Génie mécanique

Nombre total de résultats : 194
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Identification of the elasto-viscoplastic parameters for a thermoplastic polymer by instrumented indentation

A. Mokhtari, N. TALA IGHIL  (2018)

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


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

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

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)

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


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

Étude expérimentale du délaminageen mode I des tubes fabriquéspar enroulement filamentaire

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

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

Computational study of droplet breakup in a trapped channel configurationusing volume of fluid method

T. CHEKIFI  (2018)

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

Computational Investigation of Droplets Behaviour inside Passive Microfluidic Oscillator

T. CHEKIFI, B. dennai, R. Khelfaoui  (2017)

Recently, modeling immiscible fluids such as oil and water have been a classical research topic. Droplet-based microfluidics presents a unique platform for mixing, reaction, separation, dispersion of drops and many other functions. In this paper, we suggest a numerical CFD study of microfluidic oscillator with two different lengths of feedback loop. In order to produce simultaneous droplets of gasoil on water, a typical geometry that includes double T-junction is connected to the fluidic oscillator. Droplets production is computed by volume-of-fluid method (VOF). Flow oscillations of droplets were triggered by the Coanda effect of jet flow. The aim of work is to get a high oscillation frequency in the output of this passive device, the influence of hydrodynamics and physics parameters on the droplets frequency in the output of our microsystem is also investigated, the computational results show that, the length of feedback loop, operating pressure and interfacial tension have a significant effect on the droplets dynamic inside microfluidic oscillator. Across the range of low Reynold number, the droplets generation and its dynamics have been accurately controlled by adjusting applying pressure ratio of two phases. Voir les détails

Mots clés : Droplet, microfluidics, fluidic oscillator, CFD and VOF (volume of fluid method).


Chekifi Tawfiq (2016)
Thèse de doctorat

Ces travaux de recherche s’inscrivent d’une part dans une thématique demicrofluidique digitale : La microfluidique se propose d’imaginer de nouvelles techniquesadaptées aux microsystèmes et permettent d’attribuer aux microsystèmes des propriétésd’écoulements performantes malgré le caractère fortement laminaire de ces écoulements.Un aperçu général sur la microfluidique de microgoutte est présenté, incluant unaperçu bref des techniques de fabrication et des techniques de conception des microsystèmes.Une partie de notre travail porte sur les travaux antérieurs des écoulements dans les microscanaux. Nous exposons ensuite les détails des simulations numériques (en utilisant le codecommercial, Fluent) concernant l’analyse des micro-écoulements liquides.La génération de microgouttes s’effectue habituellement par agitation mécaniquevigoureuse. Les systèmes microfluidiques offrent une alternative aux systèmes classiques.Pour cela, il existe différentes techniques d’émulsifications microfluidiques.Les microstructures véhiculent localement des quantités beaucoup moins importantes deréactif que les procédés classiques, ils permettent aussi de travailler dans des conditions desécurité quasi maximales mais aussi d’augmenter la sélectivité chimique des réactions.La première technique développée pour générer des gouttes de façon contrôlée enmicrosystème est la jonction-T, Les microgouttes générées nécessitent des techniques demanipulation pour gérer et contrôler ces microgouttes. Dans cette étude, nous avons proposédes géométries à l’objectif de produire et manipuler par voie hydrodynamique lesmicrogouttes. Des résultats importants ont été obtenus dans les deux approches (numérique àl’aide de code commercial Fluent et expérimental à travers les moyens disponibles). Voir les détails

Mots clés : Microfluidique, microcanaux, microgoutte, écoulement dispersé, production des microgouttes, manipulation des microgouttes, simulation CFD (méthode de VOF)

Contribution à l’analyse de l’endommagement des matériauxcomposites

REKBI Fares Mohamed Laid (2016)
Thèse de doctorat

The composite materials with an organic matrix have become a serious competitor to traditional materials in avariety of industrial and domestic areas. However the inter-laminar defects induced during implementation or duringstress are the main sources of its progressive damage. The promotion and use of these materials require the study of themechanical behavior and the various formes of damage. The main of this work is study the mechanical behavior anddamage of tubular composite materials with glass fiber and organic matrix obtained by the filament winding method.The experimental investigation is to cut specimens from composite tube for determination of mechanical tensileproperties and the toughness expressed by the energy release rate of the double cantilever beam specimens atdélamination, and the evolution of resistance with R curves. The aim of numerical study is the modeling of the damagewith element finit method from « ABAQUS » logiciel for determination of the energy release rate. Voir les détails

Mots clés : Composites materials, characterization, damage, fracture, delamination, Cracking