Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L16: Focus Session: Extreme Mechanics: Origami and Structural Metamaterials |
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Sponsoring Units: GSNP DPOLY Chair: Jose Bico, ESPCI Room: 401 |
Wednesday, March 5, 2014 8:00AM - 8:36AM |
L16.00001: Capillary Aggregation of Nanofilaments into Superstructures Invited Speaker: Michael De Volder Over the past decades, methods have been developed to coat surfaces with high aspect ratio nanofilaments for applications including supercapacitors, solar cells, superhydrophobic surfaces, and biomimetic adhesives. Importantly, these nanofilaments often come in contact with wet environments during their synthesis, post-treatment, or in their final application. Because high aspect ratio nanofilaments have a very low stiffness, they can easily be manipulated by capillary interactions. Upon drying for instance, capillary forces can collapse nanofilaments into random aggregates, which is typically an unwanted effect. However, new studies show that by understanding and controlling capillary aggregation, it is possible to fabricate complex and robust architectures in a scalable manner [1]. Besides providing an overview of the above developments, this talk will focus on a process we are developing towards the capillary aggregation of vertically aligned carbon nanotubes ``forests.'' We found capillary aggregation to be an effective method for increasing nanotube packing density, but also to form complex nanotube superstructures. These were for instance integrated in microsensors and other MEMS devices. This talk is based on joint research with AJ Hart, S Tawfick, SJ Park and D Copic. \\[4pt] [1] Engineering Hierarchical Nanostructures by Elastocapillary Self-Assembly, M De Volder, AJ Hart, Angewandte Chemie, 52 (9), 2412-2425 [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L16.00002: Bad origami Scott Waitukaitis Origami research often assumes rigid plates connected by free hinges, but interesting and useful behaviors emerge if these assumptions are relaxed. I will show how breaking the rules of flat and rigid folding, $i.e.$ making ``bad origami,'' can lead to structures that exhibit mechanical rigidity and bistability. [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L16.00003: 3D Buckligami: Digital Matter Martin Van Hecke, Koen de Reus, Bastiaan Florijn, Corentin Coulais We present a class of elastic structures which exhibit collective buckling in 3D, and create these by a 3D printing/moulding technique. Our structures consist of cubic lattice of anisotropic unit cells, and we show that their mechanical properties are programmable via the orientation of these unit cells. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L16.00004: Metallurgy of Miura-ori: lattice theory for inhomogeneous deformations of origami tessellations Arthur Evans, Jesse Silverberg, Lauren McLeod, Itai Cohen, Christian Santangelo In nature, as well as in art, one often encounters thin materials that have been deformed by their environment or their creator into complex folded states; examples include the folds of the endoplasmic reticulum, the villi in the intestinal tract, and tessellated patterns in the ancient Japanese art of origami. One (engineering) advantage of creating a folded structure is that the geometric constraints associated with creasing imbues the construction with exotic mechanical properties, such as generating a material with a negative Poisson's ratio. Materials exhibiting novel behavior of this type, arising from the special properties of the unit cell, are generally classified as metamaterials. In this talk I consider a mechanical metamaterial known as Miura-ori, an origami tessellation pattern that displays soft modes and crystallographic defects not accounted for by a purely geometric theory of an infinitely thin material. I will discuss a method for deriving how inhomogeneous deformations arise from bending within Miura-ori, and show that this leads to a natural coherence length over which the inhomogeneity decays. Additionally, I will show how the modular nature of origami unit cells lends additional richness to the mechanical properties associated with deformation. [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L16.00005: Mechanics of Miura-ori Origami Lattice Defects Jesse Silverberg, Lauren McLeod, Arthur Evans, Jessica Ginepro, Christian Santangelo, Thomas Hull, Itai Cohen The mechanical properties of origami-inspired materials show remarkable potential for responsive, tunable next-generation materials. For example, the Miura-ori fold is predicted to have negative Poisson ratio and anisotropic compressive properties. Using a custom mechanical testing device and 3D laser profilometry, we investigate the moduli and the role of curvature in setting these material properties. Because defects are known to dramatically alter the bulk properties in other periodic materials, we introduce defects into the folding pattern to investigate their effects on the macroscopic mechanical properties. Interestingly, we find that a single defect increases the overall material stiffness, but the introduction of a second defect in the opposite direction can cancel out the first, tending to restore the original material properties. Moreover, these defect pairs can be arranged to form edge dislocations, grain boundaries, and many other topological configurations familiar from the study of crystallographic lattice defects. [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L16.00006: Cutting and Folding for Tunable Materials Properties Pablo Damasceno, Paul Dodd, Terry Shyu, Matthew Shlian, Max Shtein, Nicholas Kotov, Sharon Glotzer Despite the small set of building blocks used for their assembly, naturally occurring materials such as proteins show remarkable diversity in their mechanical properties ranging from something resembling rubber--low stiffness, high resilience and extensibility--to silk--high stiffness and strength. Moreover, their self-folding properties inspire the design of structures capable of tunable reconfiguration. Motivated by such versatility, we report on simulations and experiments for the design of nanocomposites sheets whose mechanical properties can be made tunable via ``secondary structures'' patterning. Our simulations reveal the main cutting features needed to obtain desired material extensibility. Additionally, we study how similar sheets could self-fold into their desired ``native'' structure via stochastic forces. Our results open the possibilities for manufacture of flexible and reconfigurable materials with targeted strength and extensibility. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L16.00007: Non-dissipative shapable sheet Naomi Oppenheimer, Thomas Witten A sheet of paper that has been crumpled and flattened retains some amount of shapability that a bare, uncrumpled, sheet does not have: when deformed by external forces, it retains the deformed shape after the forces are removed. Using a frustrated two dimensional lattice of springs, we show that such shapability can be attained in a non-dissipative system. Numerical investigations suggest an extensive number of bistable energy minima using several variants of this scheme. The numerical sheet can be bent into a nearly-closed cylinder that holds its shape. We verify that the deformed shape is locally stable and compare its bending modulus in the deformed state with that in the initial flat state. We investigate the threshold for non-elastic deformation using various kinds of forcing. [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L16.00008: Folding by Design Paul Dodd, Pablo Damasceno, Sharon Glotzer A form of self-assembly, ``self-folding'' presents an alternative approach to the creation of reconfigurable, responsive materials with applications ranging from robotics to drug design. However, the complexity of interactions present in biological and engineered systems that undergo folding makes it challenging to isolate the main factors controlling their assembly and dis-assembly. Here we use computer simulations of simple, minimalistic self-foldable structures and investigate their stochastic folding process. By dynamically accessing all the states that lead to, or inhibit, successful folding, we show that the mechanisms by which general stochastic systems can achieve their ``native'' structures can be identified and used to design rules for optimized folding propensity. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L16.00009: Auto-origami with defects: modeling blueprinted liquid crystal polymer networks Robin Selinger, Andrew Konya, Vianney Gimenez-Pinto Coupling between topological defects and curvature plays an important role in morphology and microstructural evolution of soft matter with orientational order. We explore this coupling in photoresponsive liquid crystal polymer networks (LCN), which deform under illumination by shrinking along the nematic director and expanding in orthogonal directions. If a non-uniform director field is imposed when a sample is cross-linked, known as ``blueprinting,'' illumination induces non-uniform strain, causing the sample to change shape. The 3-D director field thus encodes a complex deformation, a form of programmed auto-origami. Topological defects in the director field induce an initially flat sample to deform out-of-plane, forming structures with Gaussian curvature. Using 3-D finite element elastodynamics simulation studies, we model the actuation of a photoresponsive LCN containing high order topological defects (from $+$10 to -10) and defect arrays, and compare to recent experiments by McConney et al [1]. We also model blueprinted structures with a striped pattern of twisted domains which form tear-drop shaped accordion folds, and compare to experiments by de Haan et al [2]. Finally, we compare the physics of defect-curvature coupling in LCN with that in other materials such as lipid membranes.\\[4pt] [1] DOI: 10.1002/adma.201301891\\[0pt] [2] DOI:~10.1002/adfm.201302568 [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L16.00010: Measuring mechanical properties of thin hydrogel sheets by elasto-capillary origami. Jinhye Bae, Ryan Hayward Characterizing the mechanical properties of soft elastic materials is critical for understanding their fundamental behaviors, as well as for their use in applications as biomaterials and stimuli-responsive devices. However, quantitative measurements of soft materials, especially those with micro-scale dimensions, is challenging using conventional methods. We take advantage of the recently developed understanding of the elasto-capillary deformation of thin sheets under conditions where interfacial tension is comparable to elastic bending energy, as a means to characterize the elastic properties of micro-scale gel sheets. We first calibrate the method by studying the relationship between the minimum encapsulation length (L$_{crit})$ and the elasto-capillary length (L$_{ec})$ using commercial polymer films with known thickness and modulus, and then apply it photo-crosslinked temperature-responsive hydrogel sheets over a range of temperatures. We anticipate that surface tension will provide a versatile probe for characterizing the properties of soft materials on the micro-scale. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L16.00011: Auto-Origami and Soft Programmable Transformers: Simulation Studies of Liquid Crystal Elastomers and Swelling Polymer Gels Andrew Konya, Christian Santangelo, Robin Selinger When the underlying microstructure of an actuatable material varies in space, simple sheets can transform into complex shapes. Using nonlinear finite element elastodynamic simulations, we explore the design space of two such materials: liquid crystal elastomers and swelling polymer gels. Liquid crystal elastomers (LCE) undergo shape transformations induced by stimuli such as heating/cooling or illumination; complex deformations may be programmed by ``blueprinting'' a non-uniform director field in the sample when the polymer is cross-linked. Similarly, swellable gels can undergo shape change when they are swollen anisotropically as programmed by recently developed halftone gel lithography techniques. For each of these materials we design and test programmable motifs which give rise to complex deformation trajectories including folded structures, soft swimmers, apertures that open and close, bas relief patterns, and other shape transformations inspired by art and nature. In order to accommodate the large computational needs required to model these materials, our 3-d nonlinear finite element elastodynamics simulation algorithm is implemented in CUDA, running on a single GPU-enabled workstation. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L16.00012: Targeting Fold Stiffness to Design Enhanced Origami Structures Philip Buskohl, Giorgio Bazzan, Andrew Abbott, Michael Durstock, Richard Vaia Structures with adaptive geometry are increasingly of interest for actuation, sensing and packaging applications. Origami structures, by definition, can ``shape-shift'' between multiple geometric configurations that are predefined by a pattern of folds. Plastic deformation and local failure at the fold lines transform an originally homogenous material into a grid with locally tailored mechanical properties that bias the response of the overall structure to external loading. Typically, origami structures focus on uniformly stiff fold lines with rigid facets. In this study, we discuss how localized variations in stiffness can influence global properties, including energy budget to transition from flat to folded structure, the preferred path through configuration space, and the final mechanical response of the folded architecture. A simple, bi-stable origami fold pattern is laser machined into polypropylene sheets of different compliance and the critical load of the transition is measured. We model the structure as a truss with bar elongation, folding, and facet bending in order to predict ways to enhance or mitigate the critical load. Targeting local folding properties to modify global performance directly extends to the analysis of more complex architectures. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L16.00013: Tunable Helical Origami Zi Chen, Eric Dai, Huang Zheng Origami, the Japanese art of paper folding, is traditionally viewed as an amusing pastime and medium of artistic expression. However, in recent years, origami has begun to inspire innovations in science and engineering. For example, K. Miura led the study of a paper folding pattern in regards to deployment of solar panels to outer space, resulting in more efficient packing and unpacking of the solar panels into tightly constrained spaces. In this work, we study the geometric and mechanical properties of a twisting origami pattern. The pattern created by the fold exhibits several interesting properties, including rigid foldibility, and finely tunable helical coiling, with control over pitch, radius, and handedness of the helix. In addition, the pattern closely mimics the twist buckling patterns shown by thin materials, for example, a mobius strip. In our work, we relate the six parameters of the twisting origami pattern to generate a fully tunable graphical model of the fold. In addition, we demonstrate that the morphogenesis of such folding pattern can be modeled through finite element analysis. We hope our research into the diagonal fold brings insight into the potential scientific and engineering applications of origami and spark further research into how the traditional paper art can be applied as a simple, inexpensive model for complex problems. [Preview Abstract] |
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