Determination of probability distribution of fatigue strength and expressions of P-S-N curves

Abstract

In the present study, new procedures are developed to determine the probability distribution of fatigue strength and the expressions of P-S-N curves. The fatigue test results of 16 Mn steel and the analysis show that the fatigue strength coefficient, the theoretical endurance limit and the fatigue strength at a given life follow the log-normal distribution when the fatigue life follows the log-normal distribution; meantime, the theoretical endurance limit and the fatigue strength follow the normal distribution. The accurate expressions of P-S-N curves can be obtained from the distributions of the fatigue strength coefficient and the theoretical endurance limit in the case that the fatigue life test results follow the log-normal distribution. Also, the dispersion of fatigue life and fatigue strength are discussed. Based on the analysis given in this paper, it may be thought that it is applicable to assume the fatigue strength being a log-normal distribution in engineering applications. However, it may be questionable to assume the standard deviation of fatigue strength being constant. Finally, it should be pointed out that the procedures developed in the present study can be applied in the long life region, where the distribution of fatigue life can not be determined by experiments.