A method for repairing damaged electrical properties of a wave-absorbing honeycomb core

Abstract

The present invention relates to the technical field of aircraft absorbing honeycomb structure damage repair, specifically a method for repairing the electrical properties of damaged absorbing honeycomb cores, comprising the following steps: identifying and marking the outline of the damaged area of ​​the absorbing honeycomb core using nondestructive testing equipment; determining the material system, core cell dimensions, and electrical performance range based on the absorbing honeycomb core structural information; calculating the absorbing honeycomb core skeleton and the absorbing layer duty cycle based on the honeycomb core unit cell margins, wall thickness, and absorbing layer thickness; preparing a new absorbing honeycomb core corresponding to the size of the damaged area of ​​the absorbing honeycomb core, and using a cutting knife to cut along the periphery of the damaged area of ​​the absorbing honeycomb core to remove the damaged absorbing honeycomb core. The present invention selects a small, wave-transparent aramid paper honeycomb core as the skeleton, ensuring consistency with the absorbing honeycomb core material system and facilitating the restoration of mechanical properties. MATLAB mathematical calculation software can be used to calculate the target electrical properties of the adhesive under different small core structural parameters, enhancing the designability of the repair solution.

Description

Technical Field

[0001] The present invention relates to the technical field of damage repair of aircraft wave-absorbing honeycomb structures, and in particular to a method for repairing damaged electrical properties of a wave-absorbing honeycomb core. Background Art

[0002] On the modern information-based battlefield, detection means destruction has become a harsh reality. The release of a US spectrum warfare white paper reveals the unique role of the electromagnetic spectrum in providing combatants with tactical and strategic competitive advantages, as well as freedom of attack, maneuver, and defense. As a core element of electromagnetic spectrum warfare, stealth aircraft must possess both the dual attributes of a "wave-transmitting spear" and a "stealth shield." This requires the use of wave-transmitting materials to allow radars to see farther and strike more accurately, while simultaneously utilizing wave-absorbing materials to conceal the aircraft from enemy detection.

[0003] Aramid paper honeycomb structures, characterized by their lightweight, high flexural strength / mass ratio, strong resistance to buckling, and excellent thermal and acoustic insulation, are widely used in primary and secondary load-bearing aircraft structures. Their low dielectric constant and dielectric loss within the GHz frequency band make them transparent to radar waves, making them excellent wave-transmitting honeycombs. Aramid paper honeycombs, designed using stealth technology, exhibit radar absorption properties, making them excellent wave-absorbing honeycombs.

[0004] During actual service, the absorbing honeycomb is prone to damage such as honeycomb core collapse, semi-penetration and penetration damage. The change in the equivalent circuit connection form at the damaged part causes the electrical performance of the absorbing honeycomb to decrease exponentially with the increase of the damaged area. Figure 1 Currently, traditional paper honeycomb core repair techniques for this type of honeycomb structure primarily focus on using transparent aramid paper honeycombs. These methods employ a patching method to remove the damaged honeycomb core by grinding it out, then fill it with a honeycomb core of the same specification and bond it with transparent foam adhesive to restore the damaged honeycomb's mechanical properties. However, currently, no process exists to repair absorbing honeycomb cores from the perspective of integrated load-bearing and wave-absorbing capabilities. Field repairs for damaged absorbing honeycomb cores still rely on traditional aramid paper honeycomb methods.

[0005] The following drawbacks exist during the polishing stage of the repair process: 1. When using pneumatic polishing tools to remove the damaged absorbing honeycomb core, the intact absorbing honeycomb core cells near the polishing area are often significantly deformed, resulting in changes in the equivalent circuit connection form; 2. The pneumatic polishing tool increases the surface roughness after polishing, introducing excess surface resistance in the equivalent circuit; 3. The gap between the replacement honeycomb core and the intact honeycomb core is random, making it impossible to effectively evaluate the electrical performance of the repaired absorbing honeycomb.

[0006] The following disadvantages exist in the gluing stage of the repair process: 1. The electrical properties of the foam glue are close to those of air, and the equivalent circuit connection form of the gluing area cannot be effectively repaired; 2. The foam glue has a specific thickness, which causes the hexagonal honeycomb network in the gluing area to be interrupted, which directly leads to an increase in the capacitance value in the equivalent circuit; 3. The volume of the foam glue expands when it solidifies, increasing the degree of interruption of the hexagonal honeycomb network in the gluing area and seriously increasing the capacitance value of the equivalent circuit.

[0007] Therefore, the use of traditional aramid paper honeycomb foam adhesive bonding process does not fundamentally restore the equivalent circuit connection form of the bonding area, resulting in the deterioration of the electrical performance of the absorbing honeycomb after repair, such as Figure 2 shown. Summary of the Invention

[0008] To address the above technical issues, the present invention proposes a method for repairing the electrical performance of damaged absorbing honeycomb cores. Drawing on the equivalent circuit theory of absorbing materials, the present invention uses a small core-to-large core method to address the problem of electrical performance degradation caused by damaged aircraft absorbing honeycomb cores.

[0009] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0010] A method for repairing damaged electrical properties of a wave-absorbing honeycomb core comprises the following steps:

[0011] (1) Using non-destructive testing equipment to identify and mark the outline of the damaged area of ​​the absorbing honeycomb core;

[0012] (2) Determine the material system, core cell size, and electrical performance range based on the structural information of the absorbing honeycomb core;

[0013] (3) Calculate the duty cycle of the absorbing honeycomb core skeleton and the absorbing layer based on the edge distance, wall thickness and absorbing layer thickness of the absorbing honeycomb core;

[0014] (4) preparing a new absorbing honeycomb core corresponding to the size of the damaged area of ​​the absorbing honeycomb core, and using a cutting knife to cut along the periphery of the damaged area of ​​the absorbing honeycomb core to remove the damaged absorbing honeycomb core;

[0015] (5) using the new absorbing honeycomb core prepared in step (4) for filling, and maintaining a regular hexagonal structure at the interface between the new absorbing honeycomb core and the intact absorbing honeycomb core during filling;

[0016] (6) Selecting an aramid paper honeycomb core unit cell and, based on the margins and wall thickness of the selected aramid paper honeycomb core unit cell, calculating the duty ratio of the aramid paper honeycomb and the gap between the aramid paper honeycomb and the regular hexagonal cells;

[0017] (7) Based on the metal backplane model of the absorbing material and the MATLAB mathematical calculation software, calculate the height of the repaired absorbing honeycomb and the target electrical performance range of the absorbing honeycomb corresponding to the electromagnetic reflection coefficient <-10dB at different frequency points in the studied frequency band;

[0018] (8) Based on the calculated target electrical performance range of the absorbing honeycomb at different frequencies, combined with the equivalent dielectric property constitutive matrix of the strong perturbation theory, calculate the target electrical performance range of the adhesive filled in the gap area between the aramid paper honeycomb core and the regular hexagonal cells under the long wave approximation condition;

[0019] (9) mixing the absorbing particles with the adhesive, and determining the mixing ratio of the absorbing particles to the adhesive based on the target electrical performance range of the adhesive and the dielectric mixing law;

[0020] (10) Mixing the absorbing particles with the adhesive and filling the mixture into the gap between the aramid paper honeycomb and the regular hexagonal cells;

[0021] (11) Heat and cure according to the adhesive material process;

[0022] (12) After curing, remove the vacuum bag, perform post-processing on the repaired part and use the bow frame method in GJB2038A "Test Method for Reflectivity of Radar Absorbing Materials" to test the electromagnetic reflectivity and check the repair effect.

[0023] As a further improvement of the present invention, the aramid paper skeleton selected for the wave-absorbing honeycomb structure in step (2) has a wall thickness of 0.2 mm, a side-to-side distance of 5 mm, and an absorption layer coated on the inner wall of the skeleton has a thickness of 0.15 mm.

[0024] As a further improvement of the present invention, in step (2), the real part of the dielectric constant of the absorbing honeycomb structure at a frequency of 10 GHz ranges from 2.2 to 2.6, and the imaginary part of the dielectric constant ranges from 2.4 to 2.8.

[0025] As a further improvement of the present invention, in step (iii), the duty ratio of the wave-absorbing honeycomb core skeleton is 0.08, and the duty ratio of the absorption layer is 0.13.

[0026] As a further improvement of the present invention, the cutting knife in step (iv) should cut along the honeycomb wall without damaging the corners.

[0027] As a further improvement of the present invention, the aramid paper honeycomb core unit cell selected in step (six) has a specific width-to-edge distance of 2.8 mm, a wall thickness of 0.1 mm, a duty cycle of 0.02, and a duty cycle of the gap between the aramid paper honeycomb and the regular hexagonal cells of 0.38.

[0028] As a further improvement of the present invention, the height of the absorbing honeycomb repaired in step (seven) is 15 mm, and the target value of the real part of the dielectric constant at the corresponding 10 GHz frequency point is between 1-5, and the target value of the imaginary part of the dielectric constant is between 1-3.

[0029] As a further improvement of the present invention, in step (eight), the duty cycle of the adhesive filling the gap area is 0.38, corresponding to a frequency point of 10 GHz, the target value of the real part of the dielectric constant is between 0.8-3.3, and the target value of the imaginary part of the dielectric constant is between 0.2-0.5.

[0030] As a further improvement of the present invention, step (9) specifically includes: selecting conductive carbon black with a conductivity of 2-4 S / m, mixing the conductive carbon black with epoxy resin using a high-speed ball milling method, wherein the mass fraction of the conductive carbon black is between 10% and 30%, and using acetone as a dispersant.

[0031] As a further improvement of the present invention, in step (twelve), the surface of the repair area is smoothed by post-processing.

[0032] The beneficial effects of the present invention are:

[0033] The present invention solves the problem of electrical performance degradation caused by damage to aircraft absorbing honeycombs by inserting small cores into large cores based on the equivalent circuit theory of absorbing materials. Compared with the prior art:

[0034] 1. Using a manually operated cutting knife instead of a pneumatic grinding tool can avoid deformation of the honeycomb core near the cutting area;

[0035] 2. Selecting a small wave-transmitting aramid paper honeycomb core as the skeleton ensures consistency with the wave-absorbing honeycomb core material system and helps to restore the mechanical properties;

[0036] 3. Computer programming can be used to calculate the target electrical performance of the adhesive under different small core structural parameters, enhancing the designability of the repair plan;

[0037] 4. The air column wrapped in the small core plays an important role in impedance matching, which increases the control space of the electrical properties of the adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0039] Figure 1 Schematic diagram of the damage of the absorbing honeycomb core and its equivalent circuit;

[0040] Figure 2 Schematic diagram of the traditional aramid paper honeycomb core damage repair and its equivalent circuit;

[0041] Figure 3Schematic diagram of the invention for repairing the absorbing honeycomb core by inserting the small core into the large core and its equivalent circuit. DETAILED DESCRIPTION

[0042] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0043] like Figure 3 As shown, a method for repairing damaged electrical properties of a wave-absorbing honeycomb core comprises the following steps:

[0044] (1) Using non-destructive testing equipment such as X-rays, the outline of the damaged area of ​​the absorbing honeycomb core is identified and marked. Specifically, in this embodiment, the size of the damaged area of ​​the absorbing honeycomb core is Φ120 mm.

[0045] (2) Based on the absorbing honeycomb core structure information, determine the material system, core cell dimensions, and electrical performance range. Specifically, in this embodiment, the absorbing honeycomb uses an aramid paper skeleton with a wall thickness of 0.2 mm, a width across edges of 5 mm, and an absorbing layer coated on the inner wall of the skeleton with a thickness of 0.15 mm. At a frequency of 10 GHz, the real part of the dielectric constant of the absorbing honeycomb ranges from 2.2 to 2.6, and the imaginary part of the dielectric constant ranges from 2.4 to 2.8.

[0046] (3) According to the single cell margin, wall thickness and absorption layer thickness of the absorbing honeycomb core, the duty ratios of the absorbing honeycomb core skeleton and the absorption layer are calculated respectively. Finally, the duty ratio of the absorbing honeycomb core skeleton is 0.08, and the duty ratio of the absorption layer is 0.13.

[0047] (IV) Prepare a new absorbing honeycomb core with a size of Φ120mm, and use a cutting knife to cut along the periphery of the damaged area of ​​the absorbing honeycomb core. When cutting, cut along the honeycomb wall without damaging the corners, and remove the damaged absorbing honeycomb core.

[0048] (5) Use the new absorbing honeycomb core prepared in step (4) for filling, and during filling, the interface between the new absorbing honeycomb core and the intact absorbing honeycomb core maintains a regular hexagonal structure.

[0049] (6) Selecting an aramid paper honeycomb core unit cell. Specifically, in this embodiment, an aramid paper honeycomb core unit cell with a side-to-side distance of 2.8 mm and a wall thickness of 0.1 mm is selected. Based on the side distance and wall thickness of the selected aramid paper honeycomb core unit cell, the duty ratios of the aramid paper honeycomb and the gap area between the aramid paper honeycomb and the regular hexagonal cells are calculated, respectively. Ultimately, the duty ratio of the aramid paper honeycomb is 0.02, and the duty ratio of the gap area between the aramid paper honeycomb and the regular hexagonal cells is 0.38.

[0050] (7) Based on the metal backplane model of the absorbing material and the MATLAB mathematical calculation software, the height of the repaired absorbing honeycomb and the target electrical performance range of the absorbing honeycomb corresponding to the electromagnetic reflection coefficient <-10dB at different frequency points in the studied frequency band are calculated. Finally, the height of the repaired absorbing honeycomb is obtained to be 15mm, corresponding to the frequency point of 10GHz, the target value of the real part of the dielectric constant is between 1-5, and the target value of the imaginary part of the dielectric constant is between 1-3.

[0051] (8) Based on the calculated target electrical performance range of the absorbing honeycomb at different frequency points, combined with the equivalent dielectric property constitutive matrix of the strong perturbation theory, the target electrical performance range of the adhesive filled in the gap area between the aramid paper honeycomb core and the regular hexagonal cell is calculated under the long wave approximation condition. Finally, the duty cycle of the adhesive filled in the gap area is obtained to be 0.38, corresponding to the target value of the real part of the dielectric constant at the 10 GHz frequency point between 0.8-3.3, and the target value of the imaginary part of the dielectric constant between 0.2-0.5.

[0052] (9) Mixing the absorbing particles with the adhesive. The mixing ratio of the absorbing particles to the adhesive is determined based on the target electrical performance range of the adhesive and the dielectric mixing law. Specifically, in this embodiment, conductive carbon black with a conductivity of 2-4 S / m is selected. The conductive carbon black is mixed with the epoxy resin using a high-speed ball milling method. The mass fraction of the conductive carbon black is between 10% and 30%, and acetone is used as a dispersant.

[0053] (10) Mix the absorbing particles with the adhesive and fill them into the gap between the aramid paper honeycomb and the regular hexagonal cells.

[0054] (11) Heating and curing is performed according to the adhesive material process. Specifically, in this embodiment, heating and curing is performed according to HB / Z 305-1997 "Autoclave Forming Process for Composite Materials".

[0055] (12) After curing, remove the vacuum bag, perform post-processing on the repaired part to make the surface smooth, and use the bow frame method in GJB2038A "Test method for reflectivity of radar absorbing materials" to test the electromagnetic reflectivity and check the repair effect.

[0056] The present invention solves the problem of electrical performance degradation caused by damaged aircraft absorbing honeycombs by inserting small cores into large cores based on the equivalent circuit theory of absorbing materials; deformation of the honeycomb core near the cutting area can be avoided by using a manually operated cutting knife instead of a pneumatic grinding tool; 2. By selecting a small, wave-transparent aramid paper honeycomb core as the skeleton, consistency with the absorbing honeycomb core material system is ensured, which helps to restore mechanical properties; 3. By using MATLAB mathematical calculation software to calculate the target electrical properties of the adhesive under different small core structural parameters, the designability of the repair plan is enhanced; 4. The air column wrapped in the small core plays an important role in impedance matching, which increases the control space for the electrical properties of the adhesive.

[0057] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and description merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for repairing damaged electrical properties of a microwave-absorbing honeycomb core, characterized by: The following steps are involved: (1) Using non-destructive testing equipment to identify and mark the outline of the damaged area of ​​the absorbing honeycomb core; (2) Determine the material system, core cell size, and electrical performance range based on the structural information of the absorbing honeycomb core; (3) Calculate the duty cycle of the absorbing honeycomb core skeleton and the absorbing layer based on the edge distance, wall thickness and absorbing layer thickness of the absorbing honeycomb core; (4) preparing a new absorbing honeycomb core corresponding to the size of the damaged area of ​​the absorbing honeycomb core, and using a cutting knife to cut along the periphery of the damaged area of ​​the absorbing honeycomb core to remove the damaged absorbing honeycomb core; (5) using the new absorbing honeycomb core prepared in step (4) for filling, and maintaining a regular hexagonal structure at the interface between the new absorbing honeycomb core and the intact absorbing honeycomb core during filling; (6) Selecting an aramid paper honeycomb core unit cell and, based on the margins and wall thickness of the selected aramid paper honeycomb core unit cell, calculating the duty ratio of the aramid paper honeycomb and the gap between the aramid paper honeycomb and the regular hexagonal cells; (7) Based on the metal backplane model of the absorbing material and the MATLAB mathematical calculation software, calculate the height of the repaired absorbing honeycomb and the target electrical performance range of the absorbing honeycomb corresponding to the electromagnetic reflection coefficient <-10dB at different frequency points in the studied frequency band; (8) Based on the calculated target electrical performance range of the absorbing honeycomb at different frequencies, combined with the equivalent dielectric property constitutive matrix of the strong perturbation theory, calculate the target electrical performance range of the adhesive filled in the gap area between the aramid paper honeycomb core and the regular hexagonal cells under the long wave approximation condition; (9) mixing the absorbing particles with the adhesive, and determining the mixing ratio of the absorbing particles to the adhesive based on the target electrical performance range of the adhesive and the dielectric mixing law; (10) Mixing the absorbing particles with the adhesive and filling the mixture into the gap between the aramid paper honeycomb and the regular hexagonal cells; (11) Heat and cure according to the adhesive material process; (12) After curing, remove the vacuum bag, perform post-processing on the repaired part and use the bow frame method in GJB2038A "Test Method for Reflectivity of Radar Absorbing Materials" to test the electromagnetic reflectivity and check the repair effect.

2. A method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: The aramid paper skeleton used in the wave-absorbing honeycomb structure in step (2) has a wall thickness of 0.2 mm, a side-to-side distance of 5 mm, and an absorption layer coated on the inner wall of the skeleton with a thickness of 0.15 mm.

3. A method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: In step (2), the real part of the dielectric constant of the absorbing honeycomb structure at a frequency of 10 GHz ranges from 2.2 to 2.6, and the imaginary part of the dielectric constant ranges from 2.4 to 2.

8.

4. A method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: In step (3), the duty ratio of the absorbing honeycomb core skeleton is 0.08, and the duty ratio of the absorbing layer is 0.

13.

5. The method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: In step (4), the cutting knife should cut along the honeycomb wall and should not damage the corners.

6. A method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: The aramid paper honeycomb core unit cell selected in step (six) has a specific width-to-width distance of 2.8 mm, a wall thickness of 0.1 mm, a duty cycle of 0.02, and a duty cycle of the gap between the aramid paper honeycomb and the regular hexagonal cells of 0.

38.

7. The method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: The height of the absorbing honeycomb repaired in step (seven) is 15 mm, and the target value of the real part of the dielectric constant at the 10 GHz frequency point is between 1 and 5, and the target value of the imaginary part of the dielectric constant is between 1 and 3.

8. The method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: In step (eight), the duty cycle of the adhesive filling the gap area is 0.38, corresponding to a frequency point of 10 GHz, a target value of the real part of the dielectric constant is between 0.8-3.3, and a target value of the imaginary part of the dielectric constant is between 0.2-0.

5.

9. The method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: Step (9) specifically comprises: selecting conductive carbon black with a conductivity of 2-4 S / m, mixing the conductive carbon black with epoxy resin using a high-speed ball milling method, wherein the mass fraction of the conductive carbon black is between 10% and 30%, and using acetone as a dispersant.

10. The method for repairing damaged electrical properties of a microwave-absorbing honeycomb core according to claim 1, characterized in that: In step (12), the surface of the repaired area is smoothed by post-processing.

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