Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B21: Morphing Matter: From Soft Robotics to 4D Printing IIRecordings Available
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Sponsoring Units: DSOFT GSNP DPOLY Chair: Andrej Kosmrlj, Princeton Room: McCormick Place W-185D |
Monday, March 14, 2022 11:30AM - 11:42AM |
B21.00001: Multi-functional soft robotic structure via combination of origami and kirigami Ganguk Lee, Ho-Young Kim Versatile change of shape and mechanical property can greatly enhance functionality of soft robots that need to adapt to spatiotemporally varying environmental conditions. Origami and kirigami, the ancient paper art of folding and cutting, are now widely employed to develop mechanical metamaterials and soft robots. Here, we present a highly deformable structure by operating both folds (origami) and cuts (kirigami) on a two-dimensional tessellated sheet. We demonstrate that the sheet can morph into a compactly folded state, beam, or bellow by changing the folding angle and cutting direction. In addition, the resulting structures are shown to exhibit a wide range of elastic resistance, or stiffness, depending on the direction of external force. We show that our robotic system possessing such variable shapes and stiffness can steer into cleavages of varying gaps with tunable, orientation-dependent stiffness. |
Monday, March 14, 2022 11:42AM - 11:54AM |
B21.00002: Training capacity of viscoelastic materials and failure through a dynamical transition Daniel Hexner Disordered materials can be endowed with specific elastic responses by applying a select set of training strains. The ensuing internal stresses cause plastic deformations that alter the microscopic structure, and evolve the system towards the desired elastic response. We study the complexity of responses that can be attained, as expressed in the number of sites that are simultaneously controlled. With increased complexity convergence becomes very slow. The training error decays as power-law, with an exponent that varies continuously and appears to vanish at a critical threshold. We argue that this is a dynamical transition, reminiscent of the Griffiths transition in absorbing state problems. We also study the capacity as a function of system size. Our results suggest that the capacity is extensive for near isostatic networks, and sub-extensive for over-coordinated networks. Our work explains how the presence of an exotic critical point affects the convergence of training, and may be relevant to understanding learning in physical systems. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B21.00003: Irreversible deformation of architected structures Victor Charpentier, Stephane Bourgeois, Joel Marthelot Creating a curved surface from a flat membrane has recently been made possible by architected materials. Kinematic incompatibilities of non-uniform cutting patterns generate out-of-plane displacements. The resulting deformed geometry closely matches a target shape using expansion mapping techniques between the initial and final shapes. In this work, we introduce the use of irreversible plastic deformation as a means to hold the target shape. We use numerical homogenization using finite element methods to predict the kinematics and mechanical response of the architected structure. We propose a reduced model of torsional hinges to capture the elastoplastic deformation of the structure and program the target geometry and mechanical response of the deformed structure. Finally we validate our approach experimentally and program surfaces that are mechanically functional and created using a simple actuation mechanism. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B21.00004: Fabric based flexible gripper Joel Marthelot, Ignacio Andrade-Silva We study the mechanics of curved elastic tubes consisting of two thin, flat, quasi-inextensible sheets sealed together, which react in such a way that their reference curvature is amplified when inflated. We focus on V-shaped tubes with sharp corners that deform so that the initial angle between the arms decreases upon inflation, acting as a hinge-like mechanism. We first characterize the kinematic and mechanical response of an individual hinge through a combination of experiments and finite element modeling. We build a soft gripper that consists of a star-shaped tube consisting of successive V-shaped tubes forming a closed loop. Upon inflation, the structure contracts radially and provides a flexible gripping solution with adjustable gripping force. Based on the mechanical description of individual hinges, we address the inverse problem and optimize the closed loop geometry and operational conditions to achieve a target gripping force for the gripper. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B21.00005: Magnetic Handshake Polymers with Designable Properties Hanyu Alice Zhang, Chrisy Xiyu Du, Tanner Pearson, Conrad Smart, Zexi Liang, Michael P Brenner, Paul L McEuen, Itai Cohen Magnetic handshake materials [1] have allowed for the creation of artificial homopolymer systems on the centimeter scale by using a chain of magnetic panels with a 2x2 square array of magnetic dipoles embedded within. By controlling the bending energy between adjacent panels of these systems, we can understand the physical shape of a strand, predict its persistence length behavior, and even gain selective control of the strands or get the strands to exhibit long range order via the addition of an external magnetic field. In addition, the scale-invariant nature of magnetism and geometry allows for the manufacturing of similar magnetic polymer systems on the nanometer to micrometer scale. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B21.00006: Think big: overcoming gravity in large scale shape morphing structures. Lauren Dreier, Trevor J Jones, Andrej Kosmrlj, Pierre-Thomas Brun Nature is ripe with shape morphing structures – plant leaves, organs – whose transformations are driven by differential growth. In the laboratory, these mechanisms have inspired numerous shape-shifting structures, typically relying on a change of the metrics following the application of a stimulus, e.g. temperature, UV-light, electric field, or pressure, in some carefully crafted soft materials; or else strategies to change the apparent metric, e.g. origami folds and kirigami cuts. While the later heavily rely on craftsmanship for fabrication – think of the difficulty to fold an origami – and are thereby limited in scale, the former are usually restricted to small settings (tenth of centimeters or less), where gravity is negligible or is made negligible (neutrally buoyant conditions). These limitations are an impediment to the translation of these approaches to larger length scales, where necessary stiffness competes with the ability to deform largely. Here we present preliminary results obtained in identifying strategies to overcome the aforementioned challenges. Particular attention is given to combining existing techniques, e.g. origami-like structures and pneumatic actuations, and exploring new avenues of research, e.g. the jamming of granular media enclosed in elastic structures. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B21.00007: Micrometer-sized, electrically morphing metamaterial-robots (MetaBots) Qingkun Liu, Wei Wang, Himani Sinhmar, Itay Griniasty, Michael F Reynolds, Hadas Kress-Gazit, Paul L McEuen, Itai Cohen Auxetic mechanical metamaterials provide an unparalleled platform for designing soft microrobots stemming from their large degrees of freedom, negative Poisson's ratio, and easy fabrication. Here, we demonstrate electrically programmable, micrometer-sized metamaterial-based robots (MetaBots) that could form three-dimensional (3D) surfaces from two-dimensional patterns, cycle among different shapes, and locomote in a biocompatible solvent. These MetaBots have a hierarchical structure: the repeating panels are linked by origami-based splay hinges, which are controlled by applying voltage to atomically thin surface electrochemical actuators. When we apply a voltage, the local expansions of the unit cells alter the local Gaussian curvature of the MetaBot, allowing it to reconfigure into a 3D surface. By locally actuating different subsets of the splay hinges, we can transform the MetaBot into a rich class of 3D shapes that we characterize using confocal fluorescence microscopy. Furthermore, by applying a phase delay between actuating the different hinge subsets, we break both the spatial and temporal symmetry, and drive the MetaBots to locomote in a biocompatible solution. These MetaBots could open the door to a variety of applications, including microscopic robots with distributed control, tunable optical metasurface, and medical microrobotics. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B21.00008: Shape morphing from instability and frustration Xiaofei Guo, Corentin Coulais In most studies, the occurrence of shape morphing requires either symmetry breaking or defects in undeformed structures. Furthermore shape morphing needs to be actuated by an input control, such as pneumatic networks or external magnetic fields. Here we present a new type of shape morphing method that can be achieved by the use of periodic structures. Due to the instability, the periodic structure automatically generates a frustration under a homogeneous compression. The frustration breaks the symmetry of the deformation and therefore generates a global bending deformation. Although the direction of the bending seems random, it can be manipulated by programming the geometric parameters of the structure. The presented structure has the potential to be used as a robotic arm and achieves programmable responses by simple input control. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B21.00009: Designing Oscillation Using Magnetic Handshake Materials Chrisy Xiyu Du, Ella M King, Paul L McEuen, Itai Cohen, Michael P Brenner One fascinating feature of living materials is their ability to change morphology and oscillate between different states. With oscillation, structures can perform tasks such as run and tumble locomotion or cargo delivery. Maintaining oscillation between more than two states, however, can be difficult and requires pathways for the structure to intake energy. Here, we show how to achieve such multi-state oscillation in self-assembling structures made up of Magnetic Handshake Material building blocks. Our strategy entails assembling structures that retain net magnetic dipole moments so that we can directly control the structure's motion using an external magnetic field. By inverse designing the interactions between the Magnetic Handshake building blocks and the external field, we are able to obtain multi-state oscillation cycles in structures assembled from heterogeneous magnetic clusters. These results demonstrate proof of concept designs for self-assembling microscopic magnetically actuatable machines. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B21.00010: Continuum Theory and Deformation Control in Origami Metamaterials Michael D Czajkowski, James McInerney, Andrew M Wu, Zeb Rocklin The careful addition of creases to a thin sheet according to a mechanism, such as the Miura fold pattern, unlocks a special pathway of motion that allows the macroscopic sheet to access nonlinear shape changes at very low energy cost. This special mechanism behavior makes these origami metamaterials ideal candidates for controllable soft robotics. However, even rudimentary mechanical probing of these folded sheets reveals a broad variety of soft response which does not resemble the mechanism. Recently, some of us have revealed a new principle in which a geometric compatibility relation guarantees a space of soft motions affiliated with any planar mechanism. Here, we assemble these previous works in the context of differential geometry to reveal a continuum theory governing the generic soft response of origami sheets. Despite the presence of additional compatibility requirements and local modes of deformation, known colloquially as twist and bend, these exotic soft motions remain subextensive and are encoded on the sheet boundary. Our approach, which we confirm in a variety of loading simulations, closes a gap between current theory and tangible origami sheet behavior, while also revealing rich new possibilities for the precise control of deformation via boundary actuation. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B21.00011: Mapping Actuation Pathways in Morphing Origami Structures via Graph Analysis Philip Buskohl, Matthew J Grasinger, Andrew Gillman Origami has emerged as a promising platform for morphing structures, programmable materials, and reconfigurable robotics. Origami structures exhibit novel multistability properties, which can be programmed to target specific stable states and actuation modes between configurations. Here we use stochastic search and gradient-based optimization to map out the stable states of the origami structure; and use minimum energy path methods to characterize the folding paths between states (i.e. actuation paths). Then using shape metrics, we identify intermediate branching points and bifurcations where folding paths intersect. The interaction and connectivity between various folding paths of the origami naturally leads to a graph theoretic representation where the vertices correspond to folded configurations of interest and the edges correspond to folding paths. The graph representation which emerges leads to insights on potential actuation cycles for locomotion, and for robotic reconfiguration strategies more broadly. We conclude by highlighting mechanisms for tuning certain structural and energetic properties of the graph which may have important implications for effectively utilizing origami principles in robotics. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B21.00012: Global inverse design of anisotropiclly deforming sheets using curve defects Itay Griniasty, James P Sethna, Itai Cohen Can an anisotropically-deforming, shape-shifting sheet transform into any shape? While locally the local answer is positive, the global answer, so far, has been no. Smooth solutions to the inverse design problem develop singularities within a finite distance, preventing them from covering as simple a surface as a sphere. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B21.00013: Topology mechanics in axially periodic trusses James McInerney, Xiaoming Mao Axially periodic trusses are quasi-one-dimensional networks whose zero energy modes (ZMs) correspond to complex flexural and twisting deformations within their three-dimensional embedding space that can be utilized for the actuation of mechanical structures and soft robotics. In this talk, we discuss how such trusses can be programmed to exhibit topologically protected boundary and interface ZMs and states of self stress (SSSs), which might be used to amplify mechanical response or localize stress, when the number of constraints matches the number of degrees of freedom. We distinguish between two topological classes of trusses: (1) When the coordination number is the same on every vertex, the truss generically possesses a self-duality that pairs ZMs localized to opposite boundaries, but permits the existence of novel interface ZMs between different topological phases. (2) When the coordination number varies between vertices, the aforementioned self-duality is broken and the truss can be polarized so that one end possesses an excess of ZMs. We discuss the interplay between this topological polarization with gapless translational and rotational ZMs at zero wavenumber in the one-dimensional Brillouin zone. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B21.00014: Light-driven liquid crystal elastomer kirigami: fluttering with splay and topology Vianney K Gimenez-Pinto, Juan Chen, Jinghua Jiang, Chenhui Peng Via finite element simulations, we model the actuation response of liquid crystal elastomer kirigami imprinted with topological microstructures. Microstructures include in-plane defects with a preset topological charge coexisting with director splay along sample thickness. In the spirit of kirigami (the japanese art of cutting paper), we investigate samples custom-cut to specific geometries and their corresponding out-of-plane actuation driven by light. We demostrate the actuation of a variety of samples, including the fluttering of a bio-mimetic elastomer butterfly. Our numerical studies are in remarkable agreement with experimental results and demostrate a fascinating actuation behavior arising from the interplay between microstructural topology, macroscopic geometry and stimulus-response. |
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