Mechanics of Pressure-Adaptive Honeycomb

Pressure-adaptive honeycomb is a new type of adaptive structure that can exhibit great strains by relying on a pressure differential to alter the structural stiffness. The structure consists of a grid of honeycomb cells that extend a significant length perpendicular to the plain of the hexagons. Each cell possesses a pouch that can be pressurized and alter the stiffness of the structure. An analytical model is presented that predicts the stress—strain behavior in principal directions of this pressure-adaptive honeycomb. The predictions of the analytical model are shown to correlate well to experimental tests on a 130-cell aluminum honeycomb specimen that is loaded up to compressive strains of 12.5%. Based on this model, an equivalent material stiffness is defined for the honeycomb cell walls that can be employed in a FEA. An FE approximation of a 145-cell honeycomb beam based on this equivalent material stiffness is shown to correlate well to experimental results of a three-point bend test of such a specimen. The model of equivalent material stiffness greatly reduces the complexity of the FE approximation by eliminating the need to define a pouch or an internal pressure field. Therefore, the prediction method could be used in a design tool for pressure-adaptive honeycomb structures.