Air travel may become safer as a result of research USC
will carry on as its $2 million part of a $3.8 million investigation into corrosion-induced
failure in high-performance metals used in aerospace and other demanding applications.
Supercomputing specialist Priya Vashishta and his colleagues will model the behavior
of hundreds, thousands and millions of individual atoms to gain greater understanding
of how and why alloys of titanium and other metals suffer "stress corrosion cracking"
— potentially catastrophic damage resulting from mechanical strain in chemically
unfriendly environments.
In addition to the obvious safety implications, passengers may reap a coziness
bonus.
Nanoscientists at work: Kalia (standing); Nakano (at computer) and Vashista. All have joint appointments
in the Viterbi School departments of computer science and materials science and
the College department of physics and astronomy. |
"Anyone
who has traveled on an airplane knows the air is extremely dry," said
Vashishta, who has joint appointments in the USC Viterbi School of
Engineering departments of materials science, biomedical engineering
and computer science, and in the USC College of Letters, Arts,
and Sciences department of physics and astronomy. "And this is
deliberate."
"The purpose is to minimize corrosion of the airplane — which is accelerated
by moisture — and extend its life," the scientist explained. “But if we can we
understand more precisely how corrosion takes place, we may be able to find ways
that will deal with the problem with less discomfort for travelers, while still
keeping planes airworthy."
<>Vashishta and longtime collaborators Aiichiro Nakano and Rajiv K. Kalia will
be
carrying out their investigations as part of an Information Technology Research
project funded by the National Science Foundation. Like Vashishta, Nakano and
Kalia hold joint appointments in the Viterbi School departemnts of computer science,
materials science and (for Kalia) biomedical engineering; and in the USC College
department of physics and astronomy. The trio will partner with Caltech and Purdue
on the effort, one of 120 ITR projects
funded by the NSF.
Vashishta and co-investigators will use new techniques of
nanoscience to supplement the traditional structural engineering approach, known
as "continuum mechanics." This technique involves extensive testing of pieces
of material to establish parameters of performance, which are then be expressed
as predictive equations engineers use to design structures.
This works well, Vashista said, in providing reliable forecasts of how the material
will behave when new. But it offers little guidance into how and when materials
may fail because of stress corrosion cracking (SCC) — damage from corrosion that
starts when ordinary strain
on the metal produces
tiny cracks that allow the entrance of moisture and oxygen.
|
Going nano: A crack in the surfacc of a piece of metal (black area in left hand
panel) grows out of activity of atoms at the point of cracking (right hand panel).
The study will simulate the behavior in the right hand panel, and model the consequences
backward to the effects seen on the left. |
Nanoscientific analysis can supply such guidance, Vashishsta said. The idea is
to go down to the basic atomic structure of the material and simulate the behavior
of individual atoms at the point where cracks appear in the surface.
"We start by accurately modeling the behavior of collections of a few hundred
atoms at one point; proceed from there to modeling thousands of atoms along the
surface, going to millions of atoms over a larger area," he explained.
The results of the nanoanalysis have to produce the same predictions for behavior
as the traditional continuum approach, Vashishta said. "But by understanding exactly
what is going on, in detail, at the point where the material is failing, we can
find better ways to prevent damage, and create more corrosion resistant materials."
“Corrosion is an enormously complex technological and economic problem with an
annual cost of about 3% of the US gross domestic product,” according to the proposal
for the study. “Most critical here is premature and catastrophic failure of materials
resulting from chemically influenced corrosion. …Safety and reliability [of structures]
… is endangered by the uncertainties in ...SCC. To prevent
SCC … requires that we understand the atomistic mechanisms underlying SCC.
Such understanding demands huge computational resources. Vashishta's group has
its own
480-CPU supercomputer, and also uses the 2048-CPU supercomputer at the USC center
for High Performance Computing and Communications (HPCC).
Vashishta's team is supplementing their expertise in materials
science, computing
and physics with contributions from other schools. Caltech is
contributing expertise in the force fields created by chemical
corrosion reactions, (William Goddard, Ferkel Professor of Chemistry,
Materials
Science and Applied Physics) and in traditional continuum
mechanics (Michael
Ortiz, Hayman Professor of Aerospace and Mechanical
Engineering). Purdue computer
scientist Ananth Y. Grama is also part of the project.
