IGM Agenda


IGM Colloquium: Geometric Excursions in Computational Design and Manufacturing

Prof. Horeas Ilies, University of Connecticut

Abstract:
We’ve always seemed to be able to fabricate physical artifacts before being able to formally describe what we do and how we do it. Geometry has historically, and naturally, played a key role in the development of new abstractions used to build formal models of physical artifacts and of the associated design and fabrication processes. However, these formal models as well as the associated computational tools are still playing catch up with manufacturing. For example, even as the enthusiasm for 3D printing continues to build, the computational support for this technology is not adequate. In this talk I will review some of our recent efforts in developing valuable solutions to complex (geometric) problems in computational design and manufacturing, ranging from printability analysis in robotic 3D printing, to interactive haptic assembly of complex shapes, and systematic design methods for controllable nano-machines.

Bio:
Horea Ilies is a Professor and Department Head of Mechanical Engineering at the University of Connecticut with a secondary appointment in Computer Science. He holds a Ph.D. degree in Mechanical Engineering from University of Wisconsin – Madison, and received M.S. degrees in Mechanics and ME from Michigan State University, and Technical University of Cluj, Romania. He has several years of industrial experience with Ford Motor Company in research, manufacturing, and product design and development activities. His current research interests center on theoretical and computational aspects for systematic design and manufacturing of engineered systems. Dr. Ilies has received the NSF CAREER award in 2007, as well as several Best Paper awards, and he is an elected member of Connecticut Academy of Science and Engineering (CASE).
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MEchanics GAthering -MEGA- Seminar: Talk1 - The density of interacting quasi-localised modes in amorphous solids; Talk2 - How inertia can facilitate friction; Talk3 - Sudden failure in amorphous materials during quasistatic loading

 Wencheng JiTom de GeusMarko PopovicPCSL, EPFL

The density of interacting quasi-localised modes in amorphous solids by Wencheng JiPCSL, EPFL
Abstract Amorphous solids are very common materials in our daily life, such as glass, toothpaste, mayonnaise, coffee foam, and soya beans. Unlike crystals, amorphous solids do not present topological defects due to their lack of long-range order. Instead they display excitations where a group of particles can rearrange. These essentially local excitations lead to a dipolar change of stress in the medium, which can effectively couple them. One physical quantity related to the local low-energy excitations is a quasi-localized mode whose density follows D(ω)~ω4 [2-3] in glass different from Debye theory, where ω is the vibrational frequency of the quasi-localized modes.
Here, we provide a theory for the density of quasi-localized modes for classical systems at zero temperature, which takes their interactions into account and clarifies their relationship with shear transformations [4-5]. We confirm this relationship by using the molecular dynamics simulations of quasi-statically sheared glasses. 
[1] ArXiv prepring arXiv:1806.01561.
[2] V. Gurevuch, D. Parshin, and H. Schober, Physical Review B 67, 094203 (2003).
[3] E. Lerner, G. During, and E. Bouchbinder, Physical Review Letters 117, 035501 (2016).
[4] A. Argon, Acta Mettalurgica 27, 47 (1979).
[5] J. Lin and M. Wyart, Physical Review X 6, 011005 (2016).

How inertia can facilitate friction by Tom de GeusPCSL, EPFL
Abstract We study the nucleation of slip between two sliding  solids, whereby we focus on a mesoscopic level where the disorder, introduced by the surface roughness, matters. It is at this scale that we can study how different contacts interact through the bulk’s elasticity. A result of this interaction is that the detachment of one asperity can trigger that of other contacts in its vicinity. An interesting question is if such collective effects organise into depinning-like avalanches. Vice versa this system allows the clarification of the debated roled of inertia on an avalanche-like response [1-3]. We argue that, due to the presence of rare weak sites, the response is smooth in the thermodynamic limit. At the same time we find this mechanism not to be efficient, leading to a stick-sliip response in finite systems.
[1] D.S. Fisher, K. Dahmen, S. Ramanathan, Y. Ben-Zion, PRL 78(25), 4885-4888 (1997).
[2] J.M. Schwarz, D.S. Fisher, PRE, 67(2), 021603 (2003).
[3] K. Karimi, E.E. Ferrero, J.-L. Barrat, PRE, 95(1), 013003 (2017).

Sudden failure in amorphous materials during quasistatic loading by Marko PopovicPCSL, EPFL
Abstract The response of amorphous materials to an applied strain can be continuous, or instead display a macroscopic stress drop when a shear band nucleates. Such discontinuous response can be observed if the initial configuration is very stable. We study theoretically how such brittleness emerges in athermal, quasi-statically driven, materials as their initial stability is increased. We show that this emergence is well reproduced by elasto-plastic models and is predicted by a mean field approximation, where it corresponds to a continuous transition. In mean field, failure can be forecasted from the avalanche statistics. We show that this is not the case for very brittle materials in finite dimensions due to rare weak regions where a shear band nucleates. We build an analogy with fracture mechanics predicting that their critical nucleation radius follows ac~(Σ- Σb)-2  where Σ is the stress a shear band can carry.
 
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IGM Colloquium: Building Better Batteries

Professor Vanessa Wood, https://made.ee.ethz.ch/people/prof--vanessa-wood0.html

Abstract:

Lithium ion batteries are multiscale systems, and their performance, cycle life, and safety depend critically on their structure and the homogeneity of the structure from the nanometer to centimeter length scales. In this talk, I will explain how we use a combination of experimental and computational tools to quantify structure of lithium ion battery components across multiple length scales and understand the influence of this structure on performance. We have further pioneering a number of electron, neutron, and x-ray based techniques to study and visualize dynamical phenomena and degradation mechanisms of lithium ion batteries. By better understanding and quantifying the interplay between physical and electrochemical processes, we are able to improve battery performance, extend lifespan, and improve safety through innovative chemistry and manufacturing.

Bio:
Vanessa Wood holds a Bachelors in Science from Yale University in Applied Physics (2005), a Masters in Electrical Engineering and Computer Science, Massachusetts Institute of Technology (2007), and a PhD in Electrical Engineering, Massachusetts Institute of Technology (2009). Her PhD work, with Prof. Vladimir Bulović, was focused on the development of quantum dot LED technology. From 2010-2011 she was a postdoc in Department of Materials Science and Engineering at MIT, working with Professors Yet Ming Chiang and Craig Carter on lithium ion battery flow cell technology.
In 2011, she was appointed as an assistant professor in Department of Information Technology and Electrical Engineering at the Swiss Federal Institute of Technology (ETH Zürich). She received tenure in 2014 and holds the chair in Materials and Device Engineering. She won the 2014 Science Prize in Electrochemistry endowed by BASF and Volkswagen Group and the 2018 Outstanding Young Investigator Award from the Materials Research Society.
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IGM Colloquium : Sustainable and Clean Energy Research @ REaCT

Prof. Klaus Hellgardt, https://www.imperial.ac.uk/people/k.hellgardt

Abstract:
The purpose of this seminar is to give an overview of some of the sustainable and clean energy research themes being pursued at the Reaction Engineering and Catalytic Technology group, Imperial College London. Examples will cover solar fuels, biofuels and clean fossil energy. Solar fuels examples will touch on recent work relevant to the engineering of photo-electrochemical water splitting devices.
Biofuels examples will outline our work on algae based fuels production as well as the transformation of such biomass into crude.
Clean fossil energy will focus on our most recent work in the area of methane pyrolysis.

Bio:
Klaus Hellgardt (KH) is a Professor of Chemical Engineering in the Department of Chemical Engineering at Imperial College London. He is the current Director of Undergraduate Studies. KH’s research focuses on advanced reaction engineering and applied catalysis, with specific emphasis on solar (bio)fuels, smart petrofuels engineering, kinetics, (electro-) chemical and bioreactor modeling, design and application. He is the head of the REaCT group (Reaction Engineering and Catalytic Technology). To date, his cumulative grant support exceeds £20M. He has published over 150 papers, a similar number of conference proceedings, six book chapters and eight patents.
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IGM Colloquium: Folding of a continuum and energy releasing or fluttering rods

Prof. Davide Bigoni, Department of Civil, Environmental and Mechanical Engineering
University of Trento, Italy
 

It will be shown that Cosserat elastic solids with extreme anisotropy may exhibit folding and faulting, the former being the process in which bending localizes into sharp corners separated by almost undeformed elements, while the latter corresponds to the formation of displacement jumps of finite size [1,2]. While faulting can be often observed in geological formations, folding is rarely encountered in nature and is difficult to be described within the realm of the Cauchy theory of elasticity, but is shown to become possible in constrained Cosserat elastic materials.
The nonlinear theory of elastic rods is a framework for describing bifurcation and instabilities of a number of interesting structures, showing for instance configurational forces analogous to those acting on dislocations in solids. Several problems influenced by configurational forces or involving elastic energy releases will be resented, including snaking of an elastic rod [3, 4].
The dynamics of an elastic rod in a cantilever configuration and subject to a tangential follower load of the ‘Ziegler type’ at its end (the ‘Pfluger problem’) is finally addressed. This structure is subject to a Hopf bifurcation, corresponding to the initiation of the so-called ‘flutter instability’. A new experimental set-up has been designed, produced and tested to realize the follower load. Experiments provide the evidence of flutter and divergence instability and provide the first proof that damping sources have a destabilizing effect on the system (the so-called ‘Ziegler paradox’) [5].
References
[1] Bigoni, D., Gourgiotis, P.A. (2016) Folding and faulting of an elastic continuum. Proc. Royal Soc. A 472, 20160018.
[2] Gourgiotis, P.A., Bigoni, D. (2017) The dynamics of folding instability in a constrained Cosserat medium. Phil. Trans. Royal Soc. A, 375, 20160159.
[3] Dal Corso, F., Misseroni, D., Pugno, N.M., Movchan, A.B., Movchan, N.V., Bigoni, D. (2017) Serpentine locomotion through elastic energy release. J. Royal Soc. Interface 14, 20170055.
[4] Armanini, C., Dal Corso, F., Misseroni, D., Bigoni, D. (2017) From the elastica compass to the elastica catapult: an essay on the mechanics of soft robot arm. Proc. Royal Soc. A 473, 20160870.
[5] Bigoni, D., Kirillov, O., Misseroni, D., Noselli, G.Tommasini, M. (2018) Flutter and divergence instability in the Pflüger column: Experimental evidence of the Ziegler destabilization paradox. J. Mech. Phys. Solids 116, 99-116.

Bio:
Davide Bigoni is a mechanician working in solid and structural mechanics and material modeling, wave propagation, fracture mechanics. His approach to research is the employment of a broad vision of mechanics, with a combination of mathematical modelling, numerical simulation, and experimental validation. From 2001 Davide Bigoni holds a professor position at the University of Trento, where he is leading a group of excellent researchers in the field of Solid and Structural Mechanics.
He has authored or co-authored more than 100 journal papers and has published a book on nonlinear Solid Mechanics. He was elected in 2009 Euromech Fellow (of the European Mechanics Society), has received in 2012 the Ceramic Technology Transfer Day Award (of the ACIMAC and ISTEC-CNR), in 2014 he has received the Doctor Honoris Causa degree at the Ovidius University of Constanta and in 2016 the Panetti and Ferrari Award for Applied Mechanics (from Accademia delle Scienze di Torino). He has been awarded an ERC advanced grant in 2013. He is co-editor of the Journal of Mechanics of Materials and Structures and associate Editor of Mechanics Research Communications and in the editorial board of 8 international journals.


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IGM Colloquium : Geometrically frustrated assemblies

Dr. Efi Efrati, http://www.weizmann.ac.il/complex/efrati/

Abstract:

Unlike Lego bricks that perfectly assemble next to one another, in molecular assemblies some misfit is almost always present. The molecular constituents thus must distort in order to form an aggregate, resulting in a frustrated assembly. The generation of geometric frustration from the intrinsic geometry of the constituents of a material is not only natural and ubiquitous but also leads to a striking variety of morphologies of ground states and exotic response properties.
In this talk, I will review the notion of cumulative geometric frustration and discuss two distinct examples of geometrically frustrated assemblies: liquid crystals in 2D, and twisted molecular crystals that form banded spherulites. For liquid crystal, we will present how to quantify the frustration and give specific examples that exhibit super-extensive elastic energy. Motivated by the twisted crystals observed for a wide variety of organic molecular crystals studied by the Kahr group in NYU, we study a model of frustrated assembly that in particular conveys the nano-metric pitch length of the constituents to the tens of microns pitch length observed for the twisted crystalline assemblies.

Bio:

I graduated in 2010 from the Hebrew university of Jerusalem where I did my Ph.D. under the guidance of Eran Sharon and Raz Kupferman studying frustrated elastic structures. I then moved to the James Franck Institute at the University of Chicago where I was a Simons Postdoctoral fellow. Since 2014 I have been an assistant professor in the department of Physics of complex systems at the Weizmann institute of Science.
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