Quasistatic nonlinear viscoelasticity and gradient flows

OpenAIRE

Ball, John M.; Şengül, Yasemin

2014-01-01

We consider the equation of motion for one-dimensional nonlinear viscoelasticity of strain-rate type under the assumption that the stored-energy function is λ-convex, which allows for solid phase transformations. We formulate this problem as a gradient flow, leading to existence and uniqueness of solutions. By approximating general initial data by those in which the deformation gradient takes only finitely many values, we show that under suitable hypotheses on the stored-energy function the d...

A phenomenological constitutive model for the nonlinear viscoelastic responses of biodegradable polymers

KAUST Repository

Khan, Kamran

2012-11-09

We formulate a constitutive framework for biodegradable polymers that accounts for nonlinear viscous behavior under regimes with large deformation. The generalized Maxwell model is used to represent the degraded viscoelastic response of a polymer. The large-deformation, time-dependent behavior of viscoelastic solids is described using an Ogden-type hyperviscoelastic model. A deformation-induced degradation mechanism is assumed in which a scalar field depicts the local state of the degradation, which is responsible for the changes in the material\\'s properties. The degradation process introduces another timescale (the intrinsic material clock) and an entropy production mechanism. Examples of the degradation of a polymer under various loading conditions, including creep, relaxation and cyclic loading, are presented. Results from parametric studies to determine the effects of various parameters on the process of degradation are reported. Finally, degradation of an annular cylinder subjected to pressure is also presented to mimic the effects of viscoelastic arterial walls (the outer cylinder) on the degradation response of a biodegradable stent (the inner cylinder). A general contact analysis is performed. As the stiffness of the biodegradable stent decreases, stress reduction in the stented viscoelastic arterial wall is observed. The integration of the proposed constitutive model with finite element software could help a designer to predict the time-dependent response of a biodegradable stent exhibiting finite deformation and under complex mechanical loading conditions. © 2012 Springer-Verlag Wien.

The viscoelastic properties of the cervical mucus plug

DEFF Research Database (Denmark)

Kjær Bastholm, Sara; Becher, Naja; Stubbe, Peter Reimer

2013-01-01

The objective of this study was to characterize the viscoelastic properties of cervical mucus plugs (CMPs) shed during labor at term. Spontaneously shed cervical mucus plugs from healthy women in active labor, were tested. The viscoelastic properties of cervical mucus plugs were investigated...... with using frequency and stress sweep experiments within the linear viscoelastic region. Random-effects regression was used for statistical analysis. The CMPs are solid-like viscoelastic structures and the elastic modulus dominated the viscous modulus at all frequencies. These rheological characteristics...

Design and numerical implementation of a 3-D non-linear viscoelastic constitutive model for brain tissue during impact

NARCIS (Netherlands)

Brands, D.W.A.; Peters, G.W.M.; Bovendeerd, P.H.M.

2004-01-01

Finite Element (FE) head models are often used to understand mechanical response of the head and its contents during impact loading in the head. CurrentFE models do not account for non-linear viscoelastic material behavior of brain tissue. We developed a new non-linear viscoelastic material model

Bifurcations and chaos of the nonlinear viscoelastic plates subjected to subsonic flow and external loads

International Nuclear Information System (INIS)

An, Fengxian; Chen, Fangqi

2016-01-01

Highlights: • The subharmonic bifurcations and chaotic motions are studied by means of Melnikov method. • The critical conditions for the occurrence of chaotic motions and subharmonic bifurcations are obtained. • The chaotic features on the system parameters are discussed. • The theoretical predictions are confirmed by numerical simulations. - Abstract: The subharmonic bifurcations and chaotic motions of the nonlinear viscoelastic plates subjected to subsonic flow and external loads are studied by means of Melnikov method. The critical conditions for the occurrence of chaotic motions are obtained. The chaotic features on the system parameters are discussed in detail. The conditions for subharmonic bifurcations are also obtained. For the system with no structural damping, chaotic motions can occur through infinite subharmonic bifurcations of odd orders. Furthermore, we confirm our theoretical predictions by numerical simulations. The theoretical results obtained here can help us to eliminate or suppress large nonlinear vibrations and chaotic motions of the nonlinear viscoelastic plates. Based on Melnikov method, complex dynamical behaviors of the nonlinear viscoelastic plates can be controlled by modifying the system parameters.

A phenomenological constitutive model for the nonlinear viscoelastic responses of biodegradable polymers

KAUST Repository

Khan, Kamran; El Sayed, Tamer S.

2012-01-01

We formulate a constitutive framework for biodegradable polymers that accounts for nonlinear viscous behavior under regimes with large deformation. The generalized Maxwell model is used to represent the degraded viscoelastic response of a polymer

The viscoelastic properties of the cervical mucus plug

DEFF Research Database (Denmark)

Bastholm, Sara K.; Becher, Naja; Stubbe, Peter Reimer

2014-01-01

labor. MethodsViscoelastic properties of CMPs were investigated with a dynamic oscillatory rheometer using frequency and stress sweep experiments within the linear viscoelastic region. Main outcome measuresThe rheological variables obtained were as follows: elastic modulus (G), viscous modulus (G......ObjectiveTo characterize the viscoelastic properties of cervical mucus plugs (CMPs) shed during labor at term. DesignExperimental research. SettingDepartment of Obstetrics and Gynecology, Aarhus University Hospital, Denmark. Population/SampleSpontaneously shed CMPs from 18 healthy women in active...

Fully coupled heat conduction and deformation analyses of nonlinear viscoelastic composites

KAUST Repository

Khan, Kamran

2012-05-01

This study presents an integrated micromechanical model-finite element framework for analyzing coupled heat conduction and deformations of particle-reinforced composite structures. A simplified micromechanical model consisting of four sub-cells, i.e., one particle and three matrix sub-cells is formulated to obtain the effective thermomechanical properties and micro-macro field variables due to coupled heat conduction and nonlinear thermoviscoelastic deformation of a particulate composite that takes into account the dissipation of energy from the viscoelastic constituents. A time integration algorithm for simultaneously solving the equations that govern heat conduction and thermoviscoelastic deformations of isotropic homogeneous materials is developed. The algorithm is then integrated to the proposed micromechanical model. A significant temperature generation due to the dissipation effect in the viscoelastic matrix was observed when the composite body is subjected to cyclic mechanical loadings. Heat conduction due to the dissipation of the energy cannot be ignored in predicting the factual temperature and deformation fields within the composite structure, subjected to cyclic loading for a long period. A higher creep resistant matrix material or adding elastic particles can lower the temperature generation. Our analyses suggest that using particulate composites and functionally graded materials can reduce the heat generation due to energy dissipation. © 2012 Elsevier Ltd.

Two-dimensional nonlinear dynamics of an axially moving viscoelastic beam with time-dependent axial speed

International Nuclear Information System (INIS)

Ghayesh, Mergen H.; Amabili, Marco; Farokhi, Hamed

2013-01-01

In the present study, the coupled nonlinear dynamics of an axially moving viscoelastic beam with time-dependent axial speed is investigated employing a numerical technique. The equations of motion for both the transverse and longitudinal motions are obtained using Newton’s second law of motion and the constitutive relations. A two-parameter rheological model of the Kelvin–Voigt energy dissipation mechanism is employed in the modelling of the viscoelastic beam material, in which the material time derivative is used in the viscoelastic constitutive relation. The Galerkin method is then applied to the coupled nonlinear equations, which are in the form of partial differential equations, resulting in a set of nonlinear ordinary differential equations (ODEs) with time-dependent coefficients due to the axial acceleration. A change of variables is then introduced to this set of ODEs to transform them into a set of first-order ordinary differential equations. A variable step-size modified Rosenbrock method is used to conduct direct time integration upon this new set of first-order nonlinear ODEs. The mean axial speed and the amplitude of the speed variations, which are taken as bifurcation parameters, are varied, resulting in the bifurcation diagrams of Poincaré maps of the system. The dynamical characteristics of the system are examined more precisely via plotting time histories, phase-plane portraits, Poincaré sections, and fast Fourier transforms (FFTs)

Dynamic rheological properties of viscoelastic magnetic fluids in uniform magnetic fields

International Nuclear Information System (INIS)

Yamaguchi, Hiroshi; Niu Xiaodong; Ye Xiaojiang; Li Mingjun; Iwamoto, Yuhiro

2012-01-01

The dynamic rheological properties of viscoelastic magnetic fluids in externally applied uniform magnetic fields are investigated by a laboratory-made cone-plate rheometer in this study. In particular, the effects of the magnetic field on the viscoelastic properties (the complex dynamic modulus) of the viscoelastic magnetic fluids are studied. In the investigation, three viscoelastic magnetic fluids are made by mixing a magnetic fluid and a viscoelastic fluid with different mass ratios. As a supplementation to the experimental investigation, a theoretical analysis is also presented. The present study shows that the viscosity and elasticity of the viscoelastic magnetic fluids are significantly influenced by the magnetic field and the concentrations of the magnetic particles in the test fluids. Theoretical analysis qualitatively explains the present findings. - Highlights: ► The dynamic rheological properties of the viscoelastic magnetic fluids in uniform magnetic fields are investigated. ► Both the magnetic field strength and the concentration of the magnetic particles in the fluids have significant effects on the viscosity and elasticity of the viscoelastic magnetic fluids. ► Theoretical prediction and analysis qualitatively explains the present findings.

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

Science.gov (United States)

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.

A micro-macro constitutive model for finite-deformation viscoelasticity of elastomers with nonlinear viscosity

Science.gov (United States)

Zhou, Jianyou; Jiang, Liying; Khayat, Roger E.

2018-01-01

Elastomers are known to exhibit viscoelastic behavior under deformation, which is linked to the diffusion processes of the highly mobile and flexible polymer chains. Inspired by the theories of polymer dynamics, a micro-macro constitutive model is developed to study the viscoelastic behaviors and the relaxation process of elastomeric materials under large deformation, in which the material parameters all have a microscopic foundation or a microstructural justification. The proposed model incorporates the nonlinear material viscosity into the continuum finite-deformation viscoelasticity theories which represent the polymer networks of elastomers with an elastic ground network and a few viscous subnetworks. The developed modeling framework is capable of adopting most of strain energy density functions for hyperelastic materials and thermodynamics evolution laws of viscoelastic solids. The modeling capacity of the framework is outlined by comparing the simulation results with the experimental data of three commonly used elastomeric materials, namely, VHB4910, HNBR50 and carbon black (CB) filled elastomers. The comparison shows that the stress responses and some typical behaviors of filled and unfilled elastomers can be quantitatively predicted by the model with suitable strain energy density functions. Particularly, the strain-softening effect of elastomers could be explained by the deformation-dependent (nonlinear) viscosity of the polymer chains. The presented modeling framework is expected to be useful as a modeling platform for further study on the performance of different type of elastomeric materials.

A constitutive model for developing blood clots with various compositions and their nonlinear viscoelastic behavior.

Science.gov (United States)

van Kempen, Thomas H S; Donders, Wouter P; van de Vosse, Frans N; Peters, Gerrit W M

2016-04-01

The mechanical properties determine to a large extent the functioning of a blood clot. These properties depend on the composition of the clot and have been related to many diseases. However, the various involved components and their complex interactions make it difficult at this stage to fully understand and predict properties as a function of the components. Therefore, in this study, a constitutive model is developed that describes the viscoelastic behavior of blood clots with various compositions. Hereto, clots are formed from whole blood, platelet-rich plasma and platelet-poor plasma to study the influence of red blood cells, platelets and fibrin, respectively. Rheological experiments are performed to probe the mechanical behavior of the clots during their formation. The nonlinear viscoelastic behavior of the mature clots is characterized using a large amplitude oscillatory shear deformation. The model is based on a generalized Maxwell model that accurately describes the results for the different rheological experiments by making the moduli and viscosities a function of time and the past and current deformation. Using the same model with different parameter values enables a description of clots with different compositions. A sensitivity analysis is applied to study the influence of parameter variations on the model output. The relative simplicity and flexibility make the model suitable for numerical simulations of blood clots and other materials showing similar behavior.

General decay of solutions of a nonlinear system of viscoelastic wave equations

KAUST Repository

Said-Houari, Belkacem

2011-04-16

This work is concerned with a system of two viscoelastic wave equations with nonlinear damping and source terms acting in both equations. Under some restrictions on the nonlinearity of the damping and the source terms, we prove that, for certain class of relaxation functions and for some restrictions on the initial data, the rate of decay of the total energy depends on those of the relaxation functions. This result improves many results in the literature, such as the ones in Messaoudi and Tatar (Appl. Anal. 87(3):247-263, 2008) and Liu (Nonlinear Anal. 71:2257-2267, 2009) in which only the exponential and polynomial decay rates are considered. © 2011 Springer Basel AG.

General decay of solutions of a nonlinear system of viscoelastic wave equations

KAUST Repository

Said-Houari, Belkacem; Messaoudi, Salim A.; Guesmia, Aï ssa

2011-01-01

This work is concerned with a system of two viscoelastic wave equations with nonlinear damping and source terms acting in both equations. Under some restrictions on the nonlinearity of the damping and the source terms, we prove that, for certain class of relaxation functions and for some restrictions on the initial data, the rate of decay of the total energy depends on those of the relaxation functions. This result improves many results in the literature, such as the ones in Messaoudi and Tatar (Appl. Anal. 87(3):247-263, 2008) and Liu (Nonlinear Anal. 71:2257-2267, 2009) in which only the exponential and polynomial decay rates are considered. © 2011 Springer Basel AG.

Viscoelastic properties of microfibrillated cellulose (MFC) produced from agricultural residue corn stover

Science.gov (United States)

The rheological properties of microfibrillated cellulose (MFC) produced from agricultural residue corn stover were investigated. The corn stover MFC gels exhibited concentration-dependent viscoelastic properties. Higher corn stover MFC concentrations resulted in stronger viscoelastic properties. Th...

Fully coupled heat conduction and deformation analyses of visco-elastic solids

KAUST Repository

Khan, Kamran

2012-04-21

Visco-elastic materials are known for their capability of dissipating energy. This energy is converted into heat and thus changes the temperature of the materials. In addition to the dissipation effect, an external thermal stimulus can also alter the temperature in a viscoelastic body. The rate of stress relaxation (or the rate of creep) and the mechanical and physical properties of visco-elastic materials, such as polymers, vary with temperature. This study aims at understanding the effect of coupling between the thermal and mechanical response that is attributed to the dissipation of energy, heat conduction, and temperature-dependent material parameters on the overall response of visco-elastic solids. The non-linearly viscoelastic constitutive model proposed by Schapery (Further development of a thermodynamic constitutive theory: stress formulation, 1969,Mech. Time-Depend. Mater. 1:209-240, 1997) is used and modified to incorporate temperature- and stress-dependent material properties. This study also formulates a non-linear energy equation along with a dissipation function based on the Gibbs potential of Schapery (Mech. Time-Depend. Mater. 1:209-240, 1997). A numerical algorithm is formulated for analyzing a fully coupled thermo-visco-elastic response and implemented it in a general finite-element (FE) code. The non-linear stress- and temperature-dependent material parameters are found to have significant effects on the coupled thermo-visco-elastic response of polymers considered in this study. In order to obtain a realistic temperature field within the polymer visco-elastic bodies undergoing a non-uniform heat generation, the role of heat conduction cannot be ignored. © Springer Science+Business Media, B. V. 2012.

Effect of Surface Modification of Nanosilica on the Viscoelastic Properties of Its Polystyrene Nanocomposite

Directory of Open Access Journals (Sweden)

M. Mortezaei

2008-12-01

Full Text Available The preparation and characterization of the vinyltriethoxysilane-modified silica nanoparticles were investigated. Also the surface tension of polystyrene, native (hydrophilic silica and silane-modified (hydrophobic silica were determined. Two kinds of polystyrene/silica (treated and non-treated nanocomposites were prepared with different filler loadings by solution method. Their viscoelastic properties were studied by dynamic stress controlled rotary shear rheometer. Solid-like response of polystyrene/native silica nanocomposites were observed in the terminal zone. Solid inclusionsincrease the storage modulus more than the loss modulus, hence decrease the material damping. By increasing filler volume fraction, the particles tend to agglomerate and build clusters. The presence of clusters increases the viscosity, the moduli and the viscoelastic non-linearity of the composites.Treating the filler surface reduces its tendency to agglomerate as well as the adhesion between the particles and the polystyrene, leading to lower viscosity and interfacial slippage. Also the loss modulus peak is affected significantly by the particle surface area and its surface property in silica-filled polystyrene, which corresponds to its glass transition.

Viscoelastic properties of doped-ceria under reduced oxygen partial pressure

DEFF Research Database (Denmark)

Teocoli, Francesca; Esposito, Vincenzo

2014-01-01

The viscoelastic properties of gadolinium-doped ceria (CGO) powder compacts are characterized during sintering and cooling under reduced oxygen partial pressure and compared with conventional sintering in air. Highly defective doped ceria in reducing conditions shows peculiar viscoelastic...

The nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores

International Nuclear Information System (INIS)

Yu-Lin, Feng; Xiao-Zhou, Liu; Jie-Hui, Liu; Li, Ma

2009-01-01

Based on an equivalent medium approach, this paper presents a model describing the nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores. The influences of pores' nonlinear oscillations on sound attenuation, sound dispersion and an equivalent acoustic nonlinearity parameter are discussed. The calculated results show that the attenuation increases with an increasing volume fraction of micropores. The peak of sound velocity and attenuation occurs at the resonant frequency of the micropores while the peak of the equivalent acoustic nonlinearity parameter occurs at the half of the resonant frequency of the micropores. Furthermore, multiple scattering has been taken into account, which leads to a modification to the effective wave number in the equivalent medium approach. We find that these linear and nonlinear acoustic parameters need to be corrected when the volume fraction of micropores is larger than 0.1%

Characterization of a viscoelastic heterogeneous object with an effective model by nonlinear full waveform inversion

Science.gov (United States)

Mesgouez, A.

2018-05-01

The determination of equivalent viscoelastic properties of heterogeneous objects remains challenging in various scientific fields such as (geo)mechanics, geophysics or biomechanics. The present investigation addresses the issue of the identification of effective constitutive properties of a binary object by using a nonlinear and full waveform inversion scheme. The inversion process, without any regularization technique or a priori information, aims at minimizing directly the discrepancy between the full waveform responses of a bi-material viscoelastic cylindrical object and its corresponding effective homogeneous object. It involves the retrieval of five constitutive equivalent parameters. Numerical simulations are performed in a laboratory-scale two-dimensional configuration: a transient acoustic plane wave impacts the object and the diffracted fluid pressure, solid stress or velocity component fields are determined using a semi-analytical approach. Results show that the retrieval of the density and of the real parts of both the compressional and the shear wave velocities have been carried out successfully regarding the number and location of sensors, the type of sensors, the size of the searching space, the frequency range of the incident plane pressure wave, and the change in the geometric or mechanical constitution of the bi-material object. The retrieval of the imaginary parts of the wave velocities can reveal in some cases the limitations of the proposed approach.

The role of nonlinear viscoelasticity on the functionality of laminating shortenings

Energy Technology Data Exchange (ETDEWEB)

Macias-Rodriguez, Braulio A.; Peyronel, Fernanda; Marangoni, Alejandro G.

2017-11-01

The rheology of fats is essential for the development of homogeneous and continuous layered structures of doughs. Here, we define laminating shortenings in terms of rheological behavior displayed during linear-to-nonlinear shear deformations, investigated by large amplitude oscillatory shear rheology. Likewise, we associate the rheological behavior of the shortenings with structural length scales elucidated by ultra-small angle x-ray scattering and cryo-electron microscopy. Shortenings exhibited solid-like viscoelastic and viscoelastoplastic behaviors in the linear and nonlinear regimes respectively. In the nonlinear region, laminating shortenings dissipated more viscous energy (larger normalized dynamic viscosities) than a cake bakery shortening. The fat solid-like network of laminating shortening displayed a three-hierarchy structure and layered crystal aggregates, in comparison to two-hierarchy structure and spherical-like crystal aggregates of a cake shortening. We argue that the observed rheology, correlated to the structural network, is crucial for optimal laminating performance of shortenings.

Linear viscoelastic characterization from filament stretching rheometry

DEFF Research Database (Denmark)

Wingstrand, Sara Lindeblad; Alvarez, Nicolas J.; Hassager, Ole

to measure both linear and nonlinear dynamics on a single apparatus. With a software modification to the FSR motor control, we show that linear viscoelasticity can be measured via small amplitude squeeze flow (SASF). Squeeze flow is a combination of both shear and extensional flow applied by axially......Traditionally, linear viscoelasticity is measured using small amplitude oscillatory shear flow. Due to experimental difficulties, shear flows are predominately confined to the linear and mildly nonlinear regime. On the other hand, extensional flows have proven more practical in measuring...... viscoelasticity well into the nonlinear regime. Therefore at present, complete rheological characterization of a material requires two apparatuses: a shear and an extensional rheometer. This work is focused on developing a linear viscoelastic protocol for the filament stretching rheometer (FSR) in order...

Viscoelastic properties of cellular polypropylene ferroelectrets

Czech Academy of Sciences Publication Activity Database

Gaal, M.; Bovtun, Viktor; Stark, W.; Erhard, A.; Yakymenko, Y.; Kreutzbruck, M.

2016-01-01

Roč. 119, č. 12 (2016), s. 1-12, č. článku 125101. ISSN 0021-8979 R&D Projects: GA ČR GA15-08389S Institutional support: RVO:68378271 Keywords : ferroelectrets * viscoelastic properties * ultrasonic Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.068, year: 2016

Dilational viscoelastic properties of fluid interfaces - III mixed surfactant systems

Energy Technology Data Exchange (ETDEWEB)

Djabbarah, N.F.; Wasan, D.T.

1982-01-01

The surface viscosity and elasticity of solutions of mixed surfactants were determined using the longitudinal wave technique combined with tracer particle measurements. The recent analysis of Maru et al., which was restricted to insoluble monolayers and to monolayers adsorbed from a single surfactant solution, has now been extended to multicomponent solutions. This analysis can be used not only to estimate the ''net'' viscoelastic properties at gas-liquid interfaces but also to estimate the composition as well as the intrinsic viscoelastic properties. Furthermore, when accompanied by separate measurements of shear viscoelastic properties, the above analysis can be used for the determination of dilational viscosity and elasticity. Surface viscoelasticity measurements were conducted on aqueous solutions of sodium lauryl sulfate and sodium lauryl sulfate-lauryl alcohol. Net surface viscosity and elasticity of sodium lauryl sulfate solutions increased with bulk concentration and reached a maximum at a concentration in the neighborhood of the critical micelle concentration. The presence of small amount of lauryl alcohol caused almost an order of magnitude increase in intrinsic surface viscosity and a similar increase in compositional surface elasticity. A comparison between the values of intrinsic surface viscosity and those of surface shear viscosity indicated that surface dilational viscosity exceeds surface shear viscosity by at least two orders of magnitude. These appear to be the first set of data presented hitherto for the surface dilational properties in addition to surface shear properties for the same mixed surfactant systems.

Quantitative sonoelastography for the in vivo assessment of skeletal muscle viscoelasticity

International Nuclear Information System (INIS)

Hoyt, Kenneth; Kneezel, Timothy; Castaneda, Benjamin; Parker, Kevin J

2008-01-01

A novel quantitative sonoelastography technique for assessing the viscoelastic properties of skeletal muscle tissue was developed. Slowly propagating shear wave interference patterns (termed crawling waves) were generated using a two-source configuration vibrating normal to the surface. Theoretical models predict crawling wave displacement fields, which were validated through phantom studies. In experiments, a viscoelastic model was fit to dispersive shear wave speed sonoelastographic data using nonlinear least-squares techniques to determine frequency-independent shear modulus and viscosity estimates. Shear modulus estimates derived using the viscoelastic model were in agreement with that obtained by mechanical testing on phantom samples. Preliminary sonoelastographic data acquired in healthy human skeletal muscles confirm that high-quality quantitative elasticity data can be acquired in vivo. Studies on relaxed muscle indicate discernible differences in both shear modulus and viscosity estimates between different skeletal muscle groups. Investigations into the dynamic viscoelastic properties of (healthy) human skeletal muscles revealed that voluntarily contracted muscles exhibit considerable increases in both shear modulus and viscosity estimates as compared to the relaxed state. Overall, preliminary results are encouraging and quantitative sonoelastography may prove clinically feasible for in vivo characterization of the dynamic viscoelastic properties of human skeletal muscle

Viscoelasticity and diffusional properties of colloidal model dispersions

International Nuclear Information System (INIS)

Naegele, Gerhard

2003-01-01

We examine linear viscoelastic, and translational and rotational diffusion properties of colloidal model dispersions. Theoretical results are discussed, in comparison with experiments, for monodisperse suspensions of charged and neutral colloidal spheres, and for binary dispersions of differently sized tracer and host particles. The theoretical methods employed comprise a mode-coupling scheme for Brownian particles, and a rooted cluster expansion scheme of tracer diffusion with two- and three-body hydrodynamic interactions included. We analyse in particular the validity of various empirical generalized Stokes-Einstein-Debye (SED) relations between the (dynamic) shear viscosity and translational/rotational diffusion coefficients. Some of these generalized SED relations are basic to microrheological measurements aimed at characterizing the viscoelasticity of complex fluids on the basis of the diffusional properties of immersed tracer particles

Viscoelasticity and diffusional properties of colloidal model dispersions

CERN Document Server

Naegele, G

2003-01-01

We examine linear viscoelastic, and translational and rotational diffusion properties of colloidal model dispersions. Theoretical results are discussed, in comparison with experiments, for monodisperse suspensions of charged and neutral colloidal spheres, and for binary dispersions of differently sized tracer and host particles. The theoretical methods employed comprise a mode-coupling scheme for Brownian particles, and a rooted cluster expansion scheme of tracer diffusion with two- and three-body hydrodynamic interactions included. We analyse in particular the validity of various empirical generalized Stokes-Einstein-Debye (SED) relations between the (dynamic) shear viscosity and translational/rotational diffusion coefficients. Some of these generalized SED relations are basic to microrheological measurements aimed at characterizing the viscoelasticity of complex fluids on the basis of the diffusional properties of immersed tracer particles.

Real-time simulation of the nonlinear visco-elastic deformations of soft tissues.

Science.gov (United States)

Basafa, Ehsan; Farahmand, Farzam

2011-05-01

Mass-spring-damper (MSD) models are often used for real-time surgery simulation due to their fast response and fairly realistic deformation replication. An improved real time simulation model of soft tissue deformation due to a laparoscopic surgical indenter was developed and tested. The mechanical realization of conventional MSD models was improved using nonlinear springs and nodal dampers, while their high computational efficiency was maintained using an adapted implicit integration algorithm. New practical algorithms for model parameter tuning, collision detection, and simulation were incorporated. The model was able to replicate complex biological soft tissue mechanical properties under large deformations, i.e., the nonlinear and viscoelastic behaviors. The simulated response of the model after tuning of its parameters to the experimental data of a deer liver sample, closely tracked the reference data with high correlation and maximum relative differences of less than 5 and 10%, for the tuning and testing data sets respectively. Finally, implementation of the proposed model and algorithms in a graphical environment resulted in a real-time simulation with update rates of 150 Hz for interactive deformation and haptic manipulation, and 30 Hz for visual rendering. The proposed real time simulation model of soft tissue deformation due to a laparoscopic surgical indenter was efficient, realistic, and accurate in ex vivo testing. This model is a suitable candidate for testing in vivo during laparoscopic surgery.

Viscoelastic properties of poly(butylene succinate)-co-adipate) nanocomposites

CSIR Research Space (South Africa)

Al-Thabaiti, SA

2015-03-01

Full Text Available and melt-state viscoelastic properties of neat PBSA and various nanocomposites were studied in detail. The dynamic mechanical studies demonstrated an increase in the storage modulus of PBSA matrix with organoclay loading. Melt-state rheological properties...

Development of a stress-mode sensitive viscoelastic constitutive relationship for asphalt concrete: experimental and numerical modeling

Science.gov (United States)

Karimi, Mohammad M.; Tabatabaee, Nader; Jahanbakhsh, H.; Jahangiri, Behnam

2017-08-01

Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery's nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.

Measuring cell viscoelastic properties using a force-spectrometer: influence of protein-cytoplasm interactions.

Science.gov (United States)

Canetta, Elisabetta; Duperray, Alain; Leyrat, Anne; Verdier, Claude

2005-01-01

Cell adhesive and rheological properties play a very important role in cell transmigration through the endothelial barrier, in particular in the case of inflammation (leukocytes) or cancer metastasis (cancer cells). In order to characterize cell viscoelastic properties, we have designed a force spectrometer (AFM) which can stretch cells thereby allowing measurement of their rheological properties. This custom-made force spectrometer allows two different visualizations, one lateral and one from below. It allows investigation of the effects of rheology involved during cell stretching. To test the ability of our system to characterize such viscoelastic properties, ICAM-1 transfected CHO cells were analyzed. Two forms of ICAM-1 were tested; wild type ICAM-1, which can interact with the cytoskeleton, and a mutant form which lacks the cytoplasmic domain, and is unable to associate with the cytoskeleton. Stretching experiments carried out on these cells show the formation of long filaments. Using a previous model of filament elongation, we could determine the viscoelastic properties of a single cell. As expected, different viscoelastic components were found between the wild type and the mutant, which reveal that the presence of interactions between ICAM-1 and the cytoskeleton increases the stiffness of the cell.

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

Science.gov (United States)

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

Effect of long-time immersion of soft denture liners in water on viscoelastic properties.

Science.gov (United States)

Iwasaki, Naohiko; Yamaki, Chisato; Takahashi, Hidekazu; Oki, Meiko; Suzuki, Tetsuya

2017-09-26

Aim of this study was to investigate the effect of long-time immersion of soft denture liners in 37°C water on viscoelastic properties. Six silicone-based and two acrylic resin-based soft denture liners were selected. Cylindrical specimens were stored in distilled water at 37°C for 6 months. Viscoelastic properties, which were instantaneous and delayed elastic displacements, viscous flow, and residual displacement, were determined using a creep meter, and analyzed with 2-way analysis of variance and Tukey's comparison (α=0.05). Viscoelastic properties and their time-dependent changes were varied among materials examined. The observed viscoelastic properties of three from six silicone-based liners did not significantly change after 6-month immersion, but those of two acrylic resin-based liners significantly changed with the increase of immersion time. However, the sum of initial instantaneous elastic displacement and delayed elastic displacement of two acrylic resin-based liners during 6-month immersion changed less than 10%, which might indicate clinically sufficient elastic performance.

Viscoelastic behaviour of pumpkin balloons

Science.gov (United States)

Gerngross, T.; Xu, Y.; Pellegrino, S.

2008-11-01

The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes.

Normal age-related viscoelastic properties of chondrons and chondrocytes isolated from rabbit knee

Institute of Scientific and Technical Information of China (English)

DUAN Wang-ping; SUN Zhen-wei; LI Qi; LI Chun-jiang; WANG Li; CHEN Wei-yi; Jennifer Tickner; ZHENG Ming-hao; WEI Xiao-chun

2012-01-01

Background The mechanical microenvironment of the chondrocytes plays an important role in cartilage homeostasis and in the health of the joint.The pericellular matrix,cellular membrane of the chondrocytes,and their cytoskeletal structures are key elements in the mechanical environment.The aims of this study are to measure the viscoelastic properties of isolated chondrons and chondrocytes from rabbit knee cartilage using micropipette aspiration and to determine the effect of aging on these properties.Methods Three age groups of rabbit knees were evaluated:(1) young (2 months,n=10);(2) adult (8 months,n=10);and (3) old (31 months,n=10).Chondrocytes were isolated from the right knee cartilage and chondrons were isolated from left knees using enzymatic methods.Micropipette aspiration combined with a standard linear viscoelastic solid model was used to quantify changes in the viscoelastic properties of chondrons and chondrocytes within 2 hours of isolation.The morphology and structure of isolated chondrons were evaluated by optical microscope using hematoxylin and eosin staining and collagen-6 immunofluorescence staining.Results In response to an applied constant 0.3-0.4 kPa of negative pressure,all chondrocytes exhibited standard linear viscoelastic solid properties.Model predictions of the creep data showed that the average equilibrium modulus (E∞),instantaneous modulus (E0).and apparent viscosity (μ) of old chondrocytes was significantly lower than the young and adult chondrocytes (P＜0.001);however,no difference was found between young and adult chondrocytes (P＞0.05).The adult and old chondrons generally possessed a thicker pericellular matrix (PCM) with more enclosed cells.The young and adult chondrons exhibited the same viscoelastic creep behavior under a greater applied pressure (1.0-1.1kPa) without the deformation seen in the old chondrons.The viscoelastic properties (E∞,E0,and u) of young and adult chondrons were significantly greater than that observed

Viscoelastic property identification from waveform reconstruction

Science.gov (United States)

Leymarie, N.; Aristégui, C.; Audoin, B.; Baste, S.

2002-05-01

An inverse method is proposed for the determination of the viscoelastic properties of material plates from the plane-wave transmitted acoustic field. Innovations lie in a two-step inversion scheme based on the well-known maximum-likelihood principle with an analytic signal formulation. In addition, establishing the analytical formulations of the plate transmission coefficient we implement an efficient and slightly noise-sensitive process suited to both very thin plates and strongly dispersive media.

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

Science.gov (United States)

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.

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

Science.gov (United States)

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.

Effect of viscoelastic and dielectric relaxing matrix on ferroelastic behaviour of 1-3 piezocomposites

Directory of Open Access Journals (Sweden)

R. Jayendiran

2015-02-01

Full Text Available This work focuses on evaluating the time-dependent non-linear ferroelastic behaviour of 1-3 piezocomposites under pure uni-axial compressive stress loading condition. An experimental setup is developed to study the influence of high-stress levels on the stress-strain and stress-polarization behaviour of 1-3 piezocomposites. The electro-elastic effective properties of 1-3 piezocomposites are measured experimentally based on IEEE standard and compared with the proposed numerical model using finite-element software ABAQUS. The time-dependent effective properties are evaluated using viscoelastic model and it is incorporated into a 3D micromechanical model to predict the viscoelastic behaviour of 1-3 piezocomposites under mechanical loading. The simulated results are compared with the viscoelastic behaviour of 1-3 piezocomposites obtained from experiments.

Identifying Mechanical Properties of Viscoelastic Materials in Time Domain Using the Fractional Zener Model

Directory of Open Access Journals (Sweden)

Ana Paula Delowski Ciniello

Full Text Available Abstract The present paper aims at presenting a methodology for characterizing viscoelastic materials in time domain, taking into account the fractional Zener constitutive model and the influence of temperature through Williams, Landel, and Ferry’s model. To that effect, a set of points obtained experimentally through uniaxial tensile tests with different constant strain rates is considered. The approach is based on the minimization of the quadratic relative distance between the experimental stress-strain curves and the corresponding ones given by the theoretical model. In order to avoid the local minima in the process of optimization, a hybrid technique based on genetic algorithms and non-linear programming techniques is used. The methodology is applied in the characterization of two different commercial viscoelastic materials. The results indicate that the proposed methodology is effective in identifying thermorheologically simple viscoelastic materials.

New non-linear model of groundwater recharge: Inclusion of memory, heterogeneity and visco-elasticity

Directory of Open Access Journals (Sweden)

Spannenberg Jescica

2017-09-01

Full Text Available Fractional differentiation has adequate use for investigating real world scenarios related to geological formations associated with elasticity, heterogeneity, viscoelasticity, and the memory effect. Since groundwater systems exist in these geological formations, modelling groundwater recharge as a real world scenario is a challenging task to do because existing recharge estimation methods are governed by linear equations which make use of constant field parameters. This is inadequate because in reality these parameters are a function of both space and time. This study therefore concentrates on modifying the recharge equation governing the EARTH model, by application of the Eton approach. Accordingly, this paper presents a modified equation which is non-linear, and accounts for parameters in a way that it is a function of both space and time. To be more specific, herein, recharge and drainage resistance which are parameters within the equation, became a function of both space and time. Additionally, the study entailed solving the non-linear equation using an iterative method as well as numerical solutions by means of the Crank-Nicolson scheme. The numerical solutions were used alongside the Riemann-Liouville, Caputo-Fabrizio, and Atangana-Baleanu derivatives, so that account was taken for elasticity, heterogeneity, viscoelasticity, and the memory effect. In essence, this paper presents a more adequate model for recharge estimation.

A variational constitutive framework for the nonlinear viscoelastic response of a dielectric elastomer

KAUST Repository

Khan, Kamran

2012-11-10

We formulate a variational constitutive framework that accounts for nonlinear viscous behavior of electrically sensitive polymers, specifically Dielectric Elastomers (DEs), under large deformation. DEs are highly viscoelastic and their actuation response is greatly affected in dynamic applications. We used the generalized Maxwell model to represent the viscoelastic response of DE allowing the material to relax with multiple mechanisms. The constitutive updates at each load increment are obtained by minimizing an objective function formulated using the free energy and electrostatic energy of the elastomer, in addition to the viscous dissipation potential of the dashpots in each Maxwell branch. The model is then used to predict the electromechanical instability (EMI) of DE. The electro-elastic response of the DE is verified with available analytical solutions in the literature and then the material parameters are calibrated using experimental data. The model is integrated with finite element software to perform a variety of simulations on different types of electrically driven actuators under various electromechanical loadings. The electromechanical response of the DE and the critical conditions at which EMI occurs were found to be greatly affected by the viscoelasticity. Our model predicts that under a dead load EMI can be avoided if the DE operates at a high voltage rate. Subjected to constant, ramp and cyclic voltage, our model qualitatively predicts responses similar to the ones obtained from the analytical solutions and experimental data available in the literature. © 2012 Springer-Verlag Berlin Heidelberg.

Large deflection of viscoelastic beams using fractional derivative model

International Nuclear Information System (INIS)

Bahranini, Seyed Masoud Sotoodeh; Eghtesad, Mohammad; Ghavanloo, Esmaeal; Farid, Mehrdad

2013-01-01

This paper deals with large deflection of viscoelastic beams using a fractional derivative model. For this purpose, a nonlinear finite element formulation of viscoelastic beams in conjunction with the fractional derivative constitutive equations has been developed. The four-parameter fractional derivative model has been used to describe the constitutive equations. The deflected configuration for a uniform beam with different boundary conditions and loads is presented. The effect of the order of fractional derivative on the large deflection of the cantilever viscoelastic beam, is investigated after 10, 100, and 1000 hours. The main contribution of this paper is finite element implementation for nonlinear analysis of viscoelastic fractional model using the storage of both strain and stress histories. The validity of the present analysis is confirmed by comparing the results with those found in the literature.

3D printing of an interpenetrating network hydrogel material with tunable viscoelastic properties.

Science.gov (United States)

Bootsma, Katherine; Fitzgerald, Martha M; Free, Brandon; Dimbath, Elizabeth; Conjerti, Joe; Reese, Greg; Konkolewicz, Dominik; Berberich, Jason A; Sparks, Jessica L

2017-06-01

Interpenetrating network (IPN) hydrogel materials are recognized for their unique mechanical properties. While IPN elasticity and toughness properties have been explored in previous studies, the factors that impact the time-dependent stress relaxation behavior of IPN materials are not well understood. Time-dependent (i.e. viscoelastic) mechanical behavior is a critical design parameter in the development of materials for a variety of applications, such as medical simulation devices, flexible substrate materials, cellular mechanobiology substrates, or regenerative medicine applications. This study reports a novel technique for 3D printing alginate-polyacrylamide IPN gels with tunable elastic and viscoelastic properties. The viscoelastic stress relaxation behavior of the 3D printed alginate-polyacrylamide IPN hydrogels was influenced most strongly by varying the concentration of the acrylamide cross-linker (MBAA), while the elastic modulus was affected most by varying the concentration of total monomer material. The material properties of our 3D printed IPN constructs were consistent with those reported in the biomechanics literature for soft tissues such as skeletal muscle, cardiac muscle, skin and subcutaneous tissue. Copyright © 2017 Elsevier Ltd. All rights reserved.

Integrating viscoelastic mass spring dampers into position-based dynamics to simulate soft tissue deformation in real time.

Science.gov (United States)

Xu, Lang; Lu, Yuhua; Liu, Qian

2018-02-01

We propose a novel method to simulate soft tissue deformation for virtual surgery applications. The method considers the mechanical properties of soft tissue, such as its viscoelasticity, nonlinearity and incompressibility; its speed, stability and accuracy also meet the requirements for a surgery simulator. Modifying the traditional equation for mass spring dampers (MSD) introduces nonlinearity and viscoelasticity into the calculation of elastic force. Then, the elastic force is used in the constraint projection step for naturally reducing constraint potential. The node position is enforced by the combined spring force and constraint conservative force through Newton's second law. We conduct a comparison study of conventional MSD and position-based dynamics for our new integrating method. Our approach enables stable, fast and large step simulation by freely controlling visual effects based on nonlinearity, viscoelasticity and incompressibility. We implement a laparoscopic cholecystectomy simulator to demonstrate the practicality of our method, in which liver and gallbladder deformation can be simulated in real time. Our method is an appropriate choice for the development of real-time virtual surgery applications.

SYNTHESIS OF VISCOELASTIC MATERIAL MODELS (SCHEMES

Directory of Open Access Journals (Sweden)

V. Bogomolov

2014-10-01

Full Text Available The principles of structural viscoelastic schemes construction for materials with linear viscoelastic properties in accordance with the given experimental data on creep tests are analyzed. It is shown that there can be only four types of materials with linear visco-elastic properties.

Measurement of Viscoelastic Properties of Condensed Matter using Magnetic Resonance Elastography

Science.gov (United States)

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.

Assessment of the viscoelastic mechanical properties of polycarbonate urethane for medical devices.

Science.gov (United States)

Beckmann, Agnes; Heider, Yousef; Stoffel, Marcus; Markert, Bernd

2018-06-01

The underlying research work introduces a study of the mechanical properties of polycarbonate urethane (PCU), used in the construction of various medical devices. This comprises the discussion of a suitable material model, the application of elemental experiments to identify the related parameters and the numerical simulation of the applied experiments in order to calibrate and validate the mathematical model. In particular, the model of choice for the simulation of PCU response is the non-linear viscoelastic Bergström-Boyce material model, applied in the finite-element (FE) package Abaqus®. For the parameter identification, uniaxial tension and unconfined compression tests under in-laboratory physiological conditions were carried out. The geometry of the samples together with the applied loadings were simulated in Abaqus®, to insure the suitability of the modelling approach. The obtained parameters show a very good agreement between the numerical and the experimental results. Copyright © 2018 Elsevier Ltd. All rights reserved.

Non linear viscoelastic models

DEFF Research Database (Denmark)

Agerkvist, Finn T.

2011-01-01

Viscoelastic eects are often present in loudspeaker suspensions, this can be seen in the displacement transfer function which often shows a frequency dependent value below the resonance frequency. In this paper nonlinear versions of the standard linear solid model (SLS) are investigated....... The simulations show that the nonlinear version of the Maxwell SLS model can result in a time dependent small signal stiness while the Kelvin Voight version does not....

Parameter estimation of a nonlinear Burger's model using nanoindentation and finite element-based inverse analysis

Science.gov (United States)

Hamim, Salah Uddin Ahmed

Nanoindentation involves probing a hard diamond tip into a material, where the load and the displacement experienced by the tip is recorded continuously. This load-displacement data is a direct function of material's innate stress-strain behavior. Thus, theoretically it is possible to extract mechanical properties of a material through nanoindentation. However, due to various nonlinearities associated with nanoindentation the process of interpreting load-displacement data into material properties is difficult. Although, simple elastic behavior can be characterized easily, a method to characterize complicated material behavior such as nonlinear viscoelasticity is still lacking. In this study, a nanoindentation-based material characterization technique is developed to characterize soft materials exhibiting nonlinear viscoelasticity. Nanoindentation experiment was modeled in finite element analysis software (ABAQUS), where a nonlinear viscoelastic behavior was incorporated using user-defined subroutine (UMAT). The model parameters were calibrated using a process called inverse analysis. In this study, a surrogate model-based approach was used for the inverse analysis. The different factors affecting the surrogate model performance are analyzed in order to optimize the performance with respect to the computational cost.

Growth and decay of weak disturbances in visco-elastic arteries

International Nuclear Information System (INIS)

Gaur, M.; Rai, S.K.

1996-01-01

In non-linear mathematical models of the arterial circulation, the visco-elasticity of the vessel walls has generally been neglected or only taken into account in a highly approximate manner. The object of the present paper is to provide a mathematical model for the propagation of weak disturbances in visco-elastic arteries. A differential equation governing the growth and decay of the waves has been obtained and solved analytically. It is observed that compressive pulses may grow into shock waves. A mathematical model which is based on geometrical and mechanical properties of arteries admits disturbances in the propagating pulses which are not observed in human beings under normal physiological conditions. It is also predicted that visco-elasticity delays the shock wave formation in the model. The shock wave may appear in periphery in the case of aortic insufficiency due to increased pressure at the root of aorta. The corresponding predictions are in much better agreement with in vivo measurements

Nonlinear viscoelastic behavior of shells of revolution under arbitrary loading

International Nuclear Information System (INIS)

Leonard, J.W.; Arbaki-Kanjoori, F.

1975-01-01

The requirement of some structural components such as propulsion systems and gas turbines to operate at high temperatures and pressures make the accurate evaluation of the creep phenomenon exigent (in fast breeder reactor for example). For the expected increases in operating temperatures and pressures, it becomes necessary to perform a thorough analysis of integral structural components of nuclear power plants throughout their life span. Since a large class of structures operating at elevated temperatures are composed of rotationally symmetric shells, a solution technique can be developed which involves the numerical integration of the governing shell equations. This method has been successfully applied to the static and dynamic analysis of thin elastic shells of revolution and for some cases of inelastic material behavior. It has been shown to render solutions efficiently and accurately, usually with only a fraction of computer time and storage requirements and data manipulation that is required for other numerical schemes such as the finite element method. Furthermore, the numerical integration method allows more flexibility for varying the integration step lengths than does the finite difference method and can provide uniform accuracy throughout the analysis. For nonlinear viscoelastic behavior the numerical integration technique is expected to provide similar efficiency to that obtained for the elastic problems. The computer program developed can accept time variation of material properties. Since a single form for the material constitutive law cannot encompass all materials, provisions are made so that the analysis of a very large class of material behavior can be accomplished

Magnetohydrodynamic three-dimensional flow of viscoelastic nanofluid in the presence of nonlinear thermal radiation

Energy Technology Data Exchange (ETDEWEB)

Hayat, T. [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589 (Saudi Arabia); Muhammad, Taseer, E-mail: taseer_qau@yahoo.com [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Alsaedi, A.; Alhuthali, M.S. [Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589 (Saudi Arabia)

2015-07-01

Magnetohydrodynamic (MHD) three-dimensional flow of couple stress nanofluid in the presence of thermophoresis and Brownian motion effects is analyzed. Energy equation subject to nonlinear thermal radiation is taken into account. The flow is generated by a bidirectional stretching surface. Fluid is electrically conducting in the presence of a constant applied magnetic field. The induced magnetic field is neglected for a small magnetic Reynolds number. Mathematical formulation is performed using boundary layer analysis. Newly proposed boundary condition requiring zero nanoparticle mass flux is employed. The governing nonlinear mathematical problems are first converted into dimensionless expressions and then solved for the series solutions of velocities, temperature and nanoparticles concentration. Convergence of the constructed solutions is verified. Effects of emerging parameters on the temperature and nanoparticles concentration are plotted and discussed. Skin friction coefficients and Nusselt number are also computed and analyzed. It is found that the thermal boundary layer thickness is an increasing function of radiative effect. - Highlights: • Three-dimensional boundary layer flow of viscoelastic nanofluid is examined. • Nonlinear thermal radiation is analyzed. • Brownian motion and thermophoresis effects are present. • Recently developed condition requiring zero nanoparticle mass flux is implemented. • Construction of convergent solutions of nonlinear flow is possible.

Statistical mapping of the effect of knee extension on thigh muscle viscoelastic properties using magnetic resonance elastography

International Nuclear Information System (INIS)

Barnhill, Eric; Kennedy, Paul; Van Beek, Edwin J R; Roberts, Neil; Hammer, Steven; Brown, Colin

2013-01-01

Skeletal muscle viscoelastic properties reflect muscle microstructure and neuromuscular activation. Elastographic methods, including magnetic resonance elastography, have been used to characterize muscle viscoelastic properties in terms of region of interest (ROI) measurements. The present study extended this approach to create thresholded pixel-by-pixel maps of viscoelastic properties of skeletal muscle during rest and knee extension in eleven subjects. ROI measurements were taken for individual quadricep muscles and the quadriceps region as a whole, and the viscoelastic parameter map pixels were statistically tested at positive false discovery rate q ⩽ 0.25. ROI measurements showed significant (p ⩽ 0.05) increase in storage modulus (G′) and loss modulus (G″), with G″ increasing more than G′, in agreement with previous findings. The q-value maps further identified the vastus intermedius as the primary driver of this change, with greater G″/G′ increase than surrounding regions. Additionally, a cluster of significant decrease in G″/G′ was found in the region of vastus lateralis below the fulcrum point of the lift. Viscoelastic parameter mapping of contracted muscle allows new insight into the relationship between physiology, neuromuscular activation, and human performance. (paper)

Viscoelastic properties of PLA/PCL blends compatibilized with different methods

Science.gov (United States)

Shin, Boo Young; Han, Do Hung

2017-11-01

The aim of this study was to observe changes in the viscoelastic properties of PLA/PCL (80/20) blends produced using different compatibilization methods. Reactive extrusion and high-energy radiation methods were used for blend compatibilization. Storage and loss moduli, complex viscosity, transient stress relaxation modulus, and tan δ of blends were analyzed and blend morphologies were examined. All compatibilized PLA/PCL blends had smaller dispersed particle sizes than the non-compatibilized blend, and well compatibilized blends had finer morphologies than poorly compatibilized blends. Viscoelastic properties differentiated well compatibilized and poorly compatibilized blends. Well compatibilized blends had higher storage and loss moduli and complex viscosities than those calculated by the log-additive mixing rule due to strong interfacial adhesion, whereas poorly compatibilized blends showed negative deviations due to weak interfacial adhesion. Moreover, well compatibilized blends had much slower stress relaxation than poorly compatibilized blends and didn't show tan δ plateau region caused by slippage at the interface between continuous and dispersed phases.

Nonlinear viscoelastic characterization of molten thermoplastic vulcanizates (TPV) through large amplitude harmonic experiments

Energy Technology Data Exchange (ETDEWEB)

Leblanc, Jean L. [University P. and M. Curie-Paris 6, Polymer Rheology and Processing, Vitry-sur-Seine (France)

2007-10-15

The so-called thermoplastic vulcanizates (TPV) are essentially blends of a crystalline thermoplastic polymer (e.g., polypropylene) and a vulcanizable rubber composition, prepared through a special process called dynamic vulcanization, which yields a fine dispersion of micron-size crosslinked rubber particles in a thermoplastic matrix. Such materials are by nature complex polymer systems, i.e., multiphase, heterogeneous, typically disordered materials for which structure is as important as composition. Correctly assessing their rheological properties is a challenging task for several reasons: first, even if the uniformity of their composition is taken for granted, TPV are indeed very complicated materials, not only heterogeneous but also with a morphology related to their composition; second, their morphology can be affected by the flow field used; third, the migration of small labile ingredients (e.g., oil, curative residue, etc.) can in the meantime significantly change the boundary flow conditions, for instance through self-lubrication due to phase separation of the oil, or wall slip, or both. The aims of the work reported were to investigate a series of commercial TPV through the so-called Fourier transform rheometry, a testing technique especially developed to accurately investigate the nonlinear viscoelastic domain. Results are tentatively interpreted in terms of material composition and structure. (orig.)

Nonlinear waves in viscoelastic magnetized complex astroplasmas with polarized dust-charge variations

Directory of Open Access Journals (Sweden)

Papari Das

2018-01-01

Full Text Available A nonextensive nonthermal magnetized viscoelastic astrofluid, compositionally containing nonthermal electrons and ions together with massive polarized dust micro-spherical grains of variable electric charge, is allowed to endure weakly nonlinear perturbation around its equilibrium. The nonextensivity originating from the large-scale non-local effects is included via the Tsallis thermo-statistical distribution laws describing the lighter species. Assuming the equilibrium as a homogeneous hydrostatic one, the dust polarization effects are incorporated via the conventional homogeneous polarization force law. The perturbed fluid model evolves as a unique conjugate pair of coupled extended Korteweg-de Vries (e-KdV equations. A constructed numerical tapestry shows the collective excitations of a new pair of distinct classes of nonlinear mode structures in new parametric space. The first family indicates periodic electrostatic compressive eigenmodes in the form of soliton-chains. Likewise, the second one reveals gravitational rarefactive solitary patterns. Their microphysical multi-parametric dependencies of the eigen-patterns are illustratively analyzed and bolstered. The paper ends up with some promising implications and applications in the astro-cosmo-plasmic context of wave-induced accretive triggering processes responsible for gravitationally bounded (gravito-condensed astro-structure formation, such as stellesimals, planetsimals, etc.

Nonlinear waves in viscoelastic magnetized complex astroplasmas with polarized dust-charge variations

Science.gov (United States)

Das, Papari; Karmakar, Pralay Kumar

2018-01-01

A nonextensive nonthermal magnetized viscoelastic astrofluid, compositionally containing nonthermal electrons and ions together with massive polarized dust micro-spherical grains of variable electric charge, is allowed to endure weakly nonlinear perturbation around its equilibrium. The nonextensivity originating from the large-scale non-local effects is included via the Tsallis thermo-statistical distribution laws describing the lighter species. Assuming the equilibrium as a homogeneous hydrostatic one, the dust polarization effects are incorporated via the conventional homogeneous polarization force law. The perturbed fluid model evolves as a unique conjugate pair of coupled extended Korteweg-de Vries (e-KdV) equations. A constructed numerical tapestry shows the collective excitations of a new pair of distinct classes of nonlinear mode structures in new parametric space. The first family indicates periodic electrostatic compressive eigenmodes in the form of soliton-chains. Likewise, the second one reveals gravitational rarefactive solitary patterns. Their microphysical multi-parametric dependencies of the eigen-patterns are illustratively analyzed and bolstered. The paper ends up with some promising implications and applications in the astro-cosmo-plasmic context of wave-induced accretive triggering processes responsible for gravitationally bounded (gravito-condensed) astro-structure formation, such as stellesimals, planetsimals, etc.

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

Science.gov (United States)

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.

Influence of viscoelastic property on laser-generated surface acoustic waves in coating-substrate systems

International Nuclear Information System (INIS)

Sun Hongxiang; Zhang Shuyi; Xu Baiqiang

2011-01-01

Taking account of the viscoelasticity of materials, the pulsed laser generation of surface acoustic waves in coating-substrate systems has been investigated quantitatively by using the finite element method. The displacement spectra of the surface acoustic waves have been calculated in frequency domain for different coating-substrate systems, in which the viscoelastic properties of the coatings and substrates are considered separately. Meanwhile, the temporal displacement waveforms have been obtained by applying inverse fast Fourier transforms. The numerical results of the normal surface displacements are presented for different configurations: a single plate, a slow coating on a fast substrate, and a fast coating on a slow substrate. The influences of the viscoelastic properties of the coating and the substrate on the attenuation of the surface acoustic waves have been studied. In addition, the influence of the coating thickness on the attenuation of the surface acoustic waves has been also investigated in detail.

Extensional rheometer based on viscoelastic catastrophes outline

DEFF Research Database (Denmark)

2014-01-01

The present invention relates to a method and a device for determining viscoelastic properties of a fluid. The invention resides inter alia in the generation of viscoelastic catastrophes in confined systems for use in the context of extensional rheology. The viscoelastic catastrophe is according ...... to the invention generated in a bistable fluid system, and the flow conditions for which the catastrophe occurs can be used as a fingerprint of the fluid's viscoelastic properties in extensional flow....

Changes in the texture and viscoelastic properties of bread containing rice porridge during storage.

Science.gov (United States)

Tsai, Chia-Ling; Sugiyama, Junichi; Shibata, Mario; Kokawa, Mito; Fujita, Kaori; Tsuta, Mizuki; Nabetani, Hiroshi; Araki, Tetsuya

2012-01-01

The objective of this study was to investigate the effects of rice porridge on the texture and viscoelastic properties of bread during storage. Three types of bread, wheat flour bread, 15% rice flour bread, and 15% rice porridge bread, were prepared. After baking and storing the bread for 24 h, 48 h, and 72 h at room temperature, we measured the texture and viscoelastic properties of the bread crumbs by texture profile analysis (TPA) and creep test. The 15% rice porridge bread showed a significantly higher specific volume and maintained softer crumbs than the other two types (pbread crumbs during storage.

Experimental study and constitutive modeling of the viscoelastic mechanical properties of the human prolapsed vaginal tissue.

Science.gov (United States)

Peña, Estefania; Calvo, B; Martínez, M A; Martins, P; Mascarenhas, T; Jorge, R M N; Ferreira, A; Doblaré, M

2010-02-01

In this paper, the viscoelastic mechanical properties of vaginal tissue are investigated. Using previous results of the authors on the mechanical properties of biological soft tissues and newly experimental data from uniaxial tension tests, a new model for the viscoelastic mechanical properties of the human vaginal tissue is proposed. The structural model seems to be sufficiently accurate to guarantee its application to prediction of reliable stress distributions, and is suitable for finite element computations. The obtained results may be helpful in the design of surgical procedures with autologous tissue or prostheses.

Analytical Analysis on Nonlinear Parametric Vibration of an Axially Moving String with Fractional Viscoelastic Damping

Directory of Open Access Journals (Sweden)

Ying Li

2017-01-01

Full Text Available The nonlinear parametric vibration of an axially moving string made by rubber-like materials is studied in the paper. The fractional viscoelastic model is used to describe the damping of the string. Then, a new nonlinear fractional mathematical model governing transverse motion of the string is derived based on Newton’s second law, the Euler beam theory, and the Lagrangian strain. Taking into consideration the fractional calculus law of Riemann-Liouville form, the principal parametric resonance is analytically investigated via applying the direct multiscale method. Numerical results are presented to show the influences of the fractional order, the stiffness constant, the viscosity coefficient, and the axial-speed fluctuation amplitude on steady-state responses. It is noticeable that the amplitudes and existing intervals of steady-state responses predicted by Kirchhoff’s fractional material model are much larger than those predicted by Mote’s fractional material model.

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

Science.gov (United States)

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. Copyright © 2016 Elsevier Ltd. All rights reserved.

Viscoelastic and thermal properties of woven sisal fabric reinforced natural rubber biocomposites

CSIR Research Space (South Africa)

John, MJ

2009-01-01

Full Text Available This study explores the dynamic mechanical behavior of woven sisal fabric reinforced natural rubber composites. The influence of chemical modification on the viscoelastic properties has also been determined. Moreover, the effect of frequency...

Nonlinear Forced Vibration of a Viscoelastic Buckled Beam with 2 : 1 Internal Resonance

Directory of Open Access Journals (Sweden)

Liu-Yang Xiong

2014-01-01

Full Text Available Nonlinear dynamics of a viscoelastic buckled beam subjected to primary resonance in the presence of internal resonance is investigated for the first time. For appropriate choice of system parameters, the natural frequency of the second mode is approximately twice that of the first providing the condition for 2 : 1 internal resonance. The ordinary differential equations of the two mode shapes are established using the Galerkin method. The problem is replaced by two coupled second-order differential equations with quadratic and cubic nonlinearities. The multiple scales method is applied to derive the modulation-phase equations. Steady-state solutions of the system as well as their stability are examined. The frequency-amplitude curves exhibit the steady-state response in the directly excited and indirectly excited modes due to modal interaction. The double-jump, the saturation phenomenon, and the nonperiodic region phenomena are observed illustrating the influence of internal resonance. The validity range of the analytical approximations is assessed by comparing the analytical approximate results with a numerical solution by the Runge-Kutta method. The unstable regions in the internal resonance are explored via numerical simulations.

A strain-hardening bi-power law for the nonlinear behaviour of biological soft tissues.

Science.gov (United States)

Nicolle, S; Vezin, P; Palierne, J-F

2010-03-22

Biological soft tissues exhibit a strongly nonlinear viscoelastic behaviour. Among parenchymous tissues, kidney and liver remain less studied than brain, and a first goal of this study is to report additional material properties of kidney and liver tissues in oscillatory shear and constant shear rate tests. Results show that the liver tissue is more compliant but more strain hardening than kidney. A wealth of multi-parameter mathematical models has been proposed for describing the mechanical behaviour of soft tissues. A second purpose of this work is to develop a new constitutive law capable of predicting our experimental data in the both linear and nonlinear viscoelastic regime with as few parameters as possible. We propose a nonlinear strain-hardening fractional derivative model in which six parameters allow fitting the viscoelastic behaviour of kidney and liver tissues for strains ranging from 0.01 to 1 and strain rates from 0.0151 s(-1) to 0.7s(-1). Copyright (c) 2009 Elsevier Ltd. All rights reserved.

Viscoelastic Properties of Dental Pulp Tissue and Ramifications on Biomaterial Development for Pulp Regeneration.

Science.gov (United States)

Erisken, Cevat; Kalyon, Dilhan M; Zhou, Jian; Kim, Sahng G; Mao, Jeremy J

2015-10-01

A critical step in biomaterial selection effort is the determination of material as well as the biological properties of the target tissue. Previously, the selection of biomaterials and carriers for dental pulp regeneration has been solely based on empirical experience. In this study, first, the linear viscoelastic material functions and compressive properties of miniature pig dental pulp were characterized using small-amplitude oscillatory shear and uniaxial compression at a constant rate. They were then compared with the properties of hydrogels (ie, agarose, alginate, and collagen) that are widely used in tissue regeneration. The comparisons of the linear viscoelastic material functions of the native pulp tissue with those of the 3 hydrogels revealed the gel-like behavior of the pulp tissue over a relatively large range of time scales (ie, over the frequency range of 0.1-100 rps). At the constant gelation agent concentration of 2%, the dynamic properties (ie, storage and loss moduli and the tanδ) of the collagen-based gel approached those of the native tissue. Under uniaxial compression, the peak normal stresses and compressive moduli of the agarose gel were similar to those of the native tissue, whereas alginate and collagen exhibited significantly lower compressive properties. The linear viscoelastic and uniaxial compressive properties of the dental pulp tissue reported here should enable the more appropriate selection of biogels for dental pulp regeneration via the better tailoring of gelation agents and their concentrations to better mimic the dynamic and compressive properties of native pulp tissue. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Bifurcation and chaos of an axially accelerating viscoelastic beam

International Nuclear Information System (INIS)

Yang Xiaodong; Chen Liqun

2005-01-01

This paper investigates bifurcation and chaos of an axially accelerating viscoelastic beam. The Kelvin-Voigt model is adopted to constitute the material of the beam. Lagrangian strain is used to account for the beam's geometric nonlinearity. The nonlinear partial-differential equation governing transverse motion of the beam is derived from the Newton second law. The Galerkin method is applied to truncate the governing equation into a set of ordinary differential equations. By use of the Poincare map, the dynamical behavior is identified based on the numerical solutions of the ordinary differential equations. The bifurcation diagrams are presented in the case that the mean axial speed, the amplitude of speed fluctuation and the dynamic viscoelasticity is respectively varied while other parameters are fixed. The Lyapunov exponent is calculated to identify chaos. From numerical simulations, it is indicated that the periodic, quasi-periodic and chaotic motions occur in the transverse vibrations of the axially accelerating viscoelastic beam

Modulating state transition and mechanical properties of viscoelastic resins from maize zein through interactions with plasticizers and co-proteins

NARCIS (Netherlands)

Erickson, D.P.; Renzetti, S.; Jurgens, A.; Campanella, O.H.; Hamaker, B.R.

2014-01-01

Viscoelastic properties have been observed in maize zein above its glass transition temperature; however, current understanding of how these viscoelastic polymers can be further manipulated for optimal performance is limited. Using resins formed via precipitation from aqueous ethanolic environments,

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

Science.gov (United States)

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.

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

Science.gov (United States)

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.

Global existence and nonexistence for the viscoelastic wave equation with nonlinear boundary damping-source interaction

KAUST Repository

Said-Houari, Belkacem

2012-09-01

The goal of this work is to study a model of the viscoelastic wave equation with nonlinear boundary/interior sources and a nonlinear interior damping. First, applying the Faedo-Galerkin approximations combined with the compactness method to obtain existence of regular global solutions to an auxiliary problem with globally Lipschitz source terms and with initial data in the potential well. It is important to emphasize that it is not possible to consider density arguments to pass from regular to weak solutions if one considers regular solutions of our problem where the source terms are locally Lipschitz functions. To overcome this difficulty, we use an approximation method involving truncated sources and adapting the ideas in [13] to show that the existence of weak solutions can still be obtained for our problem. Second, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term, then the solution ceases to exist and blows up in finite time provided that the initial data are large enough.

Global existence and nonexistence for the viscoelastic wave equation with nonlinear boundary damping-source interaction

KAUST Repository

Said-Houari, Belkacem; Nascimento, Flá vio A Falcã o

2012-01-01

The goal of this work is to study a model of the viscoelastic wave equation with nonlinear boundary/interior sources and a nonlinear interior damping. First, applying the Faedo-Galerkin approximations combined with the compactness method to obtain existence of regular global solutions to an auxiliary problem with globally Lipschitz source terms and with initial data in the potential well. It is important to emphasize that it is not possible to consider density arguments to pass from regular to weak solutions if one considers regular solutions of our problem where the source terms are locally Lipschitz functions. To overcome this difficulty, we use an approximation method involving truncated sources and adapting the ideas in [13] to show that the existence of weak solutions can still be obtained for our problem. Second, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term, then the solution ceases to exist and blows up in finite time provided that the initial data are large enough.

Viscoelastic and dynamic properties of embryonic stem cells

DEFF Research Database (Denmark)

Ritter, Christine

Stem cells are often referred to as the ‘holy grail’ of regenerative medicine, because they possessthe ability to develop into any cell type. The use of stem cells within medicine is currently limited bythe effectivity of differentiation and cell reprogramming protocols, making it therefore...... imperative tounderstand stem cells’ differentiation mechanisms better. Studies have shown that mechanical cuescan have an influence on stem cell fate decision. However, in order to understand the reaction of stemcells to mechanical input, one should first investigate and understand the mechanical properties...... ofthe cells themselves. In this thesis, the viscoelastic properties of mouse embryonic stem cells primedeither toward the epiblast (Epi) or the primitive endoderm (PrE) lineage were investigated.Optical tweezers were used to measure the fluctuations of endogenous lipid granules and therebydraw...

Combining adhesive contact mechanics with a viscoelastic material model to probe local material properties by AFM.

Science.gov (United States)

Ganser, Christian; Czibula, Caterina; Tscharnuter, Daniel; Schöberl, Thomas; Teichert, Christian; Hirn, Ulrich

2017-12-20

Viscoelastic properties are often measured using probe based techniques such as nanoindentation (NI) and atomic force microscopy (AFM). Rarely, however, are these methods verified. In this article, we present a method that combines contact mechanics with a viscoelastic model (VEM) composed of springs and dashpots. We further show how to use this model to determine viscoelastic properties from creep curves recorded by a probe based technique. We focus on using the standard linear solid model and the generalized Maxwell model of order 2. The method operates in the range of 0.01 Hz to 1 Hz. Our approach is suitable for rough surfaces by providing a defined contact area using plastic pre-deformation of the material. The very same procedure is used to evaluate AFM based measurements as well as NI measurements performed on polymer samples made from poly(methyl methacrylate) and polycarbonate. The results of these measurements are then compared to those obtained by tensile creep tests also performed on the same samples. It is found that the tensile test results differ considerably from the results obtained by AFM and NI methods. The similarity between the AFM results and NI results suggests that the proposed method is capable of yielding results comparable to NI but with the advantage of the imaging possibilities of AFM. Furthermore, all three methods allowed a clear distinction between PC and PMMA by means of their respective viscoelastic properties.

Linear Viscoelasticity, Reptation, Chain Stretching and Constraint Release

DEFF Research Database (Denmark)

Neergaard, Jesper; Schieber, Jay D.; Venerus, David C.

2000-01-01

A recently proposed self-consistent reptation model - alreadysuccessful at describing highly nonlinear shearing flows of manytypes using no adjustable parameters - is used here to interpretthe linear viscoelasticity of the same entangled polystyrenesolution. Using standard techniques, a relaxatio...

Effect of Age and Exercise on the Viscoelastic Properties of Rat Tail Tendon

Science.gov (United States)

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

The viscoelastic standard nonlinear solid model: predicting the response of the lumbar intervertebral disk to low-frequency vibrations.

Science.gov (United States)

Groth, Kevin M; Granata, Kevin P

2008-06-01

Due to the mathematical complexity of current musculoskeletal spine models, there is a need for computationally efficient models of the intervertebral disk (IVD). The aim of this study is to develop a mathematical model that will adequately describe the motion of the IVD under axial cyclic loading as well as maintain computational efficiency for use in future musculoskeletal spine models. Several studies have successfully modeled the creep characteristics of the IVD using the three-parameter viscoelastic standard linear solid (SLS) model. However, when the SLS model is subjected to cyclic loading, it underestimates the load relaxation, the cyclic modulus, and the hysteresis of the human lumbar IVD. A viscoelastic standard nonlinear solid (SNS) model was used to predict the response of the human lumbar IVD subjected to low-frequency vibration. Nonlinear behavior of the SNS model was simulated by a strain-dependent elastic modulus on the SLS model. Parameters of the SNS model were estimated from experimental load deformation and stress-relaxation curves obtained from the literature. The SNS model was able to predict the cyclic modulus of the IVD at frequencies of 0.01 Hz, 0.1 Hz, and 1 Hz. Furthermore, the SNS model was able to quantitatively predict the load relaxation at a frequency of 0.01 Hz. However, model performance was unsatisfactory when predicting load relaxation and hysteresis at higher frequencies (0.1 Hz and 1 Hz). The SLS model of the lumbar IVD may require strain-dependent elastic and viscous behavior to represent the dynamic response to compressive strain.

A homogenization approach for the effective drained viscoelastic properties of 2D porous media and an application for cortical bone.

Science.gov (United States)

Nguyen, Sy-Tuan; Vu, Mai-Ba; Vu, Minh-Ngoc; To, Quy-Dong

2018-02-01

Closed-form solutions for the effective rheological properties of a 2D viscoelastic drained porous medium made of a Generalized Maxwell viscoelastic matrix and pore inclusions are developed and applied for cortical bone. The in-plane (transverse) effective viscoelastic bulk and shear moduli of the Generalized Maxwell rheology of the homogenized medium are expressed as functions of the porosity and the viscoelastic properties of the solid phase. When deriving these functions, the classical inverse Laplace-Carson transformation technique is avoided, due to its complexity, by considering the short and long term approximations. The approximated results are validated against exact solutions obtained from the inverse Laplace-Carson transform for a simple configuration when the later is available. An application for cortical bone with assumption of circular pore in the transverse plane shows that the proposed approximation fit very well with experimental data. Copyright © 2017 Elsevier Ltd. All rights reserved.

A New Approach for Studying Nonlinear Dynamic Response of a Thin Plate with Internal Resonance in a Fractional Viscoelastic Medium

Directory of Open Access Journals (Sweden)

Yury A. Rossikhin

2015-01-01

Full Text Available In the previous analysis, the dynamic behaviour of a nonlinear plate embedded into a fractional derivative viscoelastic medium has been studied by the method of multiple time scales under the conditions of the internal resonances two-to-one and one-to-one, as well as the internal combinational resonances for the case when the linear parts of nonlinear equations of motion occur to be coupled. A new approach proposed in this paper allows one to uncouple the linear parts of equations of motion of the plate, while the same method, the method of multiple time scales, has been utilized for solving nonlinear equations. The influence of viscosity on the energy exchange mechanism between interacting nonlinear modes has been analyzed. It has been shown that for some internal resonances there exist such particular cases when it is possible to obtain two first integrals, namely, the energy integral and the stream function, which allows one to reduce the problem to the calculation of elliptic integrals. The new approach enables one to solve the problems of vibrations of thin bodies more efficiently.

Viscoelastic properties of sweet potato complementary porridges as influenced by endogenous amylases.

Science.gov (United States)

Nabubuya, Agnes; Namutebi, Agnes; Byaruhanga, Yusuf; Schuller, Reidar B; Narvhus, Judith; Wicklund, Trude

2017-11-01

Sweet potato ( Ipomoea batatas L.) roots contain amylolytic enzymes, which hydrolyze starch thus having the potential to affect the viscosity of sweet potato porridges provided the appropriate working conditions for the enzymes are attained. In this study, the effect of sweet potato variety, postharvest handling conditions, freshly harvested and room/ambient stored roots (3 weeks), and slurry solids content on the viscoelastic properties of complementary porridges prepared using amylase enzyme activation technique were investigated. Five temperatures (55°C, 65°C, 70°C, 75°C, and 80°C) were used to activate sweet potato amylases and the optimum temperature was found to be 75°C. Stored sweet potato roots had higher soluble solids (⁰Brix) content in the pastes compared to fresh roots. In all samples, activation of amylases at 75°C caused changes in the viscoelastic parameters: phase angle (tan δ) and complex viscosity (η * ). Postharvest handling conditions and slurry solids content significantly affected the viscoelastic properties of the porridges with flours from stored roots yielding viscous (liquid-like) porridges and fresh roots producing elastic (solid-like) porridges. Increase in slurry solids content caused reduction in the phase angle values and increase in the viscosity of the sweet potato porridges. The viscosity of the porridges decreased with storage of sweet potato roots. These results provide a possibility for exploiting sweet potato endogenous amylases in the preparation of complementary porridges with both drinkable viscosities and appropriate energy and nutrient densities for children with varying energy needs.

Trefoil factor peptide 3 is positively correlated with the viscoelastic properties of the cervical mucus plug

DEFF Research Database (Denmark)

Bastholm, Sara Kjær; Samson, Mie Hesselund; Becher, Naja

2017-01-01

The viscoelastic properties of the cervical mucus plug are considered essential for the occlusion of the cervical canal and thereby for protection against ascending infections during pregnancy. Factors controlling this property are virtually unknown. This study explores a possible role of trefoil...

Effects of Wheat Flour Dough’s Viscoelastic Level by Adding Glucose Oxidase on its Dynamic Shear Properties whatever the Strain Modes

Directory of Open Access Journals (Sweden)

Jean Didier Koffi Kouassi

2014-05-01

Full Text Available The objective of this work was to study the effects of wheat flour dough’s viscoelastic level by adding glucose oxidase (Gox on its rheological properties at dynamic shear strain mode to predict the final product quality. Dough does display a linear viscoelastic domain. Glucose oxidase (Gox was added to dough in order to enhance its viscoelasticity and to take into account the possible effects of this viscoelasticity on the results. Whatever the types of dough strain used G’ increased, tan δ decreased and led to less sticky dough. Wheat flour dough, an increase in G’ with extension may be associated to a strain-hardening phenomenon but the role of dough viscoelasticity is discussed.

Experimental and Computational Investigation of Viscoelasticity of Native and Engineered Ligament and Tendon

Science.gov (United States)

Ma, J.; Narayanan, H.; Garikipati, K.; Grosh, K.; Arruda, E. M.

The important mechanisms by which soft collagenous tissues such as ligament and tendon respond to mechanical deformation include non-linear elasticity, viscoelasticity and poroelasticity. These contributions to the mechanical response are modulated by the content and morphology of structural proteins such as type I collagen and elastin, other molecules such as glycosaminoglycans, and fluid. Our ligament and tendon constructs, engineered from either primary cells or bone marrow stromal cells and their autogenous matricies, exhibit histological and mechanical characteristics of native tissues of different levels of maturity. In order to establish whether the constructs have optimal mechanical function for implantation and utility for regenerative medicine, constitutive relationships for the constructs and native tissues at different developmental levels must be established. A micromechanical model incorporating viscoelastic collagen and non-linear elastic elastin is used to describe the non-linear viscoelastic response of our homogeneous engineered constructs in vitro. This model is incorporated within a finite element framework to examine the heterogeneity of the mechanical responses of native ligament and tendon.

Influence of Nanodisperse Metal Fillers on the Viscoelastic Properties and Processes of Mechanical Relaxation of Polymer Systems

Science.gov (United States)

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.

Nonlinear wave breaking in self-gravitating viscoelastic quantum fluid

Energy Technology Data Exchange (ETDEWEB)

Mitra, Aniruddha, E-mail: anibabun@gmail.com [Center for Plasma Studies, Department of Instrumentation Science, Jadavpur University, Kolkata, 700 032 (India); Roychoudhury, Rajkumar, E-mail: rajdaju@rediffmail.com [Advanced Centre for Nonlinear and Complex Phenomena, 1175 Survey Park, Kolkata 700075 (India); Department of Mathematics, Bethune College, Kolkata 700006 (India); Bhar, Radhaballav [Center for Plasma Studies, Department of Instrumentation Science, Jadavpur University, Kolkata, 700 032 (India); Khan, Manoranjan, E-mail: mkhan.ju@gmail.com [Center for Plasma Studies, Department of Instrumentation Science, Jadavpur University, Kolkata, 700 032 (India)

2017-02-12

The stability of a viscoelastic self-gravitating quantum fluid has been studied. Symmetry breaking instability of solitary wave has been observed through ‘viscosity modified Ostrovsky equation’ in weak gravity limit. In presence of strong gravitational field, the solitary wave breaks into shock waves. Response to a Gaussian perturbation, the system produces quasi-periodic short waves, which in terns predicts the existence of gravito-acoustic quasi-periodic short waves in lower solar corona region. Stability analysis of this dynamical system predicts gravity has the most prominent effect on the phase portraits, therefore, on the stability of the system. The non-existence of chaotic solution has also been observed at long wavelength perturbation through index value theorem. - Highlights: • In weak gravitational field, viscoelastic quantum fluid exhibits symmetry breaking instability. • Gaussian perturbation produces quasi-periodic gravito-acoustic waves into the system. • There exists no chaotic state of the system against long wavelength perturbations.

Dominant role of wormlike micelles in temperature-responsive viscoelastic properties of their mixtures with polymeric chains

KAUST Repository

Molchanov, Vyacheslav S.; Philippova, Olga E.

2013-01-01

Temperature effects on the rheological properties of viscoelastic solutions containing entangled wormlike micelles of potassium oleate and hydrophobically modified polyacrylamide were studied in a wide range of polymer concentrations. A very

Characterization of site-specific biomechanical properties of human meniscus-Importance of collagen and fluid on mechanical nonlinearities.

Science.gov (United States)

Danso, E K; Mäkelä, J T A; Tanska, P; Mononen, M E; Honkanen, J T J; Jurvelin, J S; Töyräs, J; Julkunen, P; Korhonen, R K

2015-06-01

Meniscus adapts to joint loads by depth- and site-specific variations in its composition and structure. However, site-specific mechanical characteristics of intact meniscus under compression are poorly known. In particular, mechanical nonlinearities caused by different meniscal constituents (collagen and fluid) are not known. In the current study, in situ indentation testing was conducted to determine site-specific elastic, viscoelastic and poroelastic properties of intact human menisci. Lateral and medial menisci (n=26) were harvested from the left knee joint of 13 human cadavers. Indentation tests, using stress-relaxation and dynamic (sinusoidal) loading protocols, were conducted for menisci at different sites (anterior, middle, posterior, n=78). Sample- and site-specific axisymmetric finite element models with fibril-reinforced poroelastic properties were fitted to the corresponding stress-relaxation curves to determine the mechanical parameters. Elastic moduli, especially the instantaneous and dynamic moduli, showed site-specific variation only in the medial meniscus (pmeniscus. The phase angle showed no statistically significant variation between the sites (p>0.05). The values for the strain-dependent fibril network modulus (nonlinear behaviour of collagen) were significantly different (pmeniscus only between the middle and posterior sites. For the strain-dependent permeability coefficient, only anterior and middle sites showed a significant difference (pmeniscus. This parameter demonstrated a significant difference (pmeniscus shows more site-dependent variation in the mechanical properties as compared to lateral meniscus. In particular, anterior horn of medial meniscus was the stiffest and showed the most nonlinear mechanical behaviour. The nonlinearity was related to both collagen fibrils and fluid. Copyright © 2015 Elsevier Ltd. All rights reserved.

Viscoelastic properties of bovine orbital connective tissue and fat: constitutive models.

Science.gov (United States)

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.

Unequal diffusivities case of homogeneous–heterogeneous reactions within viscoelastic fluid flow in the presence of induced magnetic-field and nonlinear thermal radiation

Directory of Open Access Journals (Sweden)

I.L. Animasaun

2016-06-01

Full Text Available This article presents the effects of nonlinear thermal radiation and induced magnetic field on viscoelastic fluid flow toward a stagnation point. It is assumed that there exists a kind of chemical reaction between chemical species A and B. The diffusion coefficients of the two chemical species in the viscoelastic fluid flow are unequal. Since chemical species B is a catalyst at the horizontal surface, hence homogeneous and heterogeneous schemes are of the isothermal cubic autocatalytic reaction and first order reaction respectively. The transformed governing equations are solved numerically using Runge–Kutta integration scheme along with Newton’s method. Good agreement is obtained between present and published numerical results for a limiting case. The influence of some pertinent parameters on skin friction coefficient, local heat transfer rate, together with velocity, induced magnetic field, temperature, and concentration profiles is illustrated graphically and discussed. Based on all of these assumptions, results indicate that the effects of induced magnetic and viscoelastic parameters on velocity, transverse velocity and velocity of induced magnetic field are almost the same but opposite in nature. The strength of heterogeneous reaction parameter is very helpful to reduce the concentration of bulk fluid and increase the concentration of catalyst at the surface.

Quantitative evaluation of the viscoelastic properties of the ankle joint complex in patients suffering from ankle sprain by the anterior drawer test.

Science.gov (United States)

Lin, Che-Yu; Shau, Yio-Wha; Wang, Chung-Li; Chai, Huei-Ming; Kang, Jiunn-Horng

2013-06-01

Biological tissues such as ligaments exhibit viscoelastic behaviours. Injury to the ligament may induce changes of these viscoelastic properties, and these changes could serve as biomarkers to detect the injury. In the present study, a novel instrument was developed to non-invasive quantify the viscoelastic properties of the ankle in vivo by the anterior drawer test. The purpose of the study was to investigate the reliability of the instrument and to compare the viscoelastic properties of the ankle between patients suffering from ankle sprain and controls. Eight patients and eight controls participated in the present study. The reliability test was performed on three randomly chosen subjects. In patient and control test, both ankles of each subject were tested to evaluate the viscoelastic properties of the ankle. The viscosity index was defined for quantitatively evaluating the viscosity of the ankle. Greater viscosity index was associated with lower viscosity. Injured and uninjured ankles of patient and both ankles of controls were compared. The instrument exhibited excellent test-retest reliability (r > 0.9). Injured ankles exhibited significantly less viscosity than uninjured ankles, since injured ankles of patients had significantly higher viscosity index (8,148 ± 5,266) compared with uninjured ankles of patients (948 ± 617; p = 0.008) and controls (1,326 ± 613; p ankle can serve as sensitive and useful clinical biomarkers to differentiate between injured and uninjured ankles. The method may provide a clinical examination for objectively evaluating lateral ankle ligament injuries.

Correlation between the viscoelastic properties of the gel layer of swollen HPMC matrix tablets and their in vitro drug release.

Science.gov (United States)

Hamed, Rania; Al Baraghthi, Tamadur; Sunoqrot, Suhair

2016-11-21

Drug release from hydroxypropyl methylcellulose (HPMC) hydrophilic matrix tablets is controlled by drug diffusion through the gel layer of the matrix-forming polymer upon hydration, matrix erosion or combination of diffusion and erosion mechanisms. In this study, the relationship between viscoelastic properties of the gel layer of swollen intact matrix tablets and drug release was investigated. Two sets of quetiapine fumarate (QF) matrix tablets were prepared using the high viscosity grade HPMC K4M at low (70 mg/tablet) and high (170 mg/tablet) polymer concentrations. Viscoelastic studies using a controlled stress rheometer were performed on swollen matrices following hydration in the dissolution medium for predetermined time intervals. The gel layer of swollen tablets exhibited predominantly elastic behavior. Results from the in vitro release study showed that drug release was strongly influenced by the viscoelastic properties of the gel layer of K4M tablets, which was further corroborated by results from water uptake studies conducted on intact tablets. The results provide evidence that the viscoelastic properties of the gel layer can be exploited to guide the selection of an appropriate matrix-forming polymer, to better understand the rate of drug release from matrix tablets in vitro and to develop hydrophilic controlled-release formulations.

Linear viscoelastic properties of aging suspensions

NARCIS (Netherlands)

Purnomo, E.H.; Purnomo, E.H; van den Ende, Henricus T.M.; Mellema, J.; Mugele, Friedrich Gunther

2006-01-01

We have examined the linear viscoelastic behavior of poly-N-isopropylacrylamide (PNIPAM) microgel suspensions in order to obtain insight in the aging processes in these densely packed suspensions at various temperatures below the volume transition temperature. The system is found to display a strong

Viscoelasticity of biomaterials

International Nuclear Information System (INIS)

Glasser, W.G.; Hatakeyama, H.

1992-01-01

Viscoelasticity 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 properties of polysacchardies, chiral and liquid crystalline solution characteristics of cellulose derivatives, and viscoelastic properties 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

Study of normal and shear material properties for viscoelastic model of asphalt mixture by discrete element method

DEFF Research Database (Denmark)

Feng, Huan; Pettinari, Matteo; Stang, Henrik

2015-01-01

In this paper, the viscoelastic behavior of asphalt mixture was studied by using discrete element method. The dynamic properties of asphalt mixture were captured by implementing Burger’s contact model. Different ways of taking into account of the normal and shear material properties of asphalt mi...

Viscoelastic nanoscale properties of cuticle contribute to the high-pass properties of spider vibration receptor (Cupiennius salei Keys).

Science.gov (United States)

McConney, Michael E; Schaber, Clemens F; Julian, Michael D; Barth, Friedrich G; Tsukruk, Vladimir V

2007-12-22

Atomic force microscopy (AFM) and surface force spectroscopy were applied in live spiders to their joint pad material located distal of the metatarsal lyriform organs, which are highly sensitive vibration sensors. The surface topography of the material is sufficiently smooth to probe the local nanomechanical properties with nanometre elastic deflections. Nanoscale loads were applied in the proximad direction on the distal joint region simulating the natural stimulus situation. The force curves obtained indicate the presence of a soft, liquid-like epicuticular layer (20-40 nm thick) above the pad material, which has much higher stiffness. The Young modulus of the pad material is close to 15 MPa at low frequencies, but increases rapidly with increasing frequencies approximately above 30 Hz to approximately 70 MPa at 112 Hz. The adhesive forces drop sharply by about 40% in the same frequency range. The strong frequency dependence of the elastic modulus indicates the viscoelastic nature of the pad material, its glass transition temperature being close to room temperature (25 +/- 2 degrees C) and, therefore, to its maximized energy absorption from low-frequency mechanical stimuli. These viscoelastic properties of the cuticular pad are suggested to be at least partly responsible for the high-pass characteristics of the vibration sensor's physiological properties demonstrated earlier.

Influence of gas injection on viscous and viscoelastic properties of Xanthan gum.

Science.gov (United States)

Bobade, Veena; Cheetham, Madalyn; Hashim, Jamal; Eshtiaghi, Nicky

2018-05-01

Xanthan gum is widely used as a model fluid for sludge to mimic the rheological behaviour under various conditions including impact of gas injection in sludge. However, there is no study to show the influence of gas injection on rheological properties of xanthan gum specifically at the concentrations at which it is used as a model fluid for sludge with solids concentration above 2%. In this paper, the rheological properties of aqueous xanthan gum solutions at different concentrations were measured over a range of gas injection flow rates. The effect of gas injection on both the flow and viscoelastic behaviour of Xanthan gum (using two different methods - a creep test and a time sweep test) was evaluated. The viscosity curve of different solid concentrations of digested sludge and waste activated sludge were compared with different solid concentrations of Xanthan gum and the results showed that Xanthan gum can mimic the flow behaviour of sludge in flow regime. The results in linear viscoelastic regime showed that increasing gas flow rate increases storage modulus (G'), indicating an increase in the intermolecular associations within the material structure leading to an increase in material strength and solid behaviour. Similarly, in creep test an increase in the gas flow rate decreased strain%, signifying that the material has become more resistant to flow. Both observed behaviour is opposite to what occurs in sludge under similar conditions. The results of both the creep test and the time sweep test indicated that choosing Xanthan gum aqueous solution as a transparent model fluid for sludge in viscoelastic regime under similar conditions involving gas injection in a concentration range studied is not feasible. However Xanthan gum can be used as a model material for sludge in flow regime; because it shows a similar behaviour to sludge. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effects of a Pseudophysiological Environment on the Elastic and Viscoelastic Properties of Collagen Gels

Science.gov (United States)

Meghezi, Sébastien; Couet, Frédéric; Chevallier, Pascale; Mantovani, Diego

2012-01-01

Vascular tissue engineering focuses on the replacement of diseased small-diameter blood vessels with a diameter less than 6 mm for which adequate substitutes still do not exist. One approach to vascular tissue engineering is to culture vascular cells on a scaffold in a bioreactor. The bioreactor establishes pseudophysiological conditions for culture (medium culture, 37°C, mechanical stimulation). Collagen gels are widely used as scaffolds for tissue regeneration due to their biological properties; however, they exhibit low mechanical properties. Mechanical characterization of these scaffolds requires establishing the conditions of testing in regard to the conditions set in the bioreactor. The effects of different parameters used during mechanical testing on the collagen gels were evaluated in terms of mechanical and viscoelastic properties. Thus, a factorial experiment was adopted, and three relevant factors were considered: temperature (23°C or 37°C), hydration (aqueous saline solution or air), and mechanical preconditioning (with or without). Statistical analyses showed significant effects of these factors on the mechanical properties which were assessed by tensile tests as well as stress relaxation tests. The last tests provide a more consistent understanding of the gels' viscoelastic properties. Therefore, performing mechanical analyses on hydrogels requires setting an adequate environment in terms of temperature and aqueous saline solution as well as choosing the adequate test. PMID:22844285

Application of nonlinear rheology to assess the effect of secondary nanofiller on network structure of hybrid polymer nanocomposites

Science.gov (United States)

Kamkar, Milad; Aliabadian, Ehsan; Shayesteh Zeraati, Ali; Sundararaj, Uttandaraman

2018-02-01

Carbon nanotube (CNT)/polymer nanocomposites exhibit excellent electrical properties by forming a percolated network. Adding a secondary filler can significantly affect the CNTs' network, resulting in changing the electrical properties. In this work, we investigated the effect of adding manganese dioxide nanowires (MnO2NWs) as a secondary nanofiller on the CNTs' network structure inside a poly(vinylidene fluoride) (PVDF) matrix. Incorporating MnO2NWs to PVDF/CNT samples produced a better state of dispersion of CNTs, as corroborated by light microscopy and transmission electron microscopy. The steady shear and oscillatory shear flows were employed to obtain a better insight into the nanofiller structure and viscoelastic behavior of the nanocomposites. The transient response under steady shear flow revealed that the stress overshoot of hybrid nanocomposites (two-fillers), PVDF/CNT/MnO2NWs, increased dramatically in comparison to binary nanocomposites (single-filler), PVDF/CNT and PVDF/MnO2NWs. This can be attributed to microstructural changes. Large amplitude oscillatory shear characterization was also performed to further investigate the effect of the secondary nanofiller on the nonlinear viscoelastic behavior of the samples. The nonlinear rheological observations were explained using quantitative nonlinear parameters [strain-stiffening ratio (S) and shear-thickening ratio (T)] and Lissajous-Bowditch plots. Results indicated that a more rigid nanofiller network was formed for the hybrid nanocomposites due to the better dispersion state of CNTs and this led to a more nonlinear viscoelastic behavior.

Viscoelastic response of hydrogel materials at finite strains

OpenAIRE

Skovly, Martin Johannessen

2015-01-01

Hydrogel materials are very soft materials consisting of polymer networks and solvent molecules. The materials may exhibit large volume changes depending on its external chemical and mechanical environment and have viscoelastic properties which is common for many polymeric materials. In order to model the material response with the finite element method, a hydrogel constitutive model have been combined with finite viscoelastic theory and the resulting viscoelastic hydrogel constitutive model ...

Uniform Decay for Solutions of an Axially Moving Viscoelastic Beam

Energy Technology Data Exchange (ETDEWEB)

Kelleche, Abdelkarim, E-mail: kellecheabdelkarim@gmail.com [Université des Sciences et de la Technologie Houari Boumediene, Faculté des Mathématiques (Algeria); Tatar, Nasser-eddine, E-mail: tatarn@Kfupm.edu.sa [King Fahd University of Petroleum and Minerals, Department of Mathematics and Statistics (Saudi Arabia)

2017-06-15

The paper deals with an axially moving viscoelastic structure modeled as an Euler–Bernoulli beam. The aim is to suppress the transversal displacement (transversal vibrations) that occur during the axial motion of the beam. It is assumed that the beam is moving with a constant axial speed and it is subject to a nonlinear force at the right boundary. We prove that when the axial speed of the beam is smaller than a critical value, the dissipation produced by the viscoelastic material is sufficient to suppress the transversal vibrations. It is shown that the rate of decay of the energy depends on the kernel which arise in the viscoelastic term. We consider a general kernel and notice that solutions cannot decay faster than the kernel.

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

Science.gov (United States)

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.

Viscoelastic material inversion using Sierra-SD and ROL

Energy Technology Data Exchange (ETDEWEB)

Walsh, Timothy [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Aquino, Wilkins [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ridzal, Denis [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kouri, Drew Philip [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); van Bloemen Waanders, Bart Gustaaf [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Urbina, Angel [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2014-11-01

In this report we derive frequency-domain methods for inverse characterization of the constitutive parameters of viscoelastic materials. The inverse problem is cast in a PDE-constrained optimization framework with efficient computation of gradients and Hessian vector products through matrix free operations. The abstract optimization operators for first and second derivatives are derived from first principles. Various methods from the Rapid Optimization Library (ROL) are tested on the viscoelastic inversion problem. The methods described herein are applied to compute the viscoelastic bulk and shear moduli of a foam block model, which was recently used in experimental testing for viscoelastic property characterization.

Evaluation of Heating and Shearing on the Viscoelastic Properties of Calcium Hydroxyapatite Used in Injection Laryngoplasty.

Science.gov (United States)

Mahboubi, Hossein; Mohraz, Ali; Verma, Sunil P

2016-03-01

To compare the viscoelastic properties of calcium hydroxyapatite (CaHA) to carboxymethylcellulose (CMC) injectables used for injection laryngoplasty and determine if they are affected by heating and shearing. Experimental. University laboratory. Vocal fold injection laryngoplasty with CaHA is oftentimes challenging due to the amount of pressure necessary to push the injectate through a needle. Anecdotal techniques, such as heating the product, have been suggested to facilitate injection. The viscoelastic properties of CaHA and CMC were measured with a rheometer. The effects of heating and shearing on sample viscoelasticity were recorded. CaHA was 9.5 times more viscous than CMC (43,100 vs 4540 Pa·s). Heating temporarily decreased the viscosity of CaHA by 32%. However, it also caused the viscosity to subsequently increase after time. Shearing of CaHA reduced its viscosity by 26%. Heating and shearing together temporarily reduced the viscosity of CaHA by 52%. A combination of heating and shearing had a more profound effect than heating or shearing alone on the viscosity of CaHA, potentially making it easier to inject temporarily. Long-term and in vivo studies are required to further analyze the effect of heating and shearing on CaHA injectables. © American Academy of Otolaryngology—Head and Neck Surgery Foundation 2016.

Viscoelasticity of biofilms and their recalcitrance to mechanical and chemical challenges

Science.gov (United States)

Peterson, Brandon W.; He, Yan; Ren, Yijin; Zerdoum, Aidan; Libera, Matthew R.; Sharma, Prashant K.; van Winkelhoff, Arie-Jan; Neut, Danielle; Stoodley, Paul; van der Mei, Henny C.; Busscher, Henk J.

2015-01-01

We summarize different studies describing mechanisms through which bacteria in a biofilm mode of growth resist mechanical and chemical challenges. Acknowledging previous microscopic work describing voids and channels in biofilms that govern a biofilms response to such challenges, we advocate a more quantitative approach that builds on the relation between structure and composition of materials with their viscoelastic properties. Biofilms possess features of both viscoelastic solids and liquids, like skin or blood, and stress relaxation of biofilms has been found to be a corollary of their structure and composition, including the EPS matrix and bacterial interactions. Review of the literature on viscoelastic properties of biofilms in ancient and modern environments as well as of infectious biofilms reveals that the viscoelastic properties of a biofilm relate with antimicrobial penetration in a biofilm. In addition, also the removal of biofilm from surfaces appears governed by the viscoelasticity of a biofilm. Herewith, it is established that the viscoelasticity of biofilms, as a corollary of structure and composition, performs a role in their protection against mechanical and chemical challenges. Pathways are discussed to make biofilms more susceptible to antimicrobials by intervening with their viscoelasticity, as a quantifiable expression of their structure and composition. PMID:25725015

The effect of rework content addition on the microstructure and viscoelastic properties of processed cheese.

Science.gov (United States)

Černíková, Michaela; Nebesářová, Jana; Salek, Richardos Nikolaos; Popková, Romana; Buňka, František

2018-04-01

The aim of this work was to add various amounts of rework (0.0 to 20.0% wt/wt) to processed cheeses with a dry matter content of 36% (wt/wt) and fat with a dry matter content of 45% (wt/wt). The effect of the rework addition on the viscoelastic properties and microstructure of the processed cheeses was observed. The addition of rework (in this case, to processed cheese with a spreadable consistency) in the amounts of 2.5, 5.0, and 10.0% (wt/wt) increased the firmness of the processed cheese. With the further addition of rework, the consistency of the processed cheeses no longer differed significantly. The conclusions obtained by the measurement of viscoelastic properties were supported by cryo-scanning electron microscopy, where fat droplets in samples with added rework of over 10.0% (wt/wt) were smaller than fat droplets in processed cheeses with lower additions of rework. Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Finite element method for viscoelastic medium with damage and the application to structural analysis of solid rocket motor grain

Science.gov (United States)

Deng, Bin; Shen, ZhiBin; Duan, JingBo; Tang, GuoJin

2014-05-01

This paper studies the damage-viscoelastic behavior of composite solid propellants of solid rocket motors (SRM). Based on viscoelastic theories and strain equivalent hypothesis in damage mechanics, a three-dimensional (3-D) nonlinear viscoelastic constitutive model incorporating with damage is developed. The resulting viscoelastic constitutive equations are numerically discretized by integration algorithm, and a stress-updating method is presented by solving nonlinear equations according to the Newton-Raphson method. A material subroutine of stress-updating is made up and embedded into commercial code of Abaqus. The material subroutine is validated through typical examples. Our results indicate that the finite element results are in good agreement with the analytical ones and have high accuracy, and the suggested method and designed subroutine are efficient and can be further applied to damage-coupling structural analysis of practical SRM grain.

Age-dependent effects of systemic administration of oxytetracycline on the viscoelastic properties of rat tail tendons as a mechanistic basis for pharmacological treatment of flexural limb deformities in foals.

Science.gov (United States)

Wintz, Leslie R; Lavagnino, Michael; Gardner, Keri L; Sedlak, Aleksa M; Arnoczky, Steven P

2012-12-01

To describe the effect of systemically administered oxytetracycline on the viscoelastic properties of rat tail tendon fascicles (TTfs) to provide a mechanistic rationale for pharmacological treatment of flexural limb deformities in foals. TTfs from ten 1-month-old and ten 6-month-old male Sprague-Dawley rats. 5 rats in each age group were administered oxytetracycline (50 mg/kg, IP, q 24 h) for 4 days. The remaining 5 rats in each age group served as untreated controls. Five days after initiation of oxytetracycline treatment, TTfs were collected and their viscoelastic properties were evaluated via a stress-relaxation protocol. Maximum modulus and equilibrium modulus were compared via a 2-way ANOVA. Collagen fibril size, density, and orientation in TTfs were compared between treated and control rats. Viscoelastic properties were significantly decreased in TTfs from 1-month-old oxytetracycline-treated rats, compared with those in TTfs from 1-month-old control rats. Oxytetracycline had no effect on the viscoelastic properties of TTfs from 6-month-old rats. Collagen fibril size, density, and orientation in TTfs from 1-month-old rats did not differ between oxytetracycline-treated and control rats. Results confirmed that systemically administered oxytetracycline decreased the viscoelastic properties of TTfs from 1-month-old rats but not those of TTfs from 6-month-old rats. The decrease in viscoelastic properties associated with oxytetracycline treatment does not appear to be caused by altered collagen fibril diameter or organization. The age-dependent effect of oxytetracycline on the viscoelastic properties of tendons may be related to its effect on the maturation of the extracellular matrix of developing tendons.

Noise Reduction Evaluation of Multi-Layered Viscoelastic Infinite Cylinder under Acoustical Wave Excitation

Directory of Open Access Journals (Sweden)

M.R. Mofakhami

2008-01-01

Full Text Available In this paper sound transmission through the multilayered viscoelastic air filled cylinders subjected to the incident acoustic wave is studied using the technique of separation of variables on the basis of linear three dimensional theory of elasticity. The effect of interior acoustic medium on the mode maps (frequency vs geometry and noise reduction is investigated. The effects of internal absorption and external moving medium on noise reduction are also evaluated. The dynamic viscoelastic properties of the structure are rigorously taken into account with a power law technique that models the viscoelastic damping of the cylinder. A parametric study is also performed for the two layered infinite cylinders to obtain the effect of viscoelastic layer characteristics such as thickness, material type and frequency dependency of viscoelastic properties on the noise reduction. It is shown that using constant and frequency dependent viscoelastic material with high loss factor leads to the uniform noise reduction in the frequency domain. It is also shown that the noise reduction obtained for constant viscoelastic material property is subjected to some errors in the low frequency range with respect to those obtained for the frequency dependent viscoelastic material.

Investigation of transient cavitating flow in viscoelastic pipes

International Nuclear Information System (INIS)

Keramat, A; Tijsseling, A S; Ahmadi, A

2010-01-01

A study on water hammer in viscoelastic pipes when the fluid pressure drops to liquid vapour pressure is performed. Two important concepts including column separation and the effects of retarded strains in the pipe wall on the fluid response have been investigated separately in recent works, but there is some curiosity as to how the results for pressure and discharge are when column separation occurs in a viscoelastic pipe. For pipes made of plastic such as polyethylene (PE) and polyvinyl chloride (PVC), viscoelasticity is a crucial mechanical property which changes the hydraulic and structural transient responses. Based on previous developments in the analysis of water hammer, a model which is capable of analysing column separation in viscoelastic pipes is presented and used for solving the selected case studies. For the column-separation modelling the Discrete Vapour Cavity Model (DVCM) is utilised and the viscoelasticity property of the pipe wall is modelled by Kelvin-Voigt elements. The effects of viscoelasticity play an important role in the column separation phenomenon because it changes the water hammer fundamental frequency and so affects the time of opening or collapse of the cavities. Verification of the implemented computer code is performed for the effects of viscoelasticity and column separation - separately and simultaneously - using experimental results from the literature. In the provided examples the focus is placed on the simultaneous effect of viscoelasticity and column separation on the hydraulic transient response. The final conclusions drawn are that if rectangular grids are utilised the DVCM gives acceptable predictions of the phenomenon and that the pipe wall material's retarded behaviour strongly dampens the pressure spikes caused by column separation.

Investigation of transient cavitating flow in viscoelastic pipes

Science.gov (United States)

Keramat, A.; Tijsseling, A. S.; Ahmadi, A.

2010-08-01

A study on water hammer in viscoelastic pipes when the fluid pressure drops to liquid vapour pressure is performed. Two important concepts including column separation and the effects of retarded strains in the pipe wall on the fluid response have been investigated separately in recent works, but there is some curiosity as to how the results for pressure and discharge are when column separation occurs in a viscoelastic pipe. For pipes made of plastic such as polyethylene (PE) and polyvinyl chloride (PVC), viscoelasticity is a crucial mechanical property which changes the hydraulic and structural transient responses. Based on previous developments in the analysis of water hammer, a model which is capable of analysing column separation in viscoelastic pipes is presented and used for solving the selected case studies. For the column-separation modelling the Discrete Vapour Cavity Model (DVCM) is utilised and the viscoelasticity property of the pipe wall is modelled by Kelvin-Voigt elements. The effects of viscoelasticity play an important role in the column separation phenomenon because it changes the water hammer fundamental frequency and so affects the time of opening or collapse of the cavities. Verification of the implemented computer code is performed for the effects of viscoelasticity and column separation - separately and simultaneously - using experimental results from the literature. In the provided examples the focus is placed on the simultaneous effect of viscoelasticity and column separation on the hydraulic transient response. The final conclusions drawn are that if rectangular grids are utilised the DVCM gives acceptable predictions of the phenomenon and that the pipe wall material's retarded behaviour strongly dampens the pressure spikes caused by column separation.

Viscoelastic gravel-pack carrier fluid

International Nuclear Information System (INIS)

Nehmer, W.L.

1988-01-01

The ability of a fluid to flow adequately into the formation during gravel-pack treatments is critical to achieving a good pack. Recent studies have indicated ''fish-eyes'' and/or ''microgels'' present in many polymer gelled carrier fluids will plug pore throats, leading to impaired leakoff and causing formation damage. Intensive manipulation of the polymer gelled fluid using shear and filter devices will help remove the particles, but it adds to the cost of the treatment in terms of equipment and manpower. Excessive shear will degrade the polymer leading to poor gravel suspension, while too little shear will cause filtration problems. A gelled carried fluid using a viscoelastic surfactant system has been found to leak off very efficiently to the formation, and cause no formation damage, without the use of shear/filter devices. Viscoelastic surfactant-base gelled fluids develop viscosity because of the association of surfactant moloecules into large rod-shaped aggregates. There is no hydration of polymer involved, so fish-eyes and microgels will not be formed in the viscoelastic fluid. A surfactant-base system having a yield point allows the gravel carrying properties to be much better than fluids gelled with conventional polymer systems (hydroxyethylcellulose [HEC]). For example, a gravel carried fluid gelled with 80 lb HEC/1,000 gal has a viscosity of about 400 cp at 170 sec/sup -1/; a viscoelastic surfactant-base system having only one-half the viscosity still flows into cores about four times more efficiently than the HEC-base fluid. The rheology, leakoff, formation damage and mixing properties of a viscoelastic, surfactant-base, gravel-pack carrier fluid are discussed

Estimation of piezoelastic and viscoelastic properties in laminated structures

DEFF Research Database (Denmark)

Araujo, A. L.; Soares, C. M. Mota; Herskovits, J.

2009-01-01

An inverse method for material parameter estimation of elastic, piezoelectric and viscoelastic laminated plate structures is presented. The method uses a gradient based optimization technique in order to solve the inverse problem, through minimization of an error functional which expresses...... the difference between experimental free vibration data and corresponding numerical data produced by a finite element model. The complex modulus approach is used to model the viscoelastic material behavior, assuming hysteretic type damping. Applications that illustrate the influence of adhesive material...

Quasi-static earthquake cycle simulation based on nonlinear viscoelastic finite element analyses

Science.gov (United States)

Agata, R.; Ichimura, T.; Hyodo, M.; Barbot, S.; Hori, T.

2017-12-01

To explain earthquake generation processes, simulation methods of earthquake cycles have been studied. For such simulations, the combination of the rate- and state-dependent friction law at the fault plane and the boundary integral method based on Green's function in an elastic half space is widely used (e.g. Hori 2009; Barbot et al. 2012). In this approach, stress change around the fault plane due to crustal deformation can be computed analytically, while the effects of complex physics such as mantle rheology and gravity are generally not taken into account. To consider such effects, we seek to develop an earthquake cycle simulation combining crustal deformation computation based on the finite element (FE) method with the rate- and state-dependent friction law. Since the drawback of this approach is the computational cost associated with obtaining numerical solutions, we adopt a recently developed fast and scalable FE solver (Ichimura et al. 2016), which assumes use of supercomputers, to solve the problem in a realistic time. As in the previous approach, we solve the governing equations consisting of the rate- and state-dependent friction law. In solving the equations, we compute stress changes along the fault plane due to crustal deformation using FE simulation, instead of computing them by superimposing slip response function as in the previous approach. In stress change computation, we take into account nonlinear viscoelastic deformation in the asthenosphere. In the presentation, we will show simulation results in a normative three-dimensional problem, where a circular-shaped velocity-weakening area is set in a square-shaped fault plane. The results with and without nonlinear viscosity in the asthenosphere will be compared. We also plan to apply the developed code to simulate the post-earthquake deformation of a megathrust earthquake, such as the 2011 Tohoku earthquake. Acknowledgment: The results were obtained using the K computer at the RIKEN (Proposal number

Lecithin-based emulsions for potential use as saliva substitutes in patients with xerostomia--viscoelastic properties.

Science.gov (United States)

Hanning, Sara M; Yu, Tao; Jones, David S; Andrews, Gavin P; Kieser, Jules A; Medlicott, Natalie J

2013-11-18

The purpose of the present study was to investigate lecithin-rice bran oil rheological properties with the view to consider these as potential saliva substitutes in patients with severe xerostomia and salivary hypofunction. Pseudo-ternary phase diagrams of rice bran oil, lecithin and water mixtures were constructed and characterised using polarising light microscopy. Viscoelastic properties, which we hypothesise are important determinants in product performance, were analysed using both flow and oscillatory rheology. Rheological properties were influenced by composition, frequency and shear stress. Frequency-dependent viscoelasticity was observed in some formulations where viscosity dominated (tanδ>1) at frequencies under 5 Hz and elasticity dominated (tanδ<1) at higher frequencies. Threshold frequencies were determined for each formulation, where a peak in loss tangent was observed, coinciding with a reduction in the storage modulus and increase in loss modulus. The frequency-dependent behaviour of emulsions are of interest because these combinations exhibit viscous behaviour at low frequencies, which may improve lubrication of the oral cavity at rest, whereas increased elasticity at higher frequencies may improve retention during higher-shear tasks such as swallowing and speaking. Copyright © 2013 Elsevier B.V. All rights reserved.

The influence of time dependent flight and maneuver velocities and elastic or viscoelastic flexibilities on aerodynamic and stability derivatives

Energy Technology Data Exchange (ETDEWEB)

Cochrane, Alexander P. [Aerospace Engineering Department, University of Glasgow, University Avenue, Glasgow, Lanarkshire (United Kingdom); Merrett, Craig G. [Mechanical and Aerospace Engineering Department, Carleton Univ., 1125 Col. By Dr., Ottawa, ON (Canada); Hilton, Harry H. [Aerospace Engineering Department in the College of Engineering and Private Sector Program Division at the National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)

2014-12-10

which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. This paper reports on analytical analyses and simulations of the effects of flexibility and time dependent material properties (viscoelasticity) on aerodynamic derivatives and on lateral, longitudinal, directional and spin stability derivatives. Cases of both constant and variable flight and maneuver velocities are considered. Analytical results for maneuvers involving constant and time dependent rolling velocities are analyzed, discussed and evaluated. The relationships between rolling velocity p and aileron angular displacement β as well as control effectiveness are analyzed and discussed in detail for elastic and viscoelastic wings. Such analyses establish the roll effectiveness derivatives (∂[p(t)])/(V{sub ∞}∂β(t)) . Similar studies involving other stability and aerodynamic derivatives are also undertaken. The influence of the twin effects of viscoelastic and elastic materials and of variable flight, rolling, pitching and yawing velocities on longitudinal, lateral and directional are also investigated. Variable flight velocities, encountered during maneuvers, render the usually linear problem at constant velocities into a nonlinear one.

The influence of time dependent flight and maneuver velocities and elastic or viscoelastic flexibilities on aerodynamic and stability derivatives

International Nuclear Information System (INIS)

Cochrane, Alexander P.; Merrett, Craig G.; Hilton, Harry H.

2014-01-01

(V REV E ). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V REV< ≧ V REV E , but furthermore does so in time at 0 < t REV ≤ ∞. This paper reports on analytical analyses and simulations of the effects of flexibility and time dependent material properties (viscoelasticity) on aerodynamic derivatives and on lateral, longitudinal, directional and spin stability derivatives. Cases of both constant and variable flight and maneuver velocities are considered. Analytical results for maneuvers involving constant and time dependent rolling velocities are analyzed, discussed and evaluated. The relationships between rolling velocity p and aileron angular displacement β as well as control effectiveness are analyzed and discussed in detail for elastic and viscoelastic wings. Such analyses establish the roll effectiveness derivatives (∂[p(t)])/(V ∞ ∂β(t)) . Similar studies involving other stability and aerodynamic derivatives are also undertaken. The influence of the twin effects of viscoelastic and elastic materials and of variable flight, rolling, pitching and yawing velocities on longitudinal, lateral and directional are also investigated. Variable flight velocities, encountered during maneuvers, render the usually linear problem at constant velocities into a nonlinear one

DYNAMIC DEFORMATION THE VISCOELASTIC TWOCOMPONENT MEDIUM

Directory of Open Access Journals (Sweden)

V. S. Polenov

2015-01-01

Full Text Available Summary. In the article are scope harmonious warping of the two-component medium, one component which are represent viscoelastic medium, hereditary properties which are described by the kernel aftereffect Abel integral-differential ratio BoltzmannVolterr, while second – compressible liquid. Do a study one-dimensional case. Use motion equation of two-component medium at movement. Look determination system these equalization in the form of damped wave. Introduce dimensionless coefficient. Combined equations happen to homogeneous system with complex factor relatively waves amplitude in viscoelastic component and in fluid. As a result opening system determinant receive biquadratic equation. Elastic operator express through kernel aftereffect Abel for space Fourier. With the help transformation and symbol series biquadratic equation reduce to quadratic equation. Come to the conclusion that in two-component viscoelastic medium exist two mode sonic waves. As a result solution of quadratic equation be found description advance of waves sonic in viscoelastic two-component medium, which physical-mechanical properties represent complex parameter. Velocity determination advance of sonic waves, attenuation coefficient, mechanical loss tangent, depending on characteristic porous medium and circular frequency formulas receive. Graph dependences of description advance of waves sonic from the temperature logarithm and with the fractional parameter γ are constructed.

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

International Nuclear Information System (INIS)

Jan, Yih-Kuen; Rong, Daqian; Lung, Chi-Wen; Cuaderes, Elena; 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. (paper)

Characterization of cell mechanical properties by computational modeling of parallel plate compression.

Science.gov (United States)

McGarry, J P

2009-11-01

A substantial body of work has been reported in which the mechanical properties of adherent cells were characterized using compression testing in tandem with computational modeling. However, a number of important issues remain to be addressed. In the current study, using computational analyses, the effect of cell compressibility on the force required to deform spread cells is investigated and the possibility that stiffening of the cell cytoplasm occurs during spreading is examined based on published experimental compression test data. The effect of viscoelasticity on cell compression is considered and difficulties in performing a complete characterization of the viscoelastic properties of a cell nucleus and cytoplasm by this method are highlighted. Finally, a non-linear force-deformation response is simulated using differing linear viscoelastic properties for the cell nucleus and the cell cytoplasm.

Forward and inverse viscoelastic wave scattering by irregular inclusions for shear wave elastography.

Science.gov (United States)

Bernard, Simon; Cloutier, Guy

2017-10-01

Inversion methods in shear wave elastography use simplifying assumptions to recover the mechanical properties of soft tissues. Consequently, these methods suffer from artifacts when applied to media containing strong stiffness contrasts, and do not provide a map of the viscosity. In this work, the shear wave field recorded inside and around an inclusion was used to estimate the viscoelastic properties of the inclusion and surrounding medium, based on an inverse problem approach assuming local homogeneity of both media. An efficient semi-analytical method was developed to model the scattering of an elastic wave by an irregular inclusion, based on a decomposition of the field by Bessel functions and on a decomposition of the boundaries as Fourier series. This model was validated against finite element modeling. Shear waves were experimentally induced by acoustic radiation force in soft tissue phantoms containing stiff and soft inclusions, and the displacement field was imaged at a high frame rate using plane wave imaging. A nonlinear least-squares algorithm compared the model to the experimental data and adjusted the geometrical and mechanical parameters. The estimated shear storage and loss moduli were in good agreement with reference measurements, as well as the estimated inclusion shape. This approach provides an accurate estimation of geometry and viscoelastic properties for a single inclusion in a homogeneous background in the context of radiation force elastography.

Implementation of viscoelastic Hopkinson bars

Directory of Open Access Journals (Sweden)

Govender R.

2012-08-01

Full Text Available Knowledge of the properties of soft, viscoelastic materials at high strain rates are important in furthering our understanding of their role during blast or impact events. Testing these low impedance materials using a metallic split Hopkinson pressure bar setup results in poor signal to noise ratios due to impedance mismatching. These difficulties are overcome by using polymeric Hopkinson bars. Conventional Hopkinson bar analysis cannot be used on the polymeric bars due to the viscoelastic nature of the bar material. Implementing polymeric Hopkinson bars requires characterization of the viscoelastic properties of the material used. In this paper, 30 mm diameter Polymethyl Methacrylate bars are used as Hopkinson pressure bars. This testing technique is applied to polymeric foam called Divinycell H80 and H200. Although there is a large body of of literature containing compressive data, this rarely deals with strain rates above 250s−1 which becomes increasingly important when looking at the design of composite structures where energy absorption during impact events is high on the list of priorities. Testing of polymeric foams at high strain rates allows for the development of better constitutive models.

Viscoelastic effect on acoustic band gaps in polymer-fluid composites

International Nuclear Information System (INIS)

Merheb, B; Deymier, P A; Muralidharan, K; Bucay, J; Jain, M; Aloshyna-Lesuffleur, M; Mohanty, S; Berker, A; Greger, R W

2009-01-01

In this paper, we present a theoretical analysis of the propagation of acoustic waves through elastic and viscoelastic two-dimensional phononic crystal structures. Numerical calculations of transmission spectra are conducted by extending the finite-difference-time-domain method to account for linear viscoelastic materials with time-dependent moduli. We study a phononic crystal constituted of a square array of cylindrical air inclusions in a solid viscoelastic matrix. The elastic properties of the solid are those of a silicone rubber. This system exhibits very wide band gaps in its transmission spectrum that extend to frequencies in the audible range of the spectrum. These gaps are characteristic of fluid matrix/air inclusion systems and result from the very large contrast between the longitudinal and transverse speeds of sound in rubber. By treating the matrix as a viscoelastic medium within the standard linear solid (SLS) model, we demonstrate that viscoelasticity impacts the transmission properties of the rubber/air phononic crystal not only by attenuating the transmitted acoustic waves but also by shifting the passing bands frequencies toward lower values. The ranges of frequencies exhibiting attenuation or frequency shift are determined by the value of the relaxation time in the SLS model. We show that viscoelasticity can be used to decrease the frequency of pass bands (and consequently stop bands) in viscoelastic/air phononic crystals

Effect of rotation on the onset of thermal convection in a viscoelastic fluid layer

Energy Technology Data Exchange (ETDEWEB)

Swamy, Mahantesh S [Department of Mathematics, Government College, Gulbarga 585 105 (India); Sidram, W, E-mail: mahantesh_swamy@yahoo.co.in [Department of Mathematics, Gulbarga University, Jnana Ganga, Gulbarga 585 106 (India)

2013-02-15

A rotating viscoelastic fluid layer heated from below is studied analytically using both linear and nonlinear stability analyses. The Oldroyd-B fluid model is employed to describe the rheological behaviour of the fluid. The Coriolis term is included in the momentum equation and the Oberbeck-Boussinesq approximation is invoked. The onset criterion for both stationary and oscillatory convection is derived as a function of Taylor number, Prandtl number and viscoelastic parameters. There is competition between the processes of rotation, viscous relaxation and thermal diffusion that causes the convection to set in through oscillatory rather than stationary modes. The rotation inhibits the onset of convection in both stationary and oscillatory modes. The stress relaxation parameter destabilizes the system towards the oscillatory mode, while the strain retardation parameter enhances the stability and this stabilization is reinforced by the rotation effect. The nonlinear theory is based on a truncated representation of the Fourier series method. The effect of rotation, viscoelastic parameters and also the Prandtl number on the transient heat transfer is presented graphically. (paper)

Characterization of the elastic and viscoelastic properties of dentin by a nanoindentation creep test.

Science.gov (United States)

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.

Postseismic viscoelastic surface deformation and stress. Part 1: Theoretical considerations, displacement and strain calculations

Science.gov (United States)

Cohen, S. C.

1979-01-01

A model of viscoelastic deformations associated with earthquakes is presented. A strike-slip fault is represented by a rectangular dislocation in a viscoelastic layer (lithosphere) lying over a viscoelastic half-space (asthenosphere). Deformations occur on three time scales. The initial response is governed by the instantaneous elastic properties of the earth. A slower response is associated with viscoelastic relaxation of the lithosphere and a yet slower response is due to viscoelastic relaxation of the asthenosphere. The major conceptual contribution is the inclusion of lithospheric viscoelastic properties into a dislocation model of earthquake related deformations and stresses. Numerical calculations using typical fault parameters reveal that the postseismic displacements and strains are small compared to the coseismic ones near the fault, but become significant further away. Moreover, the directional sense of the deformations attributable to the elastic response, the lithospheric viscoelastic softening, and the asthenospheric viscoelastic flow may differ and depend on location and model details. The results and theoretical arguments suggest that the stress changes accompanying lithospheric relaxation may also be in a different sense than and be larger than the strain changes.

3D Viscoelastic Traction Force Microscopy

Science.gov (United States)

Toyjanova, Jennet; Hannen, Erin; Bar-Kochba, Eyal; Darling, Eric M.; Henann, David L.; Franck, Christian

2014-01-01

Native cell-material interactions occur on materials differing in their structural composition, chemistry, and physical compliance. While the last two decades have shown the importance of traction forces during cell-material interactions, they have been almost exclusively presented on purely elastic in-vitro materials. Yet, most bodily tissue materials exhibit some level of viscoelasticity, which could play an important role in how cells sense and transduce tractions. To expand the realm of cell traction measurements and to encompass all materials from elastic to viscoelastic, this paper presents a general, and comprehensive approach for quantifying 3D cell tractions in viscoelastic materials. This methodology includes the experimental characterization of the time-dependent material properties for any viscoelastic material with the subsequent mathematical implementation of the determined material model into a 3D traction force microscopy (3D TFM) framework. Utilizing this new 3D viscoelastic TFM (3D VTFM) approach, we quantify the influence of viscosity on the overall material traction calculations and quantify the error associated with omitting time-dependent material effects, as is the case for all other TFM formulations. We anticipate that the 3D VTFM technique will open up new avenues of cell-material investigations on even more physiologically relevant time-dependent materials including collagen and fibrin gels. PMID:25170569

Estimation of viscoelastic parameters in Prony series from shear wave propagation

Energy Technology Data Exchange (ETDEWEB)

Jung, Jae-Wook; Hong, Jung-Wuk, E-mail: j.hong@kaist.ac.kr, E-mail: jwhong@alum.mit.edu [Department of Civil and Environmental Engineering, KAIST, 291 Deahak-ro, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Lee, Hyoung-Ki; Choi, Kiwan [Health and Medical Equipment, Samsung Electronics, 1003 Daechi-dong, Gangnam-gu, Seoul 135-280 (Korea, Republic of)

2016-06-21

When acquiring accurate ultrasonic images, we must precisely estimate the mechanical properties of the soft tissue. This study investigates and estimates the viscoelastic properties of the tissue by analyzing shear waves generated through an acoustic radiation force. The shear waves are sourced from a localized pushing force acting for a certain duration, and the generated waves travel horizontally. The wave velocities depend on the mechanical properties of the tissue such as the shear modulus and viscoelastic properties; therefore, we can inversely calculate the properties of the tissue through parametric studies.

Order, viscoelastic, and dielectric properties of symmetric and asymmetric alkyl[1]benzothieno[3,2-b][1]benzothiophenes.

Science.gov (United States)

Grigoriadis, Christos; Niebel, Claude; Ruzié, Christian; Geerts, Yves H; Floudas, George

2014-02-06

The morphology, the viscoelastic, the dielectric properties and the dynamics of phase transformation are studied in symmetrically and asymmetrically substituted alkyl[1]benzothieno[3,2-b][1]benzothiophenes (C8-BTBT) by X-ray scattering, rheology, and dielectric spectroscopy. The interlayer spacing reflects the molecular and supramolecular ordering, respectively, in the symmetrically and asymmetrically substituted BTBTs. In the asymmetric BTBT, the core layer is double in size with a broader network of intermolecular interactions though the increased S-S contacts that is prerequisite for the development of high performance OFET devices. Two crystal states with elastic and viscoelastic responses were identified in the symmetric compound. In contrast, the SmA phase in the asymmetric compound is a viscoelastic solid. A path-dependent dielectric environment with a switchable dielectric permittivity was found in both compounds by cooling below 0 °C with possible implications to charge transport. The kinetics of phase transformation to the crystalline and SmA phases revealed a nucleation and growth mechanism with rates dominated by the low activation barriers.

Dominant role of wormlike micelles in temperature-responsive viscoelastic properties of their mixtures with polymeric chains

KAUST Repository

Molchanov, Vyacheslav S.

2013-03-01

Temperature effects on the rheological properties of viscoelastic solutions containing entangled wormlike micelles of potassium oleate and hydrophobically modified polyacrylamide were studied in a wide range of polymer concentrations. A very pronounced drop of viscosity by four orders of magnitude was observed at heating from 20 to 78 °C both in the presence and in the absence of polymer indicating that the wormlike micelles are mainly responsible for this effect. The highly thermosensitive behavior was attributed to the shortening of micellar chains induced by heating. Although the decrease in viscosity is almost the same for both surfactant and surfactant/polymer systems, the absolute values of the viscosity in the presence of polymer are by few orders of magnitude higher, which is due to the formation of a common network of entangled polymer and micellar chains. As a result, the added polymer allows one to get highly temperature responsive system that keeps viscoelastic properties in a much wider range of temperatures, which makes it very promising for various practical applications. © 2012 Elsevier Inc.

A numerical method for reorientation of rotating tidally deformed viscoelastic bodies

NARCIS (Netherlands)

Hu, H.; van der Wal, W.; Vermeersen, L.L.A.

2017-01-01

Existing approaches for simulating the true polar wander (TPW) of a viscoelastic body can be divided into three categories: (i) a linear dynamic approach which uses the linearized Liouville equation (e.g., Wu and Peltier (1984) and Mitrovica et al. (2005)); (ii) a nonlinear dynamic approach which

Fully coupled heat conduction and deformation analyses of visco-elastic solids

KAUST Repository

Khan, Kamran; Muliana, Anastasia Hanifah

2012-01-01

the temperature in a viscoelastic body. The rate of stress relaxation (or the rate of creep) and the mechanical and physical properties of visco-elastic materials, such as polymers, vary with temperature. This study aims at understanding the effect of coupling

Viscoelasticity evaluation of rubber by surface reflection of supersonic wave.

Science.gov (United States)

Omata, Nobuaki; Suga, Takahiro; Furusawa, Hirokazu; Urabe, Shinichi; Kondo, Takeru; Ni, Qing-Qing

2006-12-22

The main characteristic of rubber is a viscoelasticity. So it is important to research the characteristic of the viscoelasticity of the high frequency band for the friction between a rubber material and the hard one with roughness, for instance, the tire and the road. As for the measurement of the viscoelasticity of rubber, DMA (dynamic mechanical analysis) is general. However, some problems are pointed out to the measurement of the high frequency band by DMA. Then, we evaluated the viscoelasticity characteristic by the supersonic wave measurement. However, attenuation of rubber is large, and when the viscoelasticity is measured by the supersonic wave therefore, it is inconvenient and limited in a past method by means of bottom reflection. In this report, we tried the viscoelasticity evaluation by the method of using complex surface reflection coefficient and we compared with the friction coefficient under wide-range friction velocity. As a result, some relationships had been found for two properties. We report the result that character of viscoelasticity of rubber was comparable to friction coefficient.

Using nonlinearity and spatiotemporal property modulation to control effective structural properties: dynamic rods

DEFF Research Database (Denmark)

Thomsen, Jon Juel; Blekhman, Iliya I.

2007-01-01

What are the effective properties of a generally nonlinear material or structure, whose local properties are modulated in both space and time? It has been suggested to use spatiotemporal modulation of structural properties to create materials and structures with adjustable effective properties......, and to call these dynamic materials or spatiotemporal composites. Also, according to theoretical predictions, structural nonlinearity enhances the possibilities of achieving specific effective properties. For example, with an elastic rod having cubical elastic nonlinearities, it seems possible to control......, and exemplified. Then simple approximate analytical expressions are derived for the effective wave speed and natural frequencies for one-dimensional wave propagation in a nonlinear elastic rod, where the spatiotemporal modulation is imposed as a high-frequency standing wave, supposed to be given. Finally the more...

Characterization and modeling of performance of Polymer Composites Reinforced with Highly Non-Linear Cellulosic Fibers

International Nuclear Information System (INIS)

Rozite, L; Joffe, R; Varna, J; Nyström, B

2012-01-01

The behaviour of highly non-linear cellulosic fibers and their composite is characterized. Micro-mechanisms occurring in these materials are identified. Mechanical properties of regenerated cellulose fibers and composites are obtained using simple tensile test. Material visco-plastic and visco-elastic properties are analyzed using creep tests. Two bio-based resins are used in this study – Tribest and EpoBioX. The glass and flax fiber composites are used as reference materials to compare with Cordenka fiber laminates.

Characterization and modeling of performance of Polymer Composites Reinforced with Highly Non-Linear Cellulosic Fibers

Science.gov (United States)

Rozite, L.; Joffe, R.; Varna, J.; Nyström, B.

2012-02-01

The behaviour of highly non-linear cellulosic fibers and their composite is characterized. Micro-mechanisms occurring in these materials are identified. Mechanical properties of regenerated cellulose fibers and composites are obtained using simple tensile test. Material visco-plastic and visco-elastic properties are analyzed using creep tests. Two bio-based resins are used in this study - Tribest and EpoBioX. The glass and flax fiber composites are used as reference materials to compare with Cordenka fiber laminates.

Effect of lime concentration on gelatinized maize starch dispersions properties.

Science.gov (United States)

Lobato-Calleros, C; Hernandez-Jaimes, C; Chavez-Esquivel, G; Meraz, M; Sosa, E; Lara, V H; Alvarez-Ramirez, J; Vernon-Carter, E J

2015-04-01

Maize starch was lime-cooked at 92 °C with 0.0-0.40% w/w Ca(OH)2. Optical micrographs showed that lime disrupted the integrity of insoluble remnants (ghosts) and increased the degree of syneresis of the gelatinized starch dispersions (GSD). The particle size distribution was monomodal, shifting to smaller sizes and narrower distributions with increasing lime concentration. X-ray patterns and FTIR spectra showed that crystallinity decreased to a minimum at lime concentration of 0.20% w/w. Lime-treated GSD exhibited thixotropic and viscoelastic behaviour. In the linear viscoelastic region the storage modulus was higher than the loss modulus, but a crossover between these moduli occurred in the non-linear viscoelastic region. The viscoelastic properties decreased with increased lime concentration. The electrochemical properties suggested that the amylopectin-rich remnants and the released amylose contained in the continuous matrix was firstly attacked by calcium ions at low lime levels (<0.20% w/w), disrupting the starch gel microstructure. Copyright © 2014 Elsevier Ltd. All rights reserved.

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

Science.gov (United States)

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.

Physico-chemical and viscoelastic properties of high pressure homogenized lemon peel fiber fraction suspensions obtained after sequential pectin extraction

NARCIS (Netherlands)

Willemsen, K.L.D.D.; Panozzo, A.; Moelants, K.; Debon, S.J.J.; Desmet, C.; Cardinaels, R.M.; Moldenaers, P.; Wallecan, J.; Hendrickx, M.E.G.

2017-01-01

The viscoelastic properties of high pressure homogenized lemon peel cell wall fiber suspensions, obtained after sequential selective pectin extraction, were investigated in the current study. For comparison, a general pectin extraction was additionally performed on lemon peel under acid thermal

Viscoelastic characterization of carbon fiber-epoxy composites by creep and creep rupture tests

International Nuclear Information System (INIS)

Farina, Luis Claudio

2009-01-01

One of the main requirements for the use of fiber-reinforced polymer matrix composites in structural applications is the evaluation of their behavior during service life. The warranties of the integrity of these structural components demand a study of the time dependent behavior of these materials due to viscoelastic response of the polymeric matrix and of the countless possibilities of design configurations. In the present study, creep and creep rupture test in stress were performed in specimens of unidirectional carbon fiber-reinforced epoxy composites with fibers orientations of 60 degree and 90 degree, at temperatures of 25 and 70 degree C. The aim is the viscoelastic characterization of the material through the creep curves to some levels of constant tension during periods of 1000 h, the attainment of the creep rupture envelope by the creep rupture curves and the determination of the transition of the linear for non-linear behavior through isochronous curves. In addition, comparisons of creep compliance curves with a viscoelastic behavior prediction model based on Schapery equation were also performed. For the test, a modification was verified in the behavior of the material, regarding the resistance, stiffness and deformation, demonstrating that these properties were affected for the time and tension level, especially in work temperature above the ambient. The prediction model was capable to represent the creep behavior, however the determination of the equations terms should be considered, besides the variation of these with the applied tension and the elapsed time of test. (author)

Calibration of trapping force and response function of optical tweezers in viscoelastic media

DEFF Research Database (Denmark)

Fischer, Mario; Berg-Sørensen, Kirstine

2007-01-01

, 594) is not possible as the viscoelastic properties of the bio-active medium are a priori unknown. Here, we present an approach that neither requires explicit assumptions about the size of the trapped particle nor about the viscoelastic properties of the medium. Instead, the interaction between...... the medium and the trapped particle is described in a general manner, through velocity and acceleration memory. Our method is applicable to general, at least locally homogeneous, viscoelastic media. The procedure combines active and passive approaches by the application of Onsager's regression hypothesis...

Gravitational Instability of Cylindrical Viscoelastic Medium ...

Indian Academy of Sciences (India)

similar to that of viscoelastic fluid where both properties work together. They also ... cylindrical gravitational waves provides a strong motivation in this regard. .... which represents the solenoidal character of the magnetic field and the total stress.

Influence of storage in the texture and viscoelasticity of buns of corn variety white Cariaco

Directory of Open Access Journals (Sweden)

José David Torres-González

2016-09-01

Full Text Available The objective was to determine the influence of storage time on the variation of texture and visco-elasticity of buns of corn of the white Cariaco variety. The samples were stored refrigerated at 15 °C during 15 days. Textural parameters were determined every two days, using a texture analyzer; viscoelastic properties were set by a test of relaxation and com-pression effort, adjusting the experimental data to the generalized Maxwell model. Also, to determine the model parameters described, an iterative process was performed by non-linear regression using least squares techniques damped by the Solver add-on in Excel 2013. The storage time influenced the texture profile of buns, and the increase of hardness from the eleventh day, which was attributed to moisture loss of the product during cooling. Chewiness was higher for longer storage time. Cohesiveness, adhesiveness and elasticity reported no significant differences with respect to storage time. Statistical differences were presented at initial and final relaxation speeds expressed in the Maxwell model. The experimental data were successfully fitted to the model (R2 > 0.95 which was statistically significant (p < 0.05 and the performance of the elastic module indicated that buns from the white Cariaco variety showed a characteristic behavior of a viscoelastic material, increasing its hardness during the days of storage.

Investigation of the rheological properties of human semen

Energy Technology Data Exchange (ETDEWEB)

Dunn, P.F. (Purdue Univ., West Lafayette, IN); Picologlou, B.F.

1977-01-01

The results of an investigation of the previously undetermined rheological properties of human semen using a modified, multiple-point capillary viscometer are presented. The design of a viscometer, specifically constructed to give accurate, instantaneous pressure gradient and material flow rate records of biological viscoelastic fluids whose rheological properties are possibly changing with time is given. Using this device, measurements are made on human semen immediately following ejaculation. An analytical scheme for the data reduction, suitable for non-linear viscoelastic fluids of the Maxwell-type, is offered. An expression is developed for a non-linear Maxwell-type viscoelastic fluid flow in a circular tube, relating the material's elastic properties to the distance of recoil and the pressure gradient. In the case of a power-law elastic behavior this relation couples the wall shear stress with the recoil distance through an apparent shear modulus. Previously established procedures for the viscous response analysis are utilized and an approximate non-dimensional parameter is introduced allowing one to ascertain the relative contributions of the elastic and viscous components to the rate of flow. Results show the elastic and viscous properties of human semen to be functions of time following ejaculation and frequency of ejaculation. The elastic component is found to have a linear response over the shear stress range investigated, whereas the viscous component is found to exhibit a power-law behavior. The final equilibrium state is characterized by Newtonian behavior, with mean absolute viscosity of 3.37 centipoise. Finally, similarity among all cases examined is found for each material property through consideration of a non-dimensional time, t*, determined from semen liquefaction time and time post ejaculation.

Damping Analysis of Cylindrical Composite Structures with Enhanced Viscoelastic Properties

Science.gov (United States)

Kliem, Mathias; Høgsberg, Jan; Vanwalleghem, Joachim; Filippatos, Angelos; Hoschützky, Stefan; Fotsing, Edith-Roland; Berggreen, Christian

2018-04-01

Constrained layer damping treatments are widely used in mechanical structures to damp acoustic noise and mechanical vibrations. A viscoelastic layer is thereby applied to a structure and covered by a stiff constraining layer. When the structure vibrates in a bending mode, the viscoelastic layer is forced to deform in shear mode. Thus, the vibration energy is dissipated as low grade frictional heat. This paper documents the efficiency of passive constrained layer damping treatments for low frequency vibrations of cylindrical composite specimens made of glass fibre-reinforced plastics. Different cross section geometries with shear webs have been investigated in order to study a beneficial effect on the damping characteristics of the cylinder. The viscoelastic damping layers are placed at different locations within the composite cylinder e.g. circumferential and along the neutral plane to evaluate the location-dependent efficiency of constrained layer damping treatments. The results of the study provide a thorough understanding of constrained layer damping treatments and an improved damping design of the cylindrical composite structure. The highest damping is achieved when placing the damping layer in the neutral plane perpendicular to the bending load. The results are based on free decay tests of the composite structure.

Viscoelastic property tuning for reducing noise radiated by switched-reluctance machines

Science.gov (United States)

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.

Effect of ionizing radiation on visco-elastic properties of polymethyl-methacrylate and poly-4-methylpentene-1

International Nuclear Information System (INIS)

Perepechko, I.I.; Mar'yasin, B.Ya.

1978-01-01

The effect of γ radiation on visco-elastic properties of polymethylmethacrylate (PMMA) and poly-4-methylpentene-1 (P4MPI) has been investigated by the method of the forced resonance oscillations of a cantilevered specimen. It has been shown, that the variation of the dynamic elasticity modulus of amorphous polymer when the irradiation dose increases, considerable depends on the polymer physical state during the measurement. The irradiated polymer is a binary mixture of radiolysis low-molecular products and polymer itself. The value of elasticity modulus in such a mixture is defined by the modules of different components. More complex than in PMMA in the effect of γ-radiation upon the P4MPI visco-elastic behaviour. During the P4MPI irradiation, the rebuilding of polymer supermolecular structure takes place, which results in the variation of the dynamic elasticity modulus values and in the intensity of peaks of mechanical losses

Curating viscoelastic properties of icosahedral viruses, virus-based nanomaterials, and protein cages.

Science.gov (United States)

Kant, Ravi; Rayaprolu, Vamseedhar; McDonald, Kaitlyn; Bothner, Brian

2018-06-01

The beauty, symmetry, and functionality of icosahedral virus capsids has attracted the attention of biologists, physicists, and mathematicians ever since they were first observed. Viruses and protein cages assemble into functional architectures in a range of sizes, shapes, and symmetries. To fulfill their biological roles, these structures must self-assemble, resist stress, and are often dynamic. The increasing use of icosahedral capsids and cages in materials science has driven the need to quantify them in terms of structural properties such as rigidity, stiffness, and viscoelasticity. In this study, we employed Quartz Crystal Microbalance with Dissipation technology (QCM-D) to characterize and compare the mechanical rigidity of different protein cages and viruses. We attempted to unveil the relationships between rigidity, radius, shell thickness, and triangulation number. We show that the rigidity and triangulation numbers are inversely related to each other and the comparison of rigidity and radius also follows the same trend. Our results suggest that subunit orientation, protein-protein interactions, and protein-nucleic acid interactions are important for the resistance to deformation of these complexes, however, the relationships are complex and need to be explored further. The QCM-D based viscoelastic measurements presented here help us elucidate these relationships and show the future prospect of this technique in the field of physical virology and nano-biotechnology.

Viscoelastic properties of graphene-based epoxy resins

Science.gov (United States)

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.

Viscoelastic properties of orthodontic adhesives used for lingual fixed retainer bonding.

Science.gov (United States)

Papadogiannis, D; Iliadi, A; Bradley, T G; Silikas, N; Eliades, G; Eliades, T

2017-01-01

To evaluate the viscoelastic properties of two experimental BPA-free and one BisGMA-based orthodontic resin composite adhesives for bonding fixed retainers. A commercially available BisGMA-based (TXA: Transbond LR) and two bisphenol A-free experimental adhesives (EXA and EXB) were included in the study. The viscoelastic behavior of the adhesives was evaluated under static and dynamic conditions at dry and wet states and at various temperatures (21, 37, 50°C). The parameters determined were shear modulus (G), Young's modulus (E) under static testing and storage modulus (G 1 ), loss tangent (tanδ) and dynamic viscosity (n*) under dynamic testing. Statistical analysis was performed by 2-way ANOVA and Bonferroni post-hoc tests (α=0.05). For static testing, a significant difference was found within material and storage condition variables and a significant interaction between the two independent variables (p<0.001 for G and E). EXA demonstrated the highest G and E values at 21°C/dry group. Dry specimens showed the highest G and E values, but with no significant difference from 21°C/wet specimens, except EXA in G. Wet storage at higher temperatures (37°C and 50°C) adversely affected all the materials to a degree ranging from 40 to 60% (p<0.001). For dynamic testing, a significant difference was also found in material and testing condition groups, with a significant interaction between the two independent variables (p<0.001 for G 1 and n*, p<0.01 for tanδ). Reduction in G 1 , and n* values, and increase in tanδ values were encountered at increased water temperatures. The apparent detrimental effect of high temperature on the reduction of properties of adhesives may contribute to the loss of stiffness of the fixed retainer configuration under ordinary clinical conditions with unfavorable effects on tooth position and stability of the orthodontic treatment result. Copyright © 2016 The Academy of Dental Materials. All rights reserved.

A mixed-effects model approach for the statistical analysis of vocal fold viscoelastic shear properties.

Science.gov (United States)

Xu, Chet C; Chan, Roger W; Sun, Han; Zhan, Xiaowei

2017-11-01

A mixed-effects model approach was introduced in this study for the statistical analysis of rheological data of vocal fold tissues, in order to account for the data correlation caused by multiple measurements of each tissue sample across the test frequency range. Such data correlation had often been overlooked in previous studies in the past decades. The viscoelastic shear properties of the vocal fold lamina propria of two commonly used laryngeal research animal species (i.e. rabbit, porcine) were measured by a linear, controlled-strain simple-shear rheometer. Along with published canine and human rheological data, the vocal fold viscoelastic shear moduli of these animal species were compared to those of human over a frequency range of 1-250Hz using the mixed-effects models. Our results indicated that tissues of the rabbit, canine and porcine vocal fold lamina propria were significantly stiffer and more viscous than those of human. Mixed-effects models were shown to be able to more accurately analyze rheological data generated from repeated measurements. Copyright © 2017 Elsevier Ltd. All rights reserved.

Engineering viscoelasticity

CERN Document Server

Gutierrez-Lemini, Danton

2014-01-01

Engineering Viscoelasticity covers all aspects of the thermo- mechanical response of viscoelastic substances that a practitioner in the field of viscoelasticity would need to design experiments, interpret test data, develop stress-strain models, perform stress analyses, design structural components, and carry out research work. The material in each chapter is developed from the elementary to the advanced, providing the background in mathematics and mechanics that are central to understanding the subject matter being presented. The book examines how viscoelastic materials respond to the application of loads, and provides practical guidelines to use them in the design of commercial, military and industrial applications. This book also: ·         Facilitates conceptual understanding by progressing in each chapter from elementary to challenging material ·         Examines in detail both differential and integral constitutive equations, devoting full chapters to each type and using both forms in ...

A boundary integral method for a dynamic, transient mode I crack problem with viscoelastic cohesive zone

KAUST Repository

Leise, Tanya L.; Walton, Jay R.; Gorb, Yuliya

2009-01-01

interpenetration, in contrast to the usual mode I boundary conditions that assume all unloaded crack faces are stress-free. The nonlinear viscoelastic cohesive zone behavior is motivated by dynamic fracture in brittle polymers in which crack propagation

Investigating Linear and Nonlinear Viscoelastic behaviour and microstructures of Gelatine-Multiwalled carbon nanotubes composites

KAUST Repository

Yang, Zhi

2015-12-01

We have investigated the linear and nonlinear rheology of various gelatine-multiwalled carbon nanotube (gel-MWNT) composites, namely physically-crosslinked-gelatine gel-MWNT composites, chemically-crosslinked-gelatine gel-MWNT composites, and chemically-physically-crosslinked-gelatine gel-MWNT composites. Further, the internal structures of these gel-MWNT composites were characterized by ultra-small angle neutron scattering and scanning electron microscopy. The adsorption of gelatine onto the surface of MWNT is also investigated to understand gelatine-assisted dispersion of MWNT during ultrasonication. For all gelatine gels, addition of MWNT increases their complex modulus. The dependence of storage modulus with frequency for gelatine-MWNT composites is similar to that of the corresponding neat gelatine matrix. However, by incorporating MWNT, the dependence of the loss modulus on frequency is reduced. The linear viscoelastic region is decreased approximately linearly with the increase of MWNT concentration. The pre-stress results demonstrate that the addition of MWNT does not change the strain-hardening behaviour of physically-crosslinked gelatine gel. However, the addition of MWNT can increase the strain-hardening behaviour of chemically-crosslinked gelatine gel, and chemically-physically crosslinked gelatine gel. Results from light microscopy, cryo-SEM, and USANS demonstrate the hierarchical structures of MWNT, including that tens-of-micron scale MWNT agglomerates are present. Furthermore, the adsorption curve of gelatine onto the surface of MWNT follows two-stage pseudo-saturation behaviour.

Modeling Non-Linear Material Properties in Composite Materials

Science.gov (United States)

2016-06-28

Technical Report ARWSB-TR-16013 MODELING NON-LINEAR MATERIAL PROPERTIES IN COMPOSITE MATERIALS Michael F. Macri Andrew G...REPORT TYPE Technical 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE MODELING NON-LINEAR MATERIAL PROPERTIES IN COMPOSITE MATERIALS ...systems are increasingly incorporating composite materials into their design. Many of these systems subject the composites to environmental conditions

Process-induced viscoelastic stress in composite laminates

International Nuclear Information System (INIS)

Stango, R.J.

1985-01-01

In recent years, considerable interest has developed in evaluating the stress response of composite laminates which is associated with cooling the material system from the cure temperature to room temperature. This research examines the fundamental nature of time-dependent residual-thermal stresses in composite laminates which are caused by the extreme temperature reduction encountered during the fabrication process. Viscoelastic stress in finite-width, symmetric composite laminates is examined on the basis of a formulation that employs an incremental hereditary integral approach in conjunction with a quasi-three dimensional finite element analysis. A consistent methodology is developed and employed for the characterization of lamina material properties. Special attention is given to the time-dependent stress response at ply-interface locations near the free-edge. In addition, the influence of cooling path on stress history is examined. Recently published material property data for graphite-epoxy lamina is employed in the analysis. Results of the investigation generally indicate that nominal differences between the thermoelastic and viscoelastic solutions are obtained. Slight changes of the final stress state are observed to result when different cooling paths are selected for the temperature history. The methodology employed is demonstrated to result in an accurate, efficient, and consistent approach for the viscoelastic analysis of advanced composite laminates

A boundary integral method for a dynamic, transient mode I crack problem with viscoelastic cohesive zone

KAUST Repository

Leise, Tanya L.

2009-08-19

We consider the problem of the dynamic, transient propagation of a semi-infinite, mode I crack in an infinite elastic body with a nonlinear, viscoelastic cohesize zone. Our problem formulation includes boundary conditions that preclude crack face interpenetration, in contrast to the usual mode I boundary conditions that assume all unloaded crack faces are stress-free. The nonlinear viscoelastic cohesive zone behavior is motivated by dynamic fracture in brittle polymers in which crack propagation is preceeded by significant crazing in a thin region surrounding the crack tip. We present a combined analytical/numerical solution method that involves reducing the problem to a Dirichlet-to-Neumann map along the crack face plane, resulting in a differo-integral equation relating the displacement and stress along the crack faces and within the cohesive zone. © 2009 Springer Science+Business Media B.V.

Vibration analysis of viscoelastic single-walled carbon nanotubes resting on a viscoelastic foundation

International Nuclear Information System (INIS)

Zhang, Da Peng; Lei, Yong Jun; Shen, Zhi Bin; Wang, Cheng Yuan

2017-01-01

Vibration responses were investigated for a viscoelastic Single-walled carbon nanotube (visco-SWCNT) resting on a viscoelastic foundation. Based on the nonlocal Euler-Bernoulli beam model, velocity-dependent external damping and Kelvin viscoelastic foundation model, the governing equations were derived. The Transfer function method (TFM) was then used to compute the natural frequencies for general boundary conditions and foundations. In particular, the exact analytical expressions of both complex natural frequencies and critical viscoelastic parameters were obtained for the Kelvin-Voigt visco-SWCNTs with full foundations and certain boundary conditions, and several physically intuitive special cases were discussed. Substantial nonlocal effects, the influence of geometric and physical parameters of the SWCNT and the viscoelastic foundation were observed for the natural frequencies of the supported SWCNTs. The study demonstrates the efficiency and robustness of the developed model for the vibration of the visco-SWCNT-viscoelastic foundation coupling system

Skin mechanical properties and modeling: A review.

Science.gov (United States)

Joodaki, Hamed; Panzer, Matthew B

2018-04-01

The mechanical properties of the skin are important for various applications. Numerous tests have been conducted to characterize the mechanical behavior of this tissue, and this article presents a review on different experimental methods used. A discussion on the general mechanical behavior of the skin, including nonlinearity, viscoelasticity, anisotropy, loading history dependency, failure properties, and aging effects, is presented. Finally, commonly used constitutive models for simulating the mechanical response of skin are discussed in the context of representing the empirically observed behavior.

MECHANICAL BEHAVIOR OF PRESTRESSED VISCOELASTIC ADHESIVE AREAS UNDER COMBINING LOADINGS

Directory of Open Access Journals (Sweden)

Halil Murat Enginsoy

2017-12-01

Full Text Available In this article, mechanical behaviors of adhesive tape VHB 4950 elastomeric material, which is an element of acrylic polymer group and which is in viscoelastic behavior, under different pre-stress conditions and complex forces of different geometric parameters created by combining loadings have been experimentally and numerically investigated. In experimental studies, loading-unloading cyclic tests, one of the different standardized tests for the mechanical characterization of viscoelastic material, have been applied which give the most suitable convergent optimization parameters for the finite element model. Different material models were also investigated by using the data obtained from loading-unloading test results in all numerical models. According to the experimental results, the most suitable material parameters were determined with the Abaqus Parallel Rheological Framework Model (PRF for 4 Yeoh Networks with Bergstrom-Boyce Flow model created in the Mcalibration software for finite element analysis. Subsequently, using these material parameters, finite element analysis was performed as three dimension non-linear viscoelastic with a commercial finite element software Abaqus. The finite element analysis results showed good correlation to the Force (N-Displacement (mm experimental data for maximum load-carrying capacity of structural specimens.

Floquet stability analysis of viscoelastic flow over a cylinder

KAUST Repository

Richter, David

2011-06-01

A Floquet linear stability analysis has been performed on a viscoelastic cylinder wake. The FENE-P model is used to represent the non-Newtonian fluid, and the analysis is done using a modified version of an existing nonlinear code to compute the linearized initial value problem governing the growth of small perturbations in the wake. By measuring instability growth rates over a wide range of disturbance spanwise wavenumbers α, the effects of viscoelasticity were identified and compared directly to Newtonian results.At a Reynolds number of 300, two unstable bands exist over the range 0. ≤ α≤ 10 for Newtonian flow. For the low α band, associated with the "mode A" wake instability, a monotonic reduction in growth rates is found for increasing polymer extensibility L. For the high α band, associated with the "mode B" instability, first a rise, then a significant decrease to a stable state is found for the instability growth rates as L is increased from L= 10 to L= 30. The mechanism behind this stabilization of both mode A and mode B instabilities is due to the change of the base flow, rather than a direct effect of viscoelasticity on the perturbation. © 2011 Elsevier B.V.

Floquet stability analysis of viscoelastic flow over a cylinder

KAUST Repository

Richter, David; Shaqfeh, Eric S.G.; Iaccarino, Gianluca

2011-01-01

A Floquet linear stability analysis has been performed on a viscoelastic cylinder wake. The FENE-P model is used to represent the non-Newtonian fluid, and the analysis is done using a modified version of an existing nonlinear code to compute the linearized initial value problem governing the growth of small perturbations in the wake. By measuring instability growth rates over a wide range of disturbance spanwise wavenumbers α, the effects of viscoelasticity were identified and compared directly to Newtonian results.At a Reynolds number of 300, two unstable bands exist over the range 0. ≤ α≤ 10 for Newtonian flow. For the low α band, associated with the "mode A" wake instability, a monotonic reduction in growth rates is found for increasing polymer extensibility L. For the high α band, associated with the "mode B" instability, first a rise, then a significant decrease to a stable state is found for the instability growth rates as L is increased from L= 10 to L= 30. The mechanism behind this stabilization of both mode A and mode B instabilities is due to the change of the base flow, rather than a direct effect of viscoelasticity on the perturbation. © 2011 Elsevier B.V.

Anisotropy in the viscoelastic response of knee meniscus cartilage.

Science.gov (United States)

Coluccino, Luca; Peres, Chiara; Gottardi, Riccardo; Bianchini, Paolo; Diaspro, Alberto; Ceseracciu, Luca

2017-01-26

The knee meniscus is instrumental to stability, shock absorption, load transmission and stress distribution within the knee joint. Such functions are mechanically demanding, and replacement constructs used in meniscus repair often fail because of a poor match with the surrounding tissue. This study focused on the native structure-mechanics relationships and on their anisotropic behavior in meniscus, to define the target biomechanical viscoelastic properties required by scaffolds upon loading. To show regional orientation of the collagen fibers and their viscoelastic behavior, bovine lateral menisci were characterized by second harmonic generation microscopy and through time-dependent mechanical tests. Furthermore, their dynamic viscoelastic response was analyzed over a wide range of frequencies. Multilevel characterization aims to expand the biomimetic approach from the structure itself, to include the mechanical characteristics that give the meniscus its peculiar properties, thus providing tools for the design of novel, effective scaffolds. An example of modeling of anisotropic open-cell porous material tailored to fulfill the measured requirements is presented, leading to a definition of additional parameters for a better understanding of the load transmission mechanism and for better scaffold functionality.

Stationary responses of a Rayleigh viscoelastic system with zero barrier impacts under external random excitation.

Science.gov (United States)

Wang, Deli; Xu, Wei; Zhao, Xiangrong

2016-03-01

This paper aims to deal with the stationary responses of a Rayleigh viscoelastic system with zero barrier impacts under external random excitation. First, the original stochastic viscoelastic system is converted to an equivalent stochastic system without viscoelastic terms by approximately adding the equivalent stiffness and damping. Relying on the means of non-smooth transformation of state variables, the above system is replaced by a new system without an impact term. Then, the stationary probability density functions of the system are observed analytically through stochastic averaging method. By considering the effects of the biquadratic nonlinear damping coefficient and the noise intensity on the system responses, the effectiveness of the theoretical method is tested by comparing the analytical results with those generated from Monte Carlo simulations. Additionally, it does deserve attention that some system parameters can induce the occurrence of stochastic P-bifurcation.

Impact load time histories for viscoelastic missiles

International Nuclear Information System (INIS)

Stoykovich, M.

1977-01-01

Generation of the impact load time history at the contact point between a viscoelastic missile and its targets is presented. In the past, in the case of aircraft striking containment shell structure, the impact load history was determined on the basis of actual measurements by subjecting a rigid wall to aircraft crash. The effects of elastic deformation of the target upon the impact load time history is formulated in this paper. The missile is idealized by a linear mass-spring-dashpot combination using viscoelastic models. These models can readily be processed taking into account the elastic as well as inelastic deformations of the missiles. The target is assumed to be either linearly elastic or rigid. In the case of the linearly elastic target, the normal mode theory is used to express the time-dependent displacements of the target which is simulated by lumped masses, elastic properties and dashpots in discrete parts. In the case of Maxwell viscoelastic model, the time-dependent displacements of the missile and the target are given in terms of the unknown impact load time history. This leads to an integral equation which may be solved by Laplace transformation. The normal mode theory is provided. Examples are given for bricks with viscoelastic materials as missiles against a rigid target. (Auth.)

Static viscoelasticity of biomass polyethylene composites

Directory of Open Access Journals (Sweden)

Keyan Yang

Full Text Available The biomass polyethylene composites filled with poplar wood flour, rice husk, cotton stalk or corn stalk were prepared by extrusion molding. The static viscoelasticity of composites was investigated by the dynamic thermal mechanical analyzer (DMA. Through the stress-strain scanning, it is found that the linear viscoelasticity interval of composites gradually decreases as the temperature rises, and the critical stress and strain values are 0.8 MPa and 0.03% respectively. The experiment shows that as the temperature rises, the creep compliance of biomass polyethylene composites is increased; under the constant temperature, the creep compliance decreases with the increase of content of biomass and calcium carbonate. The biomass and calcium carbonate used to prepare composites as filler can improve damping vibration attenuation and reduce stress deformation of composites. The stress relaxation modulus of composites is reduced and the relaxation rate increases at the higher temperature. The biomass and calcium carbonate used to prepare composites as filler not only can reduce costs, but also can increase stress relaxation modulus and improve the size thermostability of composites. The corn stalk is a good kind of biomass raw material for composites since it can improve the creep resistance property and the stress relaxation resistance property of composites more effectively than other three kinds of biomass (poplar wood flour, rice husk and cotton stalk. Keywords: Biomass, Composites, Calcium carbonate, Static viscoelasticity, Creep, Stress relaxation

Numerical study of propagation properties of surface plasmon polaritons in nonlinear media

KAUST Repository

Sagor, Rakibul Hasan

2016-03-29

We present a time-domain algorithm for simulating nonlinear propagation of surface plasmon polaritons (SPPs) in chalcogenide glass. Due to the high non-linearity property and strong dispersion and confinement chalcogenide glasses are widely known as ultrafast nonlinear materials. We have used the finite difference time domain (FDTD) method to develop the simulation algorithm for the current analysis. We have modeled the frequency dependent dispersion properties and third order nonlinearity property of chalcogenide glass utilizing the general polarization algorithm merged in the auxiliary differential equation (ADE) method. The propagation dynamics of the whole structure with and without third order nonlinearity property of chalcogenide glass have been simulated and the effect of nonlinearity on the propagation properties of SPP has been investigated. © 2016 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

Comparative study of viscoelastic properties using virgin yogurt

International Nuclear Information System (INIS)

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

1998-01-01

We describe six different tests used to obtain a consistent set of viscoelastic properties for yogurt. Prior to yield, the shear modulus μ and viscosity η 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's crust. The resultant shear modulus agrees with μ∼E/3 for incompressible materials, where the Young's modulus E is obtained from a stress - strain curve in compression. The tensile yield stress τ o is measured in compression and tension, with good agreement. The conventional vane and cone/plate rheometers measured a shear stress yield τ os ∼τ o /√ (3) , as expected theoretically, but the inferred 'apparent' viscosity from the cone/plate rheometer is much larger than the wave measurement due to the finite yield (τ os ≠0). Finally, we inverted an open container of yogurt for 10 6 s>η/μ 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 1998 Society of Rheology

Human amniotic epithelial cell transplantation for the repair of injured brachial plexus nerve: evaluation of nerve viscoelastic properties

Directory of Open Access Journals (Sweden)

Hua Jin

2015-01-01

Full Text Available 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 properties 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 C 6 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 C 6 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 C 6 brachial plexus nerve were mitigated by the cell transplantation, restoring the viscoelastic stress relaxation and creep properties 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 properties of the brachial plexus nerve after injury in rabbits and that viscoelasticity may be an important index for the evaluation of brachial plexus injury in animals.

Relativistic viscoelastic fluid mechanics

International Nuclear Information System (INIS)

Fukuma, Masafumi; Sakatani, Yuho

2011-01-01

A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.

Relativistic viscoelastic fluid mechanics.

Science.gov (United States)

Fukuma, Masafumi; Sakatani, Yuho

2011-08-01

A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.

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

Science.gov (United States)

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.

Finite element reduction strategy for composite sandwich plates with viscoelastic layers

Directory of Open Access Journals (Sweden)

Adriana Amaro Diacenco

2013-04-01

Full Text Available Composite materials have been regarded as a convenient strategy in various types of engineering systems such as aeronautical and space structures, as well as architecture and light industry products due to their advantages over the traditional engineering materials, such as their high strength/stiffness relation characteristics and their anti-corrosion properties. This paper is devoted to the finite element modeling of composite laminated structures incorporating viscoelastic materials to the problem of vibration attenuation. However, the typically high dimension of large finite element models of composite structures incorporating viscoelastic materials makes the numerical processes sometimes unfeasible. Within this context, emphasis is placed on a general condensation strategy specially adapted for the case of viscoelastically damped structures, in which a constant (frequency- and temperature-independent reduction basis to be enriched by static residues associated to the applied loads and the viscoelastic forces is used. After presenting the theoretical foundations, the numerical applications of composite plates treated by viscoelastic materials are addressed, and the main features of the methodology are discussed.

Finite element reduction strategy for composite sandwich plates with viscoelastic layers

Directory of Open Access Journals (Sweden)

Adriana Amaro Diacenco

2012-01-01

Full Text Available Composite materials have been regarded as a convenient strategy in various types of engineering systems such as aeronautical and space structures, as well as architecture and light industry products due to their advantages over the traditional engineering materials, such as their high strength/stiffness relation characteristics and their anti-corrosion properties. This paper is devoted to the finite element modeling of composite laminated structures incorporating viscoelastic materials to the problem of vibration attenuation. However, the typically high dimension of large finite element models of composite structures incorporating viscoelastic materials makes the numerical processes sometimes unfeasible. Within this context, emphasis is placed on a general condensation strategy specially adapted for the case of viscoelastically damped structures, in which a constant (frequency- and temperature-independent reduction basis to be enriched by static residues associated to the applied loads and the viscoelastic forces is used. After presenting the theoretical foundations, the numerical applications of composite plates treated by viscoelastic materials are addressed, and the main features of the methodology are discussed.

Effective properties of linear viscoelastic heterogeneous media: Internal variables formulation and extension to ageing behaviours

International Nuclear Information System (INIS)

Ricaud, J.M.; Masson, R.; Masson, R.

2009-01-01

The Laplace-Carson transform classically used for homogenization of linear viscoelastic heterogeneous media yields integral formulations of effective behaviours. These are far less convenient than internal variables formulations with respect to computational aspects as well as to theoretical extensions to closely related problems such as ageing viscoelasticity. Noticing that the collocation method is usually adopted to invert the Laplace-Carson transforms, we first remark that this approximation is equivalent to an internal variables formulation which is exact in some specific situations. This result is illustrated for a two-phase composite with phases obeying a compressible Maxwellian behaviour. Next, an incremental formulation allows to extend at each time step the previous general framework to ageing viscoelasticity. Finally, with the help of a creep test of a porous viscoelastic matrix reinforced with elastic inclusions, it is shown that the method yields accurate predictions (comparing to reference results provided by periodic cell finite element computations). (authors)

Analysis of Blood Flow Through a Viscoelastic Artery using the Cosserat Continuum with the Large-Amplitude Oscillatory Shear Deformation Model

DEFF Research Database (Denmark)

Sedaghatizadeh, N.; Atefi, G.; Fardad, A. A.

2011-01-01

In this investigation, semiempirical and numerical studies of blood flow in a viscoelastic artery were performed using the Cosserat continuum model. The large-amplitude oscillatory shear deformation model was used to quantify the nonlinear viscoelastic response of blood flow. The finite differenc...... method was used to solve the governing equations, and the particle swarm optimization algorithm was utilized to identify the non-Newtonian coefficients (kυ and γυ). The numerical results agreed well with previous experimental results....

Measurement of tissue viscoelasticity with ultrasound

Science.gov (United States)

Greenleaf, J. F.; Alizad, A.

2017-02-01

Tissue properties such as elasticity and viscosity have been shown to be related to such tissue conditions as contraction, edema, fibrosis, and fat content among others. Magnetic Resonance Elastography has shown outstanding ability to measure the elasticity and in some cases the viscosity of tissues, especially in the liver, providing the ability to stage fibrotic liver disease similarly to biopsy. We discuss ultrasound methods of measuring elasticity and viscosity in tissues. Many of these methods are becoming widely available in the extant ultrasound machines distributed throughout the world. Some of the methods to be discussed are in the developmental stage. The advantages of the ultrasound methods are that the imaging instruments are widely available and that many of the viscoelastic measurements can be made during a short addition to the normal ultrasound examination time. In addition, the measurements can be made by ultrasound repetitively and quickly allowing evaluation of dynamic physiologic function in circumstances such as muscle contraction or artery relaxation. Measurement of viscoelastic tissue mechanical properties will become a consistent part of clinical ultrasound examinations in our opinion.

Local linear viscoelasticity of confined fluids.

Science.gov (United States)

Hansen, J S; Daivis, P J; Todd, B D

2007-04-14

In this paper the authors propose a novel method to study the local linear viscoelasticity of fluids confined between two walls. The method is based on the linear constitutive equation and provides details about the real and imaginary parts of the local complex viscosity. They apply the method to a simple atomic fluid undergoing zero mean oscillatory flow using nonequilibrium molecular dynamics simulations. The method shows that the viscoelastic properties of the fluid exhibit dramatic spatial changes near the wall-fluid boundary due to the high density in this region. It is also shown that the real part of the viscosity converges to the frequency dependent local shear viscosity sufficiently far away from the wall. This also provides valuable information about the transport properties in the fluid, in general. The viscosity is compared with predictions from the local average density model. The two methods disagree in that the local average density model predicts larger viscosity variations near the wall-fluid boundary than what is observed through the method presented here.

Alteration of brain viscoelasticity after shunt treatment in normal pressure hydrocephalus

Energy Technology Data Exchange (ETDEWEB)

Freimann, Florian Baptist; Sprung, Christian [Charite - University Medicine Berlin, Campus Virchow-Klinikum, Neurosurgical Department, Berlin (Germany); Streitberger, Kaspar-Josche; Klatt, Dieter; Sack, Ingolf [Charite - University Medicine Berlin, Campus Charite Mitte, Department of Radiology, Berlin (Germany); Lin, Kui; McLaughlin, Joyce [Rensselaer Polytechnic Institute, Mathematics Department, Troy, NY (United States); Braun, Juergen [Charite - University Medicine Campus Benjamin Franklin, Institute of Medical Informatics, Berlin (Germany)

2012-03-15

Normal pressure hydrocephalus (NPH) represents a chronic neurological disorder with increasing incidence. The symptoms of NPH may be relieved by surgically implanting a ventriculoperitoneal shunt to drain excess cerebrospinal fluid. However, the pathogenesis of NPH is not yet fully elucidated, and the clinical response of shunt treatment is hard to predict. According to current theories of NPH, altered mechanical properties of brain tissue seem to play an important role. Magnetic resonance elastography (MRE) is a unique method for measuring in vivo brain mechanics. In this study cerebral MRE was applied to test the viscoelastic properties of the brain in 20 patients with primary (N = 14) and secondary (N = 6) NPH prior and after (91 {+-} 16 days) shunt placement. Viscoelastic parameters were derived from the complex modulus according to the rheological springpot model. This model provided two independent parameters {mu} and {alpha}, related to the inherent rigidity and topology of the mechanical network of brain tissue. The viscoelastic parameters {mu} and {alpha} were found to be decreased with -25% and -10%, respectively, compared to age-matched controls (P < 0.001). Interestingly, {alpha} increased after shunt placement (P < 0.001) to almost normal values whereas {mu} remained symptomatically low. The results indicate the fundamental role of altered viscoelastic properties of brain tissue during disease progression and tissue repair in NPH. Clinical improvement in NPH is associated with an increasing complexity of the mechanical network whose inherent strength, however, remains degraded. (orig.)

Alteration of brain viscoelasticity after shunt treatment in normal pressure hydrocephalus

International Nuclear Information System (INIS)

Freimann, Florian Baptist; Sprung, Christian; Streitberger, Kaspar-Josche; Klatt, Dieter; Sack, Ingolf; Lin, Kui; McLaughlin, Joyce; Braun, Juergen

2012-01-01

Normal pressure hydrocephalus (NPH) represents a chronic neurological disorder with increasing incidence. The symptoms of NPH may be relieved by surgically implanting a ventriculoperitoneal shunt to drain excess cerebrospinal fluid. However, the pathogenesis of NPH is not yet fully elucidated, and the clinical response of shunt treatment is hard to predict. According to current theories of NPH, altered mechanical properties of brain tissue seem to play an important role. Magnetic resonance elastography (MRE) is a unique method for measuring in vivo brain mechanics. In this study cerebral MRE was applied to test the viscoelastic properties of the brain in 20 patients with primary (N = 14) and secondary (N = 6) NPH prior and after (91 ± 16 days) shunt placement. Viscoelastic parameters were derived from the complex modulus according to the rheological springpot model. This model provided two independent parameters μ and α, related to the inherent rigidity and topology of the mechanical network of brain tissue. The viscoelastic parameters μ and α were found to be decreased with -25% and -10%, respectively, compared to age-matched controls (P < 0.001). Interestingly, α increased after shunt placement (P < 0.001) to almost normal values whereas μ remained symptomatically low. The results indicate the fundamental role of altered viscoelastic properties of brain tissue during disease progression and tissue repair in NPH. Clinical improvement in NPH is associated with an increasing complexity of the mechanical network whose inherent strength, however, remains degraded. (orig.)

The effect of viscoelasticity on the stability of a pulmonary airway liquid layer

Science.gov (United States)

Halpern, David; Fujioka, Hideki; Grotberg, James B.

2010-01-01

The lungs consist of a network of bifurcating airways that are lined with a thin liquid film. This film is a bilayer consisting of a mucus layer on top of a periciliary fluid layer. Mucus is a non-Newtonian fluid possessing viscoelastic characteristics. Surface tension induces flows within the layer, which may cause the lung's airways to close due to liquid plug formation if the liquid film is sufficiently thick. The stability of the liquid layer is also influenced by the viscoelastic nature of the liquid, which is modeled using the Oldroyd-B constitutive equation or as a Jeffreys fluid. To examine the role of mucus alone, a single layer of a viscoelastic fluid is considered. A system of nonlinear evolution equations is derived using lubrication theory for the film thickness and the film flow rate. A uniform film is initially perturbed and a normal mode analysis is carried out that shows that the growth rate g for a viscoelastic layer is larger than for a Newtonian fluid with the same viscosity. Closure occurs if the minimum core radius, Rmin(t), reaches zero within one breath. Solutions of the nonlinear evolution equations reveal that Rmin normally decreases to zero faster with increasing relaxation time parameter, the Weissenberg number We. For small values of the dimensionless film thickness parameter ɛ, the closure time, tc, increases slightly with We, while for moderate values of ɛ, ranging from 14% to 18% of the tube radius, tc decreases rapidly with We provided the solvent viscosity is sufficiently small. Viscoelasticity was found to have little effect for ɛ >0.18, indicating the strong influence of surface tension. The film thickness parameter ɛ and the Weissenberg number We also have a significant effect on the maximum shear stress on tube wall, max(τw), and thus, potentially, an impact on cell damage. Max(τw) increases with ɛ for fixed We, and it decreases with increasing We for small We provided the solvent viscosity parameter is sufficiently

Application of Linear Viscoelastic Properties in Semianalytical Finite Element Method with Recursive Time Integration to Analyze Asphalt Pavement Structure

Directory of Open Access Journals (Sweden)

Pengfei Liu

2018-01-01

Full Text Available Traditionally, asphalt pavements are considered as linear elastic materials in finite element (FE method to save computational time for engineering design. However, asphalt mixture exhibits linear viscoelasticity at small strain and low temperature. Therefore, the results derived from the elastic analysis will inevitably lead to discrepancies from reality. Currently, several FE programs have already adopted viscoelasticity, but the high hardware demands and long execution times render them suitable primarily for research purposes. Semianalytical finite element method (SAFEM was proposed to solve the abovementioned problem. The SAFEM is a three-dimensional FE algorithm that only requires a two-dimensional mesh by incorporating the Fourier series in the third dimension, which can significantly reduce the computational time. This paper describes the development of SAFEM to capture the viscoelastic property of asphalt pavements by using a recursive formulation. The formulation is verified by comparison with the commercial FE software ABAQUS. An application example is presented for simulations of creep deformation of the asphalt pavement. The investigation shows that the SAFEM is an efficient tool for pavement engineers to fast and reliably predict asphalt pavement responses; furthermore, the SAFEM provides a flexible, robust platform for the future development in the numerical simulation of asphalt pavements.

Nonlinear electrorheological instability of two Rivlin-Ericksen elastico-viscous fluids

CERN Document Server

El-Dib, Y O

2003-01-01

The behaviour of surface waves propagating between two Rivlin-Ericksen elastico-viscous fluids is examined. The investigation is made in the presence of a vertical electric field and a relative horizontal constant velocity. The influence of both surface tension and gravity force is taken into account. Due to the inclusion of streaming flow a mathematical simplification is considered. The viscoelastic contribution is demonstrated in the boundary conditions. From this point of view the approximation equations of motion are solved in the absence of viscoelastic effects. The solutions of the linearized equations of motion under nonlinear boundary conditions lead to derivation of a nonlinear equation governing the interfacial displacement and having damping terms with complex coefficients. This equation is accomplished by utilizing the cubic nonlinearity. The use of the Gardner-Morikawa transformation yields a simplified linear dispersion relation so that the periodic solution for the linear form is utilized. The ...

Viscoelastic behavior of discrete human collagen fibrils

DEFF Research Database (Denmark)

Svensson, Rene; Hassenkam, Tue; P, Hansen

2010-01-01

Whole tendon and fibril bundles display viscoelastic behavior, but to the best of our knowledge this property has not been directly measured in single human tendon fibrils. In the present work an atomic force microscopy (AFM) approach was used for tensile testing of two human patellar tendon fibr...

Experimental Viscoelastic Characterization of Corn Cob Composited ...

African Journals Online (AJOL)

The nature of viscoelasticity in biomateria1s and the techniques for characterizing their rheological properties were reviewed. Relaxation tests were performed with cylindrical samples of corn cob composites which were initially subjected to radial compression. It was found that a Maxwell model composed of two simple ...

Nonlinear transport properties of non-ideal systems

International Nuclear Information System (INIS)

Pavlov, G A

2009-01-01

The theory of nonlinear transport is elaborated to determine the Burnett transport properties of non-ideal multi-element plasma and neutral systems. The procedure for the comparison of the phenomenological conservation equations of a continuous dense medium and the microscopic equations for dynamical variable operators is used for the definition of these properties. The Mori algorithm is developed to derive the equations of motion of dynamical value operators of a non-ideal system in the form of the generalized nonlinear Langevin equations. In consequence, the microscopic expressions of transport coefficients corresponding to second-order thermal disturbances (temperature, mass velocity, etc) have been found in the long wavelength and low frequency limits

A study on creep properties of laminated rubber bearings. Pt. 1. Creep properties and numerical simulations of thick rubber bearings

International Nuclear Information System (INIS)

Matsuda, Akihiro; Yabana, Shuichi

2000-01-01

In this report, to evaluate creep properties and effects of creep deformation on mechanical properties of thick rubber bearings for three-dimensional isolation system, we show results of compression creep test for rubber bearings of various rubber materials and shapes and development of numerical simulation method. Creep properties of thick rubber bearings were obtained from compression creep tests. The creep strain shows steady creep that have logarithmic relationships between strain and time and accelerated creep that have linear relationships. We make numerical model of a rubber material with nonlinear viscoelastic constitutional equations. Mechanical properties after creep loading test are simulated with enough accuracy. (author)

Geometrically nonlinear transient vibrations of actively damped anti-symmetric angle ply laminated composite shallow shell using active fibre composite (AFC) actuators

Science.gov (United States)

Ashok, M. H.; Shivakumar, J.; Nandurkar, Santosh; Khadakbhavi, Vishwanath; Pujari, Sanjay

2018-02-01

In present work, the thin laminated composite shallow shell as smart structure with AFC material’s ACLD treatment is analyzed for geometrically nonlinear transient vibrations. The AFC material is used to make the constraining layer of the ACLD treatment. Golla-Hughes-McTavish (GHM) is used to model the constrained viscoelastic layer of the ACLD treatment in time domain. Along with a simple first-order shear deformation theory the Von Kármán type non-linear strain displacement relations are used for deriving this electromechanical coupled problem. A 3-dimensional finite element model of smart composite panels integrated with the ACLD treated patches has been modelled to reveal the performance of ACLD treated patches on improving the damping properties of slender anti-symmetric angle-ply laminated shallow shell, in controlling the transient vibrations which are geometrically nonlinear. The mathematical results explain that the ACLD treated patches considerably enhance the damping properties of anti-symmetric angle-ply panels undergoing geometrically nonlinear transient vibrations.

A finite element modeling of a multifunctional hybrid composite beam with viscoelastic materials

Science.gov (United States)

Wang, Ya; Inman, Daniel J.

2013-04-01

The multifunctional hybrid composite structure studied here consists of a ceramic outer layer capable of withstanding high temperatures, a functionally graded ceramic layer combining shape memory alloy (SMA) properties of NiTi together with Ti2AlC (called Graded Ceramic/Metal Composite, or GCMeC), and a high temperature sensor patch, followed by a polymer matrix composite laced with vascular cooling channels all held together with various epoxies. Due to the recoverable nature of SMA and adhesive properties of Ti2AlC, the damping behavior of the GCMeC is largely viscoelastic. This paper presents a finite element formulation for this multifunctional hybrid structure with embedded viscoelastic material. In order to implement the viscoelastic model into the finite element formulation, a second order three parameter Golla-Hughes-McTavish (GHM) method is used to describe the viscoelastic behavior. Considering the parameter identification, a strategy to estimate the fractional order of the time derivative and the relaxation time is outlined. The curve-fitting aspects of both GHM and ADF show good agreement with experimental data obtained from dynamic mechanics analysis. The performance of the finite element of the layered multifunctional beam is verified through experimental model analysis.

The viscoelastic characterization of polymer materials exposed to the low-Earth orbit environment

International Nuclear Information System (INIS)

Strganac, T.; Letton, A.

1992-01-01

Recent accomplishments in our research efforts have included the successful measurement of the thermal mechanical properties of polymer materials exposed to the low-earth orbit environment. In particular, viscoelastic properties were recorded using the Rheometrics Solids Analyzer (RSA 2). Dynamic moduli (E', the storage component of the elastic modulus, and E'', the loss component of the elastic modulus) were recorded over three decades of frequency (0.1 to 100 rad/sec) for temperatures ranging from -150 to 150 C. Although this temperature range extends beyond the typical use range of the materials, measurements in this region are necessary in the development of complete viscoelastic constitutive models. The experimental results were used to provide the stress relaxation and creep compliance performance characteristics through viscoelastic correspondence principles. Our results quantify the differences between exposed and control polymer specimens. The characterization is specifically designed to elucidate a constitutive model that accurately predicts the change in behavior of these materials due to exposure. The constitutive model for viscoelastic behavior reflects the level of strain, the rate of strain, and the history of strain as well as the thermal history of the material

Viscoelastic and thermal behavior of structural concrete with reference to containment vessels

International Nuclear Information System (INIS)

Stefanou, G.D.

1981-01-01

A method of numerical viscoelastic stress analysis is described suitable for concrete structures operating at elevated temperatures. The paper describes how approximate numerical methods of elastic analysis of the finite element type can be extended to incorporate the viscoelastic behavior of structural concrete of the quasi-static type. A new eight parameter viscoelastic model is proposed to represent concrete behavior in the loaded and unloaded stage. The deformational expressions for the proposed viscoelastic analogue are also developed. Finally, as a result of courve-fitting procedures, the evaluation of the creep law coefficients are obtained for creep laws appropriate to a test regime. The proposed method is of general application providing that the properties of concrete are assessed reasonably well. The analytical predictions are compared with experimental results obtained on concrete model specimens loaded for 3 1/2 months, at a temperature of 80 0 C. (author)

Properties of Love waves in a piezoelectric layered structure with a viscoelastic guiding layer

International Nuclear Information System (INIS)

Liu, Jiansheng; Wang, Lijun; Lu, Yanyan; He, Shitang

2013-01-01

A theoretical method is developed for analyzing Love waves in a structure with a viscoelastic guiding layer bounded on a piezoelectric substrate. The dispersion equation previously derived for piezoelectric Love waves propagating in the layered structure with an elastic layer is adopted for analyzing a structure with a viscoelastic layer. A Maxwell–Weichert model is introduced to describe the shear stiffness of a polymeric material. Newton’s method is employed for the numerical calculation. The dispersion equation for piezoelectric–elastic Love waves is proved suitable for solving a structure with a viscoelastic layer on a piezoelectric substrate. The theoretical results indicate that the propagation velocity of the Love wave is mainly decided by the shear stiffness of the guiding layer, whereas the propagation loss is approximately proportional to its viscosity. A detailed experimental study was conducted on a Love wave delay line fabricated on an ST-90° X quartz substrate and overlaid with various thicknesses of SU-8 guiding layers. A tail-raising caused by the viscosity of the guiding layer existed in both the calculated and the measured propagation velocities. The calculated insertion loss of the Love wave delay lines was in good agreement with the measured results. The method and the results presented in this paper are beneficial to the design of Love wave sensors with a viscoelastic guiding layer. (paper)

Quantitative characterization of viscoelastic behavior in tissue-mimicking phantoms and ex vivo animal tissues.

Directory of Open Access Journals (Sweden)

Ashkan Maccabi

Full Text Available Viscoelasticity of soft tissue is often related to pathology, and therefore, has become an important diagnostic indicator in the clinical assessment of suspect tissue. Surgeons, particularly within head and neck subsites, typically use palpation techniques for intra-operative tumor detection. This detection method, however, is highly subjective and often fails to detect small or deep abnormalities. Vibroacoustography (VA and similar methods have previously been used to distinguish tissue with high-contrast, but a firm understanding of the main contrast mechanism has yet to be verified. The contributions of tissue mechanical properties in VA images have been difficult to verify given the limited literature on viscoelastic properties of various normal and diseased tissue. This paper aims to investigate viscoelasticity theory and present a detailed description of viscoelastic experimental results obtained in tissue-mimicking phantoms (TMPs and ex vivo tissues to verify the main contrast mechanism in VA and similar imaging modalities. A spherical-tip micro-indentation technique was employed with the Hertzian model to acquire absolute, quantitative, point measurements of the elastic modulus (E, long term shear modulus (η, and time constant (τ in homogeneous TMPs and ex vivo tissue in rat liver and porcine liver and gallbladder. Viscoelastic differences observed between porcine liver and gallbladder tissue suggest that imaging modalities which utilize the mechanical properties of tissue as a primary contrast mechanism can potentially be used to quantitatively differentiate between proximate organs in a clinical setting. These results may facilitate more accurate tissue modeling and add information not currently available to the field of systems characterization and biomedical research.

Quantitative characterization of viscoelastic behavior in tissue-mimicking phantoms and ex vivo animal tissues.

Science.gov (United States)

Maccabi, Ashkan; Shin, Andrew; Namiri, Nikan K; Bajwa, Neha; St John, Maie; Taylor, Zachary D; Grundfest, Warren; Saddik, George N

2018-01-01

Viscoelasticity of soft tissue is often related to pathology, and therefore, has become an important diagnostic indicator in the clinical assessment of suspect tissue. Surgeons, particularly within head and neck subsites, typically use palpation techniques for intra-operative tumor detection. This detection method, however, is highly subjective and often fails to detect small or deep abnormalities. Vibroacoustography (VA) and similar methods have previously been used to distinguish tissue with high-contrast, but a firm understanding of the main contrast mechanism has yet to be verified. The contributions of tissue mechanical properties in VA images have been difficult to verify given the limited literature on viscoelastic properties of various normal and diseased tissue. This paper aims to investigate viscoelasticity theory and present a detailed description of viscoelastic experimental results obtained in tissue-mimicking phantoms (TMPs) and ex vivo tissues to verify the main contrast mechanism in VA and similar imaging modalities. A spherical-tip micro-indentation technique was employed with the Hertzian model to acquire absolute, quantitative, point measurements of the elastic modulus (E), long term shear modulus (η), and time constant (τ) in homogeneous TMPs and ex vivo tissue in rat liver and porcine liver and gallbladder. Viscoelastic differences observed between porcine liver and gallbladder tissue suggest that imaging modalities which utilize the mechanical properties of tissue as a primary contrast mechanism can potentially be used to quantitatively differentiate between proximate organs in a clinical setting. These results may facilitate more accurate tissue modeling and add information not currently available to the field of systems characterization and biomedical research.

Computational Viscoelasticity

CERN Document Server

Marques, Severino P C

2012-01-01

This text is a guide how to solve problems in which viscoelasticity is present using existing commercial computational codes. The book gives information on codes’ structure and use, data preparation  and output interpretation and verification. The first part of the book introduces the reader to the subject, and to provide the models, equations and notation to be used in the computational applications. The second part shows the most important Computational techniques: Finite elements formulation, Boundary elements formulation, and presents the solutions of Viscoelastic problems with Abaqus.

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

Science.gov (United States)

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

Regionally variant collagen alignment correlates with viscoelastic properties of the disc of the human temporomandibular joint.

Science.gov (United States)

Gutman, Shawn; Kim, Daniel; Tarafder, Solaiman; Velez, Sergio; Jeong, Julia; Lee, Chang H

2018-02-01

To determine the regionally variant quality of collagen alignment in human TMJ discs and its statistical correlation with viscoelastic properties. For quantitative analysis of the quality of collagen alignment, horizontal sections of human TMJ discs with Pricrosirius Red staining were imaged under circularly polarized microscopy. Mean angle and angular deviation of collagen fibers in each region were analyzed using a well-established automated image-processing for angular gradient. Instantaneous and relaxation moduli of each disc region were measured under stress-relaxation test both in tensile and compression. Then Spearman correlation analysis was performed between the angular deviation and the moduli. To understand the effect of glycosaminoglycans on the correlation, TMJ disc samples were treated by chondroitinase ABC (C-ABC). Our imaging processing analysis showed the region-variant direction of collagen alignment, consistently with previous findings. Interestingly, the quality of collagen alignment, not only the directions, was significantly different in between the regions. The angular deviation of fiber alignment in the anterior and intermediate regions were significantly smaller than the posterior region. Medial and lateral regions showed significantly bigger angular deviation than all the other regions. The regionally variant angular deviation values showed statistically significant correlation with the tensile instantaneous modulus and the relaxation modulus, partially dependent on C-ABC treatment. Our findings suggest the region-variant degree of collagen fiber alignment is likely attributed to the heterogeneous viscoelastic properties of TMJ disc that may have significant implications in development of regenerative therapy for TMJ disc. Copyright © 2017 Elsevier Ltd. All rights reserved.

Transient thermal effect, nonlinear refraction and nonlinear absorption properties of graphene oxide sheets in dispersion.

Science.gov (United States)

Zhang, Xiao-Liang; Liu, Zhi-Bo; Li, Xiao-Chun; Ma, Qiang; Chen, Xu-Dong; Tian, Jian-Guo; Xu, Yan-Fei; Chen, Yong-Sheng

2013-03-25

The nonlinear refraction (NLR) properties of graphene oxide (GO) in N, N-Dimethylformamide (DMF) was studied in nanosecond, picosecond and femtosecond time regimes by Z-scan technique. Results show that the dispersion of GO in DMF exhibits negative NLR properties in nanosecond time regime, which is mainly attributed to transient thermal effect in the dispersion. The dispersion also exhibits negative NLR in picosecond and femtosecond time regimes, which are arising from sp(2)- hybridized carbon domains and sp(3)- hybridized matrix in GO sheets. To illustrate the relations between NLR and nonlinear absorption (NLA), NLA properties of the dispersion were also studied in nanosecond, picosecond and femtosecond time regimes.

Viscoelastic Surface Waves

Science.gov (United States)

Borcherdt, R. D.

2007-12-01

General theoretical solutions for Rayleigh- and Love-Type surface waves in viscoelastic media describe physical characteristics of the surface waves in elastic as well as anelastic media with arbitrary amounts of intrinsic absorption. In contrast to corresponding physical characteristics for Rayleigh waves in elastic media, Rayleigh- Type surface waves in anelastic media demonstrate; 1) tilt of the particle motion orbit that varies with depth, and 2) amplitude and volumetric strain distributions with superimposed sinusoidal variations that decay exponentially with depth. Each characteristic is dependent on the amount of intrinsic absorption and the chosen model of viscoelasticity. Distinguishing characteristics of anelastic Love-Type surface waves include: 1) dependencies of the wave speed and absorption coefficient on the chosen model and amount of intrinsic absorption and frequency, and 2) superimposed sinusoidal amplitude variations with an exponential decay with depth. Numerical results valid for a variety of viscoelastic models provide quantitative estimates of the physical characteristics of both types of viscoelastic surface waves appropriate for interpretations pertinent to models of earth materials ranging from low-loss in the crust to moderate- and high-loss in water-saturated soils.

Viscoelastic characterization of soft biological materials

Science.gov (United States)

Nayar, Vinod Timothy

Progressive and irreversible retinal diseases are among the primary causes of blindness in the United States, attacking the cells in the eye that transform environmental light into neural signals for the optic pathway. Medical implants designed to restore visual function to afflicted patients can cause mechanical stress and ultimately damage to the host tissues. Research shows that an accurate understanding of the mechanical properties of the biological tissues can reduce damage and lead to designs with improved safety and efficacy. Prior studies on the mechanical properties of biological tissues show characterization of these materials can be affected by environmental, length-scale, time, mounting, stiffness, size, viscoelastic, and methodological conditions. Using porcine sclera tissue, the effects of environmental, time, and mounting conditions are evaluated when using nanoindentation. Quasi-static tests are used to measure reduced modulus during extended exposure to phosphate-buffered saline (PBS), as well as the chemical and mechanical analysis of mounting the sample to a solid substrate using cyanoacrylate. The less destructive nature of nanoindentation tests allows for variance of tests within a single sample to be compared to the variance between samples. The results indicate that the environmental, time, and mounting conditions can be controlled for using modified nanoindentation procedures for biological samples and are in line with averages modulus values from previous studies but with increased precision. By using the quasi-static and dynamic characterization capabilities of the nanoindentation setup, the additional stiffness and viscoelastic variables are measured. Different quasi-static control methods were evaluated along with maximum load parameters and produced no significant difference in reported reduced modulus values. Dynamic characterization tests varied frequency and quasi-static load, showing that the agar could be modeled as a linearly

Voltage-Induced Nonlinear Conduction Properties of Epoxy Resin/Micron-Silver Particles Composites

Science.gov (United States)

Qu, Zhaoming; Lu, Pin; Yuan, Yang; Wang, Qingguo

2018-01-01

The nonlinear conduction properties of epoxy resin (ER)/micron-silver particles (MP) composites were investigated. Under sufficient high intensity applied constant voltage, the obvious nonlinear conduction properties of the samples with volume fraction 25% were found. With increments in the voltage, the conductive switching effect was observed. The nonlinear conduction mechanism of the ER/MP composites under high applied voltages could be attributed to the electrical current conducted via discrete paths of conductive particles induced by the electric field. The test results show that the ER/MP composites with nonlinear conduction properties are of great potential application in electromagnetic protection of electron devices and systems.

Propagation of the Stress Wave Through the Filled Joint with Linear Viscoelastic Deformation Behavior Using Time-Domain Recursive Method

Science.gov (United States)

Wang, Rui; Hu, Zhiping; Zhang, Dan; Wang, Qiyao

2017-12-01

The dynamic behavior of filled joints is mostly controlled by the filled medium. In addition to nonlinear elastic behavior, viscoelastic behavior of filled joints is also of great significance. Here, a theoretical study of stress wave propagation through a filled rock joint with linear viscoelastic deformation behavior has been carried out using a modified time-domain recursive method (TDRM). A displacement discontinuity model was extended to form a displacement and stress discontinuity model, and the differential constitutive relationship of viscoelastic model was adopted to introduce the mass and viscoelastic behavior of filled medium. A standard linear solid model, which can be degenerated into the Kelvin and Maxwell models, was adopted in deriving this method. Transmission and reflection coefficients were adopted to verify this method. Besides, the effects of some parameters on wave propagation across a filled rock joint with linear viscoelastic deformation behavior were discussed. Then, a comparison of the time-history curves calculated by the present method with those by frequency-domain method (FDM) was performed. The results indicated that change tendencies of the transmission and reflection coefficients for these viscoelastic models versus incident angle were the same as each other but not frequency. The mass and viscosity coupling of filled medium did not fundamentally change wave propagation. The modified TDRM was found to be more efficient than the FDM.

Modeling Asymmetric Flow of Viscoelastic Fluid in Symmetric Planar Sudden Expansion Geometry Based on User-Defined Function in FLUENT CFD Package

Directory of Open Access Journals (Sweden)

Zhi-Ying Zheng

2013-01-01

Full Text Available Through embedding an in-house subroutine into FLUENT code by utilizing the functionalization of user-defined function provided by the software, a new numerical simulation methodology on viscoelastic fluid flows has been established. In order to benchmark this methodology, numerical simulations under different viscoelastic fluid solution concentrations (with solvent viscosity ratio varied from 0.2 to 0.9, extensibility parameters (100≤L2≤500, Reynolds numbers (0.1 ≤ Re ≤ 100, and Weissenberg numbers (0 ≤ Wi ≤ 20 are conducted on unsteady laminar flows through a symmetric planar sudden expansion with expansion ratio of 1: 3 for viscoelastic fluid flows. The constitutive model used to describe the viscoelastic effect of viscoelastic fluid flow is FENE-P (finitely extensive nonlinear elastic-Peterlin model. The numerical simulation results show that the influences of elasticity, inertia, and concentration on the flow bifurcation characteristics are more significant than those of extensibility. The present simulation results including the critical Reynolds number for which the flow becomes asymmetric, vortex size, bifurcation diagram, velocity distribution, streamline, and pressure loss show good agreements with some published results. That means the newly established method based on FLUENT software platform for simulating peculiar flow behaviors of viscoelastic fluid is credible and suitable for the study of viscoelastic fluid flows.

Nonlinear dynamics of structures

CERN Document Server

Oller, Sergio

2014-01-01

This book lays the foundation of knowledge that will allow a better understanding of nonlinear phenomena that occur in structural dynamics.   This work is intended for graduate engineering students who want to expand their knowledge on the dynamic behavior of structures, specifically in the nonlinear field, by presenting the basis of dynamic balance in non‐linear behavior structures due to the material and kinematics mechanical effects.   Particularly, this publication shows the solution of the equation of dynamic equilibrium for structure with nonlinear time‐independent materials (plasticity, damage and frequencies evolution), as well as those time dependent non‐linear behavior materials (viscoelasticity and viscoplasticity). The convergence conditions for the non‐linear dynamic structure solution  are studied, and the theoretical concepts and its programming algorithms are presented.  

Dynamic viscoelasticity of protease-treated rice batters for gluten-free rice bread making.

Science.gov (United States)

Honda, Yuji; Inoue, Nanami; Sugimoto, Reina; Matsumoto, Kenji; Koda, Tomonori; Nishioka, Akihiro

2018-03-01

Papain (cysteine protease), subtilisin (Protin SD-AY10, serine protease), and bacillolysin (Protin SD-NY10, metallo protease) increased the specific volume of gluten-free rice breads by 19-63% compared to untreated bread. In contrast, Newlase F (aspartyl protease) did not expand the volume of the rice bread. In a rheological analysis, the viscoelastic properties of the gluten-free rice batters also depended on the protease categories. Principal component analysis (PCA) analysis suggested that the storage and loss moduli (G' and G″, respectively) at 35 °C, and the maximum values of G' and G″, were important factors in the volume expansion. Judging from the PCA of the viscoelastic parameters of the rice batters, papain and Protin SD-AY10 improved the viscoelasticity for gluten-free rice bread making, and Protin SD-NY effectively expanded the gluten-free rice bread. The rheological properties differed between Protin SD-NY and the other protease treatments.

Frequency-dependent viscoelastic parameters of mouse brain tissue estimated by MR elastography

Energy Technology Data Exchange (ETDEWEB)

Clayton, E H; Bayly, P V [Department of Mechanical Engineering and Materials Science, Washington University in St Louis, 1 Brookings Drive, Campus Box 1185, Saint Louis, MO 63130 (United States); Garbow, J R, E-mail: clayton@wustl.edu, E-mail: garbow@wustl.edu, E-mail: pvb@wustl.edu [Biomedical Magnetic Resonance Laboratory, Department of Radiology, Washington University in St Louis, 4525 Scott Avenue, Campus Box 8227, Saint Louis, MO 63110 (United States)

2011-04-21

Viscoelastic properties of mouse brain tissue were estimated non-invasively, in vivo, using magnetic resonance elastography (MRE) at 4.7 T to measure the dispersive properties of induced shear waves. Key features of this study include (i) the development and application of a novel MR-compatible actuation system which transmits vibratory motion into the brain through an incisor bar, and (ii) the investigation of the mechanical properties of brain tissue over a 1200 Hz bandwidth from 600-1800 Hz. Displacement fields due to propagating shear waves were measured during continuous, harmonic excitation of the skull. This protocol enabled characterization of the true steady-state patterns of shear wave propagation. Analysis of displacement fields obtained at different frequencies indicates that the viscoelastic properties of mouse brain tissue depend strongly on frequency. The average storage modulus (G') increased from approximately 1.6 to 8 kPa over this range; average loss modulus (G'') increased from approximately 1 to 3 kPa. Both moduli were well approximated by a power-law relationship over this frequency range. MRE may be a valuable addition to studies of disease in murine models, and to pre-clinical evaluations of therapies. Quantitative measurements of the viscoelastic parameters of brain tissue at high frequencies are also valuable for modeling and simulation of traumatic brain injury.

Coefficient of restitution in fractional viscoelastic compliant impacts using fractional Chebyshev collocation

Science.gov (United States)

Dabiri, Arman; Butcher, Eric A.; Nazari, Morad

2017-02-01

Compliant impacts can be modeled using linear viscoelastic constitutive models. While such impact models for realistic viscoelastic materials using integer order derivatives of force and displacement usually require a large number of parameters, compliant impact models obtained using fractional calculus, however, can be advantageous since such models use fewer parameters and successfully capture the hereditary property. In this paper, we introduce the fractional Chebyshev collocation (FCC) method as an approximation tool for numerical simulation of several linear fractional viscoelastic compliant impact models in which the overall coefficient of restitution for the impact is studied as a function of the fractional model parameters for the first time. Other relevant impact characteristics such as hysteresis curves, impact force gradient, penetration and separation depths are also studied.

Effect of pH and salts on microstructure and viscoelastic properties of lemon peel acid insoluble fiber suspensions upon high pressure homogenization

NARCIS (Netherlands)

Willemsen, Katleen L.D.D.; Panozzo, Agnese; Moelants, Katlijn; Cardinaels, Ruth; Wallecan, Joël; Moldenaers, Paula; Hendrickx, Marc

2018-01-01

In the present paper the effect of pH and salts on microstructural and viscoelastic properties of lemon peel acid insoluble fiber residue (AR) suspensions upon mild and intense shearing was investigated. To this aim, AR suspensions were adjusted to a pH of 2.5 (as is), 4.5, 5.5, 7 or 10 prior to or

Modelling of Asphalt Concrete Stiffness in the Linear Viscoelastic Region

Science.gov (United States)

Mazurek, Grzegorz; Iwański, Marek

2017-10-01

Stiffness modulus is a fundamental parameter used in the modelling of the viscoelastic behaviour of bituminous mixtures. On the basis of the master curve in the linear viscoelasticity range, the mechanical properties of asphalt concrete at different loading times and temperatures can be predicted. This paper discusses the construction of master curves under rheological mathematical models i.e. the sigmoidal function model (MEPDG), the fractional model, and Bahia and co-workers’ model in comparison to the results from mechanistic rheological models i.e. the generalized Huet-Sayegh model, the generalized Maxwell model and the Burgers model. For the purposes of this analysis, the reference asphalt concrete mix (denoted as AC16W) intended for the binder coarse layer and for traffic category KR3 (5×105 controlled strain mode. The fixed strain level was set at 25με to guarantee that the stiffness modulus of the asphalt concrete would be tested in a linear viscoelasticity range. The master curve was formed using the time-temperature superposition principle (TTSP). The stiffness modulus of asphalt concrete was determined at temperatures 10°C, 20°C and 40°C and at loading times (frequency) of 0.1, 0.3, 1, 3, 10, 20 Hz. The model parameters were fitted to the rheological models using the original programs based on the nonlinear least squares sum method. All the rheological models under analysis were found to be capable of predicting changes in the stiffness modulus of the reference asphalt concrete to satisfactory accuracy. In the cases of the fractional model and the generalized Maxwell model, their accuracy depends on a number of elements in series. The best fit was registered for Bahia and co-workers model, generalized Maxwell model and fractional model. As for predicting the phase angle parameter, the largest discrepancies between experimental and modelled results were obtained using the fractional model. Except the Burgers model, the model matching quality was

A Scanning Hologram Recorded by Phase Conjugate Property of Nonlinear Crystals

DEFF Research Database (Denmark)

Zi-Liang, Ping; Dalsgaard, Erik

1996-01-01

A methode of recording a scanning hologram with phase conjugate property of nonlinear crystal is provided. The principle of recording, setup and experiments are given.......A methode of recording a scanning hologram with phase conjugate property of nonlinear crystal is provided. The principle of recording, setup and experiments are given....

Linear and Nonlinear Optical Properties of Micrometer-Scale Gold Nanoplates

International Nuclear Information System (INIS)

Liu Xiao-Lan; Peng Xiao-Niu; Yang Zhong-Jian; Li Min; Zhou Li

2011-01-01

Micrometer-scale gold nanoplates have been synthesized in high yield through a polyol process. The morphology, crystal structure and linear optical extinction of the gold nanoplates have been characterized. These gold nanoplates are single-crystalline with triangular, truncated triangular and hexagonal shapes, exhibiting strong surface plasmon resonance (SPR) extinction in the visible and near-infrared (NIR) region. The linear optical properties of gold nanoplates are also investigated by theoretical calculations. We further investigate the nonlinear optical properties of the gold nanoplates in solution by Z-scan technique. The nonlinear absorption (NLA) coefficient and nonlinear refraction (NLR) index are measured to be 1.18×10 2 cm/GW and −1.04×10 −3 cm 2 /GW, respectively. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties

Science.gov (United States)

Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon

2012-01-01

Purpose: The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F[subscript 0]) during anterior-posterior stretching. Method: Three materially linear and 3 materially nonlinear models were…

Viscoelastic and fractal characteristics of a supramolecular hydrogel hybridized with clay nanoparticles.

Science.gov (United States)

Song, Fei; Zhang, Li-Ming; Shi, Jun-Feng; Li, Nan-Nan

2010-12-01

The supramolecular hydrogels derived from low-molecular-mass gelators represent a unique class of soft matters and have important potential applications in biomedical fields, separation technology and cosmetic science. However, they suffer usually from weak mechanical and viscoelastic properties. In this work, we carry out the in situ hybridization of clay nanoparticles (Laponite RD) into the supramolecular hydrogel formed from a low-molecular-mass hydrogelator, 2,6-di[N-(carboxyethyl carbonyl)amino]pyridine (DAP), and investigate the viscoelastic and structural characteristics of resultant hybrid hydrogel. It was found that a small concentration of Laponite RD could lead to a significant increase in the storage modulus, loss modulus or complex viscosity. Compared with neat DAP hydrogel, the hybrid hydrogel has a greater hydrogel strength and a lower relaxation exponent. In particular, the enhancement of the clay nanoparticles to the viscoelastic properties of the DAP hydrogel is more effective in the case of higher DAP concentration. By relating its macroscopic elastic properties to a scaling fractal model, such a hybrid hydrogel was confirmed to be in the strong-link regime and to have a more complex network structure with a higher fractal dimension when compared with neat DAP hydrogel. Copyright © 2010 Elsevier B.V. All rights reserved.

On Lamb and Rayleigh wave convergence in viscoelastic tissues

Energy Technology Data Exchange (ETDEWEB)

Nenadic, Ivan Z; Urban, Matthew W; Aristizabal, Sara; Mitchell, Scott A; Humphrey, Tye C; Greenleaf, James F, E-mail: Nenadic.Ivan@mayo.edu [Department of Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905 (United States)

2011-10-21

Characterization of the viscoelastic material properties of soft tissue has become an important area of research over the last two decades. Our group has been investigating the feasibility of using a shear wave dispersion ultrasound vibrometry (SDUV) method to excite Lamb waves in organs with plate-like geometry to estimate the viscoelasticity of the medium of interest. The use of Lamb wave dispersion ultrasound vibrometry to quantify the mechanical properties of viscoelastic solids has previously been reported. Two organs, the heart wall and the spleen, can be readily modeled using plate-like geometries. The elasticity of these two organs is important because they change in pathological conditions. Diastolic dysfunction is the inability of the left ventricle (LV) of the heart to supply sufficient stroke volumes into the systemic circulation and is accompanied by the loss of compliance and stiffening of the LV myocardium. It has been shown that there is a correlation between high splenic stiffness in patients with chronic liver disease and strong correlation between spleen and liver stiffness. Here, we investigate the use of the SDUV method to quantify the viscoelasticity of the LV free-wall myocardium and spleen by exciting Rayleigh waves on the organ's surface and measuring the wave dispersion (change of wave velocity as a function of frequency) in the frequency range 40-500 Hz. An equation for Rayleigh wave dispersion due to cylindrical excitation was derived by modeling the excised myocardium and spleen with a homogenous Voigt material plate immersed in a nonviscous fluid. Boundary conditions and wave potential functions were solved for the surface wave velocity. Analytical and experimental convergence between the Lamb and Rayleigh waves is reported in a finite element model of a plate in a fluid of similar density, gelatin plate and excised porcine spleen and left-ventricular free-wall myocardium.

Impact load time histories for viscoelastic missiles

International Nuclear Information System (INIS)

Stoykovich, M.

1977-01-01

Generation of the impact load time history at the contact point between a viscoelastic missile and its targets is presented. In the past, in the case of aircraft striking containment shell structure, the impact load time history was determined on the basis of actual measurements by subjecting a rigid wall to aircraft crash. The effects of elastic deformation of the target upon the impact load time history is formulated in this paper. The missile is idealized by a linear mass-spring-dashpot combination using viscoelastic models. These models can readily be processed taking into account the elastic as well as inelastic deformations of the missiles. The target is assumed to be either linearly elastic or rigid. In the case of the linearly elastic target, the normal mode theory is used to express the time-dependent displacements of the target which is simulated by lumped masses, elastic properties and dashpots in discrete parts. In the case of Maxwell viscoelastic model, the time-dependent displacements of the missile and the target are given in terms of the unknown impact load time history. This leads to an integral equation which may be solved by Laplace transformation. The normal mode theory is provided. The target structure may be composed of different materials with different components. Concrete and steel structural components have inherently different viscous friction damping properties. Hence, the equivalent modal damping depends on the degree of participation of these components in the modal response. An approximate rule for determining damping in any vibration mode by weighting the damping of each component according to the modal energy stored in each component is considered

Evolution of material properties during free radical photopolymerization

Science.gov (United States)

Wu, Jiangtao; Zhao, Zeang; Hamel, Craig M.; Mu, Xiaoming; Kuang, Xiao; Guo, Zaoyang; Qi, H. Jerry

2018-03-01

Photopolymerization is a widely used polymerization method in many engineering applications such as coating, dental restoration, and 3D printing. It is a complex chemical and physical process, through which a liquid monomer solution is rapidly converted to a solid polymer. In the most common free-radical photopolymerization process, the photoinitiator in the solution is exposed to light and decomposes into active radicals, which attach to monomers to start the polymerization reaction. The activated monomers then attack Cdbnd C double bonds of unsaturated monomers, which leads to the growth of polymer chains. With increases in the polymer chain length and the average molecular weight, polymer chains start to connect and form a network structure, and the liquid polymer solution becomes a dense solid. During this process, the material properties of the cured polymer change dramatically. In this paper, experiments and theoretical modeling are used to investigate the free-radical photopolymerization reaction kinetics, material property evolution and mechanics during the photopolymerization process. The model employs the first order chemical reaction rate equations to calculate the variation of the species concentrations. The degree of monomer conversion is used as an internal variable that dictates the mechanical properties of the cured polymer at different curing states, including volume shrinkage, glass transition temperature, and nonlinear viscoelastic properties. To capture the nonlinear behavior of the cured polymer under low temperature and finite deformation, a multibranch nonlinear viscoelastic model is developed. A phase evolution model is used to describe the mechanics of the coupling between the crosslink network evolution and mechanical loading during the curing process. The comparison of the model and the experimental results indicates that the model can capture property changes during curing. The model is further applied to investigate the internal stress

Enhancement of nonlinear optical properties of compounds of silica

Indian Academy of Sciences (India)

The aim of this paper is to introduce a method for enhancing the nonlinear optical properties in silica glass by using metallic nanoparticles. First, the T-matrix method is developed to calculate the effective dielectric constant for the compound of silica glass and metallic nanoparticles, both of which possess nonlinear dielectric ...

DIFFERENTIAL EQUATION SIMULATION IN CALCULATION OF LATERAL AND TRANSVERSE-LONGITUDINAL BENDING OF FRAME STRUCTURES WITHOUT AND WITH DUE ACCOUNT OF VISCOELASTIC MATERIAL PROPERTIES

Directory of Open Access Journals (Sweden)

V. M. Ovsianko

2012-01-01

Full Text Available The paper reveals a brand-new direction in simulation of frame and continual structures while calculating static and dynamic loads and stability.  An electronic model has been synthesized  for an investigated object and then it has been analyzed not with the help of  specialized analog computing techniques but by means of high-performance software package for electronic circuit calculation using a personal computer.The given paper contains exact algebraic equations corresponding to differential equations for lateral bending calculation of frame structures without and with due account of viscoelastic material properties in compliance with the Kelvin model.The exact algebraic equation for a beam on elastic supports (or elastic Winkler foundation has been derived for quartic differential equation.The paper presents a number of exact algebraic equations which are equivalent to differential equations for transverse-longitudinal bending calculation of frame structures without and with due account of viscoelastic material properties when lateral and longitudinal loads are applied in the form of  impulses with any periods of their duration and any interchangeability. 

MEASUREMENT OF THE VISCOELASTIC PROPERTIES OF WATER-SATURATED CLAY SEDIMENTS.

Science.gov (United States)

The complex shear modulus of both kaolin -water and bentonite-water mixtures has been determined in the laboratory. The method involved measuring the...range two to forty-three kHz. Dispersed sediments behaved like Newtonian liquids. Undispersed sediments, however, were viscoelastic in character, and...their shear moduli exhibited no dependence on frequency. For undispersed kaolin mixtures, a typical result is (21.6 + i 1.2) x 1,000 dynes per square

Simulating Seismic Wave Propagation in Viscoelastic Media with an Irregular Free Surface

Science.gov (United States)

Liu, Xiaobo; Chen, Jingyi; Zhao, Zhencong; Lan, Haiqiang; Liu, Fuping

2018-05-01

In seismic numerical simulations of wave propagation, it is very important for us to consider surface topography and attenuation, which both have large effects (e.g., wave diffractions, conversion, amplitude/phase change) on seismic imaging and inversion. An irregular free surface provides significant information for interpreting the characteristics of seismic wave propagation in areas with rugged or rapidly varying topography, and viscoelastic media are a better representation of the earth's properties than acoustic/elastic media. In this study, we develop an approach for seismic wavefield simulation in 2D viscoelastic isotropic media with an irregular free surface. Based on the boundary-conforming grid method, the 2D time-domain second-order viscoelastic isotropic equations and irregular free surface boundary conditions are transferred from a Cartesian coordinate system to a curvilinear coordinate system. Finite difference operators with second-order accuracy are applied to discretize the viscoelastic wave equations and the irregular free surface in the curvilinear coordinate system. In addition, we select the convolutional perfectly matched layer boundary condition in order to effectively suppress artificial reflections from the edges of the model. The snapshot and seismogram results from numerical tests show that our algorithm successfully simulates seismic wavefields (e.g., P-wave, Rayleigh wave and converted waves) in viscoelastic isotropic media with an irregular free surface.

Parametric imaging of viscoelasticity using optical coherence elastography

Science.gov (United States)

Wijesinghe, Philip; McLaughlin, Robert A.; Sampson, David D.; Kennedy, Brendan F.

2015-03-01

We demonstrate imaging of soft tissue viscoelasticity using optical coherence elastography. Viscoelastic creep deformation is induced in tissue using step-like compressive loading and the resulting time-varying deformation is measured using phase-sensitive optical coherence tomography. From a series of co-located B-scans, we estimate the local strain rate as a function of time, and parameterize it using a four-parameter Kelvin-Voigt model of viscoelastic creep. The estimated viscoelastic strain and time constant are used to visualize viscoelastic creep in 2D, dual-parameter viscoelastograms. We demonstrate our technique on six silicone tissue-simulating phantoms spanning a range of viscoelastic parameters. As an example in soft tissue, we report viscoelastic contrast between muscle and connective tissue in fresh, ex vivo rat gastrocnemius muscle and mouse abdominal transection. Imaging viscoelastic creep deformation has the potential to provide complementary contrast to existing imaging modalities, and may provide greater insight into disease pathology.

Nonlinear branch-point dynamics of multiarm polystyrene

DEFF Research Database (Denmark)

Nielsen, Jens Kromann; Rasmussen, Henrik K.; Denberg, Martin

2006-01-01

/mol, respectively. The pom-pom was estimated to have 2.5 arms on average, while the estimate is 3.3 for the asymmetric star. The molar mass of each arm is about 27 kg/mol. The melts were characterized in the linear viscoelastic regime and by elongational rheometry in the nonlinear regime. For asymmetric star...

Brain viscoelasticity alteration in chronic-progressive multiple sclerosis.

Directory of Open Access Journals (Sweden)

Kaspar-Josche Streitberger

Full Text Available INTRODUCTION: Viscoelastic properties indicate structural alterations in biological tissues at multiple scales with high sensitivity. Magnetic Resonance Elastography (MRE is a novel technique that directly visualizes and quantitatively measures biomechanical tissue properties in vivo. MRE recently revealed that early relapsing-remitting multiple sclerosis (MS is associated with a global decrease of the cerebral mechanical integrity. This study addresses MRE and MR volumetry in chronic-progressive disease courses of MS. METHODS: We determined viscoelastic parameters of the brain parenchyma in 23 MS patients with primary or secondary chronic progressive disease course in comparison to 38 age- and gender-matched healthy individuals by multifrequency MRE, and correlated the results with clinical data, T2 lesion load and brain volume. Two viscoelastic parameters, the shear elasticity μ and the powerlaw exponent α, were deduced according to the springpot model and compared to literature values of relapsing-remitting MS. RESULTS: In chronic-progressive MS patients, μ and α were reduced by 20.5% and 6.1%, respectively, compared to healthy controls. MR volumetry yielded a weaker correlation: Total brain volume loss in MS patients was in the range of 7.5% and 1.7% considering the brain parenchymal fraction. All findings were significant (P<0.001. CONCLUSIONS: Chronic-progressive MS disease courses show a pronounced reduction of the cerebral shear elasticity compared to early relapsing-remitting disease. The powerlaw exponent α decreased only in the chronic-progressive stage of MS, suggesting an alteration in the geometry of the cerebral mechanical network due to chronic neuroinflammation.

Nonlinear finite element analyses: advances and challenges in dental applications.

Science.gov (United States)

Wakabayashi, N; Ona, M; Suzuki, T; Igarashi, Y

2008-07-01

To discuss the development and current status of application of nonlinear finite element method (FEM) in dentistry. The literature was searched for original research articles with keywords such as nonlinear, finite element analysis, and tooth/dental/implant. References were selected manually or searched from the PUBMED and MEDLINE databases through November 2007. The nonlinear problems analyzed in FEM studies were reviewed and categorized into: (A) nonlinear simulations of the periodontal ligament (PDL), (B) plastic and viscoelastic behaviors of dental materials, (C) contact phenomena in tooth-to-tooth contact, (D) contact phenomena within prosthodontic structures, and (E) interfacial mechanics between the tooth and the restoration. The FEM in dentistry recently focused on simulation of realistic intra-oral conditions such as the nonlinear stress-strain relationship in the periodontal tissues and the contact phenomena in teeth, which could hardly be solved by the linear static model. The definition of contact area critically affects the reliability of the contact analyses, especially for implant-abutment complexes. To predict the failure risk of a bonded tooth-restoration interface, it is essential to assess the normal and shear stresses relative to the interface. The inclusion of viscoelasticity and plastic deformation to the program to account for the time-dependent, thermal sensitive, and largely deformable nature of dental materials would enhance its application. Further improvement of the nonlinear FEM solutions should be encouraged to widen the range of applications in dental and oral health science.

VISCOELASTIC MODELS OF TIDALLY HEATED EXOMOONS

International Nuclear Information System (INIS)

Dobos, Vera; Turner, Edwin L.

2015-01-01

Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life has been intensely studied on solar system moons such as Europa or Enceladus where the surface ice layer covers a tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. To study the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models because it takes into account the temperature dependence of the tidal heat flux and the melting of the inner material. Using this model, we introduced the circumplanetary Tidal Temperate Zone (TTZ), which strongly depends on the orbital period of the moon and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model provides more promising results in terms of habitability because the inner melting of the body moderates the surface temperature, acting like a thermostat

VISCOELASTIC MODELS OF TIDALLY HEATED EXOMOONS

Energy Technology Data Exchange (ETDEWEB)

Dobos, Vera [Konkoly Thege Miklos Astronomical Institute, Research Centre of Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Konkoly Thege Miklós út 15-17, Budapest (Hungary); Turner, Edwin L., E-mail: dobos@konkoly.hu [Department of Astrophysical Sciences, Princeton University, 08544, 4 Ivy Lane, Peyton Hall, Princeton, NJ (United States)

2015-05-01

Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life has been intensely studied on solar system moons such as Europa or Enceladus where the surface ice layer covers a tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. To study the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models because it takes into account the temperature dependence of the tidal heat flux and the melting of the inner material. Using this model, we introduced the circumplanetary Tidal Temperate Zone (TTZ), which strongly depends on the orbital period of the moon and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model provides more promising results in terms of habitability because the inner melting of the body moderates the surface temperature, acting like a thermostat.

Topology optimization of viscoelastic rectifiers

DEFF Research Database (Denmark)

Jensen, Kristian Ejlebjærg; Szabo, Peter; Okkels, Fridolin

2012-01-01

An approach for the design of microfluidic viscoelastic rectifiers is presented based on a combination of a viscoelastic model and the method of topology optimization. This presumption free approach yields a material layout topologically different from experimentally realized rectifiers...

An optimized transversely isotropic, hyper-poro-viscoelastic finite element model of the meniscus to evaluate mechanical degradation following traumatic loading

Science.gov (United States)

Wheatley, Benjamin B.; Fischenich, Kristine M.; Button, Keith D.; Haut, Roger C.; Haut Donahue, Tammy L.

2015-01-01

Inverse finite element (FE) analysis is an effective method to predict material behavior, evaluate mechanical properties, and study differences in biological tissue function. The meniscus plays a key role in load distribution within the knee joint and meniscal degradation is commonly associated with the onset of osteoarthritis. In the current study, a novel transversely isotropic hyper-poro-viscoelastic constitutive formulation was incorporated in a FE model to evaluate changes in meniscal material properties following tibiofemoral joint impact. A non-linear optimization scheme was used to fit the model output to indentation relaxation experimental data. This study is the first to investigate rate of relaxation in healthy versus impacted menisci. Stiffness was found to be decreased (p=0.003), while the rate of tissue relaxation increased (p=0.010) at twelve weeks post impact. Total amount of relaxation, however, did not change in the impacted tissue (p=0.513). PMID:25776872

Generalized Fractional Derivative Anisotropic Viscoelastic Characterization

Directory of Open Access Journals (Sweden)

Harry H. Hilton

2012-01-01

Full Text Available Isotropic linear and nonlinear fractional derivative constitutive relations are formulated and examined in terms of many parameter generalized Kelvin models and are analytically extended to cover general anisotropic homogeneous or non-homogeneous as well as functionally graded viscoelastic material behavior. Equivalent integral constitutive relations, which are computationally more powerful, are derived from fractional differential ones and the associated anisotropic temperature-moisture-degree-of-cure shift functions and reduced times are established. Approximate Fourier transform inversions for fractional derivative relations are formulated and their accuracy is evaluated. The efficacy of integer and fractional derivative constitutive relations is compared and the preferential use of either characterization in analyzing isotropic and anisotropic real materials must be examined on a case-by-case basis. Approximate protocols for curve fitting analytical fractional derivative results to experimental data are formulated and evaluated.

Viscoelastic behavior of multiwalled carbon nanotubes into phenolic resin

Energy Technology Data Exchange (ETDEWEB)

Botelho, Edson Cocchieri; Costa, Michelle Leali; Braga, Carlos Isidoro, E-mail: ebotelho@feg.unesp.br [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Guaratingueta, SP (Brazil). Dept. de Materiais e Tecnologia; Burkhart, Thomas [Institut fuer Verbundwerkstoffe GmbH, Kaiserslautern, (Germany); Lauke, Bernd [Leibniz-Institut fuer Polymerforschung, Dresden (Germany)

2013-11-01

Nanostructured polymer composites have opened up new perspectives for multi-functional materials. In particular, carbon nanotubes (CNTs) have the potential applications in order to improve mechanical and electrical performance in composites with aerospace application. This study focuses on the viscoelastic evaluation of phenolic resin reinforced carbon nanotubes, processed by using two techniques: aqueous-surfactant solution and three roll calender (TRC) process. According to our results a relative small amount of CNTs in a phenolic resin matrix is capable of enhancing the viscoelastic properties significantly and to modify the thermal stability. Also has been observed that when is used TRC process, the incorporation and distribution of CNT into phenolic resin is more effective when compared with aqueous solution dispersion process. (author)

Magnetic and viscoelastic response of elastomers with hard magnetic filler

International Nuclear Information System (INIS)

Kramarenko, E Yu; Chertovich, A V; Semisalova, A S; Makarova, L A; Perov, N S; Khokhlov, A R; Stepanov, G V

2015-01-01

Magnetic elastomers (MEs) based on a silicone matrix and magnetically hard NdFeB particles have been synthesized and their magnetic and viscoelastic properties have been studied depending on the size and concentration of magnetic particles and the magnetizing field. It has been shown that magnetic particles can rotate in soft polymer matrix under applied magnetic field, this fact leading to some features in both magnetic and viscoelastic properties. In the maximum magnetic field used magnetization of MEs with smaller particles is larger while the coercivity is smaller due to higher mobility of the particles within the polymer matrix. Viscoelastic behavior is characterized by long relaxation times due to restructuring of the magnetic filler under the influence of an applied mechanical force and magnetic interactions. The storage and loss moduli of magnetically hard elastomers grow significantly with magnetizing field. The magnetic response of the magnetized samples depends on the mutual orientation of the external magnetic field and the internal sample magnetization. Due to the particle rotation within the polymer matrix, the loss factor increases abruptly when the magnetic field is turned on in the opposite direction to the sample magnetization, further decreasing with time. Moduli versus field dependences have minimum at non-zero field and are characterized by a high asymmetry with respect to the field direction. (paper)

Computational studies of third-order nonlinear optical properties of ...

Indian Academy of Sciences (India)

Anuj Kumar

2017-06-20

Jun 20, 2017 ... Department of Physics, Jaypee University of Engineering and Technology, Raghogarh,. Guna 473 226, India. ∗ ... properties and other molecular properties of the organic nonlinear optical crystal 2-aminopyridinium p- toluenesulphonate ... nal processing, optical limiting, optical logic gates, laser radiation ...

pH-induced contrast in viscoelasticity imaging of biopolymers

International Nuclear Information System (INIS)

Yapp, R D; Insana, M F

2009-01-01

Understanding contrast mechanisms and identifying discriminating features is at the heart of diagnostic imaging development. This paper focuses on how pH influences the viscoelastic properties of biopolymers to better understand the effects of extracellular pH on breast tumour elasticity imaging. Extracellular pH is known to decrease as much as 1 pH unit in breast tumours, thus creating a dangerous environment that increases cellular mutatation rates and therapeutic resistance. We used a gelatin hydrogel phantom to isolate the effects of pH on a polymer network with similarities to the extracellular matrix in breast stroma. Using compressive unconfined creep and stress relaxation measurements, we systematically measured the viscoelastic features sensitive to pH by way of time-domain models and complex modulus analysis. These results are used to determine the sensitivity of quasi-static ultrasonic elasticity imaging to pH. We found a strong elastic response of the polymer network to pH, such that the matrix stiffness decreases as pH was reduced; however, the viscous response of the medium to pH was negligible. While physiological features of breast stroma such as proteoglycans and vascular networks are not included in our hydrogel model, observations in this study provide insight into viscoelastic features specific to pH changes in the collagenous stromal network. These observations suggest that the large contrast common in breast tumours with desmoplasia may be reduced under acidic conditions, and that viscoelastic features are unlikely to improve discriminability.

Insoluble elastin reduces collagen scaffold stiffness, improves viscoelastic properties, and induces a contractile phenotype in smooth muscle cells.

Science.gov (United States)

Ryan, Alan J; O'Brien, Fergal J

2015-12-01

Biomaterials with the capacity to innately guide cell behaviour while also displaying suitable mechanical properties 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 viscoelastic properties 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 viscoelastic 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. Copyright © 2015 Elsevier Ltd. All rights reserved.

Asphalt Pavement Aging and Temperature Dependent Properties Using Functionally Graded Viscoelastic Model

Science.gov (United States)

Dave, Eshan V.

2009-01-01

Asphalt concrete pavements are inherently graded viscoelastic 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…

Nonlinear optical properties of colloidal silver nanoparticles produced by laser ablation in liquids

International Nuclear Information System (INIS)

Karavanskii, V A; Krasovskii, V I; Ivanchenko, P V; Simakin, Aleksandr V

2004-01-01

The optical and nonlinear optical properties of colloidal solutions of silver obtained by laser ablation in water and ethanol are studied. It is shown that freshly prepared colloids experience a full or partial sedimentation by changing their nonlinear optical properties. Aqueous colloids undergo a partial sedimentation and their nonlinear optical absorption changes to nonlinear optical transmission. The obtained results are interpreted using the Drude model for metal particles taking the particle size into account and can be explained by the sedimentation of larger silver particles accompanied by the formation of a stable colloid containing silver nanoparticles with a tentatively silver oxide shell. The characteristic size of particles forming such a stable colloid is determined and its optical nonlinearity is estimated. (nonlinear optical phenomena)

An Image-Based Finite Element Approach for Simulating Viscoelastic Response of Asphalt Mixture

Directory of Open Access Journals (Sweden)

Wenke Huang

2016-01-01

Full Text Available This paper presents an image-based micromechanical modeling approach to predict the viscoelastic behavior of asphalt mixture. An improved image analysis technique based on the OTSU thresholding operation was employed to reduce the beam hardening effect in X-ray CT images. We developed a voxel-based 3D digital reconstruction model of asphalt mixture with the CT images after being processed. In this 3D model, the aggregate phase and air void were considered as elastic materials while the asphalt mastic phase was considered as linear viscoelastic material. The viscoelastic constitutive model of asphalt mastic was implemented in a finite element code using the ABAQUS user material subroutine (UMAT. An experimental procedure for determining the parameters of the viscoelastic constitutive model at a given temperature was proposed. To examine the capability of the model and the accuracy of the parameter, comparisons between the numerical predictions and the observed laboratory results of bending and compression tests were conducted. Finally, the verified digital sample of asphalt mixture was used to predict the asphalt mixture viscoelastic behavior under dynamic loading and creep-recovery loading. Simulation results showed that the presented image-based digital sample may be appropriate for predicting the mechanical behavior of asphalt mixture when all the mechanical properties for different phases became available.

Studies of biaxial mechanical properties and nonlinear finite element modeling of skin.

Science.gov (United States)

Shang, Xituan; Yen, Michael R T; Gaber, M Waleed

2010-06-01

The objective of this research is to conduct mechanical property studies of skin from two individual but potentially connected aspects. One is to determine the mechanical properties of the skin experimentally by biaxial tests, and the other is to use the finite element method to model the skin properties. Dynamic biaxial tests were performed on 16 pieces of abdominal skin specimen from rats. Typical biaxial stress-strain responses show that skin possesses anisotropy, nonlinearity and hysteresis. To describe the stress-strain relationship in forms of strain energy function, the material constants of each specimen were obtained and the results show a high correlation between theory and experiments. Based on the experimental results, a finite element model of skin was built to model the skin's special properties including anisotropy and nonlinearity. This model was based on Arruda and Boyce's eight-chain model and Bischoff et al.'s finite element model of skin. The simulation results show that the isotropic, nonlinear eight-chain model could predict the skin's anisotropic and nonlinear responses to biaxial loading by the presence of an anisotropic prestress state.

The changes of red blood cell viscoelasticity and sports anemia in male 24-hr ultra-marathoners

Directory of Open Access Journals (Sweden)

Che-Hung Liu

2018-05-01

Full Text Available Background: In endurance sports, stress, dehydration and release of chemical factors have been associated with red blood cell (RBC alterations of structure and function, which may contribute to sports anemia, a well-observed phenomenon during long-distance running. Until now, the investigation of the changes of viscoelastic properties of RBC membrane, a decisive factor of RBC deformability to avoid hemolysis, is lacking, especially in an Oriental population. Methods: nineteen runners were prospectively recruited into our study. Hematological parameters were analyzed before and immediately after the 2015 Taipei 24H Ultra-Marathon Festival, Taiwan. Video particle tracking microrheology was used to determine viscoelastic properties of each RBC sample by calculating the dynamic elastic modulus G′(f and the viscous modulus G″(f at frequency f = 20 Hz. Results: Haptoglobin, RBC count, hemoglobin, hematocrit, mean cell hemoglobin, plasma free hemoglobin and unsaturated iron-binding capacity values of the recruited runners showed a statistically significant drop in the post-race values. Blood concentration of reticulocyte and ferritin were significantly higher at post-race compared with pre-race. 15 out of the 19 runners had a concurrent change in the elastic and the viscous moduli of their RBCs. Changes in the elastic and the viscous moduli were correlated with changes in the RBC count, hemoglobin and hematocrit. Conclusion: Viscoelasticity properties, the elastic modulus G′(f and the viscous modulus G″(f of RBCs are associated with endurance exercise-induced anemia. Keywords: Clinical sports medicine, Red blood cell, Sports anemia, Ultra-marathon, Viscoelastic properties

Pseudospectral modeling and dispersion analysis of Rayleigh waves in viscoelastic media

Science.gov (United States)

Zhang, K.; Luo, Y.; Xia, J.; Chen, C.

2011-01-01

Multichannel Analysis of Surface Waves (MASW) is one of the most widely used techniques in environmental and engineering geophysics to determine shear-wave velocities and dynamic properties, which is based on the elastic layered system theory. Wave propagation in the Earth, however, has been recognized as viscoelastic and the propagation of Rayleigh waves presents substantial differences in viscoelastic media as compared with elastic media. Therefore, it is necessary to carry out numerical simulation and dispersion analysis of Rayleigh waves in viscoelastic media to better understand Rayleigh-wave behaviors in the real world. We apply a pseudospectral method to the calculation of the spatial derivatives using a Chebyshev difference operator in the vertical direction and a Fourier difference operator in the horizontal direction based on the velocity-stress elastodynamic equations and relations of linear viscoelastic solids. This approach stretches the spatial discrete grid to have a minimum grid size near the free surface so that high accuracy and resolution are achieved at the free surface, which allows an effective incorporation of the free surface boundary conditions since the Chebyshev method is nonperiodic. We first use an elastic homogeneous half-space model to demonstrate the accuracy of the pseudospectral method comparing with the analytical solution, and verify the correctness of the numerical modeling results for a viscoelastic half-space comparing the phase velocities of Rayleigh wave between the theoretical values and the dispersive image generated by high-resolution linear Radon transform. We then simulate three types of two-layer models to analyze dispersive-energy characteristics for near-surface applications. Results demonstrate that the phase velocity of Rayleigh waves in viscoelastic media is relatively higher than in elastic media and the fundamental mode increases by 10-16% when the frequency is above 10. Hz due to the velocity dispersion of P

Quasi-Static Viscoelastic Finite Element Model of an Aircraft Tire

Science.gov (United States)

Johnson, Arthur R.; Tanner, John A.; Mason, Angela J.

1999-01-01

An elastic large displacement thick-shell mixed finite element is modified to allow for the calculation of viscoelastic stresses. Internal strain variables are introduced at the element's stress nodes and are employed to construct a viscous material model. First order ordinary differential equations relate the internal strain variables to the corresponding elastic strains at the stress nodes. The viscous stresses are computed from the internal strain variables using viscous moduli which are a fraction of the elastic moduli. The energy dissipated by the action of the viscous stresses is included in the mixed variational functional. The nonlinear quasi-static viscous equilibrium equations are then obtained. Previously developed Taylor expansions of the nonlinear elastic equilibrium equations are modified to include the viscous terms. A predictor-corrector time marching solution algorithm is employed to solve the algebraic-differential equations. The viscous shell element is employed to computationally simulate a stair-step loading and unloading of an aircraft tire in contact with a frictionless surface.

Indentation analysis of active viscoelastic microplasmodia of P. polycephalum

Science.gov (United States)

Fessel, Adrian; Oettmeier, Christina; Wechsler, Klaus; Döbereiner, Hans-Günther

2018-01-01

Simple organisms like Physarum polycephalum realize complex behavior, such as shortest path optimization or habituation, via mechanochemical processes rather than by a network of neurons. A full understanding of these phenomena requires detailed investigation of the underlying mechanical properties. To date, micromechanical measurements on P. polycephalum are sparse and lack reproducibility. This prompts study of microplasmodia, a reproducible and homogeneous form of P. polycephalum that resembles the plasmodial ectoplasm responsible for mechanical stability and generation of forces. We combine investigation of ultra-structure and dimension of P. polycephalum with the analysis of data obtained by indentation of microplasmodia, employing a novel nonlinear viscoelastic scaling model that accounts for finite dimension of the sample. We identify the multi-modal distribution of parameters such as Young’s moduls, Poisson’s ratio, and relaxation times associated with viscous processes that cover five orders of magnitude. Results suggest a characterization of microplasmodia as porous, compressible structures that act like elastic solids with high Young’s modulus on short time scales, whereas on long time-scales and upon repeated indentation viscous behavior dominates and the effective modulus is significantly decreased. Furthermore, Young’s modulus is found to oscillate in phase with shape of microplasmodia, emphasizing that modeling P. polycephalum oscillations as a driven oscillator with constant moduli is not practicable.

Model and Comparative Study for Flow of Viscoelastic Nanofluids with Cattaneo-Christov Double Diffusion.

Directory of Open Access Journals (Sweden)

Tasawar Hayat

Full Text Available Here two classes of viscoelastic fluids have been analyzed in the presence of Cattaneo-Christov double diffusion expressions of heat and mass transfer. A linearly stretched sheet has been used to create the flow. Thermal and concentration diffusions are characterized firstly by introducing Cattaneo-Christov fluxes. Novel features regarding Brownian motion and thermophoresis are retained. The conversion of nonlinear partial differential system to nonlinear ordinary differential system has been taken into place by using suitable transformations. The resulting nonlinear systems have been solved via convergent approach. Graphs have been sketched in order to investigate how the velocity, temperature and concentration profiles are affected by distinct physical flow parameters. Numerical values of skin friction coefficient and heat and mass transfer rates at the wall are also computed and discussed. Our observations demonstrate that the temperature and concentration fields are decreasing functions of thermal and concentration relaxation parameters.

A frictional contact problem for an electro-viscoelastic body

Directory of Open Access Journals (Sweden)

Mircea Sofonea

2007-12-01

Full Text Available A mathematical model which describes the quasistatic frictional contact between a piezoelectric body and a deformable conductive foundation is studied. A nonlinear electro-viscoelastic constitutive law is used to model the piezoelectric material. Contact is described with the normal compliance condition, a version of Coulomb's law of dry friction, and a regularized electrical conductivity condition. A variational formulation of the model, in the form of a coupled system for the displacements and the electric potential, is derived. The existence of a unique weak solution of the model is established under a smallness assumption on the surface conductance. The proof is based on arguments of evolutionary variational inequalities and fixed points of operators.

Pearling Instabilities of a Viscoelastic Thread

Science.gov (United States)

Deblais, A.; Velikov, K. P.; Bonn, D.

2018-05-01

Pearling instabilities of slender viscoelastic threads have received much attention, but remain incompletely understood. We study the instabilities in polymer solutions subject to uniaxial elongational flow. Two distinctly different instabilites are observed: beads on a string and blistering. The beads-on-a-string structure arises from a capillary instability whereas the blistering instability has a different origin: it is due to a coupling between stress and polymer concentration. By varying the temperature to change the solution properties we elucidate the interplay between flow and phase separation.

Nonlocal vibration and biaxial buckling of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between

Energy Technology Data Exchange (ETDEWEB)

Liu, J.C. [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); Zhang, Y.Q., E-mail: cyqzhang@zju.edu.cn [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); State Key Laboratory of Mechanical Structural Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Fan, L.F. [College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100084 (China)

2017-04-11

The general equation for transverse vibration of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between and each nanoplate subjected to in-plane edge loads is formulated on the basis of the Eringen's nonlocal elastic theory and the Kelvin model. The factors of the structural damping, medium damping, small size effect, loading ratio, and Winkler modulus and shear modulus of the medium are incorporated in the formulation. Based on the Navier's method, the analytical solutions for vibrational frequency and buckling load of the system with simply supported boundary conditions are obtained. The influences of these factors on vibrational frequency and buckling load of the system are discussed. It is demonstrated that the vibrational frequency of the system for the out-of-phase vibration is dependent upon the structural damping, small size effect and viscoelastic Pasternak medium, whereas the vibrational frequency for the in-phase vibration is independent of the viscoelastic Pasternak medium. While the buckling load of the system for the in-phase buckling case has nothing to do with the viscoelastic Pasternak medium, the buckling load for the out-of-phase case is related to the small size effect, loading ratio and Pasternak medium. - Highlights: • Vibration of double-viscoelastic-FGM-nanoplate system under in-plane edge loads is investigated. • Biaxial buckling of the system with simply supported boundary conditions is analyzed. • Explicit expression for the vibrational frequency and buckling load is obtained. • Impacts of viscoelastic Pasternak medium on vibrational frequency and buckling load are discussed. • Influences of structural damping, small size effect and loading ratio are also considered.

Ultrasound viscoelasticity assessment using an adaptive torsional shear wave propagation method

Energy Technology Data Exchange (ETDEWEB)

Ouared, Abderrahmane [Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9, Canada and Institute of Biomedical Engineering, University of Montréal, Montréal, Québec H3T 1J4 (Canada); Kazemirad, Siavash; Montagnon, Emmanuel [Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9 (Canada); Cloutier, Guy, E-mail: guy.cloutier@umontreal.ca [Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9 (Canada); Department of Radiology, Radio-Oncology and Nuclear Medicine, University of Montréal, Montréal, Québec H3T 1J4 (Canada); Institute of Biomedical Engineering, University of Montréal, Montréal, Québec H3T 1J4 (Canada)

2016-04-15

Purpose: Different approaches have been used in dynamic elastography to assess mechanical properties of biological tissues. Most techniques are based on a simple inversion based on the measurement of the shear wave speed to assess elasticity, whereas some recent strategies use more elaborated analytical or finite element method (FEM) models. In this study, a new method is proposed for the quantification of both shear storage and loss moduli of confined lesions, in the context of breast imaging, using adaptive torsional shear waves (ATSWs) generated remotely with radiation pressure. Methods: A FEM model was developed to solve the inverse wave propagation problem and obtain viscoelastic properties of interrogated media. The inverse problem was formulated and solved in the frequency domain and its robustness to noise and geometric constraints was evaluated. The proposed model was validated in vitro with two independent rheology methods on several homogeneous and heterogeneous breast tissue-mimicking phantoms over a broad range of frequencies (up to 400 Hz). Results: Viscoelastic properties matched benchmark rheology methods with discrepancies of 8%–38% for the shear modulus G′ and 9%–67% for the loss modulus G″. The robustness study indicated good estimations of storage and loss moduli (maximum mean errors of 19% on G′ and 32% on G″) for signal-to-noise ratios between 19.5 and 8.5 dB. Larger errors were noticed in the case of biases in lesion dimension and position. Conclusions: The ATSW method revealed that it is possible to estimate the viscoelasticity of biological tissues with torsional shear waves when small biases in lesion geometry exist.

Non-linear Response and Viscoelastic Properties of Lipid-Coated Microbubbles: DSPC versus DPPC

NARCIS (Netherlands)

van Rooij, T.; Luan, Y.; Renaud, G.; van der Steen, A.F.W.; Versluis, Michel; de Jong, N.; Kooiman, K.

2015-01-01

For successful in vivo contrast-enhanced ultrasound imaging (CEUS) and ultrasound molecular imaging, detailed knowledge of stability and acoustical properties of the microbubbles is essential. Here, we compare these aspects of lipid-coated microbubbles that have either

Assisted heterogeneous multinucleation and bubble growth in semicrystalline ethylene-vinyl acetate copolymer/expanded graphite nanocomposite foams: Control of morphology and viscoelastic properties

Directory of Open Access Journals (Sweden)

O. Yousefzade

2015-10-01

Full Text Available Nanocomposite foams of ethylene-vinyl acetate copolymer (EVA reinforced by expanded graphite (EG were prepared using supercritical nitrogen in batch foaming process. Effects of EG particle size, crosslinking of EVA chains and foaming temperature on the cell morphology and foam viscoelastic properties were investigated. EG sheet surface interestingly provide multiple heterogeneous nucleation sites for bubbles. This role is considerably intensified by incorporating lower loadings of EG with higher aspect ratio. The amorphous and non-crosslinked domains of EVA matrix constitute denser bubble areas. Higher void fraction and more uniform cell structure is achieved for non-crosslinked EVA/EG nanocomposites foamed at higher temperatures. With regard to the structural variation, the void fraction of foam samples decreases with increasing the EG content. Storage and loss moduli were analyzed to study the viscoelastic properties of nanocomposite foams. Surprisingly, the foaming process of EVA results in a drastic reduction in loss and storage moduli regardless of whether the thermoplastic matrix contains EG nanofiller or not. For the EVA/EG foams with the same composition, the nanocomposite having higher void fraction shows relatively lower loss modulus and more restricted molecular movements. The study findings have verified that the dynamics of polymer chains varies after foaming EVA matrix in the presence of EG.

Geometric properties of Banach spaces and nonlinear iterations

CERN Document Server

Chidume, Charles

2009-01-01

Nonlinear functional analysis and applications is an area of study that has provided fascination for many mathematicians across the world. This monograph delves specifically into the topic of the geometric properties of Banach spaces and nonlinear iterations, a subject of extensive research over the past thirty years. Chapters 1 to 5 develop materials on convexity and smoothness of Banach spaces, associated moduli and connections with duality maps. Key results obtained are summarized at the end of each chapter for easy reference. Chapters 6 to 23 deal with an in-depth, comprehensive and up-to-date coverage of the main ideas, concepts and results on iterative algorithms for the approximation of fixed points of nonlinear nonexpansive and pseudo-contractive-type mappings. This includes detailed workings on solutions of variational inequality problems, solutions of Hammerstein integral equations, and common fixed points (and common zeros) of families of nonlinear mappings. Carefully referenced and full of recent,...

Studies of the viscoelastic properties of water confined between surfaces of specified chemical nature.

Energy Technology Data Exchange (ETDEWEB)

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.

Nonlinear friction dynamics on polymer surface under accelerated movement

Directory of Open Access Journals (Sweden)

Yuuki Aita

2017-04-01

Full Text Available Nonlinear phenomena on the soft material surface are one of the most exciting topics of chemical physics. However, only a few reports exist on the friction phenomena under accelerated movement, because friction between two solid surfaces is considered a linear phenomenon in many cases. We aim to investigate how nonlinear accelerated motion affects friction on solid surfaces. In the present study, we evaluate the frictional forces between two polytetrafluoroethylene (PTFE resins using an advanced friction evaluation system. On PTFE surfaces, the normalized delay time δ, which is the time lag in the response of the friction force to the accelerated movement, is observed in the pre-sliding friction process. Under high-velocity conditions, kinetic friction increases with velocity. Based on these experimental results, we propose a two-phase nonlinear model including a pre-sliding process (from the beginning of sliding of a contact probe to the establishment of static friction and a kinetic friction process. The present model consists of several factors including velocity, acceleration, stiffness, viscosity, and vertical force. The findings reflecting the viscoelastic properties of soft material is useful for various fields such as in the fabrication of clothes, cosmetics, automotive materials, and virtual reality systems as well as for understanding friction phenomena on soft material surfaces.

Nonlinear Multigrid solver exploiting AMGe Coarse Spaces with Approximation Properties

DEFF Research Database (Denmark)

Christensen, Max la Cour; Villa, Umberto; Engsig-Karup, Allan Peter

The paper introduces a nonlinear multigrid solver for mixed finite element discretizations based on the Full Approximation Scheme (FAS) and element-based Algebraic Multigrid (AMGe). The main motivation to use FAS for unstructured problems is the guaranteed approximation property of the AMGe coarse...... properties of the coarse spaces. With coarse spaces with approximation properties, our FAS approach on unstructured meshes has the ability to be as powerful/successful as FAS on geometrically refined meshes. For comparison, Newton’s method and Picard iterations with an inner state-of-the-art linear solver...... are compared to FAS on a nonlinear saddle point problem with applications to porous media flow. It is demonstrated that FAS is faster than Newton’s method and Picard iterations for the experiments considered here. Due to the guaranteed approximation properties of our AMGe, the coarse spaces are very accurate...

Transient waves in visco-elastic media

CERN Document Server

Ricker, Norman

1977-01-01

Developments in Solid Earth Geophysics 10: Transient Waves in Visco-Elastic Media deals with the propagation of transient elastic disturbances in visco-elastic media. More specifically, it explores the visco-elastic behavior of a medium, whether gaseous, liquid, or solid, for very-small-amplitude disturbances. This volume provides a historical overview of the theory of the propagation of elastic waves in solid bodies, along with seismic prospecting and the nature of seismograms. It also discusses the seismic experiments, the behavior of waves propagated in accordance with the Stokes wave

Feasibility of Residual Stress Nondestructive Estimation Using the Nonlinear Property of Critical Refraction Longitudinal Wave

Directory of Open Access Journals (Sweden)

Yu-Hua Zhang

2017-01-01

Full Text Available Residual stress has significant influence on the performance of mechanical components, and the nondestructive estimation of residual stress is always a difficult problem. This study applies the relative nonlinear coefficient of critical refraction longitudinal (LCR wave to nondestructively characterize the stress state of materials; the feasibility of residual stress estimation using the nonlinear property of LCR wave is verified. The nonlinear ultrasonic measurements based on LCR wave are conducted on components with known stress state to calculate the relative nonlinear coefficient. Experimental results indicate that the relative nonlinear coefficient monotonically increases with prestress and the increment of relative nonlinear coefficient is about 80%, while the wave velocity only decreases about 0.2%. The sensitivity of the relative nonlinear coefficient for stress is much higher than wave velocity. Furthermore, the dependence between the relative nonlinear coefficient and deformation state of components is found. The stress detection resolution based on the nonlinear property of LCR wave is 10 MPa, which has higher resolution than wave velocity. These results demonstrate that the nonlinear property of LCR wave is more suitable for stress characterization than wave velocity, and this quantitative information could be used for residual stress estimation.

NONLINEAR MULTIGRID SOLVER EXPLOITING AMGe COARSE SPACES WITH APPROXIMATION PROPERTIES

Energy Technology Data Exchange (ETDEWEB)

Christensen, Max La Cour [Technical Univ. of Denmark, Lyngby (Denmark); Villa, Umberto E. [Univ. of Texas, Austin, TX (United States); Engsig-Karup, Allan P. [Technical Univ. of Denmark, Lyngby (Denmark); Vassilevski, Panayot S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2016-01-22

The paper introduces a nonlinear multigrid solver for mixed nite element discretizations based on the Full Approximation Scheme (FAS) and element-based Algebraic Multigrid (AMGe). The main motivation to use FAS for unstruc- tured problems is the guaranteed approximation property of the AMGe coarse spaces that were developed recently at Lawrence Livermore National Laboratory. These give the ability to derive stable and accurate coarse nonlinear discretization problems. The previous attempts (including ones with the original AMGe method, [5, 11]), were less successful due to lack of such good approximation properties of the coarse spaces. With coarse spaces with approximation properties, our FAS approach on un- structured meshes should be as powerful/successful as FAS on geometrically re ned meshes. For comparison, Newton's method and Picard iterations with an inner state-of-the-art linear solver is compared to FAS on a nonlinear saddle point problem with applications to porous media ow. It is demonstrated that FAS is faster than Newton's method and Picard iterations for the experiments considered here. Due to the guaranteed approximation properties of our AMGe, the coarse spaces are very accurate, providing a solver with the potential for mesh-independent convergence on general unstructured meshes.

Enhancing the Damping Properties of Viscoelastic Composites by Topology Optimization

DEFF Research Database (Denmark)

Andreasen, Casper Schousboe; Andreassen, Erik; Sigmund, Ole

Vibrations, if undamped, might be annoying or even dangerous. Most often some kind of damping mechanism is applied in order to limit the vibration level. Vibration insulators, for instance of rubber material, have favorable damping characteristics but lack the structural stiffness often needed...... in engineering structures. Thus, materials or composites with high stiffness and high damping are of great interest to the industry. The inherent compromise between high stiffness and high damping in viscoelastic materials has been treated theoretically [2, 3] and experimentally [1]. It has been shown that high...

Stress-based viscoelastic master curve construction of model tire tread compounds

NARCIS (Netherlands)

Maghami, S.; Dierkes, W.; Noordermeer, J.W.M.; Tolpekina, T.; Schultz, S.; Gögelein, C.; Wrana, C.; Gil-Negrete, Nere; Asier, Alonso

2013-01-01

One of the important aspects in the development of new tire compounds is the correlation between the dynamic mechanical properties of the rubber, measured on laboratory scale, and the actual tire performance. In order to predict wet traction, the viscoelastic behavior of the rubber materials at high

Characterizing viscoelasticity of unhydrolyzed chicken sternal cartilage extract suspensions: Towards development of injectable therapeutics formulations.

Science.gov (United States)

Hama, Brian; Mahajan, Gautam; Kothapalli, Chandrasekhar

2017-08-01

Exogenous delivery of cartilage extract is being explored as a promising candidate for knee arthritis treatment as it biomimics native cartilage tissue characteristics. In this study, we report on the rheological characterization of aqueous suspensions constituted from a powdered form of unhydrolyzed chicken sternum extract. The effect of particle size (as-received vs. milled), suspension fluid (water vs. PBS), and temperature (37°C vs. 4°C), on the viscoelastic properties of the sternum extract based particulate suspensions were evaluated. Results showed that these suspensions exhibit shear-thinning characteristics as shear rate (γ̇) increases, while viscosity (η), storage (G'), and loss (G″) moduli of the suspensions increased with increasing particulate loading (ϕ: 2.5-10wt%). Reducing the as-received particle size by milling decreased G', G, and η of the suspensions and increased the influence of ϕ on these properties, possibly due to improved particle packing. Replacing water with PBS had no significant effect on the rheological properties, but temperature reduction from 37°C to 4°C increased G', G", and η of the suspensions and lowered the impact of powder loading on viscoelastic properties. The suspension's time-dependent response was typical of viscoelastic materials, characterized by an asymptotical approach to a final stress (stress relaxation) or strain (creep). Results were fit to a power-law model for creep, a general relaxation model for exponential decay in stress, Carreau-Yasuda models for flow curves, and a two-parameter Liu model to identify the maximum powder loading (ϕ m ). Among the various forces involved in particle-particle interactions within these suspensions, electrostatic forces appeared to dominate the most. Such characterization of the viscoelastic nature of these suspensions would help in formulating stable injectable cartilage extract based therapeutics for in vivo applications. Copyright © 2017 Elsevier Ltd. All

The visco-elastic multilayer program VEROAD

NARCIS (Netherlands)

Hopman, P.C.

1996-01-01

The mathematical principles and derivation of a linear visco-elastic multilayer computer program are described. The mathematical derivation is based on Fourier Transformation. The program is called VEROAD, which is an acronym for Visco-Elastic ROad Analysis Delft. The program allows calculation of

Nonlinear Dielectric Properties of Yeast Cells Cultured in Different Environmental Conditions

Science.gov (United States)

Kawanishi, Gomon; Fukuda, Naoki; Muraji, Masafumi

The harmonics of the electric current through yeast suspensions, the nonlinear dielectric properties of yeast cells, have particular patterns according to the biological activity of the cells and the measurement of these patterns is a technique for determining the activity of living cells. The concentration of glucose and oxygen in yeast culture medium influences the manifestation of fermentation or respiration of yeast cells. Measurements were made with yeast cells (Saccharomyces cerevisiae) cultured aerobically and anaerobically in sufficient glucose concentration, aerobic fermentation and anaerobic fermentation, and aerobically in limited glucose concentration, respiration. The results showed that the harmonics were barely apparent for yeast cells in aerobic fermentation and respiratory; however, cells in the anaerobic fermentation displayed substantial third and fifth harmonics. We can say that environmental condition affects the yeast cells' nonlinear properties, from another viewpoint, the measurements of the nonlinear properties are available to determine the activity of yeast cells adjusted to the conditions of their cultivation.

Development of probabilistic fatigue curve for asphalt concrete based on viscoelastic continuum damage mechanics

Directory of Open Access Journals (Sweden)

Himanshu Sharma

2016-07-01

Full Text Available Due to its roots in fundamental thermodynamic framework, continuum damage approach is popular for modeling asphalt concrete behavior. Currently used continuum damage models use mixture averaged values for model parameters and assume deterministic damage process. On the other hand, significant scatter is found in fatigue data generated even under extremely controlled laboratory testing conditions. Thus, currently used continuum damage models fail to account the scatter observed in fatigue data. This paper illustrates a novel approach for probabilistic fatigue life prediction based on viscoelastic continuum damage approach. Several specimens were tested for their viscoelastic properties and damage properties under uniaxial mode of loading. The data thus generated were analyzed using viscoelastic continuum damage mechanics principles to predict fatigue life. Weibull (2 parameter, 3 parameter and lognormal distributions were fit to fatigue life predicted using viscoelastic continuum damage approach. It was observed that fatigue damage could be best-described using Weibull distribution when compared to lognormal distribution. Due to its flexibility, 3-parameter Weibull distribution was found to fit better than 2-parameter Weibull distribution. Further, significant differences were found between probabilistic fatigue curves developed in this research and traditional deterministic fatigue curve. The proposed methodology combines advantages of continuum damage mechanics as well as probabilistic approaches. These probabilistic fatigue curves can be conveniently used for reliability based pavement design. Keywords: Probabilistic fatigue curve, Continuum damage mechanics, Weibull distribution, Lognormal distribution

Viscoelastic love-type surface waves

Science.gov (United States)

Borcherdt, Roger D.

2008-01-01

The general theoretical solution for Love-Type surface waves in viscoelastic media provides theoreticalexpressions for the physical characteristics of the waves in elastic as well as anelastic media with arbitraryamounts of intrinsic damping. The general solution yields dispersion and absorption-coefficient curves for the waves as a function of frequency and theamount of intrinsic damping for any chosen viscoelastic model.Numerical results valid for a variety of viscoelastic models provide quantitative estimates of the physicalcharacteristics of the waves pertinent to models of Earth materials ranging from small amounts of damping in the Earth’s crust to moderate and large amounts of damping in soft soils and water-saturated sediments. Numerical results, presented herein, are valid for a wide range of solids and applications.

Mechanochemical pattern formation in simple models of active viscoelastic fluids and solids

Science.gov (United States)

Alonso, Sergio; Radszuweit, Markus; Engel, Harald; Bär, Markus

2017-11-01

The cytoskeleton of the organism Physarum polycephalum is a prominent example of a complex active viscoelastic material wherein stresses induce flows along the organism as a result of the action of molecular motors and their regulation by calcium ions. Experiments in Physarum polycephalum have revealed a rich variety of mechanochemical patterns including standing, traveling and rotating waves that arise from instabilities of spatially homogeneous states without gradients in stresses and resulting flows. Herein, we investigate simple models where an active stress induced by molecular motors is coupled to a model describing the passive viscoelastic properties of the cellular material. Specifically, two models for viscoelastic fluids (Maxwell and Jeffrey model) and two models for viscoelastic solids (Kelvin-Voigt and Standard model) are investigated. Our focus is on the analysis of the conditions that cause destabilization of spatially homogeneous states and the related onset of mechano-chemical waves and patterns. We carry out linear stability analyses and numerical simulations in one spatial dimension for different models. In general, sufficiently strong activity leads to waves and patterns. The primary instability is stationary for all active fluids considered, whereas all active solids have an oscillatory primary instability. All instabilities found are of long-wavelength nature reflecting the conservation of the total calcium concentration in the models studied.

Numerical study of propagation properties of surface plasmon polaritons in nonlinear media

KAUST Repository

Sagor, Rakibul Hasan; Ghulam Saber, Md.; Alsunaidi, Mohammad

2016-01-01

We present a time-domain algorithm for simulating nonlinear propagation of surface plasmon polaritons (SPPs) in chalcogenide glass. Due to the high non-linearity property and strong dispersion and confinement chalcogenide glasses are widely known

The viscoelastic properties of the protein-rich materials from the fermented hard wheat, soft wheat and barley flours

Science.gov (United States)

The linear and non-linear rheological properties 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 linear and non-linear rheologi...

Viscoelasticity-based MR elastography of skeletal muscle

International Nuclear Information System (INIS)

Klatt, Dieter; Papazoglou, Sebastian; Sack, Ingolf; Braun, Juergen

2010-01-01

An in vivo multifrequency magnetic resonance elastography (MRE) protocol was developed for studying the viscoelastic properties of human skeletal muscle in different states of contraction. Low-frequency shear vibrations in the range of 25-62.5 Hz were synchronously induced into the femoral muscles of seven volunteers and measured in a cross-sectional view by encoding the fast-transverse shear wave component parallel to the muscle fibers. The so-called springpot model was used for deriving two viscoelastic constants, μ and α, from the dispersion functions of the complex shear modulus in relaxed and in loaded muscle. Representing the shear elasticity parallel to the muscle fibers, μ increased in all volunteers upon contraction from 2.68 ± 0.23 kPa to 3.87 ± 0.50 kPa. Also α varied with load, indicating a change in the geometry of the mechanical network of muscle from relaxation (α = 0.253 ± 0.009) to contraction (α = 0.270 ± 0.009). These results provide a reference for a future assessment of muscular dysfunction using rheological parameters.

Viscoelasticity-based MR elastography of skeletal muscle

Science.gov (United States)

Klatt, Dieter; Papazoglou, Sebastian; Braun, Jürgen; Sack, Ingolf

2010-11-01

An in vivo multifrequency magnetic resonance elastography (MRE) protocol was developed for studying the viscoelastic properties of human skeletal muscle in different states of contraction. Low-frequency shear vibrations in the range of 25-62.5 Hz were synchronously induced into the femoral muscles of seven volunteers and measured in a cross-sectional view by encoding the fast-transverse shear wave component parallel to the muscle fibers. The so-called springpot model was used for deriving two viscoelastic constants, μ and α, from the dispersion functions of the complex shear modulus in relaxed and in loaded muscle. Representing the shear elasticity parallel to the muscle fibers, μ increased in all volunteers upon contraction from 2.68 ± 0.23 kPa to 3.87 ± 0.50 kPa. Also α varied with load, indicating a change in the geometry of the mechanical network of muscle from relaxation (α = 0.253 ± 0.009) to contraction (α = 0.270 ± 0.009). These results provide a reference for a future assessment of muscular dysfunction using rheological parameters.

Viscoelasticity-based MR elastography of skeletal muscle

Energy Technology Data Exchange (ETDEWEB)

Klatt, Dieter; Papazoglou, Sebastian; Sack, Ingolf [Department of Radiology, Charite-Universitaetsmedizin, Berlin (Germany); Braun, Juergen, E-mail: ingolf.sack@charite.d [Institute of Medical Informatics, Charite-Universitaetsmedizin, Berlin (Germany)

2010-11-07

An in vivo multifrequency magnetic resonance elastography (MRE) protocol was developed for studying the viscoelastic properties of human skeletal muscle in different states of contraction. Low-frequency shear vibrations in the range of 25-62.5 Hz were synchronously induced into the femoral muscles of seven volunteers and measured in a cross-sectional view by encoding the fast-transverse shear wave component parallel to the muscle fibers. The so-called springpot model was used for deriving two viscoelastic constants, {mu} and {alpha}, from the dispersion functions of the complex shear modulus in relaxed and in loaded muscle. Representing the shear elasticity parallel to the muscle fibers, {mu} increased in all volunteers upon contraction from 2.68 {+-} 0.23 kPa to 3.87 {+-} 0.50 kPa. Also {alpha} varied with load, indicating a change in the geometry of the mechanical network of muscle from relaxation ({alpha} = 0.253 {+-} 0.009) to contraction ({alpha} = 0.270 {+-} 0.009). These results provide a reference for a future assessment of muscular dysfunction using rheological parameters.

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

Science.gov (United States)

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.

Viscoelastic characteristics and phytochemical properties of purple-rice drinks following ultrahigh pressure and pasteurization

Science.gov (United States)

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.

Tissue viscoelasticity is related to tissue composition but may not fully predict the apparent-level viscoelasticity in human trabecular bone – An experimental and finite element study

DEFF Research Database (Denmark)

Ojanen, X.; Tanska, P.; Malo, M. K.H.

2017-01-01

Trabecular bone is viscoelastic under dynamic loading. However, it is unclear how tissue viscoelasticity controls viscoelasticity at the apparent-level. In this study, viscoelasticity of cylindrical human trabecular bone samples (n = 11, male, age 18–78 years) from 11 proximal femurs were charact......). These findings indicate that bone tissue viscoelasticity is affected by tissue composition but may not fully predict the macroscale viscoelasticity in human trabecular bone....

Nonlinear optical properties measurement of polypyrrole -carbon nanotubes prepared by an electrochemical polymerization method

Directory of Open Access Journals (Sweden)

Shahriari

2017-02-01

Full Text Available In this work, the optical properties dependence of Multi-Walled Carbon Nanotubes (MWNT on concentration was discussed. MWNT samples were prepared in polypyrrole by an electrochemical polymerization of monomers, in the presence of different concentrations of MWNTs, using Sodium Dodecyl-Benzen-Sulfonate (SDBS as surfactant at room temperature. The nonlinear refractive and nonlinear absorbtion indices were measured using a low power CW laser beam operated at 532 nm using z-scan method. The results show that nonlinear refractive and nonlinear absorbtion indices tend to be increased with increasing the concentration of carbon nanotubes. Optical properties of  carbone nanotubes indicate that they are good candidates for nonlinear optical devices

Improving the sustainability of asphalt pavements through developing a predictive model with fundamental material properties.

Science.gov (United States)

2009-08-01

This study presents the numerical implementation and validation of general constitutive relationships for describing the : nonlinear behavior of asphalt concrete mixes. These constitutive relationships incorporate nonlinear viscoelasticity and : visc...

Understanding viscoelasticity an introduction to rheology

CERN Document Server

Phan-Thien, Nhan

2017-01-01

This book presents an introduction to viscoelasticity, in particular, to the theories of dilute polymer solutions and dilute suspensions of rigid particles in viscous and incompressible fluids. These theories are important, not just because they apply to practical problems of industrial interest, but because they form a solid theoretical base upon which mathematical techniques can be built, from which more complex theories can be constructed, to better mimic material behaviour. The emphasis of this book is not on the voluminous current topical research, but on the necessary tools to understand viscoelasticity. This is a compact book for a first year graduate course in viscoelasticity and modelling of viscoelastic multiphase fluids. The Dissipative Particle Dynamics (DPD) is introduced as a particle-based method, relevant in modelling of complex-structured fluids. All the basic ideas in DPD are reviewed. The third edition has been updated and expanded with new results in the meso-scale modelling, links between...

Understanding Viscoelasticity An Introduction to Rheology

CERN Document Server

Phan-Thien, Nhan

2013-01-01

This book presents an introduction to viscoelasticity; in particular, to the theories of dilute polymer solutions and dilute suspensions of rigid particles in viscous and incompressible fluids. These theories are important, not just because they apply to practical problems of industrial interest, but because they form a solid theoretical base upon which mathematical techniques can be built, from which more complex theories can be constructed, to better mimic material behaviour. The emphasis is not on the voluminous current topical research, but on the necessary tools to understand viscoelasticity at a first year graduate level. The main aim is to provide a still compact book, sufficient at the level of first year graduate course for those who wish to understand viscoelasticity and to embark in modeling of viscoelastic multiphase fluids. To this end, a new chapter on Dissipative Particle Dynamics (DPD) was introduced which is relevant to model complex-structured fluids. All the basic ideas in DPD are reviewed,...

Cutting edge science: Laser surgery illuminates viscoelasticity of merotelic kinetochores.

Science.gov (United States)

Cabello, Simon; Gachet, Yannick; Tournier, Sylvie

2016-03-28

Increasing evidence in eukaryotic cells suggests that mechanical forces are essential for building a robust mitotic apparatus and correcting inappropriate chromosome attachments. In this issue, Cojoc et al. (2016. J. Cell Biol., http://dx.doi.org/10.1083/jcb.201506011) use laser microsurgery in vivo to measure and study the viscoelastic properties of kinetochores. © 2016 Cabello.

The application of large amplitude oscillatory stress in a study of fully formed fibrin clots

Science.gov (United States)

Lamer, T. F.; Thomas, B. R.; Curtis, D. J.; Badiei, N.; Williams, P. R.; Hawkins, K.

2017-12-01

The suitability of controlled stress large amplitude oscillatory shear (LAOStress) for the characterisation of the nonlinear viscoelastic properties of fully formed fibrin clots is investigated. Capturing the rich nonlinear viscoelastic behaviour of the fibrin network is important for understanding the structural behaviour of clots formed in blood vessels which are exposed to a wide range of shear stresses. We report, for the first time, that artefacts due to ringing exist in both the sample stress and strain waveforms of a LAOStress measurement which will lead to errors in the calculation of nonlinear viscoelastic properties. The process of smoothing the waveforms eliminates these artefacts whilst retaining essential rheological information. Furthermore, we demonstrate the potential of LAOStress for characterising the nonlinear viscoelastic properties of fibrin clots in response to incremental increases of applied stress up to the point of fracture. Alternating LAOStress and small amplitude oscillatory shear measurements provide detailed information of reversible and irreversible structural changes of the fibrin clot as a consequence of elevated levels of stress. We relate these findings to previous studies involving large scale deformations of fibrin clots. The LAOStress technique may provide useful information to help understand why some blood clots formed in vessels are stable (such as in deep vein thrombosis) and others break off (leading to a life threatening pulmonary embolism).

Newtonian heating effects in three-dimensional flow of viscoelastic fluid

International Nuclear Information System (INIS)

Qayyum, A.; Hayat, T.; Alhuthali, M. S.; Malaikah, H. M.

2014-01-01

A mathematical model is constructed to investigate the three-dimensional flow of a non-Newtonian fluid. An incompressible viscoelastic fluid is used in mathematical formulation. The conjugate convective process (in which heat the transfer rate from the bounding surface with a finite capacity is proportional to the local surface temperature) in three-dimensional flow of a differential type of non-Newtonian fluid is analyzed for the first time. Series solutions for the nonlinear differential system are computed. Plots are presented for the description of emerging parameters entering into the problem. It is observed that the conjugate heating phenomenon causes an appreciable increase in the temperature at the stretching wall. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Finite volume multigrid method of the planar contraction flow of a viscoelastic fluid

Science.gov (United States)

Moatssime, H. Al; Esselaoui, D.; Hakim, A.; Raghay, S.

2001-08-01

This paper reports on a numerical algorithm for the steady flow of viscoelastic fluid. The conservative and constitutive equations are solved using the finite volume method (FVM) with a hybrid scheme for the velocities and first-order upwind approximation for the viscoelastic stress. A non-uniform staggered grid system is used. The iterative SIMPLE algorithm is employed to relax the coupled momentum and continuity equations. The non-linear algebraic equations over the flow domain are solved iteratively by the symmetrical coupled Gauss-Seidel (SCGS) method. In both, the full approximation storage (FAS) multigrid algorithm is used. An Oldroyd-B fluid model was selected for the calculation. Results are reported for planar 4:1 abrupt contraction at various Weissenberg numbers. The solutions are found to be stable and smooth. The solutions show that at high Weissenberg number the domain must be long enough. The convergence of the method has been verified with grid refinement. All the calculations have been performed on a PC equipped with a Pentium III processor at 550 MHz. Copyright

Seasonality Effects on Nonlinear Properties of Hydrometeorological Records: A New Method of Data Analysis

Science.gov (United States)

Livina, V. N.; Ashkenazy, Y.; Bunde, A.; Havlin, S.

2007-12-01

Climatic time series in general, and hydrological time series in particular, exhibit pronounced annual periodicity. This periodicity and its corresponding harmonics affect the nonlinear properties of the relevant time series (i.e., the long-range volatility correlations and width of multifractal spectrum) and thus have to be filtered out before studying fractal and volatility properties. We compare several filtering techniques (one of them proposed here) and find that in order to eliminate the periodicity effect on the nonlinear properties of the time series (i.e., the volatility and multifractal properties) it is necessary to filter out the seasonal standard deviation in addition to the filtering of the seasonal mean. The obtained results indicate weak volatility correlations (weak nonlinearity) in the river data, and this can be seen using different filterings approaches. [1] Livina~V.~N., Y.~Ashkenazy, A.~Bunde, and S.~Havlin, Seasonality effects on nonlinear properties of hydrometeorological records, in Extremes, Trends, and Correlations in Hydrology and Climate (ed. by J.P.Kropp & H.-J.Schellnhuber), Springer, Berlin, submitted.

Viscoelastic Properties of Hyaluronan in Physiological Conditions [version 1; referees: 2 approved

Directory of Open Access Journals (Sweden)

Mary K. Cowman

2015-08-01

Full Text Available 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

Rough viscoelastic sliding contact: Theory and experiments

Science.gov (United States)

Carbone, G.; Putignano, C.

2014-03-01

In this paper, we show how the numerical theory introduced by the authors [Carbone and Putignano, J. Mech. Phys. Solids 61, 1822 (2013), 10.1016/j.jmps.2013.03.005] can be effectively employed to study the contact between viscoelastic rough solids. The huge numerical complexity is successfully faced up by employing the adaptive nonuniform mesh developed by the authors in Putignano et al. [J. Mech. Phys. Solids 60, 973 (2012), 10.1016/j.jmps.2012.01.006]. Results mark the importance of accounting for viscoelastic effects to correctly simulate the sliding rough contact. In detail, attention is, first, paid to evaluate the viscoelastic dissipation, i.e., the viscoelastic friction. Fixed the sliding speed and the normal load, friction is completely determined. Furthermore, since the methodology employed in the work allows to study contact between real materials, a comparison between experimental outcomes and numerical prediction in terms of viscoelastic friction is shown. The good agreement seems to validate—at least partially—the presented methodology. Finally, it is shown that viscoelasticity entails not only the dissipative effects previously outlined, but is also strictly related to the anisotropy of the contact solution. Indeed, a marked anisotropy is present in the contact region, which results stretched in the direction perpendicular to the sliding speed. In the paper, the anisotropy of the deformed surface and of the contact area is investigated and quantified.

Non-linear Shear and Uniaxial Extensional Rheology of Polyether-Ester-Sulfonate Copolymer Ionomer Melts

DEFF Research Database (Denmark)

Shabbir, Aamir; Huang, Qian; P. Baeza, Guilhem

2017-01-01

We present unique nonlinear shear and extensional rheology data of unentan-gled amorphous polyester ionomers based on polyethers and sulphonated phthalates with sodium/ lithium counterions. Previous linear viscoelastic (LVE) measurements1 showed significant elasticity in these ionomers due...

Linear and nonlinear optical properties of borate crystals as ...

Indian Academy of Sciences (India)

Unknown

crystal series, with an accuracy acceptable for materials development/design, and answer the questions often ... Optical property; nonlinear optical crystals; first principles calculation. 1. ..... system, and is not in concept suitable to excitation pro-.

Experimental Characterization of Innovative Viscoelastic Foams

Directory of Open Access Journals (Sweden)

Massimo Viscardi

2016-05-01

Full Text Available The evolutionary trend in the automotive industry has produced over time numerous performance and aesthetic innovations, however, the exponential development related to transportation technologies also introduced new requirements concerning the environmental impact [1]. The awareness of ecological issues has led to a reorganization of the evaluations and the vehicle design, currently aimed at reducing the problems that have emerged in empirical investigations and the parallel increase in environmental solutions. The vehicle renewal process involves targeted technical mutations both to observance of ecology as to the safety and comfort of the driver. New recyclable materials and more resistant have been developed in order to minimize the environmental impact of the vehicle even at the end of the operating life of its components, as well as solutions relating to the reduction of noise pollution generated as a response to the requirements of comfort. Modern research programs on a global scale have set themselves the objective of exploiting the potentiality of innovative technologies in the optimization of vehicles efficiency, the noise reduction and in the consequent reduction of fuel burn. One of the crucial topics in the greening of the new generation automotive sector is therefore the use and development of high vibro-acoustic performance materials. The goal of this research is properly focused on the analysis of viscoelastic materials appointed to increase the damping of the vibrations generated in a vehicle. The use of a viscoelastic material in this context is due to its high property to convert vibrational energy into heat, providing a significant dissipation of the vibrations. Trade-off analyses are performed in order define the stiffness and damping capacity of several viscoelastic foams with different thickness and density.

Thermal convection of viscoelastic shear-thinning fluids

International Nuclear Information System (INIS)

Albaalbaki, Bashar; Khayat, Roger E; Ahmed, Zahir U

2016-01-01

The Rayleigh–Bénard convection for non-Newtonian fluids possessing both viscoelastic and shear-thinning behaviours is examined. The Phan-Thien–Tanner (PTT) constitutive equation is implemented to model the non-Newtonian character of the fluid. It is found that while the shear-thinning and viscoelastic effects could annihilate one another for the steady roll flow, presence of both behaviours restricts the roll stability limit significantly compared to the cases when the fluid is either inelastic shear-thinning or purely viscoelastic with constant viscosity. (paper)

Rheological (visco-elastic behaviour) analysis of cyclic olefin copolymers with application to hot embossing for microfabrication

International Nuclear Information System (INIS)

Jena, R K; Chen, X; Yue, C Y; Lam, Y C

2011-01-01

Transparent, amorphous cyclic olefin copolymers (COCs) have been frequently used for the fabrication of microfluidic devices using a hot embossing technique for numerous applications. In hot embossing, the polymer is deformed near its glass transition temperature (Tg), i.e. between Tg and Tg + 60 °C where the viscoelastic properties of the material are dominant. The proper characterization of the viscoelastic properties is of interest as this can lead to a better understanding of polymer flow behaviour during microfabrication. Furthermore, the ability to model its rheological behaviour will enable the prediction of the optimal hot embossing processing parameters. We performed small amplitude oscillatory shear experiments on four grades of COCs, TOPAS-8007, TOPAS-5013, TOPAS-6015 and TOPAS-6017, in order to characterize their flow behaviour. The experiments were conducted within the frequency range from 0.01 to 500 Hz at between Tg + 20 and Tg + 60 °C. The flow properties could be represented using a generalized Maxwell viscoelastic constitutive model with Williams–Landel–Ferry-type temperature dependence. Good fit of the experimental data was obtained over a wide range of temperatures. The model could be coupled with ABAQUS finite element software to predict the optimal conditions for fabricating a capillary electrophoresis micro-chip on a TOPAS-5013 substrate by hot embossing

Approximation of Viscoelastic Stresses from Newtonian Turbulent Kinematics

Science.gov (United States)

1988-09-01

birefringence of polyethylene oxide solutions in a four roll mill. J.Poly.Sci.:Poly.Phys.Ed. 14, 1111-1119. Dandridge, A., Meeten , G.H., Layec-Raphalen, M.N...flows. Poly. Comm. 25, 144-146. Metzner, A.B., & Astarita, G . 1967 External flow of viscoelastic materials: fluid property restrictions on the use of...dumbbell model for dilute solutions. Rheol.Acta 23, 151-162. Philippoff, W. 1956 Flow-birefringence and stress. Nature 178 , 811-812. Ryskin, G . 1987a

Viscoelastic modes in chiral liquid crystals

Indian Academy of Sciences (India)

amit@fs.rri.local.net (Amit Kumar Agarwal)

our studies on the viscoelastic modes of some chiral liquid crystals using dynamic light scattering. We discuss viscoelastic ... In the vicinity of the direct beam for a sample aligned in the Bragg mode and. 297 ... experimental investigations on these modes. Duke and Du ..... scattering volume is not true in practice. In an actual ...

Numerical simulation of viscoelastic layer rearrangement in polymer melts using OpenFOAM®

Energy Technology Data Exchange (ETDEWEB)

Köpplmayr, Thomas, E-mail: tkoepplmayr@gmail.com; Mayrhofer, Elias [Institute of Polymer Extrusion and Compounding, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz (Austria)

2015-05-22

In addition to their shear-thinning behavior, polymer melts are characterized by first and second normal stress differences, which cause secondary motions. Polymer coextrusion processes involve viscoelastic two-phase flows that influence layer formation. Using polymer melts with different pigmentation makes visible the layers deformed by second normal stress differences. We used a new solver for the OpenFOAM CFD toolbox which handles viscoelastic two-phase flows. A derivative of the volume-of-fluid (VoF) methodology was employed to describe the interface. Different types of polymer melt, such as polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were investigated. In a coextrusion process, the less viscous phase usually tends to encapsulate the more viscous one. However, the different viscoelastic properties of the melts also influence interface deformation. The materials were characterized by small-amplitude oscillatory-shear rheometry, and a multimode Giesekus model was used to fit shear viscosity, storage and loss modulus. Our simulations also took interfacial tension into account. Experimental observations and corresponding numerical simulations were found to be in good accordance.

Numerical simulation of viscoelastic layer rearrangement in polymer melts using OpenFOAM®

International Nuclear Information System (INIS)

Köpplmayr, Thomas; Mayrhofer, Elias

2015-01-01

In addition to their shear-thinning behavior, polymer melts are characterized by first and second normal stress differences, which cause secondary motions. Polymer coextrusion processes involve viscoelastic two-phase flows that influence layer formation. Using polymer melts with different pigmentation makes visible the layers deformed by second normal stress differences. We used a new solver for the OpenFOAM CFD toolbox which handles viscoelastic two-phase flows. A derivative of the volume-of-fluid (VoF) methodology was employed to describe the interface. Different types of polymer melt, such as polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were investigated. In a coextrusion process, the less viscous phase usually tends to encapsulate the more viscous one. However, the different viscoelastic properties of the melts also influence interface deformation. The materials were characterized by small-amplitude oscillatory-shear rheometry, and a multimode Giesekus model was used to fit shear viscosity, storage and loss modulus. Our simulations also took interfacial tension into account. Experimental observations and corresponding numerical simulations were found to be in good accordance

Viscoelasticity promotes collective swimming of sperm

Science.gov (United States)

Tung, Chih-Kuan; Harvey, Benedict B.; Fiore, Alyssa G.; Ardon, Florencia; Suarez, Susan S.; Wu, Mingming

From flocking birds to swarming insects, interactions of organisms large and small lead to the emergence of collective dynamics. Here, we report striking collective swimming of bovine sperm, with sperm orienting in the same direction within each cluster, enabled by the viscoelasticity of the fluid. A long-chain polyacrylamide solution was used as a model viscoelastic fluid such that its rheology can be fine-tuned to mimic that of bovine cervical mucus. In viscoelastic fluid, sperm formed dynamic clusters, and the cluster size increased with elasticity of the polyacrylamide solution. In contrast, sperm swam randomly and individually in Newtonian fluids of similar viscosity. Analysis of the fluid motion surrounding individual swimming sperm indicated that sperm-fluid interaction is facilitated by the elastic component of the fluid. We note that almost all biological fluids (e.g. mucus and blood) are viscoelastic in nature, this finding highlights the importance of fluid elasticity in biological function. We will discuss what the orientation fluctuation within a cluster reveals about the interaction strength. Supported by NIH Grant 1R01HD070038.

Modeling electrically active viscoelastic membranes.

Directory of Open Access Journals (Sweden)

Sitikantha Roy

Full Text Available The membrane protein prestin is native to the cochlear outer hair cell that is crucial to the ear's amplification and frequency selectivity throughout the whole acoustic frequency range. The outer hair cell exhibits interrelated dimensional changes, force generation, and electric charge transfer. Cells transfected with prestin acquire unique active properties similar to those in the native cell that have also been useful in understanding the process. Here we propose a model describing the major electromechanical features of such active membranes. The model derived from thermodynamic principles is in the form of integral relationships between the history of voltage and membrane resultants as independent variables and the charge density and strains as dependent variables. The proposed model is applied to the analysis of an active force produced by the outer hair cell in response to a harmonic electric field. Our analysis reveals the mechanism of the outer hair cell active (isometric force having an almost constant amplitude and phase up to 80 kHz. We found that the frequency-invariance of the force is a result of interplay between the electrical filtering associated with prestin and power law viscoelasticity of the surrounding membrane. Paradoxically, the membrane viscoelasticity boosts the force balancing the electrical filtering effect. We also consider various modes of electromechanical coupling in membrane with prestin associated with mechanical perturbations in the cell. We consider pressure or strains applied step-wise or at a constant rate and compute the time course of the resulting electric charge. The results obtained here are important for the analysis of electromechanical properties of membranes, cells, and biological materials as well as for a better understanding of the mechanism of hearing and the role of the protein prestin in this mechanism.

Dynamics and Stability of Rolling Viscoelastic Tires

Energy Technology Data Exchange (ETDEWEB)

Potter, Trevor [Univ. of California, Berkeley, CA (United States)

2013-04-30

Current steady state rolling tire calculations often do not include treads because treads destroy the rotational symmetry of the tire. We describe two methodologies to compute time periodic solutions of a two-dimensional viscoelastic tire with treads: solving a minimization problem and solving a system of equations. We also expand on work by Oden and Lin on free spinning rolling elastic tires in which they disovered a hierachy of N-peak steady state standing wave solutions. In addition to discovering a two-dimensional hierarchy of standing wave solutions that includes their N-peak hiearchy, we consider the eects of viscoelasticity on the standing wave solutions. Finally, a commonplace model of viscoelasticity used in our numerical experiments led to non-physical elastic energy growth for large tire speeds. We show that a viscoelastic model of Govindjee and Reese remedies the problem.

Symmetry properties of some nonlinear field theory models

International Nuclear Information System (INIS)

Shvachka, A.B.

1984-01-01

Various approaches towards the study of symmetry properties of some nonlinear evolution equations as well as possible ways of their computer implementation using the computer algebra systems langage are discussed. Special attention is paid to the method of pseudopotential investigation of formal integrability and isovector method for the equations of balance

Measurement of the viscoelastic compliance of the eustachian tube using a modified forced-response test.

Science.gov (United States)

Ghadiali, Samir N; Federspiel, William J; Swarts, J Douglas; Doyle, William J

2002-01-01

Eustachian tube compliance (ETC) was suggested to be an important determinate of function. Previous attempts to quantify ETC used summary measures that are not clearly related to the physical properties of the system. Here, we present a new method for measuring ETC that conforms more closely to the engineering definition of compliance. The forced response test was modified to include oscillations in applied flow after the forced tubal opening. Pressure and flow were recorded during the standard and modified test in 12 anesthetized cynomolgus monkeys. The resulting pressure-flow, hysteresis loops were compared with those predicted by a simple fluid-structure model of the Eustachian tube with linear-elastic or viscoelastic properties. The tubal compliance index (TCI) and a viscoelastic compliance (C(v)) were calculated from these data for each monkey. The behavior of a viscoelastic, but not a linear elastic model accurately reproduced the experimental data for the monkey. The TCI and C(v) were linearly related, but the shared variance in these measures was only 63%. This new method for measuring ETC captures all information contained in the traditional TCI, but also provides information regarding the contribution of wall viscosity to Eustachian tube mechanics.

Viscoelastic behavior of discrete human collagen fibrils

DEFF Research Database (Denmark)

Svensson, René; Hassenkam, Tue; Hansen, Philip

2010-01-01

Whole tendon and fibril bundles display viscoelastic behavior, but to the best of our knowledge this property has not been directly measured in single human tendon fibrils. In the present work an atomic force microscopy (AFM) approach was used for tensile testing of two human patellar tendon...... saline, cyclic testing was performed in the pre-yield region at different strain rates, and the elastic response was determined by a stepwise stress relaxation test. The elastic stress-strain response corresponded to a second-order polynomial fit, while the viscous response showed a linear dependence...

Nonlinear and anisotropic tensile properties of graft materials used in soft tissue applications.

Science.gov (United States)

Yoder, Jonathon H; Elliott, Dawn M

2010-05-01

The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson's ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT. The degree of anisotropy and non-linearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue. The Alloderm graft was anisotropic in both the toe- and linear-region of the stress-strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress-strain responses, were largely isotropic, had a linear-region modulus of 18MPa, and were nonlinear. OrthADAPT was anisotropic in the linear-region (131 MPA vs 47MPa in the toe-region) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0. Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application. Copyright 2010 Elsevier Ltd. All rights reserved.

Linear and nonlinear optical properties of Sb-doped GeSe2 thin films

Science.gov (United States)

Zhang, Zhen-Ying; Chen, Fen; Lu, Shun-Bin; Wang, Yong-Hui; Shen, Xiang; Dai, Shi-Xun; Nie, Qiu-Hua

2015-06-01

Sb-doped GeSe2 chalcogenide thin films are prepared by the magnetron co-sputtering method. The linear optical properties of as-deposited films are derived by analyzing transmission spectra. The refractive index rises and the optical band gap decreases from 2.08 eV to 1.41 eV with increasing the Sb content. X-ray photoelectron spectra further confirm the formation of a covalent Sb-Se bond. The third-order nonlinear optical properties of thin films are investigated under femtosecond laser excitation at 800 nm. The results show that the third-order nonlinear optical properties are enhanced with increasing the concentration of Sb. The nonlinear refraction indices of these thin films are measured to be on the order of 10-18 m2/W with a positive sign and the nonlinear absorption coefficients are obtained to be on the order of 10-10 m/W. These excellent properties indicate that Sb-doped Ge-Se films have a good prospect in the applications of nonlinear optical devices. Project supported by the National Key Basic Research Program of China (Grant No. 2012CB722703), the National Natural Science Foundation of China (Grant No. 61377061), the Young Leaders of Academic Climbing Project of the Education Department of Zhejiang Province, China (Grant No. pd2013092), the Program for Innovative Research Team of Ningbo City, China (Grant No. 2009B217), and the K. C. Wong Magna Fund in Ningbo University, China.

Direct measurement of nonlinear properties of bipartite quantum states.

Science.gov (United States)

Bovino, Fabio Antonio; Castagnoli, Giuseppe; Ekert, Artur; Horodecki, Paweł; Alves, Carolina Moura; Sergienko, Alexander Vladimir

2005-12-09

Nonlinear properties of quantum states, such as entropy or entanglement, quantify important physical resources and are frequently used in quantum-information science. They are usually calculated from a full description of a quantum state, even though they depend only on a small number of parameters that specify the state. Here we extract a nonlocal and a nonlinear quantity, namely, the Renyi entropy, from local measurements on two pairs of polarization-entangled photons. We also introduce a "phase marking" technique which allows the selection of uncorrupted outcomes even with nondeterministic sources of entangled photons. We use our experimental data to demonstrate the violation of entropic inequalities. They are examples of nonlinear entanglement witnesses and their power exceeds all linear tests for quantum entanglement based on all possible Bell-Clauser-Horne-Shimony-Holt inequalities.

Spectral dependence of third-order nonlinear optical properties in InN

International Nuclear Information System (INIS)

Ahn, H.; Lee, M.-T.; Chang, Y.-M.

2014-01-01

We report on the nonlinear optical properties of InN measured in a wide near-infrared spectral range with the femtosecond Z-scan technique. The above-bandgap nonlinear absorption in InN is found to originate from the saturation of absorption by the band-state-filling and its cross-section increases drastically near the bandgap energy. With below-bandgap excitation, the nonlinear absorption undergoes a transition from saturation absorption (SA) to reverse-SA (RSA), attributed to the competition between SA of band-tail states and two-photon-related RSA. The measured large nonlinear refractive index of the order of 10 −10 cm 2 /W indicates InN as a potential material for all-optical switching and related applications

Structure/property relationships in non-linear optical materials

Energy Technology Data Exchange (ETDEWEB)

Cole, J M [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France); [Durham Univ. (United Kingdom); Howard, J A.K. [Durham Univ. (United Kingdom); McIntyre, G J [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

1997-04-01

The application of neutrons to the study of structure/property relationships in organic non-linear optical materials (NLOs) is described. In particular, charge-transfer effects and intermolecular interactions are investigated. Charge-transfer effects are studied by charge-density analysis and an example of one such investigation is given. The study of intermolecular interactions concentrates on the effects of hydrogen-bonding and an example is given of two structurally similar molecules with very disparate NLO properties, as a result of different types of hydrogen-bonding. (author). 3 refs.

Constitution-specific features of perspiration and skin visco-elasticity in SCM.

Science.gov (United States)

Kim, Young-Min; Ku, Boncho; Jung, Chang Jin; Kim, Jaeuk U; Jeon, Young Ju; Kim, Keun Ho; Kim, Jong Yeol

2014-01-15

Human skin properties have been used as an important diagnostic component in traditional medicine as they change with health conditions. Sasang constitutional medicine (SCM) puts emphasis on the recognition of the constitution-specific skin features prior to the diagnostic decision of health. In this work, in search of skin-characteristics effectively reflecting SCM features, we compared several skin properties such as perspiration, visco-elasticity, elasticity, and elasticity hysteresis, in several candidate body parts. We conducted a clinical study in which a total of 111 healthy females aged 50 - 70 years participated with their Sasang constitution (SC) types determined objectively by the Sasang constitutional analytic tool. Perspiration on the skin surface was estimated by using a capacitance sensor to measure the amount of moisture on the palm, forehead, and philtrum before and after a heating stimulus. We acquired the visco-elasticity, elasticity, and elasticity hysteresis at the forearm by Dermalab's elasticity sensing device. An analysis of covariance (ANCOVA) was conducted to evaluate the effect of SC on the nine skin features acquired. The visco-elasticity of the forearm of the Soeum-in (SE) group was significantly lower than that of the Taeeum-in (TE) group (F = 68.867, p elasticity hysteresis of the SE group was higher than that of the TE group (F = 10.364, p elasticity, elasticity hysteresis, perspiration on the forehead and philtrum. Our findings are based on a novel interpretation of the SCM literature and will contribute to developing the constitutional health status evaluation system in SCM.

Viscoelastic behaviour of hydrogel-based composites for tissue engineering under mechanical load.

Science.gov (United States)

Kocen, Rok; Gasik, Michael; Gantar, Ana; Novak, Saša

2017-03-06

Along with biocompatibility, bioinductivity and appropriate biodegradation, mechanical properties are also of crucial importance for tissue engineering scaffolds. Hydrogels, such as gellan gum (GG), are usually soft materials, which may benefit from the incorporation of inorganic particles, e.g. bioactive glass, not only due to the acquired bioactivity, but also due to improved mechanical properties. They exhibit complex viscoelastic properties, which can be evaluated in various ways. In this work, to reliably evaluate the effect of the bioactive glass (BAG) addition on viscoelastic properties of the composite hydrogel, we employed and compared the three most commonly used techniques, analyzing their advantages and limitations: monotonic uniaxial unconfined compression, small amplitude oscillatory shear (SAOS) rheology and dynamic mechanical analysis (DMA). Creep and small amplitude dynamic strain-controlled tests in DMA are suggested as the best ways for the characterization of mechanical properties of hydrogel composites, whereas the SAOS rheology is more useful for studying the hydrogel's processing kinetics, as it does not induce volumetric changes even at very high strains. Overall, the results confirmed a beneficial effect of BAG (nano)particles on the elastic modulus of the GG-BAG composite hydrogel. The Young's modulus of 6.6 ± 0.8 kPa for the GG hydrogel increased by two orders of magnitude after the addition of 2 wt.% BAG particles (500-800 kPa).

Theory of viscoelasticity an introduction

CERN Document Server

Christensen, R

1982-01-01

Theory of Viscoelasticity: An Introduction, Second Edition discusses the integral form of stress strain constitutive relations. The book presents the formulation of the boundary value problem and demonstrates the separation of variables condition.The text describes the mathematical framework to predict material behavior. It discusses the problems to which integral transform methods do not apply. Another topic of interest is the thermoviscoelastic stress analysis. The section that follows describes the heat conduction, glass transition criterion, viscoelastic Rayleigh waves, optimal str

The dynamic deformation of a layered viscoelastic medium under surface excitation

International Nuclear Information System (INIS)

Aglyamov, Salavat R; Karpiouk, Andrei B; Emelianov, Stanislav Y; Wang, Shang; Li, Jiasong; Larin, Kirill V; Twa, Michael

2015-01-01

In this study the dynamic behavior of a layered viscoelastic medium in response to the harmonic and impulsive acoustic radiation force applied to its surface was investigated both theoretically and experimentally. An analytical solution for a layered viscoelastic compressible medium in frequency and time domains was obtained using the Hankel transform. A special incompressible case was considered to model soft biological tissues. To verify our theoretical model, experiments were performed using tissue-like gel-based phantoms with varying mechanical properties. A 3.5 MHz single-element focused ultrasound transducer was used to apply the radiation force at the surface of the phantoms. A phase-sensitive optical coherence tomography system was used to track the displacements of the phantom surface. Theoretically predicted displacements were compared with experimental measurements. The role of the depth dependence of the elastic properties of a medium in its response to an acoustic pulse at the surface was studied. It was shown that the low-frequency vibrations at the surface are more sensitive to the deep layers than high-frequency ones. Therefore, the proposed model in combination with spectral analysis can be used to evaluate depth-dependent distribution of the mechanical properties based on the measurements of the surface deformation. (paper)

Investigation of electrokinetic and electrorheological properties of polyindole prepared in the presence of a surfactant

Energy Technology Data Exchange (ETDEWEB)

Unal, H. Ibrahim, E-mail: hiunal@gazi.edu.tr [Gazi University, Chemistry Department, Smart Materials Research Lab., Ankara (Turkey); Sahan, Bekir; Erol, Ozlem [Gazi University, Chemistry Department, Smart Materials Research Lab., Ankara (Turkey)

2012-05-15

Highlights: Black-Right-Pointing-Pointer Aggregated morphology was determined for PIN, spherical and porous hollows and everniae form morphologies were recorded for SPIN. Black-Right-Pointing-Pointer The PIN/SO and SPIN/SO systems showed almost similar electrokinetic attitudes and a typical shear thinning non-Newtonian viscoelastic behavior, vibration damping capability at elevated frequencies, and enhanced storage moduli with increasing temperature. Black-Right-Pointing-Pointer Non-linear recoverable viscoelastic manner was revealed from the creep-recovery experiments under external electric field. - Abstract: In this study, synthesis of polyindole (PIN) was carried out without and with the presence of a sodium dodecyl sulfate (SDS) surfactant (SPIN), using FeCl{sub 3} as an oxidizing agent. The synthesized materials were subjected to various characterizations techniques namely: particle size, magnetic susceptibility, elemental analysis, density, conductivity, dielectric constant, FTIR, {sup 1}H NMR, TGA, XRD, and SEM. Characterization results revealed the successful preparation of the homopolymers of PIN and SPIN. Zeta ({zeta})-potentials of the samples were measured in aqueous and non-aqueous (silicone oil, SO) media. Electrokinetic properties of PIN and SPIN in aqueous media were determined by {zeta}-potential measurements in the presence of various electrolytes (NaCl, BaCl{sub 2}, AlCl{sub 3}, Na{sub 2}SO{sub 4}) and surfactants (cetyltrimethyl ammonium bromide, SDS, and Triton X-100). Besides, the effect of pH onto {zeta}-potentials of the materials was also examined. The suspensions prepared in SO were subjected to external electric field strength and their electrorheological (ER) properties were investigated. Then the effects of shear rate, frequency, and temperature onto ER activities of the suspensions were examined. Further, creep and creep-recovery tests were applied to the PIN/SO and SPIN/SO suspension systems and reversible non-linear viscoelastic

Numerical and Experimental Low-Velocity Impact Behaivor of Sandwich Plates with Viscoelastic Core

Directory of Open Access Journals (Sweden)

Soroush Sadeghnejad

2016-03-01

Full Text Available A numerical and experimental low-velocity impact behavior of sandwich plates have been presently studied with regard to the compressibility and viscoelasticity features of their cores. Face sheets were assumed to be anisotropic composites or isotropic aluminum materials and a viscoelastic behavior has been considered for core. The boundary conditions are assumed to be simply supported or rigid. Abaqus, as FEM software, and its python script programming feature, have been used to model the specimens. To model hyper-viscoelastic nonlinear behavior of the core, Ogden hyper-foam elasticity and Prony series approach are manipulated. To solve the numerical problem, dynamic explicit solver option with sufficient solving amplitude has been used. Prony series have been used to model the core time-dependent behavior. In conjunction with a simple indentation experiment, FEM used to formulate a novel method for finding the Prony series coefficients. By performing some low-velocity impact experiments, the impact force and displacement of the composite sandwich plates have been investigated. The results indicate that increasing the structural damping increases the contact time and missing energy and decreases the stored energy of the system. The structures with composite face sheets have a minimum ratio of upper face sheet displacement to lower face sheet displacement in comparison to those with the isotropic face sheets. Impact behavior of isotropic face sheet specimens are more flattened than that of the composite face sheets. In addition, the specific energy stored in the sandwich plates with composite face sheets, on different supports, is greater than that stored in the aluminum face sheets.

A viscoelastic deadly fluid in carnivorous pitcher plants.

Science.gov (United States)

Gaume, Laurence; Forterre, Yoel

2007-11-21

The carnivorous plants of the genus Nepenthes, widely distributed in the Asian tropics, rely mostly on nutrients derived from arthropods trapped in their pitcher-shaped leaves and digested by their enzymatic fluid. The genus exhibits a great diversity of prey and pitcher forms and its mechanism of trapping has long intrigued scientists. The slippery inner surfaces of the pitchers, which can be waxy or highly wettable, have so far been considered as the key trapping devices. However, the occurrence of species lacking such epidermal specializations but still effective at trapping insects suggests the possible implication of other mechanisms. Using a combination of insect bioassays, high-speed video and rheological measurements, we show that the digestive fluid of Nepenthes rafflesiana is highly viscoelastic and that this physical property is crucial for the retention of insects in its traps. Trapping efficiency is shown to remain strong even when the fluid is highly diluted by water, as long as the elastic relaxation time of the fluid is higher than the typical time scale of insect movements. This finding challenges the common classification of Nepenthes pitchers as simple passive traps and is of great adaptive significance for these tropical plants, which are often submitted to high rainfalls and variations in fluid concentration. The viscoelastic trap constitutes a cryptic but potentially widespread adaptation of Nepenthes species and could be a homologous trait shared through common ancestry with the sundew (Drosera) flypaper plants. Such large production of a highly viscoelastic biopolymer fluid in permanent pools is nevertheless unique in the plant kingdom and suggests novel applications for pest control.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

Science.gov (United States)

Bhadauria, B. S.; Singh, M. K.; Singh, A.; Singh, B. K.; Kiran, P.

2016-12-01

In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Investigations on the visco-elastic behaviour of a human healthy heel pad: in vivo compression tests and numerical analysis

DEFF Research Database (Denmark)

Matteoli, Sara; Fontanella, Chiara G.; Carniel, Emanuele L.

2013-01-01

The aim of this study was to investigate the viscoelastic behaviour of the human heel pad by comparing the stress–relaxation curves obtained from a compression device used on an in vivo heel pad with those obtained from a threedimensional computer-based subject-specific heel pad model subjected...... numerical analyses were performed to interpret the mechanical response of heel tissues, with loading conditions and displacement rate in agreement with experimental tests. The heel tissues showed a non-linear, viscoelastic behaviour described by characteristic hysteretic curves, stress......–relaxation and viscous recovery phenomena. The reliability of the investigations was validated by the interpretation of the mechanical response of heel tissues under the application of three pistons with diameter of 15, 20 and 40 mm, at the same displacement rate of about 1.7 mm/s. The maximum and minimum relative...

Nonlinear acoustic properties of the B95 aluminum alloy and the B95/nanodiamond composite

Science.gov (United States)

Korobov, A. I.; Prokhorov, V. M.

2016-11-01

Research results for the nonlinear acoustic properties of the B95 polycrystalline aluminum alloy and the B95/nanodiamond composite have been described. The nonlinear properties of the alloys have been studied by the spectral method that measures the efficiency of generation of the second harmonic of a bulk acoustic wave at a frequency of 2 f = 10 MHz in the field of a finite-amplitude longitudinal acoustic wave at a frequency of f = 5 MHz. The results derived by this method have been compared with the results of studies of the nonlinear acoustic properties of the test alloys using the Thurston-Brugger quasi-static method.

Damping analysis of cylindrical composite structures with enhanced viscoelastic properties

DEFF Research Database (Denmark)

Kliem, Mathias; Høgsberg, Jan Becker; Vanwalleghem, Joachim

2018-01-01

is forced to deform in shear mode. Thus, the vibration energy is dissipated as low grade frictional heat. This paper documents the efficiency of passive constrained layer damping treatments for low frequency vibrations of cylindrical composite specimens made of glass fibre-reinforced plastics. Different cross...... section geometries with shear webs have been investigated in order to study a beneficial effect on the damping characteristics of the cylinder. The viscoelastic damping layers are placed at different locations within the composite cylinder e.g. circumferential and along the neutral plane to evaluate...... in the neutral plane perpendicular to the bending load. The results are based on free decay tests of the composite structure....

VISCOELASTIC STRUCTURAL MODEL OF ASPHALT CONCRETE

Directory of Open Access Journals (Sweden)

V. Bogomolov

2016-06-01

Full Text Available The viscoelastic rheological model of asphalt concrete based on the generalized Kelvin model is offered. The mathematical model of asphalt concrete viscoelastic behavior that can be used for calculation of asphalt concrete upper layers of non-rigid pavements for strength and rutting has been developed. It has been proved that the structural model of Burgers does not fully meet all the requirements of the asphalt-concrete.

Nonlinear optical properties of poly(methyl methacrylate) thin films doped with Bixa Orellana dye

Energy Technology Data Exchange (ETDEWEB)

Zongo, S., E-mail: sidiki@tlabs.ac.za [UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, POBox 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 OldFaure road, Somerset West 7129, POBox 722, Somerset West, Western Cape Province (South Africa); Kerasidou, A.P. [LUNAM Université, Université d’Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 Bd Lavoisier, 49045 Angers Cedex (France); Sone, B.T.; Diallo, A. [UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, POBox 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 OldFaure road, Somerset West 7129, POBox 722, Somerset West, Western Cape Province (South Africa); Mthunzi, P. [Council for Scientific and Industrial Research, P O Box 395, Pretoria 0001 (South Africa); Iliopoulos, K. [LUNAM Université, Université d’Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 Bd Lavoisier, 49045 Angers Cedex (France); Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas (FORTH/ICE-HT), 26504 Patras (Greece); Nkosi, M. [Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 OldFaure road, Somerset West 7129, POBox 722, Somerset West, Western Cape Province (South Africa); and others

2015-06-15

Highlights: • We studied the linear and nonlinear optical properties of hybrid Bixa Orellana dye doped PMMA thin film. • We investigated the linear optical properties by means of UV/Vis, FTIR and Fluorescence. • We used Tauc - Lorentz model to evaluate linear optical parameters (n &k) with relative maximum of 1.456 at 508.5, 523.79 and 511.9 nm for n is observed while the maximum of k varies from 0.070 to 0.080. • We evaluated nonlinear third order susceptibility which was found to be 1.00 × 10{sup −21} m{sup 2} V{sup −2} or 0.72 × 10{sup −13} esu. - Abstract: Natural dyes with highly delocalized π-electron systems are considered as promising organic materials for nonlinear optical applications. Among these dyes, Bixa Orellana dye with extended π-electron delocalization is one of the most attractive dyes. Bixa Orellana dye-doped Poly(methyl methacrylate) (PMMA) thin films were prepared through spin coating process for linear and nonlinear optical properties investigation. Atomic force microscopy (AFM) was used to evaluate the roughness of the thin films. The optical constants n and k were evaluated by ellipsometric spectroscopy. The refractive index had a maximum of about 1.456 at 508.5, 523.79 and 511.9 nm, while the maximum of k varies from 0.070 to 0.080 with the thickness. The third order nonlinear optical properties of the hybrid Bixa Orellana dye-PMMA polymer were investigated under 30 ps laser irradiation at 1064 nm with a repetition rate of 10 Hz. In particular the third-order nonlinear susceptibility has been determined by means of the Maker Fringes technique. The nonlinear third order susceptibility was found to be 1.00 × 10{sup −21} m{sup 2} V{sup −2} or 0.72 × 10{sup −13} esu. Our studies provide concrete evidence that the hybrid-PMMA composites of Bixa dye are prospective candidates for nonlinear material applications.

Nonlinear Quantum Optical Springs and Their Nonclassical Properties

International Nuclear Information System (INIS)

Faghihi, M.J.; Tavassoly, M.K.

2011-01-01

The original idea of quantum optical spring arises from the requirement of quantization of the frequency of oscillations in the Hamiltonian of harmonic oscillator. This purpose is achieved by considering a spring whose constant (and so its frequency) depends on the quantum states of another system. Recently, it is realized that by the assumption of frequency modulation of ω to ω√1+μa † a the mentioned idea can be established. In the present paper, we generalize the approach of quantum optical spring with particular attention to the dependence of frequency to the intensity of radiation field that naturally observes in the nonlinear coherent states, from which we arrive at a physical system has been called by us as nonlinear quantum optical spring. Then, after the introduction of the generalized Hamiltonian of nonlinear quantum optical spring and it's solution, we will investigate the nonclassical properties of the obtained states. Specially, typical collapse and revival in the distribution functions and squeezing parameters, as particular quantum features, will be revealed. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Melt compounding of different grades of polystyrene with organoclay. Part 2: Rheological properties

DEFF Research Database (Denmark)

Tanoue, Shuichi; Utracki, Leszek A.; Garcia-Rejon, Andrés

2004-01-01

. The rheological properties of PNC were determined under dynamic and steady state shear as well as under extensional flow conditions. At the higher clay content, dynamic strain sweep demonstrated that the storage and loss moduli decrease continuously with an increase of strain. To characterize this nonlinear...... viscoelastic behavior, the Fourier-transform rheology, was applied. The low strain frequency sweep showed that the storage and loss moduli increase with organoclay content. The extracted zero-shear viscosity data were used to calculate the intrinsic viscosity and then the aspect ratio of dispersions. In spite...

Thickness-dependent nonlinear optical properties of CsPbBr3 perovskite nanosheets.

Science.gov (United States)

Zhang, Jun; Jiang, Tian; Zheng, Xin; Shen, Chao; Cheng, Xiang'ai

2017-09-01

Halide perovskite has attracted significant attention because of excellent optical properties. Here, we study the optical properties of CsPbBr 3 perovskite nanosheets and observe that the nonlinear optical properties can be tuned by the thickness. The photoluminescence (PL) properties and nonlinear absorption effects induced by saturation absorption (SA) and two-photon absorption (TPA) in CsPbBr 3 nanosheets with different thicknesses (from 104.6 to 195.4 nm) have been studied. The PL intensity increases nearly three times with changing from the thinnest one to the thinnest under the same excitation condition. Moreover, the same phenomenon takes place no matter when SA or TPA effects happen. The PL lifetime (τ) varies inversely with the thickness. When SA happens, τ decreases from 11.54 to 9.43 ns while when TPA happens new decay channels emerge with the increase of the thickness. Besides, both saturation intensity (I sat ) and the modulation depth are proportional to the thickness (I sat rises from 3.12 to 4.79  GW/cm 2 , the modulation depth increases from 18.6% to 32.3%), while the TPA coefficient (β) is inversely proportional with the thickness (decreases from 10.94 to 4.73  cm/GW). In addition, quantum yields and thicknesses are in the direct ratio. This Letter advocates great promise for nonlinear optical property related photonics devices.

Flexural wave attenuation in a sandwich beam with viscoelastic periodic cores

Science.gov (United States)

Guo, Zhiwei; Sheng, Meiping; Pan, Jie

2017-07-01

The flexural-wave attenuation performance of traditional constraint-layer damping in a sandwich beam is improved by using periodic constrained-layer damping (PCLD), where the monolithic viscoelastic core is replaced with two periodically alternating viscoelastic cores. Closed-form solutions of the wave propagation constants of the infinite periodic sandwich beam and the forced response of the corresponding finite sandwich structure are theoretically derived, providing computational support on the analysis of attenuation characteristics. In a sandwich beam with PCLD, the flexural waves can be attenuated by both Bragg scattering effect and damping effect, where the attenuation level is mainly dominated by Bragg scattering in the band-gaps and by damping in the pass-bands. Affected by these two effects, when the parameters of periodic cores are properly selected, a sandwich beam with PCLD can effectively reduce vibrations of much lower frequencies than that with traditional constrained-layer damping. The effects of the parameters of viscoelastic periodic cores on band-gap properties are also discussed, showing that the average attenuation in the desired frequency band can be maximized by tuning the length ratio and core thickness to proper values. The research in this paper could possibly provide useful information for the researches and engineers to design damping structures.

Direct and inverse scattering for viscoelastic media

International Nuclear Information System (INIS)

Ammicht, E.; Corones, J.P.; Krueger, R.J.

1987-01-01

A time domain approach to direct and inverse scattering problems for one-dimensional viscoelastic media is presented. Such media can be characterized as having a constitutive relation between stress and strain which involves the past history of the strain through a memory function, the relaxation modulus. In the approach in this article, the relaxation modulus of a material is shown to be related to the reflection properties of the material. This relation provides a constructive algorithm for direct and inverse scattering problems. A numerical implementation of this algorithm is tested on several problems involving realistic relaxation moduli

Three Different Ways of Calibrating Burger's Contact Model for Viscoelastic Model of Asphalt Mixtures by Discrete Element Method

DEFF Research Database (Denmark)

Feng, Huan; Pettinari, Matteo; Stang, Henrik

2016-01-01

modulus. Three different approaches have been used and compared for calibrating the Burger's contact model. Values of the dynamic modulus and phase angle of asphalt mixtures were predicted by conducting DE simulation under dynamic strain control loading. The excellent agreement between the predicted......In this paper the viscoelastic behavior of asphalt mixture was investigated by employing a three-dimensional discrete element method. Combined with Burger's model, three contact models were used for the construction of constitutive asphalt mixture model with viscoelastic properties...

Viscoelastic fluid-structure interactions between a flexible cylinder and wormlike micelle solution

Science.gov (United States)

Dey, Anita A.; Modarres-Sadeghi, Yahya; Rothstein, Jonathan P.

2018-06-01

It is well known that when a flexible or flexibly mounted structure is placed perpendicular to the flow of a Newtonian fluid, it can oscillate due to the shedding of separated vortices at high Reynolds numbers. Unlike Newtonian fluids, the flow of viscoelastic fluids can become unstable even at infinitesimal Reynolds numbers due to a purely elastic flow instability that can occur at large Weissenberg numbers. Recent work has shown that these elastic flow instabilities can drive the motion of flexible sheets. The fluctuating fluid forces exerted on the structure from the elastic flow instabilities can lead to a coupling between an oscillatory structural motion and the state of stress in the fluid flow. In this paper, we present the results of an investigation into the flow of a viscoelastic wormlike micelle solution past a flexible circular cylinder. The time variation of the flow field and the state of stress in the fluid are shown using a combination of particle image tracking and flow-induced birefringence images. The static and dynamic responses of the flexible cylinder are presented for a range of flow velocities. The nonlinear dynamics of the structural motion is studied to better understand an observed transition from a symmetric to an asymmetric structural deformation and oscillation behavior.

Experimental Correlation between Nonlinear Optical and Magnetotransport Properties Observed in Au-Co Thin Films

Directory of Open Access Journals (Sweden)

Kaida Yang

2016-01-01

Full Text Available Magnetic materials where at least one dimension is in the nanometer scale typically exhibit different magnetic, magnetotransport, and magnetooptical properties compared to bulk materials. Composite magnetic thin films where the matrix composition, magnetic cluster size, and overall composite film thickness can be experimentally tailored via adequate processing or growth parameters offer a viable nanoscale platform to investigate possible correlations between nonlinear magnetooptical and magnetotransport properties, since both types of properties are sensitive to the local magnetization landscape. It has been shown that the local magnetization contrast affects the nonlinear magnetooptical properties as well as the magnetotransport properties in magnetic-metal/nonmagnetic metal multilayers; thus, nanocomposite films showcase another path to investigate possible correlations between these distinct properties which may prove useful for sensing applications.

Isolation of nanoscale exosomes using viscoelastic effect

Science.gov (United States)

Hu, Guoqing; Liu, Chao

2017-11-01

Exosomes, molecular cargos secreted by almost all mammalian cells, are considered as promising biomarkers to identify many diseases including cancers. However, the small size of exosomes (30-200 nm) poses serious challenges on their isolation from the complex media containing a variety of extracellular vesicles (EVs) of different sizes, especially in small sample volumes. Here we develop a viscoelasticity-based microfluidic system to directly separate exosomes from cell culture media or serum in a continuous, size-dependent, and label-free manner. Using a small amount of biocompatible polymer as the additive into the media to control the viscoelastic forces exerted on EVs, we are able to achieve a high separation purity (>90%) and recovery (>80%) of exosomes. The size cutoff in viscoelasticity-based microfluidics can be easily controlled using different PEO concentrations. Based on this size-dependent viscoelastic separation strategy, we envision the handling of diverse nanoscale objects, such as gold nanoparticles, DNA origami structures, and quantum dots. This work was supported financially by National Natural Science Foundation of China (11572334, 91543125).

Structure, Electronic and Nonlinear Optical Properties of Furyloxazoles and Thienyloxazoles

International Nuclear Information System (INIS)

Dagli, Ozlem; Gok, Rabia; Bahat, Mehmet; Ozbay, Akif

2016-01-01

Geometry optimization, electronic and nonlinear optical properties of isomers of furyloxazole and thienyloxazole molecules are carried out at the B3LYP/6-311++G(2d,p) level. The conformational analysis of 12 compounds have been studied as a function of torsional angle between rings. Electronic and NLO properties such as dipole moment, energy gap, polarizability and first hyperpolarizability were also calculated. (paper)

Energy decay of a viscoelastic wave equation with supercritical nonlinearities

Science.gov (United States)

Guo, Yanqiu; Rammaha, Mohammad A.; Sakuntasathien, Sawanya

2018-06-01

This paper presents a study of the asymptotic behavior of the solutions for the history value problem of a viscoelastic wave equation which features a fading memory term as well as a supercritical source term and a frictional damping term: u_{tt}- k(0) Δ u - \\int \\limits _0^{&infty } k'(s) Δ u(t-s) ds +|u_t|^{m-1}u_t =|u|^{p-1}u, { in } Ω × (0,T), u(x,t)=u_0(x,t), \\quad { in } Ω × (-∞,0]), where Ω is a bounded domain in R^3 with a Dirichlét boundary condition and u_0 represents the history value. A suitable notion of a potential well is introduced for the system, and global existence of solutions is justified, provided that the history value u_0 is taken from a subset of the potential well. Also, uniform energy decay rate is obtained which depends on the relaxation kernel -k'(s) as well as the growth rate of the damping term. This manuscript complements our previous work (Guo et al. in J Differ Equ 257:3778-3812, 2014, J Differ Equ 262:1956-1979, 2017) where Hadamard well-posedness and the singularity formulation have been studied for the system. It is worth stressing the special features of the model, namely the source term here has a supercritical growth rate and the memory term accounts to the full past history that goes back to -∞.

[Studies on the mechanical properties of the knee ligament].

Science.gov (United States)

Kubotera, D

1987-04-01

To study mechanical properties of the knee ligaments, tension tests at various speeds were performed on the knee of a dog with only the collateral ligament. The results showed that the tensile force was greater in high speed than in low speed test. The difference may be caused in a viscous property of the ligament. The mechanical properties of ligaments can therefore be treated as those of viscoelastic materials and expressed by a modified Voigt model consisting of a non-linear spring element and a dash pot component. Observations regarding the ultrastructure of human knee ligaments using an electron scanning microscope revealed wavy bundles of collagen fiber connected with coarse fibers like network running in parallel with the long axis as the main structure. The above structure and properties were considered to be the decisive factors in the mechanical actions of the knee ligament.

On the Abaqus FEA model of finite viscoelasticity

OpenAIRE

Ciambella, Jacopo; Destrade, Michel; Ogden, Ray W.

2013-01-01

Predictions of the QLV (Quasi-Linear Viscoelastic) constitutive law are compared with those of the ABAQUS viscoelastic model for two simple motions in order to highlight, in particular, their very different dissipation rates and certain shortcomings of the ABAQUS model.

Sensitivity Analysis of Viscoelastic Structures

Directory of Open Access Journals (Sweden)

A.M.G. de Lima

2006-01-01

Full Text Available In the context of control of sound and vibration of mechanical systems, the use of viscoelastic materials has been regarded as a convenient strategy in many types of industrial applications. Numerical models based on finite element discretization have been frequently used in the analysis and design of complex structural systems incorporating viscoelastic materials. Such models must account for the typical dependence of the viscoelastic characteristics on operational and environmental parameters, such as frequency and temperature. In many applications, including optimal design and model updating, sensitivity analysis based on numerical models is a very usefull tool. In this paper, the formulation of first-order sensitivity analysis of complex frequency response functions is developed for plates treated with passive constraining damping layers, considering geometrical characteristics, such as the thicknesses of the multi-layer components, as design variables. Also, the sensitivity of the frequency response functions with respect to temperature is introduced. As an example, response derivatives are calculated for a three-layer sandwich plate and the results obtained are compared with first-order finite-difference approximations.

Stress Wave Propagation in Viscoelastic-Plastic Rock-Like Materials

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Liu Lang

2016-05-01

Full Text Available Rock-like materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. They exhibit viscoelastic-plastic behavior under a high-strain-rate loading according to element model theory. This paper presents an analytical solution for stress wave propagation in viscoelastic-plastic rock-like materials under a high-strain-rate loading and verifies the solution through an experimental test. A constitutive equation of viscoelastic-plastic rock-like materials was first established, and then kinematic and kinetic equations were then solved to derive the analytic solution for stress wave propagation in viscoelastic-plastic rock-like materials. An experimental test using the SHPB (Split Hopkinson Pressure Bar for a concrete specimen was conducted to obtain a stress-strain curve under a high-strain-rate loading. Inverse analysis based on differential evolution was conducted to estimate undetermined variables for constitutive equations. Finally, the relationship between the attenuation factor and the strain rate in viscoelastic-plastic rock-like materials was investigated. According to the results, the frequency of the stress wave, viscosity coefficient, modulus of elasticity, and density play dominant roles in the attenuation of the stress wave. The attenuation decreases with increasing strain rate, demonstrating strongly strain-dependent attenuation in viscoelastic-plastic rock-like materials.

Postseismic Deformations of the Aceh, Nias and Benkulu Earthquakes and the Viscoelastic Properties of the Mantle

Science.gov (United States)

Fleitout, L.; Garaud, J.; Cailletaud, G.; Vigny, C.; Simons, W. J.; Ambrosius, B. A.; Trisirisatayawong, I.; Satirapod, C.; Geotecdi Song

2011-12-01

The giant seism of Aceh (december 2004),followed by the Nias and Bengkulu earthquakes, broke a large portion of the boundary between the Indian ocean and the Sunda block. For the first time in history, the deformations associated with a very large earthquake can be followed by GPS, in particular by the SEAMERGE (far-field) and SUGAR (near-field) GPS networks. A 3D finite element code (Zebulon-Zset) is used to model both the cosismic and the postseismic deformations. The modeled zone is a large portion of spherical shell around Sumatra extanding over more than 60 degrees in latitude and longitude and from the Earth's surface to the core-mantle boundary. The mesh is refined close to the subduction zone. First, the inverted cosismic displacements on the subduction plane are inverted for and provide a very good fit to the GPS data for the three seisms. The observed postseismic displacements, non-dimensionalized by the cosismic displacements, present three very different patterns as function of time: For GPS stations in the far-field, the total horizontal post-seismic displacement after 4 years is as large as the cosismic displacement. The velocities vary slowly over 4 years. A large subsidence affects Thailand and Malaysia. In the near-field, the postseismic displacement reaches only some 15% of the cosismic displacement and it levels off after 2 years. In the middle-field (south-west coast of Sumatra), the postseismic displacement also levels-off with time but more slowly and it reaches more than 30% of the cosismic displacement after four years. In order to fit these three distinct displacement patterns, we need to invoke both viscoelastic deformation in the asthenosphere and a low-viscosity wedge: Neither the vertical subsidence nor the amplitude of the far-field horizontal velocities could be explained by postseismic sliding on the subduction interface. The low viscosity wedge permits to explain the large middle-field velocities. The viscoelastic properties of the

Morphological, viscoelastic and mechanical characterization of polypropylene/exfoliated graphite nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Ferreira, Creusa Iara; Oliveira, Ricardo Vinicius Bof de; Mauler, Raquel Santos, E-mail: raquel.mauler@ufrgs.br [Universidade Federal do Rio Grande do Sul (PGCIMAT/IQ/UFRGS), Porto Alegre, RS (Brazil); Bianchi, Otavio [Universidade de Caxias do Sul (PGMAT/CCET/UCS), RS (Brazil); Oviedo, Mauro Alfredo Soto [Braskem S/A, Rio de Janeiro, RJ (Brazil)

2013-07-01

The viscoelastic, mechanical and morphological properties of polypropylene/exfoliated graphite nanocomposites with different contents of nanofiller were investigated. According to transmission electron microscopy results, the nanofiller particles were homogeneously dispersed in the matrix. The rheological properties indicated that incorporation of graphite improved the matrix stiffness and had a reinforcing effect. Exfoliated graphite had a weak interaction with the polypropylene. The behavior of the nanocomposites was similar to that of polypropylene in terms of the interfacial detachment inferred from the transmission electron microscopy images and of their G' (storage) and G' (loss) moduli, and viscosity. The mechanical properties of the nanocomposites compared to the matrix improved significantly for the flexural and storage moduli with little loss of impact strength. (author)

Nonlinear multigrid solvers exploiting AMGe coarse spaces with approximation properties

DEFF Research Database (Denmark)

Christensen, Max la Cour; Vassilevski, Panayot S.; Villa, Umberto

2017-01-01

discretizations on general unstructured grids for a large class of nonlinear partial differential equations, including saddle point problems. The approximation properties of the coarse spaces ensure that our FAS approach for general unstructured meshes leads to optimal mesh-independent convergence rates similar...... to those achieved by geometric FAS on a nested hierarchy of refined meshes. In the numerical results, Newton’s method and Picard iterations with state-of-the-art inner linear solvers are compared to our FAS algorithm for the solution of a nonlinear saddle point problem arising from porous media flow...

Determining the Viscosity Coefficient for Viscoelastic Wave Propagation in Rock Bars

Science.gov (United States)

Niu, Leilei; Zhu, Wancheng; Li, Shaohua; Guan, Kai

2018-05-01

Rocks with microdefects exhibit viscoelastic behavior during stress wave propagation. The viscosity coefficient of the wave can be used to characterize the attenuation as the wave propagates in rock. In this study, a long artificial bar with a readily adjustable viscosity coefficient was fabricated to investigate stress wave attenuation. The viscoelastic behavior of the artificial bar under dynamic loading was investigated, and the initial viscoelastic coefficient was obtained based on the amplitude attenuation of the incident harmonic wave. A one-dimensional wave propagation program was compiled to reproduce the time history of the stress wave measured during the experiments, and the program was well fitted to the Kelvin-Voigt model. The attenuation and dispersion of the stress wave in long artificial viscoelastic bars were quantified to accurately determine the viscoelastic coefficient. Finally, the method used to determine the viscoelastic coefficient of a long artificial bar based on the experiments and numerical simulations was extended to determine the viscoelastic coefficient of a short rock bar. This study provides a new method of determining the viscosity coefficient of rock.

Enhancement of nonlinear optical properties of compounds of silica ...

Indian Academy of Sciences (India)

Enhancement of nonlinear optical properties of compounds of silica glass and metallic nanoparticle. A GHARAATI1,∗ and A KAMALDAR1,2. 1Department of Physics, Payame Noor University, P.O. Box 19395-3697, Tehran, Iran. 2Department of Education 1, Shiraz, Iran. ∗. Corresponding author. E-mail: agharaati@pnu.ac.

Mathematical analysis of a viscoelastic-gravitational layered earth model for magmatic intrusion in the dynamic case

Directory of Open Access Journals (Sweden)

Alicia Arjona

2015-11-01

Full Text Available Volcanic areas present a lower effective viscosity than usually in the Earth's crust. It makes necessary to consider inelastic properties in deformation modelling. As a continuation of work done previously by some of the authors, this work is concerned with the proof that the perturbed equations representing the viscoelastic-gravitational displacements resulting from body forces embedded in a layered Earth model leads to a well-posed problem even for any kind of domains, with the natural boundary and transmission conditions. A homogeneous or stratified viscoelastic half-space has often been used as a simple earth model to calculate the displacements and gravity changes. Here we give a constructive proof of the existence of weak solutions and we show the uniqueness and the continuous dependence with respect to the initial data of weak solutions of the dynamic coupled viscoelastic-gravitational field equations.

Numerical simulations of viscoelastic flows with free surfaces

DEFF Research Database (Denmark)

Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri

2013-01-01

We present a new methodology to simulate viscoelastic flows with free-surfaces. These simulations are motivated by the modelling of polymers manufacturing techniques, such as extrusion and injection moulding. One of the consequences of viscoelasticity is that polymeric materials have a “memory...

A viscoelastic deadly fluid in carnivorous pitcher plants.

Directory of Open Access Journals (Sweden)

Laurence Gaume

Full Text Available BACKGROUND: The carnivorous plants of the genus Nepenthes, widely distributed in the Asian tropics, rely mostly on nutrients derived from arthropods trapped in their pitcher-shaped leaves and digested by their enzymatic fluid. The genus exhibits a great diversity of prey and pitcher forms and its mechanism of trapping has long intrigued scientists. The slippery inner surfaces of the pitchers, which can be waxy or highly wettable, have so far been considered as the key trapping devices. However, the occurrence of species lacking such epidermal specializations but still effective at trapping insects suggests the possible implication of other mechanisms. METHODOLOGY/PRINCIPAL FINDINGS: Using a combination of insect bioassays, high-speed video and rheological measurements, we show that the digestive fluid of Nepenthes rafflesiana is highly viscoelastic and that this physical property is crucial for the retention of insects in its traps. Trapping efficiency is shown to remain strong even when the fluid is highly diluted by water, as long as the elastic relaxation time of the fluid is higher than the typical time scale of insect movements. CONCLUSIONS/SIGNIFICANCE: This finding challenges the common classification of Nepenthes pitchers as simple passive traps and is of great adaptive significance for these tropical plants, which are often submitted to high rainfalls and variations in fluid concentration. The viscoelastic trap constitutes a cryptic but potentially widespread adaptation of Nepenthes species and could be a homologous trait shared through common ancestry with the sundew (Drosera flypaper plants. Such large production of a highly viscoelastic biopolymer fluid in permanent pools is nevertheless unique in the plant kingdom and suggests novel applications for pest control.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

Directory of Open Access Journals (Sweden)

Bhadauria B.S.

2016-12-01

Full Text Available In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Quantitative determination of optical trapping strength and viscoelastic moduli inside living cells

International Nuclear Information System (INIS)

Mas, Josep; Berg-Sørensen, Kirstine; Richardson, Andrew C; Reihani, S Nader S; Oddershede, Lene B

2013-01-01

With the success of in vitro single-molecule force measurements obtained in recent years, the next step is to perform quantitative force measurements inside a living cell. Optical traps have proven excellent tools for manipulation, also in vivo, where they can be essentially non-invasive under correct wavelength and exposure conditions. It is a pre-requisite for in vivo quantitative force measurements that a precise and reliable force calibration of the tweezers is performed. There are well-established calibration protocols in purely viscous environments; however, as the cellular cytoplasm is viscoelastic, it would be incorrect to use a calibration procedure relying on a viscous environment. Here we demonstrate a method to perform a correct force calibration inside a living cell. This method (theoretically proposed in Fischer and Berg-Sørensen (2007 J. Opt. A: Pure Appl. Opt. 9 S239)) takes into account the viscoelastic properties of the cytoplasm and relies on a combination of active and passive recordings of the motion of the cytoplasmic object of interest. The calibration procedure allows us to extract absolute values for the viscoelastic moduli of the living cell cytoplasm as well as the force constant describing the optical trap, thus paving the way for quantitative force measurements inside the living cell. Here, we determine both the spring constant of the optical trap and the elastic contribution from the cytoplasm, influencing the motion of naturally occurring tracer particles. The viscoelastic moduli that we find are of the same order of magnitude as moduli found in other cell types by alternative methods. (paper)

Vibration and Damping Analysis of Composite Fiber Reinforced Wind Blade with Viscoelastic Damping Control

Directory of Open Access Journals (Sweden)

Tai-Hong Cheng

2015-01-01

Full Text Available Composite materials are increasingly used in wind blade because of their superior mechanical properties such as high strength-to-weight and stiffness-to-weight ratio. This paper presents vibration and damping analysis of fiberreinforced composite wind turbine blade with viscoelastic damping treatment. The finite element method based on full layerwise displacement theory was employed to analyze the damping, natural frequency, and modal loss factor of composite shell structure. The lamination angle was considered in mathematical modeling. The curved geometry, transverse shear, and normal strains were exactly considered in present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The frequency response functions of curved composite shell structure and wind blade were calculated. The results show that the damping ratio of viscoelastic layer is found to be very sensitive to determination of magnitude of composite structures. The frequency response functions with variety of thickness of damping layer were investigated. Moreover, the natural frequency, modal loss factor, and mode shapes of composite fiber reinforced wind blade with viscoelastic damping control were calculated.

Nonlinear and Nonsymmetric Single-Molecule Electronic Properties Towards Molecular Information Processing.

Science.gov (United States)

Tamaki, Takashi; Ogawa, Takuji

2017-09-05

This review highlights molecular design for nonlinear and nonsymmetric single-molecule electronic properties such as rectification, negative differential resistance, and switching, which are important components of future single-molecule information processing devices. Perspectives on integrated "molecular circuits" are also provided. Nonlinear and nonsymmetric single-molecule electronics can be designed by utilizing (1) asymmetric molecular cores, (2) asymmetric anchoring groups, (3) an asymmetric junction environment, and (4) asymmetric electrode materials. This review mainly focuses on the design of molecular cores.

Viscoelastic and Functional Properties of Cod-Bone Gelatin in the Presence of Xylitol and Stevioside

Directory of Open Access Journals (Sweden)

Linyu Nian

2018-05-01

Full Text Available The physical, rheological, structural and functional properties of cod bone gelatin (CBG with various concentrations (0, 2, 4, 6, 10, and 15% of low-calorie sweeteners [xylitol (X and stevioside (S] to form gels were investigated. The gel strength of CBGX increased with increased xylitol due presumably to hydrogen bonds between xylitol and gelatin, but with CBGS the highest gel strength occurred when S concentration was 4%. Viscosity of CBGS samples were higher than CBGX due to S's high molecular mass. The viscoelasticity (G′ and G′′, foaming capacity and fat binding capacity of CBGX were higher while foam stability was lower. The emulsion activity and emulsion stability of CBGX were a little lower than CBGS at the same concentration. The structure of X is linear making it easier to form a dense three-dimensional network structure, while the complex cyclic structure of S had more difficulty forming a network structure with cod bone gelatin. Therefore, X may be a better choice for sweetening gelatin gels.

3D force control for robotic-assisted beating heart surgery based on viscoelastic tissue model.

Science.gov (United States)

Liu, Chao; Moreira, Pedro; Zemiti, Nabil; Poignet, Philippe

2011-01-01

Current cardiac surgery faces the challenging problem of heart beating motion even with the help of mechanical stabilizer which makes delicate operation on the heart surface difficult. Motion compensation methods for robotic-assisted beating heart surgery have been proposed recently in literature, but research on force control for such kind of surgery has hardly been reported. Moreover, the viscoelasticity property of the interaction between organ tissue and robotic instrument further complicates the force control design which is much easier in other applications by assuming the interaction model to be elastic (industry, stiff object manipulation, etc.). In this work, we present a three-dimensional force control method for robotic-assisted beating heart surgery taking into consideration of the viscoelastic interaction property. Performance studies based on our D2M2 robot and 3D heart beating motion information obtained through Da Vinci™ system are provided.

Analytical, numerical, and experimental studies of viscoelastic effects on the performance of soft piezoelectric nanocomposites.

Science.gov (United States)

Li, Jing; Zhu, Zhiren; Fang, Lichen; Guo, Shu; Erturun, Ugur; Zhu, Zeyu; West, James E; Ghosh, Somnath; Kang, Sung Hoon

2017-09-28

Piezoelectric composite (p-NC) made of a polymeric matrix and piezoelectric nanoparticles with conductive additives is an attractive material for many applications. As the matrix of p-NC is made of viscoelastic materials, both elastic and viscous characteristics of the matrix are expected to contribute to the piezoelectric response of p-NC. However, there is limited understanding of how viscoelasticity influences the piezoelectric performance of p-NC. Here we combined analytical and numerical analyses with experimental studies to investigate effects of viscoelasticity on piezoelectric performance of p-NC. The viscoelastic properties of synthesized p-NCs were controlled by changing the ratio between monomer and cross-linker of the polymer matrix. We found good agreement between our analytical models and experimental results for both quasi-static and dynamic loadings. It is found that, under quasi-static loading conditions, the piezoelectric coefficients (d 33 ) of the specimen with the lowest Young's modulus (∼0.45 MPa at 5% strain) were ∼120 pC N -1 , while the one with the highest Young's modulus (∼1.3 MPa at 5% strain) were ∼62 pC N -1 . The results suggest that softer matrices enhance the energy harvesting performance because they can result in larger deformation for a given load. Moreover, from our theoretical analysis and experiments under dynamic loading conditions, we found the viscous modulus of a matrix is also important for piezoelectric performance. For instance, at 40 Hz and 50 Hz the storage moduli of the softest specimen were ∼0.625 MPa and ∼0.485 MPa, while the loss moduli were ∼0.108 MPa and ∼0.151 MPa, respectively. As piezocomposites with less viscous loss can transfer mechanical energy to piezoelectric particles more efficiently, the dynamic piezoelectric coefficient (d' 33 ) measured at 40 Hz (∼53 pC N -1 ) was larger than that at 50 Hz (∼47 pC N -1 ) though it has a larger storage modulus. As an application of our findings

Nonlinear effects in dynamic analysis and design of nuclear power plant components: research status and needs

Energy Technology Data Exchange (ETDEWEB)

Stoykovich, M [Burns and Roe, Inc., New York (USA)

1978-10-01

This paper encompasses nonlinear effects in dynamic analysis and design of nuclear power plant facilities. The history of plasticity as a science is briefly discussed, and nonlinear cases of special interest are described. Approaches to some of the nonlinear problems are presented. These include the nonlinearity due to foundation-structure interaction associated with the base slab uplift during seismic disturbances, the nonlinear base-isolation system for the reduction of earthquake-generated forces and deformations of superstructures, nonlinear systems having restoring-force functions in case of gaps and liift-off conditions, and nonlinearity of viscoelastic systems due to inelastic deformations. Available computer programs information for the solution of various types of nonlinear problems are provided. Advantages and disadvantages of some of the nonlinear and linear analyses are discussed. Comparison of some nonlinear and linear results of analyses are presented. Conclusions are reached with regard to research status and recommendations for further studies and for performing non-linear analyses associated with the problems of nonlinearity are presented.

Nonlinear effects in dynamic analysis and design of nuclear power plant components: research status and needs

International Nuclear Information System (INIS)

Stoykovich, M.

1978-01-01

This paper encompasses nonlinear effects in dynamic analysis and design of nuclear power plant facilities. The history of plasticity as a science is briefly discussed, and nonlinear cases of special interest are described. Approaches to some of the nonlinear problems are presented. These include the nonlinearity due to foundation-structure interaction associated with the base slab uplift during seismic disturbances, the nonlinear base-isolation system for the reduction of earthquake-generated forces and deformations of superstructures, nonlinear systems having restoring-force functions in case of gaps and liift-off conditions, and nonlinearity of viscoelastic systems due to inelastic deformations. Available computer programs information for the solution of various types of nonlinear problems are provided. Advantages and disadvantages of some of the nonlinear and linear analyses are discussed. Comparison of some nonlinear and linear results of analyses are presented. Conclusions are reached with regard to research status and recommendations for further studies and for performing non-linear analyses associated with the problems of nonlinearity are presented. (Auth.)

Turbulence characteristics and mixing performances of viscoelastic fluid flow in a serpentine microchannel

International Nuclear Information System (INIS)

Tatsumi, K; Takeda, Y; Nakabe, K; Suga, K

2011-01-01

Flow velocity measurement and visualization using particle image velocimetry and fluorescent dye were carried out for a viscoelastic fluid flow in a serpentine microchannel for the purpose to quantitatively evaluate the unsteady flow characteristics that is observed even under very low Reynolds number regime due to the combined effect of the viscoelastic fluid properties and the channel shape. Sucrose water solution (Newtonian fluid) and the polyacrylamide-sucrose water solution (viscoelastic fluid) were used as working fluids. The mixing performance markedly increased when the Reynolds number exceeded a certain value in the polyacrylamide solution case. The single-point, cross-sectional and two-dimensional velocity distributions showed that low frequency fluctuation was produced in the polyacrylamide solution case. Particularly large fluctuation in the channel spanwise direction was observed in the upstream area of the serpentine channel. On the other hand, the amplitude of the fluctuation decreased in the downstream region. The fluctuation in the upstream region is believed to be generated by the flow instability at the curved part of the channel, while the fluctuations in the downstream area were attributed to the local instability and the vortices provided from the upstream region.

Nonlinear Local Deformations of Red Blood Cell Membranes: Effects of Toxins and Pharmaceuticals (Part 2

Directory of Open Access Journals (Sweden)

Alexander M. Chernysh

2018-01-01

Full Text Available Modifiers of membranes cause local defects on the cell surface. Measurement of the rigidity at the sites of local defects can provide further information about the structure of defects and mechanical properties of altered membranes.The purpose of the study: a step-by-step study of the process of a nonlinear deformation of red blood cells membranes under the effect of modifiers of different physico-chemical nature.Materials and methods. The membrane deformation of a viscoelastic composite erythrocyte construction inside a cell was studied by the atomic force spectroscopy. Nonlinear deformations formed under the effect of hemin, Zn2+ ions, and verapamil were studied.Results. The process of elastic deformation of the membrane with the indentation of a probe at the sites of local defects caused by modifiers was demonstrated. The probe was inserted during the same step of the piezo scanner z displacement; the probe indentation occured at the different discrete values of h, which are the functions of the membrane structure. At the sites of domains, under the effect of the hemin, tension areas and plasticity areas appeared. A mathematical model of probe indentation at the site of membrane defects is presented.Conclusion. The molecular mechanisms of various types of nonlinear deformations occurring under the effect of toxins are discussed. The results of the study may be of interest both for fundamental researchers of the blood cell properties and for practical reanimatology and rehabilitology. 

Nonlinear Site Response Validation Studies Using KIK-net Strong Motion Data

Science.gov (United States)

Asimaki, D.; Shi, J.

2014-12-01

Earthquake simulations are nowadays producing realistic ground motion time-series in the range of engineering design applications. Of particular significance to engineers are simulations of near-field motions and large magnitude events, for which observations are scarce. With the engineering community slowly adopting the use of simulated ground motions, site response models need to be re-evaluated in terms of their capabilities and limitations to 'translate' the simulated time-series from rock surface output to structural analyses input. In this talk, we evaluate three one-dimensional site response models: linear viscoelastic, equivalent linear and nonlinear. We evaluate the performance of the models by comparing predictions to observations at 30 downhole stations of the Japanese network KIK-Net that have recorded several strong events, including the 2011 Tohoku earthquake. Velocity profiles are used as the only input to all models, while additional parameters such as quality factor, density and nonlinear dynamic soil properties are estimated from empirical correlations. We quantify the differences of ground surface predictions and observations in terms of both seismological and engineering intensity measures, including bias ratios of peak ground response and visual comparisons of elastic spectra, and inelastic to elastic deformation ratio for multiple ductility ratios. We observe that PGV/Vs,30 — as measure of strain— is a better predictor of site nonlinearity than PGA, and that incremental nonlinear analyses are necessary to produce reliable estimates of high-frequency ground motion components at soft sites. We finally discuss the implications of our findings on the parameterization of nonlinear amplification factors in GMPEs, and on the extensive use of equivalent linear analyses in probabilistic seismic hazard procedures.

Stability properties of nonlinear dynamical systems and evolutionary stable states

Energy Technology Data Exchange (ETDEWEB)

Gleria, Iram, E-mail: iram@fis.ufal.br [Instituto de Física, Universidade Federal de Alagoas, 57072-970 Maceió-AL (Brazil); Brenig, Leon [Faculté des Sciences, Université Libre de Bruxelles, 1050 Brussels (Belgium); Rocha Filho, Tarcísio M.; Figueiredo, Annibal [Instituto de Física and International Center for Condensed Matter Physics, Universidade de Brasília, 70919-970 Brasília-DF (Brazil)

2017-03-18

Highlights: • We address the problem of equilibrium stability in a general class of non-linear systems. • We link Evolutionary Stable States (ESS) to stable fixed points of square quasi-polynomial (QP) systems. • We show that an interior ES point may be related to stable interior fixed points of QP systems. - Abstract: In this paper we address the problem of stability in a general class of non-linear systems. We establish a link between the concepts of asymptotic stable interior fixed points of square Quasi-Polynomial systems and evolutionary stable states, a property of some payoff matrices arising from evolutionary games.

Dynamical heterogeneities and mechanical non-linearities: Modeling the onset of plasticity in polymer in the glass transition.

Science.gov (United States)

Masurel, R J; Gelineau, P; Lequeux, F; Cantournet, S; Montes, H

2017-12-27

In this paper we focus on the role of dynamical heterogeneities on the non-linear response of polymers in the glass transition domain. We start from a simple coarse-grained model that assumes a random distribution of the initial local relaxation times and that quantitatively describes the linear viscoelasticity of a polymer in the glass transition regime. We extend this model to non-linear mechanics assuming a local Eyring stress dependence of the relaxation times. Implementing the model in a finite element mechanics code, we derive the mechanical properties and the local mechanical fields at the beginning of the non-linear regime. The model predicts a narrowing of distribution of relaxation times and the storage of a part of the mechanical energy --internal stress-- transferred to the material during stretching in this temperature range. We show that the stress field is not spatially correlated under and after loading and follows a Gaussian distribution. In addition the strain field exhibits shear bands, but the strain distribution is narrow. Hence, most of the mechanical quantities can be calculated analytically, in a very good approximation, with the simple assumption that the strain rate is constant.

Viscoelastic stress modeling in cementitious materials using constant viscoelastic hydration modulus

NARCIS (Netherlands)

Hansen, W.; Liu, Z.; Koenders, E.A.B.

2014-01-01

Viscoelastic stress modeling in ageing cementitious materials is of major importance in high performance concrete of low water cement ratio (e.g. w/c ~0.35) where crack resistance due to deformation restraint needs to be determined. Total stress analysis is complicated by the occurrence of internal

Abnormal viscoelastic behavior of side-chain liquid-crystal polymers

Science.gov (United States)

Gallani, J. L.; Hilliou, L.; Martinoty, P.; Keller, P.

1994-03-01

We show that, contrary to what is commonly believed, the isotropic phase of side-chain liquid-crystal polymers has viscoelastic properties which are totally different from those of ordinary flexible melt polymers. The results can be explained by the existence of a transient network created by the dynamic association of mesogenic groups belonging to different chains. The extremely high sensitivity of the compound to the state of the surfaces with which it is in contact offers us an unexpected method of studying surface states.

Effects of non-linearity of material properties on the coupled mechanical-hydraulic-thermal behavior in rock mass

International Nuclear Information System (INIS)

Kobayashi, Akira; Ohnishi, Yuzo

1986-01-01

The nonlinearity of material properties used in the coupled mechanical-hydraulic-thermal analysis is investigated from the past literatures. Some nonlinearity that is respectively effective for the system is introduced into our computer code for analysis such a coupling problem by using finite element method. And the effects of nonlinearity of each material property on the coupled behavior in rock mass are examined for simple model and Stripa project model with the computer code. (author)

Exact asymptotic relations for the effective response of linear viscoelastic heterogeneous media

Science.gov (United States)

Gallican, Valentin; Brenner, Renald; Suquet, Pierre

2017-11-01

This article addresses the asymptotic response of viscoelastic heterogeneous media in the frequency domain, at high and low frequencies, for different types of elementary linear viscoelastic constituents. By resorting to stationary principles for complex viscoelasticity and adopting a classification of the viscoelastic behaviours based on the nature of their asymptotic regimes, either elastic or viscous, four exact relations are obtained on the overall viscoelastic complex moduli in each case. Two relations are related to the asymptotic uncoupled heterogeneous problems, while the two remaining ones result from the viscoelastic coupling that manifests itself in the transient regime. These results also provide exact conditions on certain integrals in time of the effective relaxation spectrum. This general setting encompasses the results obtained in preceding studies on mixtures of Maxwell constituents [1,2]. xml:lang="fr"

Morphological, viscoelastic and mechanical characterization of polypropylene/exfoliated graphite nanocomposites

Directory of Open Access Journals (Sweden)

Creusa Iara Ferreira

2013-01-01

Full Text Available The viscoelastic, mechanical and morphological properties of polypropylene/exfoliated graphite nanocomposites with different contents of nanofiller were investigated. According to transmission electron microscopy results, the nanofiller particles were homogeneously dispersed in the matrix. The rheological properties indicated that incorporation of graphite improved the matrix stiffness and had a reinforcing effect. Exfoliated graphite had a weak interaction with the polypropylene. The behavior of the nanocomposites was similar to that of polypropylene in terms of the interfacial detachment inferred from the transmission electron microscopy images and of their G' (storage and G'' (loss moduli, and viscosity. The mechanical properties of the nanocomposites compared to the matrix improved significantly for the flexural and storage moduli with little loss of impact strength.

Morphological, viscoelastic and mechanical characterization of polypropylene/exfoliated graphite nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Ferreira, Creusa Iara; Oliveira, Ricardo Vinicius Bof de; Mauler, Raquel Santos, E-mail: raquel.mauler@ufrgs.br [Universidade Federal do Rio Grande do Sul (PGCIMAT/IQ/UFRGS), Porto Alegre, RS (Brazil); Bianchi, Otavio [Universidade de Caxias do Sul (PGMAT/CCET/UCS), RS (Brazil); Oviedo, Mauro Alfredo Soto [Braskem S/A, Rio de Janeiro, RJ (Brazil)

2013-07-01

The viscoelastic, mechanical and morphological properties of polypropylene/exfoliated graphite nanocomposites with different contents of nanofiller were investigated. According to transmission electron microscopy results, the nanofiller particles were homogeneously dispersed in the matrix. The rheological properties indicated that incorporation of graphite improved the matrix stiffness and had a reinforcing effect. Exfoliated graphite had a weak interaction with the polypropylene. The behavior of the nanocomposites was similar to that of polypropylene in terms of the interfacial detachment inferred from the transmission electron microscopy images and of their G' (storage) and G' (loss) moduli, and viscosity. The mechanical properties of the nanocomposites compared to the matrix improved significantly for the flexural and storage moduli with little loss of impact strength. (author)

Viscoelastic Flow Modelling for Polymer Flooding

Science.gov (United States)

de, Shauvik; Padding, Johan; Peters, Frank; Kuipers, Hans; Multi-scale Modelling of Multi-phase Flows Team

2015-11-01

Polymer liquids are used in the oil industry to improve the volumetric sweep and displacement efficiency of oil from a reservoir. Surprisingly, it is not only the viscosity but also the elasticity of the displacing fluid that determine the displacement efficiency. The main aim of our work is to obtain a fundamental understanding of the effect of fluid elasticity, by developing an advanced computer simulation methodology for the flow of non-Newtonian fluids through porous media. We simulate a 3D unsteady viscoelastic flow through a converging diverging geometry of realistic pore dimension using computational fluid dynamics (CFD).The primitive variables velocity, pressure and extra stresses are used in the formulation of models. The viscoelastic stress part is formulated using a FENE-P type of constitutive equation, which can predict both shear and elongational stress properties during this flow. A Direct Numerical Simulation (DNS) approach using Finite volume method (FVM) with staggered grid has been applied. A novel second order Immersed boundary method (IBM) has been incorporated to mimic porous media. The effect of rheological parameters on flow characteristics has also been studied. The simulations provide an insight into 3D flow asymmetry at higher Deborah numbers. Micro-Particle Image Velocimetry experiments are carried out to obtain further insights. These simulations present, for the first time, a detailed computational study of the effects of fluid elasticity on the imbibition of an oil phase.

Nonlinear optical properties of silicon waveguides

International Nuclear Information System (INIS)

Tsang, H K; Liu, Y

2008-01-01

Recent work on two-photon absorption (TPA), stimulated Raman scattering (SRS) and optical Kerr effect in silicon-on-insulator (SOI) waveguides is reviewed and some potential applications of these optical nonlinearities, including silicon-based autocorrelation detectors, optical amplifiers, high speed optical switches, optical wavelength converters and self-phase modulation (SPM), are highlighted. The importance of free carriers generated by TPA in nonlinear devices is discussed, and a generalized definition of the nonlinear effective length to cater for nonlinear losses is proposed. How carrier lifetime engineering, and in particular the use of helium ion implantation, can enhance the nonlinear effective length for nonlinear devices is also discussed

Linear and nonlinear properties of segmented waveguides

International Nuclear Information System (INIS)

Katz, M.

1998-07-01

This dissertation deals with Periodically Segmented Waveguides (PSW), which are applied on KTiOP0 4 (KTP) crystals, by chemical ion-exchange process. In these waveguides, the crystal polarity and refractive index are periodically modulated to obtain Quasi Phase Matching (QPM) between the fundamental and second-harmonic waves. PSW is a relatively new optical device which exhibits unique optical properties in comparison with a continuous waveguide. The possibility of utilizing the KTP-PSW as a compact, cw, blue-violet, source by doubling infra-red light, is the main motivation for studying the optical properties of KTP segmented waveguides. Nevertheless, much attention in this work is also given to the study of linear optical properties of KTP-PSW, most of which, to my best knowledge, has not been studied yet. Controlling and understanding the linear optical properties of KTP-PSW, are required, for applying the PSW as an optical device by its own, and for control and characterization of the non-linear optical properties of the waveguide. In this work the dependence of the linear optical properties of KTP-PSW on geometrical parameters (period size, duty cycle and waveguide width) were studied. The experimental measured parameters include the PSW near field and the Bragg reflections, which appear due lo the grating structure of the waveguide. The possibility of controlling the wavelength and intensity, of the segmented waveguide Bragg reflections of regular period and super-period, is shown theoretically and experimentally. An unexpected dependence was found, by the experimental measurement, between the index profile and the ion-exchanged segment area,. The segmented waveguide dispersion curve, n eff (λ) in the infra-red region was found, A main part of the research work is dedicated to the study of nonlinear characteristics of PSW. The different factors, which effect the Second Harmonic Generation (SHG), are measured experimentally and analyzed. The experimental

Complexity in modeling of residual stresses and strains during polymerization of bone cement: effects of conversion, constraint, heat transfer, and viscoelastic property changes.

Science.gov (United States)

Gilbert, Jeremy L

2006-12-15

Aseptic loosening of cemented joint prostheses remains a significant concern in orthopedic biomaterials. One possible contributor to cement loosening is the development of porosity, residual stresses, and local fracture of the cement that may arise from the in-situ polymerization of the cement. In-situ polymerization of acrylic bone cement is a complex set of interacting processes that involve polymerization reactions, heat generation and transfer, full or partial mechanical constraint, evolution of conversion- and temperature-dependent viscoelastic material properties, and thermal and conversion-driven changes in the density of the cement. Interactions between heat transfer and polymerization can lead to polymerization fronts moving through the material. Density changes during polymerization can, in the presence of mechanical constraint, lead to the development of locally high residual strain energy and residual stresses. This study models the interactions during bone cement polymerization and determines how residual stresses develop in cement and incorporates temperature and conversion-dependent viscoelastic behavior. The results show that the presence of polymerization fronts in bone cement result in locally high residual strain energies. A novel heredity integral approach is presented to track residual stresses incorporating conversion and temperature dependent material property changes. Finally, the relative contribution of thermal- and conversion-dependent strains to residual stresses is evaluated and it is found that the conversion-based strains are the major contributor to the overall behavior. This framework provides the basis for understanding the complex development of residual stresses and can be used as the basis for developing more complex models of cement behavior.

Effects of viscoelasticity in the high Reynolds number cylinder wake

KAUST Repository

Richter, David

2012-01-16

At Re = 3900, Newtonian flow past a circular cylinder exhibits a wake and detached shear layers which have transitioned to turbulence. It is the goal of the present study to investigate the effects which viscoelasticity has on this state and to identify the mechanisms responsible for wake stabilization. It is found through numerical simulations (employing the FENE-P rheological model) that viscoelasticity greatly reduces the amount of turbulence in the wake, reverting it back to a state which qualitatively appears similar to the Newtonian mode B instability which occurs at lower Re. By focusing on the separated shear layers, it is found that viscoelasticity suppresses the formation of the Kelvin-Helmholtz instability which dominates for Newtonian flows, consistent with previous studies of viscoelastic free shear layers. Through this shear layer stabilization, the viscoelastic far wake is then subject to the same instability mechanisms which dominate for Newtonian flows, but at far lower Reynolds numbers. © Copyright Cambridge University Press 2012.

Effects of viscoelasticity in the high Reynolds number cylinder wake

KAUST Repository

Richter, David; Iaccarino, Gianluca; Shaqfeh, Eric S. G.

2012-01-01

At Re = 3900, Newtonian flow past a circular cylinder exhibits a wake and detached shear layers which have transitioned to turbulence. It is the goal of the present study to investigate the effects which viscoelasticity has on this state and to identify the mechanisms responsible for wake stabilization. It is found through numerical simulations (employing the FENE-P rheological model) that viscoelasticity greatly reduces the amount of turbulence in the wake, reverting it back to a state which qualitatively appears similar to the Newtonian mode B instability which occurs at lower Re. By focusing on the separated shear layers, it is found that viscoelasticity suppresses the formation of the Kelvin-Helmholtz instability which dominates for Newtonian flows, consistent with previous studies of viscoelastic free shear layers. Through this shear layer stabilization, the viscoelastic far wake is then subject to the same instability mechanisms which dominate for Newtonian flows, but at far lower Reynolds numbers. © Copyright Cambridge University Press 2012.

Salt type and concentration affect the viscoelasticity of polyelectrolyte solutions

Science.gov (United States)

Turkoz, Emre; Perazzo, Antonio; Arnold, Craig B.; Stone, Howard A.

2018-05-01

The addition of small amounts of xanthan gum to water yields viscoelastic solutions. In this letter, we show that the viscoelasticity of aqueous xanthan gum solutions can be tuned by different types of salts. In particular, we find that the decrease in viscoelasticity not only depends, as is known, on the salt concentration, but also is affected by the counterion ionic radius and the valence of the salt.

Recent advances in elasticity, viscoelasticity and inelasticity

CERN Document Server

Rajagopal, KR

1995-01-01

This is a collection of papers dedicated to Prof T C Woo to mark his 70th birthday. The papers focus on recent advances in elasticity, viscoelasticity and inelasticity, which are related to Prof Woo's work. Prof Woo's recent work concentrates on the viscoelastic and viscoplastic response of metals and plastics when thermal effects are significant, and the papers here address open questions in these and related areas.

A comparative study of the rheological and sensory properties of a petroleum-free and a petroleum-based cosmetic cream.

Science.gov (United States)

Wang, Fan C; Marangoni, Alejandro G

A petroleum-free skin cream was developed using food-grade ingredients. The rheological and sensorial properties of this petroleum-free skin cream were compared to a commercially available petroleum-based skin cream. Specifically, large-amplitude oscillatory shear (LAOS) characterization of the two skin creams was performed. The petroleum-free skin cream showed similar linear and nonlinear viscoelastic rheological properties, comparable skin hydration functions, and consumer acceptance as the commercially available skin cream. A schematic diagram aiming to correlate the physical and sensorial properties of skin cream was also proposed at the end of the work. Results of this work could provide the cosmetic industry necessary information for the development of alternatives for petroleum-based skin creams.

Visco-Elastic Properties of Sodium Hyaluronate Solutions

Science.gov (United States)

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.

Viscoelastic characterization and self-heating behavior of laminated fiber composite driveshafts

International Nuclear Information System (INIS)

Henry, Todd C.; Bakis, Charles E.; Smith, Edward C.

2015-01-01

Highlights: • Carbon fiber composites with different matrix moduli were manufactured. • The composites are of interest for flexible driveshaft applications. • The composites are viscoelastically characterized using dynamic mechanical analysis. • The viscoelastic properties are used to predict self-heating in spinning shafts. • Measured and predicted temperatures of shafts agreed within 0.7 °C. - Abstract: The high cyclic strain capacity of fiber reinforced polymeric composites presents an opportunity to design driveshafts that can transmit high power under imperfect alignment conditions without the use of flexible couplers. In weight sensitive applications such as rotorcraft, the design of highly optimized driveshafts requires a general modeling capability that can predict a number of shaft performance characteristics—one of which is self-heating due to dynamic loading conditions. The current investigation developed three new flexible matrix composite materials of intermediate matrix modulus that, together with previously developed composites, cover the full range of material properties that are of potential interest in driveshaft design. An analytical model for the self-heating of spinning, misaligned, laminated composite shafts was refined to suit the full range of materials. Inputs to the model include ply-level dynamic material properties of the composite, cyclic strain amplitude and frequency, and various heat transfer constants related to conduction, radiation, and convection. Predictions of the surface temperature of spinning shafts correspond well with experimental measurements for bending strains of up to 2000 με, which encompasses the range of strains expected in rotorcraft driveshaft applications

Adherence performances of pressure sensitive adhesives on a model viscoelastic synthetic film: a tool for the understanding of adhesion on the human skin.

Science.gov (United States)

Renvoise, Julien; Burlot, Delphine; Marin, Gérard; Derail, Christophe

2009-02-23

This work deals with the rheological behavior and adherence properties of pressure sensitive adhesive formulations dedicated to medical applications. We have developed a specific viscoelastic substrate which mimics adhesion on human skin to measure the adherence properties of PSAs when they are stuck on the human skin. By comparing peeling results of PSAs, dedicated to medical applications, stuck on human skin and on this viscoelastic substrate we show that this substrate, based on a blend of natural proteins, presents a better representation of the interactions occurring at the skin/adhesive interface than conventional substrates used for peel test (i.e. glass and steel).

Viscoelastic fingering with a pulsed pressure signal

International Nuclear Information System (INIS)

Corvera Poire, E; Rio, J A del

2004-01-01

We derive a generalized Darcy's law in the frequency domain for a linear viscoelastic fluid flowing in a Hele-Shaw cell. This leads to an analytic expression for the dynamic permeability that has maxima which are several orders of magnitude larger than the static permeability. We then follow an argument of de Gennes (1987 Europhys. Lett. 2 195) to obtain the smallest possible finger width when viscoelasticity is important. Using this and a conservation law, we obtain the lowest bound for the width of a single finger displacing a viscoelastic fluid. When the driving force consists of a constant pressure gradient plus an oscillatory signal, our results indicate that the finger width varies in time following the frequency of the incident signal. Also, the amplitude of the finger width in time depends on the value of the dynamic permeability at the imposed frequency. When the finger is driven with a frequency that maximizes the permeability, variations in the amplitude are also maximized. This gives results that are very different for Newtonian and viscoelastic fluids. For the former ones the amplitude of the oscillation decays with frequency. For the latter ones on the other hand, the amplitude has maxima at the same frequencies that maximize the dynamic permeability

Seismic Analysis of a Viscoelastic Damping Isolator

Directory of Open Access Journals (Sweden)

Bo-Wun Huang

2015-01-01

Full Text Available Seismic prevention issues are discussed much more seriously around the world after Fukushima earthquake, Japan, April 2011, especially for those countries which are near the earthquake zone. Approximately 1.8×1012 kilograms of explosive energy will be released from a magnitude 9 earthquake. It destroys most of the unprotected infrastructure within several tens of miles in diameter from the epicenter. People can feel the earthquake even if living hundreds of miles away. This study is a seismic simulation analysis for an innovated and improved design of viscoelastic damping isolator, which can be more effectively applied to earthquake prevention and damage reduction of high-rise buildings, roads, bridges, power generation facilities, and so forth, from earthquake disaster. Solidworks graphic software is used to draw the 3D geometric model of the viscoelastic isolator. The dynamic behavior of the viscoelastic isolator through shock impact of specific earthquake loading, recorded by a seismometer, is obtained via ANSYS finite element package. The amplitude of the isolator is quickly reduced by the viscoelastic material in the device and is shown in a time response diagram. The result of this analysis can be a crucial reference when improving the design of a seismic isolator.

Nonlinear waves and pattern dynamics

CERN Document Server

Pelinovsky, Efim; Mutabazi, Innocent

2018-01-01

This book addresses the fascinating phenomena associated with nonlinear waves and spatio-temporal patterns. These appear almost everywhere in nature from sand bed forms to brain patterns, and yet their understanding still presents fundamental scientific challenges. The reader will learn here, in particular, about the current state-of-the art and new results in: Nonlinear water waves: resonance, solitons, focusing, Bose-Einstein condensation, as well as and their relevance for the sea environment (sea-wind interaction, sand bed forms, fiber clustering) Pattern formation in non-equilibrium media: soap films, chimera patterns in oscillating media, viscoelastic Couette-Taylor flow, flow in the wake behind a heated cylinder, other pattern formation. The editors and authors dedicate this book to the memory of Alexander Ezersky, Professor of Fluid Mechanics at the University of Caen Normandie (France) from September 2007 to July 2016. Before 2007, he had served as a Senior Scientist at the Institute of Applied Physi...

Nonclassical properties of a contradirectional nonlinear optical coupler

Energy Technology Data Exchange (ETDEWEB)

Thapliyal, Kishore [Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307 (India); Pathak, Anirban, E-mail: anirban.pathak@gmail.com [Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307 (India); RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. listopadu 12, 771 46 Olomouc (Czech Republic); Sen, Biswajit [Department of Physics, Vidyasagar Teachers' Training College, Midnapore 721101 (India); Perřina, Jan [RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. listopadu 12, 771 46 Olomouc (Czech Republic); Department of Optics, Palacky University, 17. listopadu 12, 771 46 Olomouc (Czech Republic)

2014-10-24

We investigate the nonclassical properties of output fields propagated through a contradirectional asymmetric nonlinear optical coupler consisting of a linear waveguide and a nonlinear (quadratic) waveguide operated by second harmonic generation. In contrast to the earlier results, all the initial fields are considered weak and a completely quantum-mechanical model is used here to describe the system. Perturbative solutions of Heisenberg's equations of motion for various field modes are obtained using Sen–Mandal technique. Obtained solutions are subsequently used to show the existence of single-mode and intermodal squeezing, single-mode and intermodal antibunching, two-mode and multi-mode entanglement in the output of contradirectional asymmetric nonlinear optical coupler. Further, existence of higher order nonclassicality is also established by showing the existence of higher order antibunching, higher order squeezing and higher order entanglement. Variation of observed nonclassical characters with different coupling constants and phase mismatch is discussed. - Highlights: • Nonclassicalities in fields propagating through a directional coupler is studied. • Completely quantum-mechanical description of the coupler is provided. • Analytic solutions of Heisenberg equations of motion for various modes are obtained. • Existence of lower order and higher order entanglement is shown. • Variation of nonclassicalities with phase-mismatch and coupling constants is studied.

Rigidity percolation in dispersions with a structured viscoelastic matrix

NARCIS (Netherlands)

Wilbrink, M.W.L.; Michels, M.A.J.; Vellinga, W.P.; Meijer, H.E.H.

2005-01-01

This paper deals with rigidity percolation in composite materials consisting of a dispersion of mineral particles in a microstructured viscoelastic matrix. The viscoelastic matrix in this specific case is a hydrocarbon refinery residue. In a set of model random composites the mean interparticle

Noise reduction of rotating machinery by viscoelastic bearing supports

NARCIS (Netherlands)

Tillema, H.G.

2003-01-01

The demand for silent rolling bearing applications, such as electric motors and gearboxes, has resulted in an investigation of viscoelastic bearing supports. By placing a thin viscoelastic layer between the bearing outer ring and the surrounding structure, vibrations of the shaft-bearing arrangement

Effect of annealing conditions on the molecular properties and wetting of viscoelastic bitumen substrates by liquids

Directory of Open Access Journals (Sweden)

Salomé dos Santos

2017-01-01

Full Text Available Typically, in the production of asphalt concrete, bitumen and mineral aggregates are heated and mixed at temperatures above 100 °C. After the mixing process bitumen ideally coats the mineral aggregates and remains in the form of thin films. Because bitumen is highly temperature sensitive, the study of its properties in terms of chemistry, microstructure and rheology as a function of different annealing conditions is very relevant. The resultant molecular properties have a direct correlation to bitumen macroscopic response to liquids such as water, which is of extreme relevance to the understanding of the detrimental effect of water on asphalt pavements. The wetting characteristics play a crucial role on the extension of detachment of bitumen from the mineral aggregates when asphalt is exposed to wet conditions. Therefore, in this work, the effect of the annealing temperature and cooling history on the chemistry, microstructure and wetting of bitumen films was studied. Crystalline microstructures were identified in bulk and on the surface of the bitumen films. Larger crystals presenting higher crystallinity degree were identified when the annealed bitumen films were cooled slowly. Moreover, higher annealing temperatures increased the oxidation level. The change of the rheological properties due to the alterations of the annealing conditions produced changes in the wetting characteristics. For instance, the advancing motion of a liquid drop on the viscoelastic bitumen substrate presented an intermittent behaviour due to the deformation of bitumen at the liquid-bitumen-air contact line. Consequently, changes in the contact angles were also observed. Keywords: Bitumen, Crystallization, Oxidation, Advancing contact angle, Wetting

Effect of enzymatic hydrolysis of starch on pasting, rheological and viscoelastic properties of milk-barnyard millet (Echinochloa frumentacea) blends meant for spray drying.

Science.gov (United States)

Kumar, P Arun; Pushpadass, Heartwin A; Franklin, Magdaline Eljeeva Emerald; Simha, H V Vikram; Nath, B Surendra

2016-10-01

The influence of enzymatic hydrolysis of starch on the pasting properties of barnyard millet was studied using a rheometer. The effects of blending hydrolyzed barnyard millet wort with milk at different ratios (0:1, 1:1, 1:1.5 and 1:2) on flow and viscoelastic behavior were investigated. From the pasting curves, it was evident that enzymatically-hydrolyzed starch did not exhibit typical pasting characteristics expected of normal starch. The Herschel-Bulkley model fitted well to the flow behaviour data, with coefficient of determination (R(2)) ranging from 0.942 to 0.988. All milk-wort blends demonstrated varying degree of shear thinning with flow behavior index (n) ranging from 0.252 to 0.647. Stress-strain data revealed that 1:1 blend of milk to wort had the highest storage modulus (7.09-20.06Pa) and an elastically-dominant behavior (phase angle <45°) over the tested frequency range. The crossover point of G' and G" shifted to higher frequencies with increasing wort content. From the flow and viscoelastic behavior, it was concluded that the 1:1 blend of milk to wort would have least phase separation and better flowability during spray drying. Copyright © 2016 Elsevier B.V. All rights reserved.

Linear Viscoelasticity of Spherical SiO 2 Nanoparticle-Tethered Poly(butyl acrylate) Hybrids

KAUST Repository

Goel, Vivek; Pietrasik, Joanna; Matyjaszewski, Krzysztof; Krishnamoorti, Ramanan

2010-01-01

The melt state linear viscoelastic properties of spherical silica nanoparticles with grafted poly(n-butyl acrylate) chains of varying molecular weight were probed using linear small amplitude dynamic oscillatory measurements and complementary linear stress relaxation measurements. While the pure silica-tethered-polymer hybrids with no added homopolymer exhibit solid-like response, addition of matched molecular weight free matrix homopolymer chains to this hybrid, at low concentrations of added homopolymer, maintains the solid-like response with a lowered modulus that can be factored into a silica concentration dependence and a molecular weight dependence. While the silica concentration dependence of the modulus is strong, the dependence on molecular weight is weak. On the other hand, increasing the amount of added homopolymer changes the viscoelastic response to that of a liquid with a relaxation time that scales exponentially with hybrid concentration. © 2010 American Chemical Society.

Linear Viscoelasticity of Spherical SiO 2 Nanoparticle-Tethered Poly(butyl acrylate) Hybrids

KAUST Repository

Goel, Vivek

2010-12-01

The melt state linear viscoelastic properties of spherical silica nanoparticles with grafted poly(n-butyl acrylate) chains of varying molecular weight were probed using linear small amplitude dynamic oscillatory measurements and complementary linear stress relaxation measurements. While the pure silica-tethered-polymer hybrids with no added homopolymer exhibit solid-like response, addition of matched molecular weight free matrix homopolymer chains to this hybrid, at low concentrations of added homopolymer, maintains the solid-like response with a lowered modulus that can be factored into a silica concentration dependence and a molecular weight dependence. While the silica concentration dependence of the modulus is strong, the dependence on molecular weight is weak. On the other hand, increasing the amount of added homopolymer changes the viscoelastic response to that of a liquid with a relaxation time that scales exponentially with hybrid concentration. © 2010 American Chemical Society.

Nonlinear continuum mechanics and large inelastic deformations

CERN Document Server

Dimitrienko, Yuriy I

2010-01-01

This book provides a rigorous axiomatic approach to continuum mechanics under large deformation. In addition to the classical nonlinear continuum mechanics - kinematics, fundamental laws, the theory of functions having jump discontinuities across singular surfaces, etc. - the book presents the theory of co-rotational derivatives, dynamic deformation compatibility equations, and the principles of material indifference and symmetry, all in systematized form. The focus of the book is a new approach to the formulation of the constitutive equations for elastic and inelastic continua under large deformation. This new approach is based on using energetic and quasi-energetic couples of stress and deformation tensors. This approach leads to a unified treatment of large, anisotropic elastic, viscoelastic, and plastic deformations. The author analyses classical problems, including some involving nonlinear wave propagation, using different models for continua under large deformation, and shows how different models lead t...

Investigation of nonlinear optical properties of various organic materials by the Z-scan method

Science.gov (United States)

Ganeev, R. A.; Boltaev, G. S.; Tugushev, R. I.; Usmanov, T.

2012-06-01

We have studied the nonlinear optical properties of various organic materials (vegetable oil, juice, wine, cognac, Coca-Cola and Fanta drinks, Nescafé coffee, tea, gasoline, clock oil, glycerol, and polyphenyl ether) that are used in everyday life. Their nonlinearities have been studied by the Z-scan method in the near-IR and visible spectral ranges. We have shown that the majority of samples possess a nonlinear absorption; however, some of the studied materials show a strong saturated absorption and nonlinear refraction. Red wine and glycerol proved to be the most interesting materials. For these samples, we have observed a change in the sign of the nonlinear absorption with increasing laser intensity, which was attributed to the competition between two-photon absorption and saturated absorption.

Viscoelastic-gravitational deformation by a rectangular thrust fault in a layered earth

International Nuclear Information System (INIS)

Rundle, J.B.

1982-01-01

Previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered, elastic-gravitational earth model. This paper extends these methods to the calculation of fully time-dependent vertical surface deformation from a rectangular, dipping thrust fault in an elastic-gravitational layer over a viscoelastic-gravitational half space. The elastic-gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the Laplace transform domain. The technique used here to invert the displacements into the time domain is the Prony series technique, wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials. Purely viscoelastic results obtained are checked against results found previously using a different inverse transform method, and agreement is excellent. A series of results are obtained for a rectangular, 30 0 dipping thrust fault in an elastic-gravitational layer over viscoelastic-gravitational half space. Time-dependent displacements are calculated out to 50 half space relaxation times tau/sub a/, or 100 Maxwell times 2tau/sub m/ = tau/sub a/. Significant effects due to gravity are shown to exist in the solutions as early as several tau/sub a/. The difference between the purely viscoelastic solution and the viscoelastic-gravitational solutions grows as time progresses. Typically, the solutions with gravity reach an equilibrium value after 10--20 relaxation times, when the purely viscoelastic solutions are still changing significantly. Additionally, the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic-gravitational problem

Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites.

Science.gov (United States)

Boland, Conor S; Khan, Umar; Ryan, Gavin; Barwich, Sebastian; Charifou, Romina; Harvey, Andrew; Backes, Claudia; Li, Zheling; Ferreira, Mauro S; Möbius, Matthias E; Young, Robert J; Coleman, Jonathan N

2016-12-09

Despite its widespread use in nanocomposites, the effect of embedding graphene in highly viscoelastic polymer matrices is not well understood. We added graphene to a lightly cross-linked polysilicone, often encountered as Silly Putty, changing its electromechanical properties substantially. The resulting nanocomposites display unusual electromechanical behavior, such as postdeformation temporal relaxation of electrical resistance and nonmonotonic changes in resistivity with strain. These phenomena are associated with the mobility of the nanosheets in the low-viscosity polymer matrix. By considering both the connectivity and mobility of the nanosheets, we developed a quantitative model that completely describes the electromechanical properties. These nanocomposites are sensitive electromechanical sensors with gauge factors >500 that can measure pulse, blood pressure, and even the impact associated with the footsteps of a small spider. Copyright © 2016, American Association for the Advancement of Science.

Analysis on nonlinear optical properties of Cd (Zn) Se quantum dots synthesized using three different stabilizing agents

Science.gov (United States)

J, Joy Sebastian Prakash; G, Vinitha; Ramachandran, Murugesan; Rajamanickam, Karunanithi

2017-10-01

Three different stabilizing agents, namely, L-cysteine, Thioglycolic acid and cysteamine hydrochloride were used to synthesize Cd(Zn)Se quantum dots (QDs). It was characterized using UV-vis spectroscopy, x-ray diffraction (XRD) and transmission electron microscopy (TEM). The non-linear optical properties (non-linear absorption and non-linear refraction) of synthesized Cd(Zn)Se quantum dots were studied with z-scan technique using diode pumped continuous wavelaser system at a wavelength of 532 nm. Our (organic) synthesized quantum dots showed optical properties similar to the inorganic materials reported elsewhere.

Linear and Nonlinear Rheology Combined with Dielectric Spectroscopy of Hybrid Polymer Nanocomposites for Semiconductive Applications

Science.gov (United States)

Kádár, Roland; Abbasi, Mahdi; Figuli, Roxana; Rigdahl, Mikael; Wilhelm, Manfred

2017-01-01

The linear and nonlinear oscillatory shear, extensional and combined rheology-dielectric spectroscopy of hybrid polymer nanocomposites for semiconductive applications were investigated in this study. The main focus was the influence of processing conditions on percolated poly(ethylene-butyl acrylate) (EBA) nanocomposite hybrids containing graphite nanoplatelets (GnP) and carbon black (CB). The rheological response of the samples was interpreted in terms of dispersion properties, filler distortion from processing, filler percolation, as well as the filler orientation and distribution dynamics inside the matrix. Evidence of the influence of dispersion properties was found in linear viscoelastic dynamic frequency sweeps, while the percolation of the nanocomposites was detected in nonlinearities developed in dynamic strain sweeps. Using extensional rheology, hybrid samples with better dispersion properties lead to a more pronounced strain hardening behavior, while samples with a higher volume percentage of fillers caused a drastic reduction in strain hardening. The rheo-dielectric time-dependent response showed that in the case of nanocomposites containing only GnP, the orientation dynamics leads to non-conductive samples. However, in the case of hybrids, the orientation of the GnP could be offset by the dispersing of the CB to bridge the nanoplatelets. The results were interpreted in the framework of a dual PE-BA model, where the fillers would be concentrated mainly in the BA regions. Furthermore, better dispersed hybrids obtained using mixing screws at the expense of filler distortion via extrusion processing history were emphasized through the rheo-dielectric tests. PMID:28336857

Linear and Nonlinear Rheology Combined with Dielectric Spectroscopy of Hybrid Polymer Nanocomposites for Semiconductive Applications

Directory of Open Access Journals (Sweden)

Roland Kádár

2017-01-01

Full Text Available The linear and nonlinear oscillatory shear, extensional and combined rheology-dielectric spectroscopy of hybrid polymer nanocomposites for semiconductive applications were investigated in this study. The main focus was the influence of processing conditions on percolated poly(ethylene-butyl acrylate (EBA nanocomposite hybrids containing graphite nanoplatelets (GnP and carbon black (CB. The rheological response of the samples was interpreted in terms of dispersion properties, filler distortion from processing, filler percolation, as well as the filler orientation and distribution dynamics inside the matrix. Evidence of the influence of dispersion properties was found in linear viscoelastic dynamic frequency sweeps, while the percolation of the nanocomposites was detected in nonlinearities developed in dynamic strain sweeps. Using extensional rheology, hybrid samples with better dispersion properties lead to a more pronounced strain hardening behavior, while samples with a higher volume percentage of fillers caused a drastic reduction in strain hardening. The rheo-dielectric time-dependent response showed that in the case of nanocomposites containing only GnP, the orientation dynamics leads to non-conductive samples. However, in the case of hybrids, the orientation of the GnP could be offset by the dispersing of the CB to bridge the nanoplatelets. The results were interpreted in the framework of a dual PE-BA model, where the fillers would be concentrated mainly in the BA regions. Furthermore, better dispersed hybrids obtained using mixing screws at the expense of filler distortion via extrusion processing history were emphasized through the rheo-dielectric tests.

Finite element implementation of a thermo-damage-viscoelastic constitutive model for hydroxyl-terminated polybutadiene composite propellant

Science.gov (United States)

Xu, Jinsheng; Han, Long; Zheng, Jian; Chen, Xiong; Zhou, Changsheng

2017-11-01

A thermo-damage-viscoelastic model for hydroxyl-terminated polybutadiene (HTPB) composite propellant with consideration for the effect of temperature was implemented in ABAQUS. The damage evolution law of the model has the same form as the crack growth equation for viscoelastic materials, and only a single damage variable S is considered. The HTPB propellant was considered as an isotropic material, and the deviatoric and volumetric strain-stress relations are decoupled and described by the bulk and shear relaxation moduli, respectively. The stress update equations were expressed by the principal stresses σ_{ii}R and the rotation tensor M, the Jacobian matrix in the global coordinate system J_{ijkl} was obtained according to the fourth-order tensor transformation rules. Two models having complex stress states were used to verify the accuracy of the constitutive model. The test results showed good agreement with the strain responses of characteristic points measured by a contactless optical deformation test system, which illustrates that the thermo-damage-viscoelastic model perform well at describing the mechanical properties of an HTPB propellant.

Linear analysis using secants for materials with temperature dependent nonlinear elastic modulus and thermal expansion properties

Science.gov (United States)

Pepi, John W.

2017-08-01

Thermally induced stress is readily calculated for linear elastic material properties using Hooke's law in which, for situations where expansion is constrained, stress is proportional to the product of the material elastic modulus and its thermal strain. When material behavior is nonlinear, one needs to make use of nonlinear theory. However, we can avoid that complexity in some situations. For situations in which both elastic modulus and coefficient of thermal expansion vary with temperature, solutions can be formulated using secant properties. A theoretical approach is thus presented to calculate stresses for nonlinear, neo-Hookean, materials. This is important for high acuity optical systems undergoing large temperature extremes.

Experimental observations of flow instabilities and rapid mixing of two dissimilar viscoelastic liquids

Directory of Open Access Journals (Sweden)

Hiong Yap Gan

2012-12-01

Full Text Available Viscoelastically induced flow instabilities, via a simple planar microchannel, were previously used to produce rapid mixing of two dissimilar polymeric liquids (i.e. at least a hundredfold different in shear viscosity even at a small Reynolds number. The unique advantage of this mixing technology is that viscoelastic liquids are readily found in chemical and biological samples like organic and polymeric liquids, blood and crowded proteins samples; their viscoelastic properties could be exploited. As such, an understanding of the underlying interactions will be important especially in rapid microfluidic mixing involving multiple-stream flow of complex (viscoelastic fluids in biological assays. Here, we use the same planar device to experimentally show that the elasticity ratio (i.e. the ratio of stored elastic energy to be relaxed between two liquids indeed plays a crucial role in the entire flow kinematics and the enhanced mixing. We demonstrate here that the polymer stretching dynamics generated in the upstream converging flow and the polymer relaxation events occurring in the downstream channel are not exclusively responsible for the transverse flow mixing, but the elasticity ratio is also equally important. The role of elasticity ratio for transverse flow instability and the associated enhanced mixing were illustrated based on experimental observations. A new parameter Deratio = Deside / Demain (i.e. the ratio of the Deborah number (De of the sidestream to the mainstream liquids is introduced to correlate the magnitude of energy discontinuity between the two liquids. A new Deratio-Demain operating space diagram was constructed to present the observation of the effects of both elasticity and energy discontinuity in a compact manner, and for a general classification of the states of flow development.

Chaos analysis of viscoelastic chaotic flows of polymeric fluids in a micro-channel

Energy Technology Data Exchange (ETDEWEB)

Lim, C. P.; Lam, Y. C., E-mail: myclam@ntu.edu.sg [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 639798 (Singapore); BioSystems and Micromechanics (BioSyM) IRG, Singapore-MIT Alliance for Research and Technology (SMART) Centre, 138602 (Singapore); Han, J. [BioSystems and Micromechanics (BioSyM) IRG, Singapore-MIT Alliance for Research and Technology (SMART) Centre, 138602 (Singapore); Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2015-07-15

Many fluids, including biological fluids such as mucus and blood, are viscoelastic. Through the introduction of chaotic flows in a micro-channel and the construction of maps of characteristic chaos parameters, differences in viscoelastic properties of these fluids can be measured. This is demonstrated by creating viscoelastic chaotic flows induced in an H-shaped micro-channel through the steady infusion of a polymeric fluid of polyethylene oxide (PEO) and another immiscible fluid (silicone oil). A protocol for chaos analysis was established and demonstrated for the analysis of the chaotic flows generated by two polymeric fluids of different molecular weight but with similar relaxation times. The flows were shown to be chaotic through the computation of their correlation dimension (D{sub 2}) and the largest Lyapunov exponent (λ{sub 1}), with D{sub 2} being fractional and λ{sub 1} being positive. Contour maps of D{sub 2} and λ{sub 1} of the respective fluids in the operating space, which is defined by the combination of polymeric fluids and silicone oil flow rates, were constructed to represent the characteristic of the chaotic flows generated. It was observed that, albeit being similar, the fluids have generally distinct characteristic maps with some similar trends. The differences in the D{sub 2} and λ{sub 1} maps are indicative of the difference in the molecular weight of the polymers in the fluids because the driving force of the viscoelastic chaotic flows is of molecular origin. This approach in constructing the characteristic maps of chaos parameters can be employed as a diagnostic tool for biological fluids and, more generally, chaotic signals.

Energia total de ruptura: um teste biomecânico para avaliação de material biológico com propriedade viscoelástica não linear Total energy of rupture: a biomechanical test to evaluate non-linear viscoelastic biological material

Directory of Open Access Journals (Sweden)

Feng Chung Wu

2004-12-01

Full Text Available Objetivo: Apresentação do teste biomecânico Energia Total de Ruptura para o estudo da resistência intrínseca de material biológico com propriedade viscoelástica não-linear representado neste trabalho por segmento íntegro de cólon descendente de rato. Métodos: Implementação do teste biomecânico Energia Total de Ruptura e do Sistema de Aquisição e Análise de dados Biomecânicos - SABI 2.0. Para esse fim, foram utilizados conceitos físico-mecânicos, computacionais e biomecânicos e como corpos de teste, 15 espécimes de cólon descendente de ratos. Resultados: O teste biomecânico Energia Total de Ruptura permitiu o cálculo da energia total acumulada necessária para promover a ruptura dos corpos de prova durante os ensaios mecânicos. Por meio da automatização e gerenciamento da aquisição e análise dos dados capturados foi possível a geração de gráficos e relatórios descritivos e estatísticos. Conclusão: Fundamentado em conceitos físico-mecânicos, computacionais e biomecânicos, o teste Energia Total de Ruptura pôde proporcionar análise matemática do comportamento dos segmentos de cólon descendente de ratos durante os ensaios, demonstrando ser um possível método de medição da resistência intrínseca desse material biológico com propriedade viscoelástica não-linear.Purpose: Presentation of the Total Energy of Rupture biomechanical test to evaluate the intrinsic resistance of the rat’s left colon which presents a non-linear viscoelastic property. Methods: Implementation of Total Energy of Rupture test (ETR and the Biomechanical Data Acquisition and Analysis System (SABI 2.0 based on physic-mechanical, computational and biomechanical concepts. Fifteen specimens of Wistar adults rat’s left colon where considered for experiments. Results: Using the TER biomechanical test it was possible calculate the accumulated total energy necessary to promote the specimens rupture during the mechanical trial. It was

Causal properties of nonlinear gravitational waves in modified gravity

Science.gov (United States)

Suvorov, Arthur George; Melatos, Andrew

2017-09-01

Some exact, nonlinear, vacuum gravitational wave solutions are derived for certain polynomial f (R ) gravities. We show that the boundaries of the gravitational domain of dependence, associated with events in polynomial f (R ) gravity, are not null as they are in general relativity. The implication is that electromagnetic and gravitational causality separate into distinct notions in modified gravity, which may have observable astrophysical consequences. The linear theory predicts that tachyonic instabilities occur, when the quadratic coefficient a2 of the Taylor expansion of f (R ) is negative, while the exact, nonlinear, cylindrical wave solutions presented here can be superluminal for all values of a2. Anisotropic solutions are found, whose wave fronts trace out time- or spacelike hypersurfaces with complicated geometric properties. We show that the solutions exist in f (R ) theories that are consistent with Solar System and pulsar timing experiments.

Predicting the flexure response of wood-plastic composites from uni-axial and shear data using a finite-element model

Science.gov (United States)

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2014-01-01

Wood-plastic composites (WPCs), commonly used in residential decks and railings, exhibit mechanical behavior that is bimodal, anisotropic, and nonlinear viscoelastic. They exhibit different stress-strain responses to tension and compression, both of which are nonlinear. Their mechanical properties vary with respect to extrusion direction, their deformation under...

On the relevance of the micromechanics approach for predicting the linear viscoelastic behavior of semi-crystalline poly(ethylene)terephtalates (PET)

International Nuclear Information System (INIS)

Diani, J.; Bedoui, F.; Regnier, G.

2008-01-01

The relevance of micromechanics modeling to the linear viscoelastic behavior of semi-crystalline polymers is studied. For this purpose, the linear viscoelastic behaviors of amorphous and semi-crystalline PETs are characterized. Then, two micromechanics modeling methods, which have been proven in a previous work to apply to the PET elastic behavior, are used to predict the viscoelastic behavior of three semi-crystalline PETs. The microstructures of the crystalline PETs are clearly defined using WAXS techniques. Since microstructures and mechanical properties of both constitutive phases (the crystalline and the amorphous) are defined, the simulations are run without adjustable parameters. Results show that the models are unable to reproduce the substantial decrease of viscosity induced by the increase of crystallinity. Unlike the real materials, for moderate crystallinity, both models show materials of viscosity nearly identical to the amorphous material

Hydrophilicity, Viscoelastic, and Physicochemical Properties Variations in Dental Bone Grafting Substitutes.

Science.gov (United States)

Trajkovski, Branko; Jaunich, Matthias; Müller, Wolf-Dieter; Beuer, Florian; Zafiropoulos, Gregory-George; Houshmand, Alireza

2018-01-30

The indication-oriented Dental Bone Graft Substitutes (DBGS) selection, the correct bone defects classification, and appropriate treatment planning are very crucial for obtaining successful clinical results. However, hydrophilic, viscoelastic, and physicochemical properties' influence on the DBGS regenerative potential has poorly been studied. For that reason, we investigated the dimensional changes and molecular mobility by Dynamic Mechanical Analysis (DMA) of xenograft (cerabone ® ), synthetic (maxresorb ® ), and allograft (maxgraft ® , Puros ® ) blocks in a wet and dry state. While no significant differences could be seen in dry state, cerabone ® and maxresorb ® blocks showed a slight height decrease in wet state, whereas both maxgraft ® and Puros ® had an almost identical height increase. In addition, cerabone ® and maxresorb ® blocks remained highly rigid and their damping behaviour was not influenced by the water. On the other hand, both maxgraft ® and Puros ® had a strong increase in their molecular mobility with different damping behaviour profiles during the wet state. A high-speed microscopical imaging system was used to analyze the hydrophilicity in several naturally derived (cerabone ® , Bio-Oss ® , NuOss ® , SIC ® nature graft) and synthetic DBGS granules (maxresorb ® , BoneCeramic ® , NanoBone ® , Ceros ® ). The highest level of hydrophilicity was detected in cerabone ® and maxresorb ® , while Bio-Oss ® and BoneCeramic ® had the lowest level of hydrophilicity among both naturally derived and synthetic DBGS groups. Deviations among the DBGS were also addressed via physicochemical differences recorded by Micro Computed Tomography, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, X-ray powder Diffractometry, and Thermogravimetric Analysis. Such DBGS variations could influence the volume stability at the grafting site, handling as well as the speed of vascularization and bone regeneration. Therefore, this

Nonlinear optical properties of an electromagnetically induced transparency medium interacting with two quantized fields

CERN Document Server

Kuang-Leman; Wu Yong Shi

2003-01-01

We study linear and nonlinear optical properties of an electromagnetically induced transparency (EIT) medium interacting with two quantized laser fields in the adiabatic EIT case. We show that the EIT medium exhibits normal dispersion. Kerr and higher-order nonlinear refractive index coefficients are also calculated in a completely analytical form. It is indicated that the EIT medium exhibits giant resonantly enhanced nonlinearities. We discuss the response of the EIT medium to nonclassical light fields and find that the polarization vanishes when the probe laser is initially in a nonclassical state of no single-photon coherence.

Fluid-structure interaction with pipe-wall viscoelasticity during water hammer

NARCIS (Netherlands)

Keramat, A.; Tijsseling, A.S.; Hou, Q.; Ahmadi, A.

2011-01-01

Fluid-structure interaction (FSI) due to water hammer in a pipeline which has viscoelastic wall behaviour is studied. Appropriate governing equations are derived and numerically solved. In the numerical implementation of the hydraulic and structural equations, viscoelasticity is incorporated using

Fluid-structure interaction with pipe-wall viscoelasticity during water hammer

NARCIS (Netherlands)

Keramat, A.; Tijsseling, A.S.; Hou, Q.; Ahmadi, A.

2012-01-01

Fluid–structure interaction (FSI) due to water hammer in a pipeline which has viscoelastic wall behaviour is studied. Appropriate governing equations are derived and numerically solved. In the numerical implementation of the hydraulic and structural equations, viscoelasticity is incorporated using

Measurements of nonlinear optical properties of PVDF/ZnO using Z-scan technique

Energy Technology Data Exchange (ETDEWEB)

Shanshool, Haider Mohammed, E-mail: haidshan62@gmail.com [Ministry of Science and Technology, Baghdad (Iraq); Yahaya, Muhammad [School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Selangor (Malaysia); Yunus, Wan Mahmood Mat [Department of Physics, Faculty of Science, University Putra Malaysia, Serdang (Malaysia); Abdullah, Ibtisam Yahya [Department of Physics, College of Science, University of Mosul, Mosul (Iraq)

2015-10-15

The nonlinear optical properties of ZnO nanoparticles dispersed in poly (vinylidene fluoride) (PVDF) polymer are investigated. PVDF/ZnO nanocomposites were prepared by mixing different concentrations of ZnO nanoparticles, as the filler, with PVDF, as the polymer matrix, using casting method. Acetone was used as a solvent for the polymer. FTIR spectra of the samples were analyzed thus confirming the formation of α and β phases. The absorbance spectra of the samples were obtained, thereby showing high absorption in the UV region. The linear absorption coefficient was calculated. The single-beam Z-scan technique was used to measure the nonlinear refractive index and the nonlinear absorption coefficient of the PVDF/ZnO nanocomposite samples. We observed that the nonlinear refractive index is in the order of 10{sup -13} cm{sup 2}/W with the negative sign, whereas the nonlinear absorption coefficient is in the order of 10{sup -8} cm/W. (author)

Discrete nonlinear Schrodinger equations with arbitrarily high-order nonlinearities

DEFF Research Database (Denmark)

Khare, A.; Rasmussen, Kim Ø; Salerno, M.

2006-01-01

-Ladik equation. As a common property, these equations possess three kinds of exact analytical stationary solutions for which the Peierls-Nabarro barrier is zero. Several properties of these solutions, including stability, discrete breathers, and moving solutions, are investigated.......A class of discrete nonlinear Schrodinger equations with arbitrarily high-order nonlinearities is introduced. These equations are derived from the same Hamiltonian using different Poisson brackets and include as particular cases the saturable discrete nonlinear Schrodinger equation and the Ablowitz...

Viscoelastic behaviour and static fatigue strength of glass/epoxy composites. Influence of hydrothermal ageing

International Nuclear Information System (INIS)

Chateauminois, Antoine

1991-01-01

As ageing strength of composites appears to be one of the main criteria of their durability, this research thesis addresses the hydrothermal ageing of unidirectional glass/epoxy composites used for load-bearing structures. After having presented the used materials (epoxy matrix, reinforcement, composite elaboration), the author present the experimental techniques: viscoelastic analysis, three-point bend static fatigue test, coupled gravimetry and calorimetry, and thermogravimetry. In the next parts, the author reports the study of water sorption processes (bibliographical study, experimental study of water sorption kinetics, experimental study of interfacial diffusion within the composite), the study of plasticizing phenomena (methodology of study of plasticizing phenomena, study of the modifications of the linear viscoelastic behaviour in the glass transition region and at room temperature, relationship between plasticizing and fatigue mechanical properties by fracture studies), and the study of irreversible degradation and damage mechanisms

Viscoelasticity, nonlinear shear start-up, and relaxation of entangled star polymers

KAUST Repository

Snijkers, Frank

2013-07-23

We report on a detailed rheological investigation of well-defined symmetric entangled polymer stars of low functionality with varying number of arms, molar mass of the arms, and solvent content. Emphasis is placed on the response of the stars in simple shear, during start-up, and for relaxation upon flow cessation. To reduce experimental artifacts associated with edge fracture (primarily) and wall slip, we employ a homemade cone-partitioned plate fixture which was successfully implemented in recent studies. Reliable data for these highly entangled stars could be obtained for Weissenberg numbers below 300. The appearance of a stress overshoot during start-up with a corresponding strain approaching a value of 2 suggests that in the investigated shear regime the stars orient but do not stretch. This is corroborated by the fact that the empirical Cox-Merx rule appears to be validated, within experimental error. On the other hand, the (shear) rate dependent steady shear viscosity data exhibit a slope smaller than the convective constraint release slope of -1 (for linear polymers) for the investigated range of rates. The broadness of the stress overshoot reflects the broad linear relaxation spectrum of the stars. The initial stress relaxation rate, reflecting the initial loss of entanglements due to the action of convective constraint release in steady shear flow, increases with Weissenberg number. More importantly, when compared against the relevant rates for comb polymers with relatively short arms, the latter are slower at larger Weissenberg numbers. At long times, the relaxation data are consistent with the linear viscoelastic data on these systems. © 2013 American Chemical Society.

Nonlinear graphene plasmonics

Science.gov (United States)

Ooi, Kelvin J. A.; Tan, Dawn T. H.

2017-10-01

The rapid development of graphene has opened up exciting new fields in graphene plasmonics and nonlinear optics. Graphene's unique two-dimensional band structure provides extraordinary linear and nonlinear optical properties, which have led to extreme optical confinement in graphene plasmonics and ultrahigh nonlinear optical coefficients, respectively. The synergy between graphene's linear and nonlinear optical properties gave rise to nonlinear graphene plasmonics, which greatly augments graphene-based nonlinear device performance beyond a billion-fold. This nascent field of research will eventually find far-reaching revolutionary technological applications that require device miniaturization, low power consumption and a broad range of operating wavelengths approaching the far-infrared, such as optical computing, medical instrumentation and security applications.

An Indentation Technique for Nanoscale Dynamic Viscoelastic Measurements at Elevated Temperature

Science.gov (United States)

Ye, Jiping

2012-08-01

Determination of nano/micro-scale viscoelasticity is very important to understand the local rheological behavior and degradation phenomena of multifunctional polymer blend materials. This article reviews research results concerning the development of indentation techniques for making nanoscale dynamic viscoelastic measurements at elevated temperature. In the last decade, we have achieved breakthroughs in noise floor reduction in air and thermal load drift/noise reduction at high temperature before taking on the challenge of nanoscale viscoelastic measurements. A high-temperature indentation technique has been developed that facilitates viscoelastic measurements up to 200 °C in air and 500 °C in a vacuum. During the last year, two viscoelastic measurement methods have been developed by making a breakthrough in suppressing the contact area change at high temperature. One is a sharp-pointed time-dependent nanoindentation technique for microscale application and the other is a spherical time-dependent nanoindentation technique for nanoscale application. In the near future, we expect to lower the thermal load drift and load noise floor even more substantially.

The rheological and fracture properties of Gouda cheese

NARCIS (Netherlands)

Luyten, H.

1988-01-01

The rheological and fracture behaviour of Gouda cheese was studied. Methods for determining these properties of visco-elastic materials are described. Application of the theory of fracture mechanics, after modification and expansion, to visco-elastic materials with a

Modelling Viscoelasticity of Loudspeaker Suspensions using Retardation Spectra

DEFF Research Database (Denmark)

Ritter, Tobias; Agerkvist, Finn T.

2010-01-01

, the viscoelastic retardation spectrum, which provides a more fundamental description of the suspension viscoelasticity, is rst used to explain the accuracy of the empirical LOG creep model (Knudsen et al.). Then, two extensions to the LOG model are proposed which include the low and high frequency limit...... of the compliance, not accounted for in the original LOG model. The new creep models are veried by measurements on two 5.5 loudspeakers with different surrounds....

Modelling water hammer in viscoelastic pipelines: short brief

Science.gov (United States)

Urbanowicz, K.; Firkowski, M.; Zarzycki, Z.

2016-10-01

The model of water hammer in viscoelastic pipelines is analyzed. An appropriate mathematical model of water hammer in polymer pipelines is presented. An additional term has been added to continuity equation to describe the retarded deformation of the pipe wall. The mechanical behavior of viscoelastic material is described by generalized Kelvin-Voigt model. The comparison of numerical simulation and experimental data from well known papers is presented. Short discussion about obtained results are given.

Human umbilical cord blood-derived stem cells and brain-derived neurotrophic factor protect injured optic nerve: viscoelasticity characterization

Directory of Open Access Journals (Sweden)

Xue-man Lv

2016-01-01

Full Text Available The optic nerve is a viscoelastic solid-like biomaterial. Its normal stress relaxation and creep properties enable the nerve to resist constant strain and protect it from injury. We hypothesized that stress relaxation and creep properties of the optic nerve change after injury. More-over, human brain-derived neurotrophic factor or umbilical cord blood-derived stem cells may restore these changes to normal. To validate this hypothesis, a rabbit model of optic nerve injury was established using a clamp approach. At 7 days after injury, the vitreous body re-ceived a one-time injection of 50 µg human brain-derived neurotrophic factor or 1 × 106 human umbilical cord blood-derived stem cells. At 30 days after injury, stress relaxation and creep properties of the optic nerve that received treatment had recovered greatly, with patho-logical changes in the injured optic nerve also noticeably improved. These results suggest that human brain-derived neurotrophic factor or umbilical cord blood-derived stem cell intervention promotes viscoelasticity recovery of injured optic nerves, and thereby contributes to nerve recovery.

Viscoelastic characterization of carbon fiber-epoxy composites by creep and creep rupture tests; Caracterizacao viscoelastica por meio de ensaios de fluencia e ruptura por fluencia de compositos polimericos de matriz de matriz de resina epoxidica e fibra de carbono

Energy Technology Data Exchange (ETDEWEB)

Farina, Luis Claudio

2009-07-01

One of the main requirements for the use of fiber-reinforced polymer matrix composites in structural applications is the evaluation of their behavior during service life. The warranties of the integrity of these structural components demand a study of the time dependent behavior of these materials due to viscoelastic response of the polymeric matrix and of the countless possibilities of design configurations. In the present study, creep and creep rupture test in stress were performed in specimens of unidirectional carbon fiber-reinforced epoxy composites with fibers orientations of 60 degree and 90 degree, at temperatures of 25 and 70 degree C. The aim is the viscoelastic characterization of the material through the creep curves to some levels of constant tension during periods of 1000 h, the attainment of the creep rupture envelope by the creep rupture curves and the determination of the transition of the linear for non-linear behavior through isochronous curves. In addition, comparisons of creep compliance curves with a viscoelastic behavior prediction model based on Schapery equation were also performed. For the test, a modification was verified in the behavior of the material, regarding the resistance, stiffness and deformation, demonstrating that these properties were affected for the time and tension level, especially in work temperature above the ambient. The prediction model was capable to represent the creep behavior, however the determination of the equations terms should be considered, besides the variation of these with the applied tension and the elapsed time of test. (author)

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

KAUST Repository

Snijkers, F.; Kirkwood, K. M.; Vlassopoulos, D.; Leal, L. G.; Nikopoulou, A.; Hadjichristidis, Nikolaos; Coppola, S.

2016-01-01

We report upon the characterization of the steady-state shear stresses and first normal stress differences as a function of shear rate using mechanical rheometry (both with a standard cone and plate and with a cone partitioned plate) and optical rheometry (with a flow-birefringence setup) of an entangled solution of asymmetric exact combs. The combs are polybutadienes (1,4-addition) consisting of an H-skeleton with an additional off-center branch on the backbone. We chose to investigate a solution in order to obtain reliable nonlinear shear data in overlapping dynamic regions with the two different techniques. The transient measurements obtained by cone partitioned plate indicated the appearance of overshoots in both the shear stress and the first normal stress difference during start-up shear flow. Interestingly, the overshoots in the start-up normal stress difference started to occur only at rates above the inverse stretch time of the backbone, when the stretch time of the backbone was estimated in analogy with linear chains including the effects of dynamic dilution of the branches but neglecting the effects of branch point friction, in excellent agreement with the situation for linear polymers. Flow-birefringence measurements were performed in a Couette geometry, and the extracted steady-state shear and first normal stress differences were found to agree well with the mechanical data, but were limited to relatively low rates below the inverse stretch time of the backbone. Finally, the steady-state properties were found to be in good agreement with model predictions based on a nonlinear multimode tube model developed for linear polymers when the branches are treated as solvent.

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

KAUST Repository

Snijkers, F.

2016-03-31

We report upon the characterization of the steady-state shear stresses and first normal stress differences as a function of shear rate using mechanical rheometry (both with a standard cone and plate and with a cone partitioned plate) and optical rheometry (with a flow-birefringence setup) of an entangled solution of asymmetric exact combs. The combs are polybutadienes (1,4-addition) consisting of an H-skeleton with an additional off-center branch on the backbone. We chose to investigate a solution in order to obtain reliable nonlinear shear data in overlapping dynamic regions with the two different techniques. The transient measurements obtained by cone partitioned plate indicated the appearance of overshoots in both the shear stress and the first normal stress difference during start-up shear flow. Interestingly, the overshoots in the start-up normal stress difference started to occur only at rates above the inverse stretch time of the backbone, when the stretch time of the backbone was estimated in analogy with linear chains including the effects of dynamic dilution of the branches but neglecting the effects of branch point friction, in excellent agreement with the situation for linear polymers. Flow-birefringence measurements were performed in a Couette geometry, and the extracted steady-state shear and first normal stress differences were found to agree well with the mechanical data, but were limited to relatively low rates below the inverse stretch time of the backbone. Finally, the steady-state properties were found to be in good agreement with model predictions based on a nonlinear multimode tube model developed for linear polymers when the branches are treated as solvent.

Fluid-structure interaction with pipe-wall viscoelasticity during water hammer

Science.gov (United States)

Keramat, A.; Tijsseling, A. S.; Hou, Q.; Ahmadi, A.

2012-01-01

Fluid-structure interaction (FSI) due to water hammer in a pipeline which has viscoelastic wall behaviour is studied. Appropriate governing equations are derived and numerically solved. In the numerical implementation of the hydraulic and structural equations, viscoelasticity is incorporated using the Kelvin-Voigt mechanical model. The equations are solved by two different approaches, namely the Method of Characteristics-Finite Element Method (MOC-FEM) and full MOC. In both approaches two important effects of FSI in fluid-filled pipes, namely Poisson and junction coupling, are taken into account. The study proposes a more comprehensive model for studying fluid transients in pipelines as compared to previous works, which take into account either FSI or viscoelasticity. To verify the proposed mathematical model and its numerical solutions, the following problems are investigated: axial vibration of a viscoelastic bar subjected to a step uniaxial loading, FSI in an elastic pipe, and hydraulic transients in a pressurised polyethylene pipe without FSI. The results of each case are checked with available exact and experimental results. Then, to study the simultaneous effects of FSI and viscoelasticity, which is the new element of the present research, one problem is solved by the two different numerical approaches. Both numerical methods give the same results, thus confirming the correctness of the solutions.

Mathematical Modeling of Uniaxial Mechanical Properties of Collagen Gel Scaffolds for Vascular Tissue Engineering

Directory of Open Access Journals (Sweden)

Ramiro M. Irastorza

2015-01-01

Full Text Available Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.. When Akaike criterion is used, the best is the Mooney-Rivlin inspired model.

Mathematical modeling of uniaxial mechanical properties of collagen gel scaffolds for vascular tissue engineering.

Science.gov (United States)

Irastorza, Ramiro M; Drouin, Bernard; Blangino, Eugenia; Mantovani, Diego

2015-01-01

Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model.

Second order nonlinear optical properties of zinc oxide films deposited by low temperature dual ion beam sputtering

International Nuclear Information System (INIS)

Larciprete, M.C.; Passeri, D.; Michelotti, F.; Paoloni, S.; Sibilia, C.; Bertolotti, M.; Belardini, A.; Sarto, F.; Somma, F.; Lo Mastro, S.

2005-01-01

We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at λ=1064 nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples

Third-order nonlinear optical properties of ADP crystal

Science.gov (United States)

Wang, Mengxia; Wang, Zhengping; Chai, Xiangxu; Sun, Yuxiang; Sui, Tingting; Sun, Xun; Xu, Xinguang

2018-05-01

By using the Z-scan method, we investigated the third-order nonlinear optical (NLO) properties of ADP crystal at different wavelengths (355, 532, and 1064 nm) and different orientations ([001], [100], [110], I and II). The experimental data were fitted by NLO theory, to give out the two photon absorption (TPA) coefficient β 2 and the nonlinear refractive index n 2. When the light source changed from a 40 ps, 1064 nm fundamental laser to a 30 ps, 355 nm third-harmonic-generation (THG) laser, the β 2 value increased about 5 times (0.2 × 10‑2 → 1 × 10‑2 cm GW‑1), and the n 2 value increased about 1.5 times (1.5 × 10‑16 → 2.2 × 10‑16 cm2 W‑1). Among all of the orientations, the [110] sample exhibits the smallest β 2, and the second smallest n 2. It indicates that this orientation and its surroundings will be the preferred directions for high-power laser applications of ADP crystal.

A nonlinear least-squares inverse analysis of strike-slip faulting with application to the San Andreas fault

Science.gov (United States)

Williams, Charles A.; Richardson, Randall M.

1988-01-01

A nonlinear weighted least-squares analysis was performed for a synthetic elastic layer over a viscoelastic half-space model of strike-slip faulting. Also, an inversion of strain rate data was attempted for the locked portions of the San Andreas fault in California. Based on an eigenvector analysis of synthetic data, it is found that the only parameter which can be resolved is the average shear modulus of the elastic layer and viscoelastic half-space. The other parameters were obtained by performing a suite of inversions for the fault. The inversions on data from the northern San Andreas resulted in predicted parameter ranges similar to those produced by inversions on data from the whole fault.

Magnetodynamic non-linearity of electric properties of uncompensated metals

International Nuclear Information System (INIS)

Sobol', V.R.; Mazurenko, O.N.

2001-01-01

Magnetodynamic non-linearity of electric properties of normal metals is investigated both experimentally and analytically provided that the drift of charge carriers of high density in crossed electric and magnetic fields results in generation of a self current field. The measurements were made on high purity polycrystalline aluminium cylindrical conductors under the action of the magnetic field, coaxial the sample axis, on the radial current. The electric potential and its nonlinear correction are determined in a wide range of energy dissipation values up to the levels corresponding to the crisis of liquid helium boiling. In the approximation of contribution additivity to the resistive effect of both the external and self magnetic field agreement between the experimental data and the results calculated using the macroscopic field equations is attained. The problems of magnetic energy concentration for cylindrical conductors is discussed in the approximation of long and short solenoids

Explicit solution for the natural frequency of structures with partial viscoelastic treatment

OpenAIRE

Høgsberg, Jan Becker

2016-01-01

The free vibration characteristics of structures with viscoelastic treatment are represented by the complex-valued natural frequencies. The assumed single mode representation associated with the low-frequency stiffness of the viscoelastic treatment is modified by a correction term representing the influence from residual vibration modes. The correction term is eliminated in terms of the corresponding natural frequency associated with the high-frequency stiffness of the viscoelastic treatment,...

Viscoelastic Earthquake Cycle Simulation with Memory Variable Method

Science.gov (United States)

Hirahara, K.; Ohtani, M.

2017-12-01

There have so far been no EQ (earthquake) cycle simulations, based on RSF (rate and state friction) laws, in viscoelastic media, except for Kato (2002), who simulated cycles on a 2-D vertical strike-slip fault, and showed nearly the same cycles as those in elastic cases. The viscoelasticity could, however, give more effects on large dip-slip EQ cycles. In a boundary element approach, stress is calculated using a hereditary integral of stress relaxation function and slip deficit rate, where we need the past slip rates, leading to huge computational costs. This is a cause for almost no simulations in viscoelastic media. We have investigated the memory variable method utilized in numerical computation of wave propagation in dissipative media (e.g., Moczo and Kristek, 2005). In this method, introducing memory variables satisfying 1st order differential equations, we need no hereditary integrals in stress calculation and the computational costs are the same order of those in elastic cases. Further, Hirahara et al. (2012) developed the iterative memory variable method, referring to Taylor et al. (1970), in EQ cycle simulations in linear viscoelastic media. In this presentation, first, we introduce our method in EQ cycle simulations and show the effect of the linear viscoelasticity on stick-slip cycles in a 1-DOF block-SLS (standard linear solid) model, where the elastic spring of the traditional block-spring model is replaced by SLS element and we pull, in a constant rate, the block obeying RSF law. In this model, the memory variable stands for the displacement of the dash-pot in SLS element. The use of smaller viscosity reduces the recurrence time to a minimum value. The smaller viscosity means the smaller relaxation time, which makes the stress recovery quicker, leading to the smaller recurrence time. Second, we show EQ cycles on a 2-D dip-slip fault with the dip angel of 20 degrees in an elastic layer with thickness of 40 km overriding a Maxwell viscoelastic half

Tensile properties of latex paint films with TiO2 pigment

Science.gov (United States)

Hagan, Eric W. S.; Charalambides, Maria N.; Young, Christina T.; Learner, Thomas J. S.; Hackney, Stephen

2009-05-01

The tensile properties of latex paint films containing TiO2 pigment were studied with respect to temperature, strain-rate and moisture content. The purpose of performing these experiments was to assist museums in defining safe conditions for modern paintings held in collections. The glass transition temperature of latex paint binders is in close proximity to ambient temperature, resulting in high strain-rate dependence in typical exposure environments. Time dependence of modulus and failure strain is discussed in the context of time-temperature superposition, which was used to extend the experimental time scale. Nonlinear viscoelastic material models are also presented, which incorporate a Prony series with the Ogden or Neo-Hookean hyperelastic function for different TiO2 concentrations.

Nonlinear optical properties of Nd3+-Li+ co-doped ZnS-PVP thin films

Science.gov (United States)

Talwatkar, S. S.; Sunatkari, A. L.; Tamgadge, Y. S.; Muley, G. G.

2018-04-01

The nonlinear optical properties of Nd3+-Li+ co-doped ZnS-PVP nanocomposite were studied using a continuous wave (CW) He-Ne laser (λ = 632.8 nm)by z-scan technique. The nonlinear refractive index (n2), absorption coefficient (β) and third order nonlinear susceptibility (χ(3)) of PVP thin films embedded with Nd3+-Li+ co-doped ZnS NPs was found in the order of 10-7 cm2/W, 10-6 cm/W and 10-7 esu respectively. The nonlinearity found increasing with Nd3+-Li+ co-dopant concentration. Based on the results, it is proposed that this material is a new class of luminescent material suitable in optoelectronics devices application, especially in light-emitting devices, electroluminescent devices, display devices, etc.

Applying DTI white matter orientations to finite element head models to examine diffuse TBI under high rotational accelerations.

LENUS (Irish Health Repository)

Colgan, Niall C

2010-12-01

The in-vivo mechanical response of neural tissue during impact loading of the head is simulated using geometrically accurate finite element (FE) head models. However, current FE models do not account for the anisotropic elastic material behaviour of brain tissue. In soft biological tissue, there is a correlation between internal microscopic structure and macroscopic mechanical properties. Therefore, constitutive equations are important for the numerical analysis of the soft biological tissues. By exploiting diffusion tensor techniques the anisotropic orientation of neural tissue is incorporated into a non-linear viscoelastic material model for brain tissue and implemented in an explicit FE analysis. The viscoelastic material parameters are derived from published data and the viscoelastic model is used to describe the mechanical response of brain tissue. The model is formulated in terms of a large strain viscoelastic framework and considers non-linear viscous deformations in combination with non-linear elastic behaviour. The constitutive model was applied in the University College Dublin brain trauma model (UCDBTM) (i.e. three-dimensional finite element head model) to predict the mechanical response of the intra-cranial contents due to rotational injury.

Unsteady Magnetized Flow and Heat Transfer of a Viscoelastic fluid over a Stretching Surface

Science.gov (United States)

Ghosh, Sushil Kumar

2017-12-01

This paper is to study the flow of heated ferro-fluid over a stretching sheet under the influence of magnetic field. The fluid considered in the present investigation is a mixture of blood as well as fluid-dispersed magnetic nano particles and under this context blood is found to be the appropriate choice of viscoelastic, Walter's B fluid. The objective of the present work is to study the effect of various parameters found in the mathematical analysis. Taking into account the blood has zero electrical conductivity, magnetization effect has been considered in the governing equation of the present study with the use of ferro-fluid dynamics principle. By introducing appropriate non-dimensional variables into the governing equations of unsteady two-dimensional flow of viscoelastic fluid with heat transfer are converted to a set of ordinary differential equations with appropriate boundary conditions. Newton's linearization technique has been employed for the solution of non-linear ordinary differential equations. Important results found in the present investigation are the substantial influence of ferro-magnetic parameter, Prandlt number and the parameter associated with the thermal conductivity on the flow and heat transfer. It is observed that the presence of magnetic dipole essentially reduces the flow velocity in the vertical direction and that helps to damage the cancer cells in the tumor region.

Viscoelastic reciprocating contacts in presence of finite rough interfaces: A numerical investigation

Science.gov (United States)

Putignano, Carmine; Carbone, Giuseppe

2018-05-01

Viscoelastic reciprocating contacts are crucial in a number of systems, ranging from sealing components to viscoelastic dampers. Roughness plays in these conditions a central role, but no exhaustive assessment in terms of influence on area, separation and friction has been drawn so far. This is due to the huge number of time and space scales involved in the problem. By means of an innovative Boundary Element methodology, which treats the time as a parameter and then requires only to discretize the space domain, we investigate the viscoelastic reciprocating contact mechanics between rough solids. In particular, we consider the alternate contact of a rigid finite-size rough punch over a viscoelastic layer: the importance of the domain finiteness in the determination of the contact area and the contact solution anisotropy is enlightened. Implications on real system may be drawn on this basis. Finally, we focus on the hysteretic cycle related to the viscoelastic tangential forces.

Nonlinear Optical Properties of Aluminum Doped Zinc Oxide

Science.gov (United States)

Otieno, Calford O.

Nonlinear optical (NLO) materials are crucial to future progress in industrial and technological applications that involve intense light-matter interaction. While ZnO-related materials are known to possess good NLO properties, existing results on ZnO and AZO (Al-doped ZnO) are mostly available at a single wavelength or limited ranges. Therefore, NLO dispersions (wavelength dependences) are not entirely studied, especially at longer wavelengths far below the bandgap. It is important to explore wavelength dependences since doping can induce a drastic change in the NLO responses at varied spectral ranges via doping-induced subgap-state contributions. We present results of our studies on nonlinear harmonic generation from our samples, which include 1) second harmonic generation and 2) third harmonic generation precisely characterized by Maker fringes as a function of both Al doping and wavelength. We exhaustively discuss the possible cause for the modified optical nonlinearities observed in our AZO thin films and give detailed comparisons of our observations with the previous studies. We also present the results of open- and close-aperture Z-scans to characterize the two-photon absorption coefficient (TPA) and the nonlinear refractive index (NLR), respectively, of the AZO films. There was no clearcut evidence of monotonic dependence of TPA and NLR on doping. This presumably indicates that the overall effect is nontrivial and should be understood in terms of combined effects of bandgap shift and crystallinity upon varying the doping level. Most intriguingly, we found that NLR values from the closed-aperture Z-scan are very large by orders of magnitude when compared with the bulk counterparts. Similar observation was made for TPA values from the open-aperture Z-scan. To countercheck very large NLO absorption, we conducted simple intensity scan by varying the incident photon number on each sample but fixing the beam area to eliminate any possible errors related to optical

Viscoelastic-Viscoplastic Modelling of the Scratch Response of PMMA

Directory of Open Access Journals (Sweden)

G. Kermouche

2013-01-01

Full Text Available This paper aims at understanding how to model the time-dependent behavior of PMMA during a scratch loading at a constant speed and at middle strain levels. A brief experimental study is first presented, consisting of the analysis of microscratches carried out at various scratching velocities and normal loads. The loading conditions have been chosen in such a way that neither (viscoelasticity nor (viscoplasticity of the PMMA may be neglected a priori. The main analyzed parameter is the tip penetration depth measured during the steady state. Then, a finite element model is used to investigate the potential of classical elastic-viscoplastic constitutive models to reproduce these experimental results. It is mainly shown that these models lead to unsatisfying results. More specifically, it is pointed out here that the time-independent Young modulus used in such models is not suitable. To take into account this feature, a viscoelastic-viscoplastic model based on the connection in series of a viscoelastic part with a viscoplastic part is proposed. It is shown that it leads to more acceptable results, which points out the importance of viscoelasticity in the scratch behavior of solid polymers.

Post-seismic relaxation theory on laterally heterogeneous viscoelastic model

Science.gov (United States)

Pollitz, F.F.

2003-01-01

Investigation was carried out into the problem of relaxation of a laterally heterogeneous viscoelastic Earth following an impulsive moment release event. The formal solution utilizes a semi-analytic solution for post-seismic deformation on a laterally homogeneous Earth constructed from viscoelastic normal modes, followed by application of mode coupling theory to derive the response on the aspherical Earth. The solution is constructed in the Laplace transform domain using the correspondence principle and is valid for any linear constitutive relationship between stress and strain. The specific implementation described in this paper is a semi-analytic discretization method which assumes isotropic elastic structure and a Maxwell constitutive relation. It accounts for viscoelastic-gravitational coupling under lateral variations in elastic parameters and viscosity. For a given viscoelastic structure and minimum wavelength scale, the computational effort involved with the numerical algorithm is proportional to the volume of the laterally heterogeneous region. Examples are presented of the calculation of post-seismic relaxation with a shallow, laterally heterogeneous volume following synthetic impulsive seismic events, and they illustrate the potentially large effect of regional 3-D heterogeneities on regional deformation patterns.

Direct measurement of the ballistic motion of a freely floating colloid in Newtonian and viscoelastic fluids.

Science.gov (United States)

Hammond, Andrew P; Corwin, Eric I

2017-10-01

A thermal colloid suspended in a liquid will transition from a short-time ballistic motion to a long-time diffusive motion. However, the transition between ballistic and diffusive motion is highly dependent on the properties and structure of the particular liquid. We directly observe a free floating tracer particle's ballistic motion and its transition to the long-time regime in both a Newtonian fluid and a viscoelastic Maxwell fluid. We examine the motion of the free particle in a Newtonian fluid and demonstrate a high degree of agreement with the accepted Clercx-Schram model for motion in a dense fluid. Measurements of the functional form of the ballistic-to-diffusive transition provide direct measurements of the temperature, viscosity, and tracer radius. We likewise measure the motion in a viscoelastic Maxwell fluid and find a significant disagreement between the theoretical asymptotic behavior and our measured values of the microscopic properties of the fluid. We observe a greatly increased effective mass for a freely moving particle and a decreased plateau modulus.

Mathematical modelling of nonlinear thermal radiation effects on EMHD peristaltic pumping of viscoelastic dusty fluid through a porous medium duct

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M.M. Bhatti

2017-06-01

Full Text Available Biologically-inspired propulsion systems are currently receiving significant interest in the aerospace sector. Since many spacecraft propulsion systems operate at high temperatures, thermal radiation is important as a mode of heat transfer. Motivated by these developments, in the present article, the influence of nonlinear thermal radiation (via the Rosseland diffusion flux model has been studied on the laminar, incompressible, dissipative EMHD (Electro-magneto-hydrodynamic peristaltic propulsive flow of a non-Newtonian (Jefferys viscoelastic dusty fluid containing solid particles through a porous planar channel. The fluid is electrically-conducting and a constant static magnetic field is applied transverse to the flow direction (channel walls. Slip effects are also included. Magnetic induction effects are neglected. The mathematical formulation is based on continuity, momentum and energy equations with appropriate boundary conditions, which are simplified by neglecting the inertial forces and taking the long wavelength and lubrication approximations. The boundary value problem is then rendered non-dimensional with appropriate variables and the resulting system of reduced ordinary differential equations is solved analytically. The impact of various emerging parameters dictating the non-Newtonian propulsive flow i.e. Prandtl number, radiation parameter, Hartmann number, permeability parameter, Eckert number, particle volume fraction, electric field and slip parameter are depicted graphically. Increasing particle volume fraction is observed to suppress temperature magnitudes. Furthermore the computations demonstrate that an increase in particle volume fraction reduces the pumping rate in retrograde pumping region whereas it causes the opposite effect in the co-pumping region. The trapping mechanism is also visualized with the aid of streamline contour plots. Increasing thermal radiation elevates temperatures. Increasing Hartmann (magnetic body

Aero-servo-viscoelasticity theory: Lifting surfaces, plates, velocity transients, flutter, and instability

Science.gov (United States)

Merrett, Craig G.

Modern flight vehicles are fabricated from composite materials resulting in flexible structures that behave differently from the more traditional elastic metal structures. Composite materials offer a number of advantages compared to metals, such as improved strength to mass ratio, and intentional material property anisotropy. Flexible aircraft structures date from the Wright brothers' first aircraft with fabric covered wooden frames. The flexibility of the structure was used to warp the lifting surface for flight control, a concept that has reappeared as aircraft morphing. These early structures occasionally exhibited undesirable characteristics during flight such as interactions between the empennage and the aft fuselage, or control problems with the elevators. The research to discover the cause and correction of these undesirable characteristics formed the first foray into the field of aeroelasticity. Aeroelasticity is the intersection and interaction between aerodynamics, elasticity, and inertia or dynamics. Aeroelasticity is well suited for metal aircraft, but requires expansion to improve its applicability to composite vehicles. The first is a change from elasticity to viscoelasticity to more accurately capture the solid mechanics of the composite material. The second change is to include control systems. While the inclusion of control systems in aeroelasticity lead to aero-servo-elasticity, more control possibilities exist for a viscoelastic composite material. As an example, during the lay-up of carbon-epoxy plies, piezoelectric control patches are inserted between different plies to give a variety of control options. The expanded field is called aero-servo-viscoelasticity. The phenomena of interest in aero-servo-viscoelasticity are best classified according to the type of structure considered, either a lifting surface or a panel, and the type of dynamic stability present. For both types of structures, the governing equations are integral

Nonlinear Dirac Equations

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Wei Khim Ng

2009-02-01

Full Text Available We construct nonlinear extensions of Dirac's relativistic electron equation that preserve its other desirable properties such as locality, separability, conservation of probability and Poincaré invariance. We determine the constraints that the nonlinear term must obey and classify the resultant non-polynomial nonlinearities in a double expansion in the degree of nonlinearity and number of derivatives. We give explicit examples of such nonlinear equations, studying their discrete symmetries and other properties. Motivated by some previously suggested applications we then consider nonlinear terms that simultaneously violate Lorentz covariance and again study various explicit examples. We contrast our equations and construction procedure with others in the literature and also show that our equations are not gauge equivalent to the linear Dirac equation. Finally we outline various physical applications for these equations.

Analysis of viscoelastic flow in tin phosphate glass

International Nuclear Information System (INIS)

Cha, Jaemin; Asida, Yuto; Takebe, Hiromichi

2011-01-01

The change of the viscoelastic flow near the imprinting temperature was analyzed by a penetration method with a commercial TMA and the result was compared with thermally-imprinted SnO-P 2 O 5 (SP) and SnO-B 2 O 3 -P 2 O 5 (SBP) glass samples by an imprint apparatus. The viscosity of SP glass increases monotonically with increasing SnO content and the specific movement is shown in viscoelastic flow under the optimized thermal imprinting temperature for SP glasses.

Blast Analysis of Laminated Glass Curtain Walls Equipped by Viscoelastic Dissipative Devices

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Chiara Bedon

2012-09-01

Full Text Available Nonlinear numerical simulations are reported for a conventional unitized laminated glass curtain wall subjected to high- and low-level air blast loading. The studied curtain wall, spanning floor to floor, consisted of a laminated glass panel, a continuous bead of structural silicone sealant, a split screw spline frame and four rigid brackets. Firstly, a linear elastic FE-model (M01 is presented to investigate dynamic stresses and deflections due to explosion, by taking into account geometrical nonlinearities. Since, in similar glazing systems, it is important to take into account the possible cracking of glass lites, a second model (M02, calibrated to previous experimental data, is proposed. In it, glass behaves as a brittle-elastic material, whereas an elastoplastic characteristic curve is assumed for mullions. As a result, the design explosion seriously affects the main components of the curtain wall, especially the bead of silicone. To address these criticalities, additional viscoelastic (VE devices are installed at the frame corners (M03. Their effectiveness explains the additional deformability provided to the conventional curtain wall, as well as the obvious dissipation of the incoming energy due to blast loading. Structural and energy capabilities provided by devices are highlighted by means of numerical simulations.

A New Hybrid Viscoelastic Soft Tissue Model based on Meshless Method for Haptic Surgical Simulation

Science.gov (United States)

Bao, Yidong; Wu, Dongmei; Yan, Zhiyuan; Du, Zhijiang

2013-01-01

This paper proposes a hybrid soft tissue model that consists of a multilayer structure and many spheres for surgical simulation system based on meshless. To improve accuracy of the model, tension is added to the three-parameter viscoelastic structure that connects the two spheres. By using haptic device, the three-parameter viscoelastic model (TPM) produces accurate deformationand also has better stress-strain, stress relaxation and creep properties. Stress relaxation and creep formulas have been obtained by mathematical formula derivation. Comparing with the experimental results of the real pig liver which were reported by Evren et al. and Amy et al., the curve lines of stress-strain, stress relaxation and creep of TPM are close to the experimental data of the real liver. Simulated results show that TPM has better real-time, stability and accuracy. PMID:24339837

Non-linear thermal and structural analysis of a typical spent fuel silo

International Nuclear Information System (INIS)

Alvarez, L.M.; Mancini, G.R.; Spina, O.A.F.; Sala, G.; Paglia, F.

1993-01-01

A numerical method for the non-linear structural analysis of a typical reinforced concrete spent fuel silo under thermal loads is proposed. The numerical time integration was performed by means of a time explicit axisymmetric finite-difference numerical operator. An analysis was made of influences by heat, viscoelasticity and cracking upon the concrete behaviour between concrete pouring stage and the first period of the silo's normal operation. The following parameters were considered for the heat generation and transmission process: Heat generated during the concrete's hardening stage, Solar radiation effects, Natural convection, Spent-fuel heat generation. For the modelling of the reinforced concrete behaviour, use was made of a simplified formulation of: Visco-elastic effects, Thermal cracking, Steel reinforcement. A comparison between some experimental temperature characteristic values obtained from the numerical integration process and empirical data obtained from a 1:1 scaled prototype was also carried out. (author)

Design, synthesis, and characterization of lightly sulfonated multigraft acrylate-based copolymer superelastomers

Energy Technology Data Exchange (ETDEWEB)

Misichronis, Konstantinos [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Wang, Weiyu [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Cheng, Shiwang [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Wang, Yangyang [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Shrestha, Umesh [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Dadmun, Mark D. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Mays, Jimmy W. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Saito, Tomonori [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division

2018-01-29

Multigraft copolymer superelastomers consisting of a poly(n-butyl acrylate) backbone and polystyrene side chains were synthesized and the viscoelastic properties of the non-sulfonated and sulfonated final materials were investigated using extensional rheology (SER3). The non-linear viscoelastic experiments revealed significantly increased true stresses (up to 10 times higher) after sulfonating only 2–3% of the copolymer while the materials maintained high elongation (<700%). The linear viscoelastic experiments showed that the storage and loss modulus are increased by sulfonation and that the copolymers can be readily tuned and further improved by increasing the number of branching points and the molecular weight of the backbone. Here, in this way, we show that by tuning not only the molecular characteristics of the multigraft copolymers but also their architecture and chemical interaction, we can acquire thermoplastic superelastomer materials with desired viscoelastic properties.