Rotating bending fatigue tests have been carried out on a notched commercially pure titanium pre-strained by 0percent and 10percent in tension. The result of fatigue tests shows that a pre-strained titanium has long fatigue life compared to an annealed one in the range of finite life. Conversely, the fatigue limit of pre-strained decreases by 12percent. The notch sensitivity of an annealed one is very low, however, 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 annealed one, multiple microcracks initiated along slip bands, within a few grains in contact at a notch and join together to grow beyond grain boundaries. On the other hand, for a pre-strained one microcracks initiated along boundaries of deformation twins within a single grain, join to be a main crack leading to a final fracture.
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