ADVANCED
MATERIALS AND CHEMICALS
Strongwell Corporation
Composite
Materials Sought as Replacement for Steel and Concrete
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In 1994, the U.S. Federal Highway Administration estimated that 230,000 of the nation's 575,000 bridges were structurally deficient or functionally obsolete, and they would require an expenditure of $130 billion in public funds in the coming years. Because steel and concrete decay cost the nation billions of dollars for repair and replacement, new technology that lengthened the functional lives and sped the repair of roadways and bridges was clearly needed. Composite materials held this promise. Strongwell Corporation, the world's largest pultruder of fiber-reinforced structural parts, applied for and was awarded $2 million in cost-shared funding from the Advanced Technology Program (ATP) to research and develop a process to manufacture large, fiber-reinforced polymer (FRP) composite structures that could reduce the cost of maintaining the country's existing civil infrastructure.
Strongwell successfully developed a manufacturing process to pultrude a 36 x 18-inch "double-web" I-beam in a vinyl ester matrix known as the EXTREN DWB. This structural shape is more complex in design and 4½ times stronger than existing composite structural shapes. The large composite structures made of these carbon and glass reinforced polymer composites have attracted interest from state transportation agencies, the offshore oil industry, the construction industry, and the defense industry. Strongwell's beams have been used successfully in two Virginia bridges, but commercialization depends on acceptance by bridge engineers, who are still awaiting test data before they commit to using this new technology. Through a joint venture with Ebert Composite Corporation, the advanced pultruding process Strongwell developed with the help of ATP is being used to manufacture composite poles and towers for electric utility companies and other industries.
COMPOSITE PERFORMANCE SCORE
(based on a four star rating)
* * *
Research and data for Status Report 94-02-0010 were collected during January - March 2002.
Finally, conservative
civil engineers have delayed the acceptance of FRP structures by regulatory
agencies. Many engineers lack confidence in composite materials for civil
infrastructure because not enough testing has been done on their long-term
durability.
Strongwell Proposes an Advanced FRP Composite
Strongwell's goal was to
design and produce a new, high-strength, advanced FRP phenolic composite that
could be used in bridge and building construction. Phenolics are
thermosetting resins that cure through a condensation reaction that produces
water that must be removed during processing.
Phenolic composites have
many desirable performance qualities, including high temperature resistance,
excellent thermal insulation, sound-damping properties, and corrosion resistance;
therefore, they last far longer than conventional materials, such as steel
and concrete.
Strongwell recognized that it would take several years for civil engineers
to accept FRP as a replacement for steel and concrete. Rigorous testing, validation,
and demonstration of this material would be required to ensure product quality
and safety. As a result, Strongwell was unable to attract either internal
or external private capital for this project because the return on investment
was expected to be greater than 10 years. Because of these barriers, Strongwell
submitted a proposal for ATP funding.
Strongwell
Identifies Benefits of Large Composite Shapes
Strongwell forecasted that $2 million from ATP could translate into savings
of billions of dollars for the bridge construction industry. Successful
completion of this research to develop large composite shapes using FRP would
represent a major breakthrough in composite technology. As an improved alternative
to conventional steel and concrete, it would provide the basis for dramatic
improvements in the U.S. road transportation system
and other civil engineering and construction applications. U.S. taxpayers
would benefit from lower life-cycle
costs of existing structures and reduced time and cost to build new structures.
A reduction in the effort required to maintain the nation's highways could
lead to less traffic disruption, which would speed the transport of U.S. products
by the trucking industry. Moreover, Strongwell envisioned that its new technology
would be used in a range of applications, including short-span bridges, offshore
oil platforms, and other industrial applications where corrosion is a problem.
Additional savings also would be realized in other industries such as aircraft
and space.
Revolutionary
Shape Solves Key Technical Challenge
Strongwell's objective was to design and produce a 36 x 18-inch FRP phenolic
and vinyl ester composite beam that could be used in bridge and building construction.
Strongwell intended to build on its expertise in pultrusion (a manufacturing
process for composites) to create a structure large enough, as well as strong
enough, for civil projects. Pultrusion is used in producing continuous lengths
of reinforced plastic parts with constant cross-sections. The process involves
pulling these raw materials through a bath of thermosetting resin and then
into a heated forming and curing die to produce composite structural shapes.
As the reinforcements are saturated with the resin mixture in the resin bath
and pulled through the die, the heat from the die initiates the hardening
of the resin, and a rigid, cured profile is formed that corresponds to the
shape of the die.
One key technical challenge was to design a structure that combined structural
strength with corrosion and chemical resistance, as well as one that performed
better than existing beams used for infrastructure. Strongwell solicited the
expertise of Dr. Abdul-Hamid Zureick, head of the structural engineering and
mechanics group of the School of Civil and Environmental Engineering at Georgia
Institute of Technology, to assist in the design of the FRP shape. Dr. Zureick
proposed a revolutionary shape that is a "double-web I" or "modified
box" beam in which two vertical webs are connected by a flange across
the top and bottom. The double-web I design improved performance, increased
the shear load distribution capability of the beam, and improved the stiffness,
making the beam resistant to bending. The box-like shape also is simple, making
it easier for Strongwell to manufacture using the complex phenolic resin process
and a vinyl ester resin system.
Another key technical challenge
was to create a pultrusion machine capable of manufacturing this large 36
x 18-inch shape while achieving a complete cure of the resin and fiber laminate.
Although the company had extensive experience creating pultruded shapes, no
shape that large had ever been pultruded using phenolics.
Manufacturing
Process Proves Successful
In
September 1996, Strongwell manufactured two 8 x 6-inch subscale prototypes
of the double-web I-beam using a fiberglass and carbon composite. The first
prototype was created with vinyl ester resin, which is less viscous
and therefore easier to use in the pultrusion process, while
offering excellent corrosion resistance and weight reduction compared with
steel. The second prototype was created with phenolic resin, which requires
a more sophisticated manufacturing process but provides the added benefit
of superior heat resistance. With the help of the Georgia Institute of Technology,
Strongwell optimized the beam shape for torque resistance, eliminating the
need for support braces. The stiffness of the subscale prototype composite
beam is roughly 6.3 msi (millions of pounds per square inch), which is more
than twice the stiffness of a standard fiberglass I-beam. The beam also performed
well in tests for fatigue, creep (or stretching under tension), and strength
under static loading. Strongwell's ability to create the 8 x 6-inch beam encouraged
the company to continue its efforts to manufacture the 36 x 18-inch shape.
However, Strongwell encountered several technical challenges as it moved forward.
The thicker, multicored, closed shape of Strongwell's 36 x 18-inch shape represented
a substantial increase in complexity from the small, square tube manufactured
using a phenolic matrix.
The pull forces
required for this project were unheard of for pultrusion, as was the design
of the saw needed to cut the beams. A machine capable of exerting 120,000
pounds of force--more than Strongwell originally anticipated would be needed--was
required to pull thousands of tightly packed fibers through a bath of polymeric
resin and into molding and curing dies of the required size and shape. Strongwell
designed and fabricated a dual-reciprocating hydraulic puller system that
uses two clamping and pulling mechanisms. This was one of the first machines
to synchronize four large cylinders at one time. At that time, the machine
had the largest pull capacity of any pultrusion machine in the world and three
times the pulling capacity of Strongwell's next-largest machine.
By the end of 1997,
Strongwell had successfully developed the manufacturing process to create
the longer double-web I-beam using both a phenolic matrix and a vinyl ester
matrix. The company later marketed the beams made with the vinyl ester resin
as the EXTREN DWB.
Strongwell proved that the dissimilar materials of carbon and glass fibers
could be combined using either a phenolic or a vinyl ester matrix to create
a large structural shape that did not delaminate. The outcome was a 36 x 18-inch
structural shape more complex in design with a much better strength-to-weight
ratio than conventional steel and concrete shapes.
The
company's other tooling accomplishments related to this project include:
Project
Title: Composite
Materials Sought as Replacement for Steel and Concrete (Innovative Manufacturing
Techniques to Produce Large Phenolic Composite Shapes)
Project:
To develop large, cost-effective,
high-performance composite shapes that last longer and are maintained more
easily than the concrete and steel that is now aging and deteriorating in
the country's transportation infrastructure.
Duration: 2/1/1995-1/31/1998
ATP Number: 94-02-0010
Funding (in thousands):
ATP Final Cost $
2,000 64%
Participant Final Cost 1,142
36%
Total
$ 3,142
Accomplishments: During
this three-year project, Strongwell achieved the following significant accomplishments:
Commercialization
Status: Strongwell continues to present and demonstrate
the EXTREN DWB beam for a variety of civil infrastructure applications.
Strongwell has installed composite beams in two bridges in Virginia and has
received substantial interest from oil companies for mobile drilling rig applications.
The company formed a joint venture company with Ebert Composite Corporation
to manufacture and sell composite poles and towers. Strongwell continues to
develop engineering design guidelines so engineers can develop and test the
applicability of FRP shapes for other large civil infrastructure projects.
Outlook: Strongwell
has received positive response to its high-performance composite shapes; however,
industry codes and design standards must be modified to accommodate composite
structures before full-scale commercialization of the technology is feasible.
Maintaining and rebuilding the U.S. roadway system using composites presents
a tremendous market opportunity well into the 21st century.
Composite Performance Score:
* * *
Focused Program: Manufacturing
Composite Structures, 1994
Company:
Strongwell Corporation
400 Commonwealth Avenue
P.O. Box 580
Bristol, VA 24203
Contact: Glenn
Barefoot
Phone: (276) 645-8000
Research and data for Status Report 94-02-0010 were collected during January
- March 2002.