Liste des publications
Preparation and characterization of spinel type Zn2TiO4 nanocomposite.
Zinc orthotitanate Zn2TiO4 spinel structures have been prepared by solid state reaction in two stages. First, a mixture of ZnO and TiO2 (67% anatase+33% rutile) in a molar ratio of 2:1 was mechanically milled for 6 and 18 h, at room temperature, in a high energy planetary ball mill under argon atmosphere. Next, the ball milled powders were calcined at 900°C for 2 h, pressed into pellets and then sintered for 4 h at 1100°C in air. Phase formation, microstructure, surface morphology and optical properties were characterized by X-ray di?raction, Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, atomic force microscopy and UV–visible spectro- photometery. The mechanical milling process for 6 h gives rise to the formation of nanocrystalline orthotitanate Zn2TiO4 (15.5%, =13.2 nm) in addition to unreacted rutile TiO2, anatase TiO2 and ZnO structures. As the milling process progresses up to 18 h, the volume fraction of Zn2TiO4 increases to about 44.5%. The sintered pellets exhibit a composite structure where about a small amount of rutile nanograins are dispersed into the Zn2TiO4 matrix. FT-IR and Raman results con?rm the biphasic character of the sintered pellets. The band gap energy is milling time dependent. It varies from 3.22 for pellet 6 h to 3.45 for pellet 18 h. Voir les détails
Mots clés : Mechanical Alloying, ZnO−TiO2 system, XRD, Raman spectroscopy, SEM
DETECTION OF BROKEN ROTOR BAR FAULT IN THE SQUIRREL CAGE INDUCTION MOTOR USING WAVELET PACKET ANALYSIS
The fault of broken rotor bars in a three phase induction motor is diagnosed by using the wavelet Packet analysis. In this paper Daubechies wavelet is selected as the wavelet base and the wavelet coefficient is obtained from the wavelet transform of current signal of the faulty induction motor. Tghe energy of wavelet components appear to be useful for detecting different electrical faults. In this paper we will study the problem of broken rotor bars Voir les détails
Mots clés : Wavelet Packet, Analysis, diagnosis fault, induction motor, broken bar
Computational study of droplet breakup in a trapped channel configurationusing volume of fluid method
Computational Fluid Dynamics is performed to numerically investigate the droplet breakup of water in oil intrapped channel configuration. The volume-of-fluid (VOF) method based the commercial code FLUENT isadopted to track the interface. Two designs are suggested to study the effect of flow conditions parameters andouter channel size on the droplet breakup mode, droplet generation frequency and size. As a function of thevelocity ratio, droplets are formed in two modes, dripping mode: droplets were generated closed to the nozzle, itwas identified at low capillary number (Ca<0.005) and jetting mode: droplets were produced after a long jet,where the capillary number Ca varies from 0.01 to 0.025. The numerical results indicated the collection channeldiameter plays potential role in the determination of droplet size and droplet generation frequency, the shearforces excreted by the continuous phase on the dispersed thread are reduced in the wider model leading to havedroplets much bigger than the narrow model, the latter produced small droplets due the high shear stressgenerated in the confinement region. Furthermore, the droplet frequency and size are found to be stronglydependent on the capillary velocity ratio. However, increasing the flow velocity ratio in both models leadsdroplets to be generated in high frequency, while the droplet length was decreasing. This work also demonstratesthat the VOF method is an effective way to simulate the droplets breakup in trapped channel geometry. Voir les détails
Mots clés : T. Chekifi
Simplified Modelling of Tandem Cold Rolling
In this paper, a calculation technique for solving the problem of regulatinginter-stand tension in a tandem cold rolling is proposed. Based on the slicesmethod, the proposed technique develops a computational model for a singlestand, and then generalizes it for five stands. The effectiveness of this technique is evaluated using experimental data acquired from tandem rolling millof IMittal steel complex of El-Hadjar-Algeria. By taking into account theelasticity of the rolls and using Newton’s method; the developed model can beused to calculate, successfully, the tensions correction of the five stands.Compared with the LAM3 software, the obtained results indicated that theproposed technique is effective and can be used to produce better performance of tandem cold rolling. Voir les détails
Mots clés : modelling, tandem cold rolling, slices method, elasticity, Newton’s method.
Simulation and Modeling of Uncertainties in the Calibration
Sensitivity analysis and uncertainty estimation are ofmajor importance for the declaration of conformity of finishedproducts. Models must be sought to analyze the test data. Themain objective of this work is to establish reliable models toanalyze our experimental data and validate them. So we havestudied and used the Monte Carlo and Bootstrap simulationmethods, we have been able to realize programs that calculate theuncertainty according to the ISO 8466 standard on X-rayfluorescence spectrometer samples from the URASM CRTIchemical analysis laboratory. Programs and interfaces are madewith Matlab (GUI). Voir les détails
Mots clés : simulation, Uncertainties, Monte Carlo, Bootstrap, calibration
Corrosion E?ects on the Magnetic Behavior of Magnetic Circuitof an Induction Machine
In This paper, the e?ect of corrosion on the magnetic behavior of a magnetic material usedas a magnetic circuit in the induction machines is studied. With this objective, the magnetic propertiesof the samples with corrosion and without corrosion were evaluated by the study of hysteresis loopsusing a homemade vibrating sample magnetometer (VSM). The magnetic parameters extracted from thehysteresis loops such as saturation magnetization, coercive, remanent magnetization, squareness ratio,magnetic permeability, and hysteresis area were analyzed. It was shown that more energy is required todemagnetize the sample with corrosion than the sample without corrosion, and the hysteresis loss in thecase of the sample with corrosion is more than the case of the sample without corrosion. These meanthat when the corrosion is presented in the magnetic circuits of the induction machine, the hysteresisloss increases, consequentially reducing the machine e?ciency. Voir les détails
Mots clés : corrosion, magnetic behavior, hysteresis loops
DAMAGE MODELLING IN THERMOPLASTIC LAMINATES REINFORCED WITH STEEL AND GLASS FIBRES UNDER QUASI-STATIC INDENTATION LOADING AT LOW-VELOCITY
This paper deals with experimental and numerical investigations of the composites damages with ductile and fragile reinforcement under quasi-static indentation loading. The main goal of the work is to increase the postdamage residual strength and ductility of thermoplastic composite. Two types of composite laminates with polypropylene (PP) matrix are tested: glass fibre laminate (GFPP) and steel fine wire mesh laminate (SWPP). The specimens are [0° 90°]2s stacking sequence and prepared by using a compression moulding technique. Quasi-static indentation tests were performed with two distinct penetration scales under low velocity (1.2 mm/min). The diameter of the hemispherical indenter is 16 mm. The failure mechanisms of composite layers were examined by the field emission scanning electron microscope (SEM). The results show that the failure mode of SWPP laminates is principally dominated by the plastic deformation component. In contrast, the GFPP laminate exhibits a fragile behaviour which is related to the fragile failure of glass fibres. In addition, the SEM shows that matrix cracking, fibre breakage, debonding and fibre pull out are the major damages observed around the indentation area. A model based on the combined use of plasticity, damage and fracture, was developed and applied to simulate quasi-static indentation behaviour and predict the resulting damage. Voir les détails
Mots clés : Indentation, laminates, damage, modelling, thermoplastics, energy absorption
Identification of the elasto-viscoplastic parameters for a thermoplastic polymer by instrumented indentation
The indentation test is a simple, fast and reliable tool that allows the determination of the materials mechanical properties from experimental load-penetration curves using the inverse computation methods. Through this approach and using the Berkovich indenter, the creep and elasto-plastic properties of the polymers were estimated. Simulations of the elasto-viscoplastic behaviour of the studied polymers under nanoindentation tests were performed. A finite element analysis was carried out to simulate the mechanical behaviour of polymers which can be defined by the Young's modulus E and the parameters (K and n) that describe the materials hardening for large deformations. The obtained functions from the numerical simulations were validated by nanoindentation and compression tests for the studied polymers. Voir les détails
Mots clés : Nano-indentation, polymers, inverse computation methods
Core-rim structure formation in TiC-Ni based cermets fabricatedby a combined thermal explosion/hot-pressing process
TiC-Ni-based cermets were obtained by thermal explosion from different elemental mixtures(Ti, C, Ni and X, where X = Cr, Mo or W) and subsequently densified by hot-pressing under acyclic load. The whole process was performed in a single stage in the same experimentaldevice according to the following thermal and pressure procedure: a heating rate ramp up to1573 K without applying any load followed by an isothermal dwelling under a compressivecyclic load of 32 MPa. The thermal explosion synthesis occurred during the heating ramp at atemperature close to 1273 K that was practically independent of the starting nominalcomposition. The influence of different refractory elements on the chemical composition andmicrostructure of cermets was studied. SEM characterization showed that only with Mo andW, the cermets developed the characteristic core-rim structure. A high densification wasachieved, but decreased when the refractory elements were added. Nevertheless, in thesecases higher hardness values were obtained. Voir les détails
Mots clés : Cermets, Thermal explosion, Core-rim microstructure, Solid-solution carbides
Photocatalytically-assisted electrooxidation of herbicide fenuron usinga new bifunctional electrode PbO2/SnO2-Sb2O3/Ti//Ti/TiO2
The degradation of the herbicide fenuron was investigated using a new porous bifunctional electrodewhere the electrooxidation takes place on one side and the photocatalysis on the other side. The characterizationof the synthetized bifunctional electrode (PbO2/SnO2-Sb2O3/Ti//Ti/TiO2) was performed byscanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction analysis andshowed that the anodic side (Ti/SnO2-Sb2O3/PbO2) is covered with a tetragonal b-PbO2 film and that thephotocatalytic side (Ti/TiO2) consists of an anatase phase of TiO2. The single application of electrooxidationachieved 87.8% fenuron degradation and 84.1% chemical oxygen demand (COD) removal whileheterogeneous photocatalysis resulted in only 59.2% and 39.7% fenuron concentration decay and CODremoval, respectively. On the other hand, the photocatalytically-assisted electrooxidation (photo-electrooxidation)performed on the bifunctional electrode provided higher performances of fenurondegradation (97.5%) and mineralization (97.4%). Investigation of operating parameters highlighted thepositive effect of increase in current density. Conversely, an increase in fenuron concentration led to adecrease in degradation rate and COD removal. It was also found that the COD removal and mineralizationefficiency are higher in a neutral medium. Voir les détails
Mots clés : Fenuron Bifunctional electrode Lead dioxide anode Electrooxidation Photo-electrooxidation