Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N07: Buckling Instabilities of Thin Materials IFocus
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Sponsoring Units: DSOFT Chair: Jovana Andrejevic, University of Pennsylvania Room: Room 130 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N07.00001: Anne Meeussen, Snap-shaping sheets Invited Speaker: Anne S Meeussen
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Wednesday, March 8, 2023 12:06PM - 12:18PM |
N07.00002: Real Shells Exhibit a Universal Localized Buckling Mode with Marginal Imperfection Dependence, Part I: Theory and Simulations Marec Serlin, Nicholas L Cuccia, Kshitij K Yadav, Sagy Lachmann, Symeon Gerasimidis, Shmuel M Rubinstein Imperfections are known to play an essential role in the buckling of a thin shell, but how they interact to control the onset of failure remains unclear. We argue that the von Kármán-Donnell equations, accounting for the shells’ underlying geometric defect structure (w0), are sufficient to predict the dynamics through buckling by comparing their numerical solutions to geometrically non-linear finite-element simulations. Both reveal that shells modeled with geometric imperfections predominantly exhibit localized buckling eigenmodes. Prior to failure, the amplitude of equilibrium radial deformations in the shape of the localized buckling eigenmode is well modeled by a saddle-node bifurcation. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N07.00003: Real Shells Exhibit a Universal Localized Buckling Mode with Marginal Imperfection Dependence, Part II: Experimental Results Nicholas L Cuccia, Marec Serlin, Kshitij K Yadav, Sagy Lachmann, Symeon Gerasimidis, Shmuel M Rubinstein An understanding of the nuanced relationship between the failure properties of real shells and their defects remains elusive. We have developed an experimental system that allows for direct, non-destructive, characterization of a commercial soda can's geometric defect structure (w0) as well as its radial deformations (w) under axial loads (Fa). We predict the initial buckling location of our imperfect shells, later confirmed with high-speed videography, using numerical solutions to the equilibrium von Kármán-Donnell equations. Poking at the predicted location enables non-destructive accurate measurements of the critical axial load (Fc) to within 1%. By imaging below Fc, we directly observe and characterize our shell's buckling eigenmode in the experimental system. Shells exhibit a localized buckling mode, consistent with simulations, whose shape is marginally dependent on the underlying defect structure of the shell. Together, these results change our fundamental understanding of the role of localization and imperfections in the failure of thin shells. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N07.00004: Investigation of the Buckling Instability in Free Thin-Shell Domes Kieran J Barvenik, Zachary Coogan, Matteo Pezzulla, Eleonora Tubaldi Shell buckling presents numerous opportunities to program fast and reversible reconfigurations into multifunctional devices. Applications such as soft actuators, locomotion systems, and biomedical instruments can leverage the diverse deformation properties of shell buckling mode shapes. Here, we investigate the buckling behavior of soft, thin-shell domes with free boundary conditions to facilitate a novel gripper design. Tuning the buckling mode and pressure could enhance the gripper's actuation speed and energy input characteristics. We will present analytical and numerical models used to find the dome's buckling pressure as a function of its material and geometric properties, such as its slenderness ratio and spherical cap angle. We analyze the shell's quasi-static response during pressurization with finite element methods (FEM), and we discuss good agreement between the two models. For experimental validation, we investigate a hemispherical soft shell with a thin film covering the leading edge to create an isolated fluid cavity. Using similar FEM, we model the fluid cavity to compare to the experimental results. Our research aims to advance knowledge about the buckling of soft, thin-shell domes and to inform the usage of hemispherical shells as soft grippers. This investigation also has the potential to pave a path forward for future research into soft devices with buckling controlled actuation. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N07.00005: A wrinkled cylindrical shell as a tunable locking material Pan Dong, Mengfei He, Nathan C Keim, Joseph D Paulsen Consider the final step to place a fitted bed sheet on a mattress. At first it is easy to pull the crumpled corner outward, until the fabric becomes taut and "locks" into place. Here, we use a thin sheet to form a system where the locking behavior is tunable: a cylindrical shell that is subjected to axial compression and twist. After an initial compression, the crumpled shell can be twisted with little resistance until it reaches a "locking angle", which coincides with the appearance of an ordered wrinkle pattern. We construct a simple geometric model to predict the locking angle as a function of the axial compression, which we cast as a phase boundary between relaxed and stretched states. We then conduct force-controlled experiments, where we apply a small tension to the shell while twisting it with a rheometer. These experiments allow us to measure the locking angle and the orientation of wrinkles, in excellent agreement with our model. Our results establish a route to a tunable locking material—a system that can be freely deformed within some interval, whose endpoints can be changed continuously over a wide range. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N07.00006: Simulations of crumpling across confinement geometries Madelyn J Leembruggen, Jovana Andrejevic, Arshad Kudrolli, Chris Rycroft From cell membranes to tectonic plates, crumpling is the result of geometric incompatibility between a thin sheet and external confinement. It's been shown that crumpling statistics progress predictably, and crumpling occurs when planar facets of a sheet fragment into smaller facets. This progression is a robust function of the geometric confinement parameter and the number of compression cycles the sheet undergoes. This fragmentation model, however, has only been analyzed in the specific context of axially compressed sheets. Through simulations and comparison to experimental data, we demonstrate that the fragmentation model for crumpling applies to thin sheets crumpled via several different confinement geometries, including radial compression and cylindrical twisting. This suggests crumpling could be described universally if the correct confinement parameter can be identified. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N07.00007: Elastic instabilities and their frustrated interactions govern the mechanics of thin crumpled sheets Yoav Lahini, Dor Shohat, Daniel Hexner A thin sheet that has been crumpled many times exhibits a range of fascinating mechanical properties, including enhanced rigidity, intermittent response to continuous drives, crackling sounds spanning many scales in intensity, slow relaxations spanning many scales in time, and perhaps most staggeringly, an ability to retain various forms of memory. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N07.00008: Crumpled Kirigami Wathsala M Amadoru Jayawardana, Zhaofan Li, Yangchao Liao, Wenjie Xia, Andrew B Croll A simple act of crumpling a 2D sheet can make a complex 3D spherical structure that creates a new bulk state with different mechanical properties than the 2D sheet from which it was made. Understanding these structures has challenged scientists for many years. Compared with sheets, crumples have a rigid structure made from long-range structural features such as folds, bends, and ridges and short-range structural features such as D-cones. In our studies, we focused on identifying the most dominant features creating the rigidity of the crumple. We studied crumples made out of different materials (Polydimethylsiloxane-PDMS, Polycarbonate-PC, and Paper) and we changed the topography of those films by adding cuts, with the motivation of disturbing the underlying structural network of long-range features in the crumple. We run simple force experiments under the confocal microscope or an Instron universal test machine to identify any changes due to the added cuts. Our main observation is that adding cuts does very little to the compressibility of the crumpled sheet. Further studies using coarse-grain molecular dynamics show similar behavior. Our simple crushing experiments and simulations strongly suggest that the long-range structural features, and the networks they create during crumpling, are not a dominant part of the problem. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N07.00009: Effect of crease curvature on structure and instabilities of the origami waterbomb base Lucia Stein-Montalvo, Jessica Flores, Sigrid Adriaenssens A straightforward folding process transforms a planar, 2D sheet into the 3D origami structure known as the waterbomb base, which consists of alternating mountain and valley folds that meet at a central vertex. Futhermore, transverse force applied to the central node of the tent-like structure drives snap-through between two bistable configurations. Thus, the waterbomb base serves as an easy-to-manufacture switching actuator, and has earned popularity in origami engineering as a result. In this work, we explore how further tunability may be accessed by introducing nonzero crease curvature, which causes facets to bend and store elastic strain energy. Through experiments and simple modeling, we show how geometry and crease curvature affect the folded shape and the loading response of this origami structure. We focus in particular on local buckling events, which precede global snap-through in the curved-crease origami waterbomb base. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N07.00010: Stress Focusing in Thin Curved Films Eric Roeschlein, Andrew B Croll Origami design requires a sheet to be bent several times, often with bends meeting at an angle. Interestingly, the vertex of two bends causes stress focusing in the form of conical structures which are known as developable cones or d-cones. In our experiments, we report the formation of d-cones far from a set of curved, fixed boundaries. This is unique compared to earlier experiments in which d-cones were physically realized though free-boundary contact geometries which involved point contact at or near the site of the asymptotically-singular structure. We experimentally study how the onset of singular behavior resulting from applied strain depends on the thickness, size, and material of the film. Along with the onset of singularities in the films, we discuss general mechanical properties and morphologies observed in experiments, and speculative on the relationships identified in our data. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N07.00011: Revealing the self-similarity of creases in thin films Yasara Dharmadasa, Francisco Lopez Jimenez Creases form on thin sheets as a result of stress singularities that occur during the folding or crumpling. This changes the geometric appearance as well as the mechanical response leading to a class of tunable structures that can display deformation patterns that are not possible in a flat sheet. The Miura-Ori pattern is an example where the folded sheet has a negative Poisson’s ratio and can bend to a saddle shape (negative gaussian curvature). Folding patterns are being utilized over a large variety of applications spanning from medical devices such as heart stents to space applications where thin membranes are folded to maximize stowage and easy deployment. Capturing the effects of a crease is important to correctly model the response of such applications. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N07.00012: The life of a wrinkle on a roller Robert S Hutton, Madison Shipp, Jerald Brown, James Hanna We present preliminary experimental and theoretical results on the nucleation and motion of wrinkles in thin sheets transiting rotating surfaces, a manufacturing-inspired problem. The draping of clothing illustrates the static form of this problem, in which wrinkles are smoothed by Gaussian effects. The dynamic problem, in which the sheets move without appreciable slippage over curved surfaces, introduces additional physics at the boundary in the form of "normal entry" kinematics. We document the nucleation, motion, reorientation, and disappearance of wrinkles on rollers and present simple analytical models to describe the observed behavior. |
Wednesday, March 8, 2023 2:18PM - 2:30PM |
N07.00013: Arrays of nanometer thick buckiling membranes used as a voltage-controllable reflective display. David Gonzalez-Medrano, Marc Z Miskin, Adia Radecka Reflective displays, which work by reflecting specific wavelengths of ambient light back at an observer, hold unique advantages. For instance, they can use low power while operating in bright environments and individual pixels can display customizable colors. While many reflected display technologies exist, they are often limited by complex fabrication or large pixel pitches on the order of hundreds of micrometers. Here we demonstrate a new approach to reflective displays based on buckling, nanometer-thick actuators. Each pixel is made from a partially transparent actuator clamped on all sides above a mirror. The actuator can buckle in response to voltage signals with a deflection on the order of the wavelength of visible light, making a voltage controllable optical resonator. We show pixel fabrication is compatible with CMOS processing, high yield, and that pixels as small as 15 microns on a side, selectively reflect colors across the visible spectrum. |
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