Porous Metamaterials with Twofold Buckling Instability
Date:
Soft porous metamaterials with periodically-distributed pores are commonly known for their auxetic behavior. This nonlinear response is the result of a short-wavelength global buckling mode under compressive loading. Unlocking new pathways to trigger global buckling mode shapes with different pores rearrangements could open new avenues for developing intelligent, programmable, and multifunctional devices. In this work, we explore a novel soft porous metamaterial that demonstrates different short-wavelength global buckling modes under positive and negative pressure. We investigate the design space to characterize this twofold buckling instability and post-buckling behavior by varying the geometric parameters of the porous metamaterial. Our investigation includes analytical critical buckling pressures, numerical simulations, and experimental validation of manufactured metamaterials tested upon inflation and deflation. In terms of applications, we demonstrate the superior capability of the pneumatically-driven metamaterial to selectively grasp slender objects with preprogrammed mode shapes. Leveraging both positive and negative pressure for actuation purposes introduces a new class of programmable buckling-based soft actuators with highly tunable reconfiguration patterns.