Honeycomb sandwich wave-absorbing structure made of variable-wall-thickness composite material and integrated preparation method of honeycomb sandwich wave-absorbing structure

Abstract

The invention belongs to the technical field of wave absorption, and provides a variable-wall-thickness composite material honeycomb interlayer wave-absorbing structure and an integrated preparation method thereof. The core structure in the middle wave-absorbing layer is composed of a plurality of variable-wall-thickness unit cell cores arranged in an array mode, the reflection frequency of electromagnetic waves in the structure can be increased, the electromagnetic wave absorption frequency band is widened, and the electromagnetic wave absorption loss is improved. The reflecting layer of the interlayer wave-absorbing structure is prepared from a composite material composed of conductive continuous fibers and high-performance thermoplastic resin, the wave-transparent layer is prepared from a composite material composed of low-dielectric-constant continuous fibers and high-performance thermoplastic resin, and the core layer is prepared from thermoplastic high-performance resin containing magnetic loss and electrical loss wave-absorbing agents. The preparation method is easy to operate, the process is stable, raw materials are wide, integrated overall printing of the complex sandwich wave-absorbing structure can be achieved, and good application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of wave-absorbing materials, and relates to a variable-thickness composite honeycomb sandwich wave-absorbing structure and an integrated preparation method thereof. Background Art

[0002] With the development of radar detection technology, the risk of weapons and equipment being tracked and destroyed is increasing. To this end, a large number of sandwich absorbing structures with both load-bearing and wave-absorbing functions are used to achieve the stealth of weapons and equipment, which has become an important way to improve their battlefield penetration capability and combat effectiveness. At present, common sandwich absorbing structures include honeycomb structure, pyramid structure, corrugated structure, etc. Among them, the honeycomb structure has the advantages of light weight, high strength, rigidity, strong design, etc. compared with other structures, and is widely used in fighter wings, tails and other parts. Traditional honeycomb sandwich absorbing structures are mostly manufactured by a split method, in which a regular hexagonal honeycomb core impregnated or sprayed with absorbent slurry is glued to the composite panels on both sides. However, when optimizing the performance of the traditional regular hexagonal honeycomb core, there are few adjustment means, the improvement of wave absorption performance is relatively limited, and the manufacturing method easily leads to insufficient core-plate interface bonding strength of the sandwich structure, which hinders the engineering application of such structures.

[0003] In response to the above problems, Chinese patent number CN 116864998 A discloses a non-integer dimensional honeycomb absorbing structure, which adds a non-integer dimensional hollow structure design on the basis of an ordinary honeycomb, thereby broadening the absorption band; Chinese patent number CN 116141804 A discloses an absorbing sandwich composite material based on a honeycomb transverse structure and its preparation method, which changes the traditional honeycomb structure into a transverse structure, increases the effective thickness relative to the incident electromagnetic wave, and achieves a broadening of the absorption band. However, the core structure involved in CN 116141804 A requires the use of a mold and is formed by a hot pressing process. This method not only relies heavily on molds, but also has a cumbersome and time-consuming preparation process. It is impossible to manufacture a core with a complex structure, and the core panels are bonded together using a split method, which is prone to problems such as cracking of the core panels.

[0004] Therefore, in order 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 type of composite honeycomb sandwich absorbing structure and its integrated preparation method. Summary of the invention

[0005] In view of the limited improvement of the wave absorption performance of the traditional regular honeycomb core structure, the unstable connection strength of the traditional core-plate interface, and the inability to quickly manufacture complex structures, the present invention provides a honeycomb sandwich structure with strong wave absorption ability and a novel plate-core-plate integrated manufacturing method. First, a variable wall thickness honeycomb core structure is proposed. The variable wall thickness design of the honeycomb core structure increases the number of electromagnetic wave reflections, thereby improving the electromagnetic wave absorption performance; in addition, a plate-core-plate structure composed of the same matrix composite material and its integrated overall printing manufacturing method are proposed, and the bonding strength of the plate-core-plate connection interface is further improved by a heat source-pressure auxiliary method, which effectively improves the overall bearing performance of the sandwich wave absorbing structure, and finally can realize the overall rapid integrated forming and manufacturing of complex sandwich wave absorbing structures.

[0006] The technical solution of the present invention:

[0007] A variable wall thickness composite honeycomb sandwich wave absorbing structure comprises an upper wave-transmitting layer, a middle wave-absorbing layer and a lower reflective layer, and the overall structure is formed in an integrated manner based on 3D printing.

[0008] The intermediate absorbing layer is composed of a plurality of single-cell cores arranged in an array, and the cross-section of the single-cell core is in the shape of a regular quadrilateral, a regular pentagon, a regular hexagon or a circle, etc., and the configuration can be changed according to requirements.

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

[0010] The maximum circumscribed circle diameter of the cross section of the single-cell core is D, and the minimum circumscribed circle diameter is d; in order to allow electromagnetic waves to enter the structure and be absorbed, the minimum circumscribed circle diameter d is greater than 1 / 10 of the wavelength of the highest frequency f2 of the measured wave band, and considering the bearing performance of the overall structure, the minimum circumscribed circle diameter d does not exceed 5 times the minimum wall thickness b (i.e. c / 10f2≤d≤5b, unit mm, c is the wave speed). Similarly, the maximum circumscribed circle diameter D is greater than 1 / 10 of the wavelength of the lowest frequency f1 of the measured wave band, and does not exceed 10 times the minimum wall thickness b (i.e. c / 10f1≤D≤10b, unit mm, c is the wave speed).

[0011] The upper wave-transmitting layer is mainly made of a composite material consisting of low dielectric constant continuous fibers and high-performance resins, and the low dielectric constant continuous fibers account for 50wt.% of the mass of the upper wave-transmitting layer. 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, wherein the conductive continuous fibers account for 50wt.% of the mass of the lower reflective layer, wherein the conductive continuous fibers include but are not limited to carbon fibers and Kevlar fibers, and the high-performance resin matrix includes but is not limited to PA, PPS, and PI.

[0013] The intermediate wave absorbing layer is mainly composed of a magnetic loss material, an electric loss absorber and a high-performance resin. The mass fraction of the magnetic loss material is in the range of 5wt.%-30wt.%, and the mass fraction of the electric loss absorber is in the range of 2wt.%-15wt.%. The magnetic loss material includes but is not limited to ferrite, ferroferric oxide and other metal powders, the electric loss absorber includes but is not limited to carbon nanotubes, graphite and other materials, and the high-performance resin includes but is not limited to PA, PPS, PI.

[0014] An integrated preparation method for a variable-thickness composite honeycomb sandwich wave-absorbing structure comprises the following steps:

[0015] (1) Selecting conductive continuous fibers and high-performance resins and melt-impregnating them through a silk making machine to obtain continuous conductive fiber prepregs; using the continuous conductive fiber prepregs to 3D print and prepare the lower reflective layer, the number of printing layers is 5-10, and the printing path is zigzag, orthogonal, or 0°, 45°, 90°, 135° directions and stacking in a cycle in sequence;

[0016] (2) Mixing the magnetic loss material, the electric loss absorber and the high-performance resin in proportion, and obtaining the absorbing wire after the action of the twin-screw mixer and the single-screw extruder, and preparing the absorbing layer by 3D printing technology using the absorbing wire, and the specific structure of the printing path is generated by the slicing software;

[0017] (3) Selecting low dielectric constant continuous fibers and high-performance resins and melt-impregnating them through a silk making machine to obtain continuous low dielectric constant fiber prepregs; using the continuous low dielectric constant fiber prepregs for 3D printing to prepare a wave-transmitting layer, the number of printing layers is 10-15 layers, and the printing path is zigzag or orthogonal;

[0018] (4) placing the three wires obtained in steps (1), (2) and (3) into a 3D printing device, and first completing the printing of the lower reflective layer on the printing platform according to the path of step (1) based on the printing path codes obtained in steps (1), (2) and (3);

[0019] (5) Switching materials, completing the printing of the middle absorbing layer on the basis of the lower reflective layer; applying 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 applying pressure behind the material extruded from the nozzle to ensure the bonding strength between the middle absorbing layer and the lower reflective layer;

[0020] (6) Switch the material again and complete the printing of the upper wave-transmitting layer on the middle wave-absorbing layer according to step (3). During the printing process, a heat source is applied 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, pressure is applied behind the material extruded from the nozzle to ensure the bonding strength between the upper transmission layer and the middle wave-absorbing layer.

[0021] Beneficial effects of the present invention: Compared with the traditional honeycomb structure, the variable wall thickness honeycomb structure proposed by the present invention changes the vertical honeycomb wall into a honeycomb wall with an inclination, the effective reflection area is increased, and the number of reflections of electromagnetic waves in the structure is increased. At the same time, the synergistic effect of the two lossy materials increases the loss of electromagnetic waves in the reflection process, broadens the electromagnetic wave absorption band, and improves the overall reflection loss of electromagnetic waves; in addition, the board-core-board 3D printing integrated manufacturing method of the sandwich absorbing structure meets the rapid prototyping and integrated forming of the complex core structure, avoiding the insufficient bonding strength of the board core caused by split manufacturing. This method is simple and easy to operate, with a wide range of raw materials, high preparation efficiency, and has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0026] Figure 5 This is a simulation curve of the wave absorption performance of a common honeycomb structure.

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

[0028] In the figure: 1-wave-transmitting layer, 2-wave-absorbing layer, 3-reflecting layer. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0030] Example 1

[0031] like Figure 1As shown, a variable wall thickness composite honeycomb sandwich absorbing structure comprises an upper wave-transmitting layer 1, a middle wave-absorbing layer 2 and a lower reflective layer 3. The wave-absorbing layer is composed of a unit cell structure array to form an overall structure with a length, width and height of 200×200mm×12mm, and the overall structure is integrated based on 3D printing.

[0032] A variable wall thickness composite material honeycomb sandwich wave absorbing structure and an integrated preparation method thereof, the preparation method is as follows:

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

[0034] (2) PA is selected as the thermoplastic resin matrix, glass fiber is selected as the wave-transmitting fiber, and carbon fiber is selected as the conductive fiber, and continuous glass fiber prepreg and continuous carbon fiber prepreg are obtained by melt impregnation in a fiber making machine;

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

[0036] (4) The number of printed layers of the wave-transmitting layer is 10, the printing layer thickness is 0.1 mm, the printing line spacing is 0.8 mm, and the printing path is zigzag;

[0037] (5) The reflective layer is printed in 5 layers, with a layer thickness of 0.2 mm and a printing line spacing of 0.8 mm. The printing path is stacked in the directions of 0°, 45°, 90°, 135°, and 0°.

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

[0039] (7) The three wires obtained in steps (1) and (2) are placed in a 3D printing device. Based on the printing code obtained in step (6), the reflective layer is first printed on the printing platform according to the path of step (3).

[0040] (8) Switching materials, completing the printing of the absorbing core structure on the basis of the reflective layer. When printing the absorbing material, a small range heat source is applied near the printing nozzle to ensure that the material temperature near the nozzle is around 218°C. At the same time, a small force pressure is applied behind the material extruded from the nozzle to ensure the bonding strength between the absorbing material and the reflective layer;

[0041] (9) Switch the material again and complete the printing of the wave-transmitting layer on the core structure according to step (4). At the same time, apply a small range heat source near the printing nozzle to ensure that the material temperature near the nozzle is around 218°C. At the same time, apply a small force pressure behind the material extruded from the nozzle to ensure the bonding strength between the transmission layer and the core layer.

[0042] The 3D printing device used in this embodiment has both heat source and pressure auxiliary functions.

[0043] Depend on Figure 4 and Figure 5 It was found that the variable wall thickness honeycomb absorbing structure of the present invention has an effective absorbing frequency band broadened from 5.5 GHz to 10.2 GHz, and a maximum absorption loss increased from -23 dB to -28.5 dB, compared with a common honeycomb structure.

Claims

1. A variable wall thickness composite honeycomb sandwich wave absorbing structure, characterized in that: The variable wall thickness composite honeycomb sandwich wave absorbing structure includes an upper wave-transmitting layer, a middle wave-absorbing layer and a lower reflective layer, and the overall structure is formed in an integrated manner based on 3D printing.

2. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 1, characterized in that: The intermediate wave absorbing layer is composed of a plurality of single-cell cores arranged in an array, and the cross-section of the single-cell core is in the shape of a regular quadrilateral, a regular pentagon, a regular hexagon or a circle.

3. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 2, characterized in that: The wall thickness of the single-cell core increases uniformly from top to bottom in the vertical direction, and its vertical height h needs to satisfy 5≤h≤25mm, and the minimum wall thickness b of the single-cell core in the vertical height direction satisfies 0.5mm≤b≤2mm.

4. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 2, characterized in that: The maximum circumscribed circle diameter of the cross section of the single-cell core is D, and the minimum circumscribed circle diameter is d; in order to allow electromagnetic waves to enter the structure and be absorbed, the minimum circumscribed circle diameter d is greater than 1 / 10 of the wavelength of the highest frequency f2 of the measured band. Taking into account the bearing performance of the overall structure, the minimum circumscribed circle diameter d does not exceed 5 times the minimum wall thickness b; the maximum circumscribed circle diameter D is greater than 1 / 10 of the wavelength of the lowest frequency f1 of the measured band and does not exceed 10 times the minimum wall thickness b.

5. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 2, characterized in that: The upper wave-transmitting layer is mainly made of a composite material consisting of low dielectric constant continuous fibers and high-performance resin, and the low dielectric constant continuous fibers account for 50wt.% of the mass of the upper wave-transmitting layer.

6. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 2, characterized in that: The lower reflective layer is mainly made of a composite material consisting of conductive continuous fibers and high-performance resin, and the conductive continuous fibers account for 50 wt.% of the mass of the lower reflective layer.

7. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 2, characterized in that: The intermediate absorbing layer is mainly composed of magnetic loss material, electric loss absorber and high-performance resin. The mass fraction of magnetic loss material is in the range of 5wt.%-30wt.%, and the mass fraction of electric loss absorber is in the range of 2wt.%-15wt.%.

8. The variable wall thickness composite honeycomb sandwich wave absorbing structure according to claim 2, characterized in that: The conductive continuous fibers include carbon fibers and Kevlar fibers; the high-performance resin matrix includes PA, PPS, and PI; the magnetic loss type material includes ferrite and ferroferric oxide; the electrical loss absorber includes carbon nanotubes and graphite; and the low dielectric constant continuous fibers include glass fibers and aramid fibers.

9. An integrated preparation method for a variable wall thickness composite honeycomb sandwich wave absorbing structure, characterized in that: The following steps are involved: (1) Selecting conductive continuous fibers and high-performance resins and melt-impregnating them through a silk making machine to obtain continuous conductive fiber prepregs; using the continuous conductive fiber prepregs to 3D print and prepare the lower reflective layer, the number of printing layers is 5-10, and the printing path is zigzag, orthogonal, or 0°, 45°, 90°, 135° directions and stacking in a cycle in sequence; (2) Mixing the magnetic loss material, the electric loss absorber and the high-performance resin in proportion, and obtaining the absorbing wire after the action of the twin-screw mixer and the single-screw extruder, and preparing the absorbing layer by 3D printing technology using the absorbing wire, and the specific structure of the printing path is generated by the slicing software; (3) Selecting low dielectric constant continuous fibers and high-performance resins and melt-impregnating them through a silk making machine to obtain continuous low dielectric constant fiber prepregs; using the continuous low dielectric constant fiber prepregs for 3D printing to prepare a wave-transmitting layer, the number of printing layers is 10-15 layers, and the printing path is zigzag or orthogonal; (4) placing the three wires obtained in steps (1), (2) and (3) into a 3D printing device, and first completing the printing of the lower reflective layer on the printing platform according to the path of step (1) based on the printing path codes obtained in steps (1), (2) and (3); (5) Switching materials, completing the printing of the middle absorbing layer on the basis of the lower reflective layer; applying 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 applying pressure behind the material extruded from the nozzle to ensure the bonding strength between the middle absorbing layer and the lower reflective layer; (6) Switch the material again and complete the printing of the upper wave-transmitting layer on the middle wave-absorbing layer according to step (3). During the printing process, a heat source is applied 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, pressure is applied behind the material extruded from the nozzle to ensure the bonding strength between the upper transmission layer and the middle wave-absorbing layer.

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