A SIMPLE ENDOCHRONIC TRANSIENT CREEP MODEL OF METALS WITH APPLICATIONS TO VARIABLE-TEMPERATURE CREEP

Similar to the theory of endochronic plasticity, modified by Valanis i n 1980, a simple endochronic transient creep model of metals is propos ed by using a definition of intrinsic time zeta, measured within the c reep strain tensor space, whose metric tensor is treated as a simple p ower form of creep strain-rate Sensitive material function. The result ing constitutive equation of creep (Endocreep) contains only three mat erial 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 jum p, are then formulated. In the applications of Endocreep on 304SS unde r variable temperature creep, data of simple creep tests, provided by Ohashi er al. at 650 degrees C, Ohno et al. at 600 degrees C, Findley and Cho at 593 degrees C-649 degrees C, are employed to determine mate rial constants. The computational results in the simulation of creep t ests under step-up and step-down temperature with constant axial stres s are found in very good agreement with data provided by Findley and C ho. However, the results reveal that the model is too simple to deal w ith the recovery response of unloading. Beside this deficiency the mod el and its computational method proposed have a potential in the futur e FEM creep analysis of general thermomechanical loading history.