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断裂是机械零件最具危险性的失效形式之一,基于理化检验方法,分析某工程车辆底盘用U形螺栓断口的宏观形貌与微观特征,确定断裂的类型、机理,进而分析断裂的原因。结果表明,U形螺栓的断裂属于高周疲劳断裂,该断裂是U形螺栓螺纹面上的加工刀痕引起的微裂纹在交变载荷作用下不断扩展的结果。另外,螺栓的表面硬度偏高使得裂纹更易扩展。最后提出提高U形螺栓螺纹机加工精度,以及改善热处理工艺等解决措施。
Fracture is one of the most dangerous failure forms of mechanical parts. Based on the physical and chemical test methods, the macro-morphology and microscopic features of the U-bolt fracture of the chassis of an engineering vehicle are analyzed to determine the type and mechanism of the fracture and analyze the causes of the fracture. The results show that the fracture of the U-shaped bolt belongs to the high-cycle fatigue fracture, which is the result of the micro-crack caused by the machining cut on the U-shaped bolt’s thread surface under the action of alternating load. In addition, the higher surface hardness of the bolt makes the crack more easily expandable. In the end, it puts forward some measures to improve the processing accuracy of the U-bolt thread machine and improve the heat treatment process.