Reasons for bolt elongation and fracture of a wheel

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.