Counterface roughness, polymer abrasive wear

Abrasive wear in polyethylene occurs when the surfaee of a sample is removed by contact with a counterface with which it is in relative motion. The surfaces of the polymer and the counterface are always rough to some extent, either by design or due to the inescapable consequences of fabrication. Thus there are always asperities that protrude above the level of the surrounding surface. It is these asperities that make contact and are sites for ductile tearing failure. Asperities may be sharp and incisive, as in the case of those found on inorganic counterfaces, such as stainless steel and emery paper, or rounded and deformable, as in the case of those found on polymer surfaces. Sharp asperities cut and scour surfaces smooth ones act by adhesion to viscoelastically shear the surface. 

The wear rates of various polymers can be related to the energy of failure and hence to their cohesive energy density under eertain conditions [56]. The cohesive energy density is a measure of the cohesion between adjacent chains in a solid and hence is a function of the molecular nature of the polymer. This relationship is found to hold true for a series of polymers subjected to abrasion by very rough surfaces as shown in Figure 44. However, when less rough counterfaces are encountered, this relationship breaks down. 

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