THE INTERLAMINAR FRACTURE PROPERTIES OF CARBON-FIBER-REINFORCED PEEK LAMINATES WITH OFFSET CENTER 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 inv estigate the effect of fiber bridging on the interlaminar fracture res istance of high performance composite materials. Fiber bridging was re duced by offsetting the two centre plies by several degrees relative t o each other. it has been shown that the fracture response of these sl ightly modified laminates is very different to that of conventional un idirectional composites. Offsetting the centre plies in double cantile ver beam specimens resulted in a change in the mode of crack propagati on from stable to unstable. The effects of varying processing paramete rs and loading rate were more pronounced in the offset specimens than in the standard unidirectional samples. It is concluded that even limi ted amounts of fiber bridging conceals the true interlaminar fracture response of many composite materials.