Application of multiaxial fatigue parameters to fretting contacts with high stress gradients

Many practical fretting contacts give rise to high stress concentrations or singularities, that cause high stress gradients. Straightforward application of initiation-based-life prediction methods can result in conservative life predictions as the high stress levels are not sustained over a critical volume. This paper uses experimental results that show a size effect with the Hertzian contact geometry to investigate the application of Smith, Watson, Topper, and Fatemi-Socie multiaxial initiation parameters to fretting fatigue. It is concluded that, for cases where a high stress gradient exists, an averaging procedure is required in order to produce an acceptable prediction of initiation life. This approach is compared to an alternative procedure based on short crack arrest and the similarities and differences are discussed.