Study On Numerical Simulation Of Welding Distortions In Huge Fabrications And Its Application

The work on numerical simulation of welding residual stress and distortion has great importance both in academy and engineering. Not only can it provide better understanding to the development and distribution of welding stress and strain, but show the influence of all kinds of different welding parameters easily while these studies are nearly impossible through only experiments. Thus, numerical simulations can provide valuable instructions for the optimization of welding technology to improve the quality of welded structures greatly.In the present paper the characteristics of welding process and their effects on numerical simulations are analyzed. It can be derived that the practical numerical analysis for large complex welded structures depend on the intelligent modeling of the dominant parameters that influence the behavior of welded region in a given process. Combining accuracy with attractive efficiency, segmented moving heat source models are established in this paper. In the new models time increments used to describe details of moving heat flux are reduced greatly, that dramatically increase analysis efficiency. Moreover, focusing on different aspects concerned, different meshing principles are proposed to ensure higher efficiency when the segmented heat source models are adopted in numerical simulations of practical welded structures. Stress simulation requires small meshes but less segments, whilst distortion implies coarse meshes and more segments. Both can afford the desired accuracy and the required solution time. The high accuracy and efficiency of the new heat source models and strategies are testified by experiments and applications in huge and complex fabrications.The numerical simulation has the advantage of systematization and flexibility, but the results must be verified through physical tests before they are used as instructions for real fabrications. For large structures, to testify the results through model tests is necessary since it is impossible to make a same size fabrication just for certification purpose. In this paper for verifying the numerical analysis results on huge fabrications,similitude principles are deduced to determine residual distortion relations between physical model and actual structures. In contrast to the similitude principles based on temperature fields, which is impractical in many cases because they require rigorous and nearly impossible technological conditions, a new similitude method aiming at studying distortion of thin-wall structures is presented. The new method is based on the relations between the elastic strain energy and distortion. By using thin-wall hypothesis and assumption of elastic strain energy distribution, it is practical to predict distortions of huge welding fabrication through integrating this method with finite element analysis.In this paper a time-dependent measuring system for welding deformation is established with high quality sensors shielded from strong welding interference, and the system has high precision and high sampling speed. Applications proved that this system can be reliably used under welding conditions and is a very useful instrument for the studies of welding deformation.For providing reliable guides to optimize welding processing technology, it is an effective way to utilize segmented moving heat source model and similitude method based on elastic strain energy synthetically. Just by reliance of the method presented above, a big challenge, the accurate controlling of welding induced distortion in the beam of a huge bridge crane, is achieved successfully with the proposed approaches in this paper. And this project also shows the high accuracy and high efficiency of the new heat source models and the practicality of the similitude method. All these efforts push forward the technology of numerical simulation and produce a great influence on welding manufacturing.