Surface phenomena Tribology

Shpenkov, G.P. (1995) Friction Surface Phenomena. Tribology Series, 29. Dowson, D. (ed.), Elsevier, Amsterdam. 

Often the production of new materials such as composite materials heavily involves processes at interfaces. Thin films on surfaces are often dominated by surface effects. Examples are latex-films, coatings, and paints. The flow behavior of powders and granular media is determined by surface forces. In tribology, wear is reduced by lubrication which again is a surface phenomenon. 

The tenn tribology translates literally into the study of nibbing . In modem parlance this field is held to include four phenomena adhesion, friction, lubrication and wear. For the most part these are phenomena that occur between pairs of solid surfaces in contact with one another or separated by a thin fluid film. Adhesion describes the resistance to separation of two surfaces in contact to while friction describes their tendency to resist shearing. Lubrication is the phenomenon of friction reduction by the presence of a fluid (or solid) film between two surfaces. Finally, w>ear describes the irreversible damage or defonnation that occurs as a result of shearing or separation. 

The data of Zink et al. (1998) illustrate the measurement by NRA of near-surface composition profiles in isotopically labelled polymer blends. If a mixture of polymers is adjacent to a phase interface (e.g. a solid or an air surface), often one of the components is preferentially attracted to the surface and will segregate to it, and this phenomenon will influence the tribological behaviour the interface (lubrication, wear and adhesion). 

Virtually in all dry sliding contacts we observe that the frictional force required to initiate motion is more than that needed to maintain the surfaces in the subsequent relative sliding thus there are two values reported for the coefficient of friction. The static coefficient of friction is used in reference to the initial movement of the object from the rest position. In this case, the F ml. The kinetic coefficient of friction is used for two surfaces in relative motion. This feature, together with the inevitable natural elasticity of any mechanical system, can often lead to the troublesome phenomenon of stick-slip motion (the displacement of surface materials with time). Displacement increases linearly with time during periods of sticking when slipping occurs, the deformed surface materials are released. Representative of dry static and kinetic coefficients of friction for various material pairs are found in tribology and physics references 11 see Table 3.1. 

An increase of temperature in tribological contact during friction is well known. It facilitates the phenomenon of selective transfer of polymer components, followed by their chemical reaction with the surface layer of metal counterface, in the case of rubber-metal friction couple. The modification can not only effect composition and structure of the surface layer of polymer but metal as well [2]. Our previous studies confirmed on the... 

A lot of studies have been conducted to evaluate the tribological properties of surface-capped copper nanoparticles. Zhou et al. [5] pointed out that the size and additive concentration of copper nanoparticles have a remarkable effect on their lubricating properties, based on the experimental results shown in Table 5.1. According to the results, DDP-capped Cu nanoparticles with grain sizes of 2 and 5 nm can improve the AW ability of LP effectively. However, DDP-capped Cu nanoparticles 12 nm in size decreased the AW ability of LP to some extent, while nonmodified copper nanoparticles (with a size of 40 nm) as additives in LP caused instant seizure under the same conditions. A rational explanation of the phenomenon... 

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