"Damage Tolerance and Durability of Fiber-Metal Laminates for Aircraft Structures"
H. T. Hahn and Jenn-Ming Yang, University of California at Los Angeles
Fiber-reinforced metal laminates (FML) are hybrid composites consisting of alternating thin layers of metal sheets and fiber-reinforced resin prepreg. The most commonly used metal for FML is aluminum, and the fibers can be Kevlar or glass. The FML with glass fibers (trade name GLARE), and Kevlar fibers (trade name ARALL) have been evaluated for potential applications in aircraft structures.
These laminates possess excellent properties of both metal and fibrous composite materials. This combination results in a new family of hybrid laminates with an ability to impede and arrest crack growth caused by cyclic loading, with excellent impact and damage tolerance characteristics and a low density. Also, the corrosion resistance is excellent because the prepreg layers are able to act as moisture barriers between the various inner aluminum layers, whereas the metal layers protect the fiber/epoxy layers from picking up moisture. The laminate also has an inherent high burn-through resistance as well as good damping and insulation properties. Furthermore, this material can be produced as sheet material, but also be cured in an autoclave as a complete structure, e.g., a large curved panel with co-cured doublers and stiffening elements.
As a result of these characteristics, GLARE laminates offer the aircraft structural designer a damage-tolerant, light-weight, cost-effective solution for many applications. GLARE laminates seem poised for a much larger future in the primary structure of pressurized transport fuselages, such as A-380. However, there are still little and insufficient information available about mechanical behavior of GLARE in published literature.
More research and testing in basic mechanical behavior such as in-plane shear strength, bearing strength and tensile/compressive behavior at different environments, estimation of fatigue lives and crack growth rates, notched sensitivity, impact behavior, delaminations and damage characterization are is necessary. This will to generate adequate data to facilitate greater utilization of GLARE in future aircraft structures.
