Wave-absorbing / bearing composite material with gradient fold sandwich structure and preparation method of wave-absorbing / bearing composite material

Abstract

The invention discloses a wave-absorbing / bearing composite material with a gradient fold sandwich structure and a preparation method thereof.The wave-absorbing / bearing composite material with the gradient fold sandwich structure comprises a transmission panel, a reflection bottom plate and a middle sandwich plate located between the transmission panel and the reflection bottom plate, and the middle sandwich plate is provided with a fold structure; the plate thickness of the middle sandwich plate is changed from thin to thick from top to bottom in the height direction of the wave-absorbing / bearing composite material, and then is changed from thick to thin; the middle sandwich plate is provided with N material gradient layers from bottom to top, any material gradient layer contains carbon fiber reinforced polyphthalamide, at least one material gradient layer located in the middle further contains carbonyl iron powder, the minimum reflection loss of the wave-absorbing / bearing composite material in the frequency band of 2-18 GHz is superior to-10 dB, and the wave-absorbing / bearing composite material has the advantages that the wave-absorbing / bearing composite material can be applied to the wave-absorbing / bearing composite material in the frequency band of 2-18 GHz; incident electromagnetic waves can be effectively absorbed, reflected signals are reduced, and then the radar stealth performance of flight equipment is improved.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorption technology, specifically relating to a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure and its preparation method. Background Technology

[0002] The widespread application of microwave absorbing structures in the field of electromagnetic stealth has increasingly highlighted the need for robust mechanical load-bearing performance. However, existing research largely focuses on improving absorption performance and expanding bandwidth, often neglecting the fact that the materials themselves cannot simultaneously bear the structural load, resulting in a single functional limitation. Therefore, developing an integrated material system that combines mechanical load-bearing capacity with efficient microwave absorption is of great significance. Furthermore, in aircraft and other equipment, areas such as ventilation openings cannot be effectively stealthed solely through shape-based stealth technology, becoming a current challenge in stealth design. Traditional two-dimensional microwave absorbing materials with upper and lower skins are constrained by their structural form and cannot meet the requirements of three-dimensional spaces with ventilation functions, necessitating the development of novel integrated load-bearing and microwave-absorbing structures.

[0003] Fiber-reinforced resin matrix composites possess good mechanical properties and certain electromagnetic wave absorption capabilities, making them a potential candidate material for 3D printing. However, current methods for absorbing electromagnetic waves typically rely solely on dielectric loss, lacking a magnetic loss mechanism, thus limiting absorption efficiency and bandwidth. Furthermore, related structural designs often focus only on mechanical load-bearing capacity, failing to systematically coordinate load-bearing and wave absorption functions, thus restricting their application in multifunctional stealth structures. Therefore, developing a 3D-printed structure with a dual electromagnetic loss mechanism that achieves integrated load-bearing and stealth capabilities has significant engineering application value. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure.

[0005] The second objective of this invention is to provide a method for preparing a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure. The composite material comprises a transmissive panel, a reflective base plate, and an intermediate sandwich plate located between the transmissive panel and the reflective base plate.

[0008] The intermediate sandwich panel has a pleated structure, and the thickness of the intermediate sandwich panel changes from thin to thick and then from thick to thin in the height direction of the wave-absorbing / load-bearing composite material from top to bottom.

[0009] The intermediate sandwich panel has N material gradient layers from top to bottom, and each material gradient layer contains carbon fiber reinforced polyphthalamide, wherein at least one of the material gradient layers in the middle also contains carbonyl iron powder.

[0010] The gradient-pleated sandwich structure of this invention, used in a microwave-absorbing / load-bearing composite material, employs a dual gradient design in both structure and composition. This combines mechanical and electromagnetic design requirements. Structurally, the middle sandwich panel features a pleated structure, with its thickness gradually decreasing from top to bottom. Mechanically, this thickness setting controls the compression sequence, delaying premature buckling of the folded walls and thus enhancing out-of-plane compressive strength. Furthermore, the two layers of material constrain overall deformation and distribute applied pressure, stabilizing the folded core material during compression. Materially, the top layer, serving as an impedance matching layer near the incident region, utilizes carbon fiber-reinforced polyphthalamide to reduce air / structural impedance mismatch and suppress front surface reflection. The middle layer, configured with added carbonyl iron powder, acts as a high-loss layer to enhance magnetic loss and promote attenuation through inherent dielectric / magnetic loss, resonance, and multiple scattering. Electromagnetically, this material gradient design aims to construct a phased energy dissipation path within the folded core material. The incident wave first passes through the wave-transmissive GFRP top layer and enters the impedance matching layer, where it suppresses front surface reflection by reducing impedance mismatch. The wave then propagates deep into the core, repeatedly reflecting between the folded surface and the reflective carbon fiber reinforced plastic (CFRP) underlayer, effectively extending the propagation path and increasing the interaction time with the loss medium. In high-loss regions (especially the C-region), enhanced magnetic loss (derived from CIP) and dielectric loss (derived from the carbon fiber and polymer matrix) jointly promote efficient attenuation. The folded geometry further promotes multipath propagation and scattering, enhancing the broadband dissipation effect.

[0011] In a preferred embodiment, the transmissive panel is selected from a glass fiber composite laminate, and the reflective substrate is selected from a carbon fiber composite laminate.

[0012] In a preferred embodiment, the intermediate sandwich panel has a periodic structure, which consists of a number of unit cell structures arranged in a periodic array between the bottom plate and the top plate. The height of the unit cell structure is 14-20 mm, the length of the unit cell structure is 30-40 mm, and the width of the unit cell structure is 16-20 mm.

[0013] In a preferred embodiment, the pleated structure of the intermediate sandwich panel is a corrugated-origination multi-level unit cell structure. In the intermediate sandwich panel, the corrugation direction is perpendicular to the origami direction. The orthogonal projection surface of the unit cell structure in the origami direction is an asymmetrical herringbone shape. The orthogonal projection surface in the corrugation direction has a convex part in the middle and concave parts on both sides, and a boss at the bottom of the unit cell structure.

[0014] In a further preferred embodiment, in the orthographic projection plane of the unit cell structure in the folding direction, the width of the two herringbone legs gradually increases from top to bottom, and then decreases again. Correspondingly, the thickness of the middle sandwich panel gradually increases from top to bottom, and then decreases again.

[0015] In a preferred embodiment, the intermediate sandwich panel is divided into four material gradient layers from top to bottom along the height direction. The first and fourth material gradient layers, which are in contact with the reflective base plate, are both carbon fiber reinforced polyphthalamide, while the second and third material gradient layers are both carbon fiber reinforced polyphthalamide / carbonyl iron powder composite materials. In the carbon fiber reinforced polyphthalamide / carbonyl iron powder composite material, the mass fraction of carbonyl iron powder is 10%-30%.

[0016] In a further preferred embodiment, the mass fraction of carbonyl iron powder in the second gradient layer is 10-20% lower than that in the third gradient layer. Further gradient settings in the second and third layers can further improve the impedance matching performance of electromagnetic waves and reduce electromagnetic reflection losses caused by impedance mismatch.

[0017] In a preferred embodiment, the mass fraction of carbon fiber in the carbon fiber reinforced polyphthalamide is 15%-20%. Controlling the mass fraction of carbon fiber in the carbon fiber reinforced polyphthalamide within the range specified in this invention yields optimal performance.

[0018] This invention also provides a method for preparing a wave-absorbing / load-bearing composite material with a gradient pleated sandwich structure. First, a model of the middle sandwich panel is constructed, and the middle sandwich panel is divided into N material gradient layers along the height direction from bottom to top. Then, according to the design, polyphthalamide granules containing carbon fibers and carbonyl iron powder are distributed to prepare N parts of filament material. The middle sandwich panel is printed according to the model of the middle sandwich panel to obtain the middle sandwich panel. Then, the middle sandwich panel is assembled with the transmission panel and the reflection base plate to obtain the final product.

[0019] In actual operation, after printing, the blank is polished to remove surface burrs and obtain the middle sandwich panel.

[0020] In a preferred embodiment, the preparation process of the filament is as follows: according to the design composition of the material gradient layer, polyphthalamide granules containing carbon fibers are separately distributed, or polyphthalamide granules containing carbon fibers and carbonyl iron powder are mixed and melt-blended, then extruded to obtain composite granules, and then the composite granules are extruded a second time to obtain the filament.

[0021] In a further preferred embodiment, the mass fraction of carbon fiber in the polyphthalamide granules is 15-20%.

[0022] In practical operation, this invention uses polyphthalamide (PA) granules containing carbon fiber (CF) and carbonyl iron powder (CIP) as raw materials. First, the PA-CF granules and CIP metal powder are fed into a twin-screw extruder for melt mixing to prepare a preliminary filament. Subsequently, the preliminary filament is processed into PA-CF-CIP composite granules through a granulation process. Finally, the obtained composite granules are subjected to secondary extrusion molding using a twin-screw extruder to prepare the final composite functional filament. Simultaneously, the model of the intermediate sandwich panel is imported into 3D printing slicing software for slicing, printing parameters are set, printing code is generated, the printing code is input into the printer, filaments with different ratios are installed in the printer's AMS, the printer is adjusted, and printing begins. After printing, the wave-absorbing / load-bearing composite material of the gradient pleated sandwich structure is post-processed to complete the fabrication.

[0023] In a preferred embodiment, the 3D printing parameters are: a printing layer height of 0.2-0.25 mm, a printing speed of 60-70 mm / s, a nozzle temperature of 280-300℃, and a heated bed temperature of 90-110℃.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] The radar-absorbing / load-bearing composite material of this invention exhibits a minimum reflection loss better than -10dB in the 2-18GHz frequency band, effectively absorbing incident electromagnetic waves and reducing reflected signals, thereby improving the radar stealth performance of flight equipment. This structure is fabricated in one piece using 3D printing technology, offering flexibility and high efficiency in molding. Furthermore, mechanical simulations and experimental verification demonstrate its excellent mechanical strength and load-bearing stability, achieving a reliable integration of electromagnetic absorption and structural load-bearing. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the load-bearing / wave-absorbing composite material of the present invention.

[0027] Figure 2 A front view of a unit cell of a load-bearing / wave-absorbing composite material with a gradient pleated core structure is shown.

[0028] Figure 3 An isometric view of a load-bearing / wave-absorbing composite material with a gradient pleated core structure is shown.

[0029] Figure 4 An isometric view of the load-bearing / wave-absorbing composite material with a pleated core structure in the comparative example is shown.

[0030] Figure 5 The reflectivity curves of this structure under TM wave polarization conditions are presented as a function of different electromagnetic wave incident angles.

[0031] Figure 6 The study shows the variation of reflectivity of the structure under TE wave polarization at different incident angles.

[0032] Figure 7 The reflectivity curves of the structure under TM wave polarization were compared under different material gradient arrangement methods.

[0033] Figure 8 This reflects the reflectivity performance of the structure under TE wave polarization under different material gradient arrangements.

[0034] Figure 9 The compressive strength curves of the sandwich structure under different material gradient arrangements are compared. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0036] Reference Figure 1 The present invention discloses a load-bearing / wave-absorbing composite material gradient pleated sandwich structure, which includes a transmission panel, a reflection base plate and an intermediate sandwich plate located between the two.

[0037] The intermediate sandwich panel has a pleated structure, and the thickness of the intermediate sandwich panel changes from thin to thick from top to bottom, and then from thick to thin again.

[0038] The intermediate sandwich panel has N material gradient layers from bottom to top, and each material gradient layer contains carbon fiber reinforced polyphthalamide, wherein at least one of the material gradient layers in the middle also contains carbonyl iron powder.

[0039] Furthermore, the transmissive panel is selected from glass fiber composite laminate, and the reflective substrate is selected from carbon fiber composite laminate.

[0040] Furthermore, the intermediate sandwich panel has a periodic structure, which consists of a number of unit cell structures arranged in a periodic array between the bottom plate and the top plate. The height of the unit cell structure is 14-20mm, the length of the unit cell structure is 30-40mm, and the width of the unit cell structure is 16-20mm.

[0041] Furthermore, the pleated structure of the intermediate sandwich panel is a corrugated-origination multi-level unit cell structure. In the intermediate sandwich panel, the corrugation direction is perpendicular to the origami direction. The orthogonal projection surface of the unit cell structure in the origami direction is an asymmetrical herringbone shape. The orthogonal projection surface in the corrugation direction has a convex part in the middle and concave parts on both sides, and a boss at the bottom of the unit cell structure.

[0042] Example 1

[0043] A method for molding and preparing a load-bearing / wave-absorbing composite gradient pleated sandwich structure, the specific steps of which are as follows:

[0044] Step 1: Processing of upper and lower layers

[0045] First, the carbon fiber / glass fiber composite laminate is cut according to the design dimensions. The cut top and bottom panels are then placed in a dust-free environment for later use. The top panel is a square panel with a side length of 20mm and a thickness of 1mm, and the bottom panel is also a square panel with a thickness of 1mm.

[0046] Step 2: Preparation of the core layer of the multilayer board

[0047] (1) A geometric model of the intermediate sandwich panel of the gradient pleated sandwich structure was established using the 3D modeling software SolidWorks. The intermediate sandwich panel adopts a corrugated-origami multi-level unit cell structure with an overall height of 20 mm. The characteristic dimensions of the unit cell in the corrugation direction and vertical direction are 15 mm and 35 mm, respectively. In the cross-sectional configuration, the corrugated panel presents an asymmetrical herringbone fold distribution. The herringbone angles α1 and α2 formed by the upper and lower edges are 56° and 77°, respectively. Furthermore, the angles β1 and β2 formed by the upper and lower edges of the lower half of the corrugated panel with the reference plane are 123° and 129°, respectively, and the bottom thickness of the corrugated panel is 2 mm. The angle between the lower side edge and the side surface of the structure in the top view is 140°. After completing the modeling, the model was exported as an STL format.

[0048] (2) Import the STL file into the slicing software Bambu Studio. According to the gradient design requirements, divide the model into 4 segments along the height direction and set the material properties of each segment in sequence: Take polyphthalamide (PA) granules containing carbon fiber (CF) and carbonyl iron powder (CIP) as raw materials, wherein the mass fraction of carbon fiber (CF) in the polyphthalamide (PA) granules is 15%; feed the PA-CF granules and CIP metal powder into a twin-screw extruder for melt mixing to prepare a preliminary filament; then, process the preliminary filament into PA-CF-CIP composite granules through a granulation process; finally, use a twin-screw extruder to perform secondary extrusion molding to prepare the final composite functional filament. In this embodiment, the specific mass fractions of carbonyl iron powder (CIP) in the filaments used are 0%, 10%, 20%, and 30%, respectively. The corresponding distribution ratios of carbonyl iron powder: carbon fiber: polyphthalamide are 0:3:7, 10:27:63, 20:24:56, and 30:21:49, respectively, and are labeled as 1, 2, 3, and 4.

[0049] Taking the 1241 model as an example: The top and bottom layers are printed using CF-PPA filament. The lower layer of the two middle layers is printed using PPA-CF-CIP filament with a CIP mass fraction of 30%, while the upper layer is printed using PPA-CF-CIP filament with a CIP mass fraction of 10%. After material distribution, slicing is performed to generate layered manufacturing data. This data is then imported into the BambuLab H2D 3D printer, and fused deposition modeling (FDM) is used with PA-CF-CIP composite filament as the raw material for printing. Key process parameters are set as follows: layer height 0.2 mm, printing speed 60 mm / s, nozzle temperature 290 ℃, and heated bed temperature 100 ℃, ultimately obtaining a one-piece, gradient-pleated sandwich core.

[0050] Step 3: Assembly of the gradient pleated sandwich structure

[0051] The upper and lower panels prepared in step 1 are bonded to the upper and lower surfaces of the core using adhesive film or structural adhesive to complete the encapsulation of the overall structure.

[0052] The reflectivity and axial compression of the load-bearing / absorbing composite gradient pleated sandwich structure were tested to evaluate the microwave absorption performance and mechanical load-bearing capacity of the broadband pleated structure microwave absorption-mechanical load-bearing structure, with reference to... Figure 3-9 Therefore, it can be seen that the solution in this embodiment is one of the better solutions.

[0053] Comparative Example 1

[0054] Other conditions are the same as in Example 1, except that the thickness of the middle sandwich panel is equal along the height direction of the microwave absorbing / load-bearing composite material, without any gradient, and its unit cell structure is as follows: Figure 4 As shown.

[0055] Figures 1 to 3 A schematic diagram of the structure described in this invention is shown. Figure 4 This is a schematic diagram of the unit cell structure of Comparative Example 1. Figure 5 and Figure 6 The reflection loss curves of the fabricated structure under different incident conditions are shown using the 1241 material composition ratio. Experimental data indicate that, 0° to 60° Within the incident angle range, the structure exhibits stable electromagnetic wave absorption performance.

[0056] Figure 7 and Figure 8 The electromagnetic properties of type 1241 gradient material structures, type 1331 gradient material structures, and non-gradient structures were compared. The results show that the type 1241 gradient structure has a wider effective absorption bandwidth (RL < -10 dB). Furthermore, [the following text appears to be incomplete and requires further context: "by..."] Figure 9It can be seen that the type 1241 gradient material structure is significantly superior to the type 1331 structure and the non-gradient structure of Comparative Example 1 in terms of mechanical properties, exhibiting higher mechanical load-bearing capacity. The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, or improvements made within the scope of the inventive concept should be included within the scope of the claims of the present invention.

Claims

1. A microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure, characterized in that: The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure includes a transmission panel, a reflective base plate, and an intermediate sandwich plate located between the transmission panel and the reflective base plate. The intermediate sandwich panel has a pleated structure, and the thickness of the intermediate sandwich panel changes from thin to thick and then from thick to thin in the height direction of the wave-absorbing / load-bearing composite material from top to bottom. The intermediate sandwich panel has N material gradient layers from bottom to top, and each material gradient layer contains carbon fiber reinforced polyphthalamide, wherein at least one of the material gradient layers in the middle also contains carbonyl iron powder.

2. The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 1, characterized in that: The transmissive panel is selected from glass fiber composite laminate, and the reflective substrate is selected from carbon fiber composite laminate.

3. The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 1, characterized in that: The intermediate sandwich panel has a periodic structure, which consists of a number of unit cell structures arranged in a periodic array between the reflective base plate and the transmissive panel. The height of the unit cell structure is 14-20mm, the length of the unit cell structure is 30-40mm, and the width of the unit cell structure is 16-20mm.

4. The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 1, characterized in that: The pleated structure of the middle sandwich panel is a corrugated-origami multi-level unit cell structure. In the middle sandwich panel, the corrugation direction is perpendicular to the origami direction. The orthogonal projection surface of the unit cell structure in the origami direction is an asymmetrical herringbone shape. The orthogonal projection surface in the corrugation direction has a convex part in the middle and concave parts on both sides, and a boss at the bottom of the unit cell structure. In the orthographic projection of the unit cell structure in the folding direction, the width of the two V-shaped legs changes from narrow to wide and then from wide to narrow from top to bottom.

5. The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 1, characterized in that: The intermediate sandwich panel is divided into four material gradient layers from bottom to top along the height direction. The first and fourth material gradient layers that are in contact with the reflective base plate are both carbon fiber reinforced polyphthalamide, while the second and third material gradient layers are both carbon fiber reinforced polyphthalamide / carbonyl iron powder composite materials. In the carbon fiber reinforced polyphthalamide / carbonyl iron powder composite material, the mass fraction of carbonyl iron powder is 10%-30%.

6. The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 5, characterized in that: The mass fraction of carbonyl iron powder in the second material gradient layer is 10-20% smaller than that in the third material gradient layer.

7. The microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 1, characterized in that: In the carbon fiber reinforced polyphthalamide, the mass fraction of carbon fiber is 15%-20%.

8. A method for preparing a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure as described in any one of claims 1-7, characterized in that: First, construct a model of the middle sandwich panel and divide it into N material gradient layers along the height direction from bottom to top. Then, according to the design, take polyphthalamide granules containing carbon fiber and carbonyl iron powder to make N parts of filament. Print the filament according to the model of the middle sandwich panel to obtain the middle sandwich panel. Then, assemble the middle sandwich panel with the transmissive panel and the reflective base plate to obtain the final product.

9. The method for preparing a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 8, characterized in that: The preparation process of the filament is as follows: according to the design composition of the material gradient layer, polyphthalamide granules containing carbon fibers are taken separately, or polyphthalamide granules containing carbon fibers and carbonyl iron powder are mixed and melt-blended, then extruded to obtain composite granules, and then the composite granules are extruded a second time to obtain the filament. In the polyphthalamide granules containing carbon fibers, the mass fraction of carbon fibers is 15-20%.

10. The method for preparing a microwave absorbing / load-bearing composite material with a gradient pleated sandwich structure according to claim 8, characterized in that: The parameters for 3D printing are as follows: layer height is 0.2-0.25 mm, printing speed is 60-70 mm / s, nozzle temperature is 280-300℃, and heated bed temperature is 90-110℃.

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