The Nature of Static Friction in Elastomers

1961 ◽  
Vol 34 (2) ◽  
pp. 461-465 ◽  
Author(s):  
G. M. Bartenev ◽  
V. V. Lavrent'ev
Keyword(s):  
Coefficient Of Friction ◽  
Dry Friction ◽  
Tangential Force ◽  
Static Friction ◽  
Initial Moment ◽  
Elastomeric Materials ◽  
The Coefficient Of Friction ◽  
Accuracy Of Measurement

Abstract 1. A method free from the shortcomings of earlier work is proposed for the measurement of the friction of elastomeric materials in the initial moment of shear. 2. From results of measurement of friction of rubber on steel it follows that static friction, determined as the coefficient of friction in the initial moment of slip, is a conventional parameter, since it depends upon the accuracy of measurement of the movement and upon the rate of application of the tangential force. 3. The conventional coefficient of static friction of elastomeric materials is particularly evident at low rates of application of the tangential force, which fact is connected with the nature of dry friction of rubberlike polymers.

Review Paper 2: Basic Principles of Dry Friction Testing

1967 ◽  
Vol 182 (7) ◽  
pp. 7-15
Author(s):  
T. H. C. Childs ◽  
D. Tabor
Keyword(s):  
Dry Friction ◽  
Review Paper ◽  
Normal Load ◽  
Tangential Force ◽  
Experimental Methods ◽  
Basic Principles ◽  
Friction Process ◽  
Friction Testing ◽  
The Coefficient Of Friction ◽  
Load Movement

Friction is the force resisting relative motion between surfaces in contact. The coefficient of friction is the ratio of the frictional force to the normal load. Consequently the measurement of friction involves measurement of a normal load, movement of a surface, and measurement of a tangential force. The first part of this review paper deals with the basic principles of the friction process. The second part is concerned with experimental methods of measuring the friction.

Frictional Vibrations

1955 ◽  
Vol 22 (2) ◽  
pp. 207-214
Author(s):  
David Sinclair
Keyword(s):  
Coefficient Of Friction ◽  
Equations Of Motion ◽  
Static Friction ◽  
Uniform Motion ◽  
Friction Characteristic ◽  
Stick Slip ◽  
The Coefficient Of Friction ◽  
Brake Lining ◽  
Solid Bodies ◽  
Frictional Vibrations

Abstract Frictional vibrations, such as stick-slip motion and automobile-brake squeal, which occur when two solid bodies are rubbed together, are analyzed mathematically and observed experimentally. The conditions studied are slow uniform motion and relatively rapid simple harmonic motion of brake lining over a cast-iron base. The equations of motion show and the observations confirm that frictional vibrations are caused primarily by an inverse variation of coefficient of friction with sliding velocity, but their form and occurrence are greatly dependent upon the dynamical constants of the mechanical system. With a constant coefficient of friction, the vibration initiated whenever sliding begins is rapidly damped out, not by the friction but by the “natural” damping of all mechanical systems. The coefficient of friction of most brake linings and other organic materials was essentially invariant with velocity, except that the static coefficient was usually greater than the sliding coefficient. Most such materials usually showed a small decrease in coefficient with increasing temperature. The persistent vibrations resulting from the excess static friction were reduced or eliminated by treating the rubbing surfaces with polar organic compounds which produced a rising friction characteristic.

Tribometer for Dry Friction Measurement

1999 ◽  
Author(s):  
Marc Brandl ◽  
Friedrich Pfeiffer
Keyword(s):  
Coefficient Of Friction ◽  
Dry Friction ◽  
Stribeck Curve ◽  
Body System ◽  
Friction Measurement ◽  
Detailed Model ◽  
The Coefficient Of Friction ◽  
Simulation Results ◽  
Multi Body

Abstract This paper deals with the measurement of dry friction. A tribometer was developed in order to identify both the sticking and the sliding coefficient of friction. The aim was to determine the so called Stribeck-curve of any material in contact. The design of the plant is presented. Avoiding errors in recalculating the coefficient of friction, a detailed model of the plant as a multi body system with motor feedback was generated. Advantages of the tribometer are shown in simulations. Some results of measurements in comparison with simulation results are presented.

scholarly journals A Technique to Determine Friction at the Fingertips

2008 ◽  
Vol 24 (1) ◽  
pp. 43-50 ◽  
Author(s):  
Adriana V. Savescu ◽  
Mark L. Latash ◽  
Vladimir M. Zatsiorsky
Keyword(s):  
Coefficient Of Friction ◽  
Normal Force ◽  
Tangential Force ◽  
Vertical Direction ◽  
Force Sensor ◽  
Displacement Method ◽  
Significant Difference ◽  
The Coefficient Of Friction ◽  
Slip Method ◽  
Slip Force

This article proposes a technique to calculate the coefficient of friction for the fingertip– object interface. Twelve subjects (6 males and 6 females) participated in two experiments. During the first experiment (the imposed displacement method), a 3-D force sensor was moved horizontally while the subjects applied a specified normal force (4 N, 8 N, 12 N) on the surface of a sensor covered with different materials (sandpaper, cotton, rayon, polyester, and silk).Thenormal forceand thetangential force(i.e., the force due to the sensor motion) were recorded. Thecoefficient of friction(µd) was calculated as the ratio between the tangential force and the normal force. In the second experiment (the beginning slip method), a small instrumented object was gripped between the index finger and the thumb, held stationary in the air, and then allowed to drop. The weight (200 g, 500 g, and 1,000 g) and the surface (sandpaper, cotton, rayon, polyester, and silk) in contact with the digits varied across trials. The same sensor as in the first experiment was used to record thenormal force(in a horizontal direction) and thetangential force(in the vertical direction). Theslip force(i.e., the minimal normal force or grip force necessary to prevent slipping) was estimated as the force at the moment when the object just began to slip. The coefficient of friction was calculated as the ratio between the tangential force and the slip force. The results show that (1) the imposed displacement method is reliable; (2) except sandpaper, for all other materials the coefficient of friction did not depend on the normal force; (3) theskin–sandpapercoefficient of friction was the highest µd= 0.96 ± 0.09 (for 4-N normal force) and theskin–rayonrayon coefficient of friction was the smallest µd= 0.36 ± 0.10; (4) no significant difference between the coefficients of friction determined with the imposed displacement method and the beginning slip method was observed. We view the imposed displacement technique as having an advantage as compared with the beginning slip method, which is more cumbersome (e.g., dropped object should be protected from impacts) and prone to subjective errors owing to the uncertainty in determining the instance of the slip initiation (i.e., impeding sliding).

Coefficients of Friction: Static Versus Dynamic

2020 ◽  
Author(s):  
Jack Youqin Huang
Keyword(s):  
Coefficient Of Friction ◽  
Frictional Force ◽  
Inertial Force ◽  
Static Friction ◽  
Theory And Practice ◽  
Dynamic Friction ◽  
Kinetic Friction ◽  
The Coefficient Of Friction ◽  
Static Versus Dynamic ◽  
New Discovery

Abstract This paper deals with the problem of static and dynamic (or kinetic) friction, namely the coefficients of friction for the two states. The coefficient of static friction is well known, and its theory and practice are commonly accepted by the academia and the industry. The coefficient of kinetic friction, however, has not fully been understood. The popular theory for the kinetic friction is that the coefficient of dynamic friction is smaller than the coefficient of static friction, by comparison of the forces applied in the two states. After studying the characteristics of the coefficient of friction, it is found that the comparison is not appropriate, because the inertial force was excluded. The new discovery in the paper is that coefficients of static friction and dynamic friction are identical. Wheel “locked” in wheel braking is further used to prove the conclusion. The key to cause confusions between the two coefficients of friction is the inertial force. In the measurement of the coefficient of static friction, the inertial force is initiated as soon as the testing object starts to move. Therefore, there are two forces acting against the movement of the object, the frictional force and the inertial force. But in the measurement of the coefficient of kinetic friction, no inertial force is involved because velocity must be kept constant.

The Influence of Surface Roughness on the Mechanism of Friction

1970 ◽  
Vol 92 (2) ◽  
pp. 264-272 ◽  
Author(s):  
T. Tsukizoe ◽  
T. Hisakado
Keyword(s):  
Surface Roughness ◽  
Metal Surface ◽  
Coefficient Of Friction ◽  
Dry Friction ◽  
Metal Surfaces ◽  
Roughness Effects ◽  
Real Area Of Contact ◽  
The Coefficient Of Friction ◽  
Tangential Forces ◽  
Soft Metal

A study was made of surface roughness effects on dry friction between two metals, assuming that the asperities are cones of the slopes which depend on the surface roughness. The theoretical explanations were offered for coefficients of friction of the hard cones and spheres ploughing along the soft metal surface. A comparison of calculated values based on these with experimental data shows good agreement. Moreover, theoretical discussion was carried out of surface roughness effects on dry friction between two metal surfaces on the basis of the analyses of the frictional mechanism for a hard slider on the metal surface. The theoretical estimation of the coefficient of friction between two metal surfaces can be carried out by using the relations between the surface roughness and the slopes of the asperities, and the coefficient of friction due to the adhesion at the interface. The experiments also showed that when two metal surfaces are first loaded normally and then subjected to gradually increasing tangential forces, real area of contact between them increases and the maximum tangential microslip of them increases with the increase of the surface roughness.

scholarly journals Sintered Hydroxyapatite Ceramic for Wear Studies

1978 ◽  
Vol 57 (7-8) ◽  
pp. 777-783 ◽  
Author(s):  
Hillar M. Rootare ◽  
John M. Powers ◽  
Robert G. Craig
Keyword(s):  
Coefficient Of Friction ◽  
Tricalcium Phosphate ◽  
Friction And Wear ◽  
Tangential Force ◽  
Hydroxyapatite Ceramic ◽  
Track Width ◽  
Failure Data ◽  
Surface Failure ◽  
Human Enamel ◽  
The Coefficient Of Friction

A sintered hydroxyapatite (HAP) ceramic for use in wear studies was prepared from a commerical tricalcium phosphate. The sintered HAP had physical properties close to those of human enamel. The coefficient of friction and wear of the sintered HAP ceramic as characterized by tangential force, track width, and surface failure data, approximated those of human enamel.

The Calculation of Roll Pressure in Hot and Cold Flat Rolling

1943 ◽  
Vol 150 (1) ◽  
pp. 140-167 ◽  
Author(s):  
E. Orowan
Keyword(s):  
Pressure Distribution ◽  
Yield Stress ◽  
Coefficient Of Friction ◽  
Static Friction ◽  
Rolled Stock ◽  
Theoretical Treatment ◽  
Frictional Drag ◽  
Roll Pressure ◽  
Plate Rolling ◽  
The Coefficient Of Friction

A numerical or graphical method is given for computing, in strip or plate rolling, the distribution of roll pressure over the arc of contact and the quantities derived from this (e.g. the vertical roll force, the torque, and the power consumption). The method avoids all mathematical approximations previously used in the theoretical treatment of rolling, and permits any given variation of the yield stress and of the coefficient of friction along the arc of contact to be taken into account. It can be used, therefore, in both hot and cold rolling, provided that the basic physical quantities (yield stress and coefficient of friction) are known. The usual assumption that the deformation could be regarded as a locally homogeneous compression has not been made, and the inhomogeneity of stress distribution has been taken into account approximately by using results derived by Prandtl and Nádai from the Hencky treatment of two-dimensional plastic deformation. It is found that the discrepancy between the roll pressure distribution curves calculated from the Kármán theory and those measured by Siebel and Lueg is due to the assumption in the theory that the frictional drag between the rolls and the rolled stock is equal to the product of the roll pressure and the coefficient of friction. If frictional effects are dominant, as in hot rolling, this product may easily exceed the yield stress in shear which is the natural upper limit to the frictional drag, and then static friction, instead of slipping, occurs. This has been taken into account in the present method, and the calculated curves of roll pressure distribution show good agreement with the curves measured by Siebel and Lueg.

An Empirical Approach to Modeling the Friction Coefficient for Wheel-Rail Contact

2009 ◽  
Author(s):  
HyunWook Lee ◽  
Corina Sandu ◽  
Carvel Holton ◽  
Mehdi Ahmadian
Keyword(s):  
Friction Coefficient ◽  
Coefficient Of Friction ◽  
Dry Friction ◽  
Damping Ratio ◽  
Contact Dynamics ◽  
Nonlinear Dependence ◽  
Accurate Estimation ◽  
Highly Nonlinear ◽  
The Coefficient Of Friction ◽  
Wheel Vibration

The coefficient of friction (CoF) is one of the most important parameters for the contact between the wheel and the rail. Accurate estimation or measurement of the CoF has a very important role, both in terms of modeling the train dynamics and in terms of reducing operational costs in the long-term. For ease of implementation, since the nature of the wheel-rail contact dynamics is very complex, the assumption of a constant CoF is still used in most theoretical studies. Nevertheless, experimental work indicates that the CoF depends on dynamic changes in various wheel-rail conditions, like sliding velocity, contact patch shape and size for stick and sliding region, wheel and rail geometry, wheel vibration, rail surface roughness and/or lubrication, etc. In this paper we present the proposed equation to model the nonlinear dry friction coefficient at the wheel-rail contact. The friction coefficient is calculated at the three different values for change in the damping ratio while maintaining all the other conditions the same. As expected, the analysis performed to estimate the dry friction coefficient based on the proposed equation and using NUCARS® simulation results shows that the coefficient of friction has a highly nonlinear dependence on its parameters.

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