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Finite element and population balance models for food-freezing processesMiller, Mark J. January 1900 (has links)
Master of Science / Department of Mechanical and Nuclear Engineering / Xiao J. Xin / Energy consumption due to dairy production constitutes 10% of all energy usage in the U.S. Food Industry. Improving energy efficiency in food refrigeration and freezing plays an important role in meeting the energy challenges of today. Freezing and hardening are important but energy-intensive steps in ice cream manufacturing. This thesis presents a series of models to address these issues. The first step taken to model energy consumption was to create a temperature-dependent ice cream material using empirical properties available in the literature. The homogeneous ice cream material is validated using finite element analysis (FEA) and previously published experimental findings. The validated model is then used to study the efficiency of various package configurations in the ice cream hardening process. The next step taken is to consider product quality by modeling the ice crystal size distribution (CSD) throughout the hardening process. This is achieved through the use of population balance equations (PBE). Crystal size and corresponding hardened ice cream coarseness can be predicted through the PBE model presented in this thesis. The crystallization results are validated through previous experimental study. After the hardening studies are presented, the topic of continuous freezing is discussed. The actual ice cream continuous freezing process is inherently complex, and therefore simplifying assumptions are utilized in this work. Simulation is achieved through combined computational fluid dynamics (CFD) and PBE modeling of a sucrose solution. By assuming constant fluid viscosity, a two-dimensional cross section is able to be employed by the model. The results from this thesis provide a practical advancement of previous ice cream simulations and lay the groundwork for future studies.
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[en] MODELING OF THERMOMECHANICAL BEHAVIOR OF SHAPE MEMORY ALLOYS / [pt] MODELAGEM DO COMPORTAMENTO TERMOMECÂNICO DAS LIGAS COM MEMÓRIA DE FORMAALBERTO PAIVA 28 May 2004 (has links)
[pt] O estudo de materiais inteligentes tem instigado várias
aplicações nas mais diversas áreas do conhecimento (da
área médica à industria aeroespacial). Os materiais mais
utilizados em estruturas inteligentes são as ligas com
memória de forma, as cerâmicas piezoelétricas, os
materiais magneto-estrictivos e os fluidos eletro-
reológicos. Nas últimas décadas, as ligas com memória de
forma vêm recebendo atenção especial, sendo utilizadas
principalmente como sensores ou atuadores. Existe uma
gama de fenômenos associados a estas ligas que podem ser
explorados. Visando uma análise mais precisa do
comportamento destes materiais, tem se tornado cada vez
maior o interesse no desenvolvimento de modelos
matemáticos capazes de descrevê-los de maneira adequada,
permitindo explorar todo o seu potencial. O objetivo
deste trabalho é propor um modelo constitutivo
unidimensional que considera quatro variantes de
microconstituintes (austenita, martensita induzida por
temperatura, martensita induzida por tensão trativa e
martensita induzida por tensão compressiva) e diferentes
propriedades para cada fase. O efeito das deformações
induzidas por temperatura é incluído na formulação. O
modelo contempla ainda o efeito das deformações plásticas
e o acoplamento entre os fenômenos de plasticidade e
transformação de fase. Além disso, são introduzidas
modificações na formulação que permitem o alargamento
do laço de histerese da curva tensão-deformação,
fornecendo resultados mais coerentes com dados
experimentais. Por fim, incorpora-se a assimetria no
comportamento tração-compressão. A validação do modelo é
obtida comparando os resultados numéricos obtidos através
do modelo com resultados experimentais encontrados na
literatura para ensaios de tração a diferentes
temperaturas e para a assimetria no comportamento tração-
compressão. / [en] The study of intelligent materials has instigated many
applications within the various knowledge areas (from
medical field to aerospace industry). The most
used materials in intelligent structures are the shape
memory alloys (SMA), the piezoelectric ceramics, the
magnetostrictive materials and the electrorheological
fluids. In the last decades, SMAs have received special
attention, being mainly used as sensors or actuators. There
is a number of phenomena related to these alloys that can
be explored. Aiming a more precise analysis of SMA
behavior, the interest on the development of mathematical
models capable of describing these phenomena properly has
grown, allowing to explore all their potential. The aim of
this work is to propose a unidimensional constitutive model
which considers four microconstituent variants (austenite,
martensite induced by temperature, martensite induced by
tensile loading and martensite induced by compressive
loading) and different material properties for each phase.
The effect of thermal strains is included in the
formulation. The model considers the effect of plastic
strains and the plastic-phase transformation coupling.
Besides, some changes are introduced in the formulation in
order to enlarge the stress-strain hysteresis loop,
resulting in better agreements with experimental data.
Eventually, the tensioncompression asymmetry is
incorporated. The model validation is obtained through
the comparison between the numerical results given by the
model and experimental results found in the literature for
tensile tests at different temperatures and for tension-
compression asymmetry.
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Novel theoretical and experimental frameworks for multiscale quantification of arterial mechanicsWang, Ruoya 14 January 2013 (has links)
The mechanical behavior of the arterial wall is determined by the composition and structure of its internal constituents as well as the applied traction-forces, such as pressure and axial stretch. The purpose of this work is to develop new theoretical frameworks and experimental methodologies to further the understanding of arterial mechanics and role of the various intrinsic and extrinsic mechanically motivating factors. Specifically, residual deformation, matrix organization, and perivascular support are investigated in the context of their effects on the overall and local mechanical behavior of the artery. We propose new kinematic frameworks to determine the displacement field due to residual deformations previously unknown, which include longitudinal and shearing residual deformations. This allows for improved predictions of the local, intramural stresses of the artery. We found distinct microstructural differences between the femoral and carotid arteries from non-human primates. These arteries are functionally and mechanically different, but are geometrically and compositionally similar, thereby suggesting differences in their microstructural alignments, particularly of their collagen fibers. Finally, we quantified the mechanical constraint of perivascular support on the coronary artery by mechanically testing the artery in-situ before and after surgical exposure.
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Constitutive Modeling and Life Prediction in Ni-Base SuperalloysShenoy, Mahesh M. 01 June 2006 (has links)
Microstructural features at different scales affect the constitutive stress-strain response and the fatigue crack initiation life in Ni-base superalloys. While numerous efforts have been made in the past to experimentally characterize the effects of these features on the stress-strain response and/or the crack initiation life, there is a significant variability in the data with sometimes contradictory conclusions, in addition to the substantial costs involved in experimental testing. Computational techniques can be useful tools to better understand these effects since they are relatively inexpensive and are not restricted by the limitations in processing techniques.
The effect of microstructure on the stress-strain response and the variability in fatigue life were analyzed using two Ni-base superalloys; DS GTD111 which is a directionally solidified Ni-base superalloy, and IN100 which is a polycrystalline Ni-base superalloy. Physically-based constitutive models were formulated and implemented as user material subroutines in ABAQUS using the single crystal plasticity framework which can predict the material stress-strain response with the microstructure-dependence embedded into them. The model parameters were calibrated using experimental cyclic stress-strain histories. A computational exercise was employed to quantify the influence of idealized microstructural variables on the fatigue crack initiation life. Understanding was sought regarding the most significant microstructure features using explicit modeling of the microstructure with the aim to predict the variability in fatigue crack initiation life and to guide material design for fatigue resistant microstructures. Lastly, it is noted that crystal plasticity models are often too computationally intensive if the objective is to model the macroscopic behavior of a textured or randomly oriented 3-D polycrystal in an engineering component. Homogenized constitutive models were formulated and implemented as user material subroutines in ABAQUS, which can capture the macroscale stress-strain response in both DS GTD111 and IN100. Even though the study was conducted on two specific Ni-base superalloys; DS GTD111 and IN100, the objective was to develop generic frameworks which should also be applicable to other alloy systems.
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Modeling of Shape Memory Alloys Considering Rate-independent and Rate-dependent Irrecoverable StrainsHartl, Darren J. 2009 December 1900 (has links)
This dissertation addresses new developments in the constitutive modeling and
structural analysis pertaining to rate-independent and rate-dependent irrecoverable
inelasticity in Shape Memory Alloys (SMAs). A new model for fully recoverable SMA
response is derived that accounts for material behaviors not previously addressed.
Rate-independent and rate-dependent irrecoverable deformations (plasticity and viscoplasticity)
are then considered. The three phenomenological models are based on
continuum thermodynamics where the free energy potentials, evolution equations, and
hardening functions are properly chosen. The simultaneous transformation-plastic
model considers rate-independent irrecoverable strain generation and uses isotropic
and kinematic plastic hardening to capture the interactions between irrecoverable
plastic strain and recoverable transformation strain. The combination of theory and
implementation is unique in its ability to capture the simultaneous evolution of recoverable
transformation strains and irrecoverable plastic strains. The simultaneous
transformation-viscoplastic model considers rate-dependent irrecoverable strain generation
where the theoretical framework is modfii ed such that the evolution of the
viscoplastic strain components are given explicitly. The numerical integration of the
constitutive equations is formulated such that objectivity is maintained for SMA
structures undergoing moderate strains and large displacements. Experimentally validated
analysis results are provided for the fully recoverable model, the simultaneous
transformation-plastic yield model, and the transformation-viscoplastic creep model.
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Constitutive modeling for biodegradable polymers for application in endovascular stentsda Silva Soares, Joao Filipe 10 October 2008 (has links)
Percutaneous transluminal balloon angioplasty followed by drug-eluting stent
implantation has been of great benefit in coronary applications, whereas in peripheral
applications, success rates remain low. Analysis of healing patterns in successful
deployments shows that six months after implantation the artery has reorganized itself to
accommodate the increase in caliber and there is no purpose for the stent to remain,
potentially provoking inflammation and foreign body reaction. Thus, a fully
biodegradable polymeric stent that fulfills the mission and steps away is of great benefit.
Biodegradable polymers have a widespread usage in the biomedical field, such as
sutures, scaffolds and implants. Degradation refers to bond scission process that breaks
polymeric chains down to oligomers and monomers. Extensive degradation leads to
erosion, which is the process of mass loss from the polymer bulk. The prevailing
mechanism of biodegradation of aliphatic polyesters (the main class of biodegradable
polymers used in biomedical applications) is random scission by passive hydrolysis and
results in molecular weight reduction and softening.
In order to understand the applicability and efficacy of biodegradable polymers, a
two pronged approach involving experiments and theory is necessary. A constitutive
model involving degradation and its impact on mechanical properties was developed
through an extension of a material which response depends on the history of the motion
and on a scalar parameter reflecting the local extent of degradation and depreciates the
mechanical properties. A rate equation describing the chain scission process confers
characteristics of stress relaxation, creep and hysteresis to the material, arising due to the entropy-producing nature of degradation and markedly different from their viscoelastic
counterparts.
Several initial and boundary value problems such as inflation and extension of
cylinders were solved and the impacts of the constitutive model analyzed. In vitro
degradation of poly(L-lactic acid) fibers under tensile load was performed and
degradation and reduction in mechanical properties was dependent on the mechanical
environment. Mechanical testing of degraded fibers allowed the proper choice of
constitutive model and its evolution. Analysis of real stent geometries was made possible
with the constitutive model integration into finite element setting and stent deformation
patterns in response to pressurization changed dramatically as degradation proceeded.
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Performance of Superelastic Shape Memory Alloy Reinforced Concrete Elements Subjected to Monotonic and Cyclic LoadingAbdulridha, Alaa 14 May 2013 (has links)
The ability to adjust structural response to external loading and ensure structural safety and serviceability is a characteristic of Smart Systems. The key to achieving this is through the development and implementation of smart materials. An example of a smart material is a Shape Memory Alloy (SMA).
Reinforced concrete structures are designed to sustain severe damage and permanent displacement during strong earthquakes, while maintaining their integrity, and safeguarding against loss of life. The design philosophy of dissipating the energy of major earthquakes leads to significant strains in the steel reinforcement and, consequently, damage in the plastic hinge zones. Most of the steel strain is permanent, thus leading to large residual deformations that can render the structure unserviceable after the earthquake. Alternative reinforcing materials such as superelastic SMAs offer strain recovery upon unloading, which may result in improved post-earthquake recovery. Shape Memory Alloys have the ability to dissipate energy through repeated cycling without significant degradation or permanent deformation. Superelastic SMAs possess stable hysteretic behavior over a certain range of temperature, where its shape is recoverable upon removal of load. Alternatively, Martensite SMAs also possess the ability to recover its shape through heating. Both types of SMA demonstrate promise in civil infrastructure applications, specifically in seismic-resistant design and retrofit of structures.
The primary objective of this research is to investigate experimentally the performance of concrete beams and shear walls reinforced with superelastic SMAs in plastic hinge regions. Furthermore, this research program involves complementary numerical studies and the development of a proposed hysteretic constitutive model for superelastic SMAs applicable for nonlinear finite element analysis. The model considers the unique characteristics of the cyclic response of superelastic materials.
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Contribution à la modélisation de l'anisotropie induite par endommagement d'un matériau agrégataire énergétique / Contribution to modeling of induced anisotropy of damage for a material aggregate explosiveBenelfellah, Abdelkibir 30 September 2013 (has links)
Le matériau composite agrégataire énergétique étudié a un comportement viscoélastique endommageable sensible à la pression de confinement et à la température. Ces travaux concernent la modélisation de l'anisotropie induite par endommagement avec deux objectifs principaux. Dans un premier temps, le caractère anisotrope de l'endommagement est mis en évidence expérimentalement. Des essais alternant tension et compression permettant d'observer l'effet unilatéral d'endommagement. Ensuite, un modèle de comportement est développé pour le matériau d'étude. Des modèles pertinents sont tout d'abord comparés. Le modèle le plus approprié est ensuite amélioré par l'ajout de mécanismes d'endommagement, d'effectivité du dommage et d'un mécanisme de plasticité. Les données expérimentales sont utilisées pour identifier les paramètres du modèle. Ce dernier a été ensuite implémenté dans un logiciel de calcul aux éléments finis (Abaqus / standard) sous la forme d'une procédure Fortran (UMAT). Différents types de chargements sont simulés et confrontés aux résultats expérimentaux. / An explosive aggregate material exhibits a visco-elastic behaviour with damage, internal friction and sensitivity to the confining pressure and temperature. This thesis focuses on the anisotropic elastic damage with unilateral effect. The first aim of this study is to highlight experimentally the anisotropic nature of the damage. Then, a new model is proposed for the studied material. This is achieved using a comparison of some relevant models in order to select the most appropriate among them. The selected model is then improved by adding unilateral effect mechanisms and plasticity. Experimental data is used to characterize the material behaviour and to determine the parameters of improved model. This model has been implemented in the finite element software (Abaqus / Standard) using Fortran procedure (UMAT) and then tested for different loads and compared with experimental results.
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Experimental characterization and modeling of the mechanical behavior of filled rubbers under cyclic loading conditions / Caractérisation expérimentale et modélisation du comportement mécanique d’élastomères chargés sous conditions de chargement cycliquesMerckel, Yannick 26 June 2012 (has links)
Les applications pour lesquelles des élastomères sont soumis à des sollicitations cycliques sont nombreuses. Des charges sont généralement utilisées afin d'améliorer leurs propriétés, cependant, elles induisent également un adoucissement important de la contrainte lors de sollicitations cycliques. A ce jour, les phénomènes physiques conduisant à l’apparition de cet adoucissement ne sont pas clairement établis et sa modélisation demeure une difficulté majeure.Afin d'étudier l'adoucissement, des élastomères chargés sont soumis à des chargements cycliques. Des méthodes de caractérisations originales sont proposées afin de quantifier les effets de l'intensité du chargement et du nombre de cycles. Pour faire le lien avec la microstructure du matériau, plusieurs mélanges de compositions différentes sont utilisés. Des chargements non proportionnels de traction uniaxiale et biaxiale sont appliqués afin de mettre en évidence l'anisotropie induite par l'adoucissement. Ces données expérimentales non conventionnelles sont utilisées afin de définir un critère général pour l'activation de l'adoucissement Mullins. Une loi de comportement fondée sur une analyse approfondie des données expérimentales est proposée. La modélisation est basée sur une approche directionnelle. L'adoucissement Mullins est modélisé en utilisant le concept d'amplification de la déformation et son activation est pilotée par un critère directionnel. La capacité du modèle à prédire les réponses d'un matériau ayant subit un historique de chargement non proportionnel est validée / Rubber-like materials are submitted to cyclic loading conditions in various applications. Fillers are always incorporated within rubber compounds. They improve the mechanical properties but induce a significant stress-softening under cyclic loadings. The physical source of the softening is not yet established and its modeling remains a challenge. For a better understanding of the softening, filled rubbers are submitted to cyclic loadings. In order to quantify the effects of the loading intensity and the number of cycles, original methods are proposed to characterize the softening. To study the influence of the material microstructure on the softening, compounds with various compositions are considered.Non proportional tensile tests including uniaxial and biaxial loading paths are applied in order to highlight the softening induced anisotropy. Such unconventional experimental data are used to provide a general criterion for the softening activation. A constitutive modeling grounded on a thorough analysis of experimental data is proposed. The model is based on a directional approach. The Mullins softening is accounted for by the strain amplification concept and is activated by a directional criterion. The model ability to predict non proportional softened material responses is demonstrated
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Performance of Superelastic Shape Memory Alloy Reinforced Concrete Elements Subjected to Monotonic and Cyclic LoadingAbdulridha, Alaa January 2013 (has links)
The ability to adjust structural response to external loading and ensure structural safety and serviceability is a characteristic of Smart Systems. The key to achieving this is through the development and implementation of smart materials. An example of a smart material is a Shape Memory Alloy (SMA).
Reinforced concrete structures are designed to sustain severe damage and permanent displacement during strong earthquakes, while maintaining their integrity, and safeguarding against loss of life. The design philosophy of dissipating the energy of major earthquakes leads to significant strains in the steel reinforcement and, consequently, damage in the plastic hinge zones. Most of the steel strain is permanent, thus leading to large residual deformations that can render the structure unserviceable after the earthquake. Alternative reinforcing materials such as superelastic SMAs offer strain recovery upon unloading, which may result in improved post-earthquake recovery. Shape Memory Alloys have the ability to dissipate energy through repeated cycling without significant degradation or permanent deformation. Superelastic SMAs possess stable hysteretic behavior over a certain range of temperature, where its shape is recoverable upon removal of load. Alternatively, Martensite SMAs also possess the ability to recover its shape through heating. Both types of SMA demonstrate promise in civil infrastructure applications, specifically in seismic-resistant design and retrofit of structures.
The primary objective of this research is to investigate experimentally the performance of concrete beams and shear walls reinforced with superelastic SMAs in plastic hinge regions. Furthermore, this research program involves complementary numerical studies and the development of a proposed hysteretic constitutive model for superelastic SMAs applicable for nonlinear finite element analysis. The model considers the unique characteristics of the cyclic response of superelastic materials.
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