Дисертації з теми "Localized strains"

In questa tesi si presenta una teoria termodinamica per continui porosi multi-fase basata sul lavoro di Biot e la relativa formulazione numerica mediante elementi finiti non convenzionali che consentono di modellare fenomeni di localizzazione delle deformazioni. In una prima fase si ricava una forma generale per le relazioni iperelastiche incrementali. Si ottengono quindi espressioni particolari per gli operatori iperelastici tangenti utilizzando argomenti tipici della teoria delle miscele. Si verifica la compatibilità di tali operatori con la suddetta teoria termodinamica utilizzando le condizioni di simmetria e di Maxwell. Fra i principali risultati della trattazione considerata vi è una semplice espressione della dissipazione, che sarà utilizzata in un approccio multi-scala alla localizzazione delle deformazioni. Si considera quindi una formulazione agli elementi finiti del modello costitutivo ot tenuto, concentrando l'attenzione sulla linearizzazione del sistema risolvente. Tra le possibili fonti di non-linearità, si considerano anche quelle dovute a condizioni al contorno unilatere sul flusso fluido, introdotte per modellare e±cacemente l'interfaccia tra mezzo poroso e atmosfera. Si analizzano semplici esempi numerici monodimensionali, allo scopo di valutare le prestazioni numeriche delle tecniche di regolarizzazione di tipo penalty e Lagrangiano aumentato utilizzate. In tali esempi si evidenzia anche l'analogia formale e numerica tra problemi di filtrazione con vincoli unilateri e problemi di contatto in assenza di attrito. Si prendono inoltre in considerazione altre situazioni di interesse pratico, come la propagazione di un fronte di saturazione in uno strato di terreno e la parziale saturzione in una diga di calcestruzzo a gravità. Per modellare meccanismi dissipativi localizzati, si analizza la presenza di discontinuità negli spostamenti e nei flussi fluidi nel caso di mezzi porosi multi-fase. Nel corrispondente metodo agli elementi finiti, l'insorgere di tali discontinuità è simulato mediante "enhancement" locale delle funzioni interpolanti. Infine, si presentano i risultati della simulazione numerica di una prova di compressione piana su un mezzo poroso parzialmente saturo. Tale simulazione consente di evidenziare tutte le caratteristiche delle formulazioni teoriche e numeriche presentate in questa tesi.
In this thesis we present a thermodynamic theory for multiphase porous continua based on Biot work and the corresponding numerical formulation by non-standard finite element methods modelling strain localization phenomena. Firstly, a general form of hyperelastic rate equations is provided. Particular expressions for hyperelastic tangent operators are then obtained by using arguments typically employed in the mixture theory. The compatibility of such operators with the aforementioned thermodynamic theory is then investigated by means of symmetry and Maxwell conditions. Among the main results of the presented formulation there is a simple expression for dissipation, that will be used in a multi-scale approach to the localization of deformations in multiphase solids. A finite element formulation of this constitutive model is then presented, focusing the attention on the linearization of the resulting solving system. Among the different sources of non-linearity, also the ones due to unilateral boundary conditions on the fluid flow are considered. Such boundary conditions are introduced to effectively model the interface between the porous solid and the atmosphere. In order to investigate numerical performance of penalty and augmented Lagrangian regularization techniques employed herein, simple one-dimensional numerical examples are considered. In these examples, both the numerical and formal analogies between seepage problems with unilateral constraints and frictionless contact problems are pointed out. Further situations of practical interest are considered, as the propagation of a saturation front in a soil sample and the partial saturation of a concrete gravity dam. To model localized dissipative mechanisms, we analyze the presence of discontinuities in displacements and fluid flows. In the corresponding finite element method, the appearance of these discontinuities is simulated by local enhancement of interpolating functions. Finally, results of the numerical simulation of a plain strain compression test on a partially saturated porous solid are presented. This simulation allows us to point out all the features of theoretical and numerical formulations presented in this thesis.

Numerical methods aid significantly the engineering efforts towards the conservation of existing masonry structures and the design of new ones. Among them, macro-mechanical finite element methods based on the smeared crack approach are commonly preferred as an affordable choice for the analysis of large masonry structures. Nevertheless, they usu-ally result in a non-realistic representation of damage as smeared over large areas of the structure, which hampers the correct interpretation of the damage pattern. Additionally, a more critical pathology of this approach is the mesh-dependency, which influences nota-bly the safety and stability predictions. To overcome these limitations, this thesis proposes a novel computational tool based on the {enrichment} of the classical smeared crack approach with a local tracking algorithm. The objective of this localized damage model is the realistic and efficient non-linear anal-ysis of masonry structures with an enhanced representation of cracking. The non-linear behaviour of masonry is simulated through the adoption of a continuum damage mechanics model with two damage indices, allowing the differentiation between the tensile and compressive mechanical responses of masonry. In this context, a novel explicit formulation for the evolution of irreversible strains is proposed and implemented. Two new expressions are derived for the regularization of the tensile and compressive softening responses according to the crack-band approach, ensuring the mesh-size objec-tivity of the damage model. The simulation of the structural behaviour of masonry structures under versatile loading and boundary conditions necessitates some developments in the context of local tracking algorithms. To this end, this thesis presents the enhancement of local tracking algorithms with novel procedures that make possible the simulation of multiple, arbitrary and inter-secting cracking under monotonic and cyclic loading. Additionally, the effect of different crack propagation criteria is investigated and the selection among more than one potential failure planes is tackled. The proposed localized damage model is validated through the simulation of a series of structural examples. These vary from small-scale tests on concrete specimens with few dominant cracks, to medium and large-scale masonry structures with multiple tensile, shear and flexural cracking. The analyses are compared with analytical, experimental and numerical results obtained with alternative methods available in the literature. Overall, the localized damage model developed in this thesis largely improves the mesh-independency of the classical smeared crack approach and reproduces crack patterns and collapse mech-anisms in an efficient and realistic way.
Los métodos numéricos son decisivos en la ingeniería para la conservación de estructuras de mampostería existentes y el diseño de estructuras nuevas. Entre ellos, los métodos macro-mecánicos de elementos finitos, basados en el concepto de fisuras distribuidas, son habitualmente los preferidos como opción asequible para el análisis de grandes estructuras de mampostería. Sin embargo, suelen resultar en a una representación poco realista del daño, distribuido en grandes áreas de la estructura, lo que impide la correcta interpretación del patrón de daño. Además, esta metodología presenta una patología más crítica, la dependencia de la malla, que influye notablemente en las predicciones de seguridad y estabilidad. Para superar estas limitaciones, esta tesis propone una nueva herramienta numérica basada en el enriquecimiento del clásico enfoque de fisuras distribuidas con un algoritmo de trazado local. El objetivo de este modelo de daño localizado es el análisis no-lineal de las estructuras de mampostería de manera realista y eficiente con una representación mejora-da de fisuras. El comportamiento no lineal de la mampostería se simula a través de la adopción de un modelo de mecánica de daño continuo con dos índices de daño, permitiendo la diferenciación entre las respuestas mecánicas de tensión y compresión de la mampostería. En este contexto, se propone e implementa una nueva formulación explícita para la evolución de deformaciones irreversibles. Se derivan dos nuevas expresiones para la regularización del ablandamiento de tracción y compresión según el ancho de banda de la fisura, garantizan-do la objetividad del modelo de daño al respecto del tamaño de la malla. La simulación del comportamiento estructural de las estructuras de mampostería en condiciones de carga y contorno generales precisa de algunos desarrollos en el contexto de los algoritmos locales de trazado. Con este objetivo, se presenta la mejora de los algoritmos locales de trazado con nuevos procedimientos que posibilitan la simulación de fisuración múltiple, arbitraria e secante bajo cargas monótonas y cíclicas. Además, se investiga el efecto de diferentes criterios de propagación de fisuras y se aborda la selección entre más de un plano de falla posible. El modelo de daño localizado propuesto se valida mediante la simulación de una serie de ejemplos estructurales. Éstos van desde pruebas a pequeña escala en probetas de hormigón, con pocas fisuras dominantes, hasta estructuras de mampostería de mediana y gran escala con fisuración múltiple de tracción, de cortante y de flexión. Los análisis se comparan con los resultados analíticos, experimentales y numéricos obtenidos con métodos alternativos disponibles en la literatura. El modelo de daño localizado mejora en gran medida la independencia de la malla del clásico método de fisuras distribuidas y reproduce patrones de daño y mecanismos de colapso de una manera eficiente y realista

The Sandia GeoModel is a continuum elastoplastic constitutive model which captures many features of the mechanical response for geological materials over a wide range of porosities and strain rates. Among the specific features incorporated into the formulation are a smooth compression cap, isotropic/kinematic hardening, nonlinear pressure dependence, strength differential effect, and rate sensitivity. This study attempts to provide enhancements regarding computational tractability, domain of applicability, and robustness of the model. A new functional form is presented for the yield and plastic potential functions. The model is also furnished with a smooth, elliptical tension cap to account for the tensile failure. This reformulation renders a more accurate, robust and efficient model as it eliminates spurious solutions attributed to the original form. In addition, this constitutive model is adopted in bifurcation analysis to track the inception of new localization and crack path propagation. For the post-localization regime, a cohesive-law fracture model, able to address mixed-model failure condition, is implemented to characterize the constitutive softening behavior on the surface of discontinuity. To capture propagating fracture, the Assumed Enhanced Strain (AES) method is invoked. Particular mathematical treatments are incorporated into the simulation concerning numerical efficiency and robustness issues. Finally, the aforementioned modified cap plasticity model is employed to investigate the nonlinear dynamic response of the earthen substructure of the rail. Studying the effects of high-speed trains on the track substructure.

L'objectif de neutralité carbone reposant massivement sur les sources d'énergie renouvelables peut être accéléré en envisageant la séquestration souterraine du CO2 et le stockage souterrain (i) de l'hydrogène produit par l'électrolyse de l'eau à partir d'électricité renouvelable et (ii) du méthane synthétisé produit par la méthanisation. Cependant, l'injection de ces fluides dans des aquifères salins profonds peut déclencher des instabilités locales sous la forme de digitations, qui sont les précurseurs d'instabilités macroscopiques telles que la microsismicité, l'affaissement ou le gonflement du sol. L'interaction entre le fluide injecté, le fluide résidentiel et le milieu poreux hôte est un problème complexe. Pour étudier la réponse d'un squelette solide percolé par un écoulement diphasique instable, une machine originale bi-axiale adaptée aux géo-matériaux partiellement saturés et fournissant un contrôle hydro- mécanique, a été mise en place. Des expériences de drainage ont été menées sur des échantillons de sable saturés en eau et chargés mécaniquement, par injection d'air via une pression capillaire imposée. Un protocol d’essai détaillant les étapes nécessaires à la réussite du test de drainage, allant de la préparation de l'échantillon à l'injection d'air, a été établi. Grâce à un système optique haute résolution, l'infiltration de l’air à travers un ou plusieurs chemins préférentiels dans le milieu granulaire, a été acquise. Le suivi du ou des doigts a nécessité le développement d'un algorithme robuste permettant la détection automatique de l'interface pour l'ensemble des images disponibles. De plus, le réarrangement de la squelette granulaire induit par la percolation du fluide a été quantifié via la corrélation d'images numériques par éléments finis. Le couplage entre la propagation de l'interface et les déformations localisées a été mesuré quantitativement en fonction du chargement mécanique, contrôlé par la contrainte effective. Les résultats ont montré une corrélation entre le chargement mécanique et la percolation hétérogène sous la forme de digitation et de déformations localisées
The goal of carbon neutrality relying massively on the renewable energy sources can be accelerated by considering underground CO2 sequestration and underground storage of (i) hydrogen produced by the water electrolysis from renewable electricity, and (ii) synthesized methane produced by the methanation. However, the injection of these fluids into deep saline aquifers, can trigger local instabilities in the form of fluid fingering, which are precursors of macroscopic instabilities such as micro-seismicity, subsidence or ground swelling. The interaction between the injected fluid, the residential one and the host porous medium is a complex problem. To investigate the response of a solid skeleton percolated by an unsteady bi-phasic flow, an original bi-axial machine adapted to partially saturated geo-materials and providing a hydro-mechanical control, has been set-up. Drainage experiments have been conducted on mechanically loaded water-saturated sand samples by injecting air via an imposed capillary pressure. A testing protocol detailing the steps required to achieve successful drainage test, starting from sample preparation to air injection, has been established. Thanks to a high resolution optical system, the air infiltration through preferential pathway(s) within the granular medium, has been acquired. The monitoring of the propagating finger(s) has required the development of robust algorithm allowing the automatic interface detection for the set of available images. In addition, the skeleton remodeling driven by the fluid percolation has been quantified via finite- element based digital image correlation. The coupling between interface propagation and localized strains has been quantitatively measured as function of the mechanical loading, controlled by the effective stress. The results have shown a correlation between mechanical loading and the heterogeneous percolation in the form of fingering and localized strains

Includes bibliographical references.
The defonnation response and subsequent tearing of built in plates subjected to central impulsive loading has been investigated experimentally in the past. Theoretical predictions of the structural response have also been made and compared to these experiments. In this thesis, a new method is developed whereby the strains within the defonned plates were measured using micrographs of the grain structure of the plate. The aim of the thesis was to gain a fuller understanding of the internal defonnation of blast loaded plate so as to enable more accurate theoretical predictions of plate defonnation and tearing. The dimensions of the grains of the plate material both in the virgin state and after defonnation were measured by image analysis of scanning electron micrographs. These measurements were processed and averaged at various points within the structure. This enabled the strain distribution throughout the defonned plate to be analysed. Tensile tests were undertaken in order to calibrate this method of strain measurement. The tests were arrested during the loading, after the specimen had undergone a known amount of strain. The strain measured from the microstructure was then compared to the strain measured during the tensile tests. The method was found to give a satisfactory measurement of the strain in the tensile tests.

Doctor of Philosophy
Department of Civil Engineering
Dunja Peric
A low ratio between the compressive strength of concrete and its cost makes concrete one of the most widely used construction materials in civil engineering. Despite of a very good response to compressive stress, concrete exhibits a low tensile strength and limited tensile strain capacity. Adding short discrete fibers to a cementitious matrix can significantly improve its performance under tensile stress, thus ultimately exhibiting a ductile behavior. Nevertheless, in spite of their beneficial properties fiber reinforced cementitious composites remain underutilized in engineering practice. One of the main reasons for this is a lack of an adequate characterization of the tensile behavior as well as a lack of analysis methods that would allow engineers to incorporate fiber reinforced structural concrete elements into their design. Therefore, this dissertation has four key objectives: 1) to computationally model a stress-strain response of high performance fiber reinforced cementitious composites in uniaxial tension and uniaxial compression prior to macro-crack localization, 2) to develop and perform a diagnostic strain localization analysis for high performance fiber reinforced cementitious composites, the results of which can characterize effects of fibers on failure precursors, 3) to devise and perform an experimental program for characterization of ultra-high performance fiber reinforced cementitious composites, and 4) to characterize a full-fledged behavior including stress-strain and stress-crack opening displacement responses of ultra-high performance fiber reinforced cementitious composites in uniaxial tension. To quantify effects of fibers on onset of strain localization in fiber reinforced cementitious composites a combined computational/analytical models have been developed. To this end, linear-elastic multi-directional fibers were embedded into a cementitious matrix. The resulting composite was described by different types of two-invariant non-associated Drucker-Prager plasticity models. In order to investigate effects of a shape of a yield surface and hardening type linear and nonlinear yield surfaces, and linear and nonlinear hardening rules were considered. Diagnostic strain localization analyses were conducted for several plane stress uniaxial tension and uniaxial compression tests on non-reinforced cementitious composites as well as on high performance fiber-reinforced cementitious composites. It was found that presence of fibers delayed the inception of strain localization in all tests on fiber-reinforced composites. Furthermore, presence of fibers exerted a more significant effect on the strain localization direction and mode in uniaxial compression than in uniaxial tension. The main objective of experimental program was to facilitate characterization of the post-cracking tensile behavior of ultra-high performance fiber reinforced cementitious composites. To this end, five different mixes of fiber-reinforced cementitious composites were cast, whereby volumetric fiber content, fiber shape and water to binder ratio were the experimental variables. Two testing methods were adopted, a direct uniaxial tension test and four-point prism bending test. Two different post-cracking behaviors were observed in direct tension tests, softening and strain hardening accompanied with multiple cracking. On the other hand, the response from prism bending tests was less scattered. Several different inverse analyses were carried out to predict stress-strain and stress-crack opening displacement responses in uniaxial tension based on the prism bending tests. The analyses resulted in worthy correlations with the experimental data, thus suggesting that the prism bending test is a viable alternative to a much more challenging to perform direct tension test for ultra-high performance fiber reinforced composites.

Computational investigation of the stability of natural slopes within a coupled hydro-mechanical approach becomes more and more attractive due to an increasing number of slope movements caused by heavy rainfall events. Seasonal cycles of summer drying and winter-spring wetting affect the stability and serviceability of natural and man-made slopes, threatening lives and property worldwide. Heavy rainfall will increase the soil moisture content and lead to a reduction in suction and a consequent weakening of the soil. As a result, the slope may fail either in a diffused or in a localized pattern. The localization process is a classical mode of mechanical instability and is described as the concentration of shear strains in narrow bands within the soil strata. As it is well-known, the width of those bands cannot be properly computed using the standard continuum mechanical approach with unstable materials (in the sense of Drucker). In the framework of the standard finite element method the computation of shear band phenomena reveals a strong mesh dependency of the numerical solution and the objectivity of the computational results is blown. Each mesh refinement results in an overall different outcome and the width of the localization band has the size of the element of the adopted mesh. In the literature two main categories of methodologies can be found for regularizing this problem. One is to simulate the formation and propagation of such discontinuities via suitable enrichment functions and is the concept of the so-called extended finite elements. The other solution is to exploit enhanced continuum theories. These theories contain an internal length scale which is an additional material parameter related to the shear band width and removes the spurious mesh sensitivity of the numerical simulation results. The present work is focused on the second category. In this context, viscoplasticity and non-local theories are adopted to effectively study strain localization mechanism, assuming the soil as a multiphase porous medium. This means that the localization analysis is considered as a fully coupled hydro-mechanical problem with the material consisting of an elasto-viscoplastic skeleton and open pores filled with incompressible liquid water and compressible gas. Both regularization techniques are physically sound. Rate dependency is experimentally motivated as the mechanical response of granular materials seems to be rapid, but not instantaneous and a viscoplastic constitutive model is able to reproduce creep and relaxation processes. The physical interpretation of the non-local theory stems from the fact that no real material is an ideal continuous medium and the evolution of the microstructure at one point influences the surrounding points when irreversible strains take place. Two types of viscoplastic models are applied; the Perzyna and the Duvaut-Lions. The former is extended with respect to the non-local integral approach. In the first part of this work, the generalized effective stress is limited by the Drucker-Prager yield criterion. The models are implemented and numerically validated in the finite element code Comes-geo and further verified by simulating an experimental plane-strain biaxial test and a benchmark slope failure problem. This work is in essence aimed at answering key questions, such as: what are the most significant influential factors in the development of strain localization for each regularization technique and what is the role of suction and drainage conditions; is the viscosity of the soil affected by the presence of water and how does this fact influence the regularizing capabilities of the method; how do the internal lengths introduced by viscosity and non-locality interact with each other and under which circumstances is the one method preferable to the other? The second half of this work comprises the extension to viscoplasticity of the existing advanced elastoplastic constitutive model for unsaturated sands developed by Buscarnera and Nova. This model allows for hydraulic bonding and debonding effects and therefore the main mechanisms of unsaturated materials are captured. The elastoplastic version of the model is first implemented in the finite element code Comes-geo and validated with results from the literature. The model is then extended to viscoplasticity and is also implemented and validated in the code. The proposed viscoplastic formulation, as further novelty, is enhanced with the dependence of the constitutive parameters on the relative density. To validate the elastoplastic model in the finite element code Comes-geo a series of tests are simulated: triaxial shear tests at different suction and net confining pressure, oedometric tests with drying and wetting paths and triaxial and plane-strain compression tests in drained and undrained conditions. The viscoplastic model is also validated through oedometric tests, creep tests and triaxial compression tests on different sand densities. The onset of shear strain localization is then studied and the finite element results are compared with the results of a theoretical stability analysis. The verification of the viscoplastic model is finalized with the simulation of a triaxial compression test. The main motivation for the present work stems from these premises and this thesis presents an efficient tool to simulate strain localization with regularization techniques, which do not need to increase the number of the state variables of the numerical model, taking into account fully coupled hydro-mechanical analysis and using advanced constitutive model for unsaturated sands. This dissertation has been performed for the first two years in the University of Padova (Italy) and for the last year at Baugrund Dresden (Germany), geotechnical design and construction company within the Marie Curie Initial Training Network project MuMoLaDe (Multiscale Modelling of Landslide and Debris flow, 7th Framework Programme of the European Union, project n. 289911, http://www.mumolade.com/). This practice is in the scope of linking academia and industry and the transfer of knowledge. In this framework, the advanced elastoplastic and elasto-viscoplastic models for unsaturated soils are implemented and validated in PLAXIS commercial finite element analysis software. The validation included single element tests of drained and undrained triaxial loading and triaxial tests at different suction levels. The implementation is verified and the effectiveness of the model is displayed by numerical simulations of a partially saturated slope failure of the laboratory scale.
Lo studio numerico della stabilità dei pendii con un approccio idro-meccanico accoppiato è sempre più importante e necessario nella pratica ingegneristica a causa del continuo aumento dei fenomeni franosi, che determinano perdite di vite umane e danni all’ambiente naturale e costruito. In genere, tali fenomeni sono provocati da eventi metereologici violenti, che determinano la riduzione delle forze capillari intergranulari e della resistenza del materiale costituente i pendii. Inoltre, anche cicli stagionali di essicazione estiva e imbibizione invernale e primaverile favoriscono l’instabilità di pendii naturali e artificiali. Il collasso dei pendii avviene con un meccanismo diffuso oppure localizzato; in quest’ultimo caso avviene mediante la formazione di zone di ampiezza limitata dette bande di taglio in cui si concentrano le deformazioni del materiale. Quando si simula numericamente il collasso causato dalla formazione di bande di taglio e si utilizza la meccanica classica del continuo di Cauchy con un modello costitutivo per materiale instabile nel senso di Drucker, è noto che la larghezza delle bande di taglio non può essere calcolata né definita nel modello. In particolare, lo studio numerico di fenomeni di localizzazione delle deformazioni con il metodo degli elementi finiti evidenzia una forte dipendenza della soluzione numerica e della larghezza delle bande di taglio dalla mesh utilizzata, con perdita della soluzione all’infittimento della mesh. Infatti, accade che la larghezza delle bande di taglio risulta fissata dalla dimensione dell’elemento finito utilizzato, tendendo a zero al tendere a zero della dimensione dell’elemento finito. Di conseguenza, per poter simulare in modo obiettivo fenomeni di localizzazione delle deformazioni, è necessario modificare (o regolarizzare) il continuo di Cauchy. In letteratura si trovano due classi principali di regolarizzazione a cui ricorrere per risolvere questo problema. Il primo propone di simulare la formazione e la propagazione delle bande di taglio utilizzando campi discontinui di spostamento, dando origine al metodo degli elementi finiti estesi (extended finite element method). Il secondo propone di arricchire il modello continuo a livello cinematico oppure a livello costitutivo (enhanced continuum theories), in modo da fornire al modello una lunghezza di scala interna da cui dipende la larghezza della banda di taglio, eliminando in questo modo il problema della mesh dipendenza citata in precedenza. Questa tesi di dottorato è svolta scegliendo di arricchire il continuo di Cauchy a livello costitutivo e individua nella viscoplasticità locale e non-locale l’approccio utile allo studio della localizzazione delle deformazioni nei suoli. Inoltre, per tenere conto delle interazioni fra la parte solida e quella fluida, i suoli sono analizzati come mezzi porosi multifase. Di conseguenza, l’analisi della localizzazione delle deformazioni nei suoli è compiuta considerando il materiale dei pendii come un mezzo poroso costituito da uno scheletro solido elasto-viscoplastico e pori contenenti acqua liquida e aria umida. La scelta delle due tecniche di regolarizzazione sopra citate è stata dettata dal loro significato fisico, in quanto la risposta meccanica dei materiali granulari non è istantanea a causa dei processi viscosi o di rilassamento. Inoltre, l’introduzione della teoria non-locale deriva dalla considerazione che nessun materiale reale è un continuo nel senso matematico, a causa dell’evoluzione della microstruttura in un punto materiale che influenza i punti del suo intorno quando si sviluppano deformazioni irreversibili. In questa tesi sono utilizzati due approcci viscoplastici: quello di Perzyna e quello di Duvaut-Lions. Il primo è stato esteso con l’approccio non-locale. Nella prima parte di questo lavoro di tesi i modelli viscoplastici sono sviluppati utilizzando il criterio di snervamento di Drucker-Prager, implementati nel codice agli elementi finiti Comes-geo, validati e verificati numericamente simulando test sperimentali di compressione biassiale in stato piano di deformazione e un test numerico di collasso di un pendio. Questa parte del lavoro ha lo scopo di rispondere alle seguenti domande-chiave sulla localizzazione delle deformazioni nei mezzi porosi viscoplastici: quali sono i fattori più importanti che influenzano lo sviluppo della bande di taglio e qual è il ruolo delle pressioni capillari e delle condizioni di drenaggio; se la viscosità dei suoli è influenzata dalla presenza dell’acqua e se influenza le proprietà di regolarizzazione del metodo locale o non-locale; come interagiscono la lunghezza di scala interna indotta dalla viscosità e quella introdotta dalla non-località; quando un metodo è preferibile ad un altro. La seconda parte di questo lavoro di tesi ha per oggetto lo sviluppo di un nuovo e avanzato modello viscoplastico a partire dal modello costitutivo elasto-plastico per le sabbie parzialmente sature proposto da Buscarnera e Nova. Questo modello permette di simulare i principali meccanismi del comportamento micromeccanico di materiali parzialmente saturi, ovvero la coesione idraulica (hydraulic bounding) e gli effetti di decoesione (debonding) nelle sabbie. Questa parte del lavoro è stata svolta in due fasi; nella prima fase si è discretizzato e implementato il modello elasto-plastico nel codice agli elementi finiti Comes-Geo, successivamente validato utilizzando risultati di letteratura. In particolare sono state simulate: test di taglio a vari valori di pressione capillare (suzione) e pressione di confinamento, test di compressione edometrica con percorsi di desaturazione e saturazione e test di compressione drenata e non drenata in condizione di stato piano di deformazione. Nella seconda fase, questo modello è stato esteso alla viscoplasticità, in modo da tener conto del comportamento viscoso delle sabbie, implementato nel codice Comes-Geo e validato simulando prove di laboratorio di letteratura. La formulazione viscoplastica proposta è stata poi arricchita formulando la dipendenza dei parametri costitutivi dalla densità relativa. Il modello viscoplastico di base e quello arricchito sono stati validati simulando prove di compressione edometrica, prove di viscosità e prove di compressione triassiale a vari valori di densità. Inoltre, con il modello arricchito, è stata simulata una prova di localizzazione su sabbie dense e sciolte e i risultati numerici ottenuti sono stati confrontati con i risultati dell’analisi di stabilità. Con questa tesi si è sviluppato uno strumento numerico efficiente per la simulazione della localizzazione delle deformazioni con metodi regolarizzati che non necessitano di aumentare il numero di variabili di stato e che utilizza modelli costitutivi avanzati considerando il comportamento idro-meccanico accoppiato delle sabbie parzialmente sature. Questo lavoro è stato svolto presso l’Università degli Studi di Padova (Italia) durante i primi due anni di dottorato e presso l’unità di ricerca e sviluppo della società di progettazione e costruzione Baugrund Dresden (Germania) durante il terzo anno di dottorato; l’attività è stata svolta all’interno del progetto Marie Curie Initial Training Network MuMoLaDe (Multiscale Modelling of Landslide and Debris flow), 7th Framework Programme of the European Union, progetto n. 289911, http://www.mumolade.com/. I modelli costitutivi avanzati elasto-plastico e viscoplastici sono stati inoltre implementati e validati anche nel codice commerciale agli elementi finiti Plaxis durante la collaborazione con Baugrund Dresden.

Listeria monocytogenes é um microrganismo conhecido como causador de enfermidades transmitidas por alimentos desde a década de 80 quando foram descritos surtos de listeriose ocorridos na América do Norte e Europa. Dentre os alimentos de origem animal que veiculam esse patógeno, as aves e seus produtos têm merecido atenção especial por parte de alguns pesquisadores devido à associação feita entre aves e uma possível contaminação durante o processamento, acarretando a contaminação dos produtos finais. Os objetivos desta pesquisa foram avaliar a ocorrência de L. monocytogenes em diferentes etapas da produção de carcaça de frango em um matadouro frigorífico situado no Estado de São Paulo; avaliar a diversidade genética e sorológica das cepas de L. monocytogenes isoladas; correlacionar a diversidade genética das cepas isoladas com a distribuição nas diferentes etapas da linha de processamento, avaliar a persistência das cepas isoladas nesse matadouro e comparar os perfis genéticos de cepas de L. monocytogenes obtidos em nosso país com aqueles obtidos em um matadouro de aves com capacidade similar na Espanha. Foram realizadas 4 amostragens nos meses de julho e novembro de 2005, e março e maio de 2006 em um matadouro situado no Estado de São Paulo. Foi examinado um total de 178 amostras de carcaças de frango, pele de pescoço e de superfícies de contato e superfícies sem contato com o alimento. Os isolados foram submetidos à caracterização de sorogrupos por Reação de Polimerização em Cadeia (multiplex PCR) e à subtipagem por Eletroforese em Gel de Campo Pulsado (PFGE). Das 178 amostras analisadas, 28 (15,7%) foram positivas para L. Monocytogenes. Dentre as amostras positivas, 12 (42,9%) foram oriundas de superfícies sem contato com o produto, 9 (32,1%) de superfícies de contato com o produto e 7 (25%) da carcaça inteira de frango, não sendo detectada L. monocytogenes em pele de pescoço de frango. Dos 41 isolados de L. monocytogenes avaliados, 11 (26,8%) pertencem ao grupo 1 (1/2a ou 3a), 5 (12,2%) ao grupo 3 (1/2b, 3b ou 7) e vinte e cinco (61%) ao grupo 4 (4b, 4d ou 4e). A análise por PFGE forneceu 9 pulsotipos AscI, 6 ApaI e 14 perfis combinados, caracterizando quatro grupos clonais. Estes grupos clonais estavam amplamente disseminados ao longo das etapas de processamento. Quando comparado com dados de estudo prévio realizado no mesmo matadouro, verifica-se a existência de cepas persistentes de L. monocytogenes no ambiente. A comparação entre os pulsotipos de L. monocytogenes isolados no Brasil e aqueles da Espanha mostrou que não há correlação genética entre as cepas, sendo gerado dos grupos distintos. Isto é uma indicação de que o comércio de carcaças de frango entre os dois países não está ocasionando a disseminação de L. monocytogenes no país importador.
Listeria monocytogenes is a well-known microorganism as cause of foodborne illness since the occurrence of the first outbreak in 1980. Among foods of animal origin that serve as vehicle of this pathogen, poultry and their products are receiving special attention due to their association with outbreaks. The aims of this research were to evaluate the occurrence of L. monocytogenes in different steps of production of chicken carcasses in an abattoir in São Paulo state; to evaluate the genetic and serological diversity of L. monocytogenes isolates; to correlate the isolates with their distribution along processing line and to evaluate the persistence of strains of L. monocytogenes in the environment and evaluate the occurrence of L. monocytogenes in different steps of production of chicken carcasses in an abattoir in Brazil and at genetically correlate our data with the ones obtained in an equivalent abattoir in Spain. Samples were collected in July and November 2005, and March and May 2006. A total of 178 samples comprising chicken carcasses, neck skin, surfaces that enter in contact with the product and surfaces that not enter in contact with product were analysed. The isolates were submitted to characterization of serogroup through multiplex PCR and subtyping using PFGE. Among 178 samples, 28 (15.7%) were positive for L. monocytogenes: 12 (42.9%) were from the surfaces that do not enter in contact with the product, 9 (32.1%) from the surfaces that enter in contact with the product and 7 (25%) from the carcasses samples. No L. monocytogenes was detected among the neck skin samples. The 41 isolates were classified as group 1 [11 (26.8%)]; group 3 [5 (12.2%)] and group 4 [25 (61%)]. The molecular typing by PFGE resulted in 9 AscI and 6 ApaI profiles, and 14 composite profiles, resulting in four clonal groups. These clonal groups were spread throughout the processing line. When these results were compared with the results obtained in a previous study, persistent strains could be observed. The comparison between pulsotypes of L. monocytogenes isolated in Brazil and those isolated in Spain showed that there is no genetic correlation between strains. Two distinct clonal groups were obtained. This results indicates that chicken carcasses trade between Brazil and Spain is not disseminating L. monocytogenes in the importer country.

The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.

O Vírus da Imunodeficiência Humana (HIV) é o agente etiológico da Síndrome da Imunodeficiência Adquirida (AIDS). A AIDS é uma doença de distribuição mundial, e estima-se que existam atualmente pelo menos 36,9 milhões de pessoas infectadas com o vírus. Durante o seu ciclo replicativo, o HIV promove diversas alterações na fisiologia da célula hospedeira a fim de promover sua sobrevivência e potencializar a replicação. A rápida progressão da infecção pelo HIV-1 em humanos e em modelos animais está intimamente ligada à função da proteína acessória Nef. Dentre as diversas ações de Nef está a regulação negativa de proteínas importantes na resposta imunológica, como o receptor CD4. Sabe-se que esta ação resulta da indução da degradação de CD4 em lisossomos, mas os mecanismos moleculares envolvidos ainda são totalmente elucidados. Nef forma um complexo tripartite com a cauda citosólica de CD4 e a proteína adaptadora 2 (AP-2), em vesículas revestidas por clatrina nascentes, induzindo a internalização e degradação lisossomal de CD4. Pesquisas anteriores demonstraram que o direcionamento de CD4 aos lisossomos por Nef envolve a entrada do receptor na via dos corpos multivesiculares (MVBs), por um mecanismo atípico, pois, embora não necessite da ubiquitinação de carga, depende da ação de proteínas que compõem os ESCRTs (Endosomal Sorting Complexes Required for Transport) e da ação de Alix, uma proteína acessória da maquinaria ESCRT. Já foi reportado que Nef interage com subunidades dos complexos AP-1, AP-2, AP-3 e Nef não parece interagir com subunidades de AP-4 e AP-5. Entretanto, o papel da interação de Nef com AP-1 e AP-3 na regulação negativa de CD4 ainda não está totalmente elucidado. Ademais, AP-1, AP-2 e AP-3 são potencialmente heterogêneos devido à existência de isoformas múltiplas das subunidades codificadas por diferentes genes. Todavia, existem poucos estudos para demonstrar se as diferentes combinações de isoformas dos APs são formadas e se possuem propriedades funcionais distintas. O presente trabalho procurou identificar e caracterizar fatores celulares envolvidos na regulação do tráfego intracelular de proteínas no processo de regulação negativa de CD4 induzido por Nef. Mais especificamente, este estudo buscou caracterizar a participação do complexo AP-1 na modulação negativa de CD4 por Nef de HIV-1, através do estudo funcional das duas isoformas de ?-adaptina, subunidades de AP-1. Utilizando a técnica de Pull-down demonstramos que Nef é capaz de interagir com ?2. Além disso, nossos dados de Imunoblot indicaram que a proteína ?2-adaptina, e não ?1-adaptina, é necessária no processo de degradação lisossomal de CD4 por Nef e que esta participação é conservada para degradação de CD4 por Nef de diferentes cepas virais. Ademais, por citometria de fluxo, o silenciamento de ?2, e não de ?1, compromete a diminuição dos níveis de CD4 por Nef da membrana plasmática. A análise por imunofluorêsncia indireta também revelou que a diminuição dos níveis de ?2 impede a redistribuição de CD4 por Nef para regiões perinucleares, acarretando no acúmulo de CD4, retirados por Nef da membrana plasmática, em endossomos primários. A depleção de ?1A, outra subunidade de AP-1, acarretou na diminuição dos níveis celulares de ?2 e ?1, bem como, no comprometimento da eficiente degradação de CD4 por Nef. Além disso, foi possível observar que, ao perturbar a maquinaria ESCRT via super-expressão de HRS (uma subunidade do complexo ESCRT-0), ocorreu um acumulo de ?2 em endossomos dilatados contendo HRS-GFP, nos quais também detectou-se CD4 que foi internalizado por Nef. Em conjunto, os resultados indicam que ?2-adaptina é uma importante molécula para o direcionamento de CD4 por Nef para a via ESCRT/MVB, mostrando ser uma proteína relevante no sistema endo-lisossomal. Ademais, os resultados indicaram que as isoformas ?-adaptinas não só possuem funções distintas, mas também parecem compor complexos AP-1 com diferentes funções celulares, já que apenas a variante AP-1 contendo ?2, mas não ?1, participa da regulação negativa de CD4 por Nef. Estes estudos contribuem para o melhor entendimento dos mecanismos moleculares envolvidos na atividade de Nef, que poderão também ajudar na melhor compreensão da patogênese do HIV e da síndrome relacionada. Em adição, este trabalho contribui para o entendimento de processos fundamentais da regulação do tráfego de proteínas transmembrana no sistema endo-lisossomal.
The Human Immunodeficiency Virus (HIV) is the etiologic agent of Acquired Immunodeficiency Syndrome (AIDS). AIDS is a disease which has a global distribution, and it is estimated that there are currently at least 36.9 million people infected with the virus. During the replication cycle, HIV promotes several changes in the physiology of the host cell to promote their survival and enhance replication. The fast progression of HIV-1 in humans and animal models is closely linked to the function of an accessory protein Nef. Among several actions of Nef, one is the most important is the down-regulation of proteins from the immune response, such as the CD4 receptor. It is known that this action causes CD4 degradation in lysosome, but the molecular mechanisms are still incompletely understood. Nef forms a tripartite complex with the cytosolic tail of the CD4 and adapter protein 2 (AP-2) in clathrin-coated vesicles, inducing CD4 internalization and lysosome degradation. Previous research has demonstrated that CD4 target to lysosomes by Nef involves targeting of this receptor to multivesicular bodies (MVBs) pathway by an atypical mechanism because, although not need charging ubiquitination, depends on the proteins from ESCRTs (Endosomal Sorting Complexes Required for Transport) machinery and the action of Alix, an accessory protein ESCRT machinery. It has been reported that Nef interacts with subunits of AP- 1, AP-2, AP-3 complexes and Nef does not appear to interact with AP-4 and AP-5 subunits. However, the role of Nef interaction with AP-1 or AP-3 in CD4 down-regulation is poorly understood. Furthermore, AP-1, AP-2 and AP-3 are potentially heterogeneous due to the existence of multiple subunits isoforms encoded by different genes. However, there are few studies to demonstrate if the different combinations of APs isoforms are form and if they have distinct functional properties. This study aim to identify and characterize cellular factors involved on CD4 down-modulation induced by Nef from HIV-1. More specifically, this study aimed to characterize the involvement of AP-1 complex in the down-regulation of CD4 by Nef HIV-1 through the functional study of the two isoforms of ?-adaptins, AP-1 subunits. By pull-down technique, we showed that Nef is able to interact with ?2. In addition, our data from immunoblots indicated that ?2- adaptin, not ?1-adaptin, is required in Nef-mediated targeting of CD4 to lysosomes and the ?2 participation in this process is conserved by Nef from different viral strains. Furthermore, by flow cytometry assay, ?2 depletion, but not ?1 depletion, compromises the reduction of surface CD4 levels induced by Nef. Immunofluorescence microscopy analysis also revealed that ?2 depletion impairs the redistribution of CD4 by Nef to juxtanuclear region, resulting in CD4 accumulation in primary endosomes. Knockdown of ?1A, another subunit of AP-1, resulted in decreased cellular levels of ?1 and ?2 and, compromising the efficient CD4 degradation by Nef. Moreover, upon artificially stabilizing ESCRT-I in early endosomes, via overexpression of HRS, internalized CD4 accumulates in enlarged HRS-GFP positive endosomes, where co-localize with ?2. Together, the results indicate that ?2-adaptin is a molecule that is essential for CD4 targeting by Nef to ESCRT/MVB pathway, being an important protein in the endo-lysosomal system. Furthermore, the results indicate that ?-adaptins isoforms not only have different functions, but also seem to compose AP-1 complex with distinct cell functions, and only the AP-1 variant comprising ?2, but not ?1, acts in the CD4 down-regulation induced by Nef. These studies contribute to a better understanding on the molecular mechanisms involved in Nef activities, which may also help to improve the understanding of the HIV pathogenesis and the related syndrome. In addition, this work contributes with the understanding of primordial process regulation on intracellular trafficking of transmembrane proteins.

A new crystal plasticity scheme for explicit time integration codes is developed based on a forward Euler algorithm in the first part of this paper. The new numerical model is incorporated in the UMAT subroutine for implementing rate dependent crystal plasticity model in LS-DYNA/Explicit. The material is modeled as a Face centered cubic (FCC) polycrystalline aggregate, and a finite element analysis based on rate-dependent crystal plasticity is developed to simulate large strain behaviour. Accordingly, an element or a number of elements of the finite element mesh is considered to represent a single crystal within the polycrystal aggregate and the constitutive response at a material point is given by the single crystal constitutive model. The second part of this thesis presents two applications of the crystal plasticity scheme used in conjunction with numerical modeling of three-dimensional (3D) real microstructures. First, finite element meshes containing both particle and texture data are created with solid elements. Particle size, location and orientation are represented by 3D ellipsoids and the elements within these ellipsoids are given rigid properties. Simulations of in-plane plane strain with different combinations of texture and particle location are performed. The effect on texture development, strain magnitudes, and strain localizations is investigated. Second, the three dimensional (3D) polycrystalline microstructure of the aluminum alloy AA5754 is modeled and subjected to three different strain rates for each strain path. The effect of strain paths, strain rates and thermal softening on the formation of localized deformation is investigated. Simulations show that strain path is the most dominant factor in localized deformation and texture evolution.

博士
國立臺灣藝術大學
創意產業設計研究所
108
With the wave of digitalization spreading all over the world, globalization and localization have continually been absorbing, integrating, transforming and regenerating, and global geography has emerged, and the globalization localized has emerged. Being one of the important forms in the creative industry, the animated film has a meaning and value which can’t be ignored towards the production and regeneration of the local culture, its development can’t only increase the value of the economy of the creative industry, but it has also multiple functions in promoting communication of culture and the expression and output of value,trust building in local culture and spirit shaping of local culture. The present research is developed around the localization of animated films across the strait, combining the study of art, communication and cognition, etc., then to construct a expression model of animated films’ localization across the strait. The present research will be processed in three phases: firstly we discuss how the authors of animated films across the strait create animated films through the conception of localization, which are finishing the coding process, writing the questionnaire, pre-researching of the questionnaire, profound interview; then through the interviews of 19 experts, it continues to explore that how the authors of animated films across the strait create animated films through the concept of localization, then to summarize the experiences expressed by localization films, to build the sketch of the expression model of localization of animate films across the strait, and then to correct and refine it , in the mean time through 426 questionnaires to verify this model and to know more deeply the knowledge of the interviewees of different background on the animated films across the strait, to understand the level of their conception and the pleasure of the normal public on animated films; at the end thorough the previous research to make the further corrections and refinement, and to make it perfect the expression model of the localized animated films. And the result expresses that the constructed expression model of localized animated films has a good effect to explore relative researches.Through personal experiences of feeling and perception , artists conceive and reflect the localized culture and then extract the codification. After the transfer, the changes, they create the animated films, at the end through 21 elements of technology, of semantic, of effect, and realize the transmission of aesthetic experiences; while the cognition of the public towards the animated films are the experiences of emotion through the seeing and the knowledge of external cognition.During this process, the empathy is created constantly with the personal experiences, and the resonance of aesthetic experiences is finally realized in the end. The encoding of the artists and the decoding of the public are a process of circulation and mixture. Audiences with different sexes, ages, professional experiences and degrees have different knowledge about the conception of animated films across the strait and the same rule is working also for audiences in different areas across the strait. Among all these elements that influence public conceptions, music, images and language are the three most important elements, in which language has the the highest influence. The audiences across the strait all think that localized music let them perceive the local culture. It is worth noting that is that Taiwanese audiences are more inclined to dialect and more concrete images while mainland audiences are more inclined to Mandarin and abstract images. After the research, it is concluded that when the expression of localization of animated films is created, we can proceed with the following methods: deriving from everyday experiences, starting from the concept of argument, forming in the construction of elements, and realizing in the the public’s recognition, encouraging communication of culture. The present research proposes that the expression of localization of animated films should be: decoding culture, opening the culture creation, adding the culture value, strengthening the culture trust, forming the culture spirit.