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Nonlinear Feature Identification of Impedance-based Structural
Amanda C. Rutherford, Gyuhae Park, Hoon Sohn and Charles R. Farrar
Engineering Sciences and Applications - Weapons Response Group,
Los Alamos National Laboratory, Los Alamos NM, 87545
The impedance-based structural health monitoring technique, which utilizes electromechanical coupling properties of
piezoelectric materials, has shown feasibility for use in a variety of structural health monitoring applications. Relying on
high frequency local excitations (typically>30 kHz), this technique is very sensitive to minor changes in structural
integrity in the near field of piezoelectric sensors. Several damage sensitive features have been identified and used
coupled with the impedance methods. Most of these methods are, however, limited to linearity assumptions of a
structure. This paper presents the use of experimentally identified nonlinear features, combined with impedance
methods, for structural health monitoring. Their applicability to )@4 damage detection in various frequency ranges is
demonstrated using actual impedance signals measured from a portal frame structure. The performance of the nonlinear
feature is compared with those of conventional impedance methods. This paper reinforces the utility of nonlinear
features in structural health monitoring and suggests that their varying sensitivity in different frequency ranges may be
leveraged for certain applications.
Keywords: Structural health monitoring, piezoelectric materials, impedance method, nonlinearity
The goal of structural heath monitoring systems is to provide a warning when damage is incipient rather than when
serious damage requiring extensive repairs has occurred. Recently, the structural community has turned its attention to
developing high-frequency, in-service damage identification techniques that provide required sensitivity to localized,
minor defects in the system. Piezoelectric materials (PZT) are particularly useful for this purpose because they can
perform both duties of sensing and actuation ("self sensing") within a local area of the structure. One example of
documented success using PZTs for self sensing is with impedance-based structural health monitoring methods (Park,
It is a well-known fact that nonlinear dynamic features of a structure are more sensitive to many common types of
damage than linear features. There are many cases where the undamaged structure responds to dynamic loading in a
predominantly linear manner and then in a nonlinear manner when the damage is present. Therefore, a combination of
the impedance methods with existing nonlinear feature extraction methods is the subject of this paper. The focus of this
study is to investigate the performance of nonlinear features, extracted using a frequency domain auto-regressive model
with exogenous inputs (ARX) model, from measured impedance signatures. This frequency domain ARX model was
originally proposed by Adams (2001). The performance of the nonlinear feature is then compared with those of
conventional impedance methods. The varying sensitivity of the extracted nonlinear features in different frequency
ranges is also analyzed.
The rest of this paper will involve introduction of the impedance method, experiments conducted on a portal frame
structure, extraction of linear and nonlinear features in various frequency ranges, qualitative comparison of features and
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Chen, Bin; Lin, Jung-Fu; Chen, Jiuhua; Zhang, Hengzhong & Zeng, Qiaoshi. Synchrotron-based high-pressure research in materials science, article, June 1, 2016; (digital.library.unt.edu/ark:/67531/metadc927636/m1/2/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.