Dissertations / Theses on the topic 'Thermomechanical Analysi'

In the aeronautics industry, the propulsion systems stand among the most advanced and critical components. Over the last 50 years, gas turbine aeroengines were subjected to intensive research to increase efficiency and reduce weight, noise and harmful emissions. Together with design optimization, breakthrough in materials science for structural applications triggered the development of the most advanced gas turbine engines. For low temperatures, basically ahead of the combustion section, lightweight Ti alloys are preferred for their good mechanical properties. For high temperatures instead, Ni-based superalloys exhibit outstanding properties up to very high temperatures despite a rather high material’s density. Research have focused on enhancing to the maximum the potential of materials in gas turbine engines. According to the application, the components experience various mechanical and environmental constraints. Special designs, manufacturing process, material compositions and protective coatings have been developed to push the limits of advanced materials. Nowadays, the attention is focused on innovative materials to replace the existing Ti and Ni based alloys leading to substantial benefits. Light weight composite materials in particular were found very attractive to replace some components’ Ti alloys. At higher temperatures, it is of great interest to replace Ni-based superalloys by materials with lower density and/or higher temperatures applications, which in turn would lead to substantial weight reduction and increase efficiency. At the highest temperatures range, in particular in the combustion chamber and high pressure turbine sections, ceramic based materials offer promising balance of properties. Research are dedicated to overcome the drawbacks of ceramics for such structural applications, and in particular their brittle fracture behavior, by addition of reinforcing fibers. At lower temperatures range, TiAl based intermetallics emerged as very promising materials at half the density of Ni-based superalloys. Significant weight reduction could be achieved by the introduction of TiAl based alloys for rotating components of the compressor and low pressure turbine. 2nd generation γ-TiAl alloys were lately introduced in GE’s GEnx and CFM’s LEAP engines. The present work concerns the fabrication by the additive manufacturing technique Electron Beam Melting of 3rd generation γ-TiAl alloys for high temperatures application in gas turbine aeroengines. EBM, building parts layer by layer according to CAD, offers many advantages compared to other manufacturing processes like casting and forging. Reported by Avio, 2nd generation γ-TiAl alloys have been successfully fabricated by EBM. To increase the material’s potential, the production of 3rd generation γ-TiAl alloys Ti-(45-46)Al-2Cr-8Nb was therefore studied. The optimization of the EBM parameters led to high homogeneity and very low post-processing residual porosity ≤ 1%. The fine equiaxed microstructure after EBM could be tailored towards the desired mechanical properties by simple heat treatment, from equiaxed to duplex to fully lamellar. In particular, a duplex microstructure composed by about 80 % lamellar grains pinned at grain boundaries by fine equiaxed grains was obtained after heat treatment slightly over the α transus temperature. The study showed that addition of a higher amount of Nb significantly increased the oxidation resistance of the material, thus increasing the application temperature range of these γ-TiAl alloys.

The behaviour of heated structures is strongly governed by thermal induced deformation and degradation of material properties. This thesis presents an augmentation of the software framework OpenSees to enable thermomechanical analysis of structures. The developments contributed to OpenSees are tested by series of benchmark cases and experimental results. OpenSees is an object-oriented, open source software framework developed at UC Berekeley for providing an advanced computational tool to simulate non-linear response of structural frames to earthquakes. OpenSees was chosen to be extended to enable the modelling of structures in fire. The development of this capability involved creating new thermal load classes to define the temperature distribution in structural members and modifying existing material classes to include temperature dependent properties according to Eurocodes. New functions were also added into the existing corotational beam/column element (2D and 3D) to apply temperature related loads. A new geometrically nonlinear shell element was created (based on the existing linear MITC4 shell element in OpenSees) using total Lagrangian formulation. Appropriate thermal load, material and section classes were also developed for enabling thermomechanical analysis using the nonlinear shell element. A number of benchmark tests were carried out to verify the performance of the new developments implemented in OpenSees. The benchmark tests involved subjecting beams and plates to a range of through depth temperature gradients with OpenSees results compared against closed form solutions. Further verification was also carried out by comparing OpenSees results with ABAQUS results. The extended OpenSees framework was also used to model experiments such as two plane steel frames at elevated temperatures, the Cardington Restrained Beam Test and the Cardington Corner Test and an earthquake damaged reinforced concrete (RC) frame subjected to a subsequent fire. The existing DruckerPrager material class in OpenSees was used to the model concrete in the composite floor in the Cardington tests and in the RC frame. The pinching material available in OpenSees was used to model the beams and columns in the RC frame to consider the cyclic degradation of strength and stiffness during the increasing cyclic displacements imposed on the RC frame before the fire. In all cases the results from OpenSees show good agreement with test data.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 152-154).
One way to increase the power of a nuclear reactor is to change the solid cylindrical fuel to Internally and Externally Cooled (I&EC) annular fuel, and adjust the flow and the core inlet coolant temperature. The switch to annular fuel allows for a 20% increase in core power density without changing the assembly size or the control rod placement. Such an approach is being considered for the Korean reactor OPR1400. The analysis of I&EC fuel with a modified version of FRAPCON-3.3 revealed that an uneven heat flux split between the outer and inner surfaces may develop which does not yield an optimal design. After optimization, it is found that excessive cladding oxidation on the inner channel of the hottest fuel pin may occur due to excessive internal heat flux, which is controlled by the gap conductance. As the gaps close asymmetrically, the MDNBR limit of 1.3 could also be violated. At the uprated power, control of the gap sizes is needed in order to satisfy the thermal-hydraulic requirements. One solution is to increase the flow rate to increase the MDNBR and to reduce the coolant temperature to decrease the cladding oxidation. Reduced-moderation Water Reactor (RMWR) is a boiling water reactor proposed to operate with mixed oxide fuel and, a harder neutron spectrum and higher local fuel burnup compared to the traditional Light Water Reactors. The fissile content of the fuel is concentrated in two pancake like regions in the core separated by a blanket (fertile-only) region.
(cont.) The FRAPCON fuel performance code has been modified to assess the behavior of the RMWR fuel pins. Properties were modified to allow for a higher concentration of plutonium oxide. A new mechanistic model was adopted to simulate the fission gas release and swelling behavior of the fuel. The gas bubble swelling at the grain edges and grain faces were modeled separately. In addition, solid fission product swelling model was modified and the effect of axial migration of the volatile fission product behavior on fuel performance was also analyzed. Specifically, the cesium migrates axially based on the evaporation/condensation mechanism. Cesium precipitation at the fuel blanket interface and the resulting excessive swelling of the fuel pin at these locations could potentially be a major source of local stresses. Furthermore, as-fabricated porosity migration, central void formation, and hot-pressing of the fuel pellet were also modeled. Finally, axial variation of the material properties was allowed to represent the active fuel region and the blanket regions. The updated version of FRAPCON (called FRAPCON-EP) was checked against experiments then used to analyze the RMWR fuel behavior to optimize various parameters such the fuel pellet smear density, plenum height, and achievable peak burnup in order to achieve performance that could satisfy the NRC requirements for fuel pins.
by Andrew Lerch.
S.M.

Cette thèse a été réalisée en cotutelle entre l'Université Technique Nationale Ivan Pul'uj de Ternopil (TNTU, Ukraine) et l’Université Blaise Pascal (Clermont-Ferrand, France). Les travaux ont été effectués au sein de l'Institut Pascal de l’Université Blaise Pascal - Clermont II, de l’IFMA et du CNRS, dans le thème scientifique Matériaux actifs et intelligents, modélisation multi-échelle de l'axe Mécanique, Matériaux et Structures, et au sein de l'Institut Français de Mécanique Avancée. La thèse présentée appartient au domaine scientifique de la mécanique de la rupture et la science des matériaux. L'objectif de la thèse est de développer la méthodologie analytique et expérimentale pour la durée de vie résiduelle des collecteurs du surchauffeur dans les centrales thermiques, en tenant compte des caractéristiques de fonctionnement de chargement thermomécanique. La prédiction de la durée de vie est une tâche cruciale pour un fonctionnement continu des éléments structuraux très chargés et fait partie d'un problème plus large, couvert dans la recherche de la résistance et la durabilité des éléments structurels à haute température dans les équipements d'énergie générateur. Le mémoire décrit l'influence de la température de fonctionnement sur la vitesse de propagation des fissures de fatigue et micromécanismes de rupture dans le matériau du collecteur de surchauffeur
This thesis was performed under the cotutelle agreement between Ternopil Ivan Pul’uj National Technical University (TNTU, Ukraine) and Blaise Pascal University (Clermont Ferrand, France). The thesis was carried out within Pascal Institute of the Blaise Pascal University - Clermont II, the IFMA and the CNRS, in the Scientific Theme “Active and Smart Materials and Multiscale Modeling” of the Mechanics, Materials and Structures Department, and within the French Institute for Advanced Mechanics. The presented thesis belongs to the scientific field of fracture mechanics and material science. The aim of the thesis is to develop the analytical and experimental methodology for the residual lifetime estimation of the superheater collectors at thermal power stations (TPS), taking into account the operational features of thermomechanical loading. Prediction of lifetime is crucial task for continuous operation of heavy loaded structural elements and is a part of a broader problem, covered in the research of the strength and durability of high temperature structural elements in power-generating equipment. The thesis describes the influence of operating temperature on the fatigue crack growth rate and fracture micromechanisms in the material of the superheater collector

Ultrasonic welding (UW), as a solid-state joining process, uses an ultrasonic energy source (usually with a frequency of 20 kHz or above) to induce oscillating shears between the faying surfaces to produce metallurgical bonds between a wide range of metal sheets [1, 2], thin foils [3], semiconductors [4], plastics [5], glass [6], and ceramics [7]. In contrast to traditional fusion welding processes, ultrasonic welding has several inherent advantages [3,8] derived from its solid-state process characteristics, and has been in use as a versatile joining method in the electronics, automotive, and aerospace industries since the 1950s

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A modelagem do acoplamento entre os fenômenos mecânicos e térmicos em sólidos inelásticos é considerada neste trabalho. O acoplamento termomecânico é importante em determinadas situações, como por exemplo, no estudo de problemas envolvendo deformações inelásticas cíclicas em estruturas metálicas. Um procedimento sistemático para obtenção de equações constitutivas termodinamicamente admissíveis é apresentado. Através deste procedimento, baseado na Termodinâmica dos Processos Irreversíveis, foi possível obter uma teoria constitutiva para modelar o comportamento anisotérmico de metais e ligas metálicas. Dois tipos de acoplamentos termomecânicos foram identificados: o acoplamento interno, associado à dissipação interna do processo mecânico, e o térmico, associado à dependência dos parâmetros das equações constitutivas com a temperatura. A teoria foi particularizada para materiais elasto-viscoplásticos. Simulações com barras foram realizadas para estudar fenômenos como o aquecimento de metais provocado por solicitações mecânicas complexas e o comportamento de metais submetidos a grandes gradientes de temperatura. Uma variável de dano foi incorporada ao modelo, permitindo estudar a influência do acoplamento termodinâmico em processos de degradação do material como fadiga de baixo ciclo.
The present work is concerned with the modeling of the coupling between mechanical and termal phenomena. The thermomechanical coupling is important in some problems like those involving inelastic cyclic deformation in metallic structures. A systematic procedure to obtain thermodynamically admissible constitutive equations is presented. Such procedure has a strong thermodynamic basis and is used to obtain a constant theory to model the anisothermal behavior of metals and alloys. Two kinds of thermomechanical couplings can be identified: the internal coupling, related with the internal dissipation in the mechanical process and the thermal coupling, related with the dependence of the material parameters in the constitutive equations on temperature. The theory is particularized to elasto-viscoplastic materials. Uniaxial simulations were performed to study the heating of metals due to complex mechanical loadings and the behavior of metals subjected to high temperature gradients. A damage variable is introduced in the model to study the influence of the thermomechanical coupling in processes involving the degradation of the material like in low-cycle fatigue.

Mestrado em Engenharia Mecânica
Atualmente, a simulação numérica de processos tecnológicos tem cada vez mais importância e é cada vez mais utilizada permitindo não só reproduzir as condições de funcionamento de determinado processo como também possibilita a previsão de possíveis falhas nos materiais. Assim, surgiu o presente trabalho para dar resposta à necessidade de conseguir caracterizar comportamentos mecânicos como a uência e a fadiga, presentes na superfície de alumínio de um queimador atmosférico, e o impacto que podem ter. Para tal, através do software de simulação numérica ANSYS, realizou-se uma análise termomecânica da respetiva superfície de queima. Em primeiro lugar, selecionou-se o modelo numérico de Norton e procedeu-se à identi cação dos respetivos parâmetros com base em duas análises distintas: uma análise analítica, com base apenas em curvas experimentais e relações analíticas; e uma análise numérica, com recurso ao módulo de otimização do ANSYS, em que os parâmetros foram iterativamente de nidos. Posteriormente, as condições fronteiras do problema foram de nidas e foi realizado um estudo de convergência da malha a usar nas simulações. Deste modo, foram obtidos os per s de temperatura, tensão e deformação ao longo da superfície de queima. Por m, considerando os fenómenos de fadiga e de uência, o tempo de vida da superfície do queimador foi estimado com base em métodos de previsão.
Nowadays, the numerical simulation of technological processes is increasingly important and used, allowing to reproduce the operation conditions of a given process and to predict possible failures in materials. Thereby, the present work emerged, to answer the need to characterize mechanical behaviors such as creep and fatigue that are present on the aluminum surface of an atmospheric burner and to understand the impact they can have. For this purpose, the FEA program ANSYS was used to perform a thermomechanical analysis of the respective surface. Firstly, the Norton's numerical model was selected, and the respective parameters were identi ed based on two di erent analyses: an analytical analysis, based only on experimental curves and analytical relationships; and a numerical analysis using the ANSYS optimization module, in which the parameters were iteratively de ned. Then, the boundary conditions of the problem were de ned, and a mesh sensitivity study was carried out. Therefore, the temperature, stress and strain pro les were obtained along the surface. Considering the fatigue and creep phenomena, the lifetime of the burner surface was estimated based on prediction methods.

This PhD is sponsored by industry and is part of a project to develop and manufacture smart electric compressor for mobile refrigeration and air conditioning applications on commercial and heavy vehicles including industrial machinery. Compact electric compressors are of great value for the future due to the growth of the electric vehicle market. Recent advancements in the field of mobile air conditioning and refrigeration have witnessed extensive use of the swashplate compressor due to its compact structure, continuous operation, small size, light weight and better thermal comfort inside the vehicle. The design of the swashplate compressor is complex so that it requires considerable contributions from different fields of engineering viz. engineering mechanics, heat transfer and fluid dynamics. The estimate of compressor performance through modelling and experiments at the early stages of design and development serves as a useful tool for the designer. The input power, torque, in-cylinder gas pressure and temperature, flow through valves, and volumetric efficiency are important parameters to characterize the compressor performance. In this thesis, a set of practical thermomechanical models are derived and validated against experiments. An ideal gas based analytical model is developed for a 10 cylinder swashplate compressor with a view to predict its performance in terms of shaft torque and mass flow rate for a given rotational speed requiring minimal computational effort to run. Three sub-models are developed to account for the piston and swashplate kinematics and dynamics through deriving expressions for piston displacement as an explicit function of angle of rotation of swashplate and interactions between forces and moments. The compression process model is formulated to predict in-cylinder temperatures and pressures during one revolution of the swashplate together with refrigerant mass flow rate in and out of the compressor. A complete time-varying model is then developed by combining above three sub-models. Results are obtained in terms of compressor torque and volumetric efficiency and agree well with experiments. Considering the importance of refrigerant flow through reed valves affecting compressor performance, a real-gas, restricted-flow valve model is also developed and compared with the ideal-gas, ideal-valve model. Real gas properties of R134a are evaluated using NIST standard reference database. A minor-loss discharge coefficient approach is used to determine the refrigerant flow rate through reed valves. The model predicts the discharge temperature, refrigerant mass flow rate and volumetric efficiency accurately as a function of rotational speed. The effect of real gas properties, heat transfer to and from the compressor wall during compression and expansion and the valve model are analyzed. The suction side valve model is found to have the largest influence on the compressor performance as a function of rpm whereas heat transfer model has the least. The key contribution of this study is in assembling a practical combination of models that is capable of capturing the essential physics without being overly complex. To the authors’ knowledge this is the first swashplate study that shows clearly the cyclic variation in thermo-physical properties. The literature shows the dynamic characteristics of the compressor are well connected with the start-up transients of the swashplate mechanism and the suction and discharge pressures. To evaluate this, an experimentally validated transient swashplate compressor model is developed including mass moment of inertia of the pistons and swashplate to evaluate the motor torque loading during compressor start-up. The effects of essential parameters such as moment of inertia, bearing torque, viscous resistance to the piston motion, suction and discharge pressures on the compressor performance are presented. The actual start-up behavior is tracked using a high-speed data logger capturing phase currents for the BLDC motor, instantaneous power and rotational speed. The suction and discharge pressures are found to have the largest influence on the starting torque whereas rotational mass moment of inertia has the least. The original contribution of this work is in deriving a transient swashplate compressor model that includes the mass moment of inertia of the swashplate mechanism and clarifying the relative importance of line pressures, viscous losses and bearing resistance on the start-up torque. Since minimizing the size of the compact Brushless DC (BLDC) motor driving the compressor is important, it is worth optimizing the cooling performance of the electric motor. An experimentally validated computational fluid dynamics (CFD) model is developed to investigate the thermal performance of an air-cooled Brushless Direct Current (BLDC) motor driving swashplate compressor. Different fin arrangements on the motor housing are analysed including small protrusions on the fin surface. The findings show greater enhancements can be achieved by adding an extra fin in the cooling flow passage rather than through the inclusion of grooved walls. Thermographs of the motor housing are found to be in close agreement with the model predictions. The key achievement of this thermal investigation is in demonstrating air-cooling is a practical and effective alternative to refrigerant cooling of compact high performance electric swashplate compressors for mobile refrigeration and air conditioning applications. The effect of thermal resistance between the windings and stator core of an air-cooled Brushless DC motor is also investigated. Measurements are found to be in close agreement with predictions. The numerical simulations suggest significant benefits of injecting encapsulation material in the stator core to enhance heat transmission from windings to the surrounding electrical steel. To confirm this, an experimental investigation is carried out by adding thermal resin to the winding slots on 2.5 kW and 4 kW brushless DC motors. The findings show that the potting material can reduce the temperature of the windings by 10 °C to 20 °C for electrical power inputs of 2.4 kW to 3.8 kW. The winding temperature is also found to be sensitive to the winding arrangement in the stator slot. With tighter, more compact windings also leading to significant temperature reductions.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

More efficiency heavy-duty vehicles are developed with higher range, updated electronic and mechanical parts. The fuel efficiency and pollution of carbon dioxide need to be lower to achieve new EU regulations. The global population increases with an increased number of heavy-duty vehicles. This, in turn, increases the emission. By taking the electrical and mechanical parts to the next step, the global emission problems can be massively reduced. Electrical machines are the next step towards a cleaner future. The main goal of this study to investigate the electrical machine’s insulation system. Thermo-mechanical stresses due to thermal cycling affect the electrical machines and its sub-components. By using a FEM application with simplified models of the electrical machine, results are obtained and discussed. Specifically, if 2D-models are sufficient enough to represent a 3D-model. How good different 2D-models can represent the 3D-model is compared and discussed in this study. A physical experimental analysis is done to verify and calibrate the FE-models. Which one of the less frequent higher amplitude or more frequent, lower amplitude thermal cycling affects the insulation system most is determined. The simulations could be done with either, coupled-temperature displacement analysis or sequentially coupled analysis. Coupled-temperature displacement is the fastest method to use in the simulation models. A 3D-model is the best way to describe an object and is therefore implemented. Two additional 2D-models are developed for faster computation and to investigate if the models can represent the three-dimensional geometry. All the models have specific boundary conditions to make the models more simplified. Sensitivity studies have been done to determine which parameter affects the induced thermo-mechanical stresses the most. A physical experimental setup is also implemented to validate and calibrate the simulation model. The result of the 3D-model is most accurate when simulating a three-dimensional object. Simulation results have shown that epoxy, one of the main components in the insulation system, is most critical in terms of reaching breakdown first, followed by paper insulation and copper coating. This is a typical result of all three simulation models. Whereas it is concluded that some 2D-models can present the 3D-model, others can’t. The dependent factor is the different cross-section of the electrical machine. The physical experiment shows similar results between simulation in terms of strain at a lower temperature, and the deviation gets larger as the temperature increases. The 3D-model is the model that has the best representation of a real electrical machine as it accounts for all the normal and shear stress components in all directions, but also because it has better boundary conditions compared to the 2D-models. The 2D-model in XY-plane has shown similar results to the 3D-model. One of the main insulation system components, epoxy, is exposed to the highest stresses compared to its yield and ultimate strength, followed by the paper insulation and copper coating. The sensitivity study has concluded that the axial length of the stator does not affect the stress amplitudes. The most critical parameter that affects the thermo-mechanical stresses is the temperature amplitude, the materials CTE and the thickness of the jointed layer. All maximum stress amplitudes of all the components are located at the free end.
Mer effektiva tunga fordon utvecklas med högre räckvidd, uppdaterade elektroniska och mekaniska delar. Bränsleeffektiviteten och föroreningen av koldioxid måste vara lägre för att uppnå nya EU-förordningar. Antalet tunga fordon ökar i takt med att den globala befolkningen ökar, detta leder i sin tur till ökad utsläpp av bland annat koldioxid. Genom att ta de elektriska och mekaniska delarna till nästa steg kan de globala utsläppsproblemen minskas massivt. Elektriska maskiner för framdrivning är nästa steg mot en renare framtid. Studiens huvudmål för att undersöka den elektriska maskinens isoleringssystem. Termomekaniska påfrestningar på grund av termisk cykling påverkar de elektriska maskinerna och dess delkomponenter. Genom att använda en FEM-applikation med förenklade modeller av den elektriska maskinen erhålls och diskuteras resultat. Specifikt om 2D-modeller är tillräckliga för att representera en 3D-modell. Hur tillräckligt de olika 2D-modeller kan representera 3D-modellen jämförs och diskuteras i denna studie. Ett fysiskt experiment utförs för att validera och kalibrera FEA-modellerna. Vilken av de mindre frekventa cykler med högre amplitud eller mer frekventa cyckler med lägre amplitud påverkar isoleringssystemet mest har undersökts. Simuleringarna kan göras med antingen, temperatur kopplad förskjutnings analys eller sekventiellt kopplad analys. Temperatur kopplad kopplad förskjutning är den snabbaste metoden att använda i simuleringsmodellerna. En 3D-modell är det bästa sättet att beskriva ett objekt och har därför implementerats. Ytterligare två, 2Dmodeller är framtagna i FEM-miljö för snabbare beräkning och för att undersöka om 2D-modellerna kan representera den tredimensionella geometrin. Samtliga tre modeller har specifika randvillkor för att förenkla modellerna. Känslighetsstudier görs för att bestämma vilken parameter som påverkar de inducerade termomekaniska spänningarna mest. Ett fysiskt experiment har utförsts för att validera och kalibrera simuleringsmodellerna. Resultatet visar att 3D-modellen representerar ett tre dimensonellt objekt bäst. Simuleringsresultat har visat att epoxy, som är en av huvudkomponenterna i isoleringssystemet, är mest kritisk när det gäller att först nå brott- och sträckgräns, följt av pappersisolering och koppar beläggningen. Detta är ett typiskt resultat av alla tre simuleringsmodeller. Slutsatsen visar att vissa 2D-modeller kan presentera 3D-modellen, andra kan inte. Den beroende faktorn beror på ur vilket tvärsnitt man tittar på den elektriska maskinen. Det fysiska experimentet visar liknande resultat jämfört med simuleringen när det gäller belastning vid en lägre temperatur, och avvikelsen blir större när temperaturen ökar. 3D-modellen, är den modell som har den bästa representationen av en riktig elektrisk maskin eftersom den inkluderar normal- och skjuvspänningskomponenter i alla riktningar. Anledningen är att den har bättre randvillkor jämfört med 2Dmodellerna. 2D-modellen i XY-planet har visat liknande resultat som 3D-modellen. En av huvudkomponenterna i isoleringssystemet, epoxy, utsätts för de högsta spänningarna jämfört med dess sträck- och den brottgräns, följt av pappersisolering och koppar beläggning. Känslighetsstudien har kommit fram till att statorns axiella längd inte påverkar spänningsamplituderna. Den mest kritiska parametern som påverkar de termomekaniska spänningarna är temperatur amplituden, materialens CTE och tjockleken på det skarvade skiktet. Alla maximala spänningsamplituder för samtliga tre komponenter är belägna i den fria änden.

This dissertation discusses the thermomechanical analyses performed on threaded fasteners and curvilinearly stiffened composite panels with internal cutouts. The former problem was analyzed using a global/local approach using the commercial finite element software ANSYS while a fully functional code using isogeometric analysis was developed from scratch for the latter. For the threaded fasteners, a global simplified 3D model is built to evaluate the deformation of the structure. A second local model reproducing accurately the threads of the fasteners is used for the accurate assessment of the stresses in the vicinity of the fasteners. The isogeometric analysis code, capable of performing static, buckling and vibration analysis on stiffened composite plates with cutouts using single patch, multiple patches and level set methods is then discussed. A novel way to achieve displacement compatibility between the panel and stiffeners interfaces is introduced. An easy way of modeling plates with complicated cutouts by using edge curves and generating a ruled NURBS surface between them is described. Influence on the critical thermal buckling load and the fundamental mode of vibration due to the presence of circular, elliptical and complicated cutouts is also investigated. Results of parametric studies are presented which show the influence of ply orientation, size and orientation of the cutout, and the position and profile of the curvilinear stiffener. The numerical examples show high reliability and efficiency when compared with other published solutions and those obtained using ABAQUS, a commercial software.
PHD

L'objectif de la thèse est d'analyser le comportement mécanique de matériaux granulaires composites bidimensionels en terme de textures granulaires en utilisant deux approches : étude expérimentale par "thermoelastic stress analysis" et étude numérique par dynamique moléculaire. Les systèmes granulaires composites sont préparés à l'aide de cylindres en polyoxyméthylène (POM) et polyéthylène haute densité (PEHD), présentant un rapport de rigidité de 4 entre eux. Différents rapports de diamètres et de nombres de particules sont considérés. Les résultats expérimentaux et numériques sont en bon accord à l'échelle macroscopique. En particulier, le réseau fort (qui est ici caractérisé par des contraintes hydrostatiques supérieures à la valeur moyenne) contient moins de 50% des particules, et présente une distribution décroissance exponentielle quel que soit le type de particules considéré pour l'analyse (particules souples, particules rigides, toutes les particules). De plus, la distribution des contacts entre particules rigides (contacts POM-POM) est anisotrope et tend à s'organiser dans le sens de la direction du chargement extérieur appliqué, tandis que les autres types de contact agissent principalement pour maintenir le système en équilibre
The main objective of our dissertation is to analyze the mechanical behavior of two-dimensional composite granular materials through the granular textures. Thermoelatic stress analysis experiments and molecular dynamics simulations are used for this purpose. The composite granular systems are prepared from polyoxymethylene (POM) and high-density polyethylene (HDPE) cylinders with a stiffness ratio of about 4 between them. Different configurations in terms of ratios of diameter size and ratio of particle numbers are systematically investigated. Experimental and numerical results are good correlated at the macroscopic scale. In particular the strong network, which is here characterized by hydrostatic stresses higher than the mean value, consists of less than 50% of all particles, and exhibits an exponential decay whatever the type of particles considered for the analysis (soft, stiff, or both types). In addition, the contact distributions between stiff particles (POM-POM contacts) is anisotropic with an effort to arrange parallel to the direction of the external applied load, whereas the other types of contacts just act to sustain the granular system in equilibrium

Gravitational Waves (GWs) are ripples in the curvature of spacetime that propagate as waves at the speed of light while travelling basically undisturbed from the moment of their creation by accelerated masses. GWs provide unique information about astrophysical sources, such as binary systems, allowing their exploration under a wide range of masses, mass ratios and physical states inaccessible otherwise and therefore opening a new window to observe the universe. The Laser Interferometry Space Antenna (LISA) mission will be a spaceborne gravitational wave observatory that is expected to be launched in 2034. The observatory will operate a near-equilateral triangle constellation of three spacecraft in formation flying around the Sun with Earth-like orbits. The observatory will establish, for the first time, a huge laser interferometer of three arms separated by 2.5 million km at pm/ p H z sensitivity, allowing detection of GW signals in the low-frequencies (mHz) regime. Using technology proven by LISA Pathfinder and GRACE-Follow on mission, the LISA metrology system will continuously operate heterodyne laser interferometers in order to measure the stretching and squeezing of space-time coupled onto their laser links as pm-level pathlength displacements and recorded as tiny µ-cycle phase fluctuations over thousands of seconds by an on-board instrument so-called Phase Measurement System (PMS) or shortly "Phasemeter”. This master thesis investigates the thermo-mechanical design of an engineering model, currently under early phases of development, for the PMS instrument onboard the LISA S/C. The mechanical enclosure has been designed following a modular approach. Each PCB will be assembled into an individual enclosure, so future upgrades in the design without affecting the entire architecture. The thermal analysis conducted so far has concluded with the feasibility of a passive thermal management system in vacuum environments, based on heat conductivity throughout the mechanical enclosure towards the instrument baseplate. In particular, the following instrument features have been included within the analysis: 1. analog signal conditioning electronics, 2. analog-to-digital conversion, and 3. FPGA core signal processing, 4. high-phase fidelity frequency synthesis and 5. frequency distribution chain, i.e., all features with the most stringent thermal requirements of the PMS-EM architecture. Although the high-power consumption demands of the instrument, the proposed thermo-mechanical design showed a suitable implementation for reliable operation of components, below maximal specified temperature ranges, allowing safe operation of the electronics over mission lifetime. As the proposed design relies only on passive conductive heat transfer methods, it is implicit a reduction of instrument complexity, avoiding complex thermal approaches based on heat pipes distributions or active control systems. Moreover, the modular approach and thermal management system enhances the integration with adjacent modules and reduce cost when assembly the instrument within the payload. In this master thesis, it has been also designed and manufactured several mechanical enclosures, together with an active thermal management system, for preliminary prototyping of analog signal acquisition electronics. These prototypes have been tested in air, setting the thermal stability requirement at the thermal reference point (TRP). Test results have verified a thermal stability requirement below 0.1 K/Hz in order to accomplish with the stringent µ-cycle phase noise performance in the mHz frequency band. Further work will test those prototypes in Vacuum conditions, consolidating thermal modelling and noise coupling as initial precursors of the PMS-EM thermally critical module developments.

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.

As the engineering profession moves from prescriptive or “deemed-to-satisfy” approaches towards design methodologies based on quantification of performance, sophisticated modelling tools are increasingly needed, especially when complex combinations of demand and capacity are encountered. Recourse is invariably made to advanced computational tools to provide high fidelity solutions to large and complex problems, such as the response of structural systems or components to thermomechanical actions. Software packages based on the finite element method are most commonly used for such analyses. There are some essential prerequisites to effective use of advanced computational software for complex nonlinear problems, which are often ignored, particularly in professional practice. These include a thorough understanding of the underlying mechanics of the problem under consideration; a good appreciation of the approximation methods for modelling the problem properly (e.g. the choice between elements, continuum or structural, low or high order interpolation, degree of mesh refinement necessary and so on); and perhaps most importantly ensuring that the software is reliable and is able to reproduce established fundamental solutions to an acceptable degree of accuracy. This thesis attempts to address most of these issues but focusses primarily on the last mentioned prerequisite and provides a range of novel and unprecedented fundamental solutions for beams, plates, and shallow shells subject to moderate or extreme thermomechanical loads such as those resulting from a fire. Geometric and material nonlinearities are included in the proposed formulations along with the most common idealised boundary conditions. Thermally induced deformations generate large displacements and require the solutions to account for geometric nonlinearity, while material nonlinearity arises from the degradation of the material at elevated temperatures. In the context of structural performance under extreme thermal action (such as fire), a finite element procedure is employed to analytically characterise generic temperature distributions through the thickness of a structural component arising from different types of fire exposure conditions including: a “short hot” fire leading to a high compartment temperature over a relatively short duration; and a “long cool” fire with lower compartment temperatures, but over a longer duration. Results have shown that despite the larger area under the long cool fire time-temperature curve, which traditionally represented the fire severity, the effect of the short hot fire on the nonlinear responses of beams, plates, and shallow shells is more pronounced. Also, the effect of temperature-dependent material properties is found to be more pronounced during the short hot fire rather than the long cool fire. Comparison studies have confirmed that while the current numerical and theoretical approaches for analysing of thin plates and shells are often computationally intensive, the proposed approach offers an adequate level of accuracy with a rapid convergence rate for such structures. The solutions developed can be used to: verify software used for modelling structural response to thermomechanical actions; help students and professionals appreciate the fundamental mechanics better; provide relatively quick solutions for component level analyses; and visualise internal load paths and stress trajectories in complex structural components such as composite shells that can help engineers develop deeper insights into the relevant mechanics. The formulations developed are versatile and can be used for other applications such as laminated composite or orthotropic shallow shells. A very significant by-product of developing such fundamental solutions is their potential use in the development of highly accurate hybrid elements for very efficient modelling of large problems. While this has not been fully developed and implemented in the current work, the requisite theoretical framework has been developed and reported in one of the appendices, which can be used to develop such elements and implement on an appropriate software platform.

Hot Plane Strain Compression (PSC) testing is a thermomechanical testing method used to simulate the deformation condition of industrial rolling. Thermomechanical processing (TMP) factors such as the amount of strain, strain rate and temperature all influence the microstructural evolution. The geometry of the PSC test sample and anvil are important factors in order to achieve the plane strain condition and acceptable strain distribution within deformed sample. Geometrical factors such as the breadth ratio (BR) relates the the samples breadth (b) to anvils face width (w) and this ratio has a significant effect on the breadth spread of the sample. The height ratio (HR) relates w to the samples height (h) and this ratio has a significant effect on the strain distribution. Two different geometric PSC testing configurations were investigated for this study, the one configuration had less favourable geometric ratios with a BR of 3 and a HR of 1 and the other configuration had more favourable ratios, with the BR of 4.62 and the HR of 1.3. This investigation is to evaluate the feasibility of a newly installed TMP machinery, the Gleeble 3800, to simulate the hot finishing rolling conditions by the use of hot PSC tests for the production of the can body stock (CBS) aluminium alloy AA3104. Single hot PSC tests were carried out at temperatures of 300, 350 and 400 ⁰C at strain rates of 10, 30 and 100 sec-1 and multi-pass hot PSC tests were carried out to simulate the different rolling passes experienced on the hot finishing rolling mill of the production of the aluminium alloy AA3104. The strain rate, temperature control, flow stress and microstructural flow were investigate to establish whether PSC testing is feasible on the Gleeble 3800.

De nombreux liquides subissent un changement de volume lorsqu'ils gèlent. Pour l'eau et certaines solutions aqueuses, l'expansion volumétrique au cours de la solidification peut entraîner une série de problèmes mécaniques. Dans l'industrie automobile, l'expansion de changement de phase (ECP) met en cause la sécurité des réservoirs des véhicules aux saisons froides. Une des questions les plus problématiques est l'expansion de la solution aqueuse d'urée (SAU) dans le réservoir du système SCR des véhicules diesels. Lorsque le liquide gèle, les composants intérieurs ainsi que le réservoir lui-même peuvent être endommagés dû à la pression apportée par la dilatation du liquide solidifié. Dans le centre , une méthode numérique est fortement attendue afin de prévoir la répartition de la température, des contraintes ainsi que de la déformation des composants lors d'un processus de solidification. Du fait que les informations sur la solution d'urée restent limitées, la structure de la glace cristalline ainsi que ses comportements mécaniques sont principalement passés en revue. La préférence d'orientation de croissance des grains de glace à l'interface de cristallisation met en évidence, l'hypothèse de l'ECP non-isotropique pour des problèmes de solidification. Une série de tests mécaniques a été réalisée afin d'obtenir les propriétés basiques de SAU à l'état solide à différentes températures. Une méthode « différence-volume » a été appliquée pour mesurer la variation de la densité de la SAU lors du processus de solidification. Pour la suite, des études analytiques thermiques et mécaniques sont effectuées. Pour l'aspect thermique, le problème classique de Stefan est passé en revue. Un schéma de différence-finie est proposé et il permet de calculer la position de l'interface et les profils de température pour un modèle sphérique. Pour l'aspect mécanique, un modèle sphérique similaire est établi à la base de l'ECP non-isotropique. Les solutions analytiques des contraintes et de la pression liquide sont présentées en fonction de la position de l'interface. Une méthode éléments-finis thermo-mécaniquement couplée est développée afin de simuler efficacement les contraintes thermiques, les déformations et la pression liquide dans un problème de solidification avec des relations constitutives de comportement non-linéaires. Les contraintes thermiques sont calculées en chaque point d'intégration en résolvant les équations elasto-viscoplastiques avec l'ECP non-isotropique. Le problème aux limites est résolu par la méthode de Newton-Raphson. Cette procédure est implémentée dans le package Abaqus via un UMAT. La méthode est validée d'abord pour les aspects algorithmiques par les solutions analytiques, puis pour les paramètres de comportement retenus par une série de tests expérimentaux. De plus, une étude de cas réaliste sur un réservoir de la SAU est introduite. Les avantages et les limitations de la méthode numérique lors d'une application sont évalués
Many liquids involve a change in volume when they freeze. For water and some aqueous solutions, the volumetric expansion during solidification may invoke a series of mechanical issues. In automobile industries, the security of tanks installed in vehicles is challenged by the Phase-Change Expansion (PCE) of the freezing liquid in cold conditions. One of the most problematic issues is the expansion of Aqueous Urea Solution (AUS) in the SCR tank of diesel vehicles. As the liquid freezes, interior components may be deformed under the stress or pressure of the expanding AUS, potentially leading to failures of the storage tank. In the product center, a numerical method is of high demand to perform thermo-mechanical analysis to predict the temperature and stress distribution during a liquid solidification process in their tanks. In this work, a bibliographic study is carried out first on the basic knowledge of the ice and AUS. Due to the very limited information on urea solution in the literature, the structure and behaviors of freshwater ice are mainly reviewed. The grain orientation preference at the growth interface of polycrystalline ice provides the evidence of non-isotropic PCE for the solidification problem. A series of mechanical tests have been performed to characterize the basic properties of the solidified AUS at different temperatures. The density evolution is measured using a volume-difference method. Then, both thermal and mechanical analytical studies are performed. The classical thermal Stefan problem is reviewed and a finite-difference scheme is proposed to calculate the interface position and temperature profiles of a spherical solidification model. Mechanically, a similar spherical model is established based on the non-isotropic PCE phenomenon of ice growth. The solutions of stress distribution and liquid pressure evolution are given as a function of the solidification interface position. Finally, an efficient thermo-mechanical FEM is proposed to evaluate the thermal stress, strain, displacement and pressure in solidification problems with highly nonlinear relations. Three particular methods for treating the liquid phase with fixed-grid approaches are introduced. The thermal stress is computed at each integration point by integrating the elasto-viscoplastic constitutive equations with non-isotropic PCE. Then, the boundary value problem is solved using the full Newton-Raphson method. This procedure is implemented into the FE package Abaqus via a UMAT subroutine. The numerical model is validated first for the algorithmic aspect by the analytical solutions, and then for the parametric calibration by a series of benchmark tests. In the end, a realistic study case on a real-size AUS storage tank is introduced. Advantages and limitations of the numerical method in the application are evaluated

This research aims at understanding the conditions that lead to reaction initiation of polymer-bonded explosives (PBXs) as they undergo mechanical and thermal processes subsequent to impact. To analyze this issue, a cohesive finite element method (CFEM) based finite deformation framework is developed and used to quantify the thermomechanical response of PBXs at the microstructure level. This framework incorporates the effects of large deformation, thermomechanical coupling, failure in the forms of micro-cracks in both bulk constituents and along grain/matrix interfaces, and frictional heating. A novel criterion for the ignition of heterogeneous energetic materials under impact loading is developed, which is used to quantify the critical impact velocity, critical time to ignition, and critical input work at ignition for non-shock conditions as functions of microstructure of granular HMX and PBX. A threshold relation between impact velocity and critical input energy at ignition for non-shock loading is developed, involving an energy cutoff and permitting the effects of microstructure and loading to be accounted for. Finally, a novel approach for computationally predicting and quantifying the stochasticity of the ignition process in energetic materials is developed, allowing prediction of the critical time to ignition and the critical impact velocity below which no ignition occurs based on basic material properties and microstructure attributes. Results are cast in the form of the Weibull distribution and used to establish microstructure-ignition behavior relations.

Applications of chromium vary widely (refractories, chemicals and metallurgical); however, the greatest benefit of chromium is its ability to improve the corrosion resistance, strength and hardness of steel. South Africa possesses approximately 75% of the viable global chromite reserves and, as a result, dominates the ferrochrome market with production in excess of 5 million mega tonnes per year - making it an industry of extreme importance to the South African economy Submerged arc ferroalloy production furnaces mainly use Soderberg electrodes - self–baking continuous electrodes that are produced in situ during furnace operation. Electrode breakings may affect a furnace in a number of ways depending on the nature and location of the break. Low furnace power input, abnormal charging and tapping conditions, as well as loss of production are among the more common negative implications associated with electrode breaks. The successful operation of Soderberg electrodes is dependent on two main factors: high quality electrode paste and effective electrode management procedures. This study focused on electrode paste quality. The raw materials utilised in the production of Soderberg electrode paste consists of calcined anthracite mixed with a tar pitch binder. In this study the focus was on the development of an experimental procedure to measure the dimensional changes of electrode paste raw materials as a function of temperature by means of thermomechanical analysis (TMA). Three uncalcined anthracite (Zululand chips, Zululand duff, and Tendele duff) and two tar pitch samples (low and high softening point pitches, i.e. LSP and HSP) were obtained from a local paste producer. Electrode graphite samples were also obtained from a local pre–baked electrode supplier. The experimental procedure for both the anthracite and tar pitches consisted of two phases: sample preparation and TMA measurements. During the sample preparation procedure for the tar pitches, the two tar pitches were heat treated in order to prevent softening in the TMA (preventing possibly damage the instrument), where after pellets were pressed for TMA measurement. The anthracite samples were calcined at 1200, 1300 and 1400°C in the anthracite sample preparation phase. TMA sample pellets of calcined and uncalcined anthracite were pressed using only water as a binder. TMA was performed on pellets produced from the heat–treated tar pitch samples, uncalcined and calcined anthracite samples, as well as core drilled pellets of the pre–baked electrode graphite. The dimensional changes of these pellets were measured, as a function of temperature, through three consecutive heating (room temperature to 1300°C) and cooling (1300°C to approximately 100°C) cycles under a N2 atmosphere. A significant shrinkage (> 12%) for both the LSP and HSP tar pitches occurred during the first TMA heating cycle. During the second and third heating cycles of the LSP and HSP tar pitches, dimensional changes were approximately 2%. This indicates that substantial structural reordering of the carbonaceous binder takes place during the first heating cycle. TMA results obtained for all three the calcined anthracite samples investigated indicated thermal dimensional changes of less than 1%. The anthracite samples calcined at the highest experimental calcination temperature (1400°C) prior to TMA analysis had the smallest dimensional changes. This confirmed that higher calcination temperatures result in a higher level of structural ordering and dimensional stability. Considering the combined calcined anthracite and tar pitches TMA results, the importance of the initial baking of a Soderberg electrode at temperatures exceeding the baking isotherm temperature (475°C) becomes apparent - the dimensional behaviour of the tar pitch binder and the calcined anthracite differ dramatically, making the newly–formed electrode very susceptible to breakage. Once structural reordering of the pitch had taken place, thermal dimensional behaviours of the materials are much more similar, significantly reducing the risk of thermal shock–induced electrode breakages. In contrast to the relatively small dimensional changes measured for the calcined anthracite samples, the shrinkages measured for the uncalcined samples during the first TMA heating/cooling cycle were substantial (6–8%). This indicates the importance of the anthracite calcination process, before the electrode paste is formulated. Improperly calcined anthracite present in electrode paste would result in additional dimensional shrinkage that would have to be accommodated in the baking of a new electrode section. Considering the large shrinkage of the tar pitch that already takes place, it is unlikely that a strong enough electrode would be formed if this occurs. From the results, it also became apparent that the anthracite with the highest fixed carbon and lowest ash contents exhibited the smallest shrinkage during in situ TMA calcination. High fixed carbon, low ash type anthracites are therefore less prone to dimensional instabilities in Soderberg electrodes, as a result of poor calcination. The dimensional changes observed in the calcined anthracites were very similar to those observed for the electrode graphite samples. The expansions/shrinkages observed in the graphite samples were mostly less than 0.5%, whereas the expansions/shrinkages observed in the various calcined anthracites were approximately 0.6 to 0.9%. The difference in the magnitude of the dimensional behaviour between the calcined anthracites and the graphite can be attributed to the fact that the graphite had already undergone maximum structural ordering (having been pre–baked at 3000°C).
Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

In the vehicle industry today materials are sought that are both light and have a high strength. One manufacturing method that can produce parts with both these properties is a method called die quenching. During die tool development simulations are used to predict the material properties in the final part and there is a continuous strive for improving the simulation tools. The aim of this report is to demonstrate how a CFD (Computational Fluid Dynamics) problem and a conjugate heat transfer problem can be set up in LS-DYNA and to evaluate how well the simulation results agree with experimental results. Simulations of the cooling of the die quenching is a first step towards performing a complete mechanical forming simulation that is coupled with CFD analysis in order to predict the final part’s material properties more accurately. In the thesis two experiments were simulated. To be able to perform such an analysis a conjugate heat transfer analysis is needed, in the thesis a heated cube was studied because it had experimental values for the temperature available. The flow in a quenching tool is also discussed and the pressure drop in the tool is compared with experimental values. Temperatures from the conjugate heat transfer are compared with experimental values and sources of errors are discussed in both simulations. The conclusion of this report is that the CFD solver in LS-DYNA is a promising tool that can be used to determine more accurate material properties of the final parts in a coupled thermomechanical forming simulation.

Nanofibrous membranes are a promising material for tailoring the properties of laminated CFRP composites by embedding them into the structure. This project aimed to understand the effect of number, position and thickness of nanofibrous modifications specifically on the damping behaviour of the resulting nano-modified CFRP composite with an epoxy matrix. An improvement of damping capacity is expected to improve a composites lifetime and fatigue resistance by prohibiting the formation of microcracks and consequently hindering delamination, it also promises a rise in comfort for a range of final products by intermission of vibration propagation and therefore diminution of noise. Electrospinning was the technique employed to produce nanofibrous membranes from a blend of polymeric solutions. SEM, WAXS and DSC were utilised to evaluate the quality of the obtained membranes before they were introduced, following a specific stacking sequence, in the production process of the laminate. A suitable curing cycle in an autoclave was applied to mend the modifications together with the matrix material, ensuring full crosslinking of the matrix and therefore finalising the production process. DMA was exercised in order to gain an understanding about the effects of the different modifications on the properties of the composite. During this investigation it became apparent that a high number of modifications of laminate CFRP composites, with an epoxy matrix, with thick rubbery nanofibrous membranes has a positive effect on the damping capacity and the temperature range the effect applies in. A suggestion for subsequent studies as well as a recommendation for the production of nano-modified CFRP structures is included at the end of this document.

Abstract In TMP quality control, on-line control applications are the goal. Reliable, versatile systems are needed for this task. Various model-based systems have been developed but their performance has not always been good enough. This study evaluated the applicability of fibre analysers utilising image analysis techniques for TMP quality control. In addition to the standard measurement results of these analysers, the values of primary measurements and the fibre images obtained with these analysers were studied. Two sets of test samples were used. The first set contained 24 samples from trials at a Scandinavian TMP plant, and this set made up the the main part of the test material. The other series was a set of 13 samples obtained from another TMP plant during a short testing period that took place between normal operation runs. In this set the quality variations were understandably smaller. Fibre size analyses were made with an optical analyser that applies image analysis techniques on single fibres. The effects of fibre length, fibre width, cell wall thickness, coarseness, fines content, fibre curl and external fibrillation on the quality potential of TMP were evaluated. Both the measured averages and the values of single fibres were used in the evaluation. A tube flow fractionator was used to evaluate fibre properties during the fractionation process. The results of the fractionation as well as the original measurement signals were used in the evaluation. Both analysers were set to save images of fibres during the analyses. These images were later analysed by using standard image analysis procedures, in order to obtain additional information of the fibres. Correlation analysis and principal component analysis were used as tools to find out dependencies between fibre properties and pulp quality. Fibre curl and fibre width were found to be the most promising fibre features for use in TMP quality evaluation with optical fibre analysers. These variables accounted for more than 70% of the variations in most of the evaluated TMP quality variables. In the tube flow fractionator results, the signals of the long fibre fraction were also able to explain over 70% of the variations in drainage, bonding strength, roughness, and porosity. The values of the fibre size analyser, together with the measurements and features derived from the images of the tube flow fractionator, provided significant additional information for quality estimation. The most important variables in TMP quality calculation were fibre curl, fibre width, and the tube flow fractionator signals for the long fibre fraction. Both the on-line analysers using image analysis for fibre measurements, and the tube flow to fractionate pulp samples before measurement, are able to provide reliable and relevant information for TMP quality control
Tiivistelmä Kuumahierteen laadunvalvonnan tavoitteena on luotettava ja monipuolinen on-line-mittauksiin perustuva laadunohjaus. Tehtävään on kehitetty mallipohjaisia järjestelmiä, mutta ne eivät ole olleet aina riittävän suorituskykyisiä. Tässä tutkimuksessa selvitettiin konenäköön perustuvien kuituanalysaattoreiden soveltuvuutta kuumahierteen laadunohjauksen tarpeisiin. Sekä analysaattoreiden tuottamaa valmista mittaustietoa, että niiden kuitukohtaisia mittaustuloksia ja kuvamateriaalia tutkittiin. Tutkimuksessa käsiteltiin kahta erillistä koesarjaa. Ensimmäinen sarja sisälsi 24 koepistettä erään TMP-laitoksen koeajosta. Nämä näytteet muodostivat pääosan testimateriaalista. Toinen sarja koostui erään toisen tehtaan tuotantomassoista otetuista 13 näytepisteestä. Tässä sarjassa laatumuutokset olivat huomattavasti vähäisempiä kuin edellisessä sarjassa. Kuidunkokoanalyysit tehtiin konenäköä soveltavalla, yksittäisiä kuituja mittaavalla laitteella. Tutkimuksessa selvitettiin kuidunpituuden, kuidun leveyden, seinämävahvuuden, pituusmassan, hienoaineen, kuidun kiharuuden ja kuidun ulkoisen fibrillaation vaikutusta kuumahierteen laatuun. Näytekohtaisten keskiarvojen lisäksi myös kuitukohtaiset tiedot analysoitiin. Virtauskenttäfraktionaattorilla tutkittiin kuitujen optisia ominaisuuksia lajittelutapahtuman aikana. Mittaustuloksista käsiteltiin sekä valmiit jaetulokset että mittaussignaalien jakautumat lajittelutapahtuman ajalta. Molempien laitteiden tallettamia kuitukuvia analysoitiin niiden mahdollisesti sisältämän mutta vielä hyödyntämättömän informaation selvittämiseksi. Analyysityökaluina käytettiin korrelaatioanalyysiä ja pääkomponenttianalyysiä. Konenäköön perustuvan kuituanalysaattorin antamista tuloksista kuidun kiharuus ja kuidun leveys osoittautuivat luotettavimmiksi laatupotentiaalin indikaattoreiksi. Selitysasteet suurimmalle osalle mitattuja massan lujuus- ja arkkiominaisuuksia olivat yli 70 %. Virtauskenttäfraktionaattorin tuloksissa pitkäkuituosuutta vastaavat signaalijakeet antoivat samaten yli 70 %:n selitysasteet suotautuvuuden, sidoslujuuden, karheuden ja huokoisuuden arvioinnille. Kuituanalysaattorin kuidunkokoarvojen ja virtauskenttäfraktionaattorin signaalijakeiden ja -jakautuma-arvojen sekä kuvapiirteiden avulla lasketut kahden muuttujan mallit toivat useimpien käsiteltyjen laatumuuttujien estimaattien selitysarvoihin merkittävää parannusta. Tärkeimmät muuttujat kuumahierteen laatupotentiaalin arvioinnissa olivat kuidun kiharuus ja kuidun leveys sekä virtauskenttäfraktionaattorin signaalijakeet. Konenäköä soveltava kuituanalysaattori ja virtauskenttäfraktionaattori soveltuvat hyvin kuumahierteen laadun valvonta- ja ohjausmallin pohjaksi

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
Great works of infrastructure such as hydroelectric plants require, in it building, large concrete volumes classified as mass concrete structures. These works of power generation are strategic and fundamental for the development of a nation. However, during construction and throughout its life they may have pathological manifestations that compromise its stability. One of the most common problems in this type of structure is cracking caused by heat generated due to the exothermic reaction of cement hydration. Therefore, we had to analyze the thermal behavior of concrete, concrete with similar consistency and resistance like the concrete utilized in construction dam, and analyze how the type of cement utilized and its contents affects these parameters. In addition, we studied the evolution of compressive strength and dynamic modulus of elasticity as the cement hydrates. Finally, we compared the thermal performance of concretes produced with the results obtained from a commercial software. To carry out the experiment, concrete blocks were produced of 1,5m with cements CP II E 32 RS and CP IV 32 with consumption 241,2 kg/m and 330,0 kg/m for thermal analysis, besides cylindrical specimens for the remaining analyzes. The results showed that the thermal behavior of concrete has a small dependence on the type of cement, however the cement content affects too much this behavior, and the cement CP IV 32 showed higher thermal variations. It was also observed that the development of compressive strength is strongly dependent on the cement content, but it has low dependency on the type of cement. Computer modeling presented satisfactory results when it was compared to results of the thermal evolution blocks.
As grandes obras de infraestrutura como as centrais hidroelÃtricas requerem na sua construÃÃo grandes volumes de concreto, sendo classificadas como estruturas de concreto massa. Essas obras de geraÃÃo de energia sÃo estratÃgicas e fundamentais para o desenvolvimento de uma naÃÃo. Entretanto, durante sua construÃÃo e ao longo de sua vida Ãtil estas podem apresentar manifestaÃÃes patolÃgicas que comprometem sua estabilidade. Um dos problemas mais comuns nesse tipo de estrutura à a fissuraÃÃo causada pela energia tÃrmica gerada devido à reaÃÃo exotÃrmica de hidrataÃÃo do cimento. Diante disso, buscou-se analisar como se dà o comportamento tÃrmico de concretos utilizados para a construÃÃo de corpo de barragem, alÃm de analisar como o tipo de cimento utilizado e o seu teor afetam a variaÃÃo de temperatura da massa de concreto e os problemas causados por essa variaÃÃo. Buscou-se ainda analisar a evoluÃÃo da resistÃncia à compressÃo e do mÃdulo de elasticidade dinÃmico à medida que o cimento se hidratava. Por fim, comparou-se o comportamento tÃrmico dos concretos produzidos com os resultados obtidos por meio de um software comercial. Para a realizaÃÃo da parte experimental produziu-se blocos de concretos de 1,5 metros cÃbicos com cimentos CP II-E 32 RS e CP IV 32 com consumo de 241,2 kg/m e 330,0 kg/m para anÃlise tÃrmica, alÃm da moldagem de corpos de prova cilÃndricos para as demais anÃlises. Os resultados apontaram que o comportamento tÃrmico do concreto apresenta uma pequena dependÃncia do tipo de cimento. Entretanto, o teor de cimento afeta fortemente esse comportamento, sendo o cimento CP IV 32 o que apresentou maiores variaÃÃes tÃrmicas. Observou-se tambÃm que a evoluÃÃo da resistÃncia à compressÃo à fortemente dependente da quantidade de cimento, mas apresenta baixa dependÃncia do tipo de cimento. A modelagem computacional apresentou resultados satisfatÃrios quando comparado aos resultados da evoluÃÃo tÃrmica dos blocos produzidos.

In response to serious environmental and economic concerns, the design and production of aircrafts have been changing profoundly over the past decades with the nose-to-tail switch from metallic materials to lightweight composite materials such as carbon fibre reinforced plastic (CFRP). In this context, the present doctoral research work aimed to contribute to the development of a CFRP booster casing, a real innovation in the field initiated and conducted by Safran Aero Boosters. More specifically, this thesis addresses the matter of joining metal/CFRP hybrid structures, which are prone to possibly detrimental residual stresses.The issue is treated with an approach combining experimental characterisation and finite element (FE) simulations. The multi-layered system’s state of damage was systematically examined on hundreds of micrographs, and the outcome of this study is presented under the form of a statistical analysis. Further, the defects’ 3D morphology is investigated by incremental polishing. A number of thermal and mechanical properties are measured by diverse physical tests on part of the constituent materials, i.e. the aerospace grade RTM6 epoxy resin, the structural Redux 322 epoxy film adhesive, and AISI 316L stainless steel. They are used as input data in a FE model of the multilayer that is developed and progressively refined to obtain detailed residual stress fields after thermal loading. These results are compared to experimental data acquired by X-ray diffraction stress analysis and with the curvature-based Stoney formula. Cohesive elements are placed at specific locations within the FE model to allow simulating progressive damage. Peel tests, mode I, mode II and mixed mode I/II fracture tests are thus performed in view of measuring the joint toughness. The results of these tests are discussed and the presence of residual stress in the fracture specimens is highlighted. Key information for the calibration of the cohesive law is finally identified via inverse FE analysis of the mode I test, this being a significant step in the process of building a damage predictive FE model of the multi-layered system.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

In this dissertation a finite element procedure using the Disturbed State Concept constitutive models is proposed for the thermomechanical analysis of electronics packaging problems. First, microelectronics packaging types and the problems facing the electronics industry are discussed. Next, the literature in the field of constitutive models and the finite element procedures available for microelectronics packaging materials and interfaces is reviewed. The previous formulation of the Disturbed State Concept is modified so that different stresses and different strains are allowed in the intact and the fully adjusted parts of the material. Furthermore, the thermo elasto-viscoplastic with disturbance constitutive model is improved to handle the continuous temperature change and the hold time. These last features enhance the model so that it can be used in a finite element code to simulate the behavior of the microelectronics packaging materials and interfaces in temperature cycling. A new finite element procedure is developed to implement the improved Disturbed State Concept formulation. The finite element procedure includes a wide range of material models, starting from the linear elastic to thermo elasto-viscoplastic with disturbance. In order to eliminate the finite element mesh sensitivity encountered in strain-softening materials, a new procedure is proposed. The Disturbed State Average Strain method reduces or eliminates the finite element mesh sensitivity. This is proved through a number of example problems. The proposed finite element procedure is verified against a number of sets of experimental data obtained from the literature.

A tetrazole is a 5-membered ring containing 4 nitrogens and 1 carbon. Due to its energetic potential and structural similarity to carboxylic acids, this ring system has a wide number of applications. In this thesis, a new and safe sustainable process to produce tetrazoles was designed that acheived high yields under mild conditions. Also, a technique was developed to form a trityl-protected tetrazole in situ. The rest of this work involved the exploitation of the energetic potential of tetrazoles. This moiety was successfully applied in polymers, ionic liquids, foams, and gels. The overall results from these experiments illustrate the fact that tetrazoles have the potential to serve as a stable alternative to the troublesome azido group common in many energetic materials. Due to these applications, the tetrazole moiety is a very important entity.

The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner.   The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner.   The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given.   The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.

Les phénomènes de contact (rugosité, frottement, usure, etc.) sont importants dans le fonctionnement des freins à friction. Ils peuvent influencer leurs performances en modifiant l'état de surface et des matériaux. Afin de cerner ce problème, les industriels se basent sur des méthodes de type essai/erreur qui sont coûteuses et peu efficaces face aux exigences actuelles.L'objectif de cette thèse est de proposer une alternative consistant à modéliser numériquement les systèmes, tels qu'un frein à friction, avec des hypothèses réalistes au niveau du contact contrairement aux approches classiques considérant le contact parfait. Ce challenge a été surmonté en développant une stratégie numérique associant un modèle macroscopique du système et plusieurs modèles micro traitant les phénomènes de contact. La modélisation microscopique du contact est faite grâce à des modèles thermique et mécanique considérant la rugosité. Le problème est résolu avec des techniques d'optimisation. Le cas d'un matériau à gradient de propriétés normal à la surface et l'usure sont aussi considérés. A partir de ces calculs, les paramètres de contact (pression, température, etc.) sont analysés en fonction des propriétés de surface et du matériau. Ensuite, le modèle macroscopique est enrichi avec ces paramètres tout en conservant la planéité des surfaces en contact. Avec cette technique, le temps de calcul est réduit en comparaison à des calculs Éléments Finis complets. Cette stratégie multi-échelle a été adoptée pour l'analyse dynamique et thermo-mécanique des freins. Les résultats des simulations numériques montrent l'impact de l'interface et de son évolution sur les performances du frein et vice-versa
Contact phenomena (roughness, friction, wear, etc.) are central to friction brake functioning as they lead to the modification of surface and material properties which may affect the braking performances. To address these issues, the manufacturers use an experimental approach based on feedback tests which is expensive and inefficient against the current requirements.The objective of this work is to propose an alternative based on numerical modeling of applications like brakes with realistic assumptions at the contact interface level, unlike the classical approaches that assume a perfect contact. This challenge has been overcome by building a numerical methodology associating a large scale model of the system and several micro scale models of contact phenomena. The micro scale contact modeling has been performed with thermal and mechanical models considering roughness. The problem is solved by means of constrained quadratic programming. A normal gradient of material properties and wear have also been considered. From this analysis, surface parameters (pressure, temperature,etc.) are analyzed depending on roughness and material properties. Thereafter, a Finite Element large scale model is embedded with these parameters while the surface is flat at this scale. With this technique, the CPU time is considerably reduced and the precision is maintained in comparison to classical Finite Element calculations. This multi-scale methodology has been used for dynamic and thermo-mechanical analyses of braking systems. The results of numerical simulations highlight the impact of the contact interface and its evolution on the system behavior, and vice versa

Epoxy resin is an important engineering material in many industries such as electronics, automotive, aerospace, etc not only because it is an excellent adhesive but also because the materials based on it provide outstanding mechanical, thermal, and electrical properties. Epoxy resin has been proved to be an excellent matrix material for the nanocomposites when including another phase such as inorganic nanofillers. The properties of a nanocomposite material, in general, are a hybrid between the properties of matrix material and the nanofillers. In this sense, the thermal, mechanical, and electrical properties of a nanocomposite may be affected by the corresponding properties of matrix material. When the sonication is used to disperse the nanofillers in the polymer matrix, with the dispersal of the nanofillers, there comes some modification in the matrix as well and it finally affects the properties of nanocomposites. In this regard, we attempted to study the thermal, mechanical, and dynamic properties of EPON 862 epoxy resin where ultrasonic processing was taken as the effect causing variable. Uncured epoxy was subjected to thermal behavior studies before and after ultrasonic treatment and the cured epoxies with amine hardener EPICURE 3223 (diethylenetriamine) after sonications were tested for mechanical and dynamic properties. We monitored the ultrasonic processing effect in fictive temperature, enthalpy, and specific heat capacity using differential scanning calorimetry. Fictive temperature decreased whereas enthalpy and specific heat capacity were found to increase with the increased ultrasonic processing time. Cured epoxy rectangular solid strips were used to study the mechanical and dynamic properties. Flexural strength at 3% strain value measured with Dillon universal testing machine under 3-point bending method was found to degrade with the ultrasonic processing. The storage modulus and damping properties were studied for the two samples sonicated for 60 minutes and 120 minutes. Our study showed that the 60 minutes sonicated sample has higher damping or loss modulus than 120 minutes sonicated sample.

Les systèmes de protection thermique ablatifs, couramment utilisés dans l'industrie de l'aérospatiale sont généralement des matériaux composites, dont la dégradation permet d'isoler thermiquement les éléments subissant des flux aérothermiques sévères. On recense dans la littérature de très nombreux systèmes, tant en terme de matrice que de type de renfort. Face à la diversité des matériaux existants et la multiplicité des sollicitations auxquelles ils peuvent être soumis, il est aujourd'hui nécessaire d'acquérir une meilleure connaissance de l'influence de la composition (matrice, renfort et porosité) de ces matériaux sur leur comportement thermique et leur tenue à l'ablation. La démarche scientifique des travaux s'articule autour d'un volet expérimental et du développement d'un modèle numérique. La caractérisation expérimentale a été construite en trois étapes, explorant chacune le comportement des matériaux à une échelle différente : le comportement thermo-chimique a été caractérisé par des essais d'ATG, de TMA et de DSC, le comportement thermique a été évalué grâce à un banc muni d'une torche oxygène acétylène. Enfin, la tenue des matériaux à un jet aérothermique sévère a été testée sur un banc d'essai équipé d'un minipropulseur. Ce dernier banc permet de tester des échantillons de plusieurs dizaines de centimètres de large et d'étudier l'impact couplé de la thermique et de l'aérodynamique. En parallèle, un modèle numérique simple simulant l'ablation a été développé et validé. L'ensemble de ces travaux ont notamment permis de mettre en évidence les liens existants entre les propriétés thermo-physiques et la tenue à l'ablation d'un matériau composite. Appuyée par des observations microscopiques des matériaux dégradés, l'étude combinée des résultats aux différentes échelles a permis de proposer des scénarii de dégradation pour chacun des matériaux. Les principaux paramètres pilotant l'avancée d'un front d'ablation ont été identifiés, l'impact primordial de la porosité a notamment été démontré
Ablative thermal protection systems, commonly used in space industry, are usually made of composite materials. The degradation of these materials in surface allows to protect essential parts against severe aerothermal fluxes. In the literature, lots of different systems are described they are constituted of different type of matrix and reinforced by several kind of fibers. The diversity of the existing thermal protection systems raises the question of the influence of the composition of the materials on the thermal and ablative performances. The developed scientific approach is based on an experimental procedure coupled with the development of a numerical simulation. The material characterization is based on three experimental steps : the thermo-chemical behavior of the materials is investigated with TGA, TMA and DSC experiments, the thermal behavior under a severe flux is evaluated by an experimental bench equipped with an oxyacetylenic torch ; finally, the ablative behavior is characterized with a small jet-nozzle impacting the sample with a severe aerothermal flux. In parallel to the experimental characterization, a numerical simulation modeling of the ablative and thermal behavior of composite materials is developed. Links existing between the thermal behavior and the ablation resistance have been demonstrated. Degradation scenarios have been proposed thanks to the combined analysis of the experimental results at each stage of the characterization. Parameters controlling the ablation have been identified, the major impact of the porosity has been particularly demonstrated

The Breeding Blanket is an essential component of the DEMO fusion reactor and its design is one of the pivotal purposes of the DEMO project. Indeed, this component has to withstand severe operating conditions, as it is directly exposed to the plasma, making its design particularly challenging. In particular, the Water-Cooled Lithium-Lead (WCLL) BB concept is one of the candidates currently considered for the conceptual design of the European DEMO reactor. The development of a robust BB system is crucial for the design of the whole DEMO reactor and the thermo-mechanical assessment of the whole BB segments is mandatory to allow checking their structural performances in different loading scenarios. In this dissertation, a multi-scale procedure, allowing to investigate in detail the thermo-mechanical performances of an entire blanket segment, is proposed. In particular, the Central Outboard Blanket (COB) segment has been considered and the results are herewith presented. The structural performances have been investigated in view of the RCC-MRx design criteria.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
É considerado neste trabalho um modelo mecânico para simulação do comportamento anisotérmico de materiais inelásticos submetidos a carregamentos dinâmicos. O trabalho tem como motivação o estudo, através de simulações numéricas, dos efeitos da propagação da onda de tensão no meio, e de fenômenos como o aquecimento e a degradação local induzida pelas deformações inelásticas. A equação da energia com seus termos de acoplamentos entre os efeitos térmico e mecânico é incluída na modelagem. A teoria constitutiva utilizada baseia-se na mecânica do dano contínuo no contexto de variáveis internas sendo particularizada para materiais elastoviscoplásticos e aplicado ao caso de uma barra solicitada axialmente. O sistema não linear de equações diferenciais parciais resultante do modelo é resolvido através do uso uma técnica de decomposição do operador que permite a aplicação de procedimentos numéricos clássicos de solução. Dentre estes procedimentos, foi usado no trabalho, o método de Glimm. Exemplos numéricos retratando a evolução do dano e da temperatura induzida pela deformação plástica devido a carregamentos de impacto e de alta frequência, são apresentados e analisados. Comparações entre simulações com os modelos isotérmico e anisotérmico permitem caracterizar as influências da equação da energia e do dano.
This work presents a mechanical model for simulating the anisothermal behavior of damageable inelastic solids under dynamical loadings. The main motivation of this study is to investigate, by means of numerical simulations, the thermomechanical coupling in a simple one-dimensional problem involving the wave propagation phenomenon in a damageable non-isothermal solid. To achieve this goal, the equation of energy is taken into account in the modeling with the coupling terms between the thermal and mechanical effects. The damageable inelastic mechanical behavior is describe by means of an internal variable constitutive theory and the analysis is restricted to elastoviscoplastic solids. The resulting system of non linear partial differential equations is solved by using an operator splitting technique, along with classical numerical procedures such as the Glimm s method. Numerical examples which illustrate the damage and temperature evolution induced by the plastic deformation process due to impact and cyclic loadings are presented and analyzed. A suitable comparative analysis between simulations with and without the thermomechanical couplings shows the situations under which these terms are relevant.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho apresenta uma técnica numérica. baseada no Método de Decomposição do Operador (Operator Splitting Method) e algorítimos sequenciais associados (product formula algorithm) para simular o fenômeno de propagação de ondas em barras elasto-viscoplásticas. Este método tem boas propriedades de estabilidade e preciaão mesmo quando um esquema explícito de baixa ordem é utilizado na integração temporal. Esta técnica numérica é usada para simular carregamentos cíclicos de alta frequência em barras de aço austenítico a altas temperaturas.
The present work presents a numerical technique ( based on the Operator Split Method associated with product formula algorithm ) for simulating the wave propagation phenomenon in bars with any kind of elastic-viecoplastic oonstitutive equations. This method has very good properties of stability and precision even if explicit time evolution schemes are used. This numerical technique is used to simulate high frequency cyclic loadings in austenitic steel bars at high temperatures.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

New stricter environmental legislation requires lower emissions and fuel consumption of automotive engines. Therefore the fuel efficiency must be increased but this leads to higher loads in the engine. As for the exhaust system it is affected by higher thermomechanical loads. Until today the turbo manifold has been nitrocarburized in order to increase the wear resistance in slip joints with other exhaust components. The problem is that there is no knowledge of how the nitrocarburizing affects the thermomechanical properties of the material. The purpose of this thesis work is to examine the difference in thermomechanical properties with and without nitrocarburizing on the three different ductile irons High Silicon, SiMo51 and SiMo1000 intended for exhaust components. Thermo-mechanical fatigue (TMF) experiments were performed on test rods to evaluate difference in number of cycles to failure. In each cycle the test-rod was affected by a combination of mechanical loads and thermal loads resembling those found on exhaust components. Light optical microscopy, scanning electron microscopy and x-ray radiography were used to examine microcracks and damage mechanisms of the materials. It was found that the nitrocarburizing did not affect the number of cycles to failure in any large extent. Further, it was also found that SiMo1000 on average has the longest lifetime followed by SiMo51 and High Silicon. Although, the difference is small for many loadings and taking a 95% confidence band into account the curves overlap for many loading cases.

Les constructeurs automobiles utilisent des aciers auto-trempant à haute résistance au bore manganèse (22MnB5) pour des questions de sécurité et environnementale. La mise en forme à chaud de tôles constituées de cet acier impose aux outillages des contraintes mécaniques sévères et un échauffement intense. L'intégration d'une fonction de cisaillage sous presse à suivre permet de répondre à des problématiques rentabilité de production, mais les lames sont confrontées à des problèmes similaires de durabilité. L'objectif de cette thèse est de comprendre la dégradation des outils de cisaillage à chaud afin de proposer des guides de choix de matériaux d'outil (X38CrMoV5-3 ou X70CrMoV5-2) et de paramètres du procédé. Cela requiert l'estimation des sollicitations mécaniques et thermiques dans la partie active de l'outil. La méthodologie développée passe par quatre étapes : une recherche bibliographique, des essais de cisaillage à chaud sur un module spécifique du pilote MEFISTO de l'ICA, le développement d'un modèle thermomécanique éléments finis de l'opération et des analyses des microstructures. Un état de l'art portant sur la définition de l'opération de découpage de tôles, sur les propriétés physiques et mécaniques du matériau de tôle et des lames, le comportement à l'interface tôle/outil et sur les techniques permettant de simuler le découpage a été proposé. Des essais sur le module de découpage ont permis d'accéder à des résultats d'effort et des observations des endommagements des lames de cisaillage. Ces informations sont utilisées pour valider le modèle de calcul éléments finis. Ce modèle montre que les contraintes mécaniques sont locales, intenses et se déplacent dans l'arête de coupe. De plus, l'échauffement de l'outil engendre une température de surface proche des températures de revenu des matériaux d'outil. La comparaison des résultats de simulation numérique et de l'étude expérimentale permettent de comprendre le lien entre les dégradations observées et les sollicitations thermomécaniques
Car manufacturers are building using a self-hardening high strength boron steel (22MnB5) for safety and environmental concerns. But the shaping of sheets made of these kind of steel imposes on tools severe mechanical stresses and strong thermal transfer. The integration of a blanking function in transfer presses is a response to reach high profitability, but blades are subjected to the same durability problems. The aim of this thesis is to understand how hot blanking tools are wearing in order to give to manufacturers tool material guidelines (X38CrMoV5-3 or X70CrMoV5-2) and process parameters guidelines. To do so, an estimation of mechanical stresses and thermal solicitation is required. The methodology is based on four steps: literature search, hot blanking trials on a specific module of ICA laboratory industrial pilot MEFISTO, finite element simulations of the operation, and microstructural analysis. The state of art is focused on the description of the operation, the physical and mechanical properties of the blank material and tools materials, the blank/tool interface behavior, and the techniques used simulate the hot blanking process. Trials on the hot blanking module provided blanking force and observations of worn blades. These informations are needed to validate the finite element model. This model shows that mechanical stresses are local, intense and slides in the blade cutting edge. Moreover, the blade heating generates a surface temperature close to tool steel tempering temperature. Experimental results compared to numerical ones allow to understand the link between thermo-mechanical stresses and how the damage occurs

[ES] Las patologías óseas provocan en gran medida discapacidad física, siendo la regeneración de tejidos vivos uno de los campos más avanzados en Ingeniería de Tejidos. Consecuentemente, grandes esfuerzos se focalizan en el estudio de nuevos materiales bioabsorbibles para tratar remodelaciones de fracturas óseas. Es por ello que este trabajo se centra en estudiar las propiedades mecánicas y la interacción de las células en función de la hidrofobicidad y la química de diferentes polímeros bioabsorbibles comparados con polímeros no-bsorbibles. Por otro lado, cargas como Hidroxiapatita (HA) y Nanotubos de Haloisita (HNTs) se utilizaron para mejorar la afinidad, interacción y proliferación de células. Para ello, inicialmente se monitorizó el efecto de las cargas inorgánicas en las propiedades estructurales del polímero bioabsorbible Policaprolactona (PCL). Por lo tanto, se estudiaron las variaciones de propiedades térmicas y mecánicas de PCL provocadas por la adición de HA y HNTs. Este estudio preliminar permitió entender el efecto sinérgico entre el polímero y los grupos funcionales de las cargas inorgánicas, estableciendo el umbral de carga y optimizando el ratio de aditivación. En términos generales, se observó una mejora de las propiedades mecánicas cuando las dos cargas se utilizan simultáneamente. Asimismo, aprovechando la forma tubular de los HNTs, estos fueron utilizados como portadores de fármacos estudiando su habilidad para ser cargado con curcumina y su habilidad para liberar en un ambiente fisiológico. Conociendo por una parte la habilidad del HA de promover la formación de hueso nuevo compuesto por apatita y colágeno; y, por otra parte, que la HA y los HNTs alteran el comportamiento hidrofóbico de los polímeros; se estudiaron los cambios morfológicos provocados por la adición de HA y HNTs en dos familias de polímeros con químicas similares pero diferente hidrofobicidad. Por consiguiente, el poliéster hidrofóbico PCL se mezcló con ácido poliláctico (PLA) y se combinó con nanopartículas de HA y HNTs. Por otra parte, el altamente hidrofóbico poli(2-hidroxietil metacrilato (PHEMA) se copolimerizó con etil metacrilato (EMA) y se aditivó con HA y HNTs. Por lo tanto, la dispersión de cargas inorgánicas en las matrices poliméricas fue estudiada, además de la formación de hidroxiapatita en la superficie del polímero, y el rátio de degradación del PCL/PLA. Se observó que la introducción de HA en polímeros con carácter hidrofílico induce un alto ratio de nucleación de hidroxiapatita y de degradación de los polímeros bioabsorbibles. Sin embargo, los HNTs tienden a formar grandes agregados cuando el carácter hidrofílico del polímero aumenta, dando lugar a puntos de inicio de grietas y fallo del material. La culminación de este estudio se alcanzó mediante la monitorización de la viabilidad celular, proliferación y morfología de las células como efecto de la superficie química de los polímeros. La hidrofobicidad de la superficie del polímero afecta a la interacción de las células y esta se puede mejorar mediante la modificación del polímero con HA y HNTs. De ese modo, el incremento de la viabilidad celular con la adición de las dos cargas inorgánicas es inducido por la generación de nuevos centros reactivos de Ca2+ y PO4 3¿presentes en la HA, y los grupos silano (Si-OH) situados en la superficie de los HNTs. Por lo tanto, se observó que, en superficies hidrofóbicas, debido a un alto ratio de llegada de proteínas, estas compiten por el espacio dando lugar a interacciones pobres entre células y polímero mostrando una geometría celular redondeada. Sin embargo, en superficies hidrofóbicas al hallarse altamente solvatadas, las proteínas inicialmente encuentran mayor dificultad para llegar a la superficie, y con ello disponen de mayor espacio para organizarse y anclarse a la superficie, dando lugar a una mayor adhesión y proliferación de las cél
[CAT] Les patologies òssies provoquen en gran mesura discapacitat física, sent la regeneració de teixits vius un dels camps més avançats en Enginyeria de Teixits. Per consegüent, grans esforços es focalitzen en l'estudi de nous materials bioabsorbibles per a tractar remodelacions de fractures òssies. És per això que aquest treball es focalitza a estudiar les propietats mecàniques i la interacció de les cèl·lules en funció de la hidrofobicitat i la química de diferents polímers bioabsorbibles comparats amb polímers no-absorbibles. D'altra banda, càrregues com Hidroxiapatita (HI HA) i Nano-tubs d'Hal·loysita (HNTs) es van utilitzar per a millorar l'afinitat, interacció i proliferació de cèl·lules. Per aquest motiu, inicialment es va monitoritzar l'efecte de les càrregues inorgàniques amb les propietats estructurals del polímer bioabsorbible Policaprolactona (PCL). Per tant, es van estudiar les variacions de propietats tèrmiques i mecàniques de PCL provocades per l'addició de HA i HNTs. Aquest estudi preliminar va permetre entendre l'efecte sinèrgic entre el polímer i els grups funcionals de les càrregues inorgàniques, establint el llindar de càrrega i optimitzant la ràtio d'aditivación. En termes generals, es va observar una millora de les propietats mecàniques quan les dues càrregues s'utilitzen simultàniament. Així mateix, aprofitant la forma tubular dels HNTs, aquests van ser utilitzats com a portadors de fàrmacs estudiant la seva habilitat per a ser carregat amb cúrcuma i la seva habilitat per a alliberar en un ambient fisiològic. Coneixent d'una banda l'habilitat de l¿HA de promoure la formació d'os nou compost per apatita i col·lagen; i, d'altra banda, que l¿HA i els HNTs alteren el comportament hidrofòbic dels polímers; es van estudiar els canvis morfològics provocats per l'addició de HA i HNTs en dues famílies de polímers amb químiques semblants però diferent hidrofobicitat. Per consegüent, el polièster hidrofòbic PCL es va mesclar amb àcid poliláctic (PLA) i es va combinar amb nanopartícules de HA i HNTs. D'altra banda, l'altament hidrofòbic poli (2-hidroxietil metacrilat (PHEMA) és va copolimeritzar amb etil metacrilat (EMA) i s'additivà amb HA i HNTs. Per tant, la dispersió de càrregues inorgàniques en les matrius polimèrica va ser estudiada, a més de la formació d¿hidroxiapatita en la superfície del polímer, i la ràtio de degradació del PCL/PLA. Es va observar que la introducció de HA en polímers amb caràcter hidrofílic indueix un alt ràtio de nucleació de hidroxiapatita i de degradació dels polímers bioabsorbibles. No obstant això, els HNTs tendeixen a formar grans agregats quan el caràcter hidrofílic del polímer augmenta, donant lloc a punts d'inici de clavills i fallada del material. La culminació d'aquest estudi es va aconseguir per mitjà del monitoratge de la viabilitat cel·lular, proliferació i morfologia de les cèl·lules com a efecte de la superfície química dels polímers. La hidrofobicitat de la superfície del polímer afecta la interacció de les cèl·lules i aquesta es pot millorar per mitjà de la modificació del polímer amb HA i HNTs. D'aquesta manera, l'increment de la viabilitat cel·lular amb l'addició de les dues càrregues inorgàniques és induït per la generació de nous centres reactius de Ca2+ i PO4 3¿ presentes en l'HA, i els grups silanol (Si-OH) situats en la superfície dels HNTs. Per tant, es va observar que en superfícies hidrofòbiques, a causa d'un alt ràtio d'arribada de proteïnes, aquestes competeixen per l'espai donant lloc a interaccions pobres entre cèl·lules i polímer mostrant una geometria cel·lular arredonida. No obstant això, en superfícies hidrofòbiques al trobar-se altament solvatades, les proteïnes inicialment troben més dificultat per a arribar a la superfície, i amb això disposen de major espai per a organitzar-se i ancorar-se a la superfície, donant lloc a una ma
[EN] Bone pathology entails an important average of physical disability, being bone tissue regeneration one of the most actively researched fields in Tissue Engineering. Accordingly, large efforts are focused on the research of novel bioabsorbable materials as a prosthesis with stiffness values similar to that of the host tissue capable of fulfilling the requirements for bone fracture remodelling. This work is focused on studying mechanical properties and cell interaction as a function of the chemical structure and hydrophobicity of different bioabsorbable polymers compared with non-absorbable polymers. Hydroxyapatite (HA) and Halloysite nanotube (HNTs) were used as fillers in order to grant better cell attachment, proliferation and differentiation along with hydrophobicity behaviour. For this end, it was aimed to firstly monitor the effects of bioactive fillers on the structural properties of bioabsorbable Polycaprolactone (PCL). Thus, mechanical and thermal properties of PCL were studied by modifying the additivation percentage of the bioactive fillers HA and HNTs. This preliminary study allowed to understand the synergic effect among the polymeric matrix and the functional groups present on the additives chemical structure by establishing the additivation threshold and optimizing the additivation rate. In general terms, a noticeable improvement of mechanical properties was achieved with the simultaneous addition of the two fillers. Additionally, taking advantages of the HNTs nano-tubular shape, those were studied as drug carrier structures and their loading and release ability with curcumin was monitored. Knowing in one side that HA promotes the formation of a layer of new bone composed of biological apatite and collagen; and in the other side, that HA and HNTs alter hydrophobicity behaviour; morphological properties supplied by both fillers were studied and compared among different pairs of polymers with similar chemical natures but different hydrophobicity. Accordingly, the hydrophobic polyester PCL was modified by its blending with Polylactic acid (PLA) and combined with HA nanoparticles and HNTs. On the other hand, the hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) was copolymerized with ethyl methacrylate (EMA) and also combined with HA and HNTs. Thus, the effect of both fillers was studied on Hydroxyapatite nucleation, distribution of the fillers into the polymeric matrices and PCL/PLA degradation rate. Therefore, it was observed that introduction of HA in polymers with moderately hydrophilic character induce a higher rate of hydroxyapatite nucleation and a faster degradation rate. However, HNTs tends to form big aggregates when the hydrophilic character increases, driving to crack initiation sites and failure of the material. The completion of this study was accomplished by means of monitoring cell viability, proliferation, and morphology on the two pairs of polymers varying the polymer's chemical surface by blending hydrophilic and hydrophobic polymers, copolymerizing monomers of opposite natures, and/or loading the polymer matrix with nanoparticles such as HA or HNTs. Polymer surface wettability is known to affect cell attachment and can be enhanced by modifying the polymer with HA and HNT. In this way, improvement in cell viability with the addition of HA and HNTs was observed due to the generation of new reactive sites with Ca2+ and PO4 3¿ groups present in HA, and silanol groups (Si-OH) located at the surfaces of HNTs. Thus, it was concluded that on hydrophobic materials, due to a faster arrival rate of proteins, those compete for surface absorption driving to low interaction sites between cells and polymer surface showing a round shape. However, on hydrophilic materials, the highly solvated surface at initial stage limits protein arrival and allowed protein rearrangement and spreading over the surface promoting cell adhesion and proliferation with better cytoskeleton spreading.
Torres Roca, E. (2019). "Halloysite nanotubes/hydroxyapatite nanocomposites as hard tissue substitutes: effect on the morphology, thermomechanical behavior and biological development of aliphatic polyesters and polymethacrylates" [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/125709
TESIS

La thermographie infrarouge est un moyen d'analyse du comportement mécanique des matériaux. Elle a connu un essor considérable depuis les années 80 avec l'apparition des premiers capteurs. Deux techniques principales ont pu être développées ; la calorimétrie quantitative et l'analyse des contraintes par thermoélasticité (TSA en anglais). Jusqu'à aujourd'hui, la majorité des travaux a été réalisée sur les métaux et les polymères. Le présent manuscrit relève le challenge d'appliquer ces techniques aux matériaux verres, en développant une méthodologie de débruitage des films thermiques, permettant de conserver la résolution spatiale des mesures thermiques. Cela permet de caractériser de forts gradients dans des champs de variations de température de faible intensité. Cette méthodologie a été utilisée pour débruiter des films thermiques d'échantillons de verre soumis à un chargement mécanique cyclique. Dans un premier temps, elle a été appliquée pour étudier la réponse thermique d'une empreinte à l'échelle microscopique. Dans un second temps, elle a été utilisée pour remonter à des champs de contraintes et de sources de chaleur à l'échelle macroscopique. Ce travail ouvre de nouvelles perspectives à l'étude du comportement thermomécanique des matériaux fragiles présentant une faible réponse thermique sous sollicitation mécanique et de forts effets de gradients spatiaux. Les applications visées sont la fissuration et l'identification de paramètres constitutifs
The infrared thermography is used to analyse the mechanical behavior of materials. Since the 80's, it has rised with the appearance of the first sensors. Two principal techniques has been developed; the quantitative calorimetry and the thermoelastic stress analysis (TSA). Until today, most of the works has been carried out on metals and polymers. This manuscript takes-up the challenge of applying these techniques to glassy materials by developing a methodology to denoise infrared movies, which allows to preserve the spatial resolution of the thermal measurement. It allows to caracterise high gradients of low temperature variation fields. This methodology has been used to denoised thermal movies of glass samples submitted to a cyclic mechanical test. In a first time, it has been applied to study the thermal response of an imprint at the microscopic scale. In a second time, stress and heat sources fields have been determined at the macroscopic scale. This work provides new possibilities to study the thermomechanical behavior of brittle materials which present a low thermal response and high spatial gradients under mechanical loading. The target applications are the cracking phenomenom and the identification of constitutive parameters