Gearbox Planetary Bearing Cage Failure Analysis

There is a constant push within the rotorcraft community to increase performance while simultaneously reducing weight in all systems. For rolling element bearings, this translates to a demand for alternative materials with lower density and improved mechanical properties. This combination of new materials and increasingly demanding application conditions goes beyond historical experiences and defined design and analysis standards. A consequence of this is that tests of these new technologies occasionally result in failure. This was the case during a recent series of gearbox tests during which two different bearing designs failed due to cage issues. The two bearing designs included cages manufactured out of different materials, and the cages failed due to two distinct failure modes (wear and structural fatigue). These test results were used to validate computational results from SKF's proprietary multibody dynamics software, BEAST (BEAring Simulation Tool). A combination of elemental testing and computational analysis is now being used to explore the feasibility of alternative material substitutions to avoid the high cost and long lead time of additional full scale testing.