Numerical Simulation of the Molten Pool of a Powder Bed

In this study, a numerical approach is developed to simulate the molten pool formation during the melting of a powder bed. It is based on a fluid formulation that allows taking into account the dynamics in the molten pool through the two effects of surface tension (including both 'curvature effect' and the 'Marangoni effect') and buoyancy. Additionally, the free surface is considered using an ALE method. The shrinkage of the powder layer after its melting and the change of the thermo-physical properties depending on the material state (powder or compact) are also modeled. As an application, a 3D thermo-fluid simulation of the powder bed melting is carried out. It is found that the powder layer porosity has a great effect on the molten pool morphology

Une stabilisation efficace de l'élément fini P1/P1 en grandes transformations

L'objectif de ce travail est de proposer un stabilisation robuste de l'élément fini P1/P1 en grandes transformations. La première partie est consacrée à l'étude des propriétés de l'élément fini P1/P1 connu pour ne pas être LBB-stable. Ensuite, une nouvelle formulation stabilisée simple et robuste est proposée afin d'éviter les modes de pression parasites pour l'analyse de structures métalliques élasto-plastiques ou élasto-viscoplastiques. Enfin, des exemples sont présentés pour illustrer l'efficacité de l'approche développée

Vademecum-based GFEM (V-GFEM): optimal enrichment for transient problems

This paper proposes a generalized finite element method based on the use of parametric solutions as enrichment functions. These parametric solutions are precomputed off-line and stored in memory in the form of a computational vademecum so that they can be used on-line with negligible cost. This renders a more efficient computational method than traditional finite element methods at performing simulations of processes. One key issue of the proposed method is the efficient computation of the parametric enrichments. These are computed and efficiently stored in memory by employing proper generalized decompositions. Although the presented method can be broadly applied, it is particularly well suited in manufacturing processes involving localized physics that depend on many parameters, such as welding. After introducing the vademecum-generalized finite element method formulation, we present some numerical examples related to the simulation of thermal models encountered in welding processes

Study of the Thermal History upon Residual Stresses during the Dry Drilling of Inconel 718

The main objective of this article was to show for the first time that heat transfer plays a major role in residual stress generation during the dry drilling of Inconel 718, and to propose a numerical strategy capable of simulating such thermo-mechanical phenomena. An X-ray diffraction (XRD) analysis shows that without lubrication, high tensile residual stresses can be observed on the surface of a deep through drilled hole. Such a situation can be highly detrimental for the fatigue lifetime of a mechanical component. A thermal history in five phases is first identified by means of temperature measurements exhibiting an overheating of approximately 500 ∘C on the created hole surface just before the end of the drilling operation. A 3D thermo-viscoplastic model is herein improved in terms of boundary conditions to show that this phenomenon is triggered by the progressive decrease in the Inconel 718 volume under the cutting zone. To the authors’ knowledge, such a phenomenon has never been reported and simulated before in the literature. Then, a 3D thermo-elasto-plastic simulation including elasticity is proposed to compute residual stresses from the thermal results of the previous model. It shows for the first time that the overheating stage induces sufficiently intense plasticity to produce high tensile residual stresses of approximately 900 MPa as we experimentally observed

Evaluation of constitutive models in predicting ratcheting responses of a structure under thermo-mechanical loadings

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A multi-phase linear kinematic elastoplastic model for the HAZ of welded S355J2 steel under low-cycle fatigue

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