汽车发动机排气门弹簧断裂失效分析

Fracture Failure Analysis of Exhaust Valve Spring of Automobile Engine

某型号汽车发动机排气门弹簧在做混合循环耐久试验时发生断裂失效。通过宏观检查、断口形貌、微区成分、化学成分、金相组织及硬度等分析手段对排气门弹簧的断裂失效原因进行分析。结果表明:排气门弹簧断裂起始源区存在氧化锆和铁硅酸盐类的非金属夹杂物,割裂了基体组织,在外界交变载荷的作用下,夹杂物边缘产生附加的应力集中,最终导致排气门弹簧发生疲劳断裂。

The fracture failure occurred in the exhaust valve spring of automobile engine during the mixed cycle durability test. In order to find out the reasons for the fracture failure, the exhaust valve spring was analyzed by means of macro inspection, fracture morphology analysis, micro-area composition analysis,chemical composition test, metallographic analysis and hardness test. The results show that the matrix structure was split by the non-metallic inclusion of Zirconia and Iron silicate in the source area of the exhaust valve spring fracture. The additional stress concentration was caused at the edge of the inclusion by the action of external alternating load, and it finally led to the fatigue fracture of exhaust valve spring.