A wave-absorbing stealth sandwich composite material and a preparation method thereof

Abstract

The application discloses a wave-absorbing and bearing integrated composite material, which comprises a three-dimensional bearing sandwich structure and a wave-absorbing foam / hollow microsphere composite filling body for filling cavities in the three-dimensional bearing sandwich structure. The three-dimensional bearing sandwich structure is a dot matrix sandwich structure, a three-dimensional spacer fabric reinforced sandwich structure or a three-dimensional woven hollow sandwich structure. The composite filling body is composed of a polymer foam matrix, a wave-absorbing functional filler and hollow microspheres with a volume fraction of 10% to 60%. The low density, low dielectric constant and multiple scattering effect of the hollow microspheres are utilized in combination with gradient distribution design, so that the structural density is significantly reduced, impedance matching is optimized, the wave-absorbing frequency band is widened, and absorption is enhanced; and the rigid microspheres simultaneously improve the compression strength of the foam. Compared with pure wave-absorbing foam filling, the density of the composite filling body is reduced by 20% to 40%, the effective wave-absorbing bandwidth is widened by more than 30%, and the compression strength is increased by 15% to 35%. The material has the characteristics of ultralightness, wide frequency and strong absorption and high bearing, and is suitable for stealth structural parts of aerospace, ships and the like.

Description

Technical Field

[0001] This invention relates to the field of structural microwave absorbing composite materials, specifically to a three-dimensional load-bearing sandwich composite material with a combination of microwave absorbing foam and hollow microspheres as the filling medium, its preparation method and application. Background Technology

[0002] With the rapid development of modern detection technology, the requirements for stealth performance in weaponry are increasing. Structural absorbing composite materials that combine load-bearing and electromagnetic wave absorption functions, by embedding electromagnetic wave absorption capabilities within the load-bearing structure, avoid the problems of weight increase, peeling, and narrow bandwidth associated with traditional coating-type absorbing materials. This has become a core requirement in fields such as aircraft fuselages, ship superstructures, and ground equipment protection. These materials not only need to achieve wide-bandwidth, high-absorption-rate absorption performance but also meet stringent requirements such as lightweight, high specific strength, and designability.

[0003] Three-dimensional lightweight sandwich structures with internally regular cavities or low-density core regions have been successively developed and used as load-bearing skeletons, mainly including lattice sandwich structures, three-dimensional spacer fabric-reinforced sandwich structures, and other three-dimensional sandwich structures. Filling the cavities of such structures with microwave-absorbing media is a direct means of achieving integrated load-bearing and microwave-absorbing capabilities. Among these, filling with microwave-absorbing foam is a common solution in existing technologies. Microwave-absorbing foam is usually obtained by foaming and molding polyurethane, phenolic, epoxy, and other polymer resin matrices, chemical foaming agents, and microwave-absorbing functional fillers (such as carbon black, carbon nanotubes, ferrite, magnetic metal micropowders, etc.). However, practice has shown that this solution has the following bottlenecks: (1) Density and wave absorption performance are in sharp conflict. In order to obtain effective absorption, a large amount of high-density wave absorber is often required, which results in the overall density of the foam being much higher than that of pure resin foam, seriously eroding the lightweight advantages of lattice structure and three-dimensional fabric structure.

[0004] (2) Narrow absorption bandwidth and poor impedance matching. The electromagnetic parameters of pure absorbing foam mainly depend on the type and amount of absorbing agent, with little room for adjustment. Its real part of dielectric constant is usually high, causing impedance mismatch with free space. Electromagnetic waves are reflected in large quantities at the surface and are difficult to penetrate into the interior of the structure and be lost. The absorption effect at low frequencies is particularly insufficient. If multi-layer matching design is used, the process complexity and structural weight will be greatly increased.

[0005] (3) Deterioration of mechanical properties. High content of microwave absorber significantly increases the brittleness of foam and reduces compressive strength and plastic deformation capacity. In the cavity of lattice or three-dimensional spaced composite materials, foam not only plays a role in absorbing waves, but also participates in the core load-bearing and panel support. Excessively brittle foam is prone to breakage under bending or impact loads, resulting in the simultaneous loss of overall structural stiffness and microwave absorption performance.

[0006] Hollow microspheres (such as hollow glass microspheres and hollow ceramic microspheres) are inorganic spherical powders with extremely low density and closed internal pores, and have been widely used in lightweight composite materials and microwave absorbing coatings. When dispersed in a microwave absorbing matrix at an appropriate volume fraction, they can significantly reduce the density and equivalent dielectric constant of the material by introducing a large number of closed pores, improve impedance matching with free space, and reduce electromagnetic wave reflection at the surface. On the other hand, the micron-sized hollow spherical shell structure causes electromagnetic waves to undergo multiple scattering, refraction, and resonance within the material, increasing the effective transmission path, thereby reducing the dependence on high-density microwave absorbing agents while maintaining or even improving microwave absorbing efficiency.

[0007] However, there are currently no literature or patent reports on the organic combination of hollow microspheres and microwave-absorbing foam, which serves as an integrated filler in hollow fabric sandwich composite materials to form a structural microwave-absorbing material that combines lightweight, broadband microwave absorption, and high load-bearing capacity. This is precisely the starting point and focus of this invention. Summary of the Invention

[0008] The purpose of this invention is to provide an integrated microwave absorption and load-bearing composite material to simultaneously solve the defects of existing microwave absorption foam filling solutions, such as high density, narrow absorption bandwidth, and mechanical degradation, and to achieve a synergistic improvement in ultra-lightweight structure, broadband strong absorption and high load-bearing capacity.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A wave-absorbing and load-bearing integrated composite material includes: a three-dimensional load-bearing sandwich structure, wherein the three-dimensional load-bearing sandwich structure includes a first panel, a second panel, and a core structure connecting the first panel and the second panel, wherein the first panel, the second panel, and the core structure together define a plurality of internal cavities or low-density regions for accommodating functional media. And, a microwave-absorbing foam / hollow microsphere composite filler densely filling the internal cavity; the composite filler is composed of a polymer foam matrix, microwave-absorbing functional fillers dispersed in the foam matrix, and hollow microspheres dispersed in the foam matrix.

[0010] The three-dimensional load-bearing sandwich structure can be any one of a lattice core structure, a three-dimensional spacer fabric reinforced sandwich structure, or a three-dimensional woven hollow sandwich structure. When a lattice core structure is used, the core structure is a periodically arranged rod or plate (such as a pyramid, tetrahedral, or Kagome lattice) made of metal, fiber-reinforced polymer, or ceramic material, and the internal cavity is an interconnected or partially interconnected three-dimensional grid cavity. When a three-dimensional spacer fabric reinforced sandwich structure is used, the first and second panels are fiber fabric layers, and the core structure is multiple connecting yarns woven integrally with the upper and lower panels, thus forming an array of continuous cavities. These structures together ensure the overall anti-debonding capability and high specific stiffness of the panels and core.

[0011] Further, the polymer foam matrix is ​​one or a combination of rigid polyurethane foam, phenolic foam, and epoxy foam; the microwave absorbing filler is at least one of carbon black, carbon nanotubes, graphene, silicon carbide whiskers, ferrite, carbonyl iron powder, and magnetic alloy micropowder. The hollow microspheres are one or more of hollow glass microspheres, hollow ceramic microspheres, hollow carbon microspheres, or hollow polymer microspheres, with a volume fraction accounting for 10% to 60% of the total volume of the composite filler, a true density of 0.1 to 0.6 g / cm³, a particle size distribution range of 10 to 150 μm, and a shell wall thickness of 0.5 to 3 μm. This parameter range can balance weight reduction, impedance regulation, and mechanical enhancement.

[0012] In a preferred embodiment, the microwave-absorbing foam / hollow microsphere composite filler exhibits an electromagnetic parameter gradient distribution along the thickness direction of the three-dimensional load-bearing sandwich structure. For example, from the first panel side to the second panel side, the volume fraction of hollow microspheres decreases, while the content of the microwave-absorbing functional filler increases. The upper region near the incident surface has a lower dielectric constant due to the high content of hollow microspheres, greatly optimizing surface impedance matching; the lower region possesses strong dielectric / magnetic loss capability due to the high content of microwave-absorbing agent. This gradient structure can further extend the effective absorption bandwidth and enhance low-frequency absorption.

[0013] The above-mentioned composite material can be prepared using one of the following methods: Method 1: In-situ composite foaming method. A liquid premix is ​​prepared by mixing a resin matrix, microwave-absorbing filler, hollow microspheres, foaming agent, and additives. This premix is ​​then injected into the cavity of the three-dimensional load-bearing sandwich structure under vacuum or pressure assistance, followed by heating to foam and cure. The aforementioned gradient distribution can be easily achieved by layering premixes with different formulations.

[0014] Method 2: Prefabricated Filling Method. A microwave-absorbing foam / hollow microsphere composite preform with a specific shape and electromagnetic parameters is prepared in advance through molding or free foaming. The preform is then cut and embedded according to the cavity geometry, and bonded to the inner wall of the cavity using a structural adhesive film or secondary adhesive injection. This method is particularly suitable for filling larger cavities in lattice structures.

[0015] It should be noted that the fibers in the fiber fabric layer can be selected from one or a combination of glass fiber, carbon fiber, quartz fiber, aramid fiber, and ultra-high molecular weight polyethylene fiber to adjust the electromagnetic permeability and load-bearing characteristics of the panel.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Significantly reduce density and achieve deep lightweighting. The introduction of hollow microspheres replaces part of the high-density microwave absorbing foam matrix. While maintaining a considerable effective content of microwave absorbing agent, the density of the composite filler can be reduced by 20% to 40% compared with pure microwave absorbing foam, thereby greatly reducing the overall weight increase of the sandwich structure, which is particularly suitable for applications such as aircraft that are highly sensitive to weight.

[0017] (2) Broaden the absorption bandwidth and improve absorption efficiency. Dispersed hollow microspheres can effectively reduce the real part of the equivalent dielectric constant of the composite filler, improve the impedance matching of the air-material interface, and reduce surface reflection; its spherical shell structure and the electromagnetic wave scattering, refraction and size resonance effect caused by multiple interfaces increase the transmission loss, so that the effective absorption bandwidth (reflection loss ≤ -10dB) is extended by more than 30% in the range of 2~18GHz compared with pure absorbing foam, and the absorption peak intensity is deepened.

[0018] (3) Enhanced load-bearing and damage resistance, improving structural reliability. Micron-sized rigid hollow microspheres act as reinforcing fillers in the foam matrix, hindering crack propagation. The compressive strength and compressive modulus can be increased by 15% to 35% compared to pure microwave absorbing foam. At the same time, the foam matrix's encapsulation of the microspheres and the mechanical interlocking and insertion constraints of the three-dimensional core structure (such as lattice rods and connecting yarns) on the filler eliminate the risks of microsphere settling, displacement, and filler debonding. The structure can still maintain structural integrity and microwave absorption stability under service environments such as vibration and impact.

[0019] (4) Excellent designability and process adaptability. This invention allows for independent control of the absorber content, hollow microsphere volume fraction, particle size, and the configuration of the three-dimensional load-bearing sandwich structure (lattice type, spaced fabric type, etc.) and the type of panel fiber. Multi-parameter synergistic optimization achieves customized load-bearing and microwave absorption integrated performance. The preparation method can utilize mature liquid infusion and in-situ foaming processes, without requiring disruptive modifications to existing production lines, which is beneficial for engineering scale-up and application. Attached Figure Description Figure 1This is a schematic diagram of a structure provided in an embodiment of the present invention.

Claims

1. A microwave absorbing and load-bearing integrated composite material, characterized in that, include: A three-dimensional load-bearing sandwich structure includes a first panel, a second panel, and a core structure connecting the first panel and the second panel, wherein the first panel, the second panel, and the core structure together enclose multiple internal cavities; and a microwave-absorbing foam / hollow microsphere composite filler densely filling the internal cavities; wherein the composite filler is composed of a polymer foam matrix, microwave-absorbing functional fillers dispersed in the foam matrix, and hollow microspheres dispersed in the foam matrix.

2. The composite material according to claim 1, characterized in that, The three-dimensional load-bearing sandwich structure is a lattice sandwich structure, a three-dimensional spacer fabric reinforced sandwich structure, or a three-dimensional woven hollow sandwich structure.

3. The composite material according to claim 2, characterized in that, The core of the dot matrix sandwich structure consists of periodically arranged rods or plates forming a pyramid, tetrahedral, or Kagome dot matrix; the core of the three-dimensional spacer fabric reinforced sandwich structure consists of multiple connecting yarns woven integrally with the first and second panels, thereby forming an array of hollow cavities.

4. The composite material according to claim 1, characterized in that, The polymer foam matrix is ​​at least one of rigid polyurethane foam, phenolic foam, and epoxy foam; the microwave absorbing filler is at least one of carbon black, carbon nanotubes, graphene, silicon carbide, ferrite, carbonyl iron powder, and magnetic alloy micro powder.

5. The composite material according to claim 1, characterized in that, The hollow microspheres are at least one of hollow glass microspheres, hollow ceramic microspheres, and hollow carbon microspheres; the volume fraction of the hollow microspheres accounts for 10% to 60% of the total volume of the composite filler, the true density is 0.1 to 0.6 g / cm³, and the particle size ranges from 10 to 150 μm.

6. The composite material according to claim 1, characterized in that, The composite filler exhibits an electromagnetic parameter gradient distribution along the thickness direction of the three-dimensional load-bearing sandwich structure; from the first panel side to the second panel side, the volume fraction of the hollow microspheres changes from high to low, while the content of the microwave absorbing functional filler changes from low to high.

7. The composite material according to any one of claims 1 to 6, characterized in that, The first panel and the second panel are made of fiber-reinforced resin-based composite material, wherein the reinforcing fibers are selected from at least one of glass fiber, carbon fiber, quartz fiber and aramid fiber.

8. The composite material according to any one of claims 1 to 6, characterized in that, The composite filler is formed by injecting a liquid premix containing polymer resin, the microwave absorbing filler and the hollow microspheres into the internal cavity, followed by in-situ foaming and curing.

9. A method for preparing the integrated microwave absorbing and load-bearing composite material according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Provide the three-dimensional load-bearing sandwich structure; S2: Mix the polymer resin, microwave absorbing filler, hollow microspheres and foaming agent evenly to obtain a liquid premix; S3: The liquid premix is ​​injected into the internal cavity of the three-dimensional load-bearing sandwich structure under vacuum or pressure assistance; S4: The liquid premix is ​​foamed and solidified in situ in the cavity to form the microwave absorbing foam / hollow microsphere composite filler.

10. The method according to claim 9, characterized in that, The infusion step involves injecting premixed materials with different formulations in layers, resulting in a composite filler with an electromagnetic parameter gradient distribution along the thickness direction, where the volume fraction of hollow microspheres decreases and the content of microwave-absorbing filler increases.

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