Fretting wear

Fretting wear is quite similar to adhesive wear in that microwelding occurs on mating surfaces. The difference is that adhesive wear is related to interfaces that are sliding across each other, while fretting wear is related to interfaces that are essentially stationary with respect to each other. However, when minute elastic deflections or slight motion actually occurs, the cyclic motion of extremely small amplitude is enough Io cause microwelding on both surfaces. Fretting wear is also known as fretting corrosion, false brinelling, friction oxidation, chafing fatigue, and wear oxidation.

Fretting frequently occurs in "stationary" joints that are "fixed" from shrinking or pressing by interference fits or by bolts, pins, rivets, or other mechanisms, and also at the various contact points in antifriction, or rolling-element, bearings. This means that nonrotating antifriction bearings that are subject to vibration over a period of time may have fretting wear wherever a ball or roller contacts a raceway under load. If the bearings subsequently rotate in normal service, they may be noisy because of the wear patterns and small indentations that are present in the raceways and the corresponding flat spots on the rolling elements. The term "false brinelling" is sometimes used to describe the indentations. However, the mechanism of failure actually is fretting wear. Fretting also is a serious problem on parts such as shafts, where it can initiate fatigue cracking on the contacting surfaces. In fact, many fatigue fractures of shafts are caused directly by fretting. Since fretting is extremely difficult to prevent, special means must be taken to prevent fracture resulting from the fretting, which can occur in the most unexpected and unlikely locations.

Because fretting wear is essentially a stationary phenomenon, the debris that is formed is retained at or near the location where it was formed. The debris usually consists of oxides of the metals contacting; with ferrous metals, it is brown, reddish, or black, depending on the type of iron oxide formed. Aluminum alloys form a black powder when fretting wear is present.