L'objectif des travaux exposés dans cette thèse est d'identifier les différentes propriétés des constituants du sandwich cousu in-situ. Cette identification est indispensable pour simuler le comportement de ce type de matériau composite à différentes sollicitations statiques ou dynamiques. Nous proposons dans cette thèse de faire Une identification dynamique faite sur un échantillon représentatif (une plaque) qui prend en compte l'hétérogénéité et complexité de la structure. Cette identification est basée sur la corrélation ent.re un essai vibratoire et un calcul par éléments finis. La corrélation se fait en minimisant une fonction coût qui porte sur le décalage entre fréquences propres expérimentales et numériques. Cette minimisation est précédée par une identification du couple (fréquence propre/mode propre) numérique et expérimental en utilisant le MAC (Modal Assurance Criterion). Pour optimiser, nous passons, dans un premier temps; par une analyse de sensibilité qui permet de classifier les paramètres en fonction de• leur importance et ainsi ne lancer le processus d'identification que sur un nombre réduit de paramètres. Nous avons appliqué cette approche sur une poutre sandwich cousue et une plaque sandwich cousue. Dans une deuxième partie de ce travail de thèse, nous avons pu mettre au profil l'aspect périodique de ces structures composites sandwichs cousues, en utilisant le théorème de Floquet-Bloch, et cela sur deux plans : l'aspect numérique pour la réduction du modèle et du temps de calcul et sur le plan physique par l'étude des bandes d'arrêt ('stopband') qui ont un intérêt applicatif assez intéressant. / The sandwich structures are well known for their high bending stiffness. This type of structure is also capable of including acoustic and thermal functionalities. However, they also have weaknesses such as the connection between the faceplate and the core and the weakness in the transverse direction due to the property of the core. The core is usually made of soft materials like foam for acoustic functionality. To overcome these weaknesses, it is possible to connect the different layers of the sandwich by transverse stitches. This is the concept of ‘stitched sandwich’. The stitch will deeply change the behavior of the structure and complicate the determination of its properties. The objective of this thesis is to identify the properties of the constituents of the stitched sandwich in situ. These properties are essential to simulate the behavior of this type of composite material under static or dynamic excitation. The identification of the properties of the constituents by mechanical tests is difficult for various reasons: the heterogeneity makes it complex to extract representative specimen; the behaviors of the constituents may change in non-in-situ tests; several different types of mechanical test, such as tensile-compression and torsion, are necessary to determine all the engineering constants in the case of orthotropic material which is common for composite materials. To overcome all these difficulties, we propose in this thesis a dynamic identification method conducted on the structure (the whole plate for example). Compared to mechanical test which is based on a sample, this method takes into account the heterogeneity and complexity of the structure. This method is based on the correlation between the vibration test and a finite element model of stitched sandwich. The parameters are identified by minimizing a cost function which can measure the gap between the experimental frequencies and the calculated frequencies. The correspondence of experimental mode and calculated mode is guaranteed by MAC (Modal Assurance Criterion). Before the optimization, we propose firstly a sensitivity analysis to classify the parameters according to their importance. Then the identification process is only conducted on a reduced number of parameters. We have applied this dynamic identification method to both a stitched sandwich beam and a stitched sandwich plate. 9 parameters of different constituents are identified in the case of plate. In the second part of this thesis, based on the theorem of Floquet-Bloch, we have profited from the periodic characteristic of the stitched sandwich structures in two aspects: in the numerical aspect, the periodicity has served to reduce the calculation of forced response of periodic structure; in the physical aspect, we have studied the stop band of stitched structures.
| Identifer | oai:union.ndltd.org:theses.fr/2017COMP2361 |
| Date | 08 June 2017 |
| Creators | Li, Nan |
| Contributors | Compiègne, Aboura, Zoheir, Ben Tahar, Mabrouk |
| Source Sets | Dépôt national des thèses électroniques françaises |
| Language | French |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation, Text |
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