Pitting Wear Review

Pitting Wear Review

Pitting wear is due to surface failure of a material as a result of stresses that exceed the endurance (fatigue) limit of the material. Metal fatigue is demonstrated by bending a piece of metal wire, such as a paper clip, back and forth until it breaks. Whenever a metal shape is deformed repeatedly, it eventually fails. A different type of deformation occurs when a ball bearing under a load rolls along its race. The bearing is flattened somewhat and the edges of contact are extended outward. This repeated flexing eventually results in microscopic flakes being removed from the bearing. Fatigue wear also occurs during sliding motion. Gear teeth frequently fail due to pitting.

While pitting is generally viewed as a mode of failure, some pitting wear is not detrimental. During the break-in period of new machinery, friction wears down working surface irregularities. This condition is considered to be nonprogressive and usually improves after the break-in period. However, parts that are continuously subjected to repeated stress will experience destructive pitting as the materials endurance limit is reached.