Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H40: Mechanical Metamaterials and Origami IFocus
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Sponsoring Units: GSNP GSOFT Chair: Chris Santangelo, University of Massachusetts Amherst Room: 343 |
Tuesday, March 15, 2016 2:30PM - 2:42PM |
H40.00001: Wave Manipulation in Metamaterials: A LEGO\textsuperscript{\textregistered} Bricks Enabled Platform Paolo Celli, Stefano Gonella In this work, we show how simple, reconfigurable arrangements of LEGO\textsuperscript{\textregistered} bricks can be turned into the building blocks of an experimental platform for the investigation of wave phenomena in metamaterial architectures. The approach involves the assembly of reconfigurable specimens consisting of patterns of bricks on a baseplate and the use of a 3D laser vibrometer to reconstruct global and local wave features. The ability to seamlessly transition between different topologies makes this an effective approach for rapid experimental verification and proof of concept in the arena of mechanical metamaterials engineering. The intuitive nature of the brick-and-baseplate assembly paradigm can also be leveraged to implement families of intuitive lab demonstrations with significant didactic and scientific outreach potential. The versatility of the platform is tested through a series of experiments that illustrate a variety of wave manipulation effects, such as waveguiding and seismic isolation, both in periodic and disordered topologies. [Preview Abstract] |
Tuesday, March 15, 2016 2:42PM - 2:54PM |
H40.00002: Transformable topological mechanical metamaterials D. Zeb Rocklin, Shangnan Zhou, Kai Sun, Xiaoming Mao We present a class of mechanical metamaterials characterized by a \emph{uniform soft deformation}---a large, zero-energy homogeneous elastic deformation mode of the structure---that may be used to induce topological transitions and dramatically change mechanical and acoustic properties of the structure. We show that the \emph{existence} of such a mode determines certain exotic mechanical and acoustic properties of the structure and its \emph{activation} can reversibly alter and tune these properties. This serves as the basis for a design principle for mechanical metamaterials with tunable properties. When the structure's uniform mode is primarily dilational (shearing) its surface (bulk) possesses phonon modes with vanishing speed of sound. Maxwell lattices comprise a subclass of such material which, owing to their critical coordination number (four, in 2D), necessarily possess such a uniform zero mode, often termed a Guest mode, and which may be \emph{topologically polarized}, such that zero modes are moved from one edge to another. We show that activating the deformation can alter the shear/dilational character of the mode and topologically polarize the structure, thereby altering the bulk and surface properties at no significant energy cost. arXiv:1510.06389 [cond-mat.soft] [Preview Abstract] |
Tuesday, March 15, 2016 2:54PM - 3:06PM |
H40.00003: Tuning the Response in Disordered Networks Nidhi Pashine, Jason W. Rocks, Irmgard Bischofberger, Carl P. Goodrich, Sidney R. Nagel, Andrea J. Liu The fact that amorphous materials are structurally different from crystals has important consequences for how the properties of a disordered structure can be tuned. We have used jamming as a method to create spring networks in both two and three dimensions. By selectively removing a small percentage of bonds, we can tune the network to have a desired response. For example, we can tune the network's Poisson ratio anywhere between the auxetic and incompressible limits. We can also produce a targeted response at a local scale; by perturbing the positions of pair of particles at one point we can tune in a desired response a large distance away. This response is similar to the allosteric regulation in proteins where a reaction at one site activates another site of the protein molecule. Experimentally, we have successfully demonstrated such mechanical networks in 2D (by laser cutting) or in 3D (3D printing). [Preview Abstract] |
Tuesday, March 15, 2016 3:06PM - 3:18PM |
H40.00004: The breakdown of breathers in the Fermi-Pasta-Ulam-Tsingou system Alexandra Westley, Rahul Kashyap, Surajit Sen It is well known that in many nonlinear lattices, remarkably stable and localized disturbances known as breathers may form. Here we discuss in short the properties of these objects in the context of the Fermi-Pasta-Ulam-Tsingou (FPUT) system which consists of a mass-spring chain, with spring potentials containing both quadratic and quartic terms. These breathers, though long-lasting, inevitably decay and eventually break apart with sudden violence. This talk in particular will focus on recent numerical work studying the lead-up to the breakdown in which the breather emits at (seemingly) random intervals solitary and anti-solitary waves in the highly nonlinear limit. Furthermore, a possible method to predict the times at which these waves are emitted by examing the frequency structure of the breather will be discussed. [Preview Abstract] |
Tuesday, March 15, 2016 3:18PM - 3:30PM |
H40.00005: Multifunctional Lattices with Low Thermal Expansion and Low Thermal Conductivity Hang Xu, Lu Liu, Damiano Pasini Systems in space are vulnerable to large temperature changes when travelling into and out of the Earth's shadow. Variations in temperature can lead to undesired geometric changes in susceptible applications requiring very fine precision. In addition, temperature-sensitive electronic equipment hosted in a satellite needs adequate thermal-control to guarantee a moderate ambient temperature. To address these specifications, materials with low coefficient of thermal expansion (CTE) and low coefficient of thermal conductivity (CTC) over a wide range of temperatures are often sought, especially for bearing components in satellites. Besides low CTE and low CTC, these materials should also provide desirable stiffness, strength and extraordinarily low mass. This work presents ultralightweight bi-material lattices with tunable CTE and CTC, besides high stiffness and strength. We show that the compensation of the thermal expansion and joint rotation at the lattice joints can be used as an effective strategy to tailor thermomechanical performance. Proof-of-concept lattices are fabricated from Al and Ti alloy sheets via a simple snap-fit technique and vacuum brazing, and their CTE and CTC are assessed via a combination of experiments and theory. [Preview Abstract] |
Tuesday, March 15, 2016 3:30PM - 3:42PM |
H40.00006: Finite-temperature twisted-untwisted transition of the kagome lattice Deshpreet Bedi, D. Zeb Rocklin, Xiaoming Mao Mechanical instability governs many fascinating phenomena in nature, including jamming, glass transitions, and structural phase transitions. Although mechanical instability in athermal systems is well understood, how thermal fluctuations modify such transitions remains largely unexplored. Recent studies reveal that, due to the large number of floppy modes that emerge at mechanical instability, intriguing new phenomena occur, such as fluctuation-driven first-order transitions and order-by-disorder. In this talk, we present an analytic study of the finite-temperature rigidity transition for the kagome lattice. Our model exhibits a zero-temperature continuous twisted-untwisted transition as the sign of the next-nearest-neighbor spring constant changes. At finite temperature, we show that the divergent contribution of floppy modes to the vibrational entropy renormalizes this spring constant, resulting in a first-order transition. We also propose an experimental manifestation of this transition in the system of self-assembling triblock Janus particles. [Preview Abstract] |
Tuesday, March 15, 2016 3:42PM - 3:54PM |
H40.00007: Topological design of torsional metamaterials Vincenzo Vitelli, Jayson Paulose, Anne Meeussen Frameworks -- stiff elements with freely hinged joints -- model the mechanics of a wide range of natural and artificial structures, including mechanical metamaterials with auxetic and topological properties. The unusual properties of the structure depend crucially on the balance between degrees of freedom associated with the nodes, and the constraints imposed upon them by the connecting elements. Whereas networks of featureless nodes connected by central-force springs have been well-studied, many real-world systems such as frictional granular packings, gear assemblies, and flexible beam meshes incorporate torsional degrees of freedom on the nodes, coupled together with transverse shear forces exerted by the connecting elements. We study the consequences of such torsional constraints on the mechanics of periodic isostatic networks as a foundation for mechanical metamaterials. We demonstrate the existence of soft modes of topological origin, that are protected against disorder or small perturbations of the structure analogously to their counterparts in electronic topological insulators. We have built a lattice of gears connected by rigid beams that provides a real-world demonstration of a torsional metamaterial with topological edge modes and mechanical Weyl modes. [Preview Abstract] |
Tuesday, March 15, 2016 3:54PM - 4:06PM |
H40.00008: Surface morphology of pre-stressed bilayer shells for tunable optical transmittance Rashed Al-Rashed, Francisco López Jiménez, Joel Marthelot, Anna Lee, Pedro Reis We introduce a new class of pre-stressed bilayer shells, whose surface morphology can be used to smoothly tune their optical transmittance by pneumatic actuation. Each sample is fabricated by pressurizing a disk made out of an optically clear silicone-based rubber to bulge it into a nearly hemispherical pre-strained shell. The surface of this shell is then taken as a substrate and coated with a thin layer of a polymer suspension with black micron-sized dye particles, which, upon curing, can make the samples opaque. The sample becomes planar when it is depressurized to remove the pre-strain, and its surface develops a complex topography that significantly affects its optical transmittance (i.e. the amount of light that passes through the sample). Re-pressurization of the samples allow for their transmittance to be smoothly tuned in a reversible manner. We explore the parameter space of the system by systematically varying its geometric and material properties. A phase diagram is then constructed where we characterize the transmittance of each of the surface patterns at varying levels of pre-strain. [Preview Abstract] |
Tuesday, March 15, 2016 4:06PM - 4:18PM |
H40.00009: Elastic theory of origami-based metamaterials Frederic Lechenault, V. Brunck, A. Reid, M. Adda-Bedia Origami offers the possibility for new metamaterials whose overall mechanical properties can be programmed by acting locally on each crease. Starting from a thin plate and having knowledge about the properties of the material and the folding procedure, one would aim to determine the shape taken by the structure at rest and its mechanical response. We introduce a vector deformation field acting on the imprinted network of creases, that allows to express the geometrical constraints of rigid origami structures in a simple and systematic way. This formalism is then used to write a general covariant expression of the elastic energy of n-creases meeting at a single vertex, and then extended to origami tesselations. The generalized waterbomb base and the Miura-Ori are treated within this formalism. For the Miura folding, we uncover a phase transition from monostable to two metastable states, that explains the efficient deployability of this structure for a given range of geometrical and mechanical parameters. [Preview Abstract] |
Tuesday, March 15, 2016 4:18PM - 4:30PM |
H40.00010: Self-Folding With Graphene Bimorphs Marc Miskin, Kyle Dorsey, Peter Rose, Itai Cohen, Paul McEuen We have developed a new technique that let us program two layer stacks, or bimorphs, made of graphene and ultra-thin films to self-fold via differential stress. Our approach works in the extreme regime of bimorph folding: we construct bimorphs that optimize folding efficiency when one layer is atomically thin. The resulting devices controllably fold to micron sized radii of curvature. By applying this technique in concert with lithographic patterning, we have produced a powerful platform to build three dimensional structures at the nanoscale. We demonstrate that this this approach is intrinsically scalable and facilities the construction of both fixed 3d structures and actuation. [Preview Abstract] |
Tuesday, March 15, 2016 4:30PM - 4:42PM |
H40.00011: The role of geometry in 4-vertex origami mechanics Scott Waitukaitis, Peter Dieleman, Martin van Hecke Origami offers an interesting design platform metamaterials because it strongly couples mechanics with geometry. Even so, most research carried out so far has been limited to one or two particular patterns. I will discuss the full geometrical space of the most common origami building block, the 4-vertex, and show how exotic geometries can have dramatic effects on the mechanics. [Preview Abstract] |
Tuesday, March 15, 2016 4:42PM - 4:54PM |
H40.00012: Generalized Bistability in Origami Cylinders Austin Reid, Mokhtar Adda-Bedia, Frederic Lechenault Origami folded cylinders (origami bellows) have found increasingly sophisticated applications in space flight, medicine, and even experimental nuclear physics. In spite of this interest, a general understanding of the dynamics of an origami folded cylinder has been elusive. By solving the fully constrained behavior of a periodic fundamental origami cell defined by unit vectors, we have found an analytic solution for all possible rigid-face states accessible from a cylindrical Miura-ori pattern. Although an idealized bellows has two rigid-face configurations over a well-defined region, a physical device, limited by nonzero material thickness and forced to balance hinge with plate-bending energy, often cannot stably maintain a stowed configuration. We have identified and measured the parameters which control this emergent bistability, and have demonstrated the ability to fabricate bellows with tunable deployability. [Preview Abstract] |
Tuesday, March 15, 2016 4:54PM - 5:06PM |
H40.00013: Origami Optimization: Role of Symmetry in Accelerating Design Philip Buskohl, Kazuko Fuchi, Giorgio Bazzan, Michael Durstock, Gregory Reich, James Joo, Richard Vaia Origami structures morph between 2D and 3D conformations along predetermined fold lines that efficiently program the form, function and mobility of the structure. Design optimization tools have recently been developed to predict optimal fold patterns with mechanics-based metrics, such as the maximal energy storage, auxetic response and actuation. Origami actuator design problems possess inherent symmetries associated with the grid, mechanical boundary conditions and the objective function, which are often exploited to reduce the design space and computational cost of optimization. However, enforcing symmetry eliminates the prediction of potentially better performing asymmetric designs, which are more likely to exist given the discrete nature of fold line optimization. To better understand this effect, actuator design problems with different combinations of rotation and reflection symmetries were optimized while varying the number of folds allowed in the final design. In each case, the optimal origami patterns transitioned between symmetric and asymmetric solutions depended on the number of folds available for the design, with fewer symmetries present with more fold lines allowed. This study investigates the interplay of symmetry and discrete vs continuous optimization in origami actuators and provides insight into how the symmetries of the reference grid regulate the performance landscape. [Preview Abstract] |
Tuesday, March 15, 2016 5:06PM - 5:18PM |
H40.00014: How do bendy straws bend? A study of re-configurability of multi-stable corrugated shells Nakul Bende, Sarah Selden, Arthur Evans, Christian Santangelo, Ryan Hayward Shape programmable systems have evolved to allow for reconfiguration of structures through a variety of mechanisms including swelling, stress-relaxation, and thermal expansion. Particularly, there has been a recent interest in systems that exhibit bi-stability or multi-stability to achieve transformation between two or more pre-programmed states. Here, we study the ubiquitous architecture of corrugated shells, such as drinking straws or bellows, which has been well known for centuries. Some of these structures exhibit almost continuous stability amongst a wide range of reconfigurable shapes, but the underlying mechanisms are not well understood. To understand multi-stability in `bendy-straw' structures, we study the unit bi-conical segment using experiments and finite element modeling to elucidate the key geometrical and mechanical factors responsible for its multi-stability. The simple transformations of a unit segment -- a change in length or angle can impart complex re-configurability of a structure containing many of these units. The fundamental understanding provided of this simple multi-stable building block could yield improvements in shape re-configurability for a wide array of applications such as corrugated medical tubing, robotics, and deployable structures. [Preview Abstract] |
Tuesday, March 15, 2016 5:18PM - 5:30PM |
H40.00015: Q: How many folded angels can we fit on the head of pin? A: 22+/-5 Itai Cohen, Tom Hull, Robert Lang, Christian Santangelo, Marc Miskin, Kyle Dorsey, Paul McEuen For centuries, origami, the Japanese art of paper folding, has been a powerful technique for transforming two dimensional sheets into beautiful three dimensional sculptures. Recently, origami has made its foray into a new realm, that of physics, where it has been revolutionizing our concept of materials design. Arguably the greatest strength of this new paradigm is the fact that origami is intrinsically scalable. Thus sculptures built at one size can be shrunk down smaller and smaller. This begs the question: what is the smallest fold one can make? Or in other words how many folded angels can we fit on the head of a pin? This talk takes a deep dive into how origami has been marching smaller and smaller in size. From folding by hand, to self-folding through shape memory alloys and even folding via polymer layers, I will argue that the ultimate limit for scaling down origami is set by folding a sheet of atomic dimensions. I will conclude by showing this vision realized in the folds of a single sheet of graphene. [Preview Abstract] |
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