Teses / dissertações sobre o tema "Milieux hétérogènes (physique) – Propriétés optiques"
Crie uma referência precisa em APA, MLA, Chicago, Harvard, e outros estilos
Veja os 47 melhores trabalhos (teses / dissertações) para estudos sobre o assunto "Milieux hétérogènes (physique) – Propriétés optiques".
Ao lado de cada fonte na lista de referências, há um botão "Adicionar à bibliografia". Clique e geraremos automaticamente a citação bibliográfica do trabalho escolhido no estilo de citação de que você precisa: APA, MLA, Harvard, Chicago, Vancouver, etc.
Você também pode baixar o texto completo da publicação científica em formato .pdf e ler o resumo do trabalho online se estiver presente nos metadados.
Veja as teses / dissertações das mais diversas áreas científicas e compile uma bibliografia correta.
Liberman, Steve. "Etude optique des nanocomposites comportant des grains métalliques : exaltation de champ, propriétés linéaires et non linéaires". Versailles-St Quentin en Yvelines, 1999. http://www.theses.fr/1999VERS0024.
Texto completo da fonteGuerra, Timothée. "Interaction lumière-matière dans des suspensions de nanoparticules : homogénéisation et conception de nouvelles propriétés optiques". Electronic Thesis or Diss., Orléans, 2024. http://www.theses.fr/2024ORLE1005.
Texto completo da fonteDisordered media composed of nanoparticles are of great importance in many applications, particularly those related to energy efficiency such as radiative cooling. Understanding the light-matter interaction is therefore essential, but highly complex. Indeed, these studies often involve solving Maxwell's equations in systems made up of thousands of particles, to take account of scattering and interference phenomena. In order to reduce the ensuing numerical burden, this thesis focuses on 2D systems, with some discussion of 3D systems. In this context, the first part of this manuscript focuses on the concept of homogenization for particle systems that are small relative to the radiation wavelength and may exhibit resonances. This study highlights exotic behaviours that allow us to discuss, among other things, the link between homogenization and coherent and incoherent parts of the scattered field.The second part is dedicated to optimizing the absorption of radiation in subwavelength plates made of nanoparticles. It is shown that the use of resonant particles only results in absorption up to 70%. However, combining them with purely scattering particles results in near-perfect absorption (∼95%), through an effect similar to critical coupling. Finally, a detailed study of the mechanisms governing absorption gain in 2D has enabled them to be reproduced in 3D systems
Berthier, Serge. "Théories de la fonction diélectrique optique des milieux inhomogènes : application aux propriétés électromagnétiques des cermets". Paris 6, 1986. http://www.theses.fr/1986PA066283.
Texto completo da fonteEl-Houdaigui, Fouad. "Problèmes d'homogénéisation pour des matériaux hétérogènes viscoplastiques". Metz, 2001. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/2001/El_Houdaigui.Fouad.SMZ0118.pdf.
Texto completo da fonteAn extension of the Eshelby problem for non-linear viscous materials is considered. An ellipsoidal heterogeneity is embedded in an infinite matrix. The material properties are assumed to be uniform within the ellipsoid and in the matrix. The problem of determining the average strain rate in the ellipsoid terms of the overall applied strain rate is solved in an approximate way. The method is based on the non-incremental tangent formulation of the non-linear matrix behavior (Molinari, A. , Canova, G. R. , Ahzi, S. , 1987. A self consistent approach of the large deformation polyctristal plasticity. Acta Metall. 35, 2983-2994). In the present work this approximate solution is verified with a good agreement by comparing to the finite element calculations for various inclusion and loading conditions. The differential scheme is using the obtained behavior of the composite depends on which phase is considered to be constituted by the inclusions. This is become the interaction is different between the inclusion and the matrix when they are exchanged. Results will be given for both cases in the applications part
Paquin, Anne. "Modélisation micromécanique du comportement élastoviscoplastique des matériaux hétérogènes". Metz, 1998. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1998/Paquin.Anne.SMZ9830.pdf.
Texto completo da fonteAgoudjil, Boudjemaa. "Étude des propriétés thermophysiques et électriques de matériaux hétérogènes". Paris 12, 2006. https://athena.u-pec.fr/primo-explore/search?query=any,exact,990003939470204611&vid=upec.
Texto completo da fonteThis work presents a comparative study of thermophysical, electrical, dielectric and rheologic properties of three composites: glass and silver coated glass spheres dispersed in EVA matrix, powders of BaTiO3 dispersed in EVA matrix and PVC matrix filled with Carbon NanoTubes. This study is devoted in the first time to the composites preparation and to the measurements of the electrical conductivity (), thermal conductivity (k), dynamic viscosity () and the relative permittivity (r) (for some composites). It was shown that both relative permittivity r and electrical conductivity depend on the fillers size. However, the effect of the particles size on the thermal and the rheologic properties can be neglected. Besides, the fillers surface is an important factor controlling the thermal and the electrical conductivities. It also follows from this study the existence of a correlation between the thermal conductivity and others properties (, and r). The second objective of this study was the improvement of a measurement method of emissivity, thermal conductivity and diffusivity. The characterisation of a reference sample (PVC) allowed the validation of the measurement protocol. This includes the reproducibility study of the method, the comparison of the results to the literature data, the analysis of the limitations of the measurement protocol and a sensitivity analysis
Ahaouari, Karima. "Contribution à la modélisation de la thermoélasticité et de l'acoustoélasticité des matériaux microhétérogènes". Metz, 1990. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1990/Ahaouari.Karima.SMZ907.pdf.
Texto completo da fonteBaron, Cécile. "Le développement en série de Peano du matricant pour l'étude de la propagation des ondes élastiques en milieux à propriétés continûment variables". Bordeaux 1, 2005. http://www.theses.fr/2005BOR13036.
Texto completo da fonteRicotti, Yann. "Détermination par éléments finis de propriétés mécaniques effectives de motifs particulaires endommagés". Lyon, INSA, 2005. http://theses.insa-lyon.fr/publication/2005ISAL0016/these.pdf.
Texto completo da fonteOne estimates, associating F. E. Simulations and analytical homogenization methods (3-phase, Willis, Mori-Tanaka, models), effective elasticity moduli of damaged composite structures (PMMA/SiC, Plaster, Al/SiC, Carbon/Carbon, glass/polymer). One compares to experimental (U. S. Or mechanical) data. One questionnes the concept of “Undamaged Equivalent Inhomogeneity”, appeared in literature. Automated meshing tools for damageable inclusional patterns have been realized (code Cast3m). For inclusion fracture or debonding study, allowing comparison and/or association to analytical approaches, imbricated ellipsoidal shapes are built. In matrix phase, cubic elements mesh – over two heterogeneity levels – assemblages of damaged elementary volumes. This meshing can be performed at the voxel scale of microtomographic images. The use of surface elements allows to follow under load a not-pre-localized damage
Chen, Fengjuan. "Modélisation micromécanique de milieux poreux hétérogènes et applications aux roches oolithiques". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0134/document.
Texto completo da fonteFocusing on the effect of shape factor on the overall effective properties of heterogeneous materials, the 1st and the 2nd Eshelby problem related to 3-D non-ellipsoidal inhomogeneities with a specific application to oolitic rocks have been discussed in the current work. Particular attention is focused on concaves shapes such as supersphere and superspheroid. For rocks, they may represent pores or solid mineral materials embbeded in the surrounding rock matrix. In the 1st Eshelby problem, Eshelby tensor interrelates the resulting strain about inclusion and eigenstrain that would have been experienced inside the inclusion without any external contraire. Calculations of this tensor for superspherical pores– both concave and convex shapes – are performed numerically. Results are given by an integration of derivation of Green’s tensor over volume of the inclusion. Comparisons with the results of Onaka (2001) for convex superspheres show that the performed calculations have an accuracy better than 1%. The current calculations have been done to complete his results. In the 2nd Eshelby problem, property contribution tensors that characterizes the contribution of an individual inhomogeneity on the overall physical properties have been numerically calculated by using Finite Element Method (FEM). Property contribution tensors of 3D non ellipsoidal inhomogeneities, such as supersphere and superspheroid, have been obtained. Simplified analytical relations have been derived for both compliance contribution tensor and resistivity contribution tensor. Property contribution tensors have been used to estimate effective elastic properties and effective conductivity of random heterogeneous materials, in the framework of Non-Interaction Approximation, Mori-Tanaka scheme and Maxwell scheme. Two applications in the field of geomechanics and geophysics have been done. The first application concerns the evaluation of the effective thermal conductivity of oolitic rocks is performed to complete the work of Sevostianov and Giraud (2013) for effective elastic properties. A two step homogenization model has been developed by considering two distinct classes of pores: microporosity (intra oolitic porosity) and meso porosity (inter oolitic porosity). Maxwell homogenization scheme formulated in terms of resistivity contribution tensor has been used for the transition from meso to macroscale. Concave inter oolitic pores of superspherical shape have been taken into account by using resistivity contribution tensor obtained thanks to FEM modelling. Two limiting cases have been considered: ‘dry case’ (air saturated pores) and ‘wet case’ (water liquid saturated pores). Comparisons with experimental data show that variations of effective thermal conductivity with porosity in the most sensitive case of air saturated porosity are correctly reproduced. Applicability of the replacement relations, initially derived by Sevostianov and Kachanov (2007) for ellipsoidal inhomogeneities, to non-ellipsoidal ones has been investigated. It it the second application of newly obtained results on property contribution tensors. We have considered 3D inhomogeneities of superspherical shape. From the results, it has been seen that these relations are valid only in the convex domain, with an accuracy better than 10%. Replacement relations can not be used in the concave domain for such particular 3D shape
Seetharamdoo, Divitha. "Étude des métamatériaux à indice de réfraction négatif : paramètres effectifs et applications antennaires potentielles". Rennes 1, 2006. http://www.theses.fr/2006REN1S013.
Texto completo da fonteKhdir, Younis Khalid. "Non-linear numerical homogenization : application to elasto-plastic materials". Thesis, Lille 1, 2014. http://www.theses.fr/2014LIL10023/document.
Texto completo da fonteThis PhD dissertation deals with the numerical homogenization of heterogeneous elastic-plastic random media via large volume computations. The dissertation is presented in two main parts. The first part is dedicated to the effective elastic-plastic response of random two-phase composites stretched under uniaxial loading. The second part is focused on the effective yield response of random porous media over a wide range of stress triaxialities. In the first part, we describe a computational homogenization methodology to estimate the effective elastic-plastic response of random two-phase composite media. The method is based on finite element simulations using three-dimensional cubic cells of different size but smaller than the deterministic representative volume element of the microstructure. In the second part, we describe using the finite element method a computational homogenization study of three-dimensional cubic cells in order to estimate the effective yield surface of random porous media containing one or two populations of voids. The representativity of the overall yield surface estimates is examined using cubic cells containing randomly distributed and oriented spheroidal voids. The computational results are compared with some existing Gurson-type yield criteria
Péralès, Frédéric. "Fissuration des matériaux à gradient de propriétés : application au zircaloy hydrure". Montpellier 2, 2005. http://www.theses.fr/2005MON20202.
Texto completo da fonteNguyen, Minh Tan. "Contribution aux méthodes de calcul des propriétés élastiques et de transport des milieux hétérogènes par la Transformée de Fourier". Thesis, Paris Est, 2018. http://www.theses.fr/2018PESC1018/document.
Texto completo da fonteThis work proposed some contributions to the homogenization methods with applications to composites materials, polycristals and porous media. The effective properties are determined by solving the unit cell problem and the corresponding Lippmann-Schwinger (LS) equation. The latter is solved by means of Neumann series. Different approaches are considered to evaluate each terms of the series using analytic or numerical approaches. In the first two chapters, we formulate a general class of LS equations for the polarization in the case of conductivity and then elasticity. The operator of the latter is optimized to obtain the best convergence of the associated Neumann series and then of the better estimate of the effective of the composite. The estimate is based on both a truncated Neumann series and an approximation of its residual. In chapter 3, we deal with the mass transport properties of porous media. Classically, the filtration law is given by the Darcy equation at the macroscopic scale. In the present work we compute the corrective terms of the Darcy equation in the situation of no strict scale separation. These corrective terms are determined numerically by solving a LS equation with a fast Fourier Transform (FFT) based iterative scheme. Finally, in chapter 4, we derivative numerically some bounds for the elastic properties of polycristals still by means of an FFT iterative scheme. The approach uses an exact description of the voronoi-unit cell geometry by using the shape functions of polygons and polyhedrons. The method is applied to polycristals constituted of cubic single crystals
Tisserand, Christelle. "Étude par chromatographie gazeuse inverse des propriétés de surface de deux formes cristallographiques d'alumines : influence de différents paramètres tels l'humidité ou le dopage en magnésie". Toulouse, INPT, 2007. http://ethesis.inp-toulouse.fr/archive/00001165/.
Texto completo da fonteEl, Moumen Ahmed. "Prévision du comportement des matériaux hétérogènes basée sur l’homogénéisation numérique : modélisation, visualisation et étude morphologique". Thesis, Lille 1, 2014. http://www.theses.fr/2014LIL10077/document.
Texto completo da fonteThe homogenization is a technique of Micro-Macro passage taking into account the influence of morphological, mechanical and statistical parameters of the representative microstructure of an heterogeneous material. Numerical modeling has contributed significantly to the development of this technique to determine the physical and mechanical properties of bi-and multi-phase heterogenous materials. The main objective of this work is the prediction of the macroscopic elastic and thermal behaviors of heterogeneous materials. The mechanical and thermal behaviors was determined numerically and compared with experimental and analytical results. The variation of the representative volume element (RVE) versus volume fraction and the contrast was analyzed. This study showed the importance of a rigorous determination of the optimal RVE size. Indeed, it must take into account several parameters such as : volume fraction, contrast, type of property and the morphology of the heterogeneity. A new concept of the equivalent morphology was proposed. This concept introduces the equivalence of the elastic and thermal characteristics of a microstructure of heterogeneous materials with complex morphology and those of a microstructure containing spherical particles. This work led us to developement of a comprehensive approach to microstructural design by integrating the real morphology of heterogeneous microstructure phases incorporating at the same time the image visualization, the morphological study and the geometric and numerical modeling
Peyrega, Charles. "Prédiction des propriétés acoustiques de matériaux fibreux hétérogènes à partir de leur microstructure 3D". Phd thesis, École Nationale Supérieure des Mines de Paris, 2010. http://pastel.archives-ouvertes.fr/pastel-00568918.
Texto completo da fonteGuérin, Romuald. "Estimation des hétérogénéités de traitement lors de la cuisson de fluides alimentaires polyphasiques en cuves mécaniquement agitées". Nancy 1, 2003. http://www.theses.fr/2003NAN10166.
Texto completo da fonteIn this work, a system that allows obtaining dynamic images of temperature fields from a set of 19 electrical property measurements of the agitated fluid via a number of electrodes which are mounted non-intrusively on the vessel boundary has been developped. Using this system, it was shown the existence of thermal gradients within the vessel. In the same time, the developed tool permits to appreciate structural heterogeneity of texturing foods during cooking from a detection algorithm based on the log-likelihood ratio and applied on the first derivative of the delivered electrical signal. Experimental studies were performed with model fluids, simulating the behavior of real food fluids. That was necessary in order to be freed from the seasonal variations of real foods and to be able to discuss the physical phenomena observed during cooking of such fluids
Mikdam, Amine. "A strong-contrast statistical theory for the effective properties in heterogeneous media : application to effective conductivity". Strasbourg, 2009. http://www.theses.fr/2009STRA6141.
Texto completo da fonteHeterogeneities of materials may be due either to different atomic or molecular organization in the same material (semi-crystalline polymer or polycrystals), or to the presence of different constituents (composite materials). To determine the physical properties of these materials, experimentations, although expensive, is still necessary. Other disadvantages such as difficulty of implementing experimental procedures complicate the work of the researchers and engineers. Therefore modeling the effective properties using analytical models is positioned as a performance alternative to facilitate the understanding of the behavior of these heterogeneous materials. Many analytical models based on the volume fraction of each phase are used to predict the effective properties of heterogeneous materials. However, these models are based on different geometrical simplifications of the real material’s microstructure. This work investigates the modeling of effective conductivity (electrical or thermal) of heterogeneous materials using statistical continuum theory. This methods use probability functions to take into account the microstructure distribution, shape of constituents and their orientations
Mejias, Alberto. "Développement de l'indentation multicyclique à l'étude des matériaux massifs, revêtus et hétérogènes". Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10058/document.
Texto completo da fonteThe assessment of mechanical properties of materials by instrumented indentation tests (IIT) have been widely performed in last years. The objective of this work is to develop a methodology to analyze the mechanical behavior of materials from the data obtained by a continuous multicycle indentation test at the microscale of loads so as to limit the problems associated with the heterogeneity of the materials and to increase the amount of data for the study of thick coatings that only nanoscale analysis does not provide in the case of heterogeneous coatings. To validate our approach, it was study the hardness and the elastic modulus of homogeneous bulk materials (carbon steels), heterogeneous dense coating (hydroxyapatite), and a two-layer coating material (Nickel-Phosphorus). The study of homogeneous bulk materials allowed us, first, to validate the methodology. It is also proposed a model to estimate the hardness and elastic modulus of hydroxyapatite coatings considering the compaction of the material during the indentation process. Second, it is proposed to associate the hardness and elastic modulus to the volume fraction of crystallinity. Finally, from the multicycle indentation tests performed on the electroless Ni-P bilayer coating, a new approach is advanced to assess the elastic modulus of each layer from the expression of the reciprocal of the contact stiffness as function of the contact area originally proposed by Tricoteaux for a monolayer system, but now linked to a multilayer model based on the weight function suggested by Korsunsky
Gavérina, Ludovic. "Caractérisation thermique de milieux hétérogènes par excitation laser mobile et thermographie infrarouge". Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0012/document.
Texto completo da fonteNowadays, composite materials are widely used in the aeronautic and aerospace industries because of their high mechanical resistance. However, they have a large heterogeneity due to the fiber and matrix they are made of. In this way, for many years, the TIC team «Thermal Imaging Fields and Characterization » from TREFLE department of I2M laboratory develops methods to measure thermal in-plane properties of heterogeneous materials such as inverses (integral transforms, double singular value decomposition…) or experimental (Flash, laser diode…) methods. The recent progress made in optical control, lasers and infrared (IR) cameras enables the development of a new scanning system (based on galvanometer-mirror) which allows the easy control of a laser hot spot spatial and temporal displacements over a plane surface. The low cost of laser diodes and optical control (galvanometric mirror) systems allows to develop a laser scanning system fixed on a test bench. We can revisit the different types of thermal excitation and realize infinite spatio-temporal combinations of thermal excitations by laser method. This is one of this thesis aims. New inverse methods based on the thermal response to an instantaneous point source heating, and temperature fields separability, have been proposed. These methods allow to estimate the thermal diffusivity tensor along the main axes of anisotropy, but also out of those axes, where it is possible to estimate the anisotropy axes orientation when the heat transfer takes place out of the image axes. These methods have produced interesting results in view of their simplicity. Moreover, they made it possible to obtain in-plane thermal diffusivities maps because, compared to the other methods, they allow to obtain, locally, thermal diffusivity tensor estimations by getting a surface heat flux map using the laser optical scanner
Pétureau, Louis. "Stratégie de couplage expérimentation/modélisation dans les matériaux hétérogènes. Identification de propriétés mécaniques locales". Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2307/document.
Texto completo da fonteThe development of identification methods of material constitutive equation parameters has become fundamental to completely know the mechanical behavior. Indeed, optical methods, such as Digital Image Correlation, allows to get kinematics quantities of the constitutive equation as vectors fields. But, stresses are usually not available experimentally and one has to identify constitutive equation parameters to compute them. Several methods have been developed and answer to that problematic but most of them suppose the materials as homogeneous. This memoir is about the application of some of these methods, such as the equilibrium gap method (EGM) and the finite element model updating method (FEMU), in the case of heterogeneous materials with complex structures where mechanical properties vary spatially in the volume. The objective is to identify these local mechanical properties which rule the measured kinematics of such materials considering the isotropic linear elasticity. Firstly, both methods are detailed, implemented and compared on 2D simulated cases. The FEMU method is preferred because it is more robust in the presence of noisy data. Based on an iterative process, a parallelisation of the algorithm is achieved in order to reduce the cost of the method. In-plane experiments on polyurethane samples where heterogeneities are controlled have validated the method. Finally, two 3D applications on a polyurethane foam material and a wood-based fibrous composite have demonstrated the interest of this approach to identify local mechanical properties. The highlighting of a relationship between identified local properties and microstructural properties of these materials is made
Kandil, Karim. "Modélisation multi-physique et multi-échelle des tissus mous stratifiés : application à la réponse multi-axiale du disque intervertébral humain". Thesis, Lille 1, 2020. http://www.theses.fr/2020LIL1I040.
Texto completo da fonteThe intervertebral disc is probably the most extraordinary tissue that the nature produces, mainly for its unusual time-dependent properties strongly influenced by the biochemical environment and the applied mechanical loading. Establishing accurate structure-property relationships for intervertebral disc annulus fibrosus tissue is a fundamental task for a reliable computer simulation of the human spine. The difficulty emanates from the multi-axiality and the anisotropy of the tissue response along with regional dependency of a complex hierarchic structure interacting with the biochemical environment. In addition, the annulus fibrosus exhibits an unusual time-dependent transversal behavior for which a complete constitutive representation is not yet developed. A physically-based chemo-viscoelastic constitutive model that takes into account an accurate disc annulus structure in relation with the biochemical environment is proposed. Numerical models of annulus specimens and lumbar functional spinal units (one disc and the adjacent vertebrae) are designed while taking into consideration the interlamellar matrix connecting the fibers-reinforced lamellae. At the specimen scale, the model capabilities are verified by experimental comparisons under various conditions in terms of osmolarity, strain-rate and multi-axiality while considering the regional dependency. Our results highlight the determinant role of the interlamellar matrix in the disc multi-axial response. The different scenarios applied to lumbar units show encouraging multi-axial predictive capabilities of our approach making it a promising tool for human spine behavior long-term prediction including age-dependency
Lux, Jérôme. "Comportement thermique macroscopique de milieux fibreux réels anisotropes : étude basée sur l'analyse d'images tridimensionnelles". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2005. http://tel.archives-ouvertes.fr/tel-00366280.
Texto completo da fonteRozanski, Adrian. "Sur la représentativité, la taille minimale du VER et les propriétés effectives de transport des matériaux composites aléatoires". Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10137/document.
Texto completo da fonteThe thesis focuses on random composites and some specific features such as: the minimum size of a representative volume element (RVE) and the determination of effective transport properties. The main objective is to formulate a computationally efficient method which would allow for quick determination of effective properties. The effective properties of transport are considered. It is shown that this class of properties can be estimated either by performing calculations over one large sample or by averaging over a sufficient number of smaller microstructure realizations. However, for a given type of microstructure; the size of such smaller realizations can not be smaller than some critical minimum size. It is shown that this critical size of RVE is strongly affected by several parameters. These are: microstructure type, volume fractions of constituents, contrast in mechanical properties of composite phases, number of performed realizations as well as a desired accuracy. Furthermore, two separate types of representativity are introduced: geometrical representativity and representativity with respect to overall transport properties. Therefore, two distinct criteria for the minimum size of RVE are formulated based on the properties of the two-point correlation function. Comparing to other methods proposed in wide literature, the criterion formulated in the thesis gives an advantage: the condition proposed includes microstructure morphology. Therefore, in order to determine the minimum size of RVE none numerical calculations like those of FE are necessary. A validation of proposed methodology is performed on several examples of 2D microstructures
Ben, Elhaj Salah Sami. "Modélisation non-locale et stochastique de matériaux à fort gradient de propriétés par développement asymptotique". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2019. http://www.theses.fr/2019ESMA0018.
Texto completo da fonteThe aim is to propose a macroscopic, deterministic and non-local model, constructed by scale transition for heterogeneous materials with high property gradients and containing a random distribution of inclusions. More precisely, the inclusions are distributed in an elastic matrix according to a stochastic ergodic process. Several non-local models exist in the literature, but they do not allow (or very little) to obtain non-local quantities and/or fields at the macroscopic scale from a scale-transition. Besides, it is often difficult to link the non-local parameters to the microstructure. To this aim, we developed a two-step approach.In the first stage, we combined the method of asymptotic developments with an energetic approach to reveal a second displacement gradient in the strain energy. The advanced model involves three homogenized elasticity tensors functions of the stochastic parameter and of the phase properties. As opposed to the literature, the model involves two characteristic lengths strongly linked to the microstructure. These lengths define two morphological representative elementary volumes on which full field simulations are performed in order to determine the macroscopic strain tensors at orders 0 and 1 involved in the formulation of the model. In order to test this first version of the model, numerical simulations were performed. The estimate of the classical part of the energy, coming from the local part of the fields, has been successfully compared to classical bounds for a composite bar consisting of a random distribution of two homogeneous and isotropic elastic materials. Then, numerical solving of the whole model including the non-local terms has been performed in the three-dimensional case. Two types of microstructures with increasing morphological complexity were used. The first ones are virtual microstructures generated from a given simple pattern randomly distributed throughout the structure and composed of a big inclusion circled by six identical small ones. The second are real microstructures of Ethylène-Propylène-Diène Monomère (EPDM) obtained by tomography and containing clusters of inclusions with complex structures.In order to obtain a macroscopic model that can be used for structure analysis, without any full field intermediate calculations, a second scale transition has been performed using stochastic variational homogenization tools in the ergodic case. More precisely, the Γ-convergence method has been used in order to have a convergence of energy rather than that of mechanical fields, aiming at keeping a strong microstructural content. In fine, the model is macroscopic, non-local, deterministic and strongly connected to the microstructure. Non-local effects are now accounted for by the presence of the second displacement gradient but also by the presence of the virtual (memory) displacement field of the inclusions. The link with microstructure is still manifest through the presence of the stochastic parameter and phase properties, but also by the presence of the asymptotic fractions of the inclusion phase in the material and in each of the morphological volumes defined by the model characteristic lengths. In order to prepare the use of the model for structure calculations, a non-local finite element enriched with Hermit-type interpolations was implemented in FoXtroT, the finite element solver of the Pprime Institute. This element takes into account the virtual (memory) displacement field related to inclusions as well as the gradients of the macroscopic and virtual displacement fields. The first numerical results on this aspect, to our knowledge never discussed in the literature, are promising
Maanane, Yassine. "Identification expérimentale de propriétés radiatives à partir de méthodes Monte Carlo Symbolique : Application aux matériaux hétérogènes à haute température". Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI093.
Texto completo da fonteThis work is about radiative heat transfer in heterogeneous materials used in high temperature applications, such as fire safety in buildings, insulation of furnaces or thermal protection for aerospace vehicles. These semitransparent materials with heterogeneous structure absorb and scatter thermal radiation, and their radiative properties at high temperatures are generally unknown. In order to accurately model radiative transfer within these materials and to quantify the impact of radiation in the global heat transfer, it is necessary to determine absorption and scattering radiative properties. In this thesis, these properties are identified by inverse method from radiative models and spectrometric measurements. Experimental identification from spectrometric measurements provides radiative properties at temperature levels close to real operating conditions for the material of interest. To carry out the analysis of the inverse problem, we develop here a methodology based on Symbolic Monte Carlo (SMC) methods. These methods allow expressing radiative fluxes as a simple function of the so-called symbolic parameters. A single calculation expresses radiative fluxes overall the parameter space, which turns out to be very useful in an inversion approach. These methods are particularly suitable for expressing radiative quantities as a function of temperature, of absorption and scattering coefficients. In this thesis, we also propose a new symbolic method based on a series expansion of orthogonal polynomials, allowing the extension of SMC methods to other types of parameters (geometric, phase function, etc.). Expressions of radiative fluxes as functions of radiative properties obtained by SMC are employed to analyze if the inverse problem is well-posed and to efficiently identify the radiative properties, while taking into account the experimental and numerical uncertainties. On the other hand, if the inverse problem is ill-posed, this method can analyze the input of other types of measurements that may allow the identification. The methodology is applied in this work to the identification of radiative properties of a family of heterogeneous materials composed of Quartz fibers
Da, Daicong. "Topological optimization of complex heterogeneous materials". Thesis, Paris Est, 2018. http://www.theses.fr/2018PESC1102/document.
Texto completo da fonteMechanical and physical properties of complex heterogeneous materials are determined on one hand by the composition of their constituents, but can on the other hand be drastically modified by their microstructural geometrical shape. Topology optimization aims at defining the optimal structural or material geometry with regards to specific objectives under mechanical constraints like equilibrium and boundary conditions. Recently, the development of 3D printing techniques and other additive manufacturing processes have made possible to manufacture directly the designed materials from a numerical file, opening routes for totally new designs. The main objectives of this thesis are to develop modeling and numerical tools to design new materials using topology optimization. More specifically, the following aspects are investigated. First, topology optimization in mono-scale structures is developed. We primarily present a new evolutionary topology optimization method for design of continuum structures with smoothed boundary representation and high robustness. In addition, we propose two topology optimization frameworks in design of material microstructures for extreme effective elastic modulus or negative Poisson's ratio. Next, multiscale topology optimization of heterogeneous materials is investigated. We firstly present a concurrent topological design framework of 2D and 3D macroscopic structures and the underlying three or more phases material microstructures. Then, multiscale topology optimization procedures are conducted not only for heterogeneous materials but also for mesoscopic structures in the context of non-separated scales. A filter-based nonlocal homogenization framework is adopted to take into account strain gradient. Finally, we investigate the use of topology optimization in the context of fracture resistance of heterogeneous structures and materials. We propose a first attempt for the extension of the phase field method to viscoelastic materials. In addition, Phase field methods for fracture able to take into account initiation, propagation and interactions of complex both matrix and interfacial micro cracks networks are adopted to optimally design the microstructures to improve the fracture resistance
Zeng, Tao. "Modélisation multi-échelle des comportements plastiques et viscoplastiques des géomatériaux polycristallins". Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10099/document.
Texto completo da fonteMost geomaterials are heterogeneous material at different scales. The macroscopic mechanical behavior of these materials depends directly on the mineralogical composition and microstructure as well as their evolution. The present study makes a simple trial to extend the most widely used polycrystalline model in metallography to a typical quasi-brittle geological material--granite. The standard yield criterion and plastic potential are modified to consider the main mechanical features of geomaterial, e.g. pressure sensitivity and plastic dilatancy. The full self-consistent model firstly proposed by Hill is adopted to relate the local fields and overall ones. And the macro response of polycrystal is determined by the classical homogenization process. The numerical implementation of local and macro stress update procedure are given and the possible difficulties encountered are pointed out. The identification of seven micromechanical parameters is briefly described. The validity of the developed model is checked through the comparisons between model's predictions and experimental data on both conventional and true triaxial compression tests, respectively
Faye, Mactar. "Structure interne et propriétés thermiques macroscopiques, application aux matériaux de construction". Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30032/document.
Texto completo da fonteThe objective of this thesis is to study the impact of the internal structure of isotropic granular materials on the macroscopic thermal properties. We have developed a model to solve the heat transfer problem within a heterogeneous three-dimensional material. This code is coupled with an algorithm generating random structure. After an experimental validation, we first generated granular materials and we characterized their internal structure; then we studied the impact of this structure on the thermal conductivity. We also developed a new experimental method for measuring the heat capacity area of a wall element with complex internal structure. The originality of this method is the coupling of an analytical model of heat capacity area, which is independent of the thermal properties of the constituents, and an experimental study
Mevel, Benoît. "Propriétés structurales, magnétiques et de transport d'alliages hétérogènes Co(x)Ag(1-x) et Ni(x)Ag(1-x)". Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10071.
Texto completo da fonteAnoukou, Kokou. "Modélisation multi-échelle du comportement mécanique de nanocomposites polymères à renforts d’argile de type montmorillonite : approche micromécanique et simulation de dynamique moléculaire". Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10139/document.
Texto completo da fontePolymer nanocomposites reinforced with clay minerals have attracted a great consideration during the last two decades. That can be explained, firstly, by the availability and the reduced production cost of the reinforcing phase, and secondly, by the remarkable improvements in physical and mechanical properties. These improvements are observed even at very low amounts of reinforcements compared to their microcomposite counterparts. The development of these new materials creates a keen interest both in academic and industrial research. However, the mechanisms responsible of these property improvements are still poorly understood and remain a major concern of researchers. This work contributes to the understanding and to the development of predictive tools of the mechanical behavior of polymer nanocomposites reinforced with montmorillonite clay using two modeling approaches: the micromechanics of heterogeneous materials and the molecular dynamics simulation. An analytical micromechanical model based on the self-consistent approach is developed. The proposed model is validated by our experimental data and those from the literature. A new molecular dynamics simulation protocol is proposed for the modeling of these nanomaterials at the nanometric scale. This approach has allowed us, inter alia, to get insight into the molecular interactions between the different components and to determine the effective elastic properties of the nanocomposite
Vallade, Alexis. "Modélisation multi-échelles des shales : influence de la microstructure sur les propriétés macroscopiques et le processus de fracturation". Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10123/document.
Texto completo da fonteThis research study aims at developing tools and numerical methods to model the influence of the microstructure of shales on macroscopic properties and cracking process. The first part of the document is dedicated to the description of a 3D Finite Elements model (E-FEM) developed to represent the microstructure and cracking phenomena. This model is part of the methods with discontinuities. Two cracking criteria are described, a mode I criteria (Rankine) and a mode II criteria (Mohr-Coulomb). These criteria will be used to characterize the influence of the microstructure of shales on the macroscopics properties in triaxial compression testing. More particularly, the impact of the presence of kerogen in the shale rock is considered. The second part presents a domain decomposition method (mortar method) used to reduce computation time. This method has the advantage of allowing the use of non-conforming mesh, so a local mesh refinement is possible. This method has been integrated into a computing code using the component-oriented programming and more specifically the CTL middleware. The computing code solves both linear and nonlinear problems using the E-FEM model. The last part concerns the study of the influence of mineralogy on the cracking process using the parallelized calculation code. A hydro-mechanical coupling model is then developed and applied to the calculation of crack to measure the impact of cracking on the shales permeability
Mann, Ruddy. "Experiments and thermomechanical modelling of braking application & friction material characterization with loading history effect". Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10016.
Texto completo da fonteThe railway high speed sector is currently expanding with an increase of the maximum operating speed and load leading to the necessity of improving the capacity of the disc braking to ensure performances despite the additional energy to dissipate. The current methodology used for the development of these material is based on trial-error experimental feedback. The goal is to develop alternative methodologies, with theoretical and numerical models for designing these components. Difficulties are the complex interactions between tribological, thermal, mechanical, chemical effects and interactions between scales from the surface to the system. This work is focused on the thermomechanical aspects with the challenge of developing a realistic numerical model and considering the material evolution assuming that this evolution affects the braking performances. In the first step, an original methodology has been developed to characterize the friction material submitted to realistic solicitations and allowing identifying bulk material behavior. Characterization has been done for different braking loading histories. Corresponding thermo-elastic-plastic behavior models have been proposed. The second step of this work is the development of a finite element model of the brake system, including the sintered material models previously identified and the evolution with loading history. The numerical results illustrate the impact of the friction material evolution regarding the braking performances. They are also compared to experimental tests carried out on a real scale braking bench
Du, Kou. "Modélisation micromécanique de géomatériaux en prenant en compte des anisotropies microstructurale et matricielle". Electronic Thesis or Diss., Université de Lorraine, 2021. http://docnum.univ-lorraine.fr/public/DDOC_T_2021_0254_DU.pdf.
Texto completo da fonteThe mechanical properties of heterogeneous geomaterials are evaluated by simultaneously taking into account the microstructural anisotropy as well as the one of matrix. To this end, the microstructural anisotropy is represented by the complexity of porous shape which is considered in the present work as concave or convex by particular attention to the superspherical and the axisymmetrical superspheroidal pores. The concentration and contribution tensors are numerically computed using Finite Element Method (FEM), which are next approximated by analytical expressions for the case of the concavity parameter being p<1, to evaluate the associated effective properties, such as effective elastic and thermal responses. Specifically, to solve the 2nd Eshelby problem (Eshelby (1961)) in the case of 3D non-ellipsoidal inhomogeneities, we make use of a recently developed adapted boundary condition (Adessina et al. (2017)) based on far-field solution (Sevostianov and Kachanov (2011)) to incorporate the matrix anisotropy and to correct the bias induced by the bounded character of the mesh domain, which allows to accelerate the computation convergence without sacrificing its accuracy. Simultaneously by complying with the numerical homogenization technique, the compliance/resistivity contribution tensors are computed for different forms of pores (particular attention of superspheroidal and superspherical ones) embedded in a transversely isotropic matrix. The proposed numerical method is shown to be efficient and accurate after several appropriate assessments and validation by comparing its predictions, in some particular cases, with analytical results and some available numerical ones. On the basis of these "3D" Finite Element Modeling, approximate relations of the property contribution tensors in the two aforementioned reference concave cases, supersphere and axisymmetric superspheroid, are developed for both elastic and thermal problems. Note here that the spherical pore (i.e. concavity parameter p=1) and circular crack (i.e. aspect ratio γ → 0), which can be considered as two particular cases, are also numerically studied. This allows to assess and validate the proposed method in the present work. Moreover, in the frame of homogenization, application to the typical porous geomaterials with transversely isotropic matrix such as clay rocks is presented to illustrate the impact of the concavity parameter and the matrix anisotropy on overall properties through several micromechanical homogenization schemes such as non-interaction approximation, Mori-Tanaka-Benveniste scheme and Maxwell scheme. The methodology of evaluation of the elastic and thermal properties of heterogeneous material aforementioned is proposed based on micromechanical homogenization via multiscale modeling. The overall properties of composites with regular pores are also predicted using direct finite element approaches and then compared against micromechanical modeling. The effect of microstructure is analyzed by considering periodic RVEs containing random arrangements of pores formed by transversely isotropic phases
Bogdan, Mateusz. "Modélisation morphologique multi-échelles de matériaux cimentaires -- Application à la prédiction de propriétés effectives de diffusion". Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0021/document.
Texto completo da fonteThe aim of the present Ph.D. is to develop a methodology and a simulation framework able to predict as accurately as possible effective properties regarding diffusion in saturated cement based materials. A sequenced multiscale framework is developed to perform numerical homogenization on diffusive properties, and thus predict effective properties. The general outline is to model every scale in concrete-like materials, from the C-S-H gel, to the concrete scale, and with the help of a proper framework, be able to predict effective properties. The methodology relies on the following key points for every considered scale :- Inclusion-matrix like morphologies are generated through level set methods applied to multi-dimensional correlated random fields. This approach, together with few morphological operations allows to generate 3D morphologies with given particle size distributions (PSD), or pore size distributions. Then, it is also possible, from the initial state, to make those morphologies evolve according to any descriptive model (e.g. in terms of volume fraction), via the level set.- The morphological description of each scale is chosen according to the most acknowledged experimentations and models. In addition, at the cement paste scale, a hydration model was developed to predict the evolution of the cement paste through time, in terms of volume fractions. The choice was made to keep a simple model (Jennings & Tennis), with few but essential input parameters (mineral cement composition, w/c ratio, PSD). It has only been modified to include recent experimental results, such as the maximal hydration degree, or the hydration rates.- The upscaling framework was built to suit every considered scale, and allows to assess effective properties based on energy conservation principles. Similar to Hill's theory for elasticity, the framework is build to ensure to proper scale separation regarding effective diffusion coefficients.- Lastely, the numerical context is based on E-FEM techniques, which allows to use unstructured meshes, on which the morphologies are projected. This way, any material discontinuity in dealt within the FE, and thus does not require averaging properties, or joint elements. Results from every scale will be used as inputs at the higher scales, and effective diffusion coefficients are thus estimated
Kossman, Stephania. "Indentation instrumentée multi-échelles de matériaux homogènes et multi-matériaux". Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10180/document.
Texto completo da fonteThe mechanical properties (hardness and elastic modulus) can be studied at different scales as a function of the composition and microstructure of materials (number of phases, constituent distribution, grain size…). In this work, we studied this mechanical response at the nano, micro and macroscopic scales, through different instruments that allow to apply loads ranging from 20 mN up to 2 kN generating penetrations depths between 100 nm up to 2.5 mm. The first stage consisted in the improvement of the experimental conditions, developing and interpreting the experimental data, following a rigorous metrological methodology, in order to achieve the connection between the results obtained at the three studied scales. These tests were performed in metallic industrial materials, which are sufficiently homogeneous at the tested penetration depths (steels and aluminum alloy). For example, we had proposed an alternative approach to the Oliver and Pharr method to fit the unloading curve to estimate the elastic modulus. Afterwards, this methodology is applied to the study of the response obtained by indentation in a composite material, which is highly heterogeneous, used in the fabrication of brake pads in the railway industry. The obtained results (spatial distribution on the surface and through the volume of hardness and elastic modulus) are going to be valuables in the applications of models to study the squeal noise during braking, looking to reduce its effects
Vasoya, Manishkumar Laxmanbhai. "Study on Tensile Failure of Highly Heterogeneous Brittle Materials". Electronic Thesis or Diss., Paris 6, 2014. http://www.theses.fr/2014PA066650.
Texto completo da fonteThe development of predictive tools that bridge microscopic to macroscopic scales in brittle fracture is the key challenge of this thesis. In the context of quasi-static planar crack propagation under mode I loading, it has been shown, using first-order weight-function perturbation approaches that, for weak heterogeneities, when the material is homogeneous in the propagation direction, the Griffith’s threshold is always reached for all points of the crack front so that the effective toughness is simply equal to the average of the local toughness. Here, we address the same problem but with stronger toughness heterogeneities. In the first part, we consider a half-plane crack embedded in an infinite body or in a finite thickness plate and we extend analytically the first-order approaches to the second-order. We show that even if Griffith’s criterion is reached all over the front, the deformations of the front may induce some second-order deviation of the effective toughness from its mean value. We also perform peeling experiments that define their range of applicability. In the second part, we consider a circular crack propagating in an axisymmetric toughness map and solved the problem numerically, for any toughness contrast and heterogeneity size, by iterating the first-order formulas. For large enough heterogeneity contrast, the Griffith’s criterion can no more be reached everywhere: some points of the front are pinned by strong impurities, while some other parts advances continuously. Correspondingly, the effective toughness is shown to decrease with size and strength of heterogeneity from the average value of the local toughness down to its minimum one
Parenteau, Thomas. "Modélisation micromécanique de composites thermoplastiques élastomères à matrice polypropylène". Phd thesis, Université de Bretagne Sud, 2009. http://tel.archives-ouvertes.fr/tel-00404452.
Texto completo da fonteL'objectif de cette étude est la caractérisation expérimentale et la modélisation du comportement mécanique de composites thermoplastiques élastomères (TPE). Ces matériaux sont composés d'une matrice en homopolymère polypropylène isotactique (PP) et de particules d'élastomère recyclées à base d'éthylène propylène diène monomère (EPDM). La nature complexe du PP nous a incité à développer un modèle micromécanique, en distinguant dans ce polymère une phase amorphe et une phase cristalline. A partir d'un motif représentatif permettant d'estimer les propriétés élastiques du PP en fonction du taux de cristallinité, un modèle micromécanique de type autocohérent généralisé est comparé à un modèle macroscopique plus simple pour décrire son comportement élastoviscoplastique. La loi de comportement des TPE est construite, via une démarche d'homogénéisation, à partir du comportement mécanique des particules d'EPDM et de la loi macroscopique déterminée pour le PP. Les prévisions des modèles sont analysées et comparées aux résultats d'essais de flexion, de traction et d'indentation. Les modèles développés ont été implantés dans le code « éléments finis » Abaqus afin de permettre le calcul de pièces industrielles.
Mnasri, Faiza. "Étude du transfert de chaleur et de masse dans les milieux complexes : application aux milieux fibreux et à l’isolation des bâtiments". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0169/document.
Texto completo da fonteInternational energy context requires a new orientation to the building sector as in construction or in renovation. Any new solution must be technically efficient and environmentally acceptable. In this thesis, the object is to achieve a numerical and experimental analysis of a building biobased materials. Some of these materials are included from the study of a transborder project to the Lorraine region (France, Belgium and Luxembourg). Indeed an Ecotransfaire project was included in this work. This project has been oriented to the development of a sustainable eco materials chain. A process of analysis has been established in order to select the materials candidates on the basis of scientific, geographical and environmental criteria. The answers are moving towards the integration of bio-based materials. These materials are subject of several heat and mass transfers phenomena. So understanding these mechanisms within a building material has been achieved firstly. This resulted on a coupled model of heat transfer, air, moisture experienced by the HAM model. This model is applied to a wooden building material whose its structure is assumed homogeneous. Then, this model was implemented and solved by the finite element method. Its numerical solution is validated by analytical results available in the literature. The study of sensitivity of the model coupling, dimensions in space, the boundary conditions and the variability of input parameters is also presented. One of the difficulties of using this model is the case of heterogeneous materials. Thus, in this work, we propose an approach of characterization of a heterogeneous lignocellulosic composite material with a porous structure. In fact, this material is composed of two components: Wood and cement. The wood is presented by a shapes aggregates with irregulars sizes and the cement is considered as the binder in the composition. The object was to predict its equivalent intrinsic properties (thermal conductivity and vapor permeability) by using the micro-tomography techniques.The methodology consists to determine the structure of the sample by taking images at the microscopic scale. Once the structure of the sample is generated, we will conduct from a reconstruction of the two-dimensional representation to a three dimensional structure by using a numerical tool which determines the equivalent properties of the 3D reconstructed domain. The permeability as well as the equivalent thermal conductivity are the two properties evaluated in this configuration. These two properties are strongly depend to the porosity and to pore distribution in the continuous phase (the solid one). Moreover the composition of the material and the volume fractions of each components influence the formation of microstructure and consequently the thermal and hydric transfers
Nguyen, Dac Loi. "Nouvelle méthodologie d'identification des propriétés mécaniques locales d'un matériau hétérogène par nanoindentation : application aux matériaux du génie civil". Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1028/document.
Texto completo da fonteThe present work proposes and develops a complete methodology for identifying the local mechanical properties of a heterogeneous material at the scale of the constitutive phases. It is a combination of very diverse skills in theory, in numerical simulation and in experimentation. More precisely, the theoretical part concerns the determination of the nano-micro relations for the indentation module; the numerical part based on the yield design theory is carried out to find the last relations applicable for the hardness; and the last part is performed to obtain homogenized properties by the experimental way using the nano-indentation technique. The experimental study of the thesis is for the purpose of determining indentation properties of different cement paste samples. A complete experimental program, is developed, which allows characterizing the main phases at the micrometric scale of this material, among which we are mainly interested in the C-S-H matrix phases. The modeling of the problem related to the penetration of an indentation point into a material is studied. For this, the first way, based on the kinematic approach of the yield design theory, consists in trying to construct ruin mechanisms analytically, then to make them evolve according to the change of the initial geometry, in order to obtain the corresponding ultimate load. The second way is then to follow the same approach, but by building numerically these ruin mechanisms. The obtained load depends naturally on the retained criteria parameters, which are determined by the combination with the experimental results. The Von-Mises and Tresca strength criteria for purely coherent materials as well as the elliptical one are examined in this work
Sacristán, López-Mingo Carlos Javier. "Etude des propriétés acoustiques et comportement à l'impact de matériaux poreux de type mousses métalliques homogènes et inhomogènes". Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS035/document.
Texto completo da fonteThis work is concerned with the theoretical and experimental study of the acoustical properties of macroscopically homogenous and inhomogeneous porous media as well as their mechanical response to impacts. The model of Johnson - Champoux - Allard appeared adapted for the acoustical modeling. This model, associated with a recently developed approach involving the concept of parallel transfer matrices has lead to a new approach of macroscopically inhomogeneous porous materials based on “mixtures of materials”. Furthermore, a parametric study of the absorption coefficient as a function of porosity and frequency has been proposed. The maximums of absorption as well as the envelop of the absorption curves have been studied as functions of porosity. First, a theoretical material with independent parameters has been studied. Real materials with nonindependent parameters were then investigated with the help of a model relating their properties to the porosity. Finally, a comparison between the acoustical and mechanical properties has been initiated in view of determining an objective criterion that will allow to propose a trade off between the two fields
Ren, Xiaotao. "Modélisation semi-analytique des pertes par courants de Foucault dans les matériaux composites". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS159/document.
Texto completo da fonteComposite materials have been widely used in Electrical Engineering, and they have stimulated a growing number of scientific research, especially when it comes to energy savings. Soft Magnetic Composites (SMC) incorporate the attributes of different constituents. They can be designed to exhibit high permeability and to dissipate low Eddy Current (EC) losses compared to more conventional structures such as laminated steel. Nevertheless, electromagnetic properties of SMC are not easily determined. Numerical tools such as finite element method (FEM) are usually employed to provide a full-field description of SMC. As the microstructure has to be finely meshed, it brings significant numerical burden and instabilities. To overcome this restriction, semi-analytical homogenization methods are adapted and applied here. They consist in developing a complex permeability model. In the complex permeability model for SMC, the static magnetic permeability and EC losses are integrated respectively as the real and imaginary part of the complex permeability. Classical estimates are applied to determine the macroscopic effective magnetic permeability. A correct determination of the effective permeability, i.e. the real part of the complex permeability, is crucial for the estimate of EC losses. EC losses formulas are derived for SMC with periodic microstructure in 2D and 3D cases. Furthermore, different approaches of field averaging are employed to obtain lower and upper bounds on the EC losses in SMC. The complex permeability model is then applied to analyze a transformer structure. The magnetic field and EC losses distribution can be obtained on the equivalent homogenized transformer. The results are compared to the full-field calculations on the heterogeneous transformer. A good consistency is observed. Finally, the effect of mechanical stress on the magnetic permeability and loss property of SMC is studied, which leads to a coupled formula of EC loss density as a function of macroscopic stress and magnetic field
Vasoya, Manishkumar Laxmanbhai. "Study on Tensile Failure of Highly Heterogeneous Brittle Materials". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066650.
Texto completo da fonteThe development of predictive tools that bridge microscopic to macroscopic scales in brittle fracture is the key challenge of this thesis. In the context of quasi-static planar crack propagation under mode I loading, it has been shown, using first-order weight-function perturbation approaches that, for weak heterogeneities, when the material is homogeneous in the propagation direction, the Griffith’s threshold is always reached for all points of the crack front so that the effective toughness is simply equal to the average of the local toughness. Here, we address the same problem but with stronger toughness heterogeneities. In the first part, we consider a half-plane crack embedded in an infinite body or in a finite thickness plate and we extend analytically the first-order approaches to the second-order. We show that even if Griffith’s criterion is reached all over the front, the deformations of the front may induce some second-order deviation of the effective toughness from its mean value. We also perform peeling experiments that define their range of applicability. In the second part, we consider a circular crack propagating in an axisymmetric toughness map and solved the problem numerically, for any toughness contrast and heterogeneity size, by iterating the first-order formulas. For large enough heterogeneity contrast, the Griffith’s criterion can no more be reached everywhere: some points of the front are pinned by strong impurities, while some other parts advances continuously. Correspondingly, the effective toughness is shown to decrease with size and strength of heterogeneity from the average value of the local toughness down to its minimum one
Niezgoda, Mathieu. "Modélisation du transfert thermique au sein de matériaux poreux multiconstituants". Phd thesis, Université d'Orléans, 2012. http://tel.archives-ouvertes.fr/tel-00829217.
Texto completo da fonteBodian, Pape Arago. "Propagation des ultrasons en milieu hétérogène et anisotrope : application à l'évaluation des propriétés d'élasticité et d'atténuation d'aciers moules par centrifugation et de soudures en Inconel". Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00679694.
Texto completo da fonteKalo, Kassem. "Caractérisation microstructurale et modélisation micromécanique de roches poreuses oolithiques". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0203/document.
Texto completo da fonteThe aim of this work is to study the influence of the microstructure of heterogeneous porous rocks on the behavior at the macroscopic scale. Thus, we characterized the microstructure and micromechanical properties (thanks to nano-indentation tests) of two porous oolitic rocks (Lavoux limestone and iron ore) to calculate their effective mechanical and thermal properties. Oolitic rocks are constituted by an assemblage of porous grains (oolites), pores and inter-granular crystals. Scanning electron microscopy and X-ray 3D Computed Tomography were used to identify the different components of these rocks. Particular attention was given to X-Ray computed tomography since this analytical method allows the characterization of the porous network (size, spatial distribution, and volume fraction), and the shapes of oolites and inter-oolitic crystals. The novelty of this work lies in taking into account the 3D real shape of pores. Hence, we approximated porous oolites by spheres and irregularly shaped pores by ellipsoids. This approximation was performed thanks to the principal component analysis (PCA), which provides the geometrical properties such as length of semi-axes and orientation of resulting ellipsoids. The sphericity of the approximated oolites was calculated and the values close to 1 allowed us to consider oolites as spheres. To verify the approximation in the case of pores, we evaluated the contribution of these irregularly shaped three-dimensional pores to the overall elastic properties. Thus, compliance contribution tensors for 3D irregular pores and their ellipsoidal approximations were calculated using the finite element method (FEM). These tensors were compared and a relative error was estimated to evaluate the accuracy of the approximation. This error produces a maximum discrepancy of 4.5% between the two solutions for pores and ellipsoids which verifies the proposed approximation procedure based on PCA. The FEM numerical method was verified by comparing the numerical solution for compliance contribution tensors of ellipsoids to the analytical solution based on Eshelby’s theory. The difference between these two solutions does not exceed 3%. The same numerical method was used to calculate thermal resistivity contribution tensors. Calculated compliance and resistivity contribution tensors were used to evaluate effective elastic properties (bulk modulus and shear coefficient) and effective thermal conductivity by considering the two-step Maxwell homogenization scheme. The results showed an important influence of the porosity on effective properties. Finally, the results obtained for irregular pores were compared to those for ellipsoidal ones and they showed a good agreement with a maximum deviation of 4% which verifies once again the approximation of irregularly shaped pores by tri-axial ellipsoids