Enhanced Life Prediction Methodologies for Engine Rotor Life
Extension, 18-9414

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Principal Investigators
Stephen J. Hudak Jr.
Michael P. Enright
R. Craig McClung

Inclusive Dates:  07/16/03 - Current

Background - The U.S. Air Force is facing a potentially large wave of turbine engine disc replacement costs during the next 8 to 10 years that are inconsistent with anticipated budgets. Consequently, the Engine Rotor Life Extension (ERLE) program was conceived by the Air Force Research Laboratory (AFRL) as a sound science and technology investment that offers the potential for significant cost-avoidance by extending the life of certain life-limiting components. The concept is to extend the life of these components by recovering the conservatism believed to exist in design and life management practices, without increasing risk, by systematically improving and more effectively integrating a number of life management technologies - life prediction, nondestructive inspection, engine health monitoring, and maintenance and repair. It is estimated that successful science and technology investments of this type could reduce the disc replacement costs by 50 percent, which would amount to a cost savings of $600M during five years. Enhancements in engine life management technology would also be applicable to developmental and future military engines, as well as to commercial engines, where safety, reliability, and cost of ownership are of paramount importance. The technologies and software being developed in this program are also expected to be of value to the power-generation industry where availability and cost of ownership are high priorities, particularly in the deregulated market. The Institute is leading a team with unique capabilities to enhance, as well as integrate, several of the above life management technologies. Other team members include Smiths Aerospace, The University of Texas at San Antonio, and Mustard Seed Software.

Approach - The approach and technical objectives of this program are to develop and demonstrate: 1) a new family of physically based, deterministic life prediction models for treating total fatigue life including crack nucleation, microcrack growth, and large crack growth; 2) an efficient probabilistic life prediction methodology based on the stochastic nature of each of the above phases of fatigue life; and 3) a methodology for enhanced engine life management based on hybridization of state-of-the-art probabilistic life prediction and classical engine health monitoring.

Accomplishments - Effort during the initial 15 months of this three-year program has focused on the development of methods to transform engine sensor data (rotor speed) into stress within the engine discs - one of the most fracture critical components of the engine. Statistical analysis of engine mission usage has been performed, and probabilistic models to project future damage based on changes in the mission planning are being developed. Application of parallel processing computing methods has resulted in significant efficiency increases associated with the computationally intensive probabilistic simulation. Synergisms have also been identified between classical diagnostic and prognostic methods, and damage-based probabilistic life prediction. Engineering assessments of the significance of these synergisms is continuing. This project has resulted in the award of a Dual Use Science and Technology Program from the Air Force Research Laboratory.

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