This study examines the use of embedded shape memory alloy (SMA)actuators for adaptive control of the themomechanical response of composite structures. Control of static and dynamic responses are demonstrated including thermal buckling, thermal post-buckling, vibration, sonic fatigue, and acoustic transmission. A thermomechanical model is presented for analyzing such shape memory alloy hybrid composite (SMAHC) structures exposed to thermal and mechanical loads. Also presented are (1) fabrication procedures for SMAHC specimens, (2) characterization of the constituent materials for model quantification, (3) development of the test apparatus for conducting static and dynamic experiments on specimens with and without SMA, (4) discussion of the experimental results, and (5) validation of the analytical and numerical tools developed in the study. The constitutive model developed to describe the mechanics of a SMAHC lamina captures the material nonlinearity with temperature of the SMA and matrix material if necessary. It is in a form that is amenable to commercial finite element (FE) code implementation. The model is valid for constrained, restrained, or free recovery configurations with appropriate measurements of fundamental engineering properties. This constitutive model is used along with classical lamination theory and the FE method to formulate the equations of motion for panel-type structures subjected to steady-state thermal and dynamic mechanical loads. Mechanical loads that are considered include acoustic pressure, inertial (base acceleration), and concentrated forces. Four solution types are developed from the governing equations including thermal buckling, thermal post-buckling, dynamic response, and acoustic transmission/radiation. These solution procedures are compared with closed-form and/or other known solutions to benchmark the numerical tools developed in this study. Practical solutions for overcoming fabrication issues and obtaining repeatable specimens are demonstrated. Results from characterization of the SMA constituent are highlighted with regard to their impact on thermomechanical modeling. Results from static and dynamic tests on a SMAHC beam specimen are presented, which demonstrate the enormous control authority of the SMA actuators. Excellent agreement is achieved between the predicted and measured responses including thermal buckling, thermal post-buckling, and dynamic response due to inertial loading. The validated model and thermomechanical analysis tools are used to demonstrate a variety of static and dynamic response behaviors associated with SMAHC structures. Topics of discussion include the fundamental mechanics of SMAHC structures, control of static (thermal buckling and post-buckling) and dynamic responses (vibration, sonic fatigue, and acoustic transmission), and SMAHC design considerations for these applications. The dynamic response performance of a SMAHC panel specimen is compared to conventional response abatement approaches. SMAHCs are shown to have significant advantages for vibration, sonic fatigue, and noise control. / Ph. D.

Este trabalho é dedicado ao estudo do comportamento a longo prazo de uma equação de placas extensíveis acoplada a uma equação de calor do tipo hiperbólico. O problema corresponde a um modelo de termo-elasticidade baseado em teorias de calor do tipo não-Fourier. Considerando que efeitos de inércia de rotação estão presentes no modelo, mostramos que o efeito dissipativo do calor e suficiente para estabilizar exponencialmente o sistema, sem dissipações adicionais. Além disso, provamos que o sistema possui um atrator global de dimensão fractal finita e também atratores exponenciais. Nossos resultados generalizam e complementam diversos trabalhos existentes / This work is concerned with long-time dynamics of solutions of extensible plate equations with thermal memory. It corresponds to a model of thermoelasticity based on a theory of non-Fourier heat flux. By considering the case where rotational inertia is present we show that the thermal dissipation is sufficient to stabilize the system exponentially and guarantee the existence of a finite-dimensional global attractor. In addition the existence of an exponential attractor and some further properties are also considered. Our results complements several existing results

Οι κατασκευές των περισσοτέρων τεχνολογικών εφαρμογών υπόκεινται σε σύνθετες θερμικές καταπονήσεις. Παράλληλα, η επεξεργασία σύγχρονων υλικών συνήθως συνδέεται με ειδικές θερμικές κατεργασίες. Η πολυπλοκότητα στη γεωμετρία των κατασκευών αυτών σε συνδυασμό με τις απότομες μεταβολές της θερμοκρασίας και γενικότερα της επιβαλλόμενης θερμικής καταπόνησης, συχνά οδηγεί στη λύση της συνέχειας των υλικών μέσω της δημιουργίας ρωγμών η οποία μειώνει τα επίπεδα αξιοπιστίας και παράλληλα αυξάνει δραματικά το κόστος συντήρησης και παραγωγής τους. Οι θερμικές φορτίσεις των ρηγματωμένων κατασκευών οι οποίες συνδέονται σχεδόν πάντα με απορρόφηση θερμότητας και επομένως ταυτόχρονη διαστολή των υλικών, οδηγούν στο λεγόμενο «κλείσιμο» της ρωγμής κατά το οποίο οι επιφάνειες της ρωγμής έρχονται τμηματικά ή και εξολοκλήρου σε επαφή δηλαδή συμβάλλουν. Εξαιτίας της πολυπλοκότητας και της μη γραμμικής φύσης του προβλήματος της επαφής, o χαρακτηρισμός της θερμικής θραύσης, υπό την παρουσία φαινομένων συμβολής των επιφανειών της, δεν έχει διερευνηθεί διεξοδικά στη βιβλιογραφία. Η επικρατούσα παραδοχή, ότι δηλαδή η ρωγμή παραμένει εντελώς ανοιχτή κατά τη θερμική φόρτιση, οδηγεί σε εσφαλμένα αποτελέσματα και επομένως δεν έχει πρακτική αξία στον κατασκευαστικό σχεδιασμό. Για το λόγο αυτό, η ανάπτυξη ενός αξιόπιστου και οικονομικού από απόψεως υπολογιστικής ισχύος αριθμητικού εργαλείου για την αντιμετώπιση τέτοιων προβλημάτων είναι αναγκαία. Η αριθμητική προσομοίωση και ο χαρακτηρισμός, μέσω της μεθόδου των συνοριακών στοιχείων, της θερμικής θραύσης η οποία επηρεάζεται από το φαινόμενο της επαφής των επιφανειών της ρωγμής είναι ο σκοπός της παρούσας διατριβής. / The structures of most technological applications are subject to complicate thermal loadings. Additionally, the processing of modern materials is usually related with special thermal treatments. The complex geometry of these structures in combination with the rabid changes of the temperature and generally with the imposed thermal load, often leads to the dissolution of continuity of the materials via the creation of cracks, fact that decreases the reliability standards and simultaneously increases dramatically the maintenance and manufacturing cost. The thermal loadings of the cracked structures which are associated with heat absorption and consequently simultaneous dilation of materials, lead to the well known crack closure phenomenon in which the surfaces of the crack come partially or even entirely into contact i.e. they interfering. Due to the complexity and non linear nature of the contact problem, the fracture characterization under crack closure phenomena has not been investigated thoroughly in the literature. The prevalent assumption, that the crack remains completely open during thermal loading, leads to inaccurate results and thus is not of practical importance in structural design. Therefore, the development of a reliable numerical tool offering low computational cost is required for the treatment of such problems. The numerical simulation and characterization, through the boundary element method, of thermal fracture that is influenced by crack closure phenomenon is the aim of the present thesis.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T11:45:07Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T11:45:07Z (GMT). No. of bitstreams: 0 / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T11:45:07Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T11:45:07Z (GMT). No. of bitstreams: 0 / O comportamento dos materiais cerâmicos quanto à resistência ao choque térmico é um tema de grande interesse, devido às aplicações em que a confiabilidade frente a variações bruscas de temperatura é necessária. Neste trabalho foi estudado como a variação na proporção dos aditivos Y2O3:Al2O3 e diferentes parâmetros no processamento do carbeto de silício sinterizado via fase líquida como, tipo e temperatura de sinterização, podem influenciar na resistência ao choque térmico deste material. As misturas foram preparadas com 90%SiC+10%Y2O3:Al2O3 em mol, variando as proporções molares dos óxidos entre 2:1 e 1:4, com e sem prévia reação dos aditivos. As misturas foram compactadas e sinterizadas em forno resistivo de grafite nas temperaturas de 1750°C, 1850°C e 1950°C e, por prensagem a quente, a 1750°C e 1850°C, sendo avaliadas quanto à densificação. Após análise dos resultados preliminares, a sinterização sem pressão e as misturas com proporções 1:3 e 1:4 de Y2O3:Al2O3 previamente reagidos foram selecionadas para o estudo da resistência ao choque térmico. Os ciclos térmicos foram realizados com aquecimento em temperaturas de 600°C, 750°C e 900°C e resfriamento brusco em água em temperatura ambiente. A avaliação das amostras quanto à resistência ao choque térmico, feita por meio da determinação de módulo de elasticidade, porosidade, resistência à flexão e por análise microestrutural de trincas. As amostras sinterizadas na temperatura de 1950°C são as que apresentam o melhor desempenho em relação à resistência ao choque térmico, enquanto a variação na proporção Y2O3:Al2O3 de 1:3 para 1:4 não altera significativamente esta propriedade. Nas condições utilizadas, a temperatura máxima de aplicação do SiC sinterizado via fase líquida deve ser limitada a 750°C, permitindo seu uso como trocadores de calor, rolamentos, mancais de bombas submersas, turbinas a gás e sensor de motores automotivos e aeronáuticos. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Este trabalho é dedicado ao estudo do comportamento a longo prazo de uma equação de placas extensíveis acoplada a uma equação de calor do tipo hiperbólico. O problema corresponde a um modelo de termo-elasticidade baseado em teorias de calor do tipo não-Fourier. Considerando que efeitos de inércia de rotação estão presentes no modelo, mostramos que o efeito dissipativo do calor e suficiente para estabilizar exponencialmente o sistema, sem dissipações adicionais. Além disso, provamos que o sistema possui um atrator global de dimensão fractal finita e também atratores exponenciais. Nossos resultados generalizam e complementam diversos trabalhos existentes / This work is concerned with long-time dynamics of solutions of extensible plate equations with thermal memory. It corresponds to a model of thermoelasticity based on a theory of non-Fourier heat flux. By considering the case where rotational inertia is present we show that the thermal dissipation is sufficient to stabilize the system exponentially and guarantee the existence of a finite-dimensional global attractor. In addition the existence of an exponential attractor and some further properties are also considered. Our results complements several existing results

The generalized radiation conditions at infinity of Sommerfeld-Kupradze type are established in the theory of thermoelasticity of anisotropic bodies. Applying the potential method and the theory of pseudodifferential equations on manifolds the uniqueness and existence theorems of solutions to the basic three-dimensional exterior boundary value problems are proved and representation formulas of solutions by potential type integrals are obtained.

This study is part of an original approach based on quantitative imaging techniques, such as Infrared Thermography, to study the damage under fretting loadings. The main objective was the establishment of new experimental method for a rapid determination of crack initiation conditions under fretting loadings, based on the analysis of the thermal signal. One other objective was the determination of the different heat sources in order to assess a local analysis of the fretting damage. This work underlined the great potential of Infrared Thermography to study this damage. / Cette étude s'inscrit dans une approche originale basée sur des techniques d'imagerie quantitatives comme la thermographie infrarouge pour étudier l'endommagement sous chargement de fretting. Le premier objectif était de développer une méthode de construction rapide de carte de fretting basée sur l'analyse du signale thermique au cours d'essais de fretting. Un deuxième objectif était de déterminer les sources de chaleurs accompagnant le fretting pour une meilleure compréhension des mécanismes d'endommagement. Ce travail a souligné le grand potentiel de la thermographie infrarouge pour l'étude de c'est phénomènes.

Cette thèse est une étude théorique d’un système d’équations de Cahn-Hilliard/Allen-Cahn couplées qui représente un mélange binaire en séparation de phase. Le but principal de l’étude est le comportement asymptotique des solutions en termes d’attracteurs exponentiels/globaux. Pour cette raison, l’existence et l’unicité de la solution sont étudiées tout d’abord. Une des principales applications de ce modèle d’équations est la cristallographie.Dans la première partie de la thèse, on examine le modèle proposé avec des conditions de type Dirichlet sur le bord et une non linéarité régulière de type polynomial : on réussit à trouver un attracteur exponentiel et par conséquence un attracteur global de dimension finie. Une non linéarité singulière de type logarithmique est ensuite prise dans la deuxième partie, cette fonction étant approchée par une suite de fonctions régulières et l’existence d’un attracteur global est démontrée sous des conditions au bord de type Dirichlet.Enfin, dans la dernière partie, le système est couplé avec une équation pour la température: suivant la loi de Fourrier premièrement, puis la loi de type III de la thermo-élasticité. Dans les deux cas, la dynamique de l’équation est étudiée et un attracteur exponentiel est trouvé malgré la difficulté créée par l’équation hyperbolique dans le deuxième cas. / This thesis is a theoretical study of a coupled system of equations of Cahn-Hilliard and Allen-Cahn that represents phase separation of binary alloys. The main goal of this study is to investigate the asymptotic behavior of the solution in terms of exponential/global attractors. For this reason, the existence and unicity of the solution are first studied. One of the most important applications of this proposed model of equations is crystallography. In the first part of the thesis, the system is studied with boundary conditions of Dirichlet type and a regular nonlinearity (a polynomial). There, we prove the existence of an exponential attractor that leads to the existence of a global attractor of finite dimension. Then, a singular nonlinearity (a logarithmic potential) is considered in the second part. This function is approximated by a sequence of regular ones and a global attractor is found.At the end, the system of equations is coupled with temperature: with the Fourrier law in the first case, then with the type III law (in the context of thermoelasticity) in the second case. The dynamics of the equations are studied and the existence of an exponential attractor is obtained.

Die Temperaturverhältnisse beim Ziehen und Wärmebehandeln von Draht werden mit mathematisch-analytischen Methoden auf der Grundlage der FOURIERschen Wärmeleitungsgleichung eingehend untersucht. Insbesondere wird unter den spezifischen Wärmeübergangsbedingungen zwischen Draht und Ziehdüse sowie zwischen Draht und Ziehtrommel deren thermische Wechselwirkung analysiert. Ein Näherungsverfahren zur Berechnung der Drahttemperaturen in Zugfolgen unter Berücksichtigung des Ziehdüseneinflusses wird angegeben und mit einem Beispiel zum Nassziehen stark verzinkten Stahldrahts illustriert. Aus geschwindigkeitsabhängig gemessenen Änderungen des Drahtdurchmessers werden unter thermoelastischer Ziehringdurchmesserkorrektur Schmierfilmdicken bestimmt. Diffusionsgleichungen werden analysiert und ein Zusammenhang zur Reaktionskinetik wird hergestellt. Ein neues reaktionskinetisches Werkstoffmodell, das insbesondere auch im Falle stärker anisothermer Verhältnisse, also bei Kurzzeitwärmebehandlung anwendbar ist, wird vorgestellt.