High-frequency impedance analysis for NDE of complex precision parts

A high-frequency, impedance-based structural health monitoring technique developed at the Center for Intelligent Material Systems and Structures (CIMSS) has been extended to the NDE of complex precision parts. Like many other non-destructive evaluation (NDE) techniques, this method relies on the detection of change in the dynamic properties of the structure when damage occurs. This NDE technique relies on the measurement of the electrical impedance at high frequencies (100 kHz - 275 kHz) with bonded non-intrusive piezoelectric actuator/sensors. Since the electrical and mechanical impedances of the bonded actuator/sensor are directly coupled, the proposed NDE method is able to detect incipient damage in the structure. Gears were chosen as complex precision parts for the experimental procedure because of their tight tolerances, high quality, and broad use. The goal is to show that incipient damage in the gear teeth, which are an extension of the cylindrical base structure, can be monitored. The most common types of damage in gears, i.e., abrasive wear and bending fatigue, were successfully detected. The impedance measurements before and after damage were converted into a scalar damage metric, which was used to detect the presence of damage when a threshold value was exceeded. Also, quality inspection was successfully demonstrated using the impedance-based technique.