MEAM Seminar Series Archive: Fall 2009
"Automotive and industrial tribology challenges"
Speaker: Andrew Jackson
Senior Scientific Advisor, Corporate Strategic Research Laboratory
ExxonMobil Research and Engineering Company
The presentation opens with a primer on tribology, the science of interacting surfaces in relative motion, and then reviews the role of tribology in the formulation of automotive and industrial lubricants. Economic drivers for engineering equipment include efficiency, reliability, maintenance costs, productivity and durability, all of which are impacted by tribology. Tribologists consider equipment in terms of the components where surface interactions take place, such as cams, bearings, gears, pistons and seals. Lubricants are formulated to control friction, wear, seizure, fatigue, deposits, sludge and corrosion.
The scale of the global lubricants business is outlined. Tribology research methods for the discovery of lubricants with enhanced performance are then briefly discussed. Examples of tribology challenges covered in the presentation include balancing fuel economy and wear protection in passenger vehicle engine oils, formulation issues facing commercial vehicle engine oils in the face of emission regulations, and efficiency and durability enhancements in gear oils and hydraulic oils.
Opportunities for improved performance of lubricants are then summarized in light of market needs and the presentation will close with thoughts on the strengths and weaknesses of lubrication technology together with a summary of automotive and industrial tribology challenges in 2009 and beyond.
Host: John Bassani
"Lipid membranes in electric fields"
Speaker: Petia Vlahovska
Assistant Professor of Engineering
Membranes that encapsulate cells and internal cellular organelles are composed primarily of lipid bilayers. In this talk I will discuss the effects of electric fields on giant vesicles (cell-size lipid membrane sacs), which serve as a useful model system to study membrane electro-deformation, -poration and -fusion.
I will present a new theory to explain vesicle shapes in alternating electric fields . The analysis is challenging because of the membrane electromechanics: First, the lipid membrane is an insulating shell impermeable to ions. Second, it is essentially a two-dimensional incompressible-fluid sheet---under stress, lipid membranes store elastic energy in bending, while polymerized membranes are more likely to be stretched and sheared. Third, lipid membranes are extremely soft and they are easily bent by the thermal noise. Our theory accounts for these three features. The vesicle shape is obtained by balancing electric, hydrodynamic, bending, and tension stresses exerted on the membrane. Our approach, which is based on force balance, also allows us to describe the time evolution of the vesicle deformation, in contrast to earlier works based on energy minimization, which are able to predict only stationary shapes.
The theoretical predictions for vesicle deformation are consistent with experiment. If the inner fluid is more conducting than the suspending medium, the vesicle always adopts a prolate shape. In the opposite case, the vesicle undergoes a transition from a prolate to oblate ellipsoid at a critical frequency, which the theory identifies with the inverse membrane charging time. At frequencies higher than the inverse Maxwell-Wagner polarization time, the electrohydrodynamic stresses become too small to alter the vesicle's quasispherical rest shape.
Our study improves understanding of the physical mechanisms underlying applications such as gene transfection and nanoparticle synthesis by vesicle electrofusion.
 P.M. Vlahovska, R. S. Gracia, S. Aranda and R. Dimova, "Electrohydrodynamic model of vesicle deformation in alternating electric fields ", Biophysical Journal, 96 pp. 4789-4803 (2009)
Host: Paulo Arratia
"Nanomanufacturing for medicine and energy"
Speaker: Shaochen Chen
Program Director for Nanomanufacturing, US National Science Foundation
Professor, Mechanical Engineering Department, The University of Texas at Austin
I will first talk about the NSF Nanomanufacturing Program and the grand challenges of nanomanufacturing research. I will then discuss my laboratory’s recent research efforts in nanophotonics that use plasmonic effects for nanoscale light manipulation and nanofabrication. I will also present several on-going projects in using such advanced micro/nano-fabrication methods for the development of biomedical micro/nano-devices and energy-on-a-chip systems.
Host: Robert Carpick
Sr. Industrial Hygienist
Environmental Health & Radiation Safety
Karen Kelley, CIH
Industrial Hygienist, Laser Safety Officer
University Information Security Specialist
* All first year MEAM graduate students must attend.
"Rational design of load bearing tissues"
Speaker: Robert Mauck
Assistant Professor of Orthopaedic Surgery and Bioengineering
McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery
University of Pennsylvania
Engineering fibrous tissues of the musculoskeletal system represents a considerable challenge due to the complex architecture and mechanical properties of the component structures. Natural healing in these dense tissues is limited as a result of the mechanically challenging environment of the damaged tissue and the hypo-cellularity and avascular nature of the extracellular matrix. When healing does occur, the ordered structure of the native tissue is replaced with a disorganized fibrous scar with inferior mechanical properties, engendering sites that are prone to re-injury. To overcome these limitations, we and others have adopted a structurally-motivated tissue engineering approach based on organized nanofibrous assemblies. These scaffolds are composed of ultra-fine biodegradable and biologic fibers that can be fabricated in such a way as to recreate the structural anisotropy typical of fiber-reinforced tissues. This straight and narrow topography not only provides tailored mechanical properties, but also serves as a 3D micro-pattern for directed tissue formation. This talk will describe the underlying technology of nanofiber production, several newly developed fabrication strategies aimed at instilling dynamic and multi-functional characteristics, and the mechanical evaluation and theoretical modeling of these scaffolds as it relates to native tissue structure and function. Several case examples where these principles have been put to test will be discussed, as will the remaining challenges and opportunities in forwarding this technology towards clinical implementation.
Host: Dawn Elliott
Adrian J. Lew
"Discontinuous Galerkin methods in solid mechanics"
Speaker: Adrian J. Lew
Assistant Professor of Mechanical Engineering
Some problems in Solid and Structural mechanics require special care when analyzed via finite element approximations. Typical examples are problems that involve kinematic constraints, such as in incompressible elasticity or Reissner-Mindlin plate models, and problems involving moving boundaries, such as evolving cracks, phase transition interfaces or shape optimizations. Nonlinearities in the material behavior only exacerbate these difficulties, and immediately rule out many of the proposed solutions.
In this talk I will show how under these circumstances Discontinuous Galerkin methods provide an attractive and advantageous alternative. The overarching idea I will convey is that by relaxing the constraint of having continuous displacements across element boundaries, Discontinuous Galerkin methods are able to impose other kinematic constraints in the problem and still provide accurate solutions. I will demonstrate it by showcasing the performance of a class of Discontinuous Galerkin methods we introduced in a variety of circumstances. First, in nonlinear elasticity problems involving different kinematic constraints. Second, in a class of immersed boundary methods, which sidestep the need for automatic remeshing in problems with evolving boundaries by embedding the boundary in any mesh. And finally, in the accurate solution of the stress and displacement fields around cracks when cracks are "embedded" in the mesh, as in extended finite element methods. Some of these ideas carry over to a wider variety of popular methods in Solid Mechanics, such as Enhanced Strain Methods.
Host: Pedro Ponte Castañeda
"Mechanics of actomyosin interaction and the role of substrate stiffness on actin network dynamics"
Speaker: Sean Sun
Associate Professor, Whiting School of Engineering
Johns Hopkins University
Myosin is a major molecular force generator in the cell. The essential features of myosin interaction with actin filaments are understood. In the cell, the interactions of myosin with F-actin, substrate adhesions and other actin-associated proteins are less clear. We will borrow ideas from mathematical models of skeletal muscle to develop simple models for integrin focal adhesions, actin cross-linking proteins and non-muscle myosin-II. When these components are combined, a dynamical picture of the actin network emerges. In this talk, we will focus on the role of cell-substrate stiffness on the actin dynamics. Possible implications for mechanical sensing by cells are discussed.
Host: Prashant Purohit
"Two problems in micron-scale fluid mechanics"
Speaker: Kenneth Breuer
Professor, Division of Engineering
I will present two excerpts from some recent work in our lab concerning the behavior of fluids at micrometer and nanometer scales.
Bacterial Microfluidics: The Physics and Engineering of Swimming Bacteria - Flagellated bacteria, such as E. Coli, propel themselves using multiple flagella - long, thin helical filaments - that are rotated using nanoscale motors. We will discuss a few aspects of the fluid mechanics associated with bacterial motility, studied using scale modeling, numerical simulations and microscale experiments. The phenomena explored include the mechanics of flagellar bundling, in which several distinct filaments combine into a single helical bundle via viscous hydrodynamic interactions, the flow fields associated with viscous helical motions, and mechanisms for hydrodynamic synchronization of adjacent flagella motion. We will also (briefly) show how the flagella motion can be harnessed in engineered systems to enhance low Reynolds number mixing, to pump fluids, and to transport objects through microfluidic systems.
"The Tail Wagging the Dog" - The Fluid Physics of Contact Droplet Deposition - Contact droplet deposition is achieved when a small rod or needle is dipped into a viscous fluid, touched to a smooth substrate and then withdrawn. The size of the resulting drop left on the substrate turns out to be a surprisingly complex function of the fluid properties, needle dimension, retraction speed, and the detailed microscale physics of the moving contact line established between the liquid, gas and substrate. As an example by varying the retraction speed alone, droplet sizes ranging from several millimeters to a few microns in diameter can be achieved. We explore this system using analytical, numerical and experimental techniques and explain the different flow regimes, and how the "tail" - the nanoscale dynamic contact line physics can "wag the dog" - the resultant droplet size.
Host: Paulo Arratia
Daniel S. Gianola
"Deformation mechanisms and size-dependent mechanical response at the nanoscale"
Speaker: Daniel S. Gianola
Skirkanich Assistant Professor
Department of Materials Science and Engineering, University of Pennsylvania
Metal nanostructures proposed as the fundamental building blocks for emerging nanotechnological devices will often be subject to extreme duress during operation, particularly high mechanical stresses. Investigations of size-dependent deformation have shown that “smaller is stronger” in metals, yet the underlying mechanisms that give rise to this departure from bulk behavior are still elusive. The emerging picture is that plasticity in extremely small volumes is fundamentally different than in large materials; the law of averages gives way to discrete processes that dominate the response. Systematically probing the mechanical response and uncovering the underlying deformation mechanisms of diminishingly small structures at the micro- and nanoscale requires new strategies and approaches that circumvent difficulties associated with handling, gripping, loading, and measuring small specimens. The need for in situ experiments that give a one-to-one correlation between mechanical response and deformation morphology is exacerbated by the fact that electron optics are needed to image and manipulate nanostructures.
In this talk, I will describe quantitative in situ tensile experiments on quasi-1D metallic nanostructures using electron and ion beam microscopies. In particular, the intimate link between pre-existing defects and flaws, which is critically tied to the materials synthesis route, and mechanical response will be discussed.
Host: Prashant Purohit
Joachim L. Grenestedt
"Lightness and speed: The future of boats, airplanes and land vehicles"
Speaker: Joachim L. Grenestedt
Professor, Department of Mechanical Engineering & Mechanics
Dr. Grenestedt will talk about various vehicles that he has been involved in designing and/or building. These range from Navy stealth ships and single engine aircraft to salt flats land speed racers. A common denominator is that they are lightweight and efficient. Most of them are built of carbon fiber or glass fiber composites. He will show some examples of where this field is heading, and he will give some personal ideas of what kinds of vehicles people may use in the future.
Host: John Bassani
Spring Berman, PhD Candidate
"Abstractions, analysis techniques, and synthesis of scalable control strategies for robot swarms"
Speaker: Spring Berman
Advisor: Vijay Kumar
Department of Mechanical Engineering and Applied Mechanics
University of Pennsylvania
Tasks that require parallelism, redundancy, and adaptation to dynamic, possibly hazardous environments can potentially be performed very efficiently and robustly by a swarm robotic system. Such a system would consist of hundreds or thousands of anonymous, resource-constrained robots that operate autonomously, with little to no direct human supervision. The massive parallelism of a swarm would allow it to perform effectively in the event of robot failures, and the simplicity of individual robots facilitates a low unit cost.
Key challenges in the development of swarm robotic systems include the accurate prediction of swarm behavior and the design of robot controllers that can be proven to produce a desired macroscopic outcome. The controllers should be scalable, meaning that they ensure system operation regardless of the swarm size. In this talk, I will present a comprehensive approach to modeling a swarm robotic system, analyzing its performance, and synthesizing scalable stochastic control policies that cause the swarm members to collectively achieve a target objective. The control policies are decentralized, computed a priori, implementable on robots with limited sensing and communication capabilities, and have theoretical guarantees on performance. I will demonstrate the application of this approach to the design of a swarm task allocation strategy that does not rely on inter-robot communication and a reconfigurable manufacturing system. My approach is inspired by the self-organized behavior of natural swarms such as ant colonies, which achieve complex tasks through the local interactions of many simple individuals.
"Polydomain liquid crystal elastomers"
Speaker: Kaushik Bhattacharya
Professor of Mechanics and Materials Science
California Institute of Technology
Liquid crystal elastomers are rubbery materials that possess liquid crystal order. They undergo a large spontaneous deformation as they undergo a symmetry-breaking isotropic to nematic transition. Consequently, they are able to display unusually soft behavior by the formation and evolution of fine-scale microstructure. This soft behavior is of interest to various applications including actuation. After a brief background, this talk will present a theory that describes the overall mechanical properties of these materials. An important outcome of the theory is to show that the soft behavior depends critically on the liquid crystal phase in which the material is cross-linked to form the elastomer. The talk will also describe recent results concerning the non-intuitive mechanical behavior of thin membranes of these materials. Joint work with John Biggins, Fehmi Cirak, Qing Long, Carl Modes and Mark Warner.
We consider the equilibrium stress strain behavior of polydomain liquid crystal elastomers. We show that there is a fundamental difference between elastomers crosslinked in the high temperature isotropic and low temperature aligned states. Those crosslinked in the isotropic state then cooled to an aligned state will exhibit extremely soft elasticity — indeed softer than any monodomain sample — and ordered director pattens characteristic of textured deformations. Those crosslinked in the aligned state will be mechanically much harder and characterized by schlieren disclination textures.
Host: Prashant Purohit
Tedori-Callinan Lecture: "Micro and nano robotics"
Learn more about the lecture here!
"Nanomechanics of nano-carbon"
Speaker: James Hone
Associate Professor, Department of Mechanical Engineering and NSEC
This talk will describe our work toward fundamental understanding of the mechanical and electromechanical properties of carbon nanotubes and graphene, and their application in nano-electromechanical devices (NEMS). Using a combination of optical characterization and electromagnetic displacement, we have measured the mechanical stiffness of individual nanotubes of known chiral index. Similar techniques have been used to measure the electromechanical response of individual nanotubes, in particular the strain-induced changes in electronic bandstructure; these measurements diverged quantitatively from previous theoretical predictions, but revision of the theory leads to excellent agreement with experiment. We have used nanoindentation to measure the elastic stiffness and ultimate strength of single graphene sheets. These measurements show that graphene is the strongest material ever measured, with an ultimate strength of 130 GPa at strain rates of over 25%. As such, it is the first material whose mechanical properties can be probed deep into the nonlinear elastic regime. We have also measured the frictional behavior of graphene, which shows an unexpected strong dependence on the number of atomic layers. Finally, we have demonstrated electronic readout of graphene nanomechanical resonators, and tested their response to changes in mass and temperature.
Host: Robert Carpick
"Microelectromechanical systems for biomolecular sensing and manipulation"
Speaker: Qiao Lin
Associate Professor of Mechanical Engineering
Microelectromechanical systems (MEMS) technology holds the potential to vitally impact biology and medicine. In particular, MEMS can be exploited as innovative tools for biological sensing and manipulation. Such miniaturized systems allow biomolecules to be interrogated in controlled micro/nanoscale environments with orders-of-magnitude reduction in the consumption of biological material. Functional and structural integration enables multi-faceted analysis of complex biomolecular processes with improved sensitivity, reliability and automation. Arrays of devices integrated in a single system afford parallelized, high-throughput processing of biological samples. Ultimately, such systems will enable novel biomolecular investigations that are unattainable with conventional technologies.
This presentation will provide a highlight of our research in applying MEMS to enable and facilitate biomolecular sensing and manipulation. One of our efforts involves manipulation of biomolecules by exploiting polymers as micro/nanofluidic functional materials. For example, highly compliant microstructures of elastomeric polymers are used as passive flow control devices, while stimulus-responsive oligonucleotides are exploited to enable active biomolecular manipulation. In another effort, we integrate sensitive MEMS transducers with microfluidic systems to enable biosensing. Examples include miniaturized affinity sensors for metabolic monitoring, and calorimetric devices for characterizing conformational transitions and interactions of biomolecules. These examples will be presented to demonstrate the potential impact of MEMS on biomedical applications.
Host: Haim Bau