Date of Award

3-2007

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

This thesis studied the effect of microstructure on the fretting fatigue behavior of IN-100. First, fretting and plain fatigue S-N curves were determined over a large range of applied stress at an identical R-ratio and for fretting tests, done with a constant contact load. It was found that fretting fatigue reduces the cycles to failure compared to plain fatigue. The half contact width was found for the specimens, the crack initiation angle was found to be 40 deg and the crack initiation location was at the trailing edge of contact for the fretting specimens. Computational work included finding the stress profile in the contact region using an analytical method and a finite element method. The analytical method computed half contact width and was found to be in good agreement with experimental half contact width. The stress profiles produced from each method were compared and found to be in good agreement. The stress profiles were used to find the Modified Shear Stress Range (MSSR) Parameter. The MSSR parameter produced results in good agreement with the experimental data for crack initiation location and fatigue life. This study found microstructure did not have an effect on the MSSR parameter for IN-100. This study also found MSSR data developed for titanium alloys did not adequately represent IN-100. The parameter also gave reasonable agreement with the experimental finding for crack initiation angle. A microstructural evaluation was done between the 7 micron grain sized material of this study and an oblong, 10 by 50 micron grained microstructure IN-100 from a previous study. The study found microstructure did have an effect on crack initiation and crack propagation, with the coarser grain structure performing better in fretting fatigue. The coarser grain structure allowed a longer initiation and crack propagation time.

AFIT Designator

AFIT-GMS-ENY-07-M02

DTIC Accession Number

ADA469926

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