Date of Award


Document Type


Degree Name

Master of Science


Department of Aeronautics and Astronautics

First Advisor

Marina Ruggles-Wrenn, PhD


Recent developments in aerospace propulsion systems, along with emerging interest in hypersonic air vehicles has emphasized the need for materials which can withstand extreme service environments. The leading candidates for the structural components expected to operate in these environments are SiC-based ceramic matrix composites (CMCs). When a CMC component is subjected to thermomechanical loads in an aggressive environment during service, surface cracks form. As steam penetrates cracks in the SiC matrix, it becomes saturated with silicic acid, (SI(OH)4) and attacks the SiC fibers. The interaction between the Hi-Nicalon™ S SiC fibers and the (SI(OH)4)-saturated steam is not fully understood, and is essential to predicting long-term durability and assuring structural integrity of SiC/SiC CMCs. This research effort focused on static fatigue of Hi-Nicalon™ S fiber tows at 500°C in air and in silicic acid-saturated steam. The fiber tows were composed of 500 fiber filaments with an average diameter of 12 µm. The applied stress ranged from 3.6 MPa to 1350 MPa. Both primary and secondary deformation regimes were observed, and steady-state strain rates were found for each test. The effects of applied load and test environment on static fatigue performance of the SiC fiber tow are discussed.

AFIT Designator


DTIC Accession Number