Propagations of the Surface Fatigue Cracks in Various Kinds of Notched Specimens

抄録

In this report, the crack propagations in several kinds of notched round bar specimens of SK 5 and SUS 50 steels are investigated. The main results are summarized as follows. (1) It is possible to estimate the S-N curves for any notched specimen by using the idea of ε₀, which has been often adopted to predict the endurance limit for crack initiation. (2) If the same crack length is obtained for the imposition of the same number of cycles, the crack propagation rates coincide with each other irrespective of the notch root radius and the materials. (3) In opposition to the results in (2), the effect of specimen shape appears on the crack propagation in the radial direction. (4) The index "m" for the formula dl/dN=CK^m or dl/dN=Cσ^m1ⁿ, is considered to be related with the gradient of S-N curve and varies from 4 to 5 depending on the stress amplitude.