Very high cycle fatigue – Is there a fatigue limit?

The paper gives an overview of the present state of research on fatigue strength and failure mechanisms at very high number of cycles (Nf > 107). Testing facilities are listed. A classification of materials with typical S–N curves and influencing factors like notches, residual stresses and environment are given. Different failure mechanisms which occur especially in the VHCF-region like subsurface failure are explained. There microstructural inhomogeneities and statistical conditions play an important role. A double S–N curve is suggested to describe fatigue behaviour considering different failure mechanisms. Investigated materials are different metals with body-centred cubic lattice like low- or high-strength steels and quenched and tempered steels but also materials with a face-centred cubic lattice like aluminium alloys and copper. Recommendations for fatigue design of components are given.