MEAM Seminar Series Fall 2017

For Summer 2017 Seminars, click here.

Seminars are held on Tuesday mornings beginning at 10:45 am in Wu and Chen Auditorium, in Levine Hall (unless otherwise noted).

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September 12

Larry L. Howell, Associate Dean and Professor of Mechanical Engineering, Brigham Young University

"Origami Art and Engineering? Surprising Opportunities for Systems with Unprecedented Performance"


For centuries origami artists have invested immeasurable effort developing origami models under extreme self-imposed constraints (e.g. only paper, no cutting or gluing, one regular-shaped sheet). The accessible and formable medium of paper has enabled swift prototyping of vast numbers of possible designs. This has resulted in stunning origami structures and mechanisms that were created in a simple medium and using a single fabrication process (folding). The origami artists’ methods and perspectives have created systems that have not previously been conceived using traditional engineering methods. Using origami-inspired methods, it may be possible to design origami-like systems, but using different materials and processes to meet emerging product requirements. This presentation will highlight research in origami-based engineering at Brigham Young University, and will include a diverse set of applications.


Larry L Howell is an Associate Dean and Professor at Brigham Young University (BYU). Prof. Howell received his B.S. degree from BYU and M.S. and Ph.D. degrees from Purdue University. Prior to joining BYU in 1994 he was a visiting professor at Purdue University, a finite element analysis consultant for Engineering Methods, Inc., and an engineer on the design of the YF-22 (the prototype for the U.S. Air Force F-22 Raptor). He is a Fellow of ASME, past chair of the ASME Mechanisms & Robotics Committee, and has been associate editor for the Journal of Mechanisms & Robotics and the Journal of Mechanical Design. He is the recipient of the ASME Machine Design Award, ASME Mechanisms & Robotics Award, Theodore von Kármán Fellowship, NSF Career Award, Purdue Outstanding Mechanical Engineer (alumni award), and the BYU Karl G. Maeser Distinguished Lecturer Award (BYU’s highest faculty award). Prof. Howell’s research focuses on compliant mechanisms, including origami-inspired mechanisms, space mechanisms, microelectromechanical systems, and medical devices. He is the co-editor of the Handbook of Compliant Mechanisms and the author of Compliant Mechanisms which are published in both English and Chinese. His lab’s work has also been reported in popular venues such as Newsweek, Scientific American, Popular Science, and the PBS documentary program NOVA.

September 19

Guy Genin, Professor of Mechanical Engineering & Materials Science, Washington University in St. Louis

"Unification Through Disarray at the Attachment of Tendon to Bone"


Joining of dissimilar materials is a fundamental challenge in engineering. Nature presents a highly effective solution at the attachment of tendon to bone ("enthesis") in the rotator cuff of the shoulder’s humeral head. The natural enthesis does not regrow following healing or surgery, resulting in inferior tissue and in post-surgical tear recurrence rates as high as 94%. My group and I therefore focus on understanding the mechanobiology of adhesion and toughening across hierarchical scales in the healthy enthesis, and on reconstituting this in healing.

Our results show the tendon to bone insertion to be a hierarchical, disordered system that uses randomness to tailor strain fields, and to maximize the fraction of tissue involved in resisting injury-level stresses. Based upon this model, we are developing two new mechano-medicine products for clinical translation: a diagnostic technology to evaluate the degree to which an enthesis is succeeding in physiological strain redistribution, and a repair technology that mimics the mesoscale function of the healthy enthesis by maximizing the fraction of tissue involved in resisting injury-level stresses. This talk will summarize our understanding of the mechanics of tendon-to-bone attachment, and describe technologies under development for improving healing.


Guy M. Genin studies the mechanobiology of interfaces and adhesion in nature and physiology. He serves as professor at Washington University in St. Louis, serving on the faculties of Mechanical Engineering & Materials Science, Biomedical Engineering, and Neurological Surgery; as Changjiang Professor at Xi'an Jiaotong University in Xi'an, China; and as co-director of the Center for Engineering Mechanobiology, a joint NSF Science and Technology Center between BU, Penn, Washington University, and several satellite sites. Prof. Genin serves as chief engineer for Washington University 's Center for Innovation in Neuroscience and Technology and is active in several start-ups. He currently serves as co-lead of the NIH/Interagency Modeling and Analysis Group's working group on integrated multiscale biomechanics experiment and modeling, and has served as an editor, guest editor, or associate editor of a number of leading journals. Prof. Genin's training includes B.S.C.E. and M.S. degrees from Case Western Reserve University, S.M. and Ph.D. degrees in solid mechanics from Harvard, and post-doctoral training at Cambridge and Brown. Prof. Genin is the recipient of a number of awards for engineering design, teaching, and research, including a Research Career Award from the NIH, the Skalak Medal from the ASME, the Northcutt-Coil Professor of the Year from Washington University, and the Yangtze River Scholar Award from the Chinese Ministry of Education. He is a fellow of ASME and AIMBE.

September 26

Changchun Liu, Research Associate Professor, University of Pennsylvania

"Towards Instrument-Free Inexpensive Point of Care Molecular Diagnostics"


In the context of precision medicine, precision diagnostics are crucial to achieving rapid and accurate diagnostics, providing the patient to the best treatment strategy. Today, cellphone technology has a growing and pervasive influence on our daily life. Especially, with the rapid development of microfluidics technology, the incorporation of microfluidics technology with cellphone technology will create a new paradigm shift towards affordable, mobile, personalized, health monitoring. In this talk, I will introduce my superhydrophobic plasma separator, molecular diagnostic chip, nuclemeter technology, electricity-free “smart cup” and their applications in disease diagnostics at the point of care.


Changchun Liu is a research associate professor in Department of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania. He received his B.S. and M.S. in Chemistry at the Yunnan University, China in 1999 and 2002, respectively, and Ph.D. in Electronic Engineering at the Institute of Electronics, Chinese Academy of Sciences (IECAS), China in 2005. He has a highly interdisciplinary background and training spanning Engineering (i.e., electronic, mechanical), Chemistry and Biomedicine. Dr. Liu's research interests include the development of microfluidic chips, BioMEMS (Biomedical MicroElectroMechanical Systems) devices, biosensors, wearable devices and their biomedical applications with a focus on point-of-care (POC) diagnostics. He is a recipient of the NIH Career Development Award (K25) in 2012, the Penn One Health Award in 2015, and the W.W. Smith Charitable Trust Research Award in 2016.

October 3: Tedori-Callinan Lecture

Gang Chen, Carl Richard Soderberg Professor of Power Engineering & Head of Department of Mechanical Engineering, Massachusetts Institute of Technology

"Innovations in Materials and Devices for Efficient Solar and Thermal Energy Utilization"


Human history has very much depended on how we used heat from the sun and terrestrial sources. Over 90% of human society’s energy input is used by first converting it into heat, and yet only 40% of the total energy input is utilized, significantly lower than what the second law of thermodynamics allows. Understanding of basic heat carrier transport and energy conversion at nanoscale can lead to new materials and devices to improve the efficiency of heat utilization. This talk will present some of our work on developing advanced materials and devices to improve the efficiency of solar and thermal energy conversion devices and systems. To lower the cost of solar energy to electricity conversion, we use nanostructures to reduce the thickness of crystalline silicon thin-film solar cells and optically-transparent and thermally-insulating aerogels to replace the vacuum-tube solar collectors in concentrated solar thermal systems. We improve thermoelectric materials via nanostructuring and demonstrate significant improvements in the efficiency of solar thermoelectric energy conversion devices. We also demonstrate the ability of boiling water under unconcentrated sunlight using spectrally selective surfaces. For terrestrial thermal systems, we show that by reflecting infrared radiation back to its emitting heat source, we can significantly improve the efficiency of converting thermally-radiated photons into electricity via thermophotovoltaic devices and the luminous efficiency of incandescent light bulbs. We can turn a battery into an efficient thermal-to-electrical energy converter by cycling it between high and low temperatures. Although polymers are usually thermal insulators, we show that they can be made as thermally conductive as metals by aligning molecular orientations. With properly chosen polymer fiber diameters, we design fabrics so that they are opaque to visible light and yet allow thermal radiation from human body to escape to environment for passively cooling. Nanoscience foundations behind these diverse innovations will be explained along the way.


Gang Chen is currently the Head of the Department of Mechanical Engineering and Carl Richard Soderberg Professor of Power Engineering at Massachusetts Institute of Technology (MIT), and is the director of the "Solid-State Solar-Thermal Energy Conversion Center (S3TEC Center)" - an Energy Frontier Research Center funded by the US Department of Energy. He obtained his PhD degree from the Mechanical Engineering Department, UC Berkeley. He was a faculty member at Duke University and UCLA, before joining MIT in 2001. He received an NSF Young Investigator Award, an R&D 100 award, an ASME Heat Transfer Memorial Award, a Nukiyama Memorial Award by the Japan Heat Transfer Society, a World Technology Network Award in Energy, an Eringen Medal from the Society of Engineering Science, and the Capers and Marion McDonald Award for Excellences in Mentoring and Advising from MIT. He is a fellow of American Association for Advancement of Science, APS, ASME, and Guggenheim Foundation. He is an academician of Academia Sinica and a member of the US National Academy of Engineering.

October 10

Katia Bertoldi, Gordon McKay Professor of Applied Mechanics, Harvard University

"Architected Materials: From Reconfigurability to Nonlinear Waves"


In the search for materials with new properties, there have been great advances in recent years aimed at the construction of architected materials, whose behaviour is governed by structure, rather than composition. Through careful design of the material’s architecture, new material properties have been demonstrated, including negative Poisson’s ratio, high stiffness-to-weight ratio and mechanical cloaking.
In this talk I will focus on two different types of architected materials. First, I will introduce a robust design strategy inspired by the snapology origami technique to create highly reconfigurable 3D architected materials comprising a periodic assembly of rigid plates and elastic hinges. Then, I will focus on soft architected materials and show that they provide an ideal environment for the propagation of nonlinear waves, since they can support a wide range of effective nonlinear behaviors that are determined by the architecture.


Katia Bertoldi is the Gordon McKay Professor of Applied Mechanics at the Harvard John A.Paulson School of Engineering and Applied Sciences. She earned master degrees from Trento University (Italy) in 2002 and from Chalmers University of Technology (Sweden) in 2003, majoring in Structural Engineering Mechanics. Upon earning a Ph.D. degree in Mechanics of Materials and Structures from Trento University, in 2006, Katia joined as a PostDoc the group of Mary Boyce at MIT. In 2008 she moved to the University of Twente (the Netherlands) where she was an Assistant Professor in the faculty of Engineering Technology. In January 2010 Katia joined the School of Engineering and Applied Sciences at Harvard University and established a group studying the mechanics of materials and structures. She is the recipient of the NSF Career Award 2011 and of the ASME's 2014 Hughes Young Investigator Award.

Dr Bertoldi’s research contributes to the design of materials with a carefully designed meso-structure that leads to novel effective behavior at the macroscale. She investigates both mechanical and acoustic properties of such structured materials, with a particular focus on harnessing instabilities and strong geometric non-linearities to generate new modes of functionality. Since the properties of the designed architected materials are primarily governed by the geometry of the structure (as opposed to constitutive ingredients at the material level), the principles she discovers are universal and can be applied to systems over a wide range of length scales.

October 13

MEAM PhD Thesis Defense

Dawei Song, Ph.D. Candidate, University of Pennsylvania
Advisor: Pedro Ponte

"Constitutive Modeling of Viscoplastic Porous Single Crystals and Polycrystals"


Modeling of the overall constitutive behavior of porous materials has been of central interest in the solid mechanics community over decades. Most studies are carried out in the context of two-phase material systems consisting of voided inclusions and an isotropic (visco)plastic matrix, as usually characterized by von Mises yield criterion or flow potential. However, for more realistic and general conditions, the material surrounding the voids exhibits anisotropic behavior, either due to local crystallography in single crystals, or to the crystallographic texture for polycrystalline aggregates.

In this talk, I will present a new homogenization-based constitutive model to estimate the macroscopic response of porous single crystals and porous polycrystals. The model makes use of the effective behavior of a linear comparison composite (LCC), whose local property is determined by a suitably designed variational principle, to determine the effective behavior of the actual nonlinear composites. The resulting estimates for the macroscopic response are guaranteed to be exact to second-order in the heterogeneity contrast, and to satisfy known bounds. In addition, consistent homogenization estimates may be obtained for the average deformation fields in the composites, which can in turn be used to determine the evolution of the microstructure at finite-strain deformations. Applications will be given for porous FCC and HCP crystals, and the predictions of the model will be compared with numerical results available in the literature.

October 17

Sarah Bergbreiter, Associate Professor of Mechanical Engineering, University of Maryland at College Park

"Microsystems-Inspired Robotics"


The ability to manufacture micro-scale sensors and actuators has inspired the robotics community for over 30 years. There have been huge success stories; MEMS inertial sensors have enabled an entire market of low-cost, small UAVs. However, the promise of ant-scale robots has largely failed. Ants can move high speeds on surfaces from picnic tables to front lawns, but the few legged microrobots that have walked have done so at slow speeds (< 1 body length/sec) on smooth silicon wafers. In addition, the vision of large numbers of microfabricated sensors interacting directly with the environment has suffered in part due to the brittle materials used in microfabrication. This talk will present our progress in the design of sensors, mechanisms, and actuators that utilize new microfabrication processes to incorporate materials with widely varying moduli and functionality to achieve more robustness, dynamic range, and complexity in smaller packages. Results include skins of soft tactile or strain sensors with high dynamic range, new models of bio-inspired jumping mechanisms, and magnetically actuated legged microrobots from 1 gram down to 1 milligram that provide insights into simple design and control for high speed locomotion in small-scale mobile robots.


Sarah Bergbreiter joined the University of Maryland, College Park in 2008 and is currently an Associate Professor of Mechanical Engineering, with a joint appointment in the Institute for Systems Research. She received her B.S.E. degree in Electrical Engineering from Princeton University in 1999, and the M.S. and Ph.D. degrees from the University of California, Berkeley in 2004 and 2007 with a focus on microrobotics. Her research uses inspiration from microsystems and biology to improve robotics performance at all scales. She has been awarded several honors including the DARPA Young Faculty Award in 2008, the NSF CAREER Award in 2011, and the Presidential Early Career Award for Scientists and Engineers (PECASE) in 2013 for her research on engineering robotic systems down to sub-millimeter size scales. She also received the Best Conference Paper Award at IEEE ICRA 2010 on her work incorporating new materials into microrobotics and the NTF Award at IEEE IROS 2011 for early demonstrations of jumping microrobots. She currently serves on DARPA’s Microsystems Exploratory Council and as an associate editor for IEEE Transactions on Robotics and ASME Journal on Mechanisms and Robotics.


Stephan Wulfinghoff, Engineer-in-Chief, Institute of Applied Mechanics, RWTH Aachen University

"Challenges in Material Modeling on Different Scales"


Multi-scale material models have numerous advantages over phenomenological approaches. In particular, they are more realistic, intuitive and comprehensive. However, they also suffer from slowness and different issues related to the small scale material behavior. Thus, there is still a long road to go until they can replace phenomenological models in everyday applications. The presentation will discuss approaches that aim to overcome the aforementioned issues. The focus will be on model order reduction techniques and material models which are particularly designed for small scale applications.


Stephan Wulfinghoff is the Engineer-in-Chief at the Institute for Applied Mechanics at the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen University, in Aachen, Germany. He is currently engaged in a Theodore von Karman Fellowship grant for research at the University of Pennsylvania, under the guidance of Dr. Pedro Ponte Castaneda. In 2014 he completed his PhD (summa cum laude) at the Karlsruhe Institute of Technology.

October 24

Daniel Steingart, Associate Professor of Mechanical and Aerospace Engineering, Princeton University

"Exploring and Exploiting Often Unwanted Coupling in Closed Electrochemical Energy Cells"


Endeavors in electrochemical energy storage are industrial masochism for the same reason they are academic hedonism: a working, rechargeable battery represents a tight coupling of multiphase phenomena across the chemical, electrical, thermal and mechanical domains. Despite these couplings, most treatments of batteries in literature emphasize the material challenges and opportunities as opposed to the system level dynamics. There good reasons for this: 1) to date, tools for examining the structure of “real” cells in operando are largely limited to synchrotron x-ray and neutron methods, 2) full cells are products engineered for application demands and not platonic ideals and 3) material improvements can have enormous impact on battery performance.

Yet understanding and examining the physical dynamics of cells in a “scaled context” is a worthwhile academic endeavor. The battery as a system presents problems that are difficult to decouple, but the study of such problems can introduce new opportunities and inform electrochemical reactor designs and material utilization strategies.

In this talk I will motivate two areas where a systems approach might be worthwhile. The first area abstracts the chemistry within a battery, almost completely, to examine what the consequences of mass transport and mass conservation have on mechanical behaviors within the cell. The second area openly go where angels fear to tread and asks “Why is a short circuit a bad thing?”


Dan Steingart is an Associate Professor in the Department of Mechanical and Aerospace Engineering and the Andlinger Center for Energy and the Environment at Princeton University. His group, the Princeton Lab for Electrochemical Engineering Systems Research, studies the interactions between materials and systems in electrochemical reactors with a focus on energy storage devices. His current research looks to exploit traditional failure mechanisms and "unwanted" interactions with batteries for systematic understanding and device enhancement. His efforts in this area over the last decade have been adopted by various industries and have led directly or indirectly to five energy related startup companies, the latest being Feasible, an effort dedicated to exploiting the inherent acoustic responses of closed electrochemical systems.

October 31

David Issadore, Assistant Professor of Bioengineering, University of Pennsylvania

"Diagnosing Disease on a Microchip: Scaling Up Micro- and Nano-Scale Diagnostics"


The transformative growth in microelectronics in the latter half of the 20th century was fueled fundamentally by the ability to simultaneously miniaturize and integrate complex circuits onto monolithic chips. The impact of this growth has been profound– computing is pervasive and portable, communication is instant and global, and information is ubiquitously gathered and shared. My research aims to harness these same electrical engineering approaches, which have enabled the microelectronic revolution, to solve high impact problems in medical diagnostics. To accomplish this goal my lab develops hybrid microchips, where microfluidics are built directly on top of semiconductor chips.

In this talk I will focus mainly on my most recent work at Penn on 'digital asays.' Digital assays — in which ultra-sensitive molecular measurements are made by performing millions of parallel experiments in picoliter droplets — have generated enormous enthusiasm due to their single molecule resolution and robustness to reaction conditions. These assays have incredible untapped potential for disease diagnostics, environmental surveillance, and biosafety monitoring, but are currently confined to laboratory settings due to the instrumentation necessary to generate, control, and measure tens of millions of independent droplets. To overcome this challenge, we are developing a hybrid microelectronic / microfluidic chip to ‘unlock’ droplet-based assays for mobile use. Our microDroplet Fluorescence Detector (µDFD) takes inspiration from cellular networks, in which phones are identified by their carrier frequency and not their particular location. In the same way, but on a much smaller scale, we screen millions of droplets per second using only a conventional smartphone camera. In collaboration with physicians at The Abramson Cancer Center, we are demonstrating the power of this approach by developing a multiplexed exosome-based point of care diagnostic for the early detection of pancreatic cancer.


David Issadore is an Assistant Professor of Bioengineering at the Univeristy of Pennsylvania. He obtained his MA and PhD in Applied Physics in 2009 at Harvard University. David Issadore's research focus is on microelectronics, microfluidics, nanomaterials and molecular targeting, and their application to medicine. These multidisciplinary skills enable him to explore new technologies that can bring medical diagnostics from expensive, centralized facilities, directly to clinical and resource-limited settings. He has developed hybrid chip designs, a portable NMR system and the micro Hall detector.

November 6

MEAM PhD Thesis Defense

Jimmy Paulos, Ph.D. Candidate, University of Pennsylvania
Advisor: Mark Yim

"Rotorcraft Blade Pitch Control Through Torque Modulation"


Micro air vehicle (MAV) technology has broken with simple mimicry of manned aircraft in order to fulfill emerging roles which demand low-cost reliability in the hands of novice users, safe operation in confined spaces, contact and manipulation of the environment, or merging vertical flight and forward flight capabilities. These specialized needs have motivated a surge of new specialized aircraft, but the majority of these design variations remain constrained by the same fundamental technologies underpinning their thrust and control. This dissertation solves the problem of simultaneously governing MAV thrust, roll, and pitch using only a single rotor and single motor. Cyclic blade pitch variations in a special passively articulated rotor are obtained by modulating the main drive motor torque in phase with the rotor rotation. Such an actuator enables new cheap, robust, and light weight aircraft by eliminating the need for the complex ancillary controls of a conventional helicopter swashplate or the distributed propeller array of a quadrotor.

An analytic model predicts the experimentally observed torque, hub speed, pitch, and flap motions of rotors from 10 cm to 100 cm in diameter. We show the operating principle scales similarly as traditional helicopter rotor technologies, but is subject to additional new dynamics and technology considerations. Conventional flight characteristics are obtained in experimental aircraft from 29 g to 870 g, none of which require more than two motors for operation. In addition, the unusual capabilities of a fully actuated MAV over six degrees of freedom were emulated using only the thrust vectoring qualities of two teetering rotors. Such independent control over forces and moments has previously been obtained by holonomic or omnidirection multirotors with at least six motors, but similar abilities can now be demonstrated using only two. Future categories of MAV enabled by this actuator are illustrated by experiments with a single actuator aircraft with spatial control and a vertical takeoff and landing airplane whose flight authority is derived entirely from two rotors.


November 7

STEM Library Resource Seminar

Douglas G. McGee, Assistant Director for STEM Libraries, University of Pennsylvania

"Patents and Startups"


Penn Libraries provides a wide array of resources to support business plan writing, market research, financing and more. Doug McGee, Engineering Librarian, will provide an overview of what’s available for students interested in entrepreneurship and start-ups can access before they graduate.

November 14

Satwindar S. Sadhal, Professor of Aerospace and Mechanical Engineering, University of Southern California

"Singular Perturbation Analysis of Drops in Acoustic Levitation Fields"


Streaming is an interesting phenomenon that arises due the nonlinear behavior of fluids undergoing oscillations. Acoustic fields typically consist of oscillatory flows that have zero mean. However, in the presence of solid boundaries, nonzero mean flow takes place in the background of the oscillatory flow. The interest in streaming has emanated from research on acoustic levitation of liquid drops, a phenomenon that consists of trapping drops in standing waves. To understand the detailed fluid dynamics of streaming in such systems, singular perturbation techniques have been employed where high frequency (w) is used to define suitable perturbation parameters (U0/wa ≪ 1 and wa2/v ≫ 1). The focus of this presentation is on the Schlichting-type streaming that takes place when an oscillating fluid interacts with a solid surface where vorticity is generated and nonlinearities set in. It has been demonstrated that this type of streaming can also occur due to interaction at fluid-fluid interfaces. Several sets of analytical solutions have been developed for flow fields around acoustically suspended drops. Among the interesting physical phenomena in this research are the existence of thin recirculating zones around the suspended particle, and the remarkable difference between the behavior of drops and solid particles.


Professor Sadhal received his PhD from Caltech in 1978 whereupon he joined the faculty at MEAM. He subsequently went on to the University of Southern California in 1982 and has been on the faculty of Aerospace and Mechanical Engineering since then. His research includes fundamental work with drops and bubbles, especially pertaining to phase change, interaction with solid surfaces, interfacial phenomena including the effect of surfactants, and interaction with acoustic levitation fields. He has also made several fundamental contributions towards thermal contact problems. More recently, he has diversified into the field of ocular drug delivery, and is developing a comprehensive mathematical model for fluid flow and transport phenomena in the eye, together with accurate experimental measurements of biophysical properties of various ocular tissue, as well as extensive model validation.

November 21


November 28

Jay D. Humphrey, John C. Malone Professor and Chair of the Department of Biomedical Engineering, Yale University

"Mechanics of Arteries in Health and Disease"


Arteries are complex structures, consisting of diverse load bearing extracellular matrix constituents and cells. Understanding the mechanics of these vessels is doubly important. Stress analyses can aid in the understanding of catastrophic failure (e.g., dissection and rupture) and similarly mechano-biological responses by cells (i.e., changes in gene expression in response to changes in stress). In this talk, we will survey different applications of mechanics (based on nonlinear continuum mechanics) to understand better the biomechanics of arteries in health and disease, including the progression of aneurysms and development of dissections.


J.D. Humphrey received the Ph.D. degree in Engineering Science and Mechanics from The Georgia Institute of Technology and completed a post-doctoral fellowship in Medicine - Cardiovascular at the Johns Hopkins University. He is currently John C. Malone Professor and Chair of Biomedical Engineering at Yale. He has authored a graduate textbook (Cardiovascular Solid Mechanics), co-authored an undergraduate textbook (An Introduction to Biomechanics), co-authored a handbook (Style and Ethics of Communication in Science and Engineering), co-edited a research text (Cardiovascular Soft Tissue Mechanics), published chapters in 20+ other books or encyclopedias, and published 230+ archival journal papers. He served for 10 years as founding co-editor-in-chief for the international journal Biomechanics and Modeling in Mechanobiology and currently serves as Chair of the US National Committee on Biomechanics. He is a Fellow of the American Institute of Medical and Biological Engineering and a Fellow of the American Society of Mechanical Engineers.

December 5

Randy H. Ewoldt, Associate Professor of Mechanical Science and Engineering, University of Illinois at Urbana-Champagn

"Sticky Droplets and Sinking Bubbles: Curious Physics of Yield-stress Fluids"


Fluids should flow, and bubbles should rise, but we consider phenomena that violate such intuition. The phenomena motivate several applications (fire suppression, spray coating, high performance concrete) and are possible due to a class of soft materials known as yield-stress fluids. Examples include gels, pastes, biopolymer hydrogels, fresh concrete, and colloidal suspensions, which reversibly transition from fluid at high stress to solid at low stress. This talk will discuss our work on droplet impacts (splashing, spreading, sticking) of these non-Newtonian fluids, as well as efforts to design these materials and use them for peculiar behavior, such as making bubbles sink. Research approaches include high-speed video, rheological characterization, structure-properties modeling, and fluid dynamics scaling analysis. Two new dimensionless groups will be described that rationalize the two phenomena of (i) splashing of yield-stress fluids and (ii) gravity-opposed motion of particles/bubbles suspended in such rheologically-complex soft materials.


Randy H. Ewoldt is an Associate Professor in the Department of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign. He has Ph.D. and S.M. degrees from MIT, and a B.S. degree from Iowa State, all in Mechanical Engineering. Before joining Illinois, he held a post-doctoral fellowship at the University of Minnesota. At Illinois, his research group studies rheology, fluid mechanics, and design of complex fluids; in particular, this includes yield stress fluids, polymer gels, biological materials, and large-amplitude oscillatory shear (LAOS) characterization. He serves on the editorial board for the Journal of Non-Newtonian Fluid Mechanics and his work has been recognized by young investigator awards from NSF, ASME, 3M, DuPont, and The Society of Rheology. In 2017 he received the Presidential Early Career Award for Science and Engineering (PECASE).