Study Of The Influence Factors On Fatigue Life Of Welded Joints Based On Field Intensity Approach

In this thesis, the effect factors on fatigue life of welded joints based on field intensity approach are studied. The effect of the joint geometry parameters, type of loading and thickness effect are analyzed. Based on the Stress Field Intensity Method of fatigue assessment of welded joints, a new hot spot stress method is proposed. When compared to the surface extrapolation technique for structural hot spot stress evaluation, the proposed method has the additional advantage in that it is able to account for the stress gradient effect and thickness effect observed in welded joints.The main contents and results are given as follows:Basic principles and procedures of the Stress Field Intensity Method of fatigue assessment of welded joints are systematically discussed. By the APDL language of Ansys, some experimental datas are used to determine radius of the stress field area of A3 annealed steel.Based on the Stress Field Intensity Method, the fatigue notch factor of welded joints is calculated by FE method.The effect of parameters such as plate thickness, weld toe radius and weld bead flank angle on the fatigue notch factor are analyzed. Based on the analysis of the calculation results, the empirical formula for evaluating the fatigue notch factor of welded joints is presented. Based on the analysis of the fatigue notch factor of welded joints, the difference between the fatigue strength of welded joints under tension load and that under bending load is presented. Also the empirical formula of thickness effect is considered and presented.Based on the empirical formula calculated by Stress Field Intensity Approach, a new hot spot stress method is proposed. The proposed method has the additional advantage in that it is able to account for the stress gradient effect and thickness effect observed in welded joints. The new method can significantly reduce fatigue data dispersity.