Date of Award

3-2005

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

Effects of temperature and shot-peening intensity on fretting fatigue behavior of Ti-6Al-4A were investigated in this study. S-N curves were obtained for both room and elevated temperatures (260 C) for two different shot-peened intensities (4A and 10A). Stress relaxation behavior under both fretting fatigue at elevated temperature and temperature exposure only were also investigated after their measurements were calculated using X-ray diffraction method. The crack initiation location and the crack angle orientation along the surface were determined using optical and scanning electron microscopy (SEM). Cracks initiated near the trailing edge of the tested specimens. Cracks initiated on the contact surface for both specimens with 4A and 10A shot-peened intensities at elevated temperature. Finite element analysis was performed by commercially available software, ABAQUS, to obtain contact region state variables such as stress, strain and displacement. Those state variables were needed for the computation of fretting fatigue parameters. Fatigue parameters, such as stress range, effective stress and modified shear stress range (MSSR), were analyzed. It was found that there was relaxation of residual compressive stress during fretting fatigue at room and elevated temperature, greater stress relaxation occurred when higher temperature was applied. Also, both 4A and 10A specimens had the same percentage of residual stress relaxation due to temperature exposure only. Further, elevated temperature conditions negate the effect of shot-peening, thereby providing no improvement in fatigue life. On the other hand shot-peening at room temperature conditions improved fatigue life due to shot-peening. Both shot-peening intensities at room temperature provided an improvement to fatigue life with the 10A providing the greatest extension to fatigue life. Also, the (MSSR) par

AFIT Designator

AFIT-GAE-ENY-05-M25

DTIC Accession Number

ADA436126

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