# Abrasion (mechanical)

Abrasion is the process of scuffing, scratching, wearing down, marring, or rubbing away. It can be intentionally imposed in a controlled process using an abrasive. Abrasion can be an undesirable effect of exposure to normal use or exposure to the elements.

## Abrasion in stone shaping

Ancient artists working in stone would use abrasion to create sculptures. The artist selected dense stones like carbonite and emory and rub them consistently against comparatively softer stones like limestone or granite. The artist would use different sizes and shapes of abrasives, or turn them in various ways as they rubbed, to create effects on the softer stone's surface. Water would be continuously poured over the surface to carry away particles. Abrasive technique in stone shaping was a long, tedious process that, with patience, resulted in eternal works of art in stone.

## Models

The Archard equation is a simple model used to describe sliding wear and is based around the theory of asperity contact.

## Abrasion resistance

The resistance of materials and structures to abrasion can be measured by a variety of test methods.[1] These often use a specified abrasive or other controlled means of abrasion. Under the conditions of the test, the results can be reported or can be compared items subjected to similar tests.

Such standardized measurements can produce two quantities: abrasion rate and normalized abrasion rate (also called abrasion resistance index). The former is the amount of mass lost per 1000 cycles of abrasion. The latter is the ratio of former with the known abrasion rate for some specific reference material.[2]

One type of instrument used to get the quantities abrasion rate and normalized abrasion rate, is the abrasion scrub tester. This instrument is made up of a mechanical arm, liquid pump, and programmable electronics. The machine draws the mechanical arm with attached brush (or sandpaper, sponge, etc.) over the surface of the material that is being tested. The operator sets a pre-programmed number of passes for a repeatable and controlled result. The liquid pump can provide detergent or other liquids to the mechanical arm during testing to simulate washing and other normal uses.[3]

The use of proper lubricants can help control abrasion in some instances. Some items can be covered with an abrasion resistant material. Controlling the cause of abrasion is sometimes an option.