CN112829400A - Structure/stealth integrated composite material and preparation method thereof - Google Patents

Structure/stealth integrated composite material and preparation method thereof Download PDF

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Publication number
CN112829400A
CN112829400A CN202110149718.7A CN202110149718A CN112829400A CN 112829400 A CN112829400 A CN 112829400A CN 202110149718 A CN202110149718 A CN 202110149718A CN 112829400 A CN112829400 A CN 112829400A
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composite material
resin
layer
based composite
stealth
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邓瑞翔
张涛
宋力昕
于云
张科
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Shanghai Institute of Ceramics of CAS
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Shanghai Institute of Ceramics of CAS
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/20—Layered products comprising a layer of metal comprising aluminium or copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/28—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42
    • B32B27/281—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42 comprising polyimides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B33/00—Layered products characterised by particular properties or particular surface features, e.g. particular surface coatings; Layered products designed for particular purposes not covered by another single class
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/06—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the heating method
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/10—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the pressing technique, e.g. using action of vacuum or fluid pressure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B38/08—Impregnating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
    • B32B5/12—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer characterised by the relative arrangement of fibres or filaments of different layers, e.g. the fibres or filaments being parallel or perpendicular to each other
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B3/00—Hulls characterised by their structure or component parts
    • B63B3/14—Hull parts
    • B63B3/68—Panellings; Linings, e.g. for insulating purposes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64C—AEROPLANES; HELICOPTERS
    • B64C1/00—Fuselages; Constructional features common to fuselages, wings, stabilising surfaces or the like
    • B64C1/06—Frames; Stringers; Longerons ; Fuselage sections
    • B64C1/12—Construction or attachment of skin panels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2255/00—Coating on the layer surface
    • B32B2255/02—Coating on the layer surface on fibrous or filamentary layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2255/00—Coating on the layer surface
    • B32B2255/20—Inorganic coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2255/00—Coating on the layer surface
    • B32B2255/26—Polymeric coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2260/00—Layered product comprising an impregnated, embedded, or bonded layer wherein the layer comprises an impregnation, embedding, or binder material
    • B32B2260/02—Composition of the impregnated, bonded or embedded layer
    • B32B2260/021—Fibrous or filamentary layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2260/00—Layered product comprising an impregnated, embedded, or bonded layer wherein the layer comprises an impregnation, embedding, or binder material
    • B32B2260/04—Impregnation, embedding, or binder material
    • B32B2260/046—Synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
    • B32B2262/10—Inorganic fibres
    • B32B2262/101—Glass fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2605/00—Vehicles
    • B32B2605/18—Aircraft

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Abstract

The invention relates to a structure/stealth integrated composite material and a preparation method thereof, wherein the structure/stealth integrated composite material comprises the following components: at least two resin-based composite material layers; at least one frequency selective surface layer sandwiched between at least two resin-based composite material layers, wherein the resin-based composite material layers and the frequency selective surface layer are alternately arranged; and the resin-based composite material layer is composed of a resin-based composite material layer and a bottommost metal reflecting layer, the relative dielectric constant of the resin-based composite material layer in a 2-20 GHz frequency band is 2-5, the frequency selection surface layer is provided with two-dimensional periodically arranged conductive patterns, the size and the geometric center distance of the adjacent conductive patterns are between 1/20 and 1/5 of the lowest corresponding wavelength of the wave-absorbing working frequency band of the structure/stealth integrated composite material, and the tensile strength of the structure/stealth integrated composite material is not less than 200 MPa.

Description

Structure/stealth integrated composite material and preparation method thereof
Technical Field
The invention relates to the technical field of radar wave absorption materials. More particularly, the present invention relates to a structural/stealth integrated material having both a radar wave absorbing function and high mechanical strength.
Background
Unmanned aerial vehicles play a great role in various fields in the world at present, and the development of a new generation of stealth unmanned aerial vehicle becomes the focus of attention in the world. Modern unmanned aerial vehicle stealth includes appearance stealth and material stealth two kinds of ways. The disadvantage of the contour stealth technique is that the aerodynamic performance of the drone is generally impaired. And further coat the absorbing material in the great position of radar cross section on unmanned aerial vehicle surface, can reduce unmanned aerial vehicle's radar cross section effectively. However, according to the working principle of the wave-absorbing material, the wider the absorption bandwidth of the wave-absorbing material, the greater the thickness of the wave-absorbing material. Even in theoretical calculation, the minimum thickness of the non-magnetic wave-absorbing material with the reflection attenuation of the frequency band of 2-18 GHz, which is additionally added outside the skin and is better than-10 dB, is 9.7mm, so that the problems of heavy weight, large thickness, high maintenance cost and the like exist, extra load can be brought to the unmanned aerial vehicle, and the implementation and application of the wave-absorbing material are greatly limited.
Disclosure of Invention
The invention aims to provide a structure/stealth integrated composite material which can realize broadband radar absorption and restrain extra load by utilizing the resonance effect of the thickness and frequency selection surface of a resin-based composite material and a preparation method thereof.
In one aspect, the present invention provides a structural/stealth integrated composite material, including: at least two resin-based composite material layers; at least one frequency selective surface layer sandwiched between at least two resin-based composite material layers, wherein the resin-based composite material layers and the frequency selective surface layer are alternately arranged; and the resin-based composite material layer is composed of a resin-based composite material layer and a bottommost metal reflecting layer, the relative dielectric constant of the resin-based composite material layer in a 2-20 GHz frequency band is 2-5, the frequency selection surface layer is provided with two-dimensional periodically arranged conductive patterns, the size and the geometric center distance of the adjacent conductive patterns are between 1/20 and 1/5 of the lowest corresponding wavelength of the wave-absorbing working frequency band of the structure/stealth integrated composite material, and the tensile strength of the structure/stealth integrated composite material is not less than 200 MPa. According to the structure of the invention, the resonance effect of the surface can be selected by utilizing the thickness and the frequency of the resin-based composite material, so that the broadband radar absorption can be realized. The material can be directly used as a skin structure material, and broadband radar wave absorption can be realized without coating a wave-absorbing coating additionally, so that the contradiction between the thickness of the wave-absorbing material and the wave-absorbing bandwidth is effectively solved, the appearance design difficulty of stealth unmanned aerial vehicles, ships and warships and the like is reduced, and the maintenance cost of stealth wave-absorbing materials such as stealth aircraft wave-absorbing materials is reduced.
The wave-absorbing working frequency band of the structure/stealth integrated composite material can fall into the range of 2-20 GHz.
The surface resistance of the conductive pattern may be between 0.01 Ω/sq and 1000 Ω/sq.
Preferably, the resin-based composite material of the resin-based composite material layer has a relative dielectric constant of 2-5 in a frequency band of 2-18 GHz.
The resin-based composite material may be a fibre-reinforced composite material. The reinforcing fiber used may be at least one of glass fiber, quartz fiber, aramid fiber, and carbon fiber. Preferably, the material of the resin-based composite material layer is at least one of glass fiber reinforced epoxy resin, glass fiber reinforced polyether ether ketone and aramid fiber reinforced epoxy resin.
The conductive pattern may be made of copper foil, aluminum foil, conductive carbon film, or ITO conductive film. The conductive pattern may be one of a square, a circular ring, a square ring, and a hexagonal ring.
The thickness of each resin-based composite material layer is less than 4 mm; the thickness of each frequency selective surface layer is less than 0.2 mm; the thickness of the metal reflective layer is 0.15mm or less. The total thickness of the structure/stealth integrated composite material is less than 20mm, and the absorption band can be 2-20 GHz.
The sheet resistance of the metal reflective layer may be not more than 15 Ω/sq.
In the case that the resin-based composite material layer is a fiber-reinforced composite material layer, the resin-based composite material layer may include a plurality of layers, for example, one or more of a-45 ° fiber layer, a +45 ° fiber layer, a 0 ° fiber layer, and a 90 ° fiber layer, wherein the direction of the fibers in the 0 ° fiber layer is perpendicular to the direction of the fibers in the 90 ° fiber layer, and the included angles between the 45 ° fiber layer, the-45 ° fiber layer, and the 0 ° fiber layer are 45 °, -45 °, respectively.
The structure/stealth integrated composite material can be applied to skin structures of airplanes and ships.
In another aspect, a method of preparing a structural/stealth integrated composite material according to an aspect of the present invention includes:
manufacturing a conductive pattern according to the set size and the distance between the geometric centers to form a frequency selection surface;
impregnating fiber cloth or fiber bundles in resin slurry to obtain a prepreg;
laying the prepreg in a mould in a preset sequence and putting the prepreg on a frequency selection surface for hot press molding; and after the hot-press molding is finished, forming a metal reflecting layer on the bottommost layer by using conductive paste or a conductive film.
Preferably, polyimide or polyethylene terephthalate is used as a base film for preparing the frequency selection surface, sodium hydroxide solution with the concentration of 0.8-2 mol per liter is used for treating the area of the base film not covered with the frequency selection surface for 0.5-1.5 hours at room temperature, and surface activation is carried out, or ammonia water solution with the mass percent of 25-33% is used for carrying out heat preservation for 4-7 hours at the temperature of 60-90 ℃ and carrying out surface activation. According to this configuration, the mechanical strength of the bonding interface between the frequency selective surface and the composite material is further increased, and good bonding between the mechanical strength of the material and the wave absorption performance is ensured.
According to the structure, the structure/stealth integrated composite material which has excellent wave-absorbing performance and inhibits extra load while ensuring the mechanical strength and the preparation method thereof can be provided.
Drawings
FIG. 1: a schematic view of the integrated structure/stealth composite material of embodiment 1;
FIG. 2: example a schematic of a structure/stealth integrated composite (left) and a top view of a frequency selective surface (1 is a glass fibre reinforced epoxy, 2 is a frequency selective surface, 3 is a conductive copper ring, d1 ═ 2mm, d2 ═ 2mm, p ═ 14.4mm, r1 ═ 7mm, r2 ═ 4.4 mm);
FIG. 3: the measured result of the wave absorption performance of the embodiment;
FIG. 4: example two schematic diagrams of structure/stealth integrated composite (left) and top view of frequency selective surface (1 is glass fibre reinforced epoxy, 2 is frequency selective surface, 3 is conductive copper ring, d1 ═ 2.5mm, d2 ═ 2.5mm, p ═ 6.8mm, a1 ═ 6mm, a2 ═ 2 mm);
FIG. 5: the second embodiment has the actual measurement result of the wave-absorbing performance;
FIG. 6 shows the variation of the wave-absorbing property of the material with the arrangement period p in example 2-2;
FIG. 7 shows the wave-absorbing performance of the material in example 2-3 as a function of the outer diameter a1 of the square ring;
fig. 8 shows the variation of the wave-absorbing performance of the material in examples 2-4 with the square ring width (ring width is (a1-a 2)/2).
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
The present disclosure relates to a structure/stealth integrated composite material (hereinafter, sometimes simply referred to as "structure/stealth integrated material") and a method for producing the same. The structure/stealth integrated material is formed by implanting at least one layer of frequency selection surface in situ in a resin-based composite material such as a fiber reinforced composite material to form a layered structure in which the resin-based material and the frequency selection surface are alternately arranged, wherein the bottommost layer is a metal reflecting layer. The thickness of the composite material is utilized to realize the resonance effect with the frequency selection surface to realize broadband wave absorption, and the composition of the composite material is utilized to realize high mechanical strength. The invention realizes high mechanical strength and microwave absorption, namely, a part of microwave energy is absorbed and the rest is reflected.
The structure/stealth integrated composite of the present disclosure comprises: at least one frequency selective surface layer between at least two resin-based composite material layers, wherein the resin-based composite material layers and the frequency selective surface layers are alternately arranged; and the resin-based composite material layer is composed of a resin-based composite material layer and a bottommost metal reflecting layer, the relative dielectric constant of the resin-based composite material layer in a 2-20 GHz frequency band is 2-5, the frequency selection surface layer is provided with two-dimensional periodically arranged conductive patterns, and the size and the geometric center distance of the adjacent conductive patterns are between 1/20 and 1/5 of the lowest corresponding wavelength of the wave-absorbing working frequency band of the structure/stealth integrated composite material.
Embodiment 1
Fig. 1 is a schematic view of a structure/stealth integrated composite material according to embodiment 1. The integrated structure/stealth composite material 10 according to embodiment 1 includes: a plurality of resin-based composite material layers 1 (in the present embodiment, fiber-reinforced resin-based composite material layers, d1 and d2 indicate the thickness ranges of the fiber-reinforced resin-based composite material); and a frequency selective surface layer 2 sandwiched between layers of a resin-based composite material. In addition, the metal reflecting layer is positioned at the bottommost layer, and the first layer defining the side on which the electromagnetic waves are incident is the topmost layer. In the present embodiment, the frequency selective surface layer is one layer, but the number of layers of the frequency selective surface layer is not limited thereto, and may be a plurality of layers, for example, 1 to 3 layers.
The frequency selective surface layer has a two-dimensional periodic arrangement of conductive patterns for constituting a frequency selective surface (frequency selective surface). In the present embodiment, the frequency selective surface layer includes a conductive metal sheet or a conductive film for constituting the conductive pattern, and a substrate (base). Alternatively, a conductive metal sheet or a conductive film without a substrate may be used.
For example, copper foil or aluminum foil can be used as the conductive metal sheet. As the conductive film, a conductive carbon film or an ITO conductive film can be used, for example. For example, a polyimide film, a PET film, polycarbonate, or polymethyl methacrylate can be used as the substrate. The surface resistance of the conductive metal sheet or the conductive film is between 0.01 omega/sq and 1000 omega/sq. On the other hand, the sheet resistance of the conductive metal sheet/conductive film is determined by the thickness of the conductive film, and generally, the larger the thickness, the smaller the sheet resistance. This thickness is on the order of about a hundred nanometers and is negligible relative to the substrate thickness. The thickness of the substrate is 0.05-0.2 mm, and the substrate plays a role (support property) of supporting the conductive film. This thickness range is easy to ensure good flexibility of the membrane, on the other hand, impedance matching design that affects the wave absorption performance is suppressed from being too thick.
The conductive pattern includes, but is not limited to, square sheets, circular rings, square rings, hexagonal rings, and the like. The geometric dimension of the adjacent conductive patterns and the space between the geometric centers (the arrangement period of the conductive patterns) are between 1/20 and 1/5 of the wavelength corresponding to the lowest limit of the wave-absorbing working frequency band of the structure/stealth integrated composite material, and preferably between 1/15 and 1/5 of the wavelength corresponding to the lowest limit of the wave-absorbing working frequency band of the structure/stealth integrated composite material. As an example, in the structural/stealth integrated composite material of example 2, which is described later, the reflection attenuation of which is better than-10 dB in the full frequency band of 5-21 GHz, 1/20-1/5 of the wavelength corresponding to the lowest limit of the wave-absorbing working frequency band is equal to 60mm (the wavelength corresponding to 5GHz radar waves) multiplied by (1/20-1/5), that is, 3-12 mm. The length direction dimension of each conductive pattern is between 1/20 and 1/5 of the wavelength corresponding to the lowest wave-absorbing working frequency band of the structure/stealth integrated composite material. The periodic unit structure with sub-wavelength size can generate resonance with electromagnetic wave. The same pattern can be formed in the same composite material, and the combination of different patterns can also be formed. The sheet resistance of the frequency selective surface (two-dimensionally and periodically arranged conductive patterns) is between 0.01 Ω/sq and 1000 Ω/sq, and loss of incident electromagnetic waves can be achieved. Here, the square resistance refers to a square resistance value of the conductive pattern. When a substrate is present, the substrate is insulated so that the conductive pattern has the same square resistance as the conductive pattern + the substrate. The square resistance value is designed based on the impedance matching principle, and the design of the square resistance value is matched with other structural parameters.
The resin-based composite material layer 1 may include a fiber-reinforced composite material, and the reinforcing fiber is selected from non-conductive fibers such as glass fiber, quartz fiber, and aramid fiber, and may be reinforced with conductive fibers such as carbon fiber. One of the two can be used, or the two can be mixed for balancing the mechanical property and the cost. For example, a fiber having high mechanical strength and high cost is used in combination with a fiber having low mechanical strength and low cost. Long fibers (not short fibers) are preferred. When the conductive fiber such as carbon fiber is used, the addition ratio of the conductive fiber without insulation treatment is generally not more than 15% when the surface of the fiber is subjected to insulation treatment or mixed with other fibers. For example, the resin-based composite material layer 1 may include glass fiber reinforced epoxy resin, glass fiber reinforced polyether ether ketone, and aramid fiber reinforced epoxy resin, which may further ensure good mechanical strength. The relative dielectric constant of the resin-based composite material in a frequency band of 2-20 GHz is preferably 2-5, and the dielectric constant is controlled in the range, so that the broadband absorption design is further facilitated. The resin-based composite material layer 1 may have a 1-4-layer structure. In the present embodiment, the resin-based composite material is symmetrically disposed on both sides (upper and lower sides in fig. 1) of the frequency selective surface layer 2, so that the frequency selective layer can be protected inside and environmental erosion can be avoided.
In the case where the resin-based composite material layer is a fiber-reinforced composite material layer, the resin-based composite material layer may include a plurality of layers of prepregs or fibers, and each layer of prepregs or fibers may be arranged in a single direction. The multilayer prepreg or the fiber structure can comprise one or more of a-45-degree fiber layer, a + 45-degree fiber layer, a 0-degree fiber layer and a 90-degree fiber layer, the direction of fibers in the 0-degree fiber layer is vertical to the direction of fibers in the 90-degree fiber layer, the included angles of the 45-degree fiber layer, the-45-degree fiber layer and the fibers in the 0-degree fiber layer are 45 degrees, -45 degrees respectively, and the direction of the fibers in the 45-degree fiber layer is vertical to the direction of the fibers in the-45-degree fiber layer. For example, the arrangement sequence (irrespective of the position of the frequency selective surface) is cycled through 0 °/45 °/90 °/90 °/45 °/0 °, 0 °/45 °/0 °, 45 °/90 °/90 °/45 ° in this order, and the fibers are arranged (laid) so as to satisfy quasi-isotropy (quasi-isotropy in the resin-based composite material), thereby ensuring uniformity of material properties, such as uniform tensile strength in each direction. Flat woven fibers may be used. The thickness of each resin-based composite material layer can be 2-4 mm. The total thickness of the structural/stealth integrated composite may be no greater than 20 mm.
The thickness of the metal reflective layer (not shown) at the lowermost layer of the integrated structure/stealth composite material 10 may be 0.05 to 0.15mm, and may be 0.1mm or less. The sheet resistance of the bottom metal reflecting layer can be set to be not more than 15 omega/sq.
According to the structure/stealth integrated composite material, the frequency selection surface layer is implanted into the resin-based composite material, the resonance effect of the thickness and the frequency selection surface of the resin-based composite material is utilized, the broadband radar absorption is realized, and the structure/stealth integrated composite material can be applied to skin structures of unmanned aerial vehicles and ship deck boards. The resin-based composite material implanted with the frequency selective surface can bear and absorb waves, broadband radar wave absorption can be achieved without additionally coating a wave-absorbing coating, the contradiction between the thickness of the wave-absorbing material and the wave-absorbing bandwidth is effectively solved (extra load is restrained), the appearance design difficulty of a stealth unmanned aerial vehicle and the like is reduced, and the maintenance cost of the stealth wave-absorbing material is reduced.
The following illustrates a method for preparing the structure/stealth integrated composite material of the present invention.
Taking the structure/stealth integrated composite material 10 of embodiment 1 as an example, the inventor adopts a coaxial transmission line method to measure the relative permittivity and the relative permeability of a resin matrix composite material such as a fiber reinforced resin matrix composite material in a frequency band of 2-20 GHz, adopts high-frequency electromagnetic simulation software, introduces the measured relative permittivity and relative permeability, and designs the structure/stealth integrated material, wherein the design parameters include: the number of layers, the thickness of each layer of resin-based composite material, and the shape, the size, the arrangement period and the surface sheet resistance of the periodic frequency selection surface among each layer of resin-based composite material.
First, a conductive pattern is made of a copper foil, an aluminum foil, a conductive carbon film, or an ITO conductive film to obtain a frequency selective surface. A frequency selective surface of a resistive film having a prescribed square resistance value is formed. For example by oxygen partial pressure control. A conductive metal sheet or a conductive film having a substrate (base film) may be engraved. The frequency selective surface conductive pattern may be engraved on the surface using a photolithography process, laser machining, or an engraving machine. When the gap between the periodic patterns is sufficiently large, a part of the resistive film substrate is removed by punching a through hole at the gap position of the periodically arranged conductive patterns, resulting in a frequency selective surface. By punching, the upper layer of glue and the lower layer of glue can circulate, and the bonding strength is further improved. Alternatively, a conductive metal sheet or a conductive film may be plated on the substrate by a magnetron sputtering process or the like. In addition, the bottom side of the resistance film substrate can be subjected to sand blasting treatment before engraving or plating, so that the surface roughness of the resistance film can be increased. The sand grains used for sand blasting are 200 meshes to 300 meshes, and the sand blasting pressure is not more than 12.5 psi. The purpose of the sand blasting is to enhance the roughness of the frequency selective surface and to enhance the strength of the bonding interface of the frequency selective surface and the resin-based composite material.
Furthermore, the mechanical strength of a resin-based composite material may be reduced to some extent by implanting a frequency selective surface layer into the resin-based composite material. In the invention, the area of the base film which is not covered by the conductive film is preferably activated, so that the mechanical strength of the multi-layer structure wave-absorbing material is further ensured. For example, a base film (a conductive pattern is coated on the base film) is prepared by using polyimide, polyethylene terephthalate, polycarbonate or polymethyl methacrylate as a frequency selection surface, a sodium hydroxide solution with the concentration of 0.8-2 mol/L is used for treating the area of the base film not coated with the frequency selection surface for 0.5-1.5 hours at room temperature to perform surface activation, or an ammonia water solution with the mass fraction of 25-33% is used for performing surface activation by keeping the temperature at 60-90 ℃ for 4-7 hours. By utilizing the self mechanical properties of resin-based composite materials such as fiber reinforced composite materials and the like and adopting the surface treatment process of the frequency selection mask, the fiber reinforced composite material implanted with the frequency selection surface still has good mechanical strength. The resin matrix composite material can not remarkably reduce the mechanical strength and is endowed with excellent wave-absorbing performance. The tensile strength of the structure/stealth integrated composite material is more than 200 MPa.
When the conductive pattern is made of a substrate-free conductive film such as a copper foil, an aluminum foil, a conductive carbon film and the like, the substrate-free conductive film with an unprocessed pattern can be coated on the surface of the oiled paper or the PET by acrylic adhesive or aqueous polyurethane adhesive with weak viscosity, after the pattern is processed, the pattern is transferred to the surface of the resin-based composite material, and then the oiled paper or the PET is removed, so that sand blasting and hole punching operations are not needed.
Next, a prepreg is prepared for forming the resin-based composite material layer. For example, a prepreg is obtained by impregnating a fiber cloth or a fiber bundle with a predetermined resin slurry.
Next, prepregs are laid up layer by layer in the mould. And after the laid prepreg reaches the designed thickness, putting the prepreg into the corresponding frequency selection surface, and then laying the subsequent prepreg and the frequency selection surface. The prepregs corresponding to the lowermost fibre-reinforced composite layer may be laid in a mould and then the remaining layers of fibre-reinforced composite material may be laid in a predetermined order or a frequency selective surface layer may be placed. And after the prepreg corresponding to the topmost fiber reinforced composite material layer is laid, curing and molding are carried out. The curing temperature can be 80-200 ℃; the pressure (hot pressing pressure) can be 1-5Mpa, or vacuum curing can also be adopted; the time can be 8-12 hours. The thickness of the laid prepreg can be enlarged by 0.2% to 5% from a specified value (corresponding to the resin-based composite material layer) according to the specific shrinkage of the composite material base material.
Next, a metal reflective layer is formed on the outer surface of one side (in fig. 1, one of the upper and lower sides) of the resin-based composite material using a conductive paste or a conductive film. The material obtained by curing can be polished, redundant resin-based composite material on the periphery is cut off, and conductive paste is sprayed on the bottommost layer or a conductive film is pasted on the bottommost layer to obtain a metal reflecting layer, so that the structure/stealth integrated material is obtained. The raw material of the metal reflective layer may use conductive paste such as conductive carbon paste, copper-clad polyimide, conductive ITO, and the like. Can be cured at 80-100 ℃ after being coated with the conductive paste.
According to the structure, all design parameters are matched and coordinated with each other, the structure/stealth integrated material is an organic whole, the equivalent dielectric constant and the equivalent magnetic conductivity of the structure/stealth integrated material can be approximately equal in a wave-absorbing frequency band, the structure/stealth integrated material is matched with free space impedance, and reflection is minimum. According to the basic principle of microwave transmission lines, due to the existence of the metal reflecting layer, electromagnetic waves are totally reflected and transmitted to zero when reaching the metal back plate. The reflected electromagnetic wave and the incident electromagnetic wave are superposed to form standing wave, if the surface resistance value is R introduced at the strongest position of the electric fieldsWill create a surface current under external field excitation, the electromagnetic energy will be completely lost by the lossy surface and converted into thermal energy. According to the invention, the structural/stealth integrated composite material can achieve the radar wave absorption effect that the reflection attenuation in the frequency band of 2-18 GHz is better than-7 dB.
The structure/stealth integrated composite material provided by the invention combines the mechanical property advantages of the resin-based composite material and the design concept of an artificial resonance structure (namely, a frequency selection surface), on one hand, the excellent mechanical property of the resin-based composite material is kept, and at least one layer of frequency selection surface is implanted in the resin-based composite material in situ, so that the resin-based composite material is endowed with excellent wave-absorbing property while the mechanical strength of the resin-based composite material is not remarkably reduced. Meanwhile, the artificial resonance structure is protected inside the resin-based composite material, the maintenance cost is low, the appearance design of the stealth unmanned aerial vehicle is greatly facilitated, extra load brought to the unmanned aerial vehicle by the stealth material is inhibited, and the contradiction between the thickness of the wave-absorbing material and the wave-absorbing bandwidth is effectively solved.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values of the following examples;
in the following examples, reagents, materials and instruments used are all conventional reagents, conventional materials and conventional instruments, which are commercially available, if not specifically mentioned, and the reagents involved therein can also be synthesized by conventional synthesis methods.
The first embodiment is as follows:
the embodiment provides a structural/stealth integrated composite material working in an X wave band;
the glass fiber reinforced epoxy resin (CYDBN-240) material of this example was used as a fiber-reinforced composite material. The dielectric constant of the material in a frequency band of 2-18 GHz is 3.8, the loss tangent of the material is 0.1 and the material is nonmagnetic when measured by a coaxial line method;
the designed frequency selection surface is a periodically arranged conductive ring, and the specific design parameters are as follows: the distance between adjacent circular rings is 14.4mm, the outer diameter of each circular ring is 7mm, the inner diameter of each circular ring is 4.4mm, the surface square resistance of each circular ring is 2 omega/sq, and the thickness of the glass fiber reinforced epoxy resin plate on the upper layer and the thickness of the glass fiber reinforced epoxy resin plate on the lower layer of the frequency selection surface are both 2 mm;
the frequency selection surface is made of copper foil, the thickness of the copper foil is 0.017mm, the copper foil covers the polyimide surface with the thickness of 0.1mm, and a circular ring array which is arranged periodically is processed by a laser engraving machine. The polyimide film surface is subjected to sand blasting treatment to improve the interface bonding strength of the frequency selective surface and the fiber reinforced composite material, and the sand grain size is 300 meshes, and the sand blasting pressure is 10 psi. Meanwhile, the polyimide film is soaked in sodium hydroxide solution with the concentration of 1.5 mol/L, the temperature is room temperature, and the time is 0.5 hour. Then, punching holes with the diameter of 2mm in the central areas of four adjacent conductive circular rings of the polyimide;
epoxy resin is coated on the woven glass fiber cloth with the thickness of 0.6mm, four layers of glass fiber cloth are paved into a mould with the size of 350mm multiplied by 350mm according to the layer-by-layer mode of 0 degree/45 degrees/0 degrees and are compressed, and the thickness of the paved layer is about 2.2 mm. Then, the prepared frequency selection surface is placed in the middle of a mould, and glass fiber cloth impregnated with epoxy resin is continuously paved layer by layer according to the angle of 0 degree/45 degrees/0 degrees. Adding a proper amount of epoxy resin into the mold until the epoxy resin just submerges the glass fiber cloth, covering the mold, and curing for 8 hours at the temperature of 80 ℃ and under the pressure of 2 MPa;
after the curing is finished, the material is taken out, the excess material is cut off, and the periphery is polished. Then, finely processing the glass fiber reinforced epoxy resin on the two sides by adopting a grinding machine, and controlling the thickness to be 2 +/-0.1 mm;
and finally, spraying a layer of conductive carbon slurry with the square resistance value of about 15 omega/sq on the lower side of the material, and curing in an oven at 80 ℃ for 12 hours to obtain the structure/stealth integrated composite material.
Example two:
the embodiment provides a structure/stealth integrated composite material with reflection attenuation superior to-10 dB in 5-21 GHz full frequency band; the glass fiber reinforced epoxy resin (CYDHD-240) material of this example was used as a fiber-reinforced composite material. The dielectric constant of the material in a frequency band of 2-25 GHz is 4.4, the loss tangent is 0.02 and the material is nonmagnetic when measured by a coaxial line method;
the designed frequency selective surface is a periodically arranged conductive square ring, and the specific design parameters are as follows: the arrangement period of the square rings is 6.8mm, the side length of the outer diameter of each square ring is 6mm, the ring width is 2mm (namely the side length of the central hollow square is 2mm), the surface sheet resistance of each square ring is 70 omega/sq, and the thickness of the glass fiber reinforced epoxy resin plate on the upper layer and the lower layer of the frequency selective surface is 2.5 mm;
PET with the thickness of 0.05mm is used as a conductive film substrate, and the surface of the PET film is subjected to sand blasting treatment by using 300-mesh sand and 10psi sand blasting pressure, so that the roughness is increased. Meanwhile, the PET film is soaked in ammonia water with the mass fraction of 33%, and the heat preservation temperature is 80 ℃ for 5 hours. The interface bonding strength of the frequency selective surface and the fiber reinforced composite material is improved. Then, an ITO film with the thickness of 70nm is plated on the treated PET film by adopting a magnetron sputtering process. Finally, processing a periodically arranged square ring array by using a laser engraving machine;
epoxy resin is coated on the woven glass fiber cloth with the thickness of 0.6mm, four layers of glass fiber cloth are paved into a mould with the size of 350mm multiplied by 350mm according to 45 degrees/90 degrees/45 degrees layer by layer and are compressed, and the thickness of the paved layer is about 2.7 mm. Then, the prepared frequency selection surface is placed in the middle of a mould, and glass fiber cloth impregnated with epoxy resin is continuously paved layer by layer according to 45 degrees/90 degrees/45 degrees. Adding a proper amount of epoxy resin into the mold until the epoxy resin just submerges the glass fiber cloth, covering the mold, and curing the epoxy resin in a hot pressing manner in an oven at the temperature of 80 ℃ for 8 hours under the pressure of 2 MPa;
after the curing is finished, the material is taken out, the excess material is cut off, and the periphery is polished. Then, finely processing the glass fiber reinforced epoxy resin on the two sides by adopting a grinding machine, and controlling the thickness to be 2.5 +/-0.2 mm;
and finally, spraying a layer of conductive carbon slurry with the square resistance value of about 15 omega/sq on the lower side of the material, and curing in an oven at 80 ℃ for 12 hours to obtain the structure/stealth integrated composite material.
The composites obtained in the examples and in the comparative examples were tested:
and (3) testing mechanical tensile strength: the tensile strengths of the examples and comparative examples were tested using a universal tensile machine according to the method specified in GBT1447-2005 "tensile Properties test methods" with example 1 being 348MPa, example 2 being 337MPa, comparative examples 1, 2 being composites with no frequency-selective surface implanted, comparative example 1 being 362MPa and comparative example 2 being 346 MPa. The mechanical strength of the examples 1 and 2 is equivalent to that of the corresponding comparative examples 1 and 2;
and (3) radar reflection attenuation performance test: according to a method specified in standard GJB2023-2011 radar absorbing material reflectivity test method, an arch method test system comprising a vector network analyzer is adopted to test radar reflection attenuation of the embodiment and the comparative example, the embodiment 1 can realize reflection attenuation superior to-27.5 dB at 12GHz, and the embodiment 2 can realize reflection attenuation superior to-10 dB at a frequency band of 5-21 GHz. While the comparative example did not show the effect of attenuating radar waves. The embodiment 1 and the embodiment 2 can not only realize the radar reflection attenuation function of a specific frequency band, but also ensure good mechanical strength.
TABLE 1
Figure BDA0002931689250000091
TABLE 2
Figure BDA0002931689250000101
As can be seen from tables 1-2, the surface treatment of the substrate of the frequency selective surface of the plastic film with the sodium hydroxide and the aqueous ammonia solution of a certain concentration can improve the bonding strength between the frequency selective surface and the composite material. Ideally, the concentration of the sodium hydroxide solution is not less than 0.8 mol per liter, so that the situation that the surface of the polyimide cannot be effectively promoted to form activated groups in a short time and the combination of the film and the composite material is promoted is avoided. When the PET substrate is treated by ammonia water, the mass percent of the ammonia water is preferably more than 25%, and the treatment is carried out for at least 4-6 hours under the condition of not less than 60 ℃, so that the composite material after the implantation frequency selection surface has good mechanical strength is further ensured.
FIG. 6 shows the wave-absorbing property of the material of example 2-2 as a function of the alignment period p. It can be seen that when the periodic unit is between 1/20 and 1/5 of the wavelength corresponding to the lowest limit of the wave-absorbing working frequency band, the periodic unit has better wave-absorbing performance;
fig. 7 shows the wave-absorbing performance of the material in examples 2-3 as a function of the outer diameter a1 of the square ring. It can be seen that as a1 increases, the absorption peak at the high-frequency end gradually moves to the high-frequency band, and the position of the absorption peak at the high-frequency band can be adjusted by adjusting a 1;
fig. 8 shows the variation of the wave-absorbing performance of the material in examples 2-4 with the square ring width (ring width is (a1-a 2)/2). It can be seen that as the loop width increases, the frequency as a whole moves to the low frequency end, and the overall position of the absorption frequency can be adjusted by adjusting the loop width.

Claims (10)

1. A structural/stealth integrated composite, comprising: at least two resin-based composite material layers; at least one frequency selective surface layer sandwiched between at least two resin-based composite material layers, wherein the resin-based composite material layers and the frequency selective surface layer are alternately arranged; and a bottom-most metal reflective layer,
the resin-based composite material constituting the resin-based composite material layer has a relative dielectric constant of 2 to 5 in a frequency band of 2 to 20GHz,
the frequency selective surface layer is provided with two-dimensional periodically arranged conductive patterns, the size of the adjacent conductive patterns and the distance between the geometric centers of the adjacent conductive patterns are between 1/20 and 1/5 of the lowest corresponding wavelength of the wave-absorbing working frequency band of the structure/stealth integrated composite material,
the tensile strength of the structure/stealth integrated composite material is not less than 200 MPa.
2. The structure/stealth integrated composite material according to claim 1, wherein the wave-absorbing working frequency band of the structure/stealth integrated composite material falls within the range of 2-20 GHz.
3. The integrated structure/stealth composite material according to claim 1 or 2, characterized in that the surface square resistance of the conductive pattern is between 0.01 Ω/sq and 1000 Ω/sq.
4. The structure/stealth integrated composite material according to any one of claims 1 to 3, wherein the resin-based composite material of the resin-based composite material layer has a relative dielectric constant of 2 to 5 in a2 to 18GHz band.
5. The structure/stealth integrated composite material according to any one of claims 1 to 4, wherein the resin-based composite material is a fiber-reinforced composite material, the reinforcing fiber used is at least one of glass fiber, quartz fiber, aramid fiber and carbon fiber, and the material of the resin-based composite material layer is preferably at least one of glass fiber-reinforced epoxy resin, glass fiber-reinforced polyether ether ketone and aramid fiber-reinforced epoxy resin.
6. The structurally/cloaking integrated composite as claimed in any of claims 1 to 5, characterized in that the conductive pattern is made of copper foil, aluminum foil, conductive carbon film or ITO conductive film, preferably the conductive pattern is one of square, circular, square, hexagonal.
7. The structurally/cloaking integrated composite as claimed in any of claims 1 to 6 wherein the sheet resistance of the metallic reflective layer is no greater than 15 Ω/sq.
8. Use of the structural/stealth integrated composite material of any one of claims 1 to 7 in an aircraft skin or ship deck structure.
9. A method of making the structural/stealth integrated composite of any one of claims 1 to 7, comprising:
manufacturing a conductive pattern according to the set size and the distance between the geometric centers to form a frequency selection surface;
impregnating fiber cloth or fiber bundles in resin slurry to obtain a prepreg;
laying the prepreg in a mould in a preset sequence and putting the prepreg on a frequency selection surface for hot press molding; and
and after the hot-press molding is finished, forming a metal reflecting layer on the bottommost layer by using the conductive paste or the conductive film.
10. The method according to claim 9, wherein a base film is prepared using polyimide, polyethylene terephthalate, polycarbonate, or polymethyl methacrylate as the frequency selective surface, and the surface activation is performed by treating a region of the base film not covering the frequency selective surface with a sodium hydroxide solution having a concentration of 0.8 to 2 mol/l at room temperature for 0.5 to 1.5 hours, or by using an aqueous ammonia solution having a mass percentage of 25 to 33% and maintaining the temperature at 60 to 90 ℃ for 4 to 7 hours.
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Cited By (3)

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CN113682009A (en) * 2021-07-06 2021-11-23 福耀玻璃工业集团股份有限公司 Tectorial membrane board assembly and vehicle
CN114348175A (en) * 2022-01-28 2022-04-15 江苏铁锚玻璃股份有限公司 Marine window with RCS stealth and bulletproof functions
CN115534421A (en) * 2022-09-26 2022-12-30 中国人民解放军国防科技大学 Ultrathin broadband high-temperature-resistant structural wave-absorbing material and preparation method thereof

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113682009A (en) * 2021-07-06 2021-11-23 福耀玻璃工业集团股份有限公司 Tectorial membrane board assembly and vehicle
CN114348175A (en) * 2022-01-28 2022-04-15 江苏铁锚玻璃股份有限公司 Marine window with RCS stealth and bulletproof functions
CN114348175B (en) * 2022-01-28 2023-12-08 江苏铁锚玻璃股份有限公司 Marine window with RCS stealth and bulletproof functions
CN115534421A (en) * 2022-09-26 2022-12-30 中国人民解放军国防科技大学 Ultrathin broadband high-temperature-resistant structural wave-absorbing material and preparation method thereof
CN115534421B (en) * 2022-09-26 2024-05-28 中国人民解放军国防科技大学 Ultra-thin broadband high-temperature-resistant structural wave-absorbing material and preparation method thereof

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