Predicting Damage in Aerospace Structures  Due to Adverse Weather Encounters
by İbrahim Güven, Mechanical and Nuclear Engineering, Virginia Commonwealth University
Date: 19.02.2024
Time: 15:30
Location: VYKM1
Abstract:
There is renewed interest in hypersonic flight with applications in defense and civilian aerospace. Nontrivial chances of weather encounters with airborne particles (raindrops, ice particulates, volcanic ash) exist at lower altitudes. Predicting structural damage due to raindrops at hypersonic velocities is an open problem owing to the complex multiphysics involved. This talk will first describe the physics of the high-speed droplet impact and then demonstrate a computational solid mechanics approach, peridynamics, for damage predictions. Droplet-shock layer interactions, coupling with computational fluid dynamics, 2D vs. 3D, and other relevant topics will be discussed. 
Short Bio:
Ibrahim Guven is an Associate Professor of Mechanical and Nuclear Engineering at Virginia Commonwealth University (VCU). He was an Assistant Professor of Materials Science and Engineering at The University of Arizona. Ibrahim spent two summers as a Faculty Fellow at the Air Force Research Laboratory. He was a Visiting Professor at the University of Rennes I, France, multiple times. Ibrahim is a recipient of the NASA Group Achievement Award for outstanding work in developing materials for space exploration, which was awarded to participants of the collaborative project he worked on alongside Prof. Wardle, US-COMP Space Technologies Research Institute.

CRSS Determination: Combining Analytical Framework and Surrogate Neural Networks
by Orçun Koray Çelebi
(University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering)
 
DATE: July 18, 2023 (Tuesday)
TIME: 14:00-15:00
ROOM: VYKM-3
 
Abstract:
 
The yield strength of a crystalline structural material is a fundamental mechanical property predominantly governed by the friction (critical) stress for a dislocation to glide. Existing approaches for critical stress determination are highly unsatisfactory because of empiricism associated with determination of dislocation “core-width” and nature of core-advance. This study proposes a predictive model addressing both shortcomings. The core-width is rigorously determined from an optimized balance between continuum strain-energy and atomistic misfit-energy of the dislocation’s core. The strain-energy is calculated using the fully-anisotropic Eshelby-Stroh formalism accommodating the inherent mixed characters of the partials constituting the extended dislocation. The misfit-energy is determined from critical fault-energies of the slip-plane input to a novel misfit-model capturing the lattice structure of the slip-plane and involving the discrete Wigner-Seitz cell area at each lattice site, advancing over an 80-year old misfit-energy model that has missed the role of both concepts. For the first time in literature, the nature of motion of the extended-dislocation’s core is rigorously derived from an optimized trajectory of its total-energy. It is shown that each partial’s core moves intermittently (“zig-zag” motion), and not together, allowing the stacking-fault width to fluctuate during advance of the extended-dislocation. The critical stress is shown to involve a trajectory-dependent combination of Schmid factors for each partial, also revealed for the first time. The proposed model is used to predict critical stress for multiple FCC and HCP materials including pure metals, solid-solution alloys, and High Entropy Alloys (HEAs), displaying excellent agreement with experiments. Further, hypothetical combinations of material properties are employed to train a machine learning-based Surrogate Neural Network (SNN), and the ones of real materials are utilized to validate the SNN model yielding a 94% accuracy for 1,033 materials. The generated dataset is used to unravel the sensitivity of each material parameter to the predicted CRSS establishing a general trend for the FCC materials guiding the field in achieving superior mechanical properties. The work opens future avenues for rapid reliable assessment of a multitude of compositions across varying lattice structures, addressing a major void in structure-property prediction for structural materials, also instrumental for ab-initio materials design.
 
Short-Bio:
 
Orcun received his B.Sc. degree in Mechanical Engineering from Bogazici University in 2018. He is currently a Ph.D. candidate in Mechanical Science and Engineering Department at University of Illinois at Urbana-Champaign. His research focuses on computational & theoretical modeling of plastic deformation mechanisms (slip and twinning) in metallic materials (pure metals, alloys, and high entropy alloys) employing Density Functional Theory (DFT), Molecular Dynamics (MD), Machine Learning (ML), and Monte-Carlo Simulations.

Human-Machine Interaction with Soft Growing Robots
by Fabio Stroppa
Kadir Has University, Department of Computer Engineering

 
DATE: Nov 29th, Tuesday
TIME: 15:00
ROOM: VYKM-2

Abstract:
Artificial intelligence and robots are becoming more autonomous every day; yet, they still rely on human intervention to accomplish certain tasks. Other times, the nature of the task itself requires robots and humans to work together. Therefore, semi-autonomous telerobotic systems allow both humans and robots to exploit their strengths, while enabling personalized execution of a remote task. However, for soft robots with kinematic structures dissimilar to those of human operators, it is unknown how the control over task execution should be allocated between the human and robot. In this talk, I will present some of the late research on interaction with soft growing robots, focusing on full teleoperated interfaces that allow for easy for matching of the human and soft robot kinematics, a wide study on interaction paradigms between humans and soft robots, and finally how to optimize the fabrication of soft robots for specific tasks.
 
Bio:
Fabio Stroppa (Eng., Ph.D.) is a researcher in Artificial Intelligence and Human-Machine Interaction. He received the B.S. and M.S. degrees in Computer Science Engineering from Polytechnic University of Bari, Bari, Italy, in 2011 and 2013, respectively, and the Ph.D. in Perceptual Robotics from Scuola Superiore Sant’Anna, Pisa, Italy in 2018. He received postdoc training at CHARM Lab, Stanford University, California, USA from 2019 to 2021. He is currently an Assistant Professor in the Department of Computer Engineering at Kadir Has University, Turkey, where he is also head of EVO Lab. His publications and main research interests deal with computer vision for control purposes of robotic devices, robotic-based neurorehabilitation, bioinformatics, virtual reality, search and optimization methods, and artificial intelligence.

Material Interfaces Inspired by Catch Bond Adhesins
by Kerim Dansuk

Northwestern University, Department of Mechanical Engineering

DATE : November 25, 2022 (Friday)
TIME : 14:00-15:00
ROOM : VYKM-4

Abstract:

Over the last few years, there has been a transition away from traditional engineering materials to new advanced materials that exhibit complex architectures with improved mechanical properties. Most of the inspiration for these new materials comes from nature, where organisms have evolved an immense variety of macro and nanoscale shapes and structures with clever mechanisms. Adhesion proteins are particularly inspiring for novel materials because they exhibit conformational dynamics that enables them to form special non-covalent interactions called ‘catch bonds’ with their ligand, where dissociation lifetime of ligand-protein complexes is enhanced by mechanical force. Intuition suggests that application of a tensile force on a chemical bond should tend to shorten the bond’s lifetime, making it more likely to break, but catch bonds defy this notion. If implemented in material systems, catch bonds are predicted to address trade-offs between strength and reconfiguration, two diametric material properties that are primarily governed by the strength of intermolecular interactions. This work is a multifaceted approach combining molecular simulations and adhesion theory to establish strategies for designing material interfaces that incorporates catch bond features. Based on adhesin properties, we proposed design guidelines for reproducing the catch bond phenomenon in synthetic systems and created mechanical designs that mimicked protein ligand interaction and exhibited catch bond behavior reliably and predictably under thermal excitations. We demonstrate that catch bond functionality can be achieved using simple molecular mechanisms and provides design rules for making catch bond nanoparticles and linkages, which paves the way for engendering emergent force-tunable interfacial kinetics in synthetic materials.

Bio:

Kerim completed his B.S. in Mechanical Engineering at Bogazici University. After finishing his PhD in Mechanical Engineering at Northwestern University, he continued to work in NU as a Postdoctoral Scholar. His research focuses on applying computational modeling and statistical thermodynamics to design procedures for nanocomposites with adhesin-inspired interfaces.

Confluence of Electrochemistry and Mechanics: From Engineering the Rechargeable Batteries to Corrosion in Extreme States

by Asghar Aryanfar

(American University of Beirut, Department of Mechanical Engineering)

DATE : October 07, 2022 (Friday)
TIME : 14:00-15:00
ROOM : VYKM-2
 
[pdf version]
Abstract:

During the recent decades, the portable electronics (cell-phones, laptops, etc.) have entered the daily lifestyle, and require exponentially-increasing versatility and computational power. Hence, they demand portable electricity source necessitating the boost in terms of energy density, safety, efficiency and sustainability. On the other hand, the ever-increasing need for harnessing the green renewable energy as a potential replacement of the pollutant fossil fuels for applications such as electric vehicles, requires their capture and management via stationary smart infrastructures. The electrochemical systems, such as rechargeable batteries are the prominent answer for the in abovementioned applications. Therefore, while the exploitation of new high-energy density materials/composites for high-power applications is unavoidable, herein we delve into the engineering of the advanced electrochemical devices (batteries) and phenomena (corrosion) as well as their coupling with the mechanics at the interfaces, by performing multi-physics modeling and electrochemical experiments as the following:

•  Dendrites: Understanding the key components driving the ionic motion and formation of the growing destructive microstructures, we devise and investigate new charging methodologies to shorten and minimize them, either by real-time tuning of the charging forms, or spectral variation in the environmental parameters. In particular, noting the significant spatiotemporal scale gap between the experiments (∼ mm, ∼ms) and typical MD simulations (∼ nm, ∼ fs), we develop a new coarsegrained (CG) predictive model which is extendable to experimental regimes. Such model which passes up the information from the lower-scale atomistic interactions provides possibility of the affordable simulation for the formation of dendritic micros-structures. (Fig. 1).
•  Corrosion: We develop a diffusion-reaction framework, coupled with external stress field during the non-stoichiometric equilibrium to address the state of corrosion of the material. The established model anticipates the mechanical failure during the prolonged oxidation and extreme temperatures, both before (Fig. 2) and after (Fig. 3) the fracture and formation of cracks.• Composites: We will establish percolation-based frameworks to analyze and enhance the electrical and thermal conductivities of the 2D (thin) and 3D (thick) binary polymer composites with inclusion of fillers with higher conductivity. In broader sense, we additionally develop percolation-based efficacy measure for fiber-reinforced concrete in flexural loading and establish computational tool for capturing the rheological properties (i.e. viscosity) of super absorbent-filled concrete. As well, using percolation tools, we develop geometric-based percolation framework for estimating the size distribution of aggregates, traditionally performed via sieve experiments.

Bio:

Asghar Aryanfar received the B.S. in Civil and Mechanical Engineering (double major, top 2%) from Sharif University of Technology, Tehran, Iran in 2009 and the M.S. and Ph.D. degrees in Mechanical Engineering from California Institute of Technology, in 2010 and 2015, respectively. He is currently Assistant Professor of Mechanical Engineering at American University of Beirut (2019−present). Prior to current position, he was visiting faculty at Caltech (2018 − 2019) as well as lecturer at Faculty of Engineering at Bahçesehir University (2016 − 2019). Before then, he was Postdoctoral Associate at University of California, Los Angeles (UCLA) (2015 − 2016). Aryanfar’s research has been in the application of multi-physics modeling and experimental electrochemistry into engineering of the energy storage and conversion devices, materials and and exploitation of their interfacial phenomena. Particularly, his research on safety of high-energy rechargeable batteries has appeared as the Cover image of the Journal of Chemical Physics and he has been interviewed in CNN for his 1st prize winning invention of novel wastewater treatment system from the Gates Foundation. Current projects are the material/interfacial physics and include analysis and design of state-of-the-art sustainable rechargeable lithium metal batteries and prediction of heterogeneous cracking behavior for electrolytic membranes exposed to extreme temperature/pressure.

Phononics at the Macroscopic and Microscopic Scales: Recent Advances in Complex Band-Structure Engineering and Atomic-Scale Resonant Thermal Transport
 
by Mahmoud I. Hussein
 
(Alvah and Harriet Hovlid Professor, Ann & H.J. Smead Department of Aerospace Engineering Sciences, Department of Physics, University of Colorado Boulder)
 
DATE : January 05, 2022 (Wednesday)
TIME : 11:00-12:00
ROOM : VYKM-1
 
PDF version
Abstract:
 
Phononics is an emerging field that seeks to elucidate the nature of intrinsic mechanical motion in both conventional and artificially structured materials, and use this knowledge to extend the boundaries of physical response at either the material or structural/device level or both. The field targets primarily acoustic, elastic, and/or thermal properties and usually involves the investigation and utilization of complex wave mechanisms encompassing one or more of a diverse range of phenomena such as dispersion, resonances, dissipation, and nonlinear interactions. The field bridges multiple disciplines across applied physics and engineering, and spans multiple scales reaching the atomic scale where a rigorous definition of phonons resides–quanta of lattice vibrations.
At the mascroscale, the mechanisms of local resonance [1] and inertial amplification [2] have been introduced intrinsically in material systems to form metamaterials with salient subwavelength band-gap properties. I will demonstrate how explicitly combining these two concepts within a single framework enriches not only the real part of the elastic band structure, but also both the imaginary wavenumber and imaginary frequency parts. The imaginary wavenumber response will be shown to produce low-frequency bounded stop bands with both strong and broadband spatial attenuation properties. Simultaneously, the imaginary frequency part of the spectrum will be seen to exhibit either enhanced or diminished dissipation, demonstrating unique temporal attenuation properties.
At the microscale, I will present the concept of a locally resonant nanophononic metamaterial (NPM) [3], of which one realization is a freestanding silicon membrane (thin film) with a periodic array of nanoscale pillars extruding out of one or both free surfaces. Heat is transported along the membrane portion of this nanostructured material as a succession of wavenumber-dependent propagating vibrational waves, phonons. The atoms making up the minuscule pillars on their part generate wavenumber-independent resonant vibrational waves, which we describe as vibrons. These two types of waves linearly interact causing a mode coupling for each pair which appears as an avoided crossing in the pillared membrane’s phonon band structure. This in turn (1) enables the generation of new modes localized in the nanopillar portion(s) and (2) reduces the base membrane phonon group velocities around the coupling regions. In addition, the phonon lifetimes drop due to changes in the scattering environment, including both phonon-phonon scattering and boundary scattering. These effects bring rise to a unique form of transport through the base membrane, namely, resonant thermal transport. The in-plane thermal conductivity decreases as a result. I will introduce the concept of an NMP and present thermal conductivity predictions using lattice-dynamics calculations and molecular dynamics simulations. Finally, the potential for this concept to produce high-efficiency thermoelectric energy conversion will be discussed and demonstrated.
 
[1] Liu, Z., Zhang, X., Mao, Y., Zhu, Y. Y., Yang, Z., Chan, C. T., and Sheng, P., “Locally resonant sonic materials,” Science 289, 1734–6, 2000.
[2] Yilmaz, C., Hulbert, G.M., and Kikuchi, N. “Phononic band gaps induced by inertial amplification in periodic media. Phys. Rev. B 76, 54309, 2007.
[3] Davis, B.L. and Hussein, M.I., “Nanophononic metamaterial: Thermal conductivity reduction by local resonance,” Phys. Rev. Lett. 112, 055505, 2014.
 
 
Short Bio:
 
Mahmoud I. Hussein is the Alvah and Harriet Hovlid Professor in the Smead Department of Aerospace Engineering Sciences, and has a courtesy and affiliate faculty appointments in the Departments of Physics and Applied Mathematics, respectively, at the University of Colorado Boulder. He is the director of the Pre-Engineering Program at the College of Engineering and Applied Science, and the director of the Phononics Laboratory. He received a BS degree from the American University in Cairo and MS degrees from Imperial College, London and the University of Michigan‒Ann Arbor. He earned his PhD from the University of Michigan in 2004, and completed postdoctoral research at the University of Cambridge from 2005-2007. Dr. Hussein received a DARPA Young Faculty Award in 2011, an NSF CAREER award in 2013, and in 2017 was honored with a Provost’s Faculty Achievement Award for Tenured Faculty at CU Boulder. He is a Fellow of ASME. In addition, he is the founding vice president of the International Phononics Society and has co-established the Phononics 20xx conference series which is widely viewed as the world’s premier event in the emerging field of phononics. Dr. Hussein’s research interests lie broadly in the fields of phononics and nonlinear wave propagation.

Quasicrystal-Induced Nucleation Mechanism in Undercooled Liquids
 

by Güven Kurtuldu

(Laboratory of Metal Physics and Technology, Department of Materials, ETH Zürich, Switzerland)
 

DATE : July 18, 2019 (Thursday)
TIME : 14:00-15:00
ROOM : VYKM-2

Abstract:

A model alloy Mg69Zn27Yb4 has recently been discovered, which concurrently forms bulk metallic glass (BMG), metastable icosahedral quasicrystals (iQCs), and two crystalline approximant phases from the melt [1]. The following phases were observed (at room temperature) at increasing cooling rate via a recently developed technique, fast differential scanning calorimetry (FDSC): (i) stable Mg and approximant Mg29Zn60Yb11 phase mixture; (ii) metastable Mg and iQC phase mixture; (iii) approximant Mg51Zn20-type metastable particles; and (iv) a glassy phase. Deploying a new experimental strategy, i.e. heating the previously solidified microstructure at ultrafast rates via FDSC, the equilibrium Mg29Zn60Yb11 phase has never been observed to form directly from the melt; instead the metastable iQC phase nucleated first in the liquid and then transformed into a stable approximant phase. Such a transition path (undercooled liquid → metastable QCs → stable equilibrium phase) has also recently been suggested to occur in Al–Zn:Cr [2] and Au–Cu–Ag:Ir [3] alloys. The observations made have significant effects on control over solidification microstructures via grain refinement. The phase transition path minimizes the free energy barrier for nucleation through an intermediate metastable quasicrystal phase due to the low solid–liquid interfacial energy of quasicrystals. The experimental results shed new light on the competition between metastable and stable crystal formation, and glass formation via system frustration associated with the presence of several free energy minima. The rapid heating strategy using FDSC may yield the discovery of hidden transient phases that are key to understanding crystallization pathways in metallic systems, as well as polymers, biological solutions and pharmaceutical substances.

[1] Kurtuldu G, Shamlaye K F, Löffler J F. Metastable-quasicrystal-induced nucleation in a bulk glass-forming liquid, PNAS, 115 (24), 6123-6128 (2018).
[2] Kurtuldu G, Jarry P, Rappaz M. Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al-Zn-Cr alloys: Can icosahedral solid clusters play a role? Acta Mater 61(19):7098–7108 (2013).
[3] Kurtuldu G, Sicco A, Rappaz M. Icosahedral quasicrystal-enhanced nucleation of the fcc phase in liquid gold alloys. Acta Mater 70:240–248 (2014).

Short Bio:

Güven Kurtuldu received his Bachelor of Science degree in 2007 and Master of Science degree in 2009 from the Department of Mechanical Engineering under the guidance of Prof. Sabri Altıntaş working on properties of boron nitride nanotube/epoxy composites at Boğaziçi University. He continued his PhD study in the group of Prof. Michel Rappaz at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland. His thesis focused on effect of minute additions of solute elements on solidification microstructures in metallic alloys. He discovered a nucleation mechanism for which formation of metastable quasicrystals from the liquid is the key to control the as-cast microstructures. He was awarded his PhD degree in 2014. After staying one year as a postdoc in the same group, he joined the group of Prof. Jörg Löffler at ETH Zürich, Switzerland. He is currently working on several projects related to quasicrystal and bulk metallic glass formation, structure of metallic liquids, development of novel experimental strategies via fast calorimetry and microstructure formation in additively manufactured alloys.

Robust Surfaces for Carbon-Free Energy Conversion
 
by Çiğdem Toparlı
 
(Massachusetts Institute of Technology, Department of Nuclear Science and Engineering)
 
DATE : June 24, 2019 (Monday)
TIME : 14:00-15:00
ROOM : VYKM-2
 
Abstract:
 
Degradation of materials results in a loss of the desired properties under service conditions, which can negatively affect the efficiency of many engineering systems. Specifically, the impacts of stability of surfaces play a crucial role on the cost and operational viability of energy conversion and storage devices. First, I will focus on the strengths of a combined, in-situ approach to surface and interface analyses, illustrated with examples from a range of application including oxygen evolution reaction (OER) catalyst and proton uptake properties of thin films. I will also discuss how the electronic and structural properties of materials affect the degradation under operation conditions. Second, I will discuss the design of slick surfaces based on Lifshitz theory to enhance the overall resistance of surfaces for buildup of corrosion scale.
 
Short Bio:
 
Dr. Toparli received her Bachelors of Science degree in Metallurgical and Material Science Engineering in 2011 from Istanbul Technical University. She pursued her PhD studies under the supervision of Prof. Dr. Andreas Erbe at Max Planck Institute for Iron Research in Germany. Her thesis focused on in situ and operando observation of passive film formation on Cu and its breakdown through oxygen evolution reaction (OER). Having been awarded her PhD degree in July 2017, she continued her work in the Interface Spectroscopy group at Max Planck Institute for Iron Research as a postdoctoral researcher for several months. She joined Prof. Dr. Bilge Yildizs’ and Prof. Dr. Michael Shorts’ group at MIT as a postdoctoral associate in January 2018. Her current work focusses on the development of hydrogen and crud resistant coatings for Nuclear applications.

Tribology of Materials Across Length Scales
 
by Ahmet Deniz Usta
 
(University of Wisconsin-Madison, Department of Mechanical Engineering)
 
DATE : May 22, 2019 (Wednesday)
TIME : 15:30-16:30
ROOM : VYKM-2
 
Abstract:
 
Designing reliable and long-lasting assembled structures with desired vibration and acoustics characteristics requires tractable models of energy dissipation and stiffness of interfaces between components. Establishing the physical-basis of such models is challenging due to various length scales and mechanisms involved in vibration transmission across interfaces. Namely, length scales from microscale roughness to waviness contribute to adhesive and frictional response of a rough interface. Besides, material damping, elastic-plastic deformations, rate-dependent material properties, surface chemistry and associated adhesion constitute the major mechanisms governing the adhesive and frictional response even for atomically smooth interfaces. In the first part of my talk, I will be presenting the results of a study on the influence of length scales and different mechanisms on overall damping and tangential stiffness of nominally flat rough surfaces. This section is intended as a summary of the main content of my PhD thesis and will conclude with a discussion on open challenges for a better understanding of interfacial damping and stiffness. In the following section, I will share my findings related to two side projects that I was involved in:

1. improved wear-resistance in laser micropolished Ti6Al4V surfaces
2. tribological and mechanical characterization of human skin substitutes and comparison with human skin.

 
Short Bio:
 
Ahmet Deniz Usta received his BS degree in mechanical engineering from Bogazici University in 2010. After working as a research assistant at the National Nanotechnology Research Center in Ankara and as a vehicle test engineer at AVL in Kocaeli, he started his PhD in the Department of Mechanical Engineering at the University of Wisconsin-Madison in 2013. As a member of Eriten Research Group, a laboratory with research interests in the areas of tribology, contact mechanics and nonlinear dynamics, he participated in several projects on the tribology of metals, polymers, paper products and biological tissues. Currently, he is a PhD candidate in the same department.

Rehabilitation in MRI via Pneumatically Driven Systems
 
by Melih Türkseven
 
(Rensselaer Polytechnic Institute, Center for Modeling, Simulation, and Imaging in Medicine)
 
DATE : December 28, 2018 (Friday)
TIME : 14:00-15:00
ROOM : VYKM 2
 
PDF version
Abstract:

Magnetic resonance imaging (MRI) has been the flagship scanning technology for brain studies over the last two decades, by virtue of its spatial resolution and ability to monitor human soft tissue. In the recent years, there has been a growing interest in developing MRI-compatible robots to exploit MRI’s capabilities for healthcare applications such as surgical operations and physical rehabilitation. Fluid-driven systems offer the ultimate MRI compliance as such systems can be built with non-ferrous materials; however, they are generally oriented for slow operationswith large time constants. Rehabilitation, on the other hand, requires a relatively larger bandwidth for a stable human-robot interaction. This talk will focus on the recent developments at Georgia Institute of Technology towards the use of pneumatically driven tele-operated systems for stroke rehabilitation in MRI. The challenges in the tele-operation of the pneumatic actuators and novel approaches to mitigate the adverse effects of long transmission in pneumatic drive will be presented. The talk will conclude with a discussion on the potential of pneumatically driven systems in human-machine interaction and the corresponding challenges.
 

Short Bio:

Melih Turkseven received his BS degree in Mechanical Engineering from Bogazici University in 2010, and Ph.D. degree in Mechanical Engineering from Georgia Institute of  Technology in 2016. As a student member of the Center of Compact and Efficient Fluid Power (CCEFP), he has worked on the design and control of an MRI-compatible rehabilitation robot at the Bio-Robotics and Human Modeling Lab, Atlanta. Currently, he is a postdoctoral research associate at the Center for Modeling, Simulation, and  Imaging in Medicine (CemSIM) at Rensselaer Polytechnic Institute. His research interests include human-robot interaction, and dynamic systems and control of compliant systems.

Advanced Locomotion Control of Exoskeleton Systems: The Role of Active and Passive Compliance
 
by Barkan Uğurlu
 
(Özyeğin University, Department of Mechanical Engineering)
 
DATE : October 26, 2018 (Friday)
TIME : 14:00-15:00
ROOM : VYKM 2
 
 
Abstract:

The exoskeleton market is exponentially growing as its market size is estimated to surpass 3.4 billion USD by 2024. Likewise, R&D activities for wearable robots and exoskeletons show a significant increase. These systems are increasingly playing an important role in robot-aided walking support, elderly care, and SCI rehabilitation. Since these systems are in physical contact with humans, adjustable physical compliance, transparency and high fidelity control techniques are of importance to shape the next-gen exoskeletons of tomorrow. With this view in mind, the first segment of my talk will succinctly address my earlier research regarding the legged locomotion control of humanoids and quadrupeds.  In the second segment of my talk, I will share my hands-on experiences on two different exoskeleton systems: i) TTI-Exo, a whole body exoskeleton built in Toyota Technological Institute, Japan, ii) XoR, the first self-balancing lower limb exoskeleton with adjustable physical compliance and active disturbance rejection capability, built at the Dept. of Brain-Robot Interface, CNS-ATR, Japan. I will emphasize how the prior hands-on experience on legged locomotion enabled me to create exoskeleton systems that have distinguishable characteristics from the others. The third segment of my talk will disclose my vision concerning the next-generation exoskeleton robots and a roadmap to realistically develop such systems.
 
Short Biography:

Barkan Ugurlu received his Ph.D. degree in Electrical and Computer Engineering from Yokohama National University, Yokohama, Japan, in March 2010. From May 2010 to March 2013, he was a Post-Doctoral Researcher, at the Istituto Italiano di Tecnologia, Genova, Italy, and Toyota Technological Institute, Nagoya, Japan. Between March 2013 and February 2015, he was a Research Scientist at the Computational Neuroscience Laboratories, Advanced Telecommunications Research Institute International (ATR), Kyoto, Japan. He currently holds an Asst. Prof. position at the Dept. of Mechanical Engineering, Ozyegin University, Istanbul, Turkey. His research interests include active orthoses and exoskeletons, robot-aided rehabilitation, humanoid/quadruped locomotion control, and human-centered manipulation. He is a Marie Skłodowska-Curie Fellow.

Autonomous Mobile Vehicles and String Stability of Interconnected Vehicles
 
by Sinan Öncü
 
(Ford Otosan, Istanbul Sancaktepe R&D Center)
 
DATE : October 19, 2018 (Friday)
TIME : 14:00-15:00
ROOM : VYKM 2
 
Abstract:
 
Part 1-Overview of Past Research Projects on Autonomous Mobile Vehicles

In this introductory part of the presentation, an overview of past research experiences on autonomous mobile vehicle platforms will be presented with some example applications within the field of automotive and robotics. Some design considerations such as sensor and actuator selections besides the different modelling and control approaches for the realizations will be discussed on the following automated vehicle platforms:
- Autonomous Parallel Parking of a Car-Like Mobile Robot,
- Yaw Stability Control of a Car with Active Steering,
- A Man-portable Rover Operating on Rough Terrains,
- Cooperative Automated Maneuvering Vehicles,
- EcoTwin: Truck Platooning on Highways,
- Clara: A Warehouse Robot with Robust Multi-Sensor Localization,
- Wasteshark: An Aqua-Drone for Cleaning Plastic Waste from the Harbors and Rivers.
 
Part 2-String Stability of Interconnected Vehicles: Network-aware Modelling, Analysis and Experiments

The ever-increasing demand for mobility in today’s life brings additional burden on the existing ground transportation and logistic infrastructure, for which a feasible solution in the near future lies in more efficient use of currently available means of transportation. For this purpose, development of Cooperative Intelligent Transportation Systems (C-ITS) technologies that contribute to improved traffic flow stability, throughput, and safety is needed. Cooperative Automated Vehicles (CAVs) being one of the promising C-ITS technologies, extends the currently available Advanced Driver Assistance Systems technologies with the addition of information exchange between vehicles through Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) wireless communication.A particularly interesting application is the vehicle platooning concept. The general objective of vehicular platooning is to pack the driving vehicles together as tightly as possible in order to increase traffic throughput while preventing amplification of disturbances throughout the string, the latter of which is known as string instability. This technology relies on longitudinal control known as Cooperative Adaptive Cruise Control (CACC). In the scope of CACC, control over a wireless communication network is the enabling technology that makes this realizable; however, given the fact that multiple nodes (vehicles) share the same medium with a limited bandwidth and capacity, wireless communication introduces network-induced imperfections such as transmission delays and packet losses. The impact of these imperfections on string stability requires a careful analysis and tradeoffs between control performance and network specifications need to be made for achieving desired performance under these network-induced constraints. Therefore, in this study we present the design of a CACC system from a Networked Control System (NCS) perspective and a novel modelling framework is introduced. This modelling framework is extended with analysis tools for string stability in the presence of network effects. These analyses can provide the designer with guidelines for making multidisciplinary design tradeoffs between control and network specifications and support the design of CACC systems that are robust to uncertainties introduced by wireless communication. Moreover, the validity of the presented analysis framework is demonstrated via experimental results performed with CACC-equipped prototype vehicles. Experimental results show that the developed NCS modelling framework captures the dependency of string stability on network-induced effects and confirm the string stable operation conditions obtained by model-based analyses.
 
Short Bio:

Sinan Öncü received the B.Sc. degree in electronics and telecommunications engineering and the M.Sc. degree in mechatronics engineering from Istanbul Technical University, Istanbul, Turkey, in 2005 and 2008, respectively, and the Ph.D. degree in mechanical engineering from the Eindhoven University of Technology, Eindhoven, The Netherlands, in 2014. From 2013 to 2016, he was affiliated with the Netherlands Organization for Applied Scientific Research (TNO), The Netherlands, where he worked as a research scientist on the realization of cooperative automated vehicle technologies and their demonstrations with prototype vehicles to governmental institutes, industrial partners, and stakeholders; amongst which are most notably: the first automated driving demo in the Netherlands on public roads in 2013, and The European Truck Platooning Challenge in 2016. Since December 2017, he works as a Senior Software Engineer at Ford Otosan in Istanbul Sancaktepe R&D Center and leads the Horizon2020 project “Optimal fuel consumption with Predictive Power Train Control and calibration for intelligent trucks” (optiTruck). His current research focuses on the development of optimization-based predictive power management control systems for heavy duty trucks. Besides his professional research activities, he is enthusiastic about motorcycles and their dynamics. He combines this interest with travelling, camping, and photography. He enjoys going on long trips with his self-instrumented motorcycle and collects road data for his hobby project on developing an advisory system for safety improvement for motorcyclists.

Bio-resorbable sensors and MEMS energy harvesters for next-generation    transient and self-powered implants
 
by Levent Beker
 
(Stanford University, Department of Chemical Engineering)
 
DATE : March 28, 2018 (Wednesday)
TIME : 13:00-14:00
ROOM : VYKM 2
 
PDF version

Abstract:

Implantable medical devices and the concept of integrating  sensors/electronics into the human body have been intriguing curiosities especially in medicine for many decades. Recent developments in microfabrication and materials science finally have enabled development of sub-mm-sized implants for monitoring of critical parameters such as blood
pressure for heart arrhythmia, pH for GI tract complications, and neural activity for prosthetic applications. However, such devices have energy related problems so that patients need to go through a risky surgery for battery replacement periodically. This talk will cover potential approaches to eliminate this problem and realize next-generation transient/self-powered implants by utilizing bio-resorbable materials or energy harvesting microsystems.

In the first part of the seminar, a bio-resorbable and battery-free implant for wireless artery pulse monitoring will be presented. Design and fabrication of the proposed implant will be detailed by emphasizing particular diseases and surgical operations that require short-term vascular monitoring. Then, the focus will be on energy harvesting implants
which can generate electrical energy within the human body for long-term implants. Widely used neural and cochlear implants increase the quality of life of patients considerably by giving them the ability to move freely and hear. However, because of their power requirement, neural implant users must undergo surgery every 2-3 years just for battery replacement, and cochlear implant users need to change battery at least twice a day. Implantable    micro-electromechanical systems (MEMS) energy harvesters can help to reduce or eliminate the battery replacement problem. In the second part of the seminar, harvesting cerebrospinal fluid (CSF) flow pressure fluctuations within lateral ventricles of the brain using an  aluminum nitride-based piezoelectric-MEMS harvester will be detailed. Concentric ring-boss
diaphragm type harvester design will be introduced, and fabrication and characterization results will be presented. In addition to the MEMS-based harvester, studies on a PVDF-based flexible energy harvester array will also be presented. Then, in the final part, converting eardrum vibrations to electrical signals to stimulate auditory nerves inside cochlea using a PZT/Si cantilever-type resonant harvester to realize a self-powered cochlear implant will be discussed briefly.

Short Bio:

Levent Beker received B.Sc. and M.Sc. degrees in Mechanical Engineering and Micro/Nanotechnology from Middle East Technical University in 2010 and 2013, respectively. During his master’s he worked on fully-implantable cochlear implants. Then, he obtained his Ph.D. in Mechanical Engineering from University of California, Berkeley in 2017 where he worked on energy harvesting from cerebrospinal fluid (CSF) flow inside the brain and pressure sensors for harsh environment applications. He is currently a post-doctoral    research fellow working with Professor Zhenan Bao in Chemical Engineering at Stanford University. His current research focuses on bio-resorbable wireless implants, flexible/stretchable sensors for electronic-skin applications. He received Postdocs at the Interface award from Stanford University, Howard Hughes Medical Institute (HHMI) International Researcher Fellowship, Best poster award at Berkeley Sensor Actuator Center’s Industry Advisory Board Conference, Outstanding presentation award at Transducers 2013 Barcelona, and Best Thesis award from Middle East Technical University.

Non-Schmid slip behavior in shape memory alloys
 
by Sertan Alkan
 
(University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering)
 
DATE : November 17, 2017 (Friday)
TIME : 13:00-14:00
ROOM : VYKM 2
 
PDF Version
 
The plastic deformation mechanisms degrading the functional properties of ordered shape memory alloys will be discussed. In particular, tension-compression slip asymmetries and anisotropic glide resistances will be interrogated on both experimental and theoretical grounds for NiTi alloy. The interplay between the atomistic scale dislocation core displacements and the applied stress tensor components will be demonstrated to play a decisive role in the deviations from the critical resolved shear stress rule, also known as non-Schmid effects.  
The theoretical predictions will be compared with the experimental glide resistance measurements on single crystals within the framework of high magnification in-situ Digital Image Correlation (DIC) technique. Physical insights from the electronic structure will be provided to build a comprehensive understanding on the underlying mechanisms for non-Schmid behavior. The theoretical and experimental anisotropic glide resistance levels will bridged to the macro-scale crystal plasticity models by generating generalized yield surfaces which can embrace the dislocation core - applied stress tensor interactions.
 
 
Short Bio: Sertan Alkan received B.S. (2010) and M.S. (2013) diplomas from Department of Mechanical Engineering at Bogazici University. He is currently a PhD. student in Mechanical Science and Engineering Department at University of Illinois at Urbana-Champaign. During his M.S., he worked on modelling mechanical response of edge cracks in shape memory alloys particularly focusing on the martensitic transformation induced toughening. His PhD. studies involve characterization of fatigue crack growth behavior in nanotwinned Ni-Co alloys via Digital Image Correlation (DIC) technique and establishing a multiscale (continuum and atomistic) theoretical model encompassing the interaction of the crack-tip emitted dislocations with the grain and twin boundaries. Currently, his research mainly focuses on characterization of the slip mediated plasticity and twinning in shape memory alloys and high entropy alloys via DIC technique and atomistic scale simulations within the framework of Density Functional Theory and Molecular Dynamics/Statics.
 

Rechargeable Next-Generation Magnesium/Oxygen Batteries
 
 by Gülin Vardar
 
(Massachusetts Institute of Technology, Nuclear Science and Engineering)
 
DATE : November 25, 2016 (Friday)
TIME : 11:00-12:00
ROOM : VYKM 2
 
PDF Version
 
Electrochemical energy storage devices that are robust, energy-dense, and cheap will accelerate the commercialization of electric vehicles.  
Magnesium/Oxygen (Mg/O2) batteries are a promising system with the potential for very high energy densities. Furthermore, a rechargeable
Mg/O2 battery could be a cheaper and potentially safer alternative to lithium Li-ion batteries currently in use. The goal of this talk is to explore candidate magnesium electrolytes for use in Mg/O2 batteries,  
and to assess the reaction mechanisms and performance of Mg/O2 cells   
that employ these electrolytes.
 
Short Bio: Gülin Vardar received B.S. diplomas from Boğaziçi University in Mechanical Engineering and Physics in 2010. She received M.S. and PhD. diplomas from the University of Michigan (Ann Arbor) in Materials Science and Engineering. She is currently a postdoctoral research associate in Massachusetts Institute of Technology.
 

Electrothermal Modeling of AlGaN/GaN Heterostructure Field Effect Transistors
 
by Nazlı Dönmezer
 
(Middle East Technical University, Department of Mechanical Engineering)
 
DATE : October 7, 2016 (Friday)
TIME : 14:00-15:00
ROOM : VYKM 2
 
Nitride-based semiconductors and materials have been promising candidates for wide variety of technological applications such as nitride based power electronics, satellite communication, and light    emitting diodes. AlGaN/GaN based Heterostructure Field Effect Transistors (HFETs), that are used in high power and frequency applications have been intensively used due to their high-efficiency    power switching and large current handling capabilities. In these devices the high power densities and localized heating form small, high temperature regions called hotspots. Analysis of the heat removal from hotspots and temperature control of the entire device is necessary for the reliable design of HFET devices. Due to the resolution limits of the current experimental characterization    techniques and the geometry of the device that limits the accurate temperature measurement, thermal simulations are necessary. The aim is to build an accurate yet efficient electro-thermal model for the analysis and improvement of HFETs.
 
 
Short Bio: Dr. Nazli Donmezer is an Assistant Professor in the Mechanical Engineering Department of Middle East Technical University. She received her PhD. from Woodruff School of Mechanical Engineering   at the Georgia Institute of Technology and her M.S. from Middle East   Technical University in 2013 and 2009 respectively. During her PhD  she  worked on the development of a multiscale model  to simulate the   thermal response of devices with nanometer sized hotspots under the   supervision of Dr. Samuel Graham. She was a recipient of the   Schlumberger "Faculty for the Future" (FFTF) scholarship during her   PhD. studies. Dr. Donmezer joined the faculty at METU in Fall 2014.   She is currently leading a research group  where the goal is to   characterize the electro-thermal behavior of  the nitride devices and materials.