Deformation and fatigue behaviors of case-hardened steels in torsion: Experiments and predictions

This study investigates cyclic deformation and fatigue behavior of case-hardened solid specimens made of 1050 steel in torsion. Specimens were case-hardened to a case depth to diameter ratio of 0.2, which is typical of many applications. von Mises criterion was found to provide good predictions of the shear cyclic deformation based on the uniaxial behaviors of the core and the case materials. Shear fatigue properties estimated from uniaxial properties by employing maximum principal strain criterion were in good agreement with experimental results. In the absence of any fatigue data, the Roessle–Fatemi hardness method in combination with the maximum principal strain criterion was found to provide excellent estimate of the shear fatigue behavior for the case-hardened specimens. It is also suggested that significant weight reduction of about 50% could be obtained by changing the solid cross section configuration to tubular configuration for shafts under pure torsion or when torque is the dominant load, while maintaining the same torque carrying capacity and fatigue life.