Mode-II Interlaminar Fracture Toughness of

The interlaminar fracture behaviour of unidirectional carbon/epoxy composites hasbeen studied under flexural loading by using end-notched flexure (ENF) speci-mens. GIIc values were calculated as total fracture toughness energy at the maxi-mum load sustained by the materials as the delamination extended. The results showed that high temperature moulding systems (XHTM45) have the highest GIIc values well above 1000 J / m2. For medium temperature systems (MTM), GIIc has also increased significantly after post cure. For compression strength after impact (CSAI), the behaviour to a certain extent is related to that found for GIIc tests. Comparison of the GIIc values with CSAI also indicated a relationship between two test results. SEM Micrographs revealed their excellent delamination resistance as good crack stoppers with the evidence of strong fibre/matrix interface. Dynamic mechanical analysis (DMA) indicated the increased Tg and modulus retention of the LTM and MTM prepregs after post-curing at elevated temperatures. The failure mechanisms seem to be different for different tough matrix materials and appear to be strongly dependent on the cure and post-curing con-ditions. This is particularly noticeable for curing at 135°C and 80°C of medium and low temperature moulding systems