In order to assess the reliability of the proposed FE model to evaluate the welding distortion, the uz (Figure 2C) displacements of the plate have been measured at some locations of the joints, by means of a Coordinate Measuring Machine (CMM).
2. Finite element model
The numerical simulation of a welding process involves the investigation of the thermo-mechanical response of the joint. This behaviour can be simulated by a numerical method, by using an uncoupled approach consisting of two consecutive analyses: the former, where the thermal problem is solved independently on the joint mechanical response, under a free-free configuration, to obtain the temperatures distribution; the latter, consisting of a subsequent mechanical analysis, where the temperatures history previously predicted at each node is used as thermal load. Such uncoupled approach, which is well established in literature for such type of analyses,17,22,34 allows saving computational costs with respect to the coupled one, with a comparable and an acceptable level of accuracy. All simulations have been carried out by means of the finite element commercial code ABAQUS® v. 6.14.
The same FE model has been used for both thermal and mechanical analyses. Concerning the mesh, 8-nodes hexahedral 3D finite elements have been used for both base and weld zones. More in detail, DC3D8 finite elements have been used for the thermal analysis, allowing introducing the temperature as unique degree of freedom, and C3D8 finite elements, characterized by the three translations as degrees of freedom, has been used for the mechanical analysis. According to Figure 3, a finer mesh has been developed for the chamfer region; a transition mesh for the HAZ (Heat Affected Zone) region and a coarser mesh, with a linear bias, for the other parts of the plate. As a result, FE model counts a total of 11904 finite elements and 14175 nodes.