Simulation numérique de l’écaillage des barrières thermiques avec couplage thermo-mécanique

Abstract : The purpose of this thesis is to perform a coupled thermomechanical simulation of the failure of thermal barrier coatings for turbine blades under service conditions. The thermal barrier coating is an insulating component applied to the single crystal Nickel-based superalloy AM1 substrate which is covered with a bond coat beforehand. The main degradation mode of those systems is due to the initiation and propagation of cracks caused by the out-of-plane undulation growth of an oxide layer formed in service. A set of numerical tools is implemented into the Finite Element code Z-set in order to perform a 3D thermomechanically coupled simulation of the failure of thermal barrier coatings for turbine blades. Inserting thermomechanical cohesive zone elements at the interface between the coating and the substrate makes it possible to account for the changes in the load transfer and the variations in the heat flux as a consequence of interface degradations. The mixed finite interface element of Lorentz based on an Augmented Lagrangian is used. The thermal barrier coating is modelled by means of thermomechanical shell elements implemented using the Continuum-Based approach to take advantage of the structural properties of the coating layer. Moreover, the partitionned CSS (Conventional Serial Staggered) algorithm used to couple thermal and mechanical problems is assessed. The limitations of sub-cycling with constant coupling time-step are shown through a simulation with crack propagation. The introduction of adaptative time-stepping allows to circumvent that issue. The numerical tools are assessed on test cases with increasing complexity. Numerical simulations on cylindrical tube with a thermal through-thickness gradient are performed with realistic loading sequences. Finally, thermomechanical simulations on turbine blades covered with thermal barrier coating are shown.
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Noémie Rakotomalala. Simulation numérique de l’écaillage des barrières thermiques avec couplage thermo-mécanique. Mécanique des matériaux [physics.class-ph]. Ecole Nationale Supérieure des Mines de Paris, 2014. Français. ⟨NNT : 2014ENMP0020⟩. ⟨tel-01153585⟩

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