Abstract: When the servo motor is in service for three months, the motor shaft suddenly breaks. Through the appearance inspection, low power observation, fracture analysis, metallographic analysis, chemical analysis and mechanical property analysis of the motor shaft, the fracture cause is explored. The results show that the fracture mode of the motor shaft is fatigue fracture. The main causes of fatigue fracture are low hardness of the shaft center leading to insufficient strength, surface mesh ferrite structure defect, and too small chamfer of the cutting groove aggravating stress concentration, and poor heat treatment process is the root cause of insufficient strength. At the same time, the corresponding improvement measures are put forward to prevent such incidents from happening again.

Key words: Servo motor; Motor shaft; Tempering treatment; Fatigue fracture; Stress concentration

摘要： 伺服电机在服役三个月时，电机轴突然断裂。通过对电机轴进行外观检查、低倍观察、 断口分析、金相分析、化学分析和力学性能分析等试验，对其断裂原因进行探究。结果表明， 电机轴断裂模式为疲劳断裂，轴心部硬度偏低导致强度不足，表层网状铁素体组织缺陷，以 及退刀槽倒角过小加剧应力集中是电机轴发生疲劳断裂的主要原因，热处理工艺欠佳是强度 不足的根本原因。同时针对该失效原因提出相应的改进措施，以避免此类事件再次发生。

关键词: 伺服电机；电机轴；调质处理；疲劳断裂；应力集中