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The contact of car tires with road tracks is a research field of high practical importance since grip properties during tire-road interaction have a direct impact on safety issues. To improve the tire properties it is necessary a deep understanding of the tire-road contact mechanics, as well as the underlying rubber friction physics. Despite this topic is widely investigated, there are no complete predictive models capable to describe the friction interaction for practical applications, for this reason, it still means a big challenge for the scientific community. Therefore, the main objective of the present research is to predict the performances of different rubber materials on dry and wet rough road tracks. The effect of many intrinsic and extrinsic factors such as substrate roughness, rubber-surface affinity, temperature, load, sliding speed, lubrication, geometrical parameters and viscoelastic material properties on contact properties and the resulting friction behavior is investigated. Hence, the complex friction process is split into different subtopics, which are analyzed and modeled. From one perspective, the contact mechanics through a 2D FEM tool is investigated on different substrates to determine the main friction contribution called hysteresis. This contribution is based on the energy losses in a broad frequency scale due to cyclic deformations of the rubber by asperities. An accompanying experimental tool based on the measurement of rubber indentation into substrate asperities is designed to provide a physical understanding of static and dynamic contact problems and to validate the FEM model. The tools developed also provide access to unavailable data, such as local pressures, dissipated energies, contact area and rubber indentation. It was also figured out the effect of rubber geometry on dynamic contact mechanics through experimental and 3D FEM simulations. On the other side, the adhesion is studied as the second main friction contribution, defined a

Tire, or in its primitive form, Wheel, an important invention for the transportation sector, has evolved from a circular block of hard and durable material to one of the most complex and influential components of an automobile. It is the only means of contact between the vehicle and the road and is responsible for generating forces and moments that impact vehicle performance, stability, and control. Tire tribology is the study of interacting surfaces in relative motion which includes friction and wear. Tire friction is an essential concept for estimating the tractive effort/ traction at the tire-road interface that further helps to determine the control and stability of the vehicle. In contrary, it also results in rolling resistance and wear. Tire and vehicle engineers are henceforth interested in a robust and efficient approach towards estimation of friction and wear. Past experimental observations using tread compound samples have revealed the different factors influencing the friction at the contacting interface. In addition, different mechanisms or components resulting in frictional losses, being Hysteretic, Adhesive and Viscous, and wear being abrasive, fatigue, adhesive and corrosive were also observed. Although experimental and empirical observations have provided us with an accurate estimation of friction and wear parameters, it is very tedious and expensive approach. Recent developments in the computational power encouraged researchers and engineers towards evolution of analytical and numerical models considering the underlying physical mechanisms at the contact interface. Past research studies developed multiscale techniques for estimation of friction coefficient due to hysteretic losses from internal damping of the rubber material because of oscillation from surface undulations. Later, contact mechanics models developed using Hertzian technique or stochastic approach were considered in conjunction with frictional losses to obtain the hysteretic component

Since the early study by Grosch in 1963 it has been known that rubber friction shows generally two maxima with respect to speed - the first one attributed to adhesion, and another at higher velocities attributed to viscoelastic losses. The theory of Klüppel and Heinrich and that of Persson suggests that viscoelastic losses crucially depend on the “multiscale” aspect of roughness and in particular on truncation at fine scales. In this study, we comment a little on both theories, giving some examples using Persson’s theory on the uncertainties involved in the truncation of the roughness spectrum. It is shown how different choices of Persson’s model parameters, for example the high-frequency cutoff, equally fit experimental data on viscoelastic friction, hence it is unclear how to rigorously separate the adhesive and the viscoelastic contributions from experiments.

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., QC 20170607

Rubber friction is an important aspect to tire engineers, material developers and pavement engineers because of its importance in the estimation of forces generated at the contact, which further helps in optimizing tire and vehicle performances, and to estimate tire wear. It mainly depends on the material properties, contact mechanics and operating condition. There are two major contributions to rubber friction, due to repeated viscoelastic deformation from undulations of surface called hysteresis and due to Vander Waals interaction of the molecules called adhesion. The study focuses on analytical modeling of friction for stationary sliding of rubber block on rough surfaces. Two novel approaches are discussed and compared. Frictional shear stress is obtained from the energy dissipated at the contact interface due to the elastic deformations of rubber block at different length scales. Contact mechanics theories based on continuity approach combined with stochastic processes to estimate the real contact area, mean penetration depth and true stresses at contact depending on operating conditions. Rubber properties are highly temperature dependent. Temperature model developed based on heat diffusion relation is integrated to consider the effects of temperature rise due to frictional heating. Model results are validated with theoretical results of literature. Simulation results of friction model is obtained for Compound A sliding on rough surface. Material properties are obtained using Dynamic Mechanical Analysis and Time temperature superposition. Influence of the friction models under different conditions are discussed. Model results are validated with experimental data from Dynamic friction tester on a 120-grit surface followed by future works.

In this presentation an advanced model of sliding friction and dynamic contact of elastomers on rough, self-affine surfaces is presented, which is shown to be useful for the prediction of tire traction on dry and wet roads. It describes the frictional force via the dissipated energy, resulting from sliding stochastic excitations of the rubber by surface asperities on various length scales [1, 2]. The effect of surface roughness is considered by surface descriptors, which are derived from a fractal analysis of the surface interface. The hysteresis response of the rubber enters through viscoelastic master curves of the complex modulus up to high frequencies. Based on this concept, stationary friction curves have been estimated numerically on a broad velocity scale, in dependence of surface roughness, load and temperature. They have been compared to experimental friction data found for filled elastomers under dry and wet conditions. In particular, the investigations have shown to be useful for predicting the traction behaviour of tyres on dry and wet roads during ABS-braking of passenger cars. Furthermore, the obtained results allow for a deeper insight into the role of adhesion in dry friction of elastomers under different contact conditions and give a closer look of the physical mechanisms occurring during a friction process, In this presentation an advanced model of sliding friction and dynamic contact of elastomers on rough, self-affine surfaces is presented, which is shown to be useful for the prediction of tire traction on dry and wet roads. It describes the frictional force via the dissipated energy, resulting from sliding stochastic excitations of the rubber by surface asperities on various length scales [1, 2]. The effect of surface roughness is considered by surface descriptors, which are derived from a fractal analysis of the surface interface. The hysteresis response of the rubber enters through viscoelastic master curves of the complex modulus up to high frequencies. Based on this concept, stationary friction curves have been estimated numerically on a broad velocity scale, in dependence of surface roughness, load and temperature. They have been compared to experimental friction data found for filled elastomers under dry and wet conditions. In particular, the investigations have shown to be useful for predicting the traction behaviour of tyres on dry and wet roads during ABS-braking of passenger cars. Furthermore, the obtained results allow for a deeper insight into the role of adhesion in dry friction of elastomers under different contact conditions and give a closer look of the physical mechanisms occurring during a friction process

There is no doubt that rubber products with high abrasion resistance are strongly demanded from a sustainable or economical point of view. It is thought that abrasion loss of rubber during friction is caused by cracks generation at the rubber surface, their propagation, and elimination of rubber pieces. Therefore, investigation on generation and propagation of rubber fracture is important to clarify rubber abrasion mechanisms. In this study, X-ray imaging method at SPring-8 is applied to directly observe crack generation and propagation during friction between rubber and a needle, and origin of rubber abrasion loss will be discussed., There is no doubt that rubber products with high abrasion resistance are strongly demanded from a sustainable or economical point of view. It is thought that abrasion loss of rubber during friction is caused by cracks generation at the rubber surface, their propagation, and elimination of rubber pieces. Therefore, investigation on generation and propagation of rubber fracture is important to clarify rubber abrasion mechanisms. In this study, X-ray imaging method at SPring-8 is applied to directly observe crack generation and propagation during friction between rubber and a needle, and origin of rubber abrasion loss will be discussed.

Elastomer seals are used in a variety of industries that require flow isolation. The characterization of the behavior of these seals remains largely unexplored and hence, this study is focused on simulating and validating the axial-compressive behavior of an annular rubber seal constrained concentrically in a pipe. The elastomer material composing the seal, was experimentally characterized for its mechanical, frictional, and viscoelastic properties and modelled using models developed by Yeoh, Thirion, and Prony respectively. A 2D axisymmetric finite-element model was developed using ANSYS 16 and used alongside the material models to simulate an axial load versus displacement curve, a contact pressure distribution, and a pipe hoop strain gradient. The results for quasi-static loading and viscoelastic effects agreed within 7% and 18% of the experimental results, respectively. It was observed that pipe geometry, rubber chemistry, frictional properties, and viscoelastic effects have significant effect on the compressive behavior of the seal.

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