A wave-absorbing honeycomb composite material for forming a curved surface and a preparation method thereof

Abstract

The present application relates to a kind of wave-absorbing honeycomb composite material and its preparation method for curved surface forming, belong to wave-absorbing material preparation technical field.The present application is designed according to electrical property, places into different electromagnetic characteristics wave-absorbing adhesive film layer in different position in the unsolidified honeycomb core material cell, electromagnetic characteristics is gradient change along the cell direction, obtains impedance matching structure, wave-absorbing honeycomb is pasted on the surface (curved surface) of mould and solidified, obtains the wave-absorbing honeycomb core material after heat setting;Upper and lower surface is respectively bonded with wave-transparent skin, obtains the wave-absorbing honeycomb composite material with excellent performance, meets the stealth demand of curved surface product.The present application provides process easy to control, wave-absorbing performance, mechanical property excellent, can be used for the wave-absorbing honeycomb composite material and preparation method for curved surface forming, with excellent wave-absorbing performance in ultra-wide frequency range.

Description

TECHNICAL FIELD

[0001] The application relates to a wave-absorbing honeycomb composite material for curved surface forming and a preparation method thereof, and belongs to the technical field of wave-absorbing material preparation. BACKGROUND

[0002] Aramid paper honeycomb is a new type of lightweight structural sandwich material, which has the advantages of low density, high mechanical property and good heat resistance, and is mainly used in lightweight sandwich structures and has been widely used in aircrafts. With the development of detection technology, the stealth demand for aircrafts is higher, that is, the wave-absorbing frequency band is wider and the absorption effect is stronger. Aramid paper honeycomb has excellent electromagnetic wave transmission performance, but does not have electromagnetic wave absorption performance, and cannot be directly used in the wave-absorbing field. The conventional method is to introduce an electromagnetic wave absorber into the wall of the aramid paper wave-transparent honeycomb to achieve this.

[0003] At present, most of the existing aramid paper wave-absorbing honeycombs are prepared by the process of first preparing ordinary aramid paper without electromagnetic loss function into aramid paper wave-transparent honeycomb, then impregnating electromagnetic wave absorber glue on the honeycomb wall of the aramid paper wave-transparent honeycomb, and finally curing and forming. In patent CN114228266A, the absorber is gradiently distributed in the direction along the honeycomb cell or perpendicular to the honeycomb cell by gradient impregnation, so that an impedance matching structure is obtained, and good wave-absorbing performance is obtained. However, the wave-absorbing honeycomb obtained by the impregnation method has the problem that the absorber is attached to the cell wall and is easy to fall off, the environmental resistance is poor, and the impregnation process is difficult to control, and the process stability is poor. The impregnation process cannot be applied to carbon fibers and magnetic fibers with large length-diameter ratio, resulting in low magnetic loss performance of the aramid paper wave-absorbing honeycomb. In addition, the controllability of the impregnation process is poor, which causes the electromagnetic performance stability of the aramid paper wave-absorbing honeycomb to be not high.

[0004] To avoid the shortcomings of the impregnated wave-absorbing honeycomb, in a patent (CN112553942A) of dielectric loss aramid paper, wave-absorbing honeycomb and preparation method, a method of adding carbon fiber absorbent to aramid paper is proposed to obtain wave-absorbing aramid paper, and then a wave-absorbing honeycomb is prepared. The advantages of this method are that the absorbent in the aramid paper has good environmental resistance, the amount of absorbent added can be accurately controlled, and the process is stable; but this method is limited by the mixing papermaking process, only fiber absorbent can be added, and the amount of absorbent added should not be too high, and it does not have excellent wave-absorbing effect in the ultra-wide frequency range, and the low-frequency effect is poor; and the traditional honeycomb preparation process is adopted, the characteristics and tension of different areas of the wave-absorbing aramid paper are different, and it is difficult to ensure the uniformity of the honeycomb cells. Another method is to apply absorbent to aramid paper to obtain wave-absorbing aramid paper, and then prepare a wave-absorbing honeycomb, such as patents CN109796624A, CN202111440881.5, CN114214871A; this method can add various types of absorbent, and a large amount of absorbent can be added to meet different wave-absorbing needs; the absorbent is coated on the surface of the aramid paper to obtain wave-absorbing aramid paper, and then a wave-absorbing honeycomb is obtained by using the traditional honeycomb preparation method. However, when preparing the wave-absorbing honeycomb by this method, stretching is required to form hexagonal cells, and when the adhesion of the absorbent coating is not enough, debonding phenomenon is easy to occur. At present, both of the above methods can obtain wave-absorbing honeycomb with stable performance and excellent environmental resistance, but the absorbent content in the honeycomb is fixed and the wave-absorbing structure design is not carried out, the overall wave-absorbing honeycomb presents a single electromagnetic characteristic, there is no impedance matching design, and it is difficult to obtain excellent ultra-wide frequency wave-absorbing performance.

[0005] In order to obtain an impedance matching structure, the commonly used method at present is to introduce a wave-absorbing layer between the honeycomb sheet layers, design a wave-absorbing structure, and obtain a wave-absorbing honeycomb composite material with good wave-absorbing performance, such as the paper A-type skin composite honeycomb structure design and its wave-absorbing performance (Journal of Composite Materials, 2022, 39(3): 1180-1185). But in this structure, stress concentration points will be formed at the intersection of the cells of the two honeycomb sheets, which are easy to damage, thereby reducing the compression resistance of the overall structure; and the number of adhesive surfaces between the honeycomb layers is large, which also affects the reliability of the overall structure.

[0006] The wave-absorbing honeycomb finally obtained in the above-mentioned researches is a flat plate, which cannot be applied to some curved surface components (such as air intakes), and the cured honeycomb cannot be bent to change shape. For homogeneous wave-absorbing honeycomb, the required curved surface shape can be obtained by processing the surface. But for the impedance matching wave-absorbing structure, the thickness of each layer cannot be changed, and cannot be processed, so the curved surface contour cannot be obtained.

[0007] A wave-absorbing honeycomb with an impedance matching structure and a preparation method thereof (CN115891293A) patent, coating the absorber on aramid paper, using the template method to prepare the wave-absorbing honeycomb, having an impedance matching structure in the cell direction. Through the unit superposition, the rod is inserted into the honeycomb cell, the pressure is applied to the honeycomb cell wall, and the bonding strength of the core strip glue is ensured. The preparation method in the patent determines that the unhardened wave-absorbing honeycomb core material cannot be used to prepare the curved wave-absorbing honeycomb. SUMMARY

[0008] The present application aims to overcome the differences in the prior art, provide a process that is easy to control, has excellent wave-absorbing performance and mechanical properties, and can be used for curved surface molding. The wave-absorbing honeycomb composite material and the preparation method have excellent wave-absorbing performance in a super wide frequency range.

[0009] The present application combines the characteristics of multi-layer wave-absorbing honeycomb and proposes a wave-absorbing honeycomb composite material with an impedance matching structure and a preparation method for curved surface molding. According to the electrical performance design, different positions in the unhardened honeycomb core material cell are inserted with wave-absorbing glue film layers with different electromagnetic properties, and the electromagnetic properties change in a gradient along the cell direction to obtain an impedance matching structure. The wave-absorbing honeycomb is attached to the surface (curved surface) of the product or mold for curing to obtain a heat-set wave-absorbing honeycomb core material; the upper and lower surfaces are respectively bonded with wave-transparent skins to obtain a wave-absorbing honeycomb composite material with excellent performance, meeting the stealth requirements of curved surface products.

[0010] The technical solution of the present application is as follows:

[0011] A wave-absorbing honeycomb composite material for curved surface molding includes an upper skin, a lower skin, a honeycomb core material, and a wave-absorbing glue film layer; the honeycomb core material is obtained by curing the unhardened honeycomb core material; the wave-absorbing glue film layer is located in the cell of the honeycomb core material, and the honeycomb core material containing the wave-absorbing glue film layer is located between the upper skin and the lower skin.

[0012] Further, according to the electrical performance design, different positions in the unhardened honeycomb core material cell are inserted with wave-absorbing glue film layers with different electromagnetic properties, and the electromagnetic properties change in a gradient along the cell direction to obtain an impedance matching structure. The unhardened honeycomb core material containing the wave-absorbing glue film layer is attached to the surface (curved surface) of the product or mold for curing to obtain a heat-set wave-absorbing honeycomb core material; the upper and lower surfaces of the wave-absorbing honeycomb core material are respectively bonded with wave-transparent skins to obtain excellent wave-absorbing performance, meeting the stealth requirements of curved surface products.

[0013] Further, the unhardened honeycomb core material is aramid paper impregnated with phenolic resin, and the solvent is removed after drying. The phenolic resin is in an unhardened state, and the unhardened honeycomb core material has a heat setting capability.

[0014] Further, the wave-absorbing adhesive film layer is composed of an absorbent, an adhesive and a carrier layer, and has a thickness of 0.2mm-2mm.

[0015] Further, the absorbent has electromagnetic loss capacity and is one or more of carbon black, graphite sheet, carbon fiber, graphene and carbon nanotube, and has a content of 0.1wt%-30wt%.

[0016] Further, the adhesive is one of epoxy resin, phenolic resin and bismaleimide resin, and is preferably phenolic resin.

[0017] Further, the carrier layer is one of quartz fiber cloth and glass fiber cloth, and has a thickness of 0.04mm-0.2mm.

[0018] Further, the type of the absorbent is determined by electrical performance design, and the optimal gradient wave-absorbing structure is calculated and optimized by using electromagnetic simulation software to determine the number of the wave-absorbing adhesive film layers, the position of the wave-absorbing adhesive film layers in the honeycomb cells, the thickness of each wave-absorbing adhesive film layer and the content of the absorbent.

[0019] Further, the upper and lower skins are wave-transparent resin-based composite materials, and each comprises a reinforcing layer and a matrix. The reinforcing layer is one of quartz fiber cloth and glass fiber cloth, and the matrix is one of epoxy resin, phenolic resin and bismaleimide resin.

[0020] A preparation method of a wave-absorbing honeycomb composite material applicable to curved surface forming is realized by the following steps:

[0021] Firstly, an uncured honeycomb core material is prepared;

[0022] Secondly, a wave-absorbing adhesive film layer is prepared;

[0023] Thirdly, the wave-absorbing adhesive film layer is placed in the cells of the uncured honeycomb core material according to the electrical performance design to obtain a wave-absorbing honeycomb core material;

[0024] Fourthly, the wave-absorbing honeycomb core material is heat set;

[0025] Fifthly, the wave-absorbing honeycomb core material is bonded with a wave-transparent skin to obtain a wave-absorbing honeycomb composite material.

[0026] Further, the uncured honeycomb core material is aramid paper impregnated with phenolic resin, and the solvent is removed after drying; the phenolic resin is in an uncured state, and the uncured honeycomb core material has heat setting capacity.

[0027] Further, the wave-absorbing glue film layer is composed of an absorbent, a glue and a bearing layer. The absorbent has electromagnetic loss capacity and is one or more of carbon black, graphite sheet, carbon fiber, graphene and carbon nanotube. The glue is one of epoxy resin, phenolic resin and bismaleimide resin, and preferably phenolic resin. The bearing layer is one of quartz fiber cloth and glass fiber cloth.

[0028] Further, the wave-absorbing glue film layer is uncured and flexible, facilitating cutting into the size and shape of the honeycomb cell. The bearing layer plays a bearing role to prevent the wave-absorbing glue film from flowing during curing.

[0029] Further, the electrical performance is designed to determine the type of absorbent, and the electromagnetic simulation software is used to calculate and optimize the best gradient wave-absorbing structure to determine the number of wave-absorbing glue film layers and the position in the honeycomb cell. Then the thickness of each wave-absorbing glue film layer and the content of the absorbent are determined.

[0030] Further, the wave-absorbing glue film layer is cut according to the size and shape of the uncured honeycomb core in the third step. Then the wave-absorbing glue film is pushed into the corresponding position in the honeycomb cell in the designed order. The size of the wave-absorbing glue film layer is slightly larger than that of the honeycomb cell, which ensures that the wave-absorbing glue film layer is placed in the cell and the position remains unchanged. Moreover, the wave-absorbing glue film layer can deform with the change of the size of the cell and be firmly bonded to the honeycomb cell wall.

[0031] Further, the wave-absorbing honeycomb core is heat set in the fourth step. The uncured wave-absorbing honeycomb is placed on the surface (curved surface) of the mold, and vacuum bag pressure or hot press tank process is used for curing. The curing temperature is 180-200 DEG C, and the curing time is 2-4 hours.

[0032] Further, the wave-absorbing honeycomb core is bonded with the wave-transparent skin. The skin is a wave-transparent fiber cloth resin-based composite material. The skin can be in a cured state or an uncured state during bonding. The skin and the wave-absorbing honeycomb core are bonded using a plate-core glue.

[0033] The beneficial effects of the present application compared with the prior art are as follows:

[0034] (1) The wave-absorbing glue film layer is placed in the uncured honeycomb cell to form an impedance matching structure, which realizes accurate control of the wave-absorbing structure. The obtained wave-absorbing honeycomb core can be formed on a curved surface to meet the stealth requirements of the curved surface component, overcoming the problem that the traditional impedance matching structure cannot change the thickness and process the curved surface.

[0035] (2) The present application places the wave-absorbing glue film layer in different positions in the honeycomb cells by physical methods, obtains the impedance matching structure, and also keeps the honeycomb cells intact, overcoming the shortcomings of the multi-layer wave-absorbing honeycomb cell wall intersection and insufficient compression resistance.

[0036] (3) The present application places the wave-absorbing glue film in the honeycomb cells, can add different types of absorbents to meet different wave-absorbing needs, and can add a large amount of absorbents to have excellent wave-absorbing effect in a super wide frequency range, overcoming the shortcomings of the existing absorbent doped aramid paper wave-absorbing honeycomb, such as limited types of absorbents (only fibrous) and low absorbent content, and also overcoming the shortcomings of the aramid paper wave-absorbing honeycomb, such as thin wave-absorbing layer thickness. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a preparation process schematic diagram of the uncured wave-absorbing honeycomb core material for curved surface forming of the present application;

[0038] Figure 2 It is a preparation flow chart of the wave-absorbing honeycomb composite material for curved surface forming of the present application;

[0039] Figure 3 It is a process schematic diagram of placing the wave-absorbing glue film in the honeycomb cells of the present application. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below through specific examples and drawings.

[0041] The present application combines the characteristics of multi-layer wave-absorbing honeycomb, proposes a wave-absorbing honeycomb composite material with impedance matching structure and a preparation method for curved surface forming. According to the electrical performance design, different types of wave-absorbing glue film layers with different electromagnetic properties are placed in different positions in the uncured honeycomb core material cells, the electromagnetic properties change in a gradient along the cell direction, the impedance matching structure is obtained, and the preparation process schematic diagram is shown in Figure 1 . The wave-absorbing honeycomb is attached to the surface (curved surface) of the product or mold for curing, and the heat-set wave-absorbing honeycomb core material is obtained; the upper and lower surfaces are respectively bonded with the wave-transparent skin, and the wave-absorbing honeycomb composite material with excellent performance is obtained, meeting the stealth requirements of curved surface products.

[0042] According to the electrical performance design, the impedance matching structure of the wave-absorbing glue film in the honeycomb core material is calculated and optimized, the types and contents of the absorbents in the wave-absorbing glue film layer are determined, the thickness of the wave-absorbing glue film layer, the number of layers of the wave-absorbing glue film layer, and the position of the wave-absorbing glue film layer in the honeycomb cell are determined. Different types and contents of absorbents are mixed with the adhesive to obtain the wave-absorbing glue film layer. The mixing and coating process in the present application is a known technology in the art, and the specific process parameters are determined according to the actual production needs.

[0043] The application also provides a wave-absorbing honeycomb composite material for curved surface forming and a preparation method thereof, which are realized through the following steps: Figure 2 The application also provides a wave-absorbing honeycomb composite material for curved surface forming and a preparation method thereof, which are realized through the following steps:

[0044] 1. Preparation of uncured honeycomb core material

[0045] The uncured honeycomb core material in this step is aramid paper impregnated with phenolic resin, and the solvent is removed after drying. The phenolic resin on the honeycomb cell wall is in an uncured state and does not undergo temperature curing. The honeycomb core material is in an uncured state and has the ability to set with the deformation of the curved surface. The preparation of the uncured honeycomb core material is a known technology in the art.

[0046] 2. Preparation of wave-absorbing adhesive film layer

[0047] According to the electrical performance design, the impedance matching structure of the wave-absorbing adhesive film in the honeycomb core material is calculated and optimized to determine the type and content of the absorber in the wave-absorbing adhesive film layer, the thickness of the wave-absorbing adhesive film layer, the number of layers of the wave-absorbing adhesive film layer, and the position of the wave-absorbing adhesive film layer in the honeycomb cell.

[0048] The wave-absorbing adhesive film layer is composed of an absorber, an adhesive, and a carrier layer. The absorber has electromagnetic loss capability and is one or more of carbon black, graphite sheet, carbon fiber, graphene, and carbon nanotube. The adhesive is one of epoxy resin, phenolic resin, and bismaleimide resin, and is preferably phenolic resin. The carrier layer is one of quartz fiber cloth and glass fiber cloth.

[0049] According to the electrical performance design, different types and contents of absorbers are mixed with the adhesive and coated on the wave-transparent carrier layer to obtain different wave-absorbing adhesive film layers. The content of the absorber in the wave-absorbing adhesive film layer is 0.1wt% to 30wt%, and the thickness is 0.2mm to 2mm. The prepared wave-absorbing adhesive film layers A1, A2, A3, A4,..., An have gradually increasing absorber content and electromagnetic parameters.

[0050] 3. Placement of wave-absorbing adhesive film layer in uncured honeycomb core material cell according to electrical performance design

[0051] The wave-absorbing adhesive film layer is cut into the shape and size of the honeycomb cell, and is placed in the uncured honeycomb core material cell in the designed order and position, as shown in Figure 3 The wave-absorbing adhesive film layer is composed of a carrier layer and a wave-absorbing layer, and when placed, the carrier layer faces down and the wave-absorbing layer faces up. The size of the wave-absorbing adhesive film layer is slightly larger than the size of the honeycomb cell, which ensures that the adhesive film layer is placed in the cell and the position remains unchanged, and can deform to some extent with the change in the size of the cell and be firmly bonded to the honeycomb cell wall.

[0052] As shown in Figure 3As shown, the wave-absorbing adhesive film layer A1 is placed at the lower part of the honeycomb core material cell, and the hard metal column is used to push the adhesive film layer from the bottom to the set position. The A2, A3,..., An adhesive film layers are sequentially placed and pushed to the corresponding positions, respectively, to obtain the uncured wave-absorbing honeycomb core material with an impedance matching structure.

[0053] 4. Heat setting of the wave-absorbing honeycomb core material

[0054] In this step, the wave-absorbing honeycomb core material is heat set by placing the uncured wave-absorbing honeycomb on the surface (curved surface) of a mold, with the lower surface of the honeycomb core material being the mold-adhering surface. The vacuum bag pressing or hot pressing tank process is used for curing, with the curing temperature being 180-200°C and the curing time being 2-4 hours.

[0055] During the heat setting process, the wave-absorbing adhesive film layer is also heated and cured. The carrier layer plays a supporting role to prevent the adhesive in the wave-absorbing layer from being diluted and to drive the absorbent to flow along the cell wall. Thus, the carrier layer plays a role in maintaining the impedance matching structure. The wave-absorbing adhesive film layer and the resin on the cell wall of the honeycomb core material are both in an uncured state, and are completely cured during the heating and holding process, thereby ensuring good adhesive strength between them.

[0056] After the wave-absorbing honeycomb core material is cured, it maintains the shape of the designed curved surface, thereby obtaining the heat-set wave-absorbing honeycomb core material.

[0057] 5. Bonding of the wave-absorbing honeycomb core material and the wave-transparent skin to obtain a wave-absorbing honeycomb composite material

[0058] The wave-transparent skin in this step is a wave-transparent fiber cloth resin-based composite material. The wave-transparent fiber cloth can be a quartz fiber cloth or a glass fiber cloth, and the resin can be an epoxy resin, a phenolic resin, a cyanate ester resin or a bismaleimide resin.

[0059] The wave-transparent fiber / resin prepreg can be directly laid on the upper and lower surfaces of the wave-absorbing honeycomb core material and placed on a curved mold for curing. Alternatively, the skin prepreg can be laid on the curved mold first, and the upper and lower skins are cured, respectively, and then the upper and lower skins are laid on the upper and lower surfaces of the wave-absorbing honeycomb core material for bonding.

[0060] The skin and the wave-absorbing honeycomb core material are bonded using a skin-core adhesive, and the bonding process is a hot pressing tank or vacuum bag process. The skin and the wave-absorbing honeycomb core material are laid on a curved mold for bonding and curing to obtain a wave-absorbing honeycomb composite material. The curing temperature is 175-185°C, and the curing time is 2-4 hours.

[0061] The application will be described in detail below in combination with the drawings and specific examples.

[0062] Example 1

[0063] Step 1, according to the actual demand, the total thickness of the wave-absorbing honeycomb composite material is determined to be 27 mm, wherein the thickness of the wave-absorbing honeycomb core material is 25 mm, the honeycomb cell shape is hexagonal, the variable length is 2.77 mm, and the upper and lower skins are both 1 mm thick quartz fiber cloth / epoxy resin composite materials.

[0064] The uncured wave-absorbing honeycomb core material is prepared by impregnating aramid paper with phenolic resin. The preparation process includes aramid paper core strip glue sticking, lamination, hot pressing, stretching, impregnation, and drying. No curing treatment is performed, and the phenolic resin on the honeycomb cell wall is in an uncured state and has heat setting capability.

[0065] Step 2, according to the wave-absorbing requirement in the 8 GHz-40 GHz frequency band, the electrical performance design of the wave-absorbing honeycomb is performed. The optimal impedance matching wave-absorbing structure is calculated using electromagnetic simulation software. The absorber in the wave-absorbing adhesive film layer is carbon black, with a thickness of 1.0 mm, and a total of six layers, A1, A2, A3, A4, A5, and A6. Among them, the bearing layer is quartz fiber cloth / epoxy resin, with a thickness of 0.1 mm; the wave-absorbing layer contains carbon black and epoxy resin, with a thickness of 0.9 mm. The mass ratio of the absorber in the wave-absorbing adhesive film layers A1, A2, A3, A4, A5, and A6 is 0.3%, 1%, 4%, 8%, 15%, and 30%, respectively. The positions of each wave-absorbing layer, i.e., the distance from the lower surface, are 23 mm, 20 mm, 16 mm, 12 mm, 6 mm, and 1 mm, respectively. From the upper surface to the lower surface of the honeycomb core material (in the direction of the honeycomb thickness), the wave-absorbing adhesive film in the honeycomb cell is A1, A2, A3, A4, A5, and A6 in turn.

[0066] The quartz fiber cloth / epoxy resin prepreg is selected as the bearing layer. According to the designed absorber content, different contents of carbon black are mixed uniformly with epoxy resin and coated on the bearing layer, wherein the bearing layer thickness is 0.1 mm, the wave-absorbing layer thickness is 0.9 mm, and the overall thickness of the wave-absorbing adhesive film layer is 1.0 mm. The obtained wave-absorbing adhesive films are A1, A2, A3, A4, A5, and A6, respectively.

[0067] Step 3, the wave-absorbing adhesive film is cut into six shapes, and the length is 2.77 mm. According to the designed order, the wave-absorbing adhesive film is sequentially placed into the honeycomb hole. First, the wave-absorbing adhesive film A1 is placed from the lower part of the honeycomb core material, and the bearing layer is below. The wave-absorbing adhesive film A1 is pushed into the hole by using a hard metal column, and the pushing depth is controlled to be 23 mm, so as to ensure that the position of the A1 layer in the honeycomb is accurate. The A2, A3, A4, A5 and A6 layers are sequentially placed into the hole, and the adhesive film is pushed into the designed position by using the metal column, and the pushing depths are 20 mm, 16 mm, 12 mm, 6 mm and 1 mm respectively. The un-cured wave-absorbing honeycomb core material with impedance matching is obtained, wherein the distance between the A1 and A6 wave-absorbing adhesive film layers and the upper and lower surfaces of the honeycomb core material is 1 mm, so as to increase the bonding strength between the plate-core adhesive bonding honeycomb core material and the skin.

[0068] Step 4, according to the actual profile of the product, a curved mold for curing the honeycomb is designed. The un-cured wave-absorbing honeycomb core material is placed on the mold surface (curved surface), and the lower surface of the honeycomb core material is the mold surface. The vacuum bag pressing process is adopted for curing, the curing temperature is 180 DEG C, and the curing time is 2 h. After curing, the wave-absorbing honeycomb core material after heat setting is obtained, and the upper and lower surfaces are marked.

[0069] Step 5, quartz fiber cloth / epoxy resin is selected as the skin material, and the thickness of the upper and lower skins is 1.0 mm. The quartz fiber cloth / epoxy resin prepreg is laid on the mold surface, and the laying thickness is 1.0 mm. The vacuum bag pressing process is adopted for curing, the curing temperature is 130 DEG C, and the curing time is 2 h, so as to obtain the upper skin. The lower skin is prepared by using the same method.

[0070] The wave-absorbing honeycomb composite material is obtained by laying and curing according to the order of the lower skin, plate-core adhesive, wave-absorbing honeycomb core material, plate-core adhesive and upper skin, and adopting the vacuum bag pressing process, and the curing temperature is 180 DEG C and the curing time is 3 h.

[0071] The wave-absorbing honeycomb composite material has good appearance and good bonding quality between the skin and the honeycomb core material; the profile is consistent with the theoretical curved surface, and the deviation is less than 0.2 mm. The wave-absorbing honeycomb composite material in the curved surface cannot test the wave-absorbing performance (reflectivity). The same process is adopted to cure the wave-absorbing honeycomb core material on the flat mold, and then the wave-absorbing honeycomb composite material (equivalent flat plate) is prepared, and the wave-absorbing performance is that the reflectivity is less than or equal to -8 dB at 1 GHz-2 GHz, the reflectivity is less than or equal to -15 dB at 2 GHz-8 GHz, the reflectivity is less than or equal to -30 dB at 8 GHz-18 GHz, and the reflectivity is less than or equal to -35 dB at 18 GHz-40 GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in the required electromagnetic wave frequency band (8 GHz-40 GHz).

[0072] The part not described in detail in the present application is the technology known to those skilled in the art.

[0073] Example 2

[0074] The wave-absorbing frequency of the wave-absorbing honeycomb composite material is mainly 2GHz-18GHz, the absorbing agent is short carbon fiber, and the mass ratio is 1%, 2%, 6%, 12%, 24%, and 30% respectively, and the rest is the same as in Example 1, thereby obtaining the wave-absorbing honeycomb composite material.

[0075] The wave-absorbing honeycomb composite material has a good appearance, the bonding quality between the skin and the honeycomb core material is good, the profile is consistent with the theoretical curve, and the deviation is less than 0.2mm. The wave-absorbing performance of the wave-absorbing honeycomb composite material (equivalent flat plate) is that the reflectivity is ≤-10dB at 1GHz-2GHz, the reflectivity is ≤-25dB at 2GHz-8GHz, the reflectivity is ≤-30dB at 8GHz-18GHz, and the reflectivity is ≤-25dB at 18GHz-40GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in the required electromagnetic wave frequency band (2GHz-18GHz).

[0076] Example 3

[0077] The wave-absorbing frequency of the wave-absorbing honeycomb composite material is mainly 1GHz-40GHz, and the thickness is 32mm, wherein the thickness of the wave-absorbing honeycomb core material is 30mm, and the thickness of the upper and lower skins is 1mm. The absorbing agent is carbon nanotube, and the wave-absorbing adhesive film layer is divided into 7 layers; each layer has a thickness of 1.5mm, wherein the bearing layer is 0.1mm, the wave-absorbing layer is 1.4mm, the absorbing agent content mass ratio is 0.5%, 1%, 2%, 4%, 8%, 16%, and 30%, and the position is 29mm, 25mm, 20mm, 15mm, 10mm, 5mm, and 1mm away from the lower surface respectively. The rest is the same as in Example 1, thereby obtaining the wave-absorbing honeycomb composite material.

[0078] The wave-absorbing honeycomb composite material has a good appearance, the bonding quality between the skin and the honeycomb core material is good, the profile is consistent with the theoretical curve, and the deviation is less than 0.2mm. The wave-absorbing performance of the wave-absorbing honeycomb composite material (equivalent flat plate) is that the reflectivity is ≤-12dB at 1GHz-2GHz, the reflectivity is ≤-23dB at 2GHz-8GHz, the reflectivity is ≤-30dB at 8GHz-18GHz, and the reflectivity is ≤-30dB at 18GHz-40GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in the required electromagnetic wave frequency band (1GHz-40GHz).

[0079] Other embodiments:

[0080] The other embodiments mainly change the thickness of the honeycomb core material, the type and content of the absorbing agent, the thickness, number of layers, and position of the wave-absorbing adhesive film layer, and have no substantial difference from the above three embodiments, and the preparation method is not changed.

[0081] Comparative Example 1: The absorber content in the wave-absorbing glue film layer is 4%, and the rest is the same as Example 1, and a wave-absorbing honeycomb composite material is obtained. The wave-absorbing honeycomb composite material has a good appearance, and the bonding quality between the skin and the honeycomb core material is good; the profile is consistent with the theoretical curved surface, and the deviation is less than 0.2 mm. The wave-absorbing performance of the wave-absorbing honeycomb composite material (equivalent flat plate) is that the reflectivity is ≤-3 dB at 1 GHz-2 GHz, ≤-10 dB at 2 GHz-8 GHz, ≤-15 dB at 8 GHz-18 GHz, and ≤-15 dB at 18 GHz-40 GHz. The wave-absorbing performance of the wave-absorbing honeycomb in the required electromagnetic wave frequency band (8 GHz-40 GHz) is poor.

[0082] Comparative Example 2: The honeycomb core material substrate is a cured honeycomb core material, and the rest is the same as Example 1, and a wave-absorbing honeycomb composite material is obtained. The wave-absorbing honeycomb composite material cannot be heat set, has a poor appearance, and the honeycomb core material has cracking phenomenon, and the bonding quality between the skin and the honeycomb core material is poor; the profile has a large difference from the theoretical curved surface, and the deviation is greater than 5 mm. The wave-absorbing performance of the wave-absorbing honeycomb composite material (equivalent flat plate) is that the reflectivity is ≤-5 dB at 1 GHz-2 GHz, ≤-15 dB at 2 GHz-8 GHz, ≤-28 dB at 8 GHz-18 GHz, and ≤-33 dB at 18 GHz-40 GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in the required electromagnetic wave frequency band (8 GHz-40 GHz). This is the wave-absorbing performance tested under the flat plate. The wave-absorbing honeycomb composite material of Comparative Example 2 cannot be heat set and bent, and cracking occurs, and cannot be used in the curved surface condition.

[0083] The specific embodiments and drawings of the present application disclosed above are intended to help understand the content of the present application and to implement the same, and those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present application. The present application should not be limited to the content disclosed in the examples and drawings of the present application, and the protection scope of the present application is defined by the scope of the claims.

Claims

1. A wave-absorbing honeycomb composite material that can be used for curved surface molding, characterized in that: The invention comprises an upper skin, a lower skin, a honeycomb core material and an absorbing film layer; the honeycomb core material is formed by curing an uncured honeycomb core material; the absorbing film layer is located in the cells of the honeycomb core material, and the honeycomb core material containing the absorbing film layer is located between the upper skin and the lower skin; the absorbing honeycomb composite material is prepared by the following steps: according to the electrical performance design, absorbing film layers with different electromagnetic properties are placed at different positions in the cells of the uncured honeycomb core material, and the electromagnetic properties change gradiently along the cell direction to obtain an impedance matching structure; the uncured honeycomb core material containing the absorbing film layer is applied to the surface of a mold and cured to obtain a heat-set absorbing honeycomb core material; the upper and lower surfaces of the absorbing honeycomb core material are respectively bonded to the upper skin and the lower skin; the absorbing film layer contains an absorbent, an adhesive and a bearing layer; The absorbent has electromagnetic loss capability and its content is 0.1wt%~30wt%; The preparation steps of the wave-absorbing honeycomb composite material that can be used for curved surface molding include: preparing an uncured honeycomb core material; preparing a wave-absorbing adhesive film layer; the wave-absorbing adhesive film layer is uncured and in a flexible state; According to the electrical performance design, a wave-absorbing adhesive film layer is inserted into the cells of the uncured honeycomb core material to obtain a wave-absorbing honeycomb core material; Heat-setting the wave-absorbing honeycomb core material; bonding the wave-absorbing honeycomb core material to the upper skin and the lower skin to obtain a wave-absorbing honeycomb composite material; The absorbing film layer is inserted by cutting the absorbing film layer according to the cell size and shape of the uncured honeycomb core material, and then pushing the absorbing film into the corresponding position in the honeycomb cells in the designed order; the size of the absorbing film layer is slightly larger than the size of the honeycomb cells, ensuring that the position of the absorbing film layer remains unchanged after being inserted into the cells, and that it can undergo a certain deformation as the cell size changes, and is firmly bonded to the honeycomb cell wall.

2. The wave-absorbing honeycomb composite material according to claim 1, characterized in that: The uncured honeycomb core material is aramid paper impregnated with phenolic resin. After drying, the solvent is removed and the phenolic resin is in an uncured state. The uncured honeycomb core material has heat setting capability.

3. The wave-absorbing honeycomb composite material according to claim 1, characterized in that: The thickness of the absorbing film layer is 0.2mm~2mm; the absorber is at least one of carbon black, graphite sheets, carbon fibers, graphene, and carbon nanotubes; the adhesive is one of epoxy resin, phenolic resin, and bismaleimide resin; the bearing layer is one of quartz fiber cloth and glass fiber cloth, with a thickness of 0.04mm~0.2mm.

4. The wave-absorbing honeycomb composite material according to claim 3, characterized in that: The type of absorber is determined by conducting electrical performance design; the optimal gradient absorbing structure is calculated and optimized using electromagnetic simulation software, and the number of absorbing film layers in the absorbing honeycomb, the position of the absorbing film layers in the honeycomb cells, the thickness of each absorbing film layer and the content of the absorber are determined.

5. The wave-absorbing honeycomb composite material according to claim 1, characterized in that: The upper skin and the lower skin are wave-transmitting resin-based composite materials, including a reinforcement layer and a matrix, wherein the reinforcement layer is one of quartz fiber cloth and glass fiber cloth; the matrix is ​​one of epoxy resin, phenolic resin, and bismaleimide resin.

6. A method for preparing the wave-absorbing honeycomb composite material that can be used for curved surface molding according to claim 1, characterized in that: The following steps are involved: preparing an uncured honeycomb core material; preparing a wave-absorbing adhesive film layer; According to the electrical performance design, a wave-absorbing adhesive film layer is inserted into the cells of the uncured honeycomb core material to obtain a wave-absorbing honeycomb core material; Heat-setting the wave-absorbing honeycomb core material; The wave-absorbing honeycomb core material is bonded to the upper skin and the lower skin to obtain a wave-absorbing honeycomb composite material.

7. The preparation method according to claim 6, characterized in that The type of absorber is determined by conducting electrical performance design; the optimal gradient absorbing structure is calculated and optimized using electromagnetic simulation software, and the number of absorbing film layers in the absorbing honeycomb, the position in the honeycomb cells, the thickness of each absorbing film layer and the content of the absorber are determined.

8. The preparation method according to claim 6, characterized in that The heat setting of the wave-absorbing honeycomb core material is performed by placing the uncured wave-absorbing honeycomb on the mold surface and curing it by vacuum bag pressing or autoclave process, with the curing temperature being 180°C to 200°C and the curing time being 2h to 4h. The wave-absorbing honeycomb core material is bonded to the upper skin and the lower skin, wherein the skin is a wave-transparent resin-based composite material, and the skin is in a cured state or an uncured state during bonding, and the skin and the wave-absorbing honeycomb core material are bonded using plate-core adhesive.

Images