Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A21: Morphing Matter: From Soft Robotics to 4D Printing IFocus Recordings Available
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Sponsoring Units: DSOFT GSNP DPOLY Chair: PT Brun, Princeton University Room: McCormick Place W-185D |
Monday, March 14, 2022 8:00AM - 8:36AM |
A21.00001: Embodied Intelligence in Liquid Crystal Elastomer Composites: From Shape Morphing to Soft Robotics Invited Speaker: Shu Yang Programmable shape-shifting materials can take different physical forms to achieve multifunctionality in a dynamic and controllable manner. By pre-programming and reprogramming molecular anisotropy in liquid crystal elastomers (LCEs) and their nanocomposites together with geometric designs in the forms of films, fibers, and microparticles, we show shape morphing from 2D to 3D with combination of curvatures. By incorporating 1D and 2D nanomaterials (e.g. cellulose nanocrystals, carbon nanotubes, graphene and gold nanorods) in LCEs, we demonstrate soft robots with tendon-like actuators that are forceful and adaptive to perform various tasks in response to heat, light, magnetic field, and electric field. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A21.00002: Viscoelastic kirigami plates Shahram Janbaz, Corentin Coulais Kirigami, the art of cutting papers, has been proven as a practical outline to fabricate flexible mechanical metamaterials with complex patterns of instability. In the absence of a well-controlled activation scheme, kirigami metamaterials may deform randomly into various 3D shapes while stretched. Here, we show how viscoelasticity can effectively control the direction of buckling and, therefore, the modes of buckling in such flat materials. Our approach enables reliable switching between various modes in response to the applied strain-rate. Our experimental study confirms the practicality of producing such “viscoelastic kirigami plates” using conventional additive manufacturing techniques. Furthermore, we show that phase-transformation via relaxation can be harnessed to conduct mechanical waves and dynamic pattern evolution in pre-stretched kirigami plates. Additionally, we developed a 1D dimensionless model that explains the requirement of soliton waves in the continuum limit. Our approach can serve as a basis for designing metamaterials with well-controlled and dynamic functionalities that inherit their properties from their viscoelastic kirigami backbone. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A21.00003: 4D-Printing of Photoswitchable Actuators Taylor H Ware Liquid crystal elastomers (LCEs) modified with a photoisomerizable chromophore can be designed to undergo reversible shape change in response to light. The return of the original shape is dictated by the chromophore isomerization kinetics. To decouple isomerization kinetics in the LCE from macroscopic shape change, a photoresponsive LCE has been synthesized with dynamic covalent crosslinking (DA), supramolecular crosslinking (UPy), and azobenzene. Dynamic covalent crosslinking of the LCE enables 3D printing to be used to process the material, which enables the patterning of shape change. During light-driven actuation, UPy crosslinks break and undergo rearrangement to lock the shape change. Locking decouples the spontaneous cis-trans isomerization of azobenzene from the shape change of the material. This material can be reversibly switched from one state to another and used in either state for indefinite periods. After UV irradiation, a LCE with 30% of the repeat units functionalized with UPy and 20% of the repeat units having a DA crosslink is able to fix between 80-95% of the shape change for more than 3 days. The initial shape can be recovered by heating to break UPy crosslinks. Moreover, this shape switching behavior can be repeatedly observed over at least 10 cycles. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A21.00004: Understanding the spring-like behavior of a creased sheet Yasara Dharmadasa, Francisco Lopez Jimenez Folding or crumpling can alter the structural response of a thin sheet due to the presence of plastic creases. This has paved the way for new engineering applications ranging from tunable meta-materials to deployable and flexible structures. To understand the behavior of a creased film, we study the mechanics of a single crease, which is the building unit cell. A crease is defined by its fold angle at rest and the stiffness of its spring-like behavior during further folding or unfolding. Our work focuses on understanding the role of geometry, material laws, and the parameters controlling the crease formation. We conduct experiments to characterize the crease behavior and compare the experimental data with analytical estimations using a 1-D elastica model and 3-D continuum finite element analysis. These tools help rationalize how the localization of plasticity results in the formation of the crease. We observe the crease length to be in the same length scale of the thickness of the sheet and provide a prediction based on curvature concentration along the arc-length. Our analysis has uncovered scaling laws across different geometries and materials that would be useful to determine the behavior of a creased sheet. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A21.00005: Design for underactuated sequencing of bistable inflatable structures Bert Van Raemdonck, Edoardo Milana, Michael De Volder, Dominiek Reynaerts, Benjamin Gorissen In inflatable soft robots, every individual actuator is an underactuated structure since it transduces a single pressure input to a deformation with essentially unlimited degrees of freedom. On a system level, however, soft robots usually are not underactuated as the pressure in each actuator is controlled independently. This requires a large volume of valves and tubing which compromises the softness and performance of the robot. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A21.00006: Smart fluidic circuits for electronics-free untethered soft robots Alberto Comoretto, Luuk C Van Laake, Johannes B Overvelde Soft robotics is a promising technology for many applications, e.g. object handling, bio-medical devices and exploration of unknown environments. However, an important drawback of (fluid-driven) soft robots is the need for hard and bulky components (valves, pumps) and electronics for their control, limiting their potential in real-life applications where tethers restrain their autonomy. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A21.00007: Inelastic deformation morphs elastic-plastic bilayers into helices, rolls, saddles, and tubes Rahul Gopalan Ramachandran, Jonah de Cortie, Spandan Maiti, Luca Deseri, Sachin Velankar A strain mismatch can induce shape changes in elastic bilayers, for example, thermally induced strain mismatch causes bending of bimetallic strips. We show elastic-plastic bilayers undergo shape changes upon stretching and then releasing them due to inelastic deformation of the plastic layer. Our experiments show that when rectangular rubber plastic bilayers are uniaxially stretched to small deformation and then released, they from arches or rolls along the direction of the applied stretch with the plastic on the outside. As the uniaxial stretch is further increased, non-Euclidean saddle shapes first appear, followed by half-tube shapes that bend perpendicular to the direction of the applied deformation with the plastic on the inside. Thus, both the sign and direction of the curvature flips as the applied stretch increases. In contrast, uniaxial strain mismatch in elastic-elastic bilayers only creates arch or roll shape along the direction of the applied stretch; strain-dependent shape changes do not appear. We show that the remarkable behavior of rubber-plastic bilayer is attributable to (1) the formation of wrinkles at the rubber plastic interface, (2) the in-plane compressive yielding in the plastic during unloading. Both these phenomena allow the strain mismatch due to Poisson effects to decouple from the strain mismatch along the stretching direction. We quantify the development of curvature in such elastic-plastic bilayers, and its dependence on thickness and width of the rectangular specimens. Interestingly, thin samples or narrow width samples readily form helical shapes with perversions similar to those seen in plant tendrils. A simple energy-based model was developed to show how the modification of strain mismatch due to inelastic deformation determines the final shape. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A21.00008: Morpho-mechanics of pressurized cellular sheets: From moss leaves to soft robotics. Thomas G Chandler, Dominic J Vella, Arezki Boudaoud, Perla Maiolino Everyday experience shows that cellular sheets are stiffened by the presence of a pressurized gas: from bicycle inner tubes to bubble wrap, the presence of an internal pressure increases the stiffness of otherwise floppy structures. The same is true for plants, with turgor pressure (due to the presence of water) taking the place of gas. However, simple attempts to rationalize this mechanical stiffening suggest that the stiffness should be independent of the pressure, at odds with everyday experience. We will present a model of single-cell-thick sheets and show how a pressure-dependent bending stiffness may arise. We will demonstrate how our model rationalizes observations of turgor-driven mechanisms in plant cells and suggests that turgor is unlikely to provide significant structural support in many monolayer leaves. However, we will show that turgor does provide a way to control the shape of the sheet, in accordance with observations of curling upon drying of moss leaves. Finally, we will present a pneumatically inflated device inspired by our model, whose cell-level asymmetry creates a curvature which mimics that of moss leaves: curved at low pressures, while flat at high pressures. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A21.00009: Pneumatic morphorods: curvilinear shape morphing and stability Trevor J Jones, Etienne Jambon-Puillet, Joel Marthelot, Pierre-Thomas Brun Flexible slender bodies are boundless in nature as versatile tools for locomotion: e.g. elephant trunks, octopus arms, cucumber tendrils. These structures have inspired an array of soft-robotic structures that bend and twist. The use of these tools outside of academic settings is still limited in part due to complex modeling of structures in 3D environment with non-trivial loads and shapes. Here we leverage bubble casting as a means to build linear actuators with controllable and tunable bending. To generate 3-D curves we cast planar curves that bend out-of-plane when inflated to generate torsion. We solve the inverse problem of mapping a 3-D curve to an initial in-plane curve using a physical analog to the Bishop Frame. We explore the mechanical response of the curves when subject to external loads and geometric constraints. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A21.00010: Controlling metric & bending in inflated fabrics. Tian Gao, José Bico, Benoît Roman Inspired from biological morphogenesis in the nature, the concept of shape morphing has received great attention in a range of fields from dynamic optics, tissue engineering, aeronautics to soft robotics. Generally, transforming a flat plate of synthetic materials into a 3D structure involves metric changes, i.e. distorting distances on the surface. However, the full control of a 3D shape also requires the control of extrinsic curvature, i.e. bending. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A21.00011: Multi-morph pneu-net systems with a single input Cheong San Kim, Han Bi Jeong, Jonghyun Ha, Anna Lee, Ho-Young Kim A variety of shape-morphing actuators are adopted as an essential element of soft robots. While most of the existing actuators morph in a single mode, e.g., bending, twisting, or stretching, under a single stimulus, here we report a soft actuation technology that can achieve multiple morphing modes under a single stimulus with different intensities. A pneu-net system with soft chambers of different cross-sectional areas or wall materials is actuated at a relatively softer region first, but increasing the actuation pressure does not bulge the chamber indefinitely. Rather, the strain-hardening effects of hyperelastic elastomers stop the initially actuated chamber from swelling. The increased pressure actuates the remaining chambers that have not gone through strain-hardening. Hence, we can achieve multiple morphing sequentially by elaborate arrangements of the chambers of different stiffnesses. We experimentally demonstrate pneu-net systems that can sequentially exhibit 'bending and stretching', 'bending and twisting', and 'bending of opposite curvature' using a single air port. Our theoretical model combined with strain-hardening measurement data allows us to predict the transient and steady-state shapes of our soft robotic systems. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A21.00012: Modeling self-folding of large-scale structures Anvitha Sudhakar, Mostafa Akbari, Masoud Akbarzadeh, Andrej Kosmrlj We study the morphing of large-scale origami-inspired active structures made from strong and lightweight biodegradable polymer composites. Such morphable structures in response to external stimuli could form the basis for sustainable architecture to reduce the cost, waste, and energy consumption of traditional construction processes. While the basic design principles of small-scale self-morphing origami are well understood, it is unclear how these designs need to be adapted, when gravitational loads become relevant. To investigate the role of gravity, we created a two-part computational model to guide the design of self-morphing large-scale origami structures. The first part, based on finite-strain theory, models individual origami folds that curve because of differential swelling/contraction across the multi-layered material. These results form the basis for the coarse-grained discrete bar-hinge model with active torsion and elastic springs, and gravitational loads. Both parts work together to relate local material/structural properties of activated folds to the global structure deployed on the ground. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A21.00013: A dynamically reprogrammable metasurface with self-evolving shape morphing Xiaoyue Ni, Yun Bai, Heling Wang, Yeguang Xue, Yuxin Pan, Jin-Tae Kim, Xinchen Ni, Tzu-Li Liu, Yiyuan Yang, Mengdi Han, Yonggang Huang, John A Rogers Achieving intelligent soft matter that can self-configure, self-adapt, and even self-evolve is of great importance for many engineering sciences. The past decade has witnessed phenomenal investment in developing responsive metamaterials that can swiftly shift their structures, and henceforth their performing functions. However, creating materials and structures with precise, complex, fast, and reversible programmability and incorporating real-time feedback remains challenging. In this work, we describe a dynamically reprogrammable mechanical metasurface with embedded actuation, sensing, and feedback-control functions for shape-morphing intelligence. The voltage-controlled Lorentz force driving a flexible, conductive 2D mesh in a static magnetic field lays the foundation for a highly integrable and scalable digital-physical interface. A custom-built stereo-imaging setup incorporating multiple webcams enables an in-situ measurement of the 3D out-of-plane deformation of the 2D precursor. With an implementation of a programmable control guided by an optimization algorithm, the metasurface acquires the ability to self-evolve to approach a given target shape in absence of presuming models. The closed-loop structure opens opportunities for physical simulations on non-linear systems. Such an experiment-driven method also exhibits superior advantages in morphing against extrinsic or intrinsic perturbations that theoretical models cannot predict or account for, including environmental changes, external loading, and sample defects. In addition to the morphing intelligence, the metasurface obtains a functional intelligence to adapt its morphology to accomplish prescribed tasks, bypassing any involvement of shape designs. Upon assignment of aims, the direct goal-oriented morphing also allows the metastructure to attain multifunctionality with an ability to decouple naturally coupled structural functions. |
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