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Conference Article: Spatial variability in the tensile strength of an extruded nuclear-grade graphite

Strizak, J.P. (Oak Ridge National Lab., TN (United States))

Abstract

This report will present the results of a study on spatial variations in the strength of nuclear-grade H-451 graphite. The tensile properties of H-451 were examined extensively in the past in order to characterize the variability of strength within billets, between billets and between lots. But the variability within a billet was, for the most part, studied only casually. The problem appeared to be the strong influence of a limited sampling plan in describing the mean strength and the variability. Therefore, an extensive, statistically sound sampling plan has been devised to fully characterize the spatial variability within a single billet. Test specimens were machined to conform to ASTM C749-87, ''Standard Test Method for Tensile Stress-Strain of Carbon and Graphite''. Test results have been obtained for four specimen sizes having gage diameters of 6.35, 9.53, 15.88, and 25.40 mm with respective gage-section volumes of 1407, 3163, 12,577, and 51,482 mm3. A new fracture model developed by Burchell was applied to the data with encouraging results. This probabilistic failure criteria combines a microstructural basis with a fracture-mechanics approach to failure.

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key words: failures; fracture mechanics; fracture properties; graphite; htgr type reactors; microstructure; probabilistic estimation; spatial distribution; tensile properties; carbon; gas cooled reactors; graphite moderated reactors; mechanical properties; reactors
Reference:
Specialists' meeting on the status of graphite development for gas cooled reactors. Tokai, Ibaraki (Japan). 9-12 Sep 1991
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--690, pp:64-69