Determination of Crack Depth Profile in Cylindrical Metallic Structures, Using Alternating Current Field Measurement Data

The paper proposes an efficient technique for reconstructing the depth profile of a surface-breaking crack in a cylindrical metal from the output signal of an alternating current field measurement (ACFM) probe. The proposed technique utilizes a pattern search algorithm that seeks to improve the predicted depth profile in each iteration by minimizing an error function. The error function quantifying the difference between the predicted and measured ACFM signals in each iteration is obtained, using a fast pseudo-analytic ACFM probe output simulator. The main feature of the proposed technique is that it requires a small pattern size that includes only a finite number of measurement points along the crack opening, improving the computational efficiency without compromising convergence rate. The efficiency of the proposed method is demonstrated by comparing the proposed method and a Genetic Algorithm for reconstructing depth profiles of several simulated and machine-made cracks with no predetermined geometries.