Abstract: Objective To investigate a typical fracture feature and its effect on failure analysis.Methods An abnormal fracture of high strength bolts in traffic accidents was examined and analyzed using metallographic analysis and mechanical testing. Results A kind of rare fracture was observed on high strength bolts,and a lot of spherical carbide was found at fatigue initiations or near tearing shoulders.Conclusion An inappropriate matching between the technique of plastic deformation and heat treatment of bolts might cause the precipitation of carbides;the carbides reduced the effective cross section areas of bolts, and induced the high stress fatigue fracture.

Key words: traffic accidents, fracture, high strength bolt, carbide

摘要： 目的研究典型断口形貌对失效分析工作的作用。方法利用金相分析、力学性能测试等方法对某交通事故中汽车车轮螺栓的异常断裂进行了检验分析。结果观察到了一种少见的高强度螺栓断口形貌,其上有聚集成群的球状碳化物,有的在疲劳裂纹的起始部位,有的在撕裂台阶的根部。结论螺栓成型时的塑性变形与热处理工艺匹配不合理可能是引起碳化物异常析出的原因,这些碳化物使螺栓的有效承载面积减小,从而引起了高应力疲劳断裂,并留下了低应力疲劳断裂的假象。

关键词: 交通事故, 疲劳断裂, 车轮螺栓, 碳化物