Viscoelastic Material Properties Research Articles

Dynamic property evaluation of pipeline clamp based on analyzing the propagation characteristics of flexural wave in pipeline

The external clamp of hydraulic pipeline plays an important role in strengthening pipeline stiffness and improving vibration attenuation ability. In this study, wave propagation method is proposed to evaluate the translational and rotational stiffness and their loss factors of the clamp by analyzing the flexural wave propagation characteristics of pipeline. In order to validate the measured dynamic properties, experimental modal analysis was performed on the two-end elastically-supported pipeline. By modelling the pipeline with translational and rotational edge restraints, the analytical modal frequency parameters, wave numbers, and waveform coefficients were obtained. By comparing of the first-order flexural mode frequencies between experiment and analysis, the dynamic stiffness predicted by the wave propagation method was validated. The effects of the magnitude of torque, direction, clamping torque cycle, and clamp size on the complex dynamic properties of pipeline clamp were investigated. The proposed wave propagation method allows non-destructive continuous monitoring of a clamp stiffness, provides additional information about the vibration attenuation feature. It has advantages in clamp applications and is an effective methodology for measuring the dynamic properties of viscoelastic materials.

Dielectric and viscoelastic properties of 3D-printed biobased materials

This study aimed to develop new biobased materials containing plasticized cellulose acetate (CA) by Fused Filament Fabrication (FFF). We investigated the influence of CA on the viscoelastic/dielectric properties and the influence of 3D printing on the dielectric properties of the polymer blends. A microstructural analysis showed that the blends had a strong heterogeneous morphology, as the two phases formed a fibrillar and lamellar structure. CA strongly increased the blend viscosity at 175 °C, multiplying by 100 times the complex viscosity between neat PLA and the blend containing 40% of CA by weight (CA-40). The addition of CA to the blends increased the dielectric constant (ε') and dielectric loss (ε''), as well as the alternative current electrical conductivity (σAC). The dielectric constant of CA (ε'CA) was proportional to its percentage in the blend, showing a behavior analogous to a rule of mixture. Moreover, the activation energy of the electrical conductivity (σDC) measured at T > 124 °C decreased with increasing CA content and was associated with the enhancement of the ionic conductivity provided by the CA and its plasticizer. A decrease in the α-relaxation temperature and the associated activation energy of the PLA was also linked to the presence of the CA plasticizer. Finally, 3D printing greatly decreased both ε', ε'' and σAC due to the internal voids induced by the 3D printing process. The porosity was measured at 12% for neat PLA and between 20% and 25% for the blends. These results showed the advantage provided by FFF technology in the production of PLA:CA blends with controlled dielectric properties, thereby favoring the use of these new materials in key dielectric areas.

A hybrid constitutive model of high-damping viscoelastic materials used for vibration control of civil structures

The dynamic mechanical properties of high-damping viscoelastic (VE) materials exhibit significant frequency and temperature dependences in the glass transition zone. However, the current state of VE constitutive models face a challenge in balancing the accuracy, simplicity, and ease of structural dynamic analysis. In this study, a power-law and exponent-law hybrid model is proposed to model the frequency-dependent and temperature-dependent complex modulus of VE materials. The equivalence of hybrid model and existing VE constitutive models is presented. A total of 12 groups of experimental data are collected to validate the accuracy of hybrid model. An efficient numerical method for the hybrid model is proposed and then validated through a viscoelastically damped frame. Results show that the hybrid model is equivalent to two rheological models or fractional derivative models owning to the unshared model coefficients. The hybrid model is superior to the eight-parameter fractional derivative model in predicting the complex modulus over a wide equivalent frequency range. The proposed numerical method performs quite well in calculating seismic responses of proportional and non-proportional damped frames.

Analysis of the Scenarios of Use of an Innovative Technology for the Fast and Nondestructive Characterization of Viscoelastic Materials in the Tires Field.

The properties of tires related to their viscoelastic behavior have a significant impact in the field of vehicle dynamics. They affect the performance and safety of a vehicle based on how they change when the tire performs in variable thermal conditions, interacts with various kinds of road surfaces, and accumulates mileage over time. To analyze and understand such properties of viscoelastic materials, destructive tests like dynamic mechanical analysis (DMA) are used, which make the tire unusable after the test; these are usually carried out on specimens cut from the zone of interest. The development of an innovative testing methodology connected to a hardware device called VESevo allows the characterization of the viscoelastic properties of tire compounds belonging to tread or other parts in a fast and nondestructive way. This new device provides valuable information about the evolution of the tire's viscoelastic properties, allowing it to monitor them throughout the whole lifecycle. In the paper, an overview of the possible sensitivities that can be investigated thanks to the VESevo is provided: The tread viscoelasticity was characterized and monitored for several tire tread compounds, over tire mileage, over tread thermal curing cycles, and as an index of the tread quality and uniformity in production. Preliminary results were collected and are presented. In the final paragraph, further recent applications developed from the tire field, which are not directly related, are reported.

Laboratory Evaluation of Tensile Creep Behavior of Concrete at Early Ages

Short-term uniaxial tensile creep tests were conducted for early-age concrete at different ages in an effort to characterize early-age concrete as an aging viscoelastic material. Based on the test results, the viscoelastic material properties of the test concrete were characterized in terms of the Dirichlet series creep compliance and relaxation modulus functions. Applications of the model to the numerical analysis of the test samples showed a good agreement between the tests and computational results for the samples tested at different ages. This paper presents the test procedures and data analysis with a brief introduction of theoretical background.

De novo design of modular protein hydrogels with programmable intra- and extracellular viscoelasticity

Relating the macroscopic properties of protein-based materials to their underlying component microstructure is an outstanding challenge. Here, we exploit computational design to specify the size, flexibility, and valency of de novo protein building blocks, as well as the interaction dynamics between them, to investigate how molecular parameters govern the macroscopic viscoelasticity of the resultant protein hydrogels. We construct gel systems from pairs of symmetric protein homo-oligomers, each comprising 2, 5, 24, or 120 individual protein components, that are crosslinked either physically or covalently into idealized step-growth biopolymer networks. Through rheological assessment, we find that the covalent linkage of multifunctional precursors yields hydrogels whose viscoelasticity depends on the crosslink length between the constituent building blocks. In contrast, reversibly crosslinking the homo-oligomeric components with a computationally designed heterodimer results in viscoelastic biomaterials exhibiting fluid-like properties under rest and low shear, but solid-like behavior at higher frequencies. Exploiting the unique genetic encodability of these materials, we demonstrate the assembly of protein networks within living mammalian cells and show via fluorescence recovery after photobleaching (FRAP) that mechanical properties can be tuned intracellularly in a manner similar to formulations formed extracellularly. We anticipate that the ability to modularly construct and systematically program the viscoelastic properties of designer protein-based materials could have broad utility in biomedicine, with applications in tissue engineering, therapeutic delivery, and synthetic biology.

Seismic performance of structure equipped with a new rubber bracing damper system

Nowadays, vibration energy absorption devices are widely implemented in many buildings subjected to severe vibration due to natural hazards, such as earthquakes, strong winds, and typhoons. Recently, viscous dampers have been commonly used in many structures as the most conventional damper type. However, the high maintenance cost resulting from oil leakage from cylinder seals has prompted researchers to seek an alternative system to viscous damper systems. Therefore, the main aim of this research is to develop a new rubber bracing damper (RBD) system by implementing high damping rubber material as a viscoelastic material to be installed in framed structures as diagonal bracing members. This will help dissipate vibration effects on the structure. To achieve this, the initial design for the RBD device has been developed, and finite-element simulation has been conducted to evaluate the behavior of the proposed RBD under various dynamic loading conditions. To define the viscoelastic material properties in finite-element modeling, high damping rubber material has been produced and experimentally tested to determine the numerical model of the material. Subsequently, the test data were utilized to develop the analytical model of the RBD device, and its performance was evaluated by applying cyclic loads and conducting nonlinear analysis. Furthermore, a series of cyclic dynamic tests with various displacement amplitudes and frequencies have been conducted on the prototype of the RBD device based on the finite-element results. Finally, to analyze the dynamic behavior of the structure equipped with RBD, a finite-element model of a three-story reinforced concrete frame structure furnished with RBD dampers has been developed. The response of the structure has been evaluated under seismic loads, and a parametric study has been conducted to investigate the response of the structures with various rubber properties. The numerical analysis results indicated that the implementation of the RBD device leads to a reduction in the occurrence of plastic hinges and lateral displacements of the structure by up to 69%. This demonstrates the efficiency of the RBD device in diminishing the seismic load effect on the structure’s response.

Into a rapid polymer characterization employing optical measurement systems and high-power ultrasonic excitation

This study presents a novel methodology for estimating the master curve of the complex modulus of viscoelastic materials using a combination of optical measurement systems and ultrasonic excitation. Traditional techniques for characterizing properties of viscoelastic materials are often time-consuming and encounter limitations that hinder their accuracy at high strain rates. To address this, a method was proposed that leverages two optical measurement systems to quickly assess material properties at multiple points on a sample. A high-power ultrasonic transducer was employed to excite the material at its first longitudinal natural frequency, creating non-uniform temperature variations and strain rates. A scanning laser Doppler vibrometer measured vibrations across the material, enabling computation of the complex modulus magnitude under varying conditions. These results were correlated with temperature readings obtained from an infrared camera. The constructed master curve using the proposed methodology closely resembled those established through quasi-static and dynamic uniaxial compression tests in the literature. Additionally, this method revealed a more substantial increase in complex modulus at high strain rates compared to traditional experiments, where this characteristic is less pronounced.

Estimating viscoelastic, soft material properties using a modified Rayleigh cavitation bubble collapse time

Accurate determination of high strain rate (>103 1/s) constitutive properties of soft materials remains a formidable challenge. Albeit recent advancements among experimental techniques, in particular inertial microcavitation rheometry (IMR), the intrinsic requirement to visualize the bubble cavitation dynamics has limited its application to nominally transparent materials. Here, in an effort to address this challenge and to expand the experimental capability of IMR to optically opaque materials, we investigated whether one could use the acoustic signature of the time interval between the bubble's maximum radius and first collapse time point, characterized as the bubble collapse time, to infer the viscoelastic material properties without being able to image the bubble directly in the tissue. By introducing a modified Rayleigh collapse time for soft materials, which is strongly dependent on the stiffness of the material at hand, we show that, in principle, one can obtain an order of magnitude or better estimate of the viscoelastic material properties of the soft material under investigation. Using a newly developed energy-based theoretical framework, we show that for materials stiffer than 10 kPa the bubble collapse time during a single bubble cavitation event can provide quantitative and meaningful information about the constitutive properties of the material at hand. For very soft materials (i.e., shear modulus less than 10 kPa), our theory shows that unless the collapse time measurement has very high precision and low uncertainties, the material property estimates based on the bubble collapse time only will not be accurate and require visual resolution of the full cavitation kinematics.

Dynamics and frequency response analysis of encapsulated microbubble under nonlinear ultrasound

Bubble dynamic behavior and frequency response of encapsulated microbubbles in nonlinear acoustic field is significant in applications such as tumor therapy, thrombolysis, tissue destruction, and ultrasonic lithotripsy. The acoustic cavitation effect includes stable cavitation and transient cavitation. The transformation from stable cavitation to transient cavitation requires a certain threshold, which is also called the transient cavitation threshold. Phospholipid-coated microbubbles are commonly used to enhance acoustic cavitation. However, the acoustic effects of different coating materials are not very clear, especially when considering the nonlinear effects caused by diffraction, scattering, and reflection during ultrasonic propagation. In this paper, the bubble dynamic behaviors and frequency responses of microbubbles under different frequencies, acoustic pressures, and viscoelastic properties of different shell materials are analyzed by coupling the Gilmore-Akulichev-Zener model with the nonlinear model of a lipid envelope and using the KZK equation to simulate the nonlinear acoustic field. At the same time, the influence of the coated material and nonlinear acoustic effects are considered. The bubble dynamic behavior and frequency response under the actually measured sound field are compared with those simulated by the KZK equation. The results show that the nonlinearity will lead the velocity of the microbubble wall to decrease, and when the pressure of ultrasound increases, the main frequency component of the microbubble oscillation increases, making the radial motion of the microbubble more violent. When the frequency changes, the closer the oscillation frequency of the microbubble is to the resonant frequency, the stronger the radial motion of the microbubble is. The coating material can change the harmonic component in the oscillation frequency. When the harmonic is close to the resonance frequency, the radial motion of the microbubble is enhanced. The elasticity of the coated material has almost no effect on the microbubble's frequency response, and the initial viscosity and surface tension of encapsulated microbubble will change the oscillation frequency distribution of encapsulated microbubble. When the initial viscosity of the coated microbubble is smaller, the subharmonic component of the microbubble oscillation increases. When the frequency of the subharmonic is closer to the resonance frequency than the main frequency, the acoustic cavitation effect is significantly enhanced. On the other hand, when the initial surface tension of the encapsulated microbubble increases, the main frequency and subharmonic component of the microbubble oscillation are enhanced, so that the acoustic cavitation effect is also enhanced. Therefore, this study can further elucidate the bubble dynamics of encapsulated microbubbles, stimulated by nonlinear ultrasound, benefiting the frequency response analysis of coated microbubbles under nonlinear acoustic fields.

Analysis of Biomechanical Properties of Adipose-Derived Hydrogels for Adipose-Derived Stromal/Stem Cell-Based Hydrogel Culture.

With the increase in decellularization of different tissue sources, an understanding of the viscoelastic properties of these soft materials is important for determining practical applications. The purpose of this chapter is to better define a series of experiments to profile important rheological properties for adipose-based hydrogels. While there are numerous mechanical characterizations that are done experimentally, the protocol outlined in this chapter provides a step-wise approach to determine the gelation characteristics and native hydrogel network properties. A more complete understanding of adipose-derived hydrogel mechanical properties would provide vital information for downstream applicability in fields such as disease modeling or soft tissue regeneration.

New methods to increasing efficiency for durability design of elastomeric bushings

The use of elastomers in modern road vehicles can solve many design conflicts in the development process. The prerequisite for this is a detailed calculability of the component properties, which are dependent on the geometric shape, the choice of material and the parameters of the manufacturing process. A robust method for calculating parameter-property relationships of elastomer bushings based on physical models and machine learning approaches allows these relationships to be calculated in the early phases of vehicle development. Viscoelastic material properties represent a major challenge for the durability design of elastomer components in load data acquisition. With the help of the modeling approaches developed here for load data analysis, load paths with elastomer bushings in the vehicle can be calculated much more accurately for high loads. A new method for experimental component validation is presented, which reduces the costly testing time for operational load tests by up to 85%. This method uses multi-axis block programs and achieves damage patterns comparable to the operational load test.

Material properties in regenerating axolotl limbs using inverse finite element analysis

BackgroundThe extracellular mechanical environment plays an important role in the skeletal development process. Characterization of the material properties of regenerating tissues that recapitulate development, provides insights into the mechanical environment experienced by the cells and the maturation of the matrix. In this study, we estimated the viscoelastic material properties of regenerating forelimbs in the axolotl (Ambystoma mexicanum) at three different regeneration stages: 27 days post-amputation (mid-late bud) and 41 days post-amputation (palette stage), and fully-grown time points. A stress-relaxation indentation test followed by two-term Prony series viscoelastic inverse finite element analysis was used to obtain material parameters. Glycosaminoglycan (GAG) content was estimated using a 1,9- dimethyl methylene blue assay. ResultsThe instantaneous and equilibrium shear moduli significantly increased with regeneration while the short-term stress relaxation time significantly decreased with limb regeneration. The long-term stress relaxation time in the fully-grown time point was significantly lower than 27 and 41 DPA groups. The GAG content was not significantly different between 27 and 41 DPA but the GAG content of cartilage in the fully-grown group was significantly greater than in 27 and 41 DPA. ConclusionsThe mechanical environment of the proliferating cells changes drastically during limb regeneration. Understanding how the tissue's mechanical properties change during limb regeneration is critical for linking molecular-level matrix production of the cells to tissue-level behavior and mechanical signals.

Dynamic micromechanical measurement of the flexural modulus of micrometre-sized diameter single natural fibres using a vibrating microcantilever technique

Abstract The dynamic response of a structure is a manifestation of its inherent characteristics, including material density, mechanical modulus, thermo- and viscoelastic properties, and geometric properties. Together, these factors influence how the material behaves in dynamic scenarios, dictating its damping properties and behaviour under varying forces. In this study we present a novel approach to accurately determine the flexural (bending) modulus of microscopic diameter natural fibres (flax) using microcantilever vibration analysis. Traditionally, the characterisation of the mechanical properties of fibres has relied on macroscopic methods such as tensile testing, which often results in high scatter in measurement data; furthermore, tensile testing does not accurately represent microscale or dynamic conditions and can be complex in terms of sample preparation and loading. To address this, we have developed a microscale technique involving the fabrication of microcantilevers using flat polypropylene support chips, inspired by microelectromechanical systems approaches. Our method provides a refined method for accurately characterising the mechanical modulus of flax fibres, with reduced data dispersion compared to traditional macroscopic testing. Furthermore, by reducing the influence of inherent fibre defects and maintaining homogeneity along the length of the fibre, our micro-scale technique provides reliable modulus determination. This work opens avenues for improved understanding and application of natural and man-made fibres, such as glass and optical fibres, in a variety of fields.

A novel methodology of predicting temperature and rate effects on tensile properties of viscoelastic materials

A novel methodology to predict the tensile properties of viscoelastic materials as a synergistic function of temperature and loading/displacement rate is presented in this paper. The model is based on the amount of energy dissipated during tensile loading, requiring less input data compared to existing models. The deformation activation energy was measured and accordingly an energy-based temperature shift factor was suggested. Additionally, to describe the material’s rate dependency, two new types of energy-based loading/displacement rate shift factors based on the Eyring and Cooperative models were derived. The shift factors were implemented into the theory of viscoelasticity to predict the material tensile behavior at different temperatures and loading/displacement rates. In addition, a new failure criterion was suggested to predict the mechanical strength of the tested materials through the definition of a critical energy level, which determined the maximum energy that a material would be able to dissipate before failure. The model was applied to two different viscoelastic materials; an epoxy adhesive, and an angle-ply glass/epoxy fiber-reinforced polymer (GFRP) composite, two common viscoelastic materials used in the structural and construction industries. To determine the accuracy of the model, the results obtained from the model were compared to the results obtained from experiments. It was observed that the suggested methodology well predicted the stress–strain curves of the tested materials in the linear region and yield stress up to the post-yield region and failure point. In addition, the strength surface of the studied materials, which showed the synchronous effect of temperature and loading/displacement rate on the ultimate tensile strength in a 3-dimensional representation, was introduced.

Investigation of the Motion of a Spherical Object Located at Soft Elastic and Viscoelastic Material Interface for Identification of Material Properties

Measuring the properties of soft viscoelastic materials is challenging. Here, the motion of a spherical object located at the soft elastic and viscoelastic material interface for the identification of material properties is thoroughly investigated. Formulations for different loading cases were derived. First, the theoretical models for a spherical object located at an elastic medium interface were derived, ignoring the medium viscosity. After summarizing the model for the force reducing to zero following the initial loading, we developed mathematical models for the force reducing to a lower non-zero value or increasing to a higher non-zero value, following the initial loading. Second, a similar derivation process was followed to evaluate the response of a spherical object located at a viscoelastic medium interface. Third, by performing systematic analyses, the theoretical models obtained via different approaches were compared and evaluated. Fourth, the measured and predicted responses of a spherical object located at a gelatin phantom interface were compared and the viscoelastic material properties were identified. It was seen that the frequency of oscillations of a spherical object located at the sample interface during loading was 10–15% different from that during unloading in the experimental studies here. The results showed that different loading cases have immense practical value and the formulations for different loading cases can provide an accurate determination of material properties in a multitude of biomedical and industrial applications.

The Importance of Bulk Viscoelastic Properties in "Self-Healing" of Acrylate-Based Copolymer Materials.

"Self-healing" has emerged as a concept to increase the functional stability and durability of polymer materials in applications and thus to benefit the sustainability of polymer-based technologies. Recently, van der Waals (vdW)-driven "self-healing" of sequence-controlled acrylate-based copolymers due to "key-and-lock"- or "ring-and-lock"-type interactions has generated considerable interest as a viable route toward engineering polymers with "self-healing" ability. This contribution systematically evaluates the time, temperature, and composition dependence of the mechanical recovery of acrylate-based copolymer and homopolymer systems subject to cut-and-adhere testing. "Self-healing" in n-butyl acrylate/methyl methacrylate (BA/MMA)- or n-butyl acrylate/styrene (BA/Sty)-based copolymers with varying composition and sequence is found to correlate with the bulk viscoelastic properties of materials and to follow a similar trend as other tested acrylate-based homo- and copolymers. This suggests that "self-healing" in this class of materials is more related to the chain dynamics of bulk materials rather than composition- or sequence-dependent specific interactions.

Design and development of a hepatic lyo-dECM powder as a biomimetic component for 3D-printable hybrid hydrogels

Bioprinting offers new opportunities to obtain reliable 3D in vitro models of the liver for testing new drugs and studying pathophysiological mechanisms, thanks to its main feature in controlling the spatial deposition of cell-laden hydrogels. In this context, decellularized extracellular matrix (dECM)-based hydrogels have caught more and more attention over the last years because of their characteristic to closely mimic the tissue-specific microenvironment from a biological point of view. In this work, we describe a new concept of designing dECM-based hydrogels; in particular, we set up an alternative and more practical protocol to develop a hepatic lyophilized dECM (lyo-dECM) powder as an ‘off-the-shelf’ and free soluble product to be incorporated as a biomimetic component in the design of 3D-printable hybrid hydrogels. To this aim, the powder was first characterized in terms of cytocompatibility on human and porcine mesenchymal stem cells (MSCs), and the optimal powder concentration (i.e. 3.75 mg ml−1) to use in the hydrogel formulation was identified. Moreover, its non-immunogenicity and capacity to reactivate the elastase enzyme potency was proved. Afterward, as a proof-of-concept, the powder was added to a sodium alginate/gelatin blend, and the so-defined multi-component hydrogel was studied from a rheological point of view, demonstrating that adding the lyo-dECM powder at the selected concentration did not alter the viscoelastic properties of the original material. Then, a printing assessment was performed with the support of computational simulations, which were useful to define a priori the hydrogel printing parameters as window of printability and its post-printing mechanical collapse. Finally, the proposed multi-component hydrogel was bioprinted with cells inside, and its post-printing cell viability for up to 7 d was successfully demonstrated.

Quantifying uniaxial prestress and waveguide effects on dynamic elastography estimates for a cylindrical rod.

Dynamic elastography attempts to reconstruct quantitative maps of the viscoelastic properties of materials by noninvasively measuring mechanical wave motion in them. The target motion is typically transversely-polarized relative to the wave propagation direction, such as bulk shear wave motion. In addition to neglecting waveguide effects caused by small lengths in one dimension or more, many reconstruction strategies also ignore nonzero, non-isotropic static preloads. Significant anisotropic prestress is inherent to the functional role of some biological materials of interest, which also are small in size relative to shear wavelengths in one or more dimensions. A cylindrically shaped polymer structure with isotropic material properties is statically elongated along its axis while its response to circumferentially-, axially-, and radially-polarized vibratory excitation is measured using optical or magnetic resonance elastography. Computational finite element simulations augment and aid in the interpretation of experimental measurements. We examine the interplay between uniaxial prestress and waveguide effects. A coordinate transformation approach previously used to simplify the reconstruction of un-prestressed transversely isotropic material properties based on elastography measurements is adapted with partial success to estimate material viscoelastic properties and prestress conditions without requiring advanced knowledge of either.

Optimal viscoelastic properties for passive damping treatments

In the context of noise and vibration control, constrained viscoelastic materials can be used to reduce structure-borne noise of vibrating structure. This passive damping treatment finds many applications due to its robustness and low cost. While several approaches are proposed in the literature to optimise the placement of constrained viscoelastic patches, few studies has been dedicated to the optimisation of the viscoelastic material's properties. The difficulty stems from their frequency-dependency. In this work, a fractional derivative model is used to describe the complex frequency-dependent viscoelastic properties. This study illustrates the effectiveness of using surrogate modeling to predict the damping performance of viscoelastic patches. A multi-model reduction method combined with a modal parameter identification method is used to build a surrogate model at a reasonable computational cost. Once trained, this metamodel is explored to optimise the parameters of the fractional derivative model, thus allowing the design optimisation of viscoelastic properties. This approach could be extended to optimise the material properties of viscoelastic foams in the low frequency range.