Change in electrical resistivity of nuclear graphite during compressive tests

Abstract

The effects of prehydrostatic loading on mechanical and physical properties were examined for two isostatistically-molded graphites, grades IG-11 and Iso-20. The increase in loading levels caused the monotonic decrease in specimen volume of both graphites, the change of which was much larger in the case of IG-11 graphite than of Iso-20. The electrical resistivity increased continuously with an increase in prehydrostatic loading levels, where the effect was more pronounced for IG-11 than for Iso-20 graphite. The manner in which the Young's moduli of the two materials changed after prehydrostatic loading was clearly different from each other, i.e., for IG-11 it decreased continuously with increasing pressure, whereas it increased at small hydrostatic pressures and leveled off above 300 MPa for Iso-20. A clear difference was also observed for the flexural strength of both materials: Its continuous decrease was caused by prehydrostatic loading for IG-11 graphite, whereas for Iso-20 it remained at the original value up to 500 MPa and decreased abruptly above that pressure level. An explanation of these features was provided from the viewpoint that microcracks are induced by hydrostatic loading.