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Dissertations / Theses on the topic 'Inhomogeneous materials'

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Published: 4 June 2021
Last updated: 30 July 2024

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1

Feder, David. "Inhomogeneous d-wave superconductors /." *McMaster only, 1997.

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2

Barabash, Sergey V. "Topics in the Physics of Inhomogeneous Materials." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1053637716.

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3

Poladian, Leon. "Effective transport and optical properties of composite materials." Phd thesis, Department of Theoretical Physics, 1990. http://hdl.handle.net/2123/11724.

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4

Koss, Robert Stephen. "Numerical studies of macroscopically disordered materials /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487322984316204.

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5

Larsson, Ashley Ian. "Mathematical aspects of wave theory for inhomogeneous materials /." Title page, table of contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phl334.pdf.

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6

Kusuma, Jeffry. "On some mathematical aspects of deformations of inhomogeneous elastic materials /." Title page, contents and summary only, 1992. http://web4.library.adelaide.edu.au/theses/09PH/09phk97.pdf.

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7

Kinkade, Kyle Richard. "Divergence form equations arising in models for inhomogeneous materials." Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/900.

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8

Azis, Mohammad Ivan. "On the boundary integral equation method for the solution of some problems for inhomogeneous media." Title page, contents and summary only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09pha995.pdf.

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Errata pasted onto front end-paper. Bibliography: leaves 101-104. This thesis employs integral equation methods, or boundary element methods (BEMs), for the solution of three kinds of engineering problems associated with inhomogeneous materials or media: a class of elliptical boundary value problems (BVPs), the boundary value problem of static linear elasticity, and the calculation of the solution of the initial-boundary value problem of non-linear heat conduction for anisotropic media.
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9

Huang, Zhoushen. "Spontaneous formation of charge inhomogeneity on silica surface immersed in water /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202007%20HUANG.

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10

Gammage, Justin Wilkinson D. S. "Damage in heterogeneous aluminum alloys /." *McMaster only, 2002.

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11

Esward, T. J. "Problems in the ultrasonic characterisation of inhomogeneous materials due to scattering." Thesis, University of Surrey, 1995. http://epubs.surrey.ac.uk/843619/.

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Ultrasound wavefronts travelling through inhomogeneous materials such as biological tissues and tissue mimics are distorted by scattering processes. It has been proposed that measurements of these transmitted wavefronts may be used to define the contribution of coherent and incoherent scattering to the attenuation coefficient of such materials, by means of a comparison between the outputs of phase sensitive and phase insensitive receivers. Measurements of the complex pressure fields transmitted by scattering specimens consisting of glass beads in silicone rubber and by specimens of ox liver, kidney and myocardium have been carried out by point- by-point mapping of the amplitude and phase of the fields using a new design of pvdf needle hydrophone in a high precision scanning tank. It is demonstrated that transmission measurements of the scattered fields are not independent of the size and location of the measurement plane, and the proposed method is unlikely to be helpful in quantifying material properties. Alternative techniques based on the measurement of the angular scattering pattern of such materials are shown to be able to characterise scattering specimens consisting of glass beads in agar and gelatin, and to be able to distinguish normal ox myocardium from ox liver and kidney.
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12

Becker, Jens. "Investigation of the microstructure of heterogeneous materials using ultrasonic waves." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/22997.

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13

Lam, Tsz-fung. "Nesting of 2D parts with complex geometry and material heterogeneity." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557005.

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14

Lam, Tsz-fung, and 林子峰. "Nesting of 2D parts with complex geometry and material heterogeneity." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557005.

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15

Wang, Feng. "A study to determine a practical technology for manufacturing components made of a multiphase perfect material." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39286630.

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16

Wang, Feng, and 王楓. "A study to determine a practical technology for manufacturing components made of a multiphase perfect material." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39286630.

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17

Lee, Chung Yung. "Bistable twised nematic liquid crystal displays by inhomogeneous alignment surfaces /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?ECED%202009%20LEE.

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18

Fang, Zhibin Sun Wei. "Image-guided modeling, fabrication and micromechanical analysis of bone and heterogeneous structure /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/549.

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19

Willett, Lori Jo. "Condensation on heterogeneous regular surfaces /." free to MU campus, to others for purchase, 1999. http://wwwlib.umi.com/cr/mo/fullcit?p9964012.

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20

Deoli, Naresh T. "Sputtering of Bi and Preferential Sputtering of an Inhomogeneous Alloy." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700021/.

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Angular distributions and total yields of atoms sputtered from bismuth targets by normally incident 10 keV -50 keV Ne+ and Ar+ ions have been measured both experimentally and by computer simulation. Polycrystalline Bi targets were used for experimental measurements. The sputtered atoms were collected on high purity aluminum foils under ultra-high vacuum conditions, and were subsequently analyzed using Rutherford backscattering spectroscopy. The Monte-Carlo based SRIM code was employed to simulate angular distributions of sputtered Bi atoms and total sputtering yields of Bi to compare with experiment. The measured sputtering yields were found to increase with increasing projectile energy for normally incident 10 keV - 50 keV Ne+ and Ar+ ions. The shapes of the angular distributions of sputtered Bi atoms demonstrated good agreement between experiment and simulation in the present study. The measured and simulated angular distributions of sputtered Bi exhibited an over-cosine tendency. The measured value of the degree of this over-cosine nature was observed to increase with increasing incident Ne+ ion energy, but was not strongly dependent on incident Ar+ ion energy. The differential angular sputtering yield and partial sputtering yields due to Ar ion bombardment of an inhomogeneous liquid Bi:Ga alloy have been investigated, both experimentally and by computer simulation. Normally incident 25 keV and 50 keV beams of Ar+ were used to sputter a target of 99.8 at% Ga and 0.2 at% Bi held at 40° C in ultra-high vacuum (UHV), under which conditions the alloy is known to exhibit extreme Gibbsian surface segregation that produces essentially a monolayer of Bi atop the bulk liquid. Angular distributions of sputtered neutrals and partial sputtering yields obtained from the conversion of areal densities of Bi and Ga atoms on collector foils were determined. The Monte-Carlo based SRIM code was employed to simulate the experiment and obtain the angular distribution of sputtered components. The angular distribution of sputtered Ga atoms, originating from underneath the surface monolayer, was measured to be sharply peaked in angle about the surface normal direction compared to the Bi atoms originating from surface monolayer. The simulation study produced contradicting results, where the species originating from surface monolayer was strongly peaked around the surface normal compared to the species originating from beneath the surface monolayer.
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21

Sreeranganathan, Arun. "Realistic micromechanical modeling and simulation of two-phase heterogeneous materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24607.

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Thesis (Ph.D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Gokhale, Arun; Committee Member: Gall, Kenneth; Committee Member: Garmestani, Hamid; Committee Member: Kurtis, Kimberly; Committee Member: Thadhani, Naresh
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22

Mao, Yuxiong. "Computer simulations of realistic three-dimensional microstructures." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33954.

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A novel and efficient methodology is developed for computer simulations of realistic two-dimensional (2D) and three-dimensional (3D) microstructures. The simulations incorporate realistic 2D and 3D complex morphologies/shapes, spatial patterns, anisotropy, volume fractions, and size distributions of the microstructural features statistically similar to those in the corresponding real microstructures. The methodology permits simulations of sufficiently large 2D as well as 3D microstructural windows that incorporate short-range (on the order of particle/feature size) as well as long-range (hundred times the particle/feature size) microstructural heterogeneities and spatial patterns at high resolution. The utility of the technique has been successfully demonstrated through its application to the 2D microstructures of the constituent particles in wrought Al-alloys, the 3D microstructure of discontinuously reinforced Al-alloy (DRA) composites containing SiC particles that have complex 3D shapes/morphologies and spatial clustering, and 3D microstructure of boron modified Ti-6Al-4V composites containing fine TiB whiskers and coarse primary TiB particles. The simulation parameters are correlated with the materials processing parameters (such as composition, particle size ratio, extrusion ratio, extrusion temperature, etc.), which enables the simulations of rational virtual 3D microstructures for the parametric studies on microstructure-properties relationships. The simulated microstructures have been implemented in the 3D finite-elements (FE)-based framework for simulations of micro-mechanical response and stress-strain curves. Finally, a new unbiased and assumption free dual-scale virtual cycloids probe for estimating surface area of 3D objects constructed by 2D serial section images is also presented.
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23

Storozhenko, V. A., A. V. Myagkiy, and R. P. Orel. "Filtering of interference of inhomogeneous regular structure in thermal non-destructive control of cellular structures." Thesis, Eskisehir technical university, 2021. https://openarchive.nure.ua/handle/document/18954.

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Honeycomb constructions are the most widely used materials in contemporary aviation and space technology. They are the basis for the housings of practically all products of this sector, where reliability of all parts should meet the in-creased requirements. Special attention is paid to the quality of composite materials and to the absence of defects such as the places of adhesion failure (exfoliation) between the skin and the honeycomb filler. Therefore, increase in the efficiency and reliability of thermal flaw detection, based on in-depth analysis of the processes of detecting defects and development of the principles of optimization of both the procedure of control and subsequent processing of the obtained information, is an important and relevant task.
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24

Luscher, Darby J. "A hierarchical framework for the multiscale modeling of microstructure evolution in heterogeneous materials." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33968.

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All materials are heterogeneous at various scales of observation. The influence of material heterogeneity on nonuniform response and microstructure evolution can have profound impact on continuum thermomechanical response at macroscopic "engineering" scales. In many cases, it is necessary to treat this behavior as a multiscale process. This research developed a hierarchical multiscale approach for modeling microstructure evolution. A theoretical framework for the hierarchical homogenization of inelastic response of heterogeneous materials was developed with a special focus on scale invariance principles needed to assure physical consistency across scales. Within this multiscale framework, the second gradient is used as a nonlocal kinematic link between the response of a material point at the coarse scale and the response of a neighborhood of material points at the fine scale. Kinematic consistency between two scales results in specific requirements for constraints on the fluctuation field. A multiscale internal state variable (ISV) constitutive theory is developed that is couched in the coarse scale intermediate configuration and from which an important new concept in scale transitions emerges, namely scale invariance of dissipation. At the fine scale, the material is treated using finite element models of statistical volume elements of microstructure. The coarse scale is treated using a mixed-field finite element approach. The coarse scale constitutive equations are implemented in a finite deformation hyperelastic inelastic integration scheme developed for second gradient constitutive models. An example problem based on an idealized porous microstructure is presented to illustrate the approach and highlight its predictive utility. This example and a few variations are explored to address the boundary-value-problem dependent nature of length scale parameters employed in nonlocal continuum theories. Finally, strategies for developing meaningful kinematic ISVs, free energy functions, and the associated evolution kinetics are presented. These strategies are centered on the goal of accurately representing the energy stored and dissipated during irreversible processes.
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25

Feng, Jianwen. "Probabilistic modelling of heterogeneous media." Thesis, Swansea University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.644724.

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26

Shen, Jeng-Jung. "Heterogeneous integration and the exploitation of strain in MBE growth : engineered substrates." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/13046.

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27

Wheaton, Chad J. "Tomographic traveltime inversion for linear inhomogeneity and elliptical anisotropy /." Internet access available to MUN users only, 2004. http://collections.mun.ca/u?/theses,69654.

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28

Specht, Paul Elliott. "Shock compression response of aluminum-based intermetallic-forming reactive systems." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47559.

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Heterogeneities at the meso-scale strongly influence the shock compression response of composite materials. These heterogeneities arise from both structural variations and differing physical/mechanical properties between constituents. In mixtures of reactive materials, such as Ni and Al, the meso-scale heterogeneities greatly affect component mixing and activation, which, in turn, can induce a chemical reaction. Cold-rolled multilayered composites of Ni and Al provide a unique system for studying the effects of material heterogeneities on a propagating shock wave, due to their full density, periodic layering, and intimate particle contacts. Computational analysis of the shock compression response of fully dense Ni/Al multilayered composites is performed with real, heterogeneous microstructures, obtained from optical microscopy, using the Eulerian hydrocode CTH. Changes in the orientation, density, structure, and strength of the material interfaces, as well as the strength of the constituents, are used to understand the influence microstructure plays on the multilayered composite response at high strain rates. The results show a marked difference in the dissipation and dispersion of the shock wave as the underlying microstructure varies. These variations can be attributed to the development of two-dimensional effects and the nature of the wave reflections and interactions. Validation of the computational results is then obtained through time-resolved measurements (VISAR, PDV, and PVDF stress gauges) performed during uniaxial strain plate-on-plate impact experiments. The experimental results prove that the computational method accurately represents the multilayered composites, thereby justifying the conclusions and trends extracted from the simulations. The reaction response of cold-rolled multilayer composites is also investigated and characterized using uniaxial stress rod-on-anvil impact experiments through post-mortem microscopy and x-ray diffraction. This extensive understanding of the shock compression response of the multilayers systems is contrasted with other composites of Ni and Al, including shock consolidated and pressed (porous) powder compacts. A comprehensive design space is then developed to assist in the understanding and design of Ni/Al composites under conditions of high pressure shock compression. Research funded by ONR/MURI grant No. N00014-07-1-0740.
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29

Simpson, William M. R. "Surprises in theoretical Casimir physics : quantum forces in inhomogeneous media." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/6338.

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This thesis considers the problem of determining Casimir-Lifshitz forces in inhomogeneous media. The ground-state energy of the electromagnetic field in a piston-geometry is discussed. When the cavity is empty, the Casimir pressure on the piston is finite and independent of the small-scale physics of the media that compose the mirrors. However, it is demonstrated that, when the cavity is filled with an inhomogeneous dielectric medium, the Casimir energy is cut-off dependent. The local behavior of the stress tensor commonly used in calculations of Casimir forces is also determined. It is shown that the usual expression for the stress tensor is not finite anywhere within such a medium, whatever the temporal dispersion or index profile, and that this divergence is unlikely to be removed by modifying the regularisation. These findings suggest that the value of the Casimir pressure may be inextricably dependent on the detailed behavior of the mirror and the medium at large wave vectors. This thesis also examines two exceptions to this rule: first, the case of an idealised metamaterial is considered which, when introduced into a cavity, reduces the magnitude of the Casimir force. It is shown that, although the medium is inhomogeneous, it does not contribute additional scattering events but simply modifies the effective length of the cavity, so the predicted force is finite and can be stated exactly. Secondly, a geometric argument is presented for determining a Casimir stress in a spherical mirror filled with the inhomogeneous medium of Maxwell's fish-eye. This solution questions the idea that the Casimir force of a spherical mirror is repulsive, but prompts additional questions concerning regularisation and the role of non-local effects in determining Casimir forces.
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30

Nam, Kyung Moon. "Modeling Terahertz Diffuse Scattering from Granular Media Using Radiative Transfer Theory." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/380.

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Terahertz (THz) spectroscopy can potentially be used to probe and characterize inhomogeneous materials, however spectroscopic identification of such materials from spectral features of diffuse returns is a relatively underdeveloped area of study. In this thesis, diffuse THz scattering from granular media is modeled by applying radiative transfer (RT) theory for the first time in THz sensing. Both classical RT theory and dense media radiative transfer (DMRT) theory based on the quasi-crystalline approximation (QCA) are used to calculate diffuse scattered intensity. The numerical solutions of the vector radiative transfer equations (VRTE) were coded and calculated in MATLAB. The diffuse scattered field from compressed Polyethylene (PE) pellets containing steel spheres was measured in both transmission and reflection using a THz time domain spectroscopy (THz-TDS) system. Measurement results showed energy redistribution by granular media due to volume scattering as well as angle dependent spectral features due to Mie scattering. The RT model was validated by successfully reproducing qualitative features observed in experimental results. Diffuse intensity from granular media containing Teflon, lactose sugar, and C4 explosive was then calculated using the RT models. Simulation results showed the amplitude of diffuse intensity is affected by factors such as grain size, fractional volume of grains, thickness of scattering layer, and scattering angles. Spectral features were also observed in the diffuse intensity spectra from media containing grains with THz spectral signatures. The simulation results suggest the possibility of identifying materials from diffuse intensity spectra.
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31

Yigitler, Huseyin. "Permanent Magnet Design And Image Reconstruction Algorithm For Magnetic Resonance Imaging In Inhomogeneous Magnetic Fields." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607627/index.pdf.

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Recently, the use of permanent magnets as magnetic field sources in biomedical applications has become widespread. However, usage of permanent magnets in magnetic resonance imaging (MRI) is limited due to their inhomogeneous magnetic field distributions. In this thesis, shape and geometry optimization of a magnet is performed. Moreover, placement of more than one magnet is optimized to obtain desired magnetic field distribution in specific region of space. However, obtained magnetic field distribution can not be used in the conventional MRI image reconstruction techniques. Consequently, an image reconstruction technique for MRI in inhomogeneous magnetic fields is developed. Apart from these, since any reconstruction technique requires signal data, an MRI simulator in inhomogeneous magnetic fields is constructed as a part of this thesis. Obtained results show that the theory developed in this thesis is valid. Consequently, new MRI devices that have permanent magnets as magnetic field sources can be constructed in the future.
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32

Kim, Kwangmoo. "Topics in the theory of inhomogeneous media composite superconductors and dielectrics /." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1180537980.

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33

Sonon, Bernard. "On advanced techniques for generation and discretization of the microstructure of complex heterogeneous materials." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209087.

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The macroscopic behavior of complex heterogeneous materials is strongly governed by the interactions between their elementary constituents within their microstructure. Beside experimental efforts characterizing the behaviors of such materials, there is growing interest, in view of the increasing computational power available, in building models representing their microstructural systems integrating the elementary behaviors of their constituents and their geometrical organization. While a large number of contributions on this aspect focus on the investigation of advanced physics in material parameter studies using rather simple geometries to represent the spatial organization of heterogeneities, few are dedicated to the exploration of the role of microstructural geometries by means of morphological parameter studies.

The critical ingredients of this second type of investigation are (I) the generation of sets of representative volume elements ( RVE ) describing the geometry of microstructures with a satisfying control on the morphology relevant to the material of interest and (II) the discretization of governing equations of a model representing the investigated physics on those RVEs domains. One possible reason for the under-representation of morphologically detailed RVEs in the related literature may be related to several issues associated with the geometrical complexity of the microstructures of considered materials in both of these steps. Based on this hypothesis, this work is aimed at bringing contributions to advanced techniques for the generation and discretization of microstructures of complex heterogeneous materials, focusing on geometrical issues. In particular, a special emphasis is put on the consistent geometrical representation of RVEs across generation and discretization methodologies and the accommodation of a quantitative control on specific morphological features characterizing the microstructures of the covered materials.

While several promising recent techniques are dedicated to the discretization of arbitrary complex geometries in numerical models, the literature on RVEs generation methodologies does not provide fully satisfying solutions for most of the cases. The general strategy in this work consisted in selecting a promising state-of-the-art discretization method and in designing improved RVE generation techniques with the concern of guaranteeing their seamless collaboration. The chosen discretization technique is a specific variation of the generalized / extended finite element method that accommodates the representation of arbitrary input geometries represented by level set functions. The RVE generation techniques were designed accordingly, using level set functions to define and manipulate the RVEs geometries.

The RVE methodologies developed are mostly morphologically motivated, incorporating governing parameters allowing the reproduction and the quantitative control of specific morphological features of the considered materials. These developments make an intensive use of distance fields and level set functions to handle the geometrical complexity of microstructures. Valuable improvements were brought to the RVE generation methodologies for several materials, namely granular and particle-based materials, coated and cemented geomaterials, polycrystalline materials, cellular materials and textile-based materials. RVEs produced using those developments have allowed extensive testing of the investigated discretization method, using complex microstructures in proof-of-concept studies involving the main ingredients of RVE-based morphological parameter studies of complex heterogeneous materials. In particular, the illustrated approach offers the possibility to address three crucial aspects of those kinds of studies: (I) to easily conduct simulations on a large number of RVEs covering a significant range of morphological variations for a material, (II) to use advanced constituent material behaviors and (III) to discretize large 3D RVEs. Based on those illustrations and the experience gained from their realization, the main strengths and limitations of the considered discretization methods were clearly identified.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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34

Fogarty, Tiernan. "Finite volume methods for acoustics and elasto-plasticity with damage in a heterogeneous medium /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6751.

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35

Narayanan, Rajesh. "Influence of rare regions on the critical properties of systems with quenched disorder /." view abstract or download file of text, 1999. http://wwwlib.umi.com/cr/uoregon/fullcit?p9948028.

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Thesis (Ph. D.)--University of Oregon, 1999.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 165-166). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9948028.
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36

Tovar, Anthony Alan. "Off-axis multimode light beam propagation in tapered lenslike media including those with spatial gain or loss variation." PDXScholar, 1988. https://pdxscholar.library.pdx.edu/open_access_etds/3839.

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The propagation of light beams in inhomogeneous dielectric media is considered. The derivation begins with first principles and remains general enough to include off-axis asymmetric multimode input beams in tapered lenslike media with spatial variations of gain or loss. The tapering of lenslike media leads to a number of important applications. A parabolic taper is proposed as a model for a heated axially stretched fiber taper, and beams in such media are fully characterized. Other models are proposed by the concatenation of a parabola with other taper functions.
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37

Le, Cor Thomas. "Etude du comportement mécanique des terrains anisotropes lors de travaux de génie civil." Thesis, Rennes, INSA, 2014. http://www.theses.fr/2014ISAR0026/document.

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Les travaux de recherche présentés dans ce manuscrit ont été menés dans le cadre d’une convention CIFRE avec le Groupe Dacquin. Le sous-sol rennais est composé, en majorité, de schistes datés du Briovérien. Ces terrains, qui peuvent être rencontrés sur une grande partie du massif armoricain, présentent des degrés d’altération et de fracturation extrêmement variables à l’échelle du bassin rennais. Cette variabilité est très difficile à prendre en compte dans le cadre de la réalisation de soutènement, tant au niveau de la conception qu’au niveau de l’exécution. Dans un premier temps, des modélisations basés sur la méthode des éléments finis (logiciel PLAXIS 2D ©) ont été entreprises afin d’évaluer l’influence de la prise en compte d’une anisotropie du terrain sur le comportement de la paroi, en termes de moments et de déplacements. Le modèle utilisé permettait de prendre en compte une anisotropie élastique combinée à un critère orienté de plasticité de type Mohr-Coulomb. Les résultats obtenus avec ce modèle, pour différentes orientations du critère de plasticité, ont été comparés à ceux obtenus avec un modèle élastique isotrope et critère de plasticité de type Mohr-Coulomb. La même étude a été menée avec un second logiciel éléments finis (CESAR-LCPC) afin de comparer les résultats obtenus. Dans les deux cas une influence importante de l’orientation du critère de plasticité a été observée pouvant conduire à des résultats plus défavorables, selon l’orientation, que ceux obtenus avec le modèle isotrope. Ces résultats ont confirmé la nécessité de mieux caractériser l’anisotropie dans des matériaux tels que les schistes Briovériens. La caractérisation du matériau a donc été menée dans un second temps sur des prélèvements répartis sur la ville de Rennes et ses alentours (lors de travaux d’excavations ou sur des talus). Elle a permis de balayer les caractéristiques des schistes de l’échelle microscopique jusqu’à l’échelle macroscopique. La caractérisation microscopique, basée sur des observations au microscope à balayage électronique, des essais de diffraction des rayons X et des observations de lames minces, a permis de mettre en évidence des variations dans la pétrographie des échantillons (schistosité, granulométrie, teneur en argiles) permettant de les différencier en deux types : grès et siltites. La caractérisation à l’échelle macroscopique a été divisée en trois axes : la caractérisation de la matrice rocheuse et de son anisotropie (essais de compression uniaxiale, mesures de vitesses de propagation d’ondes et essais au scléromètre), la caractérisation de discontinuités exprimées (cisaillement direct) et la caractérisation de la résistance à l’usure (essais de broyabilité et Micro-Deval modifiés). Les siltites se sont révélées être extrêmement sensibles à l’eau (forte diminution des caractéristiques mécaniques mesurées) tandis que les échantillons gréseux l’étaient dans une moindre mesure. L’ensemble des essais réalisés a permis d’établir des ordres de grandeurs de variations des propriétés mécaniques des schistes du Briovérien. Enfin la classification des schistes briovériens élaborés par des géotechniciens pour la seconde ligne de métro de Rennes a été complétée en vue de mieux définir les classes intermédiaires de résistance
Research work presented in this phD thesis was financed by a CIFRE grant given to Groupe Dacquin. Ground from the city of Rennes is, for the majority of it, composed of schists from the Brioverian era. These schists which can be encountered in the entire Armorican massif, present a weathering and a fracturing degree highly variable. This variability is hardly considered for the construction of retaining structure whether during the design step or the execution step. First, modellings using the finite elements method (PLAXIS 2D ©) have been carried out in order to evaluate the influence of ground anisotropy on the retaining wall behaviour (horizontal displacements and bending moments). The model used combined elastic anisotropy with an oriented plasticity criterion (type Mohr-Coulomb). Results obtained with this model, for different orientations of the plasticity criterion, were compared with the ones from the elastic isotropic model (with a Mohr-Coulomb plastic criterion). The same study was carried out with another finite elements software (CESAR-LCPC) in order to compare the results between the two sofwares. In both cases, an important influence of the orientation of the plasticity criterion was noted and lead to higher efforts in the wall, for certain orientations, compared to the isotropic model. These results confirmed the need of a better characterization of the anisotropy in materials such as Brioverian schists. In a second time, the characterization of the material was carried out on samplings spread over the city of Rennes and its area (during excavation work or on natural banks). Characterization was conducted from the microscopic to the macroscopic scale. Microscopic characterization based on observations with a scanning electron microscope, XRD analyses and thin section observations showed variations in the petrography of the samples (schistosity, granulometry, clay content) that lead to the differentiation of two types: sandstone and siltstone. The characterization at the macroscopic scale was divided into three parts: characterization of the rock matrix and its anisotropy (uniaxial compression tests, ultrasonic wave velocities and Schmidt hammer test), characterization of opened discontinuities (direct shear test) and the characterization of wear resistance (grindability and Micro-Deval tests). Siltstone samples were extremely sensitive to the water content (important decrease of the mechanical characteristics measured) whereas sandstones were less sensitive. The tests carried out lead to the definition of ranges for the mechanical properties of the Brioverian schists. Classification of Brioverian schists established by geotechnical engineers for the second subway line of Rennes was completed in order to better define the transitional states of strength of the material
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38

Höfling, Felix. "Dynamics of Rod-Like Macromolecules in Heterogeneous Materials /." Münster, Westf : Monsenstein und Vannerdat, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2930009&prov=M&dok_var=1&dok_ext=htm.

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39

Simon, Jean-Christophe. "Diffusion électromagnétique dépendante dans les milieux hétérogènes denses." Rouen, 1994. http://www.theses.fr/1994ROUES061.

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Il est montré que la diffusion électromagnétique dans les milieux hétérogènes denses fait intervenir de nombreux couplages multipolaires entre les particules. Dans ce travail, la distinction est faite entre la diffusion indépendante, couramment utilisée, et la diffusion dépendante. La première partie décrit les effets de diffusions multiple et cohérente, phénomènes liés à la diffusion indépendante. L'équation de transfert radiatif est résolue par une méthode de Monte-Carlo, et l'influence des propriétés d'absorption du milieu environnant les particules est mise en évidence. Les limites de la diffusion indépendante sont exposées à l'aide d'une expérience d'extinction par des particules de verre placées dans une cuve. La seconde partie traite de la diffusion dépendante, et décrit sa théorie. Le théorème d'addition des fonctions d'onde vectorielles harmoniques sphériques est étudié numériquement, en montrant de nombreux exemples caractéristiques. Un critère de convergence des sommations infinies intervenant dans ce théorème est testé, et nous statuons sur ses limites. Enfin, l'application de cette théorie aux milieux réels fortement concentrés est discutée, et son adaptation à l'équation de transfert radiatif est étudiée
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40

Clotet, i. Fons Xavier. "Imbibition in a model open fracture. Capillary rise, kinetic roughening, and intermittent avalanche dynamics." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284588.

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The dynamics of fractured media flows is relevant in many processes of interest that range from the micrometre to the kilometre lengthscales. Flow in disordered media has been proven to be an interesting system to study fundamental physics problems also. The goal of this Thesis is to study the spatio-temporal dynamics of the oil-air interface between displaced air and invading oil, in imbibition displacements through a model open fracture. The research combines exhaustive experimental work with accurate data analysis based on methods of nonlinear statistical physics. Imbibition is a process of fluid transport in a medium in which an invading fluid that preferentially wets the medium displaces the previously resident, immiscible fluid. According to the driving protocols we define spontaneous imbibition, in which the interface is driven at constant pressure difference between the inlet and the outlet of the medium and the flow rate is free to change in time, and forced-flow imbibition in which a constant flow rate of fluid is imposed at the inlet and the pressure difference may change in time. Our model open fracture consists of a Hele-Shaw (HS) cell, i.e. two parallel plates separated by a narrow gap spacing. Two configurations that mimic an open fracture have been explored: a flat HS cell, with constant aperture, and a HS cell with a dichotomic gap spacing randomly distributed in space (disordered cell). Silicone oils of different viscosities have been used as invading fluid. The advancement of the fluid front is recorded by using either CCD or CMOS cameras. An edge-tracking algorithm is applied to the binarized images to obtain front positions. We first study the evolution in time of the mean position of the interface in spontaneous imbibition experiments (capillary rise) through our two model open fractures. Experiments are performed with and without the presence of an effective gravity, achieved systematically tilting the cell against the advancement of the front or keeping it horizontal. Different pressure differences between the inlet and the outlet are systematically explored as well. We propose a new analytical solution for the spatially-averaged position of the imbibing front, based on a pressure balance equation, that reproduces experimental results at all times. In invasion of the disordered cell, capillary pressure and permeability variations distort imbibition fronts due to medium heterogeneities, while viscous pressure and surface tension tend to restore their flatness. As a result, the oil-air interface develops long-range correlations, with a lateral correlation length that depends on the capillary number Ca, tuned experimentally. Consequently, fronts advancing through the disordered cell are not flat during the whole experiment but get rough as the fluid penetrates the medium from an initially-flat interface to a final, statistically-invariant rough front. The kinetic roughening process, that occurs as a consequence of the competition of forces acting on the interface at different lengthscales, has been characterized in low-viscosity, forced-flow imbibition displacements obtaining a super-rough scaling scenario. The complex spatio-temporal dynamics of the front is studied at the statistically-stationary state of saturated front roughness in forced-flow experiments. We have analysed the spatial and temporal correlations of velocities of the front from the local scale, much smaller than the lateral correlation length and the characteristic length of the disorder, to the system size. Imbibition fronts exhibit burst-like dynamics, advancing by spatially-localized avalanches. These avalanches are power-law distributed in sizes and durations with exponential cutoffs. Power-law exponents are independent of the experimental conditions while the cutoffs diverge as Ca is reduced. We study also the intermittent character of these displacements by analysing different moments of the statistical distributions of velocity increments as a function of the time lag. We show that intermittency is controlled by two parameters only. The ensemble of results presented in this Thesis supports a very general picture of the nonequilibrium dynamics of slowly-driven fronts in open fractures. The lateral propagation of interfacial fluctuations is controlled by local mass conservation, through the lateral correlation length. The advancement of the interface in the direction of propagation is controlled by the characteristic extent of the disorder and by the mean front velocity.
L'objectiu de la tesi és l'estudi de la dinàmica espacio-temporal de la interfície entre aire desplaçat i oli invasor, en desplaçaments d'imbibició a través d'un model de fractura oberta. La recerca presentada combina un extens i exhaustiu treball experimental amb una anàlisi de dades acurada, basada en mètodes utilitzats en física estadística de no-equilibri. El procés d'imbibició, en que el fluid invasor mulla preferentment el medi envaït, és rellevant en diverses situacions d'interès, des de fluxos fisiològics a la irrigació del sòl i l'extracció de petroli. També és un sistema model interessant per a l'estudi de problemes de física fonamental degut a les correlacions de llarg abast que es desenvolupen al front, que indueixen una dinàmica complexa. Primer s'estudia l'avançament de la posició mitjana del front de fluid en condicions d'imbibició espontània (ascens capil•lar). Hem proposat una nova solució analítica que reprodueix els resultats experimentals tant amb presència de gravetat efectiva oposant-se a l'avançament del fluid com sense. En experiments d'imbibició forçada s'ha caracteritzat el procés d'arrugament dinàmic (kineticroughening) del front oli-aire a baixa viscositat. L'escenari d'escalament observat és super-rugós. Finalment s'ha estudiat la dinàmica del sistema en el règim estadísticament estacionari. S'han analitzat les correlacions temporals i espacials de les velocitats des de l'escala local, per sota la mida de les heterogeneïtats del desordre, fins a la mida del sistema. El front mostra una dinàmica a batzegades caracteritzada en termes d'allaus. Les mides i durades d'aquestes allaus estan distribuïdes estadísticament en llei de potències, amb exponents independents de les condicions experimentals, amb un truncament exponencial, que divergeix en reduir el nombre de capil•laritat. La intermitència del senyal s'ha quantificat i se n'ha extret els dos paràmetres que la controlen. El conjunt de resultats presentats en aquesta tesi dóna suport a una descripció molt general de la dinàmica de propagació lenta de fronts d'imbibició fora de l'equilibri en fractura oberta. La conservació local de massa controla la correlació lateral de les fluctuacions de la interfície. La longitud característica de les illes de desordre i la velocitat mitjana del front, per la seva banda, controlen l'avançament del front en la direcció de propagació.
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41

Höfling, Felix. "Dynamics of rod like macromolecules in heterogeneous materials." Münster Verl.-Haus Monsenstein und Vannerdat, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2930009&prov=M&dok_var=1&dok_ext=htm.

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42

Francescato, Pascal. "Prévision du comportement plastique des matériaux hétérogènes à constituants métalliques : application aux composites à matrice métallique à fibres continues et aux plaques perforées." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10110.

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Ce travail de these porte sur la mise en uvre numerique de la methode d'homogeneisation periodique en calcul a la rupture ou analyse limite et son application a la prevision des proprietes de resistance macroscopiques de materiaux composites a fibres longues ou de plaques metalliques perforees. La methode numerique adoptee consiste a ramener la mise en uvre des approches statique par l'interieur et cinematique par l'exterieur a la resolution d'un probleme d'optimisation lineaire pose sur le volume elementaire representatif (v. E. R. ). Les programmes numeriques font appel a une utilisation originale de la methode des elements finis avec une discretisation discontinue des differents v. E. R. Etudies ainsi qu'a une technique nouvelle de linearisation des criteres de tresca et von mises. Une premiere validation de ces methodes est faite a partir de resultats theoriques et experimentaux obtenus par ailleurs, de meme qu'une campagne experimentale est menee sur des plaques minces perforees par des trous circulaires. Ces methodes donnent une evaluation tres precise de l'anisotropie de resistance de ce type de materiau. Dans la suite, une extension de ces methodes au cas de la deformation plane generalisee et au cas general tridimensionnel est proposee afin d'etudier le comportement plastique de composites a matrice metallique (c. M. M. ). Les maillages elements finis restant plans du fait du cas des fibres continues unidirectionnelles considere ici, l'objectif est de determiner le convexe de resistance de c. M. M. Unidirectionnels sous un chargement hors axes quelconque. Dans le cas d'une interface fibre/matrice a adherence maximale, les calculs mettent clairement en evidence l'anisotropie transverse de ce type de composite, y compris dans le cas d'un v. E. R. Hexagonal. Enfin l'etude se termine par une serie de calculs prenant en compte un critere de decohesion a l'interface fibre/matrice alors que la fibre et la matrice obeissent au critere de tresca tridimensionnel isotrope. Les parametres caracteristiques du critere a l'interface sont identifies a partir d'un essai de traction simple transversalement aux fibres
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43

Benkemoun, Nathan. "Contribution aux approches multi-échelles séquencées pour la modélisation numérique des matériaux à matrice cimentaire." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2010. http://tel.archives-ouvertes.fr/tel-00657311.

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L'objectif principal de cette thèse est de développer un modèle numérique capable de proposer une représentation fine des phénomènes de fissuration pour les matériaux quasi-fragiles à matrice cimentaire. Dans ce sens, l'échelle pertinente retenue est l'échelle mesoscopique. L'échelle mesoscopique est ici de l'ordre du centimètre et le matériau peut être considéré comme bi-phasique (agrégats inclus dans un mortier, contenant lui même des inclusions de taille inférieure). Par ailleurs, de part la diversité des phénomènes de fissuration pour les matériaux quasi-fragiles comme le béton, il est nécessaire de mettre en place un modèle capable de représenter explicitement les fissures à l'interface agrégats/mortier et/ou dans n'importe quelles des deux phases (agrégats et mortier). La modélisation numérique des phénomènes de fissuration proposée s'inscrit, ici, dans le cadre de la méthode des éléments finis à discontinuité forte. Plus précisément, la fissure est ici définie comme l'apparition d'une discontinuité de déplacements ou encore d'une zone d'épaisseur nulle dans laquelle toutes les déformations sont localisées. Elle correspond au cas extrême des bandes de localisation observées dans les sols ou les roches avec une largeur des bandes tendant vers zéro. Par ailleurs, le modèle proposé intégre aussi une discontinuité faible (discontinuité de déformations) afin de capturer les hétérogénéités sans que le maillage soit contraint. Finalement le but est d'intégrer ce meso-modèle dans le cadre d'une approche multi-échelle séquencée permettant le transfert des informations du niveau mesoscopique vers le niveau macroscopique ou au moins sa borne inférieure, le Volume élémentaire Représentatif. Cette approche séquencée permet, par exemple, de déterminer une surface de rupture macroscopique (dans l'esprit d'une fonction seuil) intégrant les principales caractéristiques des matériaux cimentaires.
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44

Bhallamudi, Vidya Praveen. "Spins in heterogeneous landscapes: Consequences for transport and imaging." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306871981.

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45

Gilmore, Sean William. "Electromagnetic scattering by an inhomogeneous penetrable material with an embedded resistive sheet /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487778663284816.

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46

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.

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Ce travail concerne l’étude acoustique théorique et expérimentale des matériaux poreux à squelette métallique, macroscopiquement homogènes et inhomogènes ainsi que l’étude de leurs propriétés mécaniques de comportement au choc pour comparaison. Le modèle acoustique de Johnson -Champoux - Allard s’est montré adapté pour la modélisation acoustique. Ce modèle associé à une approche proposée récemment et utilisant le concept de matrices de transfert en parallèle a permis, dans une nouvelle approche basée sur les “mélanges de matériaux”, d’étudier les matériaux poreux macroscopiquement inhomogènes. Par ailleurs, une étude paramétrique du coefficient d’absorption en fonction de la porosité et de la fréquence a été proposée. Les maxima d’absorption ainsi que l’enveloppe des courbes d’absorption en fonction de la porosité ont été étudiés. En premier lieu, un matériau théorique à propriétés indépendantes a été étudié. Les matériaux réels à propriétés interdépendantes ont ensuite été abordés à l’aide d’un modèle reliant leurs propriétés à la porosité. Enfin, une comparaison entre les propriétés acoustiques et les propriétés mécaniques de comportement à l’impact a été initiée en vue de déterminer un critère objectif permettant de proposer un compromis entre les deux domaines
This 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
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47

Andre, Robert G. "Electromagnetic scattering analysis of a three dimensional inhomogeneous material body using the Finite Element Method /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487842372897921.

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48

Faget, Xavier. "Application expérimentale de méthodes inverses avancées pour l'imagerie des propriétés électromagnétiques d'un matériau magnéto-diélectrique." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0039/document.

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Cette thèse porte sur la caractérisation non destructive de structures 2D magnéto-diélectriques inhomogènes complexes. L’ensemble des étapes allant de l’expérience au traitement du problème inverse est traité. Dans un premier temps, un modèle direct reliant le champ diffusé aux propriétés électromagnétiques du matériau a été mis en place. Ce modèle requiert des calculs par éléments finis de la propagation de l’onde électromagnétique, en présence de l’objet observé lorsque celui-ci est positionné sur un support métallique. Une validation expérimentale a été réalisée via la mise en place d'un banc de mesure multi statique. Différentes étapes d'ajustements et d'étalonnages ont permis la réduction du bruit de mesure ainsi que des biais. L’inversion est traitée principalement par une approche linéaire, avec un choix attentif de la valeur des hyper paramètres qui y sont associés. Une fois les outils mis en place, six études ont été réalisées pour la validation de notre système d’imagerie 2D des propriétés électromagnétiques de matériaux magnéto-diélectriques inhomogènes. Cela comprend l’évaluation des incertitudes de mesure, de la résolution spatiale, la mesure de différents matériaux magnétiques et l’utilisation de différents supports à géométries variées. L’ensemble des résultats expérimentaux réalisés se place dans une hypothèse de géométrie 2D. C’est pourquoi, nous avons ensuite orienté nos travaux vers la recherche d’un design innovant permettant de faire évoluer le banc de mesure en un dispositif d’imagerie 3D. Dans cette perspective, une source secondaire vient se déplacer proche de la cible pour acquérir de l’information selon la troisième dimension
The subject of this thesis is the non-destructive characterization of complex inhomogeneous magneto-dielectric structures. Successively, the experimental developments, the modelling and the data treatments stages are addressed. A forward model that links the scattered field to the electromagnetic properties is established. This model requires some finite element computations in order to estimate the propagation of the electromagnetic wave in presence of the magneto-dielectric object which is glued on a metallic support. A multistatic bench has been designed and constructed in order to collect measured scattered fields. Several adjustments and calibration procedures have been carried out to reduce the measurement noise and biases. Next, the inverse problem has been dealt with, in order to retrieve the electromagnetic properties of the samples, from the measured scattered field. The inverse problem is mainly solved with a linear approach, with a careful selection of the hyperparameters. Once the system has been fine tuned, six studies have been realized to validate our 2D imaging system. The assessment of the measurement uncertainty, the evaluation of the spatial resolution, the characterization of various magnetics materials and the use of different supports with variable geometries have been performed. So far, all the developments were done under a 2D hypothesis. That is why, we have then focused our research on the design of a 3D innovative imaging setup. To this end, a secondary source moving close to the target has been added in order to gain information in the third direction. A numerical study has been performed to assess the expected performances of this new setup
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49

Valdez-Balderas, Daniel. "Models for inhomogeneities and thermal fluctuations in two-dimensional superconductors." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1180117179.

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50

Croizet, Didier. "Etude experimentale et numérique du comportement à haute température d'un nitrure de silicium." Paris, ENMP, 1992. http://www.theses.fr/1992ENMP0516.

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Le matériau céramique que nous avons étudié est un nitrure de silicium obtenu par frittage naturel. Ce matériau biphase est constitué d'une phase principale correspondant à une solution solide de type Sialon et d'une phase secondaire cristallisée en grenat d'yttrium et d'aluminium après traitement thermique post-frittage. Le premier point de cette étude concerne la caractérisation mécanique du matériau à haute température avec une attention toute particulière à 1250 C. A cet effet, des essais de flexion 4 points, de traction et de compression ont été réalisés en utilisant la technique du dip-test. Ceux-ci ont mis en évidence un comportement viscoplastique, asymétrique en traction-compression avec apparition d'une contrainte interne lors du processus de déformation. Sur cette base expérimentale, une loi de comportement tridimentionnelle, viscoplastique, non associée, caractérisée par un critère d'écoulement de Drucker-Prager et une règle d'écrouissage cinématique, a été proposée. Le deuxième point concerne l'implantation de lois de comportement viscoplastique dans le code d'éléments finis Zébulon. Une formulation générale de ces lois a été définie dans le cadre de la thermodynamique des processus irréversibles. La plasticité y est traitée comme un cas particulier de la viscoplasticité. Cette formulation permet d'écrire un programme standard prenant en compte le comportement non linéaire d'une grande variété de matériaux tels que les métaux, les alliages, les roches, les sols ou les céramiques. L'utilisation d'une méthode d'intégration implicite, appelée thêta-Newton, permet l'évaluation d'une matrice tangente viscoplastique
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