Damage Assessment of Structures VII

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Authors: Dan Mateescu, Yong Han, Arun Misra
Abstract: The dynamic analysis of structures with piezoelectric sensors and actuators is used in this paper to establish a method for crack detection in aerospace structures. Piezoelectric strips used as sensors and actuators are bonded on both sides of a thin structure which executes flexural oscillations. The differential voltage outputs of the piezoelectric sensors are used to detect the presence of cracks in the structure. The structural analysis uses a finite element formulation for the piezoelectric strips coupled with the structure and a nonlinear model for the cracks. This paper presents first the results of the dynamic analysis in the frequency domain of healthy and cracked plates undergoing forced flexural vibrations generated by a pair of piezoelectric actuators submitted to an oscillatory voltage excitation. The peaks in the differential voltage output obtained in the case of a cracked plate at several frequencies during the frequency sweep were found to be indicative measures for the presence of a crack in the structure. The results of the dynamic analysis in the time domain have also shown that this method has a good sensitivity in detecting cracks in the structures.
Authors: Tadeusz Uhl, Artur Hanc, Krzysztof Tworkowski, Łukasz Sekiewicz
Abstract: This paper presented idea and implementation of efficient, reliable wireless bridge monitoring system. The system using Wireless Sensor Network to collect the related environment parameters (vibrations, temperature, humidity) and transmitting data to the main server. The system eliminates stand-alone laboratory benchtop equipment sets and cable-based, hard-wired sensor networking. Modern MEMS technology for vibrations measurement and integrated humidity/temperature sensors application for structural monitoring is presented. Data collected by the wireless monitoring system is compared to data from a traditional wired monitoring system. Both – traditional and wireless collected data that can be used to accurately identify modal frequencies and mode shapes of the bridge. Case study of the system on bridge located over Vistula river in Krakow is shown.
Authors: Abdelhakim Ouahabi, Marc Thomas, Makiko Kobayashi, Cheng Kuei Jen
Abstract: A new approach is proposed for conducting structural health monitoring, based on newly developed piezoceramic sensors. They are fabricated by a sol-gel spray technique. The potential application of these sensors may be broad. These sensors have been evaluated for structural health monitoring studies. The purpose of the present study aims the detection and the localization of defects by the means of these new piezoceramic sensors. Nine sensors were integrated onto a metallic plate with moving masses. The plate was excited by an impact at a specific location and the vibratory signals from sensors were recorded simultaneously. The analysis of signals obtained from nine locations was correlated with a numerical simulation in order to identify at each time the location of the mass.
Authors: H.M. Lee, Y.H. Kwon, Hyo Seon Park, I. Lee
Abstract: To make use of a new technology in the field of structural health monitoring, various displacement measuring techniques such as a global positioning system (GPS) and vision-based techniques have been studied and proposed. It was previously introduced a new displacement measuring technique using terrestrial laser scanning (TLS) that remotely samples the surface of an object using laser pulses and generates the three-dimensional (3D) coordinates of numerous points on the surface. In this paper, for an assessment of the capabilities of the measuring technique about existing structures, the field tests for vertical displacement measurement of an existing long span steel box-girder are experimentally carried out. The performance of the technique is evaluated by comparing the displacements obtained from TLS system and displacements directly measured from linear variable displacement transducer (LVDT).
Authors: D.S. Kang, H.M. Lee, Hyo Seon Park, I. Lee
Abstract: Terrestrial laser scanning (TLS) is the technique able to acquire the dense three-dimensional (3D) coordinates effectively over entire surfaces of the objects using laser pulses. Recently, TLS is often used in various fields such as civil engineering or archeology for object modeling, volume survey of tunnel, geographic information system (GIS), and the purpose to conserve the detailed shapes of cultural heritages. However, though its applications are extended continually, an application for system identification and structural health monitoring is a beginning stage. To improve the quality of data for the model based on TLS coordinate information, the digital elevation model (DEM) constructing method is applied. In a practical point of view, since there is no need to place a strain or stress sensor to a structure to be monitored, this model could has many advantages such as no in situ instrumentation of sensors, no difficulties to reach structures or structural members, independence of natural light source and no wiring cost. For the verification of this model, experimental tests are performed with a continuous steel beam subjected to point loads.
Authors: A.M. Ali, M.M. Abdel Wahab, A.D. Crocombe, Ian A. Ashcroft
Abstract: This paper describes a dynamic test carried out on intact and damaged FRP composite beams with fixed-fixed boundary condition. Hammer excitation is used to excite the beam at fixed locations. The modal parameters are extracted from the time response using a time domain analysis, i.e. the stochastic subspace identification technique. In order to introduce damage, two sections of the beam are bonded together using an epoxy adhesive, and then a static test is carried out. For the static test, a 3-point bending -configuration is used, i.e. the beam is fixed at both ends and a static load is gradually applied in the middle of the beam using a screw jack. Different static load steps, and in turn different damage stages, are considered. After each load step, dynamic measurements are carried out. The results obtained from both tests are presented and analysed.
Authors: Marco Gherlone, Marco Di Sciuva
Abstract: The article deals with the application of a higher-order FEM approach to the analysis of the dynamic behaviour of undamaged and damaged multilayered composite plates. Some numerical examples show the accuracy of the developed plate mixed finite element, in terms of vibration frequencies and mode shapes, for different boundary conditions and with different damage geometries.
Authors: Pawel Kudela, Wiesław M. Ostachowicz, Arkadiusz Zak
Abstract: The aim of this paper is to investigate the influence of temperature fields on wave propagation in composite plates (A0 mode of the Lamb wave has been used). This phenomenon is modelled by the Spectral Element Method. For this purpose a spectral composite plate element, which enables one to take into account thermal effects, has been developed. Different temperature fields have been considered. Results of numerical simulations have been used as input data for a special damage location algorithm. The proposed damage location algorithm utilises signals registered by a clock-like sensor array. In the next step the results from crack location for different temperature fields have been compared.
Authors: Mircea Calomfirescu, Axel S. Herrmann
Abstract: This paper presents a theoretical model for anisotropic wave attenuation in composites. The model has been implemented in a software called FIBREWAVE in order to predict dispersion and attenuation of A0 Lamb wave modes. The required input data are the complex stiffness matrix coefficients of the unidirectional plies of the composites, which have been measured by an immersion technique. Good agreement has been observed between predicted and experimental group velocities and wave attenuations.
Authors: S. Gabriele, C. Valente, F. Brancaleoni
Abstract: The problem of damage identification in presence of uncertainties is faced up in the framework of interval analysis. A method previously developed by the authors in the context of model updating and global minimization for dynamic problems is applied to identify the damage in framed structures. The inclusion property of the interval analysis is exploited to find the bounds of the physical solutions. Model parameters, experimental measures and modelling errors are considered as possible sources of uncertainty. The advantages of the interval approach are discussed through numerical simulations involving the different kind of uncertainties.

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