Abstract
Neutron diffraction and synchrotron X-ray diffraction and imaging have been applied to study, in situ, the mechanical response to tensile and bending loading of polygranular Gilsocarbon nuclear grade near-isotropic graphite (grade IM1-24). Digital image correlation of X-ray radiographs and digital volume correlation of tomographs allow measurement of bulk elastic moduli and examination of the heterogeneity of deformation in the microstructure. Both the neutron and X-ray studies show the application of tensile strain reduces the bulk elastic modulus. A permanent set is observed to develop with applied tensile strain. The elastic strains within the graphite crystals were measured by diffraction; a cross-correlation analysis method has been applied for greater speed, robustness and improved precision in the measurement of the change in basal plane separation distance. In compression, a linear relation is observed between the elastic strains in the graphite crystals and the applied strain. In tension, this relationship is non-linear. The results are discussed with respect to the distribution of elastic and inelastic strain within the graphite microstructure. It is deduced that the significant residual elastic strains in the as-manufactured graphite are relaxed by microcracking as tensile strain is applied.
| Original language | English |
|---|---|
| Pages (from-to) | 285-302 |
| Number of pages | 18 |
| Journal | Carbon |
| Volume | 96 |
| DOIs | |
| State | Published - Jan 2016 |
| Externally published | Yes |
Funding
The authors are very thankful to M. Mostafavi (University of Sheffield), M. Jordan (University of Oxford) and also K. Hallam and A. Andriot (University of Bristol) for their assistance during these experiments and helpful discussions. The awards of experimental time on I12 at the Diamond Light Source (EE9036 – Strain-mapping in quasi-brittle materials by diffraction) and ENGIN-X at ISIS (RB1320187 – A Novel In-situ Approach to Evaluate the Process Zone in Quasi-brittle Materials under Bending) are acknowledged. The research was supported by the UK Engineering and Physical Science Research Council (EPSRC) under awards EP/J01992/1 , EP/J019801/1 and EP/H025286 (QUBE: QUasi-Brittle fracture: a 3D Experimentally-validated approach). Dr Brian Connolly (University of Birmingham) is thanked for the loan of the tensile loading rig, funded by EPSRC (EP/H025286/1 – Long Term, In Situ Material Degradation Studies Utilizing High Resolution Laboratory X-ray Tomography). The support of TJM by the Oxford Martin School (Nuclear Programme) and of YeV by EDF Energy, who provided the material, is gratefully acknowledged. PEJF acknowledges Wolfson College, Oxford, for facilitating the collaboration.