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This paper describes research aimed at the experimental determination of the influence of rubber hysteresis on the friction coefficient between rubber samples for making soles and granite tiles. In the experiments, four types of shoe rubber with similar hardness and different hysteresis properties and two granite tiles with different roughnesses (smooth and anti-slip) were used. The determination of rubber hysteresis was carried out experimentally on a uniaxial testing machine. The friction coefficient was measured using a device specially developed for this type of test, which was based on the pulling force method, while the measurement conditions were based on the EN 13893:2011 standard. The friction coefficient was measured at two different speeds, 50 mm/s and 300 mm/s, with different surface conditions. Using regression analysis and the Taguchi method, the data obtained from the experiments were analyzed to determine the influence of parameters on the friction coefficient. The experimental research shows that different rubber mixtures with the same or similar hardness could have different hysteresis properties but also different friction properties. [ABSTRACT FROM AUTHOR]

To explore the research status on mechanism of the skid-resistance for asphalt pavement, the related achievements of the rubber friction, the tire–road contact, and the influence factors were reviewed. The rubber friction was reviewed from the mechanism and rubber friction model. The tire-road contact was studied from the modeling methods, the evaluation methods, and the skid-resistance mechanisms at different conditions. The influence factors of skid-resistance were summarized from different designing processes. This review showed that the appropriate contact or evaluation model should be selected according to the required parameters. Although the finite element method is widely used, the accuracy of the model, the boundary conditions, and the load cases need to be further improved. The optimized aggregates and asphalt binders, reasonable gradation, reasonable geometric design, and strict construction quality control are necessary for good initial skid-resistance. Pavement texture as an important factor affecting skid-resistance should be considered in pavement gradation design, especially for wearing layer technology. [ABSTRACT FROM AUTHOR]

This study proposes a mechanical tire model with deduced friction coefficient based on multiscale friction theory. In the proposed model, the contact shape and contact pressure distribution are calculated based on the elliptical contact tire model. In the calculation of longitudinal stress in the adhesion region, not only the longitudinal deformation in length direction owing to the slip ratio, but also the nonlinear deformation in width direction owing to the tread radius are considered. The coefficient of friction in the sliding region is deduced from the viscoelasticity of tread rubber by multiscale friction theory, with contributions from adhesion and hysteresis friction. The validity of theoretical calculation of coefficient of friction was verified by linear friction tests of a rubber piece conducted under two conditions: a dry road surface and a wet road surface with a water film mixed with detergent. It was confirmed that, with appropriate parameter settings, the longitudinal stress distribution in the tire contact plane calculated by the proposed method can reproduce the experimental results by inner drum tire tester better than the classical brush model. The proposed method can be applied to rubber compound design to achieve the desired braking and driving characteristics of tires because it analytically links the longitudinal forces of tire to the viscoelasticity of tread rubber.

This paper describes research aimed at the experimental determination of the influence of rubber hysteresis on the friction coefficient between rubber samples for making soles and granite tiles. In the experiments, four types of shoe rubber with similar hardness and different hysteresis properties and two granite tiles with different roughnesses (smooth and anti-slip) were used. The determination of rubber hysteresis was carried out experimentally on a uniaxial testing machine. The friction coefficient was measured using a device specially developed for this type of test, which was based on the pulling force method, while the measurement conditions were based on the EN 13893:2011 standard. The friction coefficient was measured at two different speeds, 50 mm/s and 300 mm/s, with different surface conditions. Using regression analysis and the Taguchi method, the data obtained from the experiments were analyzed to determine the influence of parameters on the friction coefficient. The experimental research shows that different rubber mixtures with the same or similar hardness could have different hysteresis properties but also different friction properties.

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]

Abstract To explore the research status on mechanism of the skid-resistance for asphalt pavement, the related achievements of the rubber friction, the tire–road contact, and the influence factors were reviewed. The rubber friction was reviewed from the mechanism and rubber friction model. The tire-road contact was studied from the modeling methods, the evaluation methods, and the skid-resistance mechanisms at different conditions. The influence factors of skid-resistance were summarized from different designing processes. This review showed that the appropriate contact or evaluation model should be selected according to the required parameters. Although the finite element method is widely used, the accuracy of the model, the boundary conditions, and the load cases need to be further improved. The optimized aggregates and asphalt binders, reasonable gradation, reasonable geometric design, and strict construction quality control are necessary for good initial skid-resistance. Pavement texture as an important factor affecting skid-resistance should be considered in pavement gradation design, especially for wearing layer technology.

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]

Abstract 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).

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]

The viscous dissipation between rigid, randomly rough indenters and linearly elastic counter bodies sliding past them is investigated using Green’s function molecular dynamics. The study encompasses a variety of models differing in the height spectra properties of the rigid indenter, in the viscoelasticity of the elastomer, and in their interaction. All systems reveal the expected damping linear in sliding velocity v at small v and a pronounced maximum at intermediate v. Persson’s theory of rubber friction, which is adopted to the studied model systems, reflects all observed trends. However, close quantitative agreement is only found up to intermediate sliding velocities. Relative errors in the friction force become significant once the contact area is substantially reduced by sliding.

Abstract While suction cups prevail as common gripping tools for a wide range of real‐world parts and surfaces, they often fail to seal the contact interface when engaging with irregular shapes and textured surfaces. In this work, the authors propose a suction‐based soft robotic gripper where suction is created inside a self‐sealing, highly conformable and thin flat elastic membrane contacting a given part surface. Such soft gripper can self‐adapt the size of its effective suction area with respect to the applied load. The elastomeric membrane covering edge of the soft gripper can develop an air‐tight self‐sealing with parts even smaller than the gripper diameter. Such gripper shows 4 times higher adhesion than the one without the membrane on various textured surfaces. The two major advantages, underactuated self‐adaptability and enhanced suction performance, allow the membrane‐based suction mechanism to grip various three‐dimensional (3D) geometries and delicate parts, such as egg, lime, apple, and even hydrogels without noticeable damage, which can have not been gripped with the previous adhesive microstructures‐based and active suction‐based soft grippers. The structural and material simplicity of the proposed soft gripper design can have a broad use in diverse fields, such as digital manufacturing, robotic manipulation, transfer printing, and medical gripping.

While suction cups prevail as common gripping tools for a wide range of real‐world parts and surfaces, they often fail to seal the contact interface when engaging with irregular shapes and textured surfaces. In this work, the authors propose a suction‐based soft robotic gripper where suction is created inside a self‐sealing, highly conformable and thin flat elastic membrane contacting a given part surface. Such soft gripper can self‐adapt the size of its effective suction area with respect to the applied load. The elastomeric membrane covering edge of the soft gripper can develop an air‐tight self‐sealing with parts even smaller than the gripper diameter. Such gripper shows 4 times higher adhesion than the one without the membrane on various textured surfaces. The two major advantages, underactuated self‐adaptability and enhanced suction performance, allow the membrane‐based suction mechanism to grip various three‐dimensional (3D) geometries and delicate parts, such as egg, lime, apple, and even hydrogels without noticeable damage, which can have not been gripped with the previous adhesive microstructures‐based and active suction‐based soft grippers. The structural and material simplicity of the proposed soft gripper design can have a broad use in diverse fields, such as digital manufacturing, robotic manipulation, transfer printing, and medical gripping. [ABSTRACT FROM AUTHOR]

The present study is meant to obtain tribological insight into the interface of a rolling rubber wheel on a counter-surface disk based on the work of the previous study Salehi et al. (Tribol Lett 68(1):37, 2020), in which a new test method was developed to rapidly predict tire grip in a laboratory environment. A Laboratory Abrasion Tester (LAT100) was used and exploited as a tribometer. This opened a new cost- and time-effective horizon for tire material development in a laboratory environment rather than having to test tread compounds by building full-scale tires. The method was validated by a comprehensive study for six different tire tread compositions, by correlating the laboratory data for solid rubber wheels as LAT100 specimens with real tire results in two test modalities: lateral (α) and longitudinal (κ) sweep tests on a dry road. It was demonstrated that the LAT100 can be exploited to simulate the α -sweep tire tests, but not the κ -sweep. The dynamics and physics of a rolling rubber wheel on a counter-surface disk of the LAT100 test step-up are investigated utilizing the renowned physical "brush model" in comparison to full-scale tire tests. The type of test modality leads to different friction mechanisms in the contact patch even at similar test conditions. This is substantiated by recognizing the two regions: stationary and non-stationary, in the contact area which results in different friction components and mechanisms. The behavior of the rolling wheel in lateral and longitudinal movements at the same test conditions is comparable if the contributions of the mentioned regions in the contact area are similar. [ABSTRACT FROM AUTHOR]

• Low-friction/low-hysteresis rubber liners reduce the motion resistance of rollers. • Rubber-track systems with oscillating bogie wheels exhibit small internal losses. • The more road wheels, the better the efficiency of a rubber-track system. • Uniform distribution of the vehicle weight to the wheels improves the efficiency. In spite of an increasing number of rubber-tracked crawlers, the literature provides few guidelines and calculation models suitable for minimizing their internal motion resistance. This article presents a model where the internal resistance of double-flanged road wheels for rubber-tracked vehicles is calculated as a sum of the losses resulting from the indentation of the wheels into the track surface and friction of the wheels against the track guide lugs. The model allows for vertical and lateral load of the wheels, the non-uniform distribution of the wheel pressure on the track, and the relationship between the friction coefficient and normal reaction force in the interface between the wheel and track guide lugs. The model has been verified by experiments. According to the results of model computations and experiments discussed in the article, the internal losses of a given rubber-tracked undercarriage might be reduced if: the road wheels are covered with a material that exhibits low friction coefficient and mechanical hysteresis, the vehicle suspension system features oscillating bogie wheels, the undercarriage is fitted with the largest possible number of road wheels, and the vehicle weight is evenly distributed to all of the road wheels. [ABSTRACT FROM AUTHOR]

• A finite element sliding contact model between the rubber spreading roller and the cold-proof cloth was developed and verified. • The lateral offset behavior of the cold-proof cloth was investigated in dynamic conditions. • A prediction model of the lateral offset was established to optimize the spreading roller. • The optimized spreading roller effectively reduced wrinkles in the winding test of the cold-proof cloth. The groove pattern of the rubber spreading roller affected its spreading performance on the wrinkled cold-proof cloth. For analysing the spreading performance in dynamic conditions, a finite element sliding contact model between the rubber spreading roller and the cold-proof cloth was developed for studying the lateral offset with different contact pressures, slip velocities, and groove patterns of the spreading roller, which constituted a prediction model for the lateral offset. A new test device of the lateral offset was developed to compare the predictive and experimental results to verify the accuracy of the finite element model. The results showed that increasing the contact pressure was beneficial to increasing the lateral offset. The slip velocity had a significant effect on the lateral offset and the positive slip velocity promoted the lateral offset better than the negative slip velocity. The effect of groove pattern parameters on the lateral offset was independent of the slip velocity. Only the diameter, groove number, and pitch affected the lateral offset significantly. With the groove pattern parameters optimised by the prediction model, the relative error between the predictive and experimental results of the lateral offset was 8.62%, indicating the accuracy and reliability of the prediction model. Moreover, the optimised spreading roller could effectively weaken the wrinkles in the rolling experiment of the cold-proof cloth. The prediction of the lateral offset model based on the finite element analysis would be useful for the reliable design of the rubber spreading roller. [ABSTRACT FROM AUTHOR]

The paper studies the effect of adhesion and surface relief of laminated plywood on rubber friction. Samples of birch plywood are studied, the surfaces of which have different texture and roughness and are made on the basis of two different resins: phenol formaldehyde and melamine. The study of the static and dynamic friction coefficient is carried out on a tribometer according to the ring-disk contact scheme at room temperature of 23°C in the range of normal pressures from 0.1 to 0.5 MPa in dry and lubricated friction mode. The study of the adhesion properties of the coatings was carried out on an atomic force microscope with a 900 nm ball at the tip. The refined contact interaction model of the spherical tip with the plywood surface made it possible to estimate the surface energies of the coatings. The findings show that when using plywood in dry contact only, it is necessary, first of all, to increase the adhesion properties of its surface, for example by introducing filler-adhesives or using a polymer resin with increased adhesive properties as the base of the laminated coating. If it is assumed that liquids or contaminants enter the plywood surface during operation, then the best effect is the application of a two-level texture: deep dents to remove water from the contact area and surface roughness to increase adhesive properties. It should be noted that the roughness on some types of laminated films can change rapidly due to wear, therefore the use of films with increased adhesive properties is an advantage for increasing the adhesive properties of the surface of laminated plywood. [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.

In this paper, a novel portable sliding friction and wear test rig is introduced. Unlike other laboratory-based test setups, this setup can be used for both indoor and outdoor experiments. There is also no limitation on the size and type of the substrate surface that can be used for the friction and wear test in contrast to typical test rigs, which have some limitations for the size and type of substrate surface. A small six-wheel ground robot is developed to drag the sample on an arbitrary surface for a desired distance and velocity. A ground robot is an unmanned ground vehicle, capable of driving on the ground without humans on board. The speed of this robot can be measured and controlled precisely. The nominal normal load is adjusted using dead weights placed on the sample holder and the friction force is measured using a load cell. An adjustable sample holder was also designed and built to hold different-size specimens. The results of styrene–butadiene rubber block sliding on an asphalt track are presented to validate the test setup and illustrate the potential of the system for friction and wear testing. In addition, the effect of sliding velocity on the friction and wear is studied, and the correlation between the wear rate and the friction coefficient is investigated. These experimental results can be used to estimate the friction and life span of a tire tread compound on the real asphalt road. Finally, the formation of abrasion pattern observed on the rubber surface sliding on an asphalt track is discussed, which provides an insight into the understanding of dominant wear mechanism of tire tread compound on typical asphalt surfaces. [ABSTRACT FROM AUTHOR]

The evaluation of tire grip on the road is costly and consumes high energy and time, but is essential for safety. Prediction of tire grip on a laboratory scale is therefore always of interest and of utmost importance for research and material developments. It mostly suffers from lack of comparison with actual tire data. To involve all influencing factors on tire grip in a laboratory scale measurement is very complex. Therefore, it has always remained challenging to obtain a strong correlation between laboratory results and road data. In the present study, a new test method is developed for a Laboratory Abrasion Tester, LAT100, which enables to exploit the device as a tribometer. The objective was to develop a technique on a laboratory device to mimic the common test modalities for evaluating tire grip on the road with a trailer tester: lateral (α) and longitudinal (κ) sweep tests. The new method is validated by correlating the laboratory data with the two test modalities of real tire grip on a dry road using a trailer tester for six different tire tread compositions. For the LAT100 tests, solid rubber wheels are characterized at three different normal loads. The effects are comparable with actual tire data. The outcome of the new test method is in good agreement with actual tire trailer α-sweep tests. [ABSTRACT FROM AUTHOR]

We study a simple model of a conveyor belt. We calculate the relation between the torque M and the belt–pulley slip s. We present numerical results for the M(s) relation, and for the frictional energy dissipation as a function of the slip, which is important for the rubber wear. The theory includes both the belt compliance and the pulley tread block stiffness. The theory shows that to minimize the friction and the related rubber wear, the pulley–belt system should be operated not at the slip where the torque is maximal, but at a lower slip. Thus, the belt–pulley system should be slightly "oversized" for the best performance. [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.

This article presents results on studying effect of multi-walled carbon nanotubes (CNTs) on the tribological properties of frost-resistant rubber based on epichlorohydrin rubber. The sliding friction coefficient has been determined using a laboratory tribometer according to the "rubber ring-smooth steel disk" contact scheme. Rubber samples have been tested under conditions of dry friction for ranges of normal pressures of 0.1 ... 0.4 MPa, sliding velocities of 1 ... 100 mm/s for two values of the bulk temperature: 23 and −25° C. The wear rate of the samples has been determined at a temperature of 23° C, pressure of 0.4 MPa, and sliding speed of 10 mm/s. As a counterbody in experiments on the wear resistance assessment, sandpaper made of silicon carbide with a grain size of 120 and 250 microns has been used. It has been found that using CNTs as a filler for studied rubbers leads to an increase in their wear resistance. There is a multiple decrease in the wear rate when filling rubber with a small amount of CNTs (1–2 pts. wt. per 100 pts. wt. of rubber). Moreover, an improvement in physical and mechanical characteristics while maintaining high frost resistance is established. The addition of CNTs to the studied rubbers does not affect the static coefficient of friction. [ABSTRACT FROM AUTHOR]

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]

Tribological behavior of Styrene-Butadiene Rubber (SBR) compound reinforced by silica and carbon-black fillers on two different asphalt-like surfaces is studied using theoretical and experimental approaches. Linear sliding friction and wear tests were performed on two different roofing asphalt papers. The surface roughness power spectra of asphalts and the master curves of the large-strain viscoelastic modulus of SBR compound were used to model the contact area and friction coefficient theoretically. The theoretical results are in good agreement with experiment providing the tribochemical degradation is not the dominant wear mechanism. When the formation of a tribo-modified layer prevails the mechanical abrasion, the wear rate, in terms of mass loss, does not necessarily increase with the increase of frictional work as expected theoretically. • Tribological behavior of Styrene-Butadiene Rubber on asphalt papers is studied. • Theoretical approaches are used to calculate the contact area and rubber friction. • Rubber friction and wear rate are obtained experimentally and compared with theory. • A tribo-modified layer is formed on the rubber surface at high sliding velocities. • The tribo-modified layer significantly affects the tribological behavior of rubber. [ABSTRACT FROM AUTHOR]

The coefficient of friction due to bulk viscoelastic losses corresponding to multiscale roughness can be computed with Persson's theory. In the search for a more complete understanding of the parametric dependence of the friction coefficient, we show asymptotic results at low or large speed for a generalized Maxwell viscoelastic material, or for a material showing power law storage and loss factors at low frequencies. The ascending branch of friction coefficient at low speeds highly depends on the rms slope of the surface roughness (and hence on the large wave vector cutoff), and on the ratio of imaginary and absolute value of the modulus at the corresponding frequency, as noticed earlier by Popov. However, the precise multiplicative coefficient in this simplified equation depends in general on the form of the viscoelastic modulus. Vice versa, the descending (unstable) branch at high speed mainly on the amplitude of roughness, and this has apparently not been noticed before. Hence, for very broad spectrum of roughness, friction would remain high for quite few decades in sliding velocity. Unfortunately, friction coefficient does not depend on viscoelastic losses only, and moreover there are great uncertainties in the choice of the large wave vector cutoff, which affect friction coefficient by orders of magnitudes, so at present these theories do not have much predictive capability. [ABSTRACT FROM AUTHOR]

Abstract Evaluating tire grip on the road, an extremely complicated tribological system, is enormously energy and time consuming but essential for safety. To predict grip on the road, tires with four different tread compounds were tested on ABS braking distance on a dry test track. Corresponding solid rubber wheels were characterized on the Laboratory Abrasion Tester (LAT100) on four different electro-corundum discs of various grain sizes. With increasing speed the side force coefficient (SFC) decreases. A lower disc grain size induces a higher SFC. A correlation coefficient of 0.93 between the LAT100 data and road results for the four tread compounds has a high potential for predicting the car tire ABS braking distance. Graphical abstract Image 1 Highlights • Friction properties of 4 tread compounds were evaluated with a Laboratory Abrasion Tester (LAT100). • With proper parameter selection the dry friction curve of treads on the road could be mimicked. • The speed effect of the LAT100-rubber wheels were quantified. • The grain size of the LAT100 discs as counter-surface was optimized to predict ABS braking. • The results of the LAT100 correlate with the tire data with a correlation coefficient of 0.93. [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.

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]

Machine elements and mechanical components have often surfaces with anisotropic roughness, which may result from the machining processes, e.g. grinding, or from wear. Hence, it is important to understand how surface roughness anisotropy affects the contact mechanics properties, such as friction and the interface separation, which is important for lubricated contacts. Here we extend a multiscale mean-field model to the lubricated contact between a soft (e.g. rubber) elastic solid and a rigid countersurface. We consider surfaces with anisotropic surface roughness, and discuss how the fluid flow factors and friction factors depend on the roughness power spectral density, as well as on the location of roughness on the interacting solids. Finally, we present an experimental study of the lubricated sliding contact between a nitrile butadiene rubber O-ring and steel surfaces with different kinds of isotropic and anisotropic surface roughness. The good quantitative comparison between the experimental results and the theory predictions suggests that the multiscale lubrication mechanisms are accurately captured by the theory. [ABSTRACT FROM AUTHOR]

An experimental methodology for constructing a 3D friction map, which depends on normal pressure, sliding velocity, and temperature, for tire tread rubber has been presented. The methodology of constructing a 3D friction map is based on the principle of temperature-velocity superposition, which makes it possible to combine the obtained experimental data into one sculpted surface. Two types of the tread rubbers were investigated that are used in summer passenger tires and heavy-loaded all-metal tires. The results of analyzing the obtained 3D friction maps have been presented. The influence of normal pressure and sliding velocity to the amount and position of the values of coefficient of friction of the rubber sliding over the sandpaper surface with the specified abrasive grit has been considered. [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]

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.

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.

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 huge number of technological and biological systems involve the lubricated contact between rough surfaces of soft solids in relative accelerated motion. Examples include dynamical rubber seals and the human joints. In this study, we consider an elastic cylinder with random surface roughness in accelerated sliding motion on a rigid, perfectly flat (no roughness) substrate in a fluid. We calculate the surface deformations, interface separation and the contributions to the friction force and the normal force from the area of real contact and from the fluid. The driving velocity profile as a function of time is assumed to be either a sine function, or a linear multi-ramp function. We show how the squeeze-in and squeeze-out processes, occurring in accelerated sliding, quantitatively affect the Stribeck curve with respect to the steady sliding. Finally, the theory results are compared to experimental data. [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]

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. [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]

Rubber is a very flexible material with many desirable properties Which enable its broad use in engineering practice. Rubber or rubber-metal springs are widely used as anti-vibration or anti-shock components in technical systems. Rubber-metal springs are usually realized as a bonded assembly, however especially in shock absorbers, it is possible to realize free contacts between rubber and metal parts. In previous research it authors was observed that friction between rubber and metal in such case have a significant influence on the damping characteristics of shock absorber. This paper analyzes the development process of rubber or rubber-metal shock absorbers realized free contacts between the constitutive parts, starting from the design, construction, testing and operation, with special emphasis on the development of rubber-metal springs for the buffing and draw gear of railway vehicles.

One of the most important factors that affect tire friction is surface roughness, which determines the size of the real contact area, real pressure distribution on the contact interface, and scales of mechanical engagement between viscoelastic rubber and a rough substrate. The need to predict coefficient of friction (COF) for rubber on rough surfaces for applications such as traction of tires on the road surfaces led to some physical models such as Heinrich-Kluppel’s model. The current study examines the applicability of the Heinrich-Kluppel model, using different viscoelastic representations, in numerical simulations of COF for rubber, and its agreement with the experimental results. For this purpose, roughness characteristics of the surfaces and viscoelastic properties of rubber were measured by fractal analysis and dynamic-mechanical-thermal analysis (DMTA), respectively. These data were employed in the numerical code to simulate COF for a rubber sample. The model was also modified by replacing the Zener viscoelastic representation in the original model with the generalized Maxwell viscoelastic representation. On the other hand, COF for rubber was measured on the same rough surface (different sand-papers) by an in-house friction tester, and results were compared with the numerical results. It was shown that computer simulation could predict the load and speed dependence of rubber friction very well. The application of the generalized Maxwell model improved agreement between the numerical and experimental results for high sliding speeds where the Zener viscoelastic model failed to predict the right trend in variation of COF with speed. This speed range was matched with the sliding velocities in the footprint of tire under rolling conditions.

The friction of filled rubber on a rough surface is mainly determined by the rubber viscoelasticity and the surface property of multiple-scale asperities that can be represented by the power spectral density of the surface profile (i.e., power spectrum of surface roughness). This paper investigates a prediction model of rubber friction on dry and wet surfaces with large roughness under lightly squeezing, and finds a high stationary friction coefficient that depends on sliding speed. To this end, we demonstrated friction testing at low velocities with carbon-black-filled rubber and a hard substrate having self-affine surface roughness. From the experiment results, we estimated the hysteresis friction coefficient related to energy dissipation resulting from cyclic deformations of the viscoelastic rubber by applying the theory developed by Persson [(J. Chem. Phys. 115, 3840 (2001)]. We discussed the additional factor, an adhesion force, which also increases the friction coefficient. We concluded that the hysteresis loss of rubber viscoelastic deformation contributes most of the friction force, accounting for the nonlinear viscoelastic behavior of filled rubber, and that the operative surface wavelength extends to the order of micrometers.

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]

Fluid leakage out of mechanical equipment such as gearboxes, hydraulic systems, or fuel tanks could cause serious problems and thus should be avoided. Seals are extremely useful devices for preventing such fluid leakages. We have developed a theoretical approach for calculation of the leak rate of stationary rubber seals and the friction force for dynamic seals. The theory is based on a recently developed theory of contact mechanics, which we briefly review. To test the theory, we have performed both simple model experiments and experiments on engineering seal systems. We have found good agreement between the calculated and measured results, and hence our theory has the potential to improve the future design of efficient seals. We briefly review the processes that determine rubber friction on lubricated smooth and rough substrate surfaces. We present experimental friction results for lubricated surfaces, obtained using a simple Leonardo da Vinci setup. The data is analyzed using the Persson rubber friction and contact mechanics theory. [ABSTRACT FROM AUTHOR]

We discuss the influence of geometrical and rheological non-linearities on the prediction of rubber friction and true contact area for rough sliding interactions. In particular, we compare the results of a linearly-viscoelastic linear-contact model, formulated in the Fourier space, with those obtained from non-linear finite element calculations. A sinusoidal rigid profile indenting a rubber block is here considered for simplicity, whereas the effects of non-linearity are evaluated by varying the aspect ratio, loading conditions and sliding speed of the contact interface. It is found that accurate friction predictions can be obtained through the linear viscoelastic model, provided that the roughness under investigation features moderate values of root mean square slopes, whereas non-linear finite element computations should be adopted for large root mean square slopes. [ABSTRACT FROM AUTHOR]

We present the numerical results for the viscoelastic and adhesive contribution to rubber friction for a tread rubber sliding on a hard solid with a randomly rough surface. In particular, the effect of the high- and low-frequency roughness power spectrum cut-off is investigated. The numerical results are then compared to the predictions of an analytical theory of rubber friction. We show that the friction coefficient for large load is given exactly by the theory while some difference between theory and simulations occur for small loads, due to a finite sample-size effects, whereas the contact area is almost unaffected by the low frequency cut-off. Finally, the role of a finite rubber thickness on viscoelastic friction and contact area is introduced and critically discussed. Interestingly, we show that classical rough contact mechanics scaling rules do not apply for this case. [ABSTRACT FROM AUTHOR]