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In the context of soft matter and cellular mechanics, microrheology - the use of micron-sized particles to probe the frequency-dependent viscoelastic response of materials – is widely used to shed light onto the mechanics and dynamics of molecular structures. Here we present the implementation of active microrheology in an Acoustic Force Spectroscopy setup (AFMR), which combines multiplexing with the possibility of probing a wide range of forces (~ pN to ~nN) and frequencies (0.01–100 Hz). To demonstrate the potential of this approach, we perform active microrheology on biological samples of increasing complexity and stiffness: collagen gels, red blood cells (RBCs), and human fibroblasts, spanning a viscoelastic modulus range of five orders of magnitude. We show that AFMR can successfully quantify viscoelastic properties by probing many beads with high single-particle precision and reproducibility. Finally, we demonstrate that AFMR to map local sample heterogeneities as well as detect cellular responses to drugs. An in-depth characterization of single-particle active microrheology via Acoustic Force Spectroscopy shows potential to measure viscoelastic moduli spanning five orders of magnitude and local heterogeneity in collagen gels and cells. [ABSTRACT FROM AUTHOR]

Dried abalones are precious products, in which candy abalone is the most treasured one, owing to its unique taste. After rehydration and simmering, the core part tastes extraordinarily tender and viscoelastic, just like a soft candy which may almost melt in mouth. However, the reason for this has yet to be elucidated. The purpose of this study is to research the formation mechanism of the candy-like core in candy abalone. First of all, we characterized the viscoelasticity, microstructure and protein changes of candy abalone during the simmering process. The texture results indicated that the springiness and adhesiveness of candy abalone showed an increase. Scanning and transmission electron microscopy suggested that myofibrillar protein in candy abalone formed a dense three-dimensional network hydrogel structure. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis revealed such a hydrogel structure might be derived from the degradation of the myofibrillar protein during the drying process. Also, we identified degraded peptides mainly stemmed from paramyosin by mass spectrometry. Moreover, molecular dynamics simulation revealed that the hydrogen bonds and hydrophobic interactions are mainly responsible for the self-assembly of peptides during the rehydration and simmering stages. Different from reported protein hydrogels, the rheological and morphological properties of the formed peptide hydrogels in candy abalone have significant changes. In this study, we found that the myofibrillar protein of fresh abalone degraded into peptides during the drying process, which further cross-linked to form a peptide hydrogel during the rehydration and simmering stages, thereby producing a unique viscoelastic candy-like core in candy abalone. [ABSTRACT FROM AUTHOR]

In classical experiments, it has been found that a rigid cylinder can roll both on and under an inclined rubber plane with a friction force that depends on a power law of velocity, independent of the sign of the normal force. Further, contact area increases significantly with velocity with a related power law. We try to model qualitatively these experiments with a numerical boundary element solution with a standard linear solid and we find for sufficiently large Maugis–Tabor parameter λ qualitative agreement with experiments. However, friction force increases linearly with velocity at low velocities (like in the case with no adhesive hysteresis) and then decays at large speeds. Quantitative agreement with the Persson–Brener theory of crack propagation is found for the two power law regimes, but when Maugis–Tabor parameter λ is small, the cut-off stress in Persson–Brener theory depends on all the other dimensionless parameters of the problem. [ABSTRACT FROM AUTHOR]

At present, structural analysis of polymer composite materials is a highly relevant issue. The complexity of taking into account the viscoelastic stress–strain dependence and the time-dependent distribution of stress–strain state parameters over the volume occupied by a solid is a limiting factor. The relevance and demand for new efficient methods of mathematical modeling of creep and relaxation processes in viscoelastic structures are obvious. The aim of this work is to verify and validate the method for solving boundary value problems of a linear viscoelastic solid. The proposed approach is based on the formulation of the generalized principle of correspondence between elastic and viscoelastic problems, according to which a viscoelastic solution can be obtained by replacing elastic constants by some time functions, which are hereinafter called time-effective moduli. The results derived from the theoretical validation and the solution of several problems suggest that the proposed method can be used for solving problems on the stress–strain state of viscoelastic structures. [ABSTRACT FROM AUTHOR]

The esterification of starches with octenyl succinic anhydride (OSA) under alkaline conditions is a modification process that takes a long time. Ultrasound-assisted esterification was investigated as an alternative for obtaining esterified starches with higher degree of substitution (DS) and reaction efficiency (RE), which could have more possibilities of application. Andean native potato starches were subjected to a conventional esterification process (OSA) and esterification with ultrasound-assisted treatment (US-OSA). The morphological and size distribution of granules, molecular features (infrared spectroscopy and X-ray diffraction), thermal, and rheological characteristics were assessed. The DS and RE for US-OSA starches were higher than those for OSA ones. Modified starches showed some peeled granules with a few pores in their surfaces, and also, span values of US-OSA starches were lower than OSA ones. Molecular studies showed that both starches, OSA and US-OSA, did not exhibit notable differences. Enthalpy of gelatinization for US-OSA starches was lower than of OSA ones. Hence, the results suggest that the esterification process of starches can be facilitated with a green technology such as ultrasound-assisted treatment, which is fast-paced and does not change the esterified starch characteristics. [ABSTRACT FROM AUTHOR]

In this article, we revisit the Timoshenko-Boltzmann system proposed by Liu and Peng [22] and characterize the exponential stability of the associated solution semigroup by considering a more general class of memory kernels. Our main result gives a slight generalization of the stability results achieved in [19, 22]. [ABSTRACT FROM AUTHOR]

Symplectic numerical schemes for reversible dynamical systems predict the solution reliably over large times as well, and are a good starting point for extension to schemes for simulating irreversible situations like viscoelastic wave propagation and heat conduction coupled via thermal expansion occuring in rocks, plastics, biological samples etc. Dissipation error (artificial nonpreservation of energies and amplitudes) of the numerical solution should be as small as possible since it should not be confused with the real dissipation occurring in the irreversible system. In addition, the other well-known numerical artefact, dispersion error (artificial oscillations emerging at sharp changes), should also be minimal to avoid confusion with the true wavy behavior. The continuum thermodynamical aspects (respect for balances with fluxes, systematic constitutive relationships between intensive quantities and fluxes, the second law of thermodynamics with positive definite entropy production, and the spacetime-based kinematic viewpoint) prove valuable for obtaining such extended schemes and for monitoring the solutions. Generalizing earlier works in this direction, here, we establish and investigate such a numerical scheme for one-dimensional viscoelastic wave propagation in the presence of heat conduction coupled via thermal expansion, demonstrating long-term reliability and the applicability of thermodynamics-based quantities in supervising the quality of the solution. [ABSTRACT FROM AUTHOR]

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model for shear flow of thixotropic viscoelastic-plastic media is continued. For arbitrary six material parameters and an (increasing) material function that control the model, the basic properties of the families of stress-strain curves at constant strain rates and relaxation curves generated by the model, and the features of the evolution of the structuredness under these types of loading are analytically studied. The dependences of these curves on time, shear rate, initial strain and initial structuredness of the material, as well as on the material parameters and function of the model, are studied. Several indicators of the applicability of the model are found which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (unusual properties) are generated by a change in structuredness in comparison with typical stress-strain curves and relaxation curves of structurally stable materials. In particular, it has been proved that stress-strain curves can be both increasing functions and can have decreasing sections resembling a "yield tooth" or damped oscillations, that all stress-strain curves (SSCs) possess horizontal asymptotes (steady flow stress), monotonically dependent on shear rate, and flow stress increases with shear rate growth, that the instantaneous shear modulus, on the contrary, depends on the initial structuredness, but does not depend on shear rate. Under certain restrictions on the material parameters, the model is also capable of providing a bilinear form of stress-strain curves, which is typical for an ideal elastoplastic model, but with strain rate sensitivity. It has been established that the family of stress-strain curves does not have to be increasing either in initial structuredness or in shear rate: in a certain range of shear rates, in which the equilibrium position is a "mature" focus and pronounced oscillations of stress-strain curves are observed, it is possible to intertwine stress-strain curves with different shear rates. It is proved that for any material parameters and functions, all stress relaxation curves decrease and have a common zero asymptote as time tends to infinity. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves, strain rate and strain hardening, flow under constant stress and so on. [ABSTRACT FROM AUTHOR]

Viscoelastic materials (VEMs) have gained increasing popularity for their ability to dampen vibrations in various structural applications in recent years. The mechanical characteristics of VEMs can be effectively described using constitutive models featuring both integer and fractional derivatives. This study examines the mechanical behavior of VEMs using fractional Zener models with four, five, and six parameters, as well as the generalized Maxwell model with 16 parameters, which relies on integer derivatives. To accomplish this, the study formulates an optimization problem with the aim of minimizing an error function defined by the quadratic relative distance between theoretical model responses and experimental data. Solving the optimization problem involves the use of a hybrid optimization technique, which combines genetic algorithms and non-linear programming. After obtaining optimal designs for each viscoelastic model, qualitative assessments demonstrate that all analytical models provide satisfactory fits to the experimental data. Subsequently, a statistical analysis employing Akaike's Information Criterion is conducted to identify the models that best describe the mechanical behavior of the analyzed VEMs. In this quantitative evaluation encompassing all viscoelastic models, it is noted that the generalized Maxwell model with 16 terms produces a lower relative error and statistically outperforms the fractional Zener models only in a global analysis. However, in a temperature-by-temperature analysis, the GMM16 proves to be inferior to all fractional models. Furthermore, when focusing solely on the fractional models, the five-parameter Fractional Zener Model exhibits the best statistical fit to the experimental data. [ABSTRACT FROM AUTHOR]

Emulsion polymerization is an effective means of synthesizing high-molecular-weight polymers in order to reduce the consumption of fossil energy. This paper adopts isoamyl octanoate to replace white oil as the continuous phase of emulsion polymerization to synthesize the high molecular weight polyacrylamide emulsion RSE. S-80 and T-80 were chosen as the emulsifiers, and the test results showed that the HLB value is 5.72 when S-80/T-80 is 6.5. When S-80/T-80 is 6.5, the HLB value is 5.72. Water and isoamyl octanoate can produce ultra-low interfacial tension and stable arrangement in the interfacial membrane to form a stable emulsion, and the particle size is uniformly distributed in a normal manner. The test of the exothermic process of polymerization shows that the emulsion can be stabilized into nuclei, and polyacrylamide polymers with a molar mass of more than 18 million are obtained. The microstructure test observes that RSE molecules are in an aggregated state in the aqueous solution. A three-dimensional spatial network structure is formed, and the polymerization can be stabilized in a three-dimensional network structure after 120 °C, 170 s−1 shear, which still has good stability. After the variable shear performance test proved that the aqueous solution of RSE belongs to the typical non-Newtonian fluids, to shock test the viscoelasticity of different concentrations of RSE polymer, G′ > G″, the RSE solution to elasticity is dominant. In this paper, the capacity to form stable emulsions of isoamyl octanoate in the emulsion polymerization process is investigated to provide a basis for seeking the selection of a continuous phase with little environmental pollution and high functionality. [ABSTRACT FROM AUTHOR]

Contact mechanics theories are commonly developed using the half-space approximation, which may raise concerns when dealing with contact region sizes comparable to or even larger than the size of the contacting bodies. In this study, we examine the normal adhesive contact between a rigid, wavy indenter and a viscoelastic substrate with a finite thickness. To achieve this, we utilize a recently developed finite element model that incorporates adhesive interactions based on the Lennard–Jones potential law. The results demonstrate that adhesive behavior is influenced by a combination of rate and size effects. Additionally, when considering non-negligible viscous effects, an optimal thickness can be determined to maximize the pull-off stress. [ABSTRACT FROM AUTHOR]

In this paper, layered periodic foundations (LPFs) are numerically examined for their responses to longitudinal and transverse modes in the time and frequency domains. Three different unit-cells, i.e., 2-layer, 4-layer, and 6-layer unit-cells, comprising concrete/rubber, concrete/rubber/steel/rubber, and concrete/rubber/steel/rubber/lead/rubber materials, respectively, are taken into account. Also, the viscoelasticity behavior of the rubber is modeled with two factors, i.e., a frequency-independent (FI) loss factor and a linear frequency-dependent (FD) loss factor. Following the extraction of the complex dispersion curves and the identification of the band gaps (BGs), the simulations of wave transmission in the time and frequency domains are performed using the COMSOL software. Subsequent parametric studies evaluate the effects of the rubber viscoelasticity models on the dispersion curves and the wave transmission for the longitudinal and transverse modes. The results show that considering the rubber viscoelasticity enhances the wave attenuation performance. Moreover, the transverse-mode damping is more sensitive to the viscoelasticity model than its longitudinal counterpart. The 6-layer unit-cell LPF exhibits the lowest BG, ranging from 4.8 Hz to 6.5 Hz. [ABSTRACT FROM AUTHOR]

The viscoelasticity of a carbon nanotube (CNT)-laden air–water interface was characterized using two different experimental methods. The first experimental method used a Langmuir-Pockels (LP) trough coupled with a pair of oscillating barriers. The second method is termed the Bicone-Trough (BT) method, where a LP trough was custom-built and fit onto a rheometer equipped with a bicone fixture to standardize the preparation and conditioning of a particle-laden interface especially at high particle coverages. The performance of both methods was evaluated by performing Fast Fourier Transform (FFT) analysis to calculate the signal-to-noise ratios (SNR). Overall, the rheometer-based BT method offered better strain control and considerably higher SNRs compared to the Oscillatory Barriers (OB) method that oscillated barriers with relatively limited positional and speed control. For a CNT surface coverage of 165 mg/m2 and a frequency of 100 mHz, the interfacial shear modulus obtained from the OB method increased from 39 to 57 mN/m as the normal strain amplitude increased from 1 to 3%. No linear viscoelastic regime was experimentally observed for a normal strain as small as 0.5%. In the BT method, a linear regime was observed below a shear strain of 0.1%. The interfacial shear modulus decreased significantly from 96 to 2 mN/m as the shear strain amplitude increased from 0.025 to 10%. [ABSTRACT FROM AUTHOR]

Melanoma is one of the most severe cancers due to its great potential to form metastasis. Recent studies showed the importance of mechanical property assessment in metastasis formation which depends on the cytoskeleton dynamics and cell migration. Although cells are considered purely elastic, they are viscoelastic entities. Microrheology atomic force microscopy (AFM) enables the assessment of elasticity and viscous properties, which are relevant to cell behavior regulation. The current work compares the mechanical properties of human neonatal primary melanocytes (HNPMs) with two melanoma cell lines (WM793B and 1205LU cells), using microrheology AFM. Immunocytochemistry of F-actin filaments and phosphorylated focal adhesion kinase (p-FAK) and cell migration assays were performed to understand the differences found in microrheology AFM regarding the tumor cell lines tested. AFM revealed that HNPMs and tumor cell lines had distinct mechanical properties. HNPMs were softer, less viscous, presenting a higher power-law than melanoma cells. Immunostaining showed that metastatic 1205LU cells expressed more p-FAK than WM793B cells. Melanoma cell migration assays showed that WM73B did not close the gap, in contrast to 1205LU cells, which closed the gap at the end of 23 h. These data seem to corroborate the high migratory behavior of 1205LU cells. Microrheology AFM applied to HNPMs and melanoma cells allowed the quantification of elasticity, viscous properties, glassy phase, and power-law properties, which have an impact in cell migration and metastasis formation. AFM study is important since it can be used as a biomarker of the different stages of the disease in melanoma. [ABSTRACT FROM AUTHOR]

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model of the shear flow of thixotropic viscoelastic-plastic media, which takes into account the mutual influence of the deformation process and structure evolution, is carried out. A set of two nonlinear differential equations describing shear at a constant rate and stress relaxation was obtained. Assuming six material parameters and an (increasing) material function that control the model are arbitrary, the basic properties of the families of stress-strain curves at constant strain rates, stress relaxation curves (Part 2) and creep curves (Part 3) generated by the model, and the features of the evolution of the structuredness under these types of loading were analytically studied. The dependences of these curves on time, shear rate, stress level, initial strain and initial structuredness of material (for example, degree of physical crosslinking), as well as on material parameters and function governing the model, were studied. Several indicators of the model applicability are found, which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (properties) are generated by structuredness changes in comparison to typical stress-strain, relaxation and creep curves of structurally stable materials. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: the effects of creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves at a constant rate, strain rate and strain hardening, flow under constant stress, etc. The first part of the article is devoted to formulation of the model and preparation of basis for the second part: the proof of the uniqueness and stability of the equilibrium point of the nonlinear equations set, analytical study of the equilibrium point dependence on all material parameters, possible types of phase portraits and the properties of integral and phase curves of the model. [ABSTRACT FROM AUTHOR]

The problems of vibration and noise have seriously affected people's production and life. Hydrogel can be used as damping material because of its good viscoelasticity, but the current damping material is difficult to meet the needs of actual production and life because of the lack of wide damping temperature and frequency range and high loss factor. In this work, ammonium persulfate was used as both initiator and oxidant to form a mixed double network hydrogel of polyacrylamide and oxidized sodium alginate. The double network hydrogel prepared by this method has good adhesion and mechanical properties. In addition, due to the adjustable viscoelasticity of the hydrogel, the hydrogel shows excellent damping properties. When the concentration of MBA is 0.02%, it can reach the temperature range of 0-125 ℃, and the damping factor is more than 0.3. The visualization experiment proves the practical application effect of the hydrogel, so it is expected to be used as a damping material in damping, noise reduction and other fields in the future. [ABSTRACT FROM AUTHOR]

To predict the occurrence of the collapse disaster in toppling perilous rock under the action of bidirectional earthquakes, the dynamic stability and fuzzy reliability calculation method of toppling perilous rock under the action of bidirectional earthquakes is proposed. First, the mass viscoelasticity model is used to simulate two main control surfaces of toppling perilous rock, the seismic dynamic response model and motion equation of toppling perilous rock are established based on the D'Alembert principle, and the Newmark-β method is used to solve the dynamic motion equation. Then, the instability event of toppling perilous rock is considered a fuzzy event, the membership function expression of the stability coefficient of toppling perilous rock is determined based on the fuzzy failure criterion, the calculation equations of the toppling perilous rock dynamic stability coefficient and fuzzy reliability are established, and the fuzzy reliability evaluation method based on the probability distribution of reliability is proposed. Finally, the influence of different superposition modes of seismic excitation on the fuzzy reliability of toppling perilous rock is analyzed. The calculation results of toppling perilous rock in the engineering case show that the fuzzy reliability calculated after considering the fuzzy failure criterion is reduced by 10.73% to 25.66% compared with the classical reliability. Considering the bidirectional seismic excitation, the fuzzy reliability of toppling perilous rock is reduced by 5.46% to 14.89%. Compared with using the acceleration peak time encounter mode to superpose the seismic excitation, the fuzzy reliability of toppling perilous rock is reduced by 3.4% when the maximum action effect time encounter mode is adopted. [ABSTRACT FROM AUTHOR]

The response of a body described by a quasi-linear viscoelastic constitutive relation, whose material moduli depend on the mechanical pressure (that is one-third the trace of stress) is studied. The constitutive relation stems from a class of implicit relations between the histories of the stress and the relative deformation gradient. A-priori thresholding is enforced through the pressure that ensures that the displacement gradient remains small. The resulting mixed variational problem consists of an evolutionary equation with the Volterra convolution operator; this equation is studied for well-posedness within the theory of maximal monotone graphs. For isotropic extension or compression, a semi-analytic solution of the quasi-linear viscoelastic problem is constructed under stress control. The equations are studied numerically with respect to monotone loading both with and without thresholding. In the example, the thresholding procedure ensures that the solution does not blow-up in finite time. [ABSTRACT FROM AUTHOR]

Extrusion-based 3D food printers are the most widely used 3D food-printing machines. Among these, screw-based 3D food printers have insufficient knowledge of printability compared to other types of extrusion-based printers. This study aimed to analyze the extrudability and shape stability immediately after printing from the viewpoint of mechanics using a screw-based 3D food printer. A paste comprising pumpkin flakes and water was used as the model food ink. The results show that 3D printing can be stable in the flake content of 20.0–28.6 wt%. When the pumpkin flake content was 18.2 wt% or lower, the 3D-printed food was flattened, and when the flake content was 30.8 wt% or higher, the paste was difficult to extrude from the nozzle. The results suggest that extrudability is mainly affected by the loss tangent of the paste and the balance between the apparent viscosity and inner nozzle pressure. Moreover, the main factors for shape stability immediately after printing were Young's modulus and the balance between the stress applied to the printed food owing to its weight and the yield stress of the paste. Particularly, it was found that the screw-based 3D food printer has a unique characteristic in controlling extrudability compared to other extrusion-based printers because the inner nozzle pressure tends to fluctuate depending on the apparent paste viscosity. The findings of this study provide new fundamental insights into screw-based 3D food printers from viewpoints of fluid and structural mechanics. [ABSTRACT FROM AUTHOR]

A protocol study was designed to examine cutaneous behavior after continuous application of a peloid in the dry mineral residue of Lanjarón-Capuchina natural mineral water. This study aims to analyze the biomechanical behavior of normal skin using various non-invasive bioengineering techniques after the application of this peloid. We determine the effects of its application for 3 months on 38 healthy volunteers (41.4 ± 5.9 years, range 32–58) without a previous history of skin diseases by courtmetry, sebumetry, pH-metry, reviscometry, and tewametry. It was shown that the production of cutaneous sebum is significantly reduced by 6%, trans epidermal skin loss (TEWL) by 21%, skin fatigue by 30%, elasticity increased by 19%, firmness by 5%, and a skin redensification by 6% was obtained under these experimental conditions. Disparate and non-significant results were obtained concerning pH and viscoelasticity. Continuous skin care with the Lanjarón-Capuchina natural peloid modifies skin behavior, normalizing sebaceous secretion, favoring the biomechanical properties of the skin and the skin barrier function without modifying skin homeostasis. [ABSTRACT FROM AUTHOR]

A serious problem in computer simulation of a stress state of polymer structures is to validate the mathematical description of the mechanical properties of materials. The structural model of a viscoelastic material has a number of advantages in describing both the rheology of a material and strain curves of it. In this model, a material is described as a structure consisting of several elements with relatively simple rheological properties. Reproduction of a complex behavior of a material under alternating non-isothermal loading is provided through the interaction of these simple elements. A technique developed in this work for modeling a viscoelastic material is intended for strength calculations of structures made of materials operating under conditions of a long-term repetitive thermomechanical impact using the finite element method. The application of the developed procedure to a polymeric material, polymethyl methacrylate (PMMA), is considered. The results of testing this material under uniaxial compression at a constant temperature are presented. The methodology and results of identification of the developed structural model using a specialized software code are described. Formulas are obtained for the approximation of the deformation characteristics of the material at a constant strain rate and for the time dependence of the deformation of the material during its holding at a constant stress level. Approximation is an important stage in the validation of the material model, which facilitates the systematization of the initial experimental data and their further mathematical processing. The best approximation of the deformation characteristics of a viscoelastic material is provided by a hyperbolic tangent function, whereas a logarithmic function provides the best results for the deformation upon holding. Further construction of the structural model was performed by selecting sequential parameters of bilinear rheological functions of the separate elements of the model and by iterative refinement of these parameters. The simulation results are compared with the experiments performed at different strain rates and with holding at different stress levels. In this work, the results of the initial stage of the performed experimental and theoretical studies are presented. [ABSTRACT FROM AUTHOR]

The lumbopelvic muscle mechanical properties (MMPs) are clinically relevant, but their dependence on sex remains unknown. Therefore, this study aimed to identify if lumbopelvic MMPs depend on the sex in a young adult population. Thirty-five healthy nulliparous women and 35 healthy men were analyzed (age range: 18–50). Lumbopelvic MMPs, that is, tone, stiffness, elasticity, relaxation and creep, assessed with MyotonPRO®, and pelvic floor (PF) health questionnaires were compared between-sexes. Intra-group correlations between sociodemographic and clinical data, and MMPs were also determined. The MMPs of PF were different between healthy non-climacteric adults of both sexes, with women showing higher values of tone and stiffness and lower values of elasticity and viscoelastic properties than men (in all cases, p < 0.03). At lumbar level, tone and stiffness were higher for men at both sides (in all cases, p < 0.04), and relaxation was lower at left side (p = 0.02). The MMPs showed few correlations with sociodemographic data within women. However, within males, there were positive correlations for PF stiffness and viscoelastic parameters with age, BMI and function (0.334 < r < 0.591) and, at lumbar level, negative correlations for tone and stiffness (− 0.385 < r < −0.590) and positive correlations for viscoelastic properties (0.564 < r < 0.719), with BMI. This indicated that between-sexes differences of lumbopelvic MMPs depend on the specific location of assessment in healthy non-obese young individuals. Women show higher tone and stiffness and lower elasticity and viscoelasticity than men, at PF level. [ABSTRACT FROM AUTHOR]

Fracture of viscoelastic materials is considered to be a complex phenomenon due to their highly rate sensitive behavior. In this context, we are interested in the quasi-static response of a viscoelastic solid subjected to damage. This paper outlines a new incremental variational based approach and its computational implementation to model damage in viscoelastic solids. The variational formalism allows us to embed the local constitutive equations into a global incremental potential, the minimization of which provides the solution to the mechanical problem. Softening damage models in their local form are known to result in spurious mesh-sensitive results, and hence, non-locality (or regularization) has to be introduced to preserve the mathematical relevance of the problem. In the present paper, we consider two different regularization techniques for the viscoelastic damage model: a particular phase-field and a lip-field approach. The model parameters are calibrated to obtain some equivalence between both these approaches. Numerical results are then presented for the bidimensional case and both these approaches compare well. Numerical results also demonstrate the ability of the model to qualitatively represent the typical rate-dependent behaviour of the viscoelastic materials. Besides, the novelty of the present work also lies in the use of lip-field approach for the first time in a viscoelastic context. [ABSTRACT FROM AUTHOR]

Movement of cell clusters along extracellular matrices (ECM) during tissue development, wound healing, and early stage of cancer invasion involve various inter-connected migration modes such as: (1) cell movement within clusters, (2) cluster extension (wetting) and compression (de-wetting), and (3) directional cluster movement. It has become increasingly evident that dilational and volumetric viscoelasticity of cell clusters and their surrounding substrate significantly influence these migration modes through physical parameters such as: tissue and matrix surface tensions, interfacial tension between cells and substrate, gradients of surface and interfacial tensions, as well as, the accumulation of cell and matrix residual stresses. Inhomogeneous distribution of tissue surface tension along the cell–matrix biointerface can appear as a consequence of different contractility of various cluster regions. While the directional cell migration caused by the matrix stiffness gradient (i.e., durotaxis) has been widely elaborated, the structural changes of matrix surface caused by cell tractions which lead to the generation of the matrix surface tension gradient has not been considered yet. The main goal of this theoretical consideration is to clarify the roles of various physical parameters in collective cell migration based on the formulation of a biophysical model. This complex phenomenon is discussed with the help of model systems such as the movement of cell clusters on a collagen I gel matrix, simultaneously reviewing various experimental data with and without cells. [ABSTRACT FROM AUTHOR]

A unified approach to the analysis of the nonstationary vibrations of piezoelectric ceramic plane layers, cylinders, and spheres taking into account the functional inhomogeneity and viscoelasticity of the material is proposed. The standard model of vibration damping and the Kelvin–Voigt viscoelastic model are considered. The proposed approach makes it possible to study the transition of the transducer to a static state or to a steady-state vibration mode under nonstationary perturbations. The effect of functional inhomogeneity on the nonstationary vibrations of a piezoelectric element is analyzed. The damping of the vibrations and viscoelastic axisymmetric vibrations of a radially polarized cylinder under electrical and mechanical perturbation using the Heaviside function is calculated. The dynamics of damping is analyzed, and the obtained results are compared with the static solution to validate the results. The generation of voltage by a piezoceramic cylinder under mechanical axisymmetric loading is also studied taking into account the viscoelastic properties of the material. It was found that the time to reach the steady-state mode for mechanical and electrical loads is almost the same. [ABSTRACT FROM AUTHOR]

Background: Reliable numerical predictive tools are instrumental in the high-end and robust design of encapsulated electronic assemblies. Process optimization and residual stress calculations require a rigorous cure simulation, which considers the transient chemical, thermal and mechanical constitutive behavior of the curing resin. Though this subject has been widely studied for epoxy-based composite materials, fewer studies have been presented on a non-reinforced bulk of low glass-transition temperature (Tg) resin. Objective: This research aims to numerically and experimentally study the cure behavior and the development of residual stresses and strains in such epoxy based encapsulants. Methods: The computational study is performed using a commercially available finite element cure process analysis software, and the experimental study is performed by a specially designed test specimen, employing various strain sensing techniques. Results: The results show good compatibility between experimental and numerical predictions of the thermal behavior and cure-induced residual stresses, which validates the use of the simulative tool for process design. Process induced stress relaxation in the resin is numerically and experimentally demonstrated, which enables a mapping of the process stages at which full viscoelastic modeling is required. The substantial effect of chain mobility on cure shrinkage and residual stress development in this type of materials is numerically demonstrated. Conclusion: The extensive numerical and experimental investigation of the cure process performed in this study provided insights to both process modeling and design. [ABSTRACT FROM AUTHOR]

Fracture of materials with rate-dependent mechanical behaviour, e.g. polymers, is a highly complex process. For an adequate modelling, the coupling between rate-dependent stiffness, dissipative mechanisms present in the bulk material and crack driving force has to be accounted for in an appropriate manner. In addition, the resistance against crack propagation can depend on rate of deformation. In this contribution, an energetic phase-field model of rate-dependent fracture at finite deformation is presented. For the deformation of the bulk material, a formulation of finite viscoelasticity is adopted with strain energy densities of Ogden type assumed. The unified formulation allows to study different expressions for the fracture driving force. Furthermore, a possibly rate-dependent toughness is incorporated. The model is calibrated using experimental results from the literature for an elastomer and predictions are qualitatively and quantitatively validated against experimental data. Predictive capabilities of the model are studied for monotonic loads as well as creep fracture. Symmetrical and asymmetrical crack patterns are discussed and the influence of a dissipative fracture driving force contribution is analysed. It is shown that, different from ductile fracture of metals, such a driving force is not required for an adequate simulation of experimentally observable crack paths and is not favourable for the description of failure in viscoelastic rubbery polymers. Furthermore, the influence of a rate-dependent toughness is discussed by means of a numerical study. From a phenomenological point of view, it is demonstrated that rate-dependency of resistance against crack propagation can be an essential ingredient for the model when specific effects such as rate-dependent brittle-to-ductile transitions shall be described. [ABSTRACT FROM AUTHOR]

The inherent shortcomings of fully biodegradable poly(butylene adipate-co-terephthalate) (PBAT) copolyesters including low strength, modulus, and melt viscoelasticity were addressed by melt blending of PBAT with high-stiffness and biological poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB). An epoxy-based chain extender was used to increase interfacial adhesion of partially miscible PBAT/P34HB (70wt/30wt) blends. The addition of chain extender refined phase-separated morphology of blends from SEM and decreased the degree of crystallinity by DSC. Compared with neat PBAT, PBAT/P34HB blends with chain extender showed much higher melt viscosity and elasticity, as indicated by rheological properties analyses. Compared with the PBAT/P34HB blend without chain extender, the breaking strength and elongation at break of PBAT/P34HB blend with incorporation of 1 wt% ADR were increased by 91.8% and 58.7%, respectively. It could be concluded that the combination of blending and chain-extension reaction simultaneously improved the strength, elongation at break, and melt viscoelasticity, which contributed to the suitability of biodegradable polymer blends for a wider range of end-use applications. [ABSTRACT FROM AUTHOR]

Models of the internal structure of Venus have been constructed with a wide range of crustal thickness (30–70 km) and core radius (2800–3500 km). An analysis of the pressure values in the center of the planet allows us to conclude that the presence of a solid inner core is unlikely if the composition and temperature profile of Venus correspond to that of the Earth. Andrade's rheology was used to take into account the inelasticity of the interior of Venus when calculating the tidal Love numbers and the angle of delay of the tidal hump. Comparison of experimental values of the Love number k2 with the model gives the radius of the core of Venus in the range of 3100–3500 km. It is shown that to determine the characteristic viscosity of the Venusian mantle, the key factor is the determination of the angle of retardation of the tidal bulge: values of 0.9° correspond to low viscosity and high temperature, and 0.4° to high viscosity and low temperature, so the planned measurements of tidal parameters and the moment of inertia of the planet in the VERITAS and EnVision missions will be able to impose restrictions on the distribution of viscosity and temperature in the interior of Venus. [ABSTRACT FROM AUTHOR]

A new Bresse system with hybrid damping coming from elasticity, thermoelasticity, and viscoelasticity, is analyzed. The uniform (exponential) stabilization of semigroup solution is proved under the dynamic response of each hybrid damping effect. [ABSTRACT FROM AUTHOR]

Arteries exhibit fully nonlinear viscoelastic behaviours (i.e. both elastically and viscously nonlinear). While elastically nonlinear arterial models are well established, effective mathematical descriptions of nonlinear viscoelasticity are lacking. Quasi-linear viscoelasticity (QLV) offers a convenient way to mathematically describe viscoelasticity, but its viscous linearity assumption is unsuitable for whole-wall vascular applications. Conversely, application of fully nonlinear viscoelastic models, involving deformation-dependent viscous parameters, to experimental data is impractical and often reduces to identifying specific solutions for each tested loading condition. The present study aims to address this limitation: By applying QLV theory at the wall constituent rather than at the whole-wall level, the deformation-dependent relative contribution of the constituents allows to capture nonlinear viscoelasticity with a unique set of deformation-independent model parameters. Five murine common carotid arteries were subjected to a protocol of quasi-static and harmonic, pseudo-physiological biaxial loading conditions to characterise their viscoelastic behaviour. The arterial wall was modelled as a constrained mixture of an isotropic elastin matrix and four families of collagen fibres. Constituent-based QLV was implemented by assigning different relaxation functions to collagen- and elastin-borne parts of the wall stress. Nonlinearity in viscoelasticity was assessed via the pressure dependency of the dynamic-to-quasi-static stiffness ratio. The experimentally measured ratio increased with pressure, from 1.03 ± 0.03 (mean ± standard deviation) at 80–40 mmHg to 1.58 ± 0.22 at 160–120 mmHg. Constituent-based QLV captured well this trend by attributing the wall viscosity predominantly to collagen fibres, whose recruitment starts at physiological pressures. In conclusion, constituent-based QLV offers a practical and effective solution to model arterial viscoelasticity. [ABSTRACT FROM AUTHOR]

A general assumption in geodesy is that solid Earth deformation in the presence of recent hydrological and ice loading is well approximated by a purely elastic response. In cases where there is clear evidence that thermal and petrological conditions exist that favor vigorous high-temperature creep behavior, such as in the mantle beneath Iceland, Patagonia, Alaska, Japan, and Svalbard, many response models have been approximated by using a Maxwell viscoelasticity. However, non-Maxwellian transient viscoelastic rheology is required for many post-seismic relaxation studies. Here, we reconsider the solid Earth response in light of highly temperature-dependent transient viscoelastic responses currently favored in the mineral physics and seismological communities. We develop a mantle response Green’s function that accounts for the vertical isostatic motion of the mantle caused by the acceleration of ice mass loss for Greenland and Patagonia measured by spaceborne and airborne remote sensing since 1992 and 1945, respectively. The Green’s function may be used to examine how anelasticity influences the uplift associated with accelerated surface mass loss. We perform a parameter exploration of the constants that define the Extended Burgers Material model, a rheology having firm experimental and theoretical underpinnings, in order to isolate those material model parameters that have the greatest impact on anelastic-isostatic uplift over interannual and interdecadal timescales. Anelasticity corrections may be required for solid Earth vertical uplift in space gravimetric solutions for long-term hydrology and cryospheric change. [ABSTRACT FROM AUTHOR]

In this study, a salt-resistant hydrophobic association polymer (PZDY) was synthesized from acrylamide, octadecyl dimethylallyl ammonium chloride, and decane polyoxyethylene ether acrylate by aqueous polymerization. Infrared spectroscopy, fluorescence spectroscopy, scanning electron microscopy, and other characterization methods were used to study its properties and the rheological properties of the PZDY solution were analyzed. The results showed that when concentration of NaCl is less than 5 wt% and that of CaCl2 is less than 1 wt%, the viscosity of 0.4 wt% PZDY increased with an increase of the salt concentration. When the salt concentration continued to increase, the PZDY viscosity gradually decreased. Investigation of the rheological behaviors showed that the 0.6 wt% PZDY in the 5 wt% NaCl and 1 wt% CaCl2 solution could withstand temperatures up to 180 °C after being sheared for 2500 s at 170 s−1 and its viscosity exceeded 50 mPa·s. Moreover, the viscosity of the 0.6 wt% PZDY in 5 wt% NaCl increased from 104 to 205 mPa·s and that in 1 wt% CaCl2 increased from 110 to 157 mPa·s at a shear rate of 170 s–1, at 180 °C, and a shear time of less than 500 s. Meanwhile, scanning electron microscope (SEM) results showed that the salt addition enhanced the quasi-spatial network structure, with closer clustering of PZDY molecules in the NaCl solution than in the CaCl2 solution. The storage modulus (G′) and loss modulus (G″) increased with the increase of the PZDY concentration. Therefore, PZDY can be used to improve the heat and shear resistance of fracturing fluids and enhance oil recovery. [ABSTRACT FROM AUTHOR]

To understand the geomechanical implications of long-term creep (time-dependent deformation) response of gas shale, short-duration creep was recorded from laboratory triaxial tests on ten Goldwyer gas shale samples in the onshore Canning Basin at in situ stress conditions under constant differential axial stress. A simple power-law function captures primary creep behaviour involving elastic compliance constant B and time-dependent factor n. Experimental creep data revealed larger axial creep strain in clay and organic-rich rocks, than those dominated by carbonates. Anisotropic nature of creep was observed depending upon the direction of constant axial stress application (perpendicular or parallel to the bedding plane). Upon the application of linear viscoelastic theory on laboratory creep fitting coefficients, differential horizontal stress accumulation over a geological time scale was estimated from the viscoelastic stress relaxation concept. Further, this model was used to derive lithology-dependent least principal stress (Shmin) magnitude at depth for two vertical wells intersecting the Goldwyer gas shale formations. This newly proposed Shmin model was found to have a profound influence on designing hydraulic fracture simulation. Further, pore size distribution and specific surface area value SN2 were derived from low-pressure gas adsorption experiments. These physical properties along with weak mineral components were linked with creep constitutive parameters to understand the physical mechanisms of creep. A strong correlation was noted between SN2 and creep parameters n and B. Finally, an attempt was made to investigate how gas shale composition and failure frictional properties can influence shear fracturing. Highlights: Bedding perpendicular gas shales show a higher creep magnitude than their bedding parallel orientation i.e., creep deformation is anisotropic in nature. A viscoelastic stress relaxation approach can explain lithology-dependent least principal stress Shmin profile estimated from 1-D power-law creep constitutive parameters (B—elastic compliance constant, n—time-dependent factor) and with a constrain of relative variation of in situ stress magnitudes ϕ at subsurface depth. Specific surface area SN2 is a first-order proxy for continuous creep constitutive parameters prediction as well as estimation of frictional failure properties of gas shales intersecting different stratigraphic layers. [ABSTRACT FROM AUTHOR]

Dissipative particle dynamics (DPD) with bond uncrossability shows a great potential in studying entangled polymers, however relatively little is known of applicability range of entangled DPD model to be use as a model for ideal chains and properly describe the full dynamics of entangled melts. Therefore, we perform a comprehensive study on structure, dynamics and linear viscoelasticity of a typical DPD entangled model system, semiflexible linear polymer melt. These polymers obey Flory's ideality hypothesis in chain dimensions, but their local structure exhibits nonideal behavior due to weak correlated hole effect. Both monomer motion and viscoelasticity relaxation reproduce the full pictures as predicted by reptation theory. The stronger chain length dependent diffusion coefficient and relaxation time as well as dynamic moduli are in close agreement with predictions of modern tube model that accounts for additional relaxation mechanisms besides chain reptation. However, an anomalous sub-diffusive center of mass motion is observed both before and after the intermediate reptation regime and the cross-correlation between chains is not negligible even these polymers obey stress-optical law, indicating limitations of the reptation theory. Hence semiflexible linear entangled DPD model can correctly describe statics and dynamics of entangled polymer melts. [ABSTRACT FROM AUTHOR]

Mathematical modeling methodology for the viscoelasticity of oriented polymer materials, as which polymer textile materials are classified, is described. The version of mathematical modeling of the viscoelasticity of polymer materials that is based on an analytical approximation of an experimental family of relaxation and deformation curves by normalized relaxation and deformation functions on a logarithmic reduced time scale is generally accepted. [ABSTRACT FROM AUTHOR]

We propose a data mining method to extract physical phenomena from the ground vibration velocity fluctuation (GVF) which is a daily observed weak signal and has no specific waveform. Our aim is to detect any traces of the return of ground motion to its normal state after earthquakes, and the evolution of ground motion towards earthquakes in the GVF. We focus on the GVF recorded near the epicenter of the magnitude 9 Great East Japan Earthquake (GEJE). Although the GVF can be discussed in the framework of the master equation which represents the thermodynamics of a stochastically fluctuating non-equilibrium system, the relation between the thermodynamic parameters and seismology-related phenomena is hardly known. So, we introduce cellular automata (CA) to analogically interpret the physical phenomena of interest as thermodynamic parameters, and show the thermodynamic equivalence between GVF and CA. These CA-derived thermodynamic parameters are then expected to deliver physical phenomena similar to those of the target when evaluated on the GVF data. In the demonstrated example of data mining, the stress relaxation signal immediately after GEJE is discovered from the recorded GVF data by deriving the thermodynamic parameters representing the stress relaxation of CA and evaluating these thermodynamic parameters for the recorded GVF data. Furthermore, the elastic rigidity and viscosity of the underground structures are estimated from the stress relaxation signal. The novelty of this study lies in drawing attention to the GVF, and combining standard techniques of CA with GVF through the use of the master equation. [ABSTRACT FROM AUTHOR]

A high-performance bismaleimide (BMI) resin blends containing the polyaryletherketone (PAEK) were prepared. The nanomechanical behaviors, viscoelasticity, and tribological properties of the bismaleimide resins were investigated by nanoindentation/scratch methods. It was established that the hardness (H) decreased, while the elastic modulus (E) increased, i.e., a reduction of plasticity index (H /E) values through the quasi-static nano-indentation testing. Meanwhile, the indentation response was mainly affected by the plastic deformation in response to a stress. The unmodified bismaleimide resins demonstrated better load-bearing capacity and indentation recovery ability, lower penetration depth than the other three specimens. Effects of angular frequency and average contact force on the viscoelastic properties were also investigated by the dynamic nanoindentation mode. The results revealed that variations of the loss tangent curves nearly were similar to each other, first increased then decreased gradually at contact force of 150 and 300 μN. Topography and profiles of the indentation and scratch surfaces were also discussed. Based on the results of the nanoscratching tests, when the PAEK content was 10 phr, the coefficient of friction during plowing was the lowest, exhibited the better scratch/wear resistance. [ABSTRACT FROM AUTHOR]

The paper presents an analytical solution of the problem of stress relaxation in a bended viscoelastic plate. The effect of tension–compression asymmetry in the viscous properties of the material on the relaxation of the bending moment is investigated. The deformation is assumed to be finite, and the multiplicative decomposition of the deformation gradient tensor into an elastic and an inelastic part is used. Two different material models with tension–compression asymmetry are compared. [ABSTRACT FROM AUTHOR]

Theoretical asymptotic calculations linear with respect to small dimensionless amplitude of oscillations have been employed to study the influence of the viscoelastic properties of a charged droplet of an electrically conducting viscous liquid on the intensity of its electromagnetic radiation. It has been shown that allowance for the effect of viscosity relaxation leads to a decrease in the damping decrement value, which is determined by energy losses for electromagnetic wave emission, and the intensity of high-frequency electromagnetic radiation; a substantial reduction in the viscous damping decrement of small cloud droplets; and an essential dependence of the viscous damping decrement on the characteristic relaxation time. It has been found that the viscosity relaxation of a liquid has no significant effect on damped capillary oscillations and electromagnetic radiation of rain droplets. Viscoelasticity and viscosity of the liquid do not influence the conditions critical for the realization of the electrostatic instability of a droplet with respect to its own charge. [ABSTRACT FROM AUTHOR]

Obtaining accurate subsurface Q (quality factor) models using full-waveform inversion (FWI) methods remains a challenging task. The forward modeling problem of viscoelastic wave propagation can be solved by superimposing N rheological bodies of Maxwell or Zener type with generalized standard linear solid rheology. However, different approaches were proposed to calculate the attenuation sensitivity kernels in viscoelastic FWI. This study reviews and compares previous theories for constructing the viscoelastic sensitivity kernels. Furthermore, we derive the viscoelastic sensitivity kernels directly following the adjoint-state (or Lagrangian multiplier) method. Compared to previous approaches, we reveal that the Q sensitivity kernels can be calculated with adjoint memory strain variables. In the numerical experiments, different methods are used to calculate the viscoelastic sensitivity kernels for comparison. We have found that when simultaneously inverting for velocity and Q models, these methods can provide inversion results of comparable quality. However, in the event of inaccurate velocity structures, the Q sensitivity kernels calculated with memory strain variables can resolve the Q anomalies more clearly, while suffering from fewer parameter trade-offs. [ABSTRACT FROM AUTHOR]

This paper deals with a linear theory of thermoviscoelasticity within the framework of Green–Naghdi thermomechanics. We use some notation and terminology introduced by Green and Naghdi, but instead of using the entropy balance law we employ an entropy production inequality. We introduce the entropy flux tensor and present a theory of materials of Kelvin–Voigt type in which the stress tensor depends on the temperature gradients. The theory leads to a fourth-order equation for temperature. The boundary conditions for thermal displacement are presented. In the dynamical theory of anisotropic solids, we formulate boundary-initial value problems and present a uniqueness theorem. We derive the continuous dependence of solutions upon initial data and supply terms. In the case of homogeneous and isotropic bodies, we establish a representation of the solution that is expressed in terms of two potentials and present an application of this result. [ABSTRACT FROM AUTHOR]

With the increase in osteoporosis and degenerative bone and joint diseases associated with an aging population, the demand for bone tissue repair materials is rapidly increasing. Bone repair materials have evolved to composite materials with biodegradability and for emerging bone repair materials, properties such as viscoelasticity, coefficient of thermal expansion, thermal conductivity, and phase change temperature play an important role in studying the mechanical properties, thermal stability, and thus determining the application scenario of the material. Therefore, thermal analysis is necessary for bone repair. This paper reviews commonly used bone tissue repair materials and thermal analysis techniques applied to bone tissue repair studies, including thermogravimetric analysis, differential thermal analysis, differential scanning calorimetry, and dynamic mechanical analysis. The paper highlights the key role of thermal analysis in bone repair research and summarizes the application of different thermal analysis techniques in the characterization of bone repair materials. The results of this study provide a valuable reference for the thermal analysis of bone repair materials. [ABSTRACT FROM AUTHOR]

Viscoelastic seismic modeling is essential to incorporate intrinsic attenuation effects in the wave propagation. Attenuation and dispersion can be quantified in terms of the quality factor Q. The consideration of these phenomena is crucial to improve the seismic processing and imaging, mainly in very deep reservoirs, having a thick salt layer above it. This work aims to evaluate the seismic attenuation effects through the 3D finite-difference viscoelastic seismic modeling using the three classical rheological models - Maxwell (M), Kelvin-Voigt (KV) and Standard Linear Solid (SLS). These viscoelastic models are analyzed comparatively considering the seismic attributes: waveform, amplitude and phase spectra. In addition, seismic attenuation of the real seismic data from Búzios field are evaluated through a frequency analysis. Synthetic seismograms of each rheological model are generated for a multi-layered geological model considering two approaches of Q distribution: a constant Q for the entire model and different Q values per layer. The amplitude spectra of real data confirmed that the shallowest post-salt package is more dissipative than deeper regions. The analysis of synthetic data shows that KV and SLS models proved to be effective to mimic seismic wave propagation at Búzios field. Thus, the KV model can be a good approach to simulate seismic waves in anelastic media due to its lower computational cost when compared to SLS. Our results also suggest that a Q distribution per layer can yield a seismic attenuation behavior similar to that observed in the seismic data of the Búzios field. [ABSTRACT FROM AUTHOR]

General anaesthetics are widely used for their analgesic, immobilising, and hypnotic effects. The mechanisms underlying these effects remain unclear, but likely arise from alterations to cell microstructure, and potentially mechanics. Here we investigate this hypothesis using a custom experimental setup combining calcium imaging and nanoindentation to quantify the firing activity and mechanical properties of dorsal root ganglion-derived neurons exposed to a clinical concentration of 1% isoflurane gas, a halogenated ether commonly used in general anaesthesia. We found that cell viscoelasticity and functional activity are simultaneously and dynamically altered by isoflurane at different stages of exposure. Particularly, cell firing count correlated linearly with the neuronal loss tangent, the ratio of mechanical energy dissipation and storage by the cell. Our results demonstrate that anaesthetics affect cells as a whole, reconciling seemingly contradictory theories of how anaesthetics operate, and highlight the importance of considering cell mechanics in neuronal functions, anaesthesia, and clinical neuroscience in general. Despite their widespread use, the mechanisms by which general anaesthetics exert their effects remain unclear. The authors use a custom-built apparatus combining calcium imaging and nanoindentation to show that cell viscoelasticity and functional activity are simultaneously altered by the anaesthetic isoflurane, and that firing and viscoelasticity alterations are correlated. [ABSTRACT FROM AUTHOR]

The salient viscoelastic properties of aramid textile materials and methods of their study are described. Preliminary information about the viscoelasticity of the studied materials can be obtained from experimental tensile diagrams and, for a more detailed study of viscoelastic properties, mathematical modeling of relaxation or deformation processes is necessary. [ABSTRACT FROM AUTHOR]

The size and viscosity effects are noticeable at the micro-/nano scale. In the present work, the strain gradient viscoelastic solution of the mode-III crack in an infinite quasi-brittle advanced material is proposed based on the strain gradient viscoelasticity theory using the Wiener–Hopf method. The solutions to the gradient-dependent viscoelastic crack problem are obtained directly by using the correspondence principle between the strain gradient viscoelasticity and strain gradient elasticity in Maxwell's standard linear solid model. In this model, the stress near the crack tip is time-dependent and size-dependent. Besides, the stress near the crack tip is more significant than that based on gradient elasticity theory. Compared with the elastic strain gradient effect, the viscous gradient effect makes the stress field at the crack tip harden. The location and the value of maximum stress change with time, which differs from the case in strain gradient elasticity theory. The time that the normalized stress takes to stabilize also changes with the distance from the crack tip. When the viscosity effect is neglected or time tends to infinity, the strain gradient viscoelasticity theory can be reduced to the classical strain gradient elasticity theory. [ABSTRACT FROM AUTHOR]

In a recent contribution, Shrimali and Lopez-Pamies (Extreme Mech Lett 58, 101944, 2023a) have shown that the Griffith criticality condition that governs crack growth in viscoelastic elastomers can be reduced—from its ordinary form involving a historically elusive loading-history-dependent critical tearing energy T c —to a fundamental form that involves exclusively the intrinsic fracture energy G c of the elastomer. The purpose of this paper is to make use of this fundamental form to explain one of the most telltale fracture tests for viscoelastic elastomers, the so-called delayed fracture test. [ABSTRACT FROM AUTHOR]

Using the diaphragm-type air spring as the research object. The ratio of the vertical stiffness change caused by compressed air to the total vertical stiffness change was calculated, and it was determined that the nonlinearity of air spring vertical stiffness was mainly caused by the deformation stiffness of the rubber airbag. The variation law of vertical dynamic stiffness of air spring was predicted by theory: due to the material's viscoelasticity, the vertical dynamic stiffness rises as the excitation frequency rises, and the vertical dynamic stiffness decreases with the increase of excitation amplitude due to the damping of the material. An air spring finite element analysis (FEA) and experiment were conducted. The results show that the vertical dynamic stiffness obtained through simulation and experiment is consistent with the theoretical prediction, when various factors such as material nonlinearity, element coupling, and stiffness value sensitivity were considered. This proves that the predicted vertical dynamic stiffness variation law is reliable. The vertical dynamic stiffness obtained from both simulation and experiment showed a strong correlation in numerical values, which verified the accuracy of the FEA model of air spring established in this paper. [ABSTRACT FROM AUTHOR]

We show that the detachment of a flat punch from a viscoelastic substrate has a relatively simple behaviour, framed between the Kendall's elastic solution at the relaxed modulus and at the instantaneous modulus, and the cohesive strength limit. We find hardly any dependence of the pull-off force on the details of the loading process, including maximum indentation at preload and loading rate, resulting much simpler than the case of a spherical punch. Pull-off force peaks at the highest speeds of unloading, when energy dissipation is negligible, which seems to be in contrast with what suggested by the theories originated by de Gennes of viscoelastic semi-infinite crack propagation which associated enhanced work of adhesion to dissipation. [ABSTRACT FROM AUTHOR]