Determination of the numerical parameters of a continuous damage model for the structural analysis of clay brick masonry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dynamic stationary response of reinforced plates by the boundary element method

A direct version of the boundary element method (BEM) is developed to model the stationary dynamic response of reinforced plate structures, such as reinforced panels in buildings, automobiles, and airplanes. The dynamic stationary fundamental solutions of thin plates and plane stress state are used to transform the governing partial differential equations into boundary integral equations (BIEs). Two sets of uncoupled BIEs are formulated, respectively, for the in-plane state ( membrane) and for the out-of-plane state ( bending). These uncoupled systems are joined to formamacro-element, in which membrane and bending effects are present. The association of these macro-elements is able to simulate thin-walled structures, including reinforced plate structures. In the present formulation, the BIE is discretized by continuous and/or discontinuous linear elements. Four displacement integral equations are written for every boundary node. Modal data, that is, natural frequencies and the corresponding mode shapes of reinforced plates, are obtained from information contained in the frequency response functions (FRFs). A specific example is presented to illustrate the versatility of the proposed methodology. Different configurations of the reinforcements are used to simulate simply supported and clamped boundary conditions for the plate structures. The procedure is validated by comparison with results determined by the finite element method (FEM).

Anodic oxidation of formaldehyde on Pt-modified SnO2 thin film electrodes prepared by a sol-gel method

Pt-modified SnO2 electrodes were prepared onto titanium substrates in the form of thin films of similar to2 mum at different temperatures in the range from 200 to 400degreesC. Surface morphology was examined by scanning electron microscopy (SEM). It was found that Pt-SnO2 sol-gel layers are significantly rough and have a low porosity. X-ray diffraction (XRD) studies showed that the films consist of Pt nanoparticles with average size varying from about 5 to 10 nm, depending on the preparation temperature, and amorphous tin oxide. X-ray photoelectron spectroscopy (XPS) was employed to determine the superficial composition of the electrodes and demonstrated the presence of Sn4+ in all the samples. XPS spectra of the Pt 4f electrons showed the presence of Pt in the zero-valence state as well as in ionic forms. The general electrochemical behavior was characterized by cyclic voltammetry in 1 mol l(-1) HClO4 and the electrocatalytic activity towards the oxidation of formaldehyde was investigated by potential sweeps and chronoamperometry. The results obtained show that the Pt-SnO2/Ti system exhibits a significant catalytic activity for the oxidation of formaldehyde, with an onset potential below 0.1 V. (C) 2004 Elsevier Ltd. All rights reserved.

Comparative analysis of strut-and-tie models using Smooth Evolutionary Structural Optimization

The strut-and-tie models are widely used in certain types of structural elements in reinforced concrete and in regions with complexity of the stress state, called regions D, where the distribution of deformations in the cross section is not linear. This paper introduces a numerical technique to determine the strut-and-tie models using a variant of the classical Evolutionary Structural Optimization, which is called Smooth Evolutionary Structural Optimization. The basic idea of this technique is to identify the numerical flow of stresses generated in the structure, setting out in more technical and rational members of strut-and-tie, and to quantify their value for future structural design. This paper presents an index performance based on the evolutionary topology optimization method for automatically generating optimal strut-and-tie models in reinforced concrete structures with stress constraints. In the proposed approach, the element with the lowest Von Mises stress is calculated for element removal, while a performance index is used to monitor the evolutionary optimization process. Thus, a comparative analysis of the strut-and-tie models for beams is proposed with the presentation of examples from the literature that demonstrates the efficiency of this formulation. © 2013 Elsevier Ltd.

Um algoritmo para a construção de superfícies potenciais de falha em sólidos tridimensionais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise numérica de seções reforçadas de concreto armado considerando o estado inicial de tensões

O presente trabalho trata da formulação e da implementação computacional, em MATLAB^®, para a análise numérica de seções reforçadas de concreto armado, submetidas à flexão composta, considerando o estado de tensões anterior ao reforço. A referida análise se dá com a geração de diagramas de interação momento fletor esforço normal por dois métodos, quais sejam: a) varredura dos domínios de deformação da NBR6118/2003; b) determinação dos picos de diagramas momento fletor – esforço normal – curvatura. Em ambos os procedimentos utiliza-se o método numérico do ponto médio na integração do cálculo dos esforços resistentes, e o método de Newton Raphson para a obtenção de raízes é usado na determinação da deformação no eixo de referência da seção, durante a determinação dos diagramas momento fletor -esforço normal - curvatura. Preliminarmente, concluiu-se que a primeira das duas metodologias aplicadas é inviável. Posteriormente, com a confirmação da eficácia da segunda metodologia, foi possível expandir o escopo do trabalho de modo a permitir a análise de seções de formatos quaisquer executadas em várias etapas, considerando o estado de tensões inicial em cada uma das etapas. A implementação computacional referente a este trabalho se baseou no programa para análise numérica de seções SECLAB, desenvolvido pelo professor Remo Magalhães de Souza.

Micro-inverter for integrated grid-tie photovoltaic module using resonant controller

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A local-global scheme for tracking crack path in three-dimensional solids

This paper aims to contribute to the three-dimensional generalization of numerical prediction of crack propagation through the formulation of finite elements with embedded discontinuities. The analysis of crack propagation in two-dimensional problems yields lines of discontinuity that can be tracked in a relatively simple way through the sequential construction of straight line segments oriented according to the direction of failure within each finite element in the solid. In three-dimensional analysis, the construction of the discontinuity path is more complex because it requires the creation of plane surfaces within each element, which must be continuous between the elements. In the method proposed by Chaves (2003) the crack is determined by solving a problem analogous to the heat conduction problem, established from local failure orientations, based on the stress state of the mechanical problem. To minimize the computational effort, in this paper a new strategy is proposed whereby the analysis for tracking the discontinuity path is restricted to the domain formed by some elements near the crack surface that develops along the loading process. The proposed methodology is validated by performing three-dimensional analyses of basic problems of experimental fractures and comparing their results with those reported in the literature.

Effect of fiber orientation on the shear behavior of glass fiber/epoxy composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Análise crítica de um vaso de pressão do setor sucroalcooleiro

This study aims to evaluate structurally a heat exchanger that has been in operation since the mid-60's and was built COSAN for operation in one of its sugar production plants in São Paulo, this equipment as well as many similar devices are operation in plants throughout Brazil, and thus to be acquired by large corporations as in the case of COSAN, pass the scrutiny of inspection work, and work such as recalculations in the latter case in structural evaluations to verify the possible need for adjustments to project or operation and thus ensure the structural integrity of the equipment. To this were first done field survey using techniques of NDT and NDT's for determining the thickness of the main parts of the equipment, made the revaluation dimensional and existing project and considering the loads operating performing the characterization of the equipment as specified in the standard regulatory number 13 - NR13 and the other for this type of equipment and finally an analysis using a static approach, as an analysis tool using the finite element method

Estudo do efeito do processo de shot peening na taxa de propagação de trinca por fadiga na liga aeronáutica 2024 - T3

Pós-graduação em Engenharia Mecânica - FEG

Effects of selenium supplementation on serum cortisol in repeatedly handled cattle

This study evaluated the relationship between Se supplementation and serum cortisol in repeatedly handled cattle. Sixty Nellore calves were randomly distributed into four experimental groups, which were fed a mineral-protein mixture added with Se to achieve individual daily supplementation of 0 (Gc), 3.6 (G3.6), 5.4 (G5.4) and 6.4 (G6.4) mg Se. Stressful handling procedures and blood sampling were performed on days 0, 15, 30, 60, 90 and 120. Serum cortisol increased until day 90 and decreased on day 120, irrespective of Se supplementation. This finding shows that cattle reached a stress state but adapted. Cortisol and Se levels were not markedly correlated. Serum Se increased over the course of the experiment in the supplemented groups. However, because serum Se decreased in Gc, it may have mobilized to form the selenoproteins needed to remove metabolic wastes from handling-related oxidative stress.

Sviluppo di una metodologia per la modellazione geologica-geomeccanica ed il monitoraggio di reservoir adibiti a siti di stoccaggio di gas naturale

La valutazione dei rischi associati all’operatività dei sistemi di stoccaggio, quali la sismicità indotta e la subsidenza, è requisito basilare per una loro corretta gestione e progettazione, e passa attraverso la definizione dell’influenza sullo stato tensionale delle variazioni di pressione di poro nel sottosuolo. Principale scopo di questo progetto è lo sviluppo di una metodologia in grado di quantificare le deformazioni dei reservoir in funzione della pressione di poro, di tarare i modelli utilizzati con casi studio che presentino dati di monitoraggio reali, tali da consentire un confronto con le previsioni di modello. In questa tesi, la teoria delle inomogeneità è stata utilizzata, tramite un approccio semianalitico, per definire le variazioni dei campi elastici derivanti dalle operazioni di prelievo e immissione di fluidi in serbatoi geologici. Estensione, forma e magnitudo delle variazioni di stress indotte sono state valutate tramite il concetto di variazione dello sforzo critico secondo il criterio di rottura di Coulomb, tramite un’analisi numerica agli elementi finiti. La metodologia sviluppata è stata applicata e tarata su due reservoir sfruttati e riconvertiti a sistemi di stoccaggio che presentano dataset, geologia, petrofisica, e condizioni operative differenti. Sono state calcolate le variazioni dei campi elastici e la subsidenza; è stata mappata la variazione di sforzo critico di Coulomb per entrambi i casi. I risultati ottenuti mostrano buon accordo con le osservazioni dei monitoraggi, suggerendo la bontà della metodologia e indicando la scarsa probabilità di sismicità indotta. Questo progetto ha consentito la creazione di una piattaforma metodologica di rapido ed efficace utilizzo, per stimare l’influenza dei sistemi di stoccaggio di gas sullo stato tensionale della crosta terrestre; in fase di stoccaggio, permette di monitorare le deformazioni e gli sforzi indotti; in fase di progettazione, consente di valutare le strategie operative per monitorare e mitigare i rischi geologici associati a questi sistemi.

Dynamic development of hydrofractures

Natürliche hydraulische Bruchbildung ist in allen Bereichen der Erdkruste ein wichtiger und stark verbreiteter Prozess. Sie beeinflusst die effektive Permeabilität und Fluidtransport auf mehreren Größenordnungen, indem sie hydraulische Konnektivität bewirkt. Der Prozess der Bruchbildung ist sowohl sehr dynamisch als auch hoch komplex. Die Dynamik stammt von der starken Wechselwirkung tektonischer und hydraulischer Prozesse, während sich die Komplexität aus der potentiellen Abhängigkeit der poroelastischen Eigenschaften von Fluiddruck und Bruchbildung ergibt. Die Bildung hydraulischer Brüche besteht aus drei Phasen: 1) Nukleation, 2) zeitabhängiges quasi-statisches Wachstum so lange der Fluiddruck die Zugfestigkeit des Gesteins übersteigt, und 3) in heterogenen Gesteinen der Einfluss von Lagen unterschiedlicher mechanischer oder sedimentärer Eigenschaften auf die Bruchausbreitung. Auch die mechanische Heterogenität, die durch präexistierende Brüche und Gesteinsdeformation erzeugt wird, hat großen Einfluß auf den Wachstumsverlauf. Die Richtung der Bruchausbreitung wird entweder durch die Verbindung von Diskontinuitäten mit geringer Zugfestigkeit im Bereich vor der Bruchfront bestimmt, oder die Bruchausbreitung kann enden, wenn der Bruch auf Diskontinuitäten mit hoher Festigkeit trifft. Durch diese Wechselwirkungen entsteht ein Kluftnetzwerk mit komplexer Geometrie, das die lokale Deformationsgeschichte und die Dynamik der unterliegenden physikalischen Prozesse reflektiert. rnrnNatürliche hydraulische Bruchbildung hat wesentliche Implikationen für akademische und kommerzielle Fragestellungen in verschiedenen Feldern der Geowissenschaften. Seit den 50er Jahren wird hydraulisches Fracturing eingesetzt, um die Permeabilität von Gas und Öllagerstätten zu erhöhen. Geländebeobachtungen, Isotopenstudien, Laborexperimente und numerische Analysen bestätigen die entscheidende Rolle des Fluiddruckgefälles in Verbindung mit poroelastischen Effekten für den lokalen Spannungszustand und für die Bedingungen, unter denen sich hydraulische Brüche bilden und ausbreiten. Die meisten numerischen hydromechanischen Modelle nehmen für die Kopplung zwischen Fluid und propagierenden Brüchen vordefinierte Bruchgeometrien mit konstantem Fluiddruck an, um das Problem rechnerisch eingrenzen zu können. Da natürliche Gesteine kaum so einfach strukturiert sind, sind diese Modelle generell nicht sonderlich effektiv in der Analyse dieses komplexen Prozesses. Insbesondere unterschätzen sie die Rückkopplung von poroelastischen Effekten und gekoppelte Fluid-Festgestein Prozesse, d.h. die Entwicklung des Porendrucks in Abhängigkeit vom Gesteinsversagen und umgekehrt.rnrnIn dieser Arbeit wird ein zweidimensionales gekoppeltes poro-elasto-plastisches Computer-Model für die qualitative und zum Teil auch quantitativ Analyse der Rolle lokalisierter oder homogen verteilter Fluiddrücke auf die dynamische Ausbreitung von hydraulischen Brüchen und die zeitgleiche Evolution der effektiven Permeabilität entwickelt. Das Programm ist rechnerisch effizient, indem es die Fluiddynamik mittels einer Druckdiffusions-Gleichung nach Darcy ohne redundante Komponenten beschreibt. Es berücksichtigt auch die Biot-Kompressibilität poröser Gesteine, die implementiert wurde um die Kontrollparameter in der Mechanik hydraulischer Bruchbildung in verschiedenen geologischen Szenarien mit homogenen und heterogenen Sedimentären Abfolgen zu bestimmen. Als Resultat ergibt sich, dass der Fluiddruck-Gradient in geschlossenen Systemen lokal zu Störungen des homogenen Spannungsfeldes führen. Abhängig von den Randbedingungen können sich diese Störungen eine Neuausrichtung der Bruchausbreitung zur Folge haben kann. Durch den Effekt auf den lokalen Spannungszustand können hohe Druckgradienten auch schichtparallele Bruchbildung oder Schlupf in nicht-entwässerten heterogenen Medien erzeugen. Ein Beispiel von besonderer Bedeutung ist die Evolution von Akkretionskeilen, wo die große Dynamik der tektonischen Aktivität zusammen mit extremen Porendrücken lokal starke Störungen des Spannungsfeldes erzeugt, die eine hoch-komplexe strukturelle Entwicklung inklusive vertikaler und horizontaler hydraulischer Bruch-Netzwerke bewirkt. Die Transport-Eigenschaften der Gesteine werden stark durch die Dynamik in der Entwicklung lokaler Permeabilitäten durch Dehnungsbrüche und Störungen bestimmt. Möglicherweise besteht ein enger Zusammenhang zwischen der Bildung von Grabenstrukturen und großmaßstäblicher Fluid-Migration. rnrnDie Konsistenz zwischen den Resultaten der Simulationen und vorhergehender experimenteller Untersuchungen deutet darauf hin, dass das beschriebene numerische Verfahren zur qualitativen Analyse hydraulischer Brüche gut geeignet ist. Das Schema hat auch Nachteile wenn es um die quantitative Analyse des Fluidflusses durch induzierte Bruchflächen in deformierten Gesteinen geht. Es empfiehlt sich zudem, das vorgestellte numerische Schema um die Kopplung mit thermo-chemischen Prozessen zu erweitern, um dynamische Probleme im Zusammenhang mit dem Wachstum von Kluftfüllungen in hydraulischen Brüchen zu untersuchen.

Modeling mechanical response of heterogeneous materials

Heterogeneous materials are ubiquitous in nature and as synthetic materials. These materials provide unique combination of desirable mechanical properties emerging from its heterogeneities at different length scales. Future structural and technological applications will require the development of advanced light weight materials with superior strength and toughness. Cost effective design of the advanced high performance synthetic materials by tailoring their microstructure is the challenge facing the materials design community. Prior knowledge of structure-property relationships for these materials is imperative for optimal design. Thus, understanding such relationships for heterogeneous materials is of primary interest. Furthermore, computational burden is becoming critical concern in several areas of heterogeneous materials design. Therefore, computationally efficient and accurate predictive tools are highly essential. In the present study, we mainly focus on mechanical behavior of soft cellular materials and tough biological material such as mussel byssus thread. Cellular materials exhibit microstructural heterogeneity by interconnected network of same material phase. However, mussel byssus thread comprises of two distinct material phases. A robust numerical framework is developed to investigate the micromechanisms behind the macroscopic response of both of these materials. Using this framework, effect of microstuctural parameters has been addressed on the stress state of cellular specimens during split Hopkinson pressure bar test. A voronoi tessellation based algorithm has been developed to simulate the cellular microstructure. Micromechanisms (microinertia, microbuckling and microbending) governing macroscopic behavior of cellular solids are investigated thoroughly with respect to various microstructural and loading parameters. To understand the origin of high toughness of mussel byssus thread, a Genetic Algorithm (GA) based optimization framework has been developed. It is found that two different material phases (collagens) of mussel byssus thread are optimally distributed along the thread. These applications demonstrate that the presence of heterogeneity in the system demands high computational resources for simulation and modeling. Thus, Higher Dimensional Model Representation (HDMR) based surrogate modeling concept has been proposed to reduce computational complexity. The applicability of such methodology has been demonstrated in failure envelope construction and in multiscale finite element techniques. It is observed that surrogate based model can capture the behavior of complex material systems with sufficient accuracy. The computational algorithms presented in this thesis will further pave the way for accurate prediction of macroscopic deformation behavior of various class of advanced materials from their measurable microstructural features at a reasonable computational cost.