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For Diana Farkas, a researcher at the Center for Modeling and Simulation in
Materials Science at Virginia Tech
(VT), that means studying the development of fractures in intermetallic
alloys by examining the alloys, especially their defects, atom by atom.
For more than 12 years, Farkas and her research team have studied new and
promising alloys at the atomic level, looking at the bonds between atoms in
defective alloy crystals, and how they behave under different levels of
external applied stress.
The goal of the research is to develop new structural materials that
hold up to extreme heat, resist oxidation, and have a high degree of
ductility in combination with strength. The work has important
implications in the field of materials design, including aircraft and
aerospace design. It is funded by the Office of Naval Research, Division of
Materials Science and the National Science Foundation.
"We are looking at the characteristics of experimental alloys, such as
whether they are brittle or ductile, and whether they maintain their
strength at high temperatures," explains Farkas. "We look at what happens
in the propagation of fractures at the atomic level. We need to understand
the mechanisms of the fracture process in order to design materials with
improved ductility and the ability to maintain strength at high
temperatures."
Farkas gets her data from computer simulations, which are based on a
description of the atomic interaction fit to the equilibrium properties of
defective atomic crystals. She then uses a FORTRAN code to calculate the
atomistic equilibrium configuration of the defects--either cracks or plastic
deformation in the alloys. Until recently, the research team could view the
data only as two-dimensional slices on a desktop workstation. These
two-dimensional visualization packages are far from perfect; for one, they
can't handle the large number of atoms involved in the massive simulations
necessary to study the propagation of cracks. Furthermore, two-dimensional
renderings can't give a complete picture of a problem that is truly
three-dimensional in nature. But in the last few months, Farkas has been
able to "see" her data in a new and much more realistic light. Using an
application called AtomView, Farkas can now study the behavior of atoms in
propagating cracks in the immersive, three-dimensional environment of the
CAVETM.
The development of AtomView is a direct result of Virginia Tech's
involvement in the National Computational Science Alliance. John Shalf, a
visualization research programmer at the National Center for Supercomputing Applications (NCSA), the leading-edge site for the Alliance, worked with Ron Kriz of
VT's Advanced Communication
and Information Technology Center during the summer of 1997 and helped
him write an application that took Farkas's FORTRAN code
output--numerical representations of the positions of every atom in a
fracture being studied--and put it into the visual 3D form that became
AtomView. Shalf's help in creating AtomView was part of the training
offered during NCSA's Visual Supercomputing Institute, a program held each
year to help scientists utilize the tools of the CAVE and ImmersaDesk
virtual environments.
"They came to the VSI with their simulation data in hand," Shalf recalls
of the VT research team. "Because of that, it was possible for me to get
them started by helping them get a very simple application running that
could read their data." Since the Visual Supercomputing Institute, VT
researchers have taken over the development of AtomView and are busy
extending its capabilities in ways that are useful to Farkas's research
team. As a partner in the Alliance, VT researchers will continue to develop
and evaluate VR tools and applications such as AtomView in their newly
installed CAVE. When appropriate, these tools and applications will be
disseminated to other Alliance partners and the larger scientific community.
AtomView, says Kriz, is one of the first success stories to emerge from
VT's Alliance collaboration to develop and disseminate cutting-edge
visualization tools and applications. "This project was designed in the
spirit of developing CAVE applications remotely for viewing animations of
supercomputing simulations," Kriz says. "I anticipate that this CAVE
application will be further developed and shared by Virginia Tech and NCSA
as PACI partners."
For researchers like Farkas, AtomView means the opportunity to view
bigger blocks of data from any angle, and the ability to view 3D
simulations of the fracture process for the first time.
"Imagine walking between the atoms in an alloy and you get the idea of
what it is like to view this information in AtomView in the CAVE," says
Farkas. "The beauty is you are able to see something that is very close to
a real fracture, only you are seeing it at the atomic level."
According to Shalf, AtomView is a better tool for looking at alloy
fractures and defects at the atomic level because the researcher can see
many more levels of atoms at once. "They want to see what's happening at
the crack tip, and that's a phenomenon that happens in three dimensions,
not on a flat surface," he says. "You need a tool that can handle the large
number of atoms involved in 3D simulations. Using a tool like this, you can
look in three dimensions instead of one or two, and see what's happening
at all levels."
A simulation of the fracture process, for example, requires data on at
least 100,000 atoms, according to Farkas, and needs the power of 128
processors on NCSA's SGI/CRAY Origin2000 supercomputer. Utilizing the
speed and the performance of the Origin2000, Farkas hopes to soon run
AtomView simulations that examine as many as 1 million atoms.
"We are already seeing a three orders of magnitude increase in the
number of atoms we are looking at," she says. "It used to be that we barely
had enough memory on computers to handle 2D data. Now we have enough memory
to simulate materials in full 3D. We need tools to understand this 3D data
and the CAVE and AtomView are a very important part of this."
Bigger simulations that look at the mechanisms of fractures in a
realistic manner mean more information about what happens in the fracture
process, especially at the critical region of the crack tip. And
understanding what happens to cause fractures and other defects is an
important step in developing stronger, more ductile materials. It's a way
of tackling the big problems of engineering by looking at the tiniest
pieces of matter--but in ever more massive chunks.
With the bigger simulations "there is time saved and there is more
information to be studied," says Farkas. "And with the Alliance and NCSA,
there is an emphasis on collaboration instead of competition. In the long
run, you get a lot more done."
AtomView is now being refined by Farkas's research team. The current version is now
available for download at:
http://www.sv.vt.edu/future/vt-cave/VT/index.html#proj.
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