某型号车轮螺栓在装配过程中出现拉长和断裂情况。采用宏观观察、化学成分分析、力学性能测试、硬度测试、金相检验、扫描电镜及能谱分析、摩擦性能测试等方法,分析了螺栓拉长和断裂的原因。结果表明:螺栓和螺母的扭矩系数一致性较差,在装配过程中,夹紧力超过螺栓屈服强度,导致螺栓拉长;当扭矩系数过小时,夹紧力超过螺栓的抗拉强度,导致螺栓断裂。

The wheel bolts of a certain model were elongated and fractured during assembly. The causes of bolt elongation and fracture were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, hardness test, metallographic examination, scanning electron microscope and energy spectrum analysis, friction performance test. The results show that the torque coefficients of bolts and nuts were not consistent. During the assembly process, the clamping force exceeded the yield strength of bolts, resulting in bolt elongation. When the torque coefficient was too small, the clamping force exceeded the tensile strength of the bolt, resulting in the bolt fracture.