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Research Papers: Gas Turbines: Structures and Dynamics

Slow Crack Growth of a Pyroceram Glass Ceramic Under Static Fatigue Loading—Commonality of Slow Crack Growth in Advanced Ceramics

[+] Author and Article Information
Sung R. Choi

Naval Air Systems Command,
Patuxent River, MD 20670
e-mail: sung.choi1@navy.mil

D. Calvin Faucett, Brenna Skelley

Naval Air Systems Command,
Patuxent River, MD 20670

1Corresponding author.

Contributed by the International Gas Turbine Institute of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 15, 2014; final manuscript received July 24, 2014; published online September 30, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(3), 032505 (Sep 30, 2014) (7 pages) Paper No: GTP-14-1399; doi: 10.1115/1.4028393 History: Received July 15, 2014; Revised July 24, 2014

An extensive experimental work for Pyroceram™ 9606 glass–ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20–23 test specimens used at each of four applied stresses. The slow crack growth (SCG) parameters n and D were found to be n = 19 and D = 45 with a coefficient of correlation of rcoef = 0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6–1.9 with an average of msf = 1.7 ± 0.2. A life prediction using the previously determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites (CMCs) based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack growth formulation was operative, a commonality of SCG in these materials systems.

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Figures

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Fig. 1

(a) Typical fracture surface of a PyroceramTM test specimen in static fatigue and (b) EDS showing a chemical composition of the area indicated (as a circle)

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Fig. 2

Optical microscopy of fracture surface of a PyroceramTM test specimen showing the fortified layer and fracture feature [7]. The arrow indicates a failure origin. Dye penetrant was used to reveal the fortified layer. The tension side is on the top.

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Fig. 3

Scanning electron microscopy of fracture surfaces of PyroceramTM test specimens subjected to static fatigue at ambient-temperature in distilled water showing the regions of SCG and fracture origins as well: (a) test specimen subjected to the lowest applied stress of 120 MPa (life = 88 h) and (b) test specimen subjected to the highest applied stress of 170 MPa (life = 116 s)

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Fig. 4

Results of static fatigue testing for PyroceramTM glass–ceramic material conducted at ambient temperature in distilled water. The solid line represents the best-fit based on Eq. (4). Note that 20–23 test specimens were used at each of the four applied stresses.

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Fig. 5

Weibull distributions of time to failure data in static fatigue of Pyroceram™ glass–ceramic material at ambient temperature in distilled water. The lines represent the best-fit based on a two-parameter Weibull scheme, Eq. (5).

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Fig. 6

Prediction of Weibull time-to-failure distributions based on a relation of Eq. (8) for Pyroceram™ glass–ceramic material subjected to static fatigue at ambient temperature in distilled water. The best-fit lines are also included for comparison.

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Fig. 7

Results of dynamic fatigue for Pyroceram™ glass–ceramic material at ambient temperature in distilled water. The number of test specimens per test (stress) rate was 30. The inert strength was included for comparison. The line represents the best-fit based on Eq. (10).

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Fig. 8

Result of life prediction based on the dynamic fatigue data based on Eq. (13) for Pyroceram™ glass–ceramic material at ambient temperature in distilled water, showing an excellent agreement with static fatigue data

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Fig. 9

Results of life prediction in static fatigue (b) from the dynamic fatigue data (a) on advanced monolithic ceramics tested in flexure at elevated temperatures. The prediction from the dynamic fatigue data [1,20] is compared with the static fatigue data of alumina [2], NCX34 silicon nitrides [2], NC203 silicon carbide [2], and NC132 silicon nitrides [19].

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Fig. 10

Results of life prediction in static fatigue (b) from the dynamic fatigue data (a) on various CMCs tested in tension at elevated temperatures. The prediction from the dynamic fatigue data [8,9] is compared with the static fatigue data of SiC/CAS [8], SiC/MAS [8], SiC/SiC [8], and SiC/BSAS [9].

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