Дисертації з теми "Gradient de porosité"
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Boulvert, Jean. "Traitements acoustiques à porosité contrôlée pour atténuation optimale." Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1033.
This thesis exploits some of the new possibilities offered by additive manufacturing to design and optimize treatments for sound attenuation consisting in porous materials. Additive manufacturing allows to control individually each pore of a material. The porous treatment design process is turned upside down: instead of searching through a catalogue of existing materials to solve a problem, it is possible to directly design the right material by adjusting its microstructure. This research is part of a plan to reduce aircraft engine noise but extends beyond the aeronautical field, both theoretically and in terms of possible applications. A predicting method of the acoustic behaviour of porous materials produced by additive manufacturing and taking into account the impact of manufacturing defects is first introduced. Porous materials with controlled graded properties are then studied. A method for optimizing microstructural or manufacturing parameters is developed. The ability of graded porous materials to attenuate frequencies too low to be attenuated by non-graded materials is then proven and the optimal gradient for broadband attenuation is defined. The impact of the wall thickness of the pores along with the impact of transverse propagation inside porous materials is studied. Finally, a metaporous treatment allowing broadband and sub-wavelength absorption is developed. The results of this research can be applied to create porous treatments with a high noise attenuation. The analytical and numerical models used in this research are based on the hypothesis of porous materials acoustically behaving as equivalent fluids. The results are physically analyzed and experimentally validated through impedance tube testing of specimens produced by additive manufacturing
Richart, Olivier. "Les substituts osseux en hydroxyapatite : Nouveau procédé de fabrication de pièces macroporeuses à gradient de porosité." Valenciennes, 1998. https://ged.uphf.fr/nuxeo/site/esupversions/cf762061-806c-4205-b695-3f16de038391.
Sirijarukul, Suksawat. "Elaboration de membranes à traces en poly(éthylènetéréphtalate) ayant un gradient linéaire de taille de pore et une porosité constante." Montpellier 2, 2007. http://www.theses.fr/2007MON20110.
A new type of polymer track-etch membrane was produced with a gradient of pore size and another gradient of pore density along the large dimension of the membrane. Those gradients are independently very well controlled and obtained by simple procedures. In a first step, the pore density gradient is created by displacing the poly(ethyleneterephthalate) –PET- film in front of a swift heavy ions beam of varying flux. In a second step, the pore size is controlled by dipping progressively the previously ion beam exposed film into an aqueous solution of 2N NaOH at 50°C. The relationship between both gradients at any position along the membrane is predetermined before preparation: we have chosen to maintain porosity constant with a linear gradient of pore size. Scanning electron microscopy measurements allowed verification of the existence of a cylindrical pore through the whole thickness (13 µm) of the PET film after exposure to UV light centred around 312 nm. A theoretical model has been proposed which describes tangential filtration in a channel where one wall is such a membrane: the case of constant permeability leads to relatively simple analytical expressions contrary to the case of constant porosity. One cell was built up and characterized by electrical and hydraulic measurements. The membrane hydrophobic character is attenuated at high pH (10-2N NaOH) by ionization of the carboxylic groups. We showed also that varying etching time to obtain a gradient of pore size did not induce a wettability gradient provided that the material was previously exposed to UV radiation
Landron, Thomas. "effets des gradients de porosité et de contrainte sur le comportement en fatigue à grand nombre de cycles de l’alliage d’aluminium AlSi9Cu3 coulé sous pression." Electronic Thesis or Diss., Paris, HESAM, 2023. http://www.theses.fr/2023HESAE091.
This research deals with the effect of porosity and stress gradients on the high-cycle fatigue behavior (HCF) of the high-pressure die-cast (HPDC) aluminum alloy AlSi9Cu3 used by the automotive industry. The components produced by HPDC are characterized by a high level of porosity compared to other casting processes. In addition, the porosity or defect distribution within a component is highly heterogeneous and the existence of a porosity gradient between the surface and the in-bulk material is notable. Defects of different nature and size are present, including defects formed by complex three-dimensional pore networks.To study the effects of the porosity and stress gradients on the HCF behavior, a test methodology based on reducing the thickness of as-cast specimens by machining was developed. Four geometries machined from the same as-cast specimens were tested in HCF under different loading modes: plane bending and tension-compression with a load ratio R=-1. The analysis of the fatigue failure surfaces, combined with fatigue results in the form of Wöhler curves shows that fatigue behavior is controlled by the interaction between the porosity gradient and the stress gradient. The position of the crack initiation site (surface or in-bulk), the nature of the critical defects, as well as the fatigue strength are entirely determined by these two gradients.The effect of defects on the fatigue behavior was analyzed using an approach based on the Kitagawa-Takahashi diagram and the stress intensity factor threshold (Kth). This analysis shows that the fatigue strength of the material is controlled by the size of the defects in terms of the Murakami parameter (√area). The wide range of defect size and the variety of defect types makes it possible to characterize the behavior of the material in both the short crack and long crack regimes. It is observed that the position of the crack initiation site (surface or in-bulk) has only a small effect on the fatigue behavior. Thanks to a comparison between the studied alloy and other gravity-cast aluminum alloys, it is shown that both the fatigue strength and the crack propagation behavior, is partly controlled by (a) the microstructural characteristics of alloys (grain size and secondary dendrite arm spacing (SDAS)) and by (b) the monotonic and cyclic mechanical behavior of the materials.The complexity of the defect distribution (type, size and spatial distribution) complicates the characterization and modeling of the kinetics of crack propagation and their interactions with defects. To investigate this, in-situ image correlation was used to monitor crack growth during fatigue tests, with the aim of observing the crack interaction with natural defects, in bending at R=-1. The analysis of the crack growth kinetics and the fatigue failure surfaces reveals a strong interaction between fatigue cracks and defects. These interactions cause rapid crack accelerations, which drastically reduce the fatigue life. A HCF crack propagation model is proposed using an averaging approach with the Paris law. The coefficients are adjusted using the crack monitoring tests. The comparison between the simulated Wöhler curves at initial iso-defect-size and the experimental Wöhler curves shows that the propagation approach is not sufficient to account for all the stages leading to fatigue failure. It is clearly highlighted that the initiation phase must be taken into account and that the fatigue damage mechanisms, associated with defects comprised of complex three-dimensional pore networks, are extremely complex.Keywords: High cycle fatigue (HCF), microstructural heterogeneity, porosity gradient, stress gradient, aluminum alloy, high-pressure die-casting, porosity networks, fatigue life, crack – defect interaction
Verdenelli, Martine. "Elaboration par procédé sol-gel de couches minces oxydes à gradient de porosité : évaluation en tant qu'interphases dans les composites à matrice céramique SiC-SiC." Lyon 1, 2002. http://www.theses.fr/2002LYO10203.
Boulesteix, Rémy. "Densification du grenat d'yttrium et d'aluminium pur ou dopé sous forme de céramiques transparentes : relation entre microstructure et propriétés optiques : élaboration de matériaux à gradient de concentration en néodyme." Limoges, 2009. http://www.theses.fr/2009LIMO4040.
Dominguez, Nicolas. "Modélisation de la propagation ultrasonore en milieu complexe : application au contrôle non destructif et à la caractérisation de la porosité dans les matériaux composites stratifiés." Toulouse 3, 2005. http://www.theses.fr/2006TOU30235.
Vieira, Nunes Antonio Idivan. "Transport d'ions sous l'effet d'un champ électrique en milieu poreux : applications à la séparation de terres rares par électrophorèse à focalisation." Vandoeuvre-les-Nancy, INPL, 1999. http://docnum.univ-lorraine.fr/public/INPL_T_1999_VIEIRA_NUNES_A_I.pdf.
Trivalent ions of rare earth elements have very similar properties and their difficult separation each from another is usually carried out by liquid-liquid extraction or ion exchange focalisation electrophoresis represehts an alternative route to the usual techniques. The purpose of this work consisted of the fundamental investigation of ion transport phenomena in electrophoretic processes. Focalisation electrophoresis is suitable for separation of amphoteric species such as rare earth ions, using a pH gradient in the cell and upon addition of a complexed agent e. G. EDTA. This technique relies upon the difference in isoelectrical points of the considered species, being under the form of free cation near the ano'de, and in the form of anionic complexed species doser to the cathode Rare earth species are submitted to the antagonist effects of diffusion and migration, enabling their focalisation to occur at the isoelectrial point, corresponding to nil value of their effective mobility. Following a literature survey on rare earth elements and electrophoresis processes, the document describes theoretical and experimental investigations of complexation equilibria of some rare earth elements, namely lanthanum, neodymium, praseodymium and cerium, depending on pH. Values for the isoelectrical points coulb be estimated. Transport and focalisation phenomena in view of rare earth separation, are dealt in the last chapter. Investigations were first carried out without forced circulation of the electrolyte solution and the transient behavior of the system allowed operating conditions to be design and built-up of a continuos device, more suitable to separation, and provided with 42 potential and 42 temperature sensors: the results of the preliminary runs, in form of variable profiles, are presented and discussed
Os fons trivalentes de terras raras apresentam propriedades muito proximas umas das outras, o que dificulta bastante a separaçao destes elementos, sendo a extraçao por solvente e troca de ions os unicos métodos mais usados na separaçao de terras raras. No entanto, a eletroforese à focalisaçao representa uma alternativa à separaçao de terras raras como mostra este trabalho que tem como objetivo fundamental estudar os fenomenos de transportes de ions num determinado processo. Através da técnica de eletroforese à focalizaçao, é possivel separar espécies ionicas anfotéricas, como por exemplo cations de terras raras, M+3, aplicando-se um gradiente de pH na célula de separaçao e utilizando um acido como agente complexante, como por exemplo o EDTA. 0 principio deste método é baseado na diferença dos pontos isoelétricos das espécies presentes sob a forma cationica proxima ao anodo ou sob a forma do complexo ionico proximo ao catodo. Os ions de terras raras estao sempre submetidos aos efeitos da diftisao e da migraçao o que os levam a focalizarem em seus pontos isoelétricos correspondentes a mobilidade efetiva nula. Apos um èstudo bibliognifico sobre as terras raras e os processos de separaçao por eletroforese, este relatorio de tese descreve as aproximaçoes teorico e experimental de equilfbrio de complexaçao de alguns elementos de terras raras, como por exemplo: lantanio, cério, praseodimio e neodimio, em funçao do pH, hem como a estimacao do ponto isoelétrico. Os fenomenos de transporte e de focalizaçao foram abordados no ultimo capftulo, o que nos permitiu de observar as condiçoes operacionais de focalizaçao de uma espécie sem o fluxo forçado de uma soluçao. A metodologia descrita anteriormente foi utilizada para a concepçao e a realizaçao de uma célula corn circulaçao continua da soluçao num sistema dotado de 42 captores de temperaturas e 42 de potenciais. Os resultados dos primeiros testes de focalizaçao e da separaçao de dois elementos de terras raras foram apresentados e discutidos sob a forma de perfis de diferentes parametros
PLúA, Carlos. "Développement d’une stratégie d’implémentation numérique pour milieu continu poreux de 2nd gradient basée sur les éléments finis isogéométriques, application à un milieu partiellement saturé." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI019/document.
During the last decade, Isogeometric Analysis (IGA) has drawn the attention of the Finite Element community to its superior capabilities over the standard Finite Element Method (FEM). The IGA concept uses the same basis functions used in Computed Aided Design (CAD) for the approximation of the unknown fields such as displacements, pore pressure or temperature in the Finite Element solution of a (possibly coupled) thermo– hydro–mechanical problem. Among the most relevant features of IGA, its smoothness, its convergence rate and particularly its intrinsic higher–order continuity between elements represent a definite improvement over the standard FEM, which allow to obtain significant computational advantages in terms of accuracy of the solution and computa- tional efficiency.This work attempts to exploit the characteristics of IGA for the numerical solution of coupled hydro–mechanical (HM) problems in saturated and partially saturated second gradient poro–elastoplastic geomaterials. On one hand, the second gradient model belonging to the theory of continua with microstructure ensures the objectivity of the results in presence of strain localization phenomena in terms of mesh independence of the numerical solution, which cannot be achieved with classical constitutive models without an internal length scale. On the other hand, the C1–continuity achievable by means of IGA basis functions allows a straightforward implementation of such higher order constitutive models, within a HM formulation derived from the classical mixture approach. In addition, the smoothness of the IGA basis functions proved to be very efficient in the modeling of coupled processes characterized by strong hydraulic gradients – such as the simulation of the downward propagation of a saturation front in a partially saturated slope subject to rainfall infiltration. Last but not least, it is worth noting that, as compared to the existing approaches based on Lagrange multipliers, the IGA approach to the solution of coupled hydro-mechanical (HM) problems in saturated and partially saturated second gradient materials allows a dramatic reduction in the number of degrees of freedoms required to achieve the same level of accuracy. This not only results in a significant increase of the computational efficiency, but also allows to extend the complete second gradient formulation to the analysis of realistic 3D problems, the solution of which has been presented in this work for the first time.The local second gradient poro–elastoplastic formulation developed in this work is implemented in the research-oriented code GeoPDEs, a Matlab open source IGA–FEM code developed at the University of Pavia. Based on the results obtained in a large series of representative 2D and 3D initial–boundary value problems analyzed in this work, it can be concluded that the combination of IGA and the second gradient elastoplasticity represents a powerful tool for the numerical simulation of geotechnical problems characterized by strong multiphysics couplings, highly nonlinear behavior of the soil, and strongly localized displacement and pore pressure gradients
Svatík, Juraj. "Funkční pěny s gradientem hustoty." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2019. http://www.nusl.cz/ntk/nusl-401848.
Abdallah, Youssouf. "Compaction banding in high-porosity limestones : Experimental observations and modelling." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC1024.
The mechanical deformation of sedimentary rocks can give rise to the formation of compaction bands which can significantly affect the performance of geosystems. The objective of this thesis is to identify the formation of compaction bands in porous carbonate rocks in laboratory experiments and to propose a constitutive model based on second-gradient plasticity theory to account for the effect of local heterogeneity.Axisymmetric compression tests are combined with X-Ray Computed Tomography observations. Samples are imaged before and after several loading steps and at different confining pressure levels. Digital Volume Correlation technique is applied on consecutive images to build 3D deformation maps at a millimetric gauge length, which permit to identify strain localization zones. A simple method based on kinematic considerations is proposed to classify these zones. Compaction bands have been identified at high confining pressures, pure shear bands are obtained for low confinements whereas compactive shear bands are observed in the transitional regime. In contrast, a diffuse compaction occurs in hydrostatic loading conditions. 3D porosity maps are constructed at some intermediate meso-scale and superimposed on deformation maps. The heterogeneity of porosity is found to control the pattern of compaction bands, as they lay inside high-porosity zones and avoid denser zones. Grain crushing is identified as the main micromechanism of the deformation. Very fine particles fill the pores and induce a porosity reduction. Large pores are observed to remain intact in denser zones, as they are protected by a surrounding rigid lattice of cemented grains. When shear strain is identified in deformation bands, porosity heterogeneity is found to control the volumetric behavior. Along a compactive/pure shear band, some cracks are observed in denser zones, whereas grain crushing and pore filling are observed in the more porous zones. These mechanisms are responsible for a complex co-existence of local contractancy and dilatancy along shear bands.Standard constitutive elastic-plastic laws of homogeneous media are insufficient to model correctly compaction banding, as a zero-thickness band is obtained for rate-independent materials in a Cauchy continuum. To regularize this problem, higher-order continua (micromorphic media) can be considered, where internal lengths in relation with the microstructure are introduced in the constitutive relations. A particular issue of these models is to calibrate the higher-order parameters. In the framework of second-gradient plasticity theory, the yield surface depends on a hardening parameter, related to the plastic strain and its second gradient. The plastic porosity reduction is taken here as the hardening parameter. A calibration procedure of the additional higher-order parameters based on macroscopic mechanical data and the data provided by the X-Ray images is proposed. Once the model is calibrated, a linear stability analysis in axisymmetric triaxial loading is applied to predict the formation of compaction bands. The calibrated model is subsequently implemented in a finite element code, textit{Numerical Geolab}, to perform numerical simulations of the experiments. Numerical results are finally compared to the experimental observations
Ma, Yujia. "Biomimetic 3D scaffold for cancer research." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16048.
Adem, Ziad. "Etude de la diffusion des hydrocarbures dans des matériaux à porosité contrôlée par RMN à gradients de champs pulsés (PFG)." Paris 6, 2008. http://www.theses.fr/2008PA066001.
Zhang, Bohua. "The Influence of Porosity and Its Modeling on Fatigue Behavior of High Pressure Die Cast Aluminum including the Effects of Mean Stress, Stress Gradient and Specimen Size." University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1556259677391458.
Liu, Zijun. "Preparation of biodegradable polymeric scaffolds with porosity gradients and interconnected structures using a sub critical carbon dioxide foaming process." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/28003.
Castagna, Salvatore. "Thermo hydraulic behaviour of unstaturated salt aggregates." Doctoral thesis, Universitat Politècnica de Catalunya, 2007. http://hdl.handle.net/10803/6246.
El combustible nuclear es de larga duración: unas barras de uranio pueden llegar a producir energía eléctrica durante una década aproximadamente. Sin embargo, a mediados del siglo pasado se planteó el problema de los residuos nucleares. Este problema es muy complejo por que, aunque la duración del combustible sea de una década, el periodo de decaimiento es del orden de siglos.
Esta tesis quiere aportar su granito de arena a esta nueva rama de la ciencia nuclear, estudiando algunos aspectos del comportamiento geotécnico de los agregados de sal, para su uso como material de relleno en los depósitos definitivos de los residuos nucleares de mayor peligrosidad.
La regla fundamental de diseño de dichos depósitos es que su función debe desarrollarse sin la ayuda del hombre o de máquinas y que la misma naturaleza tiene que ser quien proteja al hombre del riesgo de radiaciones durante el transcurso de los siglos.
Parece que al día de hoy la solución mundialmente aceptada es la de un depósito profundo en formaciones rocosas, a veces utilizando antiguas minas, incluso de sal. Se prevé que entre esta década y la próxima entrarán en funcionamiento varios de estos depósitos en los países en que la investigación en este área está más avanzada.
En Europa se está haciendo un esfuerzo común, bajo supervisión de la Unión Europea y por medio de proyectos de investigación, para estudiar el funcionamiento del almacenamiento y la difusión de los resultados de esos estudios entre los miembros de la Unión Europea, a fin de dar el mayor provecho a las diferentes investigaciones que en la actualidad se están desarrollando en todos los centros de investigación de Europa.
Esta tesis trata sobre el comportamiento termo hidráulico de los agregados de sal debido a las altas temperaturas que el decaimiento de los residuos nucleares produce. Este fenómeno crea unos efectos en los materiales de relleno y en la formación de base de alrededor del deposito.
La tesis tiene un desarrollo básicamente experimental. En el laboratorio se realizaron fundamentalmente dos ensayos; el primero permitió determinar la curva de retención de los agregados de sal altamente compactados. Para ello se utilizó la técnica de traslación de ejes para aplicar la succión matricial y se construyó una placa de succión apta a los materiales salinos para la realización de estos ensayos.
Este ensayo permitió determinar el comportamiento de una propiedad básica de los materiales salinos no saturados, sus resultados pudieron aplicarse al resto de los trabajos que se realizaron con posterioridad en esta tesis.
El objeto del segundo ensayo de laboratorio fue reproducir los fenómenos de variación de porosidad debidos a la presencia de una diferencia de temperatura en las extremidades de la muestra.
Dicho ensayo tiene una importancia fundamental para los almacenamientos profundos, porque los residuos radiactivos serán una fuente de calor durante varios siglos y la presencia de elevadas temperaturas induce fenómenos de flujo y transporte en el contacto con los contenedores de carburante nuclear agotado. Además, en el caso de los agregados de sal, a estos fenómenos cabe añadir el intercambio de sal entre la fase sólida y la líquida (precipitación /disolución).
Para desarrollar estas pruebas de laboratorio, se dedicó una parte importante de la investigación al desarrollo y comprobación del equipo de ensayo, siendo éste poco convencional y completamente novedoso. Este último ensayo, en su segunda fase, fue convalidado mediante un modelo numérico (CODE BRIGHT). Los resultados del modelo numérico han permitido confirmar todo cuanto se determinó en la fase experimental y la importancia de la succión matricial en estos fenómenos.
Pagano, Eduardo. "OBTENÇÃO DE CERÂMICAS DE ALUMINA COM GRADIENTE FUNCIONAL DE POROSIDADE A PARTIR DE DIFERENTES TÉCNICAS." Universidade Estadual de Ponta Grossa, 2017. http://tede2.uepg.br/jspui/handle/prefix/2414.
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Neste estudo foi realizado a obtenção e caracterização de materiais cerâmicos de alumina com gradiente funcional de porosidade. Foram utilizados como os métodos de processamento a rota de freeze casting em água e a fase de sacrifício utilizando o amido. Os materiais utilizados para a produção das amostras foram a alumina e o amido de milho de pureza analítica. Foram investigadas as características de porosidade quanto a morfologia de poros, distribuição dos poros pela matriz e interferência do processamento na formação destes. Para o estudo da porosidade, os métodos de porosimetria via método de Arquimedes em água e penetração de mercúrio foram aplicados na analise desta porosidade obtida. As propriedades mecânicas, bem como o modo de fratura obtido, também foram investigadas em ensaio de compressão uniaxial em uma máquina de ensaios universal. As imagens obtidas por microscopia eletrônica de varredura auxiliaram a correlacionar os dados obtidos nos ensaios de porosimetrias com a resposta mecânica obtida do material. Os resultados obtidos entre os métodos, quanto à porosidade, revelam diferenças consideráveis na distribuição e quantidade de poros ao se comparar o freeze casting com a fase de sacrifício com amido. Porém quanto a tamanho, os valores se mantiveram bem próximos. A resistência mecânica em compressão é maior nas amostras com amido, porém estas amostras falham de forma catastrófica. As amostras de freeze casting, por sua vez, possuem menor resistência mecânica e tiveram suas fraturas influenciadas por vários fatores durante o processamento. A morfologia de poros e microestrutura apresentada pelos dois métodos aplicados são consequência direta da rota de processamento utilizada. Nas amostras por freeze casting, foram observados canais de poros. Já as amostras com amido como fase de sacrifício, os poros são arredondados e não conectados
In this study, preparation and characterization of alumina ceramic materials with functional porosity gradients were performed. Freeze casting of alumina slurries, using water as the chosen solvent, and sacrificial phase method using corn starch as sacrificial phase, were implemented. The materials used to produce the samples were alumina and analytical purity corn starch. Porosity characteristics were investigated concerning pore morphology, pore distribution in the ceramic matrix and processing route interference in pore formation. The evaluation of porosity was made utilizing porosity determination methods as mercury intrusion and Archimedes method with water as immersion liquid. The mechanical properties, as well as the fracture mode, were investigated during uniaxial compressive test in a universal testing machine. Using the images obtained by scanning electron microscopy (SEM), it was possible to correlate the data obtained in the porosimetry analysis with the mechanical response obtained from the material. In terms of porosity, the results between the processing routes reveal considerable differences in pore distribution and quantity of pores. However, the pore sizes obtained for both methods were pretty close to each other. The mechanical strength during compressive stress was higher in the samples produced via sacrificial phase method, but those samples failed catastrophically. Freeze casting samples, on the other hand, had lower mechanical resistance and their fractures were directly influenced by several factors during their assembly processing. The pore and microstructure morphology presented by both methods were direct consequence of the processing route used. In the samples produced by freeze casting, pore channels were observed. The samples produced via sacrificial phased method using corn starch presented unconnected rounded pores.
Perlot, Céline. "Influence de la décalcification de matériaux cimentaires sur les propriétés de transfert : application au stockage profond de déchets radioactifs." Toulouse 3, 2005. http://www.theses.fr/2005TOU30211.
Cementitious materials have been selected to compose engineering barrier system (EBS) of the french radioactive waste deep repository, because of concrete physico-chemical properties: the hydrates of the cementitious matrix and the pH of the pore solution contribute to radionuclides retention; furthermore the compactness of these materials limits elements transport. The confinement capacity of the system has to be assessed while a period at least equivalent to waste activity (up to 100. 000 years). His durability was sustained by the evolution of transfer properties in accordance with cementitious materials decalcification, alteration that expresses structure long-term behavior. Then, two degradation modes were carried out, taking into account the different physical and chemical interactions imposed by the host formation. The first mode, a static one, was an accelerated decalcification using nitrate ammonium solution. It replicates EBS alteration dues to underground water. Degradation kinetic was estimated by the amount of calcium leached and the measurement of the calcium hydroxide dissolution front. To evaluate the decalcification impact, samples were characterized before and after degradation in term of microstructure (porosity, pores size distribution) and of transfer properties (diffusivity, gas and water permeability). The influence of cement nature (ordinary Portland cement, blended cement) and aggregates type (lime or siliceous) was observed: experiments were repeated on different mortars mixes. On this occasion, an essential reflection on this test metrology was led. The second mode, a dynamical degradation, was performed with an environmental permeameter. It recreates the EBS solicitations ensured during the resaturation period, distinguished by the hydraulic pressure imposed by the geologic layer and the waste exothermicity. This apparatus, based on triaxial cell functioning, allows to applied on samples pressure drop between 2 and 10 MPa and temperature from 20 to 80°C. Water permeability evolution relating to experimental parameters, uncoupled or coupled, was relied to mortars microstructural modifications
Olivella, Pastallé Sebastià. "Nomsothermal multiphase flow of brine and gas through saline media." Doctoral thesis, Universitat Politècnica de Catalunya, 1995. http://hdl.handle.net/10803/6261.
Las ecuaciones de balance se han formulado teniendo en cuenta que en un medio salino existen tres especies o componentes mayoritarios. Estos son: la sal, el agua y el aire. Uno de los aspectos diferenciadores respecto a otros medios geológicos es que la fase sólida se disuelve a concentraciones elevadas en la fase liquida a la que se llama Salmuera. Otro aspecto interesante es la presencia de inclusiones de salmuera en la fase sólida. La disolución y precipitación de la sal da lugar a un mecanismo de deformación por fluencia. La forma de los granos de sal cambia por disolución en las zonas donde se concentran las tensiones y recristalizacion en las zonas de menor estado tensional. Además los granos también se deforman por el carácter muy dúctil del propio sólido cristalino. Hemos derivado una nueva ley constitutiva tensión deformación para los agregados porosos de sal, que se basa en acoplar una geometría idealizada de los granos con los mecanismos fundamentales de deformación.
Una vez que se ha desarrollado y verificado el programa de cálculo, este ha sido aplicado para el estudio de diferentes fenómenos. Presentamos el análisis de las variaciones de porosidad inducidas por gradientes de temperatura en agregados porosos de sal no saturados. Las diferencias de temperatura inducen un flujo de vapor que es contrarrestado por un flujo de salmuera. Este arrastra la sal disuelta y da lugar a un flujo de sal hacia zonas de temperatura más alta.
Carvalho, Gustavo Antoniácomi de. "PROCESSAMENTO DE CERÂMICAS COM POROSIDADE GRADUADA UTILIZANDO AS TÉCNICAS DE FREEZE CASTING E COLAGEM DE BARBOTINA." Universidade Estadual de Ponta Grossa, 2018. http://tede2.uepg.br/jspui/handle/prefix/2741.
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Cerâmicas porosas vêm ganhando visibilidade devido a algumas aplicações tecnológicas interessantes, tais como a utilização em eletrólitos sólidos, ânodos de células a combustível, filtros cerâmicos e reposição óssea e dental. Dentre elas, há especial atenção ao estudo de materiais porosos com porosidade graduada, nos quais a quantidade de poros e a morfologia dos mesmos se alteram pelo volume do material. Nesse trabalho foi realizado o processamento e caracterização de materiais cerâmicos de alumina com porosidade graduada a partir das técnicas de freeze casting e colagem de barbotina, utilizando hidróxido de alumínio e amido de arroz como fases de sacrifício. Após a conformação das amostras por esses métodos, a porosidade foi caracterizada por microscopia eletrônica de varredura, pelas medidas de porosidade aparente feita pelo Princípio de Arquimedes e pela distribuição de tamanho de poros feita pela técnica de porosimetria de mercúrio. Foi avaliada também a resistência mecânica das amostras a partir de ensaio de compressão. Foi confirmada a relação entre as amostras processados isoladamente e suas respectivas camadas nas amostras graduadas. Foi observada também uma boa interação interfacial entre cada uma das camadas das amostras graduadas. A porosidade das amostras com porosidade graduada se manteve próxima do esperado, o valor esperado foi determinado a partir da média das amostras processadas isoladamente em relação às camadas do material com porosidade graduada. O ensaio mecânico demonstrou que não houve influência das interfaces dos materiais graduados na sua resistência à compressão.
Porous ceramics have been gaining visibility due to some interesting technological applications, such as its use as solid electrolytes, fuel cell anodes, ceramic filters and bone and dental reposition. Among them, there is special care in studying graded porosity materials, where the quantity of pores and pore morphology changes through the material volume. In this work the processing and characterization of alumina ceramic materials with functionally graded porosity by freeze casting and slip casting techniques using aluminum hydroxide and rice starch as sacrificial template was performed. After conformation, the porosity was characterized through electron scanning microscopy, apparent porosity through Archimedes method and median pore size through mercury porosimetry. The mechanical resistance was also obtained by compression testing. The analysis allowed to confirm the relation between each of the isolated samples’ microstructure and its respective layer in each of the graded materials, also, the graded materials shown good interfacial interaction between each of the layers. The porosity in graded materials kept close to the expected value, which was determined by the medium value of the porosities of the isolated samples respective to the graded material. Mechanical testing shown that there was no influence of the graded material interfaces in its compressive strength.
Elfmarková, Veronika. "Vliv jemnozrnných příměsí na charakter pórového systému betonu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225906.
Ezhil, Venuswaran R. R. "Development Of Porosity Gradient Bioglass Ceramic Scaffold." Thesis, 2015. http://ethesis.nitrkl.ac.in/7864/1/2016_EVRamaRaju_611CR301.pdf.
Yu, Ya Jen, and 游雅任. "The preparation of calcium oxide platelet with porosity gradient." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/27797385062632957176.
國立臺灣大學
材料科學與工程學研究所
91
Abstract In the present study, we developed a new polycrystalline platelet. The platelet is porous with gradient distribution. One side of the platelet is a dense SiO2 layer. Other phase in the platelet is mainly calcium oxide. The amount of pores increases with the increase of the distance from SiO2 layer. The macro-structure of the calcium oxide is a mutli-layered structure, many porous are inside it. The largest diameter of this platelet is 10mm, the thickness is 20-40μm. In the present study, fish scale is used as template. The macro-structure of fish scale is a layered one. There is 40% to 80% organic protein, the rest is ceramic. We applied fish scale as template to prepare porous layered platelet by using a novel process. The process mainly composes of two stages, silica coating and reaction sintering. First stage, the acid and alkaline solutions were used to applied SiO2 coating onto fish scale with the sol-gel process. Second stage, the coated fish scale is fired within the temperature range from 10000C to 14000C in a well-controlled atmosphere. Pores are still existed after firing, the pores distributes gradiently within the platelet. This polycrystalline platelet can be used as the reinforcement material for other materials.
Chun, Hyen Chung. "Application of local porosity to define pore networks and pore geometry in soils a case study along a carbon dioxide and temperature gradient /." 2009. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000051188.
ALTMAN, Jan. "Analýza lesních porostů na vulkánu Hallasan: zhodnocení vlivu disturbancí a kompetice na růst a přežívání stromových populací na gradientu nadmořské výšky." Master's thesis, 2009. http://www.nusl.cz/ntk/nusl-51296.
Rajmonová, Lenka. "Význam remízků a jejich ekologických vlastností pro ptáky v intenzivně obhospodařované zemědělské krajině." Master's thesis, 2019. http://www.nusl.cz/ntk/nusl-404904.
POLÁČKOVÁ, Jitka. "Vliv předplodiny na výnos a kvalitu ovsa." Master's thesis, 2013. http://www.nusl.cz/ntk/nusl-154401.