A fracture criterion for nuclear graphite

Abstract

Measurements of tensile and flexural strength of a nuclear graphite using small bar specimens are reported. A theoretical model of failure is described in which critical defects are assumed to be associated with cleaved large coke particles. It is further assumed that these subcritical cracks can only extend by the cleavage of small particles which surround them. The size of the critical flaws is defined on the basis of linear elastic fracture mechanics. The model predicts the observed variation in flexural strength in three- and four-point bending as the knife edge spacings are varied. It slightly overestimates the observed ratio of tensile-to-bend strength, and this is thought to be due to some of the simplifying assumptions made in the models formulation. The potential of the model for use in engineering applications is discussed.