A hollow sphere of thermosetting resin composite material with fiber gradient structure and its preparation method

Abstract

This invention belongs to the field of composite material technology, specifically disclosing a fiber-gradient structure reinforced thermosetting resin composite hollow sphere and its preparation method. The hollow sphere comprises a core material and a composite shell layer covering the outer periphery of the core material. The composite shell layer is composed of stacked thermosetting resin / reinforcing fiber layers, and includes at least two thermosetting resin / reinforcing fiber layers. The fiber length in the thermosetting resin / reinforcing fiber layers increases in a gradient from the inner to the outer layer along the radial direction of the hollow sphere. The composite shell layer comprises, by mass, 100 parts thermosetting resin, 20-40 parts diluent, 1-5 parts silane coupling agent, 20-100 parts curing agent, 1-5 parts accelerator, and 50-300 parts reinforcing fiber. The mass ratio of the core material to a single thermosetting resin layer is 1:1-1.5. The hollow sphere has a diameter of 6-60 mm, a wall thickness of 0.3-5.0 mm, and a density of 0.2-0.5 g / cm³. 3 The static water pressure is 5-60 MPa.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a hollow sphere of thermosetting resin composite material with fiber gradient structure reinforcement and its preparation method. Background Technology

[0002] Fiber-reinforced composite hollow spheres, with their lightweight and high specific strength properties, have become key functional materials in aerospace, deep-sea engineering, and other fields. In existing technologies, these hollow spheres generally employ a structural design with uniform fiber distribution. The method for preparing large hollow spheres of composite materials for solid buoyancy materials disclosed in patent CN107805318A is the most representative. This technology uses a roller method, where the core material, resin, and fibers are fed into a roller and rolled to form the spheres, enabling the large-scale production of hollow spheres.

[0003] However, this technology and similar uniform structure solutions suffer from numerous insurmountable technical bottlenecks, failing to meet the stringent material performance requirements of high-end equipment. Firstly, there is a significant contradiction between matrix density and strength. Traditional hollow sphere matrix densities typically range from 30 to 100 kg / m³, resulting in a low strength / density ratio, making it difficult to meet the urgent needs of aerospace, deep-sea exploration, and other applications requiring lightweight, high-strength materials. Secondly, uniform fiber distribution has performance limitations. It cannot optimize fiber size and arrangement based on the stress characteristics of different locations within the shell, leading to insufficient compressive strength and interfacial bonding strength of the hollow sphere. Under load, stress concentration easily occurs at the interface, significantly reducing fatigue life. Thirdly, the manufacturing process lacks precision. Traditional processes struggle to accurately control fiber size distribution and gradient structures, resulting in high costs and an inability to precisely control structural parameters. Fourthly, the core material and shell interface exhibit poor bonding. The resin-fiber bonding method is singular, lacking optimization of bonding strength at interfaces with different layer thicknesses, leading to insufficient overall structural stability. Fifth, the ability to balance tensile and compressive stresses is weak. The uniform fiber distribution structure cannot effectively coordinate tensile and compressive stresses under complex composite stresses, which can easily lead to local failures and limit the reliability of hollow spheres under extreme working conditions.

[0004] The aforementioned defects have become the core technical challenges restricting the improvement of the performance and application expansion of composite hollow spheres, and there is an urgent need to develop new structures and preparation processes to break through the existing technical bottlenecks. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a fiber-gradient structure reinforced thermosetting resin composite hollow sphere and its preparation method. This invention addresses problems in existing technologies such as the contradiction between matrix density and strength, performance limitations due to fiber distribution uniformity, insufficient manufacturing process precision, poor core-shell interface bonding, and insufficient tensile and compressive stress balance. Through the gradient fiber structure design and precisely controlled manufacturing process of this invention, lightweight, high-strength, high-toughness, and excellent thermal protection properties of the hollow sphere are achieved.

[0006] To achieve the above objectives, one technical solution of the present invention is: a hollow sphere of a fiber gradient structure reinforced thermosetting resin composite material, comprising a core material and a composite shell layer covering the outer periphery of the core material; the composite shell layer is composed of stacked thermosetting resin / reinforcing fiber layers, and includes at least two thermosetting resin / reinforcing fiber layers; the fiber length in the thermosetting resin / reinforcing fiber layers is distributed in a gradient increasing manner from the inner layer to the outer layer along the radial direction of the hollow sphere; the diameter of the hollow sphere is 6-60 mm, the wall thickness is 0.3-5.0 mm, and the density is 0.2-0.5 g / cm³. 3 The hydrostatic pressure is 5-60 MPa; the composite shell is composed of 100 parts by mass of thermosetting resin, 20-40 parts of diluent, 1-5 parts of silane coupling agent, 20-100 parts of curing agent, 1-5 parts of accelerator, and 50-300 parts of reinforcing fiber; the mass ratio of the core material to the single thermosetting resin layer in the composite shell is 1:1-1.5.

[0007] In a preferred embodiment of the present invention, the core material is one or more of expanded polystyrene (EPS), expanded polyethylene (EPE), and expanded polypropylene (EPP).

[0008] In a preferred embodiment of the present invention, the thermosetting resin comprises one or more of epoxy resin, phenolic resin, vinyl resin and polyester resin.

[0009] In a preferred embodiment of the invention, the diluent comprises one or more glycidyl ethers.

[0010] In a preferred embodiment of the present invention, the silane coupling agent comprises one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0011] In a preferred embodiment of the present invention, the curing agent comprises one or more of amine-type and acid anhydride-type curing agents.

[0012] In a preferred embodiment of the present invention, the promoter comprises one or more of 2,4,6-tris(dimethylaminomethyl)phenol and benzyldimethylamine.

[0013] In a preferred embodiment of the present invention, the reinforcing fiber comprises one or more of carbon fiber, glass fiber, wollastonite fiber, and aramid fiber.

[0014] To achieve the above objectives, a second technical solution of the present invention is: a method for preparing hollow spheres of fiber gradient structure reinforced thermosetting resin composite material, comprising the following steps:

[0015] (1) Core material preparation: The core material is put into the air classifier to suspend it;

[0016] (2) Resin coating: The thermosetting resin, diluent, silane coupling agent, curing agent and accelerator are mixed evenly according to the composition ratio, the resulting mixed liquid is atomized using an atomizer, and the atomized liquid is sprayed onto the surface of the core material suspended in step (1).

[0017] (3) Reinforcing fiber spraying: The reinforcing fiber filaments are cut into specific lengths using a long fiber cutting spray gun, and the cut reinforcing fibers are sprayed onto the surface of the core material that has been covered with resin in step (2) to form a resin-fiber composite shell and obtain a resin fiber solid ball.

[0018] (4) Curing and molding: The resin fiber solid spheres obtained in step (3) are fed into a fluidized bed and rolled and heated in a fluidized state to form a pre-cured resin fiber solid sphere with a shell structure. Then the spheres are put into an air classifier to suspend them again.

[0019] (5) Fiber gradient structure formation: Repeat steps (2) to (4) until the density of the sphere reaches 0.2-0.5 g / cm³; by controlling the cutting length of the reinforcing fiber and the number of wrapping cycles for each spray, the reinforcing fiber forms a gradient distribution with shorter inner fiber length and longer outer fiber length in the radial direction of the sphere, thereby achieving gradient optimization of mechanical properties in different regions of the hollow sphere;

[0020] (6) Post-curing and hollow structure formation: The spheres obtained in step (5) are subjected to post-curing treatment to further improve the crosslinking degree and mechanical properties of the resin matrix. During the post-curing process, the core material melts due to the heating temperature being higher than its melting point and undergoes volume shrinkage, resulting in the formation of cavities inside the spheres, and finally obtaining hollow spheres of fiber gradient reinforced thermosetting resin composite materials with hollow structures.

[0021] In a preferred embodiment of the present invention, the airflow velocity of the air classifier in steps (1) and (4) is 0.2-1 m / s, and the flow rate is 1000-3000 m³ / s. 3 / h.

[0022] In a preferred embodiment of the present invention, the atomization pressure in step (2) is 0.5-5 bar, and the droplet size is controlled at 10-150 μm.

[0023] In a preferred embodiment of the present invention, the diameter of the reinforcing fiber in step (3) is 6-20 μm, and the length of the reinforcing fiber cut by the long fiber cutting spray gun is 50-6000 μm.

[0024] In a preferred embodiment of the present invention, the heating temperature in step (4) is 40-70°C and the heating time is 15-40 min.

[0025] In a preferred embodiment of the present invention, the post-curing temperature in step (6) is 110-150°C and the heating time is 80-150 min.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention optimizes the mechanical properties of different regions of a hollow sphere by setting a gradient distribution structure of inner short fibers and outer long fibers in the diameter direction of the hollow sphere; the inner short fibers effectively enhance the interfacial bonding strength between the core material and the shell, and the outer long fibers form a continuous reinforcing network, which significantly improves the overall compressive strength and fatigue life of the hollow sphere.

[0028] 2. This invention uses an airflow grading device to suspend the core material and precisely control the density distribution of the resin matrix, thereby realizing density gradient changes in different regions of the hollow sphere and improving the lightweight level of the material;

[0029] 3. The present invention atomizes the mixture of thermosetting resin and curing agent by atomizing and sprays it evenly onto the surface of the core material, so that the resin forms a continuous and defect-free coating layer on the surface of the sphere, thereby improving the structural integrity, thermal stability and thermal protection performance of the hollow sphere.

[0030] 4. The present invention uses a repeated wrapping and curing process to obtain hollow spheres with different density gradient levels, thereby achieving gradient-based precise control of material properties and meeting the differentiated material performance requirements of different application scenarios such as aerospace, lightweight structures, and energy absorption buffers.

[0031] 5. By adjusting key process parameters such as atomizer pressure, fiber cutting size, fluidized bed temperature and time, this invention can systematically control the fiber orientation, shell thickness, density gradient and curing degree of hollow spheres, thereby achieving precise design of material properties and controllable mass production. Attached Figure Description

[0032] Figure 1 Images showing the appearance of the hollow spheres made of carbon fiber gradient reinforced epoxy resin composite material prepared in Example 1 of this invention;

[0033] Figure 2 This is a schematic diagram of the hollow sphere structure of the carbon fiber gradient reinforced epoxy resin composite material of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0035] A fiber-gradient reinforced thermosetting resin composite hollow sphere includes a core material and a composite shell layer covering the outer periphery of the core material. The composite shell layer is composed of alternating layers of thermosetting resin and reinforcing fiber, and includes at least two thermosetting resin layers and two reinforcing fiber layers. The innermost layer of the composite shell layer is a thermosetting resin layer, and the outermost layer is a reinforcing fiber layer. The length of the reinforcing fibers in the reinforcing fiber layer increases gradually from the inner layer to the outer layer along the radial direction of the hollow sphere. The composition of the composite shell layer, by mass parts, includes 100 parts of thermosetting resin, 20-40 parts of diluent, 1-5 parts of silane coupling agent, 20-100 parts of curing agent, 1-5 parts of accelerator, and 50-300 parts of reinforcing fiber. The mass ratio of the core material to the single thermosetting resin layer in the composite shell layer is 1:1-1.5. The hollow sphere has a diameter of 6-60 mm, a wall thickness of 0.3-5.0 mm, and a density of 0.2-0.5. g / cm 3 The static water pressure is 5-60 MPa.

[0036] The core material is one or more of expanded polystyrene (EPS), expanded polyethylene (EPE), and expanded polypropylene (EPP).

[0037] The thermosetting resin includes one or more of epoxy resin, phenolic resin, vinyl resin and polyester resin.

[0038] The diluent contains one or more glycidyl ethers.

[0039] The silane coupling agent comprises one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0040] The curing agent comprises one or more of amine-type and acid anhydride-type curing agents.

[0041] The accelerator comprises one or more of 2,4,6-tris(dimethylaminomethyl)phenol and benzyldimethylamine.

[0042] The reinforcing fiber comprises one or more of carbon fiber, glass fiber, wollastonite fiber, and aramid fiber.

[0043] A method for preparing hollow spheres of a fiber-gradient structure reinforced thermosetting resin composite material includes the following steps:

[0044] (1) Core material preparation: The core material is put into the air classifier to suspend it;

[0045] (2) Resin coating: The thermosetting resin, diluent, silane coupling agent, curing agent and accelerator are mixed evenly according to the composition ratio, the resulting mixed liquid is atomized using an atomizer, and the atomized liquid is sprayed onto the surface of the core material suspended in step (1).

[0046] (3) Reinforcing fiber spraying: The reinforcing fiber filaments are cut into specific lengths using a long fiber cutting spray gun, and the cut reinforcing fibers are sprayed onto the surface of the core material that has been covered with resin in step (2) to form a resin-fiber composite shell and obtain a resin fiber solid ball.

[0047] (4) Curing and molding: The resin fiber solid spheres obtained in step (3) are fed into a fluidized bed and rolled and heated in a fluidized state to form a pre-cured resin fiber solid sphere with a shell structure. Then the spheres are put into an air classifier to suspend them again.

[0048] (5) Formation of fiber gradient structure: Repeat steps (2) to (4) until the density of the spheres reaches 0.2-0.5 g / cm³. 3 By controlling the cutting length of the reinforcing fiber and the number of wrapping cycles for each spray, a gradient distribution of the reinforcing fiber with shorter inner fiber length and longer outer fiber length is formed in the radial direction of the sphere, thereby achieving gradient optimization of the mechanical properties of different regions of the hollow sphere.

[0049] (6) Post-curing and hollow structure formation: The spheres obtained in step (5) are subjected to post-curing treatment to further improve the crosslinking degree and mechanical properties of the resin matrix. During the post-curing process, the core material melts due to the heating temperature being higher than its melting point and undergoes volume shrinkage, resulting in the formation of cavities inside the spheres, and finally obtaining hollow spheres of fiber gradient reinforced thermosetting resin composite materials with hollow structures.

[0050] In steps (1) and (4), the airflow velocity of the air classifier is 0.2-1 m / s, and the flow rate is 1000-3000 m³ / s. 3 / h.

[0051] In step (2), the atomization pressure is 0.5-5 bar, and the droplet size is controlled at 10-150 μm.

[0052] In step (3), the diameter of the reinforcing fiber is 6-20 μm, and the length of the reinforcing fiber cut by the long fiber cutting spray gun is 50-6000 μm.

[0053] In step (4), the heating temperature is 40-70℃ and the heating time is 15-40 min.

[0054] In step (6), the post-curing temperature is 110-150℃ and the heating time is 80-150 min.

[0055] The isostatic compressive strength test methods for the carbon fiber reinforced hollow spheres prepared in the following examples and comparative examples are as follows:

[0056] a: Weigh a certain mass of post-cured hollow spheres, and record it as m1;

[0057] b: Place the weighed hollow sphere into a test fixture lined with a 300-mesh filter screen, and then place it in a hydrostatic press.

[0058] c: Set the test pressure P, start the hydrostatic press, and hold the pressure for 5 minutes after the pressure is increased to the specified pressure P.

[0059] d: Reduce pressure, remove the test fixture, immerse the test sample inside the fixture in water, and wash by shaking;

[0060] e: Retrieve the hollow spheres floating on the water surface, dry them, and weigh them, recording the weight as m2;

[0061] f: Calculate the survival rate W of the hollow sphere under pressure P according to the formula W=(m2 / m1-1)×100%. If W≥95%, the hydrostatic pressure test compressive strength of the hollow sphere is considered to be P.

[0062] Example 1

[0063] like Figure 2 As shown, a carbon fiber gradient reinforced epoxy resin composite hollow sphere includes a core material and a composite shell covering the outer periphery of the core material. The composite shell is composed of stacked thermosetting resin / reinforcing fiber layers, comprising 13 layers of thermosetting resin / reinforcing fiber layers. The fiber length in the thermosetting resin / reinforcing fiber layers increases in a gradient from the inner layer to the outer layer along the radial direction of the hollow sphere. The diameter of the hollow sphere is 10-12 mm, the total shell wall thickness is 0.4-0.5 mm, and the density is 0.34 g / cm³. 3 The hydrostatic pressure is 24 MPa; the composition of the thermosetting resin layer by mass is shown in Table 1.

[0064] Table 1. Composition of the thermosetting resin layer in Example 1

[0065]

[0066] The core material is expanded polystyrene (EPS) plastic spheres with a diameter of 10-12 mm, and the reinforcing fiber is carbon fiber with a diameter of 6-8 μm.

[0067] Carbon fiber gradient reinforced epoxy resin composite hollow spheres are prepared by the following method, including the following steps:

[0068] (1) Core material preparation: Weigh 100 parts by mass of expanded polystyrene plastic balls (EPS) and add them to the air classifier. Adjust the airflow speed and flow rate (specific values ​​are shown in Table 2) to keep them in a suspended state.

[0069] (2) Resin coating: The thermosetting resin, diluent, silane coupling agent, curing agent and accelerator are mixed evenly according to the composition ratio. The amount of resin added to each layer of mixture is 110 parts by mass. The obtained mixed liquid is atomized using an atomizer. The atomization pressure is 2.4 bar and the droplet size is controlled at 60 μm. The atomized liquid is sprayed onto the surface of the core material suspended in step (1) to form a resin film and obtain a thermosetting resin layer.

[0070] (3) Fiber spraying: Use a long fiber cutting spray gun to cut the carbon fiber filament into short fibers with a length of 50-100 μm. The amount of each layer of fiber is 105 parts by mass. Spray the cut carbon fiber evenly onto the surface of the core material that has been covered with resin in step (2) to obtain a layer of reinforcing fiber and obtain a resin fiber solid ball.

[0071] (4) Curing and molding: The resin fiber solid spheres obtained in step (3) are placed in a fluidized bed, the temperature is set to 50°C, and the holding time is 25 min. The resin fiber solid spheres with shell structure are obtained by rolling heating and curing. Then the spheres are put into an air classifier to suspend them again.

[0072] (5) Fiber gradient structure formation: Repeat steps (2) to (4) until the 6-layer reinforcing fiber layer is completed. Starting from the preparation of the 7th reinforcing fiber layer, adjust the cutting length of the carbon fiber precursor in the long fiber cutting spray gun in step (3) to 120-200 μm to form the outer long fiber structure. Continue to repeat steps (2) to (4) until the 13th reinforcing fiber layer is completed.

[0073] (6) Post-curing and hollow structure formation: The spheres obtained in step (5) are placed in an oven for post-curing and core shrinkage at 110°C for 90 min, resulting in a total shell wall thickness of 0.4-0.5 mm and a density of 0.34 g / cm³. 3 The appearance morphology of carbon fiber reinforced hollow spheres with a gradient fiber length distribution is shown in the image below. Figure 1 As shown.

[0074] Table 2. Airflow velocity, flow rate, and fiber length used in each layer during the preparation process of Example 1.

[0075]

[0076] The prepared carbon fiber reinforced hollow spheres were subjected to hydrostatic pressure strength testing, and the compressive strength was 24 MPa.

[0077] Example 2

[0078] A glass fiber gradient-reinforced epoxy resin composite hollow sphere includes a core material and a composite shell covering the outer periphery of the core material; the composite shell is composed of stacked thermosetting resin / reinforcing fiber layers, comprising 29 layers of thermosetting resin / reinforcing fiber layers; the fiber length in the thermosetting resin / reinforcing fiber layers increases in a gradient from the inner layer to the outer layer along the radial direction of the hollow sphere; the hollow sphere has a diameter of 31-34 mm, a total shell wall thickness of 1.6-1.7 mm, and a density of 0.50 g / cm³. 3 The hydrostatic pressure is 52 MPa; the composition of the thermosetting resin layer by mass is shown in Table 3.

[0079] Table 3. Composition of the thermosetting resin layer in Example 2

[0080]

[0081] The core material is expanded polystyrene (EPS) plastic spheres with a diameter of 30-32 mm, and the reinforcing fiber is glass fiber with a diameter of 8-13 μm.

[0082] Glass fiber gradient reinforced epoxy resin composite hollow spheres are prepared by the following method, including the following steps:

[0083] (1) Core material preparation: Weigh 100 parts by mass of expanded polystyrene plastic balls (EPS) and add them to the air classifier. Adjust the airflow speed and flow rate (specific values ​​are shown in Table 4) to keep them in a suspended state.

[0084] (2) Resin coating: The thermosetting resin, diluent, silane coupling agent, curing agent and accelerator are mixed evenly according to the composition ratio. The amount of resin added to each layer of mixture is 120 parts by mass. The obtained mixed liquid is atomized using an atomizer. The atomization pressure is 1.7 bar and the droplet size is controlled at 45 μm. The atomized liquid is sprayed onto the surface of the core material suspended in step (1) to form a resin film and obtain a thermosetting resin layer.

[0085] (3) Fiber spraying: The glass fiber filament is cut into short fibers of 150-250μm length using a long fiber cutting spray gun. The amount of fiber in each layer is 200 parts by mass. The cut glass fiber is evenly sprayed onto the surface of the core material covered with resin in step (2) to obtain a layer of reinforcing fiber and a resin fiber solid ball.

[0086] (4) Curing and molding: The resin fiber solid spheres obtained in step (3) are placed in a fluidized bed, the temperature is set to 60℃, the holding time is 35 min, and the resin fiber solid spheres with shell structure are obtained by rolling heating and curing. Then the spheres are put into an air classifier to suspend them again.

[0087] (5) Formation of fiber gradient structure: Repeat steps (2) to (4) until 11 layers of reinforcing fiber are wrapped. Starting from the preparation of the 12th layer of reinforcing fiber, the fiber cutting size in step (3) is adjusted to 500-1000 μm, and steps (2) to (4) are repeated. When 21 layers of reinforcing fiber are wrapped, start from the preparation of the 22nd layer of reinforcing fiber, adjust the fiber cutting size in step (3) to 4000-5000 μm, and repeat steps (2) to (4) until 29 layers of reinforcing fiber are wrapped.

[0088] (6) Post-curing and formation of hollow structure: The spheres obtained in step (5) are placed in an oven for post-curing and core shrinkage at 130°C for 120 min, resulting in a total shell wall thickness of 1.6-1.7 mm and a density of 0.50 g / cm³. 3 Glass fiber reinforced hollow spheres with a fiber length gradient distribution.

[0089] Table 4. Airflow velocity, flow rate, and fiber length used in each layer during the preparation process of Example 2

[0090]

[0091] The hydrostatic strength of the prepared glass fiber reinforced hollow spheres was tested, and the compressive strength was 52 MPa.

[0092] Comparative Example 1

[0093] A conventional hollow sphere made of epoxy resin composite material with uniformly distributed glass fibers includes a core material and a composite shell covering the outer periphery of the core material; the composite shell is composed of stacked thermosetting resin / reinforcing fiber layers, comprising 29 layers of thermosetting resin / reinforcing fiber layers; the hollow sphere has a diameter of 31-34 mm, a shell wall thickness of 1.6-1.7 mm, and a density of 0.50 g / cm³. 3 The hydrostatic pressure is 40 MPa; the composition of the thermosetting resin layer is the same as in Example 2.

[0094] The preparation method of the traditional epoxy resin composite hollow sphere with uniform glass fiber distribution is the same as in Example 2, except that the length of the glass fiber used in each reinforcing fiber layer is 150-250 μm.

[0095] The hydrostatic strength of the prepared epoxy resin composite hollow spheres with uniform glass fiber distribution was tested, and the compressive strength was 40 MPa.

[0096] Compared with Example 2 and Comparative Example 1, the compressive strength of glass fiber reinforced hollow spheres reached 52 MPa in hydrostatic strength testing, which is 30% higher than that of traditional hollow spheres with uniform glass fiber distribution. The compressive strength was significantly improved because the stress transmission path was optimized by the gradient distribution of fiber length, reducing interfacial stress concentration and significantly extending the fatigue life of the hollow spheres. This is because when the fiber length is distributed in a gradient according to a certain pattern (such as gradually increasing in length from the core to the surface), the mechanical properties inside the material also change in a gradient. The shorter fibers in the core provide moderate reinforcement while avoiding internal stress concentration caused by excessive constraint. The longer fibers near the surface have stronger load-bearing and bridging capabilities, which can effectively resist external loads and crack propagation. During the stress process, the load is transferred step by step through the fibers from short to long, so that the stress transitions smoothly from the matrix to the reinforcing phase, reducing abrupt interfacial changes. This reduces local stress peaks and improves the overall load-bearing efficiency and fatigue durability of the structure.

[0097] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber-graduated-structure reinforced thermosetting resin composite hollow sphere, characterized by, The device includes a core material and a composite shell covering the outer periphery of the core material. The composite shell is composed of stacked thermosetting resin / reinforcing fiber layers, and contains at least two thermosetting resin / reinforcing fiber layers. The fiber length in the thermosetting resin / reinforcing fiber layers increases in a gradient from the inner layer to the outer layer along the radial direction of the hollow sphere. The composition of the composite shell, by mass parts, includes 100 parts of thermosetting resin, 20-40 parts of diluent, 1-5 parts of silane coupling agent, 20-100 parts of curing agent, 1-5 parts of accelerator, and 50-300 parts of reinforcing fiber. The mass ratio of the core material to the single thermosetting resin layer in the composite shell is 1:1-1.

5. The hollow sphere has a diameter of 6-60 mm, a wall thickness of 0.3-5.0 mm, a density of 0.2-0.5 g / cm3, and a hydrostatic pressure of 5-60 MPa.

2. The hollow sphere of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 1, characterized in that, The core material is one or more of expanded polystyrene plastic balls, expanded polyethylene balls, and expanded polypropylene balls.

3. The hollow sphere of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 1, characterized in that, The thermosetting resin includes one or more of epoxy resin, phenolic resin, vinyl resin and polyester resin.

4. The fiber-gradient structure reinforced thermosetting resin composite hollow sphere as described in claim 1, characterized in that, The diluent comprises one or more of glycidyl ethers; the silane coupling agent comprises one or more of γ-aminopropyltriethoxysilane and γ-glycidyl etheroxypropyltrimethoxysilane; the curing agent comprises one or more of amine-type and anhydride-type curing agents; the accelerator comprises one or more of 2,4,6-tris(dimethylaminomethyl)phenol and benzyl dimethylamine; and the reinforcing fiber comprises one or more of carbon fiber, glass fiber, wollastonite fiber, and aramid fiber.

5. A method for preparing hollow spheres of fiber-gradient structure reinforced thermosetting resin composite material as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Core material preparation: The core material is put into the air classifier to suspend it; (2) Resin coating: The thermosetting resin, diluent, silane coupling agent, curing agent and accelerator are mixed evenly according to the composition ratio, the resulting mixed liquid is atomized using an atomizer, and the atomized mixed liquid is sprayed onto the surface of the core material suspended in step (1). (3) Reinforcing fiber spraying: The reinforcing fiber filaments are cut into specific lengths using a long fiber cutting spray gun, and the cut reinforcing fibers are sprayed onto the surface of the core material that has been covered with resin in step (2) to form a resin-fiber composite shell and obtain a resin fiber solid ball. (4) Curing and molding: The resin fiber solid spheres obtained in step (3) are fed into a fluidized bed and rolled and heated in a fluidized state to form a pre-cured resin fiber solid sphere with a shell structure. Then the spheres are put into an air classifier to suspend them again. (5) Fiber gradient structure formation: Repeat steps (2) to (4) until the density of the sphere reaches 0.2-0.5 g / cm³; by controlling the cutting length of the reinforcing fiber and the number of wrapping cycles for each spray, the reinforcing fiber forms a gradient distribution with short inner fibers and long outer fibers in the radial direction of the sphere. (6) Post-curing and hollow structure formation: The spheres obtained in step (5) are post-cured. The core material melts due to the heating temperature being higher than its melting point, resulting in volume shrinkage and the formation of cavities inside the spheres. Finally, hollow spheres of fiber gradient reinforced thermosetting resin composite material with hollow structures are obtained.

6. The method for preparing hollow spheres of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 5, characterized in that, The air flow velocity of the air flow classifier in steps (1) and (4) is 0.2-1 m / s, and the flow rate is 1000-3000 m 3 / h.

7. The method for preparing hollow spheres of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 5, characterized in that, In step (2), the atomization pressure is 0.5-5 bar, and the droplet size is controlled at 10-150 μm.

8. The method for preparing hollow spheres of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 5, characterized in that, In step (3), the diameter of the reinforcing fiber is 6-20 μm, and the length of the reinforcing fiber cut by the long fiber cutting spray gun is 50-6000 μm.

9. The method for preparing hollow spheres of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 5, characterized in that, In step (4), the heating temperature is 40-70℃ and the heating time is 15-40 min.

10. The method for preparing hollow spheres of fiber-gradient structure reinforced thermosetting resin composite material as described in claim 5, characterized in that, In step (6), the post-curing temperature is 110-150℃ and the heating time is 80-150 min.

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