The eventual failure of metals, such as the aluminum in ships and airplanes,
can often be blamed on breaks, or voids, in the material’s atomic lattice.
They’re at first invisible, only microns in size, but once enough of them link
up, the metal eventually splits apart.
Cornell University engineers, trying to better
understand this process, have discovered that nanoscale voids behave
differently than the larger ones that are hundreds of thousands of atoms in
scale, studied through traditional physics. This insight could lead to improved
ability to predict how cracks grow in metals, and how to engineer better
Graduate student Linh Nguyen and Derek Warner, assistant professor of civil
and environmental engineering, reported their findings in Physical Review Letters. Using new atomistic simulation techniques,
they concluded that the smallest voids in these materials, those having
nanometer dimensions, don’t contribute in the same way as microscale voids do
in material failure at ordinary room temperatures and pressures.
When metals fail, a physical phenomenon known as plasticity often occurs,
permanently deforming, or changing the shape of the material. Previously, it
was theorized that both nanometer and microscale voids grow via plasticity as
the material fails, but the new research says otherwise.
“While this was something amenable to study with traditional atomistic
modeling approaches, the interpretation of previous results was difficult due
to a longstanding challenge of time scaling,” Warner said. “We’ve
come up with a technique to better address that.”