A phenomenological model for transient creep behaviors based on the steady state creep properties

Abstract

Traditionally, empirical equations were used to quantify the primary creep behavior in which the creep rate should not only be a function of test conditions, but also be a function of time. Even though many mathematical formulations were proposed to express the primary creep behavior, those equations are mostly descriptive but not predictive. In the present work, the authors examined the relationship between primary creep and steady state creep by measuring internal stress values with creep strain, using 99.95% pure aluminum specimens at 573 K. There are two important findings: Firstly, there exists a unique relationship among the primary creep rates, the secondary creep rates, and the ratio of the internal stresses to the applied stress. Secondly, the creep equation, including the primary stage as well as the steady state, could be rationalized with two stress terms; the applied stress and the effective stress. It is the aim of this paper to suggest a new constitutive creep rate equation, describing both the normal primary and the steady state creep behaviors, by means of using the effective stress which is changing with primary creep strain. Using this equation, the prediction of the transient creep behavior after a stress change is made,more » and compared with the experimental data.« less