Effects of prestresses on mechanical properties of isotropic graphite materials

Graphite materials which are used for plasma facing components and other co mponents are subjected to stresses due to the high heat flux from the fusio n plasma. Some mechanical properties of graphite materials can change due t o the prestresses. The property changes should be considered for the design of the plasma facing components. The purpose of this study is to examine t he effects of prestresses on the mechanical properties of isotropic graphit e materials. Compressive prestresses were applied to two kinds of isotropic fine-grained graphites (IG-430 and IC-11) at 298 K (both), 1873 K (IG-11), 2273 K (IG-11) and 2283 K (IG-430). As a result, the decrease in Young's m odulus for IG-430 due to high-temperature prestressing was 56% which was mu ch larger than the 6.4% that was due to prestressing at 298 K. The results for IG-11 were the same as those for IG-430 graphite. This finding was cons idered to be due primarily to a difference in degree of the preferred orien tation of crystallites in the graphite on the basis of the Bacon anisotropy factor (BAF) obtained from X-ray diffraction measurement of the prestresse d specimens. Furthermore, high-temperature compressive prestressing produce d an increase in the strength of the isotropic graphite, although room temp erature prestressing produced no such effect. The results obtained here sug gest that the isotropic graphite which is subjected to high-temperature com pressive stresses can become anisotropic in service. (C) 1998 Elsevier Scie nce B.V. All rights reserved.