Numerical investigation of size effect on material behaviour in micro upsetting process

Abstract

In recent years, the micro-forming technology has been becoming the hotspot of micro-manufacturing researches. However, the theory of metal forming in macro-scale cannot be used to guide the micro-forming process directly due to the size effect. In this study, a region model considering the grain shape, orientation and boundary was proposed based on Hall-Petch equation. The constitutive relationships of materials in grain region and grain-boundary region were deduced by introducing the scale parameters. To verify the proposed model, relative experiments have been designed and performed. Moreover, the finite element model of the most common micro-forming like micro upsetting was established integrating the region model. The effects of grain distribution, specimen size and grain size on material behaviour were well studied based on the simulation results. The researches in this paper will be developed to provide guidance for more complex micro-forming processes in future.