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The ductile fracture process, which consists of the nucleation, growth and coalescence of microvoids, was extensively studied for materials deforming homogeneously. For materials with a non-homogeneous deformation behavior, such as those having hexagonal closed packed (HCP) crystal structure, experimental and numerical data is lacking. Therefore, the fracture properties of materials with such HCP structure, like titanium (used in aerospace and biomedical applications), zirconium (nuclear industry) and magnesium (manufacturing industry) are not well understood. The main research objective of this Ph.D. thesis is to better understand the mechanisms governing fracture in commercially pure (CP) titanium. In particular, the effect of grain orientation on void growth is investigated. The fracture process of CP titanium was visualized in model materials containing artificial holes. These model materials were fabricated using a femtosecond laser coupled with a diffusion bonding technique to obtain voids in the interior of titanium samples. Diffusion bonding was carried out either above or below the phase transformation temperature resulting in different microstructures. Changes in void dimensions during in-situ straining were recorded in three dimensions using x-ray computed tomography. Void growth obtained experimentally was compared with the Rice and Tracey model which predicted well the average void growth. However, a large scatter in void growth was observed experimentally and was explained in terms of differences in grain orientation which was confirmed by crystal plasticity simulations. It was also shown that grain orientation has a stronger effect on void growth than intervoid spacing and material strength. Intervoid spacing, however, appears to control whether the intervoid ligament failure is ductile or brittle. While this study showed a good agreement between experiments and simulations on average, there is no direct void growth comparison for particular grain orientations. In a follow-up study, an experimental approach was developed to directly relate the growth of a void to its underlying grain orientation. This is achieved by first annealing CP titanium samples below the α-β phase transformation temperature, then performing electron backscatter diffraction iii (EBSD) and finally diffusion bonding the samples together. Samples were then tested in x-ray tomography. This study showed the importance of the local state of strain on void growth. Crystal plasticity simulations that take into account the particular grain orientation and the local state of strain were found to predict well experimental void growth. Crystal plasticity simulations confirmed that the orientation of the voidcontaining grain is more important than the orientation of surrounding grains and more important than the volume fraction of voids, in order to determine void growth. This thesis on the growth and coalescence of voids is important to validate and improve the predictions of ductile fracture models and to design new materials with improved fracture properties.

Ces travaux de thèe portent sur le développement d’un outil d’analyse numérique dédié à l’ étude de nouveaux résonateursà quartz à ondes de volume et utilisant les éléments finis. Cette méthode de caractérisation permet la détermination deséléments du schéma électrique équivalent (résistance, inductance et capacité) d’une fréquence de résonance donnée ainsique son facteur de qualité, tout en prenant en compte dans le modèle la sensibilité du cristal de quartz à la températureet aux contraintes induites par le montage. Une étape de validation est d’abord réalisée afin de vérifier nos choix, enterme de modélisation et de calcul, en confrontant les données issues de la simulation aux mesures de résonateurs déjàexistants. Les trois dispositifs analysés (40 MHz, 10 MHz et 100 MHz) montrent une bonne concordance entre théorieet expérience. Pour obtenir de tels résultats, la structure de maintien est prise en compte et modélisée sous forme dezones d’amortissement de Rayleigh lorsque le piégeage de l’énergie n’est pas optimal (présence d’un mode de plaque).Un aspect important des résonateurs est ensuite étudié : le comportement en température. En effet, les contraintes dedilatation thermique ainsi que l’évolution des coefficients élastiques en fonction de la température induisent une dérivefréquentielle. La comparaison entre théorie et expérience nous permet de vérifier l’allure des courbes et de quantifier ledegré de précision du modèle. L’effet d’une contrainte mécanique appliquée sur le pourtour de la lame de quartz est parla suite introduit dans le modèle en utilisant la méthode de perturbation de Sinha-Tiersten. Il est alors possible de définirl’impact des défauts de fabrication sur la fréquence du résonateur. Enfin, la méthode numérique est appliquée à l’étudede structures innovantes dans le cadre du projet FREQUENCE2009. Il s’agit de revisiter le concept du résonateur BVA etd’envisager des procédés de fabrication collective. L’idée consiste ainsi à remplacer le rayon de courbure d’un résonateur,dont la fréquence utile se trouve aux alentours de 9 MHz, par une série de marches, plus compatible avec les procédés dela micro électronique (DRIE : Deep Reactive Ion Etching). Bien que les résultats expérimentaux soient, dans ce cas, loin denos attentes, nous constatons que l’outil d’analyse est parfaitement capable de prédire les caractéristiques de nouvellesstructures. / This work is devoted to the development of a digital analysis tool dedicated to study new bulk acoustic waves quartz resonatorsby using finite elements. This method of characterization allows the calculation of the elements of the equivalentelectrical circuit (resistor, inductance and capacitor) of a given resonant frequency as well as the quality factor, while takinginto account its sensitivity to the temperature and to the stresses induced by the mounting support. Firstly, a validationphase is carried out in order to check our choices, in terms of modeling and computation, by comparing simulation data tothe measures of existing resonators. The three analyzed devices (40MHz, 10 MHz and 100 MHz) show good agreementbetween theory and experiment. To obtain such results, the mounting support is taken into account and modeled thanks toRayleigh damping areas when the trapping of energy is not optimal (presence of a spurious shell vibration mode). Then, animportant aspect of resonators is studied : the temperature behavior of its vibrating modes. Indeed, the thermal expansionstresses as well as the change of stiffness coefficients according to the temperature induce frequency shift. The comparisonbetween theory and experiment allows us to check the shape of curves and to quantify the accuracy of the model.Thereafter, the effect of mechanical stress applied on the edge of the blank of quartz is introduced in the model by usingthe perturbation method developed by Tiersten and Sinha. So, it is possible to define the influence of some manufacturingdefects on the resonant frequency. Finally, the digital method is applied to study innovative structures in the framework ofthe project FREQUENCE2009. The aim is to review the concept of BVA resonator and consider collective manufacturingprocesses. The idea involves replacing the radius of curvature of a resonator, for which the expected frequency is around9 MHz, by several steps, more compatible with microelectronics processes (DRIE : Deep Reactive Ion Etching). Althoughthe results are far from our expectations, we note that the analysis tool is perfectly able to anticipate the characteristics ofnew structures.

Recently, there has been a significant growth in the use of composites in sectors such as automotive, aerospace and wind energy. Composites are traditionally designed for mechanical performance in terms of strength, stiffness and impact energy absorption; however multifunctionality has become the focus of researchers and designers in recent years. Multifunctional design of composites involve adding functionality such as thermal management, radiation shielding, stealth, structural health monitoring and energy storage at material level rather than adding discrete components afterwards. The aim of the current research is to incorporate multi-functionality at tow-scale both as a processing aid during manufacture and adding additional functionality during subsequent processing. Various laboratory scale machines were developed as a part of this study to identify the ideal way to spread and incorporate metallic materials into the carbon fibre tows, thereby making them multifunctional. Manufacturing processes such as co-mingling of micro-fibres, coating with metallic powder and screen printing of metallic grid lines have been developed in this work. One of the objective of this thesis is to metallise carbon tow in order to use it in conjunction with magnetic tooling, as part of the chopped fibre preforming process developed by the University of Nottingham and Bentley Motors. The performance of the metallised tow has been evaluated using characterisation tests such as magnetic pull force test, bending rigidity test etc. Finite element models have been developed to verify the experimental results of magnetic pull force and bending properties. As observed during the research, the bending properties of the carbon tow were found to influence the accuracy of the finite element modelling significantly. Study into the bending properties of the carbon fibre and Multifunctional carbon tow using two different principles such as carbon tow bending under own weight and bending due to the application of an external force were carried out. In each case the governing mathematical models were also derived.

Structural integrity assessment of nuclear components assessed using the R6 Failure Assessment Diagram approach requires an understanding of the limiting condition in terms of both fracture and plastic collapse. For ductile materials, such as stainless steels used for nuclear components, including the primary pipe-work of a Pressurised Water Reactor (PWR), the limiting condition defined by plastic collapse is likely to occur prior to the initiation of fracture. This is due to the relatively low yield stress of the material and the high fracture toughness. If this is the case, structural integrity may be solely assessed on plastic collapse criteria, with little or no reference to fracture toughness; thus considerably simplifying the assessment procedure, whilst maintaining the integrity of the plant. Nevertheless, an in-depth understanding of fracture under plastic collapse conditions is required to make a robust case for single parameter assessments based on a plastic collapse criterion alone. The challenge in this project lay in understanding and predicting ductile fracture initiation under large-scale yielding conditions, i.e. outside the normal validity limits of conventional elastic-plastic fracture mechanics as plastic collapse conditions are achieved. The approach developed in this research has explored three fracture assessment methods: (a) two parameter fracture mechanics based on the J-integral and a refined Q-parameter calculated closer to the crack-tip under widespread plasticity than is conventionally the case, (b) two local approach methods based on critical void growth ratio defined by Rice and Tracey, and (c) a local approach method based on the critical work of fracture. All three methodologies were found to adequately describe failure across a range of constraint conditions. The fracture toughness constraint dependence of 304(L) stainless steel was studied experimentally and analytically. Significant constraint loss was shown to occur in nominally high constraint fracture toughness specimens due to extensive plastic deformation at fracture initiation. Furthermore, significant fracture toughness constraint dependence was observed experimentally. An analytical method using local approach criteria was developed to predict high constraint fracture toughness, required for structural integrity assessments, and to quantify the constraint dependence fracture toughness as a function of two parameter fracture mechanics based on the J-integral and the refined Q-parameter. The influence of constraint on the prediction of failure in a stainless steel pipe containing a fully circumferential crack of various depths was investigated analytically for a range of loading conditions. A refined constraint independent failure assessment methodology was developed using local approach analyses. Using this methodology, the pipe component was shown to consistently fail by plastic collapse irrespective of the crack depth or loading condition. The conservatism of the conventional structural integrity assessment was quantified and shown to vary with crack depth and with loading conditions. This research has suggested that failure in a 304(L) stainless steel pipe will be by plastic collapse prior to ductile initiation for a limited range of defects and loading conditions. Further analytical studies and experimental work will be required to demonstrate whether this observation is general for a wider range of defects and loading conditions.

Esta dissertação apresenta um estudo desenvolvido com o intuito de consolidar uma metodologia para a otimização de projeto de porta-sedes de uma válvula de esfera trunnion. Este trabalho está dividido em dois artigos. Primeiramente, é apresentado um estudo comparativo entre diferentes modelos de porta-sedes, realizado com o apoio do método dos elementos finitos (FEA). O porta-sede de melhor desempenho foi determinado utilizando a Função de Perda Quadrática Multivariada. O objetivo principal deste primeiro artigo é identificar os principais parâmetros da geometria de um porta-sede, que possam garantir o desempenho funcional da válvula e correspondente atendimento dos requisitos de qualidade. O segundo artigo descreve uma aplicação da metodologia de Projeto de Experimentos (DOE), conduzida com o intuito de identificar a configuração geométrica da válvula que conduza a condição ótima de funcionamento, fornecendo, desta forma, subsídio para a área de Desenvolvimento de Produtos na elaboração de válvulas mais robustas. Uma das principais contribuições deste trabalho é a constatação que os quatro fatores controláveis incluídos no estudo exercem efeito significativos sobre as variáveis de resposta utilizadas (pressão de contato e força de reação). Excetuando-se o fator “pressão de operação da válvula”, que caracteriza a condição operação, mas não é um parâmetro de projeto, o fator que revelou efeito mais pronunciado sobre as variáveis resposta foi a “área da pista de vedação”. / This thesis presents a study conducted in order to consolidate a methodology for seat-retainer design optimization of a trunnion ball valve. This work is divided in two papers. Initially a comparative study between different seat-retainer models, developed with the support of the finite element analysis (FEA), is presented. The best performance seat-retainer was determined using the Multivariate Quadratic Loss Function. The main purpose of this first article is to identify the main parameters of the seat-retainer geometry, which could ensure the functional performance of the valve and corresponding quality requirements. The second paper describes an application of Design of Experiments (DOE) methodology, conducted in order to identify the geometric configuration of the valve that leads to the optimal operating condition, providing thereby, contribution to the Product Development area in designing more robust valves. The main contribution of this work is the finding that the four control factors included in the study exert significant effect on the response variables used (contact pressure and reaction force). Except for the factor "valve operating pressure" that characterizes the operation condition, but is not a design parameter, the factor that showed more pronounced effect on the response variables was the “seat sealing area”.

Orientador: Márcio de Moraes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-24T09:12:42Z (GMT). No. of bitstreams: 1 Goulart_DouglasRangel_M.pdf: 2699898 bytes, checksum: e7d2281b73e4ff46b282bf86177c5b1a (MD5) Previous issue date: 2014 / Resumo: Apesar da evolução do tratamento das fraturas de ângulo mandibular, o conhecimento torna-se restrito quando se trata de fraturas com múltiplos traços ou perda de estrutura óssea, devido à falta de investigações específicas na área. Dessa forma, o objetivo desse trabalho é desenvolver e avaliar um novo design de placa de fixação interna para tratamento de fraturas complexas de ângulo mandibular por meio do método dos elementos finitos e teste de carregamento linear. Primeiramente foi gerado um modelo tridimensional da mandíbula fraturada no software Rhinocerus 4.0, seguida pela modelagem de placas e parafusos do sistema 2,0 mm. Os modelos foram exportados para o Ansys®, no qual foi aplicado deslocamento de 3 mm no rebordo alveolar na região que corresponde a fossa central do primeiro molar ipsilateral a fratura. Foram avaliados três grupos segundo o método de fixação interna: duas placas do sistema 2,0 mm; duas placas do sistema 2,0 mm locking; e uma placa com novo design do sistema 2,0 mm locking. O modelo computacional foi transferido para um modelo in vitro com mandíbulas de poliuretano, com os mesmos grupos de fixação e padrão de fratura mandibular. Cada grupo foi composto por cinco mandíbulas, cada amostra foi submetida ao teste de carregamento linear na máquina de ensaio universal Instron modelo 4411 até o deslocamento de 5 mm. Para o modelo computacional foi observada uma distribuição mais equilibrada de tensão no novo design de placa, além disso, a fixação com a nova placa apresentou uma tendência de manter os segmentos aproximados. Porém foi observada superioridade da força de reação do grupo com duas placas 2,0 mm locking (651,67 N). No ensaio mecânico o grupo com duas placas locking apresentou maior resistência ao deslocamento de 3 mm com diferenças estatisticamente significativa que o grupo da nova placa (one-way ANOVA; F = 4,92, p = ,013). Foi desenvolvido um modelo de placa para o tratamento de fratura de ângulo mandibular, que na análise de elementos finitos apresentou uma distribuição mais equilibrada das tensões, porém o grupo com duas placas locking apresentou maior resistência mecânica. A nova placa pode substituir duas placas convencionais sem prejuízo de resistência mecânica e com vantagens de apresentar a tendência de manter os segmentos fraturados aproximados quando submetidos a deslocamento / Abstract: Despite the developments concerning the treatment of mandibular angle fractures, knowledge becomes limited when it comes to multiple fractures lines or loss of bone due to the lack of specific investigation in this field. Thus, the aim of this work is developing and evaluating a new design of internal fixation plate for the treatment of the complex mandibular fractures by the finite element method and mechanical testing. A three dimensional model of the fractured mandible was generated in Rhinocerus 4.0 software, and also was performed the modeling of the 2.0 mm system plates. The models have been exported to ANSYS ®, in which it was performed a static application of a force to generate displacement of 3 mm in the first molar region ipsilateral to the fracture. Three groups were evaluated according to the method of internal fixation: two plates of the 2.0 mm non-locking system, two plates of 2.0 mm locking system, and a plate with new design 2.0mm locking system. The computational model was transferred to an in vitro experiment with polyurethane mandibles with the same fixation groups and fracture pattern. Each group with five mandibles was subjected to linear loading test in a universal testing machine Instron Model 4411 to the displacement of 5 mm. A more balanced distribution of stress in the new plate design was observed. In addition, the new plate modified the mechanical behavior of the fractured region with a tendency to keep the approximate segments. However, the superiority of the reaction force of the group with two 2.0mm locking plates was observed (651.67 N). In the mechanical test the group with two locking plates showed greater resistance to the 3 mm displacement with statistically significant difference than the new plate group ( one-way ANOVA , F = 4.92 , p = 013) / Mestrado / Cirurgia e Traumatologia Buco-Maxilo-Faciais / Mestre em Clínica Odontológica

Orientadores: Paulo Henrique Ferreira Caria, Felippe Bevilacqua Prado / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-26T17:30:42Z (GMT). No. of bitstreams: 1 Freire_AlexandreRodrigues_D.pdf: 4165235 bytes, checksum: 39a64cbf8afdf28035d38f8c66914ac2 (MD5) Previous issue date: 2015 / Resumo: Os fenômenos mecanobiológicos envolvem as características mecânicas do tecido, a nível microscópico, relacionadas às mudanças de metabolismo, apresentando mudanças estruturais e fisiológicas. Os estímulos mecânicos na estrutura óssea implicam na presença de tensões e deformações que resultam alterações na remodelação óssea. Nos tecidos dentoalveolares, especialmente no periodonto de suporte, são conhecidas as alterações estruturais resultantes da perda do equilíbrio da oclusão, especialmente no trauma oclusal. Para entender como ocorrem tais alterações mecânicas e respostas biológicas específicas nestes locais, estudos recentes propõem a aplicação da teoria do mecanostato associada à simulação computacional por análise de elementos finitos. Foram apresentados dois estudos para demonstrar as alterações nos estímulos mecânicos computacionalmente e relacionar com as respostas biológicas que alteraram estruturalmente o osso alveolar de suporte na região dos molares. No primeiro estudo foram utilizados animais que se submeteram à cirurgia de extração do segundo e terceiros molares inferiores, unilateralmente, permanecendo o primeiro molar em oclusal isoladamente, o qual ficou sujeito a um trauma oclusal. A oclusão no primeiro molar foi simulada por análise de elementos finitos e os resultados foram comparados com resultados em análise histológica. O estudo conclui que as regiões com aumento de compressão mecânica devido ao dente estar isolado foram compatíveis com áreas de reabsorção observadas histologicamente. O segundo estudo apresentou um modelo experimental de trauma oclusal em animais com a cimentação de resina sobre a superfície oclusal dos molares superiores, unilateralmente. A mordida posterior foi simulada em análise de elementos finitos para observar os estímulos mecânicos no osso alveolar de suporte tanto no primeiro molar superior quanto no inferior do lado com o trauma. Em comparação foi realizada microtomografia computadorizada para avaliar os efeitos biológicos resultando em alteração estrutura, na qual o volume da crista óssea alveolar foi mensurado. O estudo conclui que aumento da compressão observada computacionalmente, possibilita entender a causa da redução de volume óssea na região de interesse, sendo essa redução maior no molar superior, ou seja, com a presença do material cimentado / Abstract: The mechanobiology phenomena involve the mechanical characteristics of tissue in microscopic level, which is related to changes of metabolism and presenting structural and physiological alterations. The mechanical stimuli in bone structure imply in stresses and strain in the tissue which results in changes in bone remodeling. In dentoalveolar tissues, mainly in the supportive periodontium, the structural changes resulted by the loss of occlusal equilibrium are known. To understand how these mechanical changes occurs and its consequent biological responses, recent studies proposed the application of mechanostat theory associated to computational simulation by finite element analysis. Two studies were presented to demonstrate by computational method the changes in mechanical stimuli and relate to biological responses that resulted in structural changes in the alveolar bone support in molar region. In the first study, animals were submitted to extraction of second and third lower molars, unilaterally, and the first lower molar was kept, which was subject to occlusal stress. The molar occlusion was simulated by finite element analysis and the results were compared with histological analysis. The study concluded that the regions with increase of mechanical compression in isolated molar were compatible with resorption areas in histological observation. The second study presented an experimental model of occlusal stress in animals, where a resin block was cemented on the occlusal surface of upper molars, unilaterally. The posterior occlusion was simulated by finite element analysis to observe the mechanical stimuli both first upper and lower molars, in the same side of occlusal stress. In comparison, the micro-CT was performed to evaluate the biological effect resulting in structural changes, in which the alveolar bone crest volume was measured. The study conclude that the increase of compression, observed in computational analysis, gives the possibility to understand the cause of bone volume reduction in the region of interest, being this reduction was major in the upper molar support tissue, i.e. with the presence of cemented material / Doutorado / Anatomia / Doutor em Biologia Buco-Dental

A Finite Element Analysis (FEA) investigation of concrete tunnel systems traversing seismic faults is carried out to determine how to effectively mitigate the stresses induced in the liner when subject to fault displacement. A parametric study of various fault parameters, both in the damage zone and competent rock, is carried out to determine the site conditions which induce the most stress on the tunnel liner system. Results indicate that friction angle, cohesion, and elastic modulus of fault zones have varying effects on the stresses induced on the liner. The width of damage zone and expected displacements are also investigated and it has been shown that even small displacements over narrow damage zones, around 10 m, can still result in significant damage to the concrete liner whereas in wider damage zones the effects of the displacement are more evident. The use of flexible joints in what is known as the articulated design method is investigated to mitigate the stresses induced by fault displacement and discussed. Several orientations, lengths and variations in relative stiffness of these flexible joints are investigated to determine their optimal effectiveness. Results show that this is an effective solution which can be used in design and repair of tunnels to mitigate the stresses and resulting damages to concrete tunnel liners subject to fault displacement.

Indiana University-Purdue University Indianapolis (IUPUI) / Additively manufactured (AM) metals have been increasingly fabricated for structural applications. However, a major hurdle preventing their extensive application is lack of understanding of their mechanical properties. To address this issue, the objective of this research is to develop a computational model to simulate the creep behavior of nickel alloy 718 manufactured using the laser powder bed fusion (L-PBF) additive manufacturing process. A finite element (FE) model with a subroutine is created for simulating the creep mechanism for 3D printed nickel alloy 718 components. A continuum damage mechanics (CDM) approach is employed by implementing a user defined subroutine formulated to accurately capture the creep mechanisms. Using a calibration code, the material constants are determined. The secondary creep and damage constants are derived using the parameter fitting on the experimental data found in literature. The developed FE model is capable to predict the creep deformation, damage evolution, and creep-rupture life. Creep damage and rupture is simulated as defined by the CDM theory. The predicted results from the CDM model compare well with experimental data, which are collected from literature for L-PBF manufactured nickel alloy 718 of creep deformation and creep rupture, at different levels of temperature and stress. Using the multi-regime Liu-Murakami (L-M) and Kachanov-Rabotnov (K-R) isotropic creep damage formulation, creep deformation and rupture tests of both the secondary and tertiary creep behaviors are modeled. A single element FE model is used to validate the model constants. The model shows good agreement with the traditionally wrought manufactured 316 stainless steel and nickel alloy 718 experimental data collected from the literature. Moreover, a full-scale axisymmetric FE model is used to simulate the creep test and the capacity of the model to predict necking, creep damage, and creep-rupture life for L-PBF manufactured nickel alloy 718. The model predictions are then compared to the experimental creep data, with satisfactory agreement. In summary, the model developed in this work can reliably predict the creep behavior for 3D printed metals under uniaxial tensile and high temperature conditions.