某汽车在累计行驶600 km后其发动机气门弹簧发生断裂。采用宏观观察、化学成分分析、金相检验、硬度测试、断口分析和CT检测等方法对该气门弹簧的断裂原因进行了分析。结果表明:气门弹簧的断裂性质为疲劳断裂,喷丸过程导致弹簧内部产生凹坑缺陷,凹坑处的应力集中程度较大,在受循环往复作用力的条件下,弹簧表面形成微裂纹,并不断扩展,最终导致弹簧发生断裂。

The valve spring in an automobile engine broke after running for 600 km. The fracture reasons of the valve spring were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, hardness test, fracture analysis and CT detection. The results show that the fracture property of the valve spring was fatigue fracture. The shot peening process led to the pit defect in the spring, and the stress concentration in the pit was large. Under the condition of cyclic force, the surface of the spring formed cracks, which continue to expand, and finally caused the spring to fracture.