Liste des publications
Classification of defects by the SVM method and the Principal Component Analysis (PCA).
Analyses carried out on examples of detected defects echoes showed clearly that one can describe these detected forms according to a whole of characteristic parameters in order to be able to make discrimination between a planar defect and a volumic defect. This work answers to a problem of ultrasonics NDT like Identification of the defects. The problems as well as the objective of this realized work are divided in three parts: Extractions of the parameters of wavelets from the ultrasonic echo of the detected defect - the second part is devoted to principal components analysis (PCA) for optimization of the attributes vector. And finally to establish the algorithm of classification (SVM, Support Vector Machine) which allows discrimination between a plane defect and a volumic defect. We have completed this work by a conclusion where we draw up a summary of the completed works, as well as the robustness of the various algorithms proposed in this study. Voir les détails
Mots clés : NDT, PCA, SVM, Ultrasonics, wavelet
Contribution A La Modélisation Du Soudage TIG Des Tôles Minces D’acier Austénitique 304L Par Un Modèle Source Bi- Elliptique, Avec Confrontation Expérimentale. (Contribution to the establishment of a TIG survey of thin sheet metal steel austenitic 304L by a source bi-elliptical model, with experimental confrontation)
Ce travail contribue dans la modélisation du phénomène du soudage de l'acier inoxydable Austénitique 304L, afin d'étudier le comportement thermique d'un joint de soudure, obtenu par le procédé de soudage à l'arc électrique TIG (Tungsten-Inert-Gas). Le modèle simulant la source d'énergie de soudage, utilise une distribution surfacique Gaussienne du flux de chaleur provenant de l'arc électrique. La forme de cette source est supposée circulaire pour un premier cas et de forme bi-elliptique pour un second cas, tout en procédant à l'évaluation des champs et cycles thermiques à chaque instant, pour déterminer l'étendu des zones à risque, et l'effet de la vitesse de soudage sur ces dernières. Permettant ainsi de remonter par la suite, aux problèmes de contraintes résiduelles et déformations générées dans l'assemblage soudé. L'équation de chaleur régissant le problème est discrétisée par la méthode des volumes finis. Les calculs sont effectués en considérant que les propriétés physiques et thermiques ainsi que les conditions aux limites de convection et rayonnement, sont dépendante de la température. Pour évaluer la précision du modèle, une comparaison avec des mesures expérimentales de température d'un essai de soudage a été effectuée, les résultats indiquent un bon accord. Voir les détails
Mots clés : soudage TIG, acier 304L, source thermique bi-elliptique
Ultrasonic device calibration for estimation of retained austenite in tool steel
High percent of retained austenite in tool steel involve ill-fated effects as cracks. It is very important to control it. Ultrasonic device can be calibrated by using of ultrasonic velocities measurements. The variation of the velocities in tool steel as function of the rate of austinite is very small and require measurements with high accuracy. The calibration method is very simple and need neither mathematical methods nor simulations. Voir les détails
Mots clés : • Martensite, • Retained austenite, • Ultrasound longitudinal velocity, • Ultrasound transversal velocity
Determination of mechanical and physical properties of materials by ultrasounds
The ultrasonic waves, with the matter interaction study, is an increasingly effective tool for qualitative and/or quantitative characterization of industrial materials. In this article, we describe experimental studies, which were the work object at the Welding and Control Center (CSC), based on the measurement of some simple ultrasonic parameters such as propagation velocities and attenuation coefficients of the longitudinal and transverse waves through various samples. These measurements were taken on samples of suitable nature, shape and dimensions and eventually heat treated in order to obtain the required properties. Voir les détails
Mots clés : Ultrasounds, Attenuation, Velocity
Evolution of Widmandstaïtten structure in welding joints
The operation of welding induces a metallurgical multitude of phenomenon owing to the fact that it covers high fields' energetic thus causing important variations of the mechanical properties and microstructural of materials. The multipass welding of a HSLA steel strong thickness gives place to a variation of the microstructure of a layer to another. The thermal cycle supports the appearance of a known structure under the name of "structure of widmanstätten". The latter is supported by high heating temperatures and a fast cooling; it often germinates in the form of slat on the austenitic grain boundaries, known like ferrite of widmanstätten. But it can germinate in the form of needles in the grains on the impurities or on the precipitates, it is acicular ferrite. Impact strength and hardness tests were done on the melted zone after welding and heat treatment.The microstructural evolution of each layer influences the entire welded joint, conferring these final mechanical properties to him. Voir les détails
Mots clés : heat treatment, HSLA steels, welding, Widmanstätten structure
Signal processing for the detection of multiple imperfection echoes drowned in the structural noise
In this work, we propose to develop algorithms based on the split spectrum processing method associated with the multi-steps method based on “Group delay moving entropy” (GDME) allowing detecting and locating multiple imperfection echoes drowned in the structural noise of materials. In fact, GDME is based on the fact that defect echoes have a constant group delay while the noise has a random group delay. The investigation is performed with 4 known defect echoes with different characteristics (position, center frequency and bandwidth). The defect echo frequency is varied around the frequency of the input signal in order to evaluate, by signal to noise ratio calculation, the robustness of the detection method. The grain noise signal is generated first, by a simple clutter model which consider the noise, in the time domain, as the superimposed of signal coming from backscaterers in the medium and second, experimentally by a material with coarse grains. Voir les détails
Mots clés : Ultrasonic NDE, split spectrum processing, Signal to noise ratio, Structure noise
A 2 GHz low power, highly tunable and low phase noise monolithic LC VCO in 0.35 μm CMOS technology
In this paper, a fully integrated 2 GHz low phase noise LC-tank VCO, designed in 0.35 μm CMOS technology is presented and analyzed. The phase noise of the VCO has been greatly reduced by means of integrated source degeneration inductors. The phase noise achieved is -108, -125 dBc/Hz and -139 dBc/Hz at 100 kHz, 600 kHz and 3 MHz offsets respectively from the carrier frequency of 2 GHz, with 2.5 V power supply voltage and giving a power consumption of 10.35 mW. A 20.3% wide tuning range is achieved by means of PMOS varactors and a degeneration resistor. The tunability of the designed oscillator covers 380 MHz, from 1.68 GHz up to 2.06 GHz with a VCO gain of 280 MHz/V. The proposed VCO is fully operational under variable conditions including temperature and supply voltage variations from -40°C to 85°C and 2.5 V ±10%, respectively. Voir les détails
Mots clés : inductors, low phase noise, 0.35 μm CMOS technology
Effect of postweld heat treatment on microstructure and mechanical properties of welded 2205 duplex stainless steel
Duplex stainless steels 2205 are widely used in constructional and petrochemical applications because of their good mechanical and corrosion properties. The objective of this work was to study the influence of aging at high temperature on the austenite and d ferrite equilibrium. After welding by TIG process, duplex stainless steel was aged in the range of 800 – 1150 °C temperatures for 60 min. The microstructure was characterized by metallography and X-ray methods. The toughness of welded structure was also measured Voir les détails
Mots clés : duplex stainless steel, d ferrite, aging, grain growth, - equilibrium
A New Multistage Search of Algebraic CELP Codebooks Based on Trellis Coding
This paper proposes a new multistage technique of algebraic codebook in CELP coders called Trellis Search inspired from the Trellis Coded Quantization (TCQ). This search technique is implemented into the fixed codebook of the standard G.729 for objective evaluation on a large corpus of a testing speech database. Simulation results show that in terms of computer execution time the proposed search scheme reduces the codebook search by approximately 23% compared to the time of focused search used in the standard G.729. This yields to a reduction of about 8% in the computer execution time of the coder at the cost of a slight degradation of speech quality but perceptually not noticeable. Moreover, this new techniques shows better speech quality than the G.729A at the expense of a higher complexity. Voir les détails
Mots clés : Trellis, algebraic codebook, speech coding, CELP, G729
Superplastic deformation behavior of 7075 aluminum alloy
A study has been made to investigate the effect of a prior amount of warm rolling on the superplastic forming behavior of a standard grade 7075 aluminum alloy. The thermomechanical treatment process presented for grain refinement includes furnace cooling from the solution treatment temperature to the overaging temperature, warm rolling from 65–85% deformation, recrystallization, and artificial aging treatment. Increasing the amount of warm rolling beyond 80% deformation does not produce material with higher elongation to failure when the thermomechanical treatment process presented is used. The largest value of elongation to failure was 700%, which was obtained for a specimen having a grain size of 8 µm at a strain rate of 6×10−3S−1. The fracture surface exhibits a granular appearance indicative of an intergranular fracture mode. Dislocation activities within grains were observed, indicating the occurrence of dislocation slip during grain boundary sliding. Voir les détails
Mots clés : 7075 aluminum alloy, superplastic deformation, thermo mechanical treatment, warm rolling