Date of Award

3-2006

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

In this study, a systematic investigation of the fretting fatigue behavior of nickel alloy, IN-100 was carried out. The study includes both experimental work and the corresponding analysis of the contact conditions, and the latter is accomplished using the finite element method. Fretting fatigue tests were performed over a wide range of axial stresses to examine both low and high cycle fretting fatigue under constant contact load and the influence of different pad geometries was also explored. It was observed that fretting reduced the fatigue strength of IN- 100, and that increasing cylindrical pad radii does not have the same effect as in titanium-based alloys. The crack initiation location and orientation along the surface were measured using the Optical and Scanning Electron Microscopy (SEM). In all experiments, cracks were found to initiate near the contact zone trailing edge, and at an orientation of 45? with a scatter of 10?. Finite element analysis was conducted through the commercially available software, ABAQUS, to obtain the contact region state variables such as stress, strain and displacement. These state variables were needed for the computation and analysis of fretting fatigue crack initiation parameters which were Findley parameter, Smith-Watson-Topper (SWT) parameter, shear stress range (SSR), and modified shear stress range (MSSR). These parameters were evaluated based on their ability to predict crack location, crack initiation angle and fatigue life without dependence on contact geometry. The comparison of the analysis and the experimental results showed that fretting fatigue life is not only governed by shear stress on the critical plane, but also the normal stresses plays a role in the crack initiation mechanism. After adjusting the constants used in MSSR calculations for Ti-6Al-4V, it was found that MSSR parameter is also capable of predicting crack location, in IN-100.

AFIT Designator

AFIT-GAE-ENY-06-M22

DTIC Accession Number

ADA451210

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