Distribution Of Welding Residual Stresses In Hollow Sphere Joints And Its Influence On Joint Axial Stiffness

Welded hollow spherical joints are widely used in large span space structures due to their simple fabrication,convenient construction and flexible application.The engineering community has found that the welding residual stress has a negligible effect on the mechanical properties of hollow spherical joints,and the effect of residual stress on the overall structure has become a research hotspot.The premise of accurately considering the residual stress of the hollow spherical joint in the overall analysis of the spatial structure is to accurately analyze the residual stress distribution pattern of the welded hollow spherical joint.However,the previous research on the residual stress distribution of welded hollow sphere joints has mainly focused on the position of the weld,and it is difficult to describe the welding residual stress in a three-dimensional distribution.This paper uses ANSYS finite element software to simulate the single-channel and multi-layer welding process of ball-tube butt-joint girth welds,and summarizes the spatial distribution of welding residual stress.The residual stress of the hollow sphere joint was tested by magnetic testing to verify the finite element simulation results.On this basis,ultrasonic impact treatment was performed on the weld to produce test pieces with different welding residual stresses.Then,an axial compression test was performed to study the effect of welding residual stress on the axial stiffness of the welded hollow ball joint.The main research work of this paper is as follows:(1)Based on ANSYS finite element software,a three-dimensional solid finite element model of welded hollow ball joints was established.The transient thermal analysis method was adopted to consider the change of material performance parameters with temperature.The life and death element was used to simulate the welding process of single-pass multilayer welding process,and the three-dimensional spatial temperature field with obvious circulation characteristics was obtained.(2)Based on the welding temperature field analysis results,indirect coupling method was used to simulate the welding residual stress,and the plastic strain at each moment in the heat affected zone of the weld and the final welding residual stress of the whole model were obtained during the welding process.The analysis of the evolution law of plastic strain can clearly understand the formation process of residual stress.By drawing the plastic affected zone after cooling,it provides guidance for eliminating welding residual stress.(3)Based on the final calculation results of the welding residual stress,the distribution rules of the hollow ball and the thickness of the steel pipe are analyzed.It was found that the axial welding residual stress of the steel pipe near the weld and the residual stress in the longitude direction of the hollow ball were symmetrically distributed,and the steel pipe near the weld and the welded hollow ball showed strong bending characteristics in the thickness direction.The influence of geometrical dimension of welded hollow ball joints on residual stress of welded hollow ball joints was analyzed by parameterization.(4)Through the welding test of the test piece,the residual stress of the welded hollow ball joint was tested by magnetic measurement method to verify the finite element simulation results.On this basis,ultrasonic impact treatment was performed on the weld with ultrasonic impact equipment to produce test pieces with different welding residual stresses.(5)Anode axial compression tests were performed for welded hollow ball joint models with different residual stresses.Load-displacement curves were drawn based on the test results.The axial stiffness of welded hollow ball joints was determined by the slope of the load-displacement curve.The influence of welding residual stress on the axial stiffness of welded hollow ball joints with the geometrical dimensions(hollow ball diameter D,wall thickness t and steel pipe diameter d)was analyzed parametrically.