On size effects in torsion of multi- and polycrystalline specimens

Simulations of torsion of copper single, multi- and polycrystals are presen ted. The stress is laid on an accurate description of intragranular behavio ur, which requires the use of parallel computing. If the wire contains up t o 1000 grains, the deformation is shown to localize within some weak sectio ns of the specimen. A lower bound of a critical grain number for a multi- t o polycrystal plasticity transition is therefore established.