Development of adhesion models taking into account surface topographies and frictional power in dry wheel-rail contact on a single-wheel roller rig

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A central field of research in rail vehicle technology deals with the forces between wheel and rail and the resulting forces, stresses and deformation of the contact partners. The stresses in the contact surface and the resulting frictional forces are described in various calculation models. The surface topography, namely the microscopic structure of the contact partners, is disregarded in the usual considerations. Nevertheless, it has already been shown in different experiments that the adhesion depends on the surface roughness. By selectively setting macro slip, i.e. high sliding velocities in the wheel-rail contact, the surface can be influenced in such a way that the adhesion coefficient increases. This observed behavior offers the possibility of improving braking and traction behavior under difficult wheel-rail contact conditions. For technological use, further research is needed in this regard to produce a valid model that can subsequently be implemented in traction and braking control systems. In the research project, a novel approach is to be applied, which is characterized by the continuous monitoring of the wheel tread roughness by means of scattered light measurement method. In this method the surface is exposed to a light beam. Then, the scattered light and the distribution of the reflection angles are recorded. The surface roughness is characterized based on the frequency distribution of the angles of reflection. In order to investigate the interaction of wheel tread roughness, contact conditions, adhesion and wheel wear, experiments are to be carried out a single-wheel roller rig under dry contact contact conditions. A large parameter set for wheel-rail contact conditions during braking tests will be established on this test rig, where sliding speed, contact forces and wheel tread roughness will be measured continuously. The data obtained will be used to create empirical models which, on the one hand, can give the coefficient of adhesion taking wheel roughness into account and, on the other hand, can predict the development of wheel roughness under different contact conditions. In the next step, the models will be validated by means of repeated brake tests. Finally, the dynamic adhesion model is to be implemented in the brake controller of the test rig in order to modify the surface roughness and the adhesion coefficient in a targeted manner. The aim is to increase the coefficient of adhesion in poor contact situations so that stopping distances can be shortened.