engineering professor at the University of California,
San Diego has described in the March issue of JOM
(the Journal of the Minerals, Metals and Materials
Society) the unique properties of a new type of metallic
laminate that can serve as armor and as a replacement
for beryllium, a strong but toxic metal commonly used
in demanding aerospace applications.
"The new material we developed is environmentally
safe, and while its stiffness equals that of steel,
it's only half as dense," said Kenneth S. Vecchio,
author of the paper and a professor of mechanical
and aerospace engineering in UCSD's Jacobs School
of Engineering. "It performs spectacularly in
our depth-of-penetration ballistics tests, but we
think its greatest potential may derive from its unique
ability to have its structure and properties tailored
to meet a wide variety of application-specific engineering
The new material is made primarily
of two lightweight metals. Vecchio alternated layers
of aluminum and titanium alloy foils, and compressed
and heated them in an inexpensive energy-conserving
process. The resulting reaction generated a laminate
with two layers: a hard ceramic-like "intermetallic"
layer of titanium aluminide, and a pliable layer of
residual titanium alloy. The layers can be stacked
like 1-millimeter-thick pages of a book, and even
contoured into desired shapes prior to heating.
The laminate architecture was
chosen by Vecchio to mimic the internal structure
of the tough shell of the red abalone. This science-mimicking-biology
approach is one of an increasing number of biomimetic
research efforts at the Jacobs School of Engineering.
Faculty members are studying structural and functional
designs of everything from mollusk shells and bird
bills to sea urchin spines and other biocomposites
in the development of new smart materials and devices.
The red abalone, a seaweed-eating
snail prized as a source of mother-of-pearl jewelry,
is found off the coast of California. The mollusk
makes its dome-shaped home by slowly adding layers
of brittle calcium carbonate, each about one-thousandth
the thickness of a strand of human hair, between even
thinner layers of a stretchy protein adhesive.
"The intermetallic phase
of titanium aluminide is the complement of the mollusk's
hard calcium carbonate phase, and the titanium alloy
layer mimics the abalone shell's compliant protein
layers," said Vecchio.
In order to test the bullet-stopping
capability of his new material, Vecchio fired a heavy
tungsten alloy rod into a three-quarters-inch (2 centimeters)
thick sample at a velocity of about 2,000 mph (900
meters per second). The rod penetrated only half the
thickness of the test sample. Vecchio said the laminate
performs surprisingly well as armor and has potential
as a structural metal.
He said other types of metallic
foils containing vanadium, chromium, manganese, nickel,
cobalt, and iron have been successfully fabricated
into laminates using the same stacked foil technique.
"We've only begun to explore the possible combinations
and potential uses of these promising new materials,"
He described in his paper the
production of cavities within his laminate layers,
which were made by cutting out parts of the foil prior
to heating. In one case, he filled cavities with steel
beads, which were free to bounce within their confines
and act as highly efficient vibration dampeners. "This
vibration-dampening characteristic could be extremely
valuable in jet engines and other high-performance
applications prone to noisy vibration," said
It's also possible to include
electrical pathways within the laminates by embedding
metal or ceramic wires or fibers during fabrication,
and those components could both strengthen the material
and act as built-in sensors. In addition, Vecchio
said the laminates could be further enhanced with
the addition of materials that generate an electric
charge when mechanically deformed. Conversely, these
so-called piezoelectric materials also deform when
an electric field is applied to them.