Surface Morphing of Geometrically Patterned Active Skins
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.185
Surface Morphing of Geometrically Patterned Active Skins Yujin Park1 and Kenneth J. Loh1,2,*
1
Materials Science and Engineering Program, University of California San Diego Department of Structural Engineering, University of California San Diego *Corresponding author e-mail: [email protected]
2
ABSTRACT
Nature is ripe with biological organisms that can interact with its surroundings to continuously morph their surface texture. Many attempts have been made to optimize artificial surfaces depending on operational needs; however, most of these architected materials only focus on enhancing a specific material property or functionality. This study introduces a new class of instability-induced morphable structures, herein referred to as “Active Skins”, which enables on-demand, reversible, surface morphing through buckling-induced feature deployment. By taking advantage of a preconceived auxetic unit cell geometrical design, mechanical instabilities were introduced to facilitate rapid out-of-plane deformations when in-plane strains are applied. Here, these notches were introduced at judiciously chosen locations in an array of unit cells to elicit unique patterns of out-of-plane deformations to pave way for controlling bulk Active Skin behavior. These purposefully designed imperfections were employed for selectively actuating them for applications ranging from camouflage to surface morphing to soft robotic grippers.
INTRODUCTION Biological organisms are able to control and display various surface topographies depending on their surroundings and for various purposes, including camouflage, locomotion, signaling, and hunting [1]. Many artificial surfaces reminiscent of these unique capabilities have been produced by mimicking and replicating the complex surface geometries of different biological systems, such as shark skins for minimizing drag coefficients [2-4], lotus leaves for self-cleaning [5], and geckos’ feet for dry adhesives [6, 7], among many others. However, designing and fabricating a thin
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substrate into a programmable three-dimensional (3D) shape can be challenging and nontrivial [8]. One approach to achieve biomimetic morphogenesis and bio-inspired material shape morphing is by distributing the materials in a specific direction to obtain 3D shapes such as bending and rotations [9]. Furthermore, the usage of inhomogeneous and smart materials with isotropic or anisotropic properties enables the use of different external stimuli to actuate these structures and achieve shape morphing [10, 11]. Although this approach has led to controllable shapeshifting, they are only limited to certain materials. Furthermore, they do not leverage the material’s overall geometrical configuration for controlling their morphology,
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