Multiscale Friction Modeling for Sheet Metal Forming

The most often used friction model for sheet metal forming simulations is the relative simple Coulomb friction model. This paper presents a more advanced friction model for large scale forming simulations based on the surface change on the micro-scale. The surface texture of a material changes when two surfaces are in contact under a normal load. This is caused by flattening due to combined normal loading and stretching. The consequence of this is that shear stresses between the contacting surfaces, developed by adhesion and ploughing effects between contacting asperities, will change when the surface texture changes. A numerical procedure has been developed which accounts for the change of the surface texture on the micro-scale and its influence on the friction behavior on the macro-scale. The numerical procedure is implemented in a finite element code and applied to a full scale sheet metal forming simulation.