Fatigue crack growth rate and fracture toughness of 25 wt% silicon carbide whisker reinforced alumina composite with residual porosity

The main purpose of this study was to determine the fracture toughness and the fatigue crack growth rate behaviour of 25 wt% silicon carbide whisker reinforced alumina ceramic composite. The fracture toughness values determined using the indentation technique depended significantly on the crack length produced at the corners of the indentation which, in turn, depended on the load used for the indentation and anisotropy in orientation of whiskers in the matrix. However, the fracture toughness values determined using the precracked four-point bend specimens were in general higher than that obtained by the indentation technique and the value was 5.96 ± 0.15 M Pa m1/2. The fatigue crack growth behaviour in this material was similar to that in the case of metals. However, the exponent for the fatigue crack growth rate was 15.5, significantly higher than that usually observed in metals. The likely micromechanism of crack growth under monotonic and cyclic loading in this composite has been identified from fractography of fatigue failed samples.