Date of Award

6-2006

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

Advances in aeronautical engineering in the 21st century depend upon materials that can perform well in extreme environments such as high temperatures and oxidizing conditions. Nextel™720/Alumina (N720/A) is an oxide/oxide ceramic matrix composite with a porous alumina matrix that has been identified as a candidate material for such applications. This research investigated the effects of frequency on fatigue response of N720/A at 1200°C in both air and steam environment. Prior investigation of this material by Eber [8] in 2005 studied fatigue behavior at 1200°C in air and in steam environments at the frequency of 1.0 Hz. The current research focused on fatigue response at the frequencies of 0.1 Hz and 10 Hz. Results of mechanical testing showed a significant decrease in fatigue performance in steam versus air. Specimens tested at 0.1 Hz exhibited shorter fatigue lives and smaller strains at failure than those tested at 10 Hz. Scanning Electron Micrographs of specimen fracture surfaces revealed higher degrees of fiber pull-out and greater variation in fiber failure locations in specimens tested at 10 Hz, indicating a weakening of the fiber/matrix interface. Qualitative assessment using Energy Dispersive Spectroscopy showed correlations between frequency and amount of silicon species migration between fiber and matrix.

AFIT Designator

AFIT-GAE-ENY-06-J05

DTIC Accession Number

ADA453928

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