Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V49: Mechanics of Materials ProcessingFocus
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Sponsoring Units: GSOFT GSNP Chair: Frederick Gosselin, Ecole Polytechnique de Montreal Room: BCEC 252A |
Thursday, March 7, 2019 2:30PM - 3:06PM |
V49.00001: Plastic instabilities, mechanochemistry, and a bag of (metal) chips Invited Speaker: Koushik Viswanathan Soft and highly strain hardening metals like Ni, Al, Ta and stainless steels, are notoriously difficult to cut, earning them the moniker “gummy”. This difficulty is well-known for its commercial implications, yet its origins have remained largely mysterious. This talk presents high-speed in situ investigations of this problem in two parts. In the first, we unveil the occurrence of a highly unsteady plastic flow mode, termed sinuous flow, as the cause of this difficulty. Sinuous flow arises due to a surface plastic buckling instability and is characterized by repeated material folding, large local strains (>10) and energy dissipation. The physics of this flow, its dependence on material properties, and manifestation across metals are directly observed. In the second part, we demonstrate how sinuous flow can be perturbed using mechanochemistry. A suitable chemical medium applied to the metal surface causes a local ductile-to-brittle transition by coupling plastic instabilities with interface energetics. Consequently, surface buckling and sinuous flow are replaced by a periodic fracture instability in the presence of the medium, with near absence of defects on the cut surface and significantly lower energy dissipation (~80%). The transition in flow is also reflected in the morphologies of the resulting metal chips. This mechanochemical effect is controllable and largely material agnostic, with many chemical media working equally well across different metal systems. Additionally, the benign nature of the media presents exciting opportunities for fundamentally enhancing deformation processing of metals in industrial settings. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V49.00002: Mechanics of bilayers: What soft matter physics can teach us about shot peen forming of aircraft wing skins Frederick Gosselin, Pierre Faucheux, Martin Levesque Peening treatments (e.g., shot, laser, and cavitation peening) are ubiquitous when designing metallic parts against fatigue failure: by introducing compressive surface residual stresses that oppose crack initiation and growth, they can significantly increase the fatigue strength of treated parts. Peening induced stresses also cause distortions. Although usually seen as an unwanted side effect, these distortions can be controlled to form thin-walled structures into complex contours—a process referred to as peen forming. In this talk, we focus on modeling shot peen forming (a variant that consists in bombarding the parts with small hard shot). By analogy with thin bilayer actuated systems usually encountered in the fields of smart structures, soft robotics, and composite manufacturing, we investigate the shape and stability of peen formed parts. We also present a procedure to generate peening patterns required to form initially flat plates into a desired shape, alongside experimental validation. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V49.00003: Cutting as a Tool for Investigating Crack-Blunting-Involved Soft Fracture Bingyang Zhang, Cheng-Shen Shiang, Shelby Hutchens During tearing of soft elastomers, large deformation occurs due to crack-blunting. The incorporated material nonlinearity alters the fracture response, resulting in a measured fracture energy value higher than the prediction from network binding energy [Lake and Thomas, 1967]. To understand the dependence of fracture energy on the nonlinear constitutive response, we control the crack tip geometry via cutting. A Y-shaped cutting geometry, inspired by Lake and Yeoh (1978), uses two separated “legs” to form a cutting notch that minimizes contact friction. A blade aligned with the notch imposes its radius during cutting. We find that cutting fracture energy increases nonlinearly with large blade radii. The radius sensitivity reflects the strain-stiffening constitutive response governing crack-blunting during tearing. However, as the blade radius decreases, the effect of nonlinearity is minimized and the cutting energy plateaus to a constant that appears to scale with elastic modulus. We evaluate the potential of cutting as a method for characterizing “intrinsic” fracture energy and provide insight into the microstructural origin of the plateauing transition using cutting tests from idealized, end-linked polydimethylsiloxane (PDMS) networks. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V49.00004: Stable and collision-free manipulation of an elastic rod using multiple grippers Andy Borum Despite the widespread adoption of robots in manufacturing, many tasks that involve handling and assembly of deformable objects are still completed manually. Automating these tasks requires reasoning about deformations, instabilities, and self-contact experienced by the deformable objects. As a canonical example of such a task, I will discuss the problem of deforming a slender elastic rod into a desired configuration using two or more robotic grippers that grasp the rod at multiple points. In the case when the grippers are required to grasp the rod at fixed arc lengths, I will show that the set of all equilibrium configurations of the rod that are stable is path-connected. If the grippers are allowed to slide along the rod, I will show that the set of all equilibrium configurations that are both stable and non-self-intersecting is path-connected. The proofs of these two results are constructive and provide analytical solutions that can be exploited when designing algorithms for automated handling of slender structures. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V49.00005: Pleat formation and the geometry of pure bending Tian Yu, James Hanna We will discuss our recent attempts towards understanding the mechanics of pleat forming in soft textile sheets. This is an elastic-plastic bending process that we formulate as a variable-arc-length multi-point boundary value problem for an inextensible rod, with a moment-curvature constitutive relation as input. To determine this moment-curvature relation, we have developed a linkage mechanism that can impose an exact pure bending (constant curvature) state up to high curvatures. A simpler approximate mechanism that nearly matches the exact boundary conditions is nonetheless shown to result in significant curvature variations. Our approach is relevant to recent studies of crease formation in polymers that can inform models of folded deployable structures. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V49.00006: Mechanistic Insights into Mixed Surfactant-Biosurfactant Self-Assembly, Rheology and Surface Properties Samiul Amin, Liangchen Xu, Yao Zhou The global surfactant market is expected to reach $44.9 billion by 2022, of which 67% of the demand is from the personal care and detergents market. Due to consumers’ increasing awareness on product sustainability, the microbially produced biosurfactants are increasingly gaining the interest of the personal care industry as potential alternatives for traditional petroleum derived and chemically synthesized surfactants. However, prior to that, an understanding of how performance criteria such as rheology and interfacial properties are affected by substitution of traditional surfactants with biosurfactants is required. In this study, the effect of rhamnolipid and sophorolipid biosurfactants on the rheological response and interfacial properties of traditional surfactants such as sodium laureth sulfate and cocamidopropyl betaine is explored utilizing a range of advanced characterization techniques. Diffusing Wave Spectroscopy based Optical Microrheology is specifically carried out to gain insights into the short time dynamics in these systems and is also utilized for extracting wormlike micelle structural parameters such as contour lengths and persistance lengths. These insights are utilized to develop unique formulation design rules for biosurfactant based products. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V49.00007: Scratching viscoelastic liquids Asheesh Shukla, Nicolas Chanut, Roland JM Pellenq, Franz-Josef Ulm, Thibaut Divoux Viscoelastic materials are ubiquitous in our everyday life: from skin tissue to butter or bitumen, we are surrounded by materials that display both a viscous and an elastic response under external deformation. Beyond the linear deformation regime, such materials often exhibit complex flow profiles, from spatially heterogeneous ductile flow to crack and fractures. In this presentation, we focus on the latter category of materials and show that a scratch technique, which has been extensively applied for determining the resistance to fracture of solids, can be successfully applied to viscoelastic materials. Using a Rockwell diamond probe of conical shape mounted on a micro scratch tester (Anton Paar), we perform direct measurements of the fracture toughness of various type of bitumen samples at ambient temperature. We show that the fracture toughness of bitumen increases as a power-law of the horizontal scratch speed, independently of the vertical loading rate. The power-law exponent is characteristic of the sample and increases for decreasing penetration grade. Finally, we use the scratch test to quantify the impact of various additives (polymer, glass beads, etc.) on the fracture toughness of bitumen samples. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V49.00008: Plastic damage of soft colloidal-based amorphous materials: a mesoscopic study Cesare Cejas, Gustavo Gimenes, Patrick J Tabeling, Elisabeth Bouchaud Deformation mechanisms, notably fracture, of soft amorphous systems are not yet fully understood. Because of their complex, disordered nature, these materials break involving dissipative processes such as secondary cracking ahead of the main crack tip and local structural rearrangements. The aim of our work is to fabricate and fracture soft amorphous systems composed of large enough “atoms,” so that the above mentioned mechanisms can be observed optically. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V49.00009: 3D printing by tailored extrusion of carbon nanotube inks Crystal Owens, Gareth McKinley, John Hart 3D printing through direct-ink writing builds objects by layerwise deposition of material; and the properties of the final object are governed both by the ink and by the hierarchical organization within and across layers. In extrusion 3D printing of thermoplastics, strength and thermal stability can be improved by addition of rod-like fillers such as carbon nanotubes (CNTs) or carbon/glass microfibers. However, the mechanical properties of 3D printed objects are far from those achieved by spinning of continuous fibers out of the same material.l. We study the flow-mediated structure evolution of rigid rod-like particle-based inks using single-walled carbon nanotubes (SWCNTs) at high concentrations from 0.7-1%wt. We report the influence of processing parameters such as the flow rate, rate of elongation, and rate of reaction or diffusion on the strength, conductivity, and dimensions of the extruded filament, and of printed test artifacts. Our results suggest that 3D printing processes for architected materials can be improved by incorporating key principles of fiber spinning. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V49.00010: Electrospinning Polyelectrolytes from Complex Coacervates Xiangxi Meng, Sarah Perry, Jessica Schiffman Electrospun fibers are canvases that can be tailored towards a wide variety of applications. However, traditional electrospinning often involves organic solvents that can cause cytotoxicity concerns. Here, I will highlight our revolutionary fibers that form using only water and salt. Polyelectrolyte complexes (PECs) form due to the electrostatic complexation between oppositely-charged polymers. We have recently demonstrated that by exploiting the salt-driven plasticization of PECs, we can enable the electrospinning of ultra-stable solid fibers from an aqueous solution containing a pair of strong polyelectrolytes and salt. Electrospun PEC fiber mats are stable over a wide range of pH values, ionic strength conditions, and many organic solvents. To address the challenge of delivery, we encapsulated a library of dyes into the coacervate phase and subsequently, achieved highly-loaded electrospun fibers. Finally, I will propose a mechanistic understanding of the design rules for electrospinnable coacervates by correlating polymer chain length, with coacervate phase behavior, and as-spun fiber morphology. The overall goal of the talk is to illustrate our recent findings and how these results can guide the green engineering of multifunctional fiber mats. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V49.00011: Modeling of shot peen forming using non-Euclidean plate theory Vladislav Sushitskii, Guy Levasseur, Willem Marinus van Rees, Martin Levesque, Frederick Gosselin Shot peen forming is a versatile technique for shaping large thin panels by impacting them with thousands of high-velocity millimeter-sized shots. The process is widely used in aerospace, notably to form wing skins. Two main factors hinder the process’ efficiency: the lack of accurate and simple modeling tools and the lack of automation. Without modeling, the process’ setup relies on a lengthy trial and error procedure. Our project is intended to fill this gap and to provide the industry with a reliable and efficient modeling software. The software is based on innovative theoretical framework of non-Euclidean plate theory relying on Riemannian geometry. This theory was initially developed to describe growth-induced reconfiguration of thin organic tissues, and in terms of mechanics these processes share many similarities with peen forming. It is the incompatibility between local stretching and curvature induced by different mechanical processes that is viewed as the reason of reconfiguration. The accuracy and performance of our software were examined in laboratory conditions by comparing simulations with experimental results for the case of large 1x1m aluminum plates submitted to peen forming. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V49.00012: A deep learning approach to solving the peen forming inverse problem Wassime Siguerdidjane, Farbod Khameneifar, Frederick Gosselin, Guy Levasseur
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Thursday, March 7, 2019 5:18PM - 5:30PM |
V49.00013: The effect of cryogenic thermal cycling on potential energy states and mechanical properties of metallic glasses Nikolai Priezjev The structural relaxation, potential energy states, and mechanical properties of a model glass subjected to thermal cycling are investigated using atomistic simulations. We study a non-additive binary mixture which is annealed with different cooling rates from the liquid phase to a low temperature well below the glass transition. The thermal treatment is applied by repeatedly heating and cooling the system at constant pressure. We find that poorly annealed glasses are relocated to progressively lower levels of potential energy over consecutive cycles, whereas well annealed glasses can be rejuvenated at sufficiently large amplitudes of thermal cycling. The structural transition to different energy states is accompanied by collective nonaffine displacements of atoms that are organized into clusters, whose typical size becomes larger with increasing cooling rate or temperature amplitude. We show that the elastic modulus and the peak value of the stress overshoot exhibit distinct maxima at the cycling amplitude, which corresponds to the minimum of the potential energy. The simulation results indicate that the yielding peak as a function of the cycling amplitude for quickly annealed glasses represents a lower bound for the maximum stress in glasses prepared with lower cooling rates. |
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