某柴油发动机连杆断裂失效分析

Fracture failure analysis of diesel engine connecting rod

某型号柴油发动机发生捣缸现象,经拆解检查,系内部连杆断裂所致。用扫描电子显微镜观察连杆断面形貌,分析了连杆断裂模式;对其化学成分以及拉伸、冲击、硬度等性能进行了检测;并对断口及其附近的组织和各微区的硬度进行了分析。结果表明:连杆内螺纹表面粗糙降低了材料疲劳极限,在局部较大的工作应力作用下,从大头与杆身过渡位置的内螺纹底部优先起裂,并向两侧扩展至瞬断,并引发发动机捣缸。

The cylinder ramming phenomenon occurred in a diesel engine.After disassembly and inspection,it was due to the fracture of internal connecting rod.The fracture appearance was analyzed by scanning electron microscope(SEM)to analyze the fracture mode of the connecting rod.The chemical composition,tensile strength,impact strength and hardness were tested.Moreover,the microstructure and microhardness of the fracture and its vicinity area were analyzed.The results showed that the surface roughness of the internal thread of the connecting rod reduced the fatigue limit of the material.Under the action of large local working stress,the internal thread started to crack from the bottom of the transition position between the big end and the rod body,and then extended to both sides to the instantaneous fracture.The phenomenon of ramming cylinder was finally caused.