On size effects on fatigue properties of metal foils at micrometer scales

Fatigue behaviors of two types of polycrystalline Cu foils (i.e. foil thickness (t)-constant and grain size(d)-constant foils) with different ratios of the foil thickness to the grain size (t/d) at micrometer scales were investigated. The experimental results reveal that under total strain control the fatigue life of the foils strongly depends on the tensile plasticity of the foils and the coupled effect of t and d. The large tensile plasticity leads to the high fatigue strength of the Cu foils. The contribution of surface grains to fatigue properties becomes more and more important as decreasing t/d. The coupled effects of the geometrical scale and the microstructural scale on fatigue damage formation and crack growth resistance are analyzed and the basic mechanisms are elucidated.