A smart window is fabricated from a composite consisting of elastomeric poly(dimethylsiloxane) embedded with a thin layer of quasi‐amorphous silica nanoparticles. The smart window can be switched ...from the initial highly transparent state to opaqueness and displays angle‐independent structural color via mechanical stretching. The switchable optical property can be fully recovered after 1000 stretching/releasing cycles.
In this paper we discuss the transformation of a sheet of material into a wide range of desired shapes and patterns by introducing a set of simple cuts in a multilevel hierarchy with different ...motifs. Each choice of hierarchical cut motif and cut level allows the material to expand into a unique structure with a unique set of properties. We can reverse-engineer the desired expanded geometries to find the requisite cut pattern to produce it without changing the physical properties of the initial material. The concept was experimentally realized and applied to create an electrode that expands to >800% the original area with only very minor stretching of the underlying material. The generality of our approach greatly expands the design space for materials so that they can be tuned for diverse applications.
We use a regular arrangement of kirigami elements to demonstrate an inverse design paradigm for folding a flat surface into complex target configurations. We first present a scheme using arrays of ...disclination defect pairs on the dual to the honeycomb lattice; by arranging these defect pairs properly with respect to each other and choosing an appropriate fold pattern a target stepped surface can be designed. We then present a more general method that specifies a fixed lattice of kirigami cuts to be performed on a flat sheet. This single pluripotent lattice of cuts permits a wide variety of target surfaces to be programmed into the sheet by varying the folding directions.
Significance How can flat surfaces be transformed into useful three-dimensional structures? Recent research on origami techniques has led to algorithmic solutions to the inverse design problem of prescribing a set of folds to form a desired target surface. The fold patterns generated are often very complex and so require a convoluted series of deformations from the flat to the folded state, making it difficult to implement these designs in self-assembling systems. We propose a design paradigm that employs lattice-based kirigami elements, combining the folding of origami with cutting and regluing techniques. We demonstrate that this leads to a pluripotent design in which a single kirigami pattern can be robustly manipulated into a variety of three-dimensional shapes.
The evolution of damage due to mechanical fatigue in thin metal films on flexible substrates was investigated by in situ electrical resistance measurements. A tensile fatigue load was applied to the ...metal films by subjecting a single edge of the curved samples to repeated linear motion. The change in the resistance of the metal films was monitored in situ. Upon the nucleation of a fatigue-induced crack, the electrical resistance of the metal film began to increase. The resistance subsequently continued to increase with crack propagation. Therefore, in situ electrical resistance measurements can be used to identify the fatigue-induced crack nucleation cycle. The number of cycles required for crack nucleation decreased with the increase in the fatigue-stressed area of the samples. This behavior is attributed to an increase in the crack nucleation probability with increasing sample size. The amount of strain applied also modified the number of cycles required for crack nucleation according to the Coffin–Manson relationship. The increase in the electrical resistivity with respect to the number of fatigue cycles can be accurately predicted when the fatigue cycle is normalized by the nucleation cycle. This indicates that the fatigue lifetime is determined by crack nucleation and not by crack propagation.
Buckling is a loss of structural stability. It occurs in long slender structures or thin plate structures which is subjected to compressive forces. For the structural materials, such a sudden change ...in shape has been considered to be avoided. In this study, we utilize the Au nanowire’s buckling instability for the electrical measurement. We confirmed that the high-strength single crystalline Au nanowire with an aspect ratio of 150 and 230-nm-diameter shows classical Euler buckling under constant compressive force without failure. The buckling instability enables stable contact between the Au nanowire and the substrate without any damage. Clearly, the in situ electrical measurement shows a transition of the contact resistance between the nanowire and the substrate from the Sharvin (ballistic limit) mode to the Holm (Ohmic) mode during deformation, enabling reliable electrical measurements. This study suggests Au nanowire probes exhibiting structural instability to ensure stable and precise electrical measurements at the nanoscale.
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•A defect-free single crystalline Au nanowire shows the Euler buckling deformation•The buckling and post-buckling deformation is utilized for the electrical measurement•Contact regime changes from the Sharvin to the Holm during buckling deformation•This study suggests a nanoscale probe for the electrical and magnetic characterization
Mechanics of materials; Materials science; Mechanical processing.
We demonstrate the design and fabrication of tilted micropillar arrays on wrinkled elastomeric poly(dimethylsiloxane) as a reversibly switchable optical window. Upon re‐stretching the as‐prepared ...(opaque) film to the original pre‐strain, the grating color is restored and ∼30% transmittance is recovered. Further stretching beyond the pre‐strain makes the film more transparent. This process is fully reversible and repeatable for many cycles.
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Metal-based cellular materials with periodic structures are currently the preferred choice as bone/cartilage implants under load-bearing conditions due to their controlled pore ...interconnectivity and porosities. This report presents a new methodology for the structural analysis of periodic cellular materials using X-ray microtomography and dual-level finite element modeling (FEM). A three-dimensional (3D) structure of periodic titanium foam produced using selective laser melting (SLM) is obtained using an X-ray microtomography. A dual-level FEM based on the 3D structure is used to simulate the deformation behavior of titanium foam with a regular structure under uniaxial compression, and the computed results are compared directly with the interrupted uniaxial compression experiments performed on the deformed 3D structures. The deformation behaviors of simplified structures with cylindrical and hexahedral struts are simulated, and the computed results demonstrate that unavoidable defects in the actual structure affect the mechanical stability significantly. Additionally, buckling-induced deformation behavior is analyzed by introducing an imperfection in the actual and simplified structures. The effects of certain selected process variables, such as internal angle and diameter, are also examined through a series of process simulations.
By prescribing asymmetric ligaments with different arrangements in elastomeric porous membranes of pre‐twisted kagome lattices, the buckling instability is avoided, allowing for smooth and homogenous ...structural reconfiguration in a deterministic fashion. The stress–strain behaviors and negative Poisson's ratios can be tuned by the pre‐twisting angles.
Tapered nanopillar structures of different cross‐sectional geometries including cone‐, pencil‐like, and stepwise are prepared from anodized aluminum oxide templates. The shape effect on the adhesion ...strength is investigated in experiments and simulation. Cone‐shaped nanopillars are highly bendable under load and can recover after unloading, thus, warranting high adhesion strength, 34 N cm−2. The pencil‐like and stepwise nanopillars are, however, easily fractured and are not recoverable under the same conditions.
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