Liste des publications
Guided Wave Sensitivity for De- Bond Defects in Aluminum Skin Honeycomb Core
Sandwich plates are finding an increasing range ofapplication in the aircraft industry. The inspection of honeycomb composite structure by conventional ultrasonic technique is complexand very time consuming. The present study demonstrates a technique using guided Lamb waves at low frequencies to predict de-bond defects in aluminum skin_honeycomb core sandwich structure used in aeronautics. The numerical method was investigated for drawing the dispersion and displacement curves of ultrasonic Lamb wave propagated in Aluminum plate. An experimental study was carried out to check the theoretical prediction. The detection of unsticking between the skin and the core was tested by the two first modes for a low frequency. It was found that A0 mode is more sensitive to delamination defect compared to S0 mode. Voir les détails
Mots clés : Damage detection, delamination, guided waves, Sandwich structure
Effects of Niobium and Molybdenum on Microstructures after Hardeningand Wear Resistance of Austenitic Manganese Steel
Hadfield steel has been wildly used to manufacture railway crossings because of its excellent workhardening, high strength and toughness properties. The hardness of Hadfield steel is only about 20 HRC whensubjected to water toughening. This low hardness is usually associated with poor wear resistance and severeplastic deformation, as well as abrasion of the working surface of the railway crossing during the initial serviceperiod, which remarkably reduces its service lifetime. In this study we focus on the influence of niobium andmolybdenum on the phenomenon of surface hardening or work hardening and wear resistance. Thetransformation of austenite during operation, thus determines the steel operating lifetime, the rate oftransformation of austenite to martensite can introduce a compromise between ductility and wear resistance ofthe steel to support large efforts without breaking. The objective of this study is to improve the wear resistanceby abrasion and friction after heat treatment of manganese steel alloyed with niobium and molybdenum. Theaddition of niobium and molybdenum promotes secondary hardening and allows slower transformation ofaustenite during the heat treatment. The results showed that the introduction of niobium and molybdenum hasstrongly influenced the character of the structure crystallization before hardening (Part hardened) byprecipitation carbides form and finesse variables is observed in the microstructure before heat treatment andcomplete dissolution is noted after heat treatment, for the hardened part (work hardening) we observed agreater thickness and hardness compared to the base steel and net improvement in wear resistance. Voir les détails
Mots clés : manganese steel, Effects of Niobium and Molybdenum, Hardeningand, Hardeningand Wear Resistance
A numerical study of viscous dissipation effect on non-Newtonian fluid flow inside elliptical duct
Laminar heat transfer inside duct with elliptical cross section, subjected to uniform wall temperature is studied by taking into account the viscous dissipation. The temperatures distributions are evaluated numerically by using a dynamic Alternating Direction Implicit method (dADI). Nusselt number (Nu) is presented graphically for various Brinkman number (Br) and aspect ratio for a non-Newtonian fluid described by the power law model. The results obtained showed a good agreement with those found in the literature for fluid flow in circular cross section ducts and in elliptical cross section without viscous dissipation effects. It is shown that in the fully developed region and for Br ≠ 0, Nusselt number has a fixed asymptotic value independent of Brinkman number (Br). In the thermally developing region, it is observed a single fixed point independent of heating or cooling condition which the numerical value is equal to the asymptotic Nusselt number. Another relevant feature is that in the fully developed region, the Nusselt number increases with the aspect ratio. Voir les détails
Mots clés : Elliptical duct section, Viscous dissipation, Non-Newtonian fluids, Power law model, Laminar forced convection
Wavelet Transform for Bearing Faults Diagnosis
Fault diagnosis is useful for ensuring the safe running of machines. Vibration analysis is one of the most important techniques for fault diagnosis of rotating machinery; as the vibration signal carries the dynamic information of the system. Many signal analysis methods are able to extract useful information from vibration data. In the present work, we are interested to the vibration signal analysis by the wavelet transform. The monitoring results indicate that the wavelet transform can diagnose the abnormal change in the measured data. Voir les détails
Mots clés : fault diagnosis; vibration analysis; rotating machinery; monitoring; wavelet transform
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
Petroleum quaternary ammonium surfactants mixture synthesized from light naphtha as corrosion inhibitors for carbon steel in 1 m HCl
A quaternary ammonium cationic surfactants mixture was synthesized from light naphtha, petroleum fraction. The mixture was analyzed by Fourier transform infrared spectroscopy and UV/Visible spectroscopy and was evaluated as a corrosion inhibitor for carbon steel in 1 m HCl, by gravimetry, potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that inhibiting efficiency increased with inhibitor concentration and temperature, and was independent of pH (in the range of 0 – 4) and immersion time; its optimal value was up to 84% for 560 mg/l at 25 ° C. Experimental data showed that the cationic surfactants mixture acts as a mixed (anodic and cathodic) inhibitor and conformed to the Langmuir adsorption isotherm. Scanning electron microscopy images revealed the inhibiting capacity of the mixture against carbon steel acid corrosion. Voir les détails
Mots clés : adsorption; carbon steel; cationic surfactants mixture; corrosion inhibition; surfactants synthesis.
Prediction of the conversion efficiency of a GaSb thermophotovoltaic converter heated by radioisotope source
In recent years, Gallium Antimonide (GaSb), which has smallest bandgap among III-V semiconductors family, became the subject of extensive investigations in the field of thermophotovoltaic (TPV) converters, because of the recent improvements in optoelectronic technology. In this paper, we investigated the heat to electricity conversion efficiency of a GaSb radioisotope thermophotovoltaic (RTPV) converter, taking account of the photons with energy below the cells bandgap using a comprehensive analytical process. The results show that a conversion efficiency greater than 28% can be obtained for radiator’s temperature of 1600k, at ambiant temperature. This efficiency will decrease as the cell temperature increase. Voir les détails
Mots clés : Radioisotope, Emissivity, Thermophotovoltaic, Efficiency, Temperature
Analysis and optimization of In1-xGaxAsySb1-y thermophotovoltaic cells under low radiator temperatures
In this paper, we investigated the heat to electricity conversion efficiency of In1-xGaxAsySb1-yradioisotope thermophotovoltaic (RTPV) converter with x=0.8 and y=0.18, taking account of the photons with energy below the cells bandgap using a comprehensive analytical process. This was done with a computer program designed for this reason, which allowed the computation of the cell performance under a variety of specified incident radiation spectra as well as a variety of material parameters. The results show that for an emissivity value of 0.78, a cell thickness of about 7µm with low front recombination velocity(700cm/s),a conversion efficiency greater than 29% can be obtained for radiator’s temperature of1300°k at ambient temperature. This efficiency will decrease as the cell temperature increase. Voir les détails
Mots clés : Radioisotope, Emissivity, Recombination Velocity, Efficiency, Temperature
Study of the inhibiting effect of a quaternaryammonium surfactants mixture synthesizedfrom petroleum fraction (reformate) againstthe carbon steel corrosion in HCl 1 M
Quaternary ammonium cationic surfactants were synthesized fromreformate, a liquid mixture of hydrocarbons (aromatics, naphthenes and paraffins),via chloromethylation/quaternization sequences. The petroleum surfactants thusobtained were evaluated as corrosion inhibitors for carbon steel in 1 M HCl, bygravimetry, potentiodynamic polarization and electrochemical impedance spectroscopy.The corrosion inhibiting efficiency was assessed as functions of surfactantconcentration. The results showed that the inhibiting efficiency increased withsurfactant concentration; its optimal value of 70 % was for a surfactant concentrationof 320 mg/L at 25 C. Potentiodynamic polarization measurements showedthat the mixture acts as a mixed type inhibitor. The corrosion inhibiting mechanismis thought to proceed via an adsorption of the surfactant molecules on the steelsurface, generating a film and hindering the active sites. Our experimentaladsorption data were found to obey the Langmuir adsorption isotherm. SEM imagesof the treated specimens, revealing the likely formation of a protective film, demonstratedthe inhibiting capacity of the petroleum quaternary ammonium surfactantsagainst the carbon steel corrosion. Voir les détails
Mots clés : Corrosion inhibition Carbon steel Petroleum quaternary ammonium Cationic surfactants mixture
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