Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J17: Mechanical Metamaterials I - Novel Mechanics and Shape MorphingFocus Live
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Sponsoring Units: GSNP DSOFT DMP Chair: Lucas Meza, University of Washington |
Tuesday, March 16, 2021 3:00PM - 3:36PM Live |
J17.00001: Recent Progress on 3D Chiral Mechanical Metamaterials Invited Speaker: Martin Wegener We review our recent progress on three-dimensional (3D) microstructured chiral mechanical metamaterials. These architectures have been made by state-of-the-art 3D laser nanoprinting and more recently also by rapid multi-focus multi-photon 3D laser nanoprinting. For the latter, the metamaterials contain more than one hundred thousand unit cells and more than three hundred billion voxels. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J17.00002: Chirality-induced Normal-Shear Coupling Effects of Auxetic Chiral Mechanical Metamaterial Siyao Liu, Yaning Li Mechanical metamaterials with chiral geometry often have auxetic effects. Different from auxetic materials with symmetric geometry, such as the reentrant honeycomb, chiral mechanical metamaterials are observed to have strong normal-shear coupling effects. For example, under uni-axial load, the chiral mechanical metamaterial will experience noticeable shearing deformation, and vice versa. This is because that chiral geometry is asymmetric which would induce local rotation. It is not well understood what the relationships between the chiral geometry and the coupling effects are, and how the coupling effects influence auxeticity and other effective mechanical properties. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J17.00003: Reconfigurable Kirigami Gary Choi, Levi Dudte, L. Mahadevan Kirigami is an art form wherein cuts introduced in flat, thin sheets allows the sheet to morph from one single closed and compact configuration into a given open structure, via a coordinated rotation of the individual elements. We depart from this simple paradigm by proposing a framework for the design of compact reconfigurable kirigami patterns, which can morph from a closed and compact configuration into a deployed state conforming to any prescribed target shape, and subsequently be contracted into a different closed and compact configuration. We further establish a condition for producing reconfigurable kirigami patterns which are rigid deployable. Together this lays out a new path for designing shape-morphing mechanical metamaterials. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J17.00004: Topology Restricts Quasidegeneracy in Sheared Square Colloidal Ice Erdal C. Oguz, Antonio Ortiz ambriz, Hadas Shem-Tov, Eric Babia-Soler, Pietro Tierno, Yair Shokef <div style="direction: ltr;"> |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J17.00005: Liquid-induced topological transformations of cellular microstructures Bolei Deng, Shucong Li, Katia Bertoldi, Joanna Aizenberg The fundamental topology of cellular structures - the location, number, and connectivity of nodes and compartments - can profoundly impact their acoustic, electrical, chemical, mechanical, and optical properties, as well as heat, fluid and particle transport. Here we introduce a two-tiered dynamic strategy to achieve systematic reversible transformations of the fundamental topology of cellular microstructures that can be applied to a wide range of material compositions and geometries. Our approach only requires exposing the structure to a liquid whose composition is selected to have the ability to first infiltrate and soften the material at the molecular scale, and then, upon evaporation, to form a network of localized capillary forces at the architectural scale that zip the edges of the softened lattice into a new topological structure, which subsequently re-stiffens and remains kinetically trapped. We then harness dynamic topologies for developing active surfaces with information encryption, selective particle trapping, and tunable mechanical, chemical and acoustic properties, as well as multi-stimuli actuation. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J17.00006: Screening of topological defects in elastic metamaterials Tal Sokolov, Bar Shapira, Yohai Bar-Sinai, Michael Moshe, Yoav Lahini Elastic metamaterials are solids composed of patterned elastic building blocks. The spatial arrangement of the building blocks endows the metamaterial with unusual mechanical properties. For example, elastic sheets with periodically patterned holes have been shown to exhibit negative Poisson ratio as well as other unusual mechanical properties. Here we demonstrate experimentally, and describe analytically, an exotic mechanical response of two dimensional elastic metamaterials - screening of the long-range elastic fields induced by topological defects (disclinations). We find two forms of screening – at low porosities we observe linear screening whose strength depends on the porosity of the sheet. At higher porosities non-linear screening occurs, mediated by a reversible collapse of the holes. We further demonstrate that the recently-suggested theoretical framework of elastic charges in non-Euclidean elasticity well describes the observed linear screening effects. We discuss the limitations of the linearity assumptions, the influence of lattice symmetry of the hole pattern, and provide insights regarding the nonlinear screening behavior which requires going beyond the linear elasticity regime. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J17.00007: Systematic Exploration on the Effective Mechanical Properties of Three-Dimensional Chiral Auxetic Mechanical Metamaterials Tiantian Li, Yaning Li Chiral mechanical metamaterials have unusual mechanical and physical properties due to the chiral geometry, for example, chirality-induced auxeticity and normal-twisting coupling. In order to fully understand the deformation mechanisms of chiral mechanical metamaterials, we need to systematically explore the structural-property relationships of them and quantify their effective mechanical properties. To meet this need, a family of two-phase three-dimensional periodic chiral mechanical metamaterials are designed. Based on a monoclinic anisotropic model, an integrated numerical-analytical method is developed to model the constitutive behavior of chiral mechanical metamaterials. The effective mechanical properties of them, including effective stiffness in three different directions, the effective Poisson’s ratios, and the coupling coefficients are numerically evaluated. Our results show that the addition of the second phase can significantly increase the effective stiffness of chiral mechanical metamaterials and decrease the overall auxeticity and the chirality-induced twist under normal loadings. By jointly tailoring the chiral geometry and material combination, the effective mechanical properties and the deformation mechanisms can be effectively tuned in a large range. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J17.00008: Oligomodal Mechanical Metamaterials David Dykstra, Aleksi Bossart, Jop van der Laan, Corentin Coulais Mechanical metamaterials are artifical composites that exhibit a wide range of advanced functionalities such as negative Poisson's ratio, shape-shifting, topological protection, multistability, extreme strength-to-density ratio and enhanced energy dissipation. To date, most metamaterials have a single property, e.g. a single shape change, or are pluripotent, i.e. they can have many different responses, but require complex actuation protocols. Here, we introduce a novel class of oligomodal metamaterials that encode a few but fixed number of distinct properties that can be selectively controlled under uniaxial compression. In particular, we realise a metamaterial that has a negative (positive) Poisson's ratio for low (high) compression rate. The ability of our oligomodal metamaterials to host multiple mechanical responses within a single structure makes them an early example of multi-functional matter and paves the way towards robust and adaptable devices. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J17.00009: Totimorphs Gaurav Chaudhary, S Ganga Prasath, Edward Soucy, L. Mahadevan Morphable structures are often realized by using microscopic degrees of freedom to sculpt the free energy landscape of a material structure. Such structures can be driven by an external stimulus between different configurations that are the minima in the energy landscape. The ability to design such a free energy landscape is however limited by the constraints implied by the connectivity and geometry of the elastic structure. Here we explore a new class of pre-stressed materials that we call totimorphs, which are infinitely morphable as a result of the energy landscape being flat. We describe a mechanism by which a unit of zero stiffness structure can be assembled to create objects that can morph into multiple arbitrarily complex target shapes. We fabricate prototypes of the designed structures using additive manufacturing techniques where we observe the morphability manifest itself as soft-modes in the system. Our design strategy opens up new possibilities for fabricating shape morphing functional material structures. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J17.00010: Topological, reconfigurable load-bearing cellular origami Damiano Pasini, Amin Jamalimehr, Morad Mirzajanzadeh Metamaterials capable of reconfiguring their shape and tune their mechanical properties post fabrication are sought in a large palette of applications including deployable structures, soft robotics, and microfluids. Their performance is currently limited by three main factors: i) inability to tolerate mechanical forces unless constraints are enforced onto their architecture; ii) huge elastic anisotropy with stiffness values changing with direction over a few orders of magnitude; iii) complex and lengthy process of fabrication. Inspired by notions of origami and kirigami, we introduce here a class of reconfigurable load-bearing cellular materials that can be easily realized to reversibly fold into multiple states, lock sturdily to bear the applied loads, as well as display omnidirectional compressive stiffness. In addition, this class of reconfigurable metamaterials can undergo a range of unprecedented responses including topological switches from open to closed cell configurations, geometric changes in edge and face connectivity, as well as programmable variations in permeability and elastic properties. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J17.00011: A reprogrammable mechanical metamaterial with stable memory Tian Chen, Mark Pauly, Pedro M Reis Metamaterials are designed to realise exotic physical properties through the geometric arrangement of the underlying structural layout. Traditional mechanical metamaterials are designed to achieve functionalities such as target Poisson's ratio or shape transformation through unit cell optimisation. Once fabricated, these functionalities are programmed into the layout of the metamaterial in a way that cannot be altered. Conversely, in hard disk drives for example, each unit can be written-to or read-from on-the-fly. Here, to overcome this challenge, we demonstrate a design framework for a tileable mechanical metamaterial with stable memory at the unit cell level. Our design comprises an array of physical binary elements (m-bits), analogous to digital bits, with clearly delineated writing and reading phases. Each m-bit can be independently switched between two stable states (i.e., memory) by using magnetic actuation to move between the equilibria of a bistable shell. Under deformation, each state is associated with a significantly different mechanical response that is fully elastic. Encoding a set of binary instructions onto the tiled array yields markedly different mechanical properties. We hope that our design paradigm will instigate novel mechanical metamaterials. |
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