Date of Award

3-11-2011

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

The effects of holes on the fatigue behavior of an advanced Silicon Carbide/Silicon Carbide (SiC/SiC) ceramic matrix composite (CMC) was investigated at 1200 deg C in laboratory air and in steam environment. The composite consisted of an oxidation inhibited HyprSiC matrix reinforced with laminated Hi-Nicalon fibers woven in an eight-harness-satin weave (8HSW). Fiber preforms were coated with pyrolytic carbon (PyC) fiber coating with boron carbide overlay and were then densified with HyprSiC matrix via chemical vapor infiltration (CVI). Effects if center hole on tensile stress-strain behavior and tensile properties were evaluated at 1200 deg C. To assess the effect of holes on fatigue performance, the standard dogbone-shaped specimens with a center-hole were subjected to tension-tension fatigue tests at frequencies of 0.1, 1.0, and 10 Hz for fatigue stresses ranging from 80 to 140 MPa in air and from 100 to 140 MPa in steam. The R ratio (minimum stress to maximum stress) was 0.05. Fatigue runout was defined as 105 cycles at the frequency of 0.1 Hz and as 2x105 cycles at the frequencies of 1.0 and 10 Hz. Specimens that achieved run-out were tested in tension to failure to characterize the retained tensile properties. Composite microstructure, as well as damage and failure mechanisms were investigated.

AFIT Designator

AFIT-GAE-ENY-11-M17

DTIC Accession Number

ADA540039

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