Damage Assessment of Structures VII

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Authors: Danny L. Parker, William G. Frazier, Mathew A. Gray
Abstract: In this paper, an optimal solution method is proposed for determining the location of change, i.e. damage, within a perturbed system utilizing a nonlinear pseudo-second order search algorithm based on function evaluations and gradient information. This method is applied to damped vibrating systems and utilizes stiffness matrix sensitivities to determine the direction of search within the estimation. The site of damage (location of change) is the solution which minimizes the error between the predicted and measured change. A by-product of the Levenberg- Marquardt algorithm is an estimation of the magnitude of the change within the system which correlates to damage extent. A second-order model of a dynamic system is used, and an approximation is developed to describe small perturbations within the system.
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Authors: Oreste S. Bursi, Marco Molinari, Alireza Savadkoohi, Daniele Zonta
Abstract: Dynamic and static identification of a full scale moment-resisting steel-concrete composite structure with partial strength joints that was tested by means of the pseudo-dynamic testing technique at the ELSA laboratory of the Joint Research Centre at Ispra, Italy, is the subject of this paper. The structure was subjected to pseudo-dynamic and dynamic tests at different damage and peak ground acceleration levels; and the results were used for identifying the behaviour of the structure. Two and three-dimensional refined finite element models of the structure accompanied by a robust nonlinear optimization method, the Powell’s Dog Leg method, were updated in order to reproduce in an optimal fashion the experimental static and dynamic behaviour of the structure.
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Authors: Dionisio Bernal
Abstract: The Dynamic Damage Locating Vector (DDLV) technique localizes damage by interrogating changes in transfer matrices G. It is shown that although G cannot be computed in a stochastic setting a surrogate matrix whose null space is related to that of G can be extracted and this matrix suffices. The paper reviews the theoretical support for the DDLV approach, discusses the constraints used to obtain the surrogate for G, and illustrates the technique using a 12-DOF shear beam monitored with 6 sensors.
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Authors: Magdalena Rucka, Krzysztof Wilde
Abstract: This paper presents experimental study on dispersive waves propagation in steel rails. The propagation of longitudinal and transverse waves was generated by an impulse hammer and measured in three points. Wavelet transform (WT) and short time Fourier transform (STFT) were applied to analyze the time signals. Analysis of signal by STFT does not provide a proper timefrequency representation due to a fixed size window. The wavelet transform can effectively identify the time-frequency components in waves. The wavelet signal processing of the experimental wave propagation signals is intended to be used for rail flaw detection.
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Authors: U. Galvanetto, L. Monopoli, Cecilia Surace, Alessandra Tassotti
Abstract: The paper presents an experimental application of the Proper Orthogonal Decomposition (POD) to damage detection in steel beams. A damaged beam has been excited with a sinusoidal force, the acceleration response at points regularly spaced along the structure has been recorded and the relevant Proper Orthogonal Modes calculated. In this way it is possible to locate damage by comparing the measured dominant Proper Orthogonal Mode with a smoothed version of it which does not exhibit apparent peaks in correspondence with the damage. One of the principal advantages of the proposed damage detection technique is that it does not require vibration measurements to be performed on the undamaged structure. Moreover the ‘optimality’ of the proper orthogonal modes only requires the use of a few (one-two) of them which can be computed in real time during lab experiments or while the structure is functioning in the field.
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Authors: Fotis P. Kopsaftopoulos, Spilios D. Fassois
Abstract: This work aims at the precise assessment of a recently introduced method that, in addition to damage detection, allows for complete and accurate damage identification (localization) and magnitude estimation. The method is based on Vector–dependent Functionally Pooled (VFP) models and is capable of offering an effective and precise solution in a unified framework. The effectiveness of the method is experimentally assessed via its application to a prototype GARTEURtype laboratory scale aircraft structure.
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Authors: Roberto Spadavecchia, Alessandro de Stefano, Donato Sabia
Abstract: The reduced-order model of a time-invariant linear dynamical system, excited by a force of an impulsive type, may be readily obtained using the Ho-Kalman minimal-realization algorithm [1]. The method is based upon a particular factorization of the Hankel matrix in the Markovian representation of the discrete-time process. For stochastic systems, the applicability of the theory has been demonstrated by Akaike [2] on the assumption that the excitation is a zero-mean white noise of a gaussian type. Some of the most widely known output-only identification methods, such as Eigensystem Realization Algorithm (ERA), Canonical Variate Analysis (CVA), and Balanced Realization (BR)) are based upon the above-mentioned work, with the aid of a robust factorization technique, such as Singular-Value Decomposition (SVD). Notwithstanding the growing popularity of the above methods, some aspects of their applicability are not yet understood. Two points are of particular interest: the first regards the applicability of the theory in highly damped systems; and the second regards its applicability to systems driven by excitations different from the one hypothesized. The aim of the present work is to define a reliable test on the hypotheses. Some numerical and experimental results are presented.
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Authors: Rhys Pullin, James J. Hensman, Karen M. Holford, Keith Worden, S.L. Evans
Abstract: Acoustic emission monitoring was completed on a painted aerospace grade steel landing gear component undergoing fatigue loading until rupture. A post-test linear location analysis of the collected signals revealed eleven groups where high activity (greater than 2000 hits) occurred within a defined location, three of which corresponded in location to the position of fracture and final rupture of the specimen. Feature data, such as amplitude, rise-time, energy etc. were used to describe the identified signals in each group. A dimension reduction through principal component analysis of the feature data of all groups was performed. Results showed that high amplitude signals associated with four groups of signals arising from noise could be separated from the fracture groups. However four groups not associated with noise or the known positions of the fracture groups were not separable from the signals attributed to fractures. The paint layer of the specimen was removed and a magnetic particle investigation was completed that showed these four groups coincided with regions of additional fracture in the component.
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Authors: Daley Chetwynd, Keith Worden, Faizal Mustapha, Jem A. Rongong
Abstract: This work was conducted as part of the European Union project ARTIMA and it investigates the effectiveness of wavelets in damage detection. It examines whether a prior wavelet decomposition of Lamb wave responses facilitates the classification of structural damage. The structure in question is an aluminium plate with viscoelastic-mounted transducers, and the damage took the form of saw cuts on the plate. The novelty detection technique of outlier analysis was used to classify the damage.
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Authors: Ke Jia Xing, Claus Peter Fritzen
Abstract: The electro-mechanical (E/M) impedance-based method is one important and effective method in damage detection. The basic concept of the impedance method is to monitor the variations in the structural mechanical impedance spectrum caused by damage in the structure. Comparing the impedance spectrum to a baseline measurement of the undamaged structure, the real part of the E/M impedance reflects the state of structural health in the local area, therefore, the structural damage can be localized, a local-area self-sensing method is implemented. In this paper, an aluminium plate mounted on an electromagnetic shaker is used to detect growing fatigue damage using the impedance method. The growing damage is documented by an increase of the indicators. For the case of a static artificial damage the concept is also demonstrated to an Airbus A320 fuselage part using 9 self-sensing elements on the stringers.
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