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


 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.


 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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