Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.


A facility was demonstrated that successfully resolved problems highlighted by previous attempts to study SiC fibers in steam. Monotonic tension and creep tests were conducted to characterize the fibers. The tensile strength of the fibers showed little dependence on applied stress rate, indicating a resistance to environmentally assisted crack growth. Climb-controlled diffusion in air and grain boundary sliding in silicic acid-saturated steam were the dominant damage mechanisms. Silicic acid-saturated steam had a degrading effect on the mechanical performance of the fibers, but much less than unsaturated steam environments. The Monkman-Grant relationship was demonstrated for Hi-NicalonTM S fibers and may be used to predict creep lifetime of fibers, fiber tows, and CMCs. Microstructural analysis showed a dependence of oxide thickness on applied stress.

AFIT Designator


DTIC Accession Number