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The team was able to compress small flakes
of graphene using a combination of heat
and pressure. This process produced a
strong, stable structure whose form resem-
bles that of some corals and microscopic
creatures called diatoms. These shapes,
which have an enormous surface area in
proportion to their volume, proved to be
remarkably strong. ¡°Once we created these
3-D structures, we wanted to see what¡¯s the
limit, what¡¯s the strongest possible mate-
rial we can produce,¡± says Qin. To do that,
they created a variety of 3-D models and
then subjected them to various tests. In
computational simulations, which mimic the
loading conditions in the tensile and com-
pression tests performed in a tensile loading
machine, ¡°one of our samples has 5 per-
cent the density of steel, but 10 times the
strength,¡± Qin says.
Buehler says that what happens to their 3-D
graphene material, which is composed of
curved surfaces under deformation, resem-
bles what would happen with sheets of paper. Paper has little strength along
its length and width, and can be easily crumpled up. But when made into
certain shapes, for example rolled into a tube, suddenly the strength along
the length of the tube is much greater and can support substantial weight.
Similarly, the geometric arrangement of the graphene flakes after treatment
naturally forms a very strong configuration.
The new configurations have been made in the lab using a high-resolution,
multimaterial 3-D printer. They were mechanically tested for their tensile
and compressive properties, and their mechanical response under loading
was simulated using the team¡¯s theoretical models. The results from the
experiments and simulations matched accurately.
The new, more accurate results, based on atomistic computational modeling
by the MIT team, ruled out a possibility proposed previously by other teams:
that it might be possible to make 3-D graphene structures so lightweight
that they would actually be lighter than air, and could be used as a durable
replacement for helium in balloons. The current work shows, however, that
at such low densities, the material would not have sufficient strength and
would collapse from the surrounding air pressure.
But many other possible applications of the material could eventually be fea-
sible, the researchers say, for uses that require a (continued on page 3>>)
10 Times As Strong As Steel
Researchers design one of the strongest, lightest materials known
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Porous, 3-D forms of graphene
developed at MIT bring the strength of
2-D materials and the power of material
architecture design together
David L. Chandler, MIT News Office, Janu-
ary 6, 2017: A team of researchers at MIT
has designed one of the strongest lightweight
materials known, by compressing and fusing
flakes of graphene, a two-dimensional form
of carbon. The new material, a sponge-like
configuration with a density of just 5 percent,
can have a strength 10 times that of steel.
In its two-dimensional form, graphene is
thought to be the strongest of all known
materials. But researchers until now have had
a hard time translating that two-dimensional
strength into useful three-dimensional mate-
rials.
The new findings show that the crucial aspect
of the new 3-D forms has more to do with
their unusual geometrical configuration than
with the material itself, which suggests that
similar strong, lightweight materials could be
2017 FEB/MAR #8-1
made from a variety of materials by creating similar geometric features.
The findings are being reported today in the journal Science Advances, in
a paper by Markus Buehler, the head of MIT¡¯s Department of Civil and En-
vironmental Engineering (CEE) and the McAfee Professor of Engineering;
Zhao Qin, a CEE research scientist; Gang Seob Jung, a graduate student;
and Min Jeong Kang MEng ¡¯16, a recent graduate.
Other groups had suggested the possibility of such lightweight structures,
but lab experiments so far had failed to match predictions, with some re-
sults exhibiting several orders of magnitude less strength than expected.
The MIT team decided to solve the mystery by analyzing the material¡¯s
behavior down to the level of individual atoms within the structure. They
were able to produce a mathematical framework that very closely match-
es experimental observations.
Two-dimensional materials - basically flat sheets that are just one atom
in thickness but can be indefinitely large in the other dimensions - have
exceptional strength as well as unique electrical properties. But because
of their extraordinary thinness, ¡°they are not very useful for making 3-D
materials that could be used in vehicles, buildings, or devices,¡± Buehler
says. ¡°What we¡¯ve done is to realize the wish of translating these 2-D
materials into three-dimensional structures.¡±
3-D-printed gyroid models such as this one were used
to test the strength and mechanical properties of a new
lightweight material. Photo: Melanie Gonick/MIT