José A. Otero

Dispersion curves of shear horizontal wave surface velocities in multilayer piezoelectric systems

A precise knowledge of the frequency responses, velocity dispersion, and distinct vibration modes in multilayer piezoelectric structures would permit the optimization of new designs for electromechanical sensor, actuator, and surface acoustic wave (SAW) filter devices under broad and narrow band conditions. In this paper, the singular-value decomposition technique, combined with the global matrix method and scaling procedure, are applied for studying the solutions of shear stationary waves in symmetric multilayer composite piezoelectric systems. This approach eliminates numerical instabilities sometimes appearing in the analysis of this type of piezoelectric systems, by using a multiple scaling strategy in the global matrix processing. The dispersion curves of the surface velocities, obtained by application of the proposed approach, have shown the presence of clearly separated odd and even bands in such a type of piezoelectric devices, which is explained by considering the eigenstates of the system. Detai...

Presence of Stark ladders in scattering of shear horizontal piezoelectric waves

The global matrix techniques are used in the analysis of the Stark-Ladder resonances for transverse horizontal and surface waves in piezoelectric multilayers. Stark-Ladder resonances are observed when these waves propagate inside composites consisting of N piezoelectric layers whose piezoelectric properties obey a special linear relation. Each layer is made of materials with hexagonal 6 mm symmetry. The resonances are studied through the transmission coefficient. The transmission coefficient shows the well known band structure for a periodic piezocomposite, and when a linear term in the values of the piezoelectric parameters of the layers (which breaks the periodicity) is added, the band structure is destroyed and, in certain cases, resonances of the Stark-Ladder type are shown. The transmission coefficient is studied as a function of the properties of the materials and angle of incidence of the waves. Numerical results for two different configurations of piezocomposites are presented, one of them showing...

Numerical and analytical analyses for active fiber composite piezoelectric composite materials

This study consists of the calculation of the effective properties for active fiber composites made of either circular or square cross-section fibers not only by using finite element analysis and representative volume elements, but also based on the asymptotic homogenization method. Thus, there is an investigation about different approaches, which have specific mathematical formulations and unique characteristics. The comparison between numerical and analytical approaches shows that the numerical results are in good agreement with investigations performed by both analytical and semi-analytical methods, mainly the predictions for loading applied in fiber direction. For active fiber composites made of circular cross-section fibers, the maximum difference between asymptotic homogenization method and finite element analysis is from 1.29% to 5.49% for mechanical and piezoelectric effective properties, respectively, considering representative volume element in square arrangement. However, for active fiber composites made of square cross-section fibers, the maximum difference between semi-analytical method and finite element analysis is from 2.15% to 17.09% for mechanical and piezoelectric effective properties, respectively, considering representative volume element in square arrangement.

Unit Cell Models of Viscoelastic Fibrous Composites for Numerical Computation of Effective Properties

The paper presents an extension to viscoelastic composites of a former developed numerical homogenization procedure which was used for elastic and piezoelectric material systems. It is based on an unit cell model using the finite element method. In the paper a brief description of the basic equations and the homogenization algorithm with specific attention to the numerical model is given. The investigated composites consist of a viscoelastic matrix with unidirectional embedded cylindrical elastic fibers. Hence the homogenized behavior of the composite is also viscoelastic. Consequently the effective coefficients are time-dependent. The geometrical shape of the unit cell is rhombic which allows to analyze a wide range of nonstandard unidirectional fiber distributions. Otherwise it includes the special cases for square and hexagonal fiber arrangements which can be used for comparisons with other solutions. Here results are compared with an analytical homogenization method. Furthermore the influences of rhombic angle and fiber volume fraction on effective coefficients are investigated. In addition two limit cases are considered. One is with air as inclusions which is equivalent to a porous media and the other is the pure matrix without fibers.

Micro-Macro Characterization of Effective Properties for Fibrous Composites With Parallelogram Cells and Imperfect Contact Condition

In this work, two-phase parallel fiber-reinforced periodic piezoelectric composites are considered wherein the constituents exhibit transverse isotropy and the cells have different configurations. Two types of imperfect contact at the interface of the composites are studied: a) imperfect contact via spring model, b) three phase model. Simple closed-form formulae are obtained for the effective properties of the composites with both types of contact and different parallelogram cells by means of the asymptotic homogenization method (AHM). Some numerical examples and comparisons with other theoretical results illustrate that the model is efficient for the analysis of composites with presence of parallelogram cells and imperfect contacts.Copyright