The tangential forces in the wheel-rail-contact determine vehicle guidance as well as vehicle dynamics. The forces originate at the contact of rough surfaces at the microscopical scale. At millimeter scale, the normal pressure distribution in combination with wheel rail kinematics determine the shear stress distribution. To model adhesion on a physical base, a multiscale model with a microscopic and macroscopic level at the millimeter scale was developed.
The microscopic contact of rough surfaces is modeled in detail using a dynamic simulation. The microcontact model describes the nonlinear contact stiffness as well as the pressure dependent gap between rough surfaces. At millimeter-scale, the rolling contact model uses force-displacement relations from the microcontact model to map stick-slip effects in the contact zone elastomechanically. The model also describes the contact temperature distribution and its feedback on the level of friction. Using the Navier-Stokes-Equations, the flow of a liquid through the contact is modeled. The liquid builds up pressure, which supports a part of the normal load and thus reduces adhesion in the contact.