Frettings

Frettings is a term used in tribology to describe the wear and damage that occur at contacting surfaces subjected to small, oscillatory relative motion. The term encompasses various phenomena tied to repetitive micro-slip, including fretting wear, fretting fatigue, and fretting corrosion. Fretting wear arises from repetitive sliding at asperity contacts, causing plastic deformation, disruption of surface layers, and material removal. Fretting fatigue refers to the initiation and propagation of cracks due to cyclic micro-motions at the interface, while fretting corrosion combines mechanical wear with chemical or electrochemical attack.

The mechanisms and severity of frettings are governed by several factors, including contact pressure, the amplitude and frequency of oscillation, load history, surface roughness, material combinations, and environmental conditions such as humidity and temperature. The presence of oxide layers can influence fretting behavior, sometimes protecting surfaces and other times becoming sites for accelerated wear or corrosion when damaged. Debris formed during fretting can form abrasive paths and further accelerate material loss, while moisture and electrolytes can enhance corrosion at the wear interface.

Industrially, frettings is a critical concern in joints and fasteners, gears, bearings, and turbine blades where parts experience contact with limited mobility. Consequences include localized wear scars, pitting, crack initiation, lubricant film breakdown, and reduced fatigue life. Assessment methods include fretting wear testing and pin-on-disk experiments, with wear scars measured by profilometry and microscopic analysis to identify wear mechanisms and corrosion products.

Mitigation strategies focus on reducing micro-motion and contact pressure, improving lubrication, selecting compatible materials and coatings, increasing contact area, and employing surface treatments to enhance resistance to plastic deformation and corrosion.