What is fretting fatigue and how is it prevented in aircraft joints?

Fretting fatigue occurs when small relative motion between contacting surfaces (under cyclic loading) creates surface damage that accelerates crack initiation. In aircraft, it affects fastener holes, pin joints, and interference-fit bushings. Prevention methods include: Interference-fit fasteners (eliminate relative motion), Surface treatments (shot peening, cold expansion of holes), Low-friction coatings, Proper fastener preload (reduces slip), Fretting-resistant materials at interfaces, and Lubricants or anti-fretting compounds. Design accounts for fretting through reduced fatigue allowables at susceptible joints. Testing validates fretting performance - fatigue life reduction of 50% or more is possible without mitigation.