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August 2003
FREEDOMCar Program to Develop Future Composite Car

Automotive technology aimed primarily at increasing the fuel efficiency of propulsion systems and/or developing alternative fuels that would reduce emissions has been a concern of the U.S.

Author:
Posted on: 8/1/2003
Source: Composites Technology

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Dave Warren mug shot

A graduate of Vanderbilt University in materials science and engineering, C. David Warren is program manager for Transportation Composite Materials Research at Oak Ridge National Laboratory. He serves as the field technology manager for composites for the Department of Energy's Automotive Lightweighting Materials.

Automotive technology aimed primarily at increasing the fuel efficiency of propulsion systems and/or developing alternative fuels that would reduce emissions has been a concern of the U.S. Government and private industry since the environmental movement of the 1960s and the oil crisis of the 1970s. But in 1994, the Partnership for a New Generation of Vehicles (PNGV), formed between the U.S. Government and automakers, represented a paradigm shift from an adversarial relationship, resulting from the dictates of regulation, to a true working relationship, striving to meet environmental, economic and business goals through joint technology development. Cooperative research has been extended to the U.S. Government's FREEDOMCar initiative. Its aim is to develop technologies for the manufacture of 100-mile-per-gallon, petroleum-fueled vehicles, with a corresponding drop in emitted pollutants, or fuel cell-powered vehicles that emit only water and heat as byproducts. To build a 100-mpg vehicle, designers estimate that a 50 to 60 percent reduction in vehicle curb weight will be necessary to achieve program goals. If fuel-cell-powered vehicles are to be realized, curb weight must be reduced not only to increase fuel economy, but also to offset the weight of fuel-storage and reformer systems.

Under this program, the U.S. Department of Energy (DoE) and the Automotive Composites Consortium (ACC) — one of several cooperative, pre-competitive research consortia formed by Ford Motor Co., General Motors Corp. and DaimlerChrysler — are conducting joint composite materials research for body and chassis systems, which offer the greatest potential for vehicle weight reduction.

The ACC's first order of business was to prove that composites could meet the auto industry's functional requirements and critical crash criteria for primary structures. ACC built and crash tested a glass fiber-reinforced Ford Escort front-end structure designed for energy management. The structure met all crash criteria.

In the second phase of the research, efforts focused on developing technologies that would make glass-reinforced parts commercially viable. Program focus areas included long-term durability; adhesive joining technologies; high-volume processing of medium-to-large parts (including molding and preforming technologies); crash testing and crash modeling of composite structures; and post-assembly nondestructive evaluation. This research culminated in a manufacturability demonstration project, involving a pickup truck box and tailgate assembly based on the Chevy S-10, which was 25 percent lighter than its steel counterpart. The truck box was adhesively bonded to the supporting structure, and manufactured at a production rate of 15-parts-per-hour with no cost penalty to the consumer while meeting all durability and safety requirements. The keys to program success were (1) the development of durability-driven design guidelines, including the synergistic effects of creep, fatigue, fracture, impact, temperature extremes, fluid exposure and other environmental stressors; (2) completion of SAE standard J2253 for testing of composites; (3) the development of adhesive joint test methodologies and design approaches; (4) incorporation of the P4 preforming technology; and (5) the development of high-volume liquid molding technologies with cycle times of four minutes for very large parts. Since then, technologies used in the S-10 demonstration have been commercialized and used to manufacture an optional composite pickup box for the Chevrolet Silverado, a composite pickup bed for the Ford Explorer Sport Trac, quarter panels for the Aston Martin Vanquish and the rear cargo doors of several SUVs and minivans.

As researchers pursued more aggressive weight-reduction goals, it became clear that carbon fiber would be required to meet those goals. Today, almost all body/chassis materials research is focused on making carbon fiber composites technically and economically viable for future vehicles. Whether the program is erring by "putting all of its eggs in one basket" or wisely devoting enough resources to "achieve critical mass" is yet to be seen. Carbon fiber composites offer high stiffness and low density, but government/industry attempts to make them production-worthy involve huge challenges:

Cost. The research portfolio mandates cost reduction or at least cost parity with current steel designs. Fortunately, cost is not simply viewed as material price per pound. Instead, the total system cost is evaluated, accounting for savings in capital equipment, assembly, part count and part finishing. The largest cost reduction effort is aimed at carbon fiber itself, with ongoing research into low-cost precursors, non-thermal conversion methods, high-rate oxidation techniques and the use of novel approaches to surface activation.

Manufacturability. Cost-effective, high-volume composite processing methods are under development, using techniques that will be compatible with automotive manufacturing plants and methodologies. Most of the current manufacturing research centers on fiber-reinforced thermosets — thermoplastics work has been stalled, due to concerns about thermal expansion and creep.

Design data/test methodologies. Automotive composites are rarely laminates or sandwich structures; therefore many failure criteria used elsewhere in the composites industry are not applicable. While there is a wealth of information regarding epoxy and epoxy-like systems, automotive composites are more likely to be vinyl ester, isocyanurate or similar systems. Therefore, test methods, failure criteria and material models are being developed for the more ductile, lower Tg resin systems and less directed fiber architectures used to make auto parts.

Joinery. Significant effort is going into development of fast, reliable and repeatable, high-volume technologies for joining composites and dissimilar materials — methods that enable composite parts to be removed for repair or replacement.

Recycling and repair. Cost-effective methods for recycling and repair of composites are being developed, including technology for separating carbon fiber from cured resins and - the most difficult task — development of economically advantageous applications for recovered carbon fiber. Repair methods are still largely remove and replace, but that becomes more difficult and more expensive as the benefits of parts consolidation are realized through manufacturing developments.

The goal of current composite materials research is a mostly carbon fiber composite body-in-white (BIW) which is 60 percent lighter than comparable steel vehicles. This project's initial design phase is complete, with a proposed structure that is 67 percent lighter than the steel baseline, with greater bending and torsion stiffness. The design, based on the packaging requirements of the JA, uses 55 kg/121 lb of chopped carbon fiber and 8.2 kg/18 lb of carbon fiber fabric. Currently, tooling is being procured and installed to make the various parts of the BIW, with assembly scheduled for late 2003 or early 2004.

PNGV and FREEDOMCar are successful models for reducing U.S. dependence on foreign oil and minimizing the automobile's environmental impact. But much work remains. The automotive industry is now a global enterprise and scientific research must extend far beyond U.S. shores. The time has come for cooperation in research, not only between government and industry, but also between the governments of different countries.

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