Spatial Variability in the Tensile Strength of an Extruded Nuclear-Grade Graphite

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 strong influence of a limited sampling plan in describing the mean strength and the viability. Therefore, an extensive, statistically sound sampling plan has been devised to fully characterize the spatial variability within a single billet. 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.