The interlaminar fracture properties of carbon fiber reinforced PEEK laminates with offset centre plies

A series of mode I and mode II fracture tests have been undertaken on carbon fiber reinforced poly ether ether ketone (PEEK) in order to investigate the effect of fiber bridging on the interlaminar fracture resistance of high performance composite materials. Fiber bridging was reduced by offsetting the two centre plies by several degrees relative to each other. It has been shown that the fracture response of these slightly modified laminates is very different to that of conventional unidirectional composites. Offsetting the centre plies in double cantilever beam specimens resulted in a change in the mode of crack propagation from stable to unstable. The effects of varying processing parameters and loading rate were more pronounced in the offset specimens than in the standard unidirectional samples. It is concluded that even limited amounts of fiber bridging conceals the true interlaminar fracture response of many composite materials.