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Rensselaer Polytechnic Institute: Fitter Frames: Nanotubes Boost Structural Integrity of Composites
(M2 PressWIRE Via Acquire Media NewsEdge)
RDATE:26032009
Researchers at Rensselaer have discovered a new technique for provoking
unusual crazing behavior in epoxy composites. The crazing, which causes
the composite to deform into a network of nanoscale pillar-like fibers
that bridge together both sides of a crack and slow its growth, could
lead to tougher, more durable components for aircraft and automobiles.
New research finding could lead to more durable aircraft, automotive
components
A new research discovery at Rensselaer Polytechnic Institute could lead
to tougher, more durable composite frames for aircraft, watercraft, and
automobiles.
Epoxy composites are increasingly being incorporated into the design of
new jets, planes, and other vehicles. Composite material frames are
extremely lightweight, which lowers the overall weight of the vehicle
and boosts fuel efficiency. The downside is that epoxy composites can
be brittle, which is detrimental to its structural integrity.
Professor Nikhil Koratkar, of Rensselaer's Department of Mechanical,
Aerospace, and Nuclear Engineering , has demonstrated that
incorporating chemically treated carbon nanotubes into an epoxy
composite can significantly improve the overall toughness, fatigue
resistance, and durability of a composite frame.
When subjected to repetitive stress, a composite frame infused with
treated nanotubes exhibited a five-fold reduction in crack growth rate
as compared to a frame infused with untreated nanotubes, and a 20-fold
reduction when compared to a composite frame made without nanotubes.
This newfound toughness and crack resistance is due to the treated
nanotubes, which enhance the molecular mobility of the epoxy at the
interface where the two materials touch.
When stressed, this enhanced mobility enables the epoxy to craze - or
result in the formation of a network of pillar-like fibers that bridge
together both sides of the crack and slow its growth.
'This crazing behavior, and the bridging fibers it produces,
dramatically slows the growth rate of a crack,' Koratkar said.
'In order for the crack to grow, those fibers have to first stretch,
deform plastically, and then break. It takes a lot of energy to stretch
and break those fibers, energy that would have otherwise gone toward
enlarging the crack.'
Results of the study were published this week in the journal Small.
Epoxy composites infused with carbon nanotubes are known to be more
resistant to cracks than pure epoxy composites, as the nanotubes
stitch, or bridge, the two sides of the crack together. Infusing an
epoxy with carbon nanotubes that have been functionalized, or treated,
with the chemical group amidoamine, however, results in a completely
different bridging phenomenon.
At the interface of the functionalized nanotubes and the epoxy, the
epoxy starts to craze, which is a highly unusual behavior for this
particular type of composite, Koratkar said.
The epoxy deforms, becomes more fluid, and creates connective fibers up
to 10 microns in length and with a diameter between 100 nanometers and
1,000 nanometers.
'We didn't expect this at all. Crazing is common in certain types of
thermoplastic polymers, but very unusual in the type of epoxy composite
we used,' Koratkar said. 'In addition to improved fatigue resistance
and toughness, the treated nanotubes also enhanced the stiffness,
hardness, and strength of the epoxy composite, which is very important
for structural applications.'
Koratkar said the aircraft, boat, and automobile industries are
increasingly looking to composites as a building material to make
vehicle frames and components lighter. His research group plans to
further investigate crazing behavior in epoxy composites, in order to
better understand why the chemical treatment of nanotubes initiates
crazing.
Co-authors of the paper include Rensselaer Associate Professor Catalin
Picu , of the Department of Mechanical, Aerospace, and Nuclear
Engineering; Rensselaer doctoral students Wei Zhang and Iti Srivastava;
and Yue-Feng Zhu, professor in the Department of Mechanical Engineering
at Tsinghua University in China.
Visit Koratkar's Web site for more information on his nanomaterials
research.
CONTACT: Rensselaer Polytechnic Institute (RPI)
Tel: +1 518 276 6000
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Copyright ? 2009 M2 Communications Ltd.
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