In order to examine the fatigue life distributions, statistical fatigue tests were carried out at two stress levels by using a number of specimens having only one surface defect or having two surface defects. Theoretical interpretation was attempted on the distribution characteristics of the fatigue life from the following two view points.
(1) The fatigue life distribution of the specimens with a few surface defects is derived from that of the specimens having only one defect based on the concept of extremes distribution.
(2) The total fatigue life is separated into crack initiation and crack propagation lives, and, the distribution of total life is derived by convolution integral of the above two componental distributions.
Finally, it was shown that the experimental life distribution was successfully explained by either one of these analyses.
