Modélisation par éléments finis des phénomènes thermomécaniques et de macroségrégation dans les procédés de solidification

Abstract : This work is dedicated to the modeling of macrosegregation and deformation during solidification of castings. A two-dimensional finite element model to simulate macrosegregation due to thermal-solutal convection in the case of columnar dendritic solidification is presented. A set of volume-averaged conservation equations of energy, solute, momentum and mass is solved in conjunction with the use of the lever rule as a microsegregation model. Several formulations have been implemented, permitting a resolution with either weak or strong coupling, closed or open system. In order to improve the prediction accuracy, an algorithm for dynamic remeshing is proposed. The basic idea is to generate fine elements near the liquidus isotherm. The norm of the gradient of solid fraction is used for piloting the remeshing in the mushy zone; while the objective mesh size in the liquid is considered as a function of the distance to the liquidus isotherm. The numerical approach has been validated with a benchmark test of macrosegregation in Pb-Sn alloys taken from the literature. The influences of mesh size, time step and coupling scheme have been investigated. Sufficient fine meshes, small time step and possibly coupling iterations should be applied in order to predict segregated channels. Moreover, the efficiency of mesh adaptation is demonstrated by predictions of freckles in a case of unidirectional solidification, and of 'A-type' segregation bands in a large industrial carbon steel ingot. In the last part of this work, regarding fluid flow in the liquid induced by solidification shrinkage and thermo-convection and deformation in the solid, a thermal mechanical model has been implemented with a Eulerian-Lagrangian formulation. The alloy in the liquid state is Newtonian, and in the mushy state it is modeled by a viscoplastic continuum. Below a critical temperature the alloy is considered by a thermal elastic viscoplastic model. The thermo-mechanical simulation is used to predict the shrinkage pipe, air gap, strains and stresses.
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Submitted on : Monday, August 22, 2005 - 8:00:00 AM
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  • HAL Id : pastel-00001339, version 1

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Weitao Liu. Modélisation par éléments finis des phénomènes thermomécaniques et de macroségrégation dans les procédés de solidification. Sciences de l'ingénieur [physics]. École Nationale Supérieure des Mines de Paris, 2005. Français. ⟨NNT : 2005ENMP1283⟩. ⟨pastel-00001339⟩

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