Cohesive wear

This crude distinction between adhesive and cohesive wear mechanisms is probably oversimplified in the sense that it neglects many aspects of the interactions between bulk deformation modes and interface rheology. It has, however, the merit of making a clear distinction between wear processes which can, to some extent, be related to known bulk failure properties and... 

The relevance of bulk fracture properties has therefore been considered essentially within the context of cohesive wear modes such as abrasive and fatigue wear. During abrasive wear, the initial stage is considered to be the process of contact and scratch between the polymer surface and a sharp asperity. The accumulation of the associated microscopic failure events eventually generates wear particles and gives rise to weight loss. Early approaches initiated by Ratner and co-workers [15] and Lancaster [16] attempted to correlate the abrasive wear rate with some estimate of the work to failure of the... 

A schematic of the distinction between interfacial and cohesive wear in a polymer/rigid surface interface (after Briscoe and Sinha, 2002). 

There are two broad classifieations of wear in polymers. These are interfacial wear that generally involves the surface and cohesive wear concerned with the subsurface. More specifically, the most prevalent form of surface induced wear is adhesion, whereas that below the surface occurs principally in the form of abrasion, fatigue and chemical/corrosive effects. Figure 7.5 shows... 

Abrasion is a form of cohesive wear that can occur in two modes, viz. two-body and three-body abrasive wear. Two-body abrasion refers to a hard rough surface, of which the asperities plough through the relatively stiffer counterface. The surface penetrations cause localised plastic displacement and indentations. Three-body abrasion refers to hard particles between two sliding surfaces, ploughing through at least one of the surfaces. The two are not mutually exclusive, as two-body abrasion can often lead to three-body when hard wear particles are detached from a surface. Abrasive wear is dependent on the bulk properties of the materials and the geometry of... 

Fig. 1 Schematic description of cohesive and interfacial wear processes from the two terms non interacting model of friction (from [96]). Bulk ploughing involves the dissipation of the frictional work within a volume of the order of the cube of the contact radius. Interfacial shear corresponds to the dissipation of the frictional energy in much thinner regions and at greater energy densities. Cohesive wear processes (cracking, tearing, microcutting...) are governed by the cohesive strength of the polymer. Mechanisms such as transfer film formation correspond to interfacial wear and do not readily correlate with accessible bulk failure properties...

The interfacial term of friction is the main cause of adhesive wear and may involve processes such as stick-slip motion, transfer film formation with or without chemical bonding, chemical wear, fatigue wear, and thermal softening of the interface (2,24). The adhesive wear is promoted only when the roughness of the counterface is very low, a value where cohesive wear or ploughing due to counterface asperity interaction may be safely neglected, and the adhesive interaction between the polymer and the counterface as a result of junction growth becomes an important factor. 

A linear relationship exists between the cohesive energy density of an abrasive (10) and the WoodeU wear resistance values occurring between comndum H = 9) and diamond H = 42.5). The cohesive energy density is a measure of the lattice energy per unit volume. 

Electroplating of one metal onto another is widely used for protection against corrosion and wear or for cosmetic purposes.16 Again, the source of metal for deposition could be anodic dissolution or a prepared solution with an inert anode. In contrast to electrolytic refining, only a very thin layer (typically on the order of 1 to 10 pm) of the plating metal is wanted, but usually this layer must be uniform, cohesive, and nonporous, and often a shiny appearance is desired. To understand the roles of some of the variables in electroplating, it is useful to consider the electrodeposition... 

Lubricants are often employed to facilitate the uniform transmission of forces and reduce undesirable friction effects during compaction. Lubricants may be classified as internal or external types [2]. Internal lubricants are materials which are added to the particulate feed not only to improve its flow properties (flow into the mold or die and rearrangement during compaction) but also to assist in the release of the final agglomerate from the mold or die. Internal lubricants are generally used in quantities of % to 2%. Internal lubricants, especially when used in excess, may interfere with the optimum cohesion of clean surfaces and reduce the strength of the agglomerates produced. External lubricants are materials used to prevent friction and wear at... 

Solid-solid Adhesion Solid suspension, adhesion, cohesion, corrosion, passivation, epitaxial growth, wear, friction, diffusion, thin films, delamination, creep, mechanical stability, durability, solid state devices, blend and alloy, charge transfer, nucleation and growth abrasion... 

If one considers that wear damage also results in energy dissipation, this approach can tentatively be applied to wear. Accordingly, wear processes can be classified as cohesive or interfacial depending on the length scales associated with particles detachment mechanisms (Fig. 1). 

If sand is moist, the slope of a sand pile can be higher. A sand castle can have vertical walls when it is built of moist sand in the morning, but as the afternoon wears on and the sand dries out, it cmmbles and collapses (mass wastes) until a stable slope forms. This is because the water makes the sand more cohesive. With the proper moisture content, there will be both water and air between most of the grains of sand. The boundary between the water and the air has surface tension— the same surface tension that supports water striders or pulls liquids up a capillary tube. In moist sand, surface tension holds the grains together like a weak cement. 

Powder or particle variables o particle size o size distribution o shape o surface texture o cohesivity o surface coating o particle interaction o wear or attrition characteristic o propensity to electrostatic charge o hardness o stiffness o strength o fracture toughness... 

A high degree of lateral interaction forms a cohesive adsorbed layer which results in improved adsorption. Although this class of molecules is used in lubricants to reduce friction, they may also serve to reduce wear and protect against scuffing, particularly at low temperatures where ZDDP protective film formation rates are low. 

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