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 G16: Extreme Mechanics |
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Sponsoring Units: DSOFT Chair: Jayson Paulose, University of Oregon Room: Room 208 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G16.00001: Inflating balloons with patterned rigidity Gentian Muhaxheri, Christian Santangelo
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Tuesday, March 7, 2023 11:42AM - 11:54AM |
G16.00002: Metamaterials for reconfiguration and object classification Andres F Arrieta, Juan C Osorio, Katherine S Riley Soft metastructures have introduced new opportunities in shape adaptability and complexity reduction of soft robot sensing and controls. Metamaterials have recently been used to process information due to their ability to change its stiffness, adapt to different shapes, and complement traditional computing by introducing interaction with their environment. Metamaterials composed of different dome unit cells have gained interest due to their capabilities of exhibiting different energy minima, inversion path dependency, multiple global stable shapes, adaptability, and tunable stiffness. As each unit can be locally inverted, global scale shapes are generated due to the proximity between units and their interactions. As a result, the metastructure exhibits different global stable states depending on the unit shape and spatial distribution. This nonlinear behavior can be utilized to classify different external stimuli, informed only by the mechanical response of the structure and its interaction with the environment. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G16.00003: Wannier function representation for wave-based neural networks Sima Zahedi Fard, Paolo Tiso, Parisa Omidvar, Marc Serra Garcia Elastic systems present very low power dissipation and high nonlinearity. Therefore, they are a promising candidate for low-power internet of things devices. As an example of this potential, we recently demonstrated an elastic neural network that passively distinguishes between spoken commands, without requiring power or batteries. To translate this promise into actual devices, a challenge must be overcame: Designing elastic neural networks is computationally very hard due to the need for large-scale nonlinear simulations. Even model reduction techniques based on eigenmodes struggle in the nonlinear case because the nonlinear interactions between modes grow quadratically with the problem size. In this talk, we will present a model reduction technique based on a quadratic manifold extension of the notion of Wannier functions, that exploits localization to implement linear-time simulation of nonlinear elastic neural networks. We apply our method to phononic computing, the approach works in other wave-based information systems (photonics, microwave, etc.) |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G16.00004: An implicit simulation framework to handle frictional contact in elastic rods Dezhong Tong, Andrew Choi, Jungseock Joo, Mohammad Khalid Jawed Frictional contact is essential for understanding the assembly of rod-like structures in the practical world, for example, knots, hairs, furs, bacteria, etc. Simulating those structures with accurate frictional contact responses is challenging because of their high geometric nonlinearity. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G16.00005: A centerline-based energy model for elastic ribbons based on neural networks Shivam Kumar Panda, Qiaofeng Li, Mohammad Khalid Jawed We report a simulation framework for elastic ribbons using a neural network-based one-dimensional energy model. The discrete elastic rods (DER) algorithm, originally developed to simulate 1-D rods, was repurposed to simulate elastic ribbons. The vanilla DER could not accurately capture the coupling between the bending and the twisting energies. The discrete elastic plates (DEP) framework, on the other hand, can accurately capture the mechanical behavior of ribbons. However, a plate-based simulation is computationally much more expensive than a rod-based method. For a physically accurate simulation in a computationally efficient manner, we use a neural network as the energy model for the centerline of a ribbon in a rod-like framework. DEP simulations are used to acquire ground truth time-series data of curvatures, twists, and stretch of the centerline of the ribbon under configurations involving bending and twisting. The neural network-based energy model is trained on these data using a neural ordinary differential equation (NODE) framework. Essentially, neural networks are reducing the energy model from 2-D in DEP to 1-D in DER, which leads to a reduced number of degrees of freedom and orders of magnitude computational speed up. Our approach can be taken as an inspiration to formulate non-linear dynamics of a system using neural networks, where it is difficult to capture non-linearity using analytical expressions. Our energy model can serve as a benchmark for future analytical energy models for ribbon. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G16.00006: A geometric mapping from material orthotropy to isotropy: from square beef to rectangular tofu Wenqian Sun, Jayson J Paulose Material orthotropy means that the two fundamental elastic constants, Young's modulus and Poisson's ratio, are different along orthogonal directions; two daily-life examples are beef with muscle fibers aligned in one direction (rectilinear orthotropy) and wood with annual rings (curvilinear orthotropy). We present here a rescaling transformation which can map a rectilinearly orthotropic material into an isotropic one with a different local geometry: metaphorically, a square beef → a rectangular tofu (isotropic). The newly found rescaling transformation justifies the fact that material orthotropy was generally ignored in studies of, for instance, biological membranes; also, it can be used to study mechanical properties of structures that are made of orthotropic materials. We demonstrate the use of the rescaling transformation in the context of an indentation problem for spherical shells and establish that in the absence of pressure, an orthotropic sphere's equator (beef-like) and two poles (wood-like) have the same indentation stiffness, just like an isotropic sphere. For long cylinders, the transformation can also be applied, but in a slightly different manner. We show that the indentation stiffness of an orthotropic cylinder depends on the degree of anisotropy in a fundamentally different way than the spherical case, because the cylinder can deform isometrically. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G16.00007: Can one hear the shape of a filament? How geometry controls the localization of waves in thin elastic structures. Manu Mannattil, Chris Santangelo Several remarkable applications of metamaterials from cloaking to negative refraction subtly rely on wave localization induced by material geometry. Recent work [1] has examined how elastic waves can localize around the inflection point of a thin sheet with spatially varying curvature. Here we consider the vibrations of a curved filament explicitly accounting for both flexural deformations that predominantly bend the filament, and extensional deformations that predominantly stretch it. Using WKB asymptotics for multicomponent wave fields, we show that flexural waves get trapped around the inflection point, whereas extensional waves do not. The analytically computed frequencies of the localized flexural modes also show very good agreement with numerical results. Thus, we expect infinitely long filaments to have discrete, localized flexural modes coexisting with a continuum of extensional waves. These findings have implications on possible excitations of thin elastic structures and raise the possibility of introducing new phenomena not easily captured by effective models of flexural waves alone. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G16.00008: Regularizations of string mechanics Abhinav R Dehadrai, James Hanna We will discuss two examples of regularization in inextensible strings, as exemplified by chains or flexible cables, subject to gravity: (1) In the whipping of the free end of a falling string, velocity, acceleration, and tension follow predictable singular scalings until they peak at finite values that depend on the initial geometry. (2) In a loop of cable, the singular perturbation associated with bending elasticity allows a catenary to close upon itself; this example will clarify some misconceptions about "lariat chains" and "string shooters", in which inertia and drag are less important than they may seem. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G16.00009: New insights from an analogy between a 1d quantum particle and a 3d dynamically and helically buckled rod Tyler A Engstrom In this talk I will show how a minimally coupled nonrelativistic quantum particle in 1d is isomorphic to a much heavier, vibrating, very thin Euler-Bernoulli rod in 3d, whose ratio of bending modulus to linear density is $(hbar/2m)^2$. Axial body forces and terminal twisting couples acting on the rod play the role of scalar and vector potentials, respectively, and within the semiclassical approximation, rod inextensibility plays the role of normalization. This isomorphism leads to some new insights, particularly following the direction from quantum to classical. Among these, orbital angular momentum quantized in units of $hbar/2$ emerges when the force and couple-free inextensible rod is formed into a ring, and the ring vibrates in a toroidal helix mode. Such a ring also extends the Byers-Yang theorem to a classical object. Additionally, when the rod's axial body force is periodic, due, for example, to an alternating pattern of charged and neutral monomer blocks in a stiff polyelectrolyte, the isomorphism yields a new classical analog of a 1d Bloch electron in a magnetic field. A Zak phase can potentially be realized in this system by adiabatically varying the rod's twist. I will end with a discussion of what the isomorphism has to say about mode selection and mode coarsening in dynamical buckling. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G16.00010: Failure by design of confined architected interfaces Adrianos E.F. Athanasiadis, Michal K Budzik, Dilum N Fernando, Marcelo A. Dias In this work, we investigate the mechanical properties of conceptual adhesive joints, in which the role of the adhesive is played by an architected interface joining two plates. We present a homogenisation procedure showcasing characteristic lengths that govern the mode I fracture behaviour of architected interfaces. Hence, we augment existing theoretical frameworks providing increased accuracy and accounting for micromechanical effects. Thereafter, we model the interaction between homogenization lengths and characteristic fracture process zone lengths. The findings are compared against numerical simulations justifying the effectiveness of the method. The theoretical and numerical approaches are inter-winded, revealing a set of critical parameters that needs to be considered when designing architected interfaces subjected to failure. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G16.00011: Size scale-dependent failure of poly(methyl methacrylate) due to projectile impacts Kyle Callahan, Santanu Kundu, Katherine M Evans, Edwin P Chan, William Heard Polymer glasses, such as poly(methyl methacrylate) (PMMA), are often used in impact mitigation applications where impact-resistance, optical transparency and light-weighting are required. However, our understanding regarding the failure behavior of these materials subjected to high-velocity projectile impact from the nanoscale up to macroscale is limited. In this contribution, we study the projectile impact performance of PMMA using two different projectile impact tests. For nanoscale studies, laser-induced projectile impact testing (LIPIT) was employed to investigate the impact performance of thin PMMA films, on the order of a few hundred nanometers in thickness, at strain rates of ~105 to 107 1/s. For macroscale studies, PMMA sheets with thicknesses on the order to 10 mm were subjected to ballistic and hypervelocity impacts in the strain-rate regime of ~106 1/s. By relating the minimum perforation velocity, defined as the minimum impact velocity a material can withstand without catastrophic failure, to specimen geometry and projectile size at these two distinct sizes, we demonstrate how the size-scale of the materials system defines the mechanisms of failure and its impact resistance. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G16.00012: A study of pre-programmed soft Kirigami deployables exhibiting multistability Mrunmayi Mungekar, Vishal Kackar, Shyan Shokrzadeh, Leixin Ma, Wenzhong Yan, Vwani Roychowdhury, Mohammad Khalid Jawed We present fully soft bistable structures that morph from a planar form into pre-programmed 3D shapes. These deployables consist of trilayered composites with a central pre-stretched substrate layer sandwiched between two symmetrically placed unstretched layers on the top and the bottom. This strain mismatch leads to the buckling of the planar structure into a 3D configuration. Inspired by Kirigami, the outer layers are cut along specific patterns, which, coupled with the strain mismatch, control the final shape of the structure. We study the effect of the initial design parameters, such as material and geometric properties of the layers, Kirigami designs, and the initial pre-stretch on the final 3D shape through detailed experimental, numerical, and analytical studies. This analysis culminates in developing a machine learning-aided approach to deduce the required Kirigami design, initial pre-stretch, and size of the planar composite to achieve a specific target 3D shape. This inverse design algorithm and a highly simplified manufacturing process provide us with a platform for the rapid prototyping of fully soft multistable structures. Through this study, we successfully demonstrate the use of these Kirigami structures in creating a manual bistable soft gripper and an autonomous flytrap-inspired gripper robot. This opens up a wide arena of applications, from delicate wearable electronics to deployable aerospace structures. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G16.00013: Elastic continuum modeling of flexible planar kirigami metamaterials Yue Zheng, Ian Tobasco, Paolo Celli, Paul P Plucinsky Kirigami is increasingly being used in the design of complex devices across scales, from soft robots to aerospace structures. Kirigami metamaterials made by repeatedly cutting holes in elastic sheets exhibit exotic properties. In this talk, we will combine experiment and theory to establish a new paradigm for predicting the shape change of a kirigami metamaterial in response to loads. We first provide a coarse-graining rule linking the design of the kirigami cell to the macroscale deformations of metamaterials, which gives geometric compatibility as nonlinear partial differential equations. Next, we develop a continuum elastic model, which accounts for three sources of elasticity: a bulk term that introduces stress when the effective fields deviate from those of a local mechanism, a term that resists gradients in slit actuation, and a term that accounts for hinge bending. We also provide the corresponding finite element formulation and implement it using the commercial software Abaqus. Simulations of the model match experiments across designs and loading conditions. Our work provides a new perspective to model kirigami metamaterials with low computational cost. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G16.00014: Universal response of two-dimensional flexible structures Zeb Rocklin, Michael D Czajkowski Nature and Humanity have both discovered that simple structural motifs can generate strong yet flexible structures that offer a wide range of mechanical phenomenology. At the same time, subtle interactions can have disastrous consequences, from collapsed bridges to misfolded proteins. I will discuss recent progress towards developing unifying principles governing the complex mechanical response of flexible structures. In contrast with a conventional solid with a unique shape, such a structure possesses a rich family of ground states defined by the mathematical compatibility conditions that permit elements in different states to be joined together like jigsaw pieces. This approach captures the real-world response of various systems, including origami sheets and planar mechanical metamaterials, with differing symmetry, coordination (bond) number, symmetry and dimensionality. These give rise to a rich set of phenomena, including mechanical dualities, holographic principles, exceptional points and topologically protected states. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G16.00015: A hamiltonian approach to the bifurcating mechanics of elastocapillary shells held by needles Jean Farago, Wiebke Drenckhan An increasing number of research problems addresses the mechanical response of bubbles onto which a thin polymeric layer has been grown in a manner that their properties are governed by a complex interplay of interfacial tension and elasticity. This “elastocapillary” interplay gives rise to long-term stability or intriguing shape changing capacities and is often quantified by analyzing the inflation and deflation of a bubble held by a needle in a fluid. Even though the response of such objects to an excess pressure can be predicted using modern numerical tools, it remains important to tackle the problem via a theoretical route to reveal more clearly the underlying physics. |
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