Recent advances in the development of a general three-dimensional finite element methodology for modeling large deformation steady state behavior of tire structures is presented. The new developments outlined here include the extension of the material modeling capabilities to include viscoelastic materials and a generalization of the formulation of the rolling contact problem to include special nonlinear constraints. These constraints include normal contact load, applied torque, and constant pressure-volume. Several new test problems and examples of tire analysis are presented.
A bst rnct A tliermo-viscoplaatic computational method for hypersonic structures is presented. The method employs a unified viscoplastic constitutive niotlel implemented i n a finite elcment approach lor quasi-static tlicrinal-strrictiiral analysis. Applications ol the approach to conveclively cooled hypersonic structures illiistrate the eflcctiveness of the approach and provide insight into the transient inelastic structural behavior at elevated teniperatures.
A numerical study of dynamic instabilities and vibrations of mechanical systems with friction is presented. Of particular interest are friction-induced vibrations, self-excited oscillations and stick-slip motion. A typical pin-on-disk apparatus is modeled as the assembly of rigid bodies with elastic connections. An extended version of the Oden-Martins friction model is used to represent properties of the interface. The mechanical model of the frictional system is the basis for numerical analysis of dynamic instabilities caused by friction and of self-excited oscillations. Coupling between rotational and normal modes is the primary mechanism of resulting self-excited oscillations. These oscillations combine with high-frequency stick-slip motion to produce a significant reduction of the apparent kinetic coefficient of friction. As a particular study model, a pin-on-disk experimental setup has been selected. A good qualitative and quantitative correlation of numerical and experimental results is observed.
SUMMARYIn spite of significant advancements in automatic mesh generation during the past decade, the construction of quality finite element discretizations on complex three-dimensional domains is still a difficult and time demanding task.In this paper, the partition of unity framework used in the generalized finite element method (GFEM) is exploited to create a very robust and flexible method capable of using meshes that are unacceptable for the finite element method, while retaining its accuracy and computational efficiency. This is accomplished not by changing the mesh but instead by clustering groups of nodes and elements. The clusters define a modified finite element partition of unity that is constant over part of the clusters. This so-called clustered partition of unity is then enriched to the desired order using the framework of the GFEM.The proposed generalized finite element method can correctly and efficiently deal with: (i) elements with negative Jacobian; (ii) excessively fine meshes created by automatic mesh generators; (iii) meshes consisting of several sub-domains with non-matching interfaces. Under such relaxed requirements for an acceptable mesh, and for correctly defined geometries, today's automated tetrahedral mesh generators can practically guarantee successful volume meshing that can be entirely hidden from the user. A detailed technical discussion of the proposed generalized finite element method with clustering along with numerical experiments and some implementation details are presented.
The thermomechanical behavior of pneumatic tires is a highly complex transient phenomenon that, in general, requires the solution of a dynamic nonlinear coupled thermoviscoelasticity problem with heat sources resulting from internal dissipation and contact and friction. This highly complex and nonlinear system requires indepth knowledge of the geometry, material properties, friction coefficients, dissipation mechanisms, convective heat transfer coefficients, and many other aspects of tire design that are not fully understood at the present time. In this paper, a simplified approach to modeling this system that couples all of these phenomena in a straightforward manner is presented in order to predict temperature distributions in static and rolling tires. The model is based on a one-way coupling approach, wherein the solution of a mechanical rolling contact problem (with friction and viscoelastic material properties) provides heat source terms for the solution of a thermal problem. The thermal solution is based on the thermodynamics of irreversible processes and is performed on the deformed tire configuration. Several numerical examples are provided to illustrate the performance of the method.
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