Fatigue characteristics of ultrafine grained copper for the application to components

为了将超细晶铜应用于实际的机械结构和部件，必须阐明其疲劳损伤形成的基本机理。本文通过对超细晶铜进行等径角挤压疲劳试验，研究了试样表面疲劳损伤的形成过程。然后，裂纹扩展行为，这是需要定量估计的疲劳寿命，进行了研究，显示裂纹扩展机制的微观结构和应力幅的依赖性。为了阐明依赖性的原因，进行了两步加载疲劳试验。通过对裂纹尖端区域损伤形成和剪切带的观察，研究了高低应力幅下裂纹扩展机制的差异。此外，还研究了应力变化对表面损伤形成行为的影响。

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.