Magnetic testing selectivity improving by vibration-induction method

Аuthors

Nikolaev Y. L.^*, Chernova A. V.^**

Moscow State University of Engineering and Computer Science, 20, Stromynka str., Moscow, 107996, Russia

*e-mail: leila_nik@list.ru
**e-mail: aleks.chernova@gmail.com

Abstract

Implementation of gradiometry techniques for magnetic fields registration in the process of objects surface scanning is an effective approach to magnetic testing selectivity improving. We suggest vibratory inductive method based on induction transducer which sensitivity depends on the rate of change magnetic flux, coupled with turns of its inductance coil.

When vibrating coil moves along the surface under testing the first sign of blemish presence will be indicated by the first harmonic amplitude surge in the spectrum of induced electromotive force signal. With further movement of the coil towards the defect center a signal, representing a superposition of harmonics with frequencies ω₀ and 2ω₀, appears, with the tendency of increase in second harmonic amplitude and decrease in that of the first one. This is the second sign of a blemish presence. When the coil central section coincides with the center of fault stray magnetic field, the induced signal contains only second harmonic, which amplitude assumes the highest value. This is the third and the main sign of a blemish presence. It has a selective value with locality of flaw location.

In case of normal component testing circuit, the sign of blemish presence is revealed by a surge in the first harmonic amplitude over the fault surface.

The presented experimental data has been obtained through defected samples testing with a research facility, providing test sample movement against induction transducer according to three coordinates with resolution of 5 microns, as well as relative change of the transducer and test sample angular location.

Keywords:

magnetic testing, induction transducer, vibroscanning, induced electromotive force, selective sensitivity, localization

References

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