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Research Papers: Gas Turbines: Ceramics

Interlaminar Crack Growth Resistances of Various Ceramic Matrix Composites in Mode I and Mode II Loading

[+] Author and Article Information
Sung R. Choi1

 Naval Air Systems Command, Patuxent River, MD 20670sung.choi1@navy.mil

Robert W. Kowalik

 Naval Air Systems Command, Patuxent River, MD 20670

It is not certain as to whether the use of correction fluid might induce stress corrosion cracking due to the presence of this material on the crack surfaces. However, the depth of penetration by this material was observed to be negligible as compared to the width (b) of test specimens so that the influence was believed to be insignificant. A study of stress corrosion behavior of the correction fluid using a stress-corrosion susceptible material such as glass would be of great interest.

1

Corresponding author.

J. Eng. Gas Turbines Power 130(3), 031301 (Apr 02, 2008) (8 pages) doi:10.1115/1.2800349 History: Received May 23, 2007; Revised May 25, 2007; Published April 02, 2008

Interlaminar crack growth resistances were evaluated for five different SiC fiber-reinforced ceramic matrix composites (CMCs) including three gas-turbine grade melt-infiltrated SiCSiC composites. Modes I and II crack growth resistances, GI and GII, were determined at ambient temperature using double cantilever beam and end notched flexure methods, respectively. The CMCs exhibited GI=200500Jm2 and GII=200900Jm2. All the composites (except for one SiC/CAS composite) showed a rising R-curve behavior either in mode I or in mode II, presumably attributed to fiber bridging (in modes I and II) and frictional constraint (mode II) in the wake region of a propagating crack. A glass fiber-reinforced epoxy polymer matrix composite showed typically two to three times greater GI and eight times greater GII, compared to the CMCs. An experimental error analysis regarding the effect of the off-the-center of a crack plane on GI and GII was also made.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of test specimen/loading configurations used in (a) DCB test for mode I and (b) ENF test for mode II

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Figure 2

Typical force versus displacement curves determined in (a) DCB (mode I) test for SiC∕SiC (’90) and (b) ENF (mode II) test for SiC/CAS. Each curve numbered represents one loading(/unloading) sequence for a given crack length.

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Figure 3

Typical results of compliance-crack length relations determined for U-SiC∕SiC composite: (a) normalized crack length (a∕t) versus (compliance)1∕3 in DCB (mode I) and (b) compliance versus normalized crack length (a∕S)3 in ENF (mode II)

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Figure 4

Mode I interlaminar energy release rate (GI) as a function of crack length determined for five different SiC continuous fiber-reinforced CMCs by the DCB method. Glass/epoxy PMC was included for comparison. Different symbols for a given plot represent different test specimens.

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Figure 5

Mode II interlaminar energy release rate (GII) as a function of normalized crack length (a∕S) determined for five different SiC continuous fiber-reinforced CMCs by the ENF method. Glass/epoxy PMC was included for comparison. Different symbols for a given plot represent different test specimens.

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Figure 6

Typical example showing fiber bridging in the wake region of a propagating crack during DCB (mode I) testing for S-SiC∕SiC composite

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Figure 7

Fracture surfaces of Hi-Nic SiC∕SiC composite specimens in (a) DCB test in mode I and (b) ENF test in mode II. Note the existence of broken fibers/debris in (b) due to the frictional sliding motion of two mating crack planes in an ENF specimen.

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Figure 8

Simplified summary of interlaminar energy release rates (crack growth resistances) of CMCs, PMC, and PMMA: (a) GI by the DCB method in mode I and (b) GII by the ENF method in mode II. GI and GII of PMMA were determined by DCB and ENF, respectively, with two as-fabricated glossy test beams superglued together (28).

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Figure 9

Ratio of energy release rate (Gd∕G) as a function of h1∕h2: (a) mode I DCB test and (b) mode II ENF test, showing an error due to the off-the-center of a midcrack plane

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