Abstract in English:Smart composite structures reinforced with a periodic grid of generally orthotropic cylindrical reinforcements that also exhibit piezoelectric behavior are analyzed using the asymptotic homogenization method. The analytical expressions for the effective elastic and piezoelectric coefficients are derived. In particular, the smart orthotropic composite structures with cubic, conical and diagonal actuator and reinforcement orientations are investigated.
Abstract in English:A previous study on the characterization of effective material properties of a d15 thickness-shear piezoelectric Macro-Fibre Composite (MFC) made of seven layers (Kapton, Acrylic, Electrode, Piezoceramic Fibre and Epoxy Composite, Electrode, Acrylic, Kapton) using a finite element homogenization method has shown that the packaging reduces significantly the shear stiffness of the piezoceramic material and, thus, leads to significantly smaller effective electromechanical coupling coefficient k15 and piezoelectric stress constant e15 when compared to the piezoceramic fibre properties. Therefore, the main objective of this work is to perform a parametric analysis in which the effect of the variations of fibre volume fraction, Epoxy elastic modulus, electrode thickness and active layer thickness on the MFC effective material properties is evaluated. Results indicate that an effective d15 MFC should use relatively thick fibres having relatively high shear modulus and relatively stiff epoxy filler. On the other hand, the electrode thickness does not affect significantly the MFC performance.
Abstract in English:The purpose of this article is to present a method which consists in the development of unit cell numerical models for smart composite materials with piezoelectric fibers made of PZT embedded in a non-piezoelectric matrix (epoxy resin). This method evaluates a globally homogeneous medium equivalent to the original composite, using a representative volume element (RVE). The suitable boundary conditions allow the simulation of all modes of the overall deformation arising from any arbitrary combination of mechanical and electrical loading. In the first instance, the unit cell is applied to predict the effective material coefficients of the transversely isotropic piezoelectric composite with circular cross section fibers. The numerical results are compared to other methods reported in the literature and also to results previously published, in order to evaluate the method proposal. In the second step, the method is applied to calculate the equivalent properties for smart composite materials with square cross section fibers. Results of comparison between different combinations of circular and square fiber geometries, observing the influence of the boundary conditions and arrangements are presented.
Abstract in English:The realization of semi-active actuators by smart structures is discussed. Semi-active actuators have the advantage of consuming much less power than direct-active actuators and are appropriate for the utilization in vibration problems encountered in aeronautical applications, where the loads are in general too high for direct-active actuators to perform. The development of a compact actuator device of this class, from the design phase to the validation tests, is presented.
Abstract in English:Vibration energy harvesting with piezoelectric materials is of practical interest because of the demand for wireless sensing devices and low-power portable electronics without external power supply. For practical use of vibration energy harvester with piezoelectric materials, it is necessary to process the alternating current (AC) by using different rectifiers' circuits in order to charge batteries with direct current (DC) or to feed electronic devices. Unfortunately, most of the models used focused on simplifying the energy harvesting circuit into a simple resistive load. In the real-world applications, the energy harvesting external circuit is more complex than a simple load resistance. In this sense, the goal of the present paper is to describe a comprehensive strategy for power harvesting device to estimate the output power provided by a cantilever beam with the electrodes of the piezoceramic layers connected to a standard rectifier circuit. The true electrical components were considered in the full-wave rectifier circuit with four diodes in bridge. A very simple and comprehensive description for choosing the capacitance and resistance loads is provided. In order to illustrate the results, numerical simulations and experimental verifications are also performed to ensure the accuracy. All tests and results are described and detailed using Matlab, the SimPowerSystem toolbox of the Simulink and an experimental setup.
Abstract in English:The aim of this paper is to illustrate the active control of vibration of a flexible structure using a model-based digital controller. The state-space model of the system is derived using a system identification technique known as the Observer/Kalman Filter Identification (OKID) method together with Eigensystem Realization Algorithm (ERA). Based on the measured response of the structure to a random input, an explicit state-space model of the equivalent linear system is determined. The model is used in a Linear Quadratic Regulator (LQR) to control the first two modes of vibration of a cantilever beam using a piezoelectric actuator/sensor pair. Experimental results demonstrate the efficacy of the proposed approach.
Abstract in English:The essence of structural health monitoring (SHM) is to develop systems based on nondestructive inspection (NDI) technologies for continuous monitoring, inspection and detection of structural damages. A new architecture of a remote SHM system based on Electromechanical Impedance (EMI) measures is described in the present contribution. The proposed environment is employed to automatically monitor the structural integrity of aircrafts and is composed by sensor networks, a signal conditioning system, a data acquisition hardware and a data processing system. The obtained results allow the accomplishment of structural condition-based maintenance strategies, in opposite to those based only on the usage time of the equipment. This approach increases the operational capacity of the structure without compromising the security of the flights. As the environment continually checks for the first signs of damage, possibly reducing or eliminating scheduled aircraft inspections, it could significantly decrease maintenance and repair expenses. Furthermore, the usage of this system allows the creation of a historical database of the aircrafts structural integrity, making possible the incremental development of a Damage Prognosis System (DPS). This work presents the proposed architecture and a set of experiments that were conducted in a representative aircraft structure (aircraft window) to demonstrate the effectiveness of the proposed system.
Abstract in English:Large-scale structures are of special interest of aerospace applications, especially the ones involving smart materials. This paper deals with an archetypal system with two degrees of freedom that resembles the use of SMA elements as vibration isolation systems on a sparse aperture satellite array. The system has SMA elements in two perpendicular directions connected to a mass. Each SMA element is connected to a base structure. Imperfections are represented by establishing a comparison between two different systems: ideal and perturbed configuration system. The perturbed configuration is characterized by a situation where all SMA elements are in a stress-free state. The thermomechanical behavior of SMA elements is described by a constitutive model with internal constrains. Numerical tests of this system are of concern showing its general dynamical behavior. Periodic and chaotic motions are investigated showing the complex behaviors of this kind of system. The effect of imperfection in system dynamics is also discussed.
Abstract in English:In this paper the development of an experimental test bench to analyze and control the strain of a flexible aluminum beam subjected to external disturbances is described. In the proposed platform, strain-gauges are used to measure the strain of the beam in a single cantilever mode while Ni-Ti-Cu Shape Memory Alloy (SMA) wires are used as force actuators. Data acquisition and control system are implemented with an ADuC microcontroller. The response of the structure in open-loop was used to identify the mathematical model of the system. To find the appropriate controller and to reach the best performance of the system, it was used techniques of direct tuning (pole-zero cancellation) in the identified model. The PI controller has been used to control the strain of the beam for different types of reference signals, as square, sinusoidal and triangular. The frequencies of the reference signals have been varied to observe to which bandwidth the system can respond. Experimental results are used to demonstrate the usefulness of the PI controller in the proposed smart structure.