*WINNER* Impedance-based NDE through Instrumented Fixtures; Effects of Clamping Force on Defect-detection Capabilities

Abstract

Electromechanical impedance measurements allow for a rapid assessment of structural integrity by providing insights into its dynamic response. Several studies have shown that electromechanical impedance signatures obtained via directly bonded piezoelectric transducers can be used for non-destructive evaluation of manufactured parts. Indirect electromechanical impedance measurements, through an instrumented testbed, have also been introduced as a promising solution for a rapid evaluation of manufactured parts. While such indirect impedance measurements alleviate the need for individual parts to be instrumented, they increase the complexity of the measurement system. Factors such as fixture design, part-fixture interface, and clamping force are found to impact measurement sensitivity to manufacturing defects and anomalies.

In this study, the effect of clamping force between the instrumented fixture and the part under test on indirect electromechanical impedance measurements is investigated. A steel fixture is instrumented with macro-fiber composite piezoelectric transducers for electromechanical impedance measurement. Clamping force is measured using calibrated strain gauges. Defect-free machined steel blocks (controls) and blocks featuring manufacturing defects are selected as the test specimens. Electromechanical impedance signatures of the specimens are measured using Zurich Instruments MFIA impedance analyzer and then compared with the signature of the control specimens. Finally, the sensitivity of impedance signatures to manufacturing defects is evaluated at various clamping force levels, and recommendations are presented.