* Wear is a process of removal of material from one or both of two solid surfaces in solid state contact, occurring when two solid surfaces are in sliding or rolling motion. * The rate of removal is generally slow, but steady and continuous. Figure 1.4 shows the five main categories of wear.
* Abrasive wear occurs when material is removed from one surface by another harder material, leaving hard particles of debris between the two surfaces. * It can also be called scratching, gouging or scoring depending on the severity of wear. * Abrasive wear occurs under two conditions:
* Two body abrasion: In this condition, one surface is harder than the other rubbing surface as shown in figure 1.5(a).
Examples in mechanical operations are grinding, cutting, and machining. * Three body abrasion: In this case a third body, generally a small particle of grit or abrasive, lodges between the two softer rubbing surfaces, abrades one or both of these surfaces, as shown in figure 1.5(b).
In the microscale,
* The abrasive wear process is where asperities of the harder surface press into the softer surface, with plastic flow of the softer surface occurring around the harder asperities, as shown in figure 1.6. * This often leads to what is known as microploughing, microcutting, and microcracking, when a tangential motion is imposed.
Reduction of Abrasive Wear:
* Abrasive wear may be reduced by the introduction of hydrodynamic or elastohydrodynamic lubricants at various film thickness to separate the surfaces and to wash out any contaminant particles.
* The impingement of solid particles, or small drops of liquid or gas often cause what is known as erosion of materials and components. * Example: Ingestion of sand, Erosion of jet engine & Halicopter Blades. Erosive Wear Mechanism
* Solid particle erosion is a...