Interface fracture toughness of a multi-directional woven composite

The aim of this investigation is to measure the interface fracture toughness of a woven composite. For this purpose, double cantilever beam (DCB) specimens are tested to measure the load as the delamination grows. The specimen is composed of 15 layers of a carbon-epoxy, balanced weave with alternate layers containing fibers in the directions and the directions. A thin piece of Teflon is placed between two layers of differing directions. The specimens are analyzed by means of the finite element method and an interaction energy or -integral to determine the stress intensity factors, interface energy release rate and phase angles. The first term of the asymptotic solution for the stress and displacement fields obtained by means of the Stroh and Lekhnitskii formalisms is used to define auxiliary solutions for the -integral. The critical interface energy release rate is found and exhibits a slowly increasing resistance curve. Comparisons are made to a simple expression from the literature