关键词: 多轴疲劳, 应力幅比, 相位差, 裂纹萌生与扩展, 高温

Abstract: The thermal-mechanical coupling state of structures under multiaxial fatigue loads and high temperature is very complex, and the failure prediction methods for structures under uniaxial loads are not applicable in this case. In order to study the high temperature multiaxial fatigue failure law of 2A12-T4 aluminum alloy at 175℃, the crack initiation and propagation under different loading cycles are recorded by intermittent loading, and the effect of specific loading path on crack initiation and propagation are studied. In the condition of φ=0, the direction of crack initiation is along the MSSA plane; when the φ=45°, the direction of crack initiation is near the MSSA plane, so the maximum shear stress play a major role in the process of crack initiation. Under the λ=0.5, φ=0 and λ=1.0, φ=0, the crack initiate and propagate along the MSSA, and there is no such a transition process from stage I to stage II during the main crack propagation; under λ=0.5, φ=45° and λ=1.0, φ=45°, there is an obvious transition process from stage I to stage II. A Comparison of the relation of crack initiation period and different fatigue life of four loading paths, reveals that the increase of shear stress proportion accelerate the crack initiation period, and the existence of phase difference blocked the crack initiation.

Key words: multiaxial fatigue, stress amplitude ratio, phase angle, crack initiation and propagation, high temperature