In this study, rotating bending fatigue tests have been carriedout to investigate the fatigue strength of plain andcircumferentially notched specimens of Ti-6 Al-4 V alloy. The purposeof this work is to evaluate fatigue strength and notch sensitivityunder various kdnds of stress concentra- tions. The notch radius ofspecimens varies from ∞ (plain specimen) to 2.5, 2.0, 1.5, 1.3, 1.0,0.5, 0.4, 0.2, and 0.l mm. According to the experiment results, it isfound that the notch sensitivity of Ti-6Al-4V alloy for blunt notchis remarkably lower than that of sharper notch. The cause of thisphenomenon is considered that slip system is limited fairly due tothe crystal structure (hcp) of this kind of material. Considering tothe influence of the stress gradient there is a clear differencebetween blunt notch and sharp notch for the surface state of testedportion. The non-propagating micro- cracks at the specimen surfacecould not be observed for all notched specimens including plainspecimen subjected under the stress amplitude of fatigue limit by N=10~7 cycles.
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