Predicting fracture of laminated composites

The compressive strength of currently used carbon fiber-reinforced plastics is generally 30–40% lower than the tensile strength due to fiber microbuckling, thus it is recognized that the compressive strength is often a design-limiting consideration. The zones of compressive stresses can appear in composite structures even under tensile loads. They could be due to the presence of holes, cut-outs and cracks, or generated by impact. It has been revealed that a possible mechanism of failure initiation is fiber or layer microinstability (microbuckling) that might usually occur in regions where high stress gradients exist, for instance, on the edge of a hole or near free edges. A better understanding of the compression failure mechanisms, specific only to heterogeneous materials, is crucial to the development of improved composite materials. The task of deriving Three-Dimensional [“3-D”] analytical solutions to describe the compressive response has been considered as one of great importance. Such solutions, if obtained, enable to analyze the behavior of a structure on the wide range of material properties, and kinematic and loading boundary conditions, without the restrictions imposed by simplified approximate methods.