Dependence of Rate of Creep on the Orientation of the Tensile Axis for Heavily Oriented Graphite

Abstract

IN polycrystalline material1 general deformation by slip requires co-operative slip by five independent systems. Graphite is known to deform easily by slip along its basal plane2, but such slip contributes only two independent systems. Other deformation mechanisms, such as non-basal plane slip, grain boundary sliding or cracking, twinning, or intracrystalline cracking must therefore operate in conjunction with basal plane slip. A series of experiments was designed to determine whether basal plane slip or some other deformation mechanism was the rate controlling mechanism during creep. The dependence on orientation of the creep rate of heavily oriented graphite (ZTA, National Carbon) was used for these experiments. By applying the same tensile stress to samples the axes of which were inclined at different angles to the average c-direction, different combinations of resolved shear stress and tensile stress were applied along the basal planes, “c”-axes, and the different kinds of grain boundaries, thereby causing different creep rates.