Contact area

About: Contact area is a research topic. Over the lifetime, 12358 publications have been published within this topic receiving 256401 citations. The topic is also known as: contact patch & contact region.

Measurements of and Relation Between the Adhesion and Friction of Two Surfaces Separated by Molecularly Thin Liquid Films

Abstract: A new technique is described for sliding (shearing) two molecularly smooth surfaces laterally past each other in liquids while monitoring their exact contact area, the normal and transverse forces, and the surface separation. First, we show that the elastic deformations of two initially curved surfaces in adhesive contact are the same under static and dynamic (i.e., sliding) conditions. Detailed results are then presented of how the shear properties of thin films of water and a simple nonpolar liquid are “quantized” with the number of layers. Results with water as the intervening liquid, as well as the effects of humidity on sliding in air, reveal that more complex mechanisms are operating than with simple liquids which appear to be related to the complex “hydration” forces between two surfaces in water or in aqueous salt solutions. The results suggest a close correlation between the static forces and shear properties of very thin liquid films, and the molecular structure of the liquids confined within such films.

Thermoelastic Instabilities in the Sliding of Comforming Solids

Abstract: If two sliding solids are nominally in contact over a large area, the inevitable irregularities in the surfaces will cause the pressure distribution to be non-uniform. The generation of heat due to friction at the interface will also be non-uniform and the solids will be distorted by thermal expansion. The highest parts of the surface will carry the greatest pressure, reach the highest temperature and consequently expand more than the surroundings. Thus the thermal distortion tends to exaggerate the initial irregularity of the surface. The wear at the interface has the opposite effect, but under suitable conditions the process can be unstable. Experiments are described in which the effects of this instability are observed: the load is concentrated into a few small parts of the surface causing high local temperatures. After a few seconds, the load is transferred to a new part of the surface and, when the original contact area has returned to the temperature of the surroundings, it contracts leaving an observable depression in the surface. The scale of this process is large in comparison with the size of the surface asperities. An experimental model has been produced which demonstrates the characteristics of the instability in a simplified form. The thermal expansion drives the surfaces apart at the beginning of the cycle and this movement has been observed experimentally. An analysis of the instability is produced and a good correlation is obtained with experiment.

The mechanics of adhesion of viscoelastic solids

Abstract: The experimental study of adhesion between common solids is bedevilled by the fad that, with exception of cleaved mica, inevitable roughness of the surfaces is greater than the range of surface forces. A new situation arose with the technique of casting low-modulus rubber with an optically smooth surface. When placed in contact with each other, or with a smooth hard surface like plate glass, such specimens are sufficiently compliant to make intimate contact throughout the whole of their apparent contact area. High adhesion is then observed; in fact the measured force required to separate the surfaces is generally greatly in excess of that which would be expected from the action of surface forces alone. The measured force of adhesion is found to depend on the rate of separation and to correlate with the viscoelastic properties of the rubber. The present state of knowledge of this phenomenon is reviewed and the mechanics of the process whereby the viscoelastic properties of the solids amplify their...