Liste des publications
Application of Hybrid Wavelet-Fractal Compression Algorithm for Radiographic Images of Weld Defects
Based on the standard fractal transformation in spatial domain, simple relations may be found relating coefficients in detail subbands in the wavelet domain. In this work we evaluate a hybrid wavelet-fractal image coder, and we test its ability to compress radiographic images of weld defects. A comparative study between the hybrid coder and standard fractal compression technique have been made in order to investigate the compression ratio and corresponding quality of the image using peak signal to noise ratio. Numerical experiments using radiographic images of weld defects illustrate the superior performance of the hybrid coder compared to standard fractal algorithm. Voir les détails
Mots clés : Fractal Compression, Discrete wavelet transform, Wavelet-Fractal coder, Radiographic images of weld defects, Compression ratio, Peak signal to noise ratio
A Region-Based Model and Binary Level Set Function Applied to Weld Defects Detection in Radiographic Images
In this paper, we propose a model for active contours to detect boundaries’ objects in given image. The curve evolution is based on Chan-Vese model implemented via binary variational level set formulation. The particularity of this model is the capacity to detect boundaries’ objects without need to use gradient of the image, this property gives its several advantages: it allows detecting both contours with or without gradient, it has ability to detect automatically interior contours, and it is robust in the presence of noise. For increasing the performance of model, we introduce the level sets function to describe the active contour, the more important advantage to use level set is the ability to change topology. Experiments on synthetic and real (weld radiographic) images show both efficiency and accuracy of implemented model. Voir les détails
Mots clés : image segmentation, Curve evolution, Chan-Vese Model, EDPs, Level set, radiographic images
The Non Destructive Testing Methods Applied to Detect Cracks in the Hot Section of a Turbojet
All aircraft whatever they are; are regularly audited. These controls are mainly visual and external; other controls such as "major inspection" or "general revisions” are more extensive and require the dismantling of certain parts of the aircraft. Some parts of the aircraft remain inaccessible and are therefore more difficult to inspect (compressor, combustion chamber, and turbine). The means of detection must ensure controls either during initial construction, or at the time of exploitation of all the parts. The Non destructive testing (NDT) gathers the most widespread methods for detecting defects of a part or review the integrity of a structure. The aim of this work is to present the different (NDT) techniques and to explore their limits, taking into account the difficulties presented at the level of the hot part of a turbojet, in order to propose one or more effective means, non subjective and less expensive for the detection and the control of cracks in the hot section of a turbojet. To achieve our goal, we followed the following steps: - Acquire technical, scientific and practical basis of magnetic fields, electrical and electromagnetic, related to industrial applications primarily to electromagnetic NDT techniques. - Apply a scientific approach integrating fundamental knowledge of synthetic and pragmatic manner so as to control the implementation of NDT techniques to establish a synthesis in order to comparing between the use of different methods. - To review recent developments concerning the standard techniques and their foreseeable development: eddy current, ultrasonic guided waves ..., and the possibility of the implication of new techniques. Voir les détails
Mots clés : Combustion Chamber, Crack, Hot Section, Nondestructive Testing (NDT), turbine
Maximum Likelihood Curves for Multiple Objects Extraction: Application to Radiographic Inspection for Weld Defects Detection
This paper presents an adaptive probabilistic region-based deformable model using an explicit representation that aims to extract automatically defects from a radiographic film. To deal with the height computation cost of such model, an adaptive polygonal representation is used and the search space for the greedy-based model evolution is reduced. Furthermore, we adapt this explicit model to handle topological changes in presence of multiple defects. Voir les détails
Mots clés : Explicit deformable model, adaptive contour representation, Maximum likelihood criterion
Adaptive and Statistical Polygonal Curve forMultiple Weld Defects Detection inRadiographic Images
With the advances in computer science and artificial intelligencetechniques, the opportunity to develop computer aided techniquefor radiographic inspection in Non Destructive Testing arose. This paperpresents an adaptive probabilistic region-based deformable model usingan explicit representation that aims to extract automatically defects froma radiographic film. To deal with the height computation cost of suchmodel, an adaptive polygonal representation is used and the search spacefor the greedy-based model evolution is reduced. Furthermore, we adaptthis explicit model to handle topological changes in presence of multipledefects. Voir les détails
Mots clés : Radiographic inspection, Explicit deformable model, adaptive contour representation, Maximum likelihood criterion, Multiple contours
Influence de la précipitation secondaire sur les propriétés d'usure d'une fonte au chrome alliée
La résistance à l'usure des fontes au chrome est fonction du type d'éléments d'addition. Notre approche consiste à étudier l'effet combiné des éléments d'alliage (Ti, Mo, Mn et Nb) sur le comportement à l'usure des fontes au chrome. plusieurs techniques sont employées ( microscopie optique et MEB, DSC et DRX). Des essais d'usure par frottement et par abrasion ont complété cette étude. Les résultats obtenus montrent que l'addition des éléments d'alliage a eu un effet affinant sur la matrice. Un changement microstructural est enregistré au niveau de la matrice sous forme de précipitations proeutectiques et secondaires. Les éléments carburigènes introduits dans la fonte ont favorisé une nette augmentation de la résistance à l'usure par frottement après traitement thermique, comparativement à leur effet sur la résistance à l'abrasion. Voir les détails
Mots clés : fonte au chrome, usure, précipitations
INFLUENCE DE LA PRECIPITATION SECONDAIRE SUR LES PROPRIETES D’USURE D’UNE FONTE AU CHROME ALLIEE
Résumé –Influence de la précipitation secondaire sur les propriétés d’usure d’une fonte au chrome alliée. La résistance à l’usure des fontes au chrome est fonction du type d’éléments d’addition. Notre approche consiste à étudier l’effet combiné des éléments d’alliage (Ti, Mo, Mn et Nb) sur le comportement à l’usure des fontes au chrome. Plusieurs techniques sont employées (microscopie optique et MEB, DSC et DRX). Des essais d’usure par frottement et par abrasion ont complété cette étude. Les résultats obtenus montrent que l’addition des éléments d’alliages a eu un effet affinant sur la matrice. Un changement microstructural est enregistré au niveau de la matrice sous forme de précipitations proeutectiques et secondaires. Les éléments carburigènes introduits dans la fonte ont favorisé une nette augmentation de la résistance à l’usure par frottement après traitement thermique, comparativement à leur effet sur la résistance à l’abrasion. Voir les détails
Mots clés : fonte au chrome, usure, précipitation secondaire
Two classifiers score fusion for text independent speaker verification
Two classifiers score fusion for text independent speaker verification Voir les détails
Mots clés : GMM, SVM
Aluminium-induced crystallization ofamorphous silicon films deposited byDC magnetron sputtering on glasses
Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by ther- mal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 ◦C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum- annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evi-dence that crystallization is initiated at 450°C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 ◦C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC). Voir les détails
Mots clés : Crystallization, Thin films, Hydrogenated amorphous silicon, AIC, Raman, XRD
Effet du niobium sur la résistance à l’usured’une fonte au chrome traitée thermiquement
Chromium cast irons are well known for their wear properties. They are widelyused in engineering practices such as mining, cement industries and many others. Theirwear properties are mainly due to their microstructure which is constituted by netted M7C3type eutectic carbide held in an austenitic or martensitic matrix. Several researchers investigatedthe possibility of improving the wear properties of these cast irons by acting onthe microstructure, the morphology of the microstructural constituents as well as on theirdistribution. The present work consists in studying the effect of the niobium on the wearbehaviour of a heat treated chromium cast iron. Characterizations by optical microscopy,abrasion and friction tests are realized in order to establish the wear resistance of this castiron and also the type of microstructure having been at the origin of this improvement. Theobtained results show that the studied material is a 15% chromium white cast iron. Niobiumaddition had an effect on the microstructure as well as on the abrasion and frictionresistances of the heat treated high chromium white cast iron samples. The wear resistanceincreases with the increase of the niobium content. Voir les détails
Mots clés : Chromium cast iron, wear, eutectic carbides, alloying elements