MIXED-MODE FRACTURE IN AN INTERLEAVED CARBON-FIBER EPOXY COMPOSITE

Commercial IMS carbon-fibre/modified-thermoset prepregs (Fibredux 927) were interleaved with the same matrix resin in order to study the mec hanisms and the extent of toughening achievable by this technique. Uni directional laminates were tested in mode I, mode II and in mixed mode by means of the modified NASA mixed-mode bending rig. Significant inc reases in delamination resistance were found in all modes of loading w hen 50 and 200 mu m thick layers of the resin were placed in the centr al crack path of the laminates. The fracture data were fitted to a sim ple failure criterion and related to the predicted plastic zone sizes. Fractographic examination documents the gradual change in the microme chanisms of failure as the imposed loading mode changes. The crack pat h is observed to oscillate between the two ply boundaries, via the res in-rich layer, raising questions as to the micromechanical interpretat ion of the fracture data.