AGATE Methodology Proves Its Worth
Increased availability, lower testing costs and shorter development times are among the program's achievements.
By Barry Berenberg, Web Editor/Technical Writer | May 2003
The Advanced General Aviation Technology Experiments (AGATE) Consortium was founded in 1994 by NASA, the U.S. Federal Aviation Administration (FAA) and about 70 other members from industry, academia and other government agencies. Its mission was to revitalize the general aviation industry in the U.S., delivering more aircraft in half the development time. By improving small aircraft, the consortium hoped to shift more air travel to public-use landing facilities, decreasing dependence on the limited hub-spoke airport system. The result would be a significant increase in capacity and shorter travel times.
Source: Aero Modifications and Consulting LLC
Aero Modifications & Consulting LLC replaced the aluminum thrust reverser fairings on the Learjet Model 60 with FiberCote E-765 carbon prepreg, cutting weight by half and eliminating a recurrent cracking problem.
AGATE was to accomplish this mission through the development of affordable new technologies, standards and certification methods for airframe, cockpit, flight training systems and airspace infrastructure for single pilot, light airplanes. Program work was divided into ten technical areas or work packages. The mission of the Integrated Design & Manufacturing (ID&M) work package was to reduce airframe and propeller cost and weight. The Materials Group within ID&M was tasked with developing a design manual for the use of composites in general aviation (GA) aircraft. Its specific tasks included standardizing test methodologies, developing a database of materials properties, developing methodologies for manufacturing process control and for suppliers to incorporate new materials and processes, and shortening the materials development and certification cycle from five to three years.
In April 2001, the FAA released DOT/FAA/AR-00/47, "Material Qualification and Equivalency for Polymer Matrix Composite Material Systems," known as the AGATE methodology for short. This document presents the detailed qualification plan used to generate statistically based design allowables for composites at the lamina (ply) level. The A- and B-basis allowables give end users a statistical confidence that the material properties will be at least as good as the minimum allowables (see HPC May/June 2000, p. 27, for a more complete discussion). More specifically, the methodology covers carbon or glass prepregs that are cured and processed at 115.5°C/240°F or higher, using both autoclave and vacuum-only cure cycles. The methods also can be applied to a broader range of composite materials.
Although the AGATE program ended in November 2001, the composite qualification methodology remains an active standard today. FiberCote Industries Inc. (Waterbury, Conn., U.S.A.) and Toray Composites America Inc. (Tacoma, Wash., U.S.A.) were the first two companies to use the AGATE methodology to develop materials databases, and they have continued testing to add additional materials to the database. In July 2002, Advanced Composites Group Inc. (ACG, Tulsa, Okla., U.S.A.) added a high-temperature prepreg material. Newport Adhesives and Composites Inc. (Irvine, Calif., U.S.A.) has added an intermediate-temperature prepreg.
Qualified materials
FiberCote has applied the AGATE method to a family of materials based on its E-765 resin system. The prepregs include a T300 3K plain-weave carbon, a T300 6K 5-harness satin carbon, a T700 unidirectional carbon and a 7781 fiberglass. A T700 12K twill carbon and 12K plain-weave carbon are currently in the screening phase. The 6K satin prepreg is qualified under a 3.1 bar/45 psi autoclave cure; the other materials are qualified under vacuum bag cures. E-765 cures at 121°C/250°F and provides an 82.2°C/180°F wet service temperature.
Toray has applied AGATE to three materials based on its 2510 resin system. These prepregs include a 7781 fiberglass, a T700G 12K unidirectional carbon tape and a T700S 12K plain-weave carbon fabric. The 2510 system is designed for both autoclave and non-autoclave use. It cures at 132°C/270°F, yet provides a hot-wet glass transition temperature of 128°C/262°F (146°C/294°F dry). Although the carbon fabric is made from 12K tow, it has an areal density of 193 g/m2 (5.67 oz/yd2) — the same density as a 3K fabric. The individual fiber bundles are more like miniature unidirectional tapes than tows, making the fabric exceptionally flat and easy to handle, even on highly curved parts. The fabric also demonstrates excellent damage resistance, though Toray has not determined exactly what gives the fabric this property.
ACG is targeting more traditional aerospace materials with its HTM45, a 177°C/350°F cure, toughened epoxy system. Two forms have been tested using the AGATE methodology: a 0.368 mm/14.5 mil, 8-harness satin carbon, and a 0.20 mm/7.7 mil, plain-weave carbon. With this material, ACG is targeting military aircraft manufacturers. ACG also is applying AGATE to its MTM45 resin system, which is designed to cure between 79.4°C/175°F and 121°C/250°F. Future reinforcements to be tested include additional carbon weaves, quartz and glass fabrics, and unidirectional carbon.
Newport has applied AGATE to three material forms based on its NB 321 prepreg resin system: a 7781 glass fabric; a Grafil Inc. (Sacramento, Calif., U.S.A.) 34-700 unidirectional carbon tape; and a 3K 70P plain-weave carbon fabric. The NB 321 system cures between 135°C/275°F and 163°C/325°F. Newport also has three supplemental AGATE method material databases for use with the AGATE materials: aluminum and copper mesh lightning strike materials impregnated with NB 321; and an NB 101-compatible film adhesive. All material forms have been accepted by the FAA and are now flying on production-certified aircraft.
Source: FiberCote Industries
A skirt fairing made from FiberCote E-765 prepreg provides support for a SATCOM radome on JetBlue Airways aircraft. The housed antennas allow passengers to watch live satellite TV.
Material manufacturers seem to be unanimous in their support of the new AGATE methodology. Most aerospace materials today are currently qualified to performance-based customer specifications. To sell the material to another company, the vendor must requalify to a new specification. The result is usually a significant investment in testing of a single material that, in the end, produces duplicate data. "The advantage of the AGATE methodology," says Chris Ridgard of ACG, "is the testing is done once and offered to multiple end users. The responsibility of producing the data is more on the material supplier, with the supplier assuming responsibility for selecting the product forms, resin content and other factors that define the specification." This approach is cost-effective for both material suppliers and end users. Ultimately, the goal is to create material standards driven by industry-wide specifications instead of company specifications, analogous to the way metals are currently bought and sold. Once a material is qualified by the AGATE method, it is accepted by the FAA, Department of Defense, Department of Transportation and other organizations, provided their individual requirements are met.
