Research On Method To Predict The Fatigue Strength For Welded Steel Structures Based On The Analysis Of Residual Stress

Fatigue damage is the main damage way of welded steel structures. As the instantaneous high concentration of uniform heat input during the welding process, it's inevitable generating the residual stress after welding. Obviously, the residual stress will affect the fatigue properties of the structure. Therefore, it's of great significance to research the fatigue strength prediction method of welded steel structures based on the analysis of welding residual stress. This paper studies the contents as:Adopting with numerical simulation, finite element analysis, considering the material's thermal physical properties and mechanical properties changing with temperature, using the inside heat rate loading method to simulate welding heat source, through the APDL programming language to achieve welding mobile loading of the heat source, established a mathematical model of welding transient temperature distribution. Adopting with the finite element analysis software's function of thermal-structural coupling, considering the one-way coupling of the temperature field on the stress-strain fields, Aiming the material nonlinear transient problem of thermal stress field for the welding, using the incremental theory of plastic mechanics to calculate, Material yield follows the Mises yield condition, Behavior in plastic region follows the flow rule. Through the "birth and kill technology," dynamically simulating solder fill and solidification during welding process, established the theoretical model of the welding stress-strain field calculation.Through indirect method, respectively and numerically analyzed the welding temperature field and welding residual stress field of several types of dislocation board connectors, butt joint and T joint and other typical welded steel structures. The several typical welding steel's three-dimensional welding temperature field and three-dimensional welding residual stress field were obtained.This paper systematically studies the critical distance method, on the basis of the critical distance point method, line method, area method, the volume method and the semi-ellipse area method, established fatigue notch factor theory of the fatigue strength prediction for welded structures. through critical distance volume method, using the first average principal stress in the hemisphere region of the root of the local welded toe to describe the fatigue strength for welded steel structure, based on the considerations of many factors, such as the structure geometry, the local weld geometry, loading form, stress ratio, size effect , residual stress, by analysis to the welding residual stress field, established a theory of critical distance to predict fatigue strength of welded steel structure. Through some theoretical predictions to typical welding steel, the calculated values are in good agreement with the experimental results to verify its effectiveness.Based on the analysis of the three-dimensional welding residual stress field and critical distance theory for welded steel structures, established the S-N curve prediction model. Through the prediction to several types of dislocated board joints, butt joints and T joints by S-N curve, theoretical prediction agrees well with the experimental data to verify the validity of the method. This method is valuable for engineering applications.