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Laboratoire Energétique Mécanique Electromagnétisme (Nanterre)

Overview
Works: 22 works in 22 publications in 2 languages and 22 library holdings
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Publication Timeline
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Most widely held works by Laboratoire Energétique Mécanique Electromagnétisme (Nanterre)
Modélisation du cycle thermique des moules de fonderie sous pression by Shahab Tavakoli( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

Reducing the weight of vehicles, specially the powertrain Group, contributes to the reduction of the emissions. Today, in order to achieve this objective, the automobile parts conception (Housing gear box, Cylinder block) in lightweight materials such as aluminum and its alloys is increasing. For the mass production, aluminum alloys are formed by a foundry process called ''High Pressure Die Casting''.This process uses the metal molds. Control the thermal behavior of the mold : Heating, intern cooling (by circuit) and extern cooling, is a key point to ensure castings quality and rate of production.In this thesis, the industrial process has been detailed since the mold closing and aluminum melting injection in the die, to the mold opening time and the part (Gearbox RENAULT) ejection. Then, the mold design details, different generation of the cooling systems and the parameters of each step of the manufacturing process taking into account the actual cooling system are presented. The actual cooling systems in the dies are positioned today in empirical way. The ultimate goal of this thesis is to provide the key elements for the cooling system conception from the thermal behavior point of view. For this one, a complete modeling of the phenomena has been realized and validated by 8 thermocouples and the cooling system position has been defined from the thermal equations. The thermal cycle of the die has been optimized and allowed us to reduce and homogenize the temperature fields on the die surface during the production. The rate of production, the castings quality and the lifetime of the die have been consequently increased
Statistical signal processing exploiting low-rank priors with applications to detection in Heterogeneous Environment by Rayen Ben Abdallah( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

In this thesis, we consider first the problem of low dimensional signal subspace estimation in a Bayesian context. We focus on compound Gaussian signals embedded in white Gaussian noise, which is a realistic modeling for various array processing applications. Following the Bayesian framework, we derive algorithms to compute both the maximum a posteriori and the so-called minimum mean square distance estimator, which minimizes the average natural distance between the true range space of interest and its estimate. Such approaches have shown their interests for signal subspace estimation in the small sample support and/or low signal to noise ratio contexts. As a byproduct, we also introduce a generalized version of the complex Bingham Langevin distribution in order to model the prior on the subspace orthonormal basis. Numerical simulations illustrate the performance of the proposed algorithms. Then, a practical example of Bayesian prior design is presented for the purpose of radar detection.Second, we aim to test common properties between low rank structured covariance matrices.Indeed, this hypothesis testing has been shown to be a relevant approach for change and/oranomaly detection in synthetic aperture radar images. While the term similarity usually refersto equality or proportionality, we explore the testing of shared properties in the structure oflow rank plus identity covariance matrices, which are appropriate for radar processing. Specifically,we derive generalized likelihood ratio tests to infer i) on the equality/proportionality ofthe low rank signal component of covariance matrices, and ii) on the equality of the signalsubspace component of covariance matrices. The formulation of the second test involves nontrivialoptimization problems for which we tailor ecient Majorization-Minimization algorithms.Eventually, the proposed detection methods enjoy interesting properties, that are illustrated on simulations and on an application to real data for change detection
Contrôle actif des vibrations de structures élancées FGPM by Jonas Maruani( )

1 edition published in 2019 in French and held by 1 WorldCat member library worldwide

The aim of this thesis is to show the feasibility and the efficiency of active vibration control by structures made of functionally graded piezoelectric materials (FGPM). One bloc structure, made of FGPM, with piezoelectric properties embedded, is used to replace classical intelligent structures (a host structure equipped with piezoelectric patches) and to remove their disadvantages (stresses concentrations near interface, delamination of patches, ...).This study focuses on the FGPM's modelization, in particular on the graded behavior laws and on the development of finite elements of FGPM beams and plates. Two finite element are implemented, a beam element based on Timoshenko's kinematics and a plate element based on an adaptive kinematics. Both elements have a numerical layers approximation for the electrical potential. These two elements are used for active vibration control simulations. In the beam case, the system is governed by a linear quadratic regulator. Otherwise, for the plate a fuzzy decentralized regulator is developed and used. Both systems beam and plate are observed thanks to a Luerberger's observer. Static studies show the behavior of FGPM depending on the material gradation. In addition, active vibration simulations show the feasibility of control with both systems and the ability of fuzzy regulator to accommodate to sudden changes on external perturbations
Contribution à l'étude de la réaction sodium-eau : application à la télédétection de l'hydrogène by Mirjana Milanovic( )

1 edition published in 2020 in French and held by 1 WorldCat member library worldwide

The common thread of this work has been the safety problems of energy installations, whether they are nuclear, such as the fast neutron channel that uses sodium as a heat transfer fluid, or for hydrogen as a storage medium for renewable energies. An experimental and modelling study undertaken with CEA Cadarache first focused on understanding the poorly understood mechanism of the sodium-water reaction based on the determination of temperature and concentration fields in the immersion of a sodium ball in a volume of water. We have shown that the reaction kinetics characterized by a fairly long latency time, which we have modeled, progresses like the vapour pressure of solid and then liquid sodium until it reaches 250°C, where disintegration occurs and then the explosion, which may be of the Coulomb type. The temperature of the effluent then peaks at 1400°C. In a second part we used the developments we had previously made in the remote sensing of hydrogen by the Raman effect. The remote detection of this odorless and colorless gas is one of the conditions for the development of hydrogen, the "fuel of the future". With the picosecond laser used, and although the Raman effect is particularly weak, we can determine the concentration of a leak and also what is original the temperature of a flame at distances up to a hundred meters
Study of the electromagnetic interactions between radar equipment under integrated and compact mature : design and validation by Thtreswar Beeharry( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Metamaterials (MM) are artificially engineered sub wavelength materials that can provide exceptional electromagnetic properties. Their electromagnetic properties can be changed by changing their shapes. They have been used for the design of antennas, Radar Absorbers (RA), cloak devices and so on. In the aim of reducing electromagnetic interference in radomes of military vessels, in this thesis we have used Frequency Selective Surfaces, which are a family of MM, to design thin and broadband RA for the 1-10 GHz frequency band. The RA designed in this thesis have been studied for different polarizations (TE and TM) and for different incidence angles. The Radar Cross Section (RCS) of the developed RA have also been studied. These RA have been fabricated and an excellent agreement have been found between measured and simulated absorption results. In order to improve the cross-polarization absorption of our RA, a 'chessboard' configuration of the full structures have been proposed and studied. Furthermore, the theoretical to real thickness ratio of developed RA have been calculated and results suggest that their performances are high. Also, a theoretical study has enabled us to design conformal RA for cylindrical metallic bodies. These RA are in fact sectors of dielectrics conformed around the cylindrical target. It has been shown that the total scattering and shadow zones of cylindrical metallic bodies can be reduced. The fabrication, characterization and measurement of this concept will be a remarkable result of this thesis
Analyse entropique et exergétique des systèmes énergétiques par des représentations géométriques by Yvain Canivet( )

1 edition published in 2017 in French and held by 1 WorldCat member library worldwide

À l'heure de la prise de conscience de la finitude des ressources et du besoin grandissant d'énergie, la notion de développement durable doit prendre une place centrale dans l'évolution de la société. Pour atteindre ce but, il est maintenant reconnu, qu'un changement de consommation profond est nécessaire ; et ce, qu'il s'agisse de consommation énergétique, alimentaire ou de produits finis. Nous croyons que ce changement de paradigme n'est possible que si tous les acteurs avancent de concerts sur les différentes problématiques auxquelles nous sommes confrontées. Chacun à son échelle doit ainsi pouvoir prendre les décisions qui s'imposent à tous. C'est la logique qui a motivé l'outil d'exergo-graphie présenté dans le chapitre 3. Inscrit dans la lignée des diagrammes de Sankey, il permet de représenter les bilans exergétiques sous forme graphique afin d'en communiquer plus facilement les enseignements. Nous l'appliquons à deux cas d'analyses faites sur les installations de chauffage et de production d'ECS du bâtiment A de l'UPN. Pour chacune, nous étudions la possibilité d'une solution de production durable de la chaleur (PAC géothermique et solaire thermique). Après en avoir présenté les analyses, nous en dressons les représentations graphiques que nous comparons à celles du système actuel. Au préalable, le chapitre 1 introduit les concepts de base de l'analyse exergétique, approfondis dans le chapitre 2, au travers d'une modélisation des systèmes fluides statiques et dynamiques. Finalement, dans le chapitre 4, nous introduisons un modèle-jouet qui, proposant une représentation fractale de la chaleur, tente d'établir un lien conceptuel entre le comportement microscopique, statistique, du support de la chaleur, et les observables macroscopiques qui la caractérisent
Smart control of a soft robotic hand prosthesis by Astrid Rubiano Fonseca( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

The target of this thesis disertation is to develop a new Smart control of a soft robotic hand prosthesis for the soft robotic hand prosthesis called ProMain Hand, which is characterized by:(i) flexible interaction with grasped object, (ii) and friendly-intuitive interaction between human and robot hand. Flexible interaction results from the synergies between rigid bodies and soft bodies, and actuation mechanism. The ProMain hand has three fingers, each one is equipped with three phalanges: proximal, medial and distal. The proximal and medial are built with rigid bodies,and the distal is fabricated using a deformable material. The soft distal phalange has a new smart force sensor, which was created with the aim to detect contact and force in the fingertip, facilitating the control of the hand. The friendly intuitive human-hand interaction is developed to facilitate the hand utilization. The human-hand interaction is driven by a controller that uses the superficial electromyographic signals measured in the forearm employing a wearable device. The wearable device called MyoArmband is placed around the forearm near the elbow joint. Based on the signals transmitted by the wearable device, the beginning of the movement is automatically detected, analyzing entropy behavior of the EMG signals through artificial intelligence. Then, three selected grasping gesture are recognized with the following methodology: (i) learning patients entropy patterns from electromyographic signals captured during the execution of selected grasping gesture, (ii) performing a support vector machine classifier, using raw entropy data extracted in real time from electromyographic signals
Thermodynamic characterization of gas-aluminium deflagration products by Marie Dabos( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

The thermochemical models used today are capable of restituting experimental data of the states of stationary detonations and explosions in closed volume for CxHyOzNtAlu compositions, with a deviation from experiment of a few percent. The validation work has not yet been carried out on explosives containing aluminum particles, which oxidize in the detonation products. The thesis project is part of the development of the thermochemistry code SIAME (Aero-Thermochemical Simulation of Explosive Mechanics), for the benefit of the French General Directorate of Armaments. The objective is to study the thermochemical states of the alumina produced during the deflagration of gas-aluminium particles mixtures, in order to compare them with SIAME. It is then necessary to determine the temperature, pressure and volume fraction of alumina produced by combustion of aluminum particles for different mixtures. The different thermodynamic properties are determined by spectroscopy and by the measurements of a piezoelectric sensor. The work was focused on the improvement of an experimental setup developed at the Laboratory of Energetics, Mechanics and Electromagnetism (Paris Nanterre University), in order to conduct measurements during a deflagration. The analysis provided a better understanding of the physical phenomena involved during the deflagration and during the cooling phase, which is necessary to correctly evaluate the measured radiations for the study of alumina. After a study of the possible spectral zones to characterize alumina, an experimental campaign was conducted. The results are evaluated to determine the state of alumina from the measured radiation, by using an inversion model
Applications of Stirling engine in sustainable development : context-experimental and numerical study by Ruijie Li( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

In this work a solar powered low temperature difference Gamma type Stirling engine has been studied experimentally and numerically using an isothermal model coupled with various losses and using an objective optimization. A new model named Polytropic Stirling Model with Losses (PSML) has been proposed which was applied to the Beta type GPU-3 Stirling engine. An Alpha type integral Stirling cryocooler has been studied numerically using an isothermal model with losses. To study a Gamma type Stirling engine of our laboratory, an isothermal model coupled with finite speed method has been developed, including mass and energy balances through different spaces of the engine. The engine is divided into 3 volumes: compression volume, regeneration volume, and expansion volume. Different kind of thermal and mechanical losses have been considered in the model, in order to analyze thermodynamic processes and losses in the Stirling Engine. In addition, parameter effects on the performance of the solar powered gamma type Stirling engine have also been studied experimentally and numerically. The comparison between the experimental results and the simulation results at different phase shift between the displacer and the piston, and at different piston stroke shows that the model is convincing to predict the Stirling engine performance. Based on the Finite Physical Dimensional Thermodynamic method, a multi-objective genetic method considering output power, thermal efficiency and entropy generating rate as objective functions simultaneously, has been used to multi-objective optimize the Gamma type Stirling engine. Comparing with the ecological optimization method, the multi-objective method can better balance the three objective goals. The new model (PSML) proposed in the thesis for predicting performance of Beta or Gamma type of Stirling engine divides the working space into 5 parts (compression volume, cooler, regenerator, heater, and expansion volume). A bypass linking compression volume and expansion volume has been added in the classic adiabatic model of Stirling engine. Thus, polytropic processes have been considered in the compression and expansion volumes of the Stirling engine. The GPU-3 Stirling engine has been used to validate the new model. It was shown that the new model (PSML) predict well the output power and the thermal efficiency of the engine well. An isothermal model considering various losses was developed and presented in the last part of this thesis to study an Alpha type Stirling cryocooler, whose geometrical dimensions were measured in our laboratory. The compression and expansion volumes are supposed to be isothermal, the variation of the regenerator temperature is supposed to be linear. Energy and exergy balances of the cryocooler were developed. The effect of various parameters on the cryocooler performance (cooling power and input power) are investigated. The simulation results for PPG-102 Stirling cryocooler were compared with two other simulation results of the literature and with experimental results which indicated that this model is convincing to predict the performance of the Stirling cyocooler
Marges de conception : méthodologie de pilotage pour la justification d'ouvrages parasismiques complexes by Laurent Cadet( )

1 edition published in 2020 in French and held by 1 WorldCat member library worldwide

En matière de construction d'ouvrages parasismiques, des normes et des lois ont été mises en place afin de définir des niveaux minimums de protection.Pour autant, pour des ouvrages de catégorie d'importance élevée ou à risques spéciaux, la gestion des risques des projets peut conduire les maîtres d'ouvrages à vouloir couvrir une part de risque plus importante que ces minima réglementaires. D'autant plus qu'il est plus onéreux et plus contraignant de renforcer un ouvrage en exploitation que de le surdimensionner à sa construction. Dans ce cas, le concepteur doit alors réaliser un dimensionnement plus sévère que la réglementation applicable. Toutefois, la mise en place de ces marges ne doit pas conduire à une infaisabilité pour des raisons techniques, économiques ou calendaires.Cette thèse propose une méthodologie de choix et de gestion de ces marges au cours des différentes phases de conception. Elle s'adresse autant aux concepteurs qui doivent disposer d'outils pour retenir des hypothèses de conception raisonnées qu'aux décideurs doivent justifier du financement de ces marges et démontrer le niveau de prise en compte du risque sismique
Entropie d'échelle et statistiques intermittentes appliquées aux écosystèmes by Walid Tarraf( )

1 edition published in 2021 in French and held by 1 WorldCat member library worldwide

La biodiversité est un des enjeux internationaux qui répond explicitement à la notion du développement durable. C'est un intérêt explicite pour les besoins humains qui constitue des ressources naturelles vivantes se trouvant dans la nature. La biodiversité dans son concept fondamental est introduite par l'étude de la distribution spatiale des espèces et plus précisément la relation bien connue zone-espèces (Species Area Relationship ; SAR). La connaissance de la loi zones-espèces qui gère véritablement le phénomène de distribution spatiale des espèces nous permet de prédire la réponse de la biodiversité aux changements environnementaux à différentes échelles et d'évaluer les options politiques de conservation globale de la biodiversité. En effet, dans le cadre de cette thèse, nous proposons une nouvelle approche du phénomène de distribution spatiale des espèces et des individus en utilisant les mêmes outils et propriétés physiques que pour traiter la dynamique statistique et géométrique caractérisant le phénomène de turbulence développée. Dans ce sens, nous avons adopté la dynamique de peaux entropiques P.E décrivant le phénomène d'intermittence en turbulence. ce modèle a été appliqué sur des données expérimentales de distributions spatiales d'espèces en utilisant une géométrie simulant la distribution des individus sous une forme se rapprochant de la géométrie du Cantor à deux dimensions. Les résultats montrent que la répartition des espèces et des individus est bien décrite par le modèle des P.E. Ces deux distributions spatiales montrent une dynamique intermittente possédant une hiérarchie de peaux entropiques qui s'étend entre, un corps fractal parabolique et une crête fractale pure. On voit ainsi que les statistiques d'intermittence peuvent se produire dans des phénomènes autres que la turbulence
Prise en compte de la liaison acier béton dans le comportement d'éléments de structure en béton armé by Can Turgut( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Le comportement de l'interface acier-béton a une grande importance lorsque la fissuration des structures en béton armé est étudiée. Une approche par éléments finis a été proposée par (Torre-Casanova, 2013) et (Mang, 2016) pour représenter l'interface acier-béton dans les simulations de structures à grandes dimensions Le modèle proposé permet de calculer le glissement tangentiel entre l'acier et le béton. L'objectif de cette étude est d'améliorer ce modèle initial pour le rendre plus efficace et plus représentatif. Le document est découpé en trois parties : 1) Le modèle initial de liaison est évalué. Puis amélioré tant en chargement monotone qu'alterné. Le nouveau modèle est validé par plusieurs applications numériques. 2) L'effet de confinement est implémenté dans le modèle de liaison acier-béton. L'effet sur le comportement structural du confinement actif est étudié en utilisant le nouveau modèle. A partir des simulations proposées, il est montré, par l'utilisation du nouveau modèle, que l'effet de confinement actif peut jouer un rôle sur les comportements monotone que cyclique. 3) L'effet goujon est étudié avec le nouveau modèle liaison acier-béton. Deux campagnes expérimentales différentes sont simulées avec différents modelés de renforts (1D barre et poutre) et d'interface (liaison acier-béton et liaison parfaite). Les résultats montrent que le nouveau modèle de liaison acier-béton permet de mieux reproduire les résultats expérimentaux par rapport au modèle de liaison parfaite aux échelles globale et locale
Étude des phénomènes thermiques associés à des sollicitations mécaniques à grande vitesse by Romain Pawelko( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

When a material is subjected to a mechanical loading, part of the energy will be transformed into thermal energy and another part will be stored inside the material énergy of cold work). In the case of a dynamic loading, a localization phenomenon may occur accompanied by a significant rise in temperature which can locally reach values close to the melting point of the material. This phenomenon called adiabatic shear has many applications: high-speed machining, ballistics, cold-spray , blanking... The emitted thermal energy is an observable value which has been used in the past years in order to better understand the failure mechanisms. We have developed a device able to measure the temperature in the shear bands. The combined use of a short-wavelength streak camera and a 32- infrared detectors array allows us to limit uncertainties. An inversion program has also been developed to identify the thermal source term. Temperature measurements were also performed on composite energetic materials to better understand the reaction mechanisms
Développement d'une machine de fatigue gigacyclique en torsion pour les matériaux métalliques à haute résistance by Zhaoyi Jiang( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

This research work concerns the study of the torsional ultrasonic fatigue system of indirect type which is able to study the behavior of high-strength metallic materials, mainly in the domain of gigacyclic fatigue. With the developments of technique, there are currently two types of ultrasonic torsional system: the first one is described as "direct" and its converter delivers a rotation which allows the system vibrate in torsion; the second one is described as "indirect", which uses a longitudinal converter and requires the transformation of a translation into a rotation to create a desired torsional resonant vibration in the specimen. Firstly, the study of the indirect system could understand the fatigue behavior and the properties of this system. This study is presented with the analytical and numerical calculations in order to determine and model the indirect system. Then, the optimization of this system by using the finite element method is performed and a more efficient and robust system is developed. Some comparisons between the numerical results and calibration's results are proposed and an interpretation of differences is proposed by using new numerical simulations. Secondly, the tests of the 16MnCr5 and 50CrV4 steels of the FreqTigue project are carried out at 20 kHz and beyond 10⁸ cycles by using this optimized system. The staircase method is used in the tests to describe the S-N curve, to estimate the fatigue strength and to obtain the fatigue life. Then, the comparisons of the S-N curves at different vibration frequencies and stresses are presented, and the ruptured surfaces of the specimen are also analyzed to identify the causes of the rupture
Robust variable kinematics plate finite elements for composite structures by Thi Huyen Cham Le( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Le but de ce travail est de développer deux nouveaux éléments finis quadrilatéraux à quatre et à huit nœuds implantés dans le code commercial de calcul par Eléments Finis (EF) Abaqus pour plaques composites. Les modèles plaques à cinématique variable sont formulés dans le cadre de la formulation unifiée de Carrera (CUF), qui regroupent des descriptions de type: couche équivalente (ESL) et couches discrètes (LW), avec les variables définies par des polynômes jusqu'au 4ème ordre suivant épaisseur z. Les deux formulations variationnelles sont utilisées pour dériver les matrices des éléments finis: le Principe des Déplacements Virtuels (PVD) et le Théorème Variationnel Mixte de Reissner (RMVT). Grâce à la technique de condensation statique, une formulation hybride basée sur le RMVT est introduite. Afin d'éliminer la pathologie de verrouillage en cisaillement transverse, deux approximations compatibles pour le champ de déformations de cisaillement transverse indépendantes en z, notée QC4 et CL8, sont étendues aux éléments plaques à cinématique variable basés sur CUF. De plus, les QC4S et CL8S interpolations sont également introduites pour les contraintes de cisaillement transverse dans les éléments mixtes et les éléments hybrides. Les résultats numériques comparés à ceux disponibles dans la littérature montrent que les FE proposés sont efficaces pour modéliser des éléments finis robustes
Development of an artificial muscle for a soft robotic hand prosthesis by José Luis Ramirez Arias( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

Le thème central de cette thèse est la conception d'actionneurs doux à partir de matériaux intelligents et d'une prothèse de main robotique souple. Notre approche prends en compte les différents points qui peuvent influer sur le développement d'une stratégie d'actionnement ou d'un muscle artificiel : i) Les mécanismes et la fonctionnalité de la main humaine afin d'identifier les exigences fonctionnelles pour une prothèse de main robotique en matière de préhension. ii) L'analyse et l'amélioration des mécanismes de la main robotique pour intégrer un comportement souple dans la prothèse. iii) L'évaluation expérimentale de la prothèse de main robotique afin d'identifier les spécifications du système d'actionnement nécessaire au fonctionnement cinématique et dynamique du robot. iv) Le développement et la modélisation d'une stratégie d'actionnement utilisant des matériaux intelligents.Ces points sont abordés successivement dans les 4 chapitres de cette thèse1. Analyse du mouvement de la main humaine pour l'identification des exigences technologiques pour la prothèse de main robotique.2. Conception et modélisation de la prothèse de main robotique à comportement souple.3. Evaluation mécatronique de la prothèse de main.4. Conception d'un muscle artificiel basé sur des matériaux intelligents
Influence de la fréquence de chargement sur la résistance à l'amorçage et la croissance des fissures de fatigue dans des aciers utilisés dans des applications mécaniques exigeantes by Mohand Ouramdane Ouarabi( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

Les essais de fatigue peuvent être effectués dans une gamme de fréquences similaire, mais les fréquences les plus élevés sont généralement préférables afin de réduire le temps de test et d'obtenir des résultats dans une période raisonnable. La question reste à savoir si un effet de fréquence existe. Cette étude traite de l'effet de la fréquence de chargement sur la résistance à l'amorçage et à la propagation des fissures sur 3 matériaux (M800HY, CP1000 et DP1180) utilisés dans le domaine automobile. Deux rapports de charge (R=-1 et 0.1) et cinq fréquences de chargement (25 Hz, 30 Hz, 150 Hz et 20 kHz) ont été étudiés. Tout d'abord, nous avons réalisé des calculs par élément finis en dynamique pour dimensionner les éprouvettes et calculer l'étendue du facteur d'intensité de contrainte durant la propagation de la fissure de fatigue. Ensuite, nous avons réalisé des essais d'amorçage et de propagation. Indépendamment de la fréquence de chargement,l'amorçage de la fissure de fatigue est toujours surfacique à cause des concentrations de contraintes dues au processus de laminage ou de l'électro-galvanisation. L'observation des faciès de rupture sur éprouvettes testées à 30 Hz et 20 kHz montre que le mode de propagation est transgranulaire avec quelques localisations de rupture intergranulaire ou par clivage sur la nuance DP1180. Les stries de propagations sont présentes sur les faciès d'éprouvettes M800HY et absentes sur les faciès des deux autres nuances. La nuance DP1180 présente une meilleure résistance à l'amorçage et à la propagation de la fissure de fatigue. Concernant l'effet de la fréquence de chargement, globalement l'amorçage de la fissure de fatigue est dépendante de la fréquence de chargement, par contre, la propagation est indépendante de la fréquence
Un modèle d'évaluation de la vulnérabilité sismique du bâti existant selon l'Eurocode : essai méthodologique et application sur un territoire by Jean Lemaire( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

The seismic risk is a subject of multidisciplinary study which is the object of numerous research works. For a long time, it was studied in terms of hazard and it is only in the middle of the 20th century that we became interested in the vulnerability of the exposed elements. In spite of the multiplicity of the studies on the seismic risk, none of them adopts a global approach by using the earthquake-resistant regulations. Within the framework of thesis, we support the hypothesis that it possible to estimate the vulnerability of dwellings on the scale of several buildings by using the European standard, Eurocode 8. Using these regulations has the advantage reducing the time to study physical vulnerability by assessing the seismic resistance of a single building, where the latter represents a population of several buildings used as collective dwellings. The proposed methodology, illustrated on the example of the Mulhouse-Basel conurbation, consists of two phases. The first one consists in studying the seismic hazard of the urban area of Mulhouse and Basel through the bibliographical studies of some authors. This phase also consists in examining the compatibility of the European and Helvetian seismic regulations. Finally, a diagnosis of the existing structures and of the population is made to assess the vulnerability of these two urban territories, after a division of both cities into historic-geographical sectors. A second phase consists in proposing a simplified model of deterministic and probabilistic assessment of the vulnerability of the built, based on the new European regulation and the mechanics of the structures, to evaluate the seismic resistance of buildings. The probability aspect allowed to refine the proposed model to integrate certain uncertainties. A case study feigning an important earthquake of magnitude Mw equal to 6 on the Richter scale, integrating the phenomena of site effects as recommended by Eurocode 8, validated the application of the envisaged model. The proposed evaluation model is intended to provide a tool for assessing the vulnerability of the built without performing mechanical calculations. Thus, it aims to be accessible to all (geographers, engineers, seismologists, etc...). More generally, this model aims to provide a decision-making tool in the approach of prevention which the public authorities owe to the population, because they allow to determine the more or less big vulnerability of the studied areas
Ultrasonic fatigue study of Inconel 718 by Mengxiong Zhao( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

L'Inconel 718 est utilisé dans les disques de turbine des moteurs d'avion, de par sa haute résistance à la corrosion, à l'oxydation, au fluage et sa haute résistance mécanique à très haute température. Le nombre total de cycles de ces composants mécaniques s'élève à 109~1010 durant sa vie. Ils subissent des chargements de grande amplitude à faible fréquence, comme les forces centrifuges ou les contraintes thermiques mais aussi des chargements de faibles amplitudes à très haute fréquence, du aux vibrations des pales. Dans ce travail, on se propose d'étudier la fatigue à très grand nombre de cycles (VHCF) de l'Inconel 718 en utilisant des machines de fatigue ultrasonique, fonctionnant à 20KHz. Le système d'acquisition utilise des cartes NI et le logiciel LabView pour superviser la fréquence, la température, les déplacements durant toute la durée des tests. Des capteurs laser Keyence utilisant deux sondes pour les faces supérieure et inférieure de l'éprouvette permettent de capturer la fréquence et les modes de vibration. La différence entre les valeurs moyennes mesurées permet d'accéder à l'allongement de l'éprouvette, dû à l'auto-échauffement.3 types de matériaux avec différents traitements thermiques, AR, DA et DAHQ de l'ONERA et SAFRAN sont comparés. La différence au niveau de la taille de grain, de la phase, des précipités, ... est analysée par micrographie métallographique en utilisant un microscope optique (MO) et un microscope électronique à balayage (MEB). Le comportement en traction quasi-statique et sous chargement cyclique contrainte-déformation est aussi proposé. La transition entre durcissement et adoucissement cyclique apparait à l'issue du traitement thermique. Finalement, les surfaces de ruptures sont observées en utilisant des caméras optiques et un MEB afin d'identifier les mécanismes de ruptures de l'Inconel 718 dans le domaine de la fatigue à très grand nombre de cycles
Thermomechanical study of the gigacycle fatigue behavior of pure iron and carbon-manganese steels : influence of chemical composition and microstructure on damage and crack initiation mechanism by Xiaoxue Pu( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

This work attempts to a better understanding of the fatigue damage in ferrite-pearlite steels in the Very High Cycle Fatigue (VHCF) domain. The influences of two parameters, pearlite phase percentage and free interstitial atoms percentage in solid solution, are investigated to understand dissipative mechanisms under 20 kHz high frequency fatigue loading. In-situ infrared thermography is carried out to record the temperature changes, while fractography studies and microscope observations are conducted to investigate the dissipative mechanism on the surface of specimens.For body centered cubic (BCC) materials, under high stress amplitudes, a sudden increase of the temperature occurs without a crack initiation and fracture. The inevitable temperature increase up to hundreds of degrees at high stress amplitudes, is caused mainly by the screw dislocations mobility, which is the key to explaining the observed fatigue behavior and thermal response of BCC structure under high frequency loading. Therefore, PSBs on surface and micro-voids in matrix emerge massively, accompanying with this abrupt temperature increase. These phenomena are considered as transition of deformation mechanism from thermal regime to athermal regime. At low amplitudes, few PSBs or surface roughness are still observed on the specimen surface. Through the cycles of PSB appearance on armco-iron, it's found that PSBs are inclined to appear before 1x10(7)cycles, and PSB threshold lies below the conventional fatigue limit. The increase of pearlite phase content weakens the temperature elevation, and strengthens the fatigue properties. The presence of free interstitial atoms in steels results in appearence of a secondary temperature increase in the stabilized temperature part (100-200 degree). This behavior seems to be related to the interaction of edge dislocations with free interstitial atoms. Moreover, the remarkable hardening-softening-hardening phenomenon after the sudden temperature elevation to above 300 degree is thought as the interaction of multiplicated screw dislocations and free interstitial atoms
 
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Laboratoire énergétique mécanique électromagnétisme (EA 4416)

LEME (Nanterre)

Université Paris Nanterre . Laboratoire Energétique Mécanique Electromagnétisme

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