Liste des publications
Investigation of the Effect of Aluminum Alloy Position on ResidualStresses in Dissimilar fsw Weld by Using the Ultrasonic Method
The main goal of this study is to show the effect of the advancing side (AD) and theretreating side (RT) position on the Residual stresses and local mechanical behaviour ofdissimilar friction stir welds of aluminum alloys AA2024-T3 and AA7075-T6. Different sampleswere produced by varying the rotational speed of the tool (1200 and 1400 rpm) and the alloyposition regarding the advancing side of the tool. Ultrasonic Method has been used to evaluateResidual Stresses. This method is based on the acoustoelastic effect, which measures the velocityvariation of the elastic waves according to the stress state of the material. This can be achievedthrough a calibration test, which permits the determination of the acoustoelastic coefficient (K).The results show a tensile stress in the Nugget (N), the heat affected zone (HAZ) and acompression stress in the base metal (BM). Increasing the rotational speed reduces the amplitudeof the longitudinal residual stresses with a high reduction in the case where AA7075 - T6 is inthe advancing side whit 1400 rpm. This has been directly associated to the increase in the heatinput and the reduction of the thermal mismatch between different areas of the weld. Themicrostructure effect of aluminum alloy position acts on the acoustoelastic constant K. Thechoice of t0 corrects the overestimated residual stresses in the (HAZ) and (N). Voir les détails
Mots clés : FSW, contraintes résiduelles, microstructure, comportement mécanique, corrélation d'image numérique
Tomographic Image Reconstruction in the Case of Limited Number of X-Ray Projections Using Sinogram Inpainting
In many medicine and industry applications, a precise X-ray tomography reconstruction of the internal objects structure is of great importance for reliable interpretation data. The tomography allows obtaining a spatial distribution of the internal materials structure. In certain experiments conditions, the projection data acquisition is guided by angle limitations or a restricted angle, this requires a subsampling of the projections number or a partial data absence. Accordingly, the reconstructed images may suffer from severe artefacts especially with the presence of noise. In this context, the purpose of this paper is to propose a tomographic image reconstruction method based on FBP associated to sinogram inpainting. The studied inpainting technique is based on first order variational methods such as the Chambolle-Pock algorithm. This method allows the quality improvement of the reconstruction images tomographic with reduced number of projection. The PSNR is improved by 7 to 10 dB in the reconstructed image compared to the classical FBP reconstruction. Voir les détails
Mots clés : x-ray tomographic, image reconstruction
Inhibition Efficiency of Cinnamon Oil as a Green Corrosion Inhibitor
The corrosion inhibition efficiency of cinnamon oil for stainless steel 304 L in 0.1 and 1.0 M HCl solutions was investigatedusing electrochemical study and surface electronic observation. The potentiodynamic polarization curves showed that, independentlyof the time of immersion in 1.0% HCl, a reaction to the anode occurred, which was explained by the dissolutionof the metal due to the strong aggressiveness of the medium; the addition of 1% cinnamon oil led to a corrosion efficiencyof 84%. Furthermore, in 0.1 M aggressive medium the tests with addition of inhibitor showed that the inhibition efficiencyincreases (86.6–96.0%) with an increase in the cinnamon oil concentration from 0.5 to 5%. Scanning electron microscopeobservations of metal surface confirmed the existence of a protective adsorbed film of the inhibitor on the steel surface. Cinnamonoil can be proposed as an efficient green inhibitor of corrosion of stainless steel exposed to hydrochloric acid mediums. Voir les détails
Mots clés : Aggressive medium · Cinnamon oil · Corrosion inhibitor · Stainless steel
Fast Adapting Mixture Parameters Schemes for Probability Density Difference-Based Deformable Model
This paper presents a new region-driven active contour using the pdf difference to evolve. The pdf estimation is done via a new and fast Gaussian mixture model (GMM) parameters updating scheme. The experiments performed on synthetic and X-ray images have shown not only an accurate contour delineation but also outstanding performance in terms of execution speed compared to the GMM estimation based on EM algorithm and to non-parametric pdf estimations. Voir les détails
Mots clés : Active contour, Adaptive mixture, GMM parameters update
Unsupervised weld defect classification in radiographic images using multivariate generalized Gaussian mixture model with exact computation of mean and shape parameters
In industry, the welding inspection is considered as a mandatory stage in the process of quality assurance/quality control. This inspection should satisfy the requirements of the standards and codes governing the manufacturing process in order to prevent unfair harm to the industrial plant in construction. For this purpose, in this paper, a software specially conceived for computer-aided diagnosis in weld radiographic testing is presented, where a succession of operations of preprocessing, image segmentation, feature extraction and finally defects classification is carried out on radiographic images. The last operation which is the main contribution in this paper consists in an unsupervised classifier based on a finite mixture model using the multivariate generalized Gaussian distribution (MGGD). This classifier is newly applied on a dataset of weld defect radiographic images. The parameters of the nonzero-mean MGGD-based mixture model are estimated using the Expectation-Maximization algorithm where, exact computations of mean and shape parameters are originally provided. The weld defect database represent four weld defect types (crack, lack of penetration, porosity and solid inclusion) which are indexed by a shape geometric descriptor composed of geometric measures. An outstanding performance of the proposed mixture model, compared to the one using the multivariate Gaussian distribution, is shown, where the classification rate is improved by 3.2% for the whole database, to reach more than 96%. The efficiency of the proposed classifier is mainly due to the flexible fitting of the input data, thanks to the MGGD shape parameter. Voir les détails
Mots clés : Mixture model, Multivariate GGD, radiography, weld defect, classification
Effect of zinc/cadmium proportion in CdS layers deposited by CBD method
Cadmium poisoning and the cost of panel recovery which is very expensive and difficult in the buffer layers of CdS in solar cell, for these two drawbacks, we do a search on the effect of proportion of zinc/cadmium in the properties layers of CdS. For this, our studies study the properties of CdxZn1-xS layers deposited by chemical bath (CBD). CdZnS thin films were synthesized by chemical bath deposition (CBD) with different deposition protocols to optimize deposition parameters such as temperature, deposition time, ion concentrations and pH. The surface morphology, structural, optical and chemical properties of the CdZnS thin films were studied by SEM, XRD, Raman and UV-visible spectrophotometer. The transmittance is 80% in the visible region 300 nm - 800 nm; the crystalline structure is hexagonal and cubic, the grain size is between 9.95 to 25.82 nm. It is observed that the transmittance and the shape change with the concentration of zinc in the solution; this result favors the application of these films in solar cells application. Voir les détails
Mots clés : CdZnS, chemical bath, SEM, Raman, solar cells, Thin films
Preparation, structural and functional properties of PbTiO3-δ ceramics
In the present study, oxygen deficient PbTiO3-δ ceramics were prepared by solid state-reaction method. The formation of the pure perovskite phase with tetragonal structure was confirmed for the 800 °C/2 h calcined sample by using X-ray diffraction analysis at room temperature. Energy dispersive X-ray spectroscopy analyses confirm the creation of oxygen vacancies in the system for charge compensations, as demonstrated by the percentage of O atoms of ∼53%. The complex impedance data reveals important contributions of the oxygen vacancies to the total dielectric response that are homogeneous distributed within the sample. The room temperature magnetic properties show a weak ferromagnetic character in all the samples that might be attributed to the oxygen vacancies defects and to surface effects. Voir les détails
Mots clés : Ceramics, oxygen vacancies, EDX spectra, Dielectric properties, Magnetic Properties
Optimal Stochastic Excitation for Linear Flaw Detection in a Solid Material.
The field of ultrasonic nondestructive testing has known a great development during the recent years. In order to increase the faw detection sensitivity, many improvements have been made in the equipment and the sensors technology. In the present work, the optimal command which maximizes the flaw detection is investigated experimentally. A parametric optimization consisting of finding the optimal excitation frequency which maximizes the Euclidean distance between a reference medium and a medium with a linear faw has been obtained automatically by using the gradient descent algorithm. Moreover, the waveform excitation optimization has been considered. A set of stochastic signals have been transmitted to the medium. A closed loop optimization process based on a genetic algorithm allowed to find the optimal excitation without a priori knowledge on the shape of the signal. This optimal excitation converged to a sinusoidal pulse with the optimal frequency found by the parametric optimization. Voir les détails
Mots clés : Optimal command, nondestructive testing, Gradient descent algorithm, Genetic algorithm, Ultrasound
Study of the effect burnishing on superficial hardness and hardeningof S355JR steel using experimental planning
Surface hardness plays an important role in lifetime of a mechanical piece subjected to friction and wear. Indeed, thehardness can be improved by superficial plastic deformation processes (SDP), such as mechanical surface treatment"MST", in particular the ball burnishing. However, the treatment result of is conditioned by mastery of operationthus ensuring treated piece good mechanical and geometric properties. Experimental work was carried out byapplying the ball burnishing process on steel tensile specimens S355JR, in order to observe the influence oftreatment parameters regime on surface hardness 'Hv' and the effect of latter on tensile behavior of this steel. Twoparameters of regime were considered namely: burnishing force "Py" and number of passes "i". The relationshipbetween these parameters and microhardness measured at "Hv" surface has been highlighting using factorial plans22. Moreover a mathematical model has been obtained allowing prediction of response (Hv) as well as optimizationof parameters of treatment regime. The experimental results showed that for surface hardness Hv it is possible toreach a 45% improvement rate for a burnishing force py = 20 Kgf and a number of passages i = 3 for this material.Regarding behavior of material during tensile test, for a low burnishing force (py = 10N) and a number of passes (i= 5), the section further weakening (S = 4.14), proof than ductility of material has decreased. Voir les détails
Mots clés : Surface hardness, factorial designs, ball burnishing, Mathematical model, tensile behaviour
Effects of work hardening on mechanical metalproperties—experimental analysis and simulation by experiments
The aim of the present work is to improve the materials’ performances, particularly their elastic property based on an optimalexploitation of surface work-hardening phenomenon, using surface plastic deformation treatment (DPS). The surface of amechanical piece is considered as the most vulnerable zone that determines its mechanical performances. To improve thesurface physico-mechanical properties, the surface plastic deformation treatment (DPS) is often used. The (DPS) acts by acombined action of: surface hardening, structural modification, and the generation of the compression residual stresses, thefactors that will create a heterogeneous plastic deformation. Knowing that during operation the mechanical pieces have to besubjected to a stress smaller than the elastic limit (taking into account the safety margins), where the material behavior isreversible, and to reach the maximum allowable stresses, we have to increase the material’s elastic limits. This objective canbe realized through an optimal use of work hardening phenomenon for the treated surface by the DPS. The work hardening ischaracterized by the increase of the yield strength (Re), the surface hardness (Hv), and consequently the increase of thebrittleness. Depending on the considered metals, when the piece has a defect variation: cavity, inclusion (precipitate), orzones of different hardness, it can create a stress concentration which generates a local hardening. This phenomenon is one ofthe main causes of crack generation. In our study, we consider the influence of work hardening on the elastic behavior ofXC38 steel and aluminum alloy. Voir les détails
Mots clés : Work hardening . Hardening of materials . Mechanical surface treatment (TMS) . Burnishing