The multi-task objectives of the plan discussed in this proposal are: research the role and effects of fretting on structural life of components, develop and demonstrate the feasibility of integrating candidate fretting fatigue predictive analytic model(s) into structural integrity methods, integrate and implement the techniques for applications to present and future U.S. military weapons programs, commercial aviation, automotive, and mechanical equipment and provide industry access to the predictive tools and information for commercialization. Fretting, as defined by the American Society for Metals Handbook Volume 10: Failure Analysis and Prevention, is a wear phenomenon that occurs between two mating surfaces: it is adhesive in nature, and vibration is its essential causative factor. Usually fretting is accompanied by corrosion. In general, fretting occurs between two tight fitting surfaces that are subjected to a cyclic, relative motion of extremely small amplitude. Fretted regions are highly sensitive to fatigue cracking. Under fretting conditions fatigue cracks are nucleated at very low stresses. Nucleation of fatigue cracks in fretted regions depends mainly on the state of stress on the surface and particularly on the stresses superimposed on the cyclic stress. The time to nucleation of cracks can be significantly reduced as a result of fretting. Common sites for fretting are in joints that are bolted, keyed, pinned, press fitted, and riveted. These sites are common in the assembly of most air vehicles, ground vehicles, power plants, equipment, and machinery. All applications that have safety issues, maintenance issues, and service life requirements will benefit from quantitative methods that provide the impact of fretting on the component's service. The approach APES, Inc. proposes for this SBIR improves the Holistic Life Prediction Methodology (HLPM) and the corresponding software ECLIPSE that implements the HLPM by adding a fretting fatigue capability that will be validated and verified with experimental and field service data (if available). Phase II's product will be a robust analytical approach that adequately accounts for fretting fatigue mechanisms and influences on predicted structural lives, having tremendous potential for improving durability and damage tolerance (DADT) in many industries. The aircraft industry, both commercial and defense, will be the first industry recipient of the applications afforded by this program. Systems in the aircraft industry that will be afforded benefits by improved analytical fretting fatigue approaches include transports, fighters, helicopter, commercial, small aircraft, and their subsystems, including engines.
Keywords: Fretting Fatigue, Corrosion-Fatigue, Damage Tolerance, Structural Integrity, Life Assessments, Life Predictions, Damage Simulations.
