Architected materials that control elastic wave propagation are essential in vibration mitigation and sound attenuation. Phononic crystals and acoustic metamaterials use band-gap engineering to forbid certain frequencies from propagating through a material. However, existing solutions are limited in the low-frequency regimes and in their bandwidth of operation because they require impractical sizes and masses. Here, we present a class of materials (labeled elastic metastructures) that supports the formation of wide and low-frequency band gaps, while simultaneously reducing their global mass. To achieve these properties, the metastructures combine local resonances with structural modes of a periodic architected lattice. Whereas the band gaps in these metastructures are induced by Bragg scattering mechanisms, their key feature is that the band-gap size and frequency range can be controlled and broadened through local resonances, which are linked to changes in the lattice geometry. We demonstrate these principles experimentally, using advanced additive manufacturing methods, and inform our designs using finite-element simulations. This design strategy has a broad range of applications, including control of structural vibrations, noise, and shock mitigation. A rchitected materials exploit the geometry of their structure, which can be directly designed, to attain properties not common in bulk, continuum media. The underlying principles that determine the dynamic properties of architected materials are applicable across several length scales, and can be used to control phonons or elastic and acoustic waves, as in phononic crystals and acoustic metamaterials. In the linear regime, decreasing the size of the geometrical feature designed in the structure increases the operational frequency. This opens opportunities to control elastic/acoustic waves ranging from seismic excitations (hertz), structural vibrations (kilohertz), ultrasonic waves in microelectromechanical systems (MEMS) devices (megahertz), and thermal phonons in, e.g., thermoelectric materials (terahertz) (1-3).Advanced manufacturing techniques, such as 3D printing, have progressed over size scales, ranging from meters down to nanometers. With these techniques, complex structures can be realized in many materials such as polymers, metals, and ceramics. Here, we design and test 3D-printed, composite materials, which combine a polymeric matrix with metallic components, and present a previously unidentified type of architected materials for broadband vibration mitigation.Phononic crystals (PCs) consist of periodic arrangements of materials or components with controlled spatial sizes and elastic properties. When excited by an acoustic or elastic wave, PCs exhibit band gaps, or ranges of frequencies that cannot propagate through their bulk and decay exponentially. The band gaps in PCs arise from Bragg scattering mechanisms, and can be quite wide, making them desirable in sound mitigation and vibration absorption applications (4-8). However, the periodicity dimensi...

Morphing flat sheets into non-planar shapes enables fast and scalable manufacturing of three-dimensional objects. Here, we investigate the out-of-plane shape morphing capabilities of single-material elastic sheets with architected cut patterns. The sheets are laser-cut into an array of tiles connected by flexible hinges, which enable large deformations with small applied forces. We demonstrate that a non-periodic cut pattern can make a sheet buckle into selectable three-dimensional shapes, such as domes or patterns of wrinkles, when pulled at specific boundary points. These global buckling modes are observed in experiments, predicted by numerical simulations, and rationalized by a kinematic analysis that highlights the role of the geometric frustration arising from nonperiodicity. The study focuses initially on elastic sheets, and is later extended to sheets made of elastic-plastic materials, which can retain their shape upon load removal. arXiv:1806.10851v1 [cond-mat.soft]

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Shape‐morphing planar microstructures fabricated by direct laser writing are presented by Chiara Daraio and co‐workers in article number https://doi.org/10.1002/adma.201703024. Biomimetic lotus flowers (violet) and shark skins (green) exemplify controlled self‐bending, activated by residual stresses that emerge during photochemical shrinkage. The stress‐induced transformations enable pre‐programming of complex geometries into flat sheets to form three‐dimensional polymer structures with embedded functionality and radically reduced fabrication times. Cover idea: Andrei Constantinescu, Irina Niculescu. Graphical realization: Maria Bauhofer.

In order to validate the dark field microscopical measurements, presented in Section 5.2 of the main paper, we optically evaluate the fabricated lines on separate samples before

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The goal of the research has been to design a robotic bird that utilizes principles of nature to optimize flight. Seagulls were the preferred model for the robot because they have a large wing span that provides a more steady flight and sheds a continuous wake vortex, creating lift on both the upstroke and down-stroke of flight [1]. Research has been done on the architecture of a seagull’s wing as well as the aerodynamic features of its comprising airfoils. The robotic wings developed will capture the architecture of the seagull wings with a variety of airfoils that improve lift and reduce drag and joints that enable bending on the upstroke in the flapping motion. A main focus of this research was to study how the seagull uses air flow to improve its flight performance. The fluid mechanics of the wing was analyzed for steady and unsteady flight using Fluent code to see how seagull adapts to different flow conditions. Using the developed robotic model of the wing attempts were made to achieve the necessary wing positioning that fully complied with that of the seagull during flight. Actuation of the wings was achieved using servo motors. Fabrication of the robotic prototype involved material selection for the fuselage, wing surface and skeletal structure. At completion of the prototyping, trials were performed using stereovision to study the complex effects of unsteady flow, and to verify the computational analyses undertaken.