The role of competing mechanisms in the fatigue-life variability of a titanium and gamma-TiAl alloy

The variability in fatigue lives of an α+β titanium alloy (Ti-6Al-2Sn-4Zr-6Mo) and a γ-TiAl-based alloy in stress vs. life space resulted from superposition of variability associated with two separate mechanisms. The mean lives of the two mechanisms diverged with decreasing stress level, giving rise to the variability. A life-prediction methodology based on the variability in the worst-case mechanism is suggested. The potential for reducing uncertainty and increasing the utilization of the useful life as compared to more traditional approaches is discussed.