Wave-absorbing honeycomb composite material capable of being used for curved surface forming and preparation method of wave-absorbing honeycomb composite material

Abstract

The invention relates to a wave-absorbing honeycomb composite material capable of being used for curved surface forming and a preparation method thereof, and belongs to the technical field of wave-absorbing material preparation. According to electrical property design, wave-absorbing adhesive film layers with different electromagnetic properties are placed at different positions in cells of an uncured honeycomb core material, the electromagnetic properties change in a gradient mode in the cell direction, an impedance matching structure is obtained, a wave-absorbing honeycomb is attached to the surface (curved surface) of a mold to be cured, and the heat-set wave-absorbing honeycomb core material is obtained; the upper surface and the lower surface are respectively bonded with the wave-transparent skin, so that the wave-absorbing honeycomb composite material with excellent performance is obtained, and the stealth requirement of curved-surface products is met. The invention provides the wave-absorbing honeycomb composite material which is easy in process control, excellent in wave-absorbing property and mechanical property and capable of being used for curved surface forming and the preparation method, and the wave-absorbing honeycomb composite material has excellent wave-absorbing property in an ultra-wide frequency range.

Description

Technical Field

[0001] The invention relates to a wave-absorbing honeycomb composite material which can be used for curved surface molding and a preparation method thereof, belonging to the technical field of wave-absorbing material preparation. Background Art

[0002] Aramid paper honeycomb is a new type of lightweight structural sandwich material with the advantages of low density, high mechanical properties, and good heat resistance. It is mainly used in lightweight sandwich structures and has been widely used in aircraft. With the development of detection technology, aircraft have been asked to have a wider absorption band and a stronger absorption effect. Aramid paper honeycomb has excellent electromagnetic wave transmission performance, but does not have electromagnetic wave absorption performance, so it cannot be directly used in the field of wave absorption. The conventional idea is to achieve this by introducing electromagnetic wave absorbers on the aramid paper wave-transmitting honeycomb wall.

[0003] At present, most of the existing aramid paper absorbing honeycombs are made by first preparing ordinary aramid paper without electromagnetic loss function into aramid paper transparent honeycombs, then impregnating the honeycomb walls of the aramid paper transparent honeycombs with electromagnetic wave absorbent glue, and finally curing and forming. For example, in patent CN114228266A, by gradient impregnation, the absorbent is gradiently distributed along the honeycomb grid or in the direction perpendicular to the honeycomb grid to obtain an impedance matching structure and better absorbing performance. However, the absorbing honeycomb obtained by the impregnation method has the absorbent attached to the hole wall, which is easy to fall off, and has poor environmental resistance. In addition, the impregnation process is difficult to control and has poor process stability. The impregnation process cannot apply large aspect ratio carbon fiber and magnetic fiber absorbents, resulting in low magnetic loss performance of the aramid paper absorbing honeycomb. In addition, the impregnation process has poor controllability, resulting in low stability of the electromagnetic performance of the aramid paper absorbing honeycomb.

[0004] In order to avoid the shortcomings of impregnated absorbing honeycombs, a method of adding a carbon fiber absorbent to aramid paper to obtain absorbing aramid paper and then preparing an absorbing honeycomb is proposed in a patent for dielectric loss aramid paper, absorbing honeycomb and preparation method (CN112553942A). 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; however, this method is subject to the mixing papermaking process, and only fiber absorbents can be added, and the amount added should not be too high. It does not have excellent absorbing effect in an ultra-wide frequency range, and generally has a poor low-frequency effect; and using the traditional honeycomb preparation process, the characteristics and tension of different regions of the absorbing aramid paper are different, and it is difficult to ensure the uniformity of the honeycomb grid. Another method is to apply an absorbent on aramid paper to obtain absorbing aramid paper, and then prepare an absorbing honeycomb, such as patents CN109796624A, CN202111440881.5, and CN114214871A; this method can add various types of absorbents, and a large amount of absorbents can be added to meet different absorbing needs; the absorbent is applied to the surface of the aramid paper to obtain absorbing aramid paper, and then the absorbing honeycomb is obtained by the traditional honeycomb preparation method. However, when preparing the absorbing honeycomb by this method, it is necessary to stretch it to form a hexagonal grid. When the absorbent coating has insufficient adhesion, debonding is prone to occur. At present, both of the above methods can obtain absorbing honeycombs with stable performance and excellent environmental resistance, but the absorbent content in the honeycomb is fixed, and the absorbing structure is not designed. The absorbing honeycomb as a whole presents a single electromagnetic characteristic, and there is no impedance matching design, so it is difficult to obtain excellent ultra-wideband absorbing performance.

[0005] In order to obtain an impedance matching structure, the commonly used method is to introduce an absorbing layer between the honeycomb sheet layers, design an absorbing structure, and obtain an absorbing honeycomb composite material with good absorbing performance, such as the paper Design of Type A Skin Composite Honeycomb Structure and Its Absorption Performance (Journal of Composite Materials, 2022, 39(3): 1180-1185). However, in this structure, stress concentration points will be formed at the intersection of the two layers of honeycomb sheets, which are very easy to damage, thereby reducing the compressive strength of the overall structure; and there are many adhesive surfaces between the honeycomb layers, which will also affect the reliability of the overall structure.

[0006] The absorbing honeycombs mentioned in the above studies are all flat and cannot be used on some curved components (such as air intakes), and the cured honeycombs cannot be bent to change their shape. For homogeneous absorbing honeycombs, the required curved shape can be obtained by machining the surface. However, for impedance matching absorbing structures, the thickness of each layer cannot be changed, cannot be machined, and the outer contour of the curved surface cannot be obtained.

[0007] In the patent of an absorbing honeycomb with impedance matching structure and its preparation method (CN115891293A), an absorbent is coated on aramid paper, and an absorbing honeycomb is prepared by a template method, which has an impedance matching structure in the cell direction. By stacking the pattern units, rods are inserted into the honeycomb cells, and pressure is applied to the honeycomb cell walls to ensure the bonding strength of the core strip glue. The preparation method in this patent determines that it is impossible to prepare a curved absorbing honeycomb with uncured absorbing honeycomb core material. Summary of the invention

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

[0009] The present invention combines the characteristics of multi-layer absorbing honeycombs to propose an absorbing honeycomb composite material and a preparation method with an impedance matching structure that can be used for curved surface molding. According to the electrical performance design, absorbing adhesive 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 absorbing honeycomb is attached to the surface (curved surface) of the product or mold and cured to obtain a heat-set absorbing honeycomb core material; the upper and lower surfaces are respectively bonded to the wave-transparent skin to obtain an absorbing honeycomb composite material with excellent performance to meet the stealth requirements of curved products.

[0010] The technical solution of the present invention:

[0011] A wave-absorbing honeycomb composite material that can be used for curved surface molding comprises an upper skin, a lower skin, a honeycomb core material and a wave-absorbing adhesive film layer; the honeycomb core material is formed by curing uncured honeycomb core material; the wave-absorbing adhesive film layer is located in pores of the honeycomb core material, and the honeycomb core material containing the wave-absorbing adhesive film layer is located between the upper skin and the lower skin.

[0012] Furthermore, the absorbing honeycomb composite material is designed according to electrical properties, and absorbing adhesive 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 gradually along the cell direction to obtain an impedance matching structure. The uncured honeycomb core material containing the absorbing adhesive film layer is attached to the surface (curved surface) of the product or mold for curing 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 transparent skin to obtain excellent absorbing performance and meet the stealth requirements of curved products.

[0013] Furthermore, 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 capability.

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

[0015] Furthermore, the absorbent has electromagnetic loss capability and is one or more of carbon black, graphite flakes, carbon fibers, graphene, carbon nanotubes, etc., and the content is 0.1wt% to 30wt%.

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

[0017] Furthermore, the bearing layer is one of wave-transmitting fiber cloths such as quartz fiber cloth and glass fiber cloth, and has a thickness of 0.04 mm to 0.2 mm.

[0018] Furthermore, electrical performance design is carried out to determine the type of absorbent; electromagnetic simulation software is used to calculate and optimize the best gradient absorbing structure, 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 absorbent are determined.

[0019] Furthermore, the upper skin and the lower skin are wave-transmitting resin-based composite materials, including a reinforcing layer and a matrix, wherein the reinforcing layer is one of wave-transmitting fiber cloths such as quartz fiber cloth and glass fiber cloth; and the matrix is ​​one of epoxy resin, phenolic resin, and bismaleimide resin.

[0020] A method for preparing a wave-absorbing honeycomb composite material that can be used for curved surface molding is achieved by the following steps:

[0021] The first step is to prepare an uncured honeycomb core material;

[0022] The second step is to prepare the wave absorbing adhesive film layer;

[0023] The third step is to insert an absorbing adhesive film layer into the cells of the uncured honeycomb core material according to the electrical performance design to obtain an absorbing honeycomb core material;

[0024] The fourth step is to heat-set the wave-absorbing honeycomb core material;

[0025] The fifth step is to bond the wave-absorbing honeycomb core material to the wave-transmitting skin to obtain a wave-absorbing honeycomb composite material.

[0026] Furthermore, 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 capability.

[0027] Furthermore, the wave-absorbing adhesive film layer is composed of an absorbent, an adhesive and a bearing layer. The absorbent has electromagnetic loss capability and is one or more of carbon black, graphite flakes, carbon fibers, graphene, carbon nanotubes, etc. The adhesive is one of epoxy resin, phenolic resin, and bismaleimide resin, preferably phenolic resin. The bearing layer is one of wave-transmitting fiber cloths such as quartz fiber cloth and glass fiber cloth.

[0028] Furthermore, the absorbing adhesive film layer is uncured and in a flexible state, which is convenient for cutting into the size and shape of the honeycomb cells. The bearing layer plays a bearing role to prevent the absorbing adhesive film from thinning and flowing during the curing process.

[0029] Furthermore, electrical performance design is carried out to determine the type of absorbent. Electromagnetic simulation software is used to calculate and optimize the best gradient absorbing structure, determine the number of absorbing film layers in the absorbing honeycomb and their positions in the honeycomb cells, and then determine the thickness of each absorbing film layer and the content of the absorbent.

[0030] Furthermore, the absorbing film layer is inserted in the third step by cutting the absorbing film layer according to the cell size and shape of the uncured honeycomb core material. Then the absorbing film is sequentially pushed into the corresponding positions in the honeycomb cells according to the designed sequence. The size of the absorbing film layer is slightly larger than the size of the honeycomb cells, which ensures that the absorbing film layer is inserted into the cells and remains in the same position; and it can undergo a certain deformation as the cell size changes, and is firmly bonded to the honeycomb cell wall.

[0031] Furthermore, the fourth step is to heat-set the absorbing honeycomb core material, which is to place the uncured absorbing honeycomb on the mold surface (curved surface) and cure it by vacuum bag pressing or autoclave process. The curing temperature is 180℃~200℃ and the curing time is 2h~4h.

[0032] Furthermore, the wave-absorbing honeycomb core material is bonded to the wave-transmitting skin, and the skin is a wave-transmitting fiber cloth resin-based composite material. During bonding, the skin can be in a cured state or an uncured state. The skin and the wave-absorbing honeycomb core material are bonded using a plate-core adhesive.

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

[0034] (1) The present invention places an absorbing adhesive film layer into uncured honeycomb cells to form an impedance matching structure, thereby achieving precise control of the absorbing structure. The obtained absorbing honeycomb core material can be formed on a curved surface to meet the stealth requirements of curved surface components, thereby overcoming the problem that the absorbing honeycomb of the traditional impedance matching structure cannot change its thickness and cannot be processed to obtain a curved surface.

[0035] (2) The present invention places the absorbing film layer at different positions in the honeycomb cells by physical methods, thereby obtaining an impedance matching structure while keeping the honeycomb cells intact, thus overcoming the shortcomings of cross-linking of multi-layer absorbing honeycomb cell walls and insufficient compressive resistance.

[0036] (3) The present invention places the absorbing film into the honeycomb cells, and different types of absorbers can be added to meet different absorbing requirements; the absorber can be added in large quantities, and has excellent absorbing effect in an ultra-wide frequency range, thereby overcoming the shortcomings of the existing absorber-doped aramid paper absorbing honeycomb, such as limited absorber types (only fibrous) and low absorber content, and also overcomes the shortcomings of the thin absorbing layer thickness in the coated aramid paper absorbing honeycomb. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the preparation process of the uncured wave-absorbing honeycomb core material that can be used for curved surface molding of the present invention;

[0038] Figure 2 The present invention is a flow chart for preparing the wave-absorbing honeycomb composite material that can be used for curved surface molding;

[0039] Figure 3 It is a schematic diagram of the process of inserting the wave-absorbing adhesive film into the honeycomb cells of the present invention. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below through specific embodiments and drawings.

[0041] The present invention combines the characteristics of multi-layer absorbing honeycombs to propose an absorbing honeycomb composite material with an impedance matching structure that can be used for curved surface molding and a preparation method. According to the electrical performance design, absorbing adhesive 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 gradually along the cell direction to obtain an impedance matching structure. The schematic diagram of the preparation process is shown in Figure 1 The absorbing honeycomb is pasted on the surface (curved surface) of the product or mold and solidified to obtain the heat-set absorbing honeycomb core material; the upper and lower surfaces are bonded to the wave-transmitting skin respectively to obtain an absorbing honeycomb composite material with excellent performance to meet the stealth requirements of curved products.

[0042] According to the electrical performance design, the impedance matching structure of the wave-absorbing film in the honeycomb core material is calculated and optimized to determine the type and content of the absorbent in the wave-absorbing film layer, the thickness of the wave-absorbing film layer, the number of layers of the wave-absorbing film layer, and the position of the wave-absorbing film layer in the honeycomb cell. Absorbents of different types and contents are mixed with adhesives and coated on the wave-transmitting bearing layer to obtain a wave-absorbing film layer. The mixing and coating processes in the present invention are well known in the art, and the specific process parameters are determined according to actual production needs.

[0043] The present invention also provides Figure 2 The microwave-absorbing honeycomb composite material and preparation method thereof which can be used for curved surface molding are shown, and are realized by 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 is no longer cured by heating. The honeycomb core material is in an uncured state and has the ability to be thermally set with curved surface deformation. The preparation of uncured honeycomb core material is a well-known technology in the art.

[0046] 2. Preparation of Absorbent Film Layer

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

[0048] The wave absorbing film layer is composed of an absorbent, an adhesive and a bearing layer. The absorbent has electromagnetic loss capability and is one or more of carbon black, graphite flakes, carbon fibers, graphene, carbon nanotubes, etc. The adhesive is one of epoxy resin, phenolic resin, and bismaleimide resin, preferably phenolic resin. The bearing layer is one of wave-transmitting fiber cloths such as quartz fiber cloth and glass fiber cloth.

[0049] According to the electrical performance design, different types and contents of absorbents are mixed with adhesives and coated on the wave-transmitting bearing layer to obtain different absorbing adhesive film layers. The absorbent content in the absorbing adhesive film layer is 0.1wt% to 30wt%, and the thickness is 0.2mm to 2mm. The prepared absorbing adhesive film layers with different electromagnetic properties, A1, A2, A3, A4...An, the absorbent content and electromagnetic parameters gradually increase.

[0050] 3. Based on the electrical performance design, the uncured honeycomb core material cells are built with an absorbing film layer

[0051] Cut the absorbing film layer into the shape and size of the honeycomb cells, and place the absorbing film layer into the uncured honeycomb core cells in sequence according to the designed order and position. Figure 3 As shown. The absorbing film layer is composed of a bearing layer and an absorbing layer. When placed, the bearing layer faces downward and the absorbing layer is on top. The size of the absorbing film layer is slightly larger than the size of the honeycomb cells, ensuring that the film layer remains in the same position after being placed in the cells; and it can undergo a certain deformation as the cell size changes, and is firmly bonded to the honeycomb cell wall.

[0052] like Figure 3As shown, the absorbing film layer A1 is placed at the bottom of the honeycomb core material grid, and the film layer is pushed upward from bottom to the set position using a hard metal column. The A2, A3...An film layers are placed in sequence and pushed to the corresponding positions respectively to obtain an uncured absorbing honeycomb core material with an impedance matching structure.

[0053] 4. Heat setting of microwave-absorbing honeycomb core

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

[0055] During the heat setting process, the absorbing film layer will also heat up and solidify. Among them, the bearing layer plays a supporting role to prevent the adhesive in the absorbing layer from becoming diluted, driving the absorbent to flow along the honeycomb pore wall; thus, the bearing layer plays a role in maintaining the impedance matching structure. The resin on the absorbing film layer and the honeycomb core pore wall is in an uncured state, and will be completely cured during the heating and insulation process, ensuring good bonding strength between the two.

[0056] After the microwave-absorbing honeycomb core material is cured, the shape of the designed curved surface is maintained, thereby obtaining a heat-set microwave-absorbing honeycomb core material.

[0057] 5. The wave-absorbing honeycomb core material is bonded to the wave-transmitting skin to obtain a wave-absorbing honeycomb composite material

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

[0059] The wave-transmitting 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; or the skin prepreg can be first laid on the curved mold, and the upper and lower skins can be cured separately, and then the upper and lower skins can be laid and bonded to the upper and lower surfaces of the wave-absorbing honeycomb core material.

[0060] The skin and the absorbing honeycomb core material are bonded with plate-core adhesive, and the bonding process is autoclave or vacuum bag process, and the absorbing honeycomb composite material is obtained by laying on the curved mold for bonding and curing. The curing temperature is 175℃~185℃, and the curing time is 2h~4h.

[0061] The present invention is described in detail below with reference to the accompanying drawings and specific examples.

[0062] Example 1

[0063] Step 1. According to actual needs, the total thickness of the absorbing honeycomb composite material is determined to be 27 mm, of which the thickness of the absorbing honeycomb core material is 25 mm, the shape of the honeycomb cell is hexagonal, the 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 absorbing honeycomb core material is prepared by impregnating phenolic resin with aramid paper. The preparation process is gluing aramid paper to core strips, laminating, hot pressing, stretching, dipping, and drying. No curing treatment is performed. The phenolic resin on the honeycomb hole wall is in an uncured state and has heat setting ability.

[0065] Step 2. Design the electrical performance of the absorbing honeycomb according to the absorbing requirements in the 8GHz-40GHz frequency band. Use electromagnetic simulation software to calculate the optimal impedance matching absorbing structure. The absorber in the absorbing film layer is carbon black with a thickness of 1.0mm. There are six layers in total, namely A1, A2, A3, A4, A5, and A6. Among them, the bearing layer is quartz fiber cloth / epoxy resin with a thickness of 0.1mm; the absorbing layer contains carbon black and epoxy resin with a thickness of 0.9mm. The mass ratios of the absorbers in the absorbing film layers A1, A2, A3, A4, A5, and A6 are 0.3%, 1%, 4%, 8%, 15%, and 30%, respectively. The positions of each absorbing layer, that is, the distance from the lower surface, are 23mm, 20mm, 16mm, 12mm, 6mm, and 1mm, respectively. From the upper surface to the lower surface of the honeycomb core material (along the honeycomb thickness direction), the absorbing films in the honeycomb cells are A1, A2, A3, A4, A5, and A6 in sequence.

[0066] Quartz fiber cloth / epoxy resin prepreg was selected as the bearing layer. According to the designed absorbent content, different contents of carbon black and epoxy resin were evenly mixed and coated on the bearing layer, wherein the bearing layer thickness was 0.1 mm, the absorbing layer thickness was 0.9 mm, and the overall absorbing film thickness was 1.0 mm. The obtained absorbing films were A1, A2, A3, A4, A5, and A6.

[0067] Step 3, cut the absorbing film into six deformations, and lengthen it to 2.77mm. According to the design order, place the absorbing film into the honeycomb cells in sequence. First, the absorbing film A1 is placed from the bottom of the honeycomb core material, with the bearing layer below. The absorbing film A1 is pushed into the cells using hard metal columns, and the insertion depth is controlled to be 23mm to ensure that the position of the A1 layer in the honeycomb is accurate. Place the A2, A3, A4, A5, and A6 layers into the cells in sequence, and use metal columns to push the film into the designed position, with the insertion depths of 20mm, 16mm, 12mm, 6mm, and 1mm, respectively. An uncured absorbing honeycomb core material with impedance matching is obtained, in which the A1 and A6 absorbing film layers are 1mm away from the upper and lower surfaces of the honeycomb core material, in order to increase the bonding strength between the honeycomb core material and the skin of the plate-core adhesive bonding.

[0068] Step 4. Design a curved mold for honeycomb curing according to the actual surface of the product. Place the uncured absorbing honeycomb core material on the mold surface (curved surface), with the lower surface of the honeycomb core material as the mold surface. Use vacuum bag pressing process for curing, the curing temperature is 180℃, and the curing time is 2h. After curing, remove it to obtain the heat-set absorbing honeycomb core material, and mark the upper and lower surfaces.

[0069] Step 5: Use quartz fiber cloth / epoxy resin as the skin material, and the thickness of the upper and lower skins is 1.0 mm. Lay the quartz fiber cloth / epoxy resin prepreg on the mold surface with a thickness of 1.0 mm, and cure it by vacuum bag pressing process at a curing temperature of 130°C and a curing time of 2 hours to obtain the upper skin. Use the same method to prepare the lower skin.

[0070] The lower skin, plate-core adhesive, absorbing honeycomb core material, plate-core adhesive and upper skin were laid on the mold surface in this order and cured by vacuum bag pressing process at a curing temperature of 180°C and a curing time of 3h to obtain an absorbing honeycomb composite material.

[0071] The absorbing honeycomb composite material has a smooth 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 0.2mm. The curved absorbing honeycomb composite material cannot be tested for its absorbing performance (reflectivity). Using the same process, the absorbing honeycomb core material is cured on a flat mold, and then the absorbing honeycomb composite material (equivalent flat plate) is prepared. Its absorbing performance is 1GHz~2GHz reflectivity ≤-8dB, 2GHz~8GHz reflectivity ≤-15dB, 8GHz~18GHz reflectivity ≤-30dB, and 18GHz~40GHz reflectivity ≤-35dB. The absorbing honeycomb has excellent absorbing effect in the required electromagnetic wave frequency band (8GHz-40GHz).

[0072] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0073] Example 2

[0074] The absorbing frequency of the absorbing honeycomb composite material is mainly 2GHz-18GHz, the absorber is chopped carbon fiber, the mass ratios are 1%, 2%, 6%, 12%, 24% and 30% respectively, and the rest are the same as in Example 1, to obtain a absorbing honeycomb composite material.

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

[0076] Example 3

[0077] The absorbing frequency of the absorbing honeycomb composite material is mainly 1GHz-40GHz, and the thickness is 32mm, of which the absorbing honeycomb core material is 30mm thick, and the upper and lower skins are both 1mm thick. The absorber is carbon nanotubes, and the absorbing film layer is divided into 7 layers; each layer is 1.5mm thick, of which the bearing layer is 0.1mm, the absorbing layer is 1.4mm, the absorbent content mass ratio is 0.5%, 1%, 2%, 4%, 8%, 16%, 30% respectively, and the position, i.e. the distance from the lower surface, is 29mm, 25mm, 20mm, 15mm, 10mm, 5mm, 1mm respectively. The rest is the same as in Example 1, and a absorbing honeycomb composite material is obtained.

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

[0079] Other implementations:

[0080] Other implementations mainly involve changing the thickness of the honeycomb core material, the type and content of the absorber, the thickness, number of layers and position of the absorbing film layer, which are essentially the same as the above three implementations, and the preparation method remains unchanged.

[0081] Comparative Example 1: The absorbent content in the absorbing film layer is 4%, and the rest is the same as Example 1, to obtain an absorbing honeycomb composite material. The absorbing honeycomb composite material has a smooth and good appearance, and the bonding quality between the skin and the honeycomb core is good; the profile is consistent with the theoretical curved surface, and the deviation is less than 0.2mm. The absorbing performance of the absorbing honeycomb composite material (equivalent flat plate) is 1GHz~2GHz reflectivity ≤-3dB, 2GHz~8GHz reflectivity ≤-10dB, 8GHz~18GHz reflectivity ≤-15dB, 18GHz~40GHz reflectivity ≤-15dB. The absorbing performance of the absorbing honeycomb in the required electromagnetic wave frequency band (8GHz-40GHz) 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, to obtain an absorbing honeycomb composite material. The absorbing honeycomb composite material cannot be heat-set, has a poor appearance, cracks in the honeycomb core material, and the bonding quality between the skin and the honeycomb core material is poor; the profile is very different from the theoretical curved surface, with a deviation of more than 5mm. The absorbing performance of the absorbing honeycomb composite material (equivalent flat plate) is 1GHz~2GHz reflectivity ≤-5dB, 2GHz~8GHz reflectivity ≤-15dB, 8GHz~18GHz reflectivity ≤-28dB, and 18GHz~40GHz reflectivity ≤-33dB. The absorbing honeycomb has excellent absorbing effect in the required electromagnetic wave frequency band (8GHz-40GHz). This is the absorbing performance tested under a flat plate. The absorbing honeycomb composite material of Comparative Example 2 cannot be heat-set and bent, will crack, and cannot be used on curved surfaces.

[0083] The specific embodiments and drawings of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. It can be understood by those skilled in the art that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the contents disclosed in the embodiments and drawings of this specification, and the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A wave-absorbing honeycomb composite material that can be used for curved surface molding, characterized in that: It includes an upper skin, a lower skin, a honeycomb core material and an absorbing film layer; the honeycomb core material is formed by curing uncured honeycomb core material; the absorbing film layer is located in the pores of the honeycomb core material, and the honeycomb core material including the absorbing film layer is located between the upper skin and the lower skin.

2. The wave-absorbing honeycomb composite material according to claim 1, characterized in that: The absorbing honeycomb composite material is prepared by the following steps: according to the electrical performance design, absorbing adhesive 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 gradually along the cell direction to obtain an impedance matching structure; the uncured honeycomb core material including the absorbing adhesive film layer is attached to the surface of the mold for curing to obtain the heat-set absorbing honeycomb core material; and the upper and lower surfaces of the absorbing honeycomb core material are bonded to the upper skin and the lower skin respectively.

3. The wave-absorbing honeycomb composite material according to claim 2, characterized in that: 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 capability.

4. The wave-absorbing honeycomb composite material according to claim 1, characterized in that: The absorbing film layer comprises an absorbent, an adhesive and a bearing layer, wherein the thickness of the absorbing film layer is 0.2 mm to 2 mm; the absorbent has electromagnetic loss capability and is at least one of carbon black, graphite sheets, carbon fibers, graphene, and carbon nanotubes, with a content of 0.1 wt% to 30 wt%; 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 0.04 mm to 0.2 mm.

5. The wave-absorbing honeycomb composite material according to claim 4, characterized in that: The type of absorbent is determined by conducting electrical performance design. The best gradient absorbing structure is calculated and optimized using electromagnetic simulation software to determine 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 absorbent.

6. 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.

7. A method for preparing a wave-absorbing honeycomb composite material that can be used for curved surface molding, 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.

8. The preparation method according to claim 7, characterized in that: The absorbing film layer is uncured and in a flexible state, which is convenient for cutting into the size and shape of the honeycomb cells; the type of absorbent is determined by performing electrical performance design; the electromagnetic simulation software is used to calculate and optimize the best gradient absorbing structure, 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 absorbent are determined.

9. The preparation method according to claim 7, characterized in that: 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 positions in the honeycomb cells in sequence according to the designed sequence; the size of the absorbing film layer is slightly larger than the size of the honeycomb cells, so that the position of the absorbing film layer remains unchanged after being inserted into the cells, and it can undergo a certain deformation as the cell size changes, and is firmly bonded to the honeycomb cell wall.

10. The preparation method according to claim 7, characterized in that: The heat setting of the wave-absorbing honeycomb core material is to place the uncured wave-absorbing honeycomb on the mold surface and cure it by vacuum bag pressing or autoclave process, the curing temperature is 180°C to 200°C, and the curing time is 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-transmitting resin-based composite material, 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 by plate-core adhesive.

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