Viscoelastic Composite Materials Research Articles

On the modelling of dynamic problems for viscoelastic composites

The aim of this contribution is to show that the microstructure length-scale effect on the dynamic behaviour of viscoelastic composite materials plays a curcial role and cannot be neglected. To this end, the average refined model of the viscoelastic composites, involving the microstructure length parameters, has been formulated. The proposed model can be applied to the analysis of dynamic problems for viscoelastic periodic composite materials.

Viscoelastic composite materials for noise reduction and damage tolerance

This paper describes the concept of viscoelastic composites and how their dynamic physical characteristics may be exploited for ship applications where high vibrational damping and damage tolerance is a requirement. A mathematical model is used to describe the effect of fibre alignment on viscoelastic composite dynamic Young's Moduli and loss factors. The model, supported by experimental validation, requires the dynamic physical properties of the matrix resin for the range of operational temperatures and frequencies of interest. The model predicts that the resulting loss factor of a fibre reinforced viscoelastic resin composite behaves in an anisotropic fashion, however, damping optimisation may be achieved in two different ways dependant on the angle of fibre alignment. The implications of these findings and how the fibre alignment in a viscoelastic composite may be exploited for noise free ship and submarine machinery rafts are also discussed. Empirical studies on viscoelastic composites of this type using a drop weight impact tester have shown that their damage tolerance is superior to conventional glass reinforced polyester GRP. Although a theoretical analysis has not been made, it is implied that the viscoelastic nature of the matrix resin and its optimisation over the typical damaging impact frequencies is an important factor in absorbing the impact energy in much the same way as it is for absorbing vibrational energy. In this case the impact impluse is considered to be one particular extreme form of vibrational source. Provided the impact force can do work on the matrix, the energy will be absorbed by it if the viscoelastic nature of matrix is correct with little or no resulting damage to the composite.

Geometrically nonlinear finite element analysis of viscoelastic composite materials under mechanical and hygrothermal loads

The time-dependent response of polymeric matrix laminated composites subject to mechanical and hygrothermal loads is considered. The analysis is based on an incremental total Lagrangian formulation which allows the treatment of finite displacements and small strains. A three-dimensional degenerated finite element model is employed to analyze the plates and shells. The material is considered as linear viscoelastic and hygrothermal-rheologially simple. Numerical examples for isotropic and graphite-epoxy laminated plates and shells are presented.

Harmonic wave propagation in viscoelastic heterogeneous materials Part I: Dispersion and damping relations

An analytico-numerical method is presented to study the propagation of plane harmonic waves in infinite periodic linear viscoelastic media. Part I considers only the dispersion and attenuation of acoustical longitudinal and shear waves. To show the accuracy of the method, examples of plane harmonic wave propagation in an infinite homogeneous medium and in a periodic layered viscoelastic medium are presented. The method is then used to calculate the damping and dispersion relations for a fibre-reinforced viscoelastic composite material. The results show clearly the influence of materials' viscoelastic properties and heterogeneities on the propagation of plane harmonic waves through the media.

Mechanics of the delayed fracture of viscoelastic composite materials

Mechanics of the delayed fracture of viscoelastic composite materials

Transfer matrix of multilayered absorbing and anisotropic media. Measurements and simulations of ultrasonic wave propagation through composite materials

This paper presents an adaptation of the well-known Thomson/Haskell method to introduce anisotropic attenuation into the formulation of the transfer matrix. The expression for the transfer matrix of one elementary ply is modified to take into account the heterogeneity of the generated modes at interfaces between absorbing media. This heterogeneity depends on the direction of propagation and on the anisotropic attenuation of the ply. The transfer matrix of the stratified composite is derived classically from the multiplication of the elementary matrices and leads to the transfer function of the plate. The transmission and reflection coefficients of multilayered viscoelastic anisotropic composite materials can be computed, for any direction of propagation and for any stacking sequence, with a program that requires the viscoelastic characteristics of the ply. The method is tested with PEEK matrix/carbon fibers composites. The viscoelastic properties of the ply were previously measured with a unidirectional composite made of the same elementary ply in a frequency domain where bulk heterogeneous modes can be isolated. To extend these properties to a larger domain, the model assumes that the attenuation is proportional to the frequency. Doing so, the transmission of broadband waveforms can be computed. These waveforms are compared to experimental waveforms transmitted by composites with different stacking sequences.

Rheological structural model of a crack in a viscoelastic composite material

Rheological structural model of a crack in a viscoelastic composite material

Delayed fracture of a mass of a viscoelastic composite material with a plane circular crack

Delayed fracture of a mass of a viscoelastic composite material with a plane circular crack

Inhomogeneous wave generation and propagation in lossy anisotropic solids. Application to the characterization of viscoelastic composite materials

This article develops a method for investigating some anisotropic media, such as composites, by the use of ultrasonic waves transmitted through a plate-shaped sample immersed in water. The discussion begins with Christoffel’s equations for plane linear anelastic waves under the assumptions that for small angles of incidence the wave modes are plane and inhomogeneous and that the anisotropy is representable by hexagonal symmetry. The water–sample interface is treated using the law of Snell–Descartes for nonabsorbing media and takes into account mode conversion and the generation of acoustic surface waves. The method produces viscoelastic constants and relative attenuation coefficients as a function of the angle of refraction. The experimental measurement apparatus is described and data are given for the 25-layer unidirectional Gr/epoxy composite. Results are presented in terms of slowness, damping vector, and attenuation curves. The results are significant in that they demonstrate the anisotropy both for the elastic stiffness and the attenuation. The method appears to hold promise for characterizing some classes of anisotropic media, including 2-D composites, in terms of their anelastic behavior.

Homogenisation of a viscoelastic equation with non-periodic coefficients

SynopsisThe homogenisation of a linearly viscoelastic composite material is performed without any periodicity assumptions and with no restrictions on the initial data. A term of fading memory is evidenced in the expression of the homogenised stress tensor.

An analytical and experimental investigation of high-speed mechanisms fabricated with composite laminates

The articulating members of linkage machinery must be designed and manufactured with high stiffness-to-weight ratios in order that these machine systems operate successfully in a high-speed mode. One approach to satisfying this criterion is to exploit the high specific stiffnesses of polymeric fibrous composite laminates. In this paper, results of mechanical tests of candidate materials are presented and the material constitutive behaviour classified. A variational theorem is then derived by using the Stieltjes convolution notation which enables the equations governing the geometrically-non-linear dynamic response of linkages fabricated in linear viscoelastic composite materials to be systematically established. The formulation includes inertial terms which couple the kinematic deformations of the link material with the kinematics governing the gross motion of the linkage being analyzed. This variational principle provides the basis for a finite element formulation in which the properties of the heterogeneous, two-constituent laminates are represented by a continuum model for a homogeneous single-constituent material. The predictive capability of this model is evaluated by simulating the vibrational response of both experimental four-bar linkages and also slider-crank mechanisms fabricated with simple link geometries, prior to comparing the computer results with experimental data from these laboratory mechanisms.

Analysis of the effect of using two different strain rates on the acoustic emission in bone

To study the effect of strain rate on the acoustic emission amplitude signature of bone, bovine cortical bone was milled into standard tensile specimens which were tested at two different strain rates while being monitored with acoustic emission equipment. It was demonstrated that the amplitude distribution of the acoustic events in bone is dependent on strain rate. Greater numbers of events occurred with the slower strain rate (0.0001 s −1), but these events were of lower amplitude than those emitted during the more rapid strain rate (0.01 s −1). The plot of the cumulative event amplitude distribution followed the power-law model, and the slope of this output, the b-value, represented a signature of the amplitude distribution. The mechanical test results were consistent with the behavior of a viscoelastic multi-phase composite material.

Organization of the optimal nonsteady cooling process for a thick-wall cylindrical shell of a viscoelastic composite material

The problem of regulating the magnitude and kinetics of residual temperature stresses during the cooling of thick-wall wound cylindrical articles of reinforced composite materials has and is continuing to attract significant attention [1-16]. This has given rise to an urgent widespread problem associated with the development of progressive technological processes that would ensure the required degree of reliability of these articles with a simultaneous reduction in labor outlays and the net cost of their production.

Temperature production stresses in reinforced cylindrical shell of viscoelastic composite material

Temperature production stresses in reinforced cylindrical shell of viscoelastic composite material

Is bone a Cosserat solid?

In a viscoelastic composite material including bone, acoustic waves undergo both geometric and viscoelastic dispersions as they propagate through the medium. The viscoelastic dispersion is characterized by an increase in phase velocity with increase in frequency, while the geometric dispersion is well-known. By comparing the dispersion data on these and other types of materials, it has been noted that the increases in the ultrasonic velocities for bones are much larger than those for simple viscoelastic solids and composites, suggesting an additional dispersion mechanism. This additional dispersion can be explained by Mindlin's theory on the Cosserat continuum with microstructure.

Development of fatigue cracks in viscoelastic composite materials

Development of fatigue cracks in viscoelastic composite materials

Viscoelastic Constitutive Equations with Internal Variables and Its Application to Numerical Analysis

Constitutive equations applicable to viscoelastic materials with/without initial elastic responses are derived by using internal variables, and applied to viscoelastic composite materials. Stress analyses are carried out by the finite element method, using linear and non-linear viscoelastic constitutive queations with internal variables.

Kinetics of the development of a crack in a viscoelastic fibrous composite material

Kinetics of the development of a crack in a viscoelastic fibrous composite material

A method for determining the mode 1 delamination fracture toughness of elastic and viscoelastic composite materials

A method for determining the mode 1 delamination fracture toughness of elastic and viscoelastic composite materials

Reflection Coefficients at Collagen Interfaces in Soft Tissues

For the purpose of ultrasonic imaging, soft tissue has been modeled as a viscoelastic (Voigt) composite material consisting of collagen fibers (as the inhomogeneity) embedded in a continuum tissue (as the matrix). It is known that infarction enhances the collagen content in myocardial tissues. The published in vitro attenuation data in normal and infarcted myocardial tissues have been correlated with the Voigt body model. From the correlation parameters and mixture laws for the elastic moduli of tissue components, the bulk modulus of collagen has been estimated to be about 50–55% higher than that of the normal tissue. From a knowledge of the bulk moduli and mass densities of collagen and tissue matrix, amplitude reflection coefficients at collagen interfaces have been computed. The amplitude reflection coefficient at the saline-collagen or at the collagen-myocardium interface is about 6 times that at the saline-myocardium interface.