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Degradable polymers and hydrogels are promising classes of soft materials that have sparked the interest of the research community for many years due to their unique properties. Firstly, we investigate the viscoelastic properties of hydrogels through stress relaxation experiments to gain a better understanding of the force-dependent dynamics of these materials with the aspiration of expanding their application envelope within the biomedical field and beyond. We experimentally studied the viscoelastic behavior of 4 different types of hydrogels: covalently crosslinked polyacrylamide (PAAm), covalently crosslinked PAAm network immersed in a viscous alginate solution, ionically crosslinked alginate along with crosslinked PAAm-alginate double network. Through our investigations, we demonstrate that we can tailor the viscoelasticity of a covalently bonded PAAm network by tuning the viscosity of the solution in the gel. Moreover, based on the stress relaxation test of ionically crosslinked alginate gel and the double network gel, we have revealed the quantitative correlation between the ionic bond dissociation and force-dependent viscoelastic behavior of gels containing ionic crosslinks.Secondly, we conducted a systematic investigation on stress-assisted erosion of the photocurable and degradable elastomer poly (glycerol sebacate) acrylate (PGSA). Without external stress, we confirmed that the elastomer undergoes surface erosion in an aqueous environment. Upon the application of mechanical stress, our results revealed that the surface erosion rate was dramatically accelerated. By studying the stress corrosion cracking (SCC) phenomena, we demonstrated that the crack growth speed depends on the applied load and is significantly faster than the surface erosion rate of the elastomer. We have further shown that with decreasing the crosslink density of the elastomer, the crack growth speed during SCC can be slowed down due to the increased viscoelasticity of the material.With these reported discoveries, we hope to provide the scientific community with multiple methodologies to develop advanced polymers with tunable mechanical properties while highlighting the importance of time-dependent behavior and how it is correlated to microscopic mechanisms that take place within the polymer network including ionic debonding in hydrogels and the ester bond dissociation in PGSA.

It is a great challenge for the rational molecular design of light-emitting conjugated polymers to inherently suppress the ubiquitous coffee-ring effect (CRE), which is the critical bottleneck for ...

Composite tape springs, and a related design called a storable tubular extendable member (STEM), are used in aerospace structures as deployment mechanisms for various components on satellites, e.g., solar arrays, antennae, booms. Laminates used in their designs must be thin to prevent micro-buckling when deformed into compact stowed configurations. As a result, they have matrix dominated properties that viscoelastically evolve in time and can result in deployable space structure designs with reduced deployment torque and deployed stiffness. In order to understand how to mitigate the effects of viscoelasticity in STEM designs, this dissertation explores how laminate stacking sequence and fiber orientation affect composite viscoelastic behavior and incorporates this knowledge in a method to model the performance of a particular biaxially stowed and then deployed STEM design.To explore the effect that stacking sequence and fiber orientation have on viscoelastic behavior, tensile and four-point bend creep tests are performed on neat resin, unidirectional and plain weave lamina, and 3-ply [45PW/0/45PW] and 4-ply [0/45PW/45PW/0] laminate samples, all composed of the same epoxy resin and carbon fiber system. The results of the creep tests indicate that fibers placed in the load path, e.g., surface plies in composites under flexure loads or fibers in the direction of tensile loads, mitigate the viscoelastic creep and relaxation of the composites. The presence of elastic fibers also increases the stiffness of the laminae and laminates and reduces the degree to which they creep. The proportional viscoelastic change in the transient properties of the neat resin, lamina, and laminate, e.g., percent strain change over time at fixed stress between the initial elastic response and the equilibrium response of the material, are compared to one another. The results from indicate that the viscoelastic behavior of the resin system composing the matrix of the laminae and laminates is unchanged by the presence of fibers.An analytical model is developed to predict the viscoelastic behavior of a STEM after prolonged deformation in a state of biaxial bending, e.g., the stowed configuration. The model predicts the extent to which biaxial bending moments relax during the period of time a viscoelastic composite STEM is subjected to a state of constant biaxial bending curvature (i.e., stowage) and then predicts the resulting recovery curvature and moments after the stowed STEM is allowed to deploy. The predictions of the model for a one-dimensional beam in bending are shown to compare favorably to the predictions of validated one-dimensional beam models found in the literature.Knowledge of a STEM’s laminate flexural creep and relaxation properties is needed for the model to predict the biaxial bending curvature and moments of a STEM design. Since the available test data provides information on creep performance only, viscoelastic inversion methods are needed to obtain relaxation information. Several approaches are explored for converting the creep compliance and flexure properties that are ascertained by the tensile and four-point bending creep tests. A review of one-dimensional viscoelastic inversion methods such as Gutierrez-Lemini’s exact method shows them not to be applicable for inversion of the multidimensional creep properties of the anisotropic laminae and laminates tested for this dissertation. To accomplish the task of inverting the creep data, a Laplace transform based numerical method is developed for multidimensional viscoelastic materials. The creep properties for the neat resin, unidirectional and plain weave laminae, and 3-ply and 4-ply laminates are inverted using the Laplace transform based numerical inversion method. The flexure properties cannot be inverted because the axial/transverse flexure creep properties could not be measured by the four-point bend test method utilized. To acquire the relevant information, the inverted unidirectional and plain weave tensile creep properties are used as inputs for a viscoelastic version of classical laminate theory to predict the relaxation flexure properties of the unidirectional and plain weave laminae, and 3-ply and 4-ply laminates.

Since the multi-layered structures are widely used nowadays, and due to interesting applications of cylindrical shells, this study is dedicated to analyzing free vibrational behaviors of functionally graded saturated porous micro cylindrical shells with two nanocomposite skins. Based on Biot's assumptions, constitutive relations for the core are presented and effective properties of the skins are determined via the rule of mixture. A sinusoidal theory is used to capture the shear deformation effects, and to account for the scale effects, the modified couple stress theory is employed which suggests a material length-scale parameter for predicting the results in small-dimension. With the aid of extended form of Hamilton's principle for dynamic systems, differential equations of motion are extracted. Fourier series functions are used to obtain natural frequencies and after validating them, a set of parametric studies are carried out. The results show the significant effects of porosity and Skempton coefficient, pores placement patterns, CNTs addition and distribution patterns, temperature variations, material length-scale parameter and viscoelastic medium on the natural frequencies of the microstructure. The outcomes of this work could be used to design and manufacture more reliable micro cylindrical structures in thermo-dynamical environments.

The texture profile analysis test is an imitative test to determine texture properties of food, which quantify the consumer’s perception of eating food. The instrumental texture parameters obtained from this test depend on the specimen size and the nonstandardized test conditions. To overcome this problem, texture properties are here related to intrinsic mechanical properties, which are independent of the test conditions. Two types of materials are used to investigate the effect of viscoelasticity, plasticity and damage on the texture parameters for varying test conditions. Analytical relations between mechanical properties, test conditions, and the instrumental hardness, springiness, cohesiveness, and adhesiveness are determined. The hardness is obtained from the stiffness of the material, which is potentially rate-dependent, and the yield stress of a material in case of plasticity. The springiness is determined by the recoverable or irrecoverable strain in the material, which results from the mechanical properties in combination with the test conditions. Cohesiveness and springiness are found to be strongly related, unless structural damage is present in the material. Adhesiveness is only an indirect measure of the adhesion between the material and compression plate and depends on the test conditions and stiffness of the material. Finite element simulations reveal a decrease of hardness in case of a nonflat top surface, indicating the importance of geometrical effects.

s This paper investigates the effect of porosity on active damping of geometrically nonlinear vibrations (GNLV) of the magneto-electro-elastic (MEE) functionally graded (FG) plates incorporated with active treatment constricted layer damping (ATCLD) patches. The perpendicularly/slanted reinforced 1–3 piezoelectric composite (1–3 PZC) constricting layer. The constricted viscoelastic layer of the ATCLD is modeled in the time-domain using Golla-Hughes-McTavish (GHM) technique. Different types of porosity distribution in the porous magneto-electro-elastic functionally graded PMEE-FG plate graded in the thickness direction. Considering the coupling effects among elasticity, electrical, and magnetic fields, a three-dimensional finite element (FE) model for the smart PMEE-FG plate is obtained by incorporating the theory of layer-wise shear deformation. The geometric nonlinearity adopts the von Karman principle. The study presents the effects of a variant of a power-law index, porosity index, the material gradation, three types of porosity distribution, boundary conditions, and the piezoelectric fiber's orientation angle on the control of GNLV of the PMEE-FG plates. The results reveal that the FG substrate layers' porosity significantly impacts the nonlinear behavior and damping performance of the PMEE-FG plates.

Nanoscale macromolecular biological structures exhibit time-dependent mechanical behavior, yet a quantitative understanding of their creep and stress relaxation behavior remains elusive, largely due to experimental challenges in attaining sufficient spatial and temporal resolution and control of stress or strain in conditions that guarantee their molecular integrity. To address this gap, an experimental methodology was developed to conduct creep and stress relaxation experiments with individual mammalian collagen fibrils. An image-based edge detection method, implemented with high magnification optical microscopy and combined with closed-loop proportional–integral–derivative (PID) control, was implemented and calibrated to apply constant force or stretch ratio to individual collagen fibrils via a Microelectromechanical Systems (MEMS) device. This experimental methodology allowed for real-time control of uniaxial tensile stress or strain with ~25 nm displacement accuracy. The overall experimental system was tuned to apply step inputs with rise times below 0.5 s, less than 5% overshoot, and steady-state error smaller than 1%. Three collagen fibrils with diameters in the range 101–121 nm were subjected to creep and stress relaxation tests in the range 4–20% engineering strain, under partially hydrated conditions. The collagen fibrils demonstrated non-linear viscoelastic behavior that was described well by the adaptive quasi-linear viscoelastic model. The results of this study demonstrated for the first time that mammalian collagen fibrils, the building blocks of connective tissues, exhibit nonlinear viscoelastic behavior in their partially hydrated state.

Measuring rheological properties of cells in monolayers enables quantifying average cell properties in single experimental runs despite large cell-to-cell variations. Here, we describe how to modify a commercial rotational rheometer to accomplish the necessary precision for a monolayer rheometer and we delineate the steps for setting up experiments detecting average viscoelastic cell properties.

The chapter reviews the application of creep-recovery and oscillatory rheological tests in flour based systems, including simple flour water systems, and more complex ones, such as bread, cookies and biscuits. A theoretical introduction about the fundaments and methods of linear viscoelastic rheology is presented, including general mathematical models and their application in flour based systems. A summary of experimental conditions to perform the rheological tests is covered. Functionality of flour based systems is extremely dependent on their viscoelastic properties. Processes like mixing, pumping, lamination, baking performance have been found to be strongly dependent on the system viscoelastic properties. However, the establishment of general and well-defined relationships among viscoelastic properties and specific functionalities is quite a difficult task, still on progress.

Emulsions are an interesting class of soft materials and have a wide range of practical applications in industry and in consumer goods. To design and tailor the mechanical properties of concentrated emulsions at high droplet volume fractions for specific applications and products, it is helpful to have a good quantitative understanding of emulsion rheology. In this dissertation, we describe the improvements that we have made in the quantitative description of the linear plateau elastic shear modulus, G'p, of jammed monodisperse colloidal emulsions that are stabilized by ionic surfactant molecules. We have created an improved analytical model, which accurately describes the G'p of jammed monodisperse micro- and nano-scale emulsions. We incorporate entropic, electrostatic, and interfacial (EEI) contributions into a quasi-equilibrium free energy while retaining key aspects of random jamming of deformable droplets, and we calculate G'p via free energy minimization. This analytical EEI model successfully describes the empirically measured volume-fraction dependent G'p() for microscale emulsions and nanoemulsions without any ad hoc adjustments to the empirically measured  and with very few adjustable parameters that appear to be universal. In addition, we use this EEI model to identify different -regimes of jamming caused by electrostatic repulsions and droplet interfacial deformations. Using jammed monodisperse emulsions as model system, we have improved diffusing wave spectroscopy (DWS) microrheology analysis for quantifying the rheological properties of dense colloidal systems, particularly G'p() of jammed repulsive emulsions. We show that we can correct for collective light scattering effects present in highly scattering concentrated colloidal systems through an empirically determined average structure factor and thereby obtain corrected mean square displacements (MSDs), which lead to accurate values of G'p through the generalized Stokes-Einstein relationship (GSER) of passive microrheology. This advance enables accurate optical microrheology measurements of concentrated emulsions over a wide range of frequencies beyond the capabilities of traditional mechanical rheometers. This approach of correcting DWS MSDs for collective scattering is general and can be applied to other types of highly scattering concentrated colloidal dispersions, not just emulsions.Motivated by advances in DWS microrheology for repulsive emulsions, we perform DWS microrheology studies on depletion-induced attractive emulsions near and below the jamming volume fraction of hard spheres. By adapting the analytical approach developed for repulsive emulsions, we show that in some limits DWS microrheology of attractive emulsions can be extracted and compare accurately with macroscopic mechanical measurements. We reveal systematic features in an excess MSD that is present only for the attractive emulsions, and we attribute this excess MSD to additional dynamics of clusters of droplets that are only loosely attached to the main stress-bearing struts of the main gel network of droplets. More theoretical attention is needed in attractive emulsion systems in order to determine how to analyze DWS MSDs and predict the excess MSDs. Interestingly, these measured excess MSDs can be fit using an empirical modified bound Brownian particle equation that we created to describe these extra fluctuations in the DWS signals. This application of DWS microrheology to attractive emulsions herein serves as a basis from which additional DWS microrheology studies of attractive soft colloidal systems can be performed and analyzed.

Understanding the response of skin to superphysiological temperatures is critical to the diagnosis and prognosis of thermal injuries, and to the development of temperature-based medical therapeutics. Unfortunately, this understanding has been hindered by our incomplete knowledge about the nonlinear coupling between skin temperature and its mechanics. In Part I of this study we experimentally demonstrated a complex interdependence of time, temperature, direction, and load in skin's response to superphysiological temperatures. In Part II of our study, we test two different models of skin's thermo-mechanics to explain our observations. In both models we assume that skin's response to superphysiological temperatures is governed by the denaturation of its highly collageneous microstructure. Thus, we capture skin's native mechanics via a microstructurally-motivated strain energy function which includes probability distributions for collagen fiber orientation and waviness. In the first model, we capture skin's response to superphysiological temperatures as a transition between two states that link the kinetics of collagen fiber denaturation to fiber coiling and to the transformation of each fiber's constitutive behavior from purely elastic to viscoelastic. In the second model, we capture skin's response to superphysiological temperatures instead via three states in which a sequence of two reactions link the kinetics of collagen fiber denaturation to fiber coiling, followed by a state of fiber damage. Given the success of both models in qualitatively and quantitatively capturing our observations, we expect that our work will provide guidance for future experiments that could probe each model's assumptions toward a better understanding of skin's coupled thermo-mechanics and that our work will be used to guide the engineering design of heat treatment therapies. STATEMENT OF SIGNIFICANCE: Quantifying and modeling skin thermo-mechanics is critical to our understanding of skin physiology, pathophysiology, as well as heat-based treatments. This work addresses a lack of theoretical and computational models of the coupled thermo-mechanics of skin. Our model accounts for skin microstructure through modeling the probability of fiber orientation and fiber stress-free states. Denaturing induces changes in the stress-free configuration of collagen, as well as changes in fiber stiffness and viscoelastic properties. We propose two competing models that fit all of our experimental observations. These models will enable future developments of thermal-therapeutics, prevention and management of skin thermal injuries, and set a foundation for improved mechanistic models of skin thermo-mechanics.

This study seems to be the first effort to determine the viscoelastic properties of dilute ovalbumin colloids using dynamic-light-scattering-based optical microrheology using carboxylated melamine microparticles as the tracer probe. A generalized form of the Stokes-Einstein equation constructed based on Laplace transformation of the mean square displacement, ??r 2(t)?, was employed to compute the viscoelastic moduli (storage modulus, G?, and loss modulus, G?). ??r 2(t)? was determined to increase with time by reaching a maximum plateau at a time between 10-3 and 10-1 s with no further increase, revealing the elastic nature of dilute ovalbumin colloids within the given time. On the other hand, ovalbumin colloids exhibited different viscoelastic properties at two different frequency ranges. The measurements and interpretation of data revealed that the technique used seems to ensure a fast and effective method for measuring the viscoelastic properties of ovalbumin colloids at very low concentration levels. © 2021 ICE Publishing: All rights reserved. King Abdulaziz University, KAU: 135-197-D1439; Deanship of Scientific Research, King Saud University This work was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under grant number 135-197-D1439. The authors, therefore, gratefully acknowledge the DSR technical and financial support.

In the structural design of a roller-compacted concrete pavement (RCCP), it is crucial to estimate strain and stress developments in the RCCP slab realistically. Since the RCCP mix uses less cement and lower amount of water, shrinkage strain and concrete temperature during the hardening stage are expected to be reduced as compared to those of conventional concrete mixture, resulting in a reduction of the concrete early-age deformation and stress developments in the RCCP slab. In this paper, early-age concrete strain and stress developments in RCCP slab subjected to environmental loads were evaluated. A full-scale test section of RCCP under real climatic conditions was monitored. The early-age total strains, stress-independent strains, shrinkage strains, and coefficient of thermal expansion (CTE) of the RCCP were measured and analyzed. Using the results of measured strains, in-situ CTE and shrinkage strain, and temperature, the early-age concrete stress development is computed by incorporating a viscoelastic property of the early-age concrete. The results revealed that the shrinkage strain of the RCCP is quite low as compared to that of conventional concrete. The early-age stress developments in the RCCP slab are strongly governed by the thermal-induced stresses. Shrinkage-induced stresses were quite small and might be negligible in a preliminary estimation of early-age stress developments in the RCCP slab.

Aging can significantly affect the performance of asphalt mixtures, causing increase in stiffness, reduction in relaxation capability and increase in cracking susceptibility. It is also well known that fundamental viscoelastic properties are used for design and modelling of asphalt mixtures and pavement structures to addressing rutting, fatigue and thermal cracking concerns. The objective of this paper is to study how the viscoelastic properties of asphalt mixture change over time, and evaluate and identify the cracking and aging susceptibility of asphalt mixtures with different mix variables during material selection and mixture design. Ten mixtures are evaluated using different laboratory conditioning protocols to simulate a range of aging levels in the field. The complex modulus test is then conducted on the lab aged mixtures to measure the viscoelastic properties in order to construct the dynamic modulus and phase angle master curves. The mixture Glover-Rowe (G-Rm) parameter and the shape parameters of the dynamic modulus and phase angle master curves, including inflection point frequency (−β/γ), difference between the glassy modulus and the inflection point modulus (γ), peak value of phase angle (a) and the horizontal position (frequency) of the peak phase angle value (c), are determined and evaluated for the mixtures with different aging conditions and mix variables. The study indicates the ability of the G-Rm parameter and all the master curve shape parameters to capture the effect of different aging conditions on linear viscoelastic mixture properties, as well as the cracking and aging susceptibility of asphalt mixtures.

Biocompostable poly (glycolic acid) (PGA) crystallizes slowly under fast cooling condition, leading to poor mechanical performance of the final products. In this work, a self-nucleation (SN) route was carried out to promote the crystallization of PGA by regulating only the thermal procedure without any extra nucleating agents. When self-nucleation temperature (Ts) decreased from 250 oC to 227 oC, the nuclei density was increased, and the non-isothermal crystallization temperature (Tc) of PGA was increased from 156 oC to 197 oC and the half-life time (t0.5) of isothermal crystallization at 207 oC was decreased by 89%. Consequently, the tensile strength and the elongation at break of the PGA were increased by 12% and 189%, respectively. According to the change of Tc as a function of Ts, a three-stage temperature domain map (Domain I, II and III) was protracted and the viscoelastic behavior of the self-nucleation melt and the homogeneous melt was studied. The results indicated that interaction among PGA chains was remained in Domain IIb, which can act as pre-ordered structure to accelerate the overall crystallization rate. This work utilizes a simple and effective SN method to regulate the crystallization behavior and the mechanical properties of PGA, which may broaden the application range of resulting materials.

The vibration and vibration induced noise are the major pitfalls in textile machines especially in Power Loom. This research paper provides force transmissibility of viscoelastic material as isolator. The isolator is molded with natural rubber with shape as cone and inserted on bottom shaft of the picking cone of the Power loom. Vibration analysis is carried with Fast Fourier analyzer and application of the DEWEsoft software. The Loss factor, damping factor and force transmissibility are determined. Force transmissibility yields effectiveness of vibration isolation of the viscoelastic material. The efficiency of isolators expressed as the ratio of output displacement or force to input displacement or force and this ratio is known as transmissibility.

We design an interpenetrating network of silane-functionalized nanocomposites to enhance particle dispersity and interfacial bonding strength in nanocomposites. To qualitatively measure the enhanced particle dispersity in the nanocomposites, we carry out rheological characterizations and suggest a simple particle dispersity index from the viscoelastic responses. Yield stresses of the nanocomposites are obtained by fitting with the Carreau-Yasuda model. After comparing the yield stresses and elastic moduli of the nanocomposites during photo-polymerization, we confirm that interphase regions significantly affect the interfacial bonding and mechanical strengths. Prediction of elastic moduli of the nanocomposites by the Mori-Tanaka micromechanics model agrees well with the experimental data, verifying that a good interpenetrating network exists between the nanoparticles and matrix.

Coatings of viscous oil or viscoelastic polymer on a rigid surface transform the condensation phenomena differently. When the viscous oil is infused on low-energy rigid surfaces, the surface shows excellent water repellent behavior. On the other hand, the viscoelastic material coating exhibits a high affinity with water drop resulting in more contact angle hysteresis (CAH). We focused on the drop coalescence phenomena during condensation on viscous slippery and viscoelastic coated metallic samples in this work. We have observed that the drop coalescence on lubricant infused surfaces (LIS) significantly depends on the viscosity of the lubricant and the stability of droplet interface bilayers between the drops. The lifetime of the non-coalescence event of the droplets during condensation on high viscous liquid infused surfaces (50 cst and 500 cst) surfaces was found to be in 1–3 orders of magnitude longer compared to low viscous liquid infused surface (5 cst). Coalescence induced motion during condensation was significantly observed in high viscous liquid infused surfaces (50 cst and 500 cst) compared to low viscous lubricant infused surface (5 cst). On soft viscoelastic coating, drop coalescence during condensation event undergoes through merging of the droplets followed by relaxation of the coalesced drop by the capillary induced movement of the contact line. Key findings of this work would be helpful to comprehend the drop coalescence phenomena on viscous slippery and viscoelastic coatings in a detailed manner.

Dynamic mechanical analysis (DMA) is a technique that is used to study the viscoelastic behaviour of polymeric materials. 3D printing is one of the well-known applications of additive manufacturing techniques which has wide areas of application. In that, Fusion Deposition modelling (FDM) has very fine outcomes with better printing qualities to execute good products. In this research work, the 3D printed samples of pure ABS and PLA were examined under dynamic mechanical analysis to study the various temperature heat, absorbing, storing, and dissipating behaviour of these samples. The results show, both ABS and PLA performed well under the heat flow categories. While comparing to conventional manufacturing technologies, these 3D printed DMA results are showing some excellent results. These polymeric samples may prepare as composites and used for various applications, for better outcomes and capabilities. Storage modulus, while taking the temperature values of ABS to 90 °C maximum and for PLA about 48 °C. This will happen, but this pure form of materials printed through FDM also has such a very good energy storing capacity. Considering the loss modulus energy dissipation in the form of heat started from 110 °C, this is one of the good signs on the fabricated technique and build quality of ABS. The continues decrease in the degree of crystallinity of the PLA and ABS increases the meshing strength noted in the damping factor.

Polystyrene is thermoformed in a viscous state at temperatures corresponding to its crystalline melting point (100–140 °C). The mechanical properties of the material change with temperature since these plastics behave viscously when temperature is increased. Findings are presented during numerical simulations, implementing a viscoelastic characterization of laminated polystyrene. A viscoelastic generalized Maxwell model with Prony series is used in the simulation to replicate the thermoforming processes. The results were verified by comparing them through experimental tensile tests at different temperatures. The good agreement between the model and experimentation allows the proper selection of operating parameters such as pressure, time and temperature of the process.

High-performance polymeric membrane technology is rapidly developing worldwide with the introduction of new materials and processes. Considerable research efforts are being made to establish a polymer membrane that can be used for ultrafiltration (UF) or nanofiltration (NF) applications. The development of modified polyamide-66 polymer and its compatibility in wastewater are essential elements in the quest for advances and improvements in membrane technology. The optimized conditions for membrane synthesis are critical in making it commercially viable. Response Surface Methodology (RSM) was used to find the optimum dissolution of polyamide-66 in formic acid. A model was developed and validated with experimental data, and it showed good agreement with R2 0.9984. The optimized condition for minimizing viscosity was determined. For minimum viscosity (3.64 cp), the optimum temperature and wt.% were 20 ?C and 0.6, respectively.

Hypothesis We hypothesize that dispersed Ti3C2Tz MXene particle interactions are reflected in the bulk viscoelastic properties of the dispersions and can be analyzed using classical colloidal theory for anisotropic particles. The relevant kinetic theory for Brownian anisotropic particles is given by the Doi and Edwards (D-E) Model, and the Maxwell Model is used to fit the relaxation times as a function of frequency. Such behavior is relevant to a variety of MXene processing techniques, particularly printing and coating. Experiments Small oscillatory shear tests were performed for dilute Ti3C2Tz MXene aqueous dispersions as a function of their concentration and temperature. Scanning electron microscopy (SEM), X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), ζ potential measurements, Dynamic Light Scattering (DLS) were used to characterize the Ti3C2Tz MXene nanoparticles. Findings Ti3C2Tz dispersions show gel-like and viscous-like behavior at low and high temperatures, respectively. Experimental relaxation times fitted to the Maxwell model are found to be close to the theoretical values. However, at high temperatures, relaxation time values differ due to the inter-particle interactions, even in the dilute concentration regime. For Ti3C2Tz dispersions, aggregation, and clustering can have dramatic consequences for dispersion rheology, including gelation, as the sample transitions from liquid-like to solid-like behavior.

Selection of Bio-active coating materials plays a vital role in order to improve the life span and mechanical properties of Bio-material implants. Bio-active coating is extensively coated on the Bio-polymers such as Nylon, Polytetrafluoroethyene (Teflon) and polyvinyl chloride (PVC) to form a thin film barrier where Hydroxyapatite (HAP) is used as Bio-coating material, which is very expensive and poor in viscoelastic behavior and damping co-efficient. The objective of this paper is to select the alternative Bio-coating material by using Aluminum Oxide, Egg and Sea Shell which are easily available in nature and economical. Selected Bio-active materials are used to protect the surface area of the Bio-implant. Plasma spray technology is used to coat the Teflon, Nylon and PVC with selected coating materials. Dynamic Mechanical Analysis (DMA) test conducted on both coated and uncoated samples to examine the viscoelastic behavior and damping co-efficient of samples where Teflon, Nylon and PVC coated with Al2O3, Egg Shell and Sea Shell showed better results when compared to Hydroxyapatite (HAP).

Electrospinning is a technique used to fabricate fibrillar materials for different applications. Understanding this process allows companies to reduce efforts and to have better control of the variables present in this phenomenon. A mathematical model is described in this article for Newtonian, Giesekus, FENE-P, and Oldroyd-B approaches. This was done by using radial basis functions through a localized collocation method that has not been used before to solve this kind of problems. The solutions of the viscoelastic and electric behavior were compared with a Python solver and with a previously obtained solution by other researchers. The rheological models, showed that they can be applied according to the size of fluid polymer chains. Thus, the Giesekus model rheologically describes more accurately fluids with small polymer chains, the FENE-P model describes larger polymer chains with low extensibility, and Oldroyd-B model describes same particles as FENE-P but with infinite extensibility. An interesting case of coil-stretching was obtained using the FENE-P model where the fluid becomes Newtonian while the relaxation time increases. In conclusion, The results show that by decreasing the tensile force in the jet, thinner fibers can be obtained and this can be controlled experimentally by using polymers with low molecular weight.

This article deals with the passive damping analysis of the symmetric/asymmetric sandwich beam with viscoelastic particulate composite (VEPC) core, where solid particles are incorporated in a soft viscoelastic matrix to form VEPC. The theoretical study is performed by considering the symmetric/asymmetric beam, where top/bottom stiff layers constrain a viscoelastic core for the passive control of vibration of the overall sandwich beam. Initially, the fractional-order derivative (FOD) parameters of the VEPC are obtained for the viscoelastic constitutive model. Subsequently, an analytical model of the overall beam is developed according to FOD constitutive model and layer-wise first-order shear deformation theory (FSDT). The transient responses of the symmetric/asymmetric sandwich beam are evaluated through this analytical model to explore the change in the passive damping characteristics due to the incorporation of solid particles in a soft viscoelastic matrix. The results reveal a significant reduction in vibration amplitude or improvement in the damping ratio of the symmetric/asymmetric sandwich beam with the incorporation of solid particles in the viscoelastic matrix. The results also illustrate the optimal VEPC for enhanced passive damping of the vibration of symmetric/asymmetric sandwich beam.

In order to obtain a uniform and effectively toughened poly (lactic acid) film by blending with low content of poly (ethylene octene) (POE) with high elasticity, the tailored interfacial intermolecular interaction and entanglement between the two phases of the PLA/POE blend was innovatively constructed via the facile reactive melt blending process through the reaction of the epoxy/anhydride groups grafted on the POE chains with the end groups of PLA chains (PLA/GPOE-MPOE). It was observed that POE domains were embedded tightly in PLA matrix with a fuzzy interface and abundant interface transition area, and the impact fractured surface of the blend showed an obvious plastic deformation with less occurrence of fibrillation of PLA matrix or interfacial de-bonding. Compared with neat PLA and directly blended PLA/POE blends, the PLA/GPOE-MPOE blend exhibited much higher complex viscosity/storage modulus, much lower tanδ values in the terminal region, and obvious strain-hardening behavior. The deviation in viscoelastic behavior of PLA/GPOE-MPOE from linear PLA indicated the enhanced molecular entanglement between the long-branched chains, resulting in an enhancement of the stretching ability during biaxial drawing of the blend. Uniform PLA/GPOE-MPOE films with draw ratio as high as 7 × 7 were obtained through biaxial stretching, which showed much higher tensile strength and the elongation at break than that of neat PLA and PLA/POE film. This work provides a facile method for fabricating toughening PLA films with application potentials.

The paper presents results of studying mechanical properties of polymer composites depending on types of filler particles (granular - carbon black, nanodiamonds; layered - graphene plates; fibrous - single-walled nanotubes). These nanofillers differ greatly from each other in their structure and geometry. A significant difference in behavior of nanocomposites was revealed even with little introduction of particles into the elastomer. The highest level of reinforcement of the matrix was obtained when single-wall nanotubes and detonation nanodiamonds were used as fillers. The viscoelastic properties and the Mullins softening effect [1-4] were investigated in experiments performed with material samples subjected to complex uniaxial cyclic deformation. In these experiments, the amplitude of deformations was changed step by step; and at each step a time delay was specified to complete rearrangement processes of the material structure. It was found that a pronounced softening effect after the first cycle of deformation and significant hysteresis losses occur in the material filled with single-walled nanotubes. These characteristics are insignificant for the rest of nanocomposites until elongation increases twofold. In accordance with the obtained results, a new version of the mathematical model to describe properties of the viscoelastic polymer materials was proposed. The constants of the constitutive relations were calculated for each material; the theoretical and experimental load curves were compared. As a result, the introduced model is able to describe the behavior of elastomeric nanocomposites with a high accuracy. Moreover, this model is relatively easy to use, suitable for a wide range of strain rates and stretch ratios and does not require the entire history of deformation as needed for integral models of viscoelasticity.

Evaluating friction in human skin is important to assess its condition and the effects of skincare cosmetics. In this study, we evaluated the friction dynamics of moisturized skin to show the effects of moisturization on its mechanical properties.Friction force was evaluated using a sinusoidal motion friction evaluation system. The skin of the upper arm of 20 subjects was rubbed using a contact probe. The water content of the stratum corneum and the softness of the skin were measured using a Corneometer and a Cutometer, respectively.When human skin was treated with water or 10 wt% glycerol aqueous solution, the friction coefficients increased by 0.23 ± 0.01 and 0.17 ± 0.14, respectively, and the delay times (normalized by calculating the time interval from contact with the probe to the friction response divided by the friction time for one round trip) increased by 0.048 ± 0.034 and 0.055 ± 0.024, respectively. Three different friction profiles were observed: (a) a stable pattern, in which a smooth profile was observed during the sliding process; (b) an oscillation pattern, in which significant oscillation was obtained; and (c) a stick pattern, in which the friction coefficient increased even during the deceleration process. In the case of untreated skin, the oscillation pattern was observed for the majority of subjects. The appearance rate of the stick pattern increased by 80.3% ± 29.4% after treatment with 10 wt% glycerol aqueous solution. These characteristic friction profiles can be explained by a two-step friction model consisting of two modes: (a) friction at the skin surface and (b) the delayed response due to skin deformation.Moisturizing the skin with water or 10 wt% glycerol aqueous solution increased the friction coefficient and delay time, dramatically changing the friction profile. These changes were considered to be due to the swelling and softening of the stratum corneum and the increased true contact area between the contact probe and the skin surface.Une évaluation des effets de la friction sur la peau humaine demeure importante dans le but de juger de l'état de la peau ou de l'efficacité des produits cosmétiques pour les soins de la peau. Dans cette étude, nous avons évalué les propriétés d'une peau hydratée soumise à une friction afin d'identifier les effets de l'hydratation sur les propriétés mécaniques de la peau. MÉTHODE: Les forces de friction ont été évaluées grâce à un système d'évaluation du frottement par mouvement sinusoïdal. Une sonde de contact a été utilisée pour frotter la peau sur le haut du bras de 20 participants. La teneur en eau de la couche cornée et la souplesse de la peau ont été mesurées respectivement à l'aide d'un cornéomètre et d'un cutomètre. RÉSULTAT: Le traitement de la peau humaine avec de l'eau ou une solution de glycérol à 10% a entraîné une augmentation du coefficient de friction respectivement de 0.23 ± 0.01 et de 0.17 ± 0.14, ainsi que du délai de réaction (normalisé en divisant l'intervalle de temps entre le contact avec la sonde jusqu’à l'apparition de la réaction à la friction, par le temps de friction pour un aller-retour), de 0.048 ± 0.034 et de 0.055 ± 0.024. Trois profils de friction différents ont également été observés : (1) un modèle stable, (2) un modèle avec une grande oscillation, et (3) un modèle « collé-glissé » où le coefficient de friction augmente même pendant la décélération. Lorsque la peau est sèche, le modèle oscillant a été observé chez la majorité des participants. Le taux d'apparition du modèle « collé-glissé » a augmenté de 80.3 ± 29.4% dans le cas où la peau a été traitée avec une solution de glycérol à 10%. Ces profils caractéristiques de friction ont pu être expliqués à partir d'un modèle de friction composé de deux modes, (a) une friction à la surface de la peau et (b) un délai de réaction dû à la déformation de la peau.L'hydratation de la peau avec de l'eau ou une solution de glycérol à 10% a considérablement modifié le profil de friction en raison d'une augmentation du coefficient de friction et du délai de réaction. Nous avons estimé que ces changements sont relatifs au gonflement et à l'assouplissement de la couche cornée, engendrant une augmentation de la surface de contact réel entre la sonde de contact et la surface de la peau.

Flexible strain sensors have an irreplaceable role in critical and emerging fields, such as electronic skins, flexible robots, and prosthetics. Although numerous efforts have been made to improve sensor sensitivity to meet specific application scenarios, the signal-to-noise ratio (SNR) is an extremely critical and non-negligible indicator, which takes into account higher sensitivity, meaning that they can also detect the noise signals with high sensitivity. Coincidentally, scorpions with ultrasensitive vibration sensilla also face such a dilemma. Here, it is found that the scorpion ingeniously uses the viscoelastic material in front of its slit sensilla to realize efficient preprocessing of the signal. Its mechanism is that the loss factor of materials changes with frequency, affecting energy storage and transmission. Inspired by this ingenious strategy, a bioinspired strain sensor insensitive to a low strain rate was designed using a two-step template transfer method. As a result, its relative change in resistance reached 110% under the same strain (0.3197%) but with different strain rates (0.1 Hz and ∼20 Hz). The noncontact vibration experiments also show different responses to low-frequency vibration and high-frequency impact. Moreover, it can also be used as a typical flexible strain sensor. Under the tensile state, it has a gauge factor (GF) as high as 4596 upon 0.6% strain, and the response time is 140 ms. Therefore, it is expected that this strain sensor will be used in many important ultraprecision measurement fields, especially when the measured signal is small.

Time-dependent flow of a viscoelastic material through a wavy curved channel is studied. The flow traversing the wavy curved domain is modelled in the curvilinear coordinates. The viscoelastic fluid is described by the fluid relaxation and retardation times, and their variations are considered in relation to the flow characteristic time scale. The wavy walls of the curved channels are in sinusoidal form, with arbitrary phase difference. Using domain perturbation technique, the analytical solution of the model is obtained, including the velocity and the volumetric flow rate. The analytical solution is explained as a function of the flow domain structure, the viscoelastic fluid properties, and the flow generating force. Flow enhancement due to the flow domain is discussed; we have shown that the flow augmentation depends on the properties of the viscoelastic fluid. Furthermore, comparisons have been made with Newtonian fluid flow, and the prominent variations in the flow behaviours have been reported.

This paper aims to develop asphalt binder fatigue models by time sweep tests under constant strain. By investigating the fatigue life in neat and modified asphalts under linear and nonlinear viscoelastic responses, results were analyzed in terms of strain levels, asphalt type, and additive content. The dissipated energy and dissipated energy ratio concepts were utilized to develop the phenomenological models for estimating fatigue lives of asphalt binders. Results showed that the dissipated energy ratio-based equations give relatively identical fatigue models irrespective of the strain level or asphalt binder type. Moreover, statistical analyses were performed to investigate the contribution of each parameter in the fatigue model prediction. A comparison was made between fatigue life predictions by means of traditional and energy-based methods. Results proved that the fatigue life prediction models based on the concept of dissipated energy ratio follow a similar trend.

[EN] We report a method to locally assess the complex shear modulus of a viscoelastic medium. The proposed approach is based on the application of a magnetic force to a millimeter-sized steel sphere embedded in the medium and the subsequent monitoring of its dynamical response. A coil is used to create a magnetic field inducing the displacement of the sphere located inside a gelatin phantom. Then, a phased-array system using 3 MHz ultrasound probe operating in pulse-echo mode is used to track the displacement of the sphere. Experiments were conducted on several samples and repeated as a function of phantom temperature. The dynamic response of the sphere measured experimentally is in good agreement with Kelvin¿Voigt theory. Since the magnetic force is not affected by weak diamagnetic media, our proposal results in an accurate estimation of the force acting on the inclusion. Consequently, the estimated viscoelastic parameters show excellent robustness and the elastic modulus agrees with the measurements using a quasi-static indentation method, obtaining errors below 10% in the whole temperature range. The use of the macroscopic inclusion limits the direct application of this method in a biomedical context, but it provides a robust estimation of the elastic modulus that can be used for material characterization in industrial applications., This work was supported in part by the Spanish Ministry of Science, Innovation and Universities through the "Juan de la Cierva - Incorporacion" under Grant IJC2018-037897-I, in part by the Program "Proyectos I+D+i 2019" under Grant PID2019-111436RB-C22, in part by the Agencia Valenciana de la Innovacio under Grant INNCON/2021/8, in part by Generalitat Valenciana under Grant AICO/2020/268, and in part by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 20142020 under Grant IDIFEDER/2018/022. The work of Alejandro Cebrecos was supported by the Universitat Politecnica de Valencia under Program PAID-10-19.

Dielectric elastomer (DE) is an intelligent soft material and it is regarded as one significant artificial muscle. The nonlinear large deformation, electromechanical coupling and nonlinear viscoelasticity of DE material post great challenges for constitutive modeling and the associated dynamics. Fractional viscoelasticity has encountered some successes in the dynamics of complex materials. In the current study, a 3D constitutive relation of DE based on the fractional Kelvin-Voigt viscoelastic model by considering finite strain is established. The Cauchy stress under the condition of uniaxial and biaxial stretches is derived. The fractional dynamics equations of DE membrane are also formulated based on the virtual work principle. The composite integral rule for fractional derivative and the Runge-Kutta method are combined to numerically solve the dynamics system. The constitutive model is fitted to the uniaxial and biaxial stretch experimental data, and the material parameters are obtained. Subject to a cyclic deformation, the stress-softening effect of the DE membrane is simulated. Furthermore, the dynamics responses of DE membrane are also calculated. A convenient approach is given to evaluate the equilibrium point of the system. It reveals that the model could be used to predict the creep behaviors for both free vibration and parametric excitation vibration.

Background Modelling of needle insertion in soft tissue has developed significant interest in recent years due to its application in robot-assisted minimally invasive surgeries such as biopsies and brachytherapy. However, this type of surgery requires real-time feedback and processing which complex computational models may not be able to provide. Methods In contrast to the existing mechanics-based kinetic models, a simple multilayer tissue model using a Coupled Eulerian Lagrangian based Finite Element method has been developed using the dynamic principle. The model simulates the needle motion for flexible hollow bevel-angled needle (15° and 30°, 22 G) insertion into porcine liver tissue, which includes material parameters obtained from unconfined compression testing of porcine liver tissue. To validate simulation results, needle insertion force and cutting forces within porcine liver tissue were compared with corresponding experimental results obtained from a custom-built needle insertion system. Results For the 15° and 30° bevel-angle needles, the percentage error for cutting force (mean) of each needle compared to computational model, were 18.7% and 11.9% respectively. Varying the needle bevel angle from 30° to 15° results in an increase of the cutting force, but insertion force does not vary among the tested bevel angles. Conclusion The validation of this computationally efficient multilayer Finite Element model can help engineers to better understand the biomechanical behaviour of medical needle inside soft biological tissue. Ultimately, this multilayer approach can help advance state-of-art clinical applications such as robot-assisted surgery that requires real-time feedback and processing. Statement of Significance The significance of the work is in confirming the effectiveness of multilayer material based finite element (FE) method to model biopsy needle insertion into soft biological porcine liver tissue. A multilayer Coupled Eulerian Lagrangian (CEL) based FE modelling technique allowed testing of heterogeneous, non-linear viscoelastic porcine liver tissue in a system, so direct comparison of needle tissue interaction forces on the intrinsic material (tissue) behaviour could be made. To the best of the authors’ knowledge, the present research investigates for the first time modelling of a three dimensional (3D) hollow needle insertion using a multilayer stiffness model of biological tissue using FE based CEL method and presents a comparison of simulation results with experimental data.

The reflection and transmission problems of elastic waves through a partially saturated porous interlayer sandwiched between two elastic solid half-spaces are investigated. The partially saturated porous interlayer contains solid phase, gas phase and liquid phase. The solid frame is modeled by the fractional Zener model where the fractional order derivatives are used to describe the complex history-dependent viscoelastic behavior. Due to the coupled effects of the multiple fields, there exist three longitudinal waves and one transverse wave in the porous medium. The numerical results of reflection and transmission coefficients and the energy dissipation ratios are provided and shown graphically. The effects of the gas saturation, the interlayer thickness and the viscoelasticity of the solid frame are discussed based upon the numerical results. It is observed that the reflection and transmission coefficients and the energy dissipation ratios are affected noticeably by the gas saturation, the interlayer thickness and the viscoelasticity of the solid frame. In particular, there exists the characteristic gas saturation where the energy dissipation increases drastically.

This paper investigates the time-varying mechanical performance of partially embedded pile groups subjected to vertical loads in multilayered cross-anisotropic fractional viscoelastic saturated soils. Piles are considered as one-dimensional compression bars and the stiffness matrix of a single pile and the global stiffness matrix of partially embedded pile groups are obtained by the finite element method. Based on the boundary element method, the soil stiffness matrix is deduced by expanding the extended precise integration solution. Then, the solution for partially embedded pile groups in multilayered fractional viscoelastic saturated soils is derived by employing the boundary element-finite element coupling method. Comparisons with existing solutions and an ABAQUS model prove the correctness of the proposed method. Numerical analyses are carried out to evaluate the influences of fractional derivative order, free length, pile spacing, pile-soil stiffness ratio as well as soil stratification on the time effect of partially embedded pile groups under vertical loads.

Lubricant behaves non-Newtonian at high shear stress and high shear rate. The non-Newtonian shear behavior of oil such as shear-thinning, viscoelasticity, and limiting shear stress could have influences on almost all characteristics of an elastohydrodynamic lubrication (EHL) contact, that is, the central film thickness, the coefficient of friction, and the temperature rise in the lubricating film. For example, for lubricants of large molecular weight or of polymer blended ones, there can be inlet shear-thinning, which would reduce the EHL film thickness. For the EHL traction in a rolling/sliding EHL contact, it cannot be reasonably predicted without the consideration of non-Newtonian rheology. In EHL numerical studies, the non-Newtonian properties and the constitutive equations are expressed by the concept of generalized viscosity [Formula: see text], which can be either a function of shear rate [Formula: see text] or a function of shear stress [Formula: see text]. In this way, a non-Newtonian lubrication problem could be solved as a generalized Newtonian problem based on solvers for a Newtonian EHL problem. According to the function of the generalized viscosity [Formula: see text], numerical solutions can be classified into shear rate-based ones and shear stress-based ones. In this work, these two kinds of numerical solutions are revisited. And their efficiency is compared for a two-dimensional (2D) non-Newtonian point contact EHL problem (here 2D means non-Newtonian flow in both the x and y directions). Results show that the shear rate-based numerical solution has a higher efficiency than the shear stress-based one. The shear rate-based 2D generalized Newtonian method is more suitable to analyze multiple EHL contacts in angular contact ball bearings and gears with complex 2D flow and/or transient EHL lubrication problems.