File Name: aircraft material and hardware .zip
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. At various stages in the evolution of aeronautics, one of the foundation disciplines—aerodynamics, propulsion, control, or structures—has been either the obstacle to progress or the conduit to major improvements. They all, therefore, constitute "enabling technologies.
Providing a safe and durable structure is a matter of fundamental importance, because a functional failure of structural components usually has catastrophic results. This chapter discusses the committee's findings and recommendations regarding future materials and structures technology. The boxed material summarizes the primary recommendations that appear throughout the chapter, with specific recommendations given in order of priority, and the benefits that can be gained through research and technology development efforts aimed at advanced structures and materials.
Beyond being an enabling technology, development of the structures of airframes and engines continues to be a key element in determining the economic success of aircraft. Structural weight is the single largest item in the empty weight of an aircraft and is, therefore, a major factor in the original acquisition and operating cost and in establishing operational performance. One pound added to structural weight requires additional wing area to lift it all other flight variables being held constant , additional thrust to overcome the associated incremental drag, and additional fuel to provide the same range.
All these additions result in further increases in structure. This vicious circle converges, in typical aircraft designs, to gross weight increases from 2 to 10 times the 1-pound empty weight increase that began the cycle. The trend in aeronautical structures from all-metal construction to composite airframes, which began about 25 years ago, has reached the point at which specialized military aircraft, fighters, and vertical takeoff and landing VTOL aircraft, now have composite structures.
NASA's structures and materials program should emphasize continuing fundamental research to achieve both evolutionary and revolutionary advances in materials and structures, as well as focused technology programs in materials and structures to address specific aircraft system requirements.
This should include:. The highest priority in NASA's long-range engine materials research program should be on ceramic matrix composite developments including fabrication technology, although intermetallics should continue to be an active part of engine materials research for the longer term, with emphasis on improving damage tolerance. NASA's program of basic research in materials and structures should improve understanding of failure modes in composites, increase damage tolerance, and introduce advanced means of nondestructive evaluation.
Automated sensing and feedback control should be an increasing part of NASA's research program, capitalizing on "smart structures" advances. The introduction of metal matrix composites into high-pressure compressor disks deserves major emphasis in NASA's engine programs for the nearer term.
Commercial transports use advanced composites in essential secondary structures such as flaps and control surfaces and in some primary structure such as vertical fins.
The advantages of composite materials, as exemplified by their greater strength and stiffness per unit weight, superior fatigue and corrosion resistance for many applications, and potential for lower manufacturing costs through reduced part counts and tooling expenses, make their wide application to U. However, the slow rate at which they are being adopted is evidence that their design, analysis, manufacturing, inspection, and repair methodologies are all in a developing state.
Aircraft structural design, analysis, manufacturing and validation testing tasks have become more complex, regardless of the materials used, as knowledge is gained in the flight sciences, the variety of material forms and manufacturing processes is expanded, and aircraft performance requirements are increased. A greatly expanded design data base of applied loads is now available for more complete and thorough definition of critical design conditions, thanks to the expanding use of computational fluid dynamics CFD , advanced wind tunnel testing techniques, and increasingly comprehensive aeroelastic and structural dynamic analysis computer codes.
Similarly, computer-aided design tools make it easier and quicker to consider a much greater variety of alternative structural designs. The use of high-speed, large-memory computers permits, in turn, more detailed internal structural loads analysis for each of the many loading conditions and design alternatives, with fine grid analysis determining more precise load paths, stress distributions, and load deflection characteristics for subsequent aeroelastic analysis.
Expansion of structural synthesis, analysis, and testing capabilities and the widening options available are making the choice of materials for both the airframe and the engine one that is intrinsically woven into the structural concept, detailed part design, and manufacturing process selection. A fundamental aspect, of course, is knowledge of the physical properties of these materials. Characteristics such as static tensile strength, compression and shear strength, stiffness, fatigue resistance, fracture toughness, and resistance to corrosion or other environmental conditions, can all be important in the design.
Each of these aspects must be considered and dealt with concurrently if modern structural designs for aircraft are to approach optimum configurations and, thereby, success in international. It is most important to note that current and future materials and structures aspects of aeronautical systems, both airframes and engines, require a new level of collaboration among all of these specialists.
It will probably be necessary for each specialist to become more conversant with the fields in which the others work and, from the earliest stages of design, for all of these specialists to work together in ways that are unprecedented in the aircraft industry. To summarize, the compelling reason to apply composites and other advanced materials to the structural design of the advanced aircraft envisioned in this report is to achieve the lightest weight and most effective structure possible.
This includes a highly reliable structure that requires minimum maintenance and is durable under all applicable environmental influences. This chapter outlines the key areas of research needed and the approaches that research programs should use. Among the attributes mentioned earlier, low structural weight fraction, long life, and low costs are the principal drivers for the airframe structures of future aircraft systems described in this report.
For propulsion systems, higher specific strength and ability to withstand higher temperatures are the principal drivers.
These objectives, in turn, require advances in materials, structural design concepts, life prediction methodologies, and fabrication technologies. Applied research in structures and materials is virtually always required at some level in developing a new type of advanced aircraft.
Such applied research, specific to vehicle classes discussed in other parts of this report, is dealt with in subsequent sections of this chapter. In addition, however, there is a continuing and essential need for long-term, fundamental materials and structures research of a generic nature. An appropriate program of this kind should be guided by needs that arise in the development of generic aircraft types; it also should, by its results, change the direction of generic aircraft developments.
Thus, an appropriate fundamental program of materials and structures research should seek to provide both evolutionary and revolutionary advances in materials and structures, which will be required to sustain a leadership role in both airframe and propulsion technologies. Specific areas of fundamental research that should be considered for emphasis are outlined below.
Metallic alloys continue to be used for more than 75 percent of most airframe and propulsion systems by weight. They constitute relatively mature and reasonably well-understood classes of materials ranging from aluminum alloys for airframe structures to nickel alloys for hot sections of turbine engines. Continued research into metallics is strongly recommended, emphasizing tailoring of alloy systems to provide significant advances in such traditional areas as weight reduction and environmental resistance.
Aluminum-lithium Al-Li alloy systems, for example, promise evolutionary benefits in higher stiffness and lower density, with no reduction in structural life. Continued research efforts are required, however, to ensure that Al-Li alloys will be endowed with the balanced strength, corrosion resistance, and toughness properties necessary for cost-effective airframe structural applications.
Powder metallurgy technology is another area in which continued research efforts are warranted. Aluminum powder and rapid solidification techniques offer a wider range of chemical composition and processing options, which in turn promise alloys of improved strength, toughness, and corrosion resistance, compared to ingot metallurgy processes.
Improved titanium alloys also have great potential. Alloys capable of superplastic forming continue to promise both economic fabrication of parts with complex curvature or integral stiffeners and weight savings. Research is needed to increase allowable strain rates and, thereby, part output; to reduce cavitation flaws; and to broaden the classes of superplastically formable alloys available to structural designers.
Beyond more conventional metallic systems, research efforts in ordered alloys of the TiA1, Fe3A1, and Ni3A1 types should be substantially increased. Emphasis should be on increasing fundamental understanding of the structure-property relations in these systems and on alloy additions to enhance strength and toughness. Both airframe and propulsion systems could benefit substantially from the high strength-to-weight potential of these more unusual alloy systems.
Significant research investments are required to develop the full potential of composite materials for both airframe and engine applications. This class of materials is, in general, very large; it includes polymer matrix, metal matrix, and ceramic matrix composites CMCs , as well as continuous and discontinuous fibers. Various combinations offer differing advantages, depending, for example, on the thermal environment Figure Fibers can be entirely of one constituent material or used in combination.
Some of the more traditional potential advantages of these materials are, by now, well understood. They include higher specific relative to material mass density strength, and stiffness, and better fatigue and fracture resistance compared to metallic alloys. Hybrid materials such as those having combinations of glass and graphite reinforcements show significant improvement in tensile fracture properties versus solely graphite-reinforced laminates.
This is especially important for application to fuselage structure for penetration damage containment. Damage tolerance of these materials—particularly hybrids—is not as well understood and is an area of high potential payoff. Polymer matrix composites research appropriately deals with both the constituent materials and the way they are combined to form composites.
Improvements in carbon fiber reinforcements for polymer matrix composites are expected to continue, based on the efforts of various suppliers; government research programs in this area are not likely to be required. Understanding of the fiber matrix interface characteristics required for tougher composites, however, needs to be improved, as does knowledge of how to apply textile technology, such as stitching and weaving, successfully to improve interlaminar strength. It should be recognized that a polymer matrix structure will require appropriate adhesives, sealants, and finishes.
Research by NASA emphasizing composites with discontinuous reinforcements is recommended, based on the belief that such materials are likely to simplify fabrication. Both aluminum and titanium matrix composites with silicon carbide type reinforcements particulate, fiber, ribbon , for example,. Fabrication technology, particularly for tailored structures, should be emphasized to fully exploit the advantages of MMCs and prevent cost from becoming an insurmountable barrier.
Hybrid systems involving metal sheets interleaved with various types of reinforcements also show promise as structural materials. CMCs constitute one of the highest-risk research opportunities in the materials and structures discipline. However, the magnitude of the potential benefits from these materials for higher-temperature applications, such as uncooled turbine engine components, justifies major research efforts.
Both ceramic matrix and ceramic fiber technologies need to be pursued, along with an emphasis on improving fabrication technology. Achieving reproducibility in fiber quality, matrix features, and composite behavior is essential before these promising materials can be considered to have reached a state of technology readiness. It appears that ceramic materials of the silicon nitride and silicon carbide families should receive the greatest attention.
NASA's research efforts in structural analysis and design should focus on improving stress and deflection analysis methods; establishing proven structural dynamics and aeroelastic analyses; developing improved life prediction techniques and damage-tolerant design concepts; formulating proven methodologies for optimizing structural designs, including tailored composites; and exploiting adaptive or ''smart structures'' concepts.
Structures researchers will have to play a stronger leadership role in working with materials researchers, both in defining priorities among material properties improvements and in adapting advanced materials to innovative structural concepts. The nation's materials and structures research program should have components considering how to cause structural, dynamics, materials, control systems, and manufacturing engineers to join in simultaneous consideration of structural, materials, and fabrication technology developments at the earliest design stages.
Such "concurrent engineering" seems essential to achieving the successful application of advanced materials to aircraft structures in the time period of interest in this study. Improved structural analysis methods capable of exploiting the computational power that will be available in the near future should be a high-priority objective of structural design research.
A necessary adjunct of this is development of tools to reduce the cycle time for generating structural analysis models sufficiently that such analyses for both strength and stiffness can accompany the earliest structure design concepts considered by designers. Automated finite element mesh refinement and remeshing capabilities, which readily identify areas of high stress concentration and high strain gradients and allow crack propagation characteristics to be predicted should be developed and incorporated to the point of being standard features of structural analysis.
Formalized structural optimization techniques must become a standard computational tool for design purposes. Such techniques should also allow for choice among multiple static and dynamic analysis options e.
Integrated analysis techniques that couple structural, thermal, dynamic, aeroelastic, and control technologies are required to truly optimize a design. Experience with optimization methods to date indicates that the state of these procedures requires fundamental research and that successful application can establish major competitive advantage in the marketplace.
Factors such as broader ranges of flight conditions and larger applications of high-temperature structures will require methods for design and analysis that account for temporal and spatial variations in loading and operating conditions, material states, and variations of materials themselves throughout the structure.
NASA should pursue research to improve life prediction methods and damage-tolerant designs, closely linked to the understanding of individual material properties; to their compatibility in combination, particularly at structural joints; and to NDE techniques. Structures research should take a strong lead in integrating these technical areas to achieve more efficient designs.
Life prediction systems must include multiple failure mode assessments of complex, multiaxially. Ultimately, a probabilistic approach will be required with regard to operational loads, routine damage in service, and material properties in the delivered structure, to maximize the potential of many of the advanced materials. Stochastic analysis methods should also receive greater attention to account for more complex operational aspects of advanced aircraft systems.
Whereas the more revolutionary concepts should be taken to the proof-of-concept stage in laboratory research, composite material developments per se have outdistanced current abilities to routinely design and manufacture useful parts from them.
It is important to emphasize that the research itself should often involve close and interdependent teaming of materials researchers, fabrication technologists, and structural designers.
Such teamwork is increasingly necessary for cost-effective application.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. At various stages in the evolution of aeronautics, one of the foundation disciplines—aerodynamics, propulsion, control, or structures—has been either the obstacle to progress or the conduit to major improvements. They all, therefore, constitute "enabling technologies. Providing a safe and durable structure is a matter of fundamental importance, because a functional failure of structural components usually has catastrophic results. This chapter discusses the committee's findings and recommendations regarding future materials and structures technology. The boxed material summarizes the primary recommendations that appear throughout the chapter, with specific recommendations given in order of priority, and the benefits that can be gained through research and technology development efforts aimed at advanced structures and materials.
Includes free two year revision serice. Fasteners — Screw Threads screw nomenclature; thread forms, dimensions and tolerances for standard threads used in aircraft; measuring screw threads. Bolts, Studs, and Screws bolt types: specification, identification and marking of aircraft bolts, international standards; nuts: self locking, anchor, standard types; machine screws: aircraft specifications; Studs: types and uses, insertion and removal; self tapping screws, dowels. Locking Devices tab and spring washers, locking plates, split pins, pal-nuts, wire locking, quick release fasteners, keys, circlips, cotter pins. Aircraft Rivets types of solid and blind rivets; specifications and identification, heat treatment.
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The aim in aircraft design is to keep the stress below this point. Terms Stress is the load per unit are acting on a material Strain is the deformation of a material caused by an applied load Proportional Limit is the greatest stress at which strain deformation is directly proportional to stress. Proof Stress is a stress a material can withstand without resulting in permanent elongation of more than 0.
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