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1
Lin, Chang-Yi. "Processing and properties of functionally gradient materials." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284594.
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2
Babayi, Reza. "Fracture in functionally gradient materials, static and dynamic analyses." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq20724.pdf.
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3
Yıldırım, Uygar Güden Mustafa. "Investigation of quasi-static dynamic mechanical properties of functionally graded Sic-particulate reinforced aluminium metal matrix composites/." [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/makinamuh/T000470.doc.
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4
Gao, Xiong. "Two-dimensional exact analysis of functionally graded piezoelectric cantilevers under electric and mechanical loadings." Thesis, University of Macau, 2018. http://umaclib3.umac.mo/record=b3950671.
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5
Porter, David Scott. "Production of Functionally Gradient Materials Using Model Thermosetting Systems Cured in a Thermal Gradient." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/27874.
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Thermosetting polymers can cure at a gradient of cure temperatures due to a variety of factors, including heat transfer in the thermoset during heating and the exotherm due to the chemical reaction occurring during the cure. A new method for assessing the effect of cure conditions on mechanical behavior of toughened thermosets has been developed. Modeling of the phase separation process of a model thermoset system provided detailed understanding of the mechanism of property variation with cure temperature for this material. Subsequent characterization of gradient temperature cured samples has shown important variations, illustrating not only the importance of cure conditions, but the possibility of producing materials with new and useful properties.
A special mold was developed to cure samples in a controlled gradient of temperature. Example systems known to show pronounced variations in microstructure cured in this gradient mold showed large variations of microstructure as a function of position within the sample, corresponding to the cure temperature at that point.
A model toughened thermoset system was developed to demonstrate gradients of properties following cure in the gradient temperature mold. Cyanate ester materials were modified with hydroxyl-terminated butadiene-acrylonitrile copolymers as well as low Tg amorphous polyesters. The polyesters showed very desirable properties for a toughener, including relatively good thermo-oxidative stability in comparison with the butadiene-acrylonitrile toughener. However, the variation of properties of the cured materials with temperature was small, and to better understand the property variation possible using a gradient cure temperature technique, the butadiene-acrylonitrile toughened cyanate ester system was chosen for further study. This system showed a significant variation of glass transition temperature of the cyanate-rich phase as a function of cure temperature.
Modeling of the phase separation process of this material was varied out employing a modeling procedure developed for epoxy materials. Various characteristics of the system were determined in order to apply the model to the chosen toughened thermoset. These included viscosity, surface, and thermodynamic parameters in addition to a careful characterization of the morphological parameters developed during cure at the chosen temperatures. Results show excellent predictive capability of the model for microstructure. Prediction of phase composition as a function of cure temperature is also possible, again with good agreement with experiment results. Higher cure temperatures result in a non-equilibrium phase composition, depressing the glass transition temperature of the continuous cyanate ester rich phase. This provides a mechanism by which properties of the system change as a function of position within a gradient temperature cured sample.
Dynamic mechanical analysis was employed to characterize the relaxation properties of gradient and isothermally cured samples. The Havriliak Negami equation was chosen to describe the relaxation behavior of these samples. Comparison of the fitting of isotherms over the small, experimentally accessible range of frequencies showed that the use of time-temperature superpositioning could more reliably discern relatively small differences. The breadth of the relaxation corresponding to the glass transition of the polycyanurate phase was increased with a gradient cure temperature relative to isothermally cured samples. This increased broadness was expressed in an alternative way through the use of an autocorrelation function, which allows direct comparison of the time-dependent transition from a fully unrelaxed condition to a fully relaxed one.Ph. D.
6
Heidari, Maryam. "3D modelling of functionally graded coatings." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=215382.
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The purpose of this study is to investigate the behaviour of functionally graded materials in the coating design through analytical and numerical work. Functionally graded materials are advanced composite materials formed from two or more constituents with a continuously varying composition, which results in a continuous variation of material properties from one surface of the material to the other. The concept of functionally graded material is actively explored in coating design where structural and/or functional failures of the coating can happen due to a mismatch between the material properties of the coating and substrate, particularly at the coating/substrate interface. This work focuses on the performance of coated plates with homogeneous and graded coatings under various types of loading to develop a better understanding of their response. Firstly, the three dimensional elasticity solution for an isotropic coated plate with a stiffness gradient in the coating is extended to cover different types of applied loading and then a three dimensional elasticity solution for transversely isotropic materials with gradients in elastic properties is also developed. Based on the extended/developed solutions, a MATLAB code is created to produce a model that would enable the analysis of coated plates for a range of material, geometric and loading parameters. To test the analytical models, a finite element analysis is performed using the commercial finite element software ABAQUS, in which a user material subroutine is employed to generate a gradient in the material properties within each element and increase the accuracy of the results. All the developed analytical and numerical models are then used to carry out a comparative study of three-dimensional stress and displacement fields in the coated plates with homogeneous and graded coatings and establish the effect of various parameters such as coating thickness, coating position, plate dimensions, stiffness gradient, loading distributions and anisotropy on the coated plate response.
7
Goupee, Andrew. "Methodology for the Thermomechanical Simulation and Optimization of Functionally Graded Materials." Fogler Library, University of Maine, 2005. http://www.library.umaine.edu/theses/pdf/GoupeeA2005.pdf.
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Pelletier, Jacob Leo. "Thermoelastic Analysis and Optimization of Functionally Graded Plates and Shells." Fogler Library, University of Maine, 2005. http://www.library.umaine.edu/theses/pdf/PelletierJL2005.pdf.
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9
Akarapu, Sreekanth. "Numerical analysis of plane cracks in strain-gradient elastic materials." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Fall2005/S%5FAkarapu%5F082205.pdf.
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Kidane, Addis Asmelash. "An experimental and analytical study of graded materials under thermo-mechanical dynamic loading /." View online ; access limited to URI, 2009. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3380532.
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11
Wang, Xuan. "Synthesis of functionally graded materials via electrophoretic deposition and sintering /." Diss., Connect to a 24 p. preview or request complete full text in PDF formate. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3208812.
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12
Cantergiani, Elisa. "Mechanical Properties of Functionally Graded Materials: Carbon Gradient inside Interstitial Free Steel." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34314.
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In the last decade aluminium started to be considered as an alternative to steel to produce car body panels, especially considering the strict demands to decrease fuel consumption which require vehicle weight reduction. In order to keep their leading role, steel companies have to produce stronger materials to reduce the thickness of steel sheets used in cars and are now considering non-conventional steel making processes.
The purpose of this PhD research was to investigate the possibility of strengthening thin sheets of interstitial free steel (IF steel) by using carbon rich films deposited on the steel surface using Physical Vapour Deposition (PVD). These films then act as a carbon reservoir which upon heat treatment release carbon in the IF steel and strengthen it.
Coated tensile coupons 200 μm thick were annealed at different temperatures under high vacuum. Tensile tests show that a 100 MPa increase in yield stress can be obtained after annealing at 430 ˚C for 1h in high vacuum. The effects of annealing environment, film thickness and prestrain on carbon diffusion were also investigated. It was shown that carbon diffusion from the film to the IF steel substrate is limited by the film transformation into cementite at temperatures equal or higher than 530 ˚C.
All tensile curves showed a plastic instability known as Lüders plateau, which is undesirable as it results in surface markings on the deformed part. FEM analyses were performed to find ways to suppress the Lüders plateau, proving that increasing strain-hardening or having a graded instead of uniform carbon content through thickness can suppress or limit Lüdering.
The possibility of creating a through thickness gradient of microstructure was investigated as it could suppress Lüdering and result in higher strength. For these tests, FeC coated coupons were induction heated to 820 ˚C followed by water quenching. After only 2 minutes of heat treatment the yield stress was increased by 250 MPa and the ultimate tensile strength reached 400 MPa. With an annealing of 4 minutes, the Lüders plateau was fully suppressed and the microstructure consisted in ferrite grains and TiC nanocarbides. This work demonstrates that FeC films can be effectively used to diffuse carbon into steel and that a significant increase in mechanical properties can be obtained after a heat treatment of only a few minutes.
13
Kirugulige, Madhusudhana S. "A study of mixed-mode dynamic fracture in advanced particulate composites by optical interferometry, digital image correlation and finite element methods." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Dissertations/KIRUGULIGE_MADHUSUDHANA_29.pdf.
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14
Bell, Bryan Frederick Jr. "Functionally graded, multilayer diamondlike carbon-hydroxyapatite nanocomposite coatings for orthopedic implants." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7962.
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15
Bell, Bryan Frederick. "Functionally graded, multilayer diamondlike carbon-hydroxyapatite nanocomposite coatings for orthopedic implants." Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-06072004-131058/unrestricted/bell%5Fbryan%5Ff%5F200405%5Fms.pdf.
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Jain, Nitesh. "Experiment and analytical evaluation of dynamic fracture in graded multifunctional materials /." View online ; access limited to URI, 2005. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3188059.
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17
Nandakumar, Nagarajan Nicholson P. S. "Nickel-alumina composites and graded materials by electrophoretic deposition /." *McMaster only, 2005.
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18
Morais, Dayana Campanelli de. "Síntese, processamento e caracterização de vitrocerâmicas com gradiente funcional." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152407.
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O presente estudo teve como objetivo desenvolver vitrocerâmicas de dissilicato de lítio com gradiente funcional de densidade, inspirado no gradiente natural que existe entre o esmalte e a dentina. Primeiramente o vidro de composição: 33,33% mol de Li2O e 66,67% mol de SiO2 foi obtido pelo método fusão/resfriamento. Em seguida foram preparadas amostras com estruturas homogêneas do vidro a base de dissilicato de lítio para determinação dos melhores parâmetros de sinterização. Três diferentes tratamentos térmicos, determinados com base no resultado da análise diferencial de calorimetria foram utilizados: 850 °C/3h; 900 °C/3h e 950 °C/3h. A caracterização desses materiais foi realizada através da difração de raios X, microscopia eletrônica de varredura, método de Arquimedes e ensaio de flexão biaxial (n=10). O tratamento térmico de 950 oC obteve os melhores resultados, sendo o escolhido para a realização das próximas etapas do estudo. Com a finalidade de otimizar a estética, foi adicionada cerâmica feldspática (VITAVM®9) ao vidro SiO2-Li2O na proporção de 10%, 15% e 20% (n=30). Foi observado que a adição de 10% de VM9 não alterou a resistência do material, e quanto maior a quantidade de VM9, maior foi a translucidez e menor foram o módulo elástico e a densidade. Com isso, foram preparadas vitrocerâmicas bioinspiradas com gradiente funcional de densidade nas seguintes sequências de camadas: uma com 10% de VM9, outra com 15% e a última com 20%. Não houve diferença na resistência à flexão biaxial do grupo com gradiente, quando a camada mais densa estava voltada para o lado de tração, com o grupo com 15% de VM9 com estrutura homogênea. A translucidez do grupo com gradiente foi equivalente ao grupo homogêneo mais translúcido, com 20% de VM9. Concluiu-se que foi possível sintetizar uma vitrocerâmica de dissilicato de lítio funcionalmente graduada, onde uma boa resistência mecânica e uma boa translucidez foram unidas.
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Velo, Ani P. "Optimal Design of Gradient Fields with Applications to Electrostatics." Digital WPI, 2000. https://digitalcommons.wpi.edu/etd-dissertations/311.
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"In this work we consider an optimal design problem formulated on a two dimensional domain filled with two isotropic dielectric materials. The objective is to find a design that supports an electric field which is as close as possible to a target field, under a constraint on the amount of the better dielectric. In the case of a zero target field, the practical purpose of this problem is to avoid the so called dielectric breakdown of the material caused due to a relatively large electric field. In general, material layout problems of this type fail to have an optimal configuration of the two materials. Instead one must study the behavior of minimizing sequences of configurations. From a practical perspective, optimal or nearly optimal configurations of the two materials are of special interest since they provide the information needed for the manufacturing of optimal designs. Therefore in this work, we develop theoretical and numerical means to support a tractable method for the numerical computation of minimizing sequences of configurations and illustrate our approach through numerical examples. The same method applies if we were to replace the electric field by electric flux, in our objective functional. Similar optimization design problems can be formulated in the mathematically identical contexts of electrostatics and heat conduction."
20
Siu, Yan-kit, and 邵仁傑. "Modelling and prototyping of heterogeneous solid CAD models." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31245924.
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Koppanooru, Sampat Kumar Reddy. "Estimating Thermal Conductivity and Volumetric Specific Heat of a Functionally Graded Material using Photothermal Radiometry." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062896/.
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Functionally graded materials (FGMs) are inhomogeneous materials in which the material properties vary with respect to space. Research has been done by scientific community in developing techniques like photothermal radiometry (PTR) to measure the thermal conductivity and volumetric heat capacity of FGMs. One of the problems involved in the technique is to solve the inverse problem, i.e., estimating the thermal properties after the frequency scan has been obtained. The present work involves finding the unknown thermal conductivity and volumetric heat capacity of the FGMs by using finite volume method. By taking the flux entering the sample as periodic and solving the discretized 1-D thermal wave field equation at a frequency domain, one can obtain the complex temperatures at the surface of the sample for each frequency. These complex temperatures when solved for a range of frequencies gives the phase vs frequency scan which can then be compared to original frequency scan obtained from the PTR experiment by using a residual function. Brute force and gradient descent optimization methods have been implemented to estimate the unknown thermal conductivity and volumetric specific heat of the FGMs through minimization of the residual function. In general, the spatial composition profile of the FGMs can be approximated by using a smooth curve. Three functional forms namely Arctangent curve, Hermite curve, and Bezier curve are used in approximating the thermal conductivity and volumetric heat capacity distributions in the FGMs. The use of Hermite and Bezier curves gives the flexibility to control the slope of the curve i.e. the thermal property distribution along the thickness of the sample. Two-layered samples with constant thermal properties and three layered samples in which one of the layer has varying thermal properties with respect to thickness are considered. The program is written in Fortran and several test runs are performed. Results obtained are close to the original thermal property values with some deviation based on the stopping criteria used in the gradient descent algorithm. Calculating the gradients at each iteration takes considerable amount of time and if these gradient values are already available, the problem can be solved at a faster rate. One of the methods is extending automatic differentiation to complex numbers and calculating the gradient values ahead; this is left for future work.
22
Hána, Tomáš. "Funkční polymerní pěny." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2018. http://www.nusl.cz/ntk/nusl-376873.
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Functional polymer foams are considered as a promising field which could potentially produce foams with added value. Specifically, functionally graded foams are materials which are expected to provide better mechanical properties while preserving low density in comparison with regular foams. In this thesis, a preparation process of such foams is designed, examination of prepared structure and comparison of mechanical properties with regular foams is performed. The obtained results are discussed and further research in this field is proposed.
23
Li, Qian. "Three-dimensional analysis of functionally graded material plates, free vibration in thermal environment and thermal buckling." Thesis, University of Macau, 2008. http://umaclib3.umac.mo/record=b1783646.
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Daly, John Louis Jr. "On Comparison of Indentation Models." Scholar Commons, 2007. http://scholarcommons.usf.edu/etd/3899.
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Thin films that are functionally gradient improve the mechanical properties
of film-substrate layered materials. Mechanical properties of such materials are
found by using indentation tests. In this study, finite element models are
developed to simulate the indentation test. The models are based on an
axisymmetric half space of a specimen subjected to spherical indentation. The
film layer through the thickness is modeled to have either homogeneous material
properties or nonhomogeneous material properties that vary linearly.
Maximum indenter displacement, and maximum normal and shear
stresses at the interface are compared between the homogeneous model and
the nonhomogeneous model for pragmatic contact length to film thickness ratios
of 0.2 to 0.4, and film to substrate moduli ratios of 1 to 200 to 1.
Additionally, a coefficient is derived from regression of the stress data
produced by these models and compared to that used to define the pressure field
in the axisymmetric Hertzian contact model. The results of this study suggest
that a displacement boundary condition to an indenter produces the same results
as a pressure distribution boundary condition.
The critical normal stresses that occur between modeling a film as a
nonhomogeneous and as a homogeneous material vary from 19% for a modulus
ratio of 2.5:1 to as high as 66% for a modulus ratio of 200:1 indicating that the
modeling techniques produced very different maximum normal stresses. The
difference in the maximum shear stress between the nonhomogeneous and the
homogeneous models varied from 19% for a 2.5:1 modulus ratio to 57% for the
200:1 modulus ratio but reached values as low as 6% for the 50:1 modulus ratio.
The maximum contact depth between the nonhomogeneous and the
homogeneous models varied from 14% for the 2.5:1 case to as much as 75% in
the 200:1 case.
The results from the reapplication of the pressure field derived from the
regression coefficients and the
R2 values from these regression models indicate
the correctness of the regression model used as well as its ability to replicate the
normal stresses in the contact area and maximum indenter displacements in a
FEA model for both the homogeneous and the nonhomogeneous models for
modulus ratios ranging from 2.5:1 to 200:1.
The agreement between the regression based coefficients and the force
based coefficients suggests the validity for the use of the theoretical
axisymmetric Hertzian contact model for defining the pressure field in the contact
area and displacements for both the homogeneous case and the
nonhomogeneous case for the considered film to substrate moduli ratios and
contact length to film thickness ratios.
25
Schneider-Maunoury, Catherine. "Application de l’injection différentielle au procédé de fabrication additive DED-CLAD® pour la réalisation d’alliages de titane à gradients de compositions chimiques." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0260/document.
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Depuis 1984, les matériaux à gradients de fonction (FGM) permettent de former une barrière thermique et réduire les fortes discontinuités des propriétés entre deux matériaux de nature différente. Ces multi-matériaux, qui consistent en une variation intentionnelle de la composition chimique entrainant par conséquent une modification des propriétés microstructurales, chimiques, mécaniques et thermiques, permettent de lisser la distribution des contraintes thermiques. L’élaboration in situ de ces alliages sur mesure est rendu possible grâce à l’utilisation de procédés de fabrication additive tel que le procédé par dépôt de poudres DED-CLAD®. Ces procédés connaissent un essor considérable depuis les années 1980 et sont idéaux dans la fabrication de FGM. Dans le cadre de cette thèse CIFRE, des développements techniques ont été effectués pour adapter le procédé DED-CLAD® et permettre la réalisation de FGM. Grâce à plusieurs collaborations industrielles, une étude complète a été réalisée sur les alliages titane-molybdène et titane-niobium. Ces alliages permettent dans le premier cas de réaliser des pièces résistantes à de fortes sollicitations thermiques (secteur spatial), et dans le second cas d’associer les propriétés mécaniques et la biocompatibilité (secteur biomédical). L’originalité de cette thèse repose sur l’étude d’un gradient complet, c’est-à-dire que l’ajout en élément d’alliage varie de 0% à 100%. En effet, les études reportées dans la littérature ne font pas mentions des alliages titane-matériaux réfractaire pour des taux élevés en élément réfractaire. Les analyses microstructurale (DRX, structure cristallographique par EBSD, microstructure), chimique (EDS) et mécanique (microdureté, tests de traction et essais d’indentation instrumentée) ont mis en évidence une évolution des propriétés le long du gradients de composition. La caractérisation mécanique des échantillons par indentation instrumentée s’est par ailleurs révélée particulièrement pertinente dans les cas de ces multi-matériauxSince 1984, the Functionally Graded Material (FGM) allow to create a thermal barrier and to reduce the strong discontinuities of properties between two materials of different composition. These multimaterials,whose consist of an intentional variation in the chemical composition and, consequently, modify the microstructural, chemical, mechanical and thermal properties, lead to a smooth distribution of the thermal stress. The in-situ development of these custom-made alloys is made possible by the use of additive manufacturing processes such as the DED-CLAD® powder deposition process. These processes have grown substantially since the 1980s and are optimal for the manufacture of FGM. During this industrial thesis, technical developments have been carried out to adapt the DED-CLAD® process and to allow the manufacturing of FGM. Thanks to two industrial collaborations, a full study was carried out on titanium-molybdenum and titanium-niobium alloys. These alloys make it possible, in the first case, to produce parts resistant to strong thermal stress (space sector), and in the second case to combine mechanical properties and biocompatibility (biomedical sector). The originality of this thesis rests on the study of a complete gradient, that is the addition in alloy element varied from 0% to 100%. In fact, studies reported in the literature do not mention titanium-refractory material for high levels of refractory element. Microstructural (XRD, crystallographic analysis by EBSD technique), chemical (EDS) and mechanical (microhardness, tensile test and instrumented indentation) analyses revealed an evolution of the properties along the chemical gradient. The mechanical characterization of the sample by instrumented indentation has also proved particularly relevant in the case of these multi-materials
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Thomas, Gareth James. "Advanced materials for plasma facing components in fusion devices." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:f8ba1ae1-f303-4c32-877e-dca421a3cb5c.
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This thesis describes the design, manufacture and characterisation of thick vacuum plasma sprayed tungsten (W) coatings on steel substrates. Fusion is a potentially clean, sustainable, energy source in which nuclear energy is generated via the release of internal energy from nuclei. In order to fuse nuclei the Coulomb barrier must be breached - requiring extreme temperatures or pressures – akin to creating a ‘star in a box’. Tungsten is a promising candidate material for future fusion reactors due to a high sputtering threshold and melting temperature. However, the large coefficient of thermal expansion mismatch with reactor structural steels such as the low activation steel Eurofer’97 is a major manufacturing and in-service problem. A vacuum plasma spraying approach for the manufacture of tungsten and tungsten/steel graded coatings has been developed successfully. The use of graded coatings and highly textured 3D interface surfi-sculpt substrates has been investigated to allow the deposition of thick plasma sprayed tungsten coatings on steel substrates. Finite element models have been developed to understand the residual stresses that develop in W/steel systems and made use of experimental measurements of coating thermal history during manufacture and elastic moduli measured by nano-indentation. For both the graded and surfi-sculpt coating, the models have been used to understand the mechanism of residual stress redistribution and relief in comparison with simple W on steel coatings, particularly by consideration of stored strain energy. In the case of surfi-sculpt W coatings, the patterned substrate gave rise to regular stress concentrating features, and allowed 2mm thick W coatings to be produced reproducibly without delamination. Preliminary through thickness residual stress measurements were compared to model predictions and provided tentative evidence of significant W coating stress relief by regulated coating segmentation.
27
Schneider-Maunoury, Catherine. "Application de l’injection différentielle au procédé de fabrication additive DED-CLAD® pour la réalisation d’alliages de titane à gradients de compositions chimiques." Electronic Thesis or Diss., Université de Lorraine, 2018. http://www.theses.fr/2018LORR0260.
Full textAbstract:
Depuis 1984, les matériaux à gradients de fonction (FGM) permettent de former une barrière thermique et réduire les fortes discontinuités des propriétés entre deux matériaux de nature différente. Ces multi-matériaux, qui consistent en une variation intentionnelle de la composition chimique entrainant par conséquent une modification des propriétés microstructurales, chimiques, mécaniques et thermiques, permettent de lisser la distribution des contraintes thermiques. L’élaboration in situ de ces alliages sur mesure est rendu possible grâce à l’utilisation de procédés de fabrication additive tel que le procédé par dépôt de poudres DED-CLAD®. Ces procédés connaissent un essor considérable depuis les années 1980 et sont idéaux dans la fabrication de FGM. Dans le cadre de cette thèse CIFRE, des développements techniques ont été effectués pour adapter le procédé DED-CLAD® et permettre la réalisation de FGM. Grâce à plusieurs collaborations industrielles, une étude complète a été réalisée sur les alliages titane-molybdène et titane-niobium. Ces alliages permettent dans le premier cas de réaliser des pièces résistantes à de fortes sollicitations thermiques (secteur spatial), et dans le second cas d’associer les propriétés mécaniques et la biocompatibilité (secteur biomédical). L’originalité de cette thèse repose sur l’étude d’un gradient complet, c’est-à-dire que l’ajout en élément d’alliage varie de 0% à 100%. En effet, les études reportées dans la littérature ne font pas mentions des alliages titane-matériaux réfractaire pour des taux élevés en élément réfractaire. Les analyses microstructurale (DRX, structure cristallographique par EBSD, microstructure), chimique (EDS) et mécanique (microdureté, tests de traction et essais d’indentation instrumentée) ont mis en évidence une évolution des propriétés le long du gradients de composition. La caractérisation mécanique des échantillons par indentation instrumentée s’est par ailleurs révélée particulièrement pertinente dans les cas de ces multi-matériauxSince 1984, the Functionally Graded Material (FGM) allow to create a thermal barrier and to reduce the strong discontinuities of properties between two materials of different composition. These multimaterials,whose consist of an intentional variation in the chemical composition and, consequently, modify the microstructural, chemical, mechanical and thermal properties, lead to a smooth distribution of the thermal stress. The in-situ development of these custom-made alloys is made possible by the use of additive manufacturing processes such as the DED-CLAD® powder deposition process. These processes have grown substantially since the 1980s and are optimal for the manufacture of FGM. During this industrial thesis, technical developments have been carried out to adapt the DED-CLAD® process and to allow the manufacturing of FGM. Thanks to two industrial collaborations, a full study was carried out on titanium-molybdenum and titanium-niobium alloys. These alloys make it possible, in the first case, to produce parts resistant to strong thermal stress (space sector), and in the second case to combine mechanical properties and biocompatibility (biomedical sector). The originality of this thesis rests on the study of a complete gradient, that is the addition in alloy element varied from 0% to 100%. In fact, studies reported in the literature do not mention titanium-refractory material for high levels of refractory element. Microstructural (XRD, crystallographic analysis by EBSD technique), chemical (EDS) and mechanical (microhardness, tensile test and instrumented indentation) analyses revealed an evolution of the properties along the chemical gradient. The mechanical characterization of the sample by instrumented indentation has also proved particularly relevant in the case of these multi-materials
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Crisafulli, Daniela. "Advanced modelling of multilayered composites and functionally graded structures by means of Unified Formulation." Thesis, Paris 10, 2013. http://www.theses.fr/2013PA100055/document.
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La plupart des problèmes d'ingénierie des deux derniers siècles ont été résolus grâce à des modèles structuraux pour poutres, plaques et coques. Les théories classiques, tels que Euler-Bernoulli, Navier et de Saint-Venant pour les poutres, et Kirchhoff-Love et Mindlin-Reissner pour plaques et coques, ont permis de réduire le problème générique 3-D, dans le problème unidimensionnel pour les poutres et deux dimensionnelle pour les coques et les plaques. Théories raffinés d'ordre supérieur ont été proposées au cours du temps, comme les modèles classiques ne consentez pas à d'obtenir une complète domaine des contraintes et des déformations. La Carrera Unified Formulation (UF) a été proposé au cours de la dernière décennie, et permet de développer un grand nombre de théories structurelles avec un nombre variable d'inconnues principales au moyen d'une notation compacte et se référant à des nuclei fondamentales. Cette formulation unifiée permet de dériver carrément des modèles structurels d'ordre supérieur, pour les poutres, plaques et coques. Dans ce cadre, cette thèse vise à étendre la formulation pour l'analyse des structures fonctionnellement gradués (FGM), en introduisant aussi le problème thermo-mécanique, dans le cas des poutres fonctionnellement gradués. Suite à la formulation unifiée, les variables génériques déplacements sont écrits en termes de fonctions de base, qui multiplie les inconnues. Dans la deuxième partie de la thèse, de nouvelles fonctions de bases pour la modélisation des coques, qui représentent une approximation trigonométrique des variables déplacements, sont pris en compteMost of the engineering problems of the last two centuries have been solved thanks to structural models for both beams, and for plates and shells. Classical theories, such as Euler-Bernoulli, Navier and De Saint-Venant for beams, and Kirchhoff-Love and Mindlin- Reissner for plates and shells, permitted to reduce the generic 3-D problem, in onedimensional one for beams and two-dimensional for shells and plates. Refined higher order theories have been proposed in the course of time, as the classical models do not consent to obtain a complete stress/strain field. Carrera Unified Formulation (UF) has been proposed during the last decade, and allows to develop a large number of structural theories with a variable number of main unknowns by means of a compact notation and referring to few fundamental nuclei. This Unified Formulation allows to derive straightforwardly higher-order structural models, for beams, plates and shells. In this framework, this thesis aims to extend the formulation for the analysis of Functionally Graded structures, introducing also the thermo-mechanical problem, in the case of functionally graded beams. Following the Unified Formulation, the generic displacements variables are written in terms of a base functions, which multiplies the unknowns. In the second part of the thesis, new bases functions for shells modelling, accounting for trigonometric approximation of the displacements variables, are considered
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Schedl, Andreas [Verfasser], and Hans-Werner [Akademischer Betreuer] Schmidt. "Gradient topographies and functional gradient materials / Andreas Schedl ; Betreuer: Hans-Werner Schmidt." Bayreuth : Universität Bayreuth, 2019. http://d-nb.info/1214297544/34.
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Li, Qiyao. "Effect of Surface Functional Groups on Chondrocyte Behavior Using Molecular Gradients." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428399167.
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Dureau, Clément. "Fatigue d'aciers inoxydables austénitiques traités par grenaillage ultrasonore sévère : contributions expérimentales et numériques à l'étude de l'amorçage et la propagation des fissures." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0143.
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Dans le domaine de la fatigue à grand nombre de cycles, les fissures s'initient le plus souvent à la surface des pièces. Par conséquent, en plus des propriétés mécaniques globales, les caractéristiques de la surface et de la sous-couche, telles que la rugosité et les contraintes résiduelles affectent la durée de vie en fatigue. La rugosité a essentiellement une influence sur la phase d'amorçage des fissures. En effet, la présence d'irrégularités de surface entraine des concentrations de contraintes qui peuvent produire de fortes déformations locales et éventuellement entrainer la formation de défauts de type fissures. Par ailleurs, la présence de contraintes résiduelles affecte à la fois la phase d'amorçage et de propagation des fissures. Elles affectent la plasticité proche de la surface et influencent donc l'amorçage des fissures. De plus, en se superposant au chargement mécanique macroscopique, elles modifient localement le niveau de sollicitation et peuvent donc affecter la propagation des fissures.Le grenaillage ultrasonore (SMAT) est un traitement mécanique de surface qui consiste à bombarder un échantillon avec des billes mises en mouvement par un dispositif atteignant des fréquences de vibration de 20 kHz. Les impacts répétés entrainent une déformation plastique de la surface menant au développement de contraintes résiduelles de compression ainsi qu'un gradient de microstructure caractérisé par des zones très déformées en sous couche et des tailles de grains submicroniques en surface. Un tel traitement a été réalisé sur des aciers inoxydables austénitiques afin d'étudier l'amorçage et la propagation de fissures de fatigue dans le champ complexe de microstructure et de contraintes résiduelles induit par le SMAT.Des essais en fatigue uniaxiale à grand nombre de cycles ont été conduits à deux rapports de charge différents (en traction-compression à RTC=-1 et en traction-traction à RTT=0,1). Ils ont permis de mettre en évidence un effet variable du SMAT en fonction de la condition de chargement cyclique. En effet, pour RTC une amélioration de la limite de fatigue a été mesurée alors que pour RTT c'est un abattement de la limite de fatigue qui a été constaté. Dans le but d'expliquer cette différence, une étude approfondie des éprouvettes rompues et non-rompues de l'état initial et SMAT, a été menée. Il s'est avéré que dans les conditions de chargement étudiées, les redistributions des contraintes résiduelles peuvent être considérées comme le facteur principal permettant d'expliquer les performances variables en fatigue ainsi que les amorçages observé aux différents sites d'initiation. En considérant les contraintes résiduelles de surface stabilisées après chargement en fatigue, l'utilisation d'un critère de Crossland a permis d'expliquer à la fois l'effet du rapport de charge et du SMAT sur le comportement en fatigue à grand nombre de cycles des aciers inoxydables.Une modélisation des gradients de propriétés mécaniques et de contraintes résiduelles caractéristiques du SMAT par la méthode des éléments finis a été proposée (via ABAQUS) dans le but de comprendre et de prédire les relaxations de contraintes résiduelles. Les résultats des simulations ont été confrontés aux données obtenues expérimentalement et un très bon accord a été obtenu. La capacité du modèle à rendre compte du comportement en fatigue à faible et à grand nombre de cycles a été évaluée, et une cohérence très correcte a été obtenue entre les résultats numériques et expérimentaux.Des éprouvettes pourvues d'un défaut artificiel surfacique ont ensuite été préparées afin d'évaluer la sensibilité à la présence d'accidents géométriques, mais aussi pour suivre la propagation des fissures de fatigue par la méthode des répliques. Il a été démontré que les éprouvettes SMAT ne présentent pas une sensibilité exacerbée à la présence de défauts par rapport à l'état initial pour RTT, alors qu'à RTC une sensibilité légèrement accrue a été mesurée. [...]In the high cycle fatigue, cracks initiate most of the time at the surface of workpieces. Therefore, in addition to the overall mechanical properties, surface and sub-surface characteristics such as roughness and residual stresses affect the fatigue life. Roughness essentially influences the cracks initiation phase. Indeed, the presence of surface irregularities induces stress concentrations producing high local strains potentially leading to the formation of crack-like defects. Besides, the presence of residual stresses affects both the crack initiation and propagation phase. They affect the plasticity close to the surface and influence the crack initiation. Moreover, superposed with the macroscopic loading, they locally modify the stress field and therefore may affect the crack propagation behavior as well.The ultrasonic shot peening (SMAT) is a surface mechanical treatment which consists in impacting a sample with shots put in motion by a vibrating device operating at frequencies up to 20 kHz. The repeated impacts lead to a surface plastic strain allowing the formation of compressive residual stresses as well as a microstructure gradient characterized by highly deformed zones in the sub-surface and submicronic grain size just below the surface. Such treatment was carried out to austenitic stainless steels in order to study the fatigue crack initiation and propagation in the complex microstructure and residual stress field induced by the SMAT.Uniaxial high cycle fatigue tests have been conducted for two different load ratios (under tension-compression at RTC=-1 and under tension-tension at RTT=0.1). They allowed to highlight the variable effectiveness of the SMAT with regard of the cyclic loading conditions. Indeed, at RTC, an increase of the fatigue limit was measured whereas for RTT a reduction of the fatigue limit was observed. In order to explain this difference, an in-depth study of the initial state and SMAT treated broken and run-out samples was carried out. It turns out that under the studied loading conditions the modifications of residual stress state can be considered as the primary factor governing the varying fatigue performances and the observed triggering at different initiation sites. Considering the stabilized surface residual stress after fatigue loading, the use of a Crossland criterion allowed to explain both the effects of load ratio and SMAT on the high cycle fatigue behavior of the stainless steel.A modelling method of the mechanical properties and residual stresses gradients was then developed using the finite elements method (via ABAQUS) in order to understand and predict the residual stresses redistributions. The results of the simulations were compared to the experimental measurements, and a good agreement was observed. The capacity of the model to simulate both the strain- and stress-controlled fatigue behavior was evaluated and a good consistency between the numerical and experimental results were obtained.Specimens with an artificial surface defect were then prepared in order to evaluate the surface anomalies sensitivity, and also to study the fatigue crack propagation behavior using the surface replication method. It was shown that the SMAT samples do not exhibit an increased sensitivity to the presence of defects compared to the initial state when loaded at RTT, whereas for RTC a slightly increased sensitivity was identified. Studying the crack propagation at the surface of the specimens highlighted different behaviors for different load ratios. Also, despite the presence of a defect, the crack initiation phase remained important. Finally, crack fronts were marked by different methods which permitted plotting the fatigue crack growth curves. It was then shown that at RTC, fatigue crack growth behavior in the SMAT layer is drastically different from the initial material, whereas at RTT no difference was revealed
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Camilo, Claudia Cristiane. "Implantes de alumina em gradiente funcional de porosidade recobertos com hidroxiapatita e biovidro: avaliação da osseointegração." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/18/18146/tde-17012011-160849/.
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Esta pesquisa tem como finalidade desenvolver implantes de alumina com núcleo denso e superfície gradualmente porosa (FGM) recobertos com materiais bioativos - hidroxiapatita e biovidro. Materiais porosos são estudados como solução para a osseointegração, porém apresenta déficit nas suas propriedades mecânicas. Estruturas bifásicas foram desenvolvidas por pesquisadores com o propósito de promover crescimento tecidual, sem afetar significativamente sua propriedade mecânica, no entanto ocorre delaminação. Neste trabalho é proposta uma estrutura em gradiente funcional que visa aprimorar as propriedades mecânicas conjugadas com a sinalização celular e com integração óssea. O tamanho, a morfologia de poros e também a porosidade são parâmetros fundamentais para boa resposta tecidual e integração do implante, pois afetam a viabilidade e a afinidade celular. Para essa finalidade a busca por uma espessura efetiva de porosidade se faz fundamental para alto desempenho do implante. Peças de alumina porosas infiltradas com materiais bioativos foram fabricadas e estudadas in vivo, em tíbias de ratos da raça Wistar durante 14, 18, 21 e 28 dias, para investigar a qualidade do crescimento de tecido ósseo. O estudo com implantes porosos recobertos foi realizado para avaliar e padronizar a superfície porosa do gradiente funcional. Os animais foram analisados com densidade mineral óssea (DMO), as tíbias foram caracterizadas na interface osso-implante e nos poros com histologia, com EDS-line-scan, com radiografias e com ensaios de cisalhamento. Implantes de alumina com 70% de porosidade foram comparados com recobrimento bioativo e sem recobrimento in vivo e ex-vivo. Nos resultados, os implantes recobertos aceleram o processo de osseointegração. Essa característica foi mais evidente no período de 28 dias de implantação com aumento de 24% na tensão de cisalhamento. Após validar uma superfície porosa e osseointegrável para a superfície do gradiente funcional, foram aplicadas técnicas diferenciadas para manufaturar peças com núcleo denso e superfície com gradiente de porosidade. As peças com FGM foram manufaturadas com a utilização de duas técnicas, dipping e co-prensagem e foram analisadas com microscopia eletrônica de varredura. Com o método de manufatura de co-prensagem foram obtidas peças com superfície gradualmente porosa, com transição de densificação contínua, sem delaminação. Os implantes de alumina em gradiente funcional com 70 % de porosidade na superfície mais externa, recobertos por bioativos apresentam potencial para aplicações em implantes ósseos ou dentários.The present thesis reports on the development of alumina implants with dense core and gradually porous surface (FGM) covered with bioactive materials, hydroxyapatite (HA) and bioactive glass. Porous materials have been studied to provide tissue ingrowth, however they strongly affect the mechanical properties of the implant. Biphasic structures have been developed by some researchers to promote tissue growth without affecting the mechanical properties, although delamination may occur. This study proposes a functional gradient structure to improve both the mechanical properties of the material and cell signaling. The size and morphology of the pores as well as their porosity are key parameters for good tissue response and implant integration, since they affect the viability and cell affinity, and an effective porosity thickness becomes essential for a high performance of the implant. Porous alumina implants coated with bioactive materials were fabricated and studied in vivo in rat tibia for 14, 18, 21, and 28 days to investigate the quality of bone tissue growth. The study of porous coated implants was performed to evaluate and standardize the porous surface of the functional gradient. The animals were examined with bone mineral density (BMD), the tibiae were characterized in the bone-implant interface and the pores were analyzed with histology, EDS line-scan, X-ray and shear tests. Alumina with 70% porosity was compared with and without bioactive coating in vivo and ex vivo. The results showed that the covered implants accelerated the osseointegration process. This characteristic is more evident within 28 days of deployment with a 24% increase in shear stress. After validating a porous and osteointegrated surface for the surface of the functional gradient, several techniques were applied to manufacture parts with dense core and surface with gradient of porosity. The pieces were manufactured with FGM using two techniques, dipping and co-pressing and were analyzed by scanning electron microscopy. The manufacturing method of co-pressing allowed obtaining pieces with gradually porous surface and continuous transition of densification without delamination. On the outermost surface, alumina implants with functional gradient and 70% porosity and coated with bioactive materials presented potential for application to bone or dental implants.
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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.
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Lindsay, Marianne Rose. "Development of Lithium Disilicate Microstructure Graded Glass-Ceramic." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33243.
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The goal of this research was to create a microstructure graded glass-ceramic and investigate the resulting properties as a function of crystallization processing. The desired glass-ceramic was a lithium disilicate material that has a crystallization gradient across the sample, leading to functionally graded properties as a result of the microstructure gradient. Samples were prepared by melting and pouring glass at 1400°C, annealing at 400°C for 48 hours, and nucleating at 480°C for 2 hours. To ensure that crystallization would not occur homogeneously throughout the sample, a temperature gradient was imposed during crystallization. Samples were crystallized on a self-constructed resistance wire furnace that was open to air. Several crystallization processing parameters were tested, including high temperature for a short time and low temperature for a long time. Samples were ground and polished to 0.25 microns before characterization methods were performed. Scanning electron microscopy (SEM) showed the microstructure transition across the sample cross section, with crystals present on the crystalline side and only nuclei present on the glassy side. Raman spectroscopy showed a transformation of the characteristic spectra across the sample cross section, with defined, high-intensity peaks on the crystalline side and broad, low-intensity peaks on the glassy side. Microhardness showed a slight transition in hardness values across the sample cross section, however the variability was too great to draw any conclusions. The characterization methods showed that the desired material was created and the resulting properties were a function of the crystallization processing parameters.Master of Science
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森, 敏彦, Toshihiko MORI, 健治 広田, Kenji HIROTA, 鑑明 小林, Kanmei KOBAYASHI, 直史 助田, and Naofumi SUKEDA. "インプラントモデル材へのバイオセラミックスの傾斜機能溶射." 日本機械学会, 2001. http://hdl.handle.net/2237/9032.
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Craveiro, Flávio Gabriel da Silva. "Automated multi-material fabrication of buildings." Doctoral thesis, Universidade de Lisboa, Faculdade de Arquitetura, 2020. http://hdl.handle.net/10400.5/20170.
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Tese de Doutoramento em Arquitetura, com a especialização em Desenho e Computação apresentada na Faculdade de Arquitetura da Universidade de Lisboa para obtenção do grau de Doutor.Arquitetos e engenheiros estão sob crescente pressão para melhorar a eficiência e a eficácia do setor da arquitetura, engenharia e construção, de forma a reduzir o impacto ambiental, o uso de materiais e os custos. A eficiência de recursos, baseada numa estratégia de economia circular, considera um uso eficiente da energia, assim como dos recursos naturais e materiais. A integração de tecnologias digitais nos processos de construção permitirá uma maior flexibilidade no projeto e customização, bem como a conceção de formas complexas e novos materiais. Nos últimos anos, o interesse no desenvolvimento de tecnologias de fabricação aditiva na construção cresceu, mas encontram-se limitadas ao projeto e fabrico de componentes físicos compostos por materiais com propriedades homogéneas, garantindo a segurança estrutural, mas negligenciando o uso eficiente de recursos. Para superar tais limitações, um novo sistema de fabricação aditiva foi desenvolvido para construção automatizada, permitindo a produção de materiais compósitos heterogéneos com composição espacial variável, através da replicação de processos naturais. Pretende-se, portanto, desenvolver um sistema que permita desenhar e produzir elementos de construção heterogéneos com maior desempenho. Foi desenvolvida uma ferramenta computacional, em Grasshopper, que permite a geração automática da composição do material e o controlo o equipamento de fabricação. A interface com o utilizador permite criar elementos de construção uni ou multimaterial com gradiente de porosidade ou de material, permitindo conceber o material em resposta a requisitos termomecânicos predefinidos, otimizando o seu desempenho. Um equipamento robotizado, composto por várias bombas de material, foi desenvolvido para produzir os elementos de construção heterogéneos gerados pela ferramenta computacional. A necessidade de novos materiais para viabilizar a fabricação aditiva exigiu a realização de trabalho experimental, no qual foram avaliadas as propriedades mecânicas e térmicas de várias misturas de betão de agregados finos contendo cortiça, fibras, basalto e outros resíduos industriais. Foram utilizadas diferentes percentagens de cortiça, uma matéria-prima leve, natural e sustentável, totalmente biodegradável, renovável e reciclável. As misturas de betão com maiores quantidades de cortiça apresentam menor condutividade térmica quando comparadas com as que possuem menor percentagem ou com as que não contêm cortiça, verificando-se igualmente uma redução significativa no peso do material. A utilização de um sistema de fabricação automática que permita a extrusão aditiva betão leve de composição ajustável para a produção de elementos de construção heterogénea poderá ser uma solução eficiente para reduzir os custos energéticos e proporcionar conforto térmico aos utilizadores dos edifícios.
ABSTRACT: Architects and engineers are under increasing pressure to improve the efficiency and effectiveness of the architecture, engineering and construction (AEC) sector, reducing environmental impacts, material use and costs. Resource efficiency, based on a circular economy strategy, considers an efficient use of energy, natural resources, and materials. The integration of digital technologies into construction processes will allow for a greater flexibility in design and customization, as well the emergence of complex shapes and new materials. In recent years, the interest in developing additive manufacturing (AM) technologies in the AEC has increased, though traditional AM technologies are limited to the design and fabrication of physical components with homogeneous material properties, assuring structural safety but with no efficient use of material resources. To overcome these limitations, an AM system was developed for automated fabrication, enabling the fabrication of heterogeneous composite materials with varying material distribution, simulating nature’s structural behavior. The aim is to design and fabricate functionally graded building components with increased performance. A design system, developed in grasshopper, was designed to generate the material composition variation and control the fabrication equipment. The user interface allows creating single or multi-material building components with pore size or material gradients, permitting to design the material in response to thermo-mechanical requirements, optimizing its performance. A multi-pump robot equipment was developed to produce the generated heterogeneous building components. It was necessary to develop printable materials to enable additive fabrication, so experimental work was carried out to assess the mechanical and thermal properties of fiber cement-based concrete mixtures containing cork, basalt and other residual waste. Different percentages of cork were used, as it is a natural and sustainable lightweight raw material, completely biodegradable, renewable, and recyclable. Results show that concrete mixtures with higher quantities of cork have lower thermal conductivity compared to the ones with less percentage or no cork, as well a significant reduction in material weight. The potential use of an AM system to produce printable functionally graded lightweight concretes can be an efficient solution to reduce energy costs and provide thermal comfort for building users.
N/A
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Madec, Clémentine. "Elaboration de matériaux à gradient de fonction céramique / métal par SPS pour la protection balistique." Thesis, Dijon, 2016. http://www.theses.fr/2016DIJOS057/document.
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Les propriétés idéales d’un matériau de blindage sont la combinaison d’une extrême dureté pour casserles noyaux des projectiles et d’une grande ductilité pour résister à l’impact et arrêter les fragments du projectile. Or cettecombinaison de propriétés est incompatible avec un matériau unique. Pour pallier ce problème, les concepteurs de blindageassocient un matériau dur (céramique) à un matériau ductile (métal). Une autre solution serait de réaliser un matériauprésentant un gradient de propriétés mécaniques : dans le cas présent, d’une très grande dureté de la face avant à une grandeductilité de la face arrière. Les technologies non conventionnelles de frittage telles que le Spark Plasma Sintering (SPS)permettent d’assembler ou de fritter/assembler des matériaux aux caractéristiques aussi différentes et complémentaires. Ils’agit donc d’étudier les conditions d’assemblage ou de cofrittage de tels matériaux (dans le cas présent, Al2O3 et Ti) ainsique l’influence de la microstructure résultante de l’ensemble sur sa performance balistique.La première partie de ce travail a porté sur la caractérisation de l’alumine et du titane. Cinq poudres d’alumines ontété étudiées d’un point de vue comportement au frittage. Trois d’entre elles sont retenues en raison de leurs microstructuresintéressantes, proches en termes de densité et de taille de grains. Ces alumines ont été caractérisées mécaniquement (dureté,ténacité, résistance à la rupture) et balistiquement pour n’en garder qu’une dans la deuxième partie du travail. Le titane, frittédans les mêmes conditions que l’alumine, a montré qu’il n’avait malheureusement pas les propriétés attendues (absence deductilité).La seconde partie du travail a montré que l’obtention de MGFs sains à partir de Al2O3 et Ti uniquement est délicate,que ce soit avec un intercalaire sous forme de monocouche ou de multicouche. La forte affinité du titane avec l’oxygène(formation d’oxyde ou en insertion) et le carbone (formant des carbures), ainsi que sa réactivité avec l’alumine (produisantdes intermétalliques) rend le MGF fragile et incapable d’accommoder les contraintes résiduelles d’élaboration. L’insertiond’une faible proportion de nickel (plus ductile et moins réactif vis-à-vis de l’oxygène que le titane) dans les composites apermis d’obtenir des MGFs sains, dont le comportement balistique a pu être évaluéThe objective is to improve ballistic performance of armors. A perfect armor combines ductility to resistto the impact and high hardness to stop projectile’s fragments. However, such an association of properties is inconsistent witha single material. The solution is to perform a functionally graded material (FGM) with a ductile metal at the back side of thesample and a hard ceramic on the top side. Non-conventional technologies like Spark Plasma Sintering allow joining orsintering all types of materials with different and additional properties. Furthermore, with this technique, high heating ratescan be achieved, limiting grain growth and resulting in a fine microstructure. The goal is to study joining conditions or cosinteringof such materials (in this case, Al2O3 and Ti), as well as the resulting microstructure on the ballistic efficiency.The first part of the study focused on the characterization of alumina and titanium. Five powders of alumina werestudied from a sintering point of view. Three of which were selected because of their interesting microstructures, close indensities and grain sizes. These ceramics have been characterized mechanically (hardness, toughness and strength) andballistically. One of them is adopted to realize FGM. Titanium, sintered with the same conditions, unfortunately, doesn’t haveexpected properties (absence of ductility).The second part of the work showed that the preparation of FGM without cracks from Al2O3 and Ti only ischallenging, with an interlayer with one or more layers. The strong affinity of Ti with oxygen (formation of oxides orinsertion) with C (forming carbides) and its reactivity with alumina (forming intermetallics) make the FGM brittle and enablethe release of residual stresses during the process. By adding a low amount of nickel (more ductile and less reactive withoxygen and titanium) in composites, FGMs almost without cracks were obtained. The latter were evaluated ballistically
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Warnock, Corinne Marie. "Process Development for Compression Molding of Hybrid Continuous and Chopped Carbon Fiber Prepreg for Production of Functionally Graded Composite Structures." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1518.
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Composite materials offer a high strength-to-weight ratio and directional load bearing capabilities. Compression molding of composite materials yields a superior surface finish and good dimensional stability between component lots with faster processing compared to traditional manufacturing methods. This experimental compression molding capability was developed for the ME composites lab using unidirectional carbon fiber prepreg composites. A direct comparison was drawn between autoclave and compression molding methods to validate compression molding as an alternative manufacturing method in that lab. A method of manufacturing chopped fiber from existing unidirectional prepreg materials was developed and evaluated using destructive testing methods. The results from testing both the continuous and chopped fiber were incorporated into the design of a functionally graded hybrid continuous and chopped carbon fiber component, the manufacture of which resulted in zero waste prepreg material.
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Ther, Olivier. "Élaboration de carbures cémentés à gradient de propriétés par procédé d’imbibition réactive : Application aux inserts WC-Co et aux taillants en diamant polycristallin pour le forage pétrolier en conditions sévères." Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0067.
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Dans l'industrie du forage pétrolier, les conditions de travail de plus en plus sévères requièrent sans cesse de nouveaux outils plus résistants à l'usure abrasive et à l'impact. Afin de répondre à ce défi, les travaux présentés ici, ont pour but l'élaboration de matériaux en carbure cémenté à gradient de composition par le procédé d'imbibition réactive. Ce procédé peut être décomposé en deux procédés de gradation, à savoir : l'imbibition et le revêtement réactif. L'imbibition a pour rôle d'enrichir graduellement, en phase liante, le coeur d'une pièce en carbure cémenté dense et repose sur le principe de migration de phase liquide dans un corps solide-liquide. Le revêtement réactif est un procédé qui s'applique également sur un carbure cémenté dense sur lequel est déposé un revêtement de nitrure de bore. Après avoir atteint le liquidus de la phase liante du carbure cémenté, une précipitation de borures ternaires prend place à la surface du matériau et s'étend graduellement sur des distances millimétriques. Dans le cas de pièces industrielles (inserts tricône et supports de taillants PDC (Polycrystalline Diamond Compact)), le traitement d'imbibition réactive permet de générer des gradients de dureté pouvant atteindre 450 HV sur 25 mm. L'élaboration de tels gradients a nécessité une meilleure compréhension des cinétiques ainsi que des phénomènes mis en jeu durant l'imbibition et le revêtement réactif. Dans le cas des taillants PDC, l'influence des paramètres du procédé HPHT de synthèse de la plaquette diamantée, sur le gradient de composition présent dans le support WC-Co après imbibition réactive, a été étudiée. Ces travaux se sont également intéressés à l'effet de ces gradients de composition sur les propriétés des plaquettes diamantées ainsi obtenues. A la suite d'essais mécaniques, les inserts WC-Co et taillants PDC gradués montrent une augmentation significative de leur résistance à l'abrasion (de 30 à 100%) et de leur tenue à l'impact (de 20 à 40%)In oil drilling industry, harsher working conditions require ever new and more abrasive wear and impact resistant tools. To meet this challenge, the work presented here, is to develop graded cemented carbide materials by reactive imbibition process. This method can be divided into two gradation processes, namely, reactive coating and imbibition. Imbibition gradually enriches the core of dense cemented carbide with binder phase and is based on the principle of liquid phase migration in a solid-liquid body. Reactive coating also takes place in dense cemented carbide on which a boron nitride coating is deposited. After reaction with the WC-Co liquid binder, some ternary boride precipitations take place from surface to several millimeters deep. For industrial parts (inserts for roller cone bits and PDC (Polycrystalline Diamond Compact) cutters substrates), hardness gradients obtained can reach 450 HV on 25 mm. Such gradients development is passed through a better understanding of kinetics and phenomena occurring during imbibition and reactive coating. In case of PDC cutters, influence of HPHT process parameters, allowing diamond table synthesis, on the WC-Co substrate gradient, generated by reactive imbibition, was studied. This work was also interested in gradient effect on the obtained diamond tables properties. After mechanical tests, graded WC-Co inserts and graded PDC cutters show a significant increase of both wear resistance (from 30 to 100%) and impact resistance (from 20 to 40%)
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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.
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Mohebbi, Elaheh. "Surface supported supramolecular architectures: an experimental and modeling study." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3427304.
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L’auto-organizzazione di molecole organiche su superfici solide è uno degli approcci più diffusi per la creazione di architetture supramolecolari supportate di dimensioni controllate e con proprietà innovative. L’uso combinato di differenti interazioni di natura non covalente adsorbato–adsorbato e adsorbato–substrato consente infatti la modulazione dell’associazione di specie distinte in modo quasi altrettanto accurato che nei sistemi biologici, fonte primaria di ispirazione per ciò che può essere realizzato artificialmente. Il consenso sull’uso d’interazioni intermolecolari estese non covalenti nell’ingegnerizzazione di nanostrutture bidimensionali supportate prive di difetti è unanime. Ciononostante, i materiali così ottenuti sono spesso fragili, incapaci di resistere a condizioni aggressive, privi di stabilità meccanica ed inefficienti nei processi di trasferimento di carica intermolecolare; sono cioè materiali inadatti per applicazioni tecnologiche. La produzione di sistemi nanostrutturati supportati con proprietà predeterminate, privi di difetti e con risvolti applicativi implica quindi la sintesi di network covalenti robusti, non caratterizzati dalle limitazioni di cui sopra. In questa tesi di dottorato si è voluta esplorare sia sperimentalmente sia teoricamente la possibilità di stabilizzare covalentemente network supramolecolari funzionali in una/due dimensioni stimolando la formazione di legami covalenti tra molecole preorganizzate su una superficie.The scientific community is nowadays focused on the design and the production of nm/μm-sized systems for their relevance to nanotechnology, energy production and storage, life science and environment. Advances in high performing computing and in synthetic/characterization methods make possible devising novel rational approaches to tailor properties of low-dimensional architectures of molecular networks on inorganic substrates; i.e., to control the electron transport properties of active layers and the reactivity of selected sites. As such, the self-assembly of functional architectures on appropriate surfaces is the most promising bottom-up approach to organize and integrate single molecules on solid substrates. As a consequence of the persistent progress in computational power and multiscale material modeling, new materials are less likely to be discovered by a trial-and-error approach. This points to a paradigm shift in modeling, away from reproducing known properties of known materials and towards simulating the properties of hypothetical composites as a forerunner to get real materials with desired characteristics. The interplay among multiscale material modeling, new synthetic routes and appropriate validation experiments is crucial to design the desired behavior at each length scale. In this PhD thesis we exploited integrated methodologies to provide interpretative tools about structure and functions of organic/inorganic hybrid nanostructured materials made of molecular mono-layers deposited on technological relevant substrates, suitable for applications in strategic areas such as catalysis, artificial photosynthesis, molecular electronics-magnetism and molecular recognition.
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Maruani, Jonas. "Contrôle actif des vibrations de structures élancées FGPM." Thesis, Paris 10, 2019. http://www.theses.fr/2019PA100062.
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Cette thèse vise à montrer la faisabilité et l’efficience du contrôle actif des vibrations des structures faites à partir de matériaux piézoélectriques à gradient de propriétés (FGPM). Une structure formée d’un seul bloc, fabriquée à partir d’un FGPM, intégrant directement les propriétés piézoélectriques permet de remplacer les structures classiques dites intelligentes (une structure hôte équipée de pastilles piézoélectriques) et de supprimer les inconvénients dont souffrent ces structures (concentrations de contraintes aux interfaces, décollement des pastilles, …). La recherche se concentre sur la modélisation des FGPM, en particulier sur les lois de comportement graduelle de ce matériau et le développement d’éléments finis de structures élancées FGPM. Deux éléments sont développés, un élément de poutre basé sur la cinématique de Timoshenko et un élément de plaque basé sur une cinématique adaptative. Ces deux éléments intègrent une approximation par couches numériques pour le potentiel électrique.Ils sont utilisés pour simuler le contrôle actif des vibrations d’une poutre ou d’une plaque FGPM.Dans le cas poutre, le système est régulé par un régulateur linéaire quadratique, alors que dans le cas plaque, un régulateur flou décentralisé a été développé et utilisé. Les deux systèmes sont observés grâce à un observateur de Luenberger. Des études statiques permettent de comprendre le comportement du FGPM en fonction de sa gradation. De plus, les simulations de contrôle actif présentées montrent la faisabilité du contrôle par les deux systèmes et la capacité du régulateur flou à s’adapter facilement aux changements brutaux de perturbations extérieuresThe aim of this thesis is to show the feasibility and the efficiency of active vibration control by structures made of functionally graded piezoelectric materials (FGPM). One bloc structure, made of FGPM, with piezoelectric properties embedded, is used to replace classical intelligent structures (a host structure equipped with piezoelectric patches) and to remove their disadvantages (stresses concentrations near interface, delamination of patches, …).This study focuses on the FGPM’s modelization, in particular on the graded behavior laws and on the development of finite elements of FGPM beams and plates. Two finite element are implemented, a beam element based on Timoshenko’s kinematics and a plate element based on an adaptive kinematics. Both elements have a numerical layers approximation for the electrical potential. These two elements are used for active vibration control simulations. In the beam case, the system is governed by a linear quadratic regulator. Otherwise, for the plate a fuzzy decentralized regulator is developed and used. Both systems beam and plate are observed thanks to a Luerberger’s observer. Static studies show the behavior of FGPM depending on the material gradation. In addition, active vibration simulations show the feasibility of control with both systems and the ability of fuzzy regulator to accommodate to sudden changes on external perturbations
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"Torsional motion of a system of particles with graded couplings." 2006. http://library.cuhk.edu.hk/record=b5893052.
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Tsang Hing Wa = 梯度粒子系統的扭轉運動 / 曾慶華.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.
Includes bibliographical references (leaves 66-68).
Text in English; abstracts in English and Chinese.
Tsang Hing Wa = Ti du li zi xi tong de niu zhuan yun dong / Zeng Qinghua.
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Localization --- p.1
Chapter 1.1.1 --- Localization by Potential Confinement --- p.1
Chapter 1.1.2 --- Localization by Interference --- p.2
Chapter 1.2 --- Graded Materials --- p.2
Chapter 1.3 --- Rotational Motion --- p.3
Chapter 2 --- Torsional Motion of Rotating Particles with Graded Couplings
Chapter 2.1 --- Linear Couplings --- p.5
Chapter 2.1.1 --- Model and Formalism --- p.5
Chapter 2.1.2 --- Gradient in Coupling Constant --- p.7
Chapter 2.1.3 --- Gradient in Moment of Inertia --- p.8
Chapter 2.1.4 --- Numerical Results --- p.9
Chapter 2.1.5 --- Discussion and Conclusion --- p.14
Chapter 2.2 --- Non-Linear Couplings --- p.14
Chapter 2.2.1 --- Model and Formalism --- p.14
Chapter 2.2.2 --- Gradient in Coupling Constant --- p.16
Chapter 2.2.3 --- Gradient in Moment of Inertia --- p.16
Chapter 2.2.4 --- Numerical Results --- p.17
Chapter 2.2.5 --- Discussion and Conclusion --- p.29
Chapter 3 --- Torsional Motion of Rotating Particles with graded potential --- p.30
Chapter 3.1 --- Linear Interaction --- p.30
Chapter 3.1.1 --- Model and Formalism --- p.30
Chapter 3.1.2 --- Gradient in On-site Torsional Potential --- p.32
Chapter 3.1.3 --- Numerical Results --- p.33
Chapter 3.1.4 --- Discussion and Conclusion --- p.43
Chapter 3.2 --- Non-linear Interaction --- p.43
Chapter 3.2.1 --- Model and Formalism --- p.43
Chapter 3.2.2 --- Numerical Results --- p.45
Chapter 3.2.3 --- Chaotic Effect --- p.62
Chapter 3.2.4 --- Discussion and Conclusion --- p.64
Chapter 4 --- Conclusion --- p.65
Bibliography --- p.66
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"New wave functional materials: gradons and their implication in nano-optics." Thesis, 2006. http://library.cuhk.edu.hk/record=b6074263.
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In this thesis, we will discuss the possibility of wave manipulation by graded materials and/or systems. In contrast to the traditional inhomogeneous media, i.e. periodically modulated system and randomly disordered system, graded system demonstrates a unique way to control wave, resulting in a new type of localization-delocalization transition, which can confine the primary excitations (e.g., photons, phonons, and surface plasmons) and redistribute them spatially. This is not only of fundamental significance, but will also pave new avenue for various applications, for example, in surface elastic waves, nanooptics, and plasmonics. It also has implications with practical problems in industry such as oil probing and earthquake study.Manipulating waves (e.g., elastic or electromagnetic) inside nanostructures has attracted ever increasing interest over the past decades due to the rapid advancement of nanofabrication techniques. Particularly, interactions of light with structures modulated at the wavelength or subwavelength scale offer an opportunity to achieve novel properties and designated functionalities in nanophotonics. Notable examples include photonic crystals, various metamaterials, and plasmonic devices.
Moreover, we consider to combine the novel properties of gradons and surface plasmons (SPs), in an attempt to explore new mechanisms to manipulate SP. Firstly, we study an incrementally-spaced nanoparticle chain waveguide, in which coupled plasmon waves show a localization-delocalization transition, in analogy to the elastic gradons. Secondly, we propose waveguides using periodic plasmonic chains immersed in a graded host which can sustain "light", "heavy", and "light-heavy" plasmonic gradons. Existence of tunable passband is demonstrated in these systems.
Thus, in view of the success, we discuss many potential applications in plasmonics, such as junctions, transistors, and even on-chip integrated plasmonic-dielectric devices. In this regard, we further study the most commonly used coplanar photonic elements, i.e., ring resonators and their integrated devices. To explore the interactions between various gradons and typical excitations would be very interesting and rewarding. Our findings have important ramifications for understanding excitations with transition spectra in many condensed matter systems, ranging from ultrasonic waves, seismic waves to light waves, microwaves, as well as quantum waves.
We started with one-dimensional graded networks of coupled harmonic oscillators. By examining the vibrational mode characteristics, we have identified a new kind of vibrational excitations, which are named "gradons". The features of elastic gradon are elab orated. Gradon localization is also different from well-known mechanisms of localization transition, such as defect(s) and Anderson-type localization. Gradons in higher dimensional graded elastic networks show more intriguing behaviors; we proved the existence of "soft", "hard", and "soft-hard" gradons in two dimensional cases.
Xiao Junjun = 新型调波功能材料 : 梯度子及其在纳米光学中的应用 / 肖君军.
"May 2006."
Adviser: Kin Wah Yu.
Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1694.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2006.
Includes bibliographical references (p. 108-118).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstracts in English and Chinese.
School code: 1307.
Xiao Junjun = Xin xing diao bo gong neng cai liao : ti du zi ji qi zai na mi guang xue zhong de ying yong / Xiao Junjun.
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"Study of gradon confinements in graded elastic and plasmonic lattices." Thesis, 2009. http://library.cuhk.edu.hk/record=b6074954.
Full textAbstract:
Controlling fields and properties has attracted ever increasing interest over past decades due to the rapid advancement of nanofabrication techniques. In the field of nano-optics, to overcome the limit of signal processing speed and device scale of traditional electronic devices, optical devices using photon as the signal carriers have been chosen as the potential candidates. However, the diffraction limit of light has limited the integration of the micro-meter photonic components into electronic chips. Plasmonics offer the possibility to control electromagnetic fields at the subwavelength scale. Moreover , this controlling become tunable by introducing gradient into the material and/or structure, i.e., taking the concept of functionally graded materials (FGM) to design materials.Gradon confinements in graded materials and/or systems open a door for tunable fields-controlling, which have potential applications in a variety of fields. Our research methods and results provide an effective way to understand field localization in a variety of systems, and they can be applied to design and manufacture thermal devices and even on-chip plasmonic-optical devices.
Gradon confinements, or referred as frequency-controlled localization of fields are investigated in various graded plasmonic lattices. The correspondences between gradon confinements and Bloch oscillations as well as nonBloch oscillations are explored. By taking into account retardation and loss effects, the asymmetric localization behavior and broadband localizat ion due to graded host permittivity are studied.
This thesis will concentrate on gradon confinements, which make controlling fields and properties tunable in graded materials and/or systems. We start with investigating gradon modes and their properties in graded elastic lattices. Using the quantum-classical analogue method, the analytic envelope function is obtained and can be used to analyze the system-size dependence of inverse participation ratio of gradon modes. In damping graded elastic lattices , the frequency-dependent behavior of relaxation rate are studied analytically and numerically.
We continue to study the three-dimensional graded plasmonic lattices with fully retarded electromagnetic interactions. A generalized Ewald-Kornfeld summation formula is developed to deal with the long-range interaction. In the quasistatic limit, various plasmonic gradon modes are investigated. Taking retardation and loss into account, field localization and enhancement are calculated in three-dimensional graded plasmonic lattices with graded size, spacing, and/or host permittivity in one direction.
Zheng, Mingjie = 弹性和等离子体梯度子禁闭研究 / 郑明杰.
Adviser: Kin Wah Yu.
Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: .
Thesis (Ph.D.)--Chinese University of Hong Kong, 2009.
Includes bibliographical references (leaves 117-124) and index.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Zheng, Mingjie = Tan xing he deng li zi ti ti du zi jin bi yan jiu / Zheng Mingjie.
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Chi, Shyang-Ho, and 紀翔和. "The Study of Functional Gradient Material in composite Materials." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/87870331266188623113.
Full textAbstract:
碩士國立臺灣科技大學
營建工程系
87
The subject of this thesis mainly discusses the stress behaviors and stress intensity factors of cracks of composite material with functionally gradient material subjected to thermal loading by finite element method. There are five parts included in this thesis: (1)one material coating problem. (2)multi-layered homogeneous coating problem. (3)S-curve functionally gradient material problem. (4) anti-S-curve functionally gradient material problem. (5) the problem of FGM coating with a crack. This study indicates that the use of functionally gradient material can efficiently reduce stress concentration at the edge of the interface of the composite material. The different functionally gradient materials led to different stress distributions. Results showed that the S-curve of p=2 and metal rich functionally gradient result in better stress distribution in which there is no stress singularity and lower stress concentrations. Consequently, the debonding of the undercoat can be efficiently reduced. Moreover, in the aspect of crack problem, stress intensity factor of crack tip in S-curve functionally gradient material was concerned with Dundurs'' constants and . When α>0 and , stress intensity factor appears S-curve character by the influence of functionally gradient material disposition. While when α<0 and , the SIF of a crack in the functionally gradient material is similar with that in homogeneous material.
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Wu, Meng-Chiao, and 巫孟樵. "Study on Ballistic Resistance Performance of Gradient Sphere Functionally Graded Material." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/33947186270494782188.
Full textAbstract:
碩士國防大學理工學院
兵器系統工程碩士班
103
Ceramic composite materials are widely used in armor protection systems. The flat plate composites are commonly seen, but other structures don’t. While functionally graded material (FGM) has been drawn more and more attention in recent years and some researches focus on its ballistic resistance capability. In this work, ceramic balls with same diameter and thickness but different ingredient were made. The normal ceramic ball specimen had same ingredient and gradient ceramic ball specimen had gradually placed ingredients. 0.30〞 AP bullet was used for ballistic testing. The initial and residual velocities of those two types of specimens were measured to calculate the absorbing energy of the specimens and compare their ballistic resistance capability. ANSYS/LS-DYNA finite element software was used to do simulation analysis. The mechanical properties of the materials were obtained by experiments or references. Once the material parameters were obtained, the penetration phenomena such as residual mass of projectile, motion of projectile, ceramic crack etc. were investigated through finite element analysis. Both experimental and numerical simulation results showed that the residual velocity of projectile is lower while projectile penetrated gradient sphere ceramic composite, implying that the ballistic resistance capability of gradient sphere ceramic composite was superior compared to that of the normal ceramic ball specimen.
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Lee, Jia-Bao, and 李佳保. "Optimal Design of Functional Gradient Absorbing Materials by Taguchi-Genetic Algorithm." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/27x766.
Full textAbstract:
碩士逢甲大學
航太與系統工程學系
106
The study optimized the process and the composition of functionally gradient absorbing material of carbonyl iron powder by the Taguchi method and the genetic algorithm. In the process of fabrication, we choose carbonyl iron powder for the ball milling experiments. By using the Orthogonal Array, 1024 experiments were reduced to 16 experiments, found the optimal combination of five control factors which affect the milling result and did the confirmation experiment. Compare to the tranditional, the aspect ratio increase obviously. We made the 60wt% experiment chip with the combination of polyurethane resin and ball milling powder, measured the electromagnetic parameters by using the vector network analysis and coaxial waveguide method, and then computed the wave absorptivity with 2mm by ANSYS HFSS. However, we discovered that the higher aspect ratio is, the more possible the wave absorbing happen in low frequency at the same thickness. Afterwards, fabricate the chip, from 10wt% to 70wt% respectively with the original and the optimal ball milling process. The optimization is not only have the wave absorptivity in lower frequency but also increase -15dB wave absorptivity in identical concentration. Further, design the multi-layer functionally gradient material with the best bandwidth of absorbing by applying the Taguchi-Genetic Algorithm. At the same time, compared to the Genetic Algorithm and the Taguchi method. We proved that the Taguchi-Genetic Algorithm help a lot for this research area, moreover, the experimental efficiency can be increase dramatically.
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Jheng, Meng-jie, and 鄭盟潔. "Application in Functional Gradient Material by Using Molecular Dynamic Simulation." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/04232937084081942605.
Full textAbstract:
碩士雲林科技大學
機械工程系碩士班
97
In this study, we used the molecular dynamic (MD) method to observe the thin film growth of functional graded material (FGM). To create FGM thin film, we simulate magnetron multi-target sputtering by using MD method. During the FGM thin film growth, we discuss the effect of many parameters including FGM layers, incident energy, incident angle and substrate temperature. In the MD simulation, the Morse two-body potential was used to describe the Cu-Al atomic interaction. The parameters for the mixed interactions of Cu-Al were determined by the standard combination rules, i.e., arithmetic mean for lattice parameter, and geometric mean for energy. To increase the efficiency of simulation system, we choose cut-diameter method and Verlet combining Cell link neighbor list to reduce the unnecessary calculation. The BDT stress was used to calculate the residual stress of FGM thin film. And the mix rate was used to observe the gradient variation of FGM thin film. To evaluate the roughness of FGM thin film, Root-mean-square (RMS) and three dimension morphology were used to present these results. From the simulation results, it indicates that the formula of change time of deposition rate could be used to create the FGM thin film. When the FGM thin films of different layers were created by using different deposition rate, we found that FGM thin film could be used to reduce the residual stress in nano-scale. In addition, the results also indicate that the FGM thin film was benefit to improve the roughness of thin film. In the discussion of incident energy, when increasing the incident energy from 0.5eV to 7eV, it could make the roughness of thin film became smooth, but it also produce high residual stress. Furthermore, when the incident energy was increased to 10eV, it will increase the mix rate of the layers around the surface and result in the disappearing of the function of FGM. From the deposition result of different incident angles, we found that 60 degree could raise the RMS in the dual-target deposition, and we also found that the sputtering yield is reduced when the incident angle increases over 60 degree. Increasing the incident angle could increase the lateral motion ability of incident atoms and reduce the impact from the incident atoms onto the substrate. When the temperature was considered, increasing the temperature could improve the roughness of thin film, but it could not produce more benefit for creating FGM thin film.
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Lima, Ana Maria Rodrigues. "Desenvolvimento de superfícies em titânio com gradiente de porosidade em ligas β de titânio." Master's thesis, 2018. http://hdl.handle.net/1822/59387.
Full textAbstract:
Dissertação de mestrado integrado em Engenharia de MateriaisExistem diversos materiais utilizados na área biomédica, porém um dos mais utilizados é o titânio devido à sua boa resistência mecânica especifica, baixa densidade e boa resistência à corrosão, no entanto possui enormes desvantagens para aplicações biomédicas como a sua baixa resistência ao degaste, a formação de um filme de óxido de Ti (TiO2) bionerte e o seu elevado módulo de Young comparativamente ao osso levando ao efeito de stress-shielding. De modo a evitar ou minimizar o efeito de stress-shielding e melhorar a ligação entre o osso e o implante recorre-se a ligas de baixo módulo de Young ou então a estruturas porosas de Ti. Uma outra abordagem para solucionar esta limitação dos implantes à base de titânio e de forma a mimetizar as propriedades do osso humano, recorre-se ao desenvolvimento de materiais não homogéneos, designados materiais com gradiente funcional (FGM). A brasagem, sendo uma técnica de ligação, permite ligar materiais dissimilares, sendo possível ser usada para criar FGMs. Este trabalho teve como objetivo a produção de estruturas de Ti com gradiente de porosidade em superfícies de uma liga de Ti tipo β, Ti-15Zr-15Mo (TZM). As estruturas porosas de Ti foram processadas por metalurgia dos pós com a técnica de space-holder. De seguida, estas estruturas porosas foram ligadas à TZM recorrendo à técnica de brasagem. Após o processamento, as superfícies e as secções de corte foram caracterizadas do ponto de vista microestrutural (MO e SEM) e químico (EDS). De modo compreender o comportamento à corrosão das superfícies propostas, o potencial de circuito aberto (OCP) foi monitorizado em diferentes tempos de imersão numa solução tampão de fosfato (PBS) a 37 °C. Polarização linear foi realizada para os diferentes tempos de imersão de modo a estudar a influência de cada uma das camadas do sistema proposto. Por outro lado, a técnica de polarização potenciodinâmica foi utilizada para avaliar a taxa e resistência à corrosão. Os resultados demostraram que a interface obtida por brasagem na ligação da liga TZM e estruturas porosas de Ti teve uma clara influência no comportamento à corrosão do sistema (TZM/estrutura porosa de Ti), uma vez que apresentou taxas de corrosão superior tanto da liga TZM como das estruturas porosas.
There are several materials used in the biomedical area but one of the most used is titanium due to good mechanical strength, low density and good corrosion resistance, however it has a huge disadvantage for biomedical applications due to his high Young's modulus as compared to bone leading to stress-shielding effect. In order to solve the stress-shielding effect of the implant and to improve the connection to the human bone it is used low Young's modulus alloys and porous Ti structures. Another approach to solve this limitation of titanium based implants and to mimic the properties of human bone is to use non-homogeneous functionally gradient materials (FGM). Brazing, being a connection technique, allows to connect dissimilar materials, and may be used to create FGMs. The purpose of this work was the production β-Ti (Ti-15Mo-15Zr, TZM) based Ti structures with surface porosity gradient. Ti porous structures have been processed by powder metallurgy with the space-holder technique. Then these porous structures were joined to TZM using brazing technique. After this procedure, the surface areas and the cross-sections were characterized microstructurally (OM and SEM) and chemically (EDS). In order to understand the corrosion behaviour of the proposed areas, the open circuit potential (OCP) was monitored at different times of immersion in a phosphate buffer solution (PBS) at 37 °C. Linear polarization was measured for the different immersion times in order to study the influence of each of the layers of the proposed system. On the other hand, the potentiodynamic polarization technique was used to assess the corrosion rate and resistance. The results demonstrated that the interface obtained by brazing the alloy TZM and Ti porous structures joint had a clear influence on the corrosion behaviour of the system (TZM/Ti porous structure), since it showed higher corrosion rates than both TZM alloy and porous structures, individually.
Este estudo foi realizado no âmbito FCT/CAPES, sob Proc.° 4.4.1.00 CAPES e pela MERA-NET/0001/2015