A fatigue failure of the central driven bevel gear was found at the front end of the high pressure rotor of a small turbo-shaft engine. Taking into consideration of both the gear teeth meshing and rotor-gear coupling vibration

the vibration response of the driven bevel gear under the combined influences of tooth surface meshing excitation and rotor lateral vibration excitation was investigated. The analysis results showed that the gear teeth meshing caused the 5th nodal diameter shape vibration

while the coupled vibration of the rotor-driven gear system led to a 2× excitation and then excited the swing shape vibration of the driven bevel gear. Meanwhile

the additional constraints arousing from the gear teeth meshing changed the vibration stress distribution of the swing shape vibration

which then forced the fatigue crack to propagate radially through the gear. The distribution of vibration stress is consistent with the phenomenon of the driven gear fatigue failure

which proves the correctness of the failure mechanism analysis.