飞机转动接头失效分析

对飞机进行检查时，发现与方向舵液压机构相连接的导管断裂，转动接头卡死不能转动。用化学分析、金相检验、扫描电镜观察及能谱分析等方法对转动接头卡死及导管断裂原因进行了分析。结果表明，接管套与弯管嘴处于偏心状态，导致相互旋转受到制约，发生碾压磨损，造成过载压痕损伤，碾磨达到一定程度导致转动接头卡死；导管断裂主要是由于导管变形鼓包处强度减弱，工作过程中在位于螺帽衬套根部的导管处形成应力集中产生疲劳裂纹，当疲劳裂纹扩展到一定程度时，转动接头受到制约，造成导管被强行弯曲而引起断裂。

Failure Analysis on Rotational Joint of an Airplane

When an airplane was inspected, the pipe linked to the hydraulic-pressure framework of the rudder was found to have fractured and the rotational joint was locked. The lock cause of the rotational joint and the fracture cause of the pipe were analyzed by chemical analysis, metallographic examination, SEM and energy spectrum analysis. The results show that the joint pipe and the elbow pipe nozzle were in the eccentricity state. Rolling abrasion occurred when they revolved. When the roiling abrasion evolved to some extent, the rotational joint was locked. The fracture of the pipe was a result of the forced bend of the pipe. There existed stress concentration in the pipe near the root of the nut bush during service, and the strength of the pipe at the position of the belly decreased. Under the co-effect of stress concentration and the decreased strength, fatigue crack came into being. Because the rotational joint was restricted, the pipe was forced to bend with the propagation of the fatigue crack. Finally, the pipe fractured.