Date of Award

3-14-2014

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

Creep behavior in interlaminar shear of an oxide-oxide ceramic composite, Nextel(trade mark) 720/aluminosilicate (N720/AS), was investigated at 1100 deg C in laboratory air and in steam. The interlaminar shear strength (ILSS) was determined as 7.65 MPa. The creep behavior was examined for interlaminar shear stresses in the 2-6 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. Tertiary creep was noted in the tests performed at 6 MPa. Larger creep strains and higher creep strain rates were produced in steam. Surprisingly, the presence of steam had a beneficial effect on creep lifetimes. It appears that matrix strengthening occurred in steam, which resulted in longer creep lifetimes in interlaminar shear. Additionally, exploratory tension-torsion tests of thin-walled tubular specimens of N720/AS were performed at room temperature in air. The failure stress levels determined in tension-torsion tests and in compression tests were used together with data from literature to construct a biaxial failure envelope. The efficacy of Tsai-Wu and Tsai-Hill multiaxial failure theories was also explored.

AFIT Designator

AFIT-ENY-14-M-26

DTIC Accession Number

ADA598971

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