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Open-Lattice Composite Design Strengthens Structures
Industrial Productivity
Originating Technology/NASA Contribution
NASA has invested considerable time and energy working with
academia and private industry to develop new composite structures
that are capable of standing up to the extreme conditions
of space. Over time, such technology has evolved from traditional
monocoque designs, in which the skin of a metal structure
absorbs the majority of stress the structure is subjected
to, to more complex, geometric designs that not only offer
strength to counteract stress loads, but also add flexibility.
With an eye to next-generation space-deployable structures,
NASA is continuing to identify advanced composite materials
and designs that could eventually become the mainstay of
future missions, be it in the framework of advanced spacecraft
or in the form of extraterrestrial outposts constructed for
long-term space habitation.
One of the structures in which NASA has made an investment
is the IsoTruss grid structure, an extension of a two-dimensional
“isogrid” concept originally developed at McDonnell Douglas
Astronautics Company, under contract to NASA’s Marshall Space
Flight Center in the early 1970s. IsoTruss is a lightweight
and efficient alternative to monocoque composite structures,
and can be produced in a manner that involves fairly simple
techniques.
Partnership
In the early 1990s, NASA’s Langley Research Center helped
fund a 7-year research project that led to the development
of IsoTruss. David Jensen, a professor of civil engineering
at Utah’s Brigham Young University (BYU) and director of
the school’s Center for Advanced Structural Composites, invented
the technology, with assistance from several graduate students
and further funding from the National Science Foundation
and the Federal Highway Administration.
Passionate about aerospace, Jensen originally thought that
this would be the area in which IsoTruss would attain the
most success. The support he received from NASA was for development
of space applications, including evaluation of a proposed
solar sail that could propel a craft through space by harnessing
solar flux. According to him, a very lightweight structure
would be required to stretch the solar sail out, because
of the high costs associated with launching mass into space.
BYU inked a licensing agreement with space suit and soft
materials developer ILC Dover LP in February 2002 to evaluate
use of Jensen’s patented IsoTruss technology on NASA’s conceptual
solar sail-driven spacecraft. Though the project never came
to fruition, Jensen continues to explore aerospace applications
based on his initial support from NASA to create the technology.
Product Outcome
BYU has licensed the IsoTruss technology for use in the United
States, China, and Japan; negotiations are in process for
other parts of the world.
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The
IsoTruss technology delivers superior structural
solutions that are lighter, stronger, and more efficient
than traditional fiber-reinforced composites, metal,
or wood. |
The technology is garnering global attention, because it
is extremely lightweight and as much as 12 times stronger
than steel (depending on the application). It is typically
constructed of carbon and/or fiberglass filaments that are
interwoven in an open-lattice design—longitudinal and helical
reinforcement members forming triangles and pyramids that
distribute stresses. (The “iso” and “truss” in IsoTruss represent
the isosceles triangles that truss the pyramids that ultimately
give the structure its strength and stiffness.) According
to Jensen, the breakthrough is not the composite materials
used to fabricate the structure—as any fiber and resin combination
can be used—but the three-dimensional, spider web-like structural
design itself, since it eliminates the weight of comparable
structures, such as solid wood and tubular metal poles. In
essence, a 90-pound IsoTruss composite structure could replace
a 1,000-pound steel pole and still offer the equivalent strength.
An IsoTruss structure can be built in many different geometric
configurations and possesses many different geometric variables
so that it can be optimally tailored for myriad applications.
The open-lattice design enables a variety of standard and
innovative connections, while offering significant resistance
to column buckling.
There are many cost and environmental advantages to IsoTruss,
too: It is less expensive to manufacture, transport, and
install than wood or steel; there is little-to-no maintenance
needed, as it does not rust, corrode, or rot; it is impervious
to insect and woodpecker damage; it is easy to repair and
easy to replace, if necessary; it does not contain hazardous
or toxic chemicals; and it can be made from fully recyclable
materials. When used as utility poles, IsoTruss structures
can serve as an environmentally friendly alternative to wooden
poles, which are treated with chemical preservatives that
could potentially harm the ground and water supplies.
Furthermore, an IsoTruss structure offers superior wind resistance.
Because of its open-lattice design, wind drag is typically
reduced by 30 percent, as compared to a traditional wooden
pole. This means that an IsoTruss pole is much less susceptible
to breaking or falling when subjected to high winds—another
reason why it is a good match for utility-related applications.
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Civil
Engineering students at Brigham Young University
built an ultra-strong, super-light mountain bike
using carbon fiber IsoTrusses instead of regular
cylindrical tubes. |
IsoTruss utility pole applications are still on the horizon,
albeit with plenty of potential. According to
a Wall Street Journal article from 2000, the United States
alone requires approximately 4 million new utility poles
each year just to replace rotting wood poles,
while rapidly developing Third World countries still constructing
their power and communications distribution systems will
require hundreds of millions of poles over the next decade.
Meanwhile, IsoTruss has taken off in the form of meteorological
towers. IsoTruss Structures Inc., a Utah-based licensee of
the technology, is selling and installing meteorological
towers that are 270-feet high and one-tenth the weight of
steel, plus less expensive to manufacture and easier to install
than steel towers. These tall towers are designed to handle
harsh weather conditions, including radial ice loads up to
1/2-inch thick and strong winds up to 90 miles per hour.
The meteorological towers have been fitted with wind instrumentation
and installed near the mouth of Spanish Fork Canyon, Utah;
in Arizona and New York; and on U.S. Air Force bases, where
they are monitoring meteorological conditions in preparation
for the installation of large wind turbines that generate
electricity from wind power. Since wind characteristics vary
with height, these towers provide more accurate wind speed
and meteorological measurements, enabling better prediction
of the potential long-term energy efficiency of tall wind
turbine towers. At the Spanish Fork site, for example, tests
are being conducted to evaluate the economic and energy-saving
effects of the tower.
IsoTruss structures can also be employed as preassembled,
three-dimensional, corrosion-resistant reinforcement for
concrete structures and as standalone structural columns.
They were recently used as tilt-up wall braces in constructing
the South Towne Exposition Center, in Sandy, Utah. At this
site, it took just two workers to install these wall braces
(one to hold a brace in position and one to install the anchor),
as opposed to the five workers required to install the neighboring
steel braces (four to hold and one to install).
IsoTruss is also being considered for use in communication
towers, military structures, freeway sign support structures,
medical prostheses, farming and irrigation equipment, vehicle
and aircraft parts, and sporting goods equipment.
IsoTruss Structures Inc. and ATK Thiokol Propulsion have
agreed to collaborate on the analysis and distribution of
composite lattice structures for commercial and military
products. The pact will enable the two companies to provide
application-specific solutions to customers in the military,
international aerospace industry, and commercial markets
that rely on high-performance, lightweight structures.
In the realm of sports, there is one unique application that
may eventually see the light of day as a commercial product.
Under the tutelage of Jensen, a group of BYU engineering
students used the intertwining IsoTruss composite materials
(carbon fiber and Kevlar, in this case) to construct a mountain
bike. The longitudinal frame tubes were designed to resist
all axial and bending loads, while other IsoTruss parts were
used to support transverse sheer and torsion loads. A clear
sheathing was placed over some of the tubes to protect them
from the dirt and mud that can kick up during a ride. The
students involved with the project are touting the bike frame
to be lighter, more aerodynamic, and less breakable than
many top-of-the-line carbon fiber frames.
IsoTruss® is a registered
trademark of Brigham Young University.
Kevlar® is a registered trademark of E.I. DuPont de Nemours
and Company.
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