Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K57: The Extreme Mechanics of BalloonsFocus
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Sponsoring Units: GSNP DPOLY GSOFT Chair: PT Brun Room: BCEC 256 |
Wednesday, March 6, 2019 8:00AM - 8:36AM |
K57.00001: The Extreme Mechanics of Balloons: From Interfacial Films to Inflated Membranes and Back Invited Speaker: Joseph D Paulsen Deformable sheets are ubiquitous in nature and industry across a vast range of scales, from graphene to metal foil to the earth’s crust. Thin sheets are also central to advanced applications including flexible electronics and deployable satellites or emergency shelters. Despite their ubiquity, there are still significant fundamental challenges in predicting how a thin elastic sheet will deform under confinement, from the selection of a macroscopic deformed shape all the way down to the fine details of the microstructural features. I will discuss a suite of experiments using interfacial films and inflated membranes to address problems spanning this entire range. First, I will describe how an ultrathin polymer film wrapped around a liquid droplet adopts highly nonsymmetric shapes as the droplet size is decreased, and how this overall shape selection may be understood using a simple model wherein the exposed liquid surface area is minimized [1]. This geometric model reveals a fundamental connection between interfacial films and mylar balloons. Inspired by this connection, we are conducting experiments using inflated membranes to discover how smooth sinusoidal wrinkles transition into sharp “crumples”, a striking behavior that was originally observed on interfacial polymer films in a spherical geometry [2]. We have now isolated these buckled structures on interfacial films in hyperbolic and cylindrical geometries, suggesting that such crumples are a generic building block for confined sheets. |
Wednesday, March 6, 2019 8:36AM - 8:48AM |
K57.00002: Mechanics of interconnected balloon networks Matjaz Cebron, Miha Brojan, Andrej Kosmrlj We investigate the mechanical stability of an array of interconnected thin balloons made from hyperelastic material that are filled with incompressible fluid. Each individual balloon has a nonmonotonic relation between the volume of enclosed fluid and the pressure difference between the inside and the outside of the balloon. While an individual balloon is unstable in the region with the negative slope on the pressure-volume diagram, such state of a balloon can get stabilized when it is interconnected with other balloons. We will present conditions that have to be satisfied for the mechanical stability for the whole network of balloons. Furthermore, we will discuss the dynamics of unstable configurations, which may exhibit an interesting sequence of liquid redistributions between the connected balloons, such that the volumes of balloons change nonmonotonically, before they settle in a new stable state. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K57.00003: Beyond the smectic order: splay and amplitude modulations in wrinkle patterns Oleh Tovkach, Benjamin Davidovitch Thin solid sheets and shells tend to suppress compressive stresses by developing wrinkles -- elongated periodic undulations around a smooth enveloping shape, whose characteristic "wavelength", λ , vanishes with the solid's thickness. While an energetically-favored spacing imparts a local smectic order to the pattern, the geometric constraints underlying the mere presence of wrinkles are often incompatible with a global smectic order – implying localized defects and other meso-scale deviations from an "ideal" array of parallel, elongated wrinkles. |
Wednesday, March 6, 2019 9:00AM - 9:12AM |
K57.00004: Self-similar retraction of a shot rubber-band Alexandros Oratis, James C Bird Stretching and shooting rubber bands is a familiar experience for both children and adults, yet the initial dynamics are so quick that they are generally missed. When a cut elastic strip is stretched from its end and suddenly released, the dynamics depend on a balance of stretching and inertia. However when a rubber band is stretched, a region of high-curvature is created and it is unclear how this curvature affects the dynamics. Here, we demonstrate that during the retraction of a circular rubber band, a wavelength develops at the rear which increases in size as time progresses. Through a combination of experiments and modeling, we investigate the speed at which the back of the elastic retracts and observe a self-similar shape that depends on stretching, inertia, and bending. These retraction dynamics illuminate how a rubber band can pass by a thumb when discharged without hitting it. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K57.00005: All-in-One Design of Soft Machines Trevor Jones, Joel Marthelot, PT Brun In our world filled with human innovation and technology we hardly scratch the surface of what has been formed in nature. While we have increased our control and capabilities of machines in the thrust for biomimicry, the use of soft structures to accomplish complex tasks is still primarily the handiwork of biology. To bridge the gap on nature, we introduce an all-in-one approach to building soft machines. Using the powerful rules of fluid mechanics and silicone elastomers, fluid-mediated networks can be “frozen” to provide unique functional materials. Here a Bretherton-like technique is explored as an elongated bubble deposits a polymer melt film on the inside of tubes. The residual film undergoes drainage as the polymer melt cures into an elastic solid. We characterize these elastic networks, comprised of pneumatic bending actuators, through experiments and predictive models of their constituent parts. By means of this deep integration between the non-linear actuation and the far from equilibrium shape-morphing we reverse engineer targeted soft machines. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K57.00006: Inflatable origami-inspired structures David Melancon, Chuck Hoberman, Benjamin Gorissen, Carlos Garcia Mora, Yunfang Yang, Jason Ku, Erik Demaine, Katia Bertoldi Origami has long been used as a source of inspiration to design creative and esthetic constructions, from the iconic paper swan to facades of multi-story buildings. More recently, the rules of folding have been applied to fabricate architected materials with functional properties such as compactness, self-foldability, and multi-stability. These properties highlight the potential of origami to become a new design paradigm for rapidly deployable structures. Whereas multiple origami-inspired deployable surfaces have been reported in the literature, there is a lack of research on enclosed deployable geometries. In this work, we introduce a novel type of inflatable origami-inspired structure comprised of a polyhedron with triangular faces and elastic hinges. From simple geometry principles, this star-shaped structure possesses two compatible configurations – flat-folded and deployed – giving rise to a bi-stable behavior. The insights gained from the study of this simple geometry enable the understanding of the folding principles of a novel class of enclosed origami-inspired structures that can be deployed to different stable configurations through inflation. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K57.00007: Buckling of inflatable pouch seams James Hanna, Hee Doo Yang, Alan Asbeck Inflating a mylar balloon results in a pattern of wrinkles around its seams, and a shape with similarities to those of stuffed paper folders, tea bags, empanadas, and other objects in which the perimeters of thin sheets are attached to form a closed surface around a maximal volume. Our present interest in this problem stems from working with inflatable pouches for soft robotic actuators, made by layering textiles, plastics, and adhesives. We examine circular pouches with annular seams. Inflation of the pouch effectively provides a contractile planar constraint on the interior of the rim, leading to buckling reminiscent of prior results on swelling gel strips attached to rigid bodies. The buckling wavelength coarsens with the width of the seam, until it saturates at four cycles. We examine the effects of seam width, pouch radius, and sheet thickness on the buckling wavelength, through experiments and scaling arguments. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K57.00008: Stress Focusing in Inflated Membranes: Threshold and Morphology Raj De, Yousra Timounay, Jessica L Stelzel, Joseph D Paulsen
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Wednesday, March 6, 2019 10:00AM - 10:12AM |
K57.00009: From flat sheet to cone without cutting: the wrinkled cone Doireann O'Kiely, Joseph Blanc, Finn Box, Dominic Vella It is relatively straightforward to roll a sheet of paper into a cone, but in doing so we must “waste” some paper (either by cutting or overlapping the sheet). Here, we show how to create a cone from a very thin polystyrene sheet without cutting or overlapping – instead, the excess length generated by deforming the initially flat sheet is buffered locally by wrinkling. To realise this, we suspend a thin circular sheet on a soap film so that it is held by a small radial tension at the boundary. The sheet is deformed by indenting at the centre. Through wrinkling, the flat sheet deforms to a cone, and subsequent changes in the angle of the cone are accommodated by self-regulated adjustment of the wrinkles. Experimentally, the soap film used to apply the radial tension is deformed by (and hence opposes) wrinkling in the sheet. We discuss the implications of this for the wrinkle pattern selection. |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K57.00010: Inflating and programming flat inextensible curvilinear paths Emmanuel Siefert, Etienne Reyssat, Jose Bico, Benoit Roman Mylar balloons are popular gifts in funfairs or birthday parties. |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K57.00011: Dragonfly-inspired deployable structures: how to inflate and stay flat? Joel Marthelot, Thomas Dupuis, Pierre-Thomas Brun Programming the final shape of a soft inflatable structure is a nontrivial challenge. Such a task is routinely accomplished in nature, for example when the wing of an emerging dragonfly deploys over just a couple of minutes. This expansion is guided by a network of veins where hemolymph is injected and subsequently solidifies to generate rigidity. |
Wednesday, March 6, 2019 10:36AM - 10:48AM |
K57.00012: Sub-millimeter air-filled toroidal bubbles featuring easily reversible and rapid shape change. Paul Russo, Xujun Zhang, Andrew Gorman, Peter Yunker, Saad Bhamla, H. Qi
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Wednesday, March 6, 2019 10:48AM - 11:00AM |
K57.00013: ABSTRACT WITHDRAWN
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