TECHNOLOGY AREAS: Air Platform, Materials/Processes

ACQUISITION PROGRAM: PMA-275, V-22 Program; PMA-276, USMC Light/Attack Helicopter Program

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop and demonstrate design and manufacturing methods applicable to bead-stiffened composite airframe structures as lightweight, affordable alternatives to conventional sandwich construction with enhanced survivability in the Navy shipboard environment.

DESCRIPTION: Current composite airframe construction relies extensively upon use of metallic and nonmetallic honeycomb core. While sandwich construction is structurally efficient, it suffers from durability limitations and very high life cycle costs associated with corrosion, impact damage, maintenance and repair. As a consequence, there is a strong need for alternative materials and construction methods that are structurally efficient, durable and more affordable to manufacture and maintain.

Thin gage airframe structure is frequently limited by stability (buckling) considerations. An alternative means for improving buckling load relies upon geometrical formed part features such as beads, sine wave spars, etc. to create bending stiffness in thin web structures. This approach has long been used in metallic airframes (press formed beads, beaded lightening holes, EB welded sine wave spars, etc). Self-stiffened designs have also been demonstrated in composites, but the low elongation of continuous carbon fiber and planar, non-conformal nature of prepreg material limits the detail geometries that can be formed with high quality due to effects such as wrinkles. Furthermore, forming intricate compound contour geometry on a small scale (i.e. beads) with present material forms is labor intensive, expensive and often requires that fiber and plies be cut and patched for forming purposes, adding weight and introducing discontinuities.

PHASE I: Identify and define realistic rotorcraft airframe designs that can benefit from integrally stiffened designs. Develop realistic requirements such as geometry, tolerances, loads, frequency response, environment, damage tolerance, life-cycle costs, etc based on actual Navy rotorcraft airframe designs. Investigate manufacturing processes for integrally stiffened airframe designs and demonstrate feasibility in a laboratory environment. Demonstrate material and process, as well as their feasibility and scalability for representative rotary wing components.

PHASE II: Using a building block approach develop, demonstrate and test a realistic, full-scale structure using an integrally stiffened design that meets structural integrity, weight, damage tolerance, and other requirements. Identify nonrecurring and recurring costs as a part of a comprehensive Technology Insertion Plan.

PHASE III: Develop production quality, low-cost, low-maintenance airframe designs for military and commercial aircraft programs.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This technology (composite manufacturing process, material forms, and designs) has wide-ranging applicability in both the public and private sector. As composite materials continue to displace metals in primary and secondary airframe structure, the focus is on affordability and improving durability in the service environment. This is true from both military and commercial operators. Therefore, this technology, if successful, can lead to greater penetration of the composite airframe market with US-developed technology.

REFERENCES:
1. "Buckling of Open-Section Bead-Stiffened Composite Panels", Laananen, D. H. and Renze, S. P., Composite Structures (ISSN 0263-8223), vol. 25, no. 1-4, p. 469-476.

2. "Braided Preform Manufacturer for Large Scale, Integrally Stiffened Structures", Braley, M., SAMPE 2000 - Long Beach, CA May 21 - 25, 2000.

3. "Fiber-Placed Composite Grid-Stiffened Structures", Van West, B.P., and Wegner, P., 33rd STC - Seattle, WA - November 5 - 8, 2001.

KEYWORDS: Composite Structure; Integrally Stiffened; Bead Stiffened; Buckling; Forming; Automation

TPOC: (301)757-5531
2nd TPOC: (301)757-5524

** TOPIC AUTHOR (TPOC) **

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