Definition
A form of surface damage that occurs between two tightly fitted metal parts subjected to slight, repeated relative motion. The micro-movement wears away protective oxide films and grinds off tiny particles, which then oxidize and act as an abrasive, producing pitting and a characteristic reddish-brown or black powdery debris at the contact area.
Plain English
Damage that happens where two metal parts are pressed tightly together but vibrate or rub against each other very slightly. The tiny rubbing wears the surfaces, and the worn-off bits turn into a gritty powder that keeps making the damage worse.
Context Anchor
Seen during aircraft maintenance inspections, especially around bolted joints, engine mounts, bearings, and other places where metal parts are held tightly together.
Derivation
‘Fretting’ comes from the Old English fretan, meaning ‘to gnaw or wear away.’ It describes the slow, repeated nibbling action of one surface on another, which fits this kind of corrosion well.
Why Pilots Care
Fretting corrosion can quietly weaken structural joints and fasteners long before any visible problem appears. A mechanic who spots the telltale reddish-brown dust around a bolt or fitting has found early evidence of motion that should not be there.
Grounding Statement
Picture two tightly bolted metal surfaces vibrating slightly during flight until the contact area becomes worn and stained.
Intuition Check
Fretting corrosion is not just ordinary rust from moisture. The key idea is tiny repeated movement between touching parts, with corrosion forming where that rubbing occurs.
Example Sentence 1
During the inspection, the mechanic noticed reddish-brown powder around the wing attach bolts, a clear sign of fretting corrosion.
Example Sentence 2
Proper torque and lubrication help prevent fretting corrosion at bolted joints in the airframe.