Abstract: Gearbox is an important transmission equipment of high-speed electric multiple unit(EMU) traction system and suffer the impact mainly from the line turbulence, which induces the fatigue cracks in service. Aiming at a gearbox in this paper, the life mileage statistics of the gearbox and the crack macro analysis of the gearbox fracture section are demonstrated, the origination of fatigue crack occurs at the inside corner of the gearbox, which exists stress concentration due to the structure and some structural defects, such as pit. On the basis of the online test, the vibration acceleration signal of axle box and gearbox and the dynamic stress response of gearbox surface were received, simultaneously the modal of the gearbox was analyzed. The results show that the exciting frequency from the line turbulence is mixed with the gearbox natural frequency and the resonance of the gearbox housing happens, which induces the high dynamic stress amplitude and the gearbox housing appears the fatigue crack. This idea is helpful to ensure the high speed train running in safety and a reference to the design of the new gearbox housing is provided.

Key words: modal, resonance, wheel track turbulence, gearbox