Effects of specimen size on flow stress of micro rod specimen

来源期刊：中国有色金属学报(英文版)2009年增刊第2期

论文作者：王春举 郭斌 单德彬 孙立宁

文章页码：511 - 515

Key words：micro-forming; size effects; free surface effects; deviation; flow stress

Abstract: 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.

基金信息：the Key Program of National Natural Science Foundation of China
the Natural Science Foundation of Heilongjiang Province, China
the Doctor Programs Foundation of Ministry of Education of China for Young Scholars