FAILURE MECHANISMS IN CARBON-FIBER REINFORCED POLY(ETHER ETHER KETONE) .2. MATERIAL VARIABLES

This paper examines the effects of the polymer molecular weight, the strength of the fibre/matrix bond and the volume fraction of the fibre on the fracture behaviour of unidirectional carbon fibre/poly(ether ether ketone) (PEEK) composites. The double cantilever beam testing geometry was used throughout the fracture study and cracks were mainly propagated parallel to the individual laminates (interlaminar fracture). Varying the molecular weight reinforced the link between matrix ductility and fracture behaviour, established in the previous work by these authors, with the highest toughness for the carbon fibre/PEEK system measured for the composite with the high molecular weight matrix. The composite treated to obtain low fibre/matrix adhesion showed a reduction in toughness by limiting the energy absorption of the matrix phase. However the increase in damage and appearance of fibre/matrix debonding may account for the good crack stability seen in this material, even at low temperatures. Finally results are presented for the effect of fibre volume fraction, and it is shown that the change in behaviour is directly related to the amount of matrix material available. © 1990.