论文部分内容阅读
To analyze the effect of single grain deformation behaviors on microforming process, a crystal plasticity model is developed considering grains at free surface layer as single grains because of their less constriction in plastic deformation from the viewpoints of a metal polycrystalline structure.Based on the rate-dependent crystal plasticity theory, the analysis of the scale effect mechanism on upsetting deformation of micro rods are performed with respect to specimen dimension, original grain orientation and its distribution.The results show that flow stress decreases significantly with the scaling down of the specimen because that the grains at free surface layer can be deformed easily.Distribution of grain orientation has an evident effect on flow stress of the micro specimen, which results in the scatter of flow stress.Then, the effect becomes smaller with the progress of plastic deformation because of the grain orientation turning.For the anisotropy of single grains, inhomogeneous deformation occurs at the surface layer, and it leads to the increase of surface roughness, especially for small specimens.The effect of grain anisotropy on surface topography can be decreased by the transition grains.The simulation results are validated by upsetting deformation experiments.This indicates that the developed model is suitable for analysis of microforming processes with characteristics, such as scale dependency, scatter of flow stress and inhomogeneous deformation.