Dissertations / Theses on the topic 'Viscoelastic'
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Ruas, Henriques Isadora. "Analysis, characterization and modeling of viscoelastic and poro-viscoelastic materials." Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAC044.
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Cette thèse porte sur la modélisation et la caractérisation du comportement thermomécanique des matériaux viscoélastiques et poro-viscoélastiques. Le travail est divisé en deux parties principales : l'une concernant la technique expérimentale d'Analyse Mécanique Dynamique (DMA) et l'autre relative aux performances d'amortissement des matériaux poro-viscoélastiques. Dans la première partie, la propriété viscoélastique connue comme le module complexe mesuré par les modes de flexion du DMA est examinée théoriquement et expérimentalement. Une attention particulière est portée aux effets des modes de fonctionnement et des machines. Dans le but d'obtenir une meilleure analyse des impacts des écarts constatés, des modèles de dérivées fractionnaires (FDM) sont calibrés dans le cadre bayésien. Les résultats montrent que les DMA présentent une grande variabilité entre les modes ou les fabricants et les modèles statistiques peuvent atténuer ces problèmes. Dans la deuxième partie, la dissipation d'énergie mécanique inhérente à la viscoélasticité de trois matériaux poreux différents est explorée dans le domaine des basses fréquences. Initialement, une approche numérique est proposée pour générer des prédictions dans le domaine temporel de leur comportement hystérique sous différentes conditions de chargement. Ensuite, un modèle d'éléments finis qui considère un FDM est proposé pour décrire le comportement de panneaux simplement appuyés recouverts d'une couche libre de matériau poreux. Des expériences sont menées pour valider le modèle proposé. Enfin, une méthode inverse basée sur l'inférence bayésienne a été présentée pour identifier les propriétés viscoélastiques de ces matériaux. Les résultats de ces analyses ont montré le grand potentiel des matériaux poro-viscoélastiques à appliquer afin d'amortir les vibrations mécaniquesThis thesis deals with the modeling and characterization of the thermomechanical behavior of viscoelastic and poro-viscoelastic materials. The work is divided into two main parts: one concerning the experimental technique Dynamic Mechanical Analysis (DMA) and the other related to the damping performance of poro-viscoelastic materials. In the first part, the viscoelastic property known as complex modulus measured by the flexural modes of DMA is deeply examined theoretically and experimentally. Special attention is paid to the effects of operational modes and machines on various properties. Aiming to obtain a better analysis of the impacts of the discrepancies found, fractional derivative models (FDM) are calibrated within the Bayesian framework. Results show that DMAs have a great variability between modes or manufacturers and statistical models may mitigate these issues. In the second part, the dissipation of mechanical energy inherent to the viscoelasticity of three different porous materials is explored in the low-frequency range. Initially, a numerical approach is proposed to generate predictions in the time domain of the hysteretic behavior of the analyzed materials under different loading conditions. Then, a finite element model that considers a FDM is proposed to describe the behavior of simply supported panels covered with a free-layer of porous material. Experiments are carried out to validate the proposed model. Finally, an inverse method based on Bayesian inference was presented to identify the viscoelastic properties of these materials from vibration tests. The results of these analyses showed the great potential of poro-viscoelastic materials to be applied to damp mechanical vibrations
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Lin, Kuanchung J. "Modeling viscoelastic jets /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487594970651388.
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Inch, Scott E. "Precise energy decay rates for some viscoelastic and thermo-viscoelastic rods." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39978.
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Energy dissipation in systems with linear viscoelastic damping is examined. It is shown that in such viscoelastically damped systems the use of additional dissipation mechanisms (such as boundary velocity feedback or thermal coupling) may not improve the rate of energy decay. The situation where the viscoelastic stress relaxation modulus decreases to its (positive) equilibrium modulus at a subexponential rate, e.g., like (1 + t)-x + E, where α > 0, E > 0 is examined. In this case, the nonoscillatory modes (the so-called creep modes) dominate the energy decay rate. The results are in two parts.
In the first part, a linear viscoelastic wave equation with infinite memory is examined. It is shown that under appropriate conditions on the kernel and initial history, the total energy is integrable against a particular weight if the kinetic energy component of the total energy is integrable against the same weight. The proof uses energy methods in an induction argument. Precise energy decay rates have recently been obtained using boundary velocity feedback. It is shown that the same decay rates hold for history value problems with conservative boundary conditions provided that an a priori knowledge of the decay rate of the kinetic energy term is assumed.
In the second part, a simple linear thermo-viscoelastic system, namely, a viscoelastic wave equation coupled to a heat equation, is examined. Using Laplace transform methods, an integral representation formula for W(x,s), the transform of the displacement w(x, t), is obtained. After analyzing the location of the zeros of the appropriate characteristic equation, an asymptotic expansion for the displacement w(O,t) is obtained which is valid for large t and the specific kernel g(t) = g(–) + δtη-1 [over]Î (η), 0 < η < 1. With this expansion it is shown that the coupled system tends to its equilibrium at a slower rate than that of the uncoupled system.Ph. D.
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Tang, Bin. "Nanoindentation of viscoelastic materials." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B3655408X.
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Atsbha, Hailemariam. "Viscoelastic flows around spheres." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/7909.
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The present thesis is concerned with the flow of viscoelastic liquids in channels and around spheres contained in cylinders. Problems that have been tackled are the Poiseuille flow between parallel plates and in tubes, where all models give excellent results checked against analytical solutions for a range of elasticity levels determined by a dimensionless Weissenberg number (Ws). The drag coefficient on the sphere shows a monotonic decrease with increasing Ws, from 5.9522 for Ws = 0 to 5.4935 for Ws = 0.3. Non-zero second normal stress differences decrease the drag even further. The unbounded flow around spheres was simulated using a 50:1 diameter ratio. Findings suggest that slip on the sphere surface may be occurring at moderate to high Ws numbers, which has the effect of lowering the drag calculated on the sphere. (Abstract shortened by UMI.)
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Johnson, Mitchell A. "Viscoelastic Roll Coating Flows." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/JohnsonMA2003.pdf.
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Messalti, Mansour. "Viscoelastic damping of beams /." Online version of thesis, 1988. http://hdl.handle.net/1850/10414.
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Tang, Bin, and 唐斌. "Nanoindentation of viscoelastic materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B3655408X.
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JUNIOR, WALTER MENEZES GUIMARAES. "BUCKLING OF VISCOELASTIC STRUCTURES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9164@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEste trabalho apresenta um modelo computacional aplicável à análise de sistemas estruturais viscoelásticos submetidos a grandes deslocamentos, com particular atenção ao fenômeno da instabilidade. A discretização dos modelos é obtida através de elementos finitos isoparamétricos bidimensionais que podem ser empregados na análise de colunas, pórticos, arcos e cascas axissimétricas. A estabilidade elástica do sistema é verificada ao longo de trajetórias de equilíbrio definidas no espaço carga-deslocamentos, onde a ocorrência de pontos de bifurcação ou de pontos-limite é indicada através da troca de sinal do pivô da matriz de rigidez tangente. A inclusão de um modelo viscoelástico linear para o material possibilita a avaliação do efeito do tempo de carregamento sobre a carga de flambagem da estrutura. O mecanismo de instabilidade correspondente à flambagem viscoelástica envolve duas variáveis básicas: a magnitude da carga (carga crítica) e a duração da carga (tempo crítico). Os exemplos apresentados ilustram esses conceitos e fornecem resultados interessantes a respeito dos efeitos da viscoelasticidade sobre a flambagem em diferentes sistemas estruturais.
This thesis presents a computational model for the analysis of viscoelastic structures undergoing large displacements, with particular attention to unstable phenomena. The discrete model utilizes two-dimensional isoparametric finite elements in the analysis of columns, frames, arches and axially symmetric shells. The elastic stability of the system is verified along the equilibrium paths in the multidimensional load-displacements space, with bifurcation or limit points indicated by sign changes of the pivot of the tangent stiffness at every incremental step. A linear viscoelastic model for the material is included, allowing for the consideration of the effect of loading time on the buckling load for the structure. Thus, the mechanism leading to loss of stability, corresponding to viscoelastic buckling, involves two basic variables: load magnitude and duration of the load, designated as critical load and critical time. The examples presented herein enlighten such concepts and provide interesting results about viscoelastic effects on buckling of different structural systems.
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Ramsay, John Andrew. "Mixing of viscoelastic fluids." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7333/.
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This work investigates the laminar mixing performance of viscoelastic fluids in laboratory-scale batch stirred tanks agitated by “butterfly” impellers and in-line Kenics KM static mixers. Constant-viscosity viscoelastic (Boger) fluids were formulated to investigate viscous and elastic effects separately; multiphase viscoelastic suspensions were formulated from 40-50 volume% glass spheres in glycerol. Particle Image Velocimetry in stirred tanks agitated by high impeller-to-tank diameter ratio butterfly impellers (D/T=0.98) showed that secondary flows in Boger fluid increased solid body rotation and reduced local shear rates (≤16 s-1) compared to equivalent viscosity Newtonian fluids, though the effect was non-monotonic. Mixing times obtained from Planar Laser Induced Fluorescence (PLIF) increased by ≤23%. Positron Emission Particle Tracking in multiphase suspensions showed increased axial mixing due to more dominant secondary flows. In static mixers, Boger fluid striation patterns at the mixer outlet obtained from PLIF showed time dependence and flow instability due to reduced local shear rates. Energy consumption in all geometries displayed an increase of ≤200% with viscoelastic fluids. Using a generalised Reynolds number Reg enabled viscoelastic power draw prediction, previously only possible through empirical relationships. Overall, viscoelasticity generally increases energy consumption whilst reducing blending performance though the link between elasticity and mixing quality is highly non-linear.
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Santade, Fransber [UNESP]. "Análise dinâmica do amortecimento em estruturas compostas com material viscoelástico." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/97030.
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santade_f_me_bauru.pdf: 1882891 bytes, checksum: 8a15967197afaf47ad9929eeb4946264 (MD5)Neste trabalho foi proposto o estudo do amortecimento estrutural em vigas engastadas com adição de materiais viscoelásticos. As vigas foram montadas na condição engastada-livre e sujeitas de força na extremidade livre. Duas análises foram feitas. O primeiro modelo foi desenvolvido utilizando a Matriz de Impedância de Elemento Espectral (MEE) e o outro modelo foi desenvolvido utilizando Método dos Elementos finitos (MEF). Para validar os modelos numéricos foram realizados ensaios experimentais utilizando um acelerômetro e um martelo de impacto para obter a função de resposta em frequencia para as diferentes configurações de vigas idealizadas. Através dos resultados obtidos pode-se observar e comprovar o comportamento com frequencia de resposta do sistema e detectou-se redução de amplitude devido ao fator incremental de amortecimento viscoelástico proporcionado pelas camadas de fita (materiais viscoelásticos), comprovando assim, a importância da utilização de um material viscoelástico como atenuador de amplitudes no efeito da flexão do sistema. Os resultados experimentais foram comparados aos resultados dos modelos analíticos e numéricos de modo a se obter a validação experimental
This work proposes the study of structural damping in beams with added viscoelastic materials. The beams are mounted in a clamped-free condition and subject to force input at the free end. Two types analisis were made. The first model was developed using the Impedance Matrix of Spectral Element. The other model was developed using Finite Element Method (FEM). To validate the numerical models, experimental tests were performed using one accelerometer and a impact hammer to obtain frequency responce function of the diferente beams configurations. From the results we can observe and verify the variation in frequency response of the system and was detected amplitude reduction factor due to the incremental viscoelastic damping provided by the layers of tape (viscoelastic materials), thereby proving the importance of using a viscoelastic attenuator as possible amplitudes effect of the bending system. The results were compared to the results of analytical and numerical models in order to obtain experimental validation
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Santade, Fransber. "Análise dinâmica do amortecimento em estruturas compostas com material viscoelástico /." Bauru, 2013. http://hdl.handle.net/11449/97030.
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Orientador: Edson Antônio Capello SouzaCoorientador: Paulo José Paupitz Gonçalves
Banca: Laercio Javarez Junior
Banca: Bento Rodrigues de Pontes Junior
Resumo: Neste trabalho foi proposto o estudo do amortecimento estrutural em vigas engastadas com adição de materiais viscoelásticos. As vigas foram montadas na condição engastada-livre e sujeitas de força na extremidade livre. Duas análises foram feitas. O primeiro modelo foi desenvolvido utilizando a Matriz de Impedância de Elemento Espectral (MEE) e o outro modelo foi desenvolvido utilizando Método dos Elementos finitos (MEF). Para validar os modelos numéricos foram realizados ensaios experimentais utilizando um acelerômetro e um martelo de impacto para obter a função de resposta em frequencia para as diferentes configurações de vigas idealizadas. Através dos resultados obtidos pode-se observar e comprovar o comportamento com frequencia de resposta do sistema e detectou-se redução de amplitude devido ao fator incremental de amortecimento viscoelástico proporcionado pelas camadas de fita (materiais viscoelásticos), comprovando assim, a importância da utilização de um material viscoelástico como atenuador de amplitudes no efeito da flexão do sistema. Os resultados experimentais foram comparados aos resultados dos modelos analíticos e numéricos de modo a se obter a validação experimental
Abstract: This work proposes the study of structural damping in beams with added viscoelastic materials. The beams are mounted in a clamped-free condition and subject to force input at the free end. Two types analisis were made. The first model was developed using the Impedance Matrix of Spectral Element. The other model was developed using Finite Element Method (FEM). To validate the numerical models, experimental tests were performed using one accelerometer and a impact hammer to obtain frequency responce function of the diferente beams configurations. From the results we can observe and verify the variation in frequency response of the system and was detected amplitude reduction factor due to the incremental viscoelastic damping provided by the layers of tape (viscoelastic materials), thereby proving the importance of using a viscoelastic attenuator as possible amplitudes effect of the bending system. The results were compared to the results of analytical and numerical models in order to obtain experimental validation
Mestre
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Muravyov, Alexander. "Discrete dynamic viscoelastic systems and vibration analysis of an engine supported on viscoelastic mounts." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25124.pdf.
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Barakos, George. "Viscoelastic simulations in polymer processing." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6497.
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The scope of this thesis is the mathematical modelling and the numerical simulation of polymer processing. In recent years there has been considerable progress in understanding and modelling phenomena related to flow of polymer melts through polymer processing machinery. Much of the progress is due to the numerical solution of integral-type constitutive equations relating stress and deformation and representing the fading memory of these fluids. In this direction, an integral constitutive equation of the K-BKZ type has been used for simulating the extrusion of a Low-Density Polyethylene melt (IUPAC LDPE sample A). The influence of temperature has also been examined by performing a complete non-isothermal flow simulation. In addition, simulations have been performed for the well-known phenomenon of extrudate bending, when extrusion is performed through a flat die with walls kept at different temperatures. The simulations reveal that the combination of viscous and elastic phenomena result in a significant swelling of the extrudate characterized by a profound asymmetry. Finally, a comparison has been performed of different polyethylene melts based on the predictions of the model used. The results reveal the intense viscoelastic character of the LDPE and show clearly the importance of viscoelasticity in polymer processing. Moreover, they give a wealth of information about the influence of material properties on polymer behaviour during processing especially as far as vortex growth and extrudate swell diameter are concerned. (Abstract shortened by UMI.)
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Rensfelt, Agnes. "Nonparametric identification of viscoelastic materials." Licentiate thesis, Uppsala : Univ. : Dept. of Information Technology, Univ, 2006. http://www.it.uu.se/research/publications/lic/2006-008/2006-008.pdf.
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Stokes, Jason R. "Swirling flow of viscoelastic fluids /." Connect to thesis, 1998. http://eprints.unimelb.edu.au/archive/00000686.
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Smith, Pierre. "Viscoelastic properties of ionomeric blends." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=73990.
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Matallah, H. "Numerical simulation of viscoelastic flows." Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638026.
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In this thesis, consideration is given to two-dimensional isothermal incompressible flows of rheological complex materials. An introduction is provided on the background rheology and numerical schemes. A time stepping procedure is employed to solve steady state relevant partial differential equations, and in particular the equations of momentum, continuity and the Oldroyd-B constitutive equations. A Petrov Galerkin pressure correction method is used as the base finite element scheme. Model flows, considered as smooth and having analytical solutions are tested for accuracy. In contrast, complex benchmark problems, which may be smooth but with sharp velocity gradients, or alternatively non-smooth, are also solved to test stability and to contrast the quality of results against those in the literature. Despite the considerable effort devoted to establish sophisticated numerical methods to solve highly elastic complex flows of polymeric materials, the simulation of viscoelastic flows through complex geometries remains a challenge. One method that has found favour recently is the elastic-stress-splitting (EVSS) method. There are two features associated with this method, stress-splitting and recovery of velocity gradients. In this thesis, recovery and stress-splitting schemes for plane and axi-symmetric flows of non-Newtonian fluids are presented. Accuracy, stability and numerical performance issues are addressed for different schemes. It is established that recovery-based schemes are stable and superior in higher Deborah number attenuation over conventional and EVSS alternatives. Hence, it is shown that it is the recovery aspect that is responsible for improved stability behaviour. In this context, a 4:1 plane contraction and the flow past a cylinder in an infinite domain are used to analyse vortex activities for Newtonian and viscoelastic flows. Mesh convergence is also analysed.
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Bourne, Jeffrey Parnall. "Stress singularities in viscoelastic media." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47367.
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Sibley, David N. "Viscoelastic flows of PTT fluid." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518114.
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Aumaitre, Elodie. "Viscoelastic properties of hydrophobin layers." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607660.
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Reynolds, Matthew. "Active control of viscoelastic metamaterials." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/377011/.
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Metamaterials have been the subject of significant interest over the past decade due to their ability to produce novel acoustic behaviour beyond that seen in naturally occurring media. As well as their potential in acoustic cloaks and lenses, of particular interest is the appearance of band gaps which lead to very high levels of attenuation across the material within narrow frequency ranges. Unlike traditional periodic materials which have been employed at high frequencies, the resonant elements within metamaterials allow band gaps to form within the long wavelength limit; at low frequencies where it is most difficult to design satisfactory passive isolation solutions. Hence metamaterials may provide a useful path to high performance, low frequency isolation. Passively these band gaps occur over a narrow bandwidth, however the inclusion of active elements provide a method for enhancing this behaviour and producing attenuation over a broad band. Two active metamaterials are investigated in this thesis, first a novel viscoelastic metamaterial is developed that achieves double negativity and could be employed as a high performance vibration isolator at low frequencies. A prototype is produced, the band gap confirmed in the laboratory, and active control is applied to create a wideband region of attenuation. Next an acoustic metamaterial consisting of an array of Helmholtz resonators is presented and it is shown that such a metamaterial has a resonant band gap and dispersive density and bulk modulus. The acoustic metamaterial is produced using 3D printing techniques and the predicted behaviour confirmed in the laboratory. Finally an active Helmholtz resonator is introduced as a pathway to creating an active acoustic metamaterial and the potential for band gap and material parameter manipulation is investigated before a prototype resonator is produced and feedback controllers applied, enhancing the band gap attenuation.
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Chen, Yuanguo. "Viscoelastic Modeling of Flexible Pavement." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1258231515.
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Curry, Richard. "Implementation of viscoelastic Hopkinson bars." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10293.
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Includes bibliographical references (p. 107-112).The properties of soft, viscoelastic materials at high strain rates are important in furthering our understanding of their role during blast or impact events. Testing these soft or low impedance materials using metallic bars in a split Hopkinson pressure bar setup, poor signal to noise ratios and impedance mismatching occur. One solution is to use polymeric Hopkinson bars. In this dissertation, Polycarbonate, Polymethyl Methacrylate and Nylon are considered for use as Hopkinson bars. Conventional Hopkinson bar analysis cannot be used on the polymeric bars due to the viscoelastic nature of the bar material. As stress waves propagate along the length of the bars, viscoelastic effects result in dispersion and attenuation. The main topic of this dissertation is to account for this viscoelastic material effect.
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Moore, James D. P. "Viscoelastic modelling of crustal deformation." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6e73f2e2-a8f7-4790-8f13-f562d50302a9.
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Deformation in continents is not restricted to narrow bands but is spread over great distances within their interiors. A number of lines of evidence, including the distribution of earthquakes, reveal that the strength of different continental regions varies markedly. While it is relatively easy to qualitatively map out these variations, little progress has been made in quantifying the range of strength in the continents and identifying the physical mechanisms that control these variations. I investigate crustal deformation associated with the earthquake cycle, inflation of magma chambers beneath volcanoes, and changes in surface loads. Results of these models has important implications for our understanding of large-scale continental deformation and mountain building, in addition to both seismic and volcanic hazard assessment. Novel analytic solutions for simple shear with depth-dependent linear and non-linear viscoelastic rheologies are derived, in addition to analytical solutions for imposed harmonic tractions and displacements on an elastic layer over a Maxwell viscoelastic half space.
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West, Ray A. "Damping of elastic-viscoelastic beams /." Online version of thesis, 1992. http://hdl.handle.net/1850/11111.
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Akpan, Edem T. Gogot︠s︡i I︠U︡ G. "Viscoelastic toughening of refractory ceramics /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/284.
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Niedziela, Dariusz. "On numerical simulations of viscoelastic fluids." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981890849.
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Yapici, Kerim. "Numerical Investigation Of The Viscoelastic Fluids." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609618/index.pdf.
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Most materials used in many industries such as plastic, food, pharmaceuticals, electronics, dye, etc. exhibit viscoelastic properties under their processing or flow conditions. Due to the elasticity of such materials, deformation-stress in addition to their hydrodynamic behavior differ from simple Newtonian fluids in many important respects. Rod climbing, siphoning, secondary flows are all common examples to how a viscoelastic fluid can exhibit quite distinctive flow behavior than a Newtonian fluid would do under similar flow conditions. In industrial processes involving flow of viscoelastic materials, understanding complexities associated with the viscoelasticity can lead to both design and development of hydrodynamically efficient processes and to improved quality of the final products.
In the present study, the main objective is to develop two dimensional finite volume based convergent numerical algorithm for the simulation of viscoelastic flows using nonlinear differential constitutive equations. The constitutive models adopted are Oldroyd-B, Phan-Thien Tanner (PTT) and White-Metzner models. The semi-implicit method for the pressure-linked equation (SIMPLE) and SIMPLE consistent (SIMPLEC) are used to solve the coupled continuity, momentum and constitutive equations. Extra stress terms in momentum equations are solved by decoupled strategy. The schemes to approximate the convection terms in the momentum equations adopted are first order upwind, hybrid, power-law second order central differences and finally third order quadratic upstream interpolation for convective kinematics QUICK schemes. Upwind and QUICK schemes are used in the constitutive equations for the stresses. Non-uniform collocated grid system is employed to discretize flow geometries. As test cases, three problems are considered: flow in entrance of planar channel, stick-slip and lid driven cavity flow.
Detailed investigation of the flow field is carried out in terms of velocity and stress fields. It is found that range of convergence of numerical solutions is very sensitive to the type of rheological model, Reynolds number and polymer contribution of viscosity as well as mesh refinement. Use of White-Metzner constitutive differential model gives smooth, non oscillatory solutions to much higher Weissenberg number than Oldroyd-B and PTT models. Differences between the behavior of Newtonian and viscoelastic fluids for lid-driven cavity, such as the normal stress effects and secondary eddy formations, are highlighted.
In addition to the viscoelastic flow simulations, steady incompressible Newtonian flow of lid-driven cavity flow at high Reynolds numbers is also solved by finite volume approach. Effect of the solution procedure of pressure correction equation cycles, which is called inner loop, on the solution is discussesed in detail and results are compared with the available data in literature.
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Zhang, Mengqi. "Linear stability Analysis of Viscoelastic Flows." Thesis, KTH, Mekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95137.
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The goal of present work is to investigate the instability of jet ow, mixing layer and Poiseuille ow of viscoelastic uids. According to Boeta et al: [4], small elastic eect in Kolmogorov ow will result in increasing critical Re for hydrodynamic instability, however, at high elasticity a new instability of elastic nature occurs even at vanishing Re. This thesis aims to test this result in jet and mixing layer. In addition, linear stability analysis (modal and non-modal) of viscoelastic Poiseuille ow is carried out to understand the elastic eects on the ows of both Oldroyd-B and FENE-P model uids. Energy analysis is used to reveal the instability mechanism.
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Miller, Joel C. "Shear flow instabilities in viscoelastic fluids." Thesis, University of Cambridge, 2006. https://www.repository.cam.ac.uk/handle/1810/245318.
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This dissertation is concerned with the theoretical study of the stability of viscoelastic shear flows. It is divided into two parts: part I studies inertialess coextrusion flows at large Weissenberg number where the instabilities are due to discontinuities in the elastic properties, and part II studies the effect of elasticity on the well-known inertial instabilities of inviscid flows with inflection points. We begin part I with a previously known short-wave instability of Upper Convected Maxwell and Oldroyd–B fluids at zero Reynolds number in Couette flow. We show that if the Weissenberg number is large, the instability persists with the same growth rate when the wavelength is longer than the channel width. Intriguingly, surface tension does not modify the growth rate. Previous explanations of elastic interfacial instabilities based on the jump in normal stress at the interface cannot apply to this instability. These results are confirmed both numerically and with asymptotic methods. We then consider Poiseuille flow and show that a new class of instability exists if the interface is close to the center-line. We analyse the scalings and show that it results from a change in the boundary layer structure of the Couette instability. The growth rates can be large, and the wavespeed can be faster than the base flow advection. We are unable to simplify the equations significantly, and asymptotic results are not available, so we use numerics to verify the results. In studying these instabilities we encounter some others which we mention, but do not analyse in detail. In part II we study the effect of elasticity on the inertial instability of flows with inflection points. We show that the elasticity modifies the development of cat’s eyes. The presence of extensional flow complicates the analysis. Consequently we use the FENE–CR equations.
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Arvanitaki, A. "Adhesion and traction of viscoelastic contacts." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/8273.
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Bandey, Helen Luanne. "Viscoelastic characteristics of electroactive polymer films." Thesis, University of Leicester, 1998. http://hdl.handle.net/2381/30016.
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The quartz crystal microbalance (QCM) in association with the crystal impedance technique was used to study the viscoelastic properties of electroactive polymer films. In particular, a new analysis for the interpretation of crystal impedance data, acquired dynamically during the deposition of polyvinylferrocene (PVF) and polybithiophene (PBT), was developed and applied. Qualitatively, the raw crystal impedance data gave information on the departure from rigidity. However, for a quantitative analysis, equivalent circuit modelling was employed. The modified Butterworth Van-Dyke lumped-element equivalent circuit model was used to extract inductive and resistive components that relate to film mass and energy loss (diagnostic for film (non)-rigidity), respectively, during deposition. A new equivalent circuit fitting routine was developed that described the physical characteristics of polymer films in solution in terms of the complex shear moduli, G' (energy storage) and G'' (energy loss) of the film. The model consists of three components that take into account the viscoelastic polymer film, the deposition solution and the surface roughness features of the QCM. For PVF and PBT deposition, it was found that the shear modulus was a function of film thickness and had limiting values of G' G'' 108-109 and G' G'' 106-107 dyne cm-2, respectively. This suggests that PBT films behave as Maxwell fluids, whereas PVF films behave as rubbery solids.
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Aggarwal, Nishith. "Computational viscoelastic drop dynamics and rheology." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 122 p, 2008. http://proquest.umi.com/pqdweb?did=1456285651&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Demarquette, Nicole Raymonde. "Nonlinear viscoelastic properties of polystyrene solutions." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60004.
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In this work the nonlinear behavior of concentrated polystyrene solution was examined using sliding plate rheometer developed at McGill University. In this rheometer a novel transducer is used to measure the shear stress and an optical system is used to measure birefringence during flows involving high shear rates.The steady shear stress was found to be independent of shear rate at high shear rates. The Cox-Merz rule was found to be valid for concentrations less than 0.199 g.cm$ sp{-3}$, but a deviation from the rule was observed for higher concentrations. Sigmoidal damping functions, based on both the shear stress measurements and the birefringence measurements, were determined. The exponential stress coefficient and the third normal stress difference were calculated from experimental data for different values of exponential rate constant and different strain scale factor. The exponential rate constant was shown to have a strong influence on both the exponential stress coefficient and the third normal stress difference.
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Swarbrick, Sean James. "Finite element simulation of viscoelastic flow." Thesis, Teesside University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278423.
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Karlsson, Patrik. "Determination of viscoelastic properties of adhesives." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-35521.
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A research project at Linnaeus University focuses on optimizing theadhesives joints between wood and glass, with the aim of obtain stiffcomponents that can act as a load and stabilizing elements and still betransparent. But there is, however, still a lack of knowledge regarding theadhesive materials which need to be further investigated. This thesis focused on testing six different adhesives in relaxation and todetermine the viscosity (η) and modulus of elastic (MOE, E). Viscosity andMOE are then used in combination in a standard linear solid model (SLS)describing the viscoelasticity mathematically. Figures and tables are used topresent the results and the evaluation. The so determined parameters can beused in e.g. finite element models for the design of load bearing timber glasscomposites.
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Nkemzi, D. "Dynamics of elastic/viscoelastic sandwich plates." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334951.
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GUTIERREZ, JOSE ANGEL FLORIAN. "VISCOELASTIC FLOW THROUGH MICROCHANNELS WITH CONSTRICTION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=37214@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Alguns projetos pilotos de injeção de polímeros em campos de produção de petróleo mostraram um incremento na recuperação de óleo, embora os mecanismos que governam a dinâmica do escoamento não são bem compreendidos. Recentes investigações experimentais mostraram que as propriedades viscoelásticas de soluções poliméricas podem alterar o comportamento do escoamento na escala de poros e reduzir a saturação residual de óleo. Para entender esses fenômenos em meios porosos, é importante estudar o escoamento de soluções viscoelásticas através das gargantas dos poros. Este trabalho apresenta um estudo experimental do escoamento de uma solução viscoelástica de PEO (0,1 porcento em peso de óxido de polietileno) de alto peso molecular escoando através de uma constrição, utilizado como modelo de uma geometria de garganta de poro de um meio poroso. Medições de queda de pressão e campos de velocidade do escoamento são obtidos utilizando a técnica de velocimetria por imagem de partículas (Micro-PIV). Experimentos com uma solução viscosa de glicerina (45 porcento em peso de glicerina em água) de viscosidade similar à solução de PEO foram também realizados com a finalidade de estimar os efeitos elásticos da solução de PEO. O escoamento da solução de PEO exibiu uma queda de pressão extra (comportamento não linear) acima de uma condição crítica do escoamento, acima da qual os efeitos elásticos passam a ser preponderantes. Para toda a faixa de vazão explorada, os campos de velocidade da solução de glicerina mostraram um regime de escoamento Newtoniano, enquanto a solução de PEO apresenta instabilidade no escoamento a partir de um número de Weissenberg crítico, coincidindo com o aumento da queda de pressão. Esta instabilidade pode ser relacionada ao aumento da viscosidade extensional na entrada da garganta acima de uma determinada taxa de extensão. Os resultados obtidos indicam a variação do padrão do escoamento da solução polimérica de PEO devido à presença dos efeitos elásticos do polímero, e fornecem informações importantes sobre o comportamento das soluções poliméricas viscoelásticas em um meio poroso e que podem impactar sua utilização na recuperação melhorada de óleo.
Some pilot projects of polymer injection in oil fiel ds have shown an increase in oil recovery, although the mechanisms that govern the flow dynamics are still not well understood. Recent experimental investigations have shown that the viscoelastic properties of polymer solutions may change the pore-scale flow behavior and reduce the residual oil saturation. To understand these phenomena in porous media, it is important to understand viscoelastic flow behavior through the pores-throats. This work presents experimental study of the flow of a high molecular viscoelastic PEO solution (0.1 wt percent Polyethylene Oxide) flowing through a constricted capillary, used as model for a pore-throat geometry of a porous media. Pressure drop measurements are performed and velocity fields are obtained using the micro-particle image velocimetry (Micro-PIV) technique. Experiments with a viscous solution of glycerin (45 wt percent glycerin in water), of similar shear viscosity to the PEO solution were also performed in order to isolate the elastic effects of the PEO solution. The flow of the PEO solution exhibited an extra pressure drop (nonlinear behavior) above a critical flow condition beyond which the elastic forces become relevant. For the entire flow rate range explored, the velocity field of the glycerin solution showed a Newtonian flow regime, while the PEO solution shows instability in the flow above a critical Weissenberg number, coinciding with the onset of the extra pressure drop. This instability in the flow is associated with the high extensional viscosity near the constriction at high enough extension rates. The results show the changes in the flow pattern of the PEO polymer solution due to the presence of the elastic effects of polymer, and provide important information on how viscoelastic polymer solutions behave in a porous media and can impact their use in Enhanced Oil Recovery operations.
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Wong, Matthew Q. "Viscoelastic characterization of collagen-GAG scaffolds." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36683.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 43-45).
An experimental study was performed to determine whether or not collagen-GAG scaffolds exhibit linear viscoelastic behavior. Tension tests were performed on dry and hydrated engineered collagen-GAG scaffolds in order to develop a stress-strain curve. Strains that fell in the linear elastic region of these curves were selected and then used in stress relaxation tests that were also performed on dry and hydrated specimens. The relaxation modulus was calculated from the resulting stress relaxation curves at different strain levels and compared to each other to determine viscoelastic linearity. In addition to the determination of viscoelastic linearity, a water bath was designed in the hopes of performing stress relaxation tests in hydrated environment with the temperature maintained at 37°C, the temperature of the human body. These tests will aid in the future studies of how cells contract and apply force to the scaffolds since no previous studies have looked at the time dependent mechanical properties of these scaffolds. Moreover, the data can be used in the future to determine whether the viscoelastic response contributes to cellular processes such as migration speeds, attachment, and contraction.
by Matthew Q. Wong.
S.B.
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Byars, Jeffrey Alan. "Experimental characterization of viscoelastic flow instabilities." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/17413.
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Gerngross, Tobias. "Viscoelastic behaviour in stratospheric balloon structures." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611506.
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Puangkird, Bumroong. "Numerical simulations of complex viscoelastic flows." Thesis, Swansea University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683931.
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Wilson, Helen Jane. "Shear flow instabilities in viscoelastic fluids." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625082.
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The dissertation is concerned with the stability of channel flows of viscoelastic fluids. The content is primarily theoretical. The dissertation begins with a review of instabilities observed in experiments and then attempts to elucidate possible mechanisms using linear stability theory. The first section considers a previously known interfacial instability in coextrusion flows, whose mechanism is purely elastic. This instability is investigated in different parameter régimes for an Oldroyd-B fluid. The next section generalises the study to a continuously stratified fluid, and finds that a class of models with rapid variation in their elastic properties will also show the instability. These results are confirmed both numerically and using asymptotic methods. The fundamental mechanism of this "coextrusion" instability is the same as for the interfacial instability above. The next part concerns a shear-thinning White-Metzner fluid (i.e. a viscoelastic fluid having a relaxation time that is an instantaneous function of the local shear-rate). Evidence for another instability is found where the degree of thinning in the shear viscosity is high. The mechanism for this instability is fundamentally different from that in coextrusion. In the final section of the dissertation a study of two fluids of different constitutive types but identical base-state velocity and stress profiles shows that the criterion for the "coextrusion" instability depends on properties of the model itself. The flows in question are relevant to the practical problem of extrusion of polymeric liquids. The two instabilities found may provide mechanisms for experimental observations of helical distortions of extrudates. The demonstration that the constitutive type of a model has a crucial effect on its stability may have implications for future constitutive modelling in this field.
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Keshtiban, Ibrahim Jalili. "Numerical simulation of compressible viscoelastic flows." Thesis, Swansea University, 2004. https://cronfa.swan.ac.uk/Record/cronfa43047.
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In this work, we first present a brief introduction to flow at low Mach numbers, followed by rheological and equations of states for dense materials. Subsequently, we provide the background theory over several difficult issues encounter by compressible schemes, at low Mach numbers (singular limit of compressible flows). This would include key modifications employed to rectify density-based schemes and extending pressure-based incompressible algorithms for dealing with compressible flows. To accommodate weakly-compressible viscoelastic/viscous flows at low Mach numbers, a high-order time-marching pressure-correction algorithm has been adopted, in semi-implicit form. For discretisation of velocity and pressure equations, over the fractional stages of this pressure correction scheme, a Galerkin finite element was employed. To accommodate stress equations (considered here in Oldroyd-B form) two spatial discretisation alternatives are adopted. This encompasses a mixed finite element formulation in SUPG form, with a quadratic stress and velocity interpolations. The second scheme involves a sub-cell finite volume implementation, a hybrid fe/fv scheme for the full system. For both scheme variants, enhanced velocity gradients are acquired, via a recovery technique. Two discrete representations are proposed to interpolate density: a piecewise-constant form with gradient recovery and a linear interpolation form, akin to that on pressure. Validation on a numbers of classical benchmark problems bear out the high quality of performance of both compressible flow implementations, at low to vanishing Mach number. Neither linear, nor constant density interpolation schemes degrade the second-order accuracy of the original incompressible fractional-staged pressure-correction scheme. In viscous context, we conduct several tests on cavity and contraction flows (both Cartesian and cylindrical coordinates) for both compressible and incompressible flow settings. To validate results of our original incompressible scheme, for the cavity test problem, we compare and contrast predicted velocity fields with those in the literature. For this test problem, the effect of singularity in boundary conditions is investigated on spatial accuracy for both incompressible and compressible flows with the two density interpolations. On contraction flows, consistency is confirmed according to the two different forms of density interpolation. Capability of the scheme in dealing with very low Mach number flows is demonstrated, via adjusting Tait parameters. The scheme responses well as Mach number approaches zero (incompressible limit), and there is no obvious minimum threshold on Mach number for this scheme. We have conducted several tests, under the compressible settings on the effect of system eigenvalues on convergence patterns.
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Sopakayang, Ratchada. "Viscoelastic Models for Ligaments and Tendons." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77298.
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Collagenous tissues such as ligaments and tendons are viscoelastic materials. They exhibit a slow continuous increase in strain over time, or creep, when subjected to a constant stress and a slow continuous decrease in stress over time, or stress relaxation, when subjected to a constant strain. Moreover, the loading and unloading stress-strain curves are different when the tissues are subjected to cyclic loading, showing hysteresis and softening phenomena. The micro-structural origin of the viscoelasticity of these tissues is still unknown and the subject of debate among experts in biomechanics. Therefore, formulating viscoelastic models by accounting for the mechanical contributions of the structural components of these tissues can help in understanding the genesis of viscoelasticity.
A nonlinear viscoelastic modeling framework has been developed to describe the elastic and viscoelastic properties of ligaments and tendons by considering their main structural components, the collagen fibers and proteoglycan-rich matrix. The mathematical models derived within this framework can illustrate the tensile behavior, stress relaxation and creep by as suming that the collagen fibers are elastic and the surrounding proteoglycan-rich matrix is viscoelastic. The collagen fibers are represented by linear elastic springs that are engaged to support load at different values of the tissue's strain according to a Weibull distribution function. The mechanical contribution of the matrix is introduced via a Maxwell-type viscoelastic element arranged in parallel with the collagen fibers. According to the proposed mathematical framework, both the collagen fibers and the proteoglycan-rich matrix are responsible for resisting tensile loads. However, the collagen fibers play a significant role in creep while the proteoglycan-rich matrix has a dominant role in stress relaxation. The model parameters that define the stress relaxation and strain stiffening phenomena are estimated by using published experimental on rabbit medial collateral ligaments and are then used to predict creep.
The above modeling framework has been also extended to capture the in uence of preconditioning on the mechanical properties of ligaments and tendons. The stress softening and decrease in hysteresis that are observed during successive loading cycles in preconditioning are assumed to be determined by a decrease in the elastic properties of the collagen fibers and proteoglycan-rich matrix. Preliminary data collected on stress relaxation and preconditioning on rat medial collateral ligaments by collaborators are used to evaluate the model parameters and analyze its predictions.
The elastic and viscoelastic properties of single collagen fibers are studied by formulating a nonlinear viscoelastic framework by accounting for their main components: microfibrils, cross-links and proteoglycan-rich matrix. The model illustrates tensile behavior and stress relaxation of a single collagen fiber by assuming that the microfibrils and the cross-links are elastic and the surrounding proteoglycan-rich matrix is viscoelastic. The mechanical contribution of the microfibrils is included via a linear elastic spring while the cross-links are represented by linear elastic springs that progressively fail at different values of the tissue's strain according to an exponential distribution function. The matrix is defined by linear dashpots arranged in parallel with each single spring that represents an individual cross-link. The viscous properties of the matrix associated with the unbroken and broken cross-links are assumed to have different values. In the model formulation, the microfibrils and the cross-links are assumed to determine the elastic response of the fibers while the proteoglycan-rich matrix determines the stress relaxation. Microfibrils, cross-links and the proteoglycan-rich matrix are responsible for resisting the loading force during tensile behavior. Experimental data collected by performing incremental stress relaxation tests by other investigators on reconstituted rat tail tendons are used to estimate the parameters in the model and evaluate its performance.Ph. D.
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Wang, Qi. "Dynamics of viscoelastic slender free jets /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487693923196996.
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Yetkinler, Duran Nihat. "Viscoelastic behavior of acrylic bone cements /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu148786139602582.
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Rao, Jayathirtha M. "Viscoelastic behavior of electronic packaging materials /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487932351058575.
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Rensfelt, Agnes. "Viscoelastic Materials : Identification and Experiment Design." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-111283.
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