Prediction of Butt Welding Deformation of Curved Shell Plates by Inherent Strain Method

Abstract

In order to achieve high productivity of assembly blocks of hull structure, it is important to predict welding deformations accurately and to apply these data to the production planning. For this purpose the transient thermal-elastic-plastic analysis by FEM (finite-element method) may be utilized. However, this method is not a practical approach to analyze the deformation of large and complex structures, such as ship hull structures, in view of time and cost. Whereas the inherent strain method deals the residual strain near the weld line as the inherent strain, therefore the residual deformation can be simply calculated by elastic analysis. This method is much more practical and efficient than the transient thermal-elastic-plastic analysis. Thus, in this paper, the inherent strain method is used to predict the welding deformation of hull structures. Past research activities of the inherent strain method have been focused on the prediction of the welding deformation of small size specimens and simple shape specimens; however, very few of them treat the problem of large and complex structures. Hence, in this paper, prediction of welding deformation of curved shell plate, of which size is approximately full scale, is conducted by the inherent strain method. In applying elastic analysis to predict the welding deformation of actual hull blocks, contact condition between the plate and the positioning jig should be adequately realized in the analysis. Therefore, a practical solution is proposed to con- sider the contact condition between the plate and the jig by judging reaction forces of the jig at calculation steps. Furthermore, since the welded plates may slip on the positioning jig due to the welding deformation, rigid body motion of plates is caused. Hence this motion should be taken into account of the estimation of calculated results of FEM. In addition to the rigid body motion, coordinate system of the measured data is usually different from the calculated data, therefore, the deviation of the coordinate system must be involved. These calibrations to assess the calculated deformation by FEM are also discussed. The above prediction method is confirmed to be successful by comparing the calculated deformations and the measured ones of large size specimen of curved shell plates due to butt welding.