Foam sandwich structure composite airfoil and integral forming method thereof

Abstract

The application discloses a kind of foam sandwich structure composite wing surfaces and its forming method, belong to composite material design forming technical field.The present application is to solve the defects such as insufficient foam unloading forming pressure, volatile parts cannot be discharged in the forming process of traditional composite wing surface, mainly using mould pressing co-curing forming process, and specific structure's glue hole is designed in foam core material to optimize resin fluidity and gas discharge.The present application can effectively improve the overall quality of composite wing surface, avoid defects such as glue deficiency, bubble and delamination, ensure the uniform distribution of resin in the curing process, so as to improve the compactness, uniformity and structural stability of composite material, enhance the resistance performance and durability of product.

Description

TECHNICAL FIELD

[0001] The application provides a foam sandwich structure composite wing surface and an integral forming method thereof, and belongs to the technical field of composite material design and forming. BACKGROUND

[0002] The weight of an aircraft is closely related to its performance and economic benefits. In the development process of the aircraft, reducing the structural weight is one of the core goals. The composite wing surface is widely used in the field of aerospace due to its excellent mechanical properties, such as high specific stiffness and specific strength, and excellent fatigue resistance and corrosion resistance. In the field of composite materials, the foam sandwich structure is widely used in the manufacture of aerospace structural parts due to its light weight and high strength. However, in the traditional co-curing forming process, the foam sandwich structure usually cannot provide sufficient internal pressure to ensure that the volatiles inside the prepreg are completely discharged during the curing process, resulting in defects such as bubbles or delamination inside the resin-based composite material. The internal debonding and delamination of the composite wing surface during the forming process has a significant impact on the mechanical properties of the main load-bearing beam component of the composite material. This will cause discontinuous stress transfer inside the material, thereby affecting the overall mechanical properties. Debonding and delamination may cause problems such as reduced stiffness, reduced strength, reduced fatigue life, reduced impact performance, and reduced stability.

[0003] Therefore, how to improve the internal quality of the foam sandwich composite wing surface during the co-curing forming process and reduce the risk of delamination and debonding has become a technical problem to be solved in composite design and manufacturing. Therefore, in order to ensure the flight safety and performance of the aircraft, it is necessary to prevent and detect the debonding and delamination phenomenon inside the composite material through strict quality control and detection means, and to improve the reliability of the main load-bearing beam component through design optimization and manufacturing process improvement. SUMMARY

[0004] The purpose of the present application is to provide a foam sandwich structure composite wing surface and an integral forming method thereof, which can enhance the internal pressure during the curing process by reasonably designing the foam core material to have appropriate flow hole structure, thereby effectively removing the volatiles in the prepreg and reducing the occurrence of bubbles and delamination, and further improving the structural performance of the wing surface product.

[0005] The technical scheme adopted by the present application to achieve the purpose is as follows:

[0006] In a first aspect, the present application provides a foam sandwich structure composite wing surface, comprising a skin and an internal support structure.

[0007] The internal support structure comprises a metal joint, a foam core material and a plurality of reinforcing rib structures.

[0008] The foam core material comprises an upper wing surface and a lower wing surface, and is provided with a plurality of flow holes.

[0009] The inner embedded end of the metal joint is butted against the foam core material to form a main structure of the internal support structure;

[0010] The stiffener structure is formed by laminating multiple layers of fiber prepreg, is distributed on the foam core material at intervals, and connects the foam core material and the skin.

[0011] Preferably, at least one of the stiffener structures is wound outside the joint between the metal joint and the foam.

[0012] Preferably, a layer of adhesive film is further covered on the outer surface of the foam core material.

[0013] Preferably, the glue flow hole is a through hole or a blind hole penetrating through the foam core material.

[0014] Preferably, the shape of the glue flow hole is square, circular, triangular, or strip-shaped, etc.

[0015] Preferably, the bottom angle of the glue flow hole is a positive bevel, a negative bevel, or a round angle.

[0016] In a second aspect, the present application provides a method for integrally forming a foam sandwich structure composite wing surface, comprising the following steps:

[0017] 1) According to the number of layers and the adhesive content of the foam outer layer prepreg, the array density, depth and aperture of the glue flow hole are designed;

[0018] 2) The foam core material is machined to form the glue flow hole;

[0019] 3) The surface debris of the foam core material is cleaned, and the foam is dried;

[0020] 4) The metal joint is sandblasted, coated with adhesive, and then butted against the foam core material, and then covered with adhesive film for fixation; the fiber prepreg of the stiffener structure is laid on the foam core material for forming the internal support structure;

[0021] 5) The fiber prepreg of the skin is laid on the outside of the internal support structure to obtain a wing surface structure to be cured;

[0022] 6) The wing surface structure to be cured is loaded into a mold for hot-pressing and curing, and after cooling, the mold is demolded to obtain a foam sandwich structure composite wing surface.

[0023] Preferably, in step 1), according to the area and the number of layers of prepreg, the volume of resin to be excluded is calculated as 6% to 10% of the weight of the prepreg to determine the total volume of the glue flow hole; and the density and aperture of the glue flow hole are adjusted in combination with the resin flowability.

[0024] Preferably, in step 1), the aperture and density of the glue flow hole are determined by finite element analysis simulation or experimental forming test.

[0025] Preferably, the depth of the glue flow hole in step 1) is 1-3 times the total thickness of the fiber prepreg of the skin and the stiffener structure, and the hole area is 0.2-1 cm 2 The hole spacing is 50-200 mm.

[0026] Preferably, the drying method in step 3) is to place the foam core material in an oven, dry at 80±5℃ for 1 hour, and then heat to 130±5℃ for 3 hours.

[0027] Preferably, the layup direction of the fiber prepreg of the stiffener structure in step 4) is [0 / +45 / 0 / 0 / -45 / 0].

[0028] Preferably, the layup direction of the fiber prepreg of the skin in step 5) is [45, 0, -45, 0, 0, 0, 90, 0, 45, 0, -45, 0]s.

[0029] The beneficial effects obtained by the present application are as follows:

[0030] 1. According to the number of layers and the glue content of the foam outer layer prepreg, the array density, depth and hole diameter of the glue flow hole are designed, the more the number of layers and the higher the glue content, the more glue flow holes are designed to ensure that the resin can flow smoothly into the foam interior; the resin volume to be excluded is estimated by the area and the number of layers of the prepreg multiplied by 6%-10% of the weight of the prepreg, the total volume requirement of the glue flow hole is determined, and the density and hole diameter of the glue flow hole are adjusted according to the resin flowability, so that the design of the glue flow hole is more accurate and reasonable.

[0031] 2. By setting the glue flow hole in the foam core material, the formed volatile substances are drained to the inside of the foam during the resin curing process, avoiding the retention of volatiles and providing an exhaust passage, effectively reducing bubbles and delamination defects, improving the density and uniformity of the composite material inside, and ensuring the structural stability and durability.

[0032] 3. By reasonably designing the glue flow hole, the resin can smoothly exhaust during the curing process, the resin can fully infiltrate the fibers in the composite material, reducing the lack of glue and delamination in the skin, improving the resistance performance and durability of the composite material wing surface, and the appearance is more accurate without glue lack phenomenon.

[0033] 4. The internal support structure of the present application is coated with adhesive film and laid with stiffener prepreg, so that the wing surface can be integrally molded, without the need for upper and lower wing surface bonding, simplifying the manufacturing process, reducing production cost, improving production efficiency, and saving energy.

[0034] 5. The design of the flow holes in this invention is flexible and diverse. The number and array density of flow holes can be adjusted according to the resin content of the prepreg, the layup thickness and rheological properties. The shape of the flow holes can be square, round, triangular or rectangular. The openings can be set with positive bevels, negative bevels or rounded corners to optimize the amount of glue stored and reduce appearance defects caused by the area of ​​the holes.

[0035] 6. This invention can use simulation tools such as finite element analysis (FEA) to simulate the design of the flow holes, or verify whether the design of the flow holes meets the requirements of resin flow and venting through molding tests of experimental samples, thereby ensuring the quality of airfoil molding. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the composite material airfoil with circular blind-hole adhesive flow holes in Example 1;

[0037] Figure 2 This is a schematic diagram of the composite material airfoil with circular through-hole adhesive flow holes in Example 2;

[0038] Figure 3 This is a schematic diagram of the sandwich foam composite material wing surface with elongated chamfered adhesive flow holes in Example 3;

[0039] Figure 4 A schematic diagram illustrating the specifications for measuring the size of a single defect. Detailed Implementation

[0040] To make the various technical features, advantages, or effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings.

[0041] Example 1

[0042] This embodiment provides a foam sandwich composite material wing surface, such as... Figure 1 As shown, it includes a skin 11 and an internal support structure. The skin 11 is located on the outer layer of the overall structure and serves as the main surface of the composite material airfoil. For ease of presentation of the internal support structure, Figure 1 The skin 11 is shown in perspective. The internal support structure includes a metal joint 12, a reinforcing rib structure 13, a foam core material 14, and a film layer (not shown). The metal joint 12 is used to connect to the aircraft deployment mechanism, and its embedded end connects to the foam core material 14 to form the main frame of the internal support structure of the wing surface. The reinforcing rib structure 13 is composed of multiple layers of prepreg and is wrapped around the outside of the joint between the metal joint 12 and the foam core material 14 to provide the necessary mechanical strength. The foam core material 14 serves to reduce weight and improve thermal insulation performance. The film layer covers the outer surface of the foam core material 14, increasing the mass stability and sealing between the internal support structure and the skin 11. The foam core material 14 has an array of circular adhesive flow holes 15, which are blind holes.

[0043] The foam sandwich structure composite wing surface adopts a molding co-curing forming process, and the specific implementation process is as follows:

[0044] 1) Designing flow holes: according to the number of prepreg layers (22 layers) of the thickest area of the wing surface outer skin, the resin content (38%) of the prepreg, and the curing properties of the resin (80°C for half an hour with pressure, 120°C for 2 hours), and considering the rheological properties of the resin (the minimum viscosity value at 80°C is 5 Pa·s), the foam material is polymethacrylimide (foam pore diameter 0.2-0.4 mm). The flow hole is selected as a circular blind hole with a diameter of 2 mm. The hole depth and the hole spacing are 50 mm square array.

[0045] 2) Foam machine: use a numerical control engraving machine to process and form the foam core material, and process flow holes on the foam.

[0046] 3) Foam drying treatment: clean the debris on the surface of the foam, and perform drying treatment; preferably, the drying treatment step is to dry the foam in an oven at 80±5°C for 1 hour, and then heat it to 130±5°C for 3 hours of drying.

[0047] 4) Surface treatment and assembly: after sandblasting treatment of the metal joint, surface treatment is performed by brushing J-47B glue solution on the designed and processed foam. The joint is butted and pasted with the foam, and after ensuring that the visual bonding surface has no obvious gap, the whole is fixed by wrapping J-47A glue film. Then, lay the prepreg of the stiffener structure, the lay-up sequence is [0 / +45 / 90 / -45]s, to form the internal support structure of the composite wing surface.

[0048] 5) Lay the skin: lay the CCF800S / 3068 skin prepreg on the outer layer of the above internal support structure, the lay-up sequence is [45, 0, -45, 0, 0, 0, 90, 0, 45, 0, -45, 0]s, to get the laid wing surface.

[0049] 6) Curing forming: remove the residual glue and impurities on the surface of the mold to ensure that the surface of the mold is smooth and free of oil stains. After brushing 2720 release agent, the wing surface is loaded into the mold and the mold is completed. Push into the press to cure:

[0050] First stage: heat to 80°C, temperature difference 5°C, keep for 30 minutes;

[0051] Second stage: after removing the limiting gasket, press the press to 10 MPa, heat to 125°C, temperature difference 5°C, keep for 120 minutes. Remove the mold from the press and place it on the mold car, and naturally or with a fan to cool to below 50°C, and finally demold to get the product.

[0052] Example 2

[0053] This embodiment provides a foam sandwich composite material airfoil, the structure of which is largely the same as the airfoil in Embodiment 1, such as... Figure 2 As shown, the structure includes a skin 21 and an internal support structure. The internal support structure includes a metal joint 22, a reinforcing rib structure 23, a foam core material 24, and an adhesive film layer (not shown). The foam core material 24 has an array of circular adhesive flow holes 25, which are through holes. The skin 21 is located on the outer layer of the overall structure. To facilitate the presentation of the internal support structure, Figure 2 The skin of 21 is displayed using a perspective effect.

[0054] The composite material wing surface of this foam sandwich structure is manufactured using a compression molding and co-curing process, the specific implementation process of which is as follows:

[0055] 1) Design of resin flow holes: Based on the number of prepreg layers (22 layers) in the thickest area of ​​the outermost skin of the wing surface, the resin content of the prepreg (36%), and the curing properties of the resin (80℃ for half an hour under pressure, 120℃ for 2 hours curing), and considering the rheological properties of the resin (minimum viscosity of 12 Pa·s at 80℃), the foam material was designed as polymethacrylamide (foam pore size of 0.1 mm). The resin flow holes were selected as circular through-hole structures with a pore size of [missing information]. A square array with a hole depth of 5mm and a hole spacing of 50mm.

[0056] 2) Foam machining: The foam core material is shaped using a CNC engraving machine, and flow holes are machined on the foam.

[0057] 3) Foam drying treatment: Clean the debris on the surface of the foam and dry it; preferably, the drying treatment step is to dry the foam in an oven at 80±5℃ for 1 hour, and then raise the temperature to 130±5℃ for 3 hours.

[0058] 4) Surface Treatment and Assembly: After sandblasting the metal joints, apply J-47B adhesive to the designed and processed foam for surface treatment. Butt and bond the joints to the foam, ensuring no visible gaps on the mating surfaces, then cover the entire surface with J-47A adhesive film for fixation. Next, lay the prepreg for the reinforcing rib structure in a layup sequence of [0 / +45 / 90 / -45]s to form the internal support structure of the composite material wing.

[0059] 5) Laying the skin: CCF800S / 3068 skin prepreg is laid on the outer layer of the above-mentioned internal support structure. The layup sequence is [45,0,-45,0,0,0,90,0,45,0,-45,0]s, to obtain the laid wing surface.

[0060] 6) Curing: Remove the glue and impurities on the surface of the mold, and ensure that the surface of the mold is smooth and free of oil stains. After brushing the mold release agent 2720, the airfoil is loaded into the mold and the mold is completed. Push into the press for curing:

[0061] First stage: temperature rise to 80℃, temperature difference 5℃, holding time 30 minutes;

[0062] Second stage: After removing the limiting gasket, press the press to 10MPa, temperature rise to 125℃, temperature difference 5℃, holding time 120 minutes. Remove the mold from the press and place it on the mold car, and cool it naturally or with a fan to below 50℃, and finally demold to get the product.

[0063] Example 3

[0064] This example provides a foam sandwich structure composite wing surface, which has a structure substantially the same as the wing surface in Example 1, as shown in FIG. 1, including a skin 31 and an internal support structure, the internal support structure including a metal joint 32, a rib structure 33, a foam core 34, and a film layer (not shown), the foam core 34 having a long strip-shaped chamfered glue flow hole 35 arrayed thereon, which is a blind hole. The skin 31 is located on the outer layer of the overall structure, and for the purpose of presenting the internal support structure, Figure 3 The skin 31 is shown in perspective. Figure 3

[0065] The foam sandwich structure composite wing surface is formed by a mold pressing and co-curing process, and the specific implementation process is as follows:

[0066] 1) Design glue flow hole: According to the number of prepreg layers (26 layers) of the thickest area of the outer skin of the wing surface, the glue content of the prepreg (38%), and the curing properties of the resin (80℃ for half an hour, 120℃ for 2 hours), and considering the rheological properties of the resin (the minimum viscosity value at 80℃ is 25Pa·s), the foam material is polyurethane (foam pore size is 0.2-0.4mm). The foam core is designed to have a long strip-shaped chamfered glue flow hole with a size of 3mm×5mm, a hole depth of 3mm, and a square array with a hole spacing of 50mm.

[0067] 2) Foam machine: The foam core is processed by a numerical control engraving machine, and the glue flow hole is processed on the foam.

[0068] 3) Foam drying treatment: Clean the debris on the surface of the foam and perform drying treatment; preferably, the drying treatment step is to dry the foam in an oven at 80±5℃ for 1 hour, and then heat it to 130±5℃ for 3 hours.

[0069] ​4) Surface treatment and assembly: After sandblasting the metal joint, surface treatment is carried out with foam brushing J-47B glue solution designed and processed. The joint is butted and pasted with the foam, and after ensuring that the visual bonding surface has no obvious gap, the whole is fixed with J-47A glue film. Then, the pre-impregnated material of the reinforcing rib structure is laid, and the laying sequence is [0 / +45 / 90 / -45]s, forming the internal support structure of the composite wing surface.

[0070] 5) Skin laying: CCF800S / 3068 skin pre-impregnated material is laid on the outer layer of the above-mentioned internal support structure, and the laying sequence is [0, 45, 0, -45, 0, 0, 90, 90, 0, 45, 0, -45, 0]s, to obtain the laid wing surface.

[0071] 6) Curing molding: Remove the residual glue and impurities on the surface of the mold to ensure that the surface of the mold is smooth and free of oil stains. After brushing 2720 release agent, the wing surface is loaded into the mold and the mold is completed. Push into the press for curing:

[0072] First stage: temperature rise to 80°C, temperature difference 5°C, holding time 30 minutes;

[0073] Second stage: after removing the limiting gasket, press the press to 25MPa, temperature rise to 125°C, temperature difference 5°C, holding time 120 minutes. Remove the mold from the press and place it on the mold car, and naturally or with a fan to cool to below 50°C, and finally demold to obtain the product.

[0074] Foam sandwich structure composite wing surface test:

[0075] The foam sandwich structure composite wing surface formed by the embodiment is subjected to ultrasonic nondestructive testing to detect delamination defects, and the specific detection indexes are as follows:

[0076] Single defect size: Z≤30mm, wherein Z is the average size of the defect, defined as Z=(X+Y) / 2, X is the projection length of the defect measured perpendicular to Y, and Y is the minimum projection width of the defect.

[0077] Adjacent defect spacing: d≥200mm, i.e. the distance between two defects should be greater than or equal to 200mm.

[0078] As shown in Figure 4 The test results show that after ultrasonic testing, the foam sandwich structure composite wing surface meets the above requirements, and the detection indexes are similar to the skin defects of the pre-impregnated material skin independently molded under the same conditions. Through this detection, it is known that the problem of insufficient pressure of the wing skin caused by insufficient unloading pressure of the foam is successfully solved, and the defect that volatile components cannot be effectively extruded is avoided, thereby ensuring the overall quality and performance of the product.

[0079] The part of the present application not described in detail is the technology known to the person skilled in the art.

[0080] Although the present application has been disclosed in the above with examples, it is not intended to limit the present application, and the proper modification or equivalent replacement of the technical solution of the present application made by the person skilled in the art shall be covered in the protection scope of the present application, and the protection scope of the present application is defined by the claims.

Claims

1. A foam sandwich structure composite airfoil, characterized by, The skin and the internal support structure; The internal support structure comprises metal joints, a foam core and a plurality of stiffener structures; The foam core material comprises upper and lower wings, and is provided with a plurality of glue flow holes; the depth of the glue flow hole is 1-3 times of the total thickness of the fiber prepreg of the skin and the stiffener structure, and the hole area is 0.2-1 mm; the distance between the holes is 50-200 mm. The embedded end of the metal joint is butted against the foam core to form a main structure of the internal support structure; The stiffener structure is formed by stacking a plurality of layers of fiber prepreg and is distributed on the foam core in intervals to connect the foam core and the skin.

2. Foam sandwich structural composite airfoil according to claim 1, characterized in that At least one of the stiffener structures is wound outside the joint of the metal joint and the foam.

3. The foam sandwich structural composite airfoil of Claim 1, wherein, A layer of adhesive film is further coated on the outer surface of the foam core.

4. The foam sandwich structural composite airfoil of Claim 1, wherein, The glue flow hole is a through hole or a blind hole penetrating through the foam core; the glue flow hole has a square, circular, triangular or strip shape; and the bottom of the glue flow hole has a right angle, an inverse angle or a round angle.

5. A method of integrally forming a foam sandwich composite wing surface according to any one of claims 1 to 4, characterised in that, The method comprises the following steps: 1) According to the number of layers and the adhesive content of the foam outer layer prepreg, the array density, depth and aperture of the glue flow hole are designed; 2) The foam core is machined to form the glue flow hole; 3) The surface debris of the foam core is cleaned, and the foam is dried; 4) The metal joint is sandblasted, coated with adhesive and then butted against the foam core, and then covered with adhesive film for fixation; the fiber prepreg of the stiffener structure is laid on the foam core to form the internal support structure; 5) The fiber prepreg of the skin is laid on the outside of the internal support structure to obtain a wing surface structure to be cured; 6) The wing surface structure to be cured is loaded into a mold for hot pressing and curing, and then demolded after cooling to obtain a foam sandwich structure composite wing surface.

6. The method of claim 5, wherein, In step 1), according to the area and the number of layers of the prepreg, the volume of resin to be removed is calculated according to 6% to 10% of the weight of the prepreg to determine the total volume of the glue flow hole; the density and aperture of the glue flow hole are adjusted according to the resin flowability; and the aperture and density of the glue flow hole are determined through finite element analysis simulation or experimental forming test.

7. The method of claim 5, wherein, The depth of the flow glue hole in step 1) is 1-3 times of the total thickness of the fiber prepreg of the skin and the stiffener structure, and the hole area is 0.2-1 mm, and the hole spacing is 50-200 mm.

8. The method of claim 5, wherein, In step 3), the drying method is as follows: the foam core is placed in an oven, dried at 80±5℃ for 1 hour, and then dried at 130±5℃ for 3 hours.

9. The method of claim 5, wherein, In step 4), the fiber prepreg of the stiffener structure is laid in the direction of [0 / +45 / 0 / 0 / -45 / 0].

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