Physique
Elaboration par électrodéposition et caractérisation des couches minces de Ni/Si: Effet du potentiel de dépôt
Ni thin films deposited onto on n-Si (111) substrates using pulsed electrodeposition (PED) method show an influence of the applied potential and the Ni thickness on the structural, surface morphology, electrical and magnetic properties. Significant linearly increase in Ni thickness t (t ranges from 50 to 390 nm) has been observed with increasing applied potential (from -1.6 to -2.6 V). All samples show the polycrystalline films prefers growth with the <111> texture. The strain ε (%) is negative for all samples and their variation as a function of the applied potential has a critical value corresponding to a critical potential (VCr = -2.2 V); the stress increases up to VCr, then stress is relieved. The grain size increases monotonically with increasing Ni thickness and applied potential. Voir les détails
Mots clés : Ni thin films, electrodeposition, Structural properties, microstructure.
High overtone acoustic resonator HBAR based onIDT’s/c-tilted ZnO/Si for timing applications
In this paper, the frequency characteristics ofhigh overtone bulk acoustic modes, generated by interdigitaltransducers IDT’s on c-tilted ZnO/Si, are theoretically andexperimentally investigated. The origin and characteristics ofhigh overtone acoustic modes in ZnO piezoelectric layer onsilicon substrate are discussed and one port HBAR resonator,based on c-axis tilted ZnO/Si, is fabricated and tested bynetwork analyzer. The results achieved in this work are ofinterest in design and fabrication of radiofrequency sourcesand electronic timing devices based on thin film technology Voir les détails
Mots clés : High overtone bulk acoustic modes, HBAR resonator, piezoelectric thin film, c-tilted ZnO, Frequency characteristics
Simulation et optimisation du transfert thermique lors du soudage par friction malaxage FSW d’un métal
The Friction Stir Welding (FSW) is an assembling process of parts in the solid phase, without melting the material and without added metal. The basic concept of the FSW process is simple and consists of using a non-consumable rotational tool with a pin and shoulder shaped to provide required weld properties, where the thermal energy is generated by friction among the rotating the different. The aim of this thesis is to propose an optimization strategy using the SQP algorithm (Quadratic Sequential Programming) coupled with 3D transient heat transfer computation were used to improve the FSW process parameters. An optimization method was applied to improve the FSW welding parameters of an AA2195-T8 aluminum-lithium alloy plate. The numerical procedure proposed is based on the optimization of the spatial parameters related to the tool, ie the welding speed, the speed of rotation of the tool, the radius of the shoulder of the tool and the vertical force applied. This study aims to investigate three criteria: the control of the maximum temperature during FSW; the minimization of the HAZ length and finally the reduction of the total welding energy. The numerical study showed good agreement between the results obtained and the existing experimental data. This good agreement between the results of the two approaches would make it possible to use the proposed numerical model to predict the thermal field and the maximum value of the temperature. The optimization process has demonstrated its robustness and the main results obtained are: The optimal operating conditions allow a gain about 38% of consumed energy by FSW and a reduction of 11 % in the welding time; Applying the optimal parameters permits until a 70% decrease in the length of the Heat Affected Zone (HAZ) at every position on the weld line. Voir les détails
Mots clés : Friction Stir Welding (FSW), Heat transfer, finite volume method, SQP algorithm optimization method.
Effect of Cu/Ni Ratio on the Chemical composition, Magnetic behaviour, and Structural properties of a FeCuNi based alloy
The aim of this project is to study and understand the influence of copper and nickel concentration on the magnetic, morphological and structural properties of the Fe70Cu30-xNixalloy. The alloy was elaborated by mixing iron, nickel and copper powders by the mechanicalalloying technique for 10 hours of milling. The elements were characterised by different techniques: X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM). The X-ray diffraction study shows that the crystallite size decreases with increasing Ni. When it come to the magnetic properties, the coercivityHc and the saturation moment Ms rise from 83 Oe, 121.5 emu/g to 156 Oe, 140 emu/g respectively. Voir les détails
Mots clés : Fe70Cu30-xNix, Scanning Electron Microscope (SEM), X-ray diffraction
Caractérisation des écoulements en micro fluide par vélocimétrie à l’échelle micron appliquée aux microsystèmes
Microfluidics has been a field of research in full expansion for ten years, whose vitality is nourished by the diversity of its applications Today, new technologies indeed make it possible to manufacture electromechanical systems of micro and nanometric size, up to 'at significant levels of complexity, and equipped with all kinds of functionalities. These new possibilities have been used in aspectacular way for many applications, such as DNA microarrays, or lab-onchip. In all these systems, the problem of controlling flows in devices whose dimensions or internal patterns vary from a few hundred nanometers to a few tens of micrometers arises, this work will be devoted to an analysis and characterization of the flows applied to microsystems. Voir les détails
Mots clés : microfluidics, DNA microarrays, microsystems
Élaboration et caractérisation des matériaux nanostructures à base de Fe et Ni
The aims of this work is to understand the influence of the elaboration method , mill type, milling time and concentration on the structural, microstructural and magnetic properties of Fe80Ni20 nanostructured alloy. The production of the Fe80Ni20nanostructured alloy was carried out by the mechanical alloying technique of iron and nickel powders mixture. The elements produced (elaborated) were characterized by X-ray diffraction techniques (DRX), Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM). The X-ray diffraction study confirmed the formation of the Fe-Ni alloy after 600 min of milling with an average crystallite size of 13 nm, while the analysis of the magnetization curves of the Fe-Ni alloys, revealed original magnetic properties: super paramagnetic behavior, and especially saturation magnetization and significant coercitivity. Voir les détails
Mots clés : elaboration method, properties of Fe80Ni20, nanostructured alloy
Thermal analysis of the friction stir welding process based on boundary conditions and operating parameters
Modelling of friction stir welding (FSW) remains a complicated task, as it is crucial to predict the mechanical properties of the final welded part. This research focuses on the numerical simulation aspect of the alloy material AA2195-T8. 3D transient thermal model was applied to simulate the heat transfer phenomena in the welding phase. In this model, the FSW tool is considered as a circular heat source moving in a rectangular plate having a cooling surface and subjected to non-uniform and non-homogeneous boundary conditions. To solve the thermal problem, the finite element method was used as part of a Lagrangian formulation. The obtained results allow us to determine the maximum value of the temperature in the Nugget zone of the welded joint. Sensitivity analysis of the operating parameters was also investigated to determine the thermal cycle and the temperature distribution during this welding process. Our results were successfully compared with the ones available in the literature with good agreement. Voir les détails
Mots clés : Friction Stir Welding, Heat transfer, AA2195-T8, alloy material, parameter characterisation
Effects of Boundary Conditions and Operating Parameters on Temperature Distribution during the Friction Stir Welding Process
This work deals with a numerical simulation of the friction stir welding FSW process of alloy material AA2195-T8. A 3D transient thermal model for simulating the heat transfer phenomena in the welding phase is applied. In this model, the FSW tool is considered as a circular heat source moving in a rectangular plate having a cooling surface and subjected to nonuniformandnon-homogeneousboundaryconditions.ThethermalproblemissolvedusingthefiniteelementmethodaspartofaLagrangianformulation.TheobtainedresultsallowustodeterminethemaximumvalueofthetemperatureintheNuggetzoneoftheweldedjoint.Duringthisprocess,thethermalcycleandthetemperaturedistributionweredeterminedfordifferentvaluesoftheweldingprocessparameters.Theobtainednumericalresultsareingoodagreementwiththeoneavailableintheliterature. Voir les détails
Mots clés : Frictio n Stir Welding, Heat transfer, AA2195-T8
DNS using CLSVOF method of single micro-bubblebreakup and dynamics in ?ow focusing
Numerical simulations are performed to investigate the breakup of air bubble in ?ow focusingcon?guration; the CLSVOF (coupled level set with volume of ?uid) method is employed to track theinterface, which allows a better identi?cation of the liquid–gas interface via a function called level set. TheCFD simulations showed that the velocity ratio, the interfacial tension, the outer channel diameter, thecontinuous phase viscosity, the ori?ce width and length play an important role in the determination of the airbubble’s size and shape. However, at low capillary number, increasing the ?ow velocity ratio gives a smallerbubble size in shorter time, while the increase in interfacial tension leads to a bigger bubble. Moreover, thecarrier ?uid is found to slightly affect the bubbling mechanism, while the smallest bubbles were obtainedwith the smallest ori?ce size. In addition, three breakup regimes are observed in this device: disc-bubble(DB), elongated bubble (EB) and the slug bubble (SB) regime ?ows. This work also demonstrates that theCLSVOF is an effective method to simulate the bubbles breakup in ?ow focusing geometry. In addition, acomparison of our computational simulations with available experimental results reveals reasonably goodagreement. Voir les détails
Mots clés : Bubbling, Multiphase ?ow, CLSVOF, CFD and ?ow focusing
Simulation des ondes ultrasonores dans des matériaux anisotropes piézoélectriques :application aux capteurs électroacoustiques à ondes guidées
Ce travail est une étude numérique et expérimentale pour l’optimisation des performancesde dispositifs électroacoustiques destinés à la détection. L’effet des paramètres intrinsèques,tels que l’épaisseur de la couche piézoélectrique, la longueur d’onde acoustique et l’inclinaisondu cristal sur la vitesse de phase, le facteur de couplage électromécanique et la sensibilité auxeffets de masse, a été étudié numériquement. La méthode des éléments finis a été utilisée, dansle cas des modes de Lamb dans le ZnO/SiC, pour développer un capteur de pression et dans lecas des modes de Rayleigh, de Sezawa et de Love dans le ZnO/Si pour le développement d’uncapteur multimode destiné à la détection des liquides et des gaz. L’étude numérique etexpérimentale d’un résonateur à harmoniques élevées HBAR à base de ZnO c-incliné sur le Si confirme la possibilité de réaliser des dispositifs miniaturisés et de hautes performances à basede ZnO c-incliné. Les résultats obtenus sont importants pour la conception et la réalisation de dispositifs électroacoustiques à ondes guidées pour la détection. Voir les détails
Mots clés : ondes acoustiques, Eléments finis, Matériaux anisotropes piézoélectriques, Dispositifs électroacoustiques