Fatigue Strength of Notched Specimens under Variable Loadings

In Case of K_t=3 and 5 for 0.35% Carbon Steel

Abstract

Previously the authors carried out fatigue tests under such conditions as (1) variable loadings, (2) superposed waveform loadings and (3) intermittent waveform loadings, and applied these test results to estimate the fatigue lives of actual machines. Although many fatigue test results have been published, the data for the notched specimens, especially in the case of rotating bending, about crack initiation and crack propagation under variable loadings are very few. Therefore, in order to contribute to the study of this problem, the authors have carried out the fatigue tests for the notched specimens under two-level multiple block loadings.
The conclusions obtained from the test results are summarized to the following two points.
(1) Modified Miner's law predicts the fatigue life too short, especially in the long life range.
(2) It is, for the time being, a neccessary and inevitable expedient to predict the fatigue life by extending the S-N curve downward in a straight line and by adopting σ_eq^* and Σn_i^*, in which n₂^β is substituted for n₂ in the conventional formulas of equivalent stress σ_eq and total repeated numbers Σn_i.