Novel Techniques for Gas Turbine Engine Bearing Inspection

TECH FOCUS AREAS: General Warfighting Requirements (GWR) TECHNOLOGY AREAS: Materials; Air Platform OBJECTIVE: This topic seeks to develop a novel strategy to reduce the cost and time to inspect Silicon Nitride (Si3N4) bearing rolling elements. Concepts focus to reduce the cost and inspection time of conventional non-destructive inspection (NDI) by a margin of 30% while maintaining the current standard of inspection. The strategy should accommodate multiple sizes of rolling elements, and accommodate both rollers and ball designs. DESCRIPTION: Turbine engines utilize Si3N4 rolling element bearings within the engine. Si3N4 has become the material of choice for rolling elements in turbine engine bearings due to its ability to withstand high loads, reduce frictional heat generation in the bearing contact, and reduce overall component weight. The proliferation of Si3N4 rolling elements in all bearing locations both in the main shaft bearings and in gearbox support bearings places more importance on both the accuracy and expedience of inspection methods. The strategy should accommodate multiple sizes of rolling elements and accommodate both rollers and ball designs. PHASE I: Phase I efforts will show the feasibility for a novel concept or new method to NDI Si3N4 rolling elements. Develop a design/test strategy for evaluating the ideas and identifying the key performance parameters necessary to document ability to meet the minimum flaw size and probability of inspection requirements utilizing assets owned by AFRL. Selected companies will also develop an initial transition and business plan. PHASE II: In Phase II, the methodology developed in Phase I should be validated for additional conditions replicating those found in practice with physical testing and show feasible build processes and stable quality assurance processes. In the Phase II effort, steps should be taken to establish requirements for integration of the new inspection method into a production facility. The work should be transitioned to interested OEMs and/or bearing suppliers. PHASE III DUAL USE APPLICATIONS: Si3N4 has become the material of choice for rolling elements in turbine engine bearings for advanced military engines. Recently, this material has been implemented into large commercial engines due to the beneficial weight savings as well as improved resistance to wear and fatigue relative to metallic rolling elements. Improved inspection technologies under this effort will have a direct impact on commercial airline operators by reducing both part cost and lead time for main-shaft bearings. REFERENCES: ASTM 1417 Standard Practice for Liquid Penetrant Testing ; ASTM 165 Standard Practice for Liquid Penetrant Testing for General Industry KEYWORDS: non-destructive inspection; silicon nitride; ceramic; rolling element bearing; rolling elements; ball bearing