This is another huge advance in
fabrication possibilities coming out of nanotech. To start with we have a porous strong material
that does not crack. This sure beats a
solid bumper.
The point is that it is becoming
possible to fabricate composites at these dimensions. It will all soon find its way into
manufactured products. Let us start with
an uncrushable platform of little weight for making cars. You see where we are going quite fast. Our future electric cars will also be easily
designed to withstand a 100 mph crash into a brick wall and be almost walked
away from or certainly survivable.
It is good to see this work.
Making materials to order
by David L. Chandler
for MIT News
A team of researchers at MIT has found a way to make complex composite
materials whose attributes can be fine-tuned to give various desirable
combinations of properties such as stiffness, strength, resistance to impacts
and energy dissipation.
The key feature of the new composites is a "co-continuous"
structure of two different materials with very different properties, creating a
material combining aspects of both. The co-continuous structure means that the
two interleaved materials each form a kind of three-dimensional lattice whose
pieces are fully connected to each other from side to side, front to back, and
top to bottom.
The research - by postdoc Lifeng Wang, who worked with undergraduate
Jacky Lau and professors Mary Boyce and Edwin Thomas - was published in April in
the journal Advanced Materials.
The research was funded by the U.S. Army through MIT's Institute for Soldier
Nanotechnologies.
The initial objective of the research was to "try to design a
material that can absorb energy under extreme loading situations," Wang
explains. Such a material could be used as shielding for trucks or aircraft, he
says: "It could be lightweight and efficient, flexible, not just a solid
mantle" like most present-day armor.
In most conventional materials - even modern advanced composites - once
cracks start to form they tend to propagate through the material, Wang says.
But in the new co-continuous materials, crack propagation is limited within the
microstructure, he says, making them highly "damage tolerant" even
when subjected to many crack-producing events.
Some existing composite materials, such as carbon-carbon composites
that use fibers embedded in another material, can have great strength in the
direction parallel to the fibers, but not much strength in other directions.
Because of the continuous 3-D structure of the new composites, their strength
is nearly equal in all dimensions, Wang says.
Thomas, the Morris Cohen Professor of Materials Science and Engineering
and head of MIT's Department of Materials Science and Engineering, says that in
most existing composite materials, the fibers form disordered mass with
"zero continuity," while the other material - typically a resin that
fills the space and then hardens - is continuous and connected in three
dimensions.
The material that forms the continuous structure "tends to
dominate the properties" of the composite, he says. "But when both
materials are continuous, you can get benefits that are surprisingly
synergistic, not just additive."
In their experiments, the MIT researchers combined two polymer
materials with quite different properties: one that is glass-like, strong but
brittle, and another that is rubber-like, not so strong, but tough and resilient.
The result, Thomas says, was a material "that is stiff, strong and
tough."
In the quest for new materials with specific combinations of
properties, Thomas says, "we've pretty much exhausted the natural
homogeneous materials," but the new fabrication techniques developed in
this research can "take to another level" the material development
process.
The researchers designed the new materials through computer
simulations, then made samples that were tested under laboratory conditions.
The simulations and the experimental data "agree nicely," Thomas
says. While this initial research focused on tuning the material's mechanical
properties, the same principles could be applied to controlling a material's
electrical, thermal, optical or other properties, the researchers say.
The process could even be used to make materials with
"tunable" properties: for example, to allow certain frequencies of
phonons - waves of heat or sound - to pass through while blocking others, with
the selection of frequencies tuned through changes in mechanical pressure. It
could also be used to make materials with shape-memory properties, which could
be compressed and then spring back to a specific form.
Richard Vaia, acting chief of the Nanostructured and Biological
Materials Branch at Wright-Patterson Air Force Base in Ohio, says this work is
"an exciting demonstration of the crucial importance of architecture in
materials-by-design concepts."
Vaia says this work "provides an example of the future of
composite and hybrid materials technology where direct-write fabrication,
printing technologies and complex fiber-weaving techniques are not simply
manufacturing tools, but an integral part of a robust, implementable digital
design and manufacturing paradigm."
The next step in the research, Thomas says, is to make co-continuous
composites out of pairs of materials whose properties are even more drastically
different than those used in the initial experiments, such as metal with
ceramic, or polymer with metal. Such composites could be very different from
any materials made before, he says.
No comments:
Post a Comment