Seminars and Colloquia by Series

Friday, December 2, 2016 - 15:00 , Location: Skiles 006 , Prof. David McDowell and Shouzhi Xu , GT ME and MSE , Organizer: Sung Ha Kang

Talk by Shuozhi Xu,

Title: Algorithms and Implementation for the Concurrent Atomistic-Continuum Method.

Abstract: Unlikemany other multiscale methods, the concurrent atomistic-continuum
(CAC) method admits the migration of dislocations and intrinsic
stacking faults through a lattice while employing an underlying
interatomic potential as the only constitutive relation. Here, we
build algorithms and develop a new CAC code which runs in parallel
using MPI with a domain decomposition algorithm. New features of the
code include, but are not limited to: (i) both dynamic and
quasistatic CAC simulations are available, (ii) mesh refinement
schemes for both dynamic fracture and curved dislocation migration
are implemented, and (iii) integration points in individual finite
elements are shared among multiple processors to minimize the amount
of data communication. The CAC program is then employed to study a
series of metal plasticity problems in which both dislocation core
effects at the nanoscale and the long range stress field of
dislocations at the submicron scales are preserved. Applications
using the new code include dislocation multiplication from Frank-Read
sources, dislocation/void interactions, and dislocation/grain
boundary interactions.

Crystal plasticity modeling is useful for considering the influence of anisotropy of elastic and plastic deformation on local and global responses in crystals and polycrystals. Modern crystal plasticity has numerous manifestations, including bottom-up models based on adaptive quasi-continuum and concurrent atomistic-continuum methods in addition to discrete dislocation dynamics and continuum crystal plasticity. Some key gaps in mesoscale crystal plasticity models will be discussed, including interface slip transfer, grain subdivision in large deformation, shock wave propagation in heterogeneous polycrystals, and dislocation dynamics with explicit treatment of waves. Given the mesoscopic character of these phenomena, contrasts are drawn between bottom-up (e.g., atomistic and discrete dislocation simulations and in situ experimental observations) and top-down (e.g., experimental) information in assembling mesoscale constitutive relations and informing their parameters.
Friday, November 18, 2016 - 12:00 , Location: Skiles 006 , Luca Dieci and Sung Ha Kang , GT Math , Organizer: Sung Ha Kang
This is an information session about research opportunities related to GT MAP activities.  If you are a math graduate student, please join for free pizza as well.
Friday, October 21, 2016 - 15:00 , Location: Skiles 006 , Prof. Julian Rimoli , GT AE , Organizer: Sung Ha Kang
Most available techniques for the design of tensegrity structures can be  grouped in two categories. On the one hand, methods that rely on the  systematic application of topological and geometric rules to regular polyhedrons have been applied to the generation of tensegrity elementary  cells. On the other hand, efforts have been made to either combine  elementary cells or apply rules of self-similarity in order to generate  complex structures of engineering interest, for example, columns, beams and  plates. However, perhaps due to the lack of adequate symmetries on  traditional tensegrity elementary cells, the design of three-dimensional  tensegrity lattices has remained an elusive goal. In this work, we first  develop a method to construct three-dimensional tensegrity lattices from  truncated octahedron elementary cells. The required space-tiling  translational symmetry is achieved by performing recursive reflection  operations on the elementary cells. We then analyze the mechanical response  of the resulting lattices in the fully nonlinear regime via two distinctive approaches: we first adopt a discrete reduced-order model that explicitly accounts for the deformation of individual tensegrity members, and we then utilize this model as the basis for the development of a continuum approximation for the tensegrity lattices. Using this homogenization method, we study tensegrity lattices under a wide range of loading conditions and prestressed configurations. We present Ashby charts for yield strength to density ratio to illustrate how our tensegrity lattices can potentially achieve superior performance when compared to other lattices available in the literature. Finally, using the discrete model, we analyze wave propagation on a finite tensegrity lattice impacting a rigid wall. 
Friday, September 30, 2016 - 15:00 , Location: Skiles 257 , Tomas Zegard , GT CE , Organizer: Sung Ha Kang

Bio:  Tomas Zegard is a postdoctoral fellow in the School of Civil and Environmental Engineering at Georgia Tech. He received a PhD in Structural Engineering from the University of Illinois at Urbana-Champaign in 2014. Afterwards, he took a position at SOM LLP in Chicago, an Architecture + Engineering firm specializing in skyscrapers. He has made significant contributions to the field of topology optimization through research papers and free open-source tools.   Xiaojia Zhang is a doctoral candidate in the School of Civil and Environmental Engineering at Georgia Tech. She received her bachelor’s and master’s degrees in structural engineering from the University of Illinois at Urbana-Champaign. Her major research interests are structural topology optimization with material and geometric nonlinearity, stochastic programming, and additive manufacturing.    

Topology optimization, an agnostic design method, proposes new and innovative solutions to structural problems. The previously established methodology of sizing a defined geometry and connectivity is not sufficient; in these lie the potential for big improvements. However, topology optimization is not without its problems, some of which can be controlled or mitigated. The seminar will introduce two topology optimization techniques: one targeted at continuum, and one targeted at discrete (lattice-like) solutions. Both will be presented using state-of-the-art formulations and implementations. The stress singularity problem (vanishing constraints), the ill-posedness of the problem, the large number of variables involved, and others, continue to challenge researchers and practitioners. The presented concepts find potential applications in super-tall building designs, aircrafts, and the human body. The issue of multiple load cases in a structure, a deterministic problem, will be addressed using probabilistic methodologies. The proposed solution is built around a suitable damping scheme based on simulated annealing. A randomized approach with stochastic sampling is proposed, which requires a fraction of the computational cost compared to the standard methodologies.
Wednesday, August 17, 2016 - 09:30 , Location: Skiles 249 , Various speakers , Georgia Tech , Organizer: Sung Ha Kang
The workshop will launch the themetic semester on Material for GT-MAP activities. This is a three day workshop: The first two days (Wed, Thurs) focusing on the theme of Material, and third day includes broad research topics, open to introducing your research. See the complete Schedule.
Friday, April 22, 2016 - 15:00 , Location: Skiles 006 , Prof. Ting Zhu , Mechanical Engineering, Georgia Tech , Organizer: Sung Ha Kang
Multiscale and multiphysics materials modeling addresses the challenging materials problems that involve multiple physical phenomena at multiple spatial and temporal scales. In this talk, I will present the multiscale and mulphysics models developed in my research group with a recent focus on energy storage materials and advanced structure materials. Our study of rechargeable lithium ion batteries for energy storage applications reveals a rich spectrum of electrochemically-induced mechanical degradation phenomena. The work involves a tight coupling between multiscale chemomechanical modeling and in situ nanobattery testing. Our study of nanostructured metals and alloys elucidates the effects of nanostructures on the size-dependent ultrahigh strengths and surface/interface mediated deformation mechanisms. Finally, I will present my perspectives on the multiscale and multiphysics modeling that requires a synergistic integration of engineering physics and applied mathematics, in order to design the advanced structural and functional materials to realize their potential to the full.
Friday, April 15, 2016 - 15:00 , Location: Skiles 006 , Prof. Massimo Ruzzene , Aerospace Engineering and Mechanical Engineering, Georgia Tech , ruzzene@gatech.edu , Organizer: Sung Ha Kang
Recent breakthroughs in condensed matter physics are opening new directions in band engineering and wave manipulation. Specifically, challenging the notions of reciprocity, time-reversal symmetry and sensitivity to defects in wave propagation may disrupt ways in which mechanical and acoustic metamaterials are designed and employed, and may enable totally new functionalities. Non-reciprocity and topologically protected wave propagation will have profound implications on how stimuli and information are transmitted within materials, or how energy can be guided and steered so that its effects may be controlled or mitigated. The seminar will briefly introduce the state-of-the-art in this emerging field, and will present initial investigations on concepts exploiting electro-mechanical coupling and chiral and non-local interactions in mechanical lattices. Shunted piezo-electric patches are exploited to achieve time-modulated mechanical properties which lead to one-directional wave propagation in one-dimensional mechanical waveguides. A framework to realize helical edge states in two identical lattices with interlayer coupling is also presented. The methodology systematically leads to mechanical lattices that exhibit one-way, edge-bound, defect-immune, non-reciprocal wave motion. The presented concepts find potential application in vibration reduction, noise control or stress wave mitigation systems, and as part of surface acoustic wave devices capable of isolator, gyrator and circulator-like functions on compact acoustic platforms.
Friday, March 11, 2016 - 15:00 , Location: Skiles 006 , Prof. Glaucio H. Paulino , GT CE , Organizer: Sung Ha Kang
This talk is CANCELED.  Paulino's group's (http://paulino.ce.gatech.edu/) contributions in the area of computational mechanics spans development of methodologies to characterize deformation and fracture behavior of existing and emerging materials and structural systems, topology optimization for large-scale and multiscale/multiphysics problems, and origami. 
Friday, February 5, 2016 - 15:00 , Location: Skiles 006 , Magnus Egerstedt , ECE, Georgia Tech , Organizer: Haomin Zhou
For both talks, see details.

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