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Steel fiber reinforced concrete pipes: part 1: technological analysis of the mechanical behavior; Tubos de concreto reforçado com fibras de aço: parte 1: análise tecnológica do comportamento mecânico

Figueiredo, A. D. de; Fuente, A. de la; Aguado, A.; Molins, C.; Chama Neto, P. J.
Fonte: IBRACON - Instituto Brasileiro do Concreto Publicador: IBRACON - Instituto Brasileiro do Concreto
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.99%
This paper is the first part of an extensive work focusing the technological development of steel fiber reinforced concrete pipes (FRCP). Here is presented and discussed the experimental campaign focusing the test procedure and the mechanical behavior obtained for each of the dosages of fiber used. In the second part ("Steel fiber reinforced concrete pipes. Part 2: Numerical model to simulate the crushing test"), the aspects of FRCP numerical modeling are presented and analyzed using the same experimental results in order to be validated. This study was carried out trying to reduce some uncertainties related to FRCP performance and provide a better condition to the use of these components. In this respect, an experimental study was carried out using sewage concrete pipes in full scale as specimens. The diameter of the specimens was 600 mm, and they had a length of 2500 mm. The pipes were reinforced with traditional bars and different contents of steel fibers in order to compare their performance through the crushing test. Two test procedures were used in that sense. In the 1st Series, the diameter displacement was monitored by the use of two LVDTs positioned at both extremities of the pipes. In the 2nd Series, just one LVDT is positioned at the spigot. The results shown a more rigidity response of the pipe during tests when the displacements were measured at the enlarged section of the socket. The fiber reinforcement was very effective...

Comportamento mecânico e análise dimensional de parafusos corticais de aço inoxidável e liga de titânio submetidos a ensaios de torção ; Mechanical behavior and dimensional analysis of the stainless steel and titanium alloy córtex screws, undergone torsion testing

Shimano, Suraya Gomes Novais
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/12/2005 PT
Relevância na Pesquisa
66.06%
Parafusos corticais são uns dos implantes mais utilizados na prática cirúrgica e são normalmente compostos por ligas metálicas como o aço inoxidável F-138 e a liga de titânio 6Al-4V e, quando inseridos no organismo humano, são submetidos a diversos esforços mecânicos. Assim, é necessário avaliar as propriedades mecânicas desses implantes. Portanto, o objetivo deste estudo foi analisar o comportamento mecânico de parafusos corticais de aço inoxidável e de liga de titânio, de fabricação nacional, em ensaio de torção. Vinte parafusos de aço inoxidável foram divididos em quatro grupos (1,2,3,4) e o mesmo foi feito com os parafusos de liga de titânio. Primeiramente, suas medidas-padrão foram analisadas de acordo com a Norma Brasileira NBR ISO 5835:1996. Nos dois grupos 1 (de aço inoxidável e de liga de titânio), o ângulo de rotação foi mensurado por um goniômetro e o ensaio de torção foi manual. Já os parafusos dos dois grupos 2 foram ensaiados em uma máquina de torção. Os parafusos dos grupos 3, primeiramente, foram inseridos em cortical óssea suína e, posteriormente submetidos à torção. Nos dois grupos 4, os parafusos foram submetidos à torção sucessiva e, posteriormente submetidos à torção na máquina. Na análise estatística das propriedades mecânicas...

Argamassas com adição de fibras de polipropileno -estudo do comportamento reológico e mecânico. ; Mortars with polypropylene fibres´addition - study of the rheological and mechanical behavior.

Silva, Rosiany da Paixão
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/06/2006 PT
Relevância na Pesquisa
66.16%
Buscando evitar as anomalias surgidas nos revestimentos de argamassa, muitos projetistas e construtores têm procurado soluções alternativas, dentre as quais aparece o emprego de argamassas com adição de fibras. Porém, o conhecimento sobre o comportamento deste compósito é empírico, principalmente no Brasil, onde inexistem pesquisas sistêmicas sobre o assunto. A partir deste contexto, o presente trabalho teve por objetivo investigar a influência da adição de fibras de polipropileno em argamassas para revestimento, no que se refere ao seu comportamento reológico e mecânico. Para avaliar o comportamento reológico, foram empregadas as técnicas de ensaio dropping ball e squeeze flow, e a avaliação da aplicabilidade quanto à execução do revestimento, utilizando o conhecimento de um operário experiente. Para avaliar o comportamento mecânico, foram utilizados ensaios relativos a resistência à tração na flexão, resistência à compressão e módulo de elasticidade dinâmico. Os compósitos de argamassa produzidos no trabalho apresentam variação na matriz e no teor de fibras. A variação na matriz compreendeu o tipo de argamassa e a dosagem de água. Foram utilizadas duas argamassas, largamente empregadas no mercado da Construção Civil...

Caracterização do envelhecimento da liga 20Cr32Ni+Nb fundida por centrifugação e de seu efeito sobre o comportamento mecânico a frio.; Characterization of aging in centrifugally cast alloy 20Cr32Ni+Nb and its effects on mechanical behavior.

Monobe, Luis Shiguenobu
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 10/10/2007 PT
Relevância na Pesquisa
65.95%
Fornos petroquímicos constituem a parte mais importante da indústria de derivados de petróleo. São nesses fornos que se processam as reações químicas imprescindíveis ao processamento dos produtos que constituem nosso cotidiano, como os fertilizantes, polímeros, produtos farmacêuticos e alimentícios. Devido ao caráter fortemente endotérmico dos processos, associado a reações catalíticas provocada numa mistura reacional de vapor de água com hidrocarbonetos (caso da reforma para obtenção de hidrogênio) ou craqueamento por pirólise (processo de pirólise), estes fornos são continuamente aquecidos. Com o objetivo de aumento de produção e produtividade, os fornos têm sido submetidos a condições de temperatura e pressão cada vez mais extremas. Nos fornos de pirólise, adicionalmente tem-se aumentado consideravelmente a velocidade do fluido e para tanto têm tido as seções transversais dos condutos diminuídas levando a um aumento das tensões de trabalho. Além disso, paradas e partidas desses fornos têm se mostrado um elemento crucial na operação. É comum que durante a parada desses fornos se detecte fragilização desse material após certo tempo de serviço à temperatura de trabalho. Quedas significativas nos valores de alongamento têm sido reportadas sendo que em algumas situações...

Estudo teórico-experimental do comportamento elastoplástico de poliuretano derivado do óleo de mamona (Ricinus communis); Theoretical and experimental study of the elastoplastic behavior of the castor oil polyurethane (Ricinus communis)

Ferneda, Amauri Bravo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/09/2006 PT
Relevância na Pesquisa
56.08%
Os biopolímeros surgem como materiais alternativos no atendimento aos requisitos de desempenho que a área médica tem exigido para implantes ósseos. Nesse contexto o polímero poliuretano derivado de óleo de mamona (Ricinus communis) tem obtido lugar de destaque. Mesmo assim, esse material, considerado um biopolímero regenerador ósseo, ainda necessita de investigação mecânica consistente para uma aplicação de forma confiável. No entanto, há uma grande dificuldade em se prever o comportamento mecânico das estruturas fabricadas por biopolímeros. Diante desse fato, o presente projeto de pesquisa visa através de ensaios experimentais em amostras padronizadas para ensaios de tração e compressão, bem como, ensaios normalizados para próteses de quadril, adquirir propriedades de material adequadas para a implementação dos modelos computacionais, assim como dados de comportamento mecânico sob solicitação. De posse desses dados, através do método dos elementos finitos, são realizadas simulações computacionais com o objetivo de verificar a capacidade do modelo de material de Drucker-Prager representar o comportamento mecânico do biopolímero. Este modelo é aplicado inicialmente na simulação dos ensaios de tração e compressão e posteriormente nas simulações das próteses em biopolímero...

Estudo do comportamento mecânico na usinagem de aços inoxidáveis.; Study of mechanical behavior in stainless steel machining.

Barbosa, Patrícia Alves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/01/2014 PT
Relevância na Pesquisa
65.99%
A usinagem é caracterizada pela grande quantidade de deformação plástica localizada no material devido à formação do cavaco, de forma que existe um compromisso entre o processo de deformação, encruamento e amolecimento, pelo aumento da temperatura, gerando bandas de cisalhamento. A compreensão destas zonas cisalhamento se faz importante, por conter informações que podem ser aplicadas ao aperfeiçoamento das técnicas de usinagem relacionadas à melhoria do processo e a e à busca da inovação em materiais e ferramentas. Nesse contexto, os aços inoxidáveis, que em geral, são caracterizados como materiais de baixa usinabilidade, em consequência do elevado grau de encruamento e baixa condutividade térmica durante a usinagem, podem facilitar investigações da formação do cavaco pós-processo em razão da morfologia segmentada de seus cavacos. Para tanto, o objetivo deste trabalho foi abordar a usinagem sob a ótica da ciência do comportamento mecânico dos materiais através da avaliação das características e propriedades de três classes de aços inoxidáveis com diferentes estruturas cristalianas e microestruturas. A análise foi feita utilizando respostas de deformação, taxa de deformação, tensão, encruamento e temperatura na zona de cisalhamento primária...

Analysis of mechanical behavior in bending of polymer composites using the finite elements method

Guidi, Erick Siqueira; De Azevedo Silva, Fernando
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
66%
The use of composite materials has increased in the recent decades, mainly in the aeronautics and automotives industries. In the present study is elaborated a computational simulation program of the bending test using the finite elements method, in the commercial software ANSYS. This simulation has the objective of analyze the mechanical behavior in bending of two composites with polymeric matrix reinforced with carbon fibers. Also are realized bending tests of the 3 points to obtain the resistances of the materials. Data from simulation and tests are used to make a comparison between two failures criteria, Tsai-Wu and Hashin criterion. Copyright © 2009 SAE International.

Correlação entre transformações de fases e comportamento mecanico de ligas Ti-Nb-Sn e sua aplicação na concepção de implantes ortopedicos com propriedades otimizadas; Correlation between phase transformations and mechanical behavior of Ti-Nb-Sn alloys and its applications in the design of orthopedic implants with optimized characteristics

Eder Socrates Najar Lopes
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/07/2009 PT
Relevância na Pesquisa
56.07%
As ligas de Ti tipo β exibem versatilidade em relação a propriedades mecânicas, que podem ser controladas por tratamentos térmicos específicos. Neste trabalho foram produzidas, processadas e caracterizadas amostras de ligas Ti-Nb-Sn, objetivando a fabricação de hastes de próteses totais de quadril. O trabalho incluiu a avaliação de transformações de fase durante tratamentos térmicos, a avaliação dos efeitos de tais tratamentos na microestrutura e no comportamento mecânico e finalmente, a proposição de processo de fabricação de hastes de próteses de quadril por forjamento a frio e de tratamentos térmicos coerentes com a solicitação mecânica do componente. Os resultados obtidos permitem descrever a decomposição da martensita e a formação das fases β, ω e α. Tais informações foram aplicadas na seleção de condições ideais de tratamentos térmicos que possibilitaram o forjamento a frio com sucesso, gerando peças isentas de trincas ou outros defeitos indesejáveis. A aplicação de condições específicas de tratamento térmico a haste permitiu otimizar o comportamento mecânico da mesma. A parte superior da haste, que é submetida a esforços mais intensos, foi tratada termicamente...

Effective mechanical behavior of sandwich beams under uncoupled bending and torsion loadings

Silva, Hugo Miguel; Meireles, José F.
Fonte: Trans Tech Publications Publicador: Trans Tech Publications
Tipo: Conferência ou Objeto de Conferência
Publicado em //2014 ENG
Relevância na Pesquisa
66.03%
"International Conference on Applied Mechanics and Mechanical Automation (AMMA 2014)". Serie - Applied mechanics and materials, vol. 590; Sandwich geometries, mainly panels and beams are widely used in several transportation industries, namely aerospace, aeronautic and automotive. Sandwich geometries are known for their advantages in structural applications: high specific stiffness, low weight, and possibility of design optimization prior to manufacturing. This study aims to know the influence of the number of reinforcements (ribs), and of the thickness on the mechanical behavior of sandwich panels subjected to bending and torsion loads separately. In this study, 3 geometries are compared: simple web-core beam, corrugated core, and honeycomb core. The last 2 are asymmetric, due to the use of odd number of ribs. The influence of the geometry on the results is discussed, by means of a parameter that establishes a relation between the stiffness behavior and the mass of the object. It is shown that the all relations are non-linear, despite the elastic nature of the analysis, by means of the application of loads with low intensity.

Effect of particle morphology on the mechanical and thermo-mechanical behavior of polymer composites

Oréfice,R. L.; Hench,L. L.; Brennan,A. B.
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2001 EN
Relevância na Pesquisa
56.06%
Fiber reinforced polymer composites have been used in many applications, such as in automobile, aerospace and naval industries, due basically to their high strength-to-weight and modulus-to-weight, among other properties. Even though particles are usually not able to lead to the level of reinforcement of fibers, particle reinforced polymer composites have been proposed for many new applications due to their low cost, easy fabrication and isotropic properties. In this work, polymer composites were prepared by incorporating glass particles of different morphologies on poly(aryl sulfones) matrices. Particles with aspect ratios equal to 1, 2.5 and 10 were used. The prepared composites were characterized using electron microscopy and thermal analysis. Mechanical properties of the composites were evaluated using a four-point bending test. The thermo-mechanical behavior of the obtained composites was also investigated. The results showed that the morphology of the particles alter significantly the mechanical properties of composites. Particles with larger values of aspect ratio led to large elastic modulus but low levels of strain at failure. This result was explained by modeling the thermo-mechanical behavior of the composites using a viscoelastic model. Parameters of the model...

Mechanical behavior of silver alloys used as cast post and core in maxillary incisors

Levy Neto,Flaminio; Brito,Luciana de Moura; Elias,Antônio Carlos
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2004 EN
Relevância na Pesquisa
65.95%
This experimental "in vitro" investigation is mainly concerned with the mechanical behavior of twenty plastic analogous simulating endodonticaly treated maxillary central incisor roots, divided in two groups, which were restored with: (i) silver (10 specimens, Ag - 80%); and (ii) silver - palladium (10 specimens, Ag - 58.5% / Pd - 27.4%) cast alloys. All the restored analogous were clamped inside stainless steel cylinders filled with acrylic resin, and were tested to failure in an INSTRON machine. The static compressive loads were applied with an inclination of 45° relatively to the longitudinal direction of the teeth. On average, the specimens restored with Ag- Pd presented higher values of final failure load (i.e. fracture or excessive plastic bending) and stiffness. On the other hand, those restored with Ag presented average proportional limit loads which were, in comparison, about 5% higher.

Mechanical behavior of recycled lightweight concrete using EVA waste and CDW under moderate temperature

Santiago,E. Q. R.; Lima,P. R. L.; Leite,M. B.; Toledo Filho,R. D.
Fonte: IBRACON - Instituto Brasileiro do Concreto Publicador: IBRACON - Instituto Brasileiro do Concreto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2009 EN
Relevância na Pesquisa
65.99%
Many benefits can be achieved by using recycled waste as raw material for construction. Some of them are the reduction of the total cost of the construction, the reduction of the consumption of energy and the decrease in the use of natural materials. The construction sector can also incorporate the waste of the other industries, like the waste of the shoes industry, the Ethylene Vinyl Acetate (EVA). EVA aggregate is obtained by cutting off the waste of EVA expanded sheets used to produce insoles and innersoles of the shoes. In this work two types of recycled aggregate were used - construction and demolition waste (CDW) and EVA. The aim of this work was to study the influence of the use of these recycled aggregates, as replacement of the natural coarse aggregate, on mechanical behavior of recycled concrete. The experimental program was developed with two w/c ratio: 0.49 and 0.82. Four mixtures with produced with different aggregates substitution rates (0, 50%EVA, 50%CDW and 25%EVA-25%CDW), by volume. Compressive tests were carried out to evaluable the influence of recycled aggregate on strength, elastic modulus and Poisson coefficient. In addition, it was evaluated the effect of the moderate temperatures (50, 70 and 100º C) on stress-strain behavior of concretes studied. The results demonstrated that is possible to use the EVA waste and RCD to produces lightweight concrete. The influence of temperature was more significant only on elastic modulus of the recycled concrete with 50%EVA.

Steel fiber reinforced concrete pipes: part 1: technological analysis of the mechanical behavior

Figueiredo,A. D. de; Fuente,A. de la; Aguado,A.; Molins,C.; Chama Neto,P. J.
Fonte: IBRACON - Instituto Brasileiro do Concreto Publicador: IBRACON - Instituto Brasileiro do Concreto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2012 EN
Relevância na Pesquisa
65.99%
This paper is the first part of an extensive work focusing the technological development of steel fiber reinforced concrete pipes (FRCP). Here is presented and discussed the experimental campaign focusing the test procedure and the mechanical behavior obtained for each of the dosages of fiber used. In the second part ("Steel fiber reinforced concrete pipes. Part 2: Numerical model to simulate the crushing test"), the aspects of FRCP numerical modeling are presented and analyzed using the same experimental results in order to be validated. This study was carried out trying to reduce some uncertainties related to FRCP performance and provide a better condition to the use of these components. In this respect, an experimental study was carried out using sewage concrete pipes in full scale as specimens. The diameter of the specimens was 600 mm, and they had a length of 2500 mm. The pipes were reinforced with traditional bars and different contents of steel fibers in order to compare their performance through the crushing test. Two test procedures were used in that sense. In the 1st Series, the diameter displacement was monitored by the use of two LVDTs positioned at both extremities of the pipes. In the 2nd Series, just one LVDT is positioned at the spigot. The results shown a more rigidity response of the pipe during tests when the displacements were measured at the enlarged section of the socket. The fiber reinforcement was very effective...

Mechanical Behavior of Hydrogels for the Use of Ionic Devices

Li, Jianyu
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
EN
Relevância na Pesquisa
56.09%
Wearable and implantable devices hold great promise to transform the society by making healthcare continuous, personalized and affordable. They will enable mobile healthcare by monitoring continuously vital signals, and providing various stimulations on the human body. Conventional electronics face a primary challenge: their mechanical and electrical properties mismatch those of tissues. Stretchable electronics provide some remedies to the mechanical mismatch, but any interface between stretchable electronics and tissues must translate an electronic current into an ionic one (and vice versa). Whereas electronics struggle to solve many technical problems, ionic devices solve most of them readily. Hydrogels are the materials of choice for the use of ionic devices. They mix water, mobile ions and polymer networks at molecular scales, and thus intrinsically integrate both ionic conductivity and high stretchability. Hydrogels resemble tissues biologically, mechanically and electrically. Although several ionic devices using hydrogels have been demonstrated, the mechanical behavior of hydrogels represents one of main material constraints: complex chemomechanical interactions, poor mechanical properties and weak adhesion. To this end, this thesis focuses on the mechanical behavior of hydrogels for the use of ionic devices. This thesis first presents theoretical and experimental approaches to characterize chemomechanical interactions of gels. How applied forces...

Constitutive modeling of the finite deformation behavior of membranes possessing a triangulated networked microstructure

Arslan, Melis
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 114 p.; 5191240 bytes; 5195975 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
56.15%
Many biological, natural and synthetic materials possess a networked or micro-truss-like microstructure. In this thesis work, a general microstructurally-informed continuum level constitutive model of the large stretch behavior of membranes possessing a triangulated network or truss-like structure is developed. As a specific example, a constitutive model of the stress-strain behavior of the red blood cell membrane is developed. The mechanical behavior of the membrane of the red blood cell is governed by two primary microstructural features: the lipid bilayer and the underlying spectrin network. The lipid bilayer is analogous to a 2D fluid in that it resists changes to its planar area, yet poses little resistance to planar shear. A skeletal network of spectrin molecules is crosslinked to the lipid bilayer and provides the shear stiffness of the membrane. The planar triangulated structure of the spectrin network is used to identify a representative volume element (RVE) for the model. A strain energy density function in terms of an arbitrary planar deformation field is proposed using the RVE. Differentiation of the strain energy density function provides expressions for the general multiaxial stress-stretch behavior of the material.; (cont.) The stress-strain behavior of the membrane when subjected to uniaxial and simple shear loading conditions in different directions is given...

A study of the stretch-induced softening behavior of particle filled elastomers/

Greb, Andrea (Andrea L.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 61 leaves
ENG
Relevância na Pesquisa
56.08%
Elastomers are able to undergo relatively large deformations in an elastic manner, which makes them the material of choice for a wide range of applications. In some cases, filler particles, such as carbon black, are added to the elastomer to alter the mechanical behavior when subjected to different loading conditions. When subjected to cyclic loading conditions, elastomers undergo stress-induced softening, known as the Mullins effect, and this softening behavior is influenced by the amount of filler particle present. The softening is considered to be an evolution of the soft and hard domain microstructure of the material, with the effective soft domain increasing with stretch. In this study, finite element analysis will be used to understand the softening behavior of particle reinforced elastomers. The softening behavior of the parent elastomer will be modeled using a constitutive model proposed by Qi and Boyce (2004). Nonlinear finite element analysis using the ABAQUS code was used to model elastomers with various volume fractions of filler particles, and the stress-strain behavior of the composite and evolution of the soft domain within the matrix is computed. The addition of filler particles was found to increase the overall stiffness of the elastomer...

Mechanical behavior of hybrid 3D woven composites

Muñoz Sánchez, Raúl
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
66.11%
Unidirectional fiber-reinforced composites are widely used in the aerospace industry due to their excellent in-plane mechanical properties, high corrosion resistance, dimensional stability and fatigue life. Nevertheless, they exhibit poor delamination resistance and damage tolerance, particularly under impact. The lack of reinforcement in the through-thickness direction makes them particularly vulnerable to out-of-plane threats caused by foreign objects, such as ice slabs or open-rotor blade fragments impacting on skin fuselages. A cost-effective alternative is the use of 3D woven orthogonal reinforcements, in which delamination resistance and damage tolerance are improved by weaving a yarn in the through-thickness direction. This technique allows the combination of several fiber types (hybridization) and enables the optimization of the composite properties by varying the fiber content. Preforms may be infused by using out-of-autoclave processing techniques, such as Vacuum Assisted Resin Transfer Molding (VARTM), leading to considerable cost savings, as opposed to autoclave consolidation. Despite of the potential of these materials, the use of hybrid 3D woven composites is limited by the lack of experimental data and reliable models able to predict the mechanical response of the material. This work analyzes the mechanical behavior of a hybrid 3D woven orthogonal composite made up of a thermoset polymeric matrix (epoxy-vinylester) reinforced with carbon and glass fibers...

High temperature mechanical behavior of AI/SiC nanoscale multilayers

Lotfian, Saeid
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
56.16%
Nanoscale Al/SiC composite laminates are metal-ceramic multilayers with unique mechanical properties at ambient temperature, such as high strength, high toughness, and damage tolerance, due to the nm scale thickness of their layers. Nevertheless, nothing is known about their high temperature mechanical properties and this is a key issue both from the fundamental viewpoint as well as from the in-service behavior. This lack of information is mainly due to the difficulties associated with the characterization of the mechanical behavior of thin-films at high temperature, a rather unexplored area. High temperature instrumented nanoindentation and micropillar compression were carried out in this thesis to study the mechanical properties of Al/SiC nanolaminates as a function of layer thickness from room temperature up to 300ºC. Mechanical tests were complemented with detailed transmission electron microscopy (TEM) analysis of the deformed structures to elucidate the effect of temperature on the deformation mechanisms at the nm scale. In addition, finite element simulations of the multilayer deformation were used to clarify the influence of the Al flow stress and of the interface properties (strength, friction coefficient) on the overall stress-strain response of Al/SiC multilayers. The combination of nanoindentation...

Modeling the deformation and failure behavior of FCC and HCP nanocrystalline materials

Wei, Yujie, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 188 p.
ENG
Relevância na Pesquisa
56.08%
As foreseen by Richard Feynman in his famous talk titled There's Plenty of Room at the Bottom in 1959, scientists nowadays are miniaturizing structures in materials to achieve better performance as concerned in technical applications. Reducing grain sizes in polycrystalline materials into the range of less than 100nm, for example, could achieve extraordinary high strength in these so called nanocrystalline (nc) materials. The reduced grain size gives rise to new deformation mechanisms in nc materials. It is now widely accepted that there is a strong interplay between dislocation-based deformation in the crystalline grain interiors and the inelastic deformation mechanisms operative in the grain-boundary regions. Grain-boundary regions play an increasingly significant role as the grain size decreases below the 100nm level. In this dissertation, constitutive models have been developed to investigate the deformation mechanisms of nc materials, with focus on modeling grain-boundary decohesion in nc materials. Two micromechanical models have been developed to capture the deformation in grain boundaries in nc materials.; (cont.) To the end, a phenomenological constitutive model has been developed for powder-processed nc materials, where the plastic flow could be pressure-dependent...

Temperature and rate dependent finite strain behavior of poly(ethylene terephthalate) and poly(ethylene terephthalate)-glycol above the glass transition temperature

Dupaix, Rebecca B. (Rebecca Brown), 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 348 p.; 17043648 bytes; 17043406 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
56.09%
Poly(ethylene terephthalate) is widely used for consumer products such as drawn fibers, stretched films, and soda bottles. Much of its commercial success lies in the fact that it crystallizes at large strains during warm deformation processing. The imparted crystallinity increases its stiffness and strength, improves its dimensional stability, and increases its density. The crystallization process and the stress-strain behavior above the glass transition depend strongly on temperature, strain rate, strain magnitude, and strain state. A robust constitutive model to accurately account for this stress-strain behavior in the processing regime is highly desirable in order to predict and computationally design warm deformation processes to achieve desired end product geometries and properties. This thesis aims to better understand the material behavior above the glass transition temperature in the processing regime. It examines the strain rate, strain state, and temperature dependent mechanical behavior of two polymers: PET and PETG, an amorphous non-crystallizing copolymer of PET, in order to isolate the effects of crystallization on the stress-strain behavior. Experiments over a wide range of temperatures and strain rates were performed in uniaxial and plane strain compression. A constitutive model of the observed rate and temperature dependent stress-strain behavior was then developed. The model represents the material's resistance to deformation with two parallel elements: an intermolecular resistance to flow and a resistance due to molecular network interactions.; (cont.) The model predicts the temperature and rate dependence of many stress-strain features of PET and PETG very well...