Microstructural modelling of nuclear graphite using multi-phase models

Berre, Carole Le; Fok, S L; Marsden, Barry; Mummery, Paul; Marrow, James; Neighbour, Gareth B

doi:10.1016/j.jnucmat.2008.07.006

Cited by 28 publications

(12 citation statements)

References 22 publications

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“…The failure strain of Gilsocarbon graphite has been reported to be less than 0.3% for macroscale uniaxial tension test [45] [34]. Whereas the failure strain measured in the present work is over twice the average value ~ 0.6% with a highest value of 1.0%.…”

Section: Failure Modescontrasting

confidence: 53%

“…Secondly, the broad distribution of the measured properties at the micro-scale is due to the varying pores, defects and the It has been recognised that the measurements obtained at micro-scale provide the appropriate input parameters for computer models, in particular for the type of models based on the microstructure and the multi-phases [31][34] [35]. The model proposed by Berre et al [34] derived the elastic modulus of the individual phase by extrapolating the measured phase density using X-ray tomography between pores (zero density with E = 0 GPa) and pore-free single crystal graphite (density = 2.26 g/cm 3 with E = 19 GPa). However, some of the E values measured by the micro-cantilevers in the current work (PG25, Gilsocarbon and PGA graphites) are higher than 19 GPa, which is the minimum E for single crystal graphite.…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

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Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

Liu

Flewitt

2017

Carbon

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing AbstractThe local mechanical properties of vitreous carbon and another three porous graphite materials have been investigated using a novel in situ micro-cantilever bending approach.Vitreous carbon is used for validation of the micro-mechanical measurements. Filter graphite is a single phase material with ~52 vol.% porosity. Gilsocarbon graphite is a nuclear-grade graphite that is currently used in the advanced gas-cooled reactors in the UK with ~20 vol.% porosity in the filler particles and matrix; Pile Grade-A graphite (PGA) was extracted from a fuel brick within a Magnox reactor core with 15% weight loss due to neutron irradiation and CO 2 radiolytic oxidation. The 'true' material properties obtained at micro-scale are found to be of much higher value than those measured at the macro-scale due to different failure controlling mechanisms. In particular for the PGA graphite, the micro-mechanical tests allowed the mechanical properties of the filler particles and matrix to be measured separately.The filler particles showed a higher stiffness and flexural strength compared with the matrix indicating the different influence of neutron irradiation on these two constituents. It is demonstrated here that the local mechanical properties of carbonaceous materials with various complex microstructures and even following neutron irradiation can be successfully evaluated.

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Section: Failure Modescontrasting

confidence: 53%

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

Liu

Flewitt

2017

Carbon

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“…To apply this criterion, it is necessary to relate the stress concentration in the inclusions with the size of the volume over which this stress is reached. In Berre et al, 432 the local value of the grey levels in the reconstructed tomograms are used to measure the local density in a nuclear graphite and to generate a multiphase model. The density is then used to modulate the Young's modulus and resistance of the local element and a finite element calculation is performed to account for these fluctuations and calculate the macroscopic behaviour for samples with different structures.…”

Section: Image Based Modelling Of Composites and Multiphase Materialsmentioning

confidence: 99%

Quantitative X-ray tomography

Maire¹,

Withers²

2013

International Materials Reviews

1,089

601

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X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information needed to optimise manufacturing processes, for example sintering or solidification, or to highlight the proclivity of specific degradation processes under service conditions, such as intergranular corrosion or fatigue crack growth. Besides the repeated application of static 3D image quantification to track such changes, digital volume correlation (DVC) and particle tracking (PT) methods are enabling the mapping of deformation in 3D over time. Finally the use of CT images is considered as the starting point for numerical modelling based on realistic microstructures, for example to predict flow through porous materials, the crystalline deformation of polycrystalline aggregates or the mechanical properties of composite materials.

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“…For Gilsocarbon graphite, the typical uniaxial flexural strength has been measured to be 28 MPa [21] and the critical energy release rate to be 260 J m À2 [22]. These studies used the same Gilsocarbon grade of nuclear graphite, with a nominal void volume fraction of $20% (the flexural strength and critical energy release rate are microstructure-dependent, being affected by the porosity of graphite [68]). …”

Section: Cohesive Zone Modelmentioning

confidence: 99%

Three-dimensional crack observation, quantification and simulation in a quasi-brittle material

et al. 2013

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To investigate the fracture behaviour of polygranular graphite (a quasi-brittle material), crack propagation in a short bar chevron notched specimen was studied by synchrotron X-ray computed tomography combined with digital volume correlation. Displacements were measured within the loaded test specimen, particularly the three-dimensional (3-D) profile of crack opening displacement. Analysis of the 3-D displacement field confirmed the existence of distributed damage in a fracture process zone, which significantly increased the effective crack length. Finite element simulations affirmed that the measured crack opening profiles could be reproduced using a cohesive zone model, but not with a linear elastic analysis. Comparing the simulation to the experimental results, it was deduced that the critical strain energy release rate varied across the crack front, i.e. the fracture toughness is constraint-dependent. This is proposed to be a general characteristic of quasi-brittle materials.

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Microstructural modelling of nuclear graphite using multi-phase models

Cited by 28 publications

References 22 publications

Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

Quantitative X-ray tomography

Three-dimensional crack observation, quantification and simulation in a quasi-brittle material

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