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J. A. Greenwood

Bio: J. A. Greenwood is an academic researcher from University of Cambridge. The author has contributed to research in topics: Surface roughness & Contact area. The author has an hindex of 1, co-authored 1 publications receiving 1290 citations.

Papers
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01 Jun 1970
TL;DR: In this article, the authors give a general theory of contact between two rough plane surfaces and show that the important results of the previous models are unaffected: in particular, the load and the area of contact remain almost proportional, independently of the detailed mechanical and geometrical properties of the asperities.
Abstract: Most models of surface contact consider the surface roughness to be on one of the contacting surfaces only. The authors give a general theory of contact between two rough plane surfaces. They show that the important results of the previous models are unaffected: in particular, the load and the area of contact remain almost proportional, independently of the detailed mechanical and geometrical properties of the asperities. Further, a single-rough-surface model can always be found which will predict the same laws as a given two-rough-surface model, although the required model may be unrealistic. It does not seem possible to deduce the asperity shape or deformation mode from the load-compliance curve.

1,435 citations


Cited by
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TL;DR: In this paper, the authors present the techniques, advances, problems and likely future developments in numerical modelling for rock mechanics and discuss the value that is obtained from the modelling, especially the enhanced understanding of those mechanisms initiated by engineering perturbations.

976 citations

Journal ArticleDOI
TL;DR: In this article, an elastic-plastic asperity microcontact model for contact between two nominally flat surfaces is presented, where the transition from elastic deformation to fully plastic flow of the contacting as perity is modeled based on contact-mechanics theories in conjunction with the continuity and smoothness of variables across different modes of deformation.
Abstract: This paper presents an elastic-plastic asperity microcontact model for contact between two nominally flat surfaces. The transition from elastic deformation to fully plastic flow of the contacting asperity is modeled based on contact-mechanics theories in conjunction with the continuity and smoothness of variables across different modes of deformation. The relations of the mean contact pressure and contact area of the asperity to its contact interference in the elastoplastic regime of deformation are respectively modeled by logarithmic and fourth-order polynomial functions. These asperity-scale equations are then used to develop the elastic-plastic contact model between two rough surfaces, allowing the mean surface separation and the real area of contact to be calculated as functions of the contact load and surface plasticity index. Results are presented for a wide range of contact load and plasticity index, showing the importance of accurately modeling the deformation in the elastoplastic transitional regime of the asperity contacts. The results are also compared with those calculated by the GW and CEB models, showing that the present model is more complete in describing the contact of rough surfaces.

638 citations

Journal ArticleDOI
TL;DR: In this paper, a finite element study of elasto-plastic hemispherical contact is presented, and the results are normalized such that they are valid for macro contacts (e.g., rolling element bearings), although micro-scale surface characteristics such as grain boundaries are not considered.
Abstract: This work presents a finite element study of elasto-plastic hemispherical contact. The results are normalized such that they are valid for macro contacts (e.g., rolling element bearings) and micro contacts (e.g., asperity contact), although micro-scale surface characteristics such as grain boundaries are not considered. The material is modeled as elastic-perfectly plastic. The numerical results are compared to other existing models of spherical contact, including the fully plastic truncation model (often attributed to Abbott and Firestone) and the perfectly elastic case (known as the Hertz contact). This work finds that the fully plastic average contact pressure, or hardness, commonly approximated to be a constant factor of about three times the yield strength, actually varies with the deformed contact geometry, which in turn is dependent upon the material properties (e.g., yield strength). The current work expands on previous works by including these effects and explaining them theoretically. Experimental and analytical results have also been shown to compare well with the current work. The results are fit by empirical formulations for a wide range of interferences (displacements which cause normal contact between the sphere and rigid flat) and materials for use in other applications.

558 citations

Journal ArticleDOI
TL;DR: In this article, the effect of the mode of deformation on the value of thermal conductance of flat surfaces in contact has been investigated and explicit expressions for thermal contact conductance were derived for cases of: (1) pure plastic deformation (2) plastic deformations of the asperities and elastic deformation of the substrate, and (3) pure elastic deformations on the substrate.

519 citations

01 Jan 2014
TL;DR: In this article, a new numerical approach that is simple and robust, capable of handling three-dimensional measured engineering rough surfaces moving at different rolling and sliding velocities is presented.
Abstract: contacts is presented in this paper, using a new numerical approach that is simple and robust, capable of handling three-dimensional measured engineering rough surfaces moving at different rolling and sliding velocities. The equation system and the numerical procedure are unified for a full coverage of all the lubrication regions including the full film, mixed and boundary lubrication. In the hydrodynamically lubricated areas the Reynolds equation is used. In the asperity contact areas, where the film thickness is zero, the Reynolds equation is reduced to an expression equivalent to the mathematical description of dry contact problem. In order to save computing time, a multi-level integration method is used to calculate surface deformation. Sample cases under severe condition show that this approach is capable of analyzing different cases in a full range of l ratio, from infinitely large down to nearly zero (less than 0.03).

430 citations