Effect of Mean Stress on Fatigue Crack Initiation and Propagation : From Different Configurations of Notch

Abstract

In previous papers, the effect of a mean stress on a fatigue crack initiation and its propagation from a circular hole was estimated. It is well known that a crack initiated at a bottom of a dull notch have a large propagating rate. Therefore, a degree of the effect of the mean stress on the fatigue crack initiation and its propagating rate may be affected by sharpness of the notch.A fatigue test was additionally made with specimens containing two kinds of shapes of the notch and it is discussed how the degree of the effect of the mean stress on them is affected by sharpness of the notch and the following onclusions are obtained : (1) The mean stress does not affect the crack initiation at every shape of the notch. A life to the crack initiation at the circular hole or two slits is determined only by an alternating stress at the point inner e0 from the bottom of the each notch without regard to the shape of notch. e0 corresponds to a mean size of a ferrite patch of S35C steel used in this experiment.(2) The degree of the mean stress on the fatigue crack propagating rate decreases with sharpening of the notch and this can be explained by the behaviour of the crack propagation previously reported by the authors.