Effect of phase angle on high-cycle fatigue failure of 2A12-T4 aluminum alloy under tension-torsion non-proportional loading

Fatigue experiments were carried out to investigate the effect of phase angle on multi-axial high-cycle fatigue failure of 2A12-T4 aluminum alloy under tension-torsion non-proportional loading. The change of fatigue life with phase angle under different ratio of stress amplitude was discussed. The failure mode of specimen was studied under different phase angle when τ_a/σ_a=1 based on macro-analysis of fracture. The results showed that when ratio of stress amplitude τ_a/σ_a=1, fatigue life raised gradually with the increasing of phase angle and had an exponential relation with the sin of phase angle under the same Von-Mises equivalent stress. When phase angle increased, fatigue life raised under different ratio of stress amplitude and the change was more obvious when τ_a/σ_a=1 than others. By analysis, fracture presented a mixed mode of model I and model II. The dominant mode had a transition from model I to model II when phase angle increased.