Liste des communications
mould powders in continuous casting
Continuous casting of steel is a process in which liquid steel is continuously solidified into a strand of metal. The components of the continuous casting steel system are the ladle, tundish and mold. Mould powders are spread on the surface of the bath of the molten metal of the ladle and tundish. The quality of steel produced by continuous casting is strongly dependant on the performance of mould powders. Mould powders govern the steel production in terms of production rate, cleanliness, surface condition, defects and environment of casting operation. These powders are SiO2 oxides based materials. Diatomaceous earth, or simply diatomite, formerly called Kieselguhr, is a sedimentary rock of biological origin formed by the accumulation at the bottom of the ocean of siliceous skeletons of diatoms, or unicellular algae. Diatomite is a highly porous silica (SiO2) rich material, major applications are thermal insulation. Melting behaviour of mould powders is one of the most important performance parameters for mould powders and is mainly dependant on carbon which is an essential constituent of mould powders. Carbon blacks have lately attracted considerable attention for use in mould powders due to fine size. A study was conducted to see the effect of addition of carbon black and diatomite to natural silica (sand) for a mould powder used in Arcelor Mittal Steel Annaba. Voir les détails
Mots clés : continuous casting, mould powders, oxides, diatomite
Ultrasonic Backscatter Coefficient Estimates in a Soft Tissue Mimicking Phantom
The ultimate goal of characterization methodsbased on the backscatter coefficient (BSC) estimates isto obtain structural information about samples independentlyof the measurement system. In the current study,measurements of the BSC were obtained from TissueMimicking Materials (TMM) or phantoms. These consistedof a mixture of gelatin and distilled water containingmicroscopic graphite particles with a mean radius of 18micrometers, which were randomly distributed. Phantomsconcentrations ranged from 50 to 200 g of graphite per literof gelatin. Two BSC estimation methods were used andtheir results were compared to Faran’s scattering theorywhich allowed the estimation of the number density ofgraphite particles in the phantoms. Moreover, measurementsof the attenuation coefficient and the ultrasonicpropagation velocity in phantoms were performed. Theevolution of the attenuation coefficient and the BSC as afunction of frequency and scatterers’s concentration in afrequency range from 1.5 MHz to 6 MHz will be presentedusing two transducers of nominal frequencies 2.25 MHzand 5 MHz. Decreasing of the attenuation coefficient withfrequency and graphite concentration will be showed. Voir les détails
Mots clés : Ultrasound, Attenuation, backscattering, TMM
Application de la diffraction des rayons X à la caractérisation de la microstructure de l’acier inoxydable biphasé 2205
Dans ce travail, une caractérisation par diffraction des rayons X a été réalisée sur des échantillons d’acier inoxydable duplex 2205 afin de suivre la précipitation de la phase σ. Pour cela, une analyse métallographique (microscopie optique) a été réalisée et une caractérisation par diffraction des rayons X a été effectuée sur les échantillons en utilisant le logiciel MAUD (Materials Analysis Using Diffraction). Voir les détails
Mots clés : acier inoxydable 2005, précipitation, MAUD
Finite element delamination study of adhesively-bonded patchs used to repairs damaged jute fiber/polypropylene composites
In this work, the mechanical behavior of repaired specimens is studied from both experimental and numerical viewpoints. Tensile testing of the specimens with defect, without defect and repaired is carried out. The finite element method (FEM) model is utilized to simulate the mechanical behavior of the repaired specimen during the test. Cohesive Zone Model (CZM) was used to simulate the inter-laminar fracture of the composite, with the capability of simulating the damage initiation and evolution mechanisms of adhesives. The validations of the numerical results were carried out with the experimental results and are show to be in a good agreement. Voir les détails
Mots clés : PP/jute composite, damage, adhesive bonding, cohesive element
The Measure of the Length of the Slabs by Artificial Vision
This work consists in automate the measurement of the length of the slabs in the continuous casting machine in a steel mill. This automation will be done by an artificial vision system that implements a camera matrix and embedded vision software. First, we have to make a rigorous selection of attributes such as the margin of the field of vision, the distance between the camera and the slab, the geometric landmarks of the measure, the detection landmark of the arrival of the slab and the optical reference landmark for measure. We also established a relationship between the real length of an object and the number of pixels occupied by its image after a serie of precise tests in order to integrate it in the measure program. The measuring principle is divided into two steps: First, we make a segmentation of each image with a program developed in this sense which aims to differentiate between the slab and the roller train by reading the brightness of each pixel of the acquired image. This segmentation uses the histogram of gray levels of the slab and the roller table which were obtained after the analysis of their images in their real lighting conditions. Then, the slab is measured with another developed program which calculates the abscissa of the detection landmark of the arrival of the slab, tests the value of the gray level of the pixel of this abscissa, gives a decision signal to blowtorches, then retest the value of gray level of the same abscissa to detect the end of the slab and wait the arrival of the next slab. Both programs operate in a loop until the end of the cut of all of the slabs. At each new cutting plane of the slabs we introduce new data according to the customer's command. A study was necessary to establish a criterion for detecting the slab because the value of one pixel can not be a reference and so we chose the reading of 15 points of twenty and this criterion has yielded concrete and reliable results. A simulation with the camera matrix TVC500 and the image processing map PIP was realized in the process laboratory with success and all programs were developed with the C language. On the ground, it will require ensure a stable lighting within the cut area and a good braking system of the carriage or consider a second camera for measuring the lag of the carriage because it represents the origin landmark and thus adjust the measure. Our work will allow a better measure reliability, the possibility of its exploitation for the optimization of the cut and also the improvement of working conditions of the workers. Voir les détails
Mots clés : Artificial vision, pixel, histogram, real time, image, gray level.
Application of signal processing techniques to ultrasonic guided waves
Ultrasonic guided wave testing is an attractive alternative for large-area inspection since it offers the potential for rapid screening from a single transducer position and remote inspection of physically inaccessible areas of the structure. Compared to bulk waves, guided waves exist only in waveguides, such as plates and pipes, in which they continually interact with the boundaries of the material. Therefore they are confined and allowed to propagate over long distance. However, guided wave inspection is complex because there are many modes in plates and pipes and they are in general dispersive (their velocity is a function of frequency). In this work, the objective is to improve the time resolution and signal-to-noise ratio of signals obtained from inspection of plates by the A0 and S0 mode. The signal processing scheme used is based on deconvolution of the measured signal by matching pursuit signal decomposition. The deconvolution technique is applied to simulated signals from plates with various types of notch discontinuities. Using this technique, the separation distance between adjacent notches was estimated with high accuracy Voir les détails
Mots clés : Ultrasonic, Signal processing, Guided wave, Deconvolution
Rôle des particules intermétalliques sur la corrosion de l’alliage AA6061 en présence des chlorures et l’effet du metabisulfite
Le comportement de l’alliage d’aluminium 6061 en milieux aqueux avec la concentration 0.05 M NaCl en absence et en présence du metabisulfite de sodium à été étudié par les méthodes électrochimiques. L’étude potentiodynamique cyclique à permis de déterminer plusieurs facteurs, les potentiels de corrosion et de piqûre et le potentiel de protection. Tandis que l’étude potentiostatique à précisé l’effet du metabisulfite sur la passivité de l’alliage d’aluminium. Le pH de la solution influe sur la dégradation de la couche d’oxyde autre que la valeur neutre. L’étude micrographique à révélée l’intensité d’attaque sur les particules intermétalliques riches en Mg and Si. Voir les détails
Mots clés : corrosion, polarisation, piqûres, particules
ELABORATION D’UN CAPTEUR ÉLECTROCHIMIQUE DESTINÉ À LA DÉTECTIONDES IONS CADMIUM(II)
La détection des cations, anions est habituellement basée sur des membranes organiques. Ces membranes ionosensibles sontgénéralement préparés à partir d’un mélange de polymère de haute masse moléculaire ; d’un plastifiant / photo initiateur ;d’un ionophore et d’un sel lipophilique dissous dans un solvant organique. La performance électroanalytique d’unemembrane sensible repose sur l’ensemble complexe des fonctions des composants qui forment, et nécessite donc souventd’être optimisée. Les protocoles de la mise au point du capteur++ Cd ont été optimisés, le mélange est composé de 8%, 33% et 67 % respectivement calix [4] arène, PVC et DOP , dilué dans 0,5ml de chloroforme, ensuite un volume de5μl a été déposé sur l’électrode en platine, le temps de séchage est 2h c’est le temps nécessaire pour l’évaporation dusolvant ; le conditionnement de la membrane s’effectue par l’immersion de l’électrode modifiée dans une solution de0,1M 2 CdCl pendant 1h de temps. L'étude des transferts d'ions métalliques à l'interface d’électrode modifiéereprésente une base intéressante pour le développement de capteurs électrochimiques toutefois la spectroscopie d’impédanceélectrochimique représente un outil performant permettant d’interpréter le phénomène interfacial électrode /électrolyte. Voir les détails
Mots clés : électrodes modifiées, calix [4] arène, spectroscopie d’impédance électrochimique.
ELECTROCHEMICAL STUDY OF THE INHIBITORY EFFICACY OF TWO SCHIFF BASES SYNTHESIZED TOWARDS THE CORROSIONOF STEEL IN CONCRETE.
Corrosion of Reinforcement is a major factor limiting the life of reinforced concrete buildings. The steel in concrete can corrode when many aggressive substances penetrate into the pores of concrete containing oxygen. Various methods exist to pr otect the steel against corrosion. These methods include the use of corrosion inhibitors which is a means of protection very easy and effective. The research on the protection of steel against corrosion showed that a large number of inhibitors are organic species containing in their structure elements such as nitrogen, oxygen and sulfur. Schiff bases whose applications are very numerous are recently used and the results are very satisfactory in the solution simulating the pore water in interface (frame / concrete). For this and for the same purpose, we synthesized, characterized and st udied the inhibitory power of two Schiff bases and their initial products of synthesis: • 1, 2-dehydroacetic acid ethylene diamine (H2 L1) ; • 1, 2-dehydroacetic acid amino naphtol (H2 L2) ; • Dehydroacetic acid (DHA) • 3-amino -2-Naphtol (Amine) towards the corrosion of construction steel. The elect rochemical parameters and characteristics of the corrosion were determined by cyclic voltammetry exploiting Tafel curves by Volta Masters 4 software. The study of the corrosion inhibition by these organic compounds has led to the conclusion that they have high level of inhibition rate. Compounds (H2 L1) and (H2L2) which are original and their starting materials of synthesis show an inhibition rate close to 70% at a concentration of 10-6M for each of them in the concrete environment after four months. After seven months of immersion of rebar in concrete, the results of mechanical tests show that the compound (H2L1) improves the mechanical strength of the concrete structure but DHA affects it. This behavior can be explained by the formation of bonds between metal sites and the free electron pairs of oxygen and nitrogen. The results confirm that the structure of these heterocyclic compounds do not affect the effectiveness of inhibition of corrosion of steel in concrete. Voir les détails
Mots clés : Schiff bases, corrosion, inhibitor, concrete, 1, 2-dehydroacetic acid ethylene diamine, 2-dehydroacetic acid amino naphtol, DHA, 3-amino -2-Naphtol
Sparse Representations of Acoustic Emission Signal:Application to Damage Analysis in Glass Fiber Reinforced Composites
Sparse representation of signals has been subject of many advances during recent years especially in the field ofapplied physics. The problem is to search for the most compact representation of signals in terms of linearcombinations of elementary waveforms in an over-complete dictionary. The underlying hypothesis in most ofsparse representation problems is that if one can associate a sparse representation to a given signal, its structurereveals information directly linked to the physical nature of the addressed problem. From this point of view it hasbeen shown that sparse representation problems have closed connexions with inverse problems and sourceseparation problems. In this contribution, an application of sparse representation techniques to identify damagemechanisms from Acoustic Emission (AE) signals is presented. The sparse representation is which is based onthe continues wavelet transform. All experiments concern investigations realized on glass fibre reinforcedpolymer composites (GFRP). Voir les détails
Mots clés : acoustic emission, Signal processing, Ultrasonic, precursor damage