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Sample records for linear viscoelastic properties

  1. Quasi-linear viscoelastic properties of normal articular cartilage.

    PubMed

    Woo, S L; Simon, B R; Kuei, S C; Akeson, W H

    1980-05-01

    A combined experimental and analytical approach was used to determine the history-dependent viscoelastic properties of normal articular cartilage in tension. Specimens along the surface split line direction, taken from the middle zone of articular cartilage were subjected to relaxation and cyclic tests. A quasi-linear viscoelastic theory proposed by Fung was used in combination with the experimental results to determine the nonlinear viscoelastic properties and the elastic stress-strain relationship of normal articular cartilage.

  2. High bandwidth linear viscoelastic properties of complex fluids from the measurement of their free surface fluctuations

    NASA Astrophysics Data System (ADS)

    Pottier, Basile; Talini, Laurence; Frétigny, Christian

    2012-02-01

    We present a new optical method to measure the linear viscoelastic properties of materials, ranging from complex fluids to soft solids, within a large frequency range (about 0.1--10^4 Hz). The surface fluctuation specular reflection technique is based on the measurement of the thermal fluctuations of the free surfaces of materials at which a laser beam is specularly reflected. The propagation of the thermal surface waves depends on the surface tension, density, and complex viscoelastic modulus of the material. For known surface tension and density, we show that the frequency dependent elastic and loss moduli can be deduced from the fluctuation spectrum. Using a viscoelastic solid (a cross-linked PDMS), which linear viscoelastic properties are known in a large frequency range from rheometric measurements and the time--temperature superposition principle, we show that there is a good agreement between the rheological characterization provided by rheometric and fluctuation measurements. We also present measurements conducted with complex fluids that are supramolecular polymer solutions. The agreement with other low frequency and high frequency rheological measurements is again very good, and we discuss the sensitivity of the technique to surface viscoelasticity.

  3. Quasi-linear viscoelastic properties of fibrotic neck tissues obtained from ultrasound indentation tests in vivo.

    PubMed

    Huang, Yan-Ping; Zheng, Yong-Ping; Leung, Sing-Fai

    2005-02-01

    Hand palpation is a conventional way to assess and document soft tissue fibrosis. But it is semi-quantitative and subjective, so there is a need to develop quantitative and objective methods for this purpose. 105 patients with different degrees of radiation-induced fibrosis of soft tissue of the neck were assessed using an ultrasound indentation method. The force response was reconstructed from the indentation history using a quasi-linear viscoelastic model with four material parameters. The parameters which best curve-fitted the force response with respect to the experimentally measured one, were selected as the viscoelastic properties of the tested soft tissue. These parameters were compared among patient subgroups with different degrees of fibrosis as scored by hand palpation, and also compared with those of a control group of healthy, non-irradiated subjects. Their relation to the rotation range of the neck and the effective Young's modulus, were also assessed. Soft tissue with a more severe degree of fibrosis was associated with a larger initial stiffness and a more rapid increase in stiffness under loading. Viscoelasticity parameters could discriminate soft tissue with different degrees of clinical fibrosis and had significant correlation with clinical parameters of fibrosis. Change of viscoelastic properties is reflection of pathological modifications of components in fibrotic soft tissues. Measurement of viscoelasticity parameters of soft tissue provides a quantitative and objective approach for the researcher and clinician to quantify soft tissue fibrosis. Measurement of the change of viscoelastic properties of soft tissue provides a quantitative and objective approach for researchers and clinicians to quantify soft tissue fibrosis which is one of the most common late effects of radiotherapy.

  4. Accurate prediction of the linear viscoelastic properties of highly entangled mono and bidisperse polymer melts.

    PubMed

    Stephanou, Pavlos S; Mavrantzas, Vlasis G

    2014-06-07

    We present a hierarchical computational methodology which permits the accurate prediction of the linear viscoelastic properties of entangled polymer melts directly from the chemical structure, chemical composition, and molecular architecture of the constituent chains. The method entails three steps: execution of long molecular dynamics simulations with moderately entangled polymer melts, self-consistent mapping of the accumulated trajectories onto a tube model and parameterization or fine-tuning of the model on the basis of detailed simulation data, and use of the modified tube model to predict the linear viscoelastic properties of significantly higher molecular weight (MW) melts of the same polymer. Predictions are reported for the zero-shear-rate viscosity η0 and the spectra of storage G'(ω) and loss G″(ω) moduli for several mono and bidisperse cis- and trans-1,4 polybutadiene melts as well as for their MW dependence, and are found to be in remarkable agreement with experimentally measured rheological data.

  5. Linear and nonlinear viscoelastic modeling of ovine aortic biomechanical properties under in vivo and ex vivo conditions.

    PubMed

    Valdez-Jasso, D; Bia, D; Haider, M A; Zocalo, Y; Armentano, R L; Olufsen, M S

    2010-01-01

    This study uses linear and nonlinear viscoelastic models to describe the dynamic distention of the aorta induced by time-varying arterial blood pressure. We employ an inverse mathematical modeling approach on a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (arctangent and sigmoid) to infer vascular biomechanical properties under in vivo and ex vivo experimental conditions in ten and eleven male Merino sheep, respectively. We used the Akaike Information Criterion (AIC) as a goodness-of-fit measure. Results show that under both experimental conditions, the nonlinear models generally outperform the linear Kelvin model, as judged by the AIC. Furthermore, the sigmoid nonlinear viscoelastic model consistently achieves the lowest AIC and also matches the zero-stress vessel radii measured ex vivo. Based on these observations, we conclude that the sigmoid nonlinear viscoelastic model best describes the biomechanical properties of ovine large arteries under both experimental conditions considered in this study.

  6. Quasi-linear viscoelastic properties of the human medial patello-femoral ligament.

    PubMed

    Criscenti, G; De Maria, C; Sebastiani, E; Tei, M; Placella, G; Speziali, A; Vozzi, G; Cerulli, G

    2015-12-16

    The evaluation of viscoelastic properties of human medial patello-femoral ligament is fundamental to understand its physiological function and contribution as stabilizer for the selection of the methods of repair and reconstruction and for the development of scaffolds with adequate mechanical properties. In this work, 12 human specimens were tested to evaluate the time- and history-dependent non linear viscoelastic properties of human medial patello-femoral ligament using the quasi-linear viscoelastic (QLV) theory formulated by Fung et al. (1972) and modified by Abramowitch and Woo (2004). The five constant of the QLV theory, used to describe the instantaneous elastic response and the reduced relaxation function on stress relaxation experiments, were successfully evaluated. It was found that the constant A was 1.21±0.96MPa and the dimensionless constant B was 26.03±4.16. The magnitude of viscous response, the constant C, was 0.11±0.02 and the initial and late relaxation time constants τ1 and τ2 were 6.32±1.76s and 903.47±504.73s respectively. The total stress relaxation was 32.7±4.7%. To validate our results, the obtained constants were used to evaluate peak stresses from a cyclic stress relaxation test on three different specimens. The theoretically predicted values fit the experimental ones demonstrating that the QLV theory could be used to evaluate the viscoelastic properties of the human medial patello-femoral ligament. Copyright © 2015 Elsevier Ltd. All rights reserved.

  7. The Quasi-Linear Viscoelastic Properties of Diabetic and Non-Diabetic Plantar Soft Tissue

    PubMed Central

    Pai, Shruti; Ledoux, William R.

    2011-01-01

    The purpose of this study was to characterize the viscoelastic behavior of diabetic and non-diabetic plantar soft tissue at six ulcer-prone/load-bearing locations beneath the foot to determine any changes that may play a role in diabetic ulcer formation and subsequent amputation in this predisposed population. Four older diabetic and four control fresh frozen cadaveric feet were each dissected to isolate plantar tissue specimens from the hallux, first, third, and fifth metatarsals, lateral midfoot, and calcaneus. Stress relaxation experiments were used to quantify the viscoelastic tissue properties by fitting the data to the quasi-linear viscoelastic (QLV) theory using two methods, a traditional frequency-insensitive approach and an indirect frequency-sensitive approach, and by measuring several additional parameters from the raw data including the rate and amount of overall relaxation. The stress relaxation response of both diabetic and non-diabetic specimens was unexpectedly similar and accordingly few of the QLV parameters for either fit approach and none of raw data parameters differed. Likewise, no differences were found between plantar locations. The accuracy of both fit methods was comparable, however, neither approach predicted the ramp behavior. Further, fit coefficients varied considerably from one method to the other, making it hard to discern meaningful trends. Future testing using alternate loading modes and intact feet may provide more insight into the role that time-dependent properties play in diabetic foot ulceration. PMID:21327701

  8. The quasi-linear viscoelastic properties of diabetic and non-diabetic plantar soft tissue.

    PubMed

    Pai, Shruti; Ledoux, William R

    2011-05-01

    The purpose of this study was to characterize the viscoelastic behavior of diabetic and non-diabetic plantar soft tissue at six ulcer-prone/load-bearing locations beneath the foot to determine any changes that may play a role in diabetic ulcer formation and subsequent amputation in this predisposed population. Four older diabetic and four control fresh frozen cadaveric feet were each dissected to isolate plantar tissue specimens from the hallux, first, third, and fifth metatarsals, lateral midfoot, and calcaneus. Stress relaxation experiments were used to quantify the viscoelastic tissue properties by fitting the data to the quasi-linear viscoelastic (QLV) theory using two methods, a traditional frequency-insensitive approach and an indirect frequency-sensitive approach, and by measuring several additional parameters from the raw data including the rate and amount of overall relaxation. The stress relaxation response of both diabetic and non-diabetic specimens was unexpectedly similar and accordingly few of the QLV parameters for either fit approach and none of raw data parameters differed. Likewise, no differences were found between plantar locations. The accuracy of both fit methods was comparable, however, neither approach predicted the ramp behavior. Further, fit coefficients varied considerably from one method to the other, making it hard to discern meaningful trends. Future testing using alternate loading modes and intact feet may provide more insight into the role that time-dependent properties play in diabetic foot ulceration.

  9. The Viscoelastic Properties of Passive Eye Muscle in Primates. II: Testing the Quasi-Linear Theory

    PubMed Central

    Quaia, Christian; Ying, Howard S.; Optican, Lance M.

    2009-01-01

    We have extensively investigated the mechanical properties of passive eye muscles, in vivo, in anesthetized and paralyzed monkeys. The complexity inherent in rheological measurements makes it desirable to present the results in terms of a mathematical model. Because Fung's quasi-linear viscoelastic (QLV) model has been particularly successful in capturing the viscoelastic properties of passive biological tissues, here we analyze this dataset within the framework of Fung's theory. We found that the basic properties assumed under the QLV theory (separability and superposition) are not typical of passive eye muscles. We show that some recent extensions of Fung's model can deal successfully with the lack of separability, but fail to reproduce the deviation from superposition. While appealing for their elegance, the QLV model and its descendants are not able to capture the complex mechanical properties of passive eye muscles. In particular, our measurements suggest that in a passive extraocular muscle the force does not depend on the entire length history, but to a great extent is only a function of the last elongation to which it has been subjected. It is currently unknown whether other passive biological tissues behave similarly. PMID:19649257

  10. The viscoelastic properties of passive eye muscle in primates. II: testing the quasi-linear theory.

    PubMed

    Quaia, Christian; Ying, Howard S; Optican, Lance M

    2009-08-03

    We have extensively investigated the mechanical properties of passive eye muscles, in vivo, in anesthetized and paralyzed monkeys. The complexity inherent in rheological measurements makes it desirable to present the results in terms of a mathematical model. Because Fung's quasi-linear viscoelastic (QLV) model has been particularly successful in capturing the viscoelastic properties of passive biological tissues, here we analyze this dataset within the framework of Fung's theory.We found that the basic properties assumed under the QLV theory (separability and superposition) are not typical of passive eye muscles. We show that some recent extensions of Fung's model can deal successfully with the lack of separability, but fail to reproduce the deviation from superposition.While appealing for their elegance, the QLV model and its descendants are not able to capture the complex mechanical properties of passive eye muscles. In particular, our measurements suggest that in a passive extraocular muscle the force does not depend on the entire length history, but to a great extent is only a function of the last elongation to which it has been subjected. It is currently unknown whether other passive biological tissues behave similarly.

  11. Linear viscoelastic properties of transient networks formed by associating polymers with multiple stickers

    NASA Astrophysics Data System (ADS)

    Indei, Tsutomu; Takimoto, Jun-ichi

    2010-11-01

    We have developed a single-chain theory that describes dynamics of associating polymer chains carrying multiple associative groups (or stickers) in the transient network formed by themselves and studied linear viscoelastic properties of this network. It is shown that if the average number N¯ of stickers associated with the network junction per chain is large, the terminal relaxation time τA that is proportional to τXN¯2 appears. The time τX is the interval during which an associated sticker goes back to its equilibrium position by one or more dissociation steps. In this lower frequency regime ω <1/τX, the moduli are well described in terms of the Rouse model with the longest relaxation time τA. The large value of N¯ is realized for chains carrying many stickers whose rate of association with the network junction is much larger than the dissociation rate. This associative Rouse behavior stems from the association/dissociation processes of stickers and is different from the ordinary Rouse behavior in the higher frequency regime, which is originated from the thermal segmental motion between stickers. If N¯ is not large, the dynamic shear moduli are well described in terms of the Maxwell model characterized by a single relaxation time τX in the moderate and lower frequency regimes. Thus, the transition occurs in the viscoelastic relaxation behavior from the Maxwell-type to the Rouse-type in ω <1/τX as N¯ increases. All these results are obtained under the affine deformation assumption for junction points. We also studied the effect of the junction fluctuations from the affine motion on the plateau modulus by introducing the virtual spring for bound stickers. It is shown that the plateau modulus is not affected by the junction fluctuations.

  12. The measurement of low-frequency linear viscoelastic properties of polyolefins using creeping squeeze flow

    NASA Astrophysics Data System (ADS)

    Cua, Edwin Matthew Chua

    The characterization of the low-frequency linear viscoelastic properties of polymers is a classical problem in rheometry, especially for broad molecular weight (MW), fractional melt-flow index (MFI) polyolefins with small time-temperature shift factors. By interconversion of high-temperature, low-shear steady-viscosity data in the terminal flow regime into low-frequency data using the Cox-Merz rule, the experimental window is expanded towards lower frequencies. A squeeze-flow apparatus using Newton interferometry as a drift-free transducer to measure the gap between a spherical lens and a flat glass plate with high spatial resolution was constructed. Trials with a Newtonian silicone oil and a viscoelastic polydimethylsiloxane (PDMS) gum were undertaken to examine the various experimental factors that might contribute to errors in the calculation of the viscosity. After taking into account those factors during the runs with PDMS gum, the squeeze-flow-derived viscosities at the terminal flow regime (at shear rates accessible to a commercial rheometer) were in good agreement with low frequency dynamic data. To achieve much lower shear rates for the runs with polyolefins, an increase in the working gap range was made by switching from Newton interferometry to Fizeau interferometry. A hermetically sealed high vacuum chamber was built to allow high-temperature runs with polyolefins with minimal degradation. Interconversion of the measured viscosities of a broad MW, 1.04 MFI high-density polyethylene (HDPE) with the squeeze flow apparatus resulted in complex viscosity data at ˜10-5 rad/s, expanding the experimental window by 2 decades. The squeeze-flow derived complex viscosity data was used to decide which of the two popular viscosity models was more accurate in predicting the zero-shear rate viscosity based on its fit to dynamic data limited to higher frequencies.

  13. How preservation time changes the linear viscoelastic properties of porcine liver.

    PubMed

    Wex, C; Stoll, A; Fröhlich, M; Arndt, S; Lippert, H

    2013-01-01

    The preservation time of a liver graft is one of the crucial factors for the success of a liver transplantation. Grafts are kept in a preservation solution to delay cell destruction and cellular edema and to maximize organ function after transplantation. However, longer preservation times are not always avoidable. In this paper we focus on the mechanical changes of porcine liver with increasing preservation time, in order to establish an indicator for the quality of a liver graft dependent on preservation time. A time interval of 26 h was covered and the rheological properties of liver tissue studied using a stress-controlled rheometer. For samples of 1 h preservation time 0.8% strain was found as the limit of linear viscoelasticity. With increasing preservation time a decrease in the complex shear modulus as an indicator for stiffness was observed for the frequency range from 0.1 to 10 Hz. A simple fractional derivative representation of the Kelvin Voigt model was applied to gain further information about the changes of the mechanical properties of liver with increasing preservation time. Within the small shear rate interval of 0.0001-0.01 s⁻¹ the liver showed Newtonian-like flow behavior.

  14. Quasi-linear viscoelastic properties of costal cartilage using atomic force microscopy.

    PubMed

    Tripathy, S; Berger, E J

    2012-01-01

    Costal cartilage (CC) is one of the load-bearing tissues of the rib cage. Literature on material characterisation of the CC is limited. Atomic force microscopy (AFM) has been extremely successful in characterising the elastic properties of soft biomaterials such as articular cartilage and hydrogels, which are often the material of choice for cartilage models. But AFM data on CC are absent in the literature. In this study, AFM indentations using spherical beaded tips were performed on human CC to isolate the mechanical properties. A novel method was developed for modelling the relaxation indentation experiments based on Fung's quasi-linear viscoelasticity and a continuous relaxation spectrum. This particular model has been popular for uniaxial compression test data analysis. Using the model, the mean Young's modulus of CC was found to be about 2.17, 4.11 and 5.49 MPa for three specimens. A large variation of modulus was observed over the tissue. Also, the modulus values decreased with distance from the costochondral junction.

  15. In situ biomechanical properties of normal and diabetic nerves: an efficient quasi-linear viscoelastic approach.

    PubMed

    Chen, Rung-Jian; Lin, Chou-Ching K; Ju, Ming-Shaung

    2010-04-19

    Biomechanical properties of nerves were investigated using the quasi-linear viscoelastic model. An improved parameter estimation technique based on fast convolution was developed and tested in sciatic nerves of normal and diabetic rats. In situ dynamic compression response of sciatic nerves was obtained by a modified custom-designed compression system. Six normal and five diabetic neuropathic Wistar rats were used. The model derived from the high strain rate (0.1 s(-1)) data could predict the responses of lower strain rates (0.05 and 0.01 s(-1)) satisfactorily. The computation time was cut down 49.0% by using the newly developed technique without increasing the root-mean-square error. The percentage of stress relaxation of the diabetic and normal rats, calculated directly from the experimental data, was not significantly different (51.03+/-1.96% vs. 55.97+/-5.89%, respectively; p=0.247). After model fitting, compared with the QLV parameters of normal nerves, the smaller parameter C for diabetic nerves (0.27+/-0.06 vs. 0.20+/-0.02, p < 0.05) indicated that diabetic nerves had a smaller amplitude of viscous response (stress relaxation). The larger parameter tau(2) of diabetic nerves (199+/-153 s vs. 519+/-337 s, p<0.05) implied that diabetic nerves needed a longer relaxation period to reach equilibrium. Copyright 2009 Elsevier Ltd. All rights reserved.

  16. A method for measuring linearly viscoelastic properties of human tympanic membrane using nanoindentation.

    PubMed

    Huang, Gang; Daphalapurkar, Nitin P; Gan, Rong Z; Lu, Hongbing

    2008-02-01

    A viscoelastic nanoindentation technique was developed to measure both in-plane and through-thickness viscoelastic properties of human tympanic membrane (TM). For measurement of in-plane Young's relaxation modulus, the TM sample was clamped on a circular hole and a nanoindenter tip was used to apply a concentrated force at the center of the TM sample. In this setup, the resistance to nanoindentation displacement can be considered due primarily to the in-plane stiffness. The load-displacement curve obtained was used along with finite element analysis to determine the in-plane viscoelastic properties of TM. For measurements of Young's relaxation modulus in the through-thickness (out-of-plane) direction, the TM sample was placed on a relatively rigid solid substrate and nanoindentation was made on the sample surface. In this latter setup, the resistance to nanoindentation displacement arises primarily due to out-of-plane stiffness. The load-displacement curve obtained in this manner was used to determine the out-of-plane relaxation modulus using the method appropriate for viscoelastic materials. From our sample tests, we obtained the steady-state values for in-plane moduli as approximately 17.4 MPa and approximately 19.0 MPa for posterior and anterior portions of TM samples, respectively, and the value for through-thickness modulus as approximately 6.0 MPa for both posterior and anterior TM samples. Using this technique, the local out-of-plane viscoelastic modulus can be determined for different locations over the entire TM, and the in-plane properties can be determined for different quadrants of the TM.

  17. A discrete spectral analysis for determining quasi-linear viscoelastic properties of biological materials

    PubMed Central

    Babaei, Behzad; Abramowitch, Steven D.; Elson, Elliot L.; Thomopoulos, Stavros; Genin, Guy M.

    2015-01-01

    The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress–relaxation data by imposing a simple form upon a material's temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model's ‘box’-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material's relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material's temporal relaxation spectrum from stress–relaxation data in an unbiased way. Our ‘discrete QLV’ (DQLV) approach identifies ranges of time constants over which the Fung QLV model's typical box spectrum provides an accurate representation of a particular material's temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress–relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit. PMID:26609064

  18. A discrete spectral analysis for determining quasi-linear viscoelastic properties of biological materials.

    PubMed

    Babaei, Behzad; Abramowitch, Steven D; Elson, Elliot L; Thomopoulos, Stavros; Genin, Guy M

    2015-12-06

    The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress-relaxation data by imposing a simple form upon a material's temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model's 'box'-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material's relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material's temporal relaxation spectrum from stress-relaxation data in an unbiased way. Our 'discrete QLV' (DQLV) approach identifies ranges of time constants over which the Fung QLV model's typical box spectrum provides an accurate representation of a particular material's temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress-relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit. © 2015 The Author(s).

  19. Linear and quasi-linear viscoelastic characterization of ankle ligaments.

    PubMed

    Funk, J R; Hall, G W; Crandall, J R; Pilkey, W D

    2000-02-01

    The objective of this study was to produce linear and nonlinear viscoelastic models of eight major ligaments in the human ankle/foot complex for use in computer models of the lower extremity. The ligaments included in this study were the anterior talofibular (ATaF), anterior tibiofibular (ATiF), anterior tibiotalar (ATT), calcaneofibular (CF), posterior talofibular (PTaF), posterior tibiofibular (PTiF), posterior tibiotalar (PTT), and tibiocalcaneal (TiC) ligaments. Step relaxation and ramp tests were performed. Back-extrapolation was used to correct for vibration effects and the error introduced by the finite rise time in step relaxation tests. Ligament behavior was found to be nonlinear viscoelastic, but could be adequately modeled up to 15 percent strain using Fung's quasilinear viscoelastic (QLV) model. Failure properties and the effects of preconditioning were also examined.

  20. Linear viscoelasticity of complex coacervates.

    PubMed

    Liu, Yalin; Winter, H Henning; Perry, Sarah L

    2017-01-01

    Rheology is a powerful method for material characterization that can provide detailed information about the self-assembly, structure, and intermolecular interactions present in a material. Here, we review the use of linear viscoelastic measurements for the rheological characterization of complex coacervate-based materials. Complex coacervation is an electrostatically and entropically-driven associative liquid-liquid phase separation phenomenon that can result in the formation of bulk liquid phases, or the self-assembly of hierarchical, microphase separated materials. We discuss the need to link thermodynamic studies of coacervation phase behavior with characterization of material dynamics, and provide parallel examples of how parameters such as charge stoichiometry, ionic strength, and polymer chain length impact self-assembly and material dynamics. We conclude by highlighting key areas of need in the field, and specifically call for the development of a mechanistic understanding of how molecular-level interactions in complex coacervate-based materials affect both self-assembly and material dynamics. Copyright © 2016 Elsevier B.V. All rights reserved.

  1. Effective viscoelastic properties of shales.

    NASA Astrophysics Data System (ADS)

    Cornet, Jan; Dabrowski, Marcin; Schmid, Daniel

    2017-04-01

    Shales are often characterized as being elasto-plastic: they deform elastically for stresses below a certain yield and plastically at the limit. This approach dismisses any time dependent behavior that occurs in nature. Our goal is to better understand this time dependency by considering the visco-elastic behavior of shales before plasticity is reached. Shales are also typically heterogeneous and the question arises as to how to derive their effective properties in order to model them as a homogeneous medium. We model shales using inclusion based models due to their versatility and their ability to represent the microstructure. The inclusions represent competent quartz or calcite grains which are set in a viscous matrix made of clay minerals. Our approach relies on both numerical and analytical results in two dimension and we use them to cross check each other. The numerical results are obtained using MILAMIN, a fast-finite element solver for large problems, while the analytical solutions are based on the correspondence principle of linear viscoelasticity. This principle allows us to use the results on effective properties already derived for elastic bodies and to adapt them to viscoelastic bodies. We start by revisiting the problem of a single inclusion in an infinite medium and then move on to consider many inclusions.

  2. Viscoelastic properties of ferrofluids.

    PubMed

    Chirikov, D N; Fedotov, S P; Iskakova, L Yu; Zubarev, A Yu

    2010-11-01

    The paper deals with theoretical study of non linear viscoelastic phenomena in ferrofluids placed in magnetic field. Our attention is focused on the study of nonstationary flow and Maxwell-like relaxation of the macroscopical viscous stress after alternation of the shear rate. We propose that these phenomena can be explained by finite rate of evolution of chainlike aggregates, consisting of the ferrofluid particles. Statistical model of the chains growth-disintegration is suggested. In this model the chain-single particle mechanism of the chains evolution is considered, the effects of the chain-chain interaction are ignored. The proposed model allows us to estimate the time-dependent function of distribution over number of particles in the chain. Having determined this function and using methods of hydromechanics of ferrofluids with chainlike aggregates, we have studied evolution of the ferrofluid viscosity after stepwise alternation of the fluid shear rate. The estimated time of relaxation is in a reasonable agreement with experimental results. Thus, our analysis shows that the observed macroscopical viscoelastic phenomena in ferrofluids can be provided by evolution of the chain ensemble.

  3. Approximate Controllability Results for Linear Viscoelastic Flows

    NASA Astrophysics Data System (ADS)

    Chowdhury, Shirshendu; Mitra, Debanjana; Ramaswamy, Mythily; Renardy, Michael

    2017-09-01

    We consider linear viscoelastic flow of a multimode Maxwell or Jeffreys fluid in a bounded domain with smooth boundary, with a distributed control in the momentum equation. We establish results on approximate and exact controllability.

  4. An evaluation of the quasi-linear viscoelastic properties of the healing medial collateral ligament in a goat model.

    PubMed

    Abramowitch, Steven D; Woo, Savio L Y; Clineff, Theodore D; Debski, Richard E

    2004-03-01

    The viscoelastic properties of the healing medial collateral ligament (MCL) at 12 weeks after isolated injury were investigated in a goat model. The stress-strain relationships, static and cyclic stress-relaxation behaviors of the healing MCL up to 5% strain were determined experimentally using a femur-MCL-tibia complex. These experimental data were used in combination with the quasi-linear viscoelastic (QLV) theory of Fung (1972) to characterize the reduced relaxation function, G(t) (described by constants C, tau1, and tau2) and the elastic response, sigmae(epsilon) (described by constants A and B) of this tissue. It was found that the percentage of stress relaxation for the healing MCLs was significantly greater than those for sham-operated controls (49.0 +/- 12.1% vs. 26.5 +/- 8.1%, respectively; p < 0.05). The product of constants A x B, i.e. the initial slope of the stress-strain curves, was found to be significantly lower for healing MCLs compared to those for sham-operated controls (32.9 +/- 15.8 MPa vs. 118.8 +/- 48.3 MPa; p < 0.05). The dimensionless constant C, i.e. the magnitude of the viscous response, was nearly three times greater for healing MCLs, while constant tau1 was found to be similar between the two groups (0.80 +/- 0.43 s vs. 0.89 +/- 0.52 s, respectively). Constant tau2 for the healing MCL was significantly less than the controls (1269 +/- 38 s vs. 1845 +/- 431 s; p < 0.05) indicating that the stress relaxation reached a plateau earlier. These constants of the QLV theory used to describe the healing MCL were validated for the strain level utilized in this experiment (approximately equal to 4.5%) by predicting the peak stresses during a cyclic stress-relaxation experiment. The theoretically determined values closely matched the experimentally measured values. Thus, this study demonstrates that the QLV theory could be successfully used to describe the viscoelastic behavior of the MCL during the early phases of healing.

  5. On Wave Propagation in Linear Viscoelasticity.

    DTIC Science & Technology

    1984-07-01

    solutions to equations which model motions of viscoelastic media has received a lot of attention. In this paper , we study linear initial value problems...this paper , we study linear wave propagation in a one-dimensional viscoelastic medium. That is, we study the equation (1.1) utt(x,t) - bux,(x,t) + ft m...singularities. Throughout this paper , the operations of differentiation, convolution, and Laplace transformation should be interpreted in the sense

  6. A comparison of the quasi-static mechanical and non-linear viscoelastic properties of the human semitendinosus and gracilis tendons.

    PubMed

    Abramowitch, Steven D; Zhang, Xiaoyan; Curran, Molly; Kilger, Robert

    2010-05-01

    Over 50-% of anterior cruciate ligament reconstructions are performed using semitendinosus and gracilis tendon autografts. Despite their increased use, there remains little quantitative data on their mechanical behavior. Therefore, the objective of this study was to investigate the quasi-static mechanical and non-linear viscoelastic properties of human semitendinosus and gracilis tendons, as well as the variation of these properties along their length. Specimens were subjected to a series of uniaxial tensile tests: 1-h static stress-relaxation test, 30 cycle cyclic stress-relaxation test and load to failure test. To describe the non-linear viscoelastic behavior, the quasi-linear viscoelastic theory was utilized to model data from the static stress-relaxation experiment. The constants describing the viscoelastic behavior were similar between the proximal and distal halves of the gracilis tendon. The proximal half of the semitendinosus tendon, however, had a greater viscous response than its distal half, which was also significantly higher than the proximal gracilis tendon. In terms of the quasi-static mechanical properties, the properties were similar between the proximal and distal halves of the semitendinosus tendon. However, the distal gracilis tendon showed a significantly higher tangent modulus and ultimate stress compared to its proximal half, which was also significantly higher than the distal semitendinosus tendon. The results of this study demonstrate differences between the semitendinosus and gracilis tendons in terms of their quasi-static mechanical and non-linear viscoelastic properties. These results are important for establishing surgical preconditioning protocols and graft selection. Copyright 2009 Elsevier Ltd. All rights reserved.

  7. A quasi-linear, viscoelastic, structural model of the plantar soft tissue with frequency-sensitive damping properties.

    PubMed

    Ledoux, William R; Meaney, David F; Hillstrom, Howard J

    2004-12-01

    Little is known about the structural properties of plantar soft-tissue areas other than the heel; nor is it known whether the structural properties vary depending on location. Furthermore, although the quasi-linear viscoelastic (QLV) theory has been used to model many soft-tissue types, it has not been employed to model the plantar soft tissue. The structural properties of the plantar soft tissue were quantified via stress relaxation experiments at seven regions (subcalcaneal, five submetatarsal, and subhallucal) across eight cadaveric feet. The cadaveric feet were 36.9 +/- 17.4 (mean +/- S.D.) years of age, all free from vascular diseases and orthopedics disorders. All tests were performed at a constant environmental temperature of 35 degrees C. Stress relaxation experiments were performed; different loads were employed for different areas based on normative gait data. A modification of the relaxation spectrum employed within the QLV theory allowed for the inclusion of frequency-sensitive relaxation properties in addition to nonlinear elastic behavior. The tissue demonstrated frequency-dependent damping properties that made the QLV theory ill suited to model the relaxation. There was a significant difference between the elastic structural properties (A) of the subcalcaneal tissue and all other areas (p = 0.004), and a trend (p = 0.067) for the fifth submetatarsal to have less viscous damping (c1) than the subhallucal, or first, second, or third submetatarsal areas. Thus, the data demonstrate that the structural properties of the foot can vary across regions, but careful consideration must be given to the applied loads and the manner in which the loads were applied.

  8. Viscoelastic Properties of Polymer Blends

    NASA Technical Reports Server (NTRS)

    Hong, S. D.; Moacanin, J.; Soong, D.

    1982-01-01

    Viscosity, shear modulus and other viscoelastic properties of multicomponent polymer blends are predicted from behavior of individual components, using a mathematical model. Model is extension of two-component-blend model based on Rouse-Bueche-Zimm theory of polymer viscoelasticity. Extension assumes that probabilities of forming various possible intracomponent and intercomponent entanglements among polymer molecules are proportional to relative abundances of components.

  9. A Thermodynamic Theory Of Solid Viscoelasticity. Part 1: Linear Viscoelasticity.

    NASA Technical Reports Server (NTRS)

    Freed, Alan D.; Leonov, Arkady I.

    2002-01-01

    The present series of three consecutive papers develops a general theory for linear and finite solid viscoelasticity. Because the most important object for nonlinear studies are rubber-like materials, the general approach is specified in a form convenient for solving problems important for many industries that involve rubber-like materials. General linear and nonlinear theories for non-isothermal deformations of viscoelastic solids are developed based on the quasi-linear approach of non-equilibrium thermodynamics. In this, the first paper of the series, we analyze non-isothermal linear viscoelasticity, which is applicable in a range of small strains not only to all synthetic polymers and bio-polymers but also to some non-polymeric materials. Although the linear case seems to be well developed, there still are some reasons to implement a thermodynamic derivation of constitutive equations for solid-like, non-isothermal, linear viscoelasticity. The most important is the thermodynamic modeling of thermo-rheological complexity , i.e. different temperature dependences of relaxation parameters in various parts of relaxation spectrum. A special structure of interaction matrices is established for different physical mechanisms contributed to the normal relaxation modes. This structure seems to be in accord with observations, and creates a simple mathematical framework for both continuum and molecular theories of the thermo-rheological complex relaxation phenomena. Finally, a unified approach is briefly discussed that, in principle, allows combining both the long time (discrete) and short time (continuous) descriptions of relaxation behaviors for polymers in the rubbery and glassy regions.

  10. Viscoelastic Properties of Human Tracheal Tissues.

    PubMed

    Safshekan, Farzaneh; Tafazzoli-Shadpour, Mohammad; Abdouss, Majid; Shadmehr, Mohammad B

    2017-01-01

    The physiological performance of trachea is highly dependent on its mechanical behavior, and therefore, the mechanical properties of its components. Mechanical characterization of trachea is key to succeed in new treatments such as tissue engineering, which requires the utilization of scaffolds which are mechanically compatible with the native human trachea. In this study, after isolating human trachea samples from brain-dead cases and proper storage, we assessed the viscoelastic properties of tracheal cartilage, smooth muscle, and connective tissue based on stress relaxation tests (at 5% and 10% strains for cartilage and 20%, 30%, and 40% for smooth muscle and connective tissue). After investigation of viscoelastic linearity, constitutive models including Prony series for linear viscoelasticity and quasi-linear viscoelastic, modified superposition, and Schapery models for nonlinear viscoelasticity were fitted to the experimental data to find the best model for each tissue. We also investigated the effect of age on the viscoelastic behavior of tracheal tissues. Based on the results, all three tissues exhibited a (nonsignificant) decrease in relaxation rate with increasing the strain, indicating viscoelastic nonlinearity which was most evident for cartilage and with the least effect for connective tissue. The three-term Prony model was selected for describing the linear viscoelasticity. Among different models, the modified superposition model was best able to capture the relaxation behavior of the three tracheal components. We observed a general (but not significant) stiffening of tracheal cartilage and connective tissue with aging. No change in the stress relaxation percentage with aging was observed. The results of this study may be useful in the design and fabrication of tracheal tissue engineering scaffolds.

  11. Incorporating linear viscoelasticity into acoustic scattering theory

    NASA Astrophysics Data System (ADS)

    Hipp, Alexander K.; Adjadj, Laurent P.; Storti, Giuseppe; Morbidelli, Massimo

    2002-04-01

    The scattering theory of Epstein and Carhart [J. Acoust. Soc. Am. 25, 553-565 (1953)] and Allegra and Hawley [J. Acoust. Soc. Am. 51, 1545-1564 (1972)] is a well-established approach for the prediction of the acoustic attenuation and sound speed in suspensions and emulsions. The original theory assumes that each phase is either an elastic solid or a Newtonian liquid; incorporation of other rheological behavior generally requires rederivation of the model equations. An exception is the case of linear viscoelasticity: using a suitable stress-strain relation, the original model equations also hold for this case. In this work, it is shown that G*=G'-iG'', where G' and G'' are the storage and loss moduli of a viscoelastic material, is analogous to the shear modulus G (elastic solids) and -iωɛ (Newtonian liquids). Viscoelasticity can thus be introduced simply by using G* in place of G.

  12. Viscoelastic properties of the false vocal fold

    NASA Astrophysics Data System (ADS)

    Chan, Roger W.

    2004-05-01

    The biomechanical properties of vocal fold tissues have been the focus of many previous studies, as vocal fold viscoelasticity critically dictates the acoustics and biomechanics of phonation. However, not much is known about the viscoelastic response of the ventricular fold or false vocal fold. It has been shown both clinically and in computer simulations that the false vocal fold may contribute significantly to the aerodynamics and sound generation processes of human voice production, with or without flow-induced oscillation of the false fold. To better understand the potential role of the false fold in phonation, this paper reports some preliminary measurements on the linear and nonlinear viscoelastic behavior of false vocal fold tissues. Linear viscoelastic shear properties of human false fold tissue samples were measured by a high-frequency controlled-strain rheometer as a function of frequency, and passive uniaxial tensile stress-strain response of the tissue samples was measured by a muscle lever system as a function of strain and loading rate. Elastic moduli (Young's modulus and shear modulus) of the false fold tissues were calculated from the measured data. [Work supported by NIH.

  13. Viscoelastic properties of cellular polypropylene ferroelectrets

    NASA Astrophysics Data System (ADS)

    Gaal, Mate; Bovtun, Viktor; Stark, Wolfgang; Erhard, Anton; Yakymenko, Yuriy; Kreutzbruck, Marc

    2016-03-01

    Viscoelastic properties of cellular polypropylene ferroelectrets (PP FEs) were studied at low frequencies (0.3-33 Hz) by dynamic mechanical analysis and at high frequencies (250 kHz) by laser Doppler vibrometry. Relaxation behavior of the in-plane Young's modulus ( Y11 ' ˜ 1500 MPa at room temperature) was observed and attributed to the viscoelastic response of polypropylene matrix. The out-of-plane Young's modulus is very small ( Y33 ' ≈ 0.1 MPa) at low frequencies, frequency- and stress-dependent, evidencing nonlinear viscoelastic response of PP FEs. The high-frequency mechanical response of PP FEs is shown to be linear viscoelastic with Y33 ' ≈ 0.8 MPa. It is described by thickness vibration mode and modeled as a damped harmonic oscillator with one degree of freedom. Frequency dependence of Y33 * in the large dynamic strain regime is described by the broad Cole-Cole relaxation with a mean frequency in kHz range attributed to the dynamics of the air flow between partially closed air-filled voids in PP FEs. Switching-off the relaxation contribution causes dynamic crossover from the nonlinear viscoelastic regime at low frequencies to the linear viscoelastic regime at high frequencies. In the small strain regime, contribution of the air flow seems to be insignificant and the power-law response, attributed to the mechanics of polypropylene cell walls and closed air voids, dominates in a broad frequency range. Mechanical relaxation caused by the air flow mechanism takes place in the sound and ultrasound frequency range (10 Hz-1 MHz) and, therefore, should be taken into account in ultrasonic applications of the PP FEs deal with strong exciting or receiving signals.

  14. Modeling of linear viscoelastic space structures

    NASA Astrophysics Data System (ADS)

    McTavish, D. J.; Hughes, P. C.

    1993-01-01

    The GHM Method provides viscoelastic finite elements derived from the commonly used elastic finite elements. Moreover, these GHM elements are used directly and conveniently in second-order structural models just like their elastic counterparts. The forms of the GHM element matrices preserve the definiteness properties usually associated with finite element matrices (the mass matrix is positive definite, the stiffness matrix is nonnegative definite, and the damping matrix is positive semidefinite). In the Laplace domain, material properties are modeled phenomenologically as a sum of second-order rational functions dubbed 'minioscillator' terms. Developed originally as a tool for the analysis of damping in large flexible space structures, the GHM method is applicable to any structure which incorporates viscoelastic materials.

  15. Influence of composition fluctuations on the linear viscoelastic properties of symmetric diblock copolymers near the order-disorder transition

    SciTech Connect

    Hickey, Robert J.; Gillard, Timothy M.; Lodge, Timothy P.; Bates, Frank S.

    2015-08-28

    Rheological evidence of composition fluctuations in disordered diblock copolymers near the order disorder transition (ODT) has been documented in the literature over the past three decades, characterized by a failure of time–temperature superposition (tTS) to reduce linear dynamic mechanical spectroscopy (DMS) data in the terminal viscoelastic regime to a temperature-independent form. However, for some materials, most notably poly(styrene-b-isoprene) (PS–PI), no signature of these rheological features has been found. We present small-angle X-ray scattering (SAXS) results on symmetric poly(cyclohexylethylene-b-ethylene) (PCHE–PE) diblock copolymers that confirm the presence of fluctuations in the disordered state and DMS measurements that also show no sign of the features ascribed to composition fluctuations. Assessment of DMS results published on five different diblock copolymer systems leads us to conclude that the effects of composition fluctuations can be masked by highly asymmetric block dynamics, thereby resolving a long-standing disagreement in the literature and reinforcing the importance of mechanical contrast in understanding the dynamics of ordered and disordered block polymers.

  16. Viscoelastic properties of heavy oils

    NASA Astrophysics Data System (ADS)

    Rojas Luces, Maria Alejandra

    Rheological low frequency measurements were carried out to analyze the viscoelastic properties of four heavy oil samples. At room conditions, the heavy oil samples exhibit non-Newtonian or viscoelastic behavior since they have a viscous component and an elastic component. The latter becomes very important for temperatures below 30°C, and for seismic to ultrasonic frequencies. Above this temperature, the viscous component increases significantly in comparison to the elastic component, and for seismic frequencies heavy oils can be considered as Newtonian fluids. A new viscosity model based on the concept of activation energy was derived to predict viscosity in terms of frequency and temperature for temperatures below 60°C. A new frequency-temperature dispersion model was derived to address the variation of the complex shear modulus (G*) with frequency and temperature for the heavy oil samples. This model fits the data well for seismic and sonic frequencies but it overpredicts G* at ultrasonic frequencies.

  17. Viscoelastic properties of a synthetic meniscus implant.

    PubMed

    Shemesh, Maoz; Asher, Roy; Zylberberg, Eyal; Guilak, Farshid; Linder-Ganz, Eran; Elsner, Jonathan J

    2014-01-01

    There are significant potential advantages for restoration of meniscal function using a bio-stable synthetic implant that combines long-term durability with a dependable biomechanical performance resembling that of the natural meniscus. A novel meniscus implant made of a compliant polycarbonate-urethane matrix reinforced with high modulus ultrahigh molecular weight polyethylene fibers was designed as a composite structure that mimics the structural elements of the natural medial meniscus. The overall success of such an implant is linked on its capability to replicate the stress distribution in the knee over the long-term. As this function of the device is directly dependent on its mechanical properties, changes to the material due to exposure to the joint environment and repeated loading could have non-trivial influences on the viscoelastic properties of the implant. Thus, the goal of this study was to measure and characterize the strain-rate response, as well as the viscoelastic properties of the implant as measured by creep, stress relaxation, and hysteresis after simulated use, by subjecting the implant to realistic joint loads up to 2 million cycles in a joint-like setting. The meniscus implant behaved as a non-linear viscoelastic material. The implant underwent minimal plastic deformation after 2 million fatigue loading cycles. Under low compressive loads, the implant was fairly flexible, and able to deform relatively easily (E=120-200 kPa). However as the compressive load applied on the implant was increased, the implant became stiffer (E=3.8-5.2 MPa), to resist deformation. The meniscus implant appears well-matched to the viscoelastic properties of the natural meniscus, and importantly, these properties were found to remain stable and minimally affected by potentially degradative and loading conditions associated with long-term use.

  18. Viscoelastic properties of oat ß-glucan-rich aqueous dispersions

    USDA-ARS?s Scientific Manuscript database

    C-trim is a healthy food product containing the dietary of soluble fiber ß-glucan. The suspension of C-trim in water is a hydrocolloid biopolymer. The linear and non-linear rheological properties for suspensions of C-trim biopolymers were investigated. The linear viscoelastic behaviors for C-trim...

  19. Non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

    PubMed

    van Dam, Evelyne A; Dams, Susanne D; Peters, Gerrit W M; Rutten, Marcel C M; Schurink, Geert Willem H; Buth, Jaap; van de Vosse, Frans N

    2008-04-01

    The objective of this work was to determine the linear and non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus and to study the changes in mechanical properties throughout the thickness of the thrombus. Samples are gathered from thrombi of seven patients. Linear viscoelastic data from oscillatory shear experiments show that the change of properties throughout the thrombus is different for each thrombus. Furthermore the variations found within one thrombus are of the same order of magnitude as the variation between patients. To study the non-linear regime, stress relaxation experiments are performed. To describe the phenomena observed experimentally, a non-linear multimode model is presented. The parameters for this model are obtained by fitting this model successfully to the experiments. The model cannot only describe the average stress response for all thrombus samples but also the highest and lowest stress responses. To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis.

  20. Temperature-dependent viscoelastic properties of the human supraspinatus tendon.

    PubMed

    Huang, Chun-Yuh; Wang, Vincent M; Flatow, Evan L; Mow, Van C

    2009-03-11

    Temperature effects on the viscoelastic properties of the human supraspinatus tendon were investigated using static stress-relaxation experiments and the quasi-linear viscoelastic (QLV) theory. Twelve supraspinatus tendons were randomly assigned to one of two test groups for tensile testing using the following sequence of temperatures: (1) 37, 27, and 17 degrees C (Group I, n=6), or (2) 42, 32, and 22 degrees C (Group II, n=6). QLV parameter C was found to increase at elevated temperatures, suggesting greater viscous mechanical behavior at higher temperatures. Elastic parameters A and B showed no significant difference among the six temperatures studied, implying that the viscoelastic stress response of the supraspinatus tendon is not sensitive to temperature over shorter testing durations. Using regression analysis, an exponential relationship between parameter C and test temperature was implemented into QLV theory to model temperature-dependent viscoelastic behavior. This modified approach facilitates the theoretical determination of the viscoelastic behavior of tendons at arbitrary temperatures.

  1. Effect of interfacial viscoelasticity on the bulk linear viscoelastic moduli of globular protein solutions

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenhuan; Barman, Sourav; Christopher, Gordon F.

    2014-05-01

    The role of interfacial rheology on the bulk linear viscoelastic moduli of low concentration bovine albumin solutions is probed. Previously reported soft gel properties of these systems were attributed to either protein aggregation or organization within the bulk. Instead, these behaviors are shown to be attributable to the measurement error caused by interfacial rheology due to adsorption of bovine serum albumin to the air and water interface. Even at low bulk concentrations, fast interfacial adsorption results in erroneous measurements. When these effects are removed, the solutions are viscous dominated with a dynamic viscosity slightly larger than water.

  2. Viscoelastic properties of Ionomer Melt

    NASA Astrophysics Data System (ADS)

    Goswami, Monojoy; Kumar, Sanat

    2007-03-01

    Viscoelastic prperties of a model telechelic ionomer, i.e., a melt of non-polar polymers with a charge at each chain end along with neutralizing counterions, have been examined using molecular dynamics simulation. Equlibrium calculation of the loss modulus G^''(φ) and storage modulus G^'(φ) shows plateau at lower temperatures when the systems are not relaxed. In this situation the specific heat (Cv) peak corresponds to the self-assembly of the system, at lower temperatures the specific heat begins to plateau. Similarities of the dynamic features found for telechelic melts with those observed in glass-forming liquids and entangled polymers have been shown. Furthremore, using an athermal 'probe', the properties of these materials is being distinctly classified as 'strong' glass or physical gels.

  3. A log-linearized arterial viscoelastic model for evaluation of the carotid artery.

    PubMed

    Hirano, Harutoyo; Horiuchi, Tetsuya; Kutluk, Abdugheni; Kurita, Yuichi; Ukawa, Teiji; Nakamura, Ryuji; Saeki, Noboru; Higashi, Yukihito; Kawamoto, Masashi; Yoshizumi, Masao; Tsuji, Toshio

    2013-01-01

    This paper proposes a method for qualitatively estimating the mechanical properties of arterial walls on a beat-to-beat basis through noninvasive measurement of continuous arterial pressure and arterial diameter using an ultrasonic device. First, in order to describe the nonlinear relationships linking arterial pressure waveforms and arterial diameter waveforms as well as the viscoelastic characteristics of arteries, we developed a second-order nonlinear model (called the log-linearized arterial viscoelastic model) to allow estimation of arterial wall viscoelasticity. Next, to verify the validity of the proposed method, the viscoelastic indices of the carotid artery were estimated. The results showed that the proposed model can be used to accurately approximate the mechanical properties of arterial walls. It was therefore deemed suitable for qualitative evaluation of arterial viscoelastic properties based on noninvasive measurement of arterial pressure and arterial diameter.

  4. Determination of linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

    PubMed

    van Dam, Evelyne A; Dams, Susanne D; Peters, Gerrit W M; Rutten, Marcel C M; Schurink, Geert Willem H; Buth, Jaap; van de Vosse, Frans N

    2006-01-01

    The objective of this study is to determine whether the linear viscoelastic properties of an abdominal aortic aneurysm thrombus can be determined by rheometry. Although large strains occur in the in vivo situation, in this work only linear behavior is studied to show the applicability of the described methods. A thrombus exists of several layers that vary in composition, structure and mechanical properties. Two types of thrombus are described. In discrete transition thrombi the layers are not or at most weakly attached to each other and the structure of each layer is different. Continuous transition thrombi consist of strongly attached layers whose structure changes gradually throughout the thickness of the thrombus. Shear experiments are performed on samples from both types of thrombus on a rotational rheometer using a parallel plate geometry. In the discrete type the storage modulus G' cannot be assumed equal for the different layers. In the continuous thrombus, G', changes gradually throughout the layered structure. In both types the loss modulus, G'', does not vary throughout the thrombus. Furthermore, it was found that Time-Temperature Superposition is applicable to thrombus tissue. Since results were reproducible it can be concluded that the method we used to determine the viscoelastic properties is applicable to thrombus tissue.

  5. Viscoelastic properties of levan polysaccharides

    NASA Astrophysics Data System (ADS)

    Noll, Kenneth; Rende, Deniz; Ozisik, Rahmi; Toksoy-Oner, Ebru

    2014-03-01

    Levan is a naturally occurring polysaccharide that is composed of β-D-fructofuranose units with β(2-6) linkages between fructose rings. It is synthesized by the action of a secreted levansucrase (EC 2.4.1.10) that converts sucrose into the levan externally (exopolysaccharide). Levan is a homopolysaccharide that is non-toxic, water soluble,, and has anti-tumor activity and low immunological response. Therefore, levan presents great potential to be used as a novel functional biopolymer in foods, feeds, cosmetics, pharmaceutical and chemical industries. Despite these favorable properties, levan has a moderately low mechanical properties and poor film forming capability. In the current study, the agglomeration behavior of levan in water and in saline solutions was investigated at 298 and 310 K by dynamic light scattering and transmission electron microscopy (TEM). The viscoelastic properties of neat and oxidized levan films were studied via nanoindentation experiments in the quasi-static and dynamic modes The material is partially based upon work supported by NSF under Grant Nos. 1200270 and 1003574, and TUBITAK 111M232.

  6. Viscoelastic properties of demineralized dentin matrix.

    PubMed

    Pashley, David H; Agee, Kelli A; Wataha, John C; Rueggeberg, Frederick; Ceballos, Laura; Itou, Kousuke; Yoshiyama, Masahiro; Carvalho, Ricardo M; Tay, Franklin R

    2003-12-01

    To evaluate the viscoelastic properties of demineralized dentin matrix. Stress-relaxation studies were done on matrices in tension and strain elongation or creep studies were done in both tension and compression. Mid-coronal dentin disks were prepared from extracted unerupted human third molars. Disks were 0.5 mm thick for stress-relaxation or tensile creep experiments and 0.2-0.3 mm thick for compressive creep studies. 'I' beam specimens were prepared from dentin disks and the middle region was demineralized in 0.5 M EDTA (pH 7) for 4 days. The specimens were held in miniature friction grips in water and pulled at 100 micro m s(-1) to strains of 5, 10, 15 or 20% and then held for 10 min to follow the decay of stress over time. Creep was determined on demineralized dentin immersed in water in tension and in compression. Compressive creep was measured using an LVDT contact probe with loads of 0.02-0.5 N. Strain data were converted to compliance-time curves (strain/stress) and expressed as total compliance (J(t)), instantaneous elastic compliance (J(o)), retarded elastic compliance (J(R)) and viscous response (t/eta) or creep. The dentin matrix exhibits both stress-relaxation and creep behavior. Stress-relaxation and tensile creep were independent of strain but compressive creep rates were inversely related to compressive strain. Creep values were about 10% at low compressive strains, but fell progressively to 1% at high strains. Compliance-time curves fell with stress and came closer together. However, tensile creep was about 3% regardless of the strain. The dentin matrix exhibits viscoelastic properties, but is not linearly viscoelastic. The relatively high creep rates of the matrix under low compressive loads may cause viscous deformations in poorly infiltrated hybrid layers in resin-bonded teeth under function.

  7. Geometrically-linear and nonlinear analysis of linear viscoelastic composites using the finite element method

    NASA Astrophysics Data System (ADS)

    Hammerand, Daniel C.

    Over the past several decades, the use of composite materials has grown considerably. Typically, fiber-reinforced polymer-matrix composites are modeled as being linear elastic. However, it is well-known that polymers are viscoelastic in nature. Furthermore, the analysis of complex structures requires a numerical approach such as the finite element method. In the present work, a triangular flat shell element for linear elastic composites is extended to model linear viscoelastic composites. Although polymers are usually modeled as being incompressible, here they are modeled as compressible. Furthermore, the macroscopic constitutive properties for fiber-reinforced composites are assumed to be known and are not determined using the matrix and fiber properties along with the fiber volume fraction. Hygrothermo-rheologically simple materials are considered for which a change in the hygrothermal environment results in a horizontal shifting of the relaxation moduli curves on a log time scale, in addition to the usual hygrothermal loads. Both the temperature and moisture are taken to be prescribed. Hence, the heat energy generated by the viscoelastic deformations is not considered. When the deformations and rotations are small under an applied load history, the usual engineering stress and strain measures can be used and the time history of a viscoelastic deformation process is determined using the original geometry of the structure. If, however, sufficiently large loads are applied, the deflections and rotations will be large leading to changes in the structural stiffness characteristics and possibly the internal loads carried throughout the structure. Hence, in such a case, nonlinear effects must be taken into account and the appropriate stress and strain measures must be used. Although a geometrically-nonlinear finite element code could always be used to compute geometrically-linear deformation processes, it is inefficient to use such a code for small deformations, due to

  8. Viscoelastic properties of semiflexible filamentous bacteriophage fd.

    PubMed

    Schmidt, F G; Hinner, B; Sackmann, E; Tang, J X

    2000-10-01

    The cytoskeletal protein filament F-actin has been treated in a number of recent studies as a model physical system for semiflexible filaments. In this work, we studied the viscoelastic properties of entangled solutions of the filamentous bacteriophage fd as an alternative to F-actin with similar physical parameters. We present both microrheometric and macrorheometric measurements of the viscoelastic storage and loss moduli, G'(f ) and G"(f ), respectively, in a frequency range 0.01viscoelastic moduli can be described by power laws G'(f ) approximately f(0.9-1.2) and G"(f ) approximately f(0.7-0.9), which deviate significantly from the simple theoretical predictions of G'(f ) approximately f(2) and G"(f ) approximately f(1). The latter behavior cannot yet be understood within the framework of current theories of semiflexible filament networks. For the dynamic viscosity at the low shear rate limit, a concentration dependence of eta(0) approximately c(2.6) was found. Finally, a linear scaling of the terminal relaxation time with concentration, tau(d) approximately c, was observed.

  9. Semi-analytical computation of displacement in linear viscoelastic materials

    NASA Astrophysics Data System (ADS)

    Spinu, S.; Gradinaru, D.

    2015-11-01

    Prediction of mechanical contact performance based on elastic models is not accurate in case of viscoelastic materials; however, a closed-form description of the viscoelastic contact has yet to be found. This paper aims to advance a semi-analytical method for computation of displacement induced in viscoelastic materials by arbitrary surface tractions, as a prerequisite to a semi-analytical solution for the viscoelastic contact problem. The newly advanced model is expected to provide greater generality, allowing for arbitrary contact geometry and / or arbitrary loading history. While time-independent equations in the purely elastic model can be treated numerically by imposing a spatial discretization only, a viscoelastic constitutive law requires supplementary temporal discretization capable of simulating the memory effect specific to viscoelastic materials. By deriving new influence coefficients, computation of displacement induced in a viscoelastic material by a known but otherwise arbitrary history of surface tractions can be achieved via superposition authorized by the Boltzmann superposition theory applicable in the frame of linear viscoelasticity.

  10. Linear Viscoelasticity and Swelling of Polyelectrolyte Complex Coacervates

    NASA Astrophysics Data System (ADS)

    Hamad, Fawzi; Colby, Ralph

    2012-02-01

    The addition of near equimolar amounts of poly(diallyldimethylammonium chloride) to poly(isobutylene-alt-maleate sodium), results in formation of a polyelectrolyte complex coacervate. Zeta-potential titrations conclude that these PE-complexes are nearly charge-neutral. Swelling and rheological properties are studied at different salt concentrations in the surrounding solution. The enhanced swelling observed at high salt concentration suggests the system behaves like a polyampholyte gel, and weaker swelling at very low salt concentrations implies polyelectrolyte gel behavior. Linear viscoelastic oscillatory shear measurements indicate that the coacervates are viscoelastic liquids and that increasing ionic strength of the medium weakens the electrostatic interactions between charged units, lowering the relaxation time and viscosity. We use the time-salt superposition idea recently proposed by Spruijt, et al., allowing us to construct master curves for these soft materials. Similar swelling properties observed when varying molecular weights. Rheological measurements reveal that PE-complexes with increasing molecular weight polyelectrolytes form a network with higher crosslink density, suggesting time-molecular weight superposition idea.

  11. Viscoelastic properties of vis-breaking polypropylenes

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Moad, Graeme; Habsuda, Jana; Li, Guoxin; Nichols, Lance; Dagley, Ian; Simon, George P.

    2015-12-01

    In this work hydrogen peroxide is used as a green initiator to cause scissioning of polypropylene (PP) with water as the only by-product replacing the organic peroxides that are usually used. The rheological properties of a commercial polypropylene and of the scissioned samples are determined by dynamic rheology and an inversion procedure for converting the linear viscoelastic data into molar mass distribution has been adopted. The results presented show that the molar mass distribution of the PP polymer is narrowed on scissioning. The process is found to produce polymers similar in molecular architecture and behavior to organic peroxide cleaved materials, the results of which are given as a comparison in this work.

  12. Viscoelastic properties of 3-D braided PEEK/graphite composites

    SciTech Connect

    Hu, Jian-Ni.

    1992-01-01

    In this study, 3-D braided PEEK/AS4 graphite composites were performed and processed to investigate the viscoelastic behavior of this new system. These manufactured composites were characterized to determine their fiber volume fractions and matrix crystallinity indices using matrix digestion and wide angle x-ray diffraction. After physical characterization, the mechanical response of these composites were evaluated at various temperatures. Experimental results from tensile measurements were compared to an established fabric geometry model (FGM). This model predicts tensile modules based upon fiber and matrix properties, fiber volume fraction, and braiding angle. Model predictions and experimental results are given here, and are in good agreement with each other. In order to study the time-dependent mechanical properties of these 3-D braided composites, their stress relaxation, creep and dynamic mechanical properties were evaluated. These results were then compared to a new composite model. This model combined a Quasi/linear Viscoelastic Model (QVM) for the viscoelastic behavior of PEEK with the FGM approach to predict the viscoelastic behavior of 3-D PEEK composites. The experimental stress relaxation and creep results are in good agreement with the QVM-FGM analysis. Thus, the QVM-FGM approach was used to accurately correlate these viscoelastic properties of 3-D braided PEEK/graphite composites. Through wider use and testing, this QVM/FGM approach may be used to increase our understanding and perhaps facilitate the design of composite structures.

  13. Viscoelastic modelling of tennis ball properties

    NASA Astrophysics Data System (ADS)

    Sissler, L.; Jones, R.; Leaney, P. G.; Harland, A.

    2010-06-01

    An explicit finite element (FE) tennis ball model which illustrates the effects of the viscoelastic materials of a tennis ball on ball deformation and bounce during normal impacts is presented. A tennis ball is composed of a rubber core and a fabric cover comprised of a wool-nylon mix which exhibit non-linear strain rate properties during high velocity impacts. The rubber core model was developed and validated using low strain rate tensile tests on rubber samples as well as high velocity normal impacts of pressurised cores at velocities ranging from 15 m/s to 50 m/s. The impacts were recorded using a high speed video (HSV) camera to determine deformation, impact time and coefficient of restitution (COR). The material properties of the core model were tuned to match the HSV results. A two component anisotropic fabric model was created which included artificial Rayleigh damping to account for hysteresis effects, and the core model 'tuning' process was used to refine the cloth layer. The ball model's parameters were in good agreement with experimental data at all velocities for both cores and complete balls, and a time sequenced comparison of HSV ball motion and FE model confirmed the validity of the model.

  14. A geometrically nonlinear shell element for hygrothermorheologically simple linear viscoelastic composites

    SciTech Connect

    HAMMERAND,DANIEL C.; KAPANIA,RAKESH K.

    2000-05-01

    A triangular flat shell element for large deformation analysis of linear viscoelastic laminated composites is presented. Hygrothermorheologically simple materials are considered for which a change in the hygrothermal environment results in a horizontal shifting of the relaxation moduli curves on a log time scale, in addition to the usual hygrothermal loads. Recurrence relations are developed and implemented for the evaluation of the viscoelastic memory loads. The nonlinear deformation process is computed using an incremental/iterative approach with the Newton-Raphson Method used to find the incremental displacements in each step. The presented numerical examples consider the large deformation and stability of linear viscoelastic structures under deformation-independent mechanical loads, deformation-dependent pressure loads, and thermal loads. Unlike elastic structures that have a single critical load value associated with a given snapping of buckling instability phenomenon, viscoelastic structures will usually exhibit a particular instability for a range of applied loads over a range of critical times. Both creep buckling and snap-through examples are presented here. In some cases, viscoelastic results are also obtained using the quasielastic method in which load-history effects are ignored, and time-varying viscoelastic properties are simply used in a series of elastic problems. The presented numerical examples demonstrate the capability and accuracy of the formulation.

  15. TEMPERATURE-DEPENDENT VISCOELASTIC PROPERTIES OF THE HUMAN SUPRASPINATUS TENDON

    PubMed Central

    Huang, Chun-Yuh; Wang, Vincent M.; Flatow, Evan L.; Mow, Van C.

    2009-01-01

    Temperature effects on the viscoelastic properties of the human supraspinatus tendon were investigated using static stress-relaxation experiments and Quasi-Linear Viscoelastic (QLV) theory. Twelve supraspinatus tendons were randomly assigned to one of two test groups for tensile testing using the following sequence of temperatures: (1) 37°C, 27°C, and 17°C (Group I, n=6), or (2) 42°C, 32°C, and 22°C (Group II, n=6). QLV parameter C was found to increase at elevated temperatures, suggesting greater viscous mechanical behavior at higher temperatures. Elastic parameters A and B showed no significant difference among the six temperatures studied, implying that the viscoelastic stress response of the supraspinatus tendon is not sensitive to temperature over shorter testing durations. Using regression analysis, an exponential relationship between parameter C and test temperature was implemented into QLV theory to model temperature-dependent viscoelastic behavior. This modified approach facilitates the theoretical determination of the viscoelastic behavior of tendons at arbitrary temperatures. PMID:19159888

  16. Anisotropy of bituminous mixture in the linear viscoelastic domain

    NASA Astrophysics Data System (ADS)

    Di Benedetto, Hervé; Sauzéat, Cédric; Clec'h, Pauline

    2016-08-01

    Some anisotropic properties in the linear viscoelastic domain of bituminous mixtures compacted with a French LPC wheel compactor are highlighted in this paper. Bituminous mixture is generally considered as isotropic even if the compaction process on road or in laboratory induces anisotropic properties. Tension-compression complex modulus tests have been performed on parallelepipedic specimens in two directions: (i) direction of compactor wheel movement (direction I, which is horizontal) and (ii) direction of compaction (direction II, which is vertical). These tests consist in measuring sinusoidal axial and lateral strains as well as sinusoidal axial stress, when sinusoidal axial loading is applied on the specimen. Different loading frequencies and temperatures are applied. Two complex moduli, EI ^{*} and E_{II}^{*}, and four complex Poisson's ratios, ν_{{II-I}}^{*}, ν_{{III-I}}^{*}, ν_{{I-II}}^{*} and ν_{{III-II}}^{*}, were obtained. The vertical direction appears softer than the other ones for the highest frequencies. There are very few differences between the two directions I and II for parameters concerning viscous effects (phase angles φ(EI) and φ(E_{II}), and shift factors). The four Poisson's ratios reveal anisotropic properties but rheological tensor can be considered as symmetric when considering very similar values obtained for the two measured parameters (I-II and II-I)

  17. Viscoelastic properties of laryngeal posturing muscles

    NASA Astrophysics Data System (ADS)

    Alipour, Fariborz; Hunter, Eric; Titze, Ingo

    2003-10-01

    Viscoelastic properties of canine laryngeal muscles were measured in a series of in vitro experiments. Laryngeal posturing that controls vocal fold length and adduction/abduction is an essential component of the voice production. The dynamics of posturing depends on the viscoelastic and physiological properties of the laryngeal muscles. The time-dependent and nonlinear behaviors of these tissues are also crucial in the voice production and pitch control theories. The lack of information on some of these muscles such as posterior cricoarytenoid muscle (PCA), lateral cricoarytenoid muscle (LCA), and intraarytenoid muscle (IA) was the major incentive for this study. Samples of PCA and LCA muscles were made from canine larynges and mounted on a dual-servo system (Ergometer) as described in our previous works. Two sets of experiments were conducted on each muscle, a 1-Hz stretch and release experiment that provides stress-strain data and a stress relaxation test. Data from these muscles were fitted to viscoelastic models and Young's modulus and viscoelastic constants are obtained for each muscle. Preliminary data indicates that elastics properties of these muscles are similar to those of thyroarytenoid and cricothyroid muscles. The relaxation response of these muscles also shows some similarity to other laryngeal muscles in terms of time constants.

  18. Measurement of viscoelastic properties at small length scales for heterogeneous and nonlinear materials

    NASA Astrophysics Data System (ADS)

    Wang, Fang

    In this dissertation, advances in linear and non-linear viscoelastic analysis and experimentation have been employed to investigate the properties of materials using nanoindentation. In the first study, a general linear-viscoelastic model was developed to measure the properties of polydimethylsiloxane (PDMS) using a flat punch indenter. Subsequently, linear viscoelastic nanoindentation was used to measure the young's relaxation modulus of a locally-heterogeneous thermally-aged bismaleimide resin using a Berkovich indenter. Nanoindentation measurements were conducted on both surface and cross section of aged bismaleimide resin specimens with different aging time at 200°C and 300°C respectively to extract the oxidation effect of sample under high temperatures. Finally, nanoindentation measurements were made on human tympanic membrane specimens with using a spherical nanoindenter tip in direct contact with the collagen fiber layer. Linear viscoelastic analysis was conducted to extract the Young's relaxation modulus distributions. The study also focused on the development of non-linear viscoelastic analysis of indentation experiments. Despite the fact that the nanoindentation technique is well established for the characterization of elasto-plastic materials, nanoindentation on viscoelastic materials is not fully understood especially in nonlinear viscoelastic region. In the dissertation, a nonlinear viscoelastic model was developed and implemented in Abaqus/Implicit Code to analyze the nonlinear visceoelastic behavior of polyvinyl acetate (PVA) under nanoindentation.

  19. Viscoelastic properties of polymer based layered-silicate nanocomposites

    NASA Astrophysics Data System (ADS)

    Ren, Jiaxiang

    Polymer based layered-silicate nanocomposites offer the potential for dramatically improved mechanical, thermal, and barrier properties while keeping the material density low. Understanding the linear and non-linear viscoelastic response for such materials is crucial because of the ability of such measurements to elucidate the mesoscale dispersion of layered-silicates and changes in such dispersion to applied flows as would be encountered in processing of these materials. A series of intercalated polystyrene (and derivatives of polystyrene) layered-silicate nanocomposites are studied to demonstrate the influence of mesoscale dispersion and organic---inorganic interactions on the linear and non-linear viscoelastic properties. A layered-silicate network structure is exhibited for the nanocomposites with strong polymer-silicate interaction such as montmorillonite (2C18M) and fluorohectorite (C18F) and the percolation threshold is ˜ 6 wt % for the 2C18M based hybrids. However, the nanocomposites based on hectorite (2C18H) with weak polymer-silicate interaction exhibit liquid-like terminal zone behavior. Furthermore, the enhanced terminal zone elastic modulus and viscosity of high brominated polystyrene and high molecular weight polystyrene based 2C18M nanocomposites suggest an improved delamination and dispersion of layered-silicates in the polymer matrix. The non-linear viscoelastic properties, specifically, the non-linear stress relaxation behavior and the applicability of time---strain separability, the effect of increasing strain amplitude on the oscillatory shear flow properties, and the shear rate dependence of the steady shear flow properties are examined. The silicate sheets (or collections of sheets) exhibit the ability to be oriented by the applied flow. Experimentally, the empirical Cox - Merz rule is demonstrated to be inapplicable for the hybrids. Furthermore, the K-BKZ constitutive model is used to model the steady shear properties. While being able to

  20. Parameter estimation using the quasi-linear viscoelastic model proposed by Fung.

    PubMed

    Dortmans, L J; Sauren, A A; Rousseau, E P

    1984-08-01

    Using the quasi-linear viscoelastic model proposed by Fung for the description of the viscoelastic properties of soft biological tissues, the parameters governing their time-dependent behavior are commonly estimated from relaxation experiments. Exact quantification is possible from the response to a step change in the strain. Since it is physically impossible to realize a true step change in the strain, in practice the response to a steplike strain change is used. In the present study the discrepancies between the exact and the estimated parameter values are investigated using a hypothetical quasi-linear viscoelastic material. The parameter tau 1, governing the fast viscous phenomena, is found to be subject to the largest errors. Methods for obtaining better estimates of tau 1 are outlined in a number of special cases.

  1. A simple-shear rheometer for linear viscoelastic characterization of vocal fold tissues at phonatory frequencies

    PubMed Central

    Chan, Roger W.; Rodriguez, Maritza L.

    2008-01-01

    Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G′ and G″) of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range. PMID:18681608

  2. Quasi-linear viscoelastic behavior of the human periodontal ligament.

    PubMed

    Toms, Stephanie R; Dakin, Greg J; Lemons, Jack E; Eberhardt, Alan W

    2002-10-01

    Previous studies have not produced a comprehensive mathematical description of the nonlinear viscoelastic stress-strain behavior of the periodontal ligament (PDL). In the present study, the quasi-linear viscoelastic (QLV) model was applied to mechanical tests of the human PDL. Transverse sections of cadaveric premolars were subjected to relaxation tests and loading to failure perpendicular to the plane of section. Distinct and repeatable toe and linear regions of stress-strain behavior were observed. The amount of strain associated with the toe region differed as a function of anatomical location along the tooth root. Stress relaxation behavior was comparable for different anatomical locations. Model predicted peak tissue stresses for cyclic loading were within 11% of experimental values, demonstrating that the QLV approach provided an improved, accurate quantification of PDL mechanical response. The success of the QLV approach supports its usefulness in future efforts of experimental characterization of PDL mechanical behavior.

  3. On nonlinear viscoelastic deformations: a reappraisal of Fung's quasi-linear viscoelastic model

    PubMed Central

    De Pascalis, Riccardo; Abrahams, I. David; Parnell, William J.

    2014-01-01

    This paper offers a reappraisal of Fung's model for quasi-linear viscoelasticity. It is shown that a number of negative features exhibited in other works, commonly attributed to the Fung approach, are merely a consequence of the way it has been applied. The approach outlined herein is shown to yield improved behaviour and offers a straightforward scheme for solving a wide range of models. Results from the new model are contrasted with those in the literature for the case of uniaxial elongation of a bar: for an imposed stretch of an incompressible bar and for an imposed load. In the latter case, a numerical solution to a Volterra integral equation is required to obtain the results. This is achieved by a high-order discretization scheme. Finally, the stretch of a compressible viscoelastic bar is determined for two distinct materials: Horgan–Murphy and Gent. PMID:24910527

  4. On nonlinear viscoelastic deformations: a reappraisal of Fung's quasi-linear viscoelastic model.

    PubMed

    De Pascalis, Riccardo; Abrahams, I David; Parnell, William J

    2014-06-08

    This paper offers a reappraisal of Fung's model for quasi-linear viscoelasticity. It is shown that a number of negative features exhibited in other works, commonly attributed to the Fung approach, are merely a consequence of the way it has been applied. The approach outlined herein is shown to yield improved behaviour and offers a straightforward scheme for solving a wide range of models. Results from the new model are contrasted with those in the literature for the case of uniaxial elongation of a bar: for an imposed stretch of an incompressible bar and for an imposed load. In the latter case, a numerical solution to a Volterra integral equation is required to obtain the results. This is achieved by a high-order discretization scheme. Finally, the stretch of a compressible viscoelastic bar is determined for two distinct materials: Horgan-Murphy and Gent.

  5. Visco-elastic properties and edge stress relaxation of laminated composite materials

    SciTech Connect

    Walrath, D.E.

    1986-01-01

    Applicability of the Schapery single-integral nonlinear visco-elastic constitutive model to describe time-dependent mechanical behavior of laminated composite materials containing two visco-elastic phases was explored. Procedures to measure all five visco-elastic material properties necessary to describe visco-elastic behavior of a transversely isotropic continuous-fiber unidirectional lamina were implemented. Measurement of the through-the-thickness or interlaminar shear visco-elastic response required development of a new test methodology. The losipescu shear test method was selected for this purpose. The visco-elastic response of unidirectional DuPont Kevlar KV49/Hercules 3501-6 epoxy was measured. An automated data-reduction scheme was developed to facilitate description of visco-elastic properties using the Schapery single-integral approach. The basis for this data-reduction scheme differs from similar approaches used by other investigators in that time-superposition features of linear visco-elasticity are preserved. Finally, measured visco-elastic properties of KV49/3501-6 were used to model the interlaminar shear-stress relaxation that occurs near free edges in symmetric angle-ply laminated composite materials loaded by uniform axial extension. Interlaminar stresses induced near free edges were shown to be time-dependent for KV49/3501-6.

  6. Viscoelastic Properties of Vitreous Gel

    NASA Astrophysics Data System (ADS)

    Pirouz Kavehpour, H.; Sharif-Kashani, Pooria

    2010-11-01

    We studied the rheological properties of porcine vitreous humor using a stressed-control shear rheometer. All experiments were performed in a closed environment at body temperature to mimic in-vivo conditions. We modeled the creep deformation using a two-element retardation spectrum model. By associating each element of the model to an individual biopolymeric system in the vitreous gel, a separate response to the applied stress was obtained from each component. The short time scale was associated with the collagen structure, while the longer time scale was related to the microfibrilis and hyaluronan network. We were able to distinguish the role of each main component from the overall rheological properties. Knowledge of this correlation enables us to relate the physical properties of vitreous to its pathology, as well as optimize surgical procedures such as vitrectomy.

  7. Viscoelastic properties of entangled polymers - Ternary blends of monodisperse homopolymers

    NASA Technical Reports Server (NTRS)

    Soong, D.; Shen, M.; Hong, S. D.; Moacanin, J.; Shyu, S. S.

    1979-01-01

    In a previous publication from this laboratory, the Rouse-Bueche-Zimm molecular theory of viscoelasticity has been extended by using a transient network model to apply to binary blends of monodisperse polymers with chain entanglements. The dynamics of the entanglements were modeled both by the enhanced frictional coefficients and by the additional elastic couplings. It was recognized that entanglements not only may form between chains of the same lengths (intracomponent entanglements) but also between those of different lengths (intercomponent entanglements). At a given intercomponent entanglement, the longer chain was assumed to have the frictional coefficient of the shorter chain. Similarly, for blends consisting of several monodisperse components with different molecular weights, such modifications are also required to predict their linear viscoelastic behavior. The frequency of these interactions is assumed to be proportional to the weight ratio of the respective component chains in the blend. Equations of motion are formulated for each component and solved numerically for the relaxation time spectra. Linear viscoelastic properties such as the dynamic mechanical moduli, stress relaxation moduli, and zero-shear viscosity can then be computed for these systems by linear summation of those of the components.

  8. Linear orthotropic viscoelasticity model for fiber reinforced thermoplastic material based on Prony series

    NASA Astrophysics Data System (ADS)

    Endo, Vitor Takashi; de Carvalho Pereira, José Carlos

    2017-05-01

    Material properties description and understanding are essential aspects when computational solid mechanics is applied to product development. In order to promote injected fiber reinforced thermoplastic materials for structural applications, it is very relevant to develop material characterization procedures, considering mechanical properties variation in terms of fiber orientation and loading time. Therefore, a methodology considering sample manufacturing, mechanical tests and data treatment is described in this study. The mathematical representation of the material properties was solved by a linear viscoelastic constitutive model described by Prony series, which was properly adapted to orthotropic materials. Due to the large number of proposed constitutive model coefficients, a parameter identification method was employed to define mathematical functions. This procedure promoted good correlation among experimental tests, and analytical and numerical creep models. Such results encourage the use of numerical simulations for the development of structural components with the proposed linear viscoelastic orthotropic constitutive model. A case study was presented to illustrate an industrial application of proposed methodology.

  9. Linear orthotropic viscoelasticity model for fiber reinforced thermoplastic material based on Prony series

    NASA Astrophysics Data System (ADS)

    Endo, Vitor Takashi; de Carvalho Pereira, José Carlos

    2016-09-01

    Material properties description and understanding are essential aspects when computational solid mechanics is applied to product development. In order to promote injected fiber reinforced thermoplastic materials for structural applications, it is very relevant to develop material characterization procedures, considering mechanical properties variation in terms of fiber orientation and loading time. Therefore, a methodology considering sample manufacturing, mechanical tests and data treatment is described in this study. The mathematical representation of the material properties was solved by a linear viscoelastic constitutive model described by Prony series, which was properly adapted to orthotropic materials. Due to the large number of proposed constitutive model coefficients, a parameter identification method was employed to define mathematical functions. This procedure promoted good correlation among experimental tests, and analytical and numerical creep models. Such results encourage the use of numerical simulations for the development of structural components with the proposed linear viscoelastic orthotropic constitutive model. A case study was presented to illustrate an industrial application of proposed methodology.

  10. Discrete quasi-linear viscoelastic damping analysis of connective tissues, and the biomechanics of stretching.

    PubMed

    Babaei, Behzad; Velasquez-Mao, Aaron J; Thomopoulos, Stavros; Elson, Elliot L; Abramowitch, Steven D; Genin, Guy M

    2017-05-01

    The time- and frequency-dependent properties of connective tissue define their physiological function, but are notoriously difficult to characterize. Well-established tools such as linear viscoelasticity and the Fung quasi-linear viscoelastic (QLV) model impose forms on responses that can mask true tissue behavior. Here, we applied a more general discrete quasi-linear viscoelastic (DQLV) model to identify the static and dynamic time- and frequency-dependent behavior of rabbit medial collateral ligaments. Unlike the Fung QLV approach, the DQLV approach revealed that energy dissipation is elevated at a loading period of ∼10s. The fitting algorithm was applied to the entire loading history on each specimen, enabling accurate estimation of the material's viscoelastic relaxation spectrum from data gathered from transient rather than only steady states. The application of the DQLV method to cyclically loading regimens has broad applicability for the characterization of biological tissues, and the results suggest a mechanistic basis for the stretching regimens most favored by athletic trainers. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Viscoelastic and failure properties of spine ligament collagen fascicles.

    PubMed

    Lucas, Scott R; Bass, Cameron R; Crandall, Jeff R; Kent, Richard W; Shen, Francis H; Salzar, Robert S

    2009-12-01

    The microstructural volume fractions, orientations, and interactions among components vary widely for different ligament types. If these variations are understood, however, it is conceivable to develop a general ligament model that is based on microstructural properties. This paper presents a part of a much larger effort needed to develop such a model. Viscoelastic and failure properties of porcine posterior longitudinal ligament (PLL) collagen fascicles were determined. A series of subfailure and failure tests were performed at fast and slow strain rates on isolated collagen fascicles from porcine lumbar spine PLLs. A finite strain quasi-linear viscoelastic model was used to fit the fascicle experimental data. There was a significant strain rate effect in fascicle failure strain (P < 0.05), but not in failure force or failure stress. The corresponding average fast-rate and slow-rate failure strains were 0.098 ± 0.062 and 0.209 ± 0.081. The average failure force for combined fast and slow rates was 2.25 ± 1.17 N. The viscoelastic and failure properties in this paper were used to develop a microstructural ligament failure model that will be published in a subsequent paper.

  12. Comparison of viscoelastic properties of the pharyngeal tissue: human and canine.

    PubMed

    Kim, S M; McCulloch, T M; Rim, K

    1999-01-01

    The viscoelastic properties of the human and canine pharyngeal tissue in tension were evaluated, based on both an experimental protocol-consisting of cyclic load, tensile stress relaxation, and incremental step load tests-and the quasi-linear viscoelastic theory. The reduced stress relaxation function and the elastic response of the pharyngeal tissues were derived from the experimental results specifically obtained from those tissues. The characteristic features of viscoelastic property were obtained for both human and canine pharyngeal tissues by applying the quasi-linear viscoelastic theory and compared with each other. The material properties of the pharyngeal tissue were sought to facilitate the three-dimensional biomechanical model of the pharyngeal function by using the finite element method.

  13. Viscoelastic properties of actin-coated membranes

    NASA Astrophysics Data System (ADS)

    Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; Mackintosh, F. C.; Chatenay, D.

    2001-02-01

    In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (ω=0) two-dimensional (2D) shear modulus G02D~0.5 to 5 μN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G'2D(f )~f0.85+/-0.07] and of the bending modulus (κACM(f)~f0.55+/-0.21) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.

  14. Quasi-linear viscoelastic characterization of human hip ligaments.

    PubMed

    Kemper, Andrew R; McNally, Craig; Smith, Byron; Duma, Stefan M

    2007-01-01

    The object of this study was to develop a quasi-linear viscoelastic model for the iliofemoral and ischiofemoral hip ligaments. In order to accomplish this, a total of 56 axial tension tests were performed on 8 bone-ligament-bone specimens prepared from 4 fresh frozen male cadavers. Each specimen went through a battery of 7 tests including a series of step-and-hold tests and load-and-unload ramp tests. The bone-ligament-bone specimens were situated so that the load from a servo-hydraulic Material Testing System would be applied on the long axis of each ligament. The reduced relaxation data was fit to a two exponential damping function while the instantaneous elastic response was fit to a power-law function. These two constituents were then combined to create a single constitutive equation for each ligament. The quasi-linear viscoelastic model presented in this study can be used to improve the biofidelity of computational models of the human hip.

  15. Elastic and viscoelastic properties of a type I collagen fiber.

    PubMed

    Sopakayang, Ratchada; De Vita, Raffaella; Kwansa, Albert; Freeman, Joseph W

    2012-01-21

    A new mathematical model is presented to describe the elastic and viscoelastic properties of a single collagen fiber. The model is formulated by accounting for the mechanical contribution of the collagen fiber's main constituents: the microfibrils, the interfibrillar matrix and crosslinks. The collagen fiber is modeled as a linear elastic spring, which represents the mechanical contribution of the microfibrils, and an arrangement in parallel of elastic springs and viscous dashpots, which represent the mechanical contributions of the crosslinks and interfibrillar matrix, respectively. The linear elastic spring and the arrangement in parallel of elastic springs and viscous dashpots are then connected in series. The crosslinks are assumed to gradually break under strain and, consequently, the interfibrillar is assumed to change its viscous properties. Incremental stress relaxation tests are conducted on dry collagen fibers reconstituted from rat tail tendons to determine their elastic and viscoelastic properties. The elastic and total stress-strain curves and the stress relaxation at different levels of strain collected by performing these tests are then used to estimate the parameters of the model and evaluate its predictive capabilities.

  16. Viscoelastic properties of human cerebellum using magnetic resonance elastography.

    PubMed

    Zhang, John; Green, Michael A; Sinkus, Ralph; Bilston, Lynne E

    2011-07-07

    The cerebellum has never been mechanically characterised, despite its physiological importance in the control of motion and the clinical prevalence of cerebellar pathologies. The aim of this study was to measure the linear viscoelastic properties of the cerebellum in human volunteers using Magnetic Resonance Elastography (MRE). Coronal plane brain 3D MRE data was performed on eight healthy adult volunteers, at 80 Hz, to compare the properties of cerebral and cerebellar tissues. The linear viscoelastic storage (G') and loss moduli (G″) were estimated from the MRE wave images by solving the wave equation for propagation through an isotropic linear viscoelastic solid. Contributions of the compressional wave were removed via application of the curl-operator. The storage modulus for the cerebellum was found to be significantly lower than that for the cerebrum, for both white and grey matter. Cerebrum: white matter (mean±SD) G'=2.41±0.23 kPa, grey matter G'=2.34±0.22 kPa; cerebellum: white matter, G'=1.85±0.18 kPa, grey matter G'=1.77±0.24 kPa; cerebrum vs cerebellum, p<0.001. For the viscous behaviour, there were differences in between regions and also by tissue type, with the white matter being more viscous than grey matter and the cerebrum more viscous than the cerebellum. Cerebrum: white matter G″=1.21±0.21 kPa, grey matter G″=1.11±0.03 kPa; cerebellum: white matter G″=1.1±0.23 kPa, grey matter G″=0.94±0.17 kPa. These data represent the first available data on the viscoelastic properties of cerebellum, which suggest that the cerebellum is less physically stiff than the cerebrum, possibly leading to a different response to mechanical loading. These data will be useful for modelling of the cerebellum for a range of purposes. Copyright © 2011 Elsevier Ltd. All rights reserved.

  17. VISCOELASTIC PROPERTIES OF A BIOLOGICAL HYDROGEL PRODUCED FROM SOYBEAN OIL

    USDA-ARS?s Scientific Manuscript database

    Hydrogels formed from biopolymers or natural sources have special advantages because of their biodegradable and biocompatible properties. The viscoelastic properties of a newly developed biological hydrogel made from modified vegetable oil, epoxidized soybean oil (ESO) were investigated. The mater...

  18. Viscoelastic properties of actin-coated membranes.

    PubMed

    Helfer, E; Harlepp, S; Bourdieu, L; Robert, J; MacKintosh, F C; Chatenay, D

    2001-02-01

    In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (omega=0) two-dimensional (2D) shear modulus G(0)(2D) approximately 0.5 to 5 microN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G(')(2D)(f ) approximately f(0.85+/-0.07)] and of the bending modulus (kappa(ACM)(f) approximately f(0.55+/-0.21)) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.

  19. Measurement of the linear viscoelastic behavior of antimisting kerosene

    NASA Technical Reports Server (NTRS)

    Ferry, J. D.

    1983-01-01

    Measurements of dynamic viscoelastic properties in very small oscillating shear deformations was made on solutions of a jet fuel, Jet A, containing an antimisting polymeric additive, FM-9. A few measurements were also made on solutions of FM-9 in a mixed solvent of mineral oil, Tetralin, and 0-terphenyl. Two samples of FM-9 had approximate number-average molecular weights of 12,000,000 and 8,100,000 as deduced from analysis of the measurements. The ranges of variables were 2.42 to 4.03 g/1 in concentration (0.3 to 0.5% by weight), 1 to 35 in temperature, 1.3 to 9.4 cp in solvent viscosity, and 103 to 6100 Hz in frequency. Measurements in the Jet A solvent were made both with and without a modifying carrier. The results were compared with the Zimm theory and the viscoelastic behavior was found to resemble rather closely that of ordinary non-polar polymers in theta solvents. The relation of the results to the antithixotropic behavior of such solutions a high shear rates is discussed in terms of intramolecular and intermolecular interactions.

  20. [Viscoelastic properties of relaxed papillary muscle at physiological hypertrophy].

    PubMed

    Smoliuk, L T; Lisin, R V; Kuznetsov, D A; Protsenko, Iu L

    2012-01-01

    Viscoelastic properties of relaxed rat papillary muscles at physiological hypertrophy (intensive swimming for 5 weeks) have been obtained. It has been ascertained that viscoelastic properties of hypertrophied muscles are not significantly distinguished from those of control papillary muscles. A three-dimensional model of myocardial fascicle has been verified in compliance with experimental data of biomechanical tests of hypertrophied muscles. Elastic and viscous parameters of structural elements of the model negligibly differ from the parameters of the model of a control muscle. It is shown that physiological hypertrophy has a slight influence on viscoelastic properties of papillary muscles.

  1. A simplified approach to quasi-linear viscoelastic modeling

    PubMed Central

    Nekouzadeh, Ali; Pryse, Kenneth M.; Elson, Elliot L.; Genin, Guy M.

    2007-01-01

    The fitting of quasi-linear viscoelastic (QLV) constitutive models to material data often involves somewhat cumbersome numerical convolution. A new approach to treating quasi-linearity in one dimension is described and applied to characterize the behavior of reconstituted collagen. This approach is based on a new principle for including nonlinearity and requires considerably less computation than other comparable models for both model calibration and response prediction, especially for smoothly applied stretching. Additionally, the approach allows relaxation to adapt with the strain history. The modeling approach is demonstrated through tests on pure reconstituted collagen. Sequences of “ramp-and-hold” stretching tests were applied to rectangular collagen specimens. The relaxation force data from the “hold” was used to calibrate a new “adaptive QLV model” and several models from literature, and the force data from the “ramp” was used to check the accuracy of model predictions. Additionally, the ability of the models to predict the force response on a reloading of the specimen was assessed. The “adaptive QLV model” based on this new approach predicts collagen behavior comparably to or better than existing models, with much less computation. PMID:17499254

  2. A simplified approach to quasi-linear viscoelastic modeling.

    PubMed

    Nekouzadeh, Ali; Pryse, Kenneth M; Elson, Elliot L; Genin, Guy M

    2007-01-01

    The fitting of quasi-linear viscoelastic (QLV) constitutive models to material data often involves somewhat cumbersome numerical convolution. A new approach to treating quasi-linearity in 1-D is described and applied to characterize the behavior of reconstituted collagen. This approach is based on a new principle for including nonlinearity and requires considerably less computation than other comparable models for both model calibration and response prediction, especially for smoothly applied stretching. Additionally, the approach allows relaxation to adapt with the strain history. The modeling approach is demonstrated through tests on pure reconstituted collagen. Sequences of "ramp-and-hold" stretching tests were applied to rectangular collagen specimens. The relaxation force data from the "hold" was used to calibrate a new "adaptive QLV model" and several models from literature, and the force data from the "ramp" was used to check the accuracy of model predictions. Additionally, the ability of the models to predict the force response on a reloading of the specimen was assessed. The "adaptive QLV model" based on this new approach predicts collagen behavior comparably to or better than existing models, with much less computation.

  3. Viscoelastic properties of the ovine posterior spinal ligaments are strain dependent.

    PubMed

    Ambrosetti-Giudici, Sveva; Gédet, Philippe; Ferguson, Stephen J; Chegini, Salman; Burger, Juergen

    2010-02-01

    The biomechanical role of the posterior spinal ligaments for spinal stability has been stated in previous studies. The investigation of the viscoelastic properties of human lumbar spinal ligaments is essential for the understanding of physiological differences between healthy and degenerated tissues. The stress-relaxation behavior of biological tissues is commonly described with the quasi-linear viscoelastic model of Fung, which assumes that the stress-relaxation response is independent of the applied strain. The goal of this study was to investigate the stress-relaxation response of ovine posterior spinal ligaments at different elongations to verify the above-mentioned hypothesis. Twenty-four ovine lumbar spinal segments, consisting of only the supraspinous and interspinous ligaments and adjoining spinous processes, were elongated uniaxially to different strain levels within the physiological elastic region (5-20%). The experimental data were described with a non-linear viscoelastic model: the modified superposition method of Findley. A linear dependency of the relaxation rate to the applied strains was observed on intact segments, when both ligaments were considered, as well as on each individual ligament. This result can be applied to the human spinal ligaments, due to similarities observed between the sheep and human spinal segment under physiological loading. The non-linear viscoelastic modified superposition method of Findley is an appropriate model for describing the viscoelastic properties of lumbar spinal ligaments in vitro due to its ability to address variation in applied strain during the force relaxation measurements. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

  4. Validation of numerical results of impact of viscoelastic slug and elastic rod through viscoelastic discontinuity analysis: Standard linear solid model

    NASA Astrophysics Data System (ADS)

    Musa, A. B.

    2015-05-01

    The study is about impact of a short elastic rod (or slug) on a stationary semi-infinite viscoelastic rod. The viscoelastic materials are modeled as standard linear solid which involve three material parameters and the motion is treated as one-dimensional. We first establish the governing equations pertaining to the impact of viscoelastic materials subject to certain boundary conditions for the case when an elastic slug moving at a speed V impacts a semi-infinite stationary viscoelastic rod. The objective is to validate the numerical results of stresses and velocities at the interface following wave transmissions and reflections in the slug after the impact using viscoelastic discontinuity. If the stress at the interface becomes tensile and the velocity changes its sign, then the slug and the rod part company. If the stress at the interface is compressive after the impact, the slug and the rod remain in contact. After modelling the impact and solve the governing system of partial differential equations in the Laplace transform domain, we invert the Laplace transformed solution numerically to obtain the stresses and velocities at the interface for several viscosity time constants and ratios of acoustic impedances. In inverting the Laplace transformed equations, we used the complex inversion formula because there is a branch cut and infinitely many poles within the Bromwich contour. In the viscoelastic discontinuity analysis, we look at the moving discontinuities in stress and velocity using the impulse-momentum relation and kinematical condition of compatibility. Finally, we discussed the relationship of the stresses and velocities using numeric and the validated stresses and velocities using viscoelastic discontinuity analysis.

  5. Viscoelastic Properties of Hyaluronan in Physiological Conditions

    PubMed Central

    Cowman, Mary K.; Schmidt, Tannin A.; Raghavan, Preeti; Stecco, Antonio

    2015-01-01

    Hyaluronan (HA) is a high molecular weight glycosaminoglycan of the extracellular matrix (ECM), which is particularly abundant in soft connective tissues. Solutions of HA can be highly viscous with non-Newtonian flow properties. These properties affect the movement of HA-containing fluid layers within and underlying the deep fascia. Changes in the concentration, molecular weight, or even covalent modification of HA in inflammatory conditions, as well as changes in binding interactions with other macromolecules, can have dramatic effects on the sliding movement of fascia. The high molecular weight and the semi-flexible chain of HA are key factors leading to the high viscosity of dilute solutions, and real HA solutions show additional nonideality and greatly increased viscosity due to mutual macromolecular crowding. The shear rate dependence of the viscosity, and the viscoelasticity of HA solutions, depend on the relaxation time of the molecule, which in turn depends on the HA concentration and molecular weight. Temperature can also have an effect on these properties. High viscosity can additionally affect the lubricating function of HA solutions. Immobility can increase the concentration of HA, increase the viscosity, and reduce lubrication and gliding of the layers of connective tissue and muscle. Over time, these changes can alter both muscle structure and function. Inflammation can further increase the viscosity of HA-containing fluids if the HA is modified via covalent attachment of heavy chains derived from Inter-α-Inhibitor. Hyaluronidase hydrolyzes HA, thus reducing its molecular weight, lowering the viscosity of the extracellular matrix fluid and making outflow easier. It can also disrupt any aggregates or gel-like structures that result from HA being modified. Hyaluronidase is used medically primarily as a dispersion agent, but may also be useful in conditions where altered viscosity of the fascia is desired, such as in the treatment of muscle stiffness

  6. Matrix deposition modulates the viscoelastic shear properties of hydrogel-based cartilage grafts.

    PubMed

    Wan, Leo Q; Jiang, Jie; Miller, Diana E; Guo, X Edward; Mow, Van C; Lu, Helen H

    2011-04-01

    Hydrogel-based scaffolds such as alginate have been extensively investigated for cartilage tissue engineering, largely due to their biocompatibility, ambient gelling conditions, and the ability to support chondrocyte phenotype. While it is well established that the viscoelastic response of articular cartilage is essential for articulation and load bearing, the time-dependent mechanical properties of hydrogel-based cartilage scaffolds have not been extensively studied. Therefore, the objective of this study was to characterize the intrinsic viscoelastic shear properties of chondrocyte-laden alginate scaffolds and determine the effects of seeding density and culturing time on these properties. Specifically, the viscoelastic properties (equilibrium and dynamic shear moduli and dynamic phase shift angle) of these engineered cartilage grafts were measured under torsional shear. In addition, the rapid ramp-step shear stress relaxation of the alginate-based cartilage scaffolds was modeled using the quasi-linear viscoelastic (QLV) theory. It was found that scaffold stiffness increased with both culturing time and cell density, whereas viscosity did not change significantly with cell density (30 vs. 60 million/mL). Similar to native cartilage, the energy dissipation of engineered scaffolds under pure shear is highly correlated to the glycosaminoglycan content. In contrast, collagen content was not strongly correlated to scaffold shear modulus, especially the instantaneous shear modulus predicted by the quasi-linear viscoelastic model. The findings of this study provide new insights into the structure-function relationship of engineered cartilage and design of functional grafts for cartilage repair.

  7. Matrix Deposition Modulates the Viscoelastic Shear Properties of Hydrogel-Based Cartilage Grafts

    PubMed Central

    Wan, Leo Q.; Jiang, Jie; Miller, Diana E.; Guo, X. Edward; Mow, Van C.

    2011-01-01

    Hydrogel-based scaffolds such as alginate have been extensively investigated for cartilage tissue engineering, largely due to their biocompatibility, ambient gelling conditions, and the ability to support chondrocyte phenotype. While it is well established that the viscoelastic response of articular cartilage is essential for articulation and load bearing, the time-dependent mechanical properties of hydrogel-based cartilage scaffolds have not been extensively studied. Therefore, the objective of this study was to characterize the intrinsic viscoelastic shear properties of chondrocyte-laden alginate scaffolds and determine the effects of seeding density and culturing time on these properties. Specifically, the viscoelastic properties (equilibrium and dynamic shear moduli and dynamic phase shift angle) of these engineered cartilage grafts were measured under torsional shear. In addition, the rapid ramp-step shear stress relaxation of the alginate-based cartilage scaffolds was modeled using the quasi-linear viscoelastic (QLV) theory. It was found that scaffold stiffness increased with both culturing time and cell density, whereas viscosity did not change significantly with cell density (30 vs. 60 million/mL). Similar to native cartilage, the energy dissipation of engineered scaffolds under pure shear is highly correlated to the glycosaminoglycan content. In contrast, collagen content was not strongly correlated to scaffold shear modulus, especially the instantaneous shear modulus predicted by the quasi-linear viscoelastic model. The findings of this study provide new insights into the structure–function relationship of engineered cartilage and design of functional grafts for cartilage repair. PMID:21142626

  8. Viscoelastic effective properties of two types of heterogeneous materials.

    NASA Astrophysics Data System (ADS)

    Cornet, Jan; Dabrowski, Marcin; Schmid, Daniel

    2015-04-01

    In the past, a lot of efforts have been put to describe two end cases of rock behaviors: elasticity and viscosity. In recent years, more focus has been brought on the intermediate viscoelastic cases which describe better the rheology of rocks such as shales. Shales are typically heterogeneous and the question arises as to how to derive their effective properties so that they can be approximated as homogeneous media. This question has already been dealt with at the elastic and viscous limit but still remains for some cases in between. Using MILAMIN, a fast finite element solver for large problems, we numerically investigate different approaches to derive the effective properties of several viscoelastic media. Two types of geometries are considered: layered and inclusion based media. We focus on two dimensional plane strain problems considering two phase composites deformed under pure shear. We start by investigating the case of transversely isotropic layered media made of two Maxwell materials. Using the Backus averaging method we discuss the degree of relevance of this averaging by considering some parameters as: layer periodicity, layer thickness and layer interface roughness. Other averaging methods are also discussed which provide a broader perspective on the performances of Backus averaging. In a second part we move on to inclusion based models. The advantage of these models compared to the previous one is that they provide a better approximation to real microstructures in rocks. The setup we consider in this part is the following: some viscous circular inclusions are embedded in an elastic matrix. Both the inclusions and the matrix are homogeneous but the inclusions are purely isotropic while the matrix can also be anisotropic. In order to derive the effective viscoelastic properties of the medium we use two approaches: the self-consistent averaging and the differential effective medium theory. The idea behind self-consistency is to assume that the inclusions

  9. Real-time finite-element simulation of linear viscoelastic tissue behavior based on experimental data.

    PubMed

    Sedef, Mert; Samur, Evren; Basdogan, Cagatay

    2006-01-01

    The lack of experimental data on the viscoelastic material properties of live organ tissues has been a significant obstacle in the development of realistic models. A real-time and realisti finite-element simulation of viscoelastic tissue behavior using experimental data collected by a robotic indenter offers one solution.

  10. Generalization of the ordinary state-based peridynamic model for isotropic linear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Delorme, Rolland; Tabiai, Ilyass; Laberge Lebel, Louis; Lévesque, Martin

    2017-02-01

    This paper presents a generalization of the original ordinary state-based peridynamic model for isotropic linear viscoelasticity. The viscoelastic material response is represented using the thermodynamically acceptable Prony series approach. It can feature as many Prony terms as required and accounts for viscoelastic spherical and deviatoric components. The model was derived from an equivalence between peridynamic viscoelastic parameters and those appearing in classical continuum mechanics, by equating the free energy densities expressed in both frameworks. The model was simplified to a uni-dimensional expression and implemented to simulate a creep-recovery test. This implementation was finally validated by comparing peridynamic predictions to those predicted from classical continuum mechanics. An exact correspondence between peridynamics and the classical continuum approach was shown when the peridynamic horizon becomes small, meaning peridynamics tends toward classical continuum mechanics. This work provides a clear and direct means to researchers dealing with viscoelastic phenomena to tackle their problem within the peridynamic framework.

  11. Adjustment of the human arm viscoelastic properties to the direction of reaching.

    PubMed

    Frolov, A A; Prokopenko, R A; Dufossè, M; Ouezdou, F B

    2006-02-01

    The viscoelastic properties of the human arm were measured by means of short force perturbations during fast reaching movements in two orthogonal directions. A linear spring model with time delay described the neuromuscular system of the human arm. The obtained viscoelastic parameters ensured movement stability in spite of the time delay of 50 ms. The stiffness and viscosity ellipses appeared to be predominantly orthogonal to the movement direction, which reduced the effect of force perturbation in the direction orthogonal to the reaching movement. Thus, it can be argued that the viscoelastic properties of the neuromuscular system of the human arm are adjusted to the direction of movement according to a "path preserving" strategy, which minimizes the deviation of the movement path from a straight line, when exposed to an unexpected external force.

  12. Characterization of damping properties of nonlinear viscoelastic materials

    NASA Astrophysics Data System (ADS)

    Ganeriwala, Surendra N.

    1995-05-01

    The dynamic behavior of most polymeric materials become non-linear at a moderately large strain amplitude excitation. In order to optimize their uses for noise and vibration attenuation, it is necessary to characterize their damping properties as a function of strain amplitude. This work reports the strain amplitude dependent non-linear dynamic behavior of two elastomer compounds, NBR and Neoprene, studied at various frequencies and strain amplitudes using the Fourier transform mechanical analysis (FTMA) technique, developed by us. The basic theory and experimental results are presented for a one-dimensional isothermal simple shear deformation. The Green-Rivlin constitutive equation was used to model the observed behavior. The results indicate that a complete characterization of non-linear dynamic properties is rather complex. The energy dissipation is governed, however, by a simple mechanism. It is shown that the energy dissipation is governed only by the first harmonic loss modulus term of the Green-Rivlin representation, but the energy storage is related to many material functions. An expression for the energy dissipation of a non-linear viscoelastic material is derived. It is also shown that irrespective of the material constitutive law the energy dissipation can occur only at the frequency of excitation but it can be stored in a complex manner. The results are rather generalized to show that the amplitude dependence can be modeled by a power law function. It is also shown that an examination of the stress Fourier spectra can give a quantitative indication of material non-linearity and suggest a direction for developing an adequate model of these complex materials.

  13. Dynamic tensile properties of bovine periodontal ligament: A nonlinear viscoelastic model.

    PubMed

    Oskui, Iman Z; Hashemi, Ata

    2016-03-21

    As a support to the tooth, the mechanical response of the periodontal ligament (PDL) is complex. Like other connective tissues, the PDL exhibits non-linear and time-dependent behavior. The viscoelasticity of the PDL plays a significant role in low and high loading rates. Little information, however, is available on the short-term viscoelastic behavior of the PDL. Also, due to the highly non-linear stress-strain response, it was hypothesized that the dynamic viscoelastic properties of the PDL would be greatly dependent on the preload. Therefore, the present study was designed to explore the dynamic tensile properties of the bovine PDL as a function of loading frequency and preload. The in vitro dynamic tensile tests were performed over a wide range of frequencies (0.01-100Hz) with dynamic force amplitude of 1N and different preloads of 3, 5 and 10N. The generalized Maxwell model was utilized to describe the non-linear viscoelastic behavior of the PDL. The low loss factor of the bovine PDL, measured between 0.04 and 0.08, indicates low energy dissipation due to the high content of collagen fibers. Moreover, the influence of viscous components in the linear region of the stress-strain curve (10N preload) was lower than those of the toe region (3N preload). The data reported in this study could be used in developing accurate computational models of the PDL.

  14. Analyzing and improving viscoelastic properties of high density polyethylene

    NASA Astrophysics Data System (ADS)

    Ahmed, Reaj Uddin

    2011-12-01

    High Density Polyethylene (HDPE) is closely packed, less branched polyethylene having higher mechanical properties, chemical resistance, and heat resistance than Low Density Polyentylene (LDPE). Better properties and cost effectiveness make it an important raw material over LDPE in packaging industries. Stacked containers made of HDPE experience static loading and deformation strain during their storage period in a warehouse. As HDPE is a viscoelastic material, dimensional stability of stacked HDPE containers depends on time dependent properties such as creep and stress relaxation. Now, light weighting is a driving force in packaging industries, which results in lower production costs but performance of the product becomes a challenge. Proper understanding of the viscoelastic properties of HDPE, with relevant FE simulation can facilitate improved designs. This research involves understanding and improving viscoelastic properties, creep behavior, and stress relaxation of HDPE. Different approaches were carried out to meet the objectives. Organic filler CaCO3 was added to HDPE at increasing weight fractions and corresponding property changes were investigated. Annealing heat treatments were also carried out for potential property improvements. The effect of ageing was also investigated on both annealed and non annealed HDPE. The related performance of different water bottles against squeeze pressure was also characterized. Both approaches, incorporation of CaCO3 and annealing, showed improvements in the properties of HDPE over neat HDPE. This research aids finding the optimum solution for improving viscoelastic properties, stress relaxation, and creep behavior of HDPE in manufacturing.

  15. Utilization of polymer viscoelastic properties in acoustic wave sensor applications

    NASA Astrophysics Data System (ADS)

    Martin, Stephen J.; Ricco, Antonio J.; Frye, G. C.

    The changes which occur in polymer viscoelastic properties in response to cross-linking reactions and due to absorption of gas phase species were used advantageously in several acoustic wave-based sensor applications. When a polymer film is present on the surface of an acoustic wave device, changes in the visoelastic properties of the film induce changes in wave porpagation velocity and attenuation, providing two sensor responses. Film changes which occur polymer cross-linking allow photopolymerization to be monitored in real time using acoustic devices. A photoaction spectrum of photoresist reveals the cross-linking wavelength with maximum quantum yield. Changes in the viscoelastic properties of a polysiloxane film induces by vapor absorption are found to be unique for each of several species, enabling differentiation of species with a single film. A Maxwell model for polymer viscoelasticity, in combination with mass loading effects, provides a sound theoretical basis for explaining observed results for both polysiloxane and polybytadiene/polystyrene copolymer films.

  16. Viscoelastic properties of healthy human artery measured in saline solution by AFM based indentation technique

    SciTech Connect

    Lundkvist, A.; Lilleodden, E.; Sickhaus, W.; Kinney, J.; Pruitt, L.; Balooch, M.

    1998-02-09

    Using an Atomic Force Microscope with an attachment for indentation, we have measured local, in vitro mechanical properties of healthy femoral artery tissue held in saline solution. The elastic modulus (34. 3 kPa) and viscoelastic response ({tau}sub{epsilon} {equals} 16.9 s and {tau}sub{sigma} {equals} 29.3 s) of the unstretched,intimal vessel wall have been determined using Sneddon theory and a three element model(standard linear solid) for viscoelastic materials. The procedures necessary to employ the indenting attachment to detect elastic moduli in the kPa range in liquid are described.

  17. A quasi-correspondence principle for Quasi-Linear viscoelastic solids

    NASA Astrophysics Data System (ADS)

    Rajagopal, K. R.; Wineman, A. S.

    2008-03-01

    In this paper we show that the correspondence principle that allows one to obtain solutions to boundary-initial value problems for Linear viscoelastic solids from solutions to that for a linearized elastic solid can be extended, in many circumstances, to the case of the Quasi-Linear viscoelastic solids introduced by Fung. We illustrate the ability to generalize the correspondence principle by considering a variety of problems including torsion, transverse loading of beams and several problems that involve a single non-zero stress component. This extension is however not possible for certain classes of problems and we present a specific example where the correspondence principle breaks down. The correspondence principle between Linear elasticity and Linear viscoelasticity also breaks down under certain conditions, however the correspondence between the solutions for Linear viscoelasticity and Quasi-Linear viscoelasticity is even more fragile in that it breaks down while the classical correspondence works, and hence we refer to the correspondence as a quasi-correspondence principle.

  18. Micromechanics of transformation fields in ageing linear viscoelastic composites: effects of phase dissolution or precipitation

    NASA Astrophysics Data System (ADS)

    Honorio, Tulio

    2017-02-01

    Transformation fields, in an affine formulation characterizing mechanical behavior, describe a variety of physical phenomena regardless their origin. Different composites, notably geomaterials, present a viscoelastic behavior, which is, in some cases of industrial interest, ageing, i.e. it evolves independently with respect to time and loading time. Here, a general formulation of the micromechanics of prestressed or prestrained composites in Ageing Linear Viscoelasticity (ALV) is presented. Emphasis is put on the estimation of effective transformation fields in ALV. The result generalizes Ageing Linear Thermo- and Poro-Viscoelasticity and it can be used in approaches coping with a phase transformation. Additionally, the results are extended to the case of locally transforming materials due to non-coupled dissolution and/or precipitation of a given (elastic or viscoelastic) phase. The estimations of locally transforming composites can be made with respect to different morphologies. As an application, estimations of the coefficient of thermal expansion of a hydrating alite paste are presented.

  19. Viscoelastic properties of high solids softwood kraft black liquors

    SciTech Connect

    Zaman, A.A.; Fricke, A.L. . Dept. of Chemical Engineering)

    1995-01-01

    The linear viscoelastic functions of several softwood slash pine kraft black liquors from a two level, four variable factorially designed pulping experiment were determined for solids concentrations from 65% to 81% and temperatures from 40 to 85 C. At high solids and lower temperatures, black liquors behave like un-cross-linked polymers.The exact level of dynamic viscosity and storage modulus at any given condition is dependent upon the solids composition which will vary from liquor to liquor. The linear viscoelastic functions were described using Cross and Carreau-Yasuda models. Superposition principles developed for polymer melts and concentrated polymer solutions were applied to obtain reduced correlations for dynamic viscosity and storage modulus. The data for dynamic viscosity were shifted over the whole range of temperature, solids concentrations, and frequency, and a single curve for dynamic viscosity behavior of every liquor was obtained. The data for storage modulus did not superimpose into a single curve for the effects of solids concentration. The reduced correlations were used to estimate the viscoelasticity of the liquors near normal firing conditions and found that black liquors will not have any problem in droplet formation for concentrations up to 81% solids and temperatures above 120 C. The viscometric and linear viscoelastic functions of black liquors were compared (Cox-Merz rule), and it was shown that at sufficiently low shear rates and frequencies both shear viscosity and the magnitude of the complex viscosity approach zero shear rate viscosity.

  20. A surface wave elastography technique for measuring tissue viscoelastic properties.

    PubMed

    Zhang, Xiaoming

    2017-04-01

    A surface wave elastography method is proposed to study the viscoelastic properties of skin by measuring the surface wave speed and attenuation on the skin. Experiments were carried out on porcine skin tissues. The surface wave speed is measured by the change of phase with distance. The wave attenuation is measured by the decay of wave amplitude with distance. The change of viscoelastic properties with temperature was studied at room and body temperatures. The wave speed was 1.83m/s at 22°C but reduced to 1.52m/s at 33°C. The viscoelastic ratio was almost constant from 22°C to 33°C. Fresh and decayed tissues were studied. The wave speed of the decayed tissue increased from 1.83m/s of fresh state to 2.73m/s. The viscoelastic ratio was 0.412/mm at the decayed state compared to 0.215/mm at the fresh state. More tissue samples are needed to study these viscoelastic parameters according to specific applications. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

  1. An axisymmetric boundary integral model for incompressible linear viscoelasticity: application to the micropipette aspiration contact problem.

    PubMed

    Haider, M A; Guilak, F

    2000-06-01

    The micropipette aspiration test has been used extensively in recent years as a means of quantifying cellular mechanics and molecular interactions at the microscopic scale. However, previous studies have generally modeled the cell as an infinite half-space in order to develop an analytical solution for a viscoelastic solid cell. In this study, an axisymmetric boundary integral formulation of the governing equations of incompressible linear viscoelasticity is presented and used to simulate the micropipette aspiration contact problem. The cell is idealized as a homogeneous and isotropic continuum with constitutive equation given by three-parameter (E, tau 1, tau 2) standard linear viscoelasticity. The formulation is used to develop a computational model via a "correspondence principle" in which the solution is written as the sum of a homogeneous (elastic) part and a nonhomogeneous part, which depends only on past values of the solution. Via a time-marching scheme, the solution of the viscoelastic problem is obtained by employing an elastic boundary element method with modified boundary conditions. The accuracy and convergence of the time-marching scheme are verified using an analytical solution. An incremental reformulation of the scheme is presented to facilitate the simulation of micropipette aspiration, a nonlinear contact problem. In contrast to the halfspace model (Sato et al., 1990), this computational model accounts for nonlinearities in the cell response that result from a consideration of geometric factors including the finite cell dimension (radius R), curvature of the cell boundary, evolution of the cell-micropipette contact region, and curvature of the edges of the micropipette (inner radius a, edge curvature radius epsilon). Using 60 quadratic boundary elements, a micropipette aspiration creep test with ramp time t* = 0.1 s and ramp pressure p*/E = 0.8 is simulated for the cases a/R = 0.3, 0.4, 0.5 using mean parameter values for primary chondrocytes

  2. Identification of the Hereditary Kernels of Isotropic Linear Viscoelastic Materials in Combined Stress State. 2. Proportional deviators

    NASA Astrophysics Data System (ADS)

    Golub, V. P.; Maslov, B. P.; Fernati, P. V.

    2016-11-01

    The relationships between the hereditary and creep kernels are established. The hereditary kernels define the scalar properties of isotropic linear viscoelastic materials in a combined stress state. The creep kernels are obtained in uniaxial-tension and pure-torsion tests. The constitutive equations are chosen so as to meet the hypothesis of proportional deviators. The problems of analyzing the creep deformation and stress relaxation of thin-walled tubular specimens under combined tension and torsion are solved and tested experimentally

  3. Numerical simulation of blood flow through a capillary using a non-linear viscoelastic model.

    PubMed

    Shariatkhah, Amin; Norouzi, Mahmood; Nobari, Mohammad Reza Heyrani

    2016-01-01

    In this article, a periodic developing blood flow in a capillary is simulated using a non-linear viscoelastic model for the first time. Here, the Giesekus model is used as the constitutive equation, and based on the experimental data, the best value for the mobility factor and zero shear rate viscosity are derived. The numerical solution of the problem is obtained using the finite volume method. The algorithm of the solution is pressure implicit with splitting of operators (PISO). The simulation carried out using the Giesekus, Oldroyd-B and Newtonian models and the results indicate that the Giesekus model presents a more accurate solution for the stress and velocity fields than the Newtonian and Oldroyd-B models. The previous studies on this problem were restricted to the linear and quasi-linear viscoelastic models. It is shown that only non-linear viscoelastic models can accurately describe the experimental data of unsteady blood flow in capillaries.

  4. Linear and Nonlinear Viscoelastic Modeling of Aorta and Carotid Pressure-Area Dynamics under in vivo and ex vivo Conditions

    PubMed Central

    Valdez-Jasso, Daniela; Bia, Daniel; Zócalo, Yanina; Armentano, Ricardo L.; Haider, Mansoor A.; Olufsen, Mette S.

    2013-01-01

    A better understanding of the biomechanical properties of the arterial wall provides important insight into arterial vascular biology under normal (healthy) and pathological conditions. This insight has potential to improve tracking of disease progression and to aid in vascular graft design and implementation. In this study, we use linear and nonlinear viscoelastic models to predict biomechanical properties of the thoracic descending aorta and the carotid artery under ex vivo and in vivo conditions in ovine and human arteries. Models analyzed include a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (an arctangent and a sigmoid model) that relate changes in arterial blood pressure to the vessel cross-sectional area (via estimation of vessel strain). These models were developed using the framework of Quasilinear Viscoelasticity (QLV) theory and were validated using measurements from the thoracic descending aorta and the carotid artery obtained from human and ovine arteries. In vivo measurements were obtained from ten ovine aortas and ten human carotid arteries. Ex vivo measurements (from both locations) were made in eleven male Merino sheep. Biomechanical properties were obtained through constrained estimation of model parameters. To further investigate the parameter estimates we computed standard errors and confidence intervals and we used analysis of variance to compare results within and between groups. Overall, our results indicate that optimal model selection depends on the arterial type. Results showed that for the thoracic descending aorta (under both experimental conditions) the best predictions were obtained with the nonlinear sigmoid model, while under healthy physiological pressure loading the carotid arteries nonlinear stiffening with increasing pressure is negligible, and consequently, the linear (Kelvin) viscoelastic model better describes the pressure-area dynamics in this vessel. Results

  5. Earthquake Cycle Simulations with Rate-and-State Friction and Linear and Nonlinear Viscoelasticity

    NASA Astrophysics Data System (ADS)

    Allison, K. L.; Dunham, E. M.

    2016-12-01

    We have implemented a parallel code that simultaneously models both rate-and-state friction on a strike-slip fault and off-fault viscoelastic deformation throughout the earthquake cycle in 2D. Because we allow fault slip to evolve with a rate-and-state friction law and do not impose the depth of the brittle-to-ductile transition, we are able to address: the physical processes limiting the depth of large ruptures (with hazard implications); the degree of strain localization with depth; the relative partitioning of fault slip and viscous deformation in the brittle-to-ductile transition zone; and the relative contributions of afterslip and viscous flow to postseismic surface deformation. The method uses a discretization that accommodates variable off-fault material properties, depth-dependent frictional properties, and linear and nonlinear viscoelastic rheologies. All phases of the earthquake cycle are modeled, allowing the model to spontaneously generate earthquakes, and to capture afterslip and postseismic viscous flow. We compare the effects of a linear Maxwell rheology, often used in geodetic models, with those of a nonlinear power law rheology, which laboratory data indicates more accurately represents the lower crust and upper mantle. The viscosity of the Maxwell rheology is set by power law rheological parameters with an assumed a geotherm and strain rate, producing a viscosity that exponentially decays with depth and is constant in time. In contrast, the power law rheology will evolve an effective viscosity that is a function of the temperature profile and the stress state, and therefore varies both spatially and temporally. We will also integrate the energy equation for the thermomechanical problem, capturing frictional heat generation on the fault and off-fault viscous shear heating, and allowing these in turn to alter the effective viscosity.

  6. Flexible microfluidic device for mechanical property characterization of soft viscoelastic solids such as bacterial biofilms

    PubMed Central

    Hohne, Danial N.; Younger, John G.; Solomon, Michael J.

    2009-01-01

    We introduce a flexible microfluidic device to characterize the mechanical properties of soft viscoelastic solids such as bacterial biofilms. In the device, stress is imposed on a test specimen by application of a fixed pressure to a thin, flexible poly(dimethyl siloxane) (PDMS) membrane that is in contact with the specimen. The stress is applied by pressurizing a microfabricated air channel located above the test area. The strain resulting from the applied stress is quantified by measuring the membrane deflection with a confocal laser-scanning microscope. The deflection is governed by the viscoelastic properties of the PDMS membrane and of the test specimen. The relative contributions of the membrane and test material to the measured deformation are quantified by comparing a finite element analysis and an independent (control) measurement of the PDMS membrane mechanical properties. The flexible microfluidic rheometer was used to characterize both the steady-state elastic modulus and transient strain recoil of two soft materials: gellan gums and bacterial biofilms. The measured linear elastic moduli and viscoelastic relaxation times of gellan gum solutions were in good agreement with the results of conventional mechanical rheometry. The linear Young’s moduli of biofilms of Staphylococcus epidermidis and Klebsiella pneumoniae, which could not be measured using conventional methods, were found to be 3.2 kPa and 1.1 kPa, respectively, and the relaxation time of the S. epidermidis biofilm was 13.8 s. Additionally, strain hardening was observed in all the biofilms studied. Finally, design parameters and detection limits of the method show that the device is capable of characterizing soft viscoelastic solids with elastic moduli in the range of 102 – 105 Pa. The flexible microfluidic rheometer addresses a need for mechanical property characterization of soft viscoelastic solids common in fields such as biomaterials, food and consumer products. It requires only ~ 200 p

  7. Viscoelastic and optical properties of four different PDMS polymers

    NASA Astrophysics Data System (ADS)

    Deguchi, Shinji; Hotta, Junya; Yokoyama, Sho; Matsui, Tsubasa S.

    2015-09-01

    Polydimethylsiloxane (PDMS) is the most commonly used silicone elastomer with a wide range of applications including microfluidics and microcontact printing. Various types of PDMS are currently available, and their bulk material properties have been extensively investigated. However, because the properties are rarely compared in a single study, it is often unclear whether the large disparity of the reported data is attributable to the difference in methodology or to their intrinsic characteristics. Here we report on viscoelastic properties and optical properties of four different PDMS polymers, i.e. Sylgard-184, CY52-276, SIM-360, and KE-1606. Our results show that all the PDMSs are highly elastic rather than viscoelastic at the standard base/curing agent ratios, and their quantified elastic modulus, refractive index, and optical cleanness are similar but distinct in magnitude.

  8. The analytical representation of viscoelastic material properties using optimization techniques

    NASA Technical Reports Server (NTRS)

    Hill, S. A.

    1993-01-01

    This report presents a technique to model viscoelastic material properties with a function of the form of the Prony series. Generally, the method employed to determine the function constants requires assuming values for the exponential constants of the function and then resolving the remaining constants through linear least-squares techniques. The technique presented here allows all the constants to be analytically determined through optimization techniques. This technique is employed in a computer program named PRONY and makes use of commercially available optimization tool developed by VMA Engineering, Inc. The PRONY program was utilized to compare the technique against previously determined models for solid rocket motor TP-H1148 propellant and V747-75 Viton fluoroelastomer. In both cases, the optimization technique generated functions that modeled the test data with at least an order of magnitude better correlation. This technique has demonstrated the capability to use small or large data sets and to use data sets that have uniformly or nonuniformly spaced data pairs. The reduction of experimental data to accurate mathematical models is a vital part of most scientific and engineering research. This technique of regression through optimization can be applied to other mathematical models that are difficult to fit to experimental data through traditional regression techniques.

  9. Analytical model for nanoscale viscoelastic properties characterization using dynamic nanoindentation

    NASA Astrophysics Data System (ADS)

    Yuya, Philip A.; Patel, Nimitt G.

    2014-08-01

    In the last few decades, nanoindentation has gained widespread acceptance as a technique for materials properties characterization at micron and submicron length scales. Accurate and precise characterization of material properties with a nanoindenter is critically dependent on the ability to correctly model the response of the test equipment in contact with the material. In dynamic nanoindention analysis, a simple Kelvin-Voigt model is commonly used to capture the viscoelastic response. However, this model oversimplifies the response of real viscoelastic materials such as polymers. A model is developed that captures the dynamic nanoindentation response of a viscoelastic material. Indenter tip-sample contact forces are modelled using a generalized Maxwell model. The results on a silicon elastomer were analysed using conventional two element Kelvin-Voigt model and contrasted to analysis done using the Maxwell model. The results show that conventional Kelvin-Voigt model overestimates the storage modulus of the silicone elastomer by ~30%. Maxwell model represents a significant improvement in capturing the viscoelastic material behaviour over the Voigt model.

  10. A rate insensitive linear viscoelastic model for soft tissues

    PubMed Central

    Zhang, Wei; Chen, Henry Y.; Kassab, Ghassan S.

    2012-01-01

    It is well known that many biological soft tissues behave as viscoelastic materials with hysteresis curves being nearly independent of strain rate when loading frequency is varied over a large range. In this work, the rate insensitive feature of biological materials is taken into account by a generalized Maxwell model. To minimize the number of model parameters, it is assumed that the characteristic frequencies of Maxwell elements form a geometric series. As a result, the model is characterized by five material constants: μ0, τ, m, ρ and β, where μ0 is the relaxed elastic modulus, τ the characteristic relaxation time, m the number of Maxwell elements, ρ the gap between characteristic frequencies, and β = μ1/μ0 with μ1 being the elastic modulus of the Maxwell body that has relaxation time τ. The physical basis of the model is motivated by the microstructural architecture of typical soft tissues. The novel model shows excellent fit of relaxation data on the canine aorta and captures the salient features of vascular viscoelasticity with significantly fewer model parameters. PMID:17512585

  11. Fractional characteristic times and dissipated energy in fractional linear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Colinas-Armijo, Natalia; Di Paola, Mario; Pinnola, Francesco P.

    2016-08-01

    In fractional viscoelasticity the stress-strain relation is a differential equation with non-integer operators (derivative or integral). Such constitutive law is able to describe the mechanical behavior of several materials, but when fractional operators appear, the elastic and the viscous contribution are inseparable and the characteristic times (relaxation and retardation time) cannot be defined. This paper aims to provide an approach to separate the elastic and the viscous phase in the fractional stress-strain relation with the aid of an equivalent classical model (Kelvin-Voigt or Maxwell). For such equivalent model the parameters are selected by an optimization procedure. Once the parameters of the equivalent model are defined, characteristic times of fractional viscoelasticity are readily defined as ratio between viscosity and stiffness. In the numerical applications, three kinds of different excitations are considered, that is, harmonic, periodic, and pseudo-stochastic. It is shown that, for any periodic excitation, the equivalent models have some important features: (i) the dissipated energy per cycle at steady-state coincides with the Staverman-Schwarzl formulation of the fractional model, (ii) the elastic and the viscous coefficients of the equivalent model are strictly related to the storage and the loss modulus, respectively.

  12. Sucrose ester nanodispersions: microviscosity and viscoelastic properties.

    PubMed

    Ullrich, Sebastian; Metz, Hendrik; Mäder, Karsten

    2008-10-01

    Sucrose esters have the potential to enhance both drug solubility and drug absorption. They are therefore alternatives to the widely used glycerides in the formulation of lipid-based drug delivery systems. A simple production of aqueous nanosized drug carrier systems consisting of amphiphilic sucrose fatty acid esters using exclusively nontoxic materials has been achieved. By only using 2 wt% of the emulsifier a high viscosity of the sample could be reached. Diverse history of fabrication led to the differences in the macroviscosity of SE dispersions with equal chemical composition. Combining the well-established oscillating rheology with the electron paramagnetic resonance technique, three orders of magnitude difference in macroviscosity between the dispersions containing 2 wt% of the amphiphilic SE were obtained, whereas the viscosities at the molecular level were all close to the viscosity of water. Viscoelastic behaviour could also be shown for these systems. TEM experiments visualized coexisting irregular micelles and lamellar structures in the SE dispersions. The results are important to understand the complex LDDS based on amphiphilic SE.

  13. A new device for measuring the viscoelastic properties of hydrated matrix gels.

    PubMed

    Parsons, Jeffrey W; Coger, Robin N

    2002-04-01

    Determinations of the viscoelastic properties of extracellular matrices (ECMs) are becoming increasingly important for accurate predictive modeling of biological systems. Since the interactions of the cells with the ECM and surrounding fluid (e.g., blood, media) each affect cell behavior; it is advantageous to evaluate the ECM's material properties in the presence of the hydrating fluid. Conventional rheometry methods evaluate the bulk material properties of gel materials while displacing the hydrating liquid film. Such systems are therefore nonideal for testing materials such as ECMs, whose properties change with dehydration. The new patent pending, piezoelectrically actuated linear rheometer is designed to eliminate this problem. It uses a single cantilever to apply an oscillating load to the gel and to sense the gel's deflection. Composed of two thin film piezopolymer layers, the cantilever uses one layer as the actuator, and the second piezopolymer layer to measure the lateral movement of its attached probe. The viscoelastic nature of the ECM adds stiffness and damping to the system, resulting in the attenuation and phase shift of the sensor's output voltage. From these parameters, the ECM's shear storage and loss moduli are then determined. Initial tests on the BioMatrix I and type I collagen ECMs reveal that the first prototype of the piezoelectrically actuated linear rheometer is capable of accurately determining the trend and order of magnitude of an ECM's viscoelastic properties. In this paper, details of the rheometer's design and operating principles are described.

  14. Measuring Cell Viscoelastic Properties Using a Microfluidic Extensional Flow Device.

    PubMed

    Guillou, Lionel; Dahl, Joanna B; Lin, Jung-Ming G; Barakat, AbduI I; Husson, Julien; Muller, Susan J; Kumar, Sanjay

    2016-11-01

    The quantification of cellular mechanical properties is of tremendous interest in biology and medicine. Recent microfluidic technologies that infer cellular mechanical properties based on analysis of cellular deformations during microchannel traversal have dramatically improved throughput over traditional single-cell rheological tools, yet the extraction of material parameters from these measurements remains quite complex due to challenges such as confinement by channel walls and the domination of complex inertial forces. Here, we describe a simple microfluidic platform that uses hydrodynamic forces at low Reynolds number and low confinement to elongate single cells near the stagnation point of a planar extensional flow. In tandem, we present, to our knowledge, a novel analytical framework that enables determination of cellular viscoelastic properties (stiffness and fluidity) from these measurements. We validated our system and analysis by measuring the stiffness of cross-linked dextran microparticles, which yielded reasonable agreement with previously reported values and our micropipette aspiration measurements. We then measured viscoelastic properties of 3T3 fibroblasts and glioblastoma tumor initiating cells. Our system captures the expected changes in elastic modulus induced in 3T3 fibroblasts and tumor initiating cells in response to agents that soften (cytochalasin D) or stiffen (paraformaldehyde) the cytoskeleton. The simplicity of the device coupled with our analytical model allows straightforward measurement of the viscoelastic properties of cells and soft, spherical objects.

  15. Nonlinear simulation and linear stability analysis of viscous fingering instability of viscoelastic liquids

    NASA Astrophysics Data System (ADS)

    Shokri, H.; Kayhani, M. H.; Norouzi, M.

    2017-03-01

    In this study, the viscous fingering instability of miscible displacement involving a viscoelastic fluid is investigated using both linear stability analysis and computational fluid dynamics for the first time. The Oldroyd-B model is used as the constitutive equation of a viscoelastic fluid. Here, it is assumed that one of the displacing fluids or the displaced one is viscoelastic. In linear stability analysis, the quasi-steady state approximation and six order shooting method are used to predict the growth rate of the disturbance in the flow. It is shown that the flow is more stabilized when the elasticity (Weissenberg number) of the displaced or displacing viscoelastic fluid is increased. In the nonlinear simulation, using the spectral method based on Hartley transforms and the fourth-order Adams-Bashforth technique, the effect of the viscoelastic fluid on this instability has been studied. Evaluation of concentration contours, mixing length, sweep efficiency, and transversely average concentration show that the elasticity has a significant effect on the fingering instability and the flow becomes more stable by increasing the Weissenberg number.

  16. Chemical control of the viscoelastic properties of vinylogous urethane vitrimers

    NASA Astrophysics Data System (ADS)

    Denissen, Wim; Droesbeke, Martijn; Nicolaÿ, Renaud; Leibler, Ludwik; Winne, Johan M.; Du Prez, Filip E.

    2017-03-01

    Vinylogous urethane based vitrimers are polymer networks that have the intrinsic property to undergo network rearrangements, stress relaxation and viscoelastic flow, mediated by rapid addition/elimination reactions of free chain end amines. Here we show that the covalent exchange kinetics significantly can be influenced by combination with various simple additives. As anticipated, the exchange reactions on network level can be further accelerated using either Brønsted or Lewis acid additives. Remarkably, however, a strong inhibitory effect is observed when a base is added to the polymer matrix. These effects have been mechanistically rationalized, guided by low-molecular weight kinetic model experiments. Thus, vitrimer elastomer materials can be rationally designed to display a wide range of viscoelastic properties.

  17. Chemical control of the viscoelastic properties of vinylogous urethane vitrimers

    PubMed Central

    Denissen, Wim; Droesbeke, Martijn; Nicolaÿ, Renaud; Leibler, Ludwik; Winne, Johan M.; Du Prez, Filip E.

    2017-01-01

    Vinylogous urethane based vitrimers are polymer networks that have the intrinsic property to undergo network rearrangements, stress relaxation and viscoelastic flow, mediated by rapid addition/elimination reactions of free chain end amines. Here we show that the covalent exchange kinetics significantly can be influenced by combination with various simple additives. As anticipated, the exchange reactions on network level can be further accelerated using either Brønsted or Lewis acid additives. Remarkably, however, a strong inhibitory effect is observed when a base is added to the polymer matrix. These effects have been mechanistically rationalized, guided by low-molecular weight kinetic model experiments. Thus, vitrimer elastomer materials can be rationally designed to display a wide range of viscoelastic properties. PMID:28317893

  18. Inverting Glacial Isostatic Adjustment beyond linear viscoelasticity using Burgers rheology

    NASA Astrophysics Data System (ADS)

    Caron, L.; Greff-Lefftz, M.; Fleitout, L.; Metivier, L.; Rouby, H.

    2014-12-01

    In Glacial Isostatic Adjustment (GIA) inverse modeling, the usual assumption for the mantle rheology is the Maxwell model, which exhibits constant viscosity over time. However, mineral physics experiments and post-seismic observations show evidence of a transient component in the deformation of the shallow mantle, with a short-term viscosity lower than the long-term one. In these studies, the resulting rheology is modeled by a Burgers material: such rheology is indeed expected as the mantle is a mixture of materials with different viscosities. We propose to apply this rheology for the whole viscoelastic mantle, and, using a Bayesian MCMC inverse formalism for GIA during the last glacial cycle, study its impact on estimations of viscosity values, elastic thickness of the lithosphere, and ice distribution. To perform this inversion, we use a global dataset of sea level records, the geological constraints of ice-sheet margins, and present-day GPS data as well as satellite gravimetry. Our ambition is to present not only the best fitting model, but also the range of possible solutions (within the explored space of parameters) with their respective probability of explaining the data. Our first results indicate that compared to the Maxwell models, the Burgers models involve a larger lower mantle viscosity and thicker ice over Fennoscandia and Canada.

  19. Characterization of viscoelastic soft tissue properties from in vivo animal experiments and inverse FE parameter estimation.

    PubMed

    Kim, Jung; Srinivasan, Mandayam A

    2005-01-01

    Soft tissue characterization and modeling based on living tissues has been investigated in order to provide a more realistic behavior in a virtual reality based surgical simulation. In this paper, we characterize the nonlinear viscoelastic properties of intra-abdominal organs using the data from in vivo animal experiments and inverse FE parameter estimation algorithm. In the assumptions of quasi-linear-viscoelastic theory, we estimated the viscoelastic and hyerelastic material parameters to provide a physically based simulation of tissue deformations. To calibrate the parameters to the experimental results, we developed a three dimensional FE model to simulate the forces at the indenter and an optimization program that updates new parameters and runs the simulation iteratively. We can successfully reduce the time and computation resources by decoupling the viscoelastic part and nonlinear elastic part in a tissue model. The comparison between simulation and experimental behavior of pig intra abdominal soft tissue are presented to provide a validness of the tissue model using our approach.

  20. Viscoelastic properties of poly(ethylene oxide) solution.

    PubMed

    Yu, D M; Amidon, G L; Weiner, N D; Goldberg, A H

    1994-10-01

    The viscoelastic properties of poly(ethylene oxide) (PEO) solution were investigated using the dynamic oscillatory testing technique. With this technique, the effect of PEO molecular weight (MW), concentration, composition of mixed solvent systems consisting of propylene glycol, glycerol formal, and water, and the effect of NaCl salt on the viscoelastic properties of PEO solution were determined. Dynamic moduli (G1, G2), magnitude of complex viscosity (magnitude of eta*), and loss tangent (tan delta) were examined over a frequency range of 10(-3)-2.5 Hz at 30 degrees C. The results indicated that low MW PEOs show liquidlike behavior while high elasticity is exhibited by high MW PEOs due to entanglement formation. The complex viscosity, magnitude of eta*, exhibits shear thinning (power-law) characteristics under oscillatory measurements. The relationship between steady shear and complex viscosities follows the Cox-Merz rule over the shear rate and frequency region studied. Both the storage (G1) and loss (G2) modulus increase drastically as the proportion of water in the mixed solvent system increases. Similarly, both G1 and G2 are found to increase while the tan delta decreases with increasing concentration of PEOs. The addition of up to 2% w/w NaCl in an aqueous solution of 10% w/w 2 million MW PEO has no observed detrimental effect on the viscoelastic behavior.

  1. Non-linear dynamics of viscoelastic liquid trilayers subjected to an electric field

    NASA Astrophysics Data System (ADS)

    Karapetsas, George; Bontozoglou, Vasilis

    2014-11-01

    The scope of this work is to investigate the non-linear dynamics of the electro-hydrodynamic instability of a trilayer of immiscible liquids. We consider the case of a polymer film which is separated from the top electrode by two viscous fluids. We develop a computational model and carry out 2D numerical simulations fully accounting for the flow and electric field in all phases. For the numerical solution of the governing equations we employ the mixed finite element method combined with a quasi-elliptic mesh generation scheme which is capable of following the large deformations of the liquid-liquid interface. We model the viscoelastic behavior using the Phan-Thien and Tanner (PTT) constitutive equation taking fully into account the non-linear elastic effects as well as a varying shear and extensional viscosity. We perform a thorough parametric study and investigate the influence of the electric properties of fluids, applied voltage and various rheological parameters. The authors acknowledge the support by the General Secretariat of Research and Technology of Greece under the action ``Supporting Postdoctoral Researchers'' (Grant Number PE8/906), co-funded by the European Social Fund and National Resources.

  2. High-frequency viscoelastic shear properties of vocal fold tissues: implications for vocal fold tissue engineering.

    PubMed

    Teller, Sean S; Farran, Alexandra J E; Xiao, Longxi; Jiao, Tong; Duncan, Randall L; Clifton, Rodney J; Jia, Xinqiao

    2012-10-01

    The biomechanical function of the vocal folds (VFs) depends on their viscoelastic properties. Many conditions can lead to VF scarring that compromises voice function and quality. To identify candidate replacement materials, the structure, composition, and mechanical properties of native tissues need to be understood at phonation frequencies. Previously, the authors developed the torsional wave experiment (TWE), a stress-wave-based experiment to determine the linear viscoelastic shear properties of small, soft samples. Here, the viscoelastic properties of porcine and human VFs were measured over a frequency range of 10-200 Hz. The TWE utilizes resonance phenomena to determine viscoelastic properties; therefore, the specimen test frequency is determined by the sample size and material properties. Viscoelastic moduli are reported at resonance frequencies. Structure and composition of the tissues were determined by histology and immunochemistry. Porcine data from the TWE are separated into two groups: a young group, consisting of fetal and newborn pigs, and an adult group, consisting of 6-9-month olds and 2+-year olds. Adult tissues had an average storage modulus of 2309±1394 Pa and a loss tangent of 0.38±0.10 at frequencies of 36-200 Hz. The VFs of young pigs were significantly more compliant, with a storage modulus of 394±142 Pa and a loss tangent of 0.40±0.14 between 14 and 30 Hz. No gender dependence was observed. Histological staining showed that adult porcine tissues had a more organized, layered structure than the fetal tissues, with a thicker epithelium and a more structured lamina propria. Elastin fibers in fetal VF tissues were immature compared to those in adult tissues. Together, these structural changes in the tissues most likely contributed to the change in viscoelastic properties. Adult human VF tissues, recovered postmortem from adult patients with a history of smoking or disease, had an average storage modulus of 756±439 Pa and a loss tangent of 0

  3. Characterization of Viscoelastic Properties of Polymeric Materials Through Nanoindentation

    NASA Technical Reports Server (NTRS)

    Odegard, G. M.; Bandorawalla, T.; Herring, H. M.; Gates, T. S.

    2003-01-01

    Nanoindentation is used to determine the dynamic viscoelastic properties of six polymer materials. It is shown that varying the harmonic frequency of the nanoindentation does not have any significant effect on the measured storage and loss moduli of the polymers. Agreement is found between these results and data from DMA testing of the same materials. Varying the harmonic amplitude of the nanoindentation does not have a significant effect on the measured properties of the high performance resins, however, the storage modulus of the polyethylene decreases as the harmonic amplitude increases. Measured storage and loss moduli are also shown to depend on the density of the polyethylene.

  4. Tensile Properties and Viscoelastic Model of a Polyimide Film

    NASA Astrophysics Data System (ADS)

    Zhang, Shengde; Mori, Syuhei; Sakane, Masao; Nagasawa, Tadashi; Kobayashi, Kaoru

    This paper presents tensile properties of a polyimide thin film used in electronic devices. Tensile tests were performed to determine Young's modulus, proportional limit, yield stress, ultimate tensile strength and elongation of the polyimide film. Effects of strain rate and temperature on the tensile properties were discussed. There was a little effect of strain rate on Young's modulus but proportional limit, yield stress and ultimate tensile strength increased with increasing strain rate. Only elongation decreased with strain rate. Young's modulus, proportional limit, yield stress and ultimate tensile strength decreased with increasing temperature, but elongation increased. Applicability of a viscoelastic model for describing the stress-strain curves of the polyimide film was discussed.

  5. Dynamic analysis of linear viscoelastic cylindrical and conical helicoidal rods using the mixed FEM

    NASA Astrophysics Data System (ADS)

    Eratlı, Nihal; Argeso, Hakan; Çalım, Faruk F.; Temel, Beytullah; Omurtag, Mehmet H.

    2014-08-01

    The objective of this study is to investigate the influence of the rotary inertia on dynamic behavior of linear viscoelastic cylindrical and conical helixes by means of the Laplace transform-mixed finite element formulation and solution. The element matrix is based on the Timoshenko beam theory. The influence of rotary inertias is considered in the dynamic analysis, which is original in the literature. Rectangular, sine and step type of impulsive loads are applied on helices having rectangular cross-sections with various aspect ratios. The Kelvin and standard models are used for defining the linear viscoelastic material behavior; and by means of the correspondence principle (the elastic-viscoelastic analogy), the material parameters are replaced with their complex counterparts in the Laplace domain. The analysis is carried out in the Laplace domain and the results are transformed back to time space numerically by modified Durbin's algorithm. First, the solution algorithm is verified using the existing open sources in the literature and afterwards some benchmark examples such as conical viscoelastic rods are handled.

  6. Numerical simulation of a relaxation test designed to fit a quasi-linear viscoelastic model for temporomandibular joint discs.

    PubMed

    Commisso, Maria S; Martínez-Reina, Javier; Mayo, Juana; Domínguez, Jaime

    2013-02-01

    The main objectives of this work are: (a) to introduce an algorithm for adjusting the quasi-linear viscoelastic model to fit a material using a stress relaxation test and (b) to validate a protocol for performing such tests in temporomandibular joint discs. This algorithm is intended for fitting the Prony series coefficients and the hyperelastic constants of the quasi-linear viscoelastic model by considering that the relaxation test is performed with an initial ramp loading at a certain rate. This algorithm was validated before being applied to achieve the second objective. Generally, the complete three-dimensional formulation of the quasi-linear viscoelastic model is very complex. Therefore, it is necessary to design an experimental test to ensure a simple stress state, such as uniaxial compression to facilitate obtaining the viscoelastic properties. This work provides some recommendations about the experimental setup, which are important to follow, as an inadequate setup could produce a stress state far from uniaxial, thus, distorting the material constants determined from the experiment. The test considered is a stress relaxation test using unconfined compression performed in cylindrical specimens extracted from temporomandibular joint discs. To validate the experimental protocol, the test was numerically simulated using finite-element modelling. The disc was arbitrarily assigned a set of quasi-linear viscoelastic constants (c1) in the finite-element model. Another set of constants (c2) was obtained by fitting the results of the simulated test with the proposed algorithm. The deviation of constants c2 from constants c1 measures how far the stresses are from the uniaxial state. The effects of the following features of the experimental setup on this deviation have been analysed: (a) the friction coefficient between the compression plates and the specimen (which should be as low as possible); (b) the portion of the specimen glued to the compression plates (smaller

  7. Trabeculated embryonic myocardium shows rapid stress relaxation and non-quasi-linear viscoelastic behavior.

    PubMed

    Miller, C E; Wong, C L

    2000-05-01

    Passive viscoelastic behavior is important in embryonic cardiovascular function, influencing the rate and magnitude of contraction and relaxation. We hypothesized that if viscoelastic behavior is influenced by interstitial fluid flow, then the stage-21 (312d) and stage-24 (4d) chick myocardium with large intertrabecular spaces will exhibit much different viscoelastic behavior than stage-16 (212d) and stage-18 (3d) compact myocardium and a non-quasi-linear response. Excised left ventricular sections were tested with ramp-and-hold stress relaxation tests at axial stretch ratios of 1.05:1.1:1.2:1.3. The measured stress relaxation was much more rapid than previously observed in the compact, non-trabeculated myocardium. The reduced relaxation curves depended significantly on the stretch level. A continuous-spectrum quasi-linear relaxation function described their shape well but the model-fit parameters also depended on the stretch level. Sinusoidal stretching of ventricular sections at rates from 0.2 to 25Hz showed that the steepening of stress-strain curves with increasing strain rate was half as much as predicted by a quasi-linear model. Hysteresis ranged from 25-35%, varied little with loading rate from 0.2 to 8Hz, and was twice that predicted from a quasi-linear model. Doubling the viscosity of the perfusate in stress-relaxation tests produced increased stiffness and decreased relaxation rate. These results demonstrate that the passive viscoelastic behavior of the trabeculated embryonic myocardium is markedly different from that of younger, compact myocardium and is not quasi-linear.

  8. Imaging the Viscoelastic Properties of Tissue

    NASA Astrophysics Data System (ADS)

    Fatemi, Mostafa; Greenleaf, James F.

    Elasticity and viscosity of soft tissues are often related to pathology. These parameters, along with other mechanical parameters, determine the dynamic response of tissue to a force. Tissue mechanical response, therefore, may be used for diagnosis. Measuring and imaging of the mechanical properties of tissues is the aim of a class of techniques generally called elasticity imaging or elastography. The general approach is to measure tissue motion caused by a force or displacement and use it to reconstruct the elastic parameters of the tissue. The excitation stress can be either static or dynamic (vibration). Dynamic excitation is of particular interest because it provides more comprehensive information about tissue properties in a spectrum of frequencies. In one approach an external stress field must pass through the superficial portion of the object before reaching the region of interest within the interior. An alternative strategy is to apply a localized stress directly in the region of interest. One way to accomplish this task is to use the radiation force of ultrasound. This approach offers several benefits, including: (a) safety - acoustic energy is a noninvasive means of exerting force; (b) adaptability - existing ultrasound technology and devices can be readily modified for this purpose; (c) remoteness - radiation force can be generated remotely inside tissue without disturbing its superficial layers; (d) localization - the radiation stress field can be highly localized, thus allowing for precise positioning of the excitation point; and (e) a wide frequency spectrum. Several methods have been developed for tissue probing using the dynamic radiation force of ultrasound, including: (a) transient methods which are based on impulsive radiation force; (b) shear-wave methods which are based on generation of shear-waves; and (c) vibro-acoustography, recently developed by the authors, where a localized oscillating radiation force is applied to the tissue and the

  9. Viscoelastic properties of passive skeletal muscle in compression: stress-relaxation behaviour and constitutive modelling.

    PubMed

    Van Loocke, M; Lyons, C G; Simms, C K

    2008-01-01

    The compressive properties of skeletal muscle are important in impact biomechanics, rehabilitation engineering and surgical simulation. However, the mechanical behaviour of muscle tissue in compression remains poorly characterised. In this paper, the time-dependent properties of passive skeletal muscle were investigated using a combined experimental and theoretical approach. Uniaxial ramp and hold compression tests were performed in vitro on fresh porcine skeletal muscle at various rates and orientations of the tissue fibres. Results show that above a very small compression rate, the viscoelastic component plays a significant role in muscle mechanical properties; it represents approximately 50% of the total stress reached at a compression rate of 0.5% s(-1). A stiffening effect with compression rate is observed especially in directions closer to the muscle fibres. Skeletal muscle viscoelastic behaviour is thus dependent on compression rate and fibre orientation. A model is proposed to represent the observed experimental behaviour, which is based on the quasi-linear viscoelasticity framework. A previously developed strain-dependent Young's Moduli formulation was extended with Prony series to account for the tissue viscoelastic properties. Parameters of the model were obtained by fitting to stress-relaxation data obtained in the muscle fibre, cross-fibre and 45 degrees directions. The model then successfully predicted stress-relaxation behaviour at 60 degrees from the fibre direction (errors <25%). Simultaneous fitting to data obtained at compression rates of 0.5% s(-1), 1%s(-1) and 10% s(-1) was performed and the model provided a good fit to the data as well as good predictions of muscle behaviour at rates of 0.05% s(-1) and 5% s(-1) (errors <25%).

  10. Shear viscoelastic properties of liquids and their boundary layers.

    PubMed

    Badmaev, Badma B; Dembelova, Tuyana S; Damdinov, Bair B

    2003-07-01

    An acoustical resonance method with piezoquartz vibrator was used in the experimental determination of shear elasticity modulus and a tangent of mechanical loss angle of studied liquids and their boundary layers. It has been shown that liquid has an earlier unknown low frequency (approx. 100 kHz) viscoelastic relaxation process. The experimental results of investigation of low frequency shear elasticity of different class of liquids and their solutions have been presented. An experimental research of shear properties in dependence on shear deformation rate has been carried out. The possibility of the discovery of anomalous high viscosity of liquids has also been considered.

  11. Extraction of quasi-linear viscoelastic parameters for lower limb soft tissues from manual indentation experiment.

    PubMed

    Zheng, Y P; Mak, A F

    1999-06-01

    A manual indentation protocol was established to assess the quasi-linear viscoelastic (QLV) properties of lower limb soft tissues. The QLV parameters were extracted using a curve-fitting procedure on the experimental indentation data. The load-indentation responses were obtained using an ultrasound indentation apparatus with a hand-held pen-sized probe. Limb soft tissues at four sites of eight normal young subjects were tested in three body postures. Four QLV model parameters were extracted from the experimental data. The initial modulus E0 ranged from 0.22 kPa to 58.4 kPa. The nonlinear factor E1 ranged from 21.7 kPa to 547 kPa. The time constant tau ranged from 0.05 s to 8.93 s. The time-dependent materials parameter alpha ranged from 0.029 to 0.277. Large variations of the parameters were noted among subjects, sites, and postures.

  12. Constitutive models for linear compressible viscoelastic flows of simple liquids at nanometer length scales

    NASA Astrophysics Data System (ADS)

    Chakraborty, Debadi; Sader, John E.

    2015-05-01

    Simple bulk liquids such as water are commonly assumed to be Newtonian. While this assumption holds widely, the fluid-structure interaction of mechanical devices at nanometer scales can probe the intrinsic molecular relaxation processes in a surrounding liquid. This was recently demonstrated through measurement of the high frequency (20 GHz) linear mechanical vibrations of bipyramidal nanoparticles in simple liquids [Pelton et al., "Viscoelastic flows in simple liquids generated by vibrating nanostructures," Phys. Rev. Lett. 111, 244502 (2013)]. In this article, we review and critically assess the available constitutive equations for compressible viscoelastic flows in their linear limits—such models are required for analysis of the above-mentioned measurements. We show that previous models, with the exception of a very recent proposal, do not reproduce the required response at high frequency. We explain the physical origin of this recent model and show that it recovers all required features of a linear viscoelastic flow. This constitutive equation thus provides a rigorous foundation for the analysis of vibrating nanostructures in simple liquids. The utility of this model is demonstrated by solving the fluid-structure interaction of two common problems: (1) a sphere executing radial oscillations in liquid, which depends strongly on the liquid compressibility and (2) the extensional mode vibration of bipyramidal nanoparticles in liquid, where the effects of liquid compressibility are negligible. This highlights the importance of shear and compressional relaxation processes, as a function of flow geometry, and the impact of the shear and bulk viscosities on nanometer scale flows.

  13. The constitutive behaviour of passive heart muscle tissue: a quasi-linear viscoelastic formulation.

    PubMed

    Huyghe, J M; van Campen, D H; Arts, T; Heethaar, R M

    1991-01-01

    A quasi-linear viscoelastic law with a continuous relaxation spectrum describing triaxial constitutive behaviour of heart muscle tissue is presented. The elastic response of the viscoelastic law is anisotropic, while the relaxation behaviour is assumed isotropic. The law is designed for a biphasic description (fluid-solid) of the myocardial tissue. Biaxial and uniaxial stress-strain curves from the literature are used to evaluate the parameters of the model. The non-linear elastic response, the difference between fibre and cross-fibre stiffness, the phenomenon of stress relaxation, the stiffening of the stress-strain relationship with increasing strain rate and the weak frequency dependency of the dissipated energy during cyclic loading are fairly well described by the proposed law. However, it is found that the model produces realistic values for the dissipated energy during cyclic loading only when relaxation parameter values are chosen which result in an overestimation of the stress relaxation data by more than 100%. This finding may indicate non-quasi-linearity of viscoelasticity of passive heart muscle tissue.

  14. Micro-Mechanical Viscoelastic Properties of Crosslinked Hydrogels Using the Nano-Epsilon Dot Method.

    PubMed

    Mattei, Giorgio; Cacopardo, Ludovica; Ahluwalia, Arti

    2017-08-02

    Engineering materials that recapitulate pathophysiological mechanical properties of native tissues in vitro is of interest for the development of biomimetic organ models. To date, the majority of studies have focused on designing hydrogels for cell cultures which mimic native tissue stiffness or quasi-static elastic moduli through a variety of crosslinking strategies, while their viscoelastic (time-dependent) behavior has been largely ignored. To provide a more complete description of the biomechanical environment felt by cells, we focused on characterizing the micro-mechanical viscoelastic properties of crosslinked hydrogels at typical cell length scales. In particular, gelatin hydrogels crosslinked with different glutaraldehyde (GTA) concentrations were analyzed via nano-indentation tests using the nano-epsilon dot method. The experimental data were fitted to a Maxwell Standard Linear Solid model, showing that increasing GTA concentration results in increased instantaneous and equilibrium elastic moduli and in a higher characteristic relaxation time. Therefore, not only do gelatin hydrogels become stiffer with increasing crosslinker concentration (as reported in the literature), but there is also a concomitant change in their viscoelastic behavior towards a more elastic one. As the degree of crosslinking alters both the elastic and viscous behavior of hydrogels, caution should be taken when attributing cell response merely to substrate stiffness, as the two effects cannot be decoupled.

  15. Micro-Mechanical Viscoelastic Properties of Crosslinked Hydrogels Using the Nano-Epsilon Dot Method

    PubMed Central

    Cacopardo, Ludovica; Ahluwalia, Arti

    2017-01-01

    Engineering materials that recapitulate pathophysiological mechanical properties of native tissues in vitro is of interest for the development of biomimetic organ models. To date, the majority of studies have focused on designing hydrogels for cell cultures which mimic native tissue stiffness or quasi-static elastic moduli through a variety of crosslinking strategies, while their viscoelastic (time-dependent) behavior has been largely ignored. To provide a more complete description of the biomechanical environment felt by cells, we focused on characterizing the micro-mechanical viscoelastic properties of crosslinked hydrogels at typical cell length scales. In particular, gelatin hydrogels crosslinked with different glutaraldehyde (GTA) concentrations were analyzed via nano-indentation tests using the nano-epsilon dot method. The experimental data were fitted to a Maxwell Standard Linear Solid model, showing that increasing GTA concentration results in increased instantaneous and equilibrium elastic moduli and in a higher characteristic relaxation time. Therefore, not only do gelatin hydrogels become stiffer with increasing crosslinker concentration (as reported in the literature), but there is also a concomitant change in their viscoelastic behavior towards a more elastic one. As the degree of crosslinking alters both the elastic and viscous behavior of hydrogels, caution should be taken when attributing cell response merely to substrate stiffness, as the two effects cannot be decoupled. PMID:28767075

  16. Investigation of multilayer printed circuit board (PCB) film warpage using viscoelastic properties measured by a vibration test

    NASA Astrophysics Data System (ADS)

    Joo, Sung-Jun; Park, Buhm; Kim, Do-Hyoung; Kwak, Dong-Ok; Song, In-Sang; Park, Junhong; Kim, Hak-Sung

    2015-03-01

    Woven glass fabric/BT (bismaleimide triazine) composite laminate (BT core), copper (Cu), and photoimageable solder resist (PSR) are the most widely used materials for semiconductors in electronic devices. Among these materials, BT core and PSR contain polymeric materials that exhibit viscoelastic behavior. For this reason, these materials are considered to have time- and temperature-dependent moduli during warpage analysis. However, the thin geometry of multilayer printed circuit board (PCB) film makes it difficult to identify viscoelastic characteristics. In this work, a vibration test method was proposed for measuring the viscoelastic properties of a multilayer PCB film at different temperatures. The beam-shaped specimens, composed of a BT core, Cu laminated on a BT core, and PSR and Cu laminated on a BT core, were used in the vibration test. The frequency-dependent variation of the complex bending stiffness was determined using a transfer function method. The storage modulus (E‧) of the BT core, Cu, and PSR as a function of temperature and frequency were obtained, and their temperature-dependent variation was identified. The obtained properties were fitted using a viscoelastic model for the BT core and the PSR, and a linear elastic model for the Cu. Warpage of a line pattern specimen due to temperature variation was measured using a shadow Moiré analysis and compared to predictions using a finite element model. The results provide information on the mechanism of warpage, especially warpage due to temperature-dependent variation in viscoelastic properties.

  17. Elastic and viscoelastic mechanical properties of brain tissues on the implanting trajectory of sub-thalamic nucleus stimulation.

    PubMed

    Li, Yan; Deng, Jianxin; Zhou, Jun; Li, Xueen

    2016-11-01

    Corresponding to pre-puncture and post-puncture insertion, elastic and viscoelastic mechanical properties of brain tissues on the implanting trajectory of sub-thalamic nucleus stimulation are investigated, respectively. Elastic mechanical properties in pre-puncture are investigated through pre-puncture needle insertion experiments using whole porcine brains. A linear polynomial and a second order polynomial are fitted to the average insertion force in pre-puncture. The Young's modulus in pre-puncture is calculated from the slope of the two fittings. Viscoelastic mechanical properties of brain tissues in post-puncture insertion are investigated through indentation stress relaxation tests for six interested regions along a planned trajectory. A linear viscoelastic model with a Prony series approximation is fitted to the average load trace of each region using Boltzmann hereditary integral. Shear relaxation moduli of each region are calculated using the parameters of the Prony series approximation. The results show that, in pre-puncture insertion, needle force almost increases linearly with needle displacement. Both fitting lines can perfectly fit the average insertion force. The Young's moduli calculated from the slope of the two fittings are worthy of trust to model linearly or nonlinearly instantaneous elastic responses of brain tissues, respectively. In post-puncture insertion, both region and time significantly affect the viscoelastic behaviors. Six tested regions can be classified into three categories in stiffness. Shear relaxation moduli decay dramatically in short time scales but equilibrium is never truly achieved. The regional and temporal viscoelastic mechanical properties in post-puncture insertion are valuable for guiding probe insertion into each region on the implanting trajectory.

  18. Probing viscoelastic surfaces with bimodal tapping-mode atomic force microscopy: Underlying physics and observables for a standard linear solid model.

    PubMed

    Solares, Santiago D

    2014-01-01

    This paper presents computational simulations of single-mode and bimodal atomic force microscopy (AFM) with particular focus on the viscoelastic interactions occurring during tip-sample impact. The surface is modeled by using a standard linear solid model, which is the simplest system that can reproduce creep compliance and stress relaxation, which are fundamental behaviors exhibited by viscoelastic surfaces. The relaxation of the surface in combination with the complexities of bimodal tip-sample impacts gives rise to unique dynamic behaviors that have important consequences with regards to the acquisition of quantitative relationships between the sample properties and the AFM observables. The physics of the tip-sample interactions and its effect on the observables are illustrated and discussed, and a brief research outlook on viscoelasticity measurement with intermittent-contact AFM is provided.

  19. Continuous Shear Wave Elastography: a New Method to Measure in-vivo Viscoelastic Properties of Tendons

    PubMed Central

    Cortes, Daniel H.; Suydam, Stephen M.; Silbernagel, Karin Grävare; Buchanan, Thomas S.; Elliott, Dawn M.

    2015-01-01

    Viscoelastic mechanical properties are frequently altered after tendon injuries and during recovery. Therefore, non-invasive measurements of shear viscoelastic properties may help evaluate tendon recovery and compare the effectiveness of different therapies. The objectives of this study are to present an elastography method to measure localized viscoelastic properties of tendon and to present initial results in healthy and injured human Achilles and semitendinosus tendons. The technique used an external actuator to generate the shear waves in the tendon at different frequencies and plane wave imaging to measure shear wave displacements. For each of the excitation frequencies, maps of direction specific wave speeds were calculated using Local Frequency Estimation. Maps of viscoelastic properties were obtained using a pixel wise curve-fit of wave speed and frequency. The method was validated by comparing measurements of wave speed in agarose gels to those obtained using magnetic resonance elastography. Measurements in human healthy Achilles tendons revealed a pronounced increase in wave speed as function of frequency that highlights the importance of tendon viscoelasticity. Additionally, the viscoelastic properties of the Achilles tendon were larger than those reported for other tissues. Measurements in a tendinopathic Achilles tendon showed that it is feasible to quantify local viscoeasltic properties. Similarly, measurement in the semitendinosus tendon showed a substantial differences in viscoelastic properties between the healthy and contralateral tendons. Consequently, this technique has the potential of evaluating localized changes in tendon viscoelastic properties due to injury and during recovery in a clinical setting. PMID:25796414

  20. Linear oscillation of gas bubbles in a viscoelastic material under ultrasound irradiation

    SciTech Connect

    Hamaguchi, Fumiya; Ando, Keita

    2015-11-15

    Acoustically forced oscillation of spherical gas bubbles in a viscoelastic material is studied through comparisons between experiments and linear theory. An experimental setup has been designed to visualize bubble dynamics in gelatin gels using a high-speed camera. A spherical gas bubble is created by focusing an infrared laser pulse into (gas-supersaturated) gelatin gels. The bubble radius (up to 150 μm) under mechanical equilibrium is controlled by gradual mass transfer of gases across the bubble interface. The linearized bubble dynamics are studied from the observation of spherical bubble oscillation driven by low-intensity, planar ultrasound driven at 28 kHz. It follows from the experiment for an isolated bubble that the frequency response in its volumetric oscillation was shifted to the high frequency side and its peak was suppressed as the gelatin concentration increases. The measurement is fitted to the linearized Rayleigh–Plesset equation coupled with the Voigt constitutive equation that models the behavior of linear viscoelastic solids; the fitting yields good agreement by tuning unknown values of the viscosity and rigidity, indicating that more complex phenomena including shear thinning, stress relaxation, and retardation do not play an important role for the small-amplitude oscillations. Moreover, the cases for bubble-bubble and bubble-wall systems are studied. The observed interaction effect on the linearized dynamics can be explained as well by a set of the Rayleigh–Plesset equations coupled through acoustic radiation among these systems. This suggests that this experimental setup can be applied to validate the model of bubble dynamics with more complex configuration such as a cloud of bubbles in viscoelastic materials.

  1. Linear oscillation of gas bubbles in a viscoelastic material under ultrasound irradiation

    NASA Astrophysics Data System (ADS)

    Hamaguchi, Fumiya; Ando, Keita

    2015-11-01

    Acoustically forced oscillation of spherical gas bubbles in a viscoelastic material is studied through comparisons between experiments and linear theory. An experimental setup has been designed to visualize bubble dynamics in gelatin gels using a high-speed camera. A spherical gas bubble is created by focusing an infrared laser pulse into (gas-supersaturated) gelatin gels. The bubble radius (up to 150 μm) under mechanical equilibrium is controlled by gradual mass transfer of gases across the bubble interface. The linearized bubble dynamics are studied from the observation of spherical bubble oscillation driven by low-intensity, planar ultrasound driven at 28 kHz. It follows from the experiment for an isolated bubble that the frequency response in its volumetric oscillation was shifted to the high frequency side and its peak was suppressed as the gelatin concentration increases. The measurement is fitted to the linearized Rayleigh-Plesset equation coupled with the Voigt constitutive equation that models the behavior of linear viscoelastic solids; the fitting yields good agreement by tuning unknown values of the viscosity and rigidity, indicating that more complex phenomena including shear thinning, stress relaxation, and retardation do not play an important role for the small-amplitude oscillations. Moreover, the cases for bubble-bubble and bubble-wall systems are studied. The observed interaction effect on the linearized dynamics can be explained as well by a set of the Rayleigh-Plesset equations coupled through acoustic radiation among these systems. This suggests that this experimental setup can be applied to validate the model of bubble dynamics with more complex configuration such as a cloud of bubbles in viscoelastic materials.

  2. Explicit causal relations between material damping ratio and phase velocity from exact solutions of the dispersion equations of linear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Meza-Fajardo, Kristel C.; Lai, Carlo G.

    2007-12-01

    The theory of linear viscoelasticity is the simplest constitutive model that can be adopted to accurately predict the small-strain mechanical response of materials exhibiting the ability to both store and dissipate strain energy. An important result implied by this theory is the relationship existing between material attenuation and the velocity of propagation of a mechanical disturbance. The functional dependence of these important parameters is represented by the Kramers-Kronig (KK) equations, also known as dispersion equations, which are nothing but a statement of the necessary and sufficient conditions to satisfy physical causality. This paper illustrates the derivation of exact solutions of the KK equations to provide explicit relations between frequency-dependent phase velocity and material damping ratio (or equivalently, quality factor). The assumptions that form the basis of the derivation are not beyond those established by the standard theory of viscoelasticity for a viscoelastic solid. The explicit expression for phase velocity as a function of damping ratio was derived by means of the theory of linear singular integral equations, and in particular by the solution of the associated Homogeneous Riemann Boundary Value Problem. It is shown that the same solution may be obtained also by using the implications of physical causality on the Fourier Transform. On the other hand, the explicit solution for damping ratio as a function of phase velocity was found through the components of the complex wavenumber. The exact solutions make it possible to obtain frequency-dependent material damping ratio solely from phase velocity measurements, and conversely. Hence, these relations provide an innovative and inexpensive tool to determine the small-strain dynamic properties of geomaterials. It is shown that the obtained rigorous solutions are in good agreement with well-known solutions based on simplifying assumptions that have been developed in the fields of seismology

  3. Non-Newtonian and Viscoelastic Properties of Lava Flows

    NASA Astrophysics Data System (ADS)

    Bagdassarov, N. S.

    2004-12-01

    Lava flow models require an in-depth knowledge of the rheological properties of lava. Previous measurements have shown that, at typical eruption temperatures, lavas are non-Newtonian. The reasons for this include the formation and destruction of crystal networks and bubble deformation during shear. The effects of bubbles are investigated experimentally in this contribution using analogue fluids with bubble concentrations <20%. The shear-thinning behaviour of bubbly liquids noted by previous workers is shown to be dependent on the previous shearing history of the fluid. This thixotropic behaviour, which was investigated using a rotational vane viscometer, is caused by delayed bubble deformation and recovery when subjected to changes in shear stress. A rotational vane viscometer and torsional deformation apparatus were used to investigate the rheological properties of bubbly liquids and foams in order to determine a viscoelastic transition. These experiments have shown that the foams tested are viscoelastic power law fluids with a yield strength. Non-Newtonian properties and yield strength of foams are shown to be a probable cause of accelerating flow fragmentation in tube flow experiments on expanding foams. The flow of a bubbly fluid through a narrowing conduit may cause a pulsating regime of a flow due to periodic slip and slip-free boundary conditions near the walls of a conduit. Slip boundary conditions can lead to instability in viscoelastic shear flow causing short wavelength fluctuations at high shear rates. This mechanism may also take place during explosive volcanic eruptions. The frequency and amplitude of oscillation shear affect the structure of lavas which are thixotropic non-Newtonian liquids. The frequency dependent structure of lavas can be identified via frequency hysteresis and time-evolution of internal friction and viscosity. The rheological properties of basaltic lavas from Etna, Hawai'i and Vesuvius have been investigated at temperatures

  4. Attenuation and Shock Waves in Linear Hereditary Viscoelastic Media; Strick-Mainardi, Jeffreys-Lomnitz-Strick and Andrade Creep Compliances

    NASA Astrophysics Data System (ADS)

    Hanyga, Andrzej

    2014-09-01

    Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by Strick and Mainardi (Geophys J R Astr Soc 69:415-429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.

  5. Finite element fluid flow computations through porous media employing quasi-linear and nonlinear viscoelastic models

    NASA Astrophysics Data System (ADS)

    Alakus, Bayram

    Mathematical modeling involving porous heterogeneous media is important in a number of composite manufacturing processes, such as resin transfer molding (RTM), injection molding and the like. Of interest here are process modeling issues as related to composites manufacturing by RTM, because of the ability of the method to manufacture consolidated net shapes of complex geometric parts. In this research, we propose a mathematical model by utilizing the local volume averaging technique to establish the governing equations and therein provide finite element computational developments to predict the flow behavior of a viscous and viscoelastic fluid through a porous fiber network. The developments predict the velocity, pressure, and polymeric stress by modeling the conservation laws (e.g. mass and momentum) of the flow field coupled with constitutive equations for polymeric stress field. The governing equations of the flow are averaged for the fluid phase. Furthermore, the simulations target a variety of viscoelastic models (e.g. Newtonian model, Upper-Convected-Maxwell Model, Oldroyd-B model and Giesekus model) to provide a fundamental understanding of the elastic effects on the flow field. To solve the complex coupled nonlinear equations of the mathematical model described above, a combination of Newton linearization and the Galerkin and Streamline-Upwinding-Petrov-Galerkin (SUPG) finite element procedures are employed to accurately capture the representative physics. The formulations are first validated with available test cases of viscoelastic flows without porous media. Therein, the simulations are described for viscoelastic flow through porous media and the comparative results of different constitutive models are presented and discussed at length.

  6. Quasi-linear viscoelastic modeling of arterial wall for surgical simulation.

    PubMed

    Yang, Tao; Chui, Chee Kong; Yu, Rui Qi; Qin, Jing; Chang, Stephen K Y

    2011-11-01

    Realistic soft tissue deformation modeling and haptic rendering for surgical simulation require accurate knowledge of tissue material characteristics. Biomechanical experiments on porcine tissue were performed, and a reduced quasi-linear viscoelastic model was developed to describe the strain-dependent relaxation behavior of the arterial wall. This information is used in surgical simulation to provide a realistic sensation of reduction in strength when the user holds a virtual blood vessel strained at different levels. Twelve pieces of porcine abdominal artery were tested with uniaxial elongation and relaxation test in both circumferential and longitudinal directions. The mechanical property testing system consists of automated environment control, testing, and data collection mechanism. A combined logarithm and polynomial strain energy equation was applied to model the elastic response of the specimens. The reduced relaxation function was modified by integrating a rational equation as a corrective factor to precisely describe the strain-dependent relaxation effects. The experiments revealed that (1) stress is insensitive to strain rate in arterial tissue when the loading rate is low, and (2) the rate of stress relaxation of arterial wall is highly strain dependent. The proposed model can accurately represent the experimental data. Stress-strain function derived from the combined strain energy function is able to fit the tensile experimental data with R(2) equals to 0.9995 in circumferential direction and 0.999 in longitudinal direction. Modified reduced relaxation function is able to model the strain-dependent relaxation with R(2) equals to 0.9686 in circumferential direction and 0.988 in longitudinal direction. The proposed model, based on extensive biomechanical experiments, can be used for accurate simulation of arterial deformation and haptic rendering in surgical simulation. The resultant model enables stress relaxation status to be determined when subjected

  7. Viscoelastic Timoshenko beam theory

    NASA Astrophysics Data System (ADS)

    Hilton, Harry H.

    2009-03-01

    The concept of elastic Timoshenko shear coefficients is used as a guide for linear viscoelastic Euler-Bernoulli beams subjected to simultaneous bending and twisting. It is shown that the corresponding Timoshenko viscoelastic functions now depend not only on material properties and geometry as they do in elasticity, but also additionally on stresses and their time histories. Possible viscoelastic definitions are formulated and evaluated. In general, the viscoelastic relations are sufficiently complicated so that the elastic-viscoelastic correspondence principle (analogy) cannot be applied. This is particularly true for, but not limited to, elastic shear coefficients which are Poisson ratio dependent. Expressions for equivalent viscoelastic Timoshenko shear functions must, therefore, be derived de novo on a case by case basis, taking in to account specific relaxation moduli, stresses, temperatures and their time histories. Thus the elastic simplicity and generality is lost and hence rendering the use of viscoelastic Timoshenko shear functions as highly impractical. Consequently, it is necessary to directly solve the coupled viscoelastic beam governing relations for bending and twisting deflections by using appropriate solution protocols as discussed herein.

  8. Viscoelastic properties of sterically stabilised emulsions and their stability.

    PubMed

    Tadros, Tharwat

    2015-08-01

    The interaction forces between emulsion droplets containing adsorbed polymeric surfactants and the theory of steric stabilisation are briefly described. The results for the viscoelastic properties of O/W emulsions that are stabilised with partially hydrolysed poly(vinyl acetate) that is commonly referred to as poly(vinyl alcohol) (PVA) with 4% vinyl acetate are given. The effect of the oil volume fraction, addition of electrolytes and increasing temperature is described. This allows one to obtain various parameters such as the adsorbed layer thickness, the critical flocculation concentration of electrolyte (CFC) and critical flocculation temperature (CFT) at constant electrolyte concentration. The viscoelastic properties of O/W emulsions stabilised with an A-B-A block copolymer of polyethylene oxide (A) and polypropylene oxide (B) are described. These emulsions behave as viscoelastic liquids showing a cross-over-point between G' (the elastic component of the complex modulus) and G″ (the viscous component of the complex modulus) at a characteristic frequency. Plots of G' and G″ versus oil volume fraction ϕ show the transition from predominantly viscous to predominantly elastic response at a critical volume fraction ϕ(c). The latter can be used to estimate the adsorbed layer thickness of the polymeric surfactants. Results are also shown for W/O emulsions stabilised with an A-B-A block copolymer of polyhydroxystearic acid (PHS, A) and polyethylene oxide (PEO, B). The viscosity volume fraction curves could be fitted to the Dougherty-Krieger equation for hard-spheres. The results could be applied to give an estimate of the adsorbed layer thickness Δ which shows a decrease with increase of the water volume fraction. This is due to the interpenetration and/or compression of the PHS layers on close approach of the water droplets on increasing the water volume fraction. The last section of the review gives an example of O/W emulsion stability using an AB(n) graft

  9. Nanoscale viscoelastic properties and adhesion of polydimethylsiloxane for tissue engineering

    NASA Astrophysics Data System (ADS)

    Chen, J.; Wright, K. E.; Birch, M. A.

    2014-02-01

    It has shown that altering crosslink density of biopolymers will regulate the morphology of Mesenchymal Stem Cells (MSCs) and the subsequent MSCs differentiation. These observations have been found in a wide range of biopolymers. However, a recent work published in Nature Materials has revealed that MSCs morphology and differentiation was unaffected by crosslink density of polydimethylsiloxane (PDMS), which remains elusive. To understand such unusual behaviour, we use nanoindentation tests and modelling to characterize viscoelastic properties and surface adhesion of PDMS with different base:crosslink ratio varied from 50:1 (50D) to 10:1 (10D). It has shown that lower crosslink density leads to lower elastic moduli. Despite lower nanoindentation elastic moduli, PDMS with lowest crosslink density has higher local surface adhesion which would affect cell-biomaterials interactions. This work suggests that surface adhesion is likely another important physical cue to regulate cell-biomaterials interactions. [Figure not available: see fulltext.

  10. Viscoelastic Properties of the Aortic Valve Interstitial Cell

    PubMed Central

    Merryman, W. David; Bieniek, Paul D.; Guilak, Farshid; Sacks, Michael S.

    2013-01-01

    There has been growing interest in the mechanobiological function of the aortic valve interstitial cell (AVIC), due to its role in valve tissue homeostasis and remodeling. In a recent study we determined the relation between diastolic loading of the AV leaflet and the resulting AVIC deformation, which was found to be substantial. However, due to the rapid loading time of the AV leaflets during closure (~0.05 s), time-dependent effects may play a role in AVIC deformation during physiological function. In the present study, we explored AVIC viscoelastic behavior using the micropipette aspiration technique. We then modeled the resulting time-length data over the 100 sec test period using a standard linear solid (SLS) model which included Boltzmann superposition. To quantify the degree of creep and stress relaxation during physiological timescales, simulations of micropipette aspiration were preformed with a valve loading time of 0.05 s and a full valve closure time of 0.3 s. The 0.05 s loading simulations suggest that, during valve closure, AVICs act elastically. During diastole, simulations revealed creep (4.65%) and stress relaxation (4.39%) over the 0.3 s physiological timescale. Simulations also indicated that if Boltzmann superposition was not used in parameter estimation, as in much of the micropipette literature, creep and stress relaxation predicted values were nearly doubled (7.92% and 7.35%, respectively). We conclude that while AVIC viscoelastic effects are negligible during valve closure, they likely contribute to the deformation time-history of AVIC deformation during diastole. PMID:19275434

  11. Viscoelastic shear properties of porcine temporomandibular joint disc

    PubMed Central

    Wu, Yongren; Kuo, Jonathan; Wright, Gregory J.; Cisewski, Sarah E.; Wei, Feng; Kern, Michael J.; Yao, Hai

    2016-01-01

    Objectives To investigate the intrinsic viscoelastic shear properties in porcine TMJ discs. Materials and Methods Twelve fresh porcine TMJ discs from young adult pigs (6-8 months) were used. Cylindrical samples (5 mm diameter) with uniform thickness (~1.2 mm) were prepared from five regions of the TMJ disc. Torsional shear tests were performed under 10% compressive strain. Dynamic shear was applied in two methods: (1) a frequency sweep test over the frequency range of 0.01-10 rad/s with a constant shear strain amplitude of 0.025 rad, and (2) a strain sweep test over the range of 0.005-0.05 rad at a constant frequency of 10 rad/s. Transient stress-relaxation tests were also performed to determine the equilibrium shear properties. Results As the frequency increased in the frequency sweep test, the dynamic shear complex modulus increased, with values ranging from 7 to 17 kPa. The phase angle, ranging from 11 to 15 degrees, displayed no pattern of regional variation as the frequency increased. The dynamic shear modulus decreased as the shear strain increased. The equilibrium shear modulus had values ranging from 2 to 4.5 kPa. The posterior region had significantly higher values for dynamic shear modulus than those in the anterior region while no significant regional difference was found for equilibrium shear modulus. Conclusion Our results suggest that the intrinsic region-dependent viscoelastic shear characteristics of TMJ disc may play a crucial role in determining the local strain of the TMJ disc under mechanical loading. PMID:25865544

  12. The effects of refreezing on the viscoelastic and tensile properties of ligaments.

    PubMed

    Moon, Daniel K; Woo, Savio L-Y; Takakura, Yoshiyuki; Gabriel, Mary T; Abramowitch, Steven D

    2006-01-01

    Biomechanical testing protocols for ligaments can be extensive and span two or more days. During this time, a specimen may have to undergo more than one cycle of freezing and thawing. Thus, the objective of this study was to evaluate the effects of refreezing on the viscoelastic and tensile properties of ligaments. The femur-medial collateral ligament-tibia complexes (FMTC) from six pairs of rabbit knees were used for this study. Following sacrifice, one leg in each pair was assigned to the fresh group and the FMTC was immediately dissected and prepared for testing. The contralateral knees were fresh-frozen at -20 degrees C for 3 weeks, thawed, dissected and then refrozen for one additional week before being tested as the refrozen group. The cross-sectional area and shape of the medial collateral ligament (MCL) was measured using a laser micrometer system. Stress relaxation and cyclic stress-relaxation tests in uniaxial tension were performed followed by a load to failure test. When the viscoelastic behavior of the MCL was described by the quasi-linear viscoelastic (QLV) theory, no statistically significant differences could be detected for the five constants (A, B, C, tau1, and tau2) between the fresh and refrozen groups (p > or = 0.07) based on our sample size. In addition, the structural properties of the FMTCs and the mechanical properties of the MCLs were also found to be similar between the two groups (p > or = 0.68). These results suggest that careful refreezing of the specimens had little or no effect on the biomechanical properties measured.

  13. Determination of the Constitutive Constants of Non-Linear Viscoelastic Materials

    NASA Astrophysics Data System (ADS)

    Goh, S. M.; Charalambides, M. N.; Williams, J. G.

    2004-09-01

    A simple method for computing the strain and the time dependent constants for non-linear viscoelastic materials is presented. The method is based on the finite time increment formulation of the convolution integral, and is applicable for materials which exhibit separable strain and time variables. The strain-dependent function can take any form including the hyperelastic potentials such as the Mooney-Rivlin strain energy function. The time-dependent function is based on the Prony series. The attraction of the method is that true material constants can be computed for any deformation history.

  14. Determining the parameters of the fractional exponential heredity kernels of linear viscoelastic materials

    NASA Astrophysics Data System (ADS)

    Golub, V. P.; Fernati, P. V.; Lyashenko, Ya. G.

    2008-09-01

    The parameters of the fractional exponential creep and relaxation kernels of linear viscoelastic materials are determined. Methods that approximate the kernel by using the Mittag-Leffler function, the Laplace-Carson transform, and direct approximation of the creep function by the original equation are analyzed. The parameters of fractional exponential kernels are determined for aramid fibers, parapolyamide fibers, glass-reinforced plastic, and polymer concrete. It is shown that the kernel parameters calculated through the direct approximation of the creep function provide the best agreement between theory and experiment. The methods are experimentally validated for constant-stress and variable-stress loading in the modes of additional loading and complete unloading

  15. Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation.

    PubMed

    Gayle, Andrew J; Cook, Robert F

    An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes.

  16. Active microrheology reveals molecular-level variations in the viscoelastic properties of Chaetopterus mucus

    NASA Astrophysics Data System (ADS)

    Weigand, William; Messmore, Ashley; Anderson, Rae

    The sea annelid, Chaetopterus Variopedatus, secretes a bioluminescent mucus that also exhibits complex viscoelastic properties. The constituents of the mucus are relatively unknown but it does play an important role in the development of the worms' parchment-like housing tubes. In order to determine how and why this mucus can exhibit material properties ranging from fluidity to rigidity we perform microrheology experiments. We determine the microscale viscoelastic properties by using optical tweezers to produce small oscillations in the mucus which allow us to determine both the linear storage and loss moduli (G',G'') along with the viscosity of the fluid. By varying the size of the microspheres (2-10 µm) and oscillation amplitude (.5-10 µm) we are able to determine the dominant intrinsic length scales of the molecular mesh comprising the mucus. By varying the oscillation frequency (1-15Hz) we determine the crossover frequency at which G' surpasses G'', to quantify the longest relaxation time of the mesh network. Initial results show a strong dependence on bead size which indicate that the dominant entanglement lengthscale of the mucus mesh is ~5 um. Microspheres of this size exhibit a wide variety of stress responses in different regions of the mucus demonstrating the substantial microscale heterogeneity of the mucus. We carry out measurements on a population of worms of varying size and age to determine mucus variability between worms.

  17. A comparative study on the viscoelastic properties of human and animal lenses.

    PubMed

    Sharma, P K; Busscher, H J; Terwee, T; Koopmans, S A; van Kooten, T G

    2011-11-01

    A new method of compression between two parallel plates is used to measure the viscoelastic properties of whole and decapsulated human lenses and compare them with other animal species. Compressive load relaxation was performed by deforming the lens by 10% and measuring the force relaxation response for 100 s to obtain thickness, stiffness and relaxation of the induced loading force and Maxwell parameters for human, monkey, porcine and leporine whole and decapsulated lenses. Thickness and percentage loading force relaxation increased linearly with lens age, whereas stiffness and induced loading force increased exponentially. Human and monkey lenses aged at different rates. Loading force relaxation in a generalized Maxwell model was described by three time constants ranging from 1 to 1000 s. Compressive load relaxation is a very versatile method to study the viscoelastic properties of whole and decapsulated lenses and potentially also artificial accommodating lenses. The data presented in the study will help researchers choose the most suitable animal lenses based on the desired properties and age to be mimicked from the human lenses.

  18. Continuous Shear Wave Elastography: A New Method to Measure Viscoelastic Properties of Tendons in Vivo.

    PubMed

    Cortes, Daniel H; Suydam, Stephen M; Silbernagel, Karin Grävare; Buchanan, Thomas S; Elliott, Dawn M

    2015-06-01

    Viscoelastic mechanical properties are frequently altered after tendon injuries and during recovery. Therefore, non-invasive measurements of shear viscoelastic properties may help evaluate tendon recovery and compare the effectiveness of different therapies. The objectives of this study were to describe an elastography method for measuring localized viscoelastic properties of tendons and to discuss the initial results in healthy and injured human Achilles and semitendinosus tendons. The technique used an external actuator to generate the shear waves in the tendon at different frequencies and plane wave imaging to measure shear wave displacements. For each of the excitation frequencies, maps of direction-specific wave speeds were calculated using local frequency estimation. Maps of viscoelastic properties were obtained using a pixel-wise curve fit of wave speed and frequency. The method was validated by comparing measurements of wave speed in agarose gels with those obtained using magnetic resonance elastography. Measurements in human healthy Achilles tendons revealed a pronounced increase in wave speed as a function of frequency, which highlights the importance of tendon viscoelasticity. Additionally, the viscoelastic properties of the Achilles tendon were larger than those reported for other tissues. Measurements in a tendinopathic Achilles tendon indicated that it is feasible to quantify local viscoelastic properties. Similarly, measurement in the semitendinosus tendon revealed substantial differences in viscoelastic properties between the healthy and contralateral tendons. Consequently, this technique has the potential to evaluate localized changes in tendon viscoelastic properties caused by injury and during recovery in a clinical setting. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  19. Viscoelastic properties of the contracting detrusor. I. Theoretical basis.

    PubMed

    Venegas, J G

    1991-08-01

    This paper presents the theoretical basis for estimating the detrusor's viscoelastic properties using the small-amplitude oscillatory perturbations technique. Three possible configurations of the simplest second-order lumped-parameter model of the bladder were analyzed to derive equations of the parameters incremental resistance (R) and incremental elastance (K) in terms of the experimentally measurable magnitude and phase of hydrodynamic stiffness. In model I, single viscous, elastic, and inertial elements were assumed to to be connected in series. In model III the elastic and viscous elements were connected in series, but the inertial element was connected in parallel. With the assumption of a spherical geometry of the bladder, equations were also derived to obtain the bladder wall mechanical properties, spring incremental constant (S), and muscle incremental viscosity (b) as functions of bladder volume and the hydrodynamic properties R and K. Integration of the incremental equation describing the viscous component yields an expression that fits well the force-velocity experimental data from bladder strips reported by others. This finding suggests that muscle viscosity measured with the small-amplitude oscillations and analyzed with the proper theoretical model may be related to the force-velocity characteristics of the muscle. The equations delivered here form the basis for analyzing the experimental data described in the companion paper.

  20. Small strain vibration of a continuous, linearized viscoelastic rod of expanded polymer cushion material

    NASA Astrophysics Data System (ADS)

    Batt, Gregory S.; Gibert, James M.; Daqaq, Mohammed

    2015-08-01

    In this paper, the free and forced vibration response of a linearized, distributed-parameter model of a viscoelastic rod with an applied tip-mass is investigated. A nonlinear model is developed from constitutive relations and is linearized about a static equilibrium position for analysis. A classical Maxwell-Weichert model, represented via a Prony series, is used to model the viscoelastic system. The exact solution to both the free and forced vibration problem is derived and used to study the behavior of an idealized packaging system containing Nova Chemicals' Arcel® foam. It is observed that, although three Prony series terms are deemed sufficient to fit the static test data, convergence of the dynamic response and study of the storage and loss modulii necessitate the use of additional Prony series terms. It is also shown that the model is able to predict the modal frequencies and the primary resonance response at low acceleration excitation, both with reasonable accuracy given the non-homogeneity and density variation observed in the specimens. Higher acceleration inputs result in softening nonlinear responses highlighting the need for a nonlinear elastic model that extends beyond the scope of this work. Solution analysis and experimental data indicate little material vibration energy dissipation close to the first modal frequency of the mass/rod system.

  1. Non-linear analysis and the design of Pumpkin Balloons: stress, stability and viscoelasticity

    NASA Astrophysics Data System (ADS)

    Rand, J. L.; Wakefield, D. S.

    Tensys have a long-established background in the shape generation and load analysis of architectural stressed membrane structures Founded upon their inTENS finite element analysis suite these activities have broadened to encompass lighter than air structures such as aerostats hybrid air-vehicles and stratospheric balloons Winzen Engineering couple many years of practical balloon design and fabrication experience with both academic and practical knowledge of the characterisation of the non-linear viscoelastic response of the polymeric films typically used for high-altitude scientific balloons Both companies have provided consulting services to the NASA Ultra Long Duration Balloon ULDB Program Early implementations of pumpkin balloons have shown problems of geometric instability characterised by improper deployment and these difficulties have been reproduced numerically using inTENS The solution lies in both the shapes of the membrane lobes and also the need to generate a biaxial stress field in order to mobilise in-plane shear stiffness Balloons undergo significant temperature and pressure variations in flight The different thermal characteristics between tendons and film can lead to significant meridional stress Fabrication tolerances can lead to significant local hoop stress concentrations particularly adjacent to the base and apex end fittings The non-linear viscoelastic response of the envelope film acts positively to help dissipate stress concentrations However creep over time may produce lobe geometry variations that may

  2. Characterization of the linearly viscoelastic behavior of human tympanic membrane by nanoindentation.

    PubMed

    Daphalapurkar, Nitin P; Dai, Chenkai; Gan, Rong Z; Lu, Hongbing

    2009-01-01

    Human tympanic membrane (or eardrum) is composed of three membrane layers with collagen fibers oriented in the radial and circumferential directions, and exhibits viscoelastic behavior with membrane (or in-plane) properties different from through-thickness (or out-of-plane) properties. Due to the interaction of bundled fibers and ground substance, which is inhomogeneous, these properties could change with locations. In this paper, we use nanoindentation techniques to measure the viscoelastic functions of four quadrants of tympanic membrane (TM). For measurement of in-plane Young's relaxation modulus we fixed a sectioned quadrant of the TM on a circular hole and used a spherical nanoindenter tip to apply force at the center of the suspended circular portion of the specimen. An inverse problem solving methodology was employed using finite element method to determine the average in-plane Young's relaxation modulus of the TM quadrant. Results indicate that the in-plane steady-state Young's relaxation modulus for four quadrants of the TM does not vary significantly. However, a variation of the modulus from 25.73 MPa to 37.8 MPa was observed with measurements from different individuals. For measurement of Young's relaxation modulus in the through-thickness direction a spherical indenter tip was used to indent into different locations on the surface of the TM specimen supported by a substrate. Viscoelastic contact mechanics analysis of the load-displacement curve, representative primarily of the through-thickness stiffness of the TM, was conducted to extract the Young's relaxation modulus in the out-of-plane direction. Results indicate a wide variation in steady-state Young's relaxation modulus, from 2 MPa to 15 MPa, in the through-thickness direction over the TM.

  3. A Comparison of the Quasi-static Mechanical and Nonlinear Viscoelastic Properties of the Human Semitendinosus and Gracilis Tendons

    PubMed Central

    Abramowitch, Steven D.; Zhang, Xiaoyan; Curran, Molly; Kilger, Robert

    2010-01-01

    Background Over fifty-percent of anterior cruciate ligament reconstructions are performed using semitendinosus and gracilis tendon autografts. Despite their increased use, there remains little quantitative data on their mechanical behavior. Therefore, the objective of this study was to investigate the quasi-static mechanical and nonlinear viscoelastic properties of human semitendinosus and gracilis tendons, as well as the variation of these properties along their length. Methods Specimens were subjected to a series of uniaxial tensile tests: one-hour static stress-relaxation test, 30-cycle cyclic stress-relaxation test and load to failure test. To describe the nonlinear viscoelastic behavior, the quasi-linear viscoelastic theory was utilized to model data from the static stress relaxation experiment. Findings The constants describing the viscoelastic behavior were similar between the proximal and distal halves of the gracilis tendon. The proximal half of the semitendinosus tendon, however, had a greater viscous response than its distal half, which was also significantly higher than the proximal gracilis tendon. In terms of the quasi-static mechanical properties, the properties were similar between the proximal and distal halves of the semitendinosus tendon. However, the distal gracilis tendon showed a significantly higher tangent modulus and ultimate stress compared to its proximal half, which was also significantly higher than the distal semitendinosus tendon. Interpretation The results of this study demonstrate differences between the semitendinosus and gracilis tendons in terms of their quasi-static mechanical and nonlinear viscoelastic properties. These results are important for establishing surgical preconditioning protocols and graft selection. PMID:20092917

  4. Viscoelastic properties of vascular endothelial cells exposed to uniaxial stretch

    NASA Astrophysics Data System (ADS)

    Osterday, Kathryn; Chew, Thomas; Loury, Phillip; Haga, Jason; Del Alamo, Juan C.; Chien, Shu

    2011-11-01

    Vascular endothelial cells (VECs) line the interior of blood vessels and regulate a variety of functions in the cardiovascular system. It is widely accepted that VECs will remodel themselves in response to mechanical stimuli, but few studies have analyzed the mechanical properties of these cells under stretch. We hypothesize that uniaxial stretch will cause an anisotropic realignment of actin filaments, and a change in the viscoelastic properties of the cell. To test this hypothesis, VECs were grown on a thin, transparent membrane mounted on a microscope. The membrane was stretched, consequently stretching the cells. Time-lapse sequences of the cells were taken every hour with a time resolution of 10 Hz. The random trajectories of intracellular endogenous particles were tracked using in-house algorithms. These trajectories were analyzed using a novel particle tracking microrheology formulation that takes into account the anisotropy of the cytoplasm of VECs. Supported by NSF CBET-1055697 CAREER Award (JCA) and NIH grants BRP HL064382 (SC), 1R01 HL080518 (SC).

  5. Viscoelastic properties of an aesthetic translucent orthodontic wire.

    PubMed

    Goldberg, A Jon; Liebler, Stephenie A H; Burstone, Charles J

    2011-12-01

    The objective of this study was to evaluate the time-dependent viscoelastic properties of an aesthetic orthodontic archwire. The wire is based on a recently developed translucent polyphenylene thermoplastic, whose rigid molecular structure provides high strength. While the wire has good instantaneous mechanical properties, over time all polymers may relax so it is important to understand the potential impact of the relaxation on orthodontic force systems. Four samples of 0.020 inch round and six samples of 0.021 × 0.025 inch rectangular wire were loaded in tension to a range of initial stresses, and relaxation of the stress was monitored for 7 days. Sixty-three additional samples were maintained in edgewise bracket pairs with vertical displacement for up to 6 weeks. The deformation of these wires was measured immediately after removal from the brackets and for 2 days as the samples recovered. Tensile stress decayed about 10-30 per cent over 24-48 hours depending on the initial stress. The relaxation behaviour was proportional to the initial tensile strain and therefore these data were combined into a single curve using regression. Deformation of the samples placed in the bracket pairs increased with increasing vertical displacement and time, evaluated with analysis of variance, but 19-100 per cent of the deformation was recoverable. The force systems from polyphenylene wires could vary with time and activation, but this behaviour is predictable.

  6. Radiation force imaging of viscoelastic properties with reduced artifacts.

    PubMed

    Viola, Francesco; Walker, William F

    2003-06-01

    It is well-known that changes in the mechanical properties of tissues are correlated with the presence of disease. In the eye, for example, the vitreous body undergoes dramatic changes in mechanical properties during age-related degradation. These changes may play a significant role in the formation of retinal detachment or other vitreoretinal diseases. We previously presented a noninvasive method called kinetic acoustic vitreoretial examination (KAVE), which may be used to detect these mechanical changes. KAVE uses acoustic radiation force as a means to produce small, localized displacements within the tissues. Returning echoes are processed using ultrasonic motion tracking so that the response of the tissue to the induced force can be evaluated. By repeating this process at a number of locations, images depicting viscoelastic properties of tissues can be formed. Through the combination of appropriate mechanical modeling and signal processing, we are able to generate images of parameters such as relative mass, relative elasticity, and relative viscosity. These parameters are called relative because they depend on the force applied, which is typically unknown. In this paper, we present new force-free images depicting the time constant tau, the damping ratio xi, and the natural frequency omega of the phantom material. These images are significant in that they lack the artifacts common in the relative property images. Experiments were conducted on a set of three acrylamide-based phantoms with varying gel concentrations. We present images depicting B-mode echogenicity, maximum radiation force-induced displacement, relative material parameters, and force-free characteristics of the series of phantoms. The presented force-free images depict mechanical properties without artifacts from local force variation due to acoustic reflection, refraction, and attenuation. Force-free images should prove particularly useful for in vivo imaging through inhomogeneous tissues.

  7. The Viscoelastic Properties of Passive Eye Muscle in Primates. III: Force Elicited by Natural Elongations

    PubMed Central

    Quaia, Christian; Ying, Howard S.; Optican, Lance M.

    2010-01-01

    We have recently shown that in monkey passive extraocular muscles the force induced by a stretch does not depend on the entire length history, but to a great extent is only a function of the last elongation applied. This led us to conclude that Fung's quasi-linear viscoelastic (QLV) model, and more general nonlinear models based on a single convolution integral, cannot faithfully mimic passive eye muscles. Here we present additional data about the mechanical properties of passive eye muscles in deeply anesthetized monkeys. We show that, in addition to the aforementioned failures, previous models also grossly overestimate the force exerted by passive eye muscles during smooth elongations similar to those experienced during normal eye movements. Importantly, we also show that the force exerted by a muscle following an elongation is largely independent of the elongation itself, and it is mostly determined by the final muscle length. These additional findings conclusively rule out the use of classical viscoelastic models to mimic the mechanical properties of passive eye muscles. We describe here a new model that extends previous ones using principles derived from research on thixotropic materials. This model is able to account reasonably well for our data, and could thus be incorporated into models of the eye plant. PMID:20221406

  8. The viscoelastic properties of passive eye muscle in primates. III: force elicited by natural elongations.

    PubMed

    Quaia, Christian; Ying, Howard S; Optican, Lance M

    2010-03-08

    We have recently shown that in monkey passive extraocular muscles the force induced by a stretch does not depend on the entire length history, but to a great extent is only a function of the last elongation applied. This led us to conclude that Fung's quasi-linear viscoelastic (QLV) model, and more general nonlinear models based on a single convolution integral, cannot faithfully mimic passive eye muscles. Here we present additional data about the mechanical properties of passive eye muscles in deeply anesthetized monkeys. We show that, in addition to the aforementioned failures, previous models also grossly overestimate the force exerted by passive eye muscles during smooth elongations similar to those experienced during normal eye movements. Importantly, we also show that the force exerted by a muscle following an elongation is largely independent of the elongation itself, and it is mostly determined by the final muscle length. These additional findings conclusively rule out the use of classical viscoelastic models to mimic the mechanical properties of passive eye muscles. We describe here a new model that extends previous ones using principles derived from research on thixotropic materials. This model is able to account reasonably well for our data, and could thus be incorporated into models of the eye plant.

  9. Time-resolved photoacoustic measurement for evaluation of viscoelastic properties of biological tissues

    NASA Astrophysics Data System (ADS)

    Zhao, Yue; Chen, Conggui; Liu, Hongwei; Yang, Sihua; Xing, Da

    2016-11-01

    In this letter, we proposed a method for viscoelastic characterization of biological tissues based on time-resolved photoacoustic measurement. The theoretical and experimental study was performed on the influence of viscoelasticity effects on photoacoustic generation. Taking the time delay between the photoacoustic signal and the exciting laser, the viscoelasticity distribution of biological tissues can be mapped. To validate our method, gelatin phantoms with different densities were measured. We also applied this method in discrimination between fat and liver to confirm the usefulness of the viscoelastic evaluation. Furthermore, pilot experiments were performed on atherosclerosis artery from an apolipoprotein E-knockout mouse to show the viscoelastic characterization of atherosclerotic plaque. Our results demonstrate that this technique has the potential for visualizing the biomechanical properties and lesions of biological tissues.

  10. Interrogating the viscoelastic properties of tissue using viscoelastic response (VISR) ultrasound

    NASA Astrophysics Data System (ADS)

    Selzo, Mallory Renee

    Affecting approximately 1 in 3,500 newborn males, Duchenne muscular dystrophy (DMD) is one of the most common lethal genetic disorders in humans. Boys with DMD suffer progressive loss of muscle strength and function, leading to wheelchair dependence, cardiac and respiratory compromise, and death during young adulthood. There are currently no treatments that can halt or reverse the disease progression, and translating prospective treatments into clinical trials has been delayed by inadequate outcome measures. Current outcome measures, such as functional and muscle strength assessments, lack sensitivity to individual muscles, require subjective effort of the child, and are impacted by normal childhood growth and development. The goal of this research is to develop Viscoelastic Response (VisR) ultrasound which can be used to delineate compositional changes in muscle associated with DMD. In VisR, acoustic radiation force (ARF) is used to produce small, localized displacements within the muscle. Using conventional ultrasound to track the motion, the displacement response of the tissue can be evaluated against a mechanical model. In order to develop signal processing techniques and assess mechanical models, finite element method simulations are used to model the response of a viscoelastic material to ARF excitations. Results are then presented demonstrating VisR differentiation of viscoelastic changes with progressive dystrophic degeneration in a dog model of DMD. Finally, clinical feasibility of VisR imaging is demonstrated in two boys with DMD.

  11. Viscoelastic Properties of Polymer Networks: A Study Using Optical Tweezers

    NASA Astrophysics Data System (ADS)

    Valentine, Megan T.; Dewalt, Luke E.; Ou-Yang, H. Daniel

    1996-03-01

    We report a study of the viscoelastic response of a gel-network of polystyrene latex spheres embedded in telechelic poly(ethylene oxide). We measure, using a position sensitive detector, the in-phase and out-of-phase responses of one sphere relative to the harmonic displacement of the optical tweezers. With this set-up we can study the viscoelastic responses over a broad range of frequencies and shear rates. We will be reporting the dynamics of polymer-polymer and particle-polymer interactions from the viscoelastic data.

  12. Molecular dynamics simulations of the structural, mechanical and visco-elastic properties of polymer nanocomposites filled with grafted nanoparticles.

    PubMed

    Shen, Jianxiang; Liu, Jun; Li, Haidong; Gao, Yangyang; Li, Xiaolin; Wu, Youping; Zhang, Liqun

    2015-03-21

    Through coarse-grained molecular dynamics simulations, we have studied the effects of grafting density (Σ) and grafted chain length (Lg) on the structural, mechanical and visco-elastic properties of end-grafted nanoparticles (NPs) filled polymer nanocomposites (PNCs). It is found that increasing the grafting density and grafted chain length both enhance the brush/matrix interface thickness and improve the dispersion of NPs, but there seems to exist an optimum grafting density, above which the end-grafted NPs tend to aggregate. The uniaxial stress-strain behavior of PNCs is also examined, showing that the tensile stress is more enhanced by increasing Lg compared to increasing Σ. The tensile modulus as a function of the strain is fitted following our previous work (Soft Matter, 2014, 10, 5099), exhibiting a gradually reduced non-linearity with the increase of Σ and Lg. Meanwhile, by imposing a sinusoidal external shear strain, for the first time we probe the effects of Σ and Lg on the visco-elastic properties such as the storage modulus G', loss modulus G'' and loss factor tan δ of end-grafted NPs filled PNCs. It is shown that the non-linear relation of G' and G'' as a function of shear strain amplitude decreases with the increase of Σ and Lg, which is consistent with experimental observations. We infer that the increased mechanical and reduced non-linear visco-elastic properties are correlated with the enhanced brush/matrix interface and therefore better dispersion of NPs and stronger physical cross-linking. This work may provide some rational means to tune the mechanical and visco-elastic properties of end-grafted NPs filled polymer nanocomposites.

  13. Physical aging effects on the compressive linear viscoelastic creep of IM7/K3B composite

    NASA Technical Reports Server (NTRS)

    Veazie, David R.; Gates, Thomas S.

    1995-01-01

    An experimental study was undertaken to establish the viscoelastic behavior of 1M7/K3B composite in compression at elevated temperature. Creep compliance, strain recovery and the effects of physical aging on the time dependent response was measured for uniaxial loading at several isothermal conditions below the glass transition temperature (T(g)). The IM7/K3B composite is a graphite reinforced thermoplastic polyimide with a T(g) of approximately 240 C. In a composite, the two matrix dominated compliance terms associated with time dependent behavior occur in the transverse and shear directions. Linear viscoelasticity was used to characterize the creep/recovery behavior and superposition techniques were used to establish the physical aging related material constants. Creep strain was converted to compliance and measured as a function of test time and aging time. Results included creep compliance master curves, physical aging shift factors and shift rates. The description of the unique experimental techniques required for compressive testing is also given.

  14. Comparative study of viscoelastic properties using virgin yogurt

    SciTech Connect

    Dimonte, G.; Nelson, D.; Weaver, S.; Schneider, M.; Flower-Maudlin, E.; Gore, R.; Baumgardner, J.R.; Sahota, M.S.

    1998-07-01

    We describe six different tests used to obtain a consistent set of viscoelastic properties for yogurt. Prior to yield, the shear modulus {mu} and viscosity {eta} are measured nondestructively using the speed and damping of elastic waves. Although new to foodstuffs, this technique has been applied to diverse materials from metals to the earth{close_quote}s crust. The resultant shear modulus agrees with {mu}{approximately}E/3 for incompressible materials, where the Young{close_quote}s modulus E is obtained from a stress{endash}strain curve in compression. The tensile yield stress {tau}{sub o} is measured in compression and tension, with good agreement. The conventional vane and cone/plate rheometers measured a shear stress yield {tau}{sub os}{approximately}{tau}{sub o}/{radical} (3) , as expected theoretically, but the inferred {open_quotes}apparent{close_quotes} viscosity from the cone/plate rheometer is much larger than the wave measurement due to the finite yield ({tau}{sub os}{ne}0). Finally, we inverted an open container of yogurt for 10{sup 6} s{gt}{eta}/{mu} and observed no motion. This demonstrates unequivocally that yogurt possesses a finite yield stress rather than a large viscosity. We present a constitutive model with a pre-yield viscosity to describe the damping of the elastic waves and use a simulation code to describe yielding in complex geometry. {copyright} {ital 1998 Society of Rheology.}

  15. Viscoelastic Properties and Dynamics of Porcine Gastric Mucin

    SciTech Connect

    Celli,J.; Gregor, B.; Turner, B.; Afdhal, N.; Bansil, R.; Erramilli, S.

    2005-01-01

    Gastric mucin is a glycoprotein known to undergo a pH-dependent sol-gel transition that is crucial to the protective function of the gastric mucus layer in mammalian stomachs. We present microscope-based dynamic light scattering data on porcine gastric mucin at pH 6 (solution) and pH 2 (gel) with and without the presence of tracer particles. The data provide a measurement of the microscale viscosity and the shear elastic modulus as well as an estimate of the mesh size of the gel formed at pH 2. We observe that the microscale viscosity in the gel is about 100-fold lower than its macroscopic viscosity, suggesting that large pores open up in the gel reducing frictional effects. The data presented here help to characterize physiologically relevant viscoelastic properties of an important biological macromolecule and may also serve to shed light on diffusive motion of small particles in the complex heterogeneous environment of a polymer gel network.

  16. The influence of physiological aging and atrophy on brain viscoelastic properties in humans.

    PubMed

    Sack, Ingolf; Streitberger, Kaspar-Josche; Krefting, Dagmar; Paul, Friedemann; Braun, Jürgen

    2011-01-01

    Physiological aging of the brain is accompanied by ubiquitous degeneration of neurons and oligodendrocytes. An alteration of the cellular matrix of an organ impacts its macroscopic viscoelastic properties which can be detected by magnetic resonance elastography (MRE)--to date the only method for measuring brain mechanical parameters without intervention. However, the wave patterns detected by MRE are affected by atrophic changes in brain geometry occurring in an individual's life span. Moreover, regional variability in MRE-detected age effects is expected corresponding to the regional variation in atrophy. Therefore, the sensitivity of brain MRE to brain volume and aging was investigated in 66 healthy volunteers aged 18-72. A linear decline in whole-brain elasticity was observed (-0.75%/year, R-square = 0.59, p<0.001); the rate is three times that determined by volume measurements (-0.23%/year, R-square = 0.4, p<0.001). The highest decline in elasticity (-0.92%/year, R-square = 0.43, p<0.001) was observed in a region of interest placed in the frontal lobe with minimal age-related shrinkage (-0.1%, R-square = 0.06, p = 0.043). Our results suggest that cerebral MRE can measure geometry-independent viscoelastic parameters related to intrinsic tissue structure and altered by age.

  17. Measurement of nonlinear viscoelastic properties of fluids using Dynamic Acoustoelastic Testing

    NASA Astrophysics Data System (ADS)

    Trarieux, C.; Callé, S.; Poulin, A.; Tranchant, J.-F.; Moreschi, H.; Defontaine, M.

    2012-12-01

    A nonlinear ultrasound-based method called Dynamic Acoustoelastic Testing (DAET) is used to assess nonlinear viscoelastic properties of fluids. This method is based on the interaction between two elastic waves: a low-frequency (LF) sinusoidal wave (4 kHz) to successively compress and expand the liquid as a bulk stress, and ultrasound (US) pulses (1 MHz) to simultaneously probe the sample at different states of the quasi-hydrostatic pressure. The DAET method provides estimations of the elastic nonlinearities issued from the Time Of Flight Modulations (TOFM) of the US pulses. The TOFM is plotted as a function of the LF acoustic pressure, allowing an estimation of the nonlinear elastic parameter B/A. In this study, we first present the results obtained in Newtonian fluids such as water and silicone oils. Simple viscoelastic gels (Carbomers and Xanthan gums) have also been tested exhibiting the same behavior: TOFM linearly related to LF pressure amplitude corresponding to classical quadratic nonlinearity. Finally, preliminary DAET measurements have been performed in biphasic systems composed of hard glass beads in a gel-based matrix and in gelatin during a gelation process.

  18. Viscoelastic and fatigue properties of model methacrylate-based dentin adhesives

    PubMed Central

    Singh, Viraj; Misra, Anil; Marangos, Orestes; Park, Jonggu; Ye, Qiang; Kieweg, Sarah L.; Spencer, Paulette

    2013-01-01

    The objective of the current study is to characterize the viscoelastic and fatigue properties of model methacrylate-based dentin adhesives under dry and wet conditions. Static, creep, and fatigue tests were performed on cylindrical samples in a 3-point bending clamp. Static results showed that the apparent elastic modulus of the model adhesive varied from 2.56 to 3.53 GPa in the dry condition, and from 1.04 to 1.62 GPa in the wet condition, depending upon the rate of loading. Significant differences were also found for the creep behavior of the model adhesive under dry and wet conditions. A linear viscoelastic model was developed by fitting the adhesive creep behavior. The developed model with 5 Kelvin Voigt elements predicted the apparent elastic moduli measured in the static tests. The model was then utilized to interpret the fatigue test results. It was found that the failure under cyclic loading can be due to creep or fatigue, which has implications for the failure criterion that are applied for these types of tests. Finally, it was found that the adhesive samples tested under dry conditions were more durable than those tested under wet conditions. PMID:20848661

  19. Viscoelastic properties of graphene-based epoxy resins

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Fierro, Annalisa; Rosolia, Salvatore; Raimondo, Marialuigia; Lafdi, Khalid; Guadagno, Liberata

    2015-12-01

    In this paper the viscoelastic properties of an epoxy resin filled with graphene-based nanoparticles have been investigated in the liquid state, before curing, by means of a rotational rheometer equipped with a parallel plate geometry. Exfoliated graphite was prepared using traditional acid intercalation followed by a sudden treatment at high temperature (900°C). The percentage of exfoliated graphite was found to be 56%. The epoxy matrix was prepared by mixing a tetrafunctional precursor with a reactive diluent which produces a significant decrease in the viscosity of the epoxy precursor so that the dispersion step of nanofillers in the matrix can easily occur. The hardener agent, the 4,4-diaminodiphenyl sulfone (DDS), was added at a stoichiometric concentration with respect to all the epoxy rings. The inclusion of the partially exfoliated graphite (pEG) in the formulated epoxy mixture significantly modifies the rheological behaviour of the mixture itself. The epoxy mixture, indeed, shows a Newtonian behaviour while, at 3 wt % pEG content, the complex viscosity of the nanocomposite clearly shows a shear thinning behaviour with η* values much higher at the lower frequencies. The increase in complex viscosity with the increasing of the partially exfoliated graphite content was mostly caused by a dramatic increase in the storage modulus. All the graphene-based epoxy mixtures were cured by a two-stage curing cycles: a first isothermal stage was carried out at the lower temperature of 125°C for 1 hour while the second isothermal stage was performed at the higher temperature of 200°C for 3 hours. The mechanical properties of the cured nanocomposites show high values in the storage modulus and glass transition temperature.

  20. An approach to determine pressure profile generated by compression bandage using quasi-linear viscoelastic model.

    PubMed

    Kumar, Bipin; Das, Apurba; Alagirusamy, R

    2012-09-01

    Understanding the stress relaxation behavior of the compression bandage could be very useful in determining the behavior of the interface pressure exerted by the bandage on a limb during the course of the compression treatment. There has been no comprehensive study in the literature to investigate the pressure profile (interface pressure with time) generated by a compression bandage when applied at different levels of strain. The present study attempts to describe the pressure profile, with the use of a quasi-linear viscoelastic model, generated by a compression bandage during compression therapy. The quasi-linear viscoelastic (QLV) theory proposed by Fung (Fung, 1972, "Stress Strain History Relations of Soft Tissues in Simple Elongation," Biomechanics: Its Foundations and Objectives, Y. C. Fung, N. Perrone, and M. Anliker, eds., Prentice-Hall, Englewood Cliffs, NJ, pp. 181-207). was used to model the nonlinear time- and history-dependent relaxation behavior of the bandage using the ramp strain approach. The regression analysis was done to find the correlation between the pressure profile and the relaxation behavior of the bandage. The parameters of the QLV model, describing the relaxation behavior of the bandage, were used to determine the pressure profile generated by the bandage at different levels of strain. The relaxation behaviors of the bandage at different levels of strain were well described by the QLV model parameters. A high correlation coefficient (nearly 0.98) shows a good correlation of the pressure profile with the stress relaxation behavior of the bandage.The prediction of the pressure profile using the QLV model parameters were in agreement with the experimental data. The pressure profile generated by a compression bandage could be predicted using the QLV model describing the nonlinear relaxation behavior of the bandage. This new application of the QLV theory helps in evaluating the bandage performance during compression therapy as scientific wound

  1. A multiscale model for predicting the viscoelastic properties of asphalt concrete

    NASA Astrophysics Data System (ADS)

    Garcia Cucalon, Lorena; Rahmani, Eisa; Little, Dallas N.; Allen, David H.

    2016-08-01

    It is well known that the accurate prediction of long term performance of asphalt concrete pavement requires modeling to account for viscoelasticity within the mastic. However, accounting for viscoelasticity can be costly when the material properties are measured at the scale of asphalt concrete. This is due to the fact that the material testing protocols must be performed recursively for each mixture considered for use in the final design.

  2. Vitreous cryopreservation maintains the viscoelastic property of human vascular grafts.

    PubMed

    Thakrar, Raj R; Patel, Vishal P; Hamilton, George; Fuller, Barry J; Seifalian, Alexander M

    2006-05-01

    Assess the effects of cryopreservation (cryo) and vitrification (vitro) on the viscoelastic properties of blood vessels. Human external Iliac artery vessels were harvested from liver organ donors (n=8). In each case the vessel was segmented into 3 equal parts, which were randomly placed in one of 3 categories: Fresh (stored in 4 degrees C UW for 6 h), Cryo (Placed in 10% Dulbecco's modified Eagle medium (DMEM) and slowly frozen to -196 degrees C), or Vitro (Placed in 40% DMEM and rapidly cooled to -196 degrees C). A pulsatile flow circuit was used to perfuse arterial segments at physiological pulse pressure and flow. Intraluminal pressure was measured using a Millar Mikro-tip catheter transducer, and vessel wall motion was determined with duplex ultrasonography coupled with a novel echo-locked vessel wall tracking system. Diametrical compliance (DC), Petersons elastic modulus (Ep), and stiffness index (beta) were then calculated for each of the three groups over 3 mean pressure ranging from 40 to 80 mmHg. The change in the viscous component of arterial wall (lag phase angle, theta) was calculated from hysteresis plots. No significant changes were observed in the elastic properties of fresh and vitrified vessels (P>0.05 for each of DC, Ep, and beta). Similarly, variation in the wall viscosity between fresh and vitrified vessels appeared to be nonsignificant (theta=12.60+/-4.04 vs. 17.60+/-1.14, respectively). In contrast, statistical analysis of results obtained for cryopreserved vessels to the fresh vessels showed significant reduction in elastic parameter values. There was also a significant increase in the phase angle theta of the cryopreserved vessels (theta=24.30+/-6.32; P<0.001) compared with fresh vessel. Results suggest that vitrification maintains both elastic and viscous components of the mechanical properties of vascular grafts, which is positively correlated with their functional patency. In contrast, damage caused during cryopreservation significantly

  3. Intraluminal mapping of tissue viscoelastic properties using laser speckle rheology catheter (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Hosoda, Masaki; Tshikudi, Diane M.; Nadkarni, Seemantini K.

    2016-03-01

    A number of disease conditions including coronary atherosclerosis, peripheral artery disease and gastro-intestinal malignancies are associated with alterations in tissue mechanical properties. Laser speckle rheology (LSR) has been demonstrated to provide important information on tissue mechanical properties by analyzing the time scale of temporal speckle intensity fluctuations, which serves as an index of tissue viscoelasticity. In order to measure the mechanical properties of luminal organs in vivo, LSR must be conducted via a miniature endoscope or catheter. Here we demonstrate the capability of an omni-directional LSR catheter to quantify tissue mechanical properties over the entire luminal circumference without the need for rotational motion. Retracting the catheter using a motor-drive assembly enables the reconstruction of cylindrical maps of tissue mechanical properties. The performance of the LSR catheter is tested using a luminal phantom with mechanical moduli that vary in both circumferential and longitudinal directions. 2D cylindrical maps of phantom viscoelastic properties are reconstructed over four quadrants of the coronary circumference simultaneously during catheter pullback. The reconstructed cylindrical maps of the decorrelation time constants easily distinguish the different gel components of the phantom with different viscoelastic moduli. The average values of decorrelation times calculated for each gel component of the phantom show a strong correspondence with the viscoelastic moduli measured via standard mechanical rheometry. These results highlight the capability for cylindrical mapping of tissue viscoelastic properties using LSR in luminal organs using a miniature catheter, thus opening the opportunity for improved diagnosis of several disease conditions.

  4. Interface transferring mechanism and error modification of FRP-OFBG strain sensor based on standard linear viscoelastic model

    NASA Astrophysics Data System (ADS)

    Li, Jilong; Zhou, Zhi; Ou, Jinping

    2006-03-01

    This paper presents the interface transferring mechanism and error modification of the Fiber Reinforced Polymer-Optical Fiber Bragg Grating (FRP-OFBG) sensing tendons, which including GFRP (Glass Fiber Reinforced Polymer) and CFRP (Carbon Fiber Reinforced Polymer), using standard linear viscoelastic model. The optical fiber is made up of glass, quartz or plastic, et al, which creep strain is very small at room temperature. So the tensile creep compliance of optical fiber is independent of time at room temperature. On the other hand, the FRP (GFRP or CFRP) is composed of a kind of polymeric matrix (epoxy resins or the others) with glass, carbon or aramid fibers, which shear creep strain is dependent of time at room temperature. Hence, the standard linear viscoelastic model is employed to describe the shear creep compliance of FRP along the fiber direction. The expression of interface strain transferring mechanism of FRP-OFBG sensors is derived based on the linear viscoelastic theory and the analytic solution of the error rate is given by the inverse Laplace transform. The effects of FRP viscoelasticity on the error rate of FRP-OFBG sensing tendons are included in the above expression. And the transient and steady-state error modified coefficient of FRP-OFBG sensors are obtained using initial value and final value theorems. Finally, a calculated example is given to explain the correct of theoretical prediction.

  5. Modeling of Viscoelastic Properties of Porous Rocks Saturated with Viscous Fluid at Seismic Frequencies at the Core Scale

    NASA Astrophysics Data System (ADS)

    Schmitt, D. R.; Wang, Z.; Wang, F.; Wang, R.

    2015-12-01

    Currently the moduli and velocities of rocks at seismic frequencies are usually measured by the strain-stress method in lab. However, such measurements require well-designed equipment and skilled technicians, which greatly hinders the experimental investigation on the elastic and visco-elastic properties of rocks at seismic frequencies. We attempt to model the dynamic moduli of porous rocks saturated with viscous fluid at seismic frequencies on core scale using the strain-stress method, aiming to provide a complement to real core measurements in lab. First, we build 2D geometrical models containing the pore structure information of porous rocks based on the digital images (such as thin section, SEM, CT, etc.) of real rocks. Then we assume the rock frames are linearly elastic, and use the standard Maxwell spring-dash pot model to describe the visco-elastic properties of pore fluids. Boundary conditions are set according to the strain-stress method; and the displacement field is calculated using the finite element method (FEM). We numerically test the effects of fluid viscosity, frequency, and pore structure on the visco-elastic properties based on the calculation results. In our modeling, the viscosity of the pore fluid ranges from 103mPas to 109mPas; and the frequency varies from 5Hz to 500Hz. The preliminary results indicate that the saturated rock behaves stiffer and shows larger phase lag between stress and strain when the viscosity of the pore fluid and (or) the frequency increase.

  6. Assessing the viscoelastic properties of thrombus using a solid-sphere-based instantaneous force approach.

    PubMed

    Huang, Chih-Chung; Shih, Cho-Chiang; Liu, Ting-Yu; Lee, Po-Yang

    2011-10-01

    The viscoelastic properties of thrombus play a significant role when the clot closes a leak in a vessel of the blood circulation. The common method used to measure the viscoelastic properties of a clot employs a rheometer but this might be unsuitable due to the clot fiber network being broken up by excessive deformation. This study assessed the feasibility of using a novel acoustic method to assess the viscoelastic properties of blood clots. This method is based on monitoring the motion of a solid sphere in a blood clot induced by an applied instantaneous force. Experiments were performed in which a solid sphere was displaced by a 1 MHz single-element focused transducer, with a 20 MHz single-element focused transducer used to track this displacement. The spatiotemporal behavior of the sphere displacement was used to determine the viscoelastic properties of the clot. The experimental system was calibrated by measuring the viscoelastic modulus of gelatin using different types of solid spheres embedded in the phantoms and, then, the shear modulus and viscosity of porcine blood clots with hematocrits of 0% (plasma), 20% and 40% were assessed. The viscoelastic modulus of each clot sample was also measured directly by a rheometer for comparison. The results showed that the shear modulus increased from 173 ± 52 (mean ± SD) Pa for 40%-hematocrit blood clots to 619.5 ± 80.5 Pa for plasma blood clots, while the viscosity decreased from 0.32 ± 0.07 Pa∙s to 0.16 ± 0.06 Pa∙s, respectively, which indicated that the concentration of red blood cells and the amount of fibrinogen are the main determinants of the clot viscoelastic properties.

  7. VISCEL: A general-purpose computer program for analysis of linear viscoelastic structures (user's manual), volume 1

    NASA Technical Reports Server (NTRS)

    Gupta, K. K.; Akyuz, F. A.; Heer, E.

    1972-01-01

    This program, an extension of the linear equilibrium problem solver ELAS, is an updated and extended version of its earlier form (written in FORTRAN 2 for the IBM 7094 computer). A synchronized material property concept utilizing incremental time steps and the finite element matrix displacement approach has been adopted for the current analysis. A special option enables employment of constant time steps in the logarithmic scale, thereby reducing computational efforts resulting from accumulative material memory effects. A wide variety of structures with elastic or viscoelastic material properties can be analyzed by VISCEL. The program is written in FORTRAN 5 language for the Univac 1108 computer operating under the EXEC 8 system. Dynamic storage allocation is automatically effected by the program, and the user may request up to 195K core memory in a 260K Univac 1108/EXEC 8 machine. The physical program VISCEL, consisting of about 7200 instructions, has four distinct links (segments), and the compiled program occupies a maximum of about 11700 words decimal of core storage.

  8. A self-consistent estimate for linear viscoelastic polycrystals with internal variables inferred from the collocation method

    NASA Astrophysics Data System (ADS)

    Vu, Q. H.; Brenner, R.; Castelnau, O.; Moulinec, H.; Suquet, P.

    2012-03-01

    The correspondence principle is customarily used with the Laplace-Carson transform technique to tackle the homogenization of linear viscoelastic heterogeneous media. The main drawback of this method lies in the fact that the whole stress and strain histories have to be considered to compute the mechanical response of the material during a given macroscopic loading. Following a remark of Mandel (1966 Mécanique des Milieux Continus(Paris, France: Gauthier-Villars)), Ricaud and Masson (2009 Int. J. Solids Struct. 46 1599-1606) have shown the equivalence between the collocation method used to invert Laplace-Carson transforms and an internal variables formulation. In this paper, this new method is developed for the case of polycrystalline materials with general anisotropic properties for local and macroscopic behavior. Applications are provided for the case of constitutive relations accounting for glide of dislocations on particular slip systems. It is shown that the method yields accurate results that perfectly match the standard collocation method and reference full-field results obtained with a FFT numerical scheme. The formulation is then extended to the case of time- and strain-dependent viscous properties, leading to the incremental collocation method (ICM) that can be solved efficiently by a step-by-step procedure. Specifically, the introduction of isotropic and kinematic hardening at the slip system scale is considered.

  9. Atomic force microscopy indentation and inverse analysis for non-linear viscoelastic identification of breast cancer cells.

    PubMed

    Nguyen, Nhung; Shao, Yue; Wineman, Alan; Fu, Jianping; Waas, Anthony

    2016-07-01

    Breast cancer cells (MCF-7 and MCF-10A) are studied through indentation with spherical borosilicate glass particles in atomic force microscopy (AFM) contact mode in fluid. Their mechanical properties are obtained by analyzing the recorded reaction force-time response. The analysis is based on comparing experimental data with predictions from finite element (FE) simulation. Here, FE modeling is employed to simulate the AFM indentation experiment which is neither a displacement nor a force controlled test. This approach is expected to overcome many underlying problems of the widely used models such as Hertz contact model due to its capability to capture the contact behaviors between the spherical indentor and the cell, account for cell geometry, and incorporate with large strain theory. In this work, a non-linear viscoelastic (NLV) model in which the viscoelastic part is described by Prony series terms is used for the constitutive model of the cells. The time-dependent material parameters are extracted through an inverse analysis with the use of a surrogate model based on a Kriging estimator. The purpose is to automatically extract the NLV properties of the cells with a more efficient process compared to the iterative inverse technique that has been mostly applied in the literature. The method also allows the use of FE modeling in the analysis of a large amount of experimental data. The NLV parameters are compared between MCF-7 and MCF-10A and MCF-10A treated and untreated with the drug Cytochalasin D to examine the possibility of using relaxation properties as biomarkers for distinguishing these types of breast cancer cells. The comparisons indicate that malignant cells (MCF-7) are softer and exhibit more relaxation than benign cells (MCF-10A). Disrupting the cytoskeleton using the drug Cytochalasin D also results in a larger amount of relaxation in the cell's response. In addition, relaxation properties indicate larger differences as compared to the elastic moduli

  10. The Viscoelastic Properties of Nematic Monodomains Containing Liquid Crystal Polymers.

    NASA Astrophysics Data System (ADS)

    Gu, Dongfeng

    The work presented here investigates the viscoelastic properties of nematic materials containing liquid crystal polymers (LCP). We focus on how the elastic constants and the viscosity coefficients of the mixture systems are influenced by polymer architectures. In dynamic light scattering studies of the relaxation of the director orientation fluctuations for the splay, twist, and bend deformation modes, decrease of the relaxation rates was observed when LCPs were dissolved into low molar mass nematics (LMMN). For the side-chain LCPs, the slowing down in the bend mode is comparable to or larger than those of the splay and twist modes. For main-chain LCPs, the relative changes in the relaxation rates for the twist and splay modes are about one order of magnitude larger than that for the bend mode. The results of light scattering under an electric field show that the decrease in the twist relaxation rate is due to a large increase in the twist viscosity and a minor decrease in the twist elastic constant. These changes were found to increase with decrease of the spacer length, with increase of molecular weight, and with decrease of the backbone flexibility. In Freedericksz transition measurements, the splay and bend elastic constants and the dielectric anisotropies of the nematic mixtures were determined and the values are 5~15% lower than those of the pure solvent. From the analysis of the results of Freedericksz transition and light scattering experiments, a complete set of the elastic constants and viscosity coefficients corresponding to the three director deformation modes were obtained for the LCP mixtures. The changes in the viscosity coefficients due to addition of LCPs were analysed to estimate the anisotropic shapes of the polymer backbone via a hydrodynamic model. The results suggest that an oblate backbone configuration is maintained by the side-chain LCPs and a prolate chain configuration appears for the main-chain LCPs. The rheological behavior of a side

  11. Determinants of ovine compact bone viscoelastic properties: effects of architecture, mineralization, and remodeling.

    PubMed

    Les, C M; Spence, C A; Vance, J L; Christopherson, G T; Patel, B; Turner, A S; Divine, G W; Fyhrie, D P

    2004-09-01

    Significant decreases in ovine compact bone viscoelastic properties (specifically, stress-rate sensitivity, and damping efficiency) are associated with three years of ovariectomy and are particularly evident at higher frequencies [Proc. Orthop. Res. Soc. 27 (2002) 89]. It is unclear what materials or architectural features of bone are responsible for either the viscoelastic properties themselves, or for the changes in those properties that were observed with estrogen depletion. In this study, we examined the relationship between these viscoelastic mechanical properties and features involving bone architecture (BV/TV), materials parameters (ash density, %mineralization), and histologic evidence of remodeling (%remodeled, cement line interface). The extent of mineralization was inversely proportional to the material's efficiency in damping stress oscillations. The damping characteristics of bone material from ovariectomized animals were significantly more sensitive to variation in mineralization than was bone from control animals. At low frequencies (6 Hz or less), increased histologic evidence of remodeling was positively correlated with increased damping efficiency. However, the dramatic decreases in stress-rate sensitivity that accompanied 3-year ovariectomy were seen throughout the bone structure and occurred even in areas with little or no secondary Haversian remodeling as well as in areas of complete remodeling. Taken together, these data suggest that, while the mineral component may modify the viscoelastic behavior of bone, the basic mechanism underlying bone viscoelastic behavior, and of the changes in that behavior with estrogen depletion, reside in a non-mineral component of the bone that can be significantly altered in the absence of secondary remodeling.

  12. Laser Speckle Rheology for evaluating the viscoelastic properties of hydrogel scaffolds

    NASA Astrophysics Data System (ADS)

    Hajjarian, Zeinab; Nia, Hadi Tavakoli; Ahn, Shawn; Grodzinsky, Alan J.; Jain, Rakesh K.; Nadkarni, Seemantini K.

    2016-12-01

    Natural and synthetic hydrogel scaffolds exhibit distinct viscoelastic properties at various length scales and deformation rates. Laser Speckle Rheology (LSR) offers a novel, non-contact optical approach for evaluating the frequency-dependent viscoelastic properties of hydrogels. In LSR, a coherent laser beam illuminates the specimen and a high-speed camera acquires the time-varying speckle images. Cross-correlation analysis of frames returns the speckle intensity autocorrelation function, g2(t), from which the frequency-dependent viscoelastic modulus, G*(ω), is deduced. Here, we establish the capability of LSR for evaluating the viscoelastic properties of hydrogels over a large range of moduli, using conventional mechanical rheometry and atomic force microscopy (AFM)-based indentation as reference-standards. Results demonstrate a strong correlation between |G*(ω)| values measured by LSR and mechanical rheometry (r = 0.95, p < 10‑9), and z-test analysis reports that moduli values measured by the two methods are identical (p > 0.08) over a large range (47 Pa – 36 kPa). In addition, |G*(ω)| values measured by LSR correlate well with indentation moduli, E, reported by AFM (r = 0.92, p < 10‑7). Further, spatially-resolved moduli measurements in micro-patterned substrates demonstrate that LSR combines the strengths of conventional rheology and micro-indentation in assessing hydrogel viscoelastic properties at multiple frequencies and small length-scales.

  13. Estimating material viscoelastic properties based on surface wave measurements: a comparison of techniques and modeling assumptions.

    PubMed

    Royston, Thomas J; Dai, Zoujun; Chaunsali, Rajesh; Liu, Yifei; Peng, Ying; Magin, Richard L

    2011-12-01

    Previous studies of the first author and others have focused on low audible frequency (<1 kHz) shear and surface wave motion in and on a viscoelastic material comprised of or representative of soft biological tissue. A specific case considered has been surface (Rayleigh) wave motion caused by a circular disk located on the surface and oscillating normal to it. Different approaches to identifying the type and coefficients of a viscoelastic model of the material based on these measurements have been proposed. One approach has been to optimize coefficients in an assumed viscoelastic model type to match measurements of the frequency-dependent Rayleigh wave speed. Another approach has been to optimize coefficients in an assumed viscoelastic model type to match the complex-valued frequency response function (FRF) between the excitation location and points at known radial distances from it. In the present article, the relative merits of these approaches are explored theoretically, computationally, and experimentally. It is concluded that matching the complex-valued FRF may provide a better estimate of the viscoelastic model type and parameter values; though, as the studies herein show, there are inherent limitations to identifying viscoelastic properties based on surface wave measurements. © 2011 Acoustical Society of America

  14. Lamb Wave Dispersion Ultrasound Vibrometry (LDUV) Method for Quantifying Mechanical Properties of Viscoelastic Solids

    PubMed Central

    Nenadic, Ivan Z.; Urban, Matthew W.; Mitchell, Scott A.; Greenleaf, James F.

    2011-01-01

    Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of Shearwave Dispersion Ultrasound Vibrometry (SDUV), a noninvasive ultrasound based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb wave Dispersion Ultrasound Vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb waves and measure the dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb wave model was fitted to the wave speed dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb wave dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify mechanical properties of soft tissues with a plate-like geometry. PMID:21403186

  15. Viscoelastic and dynamic nonlinear properties of airway smooth muscle tissue: roles of mechanical force and the cytoskeleton.

    PubMed

    Ito, Satoru; Majumdar, Arnab; Kume, Hiroaki; Shimokata, Kaoru; Naruse, Keiji; Lutchen, Kenneth R; Stamenovic, Dimitrije; Suki, Béla

    2006-06-01

    The viscoelastic and dynamic nonlinear properties of guinea pig tracheal smooth muscle tissues were investigated by measuring the storage (G') and loss (G") moduli using pseudorandom small-amplitude length oscillations between 0.12 and 3.5 Hz superimposed on static strains of either 10 or 20% of initial length. The G" and G' spectra were interpreted using a linear viscoelastic model incorporating damping (G) and stiffness (H), respectively. Both G and H were elevated following an increase in strain from 10 to 20%. There was no change in harmonic distortion (K(d)), an index of dynamic nonlinearity, between 10 and 20% strains. Application of methacholine at 10% strain significantly increased G and H while it decreased K(d). Cytochalasin D, isoproterenol, and HA-1077, a Rho-kinase inhibitor, significantly decreased both G and H but increased K(d). Following cytochalasin D, G, H, and K(d) were all elevated when mean strain increased from 10 to 20%. There were no changes in hysteresivity, G/H, under any condition. We conclude that not all aspects of the viscoelastic properties of tracheal smooth muscle strips are similar to those previously observed in cultured cells. We attribute these differences to the contribution of the extracellular matrix. Additionally, using a network model, we show that the dynamic nonlinear behavior, which has not been observed in cell culture, is associated with the state of the contractile stress and may derive from active polymerization within the cytoskeleton.

  16. Structural and viscoelastic properties of actin networks formed by espin or pathologically relevant espin mutants.

    PubMed

    Lieleg, Oliver; Schmoller, Kurt M; Purdy Drew, Kirstin R; Claessens, Mireille M A E; Semmrich, Christine; Zheng, Lili; Bartles, James R; Bausch, Andreas R

    2009-11-09

    The structural organization of the cytoskeleton determines its viscoelastic response which is crucial for the correct functionality of living cells. Both the mechanical response and microstructure of the cytoskeleton are regulated on a microscopic level by the local activation of different actin binding and/or bundling proteins (ABPs). Misregulations in the expression of these ABPs or mutations in their sequence can entail severe cellular dysfunctions and diseases. Here, we study the structural and viscoelastic properties of reconstituted actin networks cross-linked by the ABP espin and compare the obtained network properties to those of other bundled actin networks. Moreover, we quantify the impact of pathologically relevant espin mutations on the viscoelastic properties of these cytoskeletal networks.

  17. Time-Dependent Morphologies and Viscoelastic Properties of Block Copolymers.

    DTIC Science & Technology

    1982-03-15

    been shown proportional to the relative amounts of those phases (17). Diamant and coworkers (14-16) showed that the viscoelastic behavior between the...traditionally been associated with the re- lative amounts of styrene and butadiene in their respective domains (35). Recently, Diamant and coworkers (14-i6...understood at present. However, Diamant and coworkers (14-16) showed that a maximum in G"(T) between the two main transitions could be attributed to a "bulge

  18. Effect of Solar Radiation on Viscoelastic Properties of Bovine Leather: Temperature and Frequency Scans

    NASA Astrophysics Data System (ADS)

    Nalyanya, Kallen Mulilo; Rop, Ronald K.; Onyuka, Arthur S.

    2017-04-01

    This work presents both analytical and experimental results of the effect of unfiltered natural solar radiation on the thermal and dynamic mechanical properties of Boran bovine leather at both pickling and tanning stages of preparation. Samples cut from both pickled and tanned pieces of leather of appropriate dimensions were exposed to unfiltered natural solar radiation for time intervals ranging from 0 h (non-irradiated) to 24 h. The temperature of the dynamic mechanical analyzer was equilibrated at 30°C and increased to 240°C at a heating rate of 5°C \\cdot Min^{-1}, while its oscillation frequency varied from 0.1 Hz to 100 Hz. With the help of thermal analysis (TA) control software which analyzes and generates parameter means/averages at temperature/frequency range, the graphs were created by Microsoft Excel 2013 from the means. The viscoelastic properties showed linear frequency dependence within 0.1 Hz to 30 Hz followed by negligible frequency dependence above 30 Hz. Storage modulus (E') and shear stress (σ ) increased with frequency, while loss modulus (E''), complex viscosity (η ^{*}) and dynamic shear viscosity (η) decreased linearly with frequency. The effect of solar radiation was evident as the properties increased initially from 0 h to 6 h of irradiation followed by a steady decline to a minimum at 18 h before a drastic increase to a maximum at 24 h. Hence, tanning industry can consider the time duration of 24 h for sun-drying of leather to enhance the mechanical properties and hence the quality of the leather. At frequencies higher than 30 Hz, the dynamic mechanical properties are independent of the frequency. The frequency of 30 Hz was observed to be a critical value in the behavior in the mechanical properties of bovine hide.

  19. Impact of leg lengthening on viscoelastic properties of the deep fascia

    PubMed Central

    Wang, Hai-Qiang; Wei, Yi-Yong; Wu, Zi-Xiang; Luo, Zhuo-Jing

    2009-01-01

    Background Despite the morphological alterations of the deep fascia subjected to leg lengthening have been investigated in cellular and extracellular aspects, the impact of leg lengthening on viscoelastic properties of the deep fascia remains largely unknown. This study aimed to address the changes of viscoelastic properties of the deep fascia during leg lengthening using uniaxial tensile test. Methods Animal model of leg lengthening was established in New Zealand white rabbits. Distraction was initiated at a rate of 1 mm/day and 2 mm/day in two steps, and preceded until increases of 10% and 20% in the initial length of tibia had been achieved. The deep fascia specimens of 30 mm × 10 mm were clamped with the Instron 1122 tensile tester at room temperature with a constant tensile rate of 5 mm/min. After 5 load-download tensile tests had been performed, the specimens were elongated until rupture. The load-displacement curves were automatically generated. Results The normal deep fascia showed typical viscoelastic rule of collagenous tissues. Each experimental group of the deep fascia after leg lengthening kept the properties. The curves of the deep fascia at a rate of 1 mm/day with 20% increase in tibia length were the closest to those of normal deep fascia. The ultimate tension strength and the strain at rupture on average of normal deep fascia were 2.69 N (8.97 mN/mm2) and 14.11%, respectively. The increases in ultimate tension strength and strain at rupture of the deep fascia after leg lengthening were statistically significant. Conclusion The deep fascia subjected to leg lengthening exhibits viscoelastic properties as collagenous tissues without lengthening other than increased strain and strength. Notwithstanding different lengthening schemes result in varied viscoelastic properties changes, the most comparable viscoelastic properties to be demonstrated are under the scheme of a distraction rate of 1 mm/day and 20% increase in tibia length. PMID:19698092

  20. Quasi-Linear Viscoelastic theory applied to internal shearing of porcine aortic valve leaflets.

    PubMed

    Carew, E O; Talman, E A; Boughner, D R; Vesely, I

    1999-08-01

    The elements of Quasi-Linear Viscoelastic (QLV) theory have been applied to model the internal shear mechanics of fresh and glutaraldehyde-fixed porcine aortic valve leaflets. A novel function estimation method was used to extract the material functions from experimental shear data obtained at one strain rate, and the model was used to predict the material response at different strain rates. In general, experiments and predictions were in good agreement, the larger discrepancies being in the prediction of peak stresses and hysteresis in cyclic shear. In shear, fixed tissues are stiffer (mean initial shear modulus, 13 kPa versus 427 Pa), take longer to relax to steady state (mean tau 2 4,736 s versus 1,764 s) with a slower initial relaxation rate (mean magnitude of G(0), 1 s-1 versus 5 s-1), and relax to a lesser extent than fresh tissues (mean percentage stress remaining after relaxation, 60 versus 45 percent). All differences were significant at p = 0.04 or less, except for the initial relaxation slope. We conclude that shear experiments can complement traditional tensile and biaxial experiments toward providing a complete mechanical description of soft biomaterials, particularly when evaluating alternative chemical fixation techniques.

  1. On the use of a loudspeaker for measuring the viscoelastic properties of sound absorbing materials.

    PubMed

    Doutres, Olivier; Dauchez, Nicolas; Génevaux, Jean-Michel; Lemarquand, Guy

    2008-12-01

    This paper investigates the feasibility to use an electrodynamic loudspeaker to determine viscoelastic properties of sound-absorbing materials in the audible frequency range. The loudspeaker compresses the porous sample in a cavity, and a measurement of its electrical impedance allows one to determine the mechanical impedance of the sample: no additional sensors are required. Viscoelastic properties of the material are then estimated by inverting a 1D Biot model. The method is applied to two sound-absorbing materials (glass wool and polymer foam). Results are in good agreement with the classical compression quasistatic method.

  2. The prediction of long term viscoelastic properties of fiber reinforced plastics

    NASA Technical Reports Server (NTRS)

    Brinson, H. F.; Dillard, D. A.

    1982-01-01

    A method for the experimental and analytical accelerated characterization of long term viscoelastic properties is presented. The time-temperature-stress superposition principle (TTSSP) is shown to serve as the basis for determining long term compliance data from short term creep test results. Nonlinear viscoelastic theories are discussed to provide the framework for the mathematically modeling of such a process. A time dependent Tsai-Hill-Zhurkov failure theory is used to determine long term failure properties from short term data. Compliance and failure data are incorporated in an incremental lamination theory to make long term laminate predictions. Comparisons are made between theory and experiment.

  3. The prediction of long term viscoelastic properties of fiber reinforced plastics

    NASA Technical Reports Server (NTRS)

    Brinson, H. F.; Dillard, D. A.

    1982-01-01

    A method for the experimental and analytical accelerated characterization of long term viscoelastic properties is presented. The time-temperature-stress superposition principle (TTSSP) is shown to serve as the basis for determining long term compliance data from short term creep test results. Nonlinear viscoelastic theories are discussed to provide the framework for the mathematically modeling of such a process. A time dependent Tsai-Hill-Zhurkov failure theory is used to determine long term failure properties from short term data. Compliance and failure data are incorporated in an incremental lamination theory to make long term laminate predictions. Comparisons are made between theory and experiment.

  4. Viscoelastic Properties of Confluent MDCK II Cells Obtained from Force Cycle Experiments.

    PubMed

    Brückner, Bastian Rouven; Nöding, Helen; Janshoff, Andreas

    2017-02-28

    The local mechanical properties of cells are frequently probed by force indentation experiments carried out with an atomic force microscope. Application of common contact models provides a single parameter, the Young's modulus, to describe the elastic properties of cells. The viscoelastic response of cells, however, is generally measured in separate microrheological experiments that provide complex shear moduli as a function of time or frequency. Here, we present a straightforward way to obtain rheological properties of cells from regular force distance curves collected in typical force indentation measurements. The method allows us to record the stress-strain relationship as well as changes in the weak power law of the viscoelastic moduli. We derive an analytical function based on the elastic-viscoelastic correspondence principle applied to Hertzian contact mechanics to model both indentation and retraction curves. Rheological properties are described by standard viscoelastic models and the paradigmatic weak power law found to interpret the viscoelastic properties of living cells best. We compare our method with atomic force microscopy-based active oscillatory microrheology and show that the method to determine the power law coefficient is robust against drift and largely independent of the indentation depth and indenter geometry. Cells were subject to Cytochalasin D treatment to provoke a drastic change in the power law coefficient and to demonstrate the feasibility of the approach to capture rheological changes extremely fast and precisely. The method is easily adaptable to different indenter geometries and acquires viscoelastic data with high spatiotemporal resolution. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  5. Impact of gas injection on the apparent viscosity and viscoelastic property of waste activated sewage sludge.

    PubMed

    Bobade, Veena; Baudez, Jean Christophe; Evans, Geoffery; Eshtiaghi, Nicky

    2017-05-01

    Gas injection is known to play a major role on the particle size of the sludge, the oxygen transfer rate, as well as the mixing efficiency of membrane bioreactors and aeration basins in the waste water treatment plants. The rheological characteristics of sludge are closely related to the particle size of the sludge floc. However, particle size of sludge floc depends partly on the shear induced in the sludge and partly on physico-chemical nature of the sludge. The objective of this work is to determine the impact of gas injection on both the apparent viscosity and viscoelastic property of sludge. The apparent viscosity of sludge was investigated by two methods: in-situ and after sparging. Viscosity curves obtained by in-situ measurement showed that the apparent viscosity decreases significantly from 4000 Pa s to 10 Pa s at low shear rate range (below 10 s(-1)) with an increase in gas flow rate (0.5LPM to 3LPM); however the after sparging flow curve analysis showed that the reduction in apparent viscosity throughout the shear rate range is negligible to be displayed. Torque and displacement data at low shear rate range revealed that the obtained lower apparent viscosity in the in-situ method is not the material characteristics, but the slippage effect due to a preferred location of the bubbles close to the bob, causing an inconsistent decrease of torque and increase of displacement at low shear rate range. In linear viscoelastic regime, the elastic and viscous modulus of sludge was reduced by 33% & 25%, respectively, due to gas injection because of induced shear. The amount of induced shear measured through two different tests (creep and time sweep) were the same. The impact of this induced shear on sludge structure was also verified by microscopic images. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. In search of validated measurements of the properties of viscoelastic materials by indentation with sharp indenters

    NASA Astrophysics Data System (ADS)

    Monclus, M. A.; Jennett, N. M.

    2011-03-01

    Industry requires validated high-resolution methods for the characterisation viscoelastic materials to obtain local (or small volume) polymer properties for input to part design (e.g. micro-mouldings, packaging, coatings, composite interfaces, etc.). This paper examines the capability of dynamic (oscillatory) indentation (DI) and simple force-controlled "force-increase ramp and hold" indentation creep methods to deliver equivalent results compatible with those obtained on the same materials by dynamic mechanical analysis (DMA) and uniaxial tensile testing. We test three commercial polymers (two photo stress materials and polyoxymethylene (POM)). A creep analysis based on conical-pyramidal elastic-viscoelastic correspondence 1 and a three-element standard linear solid (SLS) model is used to give an output of two elastic moduli (E 1 and E 2) and a viscosity (η). Mathematically, E 1, E 2 and η can be used to calculate loss and storage modulus values at any frequency without further measurement. Indentation creep results obtained using various maximum forces (P max) and two indenter geometries (pyramidal (Berkovich) and conical (0.6 µm tip radius)) are compared with DI and DMA measurements at 40 Hz on the same materials and with tensile data from the POM sample fitted using the same SLS creep model. Between-method agreement of storage modulus values for all materials is sufficient to suggest that a route to validated measurement methods is available. However, simple models (as commonly used in DI and DMA) are inadequate to generate reproducible quantitative values for viscosity parameters. We show that more complex models are necessary to successfully produce loss/viscosity parameters that are equivalent.

  7. Pedestrian injuries: viscoelastic properties of human knee ligaments at high loading rates.

    PubMed

    van Dommelen, J A W; Jolandan, M Minary; Ivarsson, B J; Millington, S A; Raut, M; Kerrigan, J R; Crandall, J R; Diduch, D R

    2005-09-01

    Accidents involving pedestrians are very common, and often lead to severe injuries to the lower extremities. In a large portion of pedestrian-automobile collisions, knee ligament injuries are sustained. In this study, the viscoelastic properties of the four major human knee ligaments were investigated at loading rates representative for pedestrian-automobile collisions. Bone-ligament-bone specimens were tested in knee distraction loading. The collateral ligaments and the separate functional bundles of the cruciate ligaments were tested in the anatomical position corresponding to a fully extended knee. A series of step-and-hold tests and ramp tests at different rates were conducted to characterize the time-dependent behavior of the knee ligaments for deformation rates associated with the pedestrian impact loading environment. The quasi linear viscoelastic (QLV) theory was used to describe the structural response of the knee ligaments and averaged parameters for this model were determined. The QLV theory was found to be applicable for the time range that is relevant for pedestrian-automobile collisions. The structural behavior of the knee ligaments was found to be particularly rate-sensitive for high elongation rates, as occur during these collisions. The ligament stiffness was found to increase with age for both the collateral ligaments and with weight for the medial collateral ligament. For the loading conditions that are relevant for pedestrian-automobile collisions, the use of the QLV model for the description of the mechanical behavior of knee ligaments is appropriate. The rate-sensitivity is particularly important for these extreme loading conditions. The relaxation behavior was found to be consistent between different ligament types and samples. Variations due to donor anthropometry were found predominantly for the instantaneous elastic behavior.

  8. Viscoelastic Properties of the Chinese Fir (Cunninghamia lanceolata) during Moisture Sorption Processes Determined by Harmonic Tests

    PubMed Central

    Zhan, Tianyi; Lu, Jianxiong; Jiang, Jiali; Peng, Hui; Li, Anxin; Chang, Jianmin

    2016-01-01

    Measured by harmonic tests, the viscoelastic properties of Chinese fir during moisture sorption processes were examined under three relative humidity (RH) modes: RHramp, RHisohume, and RHstep. The stiffness decreased and damping increased as a function of the moisture content (MC), which is presumed to be the effect of plasticization and an unstable state. The increasing damping was associated with the breaking of hydrogen bonds and the formation of free volume within polymer networks. The changes of loss modulus ratio at 1 and 20 Hz, E″1Hz/E″20Hz, proved the changing trend of the unstable state. Higher ramping rates aggravated the unstable state at the RHramp period, and higher constant RH levels provided more recovery of the unstable state at the RHisohume period. Changes of viscoelastic properties were associated with RH (varied or remained constant), and the application of Boltzmann’s superposition principle is a good approach to simulate viscoelasticity development. PMID:28774140

  9. The viscoelastic properties of microvilli are dependent upon the cell-surface molecule.

    PubMed

    Python, Johanne L; Wilson, Kristal O; Snook, Jeremy H; Guo, Bin; Guilford, William H

    2010-07-02

    We studied at nanometer resolution the viscoelastic properties of microvilli and tethers pulled from myelogenous cells via P-selectin glycoprotein ligand 1 (PSGL-1) and found that in contrast to pure membrane tethers, the viscoelastic properties of microvillus deformations are dependent upon the cell-surface molecule through which load is applied. A laser trap and polymer bead coated with anti-PSGL-1 (KPL-1) were used to apply step loads to microvilli. The lengthening of the microvillus in response to the induced step loads was fitted with a viscoelastic model. The quasi-steady state force on the microvillus at any given length was approximately fourfold lower in cells treated with cytochalasin D or when pulled with concanavalin A-coated rather than KPL-1-coated beads. These data suggest that associations between PSGL-1 and the underlying actin cytoskeleton significantly affect the early stages of leukocyte deformation under flow.

  10. Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation

    PubMed Central

    Gayle, Andrew J.; Cook, Robert F.

    2016-01-01

    An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes. PMID:27563168

  11. Non-linear visco-elastic analysis and the design of super-pressure balloons : stress, strain and stability

    NASA Astrophysics Data System (ADS)

    Wakefield, David

    approach to stress and stability analysis inherent in inTENS, and focuses in particular on: Implementation of an alternative application of the Incremental Schapery Rand (ISR) representation of the non-linear visco-elastic response of the polyethylene balloon film. This is based upon the relaxation modulus, rather than the creep compliance, and as such fits more efficiently into the Dynamic Relaxation analysis procedure used within inTENS. Comparisons of results between the two approaches are given. Verification of the material model by comparison with material tests. Verification of the application to pumpkin balloon structures by comparison with scale model tests. Application of inTENS with ISR to time-stepping analyses of a balloon flight including diurnal variations of temperature and pressure. This includes the demonstration of a method for checking the likely hood of overall instability developing at any particular time in the flight as both balloon geometry and film properties change due to visco-elastic effects.

  12. Estimation of the viscoelastic properties of vessel walls using a computational model and Doppler ultrasound

    NASA Astrophysics Data System (ADS)

    Balocco, Simone; Basset, Olivier; Courbebaisse, Guy; Boni, Enrico; Frangi, Alejandro F.; Tortoli, Piero; Cachard, Christian

    2010-06-01

    Human arteries affected by atherosclerosis are characterized by altered wall viscoelastic properties. The possibility of noninvasively assessing arterial viscoelasticity in vivo would significantly contribute to the early diagnosis and prevention of this disease. This paper presents a noniterative technique to estimate the viscoelastic parameters of a vascular wall Zener model. The approach requires the simultaneous measurement of flow variations and wall displacements, which can be provided by suitable ultrasound Doppler instruments. Viscoelastic parameters are estimated by fitting the theoretical constitutive equations to the experimental measurements using an ARMA parameter approach. The accuracy and sensitivity of the proposed method are tested using reference data generated by numerical simulations of arterial pulsation in which the physiological conditions and the viscoelastic parameters of the model can be suitably varied. The estimated values quantitatively agree with the reference values, showing that the only parameter affected by changing the physiological conditions is viscosity, whose relative error was about 27% even when a poor signal-to-noise ratio is simulated. Finally, the feasibility of the method is illustrated through three measurements made at different flow regimes on a cylindrical vessel phantom, yielding a parameter mean estimation error of 25%.

  13. Estimation of the viscoelastic properties of vessel walls using a computational model and Doppler ultrasound.

    PubMed

    Balocco, Simone; Basset, Olivier; Courbebaisse, Guy; Boni, Enrico; Frangi, Alejandro F; Tortoli, Piero; Cachard, Christian

    2010-06-21

    Human arteries affected by atherosclerosis are characterized by altered wall viscoelastic properties. The possibility of noninvasively assessing arterial viscoelasticity in vivo would significantly contribute to the early diagnosis and prevention of this disease. This paper presents a noniterative technique to estimate the viscoelastic parameters of a vascular wall Zener model. The approach requires the simultaneous measurement of flow variations and wall displacements, which can be provided by suitable ultrasound Doppler instruments. Viscoelastic parameters are estimated by fitting the theoretical constitutive equations to the experimental measurements using an ARMA parameter approach. The accuracy and sensitivity of the proposed method are tested using reference data generated by numerical simulations of arterial pulsation in which the physiological conditions and the viscoelastic parameters of the model can be suitably varied. The estimated values quantitatively agree with the reference values, showing that the only parameter affected by changing the physiological conditions is viscosity, whose relative error was about 27% even when a poor signal-to-noise ratio is simulated. Finally, the feasibility of the method is illustrated through three measurements made at different flow regimes on a cylindrical vessel phantom, yielding a parameter mean estimation error of 25%.

  14. Importance of Viscoelastic Property Measurement of a New Hydrogel for Health Care

    NASA Astrophysics Data System (ADS)

    Roy, Niladri; Saha, Nabanita; Kitano, Takeshi; Saha, Petr

    2009-07-01

    A simple technology based new hydrogel "PVP-CMC-BA" has been prepared by the scientists of Tomas Bata University in Zlin, Czech Republic. Its swelling property (in presence of water, human blood and different pH), antimicrobial property (in presence of skin infection causing agents like: Staphylococcus aureus; bacteria and Candida albicans; fungi) and viscoelastic properties such as storage modulus (G'), loss modulus (G") and complex viscosity (η*) were investigated at room temperature (25-28° C) which demonstrate that PVP-CMC-BA hydrogel is maintaining requisite properties for health care application, specially as a wound dressing material. The elasticity and antimicrobial property of PVP-CMC-BA is directly correlated with percentage of boric acid, an antiseptic agent. The consequential values of viscoelastic properties of the hydrogel (before drying) enable us to understand its specific flexible condition to apply on the surface of human body.

  15. Influence of jet-cooking Prowashonupana barley flour on phenolic composition, antioxidant activities, and viscoelastic properties

    USDA-ARS?s Scientific Manuscript database

    The influence of jet-cooking Prowashonupana barley flour on total phenolic contents, antioxidant activities, water holding capacities, and viscoelastic properties was studied. Barley flour was jet-cooked without or with pH adjustment at 7, 9, or 11. Generally, the free phenolic content and antioxi...

  16. Rheology of the vitreous gel: effects of macromolecule organization on the viscoelastic properties.

    PubMed

    Sharif-Kashani, Pooria; Hubschman, Jean-Pierre; Sassoon, Daniel; Kavehpour, H Pirouz

    2011-02-03

    The macromolecular organization of vitreous gel is responsible for its viscoelastic properties. Knowledge of this correlation enables us to relate the physical properties of vitreous to its pathology, as well as optimize surgical procedures such as vitrectomy. Herein, we studied the rheological properties (e.g. dynamic deformation, shear stress-strain flow, and creep compliance) of porcine vitreous humor using a stressed-control shear rheometer. All experiments were performed in a closed environment with the temperature set to that of the human body (i.e. 37°C) to mimic in-vivo conditions. We modeled the creep deformation using the two-element retardation spectrum model. By associating each element of the model to an individual biopolymeric system in the vitreous gel, a distinct response to the applied stress was observed from each component. We hypothesized that the first viscoelastic response with the short time scale (~1 s) is associated with the collagen structure, while the second viscoelastic response with longer time scale (~100 s) is related to the microfibrilis and hyaluronan network. Consequently, we were able to differentiate the role of each main component from the overall viscoelastic properties.

  17. Viscoelastic Properties of Extracellular Polymeric Substances Can Strongly Affect Their Washing Efficiency from Reverse Osmosis Membranes.

    PubMed

    Ferrando Chavez, Diana Lila; Nejidat, Ali; Herzberg, Moshe

    2016-09-06

    The role of the viscoelastic properties of biofouling layers in their removal from the membrane was studied. Model fouling layers of extracellular polymeric substances (EPS) originated from microbial biofilms of Pseudomonas aeruginosa PAO1 differentially expressing the Psl polysaccharide were used for controlled washing experiments of fouled RO membranes. In parallel, adsorption experiments and viscoelastic modeling of the EPS layers were conducted in a quartz crystal microbalance with dissipation (QCM-D). During the washing stage, as shear rate was elevated, significant differences in permeate flux recovery between the three different EPS layers were observed. According to the amount of organic carbon remained on the membrane after washing, the magnitude of Psl production provides elevated resistance of the EPS layer to shear stress. The highest flux recovery during the washing stage was observed for the EPS with no Psl. Psl was shown to elevate the layer's shear modulus and shear viscosity but had no effect on the EPS adhesion to the polyamide surface. We conclude that EPS retain on the membrane as a result of the layer viscoelastic properties. These results highlight an important relation between washing efficiency of fouling layers from membranes and their viscoelastic properties, in addition to their adhesion properties.

  18. Constitutive Equations: Plastic and Viscoelastic Properties. (Latest citations from the Aerospace Database)

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The bibliography contains citations concerning analytical techniques using constitutive equations, applied to materials under stress. The properties explored with these techniques include viscoelasticity, thermoelasticity, and plasticity. While many of the references are general as to material type, most refer to specific metals or composites, or to specific shapes, such as flat plate or spherical vessels.

  19. Dynamic Viscoelasticity and Surface Properties of Porcine Left Anterior Descending Coronary Arteries.

    PubMed

    Burton, Hanna E; Freij, Jenny M; Espino, Daniel M

    2017-03-01

    The aim of this study was, for the first time, to measure and compare quantitatively the viscoelastic properties and surface roughness of coronary arteries. Porcine left anterior descending coronary arteries were dissected ex vivo. Viscoelastic properties were measured longitudinally using dynamic mechanical analysis, for a range of frequencies from 0.5 to 10 Hz. Surface roughness was calculated following three-dimensional reconstructed of surface images obtained using an optical microscope. Storage modulus ranged from 14.47 to 25.82 MPa, and was found to be frequency-dependent, decreasing as the frequency increased. Storage was greater than the loss modulus, with the latter found to be frequency-independent with a mean value of 2.10 ± 0.33 MPa. The circumferential surface roughness was significantly greater (p < 0.05) than the longitudinal surface roughness, ranging from 0.73 to 2.83 and 0.35 to 0.92 µm, respectively. However, if surface roughness values were corrected for shrinkage during processing, circumferential and longitudinal surface roughness were not significantly different (1.04 ± 0.47, 0.89 ± 0.27 µm, respectively; p > 0.05). No correlation was found between the viscoelastic properties and surface roughness. It is feasible to quantitatively measure the viscoelastic properties of coronary arteries and the roughness of their endothelial surface.

  20. Constitutive Equations: Plastic and Viscoelastic Properties. (Latest citations from the Aerospace Database)

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The bibliography contains citations concerning analytical techniques using constitutive equations, applied to materials under stress. The properties explored with these techniques include viscoelasticity, thermoelasticity, and plasticity. While many of the references are general as to material type, most refer to specific metals or composites, or to specific shapes, such as flat plate or spherical vessels.

  1. Effects of swelling on the viscoelastic properties of polyester films made from glycerol and glutaric acid

    USDA-ARS?s Scientific Manuscript database

    Viscoelastic properties have been determined for poly(glycerol-co-glutaric acid) films synthesized from Lewis acid-catalyzed polyesterifications. The polymers were prepared by synthesizing polymer gels that were subsequently cured at 125 degrees C to form polymer films. The polymers were evaluated ...

  2. A Rapid Small-Scale Method to Evaluate Dough Viscoelastic Properties

    USDA-ARS?s Scientific Manuscript database

    Dough viscoelastic properties are of special interest to bakers and wheat breeders. Dough extensibility (DE) and resistance to extension (RE) influence each step of the baking process as well as product end-use quality, and thus are important quality factors to consider in wheat breeding programs. T...

  3. Indentation testing and optimized property identification for viscoelastic materials using the finite element method

    NASA Astrophysics Data System (ADS)

    Resapu, Rajeswara Reddy

    The most common approaches to determining mechanical material properties of materials are tension and compression tests. However, tension and compression testing cannot be implemented under certain loading conditions (immovable object, not enough space to hold object for testing, etc). Similarly, tensile and compression testing cannot be performed on certain types of materials (delicate, bulk, non-machinable, those that cannot be separated from a larger structure, etc). For such cases, other material testing methods need to be implemented. Indentation testing is one such method; this approach is often non-destructive and can be used to characterize regions that are not compatible with other testing methods. However, indentation testing typically leads to force-displacement data as opposed to the direct stress-strain data normally used for the mechanical characterization of materials; this data needs to be analyzed using a suitable approach to determine the associated material properties. As such, methods to establish material properties from force-displacement indentation data need to be identified. In this work, a finite element approach using parameter optimization is developed to determine the mechanical properties from the experimental indentation data. Polymers and tissues tend to have time-dependent mechanical behavior; this means that their mechanical response under load changes with time. This dissertation seeks to characterize the properties of these materials using indentation testing under the assumption that they are linear viscoelastic. An example of a material of interest is the polymer poly vinyl chloride (PVC) that is used as the insulation of some aircraft wiring. Changes in the mechanical properties of this material over years of service can indicate degradation and a potential hazard to continued use. To investigate the validity of using indentation testing to monitor polymer insulation degradation, PVC film and PVC-insulated aircraft wiring are

  4. Tissue structure and inflammatory processes shape viscoelastic properties of the mouse brain.

    PubMed

    Millward, Jason M; Guo, Jing; Berndt, Dominique; Braun, Jürgen; Sack, Ingolf; Infante-Duarte, Carmen

    2015-07-01

    Magnetic resonance elastography (MRE) is an imaging method that reveals the mechanical properties of tissue, modelled as a combination of " viscosity" and " elasticity" . We recently showed reduced brain viscoelasticity in multiple sclerosis (MS) patients compared with healthy controls, and in the relapsing-remitting disease model experimental autoimmune encephalomyelitis (EAE). However, the mechanisms by which these intrinsic tissue properties become altered remain unclear. This study investigates whether distinct regions in the mouse brain differ in their native viscoelastic properties, and how these properties are affected during chronic EAE in C57Bl/6 mice and in mice lacking the cytokine interferon-gamma. IFN-γ(-/-) mice exhibit a more severe EAE phenotype, with amplified inflammation in the cerebellum and brain stem. Brain scans were performed in the sagittal plane using a 7 T animal MRI scanner, and the anterior (cerebral) and posterior (cerebellar) regions analyzed separately. MRE investigations were accompanied by contrast-enhanced MRI scans, and by histopathology and gene expression analysis ex vivo. Compared with the cerebrum, the cerebellum in healthy mice has a lower viscoelasticity, i.e. it is intrinsically " softer" . This was seen both in the wild-type mice and the IFNγ(-/-) mice. During chronic EAE, C57Bl/6 mice did not show altered brain viscoelasticity. However, as expected, the IFNγ(-/-) mice showed a more severe EAE phenotype, and these mice did show altered brain elasticity during the course of disease. The magnitude of the elasticity reduction correlated with F4/80 gene expression, a marker for macrophages/microglia in inflamed central nervous system tissue. Together these results demonstrate that MRE is sensitive enough to discriminate between viscoelastic properties in distinct anatomical structures in the mouse brain, and to confirm a further relationship between cellular inflammation and mechanical alterations of the brain. This

  5. Imaging viscoelastic properties of live cells by AFM: power-law rheology on the nanoscale.

    PubMed

    Hecht, Fabian M; Rheinlaender, Johannes; Schierbaum, Nicolas; Goldmann, Wolfgang H; Fabry, Ben; Schäffer, Tilman E

    2015-06-21

    We developed force clamp force mapping (FCFM), an atomic force microscopy (AFM) technique for measuring the viscoelastic creep behavior of live cells with sub-micrometer spatial resolution. FCFM combines force-distance curves with an added force clamp phase during tip-sample contact. From the creep behavior measured during the force clamp phase, quantitative viscoelastic sample properties are extracted. We validate FCFM on soft polyacrylamide gels. We find that the creep behavior of living cells conforms to a power-law material model. By recording short (50-60 ms) force clamp measurements in rapid succession, we generate, for the first time, two-dimensional maps of power-law exponent and modulus scaling parameter. Although these maps reveal large spatial variations of both parameters across the cell surface, we obtain robust mean values from the several hundreds of measurements performed on each cell. Measurements on mouse embryonic fibroblasts show that the mean power-law exponents and the mean modulus scaling parameters differ greatly among individual cells, but both parameters are highly correlated: stiffer cells consistently show a smaller power-law exponent. This correlation allows us to distinguish between wild-type cells and cells that lack vinculin, a dominant protein of the focal adhesion complex, even though the mean values of viscoelastic properties between wildtype and knockout cells did not differ significantly. Therefore, FCFM spatially resolves viscoelastic sample properties and can uncover subtle mechanical signatures of proteins in living cells.

  6. Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency.

    PubMed

    Bates, J H; Milic-Emili, J

    1993-01-01

    We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work (WI) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while WI was found to increase slowly with frequency above its optimum. In contrast, both WI and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the WI criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.

  7. Measurement of viscoelastic properties of in vivo swine myocardium using lamb wave dispersion ultrasound vibrometry (LDUV).

    PubMed

    Urban, Matthew W; Pislaru, Cristina; Nenadic, Ivan Z; Kinnick, Randall R; Greenleaf, James F

    2013-02-01

    Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb wave dispersion ultrasound vibrometry (LDUV) is a shear wave-based method that uses wave velocity dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of wave propagation were measured over the 50-400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb wave model to obtain estimates of the shear elasticity, μ(1), and viscosity, μ(2) as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb wave model was also studied using simulated data. We demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.

  8. Measurement of viscoelastic properties of in vivo swine myocardium using Lamb Wave Dispersion Ultrasound Vibrometry (LDUV)

    PubMed Central

    Urban, Matthew W.; Pislaru, Cristina; Nenadic, Ivan Z.; Kinnick, Randall R.; Greenleaf, James F.

    2012-01-01

    Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb Wave Dispersion Ultrasound Vibrometry (LDUV) is a shear wave-based method that uses wave velocity dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of wave propagation were measured over the 50–400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb wave model to obtain estimates of the shear elasticity, μ1, and viscosity, μ2 as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb wave model was also studied using simulated data. We demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle. PMID:23060325

  9. Microscale characterization of the viscoelastic properties of hydrogel biomaterials using dual-mode ultrasound elastography.

    PubMed

    Hong, Xiaowei; Stegemann, Jan P; Deng, Cheri X

    2016-05-01

    Characterization of the microscale mechanical properties of biomaterials is a key challenge in the field of mechanobiology. Dual-mode ultrasound elastography (DUE) uses high frequency focused ultrasound to induce compression in a sample, combined with interleaved ultrasound imaging to measure the resulting deformation. This technique can be used to non-invasively perform creep testing on hydrogel biomaterials to characterize their viscoelastic properties. DUE was applied to a range of hydrogel constructs consisting of either hydroxyapatite (HA)-doped agarose, HA-collagen, HA-fibrin, or preosteoblast-seeded collagen constructs. DUE provided spatial and temporal mapping of local and bulk displacements and strains at high resolution. Hydrogel materials exhibited characteristic creep behavior, and the maximum strain and residual strain were both material- and concentration-dependent. Burger's viscoelastic model was used to extract characteristic parameters describing material behavior. Increased protein concentration resulted in greater stiffness and viscosity, but did not affect the viscoelastic time constant of acellular constructs. Collagen constructs exhibited significantly higher modulus and viscosity than fibrin constructs. Cell-seeded collagen constructs became stiffer with altered mechanical behavior as they developed over time. Importantly, DUE also provides insight into the spatial variation of viscoelastic properties at sub-millimeter resolution, allowing interrogation of the interior of constructs. DUE presents a novel technique for non-invasively characterizing hydrogel materials at the microscale, and therefore may have unique utility in the study of mechanobiology and the characterization of hydrogel biomaterials.

  10. Laser Speckle Rheology for evaluating the viscoelastic properties of hydrogel scaffolds

    PubMed Central

    Hajjarian, Zeinab; Nia, Hadi Tavakoli; Ahn, Shawn; Grodzinsky, Alan J.; Jain, Rakesh K.; Nadkarni, Seemantini K.

    2016-01-01

    Natural and synthetic hydrogel scaffolds exhibit distinct viscoelastic properties at various length scales and deformation rates. Laser Speckle Rheology (LSR) offers a novel, non-contact optical approach for evaluating the frequency-dependent viscoelastic properties of hydrogels. In LSR, a coherent laser beam illuminates the specimen and a high-speed camera acquires the time-varying speckle images. Cross-correlation analysis of frames returns the speckle intensity autocorrelation function, g2(t), from which the frequency-dependent viscoelastic modulus, G*(ω), is deduced. Here, we establish the capability of LSR for evaluating the viscoelastic properties of hydrogels over a large range of moduli, using conventional mechanical rheometry and atomic force microscopy (AFM)-based indentation as reference-standards. Results demonstrate a strong correlation between |G*(ω)| values measured by LSR and mechanical rheometry (r = 0.95, p < 10−9), and z-test analysis reports that moduli values measured by the two methods are identical (p > 0.08) over a large range (47 Pa – 36 kPa). In addition, |G*(ω)| values measured by LSR correlate well with indentation moduli, E, reported by AFM (r = 0.92, p < 10−7). Further, spatially-resolved moduli measurements in micro-patterned substrates demonstrate that LSR combines the strengths of conventional rheology and micro-indentation in assessing hydrogel viscoelastic properties at multiple frequencies and small length-scales. PMID:27905494

  11. Viscoelastic properties of cell walls of single living plant cells determined by dynamic nanoindentation.

    PubMed

    Hayot, Céline M; Forouzesh, Elham; Goel, Ashwani; Avramova, Zoya; Turner, Joseph A

    2012-04-01

    Plant development results from controlled cell divisions, structural modifications, and reorganizations of the cell wall. Thereby, regulation of cell wall behaviour takes place at multiple length scales involving compositional and architectural aspects in addition to various developmental and/or environmental factors. The physical properties of the primary wall are largely determined by the nature of the complex polymer network, which exhibits time-dependent behaviour representative of viscoelastic materials. Here, a dynamic nanoindentation technique is used to measure the time-dependent response and the viscoelastic behaviour of the cell wall in single living cells at a micron or sub-micron scale. With this approach, significant changes in storage (stiffness) and loss (loss of energy) moduli are captured among the tested cells. The results reveal hitherto unknown differences in the viscoelastic parameters of the walls of same-age similarly positioned cells of the Arabidopsis ecotypes (Col 0 and Ws 2). The technique is also shown to be sensitive enough to detect changes in cell wall properties in cells deficient in the activity of the chromatin modifier ATX1. Extensive computational modelling of the experimental measurements (i.e. modelling the cell as a viscoelastic pressure vessel) is used to analyse the influence of the wall thickness, as well as the turgor pressure, at the positions of our measurements. By combining the nanoDMA technique with finite element simulations quantifiable measurements of the viscoelastic properties of plant cell walls are achieved. Such techniques are expected to find broader applications in quantifying the influence of genetic, biological, and environmental factors on the nanoscale mechanical properties of the cell wall.

  12. Viscoelastic properties of cell walls of single living plant cells determined by dynamic nanoindentation

    PubMed Central

    Hayot, Céline M.; Forouzesh, Elham; Goel, Ashwani; Avramova, Zoya; Turner, Joseph A.

    2012-01-01

    Plant development results from controlled cell divisions, structural modifications, and reorganizations of the cell wall. Thereby, regulation of cell wall behaviour takes place at multiple length scales involving compositional and architectural aspects in addition to various developmental and/or environmental factors. The physical properties of the primary wall are largely determined by the nature of the complex polymer network, which exhibits time-dependent behaviour representative of viscoelastic materials. Here, a dynamic nanoindentation technique is used to measure the time-dependent response and the viscoelastic behaviour of the cell wall in single living cells at a micron or sub-micron scale. With this approach, significant changes in storage (stiffness) and loss (loss of energy) moduli are captured among the tested cells. The results reveal hitherto unknown differences in the viscoelastic parameters of the walls of same-age similarly positioned cells of the Arabidopsis ecotypes (Col 0 and Ws 2). The technique is also shown to be sensitive enough to detect changes in cell wall properties in cells deficient in the activity of the chromatin modifier ATX1. Extensive computational modelling of the experimental measurements (i.e. modelling the cell as a viscoelastic pressure vessel) is used to analyse the influence of the wall thickness, as well as the turgor pressure, at the positions of our measurements. By combining the nanoDMA technique with finite element simulations quantifiable measurements of the viscoelastic properties of plant cell walls are achieved. Such techniques are expected to find broader applications in quantifying the influence of genetic, biological, and environmental factors on the nanoscale mechanical properties of the cell wall. PMID:22291130

  13. Influence of Reversibly Associating Side Group Bond Strength on Viscoelastic Properties of Polymer Melts

    NASA Astrophysics Data System (ADS)

    Lewis, Christopher; Stewart, Kathleen; Anthamatten, Mitchell

    2013-03-01

    Reversible hydrogen-bonding between side-groups of linear polymers can sharply influence a material's dynamic mechanical behavior, giving rise to valuable shape memory and self-healing properties. Here, we investigate how bond-strength affects the bulk rheological behavior of functional poly(n-butyl acrylate) (PBA) melts. A series of random copolymers containing three different reversibly bonding groups (aminopyridine, carboxylic acid, and ureidopyrimidinone) were synthesized to systematically vary the side-group hydrogen bond strength (~26, 40, 70 kJ/mol). The materials' volumetric hydrogen-bond energy densities can be tuned by adjusting the side-group composition. By comparing the viscoelastic behavior of materials containing an equivalent bond energy density, with different bonding groups, the efficacy and cooperativity of reversible binding can be directly examined. Melt rheology results are interpreted using a state-of-ease model that assumes continuous mechanical equilibrium between applied stress and resistive stresses of entropic origin arising from a network of reversible bonds. The authors acknowledge support from funding provided by the National Science Foundation under Grant DMR-0906627

  14. Viscoelastic shear properties of human vocal fold mucosa: theoretical characterization based on constitutive modeling.

    PubMed

    Chan, R W; Titze, I R

    2000-01-01

    The viscoelastic shear properties of human vocal fold mucosa (cover) were previously measured as a function of frequency [Chan and Titze, J. Acoust. Soc. Am. 106, 2008-2021 (1999)], but data were obtained only in a frequency range of 0.01-15 Hz, an order of magnitude below typical frequencies of vocal fold oscillation (on the order of 100 Hz). This study represents an attempt to extrapolate the data to higher frequencies based on two viscoelastic theories, (1) a quasilinear viscoelastic theory widely used for the constitutive modeling of the viscoelastic properties of biological tissues [Fung, Biomechanics (Springer-Verlag, New York, 1993), pp. 277-292], and (2) a molecular (statistical network) theory commonly used for the rheological modeling of polymeric materials [Zhu et al., J. Biomech. 24, 1007-1018 (1991)]. Analytical expressions of elastic and viscous shear moduli, dynamic viscosity, and damping ratio based on the two theories with specific model parameters were applied to curve-fit the empirical data. Results showed that the theoretical predictions matched the empirical data reasonably well, allowing for parametric descriptions of the data and their extrapolations to frequencies of phonation.

  15. Influences of viscoelastic properties of one-part epoxy adhesives on automotive dispensing

    NASA Astrophysics Data System (ADS)

    Dakin, Suzanne Irene Mcaleer

    The rheological properties of automotive adhesives were investigated to help understand how these properties may influence the performance of streaming dispensing processes used in automotive manufacturing. The rheological investigation included examining the base epoxies of the adhesives and two filler components: fumed silica and a spherical glass filler. Although the base epoxies are similar in chemical composition and viscosity, one exhibited non-linear elastic properties while the other did not. The enhancement of non-linear elastic properties due to the presence of fillers only occurred in the epoxy, which exhibited normal forces without fillers. Time temperature superposition was successfully applied to create master rheological curves for shear and viscoelastic properties. The shear rate range of the master viscosity curves extended to shear rates similar to shear rates of streaming dispensing. The non-linear elastic response differences of the materials played an important role in how well the materials dispensed with streaming. Dispensing studies of the adhesives using unwetted nozzles with a Graco Ultra-Flo 10 dispensing, indicated that deviations from centerline (DFC) increased as Re and De numbers increased. The adhesive, which exhibited an elastic response, looped and deviated out of view of the camera under unwetted nozzle conditions making quantifying distance from center impossible. Therefore, the adhesives and the epoxies were dispensed using a wetted nozzle. In-flight dispensed streams were photographed and DFC were recorded at distances of 2-cm and 4-cm from nozzle tip. Even under wetted nozzle conditions, the adhesive, which exhibited an elastic response during shear testing, streamed worse than the adhesive that had no detectable normal force response. Under wetted nozzle conditions, the effect of De (increase in DFC as De increases) is masked by the large stabilizing effect of Re. Therefore, the data was analyzed with respect to Re and N1/tau

  16. Viscoelastic Properties of a Hierarchical Model of Soft Biological Tissue: Two-Dimensional and Three-Dimensional Cases

    NASA Astrophysics Data System (ADS)

    Posnansky, Oleg

    2016-09-01

    The measuring of viscoelastic response is widely used for revealing information about soft matter and biological tissue noninvasively. This information encodes intrinsic dynamic correlations and depends on relations between macroscopic viscoelasticity and structure at the mesoscopic scale. Here we show numerically that the frequency dependent dynamical shear moduli distinguish between the mesoscopic architectural complexities and sensitive to the Euclidean dimensionality. Our approach enables the explanation of two- and three-dimensional viscoelastic experiments by objectively choosing and modeling the most relevant architectural features such as the concentration of compounds and intra-model hierarchical characteristics of physical parameters. Current work provides a link between the macroscopical effective viscoelastic properties to viscoelastic constants and network geometry on the mesoscale. Besides of this we also pay attention to the analytical properties of generalized susceptibility function of considered constitutive model accounting principles of causality.

  17. Piezoelectric generation of extensional waves in a viscoelastic bar by use of a linear power amplifier: Theoretical basis

    NASA Astrophysics Data System (ADS)

    Jansson, A.; Lundberg, B.

    2007-09-01

    A system consisting of a linear power amplifier driving a piezoelectric actuator pair attached to a long viscoelastic bar is analysed. Coupled piezoelectric theory is used, and allowance is made for the dynamics of the amplifier and of the actuators. Formulae are derived for the relation between the input voltage to the amplifier and the normal force associated with extensional waves generated in the bar and for the load impedance constituted by the actuator-bar assembly. It is established that the mechanical work performed on the external parts of the bar at the actuator/bar interfaces is at most equal to the electrical energy supplied by the amplifier. The results are applied to a three-parameter viscoelastic bar and to an elastic bar, and the effects of the cut-off frequency, without load, and the output impedance of the amplifier are examined. For the elastic bar, sharp response minima occur at frequencies that are integral multiples of the inverse transit time through the actuator region. For the viscoelastic bar, the corresponding minima are less sharp and deep. The input voltage to the amplifier required to produce a desired output wave at the actuator/bar interfaces can be determined provided that the spectrum of this wave is not too broad.

  18. Visco-Elastic Properties of Sodium Hyaluronate Solutions

    NASA Astrophysics Data System (ADS)

    Kulicke, Werner-Michael; Meyer, Fabian; Bingöl, Ali Ö.; Lohmann, Derek

    2008-07-01

    Sodium Hyaluronate (NaHA) is a member of the glycosaminoglycans and is present in the human organism as part of the synovial fluid and the vitreous body. HA is mainly commercialized as sodium or potassium salt. It can be extracted from cockscombs or can be produced by bacterial fermentation ensuring a low protein content. Because of its natural origin and toxicological harmlessness, NaHA is used to a great extent for pharmaceutical and cosmetic products. In medical applications, NaHA is already being used as a component of flushing and stabilizing fluids in the treatment of eye cataract and as a surrogate for natural synovial fluid. Another growing domain in the commercial utilization of NaHA is the field of skin care products like dermal fillers or moisturizers. In this spectrum, NaHA is used in dilute over semidilute up to concentrated (0viscoelastic behavior. We therefore present in this contribution the results of a comprehensive investigation of the viscous and elastic material functions of different NaHA samples. This includes, besides shear flow and oscillatory experiments, the performance of rheo-optical measurements in order to determine the elastic component in the range of low shear rates and low concentrations.

  19. Lyotropic chromonic liquid crystals: From viscoelastic properties to living liquid crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Shuang

    Lyotropic chromonic liquid crystal (LCLC) represents a broad range of molecules, from organic dyes and drugs to DNA, that self-assemble into linear aggregates in water through face-to-face stacking. These linear aggregates of high aspect ratio are capable of orientational order, forming, for example nematic phase. Since the microscopic properties (such as length) of the chromonic aggregates are results of subtle balance between energy and entropy, the macroscopic viscoelastic properties of the nematic media are sensitive to change of external factors. In the first part of this thesis, by using dynamic light scattering and magnetic Frederiks transition techniques, we study the Frank elastic moduli and viscosity coefficients of LCLC disodium cromoglycate (DSCG) and sunset yellow (SSY) as functions of concentration c , temperature T and ionic contents. The elastic moduli of splay (K1) and bend (K3) are in the order of 10pN, about 10 times larger than the twist modulus (K2). The splay modulus K1 and the ratio K1/K3 both increase substantially as T decreases or c increases, which we attribute to the elongation of linear aggregates at lower T or higher c . The bend viscosity is comparable to that of thermotropic liquid crystals, while the splay and twist viscosities are several orders of magnitude larger, changing exponentially with T . Additional ionic additives into the system influence the viscoelastic properties of these systems in a dramatic and versatile way. For example, monovalent salt NaCl decreases bend modulus K3 and increases twist viscosity, while an elevated pH decreases all the parameters. We attribute these features to the ion-induced changes in length and flexibility of building units of LCLC, the chromonic aggregates, a property not found in conventional thermotropic and lyotropic liquid crystals form by covalently bound units of fixed length. The second part of the thesis studies a new active bio-mechanical hybrid system called living liquid crystal

  20. Effect of viscoelastic properties of plantar soft tissues on plantar pressures at the first metatarsal head in diabetics with peripheral neuropathy.

    PubMed

    Jan, Yih-Kuen; Lung, Chi-Wen; Cuaderes, Elena; Rong, Daqian; Boyce, Kari

    2013-01-01

    Diabetic foot ulcers are one of the most serious complications associated with diabetes mellitus. Current research studies have demonstrated that biomechanical alterations of the diabetic foot contribute to the development of foot ulcers. However, the changes of soft tissue biomechanical properties associated with diabetes and its influences on the development of diabetic foot ulcers have not been investigated. The purpose of this study was to investigate the effect of diabetes on the biomechanical properties of plantar soft tissues and the relationship between biomechanical properties and plantar pressure distributions. We used the ultrasound indentation tests to measure force-deformation relationships of plantar soft tissues and calculate the effective Young's modulus and quasi-linear viscoelastic parameters to quantify biomechanical properties of plantar soft tissues. We also measured plantar pressures to calculate peak plantar pressure and plantar pressure gradient. Our results showed that diabetics had a significantly greater effective Young's modulus and initial modulus of quasi-linear viscoelasticity compared to non-diabetics. The plantar pressure gradient and biomechanical properties were significantly correlated. Our findings indicate that diabetes is linked to an increase in viscoelasticity of plantar soft tissues that may contribute to a higher peak plantar pressure and plantar pressure gradient in the diabetic foot.

  1. Altered viscoelastic properties of stroke-affected muscles estimated using ultrasound shear waves - Preliminary data.

    PubMed

    Rasool, Ghulam; Wang, Allison B; Rymer, William Z; Lee, Sabrina S M

    2016-08-01

    As a result of a brain injury such as stroke, the skeletal muscles may undergo numerous structural and functional alterations. These abnormal changes are linked to muscle weakness, joint contracture, and abnormal muscle tone and eventually, result in motor impairment. A subset of these alterations affects passive muscle stiffness, i.e., viscoelastic properties. However, in vivo estimation of changes in viscoelastic properties is a challenging task. Here, we used the shear wave velocity, estimated through ultrasound SuperSonic imaging (SSI), as a surrogate for viscoelastic properties. We estimated shear wave group and phase velocities (dispersion), and thus, quantified both elasticity and viscosity of the muscle tissue, respectively in muscles of hemiplegic stroke survivors. In these individuals, we found significantly higher group and phase velocities in the stroke-affected muscles (p<; 05) compared to those of the contralateral non-affected side. We hypothesize that in addition to changes in neural and contractile properties, there are also, changes in elastic and tissue dispersive properties through local mechanisms. An enhanced understanding of post-stroke changes in skeletal muscles will lead to better and targeted interventions for rehabilitation.

  2. Effects of immediate vs. delayed massage-like loading on skeletal muscle viscoelastic properties following eccentric exercise.

    PubMed

    Crawford, Scott K; Haas, Caroline; Butterfield, Timothy A; Wang, Qian; Zhang, Xiaoli; Zhao, Yi; Best, Thomas M

    2014-06-01

    This study compared immediate versus delayed massage-like compressive loading on skeletal muscle viscoelastic properties following eccentric exercise. Eighteen rabbits were surgically instrumented with peroneal nerve cuffs for stimulation of the tibialis anterior muscle. Rabbits were randomly assigned to a massage loading protocol applied immediately post exercise (n=6), commencing 48h post exercise (n=6), or exercised no-massage control (n=6). Viscoelastic properties were evaluated in vivo by performing a stress-relaxation test pre- and post-exercise and daily pre- and post-massage for four consecutive days of massage loading. A quasi-linear viscoelastic approach modeled the instantaneous elastic response (AG0), fast (g1(p)) and slow (g2(p)) relaxation coefficients, and the corresponding relaxation time constants τ1 and τ2. Exercise increased AG0 in all groups (P<0.05). After adjusting for the three multiple comparisons, recovery of AG0 was not significant in the immediate (P=0.021) or delayed (P=0.048) group compared to the control group following four days of massage. However, within-day (pre- to post-massage) analysis revealed a decrease in AG0 in both massage groups. Following exercise, g1(p) increased and g2(p) and τ1 decreased for all groups (P<0.05). Exercise had no effect on τ2 (P>0.05). After four days of massage, there was no significant recovery of the relaxation parameters for either massage loading group compared to the control group. Our findings suggest that massage loading following eccentric exercise has a greater effect on reducing muscle stiffness, estimated by AG0, within-day rather than affecting recovery over multiple days. Massage loading also has little effect on the relaxation response. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Effects of Immediate vs. Delayed Massage-like Loading on Skeletal Muscle Viscoelastic Properties Following Eccentric Exercise

    PubMed Central

    Crawford, Scott K.; Haas, Caroline; Wang, Qian; Zhang, Xiaoli; Zhao, Yi; Best, Thomas M.

    2014-01-01

    Background This study compared immediate versus delayed massage-like compressive loading on skeletal muscle viscoelastic properties following eccentric exercise. Methods Eighteen rabbits were surgically instrumented with peroneal nerve cuffs for stimulation of the tibialis anterior muscle. Rabbits were randomly assigned to a massage loading protocol applied immediately post exercise (n=6), commencing 48 hours post exercise (n=6), or exercised no-massage control (n=6). Viscoelastic properties were evaluated in vivo by performing a stress-relaxation test pre- and post-exercise and daily pre- and post-massage for four consecutive days of massage loading. A quasi-linear viscoelastic approach modeled the instantaneous elastic response (AG0), fast ( g1p) and slow ( g2p) relaxation coefficients, and the corresponding relaxation time constants τ1 and τ2. Findings Exercise increased AG0 in all groups (P<0.05). After adjusting for the three multiple comparisons, recovery of AG0 was not significant in the immediate (P=0.021) or delayed (P=0.048) groups compared to the control group following four days of massage. However, within-day (pre- to post-massage) analysis revealed a decrease in AG0 in both massage groups. Following exercise, g1p increased and g2p and τ1 decreased for all groups (P<0.05). Exercise had no effect on τ2 (P>0.05). After four days of massage, there was no significant recovery of the relaxation parameters for either massage loading group compared to the control group. Interpretation Our findings suggest that massage loading following eccentric exercise has a greater effect on reducing muscle stiffness, estimated by AG0, within-day rather than affecting recovery over multiple days. Massage loading also has little effect on the relaxation response. PMID:24861827

  4. Comparison of viscoelastic properties of suture versus porcine mitral valve chordae tendineae.

    PubMed

    Cochran, R P; Kunzelman, K S

    1991-12-01

    Recent reports have advocated the use of polytetrafluoroethylene (PTFE) suture for replacement or reinforcement of ruptured or elongated mitral valve chordae tendineae. The mechanical properties of PTFE (Gore-Tex) and other sutures were determined and compared to those of porcine mitral valve chordae. The results were analyzed to assess how closely chordal mechanical function may be simulated by synthetic suture materials. Chordae tendineae and suture samples were tested in uniaxial tension using an INSTRON Model 1000 at strain rates of 5 and 10 mm/min. The stress (g/mm2) was plotted versus strain, and the elastic modulus determined as the slope of the curve. Chordae tendineae exhibited a nonlinear viscoelastic stress/strain behavior. The elastic modulus of both suture types tested was significantly higher than that of the chordae. However, the PTFE suture did exhibit some viscoelastic characteristics (hysteresis and creep) that begin to approach the chordal behavior. Chordal viscoelastic behavior results from the inherent composite structure (collagen, elastin, endothelium, water, and ground substance). As yet, no synthetic materials are able to imitate this behavior with the appropriate tensile strength and fatigue resistant characteristics. At present, PTFE appears to be the best synthetic alternative for chordal replacement, due to its limited viscoelastic capabilities. Nevertheless, the need to more nearly approximate the mechanical behavior of mitral valve chordae tendineae with synthetic material warrants further investigation.

  5. Methods for quasi-linear viscoelastic modeling of soft tissue: application to incremental stress-relaxation experiments.

    PubMed

    Sarver, Joseph J; Robinson, Paul S; Elliott, Dawn M

    2003-10-01

    The quasi-linear viscoelastic (QLV) model was applied to incremental stress-relaxation tests and an expression for the stress was derived for each step. This expression was used to compare two methods for normalizing stress data prior to estimating QLV parameters. The first and commonly used normalization method was shown to be strain-dependent. Thus, a second normalization method was proposed and shown to be strain-independent and more sensitive to QLV time constants. These analytical results agreed with representative tendon data. Therefore, this method for normalizing stress data was proposed for future studies of incremental stress-relaxation, or whenever comparing stress-relaxation at different strains.

  6. Monitoring of peripheral vascular condition using a log-linearized arterial viscoelastic index during endoscopic thoracic sympathectomy.

    PubMed

    Hirano, Hiroki; Horiuchi, Tetsuya; Hirano, Harutoyo; Kurita, Yuichi; Ukawa, Teiji; Nakamura, Ryuji; Saeki, Noboru; Yoshizumi, Masao; Kawamoto, Masashi; Tsuji, Toshio

    2013-01-01

    This paper proposes a novel technique to support the monitoring of peripheral vascular conditions using biological signals such as electrocardiograms, arterial pressure values and pulse oximetry plethysmographic waveforms. In this approach, a second-order log-linearized model (referred to here as a log-linearized peripheral arterial viscoelastic model) is used to describe the non-linear viscoelastic relationship between blood pressure waveforms and photo-plethysmographic waveforms. The proposed index enables estimation of peripheral arterial wall stiffness changes induced by sympathetic nerve activity. The validity of the method is discussed here based on the results of peripheral vascular condition monitoring conducted during endoscopic thoracic sympathectomy (ETS). The results of ETS monitoring showed significant changes in stiffness variations between the periods before and during the procedures observed (p < 0.01) as well as during and after them (p < 0.01), so that it was confirmed that sympathetic nerve activity is drastically decreased in the area around the monitoring site after the thoracic sympathetic nerve trunk on the monitoring side is successfully blocked. In addition, no change was observed in the values of the proposed index during the ETS procedure on the side opposite that of the monitoring site. The experimental results obtained clearly show the proposed method can be used to assess changes in sympathetic nerve activity during ETS.

  7. Characterization of the passive responses of live skeletal muscle using the quasi-linear theory of viscoelasticity.

    PubMed

    Best, T M; McElhaney, J; Garrett, W E; Myers, B S

    1994-04-01

    The tensile viscoelastic responses of live, innervated rabbit skeletal muscle were measured and characterized using the quasi-linear model of viscoelasticity. The tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of anesthetized New Zealand white rabbits were surgically exposed and tested under in vivo conditions. Rate sensitivity of the force-time history was observed in response to constant velocity testing at rates from 0.01 to 2.0 Hz. Average hysteresis energy, expressed as a percentage of maximum stored strain energy, was 39.3 +/- 5.4% and was insensitive to deformation rate. The quasi-linear model, with constants derived from relaxation testing, was able to describe and predict these responses with correlation exceeding the 99% confidence interval for the 132 constant velocity tests performed (rmean = 0.9263 +/- 0.0373). The predictive ability of this model was improved when compressive loading effects on the muscle were neglected, rmean = 0.9306 +/- 0.0324. The rate insensitivity of hysteresis energy was predicted by the model; however, the absolute value of the hysteresis was underestimated (30.2 +/- 4.0%). Both muscles demonstrated strikingly different elastic functions. Geometric normalization of these responses (stress and strain) did not result in a single elastic function capable of describing both muscles. Based on these results, the quasi-linear model is recommended for the characterization of the structural responses of muscle; however, further investigation is required to determine the influence of muscle geometry and fiber architecture on the elastic function.

  8. Numerical predictions of viscoelastic properties and dynamic moduli of innovative pothole patching materials

    NASA Astrophysics Data System (ADS)

    Yuan, K. Y.; Yuan, W.; Ju, J. W.; Yang, J. M.; Kao, W.; Carlson, L.

    2013-04-01

    As asphalt pavements age and deteriorate, recurring pothole repair failures and propagating alligator cracks in the asphalt pavements have become a serious issue to our daily life and resulted in high repairing costs for pavement and vehicles. To solve this urgent issue, pothole repair materials with superior durability and long service life are needed. In the present work, revolutionary pothole patching materials with high toughness, high fatigue resistance that are reinforced with nano-molecular resins have been developed to enhance their resistance to traffic loads and service life of repaired potholes. In particular, DCPD resin (dicyclopentadiene, C10H12) with a Rhuthinium-based catalyst is employed to develop controlled properties that are compatible with aggregates and asphalt binders. In this paper, a multi-level numerical micromechanics-based model is developed to predict the viscoelastic properties and dynamic moduli of these innovative nano-molecular resin reinforced pothole patching materials. Irregular coarse aggregates in the finite element analysis are modeled as randomly-dispersed multi-layers coated particles. The effective properties of asphalt mastic, which consists of fine aggregates, tar, cured DCPD and air voids are theoretically estimated by the homogenization technique of micromechanics in conjunction with the elastic-viscoelastic correspondence principle. Numerical predictions of homogenized viscoelastic properties and dynamic moduli are demonstrated.

  9. Comparison of the viscoelastic properties of cells from different kidney cancer phenotypes measured with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Rebelo, L. M.; de Sousa, J. S.; Mendes Filho, J.; Radmacher, M.

    2013-02-01

    The viscoelastic properties of human kidney cell lines from different tumor types (carcinoma (A-498) and adenocarcinoma (ACHN)) are compared to a non-tumorigenic cell line (RC-124). Our methodology is based on the mapping of viscoelastic properties (elasticity modulus E and apparent viscosity η) over the surface of tens of individual cells with atomic force microscopy (AFM). The viscoelastic properties are averaged over datasets as large as 15000 data points per cell line. We also propose a model to estimate the apparent viscosity of soft materials using the hysteresis observed in conventional AFM deflection-displacement curves, without any modification to the standard AFM apparatus. The comparison of the three cell lines show that the non-tumorigenic cells are less deformable and more viscous than cancerous cells, and that cancer cell lines have distinctive viscoelastic properties. In particular, we obtained that ERC-124 > EA-498 > EACHN and ηRC-124 > ηA-498 > ηACHN.

  10. Measurement of Viscoelastic Properties of Condensed Matter using Magnetic Resonance Elastography

    NASA Astrophysics Data System (ADS)

    Gruwel, Marco L. H.; Latta, Peter; Matwiy, Brendon; Sboto-Frankenstein, Uta; Gervai, Patricia; Tomanek, Boguslaw

    2010-01-01

    Magnetic resonance elastography (MRE) is a phase contrast technique that provides a non-invasive means of evaluating the viscoelastic properties of soft condensed matter. This has a profound bio-medical significance as it allows for the virtual palpation of areas of the body usually not accessible to the hands of a medical practitioner, such as the brain. Applications of MRE are not restricted to bio-medical applications, however, the viscoelastic properties of prepackaged food products can also non-invasively be determined. Here we describe the design and use of a modular MRE acoustic actuator that can be used for experiments ranging from the human brain to pre-packaged food products. The unique feature of the used actuator design is its simplicity and flexibility, which allows easy reconfiguration.

  11. The viscoelastic properties of chromatin and the nucleoplasm revealed by scale-dependent protein mobility.

    PubMed

    Erdel, Fabian; Baum, Michael; Rippe, Karsten

    2015-02-18

    The eukaryotic cell nucleus harbours the DNA genome that is organized in a dynamic chromatin network and embedded in a viscous crowded fluid. This environment directly affects enzymatic reactions and target search processes that access the DNA sequence information. However, its physical properties as a reaction medium are poorly understood. Here, we exploit mobility measurements of differently sized inert green fluorescent tracer proteins to characterize the viscoelastic properties of the nuclear interior of a living human cell. We find that it resembles a viscous fluid on small and large scales but appears viscoelastic on intermediate scales that change with protein size. Our results are consistent with simulations of diffusion through polymers and suggest that chromatin forms a random obstacle network rather than a self-similar structure with fixed fractal dimensions. By calculating how long molecules remember their previous position in dependence on their size, we evaluate how the nuclear environment affects search processes of chromatin targets.

  12. The viscoelastic properties of chromatin and the nucleoplasm revealed by scale-dependent protein mobility

    NASA Astrophysics Data System (ADS)

    Erdel, Fabian; Baum, Michael; Rippe, Karsten

    2015-02-01

    The eukaryotic cell nucleus harbours the DNA genome that is organized in a dynamic chromatin network and embedded in a viscous crowded fluid. This environment directly affects enzymatic reactions and target search processes that access the DNA sequence information. However, its physical properties as a reaction medium are poorly understood. Here, we exploit mobility measurements of differently sized inert green fluorescent tracer proteins to characterize the viscoelastic properties of the nuclear interior of a living human cell. We find that it resembles a viscous fluid on small and large scales but appears viscoelastic on intermediate scales that change with protein size. Our results are consistent with simulations of diffusion through polymers and suggest that chromatin forms a random obstacle network rather than a self-similar structure with fixed fractal dimensions. By calculating how long molecules remember their previous position in dependence on their size, we evaluate how the nuclear environment affects search processes of chromatin targets.

  13. In Vivo Evaluation of the Mechanical and Viscoelastic Properties of the Rat Tongue.

    PubMed

    Loro, Emanuele; Wang, Stephen H; Schwab, Richard J; Khurana, Tejvir S

    2017-07-06

    The tongue is a highly innervated and vascularized muscle hydrostat on the floor of the mouth of most vertebrates. Its primary functions include supporting mastication and deglutition, as well as taste-sensing and phonetics. Accordingly, the strength and volume of the tongue can impact the ability of vertebrates to accomplish basic activities such as feeding, communicating, and breathing. Human patients with sleep apnea have enlarged tongues, characterized by reduced muscle tone and increased intramuscular fat that can be visualized and quantified by magnetic resonance imaging (MRI). The abilities to measure force generation and viscoelastic properties of the tongue constitute important tools for obtaining functional information to correlate with imaging data. Here, we present techniques for measuring tongue force production in anesthetized Zucker rats via electrical stimulation of the hypoglossal nerves and for determining the viscoelastic properties of the tongue by applying passive Lissajous force/deformation curves.

  14. Non linear viscoelasticity applied for the study of durability of polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Cardon, A.; Brinson, H. F.; Hiel, C. C.

    1989-01-01

    A methodology is described for the durability analysis of polymer matrix composites, based on nonlinear viscoelasticity theory. The durability analysis is performed on the basis of a certain number of tests carried out on limited and, if possible, short time scale by the use of accelerating factors. The method was applied to thermomatrix composites under uniaxial and biaxial loadings, showing satisfactory agreement between the life-time predictions and the published data on real-time behavior.

  15. Viscoelastic properties of passive skeletal muscle in compression-cyclic behaviour.

    PubMed

    Van Loocke, M; Simms, C K; Lyons, C G

    2009-05-29

    Skeletal muscle relaxation behaviour in compression has been previously reported, but the anisotropic behaviour at higher loading rates remains poorly understood. In this paper, uniaxial unconfined cyclic compression tests were performed on fresh porcine muscle samples at various fibre orientations to determine muscle viscoelastic behaviour. Mean compression level of 25% was applied and cycles of 2% and 10% amplitude were performed at 0.2-80Hz. Under cycles of low frequency and amplitude, linear viscoelastic cyclic relaxation was observed. Fibre/cross-fibre results were qualitatively similar, but the cross-fibre direction was stiffer (ratio of 1.2). In higher amplitude tests nonlinear viscoelastic behaviour with a frequency dependent increase in the stress cycles amplitude was found (factor of 4.1 from 0.2 to 80Hz). The predictive capability of an anisotropic quasi-linear viscoelastic model previously fitted to stress-relaxation data from similar tissue samples was investigated. Good qualitative results were obtained for low amplitude cycles but differences were observed in the stress cycle amplitudes (errors of 7.5% and 31.8%, respectively, in the fibre/cross-fibre directions). At higher amplitudes significant qualitative and quantitative differences were evident. A nonlinear model formulation was therefore developed which provided a good fit and predictions to high amplitude low frequency cyclic tests performed in the fibre/cross-fibre directions. However, this model gave a poorer fit to high frequency cyclic tests and to relaxation tests. Neither model adequately predicts the stiffness increase observed at frequencies above 5Hz. Together with data previously presented, the experimental data presented here provide a unique dataset for validation of future constitutive models for skeletal muscle in compression.

  16. Viscoelastic and Transport Properties of Sulfonated PS-PIB-PS Block Copolymers

    DTIC Science & Technology

    2001-05-01

    000 1200 Time (min) Figure 13. IR intensity vs. time for ethanol through three sulfonated P5-PIB- PS membranes. Figure 14 shows a comparison of four ...sulfonated PS -PIB- PS membrane. Table 1 shows a comparison of the equilibrium sorbtion values for the four alcohols in the sulfonated PS -PIB- PS . Table 1...Army Research Laboratory Aberdeen Proving Ground, MD 21005-5069 ARL-TR-2482 May2001 Viscoelastic and Transport Properties of Sulfonated PS -PIB- PS

  17. Constitutive Equations: Plastic and Viscoelastic Properties. (Latest Citations from the Aerospace Database)

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The bibliography contains citations concerning analytical techniques using constitutive equations, applied to materials under stress. The properties explored with these techniques include viscoelasticity, thermoelasticity, and plasticity. While many of the references are general as to material type, most refer to specific metals or composites, or to specific shapes, such as flat plate or spherical vessels. (Contains 50-250 citations and includes a subject term index and title list.)

  18. Constitutive Equations: Plastic and Viscoelastic Properties. (Latest Citations from the Aerospace Database)

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The bibliography contains citations concerning analytical techniques using constitutive equations, applied to materials under stress. The properties explored with these techniques include viscoelasticity, thermoelasticity, and plasticity. While many of the references are general as to material type, most refer to specific metals or composites, or to specific shapes, such as flat plate or spherical vessels. (Contains 50-250 citations and includes a subject term index and title list.)

  19. The viscoelastic properties of the vitreous humor measured using an optically trapped local probe

    NASA Astrophysics Data System (ADS)

    Watts, Fiona; Tan, Lay Ean; Tassieri, Manlio; McAlinden, Niall; Wilson, Clive G.; Girkin, John M.; Wright, Amanda J.

    2011-10-01

    We present results demonstrating for the first time that an optically trapped bead can be used as a local probe to measure the variation in the viscoelastic properties of the vitreous humor of a rabbit eye. The Brownian motion of the optically trapped bead was monitored on a fast CCD camera on the millisecond timescale. Analysis of the bead trajectory provides local information about the viscoelastic properties of the medium surrounding the particle. Previous, bulk, methods for measuring the viscoelastic properties of the vitreous destroy the sample and allow only a single averaged measurement to be taken per eye. Whereas, with our approach, we were able to observe local behaviour typical of non-Newtonian and gel-like materials, along with the homogenous and in-homogeneous nature of different regions of the dissected vitreous humor. The motivation behind these measurements is to gain a better understanding of the structure of the vitreous humor in order to design effective drug delivery techniques. In particular, we are interested in methods for delivering drug to the retina of the eye in order to treat sight threatening diseases such as age related macular degeneration.

  20. Viscoelastic properties of the ferret brain measured in vivo at multiple frequencies by magnetic resonance elastography

    PubMed Central

    Feng, Y.; Clayton, E.H.; Chang, Y.; Okamoto, R.J.; Bayly, P.V.

    2013-01-01

    Characterization of the dynamic mechanical behavior of brain tissue is essential for understanding and simulating the mechanisms of traumatic brain injury (TBI). Changes in mechanical properties may also reflect changes in the brain due to aging or disease. In this study, we used magnetic resonance elastography (MRE) to measure the viscoelastic properties of ferret brain tissue in vivo. Three-dimensional (3D) displacement fields were acquired during wave propagation in the brain induced by harmonic excitation of the skull at 400 Hz, 600 Hz and 800 Hz. Shear waves with wavelengths on the order of millimeters were clearly visible in the displacement field, in strain fields, and in the curl of displacement field (which contains no contributions from longitudinal waves). Viscoelastic parameters (storage and loss moduli) governing dynamic shear deformation were estimated in gray and white matter for these excitation frequencies. To characterize the reproducibility of measurements, two ferrets were studied on three different dates each. Estimated viscoelastic properties of white matter in the ferret brain were generally similar to those of gray matter and consistent between animals and scan dates. In both tissue types G′ increased from approximately 3 kPa at 400 Hz to 7 kPa at 800 Hz and G″ increased from approximately 1 kPa at 400 Hz to 2 kPa at 800 Hz. These measurements of shear wave propagation in the ferret brain can be used to both parameterize and validate finite element models of brain biomechanics. PMID:23352648

  1. Ultrasonic and Viscoelastic Properties of Small-Volume Mesogen Samples at the Phase Transition

    NASA Astrophysics Data System (ADS)

    Maksimochkin, G. I.; Pasechnik, S. V.; Usol'Zeva, N. V.; Bykova, V. V.

    2010-06-01

    The ultrasonic method is very informative for research of viscoelastic properties of mesogens at changing thermodynamic parameters of state. At phase transitions, anomalies of the velocity of propagation and coefficient of absorption of ultrasound waves as well as of viscoelastic properties are observed. These anomalies for liquid crystals are most pronounced at frequencies lower that 1 MHz. Up to now acoustic resonators with volumes of about 5 cm3 have been used, which considerably prevents the application of this method for science-based newly synthesized mesogenic compounds. This article presents experimental results obtained by means of a new resonator method with samples with volumes of 0.06 cm3 to 0.15 cm3. The velocity and coefficient of absorption of ultrasound were measured at frequencies from 0.68 MHz to 1.63 MHz for four mesogens: esters of alkyloxyphenylcyclo-hexane-2-carbonic acid and n-amylphenol. It has been shown that temperature dependencies of ultrasonic parameters obtained in small-volume cells correspond to those established previously by traditional methods using measuring cells with larger volumes. It is also shown that the temperature dependencies of the bulk viscosity and the bulk elasticity modulus derived from our ultrasonic measurements, in general features, duplicate the corresponding dependencies obtained by standard methods. It confirms that the proposed acoustic method is suitable for routine investigations of viscoelastic properties of small-volume samples of mesogenic compounds.

  2. Local Viscoelastic Properties of Live Cells Investigated Using Dynamic and Quasi-Static Atomic Force Microscopy Methods

    PubMed Central

    Cartagena, Alexander; Raman, Arvind

    2014-01-01

    The measurement of viscoelasticity of cells in physiological environments with high spatio-temporal resolution is a key goal in cell mechanobiology. Traditionally only the elastic properties have been measured from quasi-static force-distance curves using the atomic force microscope (AFM). Recently, dynamic AFM-based methods have been proposed to map the local in vitro viscoelastic properties of living cells with nanoscale resolution. However, the differences in viscoelastic properties estimated from such dynamic and traditional quasi-static techniques are poorly understood. In this work we quantitatively reconstruct the local force and dissipation gradients (viscoelasticity) on live fibroblast cells in buffer solutions using Lorentz force excited cantilevers and present a careful comparison between mechanical properties (local stiffness and damping) extracted using dynamic and quasi-static force spectroscopy methods. The results highlight the dependence of measured viscoelastic properties on both the frequency at which the chosen technique operates as well as the interactions with subcellular components beyond certain indentation depth, both of which are responsible for differences between the viscoelasticity property maps acquired using the dynamic AFM method against the quasi-static measurements. PMID:24606928

  3. Viscoelastic properties of human and bovine articular cartilage: a comparison of frequency-dependent trends.

    PubMed

    Temple, Duncan K; Cederlund, Anna A; Lawless, Bernard M; Aspden, Richard M; Espino, Daniel M

    2016-10-06

    The purpose of this study was to compare the frequency-dependent viscoelastic properties of human and bovine cartilage. Full-depth cartilage specimens were extracted from bovine and human femoral heads. Using dynamic mechanical analysis, the viscoelastic properties of eight bovine and six human specimens were measured over the frequency range 1 Hz to 88 Hz. Significant differences between bovine and human cartilage viscoelastic properties were assessed using a Mann-Whitney test (p < 0.05). Throughout the range of frequencies tested and for both species, the storage modulus was greater than the loss modulus and both were frequency-dependent. The storage and loss moduli of all human and bovine cartilage specimens presented a logarithmic relationship with respect to frequency. The mean human storage modulus ranged from 31.9 MPa to 43.3 MPa, while the mean bovine storage modulus ranged from 54.0 MPa to 80.5 MPa; bovine storage moduli were 1.7 to 1.9 times greater than the human modulus. Similarly, the loss modulus of bovine cartilage was 2.0 to 2.1 times greater than human. The mean human loss modulus ranged from 5.3 MPa to 8.5 MPa while bovine moduli ranged from 10.6 MPa to 18.1 MPa. Frequency-dependent viscoelastic trends of bovine articular cartilage were consistent with those of human articular cartilage; this includes a similar frequency dependency and high-frequency plateau. Bovine cartilage was, however, 'stiffer' than human by a factor of approximately 2. With these provisos, bovine articular cartilage may be a suitable dynamic model for human articular cartilage.

  4. High Resolution Imaging of Viscoelastic Properties of Intracranial Tumours by Multi-Frequency Magnetic Resonance Elastography.

    PubMed

    Reiss-Zimmermann, M; Streitberger, K-J; Sack, I; Braun, J; Arlt, F; Fritzsch, D; Hoffmann, K-T

    2015-12-01

    In recent years Magnetic Resonance Elastography (MRE) emerged into a clinically applicable imaging technique. It has been shown that MRE is capable of measuring global changes of the viscoelastic properties of cerebral tissue. The purpose of our study was to evaluate a spatially resolved three-dimensional multi-frequent MRE (3DMMRE) for assessment of the viscoelastic properties of intracranial tumours. A total of 27 patients (63 ± 13 years) were included. All examinations were performed on a 3.0 T scanner, using a modified phase-contrast echo planar imaging sequence. We used 7 vibration frequencies in the low acoustic range with a temporal resolution of 8 dynamics per wave cycle. Post-processing included multi-frequency dual elasto-visco (MDEV) inversion to generate high-resolution maps of the magnitude |G*| and the phase angle φ of the complex valued shear modulus. The tumour entities included in this study were: glioblastoma (n = 11), anaplastic astrocytoma (n = 3), meningioma (n = 7), cerebral metastasis (n = 5) and intracerebral abscess formation (n = 1). Primary brain tumours and cerebral metastases were not distinguishable in terms of |G*| and φ. Glioblastoma presented the largest range of |G*| values and a trend was delineable that glioblastoma were slightly softer than WHO grade III tumours. In terms of φ, meningiomas were clearly distinguishable from all other entities. In this pilot study, while analysing the viscoelastic constants of various intracranial tumour entities with an improved spatial resolution, it was possible to characterize intracranial tumours by their mechanical properties. We were able to clearly delineate meningiomas from intraaxial tumours, while for the latter group an overlap remains in viscoelastic terms.

  5. Deformation and relaxation of an incompressible viscoelastic body with surface viscoelasticity

    NASA Astrophysics Data System (ADS)

    Liu, Liping; Yu, Miao; Lin, Hao; Foty, Ramsey

    2017-01-01

    Measuring mechanical properties of cells or cell aggregates has proven to be an involved process due to their geometrical and structural complexity. Past measurements are based on material models that completely neglect the elasticity of either the surface membrane or the interior bulk. In this work, we consider general material models to account for both surface and bulk viscoelasticity. The boundary value problems are formulated for deformations and relaxations of a closed viscoelastic surface coupled with viscoelastic media inside and outside of the surface. The linearized surface elasticity models are derived for the constant surface tension model and the Helfrich-Canham bending model for coupling with the bulk viscoelasticity. For quasi-spherical surfaces, explicit solutions are obtained for the deformation, stress-strain and relaxation behaviors under a variety of loading conditions. These solutions can be applied to extract the intrinsic surface and bulk viscoelastic properties of biological cells or cell aggregates in the indentation, electro-deformation and relaxation experiments.

  6. Relationship between powder surface characteristics and viscoelastic properties of powder-filled semisolids.

    PubMed

    Radebaugh, G W; Simonelli, A P

    1985-01-01

    The viscoelastic properties of dispersions of powdered zinc oxide in anhydrous lanolin and colloidal sulfur in anhydrous lanolin were characterized by dynamic mechanical testing. The elastic shear modulus, G', viscous shear modulus, G", and loss tangent (damping), tan delta, were determined as a function of shear frequency, v, temperature, T, and volume fraction of powder, phi 2. A priori, it might be expected that zinc oxide and colloidal sulfur would elicit different viscoelastic properties due to their contrasting surface characteristics; zinc oxide has a hydrophilic surface and colloidal sulfur has a hydrophobic surface. Even though constitutive mathematical models, derived to predict the mechanical behavior of solid-filled polymeric materials, were not designed to account for differences in surface characteristics of the filler, the findings of these experiments show that these models are useful in explaining the differences in viscoelastic behavior of powder-filled semisolids due to surface characteristics of the filler. One model of particular value was the Kerner equation. With it, mechanisms were postulated for zinc oxide-zinc oxide interactions, sulfur-sulfur interactions, zinc oxide-anhydrous lanolin interactions, and sulfur-anhydrous lanolin interactions, within dispersions as a function of nu, T, and phi 2. In addition, damping was used to further identify the influence of temperature. Data obtained from three temperatures, where anhydrous lanolin exists in three different structural states, shows that the influence of the powder on damping is not only determined by the surface characteristics of the powder but also the structural state of anhydrous lanolin.

  7. Quantitative characterization of viscoelastic properties of human prostate correlated with histology.

    PubMed

    Zhang, Man; Nigwekar, Priya; Castaneda, Benjamin; Hoyt, Kenneth; Joseph, Jean V; di Sant'Agnese, Anthony; Messing, Edward M; Strang, John G; Rubens, Deborah J; Parker, Kevin J

    2008-07-01

    Quantification of mechanical properties of human prostate tissue is important for developing sonoelastography for prostate cancer detection. In this study, we characterized the frequency-dependent complex Young's modulus of normal and cancerous prostate tissues in vitro by using stress relaxation testing and viscoelastic tissue modeling methods. After radical prostatectomy, small cylindrical tissue samples were acquired in the posterior region of each prostate. A total of 17 samples from eight human prostates were obtained and tested. Stress relaxation tests on prostate samples produced repeatable results that fit a viscoelastic Kelvin-Voigt fractional derivative (KVFD) model (r(2)>0.97). For normal (n = 8) and cancerous (n = 9) prostate samples, the average magnitudes of the complex Young's moduli (|E*|) were 15.9 +/- 5.9 kPa and 40.4 +/- 15.7 kPa at 150 Hz, respectively, giving an elastic contrast of 2.6:1. Nine two-sample t-tests indicated that there are significant differences between stiffness of normal and cancerous prostate tissues in the same gland (p < 0.01). This study contributes to the current limited knowledge on the viscoelastic properties of the human prostate, and the inherent elastic contrast produced by cancer.

  8. Viscoelastic properties of tablets from Osborne fractions, pentosans, flour and bread evaluated by creep tests

    NASA Astrophysics Data System (ADS)

    Escalante-Aburto, Anayansi; de Dios Figueroa-Cárdenas, Juan; Véles-Medina, José Juan; Ponce-García, Néstor; Hernández-Estrada, Zorba Josué; Rayas-Duarte, Patricia; Simsek, Senay

    2017-07-01

    Little attention has been given to the influence of non-gluten components on the viscoelastic properties of wheat flour dough, bread making process and their products. The aim of this study was to evaluate by creep tests the viscoelastic properties of tablets manufactured from Osborne solubility fractions (globulins, gliadins, glutenins, albumins and residue), pentosans, flour and bread. Hard and soft wheat cultivars were used to prepare the reconstituted tablets. Sintered tablets (except flour and bread) showed similar values to those obtained from the sum of the regression coefficients of the fractions. Gliadins and albumins accounted for about 54% of the total elasticity. Gliadins contributed with almost half of the total viscosity (45.7%), and showed the highest value for the viscosity coefficient of the viscous element. When the effect of dilution was evaluated, the residue showed the highest instantaneous elastic modulus (788.2 MPa). Retardation times of the first element (λ1 3.5 s) were about 10 times lower than the second element (λ2 39.3 s). The analysis of compliance of data corrected by protein content in flour showed that the residue fraction presented the highest values. An important contribution of non-gluten components (starch, albumins and globulins) on the viscoelastic performance of sintered tablets from Osborne fractions, flour and bread was found.

  9. Soft viscoelastic properties of nuclear actin age oocytes due to gravitational creep

    PubMed Central

    Feric, Marina; Broedersz, Chase P.; Brangwynne, Clifford P.

    2015-01-01

    The actin cytoskeleton helps maintain structural organization within living cells. In large X. laevis oocytes, gravity becomes a dominant force and is countered by a nuclear actin network that prevents liquid-like nuclear bodies from immediate sedimentation and coalescence. However, nuclear actin’s mechanical properties, and how they facilitate the stabilization of nuclear bodies, remain unknown. Using active microrheology, we find that nuclear actin forms a weak viscoelastic network, with a modulus of roughly 0.1 Pa. Embedded probe particles subjected to a constant force exhibit continuous displacement, due to viscoelastic creep. Gravitational forces also cause creep displacement of nuclear bodies, resulting in their asymmetric nuclear distribution. Thus, nuclear actin does not indefinitely support the emulsion of nuclear bodies, but only kinetically stabilizes them by slowing down gravitational creep to ~2 months. This is similar to the viability time of large oocytes, suggesting gravitational creep ages oocytes, with fatal consequences on long timescales. PMID:26577186

  10. Comparison of dynamic viscoelastic and physicochemical properties of pressurised and pasteurised longan juices with xanthan addition.

    PubMed

    Chaikham, Pittaya; Apichartsrangkoon, Arunee

    2012-10-15

    Physical and biochemical properties of pressurised and pasteurised longan juices with various xanthan additions, such as viscoelastic behaviour, colour L (lightness), -a(*) (greenness), b(*) (yellowness), ΔE (total different colours) and BI (Browning Index) parameters, polyphenol oxidase (PPO) activity, ascorbic acid, gallic acid, ellagic acid, total phenols and antioxidant capacity (DPPH assay) were studied. Viscoelastic determination indicated that longan juice with 0.15% xanthan addition was optimal for a fruit drink. Colour parameters showed pressurised longan juice at 500 MPa was brighter and more transparent than fresh and other processed juices. PPO was completely inactivated in pasteurised juices, whereas in pressurised juices at 300 and 500 MPa, the activities were more than 100% and 95-99%, respectively. Bioactive components including ascorbic acid were significantly reduced according to treatment severities, whereas gallic and ellagic acids were relatively stable in all processed juices. Total phenols and DPPH radical-scavenging activity decreased significantly on pasteurisation, but were stable on pressurisation.

  11. Soft viscoelastic properties of nuclear actin age oocytes due to gravitational creep.

    PubMed

    Feric, Marina; Broedersz, Chase P; Brangwynne, Clifford P

    2015-11-18

    The actin cytoskeleton helps maintain structural organization within living cells. In large X. laevis oocytes, gravity becomes a dominant force and is countered by a nuclear actin network that prevents liquid-like nuclear bodies from immediate sedimentation and coalescence. However, nuclear actin's mechanical properties, and how they facilitate the stabilization of nuclear bodies, remain unknown. Using active microrheology, we find that nuclear actin forms a weak viscoelastic network, with a modulus of roughly 0.1 Pa. Embedded probe particles subjected to a constant force exhibit continuous displacement, due to viscoelastic creep. Gravitational forces also cause creep displacement of nuclear bodies, resulting in their asymmetric nuclear distribution. Thus, nuclear actin does not indefinitely support the emulsion of nuclear bodies, but only kinetically stabilizes them by slowing down gravitational creep to ~2 months. This is similar to the viability time of large oocytes, suggesting gravitational creep ages oocytes, with fatal consequences on long timescales.

  12. Calculation by iterative method of linear viscoelastic plate under biaxial tension

    NASA Astrophysics Data System (ADS)

    Svetashkov, A. A.; Miciński, J.; Manabaev, K. K.; Vakurov, A. A.

    2017-02-01

    In this paper, we used the iterative solution algorithm, proposed in the work of Pavlov and Svetashkova. This algorithm results in a complete separation of spatial and temporal variables, if we set up the boundary loads and (or) volumetric forces in the same kind. In this paper, we have examined the stress-strain state of a viscoelastic plate, and the results of the calculation displacements, stresses are given. In addition, we made a comparison of the calculation indices rate of convergence for the iterative process with their theoretical values.

  13. Single-Specimen Technique to Establish the J-Resistance of Linear Viscoelastic Solids with Constant Poisson's Ratio

    NASA Technical Reports Server (NTRS)

    Gutierrez-Lemini, Danton; McCool, Alex (Technical Monitor)

    2001-01-01

    A method is developed to establish the J-resistance function for an isotropic linear viscoelastic solid of constant Poisson's ratio using the single-specimen technique with constant-rate test data. The method is based on the fact that, for a test specimen of fixed crack size under constant rate, the initiation J-integral may be established from the crack size itself, the actual external load and load-point displacement at growth initiation, and the relaxation modulus of the viscoelastic solid, without knowledge of the complete test record. Since crack size alone, of the required data, would be unknown at each point of the load-vs-load-point displacement curve of a single-specimen test, an expression is derived to estimate it. With it, the physical J-integral at each point of the test record may be established. Because of its basis on single-specimen testing, not only does the method not require the use of multiple specimens with differing initial crack sizes, but avoids the need for tracking crack growth as well.

  14. Morphology and viscoelastic properties of sealing materials based on EPDM rubber.

    PubMed

    Milić, J; Aroguz, A; Budinski-Simendić, J; Radicević, R; Prendzov, S

    2008-12-01

    In this applicative study, the ratio of active and inactive filler loadings was the prime factor for determining the dynamic-mechanical behaviour of ethylene-propylene-diene monomer rubbers. Scanning electron microscopy was used to study the structure of reinforced dense and microcellular elastomeric materials. The effects of filler and blowing agent content on the morphology of composites were investigated. Microcellular samples cured in salt bath show smaller cells and uniform cell size compared with samples cured in hot air. Dynamic-mechanical thermal analysis showed appreciable changes in the viscoelastic properties by increasing active filler content, which could enable tailoring the material properties to suit sealing applications.

  15. Measurement of visco-elastic properties of breast-tissue mimicking materials using diffusing wave spectroscopy.

    PubMed

    Devi, C Usha; Bharat Chandran, R Sreekumari; Vasu, R Mohan; Sood, Ajay K

    2007-01-01

    Diffusing wave spectroscopy (DWS), without the use of tracer particles, has been used to study the internal dynamics of polyvinyl alcohol (PVA) phantoms, which mimic the properties of normal and malignant breast tissues. From the measured intensity autocorrelations, the mean square displacement (MSD) of phantom meshing is estimated, leading to the storage and loss moduli of the medium covering frequencies up to 10 KHz. These are verified with independent measurements from a dynamic mechanical analyzer (DMA) at low frequencies. We thus prove the usefulness of DWS to extract visco-elastic properties of the phantom and its possible application in detecting malignancy in soft tissues.

  16. Viscoelastic Properties and Morphology of Mumio-based Medicated Hydrogels

    NASA Astrophysics Data System (ADS)

    Zandraa, Oyunchimeg; Jelínková, Lenka; Roy, Niladri; Sáha, Tomáš; Kitano, Takeshi; Saha, Nabanita

    2011-07-01

    Novel medicated hydrogels were prepared (by moist heat treatment) with PVA, agar, mumio, mare's milk (MM), seabuckthorn oil (SB oil) and salicylic acid (SA) for wound dressing/healing application. Scanning electron micrographs (SEM) show highly porous structure of these hydrogels. The swelling behaviour of the hydrogels in physiological solution displays remarkable liquid absorption property. The knowledge obtained from rheological investigations of these-systems may be highly useful for the characterization of the newly developed topical formulations. In the present study, an oscillation frequency sweep test was used for the evaluation of storage modulus (G'), loss modulus (G″), and complex viscosity (η*) of five different formulations, over an angular frequency range from 0.1 to 100 rad.s-1. The influence of healing agents and swelling effect on the rheological properties of mumio-based medicated hydrogels was investigated to judge its application on uneven surface of body.

  17. Viscoelastic Properties of Fluorinated Ethylene-Propylene (FEP) Random Copolymers

    NASA Astrophysics Data System (ADS)

    Curtin, Megan; Wright, Benjamin; Ozisik, Rahmi

    Florinated ethylene-propylene (FEP) random copolymers contain tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) repeat units. FEP is an excellent alternative to poly(tetrafluoroethylene), PTFE, which cannot be melt processed due to its high molecular weight and extensive crystallinity. On the other hand, FEP is a melt processible polymer and offers similar if not the same properties as PTFE. Many studies have been performed on FEP over the years, however, the properties of these polymers strongly depend on the HFP concentration and molecular weight (distribution). Just like PTFE, FEP cannot be dissolved in many solvents, therefore, obtaining molecular weight distribution of these polymers is not possible with commonly used methods. In the current study, we perform rheological analysis of various FEPs and obtain their molecular weight distributions by employing the Tuminello method. This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1538730.

  18. A new method to improve the clinical evaluation of cystic fibrosis patients by mucus viscoelastic properties.

    PubMed

    Tomaiuolo, Giovanna; Rusciano, Giulia; Caserta, Sergio; Carciati, Antonio; Carnovale, Vincenzo; Abete, Pasquale; Sasso, Antonio; Guido, Stefano

    2014-01-01

    In cystic fibrosis (CF) patients airways mucus shows an increased viscoelasticity due to the concentration of high molecular weight components. Such mucus thickening eventually leads to bacterial overgrowth and prevents mucus clearance. The altered rheological behavior of mucus results in chronic lung infection and inflammation, which causes most of the cases of morbidity and mortality, although the cystic fibrosis complications affect other organs as well. Here, we present a quantitative study on the correlation between cystic fibrosis mucus viscoelasticity and patients clinical status. In particular, a new diagnostic parameter based on the correlation between CF sputum viscoelastic properties and the severity of the disease, expressed in terms of FEV1 and bacterial colonization, was developed. By using principal component analysis, we show that the types of colonization and FEV1 classes are significantly correlated to the elastic modulus, and that the latter can be used for CF severity classification with a high predictive efficiency (88%). The data presented here show that the elastic modulus of airways mucus, given the high predictive efficiency, could be used as a new clinical parameter in the prognostic evaluation of cystic fibrosis.

  19. Role of EVA viscoelastic properties in the protective performance of a sport shoe: computational studies.

    PubMed

    Even-Tzur, Nurit; Weisz, Ety; Hirsch-Falk, Yifat; Gefen, Amit

    2006-01-01

    Modern sport shoes are designed to attenuate mechanical stress waves, mainly through deformation of the viscoelastic midsole which is typically made of ethylene vinyl acetate (EVA) foam. Shock absorption is obtained by flow of air through interconnected air cells in the EVA during shoe deformation under body-weight. However, when the shoe is overused and air cells collapse or thickness of the EVA is reduced, shock absorption capacity may be affected, and this may contribute to running injuries. Using lumped system and finite element models, we studied heel pad stresses and strains during heel-strike in running, considering the viscoelastic constitutive behavior of both the heel pad and EVA midsole. In particular, we simulated wear cases of the EVA, manifested in the modeling by reduced foam thickness, increased elastic stiffness, and shorter stress relaxation with respect to new shoe conditions. Simulations showed that heel pad stresses and strains were sensitive to viscous damping of the EVA. Wear of the EVA consistently increased heel pad stresses, and reduced EVA thickness was the most influential factor, e.g., for a 50% reduction in thickness, peak heel pad stress increased by 19%. We conclude that modeling of the heel-shoe interaction should consider the viscoelastic properties of the tissue and shoe components, and the age of the studied shoe.

  20. Internal structure and thermo-viscoelastic properties of agar ionogels.

    PubMed

    Sharma, Anshu; Rawat, Kamla; Solanki, Pratima R; Aswal, V K; Kohlbrecher, J; Bohidar, H B

    2015-12-10

    Ionic liquids (IL) can alter the physical properties of agar hydrogels. Rheology studies show that gels with wide range of storage moduli (gel strength) G0 values ranging from 1 to 20 KPa could be made in imidazolium based IL solutions where the IL concentration may not exceed 5% (w/v). Gelation and gel melting temperatures (tgel and Tm) could be altered by as much as ≈ 10 °C. Small angle neutron scattering studies revealed the presence of fibre bundles of agar double helices having typical length of 120 nm that increased to ≈ 180 nm under favorable conditions. These structures gain flexibility from the cladding of the agar bundles by IL molecules which in turn caused partial charge neutralization of its surface. Raman spectroscopy revealed differential hydration of these bundles. It was found that IL molecules with longer alkyl chain (more hydrophobic) altered the gel homogeneity, and changed its thermal and mechanical properties significantly. Therefore, customization of agar hydrogels in green solvent medium (IL solutions) widens the scope of its application potential that may include sensing. Copyright © 2015 Elsevier Ltd. All rights reserved.

  1. Human cervical spine ligaments exhibit fully nonlinear viscoelastic behavior.

    PubMed

    Troyer, Kevin L; Puttlitz, Christian M

    2011-02-01

    Spinal ligaments provide stability and contribute to spinal motion patterns. These hydrated tissues exhibit time-dependent behavior during both static and dynamic loading regimes. Therefore, accurate viscoelastic characterization of these ligaments is requisite for development of computational analogues that model and predict time-dependent spine behavior. The development of accurate viscoelastic models must be preceded by rigorous, empirical evidence of linear viscoelastic, quasi-linear viscoelastic (QLV) or fully nonlinear viscoelastic behavior. This study utilized multiple physiological loading rates (frequencies) and strain amplitudes via cyclic loading and stress relaxation experiments in order to determine the viscoelastic behavior of the human lower cervical spine anterior longitudinal ligament, the posterior longitudinal ligament and the ligamentum flavum. The results indicated that the cyclic material properties of these ligaments were dependent on both strain amplitude and frequency. This strain amplitude-dependent behavior cannot be described using a linear viscoelastic formulation. Stress relaxation experiments at multiple strain magnitudes indicated that the shape of the relaxation curve was strongly dependent on strain magnitude, suggesting that a QLV formulation cannot adequately describe the comprehensive viscoelastic response of these ligaments. Therefore, a fully nonlinear viscoelastic formulation is requisite to model these lower cervical spine ligaments during activities of daily living. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  2. Measurement of quantitative viscoelasticity of bovine corneas based on lamb wave dispersion properties.

    PubMed

    Zhang, Xinyu; Yin, Yin; Guo, Yanrong; Fan, Ning; Lin, Haoming; Liu, Fulong; Diao, Xianfen; Dong, Changfeng; Chen, Xin; Wang, Tianfu; Chen, Siping

    2015-05-01

    The viscoelastic properties of the human cornea can provide valuable information for clinical applications such as the early detection of corneal diseases, better management of corneal surgery and treatment and more accurate measurement of intra-ocular pressure. However, few techniques are capable of quantitatively and non-destructively assessing corneal biomechanics in vivo. The cornea can be regarded as a thin plate in which the vibration induced by an external vibrator propagates as a Lamb wave, the properties of which depend on the thickness and biomechanics of the tissue. In this study, pulses of ultrasound radiation force with a repetition frequency of 100 or 200 Hz were applied to the apex of corneas, and the linear-array transducer of a SonixRP system was used to track the tissue motion in the radial direction. Shear elasticity and viscosity were estimated from the phase velocities of the A0 Lamb waves. To assess the effectiveness of the method, some of the corneas were subjected to collagen cross-linking treatment, and the changes in mechanical properties were validated with a tensile test. The results indicated that the shear modulus was 137 ± 37 kPa and the shear viscosity was 3.01 ± 2.45 mPa · s for the group of untreated corneas and 1145 ± 267 kPa and was 0.16 ± 0.11 mPa · s for the treated group, respectively, implying a significant increase in elasticity and a significant decrease in viscosity after collagen cross-linking treatment. This result is in agreement with the results of the mechanical tensile test and with reports in the literature. This initial investigation illustrated the ability of this ultrasound-based method, which uses the velocity dispersion of low-frequency A0 Lamb waves, to quantitatively assess both the elasticity and viscosity of corneas. Future studies could discover ways to optimize this system and to determine the feasibility of using this method in clinical situations. Copyright © 2015 World Federation for Ultrasound

  3. Viscoelastic Properties Measurement of Human Lymphocytes by Atomic Force Microscopy Based on Magnetic Beads Cell Isolation.

    PubMed

    Li, Mi; Liu, Lianqing; Xiao, Xiubin; Xi, Ning; Wang, Yuechao

    2016-03-28

    Cell mechanics has been proved to be an effective biomarker for indicating cellular states. The advent of atomic force microscopy (AFM) provides an exciting instrument for measuring the mechanical properties of single cells. However, current AFM single-cell mechanical measurements are commonly performed on cell lines cultured in vitro which are quite different from the primary cells in the human body. Investigating the mechanical properties of primary cells from clinical environments can help us to better understand cell behaviors. Here, by combining AFM with magnetic beads cell isolation, the viscoelastic properties of human primary B lymphocytes were quantitatively measured. B lymphocytes were isolated from the peripheral blood of healthy volunteers by density gradient centrifugation and CD19 magnetic beads cell isolation. The activity and specificity of the isolated cells were confirmed by fluorescence microscopy. AFM imaging revealed the surface topography and geometric parameters of B lymphocytes. The instantaneous modulus and relaxation time of living B lymphocytes were measured by AFM indenting technique, showing that the instantaneous modulus of human normal B lymphocytes was 2~3 kPa and the relaxation times were 0.03~0.06 s and 0.35~0.55 s. The differences in cellular visocoelastic properties between primary B lymphocytes and cell lines cultured in vitro were analyzed. The study proves the capability of AFM in quantifying the viscoelastic properties of individual specific primary cells from the blood sample of clinical patients, which will improve our understanding of the behaviors of cells in the human body.

  4. Viscoelastic properties of actin networks influence material transport

    NASA Astrophysics Data System (ADS)

    Stam, Samantha; Weirich, Kimberly; Gardel, Margaret

    2015-03-01

    Directed flows of cytoplasmic material are important in a variety of biological processes including assembly of a mitotic spindle, retraction of the cell rear during migration, and asymmetric cell division. Networks of cytoskeletal polymers and molecular motors are known to be involved in these events, but how the network mechanical properties are tuned to perform such functions is not understood. Here, we construct networks of either semiflexible actin filaments or rigid bundles with varying connectivity. We find that solutions of rigid rods, where unimpeded sliding of filaments may enhance transport in comparison to unmoving tracks, are the fastest at transporting network components. Entangled solutions of semiflexible actin filaments also transport material, but the entanglements provide resistance. Increasing the elasticity of the actin networks with crosslinking proteins slows network deformation further. However, the length scale of correlated transport in these networks is increased. Our results reveal how the rigidity and connectivity of biopolymers allows material transport to occur over time and length scales required for physiological processes. This work was supported by the U. Chicago MRSEC

  5. Viscoelastic properties of kenaf reinforced unsaturated polyester composites

    NASA Astrophysics Data System (ADS)

    Osman, Ekhlas A.; Mutasher, Saad A.

    2014-03-01

    In order to quantify the effect of temperature on the mechanical and dynamic properties of kenaf fiber unsaturated polyester composites, formulations containing 10 wt.% to 40 wt.% kenaf fiber were produced and tested at two representative temperatures of 30°C and 50°C. Dynamic mechanical analysis was performed, to obtain the strain and creep compliance for kenaf composites at various styrene concentrations. It is possible to obtain creep curves at different temperature levels which can be shifted along the time axis to generate a single curve known as a master curve. This technique is known as the time-temperature superposition principle. Shift factors conformed to a William-Landel-Ferry (WLF) equation. However, more long term creep data was needed in order to further validate the applicability of time-temperature superposition principle (TTSP) to this material. The primary creep strain model was fitted to 60 min creep data. The resulting equation was then extrapolated to 5.5 days; the creep strain model of power-law was successfully used to predict the long-term creep behavior of natural fiber/thermoset composites.

  6. Morphological, physicochemical, and viscoelastic properties of sonicated corn starch.

    PubMed

    Mohammad Amini, Asad; Razavi, Seyed Mohammad Ali; Mortazavi, Seyed Ali

    2015-05-20

    In the present work, different parameters of ultrasound treatment were studied for physical modification of corn starch. The results revealed that the influence of sonication strongly depends on temperature (25-65 °C) and exposure time (5-15 min), while concentration (10-20% w/w) and ultrasound amplitude (50 and 100%) have little influence on functional and rheological properties. SEM micrographs demonstrated the damage induced by ultrasound on starch granules' surface. The solubility, swelling power, and gel clarity were increased. Ultrasonication decreased the gelatinisation enthalpy and temperature range while the X-ray pattern and crystallinity remained almost unchanged, except for samples treated at onset temperature as measured by DSC. The pseudoplasticity and consistency coefficient decreased; also, apparent viscosity diminished prominently. The pasting behaviour of samples was altered without any clear change in gel strength characterised by loss factor. The results of the present work provide further insight into the mode of action of ultrasound on modifying corn starch granules.

  7. In vivo brain viscoelastic properties measured by magnetic resonance elastography.

    PubMed

    Green, Michael A; Bilston, Lynne E; Sinkus, Ralph

    2008-08-01

    Magnetic resonance elastography (MRE) is a non-invasive imaging technique used to visualise and quantify mechanical properties of tissue, providing information beyond what can be currently achieved with standard MR sequences and could, for instance, provide new insight into pathological processes in the brain. This study uses the MRE technique at 3 T to extract the complex shear modulus for in vivo brain tissue utilizing a full three-dimensional approach to reconstruction, removing contributions of the dilatational wave by application of the curl operator. A calibrated phantom is used to benchmark the MRE measurements, and in vivo results are presented for healthy volunteers. The results provide data for in vivo brain storage modulus (G'), finding grey matter (3.1 kPa) to be significantly stiffer than white matter (2.7 kPa). The first in vivo loss modulus (G'') measurements show no significant difference between grey matter (2.5 kPa) and white matter (2.5 kPa).

  8. Measuring tendon properties in mdx mice: cell viability and viscoelastic characteristics.

    PubMed

    Rizzuto, E; Musarò, A; Catizone, A; Del Prete, Z

    2009-10-16

    Muscular dystrophy is a genetic disorder of skeletal muscle characterized by progressive muscle weakness. Here we assessed whether muscle wasting affects cell viability and mechanical properties of extensor digitorum longus (EDL) and of tibialis anterior (TA) tendons from mdx dystrophic mice compared to wild type (WT) mice. mdx mice represent the classical animal model for human Duchenne muscular dystrophy, and show several signs of the pathology, including a decrease in specific force and an increase of fibrotic index. Cell viability of tendons was evaluated by histological analysis, and viscoelastic properties have been assessed by a rapid measurement protocol that allowed us to compute, at the same time, tissue complex compliance for all the frequencies of interest. Confocal microscopy and mechanical properties measurements revealed that mdx tendons, compared to WT ones, have an increase in the number of dead cells and a significant reduction in tissue elasticity for all the frequencies that were tested. These findings indicate a reduced quality of the tissue. Moreover, mdx tendons have an increase in the viscous response, indicating that during dynamic loading, they dissipate more energy compared to WT. Our results demonstrate that muscular dystrophy involves not only muscle wasting, but also alteration in the viscoelastic properties of tendons, suggesting a paracrine effect of altered skeletal muscle on tendinous tissue.

  9. Steady flow and viscoelastic properties of lubricating grease containing various thickener concentrations.

    PubMed

    Yeong, S K; Luckham, P F; Tadros, Th F

    2004-06-01

    The flow and viscoelastic properties of a lubricating grease formed from a thickener composed of lithium hydroxystearate and a high-boiling-point mineral oil were investigated as a function of thickener concentration. The flow properties of grease were measured using continuous shear rheometry, while the viscoelastic properties were measured using oscillatory shear measurements. The flow properties show that grease is a shear-thinning fluid with a yield stress that increases with thickener concentration. At concentrations of lithium hydroxystearate greater than 5% by volume, the storage modulus, G', was found to be greater than the loss modulus, G", with both moduli increasing with increasing thickener concentration, below this critical concentration G" was greater than G'. Slip at the wall of the measuring platens was a major problem encountered during the rheological measurement of grease, this is hardly surprising, and greases are designed to slip in their lubricating functions. Therefore the measuring platens were roughened by sandblasting and significantly higher yield values were recorded with the roughened geometries. Creep experiments were also performed. In the creep test, yield stresses of greases could be obtained. Zero shear viscosity was also calculated from the creep experiment and as a result viscosities over nine orders of magnitude were obtained. The power law index of the scaling law of the elastic modulus and yield stress with increasing volume fraction was found to be 4.7+/-0.2 suggesting that the flocculation of the particles that compose the grease is likely to be of the chemically limited aggregation variety.

  10. Viscoelastic properties of the ferret brain measured in vivo at multiple frequencies by magnetic resonance elastography.

    PubMed

    Feng, Y; Clayton, E H; Chang, Y; Okamoto, R J; Bayly, P V

    2013-03-15

    Characterization of the dynamic mechanical behavior of brain tissue is essential for understanding and simulating the mechanisms of traumatic brain injury (TBI). Changes in mechanical properties may also reflect changes in the brain due to aging or disease. In this study, we used magnetic resonance elastography (MRE) to measure the viscoelastic properties of ferret brain tissue in vivo. Three-dimensional (3D) displacement fields were acquired during wave propagation in the brain induced by harmonic excitation of the skull at 400 Hz, 600 Hz and 800 Hz. Shear waves with wavelengths in the order of millimeters were clearly visible in the displacement field, in strain fields, and in the curl of displacement field (which contains no contributions from longitudinal waves). Viscoelastic parameters (storage and loss moduli) governing dynamic shear deformation were estimated in gray and white matter for these excitation frequencies. To characterize the reproducibility of measurements, two ferrets were studied on three different dates each. Estimated viscoelastic properties of white matter in the ferret brain were generally similar to those of gray matter and consistent between animals and scan dates. In both tissue types G' increased from approximately 3 kPa at 400 Hz to 7 kPa at 800 Hz and G″ increased from approximately 1 kPa at 400 Hz to 2 kPa at 800 Hz. These measurements of shear wave propagation in the ferret brain can be used to both parameterize and validate finite element models of brain biomechanics. Copyright © 2013 Elsevier Ltd. All rights reserved.

  11. Flow-Mediated Change in Viscoelastic Property of Radial Arterial Wall Measured by 22 MHz Ultrasound

    NASA Astrophysics Data System (ADS)

    Ikeshita, Kazuki; Hasegawa, Hideyuki; Kanai, Hiroshi

    2009-07-01

    The endothelial dysfunction is considered to be an initial step in atherosclerosis. Additionally, it was reported that the smooth muscle, which constructs the media of the artery, changes its characteristics owing to atherosclerosis. Therefore, it is essential to develop a method of assessing the regional endothelial function and mechanical properties of the arterial wall. To evaluate the endothelial function, a conventional technique of measuring the transient change in the diameter of the brachial artery caused by flow-mediated dilation (FMD) after the release of avascularization is used. However, this method can not evaluate the mechanical properties of the wall. We previously developed a method for the simultaneous measurements of waveforms of radial strain and blood pressure in the radial artery. In this study, the viscoelasticity of the arterial wall was estimated from the measured stress-strain relationship using the least-squares method and the transient changes in the mechanical properties of the arterial wall ware revealed. From in vivo experimental results, the stress-strain relationship showed a hysteresis loop and viscoelasticity was estimated by the proposed method. The slope of the loop decreased owing to FMD, which resulted in the decrease in estimated elastic modulus. The increase in the area of the loop occurred after recirculation, which corresponds to the increase in the ratio of the loss modulus (depends on viscosity) to the elastic modulus when the Voigt model is assumed. In this study, the variance in estimates was evaluated by in vivo measurement for 10 min. The temporal decrease in static elasticity after recirculation due to FMD was much larger than the evaluated variance. These results show a potential of the proposed method for the thorough analysis of the transient change in viscoelasticity due to FMD.

  12. Prediction of fish body's passive visco-elastic properties and related muscle mechanical performance in vivo during steady swimming

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Yu, YongLiang; Tong, BingGang

    2014-01-01

    For attaining the optimized locomotory performance of swimming fishes, both the passive visco-elastic properties of the fish body and the mechanical behavior of the active muscles should coordinate with the fish body's undulatory motion pattern. However, it is difficult to directly measure the visco-elastic constitutive relation and the muscular mechanical performance in vivo. In the present paper, a new approach based on the continuous beam model for steady swimming fish is proposed to predict the fish body's visco-elastic properties and the related muscle mechanical behavior in vivo. Given the lateral travelling-wave-like movement as the input condition, the required muscle force and the energy consumption are functions of the fish body's visco-elastic parameters, i.e. the Young's modulus E and the viscosity coefficient µ in the Kelvin model. After investigating the variations of the propagating speed of the required muscle force with the fish body's visco-elastic parameters, we analyze the impacts of the visco-elastic properties on the energy efficiencies, including the energy utilization ratios of each element of the kinematic chain in fish swimming and the overall efficiency. Under the constraints of reasonable wave speed of muscle activation and the physiological feasibility, the optimal design of the passive visco-elastic properties can be predicted aiming at maximizing the overall efficiency. The analysis is based on the small-amplitude steady swimming of the carangiform swimmer, with typical Reynolds number varying from 2.5×104 to 2.5×105, and the present results show that the non-dimensional Young's modulus is 112±34, and the non-dimensional viscosity coefficient is 13 approximately. In the present estimated ranges, the overall efficiency of the swimming fish is insensitive to the viscosity, and its magnitude is about 0.11±0.02, in the predicted range given by previous study.

  13. Corneal Viscoelastic Properties from Finite-Element Analysis of In Vivo Air-Puff Deformation

    PubMed Central

    Kling, Sabine; Bekesi, Nandor; Dorronsoro, Carlos; Pascual, Daniel; Marcos, Susana

    2014-01-01

    Biomechanical properties are an excellent health marker of biological tissues, however they are challenging to be measured in-vivo. Non-invasive approaches to assess tissue biomechanics have been suggested, but there is a clear need for more accurate techniques for diagnosis, surgical guidance and treatment evaluation. Recently air-puff systems have been developed to study the dynamic tissue response, nevertheless the experimental geometrical observations lack from an analysis that addresses specifically the inherent dynamic properties. In this study a viscoelastic finite element model was built that predicts the experimental corneal deformation response to an air-puff for different conditions. A sensitivity analysis reveals significant contributions to corneal deformation of intraocular pressure and corneal thickness, besides corneal biomechanical properties. The results show the capability of dynamic imaging to reveal inherent biomechanical properties in vivo. Estimates of corneal biomechanical parameters will contribute to the basic understanding of corneal structure, shape and integrity and increase the predictability of corneal surgery. PMID:25121496

  14. Enhanced viscoelastic property of iron oxide nanoparticle decorated organoclay fluid under magnetic field

    NASA Astrophysics Data System (ADS)

    Son, You-Hwan; Jung, Youngsoo; Roh, Heesuk; Lee, Jung-Kun

    2017-08-01

    Stable hydrophobic nanocomposites of magnetic nanoparticles and clay are prepared by the self-assembly of magnetite (Fe3O4) nanoparticles on surfaces of exfoliated clay platelets. Due to the attractive interaction between hydrophobic groups, oleic acid coated nanoparticles are strongly attached to the surface of cetyl trimethylammonium cation coated clay platelets in organic media. Crystal structure and magnetic property of composite particles are examined using electron microscopy, x-ray diffractometer and vibration sample magnetometer. In addition, composite particles are dispersed in mineral oil and rheological properties of composite particle suspensions are characterized using steady-state and oscillatory measurements. Magnetite nanoparticle decorated organoclay forms a tunable network in mineral oil. When a magnetic field is applied, the composite particle fluid exhibits higher storage modulus and maintains a solid-like property at larger strain. Our results show that the viscoelastic property of the magnetite nanoparticle decorated organoclay fluid is controlled by applying external magnetic field.

  15. Corneal viscoelastic properties from finite-element analysis of in vivo air-puff deformation.

    PubMed

    Kling, Sabine; Bekesi, Nandor; Dorronsoro, Carlos; Pascual, Daniel; Marcos, Susana

    2014-01-01

    Biomechanical properties are an excellent health marker of biological tissues, however they are challenging to be measured in-vivo. Non-invasive approaches to assess tissue biomechanics have been suggested, but there is a clear need for more accurate techniques for diagnosis, surgical guidance and treatment evaluation. Recently air-puff systems have been developed to study the dynamic tissue response, nevertheless the experimental geometrical observations lack from an analysis that addresses specifically the inherent dynamic properties. In this study a viscoelastic finite element model was built that predicts the experimental corneal deformation response to an air-puff for different conditions. A sensitivity analysis reveals significant contributions to corneal deformation of intraocular pressure and corneal thickness, besides corneal biomechanical properties. The results show the capability of dynamic imaging to reveal inherent biomechanical properties in vivo. Estimates of corneal biomechanical parameters will contribute to the basic understanding of corneal structure, shape and integrity and increase the predictability of corneal surgery.

  16. Viscoelastic properties and efficient acoustic damping in confined polymer nano-layers at GHz frequencies

    NASA Astrophysics Data System (ADS)

    Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas

    2016-09-01

    We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids.

  17. Viscoelastic properties and efficient acoustic damping in confined polymer nano-layers at GHz frequencies

    PubMed Central

    Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas

    2016-01-01

    We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids. PMID:27633351

  18. Viscoelastic properties of the nematode Caenorhabditis elegans, a self-similar, shear-thinning worm.

    PubMed

    Backholm, Matilda; Ryu, William S; Dalnoki-Veress, Kari

    2013-03-19

    Undulatory motion is common to many creatures across many scales, from sperm to snakes. These organisms must push off against their external environment, such as a viscous medium, grains of sand, or a high-friction surface; additionally they must work to bend their own body. A full understanding of undulatory motion, and locomotion in general, requires the characterization of the material properties of the animal itself. The material properties of the model organism Caenorhabditis elegans were studied with a micromechanical experiment used to carry out a three-point bending measurement of the worm. Worms at various developmental stages (including dauer) were measured and different positions along the worm were probed. From these experiments we calculated the viscoelastic properties of the worm, including the effective spring constant and damping coefficient of bending. C. elegans moves by propagating sinusoidal waves along its body. Whereas previous viscoelastic approaches to describe the undulatory motion have used a Kelvin-Voigt model, where the elastic and viscous components are connected in parallel, our measurements show that the Maxwell model, where the elastic and viscous components are in series, is more appropriate. The viscous component of the worm was shown to be consistent with a non-Newtonian, shear-thinning fluid. We find that as the worm matures it is well described as a self-similar elastic object with a shear-thinning damping term and a stiffness that becomes smaller as one approaches the tail.

  19. Viscoelastic properties of the nematode Caenorhabditis elegans, a self-similar, shear-thinning worm

    PubMed Central

    Backholm, Matilda; Ryu, William S.; Dalnoki-Veress, Kari

    2013-01-01

    Undulatory motion is common to many creatures across many scales, from sperm to snakes. These organisms must push off against their external environment, such as a viscous medium, grains of sand, or a high-friction surface; additionally they must work to bend their own body. A full understanding of undulatory motion, and locomotion in general, requires the characterization of the material properties of the animal itself. The material properties of the model organism Caenorhabditis elegans were studied with a micromechanical experiment used to carry out a three-point bending measurement of the worm. Worms at various developmental stages (including dauer) were measured and different positions along the worm were probed. From these experiments we calculated the viscoelastic properties of the worm, including the effective spring constant and damping coefficient of bending. C. elegans moves by propagating sinusoidal waves along its body. Whereas previous viscoelastic approaches to describe the undulatory motion have used a Kelvin–Voigt model, where the elastic and viscous components are connected in parallel, our measurements show that the Maxwell model, where the elastic and viscous components are in series, is more appropriate. The viscous component of the worm was shown to be consistent with a non-Newtonian, shear-thinning fluid. We find that as the worm matures it is well described as a self-similar elastic object with a shear-thinning damping term and a stiffness that becomes smaller as one approaches the tail. PMID:23460699

  20. Identification of the Hereditary Kernels of Isotropic Linear Viscoelastic Materials in Combined Stress state. 1. Superposition of Shear and Bulk creep

    NASA Astrophysics Data System (ADS)

    Golub, V. P.; Maslov, B. P.; Fernati, P. V.

    2016-03-01

    Relations between the shear and bulk creep kernels of an isotropic linear viscoelastic material in combined stress state and the longitudinal and shear creep kernels constructed from data of creep tests under uniaxial tension and pure torsion are formulated. The constitutive equations of viscoelasticity for the combined stress state are chosen in the form of a superposition of the equation for shear strains and the equation for bulk strains. The hereditary kernels are described by Rabotnov's fractional-exponential functions. The creep strains of thin-walled pipes under a combination of tension and torsion or tension and internal pressure are calculated

  1. Viscoelastic Properties of Healthy Achilles Tendon are Independent of Isometric Plantar Flexion Strength and Cross-Sectional Area

    PubMed Central

    Suydam, Stephen M.; Soulas, Elizabeth M.; Elliott, Dawn M.; Silbernagel, Karin Gravare; Buchanan, Thomas S.; Cortes, Daniel H.

    2015-01-01

    Changes in tendon viscoelastic properties are observed after injuries and during healing as a product of altered composition and structure. Continuous Shear Wave Elastography is a new technique measuring viscoelastic properties of soft tissues using external shear waves. Tendon has not been studied with this technique, therefore, the aims of this study were to establish the range of shear and viscosity moduli in healthy Achilles tendons, determine bilateral differences of these parameters and explore correlations of viscoelasticity to plantar flexion strength and tendon area. Continuous Shear Wave Elastography was performed over the free portion of both Achilles tendons from 29 subjects. Isometric plantar flexion strength and cross sectional area were measured. The average shear and viscous moduli was 83.2kPa and 141.0Pa-s, respectively. No correlations existed between the shear or viscous modulus and area or strength. This indicates that viscoelastic properties can be considered novel, independent biomarkers. The shear and viscosity moduli were bilaterally equivalent (p=0.013,0.017) which allows determining pathologies through side-to-side deviations. The average bilateral coefficient of variation was 7.2% and 9.4% for shear and viscosity modulus, respectively. The viscoelastic properties of the Achilles tendon may provide an unbiased, non-subjective rating system of tendon recovery and optimizing treatment strategies. PMID:25882209

  2. Effect of Xyloglucan Oligosaccharides on Growth, Viscoelastic Properties, and Long-Term Extension of Pea Shoots.

    PubMed Central

    Cutillas-Iturralde, A.; Lorences, E. P.

    1997-01-01

    The growth-promoting effect of xyloglucan-derived oligosaccharides was investigated using a bioassay with entire pea (Pisum sativum L., var Alaska) shoots. After a 24-h incubation period at 25[deg]C, xyloglucan oligosaccharide (XGO) solutions with concentrations of 10-6 M notably increased the growth rate of pea shoots, whereas the same oligosaccharides at 10-7 M were less effective. To investigate the possible correlation between growth rate changes in the XGO-treated shoots and changes in the wall mechanical properties of their growing regions (third internodes), we used a short-term creep assay. The promotion of elongation by XGOs was reflected in an enhancement of the viscoelasticity of the growing regions of the shoots. To show whether this effect on wall viscoelastic properties was the cause or a consequence of their growth promotion, we tested the effect of XGOs on the long-term extension of isolated cell walls. We characterized an acid-induced extension in isolated cell walls from pea shoots that was not inhibited by preincubation in neutral buffers. Exogenously added XGOs did not alter the pattern of pea segment extension at any pH tested, indicating that XGOs have no direct effect on cell wall viscoelasticity. Finally, preincubation of pea segments in neutral buffers with XGOs enhanced their capacity to extend under acidic conditions. This finding suggests that XGOs at a neutral pH can act via transglycosylation, weakening the wall matrix and making the wall more responsive to other mechanisms of acid-induced extension as an expansin-mediated extension. PMID:12223593

  3. The effective ratio of acoustic impedance in predicting stress and velocity of wave propagation in viscoelastic material (standard linear solid model)

    NASA Astrophysics Data System (ADS)

    Musa, Abu Bakar

    2013-09-01

    The study is about impact of a short elastic rod(or slug) on a stationary semi-infinite viscoelastic rod. The viscoelastic materials are modeled as standard linear solid which involve three material parameters and the motion is treated as one-dimensional. We first establish the governing equations pertaining to the impact of viscoelastic materials subject to certain boundary conditions for the case when an elastic slug moving at a speed V impacts a semi-infinite stationary viscoelastic rod. The objective is to predict stresses and velocities at the interface following wave transmissions and reflections in the slug after the impact using viscoelastic discontinuity. If the stress at the interface becomes tensile and the velocity changes its sign, then the slug and the rod part company. If the stress at the interface is compressive after the impact, the slug and the rod remain in contact. In the process of predicting the stress and velocity of wave propagation using viscoelastic discontinuity, the Z-effective which is the effective ratio of acoustic impedance plays important role. It can be shown that effective ratio of acoustic impedance can help us to determine whether the slug and the rod move together or part company after the impact. After modeling the impact and solve the governing system of partial differential equations in the Laplace transform domain. We invert the Laplace transformed solution numerically to obtain the stresses and velocities at the interface for several viscosity time constants and ratios of acoustic impedances. In inverting the Laplace transformed equations, we used the complex inversion formula because there is a branch cut and infinitely many poles within the Bromwich contour. In the discontinuity analysis, we look at the moving discontinuities in stress and velocity using the impulse-momentum relation and kinematical condition of compatibility. Finally, we discussed the relationship of the stresses and velocities using numeric and the

  4. Inverting Glacial Isostatic Adjustment beyond linear viscoelasticity using the Burgers rheology

    NASA Astrophysics Data System (ADS)

    Caron, Lambert; Greff-Lefftz, Marianne; Fleitout, Luce; Métivier, Laurent; Rouby, Hélène

    2015-04-01

    In Glacial Isostatic Adjustment (GIA) inverse modeling, the usual assumption for the mantle rheology is the Maxwell model, which exhibits constant viscosity over time. However, mineral physics experiments and post-seismic observations show evidence of a transient component in the deformation of the shallow mantle, with a short-term viscosity lower than the long-term one. In these studies, the resulting rheology is modeled by a Burgers material: such rheology is indeed expected as the mantle is a mixture of materials with different viscosities. We propose to apply this rheology for the whole viscoelastic mantle, and, using a Bayesian MCMC inverse formalism for GIA during the last glacial cycle, study its impact on estimations of viscosity values, elastic thickness of the lithosphere, and ice distribution. To perform this inversion, we use a global dataset of sea level records, the geological constraints of ice-sheet margins, and present-day GPS data as well as satellite gravimetry. Our ambition is to present not only the best fitting model, but also the range of possible solutions (within the explored space of parameters) with their respective probability of explaining the data. Our results show that the Burgers model is able to fit the dataset as well as the Maxwell model, but would imply a larger lower mantle viscosity, thicker ice sheets over Fennoscandia and Canada, and thinner ice sheets over Antarctica and Greenland.

  5. A Study on the Influence of Process Parameters on the Viscoelastic Properties of ABS Components Manufactured by FDM Process

    NASA Astrophysics Data System (ADS)

    Dakshinamurthy, Devika; Gupta, Srinivasa

    2016-06-01

    Fused Deposition Modelling (FDM) is a fast growing Rapid Prototyping (RP) technology due to its ability to build parts having complex geometrical shape in reasonable time period. The quality of built parts depends on many process variables. In this study, the influence of three FDM process parameters namely, slice height, raster angle and raster width on viscoelastic properties of Acrylonitrile Butadiene Styrene (ABS) RP-specimen is studied. Statistically designed experiments have been conducted for finding the optimum process parameter setting for enhancing the storage modulus. Dynamic Mechanical Analysis has been used to understand the viscoelastic properties at various parameter settings. At the optimal parameter setting the storage modulus and loss modulus of the ABS-RP specimen was 1008 and 259.9 MPa respectively. The relative percentage contribution of slice height and raster width on the viscoelastic properties of the FDM-RP components was found to be 55 and 31 % respectively.

  6. An improved method to analyze the stress relaxation of ligaments following a finite ramp time based on the quasi-linear viscoelastic theory.

    PubMed

    Abramowitch, Steven D; Woo, Savio L

    2004-02-01

    The quasi-linear viscoelastic (QLV) theory proposed by Fung (1972) has been frequently used to model the nonlinear time- and history-dependent viscoelastic behavior of many soft tissues. It is common to use five constants to describe the instantaneous elastic response (constants A and B) and reduced relaxation function (constants C, tau 1, and tau 2) on experiments with finite ramp times followed by stress relaxation to equilibrium. However, a limitation is that the theory is based on a step change in strain which is not possible to perform experimentally. Accounting for this limitation may result in regression algorithms that converge poorly and yield nonunique solutions with highly variable constants, especially for long ramp times (Kwan et al. 1993). The goal of the present study was to introduce an improved approach to obtain the constants for QLV theory that converges to a unique solution with minimal variability. Six goat femur-medial collateral ligament-tibia complexes were subjected to a uniaxial tension test (ramp time of 18.4 s) followed by one hour of stress relaxation. The convoluted QLV constitutive equation was simultaneously curve-fit to the ramping and relaxation portions of the data (r2 > 0.99). Confidence intervals of the constants were generated from a bootstrapping analysis and revealed that constants were distributed within 1% of their median values. For validation, the determined constants were used to predict peak stresses from a separate cyclic stress relaxation test with averaged errors across all specimens measuring less than 6.3 +/- 6.0% of the experimental values. For comparison, an analysis that assumed an instantaneous ramp time was also performed and the constants obtained for the two approaches were compared. Significant differences were observed for constants B, C, tau 1, and tau 2, with tau 1 differing by an order of magnitude. By taking into account the ramping phase of the experiment, the approach allows for viscoelastic

  7. OREGANO_VE: a new parallelised 3D solver for the general (non-)linear Maxwell visco-elastic problem: validation and application to the calculation of surface deformation in the earthquake cycle

    NASA Astrophysics Data System (ADS)

    Yamasaki, Tadashi; Houseman, Gregory; Hamling, Ian; Postek, Elek

    2010-05-01

    We have developed a new parallelized 3-D numerical code, OREGANO_VE, for the solution of the general visco-elastic problem in a rectangular block domain. The mechanical equilibrium equation is solved using the finite element method for a (non-)linear Maxwell visco-elastic rheology. Time-dependent displacement and/or traction boundary conditions can be applied. Matrix assembly is based on a tetrahedral element defined by 4 vertex nodes and 6 nodes located at the midpoints of the edges, and within which displacement is described by a quadratic interpolation function. For evaluating viscoelastic relaxation, an explicit time-stepping algorithm (Zienkiewicz and Cormeau, Int. J. Num. Meth. Eng., 8, 821-845, 1974) is employed. We test the accurate implementation of the OREGANO_VE by comparing numerical and analytic (or semi-analytic half-space) solutions to different problems in a range of applications: (1) equilibration of stress in a constant density layer after gravity is switched on at t = 0 tests the implementation of spatially variable viscosity and non-Newtonian viscosity; (2) displacement of the welded interface between two blocks of differing viscosity tests the implementation of viscosity discontinuities, (3) displacement of the upper surface of a layer under applied normal load tests the implementation of time-dependent surface tractions (4) visco-elastic response to dyke intrusion (compared with the solution in a half-space) tests the implementation of all aspects. In each case, the accuracy of the code is validated subject to use of a sufficiently small time step, providing assurance that the OREGANO_VE code can be applied to a range of visco-elastic relaxation processes in three dimensions, including post-seismic deformation and post-glacial uplift. The OREGANO_VE code includes a capability for representation of prescribed fault slip on an internal fault. The surface displacement associated with large earthquakes can be detected by some geodetic observations

  8. Assessment of the viscoelastic and oscillation properties of a nano-engineered multimodality contrast agent.

    PubMed

    Kothapalli, Satya V V N; Oddo, Letizia; Paradossi, Gaio; Brodin, Lars-Åke; Grishenkov, Dmitry

    2014-10-01

    Combinations of microbubbles (MBs) and superparamagnetic iron oxide nanoparticles (SPIONs) are used to fabricate dual contrast agents for ultrasound and MRI. This study examines the viscoelastic and oscillation characteristics of two MB types that are manufactured with SPIONs and either anchored chemically on the surface (MBs-chem) or physically embedded (MBs-phys) into a polymer shell. A linearized Church model was employed to simultaneously fit attenuation coefficients and phase velocity spectra that were acquired experimentally. The model predicted lower viscoelastic modulus values, undamped resonance frequencies and total damping ratios for MBs-chem. MBs-chem had a resonance frequency of approximately 13 MHz and a damping ratio of approximately 0.9; thus, MBs-chem can potentially be used as a conventional ultrasound contrast agent with the combined functionality of MRI detection. In contrast, MBs-phys had a resonance frequency and damping of 28 MHz and 1.2, respectively, and requires further modification of clinically available contrast pulse sequences to be visualized.

  9. Viscoelastic properties and residual strain in a tensile creep test on bovine temporomandibular articular discs.

    PubMed

    Tanaka, E; Tanaka, M; Aoyama, J; Watanabe, M; Hattori, Y; Asai, D; Iwabe, T; Sasaki, A; Sugiyama, M; Tanne, K

    2002-02-01

    This study was designed to evaluate the creep characteristics and residual strain of bovine temporomandibular joint (TMJ) discs in tension. Twenty discs were divided into three specimens each: central, lateral and medial regions. Tension of 1.0 MPa was applied and sustained for 20 min to the specimens from 10 right-side discs, and tension of 1.5 MPa to specimens from 10 left-side discs. After the period of tension for creep, the specimens were removed from the tension devices and restoration observed for 20 min. Time-dependent creep curves showed a marked change in strain during the initial 5s. The essential time delay in strain ceased after 2 min, and strain reached an almost steady level after 3 min. At a tensile stress of 1.5 MPa, a strain of 14.5% on average was produced after 20 min creep in the central specimens; peripheral specimens showed strains of 12.4% on average. There were significant differences in strain between the central and peripheral specimens. The residual strain after 20 min restoration was 0.93% on average and there were no significant regional differences. This creep feature could be well represented by a generalized linear viscoelastic model. It was concluded that the regional differences in viscoelasticity might be caused by the complicated articulating functions of the TMJ, and that the residual strain caused by sustained stress could be an important factor in disc deformation.

  10. Numerical evaluation of implantable hearing devices using a finite element model of human ear considering viscoelastic properties.

    PubMed

    Zhang, Jing; Tian, Jiabin; Ta, Na; Huang, Xinsheng; Rao, Zhushi

    2016-08-01

    Finite element method was employed in this study to analyze the change in performance of implantable hearing devices due to the consideration of soft tissues' viscoelasticity. An integrated finite element model of human ear including the external ear, middle ear and inner ear was first developed via reverse engineering and analyzed by acoustic-structure-fluid coupling. Viscoelastic properties of soft tissues in the middle ear were taken into consideration in this model. The model-derived dynamic responses including middle ear and cochlea functions showed a better agreement with experimental data at high frequencies above 3000 Hz than the Rayleigh-type damping. On this basis, a coupled finite element model consisting of the human ear and a piezoelectric actuator attached to the long process of incus was further constructed. Based on the electromechanical coupling analysis, equivalent sound pressure and power consumption of the actuator corresponding to viscoelasticity and Rayleigh damping were calculated using this model. The analytical results showed that the implant performance of the actuator evaluated using a finite element model considering viscoelastic properties gives a lower output above about 3 kHz than does Rayleigh damping model. Finite element model considering viscoelastic properties was more accurate to numerically evaluate implantable hearing devices.

  11. Revealing region-specific biofilm viscoelastic properties by means of a micro-rheological approach.

    PubMed

    Cao, Huayu; Habimana, Olivier; Safari, Ashkan; Heffernan, Rory; Dai, Yihong; Casey, Eoin

    2016-01-01

    Particle-tracking microrheology is an in situ technique that allows quantification of biofilm material properties. It overcomes the limitations of alternative techniques such as bulk rheology or force spectroscopy by providing data on region specific material properties at any required biofilm location and can be combined with confocal microscopy and associated structural analysis. This article describes single particle tracking microrheology combined with confocal laser scanning microscopy to resolve the biofilm structure in 3 dimensions and calculate the creep compliances locally. Samples were analysed from Pseudomonas fluorescens biofilms that were cultivated over two timescales (24 h and 48 h) and alternate ionic conditions (with and without calcium chloride supplementation). The region-based creep compliance analysis showed that the creep compliance of biofilm void zones is the primary contributor to biofilm mechanical properties, contributing to the overall viscoelastic character.

  12. Surface viscoelastic properties of spread ferroelectric liquid crystal monolayer on air-water interface

    NASA Astrophysics Data System (ADS)

    Kaur, Ramneek; Bhullar, Gurpreet Kaur; Raina, K. K.

    2013-06-01

    Ferroelectric Liquid crystal having Smectic C* phase at room temperature was capable of forming Langmuir monolayer due to presence of both hydrophilic and hydrophobic groups in it. Surface viscoelasticity properties of FLC monolayer spread on water surface had been determined by dynamic oscillation method and discussed as a function of surface pressure. Dynamic viscoelastic properties such as G (Elastic modulus), G' (storage (elastic) modulus), G' (Loss (viscous) modulus) and phase change with sinusoidal oscillation had been measured at phase changing surface pressure values. As monolayer was becoming condensed, increasing trend was observed in G' values while G' was decreasing. At higher frequencies, viscous modulus G' had negative values. This relaxation phenomenon was probably caused by conformational rearrangements that acted to fluidize monolayer. Phase change tan θ was positive, response in surface pressure was ahead of the de-formation in area and the monolayer had positive dilatational viscosity. Phase change tan θ was negative, response in surface pressure was hysteretic to the deformation in area, and negative dilatational viscosity had been observed. Studies of monolayer in barrier oscillating mode provided us the surface pressure which was most suitable for Langmuir Blodgett monolayer deposition.

  13. Characterizing the viscoelastic properties of thin hydrogel-based constructs for tissue engineering applications.

    PubMed

    Ahearne, Mark; Yang, Ying; El Haj, Alicia J; Then, Kong Y; Liu, Kuo-Kang

    2005-12-22

    We present a novel indentation method for characterizing the viscoelastic properties of alginate and agarose hydrogel based constructs, which are often used as a model system of soft biological tissues. A sensitive long working distance microscope was used for measuring the time-dependent deformation of the thin circular hydrogel membranes under a constant load. The deformation of the constructs was measured laterally. The elastic modulus as a function of time can be determined by a large deformation theory based on Mooney-Rivlin elasticity. A viscoelastic theory, Zener model, was applied to correlate the time-dependent deformation of the constructs with various gel concentrations, and the creep parameters can therefore be quantitatively estimated. The value of Young's modulus was shown to increase in proportion with gel concentration. This finding is consistent with other publications. Our results also showed the great capability of using the technique to measure gels with incorporated corneal stromal cells. This study demonstrates a novel and convenient technique to measure mechanical properties of hydrogel in a non-destructive, online and real-time fashion. Thus this novel technique can become a valuable tool for soft tissue engineering.

  14. Characterizing the viscoelastic properties of thin hydrogel-based constructs for tissue engineering applications

    PubMed Central

    Ahearne, Mark; Yang, Ying; El Haj, Alicia J; Then, Kong Y; Liu, Kuo-Kang

    2005-01-01

    We present a novel indentation method for characterizing the viscoelastic properties of alginate and agarose hydrogel based constructs, which are often used as a model system of soft biological tissues. A sensitive long working distance microscope was used for measuring the time-dependent deformation of the thin circular hydrogel membranes under a constant load. The deformation of the constructs was measured laterally. The elastic modulus as a function of time can be determined by a large deformation theory based on Mooney–Rivlin elasticity. A viscoelastic theory, Zener model, was applied to correlate the time-dependent deformation of the constructs with various gel concentrations, and the creep parameters can therefore be quantitatively estimated. The value of Young's modulus was shown to increase in proportion with gel concentration. This finding is consistent with other publications. Our results also showed the great capability of using the technique to measure gels with incorporated corneal stromal cells. This study demonstrates a novel and convenient technique to measure mechanical properties of hydrogel in a non-destructive, online and real-time fashion. Thus this novel technique can become a valuable tool for soft tissue engineering. PMID:16849205

  15. Influence of Chemical Heterogeneity on the Viscoelastic Properties of Polystyrene-b-Poly(alkyl methacrylate) Baroplastics

    NASA Astrophysics Data System (ADS)

    Abdulahad, Asem; Ryu, Chang Y.

    2011-03-01

    The development of purification and fractionation techniques of block copolymers is important for overcoming the synthetic difficulty of preparing well-defined block copolymers using various living polymerization techniques. A large scale separation technique would lead us to obtaining sufficient amounts of homopolymer-free block copolymers for subsequent physical characterization. This can potentially aid in the elucidation of the role of chemical heterogeneity on the thermodynamic transitions and viscoelastic properties of block copolymer materials. Atom transfer radical polymerization by the activators regenerated by electron transfer method (ARGET-ATRP) was used to prepare a series of polystyrene-b-poly(alkyl methacrylate) copolymers that would inherently consist of homopolymers and a high polydispersity. Leveraging the understanding of polymer adsorption/desorption in solution onto silica and C18-modified silica surfaces during HPLC, we demonstrate how a large scale purification and fraction is achievable using flash chromatography. Finally, the viscoelastic properties of the purified, homopolymer-free block copolymers will be discussed. NSF PIRE Polymer Program.

  16. Alterations in viscoelastic properties following premature birth may lead to hypertension and cardiovascular disease development in later life.

    PubMed

    Tauzin, L

    2015-01-01

    The aim of this review was to identify the underlying relationship between preterm birth and the development of cardiovascular diseases. Preterm birth significantly affects the elastin content and viscoelastic properties of the vascular extracellular matrix in human arteries. Inadequate elastin synthesis during early development may cause a permanent increase in arterial stiffness in adulthood. Early and permanent alterations in viscoelastic properties may lead to hypertension and cardiovascular disease development in adults born prematurely. ©2014 Foundation Acta Paediatrica. Published by John Wiley & Sons Ltd.

  17. Viscoelastic properties of bronchial mucus after respiratory physiotherapy in subjects with bronchiectasis.

    PubMed

    Ramos, Ercy M C; Ramos, Dionei; Moreira, Graciane L; Macchione, Mariangela; Guimarães, Eliane T; Rodrigues, Fernanda Maria M; de Souza, Altay Alves Lino; Saldiva, Paulo H N; Jardim, José R

    2015-05-01

    Previous studies have evaluated the effectiveness of postural drainage (PD), percussion (PERC), the coughing technique (CT), and other types of coughing in subjects with bronchiectasis. However, the application times of these techniques and the quality of the expectorated mucus require further study. The aim of our study was to evaluate the effectiveness of PD, percussion, CT, and huffing in subjects with bronchiectasis and assess the quantity and quality of bronchial mucus produced (measurement of wet and dry weight and determination of viscoelastic properties). Twenty-two subjects with stable bronchiectasis (6 men; mean age: 51.5 y) underwent 4 d of experimental study (CT, PD+CT, PD+PERC+CT, and PD+huffing). The techniques were performed in 3 20-min periods separated by 10 min of rest. Before performing any technique (baseline) and after each period (30, 60, and 90 min), expectorated mucus was collected for analysis of viscoelasticity. A significant increase in the dry weight/wet weight ratio was found after 60 min of PD+PERC+CT (P = .01) and 90 min of PD+huffing (P = .03) and PD+PERC+CT (P = .007) in comparison with CT. PD+PERC+CT and PD+huffing led to the greatest removal of viscoelastic mucus at 60 min (P = .02 and P = .002, respectively) and continued to do so at 90 min (P = .02 and P = .01, respectively) in comparison with CT. An interaction effect was found, as all techniques led to a greater removal of elastic mucus in comparison with CT at 60 min (PD+CT, P = .001; PD+PERC+CT, P < .001; PD+huffing, P < .001), but only PD+PERC+CT and PD+huffing led to a greater removal of elastic mucus than CT at 90 min (P < .001 and P = .005, respectively). PD+PERC+CT and PD+huffing performed similarly regarding the removal of viscoelastic mucus in 2 and 3 20-min periods separated by 10 min of rest. PD+PERC+CT led to the greatest removal of mucus in the shortest period (2 20-min periods separated by 10 min of rest). Copyright © 2015 by Daedalus Enterprises.

  18. Modeling and Testing of the Viscoelastic Properties of a Graphite Nanoplatelet/Epoxy Composite

    NASA Technical Reports Server (NTRS)

    Odegard, Gregory M.; Gates, Thomas S.

    2005-01-01

    In order to facilitate the interpretation of experimental data, a micromechanical modeling procedure is developed to predict the viscoelastic properties of a graphite nanoplatelet/epoxy composite as a function of volume fraction and nanoplatelet diameter. The predicted storage and loss moduli for the composite are compared to measured values from the same material using three test methods; Dynamical Mechanical Analysis, nanoindentation, and quasi-static tensile tests. In most cases, the model and experiments indicate that for increasing volume fractions of nanoplatelets, both the storage and loss moduli increase. Also, the results indicate that for nanoplatelet sizes above 15 microns, nanoindentation is capable of measuring properties of individual constituents of a composite system. Comparison of the predicted values to the measured data helps illustrate the relative similarities and differences between the bulk and local measurement techniques.

  19. Application of dynamic mechanical testing to characterize the viscoelastic properties of powder-filled semisolids.

    PubMed

    Radebaugh, G W; Simonelli, A P

    1984-05-01

    A nondestructive technique, dynamic mechanical testing, was used to characterize the viscoelastic properties of dispersions of powdered starch in anhydrous lanolin. The elastic shear modulus (G'), viscous shear modulus (G"), and loss tangent (damping; tan delta) were determined as a function of shear frequency, temperature, and the volume fraction of starch. The results of these studies show that constitutive mathematical models, derived to predict the mechanical behavior of solid-filled polymeric materials, can be applied to solid-filled semisolid pharmaceuticals. In particular, the Kerner equation was useful in describing the influence of starch on the G' of the dispersions. Even though the Kerner equation was unable to predict viscoelastic behavior at all shear frequencies, temperatures, and starch volume fractions, it proved beneficial in postulating mechanisms for starch-starch and starch-anhydrous lanolin interactions within the dispersions. In addition, damping was able to differentiate the influence of temperature. Data obtained from three temperature ranges, where anhydrous lanolin exists in three different structural states, shows that the influence of starch on damping is dictated by the structural state of anhydrous lanolin.

  20. Interrelationship between the zeta potential and viscoelastic properties in coacervates complexes.

    PubMed

    Espinosa-Andrews, Hugo; Enríquez-Ramírez, Karina Esmeralda; García-Márquez, Eristeo; Ramírez-Santiago, Cesar; Lobato-Calleros, Consuelo; Vernon-Carter, Jaime

    2013-06-05

    The formation of the complex coacervate (CC) phases between gum Arabic (GA) and low molecular weight chitosan (Ch) and the interrelationship between the zeta-potential and viscoelastic properties of the coacervate phase were investigated. The maximum charge difference of biopolymers stock dispersion was displayed in a range of pH between 4.0 and 5.5. Titration experiment between the oppositely charged biopolymers showed that the isoelectric point was found at a biopolymers mass ratio (R[GA:Ch]) of R[5.5:1]. Turbidity, size and ζ-potential of the soluble complexes (SC) showed an interrelation with the complex coacervate yield (CCY). Higher CCY values (82.2-88.1%) were obtained in the range from R[3:1] to R[5.5:1]. Change the R[GA:Ch] in dispersion, make possible to produce CC's phases exhibiting cationic (R[1:1] and R[3:1]), neutral (R[5.5:1]) or anionic (R[9:1] and R[7:1]) charged. All CC's exhibited liquid-viscoelastic behavior at lower frequencies and a crossover between G″ and G' at higher frequencies. Copyright © 2013 Elsevier Ltd. All rights reserved.

  1. Characterization of the elastic and viscoelastic properties of dentin by a nanoindentation creep test.

    PubMed

    Chuang, Shu-Fen; Lin, Shih-Yun; Wei, Pal-Jen; Han, Chang-Fu; Lin, Jen-Fin; Chang, Hsien-Chang

    2015-07-16

    Dentin is the main supporting structure of teeth, but its mechanical properties may be adversely affected by pathological demineralization. The purposes of this study were to develop a quantitative approach to characterize the viscoelastic properties of dentin after de- and re-mineralization, and to examine the elastic properties using a nanoindentation creep test. Dentin specimens were prepared to receive both micro- and nano-indentation tests at wet and dry states. These tests were repeatedly performed after demineralization (1% citric acid for 3 days) and remineralization (artificial saliva immersion for 28 days). The nanoindentation test was executed in a creep mode, and the resulting displacement-time responses were disintegrated into primary (transient) and secondary (viscous) creep. The structural changes and mineral densities of dentin were also examined under SEM and microCT, respectively. The results showed that demineralization removed superficial minerals of dentin to the depth of 400 μm, and affected its micro- and nano-hardness, especially in the hydrate state. Remineralization only repaired the minerals at the surface layer, and partially recovered the nanohardness. Both the primary the secondary creep increased in the demineralized dentin, while the hydration further enhanced creep deformation of untreated and remineralized dentin. Remineralization reduced the primary creep of dentin, but did not effectively increase the viscosity. In conclusion, water plasticization increases the transient and viscous creep strains of demineralized dentin and reduces load sustainability. The nanoindentation creep test is capable of analyzing the elastic and viscoelastic properties of dentin, and reveals crucial information about creep responses. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Viscoelastic properties of bovine orbital connective tissue and fat: constitutive models.

    PubMed

    Yoo, Lawrence; Gupta, Vijay; Lee, Choongyeop; Kavehpore, Pirouz; Demer, Joseph L

    2011-12-01

    Reported mechanical properties of orbital connective tissue and fat have been too sparse to model strain-stress relationships underlying biomechanical interactions in strabismus. We performed rheological tests to develop a multi-mode upper convected Maxwell (UCM) model of these tissues under shear loading. From 20 fresh bovine orbits, 30 samples of connective tissue were taken from rectus pulley regions and 30 samples of fatty tissues from the posterior orbit. Additional samples were defatted to determine connective tissue weight proportion, which was verified histologically. Mechanical testing in shear employed a triborheometer to perform: strain sweeps at 0.5-2.0 Hz; shear stress relaxation with 1% strain; viscometry at 0.01-0.5 s(-1) strain rate; and shear oscillation at 1% strain. Average connective tissue weight proportion was 98% for predominantly connective tissue and 76% for fatty tissue. Connective tissue specimens reached a long-term relaxation modulus of 668 Pa after 1,500 s, while corresponding values for fatty tissue specimens were 290 Pa and 1,100 s. Shear stress magnitude for connective tissue exceeded that of fatty tissue by five-fold. Based on these data, we developed a multi-mode UCM model with variable viscosities and time constants, and a damped hyperelastic response that accurately described measured properties of both connective and fatty tissues. Model parameters differed significantly between the two tissues. Viscoelastic properties of predominantly connective orbital tissues under shear loading differ markedly from properties of orbital fat, but both are accurately reflected using UCM models. These viscoelastic models will facilitate realistic global modeling of EOM behavior in binocular alignment and strabismus.

  3. Viscoelastic properties of bovine orbital connective tissue and fat: constitutive models

    PubMed Central

    Yoo, Lawrence; Gupta, Vijay; Lee, Choongyeop; Kavehpore, Pirouz

    2012-01-01

    Reported mechanical properties of orbital connective tissue and fat have been too sparse to model strain–stress relationships underlying biomechanical interactions in strabismus. We performed rheological tests to develop a multi-mode upper convected Maxwell (UCM) model of these tissues under shear loading. From 20 fresh bovine orbits, 30 samples of connective tissue were taken from rectus pulley regions and 30 samples of fatty tissues from the posterior orbit. Additional samples were defatted to determine connective tissue weight proportion, which was verified histologically. Mechanical testing in shear employed a triborheometer to perform: strain sweeps at 0.5–2.0 Hz; shear stress relaxation with 1% strain; viscometry at 0.01–0.5 s−1 strain rate; and shear oscillation at 1% strain. Average connective tissue weight proportion was 98% for predominantly connective tissue and 76% for fatty tissue. Connective tissue specimens reached a long-term relaxation modulus of 668 Pa after 1,500 s, while corresponding values for fatty tissue specimens were 290 Pa and 1,100 s. Shear stress magnitude for connective tissue exceeded that of fatty tissue by five-fold. Based on these data, we developed a multimode UCM model with variable viscosities and time constants, and a damped hyperelastic response that accurately described measured properties of both connective and fatty tissues. Model parameters differed significantly between the two tissues. Viscoelastic properties of predominantly connective orbital tissues under shear loading differ markedly from properties of orbital fat, but both are accurately reflected using UCM models. These viscoelastic models will facilitate realistic global modeling of EOM behavior in binocular alignment and strabismus. PMID:21207094

  4. Dynamic crack propagation in a viscoelastic strip

    NASA Astrophysics Data System (ADS)

    Popelar, C. H.; Atkinson, C.

    1980-04-01

    THE DYNAMIC PROPAGATION of a semi-infinite crack in a finite linear viscoelastic strip subjected to Mode I loading is investigated. Through the use of integral transforms the problem is reduced to solving a Wiener-Hopf equation. The asymptotic properties of the transforms are exploited to establish the stress intensity factor. Plane-stress and plane-strain stress intensity factors as a function of crack speed for both fully-clamped and shear-free lateral boundaries are presented for the standard linear viscoelastic solid. Comparisons are made with previously obtained asymptotic stress intensity factors and with stress intensity factors for the equivalent elastic strips.

  5. The viscoelastic properties of processed cheeses depend on their thermal history and fat polymorphism.

    PubMed

    Gliguem, Hela; Lopez, Christelle; Michon, Camille; Lesieur, Pierre; Ollivon, Michel

    2011-04-13

    Both the composition and the thermal kinetics that are applied to processed cheeses can affect their texture. This study investigated the effect of the storage conditions and thermal history on the viscoelastic properties of processed cheese and the physical properties of the fat phase. The microstructure of processed cheese has been characterized. Using a combination of physical techniques such as rheometry, differential scanning calorimetry, and X-ray diffraction, the partial crystallization of fat and the polymorphism of triacylglycerols (TG; main constituents of milk fat) were related to changes in the elastic modulus and tan δ as a function of temperature. In the small emulsion droplets (<1 μm) dispersed in processed cheeses, the solid fat phase was studied at a molecular level and showed differences as a function of the thermal history. Storage of processed cheese at 4 °C and its equilibration at 25 °C lead to partial crystallization of the fat phase, with the formation of a β' 2 L (40.9 Å) structure; on cooling at 2 °C min(-1), the formation of an α 3 L (65.8 Å) structure was characterized. The cooling of processed cheese from 60 to -10 °C leads to the formation of a single type of crystal: α 3 L (72 Å). Structural reorganizations of the solid fat phase characterized on heating allowed the interpretation of the elastic modulus evolution of processed cheese. This study evidenced polymorphism of TG in a complex food product such as processed cheese and allowed a better understanding of the viscoelastic properties as a function of the thermal history.

  6. The prediction of stress-relaxation of ligaments and tendons using the quasi-linear viscoelastic model.

    PubMed

    Defrate, L E; Li, G

    2007-07-01

    Recent studies have questioned the ability of the quasi-linear viscoelastic (QLV) model to predict stresses and strains in response to loading conditions other than those used to fit the model. The objective of this study was to evaluate the ability of several models in the literature to predict the elastic stress response of ligament and tendon at strain levels higher than the levels used to fit the model. The constitutive models were then used to evaluate the ability of the QLV model to predict the overall stress response during stress relaxation. The models expressing stress as an exponential function of strain significantly overestimated stress when used at higher strain levels. The polynomial formulation of the Mooney-Rivlin model more accurately predicted the stress-strain behavior of ligament and tendon. The results demonstrate that the ability of the QLV model to accurately predict the stress-relaxation response is dependent in part on the accuracy of the function used to model the elastic response of the soft tissue.

  7. Time-dependent viscoelastic properties of Oldroyd-B fluid studied by advection-diffusion lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Lee, Young Ki; Ahn, Kyung Hyun; Lee, Seung Jong

    2017-05-01

    Time-dependent viscoelastic properties of Oldroyd-B fluid were investigated by lattice Boltzmann method (LBM) coupled with advection-diffusion model. To investigate the viscoelastic properties of Oldroyd-B fluid, realistic rheometries including step shear and oscillatory shear tests were implemented in wide ranges of Weissenberg number (Wi) and Deborah number (De). First, transient behavior of Oldroyd-B fluid was studied in both start up shear and cessation of shear. Stress relaxation was correctly captured, and calculated shear and normal stresses agreed well with analytical solutions. Second, the oscillatory shear test was implemented. Dynamic moduli were obtained for various De regime, and they showed a good agreement with analytical solutions. Complex viscosity derived from dynamic moduli showed two plateau regions at both low and high De limits, and it was confirmed that the polymer contribution becomes weakened as De increases. Finally, the viscoelastic properties related to the first normal stress difference were carefully investigated, and their validity was confirmed by comparison with the analytical solutions. From this study, we conclude that the LBM with advection-diffusion model can accurately predict time-dependent viscoelastic properties of Oldroyd-B fluid.

  8. Effect of sexual maturation on thermal stability, viscoelastic properties, and texture of rainbow trout, Oncorhynchus mykiss, fillets

    USDA-ARS?s Scientific Manuscript database

    The nutrient and energy demand of sexual maturation in many fish cultivars causes structural change to key contractile proteins and thereby, affects fillet firmness. Thermal denaturation and viscoelastic properties of white muscle from diploid (2N; fertile) and triploid (3N; sterile) female rainbow...

  9. An inverse method for determining the spatially resolved properties of viscoelastic-viscoplastic three-dimensional printed materials.

    PubMed

    Chen, X; Ashcroft, I A; Wildman, R D; Tuck, C J

    2015-11-08

    A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic-viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic-viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance.

  10. Influence of Nanodisperse Metal Fillers on the Viscoelastic Properties and Processes of Mechanical Relaxation of Polymer Systems

    NASA Astrophysics Data System (ADS)

    Kolupav, B. B.; Kolupaev, B. S.; Levchuk, V. V.; Maksimtsev, Yu. R.; Sidletskii, V. A.

    2017-05-01

    The results of research into the viscoelastic properties and processes of mechanical relaxation of polyvinylchloride (PVC) containing Cu nanoparticles obtained by means of electroerosion crushing and electrohydraulic destruction of agglomerates of disperse Cu in the presence of an ultrasonic field are presented. It is shown that, in the case of longitudinal shear deformation at a frequency of 0.4 × 106 s-1 over a wide range of temperatures and content of ingredients, viscoelastic phenomena depending on structural changes in the PVC system occur. An analysis of quantitative results of the elastic and viscoelastic deformation of a body is carried out taking into account the energy and entropy components of interaction of the polymer and filler at their interface.

  11. Studies of the viscoelastic properties of water confined between surfaces of specified chemical nature.

    SciTech Connect

    Houston, Jack E.; Grest, Gary Stephen; Moore, Nathan W.; Feibelman, Peter J.

    2010-09-01

    This report summarizes the work completed under the Laboratory Directed Research and Development (LDRD) project 10-0973 of the same title. Understanding the molecular origin of the no-slip boundary condition remains vitally important for understanding molecular transport in biological, environmental and energy-related processes, with broad technological implications. Moreover, the viscoelastic properties of fluids in nanoconfinement or near surfaces are not well-understood. We have critically reviewed progress in this area, evaluated key experimental and theoretical methods, and made unique and important discoveries addressing these and related scientific questions. Thematically, the discoveries include insight into the orientation of water molecules on metal surfaces, the premelting of ice, the nucleation of water and alcohol vapors between surface asperities and the lubricity of these molecules when confined inside nanopores, the influence of water nucleation on adhesion to salts and silicates, and the growth and superplasticity of NaCl nanowires.

  12. Effects of multiwall carbon nanotubes on viscoelastic properties of magnetorheological elastomers

    NASA Astrophysics Data System (ADS)

    Aziz, Siti Aishah Abdul; Amri Mazlan, Saiful; Intan Nik Ismail, Nik; Ubaidillah, U.; Choi, Seung-Bok; Khairi, Muntaz Hana Ahmad; Azhani Yunus, Nurul

    2016-07-01

    The effect of different types of multiwall carbon nanotubes (MWCNTs) on the morphological, magnetic and viscoelastic properties of magnetorheological elastomers (MREs) are studied in this work. A series of natural rubber MRE are prepared by adding MWCNTs as a new additive in MRE. Effects of functionalized MWCNT namely carboxylated MWCNT (COOH-MWCNT) and hydroxylated MWCNT (OH-MWCNT) on the rheological properties of MREs are investigated and the pristine MWCNTs is referred as a control. Epoxidised palm oil (EPO) is used as a medium to disperse carbonyl iron particle (CIP) and sonicate the MWCNTs. Morphological and magnetic properties of MREs are characterized by field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. Rheological properties under different magnetic field are evaluated by using parallel plate rheometer. From the results obtained, FESEM images indicate that COOH-MWCNT and CIP have better compatibility which leads to the formation of interconnected network in the matrix. In addition, by adding functionalized COOH-MWCNT, it is shown that the saturation magnetization is 5% higher than the pristine MWCNTs. It is also found that with the addition of COOH-MWCNT, the magnetic properties are improved parallel with enhancement of MR effect particularly at low strain amplitude. It is finally shown that the use of EPO also can contribute to the enhancement of MR performance.

  13. From Brittle to Pliant Viscoelastic Materials with Solid State Linear Polyphosphonium - Carboxylate Assemblies

    PubMed Central

    Godeau, Guilhem; Navailles, Laurence; Nallet, Frédéric; Lin, Xinrong; McIntosh, Thomas J.; Grinstaff, Mark W.

    2013-01-01

    A polystyrenylphosphonium polymer was synthesized and complexed with various carboxylic acid derivatives to form new solid-state polyelectrolyte-surfactant assemblies. The properties of these ionic materials were highly dependent on the nature of the anion and included a brittle material, a rubbery ball that bounces, or a sticky fiber. The values for the equilibrium modulus, storage modulus, and loss modulus were dependent on the composition of the carboxylic acid and the number of electrostatic interactions. Small-angle X-ray scattering studies on the supramolecular assemblies confirmed a bilayer structure for two of the assemblies. PMID:24511156

  14. Morphology, absorptivity and viscoelastic properties of mineralized PVP-CMC hydrogel

    NASA Astrophysics Data System (ADS)

    Saha, Nabanita; Shah, Rushita; Vyroubal, Radek; Kitano, Takeshi; Saha, Petr

    2013-04-01

    A simple liquid diffusion mineralization technique was applied for the incorporation of calcium carbonate (CaCO3) in PVP-CMC hydrogel. The hydrogel was prepared 6.5 mm thick to achieve around 1 mm thick sample after mineralization of hydrogel matrix with calcite. The calcite crystals were round shaped and organized as building blocks inside the porous three dimensional cross linked structure of the PVP-CMC hydrogel. The present study was designed to evaluate the properties of mineralized (calcite) hydrogel with respect to freshly prepared hydrogel and those swelled in water (H2O) after drying. The viscoelastic properties of swelled and mineralized samples were reported though the dry PVP-CMC hydrogel were swelled and mineralized with calcite until 150 min. It is observed that there is not much difference in elastic property of fresh and 60 min mineralized hydrogels but the values of elastic property are decreased in the case of swelled hydrogels. It is interesting that in case of swelled samples the values of complex viscosity (η*) are increased with the increase of swelling time after 90 min but in case of calcite hydrogel the values (η*) are gradually decreased with the increase of time.

  15. Chemical and antimicrobial treatments change the viscoelastic properties of bacterial biofilms.

    PubMed

    Jones, Warren L; Sutton, Michael P; McKittrick, Ladean; Stewart, Philip S

    2011-02-01

    Changes in the viscoelastic material properties of bacterial biofilms resulting from chemical and antimicrobial treatments were measured by rheometry. Colony biofilms of Staphylococcus epidermidis or a mucoid Pseudomonas aeruginosa were subjected to a classical creep test performed using a parallel plate rheometer. Data were fit to the 4-parameter Burger model to quantify the material properties. Biofilms were exposed to the chloride salts of several common mono-, di-, and tri- valent cations, and to urea, industrial biocides, and antibiotics. Many of these treatments resulted in statistically significant alterations in the material properties of the biofilm. Multivalent cations stiffened the P. aeruginosa biofilm, while ciprofloxacin and glutaraldehyde weakened it. Urea, rifampin, and a quaternary ammonium biocide weakened the S. epidermidis biofilm. In general, there was no correspondence between the responses of the two different types of biofilms to a particular treatment. These results underscore the distinction between the killing power of an antimicrobial agent and its ability to alter biofilm mechanical properties and thereby influence biofilm removal. Understanding biofilm rheology and how it is affected by chemical treatment could lead to improvements in biofilm control.

  16. Stochastic stability properties of jump linear systems

    NASA Technical Reports Server (NTRS)

    Feng, Xiangbo; Loparo, Kenneth A.; Ji, Yuandong; Chizeck, Howard J.

    1992-01-01

    Jump linear systems are defined as a family of linear systems with randomly jumping parameters (usually governed by a Markov jump process) and are used to model systems subject to failures or changes in structure. The authors study stochastic stability properties in jump linear systems and the relationship among various moment and sample path stability properties. It is shown that all second moment stability properties are equivalent and are sufficient for almost sure sample path stability, and a testable necessary and sufficient condition for second moment stability is derived. The Lyapunov exponent method for the study of almost sure sample stability is discussed, and a theorem which characterizes the Lyapunov exponents of jump linear systems is presented.

  17. Viscoelastic properties of human mesenchymally-derived stem cells and primary osteoblasts, chondrocytes, and adipocytes

    PubMed Central

    Darling, Eric M.; Topel, Matthew; Zauscher, Stefan; Vail, Thomas P.; Guilak, Farshid

    2010-01-01

    The mechanical properties of single cells play important roles in regulating cell-matrix interactions, potentially influencing the process of mechanotransduction. Recent studies also suggest that cellular mechanical properties may provide novel biological markers, or “biomarkers,” of cell phenotype, reflecting specific changes that occur with disease, differentiation, or cellular transformation. Of particular interest in recent years has been the identification of such biomarkers that can be used to determine specific phenotypic characteristics of stem cells that separate them from primary, differentiated cells. The goal of this study was to determine the elastic and viscoelastic properties of three primary cell types of mesenchymal lineage (chondrocytes, osteoblasts, and adipocytes) and to test the hypothesis that primary differentiated cells exhibit distinct mechanical properties compared to adult stem cells (adipose-derived or bone marrow-derived mesenchymal stem cells). In an adherent, spread configuration, chondrocytes, osteoblasts, and adipocytes all exhibited significantly different mechanical properties, with osteoblasts being stiffer than chondrocytes and both being stiffer than adipocytes. Adipose-derived and mesenchymal stem cells exhibited similar properties to each other, but were mechanically distinct from primary cells, particularly when comparing a ratio of elastic to relaxed moduli. These findings will help more accurately model the cellular mechanical environment in mesenchymal tissues, which could assist in describing injury thresholds and disease progression or even determining the influence of mechanical loading for tissue engineering efforts. Furthermore, the identification of mechanical properties distinct to stem cells could result in more successful sorting procedures to enrich multipotent progenitor cell populations. PMID:17825308

  18. Temoporfin-loaded liposomal gels: viscoelastic properties and in vitro skin penetration.

    PubMed

    Dragicevic-Curic, Nina; Winter, Sven; Stupar, Mirjana; Milic, Jela; Krajisnik, Danina; Gitter, Burkhard; Fahr, Alfred

    2009-05-21

    Temoporfin (mTHPC) is a potent second-generation photosensitizer. The primary object of this study was to develop a topical mTHPC-loaded liposomal hydrogel able to deliver mTHPC into the stratum corneum (SC) and deeper skin layers. This study was conducted (1) to determine the effect of carbomer concentration, used as a gelling agent, and the effect of phosphatidylcholine (PC) content of lecithin, used for the liposome preparation, on viscoelastic properties and viscosity of liposomal gels and (2) to determine the relationship between rheological properties of gels and the skin penetration of mTHPC. Liposomal hydrogels revealed plastic flow behaviour. The increase of carbomer concentration induced a domination of elastic over viscous behaviour of gels. There was an inverse relationship between the elasticity of gels and mTHPC-penetration. Viscosity also increased with the increment of carbomer concentration, reducing the mTHPC-penetration. Liposomal gels containing lecithin of smaller PC-content (i.e. smaller purity) exhibited a more elastic solid behaviour than gels containing lecithin with high PC-content, and showed smaller mTHPC-penetration. The gel containing 0.75%, w/w, carbomer and lecithin with high PC-content was considered to be the optimal formulation, since it delivered high amounts of mTHPC to the SC and deeper skin layers, and it possessed desirable rheological properties.

  19. Viscoelastic Properties of Differentiating Blood Cells Are Fate- and Function-Dependent

    PubMed Central

    Ekpenyong, Andrew E.; Whyte, Graeme; Chalut, Kevin; Pagliara, Stefano; Lautenschläger, Franziska; Fiddler, Christine; Paschke, Stephan; Keyser, Ulrich F.; Chilvers, Edwin R.; Guck, Jochen

    2012-01-01

    Although cellular mechanical properties are known to alter during stem cell differentiation, understanding of the functional relevance of such alterations is incomplete. Here, we show that during the course of differentiation of human myeloid precursor cells into three different lineages, the cells alter their viscoelastic properties, measured using an optical stretcher, to suit their ultimate fate and function. Myeloid cells circulating in blood have to be advected through constrictions in blood vessels, engendering the need for compliance at short time-scales (minutes), compared to undifferentiated cells. These findings suggest that reduction in steady-state viscosity is a physiological adaptation for enhanced migration through tissues. Our results indicate that the material properties of cells define their function, can be used as a cell differentiation marker and could serve as target for novel therapies. PMID:23028868

  20. Viscoelastic Properties of Collagen-Adhesive Composites under Water Saturated and Dry Conditions

    PubMed Central

    Singh, Viraj; Misra, Anil; Parthasarathy, Ranganathan; Ye, Qiang; Spencer, Paulette

    2014-01-01

    To investigate the time and rate dependent mechanical properties of collagen-adhesive composites, creep and monotonic experiments are performed under dry and wet conditions. The composites are prepared by infiltration of dentin adhesive into a demineralized bovine dentin. Experimental results show that for small stress level under dry conditions, both the composite and neat adhesive have similar behavior. On the other hand, in wet conditions, the composites are significantly soft and weak compared to the neat adhesives. The behavior in the wet condition is found to be affected by the hydrophilicity of both the adhesive and collagen. Since the adhesive-collagen composites area part of the complex construct that forms the adhesive-dentin interface, their presence will affect the overall performance of the restoration. We find that Kelvin-Voigt model with at least 4-elements is required to fit the creep compliance data, indicating that the adhesive-collagen composites are complex polymers with several characteristics time-scales whose mechanical behavior will be significantly affected by loading rates and frequencies. Such mechanical properties have not been investigated widely for these types of materials. The derived model provides an additional advantage that it can be exploited to extract other viscoelastic properties which are, generally, time consuming to obtain experimentally. The calibrated model is utilized to obtain stress relaxation function, frequency-dependent storage and loss modulus, and rate dependent elastic modulus. PMID:24753362

  1. Investigation of the Non-Linear Viscoelastic Behavior of Lightly Cross-linked SBR: The Need for a New Modeling Perspective

    NASA Astrophysics Data System (ADS)

    Caruthers, James; Bhattacharya, Aparajita; Medvedev, Grigori

    2010-03-01

    An extensive set of both linear and non-linear mechanical experiments including non-linear stress-strain behavior and non-linear creep/recovery has been carried out on a lightly cross-linked SBR. The results have been obtained for a wide range of temperatures, extension rates and stretch ratios. The data set reveals an unexpectedly rich behavior, which cannot be predicted by the traditional constitutive models that are based on an additive combination of hyperelastic and quasi-linear viscoelastic contributions. The inability of traditional constitutive models to describe the data is particularly striking for a high extension rate deformation followed by a slow extension rate (e.g. creep) as contrasted to deformations at slow extension rates. The hyperelastic model of rubber elasticity is shown to provide a satisfactory description of the equilibrium behavior; thus, the results in the current study indicate the need for the development of a new type viscoelastic model for elastomers. Potential candidates for the needed constitutive description will be discussed.

  2. A micromechanical approach to elastic and viscoelastic properties of fiber reinforced concrete

    SciTech Connect

    Pasa Dutra, V.F.; Maghous, S. Campos Filho, A.; Pacheco, A.R.

    2010-03-15

    Some aspects of the constitutive behavior of fiber reinforced concrete (FRC) are investigated within a micromechanical framework. Special emphasis is put on the prediction of creep of such materials. The linear elastic behavior is first examined by implementation of a Mori-Tanaka homogenization scheme. The micromechanical predictions for the overall stiffness prove to be very close to finite element solutions obtained from the numerical analysis of a representative elementary volume of FRC modeled as a randomly heterogeneous medium. The validation of the micromechanical concepts based on comparison with a set of experiments, shows remarkable predictive capabilities of the micromechanical representation. The second part of the paper is devoted to non-ageing viscoelasticity of FRC. Adopting a Zener model for the behavior of the concrete matrix and making use of the correspondence principle, the homogenized relaxation moduli are derived analytically. The validity of the model is established by mean of comparison with available experiment measurements of creep strain of steel fiber reinforced concrete under compressive load. Finally, the model predictions are compared to those derived from analytical models formulated within a one-dimensional setting.

  3. Single Microbubble Measurements of Lipid Monolayer Viscoelastic Properties for Small-Amplitude Oscillations.

    PubMed

    Lum, Jordan S; Dove, Jacob D; Murray, Todd W; Borden, Mark A

    2016-09-20

    Lipid monolayer rheology plays an important role in a variety of interfacial phenomena, the physics of biological membranes, and the dynamic response of acoustic bubbles and drops. We show here measurements of lipid monolayer elasticity and viscosity for very small strains at megahertz frequency. Individual plasmonic microbubbles of 2-6 μm radius were photothermally activated with a short laser pulse, and the subsequent nanometer-scale radial oscillations during ring-down were monitored by optical scatter. This method provided average dynamic response measurements of single microbubbles. Each microbubble was modeled as an underdamped linear oscillator to determine the damping ratio and eigenfrequency, and thus the lipid monolayer viscosity and elasticity. Our nonisothermal measurement technique revealed viscoelastic trends for different lipid shell compositions. We observed a significant increase in surface elasticity with the lipid acyl chain length for 16 to 20 carbons, and this effect was explained by an intermolecular forces model that accounts for the lipid composition, packing, and hydration. The surface viscosity was found to be equivalent for these lipid shells. We also observed an anomalous decrease in elasticity and an increase in viscosity when increasing the acyl chain length from 20 to 22 carbons. These results illustrate the use of a novel nondestructive optical technique to investigate lipid monolayer rheology in new regimes of frequency and strain, possibly elucidating the phase behavior, as well as how the dynamic response of a microbubble can be tuned by the lipid intermolecular forces.

  4. The effect of overshooting the target strain on estimating viscoelastic properties from stress relaxation experiments.

    PubMed

    Gimbel, Jonathan A; Sarver, Joseph J; Soslowsky, Louis J

    2004-12-01

    Tendon's mechanical behaviors have frequently been quantified using the quasi-linear viscoelastic (QLV) model. The QLV parameters are typically estimated by fitting the model to a single-step stress relaxation experiment. Unfortunately, overshoot of the target strain occurs to some degree in most experiments. This has never been formally investigated even though failing to measure, minimize, or compensate for overshoot may cause large errors in the estimation of parameters. Therefore, the objective of this study was to investigate the effect of overshoot on the estimation of QLV parameters. A simulated experiment was first performed to quantify the effect of different amounts of overshoot on the estimated QLV parameters. Experimental data from tendon was then used to determine if the errors associated with overshoot could be reduced when a direct fit is used (i.e., the actual strain history was used in the curve fit). We found that both the elastic and viscous QLV parameters were incorrectly estimated if overshoot was not properly accounted for in the fit. Furthermore, the errors associated with overshoot were partially reduced when overshoot was accounted for using a direct fit. A slow ramp rate is recommended to limit the amount of overshoot and a direct fit is recommended to limit the errors associated with overshoot, although other approaches such as adjusting the control system to limit overshoot could also be utilized.

  5. Elastic modulus and viscoelastic properties of full thickness skin characterised at micro scales.

    PubMed

    Crichton, Michael L; Chen, Xianfeng; Huang, Han; Kendall, Mark A F

    2013-03-01

    The recent emergence of micro-devices for vaccine delivery into upper layers of the skin holds potential for increased immune responses using physical means to target abundant immune cell populations. A challenge in doing this has been a limited understanding of the skin elastic properties at the micro scale (i.e. on the order of a cell diameter; ~10 μm). Here, we quantify skin's elastic properties at a micro-scale by fabricating customised probes of scales from sub- to super-cellular (0.5 μm-20 μm radius). We then probe full thickness skin; first with force-relaxation experiments and subsequently by elastic indentations. We find that skin's viscoelastic response is scale-independent: consistently a ~40% decrease in normalised force over the first second, followed by further 10% reduction over 10 s. Using Prony series and Hertzian contact analyses, we determined the strain-rate independent elastic moduli of the skin. A high scale dependency was found: the smallest probe encountered the highest elastic modulus (~30 MPa), whereas the 20 μm radius probe was lowest (below 1 MPa). We propose that this may be a result of the load distribution in skin facilitated by the hard corneocytes in the outermost skin layers, and softer living cell layers below. Copyright © 2012 Elsevier Ltd. All rights reserved.

  6. An acoustic wave biosensor for probing the viscoelastic properties of living cells

    NASA Astrophysics Data System (ADS)

    Li, Fang; Wang, James H.-C.; Wang, Qing-Ming

    2006-05-01

    The thickness shear mode (TSM) resonator attached with living cells has been shown to be an effective functional biosensing device to monitor the process of cell adhesion to a surface. In this study, we first monitored the dynamic process of cell attachment and spreading as a function of cell seeding densities. Based on the steady state of cell adhesion to the substrate, a multilayer sensor structure model including a quartz substrate, a cell-substrate interfacial layer and a cell layer was constructed. The thickness of cell-substrate interfacial layer and the viscoelastic properties of human skin fibroblasts (HSF) were then determined by fitting experimental results with the theoretical model. It has been obtained that the thickness of the cell-substrate interfacial layer is 60-80 nm, and the elastic module and viscosity of cell layers are about 13 KPa and 3-4 mPa's respectively. These results are in a good agreement with those measured by other techniques, such as magnetic bead microrheometry, atomic force microscopy (AFM) and Surface Plasmon Resonance Microscopy (SPRM). In addition, knowing that the actin cytoskeleton is important for the mechanical properties of living cells, we investigated the motional resistance change caused by the disruption of actin cytoskeleton induced by fungal toxin Cytochalasin D in the human skin fibroblasts. The results indeed indicate the direct correlation between resistance changes and the disruption of actin cytoskeleton, which are again consistent with the results observed by fluorescence images.

  7. Preparation and characterization of herbal creams for improvement of skin viscoelastic properties.

    PubMed

    Ahshawat, M S; Saraf, S; Saraf, S

    2008-06-01

    The aim of this study was to formulate and evaluate herbal cosmetic creams for their improvement of skin viscoelastic and hydration properties. The cosmetic cream formulations were designed by using ethanolic extracts of Glycyrriza glabra, Curcuma longa (roots), seeds of Psorolea corlifolia, Cassia tora, Areca catechu, Punica granatum, fruits of Embelica officinale, leaves of Centella asiatica, dried bark of Cinnamon zeylanicum and fresh gel of Aloe vera in varied concentrations (0.12-0.9%w/w) and characterized using physicochemical and physiological measurements. The ethanolic extracts of herbs were incorporated in a cream base that is prepared by a phase inversion emulsification technique. The cream base was prepared by utilizing oil of Prunus amagdalus, Sesamum indicum, honey, cetyl alcohol, stearic acid, polysorbate monoleate, sorbitan monostearate, propylene glycol and glycerin. Physicochemical assessments and microbiological testing were completed for all formulations according to the methods of the Indian Standard Bureau. The studies were carried out for 6 weeks on normal subjects (6 males and 12 females, between 22 and 50 years) on the back of their volar forearm for evaluation of viscoelastic properties in terms of extensibility via a suction measurement, firmness using laboratory fabricated instruments such as ball bouncing and skin hydration using electric (resistance) measurement methods. The physicochemical parameters of formulations CAA1-CAA6, i.e. pH, acid value, saponification value, viscosity, spreadability, layer thickness microbial count and skin sensitivity were found to be in the range of 5.01 +/- 0.4-6.07 +/- 0.6, 3.3-5.1 +/- 0.2, 20-32, 5900-6755 cps, 60-99%, 25-50 mum, 31-46 colony-forming units (CFU) and a 0-1 erythema score. The formulations, CAA4 and CAA5, showed an increase in percentage extensibility (32.27 +/- 1.7% and 29.89 +/- 1.64%, respectively), firmness (28.86 +/- 0.86% and 29.89 +/- 2.8%, respectively) and improved skin

  8. RLC model of visco-elastic properties of the chest wall

    NASA Astrophysics Data System (ADS)

    Aliverti, Andrea; Ferrigno, Giancarlo

    1996-04-01

    The quantification of the visco-elastic properties (resistance (R), inertia (L) and compliance (C)) of the different chest wall compartments (pulmonary rib cage,diaphragmatic rib cage and abdomen) is important to study the status of the passive components of the respiratory system, particularly in selected pathologies. Applying the viscoelastic-electrical analogy to the chest wall, we used an identification method in order to estimate the R, L and C parameters of the different parts of the chest, basing on different models; the input and output measured data were constituted by the volume variations of the different chest wall compartments and by the nasal pressure during controlled intermittent positive pressure ventilation by nasal mask, while the parameters of the system (R, L and C of the different compartments) were to be estimated. Volumes were measured with a new method, recently validated, based on an opto-electronic motion analyzer, able to compute with high accuracy and null invasivity the absolute values and the time variations of the volumes of each of the three compartments. The estimation of the R, L and C parameters has been based on a least-squared criterion, and the minimization has been based on a robustified iterative Gauss-Newton algorithm. The validation of the estimation procedure (fitting) has ben performed computing the percentage root mean square value of the error between the output real data and the output estimated data. The method has been applied to 2 healthy subjects. Also preliminary results have been obtained from 20 subjects affected by neuromuscular diseases (Duchenne Muscular Dystrophy (DMD) and Spinal Muscle Atrophy (SMA)). The results show that: (a) the best-fitting electrical models of the respiratory system are made up by one or three parallel RLC branches supplied by a voltage generator (so considering inertial properties, particularly in the abdominal compartment, and not considering patient/machine connection); (b) there

  9. Determining the viscoelastic properties obtained by depth sensing microindentation of epoxy and polyester thermosets using a new phenomenological method

    NASA Astrophysics Data System (ADS)

    Kohl, James G.; Schwarzer, Norbert; Ngo, Truc T.; Favaro, Gregory; Rengnet, Eric; Bierwisch, Nick

    2015-01-01

    Epoxy and polyester thermosets are currently used as the polymer matrix material for many fiber-reinforced composite systems. The viscoelastic properties of these materials were investigated in this study by use of depth sensing microindentation. The microindentation tests performed had the load being applied at a rapid loading rate to a maximum load. This maximum load was held constant while the stylus continued to sink. It was then unloaded at a nominal rate. A new phenomenological model developed by Schwarzer in 2014 was used in this work to determine the viscoelastic properties. Two approaches or methods were used. The first method involved determining the three parameters by using hold time data combined with unloading data (this method is referred to in this work as ‘hold time method’). The second method used only the unloading data (this method is referred to in this work as ‘unloading method’). It was shown that the properties determined by the two methods are not the same but are dependent upon the strain rate behavior during the indentation test. Low load scratch tests were also performed. It was seen that as the sliding speed increased the depth of penetration decreased resulting in the coefficient of friction also decreasing. An understanding of the viscoelastic properties at the surface and how they affect friction are important in studying wear of these materials.

  10. Nanoindentation methods to measure viscoelastic properties of single cells using sharp, flat, and buckling tips inside ESEM.

    PubMed

    Ahmad, Mohd Ridzuan; Nakajima, Masahiro; Kojima, Seiji; Homma, Michio; Fukuda, Toshio

    2010-03-01

    In this paper, methods to measure viscoelastic properties of time-dependent materials are proposed using sharp, flat, and buckling tips inside an environmental SEM. Single W303 yeast cells were employed in this study. Each of the tips was used to indent single cells in a nanoindentation test. Three loading histories were used: 1) a ramp loading history, in which a sharp indenter was used; 2) a step loading history, in which a flat indenter was implemented; and 3) a fast unloading history, in which a buckling nanoneedle was applied. Analysis of the viscoelastic properties of single cells was performed for each of the loading histories by choosing an appropriate theory between the correspondence principle and the functional equation. Results from each of the tests show good agreement, from which strong conclusion can be drawn.

  11. Microstructure and textural and viscoelastic properties of model processed cheese with different dry matter and fat in dry matter content.

    PubMed

    Černíková, Michaela; Nebesářová, Jana; Salek, Richardos Nikolaos; Řiháčková, Lada; Buňka, František

    2017-04-05

    The aim of this work was to examine the effect of a different dry matter (DM) contents (35 and 45% wt/wt) and fat in DM contents (40 and 50% wt/wt) on the textural and viscoelastic properties and microstructure of model processed cheeses made from real ingredients regularly used in the dairy industry. A constant DM content and constant fat in DM content were kept throughout the whole study. Apart from the basic chemical parameters, textural and viscoelastic properties of the model samples were measured and scanning electron microscopy was carried out. With increasing DM content, the rigidity of the products increased and the size of the fat globules in the model samples of the processed cheeses decreased. With increasing fat in DM content, the rigidity of the processed cheeses decreased and the size of the fat globules increased.

  12. Investigation into viscoelastic properties of free-standing DPPC lipid bilayer via molecular dynamics and inverse finite element analysis

    NASA Astrophysics Data System (ADS)

    Momeni Bashusqeh, Saeed; Rastgoo, Abbas

    2017-10-01

    In the current study, the viscoelastic properties of the free-standing DPPC lipid bilayer are investigated using coarse-grained molecular dynamics (CG-MD) and inverse finite element (FE) methods. As the first step, the CG-MD method is employed to simulate the loading/relaxation of a free-standing DPPC lipid bilayer in an indentation experiment. Then the experiment is simulated using the FE method, in which viscoelastic properties of the bilayer are chosen by a genetic algorithm. At each optimization step, the force–time curve is extracted and evaluated with respect to the curve obtained from the CG-MD simulation. The optimization process is continued until a sufficiently good accordance is acquired between the force–time curves obtained from the FE and CG-MD simulations. The material’s behavior in the FE simulation is represented by a two-term Prony model which comprises three unknown constants; the instantaneous Young’s modulus, the steady-state Young’s modulus and the relaxation time constant, which are obtained through optimization. The effects of various simulation parameters, such as indentation speed, the shape of the indenter, the size of the bilayer and temperature, on the viscoelastic properties of the bilayer are also studied and discussed.

  13. Comparison of viscoelastic property characterization of plastisol phantoms with magnetic resonance elastography and high-frequency rheometry.

    PubMed

    Lefebvre, P M; Koon, K Tse Ve; Brusseau, E; Nicolle, S; Palieme, J-F; Lambert, S A; Grenier, D

    2016-08-01

    This study aims at evaluating Magnetic Resonance Elastography (MRE) as a reliable technique for the characterization of viscoelastic properties of soft tissues. Three phantoms with different concentrations of plastisol and softener were prepared in order to mechanically mimic a broad panel of healthy and pathological soft tissues. Once placed in a MRI device, each sample was excited by a homemade external driver, inducing shear waves within the medium. The storage (G') and loss (G") moduli of each phantom were then reconstructed from MRE acquisitions over a frequency range from 300 to 1,000 Hz, by applying a 2D Helmholtz inversion algorithm. At the same time, mechanical tests were performed on four samples of each phantom with a High-Frequency piezo-Rheometer (HFR) over an overlapping frequency range (from 160 to 630 Hz) with the same test conditions (temperature, ageing). The comparison between both techniques shows a good agreement in the measurement of the storage and loss moduli, underlying the capability of MRE to noninvasively assess the complex shear modulus G* of a medium and its interest for investigating the viscoelastic properties of living tissues. Moreover, the phantoms with varying concentrations of plastisol used in this study show interesting rheological properties, which make them good candidates to simulate the broad variety of viscoelastic behaviors of healthy and pathological soft tissues.

  14. Monitoring the Changes of Material Properties at Bone-Implant Interface during the Healing Process In Vivo: A Viscoelastic Investigation

    PubMed Central

    Chen, Hsiang-Ho; Lai, Wei-Yi; Chee, Tze-Jian

    2017-01-01

    The aim of this study was to monitor the changes of viscoelastic properties at bone-implant interface via resonance frequency analysis (RFA) and the Periotest device during the healing process in an experimental rabbit model. Twenty-four dental implants were inserted into the femoral condyles of rabbits. The animals were sacrificed immediately after implant installation or on day 14, 28, or 56 after surgery. Viscoelastic properties at bone-implant interface were evaluated by measuring the implant stability quotient (ISQ) using RFA and by measuring the Periotest values (PTVs) using the Periotest device. The bone/implant specimens were evaluated histopathologically and histomorphometrically to determine the degree of osseointegration (BIC%). The BIC% values at different time points were then compared with the corresponding ISQ values and PTVs. The mean ISQ value increased gradually and reached 81 ± 1.7 on day 56, whereas the mean PTV decreased over time, finally reaching −0.7 ± 0.5 on day 56. Significant correlations were found between ISQ and BIC% (r = 0.701, p < 0.001), PTV and BIC% (r = −0.637, p < 0.05), and ISQ and PTV (r = −0.68, p < 0.05). These results show that there is a positive correlation between implant stability parameters and peri-implant-bone healing, indicating that the RFA and Periotest are useful for measuring changes of viscoelastic properties at bone-implant interface and are reliable for indirectly predicting the degree of osseointegration. PMID:28373978

  15. Dynamics of viscoelastic properties of rat cardiac sarcomeres during the diastolic interval: involvement of Ca2+.

    PubMed Central

    Stuyvers, B D; Miura, M; ter Keurs, H E

    1997-01-01

    1. Cardiac sarcomere stiffness was investigated during diastole in eighteen trabeculae dissected from the right ventricle of rat heart. The trabeculae were stimulated at 0.5 Hz, in a modified Krebs-Henseleit solution (pH, 7.4; 25 degrees C). Sarcomere length (SL) was measured using high resolution (+/-2 nm) laser diffraction techniques. Force (F) was measured with a silicon strain gauge. 2. SL increased exponentially (amplitude, 25 +/- 9 nm; n = 15) throughout diastole. This increase occurred even at slack SL, showing that this phenomenon was due to an internal expansion. The majority of the muscles showed discrete spontaneous fluctuations of SL (amplitude < 20 nm) starting approximately 1 s after the end of the twitch. 3. The intracellular free Ca2+ concentration ([Ca2+]i) was measured from the fluorescence of microinjected fura-2 salt in seven trabeculae under the same experimental conditions. [Ca2+]i continuously declined (from 240 to 90 nM) during diastole following a monoexponential time course (time constant, 210-325 ms). 4. The stiffness of the sarcomere was evaluated at 10, 30, 50, 70 and 90% of diastole using bursts (30 ms) of 500 Hz sinusoidal perturbations of muscle length (amplitude of SL oscillations < 30 nm). At 1 nM external Ca2+ concentration ([Ca2+]o), the average stiffness modulus (Mod) increased from 9.3 +/- 0.6 to 12 +/- 0.6 nN mm-2 micron-1 (n = 18; P < 0.05), while the average phase shift (phi) between F and SL signals decreased from 84 +/- 3 to 73 +/- 4 deg (n = 18; P < 0.05) between 10 and 90% during diastole. The increase in Mod and the decrease in phi reversed when spontaneous activity occurred. When [Ca2+]o was raised to 2 mM, the stiffness time course reversed approximately 450 ms earlier, simultaneously with the occurrence of spontaneous activity. 5. Our results show that diastole is only an apparent steady state and suggest that the structural system responsible for the viscoelastic properties of the sarcomere is regulated by [Ca2+]i

  16. Nano confinement effects on dynamic and viscoelastic properties of Selenium Films

    NASA Astrophysics Data System (ADS)

    Yoon, Heedong; McKenna, Gregory

    2015-03-01

    In current study, we use a novel nano bubble inflation technique to study nano confinement effects on the dynamic and viscoelastic properties of physical vapor deposited Selenium films. Film thicknesses ranged from 60 to 260 nm. Creep experiments were performed for the temperatures ranging from Tg,macroscopic-14 °C to Tg,\\ macroscopic + 19 °C. Time temperature superposition and time thickness superposition were applied to create reduced creep curves, and those were compared with macroscopic data [J. Non-Cryst. Solids. 2002, 307, 790-801]. The results showed that the time temperature superposition was applicable in the glassy relaxation regime to the steady-state plateau regime. However in the long time response of the creep compliance, time thickness superposition failed due to the thickness dependence on the steady-state plateau. It was observed that the steady state compliance increased with film thickness. The thickness dependence on the plateau stiffening followed a power law of DPlateau ~ h2.46, which is greater than observed in organic polymers where the exponents observed range from 0.83 to 2.0 [Macromolecules. 2012, 45 (5), 2453-2459]. National Science Foundation Grant No. CHE 1112416 and John R. Bradford Endowment at Texas Tech

  17. Interactions of glycosphingolipids and lipopolysaccharides with silica and polyamide surfaces: adsorption and viscoelastic properties.

    PubMed

    Gutman, Jenia; Kaufman, Yair; Kawahara, Kazuyoshi; Walker, Sharon L; Freger, Viatcheslav; Herzberg, Moshe

    2014-06-09

    Bacterial outer membrane components play a critical role in bacteria-surface interactions (adhesion and repulsion). Sphingomonas species (spp.) differ from other Gram-negative bacteria in that they lack lipopolysaccharides (LPSs) in their outer membrane. Instead, Sphingomonas spp. outer membrane consists of glycosphingolipids (GSLs). To delineate the properties of the outer membrane of Sphingomonas spp. and to explain the adhesion of these cells to surfaces, we employed a single-component-based approach of comparing GSL vesicles to LPS vesicles. This is the first study to report the formation of vesicles containing 100% GSL. Significant physicochemical differences between GSL and LPS vesicles are reported. Composition-dependent vesicle adherence to different surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D) technology was observed, where higher GSL content resulted in higher mass accumulation on the sensor. Additionally, the presence of 10% GSL and above was found to promote the relative rigidity of the vesicle obtaining viscoelastic ratio of 30-70% higher than that of pure LPS vesicles.

  18. Effects of thermal cycling on dynamic viscoelastic properties of four commercial resins for crown and bridge.

    PubMed

    Fujii, K; Miura, K; Omori, K; Arikawa, H; Kanie, T; Inoue, K

    1999-12-01

    To elucidate the effects of thermal cycling on the viscoelastic properties of four commercial resins for crown and bridge, dynamic shear modulus (G'), mechanical loss tangent (tan delta), Knoop hardness, water sorption and appearance of specimen surfaces before and after thermal cycling test were determined. The changes of G' and tan delta for two materials were insignificant with increased repetitions of thermal cycling. Those of the other two materials were statistically significant: in particular, G' at temperatures above 60 degrees C was inclined to increase slightly and tan delta decreased considerably. While the Knoop hardness of the materials was a little decreased over a number of 75,000 thermal cycles, the water sorption almost attained an equilibrium in uptake after 14,000 thermal cycles. Furthermore, cracks on the specimen surface were observed after 37,500 to 75,000 thermal cycles. From these results, the deterioration of materials was observed as damage to the specimen surface. Moreover, it could be presumed that the materials would be further polymerized during the period of thermal cycling.

  19. Gelation kinetics and viscoelastic properties of pluronic and α-cyclodextrin-based pseudopolyrotaxane hydrogels.

    PubMed

    Pradal, Clementine; Jack, Kevin S; Grøndahl, Lisbeth; Cooper-White, Justin J

    2013-10-14

    The results of a systematic investigation into the gelation behavior of α-cyclodextrin (α-CD) and Pluronic (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers) pseudopolyrotaxane (PPR) hydrogels are reported here in terms of the effects of temperature, α-CD concentration, and Pluronic type (Pluronic F68 and Pluronic F127). It was found that α-CD significantly modifies the gelation behavior of Pluronic solutions and that the PPR hydrogels are highly sensitive to changes in the α-CD concentration. In some cases, the addition of α-CD was found to be detrimental to the gelation process, leading to slower gelation kinetics and weaker gels than with Pluronic alone. However, in other cases, the hydrogels formed in the presence of the α-CDs reached higher moduli and showed faster gelation kinetics than with Pluronic alone and in some instances α-CD allowed the formation of hydrogels from Pluronic solutions that would normally not undergo gelation. Depending on composition and ratio of α-CD/Pluronic, these highly viscoelastic hydrogels displayed elastic shear modulus values ranging from 2 kPa to 7 MPa, gelation times ranging from a few seconds to a few hours and self-healing behaviors post failure. Using dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS), we probed the resident structure of these systems, and from these insights we have proposed a new molecular mechanism that accounts for the macroscopic properties observed.

  20. Viscoelastic properties of an exopolysaccharide: Aeromonas gum, produced by Aeromonas nichidenii 5797.

    PubMed

    Xu, Xiaojuan; Chen, Pan; Zhang, Lina

    2007-01-01

    The viscoelastic properties of Aeromonas (A) gum in water were investigated by using the Rheometric Scientific ARES controlled strain rheometer. An intrinsic viscosity of 8336 ml/g was obtained according to the Fuoss-Straus equation. The effect of salt concentration on intrinsic viscosity revealed that the A gum exists as semiflexible chain. Typical shear-thinning (pseudoplastic) behavior was observed at concentrations higher than 0.52%. The zero shear viscosity (eta(0)) increased with increasing polysaccharide concentration (c) showing a gradient of approximately 1.0, 2.9 and 4.8 in different concentration domains. The critical concentrations c* and c**, at which the transitions from a dilute solution of independently moving chains to semidilute and then concentrated domains occurred, were determined roughly to be 1.2% and 3.5%. The results from dynamic experiments revealed that the A gum solution shows characteristics of polymer solutions without any evidence of gel-like character. All the results from steady and dynamic tests suggest that the A gum is a non-gelling polysaccharide. The temperature dependence of apparent viscosity was described by Arrhenius equation and the flow activation energy was estimated to be 45.2 kJ/mol, which is independent on polymer concentration.

  1. Effect of Age and Exercise on the Viscoelastic Properties of Rat Tail Tendon

    PubMed Central

    LaCroix, Andrew S.; Duenwald-Kuehl, Sarah E.; Brickson, Stacey; Akins, Tiffany L.; Diffee, Gary; Aiken, Judd; Vanderby, Ray; Lakes, Roderic S.

    2013-01-01

    Tendon mechanical properties are thought to degrade during aging but improve with exercise. A remaining question is whether exercise in aged animals provides sufficient regenerative, systemic stimulus to restore younger mechanical behaviors. Herein we address that question with tail tendons from aged and exercised rats, which would be subject to systemic effects but not direct loading from the exercise regimen. Twenty-four month old rats underwent one of three treadmill exercise training protocols for 12 months: sedentary (walking at 0° incline for 5 min/day), moderate (running at 0° incline for 30 min/day), or high (running at 4° incline for 30 min/day). A group of 9 month old rats were used to provide an adult control, while a group of 3 month old rats provided a young control. Tendons were harvested at sacrifice and mechanically tested. Results show significant age-dependent differences in modulus, ultimate stress, relaxation rate, and percent relaxation. Relaxation rate was strain-dependent, consistent with nonlinear superposition or Schapery models but not with quasilinear viscoelasticity (QLV). Trends in exercise data suggest that with exercise, tendons assume the elastic character of younger rats (lower elastic modulus and ultimate stress). PMID:23549897

  2. Cell adaptation to a physiologically relevant ECM mimic with different viscoelastic properties

    PubMed Central

    Ghosh, Kaustabh; Pan, Zhi; Guan, E; Ge, Shouren; Liu, Yajie; Nakamura, Toshio; Ren, Xiang-Dong; Rafailovich, Miriam; Clark, Richard A.F.

    2009-01-01

    To successfully induce tissue repair or regeneration in vivo, bioengineered constructs must possess both optimal bioactivity and mechanical strength. This is because cell interaction with the extracellular matrix (ECM) produces two different but concurrent signaling mechanisms: ligation-induced signaling, which depends on ECM biological stimuli, and traction-induced signaling, which depends on ECM mechanical stimuli. In this report, we provide a fundamental understanding of how alterations in mechanical stimuli alone, produced by varying the viscoelastic properties of our bioengineered construct, modulate phenotypic behavior at the whole-cell level. Using a physiologically-relevant ECM mimic composed of hyaluronan and fibronectin, we found that adult human dermal fibroblasts modify their mechanical response in order to match substrate stiffness. More specifically, the cells on stiffer substrates had higher modulus and a more stretched and organized actin cytoskeleton (and vice versa), which translated into larger traction forces exerted on the substrate. This modulation of cellular mechanics had contrasting effects on migration and proliferation, where cells migrated faster on softer substrates while proliferating preferentially on the stiffer ones. These findings implicate substrate rigidity as a critical design parameter in the development of bioengineered constructs aimed at eliciting maximal cell and tissue function. PMID:17049594

  3. Viscoelastic characteristics and phytochemical properties of purple-rice drinks following ultrahigh pressure and pasteurization

    NASA Astrophysics Data System (ADS)

    Worametrachanon, Srivilai; Apichartsrangkoon, Arunee

    2014-10-01

    This study investigated how pressure (500, 600 MPa/20 min) altered the viscoelastic characteristics and phytochemical properties of germinated and non-germinated purple-rice drinks in comparison with pasteurization. Accordingly, color parameters, storage and loss moduli, anthocyanin content, γ-oryzanol, γ-aminobutyric acid (GABA), total phenolic compounds and 2,2-diphenyl-1-picrylthydrazyl (DPPH) capacity of the processed drinks were determined. The finding showed that germinated and pressurized rice drink had lower Browning Index than the non-germinated and pasteurized rice drink. The plots of storage and loss moduli for processed rice drinks indicated that time of pressurization had greater impact on gel structural modification than the level of pressure used. The phytochemicals, including total phenolics, and DPPH capacity in pressurized rice drinks retained higher quantity than those in pasteurized drink, despite less treatment effects on anthocyanin. On the contrary, both γ-oryzanol and GABA were found in high amounts in germinated rice drink with little variation among processing effects.

  4. Comparison of viscoelastic properties of walls and functional characteristics of valves in lymphatic and venous vessels.

    PubMed

    Ohhashi, T

    1987-12-01

    The principal function of the lymphatic and venous system is to maintain a favorable environment for cells of the body. As a consequence mainly of hydrostatic forces, shifts of fluid usually occur between the vascular system and the extracellular space. To compensate for these shifts the veins are capable of active and passive changes in capacity that serve to modulate the filling pressure of the heart by adjusting the central blood volume. In addition to the venous function, the lymphatic function also contributes to compensate for the fluid shifts by drainage from the interstitial space. Namely, the general function of the lymphatic system is to return fluid and protein which escapes from the blood capillaries to the lymph circulation. To elucidate the mode of venous and lymph transport, therefore, it is of essential importance to obtain basic knowledge of the mechanical characteristics of the walls of the vessels and the functional characteristics of the lymphatic and venous valves dividing two adjacent compartments. In this communication, in order to answer the question, "Are Lymphatics Different From Blood Vessels?", I would like to review a comparison of viscoelastic properties of walls and functional characteristics of valves in lymph and venous vessels by use of our original data obtained with isolated canine veins and thoracic ducts and with isolated bovine mesenteric lymphatics (1-9).

  5. Experimental methods for the characterization of the frequency-dependent viscoelastic properties of soft materials

    PubMed Central

    Kazemirad, Siavash; K. Heris, Hossein; Mongeau, Luc

    2013-01-01

    A characterization method based on Rayleigh wave propagation was developed for the quantification of the frequency-dependent viscoelastic properties of soft materials at high frequencies; i.e., up to 4 kHz. Planar harmonic surface waves were produced on the surface of silicone rubber samples. The phase and amplitude of the propagating waves were measured at different locations along the propagation direction, which allowed the calculation of the complex Rayleigh wavenumbers at each excitation frequency using a transfer function method. An inverse wave propagation problem was then solved to obtain the complex shear/elastic moduli from the measured wavenumbers. In a separate, related investigation, dynamic indentation tests using atomic force microscopy (AFM) were performed at frequencies up to 300 Hz. No systematic verification study is available for the AFM-based method, which can be used when the dimensions of the test samples are too small for other existing testing methods. The results obtained from the Rayleigh wave propagation and AFM-based indentation methods were compared with those from a well-established method, which involves the generation of standing longitudinal compression waves in rod-shaped test specimens. The results were cross validated and qualitatively confirmed theoretical expectations presented in the literature for the frequency-dependence of polymers. PMID:23654420

  6. Viscoelastic properties, creep behavior and degree of conversion of bulk fill composite resins.

    PubMed

    Papadogiannis, D; Tolidis, K; Gerasimou, P; Lakes, R; Papadogiannis, Y

    2015-12-01

    The aim of this study was to investigate the viscoelastic properties and creep behavior of bulk fill composites under different conditions and evaluate their degree of conversion. Seven bulk fill composites were examined: everX Posterior (EV), SDR (SD), SonicFill (SF), Tetric EvoCeram Bulk Fill (TE), Venus Bulk Fill (VE), x-tra base (XB) and x-tra fil (XF). Each material was tested at 21°C, 37°C and 50°C under dry and wet conditions by applying a constant torque for static and creep testing and dynamic torsional loading for dynamic testing. Degree of conversion (%DC) was measured on the top and bottom surfaces of composites with ATR-FTIR spectroscopy. Statistical analysis was performed with two-way ANOVA, Bonferroni's post hoc test and Pearson's correlation coefficient. Shear modulus G ranged from 2.17GPa (VE) to 8.03GPa (XF) and flexural modulus E from 6.16GPa (VE) to 23GPa (XF) when the materials were tested dry at 21°C. The increase of temperature and the presence of water lead to a decline of these properties. Flowable materials used as base composites in restorations showed significantly lower values (p<0.05) than non-base composites, while being more prone to creep deformation. %DC ranged from 47.25% (XF) to 66.67% (SD) at the top material surface and 36.06% (XF) to 63.20% (SD) at the bottom. Bulk fill composites exhibited significant differences between them with base flowable materials showing in most cases inferior mechanical properties and higher degree of conversion than restorative bulk fill materials. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  7. Viscoelastic properties of normal and cancerous human breast cells are affected differently by contact to adjacent cells.

    PubMed

    Schierbaum, Nicolas; Rheinlaender, Johannes; Schäffer, Tilman E

    2017-04-07

    Malignant transformation drastically alters the mechanical properties of the cell and its response to the surrounding cellular environment. We studied the influence of the physical contact between adjacent cells in an epithelial monolayer on the viscoelastic behavior of normal MCF10A, non-invasive cancerous MCF7, and invasive cancerous MDA-MB-231 human breast cells. Using an atomic force microscopy (AFM) imaging technique termed force clamp force mapping (FCFM) to record images of the viscoelastic material properties of sparse and confluent cells, we found that normal MCF10A cells are stiffer and have a lower fluidity when at confluent than at sparse density. Contrarily, cancerous MCF7 and MDA-MB-231 cells do not stiffen and do not decrease their fluidity when progressing from sparse to confluent density. The behavior of normal MCF10A cells appears to be governed by the formation of stable cell-cell contacts, because their disruption with a calcium-chelator (EGTA) causes the stiffness and fluidity values to return to those at sparse density. In contrast, EGTA-treatment of MCF7 and MDA-MB-231 cells does not change their viscoelastic properties. Confocal fluorescence microscopy showed that the change of the viscoelastic behavior in MCF10A cells when going from sparse to confluent density is accompanied by a remodeling of the actin cytoskeleton into thick stress fiber bundles, while in MCF7 and MDA-MB-231 cells the actin cytoskeleton is only composed of thin and short fibers, regardless of cell density. While the observed behavior of normal MCF10A cells might be crucial for providing mechanical stability and thus in turn integrity of the epithelial monolayer, the dysregulation of this behavior in cancerous MCF7 and MDA-MB-231 cells is possibly a central aspect of cancer progression in the epithelium.

  8. On the Energy Release Rate for Dynamic Transient Anti-Plane Shear Crack Propagation in a General Linear Viscoelastic Body

    DTIC Science & Technology

    1988-09-01

    properties.> Moreover, it is found that whether or not a failure zone is incorporated into the model si nif icantly influences both quantitatively and...Moreover, it is found that whether or not a failure zone is incorporated into the model significantly influences both quantitatively and...Hopf technique, Willis constructed the dynamic stress intensity factor (SIP) for a standard linear solid material model and general crack face

  9. Temperature Dependence of the Viscoelastic Properties of a Confined Liquid Polymer Measured by Using an Oscillating Optical Fiber Probe

    NASA Astrophysics Data System (ADS)

    Itoh, Shintaro; Fukuzawa, Kenji; Hamamoto, Yuya; Zhang, Hedong

    2010-08-01

    We measured the temperature dependence of the viscoelastic properties of a liquid polymer confined and sheared within a nanometer-sized gap. In the viscoelastic measurements, we used the fiber wobbling method, a highly sensitive method that we have developed for measuring shear forces. As a liquid sample, we used the fluoropolyether lubricant Fomblin Zdol4000. Our experimental results showed that the temperature dependence of the viscosity was well expressed by the well-known Andrade equation, even in the confined state. The activation enthalpy was calculated by assuming that Eyring's theory of viscosity holds for gaps of a width ranging from 100 nm down to a few nanometers. We observed a significant decrease in the activation enthalpy for gaps smaller than 10 nm. Elasticity, which only appeared for confinement in gaps smaller than 10 nm, roughly decreased with increasing temperature.

  10. Impact of Texture Heterogeneity on Elastic and Viscoelastic Properties of Carbonates

    NASA Astrophysics Data System (ADS)

    Sharma, Ravi

    This thesis discusses the impacts of fabric heterogeneity, fluids and fluid saturations, effective pressures, and frequency of investigation on the elastic and viscoelastic properties of calcite-rich limestone and chalk formations. Carbonate reservoirs have been analyzed either with empirical relations and analogs from siliciclastic reservoirs or using simplistic models. However, under the varying parameters mentioned above, their seismic response can be very different. The primary reason is because these rocks of biochemical origins readily undergo textural changes and support heterogeneous distribution of fluid flow and elastic properties. Thus, many current rock physics models are unable to predict the time-lapse elastic response in these reservoirs. I have measured elastic properties of calcite rich rocks in the seismic frequency range of 2 to 2000 Hz and at the ultrasonic frequency of 800 kHz. The samples selected for this study represent the typical heterogeneities found in carbonate formations. These measurements covering a large frequency range provide an understanding of the dispersion and attenuation mechanisms during seismic wave propagation in the subsurface. I find that a heterogeneous formation shows significant velocity dispersion and attenuations when saturated with brine, and even more on saturation with CO2. I also show that the shear modulus of carbonate rocks changes significantly (from 8% for brine saturation to 70% for CO2 saturation) upon fluid saturation with polar fluids. I evaluated rock physics models, such as Gassmann's and with uniform and patchy fluid substitution, and Hashin-Shtrikman to predict saturated elastic properties in carbonates. Fluid sensitivity is directly related to the initial stiffness of the rock instead of porosity, as normally assumed. The Gassmann model can predict elastic properties for uniform saturations - mostly in homogenous rocks. Heterogeneous rocks, however, are better modeled using a patchy fluid saturation

  11. The role of isocyanates in determining the viscoelastic properties of polyurethane

    NASA Astrophysics Data System (ADS)

    AqilahHamuzan, Hawa; Badri, Khairiah Haji

    2016-11-01

    Polyurethane (PU) has a unique structure that is dependent on the structure of the starting material used. This research focused on investigating the role of isocyanate groups (NCO) in the determination of the viscoelastic properties of the polymer. Monoester polyol was reacted with three different diisocyanates separately by prepolymerization method. The diisocyanates used were 2,4-diphenyl methane diisocyanate (MDI), toluene 2,4-diisocyanate (TDI) and isophoronediisocyanate (IPDI). Acetone was used as a solvent. IPDI, MDI and TDI were reacted with monoester polyol at ratios of 10:9, 10:10, 10:12 and 10:14 (polyol:diisocyanate). Then, the PU foams produced by the curing process were analyzed by Fourier Transform infrared spectroscopy (FTIR). The FTIR spectra showed the presence of the amide peak (-NH) and the absence of hydroxyl peak (-OH) indicated that the reaction between polyol and diisocyanate has occurred. However, the soxhlet extraction showed that only MDI-based PUs contain crosslinking bond. These cross-linking bond at the ratio of 10:10, 10:12 and 10:14 were 41.3 %,61.1 % and 74.1 % respectively. Thermal properties of the PU foams were determined by differential scanning calorimetry (DSC) and thermogravimetry (TGA) techniques. MDI-based PUs and TDI-based PUs show two values of Tg while IPDI-based PUs only show one Tg value. The tensile strains of PU foams decreased with increasing ratio of isocyanate. Meanwhile, PU foams with ratio of polyol to isocyanate at 10:12 showed the highest tensile stress and modulus compared to at 10:10 and 10:14.

  12. Cervids With Different Vocal Behavior Demonstrate Different Viscoelastic Properties of Their Vocal Folds

    PubMed Central

    Riede, Tobias; Lingle, Susan; Hunter, Eric J.; Titze, Ingo R.

    2014-01-01

    The authors test the hypothesis that vocal fold morphology and biomechanical properties covary with species-specific vocal function. They investigate mule deer (Odocoileus hemionus) vocal folds, building on, and extending data on a related cervid, the Rocky Mountain elk (Cervus elaphus nelsoni). The mule deer, in contrast to the elk, is a species with relatively little vocal activity in adult animals. Mule deer and elk vocal folds show the typical three components of the mammalian vocal fold (epithelium, lamina propria and thyroarytenoid muscle). The vocal fold epithelium and the lamina propria were investigated in two sets of tensile tests. First, creep rupture tests demonstrated that ultimate stress in mule deer lamina propria is of the same magnitude as in elk. Second, cyclic loading tests revealed similar elastic moduli for the vocal fold epithelium in mule deer and elk. The elastic modulus of the lamina propria is also similar between the two species in the low-strain region, but differs at strains larger than 0.3. Sex differences in the stress–strain response, which have been reported for elk and human vocal folds, were not found for mule deer vocal folds. The laminae propriae in mule deer and elk vocal folds are comparatively large. In general, a thick and uniformly stiff lamina propria does not self-oscillate well, even when high subglottic pressure is applied. If the less stiff vocal fold seen in elk is associated with a differentiated lamina propria it would allow the vocal fold to vibrate at high tension and high subglottic pressure. The results of this study support the hypothesis that viscoelastic properties of vocal folds varies with function and vocal behavior. PMID:19603411

  13. Viscoelastic properties of rabbit osteoarthritic menisci: A correlation with matrix alterations.

    PubMed

    Levillain, A; Magoariec, H; Boulocher, C; Decambron, A; Viateau, V; Hoc, T

    2017-01-01

    The aim of this study was to evaluate the effect of early osteoarthritis (OA) on the viscoelastic properties of rabbit menisci and to correlate the mechanical alterations with the microstructural changes. Anterior Cruciate Ligament Transection (ACLT) was performed in six male New-Zealand White rabbits on the right knee joint. Six healthy rabbits served as controls. Menisci were removed six weeks after ACLT and were graded macroscopically. Indentation-relaxation tests were performed in the anterior and posterior regions of the medial menisci. The collagen fibre organization and glycosaminoglycan (GAG) content were assessed by biphotonic confocal microscopy and histology, respectively. OA menisci displayed severe macroscopic lesions compared with healthy menisci (p=0.009). Moreover, the instantaneous and equilibrium moduli, which were 2.9±1.0MPa and 0.60±0.18MPa in the anterior region of healthy menisci, respectively, decreased significantly (p=0.03 and p=0.004, respectively) in OA menisci by 55% and 57%, respectively, indicating a global decrease in meniscal stiffness in this region. The equilibrium modulus alone decreased significantly (p=0.04) in the posterior region, going from 0.60±0.18MPa to 0.26±012MPa. This induced a loss of tissue elasticity. These mechanical changes were associated in the posterior region with a structural disruption of the superficial layers, from which the tie fibres emanate, and with a decrease in the GAG content in the anterior region. Consequently, the circumferential collagen fibres of the deep zone were dissociated and the collagen bundles were less compact. Our results demonstrate the strong meniscal modifications induced by ACLT at an early stage of OA and highlight the relationship between structural and chemical matrix alterations and mechanical properties.

  14. Cervids with different vocal behavior demonstrate different viscoelastic properties of their vocal folds.

    PubMed

    Riede, Tobias; Lingle, Susan; Hunter, Eric J; Titze, Ingo R

    2010-01-01

    The authors test the hypothesis that vocal fold morphology and biomechanical properties covary with species-specific vocal function. They investigate mule deer (Odocoileus hemionus) vocal folds, building on, and extending data on a related cervid, the Rocky Mountain elk (Cervus elaphus nelsoni). The mule deer, in contrast to the elk, is a species with relatively little vocal activity in adult animals. Mule deer and elk vocal folds show the typical three components of the mammalian vocal fold (epithelium, lamina propria and thyroarytenoid muscle). The vocal fold epithelium and the lamina propria were investigated in two sets of tensile tests. First, creep rupture tests demonstrated that ultimate stress in mule deer lamina propria is of the same magnitude as in elk. Second, cyclic loading tests revealed similar elastic moduli for the vocal fold epithelium in mule deer and elk. The elastic modulus of the lamina propria is also similar between the two species in the low-strain region, but differs at strains larger than 0.3. Sex differences in the stress-strain response, which have been reported for elk and human vocal folds, were not found for mule deer vocal folds. The laminae propriae in mule deer and elk vocal folds are comparatively large. In general, a thick and uniformly stiff lamina propria does not self-oscillate well, even when high subglottic pressure is applied. If the less stiff vocal fold seen in elk is associated with a differentiated lamina propria it would allow the vocal fold to vibrate at high tension and high subglottic pressure. The results of this study support the hypothesis that viscoelastic properties of vocal folds varies with function and vocal behavior.

  15. Effects of resistance and stretching training programmes on the viscoelastic properties of human tendon structures in vivo.

    PubMed

    Kubo, Keitaro; Kanehisa, Hiroaki; Fukunaga, Tetsuo

    2002-01-01

    The present study examined whether resistance and stretching training programmes altered the viscoelastic properties of human tendon structures in vivo. Eight subjects completed 8 weeks (4 days per week) of resistance training which consisted of unilateral plantar flexion at 70 % of one repetition maximum with 10 repetitions per set (5 sets per day). They performed resistance training (RT) on one side and resistance training and static stretching training (RST; 10 min per day, 7 days per week) on the other side. Before and after training, the elongation of the tendon structures in the medial gastrocnemius muscle was directly measured using ultrasonography, while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force (F(m)) and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the F(m)-L loop to the area beneath the load portion of the curve. The stiffness increased significantly by 18.8 +/- 10.4 % for RT and 15.3 +/- 9.3 % for RST. There was no significant difference in the relative increase of stiffness between RT and RST. The hysteresis, on the other hand, decreased 17 +/- 20 % for RST, but was unchanged for RT. These results suggested that the resistance training increased the stiffness of tendon structures as well as muscle strength and size, and the stretching training affected the viscosity of tendon structures but not the elasticity.

  16. Effects of resistance and stretching training programmes on the viscoelastic properties of human tendon structures in vivo

    PubMed Central

    Kubo, Keitaro; Kanehisa, Hiroaki; Fukunaga, Tetsuo

    2002-01-01

    The present study examined whether resistance and stretching training programmes altered the viscoelastic properties of human tendon structures in vivo. Eight subjects completed 8 weeks (4 days per week) of resistance training which consisted of unilateral plantar flexion at 70 % of one repetition maximum with 10 repetitions per set (5 sets per day). They performed resistance training (RT) on one side and resistance training and static stretching training (RST; 10 min per day, 7 days per week) on the other side. Before and after training, the elongation of the tendon structures in the medial gastrocnemius muscle was directly measured using ultrasonography, while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force (Fm) and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the Fm-L loop to the area beneath the load portion of the curve. The stiffness increased significantly by 18.8 ± 10.4 % for RT and 15.3 ± 9.3 % for RST. There was no significant difference in the relative increase of stiffness between RT and RST. The hysteresis, on the other hand, decreased 17 ± 20 % for RST, but was unchanged for RT. These results suggested that the resistance training increased the stiffness of tendon structures as well as muscle strength and size, and the stretching training affected the viscosity of tendon structures but not the elasticity. PMID:11773330

  17. Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

    PubMed Central

    2016-01-01

    Summary Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip–sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young’s modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip–sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information. PMID:27335746

  18. Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions.

    PubMed

    Solares, Santiago D

    2016-01-01

    Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information.

  19. Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: Coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

    DOE PAGES

    Solares, Santiago D.

    2016-04-15

    Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surfacemore » as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single-and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. As a result, a multifrequency AFM simulation tool based on the above sample model is provided as supporting information.« less

  20. Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: Coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

    SciTech Connect

    Solares, Santiago D.

    2016-04-15

    Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single-and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. As a result, a multifrequency AFM simulation tool based on the above sample model is provided as supporting information.

  1. Viscoelastic property tuning for reducing noise radiated by switched-reluctance machines

    NASA Astrophysics Data System (ADS)

    Millithaler, Pierre; Dupont, Jean-Baptiste; Ouisse, Morvan; Sadoulet-Reboul, Émeline; Bouhaddi, Noureddine

    2017-10-01

    Switched-reluctance motors (SRM) present major acoustic drawbacks that hinder their use for electric vehicles in spite of widely-acknowledged robustness and low manufacturing costs. Unlike other types of electric machines, a SRM stator is completely encapsulated/potted with a viscoelastic resin. By taking advantage of the high damping capacity that a viscoelastic material has in certain temperature and frequency ranges, this article proposes a tuning methodology for reducing the noise emitted by a SRM in operation. After introducing the aspects the tuning process will focus on, the article details a concrete application consisting in computing representative electromagnetic excitations and then the structural response of the stator including equivalent radiated power levels. An optimised viscoelastic material is determined, with which the peak radiated levels are reduced up to 10 dB in comparison to the initial state. This methodology is implementable for concrete industrial applications as it only relies on common commercial finite-element solvers.

  2. Modeling of viscoelastic properties of nonpermeable porous rocks saturated with highly viscous fluid at seismic frequencies at the core scale

    NASA Astrophysics Data System (ADS)

    Wang, Zizhen; Schmitt, Douglas R.; Wang, Ruihe

    2017-08-01

    A core scale modeling method for viscoelastic properties of rocks saturated with viscous fluid at low frequencies is developed based on the stress-strain method. The elastic moduli dispersion of viscous fluid is described by the Maxwell's spring-dash pot model. Based on this modeling method, we numerically test the effects of frequency, fluid viscosity, porosity, pore size, and pore aspect ratio on the storage moduli and the stress-strain phase lag of saturated rocks. And we also compared the modeling results to the Hashin-Shtrikman bounds and the coherent potential approximation (CPA). The dynamic moduli calculated from the modeling are lower than the predictions of CPA, and both of these fall between the Hashin-Shtrikman bounds. The modeling results indicate that the frequency and the fluid viscosity have similar effects on the dynamic moduli dispersion of fully saturated rocks. We observed the Debye peak in the phase lag variation with the change of frequency and viscosity. The pore structure parameters, such as porosity, pore size, and aspect ratio affect the rock frame stiffness and result in different viscoelastic behaviors of the saturated rocks. The stress-strain phase lags are larger with smaller stiffness contrasts between the rock frame and the pore fluid. The viscoelastic properties of saturated rocks are more sensitive to aspect ratio compared to other pore structure parameters. The results suggest that significant seismic dispersion (at about 50-200 Hz) might be expected for both compressional and shear waves passing through rocks saturated with highly viscous fluids.Plain Language SummaryWe develop a core scale modeling method to simulate the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of rocks saturated with viscous fluid at low frequencies based on the stress-strain method. The elastic moduli dispersion of viscous fluid is described by the Maxwell's spring-dash pot model. By using this modeling method, we numerically test</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27322412','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27322412"><span>Evaluation of <span class="hlt">visco-elastic</span> <span class="hlt">properties</span> of conditioned wheat kernels and their doughs using a compression test under small strain.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ponce-García, Néstor; Ramírez-Wong, Benjamín; Torres-Chávez, Patricia I; Figueroa-Cárdenas, Juan de Dios; Serna-Saldívar, Sergio O; Cortez-Rocha, Mario O; Escalante-Aburto, Anayansi</p> <p>2017-03-01</p> <p>The aim of this research was to evaluate the <span class="hlt">visco-elastic</span> <span class="hlt">properties</span> of conditioned wheat kernels and their doughs by applying the compression test under a small strain. Conditioned wheat kernels and their doughs, from soft and hard wheat classes were evaluated for total work (Wt ), elastic work (We ) and plastic work (Wp ). Soft wheat kernels showed lower We than Wp , while the hard wheat kernels had a We that was higher than Wp . Regarding dough <span class="hlt">visco-elasticity</span>, cultivars from soft and hard wheat showed higher Wp than We . The degree of elasticity (DE%) of the conditioned wheat kernel related to its dough decreased ∼46% in both wheat classes. The Wt , We and Wp from the soft wheat kernel and dough correlated with physico-chemical and farinographic flour tests. The Wt , Wp and the maximum compression force (Fmax ) of the dough from hard wheat class presented highly significant negative correlations with wet gluten. The <span class="hlt">visco-elasticity</span> parameters from compression test presented significant differences among conditioned wheat classes and their doughs. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20887017','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20887017"><span>Effect of preservation period on the <span class="hlt">viscoelastic</span> material <span class="hlt">properties</span> of soft tissues with implications for liver transplantation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ocal, Sina; Ozcan, M Umut; Basdogan, Ipek; Basdogan, Cagatay</p> <p>2010-10-01</p> <p>The liver harvested from a donor must be preserved and transported to a suitable recipient immediately for a successful liver transplantation. In this process, the preservation period is the most critical, since it is the longest and most tissue damage occurs during this period due to the reduced blood supply to the harvested liver and the change in its temperature. We investigate the effect of preservation period on the dynamic material <span class="hlt">properties</span> of bovine liver using a <span class="hlt">viscoelastic</span> model derived from both impact and ramp and hold experiments. First, we measure the storage and loss moduli of bovine liver as a function of excitation frequency using an impact hammer. Second, its time-dependent relaxation modulus is measured separately through ramp and hold experiments performed by a compression device. Third, a Maxwell solid model that successfully imitates the frequency- and time-dependent dynamic responses of bovine liver is developed to estimate the optimum <span class="hlt">viscoelastic</span> material coefficients by minimizing the error between the experimental data and the corresponding values generated by the model. Finally, the variation in the <span class="hlt">viscoelastic</span> material coefficients of bovine liver are investigated as a function of preservation period for the liver samples tested 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, and 48 h after harvesting. The results of our experiments performed with three animals show that the liver tissue becomes stiffer and more viscous as it spends more time in the preservation cycle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25448585','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25448585"><span>Effect of carbamazepine on <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> and hot melt extrudability of Soluplus ®.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gupta, Simerdeep Singh; Parikh, Tapan; Meena, Anuprabha K; Mahajan, Nidhi; Vitez, Imre; Serajuddin, Abu T M</p> <p>2015-01-15</p> <p>The purpose of this study was to apply <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of polymer and drug-polymer mixtures to determine processing conditions for the preparation of amorphous solid dispersion by melt extrusion. A poorly water-soluble drug, carbamazepine (CBZ), was mixed with Soluplus(®) as the carrier. Torque analysis using a melt extruder was performed at 10, 20 and 30% w/w drug concentrations and the effect of barrel temperature was studied. Viscosity of the mixtures either at fixed temperatures with different angular frequencies or as a function of temperature with the same frequency was studied using a rheometer. The viscosity of Soluplus(®) and the torque exerted on the twin screws decreased with the increase in CBZ concentration. The viscosity versus temperature plots for different CBZ concentrations were parallel to each other, without the drug melting transition, indicating complete drug-polymer miscibility. Thus, the drug-polymer mixtures could be extruded at temperature as low as 140°C with 10% w/w drug load, 135°C with 20% w/w drug and 125°C with 30% w/w drug, which were, respectively, ∼ 50°C, 55°C and 65°C below the melting point of 191°C for CBZ. The differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) analyses of the binary mixtures extruded at 125-150°C showed absence of crystalline drug. A systematic study of miscibility and extrudability of drug-polymer mixtures by rheological and torque analysis as a function of temperature will help formulators select optimal melt extrusion processing conditions to develop solid dispersions. Copyright © 2014 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008MTDM...12..221P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008MTDM...12..221P"><span>Hygrothermal characterization of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of Gore-Select® 57 proton exchange membrane</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Patankar, Kshitish A.; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Budinski, Michael K.; Gittleman, Craig S.</p> <p>2008-09-01</p> <p>When a proton exchange membrane (PEM) based fuel cell is placed in service, hygrothermal stresses develop within the membrane and vary widely with internal operating environment. These hygrothermal stresses associated with hygral contraction and expansion at the operating conditions are believed to be critical in membrane mechanical integrity and durability. Understanding and accurately modeling the <span class="hlt">viscoelastic</span> constitutive <span class="hlt">properties</span> of a PEM is important for making hygrothermal stress predictions in the cyclic temperature and humidity environment of operating fuel cells. The tensile stress relaxation moduli of a commercially available PEM, Gore-Select® 57, were obtained over a range of humidities and temperatures. These tests were performed using TA Instruments 2980 and Q800 dynamic mechanical analyzers (DMA), which are capable of applying specified tensile loading conditions on small membrane samples at a given temperature. A special humidity chamber was built in the form of a cup that encloses tension clamps of the DMA. The chamber was inserted in the heating furnace of the DMA and connected to a gas humidification unit by means of plastic tubing through a slot in the chamber. Stress relaxation data over a temperature range of 40 90°C and relative humidity range of 30 90% were obtained. Thermal and hygral master curves were constructed using thermal and hygral shift factors and were used to form a hygrothermal master curve using the time temperature moisture superposition principle. The master curve was also constructed independently using just one shift factor. The hygrothermal master curve was fitted with a 10-term Prony series for use in finite element software. The hygrothermal master curve was then validated using longer term tests. The relaxation modulus from longer term data matches well with the hygrothermal master curve. The long term test showed a plateau at longer times, suggesting an equilibrium modulus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21797737','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21797737"><span>The role of alginate in Pseudomonas aeruginosa EPS adherence, <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> and cell attachment.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Orgad, Oded; Oren, Yoram; Walker, Sharon L; Herzberg, Moshe</p> <p>2011-08-01</p> <p>Among various functions, extracellular polymeric substances (EPS) provide microbial biofilms with mechanical stability and affect initial cell attachment, the first stage in the biofilm formation process. The role of alginate, an abundant polysaccharide in Pseudomonas aeruginosa biofilms, in the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> and adhesion kinetics of EPS was analyzed using a quartz crystal microbalance with dissipation (QCM-D) monitoring technology. EPS was extracted from two P. aeruginosa biofilms, a wild type strain, PAO1, and a mucoid strain, PAOmucA22 that over-expresses alginate production. The higher alginate content in the EPS originating from the mucoid biofilms was clearly shown to increase both the rate and the extent of attachment of the EPS, as well as the layer's thickness. Also, the presence of calcium and elevated ionic strength increased the thickness of the EPS layer. Dynamic light scattering (DLS) showed that the presence of calcium and elevated ionic strength induced intermolecular attractive interactions in the mucoid EPS molecules. For the wild type EPS, in the presence of calcium, an elevated shift in the distribution of the diffusion coefficients was observed with DLS due to a more compacted conformation of the EPS molecules. Moreover, the alginate over-expression effect on EPS adherence was compared to the effect of alginate over-expression on P. aeruginosa cell attachment. In a parallel plate flow cell, under similar hydraulic and aquatic conditions as those applied for the EPS adsorption tests in the QCM-D flow cell, reduced adherence of the mucoid strain was clearly observed compared to the wild type isogenic bacteria. The results suggest that alginate contributes to steric hindrance and shielding of cell surface features and adhesins that are known to promote cell attachment. © 2011 Taylor & Francis</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040088328&hterms=Muscle+hypertrophy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DMuscle%2Bhypertrophy','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040088328&hterms=Muscle+hypertrophy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DMuscle%2Bhypertrophy"><span><span class="hlt">Viscoelastic</span> <span class="hlt">properties</span> of pressure overload hypertrophied myocardium: effect of serine protease treatment</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stroud, Jason D.; Baicu, Catalin F.; Barnes, Mary A.; Spinale, Francis G.; Zile, Michael R.</p> <p>2002-01-01</p> <p>To determine whether and to what extent one component of the extracellular matrix, fibrillar collagen, contributes causally to abnormalities in <span class="hlt">viscoelasticity</span>, collagen was acutely degraded by activation of endogenous matrix metalloproteinases (MMPs) with the serine protease plasmin. Papillary muscles were isolated from normal cats and cats with right ventricular pressure overload hypertrophy (POH) induced by pulmonary artery banding. Plasmin treatment caused MMP activation, collagen degradation, decreased the elastic stiffness constant, and decreased the viscosity constant in both normal and POH muscles. Thus, whereas many mechanisms may contribute to the abnormalities in myocardial <span class="hlt">viscoelasticity</span> in the POH myocardium, changes in fibrillar collagen appear to play a predominant role.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040088328&hterms=HYPERTROPHY&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DHYPERTROPHY','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040088328&hterms=HYPERTROPHY&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DHYPERTROPHY"><span><span class="hlt">Viscoelastic</span> <span class="hlt">properties</span> of pressure overload hypertrophied myocardium: effect of serine protease treatment</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stroud, Jason D.; Baicu, Catalin F.; Barnes, Mary A.; Spinale, Francis G.; Zile, Michael R.</p> <p>2002-01-01</p> <p>To determine whether and to what extent one component of the extracellular matrix, fibrillar collagen, contributes causally to abnormalities in <span class="hlt">viscoelasticity</span>, collagen was acutely degraded by activation of endogenous matrix metalloproteinases (MMPs) with the serine protease plasmin. Papillary muscles were isolated from normal cats and cats with right ventricular pressure overload hypertrophy (POH) induced by pulmonary artery banding. Plasmin treatment caused MMP activation, collagen degradation, decreased the elastic stiffness constant, and decreased the viscosity constant in both normal and POH muscles. Thus, whereas many mechanisms may contribute to the abnormalities in myocardial <span class="hlt">viscoelasticity</span> in the POH myocardium, changes in fibrillar collagen appear to play a predominant role.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22200611','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22200611"><span>Assessing <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of chitosan scaffolds and validation with cyclical tests.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ratakonda, Swapnika; Sridhar, Upasana M; Rhinehart, R Russell; Madihally, Sundararajan V</p> <p>2012-04-01</p> <p>We evaluated and modeled the <span class="hlt">viscoelastic</span> characteristics of chitosan and chitosan-gelatin scaffolds prepared using a freeze-drying technique. Chitosan and chitosan-gelatin solutions (0.5 and 2 wt.%) were frozen at -80°C and freeze-dried. Using the scaffolds, uniaxial tensile <span class="hlt">properties</span> were evaluated under physiological conditions (hydrated in phosphate buffered saline at 37°C) at a cross-head speed of 0.17 mms(-1) (10 mm min(-1)). From the break strain, the limit of strain per ramp was calculated to be 5% and the samples were stretched at a strain rate of 2.5%s(-1). The ramp-and-hold type of stress-relaxation test was performed for five successive stages. Chitosan and chitosan-gelatin showed nearly 90% relaxation of stress after each stage. The relaxation behavior was independent of the concentration of chitosan and gelatin. Also, changes in the microstructure of the tested samples were evaluated using an inverted microscope. The micrographs acquired after relaxation experiments showed orientation of pores, suggesting the retention of the stretched state even after many hours of relaxation. Based on these observations, two models (i) containing a hyper-elastic spring (containing two parameters) and (ii) retaining pseudo-components (containing three parameters) were developed in Visual Basic Applications accessed through MS Excel. The models were used to fit the experimental stress-relaxation data and the parameters obtained from modeling were used to predict their respective cyclic behaviors, which were compared with cyclical experimental results. These results showed that the model could be used to predict the cyclical behavior under the tested strain rates. The model predictions were also tested using cyclic <span class="hlt">properties</span> at a lower strain rate of 0.0867%s(-1) (5%min(-1)) for 0.5 wt.% scaffolds but the model could not predict cyclical behavior at a very slow rate. In summary, the pseudo-component modeling approach can be used to model the sequential strain</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Finite+AND+elements+AND+method&id=ED526006','ERIC'); return false;" href="http://eric.ed.gov/?q=Finite+AND+elements+AND+method&id=ED526006"><span>Asphalt Pavement Aging and Temperature Dependent <span class="hlt">Properties</span> Using Functionally Graded <span class="hlt">Viscoelastic</span> Model</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Dave, Eshan V.</p> <p>2009-01-01</p> <p>Asphalt concrete pavements are inherently graded <span class="hlt">viscoelastic</span> structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions being the major cause of non-homogeneity. Current pavement analysis and simulation procedures dwell on the use of layered approach to account for these non-homogeneities. The conventional…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AIPC.1032..268G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AIPC.1032..268G"><span>Passive <span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Costameres in EDL Skeletal Muscle in Normal and Dystrophin Null Mice</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>García-Pelagio, Karla P.; Bloch, Robert J.; Ortega, Alicia; Gonzalez-Serratos, Hugo</p> <p>2008-08-01</p> <p>Costameres at the sarcolemmal skeletal myofibers transmit the lateral force generated by myofibrils from them to the extracellular matrix. We used an elastimeter method by which sucking pressure is applied through a micropipette to the surface membrane of single mice myofibers of the Extensor digitorum longus to measure the <span class="hlt">viscoelasticity</span> of the sarcolemma-costamere complex as a function of sarcomere length (SL). Constant suction pressure applied to the sarcolemma generated a sarcolemmal-costamere-myofibril bleb of variable height depending on the sucking pressure and SL. It took some time for the bleb to reach a stable height after applying the pressure. This time delay indicates that the sarcolemma-costamere-myofibril system acts as a <span class="hlt">viscoelastic</span> system. We undertook the present experiments to measure the height stabilization time of the bleb at different sarcomere lengths from which we estimated the <span class="hlt">viscoelastic</span> parameters of the system. The time course of the bleb formation was biphasic and reached a plateau between 3.5 to 1.3 and 4.9 to 3.5 min for normal and dystrophic mice respectively depending on SL of 3.0 to 5.6 μm. Based on a Maxwell-Voigt system we found the <span class="hlt">viscoelastic</span> parameters such as viscosity, friction coefficient and the costameres (k) and sarcolemma (k1) elasticity constants.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=217856','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=217856"><span><span class="hlt">Viscoelastic</span> <span class="hlt">properties</span> of a bio-hydrogel produced from soybean oil</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>Hydrogels are a class of <span class="hlt">viscoelastic</span> materials that have many biomedical utilization potentials, such as drug delivery, wound care product, breast implant materials, and tissue engineering, etc. Hydrogels produced from biopolymers and/or natural sources have particular advantages in vivo applicati...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=fems&id=ED526006','ERIC'); return false;" href="https://eric.ed.gov/?q=fems&id=ED526006"><span>Asphalt Pavement Aging and Temperature Dependent <span class="hlt">Properties</span> Using Functionally Graded <span class="hlt">Viscoelastic</span> Model</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Dave, Eshan V.</p> <p>2009-01-01</p> <p>Asphalt concrete pavements are inherently graded <span class="hlt">viscoelastic</span> structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions being the major cause of non-homogeneity. Current pavement analysis and simulation procedures dwell on the use of layered approach to account for these non-homogeneities. The conventional…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28753687','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28753687"><span>Strain-Level Dependent Nonequilibrium Anisotropic <span class="hlt">Viscoelasticity</span>: Application to the Abdominal Muscle.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Latorre, Marcos; Montáns, Francisco J</p> <p>2017-10-01</p> <p>Soft connective tissues sustain large strains of <span class="hlt">viscoelastic</span> nature. The rate-independent component is frequently modeled by means of anisotropic hyperelastic models. The rate-dependent component is usually modeled through <span class="hlt">linear</span> rheological models or quasi-<span class="hlt">linear</span> <span class="hlt">viscoelastic</span> (QLV) models. These <span class="hlt">viscoelastic</span> models are unable, in general, to capture the strain-level dependency of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> present in many <span class="hlt">viscoelastic</span> tissues. In <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> models, strain-level dependency is frequently accounted for by including the dependence of multipliers of Prony series on strains through additional evolution laws, but the determination of the material parameters is a difficult task and the obtained accuracy is usually not sufficient. In this work, we introduce a model for fully nonlinear <span class="hlt">viscoelasticity</span> in which the instantaneous and quasi-static behaviors are exactly captured and the relaxation curves are predicted to a high accuracy. The model is based on a fully nonlinear standard rheological model and does not necessitate optimization algorithms to obtain material parameters. Furthermore, in contrast to most models used in modeling the <span class="hlt">viscoelastic</span> behavior of soft tissues, it is valid for the large deviations from thermodynamic equilibrium typically observed in soft tissues.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24211612','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24211612"><span>Nonlinear <span class="hlt">viscoelastic</span> characterization of the porcine spinal cord.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shetye, Snehal S; Troyer, Kevin L; Streijger, Femke; Lee, Jae H T; Kwon, Brian K; Cripton, Peter A; Puttlitz, Christian M</p> <p>2014-02-01</p> <p>Although quasi-static and quasi-<span class="hlt">linear</span> <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the spinal cord have been reported previously, there are no published studies that have investigated the fully (strain-dependent) nonlinear <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the spinal cord. In this study, stress relaxation experiments and dynamic cycling were performed on six fresh porcine lumbar cord specimens to examine their <span class="hlt">viscoelastic</span> mechanical <span class="hlt">properties</span>. The stress relaxation data were fitted to a modified superposition formulation and a novel finite ramp time correction technique was applied. The parameters obtained from this fitting methodology were used to predict the average dynamic cyclic <span class="hlt">viscoelastic</span> behavior of the porcine cord. The data indicate that the porcine spinal cord exhibited fully nonlinear <span class="hlt">viscoelastic</span> behavior. The average weighted root mean squared error for a Heaviside ramp fit was 2.8 kPa, which was significantly greater (p<0.001) than that of the nonlinear (comprehensive <span class="hlt">viscoelastic</span> characterization method) fit (0.365 kPa). Further, the nonlinear mechanical parameters obtained were able to accurately predict the dynamic behavior, thus exemplifying the reliability of the obtained nonlinear parameters. These parameters will be important for future studies investigating various damage mechanisms of the spinal cord and studies developing high-resolution finite elements models of the spine. Copyright © 2013 Acta Materialia Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4059047','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4059047"><span>Nonlinear <span class="hlt">Viscoelastic</span> Characterization of the Porcine Spinal Cord</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Shetye, Snehal; Troyer, Kevin; Streijger, Femke; Lee, Jae H. T.; Kwon, Brian K.; Cripton, Peter; Puttlitz, Christian M.</p> <p>2014-01-01</p> <p>Although quasi-static and quasi-<span class="hlt">linear</span> <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the spinal cord have been reported previously, there are no published studies that have investigated the fully (strain-dependent) nonlinear <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the spinal cord. In this study, stress relaxation experiments and dynamic cycling were performed on six fresh porcine lumbar cord specimens to examine their <span class="hlt">viscoelastic</span> mechanical <span class="hlt">properties</span>. The stress relaxation data were fitted to a modified superposition formulation and a novel finite ramp time correction technique was applied. The parameters obtained from this fitting methodology were used to predict the average dynamic cyclic <span class="hlt">viscoelastic</span> behavior of the porcine cord. The data indicate that the porcine spinal cord exhibited fully nonlinear <span class="hlt">viscoelastic</span> behavior. The average weighted RMSE for a Heaviside ramp fit was 2.8kPa, which was significantly greater (p < 0.001) than that of the nonlinear (comprehensive <span class="hlt">viscoelastic</span> characterization (CVC) method) fit (0.365kPa). Further, the nonlinear mechanical parameters obtained were able to accurately predict the dynamic behavior, thus exemplifying the reliability of the obtained nonlinear parameters. These parameters will be important for future studies investigating various damage mechanisms of the spinal cord and studies developing high resolution finite elements models of the spine. PMID:24211612</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002ASAJ..111.2480C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002ASAJ..111.2480C"><span>Nonlinear <span class="hlt">viscoelastic</span> response of vocal-fold tissues</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chan, Roger W.</p> <p>2002-05-01</p> <p>Previous rheological measurements of the <span class="hlt">viscoelastic</span> shear <span class="hlt">properties</span> of vocal-fold tissues have focused on the <span class="hlt">linear</span> regime, in the small strain region typically with γ0<=1.0%. This imposed limit was necessary in order for the theory of <span class="hlt">linear</span> <span class="hlt">viscoelasticity</span> to be valid, yielding dynamic shear data that can be applicable for the biomechanical modeling of small-amplitude vocal-fold oscillation. Nonetheless, as the physiological range of phonation does involve more than small-amplitude oscillation, the large strain <span class="hlt">viscoelastic</span> behaviors of vocal-fold tissues are equally important and remain to be quantified. This paper reports preliminary measurements of some of these <span class="hlt">viscoelastic</span> behaviors in large strain shear. Excised sheep vocal-fold mucosal tissues were subject to stress relaxation, constant stress, and constant strain rate tests in a controlled-strain torsional rheometer. Results showed that vocal-fold tissues demonstrate nonlinear <span class="hlt">viscoelastic</span> response in shear, including stress relaxation that is dependent on strain and strain creep that is dependent on stress. These findings cannot be adequately described by Y. C. Fung's quasilinear <span class="hlt">viscoelasticity</span> formulation, which assumes strain dependence and time dependence to be separable. A more general constitutive model is being developed to better characterize the observed nonlinear response.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016IJCEM..17..137U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016IJCEM..17..137U"><span>Contribution of material <span class="hlt">properties</span> of cellular components on the <span class="hlt">viscoelastic</span>, stress-relaxation response of a cell during AFM indentation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Unnikrishnan, Ginu U.; Unnikrishnan, Vinu U.; Reddy, J. N.</p> <p>2016-05-01</p> <p>The close relationship between the mechanical <span class="hlt">properties</span> of biological cells, namely, elasticity, viscosity, and the state of its disease condition has been widely investigated using atomic force microscopy (AFM). In this study, computational simulation of the AFM indentation is carried out using a finite element (FE) model of an adherent cell. A parametric evaluation of the material <span class="hlt">properties</span> of the cellular components on the <span class="hlt">viscoelastic</span>, stress-relaxation response during AFM indentation is performed. In addition, the loading rate, the size of the nucleus, and the geometry of the cell are varied. From the present study, it is found that when comparing the material <span class="hlt">properties</span> derived from experimental force-deflection curves, the influence of loading rates should be accommodated. It also provides a framework that can quantify the variation of the mechanical <span class="hlt">property</span> with various stages of malignancy of the cancer cell, a potential procedure for cancer diagnosis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JSV...332.6177W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JSV...332.6177W"><span>Finite element analysis and experimental study on dynamic <span class="hlt">properties</span> of a composite beam with <span class="hlt">viscoelastic</span> damping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Ya; Inman, Daniel J.</p> <p>2013-11-01</p> <p>This paper investigates the frequency dependent <span class="hlt">viscoelastic</span> dynamics of a multifunctional composite structure from finite element analysis and experimental validation. The frequency-dependent behavior of the stiffness and damping of a <span class="hlt">viscoelastic</span> material directly affects the system's modal frequencies and damping, and results in complex vibration modes and differences in the relative phase of vibration. A second order three parameter Golla-Hughes-McTavish (GHM) method and a second order three fields Anelastic Displacement Fields (ADF) approach are used to implement the <span class="hlt">viscoelastic</span> material model, enabling the straightforward development of time domain and frequency domain finite elements, and describing the frequency dependent <span class="hlt">viscoelastic</span> behavior. Considering the parameter identification a strategy to estimate the fractional order of the time derivative and the relaxation time is outlined. Agreement between the curve fits using both the GHM and ADF and experiment is within 0.001 percent error. Continuing efforts are addressing the material modulus comparison of the GHM and the ADF model. There may be a theoretical difference between <span class="hlt">viscoelastic</span> degrees of freedom at nodes and elements, but their numerical results are very close to each other in the specific frequency range of interest. With identified model parameters, numerical simulation is carried out to predict the damping behavior in its first two vibration modes. The experimental testing on the layered composite beam validates the numerical predication. Experimental results also show that elastic modulus measured from dynamic response yields more accurate results than static measurement, such as tensile testing, especially for elastomers. The viscoelatic layer is augmented with the inclusion of a shear angle associated with transverse shear in addition to Euler-Bernoulli hypotheses. >The other four layers are assumed to be elastic; Euler-Bernoulli bending assumption applies; Transverse and rotatory</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22014563','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22014563"><span>Relation between EPS adherence, <span class="hlt">viscoelastic</span> <span class="hlt">properties</span>, and MBR operation: Biofouling study with QCM-D.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sweity, Amer; Ying, Wang; Ali-Shtayeh, Mohammed S; Yang, Fei; Bick, Amos; Oron, Gideon; Herzberg, Moshe</p> <p>2011-12-01</p> <p>Membrane fouling is one of the main constraints of the wide use of membrane bioreactor (MBR) technology. The biomass in MBR systems includes extracellular polymeric substances (EPS), metabolic products of active microbial secretion that adversely affect the membrane performance. Solids retention time (SRT) in the MBR is one of the most important parameters affecting membrane fouling in MBR systems, where fouling is minimized at optimal SRT. Among the operating parameters in MBR systems, SRT is known to strongly influence the ratio of proteins to polysaccharides in the EPS matrix. In this study, we have direct evidence for changes in EPS adherence and <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> due to changes in the sludge removal rate that strongly correlate with the membrane fouling rate and EPS composition. EPS were extracted from a UF membrane in a hybrid growth MBR operated at sludge removal rates of 59, 35.4, 17.7, and 5.9 L day(-1) (corresponding SRT of 3, 5, 10, and 30 days, respectively). The EPS adherence and adsorption kinetics were carried out in a quartz crystal microbalance with dissipation monitoring (QCM-D) technology in several adsorption measurements to a gold sensor coated with Polyvinylidene Fluoride (PVDF). EPS adsorption to the sensor surface is characterized by a decrease of the oscillation frequency and an increase in the dissipation energy of the sensor during parallel flow of aqueous media, supplemented with EPS, above the sensor surface. The results from these experiments were further modeled using the Voigt based model, in which the thickness, shear modulus, and shear viscosity values of the adsorbed EPS layers on the PVDF crystal were calculated. The observations in the QCM-D suggested that the elevated fouling of the UF membrane is due to higher adherence of the EPS as well as reduction in viscosity and elasticity of the EPS adsorbed layer and elevation of the EPS fluidity. These results corroborate with confocal laser scanning microscopy (CLSM) image</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4392674','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4392674"><span>Human amniotic epithelial cell transplantation for the repair of injured brachial plexus nerve: evaluation of nerve <span class="hlt">viscoelastic</span> <span class="hlt">properties</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jin, Hua; Yang, Qi; Ji, Feng; Zhang, Ya-jie; Zhao, Yan; Luo, Min</p> <p>2015-01-01</p> <p>The transplantation of embryonic stem cells can effectively improve the creeping strength of nerves near an injury site in animals. Amniotic epithelial cells have similar biological <span class="hlt">properties</span> as embryonic stem cells; therefore, we hypothesized that transplantation of amniotic epithelial cells can repair peripheral nerve injury and recover the creeping strength of the brachial plexus nerve. In the present study, a brachial plexus injury model was established in rabbits using the C6 root avulsion method. A suspension of human amniotic epithelial cells was repeatedly injected over an area 4.0 mm lateral to the cephal and caudal ends of the C6 brachial plexus injury site (1 × 106 cells/mL, 3 μL/injection, 25 injections) immediately after the injury. The results showed that the decrease in stress and increase in strain at 7,200 seconds in the injured rabbit C6 brachial plexus nerve were mitigated by the cell transplantation, restoring the <span class="hlt">viscoelastic</span> stress relaxation and creep <span class="hlt">properties</span> of the brachial plexus nerve. The forepaw functions were also significantly improved at 26 weeks after injury. These data indicate that transplantation of human amniotic epithelial cells can effectively restore the mechanical <span class="hlt">properties</span> of the brachial plexus nerve after injury in rabbits and that <span class="hlt">viscoelasticity</span> may be an important index for the evaluation of brachial plexus injury in animals. PMID:25883625</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25883625','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25883625"><span>Human amniotic epithelial cell transplantation for the repair of injured brachial plexus nerve: evaluation of nerve <span class="hlt">viscoelastic</span> <span class="hlt">properties</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jin, Hua; Yang, Qi; Ji, Feng; Zhang, Ya-Jie; Zhao, Yan; Luo, Min</p> <p>2015-02-01</p> <p>The transplantation of embryonic stem cells can effectively improve the creeping strength of nerves near an injury site in animals. Amniotic epithelial cells have similar biological <span class="hlt">properties</span> as embryonic stem cells; therefore, we hypothesized that transplantation of amniotic epithelial cells can repair peripheral nerve injury and recover the creeping strength of the brachial plexus nerve. In the present study, a brachial plexus injury model was established in rabbits using the C6 root avulsion method. A suspension of human amniotic epithelial cells was repeatedly injected over an area 4.0 mm lateral to the cephal and caudal ends of the C6 brachial plexus injury site (1 × 10(6) cells/mL, 3 μL/injection, 25 injections) immediately after the injury. The results showed that the decrease in stress and increase in strain at 7,200 seconds in the injured rabbit C6 brachial plexus nerve were mitigated by the cell transplantation, restoring the <span class="hlt">viscoelastic</span> stress relaxation and creep <span class="hlt">properties</span> of the brachial plexus nerve. The forepaw functions were also significantly improved at 26 weeks after injury. These data indicate that transplantation of human amniotic epithelial cells can effectively restore the mechanical <span class="hlt">properties</span> of the brachial plexus nerve after injury in rabbits and that <span class="hlt">viscoelasticity</span> may be an important index for the evaluation of brachial plexus injury in animals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9950649','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9950649"><span>Powder densification. 1. Particle-particle basis for incorporation of <span class="hlt">viscoelastic</span> material <span class="hlt">properties</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lum, S K; Duncan-Hewitt, W C</p> <p>1999-02-01</p> <p>The present investigation was undertaken to examine the basic unit of densification: the particle-particle indentation. The true interparticle contact area that is established during densification ultimately determines the quality of the tablet compact. By examining the interfacial contact between mutually indenting <span class="hlt">viscoelastic</span> particles, the process of contact evolution may be represented in mathematical form through extension of the classical Hertzian elastic contact description to encompass material <span class="hlt">viscoelastic</span> terms. In this way, the time-dependent response of materials to applied loads may be addressed explicitly. The effects of rates of applied loading and maximum load levels were also considered. This analysis was based on <span class="hlt">viscoelastic</span> stress data collected using an instrumented Instron analyzer during the densification of PMMA/coMMA, a pharmaceutical polymeric coating material. A crossed cylinder matrix compaction geometry was used to simulate the geometry of two mutually indenting spherical particles. Numerical and graphical solutions delineating the relationship between contact area evolution and the prescribed loading force are presented. This particle-particle description of the contacting interface serves as a unit basis for describing the entire powder bed. The powder bed may ultimately be modeled as a collection of these particles in contact.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24011778','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24011778"><span>Reconstructing 3-D maps of the local <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> using a finite-amplitude modulated radiation force.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Giannoula, Alexia; Cobbold, Richard; Bezerianos, Anastasios</p> <p>2014-02-01</p> <p>A modulated acoustic radiation force, produced by two confocal tone-burst ultrasound beams of slightly different frequencies (i.e. 2.0 MHz ± Δf/2, where Δf is the difference frequency), can be used to remotely generate modulated low-frequency (Δf ≤ 500 Hz) shear waves in attenuating media. By appropriately selecting the duration of the two beams, the energy of the generated shear waves can be concentrated around the difference frequency (i.e., Δf ± Δf/2). In this manner, neither their amplitude nor their phase information is distorted by frequency-dependent effects, thereby, enabling a more accurate reconstruction of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span>. Assuming a Voigt <span class="hlt">viscoelastic</span> model, this paper describes the use of a finite-element-method model to simulate three-dimensional (3-D) shear-wave propagation in <span class="hlt">viscoelastic</span> media containing a spherical inclusion. Nonlinear propagation is assumed for the two ultrasound beams, so that higher harmonics are developed in the force and shear spectrum. Finally, an inverse reconstruction algorithm is used to extract 3-D maps of the local shear modulus and viscosity from the simulated shear-displacement fields based on the fundamental and second-harmonic component. The quality of the reconstructed maps is evaluated using the contrast between the inclusion and the background and the contrast-to-noise ratio (CNR). It is shown that the shear modulus can be accurately reconstructed based on the fundamental component, such that the observed contrast deviates from the true contrast by a root-mean-square-error (RMSE) of only 0.38 and the CNR is greater than 30 dB. If the second-harmonic component is used, the RMSE becomes 1.54 and the corresponding CNR decreases by approximately 10-15 dB. The reconstructed shear viscosity maps based on the second harmonic are shown to be of higher quality than those based on the fundamental. The effects of noise are also investigated and a fusion operation between the two spectral components is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=257965','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=257965"><span>The <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the protein-rich materials from the fermented hard wheat, soft wheat and barley flours</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>The <span class="hlt">linear</span> and non-<span class="hlt">linear</span> rheological <span class="hlt">properties</span> of the suspensions for the hard red spring wheat (HRS) flour, soft wheat (Pastry) flour, barley flour, as well as the remain residues of HRS flour, Pastry flour, and barley flour after fermentation were investigated. The <span class="hlt">linear</span> and non-<span class="hlt">linear</span> rheologi...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27142723','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27142723"><span><span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Core-Shell-Structured, Hemicellulose-Rich Nanofibrillated Cellulose in Dispersion and Wet-Film States.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tanaka, Reina; Saito, Tsuguyuki; Hänninen, Tuomas; Ono, Yuko; Hakalahti, Minna; Tammelin, Tekla; Isogai, Akira</p> <p>2016-06-13</p> <p>We report the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of core-shell-structured, hemicellulose-rich nanofibrillated cellulose (NFC) in dispersion and wet-film states. The hemicellulose-rich NFC (hemicellulose neutral sugars 23%, carboxylate 0.2 mmol g(-1)), prepared from Japanese persimmons, had a core crystallite thickness of 2.3 nm and unit fibril thickness of 4.2 nm. A carboxylate-rich NFC (hemicellulose neutral sugars 7%, carboxylate 0.9 mmol g(-1)) with crystallite and fibril widths of 2.5 and 3.3 nm, respectively, was used as a reference. The solid-concentration dependencies of the storage moduli of gel-like water dispersions of the hemicellulose-rich NFC were weaker than those of carboxylate-rich NFC, and the dispersions were loosely flocculated even at high salt concentrations and low pH values. The <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of wet NFC films were similar to those of their dispersions; the hemicellulose-rich NFC films were significantly less sensitive to salt concentration and pH and were soft and swollen at high salt concentrations and low pH values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26431909','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26431909"><span>Insoluble elastin reduces collagen scaffold stiffness, improves <span class="hlt">viscoelastic</span> <span class="hlt">properties</span>, and induces a contractile phenotype in smooth muscle cells.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ryan, Alan J; O'Brien, Fergal J</p> <p>2015-12-01</p> <p>Biomaterials with the capacity to innately guide cell behaviour while also displaying suitable mechanical <span class="hlt">properties</span> remain a challenge in tissue engineering. Our approach to this has been to utilise insoluble elastin in combination with collagen as the basis of a biomimetic scaffold for cardiovascular tissue engineering. Elastin was found to markedly alter the mechanical and biological response of these collagen-based scaffolds. Specifically, during extensive mechanical assessment elastin was found to reduce the specific tensile and compressive moduli of the scaffolds in a concentration dependant manner while having minimal effect on scaffold microarchitecture with both scaffold porosity and pore size still within the ideal ranges for tissue engineering applications. However, the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> were significantly improved with elastin addition with a 3.5-fold decrease in induced creep strain, a 6-fold increase in cyclical strain recovery, and with a four-parameter <span class="hlt">viscoelastic</span> model confirming the ability of elastin to confer resistance to long term deformation/creep. Furthermore, elastin was found to result in the modulation of SMC phenotype towards a contractile state which was determined via reduced proliferation and significantly enhanced expression of early (α-SMA), mid (calponin), and late stage (SM-MHC) contractile proteins. This allows the ability to utilise extracellular matrix proteins alone to modulate SMC phenotype without any exogenous factors added. Taken together, the ability of elastin to alter the mechanical and biological response of collagen scaffolds has led to the development of a biomimetic biomaterial highly suitable for cardiovascular tissue engineering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT.......381C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT.......381C"><span><span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Polymers: A Comparison of Micro and Macro Scales</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Champhekar, Mangesh</p> <p></p> <p> annealing time. The decreasing hardness and modulus of the samples with increasing contact depth or indentation depth (for rubbers) was attributed to interplay between the instrumental/analysis errors and material <span class="hlt">properties</span>. Dynamic nanoindentation studies were also carried out on the three amorphous glassy materials (a-PS, HIPS, ABS), the four rubbers (SBR, NR, neoprene, PDMS) and the PLLA samples. The storage modulus (E') and loss modulus (E'') values obtained by dynamic nanoindentation were compared with those obtained from conventional DMA testing and a good level of agreement was observed, with the values obtained from nanoindentation ca. 2-3 times higher than those obtained from conventional DMA testing depending upon the material under consideration. The reason for this observation is currently unknown, as there is no physical basis available in the literature to compare the values on different length scales since the methods of analysis used to extract the values of E' and E'' and the mode of deformation used is different for both the methods. However, the level of agreement between the two methods shows that dynamic nanoindentation is a powerful tool to capture the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of polymers on smaller length scales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26102894','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26102894"><span>5B.05: MARFAN SYNDROME: ASSESSMENT OF AORTIC DISSECTION RISK BY ANALYSIS OF AORTIC <span class="hlt">VISCOELASTIC</span> <span class="hlt">PROPERTIES</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Grillo, A; Pini, A; Marelli, S; Gan, L; Giuliano, A; Trifirò, G; Santini, F; Salvi, L; Salvi, P; Viecca, F; Carretta, R; Parati, G</p> <p>2015-06-01</p> <p>Marfan syndrome is an autosomal dominant genetic disorder characterized by an abnormal fibrillin-1 synthesis. Aortic root dilation and dissection are the main problems affecting patients prognosis in these patients. Their pharmacological prophylaxis with losartan or with a beta-blocker counteracts the aortic root dilation, but a close follow-up is required to assess therapeutic response rate and to identify non-responders. Unfortunately genotype-phenotype studies do not allow to determine the exact risk profile in these patients and there is no reliable method to accurately predict their risk of aortic dissection. Aim of this study was to evaluate non-invasive markers for identification of Marfan patients at higher risk of aortic complications. We studied 187 Marfan patients (identified according to 2010 Revised Ghent Criteria and positive genetic analysis), age 32.3 ± 16.5 yrs (mean ± SD). 52 patients (27.8%) had undergone surgical ascending aorta replacement (David or Bentall procedure). Central pressure curves were recorded by PulsePen tonometer, and the aortic <span class="hlt">viscoelastic</span> aortic <span class="hlt">properties</span> were studied by determination of carotid-femoral pulse wave velocity (PWV). With reference to the age related distribution of PWV values in a normal population, defined according to Arterial-Stiffness-Collaboration, PWV mean values in Marfan patients corresponded to 60th percentile in non- operated patients and to the 67th percentile in those operated. Adult Marfan patients (n = 146) generally displayed a low blood pressure, because of the pharmacological prophylaxis, and were compared with a population of 189 adult healthy subjects (81 males), matched by age (38 ± 13 vs 38 ± 16 yrs.), heart rate (64 ± 9 bpm vs 64 ± 11 bpm) and blood pressure (mean BP = 78 ± 9 mmHg vs 79 ± 4 mmHg) values. Average PWV value was higher than in healthy controls (PWV = 7.0 ± 1.7) both in not operated (PWV = 7.6 ± 1.6; p = 0</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.4955B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.4955B"><span>Grain size-sensitive <span class="hlt">viscoelastic</span> relaxation and seismic <span class="hlt">properties</span> of polycrystalline MgO</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barnhoorn, A.; Jackson, I.; Fitz Gerald, J. D.; Kishimoto, A.; Itatani, K.</p> <p>2016-07-01</p> <p>Torsional forced-oscillation experiments on a suite of synthetic MgO polycrystals, of high-purity and average grain sizes of 1-100 µm, reveal strongly <span class="hlt">viscoelastic</span> behavior at temperatures of 800-1300°C and periods between 1 and 1000 s. The measured shear modulus and associated strain energy dissipation both display monotonic variations with oscillation period, temperature, and grain size. The data for the specimens of intermediate grain size have been fitted to a generalized Burgers creep function model that is also broadly consistent with the results for the most coarse-grained specimen. The mild grain size sensitivity for the relaxation time τL, defining the lower end of the anelastic absorption band, is consistent with the onset of elastically accommodated grain boundary sliding. The upper end of the anelastic absorption band, evident in the highest-temperature data for one specimen only, is associated with the Maxwell relaxation time τM marking the transition toward viscous behavior, conventionally ascribed a stronger grain size sensitivity. Similarly pronounced <span class="hlt">viscoelastic</span> behavior was observed in complementary torsional microcreep tests, which confirm that the nonelastic strains are mainly recoverable, i.e., anelastic. With an estimated activation volume for the <span class="hlt">viscoelastic</span> relaxation, the experimentally constrained Burgers model has been extrapolated to the conditions of pressure and temperature prevailing in the Earth's uppermost lower mantle. For a plausible grain size of 10 mm, the predicted dissipation Q-1 ranges from 10-3 to 10-2 for periods of 3-3000 s. Broad consistency with seismological observations suggests that the lower mantle ferropericlase phase might account for much of its observed attenuation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26415744','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26415744"><span>Mapping <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of healthy and pathological red blood cells at the nanoscale level.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ciasca, G; Papi, M; Di Claudio, S; Chiarpotto, M; Palmieri, V; Maulucci, G; Nocca, G; Rossi, C; De Spirito, M</p> <p>2015-10-28</p> <p>In order to pass through the microcirculation, red blood cells (RBCs) need to undergo extensive deformations and to recover the original shape. This extreme deformability is altered by various pathological conditions. On the other hand, an altered RBC deformability can have major effects on blood flow and can lead to pathological implications. The study of the <span class="hlt">viscoelastic</span> response of red blood cells to mechanical stimuli is crucial to fully understand deformability changes under pathological conditions. However, the typical erythrocyte biconcave shape hints to a complex and intrinsically heterogeneous mechanical response that must be investigated by using probes at the nanoscale level. In this work, the local <span class="hlt">viscoelastic</span> behaviour of healthy and pathological red blood cells was probed by Atomic Force Microscopy (AFM). Our results clearly show that the RBC stiffness is not spatially homogeneous, suggesting a strong correlation with the erythrocyte biconcave shape. Moreover, our nanoscale mapping highlights the key role played by viscous forces, demonstrating that RBCs do not behave as pure elastic bodies. The fundamental role played by viscous forces is further strengthened by the comparison between healthy and pathological (diabetes mellitus) RBCs. It is well known that pathological RBCs are usually stiffer than the healthy ones. Our measures unveil a more complex scenario according to which the difference between normal and pathological red blood cells does not merely lie in their stiffness but also in a different dynamical response to external stimuli that is governed by viscous forces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25637822','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25637822"><span>The relationship between mechanical <span class="hlt">properties</span> and ballistic penetration depth in a <span class="hlt">viscoelastic</span> gel.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mrozek, Randy A; Leighliter, Brad; Gold, Christopher S; Beringer, Ian R; Yu, Jian H; VanLandingham, Mark R; Moy, Paul; Foster, Mark H; Lenhart, Joseph L</p> <p>2015-04-01</p> <p>The fundamental material response of a <span class="hlt">viscoelastic</span> material when impacted by a ballistic projectile has important implication for the defense, law enforcement, and medical communities particularly for the evaluation of protective systems. In this paper, we systematically vary the modulus and toughness of a synthetic polymer gel to determine their respective influence on the velocity-dependent penetration of a spherical projectile. The polymer gels were characterized using tensile, compression, and rheological testing taking special care to address the unique challenges associated with obtaining high fidelity mechanical data on highly conformal materials. The depth of penetration data was accurately described using the elastic Froude number for <span class="hlt">viscoelastic</span> gels ranging in Young's modulus from ~60 to 630 kPa. The minimum velocity of penetration was determined to scale with the gel toughness divided by the gel modulus, a qualitative estimate for the zone of deformation size scale upon impact. We anticipate that this work will provide insight into the critical material factors that control ballistic penetration behavior in soft materials and aid in the design and development of new ballistic testing media.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15299251','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15299251"><span>The role of <span class="hlt">viscoelasticity</span> of collagen fibers in articular cartilage: theory and numerical formulation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, L P; Herzog, W</p> <p>2004-01-01</p> <p>The relative importance of fluid-dependent and fluid-independent transient mechanical behavior in articular cartilage was examined for tensile and unconfined compression testing using a fibril reinforced model. The collagen matrix of articular cartilage was modeled as <span class="hlt">viscoelastic</span> using a quasi-<span class="hlt">linear</span> <span class="hlt">viscoelastic</span> formulation with strain-dependent elastic modulus, while the proteoglycan matrix was considered as <span class="hlt">linearly</span> elastic. The collagen <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> were obtained by fitting experimental data from a tensile test. These <span class="hlt">properties</span> were used to investigate unconfined compression testing, and the sensitivity of the <span class="hlt">properties</span> was also explored. It was predicted that the stress relaxation observed in tensile tests was not caused by fluid pressurization at the macroscopic level. A multi-step tensile stress relaxation test could be approximated using a hereditary integral in which the elastic fibrillar modulus was taken to be a <span class="hlt">linear</span> function of the fibrillar strain. Applying the same formulation to the radial fibers in unconfined compression, stress relaxation could not be simulated if fluid pressurization were absent. Collagen <span class="hlt">viscoelasticity</span> was found to slightly weaken fluid pressurization in unconfined compression, and this effect was relatively more significant at moderate strain rates. Therefore, collagen <span class="hlt">viscoelasticity</span> appears to play an import role in articular cartilage in tensile testing, while fluid pressurization dominates the transient mechanical behavior in compression. Collagen <span class="hlt">viscoelasticity</span> plays a minor role in the mechanical response of cartilage in unconfined compression if significant fluid flow is present.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26298748','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26298748"><span>Textural and cooking <span class="hlt">properties</span> and <span class="hlt">viscoelastic</span> changes on heating and cooling of Balkan cheeses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Guinee, T P; Pudja, P; Miočinović, J; Wiley, J; Mullins, C M</p> <p>2015-11-01</p> <p>The growth in food service and prepared consumer foods has led to increasing demand for cheese with customized textural and cooking characteristics. The current study evaluated Kačkavalj, Kačkavalj Krstaš, and Trappist cheeses procured from manufacturing plants in Serbia for texture profile characteristics, flow and extensibility of the heated cheese, and changes in <span class="hlt">viscoelasticity</span> characteristics during heating and cooling. Measured <span class="hlt">viscoelastic</span> parameters included elastic modulus, G', loss modulus, G″, and loss tangent, LT (G″/G'). The melting temperature and congealing temperature were defined as the temperature at which LT=1 during heating from 25 to 90°C and on cooling from 90 to 25°C. The maximum LT during heating was as an index of the maximum fluidity of the molten cheese. Significant variation was noted for the extent of flow and extensibility of the heated cheeses, with no trend of cheese type. As a group, the Kačkavalj cheeses had relatively high levels of salt-in-moisture and pH 4.6-soluble N and low protein-to-fat ratio and levels of αs1-CN (f24-199). They fractured during compression to 75%; had relatively low values of cohesiveness, chewiness, and springiness; melted at ~70 to 90°C; reached maximum LT at 90°C; and congealed at 58 to 63°C. Conversely, the Kačkavalj Krstaš and Trappist cheeses had low levels of primary proteolysis and salt-in-moisture content and a high protein-to-fat ratio. They did not fracture during compression, had high values for cohesiveness and chewiness, melted at lower temperatures (56-62°C), attained maximum fluidity at a lower temperature (72-78°C), and congealed at 54 to 69°C. There was a hysteretic dependence of G' and LT on temperature for all cheeses, with the LT during cooling being higher than that during heating, and G' during cooling being lower or higher than the equivalent values during heating depending on the cheese type. Monitoring the dynamic changes in <span class="hlt">viscoelasticity</span> during heating and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EPJP..131..437K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EPJP..131..437K"><span>Influence of the combined effect of magnetic field and rotation on the onset of a non-Newtonian <span class="hlt">viscoelastic</span> nanofluid layer: <span class="hlt">Linear</span> and nonlinear analyses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Khurana, Meenakshi; Rana, Puneet; Srivastava, Sangeet</p> <p>2016-12-01</p> <p>In the present paper, we present both <span class="hlt">linear</span> and nonlinear analyses to investigate thermal instability on a rotating non-Newtonian <span class="hlt">viscoelastic</span> nanofluid layer under the influence of a magnetic field. In the <span class="hlt">linear</span> stability analysis, the stationary and oscillatory modes of convection are obtained for various controlling parameters using the normal mode technique. Both Nusselt and Sherwood numbers are calculated after employing the minimal truncated Fourier series to steady and unsteady state. The main findings conclude that rotation and strain retardation parameter increase the value of the critical Rayleigh number in the neutral stability curve which delays the onset of convection in the nanofluid layer while the stress relaxation parameter enhances the convection. The magnetic field stabilizes the system for low values of the Taylor number (rotation) but an inverse trend is observed for high Taylor number. Both Nusselt and Sherwood numbers initially oscillate with time until the steady state prevails and they decrease with both Chandrasekhar and Taylor numbers. The magnitude of the streamlines and the contours of both isotherms and iso-nanohalines concentrate near the boundaries for large values of Ra, indicating an increase in convection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17604330','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17604330"><span><span class="hlt">Viscoelasticity</span> reduces the dynamic stresses and strains in the vessel wall: implications for vessel fatigue.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Wei; Liu, Yi; Kassab, Ghassan S</p> <p>2007-10-01</p> <p>The mechanical behavior of blood vessels is known to be <span class="hlt">viscoelastic</span> rather than elastic. The functional role of <span class="hlt">viscoelasticity</span>, however, has remained largely unclear. The hypothesis of this study is that <span class="hlt">viscoelasticity</span> reduces the stresses and strains in the vessel wall, which may have a significant impact on the fatigue life of the blood vessel wall. To verify the hypothesis, the pulsatile stress in rabbit thoracic artery at physiological loading condition was investigated with a quasi-<span class="hlt">linear</span> <span class="hlt">viscoelastic</span> model, where the normalized stress relaxation function is assumed to be isotropic, while the stress-strain relationship is anisotropic and nonlinear. The artery was subjected to the same boundary condition, and the mechanical equilibrium equation was solved for both the <span class="hlt">viscoelastic</span> and an elastic (which has a constant relaxation function) model. Numerical results show that, compared with purely elastic response, the <span class="hlt">viscoelastic</span> <span class="hlt">property</span> of arteries reduces the magnitudes and temporal variations of circumferential stress and strain. The radial wall movement is also reduced due to <span class="hlt">viscoelasticity</span>. These findings imply that <span class="hlt">viscoelasticity</span> may be beneficial for the fatigue life of blood vessels, which undergo millions of cyclic mechanical loadings each year of life.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24751065','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24751065"><span>Influence of different purification and drying methods on rheological <span class="hlt">properties</span> and <span class="hlt">viscoelastic</span> behaviour of durian seed gum.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Amid, Bahareh Tabatabaee; Mirhosseini, Hamed</p> <p>2012-09-01</p> <p>The aim of the present study was to investigate the effects of different purification and drying methods on the <span class="hlt">viscoelastic</span> behaviour and rheological <span class="hlt">properties</span> of durian seed gum. The results indicated that the purified gum A (using isopropanol and ethanol) and D (using hydrochloric acid and ethanol) showed the highest and lowest viscosity, respectively. Four drying techniques included oven drying (105 °C), freeze drying, spray drying and vacuum oven drying. In the present work, all purified gums exhibited more elastic (gel-like) behaviour than the viscous (liquid-like) behaviour (G″<G'). The current study revealed that all drying methods led to significantly diminish the elastic (G') and viscous modulus (G″) of durian seed gum. The freeze-dried gum and oven-dried (105 °C) gum exhibited the highest and lowest viscous modulus (G″), respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Nanos...717030C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Nanos...717030C"><span>Mapping <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of healthy and pathological red blood cells at the nanoscale level</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ciasca, G.; Papi, M.; di Claudio, S.; Chiarpotto, M.; Palmieri, V.; Maulucci, G.; Nocca, G.; Rossi, C.; de Spirito, M.</p> <p>2015-10-01</p> <p>In order to pass through the microcirculation, red blood cells (RBCs) need to undergo extensive deformations and to recover the original shape. This extreme deformability is altered by various pathological conditions. On the other hand, an altered RBC deformability can have major effects on blood flow and can lead to pathological implications. The study of the <span class="hlt">viscoelastic</span> response of red blood cells to mechanical stimuli is crucial to fully understand deformability changes under pathological conditions. However, the typical erythrocyte biconcave shape hints to a complex and intrinsically heterogeneous mechanical response that must be investigated by using probes at the nanoscale level. In this work, the local <span class="hlt">viscoelastic</span> behaviour of healthy and pathological red blood cells was probed by Atomic Force Microscopy (AFM). Our results clearly show that the RBC stiffness is not spatially homogeneous, suggesting a strong correlation with the erythrocyte biconcave shape. Moreover, our nanoscale mapping highlights the key role played by viscous forces, demonstrating that RBCs do not behave as pure elastic bodies. The fundamental role played by viscous forces is further strengthened by the comparison between healthy and pathological (diabetes mellitus) RBCs. It is well known that pathological RBCs are usually stiffer than the healthy ones. Our measures unveil a more complex scenario according to which the difference between normal and pathological red blood cells does not merely lie in their stiffness but also in a different dynamical response to external stimuli that is governed by viscous forces.In order to pass through the microcirculation, red blood cells (RBCs) need to undergo extensive deformations and to recover the original shape. This extreme deformability is altered by various pathological conditions. On the other hand, an altered RBC deformability can have major effects on blood flow and can lead to pathological implications. The study of the <span class="hlt">viscoelastic</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004SPIE.5331..118M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004SPIE.5331..118M"><span>Optical tweezers study of <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> in the outer hair cell plasma membrane</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Murdock, David R.; Ermilov, Sergey A.; Qian, Feng; Brownell, William E.; Anvari, Bahman</p> <p>2004-06-01</p> <p>An optical tweezers system was used to study the mechanical characteristics of the outer hair cell (OHC) lateral wall by forming plasma membrane tethers. A 2nd order generalized Kelvin model was applied to describe the <span class="hlt">viscoelastic</span> behavior of OHC membrane tethers. The measured parameters included equilibrium tethering force, (Feq), force relaxation times (τ), stiffness values (κ), and coefficients of friction (μ). An analysis of force relaxation in membrane tethers indicated that the force decay is a biphasic process containing both an elastic and a viscous phase. In general, we observed an overall negative trend in the measured parameters upon application of the cationic amphipath chlorpromazine (CPZ). CPZ was found to cause up to a 40 pN reduction in Feq in OHCs. A statistically significant reduction in relaxation times and coefficients of friction was also observed, suggesting an increase in rate of force decay and a decrease in plasma membrane viscosity.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/6864483','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/6864483"><span>Temperature-frequency equivalence of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of anhydrous lanolin USP.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Radebaugh, G W; Simonelli, A P</p> <p>1983-04-01</p> <p>Methods of data analysis novel to pharmaceutical semisolids have been applied to the dynamic mechanical data obtained for anhydrous lanolin USP. It was found that the <span class="hlt">viscoelastic</span> parameters determined over a wide range of temperatures and shear frequencies could be superposed. Elastic moduli (G') and viscous moduli (G") obtained at low temperatures (T) and frequencies (nu), were equivalent to moduli obtained at high T and nu. Empirical shifts of modulus versus shear frequency data obtained at different temperatures were used to produce G' and G" versus nu master curves (complete log modulus versus log frequency behavior at a constant temperature). A method of reduced variables, in conjunction with an Arrhenius-type relation, proved useful in calculating the energy of activation for the structural processes involved in a major mechanical transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910021029','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910021029"><span>Composite propellant technology research: Mechanical <span class="hlt">property</span> characterization</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bower, Mark V.</p> <p>1991-01-01</p> <p>Proof for the existence of a single Poisson's ratio function in isotropic <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> materials is presented. An in-depth discussion is given of three dimensional <span class="hlt">viscoelastic</span> material <span class="hlt">properties</span> and their relationships to <span class="hlt">linear</span> isotropic and orthotropic <span class="hlt">viscoelastic</span> materials. A discussion of the alternate invariant definition as used by Abaqus and how it relates to the form used by Dr. S. Peng is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26399307','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26399307"><span>Corneal hyper-<span class="hlt">viscoelastic</span> model: derivations, experiments, and simulations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Su, Peng; Yang, Yang; Xiao, Jingjing; Song, Yanming</p> <p>2015-01-01</p> <p>The aim of this study is to propose a method to construct corneal biomechanical model which is the foundation for simulation of corneal microsurgery. Corneal material has two significant characteristics: hyperelastic and <span class="hlt">viscoelastic</span>. Firstly, Mooney-Rivlin hyperelastic model of cornea obtained based on stored-energy function can be simplified as a <span class="hlt">linear</span> equation with two unknown parameters. Then, modified Maxwell <span class="hlt">viscoelastic</span> model of the cornea, whose analytical form is consistent with the generalized Prony-series model, is proposed from the perspective of material mechanics. Parameters of the model are determined by the uniaxial tensile tests and the stress-relaxation tests. Corneal material <span class="hlt">properties</span> are simulated to verify the hyper-<span class="hlt">viscoelastic</span> model and measure the effectiveness of the model in the finite element simulation. On this basis, an in vivo model of the corneal is built. And the simulation of extrusion in vivo cornea shows that the force is roughly nonlinearly increasing with displacement, and it is consistent with the results obtained by extrusion experiment of in vivo cornea. Conlusions: This paper derives a corneal hyper-<span class="hlt">viscoelastic</span> model to describe the material <span class="hlt">properties</span> more accurately, and explains the mathematical method for determination of the model parameters. The model is an effective biomechanical model, which can be directly used for simulation of trephine and suture in keratoplasty. Although the corneal hyper-<span class="hlt">viscoelastic</span> model is taken as the object of study, the method has certain adaptability in biomechanical research of ophthalmology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1049560','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1049560"><span><span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span>, Ionic Conductivity, and Materials Design Considerations for Poly(styrene-b-ethylene oxide-b-styrene)-Based Ion Gel Electrolytes</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zhang, Sipei; Lee, Keun Hyung; Sun, Jingru; Frisbie, C. Daniel; Lodge, Timothy P.</p> <p>2013-03-07</p> <p>The <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> and ionic conductivity of ion gels based on the self-assembly of a poly(styrene-b-ethylene oxide-b-styrene) (SOS) triblock copolymer (M{sub n,S} = 3 kDa, M{sub n,O} = 35 kDa) in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMI][TFSA]) were investigated over the composition range of 10-50 wt % SOS and the temperature range of 25-160 C. The poly(styrene) (PS) end-blocks associate into micelles, whereas the poly(ethylene oxide) (PEO) midblocks are well-solvated by this ionic liquid. The ion gel with 10 wt % SOS melts at 54 C, with the longest relaxation time exhibiting a similar temperature dependence to that of the viscosity of bulk PS. However, the actual values of the gel relaxation time are more than 4 orders of magnitude larger than the relaxation time of bulk PS. This is attributed to the thermodynamic penalty of pulling PS end-blocks through the PEO/[EMI][TFSA] matrix. Ion gels with 20-50 wt % SOS do not melt and show two plateaus in the storage modulus over the temperature and frequency ranges measured. The one at higher frequencies is that of an entangled network of PEO strands with PS cross-links; the modulus displays a quadratic dependence on polymer weight fraction and agrees with the prediction of <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> theory assuming half of the PEO chains are elastically effective. The frequency that separates the two plateaus, {omega}{sub c}, reflects the time scale of PS end-block pull-out. The other plateau at lower frequencies is that of a congested micelle solution with PS cores and PEO coronas, which has a power law dependence on domain spacing similar to diblock melts. The ionic conductivity of the ion gels is compared to PEO homopolymer solutions at similar polymer concentrations; the conductivity is reduced by a factor of 2.1 or less, decreases with increasing PS volume fraction, and follows predictions based on a simple obstruction model. Our collective results allow the formulation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhyE...85..109S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhyE...85..109S"><span>Wave dispersion of carbon nanotubes conveying fluid supported on <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> two-parameter foundation including thermal and small-scale effects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sina, Nima; Moosavi, Hassan; Aghaei, Hosein; Afrand, Masoud; Wongwises, Somchai</p> <p>2017-01-01</p> <p>In this paper, for the first time, a nonlocal Timoshenko beam model is employed for studying the wave dispersion of a fluid-conveying single-walled carbon nanotube on <span class="hlt">Viscoelastic</span> Pasternak foundation under high and low temperature change. In addition, the phase and group velocity for the nanotube are discussed, respectively. The influences of Winkler and Pasternak modulus, homogenous temperature change, steady flow velocity and damping factor of <span class="hlt">viscoelastic</span> foundation on wave dispersion of carbon nanotubes are investigated. It was observed that the characteristic of the wave for carbon nanotubes conveying fluid is the normal dispersion. Moreover, implying <span class="hlt">viscoelastic</span> foundation leads to increasing the wave frequencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25728914','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25728914"><span><span class="hlt">Viscoelasticity</span> of hyaluronic acid-gelatin hydrogels for vocal fold tissue engineering.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kazemirad, Siavash; Heris, Hossein K; Mongeau, Luc</p> <p>2016-02-01</p> <p>Crosslinked injectable hyaluronic acid (HA)-gelatin (Ge) hydrogels have remarkable <span class="hlt">viscoelastic</span> and biological <span class="hlt">properties</span> for vocal fold tissue engineering. Patient-specific tuning of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of this injectable biomaterial could improve tissue regeneration. The frequency-dependent <span class="hlt">viscoelasticity</span> of crosslinked HA-Ge hydrogels was measured as a function of the concentration of HA, Ge, and crosslinker. Synthetic extracellular matrix hydrogels were fabricated using thiol-modified HA and Ge, and crosslinked by poly(ethylene glycol) diacrylate. A recently developed characterization method based on Rayleigh wave propagation was used to quantify the frequency-dependent <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of these hydrogels, including shear storage and loss moduli, over a broad frequency range; that is, from 40 to 4000 Hz. The <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the hydrogels increased with frequency. The storage and loss moduli values and the rate of increase with frequency varied with the concentrations of the constituents. The range of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the hydrogels was within that of human vocal fold tissue obtained from in vivo and ex vivo measurements. Frequency-dependent parametric relations were obtained using a <span class="hlt">linear</span> least-squares regression. The results are useful to better fine-tune the storage and loss moduli of HA-Ge hydrogels by varying the concentrations of the constituents for use in patient-specific treatments. © 2015 Wiley Periodicals, Inc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4551655','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4551655"><span><span class="hlt">Viscoelasticity</span> of hyaluronic acid-gelatin hydrogels for vocal fold tissue engineering</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kazemirad, Siavash; Heris, Hossein K.; Mongeau, Luc</p> <p>2015-01-01</p> <p>Cross-linked injectable hyaluronic acid-gelatin hydrogels have remarkable <span class="hlt">viscoelastic</span> and biological <span class="hlt">properties</span> for vocal fold tissue engineering. Patient-specific tuning of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of this injectable biomaterial could improve tissue regeneration. The frequency-dependent <span class="hlt">viscoelasticity</span> of cross-linked hyaluronic acid-gelatin hydrogels was measured as a function of the concentration of hyaluronic acid, gelatin, and cross-linker. Synthetic extracellular matrix hydrogels were fabricated using thiol-modified hyaluronic acid and gelatin, and cross-linked by Poly(ethylene glycol)diacrylate. A recently developed characterization method based on Rayleigh wave propagation was used to quantify the frequency-dependent <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of these hydrogels, including shear storage and loss moduli, over a broad frequency range; i.e., from 40 to 4000 Hz. The <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the hydrogels increased with frequency. The storage and loss moduli values and the rate of increase with frequency varied with the concentrations of the constituents. The range of the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of the hydrogels was within that of human vocal fold tissue obtained from in vivo and ex vivo measurements. Frequency-dependent parametric relations were obtained using a <span class="hlt">linear</span> least-squares regression. The results are useful to better fine-tune the storage and loss moduli of hyaluronic acid-gelatin hydrogels by varying the concentrations of the constituents for use in patient-specific treatments. PMID:25728914</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1011924','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1011924"><span>Modeling Non-<span class="hlt">Linear</span> Material <span class="hlt">Properties</span> in Composite Materials</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2016-06-28</p> <p>Technical Report ARWSB-TR-16013 MODELING NON-<span class="hlt">LINEAR</span> MATERIAL <span class="hlt">PROPERTIES</span> IN COMPOSITE MATERIALS Michael F. Macri Andrew G...REPORT TYPE Technical 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE MODELING NON-<span class="hlt">LINEAR</span> MATERIAL <span class="hlt">PROPERTIES</span> IN COMPOSITE MATERIALS ...systems are increasingly incorporating composite materials into their design. Many of these systems subject the composites to environmental conditions</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4405169','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4405169"><span>Derivation and Analysis of <span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> in Human Liver: Impact of Frequency on Fibrosis and Steatosis Staging</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Nightingale, Kathryn R.; Rouze, Ned C.; Rosenzweig, Stephen J.; Wang, Michael H.; Abdelmalek, Manal F.; Guy, Cynthia D.; Palmeri, Mark L.</p> <p>2015-01-01</p> <p>Commercially-available shear wave imaging systems measure group shear wave speed (SWS) and often report stiffness parameters applying purely elastic material models. Soft tissues, however, are <span class="hlt">viscoelastic</span>, and higher-order material models are necessary to characterize the dispersion associated with broadband shearwaves. In this paper, we describe a robust, model-based algorithm and use a <span class="hlt">linear</span> dispersion model to perform shearwave dispersion analysis in traditionally “difficult-to-image” subjects. In a cohort of 135 Non-Alcoholic Fatty Liver Disease patients, we compare the performance of group SWS with dispersion analysis-derived phase velocity c(200 Hz) and dispersion slope dc/df parameters to stage hepatic fibrosis and steatosis. AUROC analysis demonstrates correlation between all parameters (group SWS, c(200 Hz), and, to a lesser extent dc/df) and fibrosis stage, while no correlation was observed between steatosis stage and any of the material parameters. Interestingly, optimal AUROC threshold SWS values separating advanced liver fibrosis (≥F3) from mild-to-moderate fibrosis (≤F2) were shown to be frequency dependent, and to increase from 1.8 to 3.3 m/s over the 0–400 Hz shearwave frequency range. PMID:25585400</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19819320','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19819320"><span>Characterization of physical and <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of polymer films for coating applications under different temperature of drying and storage.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Perfetti, G; Jansen, K M B; Wildeboer, W J; van Hee, P; Meesters, G M H</p> <p>2010-01-15</p> <p>The increasing tendency to enhance consumer products with added functionality is leading to ever more complex products. Nowadays more and more particulate products are coated to give the product specific functionalities. An appropriate approach is needed to be able to satisfy customer's requirements. In this work, three reference well-known coating agents, namely two grades of hydroxypropyl methylcellulose (HPMC) and one polyvinyl alcohol (PVA) were selected and investigated. Aqueous solutions of such polymers were obtained and viscosity and shear stress were measured function of shear rate, temperature and polymer concentration. The viscosities of the solutions appear to be mainly shear rate independent, they clearly show Newtonian behaviour. Drying and storage conditions influence on morphology and structure of the cast films were evaluated using scanning electron microscope (SEM). Dynamic mechanical thermal analysis (DMTA) experiments were carried out on HPMC and PVA cast films to assess the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> over wide temperature-frequency range. The time-temperature superposition principle was used to determine the shift factor, aT, and to compose a master curve. Magnitudes and profiles of storage modulus, E', loss modulus, E'', and tan delta master curves are discussed with relation to drying and storage conditions. No impact of drying temperature on the polymer <span class="hlt">properties</span> was observed whereas the effect of storage temperature resulted to be relevant in terms of shifts in glass transition temperature and, only partially, changes in the magnitudes of E' and E''.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27090523','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27090523"><span>Structure-induced nonlinear <span class="hlt">viscoelasticity</span> of non-woven fibrous matrices.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rizvi, Mohd Suhail; Pal, Anupam; Das, Sovan Lal</p> <p>2016-12-01</p> <p>Fibrous materials are widely utilized as tissue engineering scaffolds for tissue regeneration and other bioengineering applications. The structural as well as mechanical characteristics of the fibrous matrices under static and dynamic mechanical loading conditions influence the response of the cells. In this paper, we study the mechanical response of the non-woven fibrous matrices under oscillatory loading conditions and its dependence on the structural <span class="hlt">properties</span> of fibrous matrix. We demonstrate that under oscillatory shear and elongation, the fibrous matrices demonstrate nonlinear <span class="hlt">viscoelasticity</span> at all strain amplitudes. This is contrary to the behavior of other soft polymeric materials for which nonlinearity in the <span class="hlt">viscoelastic</span> response vanishes for small strains. These observations suggest that despite their prevalence, the measures of <span class="hlt">linear</span> <span class="hlt">viscoelasticity</span> (e.g., storage and loss moduli) are inadequate for the general description of the <span class="hlt">viscoelastic</span> nature of the fibrous materials. It was, however, found that <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> nature of fibrous matrices for small amplitudes is restored when a pre-stretch is applied to the fibrous matrix along with oscillatory strains. Further, we also explored the influence of the structural <span class="hlt">properties</span> of the fibrous matrices (fiber orientation, alignment and curvature) on their <span class="hlt">viscoelastic</span> nature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6385392','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6385392"><span><span class="hlt">Viscoelasticity</span> of biomaterials</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Glasser, W.G.; Hatakeyama, H.</p> <p>1992-01-01</p> <p><span class="hlt">Viscoelasticity</span> of Biomaterials is divided into three sections. The first offers a materials design lesson on the architectural arrangement of biopolymers in collagen. Included also are reviews on solution <span class="hlt">properties</span> of polysacchardies, chiral and liquid crystalline solution characteristics of cellulose derivatives, and <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of wood and wood fiber reinforced thermoplastics. The second section, Biogels and Gelation, discusses the molecular arrangements of highly hydrated biomaterials such as mucus, gums, skinlike tissue, and silk fibroin. The physical effects that result from the transition from a liquid to a solid state are the subject of the third section, which focuses on relaxation phenomena. Gel formation, the conformation of domain structures, and motional aspects of complex biomaterials are described in terms of recent experimental advances in various fields. A relevant chapter on the effects of ionizing radiation on connective tissue is abstracted separately.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.8900T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.8900T"><span><span class="hlt">Viscoelastic</span> <span class="hlt">properties</span> combined with relevant boundary conditions can produce the arctangent shape of the geodetic displacement field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Traore, N.; Le Pourhiet, L.; Frelat, J.; Rolandone, F.; Meyer, B.</p> <p>2012-04-01</p> <p>The screw dislocation model (Weertman & Weertman, 1966) gives the horizontal displacement u as a function of the vertical distance d to the dislocation, the horizontal distance x and the slip s on each side of the dislocation. u = - (s/π) arctan(x/d) Savage and Burford (1973) interpreted this model in terms of horizontal displacement across a strike slip fault which is locked down to depth d, s being the plate velocity. Because of its simplicity and because the arctangent shape well represents the displacement that can be measured around most of the major strike slip faults, this model is commonly used to match geodetic data. We present numerical simulations that have been made with the software CASTEM, a finite element code for structural and mechanical modeling. The models are rectangular boxes that have elastic or <span class="hlt">viscoelastic</span> <span class="hlt">properties</span>, and three different kinds of conditions are applied on the boundaries of the domain that may have an impact on the localization of the displacement near the fault plane. The first boundary condition imposes the displacement under the plate, this case has been chosen because of its similarity to the Weertman's screw dislocation model. The second boundary condition imposes the displacement in the front, it corresponds to an extrusion. For the third boundary condition, the displacement is imposed laterally and simulates the general plate motion that drags the domain on both sides. We found that the displacement at the free surface does not fit an arctangent in all cases. If a perfectly elastic, homogeneous domain is used, only the first two types of boundary conditions lead to a displacement field resembling the geodetic data. This is awkward since the third kind of boundary conditions seems to be geologically the more relevant one. We then introduced local rheological modifications to reduce locally the equivalent elastic plate thickness in the vicinity of the fault. This is achieved by introducing a <span class="hlt">viscoelastic</span> relaxation in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006SPIE.6343E..3CR','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006SPIE.6343E..3CR"><span><span class="hlt">Linear</span> and nonlinear optical <span class="hlt">properties</span> of a rotaxane molecule</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rau, Ilena; Czaplicki, Robert; Humeau, Adeline; Luc, Jerome; Sahraoui, Bouchta; Boudebs, Georges; Kajzar, François; Leigh, David A.; Berna-Canovas, Jose</p> <p>2006-09-01</p> <p>In this paper the recent results of our studies of <span class="hlt">linear</span> and nonlinear optical <span class="hlt">properties</span> of a selected rotaxane are presented and discussed. The studied rotaxane can be processed into good optical quality thin films by vacuum evaporation. The <span class="hlt">linear</span> optical <span class="hlt">properties</span> of rotaxane solutions were studied by the UV-VIS spectroscopy and the nonlinear optical <span class="hlt">properties</span> by the picosecond degenerate four wave mixing and Z-scan methods. The results show important rotational contribution to the nonlinear index of refraction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AIPC.1664c0003F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AIPC.1664c0003F"><span>The effect of water absorption on the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of poly(styrene-block-isobutylene-block-styrene) for use in biomedical applications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fittipaldi, Mauro; Rodriguez, Luis A.; Grace, Landon R.</p> <p>2015-05-01</p> <p>The decrease in glass transition temperature and change in creep compliance due to water diffusion in a biocompatible thermoplastic elastomer was studied and quantified. Knowledge of the mechanical and <span class="hlt">viscoelastic</span> performance of the styrene-isobutylene-styrene block (SIBS) copolymer is important to determine the feasibility of certain in-vivo applications. Furthermore, the deterioration in these types of <span class="hlt">properties</span> due to the plasticizing effect of water must be well understood for long term usage. Samples were formed with an injection molding press and fully dried prior to immersion in distilled water at 37°C. Water diffusion kinetics were studied for four different SIBS copolymers of varying molecular weight and styrene content by measuring weight changes as a function of time. These gravimetric diffusion studies showed an inverse relationship between diffusivity and styrene content and molecular weight for the first thousand hours of immersion. Measurements of storage modulus, loss modulus, tangent delta, strain recovery and creep compliance were performed using a dynamic mechanical analyzer for the high molecular weight, high styrene content SIBS version at different absorbed water contents. A measurable and nearly <span class="hlt">linear</span> decrease of the glass transition temperature and creep recovery with respect to water content was observed for the samples tested even at relatively low water content: an increase in water content of 0.27% correlated to a decrease of 4°C in glass transition temperature while a 0.16% weight increase corresponded to a 12.5% decrease in creep recovery. These quantified material <span class="hlt">properties</span> restrict the use of SIBS in certain implantable operations that undergo cyclic strains, and in sterilization techniques that require high temperatures. As such, they are important to understand in order to determine the viability of in vivo usage of this biocompatible polymer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/7241345','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/7241345"><span><span class="hlt">Viscoelastic</span> stress/strain behavior of pharmaceutical tablets: analysis during unloading and postcompression periods.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rippie, E G; Danielson, D W</p> <p>1981-05-01</p> <p>The processes of nonequilibrium generation and decay of axial and radial stresses within tablet compacts were analyzed in terms of three-dimensional <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> theory. A rotary tablet press was instrumented to measure punch and die wall stresses during the compression and postcompression periods. Following compression, tablets were permitted to remain at the compression site within the die, and the die wall stress was followed. Microcrystalline cellulose, spray-processed lactose, and sulfacetamide are known to have different compression characteristics and were found to differ significantly in their <span class="hlt">viscoelastic</span> parameters. Compacts assumed their final <span class="hlt">viscoelastic</span> state prior to the time of punch separation. Theory permits separation of material behavior into dilation and distortion components. Dilation, thought to be dependent on voids, was elastic in all cases. Distortion effects could be described well by a Kelvin solid model. Results indicate that <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> are functions of compression conditions and may be useful in adjusting compression conditions to avoid problems such as capping.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21599305','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21599305"><span>Mathematical model of Rayleigh-Taylor and Richtmyer-Meshkov instabilities for <span class="hlt">viscoelastic</span> fluids.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rollin, Bertrand; Andrews, Malcolm J</p> <p>2011-04-01</p> <p>We extended the Goncharov model [V. N. Goncharov, Phys. Rev. Lett. 88, 134502 (2002)] for nonlinear Rayleigh-Taylor instability of perfect fluids to the case of Rivlin-Ericksen <span class="hlt">viscoelastic</span> fluids [R. S. Rivlin and J. L. Ericksen, Rat. Mech. Anal. 4, 323 (1955)], with surface tension. For Rayleigh-Taylor instability, viscosity, surface tension, and <span class="hlt">viscoelasticity</span> decrease the exponential growth rate predicted by <span class="hlt">linear</span> stability analysis. In particular, we find that viscosity and surface tension decrease the terminal bubble velocity, whereas <span class="hlt">viscoelasticity</span> is found to have no effect. All three <span class="hlt">properties</span> increase the saturation height of the bubble. In Richmyer-Meshkov instability, the decay of the asymptotic velocity depends on the balance between viscosity and surface tension, and <span class="hlt">viscoelasticity</span> tends to slow the asymptotic velocity decay.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24567881','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24567881"><span>Effect of the loading duration on the <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> parameters of tropical wood: case of Tectona grandis L.f (Teak) and Diospyros mespiliformis (Ebony) of Benin Republic.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Houanou, Agapi Kocouvi; Tchéhouali, Adolphe Dèfodji; Foudjet, Amos Erick</p> <p>2014-01-01</p> <p>Judicious and regulated use of wood as a building material is better than that of many other conventional materials in terms of environmental issues of this century. The study of the behavior of wood requires a better understanding of the characteristics in different possible cases of loading including loads applied instantly, loads applied for a short time and loads applied for a long time. The purpose of this study is to evaluate the influence of the loading duration on the <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> parameters of tropical wood in creep test. Creep tests conducted on two species of tropical wood, Tectona grandis L.f and Diospyros mespiliformis, were carried out for a total loading duration of 15 hours by subjecting samples to bending test through with equal strain in all sections. After measuring the instantaneous deflection, the other measurements were carried out at regular time each 30 minutes. Each recorded deflection was converted into longitudinal deformation and the data were analyzed by considering fourteen loading durations. Using the least squares method, the dynamic modulus of elasticity and the modulus of dynamic viscosity were determined for each loading time. The results showed that the loading time has no influence on the modulus of dynamic viscosity. On the other hand, the dynamic modulus of elasticity decreases and tends towards zero. Good agreement between creep test data and dynamic modulus of elasticity was found using mathematical function in power. Suitably, the "power" function established between the elastic dynamic modulus and the loading duration can be used to extrapolate deformations values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23834833','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23834833"><span>A new highly <span class="hlt">viscoelastic</span> hyaluronic acid gel: rheological <span class="hlt">properties</span>, biocompatibility and clinical investigation in esthetic and restorative surgery.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Iannitti, Tommaso; Bingöl, Ali Ö; Rottigni, Valentina; Palmieri, Beniamino</p> <p>2013-11-18</p> <p>Nowadays there is an increased demand for safe and effective volume enhancing fillers to achieve soft tissue augmentation in order to overcome tissue defects and aging-associated skin changes. In the present study we characterized the rheological and biological <span class="hlt">properties</span> of Variofill(®), a new highly <span class="hlt">viscoelastic</span> hyaluronic acid gel, by investigating the local effects following subcutaneous implantation in the rat to detect the host-tissue reactions and biodegradation over 18 months. We also investigated, for the first time, the application of Variofill(®) in esthetic and restorative surgery in two medical case reports. In the first case report we successfully performed Variofill(®) treatment to improve facial scars in a patient previously involved in a car crash. In the second case report we carried out a novel procedure involving a high-dose (1000 ml) injection of Variofill(®) into the dermis and subcutis of the abdominal quadrants in order to allow a classic reconstructive procedure of the abdominal wall in a patient presenting a wide incisional hernia.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24732519','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24732519"><span>Ultrasound-stimulated vibro-acoustography for high-resolution differentiation based on <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of tissue mimicking phantoms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maccabi, Ashkan; Arshi, Armin; Garritano, James; Saddik, George; Kohanbash, Elnaz; Tajudeen, Bobby A; St John, Maie; Grundfest, Warren S; Taylor, Zachary D</p> <p>2014-01-01</p> <p>In the absence of an imaging technique that provides imagery of diseased tissue with high diagnostic accuracy and contrast, surgeons must often excise excess healthy tissue surrounding neoplasms to ensure complete removal of malignant tissues. Additional approaches that are commonly used in the detection of tumor regions include palpation and conventional ultrasound to locate the affected area. However, these techniques suffer from limitations such as minimal specificity and lack of depth penetration. Lack of specificity results in the production of unclear diseased tissue regions, and therefore fails to offer surgeons a reliable and accurate image guidance tool. The proposed work provides an alternative diagnostic modality termed ultrasound-stimulated vibro-acoustography (USVA) that aims to generate detailed images characterized by <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of tissues. We demonstrate selective imaging using phantom tissue samples of polyvinyl alcohol (PVA) that are altered and arranged into unique geometries of varying elastic topology. Determining the precision and sensitivity of the USVA imaging system in identifying boundary regions as well as intensity ranges associated with tissue phantom targets will provide additional important information to allow for a non-invasive tool to distinguish diseased tissues from normal tissues in an in vivo setting.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22100084','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22100084"><span>The nonlinear elastic and <span class="hlt">viscoelastic</span> passive <span class="hlt">properties</span> of left ventricular papillary muscle of a guinea pig heart.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hassan, M A; Hamdi, M; Noma, A</p> <p>2012-01-01</p> <p>The mechanical behavior of the heart muscle tissues is the central problem in finite element simulation of the heart contraction, excitation propagation and development of an artificial heart. Nonlinear elastic and <span class="hlt">viscoelastic</span> passive material <span class="hlt">properties</span> of the left ventricular papillary muscle of a guinea pig heart were determined based on in-vitro precise uniaxial and relaxation tests. The nonlinear elastic behavior was modeled by a hypoelastic model and different hyperelastic strain energy functions such as Ogden and Mooney-Rivlin. Nonlinear least square fitting and constrained optimization were conducted under MATLAB and MSC.MARC in order to obtain the model material parameters. The experimental tensile data was used to get the nonlinear elastic mechanical behavior of the heart muscle. However, stress relaxation data was used to determine the relaxation behavior as well as viscosity of the tissues. Viscohyperelastic behavior was constructed by a multiplicative decomposition of a standard Ogden strain energy function, W, for instantaneous deformation and a relaxation function, R(t), in a Prony series form. The study reveals that hypoelastic and hyperelastic (Ogden) models fit the tissue mechanical behaviors well and can be safely used for heart mechanics simulation. Since the characteristic relaxation time (900 s) of heart muscle tissues is very large compared with the actual time of heart beating cycle (800 ms), the effect of viscosity can be reasonably ignored. The amount and type of experimental data has a strong effect on the Ogden parameters. The in vitro passive mechanical <span class="hlt">properties</span> are good initial values to start running the biosimulation codes for heart mechanics. However, an optimization algorithm is developed, based on clinical intact heart measurements, to estimate and re-correct the material parameters in order to get the in vivo mechanical <span class="hlt">properties</span>, needed for very accurate bio-simulation and for the development of new materials for the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSV...386..242V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSV...386..242V"><span>The advantage of <span class="hlt">linear</span> <span class="hlt">viscoelastic</span> material behavior in passive damper design-with application in broad-banded resonance dampers for industrial high-precision motion stages</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Verbaan, Cornelis A. M.; Peters, Gerrit W. M.; Steinbuch, Maarten</p> <p>2017-01-01</p> <p>In this paper we demonstrate the advantage of applying <span class="hlt">viscoelastic</span> materials instead of purely viscous materials as damping medium in mechanical dampers. Although the loss modulus decreases as function of frequency in case of <span class="hlt">viscoelastic</span> behavior, which can be interpreted as a decrease of damping, the <span class="hlt">viscoelastic</span> behavior still leads to an increased modal damping for mechanical structures. This advantage holds for inertial-mass-type dampers that are tuned for broad-banded resonance damping. It turns out that an increase of the storage modulus as function of frequency contributes to the effectiveness of mechanical dampers with respect to energy dissipation at different mechanical resonance frequencies. It is shown that this phenomenon is medium specific and is independent of the amount of damper mass.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993PhDT........54S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993PhDT........54S"><span>A finite element formulation for the time domain vibration analysis of an elastic-<span class="hlt">viscoelastic</span> structure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Szumski, Richard Gerard</p> <p>1993-01-01</p> <p>The equations of motion for the vibration study of a partially elastic and partially <span class="hlt">linearly</span> <span class="hlt">viscoelastic</span> structure are developed in the time domain. The unique feature of these equations is that they contain both differential and integral terms. The integral terms are convolution integrals whose convolution is made between the time derivative of the <span class="hlt">viscoelastic</span> relaxation modulus and the displacement history. They account for <span class="hlt">viscoelastic</span> damping of the structure. The equations are simplified through the solution of a real eigenvalue problem which is subsequently used to decouple all but the damping term. A numerical solution procedure is presented using the finite element method for the spatial domain and a Runge Kutta-Verner numerical integration routine for temporal domain of the problem. Partial decoupling of the equations of motion reduces computation time and saves storage space. The convolution integrals are evaluated at each time step using the trapezoidal rule. Two new <span class="hlt">viscoelastic</span> constitutive laws are introduced that are shown to characterize material <span class="hlt">properties</span> over a broad frequency spectrum with few material parameters. They are convenient to work with because they have simple rational forms in both the time and frequency domains and also unconditionally obey the second law of thermodynamics. To verify the theory, computer program, and new <span class="hlt">viscoelastic</span> constitutive laws, a simple elastic-<span class="hlt">viscoelastic</span> structure known as a constrained layer damper was constructed and tested. The displacement history of the constrained layer damper was measured as an initial static displacement was suddenly released. Good agreement was obtained between the measurements and the numerical simulation of the same event using the theory developed here with the new constitutive laws. The solution procedure is a viable method for solving for the vibratory response of <span class="hlt">viscoelastically</span> damped structures and is suitable for large-scale finite element analysis through a modified</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28317718','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28317718"><span>Effect of coacervation conditions on the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of N,O-carboxymethyl chitosan - gum Arabic coacervates.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Huang, Guo-Qing; Du, Yan-Li; Xiao, Jun-Xia; Wang, Guan-Yun</p> <p>2017-08-01</p> <p>The effects of coacervation acidity, phase separation temperature, ionic strength, and biopolymer ratio on the <span class="hlt">viscoelasticity</span> of the N,O-carboxymethyl chitosan (NOCC) - gum Arabic (GA) coacervate were investigated by using coacervate yield as the indicator of electrostatic interaction strength. The strongest interaction between NOCC and GA occurred at pH 3.0, whereas the highest modulus values were found in the coacervate separated at pH 6.0. The coacervate yield did not vary with phase separation temperature in the range 4-55°C, but the coacervate <span class="hlt">viscoelasticity</span> declined as the temperature increased from 25°C to 45°C and then peaked at 55°C. The presence of NaCl weakened the electrostatic interaction between the two polyelectrolytes, but no dose-dependent reduction in <span class="hlt">viscoelasticity</span> was observed for their coacervates. Besides, the highest electrostatic interaction strength and coacervate <span class="hlt">viscoelasticity</span> were recorded at different GA to NOCC ratios. It is proposed that the strength of electrostatic interaction is not the only parameter that determines the <span class="hlt">viscoelasticity</span> of the NOCC - GA coacervate. Copyright © 2017 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=208888','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=208888"><span>A new soy-based hydrogels: development, <span class="hlt">viscoelastic</span> <span class="hlt">properties</span>, and application for controlled drug release</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>Hydrogels have been widely studied due to their potential application in drug delivery systems as they are capable of forming aggregates in aqueous solutions. Hydrogels formed from biopolymers or natural sources have special advantages because of their biodegradable and biocompatible <span class="hlt">properties</span>. I...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=233144','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=233144"><span><span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Rubber Composites Reinforced by Wheat Gluten and Starch Co-filler</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>Due to different abilities of wheat gluten (WG) and wheat starch (WS) to increase the modulus of rubber composites, the composite <span class="hlt">properties</span> can be adjusted by varying the ratio of WG to WS as a co-filler. This study shows that the co-filler composites became more temperature dependent as the WG co...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=231045','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=231045"><span>Effect of Hydrolyzed Wheat Gluten and Starch Ratio on the <span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Rubber Composites</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>The hydrolyzed wheat gluten (WG) and wheat starch (WS) showed substantial reinforcement effects in rubber composites. Due to different abilities of WG and WS to increase the modulus of rubber composites, the composite <span class="hlt">properties</span> can be adjusted by varying the ratio of WG and WS as a co-filler. The...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=231386','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=231386"><span><span class="hlt">Viscoelastic</span> <span class="hlt">properties</span> of kenaf bast fiber in relation to stem age</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>Natural fibers traditionally used for cordage are proving valuable for advanced industrial applications due in part to beneficial physical and chemical <span class="hlt">properties</span>, but also because they are a renewable and biodegradable resource. Kenaf (Hibiscus cannabinus L., Malvaceae) produces high yields of lig...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=233561','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=233561"><span><span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Rubber Composites Reinforced by Wheat Gluten and Wheat Starch Co-filler</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>Due to different abilities of wheat gluten (WG) and wheat starch (WS) to increase the modulus of rubber composites, the composite <span class="hlt">properties</span> can be adjusted by varying the ratio of WG to WS as a co-filler. This study shows that the co-filler composites became more temperature dependent as the WG co...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvE..92d2314S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvE..92d2314S"><span><span class="hlt">Linear</span> and nonlinear magnetic <span class="hlt">properties</span> of ferrofluids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Szalai, I.; Nagy, S.; Dietrich, S.</p> <p>2015-10-01</p> <p>Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic <span class="hlt">properties</span> of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001), 10.1103/PhysRevE.64.041405] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983), 10.1080/00268978300100621] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26565247','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26565247"><span><span class="hlt">Linear</span> and nonlinear magnetic <span class="hlt">properties</span> of ferrofluids.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Szalai, I; Nagy, S; Dietrich, S</p> <p>2015-10-01</p> <p>Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic <span class="hlt">properties</span> of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001)] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983)] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/2720066','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/2720066"><span>Cell poking: quantitative analysis of indentation of thick <span class="hlt">viscoelastic</span> layers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Duszyk, M; Schwab, B; Zahalak, G I; Qian, H; Elson, E L</p> <p>1989-04-01</p> <p>A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized <span class="hlt">viscoelastic</span> polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a <span class="hlt">linear</span> <span class="hlt">viscoelasticity</span> theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative <span class="hlt">viscoelastic</span> material <span class="hlt">properties</span> from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1330552','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1330552"><span>Cell poking: quantitative analysis of indentation of thick <span class="hlt">viscoelastic</span> layers.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Duszyk, M; Schwab, B; Zahalak, G I; Qian, H; Elson, E L</p> <p>1989-01-01</p> <p>A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized <span class="hlt">viscoelastic</span> polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a <span class="hlt">linear</span> <span class="hlt">viscoelasticity</span> theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative <span class="hlt">viscoelastic</span> material <span class="hlt">properties</span> from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells. PMID:2720066</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvE..94f2705T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvE..94f2705T"><span><span class="hlt">Viscoelastic</span> nematodynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Turzi, Stefano S.</p> <p>2016-12-01</p> <p>Nematic liquid crystals exhibit both crystallike and fluidlike features. In particular, the propagation of an acoustic wave shows an interesting occurrence of some of the solidlike features at the hydrodynamic level, namely, the frequency-dependent anisotropy of sound velocity and acoustic attenuation. The non-Newtonian behavior of nematics also emerges from the frequency-dependent viscosity coefficients. To account for these phenomena, we put forward a <span class="hlt">viscoelastic</span> model of nematic liquid crystals, and we extend our previous theory to fully include the combined effects of compressibility, anisotropic elasticity, and dynamic relaxation, at any shear rate. The low-frequency limit agrees with the compressible Ericksen-Leslie theory, while at intermediate frequencies the model correctly captures the relaxation mechanisms underlying finite shear and bulk elastic moduli. We show that there are only four relaxation times allowed by the uniaxial symmetry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4581979','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4581979"><span>Investigation of Mechanisms of <span class="hlt">Viscoelastic</span> Behavior of Collagen Molecule</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ghodsi, Hossein; Darvish, Kurosh</p> <p>2015-01-01</p> <p>Unique mechanical <span class="hlt">properties</span> of collagen molecule make it one of the most important and abundant proteins in animals. Many tissues such as connective tissues rely on these <span class="hlt">properties</span> to function properly. In the past decade, molecular dynamics (MD) simulations have been used extensively to study the mechanical behavior of molecules. For collagen, MD simulations were primarily used to determine its elastic <span class="hlt">properties</span>. In this study, constant force steered MD simulations were used to perform creep tests on collagen molecule segments. The mechanical behavior of the segments, with lengths of approximately 20 (1X), 38 (2X), 74 (4X), and 290 nm (16X), was characterized using a quasi-<span class="hlt">linear</span> model to describe the observed <span class="hlt">viscoelastic</span> responses. To investigate the mechanisms of the <span class="hlt">viscoelastic</span> behavior, hydrogen bonds (H-bonds) rupture/formation time history of the segments were analyzed and it was shown that the formation growth rate of H-bonds in the system is correlated with the creep growth rate of the segment ( β = 2.41 βH). In addition, a <span class="hlt">linear</span> relationship between H-bonds formation growth rate and the length of the segment was quantified. Based on these findings, a general <span class="hlt">viscoelastic</span> model was developed and verified where, using the smallest segment as a building block, the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of larger segments could be predicted. In addition, the effect of temperature control methods on the mechanical <span class="hlt">properties</span> were studied, and it was shown that application of Langevin Dynamics had adverse effect on these <span class="hlt">properties</span> while the Lowe-Anderson method was shown to be more appropriate for this application. This study provides information that is essential for multi-scale modeling of collagen fibrils using a bottom-up approach. PMID:26256473</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26256473','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26256473"><span>Investigation of mechanisms of <span class="hlt">viscoelastic</span> behavior of collagen molecule.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ghodsi, Hossein; Darvish, Kurosh</p> <p>2015-11-01</p> <p>Unique mechanical <span class="hlt">properties</span> of collagen molecule make it one of the most important and abundant proteins in animals. Many tissues such as connective tissues rely on these <span class="hlt">properties</span> to function properly. In the past decade, molecular dynamics (MD) simulations have been used extensively to study the mechanical behavior of molecules. For collagen, MD simulations were primarily used to determine its elastic <span class="hlt">properties</span>. In this study, constant force steered MD simulations were used to perform creep tests on collagen molecule segments. The mechanical behavior of the segments, with lengths of approximately 20 (1X), 38 (2X), 74 (4X), and 290 nm (16X), was characterized using a quasi-<span class="hlt">linear</span> model to describe the observed <span class="hlt">viscoelastic</span> responses. To investigate the mechanisms of the <span class="hlt">viscoelastic</span> behavior, hydrogen bonds (H-bonds) rupture/formation time history of the segments were analyzed and it was shown that the formation growth rate of H-bonds in the system is correlated with the creep growth rate of the segment (β=2.41βH). In addition, a <span class="hlt">linear</span> relationship between H-bonds formation growth rate and the length of the segment was quantified. Based on these findings, a general <span class="hlt">viscoelastic</span> model was developed and verified here, using the smallest segment as a building block, the <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of larger segments could be predicted. In addition, the effect of temperature control methods on the mechanical <span class="hlt">properties</span> were studied, and it was shown that application of Langevin Dynamics had adverse effect on these <span class="hlt">properties</span> while the Lowe-Anderson method was shown to be more appropriate for this application. This study provides information that is essential for multi-scale modeling of collagen fibrils using a bottom-up approach. Copyright © 2015 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27606621','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27606621"><span>Mechanically <span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> of Cellulose Nanocrystals Skeleton Reinforced Hierarchical Composite Hydrogels.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yang, Jun; Han, ChunRui</p> <p>2016-09-28</p> <p>With inspiration from the concept of natural dynamic materials, binary-component composite hydrogels with excellent mechanical <span class="hlt">properties</span> and recovery capability were prepared from the cellulose nanocrystal (CNC) skeleton reinforced covalently cross-linked polyacrylamide (PAAm) networks. The hierarchical skeleton obtained by freeze-drying of CNC aqueous suspension was directly impregnated into acrylamide (AAm) monomer solution, and in situ polymerization occurred in the presence of hydrophilic cross-linker PEGDA575. Under stress, hydrogen bonds at the interface between CNC and PAAm as well as inside the CNC skeleton acted as sacrificial bonds to dissipate energy, while the covalently cross-linked PAAm chains bind the network together by providing adhesion to CNC and thereby suppress the catastrophic craze propagation. The above synergistic effects of the CNC skeleton and the elastic PAAm network enabled the composite hydrogels to withstand up to 181 kPa of tensile stress, 1.01 MPa of compressive strength, and 1392% elongation at break with the fracture energy as high as 2.82 kJ/m(2). Moreover, the hydrogels recovered more than 70% elasticity after eight loading-unloading cycles, revealing excellent fatigue resistance. The depth-sensing instrumentation by indentation test corroborated that the CNC skeleton contributed simultaneous improvements in hardness and elasticity by as much as 500% in comparison with the <span class="hlt">properties</span> of the pristine PAAm hydrogels. This elegant strategy by using the CNC skeleton as a reinforcing template offers a new perspective for the fabrication of robust hydrogels with exceptional mechanical <span class="hlt">properties</span> that may be important for biomedical applications where high strength is required, such as scaffolds for tissue engineering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860056890&hterms=RATE+CHANGE&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DRATE%2BOF%2BCHANGE','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860056890&hterms=RATE+CHANGE&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DRATE%2BOF%2BCHANGE"><span>Ultrasonic characterization of changes in <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of epoxy during cure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Winfree, W. P.; Parker, F. R.</p> <p>1985-01-01</p> <p>A technique for using the longitudinal velocity (LV) of an ultrasonic wave to monitor the extent of cross linking (CL) during the cure of thermosetting resins is described. The method was developed by monitoring the rate of change in LV during the cure of a bisphenol-A epoxy resin with an amine adduct. The experiment included variations in the temperature and stoichiometry in order to express the rate of change in terms of the reaction kinetics. The pulse-echo method was used with a single transducer operating at 20 MHz. Numerical models were defined to account for the acoustic response of a single layer, the attenuation and the reflection coefficient. A <span class="hlt">linear</span> relationship was observed between the inverse of the temperature and the log of the rate of change in the velocity, supporting the theory that the velocity could be used to monitor the extent of the cross-linking reaction. An activation energy of 11.9 kcal/mole was calculated for the mixture being investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22503483','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22503483"><span>Textural and <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> of pork frankfurters containing canola-olive oils, rice bran, and walnut.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Álvarez, D; Xiong, Y L; Castillo, M; Payne, F A; Garrido, M D</p> <p>2012-09-01</p> <p>Textural, rheological and microstructural <span class="hlt">properties</span> of frankfurters made with 20% pork backfat, 20% canola or 20% canola-olive (3:1) oils, including rice bran (RB) and walnut extract (WE) as macronutrients (2.5%) were investigated. Textural parameters, including hardness, gumminess and rupture-force, were highly (P<0.05) influenced by the fat-oil composition. Addition of RB or WE in vegetable oil emulsions improved textural consistency (P<0.05). However, RB addition reduced gelling capacity, suggesting antagonistic interactions between fiber and oil droplets. Vegetable oil addition favored gel network formation, and, when combined with WE, showed the highest improvement of gel elasticity. These textural and gelling <span class="hlt">properties</span> were corroborated by frankfurter micrographs, which revealed interactions between vegetable oils, RB, or WE with protein matrix and fat globules affecting these parameters. The results suggest that functional plant-derived ingredients can be valuable to the modification of frankfurter formulations for improved nutrition and as well as textural quality. Copyright © 2012 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4624407','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4624407"><span>Shear-Thinning Supramolecular Hydrogels with Secondary Autonomous Covalent Crosslinking to Modulate <span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> In Vivo</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Rodell, Christopher B.; MacArthur, John W.; Dorsey, Shauna M.; Wade, Ryan J.; Wang, Leo L.; Woo, Y. Joseph</p> <p>2015-01-01</p> <p>Clinical percutaneous delivery of synthetically engineered hydrogels remains limited due to challenges posed by crosslinking kinetics – too fast leads to delivery failure, too slow limits material retention. To overcome this challenge, we exploit supramolecular assembly to localize hydrogels at the injection site and introduce subsequent covalent crosslinking to control final material <span class="hlt">properties</span>. Supramolecular gels were designed through the separate pendant modifications of hyaluronic acid (HA) by the guest-host pair cyclodextrin and adamantane, enabling shear-thinning injection and high target site retention (>98%). Secondary covalent crosslinking occurred via addition of thiols and Michael-acceptors (i.e., methacrylates, acrylates, vinyl sulfones) on HA and increased hydrogel moduli (E=25.0±4.5kPa) and stability (>3.5 fold in vivo at 28 days). Application of the dual-crosslinking hydrogel to a myocardial infarct model showed improved outcomes relative to untreated and supramolecular hydrogel alone controls, demonstrating its potential in a range of applications where the precise delivery of hydrogels with tunable <span class="hlt">properties</span> is desired. PMID:26526097</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030020936&hterms=clay&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dclay','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030020936&hterms=clay&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dclay"><span><span class="hlt">Viscoelastic</span> and Mechanical <span class="hlt">Properties</span> of Thermoset PMR-type Polyimide-Clay Nanocomposites</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Abdalla, Mohamed O.; Dean, Derrick; Campbell, Sandi</p> <p>2002-01-01</p> <p>High temperature thermoset polyimide-clay nanocomposites were prepared by blending 2.5 and 5 wt% of an unmodified Na(+-) montmorillonite (PGV) and two organically modified FGV (PGVCl0COOH, PGVC12) with a methanol solution of PMR-15 precursor. The methanol facilitated the dispersal of the unmodified clay. Dynamic mechanical analysis results showed a significant increase in the thermomechanical <span class="hlt">properties</span> (E' and E") of 2.5 wt% clay loaded nanocomposites in comparison with the neat polyimide. Higher glass transition temperatures were observed for 2.5 wt% nanocomposites compared to the neat polyimide. Flexural <span class="hlt">properties</span> measurements for the 2.5 wt% nanocomposites showed a significant improvement in the modulus and strength, with no loss in elongation. This trend was not observed for the 5 wt% nanocomposites. An improvement in the CTE was observed for the PGV/PMR-15 nanocomposites, while a decrease was observed for the organically modified samples. This was attributed to potential variations in the interface caused by modifier degradation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995JAP....78.5953N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995JAP....78.5953N"><span>Atomic force microscopy imaging of <span class="hlt">viscoelastic</span> <span class="hlt">properties</span> in toughened polypropylene resins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nysten, Bernard; Legras, Roger; Costa, Jean-Louis</p> <p>1995-11-01</p> <p>The bulk morphology of two toughened polypropylene/(ethylene propylene)copolymer resins (PP/EP) presenting different impact resistances has been studied by means of different atomic force microscopy techniques: contact atomic force microscopy, lateral force microscopy (LFM), and force modulation microscopy (FMM). The three techniques reveal two different morphologies as observed in transmission electronic microscopy. In LFM, a higher friction force is observed on the rubbery phase which has the lower Young's modulus confirming the relationship between friction force and elastic <span class="hlt">properties</span>. In force modulation, the elastic moduli is found to be much lower on the EP nodules in both resins. FMM also reveals that the difference of viscous response between the PP matrix and the EP nodules is much lower in the resin which is less impact resistant.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3506395','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3506395"><span><span class="hlt">Viscoelastic</span> <span class="hlt">Properties</span> and Nano-scale Structures of Composite Oligopeptide-Polysaccharide Hydrogels</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hyland, Laura L.; Taraban, Marc B.; Feng, Yue; Hammouda, Boualem; Yu, Y. Bruce</p> <p>2012-01-01</p> <p>Biocompatible and biodegradable peptide hydrogels are drawing increasing attention as prospective materials for human soft tissue repair and replacement. To improve the rather unfavorable mechanical <span class="hlt">properties</span> of our pure peptide hydrogels, in this work we examined the possibility of creating a double hydrogel network. This network was created by means of the co-assembly of mutually attractive but self-repulsive oligopeptides within an already existing fibrous network formed by the charged, biocompatible polysaccharides chitosan, alginate, and chondroitin. Using dynamic oscillatory rheology experiments, it was found that the co-assembly of the peptides within the existing polysaccharide network resulted in a less stiff material as compared to the pure peptide networks (the elastic modulus G′ decreased from 90 kPa to 10 kPa). However, these composite oligopeptide-polysaccharide hydrogels were characterized by a greater resistance to deformation (the yield strain γ grew from 4 % to 100 %). Small-angle neutron scattering (SANS) was used to study the 2D cross-sectional shapes of the fibers, their dimensional characteristics and the mesh sizes of the fibrous networks. Differences in material structures found with SANS experiments confirmed rheology data showing that incorporation of the peptides dramatically changed the morphology of the polysaccharide network. The resulting fibers were structurally very similar to those forming the pure peptide networks, but formedless stiff gels because of their markedly greater mesh sizes. Together, these findings suggest an approach for the development of highly deformation-resistant biomaterials. PMID:21994046</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...632418J','NASAA