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Biomolecular condensates are viscoelastic materials defined by time-dependent, sequence-specific complex shear moduli. Here, we show that viscoelastic moduli can be computed directly using a generalization of the Rouse model that leverages information regarding intra- and inter-chain contacts, which we extract from equilibrium configurations of lattice-based Metropolis Monte Carlo (MMC) simulations of phase separation. The key ingredient of the generalized Rouse model is a graph Laplacian that we compute from equilibrium MMC simulations. We compute two flavors of graph Laplacians, one based on a single-chain graph that accounts only for intra-chain contacts, and the other referred to as a collective graph that accounts for inter-chain interactions. Calculations based on the single-chain graph systematically overestimate the storage and loss moduli, whereas calculations based on the collective graph reproduce the measured moduli with greater fidelity. However, in the long time, low-frequency domain, a mixture of the two graphs proves to be most accurate. In line with the theory of Rouse and contrary to recent assertions, we find that a continuous distribution of relaxation times exists in condensates. The single crossover frequency between dominantly elastic vs dominantly viscous behaviors does not imply a single relaxation time. Instead, it is influenced by the totality of the relaxation modes. Hence, our analysis affirms that viscoelastic fluid-like condensates are best described as generalized Maxwell fluids. Finally, we show that the complex shear moduli can be used to solve an inverse problem to obtain the relaxation time spectra that underlie the dynamics within condensates. This is of practical importance given advancements in passive and active microrheology measurements of condensate viscoelasticity. [ABSTRACT FROM AUTHOR]

The dynamics of viscoelastic fluids are governed by a memory function, essential yet challenging to compute, especially when diffusion faces boundary restrictions. We propose a computational method that captures memory effects by analyzing the time-correlation function of the pressure tensor, a viscosity indicator, through the Stokes–Einstein equation's analytic continuation into the Laplace domain. We integrate this equation with molecular dynamics simulations to derive necessary parameters. Our approach computes nuclear magnetic resonance (NMR) line shapes using a generalized diffusion coefficient, accounting for temperature and confinement geometry. This method directly links the memory function with thermal transport parameters, facilitating accurate NMR signal computation for non-Markovian fluids in confined geometries. [ABSTRACT FROM AUTHOR]

We consider a cylinder immersed in viscous fluid moving near a flat substrate covered by an incompressible viscoelastic fluid layer, and study the effect of the fluid viscoelasticity on the lift force exerted on the cylinder. The lift force is zero when the viscoelastic layer is not deformed, but becomes non-zero when it is deformed. We calculate the lift force by considering both the tangential stress and the normal stress applied at the surface of the viscoelastic layer. Our analysis indicates that as the layer changes from the elastic limit to the viscous limit, the lift force decreases with the decrease of the Deborah number (De). For small De, the effect of the layer elasticity is taken over by the surface tension and the lift force can become negative. We also show that the tangential stress and the interface slip velocity (the surface velocity relative to the substrate), which have been ignored in the previous analysis, give important contributions to the lift force. Especially for thin elastic layers, they give dominant contributions to the lift force. [ABSTRACT FROM AUTHOR]

We investigate the cross-diffusion on MHD mixed convective thermo-solutal transport in viscoelastic fluid from a nonlinear stretching sheet. The novelty of the work is the analytical evaluation of the nonlinear stretching sheet in a porous medium with a variable magnetic parameter and radiative flux. Also, thermo-solutal transport of a mixed convective flow is analyzed with Dufour and Soret effects in the presence of the chemical reaction, heat source/sink. The governing PDEs are reduced into ODEs by similarity variables. ODEs were tackled analytically using the homotopy analysis method (HAM). The analysis is carried out up to the 15th order of approximation. HAM contains an h-curve, allowing a flexible method of controlling the series solution convergence area. Graphs and tables are plotted to analyze the influence of different parameters on the fluid. Rates of heat and mass flux are depicted using tables. Our results indicate that the increasing viscoelastic flow enhances the boundary layer, and the thermal boundary layer reduces as radiation enhances. The numerical demonstrations of the wall drag coefficient, Nusselt number and Sherwood number have been tabulated. The growing parameters are taken as 0. 5 ≤ M ≤ 2. 0 , 0. 1 ≤ Ri ≤ 0. 7 , 0. 3 ≤ K 0 ≤ 0. 9 , 0. 5 ≤ f w ≤ 2. 0 , 1 ≤ Rd ≤ 4 , 0. 3 ≤ Pr ≤ 0. 9 and 0. 5 ≤ K 2 ≤ 2. 0. [ABSTRACT FROM AUTHOR]

Triply periodic minimal surface (TPMS) structures with excellent properties of stable energy absorption, light weight, and high specific strength could potentially spark immense interest for novel and programmable functions by combining smart materials, e.g. shape memory polymers (SMPs). This work proposes TPMS lattices with hybrid configurations and materials that are composed of viscoelastic and shape-memory materials with the aim to bring temperature-dependent mechanical properties and additional dissipation mechanisms. Different configurations and diverse materials of polylactic acid (PLA), fiber-reinforced PLA, and polydimethylsiloxane (PDMS) are induced, generating five types of TPMS lattices, including (Schoen’s I-WP) IWP uniform lattice, IWP lattice with density gradient, hybrid configurations, hybrid materials, and filled PDMS, which are fabricated by 3D printing. The fracture morphologies and the distribution of carbon fibers are demonstrated via scanning electron microscopy with a focus on the influence of carbon fiber on shape-memory and mechanical properties. Shape recovery tests are conducted, which proves good shape memory properties and reusable capability of TPMS lattice. The combined methods of experiments and numerical simulation are adopted to evaluate mechanical properties, which presents multi-stage energy absorption ability and tunable vibration isolation performances associated with temperature and hybridization designs. This work can promote extensive research and provide substantial opportunities for TPMS lattices in the development of functional applications. [ABSTRACT FROM AUTHOR]

This study examines the stability of double-diffusive convection in a Kuvshiniski viscoelastic nanofluid, in which the fluid is affected by two fields (such as temperature and salinity) that influence its density. The classical Fick’s law, which assumes an immediate response of temperature to the heat flux gradient, is not entirely correct because it suggests an instantaneous reaction at all points, which is not entirely accurate since information propagates at a finite speed. This shortcoming of Fick’s law leads us to consider the Maxwell–Cattaneo effect (MC effect). Thus, our research focuses on Maxwell–Cattaneo double-diffusive convection in a horizontal layer of a porous medium saturated with viscoelastic nanofluid. Here, the fluid’s small dimensions result in its relaxation time being comparable to its thermal diffusion time, necessitating the use of the Maxwell–Cattaneo relationship. The behavior of viscoelastic nanofluids is described by a constitutive equation of the Kuvshiniski kind, and for the porous medium, Brinkman–Darcy model is considered. The nanofluid model includes the effects of Brownian diffusion and thermophoresis, with the assumption that the flux of the nanoparticle volume fraction is zero at the isothermal boundaries. The framework of linear and nonlinear stability theory leads the analysis. By applying linear stability theory with the help of normal mode technique, the conditions for the occurrence of both stationary and oscillatory convective motions are found in terms of a critical thermal Rayleigh number. The Kuvshiniski viscoelastic fluid exhibits Newtonian behavior in a state of stationary convection. We have discussed two cases for oscillatory convection that are when (i) Maxwell–Cattaneo coefficient for temperature (C T ) = 0 and (ii) Maxwell–Cattaneo coefficient for salinity (C C ) = 0. Convective heat and mass transfers are determined using a weakly nonlinear stability analysis. The effects of various factors on oscillatory and stationary states as well as the mass and heat transport are depicted graphically. It is found that with increase in the value of Kuvshiniski parameter F, thermal Rayleigh number Ra also increases for both cases C T = 0 and C C = 0. Ra drops with increasing values of modified diffusivity ratio N A and thermosolutal Lewis number Ls for both stationary as well as oscillatory convection. With increase in the value of Darcy number Da, an interesting pattern can be seen. For stationary convection, Ra increases with Da, but it has reverse effect on oscillatory convection (for both the cases). Streamlines, isotherms, and isohalines are also examined. [ABSTRACT FROM AUTHOR]

We propose an SPH‐based method for simulating viscoelastic non‐Newtonian fluids within a multiphase framework. For this, we use mixture models to handle component transport and conformation tensor methods to handle the fluid's viscoelastic stresses. In addition, we consider a bonding effects network to handle the impact of microscopic chemical bonds on phase transport. Our method supports the simulation of both steady‐state viscoelastic fluids and discontinuous shear behavior. Compared to previous work on single‐phase viscous non‐Newtonian fluids, our method can capture more complex behavior, including material mixing processes that generate non‐Newtonian fluids. We adopt a uniform set of variables to describe shear thinning, shear thickening, and ordinary Newtonian fluids while automatically calculating local rheology in inhomogeneous solutions. In addition, our method can simulate large viscosity ranges under explicit integration schemes, which typically requires implicit viscosity solvers under earlier single‐phase frameworks. [ABSTRACT FROM AUTHOR]

Biomaterials such as spider silk and mussel byssi are fabricated by the dynamic manipulation of intra‐ and intermolecular biopolymer interactions. Organisms modulate solution parameters, such as pH and ion co‐solute concentration, to effect these processes. These biofabrication schemes provide a conceptual framework to develop new dynamic and responsive abiotic soft material systems. Towards these ends, the chemical diversity of readily available ionic compounds offers a broad palette to manipulate the physicochemical properties of polyelectrolytes via ion‐specific interactions. In this study, we show for the first time that the ion‐specific interactions of biomimetic polyelectrolytes engenders a variety of phase separation behaviors, creating dynamic thermal‐ and ion‐responsive soft matter that exhibits a spectrum of physical properties, spanning viscous fluids to viscoelastic and viscoplastic solids. These ion‐dependent characteristics are further rendered general by the merger of lysine and phenylalanine into a single, amphiphilic vinyl monomer. The unprecedented breadth, precision, and dynamicity in the reported ion‐dependent phase behaviors thus introduce a broad array of opportunities for the future development of responsive soft matter; properties that are poised to drive developments in critical areas such as chemical sensing, soft robotics, and additive manufacturing. [ABSTRACT FROM AUTHOR]

This paper is devoted to the analysis of an n -dimensional model which describes thermoviscoelastic materials. With careful use of the standard energy method, we obtain the global existence and asymptotic decay of solutions for n ≥ 1 , provided that the initial data are smooth and sufficiently small in L 2 -Sobolev space. [ABSTRACT FROM AUTHOR]

Attaching viscoelastic materials (VEMs) to structures has been widely used to improve structural dynamic properties. Nevertheless, the adhesion of VEMs inevitably leads to the increase in overall structural mass. Topology optimization is one of the most effective methods to tackle this contradiction. In the traditional topology optimization, VEMs damping cores in constrain layer damping (CLD) sandwich structures are often simplified into linear elastic materials with constant parameters, usually ignoring their frequency-dependent and temperature-dependent dynamic characteristics, which will cause the distortion of the optimization results. Therefore, we propose a topology optimization method for CLD sandwich panels with a frequency-dependent VEM damping core considering steady-state free vibration in this study, where the anelastic displacement fields (ADF) model is adopted to combine the derived frequency-dependent complex constitutive relationship with the layerwise finite element (LFE) model, and the iterative modal strain energy (IMSE) method is used to determine the modal parameters of the CLD sandwich panels. The results of numerical examples show that the proposed method in this study not only has the advantages of simple and intuitive model, high calculation efficiency, and accuracy but also can achieve relatively good dynamic properties of the CLD sandwich structures. [ABSTRACT FROM AUTHOR]

Much attention has been focused on viscoelastic microfluidics which can be widely used for the focusing and separation of particles/cells in continuous flows without any external force or energy. In this study, we demonstrate that microparticles can be separated by the elasto-inertial focusing and the concentration gradient of viscoelastic fluid in a microchannel with a rhombic cross-sectional shape. We have already presented a simple and robust fabrication method for microchannel with the rhombic cross-section, which was used for particle focusing in viscoelastic polyethylene oxide (PEO) solution. Using the fabricated microfluidic device, we observed the behavior of particles by size in viscoelastic fluids with various concentration gradients and presented their focusing and separation. Separation experiments were performed on 12, 5.0, and 2.1 µm particles, and the optimal separation conditions were sought according to flow rate, sample-to-sheath flow rate ratio, and PEO concentration gradient. [ABSTRACT FROM AUTHOR]

In this paper, we study the creep phenomena for self-similar models of viscoelastic materials and derive a generalization of the Kelvin–Voigt model in the framework of fractal continuum calculus. Creep compliance for the Kelvin–Voigt model is extended to fractal manifolds through local fractal-continuum differential operators. Generalized fractal creep compliance is obtained, taking into account the intrinsic time τ and the fractal dimension of time-scale β. The model obtained is validated with experimental data obtained for resin samples with the fractal structure of a Sierpinski carpet and experimental data on rock salt. Comparisons of the model predictions with the experimental data are presented as the curves of slow continuous deformations. [ABSTRACT FROM AUTHOR]

The paper is devoted to the modeling of nonlinear viscoelastic materials. The constitutive equations are considered in differential form via relations between strain, stress, and their derivatives in the Lagrangian description. The thermodynamic consistency is established by using the Clausius–Duhem inequality through a procedure that involves two uncommon features. Firstly, the entropy production is regarded as a positive-valued constitutive function per se. This view implies that the inequality is in fact an equation. Secondly, this statement of the second law is investigated by using an algebraic representation formula, thus arriving at quite general results for rate terms that are usually overlooked in thermodynamic analyses. Starting from strain-rate or stress-rate equations, the corresponding finite equations are derived. It then emerges that a greater generality of the constitutive equations of the classical models, such as those of Boltzmann and Maxwell, are obtained as special cases. [ABSTRACT FROM AUTHOR]

Existing research shows that using waterborne epoxy resin (WER) instead of emulsified asphalt as the binder for cold mix asphalt (CMA) can enhance the rutting resistance, high-temperature performance, fracture performance, and early performance of CMA. In order to eliminate the potential drawbacks such as insufficient strength and low-temperature performance of CMA during application, a novel method was proposed in this study for the preparation of waterborne epoxy-acrylate resin (WER), specifically tailored to modify emulsified asphalt, resulting in waterborne epoxy-acrylate resin emulsified asphalt (WEREA). The modification effect of WER on emulsified asphalt was evaluated through rheological tests and direct tensile tests. A modified design method based on the conventional Marshall design method was proposed to determine the optimal mix proportions, including the key parameters of specimen compaction and curing. The results revealed that the incorporation of WER led to a substantial improvement in the complex shear modulus and a concurrent decrease in the phase angle. When the temperature exceeded 60 °C, the phase angle exhibited a diminishing trend, indicative of a reduced viscosity as temperatures escalated. As the WER content increased, a decrease in the direct tensile strain rate was observed, accompanied by a substantial elevation in direct tensile strength. At various stress levels, the shear strain of WEREA decreases with increased content of WER, indicating that the incorporation of WER can enhance the hardness of emulsified asphalt and improve its deformation resistance. The results from MSCR tests indicate that WER could significantly improve the elasticity and hardness of emulsified asphalt, transitioning it from a viscoelastic material to an elastic material, thereby improving its deformation resistance, resistance to rutting, and high-temperature performance. The results of fatigue life are consistent with those of the amplitude sweep, both reflecting the improvement of resistance to deformation of emulsified asphalt by WER. This indicates that WER has a significant improving effect on the fatigue resistance of emulsified asphalt. Furthermore, the Marshall design tests further confirmed the advantages of WEREA in asphalt mixtures. The optimal preparation for the WEREA mixture was proposed as follows: double-sided compaction for 50 times each, aging at 60 °C for 48 h, optimal moisture content of 5.14%, cement content of 2.5%, and emulsion content of 8.4%. The optimal mix proportions identified through these tests yielded asphalt mixtures with significantly improved stability, reduced flow value, and enhanced rutting resistance compared to the hot-mix asphalt mixture (HMA) of AC-16. These findings suggest that WEREA has the potential to significantly enhance the durability and longevity of asphalt pavements. For future applications, it can be explored for use in producing cold recycled asphalt mixtures. In addition to designing the WEREA mixture according to AC-16 gradation, consideration can also be given to using a gradation with a smaller nominal maximum aggregate size for the application in the surface layer or ultra-thin wearing course. [ABSTRACT FROM AUTHOR]

Relaxation time and frequency spectra are not directly available by measurement. To determine them, an ill-posed inverse problem must be solved based on relaxation stress or oscillatory shear relaxation data. Therefore, the quality of spectra models has only been assessed indirectly by examining the fit of the experiment data to the relaxation modulus or dynamic moduli models. As the measures of data fitting, the mean sum of the moduli square errors were usually used, the minimization of which was an essential step of the identification algorithms. The aim of this paper was to determine a relaxation spectrum model that best approximates the real unknown spectrum in a direct manner. It was assumed that discrete-time noise-corrupted measurements of a relaxation modulus obtained in the stress relaxation experiment are available for identification. A modified relaxation frequency spectrum was defined as a quotient of the real relaxation spectrum and relaxation frequency and expanded into a series of linearly independent exponential functions that are known to constitute a basis of the space of square-integrable functions. The spectrum model, given by a finite series of these basis functions, was assumed. An integral-square error between the real unknown modified spectrum and the spectrum model was taken as a measure of the model quality. This index was proved to be expressed in terms of the measurable relaxation modulus at uniquely defined sampling instants. Next, an empirical identification index was introduced in which the values of the real relaxation modulus are replaced by their noisy measurements. The identification consists of determining the spectrum model that minimizes this empirical index. Tikhonov regularization was applied to guarantee model smoothness and noise robustness. A simple analytical formula was derived to calculate the optimal model parameters and expressed in terms of the singular value decomposition. A complete identification algorithm was developed. The analysis of the model smoothness and model accuracy for noisy measurements was carried out. The equivalence of the direct identification of the relaxation frequency and time spectra has been demonstrated when the time spectrum is modeled by a series of functions given by the product of the relaxation frequency and its exponential function. The direct identification concept can be applied to both viscoelastic fluids and solids; however, some limitations to its applicability have been pointed out. Numerical studies have shown that the proposed identification algorithm can be successfully used to identify Gaussian-like and Kohlrausch–Williams–Watt relaxation spectra. The applicability of this approach to determining other commonly used classes of relaxation spectra was also examined. [ABSTRACT FROM AUTHOR]

This research aims to enhance industrial processes and address environmental issues by studying the effects of suction and injection on the Couette flow of a viscoelastic dusty fluid over a porous oscillating plate in a rotating frame. We investigate how these factors influence fluid flow, heat, mass, and temperature transfer rates. Suction and blowing are common techniques for controlling fluid flow in conduits. The study considers the impact of the right plate's oscillation on fluid velocity along the x‐axis, as well as mass diffusion and thermal effects from the heating of the right plate. Due to the rotation, the velocities of both the fluid and dust particles exhibit complex primary and secondary behaviors. Also considered the dust particles are homogenously distributed in the base fluid. Furthermore, the variable temperature and concentration are associated with boundary conditions. We develop a mathematical model using partial differential equations (PDEs) to describe these phenomena. The governing equations are non‐dimensionalized and transformed into ordinary differential equations (ODEs) using periodic solutions and solved via the Poincare‐Lighthill perturbation method. Key engineering parameters such as the Sherwood number, Nusselt number, and skin friction are calculated. The study reveals the influence of uniform suction/injection on velocity and temperature distributions, showing that suction can significantly alter boundary layer development, even under resonance conditions. The radiation parameter, Grashof number, and second‐grade parameter cause a decrease in skin friction as their values increase. On the other hand, suction, rotation, magnetic, dusty fluid, and Reynold numbers cause a rise in skin friction.The objective of this research is to improve industrial processes and tackle environmental issues by examining the effects of suction and injection on the Couette flow of a viscoelastic dusty fluid over a porous oscillation plate in a rotating frame. The purpose of this study is to determine how suction/injection influences the Couette flow of a viscoelastic dusty fluid, as well as the heat, mass, and temperature transfer rates across a porous, oscillating plate in a rotating frame. It also takes heat transfer into account. When manipulating the flow of a fluid via a conduit, suction and blowing are common methods. As the right plate oscillates, the x‐axis becomes the primary consideration for fluid velocity. We also take into account the mass diffusion and thermal influence on the flow from the right plate's heating. As a consequence of the spin, the fluid, and dust particles have velocities that are both secondary and primary, making them complicated. Using PDEs, we may translate the aforementioned physical phenomena into a mathematical model of the relevant flow regime. The system of governing equations is non‐dimensionalized by the use of appropriate nondimensional variables. The system of PDEs is transformed into a system of ODEs with the help of assumed periodic solutions and then solved by the perturb solution with the help of Poincare‐Lighthill perturbation methods. We also calculate the Sherwood number, the Nusselt number, and the skin friction, all of which are of relevance to engineers. We also examine how changing these variables affects the velocity distributions of skin friction, viscoelastic fluid, and dust particles. We look at how uniform suction/injection affects the speed and temperature distributions. It is important to note that even in the resonance instance, suction/ injection directs the boundary layer to develop unexpectedly. [ABSTRACT FROM AUTHOR]

[Display omitted] Plant leaves have to deal with various environmental influences. While the mechanical properties of petiole and lamina are generally well studied, only few studies focused on the properties of the transition zone joining petiole and lamina. Especially in peltate leaves, characterised by the attachment of the petiole to the abaxial side of the lamina, the 3D leaf architecture imposes specific mechanical stresses on the petiole and petiole-lamina transition zone. Several principles of internal anatomical organisation have been identified. Since the mechanical characterisation of the transition zone by direct measurements is difficult, we explored the mechanical properties and load-bearing mechanisms by finite-element simulations. We simulate the petiole-lamina transition zone with five different fibre models that were abstracted from CT data. For comparison, three different load cases were defined and tested in the simulation. In the proposed model, the fibres are represented in a smeared sense, where we considered transverse isotropic behavior in elements containing fibres. In a pre-processing step, we determined the fibre content, direction, and dispersion and fed them into our model. The simulations show that initially, matrix and fibres carry the load together. After relaxation of the stresses in the matrix, the fibres carry most of the load. Load dissipation and stiffness differ according to fibre arrangement and depend, among other things, on orientation and cross-linking of the fibres and fibre amount. Even though the presented method is a simplified approach, it is able to show the different load-bearing capacities of the presented fibre arrangements. In plant leaves, the petiole-lamina transition zone is an important structural element facilitating water and nutrient transport, as well as load dissipation from the lamina into the petiole. Especially in peltate leaves, the 3D leaf architecture imposes specific mechanical stresses on the petiole-lamina transition zone. This study aims at investigating its mechanical behavior using finite-element simulations. The proposed continuum mechanical anisotropic viscoelastic material model is able to simulate the transition zone under different loads while also considering different fibre arrangements. The simulations highlight the load-bearing mechanisms of different fibre organisations, show the mechanical significance of the petiole-lamina transition zone and can be used in the design of a future biomimetic junction in construction. [ABSTRACT FROM AUTHOR]

Determining the creep function of viscoelastic pipes is one of the challenges of modeling these pipes to calibrate or determine defects. The present research aims to determine the creep function of viscoelastic pipes using transient flow pressure in the time and frequency domains. For this purpose, the proposed method is first implemented using a numerical example. The numerical part investigated the effect of signal sample size, the number of Kelvin-Voigt (K-V) elements, repeatability, and decision variables. Then, using an experimental test, the desired methodology has been evaluated. In this research, the K-V mechanical model was used to define the creep function, and its parameters, including elastic pressure wave speed, retardation times, and creep complaint coefficients, were calibrated. The results showed that using pressure signals in both time and frequency domains provides stable results for the investigated pipeline. Examining the effect of signal size showed that the creep function can be estimated with reasonable accuracy in the time domain with a few initial cycles. Also, 14.33 dimensionless frequency for a simple reservoir-pipe-valve system can provide accurate results in the frequency domain. The results of this research can be used as a suitable pre-processing to reduce the dimensions of inputs in models based on artificial intelligence. [ABSTRACT FROM AUTHOR]

Maxwell model is one of the most outstanding and widely used models for the description of viscoelastic materials. In this study, we use an efficient meshfree technique based on the Moving Kriging (MK) interpolation for the numerical solution of Magnetohydrodynamic (MHD) flow of fractional Maxwell fluid. In this scheme to discretize this equation in time and space variables, we use the finite difference method and MK interpolation shape functions, respectively. Also, we calculate the local weak form for every node instead of the computation of the global weak form for the global domain. So, we reduce such problems to a system of algebraic equations. To indicate the efficiency of the present scheme, four examples are discussed in various types of domains and with uniform and nonuniform nodal distribution in 2D cases. Also, to show the validity of the method in this example, a comparison with a valid method has been made. Moreover, in the last example, the accuracy of our scheme in the 3D case is illustrated for the fractional telegraph equation. [ABSTRACT FROM AUTHOR]

This theoretical work deals with delamination in U-shaped load-carrying structural members. The latter represent multilayered functionally graded systems of non-linear viscoelastic behaviour. The right-hand vertical part of the structure under consideration is delaminated. The structure is clamped in the lower end of the left-hand vertical part. Besides, the structure is supported by a rotational spring which has non-linear elastic behaviour. The strain energy release rate is derived by using an approach that is based on analysis of equilibrium of the various components of the U-shaped structure. The solution derived is checked-up by applying the method of the integral J. The dependence of the strain energy release rate on different parameters is studied and presented in form of various graphs. Analysis of a U-shaped structural member with two rotational spring supports also is carried-out and the strain energy release rate obtained is compared with that in the U-shaped structure with one rotational spring support. [ABSTRACT FROM AUTHOR]

The injection of viscoelastic fluids into the oil-bearing formations to push the bypassed and entrapped oil toward the producers is a widely accepted technique known for creating a stable displacement front and piston-like displacement, leading to Enhanced Oil Recovery (EOR). However, the sweep efficiency of such complex fluids in stratified formations is still a topic of debate in the literature and is problematic, particularly in harsh reservoir conditions. This research concerns how the inclusion of nanoparticles into the polymer solution could affect the porous media flow of polymeric fluids in multilayered reservoirs. Accordingly, validated core-scale numerical models for polymer flood and polymer nanohybrid flood were upscaled to develop a reservoir-scale model. Through numerical simulations using a compositional reservoir simulator, the simultaneous flow of crude oil and polymer nanohybrids in both low and high-permeable layers of the reservoir were scrutinized. The numerical outputs showed that, compared with polymer flood, the flow dynamics of the polymer nanohybrids in different layers of the reservoir are more favorable, which resulted in improved oil recovery of over 20% of Residual Oil In Place (ROIP). Additionally, our numerical findings indicated that the polymer nanohybrids could exhibit lower polymer adsorption and acceptable salt tolerance in porous media. [ABSTRACT FROM AUTHOR]

Specialized cilia known as ependymal cilia help the cerebrospinal fluid, which is important for nutrient delivery and waste elimination, to circulate in the brain. Many species rely on cilia and flagella for fluid movement and motility. Cilia and flagella, for instance, produce propulsive forces that allow unicellular creatures like Paramecium and Euglena to move through their surroundings. Ciliary transport plays a role in the flow of egg cells, or oocytes, via the fallopian tubes in the female reproductive system. The transfer of the egg towards the uterus is facilitated by the synchronized wave‐like motion produced by the cilia lining the fallopian tubes. Like this, ciliary transport in men aids in the passage of sperm cells via the epididymis. Many scientists and researchers are studying the mechanics of cilia motion and the properties of the viscoelastic fluid layer to develop new treatments and applications in biomedical engineering and for some diseases. Motivated by a wide range of biological applications, the objective of this study is to investigate the heat and mass transfer flow of tri‐layered Newtonian fluids flowing with the help of ciliary beating in a Cartesian coordinate. The fluid is incompressible, and fluid layers are not intermixed. The fluid flow with heat and mass transfer is first modelled in wave and then transmuted into fixed. Solutions for temperature profile, velocity distribution, stresses and concentration distribution are obtained. The influence of incipient parameters is displayed with graphs and plotted with the computational software MATHEMATICA 13.0 in the results section. The key findings obtained from graphs show that the maximum magnitude for temperature and velocity is achieved in the middle layer of fluid whereas in the outer layer concentration profile is maximum. It is predicted that this approach will make an essential contribution to the progress and enhancement of various types of drug delivery systems in the biomedical industry and biomechanics. [ABSTRACT FROM AUTHOR]

Aiming at the functional self-lubricating liquid film assisted in-mold micro assembly molding of the micro universal spherical revolute motion pair, the key technical issue to achieve precise control of its manufacturing accuracy is to clarify the multi field collaborative coupling evolution law among the diameter manufacturing tolerance of the micro assembly interface, viscoelastic thermal fluid solid coupling impact load, the thickness of continuous phase transformation evolution zone, thermal viscoelastic plastic stress, and melt viscoelastic characteristics. The research results indicated that the diameter manufacturing tolerance of the micro assembly interface was controlled by the viscoelastic characteristics of the secondary injection molding melt. When the reference viscosity increased from 2 267 to 15 000 Pa*s, the diameter manufacturing tolerance of the micro assembly interface increased by 72. 7 % from 11 to 19 μm. When the relaxation time increased from 0. 05 to 0. 25 s, the diameter manufacturing tolerance of the micro assembly interface decreased by 38. 7 % from 31 to 19 μm. To meet the industry standard of dimensional manufacturing tolerance technical indicators ≤ 30 μm, it is not advisable to use a high elastic melt with a relaxation time ≤ 0. 05 s for the functional self-lubricating liquid film assisted in-mold micro assembly molding. [ABSTRACT FROM AUTHOR]

To fertilize eggs, sperm must pass through narrow, complex channels filled with viscoelastic fluids in the female reproductive tract. While it is known that the topography of the surfaces plays a role in guiding sperm movement, sperm have been thought of as swimmers, i.e., their motility comes solely from sperm interaction with the surrounding fluid, and therefore, the surfaces have no direct role in the motility mechanism itself. Here, we examined the role of solid surfaces in the movement of sperm in a highly viscoelastic medium. By visualizing the flagellum interaction with surfaces in a microfluidic device, we found that the flagellum stays close to the surface while the kinetic friction between the flagellum and the surface is in the direction of sperm movement, providing thrust. Additionally, the flow field generated by sperm suggests slippage between the viscoelastic fluid and the solid surface, deviating from the no-slip boundary typically used in standard fluid dynamics models. These observations point to hybrid motility mechanisms in sperm involving direct flagellum-surface interaction in addition to flagellum pushing the fluid. This finding signifies an evolutionary strategy of mammalian sperm crucial for their efficient migration through narrow, mucus-filled passages of the female reproductive tract. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of polymer adhesives is influenced by the environmental conditions leading to ageing and affecting the integrity of the material. The polymer adhesives have hygroscopic behaviour and tend to absorb moisture from the environment, causing the material to swell without applying external load. The focus of the work is to investigate the viscoelastic material behaviour under ageing conditions. The constitutive equations and the governing equations to numerically investigate the fracture in swollen viscoelastic material are discussed to describe the numerical implementation. Phase-field damage modelling has been used in numerical studies of ductile and brittle materials for a long time. The finite-strain phase-field damage model is used to investigate the fracture behaviour in aged viscoelastic polymer adhesives. The finite-strain viscoelastic model is formulated based on the continuum rheological model by combining spring and Maxwell elements in parallel. Commercially available post-cured crosslinked polyurethane adhesives are used in the current investigation. Post-cured samples of crosslinked polyurethane adhesives are prepared for different humidity conditions under isothermal conditions. These aged samples are used to perform tensile and tear tests and the test data are used to identify the material parameters from the curve fitting process. The experiment and simulation are compared to relate the findings and are the first step forward to improve the method to model crosslinked polymers. [ABSTRACT FROM AUTHOR]

Bioconvective non-Newtonian fluids with motile microorganisms have diverse applications in biology and medicine, offering numerous research opportunities. This article presents a comprehensive investigation into the non-similar analysis of bio-convective micropolar flow induced by a Darcy-Forchheimer exponentially stretchable sheet, considering the effects of suction/injection and thermal radiation in a three-dimensional framework. The fluid under scrutiny is a viscoelastic tangent hyperbolic nanofluid, the impact of Cattaneo-Christov heat subjected to Riga plate is considered for novelty. The role of activation energy and heat source are also computed. The governing equations of viscoelastic tangent hyperbolic nanofluids are transformed into couple of ordinary differential equations via similarity approximations. The resulting ODEs are tackled numerically via bvp4c tool of MATLAB. The impression of appropriate parameters like magnetic parameter, bio-convection parameter, viscoelasticity parameter suction/injection parameter etc. on involved profiles are computed via graphical and tabulated trends. It is observed that velocity layer f ′ is dwindled for growing value of Forchheimer number Fr , while reverse relation in velocity curve is noted for developing value of mixed convection parameter δ. Micropolar fluids find biomedical engineering applications in modeling blood flow in microvessels, understanding cerebrospinal fluid dynamics, and optimization of biomedical devices and therapies and simulating drug delivery in tissues. [ABSTRACT FROM AUTHOR]

The high temperature co‐curing damping composite was investigated by co‐curing technology to improve the mechanical property and damping performance of the traditional fiber reinforced resin matrix composite. Fluororubber with stable chemical properties and high‐temperature resistance was used as the core layer of novel carbon fiber reinforced bismaleimide resin matrix High‐temperature Co‐curing Damping Sandwich Composites (HCDSC). The curing temperature and curing time of fluororubber were consistent with that of bismaleimide resin by adjusting the formula. The viscoelastic damping properties and thermal stability of zinc methacrylate reinforced fluororubber were investigated in detail. Static mechanical tests, modal tests and interfacial shear tests prove that HCDSC display excellent mechanical and damping properties. The interfacial microscopic analysis reveals that viscoelastic sandwich materials are closely bonded with the composites. The dynamic characteristics of damping sandwich composite plate with fixed support on four sides is analyzed theoretically, and the vibration equilibrium equation of composite plate is derived by combining first‐order shear deformation theory, variational principle, and Hamilton principle. The damping performance of the composite plate are discussed through modal tests to verify the accuracy of theoretical derivation. This research is of great significance to solve the problem of structural dynamics, and provides a new idea for the design of structural and functional composite materials. Highlights: A viscoelastic damping material with large damping and high strength was prepared.The dynamic performance of co‐curing sandwich composite structures was studied.The free vibration of composite structures was explored via experiment and theory. [ABSTRACT FROM AUTHOR]

Roll coating is a popular method for applying a thin coating film to a continuous substrate, such as paper or foil. This study aims to investigate analytically the fluid flow through counter rotating rolls using a non-Newtonian model. The governing equation for the constitutive of the Oldroyd-B as a non-Newtonian fluid with momentum equation has been discovered. The nondimensionalizing of the fluid flow equations is done by using suitable dimensionless parameters. The equations are then simplified by using Lubrication Approximation Theory (LAT) to obtain the solution for various quantities. Analytical solutions for the velocity distribution, pressure and pressure gradients have been obtained by regular perturbation method. Numerical integration has been used to calculate separation point, coating thickness, separation force and power input of the fluid. The effect of involved parameter such as Weissenberg number We and viscosity on velocities, pressure gradient and pressure is presented in a variety of graphs and several other results are shown in tables. It has been observed that as the modified capillary number N C a 2 increases, the separation point moves toward the nip region, whereas the coating thickness declines. It has been witnessed that the We serves as the controlling parameter for flow rate, pressure distribution and power input, whereas for the coating thickness, the separation force increases, which are important for coating industries. [ABSTRACT FROM AUTHOR]

Many biological fluids are composed of suspended polymers immersed in a viscous fluid. A prime example is mucus, where the polymers are also known to form a network. While the presence of this microstructure is linked with an overall non-Newtonian response of the fluid, swimming cells and microorganisms similar in size to the network pores and polymer filaments instead experience the heterogeneous nature of the environment, interacting directly with the polymers as obstacles as they swim. To characterise and understand locomotion in these heterogeneous environments, we simulate the motion of an undulatory swimmer through three-dimensional suspensions and networks of elastic filaments, exploring the effects of filament and link compliance and filament concentration up to 20 % volume fraction. For compliant environments, the swimming speed increases with filament concentration to values approximately 10 % higher than in a viscous fluid. In stiffer environments, a non-monotonic dependence is observed, with an initial increase in speed to values 5 % greater than in a viscous fluid, followed by a dramatic reduction to speeds just a fraction of its value in a viscous fluid. Velocity fluctuations are also more pronounced in stiffer environments. We demonstrate that speed enhancements are linked to hydrodynamic interactions with the microstructure, while reductions are due to the filaments restricting the amplitude of the swimmer's propulsive wave. Unlike previous studies where interactions with obstacles allowed for significant enhancements in swimming speeds, the modest enhancements seen here are more comparable to those given by models where the environment is treated as a continuous viscoelastic fluid. [ABSTRACT FROM AUTHOR]

Steel bridge, as one of the main structural types in bridge design, has been widely used in rail transit. However, the train-induced vibro-acoustic problem of the bridge has become increasingly prominent. The vibration and noise characteristics must be more significant and complex than steel truss bridge because of too many components. Viscoelastic damping materials (VDMs) have the characteristics of both viscous liquid and elastic solid, and have better damping performance than other damping materials. Therefore, VDM plays an important role in vibration and noise reduction technology. In applications, VDM is usually combined with constraining materials to form composite viscoelastic damping materials (CVDM). In this paper, based on the dynamic receptance method and superposition principle, the coupling model of vehicle–track–bridge in the frequency domain is first established, and then the vibration and noise prediction model of a steel truss bridge with CVDM is established based on RUK theory and statistical energy analysis (SEA) method. Based on the prediction model, the natural dynamic characteristics of typical components of steel truss bridges with CVDM were investigated, and the control mechanism and influence rule of CVDM on train-induced vibration and noise of steel bridges were revealed. [ABSTRACT FROM AUTHOR]

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A modified Rayleigh–Lamb equation has been derived which takes account of the radial oscillations of a gas bubble coated with a hyperelastic shell and found in a viscoelastic liquid. The hyperelasticity of the shell is taken account of on the basis of the Mooney–Rivlin model, and the viscoelasticity of the liquid, according to the Zener model in whose particular cases the Kelvin–Voigt and Maxwell models are followed. Numerical calculations have been carried out. An analysis has been made of the influence of the dimension of the bubble′s shell and its rigidity, the shear modulus of the shell and the carrier liquid, and also the difference in rheological models on the radial dynamics of the gas bubble in the external acoustic field. A mathematical model has been constructed which determines the propagation of acoustic waves in the viscoelastic liquid with encapsulated gas bubbles. A study has been made of the difference in rheological models of the elastic carrier liquid, and also of the influence of the shell thickness on the dynamics of acoustic waves. [ABSTRACT FROM AUTHOR]

Dynamic neutralizers, also known as dynamic absorbers, are efficient means of mitigating vibrations in structures. They have been particularly effective in addressing broad-band passive vibration control in structures with high modal density through the use of multi-degrees of freedom (MDoF) and viscoelastic materials (VEMs). Therefore, sandwich-type or constrained-layer beams can offer great potential when used as MDoF control devices. However, there is limited literature exploring these structures as auxiliary systems, with coupling typically assumed to be single-point and limited to only translational degrees of freedom (DoFs). In this context, this article presents a methodology to determine the dynamic behavior of a compound system, coupling the displacement and rotation DoFs between a metal structure–referred to as the primary system–and a MDoF auxiliary system. The coupling is achieved by utilizing an equivalent dynamic stiffness obtained at the base of the auxiliary system through ANSYS finite-element software, providing a robust and comprehensive approach. A Matlab code transfers the auxiliary system's geometry and properties to ANSYS, where the dynamic stiffness at the base is determined and subsequently coupled to the primary system. A MDoF auxiliary system of the constrained-layer type with VEM was studied, and both single-point and distributed coupling were analyzed. The auxiliary system was attached to a cantilever metal beam for numerical and experimental validation. The proposed generalized equivalent dynamic stiffness model accurately estimates the response of the compound system, offering a 25% reduction in response computation time compared to the finite-element model of the complete compound system. This methodology enables the accurate representation of compound system dynamics while minimizing computational time, making it valuable for the optimal design of a set of MDoF viscoelastic dynamic neutralizers. [ABSTRACT FROM AUTHOR]

The basic design of a Love wave (LW) bio-sensor contains the loading of a viscoelastic liquid on top of a layered structure with distinct viscoelastic properties. Changes in the characteristics of the propagating acoustic wave caused by biochemical interactions at the sensing area can be detected at the output Inter digital transducer (IDT). The propagation of the anti-plane (AP) wave is discussed in this work in a layered structure of piezo-flexo-electric (PFE) layer bonded with a PFE half-space having a soft reinforced layer at the interface. The free surface of the PFE layer is loaded with viscous liquid. The viscosity of the loaded liquid introduces losses and results in the damping of the wave. For the formulation of the problem with interface energy, the Gurtin–Murdoch approach is used. Using suitable conditions, a dispersion relation for propagating waves is derived in complex form. On separating the dispersion relation in real and non-real parts, the expressions relating the phase and damp velocities with wave number are derived. The obtained theoretical results are portrayed for the numerical data of PFE materials and distinct data of the interface layer. The obtained results are validated with pre-existing literature. [ABSTRACT FROM AUTHOR]

The force and mechanical power required to maintain the simple harmonic motion (SHM) of the upper circular surface squeezing a viscoelastic fluid film is analyzed. The amplitude of the displacement of the upper surface is very small compared to the gap width as a function of time. The smoothness of the upper and lower surfaces is characterized by the slip model with two constant parameters, a slip length and a critical surface shear stress. The nonlinear convection terms in the momentum equation are neglected since the viscous forces dominate the inertial forces. The acceleration and deceleration terms are retained since the upper plate oscillates harmonically and the velocity in the fluid is strictly periodic. An exact solution of the governing equations is found as a function of the Deborah number, the Womersley number, the slip length, and the critical surface shear stress. A circular region without slip condition, bounded by a time-dependent radius, appears when the shear stress of the fluid does not exceed a critical surface shear stress. In addition, an annular region with slip up to the radius of the disk appears when the critical surface shear stress is exceeded. Our results show that viscoelastic and hydrophobic effects together with the Womersley number and a critical surface stress cause changes in the amplitude and phase lag of the waveform of the time-dependent radius and the force acting on the wall surface to maintain the SHM of the upper disk. [ABSTRACT FROM AUTHOR]

We introduce a class of continuum mechanical models aimed at describing the behavior of viscoelastic fluids by incorporating concepts originated in the theory of solid plasticity. Within this class, even a simple model with constant material parameters is able to qualitatively reproduce a number of experimental observations in both simple shear and extensional flows, including linear viscoelastic properties, the rate dependence of steady-state material functions, the stress overshoot in incipient shear flows, and the difference in shear and extensional rheological curves. Furthermore, by allowing the relaxation time of the model to depend on the total strain, we can reproduce some experimental observations of the non-attainability of steady flows in uniaxial extension and link this to a concept of polymeric jamming or effective solidification. Remarkably, this modeling framework helps in understanding the interplay between different mechanisms that may compete in determining the rheology of non-Newtonian materials. [ABSTRACT FROM AUTHOR]

In this work, an improved anisotropic k-ε-v2-f model based on the finite extensible nonlinear elastic model with the Peterlin approximation for viscoelastic channel flows is proposed. This model is tested using direct numerical simulation (DNS) data for friction Reynolds numbers (Reτ) in the range of 120–1000, friction Wiesenberg numbers (Wiτ) in the range of 25–116, viscosity ratios (β) in the range of 0.6–0.9, and maximum polymer extensibility values (L2) in the range of 900–14 400. The flow characteristics of viscoelastic fluids with various parameters obtained from the new model agree well with existing DNS results. By adding closures for the flow, shear, and transverse components, the incomplete prediction of nonlinear terms from interactions between the fluctuating components of the conformation and velocity gradient tensors is improved. Compared with DNS results, these closures can fully obtain each component and significantly improve the accuracy of the flow direction component in the intermediate and high drag reduction regimes. Furthermore, the model in this paper retains the advantages of an anisotropic model, does not require a damping function, is simple to construct, and is easily extended to a variety of bounded flows. [ABSTRACT FROM AUTHOR]

We study a linear stability of a resting state for flows of incompressible viscoelastic fluid in an infinite cylindrical channel under the influence of an external uniform magnetic field directed parallel to the cylinder axis (we use a generalized rheological Vinogradov–Pokrovski model as mathematical model) in a class of axisymmetric periodic along the axial variable flows. We establish that for some values of the parameters in the case of an absolute conductivity b m = 0 , the magnetic field can substantially lessen the real part of an exponent for perturbations of the radial velocity component, which is the main element of the instability development. For general case b m ≠ 0 , we justify the possibility of removing the instability based on the performed calculations. [ABSTRACT FROM AUTHOR]

This study delves into the phenomenon of air cavity formation resulting from sphere-liquid impacts, a subject of enduring scientific interest with broad interdisciplinary applications. The actual cavity and air bubble volumes following cavity rupture are for the first time measured and analyzed, in correlation with the thinning of the air filament. Utilizing direct visualization and an original image processing technique, we introduce a method for these precise measurements. We have explored the dynamics of this phenomenon across various fluids, including sunflower oil, glycerin, and polyethylene oxide (PEO) viscoelastic solutions. Impact velocity and fluid properties dictate not only the topology of the air cavity but also the volume dynamics and the evolution of the air thread near cavity rupture. Experiments with PEO solutions show that increasing polymer concentration influences elasticity, resulting in narrower cavity interfaces and reduced air volume attached to the sphere after cavity rupture. The asymmetry of the air cavity is diminished with increasing viscosity and is amplified in the presence of fluid elasticity. Insights into cavity shapes generated by the impact of a spherical body in a liquid, and correlating cavity dynamics with fluid properties, contribute to advancing knowledge in various fields, from solid–fluid interaction and rheology to biomechanics and biology. [ABSTRACT FROM AUTHOR]

The effects of viscoelasticity on the stability and morphology of the liquid cone in liquid–liquid flow focusing are investigated experimentally and numerically. The particle tracers are utilized in experiments to visualize the flow fields, and the Oldroyd-B model is applied in numerical simulations to describe the viscoelastic characteristics of the liquid cone. Based on the quantitative analyses on the elastic stresses and forces inside the cone, the influence of viscoelasticity on the startup process of the liquid cone is first investigated. The stretching and shrinking stages of the viscoelastic cone are identified, and the startup process of the Newtonian cone is also studied for comparison. By considering the force balance at local jet position, a scaling analysis is proposed to give the criterion for the establishment of the stable cone, which indicates that the axial elastic stress can promote the cone stability. Upon a stable liquid cone, the influences of viscoelasticity on the interface profile and flow field of the cone are further analyzed, indicating that an increase in viscoelasticity leads to more shrinkage of the cone interface. The shrinkage of cone leads to the acceleration of focused liquid and thus the decrease in the recirculation flow size. This fundamental work provides scientific guidance for understanding the influences of viscoelasticity in flow focusing process, contributing to the industrial applications of microdroplets production. [ABSTRACT FROM AUTHOR]

Solute transport in pulsatile viscoelastic fluid flow is relevant in nutrient transport and drug delivery in blood flow. Previous studies have extensively analyzed the effect of the shear-thinning nature of the blood but neglected the elastic property. The present study aims to fill this lacuna by analyzing the role of blood viscoelasticity on solute transport. To accomplish this, we study solute transport for a non-uniformly distributed solute slug in the pulsatile flow of an Oldroyd-B fluid through a tube in the presence of wall absorption. We employ Gill's procedure and Aris' method of moments to compute the transport coefficients K m (t) (m ≤ 4). We also numerically solve the species transport equation using a finite difference scheme to directly determine local solute concentration C (t , z , r). Consistent results for a non-viscoelastic fluid predict a negative convection coefficient K1 and a positive effective diffusivity K2 for realistic values of the parameters. However, the present analysis predicts positive K1 and negative K2 for small tubes due to flow reversal caused by the fluid elasticity. For high Λ 1 , the amplitude of oscillation for K1 and K2 exhibits scaling K 1 ∼ Λ 1 1.5 and K 2 ∼ Λ 1 2 indicating an enhancement in the dispersion due to fluid elasticity, where Λ 1 is the dimensionless relaxation time. The analysis of the skewness and (excess) kurtosis coefficients reveals inconsistency in previous studies on Newtonian fluids. Thus, we present consistent results not only for a viscoelastic fluid but also for a Newtonian fluid subjected to a pulsatile pressure gradient. In addition, the solute dispersion is significantly influenced by the non-uniformity of a solute slug. As the radius of a slug increases, solute dispersion reduces in short and moderate times; however, at large times, it is independent of the radius of a slug. [ABSTRACT FROM AUTHOR]

Polyamide 6 (PA6) film as a typical viscoelastic material, satisfies the time–temperature superposition (TTS), and demonstrates obvious dynamic strain amplitude and frequency correlation under dynamic load. The investigation of the dynamic mechanical behavior of PA6 film is essential to ensure the safety of these materials in practical applications. In addition, dynamic mechanical property testing under conventional experimental conditions generally focuses on the short-term mechanical performance of materials. Therefore, the dynamic viscoelasticity of PA6 film was tested using a dynamic thermo-mechanical analyzer (DMA) in this study, and the complex modulus master curve was constructed based on time–temperature superposition (TTS) to realize the accelerated characterization of long-term mechanical properties. Furthermore, according to experimentally obtained asymmetric characteristics of the Cole–Cole diagram and the loss modulus master curve of the PA6 film, the parameter distribution of the fractional Zener model and the modified fractional Zener model were compared, and the asymmetric dynamic viscoelastic response of PA6 film under different conditions was systematically investigated using these models. The results indicate that the modified fractional Zener model can truly describe the dynamic asymmetric characteristics of PA6 film, verify the feasibility and advantages of the modified fractional rheological model, and provide some theoretical guidance for exploring the tensile rheological mechanism of PA6 film. [ABSTRACT FROM AUTHOR]

The rheological characterization of complex liquids is of great importance in many applications. Among the properties that can be measured, the relaxation time has great relevance, as it provides a measure of fluid elasticity. In this work, we propose a novel method to estimate the longest relaxation time of viscoelastic fluids by applying machine learning to microfluidics. Specifically, we train a long-short term memory (LSTM) neural network to identify the Weissenberg number that characterizes the dynamics of trains of rigid particles suspended in a viscoelastic liquid flowing in a cylindrical microchannel. We first study the effect of the Weissenberg number on the evolution of the microstructure through numerical simulations. An in silico dataset consisting of the distributions of the interparticle distances at different channel sections is built and used to train the network. The performance of the LSTM model is tested on both classification and regression problems. The proposed method is nonintrusive, requires a simple setup, and can in principle be used to measure other properties of the fluid. [ABSTRACT FROM AUTHOR]

We report the first-ever complete measurement of MAOStress material functions, which reveal that stress can be more fundamental than strain or strain rate for understanding linearity limits as a function of Deborah number. The material used is a canonical viscoelastic liquid with a single dominant relaxation time: polyvinyl alcohol (PVA) polymer solution cross-linked with tetrahydroborate (Borax) solution. We outline experimental limit lines and their dependence on geometry and test conditions. These MAOStress measurements enable us to observe the frequency dependence of the weakly nonlinear deviation as a function of stress amplitude. The observed features of MAOStress material functions are distinctly simpler than MAOStrain, where the frequency dependence is much more dramatic. The strain-stiffening transient network model was used to derive a model-informed normalization of the nonlinear material functions that accounts for their scaling with linear material properties. Moreover, we compare the frequency dependence of the critical stress, strain, and strain-rate for the linearity limit, which are rigorously computed from the MAOStress and MAOStrain material functions. While critical strain and strain-rate change by orders of magnitude throughout the Deborah number range, critical stress changes by a factor of about 2, showing that stress is a more fundamental measure of nonlinearity strength. This work extends the experimental accessibility of the weakly nonlinear regime to stress-controlled instruments and deformations, which reveal material physics beyond linear viscoelasticity but at conditions that are accessible to theory and detailed simulation. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the mechanical stresses and strains acting on pharmaceutical glass tubing vials during freezing and thawing of model pharmaceutical formulations. Strain measurements were conducted inside of a laboratory-scale freeze-dryer using a custom wireless sensor. In both sucrose and trehalose formulations at concentrations between 5 % and 20 % w/v, the strain measurements initially increased before peaking in magnitude at temperatures close to the respective glass transition temperatures of the maximally freeze concentrated solutes, Tg'. We attribute this behavior to a shift in the mechanical properties of the frozen system from a purely elastic glass below Tg' to a viscoelastic rubber-like material above Tg'. That is, when the interstitial region becomes mechanically compliant at temperature above Tg'. The outputs were less predictable below 5 % w/v and tended to exhibit two separate peaks in strain output, one near the equilibrium melting temperature of pure ice and the other near Tg'. The peaks merged at concentrations between 4 and 5 % w/v where the largest strain magnitude was observed. The strain on primary packaging has traditionally been applied to evaluate the risk of damage or breakage due to, for example, crystallization of excipients. However, data collected during this study suggest there may be utility in formulation design or as a process analytical technology to minimize potentially destabilizing stresses and strains in the frozen formulation. [ABSTRACT FROM AUTHOR]

The current investigation focuses on examining viscous corrections for viscous potential flow (VCVPF) analysis concerning the Rayleigh–Taylor instability occurring at the interface of a Rivlin–Ericksen (R–E) viscoelastic fluid and a viscous fluid during the transfer of heat and mass between phases. The R–E model is a fundamental framework in the study of viscoelastic fluids, providing insights into their complex rheological behavior. It characterizes the material's response to both deformation and flow, offering valuable predictions for various industrial and biological applications. Within the framework of viscous potential flow (VPF) theory, viscosity is exclusively accounted for in the normal stress balance equation, disregarding the influence of shearing stress entirely. This study introduces a viscous pressure term into the normal stress balance equation alongside the irrotational pressure, presuming that this addition will improve the discontinuity of tangential stresses at the fluid interface. Through derivation of a dispersion relationship and subsequent theoretical and numerical stability analyses, the stability of the interface is investigated across various physical parameters. Multiple plots are generated using the dispersion relation, and a comparative analysis between VPF and VCVPF is conducted to establish improved stability criteria. The investigation highlights that the combined impact of heat/mass transport and shearing stress serves to delay the instability of the interface. [ABSTRACT FROM AUTHOR]

Due to its high effectiveness and low cost, viscoelastic damper (VED) is a commonly used type of passive energy dissipation device to reduce structural vibrations and responses against earthquakes and strong winds. Over the past decades, scholars have developed new types of VEDs to be installed at different structural locations. These VEDs offer better post-disaster recoverability and smarter behaviors for structures. Nonetheless, existing efforts of various VEDs and the technologies supporting VEDs were seldomly summarized. This article presents a critical state-of-art review of the existing research on VEDs, hybrid VED devices, and the design methods for structures installed with VEDs. First, the VEDs are classified based on the design locations in building structures, including VEDs used as coupling beams and damping walls, installed in braces and beam-column joints, and used to connect parallel structures. In addition to these classic VEDs, the study presents the high-performance VEDs and the corresponding techniques, such as the combined usage with other materials and/or devices. Furthermore, as an important contribution to the presented work, various design methods for structures enhanced by VEDs were systematically summarized. These methods considered different evaluation parameters aiming at different design targets. Finally, this article identifies and highlights research challenges in the existing studies. Possible improvements that could be made in the future were also provided. [ABSTRACT FROM AUTHOR]

This paper solves the dynamic contact problem when a rigid flat punch indents into an exponentially graded (FG) viscoelastic coated homogeneous half-plane. A harmonic vertical force is applied to the FG coating, and the solution is obtained for the stress and displacement for both the FG viscoelastic coating and the half-plane using the Helmholtz functions and the Fourier integral transform technique. By applying specific boundary conditions, the contact mechanics problem is converted into a singular integral equation of the first kind. This equation is then solved numerically using the Gauss-Chebyshev integration formulas. The analysis provides detailed insights into how various parameters—such as external excitation frequency, loss factor ratio, Young's modulus ratio, density ratio, Poisson's ratio, indentation load, and punch length—affect the dynamic contact stress and dynamic in-plane stress. [ABSTRACT FROM AUTHOR]

Improving the physico-mechanical characteristics of bitumen is a constant and pressing problem in road construction. The issue is solved by modifying bitumen with various additives, one of which is a nanostructured modifier. This paper examines the effect of adding a natural mineral, shungite, to bitumen from the Koksu deposit (Kazakhstan) after grinding under different conditions. The mechanochemical activation of shungite made it possible to obtain samples with an average particle diameter of up to 3 μm. Using scanning electron microscopy, nanostructured particles with sizes of up to 100 nm were discovered in their structure. The effect of nanostructured shungite on the rheological characteristics of bitumen—elasticity and loss moduli, and loss tangent at high and low temperatures—was studied. The transition temperatures of bitumen from the viscoelastic to the liquid state were established, and their shift to the region of elevated temperatures when modified with ground shungite are shown. The presence of organic and inorganic components in the composition of shungite—carbon, silica, and metal oxides—has a beneficial effect on the rheological properties of bitumen by forming bonds with resinous asphaltene components of bitumen. The use of bitumen modified with nanostructured shungite makes it possible to replace the polymer modifier with a natural mineral to improve the quality of the road surface. [ABSTRACT FROM AUTHOR]

Recently, the theory of stochastic equations has been actively developing. Here it is worth noting the classical direction of research by Ito – Stratonovich – Skorokhod.Its main problem is to overcome the difficulties associated with the differentiation of a non-differentiable (in ”the usual sense”) Wiener process. It is also necessary to note the approach of I.V. Melnikova, within the framework of which stochastic equations are considered in Schwarz spaces using the generalized derivative. Our research will use methods and results of the theory, which is based on the concept of the Nelson – Glicklich derivative. Most studies consider the Cauchy problem for stochastic equations. In this article, instead of the Cauchy condition, it is proposed to consider a multipoint initial-final value condition. The obtained abstract results are used to analyze the solvability of the stochastic Oskolkov system, which models the dynamics of the velocity and pressure of a viscoelastic incompressible fluid. It is considered with a no-slip boundary condition and a multipoint initial-final value condition. The main result of the article is the proof of the solvability of the posed problem. [ABSTRACT FROM AUTHOR]