Abstract
Mechanical metamaterials are a sub-category of designer materials where the geometry of the material at the small-scale is rationally designed to give rise to unusual properties and functionalities. Here, we propose the concept of “action-at-a-distance” metamaterials where a specific pattern of local deformation is programmed into the fabric of (cellular) materials. The desired pattern of local actuation could then be achieved simply through the application of one single global and far-field force. We proposed graded designs of auxetic and conventional unit cells with changing Poisson’s ratios as a way of making “action-at-a-distance” metamaterials. We explored five types of graded designs including linear, two types of radial gradients, checkered, and striped. Specimens were fabricated with indirect additive manufacturing and tested under compression, tension, and shear. Full-field strain maps measured with digital image correlation confirmed different patterns of local actuation under similar far-field strains. These materials have potential applications in soft (wearable) robotics and exosuits.
Highlights
Designer materials, where rationally designed geometry at the small-scale gives rise to unusual material properties at the macro-scale, are often called metamaterials
Development of complex actuators is one of the areas that could benefit from such “designer materials.”
We present a new type of metamaterials where the material is designed to exhibit a pattern of spatially distributed local actuation that is regulated by one single force applied at the boundaries of the material
Summary
Designer materials, where rationally designed geometry at the small-scale gives rise to unusual material properties at the macro-scale, are often called metamaterials. N = 16, h = 0.0075 m, l0 = 0.003 33 m, θ0 = 54◦, t = 0.0012 m, and Es = 721 kPa. Similar analytical relationships cannot be obtained for the other types of graded specimens, i.e., striped, checkered, and radial gradients.
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