Liste des publications

Nombre total de résultats : 541
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Numerical and Experimental Investigation of FluidicMicrodrops Manipulation by Fluidic Mono-Stable Oscillator

T. CHEKIFI, B. dennai, R. Khelfaoui, A. Maazouzi  (2016)
Publication

A numerical and experimental study of passive microdrops manipulation hasbeen presented. This paper focuses on the modeling of micro-oscillators systemswhich are composed by passive amplifier without moving part. The characteristicsize of the channels is generally about 35 ¹mof depth. The numerical results indicatethat the production and manipulation of microdrops are possible with passivedevice within a typical oscillators chamber of 2:25 mm diameter and 0:20 mmlength when the Reynolds number is Re = 490. The novel microdrops methodthat is presented in this study provides a simple solution about the production ofmicrodrops problems in micro system. We undertake an experimental step. Thefirst part is based on realization of sample oscillator; the second part is consistedof visualization of the microdrops production and its manipulation. Voir les détails

Mots clés : microdrop, fluidic oscillator, CFD

MicroFluidic Oscillator: A Technical Solutionfor MicroMixture

B. dennai, A. BENTALEB, T. CHEKIFI, R. Khelfaoui, A. Abenbi  (2015)
Publication

The diffusion flux given by the Fick’s law characterizethe mixing rate. A passive mixingstrategy is proposed to enhance mixing of two fluids through perturbed jet low. A numerical studyof passive mixers has been presented. This paper is focused on the modeling of a micro-injectionsystems composed of passive amplifier without mechanical part. The micro-system modeling isbased on geometrical oscillators form. An asymmetric micro-oscillator design based on amonostable fluidic amplifier is proposed [2,7]. The characteristic size of the channels is generallyabout a few hundred of microns. The numerical results indicate that the mixing performance can beas high as 99 % within a typical mixing chamber of0.20 mm diameter inlet and 2.0 mm distance ofnozzle - spliter. In addition, the results confirm that self-rotation in the circular mixer significantlyenhances the mixing performance. The novel micro mixing method presented in this study providesa simple solution to mixing problems in microsystem. Voir les détails

Mots clés : Micro oscillator, modeling, Micro mixture, diffusion, Size effect.

Effect of Geometrical Parameters on Vortex Fluidic Oscillators Operating with Gases and Liquids

T. CHEKIFI, B. dennai, R. Khelfaoui  (2018)
Publication

The fluidic oscillator is an interesting device developed for passive flow measurement. These microsystems can produce a high oscillating jet frequency with high flow velocity. The main advantages of fluidic oscillators are that no moving parts is included in the device. Commercial CFD code FLUENT was used to perform analysis of flows in fluidic oscillator. Numerical simulations were carried out for different flow conditions, where water and air were used as working fluids. The oscillation frequencies were identified by the discrete fast Fourier transform method (FFT). Furthermore a low-pressure vortex of fluid flow in the oscillating chamber was observed. The effect of the operating pressure and the oscillating chamber shape on the fluidic oscillator performance is investigated. Moreover the velocity fluctuations of the feedback flows through both feedback channels and the output were determined quantitatively. In addition, the behaviour of the low-pressure vortex in both models is analysed. Also, numerical result revealed small vortices are developed at the end of nozzle while oscillation, which maintains the deflection of jet flow between attachments wall. Comparison of our numerical simulations with available results showed reasonably and good agreement. Voir les détails

Mots clés : fluidic oscillator, CFD, oscillating chamber, vortex, size effect, Coanda effect.

Identification of the elasto-viscoplastic parameters for a thermoplastic polymer by instrumented indentation

A. Mokhtari, N. TALA IGHIL  (2018)
Publication

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

DAMAGE MODELLING IN THERMOPLASTIC LAMINATES REINFORCED WITH STEEL AND GLASS FIBRES UNDER QUASI-STATIC INDENTATION LOADING AT LOW-VELOCITY

M’hamed Mahdad, Aicha Ait Saada, Idir Belaidi, Ahcene MOKHTARI, Adel Benidir  (2018)
Publication

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

Tomographic Image Reconstruction in the Case of Limited Number of X-Ray Projections Using Sinogram Inpainting

a.allag, a.benammar, R.Drai, T.BOUTKEDJIRT  (2019)
Publication

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

Investigation of the Effect of Aluminum Alloy Position on ResidualStresses in Dissimilar fsw Weld by Using the Ultrasonic Method

I.Hadji, R.Badji, M.Gaceb, N.Kherrouba, L.Rabahi  (2019)
Publication

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

Corrosion E?ects on the Magnetic Behavior of Magnetic Circuitof an Induction Machine

ALLOU Djilali, KHORCHEF Mohamed, M’hamed Ouadah, Omar TOUHAMI, Rachid IBTIOUEN  (2018)
Publication

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

CHARACTERIZATION OF IRON ORE AND SCALE FOR SYNTHESIZING VINYL PAINT

Mohammed Tayeb, ABEDGHARS Mokhtar GHERS, Salah Bouhouche, Belgacem BEZZINA  (2019)
Publication

As part of the development of iron ore deposits in Algeria and a concern for the preservation of the environment, we are planning to characterize two materials for a possible synthesis of vinyl paint in this study. Iron ore is a red iron oxide pigment with an oolitic structure containing phosphorus. The second material is a steel by-product (scale) that should be recycled. This study covers the characterization of these two components through Chemical analysis, Particle size analysis, Thermal analysis (TGA, DSC), the Observation by SEM, X-Ray Diffraction analysis and Spectrophotometric analysis. Chemical analysis showed that the pigment contains 53.18% of total iron and mostly the gangue is dominated by silica and alumina. Scale in turn contains 73.83% of iron in the form of iron oxides (FeO, Fe3O4 and Fe2O3). Grinding tests illustrated that the scale is much more suitable for grinding than pigment. The granulometric analysis gave a volume distribution of the particles with a size between 0.7 and 32 µm for scale and 0.6 to 40 µm for the pigment and their specific areas are 1.6 and 1.5 m2/g. TGA and DSC showed that the iron pigment loses weight with phase dissolution by consuming energy when the temperature increases. Scale gains weight by the formation of a new phase with heat. Scanning electron microscope of red iron pigment showed a grain aggregate formed rounded over at least iron oxide and gangue. The EDS analysis illustrated a predominance of iron with four predominant oxides in the case of iron ore deposits. Chemical elements forming these four oxides are silicon, calcium, aluminum and magnesium. The SEM of scale showed a homogeneous structure composed of sizes of iron oxide grains and shapes ranging from 1 µm to 10 µm. X-ray diffraction analysis showed that the iron in the pigment is in the form of hematite (Fe2O3) and goethite (FeO(OH)). A tiny portion is combined with silica as fayalite (Fe2SiO4). The iron in the calamine is in the form of the three oxides (FeO, Fe2O3 and Fe3O4). Spectrophotometric tests showed that both materials have virtually no absorption and maximum reflection (100%) in the visible range Voir les détails

Mots clés : Pigment iron, scale (calamine), Simultaneous thermal analysis, X-ray diffraction, Spectrophotometry

Étude expérimentale du délaminageen mode I des tubes fabriquéspar enroulement filamentaire

F M L.REKBI, M.Hecini, A.KHECHAI  (2015)
Publication

The good behavior of composite materials under mechanical loading, make it aserious competitor to traditional materials. Inter laminar defects induced duringimplementation or during stress are the main sources of its interlaminar progressive damagecausing separation of the layers known as the delamination. This work is an experimentalstudy of mode I delamination of a laminated composite [±θ°] manufactured as a tube by thefilament winding process. Technical delamination characterization by DCB test specimens(Double Cantilever Beam) are used to determine the energy release rate in mode I andevolution of delamination resistance curves R. Tests were performed according to ASTMD5528 standard and the energy release rate in mode I (GIC) of two configurations isdetermined by the method of Berry. Voir les détails

Mots clés : matériaux composites, enroulement filamentaire, endommagement, délaminage, mode I, taux de restitution d’énergie, courbes-R