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 Lyon
Doctorant : Bhaawan GUPTA
Laboratoire INSA : LGEF
Cotutelle internationale : Université de Tohoku (Sendai, Japon)
Ecole doctorale : ED 162 MEGA
Under 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.