Enhancement of a Constitutive Friction Law by Considering Plastic Smoothing of Rough Surfaces in Dependency on the Bulk Stresses

The aim of this work is the improvement of a constitutive friction law which has been identified for the specific demands of sheet-bulk metal-forming. The constitutive friction law determines the friction shear stress in dependency on the plastic smoothing of the surface roughness, which also affects the real contact area. An experimental setup is introduced to determine the change of the surface roughness, which is influenced by the tensile bulk stress in the workpiece. In order to model the experimental results, a well-established half-space model is presented and improved to consider strain hardening. The half-space model is used to determine the change of the contact area as a function of the tensile bulk stress. This interdependency is also reflected by the proposed constitutive friction law.