Non-local stress gradient approach for multiaxial fatigue of defective material

The fatigue crack initiation from a surface defect is analysed by means of a new attempt based on multiscale reduction of the stress distribution along the potential crack initiation plane. The reduction is performed by averaging process for shear and normal stresses over two critical areas (multiscale concept). The Matake multiaxial fatigue failure criterion was used to combine the effect of the reduced shear and normal stresses and to calculate the equivalent fatigue strength. The results were verified on defective material subjected to proportional loading. Elastic-plastic numerical simulations were performed for each defect geometry and type of loading (tension, torsion, and tension-torsion) to determine stress distribution. The analysis reveals that the proper calculation of the fatigue limit for defective materials requires performing the averaging process for shear and normal stresses separately.