1 / 24

1 Dong Liu, 1 Peter Heard, 2 Soheil Nakhodchi, 1,3 Peter EJ Flewitt

Small-scale Approaches to Evaluate the Mechanical Properties of Quasi-brittle Reactor Core Graphite. 1 Dong Liu, 1 Peter Heard, 2 Soheil Nakhodchi, 1,3 Peter EJ Flewitt 1 Interface Analysis Centre, School of Physics, University of Bristol, Bristol, BS8 1TL, UK

silas-lester
Télécharger la présentation

1 Dong Liu, 1 Peter Heard, 2 Soheil Nakhodchi, 1,3 Peter EJ Flewitt

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Small-scale Approaches to Evaluate the Mechanical Properties of Quasi-brittle Reactor Core Graphite 1Dong Liu, 1Peter Heard, 2Soheil Nakhodchi, 1,3Peter EJ Flewitt 1Interface Analysis Centre, School of Physics, University of Bristol, Bristol, BS8 1TL, UK 2Department of Engineering, University of Bristol, Bristol, BS8 1TR, UK 3HH Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, UK Symposium on Graphite Testing for Nuclear Applications: the Significance of Test Specimen Volume and Geometry and the Statistical Significance of Test Specimen Population

  2. Content • Background • Measurement methods • Four-point bending (centimetre) • Brazilian disc (millimetre) • Micro-scale cantilever (micrometre) • Nano-indentation (micrometre) • Concluding comments Symposium on Graphite Testing for Nuclear Applications

  3. Background • Important to be able to measure the mechanical properties of both virgin and irradiated graphites. • Test samples obtained by trepanning from bricks or from monitoring schemes. These provide centimetre scale test specimens. • Ideally like to reduce specimen size. The use of small scale test specimens offers benefits when handling irradiated reactor core graphite. • How small can specimens be to achieve representative data. • Scaling over length is always a challenge. • Aim to explore the potential benefits, difficulties and value of small scale mechanical tests for this particular application. Symposium on Graphite Testing for Nuclear Applications

  4. Background PGA graphite • Quasi-brittle behaviour Gilsocarbon graphite Symposium on Graphite Testing for Nuclear Applications

  5. Four-point bending (PGA graphite) • Virgin and irradiated PGA graphite • Cross-section: 25 mm x 25 mm • 20% porosity – virgin PGA graphite • 48% porosity – irradiated PGA graphite 150 mm 50 mm Symposium on Graphite Testing for Nuclear Applications

  6. Four-point bending (PGA graphite) • Load-displacement curve • Reloading follows the linear route of the previous cycle • Residual permanent displacement • Peak load and post peak softening is visible • Linear variable differential transformer (LVDT) for vertical displacement measurement Peak load = 1370 N 1200 N 900 N 600 N 0.07 mm Symposium on Graphite Testing for Nuclear Applications

  7. Four-point bending (PGA graphite) • Mechanical properties (Along the extrusion direction for PGA) Symposium on Graphite Testing for Nuclear Applications

  8. Brazilian disc (Gilsocarbon and PGA graphite) • Experimental setup • PGA graphite disc • 12 mm dia. x 6 mm • Gilsocarbon graphite disc • 12 mm dia. x 6.0 mm • 12 mm dia. x 4.3 mm • 12 mm dia. x 4.0 mm • 12 mm dia. x 3.8 mm Gilsocarbon graphite 12 mm Symposium on Graphite Testing for Nuclear Applications

  9. Brazilian disc (Gilsocarbon and PGA graphite) • Experimental setup • South Bay Technology Inc. Model 650 low speed diamond wheel saw • Deben compression / tensile stage (MicroTest 2000 model, Gatan Ltd., Abingdon, Oxon, UK) • Compression speeds of between 0.033 and 0.4 mm/min • Load cell with maximum of 2 KN • Curved anvils with distributed load Curved anvil Curved anvil Symposium on Graphite Testing for Nuclear Applications

  10. Brazilian disc (Gilsocarbon and PGA graphite) • Load-displacement curve (12 mm dia. x 6 mm disc) Symposium on Graphite Testing for Nuclear Applications

  11. Brazilian disc (Gilsocarbon and PGA graphite) • Load-displacement curve (12 mm dia. x 4 mm disc) GILSO Symposium on Graphite Testing for Nuclear Applications

  12. Brazilian disc (Gilsocarbon and PGA graphite) • Mechanical properties (VE=vertical to extrusion direction) Fractured surface of Gilsocarbon graphite 400 μm Symposium on Graphite Testing for Nuclear Applications

  13. Micro-scale cantilever beams (Gilsocarbon) Step I • A new approach is developed to prepare beams • Dualbeam workstation (FEI Helios NanoLab 600i Workstation) • Force measurement system (FMS) (Kleindiek Nanotechnik) • Select specific microstructure features Step II Symposium on Graphite Testing for Nuclear Applications

  14. Micro-scale cantilever beams (Gilsocarbon) 5 μm Symposium on Graphite Testing for Nuclear Applications

  15. Merits of new method • No tapering • The root is visible • Fracture surface exposed • View specimen throughout the test 5 μm 1 μm Symposium on Graphite Testing for Nuclear Applications

  16. Loading approach • Multiple loading cycles • Vary loading directions • Imaging at a load on hold 4 μm Symposium on Graphite Testing for Nuclear Applications

  17. Loading curves • Linear → softening → Linear • Direction dependent properties Symposium on Graphite Testing for Nuclear Applications

  18. Mechanical properties Symposium on Graphite Testing for Nuclear Applications

  19. Nano-indentation Experimental and specimens • Cylinder Gilsocarbon graphite specimen (22 mm dia. x 30 mm thickness) • Agilent Nano Indenter G200 (Culham Centre for Fusion Energy, Materials Facility, UK) • A square array of 5 x 5 of distributed indents are performed on the flat surface • Berkovich diamond tip • Load control with the maximum load of 10 mN and peak hold time of 10 s • Select specific microstructure features Symposium on Graphite Testing for Nuclear Applications

  20. Nano-indentation Symposium on Graphite Testing for Nuclear Applications

  21. Summary of data Symposium on Graphite Testing for Nuclear Applications

  22. Concluding comments • Small-scale testing is a powerful approach to explore mechanical properties of quasi-brittle materials • Properties measured depend upon length scale of tests • Centimetre scale tests provide representative global measurements • Millimetre scale tests could provide representative global values if sufficient tests conducted to sample the material – requires statistical analysis of these data as porosity increases this becomes more difficult • Micro-scale and below provide measurements for specific micro-scale features • Important to understand what information is required for a particular application Symposium on Graphite Testing for Nuclear Applications

  23. Acknowledgement We acknowledge the financial support from EPSRC funded project – QUBE (QUasi-Brittle fracture: a 3D Experimentally-validated approach). Grant number: EP/J019801/1. The Materials Research Laboratory at the Culham Centre for Fusion Energy was used for the nano-indentation on Gilsocarbon graphite. Symposium on Graphite Testing for Nuclear Applications

  24. Guess which is the author Symposium on Graphite Testing for Nuclear Applications

More Related