Although applicable to any laminates, the present invention and the problem on which this invention is based will be described in detail with respect to fiber glass-aluminum laminates in aircraft construction.
Aluminum which is traditionally used as a standard material in aircraft construction is increasingly being replaced by novel materials, such as fiber-reinforced plastics materials or fiber-metal laminates, in which layers of fiber-reinforced plastics materials and metals are joined to form a laminate.
For example, large areas of the outer shell of the commercial aircraft Airbus A380 are produced from a fiber-metal laminate known under the name of GLARE (glass-fiber reinforced aluminum). This material consists of alternating layers, in each case only a few tenths of a millimeter thick, of aluminum and a glass fiber-reinforced epoxy resin plastics material which are bonded together under pressure during production. Important advantages of such laminates over aluminum are, for example favorable burn through and impact behavior as well as increased tear strength.
During regular flight operation of an aircraft, during loading and unloading, maneuvering on the ground, during lightning strike, maintenance and in other situations, the outer shell frequently suffers relatively slight damage, for example scratches. To be able to remedy damage of this type quickly and reliably, various standardized repair methods are used on conventional aircraft outer shells made of aluminum.
For example, according to one such repair method, scratches in the outer shell are ground out and polished with hand-held tools driven by compressed air. Another repair method comprises drilling or rubbing holes to seat repair bushes.
If repair methods of this type are applied analogously to the case of damage to outer shells consisting of a laminate, for example outer shells made from GLARE, the problem arises when a scratch is ground out for example, that the top layer of the laminate which, in the case of GLARE consists of aluminum, is penetrated and the underlying fiber layer is damaged, which impairs the stability of the fiber layer.
When holes are drilled and rubbed using hand-held tools, the precision required for seating the repair bushes is not achieved, because the fibers in penetrated fiber layers of the laminate exert a laterally deflecting force on the tool. An alternative method of guiding the repair bushes through a structure located behind the outer shell weakens this structure and is not always possible, or is only possible at great expense.