Search

Certain frequency ranges where waves do not propagate, and thus, vibrations are suppressed, are called band gaps. In the present paper, the appearance and the behavior of such areas are investigated on star-shaped auxetic microstructures, which are equipped with shunted piezoelectric elements. The optimal position of the piezoelectric patches is found using genetic algorithms, considering the maximization of the electromechanical coupling coefficient. A genetic algorithm is also used for the calculation of the values of the electrical parameters of the resonant shunt circuit, with objective the maximization of certain band gaps. The results indicate that the proposed technique can be used for the maximization of band gaps at certain frequency ranges, as well as at frequency bands which have not been considered in the optimization problem of the mechanical microstructure. [ABSTRACT FROM AUTHOR]

A band gap region, or simply a band gap, is a range of frequencies where vibrations of certain frequency ranges are isolated. In the present paper, such ranges are sought through the study of different cases for the shape of the unit cells of a lattice, i.e., of an assembly of classical structural elements, such as beams and plates. A lattice with a specific, special designed microstructure is considered in the present investigation. Each particular cell of the examined lattice is studied as a classical composite material consisting of a matrix and the reinforcing core (e.g., matrix-fiber composite), and it is discretized by using two-dimensional plane stress finite elements. The form of the core of the unit cells can be of several shapes, e.g., quadratic, circular, and star. Some of these shapes provide the whole lattice with auxetic behavior, with negative Poisson's ratio at the homogenized properties. The shape and the microstructure of the lattice is optimized in order to achieve isolation of the desired frequencies. A first attempt on the optimization of star-shaped microstructures is also presented. The optimization is carried out using powerful global optimization methods, such as the genetic algorithms. Results indicate that band gaps may appear in both conventional and auxetic microstructures. Moreover, the appearance and the size of the band gaps depend on the selected microstructure. [ABSTRACT FROM AUTHOR]

Delamination between the layers of smart composite beams is a possible failure type. The effectiveness of active vibration control, when delamination appears, is investigated in this article. In particular, optimized fuzzy controllers are developed and tested on partially delaminated piezocomposites. A finite element model based on layerwise theory, which incorporates the electromechanical coupling and the adhesive layer, is first developed. Delamination is considered by nonlinear structural analysis techniques and is used for the creation of realistic partially delaminated structures. Fuzzy controllers are built and applied to the smart structure. The fine-tuning of the parameters of control is done using genetic algorithms. Based on the results obtained from the numerical investigation, the applicability of fine-tuned fuzzy controllers, even in the case of partial delamination, is shown. According to different delamination scenarios, which were tested in this work, the design of adaptive fuzzy controllers, robust against delamination, is feasible. [ABSTRACT FROM AUTHOR]