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The friction performance of tread rubber is related to the safety of the vehicle during driving, especially in terms of shifting speeds, cornering, and changing environmental factors. The experimental design used in this paper employed a self-developed automatic multi-working-condition friction tester to investigate the correlation between the friction coefficient of three tread formulations and various factors, including speed, pressure, temperature, side deflection angle, and lateral camber. This experimental study demonstrates that the coefficient of friction decreases with increasing load and increases with increasing sliding velocities due to changes in adhesion friction. Due to the increasing and decreasing changes in rubber adhesion and hysteresis friction caused by temperature, the coefficient of friction shows a tendency to increase and then decrease with the increase in temperature; thus, temperature has an important effect on the coefficient of friction. Based on the basic theory of friction and experimental research, the Dorsch friction model was modified in terms of temperature, and the analytical relationship between the rubber friction coefficient and the combined variables of contact pressure, slip velocity, and temperature was established, which is more in line with the actual situation of rubber friction. The model predictions were compared with the experimental results, and the error accuracy was controlled within 5%. This verifies the accuracy of the model and provides a theoretical basis for the study of rubber friction. [ABSTRACT FROM AUTHOR]

The British pendulum tester (BPT) provides a method to measure the skid resistance of pavement, which possesses both theoretical and practical engineering significance. This article aims to establish a numerical hysteresis friction model for BPT to reproduce the dynamic motion of the slider and estimate the pavement friction based on surface texture roughness, rubber viscoelasticity property and contact characteristics. The analytical hysteresis friction model was introduced based on one of the modern rubber friction theories. As an input parameter of this model, the average penetration depth of rubber was calculated based on the interfacial separation assumption. A numerical model was established by combining the geometric and motion characteristics of BPT. To validate the model, the self-affine characteristics of texture from four types of asphalt pavement were analysed; simultaneously, the storage and the loss modulus of rubber slider at various frequencies were obtained using the Zener constitutive model. As a result, the velocity of the slider decreases gradually with the dynamic fluctuation of the friction coefficient. A significant linear correlation was found between the predicted values and the measured data. This numerical friction model performs some potential for friction estimation. However, more conditions need considering for the improvement and practicability of the model. [ABSTRACT FROM AUTHOR]

Soft-hard matter friction is a long-standing tribology problem that remains unclarified, requiring engineers to empirically predict the wear life. To clarify this issue, this study examines the transient running-in regime of rubber friction on a hard rough substrate and models the temporal wear progression using the spectrum curves of surface roughness for both materials. Performing a series of friction tests and three-dimensional surface-height measurements, the time-dependent behaviours of the power spectral densities (PSDs) are divided into two phases, namely the initial non-steady and long-term steady phases. The detailed spectral analyses of worn rubber surfaces in the initial phase lead to a blended PSD function between self-affine and K-correlation surface models, consisting of one variable (the Hurst exponent) that is saturated by the substrate self-affinity. Supported by the Greenwood--Williamson theory concerning rough contact mechanics, the volumetric estimate with the blended PSD function is used to assess the volume rate of wear debris in the steady phase, which is validated experimentally. These findings not only improve the wear predictions of soft materials from the initial measurements of worn surfaces but also help clarify the constrained multiscale mechanism of wear. [ABSTRACT FROM AUTHOR]

We study the friction when a rectangular tire tread rubber block is sliding on an ice surface at different temperatures ranging from −38 to −2 °C, and sliding speeds ranging from 3 µm/s to 1 cm/s. At low temperatures and low sliding speeds we propose that an important contribution to the friction force is due to slip between the ice surface and ice fragments attached to the rubber surface. At temperatures above −10 °C or for high enough sliding speeds, a thin premelted water film occurs on the ice surface and the contribution to the friction from shearing the area of real contact is small. In this case the dominant contribution to the friction force comes from viscoelastic deformations of the rubber by the ice asperities. We comment on the role of waxing on the friction between skis and snow (ice particles). [ABSTRACT FROM AUTHOR]

• A novel mixed visco-hyperelastic hydrodynamic lubrication model for water-lubricated rubber bearings is proposed. • The proposed model considers the multi-scale characteristics of rough surfaces, enabling a more comprehensive depiction of the contact behavior of rubber surfaces. • The proposed model can accurately analyze the mixed lubrication performance of water-lubricated rubber bearings by considering nonlinear deformation. This paper presents a novel mixed visco-hyperelastic hydrodynamic lubrication model (MVHHLM) for water-lubricated rubber bearings (WLRBs). The model is based on a fractional order differential visco-hyperelastic model and integrates Persson's multi-scale contact theory and rubber friction theory, enabling accurate analysis of the mixed lubrication performance of WLRBs with a low equilibrium modulus. In this work, the validity of the hydrodynamic pressure prediction for WLRBs is supported by published experimental results. Additionally, the experimental and theoretical comparisons validate that the multi-scale rubber friction theory based on viscoelastic dissipation effectively predicts the friction coefficient of WLRBs, thereby confirming the effectiveness of the proposed model. Compared to the classical Greenwood and Tripp (GT) contact model, the present model considers the multi-scale characteristics of rough surfaces, which enables a more accurate description of the contact properties of randomly rough surfaces. The simulation results also demonstrate the necessity of replace traditional linear viscoelastic models with visco-hyperelastic models for rubber-like bearings. Furthermore, the influence of various parameters on the mixed lubrication performance of WLRB was further investigated. The findings demonstrate that the mixed lubrication performance of WLRBs can be improved by increasing the radius clearance and equilibrium modulus, reducing the characteristic scale and rubber thickness. Additionally, the influence of rotational speed on the mixed lubrication performance of WLRBs becomes more pronounced as the average relaxation time increases. [Display omitted] [ABSTRACT FROM AUTHOR]

Modeling the real contact area plays a key role in every tribological process, such as friction, adhesion, and wear. Contact between two solids does not necessarily occur everywhere within the apparent contact area. Considering the multiscale nature of roughness, Persson proposed a theory of contact mechanics for a soft and smooth solid in contact with a rigid rough surface. In this theory, he assumed that the vertical displacement on the soft surface could be approximated by the height profile of the substrate surface. Although this assumption gives an accurate pressure distribution at the interface for complete contact, when no gap exists between two surfaces, it results in an overestimation of elastic energy stored in the material for partial contact, which typically occurs in many practical applications. This issue was later addressed by Persson by including a correction factor obtained from the comparison of the theoretical results with molecular dynamics simulation. This paper proposes a different approach to correct the overestimation of vertical displacement in Persson's contact theory for rough surfaces with self-affine fractal properties. The results are compared with the correction factor proposed by Persson. The main advantage of the proposed method is that it uses physical parameters such as the surface roughness characteristics, material properties, sliding velocity, and normal load to correct the model. This method is also implemented in the theory of rubber friction. The results of the corrected friction model are compared with experiments. The results confirm that the modified model predicts the friction coefficient as a function of sliding velocity more accurately than the original model. [ABSTRACT FROM AUTHOR]

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Here, the authors propose an energy method to obtain the friction coefficient of a rubber block sliding on self-affine substrates via simulation. Due to the multi-scale property, the rough surfaces are modelled with four harmonic rigid frictionless roads. As the rubber block is a viscoelastic solid, energy dissipation in the contact area results in friction. The authors propose a new simulation method to obtain friction coefficient through energy dissipation. With different loads and sliding velocities, the change law of friction coefficient is calculated. The authors design a test instrument to verify the friction coefficients of rubber on some certain surface. The findings of this research constitute a theoretical basis for safe tire design and tire grip improvements.

Here, the authors propose an energy method to obtain the friction coefficient of a rubber block sliding on self-affine substrates via simulation. Due to the multi-scale property, the rough surfaces are modelled with four harmonic rigid frictionless roads. As the rubber block is a viscoelastic solid, energy dissipation in the contact area results in friction. The authors propose a new simulation method to obtain friction coefficient through energy dissipation. With different loads and sliding velocities, the change law of friction coefficient is calculated. The authors design a test instrument to verify the friction coefficients of rubber on some certain surface. The findings of this research constitute a theoretical basis for safe tire design and tire grip improvements. [ABSTRACT FROM AUTHOR]

Rubber friction characteristics, which specify the sliding friction coefficient as a function of sliding speed, contact pressure etc., are required for tire models and have a substantial influence on their results. Classically, friction characteristics are determined based on sliding body measurements. In this paper, a new method is presented, which can be used to determine friction data for wet track conditions based on Grosch-wheel (solid rubber wheel) measurements. The aim is to represent more realistic contact conditions due to the rolling contact of such a wheel. When modeling tire characteristics, we show, that compared to friction characteristics obtained from sliding body measurements better results can be achieved by using the characteristics of the method mentioned in this paper. [ABSTRACT FROM AUTHOR]

To provide a potential method for predicting friction coefficients with pavement texture parameters, the Hilbert-Huang Transformation was used to extract relevant parameters from the pavement profile. Eight parameters of the Optimal Intrinsic Mode Function (OIMF) were calculated based on the Hilbert-Huang Transformation. A correlation analysis was conducted between these parameters and friction, taking into account the influence of velocity. Furthermore, a multiple linear regression model was developed to explore friction prediction. The results revealed that the parameter representing the peak density divided by sharpness in the OIMF exhibited the strongest correlation with friction (R2 =0.78), with this correlation being influenced by velocity. The multiple regression model may provide a reliable method for friction prediction (R2 =0.77), and the predicted friction coefficients demonstrated no significant deviation from the measured values (p-value < 0.0001). • Proposed a high- R2 texture profile parameter with friction using HHT method. • Investigated effects of velocity on R2 between texture parameters and friction. • A multiple regression model based on HHT is developed for friction prediction. [ABSTRACT FROM AUTHOR]

We discuss on the rough contact mechanics in presence of a graded viscoelastic solid. In particular, we derive the effective surface admittance of a stepwise or continuously-graded half-space, which is then embedded in a Fourier-based residuals molecular dynamics formulation of the contact mechanics. The viscoelastic multilayer theory, which is of general applicability, is then applied to discuss on the role of small-scale wavelengths on polymer friction and contact area. We demonstrate that the rough contact mechanics exhibits effective interface properties which converge to asymptotes upon increase of the small-scale roughness content, when a more realistic rheology of the confinement is taken into account. [ABSTRACT FROM AUTHOR]

A multiscale finite element framework for the calculation of sliding rubber samples on rough surfaces is proposed. The two essential physical contributions hysteresis and adhesion are modelled. Hysteresis originating from the viscoelastic nature of rubber materials is included directly by incorporating the rough surface in the calculation with microscopic details and without transformations or a reconstruction of the surface. The adhesive interaction is introduced by a macroscopic shear stress law coupled to the hysteresis simulation by the evaluation of the relative contact area. The assumed mechanisms and the framework are explained in detail and are used to validate the method for experimental results of different materials for low sliding speeds. [ABSTRACT FROM AUTHOR]

Rubber friction depends on the surface roughness of the counter surface, e.g. a road surface. We have measured the friction for two rubber compounds sliding on randomly rough surfaces produced by 3D-printing. The surfaces had different macro-roughness and the friction experiments were performed over six decades in speeds, from 10 −6 m s −1 to 1 m s −1 , on both dry and lubricated substrates. The viscoelastic modulus master curves of the rubber compounds, and their large-strain effective modulus were obtained from dynamic mechanical analysis (DMA). The measured friction coefficients were compared to the calculations of rubber friction using Persson's contact mechanics theory. The role of the macro-level roughness is discussed. [ABSTRACT FROM AUTHOR]

Predicting tyre–road friction requires various inputs that are known with differing levels of confidence. This paper studies the prediction and associated experimental confirmation of rubber friction on real roads at high sliding speeds. Friction predictions are obtained from Persson's flash temperature model: the topography of the road surface is measured using an optical profilometer, while the rubber's viscoelastic modulus is obtained through Dynamic Mechanical Analysis. A newly developed friction tester performs in-situ friction measurements, while controlling and monitoring bulk and contact surface temperature, respectively. Local topographical road roughness variations were identified as a major contributing factor leading to predicted friction variations of over 50%, while the flash temperature predictions showed good correlation with temperature measurements from near the rubber–road interface. • Rubber friction testing with flash temperature measurement under real conditions. • Persson's flash temperature model without adhesion showed agreement with experiment. • Rubber background temperature is less important in practical situations. • Partial validation of flash temperature predictions. [ABSTRACT FROM AUTHOR]

In order to investigate hysteresis friction separately from other friction contributions (mainly adhesive friction), linear friction tests are performed with cut out tread specimens from passenger car tires on 3D-printed sinusoidal surfaces under dry and wet conditions. In this work, a multiscale approach based on the finite element method (FEM) is used to reproduce the hysteresis friction features obtained in the laboratory. On each scale, finite element simulations at block level are evaluated at different contact pressure, sliding velocity and temperature conditions, which are homogenized with respect to time, to build up a friction characterization for the next coarser scale. The height difference correlation function is applied to consider microscopic asperities, which originate from the printing process. Using the Williams - Landel - Ferry equation, the thermal influence on the viscoelastic rubber material is taken into account. By comparing the output of the friction tests against the results of the multiscale simulations, an analysis of contact temperature as well as friction contribution of each length scale is enabled. • Friction tests on 3D-printed surfaces at dry and different wet conditions. • Numerical friction approach to compute scale-dependent hysteresis friction. • Numerical validation of multiscale friction model. • Numerical studies of micro- and macroscale hysteresis friction. • Comparison of experimental and simulated friction results. [ABSTRACT FROM AUTHOR]

In this study, the work of Mofidi et al., 2008 [6] is cited and the focus is put on the finding that the friction reported for lubricated apparently smooth surfaces (sealing applications) may be dominated by micro- or surface roughness generated hysteresis. Contrary to the very high coefficients of friction measured, Mofidi et al. did not analyze their test results and test configuration in depth and did not compare their results to experimental observations taken from the literature. In this study, the author makes an attempt to meet these needs and reanalyze/reinterpret the results of Mofidi et al. [ABSTRACT FROM AUTHOR]

The most important contribution to rubber friction on rough surfaces is the so-called hysteresis. The excitation of the viscoelastic material is induced by the surface asperities. Hysteresis friction originates from the internal energy dissipation. Since the roughness occurs over a wide range of length scales, in this work a multiscale FEM approach is developed to solve the problem with acceptable computational costs. A split of the surface in macroscopic and microscopic parts is carried out via a decomposition of the power spectral density. The coupling between the scales is performed by passing of homogenized, velocity- and pressure-dependent coefficients of friction. The values are gained from frictionless calculations on the micro scale. The proposed multiscale FEM approach is analyzed and proven on an artificial sinusoidal surface. Finally, the approach is applied to a measured rough surface profile showing good agreement with experimental data for different rubber materials. [ABSTRACT FROM AUTHOR]

In most of the tribological contacts, the composition and tribological properties of the original interface will change during use. The tribo-films, with modified properties compared to the bulk, are dynamic structures that play a significant role in friction. The existence of a tribo-modified surface layer and its importance on the overall friction of elastomers has been shown both theoretically and experimentally before. The characteristics of the modified surface layer deserve specific attention since the tribological properties of elastomers in contact with a rough counter-surface are determined by these modified surfaces together with the properties of bulk of the material. Both the formation of the modified layer and the break down (wear) of it are of importance in determining the existence and thickness of the tribo-modified layer. In this study, the importance of the wear is emphasized by comparing two styrene butadiene rubber-based elastomers in contact with a granite sphere. A current status of perception of the removal and the stability of the modified surface layers on rubbers is introduced as well as experimental work related to this matter and discussion within literature. Pin-on-disk friction tests are performed on two SBR-based samples in contact with a granite sphere under controlled environmental conditions to form the modified surface layer. Although the hysteresis part of the friction force which has a minor contribution in the overall friction is not markedly different, the total measured friction coefficient differs significantly. Mechanical changes both inside and outside the wear track are determined by atomic force microscope nano-indentations at different timescales to examine the modified surface layer on the test samples. The specific wear rates of the two tribo-systems are compared, and the existence of the modified surface layer, the different measured friction coefficient and the running-in distances toward steady-state friction are explained considering different wear rates. A conceptual model is presented, correlating the energy input into the tribo-system and the existence of a modified surface layer. [ABSTRACT FROM AUTHOR]

We present a comprehensive investigation of the adhesive rubber-solid contact problem by analytical and numerical methods. Theories of rubber friction are reviewed and a new contact theory is developed. The adhesive contact problem is solved using the boundary element method. The introduction of adhesion leads to full coverage below a certain length scale. Friction coefficients are calculated from the spectral density of the rubber surface by splitting the numerical problem into two length scales. Adhesion is shown to increase friction at low velocities. The influence of filler is modeled by assuming that their size corresponds to a linear cross-over dimension separating the bulk elastomer from the composite. Finally, we discuss open problems and describe a simplified picture of rubber friction. • Adhesion increases low-velocity friction by increasing low-wavelength deformation amplitude. • Rubber has to be viewed as composite material at length scales relevant for friction. • Rubber's contour generally has a higher Hurst exponent than the substrate. • (Adhesion-induced) elastic instabilities probably determine friction at lowest velocities. [ABSTRACT FROM AUTHOR]

This article presents the development of a method for manufacturing durable countersurfaces for testing the friction of rubber samples in a laboratory. The surface sample was designed to replicate the surface roughness characteristics of a predefined road surface. Four different types of samples were manufactured: two bitumen bound stone mastic asphalt samples, one concrete bound sample, and one epoxy bound sample. In addition, the surfaces were sandblasted to remove binder from the top of the surface. The similarity in surface roughness between the predefined target road surface and the laboratory surface samples was evaluated using optical 3D surface roughness measurements and surface roughness power spectrums. The durability of the surfaces was investigated by repeated dry rubber sliding friction tests. It was found that out of the studied surface samples the best one to both replicate the surface characteristics of the target surface and to produce a durable surface in terms of wear was the one using epoxy resin as a binder. By replacing bitumen with epoxy, more friction tests could be run without significant changes in the surface topography or rubber friction. In addition a reasonable correlation between the surface roughness power spectrums and the friction results was found, which supports the use of roughness power spectrums as a roughness metric for road surfaces in the context of rubber friction. [ABSTRACT FROM AUTHOR]

Abstract: Stick–slip behaviour is a common but not entirely understood tribological phenomenon. The sliding motion of a rubber sample was studied on a glass plate. The local sliding velocity field of the contact area was calculated by means of Digital Image Correlation and compared to the measured friction force. It was observed that the sliding of individual sipes nucleates from the side edge, whereas the sliding of a tread block propagates from the leading edge. Phase shifts between tread block detachments were observed. Furthermore, a velocity field for a precursor is presented which indicates only the local sliding of the contact without the triggering of a global detachment. The relevance of the result for rougher surfaces is discussed. [Copyright &y& Elsevier]

Highlights: [•] Computational homogenization is applied to rubber friction on a rough surface. [•] A highly accurate isogeometric computational framework is developed. [•] An accurate choice of the representative volume element is performed. [•] The variation of the friction coefficient with pressure and velocity is predicted. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a finite element based methodology for obtaining pressure dependent friction laws from experimental tribometer tests on rubber–metal contacts. Tribometer tests are simulated for analyzing the area of contact and obtaining an approximation to the contact pressure distribution in the test. The proposed methodology will be applied to the evaluation of experimental results from tribometer tests run in flat on flat and flat on cylinder configurations, for which flat and cylindrical countermaterials have been produced with very similar surface morphologies and, therefore, theoretically the same pressure-dependent friction law. [Copyright &y& Elsevier]

Abstract: We study the role of rubber friction in tire traction with special emphasis on the load and velocity dependence of the friction coefficient. In the first part, we present some basic concepts of contact mechanics of slipping tires and analyze the influence of energy dissipation due to tread deformation on the friction force. Then, we apply a recently developed model of hysteresis and adhesion friction of rubber on self-affine road surfaces for estimating the load dependence of the kinetic friction coefficient in the contact area of slipping tires. In this context the impact of track morphology (sharp or blunt) on the kinetic friction characteristics is demonstrated. Finally, using the brush model for slipping tires we discuss consequences of the load dependence of the kinetic friction coefficient with respect to the overall tire friction and slip characteristics. We show that due to the presence of a load dependence of the local rubber-road friction coefficient the tread contact patch is globally never entirely in a fully sliding situation. The presented results yield a contribution to an improved physical understanding of the dynamic frictional contact of tires with road tracks during cornering and braking, especially in the case of cars equipped with Anti-Blocking Systems (ABSs). [Copyright &y& Elsevier]

In this paper a numerical model for the analysis of coupled thermo-mechanical frictional contact problems of rubber blocks on rough surfaces is presented. The formulations for the interface shear stresses and the heat fluxes are motivated by a theoretical examination of the process of rubber friction. In general, these quantities depend explicitly on contact pressure, the sliding velocity, and the surface temperature. Several parameters in the model allow for consideration of the influence of different rubber compounds, rubber block geometries and road surfaces. The experimental setup used for the identification of these parameters and the validation of the contact model are briefly explained. The obtained results demonstrate the experimentally observed sensitivity of the system to changes in contact pressure, sliding velocity, and rubber compound. The numerical model was implemented in the commercial finite element code ABAQUS. The simulation of a sliding rectangular rubber tread block demonstrates how the contact model performs. The comparison of numerical and experimental results shows good agreement. [ABSTRACT FROM AUTHOR]

Rubber friction has received much attention because of its practical importance for modelling, for example, tyre-road friction. Many experiments were carried out and a number of theories were proposed to investigate and explain its behaviour and dependency on external conditions such as temperature and velocity. However, only a few published articles describe the observed dynamic friction behaviour using compact analytical models. Models for dry friction, such as the Dahl and LuGre models and their several variations, have been proposed to describe rubber friction. Unfortunately, they cannot reproduce many important and specific phenomena observed in experiments focused on rubber friction. In this paper, we propose a simple analytical friction model suitable to simulate the dynamic friction behaviour of rubber-like materials on rigid surface. Phenomena such as pre-sliding, sticking/sliding transitions, relaxation of the friction force at standstill and stick-slip effects can be accurately modelled. We validated the model with several experiments, obtaining a good agreement between simulation and measurements. In addition, we propose a two-dimensions (2D) extension of the model, to broaden the field of cases, in which it can be used. The capability of the model to simulate 2D anisotropic friction behaviour was validated with measurements of a vehicle tyre. • Compact analytical model for dynamic friction behaviour. • Model captures pre-sliding, sticking/sliding transition, relaxation, stick-slip. • Extension to 2D for friction behaviour with combined motion on the surface. • Excellent predictive qualities and agreement with experiments. • Significant improvement over established models such as Coulomb, Dahl and LuGre. [ABSTRACT FROM AUTHOR]

Rubber-like materials are widely used in mechanical systems. Schallamach waves appear in friction process due to their small elastic modulus and relatively large surface adhesion energy, which may cause some negative influences, such as additional vibration and singular wear. In-depth researches into the characteristics and mechanism of Schallamach waves are of great significance to development and application of rubber-like materials. Therefore, the nucleation and propagation law of Schallamach waves are investigated by using in-situ experiments and 3D finite element simulation method. Results indicate that small wrinkles appear firstly at the edges of contact regions. Here, the small wrinkles propagate towards the centers of the contact regions in a spiral manner, which is analyzed by using elastic theory. The first Schallamch wave forms on the sides of the contact region, while the subsequent waves nucleate at the front of the contact region. Then, In-situ experiments are carried out to study the influences of materials ratios and sliding velocity on the behaviors of Schallamach waves. Based on the finite element model, analysis results reveal the law of propagation speed, wave length and wave amplitude of Schallamach waves, and the relationship between contact area and force (frictional and vertical force). There is basically no sliding exiting in the contact interface during friction process, and in some extent the Schallamach waves play a lubricating role. • A three-dimensional finite element model is built to simulate both the nucleation and progression of Schallamach waves for the first time. • The evolution process of small wrinkles on the edge of the contact area is analyzed in detail. • The first Schallamach wave is different from that of steady-state slip, the former is formed on both sides of the contact area, and the latter is formed in front of the contact area. • The wavelength, amplitude and velocity of Schallamach wave are analyzed by in situ experiment and 3D simulation. • The corresponding relationships among friction force, vertical force, contact area and surface deformation are obtained by 3D FEA. [ABSTRACT FROM AUTHOR]

The future evolution of autonomous mobility and road transportation will require substantial improvements in tyre adherence optimization. As new technologies being deployed in tyre manufacturing reduce total vehicle energy consumption, the contribution of tyre friction for safety and performance enhancement continues to increase. For this reason, the tyre's grip is starting to drive the focus of many tyre developments nowadays. This is because the tread compound attitude to maximize the interaction forces with the ground is the result of a mix of effects, involving polymer viscoelastic characteristics, road roughness profiles and the conditions under which each tyre works during its lifespan. In such a context, mainly concerning the automotive market, the testing, analysis and objectivation of the friction arising at the tread interface is performed by means of specific test benches called friction testers. This paper reviews the state of the art in such devices' development and use, with a global overview of the measurement methodologies and with a classification based on the working and specimen motion principle. Most tyre friction testers allow one to manage the relative sliding speed and the contact pressure between the specimen and the counter-surface, while just some of them are able to let the user vary the testing temperature. Few devices can really take into account the road real roughness, carrying out outdoor measurements, useful because they involve actual contact phenomena, but very complex to control outside the laboratory environment. [ABSTRACT FROM AUTHOR]

A mathematical model developed previously for predicting adhesive sliding friction of rubber on a hard surface in the presence of Schallamach waves is extended here to include global effects of viscoelasticity, besides the previously included viscoelastic effects in the neighborhood of the debond (shear crack) tips; the crack tip model is unchanged. We find that global viscoelasticity limits the maximum sliding speed and minimum wavelength for which a wave train can exist and, as expected, increases the friction force. The model is shown to improve upon the agreement with experimental data on wave speed and wavelength in the previous paper. • This paper extends a previously developed model to include global viscoelastic effects. • It is shown there is a critical sliding speed above which Schallamach waves cannot exist because of global viscoelasticity. • There is also a lower limit on wave length. • The model and available experimental data are in very good agreement. [ABSTRACT FROM AUTHOR]

The authors propose a new philosophy and theory for rubber friction and wear that are significantly different from the existing classical theories. Several distinctive features of rubber friction such as the exceedingly high friction coefficient and the intense stick-slip motion during frictional sliding all result from the sticky surface behavior exhibited by a cross-linked rubber, where there is a meniscus force brought about at the interface between the rubber and the rigid surface. The total friction coefficient μ all incorporates three factors including an adhesion term μ adh , a deformation term μ def and a crack formation term μ crac. This generates an equation μ all = μ adh + μ def + μ crac ≒ K 1 ηv [ 1 + K 2 ( tanδ 2 ) + 2 K ε c) E - 7 / 6 W 1 / 6 ] where η is the viscosity of the uncross-linked phase, E the modulus of the cross-linked rubber, v sliding velocity, c crack length, W normal load, K 1 , K 2 , K ε are all coefficients whose characteristics also govern rubber wear. The adhesion term is the most dominant factor during rubber friction, which roughly contributes about 70–80% of the total friction coefficient according to a very rough estimation. The close relationships between the observed stick-slip motion, abrasion pattern formation and wear have been verified experimentally. The abrasion pattern is initiated by the high frequency vibration and the steady abrasion pattern together with steady wear is promoted by the stick-slip motion. Steady wear rate V ˙ could be estimated theoretically as a function of the steady abrasion pattern distance D ab using an equation V ˙ = k'D ab 3, which indicates that many of the characteristics observed in rubber wear are also fundamentally governed by the intense stick-slip motion induced by the sticky rubber surface. This figure shows schematically the meniscus formation by the uncross-linked phase and the Van der Waals contact by the cross-linked phase in the interface between the cross-linked rubber and solid, where the meniscus force generates the most significant adhesion friction coefficient for rubber friction together with high surface stickiness and violent stick-slip motion. Image 1 • A new theory of rubber friction, one that differs significantly from the existing classical theories, is proposed. • The adhesive component dominates the friction coefficient of rubber, comprising almost 70–80% of its magnitude. • The close relationship between stick-slip motion, abrasion pattern formation, and wear were validated by both experiments and theory. [ABSTRACT FROM AUTHOR]

A mathematical model is developed for predicting adhesive sliding friction of rubber on a hard surface in the presence of propagating detachments or buckles known as Schallamach waves. The rubber is assumed to be elastic apart from a small zone at the leading edge of each detachment where viscoelasticity is significant. We assume the rubber is in a state of plane strain, and both contact surfaces are flat. Linear elasticity is used, together with the Fast Fourier Transform, for the wave analysis. Nonlinear elasticity is used with the finite element method to illustrate the detachment initiation. The model is shown to agree quite well with experimental data from three sources, despite the use of hemispherical sliders. • An analyical model is developed for predicting rubber friction due to adhesion. • The model and available experimental data are in reasonable agreement. • Criteria for existence of Schallamach waves are established. • A finite element model shows how these waves develop. • An experimental program is proposed for a more complete comparison with theory. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We study the adhesion and friction for three tire tread rubber compounds. The adhesion study is for a smooth silica glass ball in contact with smooth sheets of the rubber in dry condition and in water. The friction studies are for rubber sliding on smooth glass, concrete, and asphalt road surfaces. We have performed the Leonardo da Vinci-type friction experiments and experiments using a linear friction tester. On the asphalt road, we also performed vehicle breaking distance measurements. The linear and non-linear viscoelastic properties of the rubber compounds were measured in shear and tension modes using two different Dynamic Mechanical Analysis (DMA) instruments. The surface topography of all surfaces was determined using stylus measurements and scanned-in silicon rubber replicas. The experimental data were analyzed using the Persson contact mechanics and rubber friction theory. [ABSTRACT FROM AUTHOR]