Extension to finite life of a failure assessment diagram for contact fatigue loading

The paper presents an extension to finite life of a failure assessment diagram recently proposed for components subjected to rolling contact loading. The approach considers inherent defects, like inclusions, as potential sources of crack initiation and propagation. A predictive model based on the critical distance theory was proposed for this aim, allowing to define iso-life curves, represented by a quarter of ellipse in the diagram. For working conditions exceeding shakedown, an approach to calculate finite life due to ratcheting was also presented, by comparing cumulated shear strain with the critical one. The proposed approach was used to predict the number of cycles to failure of disk specimens made of SAE 5135 gear steel and compared with the results of previously carried out rolling contact fatigue tests. The agreement between predicted and experimental specimens life resulted good, showing the effectiveness of the approach.