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 C17: Textiles and Topology II: Filaments and TanglesFocus Live
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Sponsoring Units: GSNP DSOFT DPOLY Chair: Michael Dimitriyev, University of Massachusetts Amherst |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C17.00001: The generalized capstan equation:
contact mechanics between an elastic rod and a frictional rigid cylinder Paul Grandgeorge, Tomohiko Sano, Pedro M Reis The Euler-Eytelwein equation for the classic capstan problem is often used to model the mechanics of entangled filaments in frictional contact, such as in the cases of ropes wound around poles or belts driven by pulleys. This modeling framework predicts an exponential tension growth along a filament of vanishing thickness and zero bending stiffness, in frictional contact with a rigid cylinder. However, in many physical settings, the sliding filament is neither infinitely thin nor perfectly flexible, thus violating the capstan equation’s underlying assumptions. In this talk, we present an enhanced capstan model based on Kirchhoff-rod theory, which considers both the thickness and elasticity of the sliding filament. Contrary to existing adaptations of the capstan equation, we assume that the extent of the contact region between the filament and the rigid cylinder is unknown a priori. Our results highlight the role of elasticity in setting the contact geometry. In turn, this nontrivial geometry strongly influences the force transmission along the sliding filament. Specifically, we investigate custom-made elastomeric rods, as well as engineering driving belts. Throughout, we validate our modeling assumptions through a combination of FEM and precision model experiments. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C17.00002: Packing Architecture and Mechanical Behaviors of Flexible Filaments Confined in Vesicles Xin Yi, Chao Shi The mechanical interplay between flexible nanofibers and vesicles, is of essential importance not only to the investigation of various cell activities, such as cell shape control cell division and cell movement, but also to the applications on biomedical engineering including drug delivery system and biomedical imaging, as well as nanomaterial hazard prevention. Here we present our recent theoretical work on how packing architectures and mechanical behaviors of confined flexible nanofibers in vesicles are regulated by the the filament length and rigidities. In the case of a single open filament in vesicle, characteristic vesicle configurations such as cherrylike, lemonlike and dropletlike shapes are observed as filaments become more flexible. In the case of a single closed filaments, stiff and short filaments adopt planar shapes such as circles and ellipses, while soft and long filaments exhibit large deformation and adopt tennis seamline and eightlike configurations. Corresponding morphological phase diagrams are determined. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C17.00003: Time-dependent Knotting of Agitated Chains Ingrid Gendron, Katherine Savard, Xavier Capaldi, Luc Capaldi, Zezhou Liu, Lili Zeng, Walter Reisner Agitated strings serve as powerful macroscopic models of knot formation, providing insight in knotting dynamics at the microscale while retaining the ability to explicitly characterize knot topology. Here we present an experimental setup in which knot formation is driven by a tumbling motion along with a software interface to process complex knot data with high crossing numbers. Using this setup, we characterize knotting probability, knot complexity and knot formation dynamics for knots with as many as 50 crossings. We find that the probability of knotting saturates below 80% within 100 seconds of tumbling and that this saturation probability does not increase for chains above a critical length. This is an indication of non-equilibrium knot-formation conditions in our experiment. Despite this saturation in knot formation, we show that longer chains still tend to form knots of higher complexity, likely due to the mobility of the free end which can access a greater number of loops during tumbling. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C17.00004: Bioinspired architected composites with enhanced energy absorption Huan Jiang, Yanyu Chen Inspired by the multiscale configuration of the microstructure of cork, here we create a new type of lightweight architected composite structure with a multilayered arrangement of hard brittle and soft flexible phases. The experiments show that this architected material can absorb four times of energy that of a conventional cellular structure under compressive strains up to 70%. Finite element simulations and 2D digital image correlation (DIC) were conducted to explain the failure mechanisms. It was found that this bioinspired architected composite provides a more uniform strain distribution and higher stress transfer efficiency with a progressive failure mode. Cyclic loading tests were performed to evaluate the shape recoverability. It was shown that the proposed architecture possesses exceptional shape recoverability under the compressive strain of 40%. These remarkable characteristics result from the interplay between soft and hard phase. Intrinsically, the soft phase plays an essential role in absorbing elastic energy during loading and then releasing the stored energy while unloading. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C17.00005: Percolation Threshold of Kinetoplast DNA Networks Joshua Ragotskie, Nathaniel Morrison, Ryan Blair, Alexander Klotz Kinetoplasts are chainmail-like networks of connected DNA loops: we are interested in how their connected topology affects their physical properties. Kinetoplasts have a loop of excess of DNA linkages their edges like the elastic band in a shower cap, but previous topological estimates did not account for this boundary loop. We intend to measure the deformation of kinetoplasts and their topology by measuring their percolation threshold: a critical point at which a sufficient number of links are removed from the structure and it is destroyed. Our numerical simulations based on lattice graphs indicate that the presence of an edge loop leads to two percolation thresholds. We probe the percolation threshold of Crithidia fasciculata kinetoplasts experimentally by staining them with YOYO-1 and examining their disintegration under bright light due to photo-induced double-strand breakage. We observe the outer loop or fragments thereof surviving after the breaks in the interior of each kinetoplast reach percolation, supporting our predictions. With this protocol we can study the mechanics of membranes with varied bending rigidity, and we observe that dynamics are slowed by link removal. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C17.00006: Emergent plasticity and hysteresis in disordered packings of filaments. Nichalas Weiner, Yashraj Bhosale, Hunter King, Mattia Gazzola A bird's cup-nest can be viewed as a disordered packing of slender grains, defined by average quantities -- coordination number and packing fraction; and dependent on grain properties -- flexibility, friction, and aspect ratio. Experimental data from packings of varying aspect ratio grains, subject to cyclic, quasi-static, oedometric compression reveal two distinctly meta- mechanical responses: plasticity associated with rearrangement without damage; and hysteresis associated with static friction rather than viscoelasticity. These qualitative behaviors appear to be common across systems of round grains to extremely fine fibers. One-to-one numerical simulations allow us to relate otherwise inaccessible micromechanical quantities such as contact distributions to bulk behaviors, confirming underlying assumptions regarding their origin. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C17.00007: Energy Harvesting in Soft Materials Nilanjana Ghosh, Derek A. Paley There is a growing demand to increase energy efficiency in robotic applications. Although energy density in batteries has been steadily increasing, a long-duration mission with onboard energy storage increases the weight and volume of the robotic platform. In an underwater robot, an onboard power supply may add to the overall weight of the robot but is offset by the corresponding increase in buoyancy. Nonetheless, it is of interest to avoid recovering underwater robots to swap or re-charge batteries. Prolonged deployments of soft underwater robots can be achieved by harvesting energy from fluid-structure interactions. For example, energy can be harvested using piezoelectric or triboelectric effect. This talk will focus on ongoing dynamic modeling and control of piezoelectric energy harvesting in soft underwater robots. We use planar Discrete Elastic Rod theory combined with an equivalent circuit models of a piezoelectric device to describe energy generation during stretching and bending motion of a soft robotic appendage in a fluid. Parametric studies are planned to determine the optimal energy generation and performance. This work seeks to open new areas for improved energetics of underwater robotics, particularly those constructed from soft, flexible materials. |
Monday, March 15, 2021 4:24PM - 5:00PM Live |
C17.00008: Let me spin you a yarn: fiber geometry and the elasticity of twisted filaments Invited Speaker: Daria Atkinson Flexible bundles of twisted filaments are found in myriad materials across lengthscales, from biopolymers like DNA to more familiar yarns and cables. Ordered ground states in filament bundles, however, are highly geometrically constrained, and we show that only two families of filament textures permit equidistance between the constituent filaments---the developable domains, which can bend, but not twist, and the helical domains, which can twist uniformly, but not bend. Because of this, the spacing between filaments varies along their length when twisted bundles bend, and so two dimensional descriptions, like those used to describe columnar liquid crystals, are inadequate. To better describe the elasticity of non-equidistant bundles, we must account for invariance under reptations: continuous zero energy deformations corresponding to displacements along the filaments. The resulting force balance equations show that constant spacing plays an essential role in the mechanics of filament bundles, with deviations from equidistance generating forces along the filament tangents. We use this gauge-theoretic description of filaments' elasticity to describe the low energy configurations of weakly curved twisted toroidal bundles, showing that this longitudinal frustration leads to an effective bending stiffness which is independent of the filaments' flexibility, and instead determined by the bundle's twist. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C17.00009: Physical trefoil knots: elastic deformation and failure Paul Johanns, Paul Grandgeorge, Tomohiko Sano, Changyeob Baek, John H. Maddocks, Pedro M Reis In its open conformation, the trefoil knot sets the basis of most functional knots. Although the trefoil knot has been studied in the realm of knot theory, their physical counterparts are not investigated thus far. To understand the local geometry of this fundamental knot, we constructed both open and closed physical trefoil knots tied in an elastic rod. We evaluated the influence of elasticity of our physical knot realizations, taking existing geometric models as a reference. Specifically, a combination of X-ray tomography and finite element simulations allowed us to systematically explore the self-contact regions, curvature profiles, and contact pressure. Our findings revealed significant rod constrictions at the entrance/exit of the tight open knot, which could act as precursors for potential spots of structural weakness. Further, we study the effect of local plastic deformation in tight functional knots, including elasto-plastic material filaments. The physical insight gained from this experimental characterization will give us a better understanding of how plastic necking emerges during the tightening process of an initially loose knot with elastic filament squeezing. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C17.00010: Towards an understanding of the mechanical response of aramid fibers at the filament scale Clotilde Richard, Sébastien Joannès, Alba Marcellan Technical fibers, and especially aromatic polyamide fibers, known as aramid fibers, are used as reinforcements in high performance composites. Mechanical characterization at the single fiber scale is challenging, especially when the diameter is as small as 12 µm, but essential to optimize performances at the product scale. In this work, we developed multiaxial characterization techniques at the filament scale. |
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