中文摘要：

在应变控制下对7075-T7451铝合金实心棒带U型环状缺口试件进行拉一扭比例、非比例恒幅和随机加载疲劳试验。查明名义剪切应力最大值与轴向应力最大值的下降规律，并用两者最先开始下降时的循环数比值来评估裂纹萌生寿命。利用弹塑性有限元法分析不同加载条件下试件缺口根部的循环应力、应变响应。基于有限元计算得到的应力、应变结果，采用拉伸型多轴疲劳损伤模型预测随机加载条件下缺口试件的疲劳裂纹萌生寿命，计算结果与试验得到的寿命比较吻合。

英文摘要：

Tension-torsion proportional, non-proportional and random loading tests are carried out for 7075-T7451 aluminum alloy bar specimens with U-notched ring under strain control. The decline behavior of the maximum nominal shear stress and the maximum axial stress is discussed, and then the crack initiation life is defined as the cyclic ratio when the one of these two stresses began to decline. In order to obtain the local stress and strain data near the notch root of the specimens, the behaviors of multi-axial cyclic stress-strain are simulated using finite element method under different loading conditions. Based on the results of finite element analysis, fatigue life is predicted with the tensile multiaxial fatigue damage model, and the results show a good agreement with the experimental life.