Fretting Wear Failures
Résumé
FRETTING is a wear phenomenon that occurs between two mating surfaces; initially, it is adhesive in nature, and vibration or small-amplitude oscillation is an essential causative factor. Fretting generates wear debris which oxidizes leading to a corrosion-like morphology. Fretting of ferrous materials in air produces a characteristic reddish-brown debris of ferric oxide, which, when mixed with oil or grease, produces debris that is often Referred to as “blood,” “cocoa,” or “red mud.” Hence in components that are lubricated so that ordinary corrosion is not likely to occur, the presence of reddish brown debris is indicative of fretting. Fretting also occurs in noble materials, such as gold, platinum, and cupric oxide in connectors. If fretting occurs in an inert or protective atmosphere, oxide debris cannot be formed leading to a full adhesive wear response with little debris produced. The general characteristics of fretting wear, with an emphasis on steel, are reviewed in this article. This review is followed by several examples of failures related to fretting wear. Common sites for fretting are in joints that are bolted, keyed, pinned, press-fitted, or riveted; in oscillating bearings, splines, press fits on shafts; and in universal joints and orthopedic implants. Generally, fretting occurs at contacting surfaces that are intended to be fixed in relation to each other but that actually undergo small oscillating motion usually induced by vibration. Other situations concern cyclic thermal dilatation and contact between balls and raceways in bearings and between mating surfaces in oscillating bearings and flexible couplings.