Research on causes of fatigue cracking in the motor hangers of high-speed trains induced by current fluctuation

Abstract Motor hangers are key components of high-speed trains. Local cracking of motor hangers in service is investigated in this study by employing fracture analysis, on-track tests, finite element analysis, etc., to determine the cause of failure. Macro- and microfracture analyses show that cracks originate from weld defects and propagate to the external surface of the lower cover plate. Time domain, frequency domain, and time-frequency domain analyses indicate that both of the dominant frequencies of the stress and the vibration acceleration are 100 Hz, which are consistent with the pulsating torque frequency. The pulsating torque of the motor induced by the current fluctuation excites the resonance mode of the motor hanger, which brings out the possibility of fatigue crack initiation and propagation under operating conditions. The results show that welding defects reduce the fatigue strength of the weld, and high-amplitude and high-frequency vibrations caused by the pulsating torque of the motor eventually lead to the failure of the motor hanger. The study provides a reference for the structural design of a bogie drive system.