Finite element analysis of compressible viscoplasticity using a three-field formulation: Application to metal powder hot compaction

International audienceIn the present study, a finite element model has been formulated to simulate the hot forging stage in powder metallurgy manufacturing route. The compacted material is assumed to obey a purely viscoplastic compressible flow rule. A three-field formulation (velocity, volumetric strain rate and pressure) has been developed. The associated three-dimensional finite element discretization is detailed. In order to take advantage of an automatic remeshing procedure for linear tetrahedra, the compatible P1+/P1/P1 element is used (4-node element plus additional degrees of freedom and bubble interpolation for velocity). The complete model includes thermomechanical coupling and friction. The formulation is validated versus an analytic solution of uniaxial free compaction and applied to the hot forging of an automotive connecting rod preform

Two-Phase Multiscale FEM Modelling of Macrosegregation Formation in Steel Slabs

International audienceThe conservation equations of a coupled thermomechanical - solute transport model to be applied in mushy zones are first recalled. Then the numerical implementation is discussed, in the context of steel continuous casting modeling. Application to the study of the end of solidification is then considered and the effects of soft reduction process are discussed

La critique saint-simonienne de la secte des économistes : un positionnement original

L'antiphysiocratie des saint-simoniens peut paraître assez naturelle. En effet, une doctrine saint-simonienne réputée pour son industrialisme utopiste ne pouvait, semble t-il, que s'opposer à ce que Smith a appelé le "système agricole". Cette interprétation, sans être totalement erronée, est une réduction abusive du point de vue saint-simonien. En effet, si, au début du XIXème siècle, les saint-simoniens peuvent être rangés dans la catégorie des "néo-smithiens" qui réfutent la thèse selon laquelle la terre est à l'origine de la richesse, ils le font à partir d'une approche spécifique, opposant oisifs et travailleurs. Cette partition modifie les débats classiques concernant le rôle des diverses classes et des revenus qui y sont associés, tout en légitimant un programme anti-physiocrate, opposé au rôle économique et politique des propriétaires fonciers. Pour autant, les saint-simoniens ne se contentent pas de cette opposition : ils soutiennent la méthode de Quesnay et sa définition de l'économie politique. Selon eux, il faut raisonner à partir d'un système, et une philosophie générale des rapports sociaux doit précéder la science des richesses. Même si la nature de cette philosophie diffère (droit naturel vs évolutionnisme historique et physiologique), cette communauté de vue revendiquée concernant la méthode et le refus d'autonomie de l'économie politique conduit les saint-simoniens à une définition et un usage originaux de leur antiphysiocratie, dans le contexte du premier tiers du XIXème siècle

Saint-Simonism and Utilitarianism: the history of a paradox. Bentham's Defence of Usury under Saint-Amand Bazard's Interpretation

This article reveals and studies the connections between Bentham's Defence of Usury (1787) and Saint-Amand Bazard (1791-1832), a founder of Saint-Simonianism. We first traces Bazard's exposure to Bentham through his unknown friendship with Bentham's publisher Etienne Dumont. After introducing in details the Saint-Simonian views on interest and money, we examines the significance of Bazard's translation of Defence of Usury and his shared opposition against usure laws. We explain why the puzzling reference to Benthamite utilitarianism is not fortuitous but appears to justify a common ground between Bentham's utilitarism and Saint-Simonianism. This connection did not survive the July Revolution

Direct modeling of material deposit and identification of energy transfer in gas metal arc welding

International audiencePurpose - The purpose of this paper is to present original methods related to the modeling of material deposit and associated heat sources for finite element simulation of gas metal arc welding (GMAW). Design/methodology/approach - The filler deposition results from high-frequency impingements of melted droplets. The present modeling approach consists of a time-averaged source term in the mass equation for selected finite elements in the fusion zone. The associated expansion of the mesh is controlled by means of adaptive remeshing. The heat input includes a volume source corresponding to the droplets energy, for which a model from the literature is expressed in coherency with mass supply. Finally, an inverse technique has been developed to identify different model parameters. The objective function includes the differences between calculations and experiments in terms of temperature, but also shape of the fusion zone. Findings - The proposed approach for the modeling of metal deposition results in a direct calculation of the formation of the weld bead, without any a priori definition of its shape. Application is shown on GMAW of steel 316LN, for which parameters of the model have been identified by the inverse method. They are in agreement with literature and simulation results are found quite close to experimental measurements. Originality/value - The proposed algorithm for material deposit offers an alternative to the element activation techniques that are commonly used to simulate the deposition of filler metal. The proposed inverse method for parameter identification is original in that it encompasses an efficient and convenient technique to take into account the shape of the fusion zone

A two-dimensional finite element thermomechanical approach to a global stress-strain analysis of steel continuous casting

International audienceThis paper addresses the two-dimensional finite element simulation of steel continuous casting using a global non steady-state approach. The method aims at the calculation of the thermomechanical state (temperature, deformation, stresses) of steel all along the continuous casting machine. Both plane deformation and axisymmetric versions have been developed. The first one addresses the simulation of continuous casting of slabs, taking into account the possible curvature of the machine, whereas the second one applies to cylindrical billets. The implementation of the method is validated by comparison with results from the literature. It is applied to the study of a slab continuous caster for which successive depressive and compressive stress states are revealed in the secondary cooling region

Adaptive anisotropic mesh technique for coupled problems: application to welding simulation

International audienceA major problem arising in finite element analysis of coupled problems, such as welding for instance, is the control of the mesh, that is an appropriate mastering of the spatial discretization to get accurate results in a minimum computer time. The present anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error and recovery of the second derivatives of different fields involved in the finite element calculation. Error indicators are derived to define an anisotropic mesh metric field, which is an input of the pre existing 3D remeshing procedure. The mesh metric consists of a combination of several metrics, each corresponding to the error estimation associated with a selected field of the solution produced (temperature, phase fraction, stress component). Mesh modifications are used to anisotropically and continuously adapt the mesh. We demonstrate the efficiency of the method by applying it to a coupled thermal-mechanical-metallurgical simulation of arc welding. We demonstrate that the use of an anisotropic adaptive finite element method can result in an order of magnitude reduction in computing time with no loss of accuracy compared to analyses obtained with isotropic meshes

Monetary Policy and Value Judgments : Did we forget Myrdal's legacy ?

Myrdal's works are usually analysed with a dual and separated point of view : on the one hand the methodological papers concerning the value problem and based on a strong non neutrality thesis ; on the other part the theoretical analysis concerning monetary theory and policy, with a Wicksellian filiation. In fact both the dimensions are strongly connected by a common way : the application of the Hägerström's Swedish guillotine between is and ought, but also the construction of a bridge between economic science and political views on social engineering and economic policy. Myrdal wants to address this problem : how economic science can become politically relevant ? This paper analyses two stages of that unique project : the proposition of a "technology of economics" (1930), and the selection process for a "norm for monetary policy" (1939). It shows that Myrdal distorts an initial end and means scheme by proposing some intermediary concepts between positive and normative fields. From a theoretical and statistical framework and an explicit value judgment these concepts enable to elaborate an iterative tree of selection of a speci-c monetary policy. If the Myrdal's project encounters difficulties in conciliating a non-cognitivist thesis with economic prescriptions and in proposing a tractable method, it remains an important benchmark for the analysis of the links between positive and normative views concerning monetary policy

A Partitioned Fluid-Structure Interaction Approach during Steel Solidification: Application to the Simulation of Ingot Casting

International audienceOne of the critical challenges encountered when modeling a thermo-mechanical problem in the context of steel casting processes, is to achieve a concurrent and efficient computation of fluid flow (ingot mould filling, nozzle jet in continuous casting) and solid mechanics (stress-strain in solidified regions). This is of crucial importance in industry for the prediction of surface or sub-surface cracks for instance that may initiate in solidified regions during the filling stage of ingot casting, or in the mould region during continuous casting. The current state-of-the-art [15-17-21] consists in separating the analysis in two distinct stages: fluid flow using CFD codes and stress-strain analysis using structural codes. This induces several drawbacks regarding practical use and computational efficiency. A monolithic formulation, treating the fluid-solid interaction (FSI) may be investigated but is not adapted to the context of solidification, because of huge differences between liquid viscosity and solid consistency. It is then preferable to consider this FSI problem as a weak interaction problem, for which a partitioned formulation is more efficient than a monolithic one. Therefore, a two-step resolution strategy combining fluid flow and solid mechanics has been developed. Liquid flow (natural convection or filling flow), thermal dilatation as well as thermally induced deformation of the solid phase are accounted for

Solidification macroprocesses - Thermal-mechanical Modeling of Stress, Distortion and Hot Tearing)

http://www.crcpress.com/product/isbn/9780849332166International audienceThe application of numerical methods to the mechanical modeling in solidification analysis has received a continuously growing interest over the last twenty years. After having concentrated their efforts on the thermal and microstructural predictions, research teams have been more and more interested in the coupled thermomechanical analysis. These developments have been motivated by the efforts done by the casting industry to increase the quality of final products while lowering the costs. Manufacturers are then interested in the development of new numerical tools able to model the thermomechanical response of castings during the processes. Accurate calculation of stress and distortions during casting is just the first step, however, as engineers are more interested in their practical consequences. These include residual stress and distortion, and defects such as segregation and the formation of cracks such as hot tears. As computing power and software tools advance, it is becoming increasingly possible to perform useful mechanical analysis of castings and these important related behaviors