Young's modulus of pyrolytic carbon in relation to preferred orientation

Abstract

Expressions are derived which express Young's modulus of an anisotropic aggregate of hexagonal crystallites in terms of the single-crystal elastic constants and functions of the preferred orientation, assuming either a constant tensile strain or a constant tensile stress throughout the aggregate. Measurements of Young's modulus and preferred orientation on a number of pyrolytic carbons with different anisotropies show that the ‘constant stress’ model represents a good approximation of the behaviour of these materials. Young's modulus of polycrystalline nuclear graphite, whose dislocations have been pinned by a low-temperature neutron irradiation, agrees with the same model.