Study on the Overload and Dwell-Fatigue Property of Titanium Alloy in Manned Deep Submersible
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e Overload and Dwell-Fatigue Property of Titanium Alloy in Manned Deep Submersible WANG Ke, WU Li, LI Yong-zheng*, SUN Xiao-peng School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China Received November 5, 2019; revised June 11, 2020; accepted July 22, 2020 ©2020 Chinese Ocean Engineering Society and Springer-Verlag GmbH Germany, part of Springer Nature Abstract With the rapid development of ocean technology, the deep-sea manned submersible is regarded as a high-tech equipment for the exploration and exploitation of ocean resources. The safety of manned cabin has a decisive effect on the whole system. Ti-6Al-4V with the superior strength-to-weight ratio and corrosion resistance has been used for the manned cabin. The manned cabin experiences loading spectrum with different maximum stresses and different dwell time during their service life. The load sequence effects on dwell fatigue crack growth behavior of Ti-6Al-4V under different dwell time are investigated experimentally in this paper. The experimental results show that the crack tip plastic zone is enlarged by the dwell time and the overload retardation zone increases with dwell time under the same overload rate. A dwell fatigue crack growth model is proposed by modifying the crack tip plastic zone under the loading history with combinations of the single overload and dwell time factors are included in the modified model. Based on the experimental data, the overload retardation zone and the crack growth rates of Ti-6Al-4V are predicted by the modified model. A reasonable model for the load sequence effect on the dwell fatigue crack growth rates of Ti-6Al-4V is verified. Key words: manned cabin, dwell fatigue crack growth rate, Ti-6Al-4V, load sequence effect Citation: Wang, K., Wu, L., Li, Y. Z., Sun, X. P., 2020. Study on the overload and dwell-fatigue property of titanium alloy in manned deep submersible. China Ocean Eng., 34(5): 738–745, doi: https://doi.org/10.1007/s13344-020-0067-8
1 Introduction During the service life, the manned deep submersible will inevitably go through the process of diving, working and floating. In this process, the pressure shell of the deep submersible will experience the dwell load in each cycle except for the normal cyclic loading (Lei et al., 2010). Then the fatigue problem of the pressure hull is actually a dwellfatigue problem. Owing to the complexity of severe marine environment and the uncertainty of the operating process of the deep submersible, the influence of random loads such as overload on the dwell fatigue growth rates should be studied to ensure the safety of the pressure hull of the deep submersible. The crack growth rate of metal materials under an overload condition can be divided into three stages: instantaneous acceleration, retardation, and recovery (Wang et al., 2017; Li, 2015). The fatigue crack growth rate of metal material will be obviously reduced
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