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TL;DR: In this article, the authors proposed a new theory of elastic contact, which is more closely related to real surfaces than earlier theories, and showed how the contact deformation depends on the topography of the surface, and established the criterion for distinguishing surfaces which touch elastically from those which touch plastically.
Abstract: It is usually assumed that the real area of contact between two nominally flat metal surfaces is determined by the plastic deformation of their highest asperities. This leads at once to the result that the real area of contact is directlyproportional to the load and independent of the apparent area-a result with many applications in the theories of electric contacts and friction. Archard pointed out that plastic deformation could not be the universal rule, and introduced a model which showed that, contrary to earlier ideas, the area of contact could be proportional to the load even with purely elastic contact. This paper describes a new theory of elastic contact, which is more closely related to real surfaces than earlier theories. We show how the contact deformation depends on the topography of the surface, and establish the criterion for distinguishing surfaces which touch elastically from those which touch plastically. The theory also indicates the existence of an 'elastic contact hardness', a composite quantity depending on the elastic properties and the topography, which plays the same role in elastic contact as the conventional hardness does in plastic contact. A new instrument for measuring surface topography has been built; with it the various parameters shown by the theory to govern surface contact can be measured experimentally. The typical radii of surface asperities have been measured. They were found, surprisingly, to be orders of magnitude larger than the heights of the asperities. More generally we have been able to study the distributions of asperity heights and of other surface features for a variety of surfaces prepared by standard techniques. Using these data we find that contact between surfaces is frequently plastic, as usually assumed, but that surfaces which touch elastically are by no means uncommon in engineering practice.
5,371 citations
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TL;DR: In this article, the Hertzian theory of elastic contact between spheres is extended by considering one of the spheres to be rough, so that contact occurs, as in practice, at a number of discrete microcontacts.
Abstract: The Hertzian theory of elastic contact between spheres is extended by considering one of the spheres to be rough, so that contact occurs, as in practice, at a number of discrete microcontacts. It is found that the Hertzian results are valid at sufficiently high loads, but at lower loads the effective pressure distribution is much lower and extends much further than for smooth surfaces. The relevance to the physical-contact theory of friction and electric contact is considered.
644 citations
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TL;DR: In this paper, a method of finding the resistance of a cluster of micro-contacts is derived, and it is shown that the resistance may be regarded as the sum of the parallel resistance of the microcontacts and an interaction term often related to the extent of the cluster and not to the number or size of individual contacts.
Abstract: The relation between the area of contact and the constriction resistance which holds for a single circular contact spot is widely used in electric contact theory, although the normal mode of contact is by a large number of microcontacts. A method of finding the resistance of a cluster of microcontacts is derived, and it is shown that the resistance may be regarded as the sum of the parallel resistance of the microcontacts and an interaction term often related to the extent of the cluster and not to the number or size of the individual contacts. The resistance is often close to that found by assuming that the entire area covered by the cluster is a single conducting spot. The known agreement between areas of contact found from resistance measurements and by other methods is therefore puzzling - until it is realized that the other methods also give only an apparent area: the real area of contact in, for example, a Brinell indentation is a small fraction of the area of the indentation. Thus from the point of view of electric contact theory the system is self-consistent, although the real area of contact is now seen to play no part in it: the implications for the theory of friction are more profound.
568 citations
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02 May 1995TL;DR: In this article, a tool with a battery, an electrical motor, and a control system has a trigger control that connects the battery to a timer and a voltage monitor, and when the user is not actuating the user actuated switch, the timer can supply electricity to the control system.
Abstract: A tool with a battery, an electrical motor, and a control system. The control system has a trigger control that connects the battery to a timer and a voltage monitor. The trigger control has a user actuated switch and a timer actuated switch. At the end of a tool operational cycle, when the user is not actuating the user actuated switch, the timer actuated switch can supply electricity to the control system. After a predetermined period of time, the timer actuated switch can then automatically electrically disconnect the control system from the battery to conserve battery power.
375 citations
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TL;DR: In this paper, an energy-balance argument is used to obtain dimensionless relations between the load, separation, and degree of contact, in terms of the height distribution of the surface.
Abstract: The treatment of plastic contact developed in this paper is based on three physical observations: that the total volume of metal is not changed by plastic deformation; that the mean indentation pressure is a well-defined material constant applicable to the whole range of likely asperity shapes; and that the displaced material reappears as a uniform rise in the non-contacting surface. An energy-balance argument is used to obtain dimensionless relations between the load, separation, and degree of contact, in terms of the height distribution of the surface. A fourth observation is then added: that the height distributions of many engineering surfaces are, to a good approximation, Gaussian. The relations are worked out in detail for this height distribution and compared with experimental observations. The treatment accurately predicts the behaviour up to extremely high loads; and accounts for the remarkable persistence of asperities on rough surfaces in plastic contact. The argument, and the main supporting experiments, were conceived in terms of the contact of a uniformly loaded nominally flat surface, but the extention to local indentations is quite straightforward. It is shown that for local indentations in homogeneous bodies the real area of contact is always one half of the nominal area. This unexpected result is in fact accurately confirmed by experiment. The treatment also discusses the effect of a hard or soft surface layer on the indented body, and again the predictions are supported by practical measurements.
341 citations
Authors
Showing all 266 results
Name | H-index | Papers | Citations |
---|---|---|---|
J. A. Greenwood | 24 | 31 | 8591 |
Rocco J. Noschese | 17 | 35 | 880 |
Heinz Piorunneck | 8 | 11 | 336 |
Glenn M. Friedman | 7 | 13 | 139 |
Richard Chadbourne | 7 | 10 | 111 |
James D. Anderson | 6 | 18 | 112 |
Irving F Matthysse | 6 | 15 | 114 |
Urs F. Nager | 6 | 8 | 159 |
Lazar Michael | 6 | 7 | 64 |
Schrader Gary E | 5 | 9 | 91 |
Gennaro L. Pecora | 5 | 7 | 107 |
John C. Collier | 5 | 8 | 101 |
Raymond C. Logue | 5 | 5 | 221 |
Edward S Raila | 5 | 10 | 63 |
Neil P. Ferraro | 5 | 7 | 129 |