Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S56: Interactions of Elastic Structures with Fluids and Granular Matter IFocus
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Sponsoring Units: GSNP DPOLY Chair: Douglas Holmes, Virginia Tech Room: BCEC 255 |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S56.00001: Interactions of slender elastic structures with complex media like granular materials Invited Speaker: Evelyne Kolb Slender elastic structures are extremely flexible and get easily unstable. As a consequence of their high geometrical aspect ratio, slender structures can be sensitive to low forces of various origins and exhibit complex mechanical behaviors due to the associated couplings with the surrounding medium, whatever it is (fluid, elastic medium, gels, frictional substrate, granular material…). |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S56.00002: Elastogranular Packing of a Loop David Jay Schunter, Jr., Regina K. Czech, Douglas Peter Holmes Confined thin structures are ubiquitous in nature. Spatial constraints have led to novel packing strategies at both the micro-scale, as when DNA packages inside a capsid, and the macro-scale, observable in plant root development. Previous work has focused on growing thin structures confined by rigid boundaries. Comparatively, much less is known about the behavior of slender growing structures constrained by deformable boundaries, such as granular materials. By varying the arc length of an elastic loop injected into a granular array of mono-disperse, soft, spherical grains of varying initial number density φ0, we investigate the resulting behavior of this model elastogranular system. At low φ0, the elastic loop deforms as though it were hitting a flat surface by periodically folding into the array. Above a critical packing fraction φc, local re-orientations of grains cause the elastic loop to deform as though striking a curved surface, leading to the emergence of a distinct circular packing morphology. These results will bring new insight into the packing behavior of wires and thin sheets (where the same morphologies have been observed) and will be relevant to modeling animal burrowing & locomotive strategies, and developing smart, steerable needles. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S56.00003: Elastic tweezers for a vibrated granular bead Paul Rambach, Thomas Salez, Yacine Amarouchene, Pascal Damman Optical tweezers are usually used to capture colloidal particles. In this talk, we will show that this method can be transferred in the realm of vibrated granular matter. It has been shown that the velocity distribution of mechanically vibrated beads is gaussian provided that a randomization of the collisions is achieved. This can be done via a rough surface, a layer of glued beads for instance. First we checked that a bead on top of a such rough surface undergoes a Brownian motion. Then we attached the bead to a flexible string and analyzed the fluctuations of motion. It revealed the drastic influence of the string elasticity, acting as a confining potential. This being equivalent to the harmonic potential achieved with optical tweezers. This new experimental setup paves the way to study stochastic behavior of small particles that should mimic colloidal suspension in 2D. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S56.00004: Using an Olami-Feder-Christensen model with velocity weakened friction and variable stress transfer range to model slip-stick behavior in a sheared granular fault gouge system Rachele Dominguez We present a variant of the Olami-Feder-Christensen (OFC) model with variable stress transfer range and a residual stress modified according to a velocity weakened friction force. The model displays dynamical modes similar to those observed in a sheared granular fault gouge laboratory system. For long stress transfer ranges, we find dynamical phases including a steady sliding state, a stick-slip state with periodic system-wide slipping events, and an intermittent state with both steady sliding and occasional slipping. For medium stress transfer ranges, we find additionally intermediate phases with large slipping events occurring in localized patches of the system. We compare simulation results of the model to laboratory results for the sheared granular fault gauge system. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S56.00005: Mechanical properties of jammed elastogranular columns Xin Jiang, Mo Eydani, Kate Flanagan, Casey Ricks, Douglas Peter Holmes Composite materials have unique properties due to the creative assemblies of their constituents. A mixture of grains and rods can enable the formation of stable structures via granular jamming. Understanding how these constituents govern the mechanical properties of the jammed structures is crucial for devising relevant engineering designs. Here, we examine freestanding columns composed of rocks and strings, and propose a simple physical model to explain the resulting structure’s mechanical behavior. The results indicate that exterior fiber mainly contributes to stiffness, while interior fiber increases the resilience and toughness of the structures. By assembling the grains and rods in a programmable way, structures with robust mechanical properties can be formed. The results provide guidelines that allow the design of jammed elastogranular structures with desired mechanical properties. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S56.00006: Scaling Effects in Composite Elastogranular Materials Mo Eydani, Xin Jiang, Casey Ricks, Kate Flanagan, Douglas Peter Holmes Composite elastogranular materials combine the characteristics of their constituents, resulting in interesting and distinct mechanical properties. In this study, the effect of scale on the mechanical properties of composite string-rock materials comprised of elastic fibers embedded in a granular rock matrix is investigated. An experimental study is carried out to explore whether the relative global size of a composite elastogranular medium affects its bulk mechanical properties. In particular, the stiffness, strength and ratcheting-like behavior of string-rock composite is investigated for a cylindrical form. The stiffness of composite string-rock columns is shown to be scale-independent while the strength and compaction are observed to be driven by the scale. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S56.00007: Modeling the physical constraints of latch mediated, spring actuated systems Mark Ilton, Andres Cook, Nicholas Heller, S. N. Patek, Alfred Crosby, Sarah Bergbreiter, Emanuel Azizi, Gregory P. Sutton, Sarah Longo, Sathvik Divi, Crystal Reynaga, Jeffrey Olberding, Ryan St Pierre, Suzanne Cox Certain plants and animals utilize elastic structures made of biomaterials to actuate rapid movements. In some of the most extreme cases, which inclues mantis shrimp and trap-jaw ants, a latching mechanism is used to control the spatio-temporal flow of energy from the organism to their environment. In this work, we model the physical constraints of latch mediated, spring actuated systems. An integrated approach rooted in physical principles that includes the loading and release of energy from these systems is presented. This approach reveals the inherent tunability of these systems, and is applicable to both biological and synthetic systems. We identify critical transitions that depend on the materials properties and geometry of the spring and latch components. The resulting kinetic energy output of these systems is ultimately limited by physical constraints placed on the organism by interaction with their environment and their control dynamics. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S56.00008: Elastic feathers spread impact force Sunghwan Jung, kinjal Bhar, Brian Chang, Lorian Staker, Emmanuel Virot, Romain Paris, Christophe Clanet Northern Gannets are seabirds that frequently employ a hunting tactic called ‘plunge-diving’ in which they dive through the water surface at high-speeds to catch underwater prey; often reaching speeds of up to 24 m/s at the moment of impact. It can result in forces as high as 500 N acting on the bird’s neck during impact, yet the bird escapes uninjured, despite making 20-100 dives per foraging trip. However, little is known about how such high impact forces affect the rest of the body. The goal of this study is to investigate the role played by the feathers in spreading the hydrodynamic impact force on the skin around the impact zone. We model the feathers as elastic beams taking into account their pre-curvature and non-uniform cross-section. Results from our experiments with polycarbonate beams suggest that the interaction of feathers on the skin patch redistributes the force, thereby reducing the impact on any particular area of the skin. |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S56.00009: Entanglement of Elastic Fibers in low Reynolds Fluid Flow Hossein Sharifazadeh, Yayun Du, Ali Beyzavi, Mohammad Khalid Jawed We report a discrete differential geometry based simulation for entanglement of elastic rods that couples the structural elasticity, hydrodynamic loading, and rod-rod contact. In nature, such entanglement can play a beneficial role, e.g. bundling in bacterial flagella; however, can also be a nuisance, e.g. trichobezoar (hairball) in human stomach. We consider a model system where elastic rods are injected, at a controlled velocity, one after another into a spherical tank full of viscous fluid. The simulation tool for this process is a combination of the following four components: the Discrete Elastic Rods algorithm for the elasticity of the rods, the modified mass method to impose the boundary condition, a penalty force-based collision detection and handling algorithm, and the Resistive Force Theory for hydrodynamic loading. We conduct experiments with a collaborative robot that injects the rods at a prescribed velocity and video records the process. In both experiments and simulations, we find that entanglement process is governed by the ratio of the elastic bending forces to the viscous forces. By exploring parameter space, we construct phase boundaries delineating the regions of entanglement. |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S56.00010: Formation mechanism and morphological behavior of high aspect-ratio folds in compressed films Derek Breid, Sachin Velankar A thin, rigid film that is subjected to compression can exhibit a variety of buckling modes depending on the nature of the applied compression and the boundary conditions at the film surface and edges. Among the lesser-known buckling modes is the development of sharp, tall folds which are typically observed as a response to a swelling stress in a confined region of a larger film. Here, we conduct experiments to identify the essential physics underlying fold growth and the effect of constraints on the mode of buckling. We show that the folding mechanism is not limited to cases of rapid swelling, but emerges more generally in any compressed thin film which is imperfectly bound to a solid substrate. The only essential condition to achieve this mode of buckling is that the film must be able to slide along the substrate without allowing air or fluid to intrude between the film and the substrate. We demonstrate that this can occur through purely mechanical application of stress. We also show the effects of the size of the compressed region, the film thickness, and the stress application rate using swelling-based methods, and characterize our results using a model combining Flory-Rehner swelling theory with buckle initiation mechanics. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S56.00011: Rate-controlled wrinkling and folding of thin elastic films bonded to viscous substrates Sachin Velankar, Sourav Chatterjee, Junyu Yang, Rui Huang, Xianheng Guan, Luka Pocivavsek, Enrique Cerda We examine the buckling of a thin elastic film floating on a viscous liquid layer which is itself supported on a prestretched rubber sheet. Releasing the prestretch in the rubber at a controlled rate induces viscous stress in the liquid, which compresses the elastic film, causing buckling. This approach allows compressive strains of several ten percent to be applied. Experiments and simulations show that two different buckle modes can appear. The first is that the elastic film develops roughly sinusoidal wrinkles. Wrinkling can be captured qualitatively by a linear stability analysis starting from a stress state that is calculated from a shear lag approach (Chatterjee, Soft Matter, 2015). The second is the appearance of tall, well-spaced folds which tend to appear at small liquid layer thickness. Folds are separated by regions where the film remains more-or-less flat. To our knowledge, the appearance of such folds in elastic films bonded to viscous supports is a new discovery. While their exact origin remains unclear, we argue that folds are energetically favorable (i.e. reduce bending energy more) as compared to wrinkles. But because folds can take a long time to develop, wrinkles may appear as a temporary intermediate state. |
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