On the Development of a Mixed Mode Tensile-Shear Interlaminar Fracture Criterion for Graphite-Epoxy Composites

Abstract

Along with the recent increase in the use of advanced composite materials in primary aircraft structures, has come the need for a quantitative approach to inspection and damage tolerance of these materials. Not only must allowable flaw limits be determined, but damage growth rates must also be known in order to provide a rational basis for establishing inspection intervals. There have been numerous efforts [1–9] to make use of linear elastic fracture mechanics to describe the behaviour of flawed composite materials. However, when fracture of the fibres is predominant, it is found [1–4] that flaw propagation involves the growth of a damage affected zone rather than the self-similar extension of a single crack as is normally the case in fracture mechanics. On the other hand where fibre breakage is restricted such as in the longitudinal splitting of unidirectional composite materials or in the interlaminar fracture of laminated composites, flaw growth is more likely to remain on a single fracture plane [5–9].