Influence Of Equatorial Weld Residual Stress On Mechanical Properties Of Spherical Pressure Shell

When deep-sea pressure resistant structures are in underwater scientific research operations,it is inevitable to bear the pressure of sea water,which is usually relatively large.It is necessary to fully consider the influence of various factors in the design and construction to ensure that the structure will not suffer structural damage during service.Due to the limitations of the existing manufacturing technology,shell structure is usually processed and manufactured by welding,so that the structure will inevitably produce plastic deformation,which will have a relatively obvious impact on the mechanical properties of the pressureresistant structure.Therefore,it is of great engineering practical significance and value to study the mechanical properties of titanium alloy spherical shell considering the influence of equatorial weld residual stress.In this paper,the numerical simulation and experimental study on the welding residual stress of Ti80 butt welding thick plate were carried out respectively.The numerical simulation results were compared with the measured values of the test,which verified the rationality of the numerical simulation method.On this basis,the numerical simulation analysis of equatorial weld residual stress of Ti80 spherical pressure shell and Ti62-A spherical pressure shell was carried out respectively.The influence of opening on equatorial weld residual stress of Ti62-A spherical pressure shell and the ultimate strength of Ti80 spherical pressure shell were studied considering the influence of equatorial weld residual stress.In addition,the influence of external pressure on the residual stress of the equatorial weld of Ti80 spherical pressure shell and the ultimate strength of the spherical shell under external pressure were studied.Finally,the fatigue strength of Ti80 spherical pressure shell considering the residual stress of equatorial weld and the effect of heat treatment was studied.The main conclusions of this thesis are as follows:(1)The transverse welding residual stress on the vertical weld path of Ti80 butt welding thick plate is tensile stress,which presents an asymmetrical distribution trend.The longitudinal welding residual stress is a large tensile stress,which exceeds the yield strength value of the material.The residual stress of longitudinal welding along the weld path and along the weld toe is tensile stress.The numerical simulation results are basically consistent with the experimental results,and the error is within a reasonable range,which verifies the rationality of the numerical simulation method.(2)The transverse residual stress and the longitudinal residual stress on the vertical weld path and along the weld path of the inner shell of the Ti80 spherical pressure shell are the residual tensile stress.The lateral residual stress along the weld path and the vertical weld path on the outer surface of the Ti80 spherical pressure shell is compressive stress,while the longitudinal residual stress is tensile stress.The transverse residual stress of Ti80 spherical pressure shell along the path of shell thickness is compressive stress near the shell area and tensile stress near the inner shell area.The residual stress of longitudinal welding is tensile stress,and the stress value is near the yield strength of the material.(3)The distribution trend of equatorial weld residual stress in vertical weld and along weld path of Ti62-A intact spherical shell is consistent with that of equatorial weld residual stress in corresponding path of Ti80 spherical pressure shell.The effect of opening on the equatorial weld residual stress of Ti62-A spherical pressure shell is not obvious.Increasing the radius of the hole has little effect on the residual stress of the equatorial weld.(4)When the residual stress of equatorial weld is considered,the ultimate strength of Ti80 spherical pressure shell is reduced compared with that when the residual stress of equatorial weld is not considered.The external pressure load has no obvious effect on the residual stress of the equatorial weld seam of Ti80 spherical pressure shell.External pressure has little effect on the ultimate strength of Ti80 spherical pressure shell.(5)The number of cycles in the inner shell of Ti80 spherical pressure shell is less than the number of cycles in the outer shell,and the number of cycles in the heat treatment is less than the number of cycles in the heat treatment,and the fatigue life is improved significantly after the heat treatment.The number of dives of general deep submersible is far less than the number of cycles obtained by fatigue calculation,therefore,Ti80 spherical pressure shell generally will not appear fatigue problems.