Page 7 - РОЗДІЛ 1

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Distinct features of the MAE signal are found, in particular, the random occurrence

of individual events in time, time boundedness, and amplitude randomness. The model

of the MAE signal in the framework of statistical model of the random impulse flow is

developed. The impulse, time and spectral characteristics of the pulse signal at the

output of the primary piezoelectric converter are singled out. Informative parameters of

the MAE signal and algorithms for their estimation together with an experimental

verification have been proposed and substantiated.

Based on the examination of the influence of experimental factors on the MAE

signal parameters for ferromagnet samples make from nickel and steel, the induction

amplitude of the re-magnetized field, the thickness of the non-magnetic interlayer and

the thickness of the sample cause changes in the amplitude, shape of the envelope, and

duration of the recorded signal are established.

To eliminate the effect of the re-magnetization conditions on change of the

parameters of the MAE signal, means and algorithms for stabilization of the re-

magnetization current amplitude and the re-magnetisation field induction are developed.

They effectively optimize the signal registration procedure and ensures the compa-

rability of diagnostic results.

The evaluation of physicochemical and mechanical properties, in particular,

structural composition, heat treatment, hydrogen and corrosion degradation of
ferromagnetic materials on the change of informative MAE parameters is carried out.

For samples of steel and nickel that are subjected to tensile load, the estimations of
distribution of pulse amplitudes of the MAE signal for various values of the applied

load are obtained. The dependences of the attenuation coefficients of the approximate

exponentials of the obtained estimates of the amplitude distributions on the applied load

are plotted. These dependencies can be used as calibration curves for diagnostics of

residual stresses in ferromagnetic objects of long-term exploitation.

Based on the research carried out in the thesis, a new applied technique to

diagnosing the stress state of ferromagnetic materials are developed and its

experimental testing on long-exploitation pipe steels is performed. In particular, the

impact of structural inhomogeneities of various zones of long-exploitation pipe steels is