Soutenance de thèse : Bhaawan GUPTA le 23/09/2019

« Advanced  Electromagnetic  Non-destructive  Testing  on  Creep Degraded  High  Chromium  Ferritic  Steels:  Characterization, Modelling and Physical Interpretation »23/09/2019 - 14h00 - Amphithéâtre OUEST (Bâtiment des Humanités) de l’INSA LyonDoctorant : Bhaawan GUPTALaboratoire INSA : LGEFCotutelle internationale : Université de Tohoku (Sendai, Japon)Ecole doctorale : ED 162  MEGAUnder  constant  high  temperatures  and  pressure,  the  material  undergoes  mechanical  creep degradation  which  leads  to  microstructural  changes.  These  microstructural  changes  if  not monitored  on  time,  can  lead  to  some  serious  fatal  accidents  such  as  in  power  plants.  To investigate these microstructural changes, the material has to be shaped in a certain specific shape  and  size  to  have  the  imaging  analysis  using  Scanning  electron  microscopy,  Electron backscatter diffraction etc. which are destructive in nature and involve high equipment cost.In order to overcome this issue, this thesis work, incorporates three different non-destructive techniques, to study the evolution of magnetic signatures with respect to the level of rupture they are exposed to. It is legitimate to assume that all the microstructural changes that occur in  the  material  can  be  reflected  in  the  corresponding  magnetic  signatures  measured.  The material that has been studied here is high chromium creep degraded steel which is used in the thermal power plant. The magnetic signatures are evaluated in terms of microstructural information  to  draw  the  conclusions.  Some  magnetic  parameters  from  the  curves,  such  as coercivity,  magnetic  reversibility  are  derived  which  show  strong  correlations  with  the microstructure.  Similarly,  techniques  based  on  Hysteresis  curves,  and  magnetic  Barkhausen Noise  are  also  implemented.  To  further  quantify  the  results  obtained  from  the  magnetic signatures of the materials, a model has been developed to derive model parameters in order to  physically  interpret  the  microstructural  changes.  The  modelling  technique  will  help  in overcoming  the  issue  of  lack  of  standards  in  NDT,  irrespective  of  the  experimental  set-up involved. The parameters are compared to reveal sensitivity based on the technique.Finally, conclusion has been drawn to check which parameters are correlated to microstructure for a particular NDT technique used.