Preparation method of wave-absorbing-bearing integrated carbon fiber fabric composite material capable of regulating and controlling periodic gradient impedance

Abstract

The invention belongs to the technical field of special functional coatings, and particularly relates to a preparation method of a wave-absorbing-bearing integrated carbon fiber fabric composite material capable of regulating and controlling periodic gradient impedance. Based on existing long carbon fibers, modified carbon fibers are obtained; adopting a waveguide method to test the dielectric constant of the X-band resin matrix, and calculating the effective dielectric constant of the modified carbon fiber; on the basis of the effective dielectric constant and the dielectric constant of the resin matrix, COMSOL finite element analysis global optimization is carried out, and structural parameters of the carbon fiber woven body are obtained; the preparation method comprises the following steps: inputting structural parameters into a braiding machine, preparing a carbon fiber braided body by adopting a modified carbon fiber braiding and silicon dioxide fiber frame auxiliary method, then immersing the carbon fiber braided body into a mixed solution of a resin matrix and a curing agent, and completing a curing process in a mold to complete preparation. The wave absorbing-bearing integrated carbon fiber fabric composite material capable of regulating and controlling the periodic gradient impedance is obtained. The method is used for solving the technical problems that the wave-absorbing frequency band of a powder material is narrow, the anisotropy of the wave-absorbing performance of a long fiber woven plane structure is obvious, and the regulation and control rule of a periodic unit on a dielectric constant is not clear.

Description

Technical Field

[0001] The present invention belongs to the technical field of special functional coatings, and particularly relates to a preparation method of a wave-absorbing and load-bearing integrated carbon fiber fabric composite material with a regulated periodic gradient impedance. The composite material prepared by the method of the present invention is a wave-absorbing and load-bearing integrated carbon fiber fabric, which has broad application prospects in the field of electromagnetic wave absorption materials. Background Art

[0002] With the rapid development of radio technology and 5G communication, electromagnetic protection materials are the key to addressing the current electromagnetic pollution problem. For wave-absorbing materials, a simple wave-absorbing coating has a narrow effective wave-absorbing frequency band, a large filling ratio, and low mechanical strength. Once damaged, it is difficult to repair, and the maintenance cost is high, making it difficult to achieve large-area applications. With the increasing demand for the electromagnetic protection, load-bearing function, acid-base resistance, and moisture resistance of wave-absorbing materials, the demand for structural-load-bearing thin materials has gradually emerged, and the research and development of new electromagnetic protection materials have become a hot issue. The new wave-absorbing materials with integrated structure-load-bearing functions play an important role in 5G networks, medical protection, equipment anti-interference, electromagnetic pollution, etc. On the one hand, traditional powder materials have a large filling ratio and are difficult to achieve lightweight, and at the same time, maintenance is difficult. There is an urgent need to adopt wave-absorbing materials with lower costs, smaller filling ratios, and more convenient maintenance. On the other hand, during the use of protective coatings, under the threats of environments such as rain, sand, high and low temperatures, a stealth coating with both wave-absorbing function and mechanical strength, that is, a structure-functional integrated material, is of great significance for the application range and long-term protection effect of the coating. The solution to these problems requires the development and further breakthrough of wave-absorbing and load-bearing integrated high-performance wave-absorbing composite materials.

[0003] Carbon materials have always been the focus of research on microwave absorption materials due to their strong attenuation ability. In particular, carbon fiber materials have excellent conductive loss and a large aspect ratio. However, their impedance matching is poor. In response to the impedance mismatch state of carbon fibers, researchers have designed many modification schemes around carbon fibers: using short carbon fibers and compounding them with magnetic materials, dielectric materials, and carbon materials to construct a gradient impedance periodic structure of a cone-like material; or using long continuous carbon fibers and compounding them with magnetic materials and dielectric materials with lower conductivity to improve their impedance matching. However, the microwave absorption performance of the planar design woven structure shows a large degree of anisotropy. Since carbon fibers themselves have strong attenuation ability and can also be used as a mechanical reinforcement phase in composites, it is feasible to achieve the integration of microwave absorption and load-bearing functions by constructing a periodic structure woven body with a gradient impedance design of carbon fibers to reinforce the resin matrix composite. It can be reasonably inferred that after interfacial modification of carbon fiber materials, by means of simulation and design of their periodic structure, and by designing a suitable impedance gradient through an arched resonant cavity, the impedance matching can be greatly improved, the strong attenuation ability and mechanical strength of carbon fibers can be maximally exerted, and broadband absorption insensitive to the incident angle and incident direction and the integration of load-bearing functions in the composite material can be achieved, meeting the requirements of high-efficiency stealth and anti-strike of new microwave absorption materials. Summary of the Invention

[0004] The present invention provides a preparation method for a microwave absorption-load-bearing integrated carbon fiber fabric composite material with a regulated periodic gradient impedance, so as to solve the technical problems of a narrow microwave absorption frequency band of powder materials, obvious anisotropy of the microwave absorption performance of a long fiber woven planar structure, and unclear regulation law of the periodic unit on the dielectric constant.

[0005] The present invention is realized through the following technical solutions:

[0006] A preparation method for a microwave absorption-load-bearing integrated carbon fiber fabric composite material with a regulated periodic gradient impedance, the preparation method comprising the following steps:

[0007] Step 1: Based on existing long carbon fibers, obtain modified carbon fibers;

[0008] Step 2: Use the waveguide method to measure the dielectric constant of the resin matrix in the X band, and calculate the equivalent dielectric constant of the modified carbon fibers in Step 1;

[0009] Step 3: Based on the equivalent dielectric constant in Step 2 and the dielectric constant of the resin matrix, perform global optimization of COMSOL finite element analysis to obtain the structural parameters of the carbon fiber woven body;

[0010] Step 4: Input the structural parameters in Step 3 into a knitting machine, and use the method of modified carbon fiber knitting assisted by a silica fiber framework to prepare a carbon fiber knitted body. Then immerse the carbon fiber knitted body in a mixed solution of a resin matrix and a curing agent, and complete the curing process in a mold to complete the preparation and obtain the wave-absorbing and load-bearing integrated carbon fiber fabric composite material with regulated periodic gradient impedance.

[0011] Further, Step 1 is specifically as follows: Immerse long carbon fibers in p-xylene for degumming in an oil bath to obtain smooth long carbon fibers, perform oxidation treatment with a nitric acid solution, then catalyze with an acetone solution of ferric chloride, and then immerse them in a glucose solution to coat a carbon coating by a hydrothermal method to obtain modified carbon fibers.

[0012] Further, Step 2 is specifically as follows: Use the waveguide method to measure the dielectric constant of the resin matrix in the X band. Make a mixture of the modified carbon fibers obtained in Step 1 into short carbon fibers and paraffin, measure the dielectric constant of the mixture, and calculate the equivalent dielectric constant of the modified carbon fibers through the maxwell-garnett equivalent medium model;

[0013] Further, the maxwell-garnett equivalent medium model is:

[0014]

[0015] Converted to:

[0016] Among them

[0017]

[0018] Among them, ε eff is the complex dielectric constant of the resin matrix, ε m is the complex dielectric constant of the short carbon fibers; ε i is the equivalent dielectric constant of the modified carbon fibers, f is the volume fraction of the short carbon fibers, N j(x，y，z) is the depolarization factor along the three axes of the short carbon fibers, a x is the semi-major axis along the x-axis direction of the short carbon fibers, a y is the semi-major axis along the y-axis direction of the short carbon fibers, a z is the semi-major axis along the z-axis direction of the short carbon fibers, and s is the characteristic length in each direction of the dispersed short carbon fibers.

[0019] Further, step 3 is specifically as follows: the equivalent dielectric constant of the modified carbon fiber obtained in step 2 and the dielectric constant of the resin matrix are respectively imported into the material library of the model. The initial model is a periodic structure composed of arch cavities. The periodic boundary conditions, wave equation, impedance matching layer, air layer, and perfect electric conductor of the initial model are set. Taking the wideband effective absorption from 1 - 18 GHz as the target, COMSOL finite element analysis global optimization is carried out to obtain the structural parameters of the carbon fiber braid.

[0020] Further, the structural parameters of the carbon fiber braid are obtained by using the COMSOL finite element analysis global optimization method. A random initial model structure is established. The wave equation of the COMSOL RF module is designed, the periodic boundary conditions in the x and y directions are set, and a perfect electric conductor is set below the periodic structure composite material. The incident electromagnetic wave is incident from top to bottom along the -z direction, and the reflection loss curve is monitored and obtained by a monitor behind the radiation source; the adjustment module is run, and the objective function is set RL represents the reflection loss value corresponding to each frequency with a step size of 0.08 GHz in the range from 1 - 18 GHz, and the adjustment target is that F reaches the minimum value.

[0021] Further, the structural parameters include: the number of carbon fiber bundles in the x and y directions, the width and height of the carbon fiber bundles, the bundle spacing of the carbon fiber bundles in the y direction, the overlapping relationship of the carbon fiber bundles, and the height of the arch resonance cavity formed by the undulation of the carbon fiber in the z-axis direction in the braid.

[0022] Further, step 4 is specifically as follows: a braid structure is prepared according to the structural parameters obtained in step three, where there is 1 carbon fiber bundle in the x direction, 3 carbon fiber bundles in the y direction, the bundle spacing of the carbon fiber bundles in the y direction is 1 mm, the height of the carbon fiber bundle is 0.5 mm, the width is 1 mm, and the height of the arch resonance cavity is 7 mm, 14 mm, or 20 mm.

[0023] An impedance gradient designed long fiber braided wave-absorbing and load-bearing integrated composite material prepared by the above method is applied to the field of electromagnetic wave absorption materials.

[0024] A computer-readable storage medium stores a computer program therein, and when the computer program is executed by a processor, the method as described above is implemented.

[0025] The beneficial effects of the present invention are:

[0026] The present invention synthesizes a composite material using commercial materials, and the synthesis process does not require complex equipment and a harsh experimental environment, and can achieve automated and large-scale production;

[0027] In the product of the present invention, the content of carbon fiber is only 3-5 vol.%, and by constructing a single-layer long fiber woven body, the original cost of the material is reduced, and cost reduction and process simplification can be achieved;

[0028] The present invention provides a design scheme for a wave-absorbing and load-bearing integrated carbon fiber fabric composite material that starts from impedance gradient design to regulate periodic structures;

[0029] The material prepared by the present invention is a periodic structure composite wave-absorbing material with wide frequency band, strong absorption, approximate isotropy, light weight and load-bearing function. When the undulation height of a 18 cm × 18 cm large plate sample is 14 mm, the maximum reflection loss is -61.84 dB. When the electric field is perpendicular to two adjacent sides respectively, the effective absorption bandwidths are 11.67 GHz and 10.87 GHz respectively, and the density is 0.085 g / cm 3 , and the areal density is 1.45 g / cm 2 . When the loads are distributed along two adjacent sides of the periodic unit respectively, the flexural strengths are 110.5 MPa and 80.5 MPa respectively.

[0030] The impedance gradient-designed carbon fiber woven body composite material prepared by the present invention, in which the carbon fiber woven body is a strong attenuation phase, has a strong attenuation effect on the electromagnetic waves entering the material, and is also a mechanical strengthening phase. Through impedance gradient design, the carbon fiber woven body layer can be regarded as a conical array structure, the height of the arched resonant cavity is adjusted, a reasonable impedance gradient is constructed, the impedance difference of each dielectric layer is reduced, the impedance matching of long carbon fibers is improved, and the balance between impedance matching and attenuation ability is achieved. In addition, the high conductivity of long carbon fibers themselves, the introduction of amorphous carbon on the surface, and the resonance between periodic structures will enhance interfacial polarization, conductance polarization and resonance loss. To sum up, through the design of impedance gradient, while improving impedance matching, strong attenuation ability is also achieved, thereby obtaining excellent electromagnetic wave absorption performance. Brief Description of the Drawings

[0031] Figure 1 is the morphology diagram of the modified carbon fiber prepared in the example and the comparative sample (CF);

[0032] Figure 2 is the wetting angle test diagram of the modified carbon fiber prepared in the example and the comparative sample (CF);

[0033] Figure 3 is the real part diagram of the dielectric constant of the modified carbon fiber prepared in the example and the comparative sample (CF);

[0034] Figure 4 is the imaginary part diagram of the dielectric constant of the modified carbon fiber prepared in the example and the comparative sample (CF);

[0035] Figure 5It is the reflection loss curve of the coaxial ring sample with a chopped length of 1 mm and a filling ratio of 1 vol.% of the contrast sample (CF);

[0036] Figure 6 It is the reflection loss curve of the coaxial ring sample with a chopped length of 1 mm and a filling ratio of 1 vol.% of the modified carbon fiber CF-1 prepared in Example 2;

[0037] Figure 7 It is the reflection loss curve of the coaxial ring sample with a chopped length of 1 mm and a filling ratio of 1 vol.% of the modified carbon fiber CF-2 prepared in Example 1;

[0038] Figure 8 It is the reflection loss curve of the coaxial ring sample with a chopped length of 1 mm and a filling ratio of 1 vol.% of the modified carbon fiber CF-3 prepared in Example 3;

[0039] Figure 9 It is the dielectric constant diagram of the waveguide sample in the X-band made of the resin matrix described in Step 2 of Example 1;

[0040] Figure 10 It is the equivalent dielectric constant diagram of the modified carbon fiber CF-2 obtained in Step 2 of Example 1;

[0041] Figure 11 It is the comparison diagram of the calculation results of the dielectric constant and the equivalent dielectric constant of the coaxial ring prepared with a filling ratio of 1 vol.% of the 1 mm chopped fiber of the modified carbon fiber CF-2 obtained in Step 2 of Example 1;

[0042] Figure 12 It is the comparison diagram of the calculation results of the dielectric constant and the equivalent dielectric constant of the coaxial ring prepared with a filling ratio of 1 vol.% of the 2 mm chopped fiber of the modified carbon fiber CF-2 obtained in Step 2 of Example 1;

[0043] Figure 13 It is the comparison diagram of the calculation results of the dielectric constant and the equivalent dielectric constant of the coaxial ring prepared with a filling ratio of 2 vol.% of the 1 mm chopped fiber of the modified carbon fiber CF-2 obtained in Step 2 of Example 1;

[0044] Figure 14 It is the comparison diagram of the calculation results of the dielectric constant and the equivalent dielectric constant of the coaxial ring prepared with a filling ratio of 2 vol.% of the 2 mm chopped fiber of the modified carbon fiber CF-2 obtained in Step 2 of Example 1;

[0045] Figure 15 It is the comparison diagram of the reflection loss and the simulation results of the waveguide sample composed of the periodic structure unit corresponding to the optimization result in Step 3 of Example 1;

[0046] Figure 16It is the three-dimensional data summary result diagram corresponding to the optimization results of frequency, reflection loss, and arch cavity height in Step 3 of Example 1;

[0047] Figure 17 It is the contour map of the three-dimensional data summary result corresponding to the optimization result in Step 3 of Example 1;

[0048] Figure 18 It is the reflection loss diagram in the X direction of the large plate samples with arch cavity heights of 7 mm and 14 mm respectively of the carbon fiber braided body obtained in Example 1;

[0049] Figure 19 It is the reflection loss diagram in the Y direction of the large plate samples with arch cavity heights of 7 mm and 14 mm respectively of the carbon fiber braided body obtained in Example 1;

[0050] Figure 20 It is the reflection loss diagram obtained by testing different electromagnetic wave incident angles in the X direction of the TE mode of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in Example 1;

[0051] Figure 21 It is the reflection loss diagram obtained by testing different electromagnetic wave incident angles in the X direction of the TM mode of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in Example 1;

[0052] Figure 22 It is the reflection loss diagram obtained by testing different electromagnetic wave incident angles in the Y direction of the TE mode of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in Example 1;

[0053] Figure 23 It is the reflection loss diagram obtained by testing different electromagnetic wave incident angles in the Y direction of the TM mode of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in Example 1;

[0054] Figure 24 It is the RCS diagram obtained by simulation calculation of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in Example 1 at 12 GHz in the TM mode;

[0055] Figure 25 It is the RCS diagram obtained by simulation calculation of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in Example 1 at 12 GHz in the TE mode;

[0056] Figure 26 It is the reflection loss diagram obtained when electromagnetic waves are incident from the X direction on the large plate samples with arch cavity heights of 7 mm, 14 mm, and 20 mm respectively of the carbon fiber braided body obtained in Example 1;

[0057] Figure 27 The reflection loss diagrams obtained when electromagnetic waves are incident from the Y direction on large plate samples with arch cavity heights of 7 mm, 14 mm, and 20 mm respectively of the carbon fiber braided body obtained in the first embodiment;

[0058] Figure 28 The flexural strength test diagram of the corresponding structural unit of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braided body obtained in the first embodiment.

[0059] Figure 29 It is the method flow chart of the present invention. Detailed implementation manners

[0060] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are presented to thoroughly understand the embodiments of the present application. However, those skilled in the art should clearly understand that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present application.

[0061] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of the described features, wholes, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0062] It should also be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification of the present application and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0063] Next, in combination with the attached Figure 1-29 of the specification of the present application, the technical solutions in the embodiments of the present application are described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0064] Many specific details are set forth in the following description to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0065] A preparation method of a wave-absorbing and load-bearing integrated carbon fiber fabric composite material for regulating periodic gradient impedance, the preparation method comprising the following steps:

[0066] Step 1: Based on existing long carbon fibers, obtain modified carbon fibers;

[0067] Step 2: Use the waveguide method to measure the dielectric constant of the resin matrix in the X-band, and calculate the equivalent dielectric constant of the modified carbon fibers in Step 1;

[0068] Step 3: Based on the equivalent dielectric constant in Step 2 and the dielectric constant of the resin matrix, perform global optimization by COMSOL finite element analysis to obtain the structural parameters of the carbon fiber braid;

[0069] Step 4: Input the structural parameters in Step 3 into a knitting machine, and use the method of knitting with modified carbon fibers and assisted by a framework of silica fibers to prepare a carbon fiber braid. Then immerse the carbon fiber braid in a mixed solution of a resin matrix and a curing agent, and then complete the curing process in a mold to complete the preparation and obtain the wave-absorbing and load-bearing integrated carbon fiber fabric composite material for regulating periodic gradient impedance.

[0070] Further, Step 1 is specifically as follows: Immerse the long carbon fibers in p-xylene for oil bath degumming to obtain smooth long carbon fibers, perform oxidation treatment with a nitric acid solution, then catalyze with an acetone solution of ferric chloride, and then immerse them in a glucose solution, and coat a carbon coating by hydrothermal method to obtain modified carbon fibers.

[0071] In the degumming process, the long carbon fibers are immersed in p-xylene for oil bath and stirred, the oil bath temperature is controlled at 140°C, the oil bath time is 3 h, and the stirring speed is 200 - 300 r / min.

[0072] The oxidation treatment is to place the long carbon fibers in a nitric acid solution for water bath, control the water bath temperature at 90°C, the time at 2 h, and the stirring speed at 200 - 300 r / min. The nitric acid solution is prepared by mixing concentrated nitric acid and deionized water, and the volume ratio of concentrated nitric acid to deionized water is 100:110.

[0073] In Step 1, the oxidized long carbon fibers are soaked in an acetone solution of ferric chloride for room temperature soaking for 12 h, wherein the mass-volume ratio of ferric chloride to acetone is 16.218 g:120 mL.

[0074] The mass concentration of glucose in the glucose solution is 10 - 30%; the hydrothermal method controls the water bath temperature at 200°C, the time at 7 h, and then washes with deionized water.

[0075] Further, step 2 is specifically as follows: The waveguide method is used to measure the dielectric constant of the X-band resin matrix. The modified carbon fibers obtained in step 1 are made into a mixture of short carbon fibers and paraffin, and the dielectric constant of the mixture is measured. Then, the equivalent dielectric constant of the modified carbon fibers is calculated through the Maxwell-Garnett equivalent medium model;

[0076] Further, the Maxwell-Garnett equivalent medium model is as follows:

[0077]

[0078] Converted to:

[0079] Among them

[0080]

[0081] Among them, ε eff is the complex dielectric constant of the resin matrix, and ε m is the complex dielectric constant of the short carbon fibers; ε i is the equivalent dielectric constant of the modified carbon fibers, f is the volume fraction of the short carbon fibers, N j(x，y，z) is the depolarization factor along the three axes of the short carbon fibers, a x is the semi-major axis along the x-axis direction of the short carbon fibers, a y is the semi-major axis along the y-axis direction of the short carbon fibers, a z is the semi-major axis along the z-axis direction of the short carbon fibers, and s is the characteristic length in all directions of the dispersed short carbon fibers.

[0082] Further, step 3 is specifically as follows: The equivalent dielectric constant of the modified carbon fibers obtained in step 2 and the dielectric constant of the resin matrix are respectively imported into the material library of the model. The initial model is a periodic structure composed of arch cavities. The periodic boundary conditions, wave equation, impedance matching layer, air layer, and perfect electric conductor of the initial model are set. With the goal of broadband effective absorption from 1 - 18 GHz, global optimization of COMSOL finite element analysis is carried out to obtain the structural parameters of the carbon fiber braid.

[0083] Further, the global optimization method of COMSOL finite element analysis is used to obtain the structural parameters of the carbon fiber braid. A random initial model structure is established, the wave equation of the COMSOL RF module is designed, the periodic boundary conditions in the x and y directions are set, and a perfect electric conductor is set below the periodic structure composite material. The incident electromagnetic wave is incident from top to bottom along the -z direction, and the reflection loss curve is monitored and obtained by the monitor behind the radiation source; the adjustment module is run, and the objective function is set RL represents the reflection loss value corresponding to each frequency with a step size of 0.08 GHz in the range of 1 - 18 GHz, and the adjustment target is for F to reach the minimum value.

[0084] Furthermore, the structural parameters include: the number of carbon fiber bundles in the x and y directions, the width and height of the carbon fiber bundles, the bundle spacing of the carbon fiber bundles in the y direction, the overlapping relationship of the carbon fiber bundles, and the height of the arched resonant cavity formed by the undulation of the carbon fibers in the z-axis direction in the braided body.

[0085] Furthermore, step 4 is specifically as follows: prepare a braided body structure according to the structural parameters obtained in step three, where there is 1 carbon fiber bundle in the x direction, 3 carbon fiber bundles in the y direction, the bundle spacing of the carbon fiber bundles in the y direction is 1 mm, the height of the carbon fiber bundles is 0.5 mm, the width is 1 mm, and the height of the arched resonant cavity is 7 mm, 14 mm, or 20 mm.

[0086] The resin matrix is E51 resin, the curing agent is T30, and the mass ratio of the resin matrix to the curing agent is 3:1.

[0087] The present invention utilizes the relatively high - height arched cavities formed by the overlapping of fibers in the braided body material to achieve impedance gradient design. It has broad development space to simultaneously achieve high - performance wave absorption and load - bearing functions through carbon fibers. Using carbon fibers as wave - absorbing agents and silica fibers to construct a three - dimensional positioning network, the preparation of a carbon fiber periodic structure braided body can be conveniently realized through an automatic braiding technique. Due to the relatively high height of the arched cavities, when electromagnetic waves are incident on the surface of the sample, they pass through the gradient impedance layer of air - resin matching layer - carbon fiber fabric in sequence. The gradient impedance layer is a conical - like structure. If it is divided into several layers in the vertical direction, the carbon fiber content in the uppermost layer is less and the resin content is more, and the impedance is slightly lower than that of the resin layer. As the vertical height decreases, the impedance gradually decreases, forming an impedance gradient structure with the air and resin layers, which is conducive to the entry of electromagnetic waves into the material and their gradual consumption. The design of interface polarization, conductance polarization, resonance loss, and impedance gradient jointly promotes the improvement of wave - absorption performance.

[0088] Specifically, Example 1:

[0089] A preparation method of a wave - absorbing and load - bearing integrated carbon fiber fabric composite material for regulating periodic gradient impedance is specifically carried out according to the following steps:

[0090] Step 1: Immerse 10 g of long carbon fibers in 250 mL of p-xylene for degumming in an oil bath. Control the oil bath temperature at 140 °C, the oil bath time at 3 h, and the stirring speed at 200 - 300 r / min. Then wash successively with absolute ethanol and deionized water to obtain smooth long carbon fibers. Then place the long carbon fibers in a nitric acid solution for oxidation treatment in a water bath. Control the water bath temperature at 90 °C, the time at 2 h, and the stirring speed at 200 - 300 r / min. The nitric acid solution is prepared by mixing 100 mL of concentrated nitric acid and 110 mL of deionized water; wash with deionized water until neutral to obtain oxidized carbon fibers; immerse the oxidized carbon fibers in an acetone solution of ferric chloride for room temperature soaking for 12 h, take them out and dry at 90 °C for 12 h to obtain carbon fibers with attached catalysts, where the acetone solution of ferric chloride is prepared by mixing 16.218 g of ferric chloride and 120 mL of acetone; then immerse them in a glucose solution and coat a carbon layer by hydrothermal method, where the mass concentration of glucose in the glucose solution is 20%, and the hydrothermal method controls the water bath temperature at 200 °C and the time at 7 h. Then wash with deionized water to obtain modified carbon fibers (CF-2);

[0091] Step 2: Use the waveguide method to measure the dielectric constant of the X-band resin matrix E51 resin. Cut the modified carbon fibers obtained in Step 1 into short carbon fibers with a length of 1 mm, and then mix them with paraffin at a filling ratio of 2 vol.% to form a mixture. Measure the dielectric constant of the mixture, and convert it to

[0092] the equivalent dielectric constant of the modified carbon fibers through the Maxwell-Garnett equivalent medium model combined with to calculate the equivalent dielectric constant of the modified carbon fibers;

[0093] where ε eff is the complex dielectric constant of the resin matrix, ε m is the complex dielectric constant of the short carbon fibers; ε i is the equivalent dielectric constant of the modified carbon fibers, f is the volume fraction of the short carbon fibers, N j(x，y，z) is the depolarization factor along the three axes of the short carbon fibers, a x is the semi-major axis along the x-axis direction of the short carbon fibers, a y is the semi-major axis along the y-axis direction of the short carbon fibers, a z is the semi-major axis along the z-axis direction of the short carbon fibers, and s is the characteristic size of the dispersed short carbon fibers in all directions;

[0094] where ε eff is the complex dielectric constant of the resin matrix, ε m is the complex dielectric constant of the short carbon fibers; ε i is the equivalent dielectric constant of the modified carbon fibers, f is the volume fraction of the short carbon fibers, N j(x，y，z)is the depolarization factor along the three axes of the short carbon fiber, a x is the semi-major axis along the x-axis direction of the short carbon fiber, a y is the semi-major axis along the y-axis direction of the short carbon fiber, a z is the semi-major axis along the z-axis direction of the short carbon fiber;

[0095] Step 3: Import the equivalent dielectric constant of the modified carbon fiber obtained in Step 2 and the dielectric constant of the resin matrix into the material library of the model. The initial model is a periodic structure composed of arched cavities. The structural parameters of the carbon fiber braid are obtained by using the global optimization method of COMSOL finite element analysis. Design the wave equation of the COMSOL RF module, set the periodic boundary conditions in the x and y directions, and set a perfect electric conductor under the periodic structure composite material. The incident electromagnetic wave is incident from top to bottom along the -z direction, and the reflection loss curve is monitored and obtained by the monitor behind the radiation source; Run the optimization module, set the objective function RL represents the reflection loss value corresponding to each frequency with a step size of 0.08 GHz in the range of 1 - 18 GHz. Adjust the target to make F reach the minimum value, and obtain the structural parameters of the carbon fiber braid, including the number of carbon fiber bundles in the x and y directions, the width and height of the carbon fiber bundles, the bundle spacing of the carbon fiber bundles in the y direction, the overlapping relationship of the carbon fiber bundles, and the height of the arched resonant cavity formed by the undulation of the carbon fiber in the z-axis direction of the braid. Specifically: there is 1 carbon fiber bundle in the x direction and 3 carbon fiber bundles in the y direction of the carbon fiber periodic braided structure, the distance between the carbon fiber bundles in the y direction is 1 mm, the height of the carbon fiber bundle is 0.5 mm, the width is 1 mm, and the height of the arched resonant cavity of the carbon fiber braid is 7 mm, 14 mm or 20 mm;

[0096] Step 4: Input the structural parameters obtained in Step 3 into the braiding machine, and use the method of assisting with the frame of modified carbon fiber braiding and silica fiber to prepare the carbon fiber braid. Then immerse the carbon fiber braid in the mixed solution of the resin matrix and the curing agent. The resin matrix is E51 resin, the curing agent is T30, and the mass ratio of the resin matrix to the curing agent is 3:1. Then vacuum outgas for 30 min in the mold and place it at room temperature for 48 h to complete the preparation and obtain the integrated carbon fiber fabric composite material with wave absorption and load-bearing functions of regulating periodic gradient impedance.

[0097] Prepare test samples:

[0098] Cut the carbon fiber coated with a carbon coating, that is, the modified carbon fiber (CF-2) prepared in Example 1, into 1 mm lengths, put it into paraffin according to a volume ratio of 2 vol.%, and ultrasonically disperse it at 70 °C for 30 min. Place the sample in a mold to obtain a coaxial ring with an outer diameter of 7 mm, an inner diameter of 3 mm, and a height of 3 mm;

[0099] Put the carbon fiber braid with an arch cavity height of 14 mm prepared in Example 1 into a mold. Pour E51 resin and T30 curing agent into the silicone mold according to a mass ratio of 3:1, and prepare a composite material which is cut into a cube sample with a side length of 18 cm and a height of 1.5 cm;

[0100] Cut the samples with an arch cavity height of 14 mm obtained in Step 4 of Example 1 into strip samples of 40 mm×10 mm×15 mm along the X and Y directions of the periodic structure respectively, and test their flexural strength at a span of 30 mm and a loading speed of 0.5 mm / min.

[0101] Prepare carbon-coated carbon fiber material samples with different carbon source concentrations:

[0102] The difference between Example 2 and Example 1 is that in Step 1, the concentration of the glucose solution is 10 wt.%, and modified carbon fiber (CF-1) is obtained.

[0103] The difference between Example 3 and Example 1 is that in Step 1, the concentration of the glucose solution is 30 wt.%, and modified carbon fiber (CF-3) is obtained.

[0104] Prepare the same test samples as in Example 1 for the comparative samples CF (smooth long carbon fiber), CF-1, and CF-3.

[0105] Test the CF-2 prepared in Example 1 together with CF, CF-1, and CF-3.

[0106] Samples with different short cut lengths and filling ratios:

[0107] Cut CF-2 into short cut carbon fibers with lengths of 1 mm and 2 mm, and mix them with paraffin at filling ratios of 1 vol.% and 2 vol.% respectively to prepare coaxial samples with an inner diameter of 3 mm and an outer diameter of 7 mm.

[0108] Prepare the same test samples as in Example 1 for the comparative samples of CF-2 with different short cut lengths and different filling ratios.

[0109] Test the samples of CF-2 with different short cut lengths and different filling ratios prepared in Example 1.

[0110] Samples with different arch cavity heights:

[0111] In Step 3 of Example 1, carbon fiber braids were prepared according to the other two arch cavity heights of 7 mm and 20 mm obtained through global optimization. The E51 resin and T30 curing agent were poured into a silicone mold according to a mass ratio of 3:1 to prepare cubes with side lengths of 18 cm and heights of 8 mm, 15 mm, and 21 mm respectively, which are the large plate samples CFM3P1-7 mm, CFM3P1-14 mm, and CFM3P1-20 mm with different braided body arch cavity heights.

[0112] The CFM3P1-7 mm, CFM3P1-14 mm, and CFM3P1-20 mm prepared in Example 1 were tested.

[0113] The test results of the equivalent dielectric constant of the CF-2 fiber obtained in Step 2 of Example 1 and the reflection loss of samples with different short cut lengths and filling ratios are as Figure 10-14 shown, which can prove the reliability of the calculation results of the equivalent dielectric constant of long continuous carbon fibers.

[0114] Figure 16 is the three-dimensional data summary result diagram corresponding to the optimization results of frequency, reflection loss, and arch cavity height in Step 3 of Example 1; Figure 17 is the contour map of the three-dimensional data summary result corresponding to the optimization result in Step 3 of Example 1; The simulation results show that there is a relatively wide effective absorption bandwidth when the arch cavity height is 7 mm and 14 mm.

[0115] The carbon fiber periodic structure braided body material with an arch cavity height of 14 mm prepared in Example 1 and samples with arch cavity heights of 7 mm and 20 mm were tested using the arch method.

[0116] The morphology diagrams of the modified carbon fibers prepared in the examples and the control sample (CF) are as Figure 1 shown. It can be seen that as the glucose concentration increases, the thickness of the carbon coating gradually increases.

[0117] The wetting angle test diagrams of the modified carbon fibers prepared in the examples and the control sample (CF) are as Figure 2 shown. It can be seen that CF-2 has the smallest wetting angle.

[0118] The reflection loss test results of the modified carbon fibers prepared in the examples and the control sample (CF) are as Figure 5-8 shown. It can be seen that CF-2 has the widest effective absorption bandwidth EAB.

[0119] Figure 18The reflection loss diagrams in the X direction of the large plate samples with arch cavity heights of 7 mm and 14 mm respectively of the carbon fiber braid obtained in Example 1 are shown. It can be seen that the effective absorption bandwidth of CFM3P1 - 7 mm is 7 GHz, the minimum reflection loss is -18.5 dB, and two loss peaks appear; the effective absorption bandwidth of CFM3P1 - 14 mm is 11.02 GHz, the minimum reflection loss is -32.4 dB, three loss peaks appear, and the loss peaks gradually shift to lower frequencies.

[0120] Figure 19 The reflection loss diagrams in the Y direction of the large plate samples with arch cavity heights of 7 mm and 14 mm respectively of the carbon fiber braid obtained in Example 1 are shown. It can be seen that the effective absorption bandwidth of CFM3P1 - 7 mm is 9.2 GHz, the minimum reflection loss is -40.7 dB, and two loss peaks appear; the effective absorption bandwidth of CFM3P1 - 14 mm is 11.8 GHz, the minimum reflection loss is -62.9 dB, three loss peaks appear, showing a trend that as the arch cavity height increases, the loss peaks shift to lower frequencies; from Figure 18 、 19 it can be seen that CFM3P1 - 7 mm still has obvious anisotropic characteristics in the effective absorption bandwidth, but the effective absorption bandwidths in the X and Y directions of CFM3P1 - 14 mm are not much different, showing isotropic characteristics in broadband absorption.

[0121] Figure 20 The reflection loss diagram obtained by testing different electromagnetic wave incident angles in the X direction of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braid obtained in Example 1 in the TE mode is shown. The test results show that at different incident angles, CFM3P1 - 14 mm maintains effective absorption in the range of 7 - 18 GHz, and even when the incident angle is 45°, effective absorption peaks also appear at 3.52 - 4.7 GHz.

[0122] Figure 21 The reflection loss diagram obtained by testing different electromagnetic wave incident angles in the X direction of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braid obtained in Example 1 in the TM mode is shown. The test results show that at different incident angles, CFM3P1 - 14 mm maintains effective absorption in the range of 7.27 - 18 GHz, and even when the incident angle is 45°, effective absorption peaks also appear at 3.52 - 4.68 GHz.

[0123] Figure 22It is the reflection loss diagram obtained by testing the Y direction of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braid obtained in Example 1 at different electromagnetic wave incident angles in the TE mode. The test results show that at different incident angles, CFM3P1-14 mm maintains effective absorption in the range of 7.75-18 GHz.

[0124] Figure 23 It is the reflection loss diagram obtained by testing the Y direction of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braid obtained in Example 1 at different electromagnetic wave incident angles in the TM mode. The test results show that at different incident angles, CFM3P1-14 mm maintains effective absorption in the range of 6.08-18 GHz. When the incident angle is 45°, it maintains effective absorption in the range of 4.6-18 GHz. From the above results, it can be shown that the wave absorption performance of the CFM3P1-14 mm gradient-designed carbon fiber braid periodic structure composite material is less affected by the incident angle and polarization mode.

[0125] Figure 26 It is the reflection loss diagram obtained when electromagnetic waves are incident from the X direction on large plate samples with arch cavity heights of 7 mm, 14 mm, and 20 mm of the carbon fiber braid obtained in Example 1. The test results show that CFM3P1-20 mm achieves effective absorption in the range of 8.07-18 GHz, and the minimum reflection loss is -29.42 dB;

[0126] Figure 27 It is the reflection loss diagram obtained when electromagnetic waves are incident from the Y direction on large plate samples with arch cavity heights of 7 mm, 14 mm, and 20 mm of the carbon fiber braid obtained in Example 1. The test results show that CFM3P1-20 mm achieves effective absorption in the range of 3.45-18 GHz, and the minimum reflection loss is -29.79 dB, achieving effective absorption in a wider frequency range, which proves the rationality of the impedance gradient design;

[0127] Figure 28 It is the flexural strength test diagram of the corresponding structural unit of the large plate sample with an arch cavity height of 14 mm of the carbon fiber braid obtained in Example 1. The flexural strength of pure resin is only 32.2 MPa. The flexural strength of the carbon fiber braid composite material in the X direction is 80.5 MPa, which is 2.5 times the original. The flexural strength in the Y direction is 110.5 MPa, which is 3.43 times the original. It proves that the carbon fiber braid effectively enhances the matrix in the composite material, and while enhancing the wave absorption performance, it also enhances the mechanical properties, and successfully prepares a wave absorption-bearing integrated composite material through gradient design.

[0128] Embodiment 2

[0129] An embodiment of the present invention provides an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. Among them, the memory is used to store software programs and modules, and the processor executes various functional applications and data processing by running the software programs and modules stored in the memory. The memory and the processor are connected through a bus. Specifically, when the processor runs the computer program stored in the memory, any step in the first embodiment is implemented.

[0130] It should be understood that in the embodiment of the present invention, the so-called processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), off-the-shelf programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0131] The memory may include a read-only memory, a flash memory, and a random access memory, and provides instructions and data to the processor. A part or all of the memory may also include a non-volatile random access memory.

[0132] As can be seen from the above, the electronic device provided by the embodiment of the present invention can implement the preparation method of the wave-absorbing and load-bearing integrated carbon fiber fabric composite material for regulating the periodic gradient impedance as described in the first embodiment by running a computer program. The present invention adopts a finite element simulation scheme, and the arched resonant cavity in the periodic structure realizes isotropic broadband effective absorption. The composite material has the characteristics of light weight, broadband, high-performance absorption, and high flexural strength. The composite material prepared by the present invention is applied in the field of electromagnetic wave-absorbing materials.

Claims

1. A method for preparing a wave absorbing and load-bearing integrated carbon fiber fabric composite material with regulated periodic gradient impedance, characterized in that: The preparation method comprises the following steps: Step 1: Based on the existing long carbon fiber, a modified carbon fiber is obtained; Step 2: Use the waveguide method to test the dielectric constant of the X-band resin matrix and calculate the equivalent dielectric constant of the modified carbon fiber in step 1; Step 3: Based on the equivalent dielectric constant of step 2 and the dielectric constant of the resin matrix, perform COMSOL finite element analysis global optimization to obtain the structural parameters of the carbon fiber braid; Step 4: Input the structural parameters of step 3 into a braiding machine, adopt a modified carbon fiber weaving and silica fiber frame-assisted method to prepare a carbon fiber braid, then immerse the carbon fiber braid in a mixture of a resin matrix and a curing agent, and then complete the curing process in a mold to complete the preparation and obtain the wave absorbing-load-bearing integrated carbon fiber fabric composite material with regulated periodic gradient impedance.

2. The preparation method according to claim 1, characterized in that: Specifically, the step 1 comprises the following steps: immersing the long carbon fiber in an oil bath in p-xylene to remove the glue, obtaining a smooth long carbon fiber, performing an oxidation treatment with a nitric acid solution, then catalyzing with an acetone solution of ferric chloride, and then immersing the long carbon fiber in a glucose solution, and coating the carbon coating with a hydrothermal method to obtain a modified carbon fiber.

3. The preparation method according to claim 1, characterized in that: Specifically, step 2 is to test the dielectric constant of the X-band resin matrix by a waveguide method, make the modified carbon fiber obtained in step 1 into a mixture of chopped carbon fiber and paraffin, test the dielectric constant of the mixture, and calculate the equivalent dielectric constant of the modified carbon fiber by the Maxwell-Gamett equivalent medium model.

4. The preparation method according to claim 3, characterized in that: The Maxwell-Garnett equivalent medium model is: Translates to: in Among them, ε eff is the complex dielectric constant of the resin matrix, ε m is the complex dielectric constant of chopped carbon fiber; ε i is the equivalent dielectric constant of the modified carbon fiber, f is the volume fraction of the chopped carbon fiber, N j(x，y，z) is the depolarization factor along the three axes of the chopped carbon fiber, a x is the semi-major axis along the x-axis direction of the chopped carbon fiber, a y is the semi-major axis along the y-axis direction of the chopped carbon fiber, a z is the semi-major axis along the z-axis direction of the chopped carbon fiber, and s is the characteristic length of the dispersed chopped carbon fiber in each direction.

5. The preparation method according to claim 1, characterized in that: Specifically, the step 3 is to import the equivalent dielectric constant of the modified carbon fiber and the dielectric constant of the resin matrix obtained in step 2 into the material library of the model respectively, the initial model is a periodic structure composed of an arched cavity, and the periodic boundary conditions, wave equations, impedance matching layers, air layers and ideal conductors of the initial model are set. With the goal of 1-18 GHz broadband effective absorption, COMSOL finite element analysis global optimization is performed to obtain the structural parameters of the carbon fiber braid.

6. The preparation method according to claim 5, characterized in that: The structural parameters of the carbon fiber braid are obtained by using the COMSOL finite element analysis global optimization method. A random initial model structure is established. The wave equation of the COMSOL RF module is designed, periodic boundary conditions in the x and y directions are set, and a perfect conductor is set under the periodic structure composite material. The incident electromagnetic wave is incident from top to bottom along the -z direction. The monitor behind the radiation source monitors and obtains the reflection loss curve; run the adjustment module and set the objective function RL represents the reflection loss value corresponding to each frequency in the range of 1-18 GHz with a step size of 0.08 GHz, and the adjustment target is to minimize F.

7. The preparation method according to claim 6, characterized in that: The structural parameters include: the number of carbon fiber bundles in the x and y directions, the width and height of the carbon fiber bundles, the bundle spacing of the carbon fiber bundles in the y direction, the overlapping relationship of the carbon fiber bundles and the height of the arched resonance cavity formed by the undulation of the carbon fibers in the braided body in the z-axis direction.

8. The preparation method according to claim 1, characterized in that: Specifically, step 4 is to prepare a woven body structure according to the structural parameters obtained in step 3, wherein there is 1 carbon fiber bundle in the x-direction, 3 carbon fiber bundles in the y-direction, the bundle spacing of the carbon fiber bundles in the y-direction is 1 mm, the height of the carbon fiber bundle is 0.5 mm, the width is 1 mm, and the height of the arched resonant cavity is 7 mm, 14 mm or 20 mm.

9. An integrated wave absorbing and load-bearing composite material of long fiber braided body with impedance gradient design prepared by the method according to any one of claims 1 to 8, which is applied in the field of electromagnetic wave absorbing materials.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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