The residual strain of polycrystalline graphite. I

The stress dependence of the residual strain of various polygraphites is investigated to make clear whether Jenkins' expressions for the residual strain are in agreement with the experimental data. Studies are also made on the effect of neutron irradiation at high temperatures on the stress dependence of the strain. The relationship between residual strain and applied stress can be approximately expressed as epsilon0 = C(sigma/ sigmasub(f)sup(n) over a wide range of applied stress. Here, epsilon0, sigma and sigmasub(f) denote residual strain, applied stress and fracture stress, respectively. C and n are constants which depend on both the kind of graphite and the specimen orientation. The values of n for various graphites are not necessarily equal to or larger than two. These facts are inconsistent with the equations of Jenkins. The values of n and C are decreased by neutron irradiation at temperatures from 820 to 9200C to a fluence of 3-9 x 1020n/cm2 (E>0.18 MeV). This is explained by the change in the population of cracks in the specimen caused by neutron irradiation. (Auth.)