连杆螺栓断裂失效分析

发动机连杆螺栓发生断裂失效，通过断口宏微观观察、金相组织检查、硬度及拉伸性能测试、螺纹尺寸测量和化学成分分析，对连杆螺栓断裂原因进行了分析。结果表明：螺栓的断裂性质为疲劳断裂；螺栓的金相组织及化学成分未见异常，硬度及拉伸性能符合要求，螺纹尺寸不符合标准要求。综合分析认为：螺栓发生松动是螺栓断裂的根本原因；螺栓松动与装配时预紧力过小和螺纹直径偏小有关。针对断裂原因，提出了预防措施。

Analysis on Fracture of Connecting Rod Bolt

Connecting rod bolt in an engine fractured. Macro and micro observation, metallurgical structure examination, hardness testing, tensile properties testing, dimensional measurement and chemical analysis were carried out to find out the cause of the connecting rod bolt fracture. The results show that bolt fracture mode was fatigue. Their metallurgical structure, hardness, tensile properties and chemical composition were all in the range of standard, but screw thread size was out the range of standard. So it can be concluded that bolt looseness was the basic reason of the failure. The bolt looseness caused by lower proload when assembly and smaller size of the blot. Based on the analysis result, some measures were put forward.