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Novel Extensible Design Approaches for Advanced Aircraft Composite Structural Architectures


OBJECTIVE: Define a low-level stochastically verified composite structural toolset geared towards expediting aircraft design and development, while at the same time leveraging building-block approach to structural verification for enhanced airframe assurance. DESCRIPTION: Advanced composite structures enable high performance aerospace structures, including extensive tailoring to particular applications, fastener elimination, weight reduction, improvements in fatigue resistance, and corrosion prevention. Some essential challenges for modern composite design, fabrication, and certification include the integration of structural design detail with repeatable manufacturing processes, which must include both material and process control. Typically, the design problem is dominated by considerations of design details, manufacturing flaws, and service damage, all of which cause local stress concentrations. Robust approaches to structural assurance explore strength, fatigue, and damage tolerance issues, and tend to have a high dependency on multiscale sample tests. This design and testing approach tends to have enormous cost and schedule impacts, effectively raising the barrier to entry of advanced composite structures into major DoD platforms. This effort intends to develop structural architectures that speed development and qualification of composite aircraft, which has broad benefits to DoD, DARPA, and the private sector in reducing cost, increasing content re-use, and improving time-to-market. In particular, novel solutions are sought that would allow extensive reuse of parametric elements in structural design of composites to achieve expedited design, verification, validation, and airworthiness certification or qualification. By raising the level of structural design abstraction to higher orders, both design engineering and verification activities could be effectively abbreviated while increasing design confidence. While conventional design processes use a set of material allowables verified at coupon level, the end goal of this effort would be to develop a stochastically validated, open, extensible database typical aircraft component geometries, which include allowable properties, based on key parameters for geometry, materials, and defined manufacturing process standards. These properties should be applicable to a defined set of configurations for key primary and secondary structural elements, including for example, spars, ribs, skins, doors, landing gear, and associated composite to composite and composite to metal joints. Each of these components should include definition of parameters that permit sizing to necessary loads, and consideration of buckling and other potential failure modes of the structures based on probable load applications. For reference and guidance, one may refer to the government publication, ANC18, which defines properties for wooden aircraft structural materials and guidelines for structural member and joint design. Although obsolete, publication ANC-18 offers relevant guidance to this effort, because it provides a novel means of design rules for non-homogenous structures. Wood, considered the original filamental composite, is actually a more complex material to design with, possessing more key parameters on type, condition, and alignment of the material with loads than are normally considered for modern composites in airframes. PHASE I: Design and specify a preferred material set and set of basic components, perform analytic justification of chosen parametric geometries. Define robust approach for uncertainty characterization and tracking. Develop an analysis of predicted performance, and define key technological milestones. Phase I deliverables will include a description of the proposed material set, proposed component set, analytic justification of broad aerospace applicability, and definition of processes required to quantify and track performance uncertainty from design through certification. PHASE II: Develop, demonstrate, and validate the basic approach to component parametric definition, stochastic verification, and quantification and tracking of uncertainties. It is anticipated that this demonstration will occur in a laboratory setting, but demonstrate multiscale parametric element application, uncertainty quantification, stochastic verification, design application, process verification, and representative simulation in a certification process flow. PHASE III: This novel architectural approach has potential for use in civilcertified aircraft structures, inclusive of aircraft certified to 14 CFR PART 23 and 14 CFR PART 25. If successful, this methodology has the potential to directly transition to the Air Force Research Laboratory"s Composites Affordability Initiative. Additionally, future unmanned aircraft programs, including demonstration programs executed by DARPA, may have particular benefit from this structural architecture approach and associated methodology. An alternate military transition path would be inclusion of this structural approach into a future aircraft program of a record. REFERENCES: 1) MILHDBK17, Composite Materials Handbook 2) ANC18 Design of Wood Aircraft Structures, Code of Federal Regulations (CFR), Title 14 (Aeronautics and Space), 14 CFR Part 23, and 14 CFR Part 25, FAA Advisory Circular AC 20-107B"Composite Aircraft Structure"

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