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Tomasini, Mireille. "Instabilités engendrées par un fort cisaillement de vitesse dans un fluide compressible". Toulouse 3, 1996. http://www.theses.fr/1996TOU30066.
Pełny tekst źródłaBoutareaud, Sébastien. "MECANISMES D'AFFAIBLISSEMENT À VITESSE DE CISAILLEMENT ELEVEE: EXEMPLES DE MODELES ANALOGUES ET NUMERIQUES". Phd thesis, Université de Franche-Comté, 2007. http://tel.archives-ouvertes.fr/tel-00263691.
Pełny tekst źródłaLes propriétés hydrologiques et poro-élastiques de la gouge et de la brèche de la faille d'Usukidani ont été determinées à partir d'échantillons prélevés sur le terrain. Ces données hydrauliques ont ensuite été utilisées dans un modèle numérique afin d'évaluer l'importance du phénomène de pressurisation thermique dans le cas d'un glissement cosismique le long de la zone de glissement principale et le long de zones de glissement secondaires. Les résultats de cette modélisation suggèrent que le mécanisme de pressurisation thermique n'est efficace que si la rupture reste localisée le long des zones de glissement contenant de la gouge, avec comme facteur de contrôle l'épaisseur de cette zone de glissement.
Afin d'identifier les processus dynamiques particulaires responsables de l'affaiblissement cosismique dans la zone de glissement, plusieurs essais de friction ont été menés sur une machine à cisaillement annulaire. Ces expériences ont été conduites à des vitesses cosismiques (équivalentes à 0,09, 0,9 et 1,3 m/s) en conditions humides ou conditions sèches. Les données obtenues montrent que quelles que soient les conditions d'humidité initiales, les failles simulées montrent toutes un affaiblissement lors du déplacement. Un examen détaillé des microstructures des gouges cisaillées obtenues une fois l'équilibre frictionnel atteint permet de définir deux types de microstructures impliquant deux régimes de déformation : un régime de déformation par roulement avec la formation d'agrégats argileux, et un régime de déformation par glissement avec la formation d'une zone de cisaillement complexe localisée à l'interface gouge-éponte. L'affaiblissement observé lors des expériences semble être lié à une diminution de la proportion de grains roulants par rapport à celle de grains glissants, et semble être favorisé par le développement des agrégats argileux, lesquels sont contrôlés par la teneur en eau.
A partir d'un modèle numérique (P2 FEM) et des données de contrainte cisaillante obtenues lors des essais de friction, il a été possible de calculer l'évolution de la température de la gouge en fonction du déplacement. Les résultats suggèrent que la distance dc pourrait représenter la distance nécessaire à une faille pour produire et diffuser assez de chaleur afin de casser les ponts d'eau capillaire (forces d'adhésion) et ainsi permettre à l'eau contenue dans la gouge d'être libérée. Ce mécanisme est appelé mécanisme d'affaiblissement par drainage.
Ethier, Yannic A. "La mesure en laboratoire de la vitesse de propagation des ondes de cisaillement". Thèse, Université de Sherbrooke, 2009. http://savoirs.usherbrooke.ca/handle/11143/1929.
Pełny tekst źródłaChallouf, Walid. "Caractérisation des sols granulaires au moyen de la vitesse des ondes de cisaillement". Mémoire, Université de Sherbrooke, 2009. http://savoirs.usherbrooke.ca/handle/11143/1485.
Pełny tekst źródłaLIU, ZENG-GANG. "Comportement et modelisation des materiaux composites carbone/epoxyde en cisaillement a grande vitesse". Nantes, 1987. http://www.theses.fr/1987NANT2011.
Pełny tekst źródłaLiu, Zeng Gang. "Comportement et modélisation des matériaux composites carbone/époxyde en cisaillement à grande vitesse". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37607504t.
Pełny tekst źródłaJrad, Mohamad. "Modélisation du perçage à grande vitesse : approches analytique, numérique et expérimentale". Thesis, Metz, 2007. http://www.theses.fr/2007METZ037S/document.
Pełny tekst źródłaThe determination of the cutting forces generated during the drilling operation is an essential step in the drilling optimisation. This information is crucial for the cutting conditions determination and the tool definition. The aim of this work is to propose a predictive thermo mechanical model for the drilling process. This model is based ont the thermo mechanical oblique cutting model developed and validated in the LPMM laboratory. The parameters used in this model are the cutting angles, the cutting conditions, the behaviour of the workpiece materials and the friction conditions on tool-chip interface. After the determination of the cutting angles from the CAD definition of the drill using a mathematical geometrical model developed in this work, the cutting edges are decomposed into a series of linear oblique cutting edges. A modified version of the thermo mechanical model is then apllied on each elemental cutting edge in order to calculate the elemental cutting forces, and then the global thrust and torque are determined. Experimental dry drilling tests were performed in order to validate the presented model. The calculated and measured global torque and thrust were compared, a good agreement was obtained. In the last section a numerical model using the finite element method with two commercial codes are presented. 2D orthogonal cutting and 3D drilling simulations were carried out. Numerical simulation provides interesting information on the chip formation and on the temperature and stress distributions but the calculations are time consuming. The two proposed methods may be used as complementary approaches to optimize cutting conditions and drill geometry
Tchabat, Tcheutchoum Harlette. "Influence de la granulométrie sur la vitesse des ondes de cisaillement des sols granulaires". Mémoire, Université de Sherbrooke, 2011. http://savoirs.usherbrooke.ca/handle/11143/1613.
Pełny tekst źródłaGaudillière, Camille. "Cisaillage à grande vitesse : des essais à la simulation". Paris, ENSAM, 2011. http://www.theses.fr/2011ENAM0052.
Pełny tekst źródłaTo increase their productivity, blanking professionals are interested by an emerging process: the high speed blanking. For this process, the punch speed reaches10m/s whereas this speed does not exceed 0,1m/s for conventional blanking process. However, even if the quality of the obtained surfaces is close to those obtained with fine blanking, the occurence of hard dynamic phenomena makes difficult the deployment of the high speed blanking process. This work proposes to better control this process using experimentations and numerical simulations. An instrumented device has been designed to observe in detail the existing phenomenon during cutting. This device is similar to the industrial one. It includes a punch with non-constant sections and a matrix linked to an Hopkinson's tube in order to measure the blanking cutting forces. This measure requires a specific treatment to correct dynamic effects present in the matrix during the cutting. This treatment, which uses a calibration of the device, was validated thanks to a one-dimensional numerical model. Many observations made on the blanked surfaces have shown that adiabatic shear bands (ASB) can take place. A thermo-mechanical constitutive model (Johnson-Cook's law) of the C40 steel has been identified and used into simulations to reproduce real experimentations. The used simulation is based on a C-NEM approach (Constrained Natural Element Method). A comparative study between simulation and experimental results has been done. Results show a good correlation with experimental tests
Dolléans, Pascal. "Etude expérimentale d'écoulements de fluides viscoélastiques dans une conduite présentant une distribution périodique de brusques variations de section". Poitiers, 1996. http://www.theses.fr/1996POIT2307.
Pełny tekst źródłaAchor, Zyad Khalid. "Étude du comportement élastoviscoplastique d'un polycarbonate à grande vitesse de déformation : simulation numérique du cisaillement adiabatique". Metz, 1999. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1999/Achor_Zyad.Khalid.SMZ9932.pdf.
Pełny tekst źródłaAchor, Zyad Khalid KLEPACZKO JANUS. "ETUDE DU COMPORTEMENT ELASTOVISCOPLASTIQUE D'UN POLYCARBONATE A GRANDE VITESSE DE DEFORMATION - SIMULATION NUMERIQUE DU CISAILLEMENT ADIABATIQUE /". [S.l.] : [s.n.], 1999. ftp://ftp.scd.univ-metz.fr/pub/Theses/1999/Achor_Zyad.Khalid.SMZ9932.pdf.
Pełny tekst źródłaBen, Romdhane Mohamed. "Étude de l'influence de la granulométrie sur la vitesse des ondes de cisaillement dans les milieux granulaires". Mémoire, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/7711.
Pełny tekst źródłaRanc, Nicolas. "Etude des champs de température et de déformation dans les matériaux métalliques sollicités à grande vitesse de déformation". Paris 10, 2004. http://www.theses.fr/2004PA100135.
Pełny tekst źródłaPawelko, Romain. "Étude des phénomènes thermiques associés à des sollicitations mécaniques à grande vitesse". Thesis, Paris 10, 2018. http://www.theses.fr/2018PA100058/document.
Pełny tekst źródłaWhen 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
Bouassida, Wafi. "Conception des fondations superficielles reposant sur des sols granulaires en utilisant la vitesse des ondes de cisaillement". Mémoire, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/7708.
Pełny tekst źródłaStopin, Alexandre. "Détermination de modèle de vitesse anisotrope par tomographie de réflexion des modes de compression et de cisaillement". Université Louis Pasteur (Strasbourg) (1971-2008), 2001. http://www.theses.fr/2001STR13203.
Pełny tekst źródłaBouette, Bruno. "Propriétés en cisaillement interlaminaire de composites à fibres de carbone et matrice organique : Influence de la vitesse de sollicitation". Besançon, 1991. http://www.theses.fr/1991BESA2019.
Pełny tekst źródłaValli, Franck. "Décrochement lithosphériques dans l'ouest du plateau du Tibet : géométrie, âge, décalages cumulés et vitesse de glissement long-terme sur la Faille du Karakorum". Paris, Institut de physique du globe, 2005. http://www.theses.fr/2005GLOB0005.
Pełny tekst źródłaFaye, El Alioune. "Cisaillement pariétal et tourbillons en écoulement Taylor-Couette". Thesis, La Rochelle, 2013. http://www.theses.fr/2013LAROS393.
Pełny tekst źródłaThis work is an experimental study to highlight general mapping of the set of states obtained from the Couette laminar flow to turbulence. All experiments were performed in a device called Taylor-Couette system (TCS) which consists of two concentric cylinders with the inner cylinder rotating. The flow regimes (SPI, TVF, WVF, MWVF, TTVF), which depend mainly on the Taylor number (Ta), were obtained with or without axial flow in the TCS according to well-defined experimental protocols. We noted that the axial Reynolds number (Reax) has astabilizing effect on the flow. Using electrodiffusion method and analysis of films, the toroidal Taylor vortices, wavy or wavy modulated flow, were characterized in terms of the wall velocity gradients, wave number, axial and azimuthal wavelength, the axial velocity of vortex displacement, and there frequencies. The Taylor number has substantial effect on the evolution of these parameters in the investigated range. The use of three-segment electrodiffusion has contributed to the understanding of the mechanisms of vortex-wall interaction and the determination of the azimuthal and axial components of the wall velocity gradient
Kouitat-Njiwa, Richard. "Contribution à l'étude du taux de cisaillement d'un écoulement de Couette entre deux cylindres coaxiaux : régime de montée en vitesse". Vandoeuvre-les-Nancy, INPL, 1989. http://www.theses.fr/1989NAN10021.
Pełny tekst źródłaChaliche, Majed. "Contribution a l'etude de la conductivite thermique des fluides complexes en presence d'une vitesse de cisaillement : realisation d'un appareillage specifique". Nantes, 1988. http://www.theses.fr/1988NANT2013.
Pełny tekst źródłaScholtys, Jeremy. "Étude numérique de l'importance du cisaillement de vitesse dans le premier stade de formation des molécules dans le milieu interstellaire". Master's thesis, Université Laval, 2017. http://hdl.handle.net/20.500.11794/28239.
Pełny tekst źródłaFrom a galactic evolution standpoint, molecular clouds are important structures since they give birth to stars and their properties. Molecule formation from the neutral atomic medium, which is ubiquitous in the Galactic disc, is therefore a key step in the stellar formation process. To rapidly generate favorable conditions for molecules to appear, i.e. to obtain cold and dense gas shielded from the ionizing radiation field of the Galaxy, two numerical simulation models are considered: warm neutral atomic gas (WNM) colliding flows and WNM flows with turbulence driven in Fourier space. Together with the compression provided by these flows, the thermal instability arising from the cooling and heating processes in the interstellar medium produces long lived cold atomic neutral gas (CNM) structures that are potentiel molecular formation sites. Recent observations of diffuse gas at high galactic latitude were undertaken and display CO and OH emission peaks wherever large velocity shears in atomic hydrogen (HI) spectra are present or where HI components merge. Numerical simulations with the two models mentionned above were undertaken in order to investigate whether the amplitude of these velocity shears can be reproduced or not and to examine how they are related to cold gas. Both cloud formation models are then compared to each other and with observations of cold gas structures in the solar neighbourhood and at high galactic latitude.
LEE, WOEI-SHYAN. "Correlation entre la microstructure et les proprietes mecaniques de materiaux a base de tungstene soumis au cisaillement a grande vitesse". Nantes, 1990. http://www.theses.fr/1990NANT2024.
Pełny tekst źródłaChaliche, Majed. "Contribution à l'étude de la conductivité thermique des fluides complexes en présence d'une vitesse de cisaillement réalisation d'un appareillage spécifique /". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb376124512.
Pełny tekst źródłaKouitat, Richard. "Contribution à l'étude du taux de cisaillement d'un écoulement de Couette entre deux cylindres coaxiaux régime de montée en vitesse /". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37614791m.
Pełny tekst źródłaMohamed, Aly Ould Sidi Mohamed. "Etude d'un jet d'air plan mince à grande vitesse : action sur une plaque plane". Valenciennes, 1993. https://ged.uphf.fr/nuxeo/site/esupversions/4b2832a5-70ea-4fb4-9ac0-ad724a113a85.
Pełny tekst źródłaBrown, David Lou. "Élaboration d'une procédure de reconstitution d'échantillon de sol non cohésif, en laboratoire, à partir de la vitesse d'une onde de cisaillement". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0015/MQ61866.pdf.
Pełny tekst źródłaBrown, David Lou. "Élaboration d'une procédure de reconstitution d'échantillon de sol non cohésif, en laboratoire, à partir de la vitesse d'une onde de cisaillement". Mémoire, Université de Sherbrooke, 1999. http://savoirs.usherbrooke.ca/handle/11143/1069.
Pełny tekst źródłaYang, Hyun-Kyu. "Contribution à l'étude de matériaux composites sollicités par barres de Hopkinson, (en compression, traction et cisaillement), à grande vitesse de déformation". Nantes, 1993. http://www.theses.fr/1993NANT2101.
Pełny tekst źródłaBrown, David Lou. "Élaboration d'une procédure de reconstitution d'échantillon de sol non cohésif, en laboratoire, à partir de la vitesse d'une onde de cisaillement". Sherbrooke : Université de Sherbrooke, 2000.
Znajdź pełny tekst źródłaBouainouche, Mokrane. "Etude de l'interaction entre un jet plan à grande vitesse et un film liquide". valenciennes, 1995. https://ged.uphf.fr/nuxeo/site/esupversions/2f38b9a7-3e25-4c6f-968e-e4d2d3c14d4a.
Pełny tekst źródłaThe first part of this study deals with the modelling of the impact of a thin plane gas jet a flat plate in order to define the pressure and shear stress distributions on the wall. In the second part, these results are used to study the behavior of viscous film liquid on the strip moving upward and submitted to the jet action. The jet actions are determined by a numerical computation based on finite volume scheme. The impingement of a plane two dimensional turbulent and compressible jet is modelised using the k-ɛ model combined to the wall functions. In order to reduce the near wall gnd influence on the shear stress calculation, a hybrid wall law is proposed resulting from simultaneous use of the logarithmic law and generalized one. Pressure and shear stress distributions on the flat plane are calculated and validated by experimental data. The motion of liquid coating is modelised by taking into account the inertia terms, neglected in the previous studies. This model is applied to the galvanization process and compared with measurements obtained in various conditions
Mainsant, Guenole. "Variation de la vitesse des ondes de cisaillement lors de la transition solide-liquide au sein des argiles. Application aux glissements de terrain". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00934433.
Pełny tekst źródłaMainsant, Guenolé. "Variation de la vitesse des ondes de cisaillement lors de la transition solide-liquide au sein des argiles. Application aux glissements de terrain". Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENU005/document.
Pełny tekst źródłaLandslides affect many clay slopes in the world and regularly threaten people in urban areas mountainous. These landslides are characterized by a slow velocity but they may suddenly liquefy and accelerate unexpectedly. The solid-liquid transition on the clay has been studied of Trièves region (French Alps) using rheological experiments. They have shown the yield stress thixotropic behavior with a viscosity bifurcation which can explain the catastrophic fluidization observed in the field. This loss of material stiffness can be followed by a drop in the shear wave velocity (Vs). Inclined plane test and field experiments (Pont-Bourquin landslides in Switzerland) have both shown a precursor drop of Vs indicating that it could be a good proxy for monitoring unstable clay slope
Naji, Siwar. "La caractérisation des propriétés physiques et mécaniques des matériaux cimentaires à l'aide des ondes de cisaillement". Thèse, Université de Sherbrooke, 2016. http://hdl.handle.net/11143/9896.
Pełny tekst źródłaDelalondre, Fabien. "Modélisation et étude 3D des phénomènes adiabatiques dans les procédés de mise en forme à grande vitesse". Phd thesis, École Nationale Supérieure des Mines de Paris, 2008. http://tel.archives-ouvertes.fr/tel-00408755/en/.
Pełny tekst źródłaAl-Rafii, Mahdi. "Tenue résiduelle des assemblages boulonnés composites soumis à des impacts basse vitesse et basse énergie". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30113.
Pełny tekst źródłaThe proportion of use of composites materials in the structures of the new generation airplane is growing, for the questions of safety and costs, the manufacturers have established rules of sizing taking into account generally the specificities of the physical behavior, mechanics in particular, behavior of the composite structures. This project concerns the tolerance in damage on assemblies screwed by plates with intermediate modulus fiber carbon / epoxy matrix T800 / M21. As a first time, the mechanical behavior of bolted junctions was studied thanks to essays of traction on representative specimens of aeronautical plates assembled in single lap shear (SLS) joint. The second part of the study is consisted to impact on the assemblies in single lap close to a fastening line, understanding and modeling the residual tensile strength after impact.The last part describes the effect of low speed impact on the specimens behavior which have been submitted to initial tension (to simulate the behavior in operation of the assembly) using a specific test, to compare the effect of the impacts with and without initial tension on the residual behavior of the composite bolted joint. Finally, a numerical finite element model with a ply damage and failure behaviors, made it possible to make comparisons between tests and numerical computations for a specific lay-up. The model shows the different phases of damages and failures observed experimentally. It provides a good basis for further development of these numerical models
Mhenni, Ahmed. "Amélioration de la technique des anneaux piézoélectriques (P-RAT) à l'aide des simulations 3D". Mémoire, Université de Sherbrooke, 2016. http://hdl.handle.net/11143/9556.
Pełny tekst źródłaBillien, Magali. "Hétérogénéités de vitesse et d'atténuation du manteau supérieur à l'échelle globale par modélisation du mode fondamental des ondes de surface". Université Louis Pasteur (Strasbourg) (1971-2008), 1999. http://www.theses.fr/1999STR13035.
Pełny tekst źródłaShahsavari, Vahid. "L'application de la méthode MASW pour déterminer l'épaisseur des couches superficielles du béton". Mémoire, Université de Sherbrooke, 2011. http://savoirs.usherbrooke.ca/handle/11143/1610.
Pełny tekst źródłaMoradian, Zabihallah. "Application de la méthode d'émission acoustique pour la surveillance du comportement au cisaillement des joints actifs". Thèse, Université de Sherbrooke, 2011. http://savoirs.usherbrooke.ca/handle/11143/1961.
Pełny tekst źródłaTounsi, Rami. "Comportement des structures en nids d'abeilles sous sollicitations dynamiques mixtes compression/cisaillement et effet de l'orientation des cellules". Phd thesis, Université de Valenciennes et du Hainaut-Cambresis, 2014. http://tel.archives-ouvertes.fr/tel-01002421.
Pełny tekst źródłaMicheli, Pascal de. "Formulation explicite en tétraèdres linéaires pour la modélisation 2D et 3D de l'UGV". Paris, ENMP, 2009. http://tel.archives-ouvertes.fr/tel-00409570.
Pełny tekst źródłaThe aim of this work is to present a FE formulation particularly adapted to the simulation of high speed machining at the cutting edge level. The modelling should be able to detect the very local phenomena that could occur, with reasonable computation times. This code is implemented using the FE library CimLib, which offers robust adaptive non-structured remeshers and allows massive parallel computing. This work can be split in two parts. The first one consist in developing, implementing and validating an explicit type formulation, which is not sensitive to volumetric locking and allows using robust adaptive non-structured remeshers. Two formulations have been compared in the field of rapid dynamics: a semi-explicit one with mixed tetrahedral elements and RFB stabilization and an explicit one with modified linear tetrahedral elements. The second part of the work consists in applying the explicit formulation presented above to high speed machining. A thermal solver is implemented and coupled to the mechanical one. 2D micro machining simulations of Ti6Al4V orthogonal cutting are performed. Results are in very good agreement with literature, and important calculation time sparing is observed. The initiation and propagation of the adiabatic shear band in the chip can be analyzed in details. A R-adaptation procedure has been added to the normal remeshing procedure in order to be able to extend those results in 3D. We can then get closer of the real industrial processes, without loosing precision
RANC, Nicolas. "Etude des champs de température et de déformation dans les matériaux métalliques sollicités à grande vitesse de déformation". Phd thesis, Université de Nanterre - Paris X, 2004. http://tel.archives-ouvertes.fr/tel-00010301.
Pełny tekst źródłaMarouani, Haykel. "Etude expérimentale et modélisation numérique du poinçonnage et du cisaillage d'alliages Fe-Si : Influence de la vitesse de déformation". Compiègne, 2006. http://www.theses.fr/2006COMP1625.
Pełny tekst źródłaThis work is a part of reflexion for the elaboration of a numerical tool which measures the magnetic properties degradation of ferromagnetic alloys after cutting. Firstly, our contribution involves the characterization of the mechanical behaviour of a Fe-3%Si alloy. Then an experimental study of punching and shearing was conducted. Finally, a finite element model of these processes was proposed. The study of the material behaviour highlights a strain rate dependence of the mechanical response. Video-tensile tests allowed identifying the most suitable law. The experimental investigations on punching and shearing, under various clearances and cutting speeds, provided a rich database for the future numerical validation. Finite elements investigations require the use of suitable techniques and approaches to treat multiple non-linearities present in this kind of problem
Julea, Felicia. "Conditions de validité de l'Élastographie par Résonance Magnétique". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS053/document.
Pełny tekst źródłaMagnetic Resonance Elastography (MRE) is a imaging technique, recognized as a pertinent method for the mechanical characterization of human tissue in vivo. It offersa particular interest in clinical diagnosis because the development of a pathological process is often accompanied by modifications of the mechanical properties of diseased tissues. MRE consists of recording, along the three spatial dimensions, the displacement field induced by the propagation of a shear wave generated by excitation of the investigated tissue. Mechanical parameters such as shear wave velocity, v, and shear moduli, G' and G'', can then be mapped. The quantification of the mechanical parameters depends on the frequency of the mechanical excitation, fexc, the spatial resolution, a, the amplitude of the induced displacement field, A and the amplitude of the curl field displacement, q, with associated measurement errors, ΔA and Δq, (related to the signal-to-noise ratio, SNR) and finally the reconstruction method. All these parameters were considered to determine the precision and the accuracy of the estimated mechanical moduli and to establish the conditions of validity of MRE following the inversion of the differential equations of the displacement field. In this work, first A and A/ΔA were considered to define a validity threshold for MRE. The influence of A and A/ΔA was studied on a heterogeneous phantom acquired using a 1.5 T MRI with two different types of coils. In a first study, the displacement fields were acquired as a function of A using motion-sensitized spin-echo (REF) and gradient-echo (FFE) sequences for an isotropic spatial resolution of 1 mm. In a second study, the displacement field was acquired as a function of A using RFE for three different spatial resolutions. These studies revealed the existence of a threshold in A/ΔA beyond which the extracted parameters (G', G'') reach a plateau and the MRE is reliable. Then the number of voxels per wavelength, λ/a was considered as a parameter determining the conditions of validity of MRE. This parameter was studied according to the quality of the acquired data characterized by the ratio q//Δq. Simulations were carried in a homogeneous and isotropic elastic medium with a SNR between 5 and 30. The accuracy and the precision of the measurements were found optimal for 6 to 9 voxels per wavelength. The simulation conditions were experimentally reproduced at 2 kHz on a home-made polyvinyl alcohol phantom. The displacement fields were acquired at 11.7 T using a motion-sensitized RFE sequence with spatial resolutions ranging from 150 μm to 300 μm in order to obtain a λ/a ratio ranging from 1 to 20. The experimental results fully confirm the predictions of the simulation. The shear wave velocity decreases with λ/a. It tends towards the expected reference value when the acquisition is performed in the optimal condition, namely here when a is less than or equal to 200 μm. In addition, the standard deviation of the shear wave velocity is reduced for the optimal conditions. Therefore, accurate estimation of mechanical parameters could be deduced. This thesis first demonstrates that the precision and accuracy of MRE are optimal when the acquisitions are performed or processed for a certain wavelength sampling range determined by the SNR. We also showed that for fair comparison of the results, MRE must be carried out in a similar range of q/Δq. Taking into account the conditions of validity of MRE, determined by the ratios λ/a and q/Δq, leads to an effective quantitative measurement of the mechanical parameters making it possible to establish a relevant clinical diagnosis within the same organ, the same subject, between subjects or over time
Jeudy, Betegard. "Microzonage sismique de la ville des cayes (haïti)". Mémoire, Université de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/393.
Pełny tekst źródłaJia, Bin. "Caractérisation expérimentale et modélisation du comportement de l'acier inoxydable 304 sous différentes vitesses de déformation et températures". Thesis, Paris, ENSAM, 2019. http://www.theses.fr/2019ENAM0056.
Pełny tekst źródłaDue to the unique Transformation Induced Plasticity (TRIP) effect, 304 austenitic stainless steel (ASS) is widely used in many engineering areas. During working and manufacturing process or in service, it may undergo deformation over a wide range of strain rates and temperatures. The current work presents a systematic deformation behavior study of 304 ASS by both experiments and numerical simulations. With an original cooling device coupled to the split Hopkinson pressure bar system, the compression behavior at strain rates between 0.001 s-1 and 3000 s-1 and temperatures between -163°C and 172°C was investigated. An extension of the Rusinek-Klepaczko (RK) model considering strain-induced martensitic transformation (SIMT) phenomenon was also used to simulate the thermo-viscoplastic behavior of this steel. To study the deformation behavior at extremely high strain rates exceeding 3000 s-1, a new single shear zone (SSS) specimen has been proposed and validated. Then, the effects of strain rate between 3000 s-1 and 39000 s-1 was analyzed. Finally, with a specially designed cooling device, the ballistic impact behavior under initial projectile velocities between 80 and 180 m.s-1 and temperatures between -163°C and 200°C was studied. By comparison between experiments and numerical simulations for perforation, the previously obtained constitutive relations were validated
Blaj, Octavian. "Comment coule une pâte granulaire? Etudes des composantes primaire et secondaire et des fluctuations de l'écoulement". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00750737.
Pełny tekst źródłaBlaj, Octavian. "Comment coule une pâte granulaire ? : études des composantes primaire et secondaire et des fluctuations de l’écoulement". Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14591/document.
Pełny tekst źródłaWet granular materials are made of solid particles in high concentration, immersed in a viscous fluid. We investigated particle dynamics in a model granular suspension in Couette geometry, at low Reynolds/Taylor numbers for density and non density matched suspension. We used innovated techniques such as: Single Particle Tracking (SPT), Multi Particles Video Trajectography (MPVT) and Concentration Photometry (CP). These experiments allow us to provide information about single and collective motion of grains as well as particle repartition (local volume fraction). We investigated fully 3D velocity profiles in concentrated suspensions, diffusion coefficients, particle fluctuations and recirculation motion, also differential flows. We observe that the flow of non density matched suspensions is localized near the inner cylinder in the low shear rate regime, resulting in a sheared layer only a few particle diameters in thickness, in a way very similar to sheared dry granular materials. At high enough angular velocity, the initially localized flow crosses over to full fluidization: in this regime the granular suspension nearly behaves as a density-matched suspension. Dependence between particles’ velocity and associated fluctuation amplitude is evidenced. Experiments as velocity and concentration profiles were compared with theoretical prediction based on the force balance model and different viscometric laws were investigated for normal and shear forces