汽车发动机曲轴断裂失效分析

某厂生产的发动机曲轴在用户使用过程中，3个月内共发生了4起曲轴断裂失效事故，采用化学成分分析、金相检验、硬度测试以及断口的宏、微观形貌分析等方法对断裂曲轴进行了分析。结果表明：曲轴断裂为高周低应力弯曲疲劳断裂，导致其断裂的主要原因是在曲轴第一曲拐过渡圆角R附近的曲柄表面聚集分布着机加工刀痕，形成了应力集中；在用户行驶过程中因车况、路面等复杂因素形成的过载或冲击载荷等作用下，在第一曲拐轴颈尺附近曲柄表面应力集中的机加工刀痕处萌生疲劳裂纹，并逐步扩展直至断裂失效。

Failure Analysis on Fracture of Automotive Engine Crankshafts

There have been four cases of engine crankshafts fracture failure accidents in uses running process,and the fractured parts were analyzed by means of chemical compositions analysis,metallographic examination,hardness test and fracture analysis.The results show that the crankshafts failed in high cycle and low stress bending fatigue fracture mode,and the main reason for the fracture was that there were many gathered distribution of machining marks on the crank surface near the transition position where stress concentration formed.In the users running process,under the action of overload or impact load formed because of vehicle condition,pavement and other complex factors,fatigue cracks initiated at the stress concentrated machining marks,and the cracks gradually propagated until the engine crankshafts fractured.