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David Tabor

Bio: David Tabor is an academic researcher from University of Cambridge. The author has contributed to research in topics: Lubrication & Indentation hardness. The author has an hindex of 59, co-authored 172 publications receiving 20321 citations. Previous affiliations of David Tabor include Council for Scientific and Industrial Research & SRI International.


Papers
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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, it is shown that surface roughness can greatly reduce the adhesion between soft elastic solids and shows the importance of combining concepts of surface forces (or surface energies) with the principles of contact mechanics.

1,199 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe a study of the adhesion between elastic solids and the effect of roughness on their adhesion, showing that roughness which is small compared with the overall deformation occurring at the region of the rubber-Perspex contact can produce an extremely large reduction in adhesion.
Abstract: This paper describes a study of the adhesion between elastic solids and the effect of roughness in reducing the adhesion. The experiments were carried out between optically smooth rubber spheres and a hard smooth flat surface of Perspex which could be roughened to various degrees. The radius of the rubber spheres was varied by a factor of 8, their elastic modulus by a factor of 10, while the centre line average (c.l.a.)of the roughened Perspex surface was varied from 0.12 to 1.5 μm. The results show that c.l.a. roughnesses which are small compared with the overall deformation occurring at the region of the rubber-Perspex contact can produce an extremely large reduction in adhesion. The effect is more marked for rubbers of higher modulus. On the other hand the curvature of the sphere (over the range examined) has little influence. For this reason and because the analytical problem of a sphere on a rough flat is extremely complicated a theoretical analysis has been developed for the simpler case of a smooth flat in contact with a rough flat surface. As in Greenwood & Williamson (1966) the rough surface is modelled by asperities all of the same radius of curvature and with heights following a Gaussian distribution of standard deviation σ. The overall contact force is obtained by applying the contact theory of Johnson, Kendall & Roberts (1971) to each individual asperity. The theory predicts that the adhesion expressed as a fraction of the maximum value depends upon a single parameter, 1/Δ e ,which is the ratio between a and the elastic displacement δ C that the tip of an asperity can sustain before it pulls off from the other surface. The analysis shows that the adhesion parameter may also be regarded as representing the statistical average of a competition between the compressive forces exerted by the higher asperities trying to prize the surfaces apart and the adhesive forces between the lower asperities trying to hold the surfaces together. Although the theory is derived for two nominally plane surfaces it is found to fit the experimental results for a sphere on a flat reasonably well.

838 citations

Journal ArticleDOI
TL;DR: In this article, a direct measurement of the forces in air between two cylindrical sheets of mica arranged with their axes mutually at right angles is made using multiple beam interferometry using fringes of equal chromatic order.
Abstract: A direct measurement has been made of the forces in air between two cylindrical sheets of mica arranged with their axes mutually at right angles. The contact resembles that between a sphere and a flat. The mica sheets are glued to glass formers, their concave face being first slightly silvered. The contact region and the distance of approach are measured by multiple beam interferometry using fringes of equal chromatic order (f. e. c. o.). This gives an accuracy for the distances between the surfaces of ± 0.3 nm. Since the surfaces are molecularly smooth it is possible to bring them very close to one another. One surface is held on a rigid support, the other on a light cantilever beam. The surfaces are slowly brought together and at a critical separation ‘flick’ together. The ‘flick’ distance depends on the stiffness of the cantilever and this in turn provides a direct measure of the surface forces. By using cantilevers of different stiffnesses the method has proved effective for separations ranging from 5 to 30 nm. The results show that for separations less than about 10 nm the forces operating are ‘normal’ van der Waals forces whilst for distances greater than 20 nm they are ‘retarded’ van der Waals forces.

668 citations

Journal ArticleDOI
TL;DR: In this article, a simple theory of hardness is given, based on the theoretical work of Hencky and Ishlinsky, which explains a number of empirical relations observed in dynamic hardness measurements, and reproduces the calibration characteristics of the rebound scleroscope.
Abstract: When a hard spherical indenter is pressed into the surface of a softer metal, plastic flow of the metal specimen occurs and an indentation is formed. When the indenter is removed it is found that the permanent indentation is spherical in shape, but that its radius of curvature is greater than that of the indenter. It is generally held that this 'shallowing' effect is due to the release of elastic stresses in the material around the indentation. It is clear that if the recovery is truly elastic it should be reversible and that a second application and removal of the indenter under the original load should not change the size or shape of the indentation. Experiments show that this is the case. This means that when the original load is reapplied, the deformation of the indenter and the recovered indentation is elastic and should conform with Hertz's equations for the elastic deformation of spherical surfaces. Measurements show that there is, in fact, close agreement between the observed deformation and that calculated from Hertz's equations. These results have been applied to the case of indentations formed in a metal surface by an impacting indenter. The energy involved in the elastic recovery of the impacting surfaces is found to account for the energy of rebound of the indenter. This analysis explains a number of empirical relations observed in dynamic hardness measurements, and, in particular, reproduces the calibration characteristics of the rebound scleroscope. The results also show that for very soft metals the dynamic hardness is very much higher than the static hardness, and it is suggested that in rapid deformation of soft metals, forces of a quasi-viscous nature are involved. In the third part of the paper a simple theory of hardness is given, based on the theoretical work of Hencky and Ishlinsky. It is shown experimentally that for a material incapable of appreciable work-hardening, the mean pressure P$\_{m}$ required to produce plastic yielding is related to the elastic limit Y of the material by a relation P$\_{m}$ = cY, where c is a constant having a value between 2$\cdot $6 and 3. An empirical method is described which takes into account the work-hardening produced in metals by the indentation process itself. This results in a general relation between hardness measurements and the stress-strain characteristic of the metal, and there is close agreement between the theory and the observed results. In addition, the theory explains the empirical laws of Meyer.

560 citations


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Journal ArticleDOI
TL;DR: In this paper, the authors used a Berkovich indenter to determine hardness and elastic modulus from indentation load-displacement data, and showed that the curve of the curve is not linear, even in the initial stages of the unloading process.
Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.

22,557 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of surface energy on the contact between elastic solids is discussed and an analytical model for its effect upon the contact size and the force of adhesion between two lightly loaded spherical solid surfaces is presented.
Abstract: This paper discusses the influence of surface energy on the contact between elastic solids. Equations are derived for its effect upon the contact size and the force of adhesion between two lightly loaded spherical solid surfaces. The theory is supported by experiments carried out on the contact of rubber and gelatine spheres.

6,981 citations

Journal ArticleDOI
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.

5,771 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AU tip.
Abstract: Images and force measurements taken by an atomic‐force microscope (AFM) depend greatly on the properties of the spring and tip used to probe the sample’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment.

3,975 citations

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