Stock material or miscellaneous articles – Sheet including cover or casing – Including elements cooperating to form cells
Reexamination Certificate
2003-08-08
2004-08-03
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Sheet including cover or casing
Including elements cooperating to form cells
C428S071000, C428S116000, C428S117000, C428S156000, C428S158000, C428S159000, C428S160000, C428S161000, C428S304400, C428S309900, C428S317100, C428S314400, C428S223000, C428S297400, C029S897000, C029S897100, C029S897200, C029S897300, C029S897320, C029S402010, C029S402090, C029S402110, C029S402120, C029S402140, C029S505000, C029S525010, C029S525060, C029S525070
Reexamination Certificate
active
06770349
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sandwich structure to be used as a structural member of aircraft, rolling stock, automobiles and ships, and a method of repairing such a sandwich structure.
2. Description of the Related Art
Lightweight, reinforced metal plates of aluminum alloys have been used for forming structural members of aircraft and the like. Recently, reinforced, plate structures of a composite material and sandwich structures formed by laminating a honeycomb core between surface plates of a composite material have been prevalently used. The surface plates of a composite material are bonded to the honeycomb core with adhesive films. Usually, cell elements of a honeycomb core are bonded together with a foaming adhesive that foams in a hot pressure molding process.
When a surface plate of a composite material is damaged and needs repairing, it is general to repair the damaged surface plate by scraping off a damaged part of the surface plat, laminating adhesive layers and prepreg sheets formed by impregnating a fiber structure with a resin in a recess formed by scraping off the damaged part so as to fill up the recess, and applying heat and pressure to the layers of the prepreg sheets and the adhesive to set the layers of the prepreg sheets.
When a sandwich structure having a honeycomb core sandwiched between surface plates is damaged, it sometimes occurs that water leaks into the sandwich structure through the periphery of the sandwich structure or cracks formed in the surface plate and water collects in the sandwich structure. The water collected in the honeycomb structure diffuses throughout the sandwich structure through the foam adhesive layers bonding together the cell elements of the honeycomb core. The adhesive film used for bonding together the surface plates and the honeycomb core includes a glass fabric, a cotton fabric or a meshed carrier of synthetic fibers. Therefore, small gaps are formed between the surface plates and the honeycomb core and it is possible that the water spreads through the gaps. If water collects in the honeycomb core and the honeycomb core is made of a metal, such as an aluminum alloy, the honeycomb core will be corroded and the surface plates will separate from the honeycomb core.
Even if the honeycomb core is made of a nonmetallic material, water collected in the honeycomb core repeats freezing and evaporation according to the variation of the ambient condition of the sandwich structure to deteriorate the adhesive bonding together the surface plates and the honeycomb core and to reduce the bonding strength of the adhesive and, consequently, the surface plates separates from the honeycomb core.
The water collected in the honeycomb core increases the weight of the sandwich structure, changes the position of the center of gravity of the sandwich structure adversely affecting the dynamic characteristic of the sandwich structure. In some cases, the sandwich structure is heated at a temperature not lower than 100° C. when repairing the damaged sandwich structure. If the honeycomb core contains water, the water evaporates to increase the pressure in the sandwich structure when the sandwich structure is heated and, in the worst case, the sandwich structure will burst.
If it is known that the honeycomb core contains water, small holes are formed in the surface plate and the water is drained through the small holes or the sandwich structure is unfastened and the water is removed by suction, which, however, needs time and costs.
When fabricating a sandwich structure having portions of different thicknesses, a honeycomb core must be machined, which requires troublesome work.
When repairing a damaged portion of a sandwich structure by laminating prepreg sheets, heat and pressure must be applied to the laminated prepreg sheets to set the prepreg sheets, which needs special devices. When setting prepreg sheets by applying heat and pressure thereto, pressure and temperature must be strictly controlled, which requires very troublesome work. After completing the repair of the damaged part of the sandwich structure by setting the prepreg sheets, the adhesive bonding the laminated prepreg sheets covering the damaged part to the mother structure of the repaired part must be inspected. Thus, the repair of the damaged sandwich structure needs special devices and much time and work.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a sandwich structure capable of inhibiting the penetration of water therein and having a core that can be easily processed and to provide a method of repairing a sandwich structure by simple work.
According to a first aspect of the present invention, a sandwich structure includes a core having foam plastic core members formed of a closed-cell foam plastic material, and surface plates formed of a fiber-reinforced composite material containing hydrophobic inorganic fibers as reinforcing fibers and covering the opposite surfaces of the core, wherein the foam plastic core members are bonded together with adhesive films that do not foam, and the surface plates are bonded to the core with adhesive films not containing any carrier or a component resin of the fiber-reinforced composite material forming the surface plates.
Since the sandwich structure is provided with the foam plastic core members of a closed-cell foam plastic material, water is unable to collect in the sandwich structure. Since the foam plastic core members are bonded together with an adhesive film that does not foam and the composite surface plates are bonded to the core with an adhesive film not having any carrier or a component resin of the fiber-reinforced composite material forming the composite surface plates, any passages through which water penetrates and diffuses into the sandwich structure are not formed at all. Consequently, the sandwich structure is free from troubles due to the penetration of water into the sandwich structure.
According to a second aspect of the present invention, a sandwich structure includes a core having foam plastic core members of a closed-cell foam plastic material and honeycomb core members, and surface plates formed of a fiber-reinforced composite material containing hydrophobic inorganic fibers as reinforcing fibers and covering the opposite surfaces of the core, wherein a peripheral part of the core is formed of the foam plastic core members arranged so as to surround the honeycomb core members, the foam plastic core members are bonded together with adhesive films that do not foam, and the surface plates are bonded to the core with adhesive films not containing any carrier or a component resin of the fiber-reinforced composite material forming the surface plates.
Since the peripheral part of the sandwich structure through which water is most liable to leak into the sandwich structure is formed of the foam plastic core members, the foam plastic core members are bonded together with an adhesive film that does not foam, and the surface plates are bonded to the core with adhesive films not containing any carrier or a component resin of the fiber-reinforced composite material forming the surface plates, the sandwich structure is free from troubles due to the penetration of water into the sandwich structure. Since the core has the honeycomb core members having strength and rigidity which are generally higher than those of the foam plastic core members, the sandwich structure has a high strength and a high rigidity.
According to a third aspect of the present invention, a sandwich structure includes a core having foam plastic core members formed of a closed-cell foam plastic material and honeycomb core members, and surface plates formed of a fiber-reinforced composite material containing hydrophobic inorganic fibers as reinforcing fibers and covering the opposite surfaces of the core, wherein the core is formed by sandwiching the honeycomb core members between the foam plastic core members and bonding the foam plastic core members to the honeycomb
Bandoh Shun-ichi
Itoh Toru
Boss Wendy
Jones Deborah
Kawasaki Jukogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
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