飞机平尾大轴断裂故障分析

某型飞机在试验中平尾大轴发生断裂。通过断口的观察分析、颤裂部位的金相分析、硬度检测，确定了平尾大轴的失效模式，并对其断裂原因进行了分析。结果表明，该平尾大轴的断裂性质为腐蚀疲劳断裂，裂纹均起源于衬套与筒体间的定位焊点处；定位焊点处选用了强度远低于基体的08A钢焊丝，导致焊点强度过低，在工作载荷作用下焊点处过早萌生了裂纹，焊接工艺不当是大轴断裂的主要因素；平尾大轴简体内壁涂敷防锈漆的质量较差，导致筒体内壁出现严重腐蚀。裂纹源区有腐蚀坑，且裂纹扩展过程中均有腐蚀特征，说明防腐蚀措施不当引起的腐蚀对大轴断裂也有重要影响。

Fracture Analysis of an Horizontal Stabilizer Shaft

An horizontal stabilizer shaft fractured during fatigue test. The failure mode and cause of the shaft were investigated by fracture surface examination, metallographic analysis and hardness testing. The results show that the fracture mode of the shaft is corrosion fatigue fracture. All the cracks initiated from the welded joint between the bush and the body of the shaft. The lower strength of 08A steel welding wire resulted in the lower strength of the welded joint. As a result, the cracks initiated from the wel- ded joint under the effect of service load after a short period. The improper welding technique is a main cause for the fracture. In addition, the poor quality of the anticorrosion paint over the shaft inwall resulted in severe corrosion of the inwall. The obvious corrosion features at the fatigue source region and the extension region show that severe corrosion resulting from poor corrosion prevention is another cause for the fracture of the shaft.