Date of Award


Document Type


Degree Name

Master of Science in Aeronautical Engineering


Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD


Ceramic matrix composites (CMCs) have the potential to be utilized in applications such as hypersonic vehicles, aircraft leading edges, hot sections of engines, and rocket nozzles. Of particular interest are advanced SiC/SiC composites that can withstand the elevated temperatures and harsh oxidizing environments while maintaining their properties and structural integrity under an applied load. Steam, a major component of combustion environment, is one such aggressive oxidizing environment. As steam passes through the SiC/SiC composite, entering the composite interior through the cracks in the SiC matrix, it becomes saturated with silicic acid, Si(OH)4. Before incorporating SiC/SiC composites in the next generation aerospace engines, the long-term impacts of exposure to the aggressive saturated steam environment on the composite durability must be thoroughly examined and understood. An in-depth understanding of the composite performance demands an in-depth study and understanding of the performance of the reinforcing SiC fibers. This study investigates the static fatigue of Hi-Nicalon™ S SiC fiber tows at an intermediate temperature of 600°C in laboratory air and in silicic acid-saturated steam. The fiber tow consists of 500 fiber filaments with an average diameter of 13 μm. Static fatigue tests were performed at applied stresses ranging from 2.96 MPa to 1300 MPa. Run-out was defined as survival of 100 h at applied stress. The presence of saturated steam significantly degraded the static fatigue performance of the fiber tows at 600°C. The static fatigue lifetimes of the Hi-Nicalon™ S SiC fiber tows were decreased by one order of magnitude due to silicic acid-saturated steam.

AFIT Designator



Plain-text title: Static Fatigue of Hi-Nicalon[Trademark] S Ceramic Fiber Tows at 600°C in Air and Silicic Acid-Saturated Steam