zastosowania elektromagnetyzmu w nowoczesnych ... - PTZE

XVIII Sympozjum PTZE, Zamość 2008
APPLICATION OF ALTERNATING MAGNETIC FIELDS
FOR TECHNICAL DIAGNOSTICS
OF THE RAIL DAMAGES
Vitalij Nichoga 1, 2 , Eugeniusz Grudziński 3 ,
Petro Dub 1 , Viktor Ivanchuk 2
1 Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, Lviv, Ukraine
2
Lviv Polytechnic National University, Lviv, Ukraine
3
Wrocław University of Technology, Wrocław, Poland
One of the most important contemporary problems is the problem of diagnostics of the
technical state of engineering objects of long-term exploitation, for example, such as rails.
Electromagnetic methods, which are based on determination of the characteristics of the
electromagnetic fields radiated by inspected objects when alternating electrical currents flow
in them, are widely used in engineering practice.
Changes of the spatial structure of the external electromagnetic field of the inspected rail,
and also the quantitative estimation of its intensity and other characteristics can give useful
information about presence of cracks and other damages in mentioned above technical
objects.
Brief analysis of the most widely used modern methods of rail diagnostics are given in
the report. It is shown that now the most popular magnetic methods of the rail damages
detection are the following ones: method of metal magnetic memory (MMM) [1, 2],
magnetodynamic method [3], and alternating current field measurement (ACFM) [4, 5]
The metal magnetic memory method is based on registration and analysis of the proper
magnetic leakage fields on the object surface with the aim to determine areas of stress
concentration, defects, structure heterogeneity of metals and welded joints.
The MMM method can be used for rail diagnostics both in manual and automatic modes
[2].
The magnetodynamic (high-speed) method occupies now very important place among the
rail diagnostics methods. That method is used in non-destructive testing carriages that are
operated on the Ukrainian railways. The essence of the method consists in the following [3]:
the current is sent from the direct current source to two electromagnets situated above both
parallel rails of a track. That system creates electromagnetic excitation of rails. During the
carriage movement the magnetic flux created by the excitation source is introduced into the
rail and structural heterogeneities (track elements, rail joints, defects) cause changes in the
magnetic field distribution above the rail and so induce alternating electromotive force in the
induction sensor which signals can be seen on a display as voltage dependency upon distance.
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