Researches On The Residual Stress And Its Redistribution In The Fatigue Crack Propagation Of The Typical Welded Joints

Ships and large marine structures are mostly welded by high strength steel. During the welding process, the local non-uniform thermoplastic deformation and phase transformation were produced thermoplastic deformation and phase transformation, as well as the self-balanced residual stress. The hot spot stresses are affected by the residual stress. Therefore, the influence on the evaluation of the strength analysis would be affected. In addition, surface crack are produced easily at weld toe of the large steel structures. And then, the welding residual stress would be redistributed when the cracks generated. And, the crack would be extended under the cyclic loads, and in turn the crack propagation would be effected by the welding residual stress redistribution. The study of the welding residual stress with initial crack in structures is relatively absent at home and abroad at present. And papers of welding residual stress redistribution in the process of crack propagation for high strength steel are few published. As a result, the crack propagation in high strength steel weld welding residual stress redistribution in the study, for the accurate prediction of high strength steel welded structure fatigue strength has important reference significance. As a result, the study on the welding residual stress redistribution in the process of crack propagation for high strength steel has important reference significance for the accurate prediction of fatigue strength for high strength steel structure.The welding residual stress and its redistribution in the process of fatigue crack propagation for two typical welded joint were simulated in this paper. And the heat-elastic-plastic theory and fatigue crack propagation related theory were used for simulation. The main research work and conclusions are as follows:(1) The initial welding residual stress of the complete structure of two typical welded joint were simulated. And the distribution rules of the initial residual stress were achieved. Then, different axial tensile loads were loaded on two welded joints, and the variation of the axial welding residual stress under different loads was researched. It can be concluded that the axial tensile residual stresses of the two complete welded joints are larger in the center of the weld and near the weld toes. The residual tensile stresses near the weld were released after the axial tensile load applied. And the greater the load, the more residual tensile stress released.(2) The semi-elliptical surface crack was added near the weld toe of the two completed welded joints. And the redistribution of the residual stress of the welded joint with initial crack was calculated by the method of numerical simulation. It could be seen that: the position of the maximum residual tensile stress for two welded joint changed from the weld to the crack front after the surface crack present. The maximum residual tensile stress of the plate welded joint appeared in the deepest depth of the crack front. The maximum residual tensile stress of the tensile welded joint appeared in the two crack tips at the intersection of the crack front and the welded joint surface.(3) The axial tensile load was added on tensile welded joint with initial surface crack, and the crack extended. The residual stress distribution rule and the changing rule of the stress intensity factor considering residual stress were both calculated in the process of crack propagation. It can be seen that the initial surface crack extended when 1t axial load added. And the residual stress was redistributed. The distribution of the residual stress is same with what concluding initial crack, but the level of the stress are changed. The maximum residual tensile stress increases gradually with the continuous extension of the crack, and the crack propagation rate is becoming more and more quickly.(4) The test plan for the initial residual stress and its redistribution of the welded joint with the crack extension are researched in order to facilitate the comparison between the results of experiment and numerical simulation late.