Méthodes morphologique et par éléments finis combinées pour une nouvelle approche de la modélisation 3D du dépôt par projection dynamique par gaz froid (« cold spray »)

This study on the cold spray process aimed at achieving an original coating build-up model, capable of predicting the resulting microstructure as a function of powder morphology and process parameters. The work focused on three main interrelated subjects: 3D powder characterization, simulation of individual impacts on a flat substrate by the finite element method and deposition build-up modeling.An innovative method based on microtomographical observations was used for 3D characterization of the powder. Image analysis allowed to separate single powder particles and to gather them into a 3D collection containing approximatively 18 000 objects. Their size and shape were quantitatively measured. A cluster analysis method (K-means) was then applied to this data set to divide the particles into 7 classes based on their shape.The second main research topic consisted in performing particle impact simulations on a flat substrate by the finite element method (using the commercial software Abaqus). The use of dedicated meshing tools allowed to simulate the impact of real particles, as observed by microtomography. Scripting techniques were used to carry out a large number of these simulations but, due to limited robustness of the procedure, only few of them were successfully conducted.The third research area focused on the development of a deposition build-up model (in 2D to allow a simpler implementation). Data from finite element results were interpolated and used in an iterative simulation, where impacting particles were deposited one by one. Different approaches were tested but the development of the model could not be completed in the framework of this thesis.Model validation could be performed on finite element simulations. The two kinds of splats (Ta on Cu and Ta on Ta) were considered separately. Concerning the first, direct microtomographical imaging could be applied, due to the heterogeneity of materials. Splats were observed, individually separated and gathered in a 3D collection as done before with powder particles. Simulated and observed splats could then be compared on a statistical basis. No particular discrepancy was observed, confirming the impact simulation method used. The second kind of splats (Ta on Ta) was complicated by the homogeneity of the materials, preventing the use of microtomography. The deposition (before spraying) of a contrast layer between Ta substrate and Ta particle was tried by different techniques. The only method giving exploitable results was the chemical vapor deposition of a Fe layer onto the powder particles. However, the small number of adherent particles and the weak contrast obtained in the images prevented the use of the methods already applied to powder particles and Ta splats onto Cu.The optimization of powder granulometry and shape (towards a specific application) is one of the main expected applications of the deposition build-up model, together with the simulation of composite powders (typically, metal and oxide). The involvement of phase transformation phenomena into the model could extend its application to the whole family of thermal spray processes (plasma, HVOF, etc.) or to other additive manufacturing techniques. In general, the philosophy behind our modeling approach could be applied to every manufacturing/coating technique where the supply material is in powder form and undergoes a certain transformation during the process. Finally, the coupling of such a model with homogenization techniques would allow the prediction of macroscopic properties depending on deposit microstructure (e.g. thermal or electrical conductivity).L'objectif principal de cette étude était de réaliser une modélisation du procédé cold spray, fondée sur l'observation expérimentale et sur des modèles physiques capables de prédire la microstructure du dépôt en fonction de la morphologie de la poudre et des paramètres de projection. Pour y arriver, le travaux se sont organisés autour de trois axes principaux de recherche : caractérisation de la poudre en 3D, simulations d'impact par éléments finis et modélisation d'empilement. Un procédé innovant de caractérisation morphologique de la poudre en 3D, utilisant la microtomographie par rayons X, a été développé. Le traitement des images résultantes a permis d'isoler les particules individuelles, regroupées dans une bibliothèque 3D d'environ 18000 objets. Leur taille et forme ont été caractérisées quantitativement. La méthode de partitionnement des données dite « K-means » a été utilisée pour la répartition des particules en 7 classes de forme.Le deuxième axe de recherche portait sur la simulation d'écrasement des particules, par la méthode des éléments finis (logiciel Abaqus, approche lagrangienne). L'utilisation d'outils de maillage adaptés a permis de réaliser des simulations d'écrasement des particules réelles (en provenance de la bibliothèque 3D). L'automatisation de ces simulations visait la possibilité d'en effectuer en grand nombre mais, face aux problèmes de robustesse rencontrés, le nombre de simulations menées à bien fut limité.Le troisième axe de recherche portait sur le développement d'un modèle d'empilement itératif, fondé sur l'utilisation des résultats des simulations d'écrasement. Ce modèle a été mis en place en 2D par simplicité. Différentes implémentations ont été essayées mais leur développement ne fut pas suffisamment abouti pour l'application à des cas pratiques.La validation des modèles s'est limitée aux simulations d'impact par éléments finis. Les deux types de splats (Ta sur Cu et Ta sur Ta), exigeant de méthodes d'observation expérimentale différentes, ont été traités séparément. Les premiers ont pu être directement observés par microtomographie et regroupés dans une bibliothèque 3D des splats Ta sur Cu. Ensuite, ils ont été comparés, de façon statistique mais aussi individuellement, aux correspondants simulés sans qu'aucune divergence évidente n'apparaisse. Le cas des Ta sur Ta est, en revanche, compliqué du fait de l'homogénéité du système qui empêche l'utilisation directe de la microtomographie. Bien que différentes méthodes visant à apporter une couche du contraste entre particule et substrat aient été essayées, la construction d'une bibliothèque 3D des splats Ta sur Ta n'a pas été possible.L'optimisation des poudres (choix de la granulométrie et de la forme, en vue d'une application donnée) est une des utilisations envisagées pour le modèle d'empilement, ainsi que la simulation de la projection de poudres composites (métal et oxyde). L'inclusion dans le modèle des transformations de phase ouvrirait la porte de la famille de la projection plasma ou de la fabrication additive. Plus généralement, la philosophie derrière la modélisation d'empilement développée dans cette thèse peut être appliquée à tout procédé où l'apport de matière est fait à partir d'une « poudre » subissant une certaine transformation. Enfin, le couplage avec un modèle de comportement pourrait permettre l'estimation de certaines propriétés physiques (par exemple, les conductivités thermique et électrique), dépendant de la microstructure du dépôt

Diagnóstico de ideas previas en Física

In this work we have study the existence of mis-conceptions and students interpretation patters concerning to phenomena refered to phase change. We show the persistency of mis-conceptions in students of different levels. This students were instructed in Physics and Chemistry. Our conclusion are in concordance with Osborne's work (1983) if we take in to account that our work was made in other educational system.</p

Architectured interfaces and electrochemical modelling in an anode supported SOFC

International audienceIncreasing the SOFC performances is many-fold: i/ at low current density, through the enhancement of the catalytic properties of the electrodes, ii/ at the ohmic loss region, through lower resistance, iii/ at the high current density region, via the optimization of the electrodes microstructure. The present work proposes to explore how the corrugation of electrode/electrolyte interfaces impacts the performances of SOFCs. Taking ideas from the battery community, this approach was applied to the anode/electrolyte interface of a SOFC based on standard compositions. Patterning of this interface was achieved with different geometries at the 10-100µm scale by cold pressing. Thin electrolyte layers have been deposited on top of these architectures by different techniques. In parallel, an electrochemical model was carried out and implemented throughout the interface in FEM (finite element method) with COMSOL Multiphysics. The results showed a 25 % increase in the total current density for a certain ellipsoid geometry

Assessment of submicroscopic genetic lesions by single nucleotide polymorphism arrays in a child with acute myeloid leukemia and FLT3-internal tandem duplication

The same FLT3-internal tandem duplication (ITD) positive clone was detected at diagnosis and relapse, but not at birth, in a child with M1 acute myeloid leukemia. Single nucleotide polymorphism arrays demonstrated that chromosome 13 acquired uniparental disomy, in association with del(9q), represented a progressive event in the course of the disease, and it was responsible for the homozygous FLT3-ITD at relapse

A new approach to 3D modeling of the cold spray process, combining morphological methods and finite element simulations

L'objectif principal de cette étude était de réaliser une modélisation du procédé cold spray, fondée sur l'observation expérimentale et sur des modèles physiques capables de prédire la microstructure du dépôt en fonction de la morphologie de la poudre et des paramètres de projection. Pour y arriver, le travaux se sont organisés autour de trois axes principaux de recherche : caractérisation de la poudre en 3D, simulations d'impact par éléments finis et modélisation d'empilement. Un procédé innovant de caractérisation morphologique de la poudre en 3D, utilisant la microtomographie par rayons X, a été développé. Le traitement des images résultantes a permis d'isoler les particules individuelles, regroupées dans une bibliothèque 3D d'environ 18000 objets. Leur taille et forme ont été caractérisées quantitativement. La méthode de partitionnement des données dite « K-means » a été utilisée pour la répartition des particules en 7 classes de forme.Le deuxième axe de recherche portait sur la simulation d'écrasement des particules, par la méthode des éléments finis (logiciel Abaqus, approche lagrangienne). L'utilisation d'outils de maillage adaptés a permis de réaliser des simulations d'écrasement des particules réelles (en provenance de la bibliothèque 3D). L'automatisation de ces simulations visait la possibilité d'en effectuer en grand nombre mais, face aux problèmes de robustesse rencontrés, le nombre de simulations menées à bien fut limité.Le troisième axe de recherche portait sur le développement d'un modèle d'empilement itératif, fondé sur l'utilisation des résultats des simulations d'écrasement. Ce modèle a été mis en place en 2D par simplicité. Différentes implémentations ont été essayées mais leur développement ne fut pas suffisamment abouti pour l'application à des cas pratiques.La validation des modèles s'est limitée aux simulations d'impact par éléments finis. Les deux types de splats (Ta sur Cu et Ta sur Ta), exigeant de méthodes d'observation expérimentale différentes, ont été traités séparément. Les premiers ont pu être directement observés par microtomographie et regroupés dans une bibliothèque 3D des splats Ta sur Cu. Ensuite, ils ont été comparés, de façon statistique mais aussi individuellement, aux correspondants simulés sans qu'aucune divergence évidente n'apparaisse. Le cas des Ta sur Ta est, en revanche, compliqué du fait de l'homogénéité du système qui empêche l'utilisation directe de la microtomographie. Bien que différentes méthodes visant à apporter une couche du contraste entre particule et substrat aient été essayées, la construction d'une bibliothèque 3D des splats Ta sur Ta n'a pas été possible.L'optimisation des poudres (choix de la granulométrie et de la forme, en vue d'une application donnée) est une des utilisations envisagées pour le modèle d'empilement, ainsi que la simulation de la projection de poudres composites (métal et oxyde). L'inclusion dans le modèle des transformations de phase ouvrirait la porte de la famille de la projection plasma ou de la fabrication additive. Plus généralement, la philosophie derrière la modélisation d'empilement développée dans cette thèse peut être appliquée à tout procédé où l'apport de matière est fait à partir d'une « poudre » subissant une certaine transformation. Enfin, le couplage avec un modèle de comportement pourrait permettre l'estimation de certaines propriétés physiques (par exemple, les conductivités thermique et électrique), dépendant de la microstructure du dépôt.This study on the cold spray process aimed at achieving an original coating build-up model, capable of predicting the resulting microstructure as a function of powder morphology and process parameters. The work focused on three main interrelated subjects: 3D powder characterization, simulation of individual impacts on a flat substrate by the finite element method and deposition build-up modeling.An innovative method based on microtomographical observations was used for 3D characterization of the powder. Image analysis allowed to separate single powder particles and to gather them into a 3D collection containing approximatively 18 000 objects. Their size and shape were quantitatively measured. A cluster analysis method (K-means) was then applied to this data set to divide the particles into 7 classes based on their shape.The second main research topic consisted in performing particle impact simulations on a flat substrate by the finite element method (using the commercial software Abaqus). The use of dedicated meshing tools allowed to simulate the impact of real particles, as observed by microtomography. Scripting techniques were used to carry out a large number of these simulations but, due to limited robustness of the procedure, only few of them were successfully conducted.The third research area focused on the development of a deposition build-up model (in 2D to allow a simpler implementation). Data from finite element results were interpolated and used in an iterative simulation, where impacting particles were deposited one by one. Different approaches were tested but the development of the model could not be completed in the framework of this thesis.Model validation could be performed on finite element simulations. The two kinds of splats (Ta on Cu and Ta on Ta) were considered separately. Concerning the first, direct microtomographical imaging could be applied, due to the heterogeneity of materials. Splats were observed, individually separated and gathered in a 3D collection as done before with powder particles. Simulated and observed splats could then be compared on a statistical basis. No particular discrepancy was observed, confirming the impact simulation method used. The second kind of splats (Ta on Ta) was complicated by the homogeneity of the materials, preventing the use of microtomography. The deposition (before spraying) of a contrast layer between Ta substrate and Ta particle was tried by different techniques. The only method giving exploitable results was the chemical vapor deposition of a Fe layer onto the powder particles. However, the small number of adherent particles and the weak contrast obtained in the images prevented the use of the methods already applied to powder particles and Ta splats onto Cu.The optimization of powder granulometry and shape (towards a specific application) is one of the main expected applications of the deposition build-up model, together with the simulation of composite powders (typically, metal and oxide). The involvement of phase transformation phenomena into the model could extend its application to the whole family of thermal spray processes (plasma, HVOF, etc.) or to other additive manufacturing techniques. In general, the philosophy behind our modeling approach could be applied to every manufacturing/coating technique where the supply material is in powder form and undergoes a certain transformation during the process. Finally, the coupling of such a model with homogenization techniques would allow the prediction of macroscopic properties depending on deposit microstructure (e.g. thermal or electrical conductivity)

Unity through uniqueness : the subcultural capital of music blogs

Recent scholarship on subcultural theory has cultivated an idea of subcultural capital around common signifiers. Points of departure within subcultures have been seen as deviations or potential threats to subcultural cohesion. In this report, I use a mixed-method approach to examine the way subcultural capital is created within the digital subculture of music blogs. Focusing on North American independent rock music blogs, I use a qualitative approach to examine their aesthetic choices, and descriptive analysis informed by quantitative techniques to examine content decisions. Through these methods, I demonstrate that in this particular subculture, member uniqueness is not a factor to be glossed over or explained away. It is not a threat to subcultural unity. Rather, for this subculture at least, member uniqueness is a necessary condition for participation within the subculture. At different locations within their websites, music blogs utilize signifiers that both unite them with, and distinguish them from, others in the subculture.Radio-Television-Fil

Reduced foraging investment as an adaptation to patchy food sources: A phasic army ant simulation

International audienceColonies of several ant species within the subfamily Dorylinae alternate stereotypical discrete phases of foraging and reproduction. Such phasic cycles are thought to be adaptive because they minimize the amount of foraging and the related costs, and at the same time enhance the colony-level ability to rely on patchily distributed food sources. In order to investigate these hypotheses, we use here a simple computational approach to study the population dynamics of two species of virtual ant colonies that differ quantitatively in their foraging investment. One species, which we refer to as “phasic”, forages only half of the time, mirroring the phasic activity of some army ants; the other “non-phasic” species forages instead all the time. We show that, when foraging costs are relatively high, populations of phasic colonies grow on average faster than non-phasic populations, outcompeting them in mixed populations. Interestingly, such tendency becomes more consistent as food becomes more difficult to find but locally abundant. According to our results, reducing the foraging investment, for example by adopting a phasic lifestyle, can result in a reproductive advantage, but only in specific conditions. We thus suggest phasic colony cycles to have emerged together with the doryline specialization in feeding on the brood of other eusocial insects, a resource that is hard to obtain but highly abundant if available

Simulation study about the geometry of electrode-electrolyte contact in a SOFC

International audienceWe tested, by means of simulations, the idea of a patterned contact between composite electrode and electrolyte of a SOFC. Simulation results show that the patterned studied geometry can improve the performance of the assembly in "intermediate" conditions, i.e. when there are neither ohmic nor kinetic limitations. The gain reached up to 45 % in terms of current density drawn, with respect to a standard flat contact

A numerical study of pore formation mechanisms in aluminium cold spray coatings

International audienc

Mathematical Modeling and Simulation for Optimization of IDEAL-Cell Performance

The IDEAL-Cell is an innovative SOFC concept, comprising the anodic part of a proton conducting fuel cell (i.e., anode and protonic electrolyte) and the cathodic part of a solid oxide fuel cell (i.e., cathode and anionic electrolyte), connected through a porous composite central membrane of proton conducting and anion conducting materials where water recombination reaction between protons and oxygen ions occurs. A mathematical model for the description of transport phenomena and reactions in steady-state conditions is presented. The model is based on charge and mass balances in a continuum approach. Simulations are performed considering negligible polarization resistances due to electrochemical activations in order to evaluate the maximum performance of the cell. Simulations show that the IDEAL-Cell performance is comparable to that provided by the current state of the art for proton conducting fuel cells, and it may be further improved by reducing ohmic losses with thinner layers