高温环境2A12–T4铝合金多轴疲劳失效规律研究

许多工程结构在服役过程中往往承受着复杂的多轴疲劳载荷和热力耦合作用，仅靠常温情况下的单周载荷来简化复杂多轴载荷状态的失效预测方法将不再适用。为研究2A12–T4铝合金的高温多轴疲劳失效规律，本实验在175℃环境温度下，选取等效Von-Mise应力幅值，通过间断式加载记录不同拉扭加载循环下的裂纹萌生与扩展情况，研究特定加载路径对裂纹萌生与扩展的影响。实验结果表明，相位差为0时，裂纹萌生方向沿MSSA平面；在相位差为45°时，裂纹萌生传播方向与最大切应力平面方向相近，最大切应力在裂纹萌生过程中起到主要作用；在λ=0.5、φ=0和λ=1.0、φ=0两种情况下，裂纹萌生初期沿着最大切应力平面方向传播，传播过程中存在第I阶段向第II阶段转变的过程；在λ=0.5、φ=45°和λ=1.0、φ=45°两种情况下，不存在明显的第I阶段向第II阶段转变的过程；对比4种加载方式下的疲劳裂纹萌生期与疲劳寿命比，发现切应力比重的增大加速裂纹的萌生过程，相位差的存在阻碍了裂纹的萌生过程。

Multiaxial Fatigue Failure of 2A12-T4 Aluminum Alloy at High Temperature

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.