Failure analysis of an aero-engine inter-shaft bearing due to clearance between the outer ring and its housing

Abstract

The inter-shaft bearing is a critical but vulnerable component of dual rotors, because of the severe operational conditions and loads. This paper investigates the failure mechanism of a fractured inter-shaft bearing belonging to a high thrust-weight ratio turbofan engine. Fractographic and microscopic analyses of the fracture surfaces were conducted, followed by vibration signal processing. Finite element analyses of the outer ring were also performed considering the centrifugal, thermal, and roller-raceway loads. What’s more, using the linear elastic fracture mechanics theory, the crack growth path simulation was obtained, whose result showed good agreement with the real fracture morphologies. The results indicated that due to the clearance between the outer ring and its housing during the operation, the anti-rotation tabs of the outer ring were subjected to non-uniform load, thus several tabs might suffer large stress concentrations at the root fillets, which could lead to the crack initiation. During the following operation of the aero-engine, the crack propagated through the outer ring and cause the fatigue fracture of tabs. The investigation provided herein suggests that the outer ring and its housing should be redesigned to eliminate the clearance during the operation, an outer ring formed integrally with the bearing housing flange is one of the failure preventions of this failure mode.