晶体塑性模型分析微圆柱墩粗变形尺寸效应机理

摘要

为了分析单个晶粒变形行为对微成形的影响,将自由表面的晶粒看作单晶体构建晶体塑性模型.基于率相关晶体塑性理论,考虑试样尺寸、初始晶体取向及其分布,分析微圆柱体墩粗变形中尺寸效应机理.结果表明,流动应力随着试样尺寸的减小而明显减小,晶体取向的分布对试样流动应力具有显著影响,并随着塑性变形的进行而减小.由于单晶体的各向异性,在试样表层发生了明显的非均匀变形,这将导致表面粗糙度的增加,小尺寸试样则更加明显.过渡晶粒的存在使得晶粒各向异性对表面形貌的影响减小.模拟结果得到了实验验证,这表明所建立的模型适合于以尺寸依赖性、流动应力分散性和非均匀变形为特点的微成形工艺分析.%To analyze the effect of single grain deformation behaviors on microforming process,a crystal plasticity model was developed considering grains at free surface layer as single grains.Based on the rate-dependent crystal plasticity theory,the analysis of the scale effect mechanism on upsetting deformation of micro rods was 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.The distribution of the grain orientation has an evident effect on flow stress of the micro specimen,and the effect becomes smaller with the progress of plastic deformation.For the anisotropy of single grains,inhomogeneous deformation occurs at the surface layer,which leads to the increase of surface roughness,especially for small specimens.The effect of grain anisotropy on the 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 the analysis of microforming processes with characteristics,such as scale dependency,scatter of flow stress and inhomogeneous deformation.