Parameters Of Viscoelastic Model Research Articles

Multi-Parameter Optimization Algorithm of Frequency-Dependent Model for Viscoelastic Damping Material

In order to obtain the parameters of viscoelastic damping material model, namely GHM, which account for frequency dependence and allow time-domain analysis of viscoelastic composite structure, a new optimization algorithm which is composed of particle swarm optimization(PSO) and sequential quadratic programming (SQP) algorithm is presented . The results are compared with those of standard rheological model and fractional derivative model as well as the experiment results. The results show that the hybrid algorithm can obtain the better optimum solution for the model and have a fast convergence , it will correctly describe the constitutive characteristics of viscoelastic damping material.

A composite viscoelastic model for incorporating grain boundary sliding and transient diffusion creep; correlating creep and attenuation responses for materials with a fine grain size

A new viscoelastic creep function that incorporates both the effects of elastically-accommodated grain boundary sliding (GBS) and transient diffusion creep is proposed. It is demonstrated that this model can simultaneously describe both the transient microcreep curves and the shear attenuation/modulus dispersion in a fine-grained (d ∼ 5 µm) peridotite (olivine + 39 vol. % orthopyroxene) specimen. Low-frequency shear attenuation, , and modulus dispersion, G(ω), spectra were measured in a one-atmosphere reciprocating torsion apparatus at temperatures of 1200 ≤ T ≤ 1300°C and frequencies of 10−2.25 ≤ f ≤ 100 Hz. Reciprocating tests were complemented by a series of small stress (τ ∼ 90 kPa) microcreep experiments at the same temperatures. In contrast to previous models where the parameters of viscoelastic models are derived by fitting the Laplace transform of the creep function to measured attenuation spectra, the parameters are derived solely from the fit of the creep function to the experimental microcreep curves using different published expressions for the relaxation strength of elastically-accommodated GBS. This approach may allow future studies to better link the large dataset of steady-state creep response to the dynamic attenuation behavior.

Differential response of peripheral arterial compliance-related indices to a vasoconstrictive stimulus

Peripheral arterial elastic properties are greatly affected by cardiovascular as well as other pathologies, and their assessment can provide useful diagnostic indicators. The photoplethysmographic technique can provide finger blood volume and pressure waveforms non-invasively, which can then be processed statically or beat-to-beat to characterize parameters of the vessel wall mechanics. We employ an occlusion–deflation protocol in 48 healthy volunteers to study peripheral artery compliance-related indices over positive and negative transmural pressure values as well as under the influence of a valid vasoconstrictor (cigarette smoking). We calculate beat-to-beat indices (compliance index CI, distensibility index DI, three viscoelastic model parameters (compliance C, viscosity R and inertia L), pressure–volume loop areas A and damping factor DF as well as symmetrical (Cmax) and asymmetrical (CAmax) static compliance estimates, and their distributions over transmural pressure. All distributions are bell-shaped and centred on negative transmural pressure values. Distribution heights were significantly lower in the smoking group (w.r.t. the non-smoking group) for C, CI, DI and significantly higher in R and DF. The estimated volume signal time lag was also significantly lower in the smoking group. Left and right distribution widths were significantly different in all parameters/groups but DI (both groups), CAmax, A (smoking group) and L (non-smoking group), and positions of maxima/minima were significantly altered in CAmax, R and DF. C, DF and CI are seen to be most sensitive under this protocol, while Cmax and CAmax are seen to be insensitive. These quantities provide complementary, time- and transmural pressure-dependent information about arterial wall mechanics, and the choice of index should depend on the physiological conditions at hand as well as relevant time resolution and transmural pressure range.

Inverse viscoelastic material characterization using POD reduced-order modeling in acoustic–structure interaction

A strategy is presented for applying the proper orthogonal decomposition (POD) technique for model reduction in computational inverse solution strategies for viscoelastic material characterization. POD is used to derive a basis of optimal dimension from a selection of possible solution fields which are generated through a traditional acoustic–structure interaction finite element model for a given vibroacoustic experiment. The POD bases are applied with the Galerkin weak-form finite element method to create a reduced-order numerical model with decreased computational cost, but which still maintains accuracy close to that of the original full-order finite element model. The reduced-order model is then combined with a global optimization technique to identify estimates to the viscoelastic material properties of a fluid immersed solid from vibroacoustic tests. A strategy is also presented to select the viscoelastic parameters of the initial full-order analyses used to create the POD bases. The selection process is shown through an example to maximize the generalization capabilities of the reduced-order model over the material search space for a minimal number of full-order analyses. Two examples are then presented in which the parameters of rheological viscoelastic models are identified for solids immersed in water, which are subject to a steady-state harmonic pressure while the acoustic response is measured at a point in the surrounding fluid. The POD reduced-order models were able to generalize over the material search domains for the inverse problems. Therefore, the reduced-order solution strategy was capable of identifying accurate estimates to the viscoelastic behavior of the solids with minimal computational expense.

Identification of viscoelastic model parameters by means of cyclic nanoindentation testing

Abstract A method for the identification of model parameters describing the time-dependent material behavior by means of cyclic nanoindentation is presented. The complex shear modulus of the material sample is determined from the prescribed amplitude in the load history, the measured amplitude in the penetration history, and the phase shift between the peak values for the load and the penetration. The parameters for a specific viscoelastic model are obtained by comparing the experimentally-obtained storage and loss moduli – both depending on the frequency used during cyclic testing – with the analytical expressions for the respective viscoelastic model. The presented method is applied to low-density polyethylene, giving access to the parameters of the fractional dash-pot which is used to describe the viscoelastic behavior. The results are compared with results from nanoindentation (static) creep tests, considering different maximum loads. Finally, the performance of the presented method is assessed by comparing the creep-compliance functions corresponding to the model parameters identified by nanoindentation with the macroscopic creep-compliance function obtained from bending-beam-rheometer tests.

Parameter determination and response analysis of viscoelastic material

The parameter determination of viscoelastic material is a multi-variable, multi-aim nonlinear optimization problem, which made the optimization process very complicated. In this paper a hybrid optimal algorithm was proposed to determine the viscoelastic parameters in the constitutive relation according to the experimentally obtained mechanical properties. This algorithm merges the Broydon–Fletcher–Goldfarb–Shanno search into a genetic algorithm framework as a basic operator in order to enhance the local search capability. The proposed hybrid algorithm not only can reduce the iterative times greatly but can abolish the limitation of initial parameter values. Nonlinear material characteristic curve-fitting was carried out using the proposed algorithm and other existing approaches. And the comparison results show this algorithm is accurate and effective. The numerical simulation and experimental study of viscoelastic cantilever beam also indicates that the finite element formulation and the calculative viscoelastic model parameters are reliable. The proposed optimization method can be extended to further complex parameter estimation researches.

Study on dynamic relaxation time and modulus of cement mortar by ultrasonic technique

Ultrasonic wave technique is employed to determine relaxation time and modulus of cement mortar. First, the property of attenuation of amplitude at different cross sections of the specimen may be obtained by detecting the ultrasonic signal at the ends of specimens with different lengths. Secondly, the coefficient of attenuation of the ultrasonic wave is obtained by simulating experimental results. Thirdly, one-dimensional propagation of the ultrasonic wave in cement mortar is analysed by considering the transversal inertial effect. Two important parameters of viscoelastic constitutive model of cement mortar, namely, modulus and relaxation time, are obtained. Finally, the transversal inertial effect on the relaxation time and modulus of material is examined numerically. The results obtained show that the transversal inertial effect may lead to increase of relaxation time and modulus. The method proposed in this paper is effective to measure parameters of the constitutive relation of cement mortar by ultrasonic wave technique.

Mechanical characteristics of Asphalt-Cement Concrete foundations (ACC).

Asphalt Cement Concrete (ACC) is a new material. On the basis of Kuhn’s paradigm, conventional methods which are proper for similar road pavement materials were applied for studying the ACC. ACC is obtained from cold mixing technology such ingredients as cement-sand mortar or cement-mineral aggregate mortar, or cement-sand-mineral aggregate mortar with recycled Asphalt Concrete (AC) mixture or with recycled Mastic Asphalt (MA) mixture. Quick setting cement (CEM I 52,5 NA) is used in all mentioned cases. Novelty of the presented material is due to existence of two internal bounds - flexibility and rigidity. Such ACC parameters as stiffness, deformability and strength in general depend on type and characteristics of cementitions grout which coats applied recycled asphalt materials and fills mixture’s air voids. ACC layer stability may be predicted using viscoelastic model parameters of constitutive relations, including Burgers model, under steady and slow loadings, finally expressed by exponential formulae. This is the research study. Its basic part consists of laboratory and field testing and obtained tests results analysis. Further, road pavements were designed with subbase of ACC with improved performance comparing to typical materials.

Identification of viscoelastic properties by means of nanoindentation taking the real tip geometry into account

Motivated by recent progress in viscoelastic indentation analysis, the identification of viscoelastic properties from nanoindentation test data taking the real tip geometry into account is presented in this paper. Based on the elastic solution of the indentation problem, the corresponding viscoelastic solution is obtained by the application of the method of functional equations. This general solution, which accounts for the real geometric properties of the indenter tip, is specialized for the case of a trapezoidal load history, commonly employed in nanoindentation testing. Three deviatoric creep models, the single dash-pot, the Maxwell, and the three-parameter model are considered. The so-obtained expressions allow us to determine viscoelastic model parameters via back calculation from the measured load–penetration history. The presented approach is illustrated by the identification of short-term viscoelastic properties of bitumen. Hereby, the influence of loading rate, maximum load, and temperature on the model parameters is investigated.

Microscale characterization of bitumen – back-analysis of viscoelastic properties by means of nanoindentation

Abstract In order to understand the complex thermo-rheological behavior of asphalt, stemming from the viscoelastic nature of bitumen, the nanoindentation (NI) technique is employed. Hereby, the load history applied onto the indenter tip is characterized by a loading, holding, and unloading phase. As regards the identification of viscoelastic properties, a recently published back-analysis scheme, employing the holding phase of the NI test, is extended towards fractional-creep models. In fact, this type of model is found to perfectly describe the viscoelastic behavior of bitumen. Based on the identified viscoelastic model parameters, the influence of loading rate, maximum load, and temperature on these parameters is investigated. Hereby, the temperature dependence of creep parameters follows an Arrhenius-type law. In addition to the model parameters, application of the so-called grid-indentation technique within NI testing provides insight into the bitumen microstructure and the mechanical behavior of the different bitumen phases. The results obtained indicate the existence of a string-like microstructure embedded into a less viscous matrix material.

A non-linear viscoelastic model for ceramics at high temperatures

High-temperature mechanical behavior of ceramics is characterized by non-linear rate dependent responses, asymmetric behavior in tension and compression, and nucleation and coalescence of voids leading to rupture. Moreover, rupture experiments show considerable scatter or randomness in fatigue lives of nominally equal specimens. To capture the non-linear, asymmetric time-dependent behavior, a new non-linear viscoelastic model is proposed. Non-linearity and asymmetry are introduced in the volumetric component. To model the random formation and coalescence of voids, each element is assigned a failure strain sampled from a lognormal distribution. An element is deleted when its volumetric strain exceeds its failure strain. Temporal increases in strains produce a sequential loss of elements (a model for void nucleation and growth), which in turn leads to failure. Non-linear viscoelastic model parameters are determined from uniaxial tensile and compressive creep experiments on silicon nitride. The model is then used to predict the deformation of four-point bending and ball-on-ring specimens. Simulation is used to predict statistical moments of rupture lives. Numerical simulation results compare well with results of four-point bending experiments.

Three-dimensional viscoelastic simulation of coextrusion process: comparison with experimental data

Three-dimensional numerical simulation of viscoelastic coextrusion process has been performed and numerical results were compared with the experimental data of Karagiannis et al. (1990). By varying the magnitude of the second normal stress difference and its ratio of Fluid I and Fluid II, we were able to control the interface profile and the degree of encapsulation along the downstream direction. By increasing the parameter α (αFluid I=αFluid II) from 0.1 to 0.4 in the Giesekus model and increasing the α ratio (αFluid IαFluid II) between Fluid I and Fluid II from 2.0 to 4.0 in the permissible range of realistic polymeric systems, the interface profile and the degree of encapsulation along the downstream direction were fitted with the experimental results. There was little difference between the numerical results and the experimental data in the interface profile and the degree of encapsulation along the downstream direction when the α ratio was set to 3.0 (0.3:0.1). Fluid I with larger magnitude of the second normal stress difference protrudes into Fluid II with smaller magnitude of the second normal stress difference around the symmetric plane, while Fluid II wraps around Fluid I near the side walls. As the ξ 1 ratio (ξ 1 ,Fluid Iξ 1 ,Fluid II) increases from 1.0 to 3.0 for the two-mode Phan-Thien and Tanner model, it was found that the curvature of the interface profile increased, and the difference between the numerical results and the experimental data in the interface profile and the degree of encapsulation along the downstream direction was almost negligible when the ξ 1 ratio was set to 3.0 (0.54:0.18). Although the parameters of viscoelastic models were fitted by using the shear viscosity data only, quantitative agreements between the numerical results and the experimental coextrusion data were quite satisfactory.

ANALYSIS OF PRESSURE PULSATION IN A POWER STEERING SYSTEM

For increasing the accuracy and applicability of the simulation that has been developed to predict the pressure pulsation response in a power steering system and uses of the transfer matrix method, this report studies the influence of the viscoelastic model parameters, the hose material and the pressure intensity.Then this report compares the simulated and experimented frequency responses of realistic automotive power steering lines which have pressure hoses with tuning cables and verifies the validity of the simulation.

A viscoelastic description of the glass transition-conversion relationship for reactive polymers

The glass transition temperature,T g is a sensitive and practical parameter for following cure of reactive thermosetting systems. A new equation was developed for predicting theT g -conversion relationship based on the Dillman-Seferis viscoelastic compliance model. It assumes that the changes inT g are primarily due to changes in relaxation time as chain extension and crosslinking reduce the mobility of a polymer network. Such information is essential in combining kinetic and viscoelastic measurements, which monitor transformations of thermosets during cure. The equation derived from the viscoelastic model was shown to be applicable for a variety of experimental data. The success of the methodology was further demonstrated by comparing well-established relations, such as the Fox equation and the Di-Benedetto equation, to predictions made possible by adjusting two viscoelastic model parameters. Finally, the fitting power of the proposed equation was shown by fitting published epoxy data from the literature as well as experimental data on a relatively new resin system such as dicyanates used as a model in this study.

τ‐p SEISMIC DATA FOR VISCOELASTIC MEDIA ‐ PART 2: LINEARIZED INVERSION1

AbstractAn approach to extraction of viscoelastic parameters from seismic data is implemented and succesfully tested. Viscoelastic inversion is performed using adaptive damping factors to control the sensitivity of the viscoelastic parameters in relation to the τ‐p seismic data. A priori information is incorporated through the damping factors as standard deviations of the data and of the viscoelastic model parameters. The stability of the inversion process is controlled by the variation of the damping factors as a function of the residual errors and parameter updates at each iteration.Tests on synthetic and real data show that P‐ and S‐wave quality factors, Qp and Qs, in addition to P‐ and S‐wave velocities and density Cp, Cs and p, can be extracted from τ‐p seismic information. Singular value decomposition analysis demonstrates that estimated Qp and Qs values are more affected by the presence of data inaccuracies and noise than are those of Cp and p. Cs and Qs are not uniquely recovered due to the limited contribution of P‐S converted waves.Knowledge of the viscoelastic parameters is of particular importance in accurately describing petrophysical properties of rocks and pore fluids existing in the subsurface; this is demonstrated with real data from the Gulf of Mexico.

Viscoelastic crack analysis by the boundary integral equation method

The linear viscoelastic three-dimensional crack problem is analyzed by combining the correspondence principle and the boundary integral equation method. In a general crack analysis the usual boundary integral equations lead to a nonunique formulation of the problem, because they do not involve information about the loading on the crack surface. Here, the boundary integro-differential equations are applied to the numerical calculation of the crack opening displacement of a penny-shaped crack in an infinite linear viscoelastic body. Moreover, the influence of several parameters of the three-parameter viscoelastic model on the crack opening displacement and the incubation time is shown.

Optimization of a Viscoelastic Structure: The Seat-Belt Problem

Optimization of the parameters of elementary linear viscoelastic models is considered for the design of a lap seat belt in automobiles. The vehicle is assumed to stop abruptly on impact. The parameters are optimized to allow the speed of the vehicle before impact to have the largest permissible value consistent with constraints imposed for the safety of the user of the belt. The constraints chosen here are: (a) the maximum displacement of the body after impact is equal to or less than a prescribed critical displacement; (b) the forward speed of the body at the critical displacement does not exceed a prescribed maximum value; (c) the force exerted by the belt on the body during the motion following impact does not exceed a prescribed maximum value. It is found that the optimized Kelvin-Voigt viscoelastic model is nearly 40 percent more effective than the purely elastic material. It is nearly as effective as constant deceleration. An additional and advantageous property is proposed, moreover, for belts of viscoelastic materials. This is that the material should have a relatively low spring rate at relatively small strain rates. The optimized belts for the elementary viscoelastic models are shown to be quite stiff at low strain rates, however.

Responses of aortic smooth muscle studied in intact dogs.

ARTICLESResponses of aortic smooth muscle studied in intact dogsHP Pieper, and LT PaulHP Pieper, and LT PaulPublished Online:01 Jul 1969https://doi.org/10.1152/ajplegacy.1969.217.1.154MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByIs obstructive sleep apnoea causally related to arterial stiffness? A critical review of the experimental evidenceSleep Medicine Reviews, Vol. 17, No. 1Regulation of arterial stiffness: Cellular, molecular and neurogenic mechanismsArtery Research, Vol. 5, No. 4Arterial Mechanics in Ischemic versus Nonischemic Cardiomyopathy: Clinical and Diagnostic ImpactEchocardiography, Vol. 26, No. 7Angiotensin II contributes to arterial compliance in congestive heart failureSilvia G. Lage, Liliane Kopel, Caio C. J. Medeiros, Ricardo T. Carvalho, and Mark A. Creager1 October 2002 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 283, No. 4Smooth muscle relaxation and local hydraulic impedance properties of the aortaBernard P. Cholley, Roberto M. Lang, Claudia E. Korcarz, and Sanjeev G. Shroff1 June 2001 | Journal of Applied Physiology, Vol. 90, No. 6Aortic pressure-diameter relationship assessed by intravascular ultrasound: experimental validation in dogsStefan E. Hardt, Armin Just, Raffi Bekeredjian, Wolfgang Kübler, Hartmut R. Kirchheim, and Helmut F. Kuecherer1 March 1999 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 276, No. 3Noninvasive Evaluation of Aortic Elastic PropertiesAortic elastic properties with transesophageal echocardiography with automated border detection: Validation according to regional differences between proximal and distal descending thoracic aortaJournal of the American Society of Echocardiography, Vol. 9, No. 4Pressure-Diameter Relation of the Human AortaCirculation, Vol. 92, No. 8In Vivo Measurement of Regional Large Artery Compliance by Intravascular Ultrasound Under Pentobarbital Anesthesia2 July 2016 | Angiology, Vol. 46, No. 6Assessment of smooth muscle contribution to descending thoracic aortic elastic mechanics in conscious dogs.Circulation Research, Vol. 73, No. 6Autonomic nervous system and large conduit arteriesNitroglycerin and arterial compliance13 March 2009 | Acta Pharmacologica et Toxicologica, Vol. 59, No. S6Hemodynamic correlates of arterial complianceCatheterization and Cardiovascular Diagnosis, Vol. 12, No. 6Pressure dependence of the canine aortic characteristic impedance and the effects of alterations in smooth muscle activityMedical & Biological Engineering & Computing, Vol. 23, No. 4Measurement of arterial pressure-dimension relationships in conscious animalsAnnals of Biomedical Engineering, Vol. 12, No. 5Control of Vascular Contractility by the Cardiac PacemakerScience, Vol. 215, No. 4540The effects of phenoxybenzamine on the aortic pressure-diameter relationship in dogsExperientia, Vol. 38, No. 2Circulatory Correlates: Vascular Impedance, Resistance, and Capacity1 January 2011Effects of age on aortic pressure-diameter and elastic stiffness-stress relationships in unanesthetized sheep.Circulation Research, Vol. 44, No. 3Pulse wave propagation in arteries with consideration of prior stresses and muscle activityPolymer Mechanics, Vol. 14, No. 2Baroreceptor reflex control of arterial hemodynamics in the dog.Circulation Research, Vol. 37, No. 6Sympathetic Control of Canine Abdominal AortaCirculation Research, Vol. 33, No. 2Estimated five component viscoelastic model parameters for human arterial wallsJournal of Biomechanics, Vol. 6, No. 1Diameter and Elasticity of the Ascending Aorta during Infusion of NoradrenalineActa Physiologica Scandinavica, Vol. 83, No. 1Computer monitoring of cardiodynamics in the newbornJournal of Pediatric Surgery, Vol. 6, No. 3Effects of Altered Smooth Muscle Tone on Aortic Diameter and Aortic Baroreceptor Activity in Anesthetized RabbitsCirculation Research, Vol. 28, No. 2Large deformation of elastic tubesJournal of Biomechanics, Vol. 3, No. 6 More from this issue > Volume 217Issue 1July 1969Pages 154-160 Copyright & PermissionsCopyright © 1969 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1969.217.1.154PubMed5785873History Published online 1 July 1969 Published in print 1 July 1969 Metrics