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Theses

Réduction des vibrations de structures composites complexes par dispositifs piézoélectriques shuntés : application aux aubes de turbomachines

Abstract : This thesis concerns the vibration reduction in the low frequency range of a composite fan blade of a turbojet engine with piezoelectric devices. The interest is to increase lifespan and avoid flutter phenomena by reducing the vibration amplitude. The purpose of this thesis is to study several shunted piezoelectric devices, in the low frequency range, that can be applied to a woven composite turbojet fan blade. The targeted applications are the LEAP fan blades or the “open-rotor” fan blade, both of them required to manage a complex geometry. The solutions investigated used piezoelectric elements coupled to a passive or semi-passive circuit. The core of this thesis, still a scientific obstacle at present, is to propose efficient solutions that integrate the piezoelectric elements to the fan blades in order to meet aerodynamic constraints for this type of structure, while increasing damping level on one of the first modes of vibration. The performances of such devices are directly related to a coefficient: the electromechanical coupling factor that requires to be maximized. This coefficient depends on all the features of the structure: materials used (host composite structure, piezoelectric material), but especially the placement and geometry of the piezoelectric elements. The use of piezoelectric material connected to active, semi-passive or passive circuits has been extensively studied but the experiences almost always deal with academic cases such as beams or plates. The aim is for the developed piezoelectric device, to evaluate the damping performance of a weakly damped massive structure.A part of the work is thus to develop a predictive finite element model of the structure coupled to the piezoelectric material to quantify the performance of the device. Several solutions are tested on a simple structure to evaluate the influence on the device performance of, (1) the choice of the piezoelectric material, (2) the placement and geometry of the piezoelectric elements, and (3) of the dissipative circuit. Various integration solutions in the blade are proposed and a method for characterizing the properties of woven materials is developed in the perspective of integrating the active materials in the composite preform.This study is both numerical and experimental: a demonstrator using a composite fan blade is designed and tested in the laboratory to validate the proposed concepts.
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Submitted on : Friday, October 20, 2017 - 7:05:09 PM
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Olivier Thierry. Réduction des vibrations de structures composites complexes par dispositifs piézoélectriques shuntés : application aux aubes de turbomachines. Vibrations [physics.class-ph]. Conservatoire national des arts et metiers - CNAM, 2016. Français. ⟨NNT : 2016CNAM1111⟩. ⟨tel-01620672⟩

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