Abstract
Frequency is an important factor influencing the fatigue behavior. Regarding to the dwell fatigue, it corresponds to the effect of rise and fall time, which is also an important issue especially for the safety evaluation of structure parts under dwell fatigue loading, such as the engines of aircrafts and the pressure hulls of deep-sea submersibles. In this paper, the effect of rise and fall time (2 s, 20 s, 110 s, and 200 s) on the dwell fatigue behavior is investigated for a high strength titanium alloy Ti-6Al-2Sn-2Zr-3Mo-X with basket-weave microstructure. It is shown that the dwell fatigue life decreases with increasing the rise and fall time, which could be correlated by a linear relation in log–log scale for both the specimen with circular cross section and the specimen with square cross section. The rise and fall time has no influence on the crack initiation mechanism by the scanning electron microscope observation. The cracks initiate from the specimen surface and all the fracture surfaces present multiple crack initiation sites. Moreover, the facet characteristic is observed at some crack initiation sites for both the conventional fatigue and dwell fatigue tests. The paper also indicates that the dwell period of the peak stress reduces the fatigue life and the dwell fatigue life seems to be longer for the specimen with circular cross section than that of the specimen with square cross section.
Highlights
The dwell fatigue in titanium alloys has drawn great attention [1,2,3,4,5,6] since it was detected inRolls-Royce RB211 engines on Lockheed Tristar aircraft in the early 1970s [7,8]
This paper investigates the effect of rise and fall time on the dwell fatigue behavior of a high
This paper investigates the effect of rise and fall time on the dwell fatigue behavior of a high strength titanium alloy Ti-6Al-2Sn-2Zr-3Mo-X for the specimen with circular cross section and the strength titanium alloy Ti-6Al-2Sn-2Zr-3Mo-X for the specimen with circular cross section and the specimen with square cross section under axial loading
Summary
The dwell fatigue in titanium alloys has drawn great attention [1,2,3,4,5,6] since it was detected inRolls-Royce RB211 engines on Lockheed Tristar aircraft in the early 1970s [7,8]. It has been shown that the dwell period at the peak stress significantly reduces the fatigue life of titanium alloys in comparison with the fatigue life under the conventional fatigue loading and that the crack initiation region has the characteristic of cleavage or quasi-cleavage facets [9,10,11]. Regarding to the dwell fatigue, it corresponds to the effect of rise and fall time, which is a very important issue especially for the safety evaluation of structure parts under dwell fatigue loading. The existing studies are mainly focused on the effect of dwell period on fatigue life, crack initiation, and crack propagation, and there is no report on this issue
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