Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S16: Extreme Mechanics: Morigami, Metamaterials, and Elasticity |
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Sponsoring Units: GSNP DPOLY Chair: Gregory Grason, University of Massachusetts-Amherst Room: 401 |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S16.00001: Surface patterning by using plastic deformation Atsushi Takei, Lihua Jin, Hiroyuki Fujita We presents a method of surface patterning using plastic deformation. Localized deformation pattern is formed on a surface of a bi-layer system composed of elastic substrate and plastic thin film. With the stretch beyond the yield stress of the film, the film is deformed plastically, and the mismatch of the lengths between the film and the substrate is induced at the release of the stretch. Consequently, the mismatch induces buckling on the surface. With the stretch $\lambda_0$ > 1.5, the deformation of the surface is localized unlike conventional wrinkle patterns. The localized deformations of the bi-layer system both in one-dimension and in two-dimension are analyzed through experiments and simulations. Besides the theoretical aspect, we present that our method achieves functional surfaces such as a hydrophobic surface in a simple manner, and also present that our method can be used for surface patterning of a wide variety of geometry such as a flat plane, fiber and micro -channel. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S16.00002: Programmable Mechanical Metamaterials: BiHolar Networks Bastiaan Florijn, Corentin Coulais, Martin van Hecke We probe the mechanics of BiHolar metamaterials, 2D elastic media with a square lattice of circular holes of two different sizes. Biaxial loading of these BiHolar structures leads to a wealth of mechanical responses, including mechanically switchable hysteresis and memory effects. We show that we can program the mechanical response with the loading force and the hole size ratios [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S16.00003: Dynamics of Geometrically Reconfigurable 1D and 2D Magneto-Elastic Lattices Marshall Schaeffer, Massimo Ruzzene Periodic structures are presented that exhibit multistability due to the nonlinearities of magneto-elastic interactions and structure geometry. The multistability of these structures affords them the ability to adapt their properties though geometric reconfiguration, bringing about changes in stiffness and Poisson's ratio, and introducing anisotropy. These changes in structural properties cause drastic changes in wave propagation, which is of interest for mechanical wave control. The dynamic transformation of one-dimensional (1D) and two-dimensional (2D) lattices between stable states are studied through nonlinear numerical simulations. The analysis is conducted using a lumped mass system of magnetic particles. The structures studied include hexagonal, re-entrant, and kagome lattices. Changes in plane wave propagation properties are predicted by applying Bloch theorem to lattice unit cells with linearized interactions. Results from Bloch analysis are then verified through direct numerical simulations. The propagation of plane waves in these lattices before and after topological changes is compared, and large differences are evident. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S16.00004: Complex ordered patterns in mechanical instability induced geometrically frustrated triangular cellular structures Sung Kang, Sicong Shan, Andrej Kosmrlj, Wim Noorduin, Samuel Shian, James Weaver, David Clarke, Katia Bertoldi Geometrical frustration arises when a local order cannot propagate throughout the space due to geometrical constraints. It plays a major role in many natural and synthetic systems including water ice, spin ice, and metallic glasses. All of these geometrically frustrated systems are degenerate and tend to form disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that mechanical instabilities induce complex ordered patterns with tunability. For structures with low porosity, an ordered symmetric pattern emerges, which shows striking correlations with the ideal spin solid. In contrast, for high porosity systems, an ordered chiral pattern forms with a new spin configuration. Our analysis using a spin-like model reveals that the connected geometry of the cellular structure plays a crucial role in the formation of ordered states in this system. Since in our study geometrical frustration is induced by a mechanical instability that is scale-independent, our findings can be extended to different materials, stimuli, and length scales, providing a general strategy to study and visualize the physics of frustration. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S16.00005: Negative post-buckling stiffness of meta-beams Corentin Coulais, Johannes Overvelde, Katia Bertoldi, Martin van Hecke We study the mechanical response of meta-materials whose building blocks undergo buckling. Euler elastica theory describes buckling of slender beams and predicts a positive post-buckling stiffness. Here, we demonstrate experimentally, numerically and theoretically that this limit breaks down when beams become non-slender and that the post-buckling stiffness eventually becomes negative. We further show that the poisson ratio can play the role of an additional design parameter and demonstrate experimentally and numerically that the mechanical response of auxetic meta-beams can indeed become unstable. This paves the way to a new generation of elastic switches, that can be triggered by simple uni-axial experiments. [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S16.00006: Instability and Wave Propagation in Structured 3D Composites Narges Kaynia, Nicholas X. Fang, Mary C. Boyce Many structured composites found in nature possess undulating and wrinkled interfacial layers that regulate mechanical, chemical, acoustic, adhesive, thermal, electrical and optical functions of the material. This research focused on the complex instability and wrinkling pattern arising in 3D structured composites and the effect of the buckling pattern on the overall structural response. The 3D structured composites consisted of stiffer plates supported by soft matrix on both sides. Compression beyond the critical strain led to complex buckling patterns in the initially straight plates. The motivation of our work is to elaborate the formation of a system of prescribed periodic scatterers (metamaterials) due to buckling, and their effect to interfere wave propagation through the metamaterial structures. Such metamaterials made from elastomers enable large reversible deformation and, as a result, significant changes of the wave propagation properties. We developed analytical and finite element models to capture various aspects of the instability mechanism. Mechanical experiments were designed to further explore the modeling results. The ability to actively alter the 3D composite structure can enable on-demand tunability of many different functions, such as active control of wave propagation to create band-gaps and waveguides. [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S16.00007: Capillary Origami with a Twist Timothy Farmer, James Bird Often, when a liquid drop contacts a solid, the droplet deforms to minimize surface energy. For sufficiently thin solids, the solid can instead minimize the combined surface and elastic energy by wrapping around the drop. This mechanism has been used to direct the 3-dimensional self-assembly of 2-dimensional sheets, in a process often referred to as capillary origami. Past experiments have shown that a variety of bending modes can exist for a droplet wetting a thin elastic sheet. However, these studies have only considered interactions between materials with uniform properties and are thus limited to symmetric deformations. In this talk, we present results for asymmetric deformations obtained by controlling these elastocapillary interactions with a pattern of surface chemistries. Our results demonstrate that spontaneous twist can be initiated in a body through a combination of surface chemistry and capillarity. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S16.00008: Shape Selection in Chiral Ribbons - From Seed Pods to Supramolecular Assemblies Hillel Aharoni, Shahaf Armon, Eran Sharon We provide a geometric-mechanical model for calculating equilibrium configurations of chemical systems that self-assemble into chiral ribbon structures. The model is based on incompatible elasticity and uses dimensionless parameters to determine the equilibrium configurations. As such, it provides universal curves for the shape and energy of self-assembled ribbons. We provide quantitative predictions for the twist-to-helical transition, which was observed experimentally in many systems. In addition, we predict bi-stability of wide ribbons and also show how geometrical frustration can cause arrest of ribbon widening. Finally, we show that the model's predictions provide explanations for experimental observations in different chemical systems. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S16.00009: Metric Description of Defects in Amorphous Elastic Materials Michael Moshe, Eran Sharon, Raz Kupferman We suggest a description for dislocations, using a torsion-free Riemannian manifold equipped with a reference metric. This metric expresses the local equilibrium geometry within the material. In this description, dislocations are singularities in the intrinsic curvature structure. The model is not based on a crystalline structure; therefore it can describe dislocations even in amorphous materials. We provide explicit expression for edge dislocation, which is a dipole of curvature. Apparently, higher multipoles of curvature can be used to describe plastic deformations in amorphous materials. The model is supported with experimental results. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S16.00010: ABSTRACT MOVED TO M31.00004 |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S16.00011: Changing shape of elastic shells via electrostatic interactions Vikram Jadhao, Creighton Thomas, Monica Olvera de la Cruz Shape plays a key role in the design of synthetic structures such as biomimetic red blood cells, metallic nanocontainers and colloidal building blocks for self-assembly. It is therefore crucial to enhance our current capabilities to synthesize membranes of desired shapes with precision and provide a simple procedure to induce shape modifications. We show that Coulomb interactions can be used as a tool for designing and manipulating shapes of soft elastic shells at the nanoscale. We investigate the minimal-energy conformations of charged, elastic nanoshells subject to the constraint of fixed total volume for a wide range of electrostatic and elastic parameters. We find that the shape of the shell changes when we decrease the electrolyte concentration in the surrounding environment or increase the total charge on the shell surface. We obtain a variety of smooth shapes that include ellipsoids, discs, and bowls. A discussion on the possible origins of these shapes and related procedures to induce shape deformations is also provided. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S16.00012: Buckling of liquid crystal elastomers in confined geometries Thanh-Son Nguyen, Andrew Konya, Robin Selinger, Jonathan Selinger Liquid crystal elastomers (LCEs) are materials that combine the orientational order of liquid crystals with the elastic properties of polymer networks. Whenever the liquid-crystal order changes (by heating, cooling, or other stimuli), the shape of the polymer network changes. If the liquid-crystal director is nonuniform, then the polymer network is generally frustrated---i.e. the local director favors a certain local strain, but these strains are incompatible; they do not fit together to fill up space. As a result, the shape can become very complex, and it can only be calculated by numerical methods. In order to understand the phenomenon of frustration in LCEs, we consider simple systems where the liquid-crystal director is uniform but frustration is introduced by confinement, so that the sample cannot extend along the director. As the induced strain passes a critical threshold, the system releases part of the frustration by buckling. The simplicity of the system allows us to evaluate several properties of the buckling process analytically, including the threshold strain and the instability wavelength. The analytic results are compared with numerical finite-element simulations of the same geometries, and with related studies of other elastic sheets. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S16.00013: Mechanical properties of warped membranes Andrej Kosmrlj, Kechao Xiao, James C. Weaver, Joost J. Vlassak, David R. Nelson We explore how a frozen background metric affects the mechanical properties of solid planar membranes at zero temperature. Our focus is a special class of ``warped membranes'' with a preferred random height profile characterized by random Gaussian variables $h(q)$ in Fourier space with zero mean and variance $< |h(q)|^2 > \sim q^{-m}$. Using statistical physics tools to treat this quenched random disorder, we find that in the linear response regime, similar to thermally fluctuating polymerized membranes, an increasing scale-dependent effective bending rigidity, while the Young and the shear moduli are reduced. Compared to flat plates of the same thickness $t$, the bending rigidity of warped membranes is increased by a factor $\sim h_v/t$ while the in-plane elastic moduli are reduced by $\sim t/h_v$, where $h_v =\sqrt{ < |h(x)|^2 > }$ describes the frozen height fluctuations. Interestingly, $h_v$ is system size dependent for warped membranes characterized with $m>2$. Numerical results show good agreement with theoretical predictions, which are now being tested experimentally, where warped membranes are prepared with 3D printers. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S16.00014: The Influence of Order and Disorder on Buckling 2D granular layers Andrew B. Croll, Bekele Gurmessa, Antoinette Tordisillas, David Carey, Jingyu Shi The buckling of thin films has recently received considerable attention in both the materials and the continuum elasticity communities. To the former, elastic instabilities form a platform for the mechanical measurement of material properties under increasing degrees of confinement. To the latter, instabilities represent a testing ground for advanced elastic theory. Buckling is also of considerable importance in the evolution of granular systems, which often show deformations that resemble those of continua. Previously, we documented several differences between continuum theory and discrete elasticity in a discrete model of a thin film experimentally constructed from a well ordered (hexagonally packed) layer of colloid scale particles. Here we consider how the structure of the 2D layer influences the buckling process. In particular, we examine the details of how a complex, disordered (glassy) 2D layer resting on soft foundations responds to in-plane compressive stress. We show how the fundamental buckling lengthscale remains identical to that of ordered layers, despite considerable heterogeneity in the motion of the particles. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S16.00015: The Buckling-Fracture Transition in Non-Euclidean Plates Eran Sharon, Yael Klein Non-Euclidean Plates (NEP) are thin elastic plates, in which lateral equilibrium distances of the material are described by a non-Euclidean reference metric. Previous studies showed that such plates buckle spontaneously -- while free of external constraints. In the thin limit the geometry of the buckled configurations approaches the reference metric. In this talk we show the existence of a new, \textit{buckling to fracture}, transition in these plates. Depending on the parameters of the system, NEP might undergo fracture instability instead, or together with, buckling instability. We propose the scaling of this transition and verify it experimentally. Our observations lead us to propose an intrinsic geometrical description of fracture, which is consistent with, but different from Linear Elastic Fracture Mechanics. [Preview Abstract] |
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