• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.68-76
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• 1997

The welding-induced initial imperfections such as residual stresses and initial strains in plated structures of ships and offshore structures can be effectively evaluated by the thermal elasto-plastic analysis method proposed in this paper. In the analysis of heat conduction of plate structures, both the analytical method and the numerical method are used. For the thermal elasto-plastic analysis of plates, the finite element analysis is performed, based on the initial strain method. In the plastic domain during incremental process, the 2nd order terms of stress increments and yield stress increments were considered, so that time increment could be controlled for more stable solution. To measure temperature distribution and angular distortion of plates during welding, bead-on-plate experiment are perform with various heat input and plate thickness. Measured data show good agreement with the calculated results.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.49-60
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• 2002

Welding is essential in ship production since welding is very popular method for joining two or more metals. However, welding causes residual stress and distortion and these give a bad influence to the structure strength and assembly of ship blocks. Therefore, prediction and treatment of residual stress and distortion is a key to accuracy control in shipyard. In this paper, a computational procedure, based on thermal-elastic-plastic 3-dimensional FEA, has been suggested to simulate butt and fillet welding process. In the simulation process, temperature distribution at each time step is obtained by heat transfer analysis and then thermal deformation analysis is done with obtained temperature distributions to find the residual stress and distortion. In heat transfer analysis, enthalpy method is used to realize phase change at melting temperature. Also element birth and death method is used to simulate adding of weld metal in both heat transfer analysis and thermal elastic plastic analysis. The proposed procedure is verified by related researches and the results show good agreement with those of related researches.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.3
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• pp.104-112
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• 1997

Line heating process has been used in forming hull surfaces long before and it has depended on skillful workers. As the reduction of production cost is major concern of shipbuilding companies, line heating work must be improved for higher productivity. In this paper, as the first step to automatic hull forming, a method is proposed to predict deformations due to line heating. It includes a simplified thermal elasto-plastic analysis to increase computing efficiency and to do real time visualization of deformed shapes. For the prediction of deformation, a method to estimate heat flux of the torch is also introduced. Predicted deformations for line heated plates show good agreement with experimental results. The proposed method can be used in control and simulation of line heating process with ease.

• Proceedings of the KWS Conference
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• 1992.04a
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• pp.81-84
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• 1992

• Proceedings of the KWS Conference
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• 1992.10a
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• pp.210-212
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• 1992

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.4
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• pp.51-57
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• 1990

There exist residual stresses and deformations in welded structures because of nonuniform temperature distribution. The thermal elasto-plastic analysis is necessary to describe the behavor of the structure during welding. In this paper, we calculated the residual stresses and deformations of the welded beam using the I-dimensional layered beam theory. In the previous 1-dimensional analyses, there were restrictions that the equilibrium conditions which were effective only on beams with infinite length were used, and the boundary conditions could not be considered adequately. But, the layered beam theory based on the incremental finite element method, can overcome these restrictions. On the other hand, in the 2-dimensional analysis, the computing time is large because of many degrees of freedom, and there was inaccuracy in the calculation of welding deformations. However, the layered beam theory can take into account the variation of properties along the depth, and can reduce the degrees of freedom considerably in comparision with the 2-dimensional analysis, and shows good agreement with the experiments.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.116-127
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• 1999

Line heating is a method widely used in forming ship hull surface. From the viewpoint of mechanics it is large deformation thermal elasto-plastic problem of arbitrary shaped plate. Many researches have been carried out to resolve this problem. Especially, Jang et al.[1] proposed a simplified thermal elasto-plastic analysis method to predict effectively the deformation of plate due to line heating. In this paper, we improved the method of Jang et al.[1] by considering tension yielding in temperature decreasing stage and verified with experimental results. FEA program using MITC4 degenerated shell element was made to deal with elastic large deformation problem. The newly proposed method can be used in the simulation and control of forming hull surface for higher productivity with simplicity and efficiency.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.69-80
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• 2002

Sequential process of roll-bending and line heating has been used to deform the curved hull-plates in shipyards. A growing interest for the mechanization or automation of the line heating process has been noted. Relations between heating conditions and residual deformations are important components needed for the mechanization. The residual deformations are investigated by using a thermal elastic-plastic analysis based on the finite element analysis(FEA). Several experiments are also performed to examine the validity of the results of FEA. The input parameters of line heating are suggested by dimensional analysis of line heating. The dimensional analysis can extract the primary input-parameters of line heating. The relations between the heating conditions and the residual deformations are set up by multi-variate analysis and multiple-regression method. This study suggests a method for the relation between the heating conditions and the deformations lying under the line heating.

• Journal of Welding and Joining
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• v.10 no.4
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• pp.250-258
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• 1992

In order to clarify the mechanical behavior of welding crack and to evaluate the mechanical characteristics of welded parts in thick plate, it is very important to accurately predict the welding deformation and residual stress including transient state before welding. In this paper, the theory of a three-dimensional elasto-plastic problem for the analysis of mechanical phenomenon of welding joint on the plate is developed into an efficient and accurate method based on the finite element method, and then several examples are considered by using the proposed model. The results of numerical analyses are discussed in the viewpoint of the mechanical characteristics of the distribution of three-dimensional welding residual stresses, plastic strains and their production mechanism on the thick plate.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.110-121
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• 2000

Gas heating, high frequency induction heating and laser heating can be used as the heat-source of line heating. Most of shipyards have been using the gas heating method for line heating. It is difficult to control the residual deformation of gas heating. High frequency induction heating is more feasible for the automation of line heating rather than the gas heating method since it is easy to control the magnitude of heat input. In this study, a numerical model of high frequency induction heating process is proposed for the application of the line heating. The simulation process of the induction heating is composed of the electromagnetic analysis, the heat transfer analysis, and the thermal deformation analysis.