ORAL REFERENCE: ICF100527OR EFFECT OF FOREIGN OBJECT DAMAGE ON THE HIGH CYCLE FATIGUE STRENGTH OF TI-6AL-4V Steven R. Thompson 1 , John J. Ruschau 2 and Theodore Nicholas 1 1 U.S. Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433 USA 2 University of Dayton Research Institute, Dayton, OH 45469 USA ABSTRACT The role of residual stresses on the fatigue behavior of Ti-6Al-4V samples that had undergone foreign object damage was investigated. Real and simulated impacts were conducted using spherical projectiles launched at 300 m/s and quasi-static chisel indentation, respectively. A unique test specimen configuration that replicates the leading edge of a typical fan blade was ballistically shot at 30° with 1 mm diameter spheres, while rectangular plates were indented quasi-statically using a 2 mm diameter steel indentor at 0°. Fatigue strengths were developed for both geometries at 350 Hz. A number of specimens from both configurations were stress relief annealed, after impacting and before HCF testing, to remove residual stresses. Attempts were made to correlate the measured damage (macro- /microscopic) to the debit in fatigue strength. Results indicate that stress relief generally improves the fatigue limit stress, indicating that tensile stresses are present after both quasistatic and dynamic indentation. For the dynamic impacts, the damage induced is not as severe on the fatigue strengths as that predicted from conventional notch fatigue analysis. KEYWORDS high cycle fatigue, foreign object damage, residual stress, fatigue limit stress INTRODUCTION The fatigue behavior of airfoils in gas turbine engines that have been subjected to foreign object damage (FOD) is a complex issue due to many contributing factors. These factors include, but probably are not limited to, notch geometry causing a stress concentration, residual stress arising from plastic deformation, microstructural damage to the material from the impact event, and the formation of cracks during the impact event [1]. In addition, changes in the geometry of the airfoil edge and residual stresses due to plastic deformation may produce local stress ratios at the notch tip which are, in general, different than the farfield applied stress ratio and may drive the initiation location from surface to sub-surface [2]. This paper deals with the fatigue behavior of axial fatigue test specimens that have been
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