通过对联轴器外齿轴的刚度、疲劳强度的校核排除了超负荷运行的可能。并通过对金相和断口的分析认定 ,断裂是由于联轴器外齿轴危险截面处材料中夹杂物等缺陷引起的小裂纹造成的疲劳裂纹扩展 ,直至截面的承载面减小 ,强度不够而引起的 By checking the stiffness of the outer shaft of the coupling and checking the fatigue strength, the possibility of overloading is ruled out. And through the analysis of the metallographic and fracture, the fracture is caused by the fatigue crack growth caused by the small cracks caused by the inclusions and other defects in the material at the dangerous cross section of the outer shaft of the coupling until the bearing surface of the cross section is reduced and the strength is not enough caused