Viscoelastic Phenomena Research Articles

A New Approach to Distinguish Thixotropic and Viscoelastic Phenomena

A novel approach for distinguishing the viscoelastic and thixotropic phenomena of predisturbed and intact networks at short and long timescales of observation was proposed using stress relaxation, creep/recovery, single shear decay, and in-shear structural recovery experiments. The method was able to illustrate the connections patterns of the internal microstructure of hydrocolloids and its alteration over time. To test the universality of the new approach, we studied seven commercial and four emerging hydrocolloids. Moreover, to find out the correlation between the proposed parameters from this approach and the fundamental rheological parameters of the selected hydrocolloids, a principal component analysis (PCA) was employed, which showed an excellent correlation between the parameters of all hydrocolloids in predisturbed and intact states at short and long timescales. This work assumed that two different patterns of linkage connection exist, but the analysis can be extended to more than two connection patterns of linkages.

Investigation of the strain‐rate‐dependent mechanical behavior of a photopolymer matrix composite with fumed nano‐silica filler

With the evolution of additive manufacturing, there is an increasing demand to produce high strength and stiffness polymers. Photopolymers are very commonly used in stereolithography and fused deposition modeling processes, but their application is limited due to their low strength and stiffness values. Nano‐sized fibers or particles are generally embedded in the polymer matrix to enhance their properties. In this study, we have studied the effect of fumed nano‐sized silica filler on the elastic and viscoelastic properties of the photopolymer. The uniaxial testing coupons with different concentrations of silica filler have been fabricated via casting. We observed improvement in mechanical properties by the addition of the nano‐sized filler. As polymers exhibit time‐dependent mechanical response, we have conducted tensile tests at different strain rates as it is one of the most common modes of deformation, and is commonly used to characterize the parameters of the rate‐dependent material. We noticed significant dependence of the mechanical properties on the strain rate. quasi‐linear viscoelastic (QLV) model, which combines hyperelastic and viscoelastic phenomena, has been employed to capture the response of the material at different strain rates. We found out that the QLV model with Yeoh strain energy density function adequately describes the rate‐dependent behavior of the material and has reasonable agreement with the experimental results. POLYM. ENG. SCI., 59:1695–1700 2019. © 2019 Society of Plastics Engineers

On the asymmetric transient responses of annular/circular viscoelastic plates based on shear deformation theory: an analytical approach

ABSTRACTTransient responses of annular/circular viscoelastic plates with different boundary conditions under various asymmetric transverse excitations are thoroughly studied in the present investigation. In order to describe creep and relaxation behaviours of viscoelastic phenomena, the standard linear solid model is employed. The equations of motion are derived by employing Hamilton’s principle using the first-order shear deformation theory which it results in a system of coupled partial differential equations with variable coefficients. By applying the perturbation technique and the generalised Fourier series, the problem is solved using an analytical approach. In the parametric study, the sensitivity of the result to the geometrical and mechanical parameters is declared. The results are compared with those obtained from the classical plate theory and the finite element package.

Dynamic Modeling and Feedforward Control of Jaw Movements Driven by Viscoelastic Artificial Muscles

Artificial muscles based on dielectric elastomer actuators (DEAs) have been used to mimic the motion of the human jaw. However, DEAs show strong nonlinear behavior coupled with rate dependent viscoelastic phenomena. Under cyclic actuation, the viscoelastic creep coupled with hysteresis further makes control of these viscoelastic membranes difficult. In this paper, we develop a nonlinear dynamic model based on the principles of nonequilibrium thermodynamics to account for viscoelasticity. Furthermore, the damping and inertial effects of the jaw and membrane are taken into account, relating the deformation of the membrane to the voltage applied. Experimental results are found to be consistent with theoretical predictions. The feedforward controller is then developed based on a viscoelastic nonlinear dynamic model. The controller can be used to track the sinusoidal, triangular, and staircase trajectories accurately. Finally, a video demonstrating the jaw movement in the speech, “I Have a Dream,” by Dr. Martin Luther King Jr. has been shown to illustrate the effectiveness of the controller. This is one of the first efforts to control of soft robots driven by viscoelastic DEAs.

The Concepts and Applications of Fractional Order Differential Calculus in Modeling of Viscoelastic Systems: A Primer.

Viscoelasticity and other related phenomena are of great importance in the study of mechanical properties of materials, especially biological materials. Certain materials demonstrate some complicated behavior under mechanical tests that cannot be described by a standard linear equation (SLE), mostly due to the shape memory effect during the deformation phase. Recently, researchers have been making use of fractional calculus (FC) in order to probe viscoelasticity of such materials accurately. FC is a powerful tool for modeling complicated phenomena. In this tutorial paper, it is sought to provide clear descriptions of this powerful tool and its techniques and implementation. It is endeavored to keep the details to a minimum while still conveying a good idea of what and how can be done with this powerful tool. The reader will be provided with the basic techniques that are used to solve the fractional equations analytically and/or numerically. More specifically, simulating the shape memory phenomena with this powerful tool will be studied from different perspectives, and some physical interpretations are made in this regard. This paper is also a review of fractional order models of viscoelastic phenomena that are widespread in bioengineering. Thus, in order to show the relationship between fractional models and SLEs, a new fractal system comprising spring and damper elements is considered and the constitutive equation is approximated with a fractional element. Finally, after a brief literature review, two fractional models are utilized to investigate the viscoelasticity of the cell and a comparison is made between the findings and the experimental data from the previous models. Verification results indicate that the fractional model not only matches well with the experimental data but also can be a good substitute for previously used models.

Adaptive Observer for State and Load Force Estimation for Dielectric Electro-Active Polymer Actuator

This paper presents a nonlinear electric circuit model of the circular DEAP membrane actuator model coupled with a viscoelastic mechanical phenomena. A parameters of the model are found by parameter identification process and then an adaptive observer to estimate the real load force is applied. The authors developed an adaptive observer for state affine system for the case without knowledge of the load mass of DEAP membrane. The results are compared with experiments obtaining a good agreement.

Study of the mechanical behavior of asphalt mixtures using fractional rheology to model their viscoelasticity

This study focuses on the mechanical behavior of asphalt mixtures composed of aggregate particles attached with an asphalt binder. Asphalt mixtures are viscoelastic composite materials widely used in the construction of pavement layers. The modelling of such materials is currently done using the Burgers model. However, this model is limited when explaining some of the viscoelastic phenomena of an asphalt mixture, mainly because the Burgers model was developed for a single material with a dual nature. This work presents a new approach that provides a more appropriate framework for studying asphalt mixtures. The model assumes an aggregate particle enclosed by an asphalt material. Viscoelastic equations were developed using derivatives of fractional order. Then, the creep, recovery, and relaxation phenomena in an asphalt mixture were analyzed using the new model. Unlike the Burgers model, the new model can predict the elastic jump observed at the beginning of the creep modulus. Thus, the new model seems to describe better those practical cases of asphalt mixtures used in the construction of pavement layers. The new model can be used to modify the properties of the binder for designing optimized and more resistant asphalt mixtures.

Effect of carbon black masterbatch and polymer process aids based on fluoroelastomer and hyper branch polymers on melt fracture of bimodal polyethylene

This research has been conducted with the view of the effect of various polymeric processing aids (PPA) on the stick-slip phenomenon in polyethylene compounds. In the extrusion process of thermoplastic polymers, such as polyethylene, for proper and efficient products like wire coatings, pipes, bottles, and films, it is desirable that the final products, gain a smooth surfaces and be polished. In the industry, it is also necessary that the rate of extrusion process is as high as possible, dislike the pressure of this process is as low as possible, so that it can be used for the most part from process machines and thus reduce process costs so much as practical. In this study, MBM and MBR masterbatches (containing 35-40% carbon black) were added to high density polyethylene powder (PE100) and the effect of these masterbatches on the reduction of viscoelastic phenomenon was confirmed. In the next step, three types of PPA with commercial names of Viton, Fx and Daikin with concentrations of 50, 100 and 150 ppm were added to the PE100MBR and PE100MBM compounds to reduce the melt fracture of the samples. The capillary rheometry test determined the quantity changes in the stick-slip phenomenon. The microscopy test also showed qualitatively the changes that occurred in the extrudates. The torque meter test also determined the effect of the PPA on the ampere and the energy consumed by the extruder. Finally, samples were produced with these features due to the importance of reducing energy in the process as well as improving the quality of the extrudates. Depending on the structure of the fluoroelastomer and hyper branch polymers, it has been found that adding these kind of materials has improved processability, and finally the appearance of the product is smoother and polished.

The Gradient Flow Structure of an Extended Maxwell Viscoelastic Model and a Structure-Preserving Finite Element Scheme

An extended Maxwell viscoelastic model with a relaxation parameter is studied from mathematical and numerical points of view. It is shown that the model has a gradient flow property with respect to a viscoelastic energy. Based on the gradient flow structure, a structure-preserving time-discrete model is proposed and existence of a unique solution is proved. Moreover, a structure-preserving P1/P0 finite element scheme is presented and its stability in the sense of energy is shown by using its discrete gradient flow structure. As typical viscoelastic phenomena, two-dimensional numerical examples by the proposed scheme for a creep deformation and a stress relaxation are shown and the effects of the relaxation parameter are investigated.

Effect of a Nanodisperse Graphite on the Viscoelastic Properties of Polyvinyl Chloride

In the absence of segregation of nanodisperse graphite particles, obtained by electrolysis as a new filler of polyvinyl chloride (PVC), the viscoelastic phenomena dependent on the structural changes of a composite are investigated. The shear modulus and the volume compressibility caused by deviations of elements of the structure from the quasi-equilibrium state under the action of ultrasonic vibrations (ω = 0.4·106 0.4 · 10 s–1) are calculated at filler concentrations 0 ≤ φ ≤ 10.0 vol.% and temperatures 298 K ≤ T ≤ (Tg + 10) K. It is shown that the volume density of internal energy depends on the expectation time for the transition of structural elements through the energy barrier, the dynamic viscosity of the material, and temperature. The results of calculations serve as the basis for producing PVC systems with controllable of properties.

Investigation on Viscoelastic-Creep Behavior of the Phase-Field Crystal Method

The phase-field crystal (PFC) method is a promising computational model with atomistic resolution and diffusive time-scale. In this study, we investigated the viscoelastic-creep behavior exhibited by the PFC model. We considered a one-dimensional crystal subjected to step changes in pressure and studied the time-dependent strain response from the system. The parametric study shows that the PFC model predicts the materials with higher density to exhibit higher stiffness and lower damping capacity while an increase in temperature results in lower stiffness and damping capacity. These predictions agree with experimental observations and show promising capability of the PFC method to model viscoelastic phenomena.

Application of neural network for computing heat performance in axisymmetric viscoelastic transport: Hybrid meta heuristic techniques

Abstract Background and Objectives Genetic algorithm and Interior point algorithms individually can have reliable and effective approaches to tackle physical flow problems. However, hybrid heuristic algorithms GA-IPA has been discovered an efficient and accurate solver than GA and IPA algorithms. Methodology Mathematical development and governing equations under the channel boundaries is developed and explore with mechanism of thermal deposition. Moreover, Genetic Algorithm (GA) and Interior Point Algorithm (IPA) are explored in a hybrid arrangement for the weights optimization of ANN which optimized the performance of thermal deposition in axisymmetric viscoelastic transport phenomena. Additionally, we incorporate artificial neural networks (ANNs) architecture Schematic and workflow diagram for experimental explanation of proposed design scheme. Significances A universal function approximation technique which is known as Artificial Neural Network (ANN) has been applied in the various field of practical importance. Among these fields are control systems, system identification, time series forecasting and decision support systems. For the purpose of ANN modeling, the weights optimization is required in a supervised manner to model the desired function. Conclusions Artificial Neural Network is a stable and provide accurate and reliable solutions. For the validation purpose,we provide error graphs against number of runs.

Towards mechanical characterization of soft digital materials for multimaterial 3D-printing

We study mechanical behavior of soft rubber-like digital materials used in Polyjet multi-material 3D-printing to create deformable composite materials and flexible structures. These soft digital materials are frequently treated as linear elastic materials in the literature. However, our experiments clearly show that these materials exhibit significant non-linearities under large strain regime. Moreover, the materials demonstrate pronounced rate-dependent behavior. In particular, their instantaneous moduli as well as ultimate strain and stress significantly depend on the strain rate. To take into account both hyper- and viscoelasticity phenomena, we employ the Quasi-Linear Viscoelastic (QLV) model with instantaneous Yeoh strain-energy density function. We show that the QLV-Yeoh model accurately describes the mechanical behavior of the majority of the soft digital materials under uniaxial tension.

Conformation constraints for efficient viscoelastic fluid simulation

The simulation of high viscoelasticity poses important computational challenges. One is the difficulty to robustly measure strain and its derivatives in a medium without permanent structure. Another is the high stiffness of the governing differential equations. Solutions that tackle these challenges exist, but they are computationally slow. We propose a constraint-based model of viscoelasticity that enables efficient simulation of highly viscous and viscoelastic phenomena. Our model reformulates, in a constraint-based fashion, a constitutive model of viscoelasticity for polymeric fluids, which defines simple governing equations for a conformation tensor. The model can represent a diverse palette of materials, spanning elastoplastic, highly viscous, and inviscid liquid behaviors. In addition, we have designed a constrained dynamics solver that extends the position-based dynamics method to handle efficiently both position-based and velocity-based constraints. We show results that range from interactive simulation of viscoelastic effects to large-scale simulation of high viscosity with competitive performance.

Modeling of Viscoelastic Electromechanical Behavior in a Soft Dielectric Elastomer Actuator

Soft dielectric elastomer actuators (DEAs) exhibit interesting muscle-like behavior for the development of soft robots. However, it is challenging to model these soft actuators due to their material nonlinearity, nonlinear electromechanical coupling, and time-dependent viscoelastic behavior. Most recent studies on DEAs focus on issues of mechanics, physics, and material science, while much less importance is given to quantitative characterization of DEAs. In this paper, we present a detailed experimental investigation probing the voltage-induced electromechanical response of a soft DEA that is subjected to cyclic loading and propose a general constitutive modeling approach to characterize the time-dependent response, based on the principles of nonequilibrium thermodynamics. In this paper, some of the key observations are found as follows: 1) Creep exhibits the drift phenomenon, and is dominant during the first three cycles. The creep decreases over time and becomes less dominant after the first few cycles; 2) a significant amount of hysteresis is observed during all cycles and it becomes repeatable after the first few cycles; 3) the peak of the displacement is shifted from the peak of the voltage signal and occurs after it. To account for these viscoelastic phenomena, a constitutive model is developed by employing several dissipative nonequilibrium mechanisms. The quantitative comparisons of the experimental and simulation results demonstrate the effectiveness of the developed model. This modeling approach can be useful for control of a viscoelastic DEA and paves the way to emerging applications of soft robots.

Improved convergence based on linear and non-linear transformations at low and high Weissenberg asymptotic analysis

We investigate the accuracy and efficiency of linear and non-linear transformations on the truncated series solutions obtained by asymptotic methods for simple shear and uniaxial elongational viscoelastic flows. The Upper Convected Maxwell, Oldroyd-B, exponential and linear Phan-Thien and Tanner, Giesekus, and FENE-P differential constitutive models are used. The major dimensionless quantity of interest is the Weissenberg number (Wi) in terms of which the unknown dependent flow variables are expanded suitably in series form. The standard regular perturbation method is performed at the Newtonian limit (zero Weissenberg number), while regular or singular perturbation techniques are required to perform the analysis at the purely elastic limit (infinite Weissenberg number). It is shown that the asymptotic approximations at low Wi converge very slowly and have limited radius of convergence, while at high Wi the asymptotic approximations are very accurate even for Wi close to unity. Further improved convergence is achieved by applying a variety of techniques on the original asymptotic solutions, such as Euler's linear transform, Shanks’ non-linear transform, and Padé-type approximants. It is found that the accuracy and the radius of convergence of the transformed solutions increase substantially compared to the original ones. By combining the transformed solutions from both limits, excellent agreement with the exact solutions is demonstrated over the entire range of the Weissenberg number, from zero to infinity, except for a very narrow region close to Wi= 1/2 under uniaxial elongational flow. The results show that, contrary to intuition, viscoelastic phenomena at Wi=O(1) can be predicted accurately using non-linear analysis.

Influence of Nanodisperse Metal Fillers on the Viscoelastic Properties and Processes of Mechanical Relaxation of Polymer Systems

The results of research into the viscoelastic properties and processes of mechanical relaxation of polyvinylchloride (PVC) containing Cu nanoparticles obtained by means of electroerosion crushing and electrohydraulic destruction of agglomerates of disperse Cu in the presence of an ultrasonic field are presented. It is shown that, in the case of longitudinal shear deformation at a frequency of 0.4 × 106 s–1 over a wide range of temperatures and content of ingredients, viscoelastic phenomena depending on structural changes in the PVC system occur. An analysis of quantitative results of the elastic and viscoelastic deformation of a body is carried out taking into account the energy and entropy components of interaction of the polymer and filler at their interface.

B‐spline solution of fractional integro partial differential equation with a weakly singular kernel

The main objective of the paper is to find the approximate solution of fractional integro partial differential equation with a weakly singular kernel. Integro partial differential equation (IPDE) appears in the study of viscoelastic phenomena. Cubic B‐spline collocation method is employed for fractional IPDE. The developed scheme for finding the solution of the considered problem is based on finite difference method and collocation method. Caputo fractional derivative is used for time fractional derivative of order α, . The given problem is discretized in both time and space directions. Backward Euler formula is used for temporal discretization. Collocation method is used for spatial discretization. The developed scheme is proved to be stable and convergent with respect to time. Approximate solutions are examined to check the precision and effectiveness of the presented method.© 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1565–1581, 2017

Generalization of the ordinary state-based peridynamic model for isotropic linear viscoelasticity

This paper presents a generalization of the original ordinary state-based peridynamic model for isotropic linear viscoelasticity. The viscoelastic material response is represented using the thermodynamically acceptable Prony series approach. It can feature as many Prony terms as required and accounts for viscoelastic spherical and deviatoric components. The model was derived from an equivalence between peridynamic viscoelastic parameters and those appearing in classical continuum mechanics, by equating the free energy densities expressed in both frameworks. The model was simplified to a uni-dimensional expression and implemented to simulate a creep-recovery test. This implementation was finally validated by comparing peridynamic predictions to those predicted from classical continuum mechanics. An exact correspondence between peridynamics and the classical continuum approach was shown when the peridynamic horizon becomes small, meaning peridynamics tends toward classical continuum mechanics. This work provides a clear and direct means to researchers dealing with viscoelastic phenomena to tackle their problem within the peridynamic framework.

Effects of graphene functionalization on the long‐term behavior of epoxy/graphene composites evaluated by dynamic mechanical analysis

ABSTRACTGraphene oxide (GO) and its reduced version (RGO) were prepared and functionalized with phenyl glycidol chlorophosphate (PGC) to obtain the corresponding GO‐PGC and RGO‐PGC materials. These graphene systems were used to prepare thermosetting composites with a tetrafunctional epoxy resin, 4,4′‐methylenebis(N,N‐diglycidylaniline) (TGMDA) cured with 4,4′‐diamino‐diphenyl‐sulfone (DDS). The systems were evaluated by dynamic mechanical analysis at constant strain and temperature sweeps to estimate the viscoelastic properties and relaxation phenomena at long time, which is important for modeling the mechanical long‐term behavior. The time temperature superposition (TTS) principle was employed for the construction of a master curve. The addition of the graphene‐type fillers shifted the time when the relaxation phenomena start to occur towards higher values, suggesting a better working temperature and durability of the corresponding nanocomposites when compared to the neat epoxy network. This phenomenon is more pronounced for the systems prepared with functionalized graphenes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44816.