Contrôle Santé des Structures Composites : application à la Surveillance des Nacelles Aéronautiques.

Abstract : This work aims at designing a Structural Health Monitoring (SHM) system for complex composite structures, with an application to elements of aeronautical nacelles. This work is original and is in the framework of a project, coordinated by AIRBUS Operations SAS and headed by AIRCELLE (SAFRAN Group). The main parts of the nacelle concerned with our approach are the fan cowl (composite monolithic) and the inner fixed structure (IFS, sandwich structure with honeycomb core) of the thrust reverser. These structures made from composite materials are subjected to many damages types which can affect nacelle’s useful life (fiber breaking, delamination, crack, etc…). Furthermore these structures are exposed to many environmental constraints which are for instance important thermal variations (from -55°C to +120°C). The objective of this work is to develop a SHM system aimed at detecting and localizing these damages, before the degradation of the whole structureoccurs. Piezoelectric (PZT) actuators and sensors are bonded on the structure and they are used to generate Lamb wave signals and perform measurements. The proposed SHM approach is based on successive measurements starting from an initial state, considered as healthy and regularly conducting follow-up. The difference in signals measured between two states is analyzed in order to extract some damages-sensitivesfeatures. After validation, PZT elements were glued to the fan cowl and to the IFS as well as on representative coupons and a suitable test bench is designed in order to validate our approach. Since one has to work on difference in signals, damage detection algorithms based on statistical hypothesis testing and PrincipalComponent Analysis (PCA) have been developed and validated. This was first tested for the detection of controlled damages introduced in coupons, and thereafter on the fan cowl and IFS. Robust damage localization algorithms (including with temperature variations) based on Time-of-flight (ToF) extraction from difference in signals, were developed and validated for these structures. A Bayesian approach for uncertainties quantification in the damage localization is also developed, leading to more accuracy in the damage localization results.
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Claude Fendzi. Contrôle Santé des Structures Composites : application à la Surveillance des Nacelles Aéronautiques.. Matériaux composites et construction. Ecole nationale supérieure d'arts et métiers - ENSAM, 2015. Français. ⟨NNT : 2015ENAM0048⟩. ⟨tel-01264825⟩

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