Effects of oxidation on compressive deformation behavior of nuclear-grade isotropic graphite

Abstract

The compressive deformation behavior of a nuclear isotropic graphite oxidized stepwise up to 30% burn-off has been studied. In the case of uniform oxidation, Young's modulus and fracture strength decrease with increasing bum-off. The residual strain caused by the compression increases monotonically with increasing bum-off, while the fracture strain shows a steep increase in the burn-off range up to 5% and thereafter decreases gradually. The ratio of flow stresses between the uniformly oxidized (σ(ϵ)) and unoxidized specimens ( σ 0( ϵ)) at same total strain is independent of the strain value adopted. The ratio decreases with increasing burn-off and can be expressed as σ(ϵ) σ 0(ϵ) = ( ρ ρ 0 ) π , where ρ and ρ 0 denote the apparent densities, and n a constant empirically determined to 4.56. Through an analysis of the data obtained for uniform oxidation, stress-strain relationship as well as Young's modulus can be reproduced reasonably well for the specimen having an oxidation gradient, if the density distribution is known.