In general, wear is mechanically induced surface damage that results in the progressive removal of material due to relative motion between that surface and a contacting substance or substances. A contacting substance may consist of another surface, a fluid, or hard, abrasive particles contained in some form of fluid or suspension, such as a lubricant. As is with friction, the presence of wear can be either good or bad. Productive, controlled wear can be found in processes like machining, cutting, grinding, and polishing. However, in most technological applications, the occurrence of wear is highly undesirable, and it is an enormously expensive problem since it leads to the deterioration or failure of components. In terms of safety, it is often not as serious (or as sudden) as a fracture, and this is because the wear is usually anticipated.
Certain material characteristics such as hardness, carbide type, and volume percent can have a decided impact on the wear resistance of a material in a given application. Wear, like corrosion, has multiple types and subtypes that are predictable to some extent and are rather difficult to test and evaluate in the lab or service reliably.
Wear can be quantified (correlated) using wear rate, defined as the mass or volume of material removed per unit sliding distance. It is usually expressed in terms of the dimensionless wear coefficient (K) or as a specific wear rate (wear volume per unit applied normal load per unit sliding distance) in (mm3*Nm-1).
The most commonly used wear equation for the dry rolling–sliding condition is Archards wear equation. The wear volume (V) for unit sliding distance (S) is equal to the non-dimensional wear coefficient (K) multiplied by the applied load (Fn) divided by the hardness of the worn material.