Génie mécanique
Reliability Index of HDPE Pipe Based on Fracture Toughness
his work presents a contribution to evaluate the reliability of a high density polyethylene (HDPE) pipe using the PHIMECA Software. The critical stress intensity factor (KIC) is adopted as a criterion to the maximum limit of a numerically calculated KI. The reliability index β is obtained using failure probability and a mechanical model. It is found that at lower KIC, no safe domain for actual service pressures existed while for moderate and higher values of KIC (above 3.5 MPa.√m); the β design index is reached and even exceeded. In terms of increasing crack length, β decreased systematically for all toughness cases supporting the idea that reliability and fracture toughness designate similar properties for service life or material resistance to cracking. For a KIC=5 MPa.√m, the pipe is considered safe when crack length is below 370μm. Finally, it is shown that SDR basis is a reasonable and conservative design approach for plastic pipes. Voir les détails
Mots clés : HDPE pipe, critical stress intensity factor, crack length, SDR, reliability index, PHIMECA software
Estimated life time in an HDPE pipe with a semi-elliptical defect under internal pressure
High density polyethylene has been widely used in marine and gas transportation, storm sewers, culverts and city drainage system. Compared with other conventional pipes, it has its own advantages, such as, chemical and corrosion resistance, toughness, flexibility, easy splicing and consequent easy handling and installation. In this paper, and in order to predict the remaining lifetime of a pipe having a defect and subjected to internal pressure, it is necessary to estimate KI stress intensity factor during the propagation of the crack. The finite element method is used to assess the values of the stress intensity factor of an axially oriented semi-elliptical crack located at the inner surface of an HDPE pipe. The crack configuration is described by the relative wall thickness (t/R), the relative crack depth (a/t) and the crack aspect ratio (a/c). The lifetimes presented are discussed according to the size of the crack and the stress intensity factor in each case. Voir les détails
Mots clés : HDPE pipe, Crack, rupture, Finite Element Method FEM, stress intensity factor, Lifetime
Engineering modeling of wear profiles in tooth flank of polyamidespur gears
The present paper is a contribution in developing an engineering model expressing the evolution of tooth flank wear in polyamide spur gears as a function of number of cycles. The method is based on first observing the behavior of wear on tooth flanks in real test conditions. Then progressive flank wear profiles are plotted in order to sort out the corresponding fitting curves together with the associated mathematical equations. The general engineering model controlling the evolution of wear profile is found of the form of quadratic equation where the variable is the circular thickness of a tooth at a given depth from the top land of the tooth. The respective parameters of the engineering wear equation are determined as a function of number of revolutions of the spur gear. A wear correction parameter kw is added in order to catch up the measuring errors when plotting the wear profile curves using the proposed engineering wear model for spur gears. The data are in good agreement with that obtained from experimental measurements. Voir les détails
Mots clés : polyamide, Spur gear, wear, Tooth flank, lubrication
Reliability estimation of pressurized API 5L X70 pipeline steel under longitudinal elliptical corrosion defect.
The probabilistic approach is the best way to give realistic answers for design and maintenance and it is considered as a powerful decision-making tool. In the present paper, assessment of the failure probability of corroded pipeline subjected to internal pressure is estimated by using the first order reliability method (FORM). Measurements of defect dimensions have been achieved changed into collected by using ultra sound inspection probe through a 75-km pipeline portion on one of the main Algerian high pressure gas transportation that has been in service for 30 years. The sensitivity analyses have been carried out on random variables to identify the importance of the parameters within the reliability mechanical model. The modified B31G code has been coupled as a mechanical model, with Rackwitz optimization algorithm by using PHIMECA Software. The limit state function resumes the difference between the pipeline burst pressure and the pipeline operating pressure. The aim of the present work is to make in evidence the competitive importance of pressure service, wall thickness and the defect depth with regards to defect length and to determine the influence of the coefficients of variation on the failure probability and the remaining life of the pipeline. A diagram based on the reliability index results is proposed to predict the pipeline degradation and it can be used as a decision tool for maintenance program. Voir les détails
Mots clés : corrosion, Failure probability, Coefficient of variation, Modified ASME B31G
Correlation between defect depth and defect length through a reliability index when evaluating of the remaining life of steel pipeline under corrosion and crack defects.
Despite the various engineering models existing for lifetime investigation of hydrocarbon steel pipelines under localized corrosion and crack defects there is still a lack of information about the correlation between the two main parameters characterizing the geometrical defect model, depth and length. So the aim of the present work is a contribution in evaluating the remaining life of the pipeline using reliability analysis in order to correlate the two parameters through one common parameter, the reliability index. As a first step, the investigation is carried out on four standard and well established engineering models; Irwin, SINTAP, ASME B31G and Modified ASME B31G methods, aiming to coordinate results given by each of the four models. The potential defect depth and length correlation through a reliability index can be used as a decision-making tool to give realistic answers for replacing and/or repairing a tube subjected to internal pressure and on which flaws of different depths and lengths have been detected from inspection of a pipeline after few years of service. Voir les détails
Mots clés : corrosion, Defect, Reliability, Correlation, Sensitivity
Reliability of the High Strength Pipeline Steelunder Corrosion Defect
The demand of energy based on hydrocarbons, such as gas and oil, requires construction of more and more newpipelines. Therefore, the assessment of the remaining life of these pipeline structures became increasingly importantto ensure the continuity of production and distribution operations. The reliability of these industrial facilities islargely conditioned by specific characteristics of each system, by its conditions of use and its environment. Generally,the causes of deterioration of hydrocarbon transportation pipelines are related to the presence of apparent defects(pinholes, cracks, corrosion, etc). This study is aimed to estimate the reliability of pipeline structures. The B31Gmechanical model of degradation was used to assess the probability of failure through dimensions of defects. Voir les détails
Mots clés : Reliability, pipeline, Defects, Mechanical Model
Computational Investigation of Droplets Behaviour inside Passive Microfluidic Oscillator
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).
Modélisation du comportement et de l’endommagement des composites à matrice thermoplastique
Ce travail est dédié à l’étude d’une approche avancée basée sur la modélisation du comportement et de l’endommagement des composites à matrice thermoplastique sous chargement de traction, de cisaillement et de compression. En particulier, nous nous sommes intéressés à l’étude de l’endommagement couplé à la rupture des composites à matrice polypropylène renforcés de tissus en jute. L’augmentation de l’utilisation de ces composites dans l’industrie automobile et de sports requiert le développement de modèles constitutifs fiables pour prédire leurs réponses sous des conditions de chargement complexes. Actuellement, les modèles disponibles n’incluent pas le comportement non-linéarité et les instabilités des structures. Ce travail focalise sur le développement d’un modèle d’endommagement tenant en compte des non-linéarités matérielle et géométrique des ces composites. Ce modèle considère tous les dommages dans le plan : endommagement provoqué par la fissuration de la matrice ainsi que ceux dus à la rupture des tissus en jute dans les directions longitudinale et transversale. L’analyse de la propagation de l’endommagement, basée sur un vaste ensemble des résultats expérimentaux, combine différents modèles de la mécanique de l’endommagement afin de développer un modèle pour ces composites à matrice thermoplastique, dont la réponse des composites est gouvernée par un couplage entre l’endommagement et la rupture. Le modèle développé dépend des seuils d’endommagement, de flambage et de rupture des composites tissés provoqués par l’évolution de l’endommagement. Ce modèle est implémenté dans un logiciel d’élément fini (ABAQUS/Explicit) en utilisant la subroutine VUMAT. Les résultats des simulations présentés dans ce travail démontrent que le modèle développé peut prédire correctement la réponse statique obtenue par les mesures expérimentales. Les résultats des simulations, pour les post-flambages et les grandes déformations sont également bien prédits. Voir les détails
Mots clés : Matrice thermoplastique, endommagement, modelisation
Contribution à l’analyse de l’endommagement des matériauxcomposites
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
MICROGOUTTES : ETUDE DE LA PRODUCTION ET LA MANIPULATION DESMICROGOUTTES DANS LES ECOULEMENTS FLUIDIQUES, DANSLES MICROCANAUX, AUX PROFITS DU GENIE DES PROCEDES
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)