Orientador: Carlos Alberto Cimini Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-28T23:32:20Z (GMT). No. of bitstreams: 1 Almeida_RobertoSilvade_M.pdf: 4039070 bytes, checksum: 5f3fa81abaa6c19d365c550dd4b59dbd (MD5) Previous issue date: 2015 / Resumo: O principal objetivo deste trabalho, foi desenvolver uma metodologia para identificar impacto em placas laminadas de materiais compósitos, a fim de reduzir o tempo de inspeção e assim otimizar o intervalo de inspeção para uma determinada estrutura, já que muitas vezes é necessário interromper a sua operação. Uma compreensão abrangente dos efeitos de interação estrutura, sensores piezelétricos e objetos utilizados para aplicar cargas de impacto foi essencial. Este trabalho efetua uma análise numérica a partir dos tempos que conduziram ondas de deformação para alcançar os sensores e os seus efeitos sobre a exatidão dos resultados, obtidos pelo algoritmo desenvolvido, bem como a exatidão da metodologia aplicada. Sensores piezelétricos fabricados pela International APC e um sistema de aquisição de dados da National Instruments foram utilizados para obter respostas de ondas de tensão geradas por cargas de impacto. Uma identificação simples e robusta do impacto em tempo real com base na triangulação foi implementada. O uso de recursos computacionais através da plataforma Labview, juntamente com um algoritmo implementado no código computacional, forneceu resultados promissores, após testes realizados em configurações de placas experimentais monitoradas com redes de sensores piezelétricos. A metodologia proposta foi validada para placas de material isotrópico (aço) e anisotrópico (carbono/epóxi) apresentando bons resultados. A interface foi desenvolvida para ser aplicada a materiais com diferentes índices de anisotropia, onde se pode ajustar os valores de velocidade das ondas em diferentes direções. Observou-se que o erro máximo medido foi de 0,028 m. O código computacional apresentou-se robusto para identificar o local do impacto em qualquer ponto da placa em tempo real. Foi possível também comprovar para as diferentes massas de impacto que um procedimento simples de triangulação combinado com as características de velocidade de propagação das ondas proporciona um meio de localizar impactos / Abstract: The main objective of this work was to develop a methodology for identifying impact in laminated plates of composite materials in order to reduce inspection time and thus reduce the inspection interval for a given structure, since it is often necessary to stop its operation. A comprehensive understanding of the interaction effects of structure, piezoelectric sensors and objects used to apply impact loads was essential. This work demonstrates the numerical analysis of time leading waves of deformation to reach the sensors and their effect on not only the accuracy of the results obtained by the algorithm but also the accuracy of the methodology applied. In this work, piezoelectric sensors manufactured by International APC and data acquisition system of National Instruments were used. A simple and robust real-time impact identification based on triangulation was implemented. The use of computational resources within Labview platform along with a computer code implemented algorithm provided promising results after testing experimental settings for plates monitored with of piezoelectric sensors. The proposed methodology was validated for isotropic (steel) and anisotropic (carbon/epoxy) plate materials with fairly good results. The interface was designed to be applied to materials with different degrees of anisotropy, adjusting the values of wave velocity in different directions for composite materials. It was observed that the maximum error was 0.028 m. The computer code was robust enough to identify the impact location at any point of the plate in real time. It was also possible to demonstrate for different impact masses that a simple triangulation procedure combined with the characteristics of wave propagation provides a methodology for locating impacts / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

High-temperature piezoelectric wafer active sensors (HT-PWAS) have been developed for structure health monitoring at hazard environments for decades. Different candidates have previously been tested under 270 °C and a new piezoelectric material langasite (LGS) was chosen here for a pilot study up to 700 °C. A preliminary study was performed to develop a high temperature sensor that utilizes langasite material. The Electromechanical impedance (E/M) method was chosen to detect the piezoelectric property. Experiments that verify the basic piezoelectric property of LGS at high temperature environments were carried out. Further validations were conducted by testing structures with attached LGS sensors at elevated temperature. Additionally, a detection system simulating the working process of LGS monitoring system was developed with PZT material at room temperature. This thesis, for the first time, (to the best of author’s knowledge) presents that langasite is ideal for making piezoelectric wafer active sensors for high temperature structure health monitoring applications.

Les capteurs magnéto-électrique (ME) sont une alternative prometteuse pour mesurer de faibles signaux magnétiques. Précédemment le choix était généralement de déposer des couches minces magnétostrictives sur un matériau piézoélectrique massif conduisant à des systèmes macroscopiques de taille milllimétrique. L’intégration de ces systèmes dans des MEMS (micro-electro-mechanical systems) requiertà la fois de résoudre les problèmes d’intégration de matériaux actif sur silicium, et de mesurer des petits signaux étant donné l’importante réduction de la réponse du système lorsqu’il est miniaturisé.Dans cette optique, le premier objectif de ce travail de thèse a été d’intégrer un matériau piézoélectrique sur un substrat de silicium tout en conservant une excellente qualité cristalline. Pb(Zr ₀ , ₅ ₂Ti ₀ ,₄₈)O₃ (PZT) a été retenu pour ces excellente propriétés piézoélectriques. L’intégration de la couche mince ce fait sur silicium qui est le substrat de prédilection pour la fabrication de microsystèmes avec les procédés microélectroniques standards. La qualité cristalline des matériaux actifs est directement corrélée aux couches d'adaptation utilisées pour obtenir une bonne qualité cristalline sur silicium. Pour cel l'intégration d'une tricouche composée de zircone stabilisée à l'yttrium (YSZ), d'oxyde de cérium (CeO₂) et de SrTiO₃ permet ensuitela croissance des pérovskites d'intérêt pour le dispositif. Le choix de l’électrode conductrice inférieure (SrRuO₃ ou La ₀ ,₆₆Sr₀₃₃MnO₃ dans le cas présent) permet de contrôler l’orientation de la maille de PZT.Une première étude des propriétés piézoélectriques de la couche mince de PZT sous la forme d’une poutre libre pour son intégration dans un système magnétoélectrique a été réalisé. La mesure de la déformation de la poutre induite par l'application d'une tension électrique permet d'extraire un coefficient d₃₁ de -53pmV⁻¹, valeur inférieure au matériau massif mais à l'état de l'art dans ce type de dispositif. Dans une seconde étape, l’utilisation de la poutre comme résonateur à été étudiée. L’étude dynamique du système a permis d'obtenir la fréquence de résonance et le facteur de qualité. Le déplacement de la fréquence caractéristique du système en fonction d'une contrainte induite par une tension DC a été investigué. Enfin, l'ajout d'une couche de matériau magnétostrictif (TbFeCo) sur la poutre a finalisé la structure du capteur. Le capteur ainsi obtenu a été caractérisé et une sensibilité d’une dizaine de micro Tesla a été obtenue. / Magneto-electric (ME) sensors have been demonstrated as a promising alternative for the detection of weak magnetic signals with high sensitivity. To date, most applications focused on the use of bulk piezoelectric materials on which magnetostrictive thin films are deposited leading to millimeter-sized devices. The integration of such devices into micro-electro-mechanical systems (MEMS), bringing smaller size and lower power consumption, involves addressing several scientific issues ranging from the integration of active materials on silicon to the strong reduction in amplitude of generated signals related to the size reduction of the sensor.In this context, the first goal of this thesis work was to integrate high crystalline quality piezoelectric thin films on silicon.Pb(Zr ₓTi ₁ ₋₁)O₃ (PZT) with a morphotropic composition (x=0.52) having high electromechanical coupling factor was chosen. Silicon is a necessary template as it allows for the use of conventional clean room processes for the realization of the microsystem. The crystalline quality of the active films is directly linked to the buffer layers that promote the crystalline growth on silicon. For this purpose, Yttria-stabilized Zirconia (YSZ) was used in combination with CeO₂ and SrTiO₃ to allow further growth of epitaxial perovskites. The choice of the bottom electrode material (SrRuO₃ or La ₀ ,₆₆Sr₀₃₃MnO₃ in this work) further tunes the crystalline orientation of the PZT layer.To probe the potential of such PZT thin films for ME devices, the first step was to characterize the electromechanical properties of this material in a free standing cantilever structure. Under an applied electric field, the measured displacement of the epitaxial PZT-based cantilevers is characterized by a coefficient d₃₁ =-53pmV⁻¹ , a reduced value with respect to the bulk material but that can be enhanced by further optimizing the film growth. The second step consists in ascertaining the ability of the cantilever to be used as resonator. For that purpose, first characterizations of oscillators have been performed to extract the resonant frequencies and the associated quality factors. Then, the resonant frequency shift with DC bias-induced stress was measured. Finally, a magnetostrictive layer of TbFeCo was added on the PZT cantilevers to sense magnetic field based on the ME effect. The resulting resonant frequency shift with external applied magnetic field was characterized with a typical sensitivity of 10’s of µT.

Structural Health Monitoring is a useful tool for reducing maintenance costs and improving the life and performance of engineering structures. Impedance-Based SHM utilizes the coupled electromechanical behavior of piezoelectric materials to detect adverse changes and material and mechanical failures of structures. Environmental variables such as temperature present a challenge to assessing the veracity of damage detected through statistical modeling of impedance signals. An effective frequency shift method was developed to compensate impedance measurements for changes resulting from environmental temperature fluctuations. This thesis investigates how the accuracy of this method can be improved and be applied to a 100oF range of temperatures. Building up the idea of eliminating temperature effects from impedance measurements, this thesis investigates the possibility of using statistical moments to create a temperature independent impedance baseline. / Master of Science

Piezoelectric materials in the forms of both bulk and thin-film have been widely used as actuators and sensors due to their electromechanical coupling. The characterization of piezoelectric materials plays an important role in determining device performance and reliability. Instrumented indentation is a promising method for probing mechanical as well as electrical properties of piezoelectric materials. The use of instrumented indentation to characterize the properties of piezoelectric materials requires analytical relations. Finite element methods are used to analyze the indentation of piezoelectric materials under different mechanical and electrical boundary conditions. For indentation of a piezoelectric half space, a three-dimensional finite element model is used due to the anisotropy and geometric nonlinearity. The analysis is focused on the effect of angle between poling direction and indentation-loading direction on indentation responses. For the indentation by a flat-ended cylindrical indenter, both insulating indenter and conducting indenter without a prescribed electric potential are considered. The results reveal that both the indentation load and the magnitude of the indentation-induced potential at the contact center increase linearly with the indentation depth. For the indentation by an insulating Berkovich indenter, both frictionless and frictional contact between the indenter and indented surface are considered. The results show the indentation load is proportional to the square of the indentation depth, while the indentation-induced potential at the contact center is proportional to the indentation depth. Spherical indentation of piezoelectric thin films is analyzed in an axisymmetric finite element model, in which the poling direction is anti-parallel to the indentation-loading direction. Six different combinations of electrical boundary conditions are considered for a thin film perfectly bonded to a rigid substrate under the condition of the contact radius being much larger than the film thickness. The indentation load is found to be proportional to the square of the indentation depth. To analyze the decohesion problem between a piezoelectric film and an elastic substrate, a traction-separation law is used to control the interfacial behavior between a thin film and an electrically grounded elastic substrate. The discontinuous responses at the initiation of interfacial decohesion are found to depend on interface and substrate properties.

Cette thèse décrit le développement d'actionneurs piézoélectriques miniaturisés pour le contrôle actif d'écoulement à haute vitesse. L'objectif est de retarder la transition laminaire turbulente par le contrôle actif des ondes de Tollmien-Schlichting par introduction d'ondes artificielles à phase inversée. Le premier concept étudié dans cette thèse est un actionneur amplifié mécaniquement avec une structure de type levier élastique situé au-dessus d'une céramique piézoélectrique. Les avantages de cet actionneur sont le contrôle direct, la fonction de transfert linéaire, et le temps de réponse très rapide, ce qui facilite l'intégration dans un système asservi. Le deuxième concept est basé sur l'utilisation d'une membrane conique actionnée par un anneau piézoélectrique dans un mode propre axisymétrique. La géométrie conique focalise les ondes générées par l'anneau piézoélectrique vers le centre ou les amplitudes sont le plus importantes. Pour le control des ondes de Tollmien-Schlichting, la modulation d'amplitude est appliquée pour atteindre une gamme de fréquence large ou la fréquence porteuse est délivrée par les modes propres. Cet actionneur à l'avantage d'utiliser une membrane robuste fermée et une intégration simple. L'effet des actionneurs sur l'écoulement a été mesuré avec des capteurs film chaud dans une soufflerie en boucle ouverte. Pour les dimensions des actionneurs adaptés sur l'écoulement, l'effet désiré pour le contrôle actif de la transition a été observé. Enfin, il a été démontré que la modulation d'amplitude est une alternative intéressante si la fréquence porteuse est sélectionnée de manière optimale pour qu'elle n'agisse pas sur l'écoulement (> 40kHz).

Esta dissertação apresenta uma análise numérica do controle de vibrações estruturais através de cerâmicas piezoelétricas em extensão e em cisalhamento conectadas a circuitos ativo-passivos compostos por resistência, indutância e fonte de tensão. Para tal, um modelo de elementos finitos de vigas sanduíche com três camadas elásticas e/ou piezoelétricas foi desenvolvido. Realizou-se também uma modelagem dos componentes do circuito elétrico e seu acoplamento à estrutura gerando assim uma equação de movimento acoplada para a estrutura com elementos piezoelétricos conectados aos circuitos elétricos. Uma análise harmônica das equações obtidas foi realizada para se obter uma avaliação preliminar dos efeitos causados pelos componentes elétricos do circuito na estrutura. Observou-se que os elementos passivos do circuito, resistência e indutância, tem não somente um efeito de absorvedor dinâmico de vibrações mas, também, promovem uma amplificação da autoridade de controle no caso de se atuar através da fonte de tensão. Usando a metodologia tradicional de projeto de absorvedores dinâmicos de vibrações, derivou-se expressões para os valores de resistência e indutância de modo a maximizar o desempenho passivo do sistema. Uma análise numérica do desempenho na redução das amplitudes de vibração em um viga engastada-livre com uma cerâmica piezoelétrica em extensão ou cisalhamento foi realizada mostrando bons resultados. Em seguida, uma análise da autoridade de controle para estas estruturas foi realizada visando a implementação de um controle híbrido ativo-passivo. A parcela ativa do controle foi obtida usando-se uma estratégia de controle por retroalimentação ótima do tipo linear quadratic regulator para calcular a tensão aplicada ao circuito. Uma comparação entre os resultados mostra que o controle híbrido ativo-passivo é sempre superior aos controles puramente ativos ou passivo para os dois casos estudados, com cerâmicas piezoelétricas em extensão e cisalhamento. / This work presents a numerical analysis of the structural vibration control using piezoelectric materials in extension and shear mode connected to active-passive electric circuits composed of the resistance, inductance and voltage source. For that, a finite element model for sandwich beams with three elastic or piezoelectric layers was developed. A modeling of the electric circuit dynamics and its coupling to the structure with piezoelectric elements was also done. A harmonic analysis of the resulting equations was performed to yield a preliminary evaluation of the effects caused by the electric circuit components on the structure. It was observed that the passive circuit components not only lead to a dynamic vibration absorber effect but also to an amplification of the control authority in case of actuation using the voltage source. Using the standard methodology for the design of dynamic vibration absorbers, expressions were derived for the resistance and inductance values that optimize the passive vibration control performance of the system. A numerical analysis of the passive vibration control was performed for cantilever beams with extension and shear piezoelectric ceramics showing satisfactory results. Then, an analysis of the control authority was carried out for the same structures aiming at an active-passive vibration control. The active control was achieved using a linear quadratic regulator optimal feedback strategy to evaluate the voltage applied to the circuit. A comparison between the obtained results show that hybrid active-passive control is always superior to the purely active or purely passive control for both cases studied, with extension and shear piezoelectric ceramics.

A utilização de materiais piezoelétricos, na função de sensores e atuadores distribuídos, para o controle e monitoramento de vibrações estruturais tem um enorme potencial de aplicação nas indústrias aeronáutica, aeroespacial, automobilística e eletroeletrônica. O uso de sensores piezoelétricos integrados para monitoramento de integridade estrutural (ou detecção de falhas), em particular, tem evoluído bastante na última década. Por conseguinte, o número de técnicas utilizadas para esse fim são as mais variadas possíveis. Dentre elas estão às técnicas que avaliam o efeito dos danos em baixa freqüência usando parâmetros modais, em especial freqüências naturais e modos, ou em média-alta freqüência medindo-se a impedância/admitância eletromecânica. O objetivo dessa dissertação é desenvolver, com auxílio de um modelo 2D ANSYS em elementos finitos, uma análise de diferentes técnicas para detecção da posição e tamanho da delaminação em estruturas compósitas utilizando pastilhas piezoelétricas. Várias métricas e técnicas são avaliadas em termos de sua capacidade de identificar, com relativa acurácia, a presença, localização e severidade do dano. Os resultados mostram que ambas as técnicas modal e baseada na impedância são capazes de identificar a presença de danos do tipo delaminação, desde que as pastilhas piezoelétricas estejam próximas do dano. Também é mostrado que as técnicas baseadas na impedância parecem ser mais eficientes do que as modais para detecção da posição e tamanho da delaminação. / The use of piezoelectric materials in the function of distributed sensors and actuators for the control and monitoring of structural vibrations has enormous potential for application in the aeronautical, aerospace, automotive and electronics. The use of integrated piezoelectric sensors for structural health monitoring (or damage detection), in particular, has evolved greatly over the last decade. Consequently, the numbers of techniques used for this purpose are highly diverse. Among them are techniques that evaluate the effect of damages on low frequency modal parameters, especially natural frequencies and mode shapes, or on medium-high frequency measurements of electromechanical impedance/admittance. The objective of this dissertation is to perform, with the aid of a 2D ANSYS finite element model, an analysis of different techniques for the detection of position and size of a delamination in a composite structure using piezoelectric patches. Several metrics and techniques are evaluated in terms of their capability of identifying, with relative accuracy, the presence, location and severity of the damage. Results show that both modal and impedance-based techniques are able to identify the presence of the delamination-type damages, provided the piezoelectric patches are close enough to the damage. It is also shown that impedance-based techniques seem more effective than modal ones for the detection of delamination position and size.

Este trabalho apresenta uma modelagem de placas laminadas com sensores/atuadores piezoelétricos integrados e conectados a circuitos tipo shunt resistivo-indutivo (RL). O modelo faz uso de duas teorias de placa, FSDT (First-order Shear Deformatíon Theory) e TSDT (Third-order Shear Deformatíon Theory), e considera a possibilidade de inserção de pastilhas piezoelétricas trabalhando nos modos de extensão e cisalhamento. Um modelo de elementos finitos para placas laminadas piezoelétricas, em camada equivalente (Equivalent Single Layer), foi desenvolvido usando como graus de liberdade os deslocamentos mecânicos generalizados e a carga elétrica gerada nos circuitos acoplados. Após, uma implementação computacional foi realizada e validada através de comparações com resultados encontrados na literatura. Então, foram realizados estudos para configurações de placa laminada com diferentes quantidades de pastilhas piezoelétricas através de uma análise paramétrica para obtenção das posições de maior acoplamento entre pastilhas e estrutura para os primeiros modos de vibração da placa. Estes resultados possibilitaram a otimização da eficiência do acoplamento eletromecânico através da distribuição das pastilhas piezoelétricas para uma placa com maior quantidade de pastilhas bem como a comparação dos resultados obtidos entre as duas teorias utilizadas. / This work presents the modeling of laminate plates with embedded piezoelectric sensors and actuators connected to resistive-inductive (RL) shunt circuits. The model considers two plate theories, FSDT (First-order Shear Deformation Theory) and TSDT (Third-order Shear Deformation Theory) and allows embedded piezoelectric patches in extension and thickness-shear modes. A finite element model for piezoelectric laminate plates, using equivalent single layer (ESL), was developed considering the generalized mechanical displacements and the electric charges induced in the coupled electric circuits as degrees of freedom. Then, the model was implemented and validated by means of comparisons with results found in the literature. Thereafter, some laminate plate configurations with different numbers of piezoelectric patches were studied through a parametric analysis to obtain the positions that maximize the electromechanical coupling between patches and structure for the first vibration modes. These results allowed the optimization of the electromechanical coupling efficiency through piezoelectric patches distribution for a plate with a larger number of patches and the comparison between the results obtained with the two plate theories considered.

Les matériaux actifs, tels que les matériaux piézoélectriques et électrostrictifs, sont couramment utilisés dans la conception de dispositifs exploitant leurs propriétés respectives. La propriété principale de ces matériaux réside dans le fort couplage entre les comportements électrique et mécanique (piézoélectricité). Dans la majorité des cas, ces matériaux sont utilisés séparément. L’utilisation combinée de ces matériaux permet la réalisation de dispositifs innovants basés sur l’effet électrostrictifs: l’apparition d’une polarisation électrique induite par une contrainte mécanique et réciproquement l’apparition d’une déformation mécanique sous l’action d’un champ électrique. Les applications « support » concernent les capteurs et les actionneurs. L’étude de ce couplage passe par la caractérisation de ces matériaux, puis par la mise en place de modèles décrivant finement leurs comportements et enfin par le développement d’outils pour la conception. L’objectif de la thèse est de remplacer le matériau céramique, rigide et à faible déformation, par un film polymère nanocomposite électroactifs, présentant des grandes déformations et forces d'actionnement sous champ électrique modéré grâce à l'incorporation dans la matrice polymère de micro et nano-objets (charge) conducteurs ou semi-conducteurs. De plus, pour des applications plus spécifiques de la récupération d’énergie, la charge du film polymère par des micro et nano-objets conducteurs sera également étudiée. Idéalement, il serait très intéressant de réaliser un matériau multifonctionnel, sensible à la fois à une stimulation mécanique (propriétés de détection et/ou de récupération d’énergie par couplage électromécanique). / In the last decades, direct energy conversion devices for medium and low grades waste heat have received significant attention due to the necessity to develop more energy efficient engineering systems. A great deal of research has in recent years been carried out on harvesting energy using piezoelectric, electrostatic, electromagnetic , and thermoelectric ,transduction, with the aim of harvesting enough energy to enable data transmission. For this purpose, piezoelectric elements have been extensively used in the past; however they present high rigidity and limited mechanical strain abilities as well as delicate manufacturing process for complex shapes, making them unsuitable in many applications. Thus, recent trends in both industrial and research fields have focused on electrostrictive polymers for electromechanical energy conversion. This interest is explained by many advantages such as high productivity, flexibility, and processability. Hence, electrostrictive polymer films are much more suitable for energy harvesting devices requiring high flexibilities, such as systems in smart textiles and mobile or autonomous devices. Electrostrictive polymers can also be obtained in many different shapes and over large surfaces. . In the last years, electrostrictive polymers have been investigated as electroactive materials for energy harvesting. However for scavenging energy a static field is necessary, since this material is isotope, there is no permanent polarization compare to piezoelectric material. A solution for avoid this problem; concern the hybridization of electrostrictive polymer with electret. Finally, the implementation of electrostrictive materials is much simpler for small-scale systems (MEMS). Hence, several studies have analyzed the energy conversion performance of electrostrictive polymers, both in terms of actuation and energy harvesting.