ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
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.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1963.070070610
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