Failure Analysis of Automobile Spring

The spring(rear spring) of an automobile fractured during testing. The fail mode and cause were analyzed by appearance observation, metallographic examination and testing hardness of the spring, as well as macro-and micro-observation of the fracture surface and energy spectrum analysis (EDS). The results show that the failure mechanism of the spring was fatigue, which was caused by the burned zone induced by local high temperature contact because of spark discharge of the failure of the magnetic powder inspection machine before the shot-blasting process. The burned zone damaged surface integrity of the spring, and greatly decreased fatigue life of the spring. Under the effect of test load, fatigue crack initiated from the burned zone and the spring fractured early. Improvement measures were proposed: the main equipment and process should be supervised in order to avoid abnormal damage during production process of the spring.