This paper presents the characterization of machined long cracks by performing measurements at two different directions not necessarily orthogonal.
Without knowing the orientation of a crack two components of the secondary magnetic field created by eddy currents induced in a conductive metallic plate are measured using a probe with axial symmetry and having a giant magnetoresistor sensor (GMR) as the sensing element in the axis of the excitation coil. The orientation and the width of the crack are computed from images obtained from scanning the specimen for two different directions. Within the paper a normalization algorithm is proposed to determine the images. Then, by performing measurements at any two directions, the images obtained can be compared and the real orientation and width of the crack can be previewed. As eddy current technique is a very sensitive method, a reproducible noise is always added to the measurements and data processing is mandatory in order to improve the informative contents of the raw data.
The paper compares the experimental result obtained by scanning the conductive plate specimen in a direction perpendicular to a crack and the result obtained by previewing the orientation and width of the same crack from processing the raw data taken by scanning the plate specimen at any two scanning directions. The highest accuracy of the calculated result, obtained when two orthogonal components of the magnetic field are measured, is also computed.