Liste des publications

Nombre total de résultats : 541
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Adaptive B-Spline Model Based Probabilistic Active Contour for Weld Defect Detection in Radiographic Imaging

N. Nacereddine, L. Hamami, D. Ziou, A. B. Goumeidane  (2010)

This paper describes a probabilistic region-based deformable model using a new adaptive scheme for B-spline representation. The idea is to adapt the number of spline control points which are necessary to describe an object with complex shape. For this purpose, the curve segment length (CSL) is used as criterion. The proposed split and merge strategy on the spline model consists in: adding a new control point when CSL is greater than a certain splitting threshold so that the contour tracks all the concavities and, removing a control point when CSL is less to a certain merging threshold so that the contour aspect maintains its smoothness. Noise on synthetic and real weld radiographic images is assumed following Gaussian or Rayleigh distribution. The experiments carried out confirm the adequacy of this approach, especially in tracking pronounced concavities contained in images. Voir les détails

Mots clés : weld defect, Active contour, adaptive B-spline, split and merge operations

Design and Optimization of Friction Stir Welding Tool

Mouloud Aissani, Saliha Gachi, Fouad Boubenider, Younes Benkedda  (2010)

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

Simulation & Expérimentation en Soudage Etude du Comportement Thermique et Mécanique des Métaux à Usage Aéronautique.

AISSANI Mouloud  (2014)

La mise en œuvre de nouvelles techniques d’assemblage, en remplaçant le rivetage par le soudage, permet l’allègement des structures et des appareils à usage aéronautique. Dans le présent travail, l’intérêt est porté sur l’étude de deux procédés de soudage importants et récents qui sont le soudage par friction malaxage FSW et par l’arc électrique TIG. Dans un premier temps, une étude du comportement thermique de quelques métaux soudés par le procédé TIG, est menée. Une modélisation et des simulations numériques du transfert thermique sont réalisées, mettant en évidence l’apparition des zones à risques et l’effet des différents paramètres de soudage. Une étude expérimentale du soudage est ensuite présentée permettant une validation des résultats numériques. Dans un second temps, la conception et la réalisation d’un outil de soudage par friction malaxage FSW (Brevet 2007) sont effectuées. Des essais de soudage ont été menés par la suite avec succès. Les cordons de soudure obtenus par ces deux procédés ont été caractérisés par différentes techniques et leurs propriétés mécaniques ont été déterminées. Voir les détails

Mots clés : thermique, 3D, Essais mécaniques, acier, MEF, soudage TIG, soudage FSW, source de chaleur, alliage d’Aluminium

Analog Circuit Implementation of FractionalOrder Damped Sine and Cosine Functions

H. Nezzari, A. Charef, and D. Boucherma  (2013)

This paper introduces for thefirst time analog circuitimplementations of two fundamental linear fractional order systems whose impulse responses called fractional order damped sineand cosine functions are the inverse Laplace transform of their irrational transfer functions. These analog circuit implementationsare derived through rational function approximations of their irrational transfer functions. Voir les détails

Mots clés : Analog circuit, fractionalorder differential equation, fractional order system, irrational function, rational function.

Effect of Substrates on the Properties of ZnO ThinFilms Grown by Pulsed Laser Deposition

Adel TAABOUCHE, Abderrahmane BOUABELLOU, Fouad KERMICHE, Faouzi HANINI, Sarah MENAKH, Yacine BOUACHIBA, Tahar KERDJA, Chawki BENAZZOUZ, Mohamed BOUAFIA, Saad AMARA  (2013)

Polycrystalline zinc oxide (ZnO) thin films have been deposited at 450˚C onto glass and silicon substrates by pulsedlaser deposition technique (PLD). The used source was a KrF excimer laser (248 nm, 25 ns, 5 Hz, 2 J/cm2). The effectsof glass and silicon substrates on structural and optical properties of ZnO films have been investigated. X-ray diffraction patterns showed that ZnO films are polycrystalline with a hexagonal wurtzite—type structure with a strong (103)orientation and have a good crystallinity on monocrystalline Si(100) substrate. The thickness and compositional depthprofile were studied by Rutherford Backscattering spectrometry (RBS). The average transmittance of ZnO films deposited on glass substrate in the visible range is 70%. Voir les détails

Mots clés : ZnO, Thin films, PLD, Silicon, X-ray diffraction, Optical transmittance, RBS

Characteristics of Al-doped TiO2 thin films grown bypulsed laser deposition

Faouzi HANINI, Yacine BOUACHIBA, Fouad KERMICHE, Adel TAABOUCHE, Abderrahmane BOUABELLOU, Tahar KERDJA, Kamel Boukheddaden  (2013)

Al-doped TiO2 (TiO2:Al) thin films were deposited at 450ºC ontoglass substrates using pulsed laser deposition method. X-rays diffractionspectra showed that the obtained films are polycrystalline of anatase structurewith preferential orientation of (101) direction. AFM images, nanoparticles sizeand surface roughness mean square values showed that the surfaces of TiO2:Alfilms are smoother than that of undoped TiO2 films. A blue shift in theabsorption edge of TiO2 with increasing Al concentration in the film isnoteworthy as it leads to increase in the width of the optical transmission. Theoptical waveguiding performances of the TiO2:Al films were demonstrated byusing the m-lines spectroscopy technique and the results were correlated to thestructural properties. Spectroscopic ellipsometry was used to extract the opticalconstants of the films. The determined band gap of undoped and Al doped filmsvaries from 3.43 to 3.61 eV, which is in accordance to Burstein-Moss shift. Voir les détails

Mots clés : Al-doped TiO2, structure, morphology, optical properties, waveguide, nanoparticles

Extraction of weld defects dimension from radiographic images using the level set segmentation without re-initialization

Mohammed Halimi, Naim Ramou  (2013)

Radiographic images segmentation is the major interest for the weld defect diagnosis and monitoring in the field of industry. In this work  we present a method that takes ownership of local segmentation geodesic active contours. The goal of the method presented in this paper is to automate the process of extracting dimension of weld defects from radiographic images using level set segmentation. The information would be used in the area of nondestructive testing (NDT). This method is found to be effective and robust. Voir les détails

Mots clés : radiographic method, weld inspection, defect dimensions, Signal processing

Etude Comparative des Techniques de Filtrage Actif Sélectif par le Référentiel Synchrone de Park d-q et l’Approche FMV

Noureddine Hamouda, Kamel Eddine Hemsas, Hocine Benalla  (2014)

To minimize the total harmonic distortion (THD) and improve the power factor (PF), this paper presents a comparative study between two techniques of shunt power active filter (SPAF) by a selective action of harmonics. These two techniques are based on the SAPF of certain low frequency harmonics (5th and 7th) whose identification of the harmonics of references of the first is made by the axis synchronous d-q of the Park, and the second is done by the approach of self-tuning filter (STF) Thereafter, The active simultaneously filtering of the 5th and 7th harmonics of the current of load catches. The shapes of the signals and the THD values resulting from the results of digital simulations (Matlab-Simulink) elaborate the effectiveness and the best technique of this type of filtering. Voir les détails

Mots clés : PF, THD, Harmonics, SAPF, STF, d-q Park Synchronous Axis

Segmentation of welding defects using level set methods

HALIMI Mohammed, RAMOU Naim  (2012)

Non-destructive testing (NDT) is a technique used in science and industry to evaluate the properties of a material without causing damage. In this paper we propose a method for segmenting radiographic images of welding in order to extract the welding defects which may occur during the welding process. We study different methods of level set and choose the model adapted to our application. The methods presented here take the property of local segmentation geodesic active contours and have the ability to change the topology automatically. The computation time is considerably reduced after taking into account a new level set function which eliminates the re-initialisation procedure. Satisfactory results are obtained after applying this algorithm both on synthetic and real images. Voir les détails

Mots clés : image segmentation, Level set, weld defects, Radiographic image

Acoustic emission signal denoising to improve damage analysis in glass fibre reinforced composites

Abida Satour, Silvio Montrésor, Mourad Bentahar, Rachid Elguerjouma and Fouad Boubenider  (2014)

In this contribution, continuous wavelet denoising technique is developed to enhancethe signal to noise ratio of acoustic emission (AE) signals. The time– frequency characteristics of the recorded noise are first determined by calculating the noisewavelet coefficients. Then, an algorithm able to proceed denoising by extracting noise features from those corresponding to AE signals is developed. The denoising procedure is applied to get meaningful signals when the detection threshold is decreased from 30 dB to 25 dB. Furthermore, the spectral flatness measure was applied to eliminate signals originating from noise. Experiments were conducted on cross-ply composite specimens [±45°]6S to examine the efficacy of the proposed technique. The denoised signals were analysed using the continuous wavelet transform and were also analysed in terms of the dominant frequency band which was processed by a fast Fouriertransform. Results show that denoised low-amplitude AE hits are well correlated withhigh-amplitude AE hits (A≥30 dB) in terms of damage characterisation. Voir les détails

Mots clés : acoustic emission, polymer-based composite, Denoising, Signal processing, damage characterisation