Effects of specimen size on flow stress of micro rod specimen  

作　　者：WANG Chun-ju GUO Bin SHAN De-bin SUN Li-ning 王春举;郭斌;单德彬;孙立宁(School of Materials Science and Engineering,Harbin Institute of technology,Harbin 150001,China;Robot Institute of Technology,Harbin Institute of Technology,Harbin 150001,China)

机构地区：[1]School of Materials Science and Engineering,Harbin Institute of technology,Harbin 150001,China [2]Robot Institute of Technology,Harbin Institute of Technology,Harbin 150001,China

出　　处：《Transactions of Nonferrous Metals Society of China》2009年第S02期511-515,共5页中国有色金属学报（英文版）

基　　金：Project(50835002)supported by the Key Program of National Natural Science Foundation of China;Project(QC08C55)supported by the Natural Science Foundation of Heilongjiang Province,China;Project(200802131031)supported by the Doctor Programs Foundation of Ministry of Education of China for Young Scholars。

摘　　要：With the miniaturization of parts,size effects occur in the micro-forming processes.To investigate the effects of the specimen size on the flow stress,a series of upsetting deformation experiments were carried out at room temperature for specimens with different diameters.And the grain size of billets was changed by anneal processes to analyze the grain size effects on the size dependence of flow stress.The deviation of stress was observed.The results show that the flow stress decreases with decreasing billet dimensions.As the dislocation accumulation in free surface layer is slight,the reduction degree of flow stress becomes larger when the plastic deformation goes on.The flow stress is enlarged by grain size,which can be analyzed by the grain boundary length per area.The deviation increases with decreasing specimen size.This can be explained by the effects of grain orientation stochastic distribution according to the Schmid law.As a result,the micro-forming process must be considered from the viewpoint of polycrystalline structure,and the single grains of micro-billet dominate the deformation.

关 键 词：MICRO-FORMING size effects free surface effects deviation flow stress 

分 类 号：TG115.2[金属学及工艺—物理冶金]