Progress in uniform field eddy current methods

Two concerns identified earlier in using the uniform field eddy current method were addressed. These concerns are 1) uncertainty regarding the calibration formula that was used and 2) some cases where the inversion method underestimated crack depth. In this paper the calibration formula was rederived using a different approach. The new formula agreed with experimental data. It was also shown that a shallow and wide cylindrical recess in a high conductivity material yielded the most accurate calibration. The effect of crack closure on flaw signals was studied with a new two-dimensional model developed by Nakagawa et al. It was also demonstrated that crack closure occurrence can be detected by large deviations in the flaw signal phase away from 90 degrees. Ti-6Al-4V alloy served as a test material.