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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]

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]

Optimisation design of composite structures requires an accurate predictive model for forming behaviour. The simulation process contains a number of model parameters which include transverse and longitudinal viscosities of continuous fibre reinforced viscous composites, fundamental to predicting the shear rheology. Micromechanical interaction between fibre and matrix offers fundamental understanding of deformation mechanisms at the micro-scale level, leading to development of the fully predictive composite viscosity models, so as to eliminate any time-consuming experimental characterisation. The composite viscosity models were developed based on rheological behaviour during movement of fibres, and validation was performed using experimental results collected from the literature, indicating reasonably good agreement with the lower bound of the test data. It is suggested that non-Newtonian effects (rate dependency), viscoelastic effects and fibre rearrangement during shearing should be considered in the models to resolve the underestimation problem. [ABSTRACT FROM AUTHOR]

We continue the systematic analytical study of a nonlinear Maxwell-type constitutive equation for shear flow for thixotropic viscoelastic media accounting for interaction of deformation process and structure evolution, namely, the influence of the kinetics formation and breakage of chain cross-links, agglomerations of molecules and crystallites on viscosity and shear modulus and deformation influence on the kinetics. We formulated it in the previous article and reduced it to the set of two nonlinear autonomous differential equations for two unknown functions (namely, the stress and relative cross-links density). We examine the phase portrait of the system for arbitrary (increasing) material function and six (positive) material parameters governing the model and prove that the (unique) equilibrium point is stable and the only three cases are realized: the equilibrium point is either a stable sink, or a degenerated stable sink, or a stable spiral sink. We found criteria for every case in the form of explicit restrictions on the material function and parameters and shear rate. [ABSTRACT FROM AUTHOR]

The viscoelastic properties of dispersions of few-layer graphite fragments (LGF) and their nitrogen-doped analogs (N-LGF) in three commercially available plastic lubricants (PLM I–III) and in a model base lubricant—medical vaseline (VM) were studied by the method of oscillatory deformations. The concentration range of additives of carbon nanostructures varied from 0.1 to 1.5 wt %. At concentrations from 0.1 to 0.5 wt %, dispersions retain the viscoelastic properties of the basic PLM. At concentrations of 1.0 and 1.5 wt %, the dispersion passes into the region of a viscous state. The predominant contribution to the change in the viscoelastic properties of dispersions is the type of base substrate. Nevertheless, the effect of structural features of LGF and N-LGF additives can be clearly seen by the example of their dispersions in VM, which does not contain thickeners and other additives. The use of the Maxwell model for a viscoelastic body allowed calculating the relaxation time and correlation length of the thickener skeleton as well as explaining the change in these parameters for the studied dispersions with varying concentrations of nanocarbon structures. [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]

The rheological property of cathode slurry is commonly influenced by coating speed and mixing temperature, thereby leading to its storage stability and coating uniformity. In this study, the effect of the temperature of slurry on the rheological behaviors is investigated under various shear rates and temperatures based on steady and dynamic tests as well as theoretical models. In the flow experiments, the thixotropic behavior of the slurry is observed at all temperatures tested, and it is reduced with the increase in temperature. The experimental data is captured well by rheological models, and the model parameters are evaluated under the combined effects of shearing and temperature, resulting in two generalized state equations for the description of the flow properties of the slurry. In addition, microstructural rearrangement and polymeric entanglement at high temperatures cause viscosity and modulus to change, giving rise to complex rheological behavior in creep and oscillatory shear. Compared with slurry at 25 and 40 °C, both storage and loss moduli are dependent on oscillatory strain in the range of 0.1–1000% at 65 °C. The difference in characteristic strain corresponding to yielding and strain stiffening behavior is only observed at high temperatures, whereas relaxation times were independent of temperature in the oscillatory shear test. Understanding the effect of the temperature of slurry on rheological behaviors will be useful for improving the manufacturing efficiency of electrodes. [ABSTRACT FROM AUTHOR]

To study the overall rheological characteristics of the silicone oil-based ferrofluid, a chemical co-precipitation method was adopted for preparation, and transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were used for characterization. The average size of Fe3O4 magnetic particles was 10.4 nm and the saturation magnetization of the ferrofluid was 5.98 emu/g. Then, the fluidity, magnetoviscous effect and viscoelasticity of the ferrofluid were studied using a rotational rheometer. The results showed obvious shear thinning of the silicone oil-based ferrofluid under an external magnetic field, and the yield stress of the ferrofluid could not be accurately obtained by fitting the flow curve with an H–B model at a continuous shear rate. A strong magnetoviscous effect could be observed at different shear rates and temperatures. The magnetoviscous parameter R increased with the increase of temperature and its variation decreased with the increase of shear rate. Moreover, based on the magnetic particle chain model and the viscosity–temperature characteristics of the base carrier liquid, different mechanisms of temperature influence on the magnetoviscous effect were analyzed. Finally, a discussion of the microstructure evolution mechanism of the ferrofluid in the modulus changing with frequency was presented through the viscoelastic analysis of the silicone oil-based ferrofluid. [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 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]

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]

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]

The article touches upon an unsteady rectilinear motion of a submarine in a liquid under an ice cover. The ice cover is modeled as a viscoelastic plate. The viscoelastic properties of the ice are described using the Kelvin–Voigt model. The fluid is assumed to be inviscid and incompressible, and its motion is potential. Free surface fluid flow past system of one source and several sinks is used to simulate the motion of Joubert submarine. The solution of this problem is constructed analytically using the Fourier and Laplace transforms. Numerical results for the wave resistance and lift force acting on Joubert submarine are presented for different ice thicknesses, length-to-diameter ratio of a submarine, and the speed of the uniform motion. It is demonstrated that the use of a viscoelastic model for an ice cover results in a significant decrease in the maximum values of wave resistance and lift coefficients compared to the scenario of using an elastic plate model. The results indicate that when a submarine moves at realistic speeds (Fr < 0.7) under a thick ice cover (thicker than a meter), the wave resistance is less than for the same submarine moving under a free surface. The lift force for moving at these speeds under a thick ice cover is directed upwards. [ABSTRACT FROM AUTHOR]

Fabrication of polyethylene (PE) pipe with significantly enhanced hoop strength and burst pressure is essential necessary for high transportation requirements. In this work, biaxially oriented PE/ultrahigh molecular weight polyethylene (PE/UHMWPE) blend pipes were fabricated on self-made pipe solid-phase die drawing apparatus. Due to formation of chain entanglement network and enhanced viscoelasticity, incorporation of UHMWPE chains improved stretchability and biaxial orientation degree of blend pipe. During die drawing, formation of more miscible blend system make long UHMWPE chains be sufficiently stretched under load, and such extended-chain conformation of UHMWPE acted as shish structure and induced short PE chains to array orderly and form kebab crystals. With increasing axial draw ratio, the lamellae remarkably deviated from hoop to axial direction, while the blend pipe exhibited higher crystallinity and orientation degree than that of PE pipe, presenting a more uniform and dense biaxial orientation structure with shish-kebab crystals. As a result, the blend pipe showed roughly 99% increase in tensile strength along hoop direction and 25% increase in burst pressure, respectively. Such biaxial self-reinforced PE/UHMWPE blend pipes exhibit promising application prospect as high-pressure transportation pipelines in civil engineering. [ABSTRACT FROM AUTHOR]

This paper is a continuation of two recent publications on crack growth in viscoelastic media. It provides further theoretical results for large strains that enable prediction of crack opening displacement for comparison with experimental data in the region of the singularity. In order to achieve good agreement with experiment it was necessary to account for far-field viscoelasticity. Additionally, it is found that with large deformation throughout the singularity, the deformation consists of simple shearing and stretching normal to the crack plane. Thus, there is no significant displacement parallel to the crack plane; such simplicity exists for materials that stiffen or soften at high strains if the stress obeys a power law in strain at high strains. This finding means that, despite the frame-dependence of the theory, there is no local rotation in the singularity to affect the stress. [ABSTRACT FROM AUTHOR]

In computational models of microchannel flows, the Helmholtz–Smoluchowski slip velocity boundary condition is often used because it approximates the motion of the electric double layer without resolving the charge density profiles close to the walls while drastically reducing the computational effort needed for the flow model to be solved. Despite working well for straight channel flow of Newtonian fluids, the approximation does not work well for flow involving complex fluids and spatially varying surface potential distribution. To treat these effects using the slip velocity boundary condition, it is necessary to understand how the surface potential and fluid properties affect the slip velocity. The present analysis shows the existence of a modified electroosmotic slip velocity for viscoelastic fluids, which is strongly dependent upon Deborah number and viscosity ratio, and this modification differs significantly from the slip velocity of Newtonian fluids. An augmentation of fluid elasticity results in an asymmetric distribution of slip velocity. Nonintuitively, the modulation wavelength of the imposed surface potential contributes to changing the slip velocity magnitude and adding periodicity to the solution. The proposed electroosmotic slip velocity for viscoelastic fluid can be used in computational models of microchannel flows to approximate the motion of the electric double layer without resolving the charge density profiles close to the walls. [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]

The unloading effects induced by rock excavation on high slopes are significant, and a prestressed anchor cable is an effective reinforcement method for high-slope safety. In this work, we consider the interaction between rock creep in high slopes and the changing anchoring force of prestressed cables. We then derive theoretical solutions for the unloading rock creep and anchoring force of prestressed cables considering the coupling effect, and verify the solutions using numerical simulation. First, based on the Boussinesq problem in elastic mechanics, we simplify the problem of slope reinforcement with a single prestressed anchor cable to the problem of a concentrated force acting on a boundary of a semiinfinite medium. The concentrated force is affected by the excavation unloading effect from the slope and the anchoring forces from the anchor cables. Based on this simplification, we derive elastic solutions for the slope unloading displacement after excavation and for the anchoring force of prestressed cables. Secondly, considering rock-creep behavior and varying anchoring force, the Burgers model is used for rock masses and the elastic model is used for anchor cables. According to the coordinated deformation between rock masses and anchor cables, we obtain the analytical solutions for the rock displacement and for the anchoring force of the cables under the coupling action in the Laplace space, based on which the viscoelastic solutions for the rock displacement and for the anchoring force considering the coupling effect are solved by the Laplace inverse transform. Finally, we validate the analytical solutions by comparing against numerical simulation results with FLAC3D. A good agreement is achieved, suggesting the fidelity of the analytical solutions. The theoretical model provides a reference for studying slope reinforcement, analyzing slope rock-creep behavior and the long-term prestress of the reinforcement structure. [ABSTRACT FROM AUTHOR]

Extended-duration cyclic loading of the spine is known to be correlated to lower back pain (LBP). Therefore, it is important to understand how the loading history affects the entire structural behavior of the spine, including the viscoelastic effects. Six human spinal segments (L4L5) were loaded with pure moments up to 7.5 Nm cyclically for half an hour, kept unloaded for 15 min, and loaded with three cycles. This procedure was performed in flexion-extension (FE), axial rotation (AR), and lateral bending (LB) and repeated six times per direction for a total of 18 h of testing per segment. A Long Short-Term Memory (LSTM) Recurrent Neural Network (RNN) was trained to predict the change in the biomechanical response under cyclic loading. A strong positive correlation between the total testing time and the ratio of the third cycle to the last cycle of the loading sequence was found (BT: τ = 0.3469, p = 0.0003, RT: τ =0.1988, p = 0.0377). The moment-range of motion (RoM) curves could be very well predicted with an RNN ( R 2 =0.988), including the correlation between testing time and testing temperature as inputs. This study shows successfully the feasibility of using RNNs to predict changing moment-RoM curves under cyclic moment loading. [ABSTRACT FROM AUTHOR]

This article concerns with the study of propagation of torsional surface waves in dry sandy layer sandwiched between upper inhomogeneous half space and lower pre-stressed viscoelastic half space with non-planer boundaries. Exponential variation of inhomogeneity is taken in upper half space. Displacement components in the dry sandy layer, upper inhomogeneous half space and lower pre-stressed viscoelastic half space are found in closed form and used to derive the complex velocity equation under the suitable boundary condition using the separation of variable technique. The real part of complex velocity equation gives the dispersion relation in terms of implicit function of relevant parameters that affect the resultant torsional velocity. Four particular cases have been deduced to compare the dispersion relation obtained for the present work for validation purpose. The significant effect of inhomogeneity, corrugated boundaries, initial stress, sandiness and viscoelasticity on the phase velocity of considered torsional surface waves has been numerically simulated for a specific model and demonstrated through different graphs. [ABSTRACT FROM AUTHOR]

In a bounded domain, we consider a viscoelastic Euler–Bernoulli equation called also viscoelastic plate equation, with logarithmic nonlinearity source in the right-hand side, u tt + Δ 2 u - ∫ 0 t g (t - s) Δ 2 u (s) d s + h (u t) = | u | γ - 2 u ln | u | , where γ > 2 and the relaxation function g satisfied g ′ (t) ≤ - ξ (t) H (g (t)) , ∀ t > 0 , where H is an increasing and convex function near the origin and ξ is a nonincreasing function. In present of a nonlinear feedback on a part of the boundary, we establish, with certain initial data, a general decay results, using the multiplier method and some properties of the convex functions. Our new results generalize and significantly improve earlier results in the literature, in particular, the result of Al-Gharabli et al. (Commun Pure Appl Anal 18(1): 159–180, 2019), Al-Gharabli et al. (Math Comput Appl 27: 10, 2022), Mustafa (Evol Equ Control Theory 6(2): 61–276, 2017) and Cavalcanti et al. (J Differ Integral Equ 17: 495–510, 2004). [ABSTRACT FROM AUTHOR]

The rheology of sputum is viewed as a powerful emerging biophysical marker for monitoring muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and non-CF bronchiectasis (NCFB). However, there is no unified practice to process sputa from collection to analysis, which can lead to highly variable, and sometimes inconsistent results. The main objective of this study is to bring light into the handling of sputum samples to establish a standardised and robust protocol before rheological measurements. Sputum collected from 22 CF and 10 NCFB adults, was divided into control (vortexed and fresh: non-heated and non-frozen) and three treated conditions (either non-vortexed, heated or frozen). In addition, 6 CF expectorations were used to study the dynamics of ageing over 24 h. Sputum's mechanical properties were measured with a rotational rheometer to obtain their properties at rest, elastic ( G ′ ) and viscous moduli ( G ′ ′ ), and at the onset of flow, critical deformation ( γ c ) and critical stress ( σ c ). We demonstrate that heating sputum is completely destructive while freezing sputa at - 80 ∘ C has no discernible effect on their rheology. We also show that the variability of rheological measurements largely resulted from the sample's macroscopic heterogeneity, and can be greatly reduced by non-destructive vortex homogenisation. Finally, we observed contrasted ageing effects as a fonction of purulence: while the viscoelasticity of purulent samples reduced by half within 6 h after collection, semi-purulent samples did not evolve. These results guide towards a robust unified protocol for simple sputum handling in rheometry. We therefore suggest to vortex and snap freeze sputum samples immediately after collection when direct testing is not possible. [ABSTRACT FROM AUTHOR]

The prime thrust of this proposed mathematical model is to investigate on Love type wave propagation in a visco-porous piezoelectric waveguide with complex fluid loaded on its surface, with loosely bonded common interfaces. To describe the fluid viscoelasticity the Maxwell and Kelvin–Voigt equations are incorporated, with the aid of varying Deborah number. Solving the equation of motion for different media, namely, complex fluid layer, visco-porous piezoelectric waveguide layer, and porous half-space, a direct Sturm–Liouville problem has been formulated, which is a salient feature of this analysis. Employing suitable boundary conditions an accurate generalized complex dispersion equation is derived. To validate the results, comparison has been done with a pre-established study as a particular case, and a strong agreement is revealed. Effect of several parameters viz. fluid viscosity (glycerol concentration), fluid layer thickness, waveguide layer thickness, and bonding parameters, on the phase velocity and attenuation of Love type wave has been delineated by means of graphs. The effect of glycerol concentration and thickness of the complex fluid layer is among the key outcome of the study. It is established that Kelvin–Voigt fluid model is most appropriate when the glycerol concentration is high, as compared to other models, in the case of rapid simulation, while the Newtonian fluid model may be preferred for problems involving varying thickness of the medium. The findings of this study may be utilized in the optimal design and development of viscosity sensors Love wave fluid sensing devices. [ABSTRACT FROM AUTHOR]

There is a growing need to develop accurate nonlinear viscoelastic material models and tools that could describe the complex nonlinear behavior of being developed composite material systems at their simulations at high loads and temperatures or to move the industry towards more sustainable bio-based alternatives. Developing such models in 3D formulation for materials with changing material state due to physical aging, change of crystallinity or degree of cure is also imperative since the loading is mostly multiaxial in real-live applications and manufacturing processes. The present paper contains the derivation of two material models with varying complexity and accuracy. The incremental procedure for implementation of the nonlinear viscoelastic material model within the numerical analysis was presented. Two relatively simple simulations with the incremental methodology developed were performed, namely triaxial mechanical loading and thermal stress development during the manufacturing process. The results obtained showed significant differences between stresses calculated using 1D and 3D simulations. Significantly higher stresses obtained in 3D simulations demonstrated the necessity of 3D models. [ABSTRACT FROM AUTHOR]

Intra-articular viscoelastic supplements are commonly administered by musculoskeletal radiologists for the treatment of symptomatic osteoarthritis (OA). This article provides an overview of the putative mechanism of action of the agents, a brief review of the evidence base underlying the practice, a commentary on some of the major society guidelines regarding the treatment, and a description of the adverse events that are associated with intra-articular hyaluronic acid administration. [ABSTRACT FROM AUTHOR]

A ternary blend of poly(L-lactic acid) (PLA), poly(ε-caprolactone) (PCL) and poly(vinyl acetate) (PVAc) was melt compounded with an aim to obtain novel biodegradable blends with a balance of performance. We systematically studied the relationship between the microstructure and macroscopic properties of the ternary blends. PVAc was miscible with both PLA an PCL. It was interesting that PVAc was selectively located in the PLA matrix of PLA/PCL/PVAc ternary blends, which significantly affected the crystallization behavior, mechanical and rheological properties, and enzymatic hydrolysis rate of the blends. The inhibited crystallization of PLA was achieved, whereas the crystallization of PCL was not affected by incorporating PVAc. Unexpectedly, increases of 10%, 17% and 26% were achieved in the yield strength, breaking strength and modulus of the ternary blend with 20 wt% PVAc compared to PLA/PCL binary blend, while the elongation at break maintained above 300%. Moreover, the rheological properties was enhanced and enzymatic hydrolysis rate was decelerated by introduction of PVAc. The excellent stiffness − toughness balance coupled with the enhanced melt viscoelasticity of the blends will help to expand the property range and processing methods of biodegradable polymers. [ABSTRACT FROM AUTHOR]

A fracture energy-based constitutive model of concrete in the framework of continuum damage mechanics is formulated. Elastic, viscoelastic, and viscoplastic mechanisms are defined in a fictitious undamaged material state, the so-called effective configuration. A linear spring and a linear dashpot characterize the viscoelastic response of concrete. The viscoplastic behavior is also described using a linear spring, a nonlinear dashpot, and a slider with constant frictional resistance. The nonlinear dashpot of the viscoplastic body is formulated using a logarithmic function so that the model can reproduce valid strength magnifications under a wide range of strain rates. As a result, a consistency viscoplastic approach is obtained wherein, in contrast to the so-called overstress viscoplastic laws, the rate effects are induced in the yield surface of the model. A fracture energy-based regularization is employed to adjust the rate of damage growth to obtain mesh-objective results. The directional degradation of concrete is also characterized by a frame-independent tensorial description of damage. Next, a fully implicit return-mapping algorithm based on the Newton–Raphson scheme is proposed. The presented model is then assessed by validating its results with a series of experimental tests. In addition, the mixed-mode fracture of concrete is investigated under different strain rates, verifying the experimentally observed transition of the failure mode from a ductile flexural to a brittle diagonal failure. [ABSTRACT FROM AUTHOR]

The occurrence of barite sag in drilling fluids has relatively often been the cause for gas kicks in oilwell drilling. The subsequent absorption of gas into drilling fluid could lower the density and reduce the viscosity of the drilling fluid, thereby aggravating both pressure control and hole cleaning. In this paper, we present experimental measurements of rheological properties and barite sag in a typical North Sea oil-based drilling fluid at downhole pressure and temperature conditions. A new experimental apparatus was setup for barite sag measurements at static condition with operational temperature and pressure capabilities up to 200 °C (392°F) and 1000 bar (14,503.8 psi), respectively. Rheometry measurements were conducted on fluid samples with and without barite particles at operating conditions up to 90 °C and 100 bar. We observed that at a typical shear rate of 250 s−1, which is experienced in 8.5″ hole annulus, the viscosity of fluid sample with barite increased nearly three times as that of the fluid sample without barite as the temperature and pressure increased. However, temperature effect on viscosity dominates at high shear rates compared to pressure effect. Furthermore, the fluid samples showed more shear-thinning effect with increasing yield stress as the temperature increased. On the other hand, barite sag measurements revealed that whereas fluid samples under high pressure are less prone to sag, high temperature fluid samples, however, promote sag significantly. The data from this study are useful to validate extrapolations used in computational models and to improve understanding and operational safety of sag phenomena at downhole conditions. We also discuss the importance of this study in optimizing drilling operations. [ABSTRACT FROM AUTHOR]

We present an experimental investigation of the linear viscoelasticity for a series of covalent adaptable network (CAN) polymers of β-amino esters possessing tertiary amines at the β position of ester linkages. CAN polymers were synthesized by aza-Michael addition from di-acrylate monomers with or without β-hydroxyl groups using a tri-amine cross-linker. The prepared CAN polymers exhibited dissociative-type bond exchanges by aza-Michael reaction. The additional inclusion of β-hydroxyl group endowed them with associative-type bond exchanges by transesterification. Time–temperature superposition (TTS) was used to construct pseudo-master curves of storage, loss, and stress-relaxation moduli over wide timescales. The results showed that without transesterification, the slow kinetics of aza-Michael reaction considerably retarded terminal relaxation. The introduction of transesterification accelerated terminal relaxation rates but did not modify the overall broadness of terminal relaxation modes. Horizontal shift factors displayed Williams–Landel–Ferry (WLF) dependence below 120 °C but Arrhenius dependence above 120 °C. The former was due to slow segmental dynamics, whereas the latter reflected the characteristic of exchange reaction kinetics. In addition, we also compared and discussed two definitions of topology freezing transition temperature, an important concept for associative-type CANs. Conclusively, the topology freezing transition temperature obtained from the transition of shift factors (WLF → Arrhenius) was a more practical definition for the potential processing and applications of CAN polymers. [ABSTRACT FROM AUTHOR]

We derive a fully-discrete finite element scheme to a fractional Timoshenko beam model, which characterizes the mechanical responses of viscoelastic beams, thick beams and beams subject to high-frequency excitations by properly considering the effects of both transverse shear and rotational inertia. We prove high-order regularity of the solutions to the model and then accordingly prove error estimates of the numerical scheme. Numerical experiments are performed to substantiate the numerical analysis results and to demonstrate the effectiveness of the fractional Timoshenko beam model in modeling the mechanical vibrations of different beams, in comparison with its integer-order analogue and the widely-used integer-order and fractional Euler-Bernoulli beam models. [ABSTRACT FROM AUTHOR]

Magnetorheological finishing (MRF) is an important technique to achieve the surface precision of difficult-to-cut materials. In this paper, a wheel-type vibration-magnetorheological compound finishing is proposed in terms of reducing the unidirectional scratch caused by the wheel-type magnetorheological finishing tool and further improving the convergence rate of surface roughness. The vibration-magnetorheological coupling was realized through utilizing designed magnetorheological finishing (MRF) wheel and a nonresonant vibrational device (NRVD). Through the theoretical and experimental analysis, the surface roughness has been verified improved through increasing the normal and tangential forces, which are associated with introducing 2D vibration. The flow and viscoelastic models of the MRP fluid were established based on hydrodynamic lubrication and viscoelasticity theories. Finally, the feasibility of the proposed finishing method was verified by the results of improving surface roughness through designing reasonable processing experiment. [ABSTRACT FROM AUTHOR]

Histotripsy is a technique that uses sound waves to create cavitation microbubbles which are used in the liquefaction of tumor tissue cells. High-intensity ultrasonic waves perform the production of small vacuum microbubbles or microcavities in the liquid during the low-pressure cycle. In this work, we present the theoretical study and mathematical modeling of microbubble dynamics in histotripsy, based on the modified Keller–Miksis equation in viscoelastic biotissues. The neo-Hookean model of viscoelastic tissue (i.e., viscosity and Young modulus) is used in the formulation of the proposed study. Effect of variation in viscosity, tissue elasticity modulus and the polytropic exponent is taken into account which is applicable for the case of the rapid evolution of bubble size during histotripsy. The model is analytically solved by the modified Plesset–Zwick method, based on the initial and boundary conditions of microbubble. The given results suggest that our proposed strategy to determine the radius of microbubble cavitation with the different viscoelasticity effects through the process of microbubble dynamics plays a highly significant role on histotripsy in hydrogel. Finally, these findings enhance our comprehension of how histotripsy affects tissue with various mechanical qualities and offer a solid foundation for investigating the physical parameters in tissue fractionation. [ABSTRACT FROM AUTHOR]

We investigate the impact of viscoelastic tidal deformation of the Moon on the motion of a polar orbiter. The dissipative effects in the Moon's interior, i.e., tidal phase lags, are modeled as Fourier series sampled at given frequencies associated with linear combinations of Delaunay arguments, the fundamental parameters describing the lunar motion around the Earth and the Sun. We implement the tidal model to evaluate the temporal lunar gravity field and the induced perturbation on the orbiter. We validate the numerical scheme via a frequency analysis of the perturbed orbital motion. We show that, in the case of the Lunar Reconnaissance Orbiter at a low altitude of less than 200 km, the main lunar tides and hence the potential Love numbers around the monthly and some multiple frequencies are dynamically separable. The omission of those effects in practice introduces a position error at the level of a few decimeters within 10 days. [ABSTRACT FROM AUTHOR]

Abstract—This paper studies instability of a heavy inclusion in the Earth's upper layers by the linear theory method for small perturbations. The existence of such inclusions with increased density is associated with chemical inhomogeneity or phase transitions. The viscoelasticity of the geomaterial is described by the Maxwell rheological model. Two layouts of the inclusion with increased density are considered. The heavy inclusion in the cold upper elastic layer of the crust does not change its location under small perturbations, i.e., it is stable according to the linear theory. The heavy inclusion which is located in the hot viscous crustal layer underlying the upper cold layer, is unstable (slowly sinking into the underlying viscous mantle layers). [ABSTRACT FROM AUTHOR]

We present a complete characterization of the (uniform) exponential stabilization for a class of viscoelastic models under small delay perturbations. The main ingredient under consideration is the notion of admissible kernels. While in the standard literature it is mostly common to request a exponential/general kernel as a sufficient condition for the exponential/general stability of the whole viscoelastic system under study, here our objective is to employ the much more general concept of admissible kernels and prove that it is not only sufficient but also a necessary assumption for exponential stability in linear viscoelasticity under small delay perturbations. [ABSTRACT FROM AUTHOR]

The explicit formulas for calculating the components of the effective tensor of relaxation kernels of a two-phase layered medium with a periodic microstructure are derived. The first phase of such a medium consists of an isotropic viscoelastic material and the second phase consists of a viscous incompressible fluid. In particular, it is established that the components of this tensor depend on the volume fraction of the fluid inside a periodicity cell and do not depend on the number of layers and the distances between them. [ABSTRACT FROM AUTHOR]

Flutter is an important instability in aeroelasticity. In this work,we derive a model for this phenomenon which naturally leads to an equation similar to a van der Pol oscillator in which the friction term is given by a fractional derivative. Motivated by these considerations,we study a fractional van der Pol oscillator and show that it exhibits a Hopf bifurcation. The model is based on a one-dimensional reduction where the instabilities associated with flutter are preserved. However, due to the fractional derivative, the bifurcation analysis differs from the standard case. We present both analytical and numerical results and discuss the implications to aerodynamics. Additionally, we contrast our qualitative results with experimental data. [ABSTRACT FROM AUTHOR]

Given a positive operator A on some Hilbert space, and a nonnegative decreasing summable function μ , we consider the abstract equation with memory u ¨ (t) + A u (t) - ∫ 0 t μ (s) A u (t - s) d s = 0 modeling the dynamics of linearly viscoelastic solids. The purpose of this work is to provide numerical evidence of the fact that the energy E (t) = (1 - ∫ 0 t μ (s) d s) ‖ u (t) ‖ 1 2 + ‖ u ˙ (t) ‖ 2 + ∫ 0 t μ (s) ‖ u (t) - u (t - s) ‖ 1 2 d s of any nontrivial solution cannot decay faster than exponential, no matter how fast might be the decay of the memory kernel μ . This will be accomplished by simulating the integro-differential equation for different choices of the memory kernel μ and of the initial data. [ABSTRACT FROM AUTHOR]

Dielectric elastomers (DEs) are widely used in soft actuation and sensing. Current DE actuators require high driving electrical fields because of their low permittivity. Most of DE actuators and sensors suffer from high viscoelastic effects, leading to high mechanical loss and large shifts of signals. This study demonstrates a valuable strategy to produce polyvinyl chloride (PVC)-based elastomers with high permittivity and low viscoelasticity. The introduction of cyanoethyl cellulose (CEC) into plasticized PVC gel (PVCg) not only confers a high dielectric permittivity (18.9@1 kHz) but also significantly mitigates their viscoelastic effects with a low mechanical loss (0.04@1 Hz). The CEC/PVCg actuators demonstrate higher actuation performances over the existing DE actuators under low electrical fields and show marginal displacement shifts (7.78%) compared to VHB 4910 (136.09%). The CEC/PVCg sensors display high sensitivity, fast response, and limited signal drifts, enabling their faithful monitoring of multiple human motions. Dielectric elastomers (DEs) are widely used in soft actuators but existing DE actuators often require high driving electrical fields. Here the authors demonstrate that introducing cyanoethyl cellulose into plasticized PVC gel confers high dielectric permittivity and allows the fabrication of elastomer actuators with high permittivity and low viscoelasticity [ABSTRACT FROM AUTHOR]

In this paper, the propagation of a Rayleigh-type wave is explored in a half-space of an incompressible nematic elastomer with a uniform director aligned orthogonal to the surface. The nematic elastomer is idealized so as to fit within the framework of linear viscoelasticity theory. The governing equations of nematic elastomers are subjected to the Tiersten-type impedance boundary conditions. An explicit secular equation of the Rayleigh wave is obtained which depends upon the non-dimensional anisotropy parameter, impedance parameters, frequency, rubber relaxation time, director rotation times, and the dynamic soft elasticity of nematic elastomers. The numerical computations of the Rayleigh wave speed are restricted for the case of ideal nematic rubbers. The Rayleigh wave speed is illustrated graphically to observe the effects of non-dimensional anisotropy parameter, frequency, impedance parameters, rubber relaxation time, and director rotation times. [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]

Nanocomposite hydrogels were elaborated by the addition of citrated magnetic nanoparticles (MNPs) in sodium alginate aqueous solutions ionically crosslinked by in situ release of calcium ions from calcium carbonate (CaCO3) with gradual hydrolysis of d-glucono-δ lactone (GDL). The sol-gel transition was studied by time-resolved mechanical spectroscopy (TRMS) in the linear viscoelastic region. The power law frequency dependence of the storage and loss moduli allowed to determine the gelation time (tg), the power law relaxation exponent (Δ), and the gel stiffness (S) at the critical gel (gel at tg) for different calcium and MNP concentrations. The effect of an applied magnetic field on these parameters was also studied for the first time. The obtained results show an effect of the concentration of both calcium and MNPs on the kinetics (tg) and properties at the critical gel (S and Δ) obtaining faster kinetics and harder critical gels for higher calcium and lower MNP concentrations. Moreover, the application of the magnetic field allows to modulate the viscoelastic properties before the gel point, but no effect was observed on the structural properties of the critical gel. Finally, this work highlights how the shear viscoelastic, compressive, and swelling properties of totally gelled nanocomposite hydrogels can be successfully modulated when MNPs are introduced in the calcium alginate matrices with a good agreement between all these properties and with the properties of the critical gels. [ABSTRACT FROM AUTHOR]

Stress-relaxation and creep experiments of TB991 weld sealant were conducted at different temperatures. The effects of temperature and strain rate on the uniaxial tensile-deformation behavior were investigated. The experimental results demonstrated that the deformation behavior of the weld sealant was nonlinear. The stress-relaxation curves were close to each other, and the creep phenomenon of the materials was pronounced with increasing temperature. Further, the deformation behavior of the material exhibited a rate dependence below the glass-transition temperatures ( T g ), while the rate dependence was not significant as the temperature exceeded T g . A nonlinear viscoelastic damage constitutive model was used to describe the tensile-deformation behavior of TB991 weld sealant, and the damage-softening function in the constitutive model was modified. The comparison between the model prediction and the experimental results demonstrated that the modified constitutive model can well describe the tensile-deformation behavior of TB991 weld sealant under different temperatures and strain rates. [ABSTRACT FROM AUTHOR]

We obtain effective viscoelasticity coefficients for a heterogeneous medium based on a generalized derivative formalism that reflects internal boundaries in the heterogeneous medium. A solution is sought for the homogenized Green's function of the resulting modified operator taking into account the homogenization and subsequent analysis of the operator. Based on the obtained solution of the many-body problem in a heterogeneous medium, the effective viscoelasticity coefficients integrally take into account the microstructure of the system (physical properties and characteristic phase sizes) in explicit form. [ABSTRACT FROM AUTHOR]

Morphogenesis, tissue regeneration, and cancer invasion involve transitions in tissue morphology. These transitions, caused by collective cell migration (CCM), have been interpreted as active wetting/de-wetting transitions. This phenomenon is considered based on a model system as wetting of a cell aggregate on a rigid substrate, which includes cell aggregate movement and isotropic/anisotropic spreading of a cell monolayer around the aggregate depending on the substrate rigidity and aggregate size. This model system accounts for the transition between 3D epithelial aggregate and 2D cell monolayer as a product of: (1) tissue surface tension, (2) surface tension of substrate matrix, (3) cell–matrix interfacial tension, (4) interfacial tension gradient, (5) viscoelasticity caused by CCM, and (6) viscoelasticity of substrate matrix. These physical parameters depend on the cell contractility and state of cell–cell and cell–matrix adhesion contacts, as well as the stretching/compression of cellular systems caused by CCM. Despite extensive research devoted to study cell wetting, we still do not understand the interplay among these physical parameters which induces an oscillatory trend of cell rearrangement. This review focuses on these physical parameters in governing the cell rearrangement in the context of epithelial aggregate wetting/de-wetting, and on modeling approaches aimed at reproducing and understanding these biological systems. In this context, we not only review previously published biophysical models for cell rearrangement caused by CCM, but also propose new extensions of those models to point out the interrelation between cell–matrix interfacial tension and epithelial viscoelasticity and the role of the interfacial tension gradient in cell spreading. [ABSTRACT FROM AUTHOR]

In this paper, shaped fibers which are especially useful for radiative cooling have been firstly deposited by Electrohydrodynamic direct-writing based on Micro-Weissenberg effect (MWE). At first, The process of pumping viscoelastic fluids (polyethylene oxide) in micro-tube (non-circle nozzle) based on Micro-Weissenberg effect has been studied to reveal the mechanism of Micro-Weissenberg effect. We have found that the pumping based on MWE have obvious periodic fluctuation when the flow rate is small. Then the process of steel pins without small diameter pipes pumping viscoelastic fluid which is a continuous, less wall and controllable pumping manner have been studied in detail. It is found that the pumping based on MWE mainly stem from an interesting capillarity between two pins and the viscoelasticity of fluid. So compare with the traditional Electrohydrodynamic direct-writing, the shaped fibers have been more easily deposited by Electrohydrodynamic direct-writing based on MWE due to the capillarity and the shear thinning in Micro-Weissenberg effect. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the asymptotic stability as well as the wellposedness of the viscoelastic damped wave equation posed on a bounded domain Ω of R 2 , ∂ t 2 u - Δ u + ∫ 0 ∞ g (s) div [ a (x) ∇ u (· , t - s) ] d s + b (x) ∂ t u + f (u) = 0 , in Ω × R + , subject to a locally distributed viscoelastic effect driven by a nonnegative function a(x) which is positive around the entire neighborhood of ∂ Ω and supplemented with a frictional damping b (x) ≥ 0 acting effectively on ∂ A where A = { x ∈ Ω / a (x) = 0 } . Assuming that well-known geometric control condition (ω ′ , T 0) holds, supposing that the relaxation function g is bounded by a function that decays exponentially to zero and the function f possesses an arbitrary growth, we show that the solutions to the corresponding partial viscoelastic model decay exponentially to zero. We can also treat the focusing case for those solutions with energy less than d of the ground state, where d is the level of the Mountain Pass Theorem. [ABSTRACT FROM AUTHOR]