Experimentally informed multi-scale modelling of mechanical properties of quasi-brittle nuclear graphite

Šavija, Branko; Liu, Dong; Smith, Gillian; Hallam, K; Schlangen, Erik; Flewitt, Peter E J

doi:10.1016/j.engfracmech.2015.10.043

Cited by 46 publications

(34 citation statements)

References 20 publications

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“…This is because the microstructure tested at these two length-scales is different since the micro-scale cantilever specimens include both micro-metre and sub-micro-metre porosity, while macro-scale specimens sample pores at both micro-and macro-length scales. 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).…”

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

confidence: 99%

“…In total, eight specimens were tested and the measured properties and loading cycles are listed in Table II Table I and ref [31] (22.3 to 26.9 MPa). The large scatter at micro-scale can be attributed to the presence of micro-scale flaws and when their presence is minimal the measured properties approach the value for defect-free material.…”

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

confidence: 99%

“…For the filler particles, as shown in Table II To test the significance of these micro-scale test data for both unirradiated and irradiated PGA graphite, the values described in this paper have been used as inputs to a microstructurally based, multi-scale computer model [31]. The computer modelling was designed to predict at the macro-length-scale the load-displacement response and the deformation and fracture properties for material containing macro-porosity arising from fabrication in unirradiated material and neutron dose in an irradiated oxidising environment [31].…”

Section: Neutron Irradiationmentioning

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: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

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

confidence: 99%

Section: Neutron Irradiationmentioning

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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“…Lattice models have been used in the past to simulate deformation and fracture in quasi-brittle materials such as concrete (Bolander et al 2000;Schlangen and Garboczi 1997;Schlangen and Qian 2009), nuclear graphite (Šavija et al 2016;Smith et al 2013), and rock (Asahina et al 2014;Sands 2016). Unlike conventional approaches based on continuum mechanics, the material is discretized as a set of two-node (spring, truss, or beam) elements which can transfer forces in lattice models.…”

Section: Mechanicalmentioning

confidence: 99%

Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials: experiments and modelling

et al. 2017

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In this work, porosity-property relationships of quasi-brittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (CaSO 4 · 1/2H 2 O) and expanded spherical polystyrene beads (1.5-2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D X-ray computed tomography. Beams of the size of 20 × 20 × 150 mm were cast and loaded under fourpoint bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a lattice-based multi-scale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasi-brittle materials.

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“…Lattice models have been used in the past to simulate fracture of concrete and other heterogeneous materials (Schlangen and Van Mier, 1992, Bolander and Saito, 1998, Vasic, et al, 2005, Šavija, et al, 2016. Fracture in fibre reinforced composites can also be simulated (Bolander and Saito, 1997, Montero-Chacón, et al, 2015.…”

Section: Lattice Modellingmentioning

confidence: 99%

Influence of Cracking on Moisture Uptake in Strain-Hardening Cementitious Composites

Šavija

Luković

Schlangen

2017

J. Nanomech. Micromech.

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Strain hardening cementitious composites (SHCC) are a class of cement based materials which show strain hardening behaviour in tension. This is achieved by multiple microcracking, which results in a tightly spaced crack pattern with relatively small crack widths (50-80 micrometers (µm), in general) and high strain capacity (up to 4-5%). Due to their ductile behaviour and tight crack widths, SHCCs are commonly used for concrete repair applications. However, due to the tight crack width and crack spacing, moisture uptake by capillary suction can take place very fast. This could result in rapid access of deleterious substances, such as chloride ions, resulting in corrosion initiation. In this study, X-ray tomography is used for monitoring and quantification of water uptake in SHCC. Specimens were first loaded to different strain levels in uniaxial tension. Then, they were subjected to a capillary suction test. The performed test was subsequently modelled using a lattice model.

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Experimentally informed multi-scale modelling of mechanical properties of quasi-brittle nuclear graphite

Cited by 46 publications

References 20 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

Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials: experiments and modelling

Influence of Cracking on Moisture Uptake in Strain-Hardening Cementitious Composites

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