Consideration of grain-size effect and kinetics in the plastic deformationof metal polycrystals

This work extends the constitutive model For the prediction of grain-size d ependent hardening in f.c.c, polycrystalline metals proposed by Acharya and Beaudoin [1] (Grain-size effect in fee viscoplastic polycrystals at modera te strains, 1999, in press) to include effects of temperature and strain ra te dependence. A comparison is made between model predictions and compressi on data, taken at varying temperature and strain rate, for pure Ag having t wo different grain sizes. It is shown that an initial increase in yield str ess and concomitant decrease in hardening rate for a fine-grained material, relative to a coarse-grained counterpart, can be captured through initiali zation of a state variable serving to describe stress response at prescribe d reference conditions of temperature and strain rate. A grain-size depende nce of hardening rate during parabolic (stage III) hardening is characteriz ed by the evolution of net dislocation density in a finite element model of a polycrystal aggregate. Finally, observations from simulations of de form ation of the polycrystal aggregate are introduced into an existing macrosco pic constitutive model for metal plasticity based on the mechanical thresho ld. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.