Effects of Frequency and Environment on Fatigue Behavior of an Oxide-Oxide Ceramic Matrix Composite at 1200°C
Date of Award
Master of Science
Department of Aeronautics and Astronautics
Marina B. Ruggles-Wrenn, PhD
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  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.
DTIC Accession Number
Hetrick, Griffin, "Effects of Frequency and Environment on Fatigue Behavior of an Oxide-Oxide Ceramic Matrix Composite at 1200°C" (2006). Theses and Dissertations. 3544.