Numerical Simulation Of Welding Residual Stress Relief For Pressure Spherical Shell Of Deep Submergence Vehicle

With the rapid development of economy and the development of industrial manufacturing technology,the demand and consumption of resources are increasing in various countries.On the contrary,which has produced the trend that can’t meet the rapid development needs of the 21 st century society,which forces countries to shift their eyes from land resources to marine resources.In order to meet the demand of deep-sea resources exploitation,advanced operation equipment must be relied on,including manned submersible deep sea.The main component of the submersible is the pressure ball shell.The pressure ball shell is used to carry the underwater pressure to ensure the life safety of the deep-sea underwater workers.When the deep-sea submersible needs to work in the deep water under 800 m for a long time,titanium alloy is generally used as the metal material and the structure shape is spherical,which is due to the low density of titanium alloy.The titanium alloy materials have good corrosion resistance and low conductivity heat conductivity,which make the structure service life longer.In recent years,a large number of research and experimental results show that fatigue fracture is the key factor causing the damage of metal structures such as ships,aerospace and submersibles.And most of the fracture location is in the welding stress concentration area,which is due to the welding residual stress will cause local plastic deformation of the material.Under the interaction of alternating load and external load,the fatigue crack may be generated in the high stress area,and gradually expand,leading to the fracture of the structure.Therefore,in order to ensure the life safety of underwater workers and the normal operation of submersible equipment,it is particularly important to analyze the distribution law of welding residual stress of pressure spherical shell and eliminate it.In this paper,based on the THERMOELASTIC-PLASTIC theory,the finite element simulation software ABAQUS is used to simulate the welding of TC4 titanium alloy pressure spherical shell,analyze the distribution of residual stress,and study the effect of external pressure method and heat treatment method on residual stress relief after welding.Firstly,TC4 titanium alloy plate was established,and DFLUX compound heat source subroutine was written in Fortran.ABAQUS finite element simulation software was used to simulate the electron beam welding of TC4 titanium alloy plate.The feasibility of pyrogen model was verified by comparing the numerical simulation results with the experimental results.Secondly,the finite element model of pressure spherical shell is established,and the welding residual stress of pressure spherical shell is numerically simulated by using the same welding method.The distribution law of welding residual stress is obtained,and the results are compared with those in other literatures,which proves the accuracy of the model.Finally,the welding residual stress of pressure spherical shell is eliminated by external pressure method and heat treatment method.The results show that with the increasing of external pressure load,the welding residual stress can be released better and the elimination effect is better;Different heat treatment process parameters have different effect on residual stress relief.