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Toward Optimal Design of Piezoelectric Transducers Based on Multifunctional and Smoothly Graded Hybrid Material Systems

Rubio, Wilfredo Montealegre; Silva, Emilio Carlos Nelli; Paulino, Gláucio Hermógenes
Fonte: SAGE PUBLICATIONS LTD Publicador: SAGE PUBLICATIONS LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
156.44727%
This work explores the design of piezoelectric transducers based on functional material gradation, here named functionally graded piezoelectric transducer (FGPT). Depending on the applications, FGPTs must achieve several goals, which are essentially related to the transducer resonance frequency, vibration modes, and excitation strength at specific resonance frequencies. Several approaches can be used to achieve these goals; however, this work focuses on finding the optimal material gradation of FGPTs by means of topology optimization. Three objective functions are proposed: (i) to obtain the FGPT optimal material gradation for maximizing specified resonance frequencies; (ii) to design piezoelectric resonators, thus, the optimal material gradation is found for achieving desirable eigenvalues and eigenmodes; and (iii) to find the optimal material distribution of FGPTs, which maximizes specified excitation strength. To track the desirable vibration mode, a mode-tracking method utilizing the `modal assurance criterion` is applied. The continuous change of piezoelectric, dielectric, and elastic properties is achieved by using the graded finite element concept. The optimization algorithm is constructed based on sequential linear programming...

Tailoring vibration mode shapes using topology optimization and functionally graded material concepts

RUBIO, Wilfredo Montealegre; PAULINO, Glaucio H.; SILVA, Emilio Carlos Nelli
Fonte: IOP PUBLISHING LTD Publicador: IOP PUBLISHING LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
156.44727%
Tailoring specified vibration modes is a requirement for designing piezoelectric devices aimed at dynamic-type applications. A technique for designing the shape of specified vibration modes is the topology optimization method (TOM) which finds an optimum material distribution inside a design domain to obtain a structure that vibrates according to specified eigenfrequencies and eigenmodes. Nevertheless, when the TOM is applied to dynamic problems, the well-known grayscale or intermediate material problem arises which can invalidate the post-processing of the optimal result. Thus, a more natural way for solving dynamic problems using TOM is to allow intermediate material values. This idea leads to the functionally graded material (FGM) concept. In fact, FGMs are materials whose properties and microstructure continuously change along a specific direction. Therefore, in this paper, an approach is presented for tailoring user-defined vibration modes, by applying the TOM and FGM concepts to design functionally graded piezoelectric transducers (FGPT) and non-piezoelectric structures (functionally graded structures-FGS) in order to achieve maximum and/or minimum vibration amplitudes at certain points of the structure, by simultaneously finding the topology and material gradation function. The optimization problem is solved by using sequential linear programming. Two-dimensional results are presented to illustrate the method.; FAPESP (Sao Paulo State Foundation Research Agency)[05/01762-5]; FAPESP[08/51070-0]; CNPq (National Council for Research and Development...

Otimização topológica aplicada ao projeto de estruturas tradicionais e estruturas com gradação funcional sujeitas a restrição de tensão.; Topology optimization applied to the design of traditional structures and functionally graded structures subjected to stress constraint.

Stump, Fernando Viegas
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/05/2006 PT
Relevância na Pesquisa
188.70285%
Este trabalho apresenta a aplicação do Método de Otimização Topológica (MOT) considerando restrição de tensão mecânica em dois problemas de Engenharia: o projeto de estruturas mecânicas sujeitas a restrição de tensão e o projeto da distribuição de material em estruturas constituídas por Materiais com Gradação Funcional (MsGF). O MOT é um método numérico capaz de fornecer de forma automática o leiaute básico de uma estrutura mecânica para que esta atenda a um dado requisito de projeto, como o limite sobre a máxima tensão mecânica no componente. Os MsGF são materiais cujas propriedades variam gradualmente com a posição. Este gradiente de propriedades é obtido através da variação contínua da microestrutura formada por dois materiais diferentes. Neste trabalho o MOT foi implementado utilizando o modelo de material Solid Isotropic Microstructure with Penalization (SIMP) e o campo de densidades foi parametrizado utilizando a abordagem Aproximação Contínua da Distribuição de Material (ACDM). O modelo de material e utilizado em conjunto com um localizador de tensões, de modo a representar as tensões nas regiões com densidade intermediária. O projeto de estruturas tradicionais através do MOT possui dois problemas centrais aqui tratados: o fenômeno das topologias singulares...

Projeto de materiais piezocompósitos baseados no conceito de gradação funcional utilizando o método de otimização topológica.; Design of piezocomposite materials based on functionally graded concept by means of topology optimization method.

Vatanabe, Sandro Luis
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 09/11/2012 PT
Relevância na Pesquisa
156.44727%
Um material piezocompósito é resultante da combinação de um material piezelétrico com outros materiais não-piezelétricos, oferecendo vantagens substanciais em relação aos materiais piezelétricos convencionais. Diferentes propriedades efetivas podem ser obtidas alterando-se a fração de volume dos constituintes ou a própria topologia da célula unitária do piezocompósito. Materiais com Gradação Funcional (MGF) são materiais compósitos avançados, projetados de tal forma que sua composição varie gradualmente numa direção espacial. A vantagem do conceito MGF é não apresentar interface convencional entre os materiais da inclusão e da matriz, reduzindo assim um problema comum em materiais compósitos laminados, como por exemplo, o surgimento de concentração de tensões mecânicas. O Método de Otimização Topológica (MOT) é uma técnica computacional utilizada para se determinar a distribuição de materiais em uma estrutura ou material de forma sistemática, a fim de se extremizar uma determinada função objetivo. Assim, esse trabalho propõe uma metodologia sistemática e genérica para o projeto de materiais piezocompósitos com gradação funcional (MPGF) utilizando o MOT, tanto para aplicações quasi-estáticas...

Fabricação de ferramentas de corte em gradação funcional por Spark Plasma Sintering (SPS).; Fabrication of cutting tools from functionally graded materials using Spark Plasma Sintering (SPS).

Carneiro, Marcelo Bertolete
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/01/2014 PT
Relevância na Pesquisa
177.615%
O objetivo do trabalho foi fabricar ferramentas de corte para usinagem a partir de materiais em gradação funcional (Functionally Graded Materials FGM), fazendo uso da técnica de sinterização por plasma pulsado (Spark Plasma Sintering SPS), a qual permite taxa de aquecimento e resfriamento maior do que as técnicas tradicionais, menor temperatura e tempo de operação, melhor controle energético e alta repetibilidade. Os materiais utilizados foram pós cerâmicos a base de alumina (Al2O3-ZrO2 e Al2O3-TiC) e metal duro (WC-Co), de modo que dois insertos foram desenvolvidos, um de cerâmica branca (Al2O3-ZrO2) em gradação com metal duro e outro de cerâmica mista (Al2O3-TiC) em gradação com metal duro. A metodologia experimental levou em conta a aplicação de um modelo termomecânico para estimar a tensão residual térmica ao longo da espessura da ferramenta, estudo da influência dos parâmetros de sinterização por SPS (Temperatura e Pressão) sobre a qualidade do sinterizado (caracterização da propriedade física, densidade), com base nesses dados foi escolhida a melhor condição de operação para fabricar corpos de prova (CPs) para os ensaios mecânicos de resistência à flexão, dureza e tenacidade à fratura...

Fabricação de gradientes funcionais entre aço ferramenta e cobre por fusão seletiva a laser usando um feixe de laser pulsado Nd:YAG de alta potência para aplicações em moldes de injeção

Beal, Valter Estevão
Fonte: Florianópolis, SC Publicador: Florianópolis, SC
Tipo: Dissertação de Mestrado Formato: xxv, 232 p.| il., tabs., grafs.
ENG
Relevância na Pesquisa
212.89453%
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica; O desenvolvimento de novos produtos envolve novos materiais, processos e metodologias de projetos. Com relação a novos materiais, a otimização de forma e função num único componente pode ser obtida por Functionally Graded Materials (FGM) ou materiais com gradientes funcionais. Assim como em materiais compósitos, o emprego de FGMs explora obter com o uso de dois ou mais materiais, funções diferenciadas que produzam um componente final otimizado. Por exemplo: materiais rígidos mas leves ou duros e condutores de calor. No entanto, genericamente, FGMs possuem como diferença uma gradual transição entre cada um dos elementos que formam o componente, em oposição a transição bem definida entre os compósitos. Apesar das potenciais vantagens e aplicações, uma das principais limitações dos FGMs é a baixa complexidade obtenível pelos processos de fabricação existentes. Nos últimos 10 anos, pesquisas têm procurado obter FGMs a partir de tecnologias de fabricação por adição de camadas, também conhecidas por prototipagem rápida. Devido ao potencial de produzir virtualmente objetos de forma livre em qualquer tipo de material...

Wear, corrosion and tribocorrosion behavior of al-based composites reinforced with al-rich intermetallic compounds

Ferreira, S. C.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Dissertação de Mestrado
Publicado em 15/12/2006 ENG
Relevância na Pesquisa
203.48666%
Dissertação de Mestrado em Processamento e Caracterização de Metais; The objective of this research work was to study the degradation (corrosion and tribocorrosion) resulting from mechanical (wear) and electrochemistry (corrosion) interactions in Al/Al3Ti and Al/Al3Zr functionally graded materials (FGMs). The influence of the spatial distribution of the platelets on the corrosion and tribocorrosion behaviour was evaluated. The Al/Al3Ti and Al/Al3Zr FGMs were produced by centrifugal casting, originating samples in the form of rings that presented radial gradients of the reinforcements. The corrosion resistance of Al/Al3Ti and Al/Al3Zr FGMs was studied using electrochemical techniques namely, open circuit potential (OCP), potenciodynamic polarization and electrochemical impedance spectroscopy (EIS). Additionally, the tribocorrosion behaviour was evaluated in a pin-on-plate configuration, under reciprocating sliding. During the tribocorrosion tests, the samples were immersed in a 0.6 M NaCl solution, and the corrosion current was measured while the samples were under potentiostatic control. Through the integration of the current density curve vs. time, the electric charge was determined, allowing the electrochemical contribution to the overall degradation process to be distinguished from that arising from the mechanical wear. The synergic action mechanisms of the system were further explained based on scanning electron microscopy (SEM) analysis. The experimental results showed that the tribocorrosion degradation of these materials is governed essentially by mechanical processes. Finally...

Particle distribution and orientation in Al-Al3Zr and Al-Al3Ti FGMs produced by the centrifugal method

Sequeira, P. D.; Watanabe, Y.; Rocha, L. A.
Fonte: Trans Tech Publications Inc Publicador: Trans Tech Publications Inc
Tipo: Artigo de Revista Científica
Publicado em //2005 ENG
Relevância na Pesquisa
288.70285%
Al-Al3Zr and Al-Al3Ti functionally graded materials (FGMs) were produced by a centrifugal method from Al-5wt% Zr and Al-5wt% Ti alloys, respectively. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Microstructural characterization was performed to evaluate the intermetallic particles’ distribution and orientation. Knoop hardness tests were carried out, with the indenter’s long diameter normal to the centrifugal force direction. Both the Al3Zr and the Al3Ti intermetallic particles are platelet in morphology. These platelets tend to be oriented normal to the centrifugal force direction. Higher applied centrifugal force increases both the intermetallic platelet volume fraction as well as their orientation in the outer regions of the fabricated FGM rings. Also higher orientation and volume fraction distribution are observed in the Al- Al3Ti FGMs. Knoop hardness measurements in general follow the same trend as the intermetallic particle volume fraction for each sample.

Aluminum matrix texture and particle characterization in Al-Al3Ti FGMs produced by a centrifugal solid-particle method

Sequeira, P. D.; Watanabe, Y.; Rocha, L. A.
Fonte: Trans Tech Publications Inc. Publicador: Trans Tech Publications Inc.
Tipo: Artigo de Revista Científica
Publicado em //2005 ENG
Relevância na Pesquisa
288.70285%
The centrifugal solid-particle method has proved to be effective in producing functionally graded materials (FGMs). In this study, Al-Al3Ti FGMs, were produced by this centrifugal method, from an Al-5 wt % Ti master alloy. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Samples from the outer surface of each specimen were cut and aluminum matrix texture analyzed by Schulz reflection method. Analysis of the resulting pole figures indicates a preferred orientation along the (200) plane for the aluminum matrix crystals. Furthermore, increasing the applied centrifugal force enhances the orientation effect. Al3Ti platelet orientation and area fraction at the samples’ outer surface along three observation planes were also measured. The Al3Ti platelets in the outer region are orientated perpendicular to the centrifugal force direction along two of the observed planes, also an increase in centrifugal force leads to an increase in orientation in those two planes. The intermetallic particle volume fraction also increases with higher applied centrifugal force, although not significantly. A correlation appears to exist between particle orientation and the preferred orientation of the matrix.

Corrosion behaviour of Al/Al3Ti and Al/Al3Zr functionally graded materials produced by centrifugal solid-particle method: Influence of the intermetallics volume fraction

Ferreira, S. C.; Rocha, L. A.; Ariza, E.; Sequeira, P. D.; Watanabe, Yoshimi; Fernandes, J. C. S.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2011 ENG
Relevância na Pesquisa
188.70285%
Intermetallic particles, Al3Ti and Al3Zr were formed in Al–5mass%Ti and Al–5mass%Zr alloys, respectively, by centrifugal casting, in order to create functionally graded materials (FGMs). At present, no information is available on the influence of the amount of intermetallics on the electrochemical properties of these alloys. In this paper, the corrosion resistance of Al/Al3Ti and Al/Al3Zr FGMs was investigated by open-circuit measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Results suggests that the corrosion resistance of the FGMs is affected by galvanic effects between the intermetallic particles and the metallic matrix. Lower centrifugal forces resulted in an improvement of the electrochemical properties.

Mechanical and fatigue properties of functionally graded aluminium silicon alloys; Propriedades mecânicas e de fadiga de ligas de alumínio-silício com gradação funcional

Chirita, Georgel
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 13/10/2011 ENG
Relevância na Pesquisa
177.615%
Tese de doutoramento em Engenharia Mecânica (ramo de conhecimento em Mecânica de Materiais); Many structural components encounter service conditions and, hence, required materials performance, which vary with location within the component. It is well known that abrupt transitions in materials composition and properties within a component often result in sharp local concentrations of stress, whether the stress is internal or applied externally. It is also known that these stress concentrations are greatly reduced if the transition from one material to the other is made gradual. By definition, functionally graded materials are used to produce components featuring engineered gradual transitions in microstructure and/or composition, the presence of which is motivated by functional performance requirements that vary with location within a part. With functionally graded materials, these requirements are met in a manner that optimizes the overall performance of the component. The research on functionally graded materials (FGMs) is encouraged by the need for properties that are unavailable in any single material and the need for graded properties to offset adverse effects of discontinuities for layered materials. Centrifugal casting is a very common method for obtaining functionally graded materials...

Validation of a field technique and characterization of fecal glucocorticoid metabolite analysis in wild chimpanzees (Pan troglodytes)

Murray, Carson M; Heintz, Matthew R; Lonsdorf, Elizabeth V; Parr, Lisa A; Santymire, Rachel M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
177.615%
Monitoring adrenocortical activity in wild primate populations is critical, given the well-documented relationship between stress, health and reproduction. Although many primate studies have quantified fecal glucocorticoid metabolite (FGM) concentrations, it is imperative that researchers validate their method for each species. Here, we describe and validate a technique for field extraction and storage of FGMs in wild chimpanzees (Pan troglodytes). Our method circumvents many of the logistical challenges associated with field studies while yielding similar results to a commonly-used laboratory method. We further validate that our method accurately reflects stress physiology using an ACTH challenge in a captive chimpanzee and a FGM peak at parturition in a wild subject. Finally, we quantify circadian patterns for FGMs for the first time in this species. Understanding these patterns may allow researchers to directly link specific events with the stress response.

First Versus Second Order Latent Growth Curve Models: Some Insights From Latent State-Trait Theory

Geiser, Christian; Keller, Brian; Lockhart, Ginger
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
200.14838%
First order latent growth curve models (FGMs) estimate change based on a single observed variable and are widely used in longitudinal research. Despite significant advantages, second order latent growth curve models (SGMs), which use multiple indicators, are rarely used in practice, and not all aspects of these models are widely understood. In this article, our goal is to contribute to a deeper understanding of theoretical and practical differences between FGMs and SGMs. We define the latent variables in FGMs and SGMs explicitly on the basis of latent state-trait (LST) theory and discuss insights that arise from this approach. We show that FGMs imply a strict trait-like conception of the construct under study, whereas SGMs allow for both trait and state components. Based on a simulation study and empirical applications to the CES-D depression scale (Radloff, 1977) we illustrate that, as an important practical consequence, FGMs yield biased reliability estimates whenever constructs contain state components, whereas reliability estimates based on SGMs were found to be accurate. Implications of the state-trait distinction for the measurement of change via latent growth curve models are discussed.

Second-order homogenisation of functionnally graded materials

ANTHOINE Armelle
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Articles in Journals Formato: Printed
ENG
Relevância na Pesquisa
177.615%
The homogenisation theory for periodic composites is generalised to the case of quasi-periodic composites. In quasi-periodic composites, the unit cell does not repeat throughout the medium but gradually changes along one or more directions of periodicity (grading directions). Quasi-periodic composites are thus to functionally graded materials (FGMs) what periodic composites are to statistically uniform composite materials. Contrarily to most of the homogenisation methods applied to FGMs, the proposed second-order homogenisation theory takes explicitly into account the grading at the micro-level. The derived equivalent material happens to be a particular second gradient material in which few components of the strain gradient (second gradient of the displacement) should be taken into account in addition to the classical strains (first gradient of displacement). The second gradient theory therefore appears as the natural framework to appropriately handle functionally graded materials at the macro-level. It is worth mentioning that the presented second-order homogenisation procedure is somehow analogous to the one developed for periodic composite materials submitted to rapidly varying macroscopic strain fields as in regions of high gradients. In fact...

An??lisis por el m??todo de los elementos finitos de problemas de fractura en FGM

Mart??nez Pa??eda, Emilio
Fonte: Universidade de Granada Publicador: Universidade de Granada
Tipo: Dissertação de Mestrado
SPA
Relevância na Pesquisa
215.99602%
Los Materiales Funcionalmente Graduados (FGM ??? Functionally Graded Materials) son aquellos cuya composici??n, y por ende sus propiedades, var??an gradualmente en funci??n de la posici??n. La necesidad de entender, cuanti???car y mejorar la tenacidad de los FGMs ha tra??do consigo un especial inter??s en establecer una metodolog??a para la mec??nica de la fractura en esos materiales. Debido al alto coste y las rebuscadas instalaciones necesarias para procesar experimentalmente los FGMs, la simulaci??n num??rica del comportamiento a fractura ha adquirido especial relevancia. El objetivo de este estudio es el de desarrollar una completa metodolog??a para la simulaci??n num??rica de procesos de fractura cuasi-est??ticos en FGMs bidimensionales bajo el modo mixto de carga. Este es el modo de fractura inherente a los FGMs y es inducido en este trabajo inclinando la grieta, o con respecto a la direcci??n de carga aplicada, como en el caso de un material homog??neo, o con respecto a la direcci??n del gradiente del material, mediante una combinaci??n de ambos; las tres con???guraciones caracter????sticas del modo mixto de fractura en FGMs. A partir del m??todo de los elementos ???nitos se calculan los FITs y el t??rmino no singular del T-stress en el preciso instante de inicio de propagaci??n de la entalla y...

Estudo de materiais com gradiente funcional (MGF) a base de alumina (Al2O3) e carbeto de nióbio (NbC) obtidos por diferentes técnicas de sinterização; Study of functional gradient materials (FGM) made of alumina (Al2O3) and niobium carbide (NbC) obtained by different sintering techniques

Uehara, José Luis Hideki Sakihama
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/07/2015 PT
Relevância na Pesquisa
177.615%
No presente trabalho, peças com gradiente funcional de Al2O3 com reforço de NbC foram planejadas com o intuito de obter um MGF (material com gradiente funcional) com uma alta dureza e boa tenacidade à fratura a partir de diferentes técnicas de sinterização. Os MGFs apresentam-se como uma excelente alternativa quando é necessária a união de materiais com propriedades térmicas ou mecânicas muito diferentes, já que possuem uma transição suave de propriedades ao longo do corpo, como consequência de uma mudança gradual do teor das fases. No planejamento dos MGFs foram utilizadas análises dilatométricas para compatibilizar o comportamento durante a sinterização de cada camada e assim minimizar as tensões que ocorrem durante a retração, responsáveis por trincas e delaminações. Nos ensaios de dilatometria observou-se que a diferença máxima de retração entre os compósitos de teor de NbC variando de 5 a 30 %p é de 4,85%, assim, foram projetados MGFs com um passo de 5% de NbC, reduzindo esta diferença para 2,73%. Compósitos monolíticos de Al2O3 com diferentes teores de NbC foram sinterizadas a 1500ºC num forno convencional sob atmosfera de grafite. As densidades das peças sinterizadas foram inferiores a 90% da densidade teórica (DT)...

Fundamental solution based graded element model for steady-state heat transfer in FGM

CAO, Leilei; Wang, Hui; Qin, Qing Hua
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
177.615%
A novel hybrid graded element model is developed in this paper for investigating thermal behavior of functionally graded materials (FGMs). The model can handle a spatially varying material property field of FGMs. In the proposed approach, a new variationa

Three boundary meshless methods for heat conduction analysis in nonlinear FGMs with Kirchhoff and Laplace transformation

Fu, Zhuo-Jia; Chen, Wen; Qin, Qing Hua
Fonte: Global Science Press Publicador: Global Science Press
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
277.615%
This paper presents three boundary meshless methods for solving problems of steady-state and transient heat conduction in nonlinear functionally graded materials (FGMs). The three methods are, respectively, the method of fundamental solution (MFS), the bo

Microstructure-based modeling of elastic functionally graded materials: One dimensional case

Sharif-Khodaei, Zahra; Zeman, Jan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
195.52613%
Functionally graded materials (FGMs) are two-phase composites with continuously changing microstructure adapted to performance requirements. Traditionally, the overall behavior of FGMs has been determined using local averaging techniques or a given smooth variation of material properties. Although these models are computationally efficient, their validity and accuracy remain questionable, since a link with the underlying microstructure (including its randomness) is not clear. In this paper, we propose a modeling strategy for the linear elastic analysis of FGMs systematically based on a realistic microstructural model. The overall response of FGMs is addressed in the framework of stochastic Hashin-Shtrikman variational principles. To allow for the analysis of finite bodies, recently introduced discretization schemes based on the Finite Element Method and the Boundary Element Method are employed to obtain statistics of local fields. Representative numerical examples are presented to compare the performance and accuracy of both schemes. To gain insight into similarities and differences between these methods and to minimize technicalities, the analysis is performed in the one-dimensional setting.; Comment: 33 pages, 14 figures

Thickness-shear Frequencies of an Infinite Quartz Plate with Material Property Variation Along the Thickness

Wang, Ji; Zhang, Wenliang; Huang, Dejin; Ma, Tingfeng; Du, Jianke
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/05/2014
Relevância na Pesquisa
177.615%
Properties of the quartz crystal blank of a resonator is assumed homogeneous, uniform, and perfect in design, manufacturing, and applications. As end products, quartz crystal resonators are frequently exposed to gases and liquids which can cause surface damage and internal degradation of blanks under increasingly hostile conditions. The combination of service conditions and manufacturing process including chemical etching and polishing can inevitably modify the surface of quartz crystal blanks with changes of material properties, raising the question of what will happen to vibrations of quartz crystal resonators of thickness-shear type if such modifications to blanks are to be evaluated for sensitive applications. Such questions have been encountered in other materials and structures with property variations either on purpose or as the effect of environmental or natural processes commonly referred to as functionally graded materials, or FGMs. Analyses have been done in applications as part of studies on FGMs in structural as well as in acoustic wave device applications. A procedure based on series solutions has been developed in the evaluation of frequency changes and features in an infinite quartz crystal plate of AT-cut with the symmetric material variation pattern given in a cosine function with the findings that the vibration modes are now closely coupled. These results can be used in the evaluation of surface damage and corrosion of quartz crystal blanks of resonators in sensor applications or development of new structures of resonators.; Comment: This is to be presented and published with the 2014 IEEE International Frequency Control Symposium...