Influence of Residual Stress on the Fatigue Crack Growth Mechanism in the Al-Alloy/Hybrid MMC Bi-Material

In this research, the effect of residual stress on the fatigue crack growth behavior in an aluminum alloy-hybrid metal matrix composite (Al alloy-Hybrid MMC) bi- material system has been investigated and the fatigue life of the bi-material has been predicted based on the crack closure technique. Conventional three-point bending fatigue test was carried out in a rectangular notched specimen and the plastic replica technique was used to observe the fatigue crack growth (FCG). The residual stress was measured by the strain relieving method. The fatigue life was predicted by classifying the expression of FCG rate and the effective stress intensity factor, Δ K eff . The results show that the crack propagates slowly in the MMC layer side and maximum crack retardation occurs in the boundary region of the bi-material system due to the change of the state of residual stresses around the boundary. A curved crack front is observed in the aluminum alloy side near the boundary of the bi-material which forms a corner crack that decelerates the crack growth in the vicinity of the boundary of the bi-material even at higher Δ K .