Thermomechanical Couplings in Solids, Fracture Mechanics,
Nanostructures
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Research Group of Alan Zehnder
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Delamination of a Gr-PI composite due to water vapor pressure
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Failure envelope for polyimide near resin
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Fracture strength distribution for nanobeams coated with CH3
monolayers (blue) and H terminated
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Research in our group includes nonlinear dynamics of MEMS and
NEMS, fracture of MEMS, damage tolerance and life prediction of polymer
matrix composites, fracture mechanics, fatigue, metal cutting,
and other
investigations of thermomechanical couplings in
solids. Our work is primarily experimental, supported by theory and
computation.
We collaborate with a wide range of researchers across both the
university
and the nation.
Cornell University
Department of Theoretical and
Applied Mechanics
304 Kimball Hall
Ithaca, New York 14853
Phone: (607) 255-0824 (lab)
(607) 255-9181 (Zehnder's office)
Fax: (607) 255-2011
Send E-mail to: atz2 at cornell dot edu
On-line papers of Zehnder research group
Complete list of publications
Current Research
Projects
- Dynamics of MEMS Oscillators
- Damage Tolerance of Composite
Structures
- Life Prediction of High
Temperature Composite Materials Structural
reliability is of utmost importance in all aspects of design of space
exploration vehicles, including airframes and propulsion systems.
For space exploration light weight is also of utmost importance due to
high launch costs. We are working as part of a team that
includes faculty at Cornell and Syracuse Universities and NASA Glenn
Research Center, to develop life prediction models for high temperature
polymer matrix composites, in particular, Graphite-Polyimide (T650-35
fibers, HFPE II-52 resin). Experiments include measuring laminate
and matrix properties across the range from 20 to 350 deg. C.
Delamination of composites due to internal steam pressure developed
during rapid heating is also a focus. This work is funded
through NASA Cooperative Agreement NCC3-994, the "Constellation
University Institutes Program".
Past Projects
- Dynamic Mechanical Properties of Nanoscale Materials
Nanoscaled structures, although still large enough to obey continuum
laws
of mechanics, show surprising effects due to their small size. For
example,
the structures interact with light through heating and photo induced
stresses
in ways that can enhance the performance, i.e. increase quality factor,
of these structures. As part of the
Nanomechanics IRG
in the CCMR we focused on applying mechanics to understanding and
designing these
structures
and to measuring the mechanical properties of Si at nanometer size
scales. Research topics included limit cycles and entrainment in
optically driven MEMS and fracture testing of MEMS materials.
- Virtual Labs, Real Data for
Strength of Materials An emerging change across the
science, technology, engineering and mathematics curriculum is the
implementation of on-line, or virtual laboratories as supplements or
replacements to both homework assignments and laboratory
exercises. To test the effectiveness of such labs, a
web-based virtual laboratory on the topic of torsion of engineered and
biological materials was developed. The lab contains
extensive data sets, videos of experiments, narrated presentations on
lab practice and theory and assignments. Flexibility of use is
built into the lab by providing the capability for the web-pages to be
tailored to the needs of a particular institution. The support of
the National Science Foundation, Division of Undergraduate Education
(DUE), CCLI program, through award DUE-01227434 is gratefully
acknowledged. The Virtual Lab may be viewed at Virtual
Labs, Real Data.
- Advanced Interactive Discovery
Environment In industry and government, teams of
scientists and engineers need to work together closely to achieve their
project goals. In large projects team members may live and work
at geographically distant sites, and may work for different
organizations, making communication and interaction between the team
members difficult at best. With support from the NASA Langley
Research Center, the State of New York and the AT&T foundation,
Syracuse and Cornell Universities are conducting a study on the
effectiveness of advanced information technology tools for facilitating
communication and collaboration at a distance. This study
combines fundamental research into the design and use of the IT tools
as well as practical experience with using IT tools for distance
collaboration. Our working hypothesis is that proper use of IT
based collaboration tools can facilitate effective design collaboration
at a distance and can enhance our student’s education, better preparing
them for tomorrow’s workplace.
- Metal Cutting Heat generation due to plastic flow
and friction
in metal cutting plays an important role in determining the cutting
force,
in chip formation and in the dynamics of the cutting process.
Working
with Prof. Deng. of the Univ. of South Carolina we performed
high speed measurements of the temperature fields at the tip of a
cutting
tool. We combined these measurements with dynamic FEM simulations
of the process. Goals of the project were to verify the
performance of
the simulations by comparing the measured and predicted temperature
fields and to combine the use of experiments and simulation to
accurately determine parameters for metal cutting simulations.
This work was supported by the
National Science Foundation, through grant CMS-9700698. Abstract
on metal cutting, (120k .pdf)
- Thermal Imaging of Fracture During crack growth the
energy
of plastic deformation ahead of a crack in a ductile metal is largely
dissipated
as heat. I have performed a number of experiments working with
colleagues
at Wayne St. Univ. where we used their infrared imaging system to
determine
temperature fields in the crack region. We analyzed these
experiments to extract
from the temperature fields the energy flow to the crack tip. FEM
simulations of the experiment were performed to close the loop
between experiment and theory. We have also measured
the fraction of plastic work dissipated as heat in annealed 302 SS,
2024
Al. and commercially pure Al. It is necessary to know these
properties
for the proper analysis of dynamic plastic deformation processes such
as
metal cutting, fracture and impact. Abstract
on thermal analysis of crack tearing (150k .pdf)
- Aircraft Structural Integrity The worldwide fleet of
commercial
aircraft is aging, and as recent aircraft structural accidents have
demonstrated,
the safety of these aircraft is an important issue. In reponse to this
problem NASA started a program on aircraft stuctural integrity, which
we
are part of. Our work concentrates on fatigue crack growth in thin
sheets
of 2024-T3 aluminum under conditions of in-plane tensile and
out-of-plane
tearing loads. The work involves theory, computation and extensive
experimentation.
In a recent paper Williams meets von
Karman
we look at the validity of the small deflection plate fields in the
fracture
of pressurized and sheared plates. Some of our work is summarized
in our paper in the proceedings of the
1998
Aircraft Structural Integrity Conference, (pdf file)
Our
collaborators on this project are the faculty and students in the research
group of Prof. Anthony Ingraffea and Prof.
C.-Y. Hui.
- Dynamic Fracture Our work in this area includes
measurements
of
the fracture toughness under impact and high
speed
crack growth, and measurements and simulation of the temperature
rise at the tip of dynamically propagating cracks. Recently,
working with colleagues at Caltech, we designed, built
and
patented a 1 million frames per second IR imaging system.
This
system has been built and is being applied for the study of impact
fracture
in structural steels.
- Metal-Ceramic Composites and
Metal-ceramic and
metal-glass interface fracture One of our previous projects
involved the development and testing of novel metal-ceramic composite
materials.
In particular we worked a great deal on developing test methods for
very
small samples and on incorporating R curve effects into the
interpretation
of the experiments. Abstract
on fracture toughness testing of small samples. Composite
materials
abound with interfaces, thus interfaces between dissimilar materials
have
a strong effect on the performance of the composite. Electronics also
contain
many metal-ceramic or metal-glass interfaces. The integrity of the
interface
is crucial to the reliability, designability and performance of the
device.
We are currently working on testing and modelling interfacial fracture
toughness of metal-ceramic and metal-glass systems. Our goals are to
devise
tests that are simple to perform, accurate, and that yield meaningful
numbers
for the fracture toughness, and to quantify the change in interfacial
bond
toughness with different bonding conditions, and different interfacial
chemistry. Abstract on testing of the Ni-Alumina
interface is given here.
- Other Projects We have
worked on a number of small projects,
including
fatigue fracture in copper-Kapton laminates (working with Prof.
Daniel Swenson of Kansas State University), and modeling
fault-propagation
folding using the trishear
model, currently working with Rick
Allmendinger of the Cornell Geology Dept.
Research Team
Prof. Alan Zehnder,
Mike Czabaj, mwc35 at cornell dot edu
David Blocher, dbb74 at cornell dot edu
Graduates
Mark Thurston, Ph.D., 1994 photo
Jacob Kallivayalil, Ph.D., 1995 photo
Mark Viz, Ph.D., 1996
Shujun Tang, Ph.D., 1999 photo
Yogesh Potdar, Ph.D., 2001
Kavi Bhalla, Ph.D. 2001
Tuncay Alan, Ph.D. 2007
Peeyush Bhargava, Ph.D. 2008
Manoj Pandey, Ph.D., 2007
Tuhin Sahai, Ph.D., 2008
Henry Lee, M.Eng., 1998
Juho Chong, M.Eng., 2000
Ai-Chi Chien, M.Eng., 2001
John Antonakakis, M.S. 2005
Last updated May 23, 2008
(Alan Zehnder)