Wave absorbing-bearing integrated gradient composite structure and 3D printing forming method

Abstract

The invention relates to the technical field of wave-absorbing materials, in particular to a wave-absorbing-bearing integrated gradient composite structure and a 3D printing forming method. The wave-absorbing-bearing integrated gradient composite structure is obtained by integrally molding a wave-absorbing structure and a shielding structure through 3D printing; the shielding structure is made of conductive fiber prepreg filaments; the conductive fiber prepreg filaments are obtained by compounding conductive continuous fibers and a first thermoplastic resin matrix; the wave-absorbing structure is composed of a plurality of single-cell core array structural layers, and each single-cell core array structural layer is prepared from an electrical loss type wave-absorbing agent, low-dielectric-constant continuous fibers and a second thermoplastic resin matrix. Through collaborative optimization of a material system and structural design, integrated forming of the structure and the function is achieved, and the technical problems that an electromagnetic wave invisible structure prepared in the prior art is low in interface bonding strength, consequently, the mechanical property is insufficient, and it is difficult to consider the broadband wave absorbing performance and the high-strength bearing requirement at the same time are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and particularly relates to a wave-absorbing-carrying integrated gradient composite structure and a 3D printing forming method. BACKGROUND

[0002] With the development of electronic detection technology and precision-guided weapons, modern equipment has higher requirements for light weight, high strength and functional performance. Stealth technology, as an important means to improve the survivability of equipment, is widely used in national defense equipment, including reducing the observability of radar and electromagnetic wave and other multi-spectrum detection. Carbon-based materials and their composites have been widely used in the field of electromagnetic wave absorption and shielding due to their high electrical conductivity, low density, excellent mechanical properties and good dielectric and magnetic loss characteristics. Through composite material design, the impedance matching performance can be effectively improved to achieve wideband electromagnetic wave absorption, while the mechanical carrying capacity is also considered.

[0003] There are related researches in the prior art to explore the integrated manufacturing of electromagnetic wave stealth structure. For example, CN106250610B discloses a manufacturing method of electromagnetic wave structure stealth, which regulates the dielectric constant through unit layer grid division and wood pile unit structure, and adopts 3D printing of the wave-transparent layer and the bonding assembly of the wave-absorbing and reflecting layers to realize the combination of stealth and carrying functions. However, in the electromagnetic wave stealth structure prepared by the above method, the functional layers mainly rely on adhesive connection, the interface bonding strength is limited, the overall mechanical properties and environmental adaptability are insufficient, and the overall structure adopts a layered stacking mode, which is difficult to balance the wideband wave-absorbing performance and high-strength carrying demand. SUMMARY

[0004] In order to solve the technical problems of low interface bonding strength of the electromagnetic wave stealth structure prepared by the prior art, resulting in insufficient mechanical properties and difficulty in balancing the wideband wave-absorbing performance and high-strength carrying demand, the present application provides a wave-absorbing-carrying integrated gradient composite structure and a 3D printing forming method.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows.

[0006] This invention provides an integrated gradient composite structure for absorbing and carrying wave energy, which is formed by 3D printing of an absorbing structure and a shielding structure. The shielding structure is prepared by 3D printing of conductive fiber prepreg filaments. The conductive fiber prepreg filaments are composed of conductive continuous fibers and a first thermoplastic resin matrix. The absorbing structure is composed of multiple layers of single-cell core array structure, and along the direction towards the shielding structure, the intrinsic impedance of the multiple layers of single-cell core array structure forms a multi-layer stepped impedance distribution along the thickness direction to match the target operating frequency band. Each layer of the single-cell core array structure uses a resin-based composite material of an electrically dissipative absorbing agent and a second thermoplastic resin matrix as the absorbing filament, which is prepared by 3D printing of the absorbing filament and low dielectric constant continuous fibers. The mass percentage of the electrically dissipative absorbing agent in each layer of the single-cell core array structure is 0wt% to 30wt%.

[0007] This invention achieves integrated molding of structure and function through synergistic optimization of material system and structural design. The shielding structure is made of conductive fiber prepreg obtained by combining conductive continuous fibers and a first thermoplastic resin matrix. This provides mechanical load-bearing capacity and reflects unabsorbed electromagnetic waves back to the absorbing layer, achieving secondary energy dissipation. The absorbing structure consists of a multi-layered single-cell core array structure. The design of the resulting metamaterial gradient impedance structure is based on an impedance distribution theory model. By establishing a gradually changing dielectric constant distribution, the propagation path of the incident electromagnetic wave is controlled, and the absorption efficiency is improved.

[0008] Preferably, each layer of the unit cell core array structure is formed by arranging multiple unit cell core arrays; the thickness of each layer of the unit cell core array structure is the same. Preferably, the shape of the unit cell core is a square-hole unit cell, a honeycomb unit cell, a stepped unit cell, or a stacked unit cell.

[0009] In this invention, each layer of the unit cell core array structure is composed of arrayed unit cells. The shape of the unit cell core is a square hole unit cell, a honeycomb unit cell, a stepped unit cell, or a stacked wood unit cell. Each unit cell core is made of a resin-based composite material composed of an electrically dissipative absorbing agent and a second thermoplastic resin matrix as the absorbing filament, and is made of continuous fibers with low dielectric constant.

[0010] Preferably, the lattice constant of the unit cell core satisfies the following condition: a ≤ 0.43λ; where a represents the lattice constant of the unit cell core; and λ is the wavelength of the target operating frequency band. According to the requirements of the target operating frequency band, the spatial unit size of the absorbing structure is not smaller than the size of the unit cell core.

[0011] Preferably, the target operating frequency band of the absorbing structure is 8GHz to 18GHz, the impedance range of the absorbing structure is 90Ω to 330Ω, the lattice constant of the unit cell core is 5mm to 7mm, the column width of the unit cell core is 1.8mm to 5.4mm, and the thickness of the unit cell core is 1.95mm.

[0012] In this invention, for the target operating frequency band of 8GHz to 18GHz, the lattice constant α of the square-hole unit cell core is 5mm to 7mm, and the pillar width w is 1.8mm to 5.4mm. The design is carried out for the target operating frequency band of 8GHz to 18GHz; during testing, the frequency range used is 2GHz to 40GHz.

[0013] Preferably, the conductive continuous fiber is carbon fiber or conductive polymer fiber; the first thermoplastic resin matrix is ​​polyetheretherketone, polyamide or polyimide; the electrical loss type microwave absorber is chopped carbon fiber, carbon nanotube or graphene; the low dielectric constant continuous fiber is aramid fiber or glass fiber; and the second thermoplastic resin matrix is ​​polyetheretherketone, polyamide or polyimide.

[0014] The conductive polymer fiber is a commercially available polyester conductive filament.

[0015] In this invention, the electrical loss type microwave absorber is short-cut carbon fiber. The short-cut carbon fiber selected is TC-HC-600-S type pitch-based short-cut fiber from Shaanxi Tianze Technology Co., Ltd., model TC-HC-600-S; elongation at break ≥0.3%; material diameter 1.75mm±0.05mm; linear density 0.225g / cm³. 3 Thermal conductivity ≥ 600 W / (m·K).

[0016] In this invention, the low dielectric constant continuous fiber is aramid fiber, which is selected from 150D fiber bundles produced by DuPont, USA; the thickness is 150D; the breaking elongation is 3.9%; the melting point is 400℃; the moisture content is 3.9%; and the fiber morphology is fiber filament.

[0017] In this invention, both the first thermoplastic resin matrix and the second thermoplastic resin matrix are preferably polyamides, specifically polyhexamethylene adipamide (nylon, PA66). That is, the thermoplastic resin matrix used in both the shielding structure and the wave-absorbing structure is nylon, so that the bonding will be better when printing the overall structure.

[0018] A second aspect of this invention provides a 3D printing method for an integrated wave-absorbing and load-bearing gradient composite structure, comprising the following steps: A microwave absorbing structure model with intrinsic impedance exhibiting a multi-layered stepped impedance distribution along the thickness direction is constructed to match the target operating frequency band.

[0019] A shielding structure was prepared by using conductive fiber prepreg, which is a composite of conductive continuous fiber and a first thermoplastic resin matrix, as raw material and by 3D printing.

[0020] Based on the constructed microwave absorbing structure model, using resin-based composite fibers obtained by combining an electrical loss type microwave absorbing agent with a second thermoplastic resin matrix as microwave absorbing filaments, and using microwave absorbing filaments and low dielectric constant continuous fibers as raw materials, a microwave absorbing structure is prepared on a shielding structure using a 3D printing molding method, resulting in an integrated microwave absorbing-load-bearing gradient composite structure.

[0021] The preferred method for constructing the absorbing structure model is as follows: Single-cell cores made of different materials were constructed, and their intrinsic impedances were obtained. Based on the intrinsic impedances of the single-cell cores, a multi-layer single-cell core array structure was constructed to form an absorbing structure with the overall impedance range divided into multiple graded gradients. This reduced the impedance difference between adjacent single-cell core array structure layers. Furthermore, along the direction towards the shielding structure, the intrinsic impedance of the multi-layer single-cell core array structure layers decreased layer by layer along the thickness direction, forming a continuous gradient transition impedance distribution. The continuous gradient transition impedance distribution was discretized and transformed into a multi-layered stepped impedance distribution to meet the target operating frequency band, thus constructing the absorbing structure model.

[0022] The intrinsic impedance of a single-cell core is determined by the material (i.e., the mass percentage of the electrically dissipative absorbing agent in each layer of the single-cell core array structure is 0wt% to 30wt%) and the single-cell size (column width w). The construction sequence is to first construct different single-cell cores made of different materials, measure the intrinsic impedance of these single-cell cores, and then select single-cell cores with different impedances to classify them into multiple impedance level gradients.

[0023] Preferably, in the absorbing structure where the overall impedance range is divided into multiple graded gradients, the overall impedance range is 90Ω to 330Ω; the impedance difference between two adjacent single-cell core array structure layers is reduced to 20Ω to 40Ω.

[0024] Preferably, the shielding structure is printed using a multi-directional laminate printing method, with a layup sequence of [0 / 90]. 2s A total of 4 layers were printed; the printing parameters of the shielding structure are as follows: Printing speed 600mm / min, printing temperature 320℃, printing layer thickness 0.1mm, printing spacing 1.0mm, base plate temperature 80℃.

[0025] Preferably, the absorbing structure is printed layer by layer according to the stepped impedance distribution of the unit cell core array structure layers to form 8 layers of unit cell core array structure layers with different intrinsic impedances; the printing parameters of the absorbing structure are as follows: Printing speed 600mm / min, printing temperature 290℃, printing layer thickness 0.1mm, printing spacing 1.8mm, base plate temperature 80℃.

[0026] In this invention, the shielding structure employs symmetrical layer-by-layer printing, meaning that the sublayer composite is repeatedly laid twice followed by a single symmetrical layup. The absorbing structure is printed using a multi-nozzle parametric control method, printing layer by layer according to the gradient impedance distribution of the unit cell cores to form an 8-layer array structure of unit cell cores with different intrinsic impedances. Specifically, the absorbing structure comprises 8 layers of unit cell core array structure layers, with adjacent layers made of unit cell cores with different dielectric constants, and each layer having the same height. The absorbing structure employs a metamaterial gradient impedance matching design, dividing the impedance range of 90Ω to 330Ω into 8 gradient levels to reduce the impedance difference ΔZi between adjacent layers, thereby improving impedance matching and suppressing interface reflection.

[0027] This invention uses conductive fiber prepreg obtained by carbon fiber and nylon composite, and prepares a shielding structure through a 3D printing continuous fiber-reinforced extrusion process; short carbon fiber and nylon are mixed and processed by a mixer and extruder to obtain microwave absorbing filament, and the microwave absorbing filament is combined with aramid fiber through in-situ impregnation process multi-nozzle 3D printing technology to prepare a microwave absorbing structure; the printing path is generated by slicing software, the shielding structure is printed first, and then the microwave absorbing structure is printed on it to achieve integrated molding of composite materials.

[0028] Preferably, the single-cell core array structure layer farther away from the shielding structure is set as the top layer, and the single-cell core array structure layer closer to the shielding structure is set as the bottom layer; from the top layer to the bottom layer, the intrinsic impedance of the single-cell core array structure layer decreases layer by layer along the thickness direction, forming a continuous gradient transition impedance distribution.

[0029] The microwave absorbing structure of this invention achieves a continuous transition of electromagnetic parameters through metamaterial unit cell gradient design, forming multi-level energy dissipation channels. Optimization of unit cell core type and gradient distribution is achieved through parametric design and control, thereby balancing mechanical load-bearing performance with broadband electromagnetic absorption performance.

[0030] The metamaterial gradient impedance structure of this invention is designed based on an impedance distribution theory model. By establishing a gradually changing dielectric constant distribution, the propagation path of incident electromagnetic waves can be controlled and the absorption efficiency improved. The impedance distribution theory model is discretized, transforming the continuous gradient impedance distribution into a multi-layered stepped impedance distribution to meet the requirements of actual engineering manufacturing precision and target operating frequency band.

[0031] Preferably, the impedance range of the absorbing structure is 90Ω to 330Ω, and the impedance range covering 90Ω to 330Ω is divided into multiple graded gradients to reduce the impedance difference between adjacent unit cell subarray structure layers; the graded gradient division of the absorbing structure satisfies the following condition: 90Ω ≤Z i ≤ 330Ω; 20Ω ≤ ΔZ i ≤ 40Ω; Z i This represents the intrinsic impedance of each of the single-cell core array structure layers; ΔZ i This represents the impedance difference between two adjacent single-cell core array structure layers. Subsequently, the absorbing structure undergoes discretization to transform the continuous gradient impedance distribution into a multi-layered stepped impedance distribution to meet the requirements of the target operating frequency band.

[0032] The beneficial effects of this invention are: 1. This invention achieves an optimized combination of absorbing and shielding structures through the combined application of conductive fiber prepreg, absorbing filaments, and low-dielectric-constant continuous fibers. This allows the composite material to achieve efficient broadband absorption capabilities while maintaining mechanical load-bearing performance. The shielding structure not only provides mechanical support, but its high reflectivity also reflects unabsorbed electromagnetic waves back to the absorbing layer, achieving secondary or even multiple energy dissipation, thereby significantly enhancing the overall absorption efficiency. The absorbing structure employs a metamaterial gradient impedance matching design, enabling a continuous impedance transition within the 8GHz–40GHz frequency band, reducing interface reflections and improving electromagnetic wave incident transmission efficiency.

[0033] 2. This invention achieves a smooth impedance transition between layers by precisely selecting the type and gradient distribution of the unit cell core, forming multi-level energy dissipation channels while maintaining the overall mechanical stability of the structure. The synergistic reinforcement effect of conductive fiber prepreg, absorbing filaments, and low dielectric constant continuous fibers effectively solves the problem that traditional composite materials struggle to balance broadband absorption and high load-bearing capacity.

[0034] 3. This invention is based on an integrated molding process of 3D printing additive manufacturing. Through parametric control, it achieves synchronous integration of structure and function, avoids performance degradation caused by interface mismatch of heterogeneous materials, improves manufacturing efficiency and reliability, and provides a technical solution for the engineering application of multifunctional high-performance composite material structures. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure and electromagnetic control mechanism of Example 1.

[0036] Figure 2 This is the intrinsic impedance of a single cell in Example 1.ΔZi This is a grading chart for 20Ω.

[0037] Figure 3 This is the intrinsic impedance of a single cell in Example 1. ΔZi This is a grading chart for 30Ω.

[0038] Figure 4 This is the intrinsic impedance of a single cell in Example 1. ΔZi This is a grading chart for 40Ω.

[0039] Figure 5 It is the square-pore single-cell structure of Example 1.

[0040] Figure 6 This is a schematic diagram of a three-dimensional model of Example 1.

[0041] Figure 7 This is a physical image of the 3D printed structural sample of Example 1.

[0042] Figure 8 This is the actual test process of the bow-shaped frame test method in Example 1.

[0043] Figure 9 This is the sensitivity of the absorption performance of Example 1 to different incident angles.

[0044] Figure 10 This is the TM polarization reflection loss at different angles in Example 1.

[0045] Figure 11 This refers to the TE polarization reflection loss at different angles in Example 1.

[0046] Figure 12 The load-displacement curves and damage morphology of the quasi-static transverse compression test in Example 1 are shown. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Against this backdrop, developing a high-performance composite material structure that integrates multiple materials and functions, while maintaining excellent mechanical properties and lightweight design to meet broadband electromagnetic wave absorption requirements, possesses significant technological innovation value and engineering application potential. This requires precise control over material composition, microstructure, interface bonding, and macroscopic morphology, incorporating gradient impedance matching design into the macroscopic structure, and employing advanced manufacturing methods to achieve functional integration of the composite material structure, thereby overcoming the limitations of existing technologies in multifunctional integration and manufacturing processes.

[0050] Compared with existing solutions, the integrated microwave absorption-load-bearing gradient composite material structure and its 3D printing method proposed in this invention achieves the integration of multi-scale electromagnetic control and mechanical load-bearing by synergistically combining low-dielectric-constant continuous fibers with microwave absorption materials to form a multi-level composite material system and multi-level structure. This method avoids the interfacial mechanical degradation and performance dispersion problems caused by traditional layered adhesive bonding, effectively balancing broadband microwave absorption efficiency, shielding performance, and structural load-bearing capacity, thus overcoming the limitations of existing patents in structural design, material composites, and functional integration.

[0051] This invention proposes a material-structure-function integrated molding strategy through the synergistic design of conductive fiber prepreg, microwave absorbing filaments, and low-dielectric-constant continuous fibers. Combined with gradient impedance matching structural design, it achieves synergistic optimization of broadband electromagnetic absorption, mechanical load-bearing capacity, and lightweight design. This method integrates the microwave absorbing structure with the shielding layer by precisely controlling the unit cell geometry parameters and gradient impedance distribution. Furthermore, it utilizes parametric design and multi-material 3D printing technology to achieve integrated molding of structure and function, thereby overcoming the technical bottlenecks of traditional composite materials in multifunctional integration, impedance matching optimization, and manufacturing processes.

[0052] This invention provides a theoretical method for the design of an integrated gradient composite material structure that combines wave absorption and load bearing. By establishing a theoretical model of impedance distribution, the dielectric constant is gradually distributed along the thickness direction. The gradual dielectric constant is used to control the propagation path of electromagnetic waves, thereby improving the wave absorption efficiency.

[0053] The theoretical model is discretized to transform the continuously distributed impedance into a multi-level gradient layer structure. The size of the spatial unit is optimized in combination with the manufacturing process and the target operating frequency band to ensure impedance matching effect and fabrication feasibility.

[0054] The size of the discretized spatial unit must be no smaller than the core size of the metamaterial. The core size is typically characterized by the lattice constant α. According to metamaterial design principles, the core lattice constant should be less than 1 / 10 of the operating wavelength, and in practical studies, this can be relaxed to less than 0.43 of the operating wavelength, i.e., α ≤ 0.43λ. For the target frequency band of 8 GHz to 18 GHz, the corresponding wavelength range is 16.7 mm to 37.5 mm; therefore, the core lattice constant should be less than 7.181 mm. Considering both design requirements and process feasibility, this invention selects a lattice constant of α = 6 mm to ensure the compatibility of structural performance with 3D printing.

[0055] The method of this invention involves selecting unit cell core structures with different geometries. Constrained by both process limitations and manufacturing performance, the column width *w* of the unit cell core is adjusted within the range of the minimum printing spacing and lattice constant *a* in continuous fiber 3D printing. The mass fraction of the electrically dissipative microwave absorbing agent is controlled from 0 wt% to 30 wt% to investigate its influence on the dielectric properties of the printed filament material for the microwave absorbing structure.

[0056] The intrinsic impedance of the printed filament under different parameters was obtained based on the intrinsic impedance calculation formula. Subsequently, to cover the impedance variation range of 90Ω to 330Ω, this invention constructed... ΔZ i The three-level partitioning schemes, with 20Ω, 30Ω, and 40Ω respectively, satisfy the following level boundary: the lower limit of the lowest level ≤ unit cell. Z i Minimum value ≤ maximum level. In the three-level classification scheme, choose the one with finer impedance resolution. ΔZ i The 30Ω scheme can effectively reduce the impedance difference between adjacent layers and make the impedance of the top unit cell as close as possible to the air impedance of 377Ω, thereby further optimizing the impedance matching effect.

[0057] The solution of the present invention will Z i The impedance range of 90–330Ω is divided into eight gradient levels. The absorbing structure is designed as an eight-layer structure, with each layer consisting of an array of unit cells with different intrinsic impedances. The top layer is composed of unit cells with an intrinsic impedance closest to air impedance (377Ω), and the impedance decreases layer by layer along the thickness direction, forming a continuous gradient transition to the bottom layer. The gradient impedance design reduces the impedance difference between adjacent layers. ΔZ i This enables interface reflection suppression and impedance matching optimization, thereby improving absorption efficiency. ΔZ i =20Ω~40Ω, preferably ΔZ i =30Ω.

[0058] Formula for calculating intrinsic impedance: ;in, Z i Indicates the intrinsic impedance of the medium; Z 0 The intrinsic impedance of free space / air is 377Ω; μ r Indicates relative permeability; ε r This represents the relative permittivity.

[0059] This invention provides an integrated gradient composite material structure for both microwave absorption and load bearing, comprising a shielding structure and a microwave absorption structure. Through synergistic optimization of the material system and structural design, combined with 3D printing manufacturing technology, the structure and function are integrated into a single form. Specifically, the shielding structure is made of a composite material of conductive continuous fibers and a first thermoplastic resin matrix. The conductive continuous fibers include, but are not limited to, carbon fibers and conductive polymer fibers, and the first thermoplastic resin matrix includes, but is not limited to, PEEK, PA, and PI.

[0060] The absorbing structure consists of arrayed unit cell cores, which can be square-hole unit cells, honeycomb unit cells, stepped unit cells, or stacked unit cells, with the shape changing according to requirements.

[0061] The unit cell core of the microwave absorbing structure is made of an electrically depleting microwave absorbing agent, low-dielectric-constant continuous fibers, and a second thermoplastic resin matrix. The electrically depleting microwave absorbing agent accounts for 0 wt% to 30 wt% of the total mass. The electrically depleting microwave absorbing agent includes, but is not limited to, chopped carbon fibers, carbon nanotubes, graphene, and carbonyl iron; the low-dielectric-constant continuous fibers include, but are not limited to, aramid fibers and glass fibers; and the second thermoplastic resin matrix includes, but is not limited to, PEEK, PA, and PI.

[0062] A 3D printing method for an integrated wave-absorbing and load-bearing gradient composite material structure includes the following steps: Step 1: For the shielding structure, conductive continuous fibers and high-performance resin are used to form the composite material using continuous fiber reinforced 3D printing technology. The printing path employs multi-angle layup printing, such as [0 / 90]. ns [0 / 45 / 90 / -45] ns and [0 / ±45 / 90] ns Other ply angle settings are used to ensure structural strength and electromagnetic shielding performance.

[0063] Step 2: For the microwave absorbing structure, the microwave absorbing material filaments obtained by mixing the electrical loss type microwave absorbing agent and high performance resin powder or granules in a certain proportion through the action of a mixer and an extruder are formed by continuous fiber 3D printing process with low dielectric constant continuous fibers.

[0064] The continuous fiber reinforced composite material 3D printing technology mentioned in steps 1 and 2 includes in-situ impregnation of continuous fiber composite materials and continuous fiber composite prepreg filament 3D printing. The 3D printing process in steps 1 and 2 can be performed using a multi-nozzle 3D printing machine capable of printing multiple materials, or the shielding structure can be printed first and then the material can be changed to print the microwave absorbing structure, ensuring a tight and effective bond between the shielding structure and the microwave absorbing structure.

[0065] This invention achieves integrated molding of structural configuration and electromagnetic function through parametric control, endowing the material with excellent electromagnetic control and load-bearing performance. The composite material structure consists of a shielding structure and a wave-absorbing structure. The shielding structure uses conductive continuous fibers and a first thermoplastic resin matrix, and a lightweight, high-strength shielding base plate is constructed through multi-directional lamination printing. Utilizing its conductivity and mechanical properties, it achieves reflection and multiple scattering of incident electromagnetic waves. The wave-absorbing structure uses pitch-based short-chopped carbon fibers, a second thermoplastic resin matrix, and continuous aramid fibers for synergistic reinforcement, balancing high mechanical strength and excellent electromagnetic loss characteristics. Based on the metamaterial gradient unit cell structure design, a gradient impedance-matched absorbing layer is constructed for the 8GHz–18GHz frequency band, achieving a continuous transition of electromagnetic parameters along the thickness direction, thereby significantly improving electromagnetic wave absorption efficiency and energy dissipation capability. Tests conducted in the 2GHz–40GHz wide frequency band show that this structure possesses high-efficiency wave absorption performance, while also exhibiting high load-bearing capacity and lightweight characteristics. It overcomes the limitations of traditional metal shields, such as high density, poor corrosion resistance, and weak interfacial bonding, providing a new technical solution for the design and application of multifunctional composite material structures.

[0066] The technical solution of the present invention will be further described below through specific embodiments.

[0067] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0068] Example 1 like Figure 1 A wave-absorbing-bearing integrated gradient composite structure is obtained by 3D printing of a wave-absorbing structure and a shielding structure.

[0069] The shielding structure is obtained by 3D printing of conductive fiber prepreg. The conductive fiber prepreg is prepared by combining conductive continuous fibers and a first thermoplastic resin matrix to obtain a continuous carbon fiber reinforced polyamide matrix composite material.

[0070] In this embodiment of the invention, the shielding structure is made of a composite material consisting of conductive continuous fibers and a first thermoplastic resin matrix. This composite material provides mechanical load-bearing capacity and reflects unabsorbed electromagnetic waves back to the absorbing layer, achieving secondary energy dissipation. The shielding structure is printed using a multi-directional laminated plate method, with a layup sequence of [0 / 90]. 2s A total of four layers are printed. For example, the shielding structure uses symmetrical layup printing, that is, the sublayer composite is repeatedly laid twice and then symmetrically laid once. Specifically, the conductive continuous fiber is carbon fiber; the first thermoplastic resin matrix is ​​polyhexamethylene adipamide (nylon, PA66), with a molecular weight of 15,000 to 20,000.

[0071] The microwave absorbing structure is composed of multiple layers of single-cell core array structures, each layer consisting of multiple single-cell core arrays arranged together. The shape of the single-cell core can be a square-hole single cell, a honeycomb single cell, a stepped single cell, or a stacked single cell. In this embodiment of the invention, the microwave absorbing structure is composed of a square-hole single-cell array structure, and the overall dimensions of the structure are 180mm × 180mm × 16.5mm.

[0072] Each of the aforementioned single-cell core array structure layers is fabricated using a multi-nozzle 3D printing method with an in-situ impregnation process, consisting of an electrically depleting microwave absorbing agent, low-dielectric-constant continuous fibers, and a second thermoplastic resin matrix. The electrically depleting microwave absorbing agent accounts for 0 wt% to 30 wt% of the mass fraction of each single-cell core array structure layer.

[0073] In this embodiment of the invention, the microwave absorbing structure is printed using a multi-nozzle parametric control method, printing layer by layer according to the gradient impedance distribution of the unit cell core to form an 8-layer unit cell core array structure with different intrinsic impedances. Specifically, the electrically dissipative microwave absorbing agent is chopped carbon fiber; the low dielectric constant continuous fiber is aramid fiber; and the second thermoplastic resin matrix is ​​nylon PA66.

[0074] A 3D printing method for an integrated wave-absorbing and load-bearing gradient composite structure includes the following steps: Step 1, Selection of conductive fiber prepreg: Continuous carbon fiber reinforced polyamide matrix composite material was selected as the conductive fiber prepreg.

[0075] The continuous carbon fiber reinforced polyamide matrix composite material is an additive manufacturing-specific 1K filament, grade ATC-CA3D4-1, produced by Nanjing Advanced Thermoplastic Composites Co., Ltd. Its resin matrix is ​​polyhexamethylene adipamide (PA66), and the reinforcement is T300 grade 1K carbon fiber. It possesses excellent mechanical properties, oleophilicity, corrosion resistance, temperature resistance, and low water absorption, with a flame retardant rating of V-0. The filament diameter is available in 0.36mm or 0.40mm, the linear density is 1.4g / m³, and the recommended printing temperature range is 275℃~290℃.

[0076] The shielding structure was fabricated using a 3D printing continuous fiber-reinforced extrusion process with conductive prepreg filaments. The S-parameters of the shielding structure were obtained through shielding effectiveness testing. The shielding structure was printed using symmetrical layup printing, meaning that sublayers were repeatedly laid up twice followed by a single symmetrical layup.

[0077] Step 2, Selection of absorbing fiber and low dielectric constant continuous fiber: Nylon pitch-based chopped carbon fibers were prepared using short-cut carbon fibers as the electrical loss-generating material and polyhexamethylene adipamide (PA66) as the thermoplastic resin matrix via a mixer and an extruder. The mass percentages of short-cut carbon fibers in the nylon pitch-based chopped carbon fibers were designed to be 0 wt.%, 10 wt.%, 20 wt.%, and 30 wt.%, respectively.

[0078] Nylon pitch-based chopped carbon fiber was selected as the microwave absorbing filament, and 150D aramid fiber bundles were selected as low-dielectric-constant continuous fibers. A multi-nozzle 3D printing method with in-situ impregnation was used to composite the microwave absorbing filament with the low-dielectric-constant continuous fibers, producing a short / continuous fiber composite filament; this short / continuous fiber composite filament was then used as the microwave absorbing filament. The electromagnetic parameters of the short / continuous fiber composite filament were measured using the bow-shaped method. The in-situ impregnation multi-nozzle 3D printing method involves uniformly mixing different materials in a mixer and then extruding them into the filament required for 3D printing.

[0079] Step 3, Establishment of the absorbing structure model: A microwave absorbing structure model with an intrinsic impedance distribution exhibiting a multi-layered stepped impedance distribution along the thickness direction is constructed to match the target operating frequency band. The method for constructing the microwave absorbing structure model is as follows:

[0080] Single-cell cores made of different materials were constructed, and their intrinsic impedances were obtained. Based on the intrinsic impedances of the single-cell cores, a multi-layer single-cell core array structure was constructed to form an absorbing structure with the overall impedance range divided into multiple graded gradients. This reduced the impedance difference between adjacent single-cell core array structure layers. Furthermore, along the direction towards the shielding structure, the intrinsic impedance of the multi-layer single-cell core array structure layers decreased layer by layer along the thickness direction, forming a continuous gradient transition impedance distribution. The continuous gradient transition impedance distribution was discretized and transformed into a multi-layered stepped impedance distribution to meet the target operating frequency band, thus constructing the absorbing structure model.

[0081] The intrinsic impedance of a single-cell core is determined by the material (i.e., the mass percentage of the electrically dissipative absorbing agent in each layer of the single-cell core array structure is 0wt% to 30wt%) and the single-cell size (column width w). The construction sequence is to first construct different single-cell cores made of different materials, measure the intrinsic impedance of these single-cell cores, and then select single-cell cores with different impedances to classify them into multiple impedance level gradients.

[0082] Specifically, in the absorbing structure where the overall impedance range is divided into multiple graded levels, the overall impedance range is 90Ω to 330Ω; the impedance difference between two adjacent single-cell core array structure layers is reduced to 20Ω to 40Ω.

[0083] In this embodiment of the invention, the absorbing structure adopts a metamaterial gradient impedance matching design. Based on the propagation characteristics of electromagnetic waves, an absorbing structure model with a gradually varying dielectric constant along the thickness direction is established. By controlling the gradually varying distribution of the dielectric constant, the electromagnetic wave path is regulated, thereby improving the absorbing efficiency.

[0084] Specifically, it involves constructing an absorbing structure covering an impedance range of 90Ω to 330Ω. The absorbing structure comprises eight layers of single-cell core array structures, each of which is composed of single-cell core arrays with different intrinsic impedances.

[0085] Employing a metamaterial gradient impedance matching design, the intrinsic impedance of the top-layer unit cell core array structure is closest to the air impedance (377Ω). Furthermore, from top to bottom, the intrinsic impedance of the unit cell core array structure layers decreases layer by layer along the thickness direction, forming a continuous gradient impedance distribution. This divides the impedance range of 90Ω to 330Ω into 8 gradient levels to reduce the impedance difference between adjacent unit cell core array structure layers. ΔZ i It suppresses interface reflection, optimizes impedance matching, and improves absorption efficiency.

[0086] Specifically, the impedance difference between adjacent unit cell core subarray structural layers ΔZ i =20Ω~40Ω; preferably ΔZi =30Ω. By designing the impedance difference... ΔZ i The impedance is adjusted within the range of 20Ω to 40Ω to optimize impedance matching and absorption efficiency. The absorption structure in this embodiment of the invention achieves a continuous gradient transition of electromagnetic parameters through metamaterial unit cell gradient impedance matching design, forming multi-level energy dissipation channels.

[0087] For example, build ΔZ i The three-level division schemes are 20Ω, 30Ω, and 40Ω respectively, such as... Figures 2 to 4 As shown, its hierarchy boundary satisfies: the lowest hierarchy limit (90Ω) ≤ the single-cell core array structure layer. Z i The minimum impedance (97.7Ω) must be less than or equal to the maximum impedance (330Ω). In the three-level classification scheme, the one with the finer impedance resolution should be selected. ΔZ i The 30Ω scheme aims to reduce the impedance difference between adjacent layers. Specifically, when... ΔZ i = At 20Ω, there are three impedance levels: 190Ω~210Ω, 230Ω~250Ω, and 290Ω~310Ω. Since there are no corresponding unit cells, this classification scheme is excluded. (Comparison) ΔZ i = 30Ω and ΔZ i = 40Ω solution, because ΔZ i = The 30Ω solution offers finer impedance resolution, effectively reducing the impedance difference between adjacent layers, and was ultimately selected. ΔZ i = 30Ω solution, Z i = The 90Ω to 330Ω range is divided into 8 gradient levels.

[0088] The impedance distribution theoretical model employs discretization to transform the continuously distributed impedance into a multi-level gradient layer structure, meeting the requirements of practical engineering manufacturing precision and the target operating frequency band. Therefore, the spatial unit size is calculated based on the target operating frequency band (8GHz~18GHz), and the lattice constant 'a' of the unit cell core is designed. Specifically, the lattice constant 'a' of the unit cell core needs to satisfy a ≤ 0.43λ to meet the requirements of the target operating frequency band (8GHz~18GHz) and achieve the material's wave absorption performance. Specifically, 'a' is 5mm~7mm; considering design and process constraints, a = 6mm is selected. The spatial unit size is 0.43λ.

[0089] The unit cell core shape is chosen to be a square hole structure. Due to both process constraints and manufacturing performance factors, the pillar width w is selected from 1.8 mm to 5.4 mm, for example, 1.8 mm, 3.6 mm, and 5.4 mm. Therefore, for the target frequency band of 8 GHz to 18 GHz, the lattice constant α of the square hole unit cell core is 5 mm to 7 mm, and the pillar width w is 1.8 mm to 5.4 mm.

[0090] Based on the values ​​of a (5mm–7mm), column width w (1.8mm–5.4mm), and the mass percentage of electrical loss absorbing agent in nylon pitch-based short-cut carbon fiber (0wt%–30wt%), 12 candidate unit cell core structures were obtained. The influence of different unit cell core structures on the dielectric properties of the printed filament of the absorbing structure was investigated, and the intrinsic impedance was calculated to construct a gradient impedance matching design for an integrated gradient composite structure of absorbing and bearing.

[0091] Only by obtaining the intrinsic impedance of each unit cell core structure can we construct the gradient impedance matching of the absorbing structure based on the intrinsic impedance, so that electromagnetic waves can better enter the interior of the material and be absorbed, resulting in excellent electromagnetic wave absorption performance.

[0092] Step 4: In the modeling software, model the integrated gradient composite structure of wave absorber and load-bearing in gradient impedance matching design. The specific parameters are shown in Table 1.

[0093] The lattice constant of the square-hole unit cell core is a = 6 mm, and the column widths are a three-order gradient parameter system with w = 1.8 mm, 3.6 mm, and 5.4 mm. The thickness of the square-hole unit cell core is 1.95 mm. Figure 5 and Figure 6 As shown, the established integrated gradient composite structure model of wave absorption and load bearing is used to generate printing paths through slicing software. First, the shielding structure is printed, and then the wave absorption structure is printed on the shielding structure to achieve integrated molding of the composite material.

[0094] Table 1 Specific Parameters Note: The content of chopped carbon fibers represents the mass percentage of chopped carbon fibers in each layer of the unit cell core array structure. Intrinsic impedance calculation formula: ;in, Z i Indicates the intrinsic impedance of the medium; Z 0 The intrinsic impedance of free space / air is 377Ω; μ r Indicates relative permeability; ε r This represents the relative permittivity.

[0095] Step 5, set the printing parameters for the shielding structure: Select the multi-directional laminate printing standard n=2, that is, after the composite material sub-laminated laminate is repeatedly laid twice, a symmetrical laying and printing is performed, and the layup sequence is [0 / 90]. 2s A total of 4 layers were printed; the printing speed was 600 mm / min, the printing temperature was 320℃, the printing layer thickness was 0.1 mm, the printing spacing was 1.0 mm, and the base plate temperature was 80℃.

[0096] Step 6, set the printing parameters for the absorbing structure: printing speed 600mm / min, printing temperature 290℃, printing layer thickness 0.1mm, printing spacing 1.8mm, and base plate temperature 80℃.

[0097] Step 7: Place the two types of filaments obtained in Step 1 and Step 2 into the multi-material multi-nozzle 3D printing equipment. According to the printing path, first complete the printing of the shielding structure in the multi-material multi-nozzle 3D printing equipment.

[0098] Step 8: Change the material. The microwave-absorbing filament from Step 2 is heated and melted before being fed into the nozzle. The filament is fed into the 3D print head using a filament feed motor, where it is heated to a molten state. Under the thrust of the filament, the molten resin is transported into the nozzle.

[0099] Simultaneously, low-dielectric-constant continuous fibers are also fed into the same 3D printing head through a specialized fiber guide, traversing the entire printing head until reaching the nozzle area. During this process, the low-dielectric-constant continuous fibers are fully impregnated and coated with molten resin, forming a composite filament, thus completing the printing and fabrication of the microwave absorbing structure. The overall structure is as follows: Figure 7 As shown.

[0100] Effect verification: Example 1 uses a 0–40 GHz broadband test system constructed based on the bow-shaped frame test method to verify the multi-angle reflection loss characteristics of the integrated absorber-bearer gradient composite structure prepared in Example 1 in the 2 GFHz–18 GFHz frequency band, as well as its polarization sensitivity characteristics to linearly polarized electromagnetic waves in the 2 GHz–40 GHz frequency band. Figure 8 As shown, the integrated absorber-load-bearing gradient composite structure prepared in Example 1 was used as the sample. The sample was placed on a 180mm × 180mm metal substrate, and the substrate reflection loss was calibrated before the experiment. The sample of Example 1 underwent a quasi-static compression test using an electronic universal testing machine to complete the mechanical property test. A 12mm diameter 45# steel hemispherical indenter was used, and the loading rate was a constant rate of 1mm / min. The test results are as follows. Figure 9 As shown.

[0101] Figure 9The study verified that the integrated absorber-bearer gradient composite structure based on gradient impedance matching exhibits excellent wide-angle absorption performance in the 2GHz–18GHz frequency band. Under incident conditions of 0°, 30°, 45°, and 60°, the effective absorption bandwidth of the sample in Example 1 reached 3.45GHz, 5.1GHz, 9GHz, and 7.5GHz, respectively, with corresponding minimum reflection loss peak values ​​of -13.9dB, -16.4dB, -18.5dB, and -19.8dB. Even under a large incident angle (60°), the sample in Example 1 maintained a 7.5GHz bandwidth and a -19.8dB absorption performance, fully demonstrating the stability and effectiveness of the integrated absorber-bearer gradient composite structure in complex electromagnetic environments.

[0102] Depend on Figure 10 and Figure 11 It is evident that the integrated absorber-bearer gradient composite structure based on gradient impedance matching design exhibits excellent polarization stability and broadband absorption performance in the 2GHz–40GHz frequency band. Under 60° incident conditions, the effective absorption bandwidth for horizontal polarization (TM wave) is 27.5GHz (peak value -22.8dB), and the effective absorption bandwidth for vertical polarization (TE wave) is 23GHz (peak value -24.1dB), with a peak absorption difference of less than 3dB, indicating that the structure maintains stable and efficient absorption performance in different polarization directions. Its superior performance is mainly attributed to the symmetrical design of the carbon fiber square-hole unit cell and the uniform reinforcement effect of the continuous carbon fiber composite material in multiple directions, thereby significantly reducing the structure's sensitivity to electromagnetic wave polarization direction.

[0103] Figure 12 Mechanical experimental data showed that the load-displacement curve consisted of three stages: rise, sudden drop, and rebound. When the displacement reached 8.9 mm, the maximum load on the sample was 7.97 kN, after which failure occurred. Microscopic damage morphology analysis revealed that the core layer mainly exhibited shear-compression failure, while the panel area showed a composite damage characteristic of delamination and crack propagation. Energy integration calculations showed that the total energy absorbed by the structure was 28.3 J, which included both the energy stored from elastic deformation and the energy dissipated from plastic deformation, corresponding to the deformation stage with an indentation depth of approximately 1.5 mm.

[0104] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wave-absorbing and load-bearing integrated gradient composite structure, characterized in that, It is formed by 3D printing an integrated microwave absorbing structure and a shielding structure. The shielding structure is prepared by 3D printing of conductive fiber prepreg; the conductive fiber prepreg is made by combining conductive continuous fibers and a first thermoplastic resin matrix. The absorbing structure is composed of a multi-layer single-cell core array structure layer, and along the direction toward the shielding structure, the intrinsic impedance of the multi-layer single-cell core array structure layer forms a multi-layer stepped impedance distribution along the thickness direction to match the target operating frequency band. Each of the single-cell core array structure layers uses a resin-based composite material obtained by combining an electrically depleting microwave absorbing agent with a second thermoplastic resin matrix as the microwave absorbing filament. The microwave absorbing filament and low dielectric constant continuous fibers are prepared by 3D printing. The mass percentage of the electrically depleting microwave absorbing agent in each of the single-cell core array structure layers is 0wt% to 30wt%.

2. The integrated gradient composite structure for absorbing and bearing waves according to claim 1, characterized in that, Each of the single-cell core array structure layers is formed by arranging multiple single-cell core arrays; the thickness of each of the single-cell core array structure layers is the same.

3. The integrated gradient composite structure for absorbing and bearing waves according to claim 2, characterized in that, The shape of the unit cell core is a square-hole unit cell, a honeycomb unit cell, a stepped unit cell, or a stacked unit cell.

4. The integrated gradient composite structure for absorbing and bearing waves according to claim 2, characterized in that, The lattice constant of the unit cell core satisfies the following condition: a≤0.43λ; where a represents the lattice constant of the unit cell core; λ is the wavelength of the target operating frequency band.

5. The integrated gradient composite structure for absorbing and bearing waves according to claim 4, characterized in that, The target operating frequency band of the absorbing structure is 8GHz to 18GHz, and the impedance range of the absorbing structure is 90Ω to 330Ω; the lattice constant of the unit cell core is 5mm to 7mm, the column width of the unit cell core is 1.8mm to 5.4mm, and the thickness of the unit cell core is 1.95mm.

6. The integrated gradient composite structure for absorbing and bearing waves according to claim 1, characterized in that, The conductive continuous fiber is carbon fiber or conductive polymer fiber; the first thermoplastic resin matrix is ​​polyetheretherketone, polyamide or polyimide; The electrical loss type microwave absorber is short-cut carbon fiber, carbon nanotube or graphene; the low dielectric constant continuous fiber is aramid fiber or glass fiber; the second thermoplastic resin matrix is ​​polyetheretherketone, polyamide or polyimide.

7. A 3D printing method for the integrated wave-absorbing and load-bearing gradient composite structure as described in claim 1, characterized in that, Includes the following steps: A microwave absorbing structure model with intrinsic impedance exhibiting a multi-layered stepped impedance distribution along the thickness direction is constructed to match the target operating frequency band. A shielding structure was prepared by using a 3D printing method with conductive fiber prepreg obtained by combining conductive continuous fiber and a first thermoplastic resin matrix as raw material. Based on the constructed microwave absorbing structure model, a resin-based composite material obtained by combining an electrical loss type microwave absorbing agent with a second thermoplastic resin matrix is ​​used as the microwave absorbing filament. The microwave absorbing filament and low dielectric constant continuous fiber are used as raw materials, and a microwave absorbing structure is prepared on the shielding structure by 3D printing, resulting in an integrated microwave absorbing-load-bearing gradient composite structure.

8. The 3D printing method for the integrated wave-absorbing and load-bearing gradient composite structure according to claim 7, characterized in that, The method for constructing the microwave absorbing structure model is as follows: Construct single-cell cores made of different materials and obtain the intrinsic impedance of the single-cell cores; Based on the intrinsic impedance of the single-cell core, a multi-layer single-cell core array structure is constructed to form an absorbing structure with the overall impedance range divided into multiple levels of gradient, so as to reduce the impedance difference between two adjacent single-cell core array structure layers. Furthermore, along the direction toward the shielding structure, the intrinsic impedance of the multi-layer single-cell core array structure layer decreases layer by layer along the thickness direction, forming a continuous gradient transition impedance distribution. The impedance distribution with continuous gradient transition is discretized and transformed into a multi-layered stepped impedance distribution to meet the target operating frequency band, thus constructing an absorbing structure model.

9. The 3D printing method for the integrated wave-absorbing and load-bearing gradient composite structure according to claim 7, characterized in that, In the absorbing structure where the overall impedance range is divided into multiple graded gradients, the overall impedance range is 90Ω to 330Ω; the impedance difference between two adjacent single-cell core array structures is reduced to 20Ω to 40Ω.

10. The 3D printing method for the integrated wave-absorbing and load-bearing gradient composite structure according to claim 9, characterized in that, The shielding structure is printed using a multi-directional laminated plate method, with a layer layup sequence of [0 / 90]. 2s A total of 4 layers were printed; the printing parameters of the shielding structure are as follows: Printing speed 600mm / min, printing temperature 320℃, printing layer thickness 0.1mm, printing pitch 1.0mm, base plate temperature 80℃; The absorbing structure is printed layer by layer according to the stepped impedance distribution of the unit cell core array structure layers to form 8 layers of unit cell core array structure layers with different intrinsic impedances; the printing parameters of the absorbing structure are as follows: Printing speed 600mm / min, printing temperature 290℃, printing layer thickness 0.1mm, printing spacing 1.8mm, base plate temperature 80℃.

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