Michael Lee

Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

The fatigue behavior of an advanced silicon carbide/silicon carbide (SiC/SiC) ceramic matrix composite (CMC) was investigated at 1300 ºC in laboratory air and in steam environments. The composite was manufactured using chemical vapor infiltration (CVI). The composite consisted of an oxidation-inhibited matrix, which was comprised of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a plain weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Two specimen geometries were evaluated, a dog bone and an hourglass geometry. Tensile stress-strain behavior and tensile properties were evaluated at 1300 ºC. Tension-tension fatigue tests were conducted in both laboratory air and in steam at 1300 ºC at 1.0 Hz with a minimum to maximum stress ratio of R = 0.05. Fatigue behavior was evaluated for a maximum stress of 70-160 MPa in air and in steam environments. Fatigue run-out was defined as 2 x 105 cycles. Strain accumulation with cycles and modulus evolution with cycles were analyzed for each fatigue test. The CMC fatigue performance was affected little by the presence of steam. The fatigue limit was between 80 and 100 MPa. Retained tensile properties were characterized for all specimens that achieved fatigue run-out. Failure surfaces were examined to study composite microstructure as well as damage and failure mechanisms.

AFIT Designator

AFIT-ENY-MS-16-M-223

DTIC Accession Number

AD1054171

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