The mean stress detecting method by the nickel foil with microcircular holes uses the propagation rate of the fatigue crack, which propagates from the edge of microcircular holes. However, since the crack propagation rate does not change considerably even if the mean stress changes, it cannot be said that the accuracy of the conventional method is enough. From the above viewpoint, in this report using the nickel alloy foil with higher hardness than the nickel foil, the improvement of accuracy of this method is investigated. Namely, the effect of mean stress on fatigue crack propagation is examined under constant temperature and frequency at first. Moreover, the influence of the frequency on the sensitivity of this method is investigated. Namely, the fatigue crack propagation is examined under various frequencies, and the basic equations are proposed to obtain mean stress.
