Mark A. Bates

Date of Award

3-1991

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

The thermo-mechanical fatigue behavior of a specific unidirectional fiber reinforced titanium aluminide composite was investigated. Three test specimens were subjected to in-phase thermo-mechanical cycling and four to out- of-phase thermo-mechanical cycling. The applied maximum mechanical stresses ranged from 500-800 MPa. The stress ratio of 0.1 was used for all tests. The temperature range was from 150-650 C and the resulting fatigue lives were in the 58-1487 cycles range. The out-of-phase test specimens failed sooner compared to their respective in-phase counterparts. In order to find out why, the test results were analyzed using a simple micromechanics analysis and compared. The fracture surfaces from both test conditions were investigated using the scanning electron microscope. Additionally, the test specimens were sectioned and the fatigue damage was studied in regions away from the fracture surface using a high-power optical microscope and metallography. The stresses that occurred throughout the test cycles were analyzed and related to the observed fatigue damage. The results were compared to the existing failure model for composite materials. Additionally, the results from the in-phase and out-of-phase tests were compared to isothermal and constant load test results.

AFIT Designator

AFIT-GAE-ENY-91S-1

DTIC Accession Number

ADA241988

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