Development Of Efficient Calculation Method For Welding Residual Stress And Deformation Of Thick Steel Structures For Engineering Applications

With the rapid development of domestic energy,construction,chemical and other industries,thick steel structures are widely used.For some important parts of the steel structure under severe service environment,its structural safety and stability seem to be very important.Welding technology is an important and common processing method in the connection process of metal materials.However,welded joints have always been considered as weak positions in welded structures,especially residual stress caused by large internal restraints and high stiffness in thick joints will seriously affect the use of components.Especially for the energy and chemical industries,most of their key operating equipment are made of austenitic stainless steel and nickel-based alloys,and these materials have a very pronounced work hardening tendency,which leads to excessive residual stress after welding,these make it easy to produce stress corrosion in welded joints.In addition,welding deformation will also affect the accurate installation of components.At present,the finite element method has been used to predict welding residual stress and deformation,but for thick welded joints,the large number of weld beads and elements will make the calculation time tedious.So under the existing hardware conditions,it is particularly important to develop new calculation methods to improve calculation efficiency.In this paper,the austenitic stainless steel and nickel-based alloy materials commonly used in the energy and chemical industries are taken as the research object.Based on ABAQUS general finite element numerical simulation software,a thermal-elastic-plastic calculation method considering material nonlinearity,geometrical nonlinearity,work hardening,and annealing effect was developed to numerically simulate the residual stress and deformation of thick welded joints.Meanwhile,the residual stress distribution of the joint was actually measured by the small hole method or the sectioning method,respectively.The validity of the developed calculation method was verified by comparing the calculation results with the experimental results.Furthermore,different calculation methods are developed to improve the calculation efficiency,and the differences in calculation accuracy and efficiency between different calculation methods and conventional methods are compared.By adopting an optimized calculation method,the welding residual stress between the saddle tube and the pipe of a nuclear power nozzle is simulated,and the full release method is adopted to verify the accuracy of the calculation results.In addition,a mobile heat source model of local vacuum electron beam welding is developed based on Fortran language,and the calculation results are compared with those of traditional gas arc welding.The results show that: 1)the residual stress distribution calculated by the instantaneous heat source model and the mobile heat source model is not much different,but the time it takes to calculate the residua stress for the mobile heat source is about 10 times the instantaneous heat source.2)For the axisymmetric model and plane strain model,the difference between the residual stress distribution calculated by the 3D instantaneous heat source model and the 2D model is not large,but the time to calculate residual stress of the former is about 30 times that of the latter.3)For complex structures that cannot be simplified to a two-dimensional model,the lumped-passes method and instantaneous heat source model can be used to further improve efficiency.Specifically,lumping weld beads along the thickness direction of the plate has little effect on the calculation accuracy of the residual stress while lumping weld beads along the width direction will underestimate the transverse residual stress and cause a larger deviation.4)Compared with gas arc welding,local vacuum electron beam welding can significantly reduce welding deformation.At the same time,the range of high longitudinal tensile stress in the electron beam welded joint is significantly narrower than that produced by gas arc welding.Moreover,the maximum value of the longitudinal residual stress caused by the former is smaller than the maximum value of the longitudinal residual stress caused by the latter.The welding time of gas arc welding is about 9 h,while the welding time of local vacuum electron beam welding is about 2 min.The numerical simulation results show that the former takes about 135 h and the latter takes about 71 h.The calculation method developed in this research provides a certain theoretical basis for efficiently and accurately predicting the residual stress of welded joints of thick steel structures.At the same time,the main conclusions obtained in this paper also provide different solutions for solving the excessively long calculation time of residual stresses in thick welded joints.