically admissible due to the assumptions of equally spaced delaminations and the classical plate theory, the contact problem does not need to be considered, that is, all of the delaminated portions deform by the same amount and do not overlap one another even without any constraints. The buckling loads analytically obtained agree well with experimental and finite element results described in the associated paper. The effects of size and number of circular delaminations on the buckling and failure load are also discussed in detail.