应力集中和表面完整性对平尾大轴抗疲劳性能的影响

Effects of Stress Concentration and Surface Integrity on Anti-fatigue Performances of Horizontal Stabilizer Shaft

某型飞机平尾轴在进行台架试验时发生断裂,失效分析表明,该轴的断裂性质为疲劳断裂,裂纹起源于大轴筒体内腔变截面过渡圆弧根部的加工刀痕谷底。通过对大轴进行扫描电镜观察分析,发现使用过的旧大轴内表面存在10～16μm厚的'疏松'层,疏松层内有较多的疲劳微裂纹和孔洞,该'疏松'层是大轴服役中氧化腐蚀和疲劳损伤所形成的。'疏松'层的存在破坏了大轴的表面完整性,降低了大轴材料的抗疲劳性能。有限元建模分析表明,变截面台阶造成的结构应力集中和粗糙加工刀痕形成的附加应力集中是造成大轴疲劳断裂的力学因素,两种应力集中因素的联合作用降低了大轴的疲劳寿命,导致大轴在变截面过渡圆弧根部的加工刀痕谷底萌生疲劳裂纹。综合分析表明,大轴内表面'疏松'层的存在以及变截面台阶造成的结构应力集中和粗糙加工刀痕形成的附加应力集中是大轴发生疲劳断裂的主要原因。

A horizontal stabilizer shaft fractured during fatigue test. Failure analysis indicates that the fracture mode of the shaft is fatigue fracture. Fatigue cracks initiated from the valley of the machining marks near the fillet of the inner surface of the hollow shaft. Scanning electron microscopy analysis discovers that there is a loose layer about 10-16 μm on the inner surface of the used hollow shaft. Besides, many fatigue microcracks and holes are in the loose layer. The loose layer resulted from oxidation corrosion and fatigue damage in the use of the shaft which destroys surface integrity and weakens anti-fatigue properties of the shaft. Finite element analysis shows that the structural stress concentration and the local stress concentration resulted from the machining marks are the mechanical factors lead to fatigue failure. Comprehensive analysis shows that the loose layer and the structural stress concentration and the local stress concentration resulted from the machining marks are main reasons for fatigue fracture.