Real-time structural integrity monitoring is a concept that is becoming a reality in the
engineering community. It will soon be possible for a structure to warn the user when its
own structural integrity has been altered.
A qualitative impedance-based health monitoring technique, which can be implemented
for real-time damage evaluation of complex structures, is investigated. The basic
principle of the technique is to monitor the structure's mechanical impedance which will
be changed with the presence of damage. The mechanical impedance variations are
monitored by measuring the electrical impedance of a bonded piezoelectric
actuator/sensor (PZT). This mechanical-electrical impedance relation is due to the
electro-mechanical coupling property of piezoelectric materials. This health monitoring
technique can be easily adapted to existing structures, since only a small non-intrusive
PZT patch is needed. This impedance-based method operates at high frequencies
(generally above 100kHz), which enables it to detect incipient type damage in a localized
region. The localized sensing region offers the advantage of not being affected by nonnal
operating conditions or by changing boundary conditions. In this thesis, a complete
theoretical background on the impedance-based technique is derived. Then, the technique
is applied successfully to a variety of case studies; such as composite patch repair, aircraft
structures, precision parts, and civil infrastructure. By simplifying the impedance
measurement interpretation through a simple scalar damage metric, the real-time
implementation of the impedance-based technique has been proven feasible.
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