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Closely fitted design members, which are clamped, pressed, or shrunk together develop fretting corrosion between the mating surfaces when subjected to fluctuating stresses. Aside from the wear which changes the geometry of the mating surfaces, there also results a greatly reduced fatigue resistance. It is this latter aspect, along with means of improving the fatigue resistance, that is discussed here because of the increasing number of service failures occurring in all types of machinery and equipment due to fretting. This paper first discusses the fundamental nature of the fatigue problem associated with fretting. Eight factors are then separately treated as to how each one influences the fatigue strength regarding both the initiation and propagation of fatigue cracks. These factors include the effects of the degree of the clamping pressure, shape or geometry of assembly, fretting, residual stresses, different engineering steels and heat treatments, surface finish, simultaneous water corrosion, and type of lubricant used between the mating surfaces. After reviewing these factors it is apparent that some limited improvement in fatigue resistance may be obtained against the initiation of fatigue cracks due to fretting. Means are available for obtaining much greater improvement in fatigue resistance against fatigue crack propagation.
Horger, Oscar J.
Chief Engineer, Timken Roller Bearing Co., Canton, Ohio