车门限位臂断裂原因分析

Failure analysis of door check arm

某品牌车型的车门限位臂在耐久试验中发生断裂。通过扫描电子显微镜(SEM)观察断口微观形态、金相显微镜观察样品金相组织、硬度测试及强度转换判定其力学性能等试验分析断裂原因。结果表明:车门限位臂材料的化学成分符合规定要求;材料硬度约为规定下限值的60%,材料强度明显偏低;限位臂在循环工作载荷作用下多源疲劳断裂,疲劳源位于安装定位孔的表面棱边应力集中处。材料强度偏低是限位臂发生疲劳断裂的主要原因。

One door check arm of a brand model has broken during the endurance test. Scanning electron microscope(SEM) is used to get the fracture morphology and metallographic structure is observed under metalloscope. Hardness test together with other tests are performed for failure analysis. Test results show that: chemical composition of the door check arm meets the specified requirement, however, the material’s hardness is about 60% of the specified lower limit value which indicates that the arm has low strength. The arm works under cyclic load and fracture originates from the surface edge of the mounting hole where stress concentration tends to happen. The arm’s fracture is multi-source fatigue fracture and material’s low strength is the main reason to the fatigue failure.