Evaluation of effect of relative microstructure size on roll-forming processes of polycrystalline metal using second-order homogenization method

The friction force produced during the plastic process induces a significant strain gradient on the material. This affects the history of microstructural deformation depending on the size. The miniaturization of the product increases the importance of an accurate evaluation of the effect of friction on the size-dependent plastic process. In this study, we investigated the effect of the relative size of the polycrystalline microstructure on the roll-forming process by establishing a nonlocal finite element square (FE2) model based on the second-order homogenization method with boundary condition applicable to arbitrary contact situations including friction. Using the established model, we evaluated the effect of the relative microstructure size on the roll-forming processes. FE2 simulations clarified that the distribution of the accumulated strain was characterized by friction and the relative microstructure size. An additional shear strain occurred at the surface layer of the sheet metal during the roll-forming process. A larger additional shear strain was observed in a surface layer for the sheet metal with smaller grains, whereas a high strain gradient occurred at the polycrystalline microstructure for the sheet with a larger microstructure.