Liste des documents
Properties of Al-doped ZnO thin films grown by pulsed laser deposition on Si (100) substrates
Undoped and Al-doped ZnO (AZO) polycrystalline thin films (Al: 3, 5 at.%) have been deposited at 450°C onto Si(100) substrates by pulsed laser deposition method. A KrF excimer (248 nm, 25 ns, 2 J/cm2) was used as laser source. The study of the obtained undoped and Al-doped ZnO thin films has been accomplished using X-ray diffraction (XRD), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) techniques. The ZnO and AZO thin films deposited have been crystallised in hexagonal wurtzite-type structure with a strong (00.2) orientation. The grain sizes calculated from XRD patterns decrease from 38 to 26 nm with increasing Al doping. All nanoparticle thin films have a good surface morphology. Voir les détails
Mots clés : ZnO, Al doping, pulsed laser deposition, PLD, X-ray diffraction, XRD, atomic force microscopy, AFM, Rutherford backscattering spectrometry, RBS, nanoparticles
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 (EC) and magnetic techniques to characterize the formation and grains size variation during Mechanical Alloying (MA) and the formation of a 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 using M.A based on planetary ball mill under several milling conditions. M.A is a non-equilibrium process for materials synthesis. The structural effects of MA of powders were investigated by X-Ray diffraction analysis, SEM, microwaves, hysteresis magnetic and Eddy Current technique. Consequently, a nanostructure alloy was obtained with an average grain size of 8 nm. Experimental results show that fine nanocrystalline alloy powders prepared by mechanical milling are very promising for microwave applications and 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-Al Powder, Magnetic Properties, Mechanical Alloying, Microwave
Study of the spray to globular transition in gas metal arc welding: a spectroscopic investigation
The gas metal arc welding (GMAW) process is strongly influenced by the composition of the shielding gas. In particular, addition of CO2 increases the threshold current for the transition from unstable globular to more stable spray transfer mode. We report on the diagnostics—using optical emission spectroscopy—of a GMAW plasma in pure argon and in mixtures of argon, CO2 and N2 while operated in spray and globular transfer modes. The spatially resolved plasma parameters are obtained by applying the Abel transformation to laterally integrated emission data. The Stark widths of some iron lines are used to determine both electron density and temperature, and line intensities yield relative contents of neutral and ionized iron to argon.Our experimental results indicate a temperature drop on the arc axis in the case of spray arc transfer. This drop reduces with addition of N2 and disappears in globular transfer mode when CO2 is added. Despite the temperature increase, the electron density decreases with CO2 concentration. The highest concentration of iron is observed in the plasma column upper part (close to the anode) and for GMAW with CO2.Our results are compared with recently published works where the effect of non-homogeneous metal vapour concentration has been taken into account. Voir les détails
Mots clés : GMAW, Optical Emission Spectroscopy, Boltzmann Plot
Texture, misorientation and mechanical anisotropy in a deformed dual phase stainless steel weld joint
The deformation behavior of a duplex stainless steel weld joint is studied. A detailed texture analysis shows that the increase of the deformation percentage leads to a reinforcement of all possible {hkl}〈111〉and {hkl}〈100〉 components in austenite, and of the {hkl} 〈110〉 components in ferrite for both the base metal (BM) and the heat affected zone (HAZ). In the weld metal (WM), a strong scatter of the crystallographic orientation relationship (OR) initially found in the solidification microstructure is recorded after deformation. The analysis of the Kernel Average Misorientation (KAM) distribution shows that the deformation is more concentrated in the base metal than in the other parts of the weld joint. The final mechanical behavior studied through microhardness measurement and micromechanical calculations, allows us to separate the contribution of both microstructural and textural evolution to the overall strain hardening of the weld joint. Voir les détails
Mots clés : duplex stainless steel, deformation texture, mechanical anisotropy, TIG welding
Analysis of High Tc Superconducting Rectangular Microstrip Patches over Ground Planes with Rectangular Apertures in Substrates Containing Anisotropic Materials
A rigorous full-wave analysis of high superconducting rectangular microstrip patch over ground plane with rectangular aperture in the case where the patch is printed on a uniaxially anisotropic substrate material is presented. The dyadic Green’s functions of the considered structure are efficiently determined in the vector Fourier transform domain. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. The accuracy of the analysis is tested by comparing the computed results with measurements and previously published data for several anisotropic substrate materials. Numerical results showing variation of the resonant frequency and the quality factor of the superconducting antenna with regard to operating temperature are given. Finally, the effects of uniaxial anisotropy in the substrate on the resonant frequencies of different TM modes of the superconducting microstrip antenna with rectangular aperture in the ground plane are presented. Voir les détails
Mots clés : Anisotropic material, Anisotropic substrates, Dyadic green's functions, Operating temperature, Rectangular aperture, Rectangular microstrip patch, Superconducting microstrip antennas, Uniaxially anisotropic substrate
Resonant Frequency of Tunable Microstrip Ring Antenna Printed on Isotropic or Uniaxially Anisotropic Substrate
In this study, the resonant frequency of annular ring microstrip resonator with uniaxial anisotropic substrate and air gap layer is analyzed. The cavity model for simple ring microstrip antenna is extended with some modifications for the tunable geometry taking into account the anisotropy inthe layer. The theoretical resonant frequency results are in very good agreement with the experimental results reported elsewhere. The air gap tuning effect on the resonant characteristics is also investigated for fundamental and higher order modes. Voir les détails
Mots clés : Microstrip, Ring Antenna
Resonance of High Tc Superconducting Microstrip Patch in a Substrate-Superstrate Configuration
The effect of a protecting dielectric superstrate on the resonance of a high Tc superconducting microstrip patch is investigated. The analysis approach is based on the spectral-domain method of moments in conjunction with the complex resistive boundary condition. The complex surface impedance of the superconducting thin film is determined using London’s equation and the two-fluid model of Gorter and Casimir. Numerical results show that the resonant frequency of the high Tc superconducting rectangular patch decreases monotonically with increasing superstrate thickness, the decrease being greater for high permittivity loading. Voir les détails
Mots clés : Resonance, Microstrip antenna, Superstrate
Bearing fault diagnosis based on feature extraction and condition classification
Bearing fault diagnosis has attracted significant attention over the past few decades. It consists of two major parts: vibration signal feature extraction and condition classification for the extracted features. In this paper, feature extraction from faulty bearing vibration signals is performed by a combination of signal's time-varying statistical parameters and features obtained through the preprocessing of the vibration signal samples using Db2 discrete wavelet transform at the fifth level of decomposition. In this way, an 8-dimensional vector of the vibration signal feature is obtained. After feature extraction from vibration signal, the support vector machine (SVM) was applied to automate the fault diagnosis procedure. To improve the classification accuracy for bearing fault prediction, particle swarm optimization (PSO) is employed to simultaneously optimize the SVM kernel function parameter and the penalty parameter. The results have shown feasibility and effectiveness of the proposed approach. Voir les détails
Mots clés : Condition monitoring, Discrete wavelet transform, Roller Bearing, Particle Swarm Optimization, Statistical parameters, Support vector machine
Fusion-based shape descriptor for weld defect radiographic image retrieval
Content-based image retrieval with relevance feedback plays nowadays an important role in several machine vision applications. In this paper, such a system is proposed for weld radiograms in radiographic testing, with the aim of searching from the overall image database, interactively with the radiograph expert, discontinuities similar to some common weld defect types such as crack, lack of penetration, porosity, and solid inclusion. Therefore, shape features characterizing efficiently these defect indications are required. Two shape descriptors are proposed: a shape geometric descriptor (SGD) consisting of a set of invariant shape geometric measures chosen on the basis of their relationships with the weld defect classes and a generic Fourier descriptor (GFD) known for its discrimination powerfulness for planar filled objects. To improve the weld defect retrieval results, we propose a new fusion-based shape descriptor. The idea of the fusion strategy is to examine the compactness and the rectangularity measures in SGD and derive a criterion permitting the design of a new descriptor f(GFD,SGD) able to better discriminate, particularly, between the problematic defect classes of crack and lack of penetration. Experiments conducted on weld defect image database show the strength of the proposed hybrid descriptor compared to GFD and SGD, simply or hierarchically concatenated or used separately. Voir les détails
Mots clés : Radiographic testing, weld defect, CBIR, SGD, GFD, f(GFD, SGD)
Local Segmentation via an Implicit Region-Based Deformable Model Applied To Weld Defects Extraction
This paper is devoted to present and discuss a model that allows a local segmentation by using statistical information of a given image. It is based on Chan-Vese model, curve evolution, partial differential equations and binary level sets method. The proposed model uses the piecewise constant approximation of Chan-Vese model to compute Signed Pressure Force (SPF) function, this one attracts the curve to the true object(s)’s boundaries. The implemented model is used to extract weld defects from weld radiographic images in the aim to calculate the perimeter and surfaces of those weld defects. Encouraged resultants are obtained on synthetic and real radiographic images. Voir les détails
Mots clés : Active contour, Chan-Vese Model, binary Level set, local segmentation, weld radiographic images