Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E48: Mechanical Metamaterials IFocus
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Sponsoring Units: GSNP DBIO GSOFT DPOLY Chair: Johannes Overvelde, FOM Inst - Amsterdam Room: LACC 510 |
Tuesday, March 6, 2018 8:00AM - 8:36AM |
E48.00001: Programmable metamaterials Invited Speaker: Chiara Daraio Phononic crystals and acoustic metamaterials are materials with a tailored, architected structure, designed to achieve properties that depart from those found in natural or more “conventional” engineering materials. Initial realizations of these materials were periodic and derived their properties from an interplay of the constitutive material responses and the architected geometry. More recently, developments in the field of metamaterials focused on the effects of disorder, nonlinearities and tunability. This increasing complexity allows material designers to control more precisely wave propagation and harvest the richness of nonlinear phenomena. Current trends in phononics suggest a growing interest in the creation of metamaterials with programmable responses and metamaterials with autonomously adapting morphology. In this talk, I will highlight some of our recent work in programmable, nonlinear metamaterials and their possible application to engineering problems. |
Tuesday, March 6, 2018 8:36AM - 8:48AM |
E48.00002: Pruning bright bonds to engineer smart networks Nidhi Pashine, Daniel Hexner, Jason Rocks, Daniel Reid, Irmgard Bischofberger, Carl Goodrich, Justin Wozniak, Heinrich Jaeger, Andrea Liu, Juan De Pablo, Sidney Nagel Disordered networks made of harmonic springs can be tuned to show various unconventional responses. For example, a network could be designed to respond to an input strain with a very specific localized output at a distant site. One could also modify a network’s global mechanical properties, such as the Poisson’s ratio. We have experimentally realized both of these in physical systems [1, 2]. There are multiple pruning algorithms that can achieve such responses. We are working on algorithms that could be applied on networks in situ. We make our networks out of photoelastic material and observe them between cross polarizers. This allows us to visualize the stress distribution in these networks under various deformations. With this technique, we can apply various algorithms to an experimental system. This enables us to design networks with desirable responses without any numerical calculations. |
Tuesday, March 6, 2018 8:48AM - 9:00AM |
E48.00003: Realizable Elastic Wave Cloaking in Mechanical Metamaterials Sophia Sklan, Ronald Pak, Baowen Li Cloaking, the tailoring of wave refraction to simultaneously shield an object from waves and prevent scattering, has proven to be a powerful conceptual tool for wave control. By employing optical or acoustic metamaterials, cloaking designs of various degrees of approximation have been conceived and experimentally verified. Elastic waves, on the other hand, have proven harder to cloak. In particular, the materials necessary for an ideal elastic wave cloak must break the minor symmetry of the elasticity tensor, an effect which has not been achieved in any known material or metamaterial. We present a means of circumventing this dilemma to design a symmetrized elastic wave cloak. We demonstrate that this cloak can effectively control waves for most realistic conditions while simultaneously preserving the symmetries found in real materials. |
Tuesday, March 6, 2018 9:00AM - 9:12AM |
E48.00004: The Role of Geometry in the Design of the Pattern-transforming Metamaterials Yuzhen Chen, Lihua Jin We numerically, analytically and experimentally study how geometry alters the behaviors of the pattern-transforming metamaterials. These metamaterials contain periodic circular holes sealed by elastomeric membranes, which can buckle under critical pressure differentials and undergo a pattern transformation, yielding a large transformation strain. The results of finite element simulations reveal the key roles of the slenderest wall thickness and size of holes in determining the critical pressure differentials, transformation strains and transformation type. According to the fact uncovered in the simulations that the deformations mainly occur in the slender regions, we introduce a 1D analytical model that features a network of rigid rectangles linked by deformable slender beams, which can qualitatively capture the results observed in the simulations. Finally, we experimentally verified the crucial role of geometry and found an excellent agreement among numerical, analytical and experimental results. Our study provides a clear guideline for the design of the pattern-transforming metamaterials. |
Tuesday, March 6, 2018 9:12AM - 9:24AM |
E48.00005: Engineering disordered phononic metamaterials Henrik Ronellenfitsch, Norbert Stoop, Aden Forrow, Jorn Dunkel Spectral band gaps in phononic metamaterials prevent the conduction of sound |
Tuesday, March 6, 2018 9:24AM - 9:36AM |
E48.00006: Designing Gripper-like Architectures from Self-folded Bilayers Arif Abdullah, K Jimmy Hsia Motivated by the environmentally responsive actuation mechanisms of non-muscular plants, research efforts have been made toward the development of smart reconfigurable devices that can sense and autonomously respond to their surroundings. Tetherless self-folding microgrippers - extensively used for micro/ nano-manipulation - are examples of such engineered systems as they could be actuated on-demand by external stimuli. Being multilayer in nature, these structures rely on spatially patterned hinges for their morphing behavior, and hence they require extensive fabrication efforts. The goal of this work is to establish a design paradigm so that gripper-like architectures could be realized from simple stimuli-responsive planar bilayers (one layer expanding isotropically due to a stimulus while the other remains passive). Through a combination of finite element modeling and experiment, we investigated the stimulus-responsive behavior of bilayer stars and established the principles to achieve stable axisymmetric gripper-like shapes in a programmable manner. Thus, in addition to proposing a simpler route to achieve microgrippers, our research contributes to the rapidly emerging multidisciplinary field of stimuli-responsive self-assembly. |
Tuesday, March 6, 2018 9:36AM - 9:48AM |
E48.00007: Controlling the Deformation of Metamaterials: Corner Modes via Topology Adrien Saremi, D. Zeb Rocklin Topological metamaterials have invaded the mechanical world, demonstrating acoustic cloaking and waveguiding at finite frequencies and variable, tunable elastic response at zero frequency. Zero-frequency topological states have previously relied on the Maxwell condition, namely that the system has equal numbers of degrees of freedom and constraints. Here, we show that otherwise rigid periodic mechanical structures are described by a map with a nontrivial topological degree (a generalization of the winding number introduced by Kane and Lubensky) that creates, directs and protects modes on their boundaries. We introduce a model system consisting of rigid quadrilaterals connected via free hinges at their corners in a checkerboard pattern. This bulk structure generates a topological linear deformation mode exponentially localized in one corner, as investigated numerically and via experimental prototype. Unlike the Maxwell lattices, these structures select a single desired mode, which controls variable stiffness and mechanical amplification that can be incorporated into devices at any scale. |
Tuesday, March 6, 2018 9:48AM - 10:00AM |
E48.00008: Surface patterning and auxetic metamaterial response with magnetorheological elastomers Kostas Danas, Erato Psarra, Laurence Bodelot In this work, we propose the use of magnetorheological elastomers (MREs) as designer active materials or even metamaterials by proper combination of geometry, material selection and combined magnetomechanical loadings. Specifically, we study experimentally and numerically the response of an MRE film/substrate assembly subjected to transverse magnetic fields and in-plane pre-compressions. We show that a single material assembly allows for a single and/or double-period wrinkling as well as surface patterning by proper combination of magnetic and mechanical loads. In addition, we show critical magnetic field for wrinkling can be substantially reduced in the presence of compressive prestress of the assembly, thus opening the possibility of controlling haptic interfaces with low magnetic fields. Finally, we propose novel auxetic MREs by use of general numerical framework. |
Tuesday, March 6, 2018 10:00AM - 10:12AM |
E48.00009: Functionality enhancement in disordered metamaterial systems: the case of bandgap widening Paolo Celli, Behrooz Yousefzadeh, Chiara Daraio, Stefano Gonella The dominant approach in the design of mechanical metamaterials revolves around ordered arrangements of mesoscale constituents---e.g. resonating units in the context of wave and vibration control. In this work, we unveil through experiments a family of unique effects that challenge this paradigm and are directly enabled by the interplay between the mechanical heterogeneity and the spatial disorder of the resonators population. The experiments are carried out using reconfigurable specimens with telescopic pillars whose resonant characteristics can be agilely and intuitively tuned through simple manual operations. In particular, we demonstrate that spatial disorder can be leveraged to enhance the already remarkable broadband filtering capabilities of so-called rainbow materials, and we provide a physical rationale for this bandgap widening phenomenon. |
Tuesday, March 6, 2018 10:12AM - 10:24AM |
E48.00010: On the Duality of Complex Geometry and Material Heterogeneity in Elastodynamics: From Topographic Reliefs to Mechanical Metamaterials Ahmed Elbanna, Qianli Chen From cell membranes to mountains, and from arches to buildings, we are surrounded by countless curved systems possessing both beauty and function. |
Tuesday, March 6, 2018 10:24AM - 10:36AM |
E48.00011: Modeling continuous light-driven mechanical waves in a photoactive, nematic polymer film Micahael Varga, Robin Selinger Photoactive materials that oscillate when illuminated are of interest for applications such as self-cleaning surfaces. Using finite element simulation, we model actuation of such a device, a "blueprinted" liquid crystal polymer film with nematic director planar on one side and homeotropic on the other, as demonstrated by Gelebart et al [1]. The polymer is doped with an azoderivate that undergoes trans-cis isomerisation when illuminated and thermal relaxation when in shadow, both on the time scale of one second. When fixed to a substrate and illuminated with UV light from an oblique angle, the film generates continuous mechanical waves. Curiously, the direction of wave propagation depends on which surface is illuminated. To model actuation, we use a simplified ray tracing algorithm and a kinetic model for light-induced isomerization/relaxation. Changes in nematic order induce dynamic motion. We find the directionality of wave propagation is controlled by a self-shadowing mechanism and periodic pop-through transitions. We compare to experiment and discuss applications such as autonomous light-driven robotics. [1] AH Gelebart, DJ Mulder, M Varga, A Konya, G Vantomme, EW Meijer, RLB Selinger & DJ Broer, Nature 546, 632 (2017). |
Tuesday, March 6, 2018 10:36AM - 10:48AM |
E48.00012: Experimental Observation of Nonreciprocal Waves in a Spatiotemporally Modulated Phononic Chain Yifan Wang, Behrooz Yousefzadeh, Chiara Daraio Mechanical devices that break time-reversal symmetry are highly desirable for sound and vibration insulation, because they allow non-reciprocal wave transmission. Here, we show the first experimental demonstration of non-reciprocity in a one-dimensional phononic chain, obtained from spatio-temporal modulation of local stiffness and resonance. The modulation is controlled by electro-magnets in a discrete chain of magnetic masses connected by weakly nonlinear springs. This biased modulation breaks time-reversal symmetry and opens a bandgap in the dispersion relation, which allows uni-directional sound transmission. This work provides opportunities to build nonreciprocal devices in 1D, without using 2D topological mechanical systems. |
Tuesday, March 6, 2018 10:48AM - 11:00AM |
E48.00013: Broadband Non-reciprocity in Active-feedback Mechanical Metamaterials Corentin Coulais
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