The Effect of Stress Amplitude on Multi-axial High-cycle Fatigue Failure under Constant Amplitude Loading

Studies about the effect of stress characteristics on multi-axial high-cycle fatigue of metals are still insufficient. Up to now, little work about the effect of different ratio of stress amplitude has been done on multi-axial fatigue under the same equivalent stress. In this paper, the effect of ratio of stress amplitude, lambda = tau(alpha)/sigma(alpha) under the same Von-Mises equivalent stress is studied from theory and experiment. The results show that the main factor of multi-axial high-cycle fatigue failure is the maximum principal stress. For proportional loading, fatigue life raises when ratio of stress amplitude increase. The variety of fatigue life is not obvious when A is larger than a certain value and its value closes to that of pure torsion. For non-proportional loading, when ratio of stress amplitude increases, fatigue life raise at first, then has an inflection point. The value of,I at the inflection point changes with phase difference and its value is 0.5 while phase angle is 90 degrees. Fatigue life of uniaxial tension was lower than that of pure torsion.