Fatigue crack growth resistance from unbridged defects in continuous fibre reinforced metal matrix composites

Fatigue crack growth from through-thickness (TT) and contained part through-thickness (PTT) unbridged defects under cyclic loading has been studied at ambient temperature in a Ti-6Al-4V alloy matrix reinforced unidirectionally with continuous silicon carbide fibres. Crack growth resistance curves have been used to predict the onset of crack arrest from both TT and PTT initial unbridged defects in terms of an initial nominal applied stress intensity range. Under some conditions similar initial stress intensity ranges can promote failure from PTT cracks but arrest from TT cracks. The importance of the number of bridging fibres that are breached (and hence stressed) simultaneously is critical to the overall behaviour of the composite. Other important factors are the exact location of the notch root with respect to the initial bridging fibres, the local fibre volume fractions close to the crack plane, together with the statistical probability of isolation and failure of individual fibres. (C) 1998 Elsevier Science Ltd.