Дисертації з теми "Anisotropie materiálu"
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1
Valtrová, Martina. "Píst zážehového motoru vyráběný aditivní technologií." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-449789.
Анотація:
The first objective of this thesis was compiling research about currently produced pistons for internal combustion engines and about additive manufacturing and based on the acquired information deciding which type of piston makes the most of the advantages. Following this research, the next step was creating a design adjustment of a piston, which was previously designed with the conventional methods of manufacturing in mind, in a way that would make the best use of the different possibilities of additive manufacturing. There was also an optimisation carried out, which depicted the densities of material elements in the piston, showing where the material was less important. There were three variants of the additive manufactured piston created, ranging from a relatively conservative design, which could be theoretically produced by conventional methods with a more substantial subtraction of material added, to a design which could only be produced via additive manufacturing. A thermo-structural analysis at maximum engine load was carried out for all these piston models. Based on these data, a conclusion was made, whether the use of additive manufacturing was justified over the use of the conventional subtractive methods.
2
Belijar, Guillaume. "Anisotropic composite elaboration and modeling : toward materials adapted to systems." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30353/document.
Анотація:
L'objectif de ces travaux de thèse a été de démontrer la possibilité, en se basant sur une approche prédictive, de contrôler avec précision la fonctionnalisation d'un matériau composite, d'isotrope à anisotrope, sous l'application d'un champ électrique. Ces derniers matériaux présentent en effet un fort potentiel pour des applications futures telles que des condensateurs intégrés ou bien encore des composites conducteurs thermiques. Une première approche théorique des différentes forces et mécanismes entrant en jeux lors de l'élaboration de composites anisotropes par chaînage a permis d'identifier les paramètres impactant le procédé d'élaboration. A la suite de cette étude théorique, un modèle de formation de chaînes de particules sous champ électrique a été développé afin de prédire la dynamique de chaînage. Le modèle choisi (méthode moment dipolaire effectif) a permis la simulation de plus de 4500 particules. Les paramètres ayant au préalable été identifiés ont ensuite été mesurés. Pour la permittivité des particules, une méthode de mesure diélectrophorétique a été développée, ce qui est une première dans le cas de particules céramiques. L'élaboration des composites anisotropes a été couplé avec un suivi novateur, en temps réel, d'un marqueur (permittivité) de la formation de chaînes, permettant d'obtenir la dynamique de structuration des particules. Afin de valider l'aspect prédictif du modèle numérique, une comparaison a été effectuée entre la dynamique mesurée et simulée. Les résultats obtenus ont démontré une très bonne fiabilité des prédictions du modèle, même si des progrès sont encore réalisables aux faibles taux de chargement. Dans un dernier temps, une preuve de concept a été démontrée, de la réalisation de composites anisotropes dont les particules sont alignées perpendiculairement au champ électriqueThis study was aimed to demonstrate the possibility, based on a predictive approach, to tailor the structure of a composite from isotropic to anisotropic when applying an electric field. This composites have great potential for future applications such as embed capacitors or thermally conductive composites. A theoretical approach of the forces and mechanisms acting in the elaboration of anisotropic composites by chaining allowed identifying the key parameters. Based on this approach a model of particle chaining under electric field was established to predict the structuration dynamics. This model (effective dipole moment) allowed simulating more than 4500 particles. The parameters previously identified were then measured, and for the particle permittivity, a dielectrophoretic measurement method was developed, which was a first for ceramic particles. The elaboration of anisotropic composites was coupled to a novel on-line monitoring of a chaining marker (permittivity), allowing to obtain the structuration dynamics. To validate the predictive aspect of the model, experimental and numerical dynamics were compared showing the robustness and accuracy of the model, even if improvement is still possible at low filler content. In the last part, a proof of concept was demonstrated of the elaboration of anisotropic composites with fillers oriented normally to the direction of the electric field
3
Rebouah, Marie. "Anisotropic stress softening and viscoelasticity in rubber like materials and architectured materials." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI104.
Анотація:
Ce travail de thèse présente une étude du comportement mécanique des matériaux mous soumis à de grandes déformations. Dans ce cadre deux types de matériaux ont été considérés : des matériaux de type élastomères et des matériaux architecturés mimant des matériaux du vivant. Dans un premier temps, cette étude se focalise sur des matériaux de type élastomères pour une meilleure compréhension des phénomènes, notamment grâce à une large étude expérimentale qui n'aurait pas pu être menée sur des tissus du vivant. La caractérisation mécanique des élastomères permet de mettre en évidence différents phénomènes tel que : l'adoucissement de contrainte (aussi connu sous le nom d'effet Mullins), l'anisotropie induite, la déformation résiduelle et la viscoélasticité. Dans le but de créer un modèle capable de prendre en compte tous ces effets dans le cadre des grandes déformations, différents élastomères ont été utilisés pour mettre en évidence chacun de ces phénomènes. Ainsi, chaque matériau a permis d'isoler un phénomène afin de développer et de valider une nouvelle partie du modèle. Par la suite, des matériaux architecturés de type élastomères ont été fabriqués et utilisés pour induire une anisotropie initiale. Le modèle proposé précédemment est alors étendu à la prise en compte de cette anisotropie initiale. Une extension à la modélisation des tissus du vivant (qui sont pour la plupart initialement anisotropes) devient ainsi possible. Chaque modèle a été implanté numériquement dans un code de calcul par éléments finis (excepté pour la viscoélasticité), et la robustesse du modèle a été validée grâce à des essais expérimentaux complexes (bulge test) ou sur des structures complexes (plaque trouée)This thesis work presents a study of the mechanical behavior of soft materials submitted to large deformations. In this context two types of materials were considered: rubber like materials and architectured materials to mimic soft tissues. As a first step, this study focuses on rubber like materials for a better understanding of the phenomena, especially through an large experimental study that could not be lead on soft tissues.The mechanical characterization of the rubber like materials allows highlighting several phenomena such as: the stress softening (also known as Mullins effect), induced anisotropy, permanent set and viscoelasticity. With the aim to create a model able to take into account all these effect in the framework of large deformations, several rubber like materials were used to highlight each one of these phenomena. In this way, each material permits to isolate one phenomenon to develop and validate a new part of the model.Thereafter, architectured materials made of rubber like materials were used to induce an initial anisotropy. The model proposed previously is adapted to take into account this initial anisotropy. An extension to modeling soft tissues (most of them are initially anisotropic) becomes possible.Each model was numerically implemented in a finite element code (except for the viscoelasticity), and the robustness of the model was validated by means of complex experimental tests (bulge test) or on complex structures (holey plate)
4
Geslain, Alan. "Anisotropie naturelle et induite des matériaux poreux : étude expérimentale et modélisation." Phd thesis, Université du Maine, 2011. http://tel.archives-ouvertes.fr/tel-00718301.
Анотація:
Ce travail de thèse a pour objectif de caractériser le comportement anisotrope des mousses acoustiques. Ces matériaux, couramment employés pour lutter contre les nuisances sonores et vibratoireset sont modélisés à l'aide du modèle de Biot. Celui-ci est basé sur le formalisme de lamécanique des milieux continus à deux champs couplés, l'un associé au solide et l'autre au fluidesaturant. Nous nous intéresserons plus particulièrement dans ce travail aux paramètres du solideet aux matériaux présentant une anisotropie (c'est-à-dire des propriétés qui varient suivant lesdirections) du squelette solide. Ici, deux types d'anisotropie sont distingués, l'anisotropie naturelledu matériau et celle induite par une action extérieure, cette dernière ayant pour principale cause lacompression statique des échantillons. Par ailleurs, trois types de symétries naturelles sont considérés : isotropie, isotropie transverse avec et sans rotation de direction principale. Celles-ci sont leplus couramment rencontrées.L'analyse expérimentale du type de symétrie des mousses se fait au moyen d'un dispositif, appelé rigidimètre, qui permet de déterminer la raideur mécanique d'échantillons cubiques de moussesous hypothèse quasi-statique. Celui-ci est couplé à une mesure au vibromètre laser à balayage, permettantde mesurer le déplacement normal des faces des cubes. Des lignes de niveaux des champsde déplacements normaux surfaciques sont ainsi obtenues. Il est alors possible de classer les différentstypes d'anisotropie en analysant ces courbes de niveaux. Ainsi, avec ces a-priori, une méthodea été élaborée pour déterminer les coefficients de Poisson à l'aide de techniques de minimisationà partir des autres constantes élastiques préalablement déterminées. Ce problème est construit àpartir d'indicateurs expérimentaux et d'indicateurs provenant d'un modèle éléments finis.L'influence de la compression statique sur les modules élastiques est ensuite étudiée. Toutd'abord, la variation du module d'Young en fonction du taux de compression est caractérisée àpartir de mesures au rigidimètre. Ensuite, la variation du module de cisaillement en fonction de lacompression statique est caractérisée par une méthode d'ondes guidées (en collaboration avec laKULeuven). Il a été montré que les variations de modules élastiques pouvaient être importantespuisqu'elles peuvent atteindre 50 %. A partir de ces déterminations expérimentales, quatre zones decomportement de la mousse ont été mises en évidence. Ces quatre zones correspondent respectivementà des effets de compression, de flambement, de densification et de réarrangement des cellules.Un modèle éléments-finis microstructural, dans lequel la cellule élémentaire est modélisée par untétrakaidécaèdre de Kelvin, est enfin proposé. Celui-ci permet de modéliser les trois premièreszones, qui correspondent aux compressions statiques usuelles dans les applications acoustiques.
5
Yamashita, Tatsuya. "Analysis of anisotropic material." Ohio : Ohio University, 1996. http://www.ohiolink.edu/etd/view.cgi?ohiou1177700236.
6
Taouk, Habib. "Wave propagation in general anisotropic media." Ohio : Ohio University, 1986. http://www.ohiolink.edu/etd/view.cgi?ohiou1183380228.
7
Morris, Billy Ray. "Grain size estimation in anisotropic materials." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/20042.
8
Lakku, Pavan Misra Anil. "Anisotropic granular models for cohesive materials." Diss., UMK access, 2005.
Анотація:
Thesis (M.S.)--School of Computing and Engineering. University of Missouri--Kansas City, 2005."A thesis in civil engineering." Typescript. Advisor: Anil Misra. Vita. Title from "catalog record" of the print edition Description based on contents viewed March 12, 2007. Includes bibliographical references (leaves 75-77). Online version of the print edition.
9
Bradford, Ian David Richard. "Finite deformations of highly anisotropic materials." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334952.
10
O'Neill, J. M. "Thermoelastic stress analysis of anisotropic materials." Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376642.
11
Hsueh, Hung-Chung. "Physics of anisotropic materials under pressure." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/14119.
Анотація:
The structural, vibrational, and electronic properties of anisotropic materials under compression are comprehensively investigated in this thesis. Recent developments in the techniques of high-pressure X-ray diffraction and Raman scattering, and significant advances in first principle simulations provide detailed high-pressure studies of condensed matter systems. In view of the widely disparate strength of cohesive forces, these studies consist of ionic compounds, quasi-two dimensional semiconductors, quasi-molecular solids, and end with liquid crystals. As a result of the coexistence of different hierarchical interactions in anisotropic systems, evidence of preferential pressure-induced enhancement of weak bonding is found not only in the structural response to external hydrostatic pressure but also in vibrational and electronic behaviour. Further, the understanding of pressure-induced breakdown of rigid-layer vibrations (explored in layered compounds), pressure-induced electron transfer in molecular crystals, and strong overlap of inter- and intra-molecular vibrational modes of liquid crystals provides insight into the essential physics of flexible molecular systems.
12
Van, der Kelen Christophe. "Vibro-acoustic modelling of anisotropic poroelastic materials : characterisation of the anisotropic properties." Doctoral thesis, KTH, MWL Strukturakustik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-137809.
Анотація:
The present-day challenges in the transport industry, steered by the increasing environmental awareness, necessitate manufacturers to take measures to reduce emissions related to the movements of goods and humans. In particular, the measures aiming at a reduced mass or higher load capacity to increase fuel efficiency, generally deteriorate the noise and vibration insulation properties of their products. In order to comply with the regulations and customer demands, modern vehicles increasingly move towards a multifunctional integrated design approach, if possible for all subcomponents involved. Such a multifunctional design approach is an iterative process, evaluating the proposed solutions in every stage, and is therefore best performed in a virtual testing environment. \\Poroelastic materials are interesting to include in a multifunctional design, offering reasonably good vibro-acoustic insulation properties at a low weight penalty. These materials can also be combined in multilayer arrangements to further enhance the overall performance. \\In order to achieve an accurate modelling of the vibro-acoustic behaviour of poroelastic materials, the input data describing the material properties should be of a high quality. Two characteristics inherent to these materials encumber a precise characterisation with traditional techniques. Poro-elastic aggregates are anelastic due to the constituent material used, and anisotropic as a consequence of the production process. Characterisation techniques allowing for an accurate determination of the material properties need to take these intrinsic characteristics into account.\\The objective in this thesis is to enable the characterisation of a constitutive material model for poroelastic materials which is as general as possible, and includes the inherent material anelasticity and anisotropy. For this purpose, a set of advanced characterisation techniques has been developed to characterise the anisotropic flow resistivity tensor and the anisotropic dynamic Hooke's tensor. \\These advanced characterisation techniques are based on an inverse estimation procedure, used consistently throughout the work, and includes both experiments and numerical predictions. The property to characterise is isolated in a specially designed set-up such that it can be modelled by physics solely involving this property. The obtained experimental and numerical data then serve as the input to an optimisation, which returns the material properties for which the difference between both is as small as possible. These methods have been successfully applied to melamine foam, which is found to be both anisotropic and anelastic, confirming the need for such advanced characterisation techniques.QC 20131219
13
Renault, Amélie. "Caractérisation mécanique dynamique de matériaux poro-visco-élastiques." Thèse, Université de Sherbrooke, 2008. http://savoirs.usherbrooke.ca/handle/11143/1915.
Анотація:
Poro-viscoelastic materials are well modelled with Biot-Allard equations. This model needs a number of geometrical parameters in order to describe the macroscopic geometry of the material and elastic parameters in order to describe the elastic properties of the material skeleton. Several characterisation methods of viscoelastic parameters of porous materials are studied in this thesis. Firstly, quasistatic and resonant characterization methods are described and analyzed. Secondly, a new inverse dynamic characterization of the same modulus is developed. The latter involves a two layers metal-porous beam, which is excited at the center. The input mobility is measured. The set-up is simplified compared to previous methods. The parameters are obtained via an inversion procedure based on the minimisation of the cost function comparing the measured and calculated frequency response functions (FRF). The calculation is done with a general laminate model. A parametric study identifies the optimal beam dimensions for maximum sensitivity of the inversion model. The advantage of using a code which is not taking into account fluid-structure interactions is the low computation time. For most materials, the effect of this interaction on the elastic properties is negligible. Several materials are tested to demonstrate the performance of the method compared to the classical quasi-static approaches, and set its limitations and range of validity. Finally, conclusions about their utilisation are given.
14
Gottwald, Matthias. "Nouveaux systèmes modèles à aimantation perpendiculaire pour l'étude des effets de transfert de spin." Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10053/document.
Анотація:
Les effets de transfert de spin sont devenus un sujet de recherche majeur ces quinze dernières années. Cependant, un manque de vérifications expérimentales pour beaucoup de modèles décrivant les effets de transfert de spin peut être constaté. Ceci est surtout lié à un manque de systèmes magnétiques modèles permettant un contrôle précis des paramètres pertinents utilisés dans les modèles théoriques. Dans ce travail deux systèmes magnétiques à aimantation perpendiculaire ont été analysés : les alliages amorphes de Co1-xTbx élaborés par pulvérisation cathodique et les super-réseaux [Co/Ni](111) élaborés par épitaxie par jets moléculaires. L'anisotropie et l'aimantation, qui sont des paramètres pertinents dans beaucoup de modèles sur le transfert de spin, sont variables dans une large gamme. L'origine de cette anisotropie est discutée. La structure des domaines magnétiques est analysée et les résultats des mesures de transport sont interprétés. Pour les super-réseaux [Co/Ni](111) une forte polarisation en spin au niveau de Fermi est démontrée grâce à des expériences de photo émission résolue en spin et un coefficient d'amortissement intrinsèque [alpha] très faible est trouvé. Il est conclu que les alliages amorphes de Co1-xTbx et les super-réseaux [Co/Ni](111) sont des systèmes modèles pour le transfert de spinSpin transfer torque effects have become a research subject of high interest during the last 15 years. However, in order to probe the fundamental physics of spin transfer torque model systems are needed. For a model system it must be as simple as possible to tune the significant parameters (magnetic and structural). In this work we analyze the suitability of two materials for this need. The studied materials are amorphous Co1-xTbx alloys elaborated by sputtering and MBE grown [Co/Ni](111) superlattices. Both systems show perpendicular magnetic anisotropy (PMA), which provides a uniaxial anisotropy to the system. This anisotropy and the magnetization, which are significant parameters for many models on spin transfer torque, can be tuned in a large range of values. The origin of this PMA is discussed. The domain structure is analyzed and transport measurements are interpreted. In addition we show a strong spin polarization of the electrons close to the Fermi level by doing photoemission experiments. A small intrinsic Gilbert damping parameter [alpha] is found by FMR spectroscopy. We conclude that both materials are good candidates to be used as model systems for spin transfer torque
15
Gozhyk, Iryna. "Polarization and gain phenomena in dye-doped polymer micro-lasers." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2012. http://tel.archives-ouvertes.fr/tel-01063044.
Анотація:
The demonstration of an electrically pumped organic laser remains a major issue of organic optoelectronics for several decades. This goal requires an improved device configuration so as to reduce losses which are intrinsically higher under electrical excitation compared to optical pumping. Moreover a systematic investigation of the material properties is still missing and should lead to a reliable estimate of the lasing threshold under optical pumping, and then to a lower limit for electrical pumping. In this thesis we addressed the issue of gain and polarization properties of organic materials in the case of dye-doped polymer thin films. The originality of this work lies in the study of materials via the features of dielectric micro-lasers, allowing to investigate the issues of gain and mode coupling and the physics of open systems. We propose a quantitative description of amplification in organic materials. The "gain-loss-threshold" relation was developed and demonstrated for a Fabry-Perot type cavity, opening the way to study both amplification in organic materials and light out-coupling in dielectric micro-cavities via the lasing threshold. Within this context, different cavity shapes were studied, for instance squares, where light out-coupling takes place by diffraction at dielectric corners. We evidence that polarization properties of such lasing system originate from the intrinsic fluorescence anisotropy of dyes, which required to develop a specific anisotropic model going beyond the existing theory. We also investigated the role of the cavity geometry on the polarization states of the micro-lasers and proposed different ways to influence these features.
16
Ramteke, Ashok Lahanuji. "Multiaxial creep of isotropic and anisotropic materials." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47770.
17
Pan, Jan Wei. "On-line Nonlinear Characterization of Anisotropic Materials." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/30239.
Анотація:
This dissertation proposes a new framework to characterize the nonlinear behavior of anisotropic materials in an on-line manner. The proposed framework applies recursive estimation and a multi-linear model to characterize the nonlinear behavior of anisotropic materials on-line using full-field strains, which are capable of capturing the multi-axial information of anisotropic materials.
A stochastic method is developed to characterize the linear behavior of anisotropic materials under the influence of full-field strain measurement noise. This method first derives stochastic equations based on the formulas of energy-based characterization that utilizes the principle of ener-gy conservation, and then recursively estimates elastic constants at every acquisition of measure-ment using a Kalman filter (KF). Since the measurement model is expressed nonlinearly, the KF utilizes a Kalman gain, which is newly derived in this dissertation through variance minimization, to achieve optimal characterization. The aforementioned method, namely stochastic linear characteri-zation in this dissertation, becomes a basis of the multi-linear characterization method. This method utilizes a multi-linear model, which is defined by partitions, to characterize the nonlinear constitu-tive relations. The multi-linear characterization scales up the number of estimates and identifies the coefficients of each linear partition using the previously derived KF. The recursive updates in measurements not only removes uncertainty through sensor measurements, but also enables the on-line capability of the nonlinear characterization of anisotropic materials.
A series of numerical and experimental studies were performed to demonstrate the performance of the proposed framework in characterizing the nonlinear behavior of anisotropic materials. The validity and applicability of the proposed framework were confirmed by the comparison with the known values of the characterized constitutive relations. It was found that the proposed framework identified elastic constants that were in good agreement with known values irrespective of the spec-imen geometry. The results of the multi-linear characterization method were well correlated with known nonlinear stress-strain relations and concluded that the proposed framework is capable of characterizing adequate nonlinear behavior on-line.Ph. D.
18
Patel, Vijay. "Studies of magnetic viscosity in anisotropic materials." Thesis, Keele University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261526.
19
Jenkins, Morgan Christen. "Fresh Mix Properties and Flexural Analysis with Digital Image Correlation of Additively Manufactured Cementitious Materials." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/96560.
Анотація:
Recently, additive manufacturing (AM), or "3D printing," is expanding into civil infrastructure applications, particularly cementitious materials. To ensure the safety, health, and welfare of the public, quality assurance and quality control (QA/QC) methods via standardized testing procedures are of the upmost importance. However, QA/QC methods for these applications have yet to be established. This thesis aims to implement existing ASTM standards to characterize additive manufactured cementitious composites and to gather better information on how to tackle the challenges that are inherent when printing with cementitious materials. In this work, fresh mix properties and hardened concrete properties were investigated using current ASTM standards as a starting point for applying or adapting them for AM applications.
Specifically, this project applied existing ASTM standards for fresh mix mortars to measure setting time, flow, and early compressive strength as qualitative indicators of printability, pumpability, and buildability. The fresh mix properties were investigated for 12 different mortar mixes to demonstrate the effect that moisture content, absorption, and sand type can have on these fresh mix properties. The results for setting time and compressive strength demonstrated that there was less variability in the properties when the moisture condition of the aggregate was measured and accounted. Flow was shown to be strongly influenced by the sand type.
Additively manufactured mortars were used to print a box in a layer-by-layer process. To evaluate the effect of layering on the flexural strength, three-point bending tests were implemented using four different loading orientations to explore the anisotropic mechanical properties. The observed anisotropic behavior was corroborated with stereo-digital image correlation data showing the stress-strain and load-deflection relationships. Two orientations (A and B) demonstrated brittle behavior while the other two orientations (C and D) experienced quasi-brittle behavior. In addition, setting a minimum unit weight of 132 pcf enabled an analysis of the effect that defects had on the mechanical performance: specimens greater than 132 pcf demonstrated greater and less variable strengths than the specimens less than 132 pcf. The discussion of how defects impacted performance of the different orientations can be valuable when determining how to effectively model, design, and inspect 3D printed structures in the future.
The findings of this thesis confirm that existing ASTM standards for mortars can be modified and applied to AM cementitious composites for QA/QC. It is recommended that mixtures used in 3D printing of cementitious composites should design and accommodate the moisture condition of the aggregate to optimize the predictability of the fresh and early-age properties. For the hardened properties, it is recommended that testing procedures such as flexural testing account for anisotropic behavior. Furthermore, for implementation of 3D printed concrete structures, it is highly recommended that design is a function of loading orientation due to the anisotropic properties of the composite.Master of Science
Recently, additive manufacturing (AM), or "3D printing," is expanding into civil infrastructure applications, specifically cementitious materials such as mortar and concrete. Understanding and predicting the behavior of the materials when using this new technique is vital for quality assurance and quality control (QA/QC). However, standard test methods have yet to be established for this new construction technique. This thesis aims to use existing testing standards to characterize AM cementitious composites and to gather better information on how to tackle the challenges of printing with these materials. In this work, properties before and after the materials hardened were studied by adapting current testing standards. Specifically, this project applied existing testing standards for fresh mix mortars to measure setting time, flow, and early compressive strength. These properties can serve as indicators of specific printing requirements. The fresh mix properties were studied for 12 different mortar mixes to show the effect of moisture content, absorption, and sand type. The results suggest that there was less variability in the properties when the moisture condition and type of the aggregate was accounted. The fresh mix materials were printed in a layer-by-layer process and then hardened in place. The effects of the layers were explored by performing flexure tests using four orientations with respect to how the load was applied to the layers. The observed difference in behavior for the different orientations was supported by digital image correlation data. In addition, an analysis of the effect defects had on the performance was included. Understanding how defects impacted performance can be valuable for effectively designing 3D printed structures in the future. The results of this thesis confirm that existing testing standards for mortars can be adapted and applied to AM cementitious materials for QA/QC. It is recommended that mixtures used in 3D printing of cementitious materials should account for the moisture condition of the aggregate to improve the predictability of the fresh and early-age properties. For the hardened properties, it is recommended that the design is a function of loading orientation due to the difference in behavior for the different orientations of the material.
20
Zeissler, Alexander. "Untersuchungen zum spannungsabhängigen Materialverhalten von Asphalt." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-167970.
Анотація:
Mit dem Einzug numerischer Verfahren zur Dimensionierung von Verkehrskonstruktionen, im Speziellen für Asphaltbefestigung, werden charakteristische Materialkenngrößen benötigt. Des Weiteren wird mit der fortschreitenden Entwicklung von FEM-Programmen, die in Zusammenhang mit Strukturanalysen und Simulationsrechnungen ihren Einsatz finden, die Kenntnis detaillierter Materialkennwerte essentiell. Dass Asphalte mit ihrem charakteristischen Materialverhalten eine Temperatur- und Frequenzabhängigkeit aufweisen, ist anerkannter Stand von Wissenschaft und Technik. In Bezug auf weitere Einflussgrößen existieren nur sehr begrenzte Erkenntnisse. Im Besonderen gilt dies für Abhängigkeiten der Materialkenngrößen von aus der äußeren Beanspruchung resultierenden Spannungszuständen in der Asphaltbefestigung. Ein wesentliches Ziel der Arbeit war die Untersuchung von möglichen Spannungsabhängigkeiten der charakteristischen Materialkenngrößen von Asphalt. In diesem Zusammenhang wurden auch Fragestellungen zu anisotropen Effekten im Materialverhalten aufgegriffen. Die Untersuchungen erfolgten an zwei ausgewählten Asphaltdeckschichtmaterialien, die sich in ihrer Zusammensetzung und granularen Struktur grundlegend voneinander unterscheiden. Zum einen wurden ein Splittmastixasphalt (SMA11S mit PmB 25/55-55A) und zum anderen ein offenporiger Asphalt (PA8 mit PmB 40/100-65A) in das Versuchsprogramm aufgenommen. Die Ansprache des Materialverhaltens erfolgte versuchstechnisch mittels uniaxialer und triaxialer Versuche. Im Ergebnis der Untersuchungen zur Anisotropie von Asphaltmaterialien konnte festgestellt werden, dass die in der Regel gerichtete Verdichtung von Asphalt anisotrope Materialeigenschaften nach sich zieht, unabhängig von der Kornform der verwendeten Gesteinskörnungen und der Ausprägung der Mörtelphase. Des Weiteren war ein wesentliches Ergebnis, dass Asphaltmaterialien in weiten Bereichen der Gebrauchstemperatur ein ausgeprägtes spannungsabhängiges Materialverhalten aufweisen. Erst bei sehr tiefen Temperaturen nähert sich das Materialverhalten von Asphalt einem linear elastischen Festkörperverhalten an. Die granulare Struktur des Asphaltmaterials sowie die Ausprägung der Mörtelphase und der damit verbundenen Bindemittelfilmdicken haben maßgebenden Einfluss auf die Art und Größe der charakteristischen Materialeigenschaften sowie auf die Auswirkungen der jeweiligen Spannungsabhängigkeiten. Als Schlussfolgerung bzw. Ausblick der im Rahmen dieser Arbeit durchgeführten Untersuchungen bleibt festzuhalten, dass für die Erweiterung der Kenntnisse des grundlegenden Materialverhaltens von Asphalt weiterführende Untersuchungen speziell in Bezug auf die Eigenschaften der Einzelbestandteile sowie deren Wechselwirkungen innerhalb der Asphaltstruktur essentiell sindCharacteristic material parameters especially for asphalt pavements are required due to the introduction of numerical pavement design methods. Furthermore, the continuous development of FEM programs, which are used for structural analysis and simulation calculations, also requires the knowledge of detailed material properties. It is state of the art that asphalt shows a significant temperature and frequency dependent behavior. The knowledge regarding additional impact parameters is very limited. This is especially valid for the stress dependency of the material parameters resulting from the stress state within the asphalt pavement based on the external loads. The main aim of this work was the investigation of the possible stress dependencies of the characteristic material parameters of asphalt. In this context, questions related to the anisotropic effects of the material behavior have also been taken up. Two asphalt surface layer materials, which have significant differences in the material composition and the granular structure were investigated in this context. On the one hand a stone mastic asphalt (SMA11S with PmB 25/55-55A) and on the other hand a porous asphalt (PA8 with PmB 40/100-65A) were included in the testing scheme. Uniaxial and triaxial tests were selected to determine the material behavior at the laboratory. Within the determination of the anisotropic material behavior of asphalt, it could be proven that the usually vertical compaction direction during the compaction process effects anisotropic material properties. This behavior can be determined independent from the particle shape, the used aggregate material and the specification of the asphalt mastic. Another essential result is, that asphalt materials show a significant stress dependent material behavior in a wide range of the performance temperature. Only on very low temperatures the material behavior of asphalt can be assumed to be linear elastic. The granular structure of asphalt material as well as the specification of the asphalt mastic and the thickness of the binder between the particles have a significant influence on the type and size of the characteristic material properties and the effect of stress dependency. Finally, it can be concluded, that it is essential to investigate the material behavior of each ingredient and their interaction within the asphalt structure to expand the knowledge regarding the fundamental material behavior of asphalt
21
Huang, Weichun. "Acoustic properties of natural materials." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1031/document.
Анотація:
Dans cette thèse, nous étudions un métamatériau inspiré de la paille de blé pour l'absorption parfaite du son. Une botte de paille estidéalisée comme un milieu poreux anisotrope, composé d’un arrangement périodique très concentré de tubes creux cylindriques. L’approche théorique de ce métamatériau repose sur l'homogénéisation asymptotique à deux échelles d'un réseau perméable de résonateursparfaitement rigides dont la physique est enrichi par des résonances internes. Les principales caractéristiques de ce milieu poreux sont lacompressibilité effective négative autour de la résonance du tube et la réduction drastique de la vitesse de propagation du son (slowsound) à très basse fréquence. Une configuration optimale est conçue, basée sur la condition de couplage critique, pour laquelle la fuited’énergie du système résonnant ouvert est parfaitement compensée par les pertes intrinsèques induites par les pertes viscothermiques.Des mesures en tube à impédance sont effectuées sur des échantillons fabriqués par impression additive pour valider les résultatsthéoriques. Nous montrons que ce métamatériau est un absorbeur sub-longueur d'onde capable d’une absorption parfaite à très bassefréquence et d'introduire une quasi-bande interdite autour de la résonance du tube. De plus, la nature anisotrope de ce matériau conduit àune absorption globalement élevée à basse fréquence et ce pour toutes les incidences. Cette étude offre la possibilité de concevoir unabsorbeur acoustique sélectif en angle et en fréquence. Pour conclure, les résultats de cette thèse montrent que la paille est un boncandidat pour une absorption acoustique parfaiteStraw-inspired metamaterials for sound absorption are investigated in this Thesis. A straw stack is idealized as a highly concentratedresonant anisotropic porous medium constituted of a periodic arrangement of densely packed cylindrical hollow tubes. The approach tothis metamaterial relies on the two-scale asymptotic homogenization of a permeable array of perfectly rigid resonators, where the physicsis further enriched by tailoring inner resonances. The main features of such sound absorbing medium are the possibility for the effectivecompressibility to become negative around the tube resonance and the drastic reduction of the effective sound speed (slow sound) at verylow frequency in the system. Moreover, an optimal configuration for sound absorption is designed, based on the critical couplingcondition, in which the energy leakage out of the open resonant system is perfectly compensated by the intrinsic losses induced by thevisco-thermal losses both in the anisotropic matrix and in the resonators. Impedance tube measurements are performed on 3-D printedsamples with controlled parameters to validate the theoretical results. This metamaterial is a sub-wavelength absorber that can achievetotal absorption at a very low frequency and possesses a quasi-band-gap around the tube resonance. Furthermore, the anisotropic nature ofthe configuration gives rise to high absorption at low-frequency range for all incidences and diffuse field excitation. It paves the way tothe design of angular and frequency selective sound absorber. To conclude, the results of this Thesis show that straw is a good candidatefor perfect sound absorption
22
Guastavino, Rémi. "Elastic and acoustic characterisation of anisotropic porous materials." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4782.
Анотація:
For an accurate prediction of the low and medium frequency surface vibration and sound radiation behaviour of porous materials, there is a need to improve the means of estimating their elastic and acoustic properties. The underlying reasons for this are many and of varying origin, one prominent being a poor knowledge of the geometric anisotropy of the cell microstructure in the manufactured porous materials. Another one being, the characteristic feature of such materials i.e. that their density, elasticity and dissipative properties are highly dependent upon the manufacturing process techniques and settings used. In the case of free form moulding, the geometry of the cells and the dimensions of the struts are influenced by the rise and injection flow directions and also by the effect of gravity, elongating the cells. In addition the influence of the boundaries of the mould also introduces variations in the properties of the foam block produced. Despite these complications, the need to predict and, in the end, optimise the acoustic performance of these materials, either as isolated components or as part of a multi-layer arrangement, is growing. It is driven by the increasing demands for an acoustic performance in balance with the costs, a focus which serves to increase the need for modelling their behaviour in general and the above mentioned, inherent, anisotropy in particular. The current work is focussing on the experimental part of the characterisation of the material properties which is needed in order to correctly represent the anisotropy in numerical simulation models. Then an hybrid approach based on a combination of experimental deformation, strain field mapping, flow resistivity measurement and physically based porous material acoustic Finite Element (FE) simulation modelling is described. This inverse estimation linked with high quality measurements is crucial for the determination of the anisotropic coefficients of the porous materials is illustrated here for soft foam and fibrous wool materials.QC 20100729
23
Guastavino, Rémi. "Elastic and acoustic characterisation of anisotropic porous materials /." Stockholm : Department of Aeronautical and Vehicle Engineering, Royal Institute of Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4782.
24
Gregory, P. W. "Finite elastic-plastic deformations of highly anisotropic materials." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282601.
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Kannan, Rangaramanujam Mudumbai Kornfield Julia A. Kornfield Julia A. "Flow-induced alignment in intrinsically anisotropic polymeric materials /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10112007-104204.
26
Dib, Wassim. "Comportement mécanique de tissus à voiles, en fibres synthétiques, sous sollicitations biaxiales et déformation finie." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI006/document.
Анотація:
Ce travail concerne l'étude théorique, expérimentale et numérique du comportement mécanique de matériaux tissés et de toiles laminées à base de fibres synthétiques, destinés à la fabrication des voiles, comme le polyester ou le Kevlar. Une approche théorique originale a été proposée ; elle permet une prise en compte du comportement spécifique des fils, de l'enduction et de leurs interactions. La modélisation, qui en résulte, permet de décrire le comportement biaxial des matériaux tissés et des toiles, en chargements cycliques complexes, avec une prise en compte des déformations finies, des effets visqueux non linéaires, de l'irréversibilité indépendante du temps et de l'anisotropie. Une mise en œuvre de cette modélisation a été effectuée dans un code d'Eléments Finis, afin de produire un outil opérationnel pour le calcul des voiles. L'approche théorique proposée a été validée grâce à une étude expérimentale détaillée, qui a été réalisée sur le Dacron SF HTP Plus. Ainsi, nous avons réalisé sur ce matériau différents essais de tractions monotones et de tractions ondulées, contrôlés en déformation et en force. Certains de ces essais comportent des séquences de relaxation. Ces essais ont été réalisés dans les axes du matériau, dans le sens chaîne ou dans le sens trame, ainsi qu'en hors axes avec des orientations par rapport à la direction chaîne allant de 5° à 45°. Des résultats expérimentaux complémentaires ont également été obtenus sur une toile laminée en Kevlar X15 et sur un Dacron SF HTM simple. Enfin, une simulation de l'essai de traction biaxiale a été réalisée et a permis d'étudier l'homogénéité des champs de contrainte et de déformation de trois formes d'éprouvette différentesThis work deals with theoretical, experimental and numerical studies of the mechanical behavior of woven materials and laminated fabrics, made with synthetic fibers, for the manufacture of sails, such as polyester or Kevlar. An original theoretical approach was proposed, it allows taking into account the specific behavior of yarns, of coating and their interactions. The resulting modeling allows describing the behavior of woven materials and laminated fabrics, in the case of complex cyclic biaxial loadings, taking into account finite deformations, nonlinear viscous effects, time-independent irreversibility and anisotropy. The implementation of this modeling was performed in a finite element code, in order to produce an operational tool for the design and calculation of sails. The proposed theoretical approach has been validated through a detailed experimental study, which was conducted on material “Dacron SF HTP Plus”. Thus, we performed various monotonous and cyclic tensile tests, which were strain or load-controlled. Some of these tests include relaxation sequences. These tests were conducted in the axes of the material, in the warp and weft directions, as well as off-axis or bias orientations, from 5 ° to 45 ° with respect to the warp direction. Further experimental results were also obtained on a laminated “Kevlar X15” and a woven “Dacron SF HTM simple” fabrics. Finally, numerical simulations of the biaxial tensile test were performed and were used for studying homogeneity of the stress and the strain fields in the cases of three different contours of biaxial-tensile samples
27
Lam, Wai Sze Tiffany. "Anisotropic Ray Trace." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/556957.
Анотація:
Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3×3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for anisotropic ray tracing. This P matrix has the following characteristics: (1) Multiple P matrices are calculated to describe the polarization of the multiple eigenmodes at an anisotropic intercept. (2) Each P matrix maps the orthogonal incident basis vectors (Ê_m, Ê_n, Ŝ) before the optical interface into three orthogonal exiting vectors (a_m Ê'_m, a_n Ê'_n, Ŝ') after the interface, where a_m and a_n are the complex amplitude coefficients induced at the intercept. The ray tracing algorithms described in this dissertation handle three types of uncoated anisotropic interfaces isotropic/anisotropic, anisotropic/isotropic and anisotropic/anisotropic interfaces. (3) The cumulative P matrix associated with multiple surface interactions is calculated by multiplying individual P matrices in the order along the ray path. Many optical components utilize anisotropic materials to induce desired retardance. This important mechanism is modeled as the optical phase associated with propagation. (4) The optical path length OPL of an eigenpolarization along an anisotropic ray path is incorporated into the calculation of each P matrix. Chapter 4 presents the data reduction of the P matrix of a crystal waveplate. The diattenuation is embedded in the singular values of P. The retardance is divided into two parts: (A) The physical retardance induced by OPLs and surface interactions, and (B) the geometrical transformation induced by geometry of a ray path, which is calculated by the geometrical transform Q matrix. The Q matrix of an anisotropic intercept is derived from the generalization of s- and p-bases at the anisotropic intercept; the p basis is not confined to the plane of incidence due to the anisotropic refraction or reflection. Chapter 5 shows how the multiple P matrices associated with the eigenmodes resulting from propagation through multiple anisotropic surfaces can be combined into one P matrix when the multiple modes interfere in their overlapping regions. The resultant P matrix contains diattenuation induced at each surface interaction as well as the retardance due to ray propagation and total internal reflections. The polarization aberrations of crystal waveplates and crystal polarizers are studied in Chapter 6 and Chapter 7. A wavefront simulated by a grid of rays is traced through the anisotropic system and the resultant grid of rays is analyzed. The analysis is complicated by the ray doubling effects and the partially overlapping eigen-wavefronts propagating in various directions. The wavefront and polarization aberrations of each eigenmode can be evaluated from the electric field distributions. The overall polarization at the plane of interest or the image quality at the image plane are affected by each of these eigen-wavefronts. Isotropic materials become anisotropic due to stress, strain, or applied electric or magnetic fields. In Chapter 8, the P matrix for anisotropic materials is extended to ray tracing in stress birefringent materials which are treated as spatially varying anisotropic materials. Such simulations can predict the spatial retardance variation throughout the stressed optical component and its effects on the point spread function and modulation transfer function for different incident polarizations. The anisotropic extension of the P matrix also applies to other anisotropic optical components, such as anisotropic diffractive optical elements and anisotropic thin films. It systematically keeps track of polarization transformation in 3D global Cartesian coordinates of a ray propagating through series of anisotropic and isotropic optical components with arbitrary orientations. The polarization ray tracing calculus with this generalized P matrix provides a powerful tool for optical ray trace and allows comprehensive analysis of complex optical system.
28
Souza, Carlos Alexandre Oliveira de. "Modelagem numerica por elementos de contorno 3D de juntas coladas em estruturas aeronauticas de material composito." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263143.
Анотація:
Orientadores: Paulo Sollero, Eder Lima de AlbuquerqueDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-08-14T09:46:04Z (GMT). No. of bitstreams: 1 Souza_CarlosAlexandreOliveirade.pdf: 3303337 bytes, checksum: beed7bb6d99b6ae8f528600efe197f82 (MD5) Previous issue date: 2009
Resumo: Na indústria aeronáutica é comum o uso de juntas coladas, rebitadas e parafusadas na união de componentes ou partes estruturais. O projeto de juntas coladas é baseado em análise para a determinação das tensões normais e cisalhantes no adesivo e do campo de deslocamentos ao longo da junta. O objetivo deste trabalho é desenvolver uma ferramenta computacional, utilizando o software Matlab® para resolver numericamente o problema de juntas coladas sobrepostas (lap joints) de material compósito no contexto 3D. O método numérico empregado para a resolução das equações diferenciais que regem o problema é o Método dos Elementos de Contorno (MEC) e a Técnica das Sub-Regiões. Para a implementação são considerados elementos retangulares constantes e descontínuos, isto é, os elementos não compartilham graus de liberdade. É utilizada nesse trabalho a Solução Fundamental para Anisotropia plena obtida por meio da Transformada de Radon que já foi anteriormente implementada por Santiago (2008). Além da Solução Fundamental Anisotrópica, também é implementada uma função contendo a Solução Fundamental Isotrópica com o objetivo de validar o código através de resultados analíticos disponíveis na literatura para este caso.
Abstract: The use of bonded, riveted and bolted joints to assemble components or structural parts is inevitable in aeronautic industries. The design of bonded joints is based upon analyses to estimate peeling and shear stresses in the adhesive and the displacement field along the bonded region. The objective of this work is to develop a computational tool using the Matlab® software to solve numerically the bonded lap joints problem in composite materials for aeronautical structures in 3D context. The numerical method to be employed for solving governing differential equations is the Boundary Element Method (BEM) and Sub-Regions Technique. For this implementation, rectangular constants and discontinuous elements were considered, which means that nodes don't share degrees of freedom. In this work is used the Fundamental Solution for Anisotropy obtained by Radon transform which was previously implemented by Santiago (2008). Besides the Anisotropic Fundamental Solution, also is implemented a function containing the Isotropic Fundamental Solution with the objective of validating the code with analytical results available in literature for this case.
Universidade Estadual de Campi
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
29
Senan, Anish Sen. "Determination of the Viscoelastic Properties of General Anisotropic Materials." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/SenanAS2003.pdf.
30
Sui, Yongqiang. "Anisotropic organic materials ferroelectric crystals and spin-polarized radicals /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5933.
Анотація:
Thesis (Ph. D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Mar. 13, 2009). Includes bibliographical references.
31
Park, Jong Keun. "Anisotropic Morphologies and Properties in Perfluorosulfonate Ionomer-Based Materials." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/40486.
Анотація:
The overall goal of this investigation was to elucidate specific structure-property relationships in perfluorosulfonate ionomers (PFSIs)-related materials. The project can be broken into two primary foci. First, we explored the current state of understanding related to morphology-property relationships in PFSIs with specific attention to the nano-scale organization of the ionic and crystalline domains. Specifically, the effect of uniaxial orientation on the structure and transport properties of Nafion® membranes was examined. Small angle X-ray scattering (SAXS) experiments on dry membranes that were uniaxially elongated showed a strong anisotropic morphology which was shown to persist over the swelling process without a significant relaxation. Hermanâ s order parameters for the ionomer peak were strongly influenced by uniaxial deformation, which supports the presence of cylindrical rather than spherical morphology for ionic domains. Comparison of the water diffusion coefficients between unoriented and oriented samples revealed that uniaxial deformation of Nafion® membranes essentially enhances transport ability in one direction (i.e., the parallel to draw direction) and suppresses in the other two directions (i.e., two orthogonal directions relative to the stretching direction). Based on 1-dimensional analyses of oriented SAXS patterns at the azimuthal angle 90o, three recent models (lamellar model, semicrystalline rod-like model and fringed-micelle model) for the morphology of PFSIs were critically evaluated. The loss of meridional scattering, different orientation behavior of the crystalline and ionic domains, and inherent chain stiffness precludes the possibility of a chain-folded lamellar morphology. While the inter-aggregate dimensions remain constant at high draw ratios, the inter-crystalline spacings decrease significantly. Coupled with the distinctly different orientation behavior, these observations preclude the existence of crystallites solely within rod-like aggregates. While the worm-like ionic channel model was able to explain the behavior of SAXS and wide angle X-ray scattering (WAXS) relatively well, this model also had limitations such as (1) crystalline domains directly linked to the ionic domain (and thus a lack of amorphous domains) and (2) a presence of only a single ionic channel between two neighboring crystallites.
Second, electroactive materials, specifically ionic polymer-metal composites (IPMCs) that undergo bending motions with the stimulus of a relatively weak electric field were fabricated. To understand the role of the nanoscale morphology of the membrane matrix in affecting the actuation behavior of IPMC systems, we evaluated actuation performance of IPMCs subjected to uniaxial orientation. The PFSI nanostructure altered by uniaxial orientation mimicked the fibrillar structure of biological muscle tissue and yielded a new anisotropic actuation response. It was evident that IPMCs cut from films oriented perpendicular to the draw direction yielded displacement values that were significantly greater than that of unoriented IPMCs. In contrast, IPMCs cut from films oriented parallel to the draw direction appeared to resist bending and yield displacement values that were much less than that of the unoriented IPMC. This anisotropic actuation behavior was attributed to the contribution of the nanoscale morphology to the bulk bending modulus. Overall, this study clearly demonstrated, for the first time, the importance of the nanoscale morphology in affecting/controlling the actuation behavior in IPMC systems.Ph. D.
32
Krishnaswami, Sriram. "Development of an anisotropic yield function for porous materials /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487849377293422.
33
Degtyar, Andrei D. "Ultrasonic characterization of stressed and damaged nonhomogeneous anisotropic materials /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487948158626289.
34
Wingfield, Charles. "Fabrication of Anisotropic Sol-gel Materials by Photo-Crosslinking." VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/2706.
Анотація:
This is a report on the fabrication and characterization of anisotropic, porous materials: functionally graded cellular and compositionally anisotropic aerogels. This new class of materials was fabricated by photopolymerization of selected regions of a homogeneous monolith using visible light. Visible light is not significantly absorbed and not significantly scattered by organic molecules and oxide nanoparticles in wet gels and it allows fabrication of deeply penetrating, well-resolved patterns. Simple variations of the exposure geometry allowed fabrication of a wide variety of anisotropic materials without requiring layers or bonding.
35
Ribeiro, ferreira Ayrton. "Modélisation micromécanique du comportement effectif des matériaux ductiles poreux anisotropes." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLN013.
Анотація:
La fabrication de matériaux ductiles insère généralement des impuretés dans leurs compositions microscopiques. Ces impuretés peuvent se détacher de la matrice environnante et même se fissurer lors d’une déformation progressive. En raison de la résultante incapacité de ces particules indésirables à supporter toute contrainte, ces matériaux ductiles sont, de manière équivalente, supposés être poreux. Il a été largement démontré que la porosité joue un rôle fondamental dans les mécanismes de la rupture ductile. Depuis les années 1970, de nombreux modèles micromécaniques ont été proposés dans le but de décriremathématiquement ces mécanismes. Parmi eux, le célèbre modèle de Gurson combine la technique d’homogénéisation avec le théorème cinématique de l’analyse limite pour estimer le critère de plastification macroscopique et la loi d’évolution de la porosité des matériaux ductiles poreux. Cependant, le modèle de Gurson, ainsi que la plupart de ses extensions, ne tient compte que de la rupture ductile isotrope. Le but du présent travail est donc de contribuer à la conception de critères de plastification pour la rupture ductile des milieuxporeux anisotropes. Trois contributions principales tirant parti d’hypothèses similaires à celles du modèle de Gurson sont ici proposées. La première contribution est l’évaluation de l’influence de la morphologie des vides sur les critères de plastification macroscopique de ces classes de matériaux. La deuxième est l’inclusion d’un critère de plastification anisotrope dans la matrice du matériau, de sorte que le comportement macroscopique présente une anisotropie induite par cette matrice, y compris pour les cavités sphériques. Le troisième et dernier progrès consiste à généraliser le critère de plastification de la matrice afin d’inclure une classe de fonctions de plastification basée sur des transformations linéaires. Cette classe de fonction a été largement employée avec succès pour représenter des alliages d’aluminium à haute résistance. Les résultats ici présentés soulignent la cohérence et la robustesse des trois formulations. En outre, le rôle de la porosité sur la modélisation de la plasticité des alliages d’aluminium incite à poursuivre les travaux sur la caractérisation expérimentale des paramètres d’anisotropieThe manufacturing of ductile materials generally inserts impurities into their microscopic composition. These impurities may detach from the surrounding matrix and even crack along progressive deformation. Due to the consequent incapacity of these undesirable particles of supporting any stress, these ductile materials are equivalently assumed to be porous. Porosity has been effectively shown to play a fundamental role in the mechanisms of ductile fracture. Many micromechanical models have been proposed since the 1970s with the aim of mathematically describing these mechanisms. Among them, the acclaimed Gursonmodel combines the averaging homogenization technique with the kinematic theorem of Limit Analysis to estimate the macroscopic yield criterion and porosity evolution law of porous ductile materials. However, the Gurson model and most of its extensions only account for isotropic ductile fracture. Thus, the purpose of the present work is to contribute to the conception of yield criteria for anisotropic porous ductile rupture. Three main contributions are hereby proposed by profiting from similar hypothesis to those of the Gurson model. The first contribution is the assessment of the influence of void morphology on overall yield criteria for those classes of materials. The second is the inclusion of ananisotropic yield criterion in the material matrix so that the macroscopic behavior present matrix-induced anisotropy even for spherical cavities. The third and last advancement consists of generalizing the material matrix yield criterion of the Gurson model in order to comprehend a linear transformation-based class of yield functions that has been widely used to represent specific high strength aluminum alloys. The results hereby presented highlight the consistency and robustness of the three formulations. Moreover, the role of the porosity on the modeling of yield behavior of aluminum alloys encourages further work regarding experimental parameter characterization
36
Stangel, Anders. "Magnetocrystalline Anisotropy in(FexNi1-x)2B Materials." Thesis, Uppsala universitet, Materialteori, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-301992.
Анотація:
The magnetic properties of the (FexNi1-x)2B family of materials are explored using DFT calculations utilizing the FPLO and SPR-KKR code packages. It is found that a uniaxial magnetocrystalline anisotropy exists at around x = 0.8 with a magnetocrystalline anisotropy energy at around 0.3 MJ/m^3. A calculation of the lattice constant for these materials were attempted but failed due to the emergence of local minima and the calculations of magnetic properties were instead done using lattice parameters interpolated between known experimental values.
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Costa, Dalmo Inacio Galdêz. "Análise numérica de falhas em materiais compósitos laminados usando um critério baseado em fenômenos físicos." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263873.
Анотація:
Orientadores: Éder Lima de Albuquerque, Paulo SolleroDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Este trabalho apresenta uma análise da falha de laminados de materiais compósitos através de critérios baseados em fenômenos físicos. Formulações de elasticidade plana anisotrópica do Método dos Elementos de Contorno (MEC) e suas respectivas soluções fundamentais foram utilizados para calcular as deformações e as tensões no contorno e no domínio de cada uma das lâminas que formam o laminado. Os envelopes de falha do critério LaRC03 foram reproduzidos e comparados com os envelopes de falha dos critérios de Puck e Tsai-Wu. A variação da resistência longitudinal de uma lâmina com o ângulo de orientação das fibras foi analisada. Uma vez que as tensões foram previamente calculadas com o MEC, o critério LaRC03 foi utilizado para avaliar se há algum dano no laminado. O modo de falha também é analisado e os resultados discutidos. Os resultados para alguns problemas são apresentados e discutidos
Abstract: This work presents a formulation of failure of laminated composite materials using a criterion based on physical phenomena. The Boundary Element Method (BEM) for anisotropic plane elasticity and its respective fundamental solutions were used to compute strains and stresses at the boundary and in the domain of each of the laminae forming the laminated. The LaRC03 failure criterion envelope was reproducted and compared with Puck's and Tsai-Wu's failure criteria as well as the longitudinal strength variation of laminae with the fiber orientation angle. Since the stresses were previously computed with BEM, the LaRC03 criterion was used to evaluate if there is any damage in the laminated. Furthermore, failure modes are observed and results were discussed. Results to some problems are presented and discussed
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Xue, Yibin. "Three dimensional interface cracks in anisotropic bimaterials." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17273.
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Ahmat, idriss Hassane gogo. "Développement d'un banc ellipsométrique hyperfréquence pour la caractérisation de l'anisotropie des indices." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSES021.
Анотація:
Pour caractériser des échantillons anisotropes non transparents afin de déterminer les indices de réfraction, nous utilisons un banc ellipsométrique hyperfréquence en espace libre fonctionnant en transmission et en incidence oblique. Le système de mesure est équipé d’un ellipsomètre à trois détecteurs et d'un analyseur de réseau vectoriel (VNA source de l’énergie). Son principe est basé sur la détermination du tenseur diagonal complexe. Cela nécessite la mesure des coefficients de transmission de l'échantillon. Un étalonnage du VNA est nécessaire pour obtenir les valeurs correctes de ces coefficients. La procédure d'étalonnage utilisée pour corriger les termes d’erreurs lié à la mesure est la méthode de calibrage One Path Two Ports. Nous travaillons sur une gamme de fréquence de 26 à 30 GHzTo characterize non-transparent anisotropic samples in order to determine their refractive indices. The technic used is based on free-space oblique transmission ellipsometry in microwave frequency range (26 to 30 GHz) with a vector network analyzer (VNA). Its principle is based on the determination of complex diagonal tensor. Measurement of the sample transmission coefficients is required. Calibration of the network vector analyzer is needed to correct these coefficient values. The calibration method used to correct measurement errors is the method called One Path Two Ports
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Vladimirov, Ivaylo N. "Anisotropic material modelling with application to sheet metal forming." Aachen Shaker, 2009. http://d-nb.info/999285513/04.
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Robertson, Daniel J. "Quantifying the Nonlinear, Anisotropic Material Response of Spinal Ligaments." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/5457.
Анотація:
Spinal ligaments may be a significant source of chronic back pain, yet they are often disregarded by the clinical community due to a lack of information with regards to their material response, and innervation characteristics. The purpose of this dissertation was to characterize the material response of spinal ligaments and to review their innervation characteristics. Review of relevant literature revealed that all of the major spinal ligaments are innervated. They cause painful sensations when irritated and provide reflexive control of the deep spinal musculature. As such, including the neurologic implications of iatrogenic ligament damage in the evaluation of surgical procedures aimed at relieving back pain will likely result in more effective long-term solutions. The material response of spinal ligaments has not previously been fully quantified due to limitations associated with standard soft tissue testing techniques. The present work presents and validates a novel testing methodology capable of overcoming these limitations. In particular, the anisotropic, inhomogeneous material constitutive properties of the human supraspinous ligament are quantified and methods for determining the response of the other spinal ligaments are presented. In addition, a method for determining the anisotropic, inhomogeneous pre-strain distribution of the spinal ligaments is presented. The multi-axial pre-strain distributions of the human anterior longitudinal ligament, ligamentum flavum and supraspinous ligament were determined using this methodology. Results from this work clearly demonstrate that spinal ligaments are not uniaxial structures, and that finite element models which account for pre-strain and incorporate ligament’s complex material properties may provide increased fidelity to the in vivo condition.
42
Fard, Samad Moemen Bellah. "Modelling anisotropy in electrotechnical steels." Thesis, Cardiff University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263551.
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Siem, Ellen J. (Ellen Jane) 1979. "Thermodynamic stability and implications of anisotropic boundary particles." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/27874.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 168-180) and index.
(cont.) Generally, a boundary is nonplanar in the neighborhood of an attached particle--even when anisotropic interfacial free energies do not produce faceting-and maintains a icKy = 0 while the boundary particles maintain a nonzero ,Ky. This is consistent with independent observations of Pb-rich particles at grain boundaries in dilute Pb-AI alloys. Predicted particle/boundary morphologies give a trade-off between boundary and particle interface-a particle replaces some boundary but also produces boundary area through local distortions. This result has several implications. The transition to perfect wetting requires a larger boundary energy density. The steady-state heterogeneous nucleation rate is increased when facets appear on the nucleus, but the increase is diminished if the boundary distorts. A corollary result presented in this thesis, that particles can induce rotations or ser- ration through torques, has implications in microstructural stability and illustrates avenues for future research.
Many material properties depend on grain and phase boundary morphology. Equilibrium boundary and particle morphologies are determined by their interactions through interfacial free energy. Currently, the determination of boundary and particle morphology is, for most materials systems, experimentally difficult. This thesis demonstrates that geometric constructions from capillarity theory for anisotropic interfaces cannot predict boundary and particle morphology, even in systems with uniform temperature, pressure, and chemical potentials. In this thesis, numerical methods are developed and implemented for calculations of anisotropic particles of fixed volumes attached to one or more interfaces that are also subject to specified constraints. Some boundary properties can be found experimentally, such as: the crystallographic misorientation across the boundary, the fixed average unit normal to the boundary, the Wulff shape (W') of the boundary, and the particle W'4 within each grain or phase abutting the boundary. These properties become model parameters in addition to the W' associated with each interface. This thesis also presents methods of generating algebraic expressions for interfacial free energy densities, W' (n), that produce W for a given symmetry. Calculated examples show that equilibrium configurations are formed from portions of the boundary and particle /s and do not contain orientations absent from the respective W's. Under the constraint that the pressure difference across a boundary is zero, the boundary will develop a constant weighted mean curvature (Kic) of zero.
by Ellen J. Siem.
Ph.D.
44
Fahey, Maureen Theresa. "Nonlinear and anisotropic behavior of high performance fibers." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12468.
Анотація:
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1993.Vita.
Includes bibliographical references (leaves 228-231).
by Maureen Theresa Fahey.
Sc.D.
45
Hoefel, Simone dos Santos. "Analise de estruturas tridimensionais de laminados atraves de metodo dos elementos de contorno." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263136.
Анотація:
Orientador: Paulo SolleroTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho é desenvolvida uma formulação do método dos elementos de contorno para análise de estruturas formadas pela associação espacial de placas de laminados compósitos. Inicialmente, as formulações do método dos elementos de contorno, desenvolvida para problemas de elasticidade plana e de flexão em placas finas para materiais anisotrópicos, são associadas obtendo-se uma estrutura plana, denominada macro-elemento. Um macro-elemento contém simultaneamente os estados de flexão em placas finas e extensão (chapa) e possui quatro graus de liberdade por nó, sendo eles: deslocamento normal, tangencial e transversal e rotação normal. O modelo final assume uma associação desses macro-elementos no espaço. Cada macro-elemento é tratado como uma sub-região do MEC. As equações de cada sub-região, após as transformações de coordenadas, são acopladas através de equações de equilíbrio e compatibilidade. O tratamento numérico é feito através do método dos elementos de contorno usando elementos constantes e quadráticos. Com o objetivo de validar a formulação desenvolvida, vários exemplos numéricos são analisados, os resultados obtidos são comparados com resultados analíticos e numéricos disponíveis na literatura
Abstract: In this work a boundary element formulation is developed for the analysis of structures formed by three-dimensional association of symmetric laminated composite plates. Initially, the boundary element formulations developed for plane elasticity anisotropic problems and bending of anisotropic thin plate problems are associated in one plane structure with four degrees of freedom per node given by normal, tangential and transverse displacements and normal rotations. Then, the formulation is extended in order to allow the plane assembling of these structures. In the two-dimensional formulation, each plane element is defined as macroelement containing out-of-plane (bending) and in plane (stretching) degrees of freedom. The final system is obtained by assuming each individual plane structural element as a sub-domain. After the necessary transformation of these equations, they can be combined in order to take into account displacement compatibilities and traction equilibrium conditions. The numerical treatment is carried out by the direct boundary element method. Numerical examples are presented and their results are compared to results available in literature
Doutorado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
46
Montemezzani, Germano Luigi Montemezzani Germano Luigi Montemezzani Germano Luigi. "Optical wave manipulation and signal processing in anisotropic photorefractive materials /." Zürich : Swiss Federal Institute of Technology, Zurich, Institute of Quantum Electronics, 2003. http://e-collection.ethbib.ethz.ch/show?type=habil&nr=14.
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Tütüncü, Göknur. "Analysis and interpretation of diffraction data from complex, anisotropic materials." [Ames, Iowa : Iowa State University], 2010. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3403852.
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Elkholy, Sherif Mohamed Abdelfatah. "Direct boundary element analysis of anisotropic solids and porous materials." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187286.
Анотація:
The main objective of this dissertation is to investigate the application of the boundary element methods (BEM) to problems with anisotropic material properties in the areas of transient flow, elastostatics, and soil consolidation. The resulting BEM formulations represent a major contribution for this class of problems which has not received much of the researchers' attention. The BEM formulations developed are entirely in terms of boundary quantities which reduces the dimensionality of the problem by one. This advantage makes the BEM an attractive alternative to the more popular domain-based techniques, such as finite element and finite difference methods for this category of problems. This gives researchers and engineers a wider range of numerical analysis tools to consider when investigating a problem in the field. The above mentioned formulations have been implemented in two computer programs, TRANSBE and EL10, which can be used for transient flow and elastic analysis of bodies with anisotropic material properties. Also, a new approach, based on these two programs, is presented to perform consolidation analysis in soils with anisotropy in both elastic and flow properties. Finally, a number of problems, which cover the three areas of interest, are solved in order to verify the effectiveness and accuracy of the developed computer programs.
49
Smith, Paula Kay. "Characterizing Dielectric Tensors of Anisotropic Materials From a Single Measurement." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293464.
Анотація:
Ellipsometry techniques look at changes in polarization states to measure optical properties of thin film materials. A beam reflected from a substrate measures the real and imaginary parts of the index of the material represented as n and k, respectively. Measuring the substrate at several angles gives additional information that can be used to measure multilayer thin film stacks. However, the outstanding problem in standard ellipsometry is that it uses a limited number of incident polarization states (s and p). This limits the technique to isotropic materials. The technique discussed in this paper extends the standard process to measure anisotropic materials by using a larger set of incident polarization states. By using a polarimeter to generate several incident polarization states and measure the polarization properties of the sample, ellipsometry can be performed on biaxial materials.Use of an optimization algorithm in conjunction with biaxial ellipsometry can more accurately determine the dielectric tensor of individual layers in multilayer structures. Biaxial ellipsometry is a technique that measures the dielectric tensors of a biaxial substrate, single-layer thin film, or multi-layer structure. The dielectric tensor of a biaxial material consists of the real and imaginary parts of the three orthogonal principal indices (nₓ + ikₓ, n(y) +ik(y) and n(z) + ik(z)) as well as three Euler angles (α, β, and γ) to describe its orientation. The method utilized in this work measures an angle-of-incidence Mueller matrix from a Mueller matrix imaging polarimeter equipped with a pair of microscope objectives that have low polarization properties. To accurately determine the dielectric tensors for multilayer samples, the angle-of-incidence Mueller matrix images are collected for multiple wavelengths. This is done in either a transmission mode or a reflection mode, each incorporates an appropriate dispersion model. Given approximate a priori knowledge of the dielectric tensor and film thickness, a Jones reflectivity matrix is calculated by solving Maxwell's equations at each surface. Converting the Jones matrix into a Mueller matrix provides a starting point for optimization. An optimization algorithm then finds the best fit dielectric tensor based on the measured angle-of-incidence Mueller matrix image. This process can be applied to polarizing materials, birefringent crystals and the multilayer structures of liquid crystal displays. In particular, the need for such accuracy in liquid crystal displays is growing as their applications in industry evolve.
50
Son, Seyul. "Nonlinear Electromechanical Deformation of Isotropic and Anisotropic Electro-Elastic Materials." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/28587.
Анотація:
Electro-active polymers (EAPs) have emerged as a new class of active materials, which produce large deformations in response to an electric stimulus. EAPs have attractive characteristics of being lightweight, inexpensive, stretchable, and flexible. Additionally, EAPs are conformable, and their properties can be tailored to satisfy a broad range of requirements. These advantages have enabled many target applications in actuation and sensing. A general constitutive formulation for isotropic and anisotropic electro-active materials is developed using continuum mechanics framework and invariant theory. Based on the constitutive law, electromechanical stability of the electro-elastic materials is investigated using convexity and polyconvexity conditions. Implementation of the electro-active material model into a commercial finite element software (ABAQUS 6.9.1, PAWTUCKET, RI, USA) is presented. Several boundary and initial value problems are solved to investigate the actuation and sensing response of isotropic and anisotropic dielectric elastomers (DEs) subject to combined mechanical and electrical loads. The numerical response is compared with experimental results to validate the theoretical model.
For the constitutive formulation of the electro-elastic materials, invariants for the coupling between two families of electro-active fibers (or particles) and the applied electric field are introduced. The effect of the orientation of the electro-active fibers and the electric field on the
electromechanical coupling is investigated under equibiaxial extension. Advantage of the constitutive formulation derived in this research is that the electromechanical coupling can be illustrated easily by choosing invariants for the deformation gradient tensor, the electro-active fibers, and the electric field. For the electromechanical stability, it is shown that the stability can be controlled by tuning the material properties and the orientation of the electro-active fibers. The electromechanical stability condition is useful to build a stable free energy function and prevent the instabilities (wrinkling and electric breakdown) for the electro-elastic materials. The invariant-based constitutive formulation for the electro-elastic materials including the isotropic and anisotropic DEs is implemented into a user subroutine (UMAT in ABAQUS: user defined material) by using multiplicative decomposition of the deformation gradient and the applicability of the UMAT is shown by simulating a complicated electromechanical coupling problem in ABAQUS/CAE. Additionally, the static and dynamic sensing and actuation response of tubular DE transducers (silicone and polyacrylate materials) with respect to combined electrical and mechanical stimuli is obtained experimentally. It is shown that the silicone samples have better dynamic and static sensing characteristics than the polyacrylate. The theoretical modeling accords well with the experimental results.Ph. D.