The aim of this study is to estimate residual stresses and distortions during the assembly of dissimilar metallic materials welded by Electron Beam Welding (EBW) technique. This work is motivated by a new welding procedure for the manufacture of large speed reduction gear. The gear consists of a central hub of S275 J2G3 steel and a toothed wheel of 32CrMoV13 steel, chosen for its high fatigue performances. Preliminary experimental welding tests have shown the opening of the joint plane during the circular welding of the gear leading to lack-of-fusion defects. To improve the joining technique, a thermomechanical model has been developed to predict the opening of the joint plane during welding. A two-dimensional finite element model has been applied on a simplified geometry of smaller size. The opening of the joint plane has been modelled by two different ways, the first one uses activation / deactivation elements and the second one uses specific contact elements. Both techniques have shown similar displacements. The assumptions of plane stress or generalized plane strain are discussed. Numerical results obtained with similar metals with or without metallurgical transformations are presented. Calculations carried out with dissimilar metals are compared with experiments in terms of fusion zone size and displacements.

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