FABRICATION AND DEFORMATION OF THREE-DIMENSIONAL BIOMIMETIC CERAMIC NANO-ARCHITECTED MATERIALS
Julia Greer (Caltech), Lucas Meza (Caltech), Dongchan Jang (California Institute of Technology)
Eringen Medal Symposium in honor of G. Ravichandran
Tue 2:40 - 4:00
Salomon 001
Creation of lightweight mechanically-robust materials has been a long sought after engineering pursuit. Many naturally occurring siliceous skeletal species have remarkable mechanical strength and damage tolerance despite containing a significant fraction of weak and brittle constituent materials. Efforts have been made to mimic the hierarchy in length scale; existing biomimetic structures have demonstrated noteworthy mechanical properties but have yet to match those of biomaterials. We report fabrication and deformation of periodically arranged hollow TiN nanolattices fabricated by (1) creating a polymer scaffold using a direct laser writing two-photon lithography (2) coating it with a conformal 75nm-thick layer of titanium nitride and (3) O2 plasma etching of polymer, which produces a hollow elliptical tube structure. Characteristic dimensions of these 3D nanolattices range from nanometers (wall thickness) to microns (tube diameter) to tens of microns (unit cell) to over 100 µm in entirety. In-situ nano-mechanical experiments and FEM of compression of a single unit cell revealed tensile strengths of 1.35 GPa at elastic limit of 1.5%, in constituent solid. Structures showed no evidence of failure after 30 cycles of loading to effective tensile strain of 1.4%. Hyperelastic load-displacement response was observed experimentally and in FE simulations, likely a structural response governed by lateral-torsional buckling in elliptical beams. We discuss mechanical response of the nanolattices in the framework of size-induced material property enhancement, flaw-sensitivity at nano-scale and structural buckling instability. Amplified strength and damage tolerance in these nanolattices shed light on critical role of size effects in material properties on bulk properties of bio-ceramics. Integration of nanoscale enhanced material properties along with hierarchical structural design should enable creation of lightweight, nanoarchitected, robust structural materials.