某型起落架主起开锁作动筒堵盖开裂分析

Analysis of Cracking of Main Lift Unlocking Actuator Cover of a Type of Landing Gear

为准确定位外场某型起落架开裂原因,采用技术归零的“定位准确、机理清楚、问题复现、措施有效、举一反三”五步分析方法。对3件堵盖故障件进行了外观目视检查、微观观察、断口成分分析及显微组织检测等多角度故障分析,并随机选取了2件开锁作动筒组件,按照图样和设计要求进行了盐雾试验。通过试验,成功复现了故障现象,发现了堵盖开裂的失效机制:主起开锁作动筒堵盖的外筒螺纹部位积存腐蚀介质后,一旦螺纹表面的保护膜受损、装配时径向应力过大,便易导致堵盖分模面处流线露头,暴露的晶界成为腐蚀通道,最终引起沿晶界的应力腐蚀破坏。为解决堵盖应力腐蚀开裂问题,改进了端盖模压成型过程中分模面的角度,并在开锁作动筒装配环节采用定力矩方法,以此控制装配应力,防止类似问题的再次发生。

In order to accurately locate the cracking cause of a certain type of landing gear in the external field,it was adopted that the five-step analysis method of accurate positioning,clear mechanism,problem recurrence,effective measures and drawing a conclusion.The multi-angle fault analysis was carried out that the visual inspection,the microscopic observation,the fracture components analysis and microstructure detection of the three plug cover faults.The two lock actuator components were randomly selected and salt spray test was carried out according to the drawings and design requirements,and the fault phenomenon was successfully reproduced through tests.It was found that the failure mechanism of plug cap cracking as follows:after the corrosion medium was deposited in the outer cylinder thread of the main unlock actuator cover,once the protective film on the thread surface was damaged and the radial stress during assembly was too large,the flow line at the mold surface of the plug cap was easily exposed,and the exposed grain boundary became a corrosion channel,which finally caused stress corrosion damage along the grain boundary.In order to solve the problem of stress corrosion cracking of the plug cap,the angle of parting die surface in the process of die pressing of end cap was improved,and the fixed torque method was adopted in the assembly of unlocking actuator barrel to control the assembly stress and prevent similar problems from happening again.