Physique
NONDESTRUCTIVE EVALUATION OF THE CARBON CONTENT IN STEEL
The aim of this work is to propose an experimental method to evaluate the steel carbon content by ultrasound. The sample is immersed in a water tank in order to analyze it under various incidences of sound waves. Longitudinal wave velocities are measured by immersion by using a 5-MHz frequency probe. Transverse wave velocities are measured in a contact mode by using a 4-MHz transverse wave transducer. The attenuation coefficients of ultrasonic longitudinal and transverse waves are deduced from three successive basic echoes through the sample. The effects of some heat treatments on ultrasonic parameters are also studied. The measurement of ultrasonic parameters in steel offers an interesting possibility of tracing the carbon content and, at the same time, provides information on the steel structure and its elasticity Voir les détails
Mots clés : carbon content, steel, ultrasonic waves.
Theoretical estimation of the production of biogasfrom the landfill of Batna city and its electricalconversion by a SOFC
Amongst the interests in fuel cells is exploring the possibility of using different fuel types;one of them is biogas or Landfill gas (LFG) from landfills or from controlled digesters.Biogas; a gas produced by an anaerobic digestion of organic waste represents an environmentalproblem that could turn to a renewable energy source. The valorization ofbiogas into energy (electricity, heat, fuel) will save other sources of energy. The authors ofthe study are interested in evaluating three technologies: fuel cells, micro turbines andinternal combustion engine.In this paper, we discussed the conversion of biomass into electricity in two steps: thefirst step (biomass-to-biogas) is based on an evaluation of biogas potential generated bysolid waste of landfill the Batna city (Algeria) by the kinetic model (U.S.EPA, 1993). In thesecond step (biogas-to-electricity), the paper considers the technology of a stack of standardsolid oxide fuel cells (Ni-YSZ/YSZ/LSM) SOFC; this allowed us to determine the besttemperature, hydrogen concentration and electrolyte thickness for maximum powerdensity in the fuel cell SOFC. At a temperature T = 1273 K and thickness of electrolyte of theorder of 0.1 mm and at higher hydrogen concentration, a maximum power density ofP = 1.4 W/cm2 was obtained. Voir les détails
Mots clés : LFG, Biogas, Anaerobic digestion, Electricity, SOFC
Champ thermique sous l'effet de la réaction chimique d'une réforme de la pile à combustible à oxyde solide SOFC DIR-interne direct
Les effets directs de reformage interne dans une pile à combustible à oxyde solide (SOFC) sur les champs thermiques sont étudiés par modélisation mathématique. Cette étude présente les champs thermiques d'une pile à combustible standard (Ni-YSZ / YSZ / LSM) anode en charge. Cette étude est également faite dans le plan perpendiculaire à l'écoulement des gaz. La pile à combustible est alimenté par de l'air et de carburant, CH4, H2, CO2, CO et H2O où la naissance du phénomène de la réforme (DIR-SOFC) interne direct. Il est basé sur la réforme de réactions chimiques, de la vapeur et de réaction de reformage réaction du gaz à l'eau. Le but principal de ce travail est la visualisation des champs de température sous l'influence des réactions chimiques mondiales et la confirmation du comportement thermique de cette réaction chimique. Les champs thermiques sont obtenus par un programme informatique (Fortran). Voir les détails
Mots clés : SOFC, Direct internal reforming, Global chemical reactions, Thermal fields
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
Design and Optimisation of Circular and Inductors for Silicon-based RFIC Application
In this paper, spiral inductors for RF application, which are designed on a silicon substrate by using standards 0.35 µ m CMOS technology, are described. Analyzed and designed with ASITIC (a tool from the University of Berkeley), which accurately takes into account the parasitic effects. This study shows the possibility of obtaining an optimal inductance having a high quality factor of 15. This result is carried out without resorting to the specific processes such as the digging of the substrate under the inductors or the use of a thick layer in gold. The use of circular form, with optimization of geometrical parameters like spacing between two adjacent turn, the track width and the number of turns, can ensure high quality factors. Voir les détails
Mots clés : circular inductor, high quality factors., RF application
Propagation of Lamb waves in an immersed periodically grooved plate: Experimental detection of the scattered converted backward waves
Guided waves propagation in immersed plates with irregular surfaces has potential application to detection and assessment of the extent, depth and pattern of the irregularity. The complexity of the problem, due to the large number of involved parameters, has limited the number of existing studies. The simplest case of irregularities of practical interest is the two-dimensional corrosion profile. Even this case is in general so complex, that one can extract several amplitude dominant periodic surfaces only by using a Fourier spectrum of the surface. Guided waves in plates, with one or both free surfaces having periodic perturbations of different shapes, have been presented in specialized literature. In this paper is studied the propagation of Lamb waves in an aluminum plate with a periodic grooved surface on only one side and immersed in water. The interaction between an incident Lamb wave and the grating gives rise to retro-converted waves. Preliminary numerical simulation by the finite element method is performed in order to obtain key parameters for the experiments. It is shown that retroconverted waves radiating into the water are detectable although their amplitudes are small. The phonon relation is verified for the leaky Lamb modes. The damping coefficients of the leaky Lamb modes in the grooved immersed plate are evaluated. Voir les détails
Mots clés : Liquid–solid interfaces, Rough plate, Periodic grating, Lamb waves, Converted modes
Notch detection in copper tubes immersed in water by a compressional guided waves
Tube- or pipe-like structures are used to convey fluids such as gas, oil or water. These fluids can be transported on land, in sea or in industrial buildings. Hence, tubes can suffer from mechanical, thermal and chemical stresses. The latter, can severely damage these structures due to the oxidation phenomena. This damage weakens the structure and reveals cracks and inhomogeneities. The objective of this work is to detect and characterise damage in tubes immersed in water by a non-destructive method. This research work is devoted to the development of an experimental device. This device can detect and locate axy- and nonaxy-symmetric circumferential small notches located on the outer surface of a filled tube and immersed in water using guided waves. Different sizes of notches are milled into copper tubes with a thin wall are considered. A single transducer is used for emission and reception of leaky guided waves by using the pulse-echo technique. The compressional L(0,2)mode is launched at relatively high frequency using oblique incidence of the transducer into the fluid. By using the wave leakages, notches of small sizes are detected and located. In addition, the sensitivity of the L(0,2) mode to the radial depth and circumferential extent of notches is evaluated. A roughly linear behaviour of the amplitude reflection coefficients is revealed which is in accordance with research works found in the literature. Voir les détails
Mots clés : guided waves, Immersed tubes, Circumferential notches, Experimental device
Grain size influence on ultrasonic velocities and attenuation
During the last two decades, ultrasonic testing was developed as an efficient tool for materials characterization. Acoustical waves by their passage through materials, carry out a multitude of information contained in the signal on the mechanical and physical properties of the material under inspection. In this paper, an experimental study on steel samples has been performed to study the evolution of some ultrasonic parameters such as wave velocities and attenuation coefficients as function of the steel grains size. The experimental results obtained are discussed and analyzed in order to develop an ultrasonic non-destructive technique to grains size determination. Voir les détails
Mots clés : Ultrasonic, Grain Size, Velocity, Attenuation, Scattering
Ultrasonic characterization of materials hardness
In this paper, an experimental technique has been developed to measure velocities and attenuation of ultrasonic waves through a steel with a variable hardness. A correlation between ultrasonic measurements and steel hardness was investigated. Voir les détails
Mots clés : Ultrasounds, hardness, Velocity, Attenuation
Characterization of the deformation texture after tensile test and cold rolling of a Ti-6Al-4Vsheet alloy
The deformation texture after cold rolling and tensile test of an industrial Ti-6Al-4V sheet alloy was studied using X-ray diffraction. The alloy was subjected to a cold rolling to different thickness reductions (from 20% to 60%) and then tensile tests have been carried out along three directions relatively to the rolling direction (0°, 45° and 90°). The experimental results were compared to the existing literature and discussed in terms of active plastic deformation mechanisms. Voir les détails
Mots clés : TA6V, deformation texture, Anisotropy, Lankford