21 July 1998 Removing effects of temperature changes from piezoelectric impedance-based qualitative health monitoring
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Abstract
A high frequency NDE technique has been under investigation at the Center for Intelligent Material Systems and Structures. Physical changes in the structure cause changes in the mechanical impedance. Due to the electromechanical coupling in piezoelectric materials, this change in structural mechanical impedance cause a change in the electrical impedance of the piezoelectric sensor. Hence, by monitoring the electrical impedance and comparing this to a baseline impedance measurement, we can determine when structural damage has either occurred or is imminent. However, there are still basic research issues that need thorough investigation before full-scale development and commercialization can take place. Included in these is the effect of temperature on this impedance based NDE technique. Since piezoelectric materials exhibit strong temperature dependency and change in temperature results in marked changes in the structural dynamic responses, any variation that is associated with a change in temperature may be confused as damage. In this paper we analyze temperature effects on the electrical impedance of piezoelectric materials and the structures. We have used an empirical approach due to the complexity of the thermo-electrical- mechanical constitutive models for piezoelectric materials. Through the experimental investigations, it was found that a change in temperature modifies both the magnitude and phase of the electrical impedance of the piezoelectric sensors. A computer algorithm was developed which incorporates temperature compensation into our health monitoring applications. This compensation technique minimizes the effect of temperatures on the electrical impedance of piezoelectric sensors bonded on the structure, in the range from 80 to 160 degrees Fahrenheit. In this paper, we show how it is applied successfully to a bolted pipe structure.
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Gyuhae Park, Kazuhisa Kabeya, Harley H. Cudney, Daniel J. Inman, "Removing effects of temperature changes from piezoelectric impedance-based qualitative health monitoring", Proc. SPIE 3330, Smart Structures and Materials 1998: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (21 July 1998); doi: 10.1117/12.316963; https://doi.org/10.1117/12.316963
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