Liste des documents
APPROXIMATE MODEL FOR PREDICTING STATIC RECRYSTALLIZATION OF FERRITIC STAINLESS STEEL TYPE 430
An approximate model for predicting static recrystallisation of ferritic stainless steel type 430, in hot rolling is proposed. In this model, the effect of variables such as strain, strain rate, temperature and initial grain size were considered during hot rolling operations. A set of integrated mathematical models for predicting static recrystallisation evolution during hot rolling has been developed through laboratory research work experiments. It consists of many sub-models such as percentage of recovery, recrystallisation kinetics, time for 50 percent of recrystallisation, recrystallised grain size and grain growth. Some of the most important theoretic basic approaches to describe the kinetics of primary recrystallisation were first independently developed and comprehensive portrayed by Johnson and Mehl, Avrami as by Kolmogorov (Often named the JMAK-theory).The quantitative determination of the effects of these variables obtained, analysed and compared in the context of the recrystallisation kinetics of this material.The predicted results are in good agreement with measured of laboratory tests. The results of constitutive models based on semi empirical equations will be compared in the next publication to more sophisticated models based on cellular automata, vertex and Monte-Carlo-Potts methods. Voir les détails
Mots clés : ferritic stainless steel, hot rolling, Static recrystallisation, Mathematical model.
Débruitatge De Signal De Bruit De Barkhausenen en Utilisant La Décomposition Des Modes Empirique Pour Optimisation L’évaluation et Caractérisation Des Matériaux
Dans le domaine contrôle non destructif CND utilise les paramètres électriques et magnétiques des matériaux pour la caractérisation. Parmi ces techniques l’analyse par bruit de Barkhausen, qui est une technique récente développé grâce au progrès de l’électronique. L’information contenue dans le signal reçu offre la possibilité de déterminer plusieurs paramètres dans le but d’analyser le matériau comme toute technique de CND. Le signal de Barkhausen mesuré par l’intermédiaire d’une chaîne de contrôle réalis est noyé par le bruit (bruit blanc) et l'information de l'état des matériaux peut s’être perdue. Nous proposons dans cet article une méthode de débruitage basé sur la décomposition des modes empiriques (EMD) pour optimiser l’utilisation des indicateurs scalaires (kurtosis,RMS) et fréquentielles (FFT, spectre d’enveloppe) de l’évaluation des matériaux. L’EMD décompose d’une façon adaptative un signal en une somme de composantes oscillantes s’appelle les fonctions modales intrinsèques(IMFs) par l’utilisation un processus de tamisage. Après la décomposition on utilise le seuillage doux pour éliminer les IMFs inférieure au seuil . enfin réaliser la reconstruction du signal débruité à l’aide des IMFs débruité. Avec un bon choix du seuil et de l’ondelette utilisée, on arrive à une réduction appréciable du bruit sur le signal de barkhausen et par conséquent une amélioration des indicateurs scalaires. Les résultats obtenus montrent l'intérêt du dé-bruitage pour le contrôle des matériaux par signal de bruit de barkhausen. Voir les détails
Mots clés : bruit de barkhausen, EMD, cnd
Grey Wolf Optimization of Fractional PID controllerin Gas Metal Arc Welding process
Gas metal arc welding (GMAW) plays the greatimportance in the welding industry. This paper presents a greywolf optimization (GWO) of fractional PID controller in orderto optimize arc length and arc current in the GMAW process.Firstly, fractional PID control of gas metal arc welding system isproposed, wherein the arc length and current of welding processare controlled, then the Grey Wolf Optimization is introduced tosolve multi-objectives functions of GMAW in order to find theoptimal parameters of fractional PID controller. The obtainedresults are compared with those given by fractional PIDcontroller in which our proposed method can ensure a betterdynamic behavior of the GMAWprocess. Voir les détails
Mots clés : GMAW, MIMO system, GWO, Fractional PID controller
Effect of Welding Process on Microstructure and Mechanical Properties of Duplex Stainless Steel Welds
The purpose of this study is a comparison between the effect of two electrical arc welding processes, on the structural and mechanical behavior of 2205 duplex stainless steel weldments, the first one is the manual process GTAW and the second one is the automatic process SAW. This effect has been identified and examined in the different welding area namely, the base metal BM, the heat affected zone HAZ and the weld metal WM, using optical metallographic techniques and mechanical methods by hardness tests. Voir les détails
Mots clés : duplex stainless steel, welding, microstructure, mechanical properties
ELABORATION et CHARACTERISATION des COUCHES MINCES DES OYDES DE CUIVRES (CuO)
Copper oxide thin films were deposited by a low-cost and simple spray pyrolysis technique on glass substrate at 485°C, The aqueous copper nitrate Cu(NO3)2,6H2O with the different concentrations (0.1 M , 0.3M) used as a source of copper. The structural, morphological, and optical properties of the CuO thin films were studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-vis-spectrophotometer. The X-ray diffraction patterns confirm the presence of CuO phases with preferential orientation along (-111), (111). The optical direct gap energy for Copper oxide calculated from optical absorption measurement is 2.82 eV , which is quite comparable with the report value Voir les détails
Mots clés : Copper oxide, Spray pyrolysis, Thin films
Application of A Basquin Model On Fatigue Tests of a Fragile Materials
Cyclic tests of repeated fatigue loads were carried out in three-point bending on a fragile materials. The tests were conducted to burden with R = 0 (ratio of minimum stress to maximum stress), a charging frequency set to a minimum of 75 cycles / min, 1,25Hz and a sinusoidal signal. The specimens used were cut on medium thickness molded plaques 4 mm, dimensions of 80 mm length and 15 mm width according to the recommendations of the standard EN ISO 14125. These specimens were subjected to various loading levels versus the maximum charge of static failure in three-point bending, either: 90%, 80%, 85%, 70%, 60%, 55%, 45%, 40% for each load level, a minimum of three test specimens was tested. The curve traced Wohler is distinguished by a wide dispersion in the lifetimes between the specimens subjected to the same level of loading and tested under the same conditions of cycling and was modeled by a straight line. This dispersion is a consequence of the heterogeneity of the studied fragile materiel. Indeed, the characteristics of specimens such as reinforcement’s rate, distribution, density and shape defects and static strength are not comparable from one specimen to another. This phenomenon of dispersion that the life of forecasts studied fragile materials can be estimated with a high probability by the curve of Wöhler. However, the route of the latter giving the middle part a good and acceptable performance can still be used as a comparison corresponding to variations in compositions, test frequency, cycling parameters …. etc . The deterioration of the fragile material takes place in the early fatigue loading cycles and gradually increases on the surface and within the volume to the final fracture. The state of fatigue damage is characterized mainly by a combination of density and orientation of microcracks. The stages of evolution of the damage in the case of cyclic loading are the same as those encountered in static loading but chronology and different magnitudes. Voir les détails
Mots clés : fatigue, damage, frequency, static, Wöhler curve
Identification des Matériaux par la Méthode de Monte Carlo
Le contrôle Non Destructif (CND) par transmission de rayonnements X est un outil essentiel qui permet, d’une part, de détecter les défauts des échantillons et, d’autre part, d’identifier les imperfections engendrées sur ces derniers. En effet, le CND peut se faire expérimentalement par des mesures directes, néanmoins l’obtention de ces mesures peut être coûteuse, complexe et difficile. La simulation numérique est alors un outil de vérification et de contrôle pouvant remédier à ces inconvénients. Dans ce travail, nous proposons une méthode de simulation qui peut apporter des informations essentielles sur l’état des matériaux moyennant la connaissance des différents éléments de leur constitution. Voir les détails
Mots clés : contrôle non destructif, Rayons X, effet Compton, effet photoélectrique, Monte Carlo
Micrographic Image Segmentation using Level Set Model based on Possibilistic C-Means Clustering
Image segmentation is often required as a fundamental stage in microstructure material characterization. The objective of this work is to choose hybridization between the Level Set method and the clustering approach in order to extract the characteristics of the materials from the segmentation result of the micrographic images. More specifically, the proposed approach contains two successive necessary stages. The first one consists in the application of possibilistic c-means clustering approach (PCM) to get the various classes of the original image. The second stage is based on using the result of the clustering approach i.e. one class among the three existing classes (which interests us) as an initial contour of the level set method to extract the boundaries of interest region. The main purpose of using the result of the PCM algorithm as initial step of the level set method is to enhance and facilitate the work of the latter. Our experimental results on real micrographic images show that the proposed segmentation method can extract successfully the interest region according to the chosen class and confirm its efficiency for segmenting micrographic images of materials. Voir les détails
Mots clés : Level set, Possibilistic C-Means Clustering, micrographic images, image segmentation.
Study of the Microstructural and Mechanical Properties of a Phosphocalcic Bone Substitute
The choice of calcium phosphate materials in reconstructive surgery is justified by the surprising similarities between the composition of these materials and that of the bone. Among a multitude of bone substitutes, hydroxyapatite of chemical composition Ca10(PO4)6(OH)2 is the material most similar to natural apatites. In this study, hydroxyapatite was developed using the wet precipitation method from hydrated calcium chloride (CaCl2,12H2O) as a source of calcium and di-sodium hydrogen phosphate dihydrate (HNa2PO4,2H2O) as a source of phosphate. Vickers Microhardness tests and XRD analyzes were used for the characterization of the synthesized material. The mechanical properties namely HV, σe, and σr, KIC and microstructural like cristallite size Dhkl and degree of cristallinity Xc were discussed according to the temperatures of the heat treatments. Two temperatures were chosen 900 and 1200°C. From the results obtained, it is obvious that the variation of the different properties studied correlates with the temperature of the heat treatment. Voir les détails
Mots clés : Phosphocalcic ceramic, hydroxyapatite, Wet precipitation, hardness, Thoughness, Crytallinity
Computation Of The Energy Density Of The Adsorption Sites By Inverse Gas Chromatography
Inverse Gas Chromatography (I.G.C) technique can be used to determine the adsorption properties of the stationary phase of various materials. The problem is formulated in terms of an integral equation where the unknown is the energy density. The integral equation is a Fredholm integral equation of the first kind. Generally, integral equations cannot be solved analytically. Resort is often made to numerical methods of solutions. The kernel of the integral equation is the adsorption model. For some special models, a solution in a closed form was obtained. Some results are presented. Voir les détails
Mots clés : Inverse gas chromatography, adsorption energy, adsorption models, integral equation