Simulation of Welding Deformation for Accurate Ship Assembling (Report II) : Influence of Initial Geometrical Imperfection on Butt Welded Plate(Mechanics, Strength & Structural Design)

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Welding deformation is one of the main problems to be solved in the automation and mechanization of ship assembly. In the previous report, the in-plane transverse deformation of one-sided automatic welding on large real size plate is investigated by experiments and thermal-elastic-plastic FEM analyses. The effects of various factors, such as welding sequence, initial stress (stress existing in plate before welding), types of tab, pitch of tack welds and local heating have been clarified. It was concluded that the local heating affects the deformation significantly near the heated region. Welding sequence also has a fairly large influence on the distribution of transverse shrinkage. The most considerable finding is, however, that certain pattens of initial stress could change the deformation significantly. Therefore, it is important to clarify the effects of the initial stress in various forms. In this paper, main work is focused on the investigation of the influence of correcting groove gaps, which is one of the major causes of initial stress. To begin with, the straightness and the shapes of skin plates after parallel gas cutting are statistically surveyed to obtain types of gap and possible maximum gap. The practical methods to correct the gap are studied. Finally, the influence of the corrections is computed using thermal-elastic-plastic FEM method. The following conclusions are drawn ; (1) Most measured plates have fan-shapes or s-shapes after gas cutting. The mean value of the out of straightness is 0.87mm. (2) Correcting gap by gas heating or by a proper choice of tack welding sequence results in quite high initial stress in widespread area of the plate before welding. (3) This kind of initial stress produces an undesirable effect on the transverse deformation after welding. It causes the irregular deformation and increases the shrinkage more than two times compared to the case without initial stress.
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Simulation of Welding Deformation for Accurate Ship Assembling (Report II) : Influence of Initial Geometrical Imperfection on Butt Welded Plate(Mechanics, Strength & Structural Design)

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