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Theses

Détection et simulation d'instabilités viscoplastiques dans les disques de turbines

Abstract : When developing aeronautical turbomachinery, engine manufacturers must prove the integrity of rotating parts by certification. The regulations require that the bursting speed of the turbine disk be at least 20% higher than its operating speed. The general objective of this thesis is to predict more accurately the bursting speed of a turbine disk made of Inconel718,a nickel-based superalloy. The first step requires precise knowledge of the material’s response to several types of thermomechanical loading and is, therefore, part of a global reflection on the optimization of the geometry of the disc, the reduction of the dimensioning margins, and the reduction of the manufacturing costs. Several geometries of specimens stressed in uniaxial and biaxial tension were developed and tested at both room and high temperatures (20°C and 500°C respectively) to represent all the local solicitation states encountered by the disc in service conditions. A patent-pending laser marking technique was developed to visualize the global and local displacement fields allowing for better pattern resistance and higher resolution. An isotropic viscoplastic behavior law could be finely established by an inverse method taking into account the mechanical tests obtained on all the geometries. Among several plasticity criteria, Hosford's criterion was adopted to which was added McCormick's model to take into account the Portevin-Le Chatelier instabilities appearing at high temperature. Moreover, the incorporation of the testing machine stiffness in the model allows for a better consistency with the experimental results and significantly reduces the calculation time. A fracture criterion has been established. It is local, multiaxial, and decoupled from the behavior model. This purely phenomenological criterionis based on the Hosford triaxiality and the Lode parameter in plastic strain rate and has the particularity to account forbiaxial stress states. A fracture surface at room temperature has been obtained allowing for the prediction of bursting speeds higher than those conventionally obtained by a global approach. At high temperatures, the PLC effect generatesa redistribution of the damage field at the passing of a band delaying the appearance of a localization band lethal to the material. The fracture surface at high temperature is identical to that obtained at room temperature. Finally, all these results lead to a recommendation of a protocol for the identification of the rupture criterion applicable in the industrial field. This work could thus contribute to refining, even to optimizing, the geometrical parameters of the discaccording to desired criteria such as the location of rupture and/or the admissible speed of bursting while having better control of the margins of dimensioning and the development costs
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Submitted on : Tuesday, June 7, 2022 - 2:14:43 PM
Last modification on : Saturday, June 25, 2022 - 3:04:31 AM
Long-term archiving on: : Thursday, September 8, 2022 - 6:49:53 PM

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  • HAL Id : tel-03689634, version 1

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Natan Guillermin. Détection et simulation d'instabilités viscoplastiques dans les disques de turbines. Mécanique des matériaux [physics.class-ph]. Université Paris sciences et lettres, 2022. Français. ⟨NNT : 2022UPSLM005⟩. ⟨tel-03689634⟩

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