Effect Of Welding And Annealing Residual Stress On Fatigue Life Of Pressure Ball Shell For Deep Submersible

As an important part of the deep-sea manned submersible,the pressure-resistant spherical shell plays the role of guaranteeing the safety of researchers and equipment as well as carrying seawater pressure,and its performance directly affects the overall structural safety of the deep submersible.The pressure-resistant spherical shell is a complex welded structure,and there is a large residual stress in the weld area,which is very likely to lead to crack sprouting in the service process under the strong coupling effect of welding residual stress and deep-sea high pressure.Therefore,the assessment of the pressure-resistant spherical shell welding residual stress distribution law,optimize the annealing process parameters to reduce the residual stress,to improve the fatigue life of the pressure-resistant spherical shell has engineering guidance significance.In order to ensure the accuracy of the welding residual stress assessment model,this thesis uses a combination of conical,double ellipsoidal heat source model,the TC4 titanium alloy butt plate electron beam welding process simulation,combined with experimental data on the melt pool sample and residual stress distribution curve for comparison,the results show that the welding model can accurately simulate the electron beam welding process,and welding residual stress calculation results are more accurate.This thesis combines the TC4 titanium alloy pressure-resistant spherical shell welding and stress relief annealing process of the actual working conditions,the TC4 titanium alloy pressure-resistant spherical shell welding process and stress relief annealing process to carry out numerical simulation,analysis of temperature field changes in the welding process and its impact on the stress field distribution,to explore the pressure-resistant spherical shell surface of each weld seam welding and annealing residual stress distribution law,compared with different annealing temperature,temperature rise rate,holding time The effect of welding residual stress reduction,combined with the annealing process strain evolution law to explore the mechanism of annealing residual stress reduction.The results show that: welding residual tensile stress and compressive stress in the pressure-resistant spherical shell surface along the welding seam alternately distributed,the residual tensile stress at the entrance and exit hatch weld is larger,the value of about 1100 MPa,the pressure-resistant spherical shell need to take stress relief measures;after 500 ℃ insulation 2h annealing treatment,the maximum residual tensile stress decreased by 49.5%,the annealing temperature for the effect of residual stress reduction,heating rate and The effect of annealing temperature on the effect of residual stress reduction is larger,and the effect of heating rate and holding time on the effect of residual stress reduction is not obvious;the residual stress reduction occurs mainly in two stages of the annealing process,in the heating stage,the material yield strength decreases rapidly and the elastic deformation changes slowly,resulting in the conversion of elastic strain into plastic strain,and in the holding stage,the creep effect results in the conversion of elastic strain into creep strain,and the reduction of elastic strain results in the reduction of residual stress.Based on the linear cumulative damage theory,the residual stress of the pressureresistant spherical shell after annealing is coupled with the deep sea pressure to study the stress distribution law of the pressure-resistant spherical shell of the deep submersible under the ultimate service condition and analyze the influence of the residual stress on its fatigue life.The results show that the most prone to cracks in the access hatch weld toe area,welding residual stress will lead to a significant decrease in the fatigue life of the pressure-resistant spherical shell,after annealing treatment,the fatigue life of the fatigue life is significantly improved,welding residual stress to reduce the fatigue life of the pressure-resistant spherical shell is not negligible,annealing process to reduce the welding residual stress is essential.