Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite

James Marrow; Dan Scotson; Xiaochao Jin; Hongniao Chen; Yang Chen; Abdo Koko; Philip Earp; Houzheng Wu

doi:10.1520/STP163920210051

Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite

James Marrow, Dan Scotson, Xiaochao Jin, Hongniao Chen, Yang Chen, Abdo Koko, Philip Earp, Houzheng Wu

Department of Mechanical Engineering

Research output: Chapter or section in a book/report/conference proceeding › Chapter in a published conference proceeding

5 Citations (SciVal)

Abstract

To enable monitoring of graphite that has been exposed to irradiated, high-temperature environments, there is a need for analysis methods that are suitable for fracture toughness measurements in small test specimens. Quasistatic fracture propagation has been studied for two candidate graphites for next-generation nuclear energy, SNG742 and T220, using small specimens in the double-cleavage drilled-compression (DCDC) geometry (20 7 7 mm). Compression of the DCDC specimen initiated stable crack propagation, and the surface full-field displacements were measured by digital image correlation. A phase congruency method was applied to the displacement field to quantify the crack lengths, crack opening displacements, and crack tip opening angles. The classical analytical solution for the stress intensity factor in the DCDC specimen gave unrealistic results due to its boundary condition assumptions. A new analysis method is proposed in which the measured crack displacement field is injected as boundary conditions into a finite element model, allowing the J-integral to be evaluated via the contour integral method, which then provides the mode 1 stress intensity factor during quasistatic crack propagation. With the assumption of linear elasticity, the critical stress intensity factor in T220 was constant for crack propagation up to 6 mm and lower than that in SNG742, which showed rising fracture resistance for longer cracks. The analysis was validated using Macor, a linear elastic fine-grained glass ceramic with known fracture toughness without significant R-curve behavior. The small-specimen graphite results are consistent with the reported fracture toughness from large-specimen tests, but the values are overestimations due to the nonlinear behavior of unirradiated graphite. Methods to extract nonlinear elastic properties by inverse analysis are discussed. The outlook for fracture testing of irradiated graphite at elevated temperatures is considered.

Original language	English
Title of host publication	Graphite Testing for Nuclear Applications
Subtitle of host publication	The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments
Editors	Athanasia Tzelepi, Martin Metcalfe
Place of Publication	U. S. A.
Publisher	ASTM International
Pages	1-17
Number of pages	17
ISBN (Electronic)	9780803177253
DOIs	https://doi.org/10.1520/STP163920210051
Publication status	Published - 1 Dec 2022
Event	2021 Symposium on Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments - Virtual, Online Duration: 23 Sept 2021 → 24 Sept 2021

Publication series

Name	ASTM Special Technical Publication
Volume	STP 1639
ISSN (Print)	0066-0558

Conference

Conference	2021 Symposium on Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments
City	Virtual, Online
Period	23/09/21 → 24/09/21

Funding

The graphite test specimens were kindly provided by Sinosteel. X.-C. Jin and H. N. Chen acknowledge the support of the China Scholarship Fund (Award Nos. 201806280383 and 201906675001) that enabled their participation in this work.

Keywords

digital image correlation
fracture toughness
graphite
J-integral
small specimen

ASJC Scopus subject areas

General Materials Science

Access to Document

10.1520/STP163920210051

Cite this

Marrow, J., Scotson, D., Jin, X., Chen, H., Chen, Y., Koko, A., Earp, P., & Wu, H. (2022). Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite. In A. Tzelepi, & M. Metcalfe (Eds.), Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments (pp. 1-17). (ASTM Special Technical Publication; Vol. STP 1639). ASTM International. https://doi.org/10.1520/STP163920210051

Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite. / Marrow, James; Scotson, Dan; Jin, Xiaochao et al.
Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments. ed. / Athanasia Tzelepi; Martin Metcalfe. U. S. A.: ASTM International, 2022. p. 1-17 (ASTM Special Technical Publication; Vol. STP 1639).

Research output: Chapter or section in a book/report/conference proceeding › Chapter in a published conference proceeding

Marrow, J, Scotson, D, Jin, X, Chen, H, Chen, Y, Koko, A, Earp, P & Wu, H 2022, Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite. in A Tzelepi & M Metcalfe (eds), Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments. ASTM Special Technical Publication, vol. STP 1639, ASTM International, U. S. A., pp. 1-17, 2021 Symposium on Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments, Virtual, Online, 23/09/21. https://doi.org/10.1520/STP163920210051

Marrow J, Scotson D, Jin X, Chen H, Chen Y, Koko A et al. Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite. In Tzelepi A, Metcalfe M, editors, Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments. U. S. A.: ASTM International. 2022. p. 1-17. (ASTM Special Technical Publication). doi: 10.1520/STP163920210051

Marrow, James ; Scotson, Dan ; Jin, Xiaochao et al. / Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite. Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments. editor / Athanasia Tzelepi ; Martin Metcalfe. U. S. A. : ASTM International, 2022. pp. 1-17 (ASTM Special Technical Publication).

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abstract = "To enable monitoring of graphite that has been exposed to irradiated, high-temperature environments, there is a need for analysis methods that are suitable for fracture toughness measurements in small test specimens. Quasistatic fracture propagation has been studied for two candidate graphites for next-generation nuclear energy, SNG742 and T220, using small specimens in the double-cleavage drilled-compression (DCDC) geometry (20 7 7 mm). Compression of the DCDC specimen initiated stable crack propagation, and the surface full-field displacements were measured by digital image correlation. A phase congruency method was applied to the displacement field to quantify the crack lengths, crack opening displacements, and crack tip opening angles. The classical analytical solution for the stress intensity factor in the DCDC specimen gave unrealistic results due to its boundary condition assumptions. A new analysis method is proposed in which the measured crack displacement field is injected as boundary conditions into a finite element model, allowing the J-integral to be evaluated via the contour integral method, which then provides the mode 1 stress intensity factor during quasistatic crack propagation. With the assumption of linear elasticity, the critical stress intensity factor in T220 was constant for crack propagation up to 6 mm and lower than that in SNG742, which showed rising fracture resistance for longer cracks. The analysis was validated using Macor, a linear elastic fine-grained glass ceramic with known fracture toughness without significant R-curve behavior. The small-specimen graphite results are consistent with the reported fracture toughness from large-specimen tests, but the values are overestimations due to the nonlinear behavior of unirradiated graphite. Methods to extract nonlinear elastic properties by inverse analysis are discussed. The outlook for fracture testing of irradiated graphite at elevated temperatures is considered.",

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AU - Earp, Philip

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PY - 2022/12/1

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N2 - To enable monitoring of graphite that has been exposed to irradiated, high-temperature environments, there is a need for analysis methods that are suitable for fracture toughness measurements in small test specimens. Quasistatic fracture propagation has been studied for two candidate graphites for next-generation nuclear energy, SNG742 and T220, using small specimens in the double-cleavage drilled-compression (DCDC) geometry (20 7 7 mm). Compression of the DCDC specimen initiated stable crack propagation, and the surface full-field displacements were measured by digital image correlation. A phase congruency method was applied to the displacement field to quantify the crack lengths, crack opening displacements, and crack tip opening angles. The classical analytical solution for the stress intensity factor in the DCDC specimen gave unrealistic results due to its boundary condition assumptions. A new analysis method is proposed in which the measured crack displacement field is injected as boundary conditions into a finite element model, allowing the J-integral to be evaluated via the contour integral method, which then provides the mode 1 stress intensity factor during quasistatic crack propagation. With the assumption of linear elasticity, the critical stress intensity factor in T220 was constant for crack propagation up to 6 mm and lower than that in SNG742, which showed rising fracture resistance for longer cracks. The analysis was validated using Macor, a linear elastic fine-grained glass ceramic with known fracture toughness without significant R-curve behavior. The small-specimen graphite results are consistent with the reported fracture toughness from large-specimen tests, but the values are overestimations due to the nonlinear behavior of unirradiated graphite. Methods to extract nonlinear elastic properties by inverse analysis are discussed. The outlook for fracture testing of irradiated graphite at elevated temperatures is considered.

AB - To enable monitoring of graphite that has been exposed to irradiated, high-temperature environments, there is a need for analysis methods that are suitable for fracture toughness measurements in small test specimens. Quasistatic fracture propagation has been studied for two candidate graphites for next-generation nuclear energy, SNG742 and T220, using small specimens in the double-cleavage drilled-compression (DCDC) geometry (20 7 7 mm). Compression of the DCDC specimen initiated stable crack propagation, and the surface full-field displacements were measured by digital image correlation. A phase congruency method was applied to the displacement field to quantify the crack lengths, crack opening displacements, and crack tip opening angles. The classical analytical solution for the stress intensity factor in the DCDC specimen gave unrealistic results due to its boundary condition assumptions. A new analysis method is proposed in which the measured crack displacement field is injected as boundary conditions into a finite element model, allowing the J-integral to be evaluated via the contour integral method, which then provides the mode 1 stress intensity factor during quasistatic crack propagation. With the assumption of linear elasticity, the critical stress intensity factor in T220 was constant for crack propagation up to 6 mm and lower than that in SNG742, which showed rising fracture resistance for longer cracks. The analysis was validated using Macor, a linear elastic fine-grained glass ceramic with known fracture toughness without significant R-curve behavior. The small-specimen graphite results are consistent with the reported fracture toughness from large-specimen tests, but the values are overestimations due to the nonlinear behavior of unirradiated graphite. Methods to extract nonlinear elastic properties by inverse analysis are discussed. The outlook for fracture testing of irradiated graphite at elevated temperatures is considered.

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ER -

Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite

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Keywords

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