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Fretting fatigue experiments were conducted on 7075-T6 and 2024-T3 Aluminum alloy specimens. The primary objective of this study was to quantitatively characterize fretting damage that resulted on the fatigue specimens. Fretting fatigue experiments were performed in laboratory air at various maximum fatigue stress levels at a constant normal pressure. The hypothesis of this study was that the intensity and the nature of fretting damage would vary depending upon the applied maximum fatigue stress and the three dimensional nature of the damage that would result from fretting could be quantified. Fretting fatigue experiments were interrupted at a predetermined number of cycles to analyze the damage on the fatigue specimens. Confocal microscopy was used to analyze and quantify fretting damage. Digitized images of fretting damage were obtained from the confocal microscope, using a pixel counting software package which also allowed length measurement of fretting induced cracks on the faying surface of the fatigue specimen. In addition, fretting damage was quantified in terms of material removal by characterizing the depth as well as the geometry of fretting-generated pits on the faying surface of the specimen. Pit size in terms of pit depth (Pd), pit area (PA), and pit dimension perpendicular (PDy) as well as parallel (PDx) to the applied load also were quantified. From the confocal microscopy analysis of fretting damage, it was observed that fretting-generated multiple cracks on the faying surface could be responsible for the fracture of 7075-T6 aluminum alloy specimens whereas the fracture of 2024-T3 aluminum alloy specimen could be attributed to fretting-generated multiple pits on the faying surface. From the results, it is proposed that fretting nucleates damage of different nature depending on the material microstructure as well as its composition and the methods to alleviate fretting should consider issues pertaining to a specific material.
fretting-fatigue, fretting-nucleated-cracks, fretting-nucleated-pits, fretting-damage
Research Assistant Professor, Mechanical Engineering Department, University of Utah, Salt Lake City, Utah
Doctoral Student, Mechanical Engineering Department, University of Utah, Salt Lake City, Utah
Professor and Director, Quality and Integrity Design Engineering Center (QIDEC), Mechanical Engineering Department, University of Utah, Salt Lake City, Utah