Cosserat modelling of size effects in the mechanical behaviour of polycrystals and multi-phase materials

Classical homogenization techniques are not designed to predict the effect of the size of the constituents on the effective mechanical behaviour of he terogeneous materials. They usually take the volume fraction and, in some c ases, the morphology of phase distribution into account. This shortcoming i s related to the fact that, in crystals, the elastoviscoplastic behaviour o f each constituent within the aggregate may be different from that observed on the constituent alone (say the single crystal). Cosserat single: crysta l plasticity is used in this work to describe the influence of grain size o n the effective hardening behaviour of polycrystals. For that put-pose, thr ee-dimensional finite element calculations of periodic Cosserat multi-cryst alline aggregates of different grain sizes are provided. The polycrystal is regarded as a heterogeneous Cosserat medium and specific techniques for th e estimation of the effective properties are presented. The approach is the n applied to the case of two-phase single crystal materials for which the b ehaviour of one phase as a matrix turns out to be much harder than the isol ated phase. (C) 2000 Elsevier Science Ltd. All rights reserved.