Abstract:Nanocrystalline (NC) materials can be treated as composite materials consisting of grain and grain boundary two phases. In this paper, the incremental stress-strain relation is derived from the view point of energy balance. Finally, the stress-strain relation of different grain sizes is obtained, and also applied in pure copper under uniaxial tension. Also the effects of grain shape and statistical distribution of grain sizes on the stress-strain relation are discussed, and the results predicted by the present model are compared with experimental data.