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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems 2 Materials Development: The Process 2.1 INTRODUCTION A three-step, tiered technology development process has been used in the U.S. Air Force (USAF) for years. It is taught at the Defense Acquisition University as part of the science and technology (S&T) management courses and instantiated in Department of Defense (DOD) and Air Force regulations.1 Air Force acquisition regulations assign responsibility for the execution of S&T, the assessment of technology readiness level (TRLs), and the negotiation of technology transition agreements. The majority of these responsibilities fall on the Air Force Research Laboratory Commander.2 Unfortunately, despite the fact that this three-step development process is instantiated in the planning and budgeting process, it rarely executes as published. Funding changes, advances or delays in moving to higher TRLs, and the dynamics of the technology-push–requirements-pull relationship result in each technology’s maturation path being different. In contrast to this notional model (further discussed in Section 2.4, below), what has actually occurred with respect to the technology development process cannot be well defined, differs from one case to the next, and, most importantly, changed substantially toward the end of the 1980s. 1 Air Force Instruction, AFI 63-101. Available at http://www.af.mil/shared/media/epubs/AFI63-101. pdf. Accessed July 9, 2009. 2 Donald C. Daniel, Center for Technology and National Security Policy. 2006. “Issues in Air Force Science and Technology Funding.” National Defense University, Fort Lesley J. McNair, Washington, D.C., February.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems That change involved an increased emphasis on risk reduction and on decisions made by reliance on TRLs—considerations that now drive materials selection in engine developments (including demonstration engines) to the point that the insertion of new materials appears only tangentially in the objectives of engine test programs. Along with this paradigm shift, the evolutionary advance of traditional turbine materials, such as superalloys, has slowed. Engine designers have become averse to the increased risk of materials insertion, and so not only have once-widespread evolutionary materials and process discoveries decreased, but the funding for needed underlying developments has also been downplayed by the new paradigm change. This sentiment was expressed, for example, at the workshops leading to publication of the National Research Council (NRC) report Accelerating Technology Transition: Bridging the Valley of Death for Materials and Processes in Defense Systems, which stated, “Workshop speakers unanimously identified risk aversion as a fundamental barrier to innovation and rapid technology transition.”3 This idea can be recast as follows: More stringent DOD guidelines with respect to required TRLs for incorporation of technology drive the engine OEMs (original equipment manufacturers) to proven low-risk technologies.4 At the same time, the path to quantum changes in advancements (discussed in Section 2.3, below) appears to point toward revolutionary classes of structural materials such as ceramic-matrix composites (CMCs) for which even less of a technology base is available. The lack of data for these materials predisposes risk-averse engine designers to avoid their use. These “structural” changes in the process for the development of new materials for propulsion have also been accompanied by a distinct change in the character of materials programs at U.S. universities. All of these elements are crucial to the understanding of why things are as they are at the present time and what might be done to adapt to and perhaps improve the present state of advances in structural materials for propulsion. Understanding the notional process and what has actually occurred depends on understanding TRLs and funding definitions. These are discussed in Section 2.2, below, followed by a brief discussion in Section 2.3 of the critical role that materials development has played in advancing turbine engine performance. In Section 2.4, the nominal materials development process for propulsion materials is described. These sections are meant to place in better perspective the pre-1990s’ materials development “process”; Sections 2.5 and 2.6 then discuss how this process evolved in the changing 1990s’ environment into the present development process. Major programs that have contributed to advances in propulsion structural materials 3 National Research Council. 2004. Accelerating Technology Transition: Bridging the Valley of Death for Materials and Processes in Defense Systems. Washington, D.C.: The National Academies Press, p. 19. 4 This observation was made by project managers in the AFRL Propulsion and Power Directorate, during presentations to the committee at Wright-Patterson Air Force Base, Ohio, May 27, 2009.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems are outlined in Section 2.7; these programs were started at the beginning of the paradigm shift in the process and continue to the present with the new demonstrator-engine program, the Versatile Affordable Advanced Turbine Engine (VAATE) Program. Section 2.7 ends with a discussion of the characteristics of successful materials development programs. Section 2.8 describes the common themes for successful materials development. Section 2.9 discusses the evolution of materials science and engineering programs at U.S. universities. Section 2.10 discusses the Air Force Office of Scientific Research (AFOSR). Finally, the chapter closes in Section 2.11 with a list of findings supported by the discussion in the chapter. These findings should be helpful in providing the context for Chapter 3, an assessment of the present state of materials development. As importantly, these findings form the starting point for Chapter 5, which presents discussion of and recommendations for a way forward. 2.2 TECHNOLOGY READINESS LEVELS AND RESEARCH AND DEVELOPMENT FUNDING As mentioned above, a certain level of understanding of how risk is assessed and what types of funding are being used in DOD research and development (R&D) is needed for a discussion of the evolution of the process of materials development for propulsion. This section briefly describes these topics. 2.2.1 Technology Readiness Levels Technology readiness levels are used by U.S. government agencies to define the level to which a technology has been developed and the concomitant risk associated with attempting to incorporate the technology into a development program. Readiness levels are also used in industry in one form or another, although the descriptions used by industry may differ from those used by the government. It is generally possible to align a company’s readiness level with the government’s definitions; when a TRL is mentioned in this chapter, an attempt is made to use the government’s definition. Even so, over the years TRLs have diverged slightly in definition between those of the DOD and of NASA. The definitions of the levels used by the DOD are given in Table 2.1. 2.2.2 Definition of DOD Defense Research and Development Funding The DOD has 11 major force programs in which program 6 is for research, development, testing, and evaluation. Program 6 is further divided into five subcategories; see Figure 2.1. The subcategories for DOD research and development funding are referred to as 6.1, 6.2, and 6.3:
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems TABLE 2.1 Technology Readiness Levels in the Department of Defense (DOD) Technology Readiness Level Description 1. Basic principles observed and reported. Lowest level of technology readiness. Scientific research begins to be translated into applied research and development. Examples might include paper studies of a technology’s basic properties. 2. Technology concept and/or application formulated. Invention begins. Once basic principles are observed, practical applications can be invented. The application is speculative and there is no proof or detailed analysis to support the assumption. Examples are still limited to paper studies. 3. Analytical and experimental critical function and/or characteristic proof of concept. Active research and development is initiated. This includes analytical studies and laboratory studies to physically validate analytical predictions of separate elements of the technology. Examples include components that are not yet integrated or representative. 4. Component and/or breadboard validation in laboratory environment. Basic technological components are integrated to establish that the pieces will work together. This is “low fidelity” compared to the eventual system. Examples include integration of “ad hoc” hardware in a laboratory. 5. Component and/or breadboard validation in relevant environment. Fidelity of breadboard technology increases significantly. The basic technological components are integrated with reasonably realistic supporting elements so that the technology can be tested in a simulated environment. Examples include “high fidelity” laboratory integration of components. 6. System/subsystem model or prototype demonstration in a relevant environment. Representative model or prototype system, which is well beyond the breadboard tested for TRL 5, is tested in a relevant environment. Represents a major step up in a technology’s demonstrated readiness. Examples include testing a prototype in a high fidelity laboratory environment or in simulated operational environment. 7. System prototype demonstration in an operational environment. Prototype near or at planned operational system. Represents a major step up from TRL 6, requiring the demonstration of an actual system prototype in an operational environment, such as in an aircraft, vehicle or space. Examples include testing the prototype in a test bed aircraft. 8. Actual system completed and “flight qualified” through test and demonstration. Technology has been proven to work in its final form and under expected conditions. In almost all cases, this TRL represents the end of true system development. Examples include developmental test and evaluation of the system in its intended weapon system to determine if it meets design specifications. 9. Actual system “flight proven” through successful mission operations. Actual application of the technology in its final form and under mission conditions, such as those encountered in operational test and evaluation. In almost all cases, this is the end of the last “bug fixing” aspects of true system development. Examples include using the system under operational mission conditions. SOURCE: Reprinted from Department of Defense, 2006, Defense Acquisition Guidebook and Technology Readiness Levels, Washington, D.C.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems FIGURE 2.1 The 6.1 to 6.5 ladder: subcategories in Department of Defense program 6 for research, development, testing, and evaluation. SOURCE: Air Force Research Laboratory (AFRL). 6.1 basic research includes scientific study and experimentation to increase knowledge and understanding in science and engineering related to long-term defense needs. This research provides the foundation for technological improvements to warfighting capability. 6.2 applied research includes efforts to solve specific defense problems, short of major developments or demonstrations. This applied research category includes the development of components, models, and new concepts through in-house and industry efforts. Individual research programs often enable a variety of new systems and support a number of identified needs. 6.3 advanced technology development includes all efforts directed toward projects that have moved into the demonstration of hardware or software for operational feasibility. Experimental systems or subsystems are demonstrated in order to prove the technical feasibility and military utility of the approach selected. Advanced technology development (6.3) provides the path for the rapid insertion of new technologies or product improvements into defense systems. Continued R&D efforts beyond 6.3 require special funding aimed at the development of engine demonstrators, specific engine component developments, or support of new weapon systems or subsystems. 2.2.3 Technology Readiness Levels and Funding Definitions Technology readiness levels are aligned with funding levels in Figure 2.2. This alignment was provided by the Materials and Manufacturing Directorate of the
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems FIGURE 2.2 Alignment of technology readiness levels (TRLs) with funding levels as applied to materials for propulsion. NOTE: Acronyms are defined in Appendix F. SOURCE: Materials and Manufacturing Directorate of the Air Force Research Laboratory, October 2009. Air Force Research Laboratory, applied to materials for propulsion, and is current as of this writing. When comparing the definitions of TRLs with the purported intent of the funding levels as seen in Figure 2.2, it is clear that this alignment is somewhat subjective and could be altered. The subjectivity in defining research funding levels is clearly not limited to this particular case. In dealing with other directives within the government, the term “fundamental research” is used to cover a range of research levels and funding levels. In National Security Decision Directive 189 (NSDD 189), for example, “fundamental research” means basic and applied research in science and engineering, the results of which ordinarily are published and shared broadly within the scientific community, as distinguished from proprietary research and from industrial development, design, production, and product utilization, the results of which ordinarily are restricted for proprietary or national security reasons. Thus it is clear that the level of funding that can be interpreted as “fundamental research” is not restricted to 6.1 funding and can be the result of 6.2 and even 6.3 funding. 2.2.4 Technology Demonstration: Definitions of Milestones A, B, and C Once funding moves beyond 6.3 (see Figure 2.2) to support TRLs above 5 and 6 through technology demonstrations, the Defense Acquisition System uses the concepts of Milestones A, B, and C, which may be thought of as gates in a system development process. Concept development and refinement occur before
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems Milestone A, and further technology development to work out the concept occurs before Milestone B. Only after Milestone B does a program become an enterprise with dedicated funding behind it; the nature of systems engineering thus changes significantly after Milestone B. Figure 2.3 illustrates the milestones in conjunction with the technical review timing. These milestones can also be aligned with TRLs. Milestone B occurs at approximately TRL 6. Recall that at TRL 6, any new material must be at the point where a representative or prototype component has been tested in a relevant environment and is ready to be made into an actual prototype to be tested in an actual system environment. Without providing an exact definition of Milestone B, it can be said that its focus is a demonstration of process maturity and component development. Milestone B generally marks the end of 6.3 programs, which start at TRL 3 or 4. The major review for engineering acquisition at Milestone B is aimed at managing the risk for further development. This generally means that materials must be selected early in the process, because the use of new materials may require new designs and increase risk. By whatever process, a new material must have been matured to approximately TRL 5, bridging an ill-defined gap often described as the “valley of death.” The valley of death is associated with a disconnect between FIGURE 2.3 Milestones A, B, and C for systems engineering review. SOURCE: Reprinted from Figure 4.3, Chapter 4, p. 39, of Interim Defense Acquisition Guidebook. Available at https://acc.dau.mil/dag.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems technology development and successful application; it has been the subject of many books, studies, and discussions. The NRC report Accelerating Technology Transition: Bridging the Valley of Death for Materials and Processes in Defense Systems discusses the issue extensively.5 Overcoming this barrier requires understanding the issues associated with it and devising strategies to be more successful in bridging the barrier. Much of the information in this report is applicable to the question of determining the adequacy of strategies for continued progress in developing materials for propulsion. 2.3 THE ROLE OF MATERIALS IN THE ADVANCEMENT OF PROPULSION TECHNOLOGY Although it goes without saying that materials technology, including the development of materials and the processes to turn these materials into engine components, has contributed significantly to the advance of propulsion technology over the past six decades, a brief discussion of this point may be helpful. The advent of new materials and processes (M&P), such as vacuum melting, high-strength titanium alloys, and superalloys, has enhanced materials performance, enabling increased turbine temperatures, rotor speeds, and engine thrust at ever-increasing engine efficiencies. This advance for high-pressure turbine airfoils is chronicled in Figure 2.4, which shows how materials improvements in concert with innovative turbine blade design advances have increased turbine inlet temperatures by a factor of two between 1940 and 2006. Complementary advances for structural titanium and superalloy rotor materials have enabled increases in rotor speed and thrust. Figure 2.4 also includes a projection of possible avenues to further enhance performance if materials advances continue, but it should be noted that at present the VAATE Program (discussed in Chapter 3) is not funded to develop components with the new materials concepts indicated on the figure. Today, the array of mate rials that are being used for propulsion or that may possibly be used in future systems is both vast and diverse, representing all classes of structural materials, including metal alloys, intermetallics, ceramics, polymer-matrix composites, metal-matrix composites, and ceramic-matrix composites. The fact is that turbo-machinery continues to depend predominantly on wrought or cast metallic alloys for the majority of engine components. The latter, nonmetallic materials clearly have the potential to contribute to future propulsion advances; however, the successful insertion of these advanced materials will depend on a thorough understanding of these emerging material classes and an acknowledgment of attendant manufacturing and durability risks. 5 National Research Council. 2004. Accelerating Technology Transition: Bridging the Valley of Death for Materials and Processes in Defense Systems. Washington, D.C.: The National Academies Press.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems FIGURE 2.4 The complementary contribution of materials advance and innovative design engineering on turbine inlet temperature increases over the past six decades. NOTE: Acronyms are defined in Appendix F. SOURCE: Information from a presentation to the committee by Charles Ward, Air Force Research Laboratory, January 2009. Approved for unlimited distribution: Public Affairs Case Number 88ABW-2009-0180. Over the past six decades, continued advances in materials both enabled new Air Force systems with greater efficiency and performance and transitioned to U.S. aerospace companies, which continued to have competitive advantages. Now, however, continued investments by the Air Force and the DOD in the work needed to mature these new advanced materials to the point that they play a role in future engine advances6 appear to be downplayed. In general, this is because people appear to associate the need for continued advances in structural materials for propulsion systems with the expectations of new airframe programs in the Air Force—in this case there is a declining expectation, an expectation of fewer new airframe programs in the Air Force. However, this apparent association overlooks the role of advanced materials in upgrading existing engines. As an example, the benefits of continued technology insertion in fielded engines are well illustrated by the continued development of the PW100 and the GE110 engines. Technology insertion allowed these engines to have significant performance and durability 6 Personal communication, C. Ward, AFRL, and C. Stevens, AFRL, May 2009.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems enhancements, resulting in the improved-performance engines that powered the F-15E and the later sections of the F-16 engine. If materials development is to continue to play its historically demonstrated role in advancing engine performance, some enhanced investment will likely be needed. However, it is important to understand where this investment might best be placed, and this in turn depends on an understanding of the process that a new materials development goes through from concept to insertion. 2.4 THE NOTIONAL DEVELOPMENT PROCESS FOR PROPULSION MATERIALS FROM IDEA TO INSERTION As discussed in Section 2.5, below, the introduction of new materials into a new or demonstration engine rarely follows the specified model. But regardless of whether or not the model is followed, it is important to discuss it because it is clear that funding plans are made under the assumption that this notional development plan will be followed. The time period from the point of the introduction of a new material idea to the point at which it is seriously considered for insertion into an engine involves a long-term process that can exceed 20 years. But rather than specifying time in years, it is easier here to describe a notional process with a “timeline” in TRLs. The notional timeline given in Figure 2.5 indicates a continuous maturation of a single material from a large number of initial candidates being nurtured at the 6.1, TRL 1 level of funding and readiness. In general, funding requirements at the lowest TRL level, even for a large number of good ideas, are small compared to the costs of insertion in the final stages of development of, by then, a single material. The funding requirements are also notionally described in Figure 2.6 as a companion to Figure 2.5. As one or a few of the ideas progress into further development, during which coupons are actually produced and property information is beginning to be obtained, the cost increases above the levels provided for all of the basic-concept materials. As larger scale-up occurs, representative geometries are reduced and spin tests and other tests are run on even fewer ideas, the costs escalate again, eventually rising to a level of risk that allows a single material to be matched against a conceptual design in pre-Milestone A, TRL 4 to 5 (see the discussion of milestones, above). Finally a Milestone B point is reached, and full-scale development begins. It is difficult to ascribe actual years along the timeline axis in Figures 2.5 and 2.6, but Table 2.2 is helpful in this regard. Table 2.2 describes the nominal number of years required to bring a new material to the maturity level needed for insertion, depending on the level at which the material development starts. It is probably possible to match the “Development Phase” description in the table with a TRL level; however, for the purpose of this description, it is assumed that the TRL for the shortest development time is approximately TRL 5 or 6. At the longest devel-
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems FIGURE 2.5 Notional development technology readiness level (TRL) timeline. opment time, the TRL level is approximately TRL 1. In this regard then, one can assume that the timeline extends to 20 years or more. Section 2.5 describes how structural materials are actually brought into the engine development cycle and concludes that in order for quantum increases in performance to be made, new classes of materials beyond wrought or cast metallic alloys must be considered. If the notional process described in Figure 2.6 were to exist, however, ensuring a continuous flow of materials into new engine developments would require, as shown in Figure 2.7, that a new cycle for each new material or class of materials was reinitiated on a continuing basis. 2.5 THE HISTORICAL MATERIALS DEVELOPMENT PROCESS: HOW IT HAS ACTUALLY WORKED Rather than closely following the prescribed process described in Section 2.4, the development and application of new propulsion structural materials have historically either opportunistically exploited novel and independent discoveries or have had programs established in order to use evolutionary developments in composition,
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems TABLE 2.4 Top Federal Funders of Research by Field, Fiscal Year 2008 (percent of total funding) DOD DOE NASA HHS NSF USDA Other Engineering Aeronautical/Astronautical 44.7 2.3 22.2 0.8 3.4 0.0 10.9 Chemical 21.9 17.8 2 15.7 26.8 1.7 10.2 Civil 13.2 7.5 3.4 2.6 22.9 1.3 48.8 Electrical 44.8 3.2 2.9 4.0 22.6 0.0 6.8 Mechanical 33.6 15.5 4.5 4.1 15.5 0.3 10.5 Metallurgy and materials 44.4 13.4 2.1 2.7 23.8 0.5 12.8 Physical sciences Astronomy 3.7 2.3 55.6 0.3 21.7 0.0 10.0 Chemistry 11.0 7.2 1.3 43.5 28.1 0.5 6.4 Physics 15.0 26.5 11.7 2.8 32.9 0.2 5.6 Life sciences Biological 2.5 1.0 0.6 80.9 6.7 3.0 4.6 Agricultural 1.5 2.9 1.3 7.9 9.5 55.9 19.4 Medical 3.0 0.4 0.4 91.0 0.4 0.3 4.0 Mathematics and computer sciences Mathematics 10.8 2.9 1.1 25.6 47.2 0.9 5.6 Computer sciences 29.3 3.3 2.0 5.3 42.4 0.3 11.2 Environmental sciences Atmospheric sciences 7.1 5.0 30.0 0.3 27.0 1.2 26.7 Earth sciences 7.0 9.6 17.7 1.7 33.0 9.0 21.6 Oceanography 11.4 0.7 2.9 2.0 42.4 0.9 37.0 NOTE: Percentages greater than 40 percent are in bold to highlight dominant funders. Acronyms are defined in Appendix F. SOURCE: Adapted from National Science Foundation. 2010. Available at http://www.nsf.gov/statistics/seind10/appendix.htm#c5. amount of funds for materials systems actually declines when spread over a broader range of topics. Several programs have been started as attempts to more closely align graduate-level education in MSE with industry needs and to address the lack of process knowledge in the graduate-student pipeline. These programs were specifically aimed at increasing interactive research between universities and industry in materials development. Examples include the following: the Committee on the Survey
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems FIGURE 2.13 Constant-dollar trends in federal funding of materials engineering research, FY 1990-1997. SOURCE: Reprinted from National Research Council, Securing America’s Industrial Strength, Washington, D.C.: National Academy Press, 1999, Figure A-13. of Materials Science and Engineering (COSMAT)30 survey in 1975, Advanced Research Projects Agency (ARPA) programs requiring that the research products be of major DOD interest, NSF centers, and NASA centers. In a National Research Council report on materials science and engineering for the 1990s, it was observed that the programs mentioned above had a downside regarding the money spent as compared with the results.31 The rationale for this conclusion includes the following considerations: the monetary infusion had produced no evidence of impact on the production of advanced degrees; despite intentions 30 National Academy of Sciences. 1975. Materials and Man’s Needs: Materials Science and Engineering, Volume III, The Institutional Framework for Materials Science and Engineering, Supplementary Report of the Committee on the Survey of Materials Science and Engineering. Washington, D.C.: National Academy of Sciences. 31 National Research Council. 1989. Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Material. Washington, D.C.: National Academy Press.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems to the contrary, no mechanism for effective sharing of facilities within universities, which currently largely exist only in industry, had developed; and the degree of interdisciplinary education that was developed by these programs fell short of that expected and practiced in industry, although it did improve over what had been present in traditional departments.32 However, as will be noted in Chapter 3 of the present report, this reduction in available facilities in industry and academia is being offset at the present time by the user centers established at national laboratories. Regardless of the perceived failings of the programs referred to above, it is important to point out that decisions on both the availability and the potential use of results from research grants made to universities at the 6.1 level have a direct and profound impact on the direction of university programs. This issue is addressed in Chapter 5, but it is important to understand the funding emphasis of the university grants from the Air Force Office of Scientific Research and to compare this to the needs for materials for aerospace propulsion that will be presented in Chapter 3. 2.9.5 Summary of Observations Specifically Related to Universities The current emphasis within universities on electronic materials, biomaterials, and nanomaterials, fueled by funding thrusts, leaves little room for fundamental studies on structural, high-temperature materials. The MSE community’s embracing of the ICME methodology has the potential to shorten materials development times. Although the constraints of diverse materials systems strongly influence product design, these systems are currently considered outside the multidisciplinary design loop.33 Thus a cultural change is needed in order to include materials into the optimization process. ICME methodology must be incorporated into the MSE departments within universities. However, as the presence of MSE departments in universities continues to decline, this opportunity may be lost. For the propulsion materials enterprise to benefit from the injection of modeling and simulation tools at many levels, this methodology must be implemented at U.S. universities. At the most basic level, models can be used to increase the understanding of the behavior of current materials—mechanical behavior, environmental behavior, microstructural stability, and so on. If correctly formulated and validated, models can be predictive of incremental improvements or, best of all, 32 National Academy of Sciences. 1975. Materials and Man’s Needs: Materials Science and Engineering, Volume III, The Institutional Framework for Materials Science and Engineering, Supplementary Report of the Committee on the Survey of Materials Science and Engineering. Washington, D.C.: National Academy of Sciences, p. 212. 33 National Research Council. 2008. Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security. Washington, D.C.: The National Academies Press, p. 63.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems can point to entirely new directions for materials development. However, graduates of U.S. universities must be trained in these areas prior to joining the workforce in order to implement future change. As was well documented by case studies in the report of the NRC’s National Materials Advisory Board titled Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security,34 the integration of design and materials processing models can lead to components that are optimized for mechanical properties at the lightest weight possible. Further more, if the statistical variability inherent in materials properties can be under stood and modeled in a particular material system, then similar materials could be considered to behave in a similar fashion, and the burden of testing prior to the implementation of analogous materials could be lightened. These scenarios could speed the inclusion of “newer” materials into systems, provided that these newer materials were similar to the current bill of material. The insertion of a completely new class of materials—for example, ceramic-matrix composites—would have to be accompanied by considerable materials testing in relevant environments. The ultimate question is whether extensive modeling and simulation can take the place of materials insertion into demonstration engines, and the answer has to be: It depends. If the proposed new material is analogous to a material already used in a current system but with improved properties that will result in life extension, then the answer should be Yes. But if the material to be inserted is radically different, such as a CMC, or if a designer wishes to take advantage of a new suite of properties in a metallic material, then the new material would have to be demonstrated, first in a rig but ultimately in a demonstrator engine. Only an engine test can provide the actual environment in which a material must operate—temperature, pressure, gas environment, and stresses both static and cyclic. 2.10 PROPULSION MATERIALS RESEARCH SUPPORT FROM THE AIR FORCE OFFICE OF SCIENTIFIC RESEARCH It is clear from the preceding discussion of MSE programs that funding opportunities have a direct impact on graduate and faculty research programs at U.S. universities with respect to both in the types of projects worked on and as the preparation given to graduates. This recognition has always been at the heart of the Air Force’s support for university research. The present character of the Air Force Office of Scientific Research, which fulfills the Air Force’s primary role in university research funding, has evolved extensively from its first incarnation 34 National Research Council. 2008. Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security. Committee on Integrated Computational Materials Engineering. Washington, D.C.: The National Academies Press.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems in response to the von Karman Commission Report, funded by the Army Air Corps under Gen. Henry “Hap” Arnold, U.S. Army Air Corps, shortly after World War II. AFOSR’s present function and format can be traced to a number of major changes in the Air Force. The most significant events included the dissolution of the Aerospace Research Laboratory in the 1970s, leaving the Frank J. Seiler Research Laboratory, collocated with the Air Force Academy in Colorado Springs, as the only laboratory in the Air Force with a charter to do basic research exclusively. By then, the Seiler Laboratory reported directly to the AFOSR. Eventually the Seiler Laboratory was also dismantled, in the 1990s.35 With the dismantling of these laboratories, basic research—that is, 6.1 research—within the Air Force laboratories (now a single Air Force laboratory, the AFRL, with various directorates) is performed under grants from the AFOSR. The AFOSR now functions as a separate operating agency of the AFRL within the Air Force Materiel Command, charged with the centralized management function for Air Force basic research, to accomplish the Air Force goals outlined for scientific and engineering research. These basic research goals include the maintaining of technological superiority in scientific areas coordinated to Air Force requirements, the prevention of technological surprise, and the maintaining of a strong science and technology infrastructure, with all areas complementing the overall national research effort.36 Until the early 1990s, discretion with respect to which research projects were supported by the AFOSR was generally left to the various program managers, who were (and continue to be) required to present and defend their program portfolios at annual reviews. Since the early 1990s, the AFOSR has been required to submit proposals to an external review board for vetting and grading before the program manager is able to exercise his or her discretion in choosing which proposals are to be funded. Still, the actual character of the research sponsored by the AFOSR is heavily dependent on the personalities overseeing the various research areas as well as on the upper management of the AFOSR, which is civilian. In the area of structural materials for propulsion, a number of changes have also taken place that formed the present character of the sponsored programs. Most notable is the elimination of the Metals Program as a separate program element, subsuming its projects and those of the Ceramics Program into the Aerospace Materials Program. The following information is taken from AFOSR’s most recent board agency announcement (BAA): The objective of basic research in High Temperature Aerospace Materials is to provide the fundamental knowledge required to enable revolutionary advances in future Air Force technologies through the discovery and characterization of 35 See http://www.wpafb.af.mil/library/factsheets/factsheet.asp?id=8976. Accessed April 20, 2011. 36 Adapted from “Air Force Office of Scientific Research: A Brief Organizational History.” See http://www.wpafb.af.mil/library/factsheets/factsheet.asp?id=8976. Accessed January 11, 2005.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems high temperature materials (nominally temperatures above 1000ºC) including: ceramics, metals, hybrid systems including composites. Applications of these materials include air-breathing and rocket propulsion systems, airframe and spacecraft structures and hypersonic vehicle systems. Specifically, the program seeks proposals that advance the field of high temperature materials research through the discovery and characterization of new materials that exhibit superior structural and/or functional performance at temperatures above 1000ºC. Representative scientific topics include the development and experimental verification of theoretical and computational models of materials discovery, characterization methods for probing microstructural evolution at elevated temperatures and mechanics of materials at elevated temperatures. There is special interest in fundamental research of high temperature materials focused on understanding combined mechanical behaviors; e.g. strength and toughness as a function of thermal and acoustic loads. This focus area will require the development of new experimental and computational tools to address the complexity of thermal, acoustic, chemistry, shear or pressure loads as they relate back to the performance of the material.37 As stated at the beginning of the BAA, “AFOSR plans, coordinates, and executes the Air Force Research Laboratory’s (AFRL) basic research program in response to technical guidance from AFRL and requirements of the Air Force; fosters, supports, and conducts research within Air Force, university, and industry laboratories; and ensures transition of research results to support USAF needs.”38 Thus, there is a clear charge to support efforts that are relevant to Air Force needs and requirements and to ensure transition; however, it has been this committee’s finding that the AFOSR’s focus is on long-horizon-type efforts that, as stated in a briefing to the committee,39 are interpreted as having a 20-year horizon. The association with the Air Force needs seems to be tied to AFRL’s Focused Long Term Challenges rather than on direct input from AFRL directorate personnel. Further, to the knowledge of the committee, no transitional research is even being considered for funding. “Transitional” is interpreted here to mean moving a technology into the high 6.1 level, or at least that the Air Force has sufficient knowledge of transitional activities outside AFOSR’s funding portfolio to ensure that some of the AFOSR’s funded efforts can be considered for near-term transition. Testimony heard by this committee showed some frustration by directorate personnel in funding some of their in-house, 6.1 efforts. More surprising to this committee was the fact that these personnel saw the AFOSR as their only source of 6.1 in-house funds, being required to submit proposals to the AFOSR to be de- 37 See http://www.wpafb.af.mil/library/factsheets/factsheet.asp?id=9222. Accessed November 2009. 38 See http://www.wpafb.af.mil/shared/media/document/AFD-100217-027.pdf. Accessed November 2009. 39 “Air Force Materials Needs for Future Military Aerospace Propulsion,” briefing to the committee by Joan Fuller, AFOSR, Washington, D.C., July 20, 2009.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems cided on through comparisons with other proposals on a competitive basis at the AFOSR. Nowhere did the committee get the impression that the AFRL Materials and Manufacturing Directorate and Propulsion and Power Directorate would, by design, provide input to the formation of technical guidance from AFRL and requirements of the Air Force for which the AFOSR provided fundamental research sponsorship. It is clear from briefings to this committee that the AFRL’s directorates are somewhat dissatisfied with the backgrounds of graduates educated at U.S. universities. Further, it is clear that the emphasis in altering these backgrounds can be directly influenced through the funding of grants to universities by the AFOSR, but these apparent needs within the AFRL and the types of graduate research funded at universities appear to be in a disconnect. It is not surprising that this disconnect exists, because most of the practices by the AFOSR were developed over a period of time during which the infrastructure in government, industry, and universities was in its heyday. At that time, universities were thought of mainly in terms of providing a stream of graduates with the appropriate backgrounds to work in industry and government laboratories. Research from universities was considered to be interesting but not of immediate impact, and most of the advances in materials were attributable to researchers in the engine manufacturing and materials supplier laboratories. In some instances specific program managers within the AFOSR were in close tune with Air Force needs and were able to make immediate impacts on ongoing Air Force development needs. One of these was mentioned earlier in this chapter regarding composites. Another initiative sponsored within the AFOSR Metals Program in 2000 that had a direct impact on materials development was the AFOSR multiyear initiative Materials Engineering for Affordable New Systems (MEANS), which was intended to sponsor basic research for the expansion of scientific capability to develop and to employ analytical models of material behavior for use in design software. Part of the objective of MEANS was to develop models of materials that could be used to calculate behavior under various operating conditions, thus reducing the amount of repetitive and empirical testing then required for building a satisfactory database. Another important component was to develop software and design protocols that would permit the models so developed to be interfaced with current design software, allowing materials properties to be manipulated as part of the design space rather than to be constraints, as in the current paradigm for design. The MEANS Program was initially established for 3-year, multi-investigator projects in metallic-, ceramic-, and polymer-based composite materials. The initiative was renewed for a second 3-year period beginning in 2003, and new projects were funded. All of these projects went to university-based investigators, with some collaboration with AFRL Materials and Manufacturing Directorate investigators. The importance of the MEANS Program is even now mentioned in industry and
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems government.40 An important point is that the MEANS Program had its emphasis on computational research rather than on laboratory-type work. There appears to have been an increasing shift in AFOSR-sponsored programs toward computational efforts. It should be mentioned that the Office of Naval Research (ONR) also funds 6.1 work, but unlike the AFOSR, ONR also funds R&D that is 6.2 and above, within the Navy as well as at universities. Also, the ONR program manager is funding work that is directly related to current technical needs and issues. 2.11 FINDINGS This chapter has traced the evolution of the process of development from concept to insertion over a period from the late 1960s to the present. The field of development of new structural materials for propulsion underwent a change from a heyday that peaked in the mid-1980s to the present ebb, which is due to a number of evolving shifts in paradigms: from materials for improved performance, to development free of risk, and concentration on things other than just performance. Also in the present climate, there is a perceived lack of requirements pull on technology to re-infuse or redirect existing funds into structural materials for propulsion. There is now a large cycle time required to move promising materials from early-concept, 6.1, levels to being viable candidates for insertion in new development engines; without either reducing this cycle time to be in sync with engine development cycle times or adapting to the new realities in a more inventive way, there will be no new materials available when new-capability engine development programs re-emerge. Although near-term opportunities for new engine development programs do not appear to be on the horizon, it is almost certain that engine development opportunities will present themselves in time frames that coincide with materials development cycle times, be they in the re-engineering of existing airframes, the development of new bombers, or the development of high-performance unmanned vehicles, and other efforts. If quantum advances in performance are to be anticipated due to advances in materials and processes, which has been the historic trend (see Figure 2.3), then new types of materials other than metallics must be moved up the TRL ladder. This can be done only by interceding to change the present paradigms that have led to the drying up of the stream of new structural materials available for insertion consideration. These conclusions are summarized in the following list of specific findings supported by the material in this chapter. There were many engine development programs in the 1980s. Starting in the 1990s, fewer engines have been and are now being developed, and these fewer 40 Personal communication, Craig S. Hartley, El Arroyo Enterprises, LLC., October 8, 2009.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems engine development programs emphasize low risk (high TRL), which discourages the use of revolutionary and high-risk material insertions. Demonstration-engine programs created to improve engine performance picked up where declining engine developments left off and afforded materials development insertion opportunities. However, continuing demonstration programs have de-emphasized materials development and plan fewer engines, and the acceptable risk level of these programs is low—that is, they have high TRL requirements. Finding: The decline in new engine developments (i.e., requirements pull) and aversion to risk have led to a decrease in support and advocacy for the use of new materials in new engine designs. Despite recent improvements in the materials development process—such as standardization of the process, tighter integration of design and materials activities, and emerging application of nascent ICME technologies—the materials-development cycle remains excessively long. During the same period in which those improvements were made in the materials development process, the introduction of computational methods and more-disciplined engine development practices shortened the engine development cycle. This means that even if materials candidates at relatively high TRL are available for consideration at the beginning of an engine development, the time needed to reduce the risk of a material’s insertion no longer exists. Finding: The development cycle for materials is considerably longer than that for engines; this is a deterrent and source of risk for the introduction of new materials into propulsion systems. Historically, engine manufacturers and supplier researchers and facilities have been a major source of both invention and innovation for aerospace structural materials. However, driven in part by the decreasing opportunities for new engine developments and in part by aversion to the risk imposed by new materials insertions, a gradual decrease has occurred in the number of industrial researchers, laboratory facilities, and corporate investment in aerospace materials, which together have reduced the pace of aerospace materials innovation and the availability of new materials ready for materials insertion. The result has been the drying up of the candidate-material pipeline. The long-standing traditional, ad hoc materials development approach could not be sustained effectively as the aerospace propulsion industry matured, engine products proliferated, and competition, both domestic and global, intensified. Unstable funding and a lack of long-term funding commitments further accelerate this decline.
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems Finding: There has been a significant decline in overall infrastructure (facilities, equipment, skilled people, and so on) for materials and processing, further weakening the U.S. technology base in materials development. Nontraditional aerospace materials, such as intermetallic alloys and ceramic composite materials, have been garnering increased interest in recent years. These materials offer significant insertion benefit. However, early development efforts do not seem to address the mitigation of the risks associated with revolutionary materials, including damage tolerance and new failure modes and their consequences, or the maturity of the manufacturing infrastructure. These new materials need to be fully understood prior to commitment and production insertion. Finding: Newer structural materials that may show some promise or even the possibility for revolutionary changes, especially those discovered under AFOSR funding, are disconnected from continued efforts that begin moving them up the TRL ladder. Although the AFOSR encourages its principal investigators to be aware of Air Force needs, at present AFOSR program managers focus on long-horizon technologies. Examples of closely tied cyclic interaction of all levels of 6.1 through 6.3 efforts in nonpropulsion materials have demonstrated the advantage of closer cooperation between the AFOSR and the AFRL. If the decline in materials candidates at sufficiently high TRL to impact future engine designs is to be reversed, the AFRL and the AFOSR must exercise the available flexibility in applying funding categories. Finding: The present approach to developing new materials at the lower TRLs is inadequate for an environment with reduced infrastructure and advocacy. Although the advance of aerospace metal alloys is decelerating, these materials will likely remain the materials of choice for critical turbine hardware. Whereas traditional advances were achieved by means of compositional and processing innovation, future advances will rely more on achieving improved property balance, local properties tailored to the requirements at critical locations within a component, and hybrid structures fueled in part by ICME technologies, but these improvements must be accompanied by research in processing them. Finding: Insufficient research for processes affects even better-understood materials. Linked to all of the findings above is the distinct change in the character of materials science and engineering programs, the type of research efforts, and the concomitant qualification of graduates at U.S. universities. Influenced in part by
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Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems research grants administered by the AFOSR, some accommodation of university programs must take place if continued advances in structural materials for propulsion are to be expected. Finding: Structural materials education and research at U.S. universities have declined, and this decline is threatening the strength of the domestic structural materials engineering workforce. Although the overall funding for the general field of MSE increased somewhat during the 1990s as is demonstrated in Figure 2.13, the general impression among educators working on structural materials, as expressed by one such educator on this committee, is that since 1997 the funding in all of MSE has remained essentially level. At the same time, the number of areas of research in MSE has greatly increased, and so the funds going specifically toward structural materials have decreased.