The Static Coefficient of Friction and the Area of Contact

Parker, Ronald A.; Hatch, D. R.

doi:10.1088/0370-1301/63/3/305

Cited by 83 publications

(37 citation statements)

References 14 publications

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“…The contact model of such a sphere with radius R can be seen in figure 1, where the contact area, A, its radius a, and interference x correspond to a contact load P. Likewise, several experimental works were performed on a single spherical contact under normal loading by a rigid flat [9][10][11][12][13][14][15]. However, of these few works only Refs.…”

Section: Introductionmentioning

confidence: 99%

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In situ investigation of the contact area in elastic–plastic spherical contact during loading–unloading

et al. 2006

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The real contact area between a sphere and a flat during loading, unloading, and cyclic loading-unloading in the elastic-plastic regime of deformations was investigated experimentally. A direct optical technique was used to observe in situ the evolution of the contact area. The experimental results obtained with copper and stainless steel spheres of different diameters that were pressed against a sapphire flat were compared with existing theoretical models, and whenever possible, with previous experimental works. These models are based on the assumption of either perfect slip (i.e., frictionless) or full stick contact condition. Good agreement was found between the experimental and theoretical results for the contact area and mean contact pressure. The existing models for the unloading process fail to accurately predict the residual radius of curvature of fully unloaded spheres, and the irreversibility of multiple loading unloading cycles at least for the several initial cycles. Some recommendations to improve the models are provided.

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Section: Introductionmentioning

confidence: 99%

“…However, of these few works only Refs. [11][12][13] deal with the elastic-plastic regime of deformations, whereas Refs. [9,10] are limited to elastic deformations and Refs.…”

Section: Introductionmentioning

confidence: 99%

In situ investigation of the contact area in elastic–plastic spherical contact during loading–unloading

et al. 2006

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“…Perhaps the first publication on discrete optical measurement of single spherical contact is from 1950 by Parker and Hatch [8]. The contact area images at various normal loads were still photographed on film through a microscope at regular discrete increments of tangential loading until gross sliding begun.…”

Section: Introductionmentioning

confidence: 99%

“…The experimental system is similar to that employed in [8]. The contact images were still photographed throughout a microscope and analyzed graphically taking into consideration non-contact areas within the contact zone.…”

Section: Introductionmentioning

confidence: 99%

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A novel test rig for in situ and real time optical measurement of the contact area evolution during pre-sliding of a spherical contact

et al. 2006

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An experimental test rig was developed in order to investigate elastic-plastic single micro-spherical contact under combined normal and tangential loading. This novel apparatus allows in situ and real time direct optical measurement of the real contact area (RCA) evolution in pre-sliding. It also allows relative displacement measurements under very low rates of tangential loading (down to 0.01 N/s) to capture accurately the fine details at sliding inception. This is achieved by piezoelectric actuation in closed loop feedback control in addition to synchronization with data and image acquisition to obtain real time measurement. The RCA measurement is realized by direct optical observation technique, whereas two different image processing algorithms were implemented for the elastic and the elastic-plastic contact regimes. The various features and capabilities of the test rig are presented along with some preliminary experimental results of RCA and friction behavior to assess its performance.

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Friction and deformation of nylon. I. Experimental

Adams¹

1963

J of Applied Polymer Sci

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An apparatus which permits the simultaneous measurement of kinetic friction and contact area between polymer hemispheres and a smooth glass surface has been used to study the dependence of friction and contact area on load, specimen radius, sliding speed, and loading time. Hemispherical nylon 610 specimens of radii 0.12–0.58 cm. have been used with loads of 0.7–200 g. and sliding speeds from 10−7 to 3 × 10−2 cm./sec. All measurements were performed in air at 20°C. and 66% r.h. The contact area was estimated from optical interference fringes (Newton's rings) between the surface of the specimen and that of the glass plate, by means of a theoretical expression, experimentally verified, for the shape into which an elastic hemisphere is deformed when pressed against a rigid plane. The contact area was negligibly affected in size or shape by the presence of the tangential force of friction, in accord with the theory for the contact of elastic spheres. The deformations of the specimens were, within experimental error, completely recoverable but depended on the time of loading. The effects of changes in the four variables, load, radius, speed, and time were found to be essentially independent. Subsidiary experiments showed that both friction and contact area increased by about 10% for each factor‐of‐10 increase in loading time in the range 5–1000 sec. and that friction increased by a factor of 3 as sliding speed increased from 10−7 to 3 × 10−2 cm./sec. The main series of measurements (at constant sliding speed and loading time) showed that the dependence on load W of both the contact area A and the friction F could well be represented by the expressions: A = βWm and F = αWn (where α and β were constants for a given specimen). The values of m and n were almost independent of specimen radius and their mean values, for 15 specimens, were 0.708 ± 0.006 and 0.781 ± 0.012, respectively. The difference between these values, 0.073 ± 0.013, is statistically highly significant and in the following paper is interpreted as implying that the friction per unit area of true contact between nylon and glass increases with pressure. The dependence of A on the specimen radius R (which is included in β) was found to be as R0.576. The value of this index of R and the value of m are both consistent with a power‐law dependence of mean contact pressure on deformation (measured by the ratio of contact to specimen radius) with index 0.82. The values of α for specimens of the same radius showed too much variation for a useful estimate of the dependence of F on R to be obtained.

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The Static Coefficient of Friction and the Area of Contact

Cited by 83 publications

References 14 publications

In situ investigation of the contact area in elastic–plastic spherical contact during loading–unloading

In situ investigation of the contact area in elastic–plastic spherical contact during loading–unloading

A novel test rig for in situ and real time optical measurement of the contact area evolution during pre-sliding of a spherical contact

Friction and deformation of nylon. I. Experimental

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