Abstract
Titanium alloys such as Ti-6Al-4V are widely used in the aerospace domain worldwide; consequently, they have been extensively investigated, and the accumulated data has facilitated their use in the construction of structural members. In contrast, commercial pure (CP) Ti, which is cheaper than Ti alloys is widely used in the general industry, especially in the marine domain in Japan because it exhibits superior seawater corrosion resistance and biocompatibility. However, CP titanium has a strong anisotropy and consists of an hcp crystal structure; therefore, the strength data are insufficient owing to its short use history as a structural material, and some of its mechanical material properties remain unclear. Herein, the effect of mean stress and stress concentration on the fatigue strength of CP Grade 2 titanium was evaluated for the application range expansion of CP titanium. The results indicated that the fatigue limit in the longitudinal direction was 80–84% that in the transverse direction for smooth specimens. However, no significant difference was noted in the fatigue limit in both the directions for notched specimens. Furthermore, it was noted that it is necessary to apply at least Sa-0.5Su line to design the safe side in CP Grade 2 titanium.
Highlights
Titanium alloys such as Ti-6Al-4V are widely used in the aerospace domain worldwide; they have been extensively investigated, and the accumulated data has facilitated their use in the construction of structural members.[1,2,3] In contrast, commercial pure (CP) Ti, which is cheaper than Ti alloys is widely used in the general industry, especially in the marine domain in Japan because it exhibits superior seawater corrosion resistance and biocompatibility.CP titanium is suitable for marine material
CP titanium is considerably more influenced by the mean stress than steel materials are, and the fatigue limit decreased in a range between the Soderberg diagram and the modified Goodman diagram with increase in the mean stress
It is necessary to apply at least a Sa-0.5Su line to design the safe side in CP Grade 2 titanium
Summary
Titanium alloys such as Ti-6Al-4V are widely used in the aerospace domain worldwide; they have been extensively investigated, and the accumulated data has facilitated their use in the construction of structural members.[1,2,3] In contrast, commercial pure (CP) Ti, which is cheaper than Ti alloys is widely used in the general industry, especially in the marine domain in Japan because it exhibits superior seawater corrosion resistance and biocompatibility.CP titanium is suitable for marine material. It has begun to be used for the structural members of fishing-boat and yacht and the non-structural members including the equipment of a ship product of the severe corrosion environment such as the exhaust pipe or the seawater condenser, from about 2000. To support the fatigue design because there was no established code of the fatigue design for titanium welded structure including the titanium alloys, author studied the fatigue strength evaluation of the principal welded joints which constitutes titanium hull structure[4]. The data of fatigue strength of CP titanium as the parent material of welded structure is insufficient unlike ship's structural materials such as steel and aluminum alloys. The effect of mean stress and stress concentration on the fatigue strength of CP Grade 2 titanium was evaluated for the application range expansion of CP titanium
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