Multiscale simulation of surface roughening of a deep drawing steel due to subsurface plastic deformation

Surface roughness due to plastic deformation is important as it impacts both the surface properties of finished parts and tribological conditions during metal forming. In the present study, an approach for modeling free surface roughening due to the heterogeneous microstructure of polycrystals, where grains deform differently, is presented and validated experimentally for uniaxial tension. Roughening is modelled by finite element crystal plasticity simulations. Two methods of applying boundary conditions to the polycrystal are used. One method involves multi-scale modeling, where the continuum-scale simulation provides the submodel boundary conditions. In the second method, the elongation is applied directly by a moving periodic boundary. Material properties of DC04 steel sheet are measured by uniaxial tensile testing. Microstructure is characterized by optical microscopy and electron backscatter diffraction is used as input to generate representative simulation models. Material parameters for crystal plasticity are determined by matching simulation results to experimental stress-strain behavior. Experimental surface topography measurements by confocal microscopy after deformation are presented and compared to simulated surface topographies to assess the accuracy of the finite element model. Simulated surface roughness values of free surfaces in the model are also used as figures of merit for a convergence study of finite element parameters.