Scaling relationship in the log ?-log ? creep and stress-relaxation curves and the plastic equation of state

Abstract

The log σ-log\( \in \) curves, obtained either during creep or stress-relaxation experiments, for different strain levels or initial stresses, frequently show a scaling behaviour. It will be discussed if the scaling relationship is a sufficient condition to ensure the existence of a state variable, dependent on σ and\( \in \). The results will be applied to some constitutive equations used to describe the plastic behaviour of metals and to creep and stressrelaxation data in Zircaloy-4. Finally, it is concluded that the constitutive equations considered define a state variable in a certain range of σ and\( \in \), limited by the values of the constants characteristic of the material.