Fatigue characteristics of ultrafine grained copper for the application to components

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For the application of ultrafine grained (UFG) copper to the actual machine structures and components, the fundamental mechanism of fatigue damage formation should be clarified. In the present study, the fatigue tests of UFG copper processed by ECAP were conducted to study formation process of fatigue damage on the specimen surface. Then the crack growth behavior, which is needed to estimate quantitatively the fatigue life, was investigated, showing a dependency of microstructure and stress amplitudes on the crack growth mechanism. To clarify the reason for the dependency, two-step loading fatigue tests were conducted. Through the observations on the damage formation and shear banding around crack tip areas, the difference in crack growth mechanism between high and low stress amplitudes were studied. In addition to these, the effect of the stress change on the formation behavior of surface damage was studied.