Fracture Causes of Connecting Bolt of Metro Bogie

The connecting bolt of a metro bogie fractured. The fracture causes of the connecting bolt were analyzed by means of macroscopic observation, chemical composition analysis, tensile test, fracture analysis and metallographic analysis. The results show that the fracture property of the connecting bolt was bending fatigue fracture, and the crack originated from the root of the thread. During the installation, the residual thread glue in the internal thread hole was not checked and cleaned in time, which led to uneven force on the bolt. There was slight decarburization at the root of the thread, coupled with the alternating load caused by the vibration of the metro running. The connecting bolt of the metro bogie initiated cracks at the root of the thread, and then expanded in the form of fatigue, and finally fracture occurred.