Benchmark problems for defect size and shape determination in eddy-current nondestructive evaluation

A set of four benchmark problems is presented for verification of theoretical calculations of defect size and shape in eddy-current nondestructive evaluation. The benchmark problems are based on careful measurements of the change in coil impedance as a function of frequency for a circular air-cored coil which is scanned along the axis of an electrodischarge machined slot in a thick aluminum alloy plate. Slots of (i) semi-elliptical, and (ii) double-peaked profiles are considered. Deviations from ideal coil behavior are identified and corrected so that the final impedance data and experimental parameters can be directly used to verify theoretical inversion algorithms.