Glare (derived from GLAss REinforced laminate ) is a fiber metal laminate (FML) composed of several very thin layers of metal (usually aluminum) interspersed with layers of S-2 glass-fiber pre-preg, bonded together with a matrix such as epoxy. The uni-directional pre-preg layers may be aligned in different directions to suit predicted stress conditions. Though Glare is a composite material, its material properties and fabrication are very similar to bulk aluminum sheets. It has far less in common with composite structures when it comes to design, manufacture, inspection, or maintenance. Glare parts are constructed and repaired using mostly conventional metal working techniques. Its major advantages over conventional aluminum are:
Better "damage tolerance" behavior, especially in impact and metal fatigue. Since the elastic strain is larger than other metal materials, it can consume more impact energy. It is dented more easily but has a higher penetration resistance. Better corrosion resistance. Better fire resistance. Lower specific weight. Furthermore, the material can be tailored during design and manufacture so that the number, type and alignment of layers can suit the local stresses and shapes throughout the aircraft. This allows the production of double-curved sections, complex integrated panels, or very large sheets. While a simple manufactured sheet of Glare is three to ten times more expensive than an equivalent sheet of aluminum, considerable production savings can be made using the aforementioned optimization. A structure built with Glare is lighter and less complex than an equivalent metal structure, requires less inspection and maintenance, and has a longer lifetime-till failure. These characteristics can make Glare cheaper, lighter, and safer to use in the long run.
History Glare is a relatively successful FML, patented by the Dutch company Akzo Nobel in 1987. It entered major application in 2007, when the Airbus A380 airliner began commercial service. Much of the research and development was done in the 1970s and 1980s at the Faculty of Aerospace Engineering, Delft University of Technology, where professors and researchers advanced the knowledge of FML and earned several patents, such as a splicing technique to build wider and longer panels without requiring external joints. The development of FML reflects a long history of research that started in 1945 at Fokker, where earlier bonding experience at de Havilland inspired investigation into the improved properties of bonded aluminum laminates compared to monolithic aluminum. Later, the United States National Aeronautics and Space Administration (NASA) became interested in reinforcing metal parts with composite materials in the Space Shuttle program, which led to the introduction of fibers to the bond layers. Thus, the concept of FMLs was born. Further research and co-operation of Fokker with Delft University, the Dutch aerospace laboratory NLR, 3M, Alcoa, and various other companies and institutions led to the first FML: the Aramid Reinforced ALuminum Laminates (ARALL), which combined aluminum with aramid fibers and was patented in 1981. This material had some cost, manufacturing, and application problems; while it had very high tensile strength, the material proved suboptimal in compressive strength, off-axis loading, and cyclic loading. These issues led to an improved version with glass fiber instead of aramid fibers. Over the course of the development of the material, which took more than 30 years from start to the major application on the Airbus A380, many other production and development partners have been involved, including Boeing, McDonnell Douglas, Bombardier, and the US Air Force. Over the course of time, companies withdrew from this involvement, sometimes to come back after a couple of years. For example, Alcoa departed in 1995, returned in 2004, and withdrew again in 2010. It is alleged that disagreements between some of these partners caused Boeing to remove Glare from the cargo floor of the Boeing 777 in 1993 (before the aircraft's service entry in 1995) and blocked Bombardier's plans to use Glare in its CSeries aircraft in 2005. These strategic decisions show the dynamic nature of innovation processes.
Applications
Glare has been most often applied in the aviation field. It forms part of the Airbus A380 fuselage and the leading edge of the tail surfaces. In 1995, an aircraft freight container made out of Glare became the first container certified by the Federal Aviation Administration (FAA) for blast resistance; the container can absorb and neutralize the explosion and fire from a bomb such as the one used in the Pan Am Flight 103 disaster over Lockerbie, Scotland in 1988. Glare has also been used in the front radome bulkhead of the Bombardier Learjet 45 business jet, which was first delivered in 1998. The material was used as a cargo liner solution for regional jets, in the lower skins of the flaps in the Lockheed Martin C-130J Super Hercules military transport aircraft, and in straps for the highest loaded frames in the Airbus A400M military transporter.
Varieties and nomenclature There are six standard Glare grades (Glare1 through Glare6) with typical densities ranging from 2.38 to 2.52 grams per cubic centimetre (0.086 to 0.091 lb/cu in), which is similar to the 2.46 to 2.49 g/cm3 (0.089 to 0.090 lb/cu in) density of S-2 glass fiber. These densities are smaller than the 2.78 g/cm3 (0.100 lb/cu in) density of 2024-T3 aluminum alloy, a common aluminum alloy in aircraft structures that is also incorporated into all but one of these Glare grades. (Glare1 uses the 7475-T761 alloy instead.) As the strength of the composite varies with fiber direction, the Glare grades differ by the number and complexity of pre-preg plies and orientations within a composite layer. Each Glare grade has A and B variants that have the same number of plies but with alternate fiber orientations. The standard Glare grades are cured in an autoclave at 120 °C (248 °F) for 3.5 hours under 11-bar pressure (11 atm; 160 psi; 1,100 kPa), and they use the FM94 epoxy pre-preg.
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