Application of the cyclic R-curve method to notch fatigue analysis

• The cyclic resistance curve method is applied to predict non-propagating cracks.
• A local plastic correction to stress intensity factor has been applied.
• The model has been validated against the critical distance method.
• The higher notch-sensitivity for high strength steels can be predicted.
• The model correctly predicts the loss of fatigue resistance with increasing roughness.

The paper deals with the prediction of the fatigue limit of notched specimens. Some authors in the literature have shown that this issue can be solved by employing an approach based on critical distances, others used elastic fracture mechanics. In this paper the fatigue limit of notched specimens is given by the non-propagating condition of mechanically small surface cracks. According to the so-called cyclic R-curve method, the crack driving force of a growing small crack is compared to its resistance force, which incorporates the gradual build-up of crack closure. The fatigue limit is determined by that applied nominal stress, for which the tangency condition of crack driving and resistance force is satisfied. The approach has been modified to incorporate plasticity effects in the mechanically short crack regime and it has been applied to a mild and a high-strength steel, in case of an infinite plate with circular hole under remote tensile stress. The method has been successfully applied to the evaluation of fatigue notch-sensitivity in case of surface roughness.

Figure optionsDownload as PowerPoint slide