Nombre total de résultats : 258
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Champ thermique sous l'effet de la réaction chimique d'une réforme de la pile à combustible à oxyde solide SOFC DIR-interne direct

S. Dehimi, D. Haddad, B. Mebarki, T. Bendris, A. Aissat  (2014)

Les effets directs de reformage interne dans une pile à combustible à oxyde solide (SOFC) sur les champs thermiques sont étudiés par modélisation mathématique. Cette étude présente les champs thermiques d'une pile à combustible standard (Ni-YSZ / YSZ / LSM) anode en charge. Cette étude est également faite dans le plan perpendiculaire à l'écoulement des gaz. La pile à combustible est alimenté par de l'air et de carburant, CH4, H2, CO2, CO et H2O où la naissance du phénomène de la réforme (DIR-SOFC) interne direct. Il est basé sur la réforme de réactions chimiques, de la vapeur et de réaction de reformage réaction du gaz à l'eau. Le but principal de ce travail est la visualisation des champs de température sous l'influence des réactions chimiques mondiales et la confirmation du comportement thermique de cette réaction chimique. Les champs thermiques sont obtenus par un programme informatique (Fortran). Voir les détails

Mots clés : SOFC, Direct internal reforming, Global chemical reactions, Thermal fields

Guided Wave Sensitivity for De-Bond Defects in Aluminum Skin Honeycomb Core

A. Satour, F. Boubenider, R. Halimi, A. Badidibouda  (2013)

Sandwich plates are finding an increasing range ofapplication in the aircraft industry. The inspection of honeycomb composite structure by conventional ultrasonic technique is complexand very time consuming. The present study demonstrates a technique using guided Lamb waves at low frequencies to predict de-bond defects in aluminum skin_honeycomb core sandwich structure used in aeronautics. The numerical method was investigated for drawing the dispersion and displacement curves of ultrasonic Lamb wave propagated in Aluminum plate. An experimental study was carried out to check the theoretical prediction. The detection of unsticking between the skin and the core was tested by the two first modes for a low frequency. It was found that A0 mode is more sensitive to delamination defect compared to S0 mode. Voir les détails

Mots clés : Damage detection, delamination, guided waves, Sandwich structure

Design and Optimisation of Circular and Inductors for Silicon-based RFIC Application

ZIOUCHE Aicha, M. T. Belaroussi  (2008)

In this paper, spiral inductors for RF application, which are designed on a silicon substrate by using standards 0.35 µ m CMOS technology, are described. Analyzed and designed with ASITIC (a tool from the University of Berkeley), which accurately takes into account the parasitic effects. This study shows the possibility of obtaining an optimal inductance having a high quality factor of 15. This result is carried out without resorting to the specific processes such as the digging of the substrate under the inductors or the use of a thick layer in gold. The use of circular form, with optimization of geometrical parameters like spacing between two adjacent turn, the track width and the number of turns, can ensure high quality factors. Voir les détails

Mots clés : circular inductor, high quality factors., RF application

Propagation of Lamb waves in an immersed periodically grooved plate: Experimental detection of the scattered converted backward waves

Nadia Harhad, Mounsif Ech-Cherif El-Kettani, Hakim Djelouah, Jean-Louis Izbicki, Mihai Predoi  (2014)

Guided waves propagation in immersed plates with irregular surfaces has potential application to detection and assessment of the extent, depth and pattern of the irregularity. The complexity of the problem, due to the large number of involved parameters, has limited the number of existing studies. The simplest case of irregularities of practical interest is the two-dimensional corrosion profile. Even this case is in general so complex, that one can extract several amplitude dominant periodic surfaces only by using a Fourier spectrum of the surface. Guided waves in plates, with one or both free surfaces having periodic perturbations of different shapes, have been presented in specialized literature. In this paper is studied the propagation of Lamb waves in an aluminum plate with a periodic grooved surface on only one side and immersed in water. The interaction between an incident Lamb wave and the grating gives rise to retro-converted waves. Preliminary numerical simulation by the finite element method is performed in order to obtain key parameters for the experiments. It is shown that retroconverted waves radiating into the water are detectable although their amplitudes are small. The phonon relation is verified for the leaky Lamb modes. The damping coefficients of the leaky Lamb modes in the grooved immersed plate are evaluated. Voir les détails

Mots clés : Liquid–solid interfaces, Rough plate, Periodic grating, Lamb waves, Converted modes

Notch detection in copper tubes immersed in water by a compressional guided waves

Sonia Djili, Farouk Benmeddour, Emmanuel Moulin, Jamal Assaad, Fouad Boubenider  (2013)

Tube- or pipe-like structures are used to convey fluids such as gas, oil or water. These fluids can be transported on land, in sea or in industrial buildings. Hence, tubes can suffer from mechanical, thermal and chemical stresses. The latter, can severely damage these structures due to the oxidation phenomena. This damage weakens the structure and reveals cracks and inhomogeneities. The objective of this work is to detect and characterise damage in tubes immersed in water by a non-destructive method. This research work is devoted to the development of an experimental device. This device can detect and locate axy- and nonaxy-symmetric circumferential small notches located on the outer surface of a filled tube and immersed in water using guided waves. Different sizes of notches are milled into copper tubes with a thin wall are considered. A single transducer is used for emission and reception of leaky guided waves by using the pulse-echo technique. The compressional L(0,2)mode is launched at relatively high frequency using oblique incidence of the transducer into the fluid. By using the wave leakages, notches of small sizes are detected and located. In addition, the sensitivity of the L(0,2) mode to the radial depth and circumferential extent of notches is evaluated. A roughly linear behaviour of the amplitude reflection coefficients is revealed which is in accordance with research works found in the literature. Voir les détails

Mots clés : guided waves, Immersed tubes, Circumferential notches, Experimental device

Grain size influence on ultrasonic velocities and attenuation

A. Badidi Bouda, S. Lebaili, A. Benchaala  (2003)

During the last two decades, ultrasonic testing was developed as an efficient tool for materials characterization. Acoustical waves by their passage through materials, carry out a multitude of information contained in the signal on the mechanical and physical properties of the material under inspection. In this paper, an experimental study on steel samples has been performed to study the evolution of some ultrasonic parameters such as wave velocities and attenuation coefficients as function of the steel grains size. The experimental results obtained are discussed and analyzed in order to develop an ultrasonic non-destructive technique to grains size determination. Voir les détails

Mots clés : Ultrasonic, Grain Size, Velocity, Attenuation, Scattering

Ultrasonic characterization of materials hardness

A. Badidi Bouda, A. Benchaala, K.Alem  (2000)

In this paper, an experimental technique has been developed to measure velocities and attenuation of ultrasonic waves through a steel with a variable hardness. A correlation between ultrasonic measurements and steel hardness was investigated. Voir les détails

Mots clés : Ultrasounds, hardness, Velocity, Attenuation

Characterization of the deformation texture after tensile test and cold rolling of a Ti-6Al-4Vsheet alloy

B Mehdi, H Azzeddine, R Badji, V Ji, B Alili, D Bradai  (2015)

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

Theoretical prediction of the structural, electronic,and thermal properties of Al1-xBxAs ternary alloys

Khaled BOUBENDIRA, Hocine Meradji, Sebti Ghemid, Fouad El Haj Hassan  (2013)

First-principles calculations are performed to study the structural, electronic, and thermalproperties of the AlAs and BAs bulk materials and Al1-xBxAs ternary alloys using the fullpotential-linearized augmented plane wave method within the density functional theory.The structural properties are investigated using the Wu–Cohen generalized gradientapproximation that is based on the optimization of total energy. For band structurecalculations, both Wu–Cohen generalized gradient approximation and modified Becke-Johnson of the exchange-correlation energy and potential, respectively, are used. Thedependence of the lattice constant, bulk modulus, and band gap on the composition x wasanalyzed. The lattice constant for Al1xBxAs alloys exhibits a marginal deviation from theVegard's law. A small deviation of the bulk modulus from linear concentration depen-dence was observed for these alloys. The composition dependence of the energy band gapwas found to be highly nonlinear. Using the approach of Zunger and coworkers, themicroscopic origins of the gap bowing were detailed and explained. The quasi-harmonicDebye model was used to determine the thermal properties of alloys up to 500 K. Voir les détails

Mots clés : Band structures, First principle calculations, Ternary alloys, Thermal Properties

First principles calculations of structural, electronic and opticalproperties of Zn1-xBexSeyTe1-y quaternary alloys

A. Boumaza, O. Nemiri, K. BOUBENDIRA, S. Ghemid, H. Meradji, F. El Haj Hassan  (2014)

The structural, electronic and optical properties of Zn1-xBexSeyTe1-y quaternary alloys are investigatedusing the full potential-linearized augmented plane wave (FP-LAPW) method within density functionaltheory (DFT). We used both the Wu–Cohen and the Engel–Vosko generalized gradient approximationsof the exchange-correlation energy that are based on the optimization of the total energy and the corre-sponding potential, respectively. Some basic physical properties, such as lattice constant, bulk modulus,electronic band structures, and optical properties (dielectric constant and refractive index) are calculated,nonlinear dependence on the compositions x and y are found. In addition, the energy band gap of zinc-blende Zn1-xBexSeyTe1-y quaternary alloys lattice matched to GaAs substrate is investigated. To ourknowledge this is the first quantitative theoretical investigation on Zn1-xBexSeyTe1-y quaternary alloysand still awaits experimental confirmations Voir les détails

Mots clés : alloys, Ab initio calculations, Electronic structure, optical properties