11-05-2017, 11:54 AM
Fretting refers to wear and sometimes corrosion damage on the roughness of the contact surfaces. This damage is induced under load and in the presence of repeated relative surface movement, as induced for example by vibration. The ASM Manual on Fatigue and Fracture defines as: "A special wear process occurring in the area of contact between two materials under load and subject to a relative minute movement by vibration or some other force." Fretting significantly reduces the quality of the surface layer producing greater surface roughness and micropits; This reduces the fatigue resistance of the components.
The amplitude of the relative sliding movement is often in the range of micrometers to millimeters, but may be as low as 3 to 4 nanometers. Contact movement causes mechanical wear and transfer of material on the surface, often followed by oxidation of both the metal debris and the newly exposed metal surfaces. Because the oxidized debris is generally much more difficult than the surfaces from which it came, it often acts as an abrasive agent that increases the speed of friction and mechanical wear called false.
Friction damage in steel can be identified by the presence of a chopped surface and fine powder of "red" iron oxide similar to cocoa powder. Strictly these debris are not "rust" since their production does not require water. The particles are much harder than the contact steel surfaces, so abrasive wear is inevitable; However, no particles are required to start the fret.