This work presents a three dimensional elastic-plastic model for two hemispherical bodies sliding across one another under various preset vertical interferences. In particular, steel-on-steel and aluminum-on-copper contact situations are considered. A finite element analysis is used for the model and the parameters to investigate include stresses, deformations, contact areas, and energy loss in sliding. Both frictional and frictionless sliding are investigated. In addidition to structural loads, electromagnetic loads are considered and a framework for a electromagneticlly, structurally, and thermally coupled model is investigated.

Two topics involving irradiation damage in alpha-iron have been considered. First, damage cascades representative of those that would be induced by radiation have been simulated using molecular dynamics (MD). The number and type of defects produced are compared for pure iron and iron with a small hydrogen concentration. Second, the inter- action energy between point defects and line dislocations has been calculated for a number of configurations, using both molecular statics methods and calculations based on linear elastic continuum theory and the dipole force tensor. Results from both methods are com- pared. Results from these two topics are relevant for predicting macroscopic behaviors such as creep and plasticity in reactor structural materials.

<p>In-service inspections of high temperature pressureequipment show that weldments are prone to creep and fatiguedamage. It is not uncommon that severely damaged weldments arefound even before the design life of the component has beenreached. In order to improve this situation action has beentaken during the last decades, both from industry, universitiesand research institutes, aiming at an enhanced understanding ofthe weldment response.</p><p>The work presented in this thesis focuses on numericalsimulation of weldment creep response. For a more profoundunderstanding of the evolution of creep damage in mismatchedlow alloy weldments, simulations are performed using thecontinuum damage mechanics, CDM, concept. Both design and lifeassessment aspects are addressed. The possibility to assessseam welded pipes using results from tests of cross-weldspecimens taken out from the seam is investigated. It is foundthat the larger the cross-weld specimen the better thecorrelation. The advantage to use the CDM concept prior to aregular creep analysis is also pointed out. In order to developthe CDM analysis, a modified Kachanov-Rabotnov constitutivemodel is implemented into ABAQUS. Using this model, a secondredistribution of stresses is revealed as the tertiary creepstage is reached in the mismatched weldment.</p><p>Creep crack growth, CCG, in cross-weld compact tension, CT,specimens is investigated numerically where a fracturemechanics concept is developed in two steps. In the first one,the C^*value and an averaged constraint parameter areused for characterising the fields in the process zone, whilein the second step, the creep deformation rate perpendicular tothe crack plane and a constraint parameter ahead of the cracktip, are used as characterising parameters. The influence oftype and degree of mismatch, location of starter notch as wellas size of CT specimen, is investigated. Results show that notonly the material properties of the weldment constituentcontaining the crack, but also the deformation properties ofthe adjacent constituents, influence the CCG behaviour.Furthermore, the effect of size is influenced by the mismatchof the weldment constituents.</p><p>A circumferentially cracked girth weld with differentmismatch is assessed numerically by use of the fracturemechanics concept developed. The results show that type anddegree of mismatch have a great influence on the CCG behaviourand that C^*alone cannot characterise crack tip fields.Corresponding R5 assessments are also performed. Comparisonwith the numerical investigation shows that the assumption ofplane stress or plane strain conditions in the R5 analysis isessential for the agreement of the results. Assuming the formerresults in a relatively good agreement for the axial stressdominated cases while for the hoop stress dominated cases, R5predicts higher CCG rates by an order of magnitude.</p><p><b>Keywords:</b>ABAQUS, constraint effect, continuum damagemechanics, creep, creep crack growth, design, design code,finite element method, fracture mechanics, life assessment,mismatch, numerical simulation, weldment</p>

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Makine Eğitimi Anabilim Dalı, 2009. / Kaynakça var.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 119-127.

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-21Bitstream added on 2014-06-13T20:37:41Z : No. of bitstreams: 1 rodrigues_ea_me_bauru.pdf: 1602991 bytes, checksum: 7f755b87b5be84900b2d054f02413197 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No presente trabalho desenvolve-se um modelo constitutivo baseado na mecânica do dano contínuo para representar o comportamento de materiais que apresentam diferentes respostas quando solicitados à tração ou à compreensão. obtem-se uma representação constitutiva através da composição de modelos simples e específicos para tratar cada tipo de solicitação. Este modelo combinado é capaz inclusive de lidar com carregamentos alternados (tração e compreensão), envolvendo fechamento e reabertura de fissuras existentes. Para modelar o comportamento em compreensão emprega-se o modelo constitutivo que tem como critério de degradação o segundo invariante do tensor de tensão desviador (critério de Von Mises ou J2). Para simular o aparecimento de fissuras de tração, usa-se o modelo de dano com critério de degradação baseado na energia de deformação da parte positiva do tensor efetivas. A integração dos modelos é feita com base em tensões efetivas associadas a duas escalas distintas (escala grosseira e refinada). O modelo é apto para representar a formação de descontinuidades no campo de deslocamento (descontinuidades fortes) em materiais quase-frágeis. Nesse caso, a região de localização de deformação (zona de processo da fatura) pode ser descrita pelo modelo de dano combinado, com lei de abrandamento de tensões (softening) exponencial, que estabelece dissipação compatível com a energia de fratura. A região contínua pode ser descrita pelo modelo de dano J2, com parâmetros ajustados com base no comportamento não linear à compreensão. Valida-se o modelo proposto mediante testes básicos, focando a capacidade do modelo em representar os principais aspectos do comportamento de materiais quase-frágeis. A aplicabilidade do modelo é demonstrada através do estudo da capacidade de rotação plástica de vigas de concreto armado, confrontando-se os resultados numéricos com os experimentais / A combined constitutive model based on the Continuum Damage Mechanics (CDM) is presented to represent the nonlinear behavior of quasi-brittle materials, which present different response when subjected to tension or compreession. The constitutive model is a composition of two simple and specific models designed to treat each type of behavior. The combined model is able to deal with alternating load (tension-compression), involving formation, closure and reopening cracks. To model the compressive behavior, a degradation criterion based on the second invariant of the deviatoric part of the effective stress tensor (Von Miser or J2 criterion) is used. To simulate cracking, a damage model with degradation criterion based on the strain energy associated to the positive part the effective stress tensor is adopted. The combination of the models is made on the basis of the effective stresses associated to two distinct scales (coarse and fine scales) The model is able to represented the formation of discontinuities in the displacement field (strong discontinuities) for quasi-brittle materials. The region of strain localization (fracture process zone) is described by a softening law which establishes dissipation energy compatible with the fracture energy. The continuous region is described by the J2 damage model, with parameters ajusted to describle the compressive nonlinear behavior in compression. Some basic tests are performed to asses the ability of the model to represent the main aspects of the behavior of quasi-brittle materials. The applicability of the model is demonstrated by the study of the plastic rotation capacity of reinforced concrete beams, comparing the numerical responses with the experimental ones

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-08-29Bitstream added on 2014-06-13T19:58:09Z : No. of bitstreams: 1 lopesjunior_ja_me_bauru.pdf: 1162814 bytes, checksum: 6b95b841db7e1b2b5ce4cd33f600a04b (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Atualmente, na odontologia, após a perda de dentes por razões diversas, estes vêm sendo substituídos por implantes dentários. A importância e modelos computacionais biomecânicos é cada vez mais frequente, posto que essas ferramentas permitem simular o comportamento desses dispositivos que tentam restaurar as funções dos dentes perdidos. Como os aspectos biomecânicos de implantes são diferentes daqueles de um dente natural, circundando por um ligamento periodontal, a transferência da carga ao implante, e deste ao osso circundante, poide gerar esforços que, além de provocar falhas nas reabilitações, podem até ultrapassar o limite fisiológico e causar perda da osseointegração. Na análise desses sistemas de prótese, é essencial representar adequadamente as influências entre os diferentes componentes implante/coroa, que são comumente unidos através de parafusos. Falhas destas uniões podem prejudicar o correto funcionamento da prótese, ou até mesmo, produzir esforços não previstos, responsáveis por danos severos na prótese ou no osso. Assim, faz-se necessário descrever adequadamente o comportamento das interfaces entre os componentes dos sistemas protéticos. No presente trabalho, são utilizados elementos finitos sólidos tetraédricos com elevada razão de aspecto para representar a superfície de interface entre os componentes em contato implante/parafuso/coroa. Um modelo constitutivo de dano é empregado para reproduzir o comportamento desses elementos de interface. O modelo é desenvolvido para representar o comportamento diferenciado em tração e compressão na superfície de contato, permitir a separação dos componentes sem oferecer, praticamente, resistência, contudo, ao mesmo tempo, impedir movimentos de interpenetração no caso de solicitações compressivas no... / Currently, in dentistry, after loss of teeth for various reasons, they have been replaced by dental implants. The importance of biomechanical computer models is increasingly, since they tools allows for the simulation of the behavior of thes devices that try to restore the cunctions of missing teeth. As the biomechanical aspects of implants are different from those of natural tooth, surrounded by a periodontal ligament, the load transferred to the implant and the surrounding bone can generate stresses that, in addition to cause failures in rehabilitations, can even exceed the physiological limit and cause loss of osseointegration. In the analysis of these phosthetic systems, it is essential to adequately represent the interaction between different components that are commonly joined together by using screws. Possible joint failures can adversely affect the correct functioning of unions, or even produce stresses responsible for severe damage in prosthesis or bone. Thus, it is necessary to adequately describe the behavior of interfaces between components prosthetic systems. In this work, tetrahedral solid finite elements with high aspect ratio are used to represent the contact interface between components (implant/screw/Crown). A constitute damage model is employed to reproduce the behavior of these interface elements. The model is designed to represent the differentiated behavior in tension and compression on the contact surface, allowing the separation of the components without offering resistance, however, preventing movement of interpenetration in the case of compression on the contact. So it is expected that this... (Complete abstract click electronic access below)

abstract: With the maturity of advanced composites as feasible structural materials for various applications there is a critical need to solve the challenge of designing these material systems for optimal performance. However, determining superior design methods requires a deep understanding of the material-structure properties at various length scales. Due to the length-scale dependent behavior of advanced composites, multiscale modeling techniques may be used to describe the dominant mechanisms of damage and failure in these material systems. With polymer matrix fiber composites and nanocomposites it becomes essential to include even the atomic length scale, where the resin-hardener-nanofiller molecules interact, in the multiscale modeling framework. Additionally, sources of variability are also critical to be included in these models due to the important role of uncertainty in advance composite behavior. Such a methodology should be able to describe length scale dependent mechanisms in a computationally efficient manner for the analysis of practical composite structures. In the research presented in this dissertation, a comprehensive nano to macro multiscale framework is developed for the mechanical and multifunctional analysis of advanced composite materials and structures. An atomistically informed statistical multiscale model is developed for linear problems, to estimate and scale elastic properties of carbon fiber reinforced polymer composites (CFRPs) and carbon nanotube (CNT) enhanced CFRPs using information from molecular dynamics simulation of the resin-hardener-nanofiller nanoscale system. For modeling inelastic processes, an atomistically informed coupled damage-plasticity model is developed using the framework of continuum damage mechanics, where fundamental nanoscale covalent bond disassociation information is scaled up as a continuum scale damage identifying parameter. This damage model is coupled with a nanocomposite microstructure generation algorithm to study the sub-microscale damage mechanisms in CNT/CFRP microstructures. It is further integrated in a generalized method of cells (GMC) micromechanics model to create a low-fidelity computationally efficient nonlinear multiscale method with imperfect interfaces between the fiber and matrix, where the interface behavior is adopted from nanoscale MD simulations. This algorithm is used to understand damage mechanisms in adhesively bonded composite joints as a case study for the comprehensive nano to macroscale structural analysis of practical composites structures. At each length scale sources of variability are identified, characterized, and included in the multiscale modeling framework. / Dissertation/Thesis / Doctoral Dissertation Aerospace Engineering 2018

Orientador: Osvaldo Luís Manzoli / Banca: Plinio Glauber Carvalho dos Prazeres / Banca: Edson Antonio Capello Souza / Resumo: Atualmente, na odontologia, após a perda de dentes por razões diversas, estes vêm sendo substituídos por implantes dentários. A importância e modelos computacionais biomecânicos é cada vez mais frequente, posto que essas ferramentas permitem simular o comportamento desses dispositivos que tentam restaurar as funções dos dentes perdidos. Como os aspectos biomecânicos de implantes são diferentes daqueles de um dente natural, circundando por um ligamento periodontal, a transferência da carga ao implante, e deste ao osso circundante, poide gerar esforços que, além de provocar falhas nas reabilitações, podem até ultrapassar o limite fisiológico e causar perda da osseointegração. Na análise desses sistemas de prótese, é essencial representar adequadamente as influências entre os diferentes componentes implante/coroa, que são comumente unidos através de parafusos. Falhas destas uniões podem prejudicar o correto funcionamento da prótese, ou até mesmo, produzir esforços não previstos, responsáveis por danos severos na prótese ou no osso. Assim, faz-se necessário descrever adequadamente o comportamento das interfaces entre os componentes dos sistemas protéticos. No presente trabalho, são utilizados elementos finitos sólidos tetraédricos com elevada razão de aspecto para representar a superfície de interface entre os componentes em contato implante/parafuso/coroa. Um modelo constitutivo de dano é empregado para reproduzir o comportamento desses elementos de interface. O modelo é desenvolvido para representar o comportamento diferenciado em tração e compressão na superfície de contato, permitir a separação dos componentes sem oferecer, praticamente, resistência, contudo, ao mesmo tempo, impedir movimentos de interpenetração no caso de solicitações compressivas no... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Currently, in dentistry, after loss of teeth for various reasons, they have been replaced by dental implants. The importance of biomechanical computer models is increasingly, since they tools allows for the simulation of the behavior of thes devices that try to restore the cunctions of missing teeth. As the biomechanical aspects of implants are different from those of natural tooth, surrounded by a periodontal ligament, the load transferred to the implant and the surrounding bone can generate stresses that, in addition to cause failures in rehabilitations, can even exceed the physiological limit and cause loss of osseointegration. In the analysis of these phosthetic systems, it is essential to adequately represent the interaction between different components that are commonly joined together by using screws. Possible joint failures can adversely affect the correct functioning of unions, or even produce stresses responsible for severe damage in prosthesis or bone. Thus, it is necessary to adequately describe the behavior of interfaces between components prosthetic systems. In this work, tetrahedral solid finite elements with high aspect ratio are used to represent the contact interface between components (implant/screw/Crown). A constitute damage model is employed to reproduce the behavior of these interface elements. The model is designed to represent the differentiated behavior in tension and compression on the contact surface, allowing the separation of the components without offering resistance, however, preventing movement of interpenetration in the case of compression on the contact. So it is expected that this... (Complete abstract click electronic access below) / Mestre

A Mecânica do Dano Contínuo é atualmente uma poderosa ferramenta para se modelar o comportamento não-linear de vários materiais decorrente da evolução de um processo de microfissuração. A perda de rigidez causada pelo processo físico tem sido considerada em modelos constitutivos através de variáveis de dano escalar, vetorial ou tensorial. Quando o carregamento é proporcionalmente crescente as deformações residuais podem ser ignoradas e relações constitutivas simples podem ser obtidas, onde os efeitos do dano aparecem por uma penalização direta das propriedades elásticas. Por outro lado, efeitos de dano podem ser acoplados com deformações residuais levando a relações constitutivas mais gerais. Esse trabalho está relacionado a esses tipos de modelos assumindo que o meio ideal apresenta um comportamento elástico linear com danificação ou elastoplástico com danificação. Um dos principais aspectos discutido relaciona-se à formulação variacional, a qual está baseada em conceitos de Análise Convexa e Não-Convexa. Explorando o fato que a evolução do dano tem correspondência com a idealização de regime de encruamento negativo, a teoria de localização de deformação é abordada e um estudo da condição necessária de singularidade ou perda da condição de elipticidade é realizado. Na sequência, uma proposta preliminar para uma análise de pós-singularidade, baseada na Teoria de Bifurcação, é feita no sentido de caracterizar pontos limite ou pontos de bifurcação de solução, em sistemas conservativos. / Continuum Damage Mechanics is nowadays a powerful tool to model the non-linear behaviour of several materials due to evolution of a microcracking process. The lost of rigidity caused by such physical process has been accounted in the constitutive models through a scalar, vectorial or tensorial damage variables. When proportional loading is considered the residuals strains can be ignored and simple constitutive relations can be obtained in which damage effects appear by direct penalization of the elastic properties. On the other hand, damage effects can be coupled with residual strains leading to more general constitutive relations. This work is related to such kind of models assuming that the ideal medium presents a linear elastic-damage or an elastoplastic-damage behaviour. One of the main topics discussed is related to the variational formulation which is based on Convex and Non-Convex Analysis concepts. Exploring the fact that damage evolution has correspondence with a softening idealised regime, the strain localization theory is treated and a study of a necessary condition for singularity or ellipticity tose condition is developed. In the sequence, a introductory poscritical analysis is proposed, based in the bifurcation theory and aiming to detect if the singularity corresponds to a limit or a bifurcation point solution, in conservative systems.