Advanced Organic Composite Materials for Aircraft Structures Future Program (1987) / Chapter Skim
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'SUPPLEMENT: SUMMARY OF COMMITTEE STUDY'
'SUPPLEMENT: SUMMARY OF COMMITTEE STUDY'
Pages 17-42
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Supplement: Summary of Committee Study
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, rotorcraft, high-performance aircraft, and general aviation -- for its assessments of potential advantages, inhibiting factors, technology needs, and possible government actions. Following is a summary of these assessments.
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They can be designed precisely to net-shape with fiber orientation to give the desired stiffness and achieve maximum structural efficiency. Structural efficiency is enhanced further by the reduced susceptibility to
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Among the major inhibiting factors for all aircraft classes are the high costs of design, development (including certification) , and production of advanced organic composite structures.
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22 TABLE S-I-2 Inhibiting Factors Assessment Subject Large Transports & Airlines Rotorcraft HighPerformance Aircraft General Aviation High costs -- design, development, and production 1 1 1 I Lack of technological data base 1 1 1 1 Understanding failure mechanisms 1 1 1 1 Low tolerance to damage 1 1 1 1 Inadequate nondestructive testing 1 1 1 1 Certification difficulty 1 1 1 1 Difficulty of damage repair in field 1 1 1 2 Lack of design experience/ education 2 2 2 1 Costly maintenance and repair 2 2 2 2 High acoustic response 2 3 3 2 Limited manufacturing capability 2 2 3 2 Inconsistent manufacturing quality 2 2 2 3 Low-stress limits 2 1 1 3 Brittleness of matrices 3 2 1 3 Adverse effects of environment 3 3 3 3 Material cost 2 3 3 2 Ability to design thick-wall components 3 1 2 3 Erosion of rotor blades 3 1 3 3 Low tolerance for high temperature 3 3 1 3 KEY: l -- Very important 2 -- Important 3 -- Significant
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New Concepts and Design Innovation The full benefits of composites will not be realized until designs (and manufacturing processes) take advantage of the unique characteristics of composites and composite structures are not designed and built like metal structures.
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Failure Mode Analysis and Understanding If designs are to be sound and certifiable, failure and its progression and an understanding of how to design to avoid failure under severe operating conditions must be predictable. Analytical tools -- theoretical and/or empirical -- that provide this capability are needed to assist in design and testing for safe, long-life composite structures.
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Advanced Composites Program An advanced composite rotorcraft program that addresses generic technology development (noted in the discussion on inhibiting factors pertinent to rotorcraft) would significantly improve these aircraft.
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support fellowships and other educational endeavors to help improve the cadre of professional and support people in the field of composite aircraft structure design, development, manufacture, testing, and operation. Other subjects warranting government support, because they are important or of significant value, involve the exploration of the potential for application of new and innovative composite structures, the development of technology pertinent to damage-tolerant design, and the definition and development of an advanced composite aircraft technology program encompassing large-scale validation of analyses and small-scale experiments.
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They can handle higher temperatures than the other organic composites noted and possess higher toughness. There is also a potential for lower-cost, uniform manufacturing.
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28 TABLE S-I-5 Summary Observations -- Materials Possible Government Actions Potential Advantages Inhibiting Factors Needs EPOXV Lower costs Existing data base Experience Existing facilities Moisture damage Low toughness and ease of damage Supportability Bismaleimides/pol vim ides High High cost temperature Thermoplastics Greater reproducibility Ease of repair Higher temperature Higher toughness High cost Availability Need for high temperature and pressure for processing Raise toughness and temperature Improve processing Improve manufacturing methods Increase data base Develop measurement and evaluation techniques and processes Develop measurement and evaluation techniques and processes Develop measurement and evaluation techniques and processes Inhibiting Factors Epoxy systems are subject to strength reduction, i.e., environmental damage, due to moisture ingestion if detailed attention is not given to design. The materials have low toughness and are relatively easily damaged.
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The data in Tables S-I-6 and S-I-7 reinforce the earlier industry discussions of needs, potential advantages, inhibiting factors, and needs. Potential Advantages The government agencies see common advantages and benefits associated with advancing the state of technology of advanced organic composites.
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Air Force Research and development: thermosets -- new polymer concepts and resin characterization, processing science, ordered polymer fiber and film, molecular composites, opto-electronic materials Supportability: field repair materials, postfailure analysis, paint removal, and thermoplastic support Manufacturing technology and science: regarding computer-aided cure of complex shapes, integrated composites center, large composite aircraft Thermoplastic and organic materials for propulsion systems Federal Aviation Administration Detection of understrength bonds (all classes) Failure analysis methodology Standards for material property testing Cost-effective finite element analysis techniques for complex-load transfer areas Flammability, toxicity, and smoke characteristics of materials Damage growth analysis Repeated-load response Statistical analyses to allow reduction of mechanical testing Full-scale component response versus coupon response and data scatter Crashworthiness Lightning-strike behavior National Aeronautics and Space Administration Systems characterization: mechanical properties, damage tolerance, micromechanics/failure, and environmental effects Structural concepts, efficiency, and tailoring Gradients, discontinuities, cutouts, and damage Postbuckling and nonlinear effects and analyses Local and global structural analyses including failure mechanisms and analyses Subscale wing-box and fuselage-shell modeling Filament-wound structures Thermoplastics
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Inhibiting Factors Government agency representatives view inhibiting factors as relating to high costs; limited design, development, and testing data bases; integration of design and manufacturing; certification; and the lack of appropriately trained engineering personnel and technicians. These are the same factors considered important by the designers and manufacturers, and by the committee.
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It is recognized that the development of an advanced organic composite material technology program is indeed complex because of the generic as well as the unique considerations associated with aircraft classes and their users. Regarding materials, the agencies agree that the basic (generic)
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TABLE S-I-8 Government Agency Summary -- Technology Program Considerations, All Aircraft Classes Technology Development Effects of discontinuities; cutouts, gradients, and damage Modeling and full scale; wing boxes and fuselage shells Airframe structural integrity, landing gears, and electromagnetics Aerostructural tailoring Filament-wound structures Methods for controlling fatigue and standards for design System response to repeated loads System characteristics; mechanics, damage tolerance, failure modes, environmental effects, and energy attenuation Supportability; maintenance and repair in depot and field Testing; bond strength, standards, techniques, and instruments Lightning-strike protection without weight penalties Components and Systems. Analytical Tools Complex load transfers; finite element techniques Local and global systems including failure mechanisms Postbuckling and nonlinear effects Failures and damage growth Materials and Processing Characterization; flammability, toxicity, and smoke Improved erosion characteristics Thermoset research and technology development Thermoplastic research and technology development Materials and material forms for severe design conditions Manufacturing technology; reproducibility, automation, and effects on products Data bases Nondestructive testing Design Concepts and Innovation Low cost and weight Criteria and standards; fatigue, damage, and durability Damage tolerance and durability Survivability, crashworthiness, and fatigue life Structural concepts; efficiency and tailoring Maintainability and repairability Certification Capability Definition of processes and procedures Full scale versus coupon response and scatter Statistical analysis to reduce testing and costs Standardized processes and definitions
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With regard to materials the committee believes that the government should help develop materials system characteristics, standards, processes, and techniques for measurement and evaluation of materials, and leave focus on materials and material system development to the materials industry. The committee's key observations are the following: • Despite successful application of organic composites to aircraft, their full potential is largely unused.
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It is the view of the committee that these actions will provide the nation with the technology that will allow the design, development, and certification of cost-effective composite aircraft with high levels of confidence.
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FUTURE R&T PROGRAM New Program The committee believes that the current R&T program in government is not deep enough or broad enough to provide the data required for sound design and development of advanced organic composite aircraft with reasonable industrial risk. A new R&T program is indicated if, as a matter of national policy, the United States wants to maintain a leadership role and a competitive advantage over other nations in aircraft design, manufacturing, and sales.
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The committee believes that program funding and priority judgments need to be made in the context of specific future development program possibilities and agency budgets and priorities, and these judgments can best be made by the agencies themselves with industrial guidance and university participation. Key Barriers Barriers to the application of advanced organic composites have been discussed in detail in Section I of this Supplement.
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However, the committee believes that greater investments are required to determine the merits of these and other possible processes and forms of composite materials to enlarge this important activity. Structures A government advanced organic composites program plan should be formulated to provide a new effort in primary structures directed to design and development activity during 1990-2010.
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This effort should focus on the development of cost-effective composite structures through the definition of efficient structural arrangements that can be rapidly produced by automated material placement techniques. The government can accelerate this activity by soliciting and sponsoring research to identify new structural shapes, elements, and components that are amenable to low-cost manufacture.
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These and other data would be used to provide the integrated data bases vital to sound design, manufacture, test certification, and other matters critical to the development of effective composite aircraft. The type of data-base documentation needed has to be developed.
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, and three-dimensional weaving. GOVERNMENT PROGRAMS The committee does not believe that the government's advanced organic composites material and structure program supports the level of activity needed to realize the full potential of these materials.
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42 dissemination. It is the committee's view that it would be appropriate for NASA to take the initiative in the development of the bold new program with strong participation from the U.S.
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