Impact Of Viscoelasticity Research Articles

On the dynamic behavior of a functionally graded viscoelastic-piezoelectric composite substrate subjected to a moving line load

The present study bestows the analytical investigation of incremental mechanical stresses (compressive stress, shear, and tensile) and electrical displacements (vertical and horizontal components) induced due to a moving line load on an irregular transversely isotropic functionally graded viscoelastic-piezoelectric material (FGVPM) substrate. The closed form expressions of said induced mechanical stresses and induced electrical displacements are deduced and validated with pre-established results for electrically open and short conditions. The elastic moduli (stiffness tensors), piezoelectric moduli, dielectric moduli, elastic loss moduli, piezoelectric loss moduli, and dielectric loss moduli for a viscoelastic-piezoelectric composite are computed and used for numerical computation and graphical demonstration. The effectuality of diverse physical parameters (viz. maximum depth of irregularity, friction due to rough upper surface, functional gradient parameter, irregularity factor associated with different types of irregularity viz. rectangular irregularity, parabolic irregularity and no irregularity) on said induced stresses and electrical displacements in the aforementioned composite substrate has also been discussed. A comparative analysis has also been made to examine the impact of piezoelectricity and viscoelasticity on theon said induced mechanical stresses and induced electrical displacements. In particular, some special peculiarities are also sketched by means of graphs.

Size-dependent resonant response of a double-layered viscoelastic nanoresonator under electrostatic and piezoelectric actuations incorporating surface effects and Casimir regime

Nonlinear dynamics of a double-layer viscoelastic nanobeam embedded into an electromechanical system is investigated in this paper. The nanoelectromechanical system (NEMS) consists of two piezoelectric and Kelvin–Voigt viscoelastic nanobeams with visco-Pasternak medium in between. An electrostatic force which is the combination of DC and AC voltages is applied to the lower nanobeam through the fixed electrode. Taking into account both the small-scale effect and surface energy effect, the modified couple-stress theory together with Gurtin–Murdoch elasticity theory is implemented. As intermolecular interactions between the fixed and lower electrodes, the influence of Casimir regime on the dynamic behavior of the NEMS device is also included in the proposed model. The differential motion’s equations are derived by means of Hamilton’s principle and discretized to a set of nonlinear ODEs through Galerkin’s decomposition procedure. In order to capture the steady-state dynamic response of the system, a combined shooting and arclength continuation method is schemed. A comprehensive study has been carried out on the impact of viscoelasticity, size-dependency, surface effects, direct and alternating current voltages, piezoelectric voltage and visco-Pasternak parameters on the frequency-response behavior of the system near primary resonance. Furthermore, some bifurcation points in the frequency-response curves are addressed. The combined hardening–softening-type behaviors are observed in the dynamic response of the system. It has been shown that the nonlinear characteristics of the motion of the proposed NEMS device have sensitive-dependence on some of the mentioned parameters.

Effects of Size, Surface Energy and Casimir Force on the Superharmonic Resonance Characteristics of a Double-Layered Viscoelastic NEMS Device Under Piezoelectric Actuations

This paper investigates the nonlinear characteristics of a double-layered viscoelastic nanoelectromechanical system (NEMS) in the vicinity of superharmonic resonance. Two nanobeams are made of piezoelectric material and coupled through a visco-Pasternak medium in between. Modified couple-stress theory together with Gurtin–Murdoch surface elasticity theory is utilized to take into account the effects of size-dependency and surface energy for the nanosized structure. Kelvin–Voigt model is also implemented to consider the impact of viscoelasticity. The differential equations of motion are established based on Hamilton’s principle and decomposed to a set of nonlinear ordinary differential equations via Galerkin discretization method. Arclength continuation technique is schemed to capture the frequency–response curves near superharmonic resonance of the system. The influence of the couple-stress parameter, surface strain energy and dispersion force on the nonlinear behavior of the system near superharmonic resonance has been studied. It is observed, that the hardening and softening behaviors of the system are remarkably affected by the size and surface parameters, and interatomic Casimir force. Finally, considering all the mentioned effects, the influence of the DC and AC voltage loads on the dynamic pull-in behavior of the NEMS device is investigated. For these cases, some frequency ranges are addressed as the pull-in band in which the lower nanobeam collapses.

Investigation of Viscoelasticity in the Relationship Between Carotid Artery Blood Pressure and Distal Pulse Volume Waveforms.

We investigated the relationship between carotid artery blood pressure (BP) and distal pulse volume waveforms (PVRs) via subject-specific mathematical modeling. We conceived three physical models to define the relationship: a tube-load model augmented with a gain (TLG), Voigt (TLV), and standard linear solid (TLS) models. We compared these models using PVRs measured via BP cuffs at an upper arm and an ankle as well as carotid artery tonometry waveform collected from 133 subjects. At both upper arm and ankle, PVR was related to carotid artery tonometry by TLV and TLS models better than by TLG model; when root-mean-squared over all the subjects, the systolic and diastolic BP errors between measured carotid artery tonometry waveform and the one estimated from distal PVR reduced from 4.3mmHg and 4.6mmHg (TLG) to 1.1mmHg and 1.0mmHg (TLS) for the upper arm (p < 0.0167), and from 2.1mmHg and 1.7mmHg (TLG) to 2.1mmHg and 1.5mmHg (TLV) for the ankle. Further, TLV and TLS models exhibited superior Akaike's Information Criterion (AIC) in both locations than TLG model. However, the difference between TLG versus TLV and TLS models associated with the ankle was not large. Therefore, the relationship of central arterial BP to arm PVR arises from both wave reflection and viscoelasticity while the relationship to ankle PVR mainly arises from wave reflection. These findings may imply that an effective subject-specific transfer function for estimating accurate central arterial BP from an arm PVR should account for the impact of viscoelasticity.

Viscoelastic hydrogels for 3D cell culture

In tissues, many cells are surrounded by and interact with a three-dimensional soft extracellular matrix (ECM). Both the physical and biochemical properties of the ECM play a major role in regulating cell behaviours. To better understand the impact of ECM properties on cell behaviours, natural and synthetic hydrogels have been developed for use as synthetic ECMs for 3D cell culture. It has long been known that ECM and tissues are viscoelastic, or display a time-dependent response to deformation or mechanical loading, exhibiting stress relaxation and creep. However, only recently have there been efforts made to understand the role of the time-dependent aspects of the ECM mechanics on regulating cell behaviours using hydrogels for 3D culture. Here we review the characterization and molecular basis of hydrogel viscoelasticity and plasticity, and describe newly developed approaches to tuning viscoelasticity in hydrogels for 2D and 3D culture. Then we highlight several recent studies finding a potent impact of hydrogel stress relaxation or creep on cell behaviours such as cell spreading, proliferation, and differentiation of mesenchymal stem cells. The role of time-dependent mechanics on cell biology remains largely unclear, and ripe for further exploration. Further elucidation of this topic may substantially advance our understanding of cell-matrix interactions during development, homeostasis, wound healing, and disease, and guide the design of biomaterials for regenerative medicine.

Viscoplasticity Enables Mechanical Remodeling of Matrix by Cells

Living tissues consist largely of cells and extracellular matrices (ECMs). The mechanical properties of ECM have been found to play a key role in regulating cell behaviors such as migration, proliferation, and differentiation. Although most studies to date have focused on elucidating the impact of matrix elasticity on cell behaviors, recent studies have revealed an impact of matrix viscoelasticity on cell behaviors and reported plastic remodeling of ECM by cells. In this study, we rigorously characterized the plasticity in materials commonly used for cell culture. This characterization of plasticity revealed time-dependent plasticity, or viscoplasticity, in collagen gels, reconstituted basement membrane matrix, agarose gels, alginate gels, and fibrin gels, but not in polyacrylamide gels. Viscoplasticity was associated with gels that contained weak bonds, and covalent cross-linking diminished viscoplasticity in collagen and alginate gels. Interestingly, the degree of plasticity was found to be nonlinear, or dependent on the magnitude of stress or strain, in collagen gels, but not in the other viscoplastic materials. Viscoplastic models were employed to describe plasticity in the viscoplastic materials. Relevance of matrix viscoplasticity to cell-matrix interactions was established through a quantitative assessment of plastic remodeling of collagen gels by cells. Plastic remodeling of collagen gels was found to be dependent on cellular force, mediated through integrin-based adhesions, and occurred even with inhibition of proteolytic degradation of the matrix. Together, these results reveal that matrix viscoplasticity facilitates plastic remodeling of matrix by cellular forces.

Locally-exact homogenization of viscoelastic unidirectional composites

The elasticity-based, locally-exact homogenization theory for periodic materials with hexagonal and tetragonal symmetries is extended to accommodate linearly viscoelastic phases via the correspondence principle. The theory employs Fourier series representations for fiber and matrix displacement fields in the cylindrical coordinate system that satisfy exactly equilibrium equations and continuity conditions in the interior of the unit cell. The inseparable exterior problem requires satisfaction of periodicity conditions efficiently accomplished using previously introduced balanced variational principle which ensures rapid displacement and stress field convergence in the presence of linearly viscoelastic phases with relatively few harmonic terms. The solution’s stability and efficiency, with concommitant simplicity of input data construction, facilitate rapid identification of the impact of phase viscoelasticity and array type on homogenized moduli and local fields in wide ranges of fiber volume fraction. We illustrate the theory’s utility by investigating the impact of fiber array type and matrix viscoelastic response (constant Poisson’s ratio vs constant bulk modulus) on the homogenized response and local stress fields, reporting previously undocumented differences. Specifically, we show that initially small differences between hexagonal and square arrays are magnified substantially by viscoelasticity. New results on the transmission of matrix viscoelastic features to the macroscale are also generated in support of construction of homogenized viscoelastic functions from experimental data.

The effect of adding Fascial Manipulation® to the physical therapy plan of care for low back pain patients

Fig. 1 Block diagram model of the mechanobiological response of fibrous load bearing tissue under biophysical stimuli including the impact of viscoelasticity/viscoplasticity. (R stands for repair, ED for enzymatic degradation, MD for mechanical degradation of the extracellular matrix). chanical behaviors, FT mechanical reaction to biophysical stimuli is influenced by the type of stimulus input and the stimulus history; 3) Under macroscopic biophysical stimuli, ECM molecules are subjected to stress and strain, and could thus undergo mechanical degradation (MD). Changes to mechanical properties and ECM structure related to MD in FT and non-linear over time and heterogeneous across the tissue; 4) When FLBT are subjected to macroscopic biophysical stimuli, these stimuli are scaled down to microscopic biophysical stimuli which are, in turn, transformed into biochemical signals that the cells can sense. In response to these signals, the cell can degrade the ECM via enzymatic degradation (ED) or repair (R) it and 5) The tissue global mechanobiological response is the result of competitive dynamics between degradation and repair leading to an inverse-U relationship between stimulation and tissue quality. Conclusion: Our analysis showed that viscoelasticity and viscoplasticity of live FLBT could influence tissue mechanobiological response, but experiments are required to confirm it. The impact of viscoelasticity and viscoplasticity may prove to have significant implications for in vivo clinical applications.

Complex fluids affect low-Reynolds number locomotion in a kinematic-dependent manner

In order to improve our understanding of the self-propulsion of swimming microorganisms in viscoelastic fluids, we study experimentally the locomotion of three artificial macro-scale swimmers in Newtonian and synthetic Boger fluids. Each swimmer is made of a rigid head and a tail whose dynamics leads to viscous propulsion. By considering three different kinematics of the tail (helical rigid, planar flexible, and helical flexible) in the same fluid, we demonstrate experimentally that the impact of viscoelasticity on the locomotion speed of the swimmers depends crucially on the kinematics of the tails. Specifically, rigid helical swimmers see no change in their swimming speed, swimmers with planar rod-like flexible tails always swim faster, while those with flexible ribbon-like tails undergoing helical deformation go systematically slower. Our study points to a subtle interplay between tail deformation, actuation, and viscoelastic stresses, and is relevant to the three-dimensional dynamics of flagellated cells in non-Newtonian fluids.

Аналітичне дослідження контактної поведінки ділянки трубопроводу з в’язкопружною ремонтною накладкою

In this paper an analytical study on a stress-strain state of a steel pipeline section with a repair fi-berglass viscoelastic layer is described. The layer is considered long enough that allows to solve the problem in a flat axisymmetric statement. The analytical model including accounting of an isotropic viscoelasticity involves the need to construct and solve the boundary value problem for a system of integro-differential equations. In order to do it an approach based on a method of differentiation of integral equations is proposed. It is shown that for the initial time moment a solution of viscoelastic problem coincides with an elastic solution. Calculation results are presented as displacement and stress distributions versus radius and time curves. The viscoelastic model lets detect and discover such impor-tant properties of viscoelasticity as an increase of displacement over time and a stress relaxation in the composite layer. It is observed that at the same time the stress relaxation in the layer causes an increase of dangerous circumferential stresses in the steel pipeline. According to these results a conclusion about an impact of viscoelasticity on an overall assessment of strength of the construction is made. Also it is shown that for the specific set of physical and geometrical parameters of the construction stress relaxa-tion in layer occurs in the moment of time with a value 200 hours and the maximum circumferential stress value increases by seven percent. The time result coincide with relaxation time obtained using numerical model based on a finite-element method of a commercial computer-aided engineering com-plex. The stress increase result also responds to the numerical assessment and this value can be much higher in case of stress concentration due to presence of defects in pipeline walls. Proposed analytical model allows to save computational resources and to extend its application to more complex cases of the stress-strain state.

Impact of Viscoelasticity on the Tribological Behavior of PTFE Composites for Valve Seals Application

In this article, we studied and explored the impact of viscoelasticity on the friction and wear behavior of pure polytetrafluoroethylene (PTFE), carbon–graphite PTFE composite, and glass fiber–MoS2 PTFE composite. Tests were carried out using a specific reciprocating tribometer for valve seal application. The worn surfaces of the PTFE composites and the transfer films formed on the counterface were examined with a scanning electron microscope (SEM). Experimental results revealed that the addition of filler materials was effective in reducing the wear volume in all composites studied. In addition, the friction coefficient and wear resistance showed high sensitivity to the viscoelastic behavior of the PTFE seal. SEM investigation showed that the incorporation of particulate fillers into the PTFE matrix could dramatically reduce and stabilize the transfer films to the counterface, so they largely decreased the wear of the PTFE composites.

Fluid elasticity increases the locomotion of flexible swimmers

We conduct experiments with flexible swimmers to address the impact of fluid viscoelasticity on their locomotion. The swimmers are composed of a magnetic head actuated in rotation by a frequency-controlled magnetic field and a flexible tail whose deformation leads to forward propulsion. We consider both viscous Newtonian and glucose-based Boger fluids with similar viscosities. We find that the elasticity of the fluid systematically enhances the locomotion speed of the swimmer and that this enhancement increases with Deborah number. Using particle image velocimetry to visualize the flow field, we find a significant difference in the amount of shear between the rear and leading parts of the swimmer head. We conjecture that viscoelastic normal stresses lead to a net elastic forces in the swimming direction and thus a faster swimming speed.

Role of linear viscoelasticity and rotational diffusivity on the collective behavior of active particles

A linear dynamics scheme has been used to quantify the impact of viscoelasticity of the suspending fluid on the collective structure of active particles, including rotational diffusivity. The linear stability examines the response near an isotropic state using a mean-field theory including far-field hydrodynamic interactions of the swimmers. The kinetic model uses three possible constitutive models, the Oldroyd-B, Maxwell, and generalized linear viscoelastic models inspired by fluids like saliva, mucus, and biological gels. The perturbation growth rate has been quantified in terms of wavenumber, translational diffusivity, rotational diffusivity, and material properties of the fluids. A key dimensionless group is the Deborah number, which compares the relaxation time of the fluid with the characteristic timescale of the instability. An advantage of the model formalism is the ability to calculate some properties analytically and others efficiently numerically in the presence of rotational diffusion. The different constitutive equations examined help illustrate when and why the dispersion relation can have a peak at a particular wavenumber. The fluid properties can also change the role of rotational diffusion; diffusion always stabilizes a system in a Newtonian fluid but can destabilize a system in a Maxwell fluid.

Effect of viscoelasticity on liquid transfer during gravure printing

Roll-to-roll patterning of small-scale features on a rapidly moving web is an industrially important process with a wide array of commercial applications both old and new. Examples include magazine printing and more recently the pattering of flexible electronics. Among the many existing web coating techniques for large-scale fabrication, slit die and gravure coating are the most commonly used. In gravure coating, an engraved roller with a regular array of shallow cavities/cells is used to pick up fluid from a bath. It is then passed through a flexible doctoring blade in order to meter off excess fluid before printing the fluid onto a flexible substrate. Here we present an experimental investigation into the effect that viscoelasticity has on the dynamics of liquid transfer from an idealized gravure cell to a flat rigid substrate. Although the dynamics of the actual gravure coating process is quite complex, we chose to study a simplified process by imposing an extensional flow using a modified filament stretching rheometer in which one of the endplates is replaced by a cell containing a single truncated conical gravure cell. The deformation and stretching of the resulting liquid bridges, the motion of the contact line within the gravure cell and the total amount of fluid removed from the gravure cell are studied as a function of the imposed stretch rate, the fluid rheology, and the geometry of the gravure cell. Two different viscoelastic solutions of high molecular weight polyethylene oxide in water were studied and compared to a series of Newtonian fluids. The results show that the primary impact of viscoelasticity is the addition of an elastic stress which increases the tension along the liquid bridge and significantly increases the bridge lifetime. For stretches where the gravure cell was placed on the bottom and the top plate moved vertically, viscoelasticity was found to significantly reduce the amount of fluid transferred to the top plate. However, by placing the gravure cell on top and reversing the relative direction of the inertial and gravitational stresses, viscoelasticity was found to significantly increase the amount of fluid transferred. Increasing the stretch rate was found to amplify these observations. Finally, increasing the contact angle between the fluid and the gravure cell and decreasing the aspect ratio of the gravure cell were both found to increase the amount of fluid transferred.

Competition Between Viscoelasticity and Surfactant Dynamics in Flow Focusing Microfluidics

AbstractThe goal of this work is to quantify the impact of viscoelasticity on a tipstreaming phenomenon observed in flow focusing microfluidic devices. Tipstreaming, or thread formation, is a phenomenon caused by surfactant transport to, from, and along, deforming interfaces that leads to long filaments in microfluidic devices. Viscoelasticity also leads to stable filaments, so possible synergies are investigated here. The ability to generate extremely long and thin filaments that will break up via interfacial instabilities will lead to the formation of droplets much smaller than the device lengthscales. Viscoelastic Boger fluids are used as the dispersed phase liquid in a flow focusing device and surfactant is added to the continuous phase liquid. We find a region of operating space in which viscoelasticity appears to couple with surfactant transport to form long threads. The phenomenon is described qualitatively and is related to fluid relaxation times. magnified image

Impact of viscoelasticity on gage variation in film casting

Mathematical modeling of the melt draw step in film casting is used to understand the impact of viscoelasticity on gage variations. The thin film approximation is used to simplify the governing equations to a set of two-dimensional partial differential equations which are solved using the finite element method. Simulations using the Giesekus constitutive model show that the magnitude of thickness variations increases with increasing flow elasticity or Deborah number.

Analysis of isothermal spinning of liquid-crystalline polymers

In this paper we use the constitutive equation of Bhave et al. (1993) for rod-like, liquid-crystalline polymer solutions to analyze the isothermal, steady-state spinning of these liquids in order to understand the evolution of microstructure, predict the velocity and normal stress distributions in the filament, and examine the effect of different upstream microstructural conditions. Our analysis shows that in contrast to fiber spinning models of isotropic liquids, the velocity, structure, and stress profiles are sensitive to the choice of initial conditions. In addition we have investigated the impact of the closure approximation used in the constitutive equation of Bhave et al. on the fiber spinning problem by solving the equation for the distribution function directly; only slight changes are seen in the velocity and stress profiles. An apparent elongational viscosity defined as the ratio of normal stress difference to strain rate at the takeup compares very well with the true elongational viscosity η̄ for the model, thereby suggesting that fiber spinning flows can be used to determine η̄ for liquid-crystalline polymer solutions. Model predictions of the velocity and stress agree well with data obtained by Prilutski (1984) for HPC/acetic acid solutions. Finally, we present a linear stability analysis of the spinning problem to show the impact of viscoelasticity, inertia, gravity, and surface tension on the onset of draw resonance instabilities. The neutral stability curves obtained for dominant viscoelastic forces reflect trends in the apparent elongational viscosity. Model predictions are in qualitative agreement with the draw resonance data reported by Prilutski.