Characterization of surface-breaking cracks in metal sheets by using AC electric fields

Abstract

A surface-breaking crack in a metal sheet may be detected by passing an alternating current through the sheet and making measurements of the potential difference on the sheet’s surface. The distribution of potential on the metal surface depends on the exact geometry of the crack and the aim of this work is to predict the shape and size of a surface-breaking crack from the potential distribution. The theoretical model is formulated using the potential and streamfunction as the independent variables and the shape of the lower edge of the crack is determined from the solution of a Fredholm integral equation of the first kind. This is solved using a minimization technique which suppresses the instability of the equation. The method is tested using theoretical distributions of potential from known crack shapes and very good agreement is obtained in each case.