Experimental Study On The Effect Of Room Temperature Creep On Fatigue Life Of Titanium Alloy Materials For Pressure Hull

In recent years,more and more countries have positioned the development and utilization of deep-sea resources as important strategic goals.Therefore,the competition for marine resources has become increasingly fierce.As an important tool for deep-sea scientific expeditions,deep-sea manned submersibles play a vital role in the deep-sea geographical environment research,marine resource surveys,and deep-sea biological gene research.Titanium alloy has become the material of choice for deep-sea manned submersibles in various countries due to its excellent mechanical properties.The deep sea manned submersible's load during service can be simplified into: diving(increasing load),cruising(load maintaining)and floating(load decreasing).The load spectra used are all fatigue cycle loads,without considering the retention time.Therefore,it is necessary to carry out the retention-fatigue life test for the new titanium alloy material used for the pressure shell of the deep sea manned submersible.Titanium alloy materials for deep-sea manned submersibles work in a deep-sea environment,so they will have different degrees of creep deformation,which is different from traditional creep deformation.Creep also occurs when the yield limit is less than the yield limit.Therefore,it is extremely necessary and practical to carry out a long-term room temperature tensile creep test and fatigue performance test on a new titanium alloy material for the pressure shell of a deep sea submersible.This article takes the new titanium alloy material used for the pressure shell of deep-sea manned submersibles as the main research object,the RDL-100 electronic creep fatigue tester as the main equipment,and the basis of the theory of creep mechanics,material fatigue and fracture mechanics.The new titanium alloy material used for the pressure shell of deep-sea manned submersibles carries out long-term room temperature tensile creep test,fatigue life test and load-fatigue life test.Study the effect of room temperature tensile creep of new titanium alloys for pressure shells under different stress levels,different loading rates and loading history conditions;different stress levels and different retention times on load-fatigue of new titanium alloys for pressure shells The effect of life;the effect of different stress levels on the fatigue life of new titanium alloys for pressure shells,and the analysis of room temperature creep,fatigue life and load-fatigue life of each group of test strains over time to study room temperature creep Effect on the fatigue life of new titanium alloys for deep sea manned submersibles.The research work in this paper mainly includes the following aspects:(1)Theoretical research on creep and fatigue life.Firstly,the creep phenomenon is studied,and the research methods,characteristics,basic laws and related theoretical models of room temperature tensile creep at home and abroad are summarized and analyzed.The research focuses on the changes in the stress levels and strain rates of the creep phenomenon.Secondly,the theory of fatigue life is studied.Finally,the theory of dwell-fatigue life is studied.It provides a theoretical basis for subsequent long-term room temperature tensile creep tests at different high stress levels,fatigue life tests at different stress levels,and dwell-fatigue life tests at different retention times and stress levels.(2)Carry out room temperature tensile creep test.According to the parameters determined by the tensile test of the new titanium alloy material,a short-time room temperature tensile creep test is performed,and then a stress level interval suitable for the room-temperature tensile creep test is determined.According to the determined stress level interval,a long-term At room temperature tensile creep test,the effects of different stress levels,different loading rates,and loading history on room temperature tensile creep are obtained by analyzing the change of strain with time and the change of creep strain rate with time.(3)Carry out dwell-fatigue life test.Focus on studying the effects of dwell-fatigue life under different holding time and different stress levels,analyze and summarize the test results,and analyze the changes of cumulative strain with time and the cumulative strain with the fracture cycle under the same stress level and different holding time;Under the same load retention time and different stress levels,the cumulative strain changes with time and the cumulative strain with the fracture cycle,and the influence of load retention time and stress level on the load retention-fatigue life is obtained.(4)Research on tensile creep and fatigue life mechanism at room temperature.By comparing and comparing the cumulative strains of room temperature tensile creep,fatigue life,and dwell-fatigue life under the same stress level and the same time range,the effect mechanism of dwell time on fatigue life was studied.