Mode II delamination behavior of carbon/epoxy composites

The end-notched flexure (ENF) test was employed in an investigation of the interlaminar fracture behavior in mode II static and fatigue loading for carbon/epoxy composites T300/M10 and HTA/6376. The mode II interlaminar fracture toughness was determined by a compliance calibration method. The tests were performed in the range of the a/L ratio from 0.5 to 0.9. Both composites, T300/M10 and HTA/6376, exhibited brittle unstable and brittle stable behavior of crack growth. Stable mode II crack growth was observed during fatigue loading with R = 0.1 in a large range of cyclic strain energy release rate. A consistent relation of the crack growth rate to the cyclic strain energy release rate was obtained for both T300/M10 and HTA/6376 composites. Within the range of moderate crack growth rate, the data of mode II fatigue crack growth for the composites obeyed a power law. The trend of reduction in the crack growth rate data with degradation in the cyclic strain energy release rate suggests the presence of a threshold strain energy release rate. Compared with T300/914C, HTA/6376 and T300/M10 have a higher crack growth resistance.