Multiaxial low-cycle fatigue behavior and life prediction model for Ti-6Al-3Nb-2Zr-1Mo titanium alloy

Abstract

In this paper, a multiaxial low-cycle fatigue damage model is proposed based on the Continuum Damage Mechanics and Modified Wöhler Curve Method. The model identifies the plane with the maximum shear stress amplitude as the critical plane for fatigue damage calculation. The influence of the normal and shear stress components on the multiaxial fatigue strength is directly considered by introducing a variable stress ratio into the traditional fatigue damage model. In the comparison of the prediction results with experimental data, all life data under different loading conditions fall into the scatter band of ±1.5. Stress-controlled multiaxial low-cycle fatigue tests of Ti-6Al-3Nb-2Zr-1Mo were performed. The results indicate that under torsional and combined axial-torsional load conditions, the plane with the maximum shear stress amplitude is not unique, which leads to inconsistencies in the directions of the propagation planes of different crack sources and changes in direction of fatigue crack propagation. The symmetry of the hysteresis curves is related to the final fracture pattern. When shear stress governs fatigue failure, the hysteresis curves near failure are symmetric. In contrast, when normal stress dominates fatigue failure, the hysteresis curves near failure are asymmetric.