From: Mike Lorrey (mlorrey@datamann.com)
Date: Sun Dec 23 2001 - 07:33:05 MST
http://unisci.com/stories/20012/0607013.htm
Spaceships Made Of Concrete? Could Happen, UAH Says
With 14 years of experience and four national championships under their
belts, the idea of building a racing canoe out of concrete no longer
seems odd to engineering faculty and students at The University of
Alabama in Huntsville (UAH).
But spaceships made of concrete?
It could happen.
A unique concrete mixture developed by UAH students for their concrete
canoe has team members and their faculty advisors convinced that
concrete could be the next wonder material of the space age.
"There's a really good chance these materials will replace the aerospace
composites that are out there now," says UAH's Dr. John Gilbert. "I
think we can make structures out of concrete that are lighter and more
flexible than structures made of graphite epoxy composites."
The UAH concrete could be used to support telescopes in space, for
rocket fuselages, to build a lunar colony -- or for low-cost emergency
shelters on Earth.
"A space station wall or space telescope mount made of this might be
thicker than graphite composites, but it wouldn't necessarily be
heavier," said Gilbert, a team coach and professor of mechanical
engineering. "The concrete is the lightest part of the mixture. And
since concrete is pretty inert, it would be less vulnerable to things
like radiation or atomic oxygen erosion."
The secret is in the recipe. UAH's flexible concrete is the end product
of more than 200 different combinations that were mixed and tested. It
is made of Portland cement, glass microbeads (microscopic hollow
spheres), latex, acrylic fortifier and water.
Mix in the right proportions, then dry for 12 hours. The end product is
concrete so light that a solid block will float in water, and so
flexible it can bend without breaking.
The bending part is important, since UAH's new canoe, "Survivor," has no
internal struts or supports to stiffen the boat. Instead, it was
intentionally designed to bend and flex -- to "swim" -- as it goes
through the water.
Designing a watercraft to flex and bend is a revolutionary proposal in
civil and mechanical engineering -- fields where structures and vehicles
are normally designed and reinforced to reduce or eliminate bending and
twisting.
It's even more revolutionary that the UAH team intentionally lowered the
boat's natural harmonic, "tuning" the canoe so it reaches resonance when
it is raced at the national concrete canoe championships June 14-16 in
San Diego, California.
In engineering, resonance is almost always thought to be a bad thing.
Every object has a natural frequency or wavelength, based on its size,
shape, density and other physical properties. Matching an object's
natural frequency with outside forces, such as sound waves, releases
tremendous energy and can shake the object to pieces. That's why certain
high frequency musical notes can break glass.
Perhaps the best known example of what happens when a large structure
reaches resonance was the first Tacoma Narrows suspension bridge.
Powerful wind blowing through the bridge cables set up an extremely low
frequency hum that matched the bridge's natural frequency. The bridge
deck started to rise and fall in great waves. News film of the bridge
shaking itself to pieces on Nov. 7, 1940, is still shown on television
documentaries around the world.
In the decades that followed, special techniques were developed to help
architects and engineers avoid harmonic resonance in everything from
bridges and skyscrapers to cars and airplanes.
So why would anyone design a canoe specifically to do what the Tacoma
Narrows bridge did?
To capture that energy.
A boat moving through water sets up waves. Some waves are pushed away
and become wake. Others flow under the boat. If the boat is rigid, those
waves set up turbulence and cause drag. The boat has to fight against
those forces to move forward.
A canoe that reaches resonance in the water, however, might move with
the water rather than against it, Gilbert said. Survivor is designed to
flex during each paddle stroke, storing energy, then to release that
energy and surge forward between stokes.
"The boat surges forward and 'swims' between strokes," said Gilbert. "It
is unlike any other boat in the field. It is an entity that no one has
ever reckoned with before."
At the southeastern regional concrete canoe competition earlier this
year, the team found that the boat's flexing and bending also gives its
passengers a ride that takes some getting used to. Compared to earlier
rigid canoes, it was like the difference between riding a bicycle and
riding a camel.
"We really had to train it and ourselves," Gilbert said. "We're trying
to deal with something that's as close to a living thing as we've ever
had. You have to get used to that actually in the saddle, so to speak."
While the concrete canoe team's "tuned" technology is theoretically
sound, extensive testing that might damage the canoe will have to wait
until after the national competition. - By Phillip Gentry
This archive was generated by hypermail 2.1.5 : Sat Nov 02 2002 - 08:12:45 MST