The correct representation of tyres is one of the central challenges in full vehicle simulation. Due to the large computation time spans, MBS computations rely on tyre models with reduced structural mechanics, fulfilling the requirements of computational effort and accuracy if the model parameters are chosen correctly. However, the parameterization requires extensive and costly rig testing. A further drawback is that these parameters can not be transferred to different tyres, even ones with only slight changes. Moreover, tyre test rigs for commercial vehicles are hardly or not at all available.

Fraunhofer ITWM uses commercially available MBS tyre models like MF-Tyre, RmodK, CD-Tire or F-Tire. In addition, FEM tyre models are intensely studied and utilized. FEM models describe the tyre directly as a continuum-mechanical structure consisting of nonlinear materials for the different rubber compositions. The reinforcing layers of steel or cord for belt and carcass are embedded into the continuum elements. Such detailed description yields a large number of dofs, which prohibits the direct use of FEM tyres in full vehicle simulations.

Fraunhofer ITWM applies FEM tyre models in different areas:

Direct computation of short events

This aspect includes applications such as cleat tests which can be seen as either exceptional or misuse events, depending on the intensity of the impact. Such simulations play a leading role for the assessment of damage when using low-section tyres.
For misuse simulation, the plastic deformation of the rim is of crucial importance. The rim is modeled as a flexible body equipped with material models describing plasticity. Fraunhofer ITWM runs these simulations on high performance computing clusters with techniques of parallelization.

Parameterization of MBS tyre models using FEM computations

Detailed FEM tyre models are used to virtually undergo expensive and difficult rig testing. With these computations one determines static quantities like stiffness in lateral, longitudinal or vertical direction as well as results from handling and cleat tests. Using these results, MBS tyre model parameters are derived from a validated FEM model. One advantage is the transferability of FEM parameters allowing to derive models of similar tyres with varying geometry from one FEM model. Again, virtual rig testing is carried out to extract MBS model parameters for the modified tyres.

Model reduction

The department MDF is investigating methods of model reduction to diminish the computational effort of detailed continuum models. This can be accomplished by structural reduction as well as nonlinear mathematical model reduction (POD). Reduced models shall describe the complex nonlinear behavior of an FE-tyre but possess few degrees of freedom so that they can be included directly into MBS computations.