Construction of a composite model of decreasing flow stress scale effect

Based on the composite model of polycrystalline plastic deformation, a new composite model was built, with which the relation of flow stress to grain size, dimension and shape of the billet can be well explained. Through the comparison of this model with experimental data and the surface layer model, its rationality was testified. Based on this model, with the definition of scale effect factor, the decrease of flow stress in micro scale was discussed and predicted, and conclusions were drawn as below: with the downscaling of billet dimension, the decrease of flow stress is gradually increased; with the increase of grain size, the decrease of flow stress is also gradually increased; the shape of billet has a significant influence on the decreasing flow stress scale effect.