A Simple Scheme for Identification of A Semi-Elliptical Surface Crack from D.C. Potential Readings *

Abstract

A simple scheme was proposed for identifying the length and the depth of a semi-elliptical surface crack in a conductive body from D.C. potential readings measured at several points on the surfaces of the body. This scheme is based on the comparison of measured potential readings with theoretical ones calculated by three-dimensional boundary element analyses. For each potential reading a characteristic curve was constructed, which represented the possible combinations of the crack length and the depth, by referring to the calculated potential distributions. The intersection of the characteristic curves, which correspond to the potential values observed at several points, gives the estimation of the crack length and the depth. A sensitivity matrix was introduced to predict errors involved in the crack identification from errors in the potential measurement, and further to determine the optimum combination of locations of potential measuring probes for the identification. This scheme was applied to monitor the length and the depth of a surface crack propagating in a steel plate subjected to fatigue loadings. It was found that the proposed scheme was useful for the estimation of the length and the depth of the surface crack. The sensitivity matrix was also found to be useful to determine good combinations of probe positions.