Welding Simulation Of Large Heavy-Load Complex Contour Vacuum Vessel And Study On Method To Releve Residual Stress

The vacuum vessel is the core component of the magnetic confinement fusion reactor,mainly to support the internal components and improve the steady-state operating environment for the plasma,thus there is a high demand for vacuum vessel's size precision molding,structure stability and fatigue life.The vacuum vessel is a double shell structure with complex contour,and the section is D shape,which has the characteristics of large size,large weight,complex structure and high requirements for material properties.The vacuum vessel 8 sectors by the same structure welded together,in the manufacturing process of each 1/8 sector and by the 4 sector of the 1/32 welded together,1/32 sector is composed of 4 PS segment,and each PS segment is pressed after welding and welding parts.The vacuum vessel is composed of 8 sectors welded together,each 1/8 sector is composed of 4 sector of the 1/32 sector,1/32 sector is composed of 4 PS sgment,each PS segment by welded by welding parts in the manufacturing process.There are a lot of welding methods used in forming process of the vacuum vessel,such as:argon arc welding,electron beam welding,narrow gap welding.In the process of welding,the welding deformation will affect the forming precision of the vacuum vessel,therefore,it is very important to control the welding deformation in the welding process.In order to control the welding deformation of the vacuum vessel,the inherent strain method is used to predict the welding deformation of the vacuum vessel,the influence of welding sequence and external constraints on welding deformation are studied.The welding deformation of PS1 segment,PS2/PS4 segment,PS3 segment,1/32 sector and 1/16 sector are simulated by setting different welding sequences,in order to simulate the real welding condition,the corresponding welding parts are activated according to the welding sequences in the welding deformation simulation.According to the condition of welding deformation without external constraints,the external constraint conditions are established,in order to study the influence of external constraint on welding deformation,The results show that the welding deformation and the maximum welding deformation are different when the welding sequences are different,the welding deformation is different when the welding sequence at different condition,applying external constraint can significantly reduce the amount of welding deformation,which provides theoretical references for the actual production processing.In order to control welding deformation,the rigidity fixed method is used,which will bring larger residual stress in vacuum vessel welding,The residual stress will cause the stress corrosion and the micro crack growth of the welded structure,which has a great influence on the structural stability and fatigue life of the vacuum vessel.In order to reduce the influence of welding residual stress on the vacuum vessel,the welding residual stress should be eliminated after welding and welding.There are many ways to eliminate welding residual stress,which is affected by the structure,weight and material properties of the vacuum vessel.The method is suitable for vacuum vessel welding residual stress elimination,including heat treatment,ultrasonic peening,shot peening and vibration aging.In this paper,the welding test plate with the similar structure of the vacuum vessel is designed,and the process of narrow gap welding is simulated by using the thermo elastic plastic method,and the welding temperature field and stress field are obtained,the results show that the temperature in the welding process changes periodically,and the welding temperature field and stress field are symmetrical.The simulation results are taken as the initial conditions of trailing ultrasonic impact treatment,and the influence of the trailing ultrasonic impact treatment on the welding residual stress is simulated,the results show that the residual stress distribution of the transverse and longitudinal welding can be improved obviously with the ultrasonic impact treatment.The simulation results are taken as the initial conditions of shot peening,and the influence of the shot peening on the welding residual stress is simulated by SPH method,the results show that the SPH method can be used to simulate the shot peening process,and the shot peening treatment can improve the distribution of the residual stress in the transverse and longitudinal directions and residual compressive stress produce on the surface of the impact zone.The vibration aging treatment parameters of the PS1 section,PS2/PS4 segment,PS3 segment,1/32 sector and 1/16 sector are given by software simulation,the vibration aging treatment parameters including:support points,excitation points,exciting frequency,exciting force and exciting time.The vibration aging treatment can be completed according to the vibration aging treament parameters.The heat treatment process of the vacuum vessel is developed under the condition of considering the material properties,the deformation of the structure and the effect of the residual stress removal,the experimental study was carried out according to the heat treatment process,the results show that the amplitude of residual stress can be reduced and the distribution of welding residual stress can be improved by heat treatment.