Spatial variability in the mechanical properties of Gilsocarbon

Abstract

The objective of this study is to investigate whether there is significant spatial variability in the mechanical properties of Gilsocarbon nuclear graphite at different sections of the billet; specifically the dynamic Poisson's ratio, dynamic shear modulus, dynamic Young's modulus and density. Similar studies have been done, usually in the context of manufacturing, to assess the quality of graphite components for nuclear reactors. In this new study, the measurements have been carried out at a much higher spatial resolution than previously. A Torness/Heysham B billet was machined into cubes so that measurements could be made across the circumference and height of the billet. ASTM standards were followed to assess the measurements of the samples. The spatial variability of material properties is described and analysed statistically. The study shows that material variability is present at different heights and circumferential locations of the billet. This discovery will have a significant impact on the structural integrity and through life performance predictions made in industry; both in current and future nuclear reactors. The computer modelling of graphite components may predict different outcomes to standard analyses (that use mean values) if this variability is incorporated into the analysis workflow; specifically through stochastic modelling.

Characterisation of the spatial variability of material properties of Gilsocarbon and NBG-18 using random fields

“…In general, these random fields present similar patterns as the ones found in Figure 15. This resemblance is expected because of the relationship between density and Young's modulus values [32,38]: graphite denser areas tend to be stiffer. This fact Figure 17e to Figure 17h.…”

“…(The complete data set can be found in reference [32].) A subset of 328 samples were used for the calculations of this research and the locations of these samples are shown in Figure 2 The summary of the density and Young's modulus values for Gilsocarbon are divided in Table 1 and Table 2.…”

“…Therefore, another source of density and dynamic Young's modulus was used for the calculations of this study [26].…”

“…The position and values of density and dynamic Young's modulus for the spine sections can be found inFigure 3andFigure ,respectively. For a more detailed description of the acquisition and data information the reader is referred to Reference[32].…”

4D synchrotron X-ray microtomography of fracture in nuclear graphite after neutron irradiation and radiolytic oxidation

“…Around half of this is an open network of gas evolution and escape pores covering multiple scale-lengths (nm-to-mm), while the other half are closed pore features, specifically micro/nano-sized cracks that form due to the anisotropic contraction of crystallites during cooling after graphitisation at 2800-3000ºC [2][3][4]. Such a large and varied flaw population is heterogeneously distributed throughout the microstructure of Gilsocarbon, causing its density to display significant spatial variability [5]. This translates into slightly anisotropic (near-isotropic) properties, substantial spread in property measurements, and significant specimen size effects [6][7][8].…”