Mechanical
and Materials Engineering
Abstracts 2004-2005
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584 EBU II
Dr. Dan B. Miracle
Air Force Research Laboratory, Materials and Manufacturing Directorate
Wright-Patterson Air Force Base
An Atomic Structural Model for Metallic
Glasses
An
atomic structural model for metallic glasses has very recently been established.
Using relative atomic sizes as the primary variable, this structural model is
derived from the requirement to efficiently fill space in a system of unequal
spheres. Three separate comparisons with experimental data have been conducted
to validate this model. The first is comparison with partial radial
distribution functions, the second is with atomic coordination numbers, and the
third is a prediction of metallic glass constitution. The agreement between
experiment and predictions is good in all three cases, including a compelling
ability to explain the compositions in a wide range of simple and complex
glasses based on Zr, Pd, rare
earth metals, Al, Mg and Fe. The basic features of this model will be described
and the specific atomic arrangements that provide the ability to stabilize
metallic glasses will be discussed. Insights gained from this model will be
explored.
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479 EBU II
Sadik Esener
Electrical and
Photonics: A
Link from the Micro into the Nanoworld
Over the last decade, micro-photonics has enabled
significant progress in diverse fields including fiber optic communication,
sensing, scanning, storage, and displays. Photonics is also penetrating new
applications including lighting, biological sensing and, and intra-computer
(backplane) communication systems. Starting with accomplishments of photonics
in the “macroworld interconnects”,
this talk will explore the potential role and limitations of photonics in the
upcoming exploration of the “nanoworld” with
engineering applications in biophotonics.
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479 EBU-II
Nanometer-scale
Analysis of Grain Boundary Segregation in Metals and Alloys
Grain boundaries play a major role in determining the properties of almost all engineering materials. Very often the boundary is the source of brittle or premature failure and, therefore, its characteristics limit the performance of the material. In particular, intergranular failure is a widespread fracture mode including such undesirable phenomena as hydrogen embrittlement, temper embrittlement and liquid-metal embrittlement. A common factor in such failures is the presence of elements that segregate to the grain boundary. To understand grain boundary chemistry and its role in intergranular failure, we need to be able to characterize the boundaries in detail. Characterization can take many forms but, for a full comprehension of the problem, it is necessary to understand the crystallographic structure, the elemental chemistry and the local bonding at the boundary, often down to the nanometer level or below. Transmission electron microscopy (TEM) is unique in its ability to determine all these characteristics in a single instrument, using diverse techniques such as imaging, diffraction, X-ray and electron spectrometry) thus permitting correlation of the structure, chemistry and properties of grain boundaries. This talk will describe the application of these various TEM techniques to grain boundary segregation in a range of metals and alloys, including prospects for improved analysis via the latest generation of aberration-corrected analytical electron microscopes.
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479 EBU-II
Professor K. Komvopoulos
Department of
“Nanoscale Surface Science and Engineering –
The
Beginning of a New Era?”
Recent advances in
nanotechnology have created great demands for basic science and engineering at
the nanoscale. Because of the unique physical laws governing
material behavior at the atomic and molecular levels, new engineering
approaches and different thinking processes must be adopted. Representative
examples of nanotechnology-based accomplishments drawn from the information
storage, nano-/micro-electromechanical systems, and
biotechnology fields will be presented to illustrate the promises of
nanotechnology, in conjunction with scientific and technology challenges that
must be overcome for growth to continue.
The origins of surface forces, significance of self-affinity in surface
texture, material response to localized deformation, self-assembly of monolayers, and some unusual behavior of metallic and
polymeric surfaces at submicron and molecular levels will be discussed next.
Results from surface nanomachining, nanostructuring and nanomodification
studies performed with mechanical, electromechanical, and chemical methods,
based on microprobe, ultrafast laser, and
spectroscopy techniques, will be shown followed by selected numerical results
from nanomechanics and molecular dynamics analyses of
surface contact. The seminar will conclude with a view toward future trends and
challenges in nanoscale surface science and
engineering.
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479 EBU-II
Professor
Eduard Arzt
Deputy Managing Director
Max Planck Institut fuer Metallforschung
University of Stuttgart
Stuttgart, Germany
“Biological and
Artificial Attachment Devices: Lessons For Materials
Scientists From Flies and Geckos”
Mechanical performance governs the usefulness of many
man-made devices. In biology, mechanics is often essential for survival: this
is true on the molecular level, on the cellular level and for whole organisms.
This keynote talk will describe an interdisciplinary study involving materials
scientists, biologists, and physicist aimed at elucidating the correlation
between structure and performance of attachment devices in insects (flies,
beetles), spiders, and geckos. In all of these cases, adhesion is mediated by
the interaction of finely-structured contact elements with the different
substrates. We study the structure of these elements on the micro and nano level by different microscopy techniques including
SEM, TEM, AFM and X-ray imaging. Local mechanical properties and adhesion
forces are measured by nanomechanical test methods
and compared with predictions based on theoretical contact mechanics. For
example, it has been possible for the first time to measure the adhesion of
single gecko spatulae, with dimensions of 200 nm, to
selected substrates by atomic force microscopy. Structure, size and shape of
the contact elements are found to play important roles; in particular the
principle of “contact splitting” has been identified: finer contact elements
(down to submicron level) produce larger contact forces in heavier animals. The
actual dimensions of the contact elements follow exactly the theoretical
predictions, a relationship that covers 6 orders of magnitude in animal mass
from the fruit fly to the gecko! From our findings, important conclusions can
be drawn on the optimal design of artificial contact elements. The talk will
present first prototype adhesive surfaces produced with this insight and
identify their technical limits by introducing “adhesion mechanism maps”. These
developments have led to the design of artificial micro-attachment systems (“biomimicry”) which are potentially useful in
micro-technology.
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479 EBU-II
R. M. Brannon, Ph.D.
Geomechanics
Sandia National Laboratories
“Accepted, Rejected, and Questionable
Tenets of Phenomenological Plasticity Theory for Brittle Media”
Historically, the term
“plasticity” has been regarded in its strictly physical sense as a
form of inelasticity associated with dislocations. Applications have (until the
last few decades) typically focused on metallurgy. However, the tremendous
mathematical infrastructure developed over the last century to address
dislocation-based physical plasticity is increasingly recognized to be
applicable, with appropriate modifications, to any form of inelastic material
response that involves irreversible volume or shape changes of a material.
Perhaps with only tenuous justification, the mathematical tenets of physical viscoelasticity and viscoplasticity are now routinely
generalized to apply to brittle and polymeric materials, with the microphysical
origins of the inelastic response now including microcracking,
creep, phase transformations, and twinning in addition to dislocation evolution
at high confining pressures. At its core, mathematical plasticity is the study
of critical stress or strain thresholds, beyond which the governing equations
significantly change type. Contemporary research accounts for intrinsic spatial
mesoscale variability by replacing a discrete
stress/strain threshold with a “fuzzy” probabilistic boundary. In this broader
realm of mathematical plasticity, generalizations of classical
(dislocation-based) constraints on associativity,
isotropic/kinematic hardening, and dissipation will
be critically reviewed. Material softening and deformation induced anisotropy
(caused, for example, by microcracking) requires new
numerical methods to ensure mesh independence and stability. Examples of
“non-classical” enhancements to classical plasticity theory (such as
non-normality, Weibull-like statistics at the finite
element level, twinning saturation, and thermoelastic-plastic
coupling) will be presented, with special emphasis on risks of violating the
second law of thermodynamics, inadvertently introducing spurious numerical
instability, or introducing inadmissible discontinuous evolution of state
variables.
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479 EBU-II
Professor H.T. Soh
Program in Biomolecular Science and Engineering
Department of Mechanical & Environmental Engineering
University of California, Santa Barbara
“Searching through 50 Billion
Cells Quickly”
The capability to amplify,
that is, to create multiple copies of a particular DNA through polymerase chain
reaction (PCR) has caused a revolution in biotechnology. It has provided the means to detect genetic
mutations and pathogenic organisms including viruses
and bacteria. In this work, we propose
to address an equally fundamental need – the capability to sort, that
is, to separate and isolate particular molecules, viruses, bacteria and
other cells, from a large background of complex mixtures, at very high
throughput, purity and efficiency.
In this work, we combine a novel technique of molecular and cellular labeling with Microsytems technology to create a disposable, massively parallel, rare-cell sorting system. The physical mechanism is based on dielectrophoresis (DEP) using inhomogeneous AC electrical fields. Our approach is truly unique in two aspects: first, we label the cells with specifically engineered DEP tags, so that the differences in dielectric constants provide a large force of separation. Second, we leverage the massive parallelism – the hallmark of micro/nano fabrication technology – to create a multi-stage array of sorting chambers to exponentially enhance the performance in throughput, purity, and recovery simultaneously.
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Monday,
January 31, 2005
11:00 a.m.
479 EBU-II
Cengiz S. Ozkan
Assistant Professor of Mechanical Engineering
Co-Faculty of Electrical and Chemical Engineering
Member, Center for Nanoscience Innovation for
Conventional device fabrication strategies must be augmented by new techniques including self assembly methods in order to truly take advantage of the quantum nature of novel nanoscale electronic devices and systems. I will describe self assembly processing for the fabrication of nano-assemblies of carbon nanotubes (CNT) and quantum dots (QD). Such heterojunctions could become better alternatives for the synthesis of nanoscale devices which would preserve the electronic properties of MWCNT’s compared to configurations that depend on the bending or overlapping of CNT’s. Such configurations could be useful for the bottom-up assembly of nanoscale circuits or as drop-in technologies for the existing device platforms. During processing, CNT’s are primarily functionalized with carboxylic end groups by oxidation in concentrated sulfuric acid. Thiol stabilized QD’s in aqueous solution with amino end groups were conjugated to carbon nanotubes using the ethylene carbodiimide coupling reaction. Next, I will describe self assembly processing by making use of DNA and PNA molecules which could become more useful due to their spatial encoding capabilities for the integration of devices. Recently, we have demonstrated the formation of heterojunctions between CNTs and CVD grown ZnO, which could be useful for optoelectronics applications. Detailed chemical and physical characterization of the heterojunctions have been conducted using Fourier transform infrared spectroscopy, transmission electron microscopy and energy dispersive spectroscopy. Current research aims to combine chemically mass-produced nanoscale building blocks with biomimetic structuring schemes employing DNA recognition to encode the desired structure at various levels Next, I will discuss the applications of carbon nanotubes for biological applications including encapsulation and mass transport of DNA. We have shown by molecular dynamics computations that DNA fragments can be spontaneously inserted into carbon naotubes and this phenomenon was confirmed by experimental observations. More recently, we have demonstrated that patterned carbon nanotube substrates can be employed in achieving directed neurite growth. Potential applications of our studies include the fabrication of novel electronic and spintronic devices and biosensors, gene transfer vehicles for cell differentiation and novel tissue scaffolds.
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479 EBU-II
Professor Sia Nemat-Nasser
Distinguished Professor of Mechanics and Materials
Department of Mechanical and Aerospace Engineering
University of California, San Diego
“A
New Horizon in Engineering Sciences: Biomimetic
Multifunctional Materials”
Multifunctional structural materials possess attributes beyond the basic strength, stiffness that typically drive the science and engineering of the material for structural systems. The structural materials can be designed to have integrated electrical, magnetic, optical, locomotive, power generative, and other functionalities that work in synergy to provide advantages that reach beyond that of the sum of the individual capabilities. Materials of this kind have tremendous potential to impact future structural performance by reducing size, weight, cost, power consumption and complexity while improving efficiency, safety, and versatility. Nature offers numerous examples of materials that serve multiple functions. Biological materials routinely contain sensing, healing, actuation, and other functions built into the primary structures of an organism.
In this lecture, I will
examine the current state-of-the-art and the challenges that must be met in
order to integrate multiple functions into fiber-reinforced polymers to create
composites with basic structural attributes that can also possess tuned
thermal, electromagnetic, self-healing, environmental sensing, self- prognosis,
and energy harvesting functionalities.
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479 EBU-II
Dr. Kelly Carney
NASA Glenn Research Center
Cleveland, OH
“A Summary of the Space Shuttle
On
The Columbia Accident Investigation Board (CAIB), a group of experts
assembled to conduct an investigation independent of NASA concluded in August,
2003 that the cause of the loss of Columbia and its crew was a breach in the
left wing leading edge Reinforced Carbon-Carbon (RCC) thermal protection system
initiated by the impact of thermal insulating foam that had separated from the
orbiters external fuel tank 81 seconds into that missions launch. During reentry, this breach allowed
superheated air to penetrate behind the leading edge and erode the aluminum
structure of left wing which ultimately led to the breakup of the orbiter.
In order to gain a better understanding the foam impact on the orbiters
RCC wing leading edge, a multi-center team of NASA and Boeing impact experts
was formed to characterize the foam and RCC materials for impact analysis using
LS-Dyna.
Analytical predictions were validated with sub-component and full scale
tests.
This talk summarizes the Columbia Accident and the nearly seven month long investigation that followed. In addition, the Return to Flight analytical efforts will also be discussed, with a special emphasis on the material modeling.
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479 EBU-II
Professor Robert Hurt
Division of
“Nature's
Minuet in C: Thermal, Catalytic, and Supramolecular
Routes to New Carbon Nanomaterials”
Elemental carbon assembles into diverse nanoforms that include fullerenes, onions, shells, "horns," films, and "peapods" as well as numerous nanotube and nanofiber varieties. These exciting new nanomaterials are best understood as members of the larger carbon material family that includes sorbents, fibers, composites, and structural graphites. The lecture will cover the principles of carbon science relevant to both nanometric and macroscopic carbon materials. A range of new carbon nanoforms will then be presented, touching on synthesis, structure, and properties, as well as selected applications and their development status. Special emphasis will be given to new supramolecular routes being pursued at Brown, which are based on liquid crystal assembly and covalent capture. The talk will end with a brief discussion of the potential impacts of carbon nanomaterials on human health, and ongoing research designed to overcome this barrier to commercial success.
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479 EBU-II
Professor Bill Stronge
Dept. of Engineering
“BOUNCE OF DEFORMABLE BALLS”
Many games are played with balls that undergo rapid changes in direction and rate of spin during collisions; control of ball speed, direction and spin requires skill that determines performance in many sports. Analysis of impact of sports balls can be used to understand the dependence of bounce of balls on equipment as well as the strength and skill of players. Despite high speed photographs showing significant ball deformations during impact, dynamic analyses for impact of sports balls are almost exclusively based upon rigid-body dynamics. At impact speeds representative of ball games, this lecture obtains effects of finite deflections and a finite contact area on the changes in velocity of a thin-walled, inflated ball. Momentum flux associated with the evolving contact region is shown to be non-conservative and a significant source of energy dissipation during impact of these balls against a court surface.
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479 EBU-II
“Dimensional
Restriction for Enhanced Performance:
Thermoelectric Nanowires”
Thermoelectric materials are of interest for a wide range of engineering applications from heat pumps to power generators. Incremental performance advancements have been evident over the last decade in commercial products, but there is considerable excitement regarding the newly proposed methods for enhancing thermoelectric figure of merit through quantum confinement. At present, Bi2Te3 alloys, along with the doped ternary phases Bi2-xSbxTe3 (p-type) and Bi2Te3-xSex (n-type), are the best thermoelectric materials for application at room temperature. This presentation reviews current understanding of the path toward dimensional restriction for enhanced thermoelectric performance in these and other materials. The geometry explored here is the two-dimensionally-confined quantum wire. Results are presented comparing the electrical and thermal conductivity of nanowires (at 200 nm diameter and less) fabricated by either nano-casting or electrodeposition into porous alumina. Elemental compositions, degree of filling, morphology, internal structure, and the nature of the wire/template interfaces are also evaluated and compared using spatially-resolved methods of electron microscopy.
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479 EBU-II
Dr. Neil C.
Holmes
Lawrence
“Shock Compression: Going Beyond the Equation of State”
Shock wave research became
an important field at the dawn of the nuclear age. Its value in material
research is high because it allows us to determine equation-of-state (EOS)
information (pressure, density, energy) accurately and absolutely on a locus of
final states called the Hugoniot. Shock states achieve high pressures and
temperatures, allowing us to access to states well beyond static compression,
and providing very fast time scales. While the focus of shock wave work has
historically been EOS and other bulk properties, now our attention is turning
to experiments that probe atomic, molecular, and optical properties directly,
to states off the Hugoniot, and to experiments that
feature complex thermodynamic paths. And
getting the thermodynamics right in this is still a challenge! I will describe new research in these areas
and point to expected developments for the next decade.
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479 EBU-II
Prof. Ing. Michele Ciavarella
CNR, Politecnico di Bari
ITALY
Contact between bodies with rough surface occurs widely in engineering systems and the micro-mechanics of the contact process has a profound effect on technologically important processes such as friction, contact stiffness and electrical contact resistance. A recent theorem due to Barber shows an analogy between conductance and incremental stiffness of a contact, implying bounds on conductance based on peak-to-peak roughness. This shows that even a fractal roughness, with bounded amplitude, has a finite conductance. The analogy also permits a simple interpretation of classical results of rough contact models based on independent asperities such as Greenwood-Williamson and others. Persson's theory is an interesting application of random process theory to the contact of rough surfaces. This theory could be applied to any starting pressure distribution. In order to discuss the non-linearities of the contact problems, we consider the simplest possible models of roughness, namely a sinusoidal profile, a sinusoidal profile with random amplitude, and the superposition of two sinusoids with close wavelength and amplitude (which can also be random).
Thermoelastic contact problems can possess non-unique
and/or unstable steady-state solutions if there is frictional heating or if
there is a pressure-dependent thermal contact resistance at the interface.
These two effects have been extensively studied in isolation, but their
possible interaction has not been investigated until recently. We shall discuss
some idealized geometries in which the two effects are seen to form limiting
cases of a more general stability and existence behavior. In most cases,
frictional heating has a destabilizing effect relative to the static contact
problem, but if the thermal contact resistance is very sensitive to pressure,
cases of stabilization can be obtained. Also, the critical sliding speed
depends on the contact pressure in contrast to results obtained in the absence
of thermal contact resistance.
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479 EBU-II
Professor John Gilman
University of California, Los Angeles
Department of Materials Science and Engineering
School of Engineering and Applied Science
“Hardness
Rationalized”
The conventional wisdom is that hardness (indentation or scratch) is a somewhat chaotic, empirical property of solids. This presentation will show that, on the contrary, hardness is a well-behaved property that can be quantitatively related to other physical properties. The key is to take the type of chemical bonding into account. Metals, ionic crystals, covalent semiconductors, and metal-metalloids will be discussed. Connections with elastic stiffnesses (bulk and shear), with valence electron densities (VED), with polarizabilities, with band-gap densities, with ionic charges, and with formation energies will be derived. In addition, the connection between indentation hardnesses and "pressure induced" phase transformations will be briefly considered.
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479 EBU-II
David H. Lassila
Materials Technology Leader
Engineering Directorate
Over the past 6 years LLNL researchers and collaborators have been engaged in a comprehensive multiscale modeling program that is ultimately aimed at predicting the plastic deformation response of bcc metals. Many of the simulation tools that have been employed and further developed under this program, such as “dislocation dynamics” computer codes and 3-D molecular dynamics, have produced exciting and, in some cases, unexpected results related to dislocation mobility and hardening behaviors in bcc metals. In addition to the multiscale modeling and simulations efforts, experimental techniques have been developed specifically to validate the simulation results.
An overview of some simulation results will be presented, leading into a description of some of the experimental challenges for detailed validation efforts. Recent experimental results on the crystallographic slip behavior of Mo single crystals that have been obtained using a unique “6-degree of freedom” (6DOF) deformation experiment are presented. In this experiment, the full stress and strain tensors are determined which allows “slip system activity” during axial compression of single crystal test samples to be calculated. The results of these experiments show that slip behavior is in substantial deviation from the expected “Schmid” behavior. These experimental results bring into question some of the fundamental assumptions used in both the construction of crystal plasticity constitutive relationships and rules for dislocation mobility use in 3-D dislocation dynamics simulations.
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Information: (858) 534-3980