A method for repairing a wave-absorbing honeycomb sandwich structure penetration damage

Abstract

The application discloses a wave-absorbing honeycomb sandwich structure and a repairing method for penetration damage of the wave-absorbing honeycomb sandwich structure. The wave-absorbing honeycomb sandwich structure comprises an upper panel, a wave-absorbing honeycomb and a lower panel, and has specific dielectric properties in a 4GHz-18GHz frequency band. The repairing method comprises checking and identifying a damage area, polishing the upper panel, digging out damaged cells of the wave-absorbing honeycomb, cutting a honeycomb replacement core of the same specification, polishing the lower panel, introducing conductive paste into a glass fiber cloth and controlling the electric conductivity of the glass fiber cloth in a target range, wrapping the glass fiber cloth impregnated with the conductive paste around the periphery of the honeycomb replacement core and inserting the glass fiber cloth into a honeycomb hole, and bonding a lower panel repair disc, the wave-absorbing honeycomb, and an upper panel repair disc to obtain the wave-absorbing honeycomb sandwich structure. The wave-absorbing honeycomb sandwich structure is constructed in a dispersive manner in the 4-18GHz frequency band by using multi-resonance characteristics, has excellent electrical performance damage tolerance, the repairing method can quickly and effectively repair the wave-absorbing honeycomb damage, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of aerospace equipment design and repair, and relates to a microwave absorbing honeycomb sandwich structure and a method for repairing penetrating damage thereon, specifically a microwave absorbing honeycomb sandwich structure with high electrical performance damage tolerance and a method for repairing penetrating damage thereon. Background Technology

[0002] With the advent of various new detection radars, advanced infrared detectors, and precision-guided weapons, the new generation of aviation equipment extensively utilizes load-bearing and stealth integrated materials, exemplified by radar-absorbing honeycomb sandwich structures. The increasing complexity of the applied material systems and the high-intensity service exceeding design conditions have led to accelerated and exacerbated equipment damage, with increasingly complex causes of failure, driving the iterative upgrading of maintenance objectives and concepts. However, targeted electrical performance damage assessment and repair work has not yet been carried out for common damage forms of radar-absorbing honeycomb sandwich structures, making it difficult for equipment maintenance and support capabilities to cope with the new challenges brought about by equipment repair.

[0003] To address the aforementioned challenges, systematic work is urgently needed in two aspects: 1. At the design level of the absorbing honeycomb sandwich structure, a broadband absorbing structure design method with high electrical performance damage tolerance should be proposed to reduce the decline in absorbing performance caused by damage during the service of aerospace equipment; 2. At the design level of repair path and repair material system, a repair scheme that enables the repair material system to have a wide range of electrical performance control should be proposed. However, there are currently only two patent applications for absorbing honeycomb repair. CN113249092B proposes a repair scheme for damage to the absorbing honeycomb core using the "small core inserted into a large core" method. However, this scheme does not fundamentally solve the problem of improving the electrical performance damage tolerance of the honeycomb, and the "small core inserted into a large core" repair scheme mentioned in this scheme has a long implementation cycle and cannot achieve rapid recovery. CN115717006A uses absorbing putty to repair electrical performance damage of the honeycomb absorbing panel. However, it only provides a repair scheme for damage to the honeycomb sandwich structure panel and does not provide a repair scheme for damage to the absorbing honeycomb core that plays a absorbing role. Furthermore, its evaluation of the repair effect is only in the 8-18GHz frequency band and cannot address the repair effect on other radar detection frequency bands. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a high electrical performance damage tolerance absorbing honeycomb sandwich structure with distributed construction design in the 4-18GHz frequency band using multi-resonance characteristics. It also provides a method for repairing penetrating damage to the absorbing honeycomb sandwich structure. The method uses conductive polymer patches and glue injection repair process to enhance the designability of the electrical performance of the repair material, realizes rapid and effective repair of damage to the absorbing honeycomb sandwich structure, and thus improves the maintenance and support capabilities of the next generation of aviation equipment.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0006] A microwave absorbing honeycomb sandwich structure includes an upper panel, a microwave absorbing honeycomb, and a lower panel arranged sequentially from top to bottom. The microwave absorbing honeycomb sandwich structure has dielectric properties in the 4GHz-18GHz frequency band as shown in Table 1 below:

[0007] Table 1. Dielectric performance indicators of microwave absorbing honeycomb sandwich structures

[0008]

[0009] Preferably, the aforementioned microwave absorbing honeycomb sandwich structure comprises an aramid honeycomb structure and a conductive polymer coating applied to the inner wall of the aramid honeycomb structure pores; the pore side length of the aramid honeycomb structure is 2.75 mm to 5.5 mm, and the height of the aramid honeycomb structure is 30 mm to 36 mm; the conductive polymer coating comprises epoxy resin and conductive particles dispersed in the epoxy resin, wherein the conductive particles comprise one or more of carbon black, graphite, carbon nanotubes, and graphene, and the mass fraction of the conductive particles in the conductive polymer coating is 7% to 23%.

[0010] Preferably, in the above-mentioned absorbing honeycomb sandwich structure, the upper panel is made of glass fiber reinforced resin, and the resin used for glass fiber reinforced resin includes one or more of epoxy resin, phenolic resin, cyanate ester and polyimide; the dielectric constant of the upper panel at 10 GHz is 3.2 to 4, and the thickness of the upper panel is 1 mm to 3 mm.

[0011] In the above-mentioned absorbing honeycomb sandwich structure, preferably, the lower panel is made of carbon fiber reinforced resin, wherein the volume fraction of carbon fiber in the carbon fiber reinforced resin is 30% to 50%, and the thickness of the lower panel is 2mm to 4mm.

[0012] Preferably, in the above-mentioned absorbing honeycomb sandwich structure, the upper panel and the absorbing honeycomb sandwich, as well as the absorbing honeycomb sandwich and the lower panel, are bonded together by epoxy resin film.

[0013] As a general technical concept, the present invention also provides a method for repairing penetrating damage to the above-mentioned absorbing honeycomb sandwich structure, comprising the following steps:

[0014] (1) Inspect and identify the damaged area, draw a circle around the damaged area to enclose the damaged area, and record the radius of the circle around the damaged area as R1;

[0015] (2) Grind the upper panel of the absorbing honeycomb sandwich structure to expose the damaged pores of the absorbing honeycomb. The center of the grinding area coincides with the center of the damaged area. The grinding radius is R1+d×30, in mm, where d is the thickness of the upper panel, in mm.

[0016] (3) Remove the damaged cells of the absorbing honeycomb, forming holes in the absorbing honeycomb, and cut a replacement honeycomb core of the same specification;

[0017] (4) Grind the lower panel of the absorbing honeycomb sandwich structure to expose the damaged pores of the absorbing honeycomb. The center of the grinding area coincides with the center of the damaged area. The grinding radius is R1+d×30, in mm, where d is the thickness of the lower panel, in mm.

[0018] (5) Prepare conductive paste for preparing conductive polymer patch. Introduce conductive paste into glass fiber cloth using impregnation coating process. Control the conductivity within the target conductivity range by adjusting the number of impregnations.

[0019] (6) Wrap the glass fiber cloth impregnated with conductive paste around the honeycomb replacement core and then insert it into the holes of the absorbing honeycomb.

[0020] (7) Prepare the upper panel repair disc and the lower panel repair disc. The radius of the upper panel repair disc and the radius of the lower panel repair disc are both the grinding radius. First, use epoxy resin to bond the lower panel repair disc to the absorbing honeycomb corresponding to the grinding area. Then, use epoxy resin to inject the honeycomb replacement core and the junction area of ​​the adjacent absorbing honeycomb pores and cure it. Then, use epoxy resin to bond the upper panel repair disc to the absorbing honeycomb corresponding to the grinding area.

[0021] (8) Test the reflectivity to verify the repair effect.

[0022] In the above-mentioned method for repairing penetrating damage to the absorbing honeycomb sandwich structure, preferably, in step (5), the conductive slurry is prepared by dispersing conductive particles in epoxy resin, and the conductive particles include one or more of carbon black, graphite, carbon nanotubes and graphene, and the mass fraction of conductive particles in the conductive slurry is 7% to 15%.

[0023] In the above-mentioned method for repairing penetrating damage to the absorbing honeycomb sandwich structure, preferably, in steps (2) and (4), the grinding tools used include pneumatic grinding tools.

[0024] In the above-mentioned method for repairing penetrating damage to the absorbing honeycomb sandwich structure, preferably, in step (3), the tools used for excavation include a paper cutter, a honeycomb cutter, or a pneumatic grinding tool.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] 1. This invention provides a high electrical performance damage tolerance absorbing cellular sandwich structure. At the design level, it utilizes multi-resonance characteristics to construct the structure in a distributed manner within the 4-18GHz frequency band. For the first time, it achieves a cellular sandwich structure with a damaged area ratio of less than 72% or a penetration damage ratio of less than 18%, while the effective absorption bandwidth (frequency band corresponding to reflection loss less than -10dB) still covers 4-18GHz, thus possessing excellent electrical performance damage tolerance.

[0027] 2. This invention also provides a method for repairing penetrating damage to absorbing honeycomb sandwich structures. Furthermore, it proposes and verifies a conductive polymer patch + injection repair process for penetrating damage to high electrical performance damage tolerance absorbing honeycomb sandwich structures with multi-resonance characteristics. Compared with the traditional injection repair process, the repair material system used in this process has a wider range of electrical performance control, which greatly enhances the designability of the repair scheme and has excellent feasibility, thereby achieving rapid and effective repair of honeycomb damage. Attached Figure Description

[0028] Figure 1 These are the measured values ​​of reflection loss of the absorbing honeycomb sandwich structure in the 4-18GHz frequency band in Embodiment 1 of the present invention.

[0029] Figure 2 The diagram shows the reflection loss at different absorbing cell heights in Embodiments 1-3 of the present invention (1) and the variation of the resonant frequency point with the absorbing cell height (2).

[0030] Figure 3 The diagrams (1) and (2) show the reflection loss and impedance matching characteristics of different panel damage areas within the 4-18 GHz frequency band in Embodiment 5 of the present invention.

[0031] Figure 4 The diagrams (1) and (2) show the reflection loss and impedance matching characteristics corresponding to different penetration damage ratios within the 4-18 GHz frequency band in Embodiment 5 of the present invention.

[0032] Figure 5 The diagrams show the traditional glue injection repair method (1), the repair method for penetrating damage of the absorbing honeycomb sandwich structure of the present invention (conductive polymer patch + glue injection repair method) (2), the injection of the interface area in the traditional glue injection repair method (3), and the injection of the interface area in the repair method of the present invention (4).

[0033] Figure 6 Electrical performance parameters of the repair material at 4GHz (1) and 6GHz (2) for traditional glue injection repair methods.

[0034] Figure 7The figures (1) and (2) show the electrical performance of the repair material (glass fiber cloth impregnated with conductive slurry) in the repair method (conductive polymer patch + glue injection repair method) for penetrating damage to the absorbing honeycomb sandwich structure of the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0036] Distributed construction of multi-resonance characteristics of absorbing honeycomb sandwich structures in the 1.4-18GHz frequency band

[0037] One or more of the following materials, including but not limited to carbon black, graphite, carbon nanotubes, and graphene, are dispersed in epoxy resin to form a conductive polymer slurry, wherein the mass fraction of conductive particles is between 7% and 23%. The slurry is coated onto the inner wall of an aramid honeycomb with a pore size of 2.75 mm to 5.5 mm (preferably 3.67 mm) using a dip-coating process, wherein the aramid honeycomb height is 30-36 mm. The bulk density of the absorbing honeycomb (hexagonal pore structure) (typically 70-80 kg / m³) is controlled by varying the number of dips. 3 The equivalent dielectric constant shall be determined according to the equivalent dielectric constant (dielectric performance) index shown in Table 1.

[0038] Table 1. Dielectric performance indicators of microwave absorbing honeycomb sandwich structures

[0039]

[0040] Glass fiber reinforced resin is used as the upper panel of the absorbing honeycomb sandwich structure. The resin selected can be one or more of epoxy resin, phenolic resin, cyanate ester, and polyimide. The dielectric constant of the upper panel at 10 GHz is between 3.2 and 4, and the thickness is 1-3 mm. Carbon fiber reinforced resin is used as the lower panel (base plate) of the honeycomb sandwich structure. The thickness of the lower panel is 2-4 mm, and the carbon fiber volume fraction is between 30% and 50%. Epoxy resin film, including but not limited to, is used to bond the upper and lower panels to the honeycomb structure.

[0041] 2. A method for repairing penetrating damage to an absorbing honeycomb sandwich structure, comprising the following steps:

[0042] (1) First, identify the damaged area by visual inspection. Use a pencil and compass to draw a circle around the damaged area to enclose the damaged area, and record the radius of the circle as R1.

[0043] (2) The upper panel of the microwave absorbing honeycomb sandwich structure is polished with pneumatic polishing tools, including but not limited to pneumatic polishing tools, wherein the center of the polishing area coincides with the center of the damaged area, and the polishing radius is R1+d×40(mm), where d is the thickness of the upper panel (mm).

[0044] (3) Remove the damaged cells (damaged cores) of the absorbing honeycomb using tools including but not limited to paper cutters, honeycomb cutters or pneumatic grinding tools, and cut replacement honeycomb cores of the same specifications;

[0045] (4) Repeat the same steps as in step (2) to polish the lower panel of the absorbing honeycomb sandwich structure, that is, polish the lower panel of the absorbing honeycomb sandwich structure to expose the damaged pores of the absorbing honeycomb. The center of the polishing area coincides with the center of the damaged area. The polishing radius is R1+d×40, in mm, where d is the thickness of the lower panel, in mm.

[0046] (5) Select one or more of the following, including but not limited to carbon black, graphite, carbon nanotubes, and graphene, and disperse them in epoxy resin to form a conductive slurry. Control the mass fraction of conductive particles in the conductive slurry to be between 7% and 15%. Cut the glass fiber cloth and introduce the conductive slurry into the glass fiber cloth using an impregnation coating process. Adjust the conductivity of the glass fiber cloth by changing the number of impregnations so that its conductivity falls within the target conductivity range.

[0047] (6) Wrap the glass fiber cloth (i.e., conductive polymer patch) impregnated with conductive paste around the periphery of the honeycomb replacement core and insert it into the absorbing honeycomb holes;

[0048] (7) Use a water jet cutting machine to process the upper and lower panel circular pieces with a radius of R1+d×40 (mm) as panel repair patches. First, use epoxy resin to bond the lower panel repair circular piece to the corresponding absorbing honeycomb in the grinding area. Then, use epoxy resin to inject the honeycomb replacement core and the adjacent absorbing honeycomb grid (i.e., sandwich structure honeycomb core) interface area and cure it. Then, use epoxy resin to bond the upper panel repair circular piece to the corresponding absorbing honeycomb in the grinding area.

[0049] (8) Test the reflectivity according to GJB2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials" to verify the repair effect.

[0050] For high electrical performance damage tolerance absorbing honeycomb sandwich structures, when the proportion of penetrating damage exceeds the electrical performance damage tolerance, it is necessary to design a targeted electrical performance repair path and screen repair material systems. Figure 5This paper illustrates schematic diagrams of traditional glue-filling repair processes and the repair method proposed in this invention (i.e., conductive polymer patch + glue-filling repair process), as well as schematic diagrams of the injection interface between the two. The biggest difference between the traditional repair method and the conductive polymer patch + glue-filling repair method proposed in this invention lies in the treatment of the interface between the honeycomb replacement core and the sandwich structure honeycomb core. The electrical discontinuity at the interface places higher demands on the electrical performance of the repair material system. While the traditional repair method directly fills and injects the conductive polymer into the interface, which is convenient to implement, it has limitations such as… Figure 6 As shown, the difference between low-frequency and high-frequency repair mechanisms cannot be avoided, and the electrical properties of the damaged sandwich structure cannot be effectively repaired. Figure 6 (1) and Figure 6 (2) The electrical performance requirements of the repair material system (conductive polymer) at 4GHz and 6GHz frequencies are shown for traditional glue-filling repair methods. The dark area in the figure represents the target electrical performance range of the repair material system. Because the dielectric constant of real-world dielectric materials typically decreases with increasing frequency (dispersion effect), it is difficult to simultaneously meet the requirements. Figure 6 The electrical performance targets shown indicate that the electrical performance of traditional repair solutions is poorly controllable, making it difficult to effectively restore the electrical performance of damaged absorbing cells.

[0051] The repair method proposed in this invention utilizes conductive polymer patches to encapsulate the honeycomb replacement core, thus avoiding the adverse effects of electrical discontinuities. Epoxy resin is filled into the pores at the interface to achieve bonding. Figure 7 As shown, the repair method of the present invention has a large degree of electrical performance tunability and effectively avoids the difference between low-frequency and high-frequency repair mechanisms (the difference in repair mechanisms here refers to the loss mechanism that is mainly electromagnetic absorption at low frequency and mainly electromagnetic scattering at high frequency). Therefore, the repair method of the present invention can effectively repair the electrical performance of damaged sandwich structures.

[0052] Figure 7 The electrical performance and repair effects of the conductive polymer patch + encapsulation solution repair material system of the present invention are demonstrated. For example... Figure 7 (1) The target conductivity range of composite materials at 4GHz, 8GHz, 12GHz and 18GHz is shown, indicating that the target conductivity has a large conductivity control range at both low and high frequencies. The implementation scheme has excellent electrical performance designability and effectively solves the problem of poor controllability of electrical performance of the repair material system caused by the difference between the low-frequency and high-frequency repair mechanisms of traditional repair schemes. Figure 7 (1) The conductivity of the conductive polymer patch prepared according to the method of Example 1 is also demonstrated. Figure 7(2) The reflectivity test results in the 4-18GHz band after repair are shown, indicating that the effective absorption bandwidth after repair covers the entire 4-18GHz band, that is, the electrical performance of the absorbing cell sandwich structure is effectively repaired (such as repairing the case where the penetration damage accounts for 40%).

[0053] Example 1:

[0054] An absorbing honeycomb sandwich structure of the present invention includes an upper panel, an absorbing honeycomb (absorbing honeycomb layer) and a lower panel arranged sequentially from top to bottom. The absorbing honeycomb sandwich structure should meet the dielectric performance indicators shown in Table 1 in the 4GHz-18GHz frequency band.

[0055] Table 1. Dielectric performance indicators of microwave absorbing honeycomb sandwich structures

[0056]

[0057] In this embodiment, the absorbing honeycomb is composed of an aramid honeycomb structure and a conductive polymer coating applied to the inner wall of the aramid honeycomb structure pores. The side length of the aramid honeycomb structure pores is 3.67 mm, and the height of the aramid honeycomb structure is 30 mm. The conductive polymer coating includes epoxy resin and conductive particles dispersed in the epoxy resin. The conductive particles are carbon black and carbon nanotubes, and the mass ratio of carbon black, carbon nanotubes, and epoxy resin is 1:2:20.

[0058] In this embodiment, the upper panel is a glass fiber / epoxy resin laminate with a dielectric constant of 3.42 at 10 GHz and a thickness of 2 mm.

[0059] In this embodiment, the lower panel is a carbon fiber / epoxy resin laminate with a carbon fiber volume fraction of 50% and a thickness of 2mm.

[0060] In this embodiment, the upper panel and the absorbing honeycomb, as well as the absorbing honeycomb and the lower panel, are bonded together with epoxy resin film.

[0061] The average real part amplitude of the dielectric constant of the absorbing honeycomb sandwich structure in this embodiment is 2.63, 1.86, and 1.57 in the C-band, X-band, and Ku-band, respectively. The average imaginary part amplitude of the dielectric constant is 1.65, 1.13, and 0.47 in the C-band, X-band, and Ku-band, respectively.

[0062] The fabrication method of the microwave absorbing honeycomb sandwich structure in this embodiment includes the following steps:

[0063] A dispersion of carbon black, carbon nanotubes, and epoxy resin in a mass ratio of 1:2:20 was selected as the impregnation slurry. Aramid honeycomb with a pore side length of 3.67 mm and a height of 30 mm was selected for multiple impregnations. Each impregnation was followed by a 70°C inversion pre-curing process to ensure the conductive slurry adhered to the inner wall of the honeycomb pores. Through repeated impregnation and weighing, the bulk density of the resulting microwave absorbing honeycomb was determined to be 75 kg / m³. 3 A 2mm thick glass fiber / epoxy resin laminate was selected as the top panel and bonded with an epoxy resin film; a 2mm thick carbon fiber / epoxy resin laminate was selected as the bottom panel and bonded with an epoxy resin film, thus realizing the fabrication of the microwave absorbing honeycomb sandwich structure.

[0064] Example 2

[0065] The absorbing honeycomb sandwich structure of the present invention is basically the same as the absorbing honeycomb sandwich structure of Example 1, except that the height of the absorbing honeycomb is 33mm.

[0066] Example 3

[0067] The absorbing honeycomb sandwich structure of the present invention is basically the same as the absorbing honeycomb sandwich structure of Example 1, except that the height of the absorbing honeycomb is 36mm.

[0068] Figure 1 The reflection loss of the absorbing honeycomb sandwich structure of Example 1, designed according to the electrical performance design index in Table 1, in the 4-18 GHz frequency band is given. It shows that the absorbing honeycomb sandwich structure we proposed exhibits significant resonant behavior at 5 GHz, 8.5 GHz, 12.5 GHz and 16.5 GHz, that is, the distributed construction of multi-resonance characteristics in the 4-18 GHz frequency band is realized.

[0069] Figure 2 The measured reflection loss values ​​of the absorbing honeycomb sandwich structure with absorbing honeycomb heights of 30mm, 33mm, and 36mm are shown. Figure 2 In (1), 1, 2, 3, and 4 indicate the appearance of four typical resonant absorption peaks. Figure 2 (1) This indicates that as the height of the absorbing cell increases, all four typical resonators can exist stably in the 4-18 GHz frequency band and achieve distributed construction. Figure 2 (2) This indicates that the corresponding resonant frequency point moves linearly towards lower frequencies as the cell height increases.

[0070] Example 4

[0071] A method for repairing penetrating damage to an absorbing honeycomb sandwich structure according to the present invention, specifically for repairing a absorbing honeycomb sandwich structure with penetrating damage accounting for approximately 40%, includes the following steps:

[0072] (1) First, identify the damaged area by visual inspection. Use a pencil and compass to draw a circle around the damaged area to enclose the damaged area, and record the radius of the circle R1 = 100 mm.

[0073] (2) The upper panel of the absorbing honeycomb sandwich structure is polished by means of pneumatic polishing tools, including but not limited to, to expose the damaged pores of the absorbing honeycomb. The center of the polishing area coincides with the center of the damaged area. The polishing radius is R2=R1+d×30(mm=130mm, where d is the thickness of the upper panel. In this embodiment, the thickness of the upper panel is 1mm.

[0074] (3) Use a utility knife to remove the damaged cells of the absorbing honeycomb and cut replacement honeycomb cores of the same specifications;

[0075] (4) Repeat the same steps as in step (2) to polish the lower panel of the absorbing honeycomb sandwich structure;

[0076] (5) A dispersion of carbon black, carbon nanotubes, and epoxy resin in a mass ratio of 1:2:20 was selected as the conductive impregnation slurry. Glass fiber cloth was cut and the conductive slurry was introduced into the glass fiber cloth using an impregnation coating process. The conductivity of the glass fiber cloth impregnated with the conductive slurry was tested after different impregnation cycles to ensure that its conductivity fell within a certain range. Figure 7 (1) indicates the target conductivity range;

[0077] (6) Wrap the impregnated fiberglass cloth around the honeycomb replacement core, such as Figure 7 (2) As shown, it is inserted into the absorbing honeycomb holes;

[0078] (7) Use a water jet cutting machine to process upper and lower panel circular pieces with a radius of R2 = 130mm as panel repair patches. First, use epoxy resin to bond the lower panel repair circular piece to the corresponding absorbing honeycomb in the grinding area. Then, use epoxy resin to inject the honeycomb replacement core and the junction area of ​​the adjacent absorbing honeycomb cells (i.e. intact honeycomb cells). Curing is carried out according to the epoxy resin curing process. Then, use epoxy resin to bond the upper panel repair circular piece to the corresponding absorbing honeycomb in the grinding area.

[0079] (8) The reflectivity was tested according to GJB2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials" to verify the repair effect. The test results are shown in [reference needed]. Figure 7 (2) The reflection loss of the repaired absorbing honeycomb sandwich structure in the 4-18GHz frequency band is all <-10dB, indicating that the conductive polymer patch + glue injection repair process can effectively repair the electrical performance of the damaged sandwich structure.

[0080] Example 5: Damage tolerance assessment of the electrical performance of a multi-resonance absorbing honeycomb sandwich structure.

[0081] To highlight the unique role of distributed construction schemes with multi-resonance characteristics in improving electrical performance tolerance, Figure 3 The reflection loss and corresponding impedance matching characteristics of the absorbing honeycomb sandwich structure panel with damaged area ratios of 5%, 18%, 40%, and 72% in Example 1 are shown. Figure 3 (1) This indicates that as the proportion of damaged area increases, the absorbing honeycomb can still maintain the distributed structure with multi-resonance characteristics. Figure 3 (2) This indicates that the impedance matching mismatch between the absorbing honeycomb sandwich structure and free space is less than 0.6 in the 4-18GHz frequency band. For absorbing materials, the smaller the impedance mismatch, the better the absorbing performance. This invention can still have "controllable" impedance mismatch when the panel damage area accounts for up to 72% by using the distributed construction of multi-resonance characteristics, so that the reflection loss shows the characteristic of being insensitive to panel damage, that is, it improves the electrical performance damage tolerance of the absorbing honeycomb sandwich structure.

[0082] To further clarify the improvement effect of the design scheme proposed in this invention on the tolerance of electrical performance impairment, Figure 4 (1) and (2) illustrate the reflection loss and corresponding impedance matching characteristics of the absorbing honeycomb sandwich structure in Example 1 when the percentage of penetrating damage area is 5%, 18%, 40%, and 72%, respectively. When the percentage of penetrating damage area is less than 18%, the absorbing honeycomb sandwich structure can still maintain the distributed construction of multi-resonance characteristics, and the impedance matching mismatch with free space is less than 0.4 in the 4-18 GHz frequency band, thus enabling the effective absorption bandwidth to cover the 4-18 GHz frequency band, indicating high electrical performance damage tolerance. When the percentage of penetrating damage exceeds 18%, the multi-resonance phenomenon gradually disappears, and the impedance mismatch between the honeycomb and free space increases, manifested as a maximum impedance mismatch of 0.8 when the percentage of penetrating damage area reaches 40%, and a maximum impedance mismatch of 2.2 when the percentage of penetrating damage area reaches 72%, failing to achieve effective absorption of electromagnetic wave energy, and therefore requiring repair. In summary, the distributed construction of multi-resonance characteristics is beneficial to reducing the impedance mismatch of honeycomb damage, thereby achieving high electrical performance damage tolerance in the 4-18 GHz wideband.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method of repairing a wave-absorbing honeycomb sandwich structure penetration damage, characterized in that, The method comprises the following steps: (1) checking and identifying a damaged area, drawing a damaged area circle to envelope the damaged area, and recording a radius of the damaged area circle as R1; (2) polishing the upper panel of the wave-absorbing honeycomb sandwich structure to expose damaged cells of the wave-absorbing honeycomb, the center of the polishing area coincides with the center of the damaged area circle, and the polishing radius is R1+d*30 mm, where d is the thickness of the upper panel in mm; (3) removing the damaged cells of the wave-absorbing honeycomb to form a hole in the wave-absorbing honeycomb, and cutting a honeycomb replacement core of the same specification; (4) polishing the lower panel of the wave-absorbing honeycomb sandwich structure to expose damaged cells of the wave-absorbing honeycomb, the center of the polishing area coincides with the center of the damaged area circle, and the polishing radius is R1+d*30 mm, where d is the thickness of the lower panel in mm; (5) preparing a conductive paste for preparing a conductive polymer patch, introducing the conductive paste into a glass fiber cloth by an impregnation coating process, and controlling the electrical conductivity in a target electrical conductivity range by adjusting the impregnation times; (6) wrapping the glass fiber cloth impregnated with the conductive paste around the periphery of the honeycomb replacement core, and then inserting it into the hole of the wave-absorbing honeycomb; (7) preparing an upper panel repair disc and a lower panel repair disc, the radius of the upper panel repair disc and the radius of the lower panel repair disc are both the polishing radius, first, bonding the lower panel repair disc to the wave-absorbing honeycomb corresponding to the polishing area by using epoxy resin, then pouring epoxy resin into the junction area between the honeycomb replacement core and the adjacent wave-absorbing honeycomb cell and performing curing, and then bonding the upper panel repair disc to the wave-absorbing honeycomb corresponding to the polishing area by using epoxy resin; (8) testing reflectivity to verify the repair effect; The wave-absorbing honeycomb sandwich structure comprises an upper panel, a wave-absorbing honeycomb and a lower panel arranged in sequence from top to bottom, and the wave-absorbing honeycomb sandwich structure has the dielectric properties shown in Table 1 in the 4GHz-18GHz frequency band: Table 1 Dielectric performance index table of wave-absorbing honeycomb sandwich structure 。 2. The method of claim 1, wherein the wave-absorbing honeycomb sandwich structure penetration damage repair method is characterized by, In step (5), the conductive paste is prepared by dispersing conductive particles in epoxy resin, the conductive particles include one or more of carbon black, graphite, carbon nanotubes and graphene, and the mass fraction of the conductive particles in the conductive paste is 7%-15%.

3. The method of claim 1 or 2, wherein the wave-absorbing honeycomb sandwich structure penetration damage is repaired by the method, characterized in that, In steps (2) and (4), the polishing tool includes a pneumatic polishing tool.

4. The method of claim 1 or 2, wherein In step (3), the tool for removing includes a paper cutter, a honeycomb cutting knife or a pneumatic polishing tool.

5. The method of claim 1, wherein the wave-absorbing honeycomb sandwich structure penetration damage repair method is characterized by, The wave-absorbing honeycomb is composed of an aramid honeycomb structure and a conductive polymer coating coated on the inner wall of the hole of the aramid honeycomb structure; the cell side length of the aramid honeycomb structure is 2.75mm-5.5mm, and the height of the aramid honeycomb structure is 30mm-36mm; the conductive polymer coating comprises epoxy resin and conductive particles dispersed in the epoxy resin, the conductive particles include one or more of carbon black, graphite, carbon nanotubes and graphene, and the mass fraction of the conductive particles in the conductive polymer coating is 7%-23%.

6. The method of claim 1, wherein the wave-absorbing honeycomb sandwich structure is a wave-absorbing honeycomb sandwich structure for an aircraft. The upper panel is made of glass fiber reinforced resin, the resin used in the glass fiber reinforced resin includes one or more of epoxy resin, phenolic resin, cyanate ester and polyimide; the dielectric constant of the upper panel is 3.2-4 at 10GHz, and the thickness of the upper panel is 1mm-3mm.

7. The method of claim 1, wherein the wave-absorbing honeycomb sandwich structure is a wave-absorbing honeycomb sandwich structure for an aircraft. The lower panel is made of carbon fiber reinforced resin, the volume fraction of carbon fiber in the carbon fiber reinforced resin is 30%-50%, and the thickness of the lower panel is 2mm-4mm.

8. The method of claim 1, wherein the wave-absorbing honeycomb sandwich structure is a wave-absorbing honeycomb sandwich structure for an aircraft. The upper panel and the wave-absorbing honeycomb, and the wave-absorbing honeycomb and the lower panel are all bonded by epoxy resin adhesive film.

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