Surface Fatigue

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PITTING
Pitting can occur in a number of wear processes. Pitting is the removal or displacement of material by a fatigue action to form cavities in a surface. Pitting as part of surface fatigue. Frequently occurs in rolling element bearings, gears, worm wheels and cam paths.

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SPALLING
In this form of wear, particles fracture from a surface in the form of metal flakes. Spalling arises from the same mechanisms as pitting. It is the result of surface fatigue, and it occurs in the same types of systems. Occasionally, wear surfaces that are subject to rolling elements are electroplated for wear resistance. Such systems are very prone to spalling.

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IMPACT
Impact wear is material damage and removal by the action of repetitive impacting of two solid surfaces. As simple example of impact wear is damage that occurs on the head of a high-speed riveting hammer. The hummer plastically deform the rivet head, and there is no concern for the wear that occurs on the rivet, but the hammer suffers material attrition that eventually necessitates it replacement.

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BRINELLING
Brinelling is the wear term used to describe surface damage of solids by repeated local impact or by static overload. The origin of this term is probably from the similarity of this form of damage to a hardness indentation on a brinell hardness test.