Proceedings of the XI DINAME, 28th February-4th March, 2005 - Ouro Preto - MG - Brazil Edited by D.A. Rade and V. Steffen Jr. © 2005 - ABCM. All rights reserved. DAMAGE LOCATION IN SMART STRUCTURES USING LOW COST IMPEDANCE MEASUREMENTS Rogério Mendonça Furtado Vicente Lopes Júnior Departament of Mechanical Engineering – UNESP – Ilha Solteira Av. Brasil Centro, 56, Ilha Solteira – São Paulo, Brazil, CEP 15385-000 vicente@dem.feis.unesp.br Abstract. There are many papers available in the literature about fault detection. Each technique has advantages and disadvantages. In this work we present a non-model technique to detect and locate structural damage using vibration data measured in high frequency ranges. This technique uses signals of electrical impedance obtained from a low cost equipment constructed in the laboratory. Due the high frequency range and low voltage applied in the piezoelectric patches (usually 1 V), these measurements are very sensitive to minor structural changes in the near field of the piezoelectric sensor. So, the PZT actuator/sensor is arranged in order to define an influence area for each sensor. This technique is able to detect the damage in its early stage and to estimate the nature of damage without prior knowledge of the mathematical model of the structure. The paper shows the circuit used to construct the low cost impedance analyzer. It is an alternative equipment that was validated through a commercial equipment. The paper concludes with an experimental test in a truss structure made of aluminum beam, which has three bonded PZTs for damage characterization. Keywords: Electrical Impedance, Piezoelectric Element, Fault Detection, Smart Structures. 1. Introduction There is great interest in the engineering community, in the development of real-time, in-service health monitoring techniques to reduce cost and improve safety, based on preventive inspection schedule. Maintenance by using vibration signals inspection is classified as one of nondestructive technique for condition monitoring. The weakest point of maintenance inspection today is that there is no general function for warning when incipient damage occurs in service (Egawa, 1997). The crucial factors that are of concern when any Non-Destructive Evaluation (NDE) technique is considered are (Raju, 1998): ｾ The principle behind these techniques is “preventive inspection”, i.e., inspect the structure in question at frequent intervals in an attempt to detect damage in the early or incipient stages; ｾ The capability of the technique to perform on-line health monitoring, i.e., monitor the integrity of the structure while it is in service; ｾ Ideally, an NDE technique should rely on use of small, non-intrusive sensors and actuators. To deal with these problems, the present paper applies the concept of smart structure. The terms “smart structure”, or “intelligent material”, are fast becoming common phrases among the engineering community. These terms are used to describe a variety of modern advances in the engineering world. There is no agreement for the definition of these systems, however, the terms used in this work refer to structures with material components that are able to transform mechanical motion or force in electrical or magnetic fields, and vice versa. A list of materials employed in smart material system includes piezoelectric, electrostrictive and magnetostrictive elements, fiber optics, etc. The impedance-based health monitoring technique relies on small patches of piezoelectric (PZT) materials, surface bonded or embedded in the structure, which utilizes the electromechanical coupling property of theirs materials (Park et al., 2000). The basic principle behind this technique is the use of high frequency (typically > 10kHz) to detect changes in structural point impedance due internal cracks, surface cracks, or loose connections (Lopes et al., 2001). The electrical impedance data obtained from a piezoelectric actuator/sensor can be used to train the artificial neural network to quantify the fault severity. This technique is very sensitive to minor structural changes in the near field of the piezoelectric sensor. So, the PZT actuator/sensor is arranged in order to define an influence area for each sensor. The measuring can be made by using commercial analyzer, as for instance, HP 4192A, or any other similar equipment. These equipments are very expensive, cost approximately of US$30.000,00. Inconveniences of these equipments are the large size and heavy weight. The impedance technique uses a small subset of the capabilities of the instrument. Therefore, one other cheaper and lighter option should represent a great improvement in this proposal. The Low Cost Impedance Analyzer proposed in this paper is small and the cost is approximately US$50,00. It intends to popularize this technique.