Influence of material's ductility and local deformation mode on multiaxial fatigue response

The multiaxial fatigue behaviour of components seems to depend mainly on the ductility of the material used determined by applied manufacturing parameters. The ductility steers the damage mechanisms. While, in the case of low-ductility (brittle) materials, the normal stress (strain) is the decisive parameter, in the case of ductile materials, it is the shear stress (strain), and, for semi-ductile materials, a combination of normal and shear stresses (strains). Critical plane oriented hypotheses can consider these different parameters, but the difficulty lies in the definition of ductility and, based on this, the selection of the appropriate hypothesis. Therefore, especially for the evaluation of safety parts, experimental verifications are still necessary, because of the lack of a general multiaxial fatigue hypothesis.