Mean vs. Life-limiting Fatigue Behavior of a Nickel-based Superalloy

The mean and the life-limiting behavior under fatigue of the nickel-based superalloy, IN100, separated (or converged) as a function of stress level and dwell loading. This behavior was related to the control of the life-limiting behavior by the smallcrack growth regime, producing its much slower response to stress level and dwell-time, relative to the mean-lifetime behavior. The lifetime probability density is therefore, modeled as a superposition of the crack growth lifetime density and a meanlifetime density. The crack growth density is calculated with the help of small-crack growth data and the distribution in the crack initiation size. The mean-lifetime density is estimated from a relatively small number of total lifetime fatigue tests. In IN100, we apply this approach to predict the effects of stress level and dwell time on the lifetime distribution and the B0.1 (1 in 1000 probability of failure) lifetime limit.