| In recent years,many countries have raised the development and utilization of deep-sea energy to the height of strategic development,and the overall competition for marine energy is more serious.The pressure hull of deep-sea manned submersible is the carrier for deep-sea scientific investigation and research.It has a far-reaching impact on the exploration of deep-sea energy and the analysis of deep-sea geographical conditions.Titanium alloy is a newly developed new composite material.Relying on its strong mechanical properties,it is regarded as the primary material for deep-sea manned submersible.Considering that the pressure hull of the nuclear submarine and submarine in service needs to be affected by the trapezoidal load,that is,the load is continuously increased during the submergence,and the load remains unchanged when the submergence is carried out to a specific depth,and the floating load is continuously decreased after the completion of the work.However,for a long time,the load spectrum selected during the life assessment of pressure shell structural materials belongs to fatigue cycle load,and the influence of load holding time is not taken into account,which makes the overall assessment work lack of reliability.At the same time,deep-sea operation will bring some creep effects.Even if it is lower than the yield limit,there will be a phenomenon different from the traditional creep deformation.Based on this,it is necessary to further study the tensile creep and fatigue properties of new titanium alloy materials for pressure hull of deep-sea submersible.The research object selected in this thesis is a new type of titanium alloy material for the pressure hull of manned submersible.The test equipment is rdl-100 electronic creep fatigue testing machine.Based on the relevant theoretical points of material fatigue and Creep Mechanics,the room temperature tensile creep test,fatigue life test and load retaining fatigue life test are completed for the material to explore various stress levels The specific effects of loading rate and loading history on the room temperature tensile creep of the new titanium alloy,the specific effects of various stress levels,the load holding time at the load peak and the load waveform on the load holding fatigue life of the new titanium alloy,and the specific effects of various stress levels on the fatigue life of the new titanium alloy.Finally Based on the analysis of the changes of fatigue life and load holding fatigue life in each group of tests with time,the influence mechanism of room temperature creep on the fatigue life of new titanium alloys is summarized.The main points of this study include the following parts:(1)Theoretical analysis of creep and load retaining fatigue,analyze the influencing mechanism of creep phenomenon and influencing factors of creep,analyze the research methods and main influencing factors of load-protection-fatigue related theories,and establish basic concepts of creep and load-protection-fatigue.It provides a theoretical basis for the subsequent experimental study of creep recovery characteristics at room temperature under different high stress levels,different loading rates and different unloading times.(2)On deep-sea manned submersible was used new titanium alloy material,high stress levels and different loading rate,different discharge time of room temperature creep recovery characteristic test,through the analysis of different high stress level and loading rate,creep under different unloading time three factors of accumulated strain and creep strain rate with the change of time,The influence of different stress level,loading rate and unloading time on the creep recovery of new titanium alloy materials at room temperature was obtained.(3)Experiments on the load-preserving fatigue crack growth rate of the new titanium alloy under different waveforms were carried out to analyze the influence of changing the loading time of the upper peak and the loading time of the lower peak on the load-preserving fatigue crack growth rate of the new titanium alloy,and the influence law of different waveforms on the load-preserving fatigue crack growth behavior was obtained.(4)Based on the selected prediction model of load protection-fatigue crack growth of titanium alloy,the model was modified considering the influence of different waveforms.The loading time of upper peak and loading time of lower peak were set,and the dynamic influence law of waveforms was also taken into account.Based on the modified model,the prediction of load retaining fatigue crack growth rate of new titanium alloy under various waveform conditions can be carried out smoothly.The analysis and test results are clear,and the modified model has good accuracy advantages. |
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