Fatigue Assessment Of Welded Joints Based On Structural Stress

Welded joints is a common structure connection in industrial field which is the major fatigue area for welded structure.The safe use of welded structure is directly determined by the strength of the welded joints.So,it is very necessary to estimate fatigue strength of the welded joint.In this paper,the structural stress of weld toe were studied based on the Dong approach.The major work and achievements in this paper are as follows:1.According to the function of the nodal forces and distribution forces are equivalent,the relation between the nodal forces and the line forces cross section of eight node second-order shell element were deduced by using the finite element shape functions.Structural stress discrete formulas of solid element were given.The detail steps to solve the structural stress of solid element and shell element were given.2.In order to solve the problem that the post-processing of finite element analysis results is very complex by Dong approach,the post-processing computation program was developed by scripting language python of finite element software ABAQUS to simplify the post-processing of results data.The provisions of finite element model and specific train of thought of program development were given in ABAQUS finite element software environment.Fatigue assessment of the welded joints was realized based on Dong approach.3.The finite element models of the lap joint,T-joint,rectangular hollow section joint were established with different element type and mesh size by using finite element software ABAQUS,and then the models were solved to obtain stresses and nodal forces field.The finite element results were post-processed with the program to obtain the structural stress.It was proved that the Dong approach was insensitive to the element type and mesh size by comparing the structural stress results of welded joints with different element type and mesh size,and the validity of the program was verified.4.The structural stress results of rectangular hollow section joint with the weld profile and without weld profile were compared.The maximum structural stress result without the weld profile was bigger than that with the weld profile,but both positions of the maximum structural stress were coincident with the experimental fatigue position.The influences of thickness of weld,the size of welded leg and the type of welded end on the structural stress were discussed.The structural stress concentration factor of weld toe decreased with the increasing of the motherboard thickness,but increased with the increasing of the attachment thickness.The dispersive influence of the size of welded leg on the structural stress concentration factor of weld toe was small.The dangerous position was changed with increasing of welded end,but it is not necessary to improve the fatigue life of welded.5.The fatigue life of rear-axle welds was predicted by using the program,and compared with the experimental results.The prediction results of fatigue life and fatigue position based on Dong approach were basically coincided with the experimental results,and the validity of Dong approach was verified.