Current research efforts have focused on the synthesis of novel, segmented, cross-linked networks and thermoplastics for emerging technologies. Tailoring macromolecular structures for improved mechanical performance can be accomplished through a variety of synthetic strategies using step-growth polymerization. The synthesis and characterization of novel Michael addition networks, ionene families, and ion-containing polyurethanes are described, with the underlying theme of fundamentally investigating the structure-property relationships of novel, segmented macromolecular architectures. In addition, it was discovered that both covalent and electrostatic crosslinking play an important role in the mechanical properties of all types of polymers described herein. Novel cross-linked networks were synthesized using quantitative base-catalyzed Michael chemistry with acetoacetate and acrylate functionalities. These novel synthetic strategies offer unique thermo-mechanical performance due to the formation of a multiphase morphology. In order to fundamentally elucidate the factors that influence the kinetics of the Michael addition reaction a detailed analyses of model compounds were conducted in the presence of an in-situ IR spectrometer to optimize reaction conditions using statistical design of experiments. Networks were then prepared based on these optimized conditions. The mechanical performance was evaluated as a function of molecular weight between crosslink points. Furthermore, the incorporation of hydrogen bonding within the monomer structure enhanced mechanical performance. The changes in morphological, thermal, and mechanical properties evaluated using dynamic mechanical analysis (DMA) and tensile behavior are described. In addition, the use of preformed urethane segments provides a safer method for incorporating hydrogen bonding functional groups into macromolecules. In order to compare the thermomechanical and morphological properties of ion-containing polyurethanes to non-charged polyurethanes, poly(tetramethylene oxide)-based polyurethanes containing either a novel phosphonium diol or 1,4-butanediol chain extenders were prepared using a prepolymer method. The novel phosphonium polyurethane was more crystalline, and it was presumed that hydrogen bonding in the non-charged polyurethane restricted polymer mobility, and reduced PTMO crystallinity, and hydrogen bonding interactions were significantly reduced due to the presence of phosphonium cations. These results correlated well with mechanical property analysis. The phase separation and ionic aggregation were demonstrated via wide-angle X-ray scattering, small-angle X-ray scattering, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy during STEM imaging, as described herein. In addition, a novel polyurethane containing imidazolium cations in the hard segment was synthesized and behaved very similarly to the phosphonium cation-containing polyurethane. Ammonium ionenes, which contain quaternary nitrogen in the macromolecular repeating unit, have many potential uses in biomedical applications. They offer interesting coulombic properties, and the charge density is easily controlled through synthetic design. This property makes ionenes ideal polyelectrolyte models to investigate the influence of ionic aggregation on many physical properties. Ammonium ionenes were prepared via the Menshutkin reaction from 1,12-dibromododecane and 1,12-bis(N,N-dimethylamino)dodecane. The absolute molecular weights were determined for the first time using an on-line multi-angle laser light scattering (MALLS) in aqueous size exclusion chromatography (SEC). Tensile testing and DMA were used to establish structure-property relationships between molecular weight and mechanical properties for a series of 12,12-ammonium ionenes. Furthermore, degradation studies in the presence of base support the possibility for water-soluble coatings with excellent mechanical durability that are amenable to triggered depolymerization. A novel synthetic strategy was utilized to prepare chain extended 12,12-ammonium ionenes containing cinnamate functional groups. In the presence of UV light, the polymers chain extended, and the resulting ionenes possessed enhanced thermomechanical properties and increased molecular weight. In addition, the novel synthesis of imidazolium ionenes was demonstrated, and the charge density was tuned for appropriate applications using either low molecular weight segments or oligomeric precursors. The change in charge density had a profound role in imidazolium ionene thermal and mechanical behavior. / Ph. D.

Nanoporous (np) metals and alloys are the subject of increasing research attention due to their high surface-area-to-volume ratio. Numerous methods exist to create np metals, with dealloying being a common approach. By dissolving one or more elements from certain alloy systems, porous structure can be generated. Utilizing this method, multiple np metals, including np-Ni, np-Ir, and np-Au were created. By carefully adjusting precursor type and dealloying conditions for each system, nanoporous Ni/Ir/Au with different morphologies and even controllable ligament/pore size were achieved. The mechanical behavior of porous materials is related to their fully dense counterparts by scaling equations. Established scaling laws exist and are widely applied for low relative density, micro- and macro-scale open-cell porous materials. However, these laws are not directly applicable to nanoporous metals, due to higher relative density and nanoscale cells. In this study, scaling laws were reviewed in light of the thermomechanical behavior of multilayer np-Ir thin films subjected to thermal cycling. Thermal cycling allows measurement of biaxial modulus from thermoelastic segments, and also causes film thickness to contract, with increases in relative density. A modified scaling equation was generated for biaxial modulus of np-Ir, and differed significantly from the classic equation.

[pt] O propósito deste trabalho é propor um modelo teórico axiomático, que descreva o comportamento termomecânico de materiais granulares, fundamentado em uma descrição física simples, do que entende-se por material granular. No capítulo I, faz-se uma revisão bibliográfica, objetivando uma visão geral do estado da arte e delinear a importância do estudo de materiais granulares. No capítulo II, utiliza-se um método axiomático estabelecendo-se as equações de balanço que descrevem o comportamento termodinâmico de materiais granulares. No capítulo III, utilizando-se um outro método axiomático, analisa-se algumas condições de contorno para materiais granulares. No capítulo IV, estuda-se restrições internas em materiais granulares, exemplificando-se algumas. Finalmente no capítulo V, aplica-se o embasamento teórico dos capítulos anteriores, na solução do problema de escoamento de um material granular entre placas paralelas. / [en] The aim of this work is to establish an axiomatic theoretical model, for description of the thermomechanical behavior of granular materials, based on a simple physical description of what mean granular materials. On the first chapter, it s make an overview of the acctual state of the arte, giving the real importance of the study of granular materials. On the second chapter, by using an axiomatic method, the balances equations for thermomechanical behavior of granular materials, was established. On the the III, by using another axiomatic method, some boundary condictions for granular materials, was analysed. On the chapter IV, by using a coceptual model for internal constraints, some internal constraints for granular materials, was exemplified. At least, on chapter V, the theoretical backgoung established in the previous chapter, is applied to solve the problem of granular flow between two parallel plates.

Les systèmes multicouches à base de LTCC (Low Temperature Co-fired Ceramic) et d’or sont largement utilisés dans l’élaboration de composants multi-matériaux pour applications radiofréquences civiles et militaires. Cette technologie présente un fort potentiel de développement car elle constitue une solution de packaging des puces électroniques. Lors du processus d’élaboration de ces composants multi-matériaux (céramique-métal), la phase de co-frittage est une étape clé et critique, car elle est source d’endommagement du fait des potentiels différentiels de coefficients de dilatation et de cinétiques de retrait. Ainsi, ce travail vise le développement d’un modèle numérique simulant fidèlement le comportement thermomécanique des composants au cours de l’étape de co-frittage. A cet effet, les comportements thermomécanique et au frittage des matériaux céramiques et métalliques sélectionnés ont été finement caractérisés. Les lois de comportement ainsi identifiées ont été implémentées dans le code de calcul par éléments finis Comsol Multiphysics. La robustesse du modèle développé a été analysée par confrontation à des essais expérimentaux conduits grâce à la mise en place d’un dispositif original de suivi in situ de la déformation par ombroscopie. Ainsi, les cambrures générées lors du frittage contraint d’un bicouche à base de LTCC et lors du co-frittage d’un bicouche LTCC-or ont été caractérisées et comparées aux simulations numériques. / LTCC (Low Temperature Co-fired Ceramic) and gold multilayers systems are extensively used in the development of multi-materials components for civil and military radio-frequency applications. This technology presents a high potential of development because it provides a packaging solution for electronic chips. During the process of drafting of these multi-materials components (ceramic metal), the co-sintering step is a key and critical one, indeed it leads to damages because of potential thermal expansion coefficients and shrinkage kinetics differentials. Thus, the aim of this work is to develop a numerical model able to faithfully simulate the components thermomechanical behavior during the co-sintering stage. To achieve this, the sintering and thermomechanical behavior of the selected ceramic and metal materials have been carefully characterized. The behavior laws so identified have been implemented in the software based on the finite elements method Comsol Multiphysics. The developed model robustness has been analyzed by confrontation with experimental tests driven by the establishment of an original shadowscopy apparatus which allows the in situ strain recording. Thus, the generated curvatures during the constrained sintering of a LTCC bilayer and during a gold-LTCC bilayer co-sintering have been characterized and compared with the numerical simulations.

ZnO nanowires and nanorods are a new class of one-dimensional nanomaterials with a wide range of applications in NEMS. The motivation for this work stems from the lack of understanding and characterization of their thermomechanical behaviors essential for their incorporation in nanosystems. The overall goal of this work is to develop a fundamental understanding of the mechanisms controlling the responses of these nanostructures with focus on: (1) development of a molecular dynamics based framework for analyzing thermomechanical behaviors, (2) characterization of the thermal and mechanical behaviors in ZnO nanowires and (3) development of models for pseudoelasticity and thermal conductivity. The thermal response analyses show that the values of thermal conductivity are one order of magnitude lower than that for bulk ZnO due to surface scattering of phonons. A modified equation for phonon radiative transport incorporating the effects of surface scattering is used to model the thermal conductivity as a function of wire size and temperature. Quasistatic tensile loading of wires show that the elastic moduli values are 68.2-27.8% higher than that for bulk ZnO. Previously unknown phase transformations from the initial wurtzite (WZ) structure to graphitic (HX) and body-centered-tetragonal (BCT-4) phases are discovered in nanowires which lead to a more complete understanding of the extent of polymorphism in ZnO and its dependence on load triaxiality. The reversibility of the WZ-to-HX transform gives rise to a novel pseudoelastic behavior with recoverable strains up to 16%. A micromechanical continuum model is developed to capture the major characteristics of the pseudoelastic behavior accounting for size and temperature effects. The effect of the phase transformations on the thermal properties is characterized. Results obtained show that the WZ→HX phase transformation causes a novel transition in thermal response with the conductivity of HX wires being 20.5-28.5% higher than that of the initial WZ-structured wires. The results obtained here can provide guidance and criteria for the design and fabrication of a range of new building blocks for nanometer-scale devices that rely on thermomechanical responses.

Lors de l'opération d’usinage à grande vitesse, la résistance à l'usure des outils de coupe est améliorée par l’utilisation des revêtements mono ou multicouches sur les faces actives de l’outil. Cependant, le chargement thermomécanique généré à l'interface outil-pièce affecte considérablement les zones de contact. Par cet effet, plusieurs modes d'usure tels que la fissuration, l’abrasion, l’adhésion et le délaminage du revêtement peuvent se manifester. L'étude du comportement des revêtements et de leurs différents modes de dégradation permet de mieux comprendre leur impact sur la durée de vie de l'outil et ainsi optimiser le procédé d'usinage. Dans ce travail de thèse, une approche numérique multi-étapes a été proposée pour prédire l'usure des outils de coupe revêtus. Cette approche est composée par trois principales étapes. La première consiste à effectuer une simulation éléments finis de l’usinage pour une courte durée (jusqu’à la stabilisation du chargement à l’interface outil/pièce). La deuxième étape consiste à récupérer ce chargement et de l’utiliser comme une entrée du modèle XFEM/Level-set. Ce dernier permet d’analyser le comportement des couches de revêtement sans recours à un maillage conforme aux interfaces. Par conséquence, la distorsion du maillage est évitée lorsque le profil d'outil usé est mis à jour, ainsi que le temps de calcul CPU est drastiquement réduit. La dernière étape de cette approche consiste à calculer le taux d’usure et ainsi prédire le déplacement des nœuds de l’outil de coupe affectés par l’usure. Les essais expérimentaux ont permis d’une part d’identifier les paramètres de contact outil/pièce, et d’autre part de valider l’approche proposée / In high speed machining, wear resistance of the cutting tools is improved by depositing single or multilayered coatings on their surface. However, the thermomechanical loading generated at the tool-workpiece interface greatly affects the contact zones. For this purpose, several wear modes such as cracking, abrasion, adhesion and delamination of the coating can be occurred. The study of the coatings behavior and their different degradation modes lead to better understanding of their impact on the tool life and machining process under optimal conditions. In this PhD thesis work, a multi-step numerical approach has been proposed to predict wear of the coated cutting tools. This approach involves three main steps. The first is to perform a finite element simulation of the orthogonal cutting for a short time (until the loading stabilization at the tool/workpiece interface). The second step is to recover this loading and use it as an input for the XFEM/Level-set model. The latter allow to take into account the coating layers presence without any need of mesh conforming to the interfaces. As a result, the mesh distortion is avoided when the worn tool profile is updated, as well as the CPU calculation time is drastically reduced. The final step of this approach is to convert the wear rate equation into a nodal displacement, thus representing the cutting tool wear. Based on the experimental tests, a procedure for identifying tool/workpiece contact parameters, and for calibrating the wear equation for each coating layer has been proposed. Experimental trials have been also used to validate the proposed approach

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-26T21:22:44Z No. of bitstreams: 1 FERNANDO ANDRADE AMORIM - DISSERTAÇÃO PPGEM 2014..pdf: 6350093 bytes, checksum: 23c947f61b48ed2613bf915ed058b600 (MD5) / Made available in DSpace on 2018-04-26T21:22:44Z (GMT). No. of bitstreams: 1 FERNANDO ANDRADE AMORIM - DISSERTAÇÃO PPGEM 2014..pdf: 6350093 bytes, checksum: 23c947f61b48ed2613bf915ed058b600 (MD5) Previous issue date: 2014-08-08 / CNPq / Capes / Ligas de NiTi têm possibilitado revolucionar muitos projetos tradicionais de engenharia com suas propriedades únicas de superelasticidade (SE) e efeito de memória de forma (EMF). Com o interesse em incorporar esses materiais em diferentes aplicações e dispositivos, o desenvolvimento de tecnologia eficaz para soldagem de ligas NiTi torna-se necessário, devido ao fato de esse tipo de união proporcionar a fabricação das mais diferentes formas geométricas e combinações entre materiais similares e dissimilares. Nesse contexto, este estudo teve como objetivo geral determinar as variações das propriedades termomecânicas em juntas soldadas de fios de NiTi. Para o trabalho, fios superelásticos de uma LMF NiTi (ASTM F2063) com 0,4 e 0,9 mm de diâmetro, foram divididos em dois grupos: (a) fios sem tratamento térmico (NiTiA) e (b) fios com tratamento térmico a 400 °C durante 20 minutos (NiTi400). Em seguida estes fios foram soldados pelo processo TIG autôgeno, utilizando a soldadora Micromelt (EDG Equipamentos e Controles). A caracterização termomecânica dos fios íntegros e soldados foi realizada utilizando ensaios de calorimetria diferencial de varredura (DSC), análise dinâmico-mecânica (DMA), ensaios de tração uniaxial em diferentes temperaturas (30°C a 70°C), microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e micro indentação Vickers. Os resultados obtidos demonstraram uma boa eficiência do processo TIG ao soldar os fios NiTi de ambos os grupos. Ensaios de DSC relevaram que o processo de soldagem pode promover modificações de natureza metalúrgica aos fios de NiTi, de maneira a reduzir as temperaturas de transformações de fase. Já no que diz respeito ao aspecto mecânico, os fios soldados apresentaram resistência a ruptura por tração de até 750 MPa (NiTiA ~ 70 °C) e valores de deformações de até 8,5 % (NiTiA). / NiTi alloys enabled revolutionize many traditional engineering projects with uniques properties of superelasticity (SE) and shape memory effect (SME). Interested on incorporating these materials in different applications and devices, developments of efficient welding technology for NiTi alloys becomes necessary due to the fact that this type of process can provide many differents geometric shapes and combinations of similar and dissimilar materials. In this context, this study had as main objective to determine variations in thermomechanical properties for NiTi welded wires. For this work, superelastic NiTi SMA wire (ASTM F2063) with 0.9 to 0.4 mm in diameter were divided into two groups: (a) wires without heat treatment (NiTiA) and (b) heat treated wires at 400 ° C for 20 minutes (NiTi400). Then, these wires were welded by autogenous welding process, using the Micromelt machine (EDG, Equipment and Controls). The thermomechanical characterization of as received and as welded wires was performed by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) uniaxial tensile test at different temperatures (30°C to 70°C), optical microscopy (OM), scanning electron microscopy (SEM) and Vickers micro indentation. The results showed a good efficiency of TIG welding for every NiTi wire studied groups. DSC curves demonstrates that welding process can cause a metallurgical changes into NiTi wires, promoting changes in phase transformation temperatures. The mechanical properties of the welded wire presented a tensile rupture strength of 750 MPa (NiTi~70 °C) and strain values up to 8.5% (NiTiA).

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-27T15:46:57Z No. of bitstreams: 1 ESTEPHANIE NOBRE DANTAS GRASSI - DISSERTAÇÃO PPGEM 2014..pdf: 4659811 bytes, checksum: 9dce2fd88b57abcccbb5be6fa913cf1b (MD5) / Made available in DSpace on 2018-04-27T15:46:57Z (GMT). No. of bitstreams: 1 ESTEPHANIE NOBRE DANTAS GRASSI - DISSERTAÇÃO PPGEM 2014..pdf: 4659811 bytes, checksum: 9dce2fd88b57abcccbb5be6fa913cf1b (MD5) Previous issue date: 2014-08-01 / CNPq / Capes / As Ligas com Memória de Forma (LMF) são um importante grupo de materiais metálicos ativos que respondem a estímulos termomecânicos por meio dos fenômenos do Efeito Memória de Forma (EMF) e da Superelasticidade (SE). Ambos os efeitos permitem recuperar grandes níveis deformações por meio de aquecimento, no primeiro caso, ou do descarregamento mecânico, no segundo. As LMF de NiTi são facilmente encontradas no mercado médico e odontológico em forma de ferramentas e acessórios para tratamentos específicos. Um destes elementos são minimolas helicoidais ortodônticas de NiTi, que alcançam deformações algumas centenas de vezes maiores que elementos unidimensionais de LMF, como fios. Por outro lado, é de amplo conhecimento que uma técnica adequada para manipular propriedades mecânicas de produtos metálicos acabados, além de variar-se a configuração geométrica, é a realização de tratamentos térmicos de recozimento. Principalmente após a realização de trabalho a frio, os recozimentos são capazes de recuperar parcial ou totalmente a mobilidade atômica no metal, o que, no caso das LMF, afeta diretamente o seu comportamento termomecânico. Neste contexto, o principal objetivo deste trabalho é estudar a influência de tratamentos térmicos de recozimento sobre a resposta termomecânica de minimolas de LMF NiTi, originalmente superelásticas. Um planejamento fatorial foi usado para avaliar a influência das variáveis temperatura e tempo de recozimento sobre algumas das principais propriedades termomecânicas das minimolas: constante de mola (rigidez), módulo de elasticidade transversal, capacidade de dissipação de energia, temperaturas de transformação, histere térmica e a entalpia de transformação. Foi demonstrado que tratamentos térmicos a temperaturas na faixa de 500 oC a 600 oC são capazes de converter as minimolas de LMF NiTi do estado superelástico para o estado de atuador, pelo aparecimento do efeito memória de forma. / Shape Memory Alloys (SMA) are an important group of metallic active materials that respond to thermomechanical stimuli through the Shape Memory Effect (SME) or the Superelasticity (SE) phenomena. Both these effects are capable of retrieving large amounts of strain by simple heating, in the former case, or simple mechanical unload, in the latest case. The SMA of the NiTi family composition exhibit superior properties when compared to other compositions, including biocompability, what brings this alloy to be widely used in medical and orthodontic fields in the form of tools and accessories to specific treatments. As an example, mini coil springs of NiTi SMA presenting superelasticity reach strain levels hundreds of times higher than one-dimensional elements, such as wires. However, a more suitable technique to manipulate mechanical properties of metallic finished products is the use of heat treatments like annealing. Mainly after experiencing cold working processes, annealing treatments are capable of partially or totally recover the atomic mobility, witch directly affects thermomechanical response of SMA. In this context, this dissertation work aims to study the influence of annealing heat treatments over thermomechanical behavior of SMA NiTi mini coil springs originally presenting the SE. A factorial design was used to evaluate the influence of temperature and time of annealing over some of the main thermomechanical springs’ properties: spring constant (stiffness), shear modulus, energy dissipation capacity, phase transformation temperatures, thermal hysteresis and transformation enthalpy availability. It was demonstrated that heat treatments between 500°C and 600°C are capable of converting the superelastic state of the mini coil springs to an actuator state, as a result of the shape memory effect appearance.

L'objectif de cette thèse est d'étudier l'influence de la vitesse de déformation sur la réponse par indentation des matériaux. Les matériaux polymères thermoplastiques, notamment le Polycarbonate (PC), le Polyméthylméthacrylate (PMMA), le Polyéthylène à Haute Densité (PEHD) et le Polyamide Nylon 6.6 renforcé à 30% de fibres de verres (PA 6.6-30% GFR), ont été choisis comme matériaux d'études en raison de leur forte sensibilité à la vitesse de déformation même à température ambiante. Les deux premières parties de ce travail sont focalisées sur l'étude du comportement thermomécanique des matériaux polymères. Une étude bibliographique sur des matériaux polymères thermoplastiques, amorphes et semi-cristallins, a été effectuée afin de comprendre leur microstructure et leur mécanisme de déformation. De plus, des essais de compression simple ont été réalisés sur les matériaux d'étude à différentes vitesses de traverse constantes puis dépouillés analytiquement. Les trois derniers chapitres de cette thèse sont consacrés à la caractérisation mécanique des matériaux par indentation. En premier lieu des simulations numériques de l'essai d'indentation conique ( =70,3°) à une vitesse de pénétration constante ( = 1 µm/s) ont été effectuées à partir des paramètres de la loi de G'sell modifiée et de la loi puissance identifiés par compression. L'identification par analyse inverse des paramètres de la loi de G'sell modifiée à 7 paramètres sur des courbes pseudo-expérimentales nous a permis de confirmer la non unicité de la solution. Ainsi, nous avons effectué l'étude théorique de l'indentation sur des matériaux pseudo-expérimentaux en utilisant la loi puissance. Un nouveau concept de déformation représentative et de vitesse de déformation représentative, basé sur l'analyse du domaine de solution regroupant l'ensemble des paramètres donnant les mêmes courbes d'indentation, a été proposé. La procédure d'identification des paramètres de la loi puissance par indentation utilisant ce concept de déformation représentative et de vitesse de déformation représentative, appliquée sur un matériau pseudo-expérimental donne des résultats très satisfaisants. Sur les matériaux d'étude en revanche la méthode n'a pu révéler son potentiel puisque la loi de comportement de ces matériaux n'est pas correctement modélisée par une loi puissance sur une large plage de déformation et de vitesse de déformation. Enfin, le concept de déformation représentative et de vitesse de déformation représentative proposé dans ce travail apporte de nouveaux outils d'analyse et d'exploitation des données de l'indentation et offre des perspectives très intéressantes. / The aim of this thesis is to study the strain rate effects through materials response from indentation test. Polymeric solid material, especially Polycarbonate (PC), Polymethyl methacrylate (PMMA), High Density Polyethylene (HDPE) and Polyamide Nylon 6.6 -30% glass fiber reinforced (PA 6.6-30% GFR), were selected as study materials due to their high strain rate sensitivity even at room temperature. The first two parts of this work were focused on the study of the thermomechanical behavior of polymer materials. Bibliographical studies of thermoplastic polymer materials, amorphous and semi-crystalline, was established in order to understand their microstructure and deformation mechanism. Moreover, compression tests were performed on study materials with several crosshead speeds values then the results was exploited analytically. The last three parts were focused on mechanical characterization using Instrumented Indentation Test (IIT). Firstly, numerical simulation of a conical indentation test ( =70.3°) with a constant rate displacement ( = 1 µm/s) was established using the identified G’sell behavior parameters and the power-law parameters from compression test. Parameter identification using Inverse Analysis from numerical material shows the non-uniqueness of G’sell parameters which gives the same indentation curve. Thus, theoretical study of conical indentation test was established considering power-law model. A new concept of the representative strain and the representative strain rate, based on solution domain which associate the set of parameters leading to the same indentation curves, was proposed. Very satisfactory results was obtained when identification process using this average representative strain rate is applied to a numerical material define by a power-law model. However, this method could not show its efficiency because the mechanical behavior of the real material is not correctly modeling with a power-law at a wide range of strain and strain rate. Finally, the new concept of the representative strain and the representative strain rate proposed on this work contributes to a new investigation tools to exploit the results form IIT and provide a very interesting perspectives.

Les cavités intérieures des culasses d'aluminium sont réalisées à l'aide de noyaux de sable, qui sont constitués d'un mélange de silice et d'une résine Polyuréthane. Ils sont placés dans le moule métallique juste avant la coulée. Durant celle-ci, ils subissent la pression métallo-statique et sont soumis à des températures élevées. Sous ces conditions extrêmes, avec l'apparition de parois de plus en plus fines et de formes plus complexes, les noyaux peuvent présenter des déformations qui induisent des défauts dimensionnels sur les pièces finales.Pour contrôler la déformation des noyaux, il faut d'abord disposer d'une caractérisation robuste de leur propriétés thermiques et mécaniques, qui puisse être utilisée dans des calculs de structures simulant le flux de métal liquide, la solidification et les champs thermiques. Cette approche n'est pas encore pratiquée de façon complète dans l'industrie. Une revue de la littérature confirme que cette connaissance n'est que très parcellaire pour le moment.Le travail a donc d'abord été concentré sur la caractérisation expérimentale du comportement thermomécanique et des propriétés thermophysiques des noyaux de fonderie et du liant résine.Ensuite, un modèle de comportement capable de prendre en compte la viscosité du matériau, son endommagement, et surtout son évolution en fonction du temps et de la température en raison de la dégradation thermique du liant résine a été développé.Une éprouvette technologique a finalement été conçue et un protocole expérimental a été mis en place pour mesurer la déformation d'un noyau durant la coulée et de valider numériquement le modèle de comportement sous des chargements thermiques et mécaniques complexes. / The inner cavities of aluminum cylinder heads are made using sand cores, which are made of silica sand and of a polyurethane resin binder. The cores are placed in the metallic mold just before casting. During this stage, the cores are submitted to the metallo-static pressure and high temperatures. Under these extreme loading conditions, with the development of thinner and thinner walls with complex designs, the cores exhibit significant deformation causing dimensional defects in the final cast.To control the deformation of the sand core, it is necessary to possess a robust characterization of their thermal and mechanical properties, that could be introduced in structural computations simulating the flow of the liquid metal, the solidification and the thermal fields. This approach is still not fully in use in the industry. A review of the literature confirms that this knowledge is incomplete for the moment.The work was therefore concentrated on the experimental characterization of the thermomechanical behavior and the thermophysical properties of the foundry cores and Polyurethane resin binder.Then, a behavior model capable of taking into account the viscosity of the material, damage development, and especially its evolution as a function of time and temperature because of the thermal degradation of the binder resin was developed.A technological specimen was finally designed and an experimental protocol has been established to measure the deformation of a core during casting and numerically validate the constitutive equations under complex thermal and mechanical loadings.