Inclusion size distribution and endurance limit of a hard steel (Q1582505)

The influence of typical component characteristic like size of the highly stressed volume, stress gradient, proportional multiaxial stress state evoked by notches, on the fatigue limit of ground specimens made of the bearing steel SAE 52100 in a superclean bainitic condition is investigated. With the weakest-link concept and the Dang-Van criterion, a method is developed to predict the endurance limit as a function of the highly stressed volume. The endurance limits of smooth specimens under tension-compression, repeated tension and rotating bending are the basis of the calculation. The application of the method supplies good predictions of the measured endurance limits and shows that the effect of notches in this steel is a statistical size effect and an effect of multiaxial stresses. For this material and the presented load conditions, the ``weakest link'' can be identified as crack initiating inclusions. Their size distribution is correlated with the distribution of the random endurance limit by a Murakami-type fracture-mechanics relation between inclusion size and endurance limit. The method inherits no restrictions concerning specimen geometry and load condition, if the stress amplitude is constant, so that an application to components is possible.