Fatigue behavior of pre-strained commercially pure titanium
Kusukawa Kazuhiro; Takao Ken-ichi
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 0.25 mm. The crack initiation behavior was investigated through successive observations. On the surface of the annealed specimen, multiple micro-cracks 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. Key Words:fatigue, pre-straining, rotating bending, notch sensitivity, crack initiation, pure titanium