Resilient 3D hierarchical architected metamaterials.
Hierarchically designed structures with architectural features that span across multiple length scales are found in numerous hard biomaterials, like bone, wood, and glass sponge skeletons, as well as manmade structures, like the Eiffel Tower. It has been hypothesized that their mechanical robustness and damage tolerance stem from sophisticated ordering within the constituents, but the specific role of hierarchy remains to be fully described and understood. We apply the principles of hierarchical design to create structural metamaterials from three material systems: (i) polymer, (ii) hollow ceramic, and (iii) ceramic-polymer composites that are patterned into self-similar unit cells in a fractal-like geometry. In situ nanomechanical experiments revealed (i) a nearly theoretical scaling of structural strength and stiffness with relative density, which outperforms existing nonhierarchical nanolattices; (ii) recoverability, with hollow alumina samples recovering up to 98% of their original height after compression to ≥ 50% strain; (iii) suppression of brittle failure and structural instabilities in hollow ceramic hierarchical nanolattices; and (iv) a range of deformation mechanisms that can be tuned by changing the slenderness ratios of the beams. Additional levels of hierarchy beyond a second order did not increase the strength or stiffness, which suggests the existence of an optimal degree of hierarchy to amplify resilience. We developed a computational model that captures local stress distributions within the nanolattices under compression and explains some of the underlying deformation mechanisms as well as validates the measured effective stiffness to be interpreted as a metamaterial property.
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;
Lucas R
LR
Meza
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;
Alex J
AJ
Zelhofer
Nanotechnology Engineering, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
Nigel
N
Clarke
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;
Arturo J
AJ
Mateos
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;
Dennis M
DM
Kochmann
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125; jrgreer@caltech.edu.
Julia R
JR
Greer
D000465:Algorithms; D000537:Aluminum Oxide / Q000737:chemistry; D002516:Ceramics; D019245:Compressive Strength; D003198:Computer Simulation; D017076:Computer-Aided Design; D017709:Fractals; D006244:Hardness; D008422:Materials Testing / Q000379:methods*; D049329:Nanostructures / Q000737:chemistry; D036103:Nanotechnology; D011108:Polymers / Q000737:chemistry; D013314:Stress, Mechanical; D013718:Tensile Strength
D011108:Polymers; D000537:Aluminum Oxide
damage tolerance; hierarchical; nanolattices; recoverable; structural metamaterial