Prediction of Welding Distortions in a Complex Structure Using Finite Element Modelling: Experimental Validation

This study presents the application of finite element modelling to predict the thermal, metallurgical and mechanical effects of welding. Welding stresses and deformations are closely related phenomena. During the heating and cooling cycles thermal strains may occur in the weld and adjacent area. The strains produced during the heating and cooling stage of welding are always accompanied by plastic deformation of the metal, due to the thermal gradients and the restraint of the cold metal. The stresses resulting from these strains combine and react to produce internal forces that cause a variety of welding distortions. The FEM model developed in this work, based on the Abaqus code, is applied to a complex structure with four welds. The analysis has been able to compute the transient temperature, distortion and the stress field for a sequence of welding. The model takes into account the fixture effect, and the delay time between welds and the cool down after welding. All the thermal and mechanical properties of the metal, IN 718 superalloy for the present case, are considered; as well as convective effects. The work investigates distortions and residual stresses induced by the welding sequence using Plasma Arc Welding (PAW). A pre-calibrated moving distributed heat source model based on Goldak's double-ellipsoid heat flux distribution is implemented in the finite element simulation. Thermo-elastic-plastic properties are applied to modelling thermal and mechanical behaviour of the welded part. Prediction of temperature variations, fusion zone and heat affected zone as well as shrinkage effect, distortions and residual stresses are obtained. Finally, FE analysis results of welding distortions are compared and validated with existing experimental measurement and observations. The numerical results agree very well with those of the experimental ones.