抄録
Fatigue tests were conducted on smoothed specimens of a carbon steel, S35C, under repeated two-step loadings as well as constant amplitude stresses, and the probabilistic characteristics of fatigue lives under varying loading conditions were examined by considering the both relations of stress-plastic strain and of plastic strain-fatigue life.
The main results obtained are as follows; (1) The distribution of fatigue lives was found to be represented by log-normal distributions for both constant stress amplitude and repeated two-step loading tests. (2) Although fatigue lives under the constant stress amplitude tests showed a fairly large scatter at a stress level near the fatigue limit, those under the varying loading tests did not show such a large scatter at that level and a slightly increasing tendency of the standard deviation of fatigue life with the increase of fatigue life was found in the region below the fatigue limit. (3) Little correlation was found between the variances of the stress-plastic strain relation and of the plastic strain-fatigue life relation for the varying loading tests, and it was found that the variance of the former relation was very much smaller than that of the latter one. Therefore, the variance of the stress-fatigue life relation for the varying loading tests of a particular load pattern was concluded to be determined by the variance of the plastic strain-fatigue life relation.
