Liste des publications
Characterization of the deformation texture after tensile test and cold rolling of a Ti-6Al-4Vsheet alloy
The deformation texture after cold rolling and tensile test of an industrial Ti-6Al-4V sheet alloy was studied using X-ray diffraction. The alloy was subjected to a cold rolling to different thickness reductions (from 20% to 60%) and then tensile tests have been carried out along three directions relatively to the rolling direction (0°, 45° and 90°). The experimental results were compared to the existing literature and discussed in terms of active plastic deformation mechanisms. Voir les détails
Mots clés : TA6V, deformation texture, Anisotropy, Lankford
Comportement structural et mécanique dessoudures en aciers inoxydables austénitique etduplex réalisées par le procédé TIG
L’objet de cette étude étant de connaître lesdifférentes variations structurales et mécaniques après un cyclethermique de soudage de deux aciers inoxydables de hauteperformance (austénitique AISI 316L et duplex AISI 2205), quisont très utilisés dans tous les secteurs, particulièrementl’industrie pétrolière. On a utilisé le procédé TIG, c’est unprocédé à arc électrique, caractérisé par son apport thermiqueintense et précis aisément automatisé, l’état microstructurale desassemblages soudés a été analysées par des observationsmétallographique optique de différentes zones à savoir : la zonefondue ZF, la zone affectée thermiquement ZAT et le métal debase MB. Finalement les changements microstructurales ont étéargumentés par une filiation de micro-dureté. Voir les détails
Mots clés : Acier inoxydable austénitique, duplex, soudage TIG, micro-dureté et contrôle
Hybrid Shape Descriptors for an Improved Weld Defect Retrieval in Radiographic Testing
In this paper, four region-based shape descriptors well reported in the literature are used to characterize weld defect types of crack, lack of penetration, porosity and solid inclusion, usually encountered in radiographic testing of welds. The rectangularity and the roundness in the geometric descriptor (GEO) are used in order to propose an hybridization algorithm so that the hybrid descriptor issued from GEO and each of the other descriptors becomes more discriminant in such application where, due to bad radiographic image quality and weld defect typology, the human film interpretation is often inconsistent and labor intensive. According to the results given in the experiments, the efficiency of the proposed hybrid descriptors is confirmed on the weld defects mentioned above where, the retrieval scores are significantly improved compared to the original descriptors used separately. Voir les détails
Mots clés : Radiographic film, weld defects, shape descriptors, hybridization algorithm
First-principles calculations of the structural, electronic and optical properties of In1−xBxAsyP1−y quaternary alloys lattice matched to InP and BeS
The structural, electronic, and optical properties of the cubic In1−xBxAsyP1−y quaternary alloys lattice matched to InP and BeS have been investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). The generalized gradient approximation (GGA) of Wu and Cohen was used as the exchange correlation potential to calculate the structural and electronic properties. In addition, the alternative GGA proposed by Engel and Vosko and the modified Becke–Johnson potential are utilized to calculate the electronic properties. The computed structural and electronic properties of the binary compounds are in good agreement with the available experimental and theoretical data. For the alloys, non-linear variations of composition x and y with the lattice constant, bulk modulus, direct, indirect band gap, dielectric constant and refractive index are found. All the compounds are direct band gap excluding BP and BAs. The energy band gap of In1−xBxAsyP1−y quaternary alloys lattice matched to InP and BeS substrates is computed. Finally, the band gap of our materials is less than 3.1 eV. Thus the In1−xBxAsyP1−y quaternary alloys may possibly be used in visible light devices. Voir les détails
Mots clés : FP-LAPW, DFT, In1−xBxAsyP1−y quaternary alloys, Lattice matched
First-principle calculations of the structural, electronic, thermodynamic and thermal properties of ZnS x Se1−x ternary alloys
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ZnS x Se1−x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). In this approach the Wu–Cohen generalized gradient approximation (WC-GGA) and Perdew–Wang local density approximation (LDA) were used for the exchange–correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows a linear dependence on alloy composition with a small deviation. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Finally, the quasi-harmonic Debye model was applied to see how the thermal properties vary with temperature at different pressures Voir les détails
Mots clés : FP-LAPW, DFT, energy band structure, Thermal Properties, Debye model, critical temperature
Adsorption d’un mélange binaire «plomb-nickel» par le kaolin
Le kaolin a été utilisé comme adsorbant pour éliminer le nickel et le plomb en mono adsorption et en mélange binaire. Le processus envisagé en régime statique et en mono adsorption a montré qu’un gramme de kaolin peut fixer 43,2 mg/g de nickel et 35,69 mg/g de plomb selon le modèle de Langmuir avec une cinétique de pseudo 1er ordre où le temps du pseudo équilibre est de 16 minutes pour Ni++ et de 14 minutes pour Pb++. Le rapport d’affinité RL a montré que le kaolin présente une bonne capacité d’adsorption. Pour le mélange binaire, l’expérience a montré que l’adsorption du nickel est la plus importante et le pseudo équilibre est plus lent que celui de l’ion seul. Toutefois, nous avons représenté approximativement le mélange avec le modèle de Langmuir généralisé et Langmuir généralisé modifié, en utilisant à la fois des données en mono constituant et en mélange. De ces deux représentations, nous avons constaté une inversion de sélectivité pour le modèle de Langmuir généralisé et une isotherme proche de celle de l’expérimentale pour le modèle de Langmuir généralisé et modifié. Voir les détails
Mots clés : Eau -dépollution- plomb- nickel- adsorption- kaolin
Effects of stabilizer ratio on photoluminescenceproperties of sol-gel ZnO nano-structured thin films
Nanostructured ZnO thin films with different molar ratios of MEA to zinc acetate (0.5, 1.0, 1.5 and 2.0) have been deposited on glass substrates by a sol–gel dip coating technique. X-ray diffraction, Scanning Electron Microscopy, UV–visible spectrophotometry and photoluminescence spectroscopy have been employed to investigate the effect of MEA stabilizer ratio on structural, morphological, absorbance and emission properties of the ZnO thin films. Diffraction patterns have shown that all the films are polycrystalline and exhibit a wurtzite hexagonal structure. The c axis orientation has been enhanced with increasing stabilizer ratio. SEM micrographs have revealed that the morphology of the ZnO films depend on stabilizer ratio. The UV–visible absorption spectra have demonstrated that the optical absorption is affected by stabilizer ratio. The photoluminescence spectra have indicated one ultraviolet and two visible emission bands (green and red), while band intensities are found to be dependent on stabilizer ratio. ZnO thin films deposited at MEA ratio of 1.0 show the highest UV emission while the minimum UV emission intensity is observed in thin films deposited at ratio of 0.5 and the maximum green has been recorded for films deposited at MEA ratio of 2.0. Voir les détails
Mots clés : ZnO thin film, Sol–gel, Stabilizer ratio, Photoluminescence
Fault Diagnosis of an Induction Generator ina Wind Energy Conversion System Using SignalProcessing Techniques
In this article, a contribution to fault diagnosis of an in-duction machine in a wind energy conversion system in closed-loopoperation using a combination between short-time Fourier transformand discrete wavelet transform algorithms is proposed. An on-linefault diagnostic technique based on stator currents analysis of thesquirrel-cage induction generator is proposed to detect and localizeabnormal electrical conditions that indicate, or may lead to, a statoror rotor failure in a squirrel-cage induction generator. This techniquealso permits identification of a fault severity factor and consequentlyhelps to determine the best choice of correctivemaintenance. Further-more, a generalized model of the squirrel-cage induction generatoris used to simulate both the rotor and stator faults, taking iron losses,main flux, and cross-flux saturation into account. The efficiency ofdiagnostic procedure in closed-loop operation of the wind energyconversion system under non-stationary operating conditions is illus-trated with simulation results. Voir les détails
Mots clés : fault diagnosis;, Induction Generator;, Wind Energy Conversion System;, Signal Processing Techniques
POLYPYRROLE COATED CELLULOSIC SUBSTRATE MODIFIED BY COPPER OXIDE AS ELECTRODE FOR NITRATE ELECTROREDUCTION
The aim of this work is to synthesize polypyrrole (PPy) films on nonconducting cellulosic substrate and modified by copper oxide particles for use in the nitrate electroreduction process. Firstly, the chemical polymerization of polypyrrole onto cellulosic substrate is conducted by using FeCl3 as an oxidant and pyrrole as monomer. The thickness and topography of the diferent PPy films obtained were estimated using a profilometer apparatus. The electrochemical reactivity of the obtained electrodes was tested by voltamperometry technique and electrochemical impedance spectroscopy. Secondly, the modification of the PPy film surface by incorporation of copper oxide particles is conducted by applying a galvanostatic procedure from a CuCl2 solution. The SEM, EDX and XRD analysis showed the presence of CuO particles in the polymer films with dimensions less than 50 nm. From cyclic voltamperometry experiments, the composite activity for the nitrate electroreduction reaction was evaluated and the peak of nitrate reduction is found to vary linearly with initial nitrate concentration. Voir les détails
Mots clés : Polypyrrole, cellulosic, CuO, electrocatalysis, Nitrate
A Quantitative Comparative Study of Back Projection, Filtered Back Projection, Gradient and Bayesian Reconstruction Algorithms in Computed Tomography (CT)
Images of the inside of the human body can be obtained noninvasively using tomographic acquisition and processing techniques. In particular, these techniques are commonly used to obtain X-ray images of the human body. The reconstructed images are obtained given a set of their projections, acquired using reconstruction techniques. A general overview of analytical and iterative methods of reconstruction in computed tomography (CT) is presented in this paper, with a special focus on Back Projection (BP), Filter Back Projection (FBP), Gradient and Bayesian maximum a posteriori (MAP) algorithms. Projections (parallel beam type) for the image reconstruction are calculated analytically by defining two phantoms: Shepp-Logan phantom head model and the standard medical image of abdomen with coverage angle ranging from 0 to ± 180° with rotational increment of 10°. The original images are grayscale images of size 128 × 128, 256 × 256, respectively. The simulated results are compared using quality measurement parameters for various test cases and conclusion is achieved. Through these simulated results, we have demonstrated that the Bayesian (MAP) approach provides the best image quality and appears to be efficient in terms of error reduction. Voir les détails
Mots clés : Computed tomography, Bayesian approach, Reconstruction techniques, Filter Back Projection (FBP), Gradient algorithm