Research On Prediction Method Of Fatigue Life Of Pressure-resistant Shell Of Conical Column Considering The Release Of Welding Residual Stress

High-strength steel in ship welding process will produce high welding residual stress,and welding defects will occur during the welding process,which will accelerate the fatigue damage of the welded structure.Deep-sea pressure-resistant structures,such as submarine cone-column combined shells,are typical high-pressure shell-like structures.High welding residual stresses are prone to fatigue cracks at the joints of cones and columns,posing a great threat to submarine safety.However,the fatigue life analysis of the general welded parts does not consider the influence of the release of the welding residual stress with the cyclic load,which is an error in the fatigue life prediction.Therefore,it is very important to study the fatigue life prediction method of deep sea structures considering the release of welding residual stress under tensile cyclic loading.This paper adopted a combination of finite element simulation and experimental analysis.Firstly,the welding test and residual stress release test of high strength steel plate butt welding were carried out.Secondly,the finite element numerical calculation of welding residual stress and release was carried out and verified by the test results.Based on this,the calculation formula of welding residual stress release was proposed.At the same time,the fatigue crack growth test was carried out and the relevant parameters of the crack growth rate curve model were determined.The fatigue crack propagation prediction method considering the release of welding residual stress was proposed.Finally,the submarine cone-column pressure-resistant shell scale ratio model was taken as an example to illustrate the fatigue crack propagation calculation method and steps considering the release of welding residual stress.The main research contents of the thesis are as follows:(1)The domestic and international research status,main research contents and methods in the field of fatigue and welding residual stress research were summarized.The form,model and basic equations of welding heat source were concluded respectively,and the stress field theory of welding residual stress release process was introduced as well.At the same time,the development history of fatigue theory analysis method and the induction work of main branches were carried out.A theoretical analysis methods suitable for studying fatigue problems under cyclic loading was found by comparing the applicable objects of various methods and its advantages and disadvantages.Finally,the Extended McEvily theoretical model was determined as the main theoretical analysis method to lay the foundation for the subsequent theoretical model establishment and elastoplastic finite element method prediction.(2)The AH36 marine high-strength steel palte welding test was designed and carried out.By comparing the results of FEM with that measured test results,the accuracy of finite element numerical simulation was verified.Finally,the factors affecting the welding residual stress during the welding process were studied.(3)The welding residual stress release test of AH36 marine high-strength steel was designed and carried out.The cyclic tensile test on the welded test piece was carried out to track the residual stress release of the welding residual stresses.Then,simulation calculation through the test process was executed to verify the correctness of the simulation calculation results.Based on the formal work,the simulation of welding residual stress release under three kinds of cyclic loads was complied to propose the welding residual stress release calculation formula of the inner and the surface of the specimen,which was proved to be adaptable by the experiment data.Finally,the factors affecting the release of the welding residual stress were studied.(4)The fatigue crack growth rate test of AH36 marine high-strength steel under tensile load of different stress ratios and load sequence was carried out.The relevant parameters in the Extended McEvily model under different stress ratios were calculated to obtain the fatigue crack growth rate of the material.At the same time,the fatigue growth rate models of the material under different load sequences were proposed by the optimization of the model parameters.A fatigue life prediction method considering the release of welding residual stress was proposed,and the butt welding thin plate was taken as the research object to study the fatigue life.(5)The scale-ratio of the submarine cone-column joint was selected as the research object to study the distribution of welding residual stress,and the influence of welding sequence on the residual stress of the welded joint of the vertebral column was discussed.Based on the fatigue life analysis method of the welded parts considering welding residual stress proposed in Chapter 5,the fatigue life analysis of the convex cone at the cone-column joint was carried out.The calculation process of the method was introduced in detail,and the experimental results of the relevant literature were compared to verify the accuracy of the method.