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1
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.)
2
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.
3
Mahaffy, Rachel Elaine. "The quantitative characterization of the viscoelastic properties of cells and polymer gels /". Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004328.
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Gordnian, Kamyar. "Crystallization and thermo-viscoelastic modelling of polymer composites". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63361.
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Process models of composite materials are useful tools for understanding the effect of process parameters and variables and reducing manufacturing risks and costs. The sub-model approach for process modelling has been applied to thermoset composites since the early 1980s. In this approach, analysis is performed with different sub-models such as thermochemical, flow, void and stress, and the analysis results are sequentially transferred from one sub-model to the next, until the analysis is complete. In recent years there has been growing use of high performance thermoplastics such as PEEK and PEKK in aircraft structures, and hence process models for thermoplastics are increasingly of interest.
During processing of thermoplastic materials, the material undergoes both melting and crystallization. Therefore a major component of the thermochemical/thermophysical sub-model for process modelling of thermoplastics is the crystallization/melt kinetics model. Most of the crystallization kinetics models in the literature are only valid for either constant temperatures or cooling at constant cooling rates. Furthermore, the number of melt kinetics models is very limited and their application restricted to small heating rates. As a material point in the part may undergo complex temperature cycles, a rate-type crystallization/melt kinetics model which is independent of the temperature cycle is desired.
Another problem in processing is development of residual stresses and distortions, which are analyzed in the stress sub-model using mechanical response constitutive models such as thermo-elastic, CHILE and viscoelastic. Most thermoplastic materials such as PEEK are indeed viscoelastic, however their unrelaxed values of moduli are temperature dependent, ie their behaviour is ‘thermo-rheologically complex’.
In this thesis the crystallization and melt behaviour of PEEK carbon fibre composites is investigated using DSC experiments. A rate type crystallization kinetics model is developed for prediction of degree of crystallinity during crystallization process. A concept of ‘master melt curve’ is introduced and is used along with the crystallization kinetics model for prediction of crystallinity change during an arbitrary process. Thermo-viscoelastic behaviour of the material is studied using DMA experiments. A thermo-viscoelastic (TVE) constitutive model is developed and is generalized to three dimensional cases. Some case studies are analyzed and validity of models are investigated.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
5
Gallican, Valentin. "Homogenization estimates for polymer-based viscoelastic composite materials". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS543.
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Cette thèse porte sur l’étude de la réponse harmonique macroscopique de matériaux composites viscoélastiques à base polymère. Nous nous intéressons tout d’abord à l’étude de matériaux composites à renforts particulaires dont la matrice est modélisée à partir de modèles de Zener fractionnaires et contient des particules sphériques élastiques. Le comportement asymptotique du module complexe macroscopique est étudié à l’aide de principes de stationnarité appliqués à la viscoélasticité complexe. Il est à noter que quatre conditions exactes sont obtenues sur les modules de stockage et de perte. Les deux premières correspondent aux réponses élastiques découplées à haute et basse fréquences, tandis que les deux autres résultent du couplage viscoélastique caractérisant la phase de transition vitreuse. A partir de celles-ci, nous développons des modèles micromécaniques viscoélastiques approchés sur toute la gamme de fréquences. Les modèles approchés font intervenir des développements en séries de Dirichlet-Prony afin d’estimer le comportement viscoélastique macroscopique. Ces derniers sont présentés à l’aide du schéma GSC dans le cas de constituants isotropes et comparés à des simulations FFT réalisées sur des microstructures périodiques pour différentes fractions volumiques de particules. Nous nous attachons ensuite à modéliser la réponse d’explosifs composés de poudres de TATB avec adjonction d’une phase polymère par une approche micromécanique en deux étapes. Nous commençons par étudier l’élasticité effective de polycristaux de TATB sans liant en fonction de nombreux paramètres morphologiques. Le comportement viscoélastique macroscopique est ensuite approché par des modèles micromécaniques et comparé à des simulations FFT et des données expérimentalesThis Ph.D. work deals with the description of the time harmonic response of polymer-based viscoelastic composite materials. On the one hand, the emphasis is put on particulate-reinforced composite materials whose matrix is defined by fractional Zener models containing elastic spherical particles. The asymptotic behaviour of the overall complex moduli is studied by resorting to stationary principles for complex viscoelasticity. Four exact conditions on the storage and loss moduli are obtained. Two of them classically correspond to the uncoupled elastic responses at low and high frequencies while the two others result from the viscoelastic coupling in the transient regime. These conditions only involve the strain fields solutions of asymptotic elastic problems. Based on these conditions, we propose to develop approximate viscoelastic homogenization models for the whole frequency range. They classically make use of Dirichlet-Prony series to estimate the overall viscoelastic behaviour. Such models are presented by means of the GSC scheme for isotropic constituents and compared to FFT full-field computations carried out on periodic microstructures with various volume fractions of particles. On the other hand, we focus on the modeling of TATB-based pressed polymer-bonded explosives seen as jointed polycrystals by means of two-step multiscale modeling. We first investigate the effective elasticity of binder-free TATB-based polycrystals with respect to various morphological parameters. Afterwards, the overall viscoelastic behaviour is assessed by making use of mean-field schemes and compared to FFT full-field computations and experimental data
6
Pandey, Anurag V. "Nonlinear viscoelastic response of a thermodynamically metastable polymer melt". Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/9096.
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Ultra High Molecular Weight Polyethylene (UHMw-PE) is an engineering polymer that is widely used in demanding applications because of its un-paralleled properties such as high abrasion resistance, high-modulus and high-strength tapes and fibres, biaxial films etc. In common practice, to achieve the uniaxial and the biaxial products, the solution processing route is adopted to reduce the number of entanglements per chain, such as found in Dyneema(R) from DSM(R). Another elegant route to reduce the number of entanglements to ease solid-state processing is through controlled polymerisation using a single-site catalytic system. In this theses, how different polymerisation condition, such as temperature and time control molecular weight and the resultant entangled state in synthesised disentangled UHMw-PE is addressed. Linear dynamic melt rheology is used to follow entanglement formation in an initially disentangled melt. With the help of rheological studies, heterogeneity in the distribution of entanglements along the chain length and the crystal morphology produced during polymerisation is considered. For the understanding of influence of large shear flow on melt dynamics large amplitude oscillatory shear (LAOS) is used and the non-linear viscoelastic regime is explored. A remarkable feature of overshoot in loss (viscous) modulus with increasing deformation (strain) in UHMw-PE melt in the LAOS is observed. This observation is characteristic of colloidal systems. The role of entanglement density in the amorphous region of the synthesised disentangled UHMw-PE (semi-crystalline polymers) on the melting and crystallisation is presented. To understand the effect of topological differences on melting behaviour, nascent entangled, nascent disentangled and melt-crystallised samples have been used. The role of superheating on the melting process is also addressed. Preliminary results on characteristic melting time of a crystal using TM-DSC are also presented.
7
Kalakkunnath, Sumod. "VISCOELASTIC RELAXATION CHARACTERISTICS OF RUBBERY POLYMER NETWORKS AND ENGINEERING POLYESTERS". UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/486.
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The relaxation characteristics of rubbery poly(ethylene oxide) [PEO] networks have been investigated as a function of network composition and architecture via dynamic mechanical analysis and broadband dielectric spectroscopy. A series of model networks were prepared via UV photopolymerization using poly(ethylene glycol) diacrylate [PEGDA] as crosslinker: variations in crosslink density were achieved either by the introduction of water in the prepolymerization reaction mixture, or by the inclusion of mono-functional acrylate such as poly(ethylene glycol) methyl ether acrylate [PEGMEA] or poly(ethylene glycol) acrylate [PEGA]. Copolymerization with mono-functional acrylate led to the insertion of flexible branches along the network backbone, and the corresponding glass-rubber relaxation properties of the copolymers (i.e., Tg, relaxation breadth, fragility) were a sensitive function of network architecture and corresponding fractional free volume. Relatively subtle variations in network structure led to significant differences in relaxation characteristics, and a systematic series of studies was undertaken to examine the influence of branch length, branch end-group, and crosslinker flexibility on viscoelastic response. Dielectric spectroscopy was especially useful for the elucidation of localized, sub-glass relaxations in the polymer networks: the imposition of local constraint in the vicinity of the crosslink junctions led to the detection of a distinctive fast relaxation process in the networks that was similar to a comparable sub-glass relaxation observed in crystalline PEO and in the confined regions of PEO nanocomposites. Gas permeation studies on the model PEGDA networks confirmed their utility as highly-permeable, reverse-selective membrane materials, and strategic control of the network architecture could be used to optimize gas separation performance. Dynamic mechanical and dielectric measurements have also been performed on a semicrystalline polyester, poly(trimethylene terephthalate) [PTT], in order to assess the influence of processing history on the resultant morphology and corresponding viscoelastic relaxation characteristics. Studies on both quenched and annealed PTT revealed the presence of a substantial fraction of rigid amorphous phase (RAP) material in the crystalline samples: dielectric measurements showed a strong increase in relaxation intensity above the glass transition indicating a progressive mobilization of the rigid amorphous phase with increasing temperature prior to crystalline melting.
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Yoshikawa, Katsuyuki. "STUDIES ON NONLINEAR VISCOELASTIC BEHAVIOR OF HIGHLY ENTANGLED POLYMER SYSTEMS". Kyoto University, 2020. http://hdl.handle.net/2433/252988.
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Kamath, Vinod Mangalore. "The modelling of viscoelastic behaviour for mono- and polydisperse polymer melts". Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/272959.
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Yang, Guanwen Zhu Da-Ming. "Probing the viscoelastic response of polymer films using atomic force microscopy". Diss., UMK access, 2005.
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Thesis (M.S.)--Dept. of Physics. University of Missouri--Kansas City, 2005."A thesis in physics." Typescript. Advisor: Da-Ming Zhu. Vita. Title from "catalog record" of the print edition Description based on contents viewed June 27, 2006. Includes bibliographical references (leaves 50-52). Online version of the print edition.
11
Zhu, Jiqing. "Towards a Viscoelastic Model for Phase Separation in Polymer Modified Bitumen". Licentiate thesis, KTH, Bro- och stålbyggnad, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-163540.
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In this thesis, a review is given on the most popular polymers used today for polymer modification of bitumen. Furthermore, the development of a model for phase separation in polymer modified bitumen (PMB) is proposed, that will enable a better control and understanding of PMB phase behaviour, allowing thus to enhanced long-term performance. PMB is hereby considered as a blend and focus is placed on its structure, its equilibrium thermodynamics and its phase separation dynamics. The effects of dynamic asymmetry on phase separation in PMB are analysed with related theories and some image data. Based on the discussion in this thesis, it is concluded that the effects of dynamic asymmetry between bitumen and polymer should be taken into consideration when studying phase separation in PMB. By analysing related literature and image data, it is found that some features of viscoelastic phase separation are shown during the phase separation process in some PMBs. It is therefore possible and useful to develop a viscoelastic model for PMB to describe its phase separation behaviour. In this, the stress-diffusion coupling is expected to play a key role in the model. Finally, recommendations are made towards the future research which is needed to realize the proposed model.QC 20150409
12
Suen, Jason Ka-Chun 1973. "Multiscale simulation of viscoelastic flows : applications to kinetic theory models of polymer melts and liquid crystalline polymers". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29293.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2003.Includes bibliographical references (v. 2, leaves 351-363).
Knowing and understanding the dynamics and molecular configurations of polymer molecules is important for efficient process design and novel product development. Much research has been focused on combining molecular simulations and traditional fluid mechanics computations to simulate the behavior of polymeric liquids in a fabrication process. These simulation approaches require solution of the coupled set of the equations of change, the governing equations from kinetic theory, and the flux expressions that map molecular configurations to macroscopic quantities. Most complex flow simulations so far make use of a mixed finite element method to calculate the velocity field, with stress tensor evaluated by using a stochastic simulation method. This so-called CONNFFESSIT approach suffers from both a large memory requirement and stochastic noise. This thesis focuses on the development and application of a fully deterministic numerical approach for computing viscoelastic flows with constitutive descriptions based directly on diffusion equations from kinetic theory. The numerical approach is based on an operator splitting time integration method that decouples the calculation of microstructure by solution of a hyperbolic diffusion equation from the velocity and pressure field evolution, which is obtained by solution of a generalized Stokes problem. The generalized Stokes problem is written in the DEVSS-G formulation, where a direct interpolation of the components of the velocity gradient tensor is introduced. The efficiency and robustness of this numerical method is demonstrated through calculating the viscoelastic flows of a modified Doi model for liquid crystalline polymer and a number of reptation models for polymer melts in different flow geometries.
(cont.) Simulations of the original Doi model with the Maier-Saupe potential in a pressure-driven channel flow by Nayak showed disclination formation due to the shear-rate-dependent frequencies of the tumbling/wagging states of the Doi model in a shear or mixed shear flow. The lack of an instrinsic length scale in the model leads to an infinitesimal structure refinement that eventually causes numerical instabilities. In this thesis, the effect of concentration variation is incorporated to develop a modified Doi model for introducing an intrinsic length scale through translational diffusion. This changes the mathematical characteristics of the spatial variation of the underlying diffusion equation from that of a hyperbolic equation to that of an elliptic equation. The resulting elliptic diffusion equation is then solved by using a local discontinuous Galerkin method, where an auxillary variable is introduced to rewrite the elliptic diffusion equation into a pair of formal, hyperbolic equations, which in turn is solved by the standard discontinuous Galerkin method. Unlike the original Doi model, a steady state is reached for a variety of De. Although there is structure variation across the channel width, the director profiles point uniformly along the flow direction. The lack of disclination formation may be rectified by introducing Frank elasticity into the modified Doi model ...
by Jason Ka-Chun Suen.
Ph.D.
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RENHA, JULIA FROTA. "SIMULATION OF INJECTION PROCESS FOR VISCOELASTIC POLYMER SOLUTION IN A RESERVOIR SCALE". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27000@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCom o objetivo de aumentar a capacidade dos poços petrolíferos, métodos convencionais de recuperação são utilizados, os quais consistem na injeção de água ou gás para a manutenção da pressão do reservatório. A produção do óleo ocorre através do deslocamento do mesmo no espaço poroso, onde a água, fluido deslocante, é injetada para ocupar gradualmente o espaço do óleo, fluido deslocado. Devido aos efeitos capilares e às heterogeneidades do meio poroso, uma parcela de óleo residual acaba ficando retida no reservatório, apresentando baixo fator de recuperação de óleo devido a elevada viscosidade do óleo em relação à viscosidade do fluido injetado e altas tensões interfaciais entre os fluidos. A adição de polímeros à água garante um aumento na sua viscosidade, melhorando a razão de mobilidade água/óleo no meio poroso. Uniformizando a frente de avanço e melhorando a eficiência de varrido devido à melhora no deslocamento do óleo. O presente trabalho analisa o comportamento viscoelástico do polímero, isolando o efeito viscoso e elástico em função das taxas de cisalhamento e extensão, implementado em um modelo de simulação de injeção de polímeros na escala de reservatórios. O efeito das propriedades reológicas da solução polimérica mostram nos resultados de produção uma frente de avanço mais estável e consequentemente uma melhora na taxa de recuperação de óleo quando avaliou-se o comportamento puramente cisalhante. Entretanto uma melhora na taxa de recuperação e na estabilidade da frente de avanço para o comportamento puramente extensional só pode ser observado quando o número de capilaridade foi aumentado consideravelmente.
Aiming to increase the capacity of oil fields, conventional recovery methods are used. These methods consist in the injection of water or gas to maintain the reservoir pressure. The oil production typically takes place by displacing this oil in the porous media, where the displacing fluid (water) is injected to gradually occupy the space of the displaced fluid (oil). Since due to capillary effects and the heterogeneity of the porous media, a residual oil portion ends up trapped in the reservoir. These methods lead to low values of oil recovery factor, which occurs mainly by two factors: high viscosity of the reservoir s oil in relation to the viscosity of the injected fluid and high interfacial tension between the fluids. The addition of polymers to the water ensures an increase in the viscosity of the injected fluid, improving mobility ratio between water and oil in the porous media. Thus, standardizing forward swept and improving the swept efficiency due to improved oil displacement, which reduces the formation of preferential paths in the reservoir, usually called fingers. This paper analyzes the viscoelastic behavior of the polymer, by isolating the viscous and elastic effect in function of its extension and shear rates, implemented in a polymer injection simulation model in a reservoir scale. The effect of the rheological properties of the polymer solution show in the production results a more stable injection front and consequently an oil recovery rate improvement when evaluated as a purely shear behavior. However an improvement in the recovery rate and stability of the injection front for pure extensional behavior can only be observed when the capillary number is increased considerably.
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Dallas, Vassilios. "Multiscale structure of turbulent channel flow and polymer, dynamics in viscoelastic turbulence". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5855.
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This thesis focuses on two important issues in turbulence theory of wall-bounded flows. One is the recent debate on the form of the mean velocity profile (is it a log-law or a power-law with very weak power exponent?) and on its scalings with Reynolds number. In particular, this study relates the mean flow profile of the turbulent channel flow with the underlying topological structure of the fluctuating velocity field through the concept of critical points, a dynamical systems concept that is a natural way to quantify the multiscale structure of turbulence. This connection gives a new phenomenological picture of wall-bounded turbulence in terms of the topology of the flow. This theory validated against existing data, indicates that the issue on the form of the mean velocity profile at the asymptotic limit of infinite Reynolds number could be resolved by understanding the scaling of turbulent kinetic energy with Reynolds number. The other major issue addressed here is on the fundamental mechanism(s) of viscoelastic turbulence that lead to the polymer-induced turbulent drag reduction phenomenon and its dynamical aspects. A great challenge in this problem is the computation of viscoelastic turbulent flows, since the understanding of polymer physics is restricted to mechanical models. An effective numerical method to solve the governing equation for polymers modelled as nonlinear springs, without using any artificial assumptions as usual, was implemented here for the first time on a three-dimensional channel flow geometry. The superiority of this algorithm is depicted on the results, which are much closer to experimental observations. This allowed a more detailed study of the polymer-turbulence dynamical interactions, which yields a clearer picture on a mechanism that is governed by the polymer-turbulence energy transfers.
15
Koga(Endoh), Maya. "Studies of shear-induced structures and viscoelastic behavior in semidilute polymer solutions". 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144525.
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Tizard, Geoffrey Alexander. "Characterization of the Viscoelastic Fracture of Solvated Semi-Interpenetrating Polymer Network Silicone Hydrogels". Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/34232.
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The unique compressive, optical, and biocompatible properties of silicone hydrogels allow them to be used in a wide variety of applications in the biomedical field. However, the relatively weak mechanical behavior, as well as the highly deformable nature of these elastomeric materials, presents a myriad of challenges when attempting to understand their constitutive and fracture properties in order to improve hydrogel manufacturing and performance in applications. In this thesis, a series of experimental techniques were developed or adapted from common engineering approaches in order to investigate the effects of rate and temperature on the viscoelastic constitutive and fracture behavior of two solvated semi-interpenetrating polymer network silicone hydrogel systems.
Viscoelastic characterization of these material systems was performed by implementing a series of uniaxial tension and dynamic mechanical analysis shear tests in order to generate relevant master curves and corresponding thermal shift factors of such properties as shear relaxation modulus, dynamic moduli, and the loss factor. Concurrently, the cohesive fracture properties were studied by utilizing a â semi-infiniteâ strip geometry under constrained tension in which thin pre-cracked sheets of these cured hydrogels were exposed to several different loading conditions. Fracture tests were performed over a relevant range of temperatures and crosshead rates to determine and generate a master curve of the subcritical strain energy release rate. Experimental methods utilizing high-speed camera images and digital image correlation to monitor viscoelastic strain recovery in the wake of a propagating crack were explored. The results from this thesis may prove useful in an investigation of the interfacial fracture of these hydrogel systems on several different polymer substrates associated with an industrial manufacturing problem.Master of Science
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Schultz, Jeffrey Patrick. "Modeling Heat Transfer and Densification during Laser Sintering of Viscoelastic Polymers". Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/11091.
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Laser sintering (LS) is an additive manufacturing process which uses laser surface heating to induce consolidation of powdered materials. This work investigates some of the process-structure-property relationships for LS of viscoelastic polymers. A one-dimensional closed-form analytical solution for heating of a semi-infinite body, with a convective boundary condition, by a moving surface heat flux was developed. This solution approximates the shape of the Gaussian energy distribution of the laser beam more accurately than previous solutions in the literature. A sintering model that combines the effects of viscoelastic deformation driven by attractive surface forces and viscous flow driven by curvature-based forces was developed. The powder-bed temperature was approximated using the thermal model developed herein. The effect of the enthalpy of melting for semi-crystalline polymers was accounted for using a temperature recovery approach. Time-temperature superposition was used to account for the temperature dependence of the tensile creep compliance. The results of the combined-mechanism sintering model will be compared to the classic Mackenzie-Shuttleworth sintering model. A lab-scale LS unit was constructed to fabricate test specimens for model validation and to test the applicability of materials to LS. In this work, sintering four materials, polycarbonate (PC) and three molecular weights of polyethylene-oxide (PEO) was predicted using the aforementioned thermal and sintering models. Samples were fabricated using the lab-scale LS unit and the sintered microstructures were investigated using scanning electron microscopy. The rheologic, thermal and physical properties of the materials were characterized using standard methods and the relevant properties were used in the models. The choice of an amorphous polymer, PC, and a semi-crystalline polymer, PEO, affords comparison of the effects of the two material forms on contact growth during LS. The three molecular weights of PEO exhibit significantly different tensile creep compliances, however, the thermal and physical properties are essentially the same, and therefore the effect of molecular weight and subsequently the rheologic characteristics on contact growth during LS will be investigated. The effects of particle size, laser power, and bed temperature were also investigated.Ph. D.
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Bryant, James William Jr. "Prediction of Linear Viscoelastic Response of the Loss Shear Modulus of Polymer-Modified Binders". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/31719.
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Current mathematical models, developed on straight asphalt binders, are inadequate to characterize the frequency dependence of response of polymer-modified asphalt binders. In an earlier study at Virginia Tech, mathematical models were developed to predict the storage and loss shear moduli of polymer-modified binders. However the model developed for the loss shear moduli is limited at high frequency (G" less than or equal to 10^7.5 Pa). This thesis presents a statistical modeling of loss shear modulus of polymer (random copolymers and thermoplastic block copolymers) modified binder. Data from dynamic mechanical analysis on modified binders, at temperatures between 5 and 75°C and frequencies ranging from 0.06 to 0188.5 rad/s, were reduced to dynamic master curves of moduli, and used to develop the model. Twenty-one polymer-binder blends prepared and tested earlier at Virginia Tech where included in the study. Realistic characterization of loss shear moduli values was obtained using the Gompertz statistical model. The model was validated by using mean square error of prediction (MSEP) in which a second set of frequency data was input in the model to obtain the moduli values, which were compared to the measured data of the second set. Although this model was successfully tested for shear loss modulus prediction of polymer-modified binders, caution should be exercised when it is applied, as such a model should be able to predict the storage modulus for a known phase angle.Master of Science
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Verghese, Kandathil Eapen. "Durability of Polymer Matrix Composites for Infrastructure: The Role of the Interphase". Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28817.
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As fiber reinforced polymer matrix composites find greater use in markets such as civil infrastructure and ground transportation, the expectations placed on these materials are ever increasing. The overall cost and reliability have become the drivers of these high performance materials and have led to the disappearance of resins such as bismaleimides (BMI), cyanate esters and other high performance polyimides and epoxys. In their place polymers, such polyester and vinylester have arisen. The reinforcing fiber scenario has also undergone changes from the high quality and performance assured IM7 and AS4 to cheaper and hybrid systems consisting of both glass and low cost carbon. Manufacturing processes have had their share of changes too with processes such as pultrusion and other mass production techniques replacing hand lay-up and resin transfer molding. All of this has however come with little or no concession on material performance. The motivation of the present research has therefore been to try to improve the properties of these low cost composites by better understanding the constituent materials (fiber and matrix) and the region that lies in-between them namely the interphase. In order to achieve this, working with controls is necessary and the present discourse therefore deals with the AS4 fiber system from Hexcel Corporation and the vinyl ester resin, Derakane 441-400 from The Dow Chemical Company. The following eight chapters sum up the work done thus far on composites made with sized fibers and the above mentioned resin and fiber systems. They are in the form of publications that have either been accepted, submitted or going to be submitted to various peer reviewed journals. The sizings used have been poly(vinylpyrrolidone) PVP and Polyhydroxyether (Phenoxy) thermoplastic polymers and G' an industrial sizing material supplied by Hexcel. A number of issues have been addressed ranging from viscoelastic relaxation to enviro-mechanical durability.
Chapter 1 deals with the influence of the sizing material on the fatigue response of cross ply composites made with the help of resin infusion molding. Chapter 2 describes the effects of a controlled set of interphase polymers that have the same chemical structure but differ from each other in polarity. The importance of the atomic force microscope (AFM) to view and perform nano-indentations on the interphase regions has been demonstrated. Finally, it attempts to tie everything together with the help of the fatigue response of the different composites. Chapter 3 deals only with the vinyl ester resin and examines the influence of network structure on the molecular relaxation behavior (cooperativity) of the glassy polymer. It also tries to make connections between structural features of the glass and fracture toughness as measured in its glassy state. Chapter 4 extends the results obtained in chapter 3 to examine the cooperativity of pultruded composites made with the different sizings. A correlation between strength and cooperativity is found to exist, with systems having greater cooperativity being stronger. Chapter 5 moves into the area of hygrothermal aging of Derakane 441-400 resin. It looks specifically at identifying a mechanism for the unusual moisture uptake behavior of the polymer subjected to a thermal-spiking environment. This it does by identifying the presence of hydrogen bonding in the resin. Finally, chapters 6 to 8 present experimental and analytical results obtained on PVP K90, Phenoxy and G' sized, AS4/Derakane 411-350 LI vinyl ester composites that were pultruded at Strongwell Inc., on their lab-scale pultruder in Bristol, Virginia.Ph. D.
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Jackson, Angela. "Electrochemical quartz crystal microbalance studies of electroactive polymer films in gravimetric and viscoelastic regimes". Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/30059.
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Under rigid film conditions the Electrochemical Quartz Crystal Microbalance (EQCM) acts as a gravimetric probe for mass changes occurring during electroactive film redox switching. The sensitivity of the technique allows one to monitor redox driven population changes of both ion and solvent between an electroactive film and its bathing solution. The interpretation of EQCM data to date has mainly been of a qualitative nature. The approach taken here is a quantitative one and attempts to provide kinetic information (rate constants) for specific electro(chemical) steps. The model to be considered is an electroactive redox polymer under permselective conditions. A new 3D vector (U) representation is developed to describe the redox and compositional state of a system in terms of injected electronic charge (Q), potential (E) and a mobile species population parameter (E), which can be calculated from film mass changes (AM). Poly(vinylferrocene) is then used as a model system to validate the methodology. The kinetics of redox switching of poly(vinylferrocene) are analysed using cyclic voltammetry and quantitative data is extracted from the relative fluxes of water and counter ion during the redox cycle. Solvent populations are extracted from the data and a new theoretical model shows solvent activity parameter effects (polymer/solvent interactions) are evident during redox switching. Crystal impedance spectra provide a diagnostic for rigid vs. viscoelastic film behaviour. The evolution from gravimetric to viscoelastic responses of poly(3-methylthiophene)-loaded thickness shear mode resonators was investigated. The relationship between ion and solvent populations (composition) and shear moduli (dynamics) was explored. Extraction of viscoelastic film characteristics, i.e. shear modulus, film thickness and film density is achieved by equivalent circuit modelling. The problem of the uniqueness of fit is tackled by a new approach in which impedance and coulometric data from the acoustically thin regime define a solvent swelling factor. Extrapolation into the acoustically thick regime using the solvent swelling factor defines the film thickness and film density. The method is validated using crystal impedance data for poly(3-methylthiophene) films exposed to propylene carbonate.
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Liu, Alice Weimin. "Viscoelastic flow of polymer solutions around arrays of cylinders : comparison of experiment and theory". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10409.
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Hanna, Richard Matthew 1979. "Viscoelastic polymer analysis : experimental, data analysis, and modeling techniques applied to cellular silicone foam". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/89357.
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Elseifi, Mostafa. "Viscoelastic Modeling of Straight and Modified Binders at Intermediate and High Temperatures". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/36445.
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The increase and change in traffic loading in recent years has resulted in the introduction of a new range of high performance asphalt binders. These new binders known as modified asphalt binders, have a more complex behavior than traditional binders. A review of the current mathematical models shows that most of them suffer from different drawbacks that make them inadequate for their intended application. To describe the behavior of straight and modified binders in the thermorheologically simple linear viscoelastic region, two models are proposed. Models to characterize the absolute value of the complex shear modulus (|G*|) and the phase angle (d) were developed using the matching function approach and validated by an experimental program. The dynamic mechanical properties of two typical paving grade binders and three modified binders were tested at intermediate and high service temperatures. Short-term and long-term aging were simulated by the rolling thin film oven test and the pressure aging vessel test, respectively. A dynamic shear rheometer with parallel plate configuration was used to conduct the dynamic mechanical tests at frequencies between 0.06 to 188.5 rad/sec and temperatures ranging from 5 to 75°C. Prior to the frequency sweeps, strain sweeps were performed to establish the linear viscoelastic region. Results indicated a strong susceptibility to the defined strain at intermediate temperatures; however, strain susceptibility was less pronounced at high temperatures. Frequency sweeps were then conducted at a constant strain corresponding to greater than 95% of the initial complex shear modulus as established by AASHTO TP5 for straight asphalts. The Time-Temperature Superposition Principle was used to construct the master curves. The shift factors were determined based on the complex shear modulus master curves and verified for the phase angle, storage shear modulus and loss shear modulus.
After construction of the master curves, non-linear regression was used to fit the proposed models to the experimental data. Comparison between the measured and predicted values indicated a good agreement for frequencies higher than 10-5 rad/sec. The phase angle model was found to adequately describe unmodified binder with a small percentage of errors (less than 6%). On the other hand, the phase angle model was found unable to simulate the plateau region observed for polymer-modified binders. However, the error in this case was found to be relatively small (from zero to 10%).
The ability of the models to estimate other viscoelastic functions, e.g. storage shear modulus (G'), loss shear modulus (G"), and relaxation spectrum (H(t)), was found to be adequate.
Master of Science
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Thompson, Thaddeus. "Rheological Study of Linear and Nonlinear Viscoelastic Behavior for Silica-Reinforced Polybutadiene and Polystyrene". University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1134566032.
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Kashani, Pooria Sharif. "An ex-situ material state monitoring of curing based on viscoelastic properties in polymer composites". Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1563.
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It is well known that time and temperature are not direct measurements of either material state during cure or mechanical properties after cure in polymer composites. Rather, in current practice, the viscoelastic properties and mechanical properties during cure are merely assumed based on an extensive statistical data of time and temperature history of the material. This practice is time-consuming and costly. In this study, an ex-situ estimation of the actual material states using advanced analytical instruments has been proposed and validated. An encapsulated sample rheometer was used as the main ex-situ instrument capable of measuring with high repeatability and robustness necessary for the validation of viscoelastic curing models of composites (especially prepregs) at production level. This rheometer was coupled with Differential Scanning Calorimetry (DSC) to obtain a correlation of the key variables of curing and the actual material states. Experimental and analytical modeling studies of the viscoelastic properties and thermal properties of four commercial prepregs were conducted using these instruments. These key cure variables were directly correlated with the viscoelastic states of the material during cure. The viscoelastic properties such as storage modulus, loss modulus, and tanδ and the glass transition temperature of the Advanced Composite Group (ACG) MTM45 and MTM45-1 prepregs and Cytec 977-2 PW and 977-2 UD prepregs were measured using the rheometer during different isothermal cure cycles below the final glass transition temperature (g∞ T). Thermal analysis of 977-2 PW and 977-2 UD prepregs was obtained using the DSC and these thermal results were correlated to the rheometry measurements. Glass transition temperatures (g T) of the cure cycles were measured using both rheometry and DSC techniques. A semi-empirical curing model, based on the viscoelastic properties of prepregs, was developed and compared with the experimental data collected at a constant frequency. A process engineer could use this curing model to monitor, control, and optimize a cure process, and to aid in the curing of parts that have time and temperature history discrepancies. This model can be statistically correlated to critical composite properties and can be validated with time and temperature feedback. Therefore, temperature sensors, such as thermocouples, would remain as the primary in-situ sensors and there would be no need for material state sensors inside the autoclave or other processing units.Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Mechanical Engineering
"December 2007."
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Kashani, Pooria Sharif Minaie Bob. "An ex-situ material state monitoring of curing based on viscoelastic properties in polymer composites /". Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1563.
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Gahvari, Fariborz. "Modeling of the linear viscoelastic response of polymer modified asphalt binders at intermediate and high temperatures". Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08272007-163901/.
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Wang, FeI. "A Numerical and Experimental Study of the Thermodynamically Consistent Nonlinear Viscoelastic Response of an Expoxy Polymer in the Glassy Regime". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163791491.
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Garg, Deepak. "Simulation of Thermal Transport in a Nanocomposite Blow Mold". Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1257829799.
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Reubush, Stacey Diane. "Effects of Storage on the Linear Viscoelastic Response of Polymer-Modified Asphalt at Intermediate to High Temperatures". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/30838.
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The design and construction of roads with longer service lives is a priority of civil engineers. The selection of appropriate highway materials with respect to climatic and loading conditions may significantly increase the lifespan of pavements. One material receiving interest in the area of improved roadway performance is polymer-modified binder. The complex behavior of polymer-modified binders, particularly over time, is not yet well-understood by engineers. Therefore, an experimental study was performed to determine the effects of four years of storage at room temperatures (23°C) on the dynamic mechanical properties of polymer-modified binders at intermediate and high temperatures. A typical paving grade (AC-20) and three elastomeric modifiers, each at three concentrations were used. Initial tests were performed in 1995 to evaluate the effects of short-term aging as simulated by the Rolling Thin Film Oven Test (RTFOT) procedure. This study encompasses a second phase of testing occurring after the modified binders were stored at ambient room temperature (23°C) for four years. The study found that significant changes affecting the dynamic response of binders occur during long term storage at a temperature of 23°C. These changes are dependent on the type and concentration of modifier and may be beneficial. Additionally, four mathematical models describing the dynamic response of binders were evaluated and found to be variable in their ability to accurately predict response of modified binders. Most of these models are not well suited for prediction of the response of stored binders.Master of Science
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Debnath, Dibyendu. "SYNTHESIS AND VISCOELASTIC PROPERTIES OF GELS OBTAINED FROM LINEAR AND BRANCHED POLYMERS". University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525400236218684.
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Debnath, Dibyendu Debnath. "SYNTHESIS AND VISCOELASTIC PROPERTIES OF GELS OBTAINED FROM LINEAR AND BRANCHED POLYMERS". University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525398351097978.
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Borzacchiello, Domenico. "Three-dimensional numerical simulation of encapsulation in polymer coextrusion". Phd thesis, Université Jean Monnet - Saint-Etienne, 2012. http://tel.archives-ouvertes.fr/tel-00976093.
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The objective of the present work is the analysis of coextrusion processes by numerical simulation based on phase-field modeling of stratified confined flows. The study of such flows is motivated by the presence of complex phenomena appearing in a vast range of industrial operational coextrusion conditions due to the differences in the components properties and their viscoelastic behavior. The basic idea in coextrusion is to combine several layers of different polymers in a common die, to form a unique product with enhanced properties. However, the existence of fluid stratification in the die is responsible of a severe distortion of the interface between the fluid components, causing a loss of efficiency for the whole process. Experimental data show that, even if a stratified initial configuration is imposed at the die entry, one fluid eventually encapsulates the other in most of the flow condition analyzed. The intrinsically three-dimensional nature of this phenomenon has required the development of a three-dimensional flow solver based on the finite volume discretization of the Navier-Stokes equations for incompressible and isothermal flow, together with differential nonlinear constitutive equations (Giesekus, PTT models). The presence of two fluid phases is taken into account by a phase field model that implies the solution of an additional scalar equation to describe the evolution of the interface on a fixed Eulerian grid. This model, unlike others of the same family, has a thermodynamic derivation and can be physically interpreted. The proposed method is tested against experimental data and solutions already available in literature and a study of coextrusion in rectangular dies is performed to identify the dependence of encapsulation on the flow parameters
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Kostourou, Konstantina Verfasser], Ralf [Akademischer Betreuer] Seemann, Stephan [Akademischer Betreuer] [Herminghaus i Sarah [Akademischer Betreuer] Köster. "Dewetting of Polymer Thin Films on Viscoelastic Substrates / Konstantina Kostourou. Gutachter: Stephan Herminghaus ; Sarah Köster. Betreuer: Ralf Seemann". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2010. http://d-nb.info/1042971544/34.
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May, Jessica Anne. "Development of an Experimentally Validated Non-linear Viscoelastic Viscoplastic Model for a Novel Fuel Cell Membrane Material". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/46977.
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The proton exchange membrane (PEM) is a key component in proton exchange membrane fuel cells (PEMFCs). During standard fuel cell operation, the PEM degrades due to cyclic hygrothermal loads, resulting in performance loss or total failure. Improvement of current PEM materials and development of cheaper, more durable materials is essential to the commercialization of PEMFC technology, which may provide an attractive alternative energy source for transportation.
This dissertation investigates a new PEM material which is a blend of sulfonated perfluorocyclobutane (PFCB) and polyvinylidene fluoride (PVDF). Hereafter referred to as PFCB/PVDF, this polymer blend was developed by General Motors Company(TM) as a potential replacement for the current benchmark PEM, the DuPont(TM) product Nafion®. The PFCB/PVDF blend is less costly to manufacture than standard PEM materials and investigations into its long-term mechanical durability are ongoing.
Specifically, this document discusses the experimental and analytical work performed in the material characterization, constitutive expression development, and implementation of that expression into uniaxial and biaxial finite element geometries. Extension of the model to time-varying temperature and moisture conditions is also explored.
The uniaxial finite element model uses a non-linear viscoelastic viscoplastic (NLVE-VP) constitutive expression with parameters determined from uniaxial creep and recovery experiments at a single environmental condition. Validation tests show that this model accurately predicts results from uniaxial tension experiments, such as stress relaxation, force ramp, and multistep creep and recovery, to stresses of 8 MPa and strains approaching 15%, which is the maximum hygrothermal strain expected in an operating fuel cell.
The biaxial finite element model combines the NLVE-VP constitutive expression with the geometry of a pressure-loaded blister experiment, which better approximates fuel cell membrane constraints. Results from the biaxial model are compared to experimental results. The model accurately predicts strain in the blister test but predicts stresses that differ from those estimated from blister curvature.
Additionally, it is found that both the non-linear viscoelastic and viscoplastic parameters are functions of the operating environment. Future experimental work is needed to characterize that dependence before the constitutive model is used to simulate the response of the PFCB/PVDF blend to fuel cell operating conditions.Ph. D.
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Chan, Kathleen Joyce. "Investigation of Processing Conditions and Viscoelastic Properties on Frictional Sliding Behavior of Unidirectional Carbon Fiber Epoxy Prepreg". Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/86444.
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The quality of continuous fiber reinforced polymer matrix composite parts and structures depends strongly on the friction during the composite forming process. The two major types of friction that cause deformations during this process are ply-ply friction and tool-ply friction. One of the challenges in the composite forming process is the occurrence of wrinkling and shape distortion of the fabric caused by the surface differences between the forming tool and surface of the laminate. Frictional measurements of composites can vary widely depending on processing parameters, measurement technique, and instruments used.
In this study, a commercial rheometer was used to evaluate tool-ply friction of unidirectional carbon fiber epoxy prepreg at various contact pressures, temperatures and sliding velocities. Viscoelastic properties such as the complex viscosity (η*), storage modulus (G'), loss modulus (G"), and loss factor (tan δ) were used to determine the critical transition events (such as gelation) during cure. An understanding of changes in viscoelastic properties as a function of time, temperature, and cure provides insight for establishing a suitable processing range for compression forming of prepreg systems.
Surface imaging results were coupled with rheological results to qualitatively examine the effects of processing parameters on prepreg distortions. Changes in gap height over the measurement interval qualitatively describe the changes in contact area and contact mechanisms between the tool-ply surfaces. The results indicate that friction behavior of the prepreg system is a contribution of adhesive and frictional forces, where increase in viscosity, reduction in gap height, and cure of the sample correlate to higher friction values.Master of Science
The quality of composite parts and structures depends strongly on the friction present during the composite forming process. One of the major challenges in the forming process is the occurrence of wrinkling and shape distortions of the fabric caused by the surface differences between the forming tool and material. The presence of these defects can compromise the final material property and lead to failure when in use. Frictional measurements of composites can vary widely depending on processing parameters, measurement technique, and instruments used. The extent of interaction between the tool and surface of the material depends on the tooling height, and by extension, contact area, which cannot easily be monitored with traditional test designs. A commercial rheometer was used in this study to evaluate tool-ply friction of unidirectional carbon fiber epoxy prepreg at various contact pressures, temperatures, and sliding velocities. Gap height and torque were monitored to provide information on the frictional dependence of processing parameters. In addition, surface-imaging results were coupled with rheological results to examine the relationship between friction and fiber distortions. The understanding of changes in material property with respect to the tooling process is the key to optimizing the composite forming process.
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Carter, Justin B. "Vibration and Aeroelastic Prediction of Multi-Material Structures based on 3D-Printed Viscoelastic Polymers". Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1627048967306654.
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De, Paoli Federico. "Measuring Polydimethylsiloxane (PDMS) Mechanical Properties Using Flat Punch Nanoindentation Focusing on Obtaining Full Contact". Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5881.
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In this research, the materials used were the Polydimethylsiloxane (PDMS) polymers. PDMS mechanicals properties were measured using a customized version of the nanoindentation test using a flat punch tip. The method is proposed in Chapter 3 and it is used to calculate the elastic modulus of different PDMS samples. The samples tested were both produced specifically for this research and available in the laboratory’s storage. They all present different levels of cross-linking degree.
It is quite common to not have full contact between the cylindrical flat punch and the sample because of the unavoidable tilt. The new method guarantees establishing full contact between the sample and the tip. The tip used for this purpose is a flat punch tip. The Young’s moduli of the following samples were calculated: 10:1, 30:1 and 50:1. The Young’s moduli found were: 2.85±0.001 MPa for the 10:1 sample, 0.34±0.001 MPa for the 30:1 sample and 0.15±0.002 MPa for the 50:1 sample. All the experiments were repeated at least three times to assure the validity and the repeatability of the method. The results were then compared with values available in the literature.
The same method was applied to analyze the viscosity of the samples. Even if a mathematical result was not obtained, data and analysis through graphical representations are available in this thesis. The sample tested was a PDMS sample with a cross-linking degree of 30:1. The experiment has been repeated three times
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De, Brito Milena. "Investigation of interpenetrating polymer networks and recent UV curable chemistries". Thesis, Mulhouse, 2011. http://www.theses.fr/2011MULH5772/document.
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Le sujet de cette thèse concerne le développement et la caractérisation de résines photosensibles pour le prototypage rapide. L'étude a tout d'abord consisté à optimiser des systèmes photoréticulables commerciaux : systèmes hybrides acrylates/époxydes. La réactivité des différentes formulations préparées ainsi que leurs propriétés thermomécaniques ont pu être évaluées grâce à la spectroscopie infrarouge à transformée de Fourier résolue dans le temps (RT-FTIR) et par analyse mécanique dynamique (DMA). En parallèle, une étude plus fondamentale visant à mieux comprendre et à contrôler la formation de réseaux polymères interpénétrés simultanés méthacrylate/époxyde a été menée. L'influence de paramètres physico-chimiques tels que l'intensité lumineuse, la concentration en photoamorceur sur les propriétés finales du matériau a notamment été abordée. Ensuite, des résines dont la chimie est moins conventionnelle ont été considérées. Comme très peu de ces monomères sont disponibles commercialement, certains d'entre eux ont dû être synthétisés. Certaines formulations ont démontré non seulement une bonne réactivité mais aussi d'intéressantes propriétés thermomécaniques et une limitation du retrait de polymérisation. Finalement, une méthode de mesure du retrait linéaire simple et facile à mettre en œuvre a été mise en place afin de comparer les différents systèmes chimiques proposés au cours de la thèse. L'utilisation de cet outil est très appréciable car il pourrait permettre de choisir le type de formulations induisant le moins de retrait possible lors de la réalisation d'un objet couche par coucheThe aim of this thesis is to develop and characterize UV curable resins for rapid prototyping application. The study started with the optimization of commercially available hybrid acrylate/epoxide systems (IPNs) commonly used in this industrial field. The reactivity of the different tested formulations in conjunction with their thermomechanical properties have been assessed by means of Real time Fourier transform infrared spectroscopy (RT FTIR) and Dynamic mechanical analysis (DMA). In the meantime, a more academic study has been performed on an epoxide/methacrylate mixture in order to get a better understanding and a control of the IPN formation. The influence of the light intensity and the photoinitiator concentration on the final properties has been examined. Then, UV curable resins whose chemistry is less conventional have been considered. Owing to the lack of commercial availability of some monomers, time has been spent to synthesize them. Some formulations display promising features especially in terms of reactivity, thermomechanical properties and linear shrinkage. Finally, a simple method to measure linear shrinkage has been set up to compare the different systems proposed during the thesis and thus evidences the less shrinkable UV curable system
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Omowunmi, Sunday Chima. "Modelling the nonlinear dynamics of polymer solutions in complex flows". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/modelling-the-nonlinear-dynamics-of-polymer-solutions-in-complex-flows(3230a688-0ea4-4620-bda1-396346feb645).html.
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The flow of polymer solutions in the high Elasticity number, El, regime in complex geometries may lead to strong viscoelastic behaviour and eventually become unstable as the Weissenberg number, Wi, is increased beyond a critical level. So far, the success of numerical simulations in predicting the highly non-linear behaviour of polymer solutions in complex flows has been limited. In this thesis, selected constitutive models are evaluated under the high El flow regime in the cross-slot and contraction benchmark flows using a numerical technique based on the finite volume method. The numerical technique is implemented within the OpenFOAM framework and thoroughly validated in the benchmark flow. A modification to the FENE dumbbell model based on the non-affine deformation of polymer solutions is proposed, which enabled the prediction of some non-linear material functions and also enhanced numerical stability, allowing a higher Wi to be attained. Asymmetric flow instability in the cross-slot flow has been studied. Time-dependent stability diagrams were constructed based on Wi and the strain, ε, both of which govern the stretching of a polymer chain. In the contraction flow, elastic instability is simulated for the first time in this geometry. Substantial time-dependent asymmetric flow patterns were predicted as seen in experiments. The effect of the contraction ratio is investigated through a stability diagram. Three-dimensional finite element simulations were also carried out to study the effect of the aspect ratio in the contraction flow of a Phan-Thien-Tanner fluid. The simulations suggest that a lip vortex mechanism is a signature for the onset of strong viscoelastic behaviour.
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Tong, Xiaolong. "A Constitutive Model for Crushable Polymer Foams Used in Sandwich Panels: Theory and FEA Application". University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1596806015399848.
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Göbel, Luise [Verfasser], Andrea [Akademischer Betreuer] Osburg, Bernhard [Gutachter] Pichler i Carsten [Gutachter] Könke. "Experimental and semi-analytical multiscale approaches for the characterization of the elastic and viscoelastic behavior of polymer-modified cement-based materials / Luise Göbel ; Gutachter: Bernhard Pichler, Carsten Könke ; Betreuer: Andrea Osburg". Weimar : Professur Bauchemie und Polymere Werkstoffe, 2018. http://d-nb.info/1176197010/34.
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Singh, Hitendra Kumar. "Lifetime Prediction and Durability of Elastomeric Seals for Fuel Cell Applications". Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/27658.
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Polymer electrolyte membrane (PEM) fuel cell (FC) stacks require elastomeric gaskets for each cell to keep the reactant gases within their respective regions[1]. If any gasket degrades or fails, the reactant gases can leak or mix with each other directly during operation or standby, affecting the overall operation and performance of the FC. The elastomeric gaskets used as FC seals are exposed to a range of environmental conditions, and concurrently, subjected to mechanical compression between the bipolar plates forming the cell. The combination of mechanical stress and environmental exposure may result in degradation of the seal material[2] over a period of time. In order to address the durability and make reliability predictions, the long-term stability of the gaskets in FC assemblies is critical. The aim of this study is to investigate the performance of elastomeric seals in a simulated FC environment in the presence of mechanical stresses. The overall scope of the study includes mechanical and viscoelastic properties characterization, and lifetime durability predictions based on an accelerated characterization approach.
With the help of finite element analysis software, ABAQUS, a fixture was designed to perform strain-based accelerated characterization of seal material in air, deionized (DI) water, 50v/50v ethylene glycol/water solution, and 0.1M sulfuric acid solution. Dogbone samples were strained to different levels in the custom fixture and submerged in liquid solutions at 90°C and in air at 90°C and 120°C. It was observed that mechanical properties such as tensile strength, strain to break, 100% modulus, crosslink density, and tensile set degrade due to aging and the extent of change (increase or decrease) depends significantly on the strain level on the specimen.
Trouser tear tests were conducted on reinforced specimens in air and deionized water (DI) to evaluate the tear resistance of an elastomeric seal material intended for proton exchange membrane fuel cells. Plots relating the crack growth rate with tearing energy were obtained at various temperatures and provided significant insight into the rate and temperature dependence of the tearing strength of the seal material. Stick-slip crack propagation was observed at all temperatures and loading rates, although the behavior was suppressed significantly at low loading rates and high temperatures. Crack growth rate versus tearing energy data at different temperatures was shifted to construct a master curve and an estimate on the threshold value of tear energy was obtained which may be helpful in designing components where material tear is of concern. Strain energy release rate (SERR) value, calculated using the J-integral approach for a pre-existing crack in ABAQUS, was used to estimate the crack growth rate in a given seal cross-section to predict lifetime.
In order to assess the viscoelastic behavior and to investigate the long term stress relaxation behavior of the seal material, compression stress relaxation (CSR) tests were performed on molded seals, called as SMORS, over a range of environmental conditions using a custom-designed fixture. The effect of temperature and environment was evident on material property changes and presented in terms of momentary properties and stress relaxation behavior. Various mechanisms involved in material degradation, chain scission and crosslinking, were suggested and insights were gained into how cure state and level of antidegradants in a material dictate the material behavior during the first phase of environmental exposure leading to change in material properties. Ring samples made of silicone were also tested using the fixture to obtain insight additional into material degradation due to aging. Results presented from testing on SMORS showed a lot more variation in data as compared to neat silicone rings due to the complexity involved in making SMORS.
For understanding the deformation behavior of an elastomeric seal and its sealing performance, finite element characterization of seal cross-section was carried out on O-ring and SMORS cross-section. The effect of a seal's layout on distribution and magnitude of contact stresses and contact width was investigated for the O-ring and the information obtained thereby helped to analyze a complex assembly such as SMORS, where several interfaces and boundary conditions are involved. Stress/strain profiles were generated to visualize their concentration and distribution in the seal cross-section. Frictionless and rough interfacial conditions between seal material and platens were assumed and it was found that its effect on contact width and peak contact pressure was insignificant. Results obtained from FEA on SMORS were validated through comparison with contact mechanics approach and experimental data and it was found that Lindley's equation correlates well with experimental data whereas ABAQUS overestimates the load values at a given compression. Lindley's approach may be used to develop contact pressure profiles that may help estimate peak contact pressure at a given time so leaking can be avoided.Ph. D.
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Oliveira, Joao Antonio Pinto de. "Análise numérica de tensões induzidas pelo escoamento não isotérmico de um polímero no preenchimento de cavidades de paredes finas". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/75762.
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O processo de moldagem por injeção de peças de paredes finas apresenta diferenças significativas em relação a processos convencionais de moldagem por injeção de termoplásticos. Processos de paredes finas são caracterizados pelo preenchimento de cavidades com espessuras inferiores a 1 mm utilizando velocidades de preenchimento elevadas. Estes dois fatores afetam o desenvolvimento de tensões induzidas pelo escoamento durante o preenchimento da cavidade, sendo que não foram encontrados na literatura estudos de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas. Neste trabalho são apresentados resultados de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas em comparação com resultados de simulação com cavidades características de processos convencionais. Para o cálculo das tensões induzidas pelo escoamento foi utilizado o modelo incompressível de Leonov. Para isso foi desenvolvida uma metodologia numérica para tratar problemas não isotérmicos utilizando o pacote CFD OpenFOAM. Foi utilizada a abordagem não acoplada, ou seja, o comportamento viscoelástico não é considerado na obtenção dos campos de velocidade, pressão e temperatura. Esta metodologia foi utilizada na simulação do preenchimento de cavidades bidimensionais. Os resultados indicaram que as tensões são influenciadas fortemente pela espessura da cavidade enquanto a velocidade de escoamento causou pequena variação das tensões induzidas pelo escoamento. Este trabalho mostrou que as tensões induzidas pelo escoamento não podem ser desconsideradas na produção de peças moldadas por injeção pelo processo de paredes finas.Thin wall injection molding process of thermoplastics has significant differences compared to conventional injection molding process. Thin wall processes are characterized by cavities thinner than 1 mm and very high injection velocities. Although these two factors are expected to increase the flow induced stresses development during cavities filling, no previous study on this subject has been found in literature. In the present work, flow induced stresses under thin wall injection molding conditions are calculated using a viscoelastic model and compared to the results obtained under conventional injection conditions. In order to do this, a numerical methodology, based on the solver viscoelasticInterFoam, was developed in the OpenFOAM package to deal with the non-isothermal flow occurring during the mold filling stage. A non-coupled approach was used to calculate the stress field, i.e., the viscoelastic behavior was not considered in the determination of velocity, pressure and temperature fields. This methodology was used in the analysis of the filling stage of two-dimensional cavities. The results indicated that the cavity thickness has more influence on the flow induced stresses than the injection velocity. The obtained results also indicate that the flow induced stresses cannot be neglected in thin wall injection molding processes.
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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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Julius, Michael J. "Time, temperature and frequency viscoelastic behavior of commercial polymers". Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=2858.
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Thesis (M.S.)--West Virginia University, 2003.Title from document title page. Document formatted into pages; contains xv, 114 p. : ill. Includes abstract. Includes bibliographical references (p. 112-114).
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Martín, Guillermo Palmer. "Estudo da viscoelasticidade linear e não linear de misturas de PP/PA-6 compatibilizadas ou não". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-19042007-155843/.
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Neste trabalho estudou-se o comportamento reológico e morfológico da mistura polimérica imiscível de polipropileno e poliamida. Como resultado deste estudo obtiveram-se valores de tensão interfacial entre 10mN/m e 13mN/m. A tensão interfacial diminuiu em até 87% quando a mistura é compatibilizada com polipropileno maleado. A análise morfológica no regime de viscoelasticidade linear quando avaliada uma morfologia de emulsão de poliamida em polipropileno revelou diâmetro médio da fase dispersa entre 1,5µm e 20µm. O diâmetro das gotas da fase dispersa diminuiu com a adição de polipropileno maleado chegando a reduções de até 98%, mantendo-se constante a concentração da fase dispersa. No regime de viscoelasticidade não linear foram testados modelos para avaliar o comportamento da mistura em fluxos de cisalhamento e extensão, sendo que somente para os fluxos de extensão foi obtida boa correlação dos resultados experimentais com as previsões teóricas.Rheological and morphological behaviour of polypropylene and polyamide polymer blend was studied. The values of interfacial tension were obtained between 10mN/m and 13mN/m. The interfacial tension decreased in 87% for compatibilized blend. Morphology analysis for linear viscoelastic regime shows dispersed drop diameter between 1,5µm and 20µm. The diameter of the drops decreased with the addition of maleic polypropylene reducing until 98%, keeping constant the concentration of the disperse phase. In non linear viscoelastic regime different models were tested to evaluate the behavior of the blends in shear and elongacional flows. However, only the elongacional flow results were acquired with theoretical - experimental corroboration.
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Chaikittiratana, Arisara. "Non-linear viscoelastic strain analysis for engineering polymers". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342239.
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Ahmad, Naveed. "Passive Damping in Stiffened Structures Using Viscoelastic Polymers". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/79566.
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Noise and vibration suppression is an important aspect in the design process of structures and machines. Undesirable vibrations can cause fatigue in a structure and are, therefore, a risk to the safety of a structure. One of the most effective and widely used methods of mitigating these unwanted vibrations from a system is passive damping, by using a viscoelastic material. This dissertation will primarily focus on constrained layer passive damping treatments in structures and the investigation of associated complex modes. The key idea behind constrained damping treatment is to increase damping as affected by the presence of a highly damped core layer vibrating mainly in shear. Our main goal was to incorporate viscoelastic material in a thick stiffened panel with plate-strip stiffeners, to enhance the damping characteristics of the structure.
First, we investigated complex damped modes in beams in the presence of a viscoelastic layer sandwiched between two elastic layers. The problem was solved using two approaches, (1) Rayleigh beam theory and analyzed using the principle of virtual work, and (2) by using 2D plane stress elasticity based finite-element method. The damping in the viscoelastic material was modeled using the complex modulus approach. We used FEM without any kinematic assumptions for the transverse shear in both the core and elastic layers. Moreover, numerical examples were studied, by including complex modulus in the base and constraining layers. The loss factor was calculated by modal strain energy method, and by solving a complex eigenvalue problem. The efficiency of the modal strain energy method was tested for different loss factors in the core layer. Complex mode shapes of the beam were also examined in the study, and a comparison was made between viscoelastically damped and non-proportionally damped structures.
Secondly, we studied the free vibration response of an integrally stiffened and/or stepped plate. The stiffeners used here were plate-strip stiffeners, unlike the rib stiffeners often investigated by researchers. Both plate and stiffeners were analyzed using the first-order shear deformation theory. The deflections and rotations were assumed as a product of Timoshenko beam functions, chosen appropriately according to the given boundary conditions. Unlike Navier and Levy solution techniques, the approach used here can also be applied to fully clamped, free and cantilever supported stiffened plates. The governing differential equations were solved using the Rayleigh-Ritz method. The development of the stiffness and the mass matrices in the Ritz analysis was found to consume a huge amount of CPU time due to the recursive integration of Timoshenko beam functions. An approach is suggested to greatly decrease this amount of CPU time, by replacing the recursive integration in a loop structure in the computer program, with the analytical integration of the integrand in the loop. The numerical results were compared with the exact solutions available in the literature and the commercially available finite-element software ABAQUS. Some parametric studies were carried out to show the influence of certain important parameters on the overall natural frequencies of the stiffened plate.
Finally, we investigated the damped response of an adhesively bonded plate employing plate-strip stiffeners, using FSDT for both the plate and stiffeners. The problem was analyzed using the principle of virtual work. At first, we did not consider damping in the adhesive in order to validate our code, by comparing our results with those available in the literature as well as with the results obtained using ABAQUS 3D model. The results were found to be highly satisfactory. We also considered the effect of changing the stiffness of the adhesive layer on the vibration of the bonded system. As a second step, we included damping in the stiffened structure using complex modulus approach, a widely used technique to represent the rheology of the viscoelastic material. We observed an overall increase in the natural frequencies of the system, due to the damping provided by the viscoelastic material. Moreover, it was noticed that when the thickness of the adhesive layer is increased, the natural frequencies and loss factor of the stiffened structure decrease. A viscoelastic material with high loss factor and small thickness will be a perfect design variable to obtain overall high damping in the structure.Ph. D.
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Wu, Lei. "The dynamic properties of voided polymers". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/16968.
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