Strain/Time Relations Describing Creep

Abstract

A new equation describing recovery creep is , where ε is the strain and is the eventual steady creep rate. From one form of the equation, namely , the McVetty-Garofalo, two forms of logarithmic, and Andrade creep equations are obtained with n = 1,2, and 5/2 respectively. From another form, namely , Li's, Akulov's and McLean's equations are obtained. These and other equations which are obtained are thus systematically related to each other. The physical bases of several derivations are also shown to be similarly related.

During the deceleration from the initial creep rate to the final rate , there develops not only a balance between the rate of recovery, r, and the strain hardening coefficient, h, so that , but also a decrease in r and an increase in h which prolongs primary creep. This paper shows how to take into account the changes in r and h, and that equations which do so, whether implicitly or explicitly, describe experimental creep strain/time curves quite well.

It is thus shown that behind the present bewildering profusion of apparently unrelated equations and physical models describing creep there is a simpler situation, in which the creep equations can be systematically derived in a physically significant manner from a single expression for recovery creep. The simplification achieved is expected to have a pedagogical and a practical value for engineers and metallurgists interested in creep.