In this paper a concept of hexagonal chiral honeycomb is proposed as a truss-like internal structure for adaptive wing box configurations. In contrast with classical centresymmetric cellular structures like rectangular or hexagonal grids, the proposed honeycomb did not present inversion symmetry, and featured an in-plane negative Poisson's ratio behaviour. The cellular structure considered exhibited this Poisson's ratio behaviour under a large range of strain. A set of numerical (finite element, FE) simulations have been carried out in order to correct the initial theoretical predictions to take into account axial, shear and elastic deformations of all elements composing the unit cell when subjected to uniaxial loading. The homogenized linear elastic mechanical properties were then introduced in an FE wing box model of a racecar wing coupled to a panel code to simulate unidirectional static fluid -structure coupling between the wing box and the flow surrounding the airfoil. The cellular solid proposed as the internal layout of the wing box allowed conforming deformations with the external flow, giving a variation of the camber line and trailing edge displacement, and acting as an aileron.

The out-of-plane bending behaviour of single layer graphene sheets (SLGSs) is investigated using a special equivalent atomistic-continuum model, where the C-C bonds are represented by deep shear bending and axial stretching beams and the graphene properties by a homogenization approach. SLGS models represented by circular and rectangular plates are subjected to linear and nonlinear geometric point loading, similar to what is induced by an atomic force microscope (AFM) tip. The graphene models are developed using both a lattice and a continuum finite element discretization of the partial differential equations describing the mechanics of the graphene. The minimization of the potential energy allows us to identify the thickness, elastic parameters and force/displacement histories of the plates, in good agreement with other molecular dynamic (MD) and experimental results. We note a substantial equivalence of the linear elastic mechanical properties exhibited by circular and rectangular sheets, while some differences in the nonlinear geometric elastic regime for the two geometrical configurations are observed. Enhanced flexibility of SLGSs is observed by comparing the nondimensional force versus displacement relations derived in this work and the analogous ones related to equivalent plates with conventional isotropic materials.

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In this work the concept of using a chiral honeycomb as the internal structure for a passively morphing wing is explored. The use of a chiral honeycomb, which features an in‐plane negative Poisson's ratio, potentially offers high deformability whilst maintaining structural integrity of the wing box. A finite element simulation was carried out, coupling a complete two‐dimensional model of the wing and internal structure to a panel code flow solver. An iterative process was then used in order to predict the wing camber change with respect to airflow. The concept was validated experimentally through the construction of a prototype wing for wind‐tunnel testing. The measured response was non‐linear with respect to aerodynamic loading, but the final deflected shape at the design case compared well with the finite element prediction. The concept was proven to work for small camber changes, with larger deflections predicted by tailoring the mechanical properties of the hexachiral core. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)