Progress made in the research on load-bearing fatigue of titanium alloys for deep-sea submersible pressure chambers
The deep-sea contains biological and mineral resources. The deep-sea submersible is the main vehicle for deep-sea scientific research and resource development. The "pressure chamber" is its core component and a safety barrier for humans to enter the deep sea. For each operation of the submersible, the pressure chamber is subjected to a continuously changing seawater pressure (load-up-load-unload), and the fatigue under this load spectrum is called Dwell fatigue. The new high-strength and tough titanium alloy is the preferred material for pressure chambers, and the study of its load-bearing fatigue characteristics is of great significance for the design and reliability evaluation of deep-sea submersibles.
The study found that there are three load fatigue failure modes of pressure chamber titanium alloys, namely fatigue failure, ductility failure, and combined fatigue and ductility failure. The interaction of holding load and fatigue load accelerates the failure of the specimen and leads to competition between different failure modes. The study further found that the holding fatigue life is related to the accumulated maximum strain in the first cycle, and the two have an approximately linear relationship in the double logarithmic coordinate. The intermittent loading time has no effect on the holding fatigue behavior of titanium alloys. The experimental results and theoretical analysis reveal the fatigue mechanism of the titanium alloy under load, that is, the plastic deformation caused by the load increases the actual stress of the specimen, which promotes the expansion of cracks or damages that have been formed. The plastic strain increases the accumulation of the dwell fatigue plastic strain.
The research was completed by the LNM Microstructure Computational Mechanics Research Group of the Institute of Mechanics of the Chinese Academy of Sciences and the 702nd Research Institute of China Shipbuilding Industry Corporation. and evaluation technology research”. Relevant research results were published in the Journal of Materials Science & Technology, and Sun Chengqi from the Institute of Mechanics, Chinese Academy of Sciences is the first author and corresponding author of the paper.
