Stress Dependence of Tensile Creep Rate in Carbons and Graphites

Abstract

DESPITE the importance of carbons and graphites for very high temperature structural applications, very little is understood about the mechanisms of deformation and failure in these materials¹. In principle, the stress dependence of the creep rate offers a simple method to obtain information on which of several possible deformation mechanisms operate at high temperatures. Using the empirical relationship ε̇ = Aσⁿ, where ε̇ is the creep rate, σ is the stress and A is a proportionality constant, the stress exponent n is expected to equal one for Nabarro–Herring diffusion mass-transport creep; a much larger value of n, typically between 4 and 5, is expected for an edge dislocation climb mechanism such as occurs in many metals.