The study consists mainly of two parts. The first part is related to the dynamic strength enhancement of honeycombs under uniaxial compression. We firstly study numerically this particular phenomenon of thin-walled structure by using three micro-size FE models and this allows us to reveal the role played by lateral inertia in the dynamic enhancement. Further more, the dynamic enhancement of a series of honeycombs with different cell-size, cell-wall thickness and base material is studied experimentally and the influence of these geometric parameters and the base material on honeycomb strength as well as the dynamic enhancement rate is investigated. The second part of this study concerns the biaxial behavior of honeycombs under combined shear-compression. We firstly present a combined dynamic shear-compression loading device basing on a large-diameter Nylon Split Hopkinson Pressure Bar system. Then, a series of quasi-static and dynamic experiments on an aluminium honeycomb is performed with loading angles ranging from 0o to 60o (part of shear more and more important). It shows a strong effect of the additional shear loading to honeycomb overall strength. A notable strength enhancement under impact loading is observed for all the honeycomby b specimens. Images captured during tests permit for the determination of the two co-existing deforming patterns under combined shear-compression. Finally, the combined shear-compression tests on honeycombs are reproduced by a numerical virtual model and the separated normal and shear behaviors of honeycombs under combined shear-compression are obtained. A crushing envelope in normal strength vs. shear strength plane was obtained on the basis of these simulations, which shows an isotropic expansion behavior from the quasi-static loading to the dynamic loading.

Cette thèse est composée de deux parties. La première partie est liée à l’augmentation sous impact des résistances des nids d'abeilles en compression uniaxiale. D’abord, nous avons étudié ce phénomène particulier numériquement à l’aide des modèles éléments finis et cela nous a permis de démontrer le rôle de l’inertie latéral dans cette augmentation. Ensuite, le comportement dynamique d'une série de nids d'abeilles (tailles de cellule et épaisseurs des parois et matériau de base différents) a été étudiée expérimentalement pour confirmer les résultats de la simulation. La deuxième partie concerne le comportement biaxial de nids d'abeilles sous cisaillement-compression combinés. Nous y présenterons d'abord un dispositif pour appliquer le cisaillement-compression combiné, en utilisant un système des barres de Hopkinson viscoélastiques de grand diamètre. Une série d'essais sur des nids d'abeille en aluminium sont réalisées en statique et en dynamique, avec les angles de chargement allant de 0° à 60o (part de cisaillement de plus en plus important). Ces essais montrent un important effet du cisaillement supplémentaire sur la résistance globale du nid d'abeille. Une augmentation de la résistance sous chargement d'impact est observée pour tous les angles. Les images capturées lors des essais permettent de la détermination des deux modes de déformations coexistant sous cisaillement-compression combiné. Enfin, les essais de cisaillement-compression sur des nids d'abeilles sont reproduites numériquement afin de séparer le comportement normale et celui du cisaillement. La courbe limite dans le plan de la contrainte normale vs la contrainte du cisaillement a été obtenue, qui montre une augmentation homogène (isotropie) sous chargement dynamique. / The study consists mainly of two parts. The first part is related to the dynamic strength enhancement of honeycombs under uniaxial compression. We firstly study numerically this particular phenomenon of thin-walled structure by using three micro-size FE models and this allows us to reveal the role played by lateral inertia in the dynamic enhancement. Further more, the dynamic enhancement of a series of honeycombs with different cell-size, cell-wall thickness and base material is studied experimentally and the influence of these geometric parameters and the base material on honeycomb strength as well as the dynamic enhancement rate is investigated. The second part of this study concerns the biaxial behavior of honeycombs under combined shear-compression. We firstly present a combined dynamic shear-compression loading device basing on a large-diameter Nylon Split Hopkinson Pressure Bar system. Then, a series of quasi-static and dynamic experiments on an aluminium honeycomb is performed with loading angles ranging from 0o to 60o (part of shear more and more important). It shows a strong effect of the additional shear loading to honeycomb overall strength. A notable strength enhancement under impact loading is observed for all the honeycomby b specimens. Images captured during tests permit for the determination of the two co-existing deforming patterns under combined shear-compression. Finally, the combined shear-compression tests on honeycombs are reproduced by a numerical virtual model and the separated normal and shear behaviors of honeycombs under combined shear-compression are obtained. A crushing envelope in normal strength vs. shear strength plane was obtained on the basis of these simulations, which shows an isotropic expansion behavior from the quasi-static loading to the dynamic loading.