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Creep-Fatigue Behavior and Crack Analysis of Ti-6Al-4V ELI

As a kind of deep-sea exploration equipment, deep-sea submersible can fundamentally satisfy the deep-sea exploration mission, and it is the commanding point of marine technology development. For deep-sea submersible, the reasonable selection of manned cabin material is one of the most important factors to ensure the safety of submersible in severe environments. Titanium alloy is a key material for deep-sea engineering equipment due to its excellent material properties. The titanium alloy of pressure-resistant structure will bear creep-fatigue load when submersible is diving, rising and working underwater for a long time. Therefore, the research on creep-fatigue behavior of titanium alloy in deep-sea manned submersible has practical significance. Ti-6Al-4V ELI has a wide range of application in aerospace and deep-sea equipment because of its great plasticity, toughness, weldability, and long service life. The paper simulates the changes of load acting on Ti-6Al-4V ELI by applying trapezoidal wave at room temperature and multiple stress levels. The creep curves of Ti-6Al-4V ELI during the dwell-time stage are obtained by using creep parameters. It can be found that the addition of fatigue in the dwell-time process will decrease the overall creep strain of Ti-6Al-4V ELI, but it can increase creep rate to some extent. In addition to the creep-fatigue behavior of titanium alloy, crack analysis is also carried out in paper. By adding small crack to the spherical shell, the stress intensity factor and J-integral of crack are obtained under given stress. The numerical calculation results provide a research perspective for designers in choosing pressure-resistant materials for deep-sea equipment.