Surface morphing control of mechanical metamaterials using geometrical imperfections

Morphable structures exhibit 2D to 3D out-of-plane deformations when exposed to an external stimulus. The current state-of-the-art of morphable structures is based on smart materials or heterogeneous composite materials, where their anisotropic properties can help induce surface morphing in response to different stimuli. This work proposes an alternative approach based on bio-inspired active skins that exhibit 2D to 3D deformations when subjected to uniaxial strains. In particular, the localized compression generated from the free-hinging motion of a re-entrant auxetic geometry was used as the driving force to induce surface morphing in the form of out-of-plane deformations. The geometry was optimized to enhance this inability, which could lower the critical stress and strain for out-of-plane buckling. In addition, geometrical imperfections were introduced to facilitate controlled surface morphing (i.e., programmable buckling directions and selective deformations). Overall, this design principle validated that surface morphing could be achieved using a single material without relying on composites and materials.