The Impact Analysis Of Apparent Defects And Residual Stress On Fatigus Strength Of Steel Pipe-welded Hollow Spherical Joints

In recent years, space truss structure with its big span, advantages of light weight, fast construction, beautiful modelling is widely used in various kinds of large industrial workshop, how to ensure the safety of the node is the main research topics of this structure.At present most of the space truss structure are welded structure, welding defects are widespread in the welding process, welding which is caused by high temperature can make weld residual considerable residual stress, and sometimes even to the yield strength, these two aspects would reduce the fatigue strength of welded structure.The nodes of the past research often ignore the welding defects and the influence of residual stress, to simplify the processing node.This paper argues that the weld defects and residual stress on the influence of the steel tube-welded hollow ball node fatigue strength is very necessary.In this paper, based on the national natural science fund project "space grid structure under the action of a suspension crane fatigue problems in-depth study (51178286201-51178286201)", on the fatigue test performance of the steel tube-welded hollow ball nodes for research, the main research content is as follows: (1) Using the finite element analysis software ANSYS, the pipe connection node model theory analysis, the axial tension is obtained under the action of stress distribution regularity of tube ball connected nodes;By changing the seam width and depth of core-die, concluded under the action of axial tensile stress distribution nephogram of each model to calculate the stress concentration factor is analyzed, it is concluded that the stress concentration factor as the bite edge depth increases, and decreased with the increase of bite edge width.(2) Using finite element analysis software ANSYS, the tube ball node model, using ANSYS and unit technology and welding process simulation for hot-structure coupling function.Node welds can be divided into four, each weld is divided into12heating period, it is concluded that four weld in different periods of welding temperature field distribution;Simulate the along the weld centerline, direction of steel tube and hollow ball direction the temperature time curve of each point, accords with the basic law of heat transfer.(3) using finite element analysis software ANSYS structural unit, thermal unit can be converted to use simulation of the heat source moving unit technology for life and death, it is concluded that four weld at different stages of heating and cooling to the stress and equivalent stress distribution nephogram;Through data analysis, it is concluded that the equivalent residual stress distribution curve of periodic change, a maximum of204mpa, close to the yield;Simulate the time curve of residual stress along the direction of the center line of the weld.