某型飞机启动发电机软轴在使用160 h后发生早期失效, 采用断口观察、磨损痕迹分析、硬度测试、显微组织分析等方法对其断裂原因进行了分析。结果表明: 软轴断裂的性质为大应力低周疲劳断裂; 软轴的断裂原因为端盖和发动机法兰盘联接错位导致发动机与发电机软轴错位, 从而产生异常的弯曲应力, 正常的扭转应力与异常的弯曲应力叠加后的应力超过了软轴的疲劳强度; 通过改进定位销的高度可避免发电机软轴的断裂。

Flexible shaft of the starter-generator for a plane fractured early after serving for 160 h. In order to find out the fracture cause, fracture observation, wear trace analysis, hardness test and microstructure analysis were carried out. The results show that the fracture mode of the flexible shaft was low cycle fatigue failure under high stress. The main reason for the flexible shaft fracture was that the abnormal bending stress was caused by the dislocation of the flexible shaft of engine and generator as link dislocation of end cap and ring flange. The stress superposition of the mormal distorting and abnormal bending stress which exceeded the fatigue strength of the shaft. The fracture of the flexible shaft could be effectively prevent by improving the height of the dowels.