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Natural rubber (NR) composites have been widely applied in damping products to reduce harmful vibrations, while rubber with only a single composition barely meets performance requirements. In this study, rubber blend composites including various ratios of NR and styrene butadiene rubber (SBR) were prepared via the conventional mechanical blending method. The effects of the rubber components on the compression set, compression fatigue temperature rising and the thermal oxidative aging properties of the NR/SBR blend composites were investigated. Meanwhile, the dynamic mechanical thermal analyzer and rubber processing analyzer were used to characterize the dynamic viscoelasticity of the NR/SBR blend composites. It was shown that, with the increase in the SBR ratio, the vulcanization rate of the composites increased significantly, while the compression fatigue temperature rising of the composites decreased gradually from 47 °C (0% SBR ratio) to 31 °C (50% SBR ratio). The compression set of the composites remained at ~33% when the SBR ratio was no more than 20%, and increased gradually when the SBR ratio was more than 20%. [ABSTRACT FROM AUTHOR]

This paper presents a numerical method to solve the non-linear vibration problem of composite structures made of many unidirectional fibers/matrix layers. To take into account damping properties of structures, fractional derivative Zener model for complex moduli is used in each layer. The frequency dependence of these models leads to a non-linear vibration problem. To solve it, a High Order Newton (HON) solver based on homotopy and perturbation techniques is proposed. Thus, the initial non-linear problem turns into a set of linear systems, easier to solve. Numerical results obtained by the HON solver are compared with experimental and numerical results of literature. [ABSTRACT FROM AUTHOR]

In this paper, the stress wave propagation and attenuation laws in heterogeneous materials such as rock and concrete are investigated by equating these materials to periodic materials through the viscoelastic analogy method. Firstly, the relaxation functions and stress response curves of the periodic materials are obtained by using a novel numerical inverse transformation method based on the viscoelastic analogy theory. Then, an experimental study of stress wave propagation in slender concrete rods was carried out on a Hopkinson pressure rod platform. The results show that there is a significant attenuation trend of the stress wave during 10 times of reflections. Comparison of the numerical inverse transform results with the experimental results shows that the decay rate in the experiment is faster than that predicted by simple viscosity. Finally, the effects of geometric dispersion and frictional dissipation of energy are considered in ABAQUS finite element simulations. The finite element analysis results show that inherent viscosity in heterogeneous materials can partially explain the stress wave attenuation in concrete. The viscoelastic simulation method effectively predicts stress wave attenuation in heterogeneous materials and provides theoretical insights for engineering applications. [ABSTRACT FROM AUTHOR]

The problems of vibration and noise have seriously affected people's production and life. Hydrogel can be used as damping material because of its good viscoelasticity, but the current damping material is difficult to meet the needs of actual production and life because of the lack of wide damping temperature and frequency range and high loss factor. In this work, ammonium persulfate was used as both initiator and oxidant to form a mixed double network hydrogel of polyacrylamide and oxidized sodium alginate. The double network hydrogel prepared by this method has good adhesion and mechanical properties. In addition, due to the adjustable viscoelasticity of the hydrogel, the hydrogel shows excellent damping properties. When the concentration of MBA is 0.02%, it can reach the temperature range of 0-125 ℃, and the damping factor is more than 0.3. The visualization experiment proves the practical application effect of the hydrogel, so it is expected to be used as a damping material in damping, noise reduction and other fields in the future. [ABSTRACT FROM AUTHOR]

We advanced a novel model to calculate viscoelastic lung compliance and airflow resistance in presence of mucus, accounting for the quasi‐linear viscoelastic stress–strain response of the parenchyma (alveoli) tissue. We adapted a continuum‐based numerical modeling approach for the lung, integrating the fluid mechanics of the airflow within individual generations of the bronchi and alveoli. The model accounts for elasticity of the deformable bronchioles, resistance to airflow due to the presence of mucus within the bronchioles, and subsequent mucus flow. Simulated quasi‐dynamic inhalation and expiration cycles were used to characterize the net compliance and resistance of the lung, considering the rheology of the mucus and viscoelastic properties of the parenchyma tissue. The structure and material properties of the lung were identified to have an important contribution to the lung compliance and airflow resistance. The secondary objective of this work was to assess whether a higher frequency and smaller volume of harmonic air flow rate compared to a normal ventilator breathing cycle enhanced mucus outflow. Results predict, lower mucus viscosity and higher excitation frequency of breathing are favorable for the flow of mucus up the bronchi tree, towards the trachea. [ABSTRACT FROM AUTHOR]

Ink transfer is achieved by the squeezing and rotation of two rollers, one of which is a roller coated with a viscoelastic rubber layer. In this study, the force caused by ink hydrodynamic pressure on the rubber roller during the rotation is considered, the viscoelasticity of ink and rubber is equivalently substituted by spring-damping unit, and a rolling squeezing theoretical model of two rollers is established to study the node deformation of the rubber roller. The validity of the theoretical model is verified by experiments. Results show that the deformation of the rubber roller is greatly affected by the roller rotational speed, rubber layer thickness, and nip width. The rotational speed and nip width have a significant influence on the stiffness-damping of the ink layer and the ink force, and the rubber layer thickness has a remarkable effect on the squeezing deformation between the rollers. [ABSTRACT FROM AUTHOR]

Following the principle of constrained-layer damping (CLD), fiber-metal-elastomer laminates (FMELs) offer a high potential for damped lightweight structures, overcoming the undesirable vibration characteristics of conventional lightweight materials. While proven to be versatile and efficient, the damage-tolerance of such laminates is unexplored. This study for the first time in literature addresses the damage-tolerance of this efficient damping mechanism using a combined experimental and numerical approach. Results of experimental low-velocity impact tests on different configurations of FMELs are presented. In subsequent numerical modal analyses, different types of damage, namely delaminations, intra-ply damage and permanent deformation, are modeled and their influence on the vibrational behavior is investigated. While all types of damage influence the natural frequencies and modal damping ratios with a strong mode dependency, all laminates retain a high amount of modal damping with losses typically not higher than 15%. The results obtained reveal, that CLD is an efficient intrinsic damping measure in FMELs even in the presence of different types of damage. The key contributions of this paper include the thorough experimental characterization of low-velocity impact damages in different configurations of FMELs as well as the numerical assessment of those in frequency-domain simulations. • Low-velocity impact experiments reveal intra-ply damage, delaminations and permanent deformation as predominant damage modes. • Simulations of damaged laminates in numerous configurations reveal the influence of laminate damage on vibration behavior. • The constrained-layer damping mechanism proves to be tolerant towards impact damage. • The effects of damage on damping properties are highly mode dependent. [ABSTRACT FROM AUTHOR]

This study investigates the damping vibration mechanism of composites using a decoupled two-scale simulation with an image-based periodic representative volume element (RVE). The parameters of the macroscopic viscoelastic constitutive law for unidirectional composites were determined using a homogenization method based on the properties of the constituent and microscale image-based periodic RVE. Using the determined viscoelastic properties, a macroscale modal simulation was conducted to predict the natural frequencies, modal damping ratios, and mode shapes of composite laminates. Then, a macroscale transient vibration simulation was performed using the calculated modal shapes and damping ratios. This simulation scheme was verified by comparing the predicted natural frequencies, modal damping ratios, mode shapes, and transient vibration responses with the experimental results. Following the homogenization simulations conducted from micro to macro scales, localization simulations were carried out from macro to micro scales to explore how microscopic deformation affects macroscopic damping properties. By utilizing both bottom-up and top-down simulations, the mechanism of vibration damping is examined by considering the microscopic structure and matrix deformation. • This study investigates the damping vibration mechanism of composite materials. • A decoupled two-scale two-way simulation scheme was established. • An image-based periodic representative volume element was used as a micro-scale model. • A bottom-up simulation was able to reproduce the experimental vibration behaviors. • A top-down simulation revealed the mechanism of damping vibration of composites. [ABSTRACT FROM AUTHOR]

The free vibrations of cantilever slender beams of polymers, which are viscoelastic materials, are theoretically described using the simple Euler--Bernoulli assumption. The comparison between the theory and the experimental data collected for a thermoplastic elastomer, polyether block amide, shows very satisfactory results. Consequently, the theory is used for a thoughtful analysis of the impact of the material parameters and the beam geometry on its free vibration. Finally, the comparison of the dynamic behaviors of two polymers, using the free vibration test and a simple uniaxial tension/relaxation test, is discussed. Résumé. Les vibrations libres d'une poutre encastrée de polymère, mesurées expérimentalement sont reproduites théoriquement à l'aide de l'hypothèse des poutres d'Euler--Bernoulli, une fois le comportement viscoélastique du matériau identifié classiquement. La théorie permet alors de simplement faire varier les paramètres matériaux et géométriques de la poutre afin de tester leurs impacts sur le test de vibration libre. En utilisant l'analyse théorique et en observant la réponse de deux matériaux lors d'un essai simple de traction/ relaxation, il est possible de prédire leur comportement relatif en vibration libre. [ABSTRACT FROM AUTHOR]

This paper presents a comparative investigation into behaviors of different damping terms of viscoelastic contact models, and introduces a novel damping term with dimensional reasoning analysis and by considering the effect of relaxation time of viscoelastic spheres. Behaviors of different contact models are compared in terms of predictions of non-dimensional variables, where the influence of damping parameters on behaviors of viscoelastic models is analyzed and the relationship between non-dimensional damping parameters and the coefficient of restitution is discussed. The damping parameter related to relaxation time is found to affect behaviors of the current viscoelastic contact model significantly. Viscoelastic models of different damping terms exhibit different behaviors, especially for a heavily damped case. Comparison between simulation and free fall impact test of viscoelastic balls demonstrates that the current contact model involving relaxation time fits experimental results better than other contact models. Unlabelled Image • Contact model involving relaxation time better fits impact test of viscoelastic balls. • It established relationship between damping parameters and coefficient of restitution. • It explored damping term for viscoelastic particles by dimensional reasoning analysis. • It illustrated behaviors of viscoelastic contact models of different damping terms. [ABSTRACT FROM AUTHOR]

This paper presents a two-variable refined plate theory for free vibration of functionally graded material (FGM) plates lying on viscoelastic Winkler–Pasternak foundations. The present work aims to examine the vibrations by a higher-order shear deformation theory including a new function of warping. The governing equations are derived from the principle of virtual displacements. Some illustrative examples are given in an attempt to solve the free vibration problem of a rectangular plate with various boundary conditions. The effects of damping on free vibrations, considering various parameters, are examined in detail. In the end, it is concluded that the present results with the new shear shape function of viscoelastic foundation are found to be in good agreement with other available results and the proposed method can easily be used to solve free vibration problems of the FGM plates. [ABSTRACT FROM AUTHOR]

This study numerically investigates the mechanism of vibration damping in woven composite structures using a decoupled multi-scale simulation scheme that considers the macroscopic woven structure consisting of bundles and resin-rich regions, as well as the microscopic structure in the bundles made of fiber and resin. For efficient macroscopic modeling of complicated woven structures, the embedded element technique is introduced to utilize separate meshes for bundles and resin regions. A special treatment is introduced for volumetric integration in the mesh overlapped between bundle and resin regions, which is required to calculate the strain energy and modal damping ratio of the entire woven structure. Using the developed scheme, the natural frequencies and damping ratios of braided and laminated composite cylinders are investigated. By comparing the vibration properties of two braided composites with different braided angles and two unidirectional laminates with different fiber volume fractions, the effects of the fiber volume fraction, braided angle, and out-of-plane waviness on vibration properties are discussed. Based on the mode shape and resultant energy dissipation within each bundle and resin-rich region, the braided composite with a large braided angle exhibited the best damping properties, mainly owing to the in-plane shear deformation in the crimped braided bundles. [ABSTRACT FROM AUTHOR]

In this paper we consider a thermo-viscoelastic system of Timoshenko-type with nonlinear damping and a distributed delay acting on transverse displacement. The heat flux of the system is governed by Cattaneo's law. We use the energy method and some properties of convex functions to prove, regardless of the speeds of wave propagation, general decay estimate from which the exponential, logarithmic and polynomial types of decay are only special cases. [ABSTRACT FROM AUTHOR]

Highlights • The study aims at comparing the damping efficiency of two viscoelastic materials in an uncertain temperature context. • The damping efficiency is numerically computed using a specific complex eigenvalue analysis applied on the finite element model of a steel frame structure. • Two different adequate rheological models are introduced depending on the behavior of the materials, and the proposed models take into account the temperature dependency. • The info-gap theory is used to evaluate the modal damping performances in an uncertain temperature context when no statistical information on the temperature evolution is available. • It is shown that the best material choice changes according to the horizon of uncertainty on temperature. Abstract Viscoelastic materials are commonly used for passive treatment in many applications. They exhibit a specific behavior depending on frequency and temperature, and thus damping performances can strongly vary in an uncertain environment for which these materials can be used far from their optimal nominal value. The problem studied in this paper is the compromise to find between damping efficiency and robustness to lack-of-knowledge when using structure with viscoelastic components. This question is illustrated on a damper made of a steel frame, considering two kinds of viscoelastic materials: the tBA-PEGDMA which is a viscoelastic material that exhibits very good performances but a very sensitive behavior according to frequency and temperature, and the silicone rubber SI 965 which is less efficient but whose behavior is less frequency- and temperature-dependent than the tBA-PEGDMA. In order to evaluate the performances, a complex eigenvalue analysis is performed on the finite element model of the damper, with different rheological material models. In a very original way, the temperature is introduced in the model to investigate its influence on the modal damping. In this context, and using the developed methodologies, a robustness study is performed using the info-gap theory to evaluate the modal damping performances for the two considered viscoelastic materials in an uncertain temperature environment. It is shown that the best design choice in terms of viscoelastic behavior really depends on the degree of lack-of-knowledge: robust and better performances can be obtained while quantifying the horizon of uncertainty. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the free vibration of an oscillator containing a viscoelastic damping modeled by fractional derivative (FD). Based on the fact that the vibration has slowly changing decay rate and frequency, we present an approach to analytically obtain the initial decay rate and frequency. In addition, ordinary differential equations governing the decay rate and frequency are deduced, according to which accurate approximation is obtained for the free vibration. Numerical examples are presented to validate the accuracy and effectiveness of the presented approach. Based on the obtained results, we analyze the decay rate and the frequency of the free vibration. Emphasis is put on their time-dependence, indicating that the decay rate decreases but the frequency increases with time increasing. [ABSTRACT FROM AUTHOR]

Highlights • A 3-D formulation for vibration and damping analysis of sandwich shallow shells is presented. • Arbitrary boundary conditions including elastic ones are considered. • Frequency dependent viscoelastic models are discussed for various temperatures and boundary conditions. • New results for sandwich plate, spherical, cylindrical and hyperbolic paraboloidal shells are calculated. • 3-D modal shapes are depicted for the sandwich shallow shells. Abstract In this paper, we present an accurate three-dimensional formulation for the vibrations of the laminated and sandwich shallow shells. The sandwich structure is characterized by a thick viscoelastic core and two thin composite faces. Frequency dependent viscoelastic models are introduced in the sandwiches. Without any change in solution procedure, the formulation makes it quite easy to change the boundary conditions. The solution can be obtained by means of Rayleigh–Ritz process combined with the three-dimensional modified Fourier series which are actually assumed displacement functions. These functions, without need to meet the boundary conditions in advance, take the form of the three-dimensional Fourier series with several closed-form auxiliary functions which are supplemented to deal with the discontinuities at the boundaries in terms of displacements and its derivatives. Besides, only three assumed displacement variables are employed in the formulation which effectively reduces the computation cost. The reliability and accuracy of the method are demonstrated by numerical comparisons and examples with the constant viscoelastic models as well as the frequency dependent ones. Modal analysis and parametric studies are conducted to examine the influences of the boundary condition, dimension, lamination scheme, temperature and frequency dependence of the materials. [ABSTRACT FROM AUTHOR]

This paper focuses on the thrust ripple reduction in permanent magnet synchronous linear motors (PMSLMs), which are applied to laser cutting machines. To meet the high-precision performance requirements of laser cutting machines, a novel auxiliary suppression device, tuned viscoelastic damper (TVD), is designed to reduce the thrust ripple of PMSLM. First, TVD is designed with the structure and motion characteristics of PMSLM. The PMSLM with TVD is an integrated structure. Then, the equivalent magnetization method is used to analyze the PMSLM thrust, which is the excitation of TVD. Under the excitation of the PMSLM thrust, the damping force of TVD is expressed by the Kelvin model and validated by finite-element analysis (FEA). Subsequently, the thrust of PMSLM with TVD is obtained by adding the PMSLM thrust and TVD damping force. Finally, the thrust ripple rate is selected as a performance index of TVD in reducing the thrust ripple. Simulation is performed to confirm the theoretical analysis. A prototype of PMSLM with TVD is manufactured and experiments are conducted to validate the effectiveness of the proposed auxiliary suppression device. [ABSTRACT FROM AUTHOR]

Vibrational microplatforms that exploit complex three-dimensional (3D) architectures assembled via the controlled compressive buckling technique represent promising candidates in 3D micro-electromechanical systems (MEMS), with a wide range of applications such as oscillators, actuators, energy harvesters, etc. However, the accuracy and efficiency of such 3D MEMS might be significantly reduced by the viscoelastic damping effect that arises from material viscosity. Therefore, a clear understanding and characterization of such effects are essential to progress in this area. Here, we present a study on the viscoelastic damping effect in complex 3D structures via an analytical model and finite element analysis (FEA). By adopting the Kelvin-Voigt model to characterize the material viscoelasticity, an analytical solution is derived for the vibration of a buckled ribbon. This solution then yields a scaling law for the half-band width or the quality factor of vibration that can be extended to other classes of complex 3D structures, as validated by FEA. The scaling law reveals the dependence of the half-band width on the geometries of 3D structures and the compressive strain. The results could serve as guidelines to design novel 3D vibrational microplatforms for applications in MEMS and other areas of technology. [ABSTRACT FROM AUTHOR]

In this communication, we propose a nonlocal fractional viscoelastic model of a nanobeam resting on the fractional viscoelastic foundation and under the influence of the longitudinal magnetic field and arbitrary number of attached nanoparticles. Size effects are taken into account using the differential form of the nonlocal constitutive relation together with the fractional Kelvin-Voigt model. The governing equation for the free vibration of a nanobeam is derived, where Maxwell’s equations are used in order to represent the effect of the longitudinal magnetic field. We propose an analytical solution of the problem based on the Laplace transform, Mellin-Fourier transforms, and residue theory. From the validation study, it is shown that the obtained complex roots of the characteristic equation, where the imaginary part is the damped frequency and the real part is the damping ratio, are approximated eigenvalues of the system. In the parametric study, several numerical examples are given to investigate the influence of different parameters on complex roots as well as different masses and numbers of nanoparticles on the damped vibration behavior of a nanobeam system. [ABSTRACT FROM AUTHOR]

Many natural materials, such as shell and bone, exhibit extraordinary damping properties under dynamic outside excitations. To explore the underlying mechanism of these excellent performances, we carry out the shear-lag analysis on the unit cell in staggered composites. Accordingly, the viscoelastic properties of the composites, including the loss modulus, storage modulus, and loss factor, are derived. The damping properties (particularly, the loss modulus and loss factor) show an optimization with respect to the constituents' properties and morphology. The optimal scheme demands a proper selection of four key factors: the modulus ratio, the characteristic frequency of matrix, aspect ratios of tablets, and matrix. The optimal loss modulus is pointed out to saturate to an upper bound that is proportional to the elastic modulus of tablets when the viscosity of matrix increases. Furthermore, a loss factor even greater than one is achievable through microstructure design. Without the assumption of a uniform shear stress distribution in the matrix, the analysis and formulae reported herein are applicable for a wide range of reinforcement aspect ratios. Further, for low-frequency loading, we give practical formulae of the three indexes of damping properties. The model is verified by finite element analysis (FEA) and gives novel ideas for manufacturing high damping composites. [ABSTRACT FROM AUTHOR]

Three different dissipation models have been used to identify the increase of damping with the vibration amplitude for a rubber rectangular plate. For this purpose, a square rubber plate made of silicone with fixed edges has been tested and its linear and nonlinear responses have been measured by laser Doppler vibrometers. First, a reduced-order model, using energy based approach and global discretization, has been constructed, taking into account geometric imperfections; the linear viscous damping at each excitation level in the nonlinear regime has been identified from the experimental data. This numerical model with linear viscous damping has been widely validated and constitutes the basis for comparison with subsequent damping identifications. Then, three different single degree of freedom models have been fitted to the same experimental data; each model has a different damping description. Specifically, the models are based on a modified Duffing oscillators with linear, quadratic and cubic stiffness and: (i) a linear viscous damping; (ii) a nonlinear viscoelastic dissipation described by the loss factor; (iii) a standard linear solid viscoelastic model with nonlinear springs. The dissipation identified by the different models is discussed and confirms the major nonlinear nature of damping as a function of the vibration amplitude. [ABSTRACT FROM AUTHOR]

Nonlinear aeroelastic systems are prone to the appearance of limit cycle oscillations, bifurcations, and chaos. Such problems are of increasing concern in aircraft design since there is the need to control nonlinear instabilities and improve safety margins, at the same time as aircraft are subjected to increasingly critical operational conditions. On the other hand, in spite of the fact that viscoelastic materials have already been successfully used for the attenuation of undesired vibrations in several types of mechanical systems, a small number of research works have addressed the feasibility of exploring the viscoelastic effect to improve the behavior of nonlinear aeroelastic systems. In this context, the objective of this work is to assess the influence of viscoelastic materials on the aeroelastic features of a three-degrees-of-freedom typical section with hardening structural nonlinearities. The equations of motion are derived accounting for the presence of viscoelastic materials introduced in the resilient elements associated to each degree-of-freedom. A constitutive law based on fractional derivatives is adopted, which allows the modeling of temperature-dependent viscoelastic behavior in time and frequency domains. The unsteady aerodynamic loading is calculated based on the classical linear potential theory for arbitrary airfoil motion. The aeroelastic behavior is investigated through time domain simulations, and subsequent frequency transformations, from which bifurcations are identified from diagrams of limit cycle oscillations amplitudes versus airspeed. The influence of the viscoelastic effect on the aeroelastic behavior, for different values of temperature, is also investigated. The numerical simulations show that viscoelastic damping can increase the flutter speed and reduce the amplitudes of limit cycle oscillations. These results prove the potential that viscoelastic materials have to increase aircraft components safety margins regarding aeroelastic stability. [ABSTRACT FROM AUTHOR]

Rubber is an effective and low-cost material for mechanical vibration suppression because in the glass-transition zone it exhibits high damping abilities. However, analytical predictions of the viscoelasticity of rubber are inaccurate because viscoelasticity depends on the frequency, amplitude and pre-deformation; this inaccuracy impedes the mechanical design of rubber parts. Previously, viscoelasticity measurements under uniaxial deformation have been performed. However, the dominant parameters cannot be clarified in these tests because the strain distribution is not uniform, and the shear strain and hydrostatic pressure are cross-coupled. In this research, a new test method was studied that enabled the direct measurement of the high-frequency viscoelasticity of rubber by independently applying simple shear pre-strain and hydrostatic pressure. The viscoelasticity of nitrile rubber was measured using this method at frequencies from 200 Hz to 2000 Hz under shear pre-strain and pre-compression. The results showed that hydrostatic pressure had a much larger influence than shear pre-strain. The hydrostatic pressure should be considered as a more essential parameter than the stretch or strain in this material. [ABSTRACT FROM AUTHOR]

The viscoelastic properties of waterlogged wood (WLW) were investigated via dynamic mechanical analysis (DMA) at room temperature and under water saturated conditions, aiming at the investigation of the relationships between viscoelasticity and chemical composition. Different softwoods (SWs) and hardwoods (HWs) from several archaeological sites were sampled, which had different levels of decay (from highly-decayed to little changed). The analytical methods included lignin and holocellulose determination by Fourier transform infrared (FTIR) spectroscopy, moisture content (MC), basic density (BD), micromorphological observations, and the DMA was performed in three-point bending and submersion mode. Both HWs and SWs showed an exponential decrease of both storage modulus (E′) and loss modulus (E″), which are related to the amount of crystalline and paracrystalline cellulose left in the cell wall, respectively. The ratio E″/E′ (tanδ) varied with the frequency in different ways depending on the preservation state of the samples. Less decayed material had a higher tanδ than the fresh reference wood and lower (or similar) tanδ in the case of highly decayed samples. Accordingly, the long-term behaviour under a certain sustained load of WLW is decay dependent. [ABSTRACT FROM AUTHOR]

Owing to growing environmental awareness in green technology, the whole gamut of engineering sector has started shifting towards natural fibre-oriented materials from synthetic materials. The adequate dynamic stability and damping property are important design necessities in a polymer composite structure. Given this perspective, this paper discusses the formulation of distinct hybrid laminates with various weight ratios of jute- and linen-incorporated epoxy polymer and the influence of their weight ratios on the dynamic attributes. Dynamic mechanical thermal analysis is employed to quantify the viscoelastic attributes of the hybrid laminates. The natural frequency of cantilevered laminate beam is determined experimentally by free vibration analysis and the damping factor of the laminate beam is computed analytically by half power bandwidth technique. The cole-cole mapping analysis is made to understand the interfacial adhesion of the different laminates with hybrid configurations. The hybrid laminate with equal weight proportion of jute and linen is found to be optimal as it has exhibited maximum stiffness property and load bearing capability with high glass transition temperature. The influences of frequency on storage modulus and loss factor of the optimal hybrid laminate with respect to temperature are analysed. Several vibratory responses of the optimal hybrid laminate beam for different natural frequencies and damping factors are elicited and studied. [ABSTRACT FROM AUTHOR]

In the context of passive damping, various mechanical systems from the space industry use elastomer components (shock absorbers, silent blocks, flexible joints,…). Among other specificities, elastomers have frequency dependent characteristics. The computational cost of the associated numerical models, using viscoelastic constitutive behavior, may become too expensive during a design process. To solve this problem, the aim of this work is to propose an efficient reduced viscoelastic model of rubber devices. The first step is to choose an accurate material model that represents the viscoelasticity. The second step is to reduce the rubber device finite element model to a super-element that keeps its frequency dependent properties. This reduced model is first built by taking into account the fact that the device's interfaces are much more rigid than the rubber core. Therefore, kinematic constraints enforce the rigid body motion of these interfaces, reducing them to twelve degrees of freedom only (three rotations and three translations per face). The super-element is then built by condensing the core of the finite element model on the interfaces via a Component Mode Synthesis (CMS) method, adapted here to viscoelastic damping. As an application, the dynamic behavior of a structure supported by four rubber devices under harmonic loads is analyzed to show the efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper considers dampers comprising collections of viscoelastic particles that are subjected to vibrations whose amplitude is such that slip between particles is negligible. Energy dissipation occurs primarily by viscoelastic processes within each particle and is maximized when standing waves are set up in the granular medium. In this work, the medium is represented as an equivalent viscoelastic solid and predictions of performance employ models constructed using standard finite element software. Two numerical approaches are considered: one uses the Direct Frequency Response and the other uses standard modal analysis in conjunction with analytical expressions for energy dissipation based on the wave equation. The performance of these prediction techniques is compared with measured behavior from experiments on a box-shaped structure and a hollow composite tube assembly. The computational efficiency of the modal technique allowed a brief investigation of the effects of uncertainties in the actual nature of the granular arrangement. Results show that both prediction methods give a reasonable level of accuracy. Differences between predicted and measured behavior are shown to be of the same order as the uncertainty in the prediction itself. For the systems considered, it is shown that the methods are appropriate for acceleration amplitudes up to almost that of gravity. [ABSTRACT FROM AUTHOR]

In this study, the vibration and damping performances of flax fibre reinforced composites with an interleaved natural viscoelastic layer are investigated. The experimental analysis is studied using beam test specimens and an impulse technique in flexural vibration. Damping modeling is developed using finite element analysis which evaluates the different energies dissipated in the material directions of the layers. The results obtained show that this analysis corresponds closely to experimental results. Finally, a parametric study is carried out using finite element analysis, to investigate the effects of flax fibre directions, thickness and Young’s modulus of the natural viscoelastic layer. [ABSTRACT FROM AUTHOR]

The optimal design of viscoelastic laminated composite panels with active piezoelectric patches is addressed in this paper. Constrained optimization is conducted to determine optimal distributions of piezoelectric patches on the top and bottom surfaces of laminated plates with viscoelastic layers. The design variables are the number and position of these patches, and the objectives are the minimization of the number of patches, the maximization of the fundamental modal loss factor and the maximization of the fundamental natural frequency. The problem is solved using the Direct MultiSearch (DMS) solver for derivative-free MultiObjective Optimization (MOO). The objective functions are evaluated by a finite element model that was developed for laminated sandwich plates incorporating piezoelectric or viscoelastic layers. Trade-off Pareto optimal fronts and the respective optimal active patch configurations are obtained and the results are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Development and design of novel materials based on their micro-structural arrangements are being intensely investigated due to their wide range of real and potential applications. One of the key objectives of such design is to achieve multiple properties, which are often competing in nature (such as high stiffness-high damping, high strength-high toughness etc.), within a single composite material. In the present work we propose a novel interlocking micro-architecture design to achieve high symmetry in a plane within a composite. The present study shows that constraining a very low volume fraction of high damping polymer within this micro-architecture, together with a stiff polymer, results in a simultaneously high stiffness and high damping polymer composite. The proposed micro-architecture design possesses high symmetry that is not commonly found in fiber-reinforced polymer composites. The interlocking feature avoids use of extra adhesives for holding two adjacent building blocks. Finite element simulations are performed by considering the micro-architecture made of two widely used polymeric materials such as polymethyl methacrylate (PMMA as the stiffer building block) and polyurethane (PU as the soft viscous material). Our numerical predictions show remarkable stiffness and damping properties for the design over a wide range of frequencies. Simulations are also performed considering contact between two polymer interfaces to establish the fact that the geometric interlocking works well without any use of adhesive for holding the blocks together. Further simulations are performed under high frequency impulse pressure loading to study dynamic wave propagation through the micro-architecture that shows the near-isotropic response of the proposed micro-architecture. [ABSTRACT FROM AUTHOR]

Propagation of a torsional wave in a doubly-layered half-space structure of an initially stressed heterogeneous viscoelastic layer sandwiched between a layer and a half-space of heterogeneous dry sandy media is studied. A closed form complex expression for the velocity profile is obtained under effective boundary conditions. The real part of the complex expression provides a dispersion equation, and the imaginary part yields a damping equation. The derived dispersion and damped equations are in well agreement with the classical Love wave condition. In addition, to study the effect of the dissipation factor, the attenuation coefficient, the sandy parameters, the initial stress, the heterogeneity parameters, and the thickness ratio parameter, some noteworthy contemplations are made by numerical calculations and graphical visuals. The results of this paper may present a deeper insight into the behaviour of propagation phenomena in heterogeneous viscoelastic and heterogeneous dry sandy materials that can provide a theoretical guide for the design and optimization in the field of earthquake engineering. The study also reveals that the presence of a damping part due to viscoelasticity affects the torsional wave propagation significantly. [ABSTRACT FROM AUTHOR]

This paper presents dynamic behavior of an isotropic magnetorheological elastomer (MRE) under harmonic tensile-compressive loadings. The dynamic viscoelastic behavior of the MRE is experimentally investigated at various external magnetic fields as well as different loadings of frequency and strain. A generalized Maxwell viscoelastic model is developed to portray the relationships between the stress and strain of the MRE based on input frequency, strain, and magnetic flux density. The coefficients of the proposed model under various input conditions, such as magnetic flux density, strain amplitude, and input frequency, are calculated by implementing the least-squares method. Unlike the previous models of MRE, which mostly focused on shear mode, the present model enables to capture dynamic behavior of MRE in tensile-compressive loadings. Furthermore, tensile-compressive operation offers the most compact design in many axial loading applications such as rotor systems, MRE bearing isolators in bridges, suspension systems in cars, building isolators, and vertical vibration settings, which cannot be controlled with MRE in shear mode due to its low capacity of stiffness. The results show that the proposed model can effectively predict dynamic behavior of MREs under tensile-compressive loadings. This model is useful to simulate the performances of MRE base devices under harmonic tensile-compressive loadings. [ABSTRACT FROM PUBLISHER]

Explicit expressions for the complex longitudinal shear moduli of viscoelastic composites with arbitrary symmetric structure are obtained. Specific formulas of dissipative properties are obtained for tetragonal composites with elliptic and rectangular fibre cross-sections, as well as for hexagonal (not necessarily regular) composites with elliptic fibre cross-section. The correspondence principle and the duality rule are used. The results of calculations for particular cases agree well with the known published data. [ABSTRACT FROM AUTHOR]

Viscoelastic materials have been widely used for the purpose of passive vibration mitigation in various types of mechanical systems, including, industrial machinery, civil structures and vehicles. In this paper, the use of those materials in aeroelastic systems is investigated, with emphasis placed on the influence of the viscoelastic behavior on the flutter speeds of two-degree-of-freedom typical section models, in which viscoelastic elements are introduced in addition to elastic elements associated to heave and pitch motions. The equations of motion of the aeroelastic system are modified to account for the dependence of the viscoelastic behavior on frequency and temperature, by using the concepts of complex modulus and shift factor. The aerodynamic forces and moments in subsonic regime are modeled according to Theodorsen's method. Numerical simulations are conducted to evaluate the influence of the addition of viscoelastic elements on the flutter speed and elucidate the separated influences of stiffness and damping additions. An experimental wind tunnel setup consisting of a rigid wing supported by flexible elements in pitch and plunge motions has been modified to enable the introduction of viscoelastic elements in parallel to those flexible elements. For various configurations of viscoelastic additions, the flutter instability is characterized from vibration measurements performed for increasing flow speeds in the vicinity of the stability boundary. The experimental results are used to validate the numerical model derived for the aeroviscoelastic system and confirm both qualitatively and quantitatively the predictions of the simulations, especially the possibility of increasing the flutter speed by the inclusion of viscoelastic materials. [ABSTRACT FROM AUTHOR]

We investigate a hyperbolic PDE, modeling wave propagation in viscoelastic media, under the influence of a linear memory term of Boltzmann type, and a nonlinear damping modeling friction, as well as an energy-amplifying supercritical nonlinear source: { u t t − k ( 0 ) Δ u − ∫ 0 ∞ k ′ ( s ) Δ u ( t − s ) d s + | u t | m − 1 u t = | u | p − 1 u , in Ω × ( 0 , T ) , u ( x , t ) = u 0 ( x , t ) , in Ω × ( − ∞ , 0 ] , where Ω is a bounded domain in R 3 with a Dirichlét boundary condition. The relaxation kernel k is monotone decreasing and k ( ∞ ) = 1 . We study blow-up of solutions when the source is stronger than dissipations, i.e., p > max ⁡ { m , k ( 0 ) } , under two different scenarios: first, the total energy is negative, and the second, the total energy is positive with sufficiently large quadratic energy. This manuscript is a follow-up work of the paper [30] in which Hadamard well-posedness of this equation has been established in the finite energy space. The model under consideration features a supercritical source and a linear memory that accounts for the full past history as time goes to −∞, which is distinct from other relevant models studied in the literature which usually involve subcritical sources and a finite-time memory. [ABSTRACT FROM AUTHOR]

This article deals with the propagation of SH-wave in a vertically heterogeneous viscoelastic layer lying over a micropolar elastic half-space. Dispersion and damping equations are obtained analytically in closed form. Phase and damped velocities are computed numerically and depicted by means of a graph to exhibit the substantial effect of heterogeneity, viscoelasticity (internal friction), and micropolar parameter. As a special case of the problem, it is found that deduced dispersion relation is well in agreement to the classical-Love wave equation and damping equation vanishes identically for the isotropic case. Influence of micropolarity present in the medium of half-space is highlighted through comparative study. [ABSTRACT FROM AUTHOR]

Microstructural mechanisms such as domain switching in ferroelectric ceramics dissipate energy, the nature, and extent of which are of significant interest for two reasons. First, dissipative internal processes lead to hysteretic behavior at the macroscale (e.g., the hysteresis of polarization versus electric field in ferroelectrics). Second, mechanisms of internal friction determine the viscoelastic behavior of the material under small-amplitude vibrations. Although experimental techniques and constitutive models exist for both phenomena, there is a strong disconnect and, in particular, no advantageous strategy to link both for improved physics-based kinetic models for multifunctional rheological materials. Here, we present a theoretical approach that relates inelastic constitutive models to frequency-dependent viscoelastic parameters by linearizing the kinetic relations for the internal variables. This enables us to gain qualitative and quantitative experimental validation of the kinetics of internal processes for both quasistatic microstructure evolution and high-frequency damping. We first present the simple example of the generalized Maxwell model and then proceed to the case of ferroelectric ceramics for which we predict the viscoelastic response during domain switching and compare to experimental data. This strategy identifies the relations between microstructural kinetics and viscoelastic properties. The approach is general in that it can be applied to other rheological materials with microstructure evolution. [ABSTRACT FROM AUTHOR]

Experimental and numerical methods to identify the linear viscoelastic properties of flax fibre reinforced polymer (FFRP) composite are presented in this study. The method relies on the evolution of storage modulus and loss factor as observed through the frequency response. Free-free symmetrically guided beams were excited in the dynamic range of 10 Hz to 4 kHz with a swept sine excitation focused around their first modes. A fractional derivative Zener model has been identified to predict the complex moduli. A modified ply constitutive law has been then implemented in a classical laminates theory calculation (CLT) routine. Overall, the Zener model fitted the experimental results well. The storage modulus was not frequency dependant, while the loss factor increased with frequency and reached a maximum value for a fibre orientation of 70°. The damping of FFRP was, respectively, 5 and 2 times higher than for equivalent carbon and glass fibres reinforced epoxy composites. [ABSTRACT FROM AUTHOR]

This work deals with the viscoelasticity of the arterial wall and its influence on the pulse waves. We describe the viscoelasticity by a nonlinear Kelvin-Voigt model in which the coefficients are fitted using experimental time series of pressure and radius measured on a sheep's arterial network. We obtained a good agreement between the results of the nonlinear Kelvin-Voigt model and the experimental measurements. We found that the viscoelastic relaxation time--defined by the ratio between the viscoelastic coefficient and the Young's modulus--is nearly constant throughout the network. Therefore, as it is well known that smaller arteries are stiffer, the viscoelastic coefficient rises when approaching the peripheral sites to compensate the rise of the Young's modulus, resulting in a higher damping effect. We incorporated the fitted viscoelastic coefficients in a nonlinear 1D fluid model to compute the pulse waves in the network. The damping effect of viscoelasticity on the high-frequency waves is clear especially at the peripheral sites. [ABSTRACT FROM AUTHOR]

Lamb wave inspection is a promising structural health monitoring method for carbon fiber reinforced plastic laminates. The optimal design of the excitation waveform based on Lamb wave pulse compression is an effective way to improve the inspection resolution in elastic plates. However, due to the viscoelastic property of the composite materials, the material damping effect will influence the amplitude response of the output signals; thus, the current design strategy is no longer applicable. The purpose of this paper is to develop an excitation waveform design strategy based on pulse compression to meet the demands of high-resolution Lamb wave inspection in composite materials. Different parameters that affect the design of excitation such as material damping effect, amplitude response, relative frequency bandwidth, and the selection of excitation waveform are considered synthetically. In addition, an excitation waveform design strategy based on the corrected amplitude response is also established to eliminate the effect of material damping and thus achieve better detection resolution. Finally, an experiment was carried out on a quasi-isotropic composite plate. The experimental results validate the robustness of the amplitude response correction method and the effectiveness of the excitation waveform design strategy. [ABSTRACT FROM AUTHOR]

Granular soils and asphalt concrete materials are characterized by microstructural effects due to their micro-stiffness and micro-inertia. In this work, an attempt is made to investigate if the material microstructure in rigid and flexible pavements affects their dynamic response to loads moving with constant speed under conditions of plane strain and linearity. The rigid pavement is modeled by a homogeneous isotropic and linearly elastic with viscous damping flexural plate resting on a homogeneous isotropic microstructured linear elastic with hysteretic damping half-pane. The flexible pavement is modeled by a layered half-plane with linear isotropic microstructured layers. The top (asphalt concrete) layer is viscoelastic, while the other layers are elastic with hysteretic damping. The dynamic response of both of the above rigid and flexible pavement models to a distributed over a finite length moving load is obtained by using the complex Fourier series approach in conjunction with compatibility and equilibrium at the plate/soil (for rigid pavements) and soil layers (for flexible pavements) interfaces. The so obtained analytical/numerical response solutions for rigid and flexible pavement problems, after verification, are employed for conducting parametric studies in order to assess the microstructural effects on the response of those pavements to moving loads. It was found, at least for the pavement cases considered here, that the presence of the stiff plate in rigid pavements and the viscoelastic top layer in flexible pavements reduce considerably microstructural effects on the pavement response, rendering them not so important for usual vehicle speeds. However, for vehicle speeds very close to the critical speed, microstructural effects become very important. • Analytical/numerical solution of the dynamic response of rigid and flexible pavements to load moving with constant speed under plane strain conditions. • Material behavior in both rigid and flexible pavements is characterized by microstructural effects. • Effects of the micro-stiffness g and micro-inertia h in conjunction with viscoelasticity and the moving load speed on the response of those pavements. [ABSTRACT FROM AUTHOR]

Damping is often an invisible requirement for a good mechanical design. To render the long-term service of viscoelastic dampers, it is essential for design engineers to estimate the degradation of the damping characteristics with age. Nitrile butadiene rubber (NBR) is a widely used damping and sealing material. Viscoelastic sandwich beam configurations have been used to mount electronic components for various automobile and aerospace applications. The present work emphasizes the estimation of modal parameter degradation of NBR with age in an oxidative environment. NBR is assumed to be homogeneous and isotropic and is allowed to age naturally with no load under ambient conditions. Fourier-transform infrared spectroscopy (FTIR) was used to detect age-related changes in the functional groups of the NBR material with age. Dynamic mechanical analysis (DMA) tests were performed to relate the complex properties of naturally aged materials to those of virgin materials in the frequency and temperature domains. Mechanical tests were performed to determine the hardness, elongation break, and failure stress of the virgin NBR and naturally aged NBR. The damping ability of the NBR was investigated using an unconstrained sandwich cantilever beam with aluminum as the base material. For sinusoidal sweep excitation, the influence of viscoelasticity on structural damping was investigated. Based on the experimental results, the damping ability of the NBR has been observed to degrade with age. As the age increased, the damping ability of the NBR decreased by 8% at the first resonance frequency and by 34% at the third resonance frequency. • Deterioration of Mechanical properties of NBR with time and temperature. • Damping ability deterioration of NBR at 40 °C. • Relaxation strength and Specific damping capacity deterioration with temperature and time. • First three fundamental frequencies of Sandwich beam with time and temperature are studied. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a finite element model based on first order shear theory (zig-zag approach) to compute the damping characteristics of sandwich structures with multi-layered frequency-dependent viscoelastic cores. The model is validated versus a layerwise finite element model and used to study damping and rigidity of a laminated glass configuration with a multi-layered visco-elastic core composed of acoustic PVB and PVB. It is shown that the rigidity index of the structure (defined as the adimensionalized inverse of the maximal transverse displacement under a static load) evolves linearly with the viscoelastic layers’ thicknesses and quadratically versus elastic layer’s thickness. The first mode damping and resonant frequency show a non monotonous behaviour. In particular, the existence of an optimal faces thickness for damping is shown while a quadratic behaviour of frequency versus acoustic PVB layer thickness is reported. [ABSTRACT FROM AUTHOR]

This paper presents a simplified coupled thermal-mechanical model for the modelling of viscoelastic dampers with temperatureand frequency-dependent properties subjected to long-term and short-term dynamic loading due to wind and earthquakes. In this numerical model, the self-heating effect caused by molecular-level friction in the viscoelastic (VE) material is captured explicitly using a finite volume thermal diffusion model based only on the physical properties of the steel and VE material. The thermal model is coupled to a single degree of freedom (SDOF) mechanical model, which produces an efficient computational scheme for time-history analyses of VE dampers under both long-term and short-term loading scenarios. The predictions from the proposed model are compared with full-scale experimental results of long-duration wind loading ranging from design level events to extremely rare events, and for shorter but more intense seismic loading scenarios. It is shown that results obtained using this proposed simplified model with idealized geometry predicted well the dynamic response of the damper for all ranges of experimental results thus validating a robust physics based tool for predicting the response of VE dampers. [ABSTRACT FROM AUTHOR]

This paper presents a unified formulation for vibration and damping analysis of a sandwich beams made up of laminated composite face sheets and a viscoelastic core with arbitrary lay-ups and general boundary conditions. A modified Fourier–Ritz method is employed to derive this unified formulation based on Reddy’s higher order shear deformation theory. In composite facings, the material couplings including bending–stretching, bending–twist, and stretching–twist as well as the Poisson’s effect are taken into consideration. Regardless of boundary conditions, the displacements of each layer are expanded as the linear combination of a standard Fourier series and closed-form functions introduced to eliminate all the relevant discontinuities, ensure and accelerate the convergence of the series expansions. This method can be universally applicable to laminated sandwich beams with classical boundaries, elastic boundaries and their combinations without any special change in the solution procedure. Both convergence and accuracy are discussed and this modified Fourier–Ritz method yields many new and accurate results at a low computational cost for various boundary conditions including general elastic boundaries. Furthermore, the effects of some key parameters such as ply configuration, layer number, moduli and thickness ratios on the natural frequency and loss factor are illustrated. Especially the effects of restraints from different directions on two ends of the sandwich beam are deeply investigated. [ABSTRACT FROM AUTHOR]

A double scale asymptotic method (DSAM) is proposed for vibration modeling of large repetitive sandwich structures with a viscoelastic core. The method decomposes the initial nonlinear vibration problem into two small linear ones. The first one is defined on few basic cells while the second is a differential global amplitude equation with complex coefficients. Their numerical computations permit determination of the damping properties as well as pass and stop bands avoiding the direct computation on the whole structure. Viscoelastic frequency dependent core with fractional and anelastic displacement field models are considered. The resulting nonclassical problems are solved by asymptotic numerical method coupled with automatic differentiation. Based on the presented method, a large reduction of the needed computational time and memory is obtained. The accuracy and efficiency of the proposed method are validated with comparisons to the direct simulations by discretization of the whole structure using asymptotic numerical method coupled with automatic differentiation. [ABSTRACT FROM PUBLISHER]

Mechanical assemblies are subjected to many dynamic loads and modifications are often needed to achieve acceptable vibration levels. While modifications on mass and stiffness are well mastered, damping modifications are still considered difficult to design. The paper presents a case study on the design of a bolted connection containing a viscoelastic damping layer. The notion of junction coupling level is introduced to ensure that sufficient energy is present in the joints to allow damping. Static performance is then addressed and it is shown that localization of metallic contact can be used to meet objectives, while allowing the presence of viscoelastic materials. Numerical prediction of damping then illustrates difficulties in optimizing for robustness. Modal test results of three configurations of an assembled structure, inspired by aeronautic fuselages, are then compared to analyze the performance of the design. While validity of the approach is confirmed, the effect of geometric imperfections is shown and stresses the need for robust design. [ABSTRACT FROM AUTHOR]

Stringed instruments are made of high quality wood species from physical, mechanical and acoustical point of view, being carefully selected, kiln dried and processed under specific conditions that assure micro-structural integrity. Maple wood (Acer Pseudoplatanus) for musical instruments is used to getting back plates and sides for string instruments (violin family). This species of wood is valued for both acoustic qualities but mostly for aesthetic, using a natural defect of maple wood characterized by wavy grain. The paper presents the research on visco-elasticity behavior of maple wood with different types of grain deviation in wood from very curly maple to common maple. The storage modulus, loss modulus, damping capacity in varying temperature conditions and for different loading frequencies were determined using dynamical mechanical analysis (DMA). It was found that specimens characterized by very wavy grain shows a high damping capacity of frequency range between 33.33 to 50Hz, unlike specimens of common maple which do not have the capacity of frequency selectivity. [ABSTRACT FROM AUTHOR]

Composite and sandwich structures are appealing to many engineering fields. Despite the increased rate of application, their cost remains higher compared to traditional engineering materials. One of the reasons is the necessary use of experimental characterization and validation of materials and structures respectively. One way to reduce costs is to increase predictive capabilities of simulation software. With this respect, finite element analysis is a powerful tool. However, the finite element modelling of composites and sandwich structures requires dedicated strategies in order to account for their non-homogeneity and anisotropy. This paper presents a C 0 -continuous beam element based on the RZT which is employed to predict the dynamic response of composite and sandwich structures. In particular, structures with viscoelastic layers for vibrations reduction will be considered. The damping modelling will also be addressed. The main objective is to assess the capabilities of the RZT for both dynamic response and damping predictions of laminates and sandwiches. [ABSTRACT FROM AUTHOR]