Sliding wear processes

The formation and fracture of these junctions leads to the transfer of small fragments of material from one surface to another and finally, after many such events, the release of a year particle often in a highly oxidised state. Such a wear process is common to most sliding systems and can undoubtedly occur during fretting movements, especially if the slip amplitude is large. However, many fretting situations occur where the amplitude of slip is very small and perhaps even comparable to the dimensions of a... 

Under more severe conditions, the shear strain concentration in the subsurface layers dominates the wear process. When the coefficient of friction is less than 0.4, shear strain accumulates under repeated sliding until it reaches a critical value,... 

Table 5.6. Typical wear processes for metal-on-metal sliding systems...

Wear control by reactive film formation involves a corrosive wear process to limit the rate of an adhesive wear process. The protective film is removed during the sliding process and must be replaced in time between successive contacts. If the rate... 

Surfaces in contact and moving parallel to each other exhibit phenomena that are encountered incessantly in our everyday life. These phenomena include friction, slide, wear, and lubrication (the process used to modify friction). We could not walk without controlled friction, nor could the internal combustion engine operate without the lubrication of its moving parts. The name tribology (from the Greek tribein—to rub) is given to phenomena that involve surfaces in relative motion. 

Variations in Coefficient of Friction and Wear Depth of Various Polymers Rubbed Against Steel Disk with Sliding Distance. Figures 5 (a),(b),(c),(d) and (e) show variations in the coefficient of friction and wear depth h with the sliding distance in the wear processes of PI, PAI, PEEK, PPS and PES, respectively With all specimen polymers, the steady states of friction and wear appear following the initial transient states The wear rates of various polymers generally decrease gradually in the initial transient wear state, and the wear rates in the steady state are much lower than those in the initial transient state However, the steady state of hi er wear rates... 

PI, PAI and PEEK exhibit relatively low friction at temperatures above 200 C in their wear processes. This is due to the thick transferred polymer layer produced during sliding. The friction of PES is generally high at any temperature. 

It is interesting to note that very thick transfer films were established on smooth counterfaces (Figures 8 and 9). Such films are typically 10 ym thick and clearly submerge the details of the initial counterface profile, rather like snow drifts on the initial land topography. In this case the bulk polymer will slide on relatively thick transfer films and it will then be the Interfacial conditions between the two polymeric features which dictate the wear process, rather than the details of the burled metallic counterface. 

The wear situation is likely to be aggravated should hard additives of a coarser grain fraction be embedded in a softer matrix, such as clay, as the result of an upstream kneading process. This may lead to grain sliding wear (besides a two-body and even a proper three-body abrasive wear), which could, in the absence of an intermediate lubricating medium, have drastic consequences. Similarly, lack of an intermediate medium will favour any likely adhesive wear. 

Ge, S. and Chen, G. (1999) Fractal prediction models of sliding wear during the running-in process, Wear, 231 249-55. 

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