The purpose of this study is to investigate the plastic deformation behavior of a round bar at the roll-gap during the rolling process of a three-roll planetary mill. The analysis is carried out with the aid of a finite element program MARC adopting the large deformation - large strain theory and the updated lagrangian formulation (ULF). A mesh rezoning procedure is also adopted to improve the uncontrollable running error of elements turning inside out. The mesh system of the whole bar billet is created by using three-dimensional brick elements, and the three-dimensional elastic-plastic finite element model in MARC is chosen to perform the simulations of three-roll planetary rolling processes. The simulation examples consist of three groups. Firstly, three different friction coefficients are adopted to investigate the rolling process. Secondly, totally five different offset angles are used during the simulation of the rolling process. Finally, five different profiles of the roller are used to study the simulation of the rolling process. The successfully obtained numerical results, including equivalent von-Mises stress and plastic strain distributions, rolling force, rolling moment, billet speeds at the entrance and exit planes of the roll-gap are useful in designing the pass schedules of the three-roll planetary rolling processes.

<p>Tantalum, niobium, stainless steels, and nickel are corrosion-resistant metals that have become critical in many industrial sectors. Due to the demanding environments and temperatures in which they operate, few materials can serve as substitutes. The advantages of these materials are offset by the difficulties in their machining. Belonging to a group of metals and alloys often referred to as ‘gummy’, their poor machinability or gumminess is manifest as thick chip formation, large cutting forces, and poor finish on cut surface. Hence, machining costs can be prohibitive, and applications limited. The gumminess has been attributed broadly to their high strain-hardening capacity.</p> <p>To examine why these metals are difficult to machine, we used direct <i>in situ</i> observations of the cutting process with a high-speed imaging system, complemented by force measurements. The observations showed that chip formation occurred by repeated large-amplitude folding of the material – sinuous flow – with vortex-like components and extensive redundant deformation. The folding was particularly severe in Ta and Nb. Although Ta and Nb displayed a higher rate of fold nucleation than the Ni and stainless steel, the flow dynamics underlying chip formation across the metals was the same – sinuous flow nucleated by a plastic (buckling-type) flow instability on the workpiece surface just ahead of the advancing tool. The large strains and energy dissipation associated with sinuous flow is the reason for the poor machinability of these metals. </p> <p>Prior work with Cu and Al has shown that sinuous flow can be disrupted and replaced by an energetically more favorable (segmented) flow mode, characterized by quasi-periodic fracture, when suitable chemical media are applied to the initial workpiece surface – a mechanochemical effect. The segmented flow is beneficial for machining processes since it involves much smaller forces and plastic strains. It has been hypothesized that the chemical media influence the flow through their adsorption onto the workpiece surface, thereby altering the surface energy and/or surface stress, and effecting a local embrittlement (ductile-to-brittle transition). </p> <p>We demonstrate similar media (mechanochemical) effects and segmented flow development in cutting of the corrosion-resistant metals, with significant benefits for their machining. These benefits include > 35 percent reduction in the cutting force/energy, and an order of magnitude improvement in cut surface quality (finish, tears and residual strain). Importantly, the experiments with the corrosion-resistant metals provide strong evidence that it is indeed adsorption – not corrosion, as in case of hydrogen embrittlement – that underpins the mechanochemical effect. The experiments used chemical agents well-known for their strong adsorption to metal surfaces, namely green corrosion inhibitors (e.g., plant extracts, propolis) and other natural organic molecules (e.g., dyes, antibacterial drugs, cow’s milk). Lastly, the suitability and application of the mechanochemical effect at industrial cutting speeds is explored in turning experiments with these corrosion-resistant metals. Collectively, our observations, measurements, and analysis show that the gumminess of metals in cutting is due to sinuous flow; the gumminess can be eliminated by use of chemical media; and adsorption is the key to engendering the mechanochemical effect. Implications of the results for industrial processes ranging from machining to particle comminution, and for sustainable manufacturing are discussed.</p> <br>

High hydrodynamic pressure (HDP) treatment is a novel non-thermal technology that improves tenderness in foods by subjecting foods to underwater shock waves. In this study non-destructive and destructive testing methods, along with two mathematical models were explored to predict biomechanical behavior of beef loins subjected to HDP-treament. The first study involved utilizing ultrasound and imaging techniques to predict textural changes in beef loins subjected to HDP-treatment using Warner-Braztler shear force (WBS) scores and texture profile analysis (TPA) features for correlation. Ultrasound velocity correlated very poorly with the WBS scores and TPA features, whereas the imaging features correlated better with higher r-values. The effect of HDP-treatment variables on WBS and TPA features indicated that amount of charge had no significant effects when compared to location of sample and container size during treatment. Two mathematical models were used to simulate deformational behavior in beef loins. The first study used a rheological based modeling of protein gel as a preliminary study. Results from the first modeling study indicated no viscous interactions in the model and complete deformation failure at pressures exceeding 50 kPa, which was contrary to the real-life process conditions which use pressures in the order of MPa. The second modeling study used a finite element method approach to model elastic behavior. Shock wave was modeled as a non-linear and linear propagating wave. The non-linear model indicated no deformation response, whereas the linear model indicated realistic deformation response assuming transverse isotropy of the model beef loin. The last study correlated small- and large-strain measurements using stress relaxation and elastic coefficients of the stiffness matrix as small-strain measures and results of the study indicated very high correlation between elastic coefficients c11, c22, and c44 with TPA cohesiveness (r > 0.9), and springiness (r > 0.85). Overall results of this study indicated a need for further research in estimating mechanical properties of beef loins in order to understand the dynamics of HDP-treatment process better. / Ph. D.

[pt] Expansão de tecido é um processo fisiológico, definido como a capacidade de uma membrana biológica aumentar em área superficial devido a uma deformação imposta. É um processo que pode ser induzido artificialmente, através de técnicas ligadas à cirurgia plástica reparadora que têm como objetivo expandir a pele para a sua utilização em áreas danificadas (queimaduras, grandes cicatrizese tatuagens), reconstrução mamária (após mastectomia), entre outras. Para expandir-se a pele artificialmente, implanta-se o expansor sob a camada da pele do paciente, numa região adjacente ao local onde se deseja efetuar a reconstrução. Em seguida, através de um tubo externo, introduz-se um fluido que irá provocar o aumento do volume inicial e, consequentemente, o aumento da área superficial da pele sobre o expansor. Este é um processo lento, feito em etapas, até que se obtenha a área superficial de pele desejada para cada fim. O objetivo desta dissertação é modelar matematicamente o fenômeno da expansão axissimétrica de tecido biológico, através da teoria da viscoelasticidade para grandes deformações. / [en] Tissue expansion is a well-known plastic surgery technique, based on the ability of biologic membranes to increase its surface area when a deformation is imposed. It is used to repair a wound area (scars, burns), to remove tattoos, in breast reconstruction, etc. This involves inserting a silicon-rubber prosthesis (expander) in its collapsed state under the subcutaneous tissue of the patient, closing the incision, and then inflating the expander slowly with a saline fluid through a one way valve. The skin expands in the form of a dome in unison with the balloon underneath it. The purpose of this work is modelling mathematically axially symmetric tissue expansion of biologic tissue, using Theory of Viscoelasticity for Finite Deformations. / [es] La expansión de tejidos es un proceso fisiológico, definido como la capacidad de una membrana biológica de aumentar su área superficial como consequencia de una deformación impuesta. Este proceso, que puede ser inducido artificialmente a través de técnicas de cirurgía plástica reparadora, tiene como objetivo expandir la piel para utilizarla en áreas dañadas (ejemplo: quemaduras o grandes cicatrices), reconstrucción mamaria (después de mastectomía, etc.) Para expandir la piel artificialmente, se implanta el expansor sobre la piel del paciente, en una región adyacente al local donde se desea efectuar la reconstrucción. Enseguida se introduce, a través de un tubo externo, un fluído que provocará el aumento del volumen inicial y, consequentemente, el aumento del área superficial de la piel sobre el expansor. Éste es un proceso lento, que se realiza por etapas hasta obtener la expansión del área superficial deseada, según los fines. El objetivo de esta disertación es modelar matemáticamente el fenómeno de la expansión asimétrica de tejido biológico, a través de la teoría de la viscoelasticidad para grandes deformaciones.

Dans les propulseurs de fusée, des instabilités aéroacoustiques et des interactions de type fluide-structure sont à l'origine de fortes oscillations de poussées pouvant déranger la poussée du moteur mais également causer des dommages non négligeables. On trouve dans les moteurs de fusée des protections thermiques de face (PTF) coincées entre les pains de propergol. Leurs déplacements se trouvent être la principale cause des interactions fluide structure (IFS) présentes dans les booster. Dans ce contexte, nous avons développé une approche numérique visant à simuler les problèmes d'IFS. Notre méthode se base sur le couplage de deux codes dissociés : l'écoulement est simulé avec CARBUR tandis que la dynamique des structures déformables est traitée par MARCUS. Une loi de comportement hyperélastique a été implémentée dans CARBUR afin de simuler le mouvement des PTF. Une campagne expérimentale a été menée dans notre laboratoire sur le tube à chocs T80 et en guide de validation du couplage des codes, les résultats numériques et expérimentaux ont été confrontés. / In a solid rocket motor, high pressure oscillations induced by aeroacoustic instabilities and fluid structure interaction (FSI) may lead to disturb rocket thrust and cause damages. In the rocket motors, flexible inhibitors made of insulating material are initially bonded to the propellant, and FSI is mainly induced by their displacement. In this context, a numérical approach to simulate FSI problems has been developped. Our method is based on the coupling of two dissociated codes : fluid flow is computed with CARBUR, while the dynamics of deformable structures is simulated by MARCUS. A hyperelastic behaviour law has been implemented in MARCUS in order to simulate the movement of flexible inhibitors. An experimental approach has been leaded in the shock waves tubes (T80) in our laboratory and as a validation of FSI coupling codes, numerical and experimental results have been compared.

[pt] O estudo do comportamento de membranas quando expostas a pressões e tensões de diverssos tipos, assim como de suas propriedades mecânicas nos últimos anos vem recebendo uma notável atenção em razão da variada aplicabilidade das membranas nas mais diversas áreas da engenharia, incluindo atuadores, robótica, sensores, aeroespacial, bioengenharia e estruturas infláveis para engenharia civil. Neste trabalho será apresentado um estudo numérico e experimental de uma membrana sujeita a uma endentação e perfuração transversalmente ao seu plano indeformado, considerando-se a presença do atrito na interface membrana-endentor, fato que torna esse estudo pioneiro nesta análise. Os estudos numéricos foram feitos no software Abaqus CAE. Os ensaios experimentais têm por objetivo comprovar os resultados numéricos e assim validá-los. Foram desenvolvidos aparatos experimentais dedicados aos ensaios pretendidos devido à ausência de equipamentos no mercado que pudessem reproduzir tais ensaios. / [en] The study of membranes behavior when subjected to pressures and tensions from all kinds, as well as their mechanical properties, is receiving a noticeable attention over the last years due to various applications of membranes on various engineering fields, including, actuators, robotics, sensors, airspace, bioengineering and inflatable structures for civil engineering. On this job will be presented a numerical and experimental study of a membrane subjected to an endentation and penetration transversally to the membrane’s undeformed plane, considering friction on the interface of the membrane and endentor, which makes this study a pioneer on this kind of analysis. The numerical studies were performed on Abaqus CAE finite element software. The experimental tests are intended to validate the numerical results. Experimental apparatus were developed especially to perform the tests done in this job.

The main focus of this work lies in the simulation of the deformation of mechanical components which consist of nonlinear elastic, incompressible material and that are subject to large deformations. Starting from a nonlinear formulation one can derive a discrete problem by using linearisation techniques and an adaptive mixed finite element method. This turns out to be a saddle point problem that can be solved via a Bramble-Pasciak conjugate gradient method. With some modifications the simulation can be improved.

[pt] Esta tese tem como objetivo analisar o comportamento estático não-linear e possíveis instabilidades de membranas e cascas hiperelásticas. Uma análise experimental detalhada de membranas e cascas com diferentes geometrias e submetidas à tração axial e pressão interna uniforme é realizada. Um aparato foi desenvolvido para possibilitar a tração da estrutura enquanto a mesma era preenchida por ar. As cascas e membranas utilizadas na análise experimental são compostas por elastômero isotrópico, homogêneo e hiperelástico, o qual é modelado como um material Neo- Hookeano incompressível, descrito por uma única constante elástica, ou por material do tipo Mooney-Rivlin ou Ogden, descritos por duas constantes elásticas. Estas constantes são obtidas pela comparação de resultados experimentais e numéricos para a estrutura sob tração axial uniforme. A estrutura foi discretizada utilizando-se elementos finitos de casca ou membrana mais apropriados e as equações de equilíbrio não-lineares resultantes resolvidas usando-se o programa de elementos finitos ABAQUS. Quando a estrutura tracionada é preenchida com ar observa-se que a pressão inicialmente cresce juntamente com o volume interno até um certo valor crítico. Após atingir este valor crítico um bulbo de deformação é formado subitamente num local ao longo do comprimento da estrutura e a pressão interna decresce subitamente, entretanto o volume interno da estrutura continua a crescer. Os resultados experimentais aproximam-se de maneira satisfatória aos resultados numéricos. Uma análise paramétrica detalhada é desenvolvida para estudar a influencia da tração inicial bem como dos parâmetros geométricos no comportamento não-linear e na capacidade de carga da estrutura. A influencia de diferentes tipos de imperfeições locais também é detalhadamente analisada. / [en] This thesis investigates the large deformations of hyperelastic membranes and shells. The static nonlinear behavior and possible instabilities of the membrane are both analyzed. A detailed experimental analysis was carried out involving cylindrical membranes and shells with different geometries and initial axial forces and the influence of the axial force and the internal pressure were investigated. An apparatus was developed to support vertically the extended structure while it is filled with air. The membranes and shells used in the experiments are composed of an isotropic, homogeneous and hyperelastic rubber, which is modeled as a Neo-Hookean incompressible material, described by a single elastic constant, or a Mooney-Rivlin or Ogden material, described by two elastic constants. Theses constants were obtained by comparing the experimental and numerical solutions for the structure under traction. The structure was discretized using appropriate membrane or shell finite elements and the resulting nonlinear equilibrium equations solved using the FE software ABAQUS. When the extended structure was filled with air, it was observed that the pressure increased initially as the volume increased until a certain critical value was reached, after which a bubble was suddenly formed along the structure and the internal pressure decreased markedly with increasing volume. The experimental results are, as shown in the thesis, in satisfactory agreement with the theory. A detailed parametric analysis was also carried out to study the influence of the initial traction and geometric parameters on the non-linear behavior and load carrying capacity of the structure. The influence of different types of local imperfections was also studied in detail.

Several geotechnical processes can only be reliably interpreted by taking account of the soil-atmosphere interactions. This thesis investigates two geotechnical problems involving soil-atmosphere interactions that drive water flow through the soil skeleton in two opposite directions; Problem 1: slope failure in expansive soils induced by water infiltration, Problem 2: large strain consolidation of soft soils induced by water evaporation. Both problems are of practical interest for safe and economical design of various geotechnical infrastructures. Two major geotechnical activities in the world; namely, the construction of water transfer canal in expansive soil area in China and the deposition of oil sands and hard rock tailings in Canada can be cited as classic examples of Problems 1 and 2, respectively. In such problems, substantial zones of the domain may switch between an unsaturated and saturated condition. Therefore, rational analysis requires simultaneous modelling of both unsaturated and saturated soil behaviour. The first goal of this thesis is to investigate the influence of swelling (the most characteristic behaviour of expansive soils) on slope stability using numerical methods. Swelling of expansive soils contributes to slope instability during rainfall because of two key reasons (i) soil swelling affects the flow process that actually induces swelling, (i.e. a typical coupling phenomenon), and (ii) swelling-induced stress redistribution and displacement development. In this thesis, the first effect is studied by a coupled (mechanical-hydraulic) numerical analysis of the response of a slope to rainfall using commercial software (GeoSlope). The second effect, the swelling-induced stress redistribution and displacement development after wetting, is tracked using a newly developed numerical program. In the program strain softening behaviour is introduced into the elasto-plastic Mohr-Coulomb Model for modelling unsaturated soil. A novel stress (net stress and suction)-dependent model for moduli of elasticity, combined with the predictive model for shear strength based on Soil Water Retention Behaviour are incorporated into the numerical program to achieve a smooth transition between saturated and unsaturated states. The results show that soil swelling can decrease the factor of safety by accelerating the wetting front depth due to hydro-mechanical coupling, while changes of sliding mass geometry has a negligible influence. The change of stress regime associated with soil swelling is significant to induce plastic strain softening (swelling-induced softening) and contribute to the slope failures. The second goal of thesis is to develop a novel computer program for simulation of large strain consolidation of soft soil under both self-weight and evaporation conditions. This program is both theoretically sound and practically applicable. Several basic/advanced constitutive models for unsaturated soils, including State Surface Model (SSM), Barcelona Basic model (BBM), Glasgow Coupled model (GCM) and bounding surface water retention model, are innovatively implemented into a piece-wise linear framework solved using finite difference technique. The developed program is referred to as UNSATCON-(ML), which has been tested using (a) existing analytical/numerical solutions and (b) various laboratory and field studies for single-layer and multiple-layer deposition of hard rock and oil sands tailings. Features of UNSATCON-(ML) that are improvements over existing models typically used to analyze consolidation-desiccation in soft soils include: (i) coupling of soil large deformation with true unsaturated water flow; (ii) correct reproduction of the shrinkage behaviour of soil under evaporation-induced desiccation; (iii) smooth transition between saturated and unsaturated states despite that some selected models are established using two independent stress variables, (iv) ensuring strictly mass conservation of water, and (v) simulation of irrecoverable volume change and hydraulic hysteresis to properly analyze multilayer tailings deposition. A number of hypothetical field case analyses are carried out using UNSATCON-ML, illustrating its applicability to industry.

[pt] Desenvolveu-se estudo teórico e numérico para simular o comportamento tensão-deformação de solos e rochas. Procurou-se estabelecer modelagem constitutiva apta a representar as peculiaridades inerentes ao comportamento destes materiais sob grandes deformações e degradação da estrutura. Dentro do contexto geotécnico brasileiro, o objetivo da pesquisa foi, também, investigar uma nova abordagem constitutiva para modelar o comportamento de solos moles, solos residuais e rochas sedimentares. O trabalho está dividido nos seguintes tópicos: revisão bibliográfica; estudo de medidas de deformações e taxas objetivas de tensões; definição e desenvolvimento dos modelos constitutivos a serem testados; definição dos algoritmos de retorno para integração das equações constitutivas; implementação em elementos finitos; simulação do comportamento observado em ensaios de laboratório. Os resultados da pesquisa indicam que o comportamento viscoso da argila mole do Sarapuí pode ser reproduzido corretamente adotando-se modelo constitutivo viscoplástico. A abordagem de solo estruturado está condizente com o comportamento do arenito de Vila Velha. Por fim, para modelar o comportamento de solos residuais dentro de um novo quadro constitutivo, foi proposta uma separação das deformações irreversíveis. / [en] A theoretical and numerical study was developed to simulate the stressstrain behavior of soils and rocks, formulating constitutive models able to catch the peculiarities inherent to the behavior of these materials under large strains and structure degradation. Within the Brazilian geotechnical context, the objective of the research was also to investigate constitutive approaches to model the behavior of soft soils, residual soils and sedimentary rocks. The work is divided into the following topics: literature review; study of strain measurements and objective stress rates; definition and development of the constitutive models to be tested; definition of the return mapping algorithms for integrating the constitutive equations; finite element implementation; and simulation of the behavior observed in laboratory tests. Results indicate that the viscous behavior of the Sarapuí soft clay can be correctly reproduced by adopting a viscoplastic constitutive model. The structured soil approach appears to be consistent with the behavior of Vila Velha sandstone. Finally, a decomposition of irreversible strains was proposed to model the behavior of residual soils within a novel constitutive framework.