Executive Summary

A polymer matrix composite (PMC) consists of a thermoset or thermoplastic resin matrix reinforced by fibers that are much stronger and stiffer than the matrix. PMCs are attractive because they are lighter, stronger, and stiffer than unreinforced polymers or conventional metals, with the additional advantage that their properties and form can be tailored to meet the needs of a specific application. High-performance fiber reinforcements are of the highest interest for military and aerospace composite applications; these include carbon fibers and such organic fibers as aramids, liquid crystalline polymers, and ultrahigh-molecular-weight polyethylene.1

When high-performance carbon fibers were first developed in the 1960s, their high cost (as much as $400 to $500 per pound) limited their applications to high-value military aerospace and space systems. The results of early military composite development programs can be seen today in systems fielded by each of the military services. For example, more than 350 parts of the F-22 Raptor, accounting for 25 percent of the structural weight, are carbon-epoxy composites.2 Further, the developmental Joint Strike Fighter will be between 25 and 30 percent composite by weight. The Army now uses carbon-thermoplastic composites in high volume production of sabots for the M829A3 munition.

Composites are expected to play an even greater role in military systems of the future. The Army’s Objective Force, part of the Defense Department's (DoD’s) Future Combat System, exemplifies an ongoing transformation to an entirely new future combat system incorporating advanced materials and design concepts for munitions, armaments, and hull structures for manned and unmanned robotic vehicles that will be light enough to be rapidly deployed on C-130 aircraft. Ground vehicles in the Future Combat System will have to weigh between 10 and 20 tons and have superior mobility, transportability, survivability, and lethality for a variety of missions. The Navy is considering carbon fiber composites for next-generation topside ship structures such as destroyers, aircraft carriers, littoral combat ships, and other high-speed vehicles to satisfy the weight and performance requirements of these systems. These applications represent a possible 100-fold increase in carbon fiber usage.

High-performance organic fibers are used extensively in soldier protection systems ranging from body armor and helmets to spall liners in ground vehicles. The global war on terrorism has increased the demand for these fibers for crew protection kits and for tactical vehicles for immediate deployment, as well as for replacement components needed by forces in the field. The new M5® fiber, being developed with improved compressive properties, may enable improved structural armor applications.3

1  

The properties of composite structures depend not only on the fiber reinforcements, but also on the polymer matrix, the characteristics of the interface between the fiber and matrix, and the manufacturing process used to form the finished structure.

2  

Composites are commonly denoted by their fiber-matrix composition. A carbon-epoxy composite will consist of carbon fibers in an epoxy matrix.

3  

M5® is a registered trade name for poly{2,6-diimidazo[4,5-b:4’,5’-E]pyridinylene-1,4-(2,5-dihydroxy)phenylene}. The fiber was engineered over a 10-year period by a team of scientists led by Doetze Sikkema while working for Akzo Nobel, a pharmaceuticals, coatings, and chemical company headquartered in the Netherlands. The design



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High-Performance Structural Fibers for Advanced Polymer Matrix Composites Executive Summary A polymer matrix composite (PMC) consists of a thermoset or thermoplastic resin matrix reinforced by fibers that are much stronger and stiffer than the matrix. PMCs are attractive because they are lighter, stronger, and stiffer than unreinforced polymers or conventional metals, with the additional advantage that their properties and form can be tailored to meet the needs of a specific application. High-performance fiber reinforcements are of the highest interest for military and aerospace composite applications; these include carbon fibers and such organic fibers as aramids, liquid crystalline polymers, and ultrahigh-molecular-weight polyethylene.1 When high-performance carbon fibers were first developed in the 1960s, their high cost (as much as $400 to $500 per pound) limited their applications to high-value military aerospace and space systems. The results of early military composite development programs can be seen today in systems fielded by each of the military services. For example, more than 350 parts of the F-22 Raptor, accounting for 25 percent of the structural weight, are carbon-epoxy composites.2 Further, the developmental Joint Strike Fighter will be between 25 and 30 percent composite by weight. The Army now uses carbon-thermoplastic composites in high volume production of sabots for the M829A3 munition. Composites are expected to play an even greater role in military systems of the future. The Army’s Objective Force, part of the Defense Department's (DoD’s) Future Combat System, exemplifies an ongoing transformation to an entirely new future combat system incorporating advanced materials and design concepts for munitions, armaments, and hull structures for manned and unmanned robotic vehicles that will be light enough to be rapidly deployed on C-130 aircraft. Ground vehicles in the Future Combat System will have to weigh between 10 and 20 tons and have superior mobility, transportability, survivability, and lethality for a variety of missions. The Navy is considering carbon fiber composites for next-generation topside ship structures such as destroyers, aircraft carriers, littoral combat ships, and other high-speed vehicles to satisfy the weight and performance requirements of these systems. These applications represent a possible 100-fold increase in carbon fiber usage. High-performance organic fibers are used extensively in soldier protection systems ranging from body armor and helmets to spall liners in ground vehicles. The global war on terrorism has increased the demand for these fibers for crew protection kits and for tactical vehicles for immediate deployment, as well as for replacement components needed by forces in the field. The new M5® fiber, being developed with improved compressive properties, may enable improved structural armor applications.3 1   The properties of composite structures depend not only on the fiber reinforcements, but also on the polymer matrix, the characteristics of the interface between the fiber and matrix, and the manufacturing process used to form the finished structure. 2   Composites are commonly denoted by their fiber-matrix composition. A carbon-epoxy composite will consist of carbon fibers in an epoxy matrix. 3   M5® is a registered trade name for poly{2,6-diimidazo[4,5-b:4’,5’-E]pyridinylene-1,4-(2,5-dihydroxy)phenylene}. The fiber was engineered over a 10-year period by a team of scientists led by Doetze Sikkema while working for Akzo Nobel, a pharmaceuticals, coatings, and chemical company headquartered in the Netherlands. The design

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High-Performance Structural Fibers for Advanced Polymer Matrix Composites DEVELOPMENT OF HIGH-PERFORMANCE FIBERS The development pathways of high-performance carbon and organic fibers have been driven by decidedly different cost and performance requirements. These different pathways strongly affect the future prospects for military and commercial applications of these fibers. High-Performance Carbon Fibers Carbon fibers are typically produced by spinning and then thermally carbonizing one of three types of precursor fibers: polyacrylonitrile (PAN), pitch, or rayon. Depending on the type of precursor and the processing method, the finished carbon fiber will have a different microstructure and therefore different properties. PAN-based fibers have a disordered microstructure that typically confers higher tensile and compressive strengths, while pitch-based fibers have a more crystalline microstructure that results in a higher tensile modulus and much higher (100 times) thermal conductivity. In general, PAN-based fibers dominate applications where strength is critical, and pitch-based fibers dominate applications where heat transfer or stiffness (i.e., more than 80 Mpsi fiber modulus) is important. Around 90 percent of all commercial carbon fibers are produced by the thermal conversion of PAN precursor fibers.4 As the carbon fiber industry matured during the 1980s and costs began to decrease, a variety of commercial applications for high-performance composites emerged, including sporting goods, commercial aircraft, and industrial applications. In 2003, the world market demand for PAN-based carbon fiber was approximately 38 million pounds, divided almost equally (10 million to 13 million pounds each) among North America, Europe, and Asia. Aerospace applications predominate in North America, while industrial and aerospace applications are emphasized in Europe, and sports and leisure are the primary applications in Asia.5 As a result, DoD usage, which dominated the U.S. requirements in the 1970s and 1980s, became a smaller part of the total market. In 2003, the lowest prices observed for carbon fibers were $5.25 per pound for a standard-modulus (32 Mpsi) fiber and $17 per pound for an intermediate-modulus (42 Mpsi) fiber. The DoD market was just under 10 percent of the total U.S. carbon fiber market and 4 percent of the world carbon fiber market. Until the late 1980s, special acrylic fiber (SAF) precursor was used for nearly all PAN-based carbon fibers. This precursor fiber is produced in filament bundle (or tow) sizes of 3,000 (3k), 6,000 (6k), and 12,000 (12k) filaments, and is normally supplied on spools without applying a crimp or twist. The majority of current defense applications are based on the performance and consistency of properties provided by these small-tow, SAF-based carbon fibers. In response to the emergence and projected growth of such commercial carbon fiber markets as sporting goods, construction, and transportation, a sector of the carbon fiber industry has evolved to produce fibers in large volumes at relatively low cost. In one sector, commercially available PAN fibers are used as precursors to produce carbon fibers in large tow counts, having up to 24k filaments. These precursor fibers are normally used in the textile industry and draw on an approximately 5-billion-pound annual market to bring about lower material costs. Another sector of the fiber supply base has emerged to meet the increasing demand for commercial applications such as Boeing’s 7E7 aircraft using SAF fiber precursors. Japanese companies are establishing domestic capacity for both SAF precursor plants and fiber lines. For example, prices for T700 12k and 24k tows of $5.25 per pound, a historic low, were not uncommon in 2003. At this price, they represent a cost-competitive alternative to the large-tow-count textile-based fibers, with performance comparable to that of the current SAF fibers approved for use by DoD. The combination of lower cost potential and equivalent performance makes these fibers very attractive for future DoD systems. Today, there is another shortage of SAF-based carbon fiber and prices have risen, demonstrating that $5.25 is not a sustainable price for SAF aerospace-grade carbon fiber.     goal set by Dr. Sikkema was to develop a high-strength synthetic fiber that excelled as both a ballistic fabric and a composite material. 4   Intertech. 2004. The Global Outlook for Carbon Fiber. Proceedings of a conference in Hamburg, Germany, October 18-20. Portland, Me.: Intertech Corporation. 5   Fiber Organon. 2004. U.S. Manufactured Fiber Capacity, Production & Utilization Review. January, p. 7.

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High-Performance Structural Fibers for Advanced Polymer Matrix Composites Further, the capacity for carbon fibers is being driven by the high-volume needs of commercial applications. This may offer additional savings to DoD through economies of scale or simply increased competition to provide the best quality at the lowest price. To increase competition, DoD could take initiatives to establish second sources for all carbon fiber applications. In addition, this commercially driven capacity may provide a primary source of carbon fiber that can supply larger quantities if future expansions are fielded. For example, carbon fiber usage for next-generation ship systems such as DD(X) could exceed current domestic capacity. The continued expansion of the carbon fiber commercial market using high-quality SAF precursors should offer a measure of stability in the fiber supply chain in future DoD applications. All of these methods to produce carbon fibers for DoD have one significant factor in common, which is the cost burden of qualification and subsequent quality and acceptance testing. One straightforward way to reduce cost over the next decade is to modify specifications to reduce the qualification requirements of these advanced fibers.6 High-Performance Organic Fibers The high-performance organic fiber industry began with the commercial introduction of the meta-aramid (m-aramid) fiber Nomex in the late 1960s. Since that time, several classes of fibers have been commercialized: high-strength para-aramid (p-aramid) fibers; liquid crystalline polyester (LCP); high-performance polyethylene (PE); ultrahigh-molecular-weight polyethylene (UHMPE); and most recently poly(p-phenylene-2,6-benzobisoxazole) (PBO). A new fiber M5 (poly{2,6-diimidazo[4,5-b:4’,5’-e]pyridinylene-1,4-(2,5-dihydroxy)phenylene}), also known as PIPD, is in late development stages with the start-up of a pilot plant expected in 2005. Like the carbon fiber industry, developments in organic fiber technology during the 1970s and 1980s enabled the use of lightweight polymer-matrix composites in military and commercial applications. Unlike the carbon fiber industry, however, growth in the high-performance organic fiber industry was driven from the beginning by a combination of military and commercial applications and aerospace and non-aerospace applications. The unusual combination of mechanical, thermal, and other properties found in high-performance organic fibers (especially PBO and aramids), as well as the ability to tailor these properties for specific applications, has enabled this wide range of uses. Demand for high-performance organic fibers such as p-aramids and m-aramids grew steadily at a rate of 6 to 7 percent from the late 1970s to the mid-1990s, due to the large number of commercial applications. These two fiber types represent more than 90 percent of worldwide demand for high-performance organic fibers and can therefore be used as a good approximation of general consumption trends. By 2002, demand for p-aramid alone had risen to approximately 90 million pounds, approximately three times the demand for PAN-based carbon fiber. In the mid-1990s, substantial production capacity existed for high-performance organic fibers in the United States, Europe, and Japan. The high-performance organic fiber industry has grown steadily in recent decades and is stable. From the beginning, the industry’s dependence on high-volume commercial applications, rather than DoD applications, has contributed to its stability. Demand for high-performance organic fibers remains high as a result of their broad range of applications, and there is potential for future growth. During the past 4 to 5 years there has been significant investment in capacity for p-aramids and polyethylene fibers. While there may be room for limited capacity expansion, in the next 5 to 10 years there will be a need for additional capacity requiring a significant investment that will include ingredients and polymer and fiber production facilities. Although DoD represents only a small portion of the overall market, the specificity of DoD requirements may focus attention on issues of supply. FINDINGS AND CONCLUSIONS Fiber Supply The 2004 worldwide capacity of carbon fibers (SAF based and textile precursor based) was expected to be more than 70 million pounds. Consumption was expected to be more than 40 million 6   National Research Council. 2004. Accelerating Technology Transition. Washington, D.C.: National Academies Press.

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High-Performance Structural Fibers for Advanced Polymer Matrix Composites pounds and increasing.7 In this changing market, it appears that each carbon fiber supplier has targeted specific market segments and is building facilities and directing product portfolios to support its chosen strategies. Although some producers have indicated that the high cost of adding new facilities is a barrier to increasing capacity, DuPont, Honeywell, Dyneema, Toho, and Toray are all adding capacity in the United States. This added capacity will help to meet the anticipated shortage of carbon fiber produced with SAF precursor and meet the demand for organic fiber for military and homeland security applications. Significant investment has been made over the past 4 to 5 years in capacity for p-aramid and PE fibers. Some of this capacity has been developed for military products, but most is targeted toward nonmilitary applications. Current expansion is targeted to meet the military needs for soldier protection and homeland security. An important aspect of this continuing investment is an M5 pilot plant start-up planned for 2005. This new M5 capacity will enable ballistic and structural performance evaluation to be conducted on full-scale components. Fiber Demand As the fiber industry matured during the 1980s and costs began to decrease, a variety of commercial applications for high-performance composites emerged, including sporting goods, commercial aircraft, and various industrial applications. As a result, DoD usage, which dominated U.S. requirements in the 1970s and 1980s, became a smaller part of the total market. In 2003, the historic and unsustainably low prices observed for carbon fibers were $5.25 per pound for a standard-modulus (32 Mpsi) fiber and $17 per pound for an intermediate-modulus (42 Mpsi) fiber. The DoD market was just under 10 percent of the total U.S. market and 4 percent of the world market. Military usage is a decreasing share of the total U.S. carbon fiber market—from 43 percent in 1989 to 9 percent in 2003. Because the military usage in the total market is ever smaller—currently less than 4 percent of the world market—the installed integrated capacity in North America is adequate to supply all projected DoD needs for the next decade. In addition, the fiber modulus and strength properties of current production meet DoD's performance requirements for the near term. For the suppliers, this increasingly tight market is expected to lead to pricing structures that could support sustainable reinvestment. For the buyers, in cases where DoD relies on a sole source, prices could remain high. Significant demand from DoD combined with a technological design shift toward lighter-denier products is expected to strain existing capacity for structural organic fibers. Additional military and homeland security applications are also emerging. In particular, the demand for organic fibers is currently high to satisfy the military's need for body armor and crew protection kits for tactical vehicles. This demand is predicted to remain high for 2 years and then decrease gradually. Fiber Technology A few companies continue to invest in new carbon fiber technologies. This investment has been primarily in process improvements and better manufacturing controls to decrease variability and reduce cost rather than to improve properties. Because of this trend, any change in carbon fiber properties is expected to be evolutionary, not revolutionary. Any impact of new lower-cost technology is at least 10 years away. In the organic fiber area, M5 fiber has the potential to become a commercial fiber with a step improvement in functionality, especially to address the need for optimized structural and ballistic properties of interest to DoD. M5 has the potential to meet the future structural and ballistic needs of the Army. Existing fibers, such as Kevlar, have good ballistic properties but poor properties in compression. M5 could be an enabling technology for a new generation of soldier protection systems. Finally, although significant progress has been made in improving fiber and matrix properties and reducing material costs, similar progress has not been achieved in manufacturing technology and innovative design to lower the cost of composite structures. Composite processing remains a major opportunity for improvement. 7   Intertech. 2004. The Global Outlook for Carbon Fiber. Proceedings of a conference in Hamburg, Germany, October 18-20. Portland, Me.: Intertech Corporation.

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High-Performance Structural Fibers for Advanced Polymer Matrix Composites CONCLUSIONS AND RECOMMENDATIONS Accelerating technology transition has been identified as a key target. One method to speed new fiber technologies to market, especially for such new fibers as M5® or nanocomposite fibers, would be for DoD to provide a guaranteed initial purchase order if the pilot product meets specified property and price requirements. In the near term, DoD should provide significant funding to purchase M5 fiber and rapidly evaluate its properties and applications. Cost reduction has been identified as a key target. A clearly significant way to reduce fiber costs over the next 10 years is to reduce or modify the aerospace specifications and qualification process. The DoD should review existing and new qualifications and material specification documents and reduce testing and quality requirements where possible. To reduce acquisition costs, all major DoD programs that use fiber or prepreg should have two qualified sources. To reduce manufacturing costs in aircraft structures, DoD should invest in manufacturing technology and innovative design concept development. Promising ways to improve dimensional tolerance and reduce processing variability include investment in new continuous process controls that would contribute to controlling fiber structure and purity, prepreg properties such as fiber weight per unit length, and overall property variability. To reduce manufacturing costs across all DoD applications, DoD should initiate a program with university-industry-government participation. Promising manufacturing and design concepts should be assessed, including vacuum-assist resin transfer molding (VARTM) to replace more costly manufacturing processes. Virtual manufacturing and simulation should play an important role in accelerated insertion of materials and processes into DoD systems. Research in automation using simulation, sensing, and control systems should be pursued to advance this process from prototype to a production-ready process. Improved understanding has been identified as a key target. The DoD should take a lead in developing a better design methodology that incorporates variability and stochastic aspects of local properties into lifetime models. DoD personnel should use this improved understanding to develop new design allowables and parameters that prevent overdesign of parts and overspecification of fiber properties. The DoD should aid in developing a better understanding of new promising technologies in such areas as micron-scale fibers with nanoscale structure and new sizings with the ability to maximize structural and ballistic properties.