某空压机曲轴在车辆行驶过程中于轴颈圆角处发生断裂。通过宏观分析、扫描电镜分析、金相分析、圆角表面粗糙度测试以及硬度测试等方法对空压机曲轴的断裂原因进行了分析。结果表明:曲轴断裂为低应力下的高周疲劳断裂;裂纹起源于轴颈与轴肩圆角过渡处的加工刀痕, 经疲劳扩展后发生断裂;曲轴断裂的根本原因是圆角处加工刀痕粗大, 表面粗糙度不满足加工标准要求, 应力集中严重, 以及曲轴基体硬度偏低。最后针对曲轴断裂失效原因, 提出了相应的改进建议。

The crankshaft of an air compressor fractured at journal fillet in the vehicle driving process. Means such as macro analysis, SEM analysis, metallographic analysis, fillet surface roughness measurement and hardness test were adopted to analyze the fracture reasons of the air compressor crankshaft. The results show that the fracture of the crankshaft was low stress and high circle fatigue fracture. The fatigue crack originated from the cutting marks at the fillet position between shaft neck and shaft shoulder, and the fatigue crack propagated continuously and finally resulted in the fracture of the crankshaft. The primary causes for the fracture were that the cutting marks at fillet position were deep and thick, the surface roughness was not conform to the process criterion, the stress concentration was serious, and the hardness of crankshaft matrix was not enough. Finally based on above crankshaft fracture causes, some countermeasures were proposed.