Academic literature on the topic 'Viscoelasticity. Shear (Mechanics)'
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Journal articles on the topic "Viscoelasticity. Shear (Mechanics)"
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Azaiez, J., and G. M. Homsy. "Linear stability of free shear flow of viscoelastic liquids." Journal of Fluid Mechanics 268 (June 10, 1994): 37–69. http://dx.doi.org/10.1017/s0022112094001254.
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The effects of viscoelasticity on the hydrodynamic stability of plane free shear flow are investigated through a linear stability analysis. Three different rheological models have been examined: the Oldroyd-B, corotational Jeffreys, and Giesekus models. We are especially interested in possible effects of viscoelasticity on the inviscid modes associated with inflexional velocity profiles. In the inviscid limit, it is found that for viscoelasticity to affect the instability of a flow described by the Oldroyd-B model, the Weissenberg number, We, has to go to infinity in such a way that its ratio to the Reynolds number, G ∞ We/Re, is finite. In this special limit we derive a modified Rayleigh equation, the solution of which shows that viscoelasticity reduces the instability of the flow but does not suppress it. The classical Orr–Sommerfeld analysis has been extended to both the Giesekus and corotational Jeffreys models. The latter model showed little variation from the Newtonian case over a wide range of Re, while the former one may have a stabilizing effect depending on the product ςWe where ς is the mobility factor appearing in the Giesekus model. We discuss the mechanisms responsible for reducing the instability of the flow and present some qualitative comparisons with experimental results reported by Hibberd et al. (1982), Scharf (1985 a, b) and Riediger (1989).
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Luo, Zheng Yuan, and Bo Feng Bai. "Dynamics of capsules enclosing viscoelastic fluid in simple shear flow." Journal of Fluid Mechanics 840 (February 14, 2018): 656–87. http://dx.doi.org/10.1017/jfm.2018.88.
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Previous studies on capsule dynamics in shear flow have dealt with Newtonian fluids, while the effect of fluid viscoelasticity remains an unresolved fundamental question. In this paper, we report a numerical investigation of the dynamics of capsules enclosing a viscoelastic fluid and which are freely suspended in a Newtonian fluid under simple shear. Systematic simulations are performed at small but non-zero Reynolds numbers (i.e. $Re=0.1$) using a three-dimensional front-tracking finite-difference model, in which the fluid viscoelasticity is introduced via the Oldroyd-B constitutive equation. We demonstrate that the internal fluid viscoelasticity presents significant effects on the deformation behaviour of initially spherical capsules, including transient evolution and equilibrium values of their deformation and orientation. Particularly, the capsule deformation decreases slightly with the Deborah number De increasing from 0 to $O(1)$. In contrast, with De increasing within high levels, i.e. $O(1{-}100)$, the capsule deformation increases continuously and eventually approaches the Newtonian limit having a viscosity the same as the Newtonian part of the viscoelastic capsule. By analysing the viscous stress, pressure and viscoelastic stress acting on the capsule membrane, we reveal that the mechanism underlying the effects of the internal fluid viscoelasticity on the capsule deformation is the alterations in the distribution of the viscoelastic stress at low De and its magnitude at high De, respectively. Furthermore, we find some new features in the dynamics of initially non-spherical capsules induced by the internal fluid viscoelasticity. Particularly, the transition from tumbling to swinging of oblate capsules can be triggered at very high viscosity ratios by increasing De alone. Besides, the critical viscosity ratio for the tumbling-to-swinging transition is remarkably enlarged with De increasing at relatively high levels, i.e. $O(1{-}100)$, while it shows little change at low De, i.e. below $O(1)$.
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Nashima, Takeshi. "Method of Viscoelasticity Measurement under Shear-Flow." Nihon Reoroji Gakkaishi 48, no. 5 (December 15, 2020): 251–57. http://dx.doi.org/10.1678/rheology.48.251.
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AGGARWAL, NISHITH, and KAUSIK SARKAR. "Deformation and breakup of a viscoelastic drop in a Newtonian matrix under steady shear." Journal of Fluid Mechanics 584 (July 25, 2007): 1–21. http://dx.doi.org/10.1017/s0022112007006210.
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The deformation of a viscoelastic drop suspended in a Newtonian fluid subjected to a steady shear is investigated using a front-tracking finite-difference method. The viscoelasticity is modelled using the Oldroyd-B constitutive equation. The drop response with increasing relaxation time λ and varying polymeric to the total drop viscosity ratio β is studied and explained by examining the elastic and viscous stresses at the interface. Steady-state drop deformation was seen to decrease from its Newtonian value with increasing viscoelasticity. A slight non-monotonicity in steady-state deformation with increasing Deborah number is observed at high Capillary numbers. Transient drop deformation displays an overshoot before settling down to a lower value of deformation. The overshoot increases with increasing β. The drop shows slightly decreased alignment with the flow with increasing viscoelasticity. A simple ordinary differential equation model is developed to explain the various behaviours and the scalings observed numerically. The critical Capillary number for drop breakup is observed to increase with Deborah number owing to the inhibitive effects of viscoelasticity, the increase being linear for small Deborah number.
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AGGARWAL, NISHITH, and KAUSIK SARKAR. "Effects of matrix viscoelasticity on viscous and viscoelastic drop deformation in a shear flow." Journal of Fluid Mechanics 601 (April 25, 2008): 63–84. http://dx.doi.org/10.1017/s0022112008000451.
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The deformation of a Newtonian/viscoelastic drop suspended in a viscoelastic fluid is investigated using a three-dimensional front-tracking finite-difference method. The viscoelasticity is modelled using the Oldroyd-B constitutive equation. Matrix viscoelasticity affects the drop deformation and the inclination angle with the flow direction. Numerical predictions of these quantities are compared with previous experimental measurements using Boger fluids. The elastic and viscous stresses at the interface, polymer orientation, and the elastic and viscous forces in the domain are carefully investigated as they affect the drop response. Significant change in the drop inclination with increasing viscoelasticity is observed; this is explained in terms of the first normal stress difference. A non-monotonic change – a decrease followed by an increase – in the steady-state drop deformation is observed with increasing Deborah number (De) and explained in terms of the competition between increased localized polymer stretching at the drop tips and the decreased viscous stretching due to change in drop orientation angle. The transient drop orientation angle is found to evolve on the polymer relaxation time scale for highDe. The breakup of a viscous drop in a viscoelastic matrix is inhibited for smallDe, and promoted at higherDe. Polymeric to total viscosity ratio β was seen to affect the result through the combined parameter βDeindicating a dominant role of the first normal stress difference. A viscoelastic drop in a viscoelastic matrix with matched relaxation time experiences less deformation compared to the case when one of the phases is viscous; but the inclination angle assumes an intermediate value between two extreme cases. Increased drop phase viscoelasticity compared to matrix phase leads to decreased deformation.
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Korol, A. M., J. R. Valverde, and R. J. Rasia. "Viscoelasticity: Fractal parameters studied on mammalian erythrocytes under shear stress." Experimental Mechanics 42, no. 2 (June 2002): 172–77. http://dx.doi.org/10.1007/bf02410879.
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Helgeson, Matthew E., Norman J. Wagner, and Dimitris Vlassopoulos. "Viscoelasticity and shear melting of colloidal star polymer glasses." Journal of Rheology 51, no. 2 (March 2007): 297–316. http://dx.doi.org/10.1122/1.2433935.
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Yoshimura, Narihiko, Noboru Umemoto, and Tsunamitsu Nakahara. "Analysis of Traction Curve in Linear Region Considering Volume Viscoelasticity." Journal of Tribology 121, no. 2 (April 1, 1999): 252–58. http://dx.doi.org/10.1115/1.2833928.
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Measurements of the gradient in the linear region of traction curve, where the effects of heat generation and nonlinearity of shear viscosity can be neglected were made for two kinds of synthetic oils, DOP and 5P4E, using a traction tester improved to a precision less than 0.01 percent in slip ratio. The measured results were compared with the theoretical results based on a viscoelastic model for shear stress and on an elastic model for compressibility using primary data of the rheological properties which were obtained not by means of traction test; they were markedly less than the theoretical results under low speed for both oils and also under high speed for DOP. A new analysis of the traction was performed considering volume viscoelasticity for compressibility which relates shear viscoelasticity under high pressure. The theoretical results agree fairly with the measured results.
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Mukherjee, Swarnajay, and Kausik Sarkar. "Effects of matrix viscoelasticity on the lateral migration of a deformable drop in a wall-bounded shear." Journal of Fluid Mechanics 727 (June 21, 2013): 318–45. http://dx.doi.org/10.1017/jfm.2013.251.
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AbstractThe dynamics of a drop deforming, orienting and moving in a shear flow of a viscoelastic liquid near a wall is numerically investigated using a front-tracking finite-difference method and a semi-analytic theory. The viscoelasticity is modelled using the modified FENE-CR constitutive equation. In a Newtonian system, deformation in a drop breaks the reversal symmetry of the system resulting in a migration away from the wall. This study shows that the matrix elasticity reduces the migration velocity, the reduction scaling approximately linearly with viscoelasticity (product of the Deborah numberDeand the ratio of polymer viscosity to total viscosity$\beta $). Similar to a Newtonian system, for small Deborah numbers, the dynamics quickly reaches a quasi-steady state where deformation, inclination, as well as migration and slip velocities become independent of the initial drop–wall separation. They all approximately scale inversely with the square of the instantaneous separation except for deformation which scales inversely with the cube of separation. The deformation shows a non-monotonic variation with increasing viscoelasticity similar to the case of a drop in an unbounded shear and is found to influence little the change in migration. Two competing effects due to matrix viscoelasticity on drop migration are identified. The first stems from the reduced inclination angle of the drop with increasing viscoelasticity that tries to enhance migration velocity. However, it is overcome by the second effect inhibiting migration that results from the normal stress differences from the curved streamlines around the drop; they are more curved on the side away from the wall compared with those in the gap between the wall and the drop, an effect that is also present for a rigid particle. A perturbative theory of migration is developed for small ratio of the drop size to its separation from the wall that clearly shows the migration to be caused by the image stresslet field due to the drop in presence of the wall. The theory delineates the two competing viscoelastic effects, their relative magnitudes, and predicts migration that matches well with the simulation. Using the simulation results and the stresslet theory, we develop an algebraic expression for the quasi-steady migration velocity as a function ofCa,Deand$\beta $. The transient dynamics of the migrating drop is seen to be governed by the finite time needed for development of the viscoelastic stresses. For larger capillary numbers, in both Newtonian and viscoelastic matrices, a viscous drop fails to reach a quasi-steady state independent of initial drop–wall separation. Matrix viscoelasticity tends to prevent drop breakup. Drops that break up in a Newtonian matrix are stabilized in a viscoelastic matrix if it is initially far away from the wall. Initial proximity to the wall enhances deformation and aids in drop breakup.
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Murata, Shoichi, Akihiko Takada, and Yoshiaki Takahashi. "Structure and Viscoelasticity of Wormlike Micellar Solutions under Steady Shear Flows." Nihon Reoroji Gakkaishi 35, no. 4 (2007): 185–89. http://dx.doi.org/10.1678/rheology.35.185.
Full textDissertations / Theses on the topic "Viscoelasticity. Shear (Mechanics)"
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Olapade, Peter Ojo. "Computational studies of pair wise interactions between drops and the dynamics of concentrated emulsions at finite inertia." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 96 p, 2007. http://proquest.umi.com/pqdweb?did=1407501831&sid=11&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Silva, Thales Augusto Barbosa Pinto. "Análise do módulo de cisalhamento associado a modelo de Jeffreys modificado." Universidade Tecnológica Federal do Paraná, 2017. http://repositorio.utfpr.edu.br/jspui/handle/1/2866.
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CNPqMateriais tixotrópicos possuem aplicações industriais economicamente importantes. Modelos constitutivos descrevendo seu comportamento, propostos recentemente, são formulados por meio de um sistema acoplado de duas equações: equação constitutiva (baseada em modelos viscoelásticos clássicos) e a equação de taxa (que descreve a evolução microestrutural do material). O módulo de cisalhamento e o(s) coeficiente(s) de viscosidade são considerados, nesta classe de modelos, funções do parâmetro estrutural. As expressões utilizadas para tais funções são definidas satisfazendo limites assintóticos, de tal forma que o modelo seja fisicamente consistente. Entretanto, não há consenso quanto a forma em que as expressões são formuladas. Objetivou-se determinar o formato da função associada ao módulo de cisalhamento, a partir de dados de testes reológicos, utilizando um modelo de Jeffreys modificado. A obtenção da expressão do módulo de cisalhamento foi definida como um problema inverso e, portanto, a teoria e algumas estratégias associadas foram discutidas. Utilizou-se uma estrutura multiobjetiva juntamente com o método de regularização de Tikhonov e o critério de escolha de parâmetro curva L, para a obtenção de soluções de problemas mal-postos associados. Os algoritmos formalizados no trabalho foram implementados por meio de um código desenvolvido no MATLAB. Como resultados, uma nova proposta para a função associada ao módulo de cisalhamento foi obtida e os parâmetros associados ao modelo constituído desta nova proposta foram ajustados a dados de testes reológicos.
Thixotropic materials have economically important industrial applications. Recently proposed constitutive models describing its behavior are formulated by means of a two coupled equations system: the constitutive equation (based on viscoelastic classic models) and the rate equation (in which the microstructural evolution is described). The shear modulus and the viscosity coefficient(s) are considered, in such a class of models, as functions of the structural parameter. The expressions used for such functions are defined by satisfying some asymptotic limits, in a way that the model is physically consistent. However, there is no agreement as to the form in which the expressions are formulated. It is aimed to determine the form of shear modulus function, from rheological tests data, using a modified Jeffreys model. The obtainment of an expression for the shear modulus function is defined as an inverse problem and therefore the theory and some strategies associated were discussed. It is used a multi-objective framework together with the Tikhonov regularization method and the L-curve parameter-choice criterion in order to get the solution for associated ill-posed problems. The algorithms formalized throughout the work were implemented through a MATLAB developed code. As results, a new proposal for the shear modulus function were obtained and the parameters associated with the model constituted of this new proposal are fitted to rheological tests data.
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Bechtel, Toni M. "Micro-mechanical Modeling of Brownian Spheroids in Oscillatory Shear Flow." Research Showcase @ CMU, 2018. http://repository.cmu.edu/dissertations/1144.
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We calculate the stress response, or rheology, of a micro-mechanical model suspension of rigid, Brownian spheroids in a Newtonian fluid in an oscillatory shear flow. The straining and rotation components of a linear flow affects the microstructure, or particle orientation in space and time, and thus, the suspension stress. A statistical description of the microstructure is given by an orientation probability distribution function, which quantifies the likelihood of a particle possessing a particular orientation at an instance in time. The evolution of the microstructure results from the memory of the material, advection from the flow, and rotational Brownian motion. The macroscopic stress response is calculated from ensemble averages of the stresslet weighted by the orientation distribution function. First, we calculate the linear stress response of a dilute suspension of rigid, spheroidal, self-propelled particles under a small-amplitude oscillatory shear deformation using regular perturbation theory. The particle activity leads to a direct contribution to the material stress, via self-propulsion, and an indirect contribution due to correlated tumbling events. The mechanism and strength of self-propulsion and correlation between tumbling events can be determined from the linear stress response of an active suspension. Next, we develop a framework for determining the relaxation moduli of a viscoelastic material through the combination of a memory integral expansion and a multimode-frequency oscillatory shear flow. We analytically determine the first nonlinear relaxation modulus of the model suspension through a comparison of the second normal stress difference from the microstructural stress response, calculated via regular perturbation theory, and a co-rotational memory integral expansion. The stress response of the system is reconstructed for the start-up and cessation of steady simple shear and uniaxial extension. Finally, we numerically calculate the nonlinear viscoelasticity of the model system subject to a large-amplitude oscillatory shear flow. In a sufficiently strong flow with oscillation frequency comparable to the material relaxation rate, secondary overshoots in the stress response occur. We attribute the origin of secondary overshoots to particles undergoing a Jeffery orbit during a (half) cycle of the oscillation, analogous to the case of non-Brownian spheroids in steady shear flow.
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Alkhtany, Moshabab Mobarek H. "MODELING STRUCTURAL POLYMERIC FOAMS UNDER COMBINED CYCLIC COMPRESSION-SHEAR LOADING." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1469532064.
Full textBook chapters on the topic "Viscoelasticity. Shear (Mechanics)"
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Beris, Antony N., and Brian J. Edwards. "Incompressible Viscoelastic Fluids." In Thermodynamics of Flowing Systems: with Internal Microstructure. Oxford University Press, 1994. http://dx.doi.org/10.1093/oso/9780195076943.003.0013.
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In Part I, we discussed in detail the foundations of the bracket description of dynamical behavior, demonstrating how the generalized bracket is linked to the theories of both Hamiltonian mechanics and irreversible thermodynamics. Now it is time to discuss the various applications towards seemingly complex systems which are the main focus of this book. Specifically, we want to look at a variety of microstructured media of immediate concern in science and industry, and to illustrate the advantages of using the generalized bracket formalism over traditional techniques when developing system-particular models. As we shall also see, there are certain advantages to be gained even when we are simply expressing existing models in Hamiltonian form. The first subject that we wish to address is that of viscoelastic fluid dynamics. As the name implies, viscoelasticity characterizes the materials that possess properties intermediate to those of an elastic solid and a viscous fluid. The most characteristic property is that of limited (“fading”) memory: viscoelastic materials partially resume their previous deformation state upon removal of the externally applied forces; the smaller the duration of the application of the forces, the better the recovery. Materials of this type contain a certain degree of internal microstructure (e.g., polymeric solutions and melts, advanced composites, liquid crystals, etc.), and are very important in the processing industry where one wishes to combine the “processability” of the medium's fluidity with the “structural quality” of the internal architecture to obtain high strength/ low-weight final products. We can distinguish two types of viscoelasticity: viscoelastic solids and viscoelastic fluids characterized by the ability or lack of ability respectively, to support shear stresses at finite deformations. In the following we shall focus on the analysis of viscoelastic fluids although the approach followed applies and/or can be extended in a straightforward fashion to viscoelastic solids as well. For a description of solid viscoelasticity, the interested reader may consult one of the many excellent monographs in the area [Eringen, 1962, chs. 8, 10; Ferry, 1980; Sobotka, 1984; see also Tschoegl, 1989].
Conference papers on the topic "Viscoelasticity. Shear (Mechanics)"
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Sodeifian, Gholamhossein, Ali Haghtalab, and Amir Abdollah. "A High Shear Rate Sliding Plate Rheometer for Nonlinear Viscoelasticity." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-33740.
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In most of polymer processings, such as injection molding and extrusion, materials are subjected to high deformations. In order to study nonlinear viscoelastic properties, it is necessary to have an instrument to generate high shear rates. A new sliding plate rheometer incorporating shear stress transducer has been developed. This rheometer has been equipped with a robust servohydraulic linear actuator which can generate shear rates and frequencies up to 900 (1/S) and 500 (Hz) respectively, compared with maximum 500 (1/S) and 100 (Hz), used in latest researches. Using this system, a wider range of nonlinear viscoelasticity can be investigated.
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Murakami, K., M. Tsukune, Y. Kobayashi, M. Fujie, R. Kishimoto, T. Obata, K. Kawamura, K. Yoshida, and T. Yamaguchi. "Viscoelasticity and shear wave velocity of liver tissue evaluated by dynamic mechanical analysis." In 2015 IEEE International Ultrasonics Symposium (IUS). IEEE, 2015. http://dx.doi.org/10.1109/ultsym.2015.0289.
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Dai, Zoujun, Ying Peng, Hansen A. Mansy, Thomas J. Royston, and Richard H. Sandler. "Estimation of Local Viscoelasticity of Lungs Based on Surface Waves." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65561.
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The viscoelastic properties of lung tissue are of interest in medicine as they have been shown to be affected by various pathologies. Identifying the mechanical properties of lung tissue first requires a means of quantitatively measuring phenomena, such as mechanical wave motion, that are affected by these properties. In the present study, lung surface motion is measured on excised pig lungs to determine suitable viscoelastic models. The relation between the surface wave speed and the frequency is analyzed and different viscoelastic models are used to fit this relation. Also a more comprehensive method to evaluate the frequency-dependent shear modulus of the pig lung measuring the propagation of surface waves on the surface of the lung is presented and viscoelastic models (both of integer and fractional order) are compared to experimental results over the frequency range of 100–500 Hz.
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Renaud, Franck, Gael Chevallier, Jean-Luc Dion, and Re´mi Lemaire. "Viscoelasticity Measurement and Identification of Viscoelastic Parametric Models." In ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/detc2011-47545.
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Generally speaking, the behaviour of viscoelastic material is more complicated than the behaviour proposed by classical models as Voigt, Maxwell or Zener. The stiffness of such materials is a frequency dependent complex function. Above 1000Hz, classical measurements techniques are unable to achieve accurate measurements of the stiffness. In this paper, a new Dynamical Mechanical Analysis (DMA) tester is presented. It allows the characterization of the shear stiffness of preloaded viscoelastic materials between 200 and 3500Hz and without using frequency-temperature equivalences. Then the Generalized Maxwell model is used to describe behaviours measured with the DMA tester. A new iterative identification method of the parameter of the Generalized Maxwell model is described. This identification method is based on the asymptotes of the model.
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Sable, Peter A., Christopher H. Neel, and John P. Borg. "High Strain-rate Shear and Friction Characterization of Fully-Dense Polyurethane and Epoxy." In 2019 15th Hypervelocity Impact Symposium. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/hvis2019-047.
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Abstract The characterization of polymer behavior at high strain-rates is a critical area of research driven by the use of polymers as adhesives, structural components, or as binders for energetic systems. Previous investigations have successfully defined Hugoniot equations-of-state for many relevant polymers such as epoxy, polycarbonate, and polyether ether ketone [1]–[4].Several studies have also explored the ramifications of polymer viscoelasticity at high strain-rates and pressures. This has been observed as nonlinearities in both propagating stress wave structure and Hugoniot state spaces [5]–[7]. The mechanisms driving such behavior is hypothesized as the breakdown and extended time interaction of polymer-chains but is yet to be fully understood.
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Hu, Yingying, Shiyao Bian, Marcel Filoche, John C. Grotberg, Shuichi Takayama, and James B. Grotberg. "Rheology Effects on Mucus Plug Rupture." In ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14507.
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Human respiratory mucus has non-Newtonian rheological properties of viscoelasticity, shear-thinning and yield stress. They play significant roles in mucus clearance by ciliary motion as well as cough [5,7,9]. Mucus is hypersecreted in such lung diseases as cystic fibrosis and asthma. Mucus hypersecretion damages mucus clearance mechanism [6], and more likely causes plugs to block partial or total airways [4].
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Pataky, Todd C., and Vladimir Zatsiorsky. "Finger Pad Viscoelastic Response to Shear Load." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43359.
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Uniaxial human skin viscoelasticity has been demonstrated in vitro (Pan et al., 1998). Although some have experimentally measured in vivo finger pad viscoleasticity under normal compression (e.g. Jindirch et al., 2003), none have measured its response to shear load. Knowledge of the viscoelastic properties of the finger pad is important for understanding dynamic finger force coordination during manipulation. While finite element models (FEM) of the finger pad have been developed for dynamic loading studies (e.g. Wu et al., 2002; 2003), these models have not been validated using experimental data. The purpose of the current study was to measure the viscoelastic response of the finger pad to tangential shear load, and to compare the data with results of FEM simulations. The index, middle, ring, and little fingers of the right hand of eight subjects (age: 26.0 ± 2.3 years, height: 175.1 ± 9.5 cm, body mass: 69.3 ± 8.3 kg) were individually clamped at their distal interphalangeal joints in a custom-built device that allowed for compression of the finger pad against a multi-axis force transducer (ATI, North Carolina, USA). The transducer was topped with 100-grit sandpaper to prevent slip; the coefficient of static friction between the finger and the sandpaper was measured to be approximately 1.4. Three different levels of compressive normal force (ranging from 1 to 5 N) were applied to each finger of each subject. Subsequent tangential displacements in both the medial and lateral directions were applied in steps of 0.6 mm (to an accuracy of 0.01 mm) to the force transducer by a micrometer positioning slide (Techno, Inc., NY, USA). Since the micrometer slide was adjusted manually, the loading rate was not precisely controlled (the loading rate was estimated to be 0.6 mm/s). Thus only force relaxation was analyzed (using nonlinear regression techniques) — this was considered sufficient to compare to FEM results. The force response after full relaxation was also considered as a long-term ‘stiffness’ response. The experimental results were compared with two FEM from the literature: Wu et al. (2002) and Wu et al. (2003) that were reconstructed using ABAQUS 6.2 (ABAQUS Inc.; Pawtucket, RI, USA). Both models were 2-D plain strain models with hard normal and rough tangential contact. Both incorporated linearly elastic bone and nail components and had geometry of the average male index finger. The soft tissue of the former FEM was modeled en masse as hyperelastic skin. The soft tissue of latter model incorporated a thin skin layer with biphasic subcutaneous tissue (see the original articles for material parameters, constitutive equations, etc.). The experimental data showed tangential force relaxation on the order of 40% over an average time period of 11.2 seconds. A logarithmic function applied to the rate of change of the force relaxation successfully reproduced the relaxation curves. The long-term ‘stiffness’ was found to be linearly related to the applied shearing displacement magnitude. ANOVA found that both stiffness and the relaxation parameters were different for each finger (p<0.01). These data were also dependent on the direction of the shear load (p<0.01). While the ABAQUS models have been constructed and qualitative agreement has been found between the modeled and experimental results, a quantitative comparison has not yet been performed. The substantial relaxation and inter-finger differences may have important implications to studies of force coordination among redundant fingers. The agreement between experimental data and predictions of FEM confirm the usefulness of the FEM for soft tissue biomechanics studies.
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Chan, Roger W., and Thomas Siegmund. "Constitutive Characterization of the Nonlinear Viscoelastic Response of Vocal Fold Tissues." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32606.
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Previous empirical studies have shown that vocal fold tissues exhibit nonlinear viscoelastic behaviors under different loading conditions. Hysteresis and strain rate-dependence of stress-strain curves have been observed for different layers of vocal fold tissues when subjected to cyclic tensile loading [1,2]. Nonlinear viscoelastic response has also been described for vocal fold tissues subjected to constant strain and constant stress tests under both tensile loading and large-strain shear deformation conditions [3,4]. These findings cannot be adequately described by many of the traditional constitutive formulations of linear and quasilinear viscoelasticity. For instance, models based on Y. C. Fung’s quasilinear viscoelastic theory typically apply two separate functions to describe the time dependence and the strain dependence of stress (e.g., the reduced relaxation function G(t) and the elastic response σe(ε), respectively), and combine the two functions by the Boltzmann superposition principle [5]. Such formulations assume that time dependence and strain dependence can be separated. However, recently obtained stress relaxation data of vocal fold tissues under various magnitudes of applied shear strain indicated that they are not separable, as relaxation became slower with increasing strain [4]. This paper attempts to characterize some nonlinear viscoelastic behaviors of vocal fold tissues under tensile and shear deformation conditions based on an implementation of the Bergstrom-Boyce model [6,7].
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Chotpattananont, Datchanee, and Anuvat Sirivat. "Electrorheological Properties of Suspensions Prepared From Polythiophene Conductive Polymer." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79491.
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Electrorheological (ER) fluids are typically composed of polarizable particles dispersed in a non-conducting fluid. Upon the application of an electric field, chain-like or fibrillar aggregates of the suspended particles are oriented along the direction of the electric field, thereby inducing viscoelasticity and a drastic increase in viscosity. In our study, Poly(3-thiophene acetic acid), PTAA, has been developed for using as ER material. The rheological properties of this PTAA suspension upon the application of electric field were investigated under various deformations; oscillatory shear flow, steady shear, and creep. We found that PTAA based ER fluid exhibited viscoelastic behavior and showed the excellent responses under an applied electric field. Moreover, the ER response of this PTAA fluid was amplified with increases in electric field strength, particle concentration, and particle conductivity. Under the oscillatory shear, the dynamic moduli, G′ and G″, increased dramatically by 10 orders of magnitude, when the field strength was increased to 2 kV/mm. The suspensions exhibited a transition from fluid-like to solid-like behavior as the field strength increased. While under steady shear flow, the yield stress increased with electric field strength, E, and particle volume fraction, φ, according to a scaling law of the form, τy α Eαφγ. Furthermore, the creep curves of this ER fluid consisted of both elastic and viscous responses and this fluid exhibits partially elastic recovery after the removal of applied stress. The creep properties strongly depended on the magnitude of an applied stress.
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Almeida, Ekmagage Don N., Leela Rakesh, Stanley Hirschi, and Anja Mueller. "Solution Rheology of Saline and Polysaccharide Systems." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-15906.
Full textAbstract:
The problem of the characterization of the solution properties of water soluble polymers is long-standing. These polymers tend to form aggregated supramolecular gels that are resistant to molecular dispersion. These materials are being widely used in a variety of industrial applications. Their principle functions are as rheological modifiers, where they thicken or gel solutions in products such as hair-care, detergents, air fresheners and foods; as flocculants for particle separation as applied to water clarification, sewage, and effluent treatment, and as stabilizers to control the properties of concentrated suspension and emulsions, for example in paints, pesticides, dyes, and pharmaceutical industries. Therefore it is important to understand their rheological properties under various operating conditions such as stress, strain, temperature etc, which will induce gelation. The rheological properties of starch gels of high concentration (up to 86% starch) have been investigated before [1]. In this paper we have investigated experimentally the shear viscosity and viscoelasticity properties of saline and polysaccharide suspensions at various low concentrations and pH at different temperatures using controlled stress and strain rheometers (Vilastic-3 and AR 2000). The data were then fitted with the power law and Cross model for low and higher concentrations respectively. The present results show that the viscosity/elasticity does not significantly change for low concentrations at different pH values. The maximum viscosity/elasticity was obtained around pH 5-7.4 at higher concentrations.