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Three-Dimensional Finite Element Analysis of Three-Roll Planetary Mill ProcessesChang, Ming-Hu 26 July 2001 (has links)
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.
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Exploring the Role of Surface-Adsorbing Media in Cutting of Corrosion-Resistant MetalsJason Marion Davis (9027656) 25 June 2020 (has links)
<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>
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Non-Destructive Evaluation and Mathematical Modeling of Beef Loins Subjected to High Hydrodynamic Pressure TreatmentLakshmikanth, Anand 15 September 2009 (has links)
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.
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[pt] ANÁLISE NUMÉRICA DE MEMBRANAS E BIOMEMBRANAS VISCOELÁSTICAS SUBMETIDAS À EXPANSÃO AXISSIMÉTRICA / [es] ANÁLISIS NUMÉRICA DE MEMBRANAS Y BIOMEMBRANAS VISCOELÁSTICAS SUBMETIDAS A EXPANSIÓN ASIMÉTRICA / [en] NUMERICAL ANALYSIS OF VISCOELASTIC MEMBRANES AND BIOMEMBRANES SUBJECTED TO AXIALLY-SYMMETRIC EXPANSIONCRISTINA DE ABREU ALVIM 26 May 2000 (has links)
[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.
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Sur la compréhension des phénomènes de couplage fluide-structure dans les propulseurs de fuséeDevesvre, Julie 13 December 2011 (has links)
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.
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[en] NUMERICAL AND EXPERIMENTAL ENDENTATION ANALYSIS OF PLANE HYPERELASTIC MEMBRANES / [pt] ANÁLISE NUMÉRICA E EXPERIMENTAL DE ENDENTAÇÃO EM MEMBRANAS HIPERELÁSTICAS PLANASGUILHERME RODRIGUES SAMPAIO DE PAULA 12 January 2015 (has links)
[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.
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Fast simulation of (nearly) incompressible nonlinear elastic material at large strain via adaptive mixed FEMBalg, Martina, Meyer, Arnd 19 October 2012 (has links) (PDF)
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.
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[en] NON-LINEAR BEHAVIOR AND INSTABILITY OF HYPERELASTIC MEMBRANES AND SHELLS / [pt] COMPORTAMENTO NÃO-LINEAR E INSTABILIDADE DE MEMBRANAS E CASCAS HIPERELÁSTICASSTEFANE RODRIGUES XAVIER LOPES 21 January 2004 (has links)
[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.
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Numerical Investigation for Slope Stability of Expansive Soils and Large Strain Consolidation of Soft SoilsQi, Shunchao January 2017 (has links)
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.
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[pt] TEORIA E IMPLEMENTAÇÃO DE MODELOS CONSTITUTIVOS PARA GEOMATERIAIS / [en] THEORY AND IMPLEMENTATION OF CONSTITUTIVE MODELS FOR GEOMATERIALSALESSANDRO CIRONE 07 December 2020 (has links)
[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.
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