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 YY02: V: Mechanics and More |
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Sponsoring Units: DSOFT Chair: Yiqiu Zhao, The Hong Kong University of Science and Technology Room: Virtual Room 2 |
Wednesday, March 22, 2023 10:00AM - 10:12AM |
YY02.00001: Frank-Read Sources in Nematic Liquid Crystals: Temperature and Strain-Rate Effects Matthew J Deutsch, Cheng Long, Jonathan V Selinger, Robin L Selinger In a crystalline solid under stress, a Frank-Read (F-R) source is a pinned dislocation segment that repeatedly bows out and detaches, generating concentric dislocation loops. We study an analogous F-R mechanism in nematic liquid crystals, where a pinned disclination segment bows out and generates concentric disclination loops. We model this mechanism via a 3D Lebwohl-Lasher rotor model with a Langevin thermostat, representing a uniaxial nematic with equal Frank constants. We model a disclination half-loop pinned to a planar anchoring surface containing two point defects; loop emission is driven by applied director twist. We find that the critical elastic stress to produce loop emission drops with increasing temperature; and that the critical strain for loop emission rises as a function of increasing twist-rate. We also demonstrate that a tethered loop below the critical strain is stable at low temperature, but expands and can become unstable when heated. We compare our results with an analytical model; speculate on how engineered F-R sources can be used to modify rheology and microstructural evolution; and compare with behavior of F-R sources in crystals; and discuss other stimuli that could drive loop emission in passive and active nematics. |
Wednesday, March 22, 2023 10:12AM - 10:24AM |
YY02.00002: Constructing the transition graphs of interacting hysterons Margot Teunisse In a variety of frustrated mechanical systems, including crumpled sheets, origami structures and sheared amorphous solids, unusual pathways have been observed in response to external driving. These include breaking of return-point memory, multiperiodic response to cyclical driving, and transient memory. It turns out that such responses are captured by a model of interacting hysteretic bits, known as hysterons. While the Preisach model of non-interacting hysterons is well understood, interactions lead to a combinatorial explosion of possible responses. We present a strategy to hierarchically construct all state transition graphs for interacting hysterons. This provides us with a framework for understanding the memory phenomena that have been seen in experiment, and opens up the way for rational design of mechanical pathways. |
Wednesday, March 22, 2023 10:24AM - 10:36AM |
YY02.00003: Self folding curved origami Haotian Xiao, Tian Gao, Etienne Reyssat, Benoit Roman, Antonio DeSimone, Tiffany Cheng, Yasaman Tahouni, Ekin Sahin, Dylan Wood, Achim Menges, José Bico In traditional origami facets are connected through rectilinear creases whose angle is actively set by the operator. In a self-folding scenario, setting the folding angle along a crease requires a load concentrated along a line. As a consequence, self-folding origami structures tend to be floppy and are limited to small scales. In contrast, the bending energy of the whole area of the facets can be harvested to fold efficiently a curved crease. Such bending is readily achieved through a classical bilayer effect, which open applications to self-folding origami structures. |
Wednesday, March 22, 2023 10:36AM - 10:48AM |
YY02.00004: Morphological Computation - Nonlinear Materials for Nonlinear Control, Sensing and Computation Helmut Hauser With the rise of soft robotics the focus of the design process for machines has shifted to nonlinear materials and clever mechanisms. The underlying idea is to exploit the often nonlinear dynamics of compliant morphologies to implement beneficial functionalities. This includes the physical embodiment of control, sensing, computation and even learning. This is partly motivated by the large number of examples from Nature, where we can see that biological systems rely heavily on their body morphology to survive in and interact with a complex, noisy and often unpredictable world. Morphological features endow biological systems with impressive levels of energy efficiency, robustness, resilience, and the ability to learn in complex environments. The approach to transfer these capabilities to intelligent machines through the use of clever morphologies is often referred to as morphological computation. Opposed to classical robotics, which actively suppresses any nonlinear and complex dynamics in bodies to facilitate modeling and control, morphological computation proposes to actively embrace and exploit nonlinear dynamical features. This implies a radical shift of how we should design and built machines. In order to be able to realize the full potential of morphological computation we need better materials, more intelligent structures, and novel mechanisms that allow us to design dynamic and responsive morphologies. |
Wednesday, March 22, 2023 10:48AM - 11:00AM |
YY02.00005: Micromechanics of strain stiffening in stochastic network materials Md Nishan Parvez Many biological and man-made materials have a random fiber network as primary structural component and belong to the broad class of network materials. A subset of these materials exhibits hyperelastic behavior characterized by strong strain stiffening. In this work we evaluate the origins of strain stiffening and discuss the relative contributions of geometric and constitutive nonlinearities, and of the bending and stretching deformation modes of fibers. The deformation is strongly controlled by instability modes which emerge recurrently during deformation. We observe that the formation of stress paths is a consequence of the interplay between the bending and axial modes. The effect of the network architecture is also discussed. |
Wednesday, March 22, 2023 11:00AM - 11:12AM |
YY02.00006: Effect of concentration fluctuations in Active Polar fluids. Purnima Jain Active Polar Fluids (APF) are a system consisting of head-tail asymmetric self-propelled particles (SPPs) suspended in a fluid medium. These complex active fluids show spectacular collective behavior spanning subcellular scales to oceanic scales such as the cytoskeleton, bacterial suspensions, fish schools, e.t.c. The flocking or the ordered state where all the particles move in a common direction is not always stable to small perturbations. It can destabilize into a disordered state to form complex spatiotemporal patterns. The earlier works studied such instabilities in the Stokesian regime or in the case where concentration is assumed to be homogeneous. In our work, we study the effect of fluctuations in the concentration of "extensile" or "pusher" like polar SPPs at small Reynold's number (Re |
Wednesday, March 22, 2023 11:12AM - 11:24AM |
YY02.00007: Non-reciprocal reorientation mechanism exhibits flocking Soumen D Karmakar, Rajaraman Ganesh A non-reciprocal alignment interaction [1] that reorient the self-propulsion direction of circular disks along the inter-particle separation and away from the neighboring disks is found to exhibit flocking in a system of extremely small area fraction of 15 percent. The non-reciprocal alignment interaction is considered to be extremely short-ranged, and it effects the neighboring particles that comes within a small fraction of their diameter. Interestingly, the flocking phase is observed in a specific range of the strength of reorientational interaction [1], and the system reenters the homogeneous phase without any global dynamical ordering in the limit of large strength of alignment. Flocking bands are found to move with a speed [1], depending on the self-propulsion speed of the particles, without forming any shock front. The system is further investigated to explore the spatio-temporal correlation of various dynamical parameters. On the other hand, reversing the reorientational interaction [2] of the particles results in completely new mechanism of motility-induced phase separation. |
Wednesday, March 22, 2023 11:24AM - 11:36AM |
YY02.00008: Topological kinks in odd elastic metamaterials Jonas Veenstra Non-reciprocal interactions in mechanical materials can generate exciting material properties such as asymmetric (odd) elastic moduli. |
Wednesday, March 22, 2023 11:36AM - 11:48AM |
YY02.00009: Why do clamped sheets wrinkle under tension ? José Bico, Benoit Roman, Matteo Ciccotti, Julien renaud, ludovic brivady When a rectangular sheet has two opposite edges clamped and pulled apart, |
Wednesday, March 22, 2023 11:48AM - 12:00PM |
YY02.00010: Distinguishing strength from stability in a jammed granular column with interstitial fluid Jeffrey S Olafsen, Mihan H McKenna Taylor, Oliver-Denzil S Taylor A wide variety of data exists to describe structures composed of granular materials of different particle sizes and shapes for a variety of fluid saturations. These assays can be used to describe on a case by case basis the physical characteristics, such as s-wave and p-wave velocities that are dominated by either the granular structure or the interstitial fluid matrix. What is lacking is a more universal description of the granular+fluid system that can predict global characteristics such as strength and stability. We present a low-dimensional 'phase space' energy model that outlines contributions to relative strength and stability of a jammed system from both granular structure and interstitial fluids as determined by experimental parameters. While the model does not include higher order effects (spatial or temporal dependence of the parameters), it nonetheless demonstrates the overall role that granular temperature plays in both the relative strength and stability of the system in a manner that allows these two characteristics to be distinguished. |
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