Nacre-mimicking toughening structure and preparation process therefor

Abstract

A nacre-mimicking toughening structure and a preparation process therefor. The nacre-mimicking toughening structure comprises an upper-layer composite material (1), a lower-layer composite material (3), and an interlayer nacre-mimicking toughening structure (2) constructed from a low-dielectric sheet material and a resin matrix and located between layers of the upper-layer composite material (1) and the lower-layer composite material (3), wherein the interlayer nacre-mimicking toughening structure (2) has a high-performance soft layer / hard layer alternating nacre structure similar to that in natural shells.

Description

A nacre bionic toughening structure and its preparation process

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 202410067663.9, filed with the Patent Office of China on January 17, 2024, entitled “Nacreous layer bionic toughening structure between layers of high-speed impact-resistant and wave-transparent composite materials and its streamlined preparation process,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of composite materials, and in particular to a nacre bionic toughening structure between layers of a high-speed impact-resistant and wave-transparent composite material and a simplified preparation process thereof. Background Art

[0004] Composite materials are the main materials of radar antenna covers. While providing an electromagnetic window for the antenna system, they also need to protect it from damage from the harsh natural environment and high-speed impacts from unidentified objects outside the surface. The increasingly complex battlefield environment has put forward more stringent protection performance requirements for composite materials. Not only are they required to provide excellent wave transmission performance and maintain the overall mechanical properties of the structure in a complex and changeable battlefield environment, but they are also required to minimize their own weight to provide better maneuverability. As a new generation of protective materials, reinforced resin-based composite materials such as ultra-high molecular weight polyethylene (UHMWPE) fiber, poly(p-phenylene benzobisoxazole) fiber and aramid fiber have been research hotspots in this field in recent years, and have also been widely used. Fiber-reinforced resin-based composite materials have excellent impact resistance and protective properties, and the density is mostly 3g / cm 3 Compared to traditional metal protective materials, the following is significantly reduced, thus accelerating the development of lightweight and highly maneuverable weaponry. However, in actual applications, impacts can easily cause fiber-reinforced resin-based composite materials to delaminate and form large back protrusions. While they can effectively protect against penetrating damage, they can easily cause structural failure due to non-penetrating damage and struggle to provide the required rigidity for structural materials. To address these issues, the currently commonly used method is to increase the bonding strength between composite layers.

[0005] To resist penetrating damage, composite materials need to exhibit large in-plane tensile deformation under out-of-plane loads to fully utilize the axial tensile properties of the fibers. To resist non-penetrating damage, composite materials must exhibit high in-plane stiffness to mitigate denting deformation. Traditional research based on energy dissipation mechanisms considers penetration resistance and dent resistance to be mutually exclusive properties. For special applications, such as radar antenna covers, the low dielectric properties of the material are an unavoidable issue. This requires that while reinforcing the composite material, high dielectric materials and structures cannot be introduced.

[0006] The key to the above problems lies in the interface of the composite material. Therefore, seeking an interface toughening method with excellent fracture toughness, low plastic deformation, low dielectric and high wave transmittance is an urgent problem to be solved in the current application of composite materials in the field of radar antenna covers.

[0007] Summary of the Invention

[0008] This invention overcomes the shortcomings of existing technologies by providing a nacre-inspired bionic toughening structure between layers of high-speed impact-resistant and wave-transparent composite materials. This interlayer toughening structure exhibits low dielectric properties and high crack arrest, and its preparation process is simple and convenient. Compared to traditional single-component interlayer toughening structures, the structurally toughened composite protective material of this invention offers advantages such as low deformation, high impact resistance, low dielectric properties, and high wave transmission.

[0009] To solve the above technical problems, the present invention adopts a technical solution: a nacre bionic toughening structure between layers of high-speed impact-resistant and wave-transparent composite materials, comprising an upper composite material layer, a lower composite material layer, and an interlayer nacre bionic toughening structure constructed between the upper and lower composite material layers of a low-dielectric sheet material and a resin matrix, which has the characteristics of preventing crack propagation, improving interlayer performance, and having a low dielectric constant, similar to the high-performance soft-hard alternating nacre structure found in natural shells;

[0010] The upper composite material is selected from one of a fiber-reinforced resin-based composite material, a foam material and a honeycomb material;

[0011] The lower layer composite material is selected from one of a fiber-reinforced resin-based composite material, a foam material and a honeycomb material;

[0012] The interlayer nacre biomimetic toughening structure is an aerogel completely filled with resin. It utilizes directional freezing technology to assemble α-ZrP sheets into a continuous network structure with a specific orientation direction. The network structure is then filled with a resin matrix. Ultimately, the resin matrix forms a soft layer, and the oriented α-ZrP aerogel wall forms a hard layer, thereby constructing a nacre-like structure with alternating soft and hard layers between the composite material layers.

[0013] The resin soft layer can bond the aerogel into a whole and maintain a certain shape, transfer interlayer stress, and protect the aerogel from external erosion and damage; the low-dielectric oriented α-ZrP hard layer filled between the composite material layers in the form of aerogel has the effect of improving the mechanical properties and wave transmission performance of the interlayer toughening structure. In addition, when the overall structure is impacted, the cracks are deflected, differentiated, and terminated, thereby hindering the expansion of the main cracks between layers, thereby effectively suppressing delamination.

[0014] The interlayer nacre bionic toughening structure is applicable to the interlayers of the same or different fiber-reinforced resin composite materials, the interlayers of foams and honeycombs with discontinuous features, and the interlayers between them and fiber-reinforced resin composite materials.

[0015] As a further improvement to the technical solution of the present invention, the aerogel is obtained by directional freezing of an aqueous dispersion system of in-situ exfoliated α-ZrP nanosheets and cellulose, and has a directional orientation perpendicular to the horizontal direction, uniform wall thickness, and uniform pore distribution; the cellulose serves as a structural reinforcement framework for the oriented α-ZrP aerogel, which can enhance the structure of the oriented α-ZrP aerogel;

[0016] The in-situ exfoliated α-ZrP nanosheets are exfoliated using a small molecule substance containing amino groups as an exfoliating agent and ultrasonic-assisted exfoliation technology to obtain α-ZrP nanosheets of different two-dimensional sizes and thicknesses by controlling the exfoliation time and ultrasonic power.

[0017] The cellulose is selected from at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and bacterial cellulose.

[0018] As a further improvement of the technical solution of the present invention, the stripping agent is selected from at least one of triethanolamine, ethylenediamine and lysine.

[0019] As a further improvement of the technical solution of the present invention, the resin matrix is ​​a thermosetting resin system obtained by uniformly mixing a thermosetting resin, a curing agent and a reaction aid; the thermosetting resin is selected from at least one of an epoxy resin, an unsaturated polyester resin and a phenolic resin; the reaction aid includes any one or more mixtures of an initiator, a accelerator and a catalyst.

[0020] As a further improvement of the technical solution of the present invention, in the aqueous dispersion system of α-ZrP nanosheets and cellulose for preparing aerogel, the mass ratio of α-ZrP to cellulose is 10-5:2-1.

[0021] As a further improvement of the technical solution of the present invention, the α-ZrP nanosheet is a nano-level two-dimensional sheet material with a two-dimensional sheet size of 300 to 1700 nm and a sheet thickness of 30 to 100 nm; the thickness of the α-ZrP aerogel is 0.1 to 0.4 mm and the surface density is 20 to 100 g / m 2 .

[0022] As a further improvement of the technical solution of the present invention, the thickness of the interlayer nacre bionic toughening structure is 0.1 to 0.4 mm, the dielectric constant is 2.45 to 2.72, the loss tangent is 0.028 to 0.042, the bending strength is 100 to 130 MPa, the maximum bending strain is 4 to 6%, and the type I critical energy release rate is 1.02 to 1.58 kJ / m 2 ; The critical energy release rate of type I bonding interface is 0.7~1.2kJ / m 2 The critical energy release rate of type II bonding interface is 3.0~3.8kJ / m 2 , the interlaminar shear strength reaches 55~75MPa.

[0023] The present invention also provides a simplified preparation process for the nacreous bionic toughening structure between the layers of the high-speed impact wave-transmitting composite material, comprising the following steps:

[0024] (1) α-ZrP powder is uniformly dispersed in water, a certain amount of stripping agent is added, and the mixture is stirred until the dispersion is uniform and free of precipitation, thereby obtaining an intercalated α-ZrP dispersion; the dispersion is transferred to a cell disruptor, and the ultrasonic power and ultrasonic time are controlled to obtain α-ZrP dispersions with different stripping degrees;

[0025] (2) adding cellulose to the stripped α-ZrP dispersion obtained in step (1) and completely dissolving the cellulose to obtain a uniform aqueous dispersion; pouring the obtained uniform aqueous dispersion into a copper-bottomed mold parallel to the ground, so that the liquid nitrogen covers the copper bottom; after the aqueous dispersion is completely frozen, transferring the mold to a freeze dryer, removing the mold after drying, and obtaining an α-ZrP aerogel;

[0026] (3) Mixing the thermosetting resin and the curing agent, mechanically stirring until the color is uniform and there is no stratification, then adding the reaction aid, mechanically stirring until the color is uniform; then vacuum degassing in an oven until no bubbles are generated to obtain a resin glue solution;

[0027] (4) impregnating the α-ZrP aerogel prepared in step (2) into the resin glue prepared in step (3), evacuating the aerogel so that the resin completely fills the aerogel, raising the temperature to perform pre-curing when there are no bubbles, and taking it out after the resin matrix is ​​gelled to obtain a pre-cured body of the interlayer nacre bionic toughening structure;

[0028] (5) placing the pre-cured body of the interlayer nacre bionic toughening structure obtained in step (4) between the layers of two composite materials to be bonded, and solidifying the interlayer toughening phase and the two composite materials as a whole by liquid molding or autoclave technology to obtain a nacre bionic toughening structure between the layers of a high-speed impact-resistant and wave-transparent composite material.

[0029] As a further improvement to the technical solution of the present invention, in step (1), the power of the cell disruptor is 150 to 300 W, and the ultrasonic time is 3 to 15 minutes; in step (2), the temperature of the liquid nitrogen is -196°C; the vacuum degree of the freeze-drying is -0.05 to -0.09 MPa, the temperature is -65 to -45°C, and the time is 36 to 48 hours.

[0030] As a further improvement of the technical solution of the present invention, in step (4), the vacuum degree of vacuuming is -0.09 MPa, the pumping rate is 2 L / min, the temperature is 60-80°C, and the vacuuming time is 0.5-1 h.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The interlayer toughening method of the present invention has high interlayer performance of composite materials, can improve the critical energy release rate of the entire material, and effectively suppress interlayer delamination failure, penetrating damage and non-penetrating damage to the composite material caused by out-of-plane impact. At the same time, it also has high wave transmission performance and can be applied to fields with high requirements for the impact resistance and wave transmission performance of composite materials, such as weather radar antenna covers, vehicle-mounted antenna covers, aircraft shells, etc.

[0033] (2) The interlayer toughening structure of the present invention, the thermosetting resin system can bond the aerogel into a whole and maintain a certain shape, transfer interlayer stress, protect the aerogel from external erosion and damage, etc.; cellulose serves as a reinforcing frame of the α-ZrP aerogel structure, which plays a role in strengthening the α-ZrP aerogel structure; at the same time, α-ZrP, as a low dielectric material, is filled in the interlayer of the composite material in the form of aerogel, which can play a role in improving the interlayer phase mechanics and wave transmission performance; when the overall structure is subjected to out-of-plane impact, the cracks extend between the layers, and when reaching the aerogel wall, the aerogel wall composed of α-ZrP sheets slips, pulls out, and breaks. These methods can reduce and eliminate the stress concentration generated at the crack extension tip, consume a lot of energy, and hinder the extension of the main crack between the layers by causing the crack to deflect, differentiate, and terminate, thereby effectively suppressing delamination.

[0034] (3) The modulus of the α-ZrP layer is quite different from that of the resin matrix. Such an alternating arrangement with such a large modulus difference can also effectively prevent cracks.

[0035] (4) Aerogel can expand the interlayer space between layers, thereby increasing the glue content between the composite layers, making it more difficult for cracks to extend to the relatively fragile interface, and effectively improving the overall performance and anti-delamination performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a schematic diagram of a nacre bionic toughening structure between layers of a high-speed impact resistant and wave-transmitting composite material according to the present invention.

[0037] FIG2 is a SEM photograph of the nacre bionic toughening structure between the composite material layers prepared in Example 1 after high-speed impact.

[0038] The markings in the figure are as follows: 1-upper composite material, 2-interlayer nacre biomimetic toughening structure, 3-lower composite material, 4-α-ZrP aerogel, 5-resin matrix phase. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to specific embodiments.

[0040] Example 1

[0041] A bionic toughened nacreous layer structure with high-speed impact resistance and wave-transmitting interlayers of a glass fiber cloth reinforced epoxy resin-based composite material and an ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material, wherein the simplified preparation process comprises the following steps:

[0042] (1) Weigh 20 g of E-51 epoxy resin, add 15.8 g of anhydride curing agent hexahydrophthalic anhydride (HHPA) and 0.06 g of accelerator 2.4.6-tris(dimethylaminomethyl)phenol (DMP-30), mix well, and degas under vacuum at 50°C until no bubbles are generated to obtain epoxy resin glue;

[0043] (2) 1.43 g of α-ZrP powder was uniformly dispersed in 150 ml of deionized water, and 1.51 g of triethanolamine as an exfoliating agent was added at a molar ratio of 2:1. The mixture was stirred until the dispersion was uniform and free of precipitation to obtain an intercalated α-ZrP dispersion. The dispersion was transferred to a cell disruptor and ultrasonicated at a power of 300 W for 9 min to obtain an exfoliated α-ZrP nanosheet dispersion, wherein the average size of the α-ZrP two-dimensional sheet was 600 nm and the average sheet thickness was 40 nm.

[0044] (3) 0.4 g of hydroxyethyl cellulose was added to the prepared in situ exfoliated α-ZrP sheet dispersion until the hydroxyethyl cellulose was completely dissolved to obtain a uniform aqueous dispersion of α-ZrP / cellulose. The dispersion was then poured into a copper-bottomed mold parallel to the ground so that the liquid nitrogen covered the copper bottom. After the aqueous dispersion was completely frozen, the mold was transferred to a freeze dryer with the parameters set to a cold trap temperature of -65°C, a vacuum degree of -0.05 MPa, and freeze drying for 36 hours. After drying, the mold was removed and demolded to obtain an α-ZrP aerogel with a thickness of 0.1 mm and an area density of 40 g / m 2 ;

[0045] (4) impregnating the α-ZrP aerogel prepared in step (3) into the epoxy resin glue prepared in step (1), and evacuating the aerogel at 70°C to completely fill the resin with the aerogel at a vacuum rate of 2 L / min for 0.5 h. When there are no bubbles, the temperature is raised to 100°C for pre-curing. After the epoxy resin matrix is ​​gelled, the aerogel is taken out to obtain a pre-cured body of the interlayer toughening phase;

[0046] (5) A hard single-sided mold is used, a release agent is applied on the surface of the mold, and then a glass fiber cloth reinforced epoxy resin-based composite material, a pre-cured body of the interlayer toughening phase obtained in step (4), and an ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material are laid in sequence, and the material system is sealed on the mold with a polytetrafluoroethylene film; then a vacuum pump is connected, and the mold is transferred to a heating table, and cured at 140°C and 1 atmosphere for 3 hours to obtain a high-speed impact-resistant and wave-transparent interlayer pearl layer bionic toughening structure of the glass fiber cloth reinforced epoxy resin-based composite material and the ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material.

[0047] The preparation process of glass fiber cloth reinforced epoxy resin-based composite materials and ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite materials used for bonding is as follows:

[0048] (I) Preparation of epoxy resin glue: 150 g of E-51 epoxy resin was weighed, 118.5 g of HHPA and 0.7 g of DMP-30 were added thereto, and the mixture was mixed evenly and vacuum degassed at 50° C. until no bubbles were generated to obtain epoxy resin glue.

[0049] (II) Preparation of a glass fiber cloth reinforced epoxy resin-based composite material: A mold was coated with a release agent, and glass fiber cloth was laid in an orthogonal laying manner. After each layer was laid, it was soaked with the epoxy resin glue prepared in step (I). After laying 10 layers, the mold was wrapped with a polytetrafluoroethylene film and hot-pressed in a hot press at 100°C for 45 minutes; then the temperature was increased to 140°C and hot-pressed for 2 hours to obtain a glass fiber cloth reinforced epoxy resin-based composite material.

[0050] (III) Preparation of ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material: The mold was coated with a release agent, and ultra-high molecular weight polyethylene fiber cloth was laid in an orthogonal laying manner. After each layer was laid, it was soaked with the epoxy resin glue prepared in step (I). After laying 10 layers, the mold was wrapped with polytetrafluoroethylene film and hot pressed in a hot press at 100°C for 45 minutes; then the temperature was increased to 140°C and hot pressed for 2 hours to obtain an ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material.

[0051] Figure 2 shows an SEM image of the biomimetic toughened nacre structure between the layers of the composite material prepared in Example 1 after high-speed impact. As shown in Figure 2, the aerogel stands out between the layers in a cross-linked network structure with a specific orientation perpendicular to the horizontal direction. Residual resin matrix remains between the aerogel walls, broken by stress concentration. The aerogel walls also show varying degrees of loss due to crack propagation. These phenomena indicate improved interlayer toughness.

[0052] Comparative Example 1

[0053] A pure epoxy resin toughening structure between layers of a glass fiber cloth reinforced epoxy resin-based composite material and an ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material, the preparation process of which comprises the following steps:

[0054] (1) Same as (1) of Example 1;

[0055] (2) A hard single-sided mold is used, a mold release agent is applied on the surface of the mold, a glass fiber cloth reinforced epoxy resin-based composite material is laid, a certain thickness of the epoxy resin glue obtained in step (1) is applied thereon, and then an ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material is laid thereon, and the material system is sealed on the mold with a polytetrafluoroethylene film; then a vacuum pump is connected, the mold is transferred to a heating table, and cured at 140°C and 1 atmosphere for 3 hours to obtain a pure epoxy toughened structure between the glass fiber cloth reinforced epoxy resin-based composite material and the ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material.

[0056] The preparation process of the glass fiber cloth reinforced epoxy resin-based composite material and the ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material used for bonding is exactly the same as that in Example 1.

[0057] Comparative Example 2

[0058] A glass fiber cloth reinforced epoxy resin-based composite material and an ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material interlayer α-ZrP powder / epoxy composite toughening structure, the preparation process of which comprises the following steps:

[0059] (1) Weigh 20 g of E-51 epoxy resin, add 15.8 g of HHPA and 0.06 g of DMP-30, mix well, then add the same amount of α-ZrP powder as in Example 1, mix well, and vacuum degas at 50°C until no bubbles are generated to obtain an α-ZrP powder / epoxy composite resin glue;

[0060] (2) The same as (2) in Comparative Example 1, except that a certain thickness of α-ZrP powder / epoxy resin glue obtained in step (1) is brushed on the surface of the glass fiber cloth reinforced epoxy resin-based composite material.

[0061] The preparation process of the glass fiber cloth reinforced epoxy resin-based composite material and the ultra-high molecular weight polyethylene fiber cloth reinforced epoxy resin-based composite material used for bonding is exactly the same as that in Example 1.

[0062] Example 2

[0063] A bionic toughened pearl layer structure of a glass fiber cloth reinforced epoxy resin-based composite material and a polyvinyl chloride closed-cell foam board that resists high-speed impact and transmits waves between layers, wherein the simplified preparation process comprises the following steps:

[0064] (1) Weigh 30 g of E-51 epoxy resin, add 23.7 g of HHPA and 0.09 g of DMP-30, mix well, and vacuum degas at 50°C until no bubbles are generated to obtain epoxy resin glue;

[0065] (2) 2.15 g of α-ZrP powder was uniformly dispersed in 150 ml of deionized water, and 2.27 g of triethanolamine was added at a molar ratio of 2:1, and stirred until the dispersion was uniform and free of precipitation to obtain an intercalated α-ZrP dispersion; the dispersion was transferred to a cell disruptor and ultrasonicated at a power of 300 W for 6 min to obtain an exfoliated α-ZrP nanosheet dispersion, wherein the average size of the α-ZrP two-dimensional sheet was 1000 nm and the average sheet thickness was 60 nm;

[0066] (3) Same as (3) in Example 1; the thickness of the obtained α-ZrP aerogel is 0.2 mm and the surface density is 80 g / m 2 ;

[0067] (4) Same as (4) of Example 1;

[0068] (5) Same as (5) of Example 1, except that the cleaned polyvinyl chloride closed-cell foam board is used instead of the ultra-high molecular weight polyethylene fiber cloth to reinforce the epoxy resin-based composite material.

[0069] The preparation process of glass fiber cloth reinforced epoxy resin matrix composite material for bonding is as follows:

[0070] (I) Same as (I) of Example 1;

[0071] (II) Same as (II) in Example 1;

[0072] (III) Treatment of PVC closed-cell foam board products: Clean the surface dirt of the foam board with deionized water, and then wipe it with ethanol several times.

[0073] Comparative Example 3

[0074] A pure epoxy resin toughening structure between a glass fiber cloth reinforced epoxy resin-based composite material and a polyvinyl chloride closed-cell foam board layer, the preparation process of which comprises the following steps:

[0075] (1) Same as (1) of Example 2;

[0076] (2) A hard single-sided mold is used, a release agent is applied on the surface, a glass fiber cloth reinforced epoxy resin-based composite material is laid, a certain thickness of the epoxy resin glue obtained in step (1) is brushed on it, and then a cleaned polyvinyl chloride closed-cell foam board is laid on it, and the material system is sealed on the mold with a polytetrafluoroethylene film; then a vacuum pump is connected, and the mold is transferred to a heating table, and cured at 140°C and 1 atmosphere for 3 hours to obtain a pure epoxy toughened structure between the glass fiber cloth reinforced epoxy resin-based composite material and the polyvinyl chloride closed-cell foam board layer.

[0077] The preparation process of the glass fiber cloth reinforced epoxy resin-based composite material used for bonding and the cleaning process of the polyvinyl chloride closed-cell foam board are exactly the same as those in Example 2.

[0078] Comparative Example 4

[0079] A glass fiber cloth reinforced epoxy resin-based composite material and an α-ZrP powder / epoxy composite toughening structure between layers of a polyvinyl chloride closed-cell foam board, the preparation process of which comprises the following steps:

[0080] (1) Weigh 30 g of E-51 epoxy resin, add 23.7 g of HHPA and 0.09 g of DMP-30, mix well, add the same amount of α-ZrP powder as in Example 2, and degas under vacuum at 50° C. until no bubbles are generated to obtain an α-ZrP powder / epoxy composite resin glue solution;

[0081] (2) The same as (2) of Comparative Example 3, except that a certain thickness of α-ZrP powder / epoxy resin glue obtained in step (1) is brushed on the surface of the glass fiber cloth reinforced epoxy resin-based composite material.

[0082] The preparation process of the glass fiber cloth reinforced epoxy resin-based composite material used for bonding and the cleaning process of the polyvinyl chloride closed-cell foam board are exactly the same as those in Example 2.

[0083] Table 1 shows the properties of Examples 1-2 and Comparative Examples 1-4. The dielectric constant and dielectric loss tangent of the interlayer toughening structures in the Examples and Comparative Examples were measured using the coaxial method; the flexural strength and flexural strain were measured according to ASTM D 638, and the Type I energy release rate was measured according to ASTM D5045; the Type I energy release rate of the toughened interface was measured according to ASTM D5528, the Type II energy release rate was measured according to HB 7403, and the interlaminar shear strength was measured according to ASTM D2344.

[0084] Table 1 Performance of Examples 1-2 and Comparative Examples 1-4

[0085] As shown in Table 1, compared to comparative example, all performances of embodiment are improved. Due to the low dielectric properties possessed by the added material itself and the interlayer toughening structure obtained by using the inventive method, there is a unique class nacre brick-slurry structure, therefore, the interlayer nacre biomimetic toughening structure of the present invention, while having low dielectric constant and low dielectric loss, also has good mechanical property concurrently. In addition, interfacial energy release rate and interlaminar shear strength are significantly improved, showing that the interlayer interface toughened with the interlayer of the present invention has excellent resistance to crack generation and expansion ability, significantly improves the interlaminar fracture toughness of composite material, has broad application prospects.

[0086] In the present invention, the nacre-inspired toughening structure between the layers of the high-speed impact-resistant and wave-transparent composite material can increase the overall modulus of the material, enhancing stress transfer and thus improving the overall load-bearing performance of the structure. When the overall structure is impacted, cracks propagate between the layers. Upon reaching the aerogel wall, the aerogel wall composed of α-ZrP sheets undergoes slippage, pullout, and fracture. These processes can reduce and eliminate stress concentrations generated at the crack tip, dissipating significant energy and causing crack deflection, differentiation, and termination, hindering the propagation of the main crack between the layers and thereby inhibiting delamination. Furthermore, the modulus of the α-ZrP sheets differs significantly from that of the resin matrix. This alternating arrangement with this significant modulus difference can also effectively arrest cracks. Furthermore, the aerogel between the layers expands the interlayer space, increasing the resin content between the composite layers, making it more difficult for cracks to extend to the relatively fragile interfaces, effectively improving the overall performance and delamination resistance of the material. Furthermore, the uniquely oriented structure of the α-ZrP sheets between the layers exhibits significant interfacial effects. At the same time, α-ZrP, as a low dielectric material, is filled between the layers of the composite material in the form of aerogel, which can reduce the dielectric value of the interlayer phase.

[0087] The foregoing description is merely a specific embodiment of the present disclosure, which enables those skilled in the art to understand or implement the present disclosure. Although detailed descriptions have been made with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments, and they should all be covered by the scope of protection of the claims.

Claims

1. A nacre-inspired toughening structure for the interface of a wave-transparent composite material against high-speed impact, characterized in that, It includes an upper composite material (1), a lower composite material (3), and an interlayer nacreous bionic toughening structure (2) constructed between the upper and lower composite materials by a low-dielectric lamellar material and a resin matrix, which has a high-performance soft-hard alternating nacreous structure similar to that of natural shells, capable of preventing crack propagation, enhancing interlayer performance, and having low dielectric properties. The upper composite material (1) is selected from one of fiber-reinforced resin matrix composites, foam materials, and honeycomb materials. The lower composite material (3) is selected from one of fiber-reinforced resin matrix composites, foam materials, and honeycomb materials. The interlayer nacreous bionic toughening structure (2) is an aerogel completely filled with resin. It uses the directional freezing technique to assemble lamellar α-ZrP into a continuous network structure with a specific orientation direction, and further fills the resin matrix inside the network structure. Finally, the resin matrix forms the soft layer, and the oriented α-ZrP aerogel wall forms the hard layer, thus constructing a soft-hard alternating nacreous-like structure between the composite material layers. The resin soft layer can bond the aerogel into a whole, maintain a certain shape, transfer interlayer stress, and protect the aerogel from external erosion and damage. The low-dielectric oriented α-ZrP hard layer filled in the composite material layer in the form of aerogel has the function of enhancing the mechanical properties and wave-transmitting properties of the interlayer toughening structure. In addition, when the overall structure is impacted, it can hinder the propagation of the main crack between the layers by deflecting, differentiating, and terminating the crack, thus effectively suppressing delamination.

2. The nacre biomimetic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 1, characterized in that, The aerogel is obtained by directional freezing of an aqueous dispersion system of in-situ exfoliated α-ZrP nanosheets and cellulose, and has an aerogel with a uniform wall thickness and uniform pore distribution, oriented perpendicular to the horizontal direction. Cellulose, as the structural strengthening framework of the oriented α-ZrP aerogel, can enhance the structure of the oriented α-ZrP aerogel. The in-situ exfoliated α-ZrP nanosheets are exfoliated from the original α-ZrP nanosheets using an ultrasonic-assisted exfoliation technique with a small molecule substance containing an amino group as the exfoliating agent. Different two-dimensional sizes and thicknesses of α-ZrP nanosheets are finally obtained by controlling the exfoliation time and ultrasonic power. The cellulose is selected from at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and bacterial cellulose.

3. The nacreous layer biomimetic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 2, characterized in that, The exfoliating agent is selected from at least one of triethanolamine, ethylenediamine, and lysine.

4. The nacre-inspired toughening structure for the interlayer of the anti-high-speed impact wave-transparent composite material according to claim 1, characterized in that, The resin matrix is a thermosetting resin system obtained by uniformly mixing a thermosetting resin, a curing agent, and a reaction assistant. The thermosetting resin is selected from at least one of epoxy resin, unsaturated polyester resin, and phenolic resin. The reaction assistant includes any one or a mixture of initiators, accelerators, and catalysts.

5. The nacreous layer bionic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 2, characterized in that, In the aqueous dispersion system of α-ZrP nanosheets and cellulose for preparing the aerogel, the mass ratio of α-ZrP to cellulose is 10 - 5:2 - 1.

6. The nacreous layer bionic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 2, characterized in that, The α-ZrP nanosheets are a kind of nanoscale two-dimensional sheet material, with the two-dimensional sheet size being 300 - 1700 nm and the sheet thickness being 30 - 100 nm; the thickness of the α-ZrP aerogel is 0.1 - 0.4 mm, and the areal density is 20 - 100 g / m 2 .

7. The nacre-inspired toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 1, characterized in that, The thickness of the interlayer nacreous layer bionic toughening structure 2 is 0.1 - 0.4 mm, the dielectric constant value is 2.45 - 2.72, the tangent value of the loss angle is 0.028 - 0.042, the flexural strength is 100 - 130 MPa, the maximum flexural strain is 4 - 6%, and the critical energy release rate of Mode I is 1.02 - 1.58 kJ / m 2 ; the critical energy release rate of Mode I at the bonding interface is 0.7 - 1.2 kJ / m 2 , the critical energy release rate of Mode II at the bonding interface is 3.0 - 3.8 kJ / m 2 , and the interlayer shear strength reaches 55 - 75 MPa.

8. The simplified preparation process of the nacre biomimetic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to any one of claims 1-7, characterized in that, It includes the following steps: (1) Uniformly disperse α-ZrP powder in water, add a certain amount of exfoliating agent, and stir until the dispersion is uniform and without precipitation to obtain an intercalated α-ZrP dispersion; transfer this dispersion to a cell disruptor, control the ultrasonic power and ultrasonic time, and obtain α-ZrP dispersions with different exfoliation degrees; (2) Add cellulose to the exfoliated α-ZrP dispersion obtained in step (1) and completely dissolve the cellulose to obtain a uniform aqueous dispersion system; pour the obtained uniform aqueous dispersion system into a copper-bottom mold parallel to the ground, immerse the liquid nitrogen in the copper bottom, and after the aqueous dispersion system is completely frozen, transfer the mold to a freeze dryer, take it out and demold after drying to obtain α-ZrP aerogel; (3) Mix the thermosetting resin and the curing agent, mechanically stir until the color is uniform and there is no stratification, then add a reaction assistant thereto and mechanically stir until the color is uniform; then perform vacuum degassing in an oven until no bubbles are generated to obtain a resin glue solution; (4) Immerse the α-ZrP aerogel prepared in step (2) in the resin glue solution prepared in step (3), evacuate to completely fill the aerogel with the resin, raise the temperature for pre-curing when there are no bubbles, and take it out after the resin matrix gels to obtain a pre-cured body of the bio-inspired toughened structure with nacreous layers 2; (5) Place the pre-cured body of the bio-inspired toughened structure with nacreous layers 2 obtained in step (4) between the layers of the two composite materials to be bonded, and use liquid molding or autoclave process to integrally cure the interlayer toughening phase and the two composite materials to obtain a bio-inspired toughened structure with nacreous layers between the layers of a high-speed impact-resistant wave-transparent composite material.

9. The simplified preparation process of the nacre biomimetic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 8, characterized in that, In step (1), the power of the cell disruptor is 150 - 300 W, and the ultrasonic time is 3 - 15 min; in step (2), the temperature of the liquid nitrogen is -196 °C; the vacuum degree of the freeze drying is -0.05 - -0.09 MPa, the temperature is -65 - -45 °C, and the time is 36 - 48 h.

10. The simplified preparation process of the nacre biomimetic toughening structure between layers of the anti-high-speed impact wave-transparent composite material according to claim 8, characterized in that, In step (4), the vacuum degree of evacuation is -0.09 MPa, the pumping rate is 2 L / min, the temperature is 60 - 80 °C, and the evacuation time is 0.5 - 1 h.

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