Liste des communications
Dynamic mechanical analysis of hybrid composite laminate reinforced with glass/carbon fiber
Composite materials possess the characteristics of high stiffness and high fatigue strength, which are desirable for advanced aircraft components. However, the mechanical behavior of such materials depends upon a variety of factors such as fiber volume fraction, percentage of voids, lay-up order and reinforcement type, the effects of which are difficult to establish individually. As the damage initiates in composite materials and grows during static and cyclic loading, material properties such as modulus, residual strength and strain would vary and, in many cases, they may be significantly reduced because of the progressive accumulation of cracks and delaminations. The objective of the current study was to gain a better understanding of mechanical and dynamic mechanical properties of hybrid composite laminate reinforced with glass woven fabric, carbon woven fabric and epoxy matrix, manufactured using vacuum assisted resin molding process. Quasi-static flexural and dynamic mechanical analysis (DMA) tests were conducted on hybrid composites samples prepared according to ASTM standards. Responses of carbon/epoxy and glass/epoxy laminates were also investigated to compare with that of hybrid samples as a function of fiber content. The storage modulus (E’) was found to decrease with temperature in all cases at an oscillating frequency of 1 Hz, and hybrid composite had showed better values of E’ at glass transition temperature (Tg=96°C). Microscopic examinations indicated that flexural failure was mainly due to matrix cracking, shear failure of fiber/matrix interface and delamination. Voir les détails
Mots clés : Composite laminate, hybridation effect, glass transition temperature, dynamic mechanical analysis (DMA)
La contamination métallique des eaux lacustres des zones humides du PNEK située au Nord-Est algérien
Les lacs (Tonga, El-Mellah et Oubeira) zone de notre étude sont alimentés soit directement par les précipitations soit indirectement par les oueds (eaux des rejets) alimentant ces derniers et pouvant véhiculer des polluants toxiques. A leurs sorties des lacs les concentrations des métaux lourds dans les eaux des lacs se caractérisent soit par une baisse soit par un accroissement. A titre indicatif, les variations des concentrations au niveau des deux stations caractérisant le lac El Mellah, enregistre une baisse assez sensible en fer, en manganèse et en nickel, cette baisse s’accompagne d’un accroissement en zinc, en cuivre, en chrome et en plomb. L’échantillonnage a été réalisé suivant un pas mensuel, Les résultats montrent un accroissement des concentrations se faisant dans le sens saison sèche saison humide. Cette évolution serait liée soit à un piégeage par les sédiments provoquant ainsi la baisse remarquée soit à une forte vitesse d’écoulement entraînant d’une manière quasi-instantanée les métaux lourds vers la sortie par effet de pousse pousse. Voir les détails
Mots clés : pollution, zone humide, variations saisonnières, métaux lourds, lacs.
Contrôle des pipelines par ondes guidées:Evaluation de la méthode
La technique de contrôle par ondes guidées est nouvellement utilisée dans l'industrie pétrochimique en Algérie afin, de contrôler l’intégrité des pipelines. En effet, cette technique est la seule qui peut contrôler une distance de 200 mètres en un simple tir, et permet de détecter les corrosions le long des pipelines. L'objet de ce travail est de mener des essais pour évaluer la fiabilité de cette technique de contrôle des pipelines. En effet, les ondes guidées sont générées à l’aide des transducteurs piézoélectriques, et les fréquences utilisées varient entre 20 kHz et 100 kHz. Des essais sur un circuit de gazoduc ont été réalisés dans une usine à gaz à Hassi Messaoud. Une partie du circuit contrôlé est enterrée. Ceci nous a permis d’étudier ce cas avec ses signaux complexes. Des diminutions de matière ont été détectées et localisées par cette technique sur la partie non enterrée. Les résultats obtenus ont été confirmés par la technique classique du contrôle par ultrasons. Voir les détails
Mots clés : cnd, Ondes guidées, pipelines
Room temperature and seed layer free electrochemicalo elaboration of ZnO-nanowires and thin films highly c-axis oriented
In this present work we report the electrodeposition at room-temperature and without seed-layer of well-aligned and highly c-axis oriented ZnO nanowires and ZnO thin films.The electrodeposition was performed in a classical three electrodes electrochemical cell, under potentiostatic mode and without stiring. The substrates used were molybdenum foil, ITO-glass and aluminium foil.The electrolytic bath was initially composed of 5mM ZnCl2, 5mM H2O2 and 100 mM KCl as supporting electrolyte, the pH value being about 6.8. The ZnCl2 concentration was progressively modified, and this gives morphological modification of the deposits.Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy to give information about microstructure, morpholohy and crystalline phases.The morphology observed by SEM showed that the increasing of ZnCl2concentration will increase the average diameter of the ZnO-nanowires, until obtaining thin films. DRX spectra confirm the elaboration of ZnO-deposits with highly c-axis orientation.These important result will promote the facile use of electrodeposition to elaborate ZnO nanostructures and thin films for several technological applications as nanogenerators, SAW devices, DSSC, ETA solar-cells, water-splitting, sensing, etc. Voir les détails
Mots clés : ZnO, nanowires, thin film, electrodeposition
polypyrrole coated cellulosic substrate modified by copper oxide.
Firstly, the chemical polymerization of polpyrrole onto cellulosic substrate is conducted by using FeCl3 as an oxidant and pyrrole as monomer. Different parameters were tested (monomer concentration, duration of the experiment, nature of supporting electrolyte, temperature, etc…) in view to obtain films with different thickness and different morphologies. Thickness and topography of different PPy deposits (films) were estimated by a profilometer apparatus. The electrochemical reactivity of the obtained electrodes was tested by voltamperometry technique (CV) and electrochemical impedance spectroscopy (SIE).Secondly, the modification of the PPy film surface by incorporation of copper oxide nanoparticles is conducted by applying a galvanostatic procedure from a CuCl2 solution.Surface characterization has been carried out using scanning microscope (SEM) coupled with energy dispersive X-ray analysis (EDX), fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The analysis showed clearly the presence of the copper oxide nanoparticles (CuO and Cu2O) in the polymer films with dimensionsless than 50 nm. Voir les détails
Mots clés : modified polypyrrole, copper oxides
Mechanical properties of hybrid composites laminates reinforced with carbon and glass fibers
Composite materials possess the characteristics of high stiffness and high fatigue strength, which are desirable for advanced aircraft components. However, the mechanical behavior of such materials depends upon a variety of factors such as fiber volume fraction, percentage of voids, lay-up order and reinforcement type, the effects of which are difficult to establish individually. The objective of the current study was to gain a better understanding of mechanical properties of hybrid composite laminate reinforced with weave carbon/glass fiber manufactured using vacuum assisted resin molding process with STR Midapoxy resin. Responses of weave carbon/epoxy and weave glass/epoxy laminates were also investigated to compare with that of hybrid samples. This experimental investigation was conducted to study the effect of hybrid composite specimen subjected to in-plane tensile, three-point-bending flexural and compressive loading on a universal testing machine according to ASTM standards. The failure modes were observed using an optical microscope, and the results show that the carbon/epoxy composite laminate had the highest mechanical strength and modulus and the hybrid composites increase with increasing relative carbon fiber volume fraction. It can be concluded that improvement in the balance of stiffness and toughness in composite laminates can be realize through hybridization. Voir les détails
Mots clés : Woven fiber, hybrid effect, Composite laminate, mechanical properties
CuO grown on copper of high performance electrocatalyst for O2 electroreduction
The aim of this work is to synthesize copper oxide on copper electrode electrochemically for use in the O2 electroreduction. The growth of CuO arrays on Cu foil was demonstrated. The morphology and structure of the CuO were examined by X-ray diffraction spectroscopy. The catalytic performance of the obtained CuO/Cu electrode for O2 electroreduction was evaluated by means of cyclic voltammetry, chronoamperometry. Voir les détails
Mots clés : Copper substrate, electrocatalyst
Effet d’un traitement de surface par projection thermique sur les propriétés structurales et mécaniques d’une fonte grise
La technique de projection thermique occupe aujourd’hui une place de plus en plus importante parmi les familles de traitements de surface qui joue un rôle incontournable dans de nombreux domaines industriels particulièrement dans la mécanique. Dans ce travail, nous allons montrer l’effet d’un revêtement de molybdène déposé par le procédé de projection à flamme-fil sur les propriétés microstructurales et mécaniques d’une fonte grise à graphite lamellaire.Les caractérisations par microscopie optique, électronique à balayage et par diffraction RX ont mis en évidence le rôle de la nouvelle microstructure obtenue après projection thermique à flamme-fil dans l’amélioration des propriétés mécaniques particulièrement la résistance à l’usure par abrasion de la fonte grise à graphite lamellaire. Les résultats ont montré que le taux d’usure obtenu pour la fonte revêtue en molybdène est faible que celui de la fonte nue. Cette évolution présente une bonne concordance avec la variation de la dureté. Voir les détails
Mots clés : traitement de surface, molybdène, fonte grise, microstructure, propriétés mécaniques.
Efficient Detection Criteria for Model Order Selection of Interferometric SAR signal corrupted by multiplicative noise with a new penalty function
In this paper the problem of estimating the number of components in a multibaseline interferometric synthetic aperture radar (InSAR) signal, corrupted by complex correlated multiplicative noise in the presence of the layover phenomenon, is addressed. Research tasks were carried out by using the information theoretic criteria (ITC). It has been shown that among the ITC, one of the efficient detection criteria (EDC) achieves generally the best performance. We propose then a new penalty function for EDC. Voir les détails
Mots clés : Model order estimation, information theoretic criteria, multiplicative noise, SAR interferometry
STRUCTURAL AND MAGNETIC PROPRIETIES OF NANOSTRUCTURED Fe80CO20 POWDERS ELABORATED BY MECHANICAL ALLOYING PROCESS.
Nanostructured disordered iron–cobalt alloy of Fe–80% Co–20% composition was prepared by mechanical alloying of the elemental powders in a high-energy ball milling. The transformations occurring in the material during milling were studied with the Eddy current characterization for having the relationship with impedance, lattice parameters and crystallite size. The transformation of the phase depends upon the milling time. With the increase of milling time all Co atoms became dissolved in the bcc Fe and the final product of the MA process was the nanocrystalline Fe (Co) solid solution with a mean crystallite size of about 15 nm. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Magnetic properties were investigated and related to the microstructural changes. Voir les détails
Mots clés : Mechanical Alloying, Nanostructure materials, Eddy Current, Magnetic and mechanical properties