凸轮轴顶端断裂原因失效分析

Failure Analysis for Top Fracture of Camshaft

目的研究发动机凸轮轴和螺栓的失效原因。方法在化学成分、硬度、金相组织、断口形貌等检测分析的基础上,研究凸轮轴和螺栓的失效行为,推断整个失效过程的起因件,并分析导致其失效的原因。结果凸轮轴金相组织、表面和心部硬度无明显异常,断口表面有明显的疲劳断裂特征,裂纹起源于凸轮轴的螺栓孔壁,此处为凸轮轴热处理过程中的感应淬火和非感应淬火的交界处。结论凸轮轴顶端螺栓孔在感应淬火过程中产生尖角效应,导致螺栓孔壁被淬透,材料脆性增加,在长期使用过程中导致凸轮轴顶端疲劳断裂,进而导致连接螺栓发生断裂。

The work aims to study the causes for failure of engine camshaft and bolt.The failure behavior of the camshaft and bolt was investigated based on analysis and test of chemical composition,hardness,microstructure,and fracture morphology,etc.to deduce the part leading to the whole failure process,and analyze the cause of the failure.There was no obvious abnormity in microstructure,surface and center hardness.The fracture surface had obvious characteristics of fatigue crack and cracks originated in the bolt hole wall of the camshaft,namely the interface between induction hardening and non-induction hardening during the heat treatment of camshaft.The bolt hole on the top of camshaft generates acute angle effect during induction hardening,leading to the hardening of bolt hole wall and increasing material brittleness,thus the top of the camshaft has fatigue fracture after long-term use,causing the fracture of joint bolt.