The ASM Handbook on Fatigue and Fracture defines fretting as: "A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force."
What does your assembly consist of....bearings, bushings, roller cam or ?
Heckler
Sr. Mechanical Engineer
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(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right." -- George Best
1. using a huge number of fasteners, closely spaced and highly preloaded.
2. installing a "fretting washer" of suitable material between the mating parts.
3. selecting materials of suitable heat treat and physical properties to prevent cold welding or diffusion bonding effects at the mating interface.
4. apply barrier coatings (silver plate or moly disulfide DFL) to the mating surfaces.
5. design your joints so that the contact stresses are extremely low.
Fretting is a phenomenon that occurs at the micro level. The mating surfaces have tiny peaks or "asperities" that contact each other. Even though the mating surfaces appear smooth at the macro level, and the apparent bearing stress is well within the allowable for the materials, at the micro level the only surfaces actually contacting are the asperity tips. And the bearing stress there is enough to cause local mechanical bonding at the peak of a cyclic load. The asperity tips then break apart as the local mating surfaces unload, and a small amount of material is transfered from one side to the other. After this happens for millions of load cycles, you can see the classic pitting and material accumulation of the mating surfaces that have fretted.
