A model for anelastic relaxation controlled cyclic creep

Abstract

In the paper we derive an expression for the cyclic minimum strain rate of cyclic creep in systems where anelastic relaxation is a controlling mechanism. The cyclic creep behavior is modeled by assuming that the anelastic strain recovered during the off-load periods must first be stored during the on-load periods before nonrecoverable creep results. To perform the derivation, the time dependence of the anelastic relaxation is reported for two oxide dispersion strengthened alloys and shown to be adequately described by a double exponential function. The time dependence of the anelastic relaxation is then incorporated into an expression, generally used to describe static minimum strain rate data, to obtain the frequency dependence of the cyclic minimum strain rate. The predicted values of the derived expression using results from static creep and strain relaxation tests are in excellent agreement with the experimentally observed cyclic creep results with the use of no adjustable parameters. The proposed model of anelastic strain storage delaying nonrecoverable creep is also shown to be consistent with the observed effects of temperature and maximum load on the cyclic minimum strain rate.