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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]

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]

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]

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]

The study presents the experimental results of measurements of the relaxation time of cryogels formed from various colloid-dispersed systems based on a poly(vinyl alcohol) aqueous solution. It is shown that the value of relaxation time, which characterizes the relationship between the viscosity and elasticity of real bodies, describes the rheological properties of materials more objectively than the traditional assessment of their physical and mechanical characteristics only by the elasticity modulus of the samples. [ABSTRACT FROM AUTHOR]

The flexural wave propagation in a micro-beam mounted on viscoelastic foundation is considered in the present work. The mechanical behavior of the micro-beam is modeled by nonlocal strain gradient elasticity with the size-effects taken into account. The constraint is modeled by the Pasternak foundation with the rheology behavior modeled by fractional-order viscoelasticity. The main concerns are the dispersion and attenuation feature of five kinds of possible flexural waves derived from the governing equations of the presented micro-beam model. The influences of the nonlocal effects, strain gradient effects and the fractional-order viscoelastic effects are investigated by a parameter study in the numerical examples. This research is helpful for the design of micro-sensor, micro-actuator and energy-harvest devices in micro electric-mechanic system (MEMS). [ABSTRACT FROM AUTHOR]

The promising phase-field method has been intensively studied for crack approximation in brittle materials. The realistic representation of material degradation at a fully evolved crack is still one of the main challenges. Several energy split formulations have been postulated to describe the crack evolution physically. A recent approach based on the concept of representative crack elements (RCE) in Storm et al. (The concept of representative crack elements (RCE) for phase-field fracture: anisotropic elasticity and thermo-elasticity. Int J Numer Methods Eng 121:779–805, 2020) introduces a variational framework to derive the kinematically consistent material degradation. The realistic material degradation is further tested using the self-consistency condition, which is particularly compared to a discrete crack model. This work extends the brittle RCE phase-field modeling towards rate-dependent fracture evolution in a viscoelastic continuum. The novelty of this paper is taking internal variables due to viscoelasticity into account to determine the crack deformation state. Meanwhile, a transient extension from Storm et al. (The concept of representative crack elements (RCE) for phase-field fracture: anisotropic elasticity and thermo-elasticity. Int J Numer Methods Eng 121:779–805, 2020) is also considered. The model is derived thermodynamic-consistently and implemented into the FE framework. Several representative numerical examples are investigated, and consequently, the according findings and potential perspectives are discussed to close this paper. [ABSTRACT FROM AUTHOR]

Understanding tissue rheology is critical to accurately model the human heart. While the elastic properties of cardiac tissue have been extensively studied, its viscous properties remain an issue of ongoing debate. Here we adopt a viscoelastic version of the classical Holzapfel Ogden model to study the viscous timescales of human cardiac tissue. We perform a series of simulations and explore stress–relaxation curves, pressure–volume loops, strain profiles, and ventricular wall strains for varying viscosity parameters. We show that the time window for model calibration strongly influences the parameter identification. Using a four-chamber human heart model, we observe that, during the physiologically relevant time scales of the cardiac cycle, viscous relaxation has a negligible effect on the overall behavior of the heart. While viscosity could have important consequences in pathological conditions with compromised contraction or relaxation properties, we conclude that, for simulations within the physiological range of a human heart beat, we can reasonably approximate the human heart as hyperelastic. [ABSTRACT FROM AUTHOR]

Background: Magnetic resonance elastography (MRE) of the brain allows quantitative measurement of tissue mechanics. Multiple studies are exploring possible applications in normal pressure hydrocephalus (NPH) in clinical and paraclinical contexts. This is of great interest in neurological surgery due to challenges related to diagnosis and prediction of treatment effects. In this scoping review, we present a topical overview and discuss the current literature, with particular attention to clinical implications and current challenges. Methods: The protocol was based on the PRISMA extension for scoping reviews. After a systematic database search (PubMed, Embase, and Web of Science), the articles were screened for relevance. Thirty articles were subject to detailed screening, and key technical and clinical data items were extracted. The inclusion criteria included the use of MRE on human subjects with NPH. Results: Seven articles were included in the final study. These studies had various objectives including the role of MRE in the assessment of regional elastic changes in NPH, shunt effect, and evaluation of NPH symptoms. MRE revealed patterns of mechanical changes in NPH that differed from other dementias. Regional MRE changes were associated with specific NPH signs and symptoms. Neurosurgical shunting caused partial normalization in tissue scaffold parameters. The studies were highly heterogeneous in technical aspects and design. Conclusion: MRE studies in NPH are still limited by few participants, variable cohorts, inconsistent methodologies, and technical challenges, but the approach shows great potential for future clinical application. [ABSTRACT FROM AUTHOR]

Within a 3D concrete printing process, the fresh concrete is aging due to hydration. One of the consequences from the purely mechanical point of view is that its constitutive relation must be defined in rate form. This restriction is taken into account in this contribution and, besides on the incremental elasticity, we moreover introduce the relaxation of the internal stresses in order to describe the creep at early age. On another hand, due to the soft nature of the material, the finite strain range is herein a priori assumed. Eventual structural instabilities during the printing process can therefore be predicted as well. On another hand, with regards to the incremental formulation of the boundary value problem, the kinematics must be adapted as well. We use for this the multiplicative decomposition of the actual deformation gradient into its known part at an earlier time and the relative deformation gradient with respect to the configuration at that time. Within a Lagrangian formulation, the incremental constitutive relations and evolution equations can then be ideally defined on the above mentioned intermediate configuration prior to be transported back to the reference configuration. In particular, the early age creep is here described through an internal variable approach the evolution of which is motivated by the generalized Maxwell model. In this work, this latter is adapted for incremental viscoelasticity. Model examples are proposed and the numerical efficiency of the proposed framework is illustrated through a set of representative simulations. [ABSTRACT FROM AUTHOR]

We solve the plane problem of the theory of elasticity of anisotropic bodies with transverse shear cracks "healed" by the injection technologies, which is reduced to the solution of singular integrodifferential equations for the displacements of crack surfaces. We consider the cases of elastic and viscoelastic fillers of the cracks and evaluate the limit equilibrium state of the bodies with healed cracks according to the energy criterion. [ABSTRACT FROM AUTHOR]

Different drying accelerators were studied to improve vegetable drying: acetone (AC), ethanol (ET), isopropanol (ISO) and acetic acid (AA). Pre-treatments were performed by immersion of pumpkin cylinders. Convective drying was performed at 40 °C and air velocity 1 m/s. Different aspects were evaluated: drying kinetics, structural changes (microstructure and macrostructure), thermal profile and viscoelastic and rehydration behaviours. The microstructure was modified by pre-treatments, being more pronounced with AC and AA. Thinner cell walls, changes on turgor and extraction of components and air were reported, affecting the mass transfer. Moreover, the microstructural changes reinforced anisotropy and also affected the macrostructure, changing the viscoelastic behaviour. All pre-treatments resulted in a super-diffusive behaviour, decreasing the drying time from 9% (ISO) to 22% (AC). Possible relations were discussed among the compounds' physical properties, sample temperature profile, drying kinetics and equilibrium moisture. Rehydration was improved by ET and ISO, but impaired by AA. Although AC accelerates drying, it did not affect the rehydration. The viscoelasticity reflected the structure and composition, with the pre-treatments with higher structure modifications (AA and AC) losing elastic properties. In conclusion, the pre-treatments with isopropanol and ethanol showed better results, improving drying and rehydration, and are thus recommended. [ABSTRACT FROM AUTHOR]

Instrumented indentation has become an indispensable tool for quantitative analysis of the mechanical properties of soft polymers and biological samples at different length scales. These types of samples are known for their prominent viscoelastic behavior, and attempts to calculate such properties from the indentation data are constantly made. The simplest indentation experiment presents a cycle of approach (deepening into the sample) and retraction of the indenter, with the output of the force and indentation depth as functions of time and a force versus indentation dependency (force curve). The linear viscoelastic theory based on the elastic–viscoelastic correspondence principle might predict the shape of force curves based on the experimental conditions and underlying relaxation function of the sample. Here, we conducted a computational analysis based on this theory and studied how the force curves were affected by the indenter geometry, type of indentation (triangular or sinusoidal ramp), and the relaxation functions. The relaxation functions of both traditional and fractional viscoelastic models were considered. The curves obtained from the analytical solutions, numerical algorithm and finite element simulations matched each other well. Common trends for the curve-related parameters (apparent Young's modulus, normalized hysteresis area, and curve exponent) were revealed. Importantly, the apparent Young's modulus, obtained by fitting the approach curve to the elastic model, demonstrated a direct relation to the relaxation function for all the tested cases. The study will help researchers to verify which model is more appropriate for the sample description without extensive calculations from the basic curve parameters and their dependency on the indentation rate. [ABSTRACT FROM AUTHOR]

Cell lysates (cellular extracts) constitute a perfect imitation of the intracellular environment that can provide insight into cellular response to external stimuli. However, most of the presented results are performed for diluted lysates that do not reflect the actual properties of a crowded cellular environment. Here, we report for the first time the measurement of the viscosity and shear storage modulus of highly concentrated Escherichia coli (E. coli) lysates with and without adenosine triphosphate (ATP). By cleavage of DNA content, we showed the value of shear storage modulus G ′ decreases by 19–31% in comparison to control samples. The addition of molecules that provides energy (ATP) allowed to rebuild the structure of the lysate by reversibly increasing viscous properties over elastic ones. When the energy delivered in the form of ATP is consumed by the unliving bacterial lysate, the system returns to its initial state. [ABSTRACT FROM AUTHOR]

In this work, based on Eringen's theory of nonlocal anisotropic elasticity, the three-dimensional nonlocal anisotropic elasticity of generalized Helmholtz type is developed. The derivation of a new three-dimensional nonlocal anisotropic kernel, which is the Green function of the three-dimensional anisotropic Helmholtz equation, enables to capture anisotropic length scale effects by means of a length scale tensor, which is a symmetric tensor of rank two. The derived nonlocal kernel function possesses up to six internal characteristic lengths on the Ångström-scale. The presented theory of nonlocal elasticity possesses the appropriate property to be a generalized continuum theory of Ångström-mechanics, since the range of its validity and applicability is up to the Ångström-scale. The connection between the theory of nonlocal anisotropic elasticity and lattice theory is established. The tensor function of nonlocal elastic moduli as well as the nonlocal kernel function is given in terms of the Hessian matrix in the lattice approach. In the framework of the considered theory, the modeling of dislocations in anisotropic materials taking into consideration anisotropic dislocation core effects is presented. Important dislocation key formulas, namely the anisotropic Peach–Koehler stress formula, the Peach–Koehler force and the anisotropic Blin's formula, are derived. A major tool used in deriving the expression of anisotropic Blin's formula is Kirchner's so-called F -tensor, which is here generalized toward nonlocal anisotropic elasticity. The main feature and advantage of the derived fields, compared with the corresponding ones in classical anisotropic elasticity, is that they are free of singularities. Numerical applications to straight dislocations in bcc Fe are given, revealing the ability and advantage of the considered theory to describe adequately nonsingular anisotropic stress and self-energy fields capturing the effects of anisotropy on the Ångström-scale. [ABSTRACT FROM AUTHOR]

We introduce a novel magneto-mechanical device to simulate viscoelastic substances in a rotational rheometer. The device can serve as a calibration standard to calibrate the measurement of the viscous and elastic properties of a substance or as a benchmark for measuring methods and device testing procedures. We present the mechanical and rheological backgrounds of this device, describe its design, and present the results from basic rheometric measurements, i.e., frequency sweeps, creep recovery, and cessation-of-shear experiments. We conclude with remarks on possibilities of extending the concept by modeling a broader spectrum of substances and the application in dynamic mechanical analyzers. [ABSTRACT FROM AUTHOR]

We investigate experimentally the rheology of an active suspension of nematodes C. elegans under oscillatory shear. There are few experimental investigations and theoretical work on the oscillatory rheological properties including elastic and viscous moduli of micro-swimmer suspensions. The viscous and elastic moduli are evaluated by our experiments in the regime of linear viscoelasticity. These viscoelastic quantities are explored at low frequency given the active suspension viscosity and the shear elastic modulus. The experiments have revealed an anomalous behavior of the viscosity and the shear elastic modulus with the variation of the suspension volume fraction. The suspension relative viscosity decreased with the increase of active particles within a certain range of volume fraction. However, above a critical particle volume fraction, the relative viscosity increases. This observed increase of the viscosity for larger concentration is a direct consequence of formation of large and coherent oriented structures and active particle interactions. This collective behavior also increases the first normal stress difference N1, obtained through Cox–Merz rule. Three different regions are obtained regarding different involved mechanisms and a physical interpretation is provided based on the particles dipole stresslet. Step strain tests are carried out and the active relaxation time as a function of volume fractions are obtained. An intrinsic oscillatory behavior is observed regardless the volume fraction, showing the non-equilibrium condition of the active suspension. [ABSTRACT FROM AUTHOR]

Fractional derivative and WLF equation are effective in describing the dynamic behavior and time-temperature effect of viscoelastic damping materials, respectively. These approaches have essentially evolved from the viscoelastic constitutive behavior. Based on such intrinsic relation, a fractional time-temperature superposition principle model (FTTSPM) that integrates the fractional constitutive relation and WLF equation was proposed. The parameters of this model were determined by performing tensile and DMA tests, and the master curves at 5 °C constructed by FTTSPM and WLF equation were compared. The theoretical prediction over the extended frequency span as the master curves was made by using the fractional standard linear solid model (FSLSM) to validate FTTSPM. The numerical results show that FTTSPM conforms to the time-temperature superposition principle. The parameters α and B′ in this model denote the impact of the material and environment on the shifted factor, respectively. For the storage and loss modulus, the extended frequency obtained by FTTSPM is broader than that obtained by the WLF equation. Moreover, the evaluation of the storage and loss modulus by FTTSPM is much closer to the theoretical prediction compared with that by the WLF equation. Therefore, FTTSPM is a concise and experiment-based approach with a higher precision and greater frequency-extended capacity compared with the WLF equation. However, FTTSPM inevitably faces a vertical shift when non-thermo-rheologically simple materials are considered. The physical mechanism and practical application of FTTSPM will be examined in further research. [ABSTRACT FROM AUTHOR]

Introduction: Lamin proteins confer nuclear integrity and relay external mechanical cues that drive changes in gene expression. However, the influence these lamins have on whole-cell mechanical properties is unknown. We hypothesized that protein expression of lamins A, B1, and C would depend on the integrity of the actin cytoskeleton and correlate with cellular elasticity and viscoelasticity.Methods: To test these hypotheses, we examined the protein expression of lamins A, B1, and C across five different cell lines with varied mechanical properties. Additionally, we treated representative “soft/stiff” cell types with cytochalasin D and LMNA siRNA to determine the effect of a more compliant whole-cell phenotype on lamin A, B1 and C protein expression.Results: A positive, linear correlation existed between lamin C protein expression and average cell moduli/apparent viscosity. Though moderate correlations existed between lamin A/B1 protein expression and whole-cell mechanical properties, they were statistically insignificant. Inhibition of actin polymerization, via cytochalasin D treatment, resulted in reduced cell elasticity, viscoelasticity, and lamin A and C protein expression in “stiff” MG-63 cells. In “soft” HEK-293T cells, this treatment reduced cell elasticity and viscoelasticity but did not affect lamin B1 or C protein expression. Additionally, LMNA siRNA treatment of MG-63 cells decreased whole-cell elasticity and viscoelasticity.Conclusion: These findings suggest that lamin C protein expression is strongly associated with whole-cell mechanical properties and could potentially serve as a biomarker for mechanophenotype. [ABSTRACT FROM AUTHOR]

We present a survey of the efficient approximate methods for the evaluation of the stress concentration near notches, slits, and cavities filled with elastic or viscoelastic materials. Our main attention is given to a method based on the use of solutions of the corresponding problems for bodies with mathematical cuts along the median surfaces of the concentrators. The idea of the method is to replace an inclusion with a certain volume by a surface with unknown discontinuities of stresses and/or displacements. We describe a procedure of construction of the integral equations of the corresponding boundary-value problems used to determine the indicated discontinuities. By an example of the inhomogeneities bounded by canonical surfaces, we illustrate the efficiency of construction of approximate solutions of these problems. [ABSTRACT FROM AUTHOR]

Persistence length is one of the most interesting properties of a molecular chain, which is used to describe the stiffness of a molecule. The experimentally measured values of the persistence length of the collagen molecule are widely scattered from 14 to 180 nm. Therefore, an alternative approach is highly desirable to predict the persistence length of a molecule and also to explain the experimental results. In this paper, a nonlocal viscoelastic model is developed to obtain the persistence length of the collagen molecules in solvent. A new explicit formula is proposed for the persistence length of the molecule with the consideration of the small-scale effect, viscoelastic properties of the molecule, loading frequency, and viscosity of the solvent. The presented model indicates that there exists a range of molecule lengths in which the persistence length strongly depends on the frequency and spatial mode of applied loads, small-scale effect, and viscoelastic properties of the collagen. [ABSTRACT FROM AUTHOR]

The paper deals with numerical evaluation of the scattered wave and dynamic stress concentration fields in a finite anisotropic solid containing multiple nano-cavities. 2D plane-strain state and in-plane wave motion are assumed. The proposed mechanical model combines classical elastodynamic theory for the bulk general anisotropic solid and the Gurtin-Murdoch theory of surface elasticity assuming localized constitutive equation for the infinitely thin interface between the cavity and the matrix. The developed computational methodology is based on the following: (a) displacement boundary integral equations along existing boundaries using the analytically derived through Radon transform fundamental solution of the equation of motion of the bulk anisotropic solid; (b) non-classical boundary conditions of the Gurtin-Murdoch model along the interface between the matrix and cavities taking into consideration a jump in the stresses as one moves from the bulk material to the cavity due to the presence of surface elasticity; and (c) elastic-viscoelastic correspondence principle. The accuracy of the developed software is proven by comparisons of the obtained results solved by boundary element method and finite element method. A detailed parametric study reveals the sensitivity of the wave field to different key factors such as size, number and configuration of the cavities, surface and bulk material properties. [ABSTRACT FROM AUTHOR]

An algorithm for solving the problem of slow growth of a mode I crack with a zone of partial contact of the faces is proposed. The algorithm is based on a crack model with a cohesive zone, an iterative method of finding a solution for the elastic opening displacement, and elasto-viscoelastic analogy, which makes it possible to describe the time-dependent opening displacement in Boltzmann-Volterra form. A deformation criterion with a constant critical opening displacement and cohesive strength during quasistatic crack growth is used. The algorithm was numerically illustrated for tensile loading at infinity and two concentrated forces symmetric about the crack line that cause the crack faces to contact. When the crack propagates, the contact zone disappears and its dynamic growth begins. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of solid biological tissues has long been described using models based on classical continuum mechanics. However, the classical continuum theories of elasticity and viscoelasticity cannot easily capture the continual remodelling and associated structural changes in biological tissues. Furthermore, models drawn from plasticity theory are difficult to apply and interpret in this context, where there is no equivalent of a yield stress or flow rule. In this work, we describe a novel one-dimensional mathematical model of tissue remodelling based on the multiplicative decomposition of the deformation gradient. We express the mechanical effects of remodelling as an evolution equation for the effective strain, a measure of the difference between the current state and a hypothetical mechanically relaxed state of the tissue. This morphoelastic model combines the simplicity and interpretability of classical viscoelastic models with the versatility of plasticity theory. A novel feature of our model is that while most models describe growth as a continuous quantity, here we begin with discrete cells and develop a continuum representation of lattice remodelling based on an appropriate limit of the behaviour of discrete cells. To demonstrate the utility of our approach, we use this framework to capture qualitative aspects of the continual remodelling observed in fibroblast-populated collagen lattices, in particular its contraction and its subsequent sudden re-expansion when remodelling is interrupted. [ABSTRACT FROM AUTHOR]

Purpose: To investigate how the viscoelastic characteristics of muscles (non-neural tone, elasticity and stiffness) vary as a function of age and gender in a sample of track and field master athletes. To compare these findings with data on related sedentary subjects in literature.Methods: A total of 390 athletes (aged 35-99) were assessed during the European Master Athletics Indoor Championship 2016. A non-invasive measurement device called MyotonPro was used to measure tone, stiffness, and elasticity in the biceps brachii and rectus femoris muscles at rest. Linear regression analysis was used to assess the correlation between age and the measured parameters. To compare our results with previously reported data, we stratified participants according to gender and age.Results: Tone was found to not be dependent on age, whereas stiffness was found to be age dependent. Elasticity was found to be both physical activity and age dependent. Tone (only for men), elasticity, and stiffness were lower in master athletes than in sedentary subjects.Conclusions: Tone, elasticity, and stiffness change with aging; nevertheless, our findings suggest that physical activity can delay the effects of muscular aging, improving fitness in older people. [ABSTRACT FROM AUTHOR]

The annulus fibrosus (AF) swelling property, which is correlated with its rheological and viscoelastic properties, plays a significant role in disc nutrition and mechanical loading justification during daily activities as well as designing scaffolds for tissue engineering applications. The objective of this study was twofold: firstly to characterize the AF single lamella swelling kinetics in different regions and solutions at the temperature range of 35-40 °C and secondly to use the swelling results as a baseline to model (independent to swelling media and anatomic region) the AF single lamella swelling. It was found that the AF single lamella swelling kinetics (equilibrium swelling ratio and swelling rate) depends on anatomic region and swelling media; however, its trend for different swelling media (ionic and molecular solution) is similar and the majority of hydration occurs during first 20% of equilibrium swelling time (about 20 min). Change in swelling rate constant in circumferential direction depends on the solution type. It decreases from anterior to lateral regions for water, PBS and glucose solution and remains constant-or its change is negligible-from lateral to posterolateral regions. The effect of temperature (in the range of 35-40 °C) on swelling kinetics was seen to be negligible. It was also understood that it is possible to present a model (independent to swelling media type) to predict the swelling kinetics of posterior and posterolateral AF single lamella, as these locations are less sensitive to the swelling media. [ABSTRACT FROM AUTHOR]

We propose mixed finite element methods for the standard linear solid model in viscoelasticity and prove a priori error estimates. In our mixed formulation the governing equations of the problem become a symmetric hyperbolic system, so we can use standard techniques for a priori error estimates and time discretization. Numerical results illustrating our theoretical analysis are included. [ABSTRACT FROM AUTHOR]

We performed particle focusing in viscoelastic fluids in a straight square microchannel based on elasto-inertial focusing. Probability distribution functions (PDFs) were obtained at various flow rates (40-320 μl/h) for a broad range of medium viscoelasticity (PEO solutions) from a dilute regime (0.01-0.2 wt%) to a semi-dilute regime (0.3-1.0 wt%). To evaluate focusing efficiency, PDF values at the centerline of the microchannel were plotted as a function of three dimensionless numbers: Reynolds number ( Re), Weissenberg number ( Wi), and elasticity number ( El). Relaxation times were carefully calculated by using two different methods for each regime of medium to calculate Wi accurately. As a result, PDF at the centerline as a function of Re and El did not display any scaling tendency, but a single master curve was obtained in the plot of PDF at the centerline as a function of Wi, indicating that Wi is a more suitable parameter for manipulating elasto-inertial focusing than Re or El. In the plot of PDF versus Wi, particle focusing could be divided into two regimes at Wi = 3.16, where maximum PDF was observed. In the first regime ( Wi < 3.16), particle focusing increased rapidly with increasing Wi. However, in the second regime ( Wi > 3.16), particle focusing was no greater, but scattering increased with increasing Wi due to the shear thinning effect of suspending medium. [ABSTRACT FROM AUTHOR]

Rheological soft tissue models play an important role in designing control methods for modern teleoperation systems. In the meanwhile, these models are also essential for creating a realistic virtual environment for surgical training. The implementation of model-based control in teleoperation has been a frequently discussed topic in the past decades, offering solutions for the loss of stability caused by time delay, which is one of the major issues in long-distance force control. In this paper, mass-spring-damper soft tissue models are investigated, showing that the widely used linear models do not represent realistic behavior under surgical manipulations. A novel, nonlinear model is proposed, where mechanical parameters are estimated using curve fitting methods. Theoretical reaction force curves are estimated using the proposed model, and the results are verified using measurement results from uniaxial indentation. The model is extended with force estimation by nonuniform surface deformation, where the surface deformation function is approximated according to visual data. Results show that using the proposed nonlinear model, a good estimation of reaction force can be achieved within the range of 0-4 mm, provided that the tissue deformation shape function is appropriately approximated. [ABSTRACT FROM AUTHOR]

The paper presents mathematical formulation of a dynamic soft-contact problem consisting of a material point impacting rheological structures. Two different models were analyzed. The first model concerns a viscoelastic structure while the second one applies to the so-called fractional-elastic scheme. In both cases the formulation of the problem needs the notion of variational inequalities describing unilateral constraints. Moreover, the fractional-elastic model contains an element defined via fractional derivatives (spring-pot) that complicates the numerical solution. Thanks to the methods used in this paper, both problems were described mathematically applying appropriate systems of algebraic-differential equations. The solution of the fractional-elastic problem involving a fractional-differential equation (FDE) was obtained with the use of time-discretization schemes proposed in the literature. Selected numerical results of the initial-value problem solution, modelling a material point falling freely and impacting the rheological structures were presented. [ABSTRACT FROM AUTHOR]

Results of experimental investigation of the low-frequency shear elasticity of liquids depending on the angle of shear strain are presented. A cluster model of the liquid structure is suggested to explain the low-frequency viscoelastic relaxation. [ABSTRACT FROM AUTHOR]

In this paper, we show that circularly polarized transverse stress waves, standing shear stress waves, and oscillatory shear stress waves can propagate in a new class of viscoelastic solid bodies which are a subclass of bodies described by implicit constitutive theories. The class of models that is being considered includes as sub-classes, the classical Kelvin-Voigt model, the new models introduced by Rajagopal wherein the Cauchy-Green tensor is a non-linear function of the stress, and the Navier-Stokes fluid model. The solutions established in this paper are generalizations of solutions that have been established within the context of nonlinear elasticity by Carroll, and Destrade and Saccomandi, to the new class of elastic and viscoelastic bodies that are being considered. [ABSTRACT FROM AUTHOR]

This work is focused on the magnetic response of magnetoactive elastomer (MAE) based on silicone polymer matrices filled with magnetic particles of magnetically hard NdFeB-alloy. Viscoelastic properties of MAE were studied by the method of oscillation shear. After magnetization in an external magnetic field of 2 T MAE samples demonstrate more than two-time increase in the storage and loss moduli and 25% increase in the loss factor. Performed study of the damping properties of the materials has shown that the oscillation time of the pendulum hammering the magnetized sample is in two times shorter than in case of the non-magnetized sample. Viscoelastic and damping properties of MAE are defined by magnetic interactions between the magnetized particles of the magnetic filler. [ABSTRACT FROM AUTHOR]

Filled elastomers usually show a pronounced viscoelastic behaviour with long relaxation times. The basic elasticity of the material represents the basis for the complete viscoelastic material model. The important problem is that the long relaxation times lead to a very difficult experimental procedure in order to get the appropriate experimental data. An adequate pretreatment of the material can significantly reduce the experimental duration. This effect has been seen for different types of filled elastomers and has been investigated in detail for a carbon black-filled ethylene propylene diene monomer (EPDM). In the present work, the single steps in the development of the material model for this EPDM are presented, including the basic elasticity, viscoelastic behaviour for moderate strain rates and the Payne effect as a softening effect. An adequate pretreatment can reduce the experimental duration to get the basic elasticity. By using the material model, an optimisation of this experimental pretreatment process is determined for uniaxial loadings. The result of this optimisation can also be seen for different kinds of filled elastomers. Finally, the question whether these conclusions can also be transferred to biaxial deformations is discussed and experimentally examined. [ABSTRACT FROM AUTHOR]

We review the anomalous behavior of solid He at low temperatures with particular attention to the role of structural defects present in solid. The discussion centers around the possible role of two level systems and structural glassy components for inducing the observed anomalies. We propose that the origin of glassy behavior is due to the dynamics of defects like dislocations formed in He. Within the developed framework of glassy components in a solid, we give a summary of the results and predictions for the effects that cover the mechanical, thermodynamic, viscoelastic, and electro-elastic contributions of the glassy response of solid He. Our proposed glass model for solid He has several implications: (1) The anomalous properties of He can be accounted for by allowing defects to freeze out at lowest temperatures. The dynamics of solid He is governed by glasslike (glassy) relaxation processes and the distribution of relaxation times varies significantly between different torsional oscillator, shear modulus, and dielectric function experiments. (2) Any defect freeze-out will be accompanied by thermodynamic signatures consistent with entropy contributions from defects. It follows that such entropy contribution is much smaller than the required superfluid fraction, yet it is sufficient to account for excess entropy at lowest temperatures. (3) We predict a Cole-Cole type relation between the real and imaginary part of the response functions for rotational and planar shear that is occurring due to the dynamics of defects. Similar results apply for other response functions. (4) Using the framework of glassy dynamics, we predict low-frequency yet to be measured electro-elastic features in defect rich He crystals. These predictions allow one to directly test the ideas and very presence of glassy contributions in He. [ABSTRACT FROM AUTHOR]

An apparatus for measurement of mechanocaloric effect in rubber has been constructed and tested by measuring the thermal response of three rubber materials to mechanical strain. The results obtained were satisfactory. Detailed measurement has been performed on these materials. The entropy changes that accompany elongation were calculated from the experimental results and compared with those derived from literature data and statistical theory of the macromolecular chain. A dissipative effect was found to accompany the rapid deformation of rubber and attributed to viscoelastic irreversibility. An experimental procedure to eliminate this effect was identified. The apparatus, assembled with the readily available components, will be a useful device for introducing the entropy concept in thermodynamics courses. [ABSTRACT FROM AUTHOR]

On the basis of a mixed statement (velocity-strain), we complete the development of a general theory of completely conservative adjoint-coordinated difference schemes for dynamic problems of linear elasticity and viscoelasticity. In particular, our explicitly solvable discrete models permit controlling the total energy imbalance and have the same parallelization degree as the conventional explicit schemes. [ABSTRACT FROM AUTHOR]

Instrumented indentation is used to measure the complex modulus of highly plasticized polyvinyl chloride (HP-PVC) and four kinds of polyethylene over the frequency range of 1-50Hz. Over this range, the loss factor for the HP-PVC increases from 0.3 to 1, making this an ideal material for damping out noise and vibration. The storage moduli for the four polyethylene samples are ordered according to density, with the lowest-density material have the lowest storage modulus. Results for both storage modulus and loss factor compare well with published results obtained by dynamic mechanical analysis for nominally similar materials. [ABSTRACT FROM AUTHOR]

With the recent well-being trend, a great deal of effort has been made to develop instant fried noodles with beneficial health effects. Thus, β-glucan-enriched materials (BGEMs) were obtained from Lentinus edodes mushroom and their effects on the quality attributes of instant fried noodles were characterized in terms of rheological, textural, and oil-resisting properties. When BGEMs were mixed with wheat flour, different thermomechanical profiles were observed by a Mixolab, enhancing dough stability and water absorption. The use of BGEMs raised the viscoelastic properties of noodle dough with a great increase in the elastic property. In addition, the dough samples prepared with more BGEMs exhibited greater elongational viscosity. In the case of fried noodle strands, the incorporation of BGEMs led to a significant increase in the breaking stress and produced a surface microstructure with smaller voids. Moreover, the oil uptake of fried noodles containing BGEMs was significantly reduced by 22%. Therefore, it showed that BGEMs had positive impacts on the quality attributes of instant fried noodles and could also be used as an oil barrier to produce fried noodles with a reduced content of oil and calories. [ABSTRACT FROM AUTHOR]

The tension force of a thinning high-molecular polymer solution filament is measured using the filament itself as a force sensor. The axial filament stresses and the effects of fluid flow from the filament into adjacent drops are estimated. It is shown that these effects are insignificant for polymer solutions in a low-viscosity solvent (water) but substantial for solutions in a high-viscosity fluid (glycerine). A modification of the standard rheological capillary filament method is proposed. This modification makes it possible to exclude any hypotheses concerning the stress distribution pattern within the filament. Periodic transverse oscillations of the filament axis are revealed and analyzed. [ABSTRACT FROM AUTHOR]

Results related to the buckling delamination of elastic and viscoelastic composite plates are reviewed and analyzed. They have been obtained during the last fifteen years by the author and his students. The plates contain cracks whose faces have initial infinitesimal imperfections. The evolution of the imperfections under compression of the plates is studied, and the values of critical parameters are determined from a criterion of initial imperfection. The study is performed with the use of 3D geometrically nonlinear field equations. In the present paper, the historical background of the problems is outlined considered, general remarks about the field equations and solution method are made, and problems related to the plane strain state are reviewed. [ABSTRACT FROM AUTHOR]

In this paper, we deal with the mechanical behaviour of elastomeric sole shoes subjected to bending. First, a methodology for material parameter identification is described for a visco-hyperelastic constitutive law with discontinuous damage, modelling the Mullins effect. This constitutive law was implemented in the finite element software CODE-ASTER (Abbas and Baranger ). Then, numerical results of the bending behaviour of a simple geometric shoe sole model are compared to experimental measurements obtained with a stereoscopic vision system. Finally, an industrial application of dynamic bending sole shoe is presented and experimental results and simulated load history are compared. [ABSTRACT FROM AUTHOR]

For the integrodifferential equation that corresponds to the two-dimensional viscoelasticity problem, we study the problem of determining the density, the elasticity coefficient, and the spaceintegral term in the equation. We assume that the sought functions differ from the given constants only inside the unit disk D = { x ∈ ℝ | | x| < 1}. As information for solving this inverse problem, we consider the one-parameter family of solutions to the integrodifferential equation corresponding to impulse sources localized on straight lines and, on the boundary of D, there are defined the traces of the solutions for some finite time interval. It is shown that the use of a comparatively small part of the given information about the kinematics and the elements of dynamics of the propagating waves makes it possible to reduce the problem under consideration to three consecutively and uniquely solvable inverse problems that together give a solution to the initial inverse problem. [ABSTRACT FROM AUTHOR]

Polymer composites that can be folded into different angles and upon reheating come back to their original shapes are called elastic memory composites (EMC). This is particularly attractive for the development of large deployable space-based sensors which can be stowed during launch and deployed in orbit. However, the dynamics of deployment (rate and precision) is important considering the high levels of positional sensitivity of such structures. The rate of deployment of the composite depends on the viscoelastic properties of the EMC polymer and the elastic properties of the fibers. In this paper first the experimental setup for deployment data acquisition and resin viscoelastic properties is discussed and then an analytical prediction model (based on micro-mechanics) is developed. The analytical model is validated by excellent correlation with the deployment test data. [ABSTRACT FROM AUTHOR]

A linear viscoporoelastic model is developed to describe the problem of reflection and transmission of an obliquely incident plane P-wave at the interface between an elastic solid and an unsaturated poroelastic medium, in which the solid matrix is filled with two weakly coupled fluids (liquid and gas). The expressions for the amplitude reflection coefficients and the amplitude transmission coefficients are derived by using the potential method. The present derivation is subsequently applied to study the energy conversions among the incident, reflected, and transmitted wave modes. It is found that the reflection and transmission coefficients in the forms of amplitude ratios and energy ratios are functions of the incident angle, the liquid saturation, the frequency of the incident wave, and the elastic constants of the upper and lower media. Numerical results are presented graphically. The effects of the incident angle, the frequency, and the liquid saturation on the amplitude and the energy reflection and transmission coefficients are discussed. It is verified that in the transmission process, there is no energy dissipation at the interface. [ABSTRACT FROM AUTHOR]

The Cox-Merz rule and Laun's rule are two empirical relations that allow the estimation of steady shear viscosity and first normal stress difference, respectively, using small amplitude oscillatory shear measurements. The validity of the Cox-Merz rule and Laun's rule imply an agreement between the linear viscoelastic response measured in small amplitude oscillatory shear and the nonlinear response measured in steady shear flow measurements. We show that by using a lesser-known relationship also proposed by Cox and Merz, in conjunction with Laun's rule, a relationship between the rate-dependent steady shear viscosity and the first normal stress difference can be deduced. The new empirical relation enables a priori estimation of the first normal stress difference using only the steady flow curve (i.e., viscosity vs shear rate data). Comparison of the estimated first normal stress difference with the measured values for six different polymer solutions and melts show that the empirical rule provides values that are in reasonable agreement with measurements over a wide range of shear rates, thus deepening the intriguing connection between linear and nonlinear viscoelastic response of entangled polymeric materials. [ABSTRACT FROM AUTHOR]

A simulation technique to deal with transient dynamic contact of tire rubber compounds on rough road surfaces is presented. The segment-to-surface approach is used for modeling the contact between tire tread rubber and road track. While the rubber components are deformable and described by a sophisticated viscoelastic damage constitutive model, the road surface is assumed to be rigid and characterized by an analytical function. A spectral approach based on an inverse computation of the 2D-Fast Fourier transform has been suggested for the reconstruction of rough surface profiles. The Newmark time-stepping method is used for the integration of transient dynamic equations. With the so-called contact-stabilized Newmark method the spurious oscillation at contact boundary has been removed. The detailed investigation on the dynamic contact of inelastic rubber block with rough road surfaces has been made. The robustness of the contact-stabilized Newmark method within a finite deformation framework is underlined by numerical studies, in which it is compared with several dissipation-based stabilization techniques selected from literature. [ABSTRACT FROM AUTHOR]

The article deals with a study which developed an experimental method for determining the viscoelastic behavior of a sedimentary rock. The viscoelastic behavior of a sedimentary rock was investigated through a series of impact tests. It relates how the frequency dependence of the viscoelastic storage modulus and loss modulus is obtained. It describes the rock viscosity and its effect on stress wave propagations in the sedimentary rock.

Properties determined from the microscopic stress tensor are discussed for the related systems of a steeply repulsive pair potential and hard spheres. The microscopic stress tensors determined from the local conservation law for momentum are different in these two cases. Consequences are discussed for both fluid and solid phases. [ABSTRACT FROM AUTHOR]