Achieving the theoretical limit of strength in shell-based carbon nanolattices

Abstract

Recent developments in mechanical metamaterials exemplify a new paradigm shift called mechanomaterials, in which mechanical forces and designed geometries are proactively deployed to program material properties at multiple scales. Here, we designed shell-based micro-/nanolattices with I-WP (Schoen’s I-graph–wrapped package) and Neovius minimal surface topologies. Following the designed topologies, polymeric microlattices were fabricated via projection microstereolithography or two-photon lithography, and pyrolytic carbon nanolattices were created through two-photon lithography and subsequent pyrolysis. The shell thickness of created lattice metamaterials varies over three orders of magnitude from a few hundred nanometers to a few hundred micrometers, covering a wider range of relative densities than most plate-based micro-/nanolattices. In situ compression tests showed that the measured modulus and strength of our shell-based micro-/nanolattices with I-WP topology are superior to those of the optimized plate-based lattices with cubic and octet plate unit cells and truss-based lattices. More strikingly, when the density is larger than 0.53 g cm −3 , the strength of shell-based pyrolytic carbon nanolattices with I-WP topology was found to achieve its theoretical limit. In addition, our shell-based carbon nanolattices exhibited an ultrahigh strength of 3.52 GPa, an ultralarge fracture strain of 23%, and an ultrahigh specific strength of 4.42 GPa g −1 cm 3 , surpassing all previous micro-/nanolattices at comparable densities. These unprecedented properties can be attributed to the designed topologies inducing relatively uniform strain energy distributions and avoiding stress concentrations as well as the nanoscale feature size. Our study demonstrates a mechanomaterial route to design and synthesize micro-/nanoarchitected materials.

Elastically Isotropic Truss‐Plate‐Hybrid Hierarchical Microlattices with Enhanced Modulus and Strength

“…Both cubic and octet trusses are highly anisotropic, as their Zener ratios show significant deviation from one. [ 30 ] Figure 2d shows that the Zener ratio of ISO‐COP is very close to one in the whole range of relative densities we investigated, suggesting that ISO‐COP is elastically isotropic. This implies that when the topologies at both levels of hierarchy are isotropic, the two‐level hierarchical structure is also isotropic.…”

“…Therefore, we can fabricate hierarchical architected materials composed of metals, alloys, or ceramics and scale the overall structures up to the larger scale, which facilitates the potential structural applications of hierarchical architected materials. Through high-resolution additive manufacturing techniques (for example, two-photon lithography) and subsequent post-treatment processes (such as pyrolysis, [30,34] nickel-catalyzed templating-pyrolysis, [35,36] electroless plating and etching [37] ), hierarchical architected materials with nanoscale feature size can be fabricated and be expected to exhibit superior strength due to the size strengthening effect. [38] Notably, there exists a trade-off between printing resolution and dimension for all high-resolution additive manufacturing techniques.…”

Flexible Impact-Resistant Composites with Bioinspired Three-Dimensional Solid–Liquid Lattice Designs

“…Keeping the cell length ( L c ) as a constant and replacing all flat surfaces into continuous concave and convex surfaces, Schwarz Primitive (SP) and connected sphere (CS) lattices can be further constructed (Figure a). Additionally, the Schwarz Primitive (SP) cell is a minimal surface configuration with zero mean curvature, which is usually adopted to offer a high-specific stiffness . Based on the coordinate system described in Figure a, the outer surface of SP cell can be described using the following equation: cos nobreak0em.25em⁡ ω x + cos nobreak0em.25em⁡ ω y + cos nobreak0em.25em⁡ ω z = C where ω = 2π/ L c , C is a dimensionless shape control parameter, and L c is the length of adopted cubic unit.…”

Porous Microneedles for Therapy and Diagnosis: Fabrication and Challenges

“…The lattice structure, for example, is a three-dimensional open-cell structure formed by one or more repeating unit cell spatial arrangements with edges and faces that can have excellent mechanical properties (even near the theoretical limit) through design and structural optimization. 88 Recent work by researchers 89 involved the fabrication of shell-based carbon nanolattices using projection microstereolithography or twophoton lithography. These nanolattices displayed extremely high strengths of 3.52 GPa, extremely large fracture strains of 23%, and extremely high specific strengths of 4.42 GPa/(g/ cm 3 ).…”