Variable-wall-thickness composite honeycomb sandwich wave-absorbing structure and integrated preparation method thereof

Abstract

This invention belongs to the field of microwave absorption technology and provides a variable-wall-thickness composite honeycomb sandwich microwave absorbing structure and its integrated fabrication method. The core structure of the intermediate absorbing layer consists of several arrayed variable-wall-thickness unit cells, which increases the number of electromagnetic wave reflections within the structure, broadens the electromagnetic wave absorption bandwidth, and improves electromagnetic wave absorption loss. The reflective layer of the sandwich microwave absorbing structure is made of a composite material composed of conductive continuous fibers and high-performance thermoplastic resin; the transparent layer is made of a composite material composed of low-dielectric-constant continuous fibers and high-performance thermoplastic resin; and the core layer is made of a thermoplastic high-performance resin containing magnetic and electrical loss absorbing agents. The fabrication method of this invention is simple to operate, has a stable process, uses widely available raw materials, and can achieve integrated printing of complex sandwich microwave absorbing structures, showing great application potential.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, and relates to a variable wall thickness composite honeycomb sandwich microwave absorbing structure and its integrated preparation method. Background Technology

[0002] With the development of radar detection technology, the risk of weapons and equipment being tracked and destroyed is increasing. Therefore, the widespread adoption of sandwich-type radar-absorbing structures that combine load-bearing and radar-absorbing functions to achieve stealth capabilities has become an important way to enhance the battlefield penetration capability and combat effectiveness of weapons and equipment. Currently, common sandwich-type radar-absorbing structures include honeycomb structures, pyramid structures, and corrugated structures. Among them, honeycomb structures have advantages over other structures, such as light weight, high strength and rigidity, and strong design flexibility, and are widely used in fighter jet wings, tail fins, and other parts. Traditional honeycomb sandwich-type radar-absorbing structures are mostly manufactured using a split method, bonding a regular hexagonal honeycomb core impregnated or sprayed with radar-absorbing agent slurry to the two side composite panels. However, when optimizing the performance of traditional regular hexagonal honeycomb cores, there are limited adjustment methods, resulting in limited improvement in radar absorption performance. Furthermore, this manufacturing method easily leads to insufficient bonding strength between the core and the panels in the sandwich structure, hindering the engineering application of this type of structure.

[0003] To address the above issues, Chinese patent CN 116864998 A discloses a non-integer dimension honeycomb absorbing structure, which adds a non-integer dimension hollow structure design to the ordinary honeycomb structure, thus broadening the absorption bandwidth. Chinese patent CN 116141804 A discloses a honeycomb transverse structure-based absorbing sandwich composite material and its preparation method, which changes the traditional honeycomb structure to a transverse structure, increasing the effective thickness relative to the incident electromagnetic wave and achieving a broadening of the absorption bandwidth. However, the core structure involved in CN 116141804 A requires the use of a mold and is formed by hot pressing. This method not only heavily relies on molds, but also has a cumbersome and time-consuming preparation process, making it impossible to manufacture cores with complex structures. Furthermore, the use of a split method to bond the core boards together makes it prone to problems such as core board cracking.

[0004] Therefore, to meet the requirements of wide absorption band of complex sandwich absorbing structures, as well as the manufacturing requirements of high strength and rapid prototyping, it is necessary to design a new composite honeycomb sandwich absorbing structure and its integrated preparation method. Summary of the Invention

[0005] To address the limitations of traditional regular honeycomb core structures in improving electromagnetic wave absorption performance, the unstable connection strength at the interface between traditional core and panel, and the inability to rapidly manufacture complex structures, this invention provides a honeycomb sandwich structure with strong electromagnetic wave absorption capabilities and a novel integrated panel-core-panel manufacturing method. First, a variable wall thickness honeycomb core structure is proposed. By increasing the number of electromagnetic wave reflections through the variable wall thickness design of the honeycomb core structure, the electromagnetic wave absorption performance is improved. Furthermore, a panel-core-panel structure composed of the same matrix composite material and its integrated printing manufacturing method are proposed. A heat source-pressure assisted method is used to further enhance the bonding strength at the panel-core-panel interface, effectively improving the overall load-bearing capacity of the sandwich microwave absorbing structure. Ultimately, this enables the rapid integrated molding and manufacturing of complex sandwich microwave absorbing structures.

[0006] The technical solution of this invention:

[0007] A variable wall thickness composite honeycomb sandwich absorbing structure includes an upper wave-transmitting layer, a middle wave-absorbing layer and a lower reflective layer. The overall structure is integrally formed by 3D printing.

[0008] The intermediate absorbing layer is composed of several unit cells arranged in an array. The cross-sectional shape of the unit cells can be a regular square, a regular pentagon, a regular hexagon, or a circle, and the configuration can be changed according to the requirements.

[0009] The wall thickness of the unit cell core increases uniformly from top to bottom in the vertical direction, and its vertical height h must satisfy 5≤h≤25mm. The minimum wall thickness b in the vertical height direction of the unit cell core must satisfy 0.5mm≤b≤2mm.

[0010] The maximum circumscribed circle diameter of the unit cell core is D, and the minimum circumscribed circle diameter is d. To ensure that electromagnetic waves are absorbed when they enter the structure, the minimum circumscribed circle diameter d is greater than the highest frequency of the measured waveband. The minimum circumscribed circle diameter d should not exceed 5 times the minimum wall thickness b (i.e., c / 10) while considering the overall structural load-bearing capacity. ≤d≤5b (unit: mm, c is wave velocity). Similarly, the maximum circumscribed circle diameter D is greater than the lowest frequency of the measured band. One-tenth of the wavelength, not exceeding ten times the minimum wall thickness b (i.e., c / 10). ≤D≤10b, unit mm, c is wave velocity).

[0011] The upper wave-transparent layer is mainly made of a composite material composed of low dielectric constant continuous fibers and high-performance resin, with the low dielectric constant continuous fibers accounting for 50 wt.% of the mass of the upper wave-transparent layer. Among them, the low dielectric constant continuous fibers include, but are not limited to, glass fibers and aramid fibers, and the high-performance resin matrix includes, but is not limited to, PA, PPS, and PI.

[0012] The lower reflective layer is mainly made of a composite material composed of conductive continuous fibers and high-performance resin, with the conductive continuous fibers accounting for 50 wt.% of the mass of the lower reflective layer. The conductive continuous fibers include, but are not limited to, carbon fiber and Kevlar fiber, and the high-performance resin matrix includes, but is not limited to, PA, PPS, and PI.

[0013] The intermediate absorbing layer is mainly composed of magnetic loss material, electrical loss absorbing agent, and high-performance resin. The mass fraction of magnetic loss material ranges from 5 wt.% to 30 wt.%, and the mass fraction of electrical loss absorbing agent ranges from 2 wt.% to 15 wt.%. Magnetic loss material includes, but is not limited to, ferrite, iron(III) oxide, and other metal powders; electrical loss absorbing agent includes, but is not limited to, carbon nanotubes, graphite, and other materials; and high-performance resin includes, but is not limited to, PA, PPS, and PI.

[0014] An integrated fabrication method for a variable wall thickness composite honeycomb sandwich microwave absorbing structure includes the following steps:

[0015] (1) Select conductive continuous fibers and high-performance resins and melt impregnate them with a filament making machine to obtain continuous conductive fiber prepreg; use the continuous conductive fiber prepreg to 3D print the lower reflective layer, the number of printing layers is 5-10, and the printing path is zigzag, orthogonal or 0°, 45°, 90°, 135° direction to stack the layers in a cyclic manner.

[0016] (2) Magnetic loss material, electrical loss absorbing agent and high performance resin are mixed in proportion and obtained by a twin-screw mixer and a single-screw extruder. The absorbing wire is then used to prepare the absorbing layer by 3D printing technology. The specific structure of the printing path is generated by slicing software.

[0017] (3) Select low dielectric constant continuous fibers and high performance resins and melt impregnate them with a filament making machine to obtain continuous low dielectric constant fiber prepreg; use the continuous low dielectric constant fiber prepreg to 3D print a wave-transparent layer, with 10-15 layers printed and the printing path being zigzag or orthogonal.

[0018] (4) Place the three types of filaments obtained in steps (1), (2), and (3) into the 3D printing equipment. Based on the printing path code obtained in steps (1), (2), and (3), first complete the printing of the lower reflective layer on the printing platform according to the path in step (1).

[0019] (5) Switch materials and print the intermediate absorbing layer on the basis of the lower reflective layer; apply a heat source near the printing nozzle to ensure that the temperature of the material near the nozzle is at the melting point of the high-performance resin, and apply pressure after the material is extruded from the nozzle to ensure the bonding strength between the intermediate absorbing layer and the lower reflective layer.

[0020] (6) Switch materials again and print the upper wave-transmitting layer on the middle absorbing layer according to step (3). During the printing process, apply a heat source near the printing nozzle to ensure that the temperature of the material near the nozzle is at the melting point of the high-performance resin. At the same time, apply pressure after the material is extruded from the nozzle to ensure the bonding strength between the upper wave-transmitting layer and the middle absorbing layer.

[0021] The beneficial effects of this invention are as follows: Compared to traditional honeycomb structures, the variable wall thickness honeycomb structure proposed in this invention replaces the vertical honeycomb walls with inclined honeycomb walls, increasing the effective reflective area and the number of reflections of electromagnetic waves within the structure. Simultaneously, the synergistic effect of the two lossy materials increases the loss of electromagnetic waves during reflection, broadening the electromagnetic wave absorption bandwidth and improving the overall electromagnetic wave reflection loss. Furthermore, the integrated 3D printing manufacturing method of the sandwich-core-plate absorber structure satisfies the requirements for rapid prototyping and integrated forming of complex core structures, avoiding insufficient bonding strength between the core and plate caused by separate manufacturing. This method is simple to operate, uses widely available raw materials, has high preparation efficiency, and has excellent application prospects. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the variable wall thickness composite honeycomb sandwich microwave absorbing structure of the present invention.

[0023] Figure 2 This is a top view of the unit cell structure of the variable wall thickness composite honeycomb sandwich microwave absorbing core of the present invention.

[0024] Figure 3 This is an axonometric view of the unit cell structure of the variable wall thickness composite honeycomb sandwich absorbing core of the present invention.

[0025] Figure 4 This is a schematic diagram of the reflective layer path of the variable wall thickness composite honeycomb sandwich absorbing structure of the present invention.

[0026] Figure 5 The simulation curves show the microwave absorption performance of a typical honeycomb structure.

[0027] Figure 6 This is a simulation curve of the microwave absorption performance of the variable wall thickness composite honeycomb sandwich microwave absorbing core structure of the present invention.

[0028] In the diagram: 1-wave-transmitting layer, 2-wave-absorbing layer, 3-reflecting layer. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0030] Example 1

[0031] like Figure 1As shown, a variable wall thickness composite honeycomb sandwich absorbing structure is composed of an upper wave-transmitting layer 1, a middle wave-absorbing layer 2 and a lower reflective layer 3. The wave-absorbing layer is formed by an array of unit cell structures, forming an overall structure with length, width and height dimensions of 200×200mm×12mm. The overall structure is integrally formed by 3D printing.

[0032] A variable wall thickness composite honeycomb sandwich microwave absorbing structure and its integrated fabrication method are described below:

[0033] (1) PA was selected as the thermoplastic resin matrix, and iron oxide and carbon nanotubes were selected as magnetic loss type and electrical loss type microwave absorbers, respectively. PA resin powder was mixed with iron oxide powder and carbon nanotube powder at mass fractions of 65%, 25% and 6%, respectively. A wire with a diameter of about 1.5-1.75 mm was obtained by using a twin-screw mixer and a single-screw extruder. The electromagnetic parameters of Fe3O4 / CNTs / PA material were measured by waveguide method.

[0034] (2) PA is selected as the thermoplastic resin matrix, glass fiber is selected as the wave-transparent fiber, and carbon fiber is selected as the conductive fiber. The fiber is melt-impregnated by a fiber making machine to obtain continuous glass fiber prepreg and continuous carbon fiber prepreg.

[0035] (3) Model the variable thickness honeycomb structure in SOLIDWOREKS. The minimum cross-sectional circumscribed circle diameter d=5mm, the maximum cross-sectional circumscribed circle diameter D=15mm, the minimum wall thickness in the height direction b=1mm, the honeycomb height h=10mm, and the overall structure is composed of a single cell structure array.

[0036] (4) The number of transparent layers is 10, the layer thickness is 0.1mm, the line spacing is 0.8mm, and the printing path is zigzag.

[0037] (5) The number of reflective layer printing layers is 5, the printing layer thickness is 0.2mm, the printing line spacing is 0.8mm, and the printing path is 0°, 45°, 90°, 135° and 0° direction stacked layer by layer.

[0038] (6) Slice the core structure model, the wave-transmitting layer path and the reflective layer path to obtain their respective gcode codes, and then obtain the printing code of the sandwich absorbing structure that can be recognized by the printer.

[0039] (7) Place the three types of filaments obtained in steps (1) and (2) into the 3D printing equipment. Based on the printing code obtained in step (6), first complete the printing of the reflective layer on the printing platform according to the path in step (3).

[0040] (8) Switch materials and print the absorbing core structure on the basis of the reflective layer. When printing the absorbing material, apply a small heat source near the printing nozzle to ensure that the material temperature near the nozzle is about 218°C. At the same time, apply a small force after the material is extruded from the nozzle to ensure the bonding strength between the absorbing material and the reflective layer.

[0041] (9) Change the material again and print the wave-transmitting layer on the core structure according to step (4). At the same time, apply a small heat source near the printing nozzle to ensure that the material temperature near the nozzle is about 218°C. At the same time, apply a small force after the material is extruded from the nozzle to ensure the bonding strength between the wave-transmitting layer and the core layer.

[0042] The 3D printing equipment used in this embodiment also has a heat source-pressure auxiliary function.

[0043] Depend on Figure 5 and Figure 6 It was found that, compared with ordinary honeycomb structures, the variable wall thickness honeycomb absorbing structure of the present invention has an effective absorption frequency band that is broadened from 5.5GHz to 10.2GHz, and the maximum absorption loss is increased from -23dB to -28.5dB.

Claims

1. A variable wall thickness composite honeycomb sandwich microwave absorbing structure, characterized in that, The variable wall thickness composite honeycomb sandwich absorbing structure includes an upper wave-transmitting layer, a middle wave-absorbing layer and a lower reflective layer. The overall structure is integrally formed by 3D printing. The intermediate absorbing layer is composed of several unit cells arranged in an array. The cross-sectional shape of the unit cells is a regular square, a regular pentagon, a regular hexagon, or a circle. The wall thickness of the unit cell core increases uniformly from top to bottom in the vertical direction, and its vertical height h must satisfy 5≤h≤25mm. The minimum wall thickness b in the vertical height direction of the unit cell core must satisfy 0.5mm≤b≤2mm. The maximum circumscribed circle diameter of the unit cell core is D, and the minimum circumscribed circle diameter is d. To ensure that electromagnetic waves are absorbed when they enter the structure, the minimum circumscribed circle diameter d is greater than the highest frequency of the measured waveband. The minimum circumscribed circle diameter d should not exceed 5 times the minimum wall thickness b, while considering the overall structural load-bearing capacity; the maximum circumscribed circle diameter D should be greater than the lowest frequency of the measured band. One-tenth of the wavelength, not exceeding ten times the minimum wall thickness b.

2. The variable wall thickness composite honeycomb sandwich microwave absorbing structure according to claim 1, characterized in that, The upper wave-transparent layer comprises a composite material consisting of low dielectric constant continuous fibers and high performance resin, with the low dielectric constant continuous fibers accounting for 50 wt.% of the mass of the upper wave-transparent layer.

3. The variable wall thickness composite honeycomb sandwich microwave absorbing structure according to claim 2, characterized in that, The lower reflective layer comprises a composite material consisting of conductive continuous fibers and high-performance resin, with the conductive continuous fibers accounting for 50 wt.% of the mass of the lower reflective layer.

4. The variable wall thickness composite honeycomb sandwich microwave absorbing structure according to claim 3, characterized in that, The intermediate absorbing layer comprises magnetic loss material, electrical loss absorbing agent and high performance resin, with the magnetic loss material accounting for 5 wt.%-30 wt.% by mass and the electrical loss absorbing agent accounting for 2 wt.%-15 wt.% by mass.

5. The variable wall thickness composite honeycomb sandwich microwave absorbing structure according to claim 4, characterized in that, The conductive continuous fibers include carbon fiber and Kevlar fiber; the high-performance resins include PA, PPS, and PI; the magnetic loss materials include ferrite and iron(III) oxide; the electrical loss absorbing agents include carbon nanotubes and graphite; and the low dielectric constant continuous fibers include glass fiber and aramid fiber.

6. An integrated fabrication method for a variable wall thickness composite honeycomb sandwich microwave absorbing structure as described in claim 1, characterized in that, Includes the following steps: (1) Select conductive continuous fibers and high-performance resins and melt impregnate them with a filament making machine to obtain continuous conductive fiber prepreg; use the continuous conductive fiber prepreg to 3D print the lower reflective layer, the number of printing layers is 5-10, and the printing path is zigzag, orthogonal or 0°, 45°, 90°, 135° direction to stack the layers in a cyclic manner. (2) Magnetic loss material, electrical loss absorbing agent and high performance resin are mixed in proportion and obtained by a twin-screw mixer and a single-screw extruder. The absorbing wire is then used to prepare the absorbing layer by 3D printing technology. The specific structure of the printing path is generated by slicing software. (3) Select low dielectric constant continuous fibers and high performance resins and melt impregnate them with a filament making machine to obtain continuous low dielectric constant fiber prepreg; use the continuous low dielectric constant fiber prepreg to 3D print a wave-transparent layer, with 10-15 layers printed and the printing path being zigzag or orthogonal. (4) Place the three types of filaments obtained in steps (1), (2), and (3) into the 3D printing equipment. Based on the printing path code obtained in steps (1), (2), and (3), first complete the printing of the lower reflective layer on the printing platform according to the path in step (1). (5) Switch materials and print the intermediate absorbing layer on the basis of the lower reflective layer; apply a heat source near the printing nozzle to ensure that the temperature of the material near the nozzle is at the melting point of the high-performance resin, and apply pressure after the material is extruded from the nozzle to ensure the bonding strength between the intermediate absorbing layer and the lower reflective layer. (6) Switch materials again and print the upper wave-transparent layer on the middle absorbing layer according to step (3). During the printing process, apply a heat source near the printing nozzle to ensure that the temperature of the material near the nozzle is at the melting point of the high-performance resin. At the same time, apply pressure after the material is extruded from the nozzle to ensure the bonding strength between the upper wave-transparent layer and the middle absorbing layer.

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