Grain-size dependent accommodation due to intragranular distributions of dislocation loops

• Published in: Acta materialia 2009-03, Vol.57 (5), p.1347-1356
• Main Authors: Richeton, T., Berbenni, S., Berveiller, M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Bauschinger effect; Dislocation loops; Engineering Sciences; Exact sciences and technology; Grain size; Internal stresses; Materials; Mechanics; Metals. Metallurgy; Micromechanical modelling; Physics
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2008.11.024

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