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 B17: Textiles and topology I: Sheets, Entanglement and ElasticityFocus Live
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Sponsoring Units: GSNP DSOFT Chair: Daria Atkinson, University of Massachusetts Amherst |
Monday, March 15, 2021 11:30AM - 12:06PM Live |
B17.00001: Mechanics-based simulation of textiles Invited Speaker: Christopher Rycroft Textiles have a myriad of uses in modern life, from clothing to filters to ship sails, and are also promising candidates for use in next-generation soft robotic devices. Here, we develop a high-performance code for simulating textiles at the level of individual yarns. Each yarn is represented using a spline basis and is simulated using Lagrangian dynamics to take into account stretching, bending, friction, and contact. After calibrating physical parameters for an individual yarn, we demonstrate that our code can make quantitative predictions about the stress–strain responses of macroscopic textile samples. These simulations therefore form the foundation of a systematic analysis of the macroscopic properties of textiles in terms of yarn topology and mechanics. |
Monday, March 15, 2021 12:06PM - 12:18PM Live |
B17.00002: Linked loops on a lattice: Formulating knitted fabric elasticity with coarse-grained curve mechanics Michael Dimitriyev, Krishma Singal, Elisabetta Matsumoto Knitted fabric is a 2D mechanical metamaterial constructed from loops of quasi-1D yarn, topologically entangled in 3D. Different fabrics are designed by combining knitted stitches, the basic unit of linked yarn, in a variety of patterns. One stitch can be transformed into another merely by swapping the order in which segments of yarn cross over each other. It is therefore remarkable that different stitch patterns give rise to dramatically different macroscopic elastic responses. We explore this relationship between microstructure and macroscopic response by coarse-graining the yarn-level mechanics. This leads to a reduced lattice model that depends only on the configurations and spatial arrangements of the cross-over regions. In the low-stress regime, the fabric elasticity is governed by collective deformations of the cross-over regions and thus depends on stitch pattern. In the high-stress regime, the yarn mechanics within individual cross-overs is dominant, leading to nonlinear strain-stiffening that is observed in experiments. To conclude, we show how this coarse-grained model additionally provides a microscopic basis for the mechanics of curved fabric. |
Monday, March 15, 2021 12:18PM - 12:30PM Live |
B17.00003: Quantifying the Elastic Nature of Knitted Materials Krishma Singal, Michael Dimitriyev, Elisabetta Matsumoto Knitted materials involve the manipulation of a 1D material into a complex 2D sheet. We manipulate yarn into a lattice of slip-knots, known as stitches, where the types of stitches have significant impact on the resulting fabric and its elastic properties. The constituent yarn is normally inextensible, yet when manipulated into these stitches, the fabric possesses emergent elastic behavior. We show through uniaxial applied strain experiments that the bulk stress-strain relationship of knitted fabrics have two key regimes: a linear response in the low stress regime and a nonlinear response with increasing stress. The length of the low stress regime corresponds to the softness of the fabrics and how extensile the stitch patterns are from their topology. The nonlinear regime stems from the yarn to yarn interactions; eventually as the stitches are stretched, they reach a point where the stitch can no longer deform and the yarn must stretch. We characterize the non-affine deformation of the fabrics by tracking a 5 by 5 grid of points while undergoing deformation. We quantify the programmable nature of knitting and extract parameters to create a continuum model of knitted materials. |
Monday, March 15, 2021 12:30PM - 12:42PM Live |
B17.00004: A formal language for describing knitted textiles using swatches Shashank Markande, Elisabetta Matsumoto Knitted textiles are a type of 2D programmable material. Their emergent elastic behavior can be 'coded' in by changing the entanglement of yarn at the stitch level. Therefore, the natural formulation to describe and study complex knitted textiles is a language with a grammar. We propose such a framework, where the alphabet is composed of irreducible swatches -- knitable textile knots and links -- that can be concatenated leading to higher order or compound swatches. In this talk, first we define what are irreducible and reducible/compound swatches -- analogous to prime factorization of natural numbers. Then a set of operations acting on two or more swatches is described to define the syntax and grammatical structures of the proposed language of knitted textiles. Using this approach, we then quantify an upper bound on the number of words of fixed length in the vocabulary of the language corresponding to a knitting protocol capable of generating a finite alphabet. This work is supported by the NSF grant, NSF DMR1847172. |
Monday, March 15, 2021 12:42PM - 12:54PM Live |
B17.00005: Leveraging Temporal Constraints for Simplified Knit Representation Jenny Lin, James McCann Knitting is a fabrication technique capable of producing incredibly complex shapes with a wide range of mechanical properties from a single, continous strand of yarn. This flexibility, however, also means that the underlying structure can be extremely complex, which makes reasoning about said structure equally difficult. While it is possible to describe the yarn geometry using knot theory, the difficulty of the knot equivalence problem means either the scale or the type of knit object must be limited to make computation on this representation tractable. To address this, our work seeks to leverage the temporal constraint inherent in the knitting process. By assuming the knitting process consumes yarn monotonically (a fact which holds true for the most common knit operations), we can establish an order on the loops produced by the knitting process. This allows each loop to be treated as a strand within a braid, a group that is much easier to compute equivalence on than knots. A simple representation would open the avenue for applications such as yarn level simulation and fast pattern validation. |
Monday, March 15, 2021 12:54PM - 1:06PM Live |
B17.00006: Tensional twist-folding and scrolling of sheets Julien Chopin, Arshad Kudrolli The simple act of twisting a flat sheet has been used since ancient time in making surgical sutures, food packaging, redeployable fabric wearables, and has been proposed more recently as a strategy to make multifonctinal yarns. In this talk, we will discuss experiments where hyperelastic sheets are undergoing extremely large shape change as they are held under tension and twisted way above the initial wrinkling instability. Using 3D shape reconstruction based on x-ray Computed Tomography, we demonstrate that the wrinkles grow in amplitude and localize to form a star-shaped accordion folded spiral structure with self-contact at a half-turn. As the twist is increased further, a nestled helical structure forms at the waist, before a secondary instability occurs which leads to recursive folding and a scrolled yarn. We found that each of the major shape transformations causes the rate of change of applied torque to change sign, leading to a sawtooth variation with twist. We will present a tensional twist-folding model that quantitatively explains the morphologies observed and associated mechanical response and can serve as a guide for fabrication of yarns with precise control of crosssectional architecture. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B17.00007: Designing Knitted Fabrics with Programmable Properties Xiaoxiao Ding, Christopher Rycroft Programmable materials that are engineered to be highly dynamic in form and function have attracted research interests in the most recent decade. We believe that knitted fabrics can also be programmable and yield an enormous design space to explore: in addition to varying the fiber mechanical properties, there is a whole gamut of topological relations for how the fibers are knitted together. Here, we develop a simulation framework for modeling fabrics at the level of individual fibers, which we quantitatively validate against experiment. We use this framework to systematically explore how the macroscopic mechanical properties of knitted fabrics depend on the knit topology. We consider both fabrics made of a single knit topology, plus composite fabrics where multiple knit topologies are present. Our framework allows us to understand the interplay of knit topology, geometry, and elasticity, and permits the design of knitted fabrics with programmable properties. |
Monday, March 15, 2021 1:18PM - 1:30PM Live |
B17.00008: Improving Fit on Clothing using Bent Seams Lewis Campbell, Kelly Delp, Elisabetta Matsumoto Traditionally, clothes are designed to take advantage of right-left symmetry and to accommodate the differences between the front and back of the human body. This results in flat pattern pieces shaped for the front and back geometries, then attached by seams that run parallel to the line of symmetry. Therefore, the fit of clothing is defined by the property of the material and shape of the two-dimensional pieces that meet at the seams. Seams are simple surface arc curves which are chosen to create positive or negative curvature. Here we study the way seams made from complicated curves can distribute curvature more evenly across the entire garment. For discrete surfaces, Gaussian curvature at a point is given by the angle defect. However, we can smear out this angle defect by locally bending the curve. The bending process adds or subtracts to the angle defect causing positive or negative curvature. By implementing these bent seams, a better fit is achieved for the human body. |
Monday, March 15, 2021 1:30PM - 1:42PM Live |
B17.00009: Cohesion of a bird nest. Theo Godefroy, Ignacio Andrade-Silva, Olivier Pouliquen, Joel Marthelot Anyone who has tried to pick up pine needles knows that the more we compress the aggregate the easiest it is shaped into a complex geometrical form. One striking difference between aggregates of flexible frictional fibers and other granular materials like rigid spheres is the effective cohesion of their assembly. We need to add glue or water capillary bridges between grains to shape aggregates of spherical particles and build sandcastles. For fibers, no need for glue to build a nest. Here we study an assembly of monodisperse flexible fibers. We first use X-ray microtomography to characterize the geometry of the initial assembly, the number of frictional points and bending curvatures of the fibers. Using force-displacement measurements, we characterize the variation of the macroscopic cohesive strength of the aggregate with the geometry of the fibers, the fibers mechanical properties and the packing preparation. Finally, we relate the macroscopic mechanical behavior of the assembly with the filament reorganization at the microscopic scale. |
Monday, March 15, 2021 1:42PM - 1:54PM Live |
B17.00010: Every mechanism in 2d generates an exotic space of soft modes Michael Czajkowski, Zeb Rocklin Mechanical metamaterials can be designed with special deformation pathways (mechanisms) that allow them to change shape dramatically with little energetic cost. However, even in materials designed around a uniform mechanism, experiments reveal ubiquitous nonuniform deformations. Here, we show that the mechanism constitutes an approximate local symmetry of the material, and that in 2d each distinct mechanism generates a unique class of nonuniform deformations lower in energy than standard elastic modes. We introduce an illustrative new class of general mechanisms in lattices of corner-sharing quadrilaterals and use them to show that these modes are governed by a single second-order nonlinear differential equation which guarantees mechanical compatibility. This equation induces a bulk-boundary correspondence in which specifying the amplitude of the mode on the boundary fixes the deformation of the bulk, irrespective of additional microscopic details, which we then exploit to achieve on-demand target shapes. Our investigation shows that a single mechanism in 2d will generically give rise to an exotic space of nonlinear nonuniform soft modes, while in higher dimensions multiple mechanisms must be at play simultaneously to generate such nontrivial spaces of soft motions. |
Monday, March 15, 2021 1:54PM - 2:06PM Live |
B17.00011: Knit architectures for sensing and actuation Vanessa Sanchez, Robert J Wood The field of robotics has begun to adopt textiles as materials of choice for wearable robots and smart garments due to their light weight, high flexibility, and breathability. To realize an entire wearable robot, many subsystems must be considered including sensors, actuators, and integration components, all requiring specialized mechanical properties. Current cut-and-sew manufacturing strategies pair these discrete textile components together; however, they are effort-intensive and can lead to failure at connection points. Weft knitting represents an especially promising alternative for creating fully integrated wearable robots because it uses only a single additive manufacturing process, and because of the mechanical diversity achievable through varying the topology via stitch design. Surprisingly, knit actuators and sensors have predominantly utilized jersey and garter structures to date. Here we explore a candidate structure to program fluidic actuation and a candidate structure to improve resistive strain sensing sensitivity, both using alternative knit stitches. We evaluate how features of the textile structure, including yarn linearity, intersections, and yarn stiffness, program the fabric mechanics necessary for these applications. |
Monday, March 15, 2021 2:06PM - 2:18PM On Demand |
B17.00012: A soft adaptive gripper for extremely small or flexible objects Uhsang Ahn, Subyeong Ku, Yong-Lae Park, Ho-Young Kim Recent developments in soft grippers have shown promise in manipulating a wide variety of objects through utilization of various gripping mechanisms, such as granular jamming and multi-fingered grippers. However, manipulation of small bodies or extremely flexible sheets, such as pins, porous fabrics, and biological membranes, remains difficult. Here we present a soft, pneumatically-actuated gripper that exploits the buckling effect of an elastic membrane to either engulf sub-millimetric objects or pinch and separate flexible sheets from a stack. Our gripper is also able to lift thin sheets, whether artificial or biological, using their edges without causing folds or creases. We further show that important information for dexterous manipulation, such as success or failure of grasping and the dimensions and the material properties of the target object, can be detected by embedded soft capacitive sensors. Models for the gripping and the sensing principles are suggested and potential applications in manufacturing and medicine are explored. |
Monday, March 15, 2021 2:18PM - 2:30PM On Demand |
B17.00013: Dual curvature control using pneumatic actuators Han Bi Jeong, Cheong San Kim, Jonghyun Ha, Seungjoo Lee, Anna Lee, Ho-Young Kim Pneu-Nets, or pneumatic networks have widely been used as extremely light soft actuators capable of gripping and performing a variety of locomotion such as forward and twisting movements. However, when dealing with sophisticated movements involving Pneu-Nets, previous researchers have used separate compartments to form a large system of Pneu-Nets to activate each channel in order to achieve a complex shape or function. Here, we present a novel design strategy of Pneu-Nets to achieve complex forms (dual curvature) from a single channel with a single compartment. Using the idea of strain hardening of hyperelastic elastomers, when controlled precisely to activate different regions of the same compartment, depending on the pressure of air which is present in the channels, two different forms or curvatures can be obtained from a single input to sequentially bend, stretch, and twist. Using Abaqus simulations, along with tensile tests on several combinations of commercial elastomers, Pneu-Nets with dual curvatures are designed and experimentally demonstrated to introduce a new paradigm in the field of soft actuators. |
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