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Research Papers: Gas Turbines: Coal, Biomass, and Alternative Fuels

Creep in Interlaminar Shear of an Oxide/Oxide Ceramic-Matrix Composite at Elevated Temperature1

[+] Author and Article Information
M. B. Ruggles-Wrenn

Department of Aeronautics and Astronautics,
Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433-7765
e-mail: marina.ruggles-wrenn@afit.edu

S. R. Hilburn

Department of Aeronautics and Astronautics,
Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433-7765

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 13, 2015; final manuscript received July 30, 2015; published online September 1, 2015. Editor: David Wisler.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Eng. Gas Turbines Power 138(2), 021401 (Sep 01, 2015) (8 pages) Paper No: GTP-15-1270; doi: 10.1115/1.4031304 History: Received July 13, 2015

Creep behavior in interlaminar shear of an oxide–oxide ceramic composite was evaluated at 1100 °C in laboratory air and in steam environment. The composite (N720/AS) consists of a porous aluminosilicate matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The interlaminar shear properties were measured. The interlaminar shear strength (ILSS) was determined as 7.6 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 tests performed at 6 MPa. Creep run-out defined as 100 hrs at creep stress was not achieved in any of the tests. Larger creep strains and higher creep strain rates were produced in steam. However, the presence of steam had a beneficial effect on creep lifetimes. Composite microstructure, as well as damage and failure mechanisms, was investigated.

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Figures

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Fig. 3

Creep strain versus time curves N720/AS CMC obtained at applied interlaminar shear stresses in the 2–6 MPa range at 1100 °C in air and in steam

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Fig. 2

Interlaminar shear stress versus compressive strain curves for N720/AS at 1100 °C in air

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Fig. 1

(a) DNS specimen, (b) notch details, and (c) prospective shear plane

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Fig. 4

Minimum creep rate as a function of applied interlaminar shear stress for N720/AS CMC at 1100 °C in air and in steam

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Fig. 5

Interlaminar shear stress versus time to rupture for N720/AS CMC at 1100 °C in air and in steam

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Fig. 6

Fracture surface of the DNS specimen tested in compression to failure at 1100 °C in air. Test duration < 10 s. Failure occurs mainly through interply delamination.

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Fig. 7

Fracture surface of the DNS specimen tested in creep at 6 MPa at 1100 °C in air, tf = 14.1 hrs. Failure occurs through combined fiber fracture and interply delamination.

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Fig. 8

Fracture surface of the DNS specimen tested in creep at 2 MPa at 1100 °C in air, tf = 78.3 hrs. Extensive fiber fracture and matrix damage are evident.

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Fig. 9

Fracture surfaces of the DNS specimens tested in creep at 6 MPa at 1100 °C in steam, tf = 22.7 hrs. Fiber fracture is the dominant failure mechanism.

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Fig. 10

Fracture surface of the DNS specimen tested in creep at 2 MPa at 1100 °C in steam, tf = 96.9 hrs. Widespread fiber-matrix bonding is evident.

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