Construction of Material Constitutive Relationship Based on Surface-Layer Model at Micro/Mesoscopic Scale

Abstract

Micro-forming process get extensive attention in the last decades as the rapid development of micro-manufacturing technology. But the traditional metal plastic forming theory becomes no longer applicable in micro-forming process because of the so-called size effect. Many factors such as size effect, grain boundary and grain orientation should be considered to reveal the plastic deformation behaviors of metal material in micro/mesoscopic scale. In this paper, on the basis of classical Hall-Petch relationship, combining the surface layer model and composite model, a constitutive model of material in micro/mesoscopic scale was established with further consideration of grain orientation. The micro-compression experiment of pure copper specimens with different diameters and grain sizes was conducted. Based on the experiment results, the established constitutive relationship was determined and verified, and high consistence and accuracy were found. Finally, the finite element model of micro specimen was built based on the established constitutive model and Voronoi method. Then the numerical simulation of upsetting process of the pure copper was executed, which showed that the simulation results could well reflect the flow stress and deformation of the material at micro/mesoscopic scale, and further proved the availability of the proposed model.