Design and characterization of an orthotropic accordion cellular honeycomb as one-dimensional morphing structures with enhanced properties

This study develops the governing equations and characterizes the mechanical properties of a new orthotropic accordion morphing honeycomb structure containing periodic arrays of U-type beams reinforced with glass fibers. Castigliano’s second theorem is modified to develop the analytical equations to predict the deformation behavior of a single orthotropic ply under a combined axial, bending, and shear loadings. Accordingly, the elastic properties of the orthotropic structure including elastic stiffness, shear stiffness, and in-plane Poisson’s ratios are calculated by the developed equations. The honeycomb structure is manufactured by 3D printing, and the samples are subjected to tensile tests to experimentally validate the analytical solutions. Multiple finite element simulations are also used to validate the results. A good agreement is observed between the analytical solution, the experiments, and simulations, confirming the robustness of the analytical solution to predict the full elastic properties of the composite cellular. The results show that the periodic arrays of U-type and vertical beams can generate low in-plane stiffness in the morphing direction and high in-plane stiffness in the transverse direction, respectively. A zero Poisson’s ratio feature is achieved by employing straight beams which result in a high stiffness in the perpendicular direction. The proposed accordion cellular honeycomb structure exhibits the flexible response along the accordion shape direction, with a significant stiffness in its transverse direction. Moreover, the new orthotropic structure has considerably greater strain to failure in the morphing direction compared with a conventional isotropic configuration. These features prove that this type of structure can be applied for the aerospace morphing structures such as wings.