Eddy Current Probe Signals Due to a Crack at a Right-Angled Corner

Abstract

In eddy current testing, a flaw in a metal is detected when it gives rise to a change in the electrical impedance of the probe that induces current in the material. Theoretical models and computer codes have been developed to predict the probe signals as an aid to improving inspections and the interpretation of measurements. Model calculations can be efficient for a restricted class of problems in which the conductor geometry is simple, such as an infinite plate or tube. The computational cost is usually low in such cases because dedicated Green's kernels are available, allowing numerical approximations of integral equations to be found using only a few unknowns to represent the field in the flaw region. In this study, the aim has been to perform eddy current calculations on corner cracks efficiently using an approximate Green's function for a conductive quarter-space, thereby extending the class of problems that benefit from the use of a dedicated kernel. The properties of the kernel mean that numerical solutions based on boundary or volume elements can be found for an edge crack by rendering as a discrete approximation only the field at the surface of the flaw or the field within it respectively. Volume element calculations have been carried out to determine the field at a corner crack and from it the probe response. Comparisons of the calculated probe impedance due to edge notches show good agreement with experimental measurements.