<p>It is well known that elastic structures can undergo large deformations, and instabilities can be triggered when subjected to mechanical loadings. Researchers have shown that metamaterials with arrays of pores/voids present interesting mechanical instabilities (i.e. buckling) under uniaxial compression or negative pressure (i.e. vacuum). However, this instability has never been observed with positive pressure and, as of now, it does not exist a metamaterial able to experience buckling instability upon inflation. We investigate numerically and experimentally a novel 3D cellular-based structure composed of an elastomeric material with two faces embedded with periodic arrays of pores and a cavity within it. Upon inflation, a cascade effect of instabilities is triggered such that the walls of the pores buckle in a diamond-like pattern buckling mode. We characterize experimentally the inflatable metamaterial both upon inflation and deflation through pressure-volume (p-V) curves, change of porosity, and variation of equivalent Poisson’s ratio. With a single pressure input, different regimes with tunable effective stiffness (proportional to the slope of the p-V curves) are identified and the richness of nonlinear behavior of the metamaterial is explored. A numerical finite element (FE) model is developed to validate the experimental findings. Dynamic implicit analyses are used to mimic the experiments and replicate the p-V curves with an excellent agreement. Specifically, the critical pressure of the buckling mode that produces the synergetic diamond-shape rearrangement of through-holes patterns is obtained both in the experiments and numerical simulations. The numerical model represents a perfect framework to explore the design space and identify the geometrical parameters (porosity, cylinder thickness, external walls, lattice shape) that control the nonlinear metamaterial response. We use the FE model as a predictive tool to describe the tunable behavior of the metamaterial with pores of different initial shapes and size. This will allow to expand the design space by localizing and eventually sequencing the buckling instability with different critical pressure thresholds. The proposed meta-structure represents a unique platform for tunable and complex mechanical responses with reversible pattern reconfigurations triggered by preprogrammed structural instabilities. This transformative material shows local and global properties that can be controlled and switched on-the-fly with a simple pressure input. Potential applications span from bio-prostheses, foams with superior acoustic and damping properties, aerospace structures, and soft robotics. We will show how the multicellular metamaterial can be used as a soft distributed gripper able to grasp delicate filaments, such as marine algae, by applying a distributed load below the grasped-object fracture point.</p>

Programming Buckling Instability Upon Inflation in Soft Metamaterials

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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