Transient creep and recovery in graphite

Abstract

Abstract A simple formal theory of creep in graphite is derived in which both forward and reverse thermally activated processes are considered. During the creep an internal back stress develops which reduces the rate of the forward process and increases the rate of the reverse process. At intermediate times the creep equation derived from the theory approximates to a logarithmic creep law of the form: However, the creep rate at small times, and the total strain at infinite time, are both finite. Recovery of creep strain on removal of stress is predicted to obey the same law. The creep laws are shown to agree with experimental creep data at temperatures below 1500°c in their general form and in the linear dependence of K on both the temperature and the applied stress. Finally, a more specific model in terms of dislocation movement across periodic energy barriers is shown to be in fair agreement with the formal theory.