Fast Prediction of Welding Distortion Using ISM and i-ISM with Experimental Validation

摘要

Welding mechanics plays an important role in the design of weldingjoint to minimize the residual distortion and stress. In the past decades,the TEP-FEM (thermal elastic-plastic finite element method) hasshown its excellent capability in tracing the stress and strain duringwelding. Nevertheless, the computation expense in aspect of CPU timeand computer memory becomes a big issue when the finite elementmodel is large. For practical welded structures, the elements requiredfor a transient thermal mechanical analysis can easily reach severalmillions, which make the computation difficult to run on moderncomputers or cost too much time to complete. In order to improve thecomputing speed while maintaining the accuracy, the ISM (iterativesubstructure method) was developed about ten years ago. According tothe temperature distribution, the FE model (Region A) was divided intostrongly nonlinear region B (near heat source) and weakly nonlinearregion A-B (rest part excluding B). The A-B and B regions are solvedseparately, and balance on the boundary between the regions is realizedby iterative calculations. Recently, the i-ISM (inherent strain basedISM) was proposed by introducing the concept of inherent strain intothe ISM scheme. The region C which covers a part large enough aroundthe heat source can be solved by fixing its boundary for a time intervaland then it is released to solve the global model. This approach is basedon the fact that strain in the rest part beyond C region will not changeappreciably. To validate the two schemes ISM and i-ISM, experimenton a fillet welding model was carried out and three deformationcomponents namely longitudinal shrinkage, transverse shrinkage andangular distortion were measured after welding. Analysis byconventional FEM, and ISM were then performed on the same model.Furthermore, a large scale model with nearly two millions of DOF(degree of freedom) was simulated by ISM and i-ISM. Finally, theaccuracy and efficiency of the proposed methods have been confirmed.