MEAM Seminar Series Spring 2016
For Fall 2015 Seminars, click here.
Seminars are held on Tuesday mornings, with coffee at 10:30 am in the Levine Hall Mezzanine and the seminar beginning at 10:45 am in Wu and Chen Auditorium (unless otherwise noted).
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Monday, January 11: Special Seminar
James Pikul, Post-Doctoral Associate, Department of Mechanical and Aerospace Engineering, Cornell University
9:00 am, Wu and Chen Auditorium
"Design and Fabrication of High Power Microbatteries and High Specific Strength Cellular Solids from Mesostructured Hierarchical Materials"
An emerging paradigm in engineering design is the development of materials by constructing hierarchical assemblies of simple building blocks into complex architectures that address physics at multiple length scales. These hierarchical materials are increasingly important for the next generation of mechanical, electrical, chemical, and biological technologies. However, fabricating hierarchical materials with nm control over multiple chemistries in a scalable fashion is a challenge yet to be overcome. This talk reports the design and fabrication of hierarchical microbattery electrodes that demonstrate unprecedented power density as well as large area cellular solids with controllable moduli and high specific strengths.
The microbatteries have up to 7.4 mW cm-2 m-1 power density, which equals or exceeds that of the best supercapacitors and is 2000 times greater than other microbatteries. The three-dimensional bicontinuous interdigitated microelectrode architecture improves power performance by simultaneously controlling ion and electron transport distances through the anode, cathode, and electrolyte. The low internal transport resistances reduce the microbattery internal heat generation by more than 50% at normal (0.1 – 10 C) discharge rates. Self-assembly and electrochemical deposition techniques integrate large volume fractions of high capacity materials into the microbattery architecture to enable up to 45.5 µWh cm-2 µm-1 energy densities, which is greater than previously reported three-dimensional microbatteries and comparable to commercially available lithium-based batteries, while maintaining high power density. A one dimensional electrochemical model of the microbatteries enables the development of battery design rules that suggest a 10X improvement in battery power performance is possible.
In addition, the electrode architecture has high specific compressive strengths up to 0.23 MPa / (kg m−3) and Young’s moduli that can be varied from 2.0 to 44.3 GPa. The specific strength is greater than most high strength steels and titanium alloys and is due to the size based strengthening of the nanometer scale struts in the porous architecture. The excellent mechanical properties, combined with the ability to precisely control chemistry, can be utilized to develop next generation multifunctional materials for energy, robotics, and medical applications.
James Pikul earned his B.S. (2009) M.S. (2011) and Ph.D. (2015) in Mechanical Engineering from University of Illinois at Urbana-Champaign under the advisement of Professors William P. King (Mechanical Engineering) and Paul V. Braun (Materials Science). He was a Department of Energy Office of Science Graduate Research Fellow and University of Illinois Carver Fellow. His Ph.D. research focused on the self-assembly and electrochemical fabrication of ultra-high power microbatteries and large area, high strength cellular solids. For this work, he won the Materials Research Society Gold Award. James has authored nine journal papers, four conference papers, and a patent application. His articles inNature CommunicationsandPNAShave generated significant interest in the popular media, having been featured in BBC, Discovery News, Yahoo News, arstechnica, Engadget, and many other outlets.
James Pikul is currently a post-doctoral scholar in the Organic Robotics Laboratory at Cornell University under Professors Robert Shepherd (Mechanical Engineering) and Itai Cohen (Physics). In this position, he continues to develop advances in multi-scale manufacturing to enable critically important technologies. He is currently developing soft robotic rovers for extraterrestrial oceans for NASA and manufacturing technologies for adaptive camouflage for the US Army.
Cynthia Sung, PhD Candidate, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology
"Computational Tools for Robot Design: A Composition Approach"
As robots become more prevalent in society, they must develop an ability to deal with more diverse situations. This ability entails customizability of not only software intelligence, but also of hardware. However, designing a functional robot remains challenging and often involves many iterations of design and testing even for skilled designers. My goal is to create computational tools for making functional machines, allowing future designers to quickly improvise new hardware in response to unexpected circumstances.
In this talk, I will discuss one possible approach to automated design using composition. I will describe our origami-inspired print-and-fold process that allows entire robots to be fabricated within a few hours, and I will demonstrate how foldable modules can be composed together to create foldable mechanisms and robots. The modules are represented parametrically, enabling a small set of modules to describe a wide range of geometries and also allowing geometries to be optimized in a straightforward manner. I will also introduce a tool that we have developed that combines this composition approach with simulations to help human designers of all skill levels to design and fabricate custom functional robots.
Cynthia Sung is a Ph.D. candidate in the Computer Science and Artificial Intelligence Laboratory at the Massachusetts Institute of Technology (MIT). She received a B.S. in Mechanical Engineering from Rice University in 2011 and an M.S. in Electrical Engineering and Computer Science from MIT in 2013. Her research interests include computational design, folding theory, and rapid fabrication, and her current work focuses on algorithms for synthesis and analysis of engineering designs.
Thursday, January 28: Special Seminar
Arthur W. Mahoney, Postdoctoral Fellow in the Medical Engineering and Discovery Laboratory at Vanderbilt University
1:30 p.m., Singh Center for Nanotechnology, 3205 Walnut Street, Glandt Forum (third floor)
"Wireless Magnetic Devices and Needle-sized Tentacles Inside the Body: Robots That Help Surgeons Save Lives"
Robotic technology has transformed the operating room by giving surgeons access to confined regions of the human body with dexterity as good as their own hands. But there are still areas of the human body that surgeons consider to be “inoperable” in a safe way. This talk is about emerging robotic technologies that push the frontiers of where robots can reach in the human body. My talk will cover how the physics of magnetism and elasticity can be exploited to create miniature magnetic wireless robots that navigate through the pathways of the human body, and needle-sized elastic tentacle robots that can maneuver around corners to deliver dextrous tools without any incisions in the skin. These devices can become interactive diagnostic and interventional instruments that push the boundaries ofinoperable disease when they are combined with perception and intelligence. A major theme of this talk is that the robots in the future operating room must be "smart- by-design,"that is, mechanically designed with perception and intelligence in mind.
Dr. Art Mahoney is a Postdoctoral Fellow in the Medical Engineering and Discovery Laboratory at Vanderbilt University. He earned undergraduate degrees in computer science and computational mathematics from Utah State University, and his Ph.D. degree from the School of Computing at the University of Utah as a member of the Utah Telerobotics Laboratory. His graduate research was on magnetically controlled robots in the human body with Dr. Jake Abbott. Dr. Mahoney’s postdoctoral work focuses on design, planning, and sensing for flexible minimally-invasive surgical robots with Dr. Robert Webster. Aside from his postdoctoral and graduate work, he has conducted research in computational search methods for discovering new cancer therapies, parallel computing, and robot motion planning. He is the recipient of an NSF Graduate Research Fellowship and is a Hertz Fellowship Finalist.
Rodrigo A. Bernal, Postdoctoral Researcher, Department of Mechanical Engineering and Applied Mechanics,
University of Pennsylvania
"Mechanical and Electromechanical Properties of Nanowires for Sensors and Electronics"
Nanowires are envisioned as components of future sensors, electronics, nanostructured materials, among many applications. This technological relevance has stimulated research in the characterization and understanding of their physical properties. In this talk, I will present results on the mechanical and electromechanical characterization of metallic and semiconducting nanowires, obtained with in-situ electron microscopy experiments. By allowing visualization of the materials at high resolution during characterization, in-situ experiments allow us to draw insights on the fundamental mechanisms controlling nanowire properties.
In the context of semiconducting specimens, we characterized the elastic modulus of gallium nitride nanowires. We find that below 20 nm in diameter, the nanowires display enhanced elastic modulus, due to reduced interatomic spacing near the surface. For metallic specimens, we characterized the tensile behavior of fivefold-twinned silver nanowires below 120 nm in diameter. We observe the Bauschinger effect and recoverable plasticity, and establish these behaviors are caused by reversible dislocation activity promoted by the twinned structure. For both semiconducting and metallic specimens, complementary atomistic simulations agree with the experimental results. Leveraging the experience acquired on mechanical testing, we implemented a MEMS (Microelectromechanical System) device for electromechanical characterization. We characterized the piezoresistance of n-doped silicon nanowires, which is found to be of the same order of magnitude as bulk.
The ability to characterize both the mechanical properties of nanomaterials, and the effect of mechanical deformation on other properties, such as electron transport, will pave the way for the discovery of novel multiphysics phenomena, which will underpin the next generation of sensors and electronics.
Rodrigo Bernal was born and raised in Colombia. He earned B.Sc. degrees in Mechanical and Electronics Engineering from the University of the Andes, in Bogotá. After this, he moved to the U.S to pursue a Ph.D. in Mechanical Engineering at Northwestern University, under the advisement of Prof. Horacio Espinosa, graduating in 2014. At Northwestern, he investigated the mechanical and electromechanical properties of metallic and semiconducting nanowires, employing in-situ Scanning and Transmission Electron Microscopy (SEM/TEM). Currently, he is a postdoctoral researcher in the Mechanical Engineering and Applied Mechanics Department, at the University of Pennsylvania, supervised by Prof. Robert Carpick. He is investigating the fundamental mechanisms of wear and friction in advanced carbon-based materials. His future research interests are in the area of nanomechanical multiphysics: nanoscale phenomena where mechanical deformation can control and tune other properties such as electrical, thermal or chemical.
Monday, February 8: Special Seminar
Jordan R. Raney, Postdoctoral Fellow,Wyss Institute for Biologically Inspired Engineering, Harvard University
9:00 a.m., Towne 337
"Mechanics By Design: 3D Printing Architected Engineering Materials With Unprecedented Control of Mechanical Properties"
Natural structural materials such as wood possess highly heterogeneous mesoscale architectures, with hierarchical structure, spatially-varying fiber alignment, non-uniform density, graded porosity, and multifunctionaliMty. These features are the result of localized structural and compositional optimization, producing maximal bulk mechanical properties that greatly exceed those of the constituent materials. In contrast, due to the limitations of current manufacturing processes, synthetic engineering materials typically lack these heterogeneous features that are associated with optimized mesoscale structure. As a result, they lack the level of performance (as defined by metrics such as strength, toughness, mass efficiency, etc.) that is ultimately possible. Additive manufacturing techniques have begun to enable more complicated mesoscale features in synthetic material systems, but many challenges remain. Here, direct write 3D printing is applied to the construction of architected engineering materials with the goal of enabling unprecedented control of mechanical properties. Two example material systems will be discussed: (i) beam-based soft materials that make use of bistability to controllably store and release elastic strain energy; and (ii) bioinspired fiber composites with fiber alignment that can be locally, heterogeneously assigned to achieve excellent mass efficiency and control of strain and failure localization.
Jordan R. Raney is a Postdoctoral Fellow in the John A. Paulson School of Engineering and Applied Sciences and the Wyss Institute for Biologically Inspired Engineering at Harvard University. His research focuses on the mechanics and fabrication of novel material architectures, including hierarchical, heterogeneous, fibrous, and soft systems. He received his Ph.D. in materials science at the California Institute of Technology, where he was the recipient of a National Defense Science & Engineering Graduate Fellowship and the Demetriades-Tsafka-Kokkalis Prize in Nanotechnology for his dissertation.
Jeremy D. Brown, Postdoctoral Research Fellow, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania
"Smart Haptic Displays for Dextrous Manipulation of Telerobots"
The human body is capable of dexterous manipulation in many different environments. Some environments, however, are challenging to access because of distance, scale, and limitations of the body itself. In many of these situations, access can be effectively restored via a telerobot, in which a human remotely controls a robot to perform the task. Dexterous manipulation through a telerobot is currently limited, and will be possible only if the interface between the operator’s body and the telerobot is able to accurately relay any sensory feedback resulting from the telerobot’s interactions in the environment.
This talk will focus on the scientific investigation of high fidelity haptic interfaces that adequately translate the interactions between the telerobot and its environment to the operator’s body through the sense of touch. I will introduce the theme of “Smart Haptic Displays,” which are capable of modulating their own dynamic properties to compensate for the dynamics of the body and the telerobot to ensure the environment dynamics are accurately presented to the operator. Along the way, I will highlight contributions I have already made for two specific telerobots: upper-limb prostheses and minimally invasive surgical robots. These contributions include an empirical validation of the utility of force feedback in body-powered prostheses and the creation of a testbed to compare various haptic displays for pinching palpation in robotic surgery. Finally, I will briefly introduce a novel approach I am currently investigating that utilizes haptic signals to automatically predict a surgical trainee’s skill on a minimally invasive surgical robotic platform. As this work progresses, it will lead to the creation of interfaces that provide the rich haptic sensations the body has come to expect, and will allow for dexterous manipulation in any environment whether or not access is mediated through a telerobot.
Jeremy D. Brown is a Postdoctoral Research Fellow in the Department of Mechanical Engineering and Applied Mechanics and the Haptics Group in the GRASP Lab at the University of Pennsylvania. He earned undergraduate degrees in applied physics and mechanical engineering from Morehouse College and the University of Michigan, and a PhD degree in mechanical engineering from the University of Michigan, where he worked in the HaptiX Laboratory. His research focuses on the interface between humans and robots with a specific focus on medical applications and haptic feedback. He was honored to receive several awards including the National Science Foundation (NSF) Graduate Research Fellowship and the Penn Postdoctoral Fellowship for Academic Diversity.
Thursday, February 18: Special Seminar
3:00 p.m., Berger Auditorium, Skirkanich Hall
Christopher Boyce, Post-doctoral researcher at Princeton University in the Multiphase Flow Group in the Department of Chemical and Biological Engineering
"Tomographic Imaging and Computational Modeling of Fluid-Particle Flow Systems"
Fluid-particle flows exhibit fascinating and complex physical phenomena which defy the traditional divisions between solid, liquid and gas. These flows also form the basis of many process units, such as fluidized beds, which perform vital operations in industries ranging from fuel and electricity generation to polymer production to pharmaceutical manufacturing. Recent and renewed attention focuses on their potential in providing clean energy solutions, for example, in chemical looping combustion, a process for burning coal, natural gas and biomass with efficient carbon capture. Fluidized beds and other fluid-particle flow systems are widely used because their dynamics allow for efficient particle transport and mixing as well as interphase heat and mass transport. These dynamics also create fascinating physical phenomena, such as bubbles rising through granular material in a liquid-like state, and hydrodynamic effects coupled with chemical reactions, species transport and inter-particle forces generate a range of multi-physics problems. With such complex dynamics, we have only begun to scratch the surface of understanding the fundamental science of these systems, despite decades of industrial use.
Two historic limitations in scientific research of fluid-particle flow systems have been: (1) a lack of non-invasive experimental techniques for measuring the multi-physics of these opaque, 3D systems and (2) difficulties in developing models which account for the various physics of these systems on all of the necessary length and time scales. Exciting advances in tomographic imaging and computational modeling have now opened the door to provide crucial new insights into the governing physics, statistics and evolution of these flow systems. This talk will center on the advancement and use of magnetic resonance imaging (MRI) to study the hydrodynamics of the gas and solid phases, as well as multi-scale modeling techniques accounting for complex inter-particle forces.
Chris Boyce is a post-doctoral researcher at Princeton University in the Multiphase Flow Group in the Department of Chemical and Biological Engineering. He studied as an undergraduate at MIT, earning a double-major in Chemical Engineering and Physics with a minor in Nuclear Science and Engineering. As a Gates Cambridge Scholar, he obtained his PhD at the University of Cambridge in Chemical Engineering as a member of Trinity College. Chris has been studying the science underlying energy-related systems since he was an undergraduate and has acquired expertise in uncovering the physics of fluidization using magnetic resonance imaging (MRI) coupled with multiscale modeling.
Thursday, February 25: Special Seminar
1:30 p.m., Glandt Forum, Singh Center
Hunter Gilbert, research assistant and PhD candidate, Medical Engineering and Discovery Lab, Vanderbilt University
"Tentacle Robots for Minimally Invasive Surgery: Model-based Analysis and Design"
Surgeons and engineers are together pushing towards surgical procedures that are less invasive, resulting in fewer complications, less scarring, and faster recovery times. Tentacle-like robots with flexible backbones have enabled new applications of robotics and driven the development of new modeling and analysis techniques. The concentric tube robot is one type of flexible robot that is poised to enable new minimally invasive surgical procedures. They consist of multiple precurved, superelastic Nitinol tubes nested within one another, and they are needle-sized devices that can provide robotic dexterity in difficult-to-reach sites within the human body. They can also be designed as “steerable needles” that provide curved access to obscured sites in order to deliver therapy or take biopsy samples. In this presentation, I describe the model-based analysis and design of these robots that enable them to perform surgeries and needle-based procedures safely and effectively. I will also discuss two applications for these robots in the treatment of pituitary tumors and epilepsy.
Hunter Gilbert is currently a research assistant and Ph.D. candidate in the Medical Engineering and Discovery Lab at Vanderbilt University in Nashville, TN. He obtained the B.S. degree in Mechanical Engineering from Rice University in Houston, TX in 2010, and received the NSF Graduate Research Fellowship in 2012. His research interests center around the modeling of flexible robots and the use of engineering principles to improve surgical outcomes.
Thursday, March 3: Special Seminar
3:00 p.m., Berger Auditorium, Skirkanich Hall
Luigi Perotti, Postdoctoral Scholar, University of California, Los Angeles (UCLA)
"Modeling Cardiac Mechanics and Electrophysiology"
Heart failure (HF) is a leading cause of death in developed countries, yet its underlying mechanisms are not well understood. This lack of understanding limits our ability to diagnose the onset of HF and to identify effective therapies. In this context, computational models are able to interpret patient specific experimental data, expose the causal factors of HF, and provide insights into interventional and pharmacological therapies.
First we present a new framework to identify changes in the material properties of passive myocardium, which underlie several forms of heart disease. This novel approach is based on clinical data that can be acquired routinely for HF patients, is formulated in finite kinematics, and results in unique material properties that, as a result, can be used as diagnostic markers. We validate our approach using in silico generated data and present a new strategy to formulate material laws that optimally describe available experiments and can be applied to future in vivo data.
Cardiac dysfunction is related not only to changes in the myocardium mechanical response but also to compromised cardiac electrical activity. In the second part of my talk I will discuss our validated electrophysiology model of a rabbit heart to study the risk of ventricular fibrillation (VF) in patients affected by congestive HF. Our multiscale model is based on an anatomically accurate heart geometry obtained from MRI, fiber directions obtained from DTMRI, a Purkinje activation network, and experimentally based ionic cellular models. This computational model led to the discovery of a new mechanism for the onset of VF and can be employed for studying interventional and pharmacological therapies.
Luigi Perotti received his Laurea (B.S./M.S.) degree in Civil Engineering from Politecnico di Milano, Italy, in 2004. Subsequently he continued his studies in Mechanical Engineering at the California Institute of Technology where he received his M.S. in 2006 and his Ph.D. with a minor in Applied and Computational Mathematics in 2011. During his Ph.D. research he worked in Dr. Ortiz's group on developing new finite elements and mesh-free methods for plates and shells and on modeling the response of fiber composite sandwich structures to underwater explosions. At the end of 2011, he joined Dr. Klug’s group in the Mechanical and Aerospace Engineering department at UCLA to pursue his research interests in biomechanics. Since then he has worked on several multidisciplinary projects involving collaborations across the Departments of Physics, Bioengineering, Radiology, and the School of Medicine to study both the assembly and maturation of viral capsids, and cardiac mechanics and electrophysiology using computational and continuum mechanics models. In 2014 he received the American Heart Association postdoctoral fellowship and joined Dr. Ennis' group in the Bioengineering and Radiological Sciences departments at UCLA to develop advanced methods for evaluating cardiac mechanics of the failing heart.
SPRING BREAK: NO SEMINAR
Thursday, March 10: Special Seminar
10:30 a.m., Towne 337
Daniel Chenet, Ph.D., Department of Mechanical Engineering, Columbia University
"Van der Waals Heterostructures of 2D Materials: Synthesis, Characterization, & Applications"
Two-dimensional materials offer extraordinary potential in the fields of on-chip optoelectronics, flexible electronics, and transparent display technologies, to name a few. Enabling the advancement of this technology is (1) our development of spectroscopic techniques to study the structure-property-function relationship, and (2) our ability to fabricate high-quality devices using van der Waals heterostructures. Van der Waals heterostructures, which require the layer-by-layer deposition or transfer of structurally and electronically dissimilar 2D materials, enable us to develop new functionalities and to study both material and device performance in ultra-clean and air-stable conditions. In this presentation, I will discuss our recent works on both of these fronts, specifically focusing on spectroscopic techniques for studying anisotropic 2D semiconductors and 2D phase change alloys as well as 2D optoelectronics using air-sensitive low bandgap semiconductors.
Daniel Chenet completed his Ph.D. in March 2016 at Columbia University in the Department of Mechanical Engineering working in James Hone's Laboratory for Nanomaterials, Nanomechanics, and Nanofabrication. He joined Columbia University in 2010 as a CU Presidential Fellow and a GEM Ph.D. Fellow. Prior to joining Columbia, he was a jazz performance major at CUNY-City College and still enjoys playing music in his free time.
Thursday, March 24: Special Seminar
3:00 p.m., Berger Auditorium, Skirkanich Hall
Anirudha Majumdar, Ph.D. Candidate, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology
"Control of Agile Robots in Complex Environments with Formal Safety Guarantees"
The goal of my research is to develop algorithmic and theoretical techniques that push highly agile robotic systems to the brink of their hardware limits while guaranteeing that they operate in a safe manner despite uncertainty in the environment and dynamics.
In this talk, I will describe my work on algorithms for the synthesis of feedback controllers that come with associated formal guarantees on the stability of the robot and show how these controllers and certificates of stability can be used for robust planning in environments previously unseen by the system. In order to make these results possible, my work connects deeply to computational tools such as sums-of-squares (SOS) programming and semidefinite programming from the theory of mathematical optimization, along with approaches from nonlinear control theory.
I will describe this work in the context of the problem of high-speed unmanned aerial vehicle (UAV) flight through cluttered environments previously unseen by the robot. In this context, the tools I have developed allow us to guarantee that the robot will fly through its environment in a collision-free manner despite uncertainty in the dynamics (e.g., wind gusts or modeling errors). The resulting hardware demonstrations on a fixed-wing airplane constitute one of the first examples of provably safe and robust control for robotic systems with complex nonlinear dynamics that need to plan in realtime in environments with complex geometric constraints.
Anirudha Majumdar is a Ph.D. candidate in the Electrical Engineering and Computer Science department at MIT. He is a member of the Robot Locomotion Group at the Computer Science and Artificial Intelligence Lab and is advised by Prof. Russ Tedrake. Ani received his undergraduate degree in Mechanical Engineering and Mathematics from the University of Pennsylvania, where he was a member of the GRASP lab. His research is primarily in robotics: he works on algorithms for controlling highly dynamics robots such as unmanned aerial vehicles with formal guarantees on the safety of the system. Ani's research has been recognized by the Siebel Foundation Scholarship and the Best Conference Paper Award at the International Conference on Robotics and Automation (ICRA) 2013.
April 4: MEAM Ph.D. Defense
4:30 p.m., Room 227, Towne Building
Sheng Mao, Ph.D. Candidate
Advisor: Prashant K. Purohit
"Continuum and Computational Modeling of Flexoelectricity"
A material is said to be flexoelectric when it polarizes in response to strain gradients. The phenomenon is well known in liquid crystals and biomembranes but has received less attention in hard materials such as ceramics. With the advent of nanotechnology, flexoelectric effect in solid structures is gaining increasing prominence. For instance, gradient-engineered epitaxial films, mechanical rotation of ferroelectric polarization, making piezoelectric structures from non-piezoelectric materials. It also inspires ways of enhanced energy harvesting. To better understand this effect, a systematic continuum model is built, starting from fundamental theory to computational techniques.
On the theoretical end, a model is established for a flexoelectric solid under small deformation and linear constitutive relation. Gradient raises the order of the governing PDE’s and a Navier equation is obtained for isotropic case, which resembles that of Mindlin’s in gradient elasticity. Based on this theoretical model, various boundary value problems can be solved with analytic solutions, including torsion, beam bending, pressurized disk/cylinder, etc. We predict size-dependent electromechanical properties and flexoelectric modulation of material behavior. We also look at the interplay of flexoelectricity with defects. Defects have a strong gradient field around them—so do we expect flexoelectric effect. We quantify this expectation by computing analytic solutions of displacement, stress and polarization fields near different types of defects in flexoelectric solids, namely point defects, line defects (dislocations) and cracks. Our solution can make connections to non-local piezoelectric theory, gradient elasticity theory and some well-known experimental results. Our crack asymptotic analysis can be used in classical criterion to make predictions on crack growth as well as material fracture.
Based on the above theoretical/analytic results, for the sake of studying more sophisticated problems of flexoelectric effect in solids, we derive a computational theory of simulating flexoelectric effect in solids. We circumvented the challenge of higher-order PDE’s by introducing a “mixed” formulation where both displacement and displacement gradients are treated as “independent” variables. Based on this idea, a weak formulation for flexoelectric solids can be derived. A new III9-87 element is used and clears the patch tests. The proposed technique gives excellent agreement to benchmark problems with known analytic solutions. Moreover, the technique is used to study the classical problem of a plate with a hole. We study the size-effect and the flexoelectric reduction of the stress concentration factor. We also study the shape effect. We demonstrate how non-centrosymmetric defects could help make piezoelectric nano-structures from centro-symmetric and even isotropic materials.
David L. Burris, Associate Professor, Department of Mechanical Engineering, University of Delaware
"New Insights into Joint Lubrication, Health, and Replacement"
Animal joints operate with friction coefficients in the range from 0.005-0.02. Such values suggest hydrodynamic fluid film lubrication until it is realized that friction is just as low at zero speed where hydrodynamics vanish. These extraordinarily low friction coefficients are ~5x below those of ice on ice, ~10x below those of Teflon, and ~20x below those of well-lubricated metal bearings.
The mechanisms underlying these unique tribological properties of joints remains a topic of great scientific interest and uncertainty. Biomechanics textbooks typically suggest that joints are lubricated by fluid films during articulation and boundary lubrication once fluid films collapse during sitting and standing. As a result, joint replacement devices have evolved to possess harder, smoother, and more conforming surfaces in an effort to promote fluid films and resist damage during contact. However, there are strong competing arguments in the literature against the fluid film joint lubrication hypothesis on the basis that the cartilage ‘surface’ is ~80% pores. Supporters of interstitial lubrication believe that the pressurized interstitial fluid near the contact hydrostatically supports the contact force, which simultaneously explains its remarkable mechanical and tribological properties. Because these competing hypotheses suggest two completely different approaches to joint replacement, the matter is far more important than simple academic curiosity.
This talk outlines our work over the last five years to clarify the problem of cartilage/joint lubrication using novel in-situ tribometry approaches. By measuring the interstitial pressurization response of cartilage during friction experiments, we are able to experimentally isolate lubrication contributions from fluid films and interstitial pressures. Our results indicate that friction in joints is primarily reduced by interstitial pressure, not by fluid films. Unlike artificial joints, interstitial pressure in cartilage of natural joints keeps friction low for many hours of sitting and standing until the majority of the interstitial fluid has been ‘wrung out’. Given the infrequency with which joints actually move, we believe this feature is absolutely critical for long term wear prevention. However, it is not known how fluid re-enters cartilage once removed. Our results demonstrate how this happens and explain why the experimental measurements in the literature support two seemingly conflicting mechanisms. During articulation after wring out, external hydrodynamic pressures develop and drive fluid into the porous contacting surfaces (rather than between them) to restore hydration and interstitial lubrication. The results explain why cartilage in our joints doesn’t ‘deflate’ over time and why being overly sedentary increases a person’s risk of joint disease. Finally, they suggest that a biomimetic joint replacement material must be soft in compression, porous, fluid soaked and stiff in tension; this suggests that existing hydrogels are the perfect foundation but must be reinforced such that they become many times stiffer in tension than compression (e.g. with a fibrous, collagen-like scaffold).
Dr. Burris received his Ph.D. in 2007 from the University of Florida. He is currently an Associate Professor in Mechanical Engineering at the University of Delaware with a joint appointment in Biomedical Engineering. He has 4 patents and 47 peer-reviewed journal publications. He is the recipient of the ASME Marshall B. Peterson award, the ASME Burt L. Newkirk award, the ASME Pi Tau Sigma Gold Medal, the AFOSR Young Investigator award, and the University of Florida Outstanding Young Alumnus award.
Thursday, April 14: Special Seminar
10:00 a.m., Room 337, Towne Building
Qingze Zhao, Ph.D. Candidate
Advisor: Prashant K. Purohit
"Phase Boundary Propagation in Mass Spring Chains and Long Molecules"
Martensitic phase transitions in crystalline solids have been studied and utilized for many technological applications, including bio-medical devices. These transitions typically proceed by the nucleation and propagation of interfaces, or phase boundaries. Over the last few decades, a continuum theory of phase transitions has emerged under the framework of thermoelasticity to study the propagation of these phase boundaries. It is now well established that classical mechanical and thermodynamic principles are not sufficient to describe their motion within a continuum theory, and a kinetic relation must be supplied to complete the constitutive description.
The goal of my research is to study phase transition theory especially the kinetic relation in 1-D system. We discrete a one-dimensional continuum into a chain of masses and springs with multi-well energy landscapes and numerically solve impact and Riemann problems in such systems. In our simulations we see propagating phase boundaries that satisfy all the jump conditions of continuum theories. By changing the boundary and initial conditions on the chains we can explore all possible phase boundary velocities and infer kinetic relations that when fed to the continuum theory give excellent agreement with our discrete mass-spring simulations.
A physical system that shares many features with the mass-spring systems analyzed in our study is DNA in single molecule extension-rotation experiments. DNA is typically modeled as a one-dimensional continuum immersed in a heat bath. At high enough tensions we can assume that bending deformations of DNA are so small that its energy depends on stretch and twist only In this situation DNA is known to undergo structural transitions when subjected to tension and torque. It is also known from fluorescence experiments that some of these transitions proceed by the motion of phase boundaries, just as in crystalline solids. Hence, we use a continuum theory to study these phase boundaries in DNA across which both the stretch and twist can jump. We show that experimental observations from many different labs on various DNA structural transitions can be quantitatively explained within our model.
April 19: Tedori-Callinan Seminar
Albert P. Pisano, NAE, Walter J. Zable Chair of Mechanical and Aerospace Engineering and Dean, Jacobs School of Engineering, University of California, San Diego
In this seminar, recent results in the dry nanoprinting of a number of structures and devices will be presented. Dry nanoprinting is a novel process by which a micro or nanofluidic template is used not only to guide the flow of one or more inks simultaneously, but also to template the final, dry printed structures and devices. The advantages of this approach include auto-registration among structures printed from multiple iinks, as well as extreme sidewall definition. Examples of functional devices made from this technology will be presented.
Albert P. Pisano began his service as Dean of the Jacobs School of Engineering on September 1, 2013. Pisano holds the Walter J. Zable Chair in Engineering and serves on the faculty of the Departments of Mechanical and Aerospace Engineering and Electrical and Computer Engineering.
Pisano is an elected member of the National Academy of Engineering for contributions to the design, fabrication, commercialization, and educational aspects of MEMS.
Prior to his appointment at UCSD, Pisano served on the UC Berkeley faculty for 30 years where he held the FANUC Endowed Chair of Mechanical Systems. Pisano was the senior co-director of the Berkeley Sensor & Actuator Center (an NSF Industry-University Cooperative Research Center), director of the Electronics Research Laboratory (UC Berkeley's largest organized research unit), and faculty head of the Program Office for Operational Excellence, among other leadership positions. Since 1983, Pisano has graduated over 40 Ph.D. and 75 M.S. students.
From 1997 to 1999, Pisano was a program manager for the MEMS Program at the Defense Advanced Research Project Agency (DARPA).
Pisano earned his undergraduate ('76) and graduate degrees ('77, '80, '81) in mechanical engineering at Columbia University. Prior to joining the faculty at UC Berkeley, he held research positions with Xerox Palo Alto Research Center, Singer Sewing Machines Corporate R&D Center and General Motors Research Labs.
Pisano's research interests include: micro-electro-mechanical systesm (MEMS) wireless sensors for harsh environments (600 degrees Celsius) such as gas turbines and geothermal wells; and additive, MEMS manufacturing techniques such as low-temperature, low-pressure nano-printing of nanoparticle inks and polymer solutions. Other research interests and activities include MEMS for a wide variety of applications, including RF components, power generation, drug delivery, strain sensors, biosensors, micro inertial instruments, disk-drive actuators and nanowire sensors. He is a co-inventor listed on more than 20 patents in MEMS and has co-authored more than 300 archival publications.
Pisano is a co-founder of ten start-up companies in the areas of transdermal drug delivery, transvascular drug delivery, sensorized catheters, MEMS manufacturing equipment, MEMS RF devices and MEMS motion sensors.
John Hart, Associate Professor, Department of Mechanical Engineering, Massachusetts Institute of Technology
"Scalability and Flexibility: Key Principles for Advanced Manufacturing Research and Education"
Advances in automation, computation, and global connectivity are enabling us to scale-up new products more quickly, and to accelerate the translation of new materials and processes to applications. In the coming years, continued population growth and resource pressures will drive compound interest in additive manufacturing for local and customized production, and in printed electronics for ubiquitous sensing and communication. I believe these dynamics present important opportunities to perform fundamental yet practical research on emerging manufacturing processes, and to accelerate innovation via hands-on education. First, I will highlight two new research projects in my group: relief printing of electronic inks using nanoporous stamps, which demonstrate 10-fold improved resolution over industrial flexography; and extrusion-based 3D printing at 10-fold greater throughput than current equipment. Second, I will describe our effort to create an open digital course on manufacturing processes which is based on the MIT core undergraduate manufacturing class (2.008), and will reflect on experiences teaching additive manufacturing to graduate students and industry audiences.
John Hart is Associate Professor of Mechanical Engineering and Mitsui Career Development Chair at MIT. Prior to joining the MIT faculty in 2013 he was Assistant Professor of Mechanical Engineering, Chemical Engineering and Art/Design, at the University of Michigan. He has Ph.D. and S.M. degrees from MIT, and a B.S.E. degree from Michigan, all in Mechanical Engineering. At MIT, John leads the Mechanosynthesis Group (http://mechanosynthesis.mit.edu), which aims to create new principles, machines, and processes for manufacturing of advanced materials. His work has been recognized by young investigator awards from NSF, ONR, AFOSR, DARPA, ASME, and SME; and he is the recipient of two R&D 100 awards.
Thursday, April 28: Special Seminar
1:30 p.m., Room 337, Towne Building
David M. Warsinger, Post Doctoral Researcher, Lienhard Research Group, Massachusetts Institute of Technology
"Saving Lives with Thermodynamics: Thermofluids and Nanoengineering for the Water-Food-Energy Nexus"
Climate change, degrading water resources, and economic and population growth are increasing the need for new science and technologies at the Water-Food-Energy Nexus. In enabling new and improved technologies to tackle these issues, a thermofluids systems approach is essential to improve efficiency, design new nanomaterials, allow for new power sources, and enable applications to agriculture. Thermodynamic design of water treatment membrane technologies such as reverse osmosis (RO) and membrane distillation (MD) leads to innovations with superhydrophobic nanostructured surfaces for enhanced heat transfer, batch cycles, new configurations, and optimal use of waste heat can more than double their efficiencies. Optimization of heat and mass transfer and chemical thermodynamics provides new guidance for the design of nanofabricated membranes. These membranes need to minimize surface energy for fouling prevention, and use multi-layer membranes of varied porosity and thermal conductivity for technologies such as membrane distillation. Thermofluid approaches are especially valuable for food needs in the developing world. Two key areas are adding refrigeration of food to the supply chain and improving the productivity of aquaculture. As demonstrated by the startup Coolify, cofounded by Dr. Warsinger, phase-change thermal storage can enable refrigeration of produce with intermittent grids or solar power. Additionally, solar-absorbing surfaces can enhance oxygenation for aquaculture through optimized natural convection. The central pieces of this approach are ideal for forming a collaborative research lab, with emphasis on conducting component level energy and second law analysis and on developing creative techniques for maximizing or minimizing heat and mass transfer.
Dr. David Warsinger completed his B.S. and M.Eng at Cornell, and his PhD in Mechanical Engineering at MIT. He completed his graduate studies in a combined 3 years. Prior to starting his PhD, David designed heating and cooling systems and performed energy and sustainability analysis at the engineering consulting firm Arup. David is a coauthor of 17 published and 5 submitted conference or journal papers and a co-inventor on 13 filed or awarded patents. David cofounded Coolify, a startup providing cold storage for farmers in developing economies, which won the national competition for the $100k Ag Innovation Prize. Recently, David received the Institute Award for Best Research Mentor for Undergraduate Students at MIT. He has also received awards for the highest GPA in his class (M.Eng.), numerous grants, a national best dissertation award, and 8 presenter awards at conferences.