Short-fiber/particle hybrid reinforcement: Effects on fracture toughness and fatigue crack growth of metal matrix composites

We have studied the effects of short-fiber/particle hybrid reinforcement on fracture toughness and fatigue crack growth in metal matrix composites. Reinforcement hybridization was achieved by a hybrid preform process, and composites were fabricated by the squeeze casting method. A16061 matrix alloy and four composites having different short-fiber/particle ratio were tested. The fracture toughness (K-IC) and the fatigue threshold (Delta K-th) increased with increasing particle contents, whereas the Paris' exponent (m) was insensitive to the short-fiber:particle ratio. These results emerged as a shift of the crack growth curve which implies on enhanced crack resistance over the entire stress intensity factor range. The positive aspect of particulate reinforcement is advocated by comparison of microstructural variables, and by observation of the crack path and surfaces. The characteristics of hybrid composites in damage tolerance are emphasized. (c) 2006 Elsevier Ltd. All rights reserved.