Proposal of estimation method for notched specimen fatigue limit of commercially pure titanium

In order to identify the fatigue limit for a sharp notched specimen of commercially pure titanium, rotating bending fatigue tests on smooth and notched specimens were curried out. In previous studies, it was found that the fatigue limit for a sharp notched specimen of commercially pure titanium could not be determined and it is not sure whether it fail over N=10 ⁷ cycles or not. Based on the experimental results, in the smooth specimen and notched specimen (p=1.0mm), they have fatigue limits and knee points, while the sharp notched specimen (p=0.1mm) does not. As an estimation method, the fatigue crack initiation of each specimen was then investigated. The investigation results are as follows. (1) The proportional relationship exists between the maximum stress K _iωa at the notch root and logarithm of the number of cycles to fatigue crack initiation N _i. (2) Based on the slope of the relationship between the maximum stress K _iωa and the number of cycles to fatigue crack initiation N _i at the notch root, there is no possibility that the fatigue crack in the same mechanism initiates over N=10 ⁷ cycles. Therefore, the stress amplitude that is not initiated the fatigue crack at N=10 ⁷ cycles is the fatigue limit.