装载机曲轴断裂原因分析

装载机累计运行1700 h后,柴油发动机曲轴发生断裂失效。通过化学成分分析、硬度检测、金相检查、断口宏观和微观分析等方法,探究曲轴断裂失效的原因。结果表明:该曲轴的失效模式为高周疲劳断裂失效,裂纹源在曲轴第6连杆颈轴颈内部深度约6 mm区域;轴颈内部未完全闭合的缩孔缺陷和呈带状聚集分布的大颗粒(Ti,Nb,V)(N,C)非金属夹杂物是曲轴断裂失效的主要原因。发动机运转过程中曲轴在服役应力的作用下,缩孔缺陷作为裂纹源在(Ti,Nb,V)(N,C)非金属夹杂物偏聚带发生裂纹扩展长大,形成轴颈内部裂缝,并持续疲劳扩展,最终发生疲劳断裂失效。

Analysis on Fracture of Loader Crankshaft

The crankshaft of the diesel engine broke and failed after the loader has been running for 1700 hours. The reasons of the crankshaft fracture failure were explored by means of the chemical composition analysis, hardness testing, metallographic structure analysis, fracture macroscopic and microscopic analysis, and other analytical methods. The results show that the failure mode of the crankshaft is high-cycle fatigue failure. The crack source is about 6 mm deep inside the journal of the 6th connecting rod of the crankshaft. The shrinkage defects which are not completely closed, and the large non-metallic inclusions (Ti,Nb,V)(N,C) which are clustered and distributed in bands inside the journal, are the main reasons for the crankshaft fracture failure. During the operation of the engine, the shrinkage hole defects acted as crack sources in the segregation zone of the (Ti,Nb,V)(N,C) non-metallic inclusions under the action of the service stress. The cracks grew and expanded to the internal cracks in the journal, and continued fatigue expansion to the final fatigue fracture failure.