Abstract
The objective of the present work is to study the thermo-mechanical behavior of the fusion welding procedure in the shipbuilding industry. For this purpose numerous experiments as well as numerical simulations were carried out using commercially available software ANSYS®15. The thermal and mechanical analysis was carried out in an uncoupled way. The heat source modeling is a major concern to obtain the correct deformation pattern of the welded structures. Here, for the Gas Metal Arc Welding (GMAW), the Goldak’s double ellipsoidal heat source model was used.
Though, for this model the heat source parameters were problem specific in each case. To overcome this shortcomings, a new way of generalized heat source model using the regression equations was developed for the Submerged Arc Welding (SAW). Here a combined vertical and horizontal ellipsoid was also taken by considering the weld pool shape obtained from experiments.
This generalized SAW heat source model can be replicated for the other welding procedures. The interruptions in the welding process is very common and unavoidable because of the complex geometry, long weld length and human fatigue. So, the effect of welding interruptions on the residual stress was carried out in this study. Short-time welding interruptions can also be treated as a case of preheat for the subsequent welding. So, the effect of preheat was correlated with the welding interruptions. A two minute weld interruption produced the similar effect of 200oC preheat. Nonlinear thermo-elastoplastic welding simulation requires huge time and computer resources. As a solution to this, an elastic method was developed based on various welding forces.
It was further extended to an elastic transient welding force method to capture the effect of welding sequences correctly. To study the effect of welding sequences four large (2438 mm x 1219 mm x 6.25 mm) orthogonally stiffened panels were welded by using GMAW. Finally to reduce the welding induced buckling distortion, an in process distortion control method called Thermo Mechanical Tensioning (TMT) was introduced. Extensive experimentation was carried out both in laboratory and in full scale in Cochin Shipyard Ltd. The TMT procedure was also numerically investigated to understand the residual stress development process during the process.
Keywords: Heat source model, 3-D Finite Element Analysis, Thermal Structural analysis, Low- Carbon steels, Weld pools, Interruption in the welding process, Residual stress, Preheat, Welding induced distortion, Inherent strain, Plastic strain, Welding force, Transient welding force, Large stiffened panels, Welding sequences, Thermo Mechanical Tensioning, Buckling distortion.
