Tesi sul tema "Effet de compression"
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Chiquier, Jean-Michel. "Compression temporelle par effet Raman intra-cavité et compression spectrale des impulsions d'un laser à excimère". Paris 11, 1988. http://www.theses.fr/1988PA112084.
Testo completoChiquier, Jean-Michel. "Compression temporelle par effet Raman intra-cavité et compression spectrale des impulsions d'un laser à excimère". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37612742x.
Testo completoNakano, Tamon. "Étude numérique de l’interaction choc/couche limite en géométrie de révolution". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2018. http://www.theses.fr/2018ESMA0013/document.
Testo completoShock wave/boundary layer interactions (SWBLI) are present in various aerospace engineering applications.They can be associated with separated regions yielding low-frequency unsteadiness, which have mainly been studied in planar geometries. The present study aims at characterizing this type of interaction in a cylindrical configuration. A direct numerical simulation solver has been developed and validated with various test cases. It is based on a high-order finite difference based hybrid schemes (6th order centered scheme/5thorder WENO), extended to curvilinear geometries. Transverse curvature effects on properties of spatially developing supersonic boundary layer at Mach 3 are first examined. It is shown that the increase of the relative curvature of the boundary layer tends to reduce the fluctuation energy at lower frequencies near the wall, while reinforcing the perturbations at higher frequencies in the upper zone of the boundary layer.In comparison with the planar case, the transverse curvature leads to a significant re-organization of the boundary layer structures and a subsequent modified behavior of the invariants of anisotropy turbulent stress tensor. It however only leads to slightly modified distributions of Reynolds stress and a rather similar overall balance of turbulent kinetic energy through the boundary layer. The second part of this study is dedicated to the unsteady motions of the shock/separation zone in a cylinder/compression flare configuration for which the full cylindrical geometry is taken into account. The shock distortions in the azimutal direction appears to be mainly associated to the organization of the upstream vortex structures and the subsequent azimutal fluctuations of the separation line. It is shown that the energy of the fluctuating wall pressure is more amplified for higher order azimutal modes. The contributions to lateral forces, associated to the first mode, are dominated by low-frequencies only upstream of the separation line in the intermittent region. They become more dominant in the middle frequency range downstream of the reattachment zone on the ramp. It is also shown that the low-frequency activity at the wall is progressively due to higher order azimuthal modes through the interaction zone
Michau, Vincent. "Conversion de fréquence et compression d'impulsion d'un laser alexandrite par diffusion Raman stimulée intracavité". Paris 11, 1988. http://www.theses.fr/1988PA112065.
Testo completoStorck-Gantois, Fanny. "Effet de la compression et de l’ajout d’additifs sur l’amélioration des performances d’un accumulateur au plomb". Paris 6, 2008. http://www.theses.fr/2008PA066370.
Testo completoMalvache, Arnaud. "Optique non-linéaire à haute intensité : Compression d'impulsions laser Interaction laser-plasma". Phd thesis, Palaiseau, Ecole polytechnique, 2011. https://theses.hal.science/index.php?halsid=uofsba7dj5fa0catc3i9mh00v0&view_this_doc=pastel-00677295&version=1.
Testo completoThis mainly theoretical PhD thesis has been done in the framework of high-order harmonics generation on solid targets using 1mJ ultrashort laser pulses (2 optical cycles) at high repetition rate (1kHz), CEP-stabilized. On the one hand, in order to fully use the laser source, I developed a simulation code of hollow-core fiber propagation. The results of this code, associated with an experimental study, allowed to push the energy limitation of this compression technique. On the other hand, I used PIC simulation and I developed a simulation model of CWE in order to quantify its dependence to the laser and plasma parameters. This work first helped to explain the CWE spectrum changes with pulse CEP. Second, by comparing theoretical results with an experimental parametric study, it provided information about the plasma conditions such as density gradient and electronic temperature
Manseau, Anthoni. "Génération d’états comprimés du champ électromagnétique micro-onde à l’aide d’un transistor à effet de champ commercial". Mémoire, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/10538.
Testo completoWouts, Jérémy. "Étude et modélisation du comportement en compression du bois sous sollicitations d'impacts". Thesis, Valenciennes, 2017. http://www.theses.fr/2017VALE0025.
Testo completoWood is a natural cellular material, which is widely and advantageously used as shock absorber for the transport of radioactive materials. Accident situations are evaluated based on the 9 m drop test, which allows us to observe the complex crushing behavior of wood. A compressive experimental study is conducted on spruce and beech wood species over a large range of strain rates (from 0.001 to 600 s−1) to investigate the effect of the loading direction and of two extreme lateral confinements. The longitudinal direction is the most sensitive to the effect of strain rate and of lateral confinements which have significant consequences on the energy absorption. Besides, the experimental investigation can be adapted to various wood species with very different mechanical properties. A strain rate dependent elastoplastic model with transversal isotropy is developed using multi-scale and micromechanics techniques. The elastic macroscopic properties of wood are estimated with a Mori-Tanaka scheme and information extracted from the microstructure. The Gurson type criterion based on the micromechanical approach of the ductile damage is used in order to describe the non linear behavior of wood, its densification regime and its compressibility as well. Additionally, uncoupled degradation parameters are applied to reproduce the failure mechanisms involved in the longitudinal response. A simplified description of wood is used within the modeling and the numerical results exhibit the good ability of the model to reproduce the various wood responses during an accident situation
Malvache, Arnaud. "Optique non-linéaire à haute intensité : Compression d'impulsions laser Interaction laser-plasma". Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00677295.
Testo completoTounsi, 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.
Testo completoANCRENAZ, PATRICK. "Influence des elements d'addition sur le comportement mecanique du cuivre sous compression : effet de la vitesse de deformation". Paris 11, 1992. http://www.theses.fr/1992PA112474.
Testo completoNoumowe, Albert. "Effet de hautes températures (20-600°C) sur le béton : cas particulier du béton a hautes performances". Lyon, INSA, 1995. http://www.theses.fr/1995ISAL0092.
Testo completoFirst of all, a general review on concretes at high temperatures is presented. The advantage of high performance concretes in nuclear power plants is underlined. The experimental investigation is carried out on two concretes (ordinary and high performance) made on the CIVAUX power plant. Cylindrical and specimens there heated to different temperatures. Measurements of temperature distributions in the concrete during heating showed high temperature differences between the center and the surface of the specimens. Eight measurements during heating up to 600°C were suitable for gathering information on micro structural changes. This permitted quantifying the specimen water loss. After a heating/cooling cycle at each target temperature, decreases were recorded in the residual compressive strength, tensile strength and modulus of elasticity. Three factors that influence concrete spalling at high temperature are investigated : heating rate, specimen dimensions and concrete age. An elastic thermal stresses analysis was conducted both analytically, and numerically by means of finite elements codes. Analysis of pore pressures in the heated concrete specimens necessitate also a numerical approach. Furthermore, the theoretical results and experimental findings showed main parameters for the understanding of the violent explosion which took place in some high performance concrete specimens the thermal gradient, the moisture content and the tensile strength
Derviaux, Christian. "Evaluation de la visibilité des effets de blocs dans le codage MPEG : application à l'amélioration de la qualité visuelle de séquences video". Valenciennes, 1998. http://www.theses.fr/1998VALE0032.
Testo completoOuarem, Abdelouahab. "Comportement mécanique et évolutions microstructurales sous compression quasi-statique et dynamique de polycristaux CFC et HC : effet de la taille des grains". Paris 13, 2012. http://scbd-sto.univ-paris13.fr/intranet/edgalilee_th_2012_ouarem.pdf.
Testo completoThe present work is devoted to the analysis of the strain rate and grain size effects on the deformation mechanism activated during plastic deformation of two polycrystalline materials: (i) zinc (Zn), a crystal with hexagonal compact packing structure, having grain size in the micro and ultrafine grain ranges (~ 300 µm and 200 nm, respectively), loaded under quasi-static and dynamic compression conditions, up to a strain rate of ~ 10⁵ s⁻¹ (by use of a Direct Impact Hopkinson Pressure Bars (DIHPB); (ii) electrodeposited nickel (Ni), a face-centered cubic structure with grain size of 5 µm deformed in compression under dynamic conditions using DIHPB. Significant differences in terms of micro-mechanisms of deformation in the two regimes were found: (i) At lower strain rates, up to ~ 10² s⁻¹, dislocation-based plasticity was observed in both Ni and Zn. Extensive twinning occurred only in the case of micrometer grain-sized Zn, indicating a grain size dependence of twinning; (ii) In the dynamic regime (> 10³ s⁻¹) plastic deformation induced a significant increase of the temperature within the samples. This increase of temperature was significant enough to induce recovery and/or dynamic recrystallization. As consequence two phenomena were observed depending on the structure under investigation: for Ni, the resulting microstructure and mechanical properties were similar to that of the initial state, dominated by annealing twins and equiaxed and randomly oriented grains. For micro-grained Zn a tremendous grain refining was found. As a consequence, twinning was inhibited. To clarify this point, additional investigations were carried out on coarse-grained CP-Ti deformed in both quasi-static and dynamic regimes. It was found that twinning was the main deformation mechanism. Indeed, the larger the strain rate and grains size, the larger the twin density. On the one hand, these results clearly demonstrate the grain size effect on the occurrence of mechanical twinning in HCP materials. On the other hand, the effect of the strain rate on twinning was found to depend on the material under investigation. Compared to Ti, the lower homologous temperature T/T m of Zn probably plays a key role, as it may induce dynamic recovery/recrystallization as far as the present experimental conditions are concerned
Roiron, Coline. "Contribution à la caractérisation thermomécanique d’un polyéthylène auto-renforcé et de ses « recyclats » : Effet des paramètres du procédé de moulage par compression". Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2022. http://www.theses.fr/2022ESMA0004.
Testo completoReducing energy consumption is an essential issue for today's society. In order to achieve a sustainable energy transition, especially in the field of transportation, new and more demanding regulations are being implemented. The keywords are to increase the proportion of recycled and recyclable materials and lightening structural parts.The use of polymers can be a solution. However, to guarantee good mechanical resistance, the use of self-reinforced composites(SRP) is a lever for action. They are composed of a polymer or a family of polymers in two physical states, one to form the matrix and the second for the reinforcement. They present a low density, interesting mechanical behavior, and increased recyclability. To understand the behavior of a self-reinforced polyethylene and to be able to consider the use of this material for a given application,it is essential to understand the behavior of each of its components. If the behavior of more conventional composites, such as glass or carbon fiber reinforced thermoplastic matrix composites, is well understood, using thermoplastic reinforcements such as UHMWPE (Ultra-High Molecular Weight PolyEthylene) within the composite makes the understanding of the behavior of SRP more complex. The impact of temperature and time on the mechanical response of the reinforcements is then examined in a first step, and the observations are related to microstructural considerations. A test protocol has been proposed and validated before hand. A solid-phase transition is highlighted around 49°C and generates an abrupt behavior change.These UHMWPE reinforcements are integrated into composites. A compression molding process is suggested to process them in a single step from a matrix in granular form. The effect of different process parameters is evaluated to propose an optimal combination.The short and long-term mechanical response in tension and creep is then analyzed, and the interest of the SRPE thus designed is highlighted. Indeed, the benefit of its use is evident, especially at low temperatures. Moreover, the presence of thermoplastic reinforcements seems to introduce additional parameters that affect the behavior of the composites and, in particular, in creep. The precise characterization and the knowledge of the transition temperatures of the latter appeared then determining, mainly since the transitions depend on the microstructure of the reinforcement and thus on the type of stretching and the applied conditions. Finally, the recyclability of the implemented composites is studied since it constitutes a driving force for the development of SRP on the market
Lavabre, Alexis. "Détection de l'effet de lentille gravitationnelle dans les données de Planck-HFI". Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00923133.
Testo completoDenay, Anne-Gaëlle. "Mécanismes et tenue mécanique long-terme de mousses polyuréthanes pures et renforcées aux températures cryogéniques". Phd thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2012. http://tel.archives-ouvertes.fr/tel-00740110.
Testo completoZhang, Liguo. "Effet de la sonication sur les propriétés mécaniques et le relargage de billes et capsules d'alginate". Compiègne, 2012. http://www.theses.fr/2012COMP1994.
Testo completoWe have investigated the effect of ultrasonic stimulation on the mechanical properties and release of alginate beads and capsules. Capsules are fabricated with the same technique of extrusion as the beads, but using a new process that has been developed. They are made of a highly-viscous liquid core enclosed in a thin hyperelastic alginate membrane. Using an ultrasonic pulse-echo technique, we have first shown that the alginate gel is quasi-incompressible and thus has a Poisson ratio very close to 0. 5. The shear modulus of the alginate beads and capsules has then been measured by compression. We have shown that they recover their mechanical properties after sonication. Still, at high intensities and/or long exposure times, sonication can lead to the rupture of the capsule membrane due to fatigue. No similar phenomenon has been observed for the beads. Release is studied by sonicating loaded beads and capsules suspended in an aqueous solution. The mass release that results from the sonication of capsules is found to be proportional to the sonication duration time and pressure wave amplitude. A possible physical interpretation is that the acoustic streaming flow induced by the ultrasonic wave enhances convection in the vicinity of the capsule membrane and thus mass release. The release from alginate beads is also increased by the ultrasonic parameters, but to a smaller extent. We have finally quantified the passive release subsequent to low-intensity sonication: it is on average identical to the one measured on non-sonicated beads and capsules. Overall the alginate gel therefore recovers its physical and mechanical properties after sonication. If sonication leads to an increase in porosity, the increase is temporary and reversible at the end of the ultrasonic stimulation
Miled, Karim. "Effet de taille dans le béton léger de polystyrène expansé". Phd thesis, Ecole des Ponts ParisTech, 2005. http://pastel.archives-ouvertes.fr/pastel-00001820.
Testo completoTekaya, Aymen. "Influence de la dimensionnalité et de la complexité d'un réseau de billes sous compression mécanique sur les transports électrique et thermique dans les milieux granulaires métalliques : de l'interface individuelle aux propriétés collectives". Amiens, 2012. http://www.theses.fr/2012AMIE0115.
Testo completoThis thesis mainly deals with the physical characterization of the electrical contact between two adjacent steel beads as well as the electro-thermal coupling taking place at the level of larger assemblies of beads. We thus show how these studies made on couples of metallic beads may be applied to granular media and even, subject to certain limitations, to ball bearings, part of tooling machines, for the detection of certain surface defects. The main part of the subject, with the experimental study, consists on the theoretical and numerical modeling of the metallic beads electrical properties and the electrical contact properties. We show how the surface state and its evolution through time are responsible for several observed phenomena. Indeed, the oxide layer present at the surface of the beads plays a key role in global electrical properties such as the hysteresis loop of the current-voltage characteristic (DC Branly effect) as well as the slow voltage relaxation. This led us to use new approaches in order to explain the experimental results. The most promising one, suggested by P. G. De Gennes for granular media, is the influence of electron tunneling process between neighboring beads which is acting through the insulating oxide layer, promoting thus quantum transport
Bulot, Nicolas. "Analyse expérimentale et modélisation numérique des mécanismes d'interactions instationnaires à proximité du pompage d'un étage de compresseur centrifuge à fort taux de compression". Thesis, Ecully, Ecole centrale de Lyon, 2010. http://www.theses.fr/2010ECDL0006.
Testo completoThe present work is in line with a collaboration between the Laboratoire de Mécanique des Fluides et d'Acoustique at École Centrale de Lyon (LMFA-ECL), Turbomeca and ONERA. The subject is focused on impeller-diffuser interaction and phenomena occurring during surge ignition of a transonic centrifugal stage with high-compression ratio at cruise rotation speed (0,927Nn). The analysed data come from three measurement devices and two kinds of numerical simulations. The 1MW LMFA-ECL test rig was used for carrying out the experiments on the centrifugal compressor stage. The global performances were obtained by pressure, temperature, mass flow rate and rotation speed measurements. The internal flow field properties were probed by Laser Doppler Anemometry (LDA) and high frequency pressure measurements. The computations were performed with the elsA software developed at ONERA. The code solves the compressible Reynolds Averaged Navier-Stokes equations associated with the two-equations (k-l) turbulence model of Smith. Two models of impeller-diffuser interaction were used to simulate the flow within the compressor. The first model is based on the Averaged Passage equations, gives a stationary description of the internal flow fields. The second model is based on the phase lagged approach and allows access to the unsteady phenomena. A good agreement between experiments and simulations was obtained, which justifies the use of the CFD results for the flow field analysis. Analysis of the flow development within the impeller were carried out for three operating points (choke, peak efficiency and close to surge). This study shows that, from choke to near surge, the development of the tip clearance vortex is the starting point of a sequence of physical mechanisms which lead to an extend of the wake of the jet-wake structure. The change in flow field at impeller exit tends to increase the upstream incidence of the vaned diffuser, especially close to the hub. The vane bow shock wave progresses in the impeller passages when the operating point moves from choke to near surge. The location of the main flow moves from suction side to pressure side of the vaned diffuser passage. The topology of the boundary layer separations within the diffuser passage is deeply affected when approaching surge. The main unsteady structures are generated by the interaction between the bow shock wave and the impeller blades. Progressive pressure waves and low Mach number flow bubbles are generated by this locally time-spaced interaction phenomenon. The pressure waves lead to strong fluctuations of the velocity field. As a consequence, the boundary layer becomes more resistant in relation to the separations (in term of time-averaged point of view). In time-averaged point of view, the low Mach number flow bubbles lead to inhomogeneous conditions at the vaned diffuser inlet along the azimuthal direction . From choke to near surge operating point, the strength of the pressure wave increases whereas the size of the low Mach number flow bubbles decreases. These conditions are quite favourable to push back the surge limit which is locally initiated in the inlet part of the vaned diffuser. The surge of the compressor is produced by a rapid change in supersonic flow structure at diffuser inlet. The pressure fluctuations due to the progressive waves lead to destabilise the new supersonic flow configuration and degenerate in the global instability of the compressor flow
Tran, Quang Vu. "Locally heterogeneous three-dimensional fibrous media : Representative elementary volumes and calculation of acoustic properties". Electronic Thesis or Diss., Université Gustave Eiffel, 2023. http://www.theses.fr/2023UEFL2081.
Testo completoThis thesis explores the complex relationship between the structures, acoustic properties, and manufacturing processes of non-woven fiber materials. Two families of composite fibrous media, derived from recycled textile fibers and recycled PET fibers, were studied, offering a diversity of polydispersity. Through microstructural characterization and numerical homogenization, this research identified key parameters associated with transport and sound absorption properties.The volume-weighted mean diameter Dv and inverse volume weighted mean diameter Div were found to be essential geometric descriptors. They explain acoustic behaviors at different frequencies, revealing that viscous and thermal exchanges occur through the widest channels of the microstructure at low frequencies; while at high frequencies, the acoustic signature is influenced by the entire microstructure, including the smallest constrictions.The original contributions of this research include (1) the development of Representative Elementary Volumes (REVs) for polydisperse fibrous media; (2) solving an optimization problem based on the degree of polydispersity; (3) and proposing an experimental technique to estimate transport properties at high frequencies.In summary, this thesis offers promising perspectives for understanding and optimizing the acoustic properties of polydisperse fibrous media while identifying crucial microstructural descriptors for these complex materials
NAVAI, FARHAD. "Etude de l'effet des contraintes mecaniques et des halogenures sur la composition des films passifs formes sur l'acier inoxydable x15crni18-8. Effet particulier des contraintes de compression". Nantes, 1997. http://www.theses.fr/1997NANT2070.
Testo completoLai, Dawei. "Contribution à la modélisation de la rupture des plaques stratifiées entaillées sous un chargement monotone ou cyclique comprenant une sollicitation de compression". Compiègne, 1988. http://www.theses.fr/1988COMPD150.
Testo completoJu, Minglei. "Contribution à la modélisation du comportement visco-hyper-élastique de mousses de polyuréthane : Validation expérimentale en quasi-statique". Thesis, Mulhouse, 2014. http://www.theses.fr/2014MULH8865/document.
Testo completoFlexible polyurethane foam is widely used in numerous applications such as acoustic, thermal and building due to its low density and its ability to absorb thermal and acoustic energy. It is also used for the comfort of the seats such as the vehicle, train, plane due to its low stiffness and its ability to absorb deformation energy. In order to optimize the comfort of the car seat, it is necessary to model the behavior of seat system, particularly the flexible component - polyurethane foam. The main objective of this study is to identify and model the quasi-static behavior of polyurethane foam under different test conditions in large deformations. Compression / decompression uniaxial unicycle and multicycle tests were carried out on three types of polyurethane foam at different strain rates, which allows us to understand the behavior of the material. The results of the tests indicate that the polyurethane foams exhibit a hyperelastic behavior and a viscoelastic behavior under large deformations. They also showed that the polyurethane foams have a stress softening phenomenon which is called 'Mullins effect' during the compression / decompression multicycle tests. In other words, the stress in first cycle is lower than the stresses in the subsequent cycles in the same deformation. ‘Mullins effect’ for the polyurethane foam is also an important study in this dissertation. Based on the experimental results and the goal of modeling quasi-static behavior of the polyurethane foam, three visco-hyperelastic models were developed. These models consist in two elements: hyperelastic models, which is normally used for description the behavior of rubber materials, and entire memory model which takes into account the history and describing the viscoelastic behavior. Model parameters were identified using appropriate identification and optimization methods. The results of modeling the mechanical behavior of the foam on the unicycle and multicycle tests were compared with experimental results. The models showed a very good competence to simulate the first cycle and the following cycles during the charge / discharge tests. Our models have proven its ability to model Mullins effect on flexible polyurethane foams. These models have been validated on three types of foam in order to present a comparative study of their effectiveness and their representativeness
Wollbrett-Blitz, Judith. "Comportement mécanique longitudinal et transverse, micro-mécanismes de déformation et effet de la température sur la fibre Kevlar® 29". Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0062/document.
Testo completoDesigning safer and lighter vehicles is a major challenge for manufacturers. Nowadays, a vehicle needs to be eco-friendly and conciliate efficiency and energy-saving. Considering these requirements, tire materials are subject to change: high performance polymers are a good replacement, in terms of weight and dissipation, for traditional reinforcements such as drawn steel. For instance, aramid strands (1000 fibres) are used because the single fibre exhibits good mechanical properties such as its high modulus (85 GPa) conferred by its anisotropy or its high temperature resistance. The mechanical performance of a Kevlar® fibre is due to its different scale organisation : the primary (molecular chains held by covalent bonds), the secondary (pleated sheets held by interactions) and the tertiary structure (sheets stacked together). Because of the cooling thermodynamics during the fabrication process, the 15 microns diameter fibre seems to have a skin/core structure with punctual more or less critical defects. To go further in the understanding of the complex structure, the contribution of the skin/core structure in the mechanical performance in the longitudinal and the transverse directions is investigated through a multi-disciplinary approach made of a numerical and an experimental study. During its use, an aramid single fibre undergoes cyclic multiaxial loading and harmful thermal treatments, at the origin of structural and mechanical properties modifications but also dissipative behaviour evolution, still misunderstood. To deal with these change in depth, an experimental and numerical multi-scale characterisation is used. Mechanical and thermal treatments are realised and their impact on the microstructure, on the deformation micromechanisms and on the mechanical properties including the dissipative behaviour are investigated. Limiting use values in terms of temperature, longitudinal and transverse stresses are highlighted in this work in order to understand modifications enhanced by the fibre life cycle
Abbas, Khaled. "Effet de traitements thermiques sur les propriétés fonctionnelles de fromages traditionnels : le cas des pâtes persillées". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00724803.
Testo completoDenay, Anne-Gaëlle. "Mécanismes et tenue mécanique long-terme de mousses polyuréthanes pures et renforcées aux températures cryogéniques". Phd thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2012. https://theses.hal.science/docs/00/74/01/10/PDF/MANUSCRIT_FINAL_THESE_AG_DENAY_14032012.pdf.
Testo completoThe general framework of the study concerns the long term creep resistance of polyurethane foams used in the wall of LNG tanks. The mechanical behavior in monotonic compression, low stress creep and dynamic mechanical analysis (DMA) has been characterized at cryogenic temperatures (-170°C) for polyurethane foam reinforced or not by the glass fiber mat. The first objective was to characterize the response and the mechanisms activated at low temperatures. The induced damage by the strong cooling of samples affects the earliest stages of deformation in compression, depending on the sample size. The micrographs and tomographic observations post-mortem did not show obvious damage. A creep recovery deformation is also observed. The second objective was to consider a prediction method for long-term creep by time-temperature equivalence in DMA. The various transitions observed between -170°VC and glass transition have been analyzed, as well as the representativeness of small samples used in this device. The results obtained in multifrequency DMA have not allowed the construction of mater curve. This approach is not the most appropriate to predict the creep behavior under low stress and long term of these foams
Bonod, Nicolas. "Méthode différentielle : développements et applications". Aix-Marseille 1, 2004. http://www.theses.fr/2004AIX11024.
Testo completoIssa, Inas. "In situ TEM nanocompression and mechanical analysis of ceramic nanoparticles". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI008/document.
Testo completoIn this study, we propose an innovative mechanical observation protocol of ceramics nanoparticles in the 100nm size range. This Protocol consists of in situ TEM nanocompression tests of isolated nanoparticles. Load–real displacements curves, obtained by Digital Image Correlation, are analyzed and these analyses are correlated with Molecular Dynamics simulations. By this protocol a constitutive law with its mechanical parameters (Young modulus, Yield stress...) of the studied material at the nano-scale can be obtained. In situ TEM nano-compression tests on magnesium oxide nanocubes are performed. Magnesium oxide is a model material and its plasticity is very well known at bulk. The MgO nanocubes show large plastic deformation, more than 50% of plastic strain without any fracture. The TEM results are correlated to MD simulations and the deformation mechanism can be identified.The size effect and the electron beam effect on the yield strength are investigated. In a second part of the dissertation, we present a study on transition alumina nanoparticles compacted in a Diamond Anvil Cell at different uniaxial pressures. Thin Foils of these compacted nanoparticles are prepared by FIB for HRTEM Observations. Their analysis reveals the plastic deformation of the nanoparticles. The crystallographic texture observed inthese compacted nanoparticles in DAC shows a preferred orientation of the {110} lattice planes, orientated perpendicular to the compression direction. This is compatible with the slip system. This argument was reinforced with a preferred orientation of slip bands observed during in situ TEM nano-compression tests. Moreover, electron diffraction patterns (Debye Scherrer) analysis on these compacted transition alumina nanoparticles reveals the decrease of the presence of gamma-alumina and the increase of delta-alumina with increasing pressure. This reveals the phase transformation with increasing pressure from gamma to delta* alumina
ZHOU, XIAO-WEI. "Contribution au comportement dynamique des materiaux metalliques : etude experimentale de l'alliage al-li en torsion et en compression, simulation numerique du processus de penetration a grande vitesse". Nantes, 1988. http://www.theses.fr/1988NANT2014.
Testo completoRedjel, Bachir. "Mécanique et mécanismes de rupture dans les matériaux composites SMC (Sheet Molding Compound)". Compiègne, 1987. http://www.theses.fr/1987COMPD067.
Testo completoCroizet, Didier. "Etude experimentale et numérique du comportement à haute température d'un nitrure de silicium". Paris, ENMP, 1992. http://www.theses.fr/1992ENMP0516.
Testo completoYang, Yanfeng. "Étude des effets des changements de trajet en emboutissage". Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE001.
Testo completoIn sheet metal forming process, the material usually undergoes large deformations, complex loading histories and its mechanical behavior can be modeled by constitutive equations. Despite the great efforts paid to develop advanced hardening models considering the Bauschinger effect, the reliability and applicability of the developed hardening models still needs to be investigated, both experimentally and theoretically. In the first part, based on the developed hardening models, some classical and advanced models are selected are implemented by using Euler explicit implementation method. After that, the developed numerical instruments in current work are applied to investigate the prediction of the yield surface evolution, which show that some apparent violation of the normality condition can be simulated using models based on associated plasticity. The second part mainly focuses on characterizing and discriminating for selecting material models. Firstly some characterizations tests including complex loading path are performed to identify material parameters and bending-under-tension discriminant test is built to investing springback behavior that can sort out the best model
Mangold, Nicolas. "Rhéologie du pergélisol de Mars : applications géomorphologiques et structurales : conséquences sur l'origine des contraintes compressives". Grenoble 1, 1997. http://www.theses.fr/1997GRE10292.
Testo completoHuet, Dominique. "Mise en oeuvre, modélisation et comparaison de trois systèmes d'amplification de puissance sous vide utilisant des plasmas sous striction magnétique". Phd thesis, Ecole Polytechnique X, 2004. http://pastel.archives-ouvertes.fr/pastel-00000943.
Testo completoAlkharabsheh, Khaled S. "Image compression and its effect on data". Huntington, WV : [Marshall University Libraries], 2004. http://www.marshall.edu/etd/descript.asp?ref=462.
Testo completoTravers, Thierry. "Compression de milieux granulaires modeles : effets des heterogeneites". Rennes 1, 1988. http://www.theses.fr/1988REN10097.
Testo completoTravers, Thierry. "Compression de milieux granulaires modèles effets des hétérogénéités /". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37618947n.
Testo completoBree, Carsten. "Self-compression of intense optical pulses and the filamentary regime of nonlinear optics". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16430.
Testo completoThis thesis discusses femtosecond filaments in dispersive dielectric media. In particular, the generation of intense, few-cycle optical pulses due to self-compression in noble gases is analyzed from a theoretical as well as from an experimental viewpoint, clearly isolating the physical mechanisms behind the observed pulse self-compression mechanism. To this end, numerical simulations of high-intensity femtosecond pulses propagating in noble gases were performed, and an analytical model of the processes leading to pulse self-compression was developed. Moreover, a theoretically predicted temporal self-healing property of femtosecond filaments is experimentally proven, demonstrating that few-cycle optical pulses can recover and even benefit from a temporary, non-adiabatic increase of dispersion and nonlinearity of the order of three magnitudes as experienced during the passage from a gaseous medium to a thin silica sample. Filamentation sets in at field strengths that approach the order of inner-atomic binding forces. At these extreme intensities, highly nonlinear effects such as multiphoton ionization or tunneling effects occur. Recent experimental investigations claim a prevalent contribution of a saturation of the optical Kerr effect in filamentation prior to the onset of Drude-contributions from ionization effects. This finding is currently controversially discussed in literature. In this thesis, an independent theoretical approach was pursued, estimating high-order contributions to the all-optical Kerr effect via a Kramers-Kronig transform of multiphoton absorption cross-sections. Quite surprisingly, while only based on first principles with some moderate approximations, the results of this analysis are in strong support of the recently suggested higher-order Kerr model.
Gan, Khong Wui. "Effect of high through-thickness compression on composite failure". Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616885.
Testo completoRagan, Paula Marie. "The effect of mechanical compression on chondrocyte gene expression". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85347.
Testo completoIncludes bibliographical references (leaves 115-122).
by Paula M. Ragan.
Ph.D.
Talal, Sina. "Effect of long-term compression on rigid polymer foams". Thesis, Kingston University, 1999. http://eprints.kingston.ac.uk/20640/.
Testo completoThorp, George. "The Effect of Compression Recovery Pants on Cycling Performance". University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1430470588.
Testo completoComstedt, Erik. "Effect of additional compression features on h.264 surveillance video". Thesis, Mittuniversitetet, Avdelningen för informationssystem och -teknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-30901.
Testo completoWaizmann, Tabea. "The effect of compression and expansion on stochastic reaction networks". Thesis, IMT Alti Studi Lucca, 2021. http://e-theses.imtlucca.it/335/1/Waizmann_phdthesis.pdf.
Testo completoMangold, Nicolas. "Rhéologie du pergélisol de Mars : applications géomorphologiques et structurales ; conséquences sur l'origine des contraintes compressives". Phd thesis, Université Joseph Fourier (Grenoble), 1997. http://tel.archives-ouvertes.fr/tel-00740850.
Testo completoMango, Omar I. K. "The effect of design parameters of compressors on the performance of domestic refrigerators". Thesis, University of Hertfordshire, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259540.
Testo completoTchiotsop, Daniel. "Modélisations polynomiales des signaux ECG. Application à la compression". Phd thesis, Institut National Polytechnique de Lorraine - INPL, 2007. http://tel.archives-ouvertes.fr/tel-00197549.
Testo completoNdebele, Nothando Elizabeth. "Clustering algorithms and their effect on edge preservation in image compression". Thesis, Rhodes University, 2009. http://hdl.handle.net/10962/d1008210.
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