Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K40: Mechanical Metamaterials and Origami IIFocus
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Sponsoring Units: GSNP GSOFT Chair: Katia Bertoldi, Harvard University Room: 343 |
Wednesday, March 16, 2016 8:00AM - 8:12AM |
K40.00001: Combinatorial Mechanical Metamaterials Martin van Hecke The structure of most mechanical metamaterials is periodic so that their design space is that of the unit cell. Here we introduce a combinatorial strategy to create a vast number of distinct mechanical metamaterials, each with a unique spatial texture and response. These are aperiodic stackings of anisotropic building blocks, and their functionality rests on both the block design and their stacking configuration which is governed by a tiling problem. We realize such metamaterials by 3D printing, and show that they act as soft machines, capable of pattern recognition and pattern analysis. [Preview Abstract] |
Wednesday, March 16, 2016 8:12AM - 8:24AM |
K40.00002: Geometry Driven Pathways in Hierarchical Mechanical Metamaterials Corentin Coulais, Alberico Sabbadini, Martin van Hecke Using exactingly positioned vacancies in flexible tessellations of squares, we create novel hierarchical mechanical metamaterials that can exhibit multiple shape changes under mechanical actuation. By designing bending, buckling and self-contact interactions, we unravel the link between geometry and dynamical pathways and engineer 2D transformers, which explore complex sequences of symmetrical shapes. [Preview Abstract] |
Wednesday, March 16, 2016 8:24AM - 8:36AM |
K40.00003: Rigidity loss in disordered network materials Wouter G. Ellenbroek, Varda F. Hagh, Avishek Kumar, M.F. Thorpe, Martin van Hecke Weakly jammed sphere packings show a very peculiar elasticity, with a ratio of compression modulus to shear modulus that diverges as the number of contacts approaches the minimum required for rigidity. Creating artificial isotropic network materials with this property is a challenge: so far, the least elaborate way to generate them is to actually simulate weakly compressed repulsive spheres. The next steps in designing such networks hinge upon a solid understanding of what properties of the sphere-packing derived network are essential for its elasticity. We elucidate the topological aspects of this question by comparing the rigidity transition in these networks to that in other random spring network models, including the common bond-diluted triangular net and a self-stress-free variant of that. We use the pebble game algorithm for identifying rigid clusters in mechanical networks to demonstrate that the marginally rigid state in sphere packings is perfectly isostatic everywhere, and the addition or removal of a single bond creates a globally stressed or globally floppy network, respectively. By contrast, the other classes of random network random networks show a more localized response to addition and removal of bonds, and, correspondingly, a more gradual rigidity transition. [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K40.00004: Foam-like compression behavior of fibrin networks Xiaojun Liang, Oleg Kim, Rustem Litvinov, John Weisel, Mark Alber, Prashant Purohit The rheological properties of fibrin networks have been of long-standing interest, especially shear and tensile responses. Their compressive behavior, however, remains unexplored. We show that the compressive behavior of fibrin networks consists of three regimes: 1) an initial linear regime, in which most fibers are straight, 2) a plateau regime, in which more and more fibers buckle and collapse, and 3) a markedly non-linear regime, in which network densification occurs by bending of buckled fibers and inter-fiber contacts. Importantly, the spatially non-uniform network deformation included formation of a moving “phase boundary” along the axis of strain, which segregated the fibrin network into two phases with different fiber densities and structure. The Young's modulus of the linear phase depends quadratically on the fibrin volume fraction while that in the densified phase depends cubically on it. The viscoelastic plateau regime corresponds to a change of volume fraction in mixture of these two phases. We model this regime using a continuum theory of phase transitions and analytically predict the storage and loss moduli. We show they are in good agreement with the experimental data. Our work shows that fibrin networks are a member of a broad class of natural cellular materials. [Preview Abstract] |
Wednesday, March 16, 2016 8:48AM - 9:00AM |
K40.00005: Topological boundary modes in jammed matter Daniel Sussman, Olaf Stenull, Tom Lubensky Granular matter at the jamming transition is poised on the brink of mechanical stability, and hence it is possible that these random systems have topologically protected surface phonons. Studying two model systems for jammed matter, we find states that exhibit distinct mechanical topological classes, protected surface modes, and ubiquitous Weyl points. The detailed statistics of the boundary modes enable tests of a standard understanding of the detailed features of the jamming transition, and show that parts of this argument are invalid. [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K40.00006: Rigidity Percolation in Mechanical Metamaterials Luuk Lubbers, Martin van Hecke We explore rigidity percolation of non-generic diluted tilings of rigid squares coupled by hinges. These compose the backbone of a range of mechanical metamaterials, and allow for a single degree of freedom motion even for full filling. We numerically study the onset and nature of additional floppy modes which arises when sufficient square tiles are removed. [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:48AM |
K40.00007: to be determined by you Invited Speaker: Julia Greer |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K40.00008: Multistable Compliant Auxetic Metamaterials Inspired by Geometric Patterns in Islamic Arts Ahmad Rafsanjani, Damiano Pasini Beyond their aesthetic significance, geometric patterns in Islamic arts can offer a rich source of inspiration that can be used to create new mechanical metamaterials. In this work, we follow this route and present a new class of compliant mechanical metamaterials which simultaneously exhibit negative Poisson's ratio and structural bistability. Designed by finite element simulations, this multifunctional metamaterial is fabricated by perforating a symmetric cut pattern into a sheet of natural rubber. Its building blocks are rotating units with square or triangular shapes connected together with compliant flexure hinges. Under the action of uniaxial extension, the relative rotation between the adjacent members triggers snap-through instability and brings together auxeticity and structural bistability. As a result, this metamaterial can accomplish reversible reconfiguration between two stable arrangements. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K40.00009: The topology of gyroscopic metamaterials Lisa M. Nash, Dustin Kleckner, Alismari Read, Vincenzo Vitelli, Ari M. Turner, William T.M. Irvine Mechanical metamaterials can have topologically protected states, much like their electronic and optical counterparts. We recently demonstrated this in experiment by building a meta-material composed of coupled gyroscopes on a honeycomb lattice. This system breaks time-reversal symmetry and exhibits topologically protected one-way edge modes. In this talk we will explore the relationship between the topology of the band structure and the geometry of the lattice. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K40.00010: Modeling the Mechanical Metamaterials with Confinement Controlled Response. NITIN SINGH, CORENTIN COULAIS, BASTIAAN FLORIJN, MARTIN VAN HECKE Much of the physics of two dimensional mechanical metamaterials can be understood from tilling of rigid-polygons connected by hinges. Here we map recently introduced programmable mechanical metamaterials which are elastic slabs patterned with circular holes of two different sizes to a tilling of hinged rectangles. Torsional springs in the hinges and linear springs at the outside of this mechanism allow us to capture the experimentally observed mechanical response, and we connect the physical design parameters to the shape of the rectangles, and the strength of the torsional springs. We finally show that this soft mechanism provides us with an inverse design tool for metamaterials. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K40.00011: Taming the Exceptional Points of Parity-Time Symmetric Acoustics Marc Dubois, Chengzhi Shi, Yun Chen, Lei Cheng, Hamidreza Ramezani, Yuan Wang, Xiang Zhang Parity-time (PT) symmetric concept and development lead to a wide range of applications including coherent perfect absorbers, single mode lasers, unidirectional cloaking and sensing, and optical isolators. These new applications and devices emerge from the existence of a phase transition in PT symmetric complex-valued potential obtained by balancing gain and loss materials. However, the systematic extension of such devices is adjourned by the key challenge in the management of the complex scattering process within the structure in order to engineer PT phase and exceptional points. Here, based on active acoustic elements, we experimentally demonstrate the simultaneous control of complex-valued potentials and multiple interference inside the structure at any given frequency. This method broadens the scope of applications for PT symmetric devices in many fields including optics, microwaves, electronics, which are crucial for sensing, imaging, cloaking, lasing, absorbing, etc. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K40.00012: Overcoming dissipation with structure: Stable propagation of mechanical signals in soft mechanical metamaterials katia bertoldi, Jordan Raney, Neel Nadkarni, Chiara Daraio, Dennis Kochmann, Jennifer Lewis Soft structures with rationally designed architectures capable of large, nonlinear deformation present opportunities for the design of unprecedented, highly-tunable devices and machines. However, the highly-dissipative nature of soft materials has inherently limited the way in which such systems can be used. Here we present an architected soft system comprised of elastomeric, bistable beam elements connected by elastomeric linear springs. The dissipative nature of the polymer readily damps linear waves, preventing propagation of any mechanical signal beyond a short distance, as expected. However, the unique architecture of the system enables propagation of stable, nonlinear solitary transition waves with constant velocity and pulse geometry over arbitrary distances. Since the high damping of the material removes all other linear, small amplitude excitations, the desired pulse propagates with high fidelity and controllability. This phenomenon can be used for control signals as we demonstrate through the design of soft diodes and soft mechanical logic gates. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K40.00013: Combinatorial Origami Peter Dieleman, Scott Waitukaitis, Martin van Hecke To design rigidly foldable quadrilateral meshes one generally needs to solve a complicated set of constraints. Here we present a systematic, combinatorial approach to create rigidly foldable quadrilateral meshes with a limited number of different vertices. The number of discrete, 1 degree-of-freedom folding branches for some of these meshes scales exponentially with the number of vertices on the edge, whilst other meshes generated this way only have two discrete folding branches, regardless of mesh size. We show how these two different behaviours both emerge from the two folding branches present in a single generic 4-vertex. Furthermore, we model generic 4-vertices as a spherical linkage and exploit a previously overlooked symmetry to create non-developable origami patterns using the same combinatorial framework. [Preview Abstract] |
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