A simple endochronic transient creep model of metals with applications to variable temperature creep

Abstract

Similar to the theory of endochronic plasticity, modified by Valanis in 1980, a simple endochronic transient creep model of metals is proposed by using a definition of intrinsic time ζ, measured within the creep strain tensor space, whose metric tensor is treated as a simple power form of creep strain-rate sensitive material function. The resulting constitutive equation of creep (Endocreep) contains only three material constants whose values can be determined completely by a simple creep test. An incremental form involving isothermally constant creep stress, with or without jump, and constant stress with temperature jump, are then formulated. In the applications of Endocreep on 304SS under variable temperature creep, data of simple creep tests, provided by Ohashi et al. at 650°C, Ohno et al. at 600°C, Findley and Cho at 593°C–649°C, are employed to determine material constants. The computational results in the simulation of creep tests under step-up and step-down temperature with constant axial stress are found in very good agreement with data provided by Findley and Cho. However, the results reveal that the model is too simple to deal with the recovery response of unloading. Beside this deficiency the model and its computational method proposed have a potential in the future FEM creep analysis of general thermomechanical loading history.