Method for reducing deformation of aircraft skin co-curing plate

Abstract

The invention discloses a method for reducing deformation of an aircraft skin co-curing plate, the aircraft skin co-curing plate comprises 1-4 wave-absorbing prepreg layers and 8-15 structural prepreg layers which are sequentially laid on the surface of a tool from bottom to top, and 1-4 flexible buffer layers are laid between the wave-absorbing prepreg layers and the structural prepreg layers. And then the wave-absorbing prepreg layer, the flexible buffer layer and the structural prepreg layer are cured and formed through a curing process. By additionally arranging the flexible buffer layer, deformation independently generated by co-curing of the wave-absorbing prepreg or the structural prepreg can be buffered, so that the deformation of the whole plate is reduced under the condition that the temperature resistance of the wave-absorbing prepreg is not changed; the flexible buffer layer is reserved along with curing extrusion in the curing process, and it can be guaranteed that the temperature resistance of the whole plate is basically unchanged; by controlling the thickness of the flexible buffer layer, the specific wave band absorption performance is improved, and the positive progressive significance is achieved for production and manufacturing of the invisible skin.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, and in particular to a method for reducing deformation of aircraft skin co-cured panels. Background Art

[0002] At present, the aircraft skin preparation plan is to first lay the absorbing prepreg on the tooling surface, and then lay the structural prepreg and adopt co-curing molding. However, since the resin formula and fiber system used by the absorbing prepreg and the structural prepreg are different, the two deform and pull each other during the co-curing process, resulting in huge overall deformation, which affects the subsequent assembly. Some technical means reduce the overall deformation of the panel by adding flexible resin to the absorbing prepreg, but there is a disadvantage of greatly reducing the glass transition temperature of the absorbing prepreg and reducing its temperature resistance. Therefore, there is an urgent need for a method to reduce the deformation of the co-cured panel of the aircraft skin while ensuring that the glass transition temperature remains unchanged. Summary of the invention

[0003] The object of the present invention is to provide a method for reducing the deformation of co-cured panels of aircraft skins, which can significantly reduce the deformation of co-cured panels and does not reduce the temperature resistance of absorbing prepregs.

[0004] The present invention is achieved through the following technical scheme: a method for reducing deformation of an aircraft skin co-cured panel, wherein the aircraft skin co-cured panel comprises 1 to 4 absorbing prepreg layers and 8 to 15 structural prepreg layers sequentially laid from bottom to top on a tooling surface, 1 to 4 flexible buffer layers are laid between the absorbing prepreg layers and the structural prepreg layers, and then the absorbing prepreg layers, the flexible buffer layers and the structural prepreg layers are cured and formed by a carbon fiber prepreg curing process.

[0005] The principle of this technical solution is to set a flexible buffer layer between the absorbing prepreg layer and the structural prepreg layer. The flexible buffer layer can buffer the deformation caused by the co-curing of the absorbing prepreg layer or the structural prepreg layer, so as to achieve a significant reduction in the deformation of the overall panel while ensuring that the temperature resistance of the absorbing prepreg remains unchanged. In addition, the flexible adhesive film is located between the absorbing prepreg and the carbon fiber prepreg, and participates in the co-curing of the overall panel. During the curing process, it is extruded and retained as the curing is carried out, which can ensure that the temperature resistance of the overall panel remains unchanged. Among them, the absorbing prepreg layer plays a role in absorbing waves, the flexible buffer layer plays a role in reducing deformation and adjusting the peak position of the absorbing peak, and the structural prepreg layer plays a role in bearing.

[0006] In order to better implement the method of the present invention, further, the absorbing prepreg layer is mainly composed of an absorbing resin layer, the absorbing resin layer is composited by an absorbent and a resin, the absorbent is at least one of carbon black and carbonyl iron, and the mass fraction of the absorbent in the absorbing resin is 0.1-99%; the mass of the absorbing resin layer per square meter is 100g-1000g.

[0007] In order to better implement the method of the present invention, further, the absorbing prepreg layer also includes a fiber carrier; the fiber carrier is made of at least one of glass fiber, aramid fiber, and glass felt.

[0008] In order to better implement the method of the present invention, further, the absorbing prepreg layer is composited by 1-2 absorbing resin layers and 1 fiber carrier layer.

[0009] In order to better implement the method of the present invention, further, the flexible buffer layer is composited by two substances A and B, wherein A is at least one of flexible resin polyurethane, natural rubber, and silicone rubber, and B is at least one of epoxy resin or bismaleimide resin.

[0010] In order to better implement the method of the present invention, further, the flexible buffer layer is also added with a curing agent and an inert accelerator, the mass ratio of the flexible buffer layer, the curing agent, and the inert accelerator is 100:1~20:1~10, and the mass of the flexible buffer layer per square meter is 10g~500g.

[0011] In order to better implement the method of the present invention, further, an inert promoter is added to both the absorbing prepreg layer and the structural prepreg layer, and the amount of the inert promoter added to the absorbing prepreg layer and the structural prepreg layer is less than the amount added to the flexible buffer layer.

[0012] In order to better implement the method of the present invention, further, the thickness of the single-layer absorbing prepreg layer is 0.1 mm to 1 mm.

[0013] In order to better implement the method of the present invention, further, the thickness of the flexible buffer layer is 0.01 mm to 0.1 mm.

[0014] In order to better implement the method of the present invention, further, the thickness of the structural prepreg layer is 0.1 mm to 1 mm.

[0015] In order to better implement the method of the present invention, further, the solidified plate formed by solidification is also encapsulated on all sides with multiple layers of adhesive absorbing materials.

[0016] In order to better implement the method of the present invention, further, the curing process is to first pressurize 0.5~0.9MPa, heat to 130℃~180℃ and cure for 4h~10h to complete the curing of the absorbing prepreg layer and the structural prepreg layer, and then heat to 190℃~220℃ and cure for 0.5h~2h to complete the curing of the flexible buffer layer.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The present invention arranges a flexible buffer layer between the absorbing prepreg and the structural prepreg. Through the curing process control, the absorbing prepreg and the structural prepreg on both sides are cured first, and the flexible buffer layer is cured later. Therefore, the flexible buffer layer can buffer the deformation caused by the co-curing of the absorbing prepreg or the structural prepreg alone, and the formula of the absorbing prepreg is not changed, thereby achieving the situation that the temperature resistance of the absorbing prepreg remains unchanged, and the deformation of the overall panel is greatly reduced; (2) In the present invention, the flexible buffer layer is located between the absorbing prepreg layer and the structural prepreg layer, and participates in the co-curing of the overall panel. During the curing process, the flexible buffer layer is squeezed out under the action of the absorbing glue material and pressure, thereby ensuring that the temperature resistance of the overall panel remains unchanged; (3) The present invention adjusts the wave-absorbing performance of the entire panel by controlling the thickness of the flexible buffer layer, thereby improving the absorption performance in a specific band, and further realizing the absorption of the specific band by the stealth skin, which has a positive progressive significance for the production and manufacturing of the stealth skin. DETAILED DESCRIPTION

[0018] In order to make the purpose, process conditions and advantages of the present invention more clearly understood, the present invention is further described in detail in conjunction with the following embodiments, but the embodiments of the present invention are not limited thereto. Without departing from the above-mentioned technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the field, which should all be included in the scope of the present invention. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] Embodiment 1: The present embodiment provides a stealth skin, which is formed by sequentially stacking 4 layers of absorbing prepreg layers, 1 layer of flexible buffer layer, and 10 layers of structural prepreg layers on the surface of the tooling and curing them into a 300mm*300mm panel using a carbon fiber prepreg curing process.

[0020] The absorbing prepreg layer is a composite layer consisting of two absorbing resin layers, upper and lower, and a glass felt layer in the middle. The absorbing resin layer is prepared by adding 50% carbonyl iron absorber to epoxy resin. The mass of the prepared absorbing resin layer is 300g per square meter and the thickness of a single layer is 0.2mm.

[0021] The flexible buffer layer is made of 87% silicone rubber, 3% curing agent, 5% inert accelerator, and 5% epoxy resin by mass. The mass of the prepared flexible buffer layer is 20g per square meter, and the thickness of the single layer is 0.05mm. The inert accelerator plays a role in delaying curing. For example, if the curing time before addition is 30 minutes, the curing time can be increased to 60 minutes by adding the inert accelerator. It should be added to the flexible buffer layer so that the flexible buffer layer can lag behind the curing of the structural layer / wave-absorbing prepreg, thereby ensuring that the flexible layer still has good flexibility during the curing process of the structural layer / wave-absorbing prepreg, and the effect of reducing deformation can be achieved. In addition, in order to ensure the curing of silicone rubber in the flexible buffer layer, a curing agent needs to be added. The curing agent is generally a common peroxide, such as benzoyl oxide, butyl tert-butyl ketone peroxide, etc.

[0022] The structural prepreg layer is composed of carbon fiber and resin.

[0023] The specific curing process is to first pressurize at 0.8 MPa, heat up to 180°C and cure for 6 hours to complete the curing of the absorbing prepreg layer and the structural prepreg layer, and then heat up to 200°C and cure for 1 hour to complete the curing of the flexible buffer layer.

[0024] The final invisible skin has an X-band vertical reflectivity of -4.7dB. The functional layer of the panel is placed downward on the table, with the highest point of the functional layer 2.5mm away from the table. The glass transition temperature of the single absorbing prepreg is 230℃.

[0025] Embodiment 2: The present embodiment provides a stealth skin, which is formed by sequentially stacking 4 layers of absorbing prepreg layers, 4 layers of flexible buffer layers, and 10 layers of structural prepreg layers on the surface of a tooling and curing them into a 300mm*300mm panel using a carbon fiber prepreg curing process.

[0026] The absorbing prepreg layer is a composite layer consisting of two absorbing resin layers, upper and lower, and a glass felt layer in the middle. The absorbing resin layer is prepared by adding 50% carbonyl iron absorber to epoxy resin. The mass of the prepared absorbing resin layer is 300g per square meter and the thickness of a single layer is 0.2mm.

[0027] The flexible buffer layer is prepared by 87% silicone rubber, 3% curing agent, 5% inert accelerator, and 5% epoxy resin by mass. The mass of the prepared flexible buffer layer is 20g per square meter and the thickness of a single layer is 0.05mm.

[0028] The structural prepreg layer is composed of carbon fiber and resin.

[0029] The specific curing process is to first pressurize at 0.8 MPa, heat up to 180°C and cure for 6 hours to complete the curing of the absorbing prepreg layer and the structural prepreg layer, and then heat up to 200°C and cure for 1 hour to complete the curing of the flexible buffer layer.

[0030] The final invisible skin has an X-band vertical reflectivity of -8.2dB. The functional layer of the panel is placed downward on the table, with the highest point of the functional layer 2.0mm away from the table. The glass transition temperature of the single absorbing prepreg is 230℃.

[0031] Embodiment 3: The present embodiment provides a stealth skin, which is formed by sequentially stacking 4 layers of absorbing prepreg layers, 1 layer of flexible buffer layer, and 10 layers of structural prepreg layers on the surface of a tooling and curing them into a 300mm*300mm panel using a carbon fiber prepreg curing process.

[0032] The absorbing prepreg layer is a composite layer consisting of two absorbing resin layers, upper and lower, and a middle layer of aramid fiber. The absorbing resin layer is prepared by adding 50% carbonyl iron absorber to epoxy resin. The mass of the prepared absorbing resin layer is 300g per square meter and the thickness of a single layer is 0.2mm.

[0033] The flexible buffer layer is prepared by 87% silicone rubber, 3% curing agent, 5% inert accelerator, and 5% epoxy resin by mass. The mass of the prepared flexible buffer layer is 20g per square meter and the thickness of a single layer is 0.05mm.

[0034] The structural prepreg layer is composed of carbon fiber and resin.

[0035] The specific curing process is to first pressurize at 0.8 MPa, heat up to 180°C and cure for 6 hours to complete the curing of the absorbing prepreg layer and the structural prepreg layer, and then heat up to 200°C and cure for 1 hour to complete the curing of the flexible buffer layer.

[0036] The final invisible skin has an X-band vertical reflectivity of -4.5dB. The functional layer of the panel is placed downward on the table, with the highest point of the functional layer 3.7mm away from the table. The glass transition temperature of the single absorbing prepreg is 230°C.

[0037] Embodiment 4: The present embodiment provides a stealth skin, which is formed by sequentially stacking 4 layers of absorbing prepreg layers, 4 layers of flexible buffer layers, and 10 layers of structural prepreg layers on the surface of a tooling and curing them into a 300mm*300mm panel using a carbon fiber prepreg curing process.

[0038] The absorbing prepreg layer is a composite layer consisting of two absorbing resin layers, upper and lower, and a glass felt layer in the middle. The absorbing resin layer is prepared by adding 50% carbonyl iron absorber to epoxy resin. The mass of the prepared absorbing resin layer is 300g per square meter and the thickness of a single layer is 0.2mm.

[0039] The flexible buffer layer is prepared by 58% silicone rubber, 2% curing agent, 5% inert accelerator, and 35% epoxy resin by mass. The mass of the prepared flexible buffer layer is 20g per square meter, and the thickness of a single layer is 0.05mm.

[0040] The structural prepreg layer is composed of carbon fiber and resin.

[0041] The specific curing process is to first pressurize to 0.56MPa, heat to 180℃ and cure for 6h to complete the curing of the absorbing prepreg layer and the structural prepreg layer, and then heat to 200℃ and cure for 1h to complete the curing of the flexible buffer layer.

[0042] The final invisible skin has an X-band vertical reflectivity of -9.6dB. The functional layer of the panel is placed downward on the table, with the highest point of the functional layer being 1.4mm away from the table. The glass transition temperature of the single absorbing prepreg is 230°C.

[0043] Embodiment 5: In order to verify the effect of the flexible buffer layer, this embodiment prepares an invisible skin without adding a flexible buffer layer on the basis of the above embodiment. The invisible skin is prepared by sequentially stacking 4 layers of absorbing prepreg layers and 10 layers of structural prepreg layers on the surface of the tooling and curing them into a 300mm*300mm panel using a carbon fiber prepreg curing process.

[0044] The absorbing prepreg layer is a composite layer consisting of two absorbing resin layers, upper and lower, and a glass felt layer in the middle. The absorbing resin layer is prepared by adding 50% carbonyl iron absorber to epoxy resin. The mass of the prepared absorbing resin layer is 300g per square meter and the thickness of a single layer is 0.2mm.

[0045] The structural prepreg layers consist of carbon fibers.

[0046] The specific curing process is to pressurize 0.8MPa, heat to 180°C and cure for 6 hours to complete the curing of the absorbing prepreg layer and the structural prepreg layer.

[0047] The final invisible skin has an X-band vertical reflectivity of -3.8dB. The functional layer of the panel is placed downward on the table, with the highest point of the functional layer being 12.6mm away from the table. The glass transition temperature of the single absorbing prepreg is 230°C.

[0048] Embodiment 6: In order to verify the influence of the flexible buffer layer on the glass transition temperature of the absorbing prepreg layer, the glass transition temperature of the absorbing prepreg is directly tested. The absorbing prepreg layer is prepared by mixing carbonyl iron, polyurethane and epoxy resin in a ratio of 50:45:5 to prepare an absorbing resin layer, the mass of which is 300g per square meter. The upper and lower absorbing prepreg layers and the middle layer of glass felt are combined to form an absorbing prepreg layer, and the thickness of the single layer is 0.2mm. The specific curing process is to pressurize 0.8MPa, heat to 180℃ and cure for 6h.

[0049] The final invisible skin has an X-band vertical reflectivity of -4.3dB. The functional layer of the panel is placed downward on the table, with the highest point of the functional layer being 5.2mm away from the table. The glass transition temperature of the separate absorbing prepreg is 182°C.

[0050] The performance of the cured panels prepared in Examples 1 to 6 above was tested, as shown in Table 1: Table 1 Performance test of cured panels

[0051] According to the content of Table 1, the glass transition temperature of the absorbing prepreg is the heat resistance of the panel. The higher the glass transition temperature, the better the heat resistance of the panel. It can be seen from the above test results that in Examples 1-4 of the present application, a flexible buffer layer is set between the absorbing prepreg and the structural prepreg. The deformation of the panel after curing is significantly reduced compared with Example 5 (without a flexible layer), which can effectively reduce deformation.

[0052] In Examples 1-4 of the present application, a flexible layer is provided between the absorbing prepreg and the structural prepreg. After curing, the glass transition temperature of the panel does not decrease compared with Example 6 (where the flexible layer is not provided and the flexible material is directly added to the absorbing prepreg), and the glass transition temperature can be maintained at 230°C, which has outstanding benefits in high temperature resistance in the aerospace field.

[0053] Embodiments 1 and 2 provide a method for changing the absorption peak position by adjusting the thickness of the flexible layer to increase the wave absorbing performance of the panel; embodiments 2 and 4 provide a method for adjusting the absorption peak position by process control.

[0054] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for reducing deformation of an aircraft skin co-cured panel, wherein the aircraft skin co-cured panel comprises 1 to 4 layers of absorbing prepreg layers and 8 to 15 layers of structural prepreg layers sequentially laid from bottom to top on a tooling surface, characterized in that: One to four layers of flexible buffer layers are laid between the absorbing prepreg layer and the structural prepreg layer, and then the absorbing prepreg layer, the flexible buffer layer and the structural prepreg layer are cured and formed through a curing process.

2. A method for reducing deformation of aircraft skin co-cured panels according to claim 1, characterized in that: The absorbing prepreg layer is mainly composed of an absorbing resin layer, which is composited by an absorbent and a resin. The absorbent is at least one of carbon black and carbonyl iron, and the mass fraction of the absorbent in the absorbing resin is 0.1-99%; the mass per square meter of the absorbing resin layer is 100g-1000g.

3. A method for reducing deformation of aircraft skin co-cured panels according to claim 2, characterized in that: The wave-absorbing prepreg layer also includes a fiber carrier; the fiber carrier is made of at least one of glass fiber, aramid fiber, and glass felt.

4. A method for reducing deformation of aircraft skin co-cured panels according to claim 3, characterized in that: The wave-absorbing prepreg layer is composited by 1-2 layers of wave-absorbing resin layers and 1 layer of fiber carrier.

5. A method for reducing deformation of aircraft skin co-cured panels according to any one of claims 2 to 4, characterized in that: The flexible buffer layer is composited by two substances A and B, wherein A is at least one of flexible resin polyurethane, natural rubber, and silicone rubber, and B is at least one of epoxy resin or bismaleimide resin.

6. A method for reducing deformation of aircraft skin co-cured panels according to claim 5, characterized in that: The flexible buffer layer is further added with a curing agent and an inert accelerator, the mass ratio of the flexible buffer layer, the curing agent and the inert accelerator is 100:1-20:1-10, and the mass of the flexible buffer layer per square meter is 10g-500g.

7. A method for reducing deformation of aircraft skin co-cured panels according to claim 6, characterized in that: Inert promoters are added to the absorbing prepreg layer and the structural prepreg layer, and the amount of the inert promoter added to the absorbing prepreg layer and the structural prepreg layer is less than the amount added to the flexible buffer layer.

8. A method for reducing deformation of aircraft skin co-cured panels according to any one of claims 1 to 4, characterized in that: The thickness of the single-layer absorbing prepreg layer is 0.1 mm to 1 mm; the thickness of the flexible buffer layer is 0.01 mm to 0.1 mm; and the thickness of the structural prepreg layer is 0.1 mm to 1 mm.

9. A method for reducing deformation of aircraft skin co-cured panels according to any one of claims 1 to 4, characterized in that: The solidified plate is also encapsulated on all sides with multiple layers of adhesive absorbing materials.

10. A method for reducing deformation of aircraft skin co-cured panels according to any one of claims 1 to 4, characterized in that: The curing process is to first pressurize 0.5~0.9MPa, heat up to 130℃~180℃ for curing for 4h~10h to complete the curing of the absorbing prepreg layer and the structural prepreg layer, and then heat up to 190℃~220℃ for curing for 0.5h~2h to complete the curing of the flexible buffer layer.

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