Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L17: Mechanical Metamaterials II - MultistabilityFocus Session Live
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Sponsoring Units: GSNP Chair: Lihua Jin, University of California, Los Angeles |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L17.00001: Multistable inflatable origami structures at themeter-scale Invited Speaker: David Melancon From stadium covers to solar sails, we rely on deployability for the design of large-scale structures that can quickly compress to a fraction of their size. Historically, two main strategies have been pursued to design deployable structures. The first and most common approach involves mechanisms comprising interconnected bar elements, which can synchronously expand and retract, occasionally locking in place through bistable elements. The second strategy instead, makes use of inflatable membranes that morph into target shapes by means of a single pressure input Neither strategy however, can be readily used to provide an enclosed domain able to lock in place after deployment: the integration of protective covering in linkage-based systems is challenging and pneumatic systems require a constant applied pressure to keep their expanded shape. Here, we draw inspiration from origami, the Japanese art of paper folding, to design rigid-walled deployable structures that are multistable and inflatable. Guided by geometric analyses and experiments, we create a library of bistable origami shapes that can be deployed through a single fluidic pressure input. We then combine these units to build functional structures at the meter-scal, such as arches and emergency shelters, providing a direct pathway for a new generation of large-scale inflatable structures that lock in place after deployment and provide a robust enclosure through their stiff faces. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L17.00002: From bifurcation to snap-through buckling of elastic thin shells for soft robotic materials Damiano Pasini, Chuan Qiao Elastic thin shells are well-known for their highly unstable post-buckling response that exhausts their pressure bearing capacity and leads to catastrophic collapse. This paper examines elastic thin shells with a large axisymmetric imperfection that can escape the classical bifurcation of perfect spherical shells. The results show that the imperfect shell undergoes snap-through buckling followed by a stable post-buckling that offers increasing resistance to pressure over a large shell deformation. In addition, a sensitivity analysis on the role of defect geometry reveals the emergence of four buckling modes. The findings show that harnessing defect geometry can be effective in programming the post-buckling characteristics and transition between buckling modes, thus offering potential routes for the design of soft metamaterials. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L17.00003: The twisting mechanics of undulated ribbons: theory and application to morphing structures Connor McMahan, Paolo Celli, Alice Lamaro, Punnathat Bordeenithikasem, Douglas Hofmann, Chiara Daraio Stress localization at compliant hinges and flexures makes it challenging to design durable, low-part-count, load bearing systems that can undergo complex and reversible changes in shape. Here, we investigate the use of bulk metallic glass (BMG) ribbons that have been thermoformed into twisted, stress-free configurations as building blocks for shape-changing structures. The post-twisting helicoidal shape allows the ribbons to have preferred bending directions that vary throughout their length. A boundary undulation allows to introduce a bias and to make some bending directions more favorable. The result is that twisted undulated ribbons behave as structural elements with multi-directional compliant joints. We join multiple ribbons to create deployable systems with complex morphing attributes enabled by the intrinsic chirality of the building blocks. The design of our structures is informed by an investigation of non-rectangular ribbon mechanics through a combination of numerical simulations, an analytical model based on a geometrically nonlinear plate theory and torsional experiments. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L17.00004: Stretching to bend: tension-induced curving of textured soft ribbons Emmanuel Siéfert, Nicolas Cattaud, Etienne Reyssat, Benoit Roman, Jose Bico A smooth elastic ribbon put under tension undergoes transverse contraction owing to Poisson effect. Thicker ribs of the same material placed on the surface of the ribbon give rise to an effective bilayer, which results in the transverse bending of the textured ribbon upon stretching. We study this phenomenon through model experiments, and describe analytically how the orientation and geometry of the decorating ribs influence the sign and amplitude of the curvature. We also describe the instability that leads to the buckling of the most slender surface ribs. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L17.00005: A reusable and rate-independent energy-absorbing metamaterial Yuzhen Chen, Lihua Jin This work reports a new strategy for designing reusable and rate-independent energy-absorbing metamaterials. Combining finite element simulations, asymptotic post-buckling analysis, and experiments, we discover that as the width-to-length ratio increases, a hyperelastic column subjected to uniaxial compression can undergo continuous buckling, snapping-through buckling, snapping-back buckling, or creasing. Harnessing the hysteretic snapping-through or snapping-back buckling of wide hyperelastic columns, we build a class of metamaterial that is capable of energy dissipation and shock attenuation. The metamaterial shows a long working distance under loading, and instantaneously recovers its original shape upon unloading, but forming a large hysteresis between loading and unloading. Such an energy-absorbing metamaterial is reusable, self-recoverable and rate-independent. By tuning the design parameters or applying a pre-load, we can tailor the peak force, the dissipated energy, and even the monostability of the metamaterial. Our study opens a new avenue to the design of reusable energy-absorbing materials for personal safety, packaging, and aircraft and vehicles crashworthiness. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L17.00006: Metamaterials that can count Lennard Kwakernaak Most metamaterials considered so far respond the same way every time they are driven. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L17.00007: Temperature-dependent critical buckling strains and elastic constants in thermalized nanoribbons David Yllanes, Paul Hanakata, Sourav Bhabesh, Mark J Bowick, David R. Nelson Studies of buckling and instabilities of thin plates date back more than two centuries. However, stability predictions, such as for the critical buckling load, can be dramatically altered for nanomembranes (e.g., graphene) when thermal fluctuations become important. We study, using theory and simulations, thin ribbons under longitudinal compressions and an out-of-plane perturbing field at a wide variety of temperatures. We find that the buckling behavior, obtained via molecular dynamics, can be described by a mean-field theory with renormalized elastic constants when the ribbon length is shorter than the persistence length. The ribbon mechanics become temperature dependent with Young’s modulus Y ∝ T-ηu/2, bending rigidity κ ∝ T η/2, and critical strain εc ∝ T (η+ηu)/2 where η = 0.67(18) and ηu = 0.41(10). These buckling exponents are close to theoretical predictions and numerical simulations normally obtained via Fourier analysis of height fluctuations of a stress-free membrane. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L17.00008: Topological defects steer stresses in two- and three-dimensional combinatorial mechanical metamaterials Ben Pisanty, Erdal C. Oguz, Cristiano Nisoli, Yair Shokef Mechanical metamaterials present a promising avenue towards seemingly impossible mechanics. They often require frustration of elementary building blocks, yet a comprehensive understanding of its role remains elusive. Relying on an analogy to ferromagnetic and antiferromagnetic binary spin interactions, we present a universal approach to detect and analyze mechanical defects in two and three dimensions and for arbitrary building blocks. We apply this method to two- and three-dimensional metamaterials, and show how topological defects can be implemented to steer stresses and strains in a controlled and non-trivial manner. This can inspire constructing materials with hitherto unknown complex mechanical response. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L17.00009: Exploiting symmetry and a new conservation law for designing multistable eight-fold origami structures Matthew Grasinger, Andrew Gillman, Philip Buskohl The nonlinearities inherent in the mechanics of origami make it a rich design space for multistable structures and metamaterials. In this talk, we investigate the multistability properties of a classic origami base: the symmetric eight-fold waterbomb. We present a design procedure for tuning the depth and the symmetry/asymmetry of its energy wells. While the waterbomb is thought to be strictly bistable, we have discovered tristable cases that can exist when the mountain and valley creases are pre-tensioned with respect to each other; that is, when the waterbomb does not have a stress-free configuration. Finally, we consider quasi-1D sheets of waterbombs. Here we discover an analog of Gauss's law in which the number of popped-up and popped-down vertices is determined simply through analysis of its boundaries. This is followed by a discussion of how the quasi-1D sheet may be designed to achieve stable states with various degeneracies, kinematics, and band-gaps. These discoveries and novel analysis techniques, as we work towards generalization, represent a powerful global design tool for useful origami structures. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L17.00010: Characterizing the mechanics of permanent creases in folded films Yasara Dharmadasa, Francisco Lopez Jimenez Folding a thin film can alter the overall response of the design, paving the path for many innovative engineering applications ranging from mechanical meta-materials to deployable and flexible structures. Creases and film panels are the building blocks for such designs, and the overall response of the design can be tuned by controlling the geometry and crease behavior. Our work focuses on characterizing the behavior of permanent creases and developing modelling techniques to predict the behavior of foldable structures. We perform experiments on the crease formation and the folding-unfolding process to characterize its properties, such as the equilibrium angle and the torsional stiffness. We rationalize the observed experimental trend with an elasto-plastic elastica beam model. Using the analytic tools, we investigate the localization of the curvature, which allows us to define a length scale of a crease. Non-dimensional analysis shows robust relationships that could extend the results to other geometries and materials. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L17.00011: Ising-like transitions and anomalous thermal expansion in fluctuating membranes with puckered impurity arrays Paul Hanakata, Abigail Plummer, David R. Nelson Idealized homogeneous membranes and membranes with various types of defects have been studied for the last thirty years. However, finite temperature investigations of membranes with a periodic array of impurities that can buckle on either side of the membrane are less common. In this work, we present molecular dynamics simulations of elastic membranes with dilational impurities arranged in a square lattice. The staggered "magnetization" of the up-down buckled impurities acts as the order parameter for a 2D Ising phase transition of the puckers in the flat phase. We find that both that the ground state and the finite temperature behavior of this system can be described as a highly compressible antiferromagnetic Ising model. Non-trivial couplings between dilations and both flexural and in-plane phonons alter the long-wavelength physics, resulting in anomalous thermal expansion. The isothermal expansion picks up a diverging specific heat singularity because the buckled puckers no longer pack efficiently as the order-disorder transition progresses. |
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