A Method to Predict the Effect of Thermal Residual Stresses on the Free-Edge Delamination Behavior of Fibre Reinforced Composite Laminates

Abstract

A method is presented which accounts for the effect of process-induced thermal residual stresses on the free-edge delamination behavior of fibre reinforced laminates. A strain energy release rate fracture mechanics formulation is derived based upon the Irwin crack closure integral. The finite element method is then used to calculate Mode I and Mode II crack opening displacements and stiffnesses for free-edge delamination cracks originating at a specified ply interface from which strain energy release rates due to thermal and mechanical loading are then obtained. The effect of processing temperature on strain energy development is included in the calculation of thermal energy release rates by using experimentally measured material property data. To verify the model, (+352/-352/02/902)s graphite-reinforced PEEK tensile test specimens were manufactured and tested to failure. Measured delamination strains agree well with predictions when the effect of thermal residual stresses is included. Neglecting residual stresses over-estimates the tensile delamination strength by approximately 32%.