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Journal ArticleDOI

Contact and Rubbing of Flat Surfaces

01 Aug 1953-Journal of Applied Physics (American Institute of Physics)-Vol. 24, Iss: 8, pp 981-988
TL;DR: In this article, the authors compared the deduced dependence of the experimental observables on the load with the experimental evidence and concluded that the most realistic model is one in which increasing the load increases both the number and size of the contact areas.
Abstract: The interpretation of certain phenomena occuring at nominally flat surfaces in stationary or sliding contact is dependent on the assumed distribution of the real area of contact between the surfaces. Since there is little direct evidence on which to base an estimate of this distribution, the approach used is to set up a simple model and compare the deduced theory (e.g., the deduced dependence of the experimental observables on the load) with the experimental evidence. The main conclusions are as follows. (a) The electrical contact resistance depends on the model used to represent the surfaces; the most realistic model is one in which increasing the load increases both the number and size of the contact areas. (b) In general, mechanical wear should also depend on the model. However, in wear experiments showing the simplest behavior, the wear rate is proportional to the load, and these results can be explained by assuming removal of lumps at contact areas formed by plastic deformation; moreover, this particular deduction is independent of the assumed model. This suggests that a basic assumption of previous theories, that increasing the load increases the number of contacts without affecting their average size, is redundant.
Citations
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Book
25 Jan 1991
TL;DR: The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws -producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events.
Abstract: This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

3,802 citations

Journal ArticleDOI
01 Nov 2000-Wear
TL;DR: In this article, the authors discuss the concept of nanocomposite coatings with high hardness and low elastic modulus, which can exhibit improved toughness, and are therefore better suited for optimising the wear resistance of real industrial substrate materials (i.e., steels and light alloys, with similarly low moduli).

2,252 citations

Journal ArticleDOI
TL;DR: The potential of wear-Mechanism diagrams is explored in this paper, where the rate and the regime of dominance of dry wear mechanisms are investigated empirically and by modelling by theoretical analysis calibrated to experiment.

961 citations

Journal ArticleDOI
TL;DR: In this article, the authors focus on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets.
Abstract: One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.

877 citations

Journal ArticleDOI
01 Mar 1995-Wear
TL;DR: Most wear models and equations in the literature were analyzed as to origin, content and applicability as discussed by the authors, and no single predictive equation or group of limited equations could be found for general and practical use.

820 citations

References
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Book
01 Jan 1954
TL;DR: Tabor and Bowden as mentioned in this paper reviewed the many advances made in this field during the past 36 years and outlined the achievements of Frank Philip Bowden, and reviewed the behavior of non-metals, especially elastomers; elastohydrodynamic lubrication; and the wear of sliding surfaces.
Abstract: Originally published in 1950, this classic book was a landmark in the development of the subject of tribology. For this edition, David Tabor has written a new preface, reviewing the many advances made in this field during the past 36 years and outlining the achievements of Frank Philip Bowden. The book covers the behavior of non-metals, especially elastomers; elastohydrodynamic lubrication; and the wear of sliding surfaces, which has gradually replaced the earlier concentration on the mechanism of friction. It remains one of the most interesting and comprehensive works available on a single branch of physics.

5,834 citations

Journal ArticleDOI
TL;DR: In this article, the transition between static and kinetic conditions when stationary metal surfaces are set into motion is determined by measuring the energy that has to be given to one of the bodies to start it moving.
Abstract: Experiments have been carried out to determine the transition between static and kinetic conditions when stationary metal surfaces are set into motion, a simple method being used which measures the energy that has to be given to one of the bodies to start it moving. The method is confined to cases in which the static coefficient exceeds the kinetic. Using a load of 1 kg and metal surfaces of various kinds, it is found that the static coefficient persists for distances of the order of 10−4 cm, and then gradually falls off to values corresponding to the kinetic coefficient. This behavior is shown to be consistent with a simple model based on the assumption that the friction force is needed to shear metallic junctions formed between the metal surfaces. The action of boundary lubricants is discussed, and it is shown that they can act either by diminishing the metallic interaction directly, or by preventing its increase during the sliding process.

375 citations

Journal ArticleDOI
TL;DR: In this paper, the wear of rubbing steel surfaces as a function of load, distance of travel, and hardness under controlled conditions was measured and the effect of all factors except adhesion was analyzed.
Abstract: Careful measurements have been made of the wear of rubbing steel surfaces as a function of load, distance of travel, and hardness under controlled conditions which eliminated the effect of all factors except adhesion. At normal pressures averaged over the apparent contact area which are less than one third the hardness of the softer material the amount of wear was found to depend linearly on the distance of travel and on the load but was independent of the apparent area of contact. At average pressures greater than one third of the hardness, the depth of wear varied linearly with the distance of travel, was independent of the apparent area of contact for a given average normal stress, but increased many fold for small increases in stress. These findings rationalize the familiar observations on the running‐in of machine surfaces. The results are discussed in the light of the current adhesion theory of dry friction.

257 citations

Journal ArticleDOI
TL;DR: In this article, a study of the friction and metallic transfer between sliding metal surfaces in the absence and in the presence of boundary lubricant films has been conducted, showing that the metallic transfer consists of a relatively small number of discrete particles and that the main function of a boundary lube is to reduce the amount of metallic interaction.
Abstract: This paper describes a study of the friction and metallic transfer between sliding metal surfaces in the absence and in the presence of boundary lubricant films One surface is made radioactive and is slid over the surface of a second, non-radioactive metal, the amount of metal transferred being detected by the blackening of a photographic plate placed in contact with the second surface The results show that, in general, the metallic transfer or 'pick-up', consists of a relatively small number of discrete particles For unlubricated surfaces the pick-up is about 40 times larger for similar than for dissimilar metals, although the coefficient of friction covers a relatively small range ($\mu \approx $ 0$\cdot $4 to $\mu \approx $ 1) With well-lubricated surfaces the friction is reduced by a factor of not more than 20 ($\mu \approx $ 0$\cdot $05), whilst the 'pick-up' may be diminished by a factor of 20,000 or more A simple analysis suggests that under these conditions the welded metallic junctions formed through the lubricant film play a very small part in determining the frictional resistance to motion Consequently two lubricants possessing widely differing abilities to protect the surfaces may give essentially the same coefficient of friction The lowest friction and 'pick-up' are observed when the lubricant film is solid As the temperature is raised a marked increase in friction and 'pick-up' occurs at a temperature close to the melting-point of the film A new observation is that at a somewhat higher temperature a further deterioration in lubricating properties occurs; although the surfaces are visibly covered with lubricant, the frictional behaviour and the metallic transfer are similar to those observed with unlubricated surfaces These changes are reversible on cooling, and it is suggested that they correspond to changes in state of the lubricant film The results provide direct support for the view that the friction between metals is due largely to the formation and shearing of metallic junctions, and that the main function of a boundary lubricant is to reduce the amount of metallic interaction The investigation also shows that the metallic transfer is immensely more sensitive to changes in surface conditions than is the coefficient of friction

110 citations

Journal ArticleDOI
TL;DR: In this article, a detailed examination of the surface damage produced during sliding shows that metallic junctions are formed and sheared during the sliding process, and it is suggested that they are produced by a cold welding of the surfaces as a result of the high localized pressures developed at the points of real contact.
Abstract: Examination of the contours of the depression in a copper surface made by a cylindrical indenter shows that although considerable bulk deformation has occurred the asperities are relatively little deformed. When a similar groove is made by sliding with a hemispherical slider, there is sufficient surface damage to obliterate completely the surface irregularities. In the presence of a lubricant, similar effects are observed, though on a reduced scale. The tops of the asperities are wiped away, showing that there is considerable interaction between the metal surfaces through the lubricant film. A detailed examination of the surface damage produced during sliding shows that metallic junctions are formed and sheared during the sliding process. These junctions are formed even when the sliding speeds are so small that the temperature rise due to frictional heating is negligible, and it is suggested that they are produced by a cold welding of the surfaces as a result of the high localized pressures developed at the points of real contact. These junctions are often strong enough to rupture the stronger of the two sliding metals. Thus when copper slides on steel (unlubricated) there is not only a marked tearing out of copper fragments from the copper surface, but also a plucking of minute particles of steel out of the steel surface. Further, the shearing of metallic junctions and the smearing of metallic fragments over the surfaces may produce considerable work hardening below the actual points of contact. Although a lubricant reduces the amount of intimate metallic contact, the investigation shows that metallic junctions are formed through the lubricant film by an essentially similar mechanism. These observations provide graphic evidence for the view that the frictional force for both clean and lubricated surfaces is due mainly to the shearing of metallic junctions formed by cold welding at the points of intimate contact. The significance of these conclusions in the burnishing of metals and in the behaviuor of bearing alloys is discussed.

56 citations