An ALE-FEM approach to the thermomechanics of solidification processes with application to prediction of pipe shrinkage

International audiencePurpose - The present paper addresses the computer modelling of pipe formation in metal castings. Design/methodology/approach - As a preliminary, a brief review of the current state-of-the-art in pipe shrinkage computation is presented. Then, in first part, the constitutive equations that have to be considered in thermomechanical computations are presented, followed by the main lines of the mechanical finite element resolution. A detailed presentation of an original arbitrary Lagrangian-Eulerian (ALE) formulation is given, explaining the connection between the Lagrangian and the quasi Eulerian zones, and the treatment of free surfaces. Findings - Whereas most existing methods are based on thermal considerations only, it is demonstrated in the current paper that this typical evolution of the free surface, originated by shrinkage at solidification front and compensating feeding liquid flow, can be effectively approached by a thermomechanical finite element analysis. Research limitations/implications - Future work should deal with the following points: identification of thermo-physical and rheological data, automatic and adaptive mesh refinement, calculation of the coupled deformation of mold components, development of a two-phase solid/liquid formulation. Practical implications - An example of industrial application is given. The proposed method has been implemented in the commercial software THERCAST® dedicated to casting simulation. Originality/value - The proposed numerical methods provide a comprehensive approach, capable of modelling concurrently all the main phenomena participating in pipe formation

Forming Process Simulation for Fabrication Optimization in Areva Creusot Forge and Industeel

International audienceThe grain size of the austenitic stainless steel is an important issue for parts such as primary pipes in nuclear power plants and more globally for metal forming. Having tools which can predict at least the final grain size distribution for these materials is strongly required. It is in this frame that ACF worked for several years with other industrial and academic partners such as INDUSTEEL CRMC, Aubert & Duval, Ascometal, CEA Valduc and CEMEF Mines ParisTech on the simulation of the recrystallization (ReX) of 304L austenitic stainless steel. Recent developments allowed simulation in a full-field context of the static recrystallization (SRX) of 304L stainless steel including a crystal plasticity formulation in a finite element (FE) context in order to model precisely the grain deformation anisotropy. This crystal plasticity model includes a decomposition of the dislocation density in SSDs (Statistically Stored Dislocations) and GNDs (Geometrically Necessary Dislocations). Including the GNDs gave better results on the localization of the strain but also allowed to define more relevant nucleation criteria. During and after ReX, the grain growth phenomenon due to capillarity effects is also modelled. To take into account capillarity effects enables to reproduce precisely the final microstructure morphology (shape of the grains, equilibrium angles at multiple junctions...). This full-field approach gives very good results for the modelling of 304L stainless steel SRX. In parallel, at plants, forging and rolling processes need to be simulated in order to optimize fabrication sequences in terms of material distortion capability versus rheological properties of these materials and in terms of grain size with potential impact on ultrasonic inspection performance. In order to verify the process capability, a reduced ¼ scale component of 304L stainless steel primary pipes has been fabricated in a similar forging sequence. Study of the recrystallization aspect at different locations of the component was part of the objectives of the project. The paper gives a view of all combined approaches: theoretical approach by recrystallization modeling as well as simulation of forging and rolling sequences with Forge® software (coupled to a mean-field metallurgical model called Thermide) and fabrication of a reduced scale part with nozzles as a test before the fabrication of the final component

Application of the arbitrary Eulerian Lagrangian finite element formulation to the thermomechanical simulation of casting processes, with focus on pipe shrinkage prediction

International audienceThe Arbitrary Lagrangian-Eulerian formulation (ALE) has become an indispensable component of finite element thermomechanical computations of casting processes. As it is an intermediate formulation between the Lagrangian formulation (material convected mesh) and the Eulerian one (fixed mesh), it allows the simultaneous computation of important phenomena: Deformation and stresses affecting solidified regions, yielding the computation of air gap evolution at part/mold interfaces. In such regions, the formulation is essentially Lagrangian. Thermosolutal convection flow in the non solidified regions; here the ALE formulation tends to a pure Eulerian one (stationary mesh). Free surface evolution at top of risers, leading to the prediction of pipe defects (macroshrinkage). In this case the ALE formulation allows the follow up of the free surface. After a brief reminder of the constitutive equations to be used in thermomechanical modeling of solidification, the mechanical equations are presented and their resolution in the context of FEM-ALE. We insist on the transport analysis, a key-point of ALE, and present a validation of the original scheme that is used here. Finally, we focus on the prediction of pipe shrinkage formation and show two industrial examples

Démarche utilisée par Creusot Forge pour l'amélioration des gammes de fabrication de ses pièces

Creusot Forge s'est tourné vers la simulation numérique afin d'améliorer et de développer ses gammes de forgeage. Les récentes évolutions du logiciel FORGE ont permis à Creusot Forge de développer une approche originale de simulation de ses opérations de forgeage et de traitement thermique visant à garantir la qualité de ses produits. Face au renouveau des programmes nucléaires civils et au développement de centrales de nouvelle génération, cette démarche a été largement utilisée en s'appuyant sur 40 années de savoir faire ainsi que sur une parfaite connaissance métallurgique de ses lingots

THERMIDE : un programme de recherche pour optimiser les opérations de mise en forme et de traitements thermiques de composants métalliques

L'objectif du programme THERMIDE est d'optimiser le procédé de fabrication des composants métalliques par une meilleure maîtrise des déformations et le contrôle de la taille de grain. Devant la complexité du problème, une attention particulière est portée à la modélisation de la recristallisation dynamique activée durant la déformation à chaud des métaux. Les applications portent sur différentes nuances d'acier pour composants nucléaires ainsi qu'un matériau « école » (le tantale). La simulation d'un traitement thermique est également abordée dans l'intention de valider le logiciel FORGE®

Dynamic recrystallization in 304L steel: Full field and mean field simulation results compared to experimental data

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Full field modeling of dynamic recrystallization in a global level set framework, application to 304L stainless steel

International audienceA new full field numerical approach for the simulation of dynamic and post-dynamic recrystallization will be detailed. A level Set framework is employed to link a crystal plasticity finite element method with the modeling of recrystallization. Plasticity is calculated through the activation of slip systems and provides predictions for both SSDs and GNDs densities. These predictions control the activation and kinetics of recrystallization. All the developments are applied on 304L stainless steel

3D Full field modelling of recrystallization in a finite element framework – application to 304L

International audienceThis paper describes a level-set framework for the full field modelling of recrystallization and grain growth in a polycrystalline material. Topological evolutions are simulated based on a kinetic law linking the velocity of the boundaries to the thermodynamic driving forces. Dynamic recrystalli- zation is also modelled by coupling the level-set method to mean field laws describing strain harde- ning mechanism and nucleation criteria. The proposed formalism enables to reach outstanding massively multi-domain computations in a front-capturing finite element framework comparatively to the state of art

Full field modeling of dynamic recrystallization in a global level set framework, application to 304L stainless steel

A new full field numerical approach for the simulation of dynamic and post-dynamic recrystallization will be detailed. A level Set framework is employed to link a crystal plasticity finite element method with the modeling of recrystallization. Plasticity is calculated through the activation of slip systems and provides predictions for both SSDs and GNDs densities. These predictions control the activation and kinetics of recrystallization. All the developments are applied on 304L stainless steel