Friction of diamond, graphite, and carbon and the influence of surface films

1951 ◽  
Vol 208 (1095) ◽  
pp. 444-455 ◽  
Keyword(s):  
Shear Strength ◽  
Large Scale ◽  
Physical Adsorption ◽  
Surface Films ◽  
Low Friction ◽  
Real Area Of Contact ◽  
Carbon And Graphite ◽  
Strong Adhesion ◽  
Frictional Behaviour ◽  
Real Area

This paper describes an experimental study of the frictional behaviour of diamond, graphite and of carbon which have been outgassed in vacuo . The removal of surface films which are normally present causes a large increase in the friction. The admission of a small amount of oxygen, water vapour or other contaminant will reduce the friction. Both physical adsorption and chemical adsorption are important. There is evidence that with clean graphite surfaces there is strong adhesion at the interface, so that when sliding takes place slip and shearing occurs beneath the surface. Carbon and graphite have a negative tem perature coefficient of friction. The low friction normally observed with diamond is due to the presence of adsorbed oxygen and other gases. The friction of clean diamond on diamond is high, and the shear strength at the interface is comparable with the shear strength of diamond. Large-scale seizure does not occur because the deformation of the diamond in the region of contact is elastic and the real area of contact necessarily remains small.

Part II. Friction of non-metals - Friction of diamond, graphite and carbon: the influence of adsorbed films

1952 ◽  
Vol 212 (1111) ◽  
pp. 485-488 ◽  
Keyword(s):  
Experimental Study ◽  
Plastic Deformation ◽  
Shear Strength ◽  
Large Scale ◽  
Physical Adsorption ◽  
Surface Films ◽  
Diamond Surfaces ◽  
Adsorbed Films ◽  
Carbon And Graphite ◽  
Frictional Behaviour

An experimental study has been made of the frictional behaviour of diamond, graphite and carbon which have been outgassed in vacuo . With carbon and graphite the friction rises to a high value when the surface films normally present are removed by outgassing. A small pressure of oxygen or water vapour restores the friction to its normal value. These results may be compared with Savage’s observations on the wear of graphite. This change is reversible on pumping out without heating, suggesting that a major factor is the physical adsorption of surface films. The friction of diamond surfaces in air is low, but on removing the surface films in vacuo it rises to a high value and the shear strength of the junction is comparable with the bulk strength of diamond. Large-scale seizure does not occur as with outgassed metals, since the deformation in the region of contact is elastic and the area of contact remains small. If the diamond slides on a metal such as platinum so that plastic deformation is possible, the area of contact becomes large and the friction is correspondingly increased.

Friction of clean metals and the influence of adsorbed films

1951 ◽  
Vol 208 (1094) ◽  
pp. 311-325 ◽  
Keyword(s):  
Room Temperature ◽  
Physical Adsorption ◽  
Surface Films ◽  
Metallic Contact ◽  
Adsorbed Films ◽  
Real Area Of Contact ◽  
Molecular Layers ◽  
Very High ◽  
Frictional Behaviour ◽  
Real Area

An experimental Study has been made of the frictional behaviour of thoroughly degassed metal surfaces. An apparatus is described, in which friction can be measured at any desired temperature up to 1200° C or more, either in vacuo or in a particular gas. It is found that when sufficiently clean metals are allowed to touch, even at room temperature, complete seizure occurs. Over the real area of contact the specimens adhere with the bulk strength of the metal, and this area increases greatly with continued sliding or attempted sliding. Various gases and vapours have been adsorbed on to the clean specimens, and their in­fluences on friction determined. These specific contaminants are most effective as lubricants where they can react with the metal to form a solid and chemically attached film which is several molecular layers in thickness. Otherwise the friction remains very high, although seizure is prevented. It is shown that physical adsorption may occur in addition, with a significant reduction in the friction. The results support the view that the friction of metals is due mainly to adhesion at the points of real contact, and is governed by the extent to which even the thinnest of surface films can reduce this metallic contact.

Introduction to the discussion: the mechanism of friction

1952 ◽  
Vol 212 (1111) ◽  
pp. 440-449 ◽  
Keyword(s):  
Large Scale ◽  
Surface Films ◽  
Local Pressure ◽  
Large Measure ◽  
Thermo Electric ◽  
The Real ◽  
Real Area Of Contact ◽  
Rough Approximation ◽  
Local Surface Temperature ◽  
Real Area

The application of the electron microscope, and of metallurgical, interferometric and other physical methods, shows that even carefully polished or cleaved surfaces have irregularities on them which are large compared with molecular dimensions. When two solids are placed together, the real area of contact is very small, so that the local pressure is high and, in general, exceeds the yield pressure, p m , of the metal. Plastic flow of the solid occurs at the summits of the irregularities so that the real area of contact A is proportional to the applied load W , i.e. A = W / p m . There is adhesion at these local regions of contact and the friction is, in a large measure, the force required to shear them. As a rough approximation F = As , where s is the shear strength of the junctions. Since A is proportional to W and independent of the size of the surfaces, this can explain the classical laws of friction. The mechanism of this process has been studied by optical and metallurgical methods and by the use of artificially radioactive metals. The strength and nature of the adhesion between metals is profoundly influenced by the oxide films which are normally present on them. It is the presence of these films which enables sliding to occur. If these surface films are removed in high vacuo and naked metals are placed in contact, there is strong adhesion—an attempt to slide them may cause further plastic deformation with consequent increase in the area of contact—and a large-scale ‘cold welding’ of the metals. If the sliding speed is appreciable, the temperature at the local points of rubbing contact will be raised. These surface temperatures have been measured by a thermo-electric method, by a visual or photographic method and by the use of an infra-red cell. All three methods give similar results and show that even at moderate speeds the local surface temperature may easily exceed 1000° C. It is limited by the melting of the metal. These high temperatures play an important part in polishing, the formation of the Beilby layer, the machining of metals and a number of other physical processes. Some low-friction materials are also described.

scholarly journals Quantification of Bolt Tension by Surface Acoustic Waves: An Experimentally Verified Simulation Study

Acoustics ◽  
2019 ◽  
Vol 1 (4) ◽  
pp. 794-807 ◽  
Author(s):  
Alhazmi ◽  
Guldiken
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Surface Acoustic Waves ◽  
Bolted Joint ◽  
Civil Infrastructures ◽  
Reflected Wave ◽  
Real Area Of Contact ◽  
Central Hypothesis ◽  
Good Agreement ◽  
Real Area

Quantifying bolt tension and ensuring that bolts are appropriately tightened for large-scale civil infrastructures are crucial. This study investigated the feasibility of employing the surface acoustic wave (SAW) for quantifying the bolt tension via finite element modeling. The central hypothesis is that the real area of contact in a bolted joint increases as the tension or preload is increased, causing an acoustical signature change. The experimentally verified 3-D simulations were carried out in two steps: A preload was first applied to the bolt body to simulate the realistic behavior of bolted joint; and the SAW propagation was then excited on the top surface of the plate to reflect from the bolted joint. The bolt tension value was varied between 4 and 24 kN (properly tightened bolt) in the steps of 4 kN to study the effect of the bolt tension. The results indicate an increased reflected wave amplitude and a gradual phase shift, up to 0.5 µs, as the bolt tension increased. Furthermore, the result shows that the distance between the first reflected wave and the source becomes shorter as the preload increases, as hypothesized. A 1.9 mm difference in the distance between the maximum and minimum preload was observed. As part of this study, the simulation results were also compared with the experimental results, and a good agreement between the simulation and experiments was demonstrated.

The friction and transfer of polytetrafluoroethylene

1964 ◽  
Vol 281 (1384) ◽  
pp. 49-61 ◽  
Keyword(s):  
Interference Microscopy ◽  
Viscous Force ◽  
Low Friction ◽  
Oriented Crystal ◽  
Rate Dependent ◽  
High Speeds ◽  
Strong Adhesion ◽  
Small Change ◽  
Frictional Behaviour ◽  
Poor Adhesion

Earlier work has shown that the friction of polytetrafluoroethylene ( PTFE ) increases with increasing velocity and decreases with rise of temperature as though a relaxation process were involved. A study by microscopy, interference microscopy and electron microscopy of the friction tracks formed when PTFE slides on itself or on ‘clean’ glass shows that there are basically two friction regimes. At high speeds or low temperatures the friction is high ( μ , = 0.07 to 0.3) and there is fairly massive transfer and movement of polymer. The details depend on the sliding conditions but in general the transfer is in the form of lumps, ribbons or sheets, the thickness generally exceeding a few tenths of a micrometre. At low speeds and moderate temperatures a very different behaviour is observed: the friction is low ( μ < 0.07) and a thin film of PTFE is laid down or drawn over the surfaces. This film may show strong adhesion to the surfaces if they are clean. It is very fibrous and has a thickness varying between about 100 and 400 Å; in addition it has a highly oriented crystal structure. The low friction under these conditions is not due to poor adhesion but to easy shear of relevant units of the PTFE crystal. As the speed of sliding is increased or the temperature diminished the viscous force to shear the film increases until a stage is reached where the shear force exceeds the strength of the boundaries between crystals or grains. The higher friction is then accompanied by the transfer of relatively large fragments of PTFE . These two régimes in the frictional behaviour may thus be interpreted in terms of a relaxation time for intra-crystalline flow. The small change in friction at higher speeds suggests that the shear of larger units within the polymer is not appreciably rate dependent.

scholarly journals Friction of Metals: A Review of Microstructural Evolution and Nanoscale Phenomena in Shearing Contacts

2021 ◽  
Vol 69 (4) ◽  
Author(s):  
Michael Chandross ◽  
Nicolas Argibay
Keyword(s):  
Shear Strength ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Low Friction ◽  
Friction Behavior ◽  
Important Conclusion ◽  
Fundamental Properties ◽  
Wide Range ◽  
Boundary Sliding ◽  
Metal Interfaces

AbstractThe friction behavior of metals is directly linked to the mechanisms that accommodate deformation. We examine the links between mechanisms of strengthening, deformation, and the wide range of friction behaviors that are exhibited by shearing metal interfaces. Specifically, the focus is on understanding the shear strength of nanocrystalline and nanostructured metals, and conditions that lead to low friction coefficients. Grain boundary sliding and the breakdown of Hall–Petch strengthening at the shearing interface are found to generally and predictably explain the low friction of these materials. While the following is meant to serve as a general discussion of the strength of metals in the context of tribological applications, one important conclusion is that tribological research methods also provide opportunities for probing the fundamental properties and deformation mechanisms of metals.

Analysis of the Real Area of Contact Between a Polymeric Magnetic Medium and a Rigid Surface

1984 ◽  
Vol 106 (1) ◽  
pp. 26-34 ◽  
Author(s):  
Bharat Bhushan
Keyword(s):  
Complex Modulus ◽  
Critical Value ◽  
Computer Applications ◽  
Hard Material ◽  
Rigid Surface ◽  
Magnetic Medium ◽  
The Real ◽  
Real Area Of Contact ◽  
The Mean ◽  
Real Area

The statistical analysis of the real area of contact proposed by Greenwood and Williamson is revisited. General and simplified equations for the mean asperity real area of contact, number of contacts, total real area of contact, and mean real pressure as a function of apparent pressure for the case of elastic junctions are presented. The critical value of the mean asperity pressure at which plastic flow starts when a polymer contacts a hard material is derived. Based on this, conditions of elastic and plastic junctions for polymers are defined by a “polymer” plasticity index, Ψp which depends on the complex modulus, Poisson’s ratio, yield strength, and surface topography. Calculations show that most dynamic contacts that occur in a computer-magnetic tape are elastic, and the predictions are supported by experimental evidence. Tape wear in computer applications is small and decreases Ψp by less than 10 percent. The theory presented here can also be applied to rigid and floppy disks.

Human Joint Performance and the Roughness of Articular Cartilage

1980 ◽  
Vol 102 (1) ◽  
pp. 50-56 ◽  
Author(s):  
T. R. Thomas ◽  
R. S. Sayles ◽  
I. Haslock
Keyword(s):  
Articular Cartilage ◽  
Heel Strike ◽  
Height Distribution ◽  
Normal Walking ◽  
Cartilage Surface ◽  
Real Area Of Contact ◽  
The Mean ◽  
Human Joints ◽  
Human Joint ◽  
Real Area

It is known that the surface of articular cartilage is rough and it has been suggested that this is likely to affect the lubrication of human joints. This paper describes the direct measurement of a cartilage surface with a stylus instrument. It is found that the height distribution is Gaussian with an inverse-square power spectrum. It is thus possible to calculate the elastic deflection of the surface under normal walking loads and it is shown that the mean separation of the cartilage surfaces in a human joint varies rather slowly with load. In one particular hip joint at heel strike the real area of contact was calculated to be about 1.3 cm2, the mean gap to be about 60 μm and the trapped volume to be about 80 percent of that when standing.

scholarly journals Basic Mechanical Parameter Relations of Soft Clay in Pearl River Delta

2014 ◽  
Vol 8 (1) ◽  
pp. 320-325 ◽  
Author(s):  
Zhangming Li ◽  
Na Qi ◽  
Zhibin Masumi ◽  
Weidi Lin
Keyword(s):  
Shear Strength ◽  
Pearl River Delta ◽  
Large Scale ◽  
Soft Clay ◽  
River Delta ◽  
Pearl River ◽  
Cylindrical Cavity Expansion ◽  
In Situ Data ◽  
The Pearl River

Basic parameters relations among CPT parameters, un-drained strength and other mechanical parameters of soft clay are presented based on an elastic-plastic solution for cylindrical cavity expansion for soil investigation in energy engineering. The relation between CPT parameters and shear strength from vane test is also presented based on the result. Thus, the CPT parameters can be determined directly by elastic parameters and shear strength or vane shear parameters and vice versa. That makes it possible to save the high test costs and provide theoretical formulas to avoid some tests which are limited due to the site and/or other condition. Results are compared between the relations and in situ data at a large-scale project in the Pearl River Delta. The results showed consistency between the relation and in situ data.

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