Study on the Residual Strain Associated with Compressive Stress Applied to Nuclear Graphites

Abstract

Constituent elements of the compressive residual strain have been examined taking account of results of deformation within grist particles, deformation of pores, and crack formation which are produced after applying compressive stress to nuclear graphites. Longitudinaland transverse residual strains associated with compressive prestress have been precisely measured at room temperature both foranisotropic and isotropic nuclear graphites. The apparent volume of specimen and the Young's modulus measured by ultrasonic method decreased in approximately proportion to the increase in the longitudinal residual strain. The transverse residual strain was an order of magnitude smaller than the longitudinal one.The deformation within grist particles was estimated to be within the limit of detection by the X-ray analysis of layer spacing and lattice strain after prestressing.These results suggest that the decrease in the apparent volume associated with increase in the compressive prestress is mainly due to the decrease in the total porosity in which the pore deformation plays an important role.The formation of crack which is taken to be a primary cause of the decrease in the Young's modulus is considered to be an element which gives a large contribution to the residual strain, together with the deformation of pores.