Liste des documents
Effect of Silicon Films Thickness on Aluminium Induced Crystallization of Hydrogene Amorphous Silicon (a-Si:H)
Hydrogenated amorphous silicon (a-Si: H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si:H/Al/glass structure with different amorphous silicon thickness ranging from 200 to 1000nm were annealed at 550°C during 4 hours in vacuum-sealed bulb. The effects of amorphous silicon thickness on optical, structural and morphological properties of the vacuum-annealed a-Si:H/Al/glass are presented in this contribution. The Raman results clearly evidenced that a-Si:H film which has the same thickness as that aluminum layer presents a better crystallisation with a peak position at about 520 cm-1, which is very similar to the Raman pattern of crystalline silicon (c-Si). The presence of a high intensity peak at 520 cm−1 suggests that the Si crystallites are formed during Al assisted crystallization. XRD measurements clearly evidence that poly-Si is successfully induced by aluminum induced crystallization of hydrogenated amorphous silicon thin films. By increasing the thickness of a-Si:H films the intensity of the peak related to Si(111) plane increases, probably due to a preferential growth of the grains in <111> direction. XRD measurements carried out on uncoated aluminum parts, reveal the presence of the peaks characteristic of crystalline silicon for the thickness of 300nm. This result clearly shows lateral crystallization with an estimated crystalline fraction of 46%. This lateral crystallization remains weak for the thick layers and was favored when the thickness ratio between Al and a-Si:H is equal to 1. Voir les détails
Mots clés : Hydrogenated amorphous silicon, Raman, AIC, Crystallisation, Thin films
Influence de L’étude des Revêtements dans La Protection des Ouvrages Métalliques
La protection contre la corrosion des ouvrages métalliques enterrés ou immergés est assurée par l'application conjointe de revêtements et d’un système de protection cathodique. Les ouvrages enterrés seront isolés du sol par des revêtements protecteurs diminuant le plus possible les surfaces de métal nu en contact avec le sol. La protection cathodique viendra compléter cette protection passive, avec efficacité, d'autant que son action ne va porter maintenant que sur de plus petites surfaces de métal en contact avec le sol. Nous aborderons dans ce travail , un calcul de la résistance transversal ou d’isolement en tenant compte des défauts de revêtement , suivi d’une analyse de leur influence sur les principaux paramètres entrant dans le dimensionnement d’un système de protection cathodique Voir les détails
Mots clés : Pipe line, X42, Protection cathodique, Défaut de Revêtement, potentiel de la conduite.
Analysis of the behavior of a galvanization by immersion by NDE
The purpose of the study is to develop a method of experimental characterization, primarily non-destructive, to evaluate the anticorrosive effectiveness of galvanized coatings applied by immersion. The method used in this work is to apply non-destructive testing appropriate and essential vis-à-vis the coatings: aging in salt spray; by electrochemical impedance, grab tests and eddy current. These tests are performed on a sample set of galvanized steel prepared in the state of the art, it will enable for us to judge the relevance of the method used, in order to describe the corrosion resistance of a coating. These results are invaluable in determining the anticorrosive protection of metallic structures exposed at corrosion problems, in particular, in the installation of duplex systems (anticorrosive coating combined with cathodic protection). Voir les détails
Mots clés : galvanization, immersion, sea water, EIS, Eddy Current, adhesion.
Propagation of Lamb Waves on an Immersed Plate Containing a Periodic Grating: Experimental study
In this paper the propagation of Lamb waves in an aluminum plate with a roughness on only one side is studied. The interaction between the incident Lamb wave and the grating gives rise to reflected converted waves. This phenomenon is studied experimentally in the case of an immersed plate in water. Our objective is to show that retroconverted waves radiating into the water are detectable although their energies are small. The damping coefficient of the propagating Lamb wave in the plate is evaluated. Preliminary numerical simulation by using a finite elements method is performed in order to help experiments. Voir les détails
Mots clés : Liquid–solid interfaces, Rough plate, Periodic grating, Lamb waves, Converted modes
EDDY CURRENT CHARACTERIZATION OF (FE65CO35)XAL1-X NANOCRYSTALLINE ALLOY SYNTHESIZED BY MECHANICAL ALLOYING PROCESS
An investigation was conducted to explore the applicability of eddy current and magnetic techniques to characterize grains size variation during mechanical alloying and the formation the new mixture due to the variation of crystallography parameters. The change in apparent density was attributable to the irregular particles of the metal powders.A series of Nanocrystalline (Fe65Co35)xAl1-x samples have been prepared, these structures are prepared using mechanical alloying based on planetary ball mill under several milling conditions. Mechanical alloying is a non-equilibrium process for materials synthesis. The structural effects of mechanical alloying of powders were investigated by X - Ray diffraction analysis, SEM, microwaves, hysteresis magnetic and eddy current technique. Consequently, alloy powder with an average grain size about of 8 nm was obtained. Experimental results show that fine nanocrystalline alloy powders prepared by mechanical milling are very promising for microwave applications. It is suggested that eddy current measurement technique is a useful tool for the characterization of Nanocrystalline materials Voir les détails
Mots clés : Eddy current, Fe-Co powder, Mechanical alloying, Magnetic properties, Microwave.
ÉTUDE ET INFLUENCE DE LA TAILLE DES CRISTALLITES SUR LE COMPORTEMENT MAGNÉTIQUE DES ALLIAGES À BASE DE FER
Les propriétés d’un matériau sont fonction de ses éléments constitutifs, mais aussi de sa structure à l’échelle micro- et nano-métrique. Si la taille du cristal diminue, la taille des domaines diminue et la structure des domaines peut changer. Tout changement dans la structure du matériau engendre des modifications du comportement magnétique tel que le champ coercitif qui est fonction de la taille grains. Ce comportement reste il valable et a le même comportement à l’échelle nanostructure? Une sérié d’échantillons a été élaborée par mécanosynthèse (le broyageà haute énergie), l’obtention d’un matériau bien défini nécessite lecontrôle d’un certain nombre de paramètres du broyage et aussi le bon conditionnementdu matériau pour sa caractérisation. La caractérisation des poudres nanostructurées fait appel à différentes techniques (la diffraction des rayons X, la microscopie à balayage électronique, la mesure magnétique a base et a haute fréquence …) dont le choix repose toutd’abord sur leur faisabilité, leur sensibilité et leur complémentarité. Une caractéristique importante des matériaux a été observée lors de l’utilisation des différentes techniques decaractérisation, c’est la variabilité des réponses obtenues selon la technique appliquée d’où la nécessité de cernercorrectement le domaine et de préciser les conditions d’application de chaque matériau nanostructuré. Voir les détails
Mots clés : Mécanosynthèse, nanostructure, ferromagnétique, champ coercitif, cristallite, hyperfréquence
Frequency and concentration dependence of the ultrasonic backscatter coefficient in a soft tissue mimicking material
In medical ultrasound, the backscatter coefficient is used to quantify the scattering properties of biological tissues. It is defined as the differential scattering cross section per unit volume for a scattering angle of 180 °.In this study, measurement of backscatter coefficient are made on Tissue mimicking Materials. These are materials whose acoustic properties (velocity, attenuation, diffusion) are close to those of biological tissues.Measurements of this coefficient have been achieved in a mixture of gelatin and distilled water containing microscopic graphite particles with mean radius of 18µm randomly distributed. Samples concentrations ranged from 50 to 200g of graphite per liter of gelatin. The backscatter coefficient was evaluated using both Sigelman and Reid and Chen methods in frequency range around 5 MHz. The evolution of this coefficient as a function of frequency and concentration of scatterers will be presented. Comparison of experimental values with those obtained from Faran theory permits estimation of number density of graphite particles in TM material. Voir les détails
Mots clés : Ultrasound, Bakscatter coefficient, Tissue mimicking material
Extraction of weld defects dimension from radiographic images using the level set segmentation without re-initialization
Radiographic images segmentation is the major interest for the weld defect diagnosis and monitoring in the field of industry. In this work we present a method that takes ownership of local segmentation geodesic active contours. The goal of the method presented in this paper is to automate the process of extracting dimension characteristics from radiographic images using level set segmentation to provide information which is used in the area of nondestructive testing (NDT). This method is found to be effective and robust. Voir les détails
Mots clés : Level set segmentation, Radiographic weld defect, weld defects Dimension, NDT
MULTIPHASE LEVEL SETS MODEL APPLIED TO WELD RADIOGRAPHIC IMAGES SEGMENTATION.
This paper is devoted to a crucial task in image analysis which is segmentation. Our aim is to give the structural form of industrial radiographic images. In this purpose, we have used an implicit region oriented deformable model. In this context the criteria to stop the curves’ evolution is the statistical information of the image grey level, this gives many advantages compared to those that used the gradient.The functional is minimized via a piecewise constant approximation and Multiphase level set. In this situation we need n level set function to represent up to 2n segments or regions. The model avoids automatically the problems of vacuum and overlap. The numerical results for synthetic and weld radiographic images are satisfactory. Voir les détails
Mots clés : Weld Radiographic image, image segmentation, Level Set Methods, Chan-Vese Model, Multiphase segmentation
New approach for the damage mechanisms identification in the glass-epoxy composites
The aim of this work is to introduce a new approach for clustering acoustic emission data occuring during the fracture process of glass fibre reinforced polymer (GFRP) plates. In particular, we have developed signal processing techniques based on continues wavelet transform (CWT) in order to isolate acoustic signature corresponding to each damage mechanism (fibre breakage, matrix cracking, etc.). Entropy criterion was used to provide selection of most significant wavelet coefficients of AE signals. Models are established in the form of dictionaries, whose elements are the waveforms collected during specific experiments in which the created damage mechanisms are well known. Dictionaries should be used to classify acoustic emission signals recorded when polymer composites are under load. Voir les détails
Mots clés : acoustic emission, wavelet transforme, damage mechanisms