Aerospace & Defense Technology - June 2024 - 35

Tech Briefs
of aeroacoustics phenomena in ducted fans exposed to a broad
spectrum of incoming turbulent flows.
" Our study sheds light on how noise is generated by futuristic
embedded ducted fans mounted on curved airframe surfaces,
revealing that noise patterns vary with fan thrust levels, offering
crucial insights for quieter next-generation aircraft design. "
This research was performed by Dr. Feroz Ahmed from Bristol's
School of Civil, Aerospace and Design Engineering under
the supervision of Professor Mahdi Azarpeyvand. For more
information, download the Technical Support Package
(free white paper) at mobilityengineeringtech.com/tsp
under the Materials category.
'Nanostitches' Enable Lighter and Tougher Composite
Materials
In research that may lead to advancements in the design of next-generation airplane and spacecraft,
MIT engineers used carbon nanotubes to prevent cracking in multilayered composites.
Massachusetts Institute of Technology, Cambridge, MA
T
o save on fuel and reduce aircraft emissions, engineers are
looking to build lighter, stronger airplanes out of advanced
composites. These engineered materials are made from high-performance
fibers that are embedded in polymer sheets. The sheets
can be stacked and pressed into one multilayered material and
made into extremely lightweight and durable structures.
But composite materials have one main vulnerability: the
space between layers, which is typically filled with polymer
" glue " to bond the layers together. In the event of an impact
or strike, cracks can easily spread between layers and weaken
the material, even though there may be no visible damage to
the layers themselves. Over time, as these hidden cracks
spread between layers, the composite could suddenly crumble
without warning.
Now, MIT engineers have shown they can prevent cracks
from spreading between composite's layers, using an approach
they developed called " nanostitching, " in which they deposit
chemically grown microscopic forests of carbon nanotubes
between composite layers. The tiny, densely packed fibers grip
and hold the layers together, like ultrastrong Velcro, preventing
the layers from peeling or shearing apart.
In experiments with an advanced composite known as thinply
carbon fiber laminate, the team demonstrated that layers
bonded with nanostitching improved the material's resistance
to cracks by up to 60 percent, compared with composites with
conventional polymers. The researchers say the results help to
address the main vulnerability in advanced composites.
" Just like phyllo dough flakes apart, composite layers can
peel apart because this interlaminar region is the Achilles' heel
of composites, " says Brian Wardle, Professor of Aeronautics and
Astronautics at MIT. " We're showing that nanostitching makes
this normally weak region so strong and tough that a crack will
not grow there. So, we could expect the next generation of aircraft
to have composites held together with this nano-Velcro,
to make aircraft safer and have greater longevity. "
Wardle and his colleagues have published their results in the
Journal ACS Applied Materials and Interfaces. The study's first
author is former MIT Visiting Graduate Student and Postdoc Carolina
Furtado, along with Reed Kopp, Xinchen Ni, Carlos Sarrado,
Estelle Kalfon-Cohen, and Pedro Camanho.
Aerospace & Defense Technology, June 2024
mobilityengineeringtech.com
35
Forest Growth
At MIT, Wardle is director of the necstlab (pronounced " next
lab " ), where he and his group first developed the concept for
nanostitching. The approach involves " growing " a forest of vertically
aligned carbon nanotubes - hollow fibers of carbon,
each so small that tens of billions of the nanotubes can stand in
an area smaller than a fingernail. To grow the nanotubes, the
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Aerospace & Defense Technology - June 2024

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