Submitted by Cássia Santos (cassia.bcufg@gmail.com) on 2017-08-30T13:26:19Z No. of bitstreams: 2 Dissertação - Paula Viana Queiroz Andrade - 2017.pdf: 2686282 bytes, checksum: d828cc8979cf594c108b844e7b806230 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-09-15T13:36:35Z (GMT) No. of bitstreams: 2 Dissertação - Paula Viana Queiroz Andrade - 2017.pdf: 2686282 bytes, checksum: d828cc8979cf594c108b844e7b806230 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-09-15T13:36:35Z (GMT). No. of bitstreams: 2 Dissertação - Paula Viana Queiroz Andrade - 2017.pdf: 2686282 bytes, checksum: d828cc8979cf594c108b844e7b806230 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-07-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work deals with analysis of the microstructures composed of metal matrix composites (MMC) and its application in Structural Engineering. The main goal of this essay is considered the potentialities and limitations when using the modeling activity suggested. For this, it is intended to consider the dissipative processes of plastification, occurring in the matrix, and phase debonding, that occurs in the matrix/inclusion interface region, where the influence of such processes on the macroscopic response of the material will be investigated. Initially, the applicability of this material in the various Engineering areas is described. For the numerical simulations of the MMC structural behavior, the von Mises model is used in the modeling of the matrix and a cohesive fracture model is used in the simulation of the phase debonding process. Inclusion is considered elastic with great rigidity. However, the dissipative processes that occur in the microstructure and that affect the macro mechanical behavior of the material are analyzed through a microscale modeling using a homogenization process based on the concept of Representative Volume Element (RVE) and the Finite Element Method (FEM). The strain and deformation are volumetric means of the respective microscopic fields on the EVR. The general objective is to verify through numerical analysis the potentialities and limitations of the use of the proposed modeling for future applications of metallic matrix composites in engineering, which shows a good representativeness of the mechanical behavior of the CMM. / Este trabalho trata de uma contribuição sobre a análise da microestrutura de materiais compósitos com matriz metálica (CMM) e sua aplicação na Engenharia Estrutural. O objetivo geral é verificar as potencialidades e limitações do emprego da modelagem proposta. Para isso, consideram-se os processos dissipativos de plastificação, que ocorre na matriz, e de descolamento, que ocorre na região de interface matriz/inclusão, onde a influência de tais processos na resposta macroscópica do material será investigada. Inicialmente, a aplicabilidade deste material nas diversas áreas de Engenharia é descrita. Para as simulações numéricas do comportamento estrutural de CMM, o modelo de von Mises é utilizado na modelagem da matriz assim como um modelo de fratura coesiva na simulação do processo de descolamento na interface. A inclusão é considerada elástica com grande rigidez. Contudo, os processos dissipativos que ocorrem na microestrutura e que repercutem no comportamento macromecânico do material são analisados através de uma modelagem na microescala utilizando um processo de homogeneização baseada no conceito de Elemento de Volume Representativo (EVR) e no Método dos Elementos Finitos (MEF). A tensão e deformação são médias volumétricas dos respectivos campos microscópicos sobre o EVR. Por fim, as análises numéricas apresentadas com o emprego da modelagem proposta evidenciam sua boa representatividade do comportamento mecânico do CMM contribuindo para futuras aplicações de compósitos de matriz metálica na engenharia.

Les matériaux architecturés font émerger de nouvelles possibilités en termes de propriétés structurales et fonctionnelles, repoussant ainsi les limites des cartes d'Ashby. Le terme "matériaux architecturés" inclus toute microstructure conçue de façon astucieuse, de sorte que certaines de ses propriétés soient optimisées. Les exemples sont nombreux : composites fibreux et particulaires, matériaux cellulaires, structures sandwiches, matériaux tissés, structures treillis, etc. Un enjeu de taille pour l'emploi de tels matériaux est la prédiction de leurs propriétés effectives. Dans ce travail, deux types de microstructures sont considérées : des structures auxétiques périodiques et des milieux fibreux aléatoires. Les auxétiques sont des matériaux apparus au milieu des années 1980, présentant un coefficient de Poisson négatif. On attend des auxétiques qu'ils présentent des propriétés mécaniques améliorées, comme le module de cisaillement ou la résistance à l'indentation. Les milieux fibreux aléatoires considérés dans ce travail sont constitués de fibres 3D infinies interpénétrantes aléatoirement distribuées et orientées. Ce type de structure aléatoire est très défavorable à la détermination d'une taille de volume élémentaire statistiquement représentatif. Pour les deux types de matériaux, l'homogénéisation numérique à l'aide de la méthode des éléments finis est implémentée dans le but d'estimer les propriétés thermiques et mécaniques effectives. / Architectured materials bring new possibilities in terms of structural and functional properties, filling gaps and pushing the boundaries of Ashby's materials maps. The term "architectured materials" encompasses any microstructure designed in a thoughtful fashion, so that some of its materials properties have been improved. There are many examples: particulate and fibrous composites, foams, sandwich structures, woven materials, lattice structures, etc. One engineering challenge is to predict the effective properties of such materials. In this work, two types of microstructures are considered: periodic auxetic lattices and stochastic fibrous networks. Auxetics are materials with negative Poisson's ratio that have been engineered since the mid-1980s. Such materials have been expected to present enhanced mechanical properties such as shear modulus or indentation resistance. The stochastic fibrous networks considered in this work is made of 3D infinite interpenetrating fibres that are randomly distributed and oriented. This case of random structure is challenging regarding the determination of a volume element size that is statistically representative. For both materials, computational homogenization using finite element analysis is implemented in order to estimate the effective thermal and mechanical properties.

Composite materials show heterogeneity at different length scales. hence concurrent multiscale analysis is the only reliable method to analyze them. But unfortunately there is no concurrent multi-scale strategy that is efficient, and accurate while addressing all kinds of problems. This lack of reliability is partly because there is no micro-mechanical model which inherently keeps all relevent global information with it. This thesis tries to fill this gap. The presented micro-mechanical model not only homogenizes the micro-structure but also keeps the global information with it. Most of the micro-mechanical models in the literature extract the Representative Volume Element (RVE) from the continuum for analysis which results in loss of information and accuracy. In the present approach also, the RVE has been extracted from the continuum but with the major difference that all the macro/meso-scopic parameters are accounted for. Five macro/meso-scopic one dimensional parameters have been defined which completely define the effect of continuum. 11 for one dimensional stretch, _1 for torsion, __ (_ = 2, 3) for bending and _33 for uniform pressurization due to the presence of the continuum. Further, the above macro/meso-scopic parameters are proven, by the asymptotic, theory to be constant at a cross section but vary, in general, over the length of the fiber. Hence, the analysis is valid for any location and is not restricted to any local domain. Three major problems have been addressed: • Homogenization and analysis of RVE without any defects • Homogenization and analysis of RVE with fiber-matrix de-bonding • Homogenization and analysis of RVE with radial matrix cracking. Variational Asymptotic Method (VAM) has been used to solve the above mentioned problems analytically. The results have been compared against standard results in the literature and against 3D FEA. At the end, results for “Radial deformation due to torsion” problem will be presented which was solved “accidentally.”

Epithelial tissues, one of the four primary tissue structures found in our human body, are known to comprise of tiny cells interconnected in a unique continuous pattern. In most cases, they serve a dual purpose of protecting the internal organs from physical damage, and at the same time, enable in facilitating inter-cellular activities and prevent pathogen break ins. While the tissue mechanics and its proliferation have been scrutinized to great detail, it is their geometric uniqueness, that has remained more or less unexplored. With an intent of doing the same, this thesis identifies and explores those geometric properties/parameters that have an influence on the micro structure’s homogenized and localized response. However, it does so by extracting the microstructures profile and representing its cell edges via three dimensional beam elements - hence the name, bio-inspired structures. The analysis is carried out by first developing a staggered Representative Volume Element (RVE)using finite elements, and identifying its appropriate size. The staggered assembly aids in minimizing boundary effects from creeping in, and at the same time, provides the requisite statistical homogeneity. This is followed by the geometry study. A wide range of epithelial geometries are considered for the study, ranging from completely isotropic skin models, to in plane anisotropic cuboidal structures and out of plane anisotropic stratified geometries. The effects of orientation, relative density and edge length are extracted and studied in great detail. It is observed that cell edges initial orientation has a direct dependence on the particle distribution, whereas the change in orientation is largely dependent on the deformation the microstructure is subjected to. Relative density is documented to show a direct correlation to a materials homogenized response i.e. larger the relative density, greater is the microstructures stiffness and homogenized stress response to the same deformation. Edge length, on the other hand is observed to showcase a downward trend on the cell edge’s axial stress. On average, in any kind of distribution and any kind of deformation, smaller cell edges are known to showcase larger stresses, as compared to the larger cell edges.

Storstadsregionernas växande befolkning, viljan att förtäta förorterna, samt miljonprogrammets stora utbud av standardiserade flerbostadshus i ytterstaden leder oss fram till examensarbetets innehåll: en studie om våningspåbyggnad på miljonprogrammets flerbostadshus. Syftet med examensarbetet är utreda miljonprogrammets potential för en vertikal förtätning. Vertikal förtätning innebär att redan befintlig bebyggelse kompletteras med ytterligare våningsplan. Syftet är även att underlätta för kommande påbyggnadsprojekt genom att lyfta fram svårigheter som ett påbyggnadsprojekt kan medföra, samt beskriva hur en våningspåbyggnad kan utföras. För att nå rapportens syfte ska följande frågeställningar besvaras: 1. Varför ska vi bygga ovanpå miljonprogrammets flerbostadshus? 2. Hur utformas en våningspåbyggnad lämpligast med avseende på stommaterial, byggmetod och installationer? 3. Vad bör särskilt beaktas vid en våningspåbyggnad? Examensarbetet kommer att studera miljonprogrammets potential för en vertikal förtätning i främst Stockholms stads förorter. Flerbostadshusens byggtekniska förutsättningar lyfts fram. Utöver det studeras lämpliga byggmetoder, stommaterial och installationslösningar för en påbyggnad. Examensarbetet avslutas med att belysa vad som särskilt bör beaktas i ett påbyggnadsprojekt. Resultatet av examensarbetet visar att miljonprogrammets flerbostadshus har god potential för en vertikal förtätning. Våningspåbyggnaden utformas lämpligast med planelement av betong om den befintliga konstruktionen tål en tung påbyggnad utan förstärkning. I annat fall konstrueras påbyggnadens stomme lämpligast av planelement av trä för miljonprogrammets flerbostadshus. För att fritt kunna utforma våningspåbyggnadens planlösning bör en balkgrund eller ett installationsgolv installeras. Där kan de nya installationerna till påbyggnaden dras. För att undvika störningar under projektets gång är områdets förutsättningar minst lika viktiga att beakta som den befintliga konstruktionens byggtekniska förutsättningar. Hyresgästernas åsikter och skyddsrumsreglerna ska även beaktas tidigt i ett våningspåbyggnadsprojekt. / The growing population in most Swedish conurbations, the desire to densify housing in the suburbs, as well as the suitability of the so called ”the Million Programme” wide range of standardized apartment buildings in the suburbs, led us to the thesis content: a study on storey extension for “the Million Programme” apartment buildings. The aim of the thesis is to facilitate the concept development phase for future storey extension projects and overall, to investigate ”the Million Programme” buildings’ potential for vertical densification. . Vertical densification means supplying additional floors on already existing buildings. To address the purpose of the report, the following questions will be answered: 1. What are the incentives for building on top of ”the Million Programme” apartment buildings? 2. How should a storey extension be designed conveniently concerning construction methods, selection of structural bearing materials and HVAC? 3. What should be considered especially during a storey extension project? The thesis will investigate potential of the buildings of ”the Million Programme” for a vertical densification, mainly in Stockholm’s suburbs. The residential buildings’ technical conditions will be highlighted. In addition, the study will also consider suitable construction methods and structural bearing materials, as well as HVAC solutions for storey extension. The thesis is rounded off by highlighting what should be considered especially during the storey extension project work to avoid or minimize disturbances during the project. The result of the thesis proves that the ”million programme” apartment buildings have good potential for a storey extension. If the existing building allows a massive storey extension without revetments, the storey extension should be made of plan elements of concrete. Otherwise the most appropriate alternative is proven to be plan elements of wood on the “million programme” apartment buildings. To freely be able to design the plan arrangements in the storey extension, an appropriate alternative is to build a beam floor or an installation floor that creates a space between the existing floor and the new floor. This space can be used for the new installations for the storey extension. Our result also proves that the area qualifications are at least as important to observe as the technical qualifications of the existing buildings. Also the opinions of the tenants in the area and shelter regulations are important things to investigate early in the project.

<p>Injection to the subcutaneous (SC) tissue is one of the preferred methods for drug delivery of pharmaceuticals, from small molecules to monoclonal antibodies. Delivery to SC has become widely popular in part thanks to the low cost, ease of use, and effectiveness of drug delivery through the use of auto-injector devices. However, injection physiology, from initial plume formation to the eventual uptake of the drug in the lymphatics, is highly dependent on SC mechanics, poroelastic properties in particular. Yet, the poroelastic properties of SC have been understudied. In this thesis, I present a two-pronged approach to understanding the poroelastic properties of SC. Experimentally, mechanical and fluid transport properties of SC were measured with confined compression experiments and compared against gelatin hydrogels used as SC-phantoms. It was found that SC tissue is a highly non-linear material that has viscoelastic and porohyperelastic dissipation mechanisms. Gelatin hydrogels showed a similar, albeit more linear response, suggesting a micromechanical mechanism may underline the nonlinear behavior. The second part of the thesis focuses on the multiscale modeling of SC to gain a fundamental understanding of how geometry and material properties of the microstructure drive the macroscale response. SC is composed of adipocytes (fat cells) embedded in a collagen network. The geometry can be characterized with Voroni-like tessellations. Adipocytes are fluid-packed, highly deformable and capable of volume change through fluid transport. Collagen is highly nonlinear and nearly incompressible. Representative volume element (RVE) simulations with different Voroni tesselations shows that the different materials, coupled with the geometry of the packing, can contribute to different material response under the different kinds of loading. Further investigation of the effect of geometry showed that cell packing density nonlinearly contributes to the macroscale response. The RVE models can be homogenized to obtain macroscale models useful in large scale finite element simulations of injection physiology. Two types of homogenization were explored: fitting to analytical constitutive models, namely the Blatz-Ko material model, or use of Gaussian process surrogates, a data-driven non-parametric approach to interpolate the macroscale response.</p>

<p>The superior high-temperature elastic-plastic properties coupled with greater damage tolerance when compared with monolithic ceramics make ceramic matrix composites, CMCs, promising candidates for challenging applications such as engine components, rocket nozzles, cutting tools and nuclear energy reactor core components. Anelastic recovery is the time-dependent back strain observed upon the load removal following creep. In whisker-reinforced CMCs this can be a factor limiting operating conditions. Plastic strain misfit between two phases is thought to be the main driver in terms of the interactions within a percolating network. However, the network deformation mechanisms are still unclear and a previous neutron diffraction study showed an unexpected decrease of peak width after creep contradicting the theoretical predictions.</p> <p>In this contribution, the finite element method (FEM) is applied to a representative volume element (RVE) with proper boundary conditions in order to simulate the creep deformation and hot pressing processes. Three geometries have been generated and studied: a 3D randomly-oriented short-fiber unit cell without fiber to fiber contact, generated by a random sequential adsorption algorithm; 3D regularly aligned single fiber unit cells; and 2D regularly aligned percolating unit cells. Deformation mechanism has been studied from an energy point of view and compared with a modified analytical model. Then a virtual diffraction model has been developed providing a framework to transfer information between the FEM simulations (strain fields) and the diffraction pattern in terms of the peak width (full width at half maximum: <strong><em>FWHM</em></strong>) and peak position as a measure of stress distribution and mean stress state respectively. Furthermore, the coupling effects of external stress, deformation mode, and thermal stress on the diffraction patterns have been studied.</p> <p>The critical importance of a percolating whisker network for the anelastic recovery is demonstrated based on the 3D multi-whisker random unit cell. Whisker bending is shown to be the dominant mechanism over contact effects during the creep deformation of a composite containing a well aligned percolating whisker network based on the 2D unit cell model. Good qualitative agreement was found between our FEM simulations and the analytical model of Wilkinson and Pompe with regards to the maximum recoverable strain and the characteristic relaxation time. The analytical model captures all the critical factors characterizing the strain recovery, e.g., the effect of creep pre-exponent constant, whisker Young’s modulus and aspect ratio. Furthermore, it is found that the deformation from an initial stress-free state inevitably introduces peak broadening of whiskers inside the matrix. Several factors determine the peak-width and -shift, i.e., creep strain, applied stress, aspect ratio and geometry. However, thermal stress from the cooling stages following creep and hot pressing processes shelters this broadening effect and complicates the trends. Wide-ranging peak-width changes from narrowing to broadening are predicted depending on the geometry and applied stress. The peak position is shifted to a lower angle due to this thermal effect. This clearly explains the contradicting phenomena motivating this work and leads to that recommendation that a diffraction source with high angular resolution is needed to detect the subtle change of peak profile during creep.</p> / Doctor of Philosophy (PhD)

Among the many active materials in use today, piezoelectric composite patches have enabled notable advances in emerging technologies such as disturbance sensing, control of flexible structures, and energy harvesting. The macro fiber composite (MFC), in particular, is well known for its outstanding performance. Multiscale models are typically required for smart-structure design with MFCs. This is due to the need for predicting the macroscopic response (such as tip deflection under a transverse load or applied voltage) while accounting for the fact that the MFC has microscale details. Current multiscale models of the MFC exclusively focus on predicting the macroscopic response with homogenized material properties. There are a limited number of homogenized properties available from physical experiments and various aspects of existing homogenization techniques for the MFC are shown here to be inadequate. Thus, new homogenized models of the MFC are proposed to improve smart-structure predictions and therefore improve device design. It is notable that current multiscale modeling efforts for MFCs are incomplete since, after homogenization, the local fields such as stresses and electric fields have not been recovered. Existing methods for obtaining local fields are not applicable since the electrodes of the MFC are embedded among passive layers. Therefore, another objective of this work was to find the local fields of the MFC without having the computational burden of fully modeling the microscopic features of the MFC over a macroscale area. This should enable smart-structure designs with improved reliability because failure studies of MFCs will be enabled. Large-scale 3D finite element (FE) models that included microscale features were constructed throughout this work to verify the multiscale methodologies. Note that after creating a free account on cdmhub.org, many files used to create the results in this work can be downloaded from https://cdmhub.org/projects/ernestocamarena.<br><br>First, the Mechanics of Structure Genome (MSG) was extended to provide a rigorous analytical homogenization method. The MFC was idealized to consist of a stack of homogeneous layers where some of the layers were homogenized with existing rules of mixtures. For the analytical model, the electrical behavior caused by the interdigitated electrodes (IDEs) was approximated with uniform poling and uniform electrodes. All other assumptions on the field variables were avoided; thus an exact solution for a stack of homogeneous layers was found with MSG. In doing so, it was proved that in any such multi-layered composite, the in-plane strains and the transverse stresses are equal in each layer and the in-plane electric fields and transverse electric displacement are constant between the electrodes. Using this knowledge, a hybrid rule of mixtures was developed to homogenize the entire MFC layup so as to obtain the complete set of effective device properties. Since various assumptions were avoided and since the property set is now complete, it is expected that greater energy equivalence between reality and the homogenized model has been made possible. The derivation clarified what the electrical behavior of a homogenized solid with internal electrodes should be—an issue that has not been well understood. The behavior was verified by large-scale FE models of an isolated MFC patch.<br> <br>Increased geometrical fidelity for homogenization was achieved with an FE-based RVE analysis that accounted for finite-thickness effects. The presented theory also rectifies numerous issues in the literature with the use of the periodic boundary conditions. The procedure was first developed without regard to the internal electrodes (ie a homogenization of the active layer). At this level, the boundary conditions were shown to satisfy a piezoelectric macrohomogeneity condition. The methodology was then applied to the full MFC layup, and modifications were implemented so that both types of MFC electrodes would be accounted for. The IDE case considered nonuniform poling and electric fields, but fully poled material was assumed. The inherent challenges associated with these nonuniformities are explored, and a solution is proposed. Based on the homogenization boundary conditions, a dehomogenization procedure was proposed that enables the recovery of local fields. The RVE analysis results for the effective properties revealed that the homogenization procedure yields an unsymmetric constitutive relation; which suggests that the MFC cannot be homogenized as rigorously as expected. Nonetheless, the obtained properties were verified to yield favorable results when compared to a large-scale 3D FE model.<br> <br>As a final test of the obtained effective properties, large-scale 3D FE models of MFCs acting in a static unimorph configuration were considered. The most critical case to test was the smallest MFC available. Since none of the homogenized models account for the passive MFC regions that surround the piezoelectric fiber array, some of the test models were constructed with and without the passive regions. Studying the deflection of the host substrate revealed that ignoring the passive area in smaller MFCs can overpredict the response by up to 20%. Satisfactory agreement between the homogenized models and a direct numerical simulation were obtained with a larger MFC (about a 5% difference for the tip deflection). Furthermore, the uniform polarization assumption (in the analytical model) for the IDE case was found to be inadequate. Lastly, the recovery of the local fields was found to need improvement.<br><br><br>

<p>Modern structural materials utilize tailored microstructures to retain peak performance within the most volatile operating conditions. Features such as grain size, grain boundary (GB) character and morphology and secondary phases are just a few of the tunable parameters. By tailoring these types of microstructural features, the deformation behavior of the material is also altered. The localization of plastic strain directly correlated to material failure. Thus, a systematic approach was utilized to understand the effect of microstructural features on the localization of plastic deformation utilizing digital image correlation (DIC). First, at the macroscopic scale, strain accumulation is known to form parallel to the plane of maximum shear stress. The local deviations in the deformation pathways at the meso-scale are investigated relative to the plane of maximum shear stress. The deviations in the deformation pathways are observed to be a function of the accumulated local plastic strain magnitude and the grain size. Next, strains characterized via DIC were used to calculate a value of incremental slip on the active slip systems and identify cases of slip transmission. The incremental slip was calculated based on a Taylor-Bishop-Hill algorithm, which determined a qualitative assessment of deformation on a given slip system, by satisfying compatibility and identifying the stress state by the principle of virtual work. Inter-connected slip bands, between neighboring grains, were shown to accumulate more incremental slip (and associated strain) relative to slip bands confined to a single grain, where slip transmission did not occur. These results rationalize the role of grain clusters which lead to intense strain accumulation and thus serve as potential sites for fatigue crack initiation. Lastly, at GB interfaces, the effect of GB morphology (planar or serrated) on the cavitation behavior was studied during elevated temperature dwell-fatigue at 700 °C. The resulting γ′ precipitate structures were characterized near GBs and within grains. Along serrated GBs coarsened and elongated <a>γ′ </a>precipitates formed and consequently created adjacent regions that were denuded of γ′ precipitates. Dwell-fatigue experiments were performed at low and high stress amplitudes which varied the amount of imparted strain on the specimens.<a> Additionally, the regions denuded of the γ′ precipitates were observed to localize strain and to be initial sites of cavitation.</a> <a>These results present a quantitative strain analysis between two GB morphologies, which provided the micromechanical rationale for the increased proclivity for serrated GBs to form cavities.</a></p>

The effective behavior of composite materials is of great interest in materials science. The properties of such a material at the macroscale can be directly coupled to the properties of the material at the microscale. The random distribution of microscopic phases can be simulated using models of stochastic geometry. Random, two-dimensional, two-phase microstructures were constructed by stochastic simulation using the planar Boolean model. An extensive study was conducted to relate the effective hyperelastic material behavior to the stochastic parameters of the Boolean model and the physical parameters of the microstructure. Well-known approaches to determine the size of the representative volume element were adapted for this context and their results were compared.