进气门外弹簧断裂原因分析

本文对某活塞发动机承受压缩交变载荷的进气门外弹簧断裂的性质及原因进行了综合分析。通过对弹簧进行断口分析、痕迹分析、金相分析、受力分析以及模拟试验等，确认了该弹簧的失效性质为起源于弹簧外表面的早期疲劳断裂。造成该弹簧早期疲劳断裂的原因为：弹簧在镀镉前电解工序过程中，弹簧外表面与阴极板电极接触放电造成电接触损伤，在弹簧表面形成了电接触损伤凹坑，导致弹簧的疲劳寿命大幅度降低，在工作载荷作用下，从电接触损伤凹坑位置萌生疲劳裂纹并发生早期疲劳断裂。

Failure Analysis of a Spring out of an Intake Valve

A spring out of an intake valve in a piston engine fractured under the effect of compressive alternate load. The failure mode and cause of the spring were investigated by fracture surface examination, metallographic analysis, stress analysis and simulation tests. It is confirmed that the failure mode of the spring is early fatigue fracture originating from the outer surface of the spring. During the grease removal process prior to overlaying cadmium, electrical contact damage occured to the spring outer surface because of discharge between the spring outer surface and the negative plate electrode. Some pits caused by electrical contact damage formed at the spring surface. As a result, the fatigue life of the spring declined greatly. Under the effect of service load, fatigue crack initiated from the pits caused by electrical contact damage and the spring fractured early.