| ABSTRACT: | VARIATION OF ELECTROMAGNETIC ACOUSTIC TRANSDUCTION SIGNALS WITH
MICROSTRESS AND ANISOTROPY IN STEEL PARTS
E. Gorkunov, S. Zadvorkin, A. Makarov, V. Solomein, and S. Rodionova
Institute of Engineering Science, Russian Academy of Sciences (Urals Branch),Yekaterinburg, Russia.
The influence of microstress on double resonant electromagnetic-acoustic transduction (EMAT) signals has
been examined in order to reveal its correlation with wear-resistance of steel parts subjected to either abrasive
wear or sliding friction. Measurements were performed on a number of samples of carbon steel and on low- and
high-alloyed steels. The samples under examination exhibited different microstress values as they were
subjected to various schedules of heat treatment and/or cold deformation. A unique relation of microstresses to
the amplitude of EMAT signals and the elastic wave velocity has been established. Besides, measurements of
hardness and wear-resistance (under abrasive and sliding friction conditions) were made on selected samples.
The results obtained give strong evidence for the relation of these important operation parameters to the
amplitude and resonant frequency of EMAT signals.
The influence of crystallographic anisotropy on EMAT signal parameters was examined on a (110) monocrystal
disc of (Fe+3%Si) transformer steel by evaluating the signal amplitude and Q-factor, the resonant frequency and
the polarizing magnetic field corresponding to the maximum signal amplitude when generating elastic and
electromagnetic waves along various crystallographic directions. Magnetic characteristics like magnetization
curves, hysteresis loop parameters, differential susceptibility, both longitudinal and transverse magnetostriction
were also measured on the disc along similar crystallographic directions. The results obtained for silicon iron
testify that the effectiveness of the resonant EMAT technique under various acoustic modes depends
significantly on a specific magnetostrictive nature of the transduction of electromagnetic and elastic waves, i.e.
that the EMAT signal anisotropy is governed by the anisotropy of magnetization and magnetostriction.
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