R. T. Ko, T. R. Boehnlein, University of Dayton Research Institute, Dayton, OH; S. Sathish, University of Dayton Research Institute, Dayton, OH, OH; M. P. Blodgett, US Air Force Research Laboratory, Wright-Patterson AFB, OH
An eddy current liftoff signal which arises from a small variation of distance between a probe and a material is often considered an undesirable test variable. Rotating the liftoff signal in the impedance plane or finding a position where the liftoff signal has the least impact on the desired signal is a routine step in an eddy current inspection. In this study, the material dependency of the liftoff signal using resonant frequency eddy current is evaluated. This is to examine the feasibility of using the liftoff signal in monitoring a small change of conductivity in materials at high frequencies beyond 12 MHz. Experimental results were obtained from materials of various conductivities as well as shot peened specimens with different peening intensities and residual stresses. Preliminary results indicated that the liftoff measurement using resonant frequency eddy current could be a potential tool for evaluating small changes of conductivity in materials.
Summary: This presentation will address the application of resonant frequency eddy current liftoff measurements for possible solutions to successful implementation of eddy current methodology for residual stress profile measurement in engine components.
