Adaptive elastic metastructures from magneto-active elastomers

In this paper, elastic wave dispersion characteristics of two novel unit-cells are numerically and experimentally studied. Based on Bloch’s theorem for infinite cellular structures, the Eigen-frequency problem for the unit-cells is solved through a finite element scheme. These novel unit-cells are inspired from Maltese-Cross shape and named unit-cell I and II, while the unit-cell II is created from replacing side ligaments of unit-cell I with triangles. It is observed that these novel unit-cells are capable of providing over 200% phononic bandgap coverage factor over the low-frequency range of 0–12 kHz. Also, the effects of replacing side ligaments with triangles on shifting bandgap pattern to lower frequencies are investigated. The unit-cells are then utilized to construct a metaplate to filter two-dimensional wave’s propagation through the plate. The plate and its cellular segment are simulated with the finite element method, and they are fabricated through laser the cutting process. Frequency analysis is performed on the numerical and experimental models, and results are compared with the bandgaps obtained from periodic Bloch’s theorem. It is shown that a perfect match is observed between experimental and numerical results. The present study provides the practical application of new phononic crystals as a frequency tool to stop the propagation of elastic waves while the location of bandgaps can be tuned with the topology of unit-cells.

Novel cross shape phononic crystals with broadband vibration wave attenuation characteristic: Design, modeling and testing

\n Band gaps in metamaterials and phononic crystals provide a way to engineer vibration mitigation into a material’s geometry. Here, we present a comprehensive experimental characterization of band gaps in lattice-resonator metastructures, which have been previously analyzed with finite element simulations, to better understand this phenomenon in 3D-printed materials. We fabricate the metastructures with a new approach to obtain multimaterial structures using stereolithography. We experimentally characterize the material’s frequency-dependent storage and loss modulus over the band gap frequencies to confirm that the measured band gaps are due to geometry and not due to material properties. Experimental results using both frequency sweep and impulse excitations show that band gaps and attenuation efficiencies strongly depend on the lattice geometry as well as loading direction, and a comparison between axial and bending excitation responses reveals frequency ranges of “fluid-like” and “optical-like” behaviors. Comparison between finite element simulations and experimental results demonstrate the robustness of the metastructure design. While the experiments used here are well established, their combination allows us to gain additional insights into band gaps measurements. Specifically, we show that the coherence function, a common concept in signal processing, is a strong predictor of band gaps in linear materials and that the attenuation efficiency inside the measured band gap can be physically limited by fluid–structure interactions.

Experimental testing of vibration mitigation in 3D printed architected metastructures

Continuous demand for the improvement of mechanical performance of engineering structures pushes the need for metastructures to fulfil multiple functions. Extensive work on lattice-based metastructure has shown their ability to manipulate wave propagation and producing bandgaps at specific frequency ranges. Enhanced customizability makes them ideal candidates for multifunctional applications. This paper explores a wide range of nonlinear mechanical behavior that can be generated out of the same lattice material by changing the building block into dome shaped structures which improves the functionality of material significantly. We propose a novel hourglass shaped lattice metastructure that takes advantage of the combination of two oppositely oriented coaxial domes, providing an opportunity for higher customizability and the ability to tailor its dynamic response. Six new classes of hourglass shaped lattice metastructures have been developed through combinations of solid shells, regular honeycomb lattices and auxetic lattices. Numerical simulation, analytical modelling, additive layer manufacturing (3D printing) and experimental testing are implemented to justify the evaluation of their mechanics and reveal the underlying physics responsible for their unusual nonlinear behaviour. We further obtained the lattice dependent frequency response and damping offered by the various classes of hourglass metastructures. This study paves the way for incorporating hourglass based oscillators to be used as building block of future mechanical metamaterials, leading to a new class of tunable metamaterial over a wide range of operating frequencies. The proposed class of metastructure will be useful in applications where lightweight and tunable properties with broadband vibration suppression and wave attenuation abilities are necessary.

/pdf/exploring-the-dynamics-of-hourglass-shaped-lattice-30wwbfq4wv.pdf

Exploring the dynamics of hourglass shaped lattice metastructures.

/pdf/optimized-structures-for-vibration-attenuation-and-sound-2fepzmbe.pdf

Optimized structures for vibration attenuation and sound control in nature: A review

Continuous demand for improvement of material performance in structural applications pushes the need for materials that are able to fulfill multiple functions. Extensive work on effective static properties of different architected materials have shown their ability to push the modulus-density design space, in terms of high effective moduli at low relative density. On the other hand, variations in geometry allow for these materials to manipulate mechanical wave propagation, producing band gaps at certain frequency ranges. The enhanced static and vibration properties of architected metamaterials make them ideal candidates for multi-functional purposes. In this paper, we take inspiration from the mass-efficient static behavior of different lattice geometries to fully explore the capabilities of a periodic and locally resonant metastructure design platform. We numerically study the influence of four different lattice topologies on the dynamic and static behavior of metastructures that combine a periodic lattice geometry with locally resonant inclusions. We analyze the influence of lattice geometry on band gap frequencies in terms of the lattice effective static properties. We show that vibration mitigation over a wide range of frequencies is achieved by tailoring the lattice geometry for constant unit cell mass and size. Specifically, by selectively placing material inside the unit cell, we achieve up to a 6-fold change of lower edge band gap frequency and up to an 8-fold change of normalized band gap width, for metastructures with low-density lattices. We introduce multi-functional performance parameters to evaluate the metastructures in terms of their effective static stiffness and band gap properties. These parameters can inform the design of tailored materials that have desired mechanical and dynamic properties for applications in e.g. aerospace and automotive components, and energy infrastructure.

/pdf/on-the-interrelationship-between-static-and-vibration-3g6zskwkk6.pdf

On the Interrelationship Between Static and Vibration Mitigation Properties of Architected Metastructures

Phononic crystals show novel characteristics when it comes to acoustic and elastic wave propagation control. Nevertheless, most studies on phononic crystals are based on a plane wave assumption because this allows for application of Bloch theorem and analysis of the infinite system based on a single unit cell. However, the plane wave assumption is not valid in the near field of a source, where the wave front takes cylindrical or spherical form. Here, we overcome this limitation by introducing the concept of effective phononic crystals, which combine periodicity with varying isotropic material properties to force periodic coefficients in the elastic equations of motion in a non-Cartesian basis. The periodic coefficients allow for band structure calculation using Bloch theorem. Using the band structure, we demonstrate band gaps and topologically protected interface modes can be obtained for cylindrically propagating waves. Through effective phononic crystals, we show how behaviors of Cartesian phononic crystals can be realized in regions close to sources, where near-field effects are non-negligible.

Ignacio Arretche

Papers

Experimental testing of vibration mitigation in 3D printed architected metastructures

On the Interrelationship Between Static and Vibration Mitigation Properties of Architected Metastructures

Effective phononic crystals for non-Cartesian elastic wave propagation

Locally Resonant Effective Phononic Crystals for Subwavelength Vibration Control of Torsional Cylindrical Waves

A process to spatially control the fraction of SS420 and bronze phases in binder jet infiltrated parts