Effects of Ambient Gases on Friction and Interfacial Resistance

1988 ◽  
Vol 110 (3) ◽  
pp. 508-515 ◽  
Author(s):  
Y.-J. Chang ◽  
D. Kuhlmann-Wilsdorf
Keyword(s):  
Contact Resistance ◽  
Coefficient Of Friction ◽  
Wear Behavior ◽  
Copper Surface ◽  
Surface Films ◽  
Electric Contact ◽  
Interfacial Resistance ◽  
Stick Slip ◽  
The Coefficient Of Friction ◽  
Ambient Gases

As is well known, ambient atmospheres can greatly affect the friction and wear behavior of metals sliding on each other, as well as the electric contact resistance between the metals. In order to better understand the mechanisms of those effects of ambient atmospheres, the coefficient of friction and the electric contact resistance have been studied for bundles of 50 micrometer thick copper wires, sliding on a polished copper surface in a specialized apparatus, called the hoop apparatus. The ambient gas was cycled between laboratory air and carbon dioxide, and between laboratory air and argon, respectively. The results indicate a reversible build-up and removal of surface films whose nature as well as speed of formation and removal depends on the gas present. Fiber bundles are used in order to eliminate the constriction resistance, so that the contact resistance is directly proportional to the specific film resistivity. The following properties were found to be affected by the ambient gases. (i) The average level of the contact resistance. (ii) The amplitude of the electric “noise.” (iii) The coefficient of friction. (iv) The difference between the static and the dynamic coefficients of friction in stick-slip motion. The results were found to be consistent with previous measurements in which the mechanism of forming wear particles was deduced from a wear chip analysis. Correspondingly they were interpreted in terms of the same wear model. This led to a further advance in the understanding of the interfacial processes accompanying sliding in this sample/substrate combination.

Friction, Wear, and Interfacial Electrical Resistance. Part I: The Hoop Apparatus

1987 ◽  
Vol 109 (4) ◽  
pp. 604-608 ◽  
Author(s):  
D. Kuhlmann-Wilsdorf ◽  
Y. J. Chang ◽  
L. B. Johnson ◽  
L. J. Bredell
Keyword(s):  
Coefficient Of Friction ◽  
Electrical Resistance ◽  
Electrical Contact ◽  
Constant Load ◽  
Simultaneous Recording ◽  
Contact Spot ◽  
Interfacial Resistance ◽  
Stick Slip ◽  
The Coefficient Of Friction ◽  
Contact Spots

An apparatus has been developed for the gathering of data from which, through suitable analysis, detailed information on the momentary condition of a sliding interface may be obtained. The information includes the number of the contact spots, the electrical resistivity of the interfacial film, and the flash temperature at the contact spots. The apparatus provides for the continuous simultaneous recording of the coefficient of friction and of the interfacial electrical resistance of a slider in stick-slip motion at constant load and controllable average speed, and/or of the interfacial resistance of a slider at constant speed under controllable load. Loads between 0.3 and 10N and speeds up to 0.15m/s may be selected, in a variety of atmospheres and ambient pressures, as the apparatus is enclosed in a bell jar. It consists of a rotating cylindrical metal hoop inside of which a metal slider moves under the forces of friction and gravity, giving stick-slip behavior full play, and a slider in fixed position subjected to controllable, hydrostatically applied loads. The entire apparatus can be used with a controlled atmosphere or vacuum. The motion of the stick-slip slider, from which the coefficient of friction is inferred, is recorded on one pen of a three-pen strip-chart recorder and the electrical contact resistances between the two sliders and the hoop on the other two pens. The dependence of contact resistance on load, obtainable from the fixed slider without removing the bell jar, permits a determination of the number of contact spots provided the constriction resistance is not negligibly small compared to the film resistance. Deliberate changes of the contact spot temperature can be made by adjusting the current through the slider/hoop interfaces.

A Bifurcation Phenomenon of Static Friction

1961 ◽  
Vol 28 (2) ◽  
pp. 213-217 ◽  
Author(s):  
F. F. Ling ◽  
R. S. Weiner
Keyword(s):  
Contact Resistance ◽  
Coefficient Of Friction ◽  
Normal Load ◽  
Pure Shear ◽  
Static Friction ◽  
The Other ◽  
Electric Contact ◽  
Bifurcation Phenomenon ◽  
The Coefficient Of Friction

Measurements are reported of electric contact resistance, actual area of contact, static friction, adhesion and pure shear for lead on lead. The data exhibit a statistical bifurcation of friction. In other words, below extreme pressures, statistically there are two branches of the coefficient of friction versus normal load relationship. The nature of one of the branches is explicable exclusively in terms of the weld-junction or adhesion theory of friction. The nature of the other, however, is not so explicable. This points to the existence of what Holm [1] called the Y-term of friction, the nature of which has yet to be satisfactorily explained.

Sliding friction and wear behavior of Al–Ni–Co–Si quasicrystalline coatings deposited by the high-velocity oxy-fuel spraying technique

2002 ◽  
Vol 17 (2) ◽  
pp. 492-501 ◽  
Author(s):  
Eric Fleury ◽  
Yu-Chan Kim ◽  
Jae-Soo Kim ◽  
Hyo-Sok Ahn ◽  
Sang-Mok Lee ◽  
...  
Keyword(s):  
Coefficient Of Friction ◽  
High Velocity ◽  
Wear Debris ◽  
Friction And Wear ◽  
Sliding Friction ◽  
Wear Behavior ◽  
Stick Slip ◽  
Friction And Wear Behavior ◽  
Test Conditions ◽  
The Coefficient Of Friction

The sliding friction and wear performance of Al–Ni–Co–Si quasicrystalline coatings deposited by the high-velocity oxy-fuel technique were investigated under dry sliding conditions. This study indicated that changes in the imposed sliding test conditions modified the friction and wear behavior of quasicrystalline coatings. Qualitative analysis of the contact interface and wear debris were performed with the aim of understanding the role of the third body on the friction and wear processes. The dependence of the coefficient of friction on the sliding velocity and counterpart material was explained by the stick-slip behavior. It was also shown that test conditions favorable for the formation of thick intermediate layers and the densification of the coating subsurface led to low wear rates. Large cylindrical particles, formed by agglomeration of small wear debris, were suggested as a beneficial factor for the reduction of the coefficient of 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.

Investigation of the friction behavior of plasma spray Mo/NiCrBSi coated brake discs

2021 ◽  
Vol 63 (3) ◽  
pp. 259-265
Author(s):  
Halil Kılıç ◽  
Cenk Mısırlı ◽  
İbrahim Mutlu
Keyword(s):  
Coefficient Of Friction ◽  
Plasma Spray ◽  
Wear Behavior ◽  
Atmospheric Plasma ◽  
Brake Disc ◽  
Friction Behavior ◽  
Braking Performance ◽  
Spray Process ◽  
The Coefficient Of Friction ◽  
Nicrbsi Coating

Abstract This paper presents the findings of comparative research conducted to find out the braking performance of a Mo/NiCrBSi coated automobile brake disc. The friction and wear behavior of the Mo/NiCrBSi coating (CD) used for the disc material was evaluated using a laboratory scale disc-pad dynamometer and compared with a reference disc (RD). The coating was deposited by means of the atmospheric plasma spray process on a grey cast iron substrate. Braking tests were performed according to the SAE-J2430 test standard. Disc microstructures were characterized by SEM and XRD. It was found that the bonding strength was good with an infinite rating between the accumulated coating layer and the substrate. The results show that the coated brake disc has a comparable coefficient of friction and that the amount of wear is lower than that of the reference disc. The addition of ductile phases to the disc coating was beneficial in reducing the coefficient of friction to an acceptable degree and also effectively improving wear resistance.

Dry Slide Wear Behavior of Graphite and SiC, TiO2 Filled the Unidirectional Glass-Epoxy Composites

2017 ◽  
Vol 25 (3) ◽  
pp. 193-198 ◽  
Author(s):  
A. Madhanagopal ◽  
S. Gopalakannan
Keyword(s):  
Wear Rate ◽  
Coefficient Of Friction ◽  
Wear Behavior ◽  
Specific Wear Rate ◽  
Dry Sliding ◽  
Testing Time ◽  
Time Duration ◽  
Sem Images ◽  
Unidirectional Glass ◽  
The Coefficient Of Friction

This study determines the friction and the wear properties of the unidirectional glass epoxy composite with Gr, SiC TiO2 powder by using pin on disk apparatus. This tribological data is obtained in dry sliding condition for a constant sliding time of 30 minutes. Test specimens are prepared using hand lay-up process and by varying the different (2, 5, 7) percentage each of graphite and SiC, TiO2 particles addition for the combination of fiber and matrix. The tests are performed by varying the operating parameters of contact pressure (p) and velocity (v). The composites (2% 5%, and 7%) are worn by dry sliding at the steel counter face under ambient conditions. The coefficient of friction reaches maximum of 0.78 at 2 kg load, 2 m/s velocity with testing time duration of 24 min. whereas 5%, 7% sample shows the coefficient of friction 0.28, 0.25 respectively. The specific wear rate value drops to 0.79 (mm3/N-m×10−6) at 2 kg load at 2 m/s velocity for the 5% specimen. The maximum reduction in the specific wear rate at 3 kg load, 1m/s velocity is 32.7 percentages, 5.63 percentages for the 5,7 percentage specimen compared to 2% specimen for the graphite and SiC, TiO2 particle filled composite specimen respectively. The SEM images are also taken to support the results.

The friction of clean crystal surfaces

1966 ◽  
Vol 295 (1442) ◽  
pp. 233-243 ◽  
Keyword(s):  
Coefficient Of Friction ◽  
High Surface ◽  
High Vacuum ◽  
Surface Films ◽  
Surface Adhesion ◽  
Crystal Surfaces ◽  
Deformation And Fracture ◽  
The Coefficient Of Friction ◽  
Molecular Layers ◽  
Frictional Behaviour

A study is made of the frictional behaviour of crystals (diamond, magnesium oxide, sapphire) sliding on themselves in high vacuum (10 -10 torr). The surface films normally present on these crystals are very tenacious but they may be worn away by repeated sliding in the same track. Under these conditions the friction of the clean crystals may increase by a factor of ten so that the coefficient of friction may rise to μ ≈ 1. The frictional rise is limited because of the elastic and brittle behaviour of the contact regions. Under these conditions subsurface deformation and fracture of the crystal occurs and this, combined with the high surface adhesion, causes pronounced wear. Adsorption of a few molecular layers of gas can again reduce the friction to a low value. The results are relevant to the operation of bearings and to the wear of surfaces in space.

scholarly journals Finger pad friction and its role in grip and touch

2013 ◽  
Vol 10 (80) ◽  
pp. 20120467 ◽  
Author(s):  
Michael J. Adams ◽  
Simon A. Johnson ◽  
Philippe Lefèvre ◽  
Vincent Lévesque ◽  
Vincent Hayward ◽  
...  
Keyword(s):  
Contact Zone ◽  
Coefficient Of Friction ◽  
Normal Load ◽  
Theoretical Models ◽  
Tactile Perception ◽  
Major Influence ◽  
Sliding Velocity ◽  
Stick Slip ◽  
The Coefficient Of Friction ◽  
Finger Pad

Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanisms. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counterintuitively, the coefficient of friction can increase by an order of magnitude in a period of tens of seconds when in contact with an impermeably smooth surface, such as glass. In contrast, the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first-order kinetics. Surprisingly, the sensitivity of the coefficient of friction to the normal load and sliding velocity is comparatively of second order, yet these dependencies provide the main basis of theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick–slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function.

Influence of Surface Roughness on Friction and Contact Resistance in Sliding Electrical Contacts

2007 ◽  
Author(s):  
Dinesh G. Bansal ◽  
Jeffrey L. Streator
Keyword(s):  
Surface Roughness ◽  
Contact Resistance ◽  
Coefficient Of Friction ◽  
Electrical Contact ◽  
Electrical Current ◽  
Electrical Contacts ◽  
Sliding Electrical Contacts ◽  
The Coefficient Of Friction ◽  
Current Densities

An experiment is conducted to investigate the role of surface roughness on the coefficient of friction and contact resistance of sliding electrical contacts. A hemispherical pin is sliding along both smooth and rough 2-meter rail surface. Tests are performed at both low and moderate sliding speed and for a range of electrical current densities, ranging from 0 to about 12 GA/m2. It was found that surface roughness had a significant influence on the coefficient of friction, with the smoother surfaces exhibiting higher coefficients of friction. Contact resistance, on the other hand, did not show as strong an effect of surface roughness, except for a few parameter combinations. At the higher current densities studied (>10 GA/m2), it was found that the contact resistance values tended to be on the order of 1 mΩ, independent of load, speed and roughness. This convergence may be due to presence of liquid metal film at the interface, which established ideal electrical contact.

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