Effect of Phase Angle on Fatigue Failure of 30CrMnSiA Steel under Tension-torsion Fatigue Loading

Tension-torsion high-cycle fatigue experiments with solid cylindrical bar specimens of 30CrMnSiA steel were carried out under different phase angles. And the experiment data, characteristics of stresses with plane orientation and fracture appearance under different loading conditions were analyzed and investigated. Experiment results show that fatigue life increases gradually with the increase of phase angle. The fatigue life is shortest for 0° phase angle, while the fatigue life is longest for 90° out-of-phase angle. It could be found from analysis of stress parameters that as the phase angle increases, the shear stress amplitude decreases and the maximum normal stress increases gradually, which are on the maximum shear stress amplitude plane close to the axial of specimen. Macro-analysis of the fracture appearances show that when the phase angle increases, the angel between crack initiation plane and specimen axial decreases, and cracks are inclined to initial and propagate on or near the maximum shear stress amplitude plane with larger maximum normal stress under proportional loading as well as non-proportional loading.