Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems (2011) / Chapter Skim
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2 Materials Development: The Process
2 Materials Development: The Process
Pages 13-67
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From page 13... ...
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)
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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.
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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 de velopment for propulsion.
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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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Continued R&D efforts beyond 6.3 require special funding aimed at the devel opment 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.
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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 fund ing levels.
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39, of Interim Defense Acquisition Guidebook. Available at https://acc.dau.mil/dag.
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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 devel opment of materials and the processes to turn these materials into engine compo nents, has contributed significantly to the advance of propulsion technology over the past six decades, a brief discussion of this point may be helpful.
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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.
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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.
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bitmapped 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 develop ments 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.
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. SOURCE: R Schafrik, GE Aircraft Engines, briefing presented at the National Research Council Workshop on Accelerating Technology Transition, Washington, D.C., November 24, 2003.
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Whether through opportunistic or Figure 2-7 concerted efforts, new materials were developed to solve known problems, to expand R01976 Propulsion a material's operational envelope, or bitmapped even to enable new engine design concepts. Although all new M&P technology introduces some technical, budgetary, and sched uling risk to an engine program, those developments that represented revolutionary departures (i.e., the first application of a materials system or manufacturing process)
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Although cases may exist, it is worth noting that the com mittee was unable to find an example of a 6.1-funded material that could be tracked through continuous development to an engine insertion. Historically, materials research was usually performed by a team that included engine manufacturers, material-forging companies, and casting suppliers, all having well-staffed research departments and facilities and vibrant, ongoing research programs.
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Considerations in determining requirements included the impact of component failure on engine operation and flight safety, prior experience with the material in other components or engines, the prior history for similar mate rials and manufacturing processes, the quantity and quality of materials data, and the maturity of as-manufactured and in-service nondestructive inspection methods. The committee notes that the TRLs listed along the bottom of Figure 2.8 in dicate the approximate point in the materials development process where a TRL would fall, even though almost no TRL language was used in the development cycles in the early years.
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The engine development cycle originally depended largely on component and engine testing to improve and validate engine designs, including constitu ent materials and processes. This make-or-break approach required a long (8 to 12 year)
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2.5.1 Case Study: Powder Metallurgy "As-HIP" Superalloys The following case study clearly changed the paradigm within the company involved for evaluation of the importance of considering risk in inserting new materials. This case and others like it throughout industry were studied by engine manufacturers and the government, leading to a new emphasis on risk aversion and the use of integrated product development teams (IPDTs)
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Unlike cast and wrought processing of highly alloyed superalloy composi tions (such as Rene '95) , early as-HIP development yielded fully dense, crack-free component pre-forms that exhibited good mechanical properties.
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1992. "Advanced Materials for Aircraft Engine Applications," Science 255(5048)
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But unfulfilled material promises, such as that described in this case study, also taught a generation of young design engineers and managers to avoid new materials technology lest they be ambushed by similar problems with the next new material. The longer-range consequences for future propulsion materials are clouded by the competitive fallout of the 1980s engine wars, the 1990s economic downturn in the propulsion business, and the resulting reduction of the overall aerospace engi neering workforce.
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Unless the engine developments are for demonstration engines FIGURE 2.10 The science and technology program of the U.S. Air Force.
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A well-known nonpropulsion materials technology maturation that made intentional use of this "simultaneous process" is the development of advanced composites. Early work showed that significant weight savings, fatigue resistance, and corrosion resistance were possible with advanced composites (i.e., laminated anisotropic fiber-reinforced materials containing high-strength and high-stiffness fibers in a polymer matrix, which was a new technology at the time)
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2.6 THE EVOLVING MATERIALS DEVELOPMENT PROCESS Although the traditional steps undertaken during M&P development are still used today, the landscape in which materials developers' work has undergone sig nificant changes. Some of these changes, which include technical, programmatic, and cultural elements, have increasingly challenged the M&P development process, have increased the risk associated with materials insertion, and have even led some engine designers and now even government-sponsored demonstration-engine programs to de-emphasize the deployment of new materials.
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Also, the application of structured engine development processes, integrated product development teams, and computer-based optimization have reduced the number of engine design iterations, further expediting the engine development cycle and in the process widening the cycle gap between the materials development cycle and the engine development cycle. Although engineers benefit from IPDTs and structured materials development processes, materials development activities remain highly dependent on costly and time-consuming experiments, processing trials, and mechanical property testing.
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But, these alternative materials systems may actually increase the development-cycle gap and pose addi tional schedule and insertion risks associated with the immaturity of the supplier base and uncertainties associated with materials defects, manufacturing flaws, and limited knowledge of failure modes and other durability issues for these newer, less-mature classes of materials. Conversely, materials development has also been aided by several changes in the propulsion engineering culture, including the adoption of IPDTs and the estab lishment of formal product development cycles and TRLs.
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, Integrated High Payoff Rocket Propulsion Technology (IHPRPT) , and Versatile Affordable Advanced Turbine Engine Program.
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The program was canceled before a demonstration vehicle was built, but the stable funding over 4 years, albeit abruptly ended, enabled significant advances in many materials classes that were to a lesser extent picked up by other programs and other means. Relevant materials advances from the NASP Program are listed below: • Titanium aluminide development and processing, • Titanium matrix composites, • Carbon-carbon, • Coatings for refractory alloys, and • High-conductivity materials.
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This lack of demonstrator engines hampered transitions of these materials out of the 6.2 level, but at least it moved select materials upward on the TRL ladder; this was particularly important to the IHPTET Program, discussed below. A number of the materials technologies that were investigated in the NASA programs are now in service, but they have required significant additional invest
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Similarly, the new superalloy disk materials, ME-3 and ME-16, are only now finding their way into newly designed engines. Integrated High Performance Turbine Engine Technology Program, 1988-2005 The IHPTET Program began in 1988 and was driven by phased goals related to the performance of gas turbine engines, the ultimate goal being a doubling of the performance (thrust to weight)
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Unlike the funding for the IHPTET Program, the funding for the IHPRPT Program has not been straight forward and has been somewhat disconnected from the program, leading to an unstable funding environment for materials research. Versatile Affordable Advanced Turbine Engine Program, 2005-2017 The ongoing VAATE Program is the follow-on program to IHPTET; the pro gram appears similar to the IHPTET Program in that it has very concrete goals, both technology goals and cost goals.
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Although those materials were not part of the IHPTET Program funding directly, IHPTET's expecting new materials to transition into IHPTET and setting the requirements for these developments led to concomitant funding from DOD materials programs to be transitioned into the demonstrator engines, and this in turn furnished a rationale for continuing the materials program funding. The importance of the availability of engines to test new materials cannot be overstated.
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However, in terms of the development of new materials for propulsion, the FLTCs give little support for the level of materials development funding at the 6.3 level and beyond that was present under the IHPTET Program. Without the pull for new materials provided in new development engines from the AFRL's Propulsion and Power Directorate and acquisition and program offices, there exists little support for the infusion of funds into new materials for propulsion within the AFRL's Materials and Manufacturing Directorate.
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• A sufficiently funded companion materials development program is tied to the goals of the overall engine/aircraft development program -- that is, a commitment to fund materials development is part of the larger technology development program. In their discussion of these elements of success before the committee, AFRL staff members17 gave as an example of a successful materials-advancing program the 1988-1991 National Aerospace Plane Program.
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. Absent any particular program, some individual or group of people must decide what needs to be done to take a promising candidate from the status of candidate to that of a viable material for consideration for insertion that can fit a system development cycle time.
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Once a material moves into a program shown in the non-AFRL section of Figure 2.10, the application must be significant, and the benefit must be clear to all parties in terms of cost, performance, or safety and acceptance of risk. Matching the benefits of a new materials technology to engine needs must be ongoing.
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The common themes for successful materials development discussed in this section are listed below: • A path to development; • Materials innovation; • Sustained development; • A partnership: government and company; • An application or need; • A significant advantage; • Low risk; • Corporate involvement: timing is important; • Manufacturing capability: a path forward and a solution to manufacturing challenges; and • A product: business opportunity. 2.8.3 Further Discussion of the Role of Funding and Champions As mentioned above, funding, at a sustained and appropriate level, is required for successful materials advancement, development, and insertion, but it is not the only reason for success or failure.
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The emphasis in the IHPTET Program, and to a lesser extent in the VAATE Program, was primar ily on performance, with high-speed flight as the focus. In high-speed flight, ram recovery temperatures present at the front face of the compressor start out much higher than in lower-Mach-number flight.
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Toward the end of the 1960s, polymeric processing and biomaterials were introduced into many university materials programs. In this environment, as materials usage changed (i.e., electronic materials, polymer composites, and metal-matrix composites)
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As MSE departments grew and graduated new PhDs without back ground in the individual disciplines, the current offerings of MSE lost depth in practical experience and/or science of specific materials. In the 1975 report Materials and Man's Needs: Materials Science and Engineering Volume III, The Institutional Framework for Materials Science and Engineering, from the National Academy of Sciences, the question was posed as to whether a truly inter disciplinary MSE program would develop or whether it might become a group of materials science offerings affiliated loosely with one another.20 This question might be more properly stated to ask whether the real difficulty in achieving genuine intel lectual innovation in curricular matters is caused by the competing interests of other existing departments.21 Current emphasis on electronic materials, biomaterials, and nanomaterials, fueled by funding thrusts, leaves little room for fundamental studies in traditional areas such as structural, high-temperature materials.
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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 52 and for FIGURE 2.12 Materials science and engineering (MSE) degrees awarded for (top)
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In a study by the National Research Council titled Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness 22 Ibid., p.
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2008. Integrated Computational Materials Engineering: A Transforma tional Discipline for Improved Competitiveness and National Security.
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Successful integration will require communication between experi mental materials research and the computer modeling of advanced materials and applications. The long-term goal of CMS is to provide a predictive understanding of materials behavior.
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Physics research funding declined throughout the 1990s, reflecting the cancel lation of several major projects such as the supercollider (in 1993) .29 A relatively steady level of funding for materials engineering has existed over the past 25 years, as shown in Figure 2.13.
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These programs were specifically aimed at increasing interactive research between universities and industry in mate rials development. Examples include the following: the Committee on the Survey
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1975. Materials and Man's Needs: Materials Science and Engineer ing, Volume III, The Institutional Framework for Materials Science and Engineering, Supplementary Report of the Committee on the Survey of Materials Science and Engineering.
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2008. Integrated Computational Materials Engineering: A Transforma tional Discipline for Improved Competitiveness and National Security.
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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 compo nents that are optimized for mechanical properties at the lightest weight possible.
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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.
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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 1000°C.
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Another initiative sponsored within the AFOSR Metals Pro gram 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 capa bility to develop and to employ analytical models of material behavior for use in design software.
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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 develop ment opportunities will present themselves in time frames that coincide with materials development cycle times, be they in the re-engineering of existing air frames, the development of new bombers, or the development of high-performance unmanned vehicles, and other efforts.
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From page 65... ...
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 inser tions, a gradual decrease has occurred in the number of industrial researchers, labo ratory 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.
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From page 66... ...
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.
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From page 67... ...
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 essen tially level.
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