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Title:
A LAMINATE STRUCTURE OF COMPOSITE MATERIAL
Document Type and Number:
WIPO Patent Application WO/2014/031047
Kind Code:
A1
Abstract:
The invention relates to a laminate structure (10, 20, 30, 40, 50) of stacked sheets of composite material and method of manufacturing a laminate structure (10, 20, 30, 40, 50) of composite material. The structure (10, 20, 30, 40, 50) comprises at least one curved portion(105, 205, 305, 325, 405A, 405B, 425A, 425B, 505) having an inner radius of curvature(R1) and an outer radius of curvature(R2). The stacked sheets (3) of composite material in the at least one curved portion(105, 205, 305, 325, 405A, 405B, 425A, 425B, 505) have a total thickness (W). Resin (21) is provided between at least two of the sheets (3) of composite material on the portions of the sheets (3) forming the at least one curved portion (105, 205, 305, 325, 405A, 405B, 425A, 425B, 505), wherein the difference between the outer radius of curvature(R2) and the inner radius of curvature(R1) is smaller than the thickness (W).

Inventors:
HALLANDER PER (SE)
PETERSSON MIKAEL (SE)
LUNDBERG ANDERS (SE)
Application Number:
SE2012/050899
Publication Date:
February 27, 2014
Filing Date:
August 24, 2012
Export Citation:
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Assignee:
SAAB AB (SE)
HALLANDER PER (SE)
PETERSSON MIKAEL (SE)
LUNDBERG ANDERS (SE)
International Classes:
B29C70/20; B29C70/34; B29C70/54; B29D99/00; B64C1/06; B64C3/18
Domestic Patent References:
WO2011142699A12011-11-17
WO2010022247A12010-02-25
WO1999047620A11999-09-23
WO2009097853A12009-08-13
Foreign References:
US5217766A1993-06-08
EP2052846A12009-04-29
US3703422A1972-11-21
US20050051262A12005-03-10
US20100140834A12010-06-10
GB2168002A1986-06-11
Other References:
FEIH S. ET AL.: "Quality assessment of curved composite components in peel joint structures", COMPOSITES: PART A, vol. 36, 2005, pages 397 - 408, XP004691963, DOI: doi:10.1016/j.compositesa.2004.02.022
NIXON J.: "The best of both worlds", REINFORCED PLASTICS, vol. 52, 2008, pages 36, 37, 39
Attorney, Agent or Firm:
ALBIHNS.ZACCO AB (Valhallavägen 117 N, Stockholm, SE)
Download PDF:
Claims:
CLAIMS

1 . A method of manufacturing a laminate structure (10, 20, 30, 40, 50) made of sheets (3) of composite material ; which structure (10, 20, 30, 40, 50) comprises at least one curved portion (105, 205A, 205B, 305, 325, 405A, 405B, 425A, 425B, 505) having an outer radius of curvature (R2), wherein the method comprises the following steps:

- providing a first semi cured lay-up (100, 213, 215, 300, 413, 415, 500) by stacking semi cured sheets (3) of composite material on a curved forming surface of a first forming tool (55, 57), thereby forming the at least one curved portion (105, 205A, 205B, 305, 325, 405A, 405B, 425A, 425B, 505), and in the same step applying resin (21 ) between at least two adjacent sheets (3) of composite material on the portions of the sheets (3) forming the at least one curved portion (105, 205A, 205B, 305, 325, 405A, 405B, 425A, 425B, 505) in order to reduce a length of the outer radius of curvature (R2),

- curing the first semi cured lay-up (100, 213, 215, 300, 413, 415, 500) in a curing tool (47),

- removing the laminate structure (10, 20, 30, 40, 50) from the curing tool (47).

2. The method according to claim 1 , wherein the step of providing the first semi cured lay-up (100, 213, 215, 300, 413, 415, 500) further comprises the step of:

- forming the first semi cured lay-up (100, 213, 215, 300, 413, 415, 500) in a second forming tool (55, 57).

3. The method according to either of claims 1 or 2, wherein the step of providing a first semi cured lay-up (100, 213, 215, 300, 413, 415, 500), further

comprises the step of:

- forming at least one flange part (207 A, 217B, 407A, 407B, 427A, 427B), and a web part (209A, 209B, 409A, 409B), and wherein the method further comprises the steps of: - providing a second semi cured lay-up (213, 215, 413, 415) comprising at least one curved portion (215A, 215B, 405A, 405B, 425A, 425B), at least one flange part (207 A, 207B, 407A, 407B, 427A, 427B), and a web part (209A, 209B, 409A, 409B)

- positioning the first semi cured lay-up (213, 215, 413, 415) adjacent the second semi cured lay-up (213, 215, 413, 415), so that an outer surface (217A, 217B , 417A, 417B) of the web part (209A, 209B, 409A, 409B) of the first cured structure element (213, 215, 413, 415) abuts an outer surface (217A, 217B, 417A, 417B) of the web part (209A, 209B, 409A, 409B) of the second cured structure element (213, 215, 413, 415), and wherein the step of curing the semi cured lay-up (100, 213, 215, 300, 413, 415, 500) in a curing tool (47) further comprises the steps of:

- curing the first and the second semi cured lay-up (100, 213, 215, 300, 413, 415, 500) in the curing tool (47).

The method according to any of claims 1 -3 wherein the sheets (3) of

composite material are prepregs.

The method according to any of claims 1 -4 wherein the resin (21 ) is a resin film.

The method according to any of claims 1 -4 wherein the resin (21 ) is a tape.

The method according to any of claims 1 -4 wherein the resin (21 ) has a curing temperature, which is lower than the curing temperature of the sheets (3) of composite material.

A laminate structure (10, 20, 30, 40, 50) made of stacked sheets (3) of composite material, which structure (10, 20, 30, 40, 50) comprises at least one curved portion (105, 205A, 205B, 305, 325, 405A, 405B, 425A, 425B, 505) characterized by resin (21 ) being provided between at least two adjacent sheets (3) of composite material on the portion of the sheets (3) forming the at least one curved portion (105, 205A, 205B, 305, 325, 405A, 405B, 425A, 425B, 505).

9. The laminate structure (10, 20, 30, 40, 50) according to claim 8, wherein the sheets (3) of composite material are prepregs. 10. The laminate structure according to claim 8, wherein the resin is a resin film.

1 1 . The laminate structure according to claim 8, wherein the resin is a tape.

12. The laminate structure according to claim 8, wherein the resin (21 ) has a

curing temperature, which is lower than the curing temperature of the sheets

(3) of composite material.

13. The laminate structure (20, 40) according to any of claims 8-12, wherein the structure (20, 40) is an aircraft laminate structure comprising a first curved portion (205A, 405A, 425A), a second curved portion (205B, 405B, 425B), a web part (209, 409), a first flange part (207A, 407A, 427A) and a second flange part (207B, 407B, 427B).

14. The structure (20) according to claim 13, wherein the structure (20) essentially has the form of a T.

15. The structure (40) according to claim 13, wherein the structure (40) essentially has the form of an I.

Description:
A LAMINATE STRUCTURE OF COMPOSITE MATERIAL

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a laminate structure made of sheets of composite material according to the preamble of claim 1 , and to a laminate structure made of sheets of composite material according to the preamble of claim 8. The present invention relates to, but is not limited to, aircraft industry.

BACKGROUND OF THE INVENTION Methods of manufacture of composite materials using "prepreg" material (layer of fibre material previously impregnated with resin) exist today. When manufacturing curved or folded structures such as aircraft shells, a stack of prepregs are formed into a curved shape in a forming tool. The shape can be double curved or single curved. Since almost no plastic deformation occurs during the forming procedure, the inner radius of curvature of the curved structure tends to be smaller than the outer radius of curvature. The difference between the inner radius of curvature and the outer radius of curvature is proportional to the thickness of the structure in the curved area. If no plastic deformation occurs at all, the difference between the inner and the outer radius of curvature will theoretically be equal to the thickness of the structure in the curved area.

When two folded L-formed stiffening elements are connected to form an upside-down T-shaped stiffening structure, which is attached to an inner surface of an aircraft structure, there will be a space under the folded portion of the T-shaped stiffening structure. This space weakens the aircraft structure and therefore it is normally filled with a so called noodle or infill. For strength reasons it is desirable to make the space as small as possible.

If the outer radius of curvature of the folded portion of the respective L-formed stiffening elements is large, the space will also be large. Therefore it is desirable to keep the outer radius of curvature of the folded portion of the respective L-formed stiffening elements as small as possible, preferably as small as the inner radius of curvature of the folded portion

It is possible to achieve a stiffening structure having the same outer radius of curvature as the inner radius of curvature by milling the structure, since the machining admits forming into almost any form. If, however, a structure is folded and formed so that the length of the inner and outer radius of curvature is the same, the forming must be obtained with plastic deformation. When forming stacked prepregs, comprising continuous fibres, into a curved surface, no plastic deformation occurs. Instead fibres in the prepregs tend to take the shortest way in the folded area. This means that the fibres don't follow the curved form. This can lead to folds or wrinkles in the curved portions of the structure and to non desired accumulations of resin. One way to solve this problem is to apply dry fibres as distance material between the prepregs in the folded area. This solution is described in the 18 th international conference on composite materials "Limitations of fibre placement techniques for variable angle tow composites and their process-induced defects" B.C.Kim, K Hazra et al, ACCIS, Bristol. However, with this solution it is still possible for the dry fibres to take a short cut. The dry fibres also increase the friction between the prepregs, which makes the forming more difficult.

The present invention will overcome the above mentioned drawbacks of the known technology. The present invention also solves the problem of how to achieve a cost- effective production of stiffened aircraft shells, where the shells at the same time will have a high strength.

SUMMARY OF THE INVENTION The invention shows a method for manufacturing a laminate structure of composite material comprising a curved portion as being defined in the introduction, the method being characterised by the steps claimed in claim 1 .

The method has the advantage that the outer radius of curvature of the curved portion can be reduced in an easy and cost effective way in comparison with the known technology. The method has also the advantage that the fibres in the laminate sheets will follow the curvature of the curved portion instead of taking short cuts, which prevents folds or wrinkles in the structure and non desired accumulations of resin.

According to an embodiment the method comprises the further step of forming the semi cured lay-up in a second forming tool. This step has the advantage that the semi cured lay-up is formed from both an inner surface and from an outer surface, which prevents air pockets and accumulations of resin.

According to a further embodiment the method comprises providing two semi cured lay-ups each comprising at least one curved portion, at least one flange part and a web part and positioning the first semi cured lay-up adjacent the second semi cured lay-up so that an outer surface of the web part of the first cured structure element abuts an outer surface of the web part of the second cured structure element. This embodiment results in a T-formed or l-formed reinforcing structure element with only a minor space under the curved portion. This has the advantage that strength of the reinforcing structure element is increased by a cost effective method.

According to a further embodiment the resin is an adhesive film or a resin film. This has the advantage that the resin can be applied quickly.

According to a further embodiment the resin is a tape. This has the advantage that the resin can be applied quickly and evenly.

According to a yet a further embodiment the resin has a curing temperature, which is lower than the curing temperature of the sheets of composite material. This has the advantage that the resin works as a forming tool, forming the sheets of composite material so that they follow the form of the resin during the curing. The invention also shows a laminate structure as being defined in the introduction, the laminate structure being characterised by the features claimed in claim 8. The laminate structure has the advantage that it is rigid without folds, wrinkles or resin accumulations, while having a relatively small outer radius of curvature.

According to an embodiment the structure essentially has the form of a T. This has the advantage that the space under the transition area between the web and the flange will be relatively small which implies that the structure element will be more rigid in comparison with traditional T-structures.

According to an embodiment the structure essentially has the form of an I. This has the advantage that the space under the transition area between the web and the flange will be relatively small which has as consequence that structure element is more rigid in comparison with traditional l-structures.

The resin may be pure. This has the advantage that the friction between the laminate sheets is reduced which facilitates the forming procedure.

The resin may also be reinforced with a nano filament such as e.g. carbon nano tubes (CNT), nano fibres or nano wires. This has the advantage that the laminate structure will be strong and durable at the same time as the method provide an extremely cost effective production of a reinforced aircraft shell. Preferably, the nano filament (CNT, nano fibre, nano multi wall filament, nano double wall filament, nano wire etc.) has a length of 0, 125 mm or less. This is suitable for a common prepreg ply having a thickness of 0, 125 mm used in the production of aircrafts. If leaning, or in the plane oriented nano filaments are used, the length preferably can be longer. The definition of nano means that a filament particle has at least one dimension not more than 200 nm. 1 nm (nanometre) is defined as 10 "9 metre (0,000 000 001 meter). Preferably, the diameter of a multiwall nano tube is 15-35 nm, suitably 18-22 nm. Suitably, the diameter of a single wall nano tube is 1 ,2 -1 ,7 nm, preferably 1 ,35-1 ,45 nm.

The sheets of composite material may be fibre reinforced resin sheets, such as for example prepregs.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example with reference to the accompanying schematic drawings of which:

Fig 1 : Figure 1 shows a cut view of a cross section of a first curved structure according to the state of the art.

Fig 2: Figure 2 shows a cut view of a cross section of a second curved

structure according to the state of the art.

Fig 3: Figure 3 shows a perspective view of the second curved structure

according to the state of the art.

Fig 4: Figure 4 shows a cut view of a cross section of a curved structure

according to a first embodiment of the present invention.

Fig 5: Figure 5 shows a cross section view of a curved structure according to a second embodiment of the present invention.

Fig 6: Figure 6 shows a cross section view of a curved structure according to a third embodiment of the present invention.

Fig 7: Figure 7 shows a cross section view of a curved structure according to a fourth embodiment of the present invention. Fig 8A: Figure 8A shows a flowchart of a method of manufacturing the structures showed in figure 4, 6 or 10. Fig 8B: Figure 8B shows a flowchart of a method of manufacturing the structures showed in figure 5 and in figure 7.

Fig 9: Figure 9 shows the curing process in the curing tool.

Fig 10: Figure 10 shows a cross section view of a curved structure according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings related to embodiments, wherein for the sake of clarity and understanding of the invention some details of no importance are deleted from the drawings.

For clarity reasons the figures are not depicted according to scale. Only three layers of sheets of composite material are shown. In reality the structures may comprise a large number of sheets of composite material.

Since a semi cured lay-up essentially preserves its shape during the curing procedure, the different portions of the semi cured lay-ups are defined in the same way, and with the same reference number, as the portions of the cured structures.

Figure 1 schematically shows a cut view of a cross section of a curved structure 1 A according to the state of the art. The structure is made of stacked prepregs 3 which are formed to a curved shape. The structure 1A comprises a curved portion 5 a flange part 7 and a web part 9. The web part 9 has an outer surface 17. The stacked prepregs have a thickness W. The curved portion 5 has an inner radius of curvature R1 and an outer radius of curvature R2. The two dotted circles only serves to illustrate the inner and the outer radius of curvature R1 , and R2, so they are not parts of the curved structure. Due to the non-plastic deformation the origin of the outer radius of curvature R2 is the same as of the inner radius of curvature R1 . The length of the outer radius of curvature R2 is equal to the sum of the length of inner radius of curvature R1 and the thickness W. This can be described with the following relation:

R2 = R1 + W

This relation is valid when the prepregs are formed without plastic deformation and is a result of simple geometrical properties. If more prepregs are applied, the thickness of the structure increases, which affects the outer radius of curvature so that the outer radius of curvature increases too.

Figure 2 shows schematically a cut view of a cross section of a further curved structure 1 B according to the state of the art. This structure 1 B has the form of an upside down T and is used as a stiffening element such as a stringer or a rib, which is connected to a shell 1 1 in an aircraft structure. The structure 1 B is also shown in a perspective view in figure 3. The structure 1 B is made of two structure elements, a first structure element 13 and a second structure element 15. Each of the first structure element 13 and the second structure element 15 are made of stacked prepregs 3 which are formed to a curved shape. The second structure element 15 has a similar shape as the first structure 1A. It comprises a curved portion 5B, a flange part 7B and a web part 9B, thereby having the shape of an L. The first structure element 13 comprises a curved portion 5A, a flange part 7A and a web part 9A. The first structure element 13 has a shape which is reversed in relation to the second structure element 15, i.e. a reversed L. Each of the respective web parts 9A and 9B has an outer surface 17A and 17B and the two structure elements 13 and 15 are attached to each other at their respective outer surfaces 17A and 17B. In this way a web part 9 of the structure 1 B is formed by the respective web parts 9A and 9B of the first structure element 13 and the second structure element 15.

Each of the first and second structure elements 13 and 15 has an inner radius of curvature R1 and an outer radius of curvature R2 and each of the stacks of prepregs 3 has a thickness W. Just like for the structure 1 A as shown in figure 1 , the length of the outer radius of curvature R2 is equal to the sum of the length of inner radius of curvature R1 and the thickness W, for each of the first and the second structure element 13 and 15. If the structure is made thicker and comprises many prepregs, the outer radius of curvature R2 of each of the respective structure elements 13 and 15 will also be large. If the curved structure 1 B is connected to a shell 1 1 of an aircraft structure (as shown in figure 2), this has as effect that a space 19 between the respective curved portions 5A and 5B and the shell 1 1 will also be large. Due to strength requirements of aircraft structures it is advantageous if this space 19 can be made as small as possible. In aircraft applications, where the strength of the aircraft structure is essential, the space 19 is normally filled with a resin. This filling is called a needle. One aim of the present invention is to obtain a smaller space 19 while still preserving the thickness of the structure. This can be obtained if the outer radius of curvature R2 can be made smaller.

Figure 4 schematically shows a cut view of a cross section of a curved structure 10 according to a first embodiment of the present invention. The figure also shows a semicured lay-up 100 of the curved structure 10. The structure 10 is made of stacked sheets 3 of composite material, which are formed to a curved shape. The structure 10 according to this embodiment comprises a curved portion 105, a flange part 107 and a web part 109. The curved portion 105 has an inner radius of curvature R1 , and an outer radius of curvature R2. The inner surface 133 of the structure 10 is defined as the surface having the inner radius of curvature R1 and the outer surface 135 of the structure 10 is defined as the surface having the outer radius of curvature R2. In order to decrease the outer radius of curvature R2 the structure 10 comprises resin 21 between the sheets 3. The resin 21 is provided on the portions of the sheets 3 which form the curved portion 105. Just as for figure 1 the two dotted circles only serves to illustrate the inner and the outer radius of curvature R1 , and R2, so they are not parts of the curved structure. Note that the origin of the outer radius of curvature R2 don't coincide with the origin of the inner radius of curvature R1 .

The structure 10 is provided with resin to such degree that the length of the outer radius of curvature R2 is smaller than the sum of the length of inner radius of curvature R1 and the thickness W, where W is equal to the thickness the structure 10 without the resin 21 . This means that the outer radius of curvature R2 is smaller than it would have been without the resin 21. The resin may e.g. be provided to an extent such that the outer radius of curvature R2 is equal to the inner radius of curvature R1 (not shown).

Figure 5 schematically shows a cut view of a cross section of a curved structure 20 according to a second embodiment of the present invention. The figure also shows a semicured lay-up 200 of the curved structure 20. The structure 20 is made of two structure elements, a first structure element 213 and a second structure element 215. Each of the first structure element 213 and the second structure element 215 are made of stacked sheets of composite material 3, which are formed to a curved shape. The second structure element 215 is similar to the structure 10. It comprises a curved portion 205B, a flange part 207B and a web part 209B, thereby having the shape of an L. The first structure element 213 comprises a curved portion 205A, a flange part 207A and a web part 209A. The first structure element 213 is reversed in relation to the second structure element 215, i.e. a reversed L. Each of the respective web parts 209A and 209B has an outer surface 217 A and 217B. The two structure elements 213 and 215 are attached to each other at their respective outer surfaces 217A and 217B. In this way the web part 209 of the structure 20 is formed by the respective web parts 209A and 209B of the first structure element 213 and the second structure element 215.

Each of the curved portions 205A and 205B has an inner radius of curvature R1 and an outer radius of curvature R2. In order to decrease the outer radius of curvature R2 of the respective structure elements 213 and 215, resin 21 is provided between adjacent sheets 3. The resin is applied on the sections of the sheets 3 which form the curved portions 205A and 205B.

The resin is applied to such degree that the length of the outer radius of curvature R2 is smaller than the sum of the length of inner radius of curvature R1 and the

thickness W, which W is equal to the thickness of the stacked sheets 3 of composite material of the respective structure elements 213 and 215 in their web- and flange parts 207, 209. The resin may e.g. be provided such that the outer radius of curvature R2 is equal to the inner radius of curvature R1 (not shown).

This structure 20 may be used as a reinforcing element such as a rib or a stringer in aircraft applications. In figure 5 the structure has been positioned on an aircraft shell 1 1 . Just as showed in accordance with the structure 1 B there is a space 219 between the respective curved portions 205A and 205B and the shell 1 1 . However, due to the decreased outer radius of curvature R2 the space 219 is much smaller than the space 19 under the structure 1 B according to the state of the art. Therefore this structure 20 according to the present embodiment is advantageous in

comparison with the structure 1 B, when it is connected to e.g. an aircraft shell 1 1.

Figure 6 schematically shows a cut view of a cross section of a curved structure 30 according to another embodiment of the present invention. The figure also shows a semicured lay-up 300 of the curved structure 30. The structure 30 is made of stacked sheets 3 of composite material, here prepregs, which are formed to a curved or curved shape. According to this embodiment the structure 30 comprises a first curved portion 305, a second curved portion 325, a first flange part 307, a second flange part 327 and a web part 309, giving the structure 30 a form of a U.

The first curved portion 305 has an inner radius of curvature R1 and an outer radius of curvature R2. The second curved portion 325 has an inner radius of curvature R1 ' and an outer radius of curvature R2. In order to decrease the outer radii R2 and R2 ' resin 21 is positioned between the sheets 3. The resin 21 is provided on the portions of the sheets 3 which form the curved portions 305 and 325.

The resin on the curved portion 305 is applied with resin to such degree that the outer radius of curvature R2 and has a desired length, i.e. the length of the outer radius of curvature R2 is smaller than the sum of the length of inner radius of curvature R1 and the thickness W, which W is equal to the thickness of the stacked sheets 3 of composite material. The resin may e.g. be provided such that the outer radius of curvature R2 is equal to the inner radius of curvature R1 (not shown).

Equivalently, the resin on the curved portion 325 is provided in an extent such that the outer radius of curvature R2 ' and has a desired length, i.e. the length of the outer radius of curvature R2 ' is smaller than the sum of the length of inner radius of curvature R1 ' and the thickness W. The resin may e.g. be provided such that the outer radius of curvature R2 ' is equal to the inner radius of curvature R1 ' (not shown).

The inner surface 333 of the structure 30 is defined as the surface comprising the inner radii R1 and R1 ' and the outer surface 335 of the structure 30 is defined as the surface comprising the outer radii R2 and R2 ' . Principally, the structure 30 is similar to the structure 10. However, the structure 30 comprises an additional curved portion 325.

Figure 7 shows schematically a cut view of a cross section of a curved structure 40 according to a yet another embodiment of the present invention. The figure also shows a semicured lay-up 400 of the curved structure 40. The structure 40

comprises a first curved portion 405A, a second curved portion 405B, a third curved portion 425A, a fourth curved portion 425 B, a first flange part 407A, a second flange part 407B, a third flange part 427A, a fourth flange part 427B and a web part 409. The structure 40 is made of two structure elements, a first structure element 413 and a second structure element 415. Each of the first structure element 413 and the second structure element 415 are made of stacked sheets 3 of composite material, which are formed to a curved shape. The second structure element 415 is similar to the structure 30 in figure 6. It comprises the second curved portion 405B, the fourth curved portion 425B, the second flange part 407B, the fourth flange part 427B and a web part 409B. The first structure element 413 is reversed in relation to the second structure element 415, i.e. a reversed U. It comprises the first curved portion 405A, the third curved portion 425A, the first flange part 407A, the third flange part 427A and a web part 409A. An outer surface 417A of the web part 409A is attached to an outer surface 417B of the web part 409B. In this way the web part 409 of the structure 40 is formed by the respective web parts 409A and 409B of the first structure element 413 and the second structure element 415. Each of the curved portions 405A, 405B, has an inner radius of curvature R1 and an outer radius of curvature R2. The curved portions 425A, 425B, have an inner radius of curvature R1 ' and an outer radius of curvature R2 ' . In order to decrease the outer radii R2 and R2 ' resin 21 is positioned between the sheets 3. The resin 21 is provided on the portions of the sheets 3 which form the curved portions 405A, 405B, 425A and 425B. The resin on the curved portions 405A and 405B is applied in an extent such that the outer radius of curvature R2 has a desired length, i.e. the length of the outer radius of curvature R2 is smaller than the sum of the length of inner radius of curvature R1 and the thickness W, which W is equal to the thickness of the stacked sheets 3 of composite material. The resin may e.g. be provided such that the outer radius of curvature R2 is equal to the inner radius of curvature R1 . The resin on the curved portions 425A and 425B is provided in an extent such that the outer radius of curvature R2 ' has a desired length, i.e. the length of the outer radius of curvature R2 ' is smaller than the sum of the length of inner radius of curvature R1 ' and the thickness W. The resin may e.g. be provided such that the outer radius of curvature R2 ' is equal to the inner radius of curvature R1 ' .

Just as for the structure 20 this structure 40 may be used in aircraft applications as a reinforcing element such as a rib or a stringer. In figure 7 the structure 40 has been positioned on a shell 1 1. Just as for the structure 1 B there is a space 419 between the respective curved portions 405A and 405B and the shell 1 1 . However, due to the decreased outer radius of curvature R2, the space 419 is much smaller than the space 19 of the structure 1 B according to the state of the art. Therefore the structure 40 according to this embodiment is advantageous, when used together with a shell 1 1 , in comparison with a structure according to the state of the art without the resin 21 .

The manufacturing method of the structures 10 or 30 is described here below. The first step A (shown in figure 8A) is to provide a semi cured lay-up 100 or 300. The semi cured lay-up later forms the actual structure 10 or 30, when it has been cured. The semi cured lay-up 100 or 300 is provided by positioning semi cured sheets 3 of composite material on a first forming tool 55 or 57 (shown in figure 9). The sheets 3 of composite material are preferably prepregs. The forming tool 55 or 57 is chosen so that the stacked sheets 3, when positioned on the first forming tool 55 or 57, obtain the desired curved form, i.e. either the form of the structure 10 with one curved portion 105 or the form of the structure 30 with two curved portions 305, 325. The forming tool 55 or 57 has a female shape or a male shape. This means that the forming tool 55 or 57 may form the semi cured lay-up 100 or 300 from the inner surface 133 or 333 or from the outer surface 135 or 335.

In order to decrease the outer radii R2 or R2 ' of the semi cured lay-up 100 or 300, resin 21 is applied between at least two of the sheets 3 of composite material on the portions of the sheets 3 forming the at least one curved portion 105, 305 and 325. The desired outer radii R2 or R2 ' determine the thickness of the resin 21 between the sheets 3, and/or the number of sheets 3 being provided with the resin.

The semi cured lay-up 100 or 300 may also be formed by a second forming tool 55 or 57 (shown in figure 9). If the first forming tool 55 or 57 is of female form, and the second forming tool 55 or 57 is of male form and inversely.

In the final step B (showed in figure 8A), the semi cured lay-up 100 or 300 is cured in a curing tool. Preferably the resin has a curing temperature, which is lower than the curing temperature of sheets 3 of composite material. In this way the resin 21 works as a forming tool, forming the sheets of composite material so that they follow the form of the resin 21 during the curing.

The manufacturing method of the structures 20 and 40 is essentially equal to the manufacturing method described here above regarding the structures 10 and 30. This manufacturing method is schematically illustrated in figure 8B. The first step A is almost similar to the first step A in figure 8A. The difference is that instead of providing one semi cured lay-up, a first semi cured lay-up 213 or 413 and a reversed second semi cured lay-up 215 or 415 are provided. In the second step A' the first semi cured lay-up 213 or 413 and the second semi cured lay-up 215 or 415 are positioned adjacent each other so that the outer surface 217A or 417A of the web part 209A or 409A of the first semi cured lay-up 213 or 413 abuts an outer surface 217B or 417B of the web part 209B or 409B of the reversed second semi cured lay- up 215 or 415. In the third step B the first semi cured lay-ups 213 or 413 and the second semi cured lay-ups 215 or 415 are co-cured in the curing tool 47.

Figure 9 illustrates the curing process of the structure 10 in a curing tool 47. The curing tool 47 comprises a vacuum bag 53, a pump 54 for pumping out air, and heating means 59. The curing procedure is as follows: The semi cured lay-up 100 is positioned on a frame 52 and it is sealed in the vacuum bag 53. The forming tools 55 and/or 57 may also be sealed within the vacuum bag. Air is evacuated from the vacuum bag 53. The semi cured lay-up is heated by means of heating means 59. Thereafter it is cooled and removed from the curing tool 47.

The present invention is of course not in any way restricted to the preferred embodiments described above, but many possibilities to modifications, or

combinations of the described embodiments, thereof should be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.

For instance, present invention can be applied to any curved structure made of sheets of composite material, being provided with resin between the sheets. An example of such a structure 50 is shown in figure 10. The figure 10 shows a cut view of the structure 50 having a curved portion 505. The figure also shows a semicured lay-up 500 of the curved structure 50. Only the curved portion 505 is showed in the figure. The rest of the structure 50 can principally have any shape. The structure 50 may also simply consist of the curved portion 505. The curved portion 505 of the structure 50 has an inner radius of curvature R1 , an outer radius of curvature R. The stacked prepregs have a thickness W (not showed). Resin 21 is provided between the sheets 3 in an extent such that the outer radius of curvature R2 has a desired length. The resin may e.g. be provided such that the outer radius of curvature R2 is equal to the inner radius of curvature R1 . The method for manufacturing the structure 50 is equal to the method for manufacturing the structures 10 and 30. This structure 50 can be used e.g. as a tool of composite material, which tool must have a certain outer radius of curvature R2.

In the figures 5 and 7 the radii R2 of the reversed structure elements are illustrated as having the same length. The structures 20 and 40 may comprise two reversed structure elements having different reversed outer radii R2. This means that the resin is not applied symmetrically on both structure elements so the space 219 or 419 under the web 209 or 409 will not be symmetrical. This embodiment is not showed.

Similarly, in the figures 5 and 7 the thickness of the first structure element is illustrated as being equal to the thickness of the second structure element. However, the thickness of the first structure element may differ from the thickness of the second structure element. This is not showed.

The word "curved" in the present application means that the structure has been bent or folded into a curved shape. The strucure is preferably curved or folded about 90°, such as shown in the figures 4-7 and 9. However, the structure may also be only slightly curved, such as e.g. 45° or less, such as shown in figure 10.

The wording radius of curvature shall be interpreted as a curvature with one radius or a curvature with several different radii.

The resin 21 may be applied as a resin film, but it may also be applied as a resin layer. The invention is particularly, but not exclusively, applicable to larger aircraft such as passenger carrying aircraft or freight carrying aircraft.




 
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