A state-dependent method to model contact nonlinearities in rolling contacts is proposed. By pre-calculation of contact stiffness and contact filters as functions of vertical relative displacement, a computationally efficient modelling approach based on a moving point force description is developed. Simulations using the state-dependent model have been analysed by comparison with measurements. Results from the investigated case consisting of a steel ball rolling over a steel beam having two different degrees of roughness - show good agreement between nonlinear simulations and measured beam vibrations. The promising results obtained with the proposed method are potentially applicable to wheel rail interaction and rolling element bearings.

A state-dependent contact model including nonlinear contact stiffness and nonlinear contact filtering is used to calculate contact forces and rail vibrations with a time-domain wheel-track interaction model. In the proposed method, the full three-dimensional contact geometry is reduced to a point contact in order to lower the computational cost and to reduce the amount of required input roughness-data. Green's functions including the linear dynamics of the wheel and the track are coupled with a point contact model, leading to a numerically efficient model for the wheel-track interaction. Nonlinear effects due to the shape and roughness of the wheel and the rail surfaces are included in the point contact model by pre-calculation of functions for the contact stiffness and contact filters. Numerical results are compared to field measurements of rail vibrations for passenger trains running at 200 kph on a ballast track. Moreover, the influence of vehicle pre-load and different degrees of roughness excitation on the resulting wheel-track interaction is studied by means of numerical predictions.

A novel test rig design is presented which enables detailed studies of the three force components generated in the impact and release phase of rolling contact between a tyre tread block and a substrate. The design of the compact internal drum test rig provides realistic impact and release angles for the tread block-substrate contact and enables force measurements at high rolling speeds with a high signal-to-noise ratio. Measurements of the rolling contact forces are presented for different values of rolling velocity, static pre-load and acceleration. It is demonstrated that this test rig provides results which contribute to the understanding of tyre--road interaction and can be used as input to modelling-based development of both tyres and roads aiming for improved handling, safety, energy efficiency and comfort.

The longitudinal and vertical contact force history of an individual truck tyre tread block in rolling contact with an asphalt surface is experimentally investigated. Different rolling velocities up to approximately 60 km/h and different amount of slip ratios are studied with the use of a novel compact internal drum test rig, leading to results with high signal-to-noise ratio. Interestingly, the longitudinal rolling contact force component and the corresponding friction coefficient exhibit substantial variations not only between the different operating conditions, but also along the contact length of individual impacts. In addition, separate investigatory characterisations for the dynamic elastic deformation of the rubber and for the sliding friction of the rubber\textendash asphalt contact are found to be useful; they provide approximate input values for an initial, promising attempt to separate the contribution from elastic deformation and that from sliding friction. Conclusively, valuable insights are gained which has the potential to further reduce the gap between physically based modelling of friction and empirically based knowledge, which are commonly used in vehicle and tyre industry.

An experimental study of the friction coefficient is performed for a tyre tread block in rolling and sliding contact with two different asphalt substrates, a smooth aluminium and an anti-slip tape substrate. The sliding friction coefficient is for all substrates seen to increase as the sliding velocity is increasing. However, the slope for the increasing friction as a function of sliding velocity differs significantly between the substrates, presumably due to differences in the respective contribution from adhesive and hysteresis friction mechanisms. Parametric studies of the rolling friction show that the choice of substrate as well as the rolling velocity and the slip ratio has significant influence on the resulting friction coefficient. A linear relation is observed between the longitudinal rolling friction coefficient measured at low values of slip ratio and the sliding friction coefficient measured at low sliding velocities. For the tests of rolling friction at higher values of slip, stick\textendash slip conditions are observed for which the frequency content of the longitudinal force is seen to vary substantially between the different operating conditions and choice of substrate. The outcomes of this study can potentially be used to improve future tyre\textendash road contacts with respect to wear, traction and noise generation.