Effect of interfacial ply orientation on the fracture toughness of a laminated graphite/epoxy composite

Abstract

Results are presented from an investigation on the effect of interfacial ply orientation on the fracture toughness of a graphitelepoxy composite. Three different mode ratios were considered: pure mode I, pure mode 11, and a single mixed-mode condition. Fracture toughness testing was performed on specimens with preimplanted delaminations at 0°100, +15/+15, +15/-15, +30°/+300 and +30°1 30 interfaces. The Double Cantilever Beam test and the End-Notched Flexure test were used to determine values of the critical strain energy release rates for mode I and mode I1 loading, respectively. A relatively new test, the Single-Leg Bending test, was used to determine the critical strain energy release rate for a single, mixed-mode condition. It was found that a 0°/00 interface corresponds to a minimum critical strain energy release rate for all three mode ratios. Fracture surface morphologies were also examined in order to determine the relationship between strain energy release rate and the amount of near tip damage. It was observed that fracture at a O0IO0 interface corresponded to the minimum amount of damage.