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Method and apparatus for diagnosing a damage in a structure

外国特許コード F120007027
掲載日 2012年11月19日
出願国 アメリカ合衆国
出願番号 86697409
公報番号 20100319452
公報番号 8371170
出願日 平成21年2月12日(2009.2.12)
公報発行日 平成22年12月23日(2010.12.23)
公報発行日 平成25年2月12日(2013.2.12)
国際出願番号 JP2009052311
国際公開番号 WO2009101978
国際出願日 平成21年2月12日(2009.2.12)
国際公開日 平成21年8月20日(2009.8.20)
優先権データ
  • 特願2008-032142 (2008.2.13) JP
  • 2009JP052311 (2009.2.12) WO
発明の名称 (英語) Method and apparatus for diagnosing a damage in a structure
発明の概要(英語) In the diagnosis of a structure, at least one electromechanical transducer is fixed to a structure as an object of diagnosis and is driven with an alternating voltage of a constant amplitude, and a current flowing through the at least one electromechanical transducer is measured.
Next, high frequency components around a driving frequency of the electromechanical transducer are separated from a signal of the current.
Next, modulation information due to a damage is extracted from amplitude and/or phase demodulation of the high frequency components.
Then a damage index is evaluated based on the modulation information.
Thus, structural health can be diagnosed with use of at least one electromechanical transducer, without baseline data, in one measurement.
従来技術、競合技術の概要(英語) BACKGROUND OF THE INVENTION
The invention relates to damage detection and structural health evaluation in various structures such as mechanical structures and facilities, buildings, civil engineering works, and aerospace structures.
Damage detection and structural health evaluation on a structure have been performed in various ways.
For example, piezoelectric impedance-based damage detection technique is used to detect a damage created in a structure in an early stage. (For example, refer to JP-A 2007-085733, JP-A 2004-028907 and JP-A 2001-099760.) In the piezoelectric impedance-based damage detection technique, a piezoelectric element is affixed on a surface of a structure, and a change in dynamic characteristics of the structure due to a damage created in the structure is detected as a change in electrical impedance of the piezoelectric element in a supersonic range between a few tens kHz to a few hundreds kHz.
The inverse of the electrical impedance (or admittance) of the piezoelectric element depends on electrostatic capacitance of the piezoelectric element and driving point mobility of the structure observed from the piezoelectric element.
When a damage is created at a structural point near the affixed point of the piezoelectric element, the driving point mobility of the structure is changed largely in a range between a few tens kHz to a few hundreds kHz, so that the electrical impedance (or admittance) of the piezoelectric element is changed largely in the range according to a relationship between the dynamic characteristics of the structure and the electrical impedance (or admittance).
Then, it is said that a very small damage is detected sensitively near the affixed point by measuring the electrical impedance of the piezoelectric element.
An impedance analyzer or a device dedicated for measuring impedance is used for the measurement of electrical impedance.
However, in the piezoelectric impedance-based damage detection technique, an effect of a damage on high frequency waves is evaluated as a frequency response (impedance).
Thus, the dynamical effect due to the damage is observed only as a time average.
A damage is viewed as a static one, and for example, various nonlinear effects and interactions with the high frequency waves are neglected at the interface of the damaged area.
Further, the evaluation is relative because a damage is detected as a "change" in electrical impedance of the piezoelectric element affixed to the structure before and after the structure is damaged, or a "baseline" data is necessary as a standard for the evaluation.
The healthy impedance or admittance as a baseline varies largely with the structure, and it also depends on the affixed point or a size of the piezoelectric element.
Therefore, the baseline cannot be predicted with a calculation or the like practically, and it has to be measured actually.
This means that structural health cannot be decided with only one measurement in principle, and it is a large problem on the application or operation of the technique.
Further, a damage in an early stage often has a form of a "hidden damage" such as a closed crack or a kissing bond, and if such a damage is not detected, it might be a very great danger on safety management.
However, a supersonic wave is transmitted through a damage such as a closed crack, so that it would be difficult to detect such a damage with the piezoelectric impedance-based damage detection technique.
On the other hand, nonlinear wave modulation-based damage detection technique is one of the techniques effective for detecting a "hidden damage" without baseline data in principle. (For example, refer to C. Liang, F. P. Sun, C. A. Rogers, An impedance method for dynamic analysis of active material systems, Journal of Vibration and Acoustics, Transactions of the ASME, Vol. 116, pp. 120-128, 1994; G. Park, H. Sohn, C. R. Farrar, D. J. Inman, Overview of piezoelectric impedance-based health monitoring and path forward, The Shock and Vibration Digest, Vol. 35, No. 6, pp. 451-463, 2003; K. E.-A. Van Den Abeele, P. A. Johnson and A. Sutin, Nonlinear elastic wave spectroscopy (NEWS) techniques to discern material damage, Part I: Nonlinear wave modulation spectroscopy (NWMS), Res Nondestr Eval, Vol. 12, pp. 17-30, 2000; V. Zaitsev, V. Gusev, B. Castagnede and P. Sas, Micro-damage detection using a modulation technique based on dissipative nonlinear effects, Proceedings of Forum Acusticum Sevilla 2002, 2002; and V. Zaitsev and P. Sas, Nonlinear response of a weakly damaged metal sample: a dissipative mechanism of vibro-acoustic interaction, Journal of Vibration and Control, Vol. 6, pp. 803-822, 2000.) In this technique, it is noted that a damage such as a crack created in a structure, a slacked bolt, or detachment at an adhering face accompanies a change in contact state between contacting faces.
Then, a change in contact state between the contacting faces due to low frequency dynamic load fluctuations is taken out as amplitude or phase modulation of high frequency waves received from an electromechanical transducer such as a piezoelectric element.
If there is no damage, no modulation occurs, and this evaluation is absolute in principle.
Thus, structural health can be decided by one data acquisition with nonlinear wave modulation-based damage detection technique.
Further, because this technique uses a change in variations of dynamic load at low frequencies exerting a damaged site, it has an advantage that a "hidden damage" can be detected in principle.
However, for nonlinear wave modulation-based damage detection technique, at least two piezoelectric elements are needed for sending and receiving high frequency waves, and this is a problem when the technique is applied to a situation wherein a space for affixing the piezoelectric elements is restricted strictly.
Therefore, it is a problem to develop a self-sensing technique using only one piezoelectric element.

特許請求の範囲(英語) [claim1]
1. A method for diagnosing a structure comprising: driving at least one electromechanical transducer fixed to a structure as an object of diagnosis with an alternating voltage of a constant amplitude, and measuring a current flowing through the at least one electromechanical transducer,
separating high frequency components around a driving frequency of the electromechanical transducer from a signal of the current,
extracting modulation information due to a damage from amplitude demodulation of the high frequency components, and
evaluating a damage index based on the modulation information.
[claim2]
2. The method according to claim 1, wherein the damage index is a ratio of amplitude of a current waveform after the demodulation to an average of the current waveform after the demodulation, and the ratio is compared with a threshold value to diagnose occurrence of a damage.
[claim3]
3. A diagnosis apparatus comprising: a separator for separating high frequency components around a driving frequency of at least one electromechanical transducer from a signal of a current flowing through the at least one electromechanical transducer when the transducer fixed to a structure as an object of diagnosis is driven with an alternating voltage of a constant amplitude,
an extractor for extracting modulation information due to a damage from amplitude demodulation of the high frequency components, and
an evaluator for evaluating a damage index based on the modulation information.
[claim4]
4. A diagnosis method comprising: driving at least one electromechanical transducer fixed to a structure as an object of diagnosis with an alternating voltage of a constant amplitude, and measuring a current flowing through the at least one electromechanical transducer,
separating high frequency components around a driving frequency of the electromechanical transducer from a signal of the current,
extracting modulation information due to a damage from phase demodulation of the high frequency components, and
evaluating a damage index based on the modulation information.
[claim5]
5. The method according to claim 4, wherein the damage index is a ratio of amplitude of a current waveform after the demodulation to an average of the current waveform after the demodulation, and the ratio is compared with a threshold value to diagnose occurrence of a damage.
[claim6]
6. The method according to claim 4, further comprising: extracting the modulation information due to the damage with amplitude demodulation of the high frequency components,
wherein the damage index is evaluated from the modulation information after the phase demodulation and the modulation information after the amplitude demodulation.
[claim7]
7. An diagnosis apparatus comprising: a separator for separating high frequency components around a driving frequency of an at least one electromechanical transducer from a signal of a current flowing through the at least one electromechanical transducer when the transducer fixed to a structure as an object of diagnosis is driven with an alternating voltage of a constant amplitude,
an extractor for extracting modulation information due to a damage from phase demodulation of the high frequency components, and
an evaluator for evaluating a damage index based on the modulation information.
[claim8]
8. The diagnosis apparatus according to claim 7, wherein the extractor further extracts modulation information due to the damage with amplitude demodulation of the high frequency components, and the evaluator evaluates the damage index from the modulation information after phase demodulation and the modulation information after amplitude demodulation.
  • 発明者/出願人(英語)
  • MASUDA ARATA
  • KYOTO INSTITUTE OF TECHNOLOGY
国際特許分類(IPC)
米国特許分類/主・副
  • 73/587
  • 73/594
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