In a study of a field such as fatigue, which depends at least partly on an ever more refined understanding of materials phenomena, there can be no final statement completely explaining the physics of the problem. In the case of some kinds of failure, such as yield, or brittle fracture of a flawed component, it is, nevertheless, possible to make simple concise statements which are of immediate usefulness to the engineering designer. In attempting to quantify fretting fatigue, even this is not possible, principally because of our incomplete understanding of the nature of crack initiation, and partly because the process is a stochastic one, depending on the vagaries of the material crystallography, surface topography and cleanliness. We should remind ourselves that the life of a crack is conveniently categorised as a two-stage process; first the crack nucleates, usually from the surface and from pre-existing defect, no matter how small that defect may be. It is this phase of the life which is so critically dependent on the quantities cited, and which is difficult to quantify. Secondly, the crack propagates, in a direction and at a rate controlled also by the state of stress, but this phase is somewhat less sensitive to the material properties obtaining within the individual grains. There is a considerable body of experimental evidence to show that fretting influences both of these processes. The goal of an engineering approach to the analysis of fretting fatigue is to quantify the effects, so as to allow the designer to estimate component life reliably using the results of basic materials tests.
KeywordsStress Intensity Factor Stress Intensity Factor Calculation Plain Fatigue Fret Fatigue Test Fret Fatigue Crack
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