Toughness of aromatic polymer composites reinforced with carbon fibres

Abstract This experimental study focuses on the toughness of a thermoplastic composite, namely, poly ether-ether-ketone (PEEK) reinforced with 60% by volume of continous carbon fibres (APC 2). Toughness is assessed using both comparative and intrinsic techniques and a critical discussion of the two approaches is presented. The comparative toughness of cross-ply and quasi-isotropic sheets of APC 2 is studied using a damage tolerance test (compression after impact) and by using an instrumented falling weight impacr test over a range of temperatures. Intrinsic toughness is discussed by applying fracture mechanics techniques to unidirectional laminates. Double cantilever beam and three-point flexure tests are used, the latter being performed in six different crack directions. Fracture toughness results are presented for APC 2 and unreinforced PEEK. An ultrasonic C-scan on impacted specimens and scanning electron microscopy on fracture surfaces are used to explore further the mechanisms of fracture, e.g. delamination, fibre breakage and matrix cracking.