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CONTENTS
Volume 5, Number 6, November 2009
 

Abstract
New insights are presented in simplified modeling and analysis of free vibrations of piezoelectric-based smart structures and systems. These consist, first, in extending the wide used piezoelectric-thermal analogy (TA) simplified modeling approach in currently static actuation to piezoelectric free-vibrations under short-circuit(SC) and approximate open-circuit (OC) electric conditions; second, the popular piezoelectric strain induced-potential (IP) simplified modeling concept is revisited. It is shown that the IP resulting frequencies are insensitive to the electric SC/OC conditions; in particular, SC frequencies are found to be the same as those resulting from the newly proposed OC TA. Two-dimensional plane strain (PStrain) and plane stress (PStress) free-vibrations problems are then analyzed for above used SC and approximate OC electric conditions. It is shown theoretically and validated numerically that, for both SC and OC electric conditions, PStress frequencies are lower than PStrain ones, and that 3D frequencies are bounded from below by the former and from above by the latter. The same holds for the modal electro-mechanical coupling coefficient that is retained as a comparator of presented models and analyses.

Key Words
piezoelectricity; free-vibration; thermal analogy; induced potential; plane strain; plane stress.

Address
Ayech Benjeddou; Institut Sup?ieur de M?anique de Paris, Structures, 3 rue Fernand Hainaut, 93407 Saint Ouen CEDEX, France

Abstract
The present paper is concerned with the design of a proper patch actuator network in order to track a desired displacement of the sidewalls of a one-storey frame structure; both, for the static and the dynamic case. Weights for each patch of the actuator network found in our previous work were based on beam theory; in the present paper a refinement of these weights by modeling the sidewalls of the frame structure as thin plates is presented. For the sake of calculating the refined weights approximate solutions of the plate equations are calculated by an extended Galerkin method. The solutions based on the analytical plate model are compared with three-dimensional Finite Element results computed in the commercially available code ANSYS. The patch actuator network is put into practice by means of four piezoelectric patches attached to each of the two sidewalls of the frame structures, to which electric voltages proportional to the analytically refined patch weights are applied. Analytical and numerical results coincide very well over a broad frequency range.

Key Words
plate theory; displacement tracking; piezoelectric actuator network.

Address
Daniel Huber; Linz Center of Mechatronics GmbH, Altenbergerstrasse 69, A-4040 Linz, Austria
Michael Krommer and Hans Irschik; Institute for Technical Mechanics, Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz, Austria

Abstract
A simple method has been developed to detect the bonding condition of active fiber composites (AFC) adhered to the surface of a host structure. Large deformation actuating capability is one of important features of AFC. Edge delamination in adhesive layer due to large interfacial shear stress at the free edge is typically resulted from axial strain mismatch between bonded materials. AFC patch possesses very good flexibility and toughness. When an AFC patch is partially delaminated from host structure, there remains sensing capability in the debonded part. The debonding size can be determined through axial resonance measured by the interdigitated electrodes symmetrically aligned on opposite surfaces of the patch. The electrical impedance and modal response of the AFC patch in part adhered to an aluminum plate were investigated in a broad frequency range. Debonding ratio of the AFC patch is in inverse proportion to the resonant frequency of the fundamental mode. Feasibility of in-situ detecting the progressive delamination between AFC patch and host plate is demonstrated.

Key Words
active fiber composite; delamination; electric impedance; resonance.

Address
Dwo-Wen Wang and Ching-Chung Yin; Department of Mechanical Engineering, National Chiao Tung University 1001 Ta Hsueh Road, Hsinchu 300, Taiwan, Republic of China

Abstract
Adaptive wings are capable of properly modifying their shape depending on the current aerodynamic conditions, in order to improve the overall performance of a flying vehicle. In this paper is presented the concept design of a small-scale compliant wing rib whose outline may be distorted in order to switch from an aerodynamic profile to another. The distortion loads are induced by shape memory alloy actuators placed within the frame of a wing section whose elastic response is predicted by the matrix method with beam formulation. Genetic optimization is used to find a wing rib structure (corresponding to the first airfoil) able to properly deforms itself when loaded by the SMA-induced forces, becoming as close as possible to the desired target shape (second airfoil). An experimental validation of the design procedure is also carried out with reference to a simplified structure layout.

Key Words
shape memory alloy; SMA actuator; adaptive wing; compliant structure; genetic algorithm.

Address
Giuseppe Mirone; Dipartimento di Ingegneria Industriale e Meccanica, University of Catania, Viale A. Doria 6, 95125 Catania, Italy

Abstract
The use of Micro-Electro-Mechanical Systems (MEMS) accelerometers in geotechnical instrumentation is relatively new but on the rise. This paper describes a new MEMS-based system for in situ deformation and vibration monitoring. The system has been developed in an effort to combine recent advances in the miniaturization of sensors and electronics with an established wireless infrastructure for on-line geotechnical monitoring. The concept is based on triaxial MEMS accelerometer measurements of static acceleration (angles relative to gravity) and dynamic accelerations. The dynamic acceleration sensitivity range provides signals proportional to vibration during earthquakes or construction activities. This MEMS-based in-place inclinometer system utilizes the measurements to obtain three-dimensional (3D) ground acceleration and permanent deformation profiles up to a depth of one hundred meters. Each sensor array or group of arrays can be connected to a wireless earth station to enable real-time monitoring as well as remote sensor configuration. This paper provides a technical assessment of MEMS-based in-place inclinometer systems for geotechnical instrumentation applications by reviewing the sensor characteristics and providing small- and full-scale laboratory calibration tests. A description and validation of recorded field data from an instrumented unstable slope in California is also presented.

Key Words
autonomous geotechnical monitoring; wireless data transmission; MEMS.

Address
V. Bennett and T. Abdoun; Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, 110 8th Street, JEC 4049, Troy, NY 12180, USA
T. Shantz; California Department of Transportation, Division of Research and Innovation, 1227 O Street, MS-83, P.O. Box 942873, Sacramento, CA 94273, USA
D. Jang; Branch A Geotechnical Design South 1, California Department of Transportation, Division of Engineering Services, Geotechnical Services, MS 5, 5900 Folsom Boulevard, Sacramento, CA 95819, USA
S. Thevanayagam; Department of Civil and Environmental Engineering, University at Buffalo, 133 Ketter Hall, Buffalo, NY 14260, USA

Abstract
Limited, noisy data in vibration testing is a hindrance to the development of structural damage detection. This paper presents a method for optimizing sensor placement and performing damage detection using finite element model updating. Sensitivity analysis of the modal flexibility matrix determines the optimal sensor locations for collecting information on structural damage. The optimal sensor locations require the instrumentation of only a limited number of degrees of freedom. Using noisy modal data from only these limited sensor locations, a method based on model updating and changes in the flexibility matrix successfully determines the location and severity of the imposed damage in numerical simulations. In addition, a steel cantilever beam experiment performed in the laboratory that considered the effects of model error and noise tested the validity of the method. The results show that the proposed approach effectively and robustly detects structural damage using limited, optimal sensor information.

Key Words
modal analysis; damage detection; flexibility matrix; PSO; FE model updating.

Address
L. Cheng and H. C. Xie; College of Civil Engineering, Shenzhen University, Shenzhen Durability Center for Civil Engineering, Shenzhen, 518060, Guangdong, China
B. F. Spencer, Jr. and R. K. Giles; Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA


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