MODELLING OF SHORT CRACK FATIGUE THRESHOLDS BY A STRIP-YIELD MODEL

Fatigue of mechanical components corresponds to the fatigue growth of very small fatigue cracks up to the final fracture. It is therefore important to try to describe small crack growth and thresholds with the Strip- Yield model, which is a common prediction tool for life estimates under variable amplitude loading. In the present paper, we apply the Strip-Yield model to the analysis of fatigue thresholds of a mild steel widely adopted for manufacturing railway axles. In particular, we have here addressed the problem of a correct definition of the constraint factor under the cyclic non-linear response of the material and of the choice of an appropriate constraint formulation. This has led to good predictions of fatigue thresholds at R=-1 for long cracks (obtained on SE(B) specimens) and for small cracks (obtained with fatigue tests on specimens containing defects).