Composite sandwich structure with integrated reinforcement area and method of producing the same
Producing a local reinforcement in a core structure of a composite sandwich structure involves forming a hole in a cover layer and the core of the sandwich structure, forming a hollow space in the core with a diameter the same as or preferably larger than that of the hole, introducing a spatial bounding device through the hole into the hollow space, seating the spatial bounding device in the hollow space to contact outwardly against parts of the core preferably by outwardly expanding the device, and introducing a filler material into the spatial bounding device. A sandwich structure includes a core between cover layers, and a local reinforcement including a hole in at least one of the cover layers, a space in the core with a larger diameter than the hole, a spiral sleeve in the space, and a filler material inside the spiral sleeve.
1. A method of producing a local reinforcement area in a core structure of a composite sandwich structure, comprising:
a) providing a composite sandwich structure including an open three-dimensional core structure and first and second cover layers applied on opposite first and second sides of said core structure, wherein said core structure comprises a folded core element having fold valleys forming open channels that are bounded between said folded core element and said first and second cover layers and that extend in a longitudinal direction of said open channels continuously along and parallel to said first and second cover layers;
b) forming a hole having a hole diameter in at least said first cover layer and in said core structure;
c) forming a hollow space having a hollow space diameter in said core structure, wherein said hollow space diameter is at least twice as large as said hole diameter, said hollow space is bounded at least partially by bounding parts of said core structure at a perimeter of said hollow space, said hollow space communicates into an adjoining open channel of said open channels, and said bounding parts of said core structure at said perimeter of said hollow space are cut edges of webs of said folded core element that were cut during said forming of said hollow space;
d) introducing a spatial boundary device comprising a spiral sleeve through said hole in said first cover layer into said hollow space in said core structure, wherein at least a partial area of said spiral sleeve is a material strip of a perforated sheet, a net, a mesh, or a woven web that has a regular pattern of openings passing therethrough;
e) outwardly expanding and seating said spiral sleeve in said hollow space so that said spiral sleeve at least partially contacts outwardly against said bounding parts of said core structure;
f) introducing a filler material into a bounded space formed within said spiral sleeve, wherein said openings serve to permit a limited discharge of said filler material out of said bounded space and into said adjoining open channel to fix said spiral sleeve in said core structure, and then hardening said filler material so as to form thereof a local reinforcement area, and
g) integrating a securing element into said local reinforcement area after the formation of said local reinforcement area.
2. The method according to claim 1 , wherein said hollow space diameter is from 3 to 20 times said hole diameter.
3. The method according to claim 1 , wherein said hole diameter of said hole in said first cover layer established in said step b) is maintained unchanged throughout said steps c), d), e), and f).
4. The method according to claim 1 , wherein said step c) of forming said hollow space comprises enlarging said hole in said core structure using an undercutting miller or an undercutting reamer reaching through said hole in said first cover layer.
5. The method according to claim 1 , wherein said spiral sleeve has variable cross section geometry, wherein said step d) is carried out with a spiral sleeve outer diameter of said spiral sleeve contracted to be smaller than or equal to said hole diameter, and wherein said step e) involves expanding said spiral sleeve outer diameter to be equal to said hollow space diameter.
6. The method according to claim 5 , wherein said spiral sleeve comprises a shape memory alloy metal, and said step e) comprises heating said hollow body to cause said shape memory alloy metal to expand.
7. The method according to claim 5 , wherein said spiral sleeve has, in an unstressed condition, said outer diameter being larger than said hole diameter and at least as large as said hollow space diameter, said step d) involves compressing said spiral sleeve to a stressed contracted condition in which said outer diameter is smaller than or equal to said hole diameter, and said step e) involves allowing said spiral sleeve to expand out of said stressed contracted condition until said outer diameter equals said hollow space diameter.
8. The method according to claim 1 , wherein said step d) involves contracting said spiral sleeve to a stressed condition and then passing said spiral sleeve through said hole in said first cover layer while said spiral sleeve is in said stressed condition, and said step e) involves expanding said spiral sleeve to an expanded condition in which said spiral sleeve is at least partially destressed relative to said stressed condition and in which said spiral sleeve contacts outwardly against said bounding parts of said core structure.
9. The method according to claim 1 , wherein said spiral sleeve achieves a stressed condition through tightly rolling said spiral sleeve, and in said stressed condition said spiral sleeve has a smaller diameter compared to a relaxed condition of said spiral sleeve.
10. The method according to claim 9 , wherein said spiral sleeve has a height corresponding to a thickness of said core structure between said cover layers.
11. The method according to claim 9 , wherein said spiral sleeve comprises an initially planar spring-elastic material strip of a synthetic plastic material.
12. The method according to claim 9 , wherein said spiral sleeve comprises a material that softens at a specified temperature, and said step e) further comprises heating said spiral sleeve to at least said specified temperature so as to soften said material and to thereby connect said spiral sleeve to said core structure by said material.
13. The method according to claim 9 , wherein said spiral sleeve comprises a material that foams-up under a specified condition, and said step e) further comprises subjecting said spiral sleeve to said specified condition so as to cause said material to foam-up and to thereby connect said spiral sleeve to said core structure by said material.
14. The method according to claim 1 , wherein the securing element comprises an insert element.
15. The method according to claim 14 , wherein said insert element is an insert nut.
16. The method according to claim 1 , further comprising boring a bored hole into said filler material of said local reinforcement, wherein a securing element is positioned in the bored hole and is secured therein in a force-transmitting manner.
17. The method according to claim 1 , wherein a sleeve wall of said spiral sleeve comprises a woven web mesh of carbon fibers and/or fiberglass fibers that are coated and/or impregnated with a synthetic plastic material so as to leave said openings open through said woven web mesh, permitting a limited discharge of said filler material out of an interior of the spiral sleeve into the surrounding core structure, and fixing the spiral sleeve in the core structure.
18. The method according to claim 1 , wherein said open channels extend continuously open in said longitudinal direction of said channels from one edge to an opposite other edge of said core structure.
19. The method according to claim 1 , wherein said filler material introduced in said step f) is a flowable filler material, wherein said local reinforcement area formed in said step f) comprises said spiral sleeve and said filler material hardened inside and outside of said spiral sleeve, whereby said hardened filler material outside of said spiral sleeve fixes said spiral sleeve to said core structure, and wherein said step g) comprises boring a hole into said hardened filler material inside of said spiral sleeve and inserting and fixing said securing element into said bored hole.