ADVANCED MATERIALS zy Aerospace Materials Research Opportunities zy ** zy By Michael Salkind* As we approach the second century of aerospace, increased emphasis is being placed on endurance, reliability, ease of man- ufacture, and lower cost, in addition to weight saving. This change in emphasis will have a major effect on not only the selection of materials, but on how materials are integrated into the total system design process. Subsonic aircraft will continue to play a major role in our future with emphasis on increased durability and lower cost. .Nonmetals that do not corrode are attractive; however, the issues of reliable fracture resistance to ensure safety and durability as well as ease of manufacture and inspection will be key. Higher performance engines and hyper- sonic aircraft will require higher temperature materials (in- cluding a substantial amount of non-metals) along with reliable toughness and ease of manufacture. In space, weight will con- tinue to be a major driving force along with the need for long term vacuum and radiation stability. Ease of assembly and multifunctional use (e.g. electrically or thermally conducting structure) will zyxwvutsr be additional needs for spacecraft materials. We have reached a point in the evolution of structural materials where we are moving away from processing naturally occur- ring materials toward synthesizing designed microstructures to perform specific functions. The mathematical modeling of microstructure-property relationships and new chemical and biotechnical synthesis techniques appear to be critical tech- nologies for the future. In addition, the future materials developer will need a broader understanding of the total struc- tural life cycle zyxwvutsr so that the impact of utilization, maintenance, and training requirements in the design of new materials can be considered. 1. Introduction For more than 40 years, mankind has not had a major war nor used a nuclear weapon in anger. The USA and USSR are experiencing a decided recent warming in relations and western economic hegemony seems to be yielding to the Pacific miracle. We are seeing more and more transnational companies which challenge some of our assumptions about national economic competitiveness and indeed the definition [*I Dr. M. Salkind Air Force Office of Scientific Research Washington, DC, 20332-6448 (USA) [**I The author would like to thank his colleagues at AFOSR, J. zyxwvutsrqponml Dimmock, G. Haritos, A. Rosenstein, L. Schioler, and D. Ulrich, for their assistance in preparing and reviewing the manuscript. Engineered Microstructures Intermetallics Advanced Composites Materials Processing of a company or a nation. In 1964, General Schriever said “The traditional geographical barriers are really meaningless in today’s world. . . (which) emphasizes. . . the inseparability of political, military, economic, and psychological fac- tors.’’[11 We are coming to grips with the facts that our envi- ronment is delicate and that our natural resources are finite. Against this background, we can conclude that the 21st cen- tury, the second century for aerospace, will surely bring great change. The first century of aerospace was clearly dominated by performance considerations. In the future we will still be pushing back the weight and temperature barriers but within the context of limited mineral, financial, and human re- sources. We will need to provide improved performance for more capable military vehicles, more economical transport vehicles, and new hypersonic vehicles and spacecraft. How- ever, these new capabilities must be more affordable, more reliable, easier to maintain, and less demanding of our envi- ronment, including our mineral and energy resources. An historical summary of tactical aircraft costs showing the in- exorable climb in unit cost, Figure 1, led Norman Augustine to postulate that: “In the year 2054, the entire defense budget will purchase just one tactical aircraft. This aircraft will have to be shared by the Air Force and Navy three and a half days each per week, ex- cept for leap year, when it will be made avail- able to the Marines for the extra day.” Augustine ’s First Law [’I Augustine’s “first law” may be amusing hyperbole, but the underlying data are real and, taken together with the global economic realities, indicate that cost must be a far more significant consideration in future aerospace systems. Maintenance costs of tactical aircraft also indicate the inexorable upward trend.‘’] Augustine concluded: “Aircraft flight in the 21st century will always be in a westerly direction, preferably superson- ic, to provide the additional hours needed each day to maintain all the broken parts.. .” Augustine’s Second Law[‘] Adv. Mater. 1989, No. zyxwvutsrqpon 5 157