Soft Mechanical MetamaterialsHarnessing Instability

Speaker : Prof. JongMin Shim, Ph.D.
Department of Civil, Structural and Environmental Engineering
State University of New York (SUNY) at Buffalo

Mechanical metamaterialsare artificial materials engineered to have unconventional mechanical properties stemming from their microstructuralgeometry rather than from their chemical composition. Initially, the concept of metamaterialsoriginated from a research community working on photonic crystals for electromagnetic waves. However, research in mechanical metamaterialshas broadened significantly and it now covers various unconventional macroscopic mechanical characteristics, which include not only dynamic properties (e.g., frequency band-gaps, dynamic modulus, dynamic density, etc.) but also static properties (e.g., extremalmodulus, negative modulus and ultra-low density). This presentation introduces a new class of deformable mechanical metamaterialscharacterized by instability.
Traditionally, the prevention of buckling is considered as a critical design criterion for structural components of mechanical systems. However, reversible and repeatable elastic buckling phenomenon can be also exploited for practical applications, as in the micro/nano-substrates of stretchable electronics. This presentation focuses on using elastic buckling to improve structural functionality through smart design, and introduces a class of continuum porous structures (e.g., 2D, spherical, and 3D structures) that show structural transformations under mechanical loading. To illustrate, the proposed 2D and 3D structures possess auxeticity(ability to have a negative Poisson’s ratio) and the spherical structures are characterized by their encapsulation capability. In particular, the pattern transformation in the 2D structures strongly affect in-plane phononicband gaps, providing opportunities for tunable phononiccrystals (e.g., noise-cancelling devices and vibration isolators). The extension of the proposed structures to general 3D geometries and fabrications at the micro-scale will open an avenue for a new class of innovative mechanical metamaterials.