Sandwich pressure-resistant shell structure and processing method thereof

Abstract

This invention provides a sandwiched pressure hull structure and its processing method, relating to an underwater vehicle structure, including an inner hull, an outer hull, and an intermediate sandwich layer located between the inner and outer hulls. The intermediate sandwich layer includes hollow glass microspheres, reinforcing fibers, and epoxy resin. The spherical hollow glass microspheres and reinforcing fibers are uniformly mixed in the epoxy resin and placed in a fluidized state between the inner and outer hulls. After vacuum curing, they form a buoyancy material located between the inner and outer hulls. This invention addresses the problems of insufficient load-bearing capacity and low specific strength and specific stiffness of the pressure hulls of underwater vehicles in the prior art.

Description

Technical Field

[0001] This invention relates to an underwater vehicle structure, and more particularly to a sandwich pressure hull structure and its processing method. Background Technology

[0002] In existing technologies, the selection of materials for pressure hulls involves two main types: metal materials and composite materials. Composite hulls have greater advantages over metal pressure hulls in terms of specific stiffness, specific strength, and sound insulation and noise reduction, and have been increasingly used in underwater vehicles. However, the commonly used composite pressure hull structures currently have the following problems: the structural utilization efficiency of single-layer carbon fiber hulls is not high, especially in terms of improving stiffness performance; in existing sandwich hull technology, the sandwich is processed separately and then bonded, which has low overall requirements for bearing external pressure loads, and the specific strength and specific stiffness of the sandwich material itself still have a lot of room for improvement; existing designs also focus more on improving the ring-shaped instability resistance, and lack attention to the axial instability resistance. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a sandwich pressure-resistant shell structure and its processing method. This structure solves the problems of insufficient load-bearing capacity, low specific strength, and low specific stiffness in the pressure-resistant shells of underwater vehicles in the prior art. Furthermore, by mixing hollow glass microspheres, reinforcing fibers, and epoxy resin and injecting them into the space between the inner and outer shells in a pre-cured fluid state, the present invention ensures a better filling rate between the inner and outer shells. This eliminates interfacial air gaps and forms a continuous force transmission path after curing, significantly improving interlayer shear strength and greatly reducing the anisotropic difference in compressive strength. Molecular-level diffusion occurs between the fluid material and the uncured layer of the shell prepreg, resulting in a peel strength of up to 120 N / cm (80% higher than that of adhesive bonding).

[0004] This invention provides the following technical solution:

[0005] A sandwich pressure-resistant shell structure and its processing method are disclosed, comprising an inner shell, an outer shell, and an intermediate sandwich layer located between the inner shell and the outer shell. The intermediate sandwich layer comprises hollow glass microspheres, reinforcing fibers, and epoxy resin. The spherical hollow glass microspheres and reinforcing fibers are uniformly mixed in the epoxy resin and placed in a fluidized state between the inner shell and the outer shell. After vacuum curing, a buoyancy material is formed between the inner shell and the outer shell.

[0006] Among them, hollow glass microspheres provide low density (0.2-0.4 g / cm³). 3The hollow glass microspheres and closed-cell structure are used to achieve buoyancy compensation, while the reinforcing fibers are used to form a three-dimensional reinforcing network to improve compressive strength and shear resistance. Epoxy resin is used as a binder to impart formability to the material and improve interfacial stress transmission. The hollow glass microspheres, reinforcing fibers and epoxy resin are mixed and poured into the inner and outer shells in a fluid state before curing. This can also ensure a better filling rate between the inner and outer shells, eliminate interfacial air gaps, and form a continuous force transmission path after curing. The interlayer shear strength is greatly improved, and the anisotropic difference in compressive strength is also greatly reduced. The fluid material diffuses at the molecular level with the uncured layer of the shell prepreg, and the peel strength can reach 120 N / cm (80% higher than the adhesive bonding process).

[0007] Preferably, the weight ratio of hollow glass microspheres, reinforcing fibers, and epoxy resin in the buoyancy material is 60% hollow glass microspheres + 30% reinforcing fibers + 10% epoxy resin. This buoyancy material ratio achieves an optimal balance between mechanical properties and buoyancy characteristics through the synergistic effect of multiple components, allowing the formed shell to withstand seawater (1.025 g / cm³). 3 It provides 17-20% net buoyancy compensation, with a compressive strength range of 85-110MPa (ASTM D695 standard), an elastic modulus range of 8-12GPa (5 times higher than pure microsphere systems), and an interlaminar shear strength range of 25-30MPa (under the bridging effect when the reinforcing fiber uses short-cut carbon fiber). In the pressure test, the volume shrinkage rate of the shell under 60MPa hydrostatic pressure is <2% (microsphere breakage rate <5%), and the buoyancy loss is <3% after 500 pressure cycles (10-60MPa). This effect is far superior to the shell structures currently available on the market.

[0008] Preferably, the thickness of the outer shell is greater than the thickness of the inner shell, and the outer diameter of the inner shell is smaller than the inner diameter of the outer shell. This way, because the outer shell needs to withstand greater circumferential stress, the increased thickness relative to the inner shell ensures that the circumferential stress level of the outer shell is comparable to that of the inner shell, thereby making the stress distribution of the overall structure more uniform and reducing the risk of inner layer interface peeling.

[0009] Preferably, the inner shell and the outer shell are preformed cylindrical shells using fiber bundles, and the fiber bundles are made of carbon fiber or glass fiber. The forming technology includes, but is not limited to, wet winding and three-dimensional weaving. The cylindricity of the inner and outer surfaces of the inner and outer shells is ensured by the male mold and machining, respectively.

[0010] Preferably, when the fiber bundle is made of carbon fiber and the inner and outer shells are formed as carbon fiber shells, the thickness ratio of the outer shell to the inner shell is in the range of 1.3:1 - 1.8:1; while when the fiber bundle is made of glass fiber and the inner and outer shells are formed as glass fiber shells, the thickness ratio of the outer shell to the inner shell is in the range of 1.8:1 - 2.5:1. This thickness ratio range can better maintain the uniformity of the overall compressive stress distribution of the shell structure. Within this range, the test surface is 12%-15% lighter than the traditional equal-thickness design while maintaining the same compressive strength. At the same time, ANSYS simulation shows that the stress non-uniformity is reduced by about 35% compared with the equal-thickness design, which is within a better range.

[0011] Preferably, in order to further increase the stability of the overall structure, the interlayer material also includes an annular composite profile and / or strip composite profile pre-formed before being placed between the inner shell and the outer shell. The base material of the annular composite profile and the strip composite profile is carbon fiber or glass fiber material, and the annular composite profile placed between the inner shell and the outer shell is also provided with a through hole so as not to obstruct the fluid injection of the buoyancy material between the inner shell and the outer shell.

[0012] Preferably, the system further includes two sets of flanges fixedly installed at both ends of the inner shell and the outer shell. The flanges are provided with an inner annular boss, a middle annular boss, and an outer annular boss. The height of the intermediate interlayer is less than the height of the inner shell and the outer shell. The two ends of the intermediate interlayer are tightly fitted with the middle annular boss of the flange. The inner shell and the outer shell are respectively nested in the inner annular boss and the outer annular boss of the flange, and are spaced apart by sealing rings. Since the two ends of the intermediate interlayer are in direct contact with the middle annular boss of the flange, the axial pressure load acting on the two ends will take the buoyancy material interlayer in the core of the intermediate interlayer as the first transmission path, effectively reducing the risk of axial instability.

[0013] Preferably, after the buoyancy material is placed in fluid form between the inner and outer shells, it is cured on a vibration table in a vacuum autoclave using a temperature-step curing method. This temperature-step curing method includes the following steps: first, curing at 55-65℃ for 1.5-2.5 hours to bring the buoyancy material to a gel state; then, raising the temperature to 75-85℃ for 3-5 hours to complete the pre-curing of the buoyancy material; and then further raising the temperature to 115-125℃ for 1.5-2.5 hours to complete the overall curing of the buoyancy material. During the curing process, a vacuum is first drawn inside the vacuum autoclave, followed by temperature... During the process of raising the temperature to 55-65℃ and maintaining it, nitrogen gas is introduced into the vacuum autoclave to maintain the pressure inside the autoclave at 0.35-0.45 MPa. When the temperature rises to above 75-85℃, nitrogen gas is continued to be introduced into the vacuum autoclave to maintain the pressure inside the autoclave at 1.05-1.15 MPa. During this process, vacuuming thoroughly removes gases, moisture, and volatile impurities from the buoyancy material. If these substances remain, they will form pores or bubbles during the curing process, leading to a decrease in material density and pressure resistance. For example, high-temperature epoxy resin potting compound will show negative effects after vacuuming. After vacuum treatment, its pressure resistance is significantly improved, enabling it to withstand higher hydrostatic pressure and meet the high pressure resistance requirements of buoyancy materials in deep-sea equipment. Maintaining a pressure of 0.4 MPa in the 0-60℃ range promotes the volatilization of low molecular weight substances within the material, further reducing porosity. Simultaneously, the pressure allows for tighter material filling, improving molding precision. Upon reaching 80℃, increasing the pressure to 1.1 MPa accelerates the curing reaction, strengthens intermolecular bonding, and makes the material structure more compact, thereby enhancing overall pressure resistance. Through gradient pressure adjustment, the material is subjected to uniform pressure during curing, avoiding localized stress concentration. Microscopic defects (such as cracks and delamination) can be addressed. For example, high-strength solid buoyancy materials (such as epoxy resin containing hollow glass microspheres) can be vacuum-cured under pressure regulation, which can improve their impact resistance by 15%-20% and extend their fatigue life by more than 30%. This is suitable for frequent ascents and descents of pressure hulls for deep-sea submersibles. Pressure control can adjust the balance between material density and strength. At 0.4 MPa, the material density decreases (buoyancy increases), while strength is maintained through high-pressure curing at 80℃, achieving "lightweight and high-strength" characteristics. For example, after this process, the density of a certain type of buoyancy material is reduced to 0.6 g / cm³. 3 Its compressive strength reaches 80MPa, meeting the dual requirements of buoyancy and structural strength for deep-sea submersibles.

[0014] A method for manufacturing a sandwich pressure-resistant shell structure, based on the aforementioned sandwich pressure-resistant shell structure, includes the following steps:

[0015] S1: Pre-form the fiber bundle into a cylindrical shell;

[0016] S2: Position two sets of cylindrical shells of different diameters onto the positioning fixture on the vibrating table inside the vacuum autoclave. The two sets of cylindrical shells are nested in a state where they are coaxial inside and out and have flush end faces. The innermost shell is the inner shell, and the outermost shell is the outer shell.

[0017] S3: A buoyancy material for filling the space between the inner and outer shells with fluid;

[0018] S4: Start the vibration platform to vibrate, and complete the overall vacuum curing operation in the vacuum autoclave;

[0019] S5: Demold the sandwich shell after curing in S4 and machine the end face so that the machined end face is compatible with the flange to be installed;

[0020] S6: Bond the end flanges of the sandwich shell after machining in S5.

[0021] The beneficial effects of this invention are:

[0022] This invention provides a sandwich pressure-resistant shell structure and its processing method, which solves the problems of insufficient load-bearing capacity and low specific strength and specific stiffness of pressure shells for underwater vehicles in the prior art. Furthermore, by mixing hollow glass microspheres, reinforcing fibers, and epoxy resin and injecting them into the space between the inner and outer shells in a pre-cured fluid state, it ensures a better filling rate between the inner and outer shells, eliminates interfacial air gaps, and forms a continuous force transmission path after curing. This significantly improves interlayer shear strength and greatly reduces the anisotropic difference in compressive strength. Molecular-level diffusion occurs between the fluid material and the uncured layer of the shell prepreg, resulting in a peel strength of up to 120 N / cm (80% higher than adhesive bonding).

[0023] This invention employs a sandwich structure, achieving higher circumferential stiffness with a lower mass than traditional structures. Specifically, the outer and inner shells are pre-formed cylindrical shells, nested coaxially. The buoyancy material is a mixture of hollow glass microspheres, reinforcing fibers, and epoxy resin, poured into the space between the outer and inner shells in a pre-cured fluid state. During curing, vibration and vacuum are applied simultaneously to aid in venting and improve the homogeneity of the sandwich material. The flange faces at both ends of the cylinder are multi-layered. The annular flange structure specifically includes an inner annular boss, a middle annular boss, and an outer annular boss. The two ends of the intermediate interlayer are in direct contact with the middle annular boss of the flange, while the inner shell and outer shell are nested within the inner annular boss and the outer annular boss of the flange, respectively, and are separated by sealing rings. Since the two ends of the intermediate interlayer are in direct contact with the middle annular boss of the flange, the axial pressure load acting on the two ends will be transmitted through the buoyancy material interlayer in the core of the intermediate interlayer as the first transmission path, effectively reducing the risk of axial instability. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0025] Figure 1 This is a cross-sectional view of the sandwich pressure-resistant shell structure of the present invention;

[0026] Figure 2 yes Figure 1 A partial schematic diagram;

[0027] Figure 3 This is a schematic diagram of the buoyancy material in this invention;

[0028] Figure 4 This is a schematic diagram illustrating the manufacturing method of injecting buoyancy material into the inner shell and outer shell according to the present invention;

[0029] Figure 5 This is a schematic diagram of the structure of the present invention, in which a cylindrical body containing interlayer material is placed inside a vacuum bag;

[0030] Figure 6 This is a schematic diagram of the manufacturing method of injecting buoyancy material into the inner shell and the outer shell in Embodiment 2 of the present invention;

[0031] Figure 7 This is a cross-sectional view of the sandwich pressure-resistant shell structure of the present invention in Embodiment 2;

[0032] Markings in the diagram:

[0033] 1. Outer shell; 2. Inner shell; 3. Intermediate layer; 301. Hollow glass microspheres; 302. Reinforcing fiber filaments; 303. Epoxy resin; 31. Annular composite profile; 32. Strip composite profile; 4. Sealing ring; 5. Flange; 51. Inner annular boss; 52. Middle annular boss; 53. Outer annular boss; 61. Vibrating table; 62. Vacuum bag. Detailed Implementation

[0034] Example 1

[0035] like Figure 1-5As shown, a sandwich pressure-resistant shell structure, in this embodiment, includes an inner shell 2, an outer shell 1, and an intermediate sandwich 3 located between the inner shell 2 and the outer shell 1. The intermediate sandwich 3 includes hollow glass microspheres 301, reinforcing fiber filaments 302, and epoxy resin 303. The spherical hollow glass microspheres 301 and reinforcing fiber filaments 302 are uniformly mixed in epoxy resin 303 and placed in the space between the inner shell 2 and the outer shell 1 in a fluid state. After vacuum curing, it forms a buoyancy material located between the inner shell 2 and the outer shell 1.

[0036] Among them, hollow glass microspheres 301 provide low density (0.2-0.4 g / cm³). 3 The hollow glass microspheres 301, reinforcing fiber 302, and epoxy resin 303 are mixed and poured into the inner shell 2 and outer shell 1 in a fluid state before curing. This ensures a better filling rate between the inner shell 2 and outer shell 1, eliminates interfacial air gaps, and forms a continuous force transmission path after curing. The interlayer shear strength is greatly improved, and the anisotropic difference in compressive strength is greatly reduced. The fluid material diffuses at the molecular level with the uncured layer of the shell prepreg, and the peel strength can reach 120 N / cm (80% higher than the adhesive bonding process).

[0037] The buoyancy material comprises hollow glass microspheres 301 (50 μm particle size), reinforcing fiber filaments 302, and epoxy resin 303 in a weight ratio of 60% hollow glass microspheres 301 (50 μm particle size) + 30% reinforcing fiber filaments 302 (6 mm diameter) + 10% epoxy resin. This buoyancy material composition achieves an optimal balance between mechanical properties and buoyancy characteristics through the synergistic effect of multiple components, enabling the formed shell to withstand seawater (1.025 g / cm³). 3 It provides 17-20% net buoyancy compensation, with a compressive strength range of 85-110MPa (ASTM D695 standard), an elastic modulus range of 8-12GPa (5 times higher than the pure microsphere system), and an interlaminar shear strength range of 25-30MPa (under the bridging effect when the reinforcing fiber 302 uses short-cut carbon fiber). In the pressure test, the volume shrinkage rate of the shell under 60MPa hydrostatic pressure is <2% (microsphere breakage rate <5%), and the buoyancy loss is <3% after 500 pressure cycles (10-60MPa). This effect is far superior to the existing shell structures on the market.

[0038] The outer shell 1 has a greater thickness than the inner shell 2, and the outer diameter of the inner shell 2 is smaller than the inner diameter of the outer shell 1. As a result, since the outer shell 1 needs to withstand greater circumferential stress, the increased thickness relative to the inner shell 2 ensures that the circumferential stress level of the outer shell 1 is comparable to that of the inner shell, thereby making the stress distribution of the overall structure more uniform and reducing the risk of inner layer interface peeling.

[0039] The inner shell 2 and the outer shell 1 are pre-formed cylindrical shells using fiber bundles. The fiber bundles are made of carbon fiber or glass fiber. The forming technology includes, but is not limited to, wet winding and three-dimensional weaving. The cylindricity of the inner and outer surfaces of the inner shell 2 and the outer shell 1 is ensured by the male mold and machining, respectively.

[0040] When the fiber bundle is made of carbon fiber, and the inner shell 2 and outer shell 1 are formed into carbon fiber shells, the thickness ratio of the outer shell 1 to the inner shell 2 ranges from 1.3:1 to 1.8:1. When the fiber bundle is made of glass fiber, and the inner shell 2 and outer shell 1 are formed into glass fiber shells, the thickness ratio of the outer shell 1 to the inner shell 2 ranges from 1.8:1 to 2.5:1. This thickness ratio range can better maintain the uniformity of the overall compressive stress distribution of the shell structure. Within this range, the test surface, while maintaining the same compressive strength, is 12%-15% lighter than the traditional equal-thickness design. At the same time, ANSYS simulation shows that the stress non-uniformity is reduced by about 35% compared to the equal-thickness design, which is within a better range.

[0041] It is known that the failure mode of underwater pressure hulls is often buckling failure, which is the elastic instability of the structure under pressure, i.e., a sudden change in geometry (such as a wavy indentation on a cylindrical shell). The material stress may be far below the ultimate tensile strength. At depths of hundreds to tens of thousands of meters, the external hydrostatic pressure of deep-sea submersible pressure hulls can reach tens to hundreds of megapascals, and the hull may fail due to local or overall buckling.

[0042] However, it's not necessarily true that the greater the thickness of the outer shell 1, the better. A thicker outer shell 1 also increases cost. To achieve maximum gain, the buckling stress (MPa) and mass cost ($) need to be optimized. Calculations show that when carbon fiber is used for the fiber bundle, the stiffness gain reaches an inflection point when the thickness ratio of the outer shell 1 to the inner shell 2 is 1.5:1 (further increasing the thickness ratio results in diminishing returns). Therefore, a ratio of 1.3-1.8:1 balances material usage and stability (accounting for over 85% of the total gain), as shown in Table 1 below.

[0043] Table 1

[0044]

[0045] Similarly, when glass fiber is used for the fiber bundle, when the thickness ratio of the outer shell 1 to the inner shell 2 is 2.2:1, the calculation shows that the stiffness gain reaches an inflection point (further increasing the thickness ratio yields diminishing returns). Therefore, a range of 1.8:1 to 2.5:1 can be selected to balance the amount of material used and the stability.

[0046] In this embodiment, a sandwich pressure-resistant shell structure further includes two sets of flanges 5 fixedly installed at both ends of the inner shell 2 and the outer shell 1. The flanges 5 are provided with an inner annular boss 51, a middle annular boss 52, and an outer annular boss 53. The height of the intermediate sandwich 3 is less than the height of the inner shell 2 and the outer shell 1. The two ends of the intermediate sandwich 3 are tightly fitted with the middle annular boss of the flange 5. The inner shell 2 and the outer shell 1 are respectively nested in the inner annular boss 51 and the outer annular boss 53 of the flange 5, and are spaced apart by sealing rings 4. Since the two ends of the intermediate sandwich 3 are in direct contact with the middle annular boss of the flange 5, the axial pressure load acting on the two ends will take the buoyancy material sandwich in the core of the intermediate sandwich 3 as the first transmission path, effectively reducing the risk of axial instability.

[0047] After the buoyancy material is placed in fluid form between the inner shell 2 and the outer shell 1, it is cured on the vibration table 61 inside the vacuum autoclave using a temperature-step curing method. The temperature-step curing method is as follows: first, it is cured at 60°C for 2 hours to make the buoyancy material into a gel state; then, the temperature is raised to 80°C and cured for 4 hours to complete the pre-curing of the buoyancy material; then, the temperature is further raised to 120°C and cured for 2 hours to complete the overall curing of the buoyancy material. During the curing process, the vacuum autoclave is first evacuated, and then the temperature is raised to 60°C and maintained while the buoyancy material is being cured. Nitrogen gas is introduced into the vacuum autoclave to maintain a pressure of 0.4 MPa. When the temperature rises above 80°C, nitrogen is continuously introduced to maintain a pressure of 1.1 MPa. During this process, vacuuming thoroughly removes gases, moisture, and volatile impurities from the buoyancy material. Residual substances can form pores or bubbles during curing, leading to reduced material density and decreased pressure resistance. For example, the pressure resistance of high-temperature epoxy resin 303 potting compound is significantly improved after vacuum treatment, enabling it to withstand higher static water pressure. The pressure is designed to meet the high pressure resistance requirements of buoyancy materials in deep-sea equipment. Maintaining a pressure of 0.4 MPa during the 0-60℃ range promotes the volatilization of low molecular weight substances within the material, further reducing porosity. Simultaneously, the pressure allows for tighter material packing, improving molding precision. Upon reaching 80℃, increasing the pressure to 1.1 MPa accelerates the curing reaction, strengthens intermolecular bonding, and makes the material structure more compact, thereby enhancing overall pressure resistance. Through gradient pressure adjustment, the material experiences uniform pressure during curing, avoiding microscopic defects (such as cracks and delamination) caused by localized stress concentration. For example, high-strength solid buoyancy materials (such as epoxy resin 303 containing hollow glass microspheres) can have their impact resistance improved by 15%-20% and their fatigue life extended by more than 30% after vacuuming and pressure-regulated curing. This is suitable for frequent ascents and descents of pressure hulls in deep-sea submersibles. Pressure control can adjust the balance between material density and strength. At 0.4 MPa, the material density decreases (buoyancy increases), while strength is maintained through high-pressure curing at 80℃, achieving "lightweight and high-strength" characteristics. For example, the density of a certain type of buoyancy material reduced to 0.6 g / cm³ after this process. 3 Its compressive strength reaches 80MPa, meeting the dual requirements of buoyancy and structural strength for deep-sea submersibles.

[0048] Example 2

[0049] like Figure 6-7As shown, a sandwich pressure-resistant shell structure is provided. In this embodiment, in order to further increase the stability of the overall structure, the sandwich material also includes an annular composite profile 31 and / or a strip composite profile 32 pre-formed before being placed between the inner shell 2 and the outer shell 1. The base material of the annular composite profile 31 and the strip composite profile 32 is carbon fiber or glass fiber material. The annular composite profile 31 placed between the inner shell 2 and the outer shell 1 is also provided with a through hole so as not to obstruct the fluid injection of the buoyancy material between the inner shell 2 and the outer shell 1.

[0050] Example 3

[0051] A method for processing a sandwich pressure-resistant shell structure, based on a sandwich pressure-resistant shell structure of Embodiment 1, includes the following steps in this embodiment:

[0052] S1: Pre-form the fiber bundle into a cylindrical shell;

[0053] S2: Position two sets of cylindrical shells of different diameters onto the positioning fixture on the vibration table 61 inside the vacuum autoclave. The two sets of cylindrical shells are nested in a state where the inner and outer shells are coaxial and the end faces are flush. The inner shell is the inner shell 2, and the outer shell is the outer shell 1.

[0054] S3: A buoyancy material for filling the space between the inner shell 2 and the outer shell 1 with fluid;

[0055] S4: Start the vibration platform to vibrate, and complete the overall vacuum curing operation in the vacuum autoclave;

[0056] S5: Demold the sandwich shell after curing in S4 and machine the end face so that the machined end face is compatible with the flange 5 to be installed;

[0057] S6: Bond the end flange 5 of the sandwich shell after machining in S5.

[0058] The working principle of this invention is:

[0059] This invention provides a sandwich pressure-resistant shell structure and its processing method, which solves the problems of insufficient load-bearing capacity and low specific strength and specific stiffness of pressure-resistant shells for underwater vehicles in the prior art. Furthermore, by mixing hollow glass microspheres 301, reinforcing fiber filaments 302, and epoxy resin 303 and injecting them into the space between the inner shell 2 and the outer shell 1 in a pre-cured fluid state, it ensures a better filling rate between the inner shell 2 and the outer shell 1. This eliminates interfacial air gaps and forms a continuous force transmission path after curing, significantly improving interlayer shear strength and greatly reducing the anisotropic difference in compressive strength. Molecular-level diffusion occurs between the fluid material and the uncured layer of the shell prepreg, resulting in a peel strength of up to 120 N / cm (80% higher than adhesive bonding).

[0060] This invention employs a sandwich structure, achieving higher circumferential stiffness with a lower mass than traditional structures. Specifically, the outer shell 1 and inner shell 2 are pre-formed cylindrical shells, coaxially nested. The buoyancy material is a mixture of hollow glass microspheres 301, reinforcing fiber filaments 302, and epoxy resin 303, which is poured into the space between the outer shell 1 and inner shell 2 in a pre-curing fluid state. During curing, vibration and vacuum are applied simultaneously to assist in venting and improve the homogeneity of the sandwich material. The flanges 5 at both ends of the cylinder have multi-layered annular end faces. The flange structure specifically includes an inner annular boss 51, a middle annular boss 52, and an outer annular boss 53. The two ends of the intermediate sandwich 3 are in direct contact with the middle annular boss of the flange 5, while the inner shell 2 and the outer shell 1 are nested in the inner annular boss 51 and the outer annular boss 53 of the flange 5, respectively, and are spaced apart by sealing rings 4. Since the two ends of the intermediate sandwich 3 are in direct contact with the middle annular boss of the flange 5, the axial pressure load acting on the two ends will take the buoyancy material sandwich in the core of the intermediate sandwich 3 as the first transmission path, effectively reducing the risk of axial instability.

[0061] In actual processing, the outer shell 1 and the inner shell 2 are coaxially assembled on the positioning fixture of the vibration table 61. The bottom end of the shell and the vibration table 61 are sealed to prevent leakage, ensuring that the fluid interlayer material does not leak during the curing process. In addition to placing the cylinder containing the interlayer material directly into the vacuum autoclave, the cylinder containing the interlayer material can also be placed in the vacuum bag 62 to ensure good sealing between the vacuum bag 62 and the vibration table 61. Then, the cylinder containing the interlayer material is simultaneously subjected to vibration and vacuuming, and placed in an oven for curing. The shell that has been completely cured is then demolded and the end face is machined. The machined end face must be compatible with the flange 5 to be installed.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sandwich pressure hull structure comprising an inner shell, an outer shell and an intermediate sandwich layer between the inner shell and the outer shell, characterized in that, The intermediate interlayer includes hollow glass microspheres, reinforcing fibers and epoxy resin. The spherical hollow glass microspheres and reinforcing fibers are uniformly mixed in epoxy resin and placed in the inner shell and outer shell in a fluid state. After vacuum curing, they form a buoyancy material located between the inner shell and the outer shell. The weight ratio of hollow glass microspheres, reinforcing fiber filaments and epoxy resin in the buoyancy material is 60% hollow glass microspheres + 30% reinforcing fiber filaments + 10% epoxy resin. The inner shell and outer shell are preformed cylindrical shells using fiber bundles, and the fiber bundles are made of carbon fiber or glass fiber. When the fiber bundle is made of carbon fiber, the inner shell and outer shell are formed into a carbon fiber shell, and the thickness ratio of the outer shell to the inner shell is in the range of 1.3:1 - 1.8:1; while when the fiber bundle is made of glass fiber, the inner shell and outer shell are formed into a glass fiber shell, and the thickness ratio of the outer shell to the inner shell is in the range of 1.8:1 - 2.5:

1. It also includes two sets of flanges fixedly installed at both ends of the inner shell and the outer shell. The flanges are provided with an inner annular boss, a middle annular boss and an outer annular boss. The height of the intermediate interlayer is less than the height of the inner shell and the outer shell. The two ends of the intermediate interlayer are tightly fitted with the middle annular boss of the flange. The inner shell and the outer shell are respectively nested in the inner annular boss and the outer annular boss of the flange, and are separated by sealing rings.

2. The sandwich pressure-resistant shell structure according to claim 1, characterized in that, The intermediate interlayer also includes an annular composite profile and / or strip composite profile pre-formed before being inserted between the inner shell and the outer shell. The base material of the annular composite profile and the strip composite profile is carbon fiber or glass fiber material, and the annular composite profile inserted between the inner shell and the outer shell is also provided with through holes.

3. The sandwich pressure-resistant shell structure according to claim 1, characterized in that, After the buoyancy material is placed in fluid form between the inner and outer shells, it is cured on a vibration table in a vacuum autoclave using a temperature-step curing method. The temperature-step curing method includes the following steps: first, curing at 55-65℃ for 1.5-2.5 hours to make the buoyancy material gel-like; then, raising the temperature to 75-85℃ for 3-5 hours to complete the pre-curing of the buoyancy material; then, continuing to raise the temperature to 115-125℃ for 1.5-2.5 hours to complete the overall curing of the buoyancy material. During the curing process, the vacuum autoclave is first evacuated, and while the temperature is raised to 55-65℃ and maintained, nitrogen gas is introduced into the vacuum autoclave to maintain the pressure inside the vacuum autoclave at 0.35-0.45 MPa. When the temperature is raised to above 75-85℃, nitrogen gas is continued to be introduced into the vacuum autoclave to maintain the pressure inside the vacuum autoclave at 1.05-1.15 MPa.

4. A method for processing a sandwich pressure-resistant shell structure, based on the sandwich pressure-resistant shell structure according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Pre-form the fiber bundle into a cylindrical shell; S2: Position two sets of cylindrical shells of different diameters onto the positioning fixture on the vibrating table inside the vacuum autoclave. The two sets of cylindrical shells are nested in a state where they are coaxial inside and out and have flush end faces. The innermost shell is the inner shell, and the outermost shell is the outer shell. S3: A buoyancy material for filling the space between the inner and outer shells with fluid; S4: Start the vibration platform to vibrate, and complete the overall vacuum curing operation in the vacuum autoclave; S5: Demold the sandwich shell after curing in S4 and machine the end face so that the machined end face is compatible with the flange to be installed; S6: Bond the end flanges of the sandwich shell after machining in S5.

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