Abstract: Based on the mechanism of micro-bulk-forming and the traditional surface layer model, the object is divided into the inner polycrystalline region, the inner region of the grains in the surface layer and the region affected by the grain boundary in the surface layer. Depending on Hall-Petch formula and introducing scale parameters, the constitutive equation of the region affected by the grain boundary is established through regressing the experiment data of the copper micro-upsetting. The micro-forming process is simulated after regionalization and discretization of the object. The simulation results reflect the characteristics of micro-forming and are consistent with the experiment result, which certify the reliability of the constitutive equation and the simulation model.

Key words: Constitutive equation, Grain boundary, Hall-Petch formulae, Micro-bulk-forming, Numerical simulation, Surface layer model