MIXED-MODE DELAMINATION BEHAVIOR OF CARBON EPOXY COMPOSITES/

The mixed-mode bending (MMB) test was employed in an investigation of delamination fracture behavior in static and fatigue loading for carbo n/epoxy composites T300/M10 and HTA/6376. As specimens were loaded at different ratios of a/L for different mixed-mode ratios, both investig ated composites exhibited brittle unstable or brittle stable behavior of crack growth. Mixed-mode delamination fracture toughness was determ ined at a/L = 0.5. Fracture surfaces of MMB specimens were examined us ing scanning electron microscopy to distinguish fracture features, Sta ble crack growth was observed over the entire range of crack lengths i nvestigated in the cyclic tests. A consistent relation of crack growth per cycle to the cyclic strain energy release rate was obtained. The trend of reduction in crack growth rate data with diminution in cyclic strain energy release rate suggests the presence of a threshold strai n energy release rate.