Exploiting Structural Instability to Design Architected Materials Having Essentially Nonlinear Stiffness

Architected materials enable unusual mechanical behavior, that is, inaccessible to existing materials. This study demonstrates an architected cell structure having a constant stress plateau extending for a very wide range of strains followed by hardening at large strains. This essentially nonlinear stiffness has attractive applications ranging from static stress redistribution to acoustic wave tailoring, yet materials exhibiting this behavior are challenging to realize practically. The authors propose designs which realize controlled essentially nonlinear response using coordinated elastic strut buckling. The authors exploit controlled asymmetric buckling of the struts’ structure to precisely tailor a wide flat stress plateau in elastomeric materials. The authors experimentally measure the effects of structural geometry and provide design guidelines to tune this exotic behavior. The authors utilize finite element simulations to isolate the core strain energy storage mechanisms governing the deformation. Owing to the 2D nature of the design, these materials can be readily fabricated in a variety of materials using laser cutting, extrusion, molding, 3D printing, and micro-lithographic methods. The proposed designs have wider constant stress plateaus than open cell foams, and as such offer new opportunities in orthopedic design, protection, packaging, as well as sonic vacua and non-reciprocal acoustic metamaterials.