Effect of forming strain on low cycle, high cycle and notch fatigue performance of automotive grade dual phase steels: A review

In many engineering structural applications, including car body structures, sheet metal formed components are used. A systematic investigation of the impact of forming strain on fatigue life is necessary for an accurate prediction of a formed component's fatigue life. The present work aims to determine the impact of diverse types of tensile pre-straining on high cycle fatigue (HCF), low cycle fatigue (LCF) and notch fatigue performance of automotive grade dual phase steels. In all examined pre-straining conditions, HCF life improves, LCF life deteriorates, and little change in notch fatigue life are observed. The most significant improvement in HCF life and deterioration in LCF life are observed for equi-biaxial and orthogonal tensile pre-straining conditions due to the rotation of maximum shear stress plane and the rotation of the deformation concentrated region around the hard martensite. As the strength improves during pre-straining, there is a corresponding increase in stress concentration around a notch, and as a result, no significant change in notch fatigue life is observed.