Modeling of quasi-stationary electromagnetic field near the conductive body for problems of eddy current magneto-optical testing
Magneto-optical (MO) eddy current (EC) inspection is a relatively new method of determining defectiveness metal structures and its capabilities are very poorly studied. The main advantage MOEC method is immediate inspection of defects visualization in real time, small size and relative ease of manufacture of main parts of the flaw detector. Represented the interest to calculate the topology of magnetic field, generated by the eddy currents, when it is scattered by defects various kinds and modeling of time-dependent distribution of EC, which is a decisive factor in the DDS registration of stroboscopic method. The simplest form of such a defect is the boundary of a flat sample. The aim of this work is to conduct mathematical modeling of magnetic fields generated by the eddy currents in the volume and on the borders of test objects, and compare the model with results of the magneto-optical experiments. The paper proposes a mathematical model of three-dimensional quasi-stationary electromagnetic field produced near the surface of a conductive test object when analyzing its defectiveness by eddy-current magneto-optical inspection. Elaborated a system of integrodifferential equations for the density of eddy currents and electrical charges. The article shows examples simulation of eddy currents in the form of topograms the resultant magnetic field near the surface of the plate, distribution z-component of the magnetic field over the surface of plate and allocation of the eddy current density vector in the volume of the plates. Investigated the theoretical 3D-dependence of the magnetic field distribution at the boundaries of the sample from its thickness, the operating frequency and phase of the registration of the dynamic domain structure of the magneto-optical sensor. For comparison the simulation results with the practice experiments were conducted to obtain images of the plate corresponding to the magneto-optical model calculations. Results from the magneto-optical experiments are in good agreement with model calculations.