Effect of nuclear irradiation on the internal friction and dynamic elastic modulus of stress-graphitized pyrolytic carbon

Abstract

The effects of room temperature irradiation on the dynamic elastic modulus, E', and the internal friction, Q −1, of graphite have been investigated over a range of reactor radiation doses (~10 12 to 10 18 nvt − > 50 keV). Well-ordered graphite formed by stress-annealing pyrolytic carbon at high temperatures was used in the experiments. Tests were conducted at audio frequencies in the temperature range from 100° to 650°K. Modulus values increased with dose at all test temperatures.Irradiation to 1.4 × 10 18 nvt resulted in a modulus increase by a factor of × 8 in the 100°–400°K range. An inverse-annealing peak, present near 500°K at lower doses, became largely masked at higher doses (1.4× 10 18 nvt). Results also indicate that threshold for detection of radiation-induced changes is surprisingly low (10 12 nvt or less).This corresponds to a fractional displacement of ~ 10 -8 atoms/atom.Accompanying changes in the internal friction for various doses are presented and discussed.Results for a Co-60 irradiated specimen are also presented to illustrate that gamma radiation (140 Mrad) produces clearly detectable changes in E'.The overall research indicates that models for radiation damage in graphite may have to be altered to account for the effects.