Magnetic shape memory alloys are active materials which deform under the application of a magnetic field or an external stress. Due to their internal friction, recognizable from the strain-stress hysteresis, this new material technology allows the design of multistable actuators. This paper describes and characterizes an innovative airflow control valve whose aperture is proportional to the deformation of the active material and thus controllable by the input voltage. The multistability of the material is partially exploited within an airflow control loop to reduce the energy losses of the valve when a specific airflow value must be hold.

The recent advancements in electronics and the advents of small scaled instruments has increased the attachment of life and functionality of devices to electrical power sources but at the same time granted the engineers and companies the ability to use smaller sources of power and batteries. Therefore, many scientists have tried to come up with new solutions for a power alternatives. Piezoelectric is a promising material which can readily produce continuous electric power from mechanical inputs. However, their power output is dependent upon several factors such as, system natural frequency, their position in the system, the direction of vibration and many other internal and external factors. In this research the working bandwidth of the system is increased through utilizing of two different piezoelectric beam in different directions. The dependency of output power with respect to rotation angle and also the frequency shift due to the rotation angle is studied.

No description available.

Stimuli-responsive polymers have aroused enormous interest in fundamental and applied polymer research in the last decades as they exhibit a spontaneous, defined, and reversible adaptation of their physicochemical properties towards environmental conditions. Their switching behavior can be triggered by external physical, chemical or biological stimuli, such as a change in temperature, pH value or the presence of certain enzymes. These materials, often referred to as 'smart' polymers, offer a huge potential for novel (bio-medical) sensors, actuators like artificial muscles and flexible robotics, drug-delivery systems, tissue engineering, and switchable catalysts. For almost all of these applications, responsive polymer chains need to be attached to interfaces such as particles or flat substrates or assembled into constrained architectures, like branched structures, micelles, or cross-linked networks. Although there are strong indications that the assembly of responsive polymers largely impacts their adaptiveness, the underlying structure–property relationships are still poorly understood. Besides the challenge of synthesizing constrained polymeric architectures precisely, the analytical characterization of their responsiveness is challenging too. Despite these obstacles, fundamental scientific characterization is an important tool for making smart polymers accessible for real-life applications. To contribute to this, the overarching objective of this work is to synthesize, characterize, adapt, and control the switching characteristics of a multi-responsive polymeric coating. The responsive polyelectrolyte, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), is covalently anchored to flat silicon substrates or gold nanoparticles via three newly developed, distinct grafting-to approaches in a controlled manner. In particular, the thermo-responsive behavior of the nanometer-thick polymer layer in aqueous solutions is being investigated using complementary in-situ techniques such as spectroscopic ellipsometry, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR spectroscopy) and atomic force microscopy (AFM). Herein, the polymer coating reveals an extraordinary responsiveness, exhibiting two distinct modes of thermo-responses, namely a lower critical solution temperature (LCST) and a multivalent ion induced upper critical solution temperature (UCST). The temperature-dependent switching characteristics of the coating, in terms of switching amplitude, temperature, and sharpness, can be tailored by secondary triggers, such as a change in the pH value, ionic strength, or type of counterions present. In addition to characterizing the interactions between the polymer layer and the aqueous environment on a molecular level, the remarkable impact of thermo-responsiveness on the surface patterning of the coating is exposed. A nanostructured surface of pinned PDMAEMA micelles of tunable size during the UCST transition is opposing a homogenous surface detected both below and above the LCST. Furthermore, the synthetic control over the grafting density of the polymer chains reveals the ambiguous influence of steric constraint on both the LCST and induced UCST transition of the coating for the first time. In summary, the in-depth physicochemical characterization of a multi-responsive polymer coating in this work marks a comprehensive contribution to fundamental advances in constrained responsive polymers and their future applications in tailoring surface properties. / Stimuli-responsive Polymere haben in den letzten Jahrzehnten ein enormes Interesse in der Grundlagen- und angewandten Polymerforschung geweckt, da sie eine spontane, definierte und reversible Anpassung ihrer physikalisch-chemischen Eigenschaften an Umweltbedingungen aufweisen. Ihr Schaltverhalten kann dabei sowohl durch externe physikalische, chemische oder biologische Reize wie zum Beispiel eine Änderung der Temperatur, des pH-Wertes bzw. der Präsenz bestimmter Enzyme, ausgelöst werden. Diese oft als 'intelligente' Polymere bezeichneten Materialien bieten ein großes Potenzial für neuartige (biomedizinische) Sensoren, Aktoren wie künstliche Muskeln und flexible Roboter, Systeme zur Abgabe von Medikamenten, Gewebezüchtung sowie schaltbare Katalysatoren. Für fast alle diese Anwendungen müssen responsive Polymerketten an Grenzflächen wie (Nano-)Partikel oder flache Substrate gebunden bzw. zu sterisch anspruchsvollen Architekturen wie verzweigten Strukturen, polymeren Mizellen oder Netzwerken zusammengefügt werden. Obwohl es deutliche Hinweise darauf gibt, dass die Assemblierung von responsiven Polymeren deren Adaptivität signifikant beeinflusst, sind die zugrunde liegenden Struktur-Eigenschafts-Beziehungen noch wenig bekannt. Neben den hohen Anforderungen der Synthese sterisch eingeschränkter Polymerarchitekturen, ist auch die analytische Charakterisierung ihrer Responsivität anspruchsvoll. Trotz dieser Herausforderungen ist gerade diese grundlegende wissenschaftliche Charakterisierung ein wichtiges Instrument, um intelligente Polymere für reale Anwendungen zugänglich zu machen. Um einen Beitrag dafür zu leisten, ist das übergeordnete Ziel dieser Arbeit die Synthese, Charakterisierung, Anpassung und Regulierung der Schalteigenschaften einer multi-responsiven Polymerbeschichtung. Der responsive Polyelektrolyt, Poly(N,N-dimethylaminoethylmethacrylat) (PDMAEMA), wird über drei neu entwickelte, unterschiedliche Pfropfansätze kontrolliert auf flachen Siliziumsubstraten oder Goldnanopartikeln kovalent verankert. Insbesondere das thermo-responsive Verhalten dieser nur wenigen nanometerdicken Beschichtung wird in wässrigen Lösungen mit komplementären in-situ Techniken wie der spektroskopischen Ellipsometrie, ATR-FTIR (attenuated total reflection Fourier-transform infrared) Spektroskopie sowie AFM (atomic force microscopy) analytisch untersucht. Hierbei zeigt die entwickelte Polymerbeschichtung eine außergewöhnliche Adaptivität bestehend aus zwei unterschiedlichen Arten der Thermoresponsivität, namentlich einer unteren kritischen Entmischungstemperatur (lower critical solution temperature, LCST) und einer durch multivalente Ionen induzierten oberen kritischen Entmischungstemperatur (upper critical solution temperture, UCST). Die Schalteigenschaften der Beschichtung in Bezug auf Schaltamplitude, -temperatur, und Schärfe des Übergangs können durch sekundäre Stimuli, wie eine Änderung des pH-Werts, der Ionenstärke oder der Art der vorhandenen Gegenionen, maßgeschneidert werden. Neben der Charakterisierung der molekularen Wechselwirkungen zwischen Polymerschicht und wässriger Umgebung, wird auch der bemerkenswerte Einfluss der Thermoresponsivität auf die Oberflächenstrukturierung der Beschichtung gezeigt. Eine Nanostrukturierung aus gepinnten PDMAEMA-Mizellen mit einstellbarer Größe während des UCST-Übergangs steht einer homogenen Oberfläche gegenüber, die sowohl unterhalb als auch oberhalb der LCST festgestellt wird. Darüber hinaus zeigt die synthetische Kontrolle der Pfropfdichte der Polymerketten erstmals den ambivalenten Einfluss sterischer Restriktionen sowohl auf den LCST als auch auf den induzierten UCST-Übergang der Beschichtung. Zusammenfassend leistet die tiefgründige physiko-chemische Charakterisierung einer multi-responsiven Polymerbeschichtung in dieser Arbeit einen umfangreichen Beitrag zum grundlegenden Verständnis gepfropfter, responsiver Polymere und ihren künftigen Anwendungen bei der gezielten Anpassung von Oberflächeneigenschaften.

Die Entwicklung neuartiger Hydrogel-basierter Sensorsysteme, die in der Lage sind den Quellgrad eines Hydrogels mittels eines Hall Sensors zu bestimmen, erfordert Gele, die über ein starkes magnetisches Feld verfügen. Die vorliegende Dissertation befasst sich mit der Entwicklung eines Stimuli-responsiven Hydrogels, welches mit einer hohen Konzentration an magnetischen Nanopartikeln beladen ist. Dazu wird ein Temperatur-sensitives Gel basierend auf Poly(N-Isopropylacrylamid) mittels Laponite® XLS vernetzt. Ein solches Nanokomposit-Hydrogel zeigt höhere Quellgrade und bessere mechanische Eigenschaften als Gele, die N,N‘-Methylenbisacrylamid als chemischen Vernetzer nutzen. Reine Chrom(IV)-oxid-, Magnetit-, Cobaltferrit und Strontiumferrit-Partikel werden während der Synthese in das Gel eingebracht. Die Reaktionsgeschwindigkeit wird mittels eines konstanten Argonstroms erhöht, so dass keine Sedimentation stattfindet. Auf diese Weise kann eine homogene Verteilung der Partikel erzielt werden. Die Oberfläche der Partikel wurde weiterhin mit 3 (Trimethoxysilyl)propylmethacrylat beschichtet, um sie in das Polymernetzwerk einzubinden. Der Einfluss unterschiedlicher Beladungen auf die Quellung und mechanischen Eigenschaften der Gele wird untersucht. Zusätzlich wurden Stärke- und Ölsäure-beschichtete Magnetit-Partikel in das Netzwerk eingebracht, um den Effekt stabilisierender Beschichtungen auf das Gel zu untersuchen. Die Hydrogel-Synthese wurde ebenfalls in einem magnetischen Feld durchgeführt, um die magnetischen Nanopartikel dauerhaft im Netzwerk auszurichten. Dies führte zur Bildung großer stabartiger Agglomerate, die sich über die gesamte Länge des Gels erstrecken. Der Einfluss dieser anisotropen Verteilung auf die mechanischen Eigenschaften wurde mittels Kompressionsmessungen untersucht. Weiterhin wurde ein neuartiges Doppelnetzwerk bestehend aus Poly(2-Acrylamido-2-methylpropansulfonsäure) und Poly(N-Isopropylacrylamid) entwickelt. Das Gel zeigt eine hohe mechanische Festigkeit, die mit Poly(2-Acrylamido-2-methylpropansulfonsäure)/Polyacrylamid-DN-Gelen vergleichbar ist und zeigt Stimuli-induzierte Entquellung durch Erhöhung der Temperatur und Ionenkonzentration. Solche Gele wurden außerdem durch in-situ Präzipitation mit Magnetit-Partikeln modifiziert. Der Einfluss auf die mechanischen Eigenschaften wird anhand von Zugversuchen untersucht.:Danksagung I Kurzfassung II Abstract III Abkürzungen und Formelzeichen VI I. Theoretischer Teil 1 1. Einleitung 1 2. Problemstellung und Zielsetzung 2 3. Theorie 4 3.1. Hydrogele 4 3.1.1. Hydrogelsynthese 5 3.1.2. Quelleigenschaften von Hydrogelen 10 3.2. Stimuli-responsive Hydrogele 15 3.2.1. Temperatur- und lösungsmittel-sensitive Hydrogele 16 3.2.2. Ionen- und pH-sensitive Hydrogele 21 3.3. Nanokomposit-Hydrogele 22 3.3.1. Nanokomposit-Hydrogele basierend auf Schichtsilikaten 24 3.3.2. Doppelnetzwerk-Hydrogele 28 3.3.3. Ferrogele 30 II. Synthese und Methoden 34 4. Synthese 34 4.1. Nanosilkat-Hydrogele 35 4.2. Nanosilkat-Ferrogele 35 4.3. Beschichtung von magnetischen Nanopartikeln mit TMSPMA 36 4.4. Ferrogele im Magnetfeld 36 4.5. PAMPS/PAAM-Doppelnetzwerk-Hydrogele 36 4.6. PAMPS/PNIPAM-Doppelnetzwerk-Hydrogele 37 4.7. In-situ-Präzipitation von Magnetit in PAMPS/PNIPAM-DN-Gelen 37 5. Charakterisierungsmethoden 38 5.1. Quellungsmessung 38 5.2. Kompression 38 5.3. Zugversuch 38 5.4. Vibrating Sample Magnetometer 39 5.5. Trübungsmessungen 39 5.6. Thermogravimetrie 39 5.7. Infrarotspektroskopie 40 5.8. Dynamische Lichtstreuung 40 III. Ergebnisse und Diskussion 41 6. Ferrogelsynthese 41 6.1. Modifizierung von Nanosilikat-Gelen mit magnetischen Nanopartikeln 42 6.2. Modifizierung von Nanokomposit-Gelen mit Stärke-beschichteten Fe3O4-Partikeln 46 6.3. Oberflächenmodifizierung magnetischer Nanopartikel mittels TMSPMA 50 6.4. Modifizierung von Nanokomposit-Gelen mit beschichteten Nanopartikeln 52 6.5. Synthese von Ferrogelen im Magnetfeld 52 7. Charakterisierung von Ferrogelen 54 7.1. Quellgrad von Ferrogelen aus dem trockenen Zustand 54 7.2. LCST-Verhalten von Ferrogelen 58 7.3. Mechanische Eigenschaften 62 8. Doppelnetzwerk-Hydrogel-Synthese 69 8.1. PAMPS/PAAM-Doppelnetzwerk-Hydrogele 69 8.2. PAMPS/PNIPAM-Doppelnetzwerk-Hydrogele 70 8.3. Temperatur-responsive Eigenschaften von PAMPS/PNIPAM-DN-Gelen 75 8.4. Einfluss der Ionenstärke auf das Quellverhalten 77 8.5. In-situ Präzipitation von Magnetit in PAMPS/PNIPAM-DN-Gelen 79 IV. Zusammenfassung und Ausblick 82 V. Literaturverzeichnis 86 Lebenslauf 91 Veröffentlichungen 93 Selbstständigkeitserklärung 94 / Developing new hydrogel based sensor systems that can measure the degree of swelling of a gel through the Hall Effect requires hydrogels emitting strong magnetic fields. The PhD thesis presented here focuses on the development of a stimuli-responsive hydrogel containing high concentrations of magnetic nanoparticles. For this purpose, temperature sensitive gels consisting of poly(N isopropylacrylamide) cross-linked with Laponite® XLS are used for their improved mechanical properties and high degree of swelling compared to chemically cross-linked hydrogels using N,N‘ methylenebisacrylamide. Pure chromium(IV) oxide, magnetite, Cobalt ferrite and strontium ferrite particles are added during the synthesis and homogeneously distributed by accelerating the reaction through the use of a constant argon flow. These particles were coated with 3 (trimethoxysilyl)propyl methacrylate to connect them to the polymer network. The effects of various particle loads on the swelling behavior and mechanical properties are investigated. Furthermore magnetite particles coated with starch and oleic acid are introduced into the system to study the effects of stabilizing coatings on the network. The hydrogel synthesis was also performed in a magnetic field to permanently align the magnetic particles in the network. This resulted in large rod-like agglomerations that span the entire length of the hydrogel. Compression measurements were performed to study the effects of a purposefully introduced anisotropic particle distribution. Additionally a new type of double network hydrogel was developed consisting of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) and poly(N-isopropylacrylamide). The gel exhibits tough mechanical properties similar to poly(2-acrylamido-2-methyl-1-propanesulfonic acid)/polyacrylamide DN-gels while showing stimuli-induced deswelling through temperature and ion concentration. Such gels were further modified with magnetite nanoparticles obtained through in-situ precipitation inside the network. The effects of the nanoparticle load on the mechanical properties are studied via tensile testing.:Danksagung I Kurzfassung II Abstract III Abkürzungen und Formelzeichen VI I. Theoretischer Teil 1 1. Einleitung 1 2. Problemstellung und Zielsetzung 2 3. Theorie 4 3.1. Hydrogele 4 3.1.1. Hydrogelsynthese 5 3.1.2. Quelleigenschaften von Hydrogelen 10 3.2. Stimuli-responsive Hydrogele 15 3.2.1. Temperatur- und lösungsmittel-sensitive Hydrogele 16 3.2.2. Ionen- und pH-sensitive Hydrogele 21 3.3. Nanokomposit-Hydrogele 22 3.3.1. Nanokomposit-Hydrogele basierend auf Schichtsilikaten 24 3.3.2. Doppelnetzwerk-Hydrogele 28 3.3.3. Ferrogele 30 II. Synthese und Methoden 34 4. Synthese 34 4.1. Nanosilkat-Hydrogele 35 4.2. Nanosilkat-Ferrogele 35 4.3. Beschichtung von magnetischen Nanopartikeln mit TMSPMA 36 4.4. Ferrogele im Magnetfeld 36 4.5. PAMPS/PAAM-Doppelnetzwerk-Hydrogele 36 4.6. PAMPS/PNIPAM-Doppelnetzwerk-Hydrogele 37 4.7. In-situ-Präzipitation von Magnetit in PAMPS/PNIPAM-DN-Gelen 37 5. Charakterisierungsmethoden 38 5.1. Quellungsmessung 38 5.2. Kompression 38 5.3. Zugversuch 38 5.4. Vibrating Sample Magnetometer 39 5.5. Trübungsmessungen 39 5.6. Thermogravimetrie 39 5.7. Infrarotspektroskopie 40 5.8. Dynamische Lichtstreuung 40 III. Ergebnisse und Diskussion 41 6. Ferrogelsynthese 41 6.1. Modifizierung von Nanosilikat-Gelen mit magnetischen Nanopartikeln 42 6.2. Modifizierung von Nanokomposit-Gelen mit Stärke-beschichteten Fe3O4-Partikeln 46 6.3. Oberflächenmodifizierung magnetischer Nanopartikel mittels TMSPMA 50 6.4. Modifizierung von Nanokomposit-Gelen mit beschichteten Nanopartikeln 52 6.5. Synthese von Ferrogelen im Magnetfeld 52 7. Charakterisierung von Ferrogelen 54 7.1. Quellgrad von Ferrogelen aus dem trockenen Zustand 54 7.2. LCST-Verhalten von Ferrogelen 58 7.3. Mechanische Eigenschaften 62 8. Doppelnetzwerk-Hydrogel-Synthese 69 8.1. PAMPS/PAAM-Doppelnetzwerk-Hydrogele 69 8.2. PAMPS/PNIPAM-Doppelnetzwerk-Hydrogele 70 8.3. Temperatur-responsive Eigenschaften von PAMPS/PNIPAM-DN-Gelen 75 8.4. Einfluss der Ionenstärke auf das Quellverhalten 77 8.5. In-situ Präzipitation von Magnetit in PAMPS/PNIPAM-DN-Gelen 79 IV. Zusammenfassung und Ausblick 82 V. Literaturverzeichnis 86 Lebenslauf 91 Veröffentlichungen 93 Selbstständigkeitserklärung 94

Smart materials are intelligent materials that change their structural, chemical, mechanical, or thermal properties in response to an external stimulus such as heat, light, and magnetic and electric fields. With the increase in usage of smart materials in many sensitive applications, the need for a remote, wireless, efficient, and biologically safe stimulus has become crucial. This dissertation addresses this requirement by using high intensity focused ultrasound (HIFU) as the external trigger. HIFU has a unique capability of maintaining both spatial and temporal control and propagating over long distances with reduced losses, to achieve the desired response of the smart material. Two categories of smart materials are investigated in this research; shape memory polymers (SMPs) and piezoelectric materials. SMPs have the ability to store a temporary shape and returning to their permanent or original shape when subjected to an external trigger. On the other hand, piezoelectric materials have the ability to convert mechanical energy to electrical energy and vice versa. Due to these extraordinary properties, these materials are being used in several industries including biomedical, robotic, noise-control, and aerospace. This work introduces two novel concepts: First, HIFU actuation of SMP-based drug delivery capsules as an alternative way of achieving controlled drug delivery. This concept exploits the pre-determined shape changing capabilities of SMPs under localized HIFU exposure to achieve the desired drug delivery rate. Second, solving the existing challenge of low efficiency by focusing the acoustic energy on piezoelectric receivers to transfer power wirelessly. The fundamental physics underlying these two concepts is explored by developing comprehensive mathematical models that provide an in-depth analysis of individual parameters affecting the HIFU-smart material systems, for the first time in literature. Many physical factors such as acoustic, material and dynamical nonlinearities, acoustic standing waves, and mechanical behavior of materials are explored to increase the developed models' accuracy. These mathematical frameworks are designed with the aim of serving as a basic groundwork for building more complex smart material-based systems under HIFU exposure. / Doctor of Philosophy / Smart materials are a type of intelligent materials that have the ability to respond to external stimuli such as heat, light, and magnetic fields. When these materials respond, they can change their structural, thermodynamical, mechanical or chemical nature. Due to this extraordinary property, smart materials are being used in many applications including biomedical, robotic, space, microelectronics, and automobile industry. However, due to increased sensitivity and need for safety in many applications, a biologically safe, wireless, and efficient trigger is required to actuate these materials. In this dissertation, sound is used as an external trigger to actuate two types of smart materials: shape memory polymers (SMPs) and piezoelectric materials. SMPs have an ability to store a temporary (arbitrarily deformed) shape and return to their permanent shape when exposed to a trigger. In this dissertation, focused sound induced thermal energy acts as a trigger for these polymers. A novel concept of focused ultrasound actuation of SMP-based drug delivery capsules is proposed as a means to solve some of the challenges being faced in the field of controlled drug delivery. Piezoelectric materials have an ability to generate electric power when an external mechanical force is applied and vice versa. In this study, sound pressure waves supply the external force required to produce electric current in piezoelectric disks, as a method for achieving power transfer wirelessly. This study aims to solve the current problem of low efficiency in acoustic power transfer systems by focusing sound waves. This dissertation addresses the fundamental physics of high intensity focused ultrasound actuation of smart materials by developing comprehensive mathematical models and systematic experimental investigations, that have not been performed till now. The developed models enable an in-depth analysis of individual parameters including nonlinear material behavior, acoustic nonlinearity and resonance phenomena that affect the functioning of these smart systems. These mathematical frameworks also serve as groundwork for developing more complex systems.

No description available.

This research undertakes the problem of vibration control of vehicular and structural systems using intelligent materials and controllable devices. Advanced modeling tools validated with experimental test data are developed to help with understanding the fundamentals as well as advanced and novel applications of smart and conventional suspension systems. The project can be divided into two major parts. The first part is focused on development of novel smart suspensions using Magneto-Rheological (MR) fluids in unique configurations in order to improve efficiency, controllability, and safety of today's vehicles. In this part of the research, attention is paid to fundamentals as well as advanced applications of MR technology. Extensive rheological studies, both theoretical and experimental, are performed to understand the basic behaviors of MR fluids as complex non-Newtonian fluids in novel applications. Using the knowledge obtained from fundamental studies of MR fluids, unique application concepts are investigated that lead to design, development, and experimental testing of two new classes of smart devices: MR Hybrid Dampers and MR Squeeze Mounts. Multiple generations of these devices are built and tested as proof of concept prototypes. Advanced physics-based mathematical models are developed for these devices. Experimental test data are used to validate the models and great agreement is obtained. The models are used as design tools at preliminary as well as detailed design stages of device development. The significant finding in this part of the research is that MR fluids can deliver a much larger window of controllable force in squeeze mode compared to shear and valve modes which can be used in various applications. The second part of the research is devoted to the development of innovative design tools for suspension design and tuning. Various components of suspension systems are studied and modeled using a new physics-based modeling approach. The component of main interest is the shim stack assembly in hydraulic dampers which is modeled using energy and variational methods. A major finding is that the shims should be modeled individually in order to represent the sliding effects properly when the shim stack is deflected. Next, the individual component models are integrated into a full suspension model. This model is then used as a tool for suspension design, synthesis, and tuning. Using this design tool, suspension engineers in manufacturing companies and other industrial sections can easily perform parametric studies without the need to carry out time consuming and expensive field and laboratory tests. / Ph. D.

In this thesis, the thermomechanical approach with internal variables has been thoroughly analyzed. This approach is based on the combination of thermodynamic principles and continuum mechanics. Therefore it reflects the physical essence of constitutive behavior of materials. Based on this approach, a one-dimensional constitutive model for the two-way shape memory effect and a one-dimensional constitutive model for piezoceramics have been developed, respectively. In modeling the two-way shape memory effect, a residual stress σ_re is introduced as a controlling parameter for the two-way shape memory effect. A further refinement of the transformation kinetics expression for two-way shape memory is derived. It is demonstrated that the material parameters required by this model can be calculated or measured using a standard materials testing apparatus. A numerical study is conducted and the effectiveness of this model is verified. In the constitutive modeling of piezoceramics, a new internal state variable is introduced to relate the macroscopic behavior of a piezoceramic with its micro-properties. A phenomenological formulation of polarization reversal is proposed, and then a fully-coupled thermo-electro-mechanical model is developed. It is shown that the theory developed can describe the electromechanical behavior of piezoceramics well. / Master of Science

O presente trabalho visa o desenvolvimento de uma formulação de um elemento finito de casca com capacidade de prever o comportamento de materiais compósitos inteligentes. Além disso, tem-se a implementação da referida formulação junto ao pacote comercial de elementos finitos Abaqus™, através de sub-rotinas em Fortran via sua ferramenta UEL (User Element). De posse da formulação implementada, realiza-se a avaliação de suas potencialidades e limitações através de estudos de casos. Para selecionar de forma criteriosa a formulação a ser avaliada, executa-se, inicialmente, uma revisão bibliográfica aprofundada sobre trabalhos relevantes na área. Posteriormente apresenta-se a fundamentação teórica da formulação selecionada, bem como uma discussão acerca dos diferentes modelos matemáticos existentes para piezeletricidade linear. Há também uma descrição sobre modelos de casca e do comportamento mecânico de materiais laminados. Além disso, tem-se que as particularidades existentes devido ao acoplamento piezoelétrico e a utilização da ferramenta UEL são discutidas. A metodologia utilizada no trabalho é abordada, evidenciando-se as diferentes etapas empregadas. Por fim, sete estudos de casos são investigados, comparando os resultados providos pelo elemento implementado via UEL com resultados da literatura, bem como, com resultados de experimentos realizados pelo Grupo de Estruturas Aeronáuticas da EESC/USP. Concluindo o trabalho, perspectivas futuras de novos projetos de pesquisas, fruto do presente trabalho, são apresentadas. Por fim, com base na análise dos resultados, conclui-se que a formulação proposta é capaz de simular o comportamento de estruturas fabricadas a partir de materiais compósitos inteligentes. No entanto, trabalhos futuros devem ser realizados com o intuito de melhorar a precisão dos resultados obtidos via UEL, sem gerar um elevado custo computacional. / The present work aims at the development of a shell finite element formulation in order to simulate the behavior of smart composite materials. Furthermore, the referred formulation is implemented within the commercial finite element package Abaqus™ by using Fortran subroutines through its UEL (User Element) tool. Based on the implemented formulation, case studies are used to evaluate its potentialities and limitations. A deep review of works in the area is carried out in order to perform a careful selection of the finite element formulation, which is implemented. After that, the theory for the selected formulation is presented, as well as a discussion of the different existing mathematical models for linear piezoelectricity. Also, a description of the mechanical behavior of laminated shells is shown. Besides, the particularities of the piezoelectric coupling and its implementations by using UEL tool are discussed. The used methodology is addressed, detailing its phases. Finally, seven case studies are investigated, comparing results provided by simulations by using the implemented element with results found in the literature and experimental results from experiments performed by the Aeronautical Structures Group of the EESC/USP. In conclusion, based on the analysis of the aforementioned results, it is established that the proposed formulation is capable of simulating the behavior of smart composite structures. However, future works should be introduced to enhance the precision of the solutions obtained through the UEL tool, without increasing the inherent computational cost.