- Award ID(s):
- 1634492
- NSF-PAR ID:
- 10142492
- Date Published:
- Journal Name:
- Journal of Applied Mechanics
- Volume:
- 87
- Issue:
- 3
- ISSN:
- 0021-8936
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
In this work, we investigate the anelastic deformation behavior of periodic three-dimensional (3D) nanolattices with extremely thin shell thicknesses using nanoindentation. The results show that the nanolattice continues to deform with time under a constant load. In the case of 30-nm-thick aluminum oxide nanolattices, the anelastic deformation accounts for up to 18.1% of the elastic deformation for a constant load of 500 μN. The nanolattices also exhibit up to 15.7% recovery after unloading. Finite element analysis (FEA) coupled with diffusion of point defects is conducted, which is in qualitative agreement with the experimental results. The anelastic behavior can be attributed to the diffusion of point defects in the presence of a stress gradient and is reversible when the deformation is removed. The FEA model quantifies the evolution of the stress gradient and defect concentration and demonstrates the important role of a wavy tube profile in the diffusion of point defects. The reported anelastic deformation behavior can shed light on time-dependent response of nanolattice materials with implication for energy dissipation applications.more » « less
-
Two-dimensional (2-D) atomically thin graphene has exhibited overwhelming excellent properties over its bulk counterpart graphite, yet the broad applications and explorations of its unprecedented properties require a diversity of its geometric morphologies, beyond its inherently planar structures. In this study, we present a self-folding approach for converting 2-D planar free-standing graphene to 2-D and 3-D folded structures through the evaporation of its liquid solutions. This approach involves competition between the surface energy of the liquid, and the deformation energy and van der Waals energy of graphene. An energy-based theoretical model is developed to describe the self-folding process during liquid evaporation by incorporating both graphene dimensions and surface wettability. The critical elastocapillary length by liquid evaporation is extracted and exemplified by investigating three typical graphene geometries with rectangular, circular and triangular shapes. After the complete evaporation of the liquid, the critical self-folding length of graphene that can enable a stable folded pattern by van der Waals energy is also obtained. In parallel, full-scale molecular dynamics (MD) simulations are performed to monitor the evolution of deformation energies and folded patterns with liquid evaporation. The simulation results demonstrate the formation of 2-D folded racket-like and 3-D folded cone-like patterns and show remarkable agreement with theoretical predictions in both energy variations and folded patterns. This work offers quantitative guidance for controlling the self-folding of graphene and other 2-D materials into complex structures by liquid evaporation.more » « less
-
Three-dimensional (3D) nanostructures play a crucial role in nanophotonics, lasers, and optical systems. This article reports on the fabrication of 3D nanostructures consisting of opal structures that are spatially aligned to an array of holes defined in the photoresist. The proposed method uses colloidal lithography to pattern a hexagonal array of holes, which are then used to direct the subsequent 3D assembly of colloidal particles. This approach allows the 3D opal structures to be aligned with the 2D array of holes, which can enhance spatial-phase coherence and reduce defects. The polymer patterns can be used as a sacrificial template for atomic layer deposition and create free-standing nanolattices. The final structure consists of a combination of nanolattice, upon which controlled deposition of opal structures is achieved. These structures result in nanostructured materials with high porosity, which is essential to create low-index materials for nanophotonics. A thick layer of titanium oxide with high refractive index is deposited over nanolattices to demonstrate the mechanical stability of underlying structures. These nanolattice structures with precisely controlled height can serve as a low-index layer and can find applications in Bragg reflectors, nanophotonics, and optical multilayers.
-
Abstract The fabrication of periodic 3D nanostructures with uniform material properties has been widely investigated and is important for applications in photonics, mechanics, and energy storage. However, creating nanostructures with spatially varying lattice geometry and material composition is still largely an unexplored challenge in nanofabrication. This work presents the fabrication of non‐uniform nanolattices by patterning multiple layers of 3D nanostructures using phase shift lithography and atomic layer deposition. By controlling the processing parameters, the lattice geometry and material composition of each individual nanolattice layer can be tailored to create arbitrary material property profiles. Using the proposed method, a five‐layer nanolattice with spatially varying porosity and oxide materials has been demonstrated. This process can be used to create gradient‐index antireflection nanostructures, and a fabricated four‐layer nanolattice structure consisting of TiO2and Al2O3with gradually varying porosity reduces more than 90% of the specular reflectance from a silicon substrate. By enabling nanolattices with arbitrary profiles in physical properties, the demonstrated technique can find broad applications in nanophotonics, graded filters, energy storage systems, and nanoarchitected films.
-
Soft machines typically exhibit slow locomotion speed and low manipulation strength because of intrinsic limitations of soft materials. Here, we present a generic design principle that harnesses mechanical instability for a variety of spine-inspired fast and strong soft machines. Unlike most current soft robots that are designed as inherently and unimodally stable, our design leverages tunable snap-through bistability to fully explore the ability of soft robots to rapidly store and release energy within tens of milliseconds. We demonstrate this generic design principle with three high-performance soft machines: High-speed cheetah-like galloping crawlers with locomotion speeds of 2.68 body length/s, high-speed underwater swimmers (0.78 body length/s), and tunable low-to-high-force soft grippers with over 1 to 10 3 stiffness modulation (maximum load capacity is 11.4 kg). Our study establishes a new generic design paradigm of next-generation high-performance soft robots that are applicable for multifunctionality, different actuation methods, and materials at multiscales.more » « less