Gaussian heat flux parameters estimation during a GTAW operation

International audienc

From liquid to solid bonding in cohesive granular media

We study the transition of a granular packing from liquid to solid bonding in the course of drying. The particles are initially wetted by a liquid brine and the cohesion of the packing is ensured by capillary forces, but the crystallization of the solute transforms the liquid bonds into partially cemented bonds. This transition is evidenced experimentally by measuring the compressive strength of the samples at regular intervals of times. Our experimental data reveal three regimes: 1) Up to a critical degree of saturation, no solid bonds are formed and the cohesion remains practically constant; 2) The onset of cementation occurs at the surface and a front spreads towards the center of the sample with a nonlinear increase of the cohesion; 3) All bonds are partially cemented when the cementation front reaches the center of the sample, but the cohesion increases rapidly due to the consolidation of cemented bonds. We introduce a model based on a parametric cohesion law at the bonds and a bond crystallization parameter. This model predicts correctly the phase transition and the relation between microscopic and macroscopic cohesion.Comment: 20

Ibuprofen loading into mesoporous silica nanoparticles using Co-Spray drying: A multi-scale study

Mesoporous Silica Nanoparticles (MSN) are used in an increasing number of applications in nanomedicine. Their synthesis and external/internal functionalization have been extensively studied as well as their biological properties. Nevertheless, the conventional drug loading processes of MSN (such as impregnation), do not enable sufficient efficiency and are difficult to consider on an industrial scale. To overcome these limitations, we implemented an innovative co-spray-drying process, using a nano spray-dryer, to load MSN with ibuprofen molecules. In this contribution, complementary techniques were used to perform a multi-scale characterization of the loaded particles. Spray-dried powders have been analysed from aggregates size and morphology to pore loading and ibuprofen conformation. This study demonstrates that ibuprofen/silica weight ratio in the initial suspension strongly affects the location (into mesopores or external) and the conformation (crystallized, amorphous or liquid-like) of ibuprofen. The quantification of each phase has allowed calculating precise loading rates and demonstrate tunable pore filling

Procédé innovant pour la formulation de nanovecteurs d’agents anticancéreux par co-spray drying

Les nanosystèmes présentent un intérêt important dans le monde biomédical, pour leur utilisation comme outilsdiagnostiquesou thérapeutiquesafin de réaliser une délivrance contrôlée de principes actifs. Parmi tous ces systèmes, les nanoparticules de silice mésoporeuse (MSN), biocompatibles et capablesde se dégrader naturellement dans le corps(Lu et al. 2007, Slowing et al. 2008), possèdent un véritable potentiel en tant que vecteurs de molécules actives.Leur capacité d’encapsulation par physisorption ou chimisorption est également un atout majeur. La silice de type MCM-41 est l’une des plus synthétiséeset utilisées, notammentgrâce à sa forteporosité et à satrès grande surface spécifique (Vallet-Regi etal. 2001, Wilczewska et al. 2012)

Etude micromécanique de la cohésion par la capillarité dans les milieux granulaires humides

The capillary cohesion in polydisperse granular media is studied at the local and macroscopic scales. At the local scale, an explicit modeling of capillary cohesion is proposed according to the characteristics of the grain-pair. The modeling of capillary force is validated by experiments performed over pairs of beads. The modeling is then implemented in a 3D numerical code based on a discrete element method, together with a numerical method for the distribution of water in the granular material. Axial compression tests are carried out numerically and experimentally. Successful comparisons between numerical and experimental macroscopic tests approve the approach allowing thus to study the macroscopic behaviour of wet granular materials

Cohésion par capillarité et comportement mécanique de milieux granulaires

The capillarity is studied in 3D polydisperse granular materials at the local and macroscopic scales. At the local scale, an explicit model of capillary cohesion is proposed. It includes a local behaviour law and a rupture criterion that depend on the characteristics of the grain pair. The model is validated by experiments on reference grain pairs. This model, intentionally simple, is implemented in a numerical code based on a 3D distinct- element algorithm, together with a numerical method for the distribution of water. Successful comparisons between numerical and experimental macroscopic tests approve the approach allowing thus to study the macroscopic behaviour of wet granular materials. Finally, the inuence of some couplings is also accounted for in order to show the sensitivity of the capillary cohesion to environmental conditions and to illustrate the potential applications of the code.La capillarité dans un milieu granulaire est étudiée aux échelles locale et macroscopique dans le cas 3D polydisperse. A l'échelle locale, un modéle explicite de cohésion par capillarité est proposé. Il comprend une loi de comportement et un critère de rupture locaux fonctions des caractéristiques du doublet. La pertinence du modèle est vérifiée expérimentalement sur des billes de verre. Il est implémenté dans un code de calcul en éléments discrets, en association avec une gestion numérique de la répartition de l'eau dans le milieu. Des essais de compression sont réalisés numériquement et expérimentalement. Leur concordance a permis de valider l'approche en éléments discrets dans le cas de la capillarité, et d'envisager l'étude du comportement macroscopique des matériaux granulaires humides. Enfin, l'influence de certains couplages est abordée afin de montrer la sensibilité de la cohésion par capillarité aux conditions environnementales ainsi que les possibilités offertes par le cod

Estimation of the Heat Flux Parameters : Application to GTA Static Welding Spot

International audienceA numerical magneto-thermo-hydrodynamic (MTHD) model coupled with an inverse optimizationmethod is developed for the identification of heat flux parameters for the Gas Tungsten Arc Welding(GTAW) process. The MTHD model is based on the four conservation equations of mass, momentum(Navier-Stokes equations), energy (heat transfer) and electric potential. The stated MTHD includes theforce term due to magnetic field in the momentum equation (Lorentz force). The transport phenomenaand the heat transfer from the electrical arc plasma to the weld pool determine the weld penetration andthe weld pool shape. In the current study an attempt has been made to replace the argon electrical arcplasma effect with a heat flux modelled by a Gaussian function on the anode surface. The majorparameters that influence the formation of weld pool shape were identified using a parametric study andare welding efficiency and base radius of the Gaussian distribution. A multivariable optimizationalgorithm based on Levenberg-Marquardt Method is used for the inverse problem. It is concluded thatalgorithm developed were able to predict the reference numerical model and demonstrated the stabilityand robustness of the algorithm using a noised input data