DYNAMIC MECHANICAL BEHAVIOR OF GRAPHITES

The stress-amplitude independent internal friction and dynamic elastic modulus of pitch-bonded natural graphite crystals and various grades of commercial graphites were measured from 4 to 750°K at frequencies in the range of 0.6 to 10 kcps. For these materials, the internal friction, which was an order of magnitude larger than that previously reported for asdeposited pyrolytic carbon and vitreous carbons, is primarily characterised by a broad peak (designated as the α peak) centered near room temperature, accompanied by an elastic modulus relaxation. The peak characteristics, including a reduction in peak height by annealing or lowdose reactor irradiation (4 × 1015 nvt), closely corresponded to that previously observed for the Bordoni peak in fcc metals. Similar to the suggested mechanism in metals, the α peak may be associated with the motion of basal plane dislocations. The investigation also revealed the presence of a small relaxation below 60°K in some graphites, and, in one case, a very sharp peak above room temperature. It is assumed that the former may be associated with impurities. The latter peak, which anneals out, is similar in some respects to a few cited cases in metals. © 1968.