Liste des documents
ANALYSE DU COMPORTEMENT MÉCANIQUE DES MATÉRIAUX COMPOSITES RENFORCÉS PAR DES FIBRES VÉGÉTALES
L’objectif de ce travail est d’analyser l’influence de l’orientation des fibres végétales, qui ont connus un intérêt particulier dans l’industrie, sur le comportement mécanique des Bio-composites. L’orientation des fibres est un paramètre significatif pour l’amélioration des propriétés mécaniques et l’amplification des contraintes induites dans le matériau et par conséquent sur la sécurité de la structure. En se basant sur la théorie classique des stratifiés, un code en Matlab a été développé, afin d’estimer les appropriés élastiques, les contraintes et les déformations induites dans le matériau composite renforcé par des fibres de Lin. Voir les détails
Mots clés : Bio-composite, Fibre Végétale, Contrainte Induites, Déformation Induite.
Bearing Fault Diagnosis Using De-noising Techniques Based on EMD Combined with Coefficients Correlation
The vibration signals of a rolling bearing contain important information which can be used in early defect detection and diagnosis. This signal is usually noisy and the information about the fault can be lost. In this paper, a new denoising method based on Empirical Mode Decomposition Iterative Interval Thresholding and estimation of the correlation coefficient (EMD-corIIT) is presented. The results are compared with others proposed methods. The application of this technique to the experimental results shows that this method can extract effectively the fault features of rolling bearing compared with the others cited methods. Voir les détails
Mots clés : Denoising EMD, thresholding, vibration signal, Bearing Fault, Correlation Coefficients
BEHAVIOURS OF DEFORMATION AND RECRYSTALLIZATION OF 3% SILICON STEEL USING WEDGE-SHAPE SPECIMEN
Hot deformation and static recrystallization behaviours of a low carbon 3% Silicon steel, which is ferritic structure at high temperatures, has been investigated using wedge-shape specimen with a single-pass hot rolling experiments. The hot-rolling tests were carried out at temperature of 900?C to 9mm thickness followed by holding at the same temperature (900oC). The volume fraction recrystallized increased with the increase in rolling reduction and holding time after rolling, although a plateau was observed in the relationship between the volume fraction recrystallized and the effective strain. The preferential area for the recrystallization was the previous grain boundaries, particularly triple points of boundaries where the strain was concentrated. An inhomogeneity of recrystallization in the transverse sections through the thickness of the deformed wedges was observed. It was concluded that in this fine grain size material of 3% Silicon steel, the knowledge of deformation and recrystallization behaviors needs better control of strain and temperature under wedge-shape material. Voir les détails
Mots clés : 3% Silicon steel, wedge-shape specimen, hot rolling, deformation variables, dynamic recovery, static recovery, static recrystallization.
X-Ray Diffraction Evaluation of Dislocation Density and Crystallite Size in the HAZ
The aim of this work is to study the effect of successive welding process on microstructure and mechanical properties of the heat affected zone (HAZ) in welded HSLA steel, employed in petroleum and gas transport. The analysis of the diffraction pattern profiles by the Rietveld refinement method (X-ray Diffraction Line Profile Analysis XRDLPA), allows obtaining detailed information on the evolution of the microstructural parameters such as the sizes of the domains consistent with diffraction (crystallite size), micro-deformations and dislocation densities. Based on the X-ray diffraction analysis (XRD) using Material Analysis Using Diffraction (MAUD) software, the results show an outstanding evolution of microstructural parameters in the HAZ, which means an increase in the crystallite size and a decrease in the dislocation density according to the number of welding process. Voir les détails
Mots clés : HSLA, XRD, dislocation density, HAZ.
Characterization of the Polylactic acid stretched uniaxial and annealed by Raman spectrometry and Differential scanning calorimetry
in this work, we have been interested in the characterization of the effect of heat treatment and mechanical treatment on the crystallinity of a polylactic acid (PLA) film by two techniques, DSC and Raman spectroscopy. the results obtained by the DSC for the stretched film shows the appearance of a broad peak of crystallization around 120 ° C, a rise in melting peak in a significant way, which shows that the uniaxial stretching has increased the crystallinity of the PLA, whereas for the annealed film appearance of a double melting peak. The results obtained by Raman spectroscopy show new peak appears at 922 cm−1 after stretching process, indicating crystallization process occurs. Voir les détails
Mots clés : Raman, DSC, PLA, crystallinity
Effect of deposition time on the properties of Cu2O thin film electrodeposited on ITO substrates
In the last few years, the scientists have researched for a sustainable, inexpensive, and efficient new materials for enhancing electrocatalytic activity and electronic energy conversion. All explored materials have provided novel and high electrical, electrochemical, magnetic and optical characteristics. Among them, Cuprous oxide (Cu2O) thin films grown by electrodeposition clearly fulfill the sustainability and the cost pre-requisites. Therefore, if they are well prepared and electrodeposited they could lead to the fabrication of highly efficient devices.In this study, we investigate the effect of deposition time on the electrochemical, structural, morphological and optical properties of Cu2O thin films. The Cu2O thin films were electrochemically elaborated on ITO substrate into a reducing sulphatic bath under pH 11 by a chronoamperometric method at a potential of −0.50V versus SCE. Deposition time was varied from 1 to 10 min. The XRD analysis indicated that the synthesized Cu2O thin films had a cubic phase with a preferred texture along (111) plane. In addition, no trace of CuO and Cu was observed. From AFM analysis, the thickness and the roughness of the thin films increase by increasing deposition time from 1 to 10 min. The surface of the deposits was become dense and compact when the deposition time increase. The optical properties of the as-deposited Cu2O thin films revealed an optical transmission of about 70% in visible light region. The optical energy band gap was estimated from Tauc extrapolation; it was found that the band gap of Cu2O thin films is 1.9-2.2 eV. A summary, the obtained Cu2O thin films have suitable and high properties. Therefore, they could be a good candidate to develop advanced electrode materials for solar cells, electrochemical sensors and electrocatalytic purposes. Voir les détails
Mots clés : Cu2O thin film, deposition time, electrodeposition
Influence of Applied Potential on the Conductivity of Polypyrrole Thin Films growing on Indium Tin Oxide
As one of the promising conducting polymers (CPs), polypyrrole (PPy) has been extensively used as active electrode material for many applications: anti-corrosive coatings, batteries, electronic devices, sensors and biomaterials. In fact, PPy is a widely studied conductive polymer due to its high environmental, thermal and chemical stability, their good electronic conductivity and ease of synthesis. Its conductivity originates from the ? electrons delocalized over the conjugated system and from the doping ions. PPy thin films can be synthesized on electrodes from organic or aqueous media by chemical and electrochemical methods. Electrochemical deposition offers a versatile and facile method since the film formation and its properties (thickness and surface topography) can be easily controlled by controlling the electropolymerization conditions, such as applied potential, current density, monomer concentration, electrolyte solutions and pH. Recently, it has been reported that properties of PPy films depend significantly on their final morphology. Therefore, synthesis of novel morphologies of PPy deposits could improve some of these properties. In this study, PPy thin films were deposited on indium tin oxide (ITO) electrode under potentiostatic control from a solution containing 0.01 M pyrrole (C4H5N) dissolved in acetonitrile (CH3CN). The influence of the applied anodic potential on the morphology, electrochemical behavior, as well as the electronic conductivity of the resulting PPy films was investigated. For this purpose, PPy films deposition was performed at three applied potentials 0.8, 1 and 1.1 V/SCE for 2 min. The obtained films were characterized by impedance spectroscopy measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Voir les détails
Mots clés : Chronoamperometry, Electrochemical polymerization, Polypyrrole, Thin films
Electrochimical oxidation of glucose by Ni-Fe nanoparticiles dispersed on polyaniline thin films
In this work we describe the electrodeposition of Ni–Fe nanostructures on polyanilyne (PAni) as templates. The conditions and parameters influence in the morphology and electrochemical activity of the electrodeposited Ni–Fe nanoparticles.The electrocatalytic properties of Ni–Fe/polyanilyne-modified electrode toward the glucose oxidation were analyzed via cyclic voltammetry and amperometry. The studies showed that Ni–Fe /PAni electrode displayed the highest electrocatalytic activity, attributed to the high density of Ni–Fe nanoparticles deposited on the polyanilyne vibreuse nanotubes support. Voir les détails
Mots clés : Ni–Fe nanoparticles, glucose, Polyanilne, cyclic voltammetry, Electrocatalytic Oxidation
Contribution to the improvement of the quality of continuous casting steels at Sider El-Hadjar-Annaba
Continuous casting is the process between steel making and rolling. It consists of turning liquid steel into slabs, blooms, or billets. The molten steel comes into contact with the mold, it will solidify and the first phases of the steel will form. This study confirms the need to check the steel quality and the continuous casting parameters such as; casting speed, extraction rate, oscillation of the mold and lubrication during primary cooling. The main objective is to build a thermal model that is an important task for predicting temperature profiles on different sides and edges of the product, in order to optimize the crust of steel. Voir les détails
Mots clés : continuous casting - steel - mold - primary cooling – slab.
Proposition of a mechanical model to predict the behaviour of a laminate bio composite material
The purpose of this paper is to develop a mechanical model able to predict the mechanical behaviour of a laminate bio-composite material reinforced by the flax fibres without necessity to the expensive experimental test. A numerical comparative modelling based on finite element method is conducted by using in one hand a several stacking sequences, and in the other hand a growing plies number in order to estimate the lateral deflexion U3 in each plies of the bio-composite subjected to compression load. Meanwhile, the proposed mathematical model can be used as a power tool decision in design and the ensuring of the structure integrity. Voir les détails
Mots clés : Bio-composite, laminate, flax, modeling