A Virtual Test Platform for Analyses of Rolling Tyres on Rigid and Deformable Terrains

Dynamic performance characteristics of wheeled vehicles highly rely on the forces/moments arising from interactions between the pneumatic tyres and the terrains. Reliable models are thus needed to estimate these forces/moments to be used in vehicle simulations for design and developments. The empirical and semi-empirical tyre models developed for vehicle dynamics simulations invariably require extensive experimental data, and may not be applicable under many practical conditions. The structural tyre models, on the other hand, are not suited for vehicle dynamics simulations due to excessive computational demands. Moreover, the tyre modeling on deformable terrains has been addressed in relatively fewer studies due to challenges associated with complex behaviors of soils under moving vehicular loads. Although the Finite Element (FE) tyre models provide accurate estimations of forces/moments on rigid surfaces, the mesh-based nature of FE models of the soils yield poor performance in modeling the soil flow beneath a rolling tyre. Alternatively, mesh-less methods such as the Smoothed Particle Hydrodynamics (SPH) have been proposed to account for large deformations and fragmentations of the soil. This dissertation research aims at development of a virtual testing environment for analyses of rolling tyre interactions on rigid and soft terrains using the FE and SPH analysis methods. The virtual platform is used for parametrization and evaluation of the terramechanics-based models as an alternative to actual experiments. A 3-D finite element model of a rolling truck tyre is developed using LS-DYNA to predict its dynamic responses at speeds up to 100 km/h. The model takes into account the complex multi-layered structures of the tyre carcass and belts. A customized pre-processing algorithm is developed to facilitate model reformulations for efficient parametric analyses. The validity of the model is demonstrated by comparing the predicted responses with the experimental data. The verified tyre model is subsequently employed to study the influences of various operating parameters on the tyre vertical and cornering properties. The modal properties of the rolling tyre are also analyzed under varying inflation pressure and vertical load, using the large-deformation finite element theory. The eigenvalues are extracted during an explicit dynamic simulation at instants when the tyre stresses reach steady state under a given loading condition. It is shown that some of the eigen-frequencies of a free tyre diverge into two distinct frequencies in the presence of ground contact of the rolling tyre. A computationally efficient model of the truck tyre is further formulated using the Part-Composite approach in LS-DYNA, where the layers of the rubber matrix and reinforcements are simplified by a single layer of shell elements with layered configuration. The validity of the simplified model is demonstrated through comparisons with the comprehensive tyre model as well as with the experimental data. It is shown that the proposed simplification substantially reduces the total number of elements and thereby enhances the computational efficiency. A computational soil model is developed using the FE and SPH methods in conjunction with a contact pressure-dependent material model based on the available test data. The soil model is initially validated in terms of volumetric deformation behavior using the experimental data. The relative merits and limitations of the FE and SPH analysis methods are illustrated to justify the use of the SPH soil model for parametrization of the terramechanics formulations characterizing the normal and shear behavior of soil. The effectiveness of parameters identification method is demonstrated via comparisons with reported data obtained from classical bevameter and triaxial force measurement devices. The soil model is subsequently integrated to the simplified pneumatic tyre and rigid wheel models for analyses of tyre forces developed while traversing different deformable terrains. The simulation results obtained for the rolling and steered tyre showed good agreements with the analytically estimated contact force/moment responses.