Layer Of Viscoelastic Material Research Articles

Fractional-Derivative Maxwell Kelvin Model for “5+4” Viscoelastic Damping Wall Subjected to Large Deformation

Considering the larger vibration amplitude and several viscoelastic material layers, a fractional-derivative Maxwell Kelvin (FDMK) viscoelastic mechanical model is proposed for “5+4” viscoelastic damping wall, which is used for vibration control of building structures. The development of the model is based on in-parallel combination of fractional Maxwell model and fractional Kelvin model. The proposed model is experimentally validated and very good agreement between predicted and experimental results was obtained. The results confirm that the FDMK model is accurate in simulating the hysteresis properties of the “5+4” viscoelastic damping wall under large deformation. From the areas of the experimental and theoretical hysteresis loops, under 300% strain, the predicted result is the most accurate in prediction of the energy dissipation and the second is the prediction under 450% strain. Moreover, from the comparisons of dynamic properties (storage modulus, loss modulus, etc.), the FDMK model works satisfactorily. The FDMK model is more sensitive in energy dissipation than in energy storage.

Design of armor for protection against blast and impact

The features of blast and impact that can damage a delicate target supported by a structure include both the peak pressure and the impulse delivered to the structure. This study examines how layers of elastic and visco-elastic materials may be assembled to mitigate these features. The impedance mismatch between two elastic layers is known to reduce the pressure, but dissipation is required to mitigate the transmitted impulse in light-weight armor. A novel design concept called impact or blast tuning is introduced in which a multi-layered armor is used to tune the stress waves resulting from an impact or blast to specific frequencies that match the damping frequencies of visco-elastic layers. The material and geometrical parameters controlling the viscous dissipation of the energy within the armor are identified for a simplified one-dimensional system, to provide insight into how the optimal design of multi-use armor might be based on this concept.

Modal Analyses of a Thin Shell with Constrained Layer Damping (CLD) Based on Rayleigh-Ritz Method

Foreign Object Debris (FOD) is debris or article alien, which may This paper presents analytical results of natural frequencies and loss factors of node-diameter and node-circumferential modes of a thin shell treated with constrained layer damping (CLD) based on Rayleigh-Ritz method. General differential equations of motion of the thin CLD shell are derived firstly by following the Donnell-Mushtari shell theory. By taking the beam characteristic functions as the admissible functions, the Rayleigh-Ritz method is employed to deduce the higher degree equations of natural frequencies of the thin CLD shell under different boundary conditions. It is confirmed that the present method is accurate and convenient so that it is applicable to the thin CLD shell compared with classic analytic method or transfer matrix method. Several examples are achieved and compared to illustrate the effects of the viscoelastic material (VEM) and constrain layer’s thickness ratios on the natural frequencies and modal loss factors, besides the effect of boundary conditions. The results show that the thickness ratio of VEM affects sensitively the modal frequencies and the total damping capacity of the thin CLD shell.

Reflection of a plane sound wave from the boundary of a heterogeneous medium consisting of elastic and viscoelastic layers

The reflection of a plane sound wave incident normally on the flat boundary of a layered heterogeneous medium is considered. The heterogeneous medium consists of periodically alternating layers of elastic and viscoelastic isotropic materials. All the layers are assumed to be parallel or perpendicular to the wavefront and each layer is much thinner than the sound wavelength. The problem is studied using a homogenized model of the layered heterogeneous medium. Specifically, the complex amplitudes of the reflected and transmitted waves are determined as functions of frequency.

The rupture of viscoelastic shell bubble under high intensity ultrasound drive

A model for encapsulated bubble (EB) used in ultrasonic therapy is presented discussing EB's finite amplitude oscillation and rupture under high intensity ultrasound drive. The shell of EB, which is the key to EB dynamics, is treated as a layer of viscoelastic material and its large deformation and stress are expressed analytically. By introducing the critical tolerable stress of the shell material, the threshold drive pressure for the rupture of an EB can be calculated in the framework of the model. The oscillation of an EB on the verge of its rupture is simulated and the results are in agreement with the reported experimental data. The relationship between the drive frequency and EB's rupture is also investigated.

Passage of a plane acoustic wave through a layered composite with components of elastic and viscoelastic materials

The problem of passage of a plane acoustic wave through a flat composite layer of finite thickness is considered. It is assumed that the composite consists of mutually alternate layers of elastic and viscoelastic materials, and all composite layers are either parallel or perpendicular to the incident-wave front. In addition, the thickness of each separate layer of the composite is considered to be much smaller than both the acoustic wavelength and the composite thickness. The formulated problem is investigated using an averaged composite model, which helps to determine the reflection and transmission factors and the change in the sound-intensity level during sound propagation through a composite layer.

Vibration and damping analysis of thick sandwich cylindrical shells with a viscoelastic core under arbitrary boundary conditions

An accurate solution approach based on the first-order shear deformation theory (FSDT) is developed for the free vibration and damping analysis of thick sandwich cylindrical shells with a viscoelastic core under arbitrary boundary conditions. Laminated and sandwich theories are employed to describe the laminated composite layers and viscoelastic material layer, respectively. The present solution is based on a set of new displacement field expression in which the displacements of the middle surface are expanded as a combination of a standard Fourier series and auxiliary functions. Due to the improved displacement expansions, rapid convergence and high accuracy can be easily obtained. The current method can be universally applicable to a variety of boundary conditions including all the classical cases, elastic restraints and their combinations. Natural frequencies and loss factors under various boundary conditions and lamination schemes are calculated, which may serve as benchmark solutions in the future. The effects of some key parameters including the boundary conditions, fiber orientation angle, and number and thickness of the layers on free vibration and damping characteristics of the shells are illustrated and analyzed.

Dynamics of frontal extension of an amoeboid cell

The acellular slime mould Physarum polycephalum forms giant plasmodia that consist of an apical zone, which is succeeded by a vast network of veins where protoplasm is periodically transported back and forth. The apical zone is formed by a dense layer of viscoelastic cell material, whose leading edge is characterized by the development of undulations, which are called fingers. The dynamics of finger formation and evolution was studied. The front is characterized by alternating events of front advancement and stagnation, which are reflected in the development of the fingers. Therefore, the dynamics of the front was divided into two distinct, periodically alternating regimes. The dispersion relations, i.e., the growth rates of fingers of different wavelengths, observed in these two regimes were found to be symmetric, except for the sign of the growth rates. Furthermore, finger splitting occurred once the fingers reached a critical curvature. Our findings are discussed in terms of the intracellular dynamics of this slime mould.

Spherical indentation analysis of stress relaxation for thin film viscoelastic materials

The mechanical testing of thin layers of soft materials is an important but difficult task. Spherical indentation provides a convenient method to ascertain material properties whilst minimising damage to the material by allowing testing to take place in situ. However, measurement of the viscoelastic properties of these soft materials is hindered by the absence of a convenient yet accurate model which takes into account the thickness of the material and the effects of the underlying substrate. To this end, the spherical indentation of a thin layer of viscoelastic solid material is analysed. It is assumed that the transient mechanical properties of the material can be described by the generalised standard linear solid model. This model is incorporated into the theory and then solved for the special case of a stress relaxation experiment taking into account the finite ramp time experienced in real experiments. An expression for the force as a function of the viscoelastic properties, layer thickness and indentation depth is given. The theory is then fitted to experimental data for the spherical indentation of poly(dimethyl)siloxane mixed with its curing agent to the ratios of 5:1, 10:1 and 20:1 in order to ascertain its transient shear moduli and relaxation time constants. It is shown that the theory correctly accounts for the effect of the underlying substrate and allows for the accurate measurement of the viscoelastic properties of thin layers of soft materials.

ACOUSTICAL SOUND PROOFING MATERIAL WITH IMPROVED FIRE RESISTANCE AND METHODS FOR MANUFACTURING SAME

A material for use in building construction (partition, wall, ceiling, floor or door) that exhibits improved acoustical sound proofing and fire resistance. The material comprises a laminated structure having as an integral part thereof one or more layers of intumescent viscoelastic material which also functions as a glue, energy dissipating layer, and a fire resistive layer; and one or more constraining layers, such as gypsum, cement, metal, cellulose, wood, or petroleum-based products such as plastic, vinyl, plastic or rubber. In one embodiment, standard wallboard, typically gypsum, comprises the external surfaces of the laminated structure.

Evaluation of the structure-induced rolling resistance (SRR) for pavements including viscoelastic material layers

This article addresses the question of whether the viscoelastic behavior of asphalt pavements, as part of the factors that impact the rolling resistance, might lead to substantially higher energy consumption of road traffic, as compared to non-dissipative pavements. In the context of sustainable development (fuel consumption, gas emission), this is a current issue for the pavement design community. This problem is tackled by a theoretical approach which consists in computing the structure-induced rolling resistance (SRR) for a vehicle by using the mechanical response of a layered viscoelastic medium excited by moving loads (i.e. tires of the vehicle). The structure-induced power dissipation is shown to be proportional to the integral over contours of the applied loads of the pavement deflection, times the outward normal to these contours. Following the developed approach, the determination of the SRR force engendered by the structure-induced dissipation is obtained from the computation of the deflection of the viscoelastic pavement to an assumed pressure distribution. Such an approach applied to a thick asphalt pavement allows the SRR for a typical road structure to be evaluated as a function of temperature and speed. A non-dimensional analysis is also presented to extend the results to some other contexts. Under the assumptions made for the derivation of the SRR, the main conclusion of the case study is that the extra fuel consumption for a vehicle resulting from the viscoelastic behavior of asphalt pavements is small.

Performance Analysis of Finite Element and Energy Based Analytical Methods for Modeling of PCLD Treated Beams

For active/passive vibration control applications, low order models of flexible structures are always preferable. Mathematical models of passive constrained layer damping (PCLD)/active constrained layer damping (ACLD) treatment generated by energy based analytical methods are of much smaller orders as compared to finite element methods (FEM). Using these analytical methods, one can get rid of complex model reduction techniques, since these model reduction techniques are subjected to errors if applied directly to PCLD or ACLD systems. However, analytical techniques cannot be applied blindly to any PCLD system. There is significant error in loss factor prediction for certain boundary conditions. This error is also dependent on the relative thicknesses of Viscoelastic material layer, constraining layer and base beam. For certain combination of the above thicknesses and under certain boundary conditions, the models generated are useless for controller design purposes. On the other hand, FEM are highly robust and can be applied easily to any set of boundary conditions with guaranteed accuracy. Also, results predicted by this method are of high accuracy for any combinations of thicknesses of different layers. The only disadvantage of this technique is the high order of the developed model. Detailed performance comparison of both the techniques to predict the modal parameters of the PCLD treated beam is presented.

Frictionless elliptical contact of thin viscoelastic layers bonded to rigid substrates

A three-dimensional unilateral contact problem for thin viscoelastic layers bonded to rigid substrates shaped like elliptic paraboloids is considered. Two cases are studied: (a) Poisson’s ratios of the layer materials are not very close to 0.5 and (b) the layer materials are incompressible with Poisson’s ratio of 0.5. Poisson’s ratios are assumed to be time independent. In the present paper we derive the general solutions to the problems of elliptical contact between thin compressible or incompressible layers of arbitrary viscoelastic materials. The approach is based on the analytical method developed by the authors for the elliptical contact of thin biphasic cartilage layers. The obtained analytical solution is valid for monotonically increasing loading conditions.

Acoustical Sound Proofing Material With Improved Damping At Select Frequencies And Methods For Manufacturing Same

Panels for use in building construction (partitions, walls, ceilings, floors or doors) which exhibit improved acoustical sound proofing in multiple specific frequency ranges comprise laminated structures having as an integral part thereof one or more layers of viscoelastic material of varied shear moduli which also function as a glue and energy dissipating layer; and, in some embodiments, one or more constraining layers, such as gypsum, cement, metal, cellulose, wood, or petroleum-based products such as plastic, vinyl, plastic or rubber. In one embodiment, standard wallboard, typically gypsum, comprises the external surfaces of the laminated structure.

Three Dimensional Vibration Transmission of a Plate on a Layer of Porous Medium Due to a Moving Load

Three-dimensional (3D) transmission of vibration in an infinite elastic thin plate on a layer of poroviscoelastic medium, due to a harmonic, rectangular moving load, is investigated theoretically based on Biot’s theory. The material of the medium is idealized as a uniform, fully saturated poroviscoelastic layer on bedrock. By introducing four scalar potential functions and Helmholtz decomposition theorem, analytical solutions of stress, displacement, and pore pressure with and without thin plate are derived using Fourier transform technique. Numerical results are obtained with the help of inverse Fourier transform and are used to analyze the influence of load velocity, porosity, permeability, relative stiffness of plate versus ground, and the thickness of plate on the vibration. Furthermore, the results are compared with the available dynamic response results of a non-moving load on a layer of viscoelastic material.

Acoustical sound proofing material

Panels for use in building construction (partitions, walls, ceilings, floors or doors) which exhibit improved acoustical sound proofing in multiple specific frequency ranges comprise laminated structures having as an integral part thereof one or more layers of viscoelastic material of varied shear moduli which also function as a glue and energy dissipating layer; and, in some embodiments, one or more constraining layers, such as gypsum, cement, metal, cellulose, wood, or petroleum-based products such as plastic, vinyl, plastic or rubber. In one embodiment, standard wallboard, typically gypsum, comprises the external surfaces of the laminated structure.

Coupling effects in dynamic calorimetry: Frequency-dependent relations for specific heat and thermomechanical responses — A one-dimensional approach based on thermodynamics with internal state variables

As shown by Christensen et al. [2], temperature-induced stresses or strains can have a strong influence on the frequency-dependent specific heat, especially of thin layers of viscoelastic materials near the glass transition. Thus, both the mathematical representation and the physical understanding of these couplings are essential for the interpretation of temperature-modulated DSC data. The approach provided in this paper is based on thermodynamics with internal state variables. It thus differs from the transfer-matrix method which has been applied in Refs. [2,29] and constitutes a thermodynamic basis from a different point of view for the interpretation of the results obtained in Refs. [2,29,32]. Furthermore, although not the object of this paper, time-domain simulations can also be done with the model presented thus allowing for the calculation of temperature-ramping experiments and effects observed therein [42]. The approach in this paper is restricted to one-dimensional states of stress and strain to focus on the main idea and keep the mathematical formalism to a minimum. The Gibbs free energy is chosen as thermodynamic potential and the primary variables – the stress and the temperature – are supplemented by a set of internal state variables which is introduced to include history-dependent and hence viscoelastic effects. The Gibbs free energy is approximated up to second order terms in the vicinity of a reference state. Employing the Legendre transform, a corresponding expression for the Helmhotz free energy is obtained. Evaluating the laws of thermodynamics, explicit frequency-dependent expressions for the specific heat under constant stress or strain, the thermal expansion behaviour as well as the mechanical response functions are obtained. Recently published formulations of the Prigogine–Defay ratio can also be derived from the proposed constitutive model.

Vibration and damping characteristics of beams with active constrained layer treatments under parametric variations

Hybrid damping designs with active piezoelectric materials and passive viscoelastic materials (VEMs) combine the advantages of both active and passive constrained layer damping (ACLD/PCLD) treatments. Researchers have established the standards for the extent and placement of the PCLD treatment for common structures. However for ACLD treatment, such detailed studies are not available. This study is aimed to examine, the effect of parametric variation of active constrained layer on the vibration control of the beams treated with optimally placed active or passive constrained layer damping patches. Finite element model is developed to model the open-loop and close-loop dynamics of active/passive constrained layer damping treated beam. The placement strategies of ACLD patches are devised using the modal strain energy (MSE) approach. Extensive experimentation studies are conducted by making twenty one separate samples of ACLD/PCLD treated beams with variations in viscoelastic material layer thickness, ACLD/PCLD patch coverage and location of the patch. Effects of key parameters, such as control gain, viscoelastic material thickness, coverage and location variation of ACLD patch on the system loss factor have been investigated. The careful analysis of results from partially covered ACLD treated beam suggests that the maximum damping of the first mode can be achieved by attaching the ACLD patch only up to 50% coverage. It also reveals that with proper choice of the control voltage and thickness, the effective loss factor can be almost doubled. The present study suggests the potential use of parametric studies that establish some guide lines for the extent and placement of the ACLD patches on the cantilevered beam.

Coupled heat conduction and deformation in a viscoelastic composite cylinder

We study the coupled problem of deformation due to mechanical and thermal loading of a composite cylinder made up of two layers of linear isotropic viscoelastic materials. The effect of a time-varying temperature field due to unsteady heat conduction on the short term and long term material response is examined in terms of the stress, displacement, and strain fields. The material properties of the two layers of the composite cylinder at any given location and time are assumed to depend on the temperature at that location at that given instant of time. Sequentially coupled analyses of heat conduction and deformation of the viscoelastic composite cylinder are carried out. Analytical solutions for the stress, strain and displacement fields of the viscoelastic composite cylinder are obtained from the corresponding solution of the linear elasticity problem by applying the Correspondence Principle. We examine the discontinuity in the hoop stress and the radial strain at the interface of the two layers caused by mismatches in material properties, during transient heat conduction. We find that the discontinuities change over time as the mismatch in the moduli of the two layers changes due to the material properties which are time-dependent. We also investigate the effect of the thermal field on the time-dependent field variables in the composite body.

Influence of vertical load models on flexible pavement response—an investigation

This paper aims to illustrate the influence of moving loads on pavement analysis, namely their characteristics and time distribution. Firstly, a state-of-the-art load model for pavement analysis is presented. Components of traffic load (contact stresses), their magnitude and time distribution, the tyre-pavement contact area and the characterization of a moving load according to dynamic and static formulations are introduced. Secondly, a study of the influence of load models (uniform vs. non-uniform distribution and non-moving vs. moving load) for pavement analysis by modelling a flexible pavement with the finite element method (FEM) is performed. The structure is modelled with DIANA software (TNO 2005), considering bituminous layers as a viscoelastic material and granular layers and foundation as a linear elastic material. The study reaches the conclusion that pavement response presents different evolutions, during loading time, depending on whether we choose a uniform or non-uniform time distribution load. Considering non-uniform distribution, the maximum value of pavement response can be much higher than those calculated for uniform distribution. It was also confirmed that the moving load character influence decreases not only with pavement depth, but also with distance from the point where the load is applied.