Abstract
Rotating bending fatigue tests have been carried out notched commercially pure titanium specimens pre-strained by 0% and 10% in tension. The result of fatigue tests shows that the pre-strained titanium has long fatigue life compared to the annealed one in the range of finite life. Conversely, the fatigue limit of the pre-strained one decreases by 12%. The notch sensitivity of the annealed specimen is very low, although it increases due to pre-straining. No non-propagating macrocrack is observed, but some microscopic non-propagating cracks are observed on a sharp notch with a radius of 0.25mm. The crack initiation behavior was investigated through successive observations. On the surface of the annealed specimen, multiple microcracks initiate along slip bands within multiple grains in contact at a notch, and join together to grow beyond grain boundaries. On the other hand, for the pre-strained one, microcracks initiate along the boundaries of deformation twins within a single grain, joining to become a main crack leading to a final fracture.
