Methods for nondestructive eddy-current testing of structural members with automatic characterization of faults

摘要

Several phenomena which occur commonly in graphite composites, as well as other materials, and which affect the impedance of an eddy- current probe have been characterized on the complex impedance plane. An eddy- current method is disclosed by which a target material is stimulated at several frequencies, the impedance of the probe is measured and compared to the impedance of reference material, and the condition of the target material is determined. The method described is capable of finding the signatures of a number of conditions commonly found by eddy- currents, and can be programmed to find others, such as conductive and non-conductive plating thicknesses, and inclusions of material with relative ferrous materials. Because the method determines faults on the normalized impedance plane, it is capable of being used on other conductive materials in addition to graphite composites. A unique technique for accurately describining the size and shape of a fault with improved resolution using nondestructive eddy-current testing is also disclosed by which faults found by two anisotropic scans of the same material are mathematically combined.