Liste des publications
Design and Optimization of Friction Stir Welding Tool
In Friction stir welding, the tool geometry plays a fundamental role to obtain suited microstructures in the weld and the heat affected zone. In this work, for obtaining an excellent weld appearance without void, cracking, or distortion, an attempt was made to select proper FSW tool for aluminium alloy. So, we have included in the tool a safety system aimed at avoiding premature damage, and allowing the measure of applied pressure. The improved tool was tested on AA2024-T4 and AA7075-T6 aluminum alloys sheets. The weld quality has been evaluated by means of a microstructure analysis and micro-hardness measurements. The capacity to increase the welding speed, the changes of the crystalline plans orientation in the mixed part of thermo-mechanically affected zone and grains sizes observed in micrographics underlines the effect of the pin geometry and its displacement. The micro-hardness curve shows good mechanical properties. Finally, obtained results show welds of very good qualities. This study opens new interesting perspectives. Voir les détails
Mots clés : Aluminium, Design, Friction Stir Welding, Metallography, Micro-hardness
Use of Guided Waves for Inspection of Composite Skin-Honeycomb Core
Sandwich plates, made of two aluminum layers and a metal honey comb core are used inthe aircraft industry. The purpose of this study is to show the ultrasonic guided waves sensibility to discover delamination in skin-honeycomb sandwich structures used in aeronautics. Separation between the skin and the core can appear during the manufacture or after use. In this work, Lamb's waves are used to control this kind of plane structure. Indeed, these waves have the advantage to putin vibration the totality of the plate that we want to control and they propagate on long distances without too much attenuation. The revealing, by the guided waves, of the unsticking which canmeet on such sandwiches, between the plate and the honeycomb core is studied and commented. Voir les détails
Mots clés : Lamb waves, Sandwich structure, Dispersion curves, Displacements.
Low-Complexity Wideband LSF Quantization Using Algebraic Trellis VQ
In this paper an algebraic trellis vector quantization (ATVQ) that introduces algebraic codebooks into trellis coded vector quantization (TCVQ) structure is presented. Low encoding complexity and minimum memory storage requirements are achieved using the proposed approach. It exploits advantages of both the TCVQ and the algebraic codebooks to know the delayed decision, the codebook widening, the low computational complexity and the no storage of the codebook. This novel vector quantization scheme is used to encode the wideband speech line spectral frequencies (LSF) parameters. Experimental results on wideband speech have shown that ATVQ yields the same performance as the traditional split vector quantization (SVQ) and the TCVQ in terms of spectral distortion (SD). It can achieve a transparent quality at 47bits/frame with a considerable reduction of memory storage and computation complexity when compared to SVQ and TCVQ. Voir les détails
Mots clés : trellis coded quantization, algebraic codebook, LSF, wideband speech coding
Design and deformation behavior of high strength Fe–Mn–Al–Cr–C duplex steel
The influence of cold rolling reduction on microstructures and mechanical properties at room temperature of the duplex Fe–28Mn–7Al–5Cr–0.3C steel was investigated. In the Fe–28Mn–7Al alloy system, the duplex microstructure was obtained by lowering the carbon content to about 0.3 wt.%. The steel was austenito-ferritic with a low to moderate stacking fault energy. Two thermomechanical cycles were performed, which included cold rolling/annealing at 1100 °C, and cold rolling/annealing at 1100 °C/cold rolling/annealing at 1000 °C. The effects produced by cold rolling on the duplex steel were grain refinement and different strain-induced marks within the ferrite and austenite phases. They were easily observed within the austenite phase at a relatively smaller reduction than within the ferrite phase. Mechanical twinning plays a dominant role within the austenite phase during deformation at room temperature, resulting in extreme mechanical properties. No edge or longitudinal cracks were observed during cold rolling of the duplex steel. Voir les détails
Mots clés : Duplex steel, Cold rolling, Annealing, Microstructures, Austenite, Ferrite
The effect of a high temperature superconducting patch on a rectangular microstrip antenna
The complex resonant frequency problem of a superconductor patch is formulated in terms of an integral equation which is the kernel of a dyadic Green's function. To include the effect of the superconductivity of the microstrip patch, the surface complex impedance of the superconductor film is introduced using the two fluids model of Gorter and Casimir. The Galerkin procedure is used in the resolution of the electric field integral equation. Numerical results concerning the effect of the operating temperature of a superconductor patch on the characteristics of the antenna are presented. Voir les détails
Mots clés : Dyadic Green's function, Galerkin procedure, HTS microstrip patch, Microstrip antenna, Superconducting patch
Air gap tuning effect on the resonant frequency and half-power bandwidth of superconducting microstrip patch
An accurate analysis of an air gap tuned high Tc superconducting microstrip antenna is presented. To include the effect of the superconductivity of the microstrip patch in the Full wave analysis of the tunable rectangular microstrip patch, a surface complex impedance is considered. This impedance is determined by using London's equation and the model of Gorter and Casimir. Numerical results obtained are found to be in excellent agreement with the theoretical and experimental data available in the literature. Finally, numerical results for the air gap tuning effect on the operating frequency and bandwidth of the high Tc superconducting microstrip antenna are also presented. Voir les détails
Mots clés : Bandwidth, natural frequencies, Accurate analysis, Air gap tuning effect, Full wave analysis, Numerical results, Operating frequency, Rectangular microstrip patch, Superconducting microstrip antennas, Superconducting microstrips
Study of High Tc Superconducting Microstrip Antenna
Resonant characteristics of microstrip antennas with superconducting films is presented. The analysis is based on a full electromagnetic wave model with London's equations and the two-fluid model. It is shown that the full-wave analysis presented here gives numerical results which are in excellent agreement with the measured data available in the literature. Re- sults showing the effect of the temperature on the resonant frequency and half-power bandwidth of superconducting microstrip antenna are given. Variations of the resonant frequency with the high Tc superconducting film thickness are also presented. Voir les détails
Mots clés : Electromagnetic waves, microstrip antennas, Superconducting films, Full wave analysis, High-T, Numerical results, Resonant characteristics, Superconducting microstrip antennas, Two fluid model
Influence de la répartition des textures sur les performances d’un palier lisse
Un intérêt progressif est accordé aux surfaces texturées dans les paliers lisses. L’utilisation desurfaces avec certaines géométries et dispositions de textures peut être une approche efficace pouraméliorer la performance d’un palier hydrodynamique.Cet article présente l’approche numérique utilisée pour analyser l’effet des textures de formesphérique sur les caractéristiques d’un contact hydrodynamique. Les résultats obtenus montrent que lescaractéristiques les plus importantes du contact comme l’épaisseur minimale du film, la pressionmaximale dans le contact, le débit axial et le couple de frottement peuvent être améliorés à travers unchoix approprié de la répartition des textures sur la surface du contact. Voir les détails
Mots clés : lubrification hydrodynamique, Lubrification à fluide non Newtonien, Tribologie des revêtements, Contact sous sollicitation de Freting, Tribologie sous champ électrique et magnétique, Méthodologie et caractérisation tribologique
Valorisation du kaolin de debagh (Guelma), Algériedans le domaine de dépollution des eaux de rejets industriels, cas du nickel.
le kaolin de debagh-guelma, traite par HCl 0,4 m, a été utilise comme support adsorbant pouréliminer le nickel contenu dans les eaux de rejet industriel en vue de leur valorisation pourêtre déversées dans la nature sans risque de contamination des eaux de surface ou des nappesphréatiques. Le processus envisage en régime statique, a 20°c, une vitesse d’agitation de l’ionde 400 tr/min et un ph = 4,4, montre qu’un gramme de kaolin purifie peut fixer selon lemodèle de Freundlich, jusqu’a 37,16 mg de nickel. Le temps de pseudo équilibre ion solide,mis en évidence dans ce travail est de 16 minutes. un pseudo premier ordre a été déterminepour la vitesse d’adsorption de l’ion a la surface du solide avec une constante de vitesseapparente (kapp ) égale a 0,14 s-1 et une énergie d’activation (ea) de 32,23 kj/mol. Enfin, nousmontrons que l’adsorption du nickel sur le kaolin purifie est soumise a l’influence de deuxzones distinctes: une zone de diffusion, dépendant de l’agitation de l’ion dans le milieuréactionnel et une zone cinétique contrôlée par la réaction. Voir les détails
Mots clés : Nickel, Kaolin, dépollution, eau de rejet
MATERIAL CHARACTERIZATION BY PULSED EDDY CURRENTM.Zergoug,N.Boucherrou
The Pulsed eddy current (PEC) application in the industrial domain is veryweak compared to conventional eddy current. Its use in detection of the defects, particularly inthe determination of corrosions .The contained information in the received signal makes itpossible to determine several parameters with an aim of analyzing material. The resultsobtained explain the behaviour of the Pulsed Eddy Currents and their influences in variouselectromagnetic parameters on the inspection. We will evaluate the aptitudes and theperformances of this technique in the determination of the characteristics materials inparticular. Also we have studied the sensitivity of the defects and other parameters in theinspection by the pulsed method and we have showed the detection of the defects into thesecond and third layers. The originality of this work consists of the material evaluation. Theapplied NDT PEC methods can characterize microstructure types, micro structural changes,hardness changes. The objective of our work is to evaluate some metallurgic characteristics bynon-destructive methods. The characterization of the structure modifications by PEC allows todetect mechanical and metallurgical parameters of materials Voir les détails
Mots clés : Pulsed eddy current, PEC, CF, NDE, NDT