Liste des documents
Fuzzy Edge Detection In Computed Tomography Through Particle Swarm Optimization
In this paper, we propose a new approach using particle swarm optimization (PSO) for image reconstructions, in which we use the fuzzy inference penalty instead of the Bayesian inference penalty, and particle swarm optimization instead of local method of optimization. We saw that the PSO algorithm just work on the behavior of the individual to reach the best result of the population. Voir les détails
Mots clés : Computed tomography, Non destructive testing, Bayesian Inference, Fuzzy inference, Particle Swarm Optimization
Finite element modeling and analysis of electromagnetic field distribution for different shapes of metallic materials
In aeronautical industry, diversity of used materials, dimensions and complexity of the parts require a specific treatment in order to fulfilling the requirements of safety and reliability.In this paper, electromagnetic problem modeling is developed in order to realize a data-processing application able to calculate electromagnetic field distribution in different mediums especially those used in aeronautics.The finite element method is successfully applied since it adapts for any selected section. The numerical results enable to determinate the field values in any point of the chosen geometry and to determine thereafter the system parameters as well as the distribution of energy. Geometry dimensions, material properties and used frequency influence on results. And for the special cases these results are compared with those given by FEMLAB code. The results are very similar with a good precision which enables usage of the developed code to carry out simulations for other geometries of materials with different proprieties. Voir les détails
Mots clés : Electromagnetic interaction, Maxwell's equations, aeronautical materials, Finite Element Method, field distributions, FEMLAB
Etude ab initio des propriétés Structurales, Magnétique etStabilité du système Fe2(Zr,Nb) dans les trois phases de Laves:C14 C15 et C36.
The pseudopotential method (PP) Based on Density Functional Theory (DFT), using theGeneralized Gradient Approximation (GGA) was applied to investigate the Fe2(Zr,Nb)system within the three Laves phases structures: Cubic C15, Hexagonal C14 and C36. Theeffects of Nb concentration on structural, magnetic and stability of the system were studied.The lattice parameters, bulk modulus and magnetic moments of the three phases werepredicted and showed a significant dependence on Nb concentration. We evidenced therigidity of the Fe2Nb was higher than the Fe2Zr one for C15, C14 and C36. The energeticphase diagram of the systems was also established by determining the heat formation and thestability of the alloys was discussed accordingly. The obtained results showed that the Lavesphase have close formation energies which suggests that the C15, C14 and C36 phases canco-exist at low-temperature. In addition, the magnetic behavior was also established and themagnetic moments were found to be on Fe atoms. Consequently, these alloys were predictedto be ferromagnetic for all phases. The obtained results were in good agreement with availabletheoretical and experimental ones. Voir les détails
Mots clés : Laves Phases, Pseudopotential Method, DFT, Heat of Formation, Stability
Electrochemical behavior of pure aluminum andaluminum alloy sacrificial anodes in seawater solution
In this paper, electrochemical dissolution processes of pure aluminum and aluminum alloy, which act as an anode for the cathodic protection of steel structures in seawater medium, were compared. In this object, the electrochemical characters of these anodes were studied in artificial seawater electrolyte by: (1)Open Circuit Potential (OCP), (2) Potentiodynamic Polarization(LP), and (3) by Electrochemical Impedance Spectroscopy (EIS) measurements. Microstructures of anodes both before and after measurements were analyzed by optical microscopy. Results indicate that Al alloy showed a considerable activation compared to pure aluminum by shifting the OCP values toward more anodic direction and by increasing the corrosion current densities. Voir les détails
Mots clés : Aluminum alloy, corrosion, electrochemical activation, sacrificial anode
Influence of heat input on microstructure and mechanical properties of Ferritic Stainless Steel welds
Ferritic stainless steels are classified as such because the predominant metallurgical phase present is ferrite. These steels are characterized by good resistance to stress corrosion cracking (SCC), pitting corrosion, crevice corrosion (particularly in chloride environments), higher thermal conductivity, low coefficient of heat dilation and lower cost, when compared to austenitic stainless steels. The combination of low cost and good properties has made ferritic stainless steel more and more attractive in various application fields, such as, heat exchangers, petroleum refining equipment, storage vessels, protection tubes, solar water heaters, and exhaust manifold applications. However, ferritic stainless steel steels are associated with many problems during the welding process. These problems are the martensite formation and grain growth, causing a reduction of ductility and toughness. For these reasons, until recently, the application of this group steels is limited in welded structures. The aim of the work is, first to characterize the weld metal, as variable GTA welding process parameters and optimize the heat input. We focused on improving tensile strength of ferritic stainless steel. The results show that, the heat input has a great influence on microstructure and mechanical proprieties of weld metal. The details of tensile tests, optical microscopic observations, microhardness, and Scanning electron microscopy (SEM) fractography, are discussed. Voir les détails
Mots clés : GTA welding, heat input, ferritic stainless steel, microstructure, mechanical properties, Fractography
Etude Microstructurale de l’Alliage nanostructuré (Fe65Co35)70Al30 obtenu par mécanosynthése
Des poudres nanostructurés de l’alliage (Fe65Co35)70Al30 sont obtenues par un broyeur à haute énergie sous une atmosphère d’argon. Des variations morphologiques et microstructurale au cours du broyage sont observées par microscopie électronique à balayage (MEB) et par diffraction des rayons X (DRX). La réduction de la taille des cristallites (16–7 nm) est accompagnée par une augmentation des microdéformations du réseau. Une phase ternaire est obtenue après 8 heures de broyage. Voir les détails
Mots clés : Poudres Fe-Co, alliage nanostructuré, Mécanosynthèse, Diffraction des rayons X
Elaboration et caractérisation d'un multimatériau WC-W-Ni obtenu par infiltration: Effet du nickel sur la consolidation du W
En pratique, l’infiltration spontanée de mélanges de poudres libres sous gravité est la plus adéquate à la réalisation des outils de forage. Les pores interconnectés des poudres libres (non compactées) sont remplis avec un métal ou alliage ayant un bas point de fusion. L’attraction capillaire constitue la force motrice de l’infiltration causant la réduction de l’énergie surfacique interfaciale. Le liquide recouvre la phase solide des poudres de la matrice. Les propriétés du consolidé final dépendent étroitement de la composition du mélange de poudres et de sa réactivité avec le liant infiltrant au cours du cycle de frittage imposé. Nous nous intéressons dans cette étude, pour mieux comprendre les phénomènes qui peuvent se manifester dans le multiconstituant WC-W-Ni (matrice d’outil de forage), àl’élaboration et à la caractérisation du consolidé W-Ni en mettanten évidence l’effet du nickel sur la consolidation de W. Voir les détails
Mots clés : Consolidation, frittage, infiltration, poudres libres, PDC
Exploitation de la propagation réverbérante des ondes élastiques dans les structures : vers un concept de réseau de capteurs SHM à basse consommation
Les méthodes de CND et d’imagerie ultrasonores classiques utilisent des sources contrˆolées et synchronisées avecles récepteurs et n’exploitent en général que les premiers paquetsd’onde des signaux enregistrés aprés propagation dansle milieu. `A l’inverse, les travaux que nous présentons iciconsistent à exploiter les signaux acoustiques dans toute leur complexité, afin d’extraire le maximum d’information à partir d’un nombre limité de capteurs. Les codas ultrasonores, notamment,issues de trajets de propagation multiples et entrelacés dans les structures offrent un moyen original d’extraire des propriétés structurelles utiles (propriétés des matériaux, dimensions,localisation des sources, d´etection et caract´erisation ded´efaut) des signaux de réverbération excités par des sourcesconnues ou non. En particulier, la possibilité d’utiliser dessources acoustiques naturelles (on parle également de sources≪ ambiantes ≫, ou encore ≪ sources d’opportunité ≫) en lieu etplace de l’émission d’ondes ultrasonores, ouvre la voie vers des réseaux de capteurs ultrasonores passifs (récepteurs uniquement), donc basse consommation et potentiellement autonomes et peuintrusifs. Nous présenterons tout d’abord quelques résultats sur l’extraction d’informations globales à partir des moyennes d’ensemble des codas de réverbération. Puis nous illustrerons la détection de défauts par la méthode de corrélation de bruit pardes exemples d’applications sur différentes structures (plaques,tubes, rails,. . . ). Voir les détails
Mots clés : ondes ´elastiques, propagation réverbérante, SHM
Parameters estimation using cuckoo search algorithm of harmonic signals in additive and multiplicative noise
In this study we present a novel approach to estimate harmonics in multiplicative and additive noise using Cuckoo search algorithm. The estimation of parameters is formulated as a nonlinear optimization problem and simulations are carried out to assess the performance of the proposed algorithm. Voir les détails
Mots clés : Cuckoo search algorithm, multiplicative noise, Additive noise, Parameters estimation, Harmonics, Metaheuristic
Effect of Welding Current on Microstructure Properties ofdissimilar metal joints
Dissimilar metal joints between X70 and duplex pipes will be required to prove their weldability in the oil and gas industry, the welds have been performed by GTA weldingprocess using alternating current, and different values of current (between 75 and 140A),without filler metal. The results show that, the heat input has a great influence on microstructure. The details of optical microscopic observations and Scanning electron microscopy (SEM) are discussed. Voir les détails
Mots clés : GTA welding, Dissimilar welding, welding current, HSLA, DSS, HAZ, microstructure