Effect of steam oxidation on strength, elastic modulus, and strain at fracture of graphite 2020. [HTGR]

Abstract

Stackpole Carbon's graphite grade 2020, a candidate material for support posts in GA HTGRs, was oxidized in steam-helium mixtures to 25 wt % burnoff. The effects of the oxidation on ultimate strength, elastic modulus, and strain at fracture are reported. A large number of nonoxidized and oxidized tensile specimens were tested to failure. Average losses of 6.7 wt % in strength and 7.4 wt % in elastic modulus at 1% burnoff were obtained. No significant change in strain at fracture was observed for burnoffs up to 5%. The elastic modulus and ultimate tensile strength of the oxidized samples correlated with bulk density. No significant radial gradients in strength or elastic modulus were observed in the log; however, slight differences in elastic modulus and strain at fracture were observed along the length of the log. Radial specimens had significantly higher strength and elastic modulus than axial specimens.