Advanced Organic Composite Materials for Aircraft Structures Future Program (1987) / Chapter Skim
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'APPENDIX A: Synopsis of Presentations to the Committee'
'APPENDIX A: Synopsis of Presentations to the Committee'
Pages 43-98
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From page 43... ...
Reinhart) The Air Force has had 8 to 10 years of operational experience with composites, with good success; composites are being used on rotor blades and other parts of helicopters and for secondary structures on other types of aircraft.
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From page 44... ...
Field repairs of composite structures are a major concern. A substantial program is in progress with emphasis on the minimization or elimination of the need for special repair equipment.
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From page 45... ...
The National Aeronautics and Space Administration (NASA) supported an extensive flight-service evaluation program for noncritical advanced organic composite components on a variety of aircraft (L-1011, B-737, CH-54B, 206-L, DC-10, and C-130)
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From page 46... ...
Work is also needed in the following areas: statistical procedures to reduce the amount of material property testing of environmentally conditioned specimens, an analysis methodology capable of predicting material and structural response due to environmental considerations for use in ultimate load static strength assessments, failure criterion, and design criteria for structural fasteners. The structural integrity of bonded structure is an area of concern.
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From page 47... ...
The objectives for thermosets and thermoplastics are: developing new material concepts and understanding of behavior, including failure mechanics; enabling innovative structural designs and applications; and assisting the achievement of "full" weight and cost savings, and performance gains in future aircraft. The structural weight savings are estimated to be in the range of 25 to 35 percent.
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From page 48... ...
are expected to contribute, in some degree, to verified, cost-effective advanced composite, primary structural concepts for wings and fuselages, and address material forms, high-performance polymers, characterization of advanced systems, composites-processing science, and structural element and structural component fabrication. The NASA program will also encompass metal matrix composites for airframe and propulsion systems through the use of a small business, innovative research proposal activity.
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From page 49... ...
In summary, the Air Force has a continuing interest in composite materials for aircraft systems with emphasis on material improvement, higher-temperature capability, supportability, durability, damage tolerance, and design and manufacturing technology development. Program plans have been defined through FY 1990 covering graphite-epoxy structures, ballistic survivability, laser survivability, and structures beyond graphite-epoxy.
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From page 50... ...
. Work is in progress to develop damage tolerance and durability criteria for composite structures, improve fatigue analytical techniques and methodology, and develop vibration reduction techniques and analytical procedures.
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From page 51... ...
, summarized the committee's activities, noting in particular the work of Workshop III, Future Composite Manufacturing Technology. The workshop was focused on the net-shape manufacturing of composite structures as part of the AFSB's examination of net-shape manufacturing.
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From page 52... ...
Compared to present conventional composite design, the proper application of advanced composites can reduce costs by some 20 to 30 percent through reduced parts, weight, and production and increased strength. Further cost reductions should be possible through innovative design, the use of computer-aided design and manufacturing (CAD/CAM)
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From page 53... ...
The introduction of composite materials in commercial aircraft structures has been slow compared to their introduction in military aircraft. Flight service components, such as the Boeing 737 spoilers and the Douglas DC-10 aft rudder, have been in commercial airline service for over 10 years without any serious material problems.
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From page 54... ...
Emphasis is being put on raising design strain levels while holding stiffness to make composites more competitive for primary structures. Current Douglas composite designs operate at low-stress levels to increase damage tolerance.
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From page 55... ...
• Analytical tools. These are generally good but not always adequately applicable to through-the-thickness forces without very complex finite element modeling.
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From page 56... ...
The most aggressive application has been in the 70-passenger ATR-72 center wing box. The introduction of composite primary structures to transports will depend on a clear understanding and response to what the industry sees as the issues related to a full commitment.
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From page 57... ...
The use of composites is almost complete, having been applied to rotor blades and hubs, fins, landing gears, pylon supports, fuselages, and, in the case of the V-22 tilt rotor, the wing. This has been driven by military requirements for higher performance and increased operability, both dictating lower weight and improved supportability.
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From page 58... ...
Work on composite rotor blades started in 1957. The decision to use composite blades for production systems was made in 1970.
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From page 59... ...
The industry also needs design guidelines for controlling failure modes. A related matter is crashworthy design concepts for primary structures.
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From page 60... ...
used mostly fiberglass epoxy for the Model 500 and Kevlar epoxy for the AH64A Apache. Parts production has principally involved 250°F curing materials and a range of conventional manufacturing processes.
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From page 61... ...
made of composite material. Many aircraft of foreign design make extensive use of organic composites.
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From page 62... ...
As for thermosets, costs need to be reduced. Technical barriers to broader use of organic composites relate to: • Material variability; • Costs from design to certification and support; • Lack of data bases and approved specifications, standards, and design allowables; • Inadequate cost bases for investment; and • Lack of confidence in new technology.
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From page 63... ...
The material characterization work has resulted in the preparation of an advanced composite design guide based on approximately 15,000 tests. Rockwell's standards and allowable design strain levels for composites are incorporated in this design handbook.
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From page 64... ...
Experience has shown these matters to be problems: out-of-plane loads -- difficult to predict, need good modeling; effects of impact damage on compressive strength -- an empirical process, need better analytical tools; environmental effects -- though generally understood, need careful design attention; bearing interaction allowable strength -- tools for analyses reasonably in hand; bonded-joint thermal mismatch -- a serious issue in need of attention; variability of bonded-joint quality -- design approaches and validation techniques needed; and durability and damage tolerance prediction -- a real problem, need prediction techniques since analytical tools are not available and designers are forced to depend upon testing. The factors that inhibit wider use of composites include: initial acquisition costs of tooling; limited service temperatures; integrity of bonded primary structure joints; areas of high-load transfer -- designers use metals since they handle concentrated loads better; supportability requirements -- difficult to identify and estimate costs since good models are not available; sensitivity to low-level impact damage; and effects of hostile threats, such as from lasers -- need to be examined.
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From page 65... ...
However, there will be a high percentage of organic composites, with metals in appropriate places, approaching 50 percent by weight and providing some 20 to 25 percent structural weight reduction. The nature of the future factory will change.
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From page 66... ...
The key to expanded use of composites and exploitation of higher-strain levels is the continued development of analytical tools that include automated design and analysis methodology. As noted, organic composites are used extensively on AV-8B aircraft.
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From page 67... ...
In addition automation of manufacturing methods, inspection procedures, processes, and tools are mandatory for cost reduction. In the long-term, expanded utilization of organic composite structures offers significant performance gains.
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From page 68... ...
All of this will help cost reduction. The matters that inhibit fuller use of organic composites include: labor, material,
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From page 69... ...
For preliminary design, "quick" design tools would be very helpful. Cost is a major deterrent to expanded use of organic composites.
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From page 70... ...
In summary, experience to date is good but cannot be extrapolated; current materials are not good enough for projected high-performance aircraft; the nature of damage sources and progression needs to be identified; work needs to be directed at defining material properties that provide a good measure of toughness; and effort needs to be put into the development of tough composite materials -- new thermosets may succeed and thermoplastics show promise. The future for organic-matrix composites is bright.
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From page 71... ...
With careful design, some of the critical certification issues can be resolved, i.e., temperature and moisture effects, material selection, fatigue and corrosion resistance, accelerated testing, and certification. However, work on the following matters is needed and very appropriate: out-of-plane failure modes, predication of full-scale structural performance, service durability of thin structures, and methodology to assess damage tolerance.
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From page 72... ...
In addition to the high potential for reduced manufacturing costs, life-cycle costs should be reduced too. Cost reductions should accrue through lower weight, smaller aircraft, higher performance, excellent fatigue and corrosion resistance, and repair simplicity.
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From page 73... ...
The technical barriers to wider use of organic composites center around correlation to analysis, data variability, flaw growth, environmental tests and methods, and professional staffing. Laminate analyses predict elastic properties, but they are inadequate for first
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From page 74... ...
Development of methods (and a handbook) addressing failure modes would be of specific value, i.e., stability, first ply failure, bearing strength, and flaw growth.
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From page 75... ...
The composite activity has a staff of 60 that is projected to grow to 244 by mid-1987. At present, for preliminary design, available industry data bases and analytical techniques are used.
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From page 76... ...
The field could be helped by having: data readily available on manufacturing discrepancies (a comprehensive research effort quantifying effects, paralleling what is done for metals, would be helpful) ; feasibility studies for primary, intermediate, and nonstructural parts for varying design strain rates; studies of hole tolerance on fatigue strength; and studies to identify design strain parameters and values.
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From page 77... ...
The market is relatively small, $350 million, compared with the estimated value of the composite components generated, $3 billion. Pertinent to the committee is the fact that an average of 3 to 5 percent of sales, some $11 million to $18 million in 1985, is applied to R&D by the material suppliers.
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From page 78... ...
through teams/consortiums with matching industry funds; the government, principally DOD, support productivity improvement technology through industry consortiums and, in addition, permit the early recovery of plant and equipment investments; and universities give attention to teaching composite design and manufacturing and give industrial engineers credentials in composite process control and automation. Union Carbide (T.
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From page 79... ...
Standardization, among users, of sample preparation, testing, and data reduction would help reduce the number of tests required and speed the development of a common data base. The result should be to reduce costs for design and production and to reduce time for response to design requirements.
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From page 80... ...
It is projected that the strength of organic composites will continue to improve. Up until 1980, improvements were due primarily to better production technique.
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From page 81... ...
Examination of the buildup of composite aircraft costs gives this relative per pound cost breakdown: graphite fibers, $20; prepregs, $40; and structures, $200 to $500 per pound. The place to get major payoff for cost reduction is in structures manufacture, not direct material costs.
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From page 82... ...
Fabrication costs are driven by lack of material uniformity, process control, and material standards. In addition, costs increase through less than optimal use of materials, possibily due to the limited fundamental understanding of the composite materials and related design experience.
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From page 83... ...
A program level review of work on the following rotorcraft subjects was presented: • Rotor-blade erosion protection; • Damage tolerance and durability of primary structures; • Fatigue methodology; • Design criteria and analysis; • Composite swashplate and hub design; • Advanced Composite Airframe Program (Bell and Sikorsky, addressing landing gears, lightning protection, internal noise, repair and maintenance, crashworthiness, and weapon interfaces) ; • Automated blade and low-cost fuselage production; • Advanced fuselage tooling; and • Single-cure, tail rotor blades.
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From page 85... ...
-- Total -- 1.75 2.2 2.3 2.5 U.S. Air Forcea Research and development 7.0 8.3 6.0 Supportability 0.2 0.5 0.9 Manufacturing technology 10.3 9.4 16.5 Structural concepts, integrity survivability, and repair 2.3 2.6 3.4 Total 19.8 20.8 26.8 Federal Aviation Administration Nondestructive inspection -- 0.1 0.1 0.1 Fuselage damage containment -- 0.1 0.1 0.4 Structural response crashworthiness ..
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From page 86... ...
• Tolerance to directed energy threats, both low- and high-energy, need to be considered in the design of composite structures. • Repairability, maintainability, and capability are needed in adverse environments.
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From page 87... ...
The 6.1 work focuses on: developing a basic understanding of composite impact damage, fatigue, fracture, and innovative concepts for damage tolerant structures; composite structural tailoring; and metal structure crack initiation and propagation. The 6.2 work encompasses: advanced design concepts, structural integrity, supportability, air loads prediction, life management, and electromagnetic compatibility.
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From page 88... ...
The first three elements of the program are directed by the Air Force Materials Laboratory and the fourth by the Flight Dynamics Laboratory at the Air Force's Wright Aeronautical Laboratory. The major elements of each of the following programs were briefly described: Organic Composites R&D • Thermoplastics • Thermosets • New polymer concepts and resin characterization • Processing science • New composites technology • Ordered polymer fiber • Ordered polymer film • Molecular composites • Opto-electronic materials • Support activity Organic Composites Supportability • Advanced field repair materials • Post-failure analysis • Paint removal • Thermoplastic support Organic Composites Manufacturing Technology • Manufacturing science -- computer-aided cure and complex shapes • Integrated composite center • Large composite aircraft • Manufacturing for thermoplastics • Radorne manufacturing technology • Composite repair center • Organic propulsion materials Structural Considerations • Structural concepts
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From page 89... ...
These data and the actual program plan by element are shown in Table A-6. Specific comments were: • At present there is an active effort to increase FY 1987 support for the mechanical material property testing, large fuselage decompression studies, and *
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From page 90... ...
reflects an increase of $10 million for materials and structures R&T related to: other composite materials program augmentation, increased computational structural mechanics effort, and R&T augmentation in rotorcraft noise and vibration. • A NASA advanced composites program would encompass: structural concepts and sizing methodology for improved local stiffness and aeroelastic tailoring;
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From page 91... ...
This type of work should continue, but at a higher (an order of magnitude) funding level to build the technology base required for design, production, test, and certification confidence, and to allow fuller application of advanced organic composites.
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From page 93... ...
TABLE A-9 Government Advanced Organic Composite Program Plan, FY 1987 (Smillion) Program Elements Design/ Materials/ Government Agency R&T Support Manufac.
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From page 94... ...
• Material costs ($ per pound) are still coming down for current materials and significant drops in cost can be expected for advanced materials with increased production volume.
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From page 95... ...
It is believed that the materials manufacturers are working on the problem of material tolerances and that government assistance in this area is not required. Logistic Support Military service representatives from the Navy/Marine Corps, Air Force, and Army briefed the committee on field experience with aircraft composite structure repair and maintenance.
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From page 96... ...
Major concerns related to composite structures are reliability, maintainability, and repair. Much of the noncombat problems are associated with work accidents, i.e., dropped tools and cart strikes.
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From page 97... ...
A Tobiason, of the ATA, invited guest of the committee, reported on recent environmental experiences with composite structures.
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