Frédéric Boitout

Prediction of welding residual distortions of large structures using a local/global approach

Prediction of welding residual distortions is more difficult than that of the microstructure and residual stresses. On the one hand, a fine mesh (often 3D) has to be used in the heat affected zone for the sake of the sharp variations of thermal, metallurgical and mechanical fields in this region. On the other hand, the whole structure is required to be meshed for the calculation of residual distortions. But for large structures, a 3D mesh is inconceivable caused by the costs of the calculation. Numerous methods have been developed to reduce the size of models. A local/global approach has been proposed to determine the welding residual distortions of large structures. The plastic strains and the microstructure due to welding are supposed can be determined from a local 3D model which concerns only the weld and its vicinity. They are projected as initial strains into a global 3D model which consists of the whole structure and obviously much less fine in the welded zone than the local model. The residual distortions are then calculated using a simple elastic analysis, which makes this method particularly effective in an industrial context. The aim of this article is to present the principle of the local/global approach then show the capacity of this method in an industrial context and finally study the definition of the local model.

Simulation thermomécanique du soudage par friction-malaxage

Le soudage par friction-malaxage est un procédé de soudage sans apport de matière où la source de chaleur provient intégralement du malaxage du matériau à souder, ainsi que de son frottement sur l’outil. Dans cet article, un modèle élément fini est proposé pour simuler le couplage thermomécanique durant la phase stationnaire du procédé. Les équations de conservation de l’énergie, de la masse et de la quantité de mouvement sont traitées à partir d’un élément fini tétraédrique. Un exemple de simulation est présenté pour un alliage d’aluminium de type 7075.

Efficient Updated-Lagrangian Simulations in Forming Processes

A new efficient updated-Lagrangian strategy for numerical simulations of material forming processes is presented in this work. The basic ingredients are the in-plane-out-of-plane PGD-based decomposition and the use of a robust numerical integration technique (the Stabilized Conforming Nodal Integration). This strategy is of general purpose, although it is especially well suited for plateshape geometries. This paper is devoted to show the feasibility of the technique through some simple numerical examples.

Numerical Simulation of TIG Welding Distortions: Distortions of a Mock-Up Representative of ITER Vacuum Vessel

Welding problems encountered in the nuclear industry have been mainly addressed by weldability tests and the analysis, development of new techniques or improvements through lesson learning. Since a decade, AREVA is developing a complementary approach based on numerical simulation. Residual stresses present in reactors do not constitute a major problem at the design stage; even though they may have a strong impact on some types of damage. Numerical welding simulation in the nuclear industry has focused mainly on residual stress prediction, which constitutes an issue for engineering. PWR components are usually massive; nevertheless distortion may also be a source of concern in component design: some structures are slender in spite of their thickness; narrow gap welding requires a close control of the groove width. AREVA, also working on a fast breeder project, the distortion problem gains in importance. In this prospect, AREVA, world energy expert, paid special attention on the numerical simulation of Gas Tungsten Arc Welding (GTAW) of a mock-up relative to the International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel (VV). One of the challenges of manufacturing the ITER vacuum vessel is the low value of acceptance level of distortion (∼ 10 mm) compared to the global dimensions of the structure (∼ 10 m). Welding simulations of a representative mock-up of VV pattern of the made of austenitic steel plates (316L(N) ITER GRADE) are carried out. The aim of the numerical simulations is to check the quality of the distortion prediction. Multi pass welding simulation reproduces the deposit of each bead by thermo-metallurgical and mechanical calculations. Distortions induced by each weld are computed using a simplified approach (local global method). This method aims at modeling long and numerous welding operations with an acceptable calculation time. Moreover, this method is improved in order to respect welding sequence with partial filling of grooves. After welding sequences, distortions are measured at some representative points of the mock-up. The paper presents the methodology of the numerical simulations and the relevant results: • Residual stress and strain fields in and near the welds (local fields), • Distortion prediction for the global structure. The comparison with experimental distortions shows that the trends of the experimental deformed shape are well represented by the simulations. Moreover, displacement magnitudes are in good agreement with measurements.Copyright