Eddy Current Image Processing for Crack Size Characterization

Estimation of crack length and depth is of considerable interest to the eddy current testing community, due to their importance in determining the relative severity of the flaw. A paper presented at the INTERMAG-MMM conference in July, 1988 proposes an automated method for estimation using eddy current image data where the material being tested is magnetic [1]. These estimates are within two to one of the correct results over a wide range of EDM slot sizes and aspect ratios, provided the slot length is at least half the mean coil radius. A second motivation for the present work is to provide a benchmark against which other techniques, or variations such as lower sampling density or different flying heights (fixed lift-off), may be measured. Since there is no obvious reason why the same methodology should not work for non-magnetic material tests, seven different sets of data on the twelve EDM slots in a calibration block were run thru a similar algorithm. A brief description of the algorithm will be given, then the data sets will be described, and the results (including some processing variations) discussed