ANALYSIS OF BEARING INCIDENTS IN AIRCRAFT GAS-TURBINE MAINSHAFT BEARINGS

An examination of approximately 200 bearing incidents in current aircraft engines has shown that damage in the bearing is initiated at the surface. Twenty-one cases were studied in detail, and five typical incidents are presented here. The initial damage was produced by abrasive particles, dents, grinding scores, skidding, large carbides and corrosion pits. The first phase of the failure mechanism appeared to be by peeling, where microscopic regions about 0.13 mm (0.005 in ) were removed from the surface, and the peels eventually developed into spalls. These mechanisms of failure are a consequence of the partial EHD lubrication utilized in these bearings, and the consequent sharing of the load by the asperities and the EHD film. Failures of this type were reproduced in test bearings run under typical engine conditions, and these tests were used to study the peeling mechanism. Techniques for the minimization of surface-initiated fatigue are also discussed.