Investigation And Application On The Analysis Methods Of Welding Distortion In Large-scale And Complex Marine Structures

Welding is a main fabricating process and widely used in industries to assemble a variety of products including ships, automobiles, trains and bridges. For example, the course of assembling ships involves of the joining of large-scale and complex blocks which are all-welded and thin-plated structures. Welding residual deformations occur during the manufacturing process. Welding residual deformations not only influence the quality but also increases the cost of structures. Although it is practically difficult to eliminate welding residual deformation completely, it is possible to produce blocks with a level of sufficient accuracy to avoid problems during the assembly process. Therefore, it is of significance to quantitatively predict and control welding residual deformation in the course of assembling large-scale and complex marine structures.In this research, the inherent strain theory is applied in the prediction of welding deformation in large-scale and complex marine structures. Key problems of this field including the establishment of inherent deformation database, determination of boundary conditions, optimum of assembly and welding sequence and the influence of forced assembly are investigated. Then, in order to help onsite engineers use FEM for predicting welding deformation conveniently, a kind of FEM pre- and post-processing software-Welding Structure Analysis System(Weld-sta) is developed. By successfully applied this software to marine structures, it can provide a guideline for the designation, determination and optimum of welding procedures.The main research contents are as follows:(1) Based on the theory of inherent strain, three methods(formula method, Thermal-Elastic-Plastic Finite Element Method(TEP FEM) and experimental method) for evaluating inherent deformation are presented. Then, a fillet welded joint is taken as an example, inherent deformations including longitudinal shrinkage and transverse shrinkage evaluated by these methods are compared. Finally, approximate formula of calculating the inherent deformation of complicated welding joints in marine structures is proposed and the method of establishing the inherent deformation database of complicated joints in marine structures is introduced.(2) In order to solve the problem of determining the boundary condition in calculating the welding deformation of large-scale and complex marine structures, inertia relief method, the inertia force of the unconstrained structure is relieved to balance the external force, is proposed. 203 block of 4250 TEU container ship is taken as an example, simulations based on inherent deformation are conducted considering the inertia relief and rigid-body motion boundary conditions. By comparing the deformation of measured point, the computational results by using inertia relief is the most approximate to measurement results compared to other cases, and it is more convenient to set the boundary condition using the proposed method which provides an effective choice for the industrial application of welding structure deformation prediction.(3) In order to consider the influence of forced assembly, a method, based on the property of connector elements in Abaqus, is developed to simulate the process of it. Firstly, a fillet joint is adopted to explain the simulated process of forced assembly. Secondly, a model with initial gaps is used to prove the reliability of this method by comparing simulated results with experimental ones. Finally, a double bottom block 303P/S of 4800 TEU container ship is taken as an example, and simulations based on inherent deformation are conducted considering forced assembly. The influence of forced assembly on deformation is discussed.(4) Based on the inherent strain theory, Welding Structure Analysis System(Weld-Sta) is developed. This software is developed by C++ and FORTRAN based on Windows platform. The design style of this software is direct and convenient for operating. Besides, practical functions including determination of welding lines, inherent deformation and boundary conditions automatically and good compatibility of computation module.(5) The double bottom block 303P/S of 4250 TEU container ship and body bolster of electric locomotive is selected as research subject. by considering the welding sequence, Welding Structure Deformation Analysis(Weld-sta) is employed to carry out analysis of welding deformation on these structures. By comparing the welding deformation predicted by simulated results including two methods-considering welding sequence and not considering welding sequence with that of measured results, the reliability of this method is confirmed. Then, by considering the designed objective optimization function the optimum program of welding procedures in assmebling 303P/S is presented.