Modélisation des propriétés thermomécaniques effectives de dépôts élaborés par projection thermique

Dans la présente étude, la conductivité thermique et le module d'élasticité de revêtementsd YPSZ élaborés par projection plasma ont été prédits par modélisations numériques 2D et3D de type différences finies et éléments finis.L'influence de la résolution d'image, de la taille et de la valeur du seuil sur les propriétésprédites du revêtement a été étudiée. En outre, les effets de la méthode numérique et du typede condition aux limites ont été étudiés. En particulier, la quantification de l'effet Knudsen(effet de raréfaction) sur le transfert de chaleur à travers une structure poreuse a été réaliséepar modélisation numérique en combinaison avec l'analyse d'image. Les conductivitéseffectives obtenues par modélisation 3D s'avèrent plus élevées que celles obtenues en 2D, etaussi en meilleur accord avec les résultats mesurés. Une corrélation 2D/3D a été trouvéepour la modélisation de la conductivité thermique : cette corrélation permet de prédire lesvaleurs 3D à partir des valeurs calculées en 2D.In the present study, the thermal conductivity and elastic modulus of thermal spray YPSZcoatings were predicted by 2D and 3D finite differences and finite elements numericalmodeling based on cross-sectional images.The influence of the image resolution, size and threshold on the predicted properties of thecoating was studied. Moreover, the effects of the numerical method and of the boundarycondition were investigated. In particular, the quantification of the Knudsen effect(rarefaction effect) on the heat transfer through a porous structure was realized by numericalmodeling in combination with image analysis. The predicted thermal conductivities obtainedby 3D modeling were found to be higher than those obtained by 2D modeling, and in betteragreement with the measured results. A 2D/3D correlation was sucessfully found for themodeling of thermal conductivity: this correlation allows predicting 3D computed valuesfrom 2D ones.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF

Preparation and characterization of magnesium coating deposited by cold spraying

Magnesium (Mg) and its alloys have a great potential as structural materials due to their beneficial combination of high strength to weight ratio, high thermal conductivity and good machinability. However, few literatures about Mg coatings fabricated by cold spraying can be found. In this study, Mg coatings were fabricated by cold spraying, and the microstructure, phase structure, oxygen content and microhardness of the coating prepared under different main gas temperatures were investigated. The critical velocity of the particle was evaluated through numerical simulations. The particle deformation behavior and bonding mechanism were discussed. The result of the oxygen content test shows that the oxygen contents of the coatings did not increase comparing with that of the feedstock powder. The simulation results show that the critical velocity of Mg particles was in a range of 653 m/s to 677 m/s. The observation of the coating fracture morphology shows that the formation of the coating was due to the intensive plastic deformation and mechanical interlocking. The microhardness of the coating increased with the increase of the main gas temperature from 350oC to 450oC due to the decrease of the coating porosity.Comment: 20 pages, 9 figur

Modélisation des procédés et des propriétés des dépôts élaborés par projection thermique

Mémoire d'habilitation à diriger des recherches Modélisation des procédés et des propriétés des dépôts élaborés par projection thermique Ecole doctorale Sciences pour l'Ingénieur et Microtechniques (SPIM) Présenté par Rodolphe BOLOT le 27 novembre 2008 à 14h30 UTBM, site de Sévenans, amphi P228

Application of FEM to Estimate Thermo-Mechanical Properties of Plasma Sprayed Composite Coatings

The presence of defects such as voids, inter-lamellar porosities or cracks causes a decrease in the effective thermal conductivity of plasma-sprayed coatings as well as a decrease in corresponding mechanical properties, such as the Young’s modulus. In general, the effective properties of thermal spray coatings are thus very different from that of bulk materials and thus have to be quantified to validate in service performances. A complementary approach allowing us to understand the relationships between the microstructure of a coating and its macro-properties is that of Finite Element Modeling (FEM). The case of composite coatings is more complicated still, due to the presence of different materials. In the present study, thermo-mechanical properties of a plasma-sprayed composite coating were estimated by numerical modeling based on FEM. The method applied uses directly cross-sectional micrographs without simplification, using a one-cell per pixel approach. Characteristics such as the thermal conductivity, the Young’s modulus, the Poisson’s ratio and the dilatation coefficient were considered. The example selected was an AlSi/polyester coating used as an abradable seal in the aerospace industry

Modélisation des écoulements de plasmas d'arc soufflé : Application à la projection de matériaux pulvérulents

The present study is devoted to the modeling of plasma spray process.Firstly, a Gibbs free energy minimization method is first used in order to determine thermodynamic properties of thermal plasmas. Transport coefficients are then deduced from kinetic theory of gases. Some numerical results are proposed.In a second step, calculated data are used in order to determine temperature and velocity fields in plasma jets and the influence of different parameters such as the turbulence model or the surrounding gas nature is shown.In a third step, the case of a plasma jet impinging on a flat plate is studied. In view of the comparison between thermal exchanges predictions and measurements taken from the literature, the proposed model seems to be able to describe impinging plasma jets successfully.The last part of the study deals with the spray of powder materials. A Lagrangian model is used for the simulation of jet/particles interactions. In the model, allowance is made for non-continuum effect, vaporization effect, internal heat conduction within particles as well as the effect of highly variable properties in the boundary layer around particles. Predictions of in-flight particles characteristics are compared with measurements obtained using an optical sensing device.The PHOENICS™ computational fluid dynamic code is used for plasma flows calculations.Cette étude s'inscrit dans le cadre de l'amélioration de la maîtrise du procédé de projection thermique à la torche à plasma d'arc soufflé.Le développement d'un code de calcul des propriétés thermodynamiques et des coefficients de transport des plasmas thermiques est réalisé dans un premier temps : les méthodes de calcul utilisées sont décrites et des résultats numériques sont présentés.Les données calculées sont utilisées dans un second temps pour permettre la détermination des champs de température et de vitesse dans les jets de plasma d'arc soufflé : l'influence de différents éléments tels que le modèle de turbulence ou la nature du gaz environnant sont mis en évidence.Le cas des jets de plasma impactant sur une surface plane est abordé dans un troisième temps : un modèle permettant la prédiction des échanges thermiques est suggéré et les flux thermiques calculés sont comparés à des résultats expérimentaux.La dernière partie est consacrée à l'étude de la projection de matériaux pulvérulents. Une approche Lagrangienne est utilisée pour simuler les interactions jet/particules. Un couplage avec l'équation de conduction de la chaleur au sein d'une particule isolée est notamment réalisé et les caractéristiques de particules en vol sont comparées à des mesures expérimentales obtenues avec un système optique.Le code de calcul PHOENICS™ est utilisé pour les calculs des écoulements de plasma

In-Flight Characteristics of Plasma Sprayed Alumina Particles: Measurements, Modeling, and Comparison

International audienc

Influence of the welding speed on the distortion of thin stainless steel plates—Numerical and experimental investigations in the framework of the food industry machines

International audienc

Application of FEM to Estimate Thermo-Mechanical Properties of Plasma Sprayed Composite Coatings

International audienceThe presence of defects such as voids, inter-lamellar porosities or cracks causes a decrease in the effective thermal conductivity of plasma-sprayed coatings as well as a decrease in corresponding mechanical properties, such as the Young’s modulus. In general, the effective properties of thermal spray coatings are thus very different from that of bulk materials and thus have to be quantified to validate in service performances. A complementary approach allowing us to understand the relationships between the microstructure of a coating and its macro-properties is that of Finite Element Modeling (FEM). The case of composite coatings is more complicated still, due to the presence of different materials. In the present study, thermo-mechanical properties of a plasma-sprayed composite coating were estimated by numerical modeling based on FEM. The method applied uses directly cross-sectional micrographs without simplification, using a one-cell per pixel approach. Characteristics such as the thermal conductivity, the Young’s modulus, the Poisson’s ratio and the dilatation coefficient were considered. The example selected was an AlSi/polyester coating used as an abradable seal in the aerospace industr

Electromagnetic–Computational Fluid Dynamics Couplings in Tungsten Inert Gas Welding Processes—Development of a New Linearization Procedure for the Joule Production Term

International audienceThe finite volume method (FVM) was used to model a tungsten inert gas (TIG) arc welding process. A two-dimensional axisymmetric model of arc plasma integrating fluid–solid coupling was developed by solving electromagnetic and thermal equations in both the gas domain and the solid cathode. In addition, two additional coupling equations were considered in the gaseous domain where the arc is generated. This model also included the actual geometry of torch components such as the gas diffuser, the nozzle, and the electrode. The model was assessed using numerous numerical examples related to the prediction of the argon plasma mass fraction, temperature distribution, velocity fields, pressure, and electric potential in the plasma. A new linearization method was developed for the source term in the energy conservation equation, allowing for the prediction of Joule effects without artificial conductibility. This new method enhances the efficiency of the classical approach used in the literature