Failure Analysis of an Inter-shaft Bearing of an Aero Gas Turbine Engine

Failure of an inter-shaft bearing in an aero gas turbine engine is investigated to determine its root cause. Teardown inspections followed by metallurgical investigations are carried out on the parts of the failed bearing. None of the components of the bearing has shown any discolouration, wear, or overheating marks. But severe flaking is observed on one side of the outer raceway. It indicates progressive fatigue due to overload. Insufficient clearance due to differential expansion of inner ring and contraction of outer ring due to heating and cooling, respectively, can also result in this type of phenomena. Maintaining oil discipline and using correct grade of oil at proper frequency can address these issues. A comprehensive engine-bearing prognostic approach may be followed utilizing available sensor information on-board the aircraft such as rotor speed, vibration, lube system information, and aircraft maneuvers to predict bearing life and incipient bearing failure. © 2015, ASM International.