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                     The thesis is submitted for Ph.D. degree in technical sciences, speciality 05.02.10 –

               Diagnostics  of  Materials  and  Constructions  (132  –  Materials  Science).  –  Karpenko

               Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, Lviv,

               2019.

                     The dissertation is aimed at solving the significant scientific and technical problem

               consists in the development of the method for diagnostic of the condition of the long-

               term exploited ferromagnetic elements of constructions on the parameters of the signal

               of magnetoelastic acoustic emission (MAE). This method is based on the analysis of the

               mechanism  of  generation  of  the  MAE,  selection  and  substantiation  of  the  statistical

               model of the registered signal, development of effective algorithms for processing the

               result  of  the  received  signals  as  well  as  the  method  for  diagnostic  of  ferromagnetic

               objects.

                     Today in the industrial complex of Ukraine, a relevant problem is the diagnostics

               of the condition of metal products and structural elements, as well as equipment, which

               has completed its design resource and needed replacement. Most of equipment in the

               industrial sector is made from steels that are ferromagnetic materials. Contacting during

               long-term  exploitation  with  a  medium  which  contains  hydrogen  or  hydrogen  sulfide,

               undergoing temperature changes, environmental influences and natural factors, and also


               stresses influences, ferromagnetic materials are degraded losing their strength properties
               and characteristics.


                     To improve the quality of technical diagnostics of the state of the materials from
               which these products are made, it is necessary to develop and apply new methods and


               means of non-destructive testing. A perspective diagnostic method is the MAE method,

               which occurs during the re-magnetization of the ferromagnet and is associated with the

               jump motion of non-180° domain walls.

                     The  dissertation  presents  a  mathematical  model  of  motion  of  non-180°  domain

               wall  during  the  ferromagnetic  re-magnetization  based  on  the  energy  approach  is

               developed. The relation ship between parameters of the jump of non-180° domain wall

               and  the  parameters  of  the  MAE  signal  and  the  tested  ferromagnetic  material  is

               established.
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