Study On Residual Stress Of Equatorial Weld Of Pressure Spherical Shell Of Deep Sea Manned Submersible

With the continuous development of marine resources,more and more attention has been paid to manned submersibles.Because of its low density,high specific strength and good corrosiveness,titanium alloy has become the first choice material for deep-sea pressure spherical shell manned submersible.The pressure spherical shell is usually welded by two hemispherical shells,with a long equatorial weld,and there is a high residual stress near the weld,which has a negative impact on the safety of the pressure spherical shell,which is one of the problems urgently needed to be studied.The pressure spherical shell of the manned submersible is generally thick,and the manufacturing cost is relatively high.The equatorial weld belongs to butt welding,because the welding residual stress of inner shell is difficult to test.Therefore,in this paper,the residual stress of Ti80 butt welded thick plate is calculated,and X-ray nondestructive testing method is used for residual stress test.On the basis of the agreement between the numerical simulation and the test results,the numerical simulation of the welding residual stress of the equatorial weld of Ti80 pressure spherical shell is carried out,and the influence of the narrow gap technology and the external pressure load on the welding residual stress of the equatorial weld of Ti80 pressure spherical shell is studied.The main research work and conclusions are as follows:(1)Based on the non-destructive testing method,the residual stress on the surface of the butt welded thick plate of Ti80 was tested and studied.The test results show that: the transverse welding residual stress on the surface of the butt welded thick plate of Ti80 presents an asymmetric bimodal tensile stress distribution,the peak value of the tensile stress is high,and the maximum value appears near the weld toe;the longitudinal welding residual tensile stress on the weld toe path is large;(2)After wire cutting,the tensile test specimens of Ti80 butt welded thick plate were obtained,and the residual stress was studied by nondestructive testing.The test results show that the residual tensile stress of transverse welding on the surface of the cut tensile specimen shows an asymmetrical bimodal distribution,and the peak value of the asymmetrical bimodal distribution is reduced to 59% compared with that of butt welded thick plate,and the position of the bimodal is close to the weld center line;(3)Based on the basic theory of thermoelastoplasticity and APDL redevelopment program of ANSYS,the welding residual stress of Ti80 butt welded thick plate is analyzed by numerical simulation.The results show that the transverse welding residual stress on the surface of thick plate presents asymmetric bimodal distribution;the welding residual stress at the weld toe and along the longitudinal direction of the weld along the Y-axis is high,and the residual stress value at the Y-axis is higher than that at the weld toe.The numerical simulation results are compared with the experimental results.The results show that the numerical simulation results of residual stress are consistent with the results of nondestructive testing,which verifies the reliability of the numerical simulation method of residual stress in this paper;(4)The influence of different welding process and tensile load on the welding residual stress on the surface of the butt welded thick plate of Ti80 is studied.The calculation results show that the welding residual stress on the surface of the butt welded thick plate decreases after adopting the narrow gap welding process,that is to say,the welding residual stress on the surface of the butt welded thick plate is smaller;the welding speed has little effect on the residual tensile stress on the surface of the thick plate,and it is transverse with the increase of the welding speed The tensile load can release the residual stress of the butt welded thick plate of Ti80,and the larger the tensile load is,the more the transverse residual tensile stress on the surface of the butt welded thick plate will release.The results show that the distribution trend and the maximum value of the residual stress of the butt welded thick plate of Ti80 and the same yield strength high strength steel have little change;(5)Based on the basic theory of thermoelastoplasticity and the finite element analysis software ANSYS,the welding residual stress of equatorial welding of high strength steel Q345 pressure spherical shell is simulated,and the rationality of the method is verified by comparing the existing literature.Based on this,the distribution rule of welding residual stress of equatorial welding of Ti80 pressure spherical shell is obtained,and the welding residual stress of the highest welding temperature to Ti80 pressure spherical shell is analyzed The results show that: in the vertical weld path of the inner and outer shell of Ti80 pressure spherical shell,the longitudinal residual stress is tensile stress,and the residual stress value of the inner shell is greater than that of the outer shell;the transverse residual stress direction is opposite,and the inner shell is tensile pressure.For the welding residual stress along the weld path,the longitudinal and transverse residual stress of the inner shell are tensile stress,and the longitudinal residual tensile stress is greater than the transverse residual tensile stress.The longitudinal residual stress of shell is tensile stress,while the transverse residual stress is compressive stress.Secondly,the higher the welding temperature,the higher the residual stress level of the equatorial weld of the Ti80 pressure spherical shell;The external pressure has little effect on the residual stress of equatorial weld of Ti80 pressure spherical shell.