Microstructural model for predicting high cycle fatigue strength in the presence of holes under proportional biaxial loading

• Presents microstructural fracture mechanics model of circular hole under biaxial load.
• Procedure for calculating the biaxial notched fatigue limit is described.
• The crack initiation point and the crack direction are predicted too.
• Good agreement with experiments from literature in pure bending and torsion.
• Location of crack initiation along hole contour depends on hole to grain size ratio.

Microstructural fracture mechanics models provide a description of short crack growth that accounts for the interaction between cracks and microstructural barriers. In these models the crack and the plastic zone are represented by a distribution of dislocations. An application to a circular notch under proportional biaxial load is shown. The procedure for calculating the biaxial notched fatigue limit is presented. The crack initiation point and the crack direction are predicted too. The results are compared with experiments from the literature for specimens with a circular hole subjected to pure bending, pure torsion and in-phase biaxial loadings. The need of a biaxial model to account for the direction of initial crack growth found in practice is established. An interesting result given by the model is the fact that the smaller the radius of the notch, the wider the region along the notch contour where the likelihood of initiation is equally high.