Repeated rotating bending fatigue tests were carried out on the notched specimens of Cr-Mo steel, SCM 4, especially at and near it's fatigue limit, and its statistical fatigue properties were investigated. The distributions of the number, depth and length of microcracks being developed were determined at various steps of fatigue lives, and the distribution shapes of fatigue lives were obtained.
A new model which can explain the statistical properties of microcracks and fatigue lives was proposed, and a new method to evaluate the distribution of lives at and near the fatigue limit was established. The new method was essentially based on the consideration of properties of microcracks and the distribution of crystallographical properties. This new method of statistical evaluation presents the so-called variable finite extreme value distribution function.
The tested lives were analysed by this evaluation method. It was revealed that the distributions of lives calculated at and near the fatigue limit were in good agreement with the test results.
