Wear(redirected from worn out)
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a change in the dimensions, shape, weight, or surface condition of a product as a result of friction on the surface layer.
The wear of machine parts, members of building structures (such as the steps of stairs), objects, clothing, and other items depends on the conditions of friction, the properties of the material, and the design of the product. Wear may be considered as a mechanical process complicated by the action of physical and chemical factors that bring about a decline in the strength of microunits of the surface layer. Depending on the conditions of external influence on the surface layer, a distinction is made between abrasive, cavitational, erosive, and other types of wear. Wear leads to a deterioration of the functional qualities of products and to the loss of their use value. Both the use of materials with high wear resistance and design concepts that assure compensation for wear, reserve durability, and so on and general reduction of friction-use of high-quality lubricant and protection from abrasion-increase resistance.
REFERENCESKhrushchov, M. M., and M. A. Babichev. Issledovaniia iznashivaniia metallov. Moscow, 1960.
Kragel’skii, I. V. Trenie i iznos. Moscow, 1968.
Tenenbaum, M. M. Iznosostoikost’konstruktsionnykh materialovidetalei mashin pri abrazivnom iznashivanii. Moscow, 1966.
M. M. TENENBAUM
the gradual loss of value (including use-value) of fixed capital stock during use caused by natural forces and extraordinary circumstances (fires, floods). Wear manifests itself in mechanical wear, corrosion, metal fatigue, deformation, and the failure of structures. The greater the wear on productive assets, the shorter will be their service life and undepreciated value. At the same time, as wear occurs during production, the value of the fixed capital stock is gradually transferred to the finished goods; the value transferred takes the form of amortization deductions. These deductions in turn are used for the modernization and/or replacement of the assets.
Wear can be minimized through timely maintenance and repair. Of particular importance is capital repair, wherein worn parts of machines and other objects are replaced with new ones, thereby preventing an excessive increase in wear. Thus, while some types of wear can be avoided, others are a normal part of operation and their prevention through capital repair is economically unjustified.
The removal of material from a solid surface as a result of sliding action. It constitutes the main reason why the artifacts of society (automobiles, washing machines, tape recorders, cameras, clothing) become useless and have to be replaced. There are a few uses of the wear phenomenon, but in the great majority of cases wear is a nuisance, and a tremendous expenditure of human and material resources is required to overcome the effects.
Adhesive wear is the only universal form of wear, and in many sliding systems it is also the most important. It arises from the fact that, during sliding, regions of adhesive bonding, called junctions, form between the sliding surfaces. If one of these junctions does not break along its original interface, then a chunk from one of the sliding surfaces will have been transferred to the other surface. In this way, an adhesive wear particle will have been formed. Initially adhering to the other surface, adhesive particles soon become loose and can disappear from the sliding system. See Friction
Abrasive wear is produced by a hard, sharp surface sliding against a softer one and digging out a groove. The abrasive agent may be one of the surfaces (such as a file), or it may be a third component (such as sand particles in a bearing abrading material from each surface). Abrasive wear coefficients are large compared to adhesive ones. Thus, the introduction of abrasive particles into a sliding system can greatly increase the wear rate; automobiles, for example, have air and oil filters to catch abrasive particles before they can produce damage.
Corrosive wear arises when a sliding surface is in a corrosive environment, and the sliding action continuously removes the protective corrosion product, thus exposing fresh surface to further corrosive attack. See Corrosion
Surface fatigue wear occurs as result of the formation and growth of cracks. It is the main form of wear of rolling devices such as ball bearings, wheels on rails, and gears. During continued rolling, a crack forms at or just below the surface and gradually grows until a large particle is lifted right out of the surface.
Most manifestations of wear are highly objectionable, but the phenomenon does have a few uses. Thus, a number of systems for recording information (pencil and paper, chalk and blackboard) operate via a wear mechanism. Some methods of preparing solid surfaces (filling, sandpapering, sandblasting) also make use of wear. See Abrasive