Summary

Many of the significant advances in aircraft and rocket propulsion have been enabled by improved materials and materials manufacturing processes. Improving the efficiency and performance of a jet engine requires higher operating temperatures in order to improve thermodynamic efficiency. To improve efficiency further, engine weight must be reduced while preserving thrust. All of these improvements require new materials with higher melting points and greater strength and durability. Improvements in rocket casing and nozzle throat materials require similar advances. The development of lighter, more durable materials capable of operating at higher temperatures allows significant improvements in engine thrust to weight, fuel-use efficiency, and service life.

The period from about 1950 to 1990 in the United States produced significant advances in propulsion performance. That period was characterized by multiple military and commercial engine development programs, a robust group of engine companies and second-tier suppliers, and significant government investment in technology development, demonstration engines, and supporting infrastructure. Together these factors resulted in significant improvements in all engine characteristics and established the United States on the leading edge of propulsion technology.

THE MATERIALS DEVELOPMENT PROCESS

A three-step, tiered technology development process has been used in the U.S. Air Force (USAF) for years. Basic research (6.1), applied research (6.2), and advanced



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Summary Many of the significant advances in aircraft and rocket propulsion have been enabled by improved materials and materials manufacturing processes. Improving the efficiency and performance of a jet engine requires higher operating tempera- tures in order to improve thermodynamic efficiency. To improve efficiency further, engine weight must be reduced while preserving thrust. All of these improvements require new materials with higher melting points and greater strength and dura- bility. Improvements in rocket casing and nozzle throat materials require similar advances. The development of lighter, more durable materials capable of operating at higher temperatures allows significant improvements in engine thrust to weight, fuel-use efficiency, and service life. The period from about 1950 to 1990 in the United States produced significant advances in propulsion performance. That period was characterized by multiple military and commercial engine development programs, a robust group of engine companies and second-tier suppliers, and significant government investment in technology development, demonstration engines, and supporting infrastructure. Together these factors resulted in significant improvements in all engine char- acteristics and established the United States on the leading edge of propulsion technology. THE MATERIALS DEVELOPMENT PROCESS A three-step, tiered technology development process has been used in the U.S. Air Force (USAF) for years. Basic research (6.1), applied research (6.2), and advanced 1

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m at e r i a l s n e e d s r & d s t r at e g y m i l i ta ry a e ro s Pac e P ro P u l s i o n 2 and for technology development (6.3) constitute the parts of the science and technology program that are managed by the Air Force Research Laboratory (AFRL). However, the National Research Council’s Committee on Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems, which conducted the present study at the request of the Department of Defense (DOD), found that although the tiered process is useful for budgeting purposes, development of materials technolo- gies rarely adhere to the process, and technology maturation is driven more by the identification of a critical need or the sponsorship of a champion within the DOD or industry. In recent years, engine development cycles have been reduced and are considerably shorter than the development cycles for new materials. This mismatch in development timelines, coupled with a reduced infrastructure for engine devel- opment within government and industry, fewer development programs (transition opportunities), and increased aversion to risk by engine program managers, has de- creased the support and advocacy for new materials development. The study found that this lack of support for new materials development has impacted the university environment. Structural materials education and research at U.S. universities have declined, and this decline in turn will threaten the viability of the domestic structural materials engineering workforce. The bottom line, according to this report, is that the current approach to developing new materials, at low levels of maturity, is inadequate for today’s envi- ronment with reduced infrastructure, fewer transition opportunities, increased risk aversion, and limited advocacy and funding. MATERIALS DEVELOPMENT ASSESSMENT The DOD and the AFRL have in the past been able to provide the USAF and U.S. industry with a global competitive advantage in materials and propulsion technology and fielded systems. However, current and future planned AFRL engine programs have a decreased level of industrial-base cooperation and materials funding. It appears that the transition from basic research, to applied research, to advanced technology development, to the manufacturing of technology is not characterized by a formal, executable process, but rather is conducted on an ad hoc basis responding to “user pull” and short-term competitive imperatives. The current planning processes of the AFRL Materials and Manufacturing Directorate and Propulsion and Power Directorate are evolving to address AFRL’s Focused Long Term Challenge (FLTC) approach. The AFRL recognizes the need for activities in the near term, intermediate term, and far term to address the full spectrum of the Air Force mission; however, the expanded scope of the Air Force mission has put significant pressure on the far-term propulsion materials funding profile. The committee believes it is essential that a balance be maintained between the near-term, intermediate-term, and far-term activities in response to the FLTC

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summary 3 demands on the one hand, and a long-term concomitant funding commitment on the other. In addition, the decline that has occurred in the number of technology dem- onstrators has significantly reduced the number of opportunities to demonstrate advanced materials and processes prior to their insertion into existing and emerg- ing propulsion systems. Although the number of planned new systems is limited, advanced materials are critical in improving existing and emerging propulsion systems to meet stated military needs. The committee believes that the AFRL’s Materials and Manufacturing Directorate and Propulsion and Power Directorate will achieve more value for their investments by increasing their communication and collaboration with the Air Force Office of Scientific Research (AFOSR), the system program offices, and industry relative to propulsion materials advances, technology readiness, and the potential payoffs of technology insertion. GLOBAL MATERIALS DEVELOPMENT ENVIRONMENT The committee conducted an open-source assessment of global materials development activities. Since the early 1990s, there has been significant investment in materials development within Europe, Russia, and Japan. The European Union established the European Technology Platform on Advanced Engineering Materials and Technologies (EuMaT).1 That organization facilitates advanced research in the development and application of advanced engineering materials and related manufacturing processes. Specific activities are funded through the contribution of industry (target: 35 percent), national governments (target: 35 percent), and the European Commission (target: 30 percent). The EuMaT strategic plan indicates funding of 4 billion euros for advanced materials development, with yearly alloca- tions ranging from 500 million euros to 2.0 billion euros. All development activities involve consortia of industry, government, and university researchers. Similar advanced materials research continues within Russia and the Ukraine and is frequently conducted in partnership with European Union researchers. Japan makes use of partnerships hosted by its national laboratories to conduct materials research. These partnerships involve one or more industry participants and university researchers. Japan has become a world leader in high-temperature materials made of ceramics and ceramic-matrix composites. The committee identified several areas in which the United States is not at the leading edge of propulsion technology. Specifically, the United States has lost competitive advantage in the following areas: the attachment of the compressor and fan blades using advanced welding processes, superplastically formed diffusion- bonded hollow fan blades, and some areas of ceramic-matrix composites. In most 1 Information on EuMaT is available at http://www.eumat.org/. Accessed December 16, 2009.

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m at e r i a l s n e e d s r & d s t r at e g y m i l i ta ry a e ro s Pac e P ro P u l s i o n 4 and for cases, this loss of competitive advantage is the result of the limited funding of U.S. research efforts and of consortia activities elsewhere in the world. Unfortunately, the loss of competitive advantage with respect to these technologies will result in a competitive disadvantage for U.S. suppliers. In order to maintain or regain the U.S. competitive advantage in the areas of propulsion materials and keep the United States on the leading edge of propulsion technology, there is a need to increase activities in new materials development and competitive 6.2 component and 6.3 demonstrator programs related to materials development and to pursue collaborative research activities within this very com- petitive global environment. INTELLECTUAL PROPERTY AND EXPORT CONTROL Collaboration between competing companies, focused principally on pre- competitive research, has led to numerous successful developments that benefit both the collaborating engine companies and, arguably, the entire materials com- munity. It remains essential in such collaborative arrangements that engine pro- ducers safeguard pre-existing competition-sensitive information and intellectual property (IP) and that these collaborative agreements between competing compa- nies fairly distribute or share newly developed IP and data rights. The committee found that this has been successfully accomplished within existing IP protection mechanisms found within export controls. Significant global investment in materials technologies has led to a highly com- petitive global environment. Future U.S. access to foreign world-class propulsion materials technology may be difficult or impossible to obtain, thereby impacting the U.S. ability to achieve advanced propulsion system capabilities. Delays and uncertainties associated with International Traffic in Arms Regulations (ITAR) requirements hamper and discourage international collaboration on research for propulsion materials. ELEMENTS OF AN EFFECTIVE RESEARCH AND DEVELOPMENT STRATEGY The following 10 elements are listed in an approximate order of impor- tance; clearly, the importance of different elements can change with specific circumstances. 1. Annual reviews of the Air Force propulsion materials requirements, objec- tives, and execution plans to adjust for budget changes and the external environment.

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summary 5 2. Better integration of AFOSR programs into Air Force propulsion materials plans and more involvement of academia and industry in the development of the plans. 3. The development of a stable, long-term materials development program that covers basic research through manufacturing and has provision for materials insertion into test engines. 4. The development of a sufficiently robust and, most important, a stable funding stream. 5. The continued development of Integrated Computational Materials Engi- neering (ICME) approaches that promise to shorten the materials develop- ment time. 6. The implementation of a systems engineering approach to propulsion materials development that includes a risk management plan aimed at inserting materials considerations early in any engine development program. 7. The use of existing engines and demonstrators to expedite materials inser- tion and technology maturation. 8. The inclusion of academia in transition research and development (R&D) both to take advantage of talent and facilities that exist at selected univer- sities around the country and to ensure the development of the required workforce. 9. The increased use of government-industry-academia partnerships to con- duct pre-competitive R&D. 10. The integration of foreign technology development and research with U.S. efforts. Opportunities for collaborative fundamental research should be pursued. CONCLUSIONS AND RECOMMENDATIONS In conclusion, the committee found that the U.S. current and planned R&D efforts are not sufficient to meet U.S. military needs or to keep the United States on the leading edge of propulsion technology. The United States has had a demonstrated process for developing state-of- the-art materials for propulsion systems, but that process needs to be updated to accommodate today’s development environment. Previous best practice for devel- oping new materials depended on a defined propulsion system need, demonstrator engines to verify the materials, and consortia of government, academia, and indus- try to develop the materials. The current plan is lacking in many of these areas. The U.S. development environment is far less robust than in the past, and significant global investment has produced a very competitive environment. The committee found that in several key technology areas (ceramics, joining processes, and super-

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m at e r i a l s n e e d s r & d s t r at e g y m i l i ta ry a e ro s Pac e P ro P u l s i o n 6 and for plastic bonded, hollow fan blades), Europe or Japan is establishing the leading edge of propulsion technology. Additionally, Japan and France are the dominant producers of carbon-carbon fiber that is used both in lightweight structures and in high-temperature carbon silica composites. There are no U.S. domestic sources for these materials. Although the number of new engine development programs in the United States has decreased, opportunities still exist to transition new materials into exist- ing engines in order to improve performance, efficiency, or durability. The com- mittee identified several challenges in materials development that must be met in order to satisfy military needs. These include the following three: 1. Currently, gas turbine efficiency, higher thrust-to-weight ratios, and opera- tion at maximum Mach numbers are limited by compressor disk materials— that is, the 1300°F limit of the compressor disk materials confines the maximum gas turbine pressure ratio to 50 to 1, although higher pressure ratios would remove all of the above limits. 2. Hydrocarbon-fueled scramjets are limited to approximately Mach 8 by the heat absorption of hydrocarbon fuel. Ceramic structures or better thermal barrier coatings are required to remove this limitation. The higher heat sink afforded by hydrogen fuel allows hydrogen scramjets to achieve ap- proximately Mach 12. The materials above would also raise this limit. 3. Rocket engines are limited by fuel/oxidizer velocities. Higher pressure ratios and lower-weight structures are needed to improve rocket engine effectiveness. In addition, the Versatile Affordable Advanced Turbine Engine (VAATE) Pro- gram could offer increased transition opportunities if better coordination occurred among the AFOSR, AFRL, industry, and academia. The committee found numerous examples of government-industry-academia consortia performing pre-competitive development activities without hindering industry’s ability to protect key intellec- tual property in the later phases of materials and process development. Because the United States trails Japan and Europe in some key propulsion materials areas, it is important that laws and practices allow the inclusion of these leading-edge areas of materials development in new government and industry consortia. DOD fund- ing agencies should identify and support, both financially and through regulatory and administrative relief, opportunities for pre-competitive collaborative research for structural propulsion materials, both domestically and with global partners. The committee makes the following recommendations: • The Air Force Research Laboratory’s Materials and Manufacturing Direc- torate and Propulsion and Power Directorate need to develop a strategy to

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summary 7 maintain or regain U.S. preeminence in propulsion materials. The strategy should include the regular review and updating of the directorates’ propul- sion materials plan, with an emphasis on the consequences of unfunded items, the changing external environment, and maintaining a balance for the near-, mid-, and far-term activities in response to the Focused Long Term Challenges and funding commitment. • The strategy for developing future aerospace propulsion materials should define a materials development program with stable and long-term fund- ing. The program should cover basic 6.1 research through 6.3 development and include manufacturing and insertion strategies. It should involve in- dustry, academia, and other government entities, and it should selectively consider global partners for pre-competitive collaboration. Essential ele- ments of the strategy include a steering committee, feedback metrics, and a risk reduction plan based on systems engineering practices. • The AFRL’s Materials and Manufacturing Directorate and Propulsion and Power Directorate should increase their communication and collaboration with the AFOSR, system program offices, industry, and academia relative to propulsion materials needs, advances, technology readiness, and the potential systems payoffs of technology insertion. • To maintain or regain the U.S. military competitive advantage in the areas of propulsion materials and to keep the United States on the leading edge of propulsion technology, there is a need for advocacy within the Office of the Secretary of Defense/Director, Defense Research and Engineering, to increase activities in new materials development and competitive 6.2 component and 6.3 demonstrator programs. • The U.S. State Department should reformulate the ITAR fundamental research exclusion to encompass all such research whether performed in academia, industry, or government. This exclusion should also apply to fun- damental research activities encompassed within larger research programs that contain other ITAR-controlled elements. • DOD funding agencies should identify and support, both financially and through regulatory and administrative relief, opportunities for pre- competitive collaborative research for structural propulsion materials, both domestically and with global partners. • For the special case of pre-competitive research with global partners, the DOD, the Department of State, and other U.S. government entities, including the Department of Commerce, should proactively encourage such pre-competitive research opportunities and develop ways to facilitate knowledge transfer within wide, acceptable boundaries. • The research activities of the Air Force Office of Scientific Research should tie more closely to AFRL propulsion materials needs so as to provide a path

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m at e r i a l s n e e d s r & d s t r at e g y m i l i ta ry a e ro s Pac e P ro P u l s i o n 8 and for to insertion. Together the AFOSR and the AFRL should develop a research portfolio that covers a wider range of near-, mid-, and far-term needs. • The United States should continue to develop computational methods to shorten materials development time and to reduce the time required for testing and materials validation so as to reduce the risk related to insertion of new materials. • The Air Force should fully implement the R&D strategy that it develops, and it should reevaluate its strategy annually. THE WAY AHEAD For many years the United States has defined the leading edge of propulsion and propulsion materials technology. This technology has provided the nation with a military and commercial competitive advantage. Due to changing priorities, atrophying infrastructure, and a much more competitive global environment, the United States must take action to regain its competitive position.