Fatigue crack propagation mechanism for SiC whisker or SiC particle reinforced aluminum matrix composites

Abstract

Fatigue crack propagation properties and fracture mechanisms were examined for three commercially fabricated aluminum matrix composites containing SiC whiskers (SiC_w) and SiC particles (SiC_p) under rotating bending condition. Fatigue crack propagation rates for SiC_w/A2024 and SiC_p/A356 composites were lower than those for unreinforced alloys at a given stress intensity factor near fatigue threshold, while the fatigue thresholds for those composites were higher than those for matrix alloys. For SiC_p/A357 composite the fatigue crack propogation rates were higher than those for SiC_p/A356 composite. Fractography revealed that the fatigue crack would propagate to the whisker/matrix interface following the formation of dimple patterns in the whisker rich zones or formation of striation patterns in the whisker poor zones for SiC_w/A2024 composites, while for SiC_p/A356 and SiC_p/A357 composites the fatigue crack would propagate in the matrix near fatigue threshold. The near final failure crack would be linked to the sub-crack initiated from the particles ahead of the main crack. The fatigue crack propagation models were proposed for discontinuous fiber reinforced aluminum matrix composites. It is suggested that the silicon carbide whiskers or particles would have a very significant effect on fatigue crack propagation properties near fatigue threshold