Viscoelastic Material Properties Research Articles

Vibration damping composition polymer materials and coatings for engineering purpose

To develop and create effective vibration-damping composite polymer materials (VDСPM) with high viscoelastic and strength properties, the choice of research objects to increase durability reduces vibration of parts and structures of machines consequently, the noise level in industrial premises is stated and substantiated. A method is described for studying the viscoelastic properties, adhesive strength, microhardness, impact strength of polymer coatings, and compositions based on them, filled with organomineral ingredients. The results of studies of the viscoelastic and physicomechanical properties of polymer composite materials based on epoxy polymers and an organomineral filler - rubber powder are presented. Based on complex analyzes and the obtained results of the study of the physicomechanical and viscoelastic properties of materials, several effective compositions of vibration-damping polymer materials using rubber powder have been developed.

Analytical solutions for the effective viscoelastic properties of composite materials with different shapes of inclusions

This paper aims to model the effect of different shapes of inclusions on the homogenized viscoelastic properties of composite materials made of a viscoelastic matrix and inclusion particles. The viscoelastic behavior of the matrix phase is modeled by the Generalized Maxwell rheology. The effective properties are firstly derived by combining the homogenization theory of elasticity and the correspondence principle. Then, the effective rheological properties in time space are explicitly derived without using the complex inverse Laplace?Carson transformation (LC). Closed-form solutions for the effective bulk and shear rheological viscoelastic properties, the relaxation and creep moduli as well as the Poisson ratio are obtained for the isotropic case with random orientation distribution and different shapes of inclusions: spherical, oblate and elongate inclusions. The developed approach is validated against the exact solutions obtained by the classical inverse LC method. It is observed that the homogenized viscoelastic moduli are highly sensitive to different shapes of inclusions.

Integrating material properties from magnetic resonance elastography into subject-specific computational models for the human brain

Advances in brain imaging and computational methods have facilitated the creation of subject-specific computational brain models that aid researchers in investigating brain trauma using simulated impacts. The emergence of magnetic resonance elastography (MRE) as a non-invasive mechanical neuroimaging tool has enabled in vivo estimation of material properties at low-strain, harmonic loading. An open question in the field has been how this data can be integrated into computational models. The goals of this study were to use a novel MRI dataset acquired in human volunteers to generate models with subject-specific anatomy and material properties, and then to compare simulated brain deformations to subject-specific brain deformation data under non-injurious loading. Models of five subjects were simulated with linear viscoelastic (LVE) material properties estimated directly from MRE data. Model predictions were compared to experimental brain deformation acquired in the same subjects using tagged MRI. Outcomes from the models matched the spatial distribution and magnitude of the measured peak strain components as well as the 95th percentile in-plane peak strains within 0.005 mm/mm and maximum principal strain within 0.012 mm/mm. Sensitivity to material heterogeneity was also investigated. Simulated brain deformations from a model with homogenous brain properties and a model with brain properties discretized with up to ten regions were very similar (a mean absolute difference less than 0.0015 mm/mm in peak strains). Incorporating material properties directly from MRE into a biofidelic subject-specific model is an important step toward future investigations of higher-order model features and simulations under more severe loading conditions. Statement of SignificanceThe study presents a method to calibrate and evaluate subject-specific finite element brain models using a combination of advanced magnetic resonance imaging (MRI) data. The imaging data is acquired in human volunteers and includes anatomical MRI, magnetic resonance elastography (MRE), and tagged MRI to generate subject-specific geometry, calibrate subject-specific material properties, and evaluate simulation response using subject-specific brain deformation. This dataset of MRE and tagged MRI allows for a unique evaluation of whether material properties from MRE can be used to create biofidelic computational models of the human brain. The study develops a calibration procedure to readily calculate linear viscoelastic material parameters from MRE data and then provides a sensitivity study of the effect of mechanical heterogeneity of the brain on simulation response. The calibrated computational models are used to simulate each subject's tagged MRI experiment; the results show good agreement between the simulated and experimental strain fields. The presented study and results will be informative in guiding the calibration of subject-specific computational brain model from experimental MRE data. The processed MRI, MRE, and tagged MRI data are publicly available at https://www.nitrc.org/projects/bbir/.

An Explicit Model to Extract Viscoelastic Properties of Cells From AFM Force-Indentation Curves

Atomic force microscopy (AFM) has become one of the most used techniques for quantifying the mechanical properties of soft materials such as living cells. AFM force-indentation curves are conventionally fitted with a Hertzian model to extract elastic properties. The elastic properties solely are, however, insufficient to describe the mechanical properties of cells. Hence, extending the quantification to assess, in addition, the viscous behavior, is necessary for a more adequate characterization of the mechanical properties. Here, we expand the analysis capabilities to describe the viscoelastic behavior of the probed materials while using the same conventional AFM force-indentation curves. Our model gives an explicit relation of force and indentation and extracts physically meaningful cell mechanical parameters. We first validated the model on simulated forceindentation curves of a viscoelastic half-infinite space. Then, we applied the fitting model to the force-indentation curves of two hydrogels with different crosslinking mechanisms, polyacrylamide and agarose. We demonstrated that the viscoelastic properties extracted using our fitting model reflected adequately the distinct nature of these hydrogels. Finally, we characterized HeLa cells in two different cell cycle phases, interphase and mitosis and showed that mitotic cells have a higher apparent elasticity and a lower apparent viscosity when compared to interphase cells. Our study provides a simple and rapid method, which can be directly integrated into the standard AFM framework, for extracting the viscoelastic properties of materials. This facilitates the exploration of advanced material properties in general and the understanding of complex biophysical processes in particular.

Ansys code applied to investigate the dynamics of composite sandwich beams

Abstract A numerical analysis of the effect of temperature on the dynamics of the sandwich beam model with a viscoelastic core is presented. The beam under analysis was described with a standard rheological model. This solution allows one to study the effect of temperature on material strength properties. Calculations were performed with the Finite Element Method in the ANSYS software. The analysis of the results of the numerical calculations showed a significant influence of temperature on the strength properties of the model under test. The analysis confirmed damping properties of viscoelastic materials.

Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates.

Ligaments including the cruciate ligaments support and transfer loads between bones applied to the knee joint organ. The functions of these ligaments can get compromised due to changes to their viscoelastic material properties. Currently there are discrepancies in the literature on the viscoelastic characteristics of knee ligaments which are thought to be due to tissue variability and different testing protocols.The aim of this study was to characterise the viscoelastic properties of healthy cranial cruciate ligaments (CCLs), from the canine knee (stifle) joint, with a focus on the toe region of the stress-strain properties where any alterations in the extracellular matrix which would affect viscoelastic properties would be seen. Six paired CCLs, from skeletally mature and disease-free Staffordshire bull terrier stifle joints were retrieved as a femur-CCL-tibia complex and mechanically tested under uniaxial cyclic loading up to 10 N at three strain rates, namely 0.1%, 1% and 10%/min, to assess the viscoelastic property of strain rate dependency. The effect of strain history was also investigated by subjecting contralateral CCLs to an ascending (0.1%, 1% and 10%/min) or descending (10%, 1% and 0.1%/min) strain rate protocol. The differences between strain rates were not statistically significant. However, hysteresis and recovery of ligament lengths showed some dependency on strain rate. Only hysteresis was affected by the test protocol and lower strain rates resulted in higher hysteresis and lower recovery. These findings could be explained by the slow process of uncrimping of collagen fibres and the contribution of proteoglycans in the ligament extracellular matrix to intra-fibrillar gliding, which results in more tissue elongations and higher energy dissipation. This study further expands our understanding of canine CCL behaviour, providing data for material models of femur-CCL-tibia complexes, and demonstrating the challenges for engineering complex biomaterials such as knee joint ligaments.

An Experimental Study on the Blood Pressure Cuff as a Transducer for Oscillometric Blood Pressure Measurements

Noninvasive blood pressure (BP) measurements still rely on empirical interpretation of arterial oscillations recorded via cuff-based oscillometric methods. Extensive effort has dedicated to establishing a theoretical basis for oscillometry, aiming at more accurate BP estimations and measurement of additional hemodynamic parameters. However, oscillometry is still a heuristic method for BP inference. Goal: This study is focused on improving our understanding of the expression of arm volume pulsations in oscillometric signals. The aim is to identify the main factors that determine the transfer function of arm volume to cuff pressure oscillations for existing cuff devices-this being an essential step in establishing a theoretical basis for oscillometry. Methods: The effects of air compression within the cuff and the influence of viscoelastic cuff material properties on the transfer function are studied by an experimental setup. Mechanical numerical modeling is used to interpret the results. Results: Air compression is found to be of adiabatic nature in the frequency range of interest. The cuff material exhibits viscous characteristics which is the cause of cuff response dependence on inflation speed, tightness of wrapping, time passed since previous measurement, and heart rate. Conclusion: It was found that typical cuffs used in clinical practice exhibit complex behavior. Cuff hardware needs to be improved to enable practical translation of pressure to arm volume oscillations. The presented characterization method contributes to standardized development of new cuff prototypes and to identification of designs, techniques, and materials with improved properties for enabling BP measurement accuracy and extraction of additional hemodynamic information.

Contribution of Bowman layer to corneal biomechanics.

To compare the elastic modulus of thin corneal lamellas using 2D stress-strain extensometry in healthy ex vivo human corneal lamellas with or without the presence of Bowman layer. Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Switzerland; ELZA Institute, Dietikon, Switzerland; Department of Ophthalmology, Philipps University of Marburg, Germany. Prospective experimental laboratory study. Healthy human corneas were stripped of Descemet membrane and the endothelium for Descemet membrane endothelial keratoplasty. After epithelium removal, corneas were divided into 2 groups. In Group 1, Bowman layer was ablated with an excimer laser (20 μm thick, 10 mm). In Group 2, Bowman layer was left intact. Then, a lamella was cut from the anterior cornea with an automated microkeratome. Elastic and viscoelastic material properties were analyzed by 2D stress-strain extensometry between 0.03 and 0.70 N. Twenty-six human corneas were analyzed. The mean lamella thickness was 160 ± 37 μm in corneas with Bowman layer and 155 ± 22 μm in corneas without. No statistically significant differences between flaps with and without Bowman layer were observed in the tangential elastic modulus between 5% and 20% strain (11.5 ± 2.9 kPa vs 10.8 ± 3.7 kPa, P > .278). The presence or absence of Bowman layer did not reveal a measurable difference in corneal stiffness. This may indicate that the removal of Bowman layer during photorefractive keratectomy does not represent a disadvantage to corneal biomechanics.

Revealing nucleoplasm mechanics by optical trapping and Brownian motion of nucleolus within mouse GV-oocytes in vivo

Optical trapping of nucleoli within nucleoplasm of living oocytes as unique model system provides non-invasive technique for investigation of nuclear environment. We employed methods of active and passive rheology to characterize rheological properties of the nucleoplasm of GV-oocytes (germinal vesicle stage) with main types of chromatin distribution in the nucleus (NSN, SN). By using of single beam optical trap, formed by a tightly focused laser radiation at 790 nm wavelength, we performed subsequent stress-relaxation tests series of nucleoli in various directions and with different amplitudes. Nucleolus of the oocyte was employed as a microprobe due to its large size and spherical shape. The characteristic nucleolus relaxation times were obtained for two types of chromatin distribution, which can subsequently be used to evaluate the viscoelastic properties of the nuclear material within oocytes with different physiological states. Motion activity of nucleoli was also extracted to evaluate local forces, acting within nucleolar environment and facilitating chromatin redistribution.

Rheological and mechanical properties of edible gel materials for 3D food printing technology

3D food printing sectors require comprehensive knowledge on viscoelastic and mechanical properties of diverse food materials in order to effectively utilize them in rapid and customized 3D production for supply and manufacturing chains. In this work, we present mechanical and rheological properties of Agar and Konjac based edible gels at different Agar and Konjac weight ratio and discuss their 3D printing performance. Gel samples with higher Konjac content positively contributed to the viscoelastic properties of the gel samples which in return has been found viable for extrusion-based 3D printing. By choosing appropriate printing parameters, different shapes are printed to demonstrate printing resolution. We expect, this study will add potential scope for evaluating and optimizing soft-gel materials for 3D food printing sector.

A nondestructive guided wave propagation method for the characterization of moisture-dependent viscoelastic properties of wood materials

The in-situ monitoring and characterization of the mechanical properties of wood and timber materials is of great importance due to their broad structural applications. The purpose of this study was to propose a nondestructive method to assess the moisture-dependent viscoelastic behavior of structural wood using the guided Lamb wave propagation. Twelve green poplar wood specimens with different moisture content (MC) underwent the Lamb wave propagation tests and the wave characteristics were acquired. The viscoelastic properties of the wood specimens, including the shear storage and shear loss moduli and the loss factor, were then estimated through the solution of the corresponding inverse Lamb wave propagation problem using the experimentally measured Lamb wave characteristics. The structural stiffness and damping of wood specimens were affected by their MC, as the Lamb wave amplitude and velocity significantly decreased with MC. While the shear storage modulus decreased with MC, the shear loss modulus and loss factor increased with MC, resulting in a higher viscoelastic behavior. The loss factor of the wood specimens was estimated to be between 5.88% and 8.49% for different classes of MC, showing an increase of 44% with MC. The Lamb wave propagation method offers a strong tool for nondestructive characterization of the viscoelastic properties of wood materials and structures over a broad MC range. Wood materials show a significant viscoelastic behavior which is highly impacted by their MC. The loss factor can play an important role in the characterization and classification of structural wood and timber with different MC.

Conductive Polymers As Hybrid Battery-Capacitor Electrode Materials

The disruption in next-generation batteries can only be realised by employing both new advanced materials and designs, eventually allowing to holistically achieve new levels of performance, safety and sustainability in a single battery system. To close the gap between high power and energy per unit weight, new materials are needed that can act as a battery and capacitor simultaneously. Conductive polymers, e.g. poly(3,4-ethylenedioxythiophene) (PEDOT), used with ionic liquids or semi-solid ionogels have recently attracted attention as hybrid battery-(pseudo)-capacitor systems, achieving a specific capacity, energy, and power of 40-180 Ah kg-1, 50-230 Wh kg-1, and 30-140 W kg-1 when used as positive electrodes in rechargeable aluminium batteries 1-4. In addition, the polymer composites are non-flammable, non-toxic, economically available and recyclable at low-cost. In comparison to other charge storage materials, like graphite, conductive polymers are less limited by their capacity as the electrode architecture can be redesigned from a conventional 2D design to an interconnected 3D electrode-electrolyte network, allowing a higher active surface, shorter charge transfer and ion diffusion paths for fast charging (up to 80C 4), and controllable electrode shapes/sizes (Figure A 3). The performance of conductive polymers can be tailored by their synthesis path and conditions 1,5. The relationship between electrode fabrication, underlying operating mechanisms, and performance was studied by in operando methods such as electrochemical atomic force microscopy (EC-AFM), and electrochemical microgravimetry (EQCM) 3.The main achievement is the visualisation of reversible morphological modifications at the nano-scale (Figure B and C 3) of the conductive polymer as a function of state-of-charge. Such changes influence significantly the viscoelastic material properties, which are linked directly to the electrochemical fabrication process 5. Overall, the findings provide an explanation why conductive polymers behave like a hybrid battery-(pseudo)-capacitor (Figure D), setting a new standard for how energy storage can be approached.[1] Heinze, J. et al. Chemical Reviews 2010, 110, 4724–4771.[2] Hudak, N.S. The Journal of Physical Chemistry 2014 , 118, 5203–5215.[3] Schoetz, T. et al. Journal of Materials Chemistry A 2018, 6, 17787–17799.[4] Schoetz, T. et al. Journal of the Electrochemical Society 2020, 28, 101176.[5] Schoetz, T. et al. Electrochimica Acta 2018 , 263, 176–183. Figure 1

A New Viscoelasticity Dynamic Fitting Method Applied for Polymeric and Polymer-Based Composite Materials.

The accurate analysis of the behaviour of a polymeric composite structure, including the determination of its deformation over time and also the evaluation of its dynamic behaviour under service conditions, demands the characterisation of the viscoelastic properties of the constituent materials. Linear viscoelastic materials should be experimentally characterised under (i) constant static load and/or (ii) harmonic load. In the first load case, the viscoelastic behaviour is characterised through the creep compliance or the relaxation modulus. In the second load case, the viscoelastic behaviour is characterised by the complex modulus, , and the loss factor, . In the present paper, a powerful and simple implementing technique is proposed for the processing and analysis of dynamic mechanical data. The idea is to obtain the dynamic moduli expressions from the Exponential-Power Law Method (EPL) of the creep compliance and the relaxation modulus functions, by applying the Carson and Laplace transform functions and their relationship to the Fourier transform, and the Theorem of Moivre. Reciprocally, once the complex moduli have been obtained from a dynamic test, it becomes advantageous to use mathematical interconversion techniques to obtain the time-domain function of the relaxation modulus, , and the creep compliance, . This paper demonstrates the advantages of the EPL method, namely its simplicity and straightforwardness in performing the desirable interconversion between quasi-static and dynamic behaviour of polymeric and polymer-composite materials. The EPL approximate interconversion scheme to convert the measured creep compliance to relaxation modulus is derived to obtain the complex moduli. Finally, the EPL Method is successfully assessed using experimental data from the literature.

Numerical simulation of creep behaviour of flexible riser inner liner

The creep behaviour of an inner liner, one of the reasons for carcass tearing, may affect the structural integrity of flexible risers. This has been previously discussed without conclusive results owing to complex structure and time-dependent material properties. The present paper proposes a numerical model for predicting creep responses by means of the finite element method. In this model, series coefficient is used to characterise the viscoelastic properties of material. Consequently, the influence of geometric parameters such as span of the carcass layer and thickness of the inner layer on the deformation is observed. Moreover, a threedimensional model assembling the carcass and inner liner was established for mechanical analysis, during which the viscoelasticity of inner liner and the internal friction of the carcass are considered, after which the stress and strain distribution on each layer under the combined external pressure and axial tensile force generated by the inner liner are obtained. Additionally, the effect of external pressures on the stress distribution of the carcass cross-section was found through sensitivity analysis.

Time–temperature superposition of asphalt materials and temperature sensitivity of rheological parameters (TSRP)

Different temperature sensitivity parameters were introduced to address the temperature susceptibility of asphalt cement, all of which used a single number to define each particular material by assuming linearity in temperature sensitivity. The time–temperature superposition principle (TTS) has been used, under different circumstances, to understand the viscoelastic properties of asphalt materials. Various empirical relationships have been developed to explain the relationship between TTS shift factors and temperature. This research evaluated the suitability of such relationships to evaluate the temperature sensitivity of viscoelastic materials and found that the modified Arrhenius equation is more fundamentally appropriate for this purpose. Results of this study showed that the temperature sensitivity of rheological parameters, introduced here, is sensitive to age hardening (for both asphalt cement and mix) and can be used to evaluate age hardening and changes in mix’s volumetric properties as well as investigating the effect of mix design properties.

General Eigensolutions for 2D Viscoelastic Materials

In recent years, viscoelastic materials have been widely used in industry, and the study of its mechanical properties has become the key of modern science and engineering. In this paper, based on Laplace integral transformation, a new analytical method is proposed to solve the mechanical problems related to viscoelastic materials. According to the variational principle and the method of separating variables, the governing equations of the basic problems are established, and all the eigensolutions of analytical forms are obtained. In the numerical calculation, the relationship between these eigensolutions and boundary conditions is studied systematically, and the time-dependent property of viscoelastic materials is well described.

Frequency dependent mechanical properties of violin varnishes and their impact on vibro-mechanical tonewood properties

Violin varnishes influence the vibrational properties of tonewood. However, the frequency dependence of the varnish influence and mechanical properties of typical varnishes has received little attention. The viscoelastic properties of various violin varnish materials over the audible frequency range were characterized by dynamic mechanical analysis. The properties of the studied varnishes showed comparable frequency dependencies. For all varnishes, E increased and tan(δ) decreased with increasing frequency. The results were in good agreement with an analytical mechanical model, which was used for additional numerical FEM calculations. The approach of numerically determining varnish-induced changes in the vibrational properties on basis of the individual wood and varnish properties was confirmed through comparison with experimental results obtained in an earlier study. The latter procedure was subsequently used to analyse varnish-induced changes in the eigenfrequencies of a violin soundboard. The results revealed that the frequency dependence of the varnish properties determined the specific influence of varnishes on the vibrational properties of tonewood, which should be taken into account when assessing the impact of varnishes.

A fractional Maxwell approach for the shock response of viscoelastic oscillator

Viscoelastic damping structures under shock loading with variable amplitude and frequency are always in the multifactorial dynamic state, of which the shock response is obviously different from that under low strain rate. In order to accurately describe the impact mechanical properties of viscoelastic damped materials, a fractional order Maxwell model (FMM) is constructed. To verify the adopted model, the dynamic experiments for different strain rates (1800 s-1, 2500 s-1, 3500 s-1 and 4000 s-1) are performed by SHPB system. The experimental stress-strain curves should be divided into three stages: the linear stage, the strain-softening stage and the strain-hardening stage. As increase with the strain rate, the peak strain, the peak stress and the curvature of the curve in strain-softening stage increase, and the hardening effect in the strain-hardening stage tends to stronger, demonstrating a distinct strain rate effect in viscoelastic damped materials. The reason is that as increase of the strain rate, the action time of external loading gets closer to the relaxation time of the molecular chain segment, indicating the apparent strain rate-dependence of molecular slip and friction. The comparisons are made between the models of FMM, fractional Kelvin-Voight, ZWT and Ogden considering the strain rate-dependent. As a fractional-order model, FMM model has the minimum mean of RMSE 0.460 among the four models. The results indicate that FMM model could accurately describe the impact mechanical behavior characteristics of viscoelastic materials in a wider range of strain rate with comprehensive superiority of higher fitting precision, fewer parameters and clear physical meaning.

Modeling thermal-visco-elastohydrodynamic lubrication (TVEHL) interfaces of polymer-based materials

This paper reports a novel thermal-visco-elasohydrodynamic lubrication (TVEHL) model for analyzing the lubrication behavior of the interface formed by an elastic sphere and a polymer half-space. The temperature-dependent viscoelastic displacement of the polymer surface is calculated through the elastic-viscoelastic correspondence theory and frequency-temperature superposition. The discrete convolution and fast Fourier transform (DC-FFT) algorithm is used for efficient solution computation. The model is verified by comparing results from its degenerated forms with those from thermal-viscoelastic (TVE) contact and thermal-elastohydrodynamic lubrication (TEHL) theories. The results from the current model with and without considering temperature effect are also compared. The new TVEHL model is explored to study the viscoelastic material property, entraining speed, sliding-to-rolling ratio, and the coupled thermal-viscoelasticity effects.

Nonlinear Dynamic Modeling of a Robotic Endoscopy Platform on Synthetic Tissue Substrates

Abstract A scaled robotic endoscopy platform (REP) was previously developed to efficiently test new control schemes in a simulated colon environment. This article presents the derivation and tuning of a nonlinear model of the REP operating on various substrates. The modeling technique and novel empirical friction profiling demonstrated here are useful for a wide variety of devices interacting with unconventional substrates. The model is first derived from the REP drivetrain inertial characteristics, and then the interaction with synthetic tissue is quantified by an automated traction measurement system for multiple substrates. The resulting model is then used with ground-truth VICON and sensor data to optimize uncertain parameters by minimizing pose error over a variety of tests and substrates. The results show an average error reduction of 67% over all tests and substrates, with a worst-case 10% open-loop final position error. The success of these results proves a robust dynamic model of the REP and its tissue interactions without the need to model complex and computationally expensive viscoelastic material properties or discrete/nonlinear events such as stalling. The resulting model will be used to develop model-based feedback control for estimation, disturbance rejection, and autonomy for the REP in an actuated colon simulator.