QUBE:- QUasi-Brittle fracture: a 3D Experimentally-validated approach
Lead Research Organisation:
University of Bristol
Department Name: Interface Analysis Centre
Abstract
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Publications
Darnbrough J
(2013)
Micro-scale testing of ductile and brittle cantilever beam specimens in situ with a dual beam workstation
in Measurement Science and Technology
Dong Liu (Author)
(2013)
Fracture characterisation of reactor core graphite under bi-axial loading
Dong Liu (Author)
(2013)
Microscale testing to evaluate the fracture characteristics of quasi-brittle
Garza C
(2016)
Closed-form solutions of hole distortion for use in deep-hole drilling measurements of residual stress in orthotropic plates
in The Journal of Strain Analysis for Engineering Design
Heard P
(2014)
Evaluation of surface deposits on the channel wall of trepanned reactor core graphite samples
in Journal of Nuclear Materials
Heard P
(2015)
Study of Reticulated Vitreous Carbon Foam as a Quasi-Brittle Material
in Key Engineering Materials
Liu D
(2017)
On the damage and fracture of nuclear graphite at multiple length-scales
in Journal of Nuclear Materials
Liu D
(2013)
Fracture Characterisation of Reactor Core Graphite under Biaxial Loading
in Key Engineering Materials
| Description | The Characteristics both physical and mechanical have been evaluated and are the subject of papers in preparation |
| Exploitation Route | Further considerations of quasi brittle materials |
| Sectors | Aerospace Defence and Marine Energy |
| Description | Build public confidence that it is safe to continue to operate the AGR fleet of nuclear power plant in the UK. |
| First Year Of Impact | 2016 |
| Sector | Energy |
| Impact Types | Societal |
| Description | Modelling at the test specimen length-scale deformation and fracture of unirradiated and irradiated Gilsocarbon graphite |
| Amount | £30,000 (GBP) |
| Organisation | EDF Energy |
| Sector | Private |
| Country | United Kingdom |
| Start | 02/2016 |
| End | 10/2016 |
| Description | Modelling the deformation and fracture of irradiated Gilsocarbon graphite |
| Amount | £27,000 (GBP) |
| Organisation | EDF Energy |
| Sector | Private |
| Country | United Kingdom |
| Start | 08/2015 |
| End | 01/2016 |
| Description | Modelling the mechanical properties of Gilsocarbon graphite |
| Amount | £27,000 (GBP) |
| Organisation | EDF Energy |
| Sector | Private |
| Country | United Kingdom |
| Start | 05/2014 |
| End | 01/2015 |
| Title | Resistivity measurement under load and temperature of graphite |
| Description | Measurement of resistivity of tensile test specimens over a temperature range developed in conjunction with Dr Bryan Roebuck at NPL |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2017 |
| Provided To Others? | No |
| Impact | Provides new insights on the fracture and deformation of reactor core type graphite |
| Description | Multiscale modelling of mechanical properties of quasi-brittle nuclear graphite |
| Organisation | Delft University of Technology (TU Delft) |
| Country | Netherlands |
| Sector | Academic/University |
| PI Contribution | Abstract Commercial graphites are used for a wide range of applications. For example, Gilsocarbon graphite is used within the reactor core of advanced gas-cooled reactors (AGRs, UK) as a moderator. In service, the mechanical properties of the graphite are changed as a result of neutron irradiation induced defects and porosity arising from radiolytic oxidation. In this paper, we discuss measurements undertaken of mechanical properties at the micro-length-scale for virgin and irradiated graphite. These data provide the necessary inputs to an experimentally-informed model that predicts the deformation and fracture properties of Gilsocarbon graphite at the centimetre length-scale, which is commensurate with laboratory test specimen data. The model predictions provide an improved understanding of how the mechanical properties and fracture characteristics of this type of graphite change as a result of exposure to the reactor service environment. Concluding Comments In Section 5, we have described and discussed results of a multi-scale model used for predicting changes in elastic properties of Gilsocarbon graphite due to service exposure to combined neutron irradiation and radiolytic oxidation. The model is founded on two underlying assumptions: (1) a good description of the material microstructure is necessary; and (2) material properties measured at the appropriate length-scale are needed to describe the deformation and fracture process in a complex multi-phase material such as Gilsocarbon graphite. The model is informed by experimental measurements of 'true' material properties. In this work, mechanical properties (elastic modulus and fracture strength) of virgin and irradiated Gilsocarbon graphite are obtained using a micro-cantilever testing technique. By testing micrometre length-scale specimens, this technique enables material properties of specific features of the microstructure to be obtained via minimisation of the influence of porosity and defects on the measurement results. This is essential for multi-phase materials that exhibit heterogeneities and porosities at multiple length-scales, such as nuclear graphite [9] and cement paste [22], [23], [24], [25]. These measurements provide the necessary input data at the micro-length-scale. In addition, a microstructural model representative of the Gilsocarbon graphite and the changes affecting it over time has been invoked. Therefore, porosity is explicitly included in the microstructural model. This procedure avoids the need for fitting parameters, so the simulation results are fully predictive and dependent on a good microstructural model. This makes data collection and property prediction cheap and efficient. Two different approaches, with varying levels of detail, have been presented: (1) a fully microstructural approach, which has been used to simulate uniaxial tension experiments on the millimetre length-scale; and (2) a statistical microstructure-informed approach, which has been used to simulate three-point bending experiments at the centimetre length-scale, with size corresponding to experiments. Simulation results have been compared to experimental data. Uniaxial tension simulations have shown excellent agreement between simulated elastic moduli and those measured for various in-service conditions. In addition, simulations have shown a shift between relatively brittle to more quasi-brittle behaviour with increasing irradiation and mass loss, signified by an increased contribution of the post-peak work of fracture, accompanied by widening of the fracture process zone. The crack propagation mode changes with increasing irradiation due to strengthening of the filler particles. While virgin condition cracks do penetrate through the filler particles, following irradiation this is not the case. For three-point bending simulations, a simplified statistical microscale approach has been adopted. While this does not explicitly use the material microstructure as input, it is informed by smaller-scale simulations. In a statistical way, this makes the proposed approach significantly less computationally expensive and, therefore, more suitable for larger specimens. Simulation results have shown good agreement with experimental data in terms of flexural strength. Although simplified, this approach is able to reproduce the main behaviours of the more detailed microstructurally-based approach (such as widening of the damage zone with increasing porosity), but with less detail. |
| Collaborator Contribution | Delft: FE modelling |
| Impact | Modelling deformation and fracture of Gilsocarbon graphite subject to service environments By:Savija, B (Savija, Branko)[ 1 ] ; Smith, GE (Smith, Gillian E.)[ 2 ] ; Heard, PJ (Heard, Peter J.)[ 2 ] ; Sarakinou, E (Sarakinou, Eleni)[ 2 ] ; Darnbrough, JE (Darnbrough, James E.)[ 2 ] ; Hallam, KR (Hallam, Keith R.)[ 2 ] ; Schlangen, E (Schlangen, Erik)[ 1 ] ; Flewitt, PEJ (Flewitt, Peter E. J.)[ 2,3 ] JOURNAL OF NUCLEAR MATERIALS Volume: 499 Pages: 18-28 DOI: 10.1016/j.jnucmat.2017.10.076 |
| Start Year | 2015 |
| Description | Multiscale modelling of mechanical properties of quasi-brittle nuclear graphite |
| Organisation | EDF Energy |
| Department | EDF Energy Nuclear Generation |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | Abstract Commercial graphites are used for a wide range of applications. For example, Gilsocarbon graphite is used within the reactor core of advanced gas-cooled reactors (AGRs, UK) as a moderator. In service, the mechanical properties of the graphite are changed as a result of neutron irradiation induced defects and porosity arising from radiolytic oxidation. In this paper, we discuss measurements undertaken of mechanical properties at the micro-length-scale for virgin and irradiated graphite. These data provide the necessary inputs to an experimentally-informed model that predicts the deformation and fracture properties of Gilsocarbon graphite at the centimetre length-scale, which is commensurate with laboratory test specimen data. The model predictions provide an improved understanding of how the mechanical properties and fracture characteristics of this type of graphite change as a result of exposure to the reactor service environment. Concluding Comments In Section 5, we have described and discussed results of a multi-scale model used for predicting changes in elastic properties of Gilsocarbon graphite due to service exposure to combined neutron irradiation and radiolytic oxidation. The model is founded on two underlying assumptions: (1) a good description of the material microstructure is necessary; and (2) material properties measured at the appropriate length-scale are needed to describe the deformation and fracture process in a complex multi-phase material such as Gilsocarbon graphite. The model is informed by experimental measurements of 'true' material properties. In this work, mechanical properties (elastic modulus and fracture strength) of virgin and irradiated Gilsocarbon graphite are obtained using a micro-cantilever testing technique. By testing micrometre length-scale specimens, this technique enables material properties of specific features of the microstructure to be obtained via minimisation of the influence of porosity and defects on the measurement results. This is essential for multi-phase materials that exhibit heterogeneities and porosities at multiple length-scales, such as nuclear graphite [9] and cement paste [22], [23], [24], [25]. These measurements provide the necessary input data at the micro-length-scale. In addition, a microstructural model representative of the Gilsocarbon graphite and the changes affecting it over time has been invoked. Therefore, porosity is explicitly included in the microstructural model. This procedure avoids the need for fitting parameters, so the simulation results are fully predictive and dependent on a good microstructural model. This makes data collection and property prediction cheap and efficient. Two different approaches, with varying levels of detail, have been presented: (1) a fully microstructural approach, which has been used to simulate uniaxial tension experiments on the millimetre length-scale; and (2) a statistical microstructure-informed approach, which has been used to simulate three-point bending experiments at the centimetre length-scale, with size corresponding to experiments. Simulation results have been compared to experimental data. Uniaxial tension simulations have shown excellent agreement between simulated elastic moduli and those measured for various in-service conditions. In addition, simulations have shown a shift between relatively brittle to more quasi-brittle behaviour with increasing irradiation and mass loss, signified by an increased contribution of the post-peak work of fracture, accompanied by widening of the fracture process zone. The crack propagation mode changes with increasing irradiation due to strengthening of the filler particles. While virgin condition cracks do penetrate through the filler particles, following irradiation this is not the case. For three-point bending simulations, a simplified statistical microscale approach has been adopted. While this does not explicitly use the material microstructure as input, it is informed by smaller-scale simulations. In a statistical way, this makes the proposed approach significantly less computationally expensive and, therefore, more suitable for larger specimens. Simulation results have shown good agreement with experimental data in terms of flexural strength. Although simplified, this approach is able to reproduce the main behaviours of the more detailed microstructurally-based approach (such as widening of the damage zone with increasing porosity), but with less detail. |
| Collaborator Contribution | Delft: FE modelling |
| Impact | Modelling deformation and fracture of Gilsocarbon graphite subject to service environments By:Savija, B (Savija, Branko)[ 1 ] ; Smith, GE (Smith, Gillian E.)[ 2 ] ; Heard, PJ (Heard, Peter J.)[ 2 ] ; Sarakinou, E (Sarakinou, Eleni)[ 2 ] ; Darnbrough, JE (Darnbrough, James E.)[ 2 ] ; Hallam, KR (Hallam, Keith R.)[ 2 ] ; Schlangen, E (Schlangen, Erik)[ 1 ] ; Flewitt, PEJ (Flewitt, Peter E. J.)[ 2,3 ] JOURNAL OF NUCLEAR MATERIALS Volume: 499 Pages: 18-28 DOI: 10.1016/j.jnucmat.2017.10.076 |
| Start Year | 2015 |
| Description | Graphite Core Committee (EDF Energy, UK) |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Industry/Business |
| Results and Impact | Specialist expert group. |
| Year(s) Of Engagement Activity | 2015,2016,2017 |