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Nombre total de résultats : 1846
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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

A Simple Efficient Finite Element for the Sandwich Plates Analysis

K. BELKAID, B. BOUBIR, N. BOUTASSETA, H. Aouaichia, N. Fergani, D. GAAGAIA  (2019)
Article de conférence

In this work, a numerical simulation has been considered of a sandwich composite panel subjected to a mechanical uniaxial load in order to study the buckling behaviors. In this study, we used the finite element Abaqus software and a simple efficient finite element model available in the literature [1] in order to: 1- Describe the fundamental buckling modes of a sandwich composite panel. 2- Understand the buckling behavior on this type of structure. 3- Validate the reply of the developed element on buckling behavior for the sandwich composite structure with the finite element ABAQUS software. Voir les détails

Mots clés : composite, sandwich, buckling modes, finite element

Effect of cold rolling on the recrystallization of 904L austenitic stainless steel

Lyacine RABAHI, Brahim MEHDI, Idir HADJI, Riad BADJI, Nabil KHERROUBA  (2019)
Article de conférence

The aim of this work is to study the recrystallization in the 904L austenitic stainless steel, which underwent a cold rolling with two different deformation amounts (50 and 90%). DSC tests have been conducted to determine the temperature range of the recrystallization. It was found that reducing the deformation amount slightly delays the recrystallization. The microstructure of the as-received alloy consists of austenitic grains recognized by the twins they contain. The deformation induced a corrugated microstructure with the presence of ribs. The XRD analysis confirmed that only γ phase peaks were present in the as-received alloy and showed that the deformation induced the extinction of γ phase peaks and the apparition of α phase peaks. Voir les détails

Mots clés : recrystallization, 904L, Cold rolling, DSC

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

Modélisation Numérique du comportement à l’endommagement d’un matériau composite

Hassani Mohamed (En préparation)
Thèse de doctorat

In this thesis, we focused on the development of micromechanical model specific to plain woven composite in order to predict their progressive damage , where the law of material behavior is considered as nonlinear elasto-plastic (this depend on tensile test results) . The first part of the work will be conducted to elaborate plain woven composite specimen and perform tensile test. After that micromechanical model would be developed in order to determine the initial effectives elastic modulus from homogenization techniques, of RVE, which can be used to relate between Mico scale and Macro scale. Subsequently, an incremental formulation of the unit cell  method will be considered taking into account the evolution of plasticity and damage. The implementation of investigated approach will be achieved through finite element code and the validation of the model will be considered in the case of a quasi-static loading. Voir les détails

Mots clés : Woven composite, damage, plasticity

Détermination des contraintes lors de l’interactionfluide Conduite avec prise en compte du phénomène de cavitation.

Hassani Mohamed (2012)
Mémoire de magister

A mathematical model has been developed to calculate the transient flow in elastic pipes. This model takes into account the interaction beetwin structure of the pipe and the fluid behavior and the cavitation phenomenon. When the liquid pressure falls below the vapour pressure, a bubbly cavitation occurs and grows in different location of the pipeline. This cavitation can produce sever damage to structure .the application of mass,momentum and energy conservation laws yields to a system of hyperbolic partial differential equations resolved by a MOC with finite differences scheme. The model is tested with experimental data. Voir les détails

Mots clés : Water hammer, transient flow, Cavitation

VISCOELASTIC EFFECTS IN ELASTIC MODULUS MEASUREMENT USING DEPTH-SENSING INDENTATION

A. Mokhtari, N.Tala-ighil, A. Brick Chaouche, Y. A. MASMOUDI  (2019)
Article de conférence

The nanoindentation test is used to determine the viscoelastic parameters of a thermoplastic polymer at ambient temperature. The aim of the study is to obtain a mean representative value taking into account the influence of the viscosity on the elastic modulus of the poypropylene. For that, Berkovich indenter has been chosen and applied load equal to 100mN. We used poypropylene as a prototype of viscoplastic material, having a creep more important than the others thermoplastic polymers. It was found that, during nanoindentation, the Young's modulus estimated by the Oliver-Pharr method is several times higher than that which is suitable. The Pile-up and viscoelasticity are usually at the cause of this failure and an analysis of their influences is attempted in this work. The loading and unloading curve obtained from FE simulation results by the nanoindentation test is then undertaken to complete the work. The various results have enabled to analyze the influence of viscosity on the elastic modulus of the polypropylene matrix. Voir les détails

Mots clés : thermoplastic polymer, Nanoindentation, constitutive behaviour, Finite Elements