Failure Analysis of an Inter-shaft Bearing of an Aero Gas Turbine Engine
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CASE HISTORY—PEER-REVIEWED
Failure Analysis of an Inter-shaft Bearing of an Aero Gas Turbine Engine R. K. Mishra • S. K. Muduli • K. Srinivasan S. I. Ahmed
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Submitted: 23 June 2014 / in revised form: 16 January 2015 / Published online: 14 February 2015 ASM International 2015
Abstract 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. Keywords
Fatigue failure SEM Spalling
R. K. Mishra (&) S. K. Muduli Regional Center for Military Airworthiness (Engines), Bangalore, Karnataka, India e-mail: [email protected] K. Srinivasan Hindustan Aeronautics Limited - Engine Division, Bangalore, India S. I. Ahmed Aeronautical Quality Assurance (Engines), Bangalore, Karnataka, India
Introduction Bearings in a gas turbine engine provide support and positioning of the rotors. They operate under extremely severe conditions of load, shaft speed, and oil temperature. Under these conditions, bearing damage can progress undetected until the bearing fails with possible secondary damage to other areas of the engine. A bearing can fail prematurely due to a variety of factors like improper designing or wrongly selecting a bearing for the required application, lack of or inadequate lubrication, impact loads, vibrations, environmental factors like operating temperature, corrosive media, moisture, dirt or handling abuse during transport, mounting, reinstallation and servicing [1]. Interruption in oil flow and ingestion of fine sand and debris into the oil circuit are harmful to the engine bearings and have resulted in many failures, causing even fatal accidents [2]. In land-based gas turbines as well as in aero engine applications, a long service life with high reliability is the prime factors while selecting a bearing. Any malfunction in the bearing system will affect the normal operation of the rotor. This may also cause rotor imbalance and high vibration, rubbing of rotor blades with casing, rise in lubrication oil temperature, and severe damage to the engine affecting its operation. Bearing failures generally amount to about 7% of all failures in the gas turbine engines and the down time greatly affects the f
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