
Conference Paper: Vibrationbased damage identification applied for composite plate: Numerical analyses
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ABSTRACT: Maintenance planning and costs are one of the greatest logistics concerns faced today by aircraft manufactures and operators. With the advancement of composite materials, other problems arrived as these materials’ behavior are still not completely understood. As such, structure health monitoring (SHM) and damage detection methods were eagerly studied in academic level in the last two decades. In particular, vibration based methods employing piezoelectric sensors and/or actuators offer a promising option, especially with the advance of piezoelectric materials such as macrofiber composites (MFCTMs) and active fiber composites (AFC) which can be incorporated directly into the composite materials. Through these methods, damage can be estimated and located by comparing the dynamic responses between the damaged and undamaged structure. This occurs as, in general, damage locally introduces changes in the mass and stiffness properties of the structure, changing the dynamic properties of a given structure such as modal shapes, natural frequencies and damping values. In this paper, a preliminary investigation in order to develop a vibrationbased damage identification method is presented, consisting on evaluating via Finite Element Method not only the mode shapes but also the Frequency Response Functions (FRFs) of undamaged and damaged composite plates. Therefore, rectangular plates made of composite material, resin epoxy and carbon fiber, were analyzed by Abaqus’ code, considering piezoelectric transducers attached in suitable positions in order to obtain the dynamic behavior of the structures. A FE mathematical formulation for laminate structures containing active piezoelectric layers was developed in order to obtain more accuracy results. Thus, a plate quadratic finite element with eight nodes and curved structures, which allows fully coupled electromechanical analyses was formulated and implemented into the Abaqus’ code, using Fortran subroutine defined as UEL (User Element). First, an undamaged composite plate was modeled using this user subroutine. Then natural frequencies and Frequency Response Functions were obtained by finite element analyses. After that, a central hole is created in the finite element model in order to simulate a specific damage. Then, the natural frequencies and Frequency Response Functions were obtained for the damaged plate. Finally, it was discussed the advantages and limitations to use vibrationbased damage detection method into the context of SHM (Structural Health Monitoring) via Finite Element approach.22nd International Congress of Mechanical Engineering (COBEM 2013), Ribeirão Preto, São Paulo, Brazil; 11/2013  Ceramics International 07/2014; 2014(40):16365. · 2.09 Impact Factor

Article: Electrostrictive effect in ferroelectrics: An alternative approach to improve piezoelectricity
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ABSTRACT: Electrostriction plays an important role in the electromechanical behavior of ferroelectrics and describes a phenomenon in dielectrics where the strain varies proportional to the square of the electric field/polarization. Perovskite ferroelectrics demonstrating high piezoelectric performance, including BaTiO3, Pb(Zr1 x Ti x )O3, and relaxorPbTiO3 materials, have been widely used in various electromechanical devices. To improve the piezoelectric activity of these materials, efforts have been focused on the ferroelectric phase transition regions, including shift the composition to the morphotropic phase boundary or shift polymorphic phase transition to room temperature. However, there is not much room left to further enhance the piezoelectric response in perovskite solid solutions using this approach. With the purpose of exploring alternative approaches, the electrostrictive effect is systematically surveyed in this paper. Initially, the techniques for measuring the electrostrictive effect are given and compared. Second, the origin of electrostriction is discussed. Then, the relationship between the electrostriction and the microstructure and macroscopic properties is surveyed. The electrostrictive properties of ferroelectric materials are investigated with respect to temperature, composition, phase, and orientation. The relationship between electrostriction and piezoelectric activity is discussed in detail for perovskite ferroelectrics to achieve new possibilities for piezoelectric enhancement. Finally, future perspectives for electrostriction studies are proposed.Applied Physics Reviews. 01/2014; 1(1):011103.
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