A grain-size dependent accommodation law for polycrystals was deduced from an inclusion/matrix problem (i.e., each grain was viewed as being embedded in an homogeneous equivalent medium) where plastic strain inside the inclusion was given as a discrete distribution of circular coaxial glide dislocation loops. The loops were assumed to be constrained at spherical grain boundaries. From thermodynamic considerations specific to a process of identical plastification in all the loops (considered to be super-dislocations), an average back-stress over the grain was derived. In order to compute the very early stages of plastic deformation in a face-centred cubic polycrystal, this back-stress was incorporated into a diluted model in terms of concentration of plastic grains. Contrary to conventional mean-field approaches, a grain-size effect was obtained for the initial overall strain-hardening behaviour. This size effect results from an intrinsic contribution of intragranular slip heterogeneities on the kinematical hardening.

Grain-Size Dependent Accommodation due to Intragranular Distributions of Dislocation Loops. T.Richeton, S.Berbenni, M.Berveiller: Acta Materialia, 2009, 57[5], 1347-56