Goodyear Medalist Lecture. Rubber Friction and its Relation to Tire Traction

2007 ◽  
Vol 80 (3) ◽  
pp. 379-411 ◽  
Author(s):  
K. A. Grosch
Keyword(s):  
Friction Coefficient ◽  
Master Curve ◽  
Normal Load ◽  
Single Point ◽  
Limited Range ◽  
Constant Load ◽  
Slip Angle ◽  
Rubber Friction ◽  
Track Surface ◽  
Laboratory Tool

Abstract Rubber friction differs from that of hard solid materials in that it is not linearly related to the normal load and it depends strongly on sliding speed and temperature. There exists an interrelation between these two variables on their effect on the friction coefficient, first observed for the viscosity of liquids and generally described by the universal WLF transformation equation. The friction coefficient at a constant load is then described by a so-called master curve. Such master curves have been obtained on different types of surface and for gum rubbers as well as filled rubbers on wet and dry surfaces and it is shown that they may also be obtained on ice. The shape of the curve and position on the log(aTv) axis depends on the polymer and the track surface structure indicating that two distinct processes determine the friction: adhesion friction akin to a molecular relaxation process and a deformation process in which energy is lost due to the cyclic deformation of the rubber by the surface asperity. To obtain such a master curve it is necessary to keep the experimental speeds so low that the temperature rise in the contact area can be neglected. In practical tire tests, sliding speeds are high and hence the temperature rises with speed. Since the WLF equation is a negative function of temperature, the range of log(aTv) is limited. If thermocouples are used as sliders on rubber, it is shown that the experimental curves as function of speed can be transformed into a part of a master curve. For compound development friction tests, a limited range of track temperatures and speeds are sufficient to ensure a high correlation with road test data. A single point laboratory measurement may correlate with road tests if carefully chosen. More usually, it leads to misleading conclusions. Side force measurements at a reasonably large slip angle also reflect the friction coefficient and are a useful laboratory tool to evaluate the traction properties of tread compounds.

A Laboratory Method to Comprehensively Evaluate Abrasion, Traction and Rolling Resistance of Tire Tread Compounds

2007 ◽  
Vol 80 (4) ◽  
pp. 580-607 ◽  
Author(s):  
M. Heinz ◽  
K. A. Grosch
Keyword(s):  
Friction Coefficient ◽  
Laboratory Test ◽  
Rolling Resistance ◽  
Limited Range ◽  
Slip Angle ◽  
Testing Conditions ◽  
Side Force ◽  
The Road ◽  
Wide Range ◽  
On The Road

Abstract A laboratory test method has been developed which allows the evaluation of diverse properties of tire tread compounds on the same sample. The laboratory test instrument consists of a rotating abrasive disk against which a rubber sample wheel runs under a given load, slip angle and speed. All three force components acting on the wheel during the tests are recorded. By changing the variable values over a wide range practically all severities encountered in tire wear are covered. The well-known fact that compound ratings depend on the road testing conditions is verified. Most compounds are only significantly distinguishable against a control over a limited range of testing conditions. Using a road test simulation computer program based on the laboratory data shows that not only ratings correspond to practical experience but also calculated absolute tire life times do. Tests on surfaces of different coarseness and sharpness indicate that sharp coarse surfaces give the best results with road tests, which of necessity are mostly carried out on public roads of differing constitution. The abrasive surface can be wetted with water at different temperatures and hence either the friction force at a locked wheel or the side force at a slipping wheel can be measured over a wide range of temperatures and speeds. At small slip angles the side force is dominated by dynamic cornering stiffness of the compound, at large slip angles by the friction coefficient. In this case, too, good correlations to road experience exist over a limited range of testing conditions. Low water temperatures and low slip speed settings in the laboratory produce side force ratings, which correlate closely with ABS braking on the road High and higher slip speeds give ratings in close agreement with locked wheel braking on the road. A heatable/coolable disk enables traction measurements on ice and newly abrasion measurements on surfaces at elevated surface temperature. Ice surface temperatures between −5 °C and −25 °C are possible. Friction measurements show that the difference in compound rating between summer and winter compounds is maintained over the whole temperature range. New investigations show not only a differentiation between different winter tire treads qualities but also an excellent correlation between tire and laboratory results. As a new topic side force measurements on dry surfaces highlight the correlation to dry handling of tires. The tire tread compound contributes to this performance through its shear stiffness and its friction coefficient. The shear stiffness contributes to the response of the tire in directional changes. The friction coefficient determines the maximum force, which can be transmitted. A simple operation possibility for evaluation of determined side forces is demonstrated. In addition to antecedent investigations the rolling resistance of the rubber wheel can be measured over a range of loads and speeds with the slip angle set at zero. Again for these new results good correlations are achieved with practical experience. In particular, the dependence of the rolling resistance on the velocity and loads are pointed out. Ultimately a good correlation between tire test and laboratory test results was demonstrated.

The Size of the Friction Coefficient Depending on the Size and Course of Normal Load

2014 ◽  
Vol 474 ◽  
pp. 303-308 ◽  
Author(s):  
Eva Labašová
Keyword(s):  
Friction Coefficient ◽  
Coefficient Of Friction ◽  
Normal Load ◽  
Testing Machine ◽  
Constant Load ◽  
Current Component ◽  
Rectangular Shape ◽  
The Coefficient Of Friction ◽  
Ring Method ◽  
Run Up

The coefficient of friction for the bronze material (CuZn25Al6) with inset graphite beds is investigated in the present paper. Friction coefficient was investigated experimentally by the testing machine Tribotestor`89 which uses the principle of the ring on ring method. Tribotestor`89 machine may be classed to the rotary tribometers. The tested sliding pairs were of the same material. The internal bushing performed a rotational movement with constant sliding speed (v = 0.8 m s-1). The external fixed bushing was exposed to the normal load, which was of different sizes and different variations. Process of load was increased from level 50 N to 200 N (400 N, 600 N) during run up 600 s, after the run up the appropriate level of load was held.The forth test had a rectangular shape of loading with direct current component 400 N and the amplitude 200 N period 600 s, the whole test took 1800 s. The obtained results reveal that friction coefficient decreases with the increase of normal load. Further, that the coefficient of friction was found smaller at constant load, as compared to rectangular shape of loading.

Mechanical Characterization Of Ultra-Thin, Hard-Disk Overcoats Using Scratch Testing And Depth-Sensing Indentation

1997 ◽  
Vol 505 ◽  
Author(s):  
J. L. Hay ◽  
R. L. White ◽  
B. N. Lucas ◽  
W. C. Oliver
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
Wear Test ◽  
Constant Load ◽  
Indentation Hardness ◽  
Depth Sensing ◽  
Small Constant ◽  
Residual Damage ◽  
20 Nm ◽  
Scratch Tests

ABSTRACTTwo series of five diamond-like carbon (DLC) coatings were sputtered under nominally identical conditions, but to different film thicknesses of 20 nm and 105 nm. First, the hardness of each sample was determined by depth-sensing indentation. Hardness measurements were substrate-affected to some extent for all samples but especially so for the 20 nm coatings. Two types of scratch tests were performed in an attempt to isolate and characterize the top coatings. The first was a wear test, which consisted of moving the sample back and forth repeatedly under a small constant load. The residual damage was inconsistent, but appeared to be a function of the composite, or substrate-affected hardness. The second test was a single-pass scratch in which the normal load was ramped linearly. For all samples, the friction coefficient was approximately constant as a function of load. Furthermore, samples with the same top coats yielded similar friction coefficients, regardless of the coating thicknesses. Friction coefficient decreased with hydrogen content and to some extent, increased with hardness, as measured on the 105 nm samples. The friction coefficient measured during a ramp-load scratch offers an alternative for characterizing ultra-thin films, when indentation alone yields measurements that are significantly affected by the substrate.

scholarly journals Soft EHL based Friction Mechanism of Unreinforced and GF-Reinforced PA66 in Contact with Steel under PAO8 Oil Lubrication

2021 ◽  
Author(s):  
Takeshi Kunishima ◽  
Gaëtan BOUVARD ◽  
Jean Christophe ABRY ◽  
Vincent FRIDRICI ◽  
Philippe KAPSA
Keyword(s):  
Friction Coefficient ◽  
Master Curve ◽  
Hydrodynamic Lubrication ◽  
Normal Load ◽  
Sliding Surface ◽  
Polyamide 66 ◽  
Oil And Grease ◽  
Oil Viscosity ◽  
Friction Mechanism ◽  
Oil Film

Abstract Polyamide 66 is widely used in polymer sliding parts including polymer gear. These parts are used under lubrication of oil and grease. In this study, the friction mechanism of the contact between polyamide 66 and a steel counterpart lubricated with additive-free polyalphaolefin8 oil was discussed by focusing on various parameters including the sliding surface roughness, normal load (contact pressure), sliding speed, temperature, and hardness of the steel counterpart. To explain the friction coefficient obtained under different test conditions, the theoretical minimum oil film thickness was calculated using the equation of the soft elastic hydrodynamic lubrication regime presented by Hamrock and Dowson considering the temperature dependence of oil viscosity and polymer mechanical properties, and the master curve of the relationship between Λ and the friction coefficient was proposed considering the change in the roughness on the sliding surface. In addition, the contributions of the oil film based on the proposed master curve and lubricated solid/solid contact based on the Bowden-Tabor theory to the friction coefficient were discussed. Furthermore, the friction mechanism using the glass fiber-reinforced PA66 composite was investigated and compared to that of the unreinforced PA66.

A Quantitative Theory for the Computation of Tire Friction Under Severe Conditions of Sliding

1986 ◽  
Vol 14 (1) ◽  
pp. 44-72 ◽  
Author(s):  
C. M. Mc C. Ettles
Keyword(s):  
Friction Coefficient ◽  
Flash Temperature ◽  
Contact Conditions ◽  
Quantitative Form ◽  
Heating Effects ◽  
Rubber Friction ◽  
Viscoelastic Effects ◽  
Tire Friction ◽  
Pavement Friction ◽  
Metal Polymer

Abstract It is proposed that tire-pavement friction is controlled by thermal rather than by hysteresis and viscoelastic effects. A numerical model of heating effects in sliding is described in which the friction coefficient emerges as a dependent variable. The overall results of the model can be expressed in a closed form using Blok's flash temperature theory. This allows the factors controlling rubber friction to be recognized directly. The model can be applied in quantitative form to metal-polymer-ice contacts. Several examples of correlation are given. The difficulties of characterizing the contact conditions in tire-pavement friction reduce the model to qualitative form. Each of the governing parameters is examined in detail. The attainment of higher friction by small, discrete particles of aluminum filler is discussed.

Lateral Tire Forces on Wet Roads

1977 ◽  
Vol 5 (2) ◽  
pp. 75-82 ◽  
Author(s):  
A. Schallamach
Keyword(s):  
Normal Load ◽  
The Self ◽  
Experimental Results ◽  
Slip Angle ◽  
Tire Model ◽  
Side Force ◽  
Tire Forces

Abstract Expressions are derived for side force and self-aligning torque of a simple tire model on wet roads with velocity-dependent friction. The results agree qualitatively with experimental results at moderate speeds. In particular, the theory correctly predicts that the self-aligning torque can become negative under easily realizable circumstances. The slip angle at which the torque reverses sign should increase with the normal load.

scholarly journals Thermomechanical Couplings in Aircraft Tire Rolling/Sliding Modeling

2011 ◽  
Vol 274 ◽  
pp. 81-90 ◽  
Author(s):  
Ange Kongo Kondé ◽  
Iulian Rosu ◽  
F. Lebon ◽  
L. Seguin ◽  
Olivier Brardo ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Thermal Effects ◽  
Coulomb Friction ◽  
Large Deformations ◽  
Element Model ◽  
Slip Angle ◽  
Tire Model ◽  
Vertical Load ◽  
Coulomb Friction Law ◽  
Lateral Friction

This paper presents a finite element model for the simulation of aircraft tire rolling. Large deformations, material incompressibility, heterogeneities of the material, unilateral contact with Coulomb friction law are taken into account. The numerical model will allow estimating the forces in the contact patch - even in critical and extreme conditions for the aircraft safety and security. We show the influence of loading parameters (vertical load, velocity, inflating pressure) and slip angle on the Self Aligning torque and on the lateral friction coefficient. A friction coefficient law corresponding to Chichinadze model is considered to take into account thermal effects in the aircraft tire model behaviour.

The Dependence of the Friction Coefficient on the Size and Course of Sliding Speed

2014 ◽  
Vol 693 ◽  
pp. 305-310 ◽  
Author(s):  
Eva Labašová
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
Testing Machine ◽  
Current Component ◽  
Sliding Speed ◽  
Rectangular Shape ◽  
Coefficient Increase ◽  
The Coefficient Of Friction ◽  
Ring Method ◽  
Run Up

The coefficient of friction for the bronze material (CuZn25Al6) with insert graphite beds and other bronze material (CuSn12) are investigated in this paper. Friction coefficient was investigated experimentally by the testing machine Tribotestor`89 which uses the principle of the ring on ring method. The external fixed bushing was exposed to the normal load of the same size in all tests. Process of load was increased from level 50 N to 600 N during run up 300 s, after the run up the appropriate level of load was held. The internal bushing performed a rotational movement with constant sliding speed. The value of sliding speed was changed individually for every sample (v = 0.2 (0.3, 0.4) m.s-1). The forth test had a rectangular shape of sliding speed with direct current component 0.3 m.s-1 and the amplitude 0.1 m.s-1 period 300 s, the whole test took 2100 s. The obtained results reveal that friction coefficient increase with the increase of sliding speed.

Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part II—Correlation With Bench Test Data

1999 ◽  
Vol 123 (1) ◽  
pp. 219-223 ◽  
Author(s):  
Ozgen Akalin ◽  
Golam M. Newaz
Keyword(s):  
Friction Coefficient ◽  
Test Data ◽  
Piston Ring ◽  
Normal Load ◽  
Test System ◽  
Mixed Lubrication ◽  
Contact Temperature ◽  
Bench Test ◽  
Crank Angle ◽  
Contact Width

A bench friction test system for piston ring and liner contact, which has high stroke length and large contact width has been used to verify the analytical mixed lubrication model presented in a companion paper (Part 1). This test system controls the speed, temperature and lubricant amount and records the friction force, loading force, crank angle signal and contact temperature data simultaneously. The effects of running speed, applied normal load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores. Friction coefficient predictions are presented as a function of crank angle position and results are compared with bench test data. Analytical results correlated well with bench test results.

scholarly journals Experimental Study on the Transition between Static and Kinetic Frictions of Steel/Shale Pairs

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Qin Lian ◽  
Chunxu Yang ◽  
Jifei Cao
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
Critical Distance ◽  
Dynamic Friction ◽  
Stick Slip ◽  
Dynamic Friction Coefficient ◽  
The Coefficient Of Friction ◽  
The Difference ◽  
Stick Slip Motion ◽  
Insight Into

The transition between static and kinetic frictions of steel/shale pairs has been studied. It was found that the coefficient of friction decreased exponentially from static to dynamic friction coefficient with increasing sliding displacement. The difference between static and dynamic friction coefficients and the critical distance Dc under the dry friction condition is much larger than that under the lubricated condition. The transition from static to dynamic friction coefficient is greatly affected by the normal load, quiescent time, and sliding velocity, especially the lubricating condition. Maintaining continuous lubrication of the contact area by the lubricant is crucial to reduce or eliminate the stick-slip motion. The results provide an insight into the transition from static to dynamic friction of steel/shale pairs.

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