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This study examines the flow dynamics and heat transfer characteristics of Maxwell fluid in a channel influenced by magnetohydrodynamics (MHD), Joule heating, thermal radiation, and boundary layer suction/blowing effects. The governing partial differential equations (PDEs) for momentum, energy, and concentration are transformed into ordinary differential equations (ODEs) using similarity transformations. The boundary value problem (BVP) is solved numerically using the bvp4c solver in MATLAB, yielding accurate solutions for velocity, temperature, and concentration profiles under various parameters. Key findings reveal that the porous parameter decreases the velocity profile but increases the temperature profile for both suction and blowing effects. Additionally, the MHD, Deborah, and Eckert numbers significantly influence the velocity and temperature profiles differently under these conditions. This study highlights the crucial role of integrating MHD, thermal, and boundary control effects to optimize performance and efficiency in engineering systems involving Maxwell fluids, with applications in polymer processing, biomedical engineering, electronics cooling, oil recovery, and chemical processing. [ABSTRACT FROM AUTHOR]

Elastic nonlinearity in sandstones is given by the combination of slow and fast effects, leading to hysteresis and relaxation of the viscoelastic properties after the sample is perturbed (conditioning). While a lot of experimental evidences of slow dynamics are available, quantification of nonclassical nonlinearity is still difficult: nonlinear indicators must be introduced which are independent of both experimental configuration and on conditioning strain amplitude, which is often difficult to quantify in an accurate way. In this contribution, we introduce and analyze some possible quantities describing nonlinear viscoelasticity in sandstones, derived from a non-equilibrium strain model. We will show that they identify real material properties, in the sense that they are not dependent on experimental details (such as experiment duration, conditioning protocol, frequency,...) and can be measured easily with good repeatability. Highlights: We quantify the temporal relaxation of viscoelastic properties of sandstones; We introduce measurable indicators allowing to quantify hysteresis, anisotropy, and relaxation in sandstones; We propose a non-equilibrium strain model to describe observed hysteresis and anisotropy in nonlinear hysteretic viscoelastic properties; We show a linear correlation exists between modulus and damping evolution during relaxation in sandstones. [ABSTRACT FROM AUTHOR]

The Chandler period of Mars is a new parameter determined from observational data that characterizes the properties of the planetary interior. Numerical modeling of the period of the Chandler wobble of Mars was performed for a number of internal structure models that satisfy not only geodetic data (moment of inertia, tidal Love number k2), but also data obtained during a seismic experiment in the years 2019–2022. To reconcile the theoretical and observed values of the Chandler wobble, it is necessary to take into account the inelasticity of the mantle. To take into account the viscoelastic behavior of the interior, the Andrade rheological model was used. It is demonstrated how the value of the Chandler period depends on the rheological model parameters. [ABSTRACT FROM AUTHOR]

An analysis and modeling of the linear viscoelastic behavior of maltenes (M) blended with styrene–butadiene–styrene block copolymer (SBS) are presented in this study. M were mixed with different amounts of SBS (Elastomer, E) (0.25–80 wt%) to investigate the effect of polymer concentration on linear viscoelastic response of the blends; storage and loss moduli were obtained from small amplitude oscillatory shear tests (SAOS). Time–temperature superposition master curves were analyzed by a Maxwell multi-modal model with up to nine relaxation times. Han, Cole–Cole and Van Gurp-Palmen diagrams were prepared from the rheological data. Two different responses were observed: At low E contents, a dispersed system rheological response was observed and verified by microscopy with elastomer as the dispersed phase and maltenes as the matrix, while at high E content the response was that of a co-continuous system. Mixtures with E > 2 wt% exhibited change in their thermomechanical properties with a phase inversion at E > 50 wt%. Furthermore, at low E concentration resins stabilize the dispersed phase by diminishing the magnitude of the viscoelastic moduli, conversely, at high E concentration a swelled polymer-rich phase creates a network that significantly influences of the viscoelastic properties. [ABSTRACT FROM AUTHOR]

Adsorptive polymer additives have been reported to improve the retention capacity of oil films under hydrodynamic lubrication and to reduce friction under boundary lubrication. These effects are believed to result from the formation of a polymer adsorption film on the surface that acts as a lubricious coating. Polymer adsorption films have become dominant in nanometer-order microscopic gaps. However, their mechanical properties are difficult to quantify. This hinders the development of polymer additives. In our previous study, we successfully measured the shear viscoelasticity of lubricants (base oils) sheared in nanogaps using an originally developed measurement method called the fiber wobbling method (FWM). In this study, we measured the shear viscoelasticity of polymer-added lubricants in nanogaps by using FWM. In addition, we developed a heating stage in the FWM to quantify the temperature dependence of shear viscoelasticity in nanogaps. As a result, the viscosity index improved and elasticity was observed in the nanogap, where the polymer adsorption film was dominant. Furthermore, our results indicated that the elasticity of the adsorbed polymer film originated from entropic elasticity. [ABSTRACT FROM AUTHOR]

Asphalt, a widely utilized binder material in pavement construction, brings notable environmental and economic advantages through its efficient and high-utilization technique of multiple recycling. Nevertheless, the microscale mechanical mechanisms and laws governing the damage evolution in asphalt during repeated aging and recycling processes remain unclear, posing challenges in determining the optimal reclamation method and timing for binder maintenance. This study seeks to bridge this gap by employing microstructural numerical simulation and viscoelastic computational methods to elucidate the fundamental changes in microstructural mechanics and relaxation spectra of asphalt binders during multiple aging and regeneration processes, ultimately enhancing the design efficiency of multiple regeneration pavements. The study's key findings revealed that aging decelerates the relaxation capacity and increases the modulus of asphalt, while regeneration reduces the modulus and enhances relaxation capacity. The initial two aging and regeneration processes significantly influenced the stress distribution in the microscopic phase of the asphalt. Following the third aging and rejuvenation, the stress threshold and area of stress concentration remained relatively unchanged. Aging and regeneration primarily alter the mechanical properties of the microscopic phase, affecting the stress relaxation capacity and complex modulus of asphalt. The present study provides a certain research basis for the micro-mechanism of multiple regeneration asphalt. [ABSTRACT FROM AUTHOR]

A conformational difference in gum arabic (GA) in aqueous and emulsion systems can influence its interaction with guar gum (GG). Therefore, in this study, the rheological and tribological properties of GG mixed with an orange oil emulsion containing GA at varying concentrations were investigated and compared with those of GG-GA mixtures. As the GA concentration was increased, the apparent viscosity of GG mixtures with either GA or GA-based emulsion (GAE) tended to decrease. Specifically, with a higher GA concentration (> 1.5%), the GG-GA mixtures showed a lower relative apparent viscosity than the GG-GAE mixtures. In contrast, except for GG-GA mixture with 6.0% GA, all other mixtures showed lower tan δ values (0.66–0.69) than GG alone (0.72), indicating an enhancement of weak gel-like properties. At a lower GA concentration (< 3.0%), GG-GA interactions in the aqueous system produced a lower relative tan δ value than those in the emulsion system, whereas the opposite result was observed with a higher GA concentration (> 4.5%). In addition, each type of mixture exhibited different tribological properties. As the GA concentration was increased, the friction coefficient (μ) values of both tended to decrease. Especially, the GG-GAE mixtures attained lower μ values than the GG-GA mixtures, thereby indicating that the former have better lubricant properties. These results demonstrated that the conformational change in GA while emulsifying oil droplets influences its interactions with GG. [ABSTRACT FROM AUTHOR]

Various stress-releasing phenomena, such as episodic tremor and slip (ETS) and low-frequency earthquakes, occur at the downdip seismogenic zone in southwest Japan. However, it is unclear how much net stress and slip deficit accumulate at these depths during the interseismic phase. Here, we perform both elastic and viscoelastic earthquake-cycle forward models and reassess the locking state in Nankai from a synthesized perspective with the aid of geodetic modeling results. Our results suggest that the overestimation of the locking depth due to ignoring Earth's viscoelasticity is much smaller (less than 5 km) in this early interseismic subduction zone compared to that (~ 10 km) of late-interseismic margins. Considering viscoelastic modeling results and other physical arguments, the preferred steady-state viscosities for the continental and oceanic mantle are 5 × 1019 Pa s and 1020 Pa s, respectively. We find a clear trade-off between the full locking depth and the width of the transition zone when explaining both horizontal and vertical geodetic data, demanding other data to further resolve this inherent ambiguity. Unlike in Cascadia, partial megathrust locking in Nankai likely penetrates into the ETS zone, leaving no intervening gap between the shallow megathrust, where hosts large earthquakes, and the ETS zone. Assuming locking extends into the downdip of the ETS zone (i.e., 40 km), we propose a preferred viscoelastic locking model with a full locking depth of 18 km and a broad transition zone spanning a 22-km depth range. In this model, the downdip half portion of the transition zone corresponds to the ETS zone, which can accumulate certain slip deficit in a largely creeping and partially locked state. However, most of the accumulated slip deficit in the ETS zone may be accommodated aseismically simultaneously by stress-releasing phenomena, leaving limited to no budget to release during future megathrust earthquakes. We suggest that precise documentation of total slip during slow slip events, along with refinement of viscoelastic locking models, will provide new insights into the net slip budget available in the ETS zone. This will help assess the potential of future coseismic and/or postseismic slip penetrating into the ETS zone in Nankai, Cascadia and other subduction zones. [ABSTRACT FROM AUTHOR]

A generalization of fractional linear viscoelasticity based on Scarpi's approach to variable-order fractional calculus is presented. After reviewing the general mathematical framework, a variable-order fractional Maxwell model is analysed as a prototypical example for the theory. Some physical considerations are then provided concerning the fractionalisation procedure and the choice of the transition functions. Lastly, the material functions for the considered model are derived and numerically evaluated for exponential-type and Mittag-Leffler-type order functions. [ABSTRACT FROM AUTHOR]

Non-linear rheological behaviours of high fluorine content fluoroelastomer (HF-FKM) mixtures with varied carbon black (CB) filling amounts were investigated. Non-linear viscoelastic characteristics of HF-FKM mixture are characterised by large amplitude oscillatory shear (LAOS) tests, correlations between rheological behaviour and CB content were then discussed. Each non-linear viscoelastic parameter of HF-FKM mixture presents a three-stage characteristic with increasing CB content, corresponding to ranges of 0–20 phr, 25–30 phr, and 35–45 phr. Three stages of viscoelasticity characteristics for HF-FKM mixtures were considered to depend on the alteration of CB-elastomer network structure with increasing CB content, corresponding to the states where continuous phase of gum, CB-elastomer mesophase and excessive CB agglomerates predominate in mixture compound, respectively. After vulcanisation, samples with 30 phr CB content show the best resilience performance against thermal ageing, contributing to the existence of CB-elastomer mesophase. Samples with 25 phr CB content possess the second lowest compression sets at 225 and 250 °C ageing conditions but perform no better than those with 35 phr at 275 °C. The reason is presumed to be that the presence of excessive CB agglomerates in HF-FKM vulcanisate reduced irreversible deformation of the CB-elastomer network under compression at elevated temperatures. [ABSTRACT FROM AUTHOR]

As temperature and salt-resistant materials, hydrophobically associating polymers can form a reversible spatial network structure through the interaction between their hydrophobic groups, effectively improve the viscosity of the polymer solution through association, and enhance the temperature and salt resistance of the polymer. Hydrophobically associating monomers have different effects on the properties of polymer solutions. Herein, acrylic acid, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid were used as hydrophilic monomers. The three hydrophobic monomers with different carbon chain lengths were prepared by the bromination reaction. Hydrophobic associating polymers DQM1-PAM, DQM2-PAM, and DQM3-PAM were prepared by aqueous solution free-radical polymerization. The structure–activity relationship of the hydrophobic monomers with different carbon chain lengths on polymers was studied. It was confirmed by Fourier-transform infrared spectroscopy and 1H-NMR that the target product was successfully synthesized. Scanning electron microscopy revealed that with increasing hydrophobic carbon chain length, the hydrophobic microarea of molecular aggregation increased, forming a closer spatial network structure. Thermogravimetric and fluorescence tests revealed that with increasing hydrophobic carbon chain length of polymer molecules, the polymerization temperature resistance increased, intermolecular association degree increased, and critical association concentration decreased. Rheological property evaluation revealed that the viscosity of 0.5% polymer DQM1-PAM, DQM2-PAM, and DQM3-PAM was 71.32, 100.21, and 118.79 mPa·s after shearing at 120 °C and 170 s−1 for 1 h. With the increase in the carbon chain length, the retention rate of shear viscosity of polymer in a salt solution increased, showing good salt resistance. Concurrently, the molecular aggregation microarea of a solution with 0.5% polymer, degree of molecular chain action, viscoelasticity of the solution (G' > G''), and thixotropic area all increased. The performance of polymer solution can be improved by modifying hydrophobically associating polymers with long carbon chains, which has a broader application. [ABSTRACT FROM AUTHOR]

We present a class of model-free Data-Driven solvers that effectively enable the utilization of in situ and in vivo imaging data directly in full-scale calculations of the mechanical response of the human brain to sonic and ultrasonic stimulation, entirely bypassing the need for analytical modeling or regression of the data. The well-posedness of the approach and its convergence with respect to data are proven analytically. We demonstrate the approach, including its ability to make detailed spatially resolved patient-specific predictions of wave patterns, using public-domain MRI images, MRE data and commercially available solid-mechanics software. [ABSTRACT FROM AUTHOR]

Understanding the viscoelastic behavior of pediatric brain tissue is critical to interpret how external mechanical forces affect head injury in children. However, knowledge of the viscoelastic properties of pediatric brain tissue is limited, and this reduces the biofidelity of developed numeric simulations of the pediatric head in analysis of brain injury. Thus, it is essential to characterize the viscoelastic behavior of pediatric brain tissue in various loading conditions and to identify constitutive models. In this study, the pediatric porcine brain tissue was investigated in compression with determine the viscoelasticity under small and large strain, respectively. A range of frequencies between 0.1 and 40 Hz was applied to determine frequency-dependent viscoelastic behavior via dynamic mechanical analysis, while brain samples were divided into three strain rate groups of 0.01/s, 1/s and 10/s for compression up to 0.3 strain level and stress relaxation to obtain time-dependent viscoelastic properties. At frequencies above 20 Hz, the storage modulus did not increase, while the loss modulus increased continuously. With strain rate increasing from 0.01/s to 10/s, the mean stress at 0.1, 0.2 and 0.3 strain increased to approximate 6.8, 5.6 and 4.4 times, respectively. The brain compressive response was sensitive to strain rate and frequency. The characterization of brain tissue will be valuable for development of head protection systems and prediction of brain injury. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the tensile creep behavior of PVC flexible composites reinforced with various aramid warp-knitted fabrics (PCRAWF). The tensile creep test of PCRAWF was conducted and the impact of various tissue structure reinforcements on the viscoelastic behavior of PCRAWF was also discussed. Dynamic mechanical analysis (DMA) tests were conducted on PCRAWF to explore the effect of temperature on the creep strain and creep recovery properties of PCRAWF. The variation in viscoelastic properties of PCRAWF with temperature was analyzed. The decomposition behavior of aramid fibers and PVC resins in a nitrogen (N2) atmosphere was analyzed using thermogravimetric analysis (TGA). The experimental results showed that as the density of the reinforcing fabric increases, the creep strain of the corresponding PCRAWF decreases. The amount of creep strain increases as the loading force increases, and the rate of increase gradually decreases. The creep strain of PCRAWF increases as the temperature rises, and the creep recovery decreases with increasing temperature. The creep strain increases by approximately 0.4–1.6% as the temperature rises from 30 °C to 60 °C, and by about 0.2–0.6% as the temperature increases from 60 °C to 90 °C. The TGA results analyzed the thermal degradation temperatures of aramid fiber and PVC composites in N2 to reach 680 °C and 480 °C, respectively. The characterization of tensile creep behavior has significant potential for predicting the long-term performance of fabric-reinforced polyvinyl chloride flexible composites. Based on the experimental results of the creep of PCRAWF, the constitutive Kelvin-Maxwell model was used to establish the constitutive equations with the experimental data for numerical simulation. [ABSTRACT FROM AUTHOR]

Previous studies have shown that engagement in even a single session of exercise can improve cognitive performance in the short term. However, the underlying physiological mechanisms contributing to this effect are still being studied. Recently, with improvements to advanced quantitative neuroimaging techniques, brain tissue mechanical properties can be sensitively and noninvasively measured with magnetic resonance elastography (MRE) and regional brain mechanical properties have been shown to reflect individual cognitive performance. Here we assess brain mechanical properties before and immediately after engagement in a high-intensity interval training (HIIT) regimen, as well as one-hour post-exercise. We find that immediately after exercise, subjects in the HIIT group had an average global brain stiffness decrease of 4.2% (p < 0.001), and an average brain damping ratio increase of 3.1% (p = 0.002). In contrast, control participants who did not engage in exercise showed no significant change over time in either stiffness or damping ratio. Changes in brain mechanical properties with exercise appeared to be regionally dependent, with the hippocampus decreasing in stiffness by 10.4%. We also found that one-hour after exercise, brain mechanical properties returned to initial baseline values. The magnitude of changes to brain mechanical properties also correlated with improvements in reaction time on executive control tasks (Eriksen Flanker and Stroop) with exercise. Understanding the neural changes that arise in response to exercise may inform potential mechanisms behind improvements to cognitive performance with acute exercise. [ABSTRACT FROM AUTHOR]

The intervertebral disc (IVD) is a complex biological structure that ensures the spine strength, stability, mobility, and flexibility. This is achieved due to its biphasic nature which is attained by its solid phase (annulus fibrosus) and fluid phases (nucleus pulposus). Hence, the IVD biomechanical response to long-term loads, which is critical as it affects hydration, and nutrients-water transport influencing disc height reduction, has been further explored and mathematically modelled in this paper. An in-vitro study was performed on seven human lumbar spine specimens (L4-5), to assess if the classical rheological models and Nutting's power law can model in a simple way the intermediate characteristics between solid and fluid of the IVD. Creep tests were conducted by applying a static compression load of 500 N for 15 min. A correlation analysis was done (Pearson, p < 0.05) between the model parameters and the maximum value of Disc Height Reduction, followed by a linear regression analysis. In summary, the long-term IVD mechanical behavior was modeled in a simple way, emphasizing that yet there is no mathematical certainty about this mechanical behavior. Hence, a future aim might be to develop intervertebral disc prostheses capable of replicating only the disc mechanical response, without necessarily considering the microscopic-level biological drivers. Therefore, a future goal is to fully understand and model the disc's mechanical response toward the design of new disc prostheses that would consider only the macroscopic aspect, without considering the biological aspects.Article highlights: Intervertebral disc (IVD) biomechanics under long-term lads is still not yet fully understood. Creep curves of IVD were modelled through rheological models and Nutting’s power law. A simplified model should be pursued to describe the IVD biomechanics, to support research into IVD replacement devices. [ABSTRACT FROM AUTHOR]

In additive manufacturing, modification of the viscosity of softened or molten metal plays a significant role in the development of mechanical properties distribution. Similar to soft polymers, molten or softened metal usually exhibits vastly different viscoelastic properties. During scratching tests, viscoelastic polymers undergo spatiotemporal stress development and relaxation, causing stress ripples to form on their surfaces. It is observed that friction stir-based solid-state manufacturing can yield similar stress ripples on softened aluminum alloys due to the linear motion of the deposition tool. Softened aluminum alloys exhibit viscoelastic and viscoplastic responses similar to polymeric material during the solid-state deposition process. In the final product, residual stress ripples appear on the surface of the metal alloy due to periodic residual stress relaxation, leading to oscillatory behavior from the bulk mechanical properties of the material. The orientation of the in-built stress pattern formed in the bulk of the additively manufactured metal alloy underneath the visually evident onion ring-like surface pattern formation is diametrically in the opposite direction. The experimentally observed results are consistent with analytical calculation and numerical simulations in terms of behaviors. [ABSTRACT FROM AUTHOR]

In this paper, the coupled linear theory of thermoviscoelasticity for porous materials is considered in which the coupled phenomenon of the following four mechanical principles is proposed: the deformation of the skeleton of a porous solid, the volume fraction concept of the pore network, Darcy's law for the flow of a fluid through a porous medium, and Fourier's law of thermal conduction. The governing systems of equations of motion and steady vibrations are proposed. The fundamental solution of the system of steady vibration equations is presented explicitly by means of elementary functions, and its basic properties are established. By virtue of Green's identity the uniqueness theorems for the classical solutions of the basic internal and external boundary value problems (BVPs) of steady vibrations are proved. Then, the surface and volume potentials are presented and their basic properties are given. Finally, the existence theorems for classical solutions of the above-mentioned BVPs are proved by means of the potential method (boundary integral equation method) and the theory of singular integral equations. [ABSTRACT FROM AUTHOR]

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model for shear flow of thixotropic viscoelastic-plastic media, which takes into account the mutual influence of the deformation process and structure evolution, is continued. A set of two nonlinear differential equations describing the processes of shear at a constant rate and stress relaxation is obtained. Equation set describing creep is derived; a general solution of the Cauchy problem for the set is constructed in an explicit form (the equations of the families of creep, and structuredness curves are derived). For arbitrary six material parameters and (increasing) material function that govern the model, basic properties of the families stress-strain curves at constant strain rates, stress relaxation curves and creep curves generated by the model, and the features of structuredness evolution under these types of loading are analytically studied. The dependences of these curves on time, shear rate, stress level, initial strain, and initial structuredness of the material, as well as on the material parameters and function of the model, are studied. Several indicators of the applicability of the model are found which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (unusual properties) are generated by a change in structuredness in comparison with typical stress-strain curves, relaxation curves, and creep curves of structurally stable materials. In particular, it is proved that creep curves always increase in time and have oblique asymptote, and structuredness under constant stress is always monotonous (unlike other loading modes), but can decrease or increase depending on the relation between the stress level and initial structuredness. The same condition controls creep curves to be convex up or down: at a certain (calculated) critical load creep curves change from convexity up (under smaller loads) to convexity down, and the structuredness becomes ascending instead of descending. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves, strain rate and strain hardening, flow under constant stress and so on. [ABSTRACT FROM AUTHOR]

Polyamides can absorb or desorb water from or to their surrounding environment. The impact of this process is significant as water molecules lead locally to a swelling and a coupling of diffusion and deformation behavior. To model these phenomena, a strongly coupled chemo-mechanical (or diffuso-mechanical) model is required, considering both local water concentration and the viscoelastic material behavior of polyamide. In the present work, we derive and apply such a model to polyamide 6. A diffusion equation describing changes in water concentration is coupled to the balance of linear momentum in polyamide 6. The interaction between deformation and concentration is derived from thermodynamic considerations by introducing a free energy consisting of a mechanical and a chemical part. The mechanical part describes a linear viscoelastic model and includes chemical strains due to the presence of water molecules. The chemical part builds upon the theory of Flory and Huggins, that takes into account changes in enthalpy and entropy of mixing due to the interaction of polymer and water molecules. The coupling of deformation to water concentration arises due to a dependency of the water flux on the hydrostatic stress inside the polyamide. We successfully apply the derived model in Finite-Element simulations to predict the drying of polyamide 6 specimens without any coupling to mechanical loads. In addition, we reproduce experimentally obtained data from relaxation measurements, where the drying of polyamide specimens leads to an increase in relaxation modulus. [ABSTRACT FROM AUTHOR]

Biodegradable green composites of poly(butylene succinate) (PBS) and poly(L-lactide) (PLA) fibers were initially melt-blended aiming to obtain balanced comprehensive properties. According to the morphological observations, the PLA fibers were uniformly embedded in the PBS matrix. Rheology measurements suggested that the incorporation of PLA fibers improved the viscoelasticity of PBS melt. The percolation network of PLA fibers was formed at content of 20 wt%. The presence of PLA fibers inhibited the crystallization and reduced the isothermal crystallization rate of PBS in the composites. Moreover, the reinforcing effect of PLA fibers on the PBS matrix was found to be very significant. The storage modulus and tensile modulus of the composite with 30 wt% PLA fibers were 74% and 94% higher than those of neat PBS, respectively. PBS/PLA fiber composites prepared by simple melt blending method displayed the combination of enhanced melt strength and modulus, while maintaining the biodegradability of PBS matrix, which is of great potential for the wider practical application of environmentally friendly polymers. [ABSTRACT FROM AUTHOR]

The use of hydrogels has exponentially increased in recent years in many fields, such as biology, medicine, pharmaceuticals, agriculture, and more. These materials are so widely used because their mechanical properties change drastically with the different chemical compositions of the constituent polymer chains, making them highly versatile for different applications. We introduce a numerical simulation tool that relies on the Discrete Element Method to reproduce and predict the behavior of hydrogel spheres. We first use a benchmark test, namely an oscillatory compression test on a single hydrogel, to calibrate the model parameters, obtaining a good agreement on the material's rheological properties. Specifically, we show that the normal modified storage and loss moduli, E' and E", obtained in the simulation match the experimental data with a small relative error, around 3%, for E' and 11% for E". This result aligns with recent work on numerical modeling of hydrogels, introducing a novel approach with bonded particles and a viscoelastic constitutive relation that can capture a wide range of applications thanks to the higher number of elements. Moreover, we validate the model on a particle-particle compression test by comparing the simulation output with the contact force in the compression direction, again obtaining promising results. [ABSTRACT FROM AUTHOR]

Non-Newtonian fluid mechanics and computational rheology widely exploit elastic dumbbell models such as Oldroyd-B and FENE-P for a continuum description of viscoelastic fluid flows. However, these constitutive equations fail to accurately capture some characteristics of realistic polymers, such as the steady extension in simple shear and extensional flows, thus questioning the ability of continuum-level modeling to predict the hydrodynamic behavior of viscoelastic fluids in more complex flows. Here, we present seven elastic dumbbell models, which include different microstructurally inspired terms, i.e., (i) the finite polymer extensibility, (ii) the conformation-dependent friction coefficient, and (iii) the conformation-dependent non-affine deformation. We provide the expressions for the steady dumbbell extension in shear and extensional flows and the corresponding viscosities for various elastic dumbbell models incorporating different microscopic features. We show the necessity of including these microscopic features in a constitutive equation to reproduce the experimentally observed polymer extension in shear and extensional flows, highlighting their potential significance in accurately modeling viscoelastic channel flow with mixed kinematics. [ABSTRACT FROM AUTHOR]

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

Accurate seismic wave modeling of viscoelastic anisotropic medium is a fundamental tool for seismic data processing, interpretation and full waveform inversion. Also, free water surface, topographic relief and irregular seabed are often encountered in practical seismic surveys. Thus, basing on the General Maxwell Body, we proposed a generalized matrix form of the velocity-stress seismic wave equation, which becomes valid for composite viscoelastic anisotropic media and satisfies the boundary conditions in presence of topographic free surfaces and irregular fluid–solid interfaces. We theoretically show that the viscoelastic effect of a medium may be considered as the intrinsic body sources accumulated in wavefield history and computed by a recursive convolution formula accurately and efficiently. We also demonstrated that such a generalized viscoelastic wave equation may be solved with the curvilinear MacCormack finite difference method and validated the accuracy and feasibility of the proposed method. The modeling results in homogeneous and heterogeneous media match well with the analytical solutions and the references yielded by the spectral element solutions. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

The mechanical behaviour of metamaterials typically depends on their microstructural configuration and composition, in addition to their relative density. The design of these materials requires extensive experiments or complex finite element models which tend to be numerically demanding. In order to understand, control and optimise the macroscopic mechanical behaviour, in this paper numerical homogenisation is applied to a simple square unit cell with a single inclusion using a combination of elastic and viscoelastic responses on the micro level. Through a systematic analysis of unit cell behaviour with increasingly complex microstructural configurations, it is shown how certain macroscale constitutive laws can be obtained in a controlled and controllable manner. [ABSTRACT FROM AUTHOR]

Phase separation and percolation contribute to phase transitions of multivalent macromolecules. Contributions of percolation are evident through the viscoelasticity of condensates and through the formation of heterogeneous distributions of nano- and mesoscale pre-percolation clusters in sub-saturated solutions. Here, we show that clusters formed in sub-saturated solutions of FET (FUS-EWSR1-TAF15) proteins are affected differently by glutamate versus chloride. These differences on the nanoscale, gleaned using a suite of methods deployed across a wide range of protein concentrations, are prevalent and can be unmasked even though the driving forces for phase separation remain unchanged in glutamate versus chloride. Strikingly, differences in anion-mediated interactions that drive clustering saturate on the micron-scale. Beyond this length scale the system separates into coexisting phases. Overall, we find that sequence-encoded interactions, mediated by solution components, make synergistic and distinct contributions to the formation of pre-percolation clusters in sub-saturated solutions, and to the driving forces for phase separation. Biomolecular condensates form via phase separation of multivalent macromolecules. Phase separation is governed by solubility whereas multivalence drives percolation, also known as gelation. The authors in this work identify the distinct energy and length scales that influence phase separation versus percolation. [ABSTRACT FROM AUTHOR]

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

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

The purpose of the study is to evaluate strain-dependent behaviour of Cold Recycled Material (CRM) mixtures using three frameworks typically applied for Hot Mix Asphalt (HMA): linear viscoelastic (LVE) limits; non-linearity directions; changes in rheological model parameters. To this aim, the complex modulus of three CRM mixtures with different bitumen-to-cement ratio (0.2, 0.6 and 1.8) was measured in cyclic compression mode, at increasing level of axial deformation (from 35 to 195 μstrain) and at three temperatures (4, 20 and 40 °C). CRM mixtures showed strong strain dependent behaviour, which does not fully comply with the LVE hypothesis. LVE limit framework is applicable, but strain limits for CRM are different from HMA. Linearity direction framework does not give unique trend, hence it is not applicable in the same way as it was developed for HMA. The most promising framework for further analysis is the change in rheological model parameters, but it requires high number of performed tests. [ABSTRACT FROM AUTHOR]

We discuss the well-posed solvability and exponential stability of solutions of abstract integro-differential equations where the kernels of integral operators are of general type and lie in the space of functions integrable on the positive half-line. The abstract integro-differential equations studied in the present paper are operator models of viscoelasticity theory problems. The proposed approach to the study of these integro-differential equations is related to an application of semigroup theory and can also be used to study other integro-differential equations containing integral terms of the Volterra convolution type. [ABSTRACT FROM AUTHOR]

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

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

The paper considers the problem of unsteady wave propagation in the cross section of an infinite hollow cylinder made of a viscoelastic functionally graded material with nonmonotonically varying properties along the radius. The cylinder is replaced by a piecewise-homogeneous one with a large number of coaxial homogeneous layers approximating the properties of the source material. Based on the previously constructed solution for a layered cylinder, wave processes in a cylinder made of a viscoelastic functionally graded material with different types of nonmonotonic inhomogeneities are studied. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

The serviceability of wooden structures involves multiphysical phenomena, notably the interactions among creep, plasticity, and damage. The influence of creep on the initialization of the damage and on its growth and spread can be adjusted by an additional alpha parameter in order to take into account the coupled effect between creep and damage more properly. We integrate an orthotropic viscoelastic model, based on the generalized Kelvin chain, with an orthotropic damage model, capturing both the immediate nonlinear elastic–plastic–damage response and the time-dependent viscous response of timber. The combination of these material models is important to obtain a realistic description of wood behavior, because the timber shows an immediate nonlinear elastic–plastic–damage response, but also the time-dependent viscous response. In this paper, we algorithmize, implement, and validate the concept of 'creep damage', a phenomenon observed in wooden structures. Benchmark tests reveal two distinct patterns of damage in beech wood, immediate postload damage that evolves over time and damage that occurs and spreads during the loading period. [ABSTRACT FROM AUTHOR]

The mechanical behavior of thermoplastics is strongly rate-dependent, and oftentimes it is difficult to find constitutive models that can accurately describe their behavior in the small to moderate strain regime. In this paper, a hyperelastic network model (modified neo-Hookean) and a set of experiments are presented. The testing consists of monotonic tensile loading as well as stress relaxation and zero stress creep. Two materials were tested, polyoxymethylene (POM) and recycled polypropylene (rPP), representing one more rigid and brittle and one softer and more ductile semi-crystalline polymer. The model contains two main novelties. The first novelty is that the stiffness is allowed to vary with the elastic deformation (in contrast to a standard neo-Hookean model). The second novelty is that the exponent governing viscous relaxation is allowed to vary with the viscous deformation. The basic features of the new model are illustrated, and the model was fitted to the experimental data. The model proved to be able to describe the experimental results well. [ABSTRACT FROM AUTHOR]

In the present work, a thorough description of the creep response of polymers in both linear and nonlinear viscoelastic domains is presented. According to the proposed model, the polymeric structure is considered as an ensemble of meso-regions linked with each other while they can cooperatively relax and change their positions. Each meso-region has its own energy barrier that needs to be overcome for a transition to occur. It was found that the distribution function, followed by the energy barriers, attains a decisive role, given that it is associated with the distribution of retardation times and with their particular effect on the materials' time evolution. The crucial role of the imposed stress in a creep experiment by its influence on the retardation time spectrum of the polymeric structure was extensively analyzed. The proposed model has been successfully validated by a series of creep data in a variety of temperatures and stress levels for polymeric materials, studied experimentally elsewhere. Furthermore, the model's capability to predict the long-term creep response was analytically shown. [ABSTRACT FROM AUTHOR]

In the process of measuring the surface tension of Ga and Ga-based liquid metals by pendant-drop method, we found that at least two factors will lead to inaccurate measurement results. For one thing, it is due to the coating of the oxide film on the surface of the pendant-droplet, which shows the viscoelasticity. For another thing, the volume of pendant-drop does not exceed the critical value to ensure the accuracy of measurement. When the volume of the pendant-drops exceeds the critical value (the volume when Worthington number > 0.4), more accurate values can be obtained by using mechanical extrusion while rapidly forming pendant-drops. The surface tensions of Ga, E-GaIn, Galinstan, and GaInSnBiZn alloys are ~ 717.2, ~ 622.8, ~ 548.8 and ~ 545.7 mN/m, respectively, and the measured results are not sensitive to atmosphere. In this study, the dispersion component of GaInSnBiZn high-entropy alloy surface tension is ~ 327.81 mN/m, accounting for about 39.19%, which indicates that the proportion of dispersion component in the surface tension of multi-component alloys is close to that of elemental (Hg). This work will provide theoretical evidence for further development and application of low melting point high-entropy alloy. [ABSTRACT FROM AUTHOR]

Ultrasonication (20 kHz, 19.9 W/10 mL sample) was used to form O/W emulsions stabilised by quinoa protein isolate (QPI) particles at 3 wt%. Effects of pH (3, 5, 7, 9) and oil volume fractions (20%, 40%, and 60%) on rheological properties and microstructural characteristics of emulsions were investigated. All emulsions show viscoelastic behaviours and form a network structure comprising aggregated oil droplets and QPI particles. Emulsions stabilised by QPI at pH 5 showed largest droplet sizes and lowest gel strength due to extensive aggregation of proteins around the isoelectric point (pI ~ 4.5). The gel strength (G´(1 Hz)) were enhanced when the oil volume fraction increased and reached ~ 1100–1350 Pa at 60% oil volume fraction at different pH. This could be attributed to a tighter packing of oil droplets at 60% oil. Confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) revealed that interdroplets bridging and voids filling of QPI particles between oil droplets are critical in formation of aggregated emulsions network. Emulsions stabilised by QPI at pH 7 and 9 possessed thinner interfacial layers compared to those at pH 3 and 5. Finally, this study shows a potential of using ultrasonication to prepare gel-like emulsions stabilised by QPI, broadening applications of quinoa proteins in making dairy substitutes with semi-solid textural characteristics. [ABSTRACT FROM AUTHOR]

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