Liste des publications
Structural modification, photoluminescence, andmagnetic property enhancement with Er3+ doping,of sol–gel TiO2 thin films
Nanocrystalline undoped and Er3+ doped TiO2 thin films were prepared by sol–gel dip-coatingtechnique onto glass substrates. Post-deposited films were annealed at 450 °C for 1 h. Differentialscanning calorimetric analysis showed that undoped film crystallization occurred at 339 °C, whileit appears at lower temperature for Er:TiO2. X-ray diffraction and Raman spectroscopy resultsindicate that the films crystallize only into anatase phase, and the crystallite size decreases from24.3 to 21.16 nm with increasing Er3+ doping ratio. The photoluminescence (PL) spectra arecomposed of two broad peaks at 520–570 nm and 640–680 nm assigned to (2H11/2, 4S3/2)–4I15/2 and4F9/2–4I15/2 transitions of Er3+ ions, respectively. PL emission intensities increase gradually raisingthe erbium doping ratio. Vibrating sample magnetometer results of undoped TiO2 thin films reveala ferromagnetic behavior at room temperature and erbium doping leads to an enhancement of thesaturated magnetic moment (Ms). Voir les détails
Mots clés : TiO2 doped Er3+, Sol–gel, Photoluminescence, Magnetic Properties
Effect of brazing current on microstructure and mechanical behavior of WC-Co/AISI 1020 steel TIG brazed joint
In this work, the WC-Co carbide/1020 steel brazed joints which were prepared by Tungsten Inert Gas (TIG) process using different brazing currents have been studied. The peak temperature reached by increasing the brazing current caused remarkable inter-diffusion of Ni, Mn, Cu and Co elements between the braze and the base materials. The higher the brazing current was, the larger the diffusion extent of these elements became and the greater the WC rearrangement occured. As the diffusion rate of Ni towards the WC-Co was enhanced through increasing brazing current, a short range diffusion of Co element towards the braze was recorded. A Special Shear Test (SST) conducted at room temperature revealed the best bonding strength for the current of 80A. Besides, hardness (HIT) and elastic modulus (EIT) values of the interfaces were situated between those of the braze and the base materials. Voir les détails
Mots clés : WC-Co cemented carbide, TIG brazing, inter-diffusion, Interface, Nano-indentation
Effect of the Inclination of Mold Walls on Primary Cooling During the Continuous Casting of Steel
The principal function of a continuous casting mold is to receive the liquid steel, and ensure its cooling in order to permit the formation of a solidified skin, and sufficiently resistant, this is the phase of primary cooling. The efficiency of this process depends on several parameters such as the casting speed, the temperature exchange between the walls of the mold and the thin crust of the slab as well as the conicity of continuous casting mold. Latter has been the subject of this work, which consists in observe the influence of the conicity of mold on the variation of the temperature field, and friction generated during lowering of the slab. the curves reflect changing the factors cited previously as a function of the conicity. The numerical simulation was conducted by FLUENT 6.0 code. Voir les détails
Mots clés : continuous casting, conicity of mold, temperature field
Thermal and mechanical properties of bio-basedplasticizers mixtures on poly (vinyl chloride)
The use of mixtures of nontoxic and biodegradable plasticizers coming from natural resources is a good way to replaceconventional phthalates plasticizers. In this study, two secondary plasticizers of epoxidized sunflower oil (ESO)and epoxidized sunflower oil methyl ester (ESOME) were synthesized and have been used with two commerciallyavailable biobased plasticizers; isosorbide diesters (ISB) and acetyl tributyl citrate (ATBC) in order to produce flexiblePVC. Different mixtures of these plasticizers have been introduced in PVC formulations. Thermal, mechanical andmorphological properties have been studied by using discoloration, thermogravimetric analysis (TGA), differentialscanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile - strain and scanning electronmicroscopy (SEM). Studies have shown that PVC plasticization and stabilization were improved by addition ofplasticizers blends containing ISB, ATBC, ESO and ESOME. An increase in the content of ESO or ESOME improvedthermal and mechanical properties, whereas ESOME/ATBC formulations exhibited the best properties. Voir les détails
Mots clés : PVC, epoxidized sunflower oil, epoxidized sunflower oil methyl ester, isosorbide diesters, acetyl tributyl citrate.
Adaptive backstepping control using combined direct and indirect σ-modification adaptation
In this paper, by using the dynamic surface control technique, an adaptive backstepping controller using combined direct and indirect σ-modification adaptation is proposed for a class of parametric strict-feedback systems. In this approach, a σ-modification parameter adaptation law that combines direct and indirect update laws is proposed. At first, the x-swapping identifier with a gradient-type update law is presented for a class of parametric strict-feedback nonlinear systems. Next, the main steps of the controller design for a class of nonlinear systems in parametric strict-feedback form are described. The closed-loop error dynamics is shown to be globally stable by using the Lyapunov stability approach. Finally, simulation results for a single-link flexible-joint robot manipulator are given to illustrate the tracking performance of the proposed adaptive control scheme. Voir les détails
Mots clés : Backstepping control, direct and indirect adaptive control, adaptive dynamic surface control, Lyapunov stability, flexible joint manipulators
Microstructural Study of Thin Films CuFe Obtained by ThermalEvaporation of Nanostructured Milled Powde
Commercial copper and iron powders were used as starting materials. These powderswere mechanically alloyed to obtain Cu(100-x) Fex supersaturated mixture. The milling duration waschosen in such a way as to obtain a nanostructured mixture and to form a supersaturated solidsolution of CuFe; the powder mixture was used to deposit CuFe on a glass substrate.The elaboration of our films has been carried out using thermal evaporation process (physical vapordeposition) under 1 × 10-6 mbar vacuum from an electrically heated tungsten boat, using thesupersaturated solid solution Cu(100-x) Fex powder obtained by mechanical alloying. The filmsdeposition has been done on glass substrates. In this study, we present the composition effect on thestructural and magnetic proprieties of Cu(100-x) Fex powder and thin films. The chemicalcomposition, structural and magnetic proprieties of milled powders and thin films were examinedby SEM, TEM, XRD, XRF and VSM. Voir les détails
Mots clés : thin film, CuFe Solid Solution, microstructure, DRX, MET, VSM
Reliability of the high strength pipeline steel under corrosion defect
The demand of energy such as hydrocarbon, gas and oil requires more and more construction of new pipeline. Therefore, the assessment of the remaining life of these pipelines structure became more and more important to ensure the continuity of production and distributions operations. The reliability of these industrial facilities is largely conditioned by specific characteristics for each system, in its conditions of use, its environment. Generally the causes of deterioration of hydrocarbon transportation pipelines are related to the presence of apparent defects (pinholes, cracks, corrosion.....etc.). This manuscript is a study to estimate the reliability of these structures. The B31G mechanical model of degradation was used to assess the probability of failure through dimensions of defects. Voir les détails
Mots clés : Reliability, pipeline, Defects, Mechanical Model.
Influence of Vanadium on the Corrosion Behavior of High Manganese Steel in 0.5 M H?SO? Solution
The effect of vanadium on the corrosion behavior of high manganese steel in 0.5 M H?SO? solution has been investigated using scanning electron microscopy, potentiodynamic polarization and impedance spectroscopy. The results have shown that the addition of vanadium to high manganese steel decreases the corrosion current density from 2.1 mA cm¯² to 1.29 mA cm¯². Impedance diagrams show the existence of a high frequency capacitive loop and a low frequency inductive loop. The addition of vanadium increases charge transfer resistance from 5.18 Ω cm² to 12.45 Ω cm². Voir les détails
Mots clés : corrosion, Manganese, EIS, Tafel
Characterization of Structural Noise Patterns and Echo Separation in the Time-Frequency Plane for Austenitic Stainless Steels.
The aim of this study is to characterize the structural noise for a better flaw detection in heterogeneous materials (steels, weld, composites...) using ultrasonic waves. For this purpose, the continuous wavelet transform is applied to ultrasonic A-scan signals acquired using an ultrasonic non destructive testing (NDT) device. The time-scale representation provided, which highlights the temporal evolution of the spectral content of the A-scan signals, is relevant but can lead to misinterpretation. The problem is to identify if each pattern from the wavelet representation is due to the structural noise or the flaw. To solve this problem, a detection technique based on statistical significance testing in the time-scale plane is used. Information about the structural noise signals is injected into the decision process using an autoregressive model, which seems relevant according to the spectral content of the signal. The approach is tested on experimental signals, obtained by ultrasonic NDT of metallic materials (austenitic stainless steel) then on a weld in this steel and indeed enables to distinguish the components of the signal as flaw echoes, which differ from the structural noise. Voir les détails
Mots clés : Austenitic stainless steels, Structural noise, Flaw detection, Wavelet transform, Autoregressive model, Significance testing
Performance evolution of fully and partially textured hydrodynamic journal bearings lubricated with two lubricants
This study investigates the evolution of the main bearing performance of partiallyand fully textured hydrodynamic journal bearing. The viscosity effect is also analysed by themean of numerical simulations for two types of oil: the oil 1 (ISO VG 32, 31.3 cSt at 40 °C)has a lower viscosity than oil 2 (ISO VG 100, 93 cSt at 40 °C). Reynolds equation is solved byfinite difference and Gauss-Seidel methods with over-relaxation for various operatingconditions. It is shown that, under hydrodynamic lubrication regime, the improvement of themost important characteristics (the friction coefficient and minimum film thickness) of atextured journal bearing depend strongly on the lubricant viscosity and the journal rotationalspeed. The fully textured journal bearing is highly favorable at very low speeds while thepartially textured journal bearing is more suitable for slightly higher speeds. The gain inbearing performance due to the texturing of the bushing disappears at a critical speed of thejournal and then, for higher rotational speeds, the presence of textures becomes detrimental. Voir les détails
Mots clés : journal bearing, texture, hydrodynamic, lubrication