Exploratory Development of Advanced Surface Flaw Detection Methods.

Development of the electric current perturbation ECP method for application to surface flaw detection in the retirement-for-cause RFC inspection system is described. Physical constraints imposed by material properties and complex geometrical features of F100 engine parts are discussed as background for the selection and preparation of specimens for experimental optimization of ECP probe design. Experimental flaw detection data are presented for simple laboratory specimens, specimens designed to simulate complex geometry features of concern in F100 engine inspection, and finally, for actual engine parts. Results demonstrate that the detection of flaws even smaller than 0.010 in. long by 0.005 in. deep is possible in blade slots. Also, from experimental data obtained in blade slot scans, preliminary estimates of the probability of detection as a function of flaw size are provided. Based on data reported here, it is concluded that ECP method has been demonstrated with the breadboard system to have the inherent sensitivity and repeatability to meet RFC requirements regarding flaw detection capability and system compatibility, and is now ready for more extensive evaluation in an actual inspection environment.