Three-Dimensional Identification of Semi-Elliptical Surface Crack by Means of Direct-Current Electrical Potential Difference Method With Multiple-Probe Sensor

A method of three-dimensional identification of a semi-elliptical surface crack by direct-current electrical potential difference method with a multiple-probe sensor was proposed and its validity was numerically examined. The condition of the surface crack embedded in a conductive plate was specified by the two-dimensional location of the crack center, (y_c, z_c), length and depth of the crack, c and a, and the surface and inward angles of the crack plane, θ_sur and θ_in. Identification was carried out based on the distribution of the electrical potential difference around the crack measured on the surface of the plate with the “multiple-probe sensor” which is composed of many probes aligned in two orthogonal directions. The location, (y_c, z_c), and surface angle, θ_sur, were evaluated using the line and point symmetries of the potential difference distribution. The inward angle, θ_in, was determined by the magnitude of symmetry of potential difference distribution with reference to the evaluated crack line. Finally, length and depth of the crack, c and a, were determined using the exact solution of potential difference for an inclined inner elliptical crack which yields similar potential difference to that of the inclined semi-elliptical surface crack. The validity of the method was numerically confirmed by carrying out the evaluation based on the result obtained by finite element analysis.