Date of Award

3-10-2010

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

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) with oxidation inhibited matrix was investigated at 1200˚C in laboratory air and in steam environments. The composite consisted of an oxidation inhibited SiC matrix reinforced with Hi-Nicalon fibers coated with pyrolytic carbon (PyC) with a boron carbide overlay woven into eight-harness-satin (8HS) weave plies. Tensile stress-strain behavior and tensile properties were evaluated at 1200˚C. Tension-tension fatigue tests were conducted in both laboratory air and in steam at 1200˚C at frequencies of 0.1 Hz, 1.0 Hz, and 10 Hz. The tension-tension fatigue tests had a ratio of minimum stress to maximum stress of R = 0.05, with maximum stresses ranging from 100 to 140 MPa in air and in steam. Fatigue run-out was defined as 105 cycles for the 0.1 Hz tests and as 2 x 105 cycles for the 1.0 Hz and 10 Hz tests. Strain accumulation with cycles and modulus evolution with cycles were analyzed for each fatigue test. The presence of steam degraded the fatigue resistance of the material at 0.1 Hz and 10 Hz. At 1.0 Hz, the presence of steam appeared to have little influence on the fatigue resistance for the fatigue stress levels < 140 MPa. The presence of steam degraded the fatigue performance of the CMC at 1.0 Hz for the fatigue stress level of 140 MPa. Fatigue limit was 100 MPa (32.6% UTS) in air and steam at 1.0 Hz and in steam at 0.1 Hz. Fatigue limit was 140 MPa (45.6%) in air at 10 Hz. Specimens that achieved run-out were subjected to tensile tests to failure to characterize the retained tensile properties. Specimens tested in air retained 42-61% of their tensile strength and specimen tested in steam retained 59-75% of their tensile strength.

AFIT Designator

AFIT-GAE-ENY-10-M07

DTIC Accession Number

ADA517389

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