A z-direction reinforced pressure-resistant sound-absorbing composite structure based on an in-situ foaming process and a preparation method thereof

Abstract

The application discloses a Z-direction reinforced pressure-resistant sound-absorbing composite structure based on an in-situ foaming process and a preparation method thereof. The Z-direction reinforced pressure-resistant sound-absorbing composite structure comprises a fiber reinforced composite material frame and an internal sound-absorbing core layer. The fiber reinforced composite material frame is formed by a 2.5D fabric reinforced resin matrix composite material formed after a hollow 2.5D fabric and a Z-direction reinforced framework are integrally and continuously connected by using a vacuum introduced resin matrix. The Z-direction reinforced framework is formed by using fibers to pull the 2.5D fabric hollow layer in the Z direction. The sound-absorbing core layer is formed by using a sound-absorbing foaming material to form an in-situ foaming process in the internal cavity of the hollow 2.5D fabric. The in-situ foaming process is used to form the sound-absorbing foaming material in the 2.5D fabric, so that the interface bonding strength of the sound-absorbing foaming material and the fabric surface layer is ensured, the contradiction between the pressure resistance and the sound-absorbing performance of the traditional sound-absorbing sandwich material is overcome, the sound-absorbing pressure-resistant structure function integration is realized, and the structural stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic materials technology, and particularly relates to a Z-axis reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming process and its preparation method. Background Technology

[0002] The stealth performance of underwater vehicles relies on highly efficient sound-absorbing materials, while the deep-sea environment places stringent requirements on the pressure resistance of these materials (e.g., a hydrostatic pressure of approximately 10 MPa at a water depth of 1000m). Traditional sound-absorbing materials (such as rubber and aluminum foam) suffer from insufficient pressure resistance and complex manufacturing processes. For example, porous foam materials are easily compressed and deformed under high pressure, leading to a sharp decline in sound absorption performance under water pressure; layered composite structures are prepared through adhesive bonding processes, resulting in low interfacial bonding strength and easy delamination failure under water pressure.

[0003] Patent CN 102930862 B describes a Z-axis reinforced underwater sound-absorbing sandwich composite material and its preparation method. The material includes a composite panel, a sound-absorbing core, and a reinforcing structure positioned between the top and bottom panels in the Z-axis (thickness direction) of the sound-absorbing core. The reinforcing structure involves machining holes in the core material, followed by threading and sewing, and then embedding titanium or stainless steel rods for pre-bonding the core material. This method requires time-consuming and labor-intensive drilling and sewing, as well as embedding and bonding of the metal support structure. The process is complex and cannot guarantee the interfacial bonding strength between the sound-absorbing core and the panel. Summary of the Invention

[0004] Based on the problems existing in the above-mentioned background technology, the present invention provides a Z-direction reinforced pressure-resistant sound-absorbing composite structure and its preparation method based on in-situ foaming process. The sound-absorbing foam material is formed in a preform such as 2.5D fabric using the in-situ foaming process, which ensures the interfacial bonding strength between the sound-absorbing foam material and the fabric surface layer, overcomes the contradiction between the pressure resistance and sound absorption performance of traditional sound-absorbing sandwich materials, realizes the integration of sound-absorbing and pressure-resistant structure functions, simplifies the Z-direction reinforcement preparation process, and improves the structural stability.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A Z-direction reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming process includes a fiber-reinforced composite material frame and an internal sound-absorbing core layer. The fiber-reinforced composite material frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-direction reinforced skeleton. The main structure of the fiber-reinforced composite frame uses hollow 2.5D fabric as the outer surface skin. The inner hollow layer uses the same type of 2.5D fabric fibers to form a Z-direction reinforcing skeleton in the Z direction. The fiber structure and size of the Z-direction reinforcing skeleton can be adjusted according to the sound absorption and pressure resistance requirements of the actual application. The recommended value is columnar fibers with a diameter of 1~9mm and a fiber spacing of 20~60mm to form a lattice structure. The Z direction is the thickness direction of the sound-absorbing core layer and the hollow 2.5D fabric. The hollow 2.5D fabric has a fiber volume content of 40% to 60%, and the surface layer thickness can be adjusted according to the needs of sound-absorbing materials in different frequency bands, with a recommended value of 2 to 100 mm; the cavity thickness is matched with the sound-absorbing core layer thickness and can be designed according to sound absorption requirements, with a recommended value of 4 to 200 mm. The sound-absorbing core layer is formed by in-situ foaming of sound-absorbing foam material in the cavity inside a 2.5D hollow fabric, achieving sound absorption performance within the designed frequency band.

[0006] Furthermore, the warp and weft yarns of the hollow 2.5D fabric described in this invention are made of glass fiber, carbon fiber or aramid fiber, and the yarn linear density is 1000~3000tex.

[0007] Furthermore, the sound-absorbing foaming material of the present invention is a polymer foaming material or an inorganic-organic hybrid foaming material, wherein the polymer foaming material is a polyurethane foaming material or a rubber foaming material, and the inorganic-organic hybrid foaming material is a ceramic microsphere / epoxy resin composite foam.

[0008] Furthermore, the present invention also provides a method for preparing the above-mentioned Z-axis reinforced pressure-resistant sound-absorbing composite structure, comprising the following steps: (1) Cut and weave 2.5D fabric into a pre-set size structure, hollow layer with a pre-set sound-absorbing core layer thickness inside, and use Z-direction traction fiber columns to connect the upper and lower fabric surfaces to form a Z-direction reinforcing skeleton to obtain a pre-formed fabric. Then, put the pre-formed fabric into a forced-air drying oven to dry and set it for later use. The drying temperature is 90~120℃, and the drying time is 1~3h; In step (1), according to the pressure resistance requirements, other Z-direction reinforcement structures are also embedded in the hollow layer of the 2.5D fabric and wrapped around the outside of the Z-direction tension fiber. The Z-direction reinforcement structure includes metal support columns or 3D printed reinforcements. The 3D printed reinforcement contains open pores with a porosity of 50-80%, which facilitates the flow of foaming adhesive. (2) The pre-formed fabric after pretreatment and drying in step (1) is laid in the mold. After the mold is closed, it fits the 2.5D fabric size and is limited to ensure that the fabric is fixed in position during the foaming process. The mold is a stainless steel male and female mold, with an injection port and an exhaust hole on each side of the mold. The mold cavity size matches the size of the preformed fabric, and the preformed fabric is embedded in the mold cavity to restrict its movement. Furthermore, the mold is provided with a limiting structure for positioning the preformed fabric. Specifically, a metal hook is inserted into the 2.5D fabric to fix it or double-sided tape is used to fix the fabric. (3) After mixing the components of the foaming material, inject it into the 2.5D hollow fabric layer in the mold through the injection port, and let the internal air out through the vent hole. After filling the cavity of the hollow 2.5D fabric, seal the injection port and the vent hole, and let the foaming material chemically foam and form itself. The foaming material mainly includes sound-absorbing foaming material and foaming agent. Specifically, the foaming material formula in the embodiment of patent CN118725238 B can be used. (4) The overall structure after foaming and molding in step (3) is injected with resin matrix using vacuum infusion process so that the fabric is completely impregnated. After the resin gels, it is placed in an oven to cure and mold. The resin matrix is ​​epoxy resin or vinyl ester resin; The vacuum level is controlled between -0.08 and -0.1 MPa.

[0009] (5) After curing and molding, demolding is performed. After demolding, the structure is trimmed to remove flash and excess material, and the composite structure described in this invention is obtained.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) The in-situ foaming Z-direction reinforcement structure deeply integrates the load-bearing skeleton with the sound absorption function. The Z-direction reinforcement frame effectively disperses hydrostatic pressure and avoids sound absorption failure caused by cavity compression and collapse. This integrated design ensures the realization of underwater acoustic stealth performance by optimizing the structural pressure resistance.

[0011] (2) By foaming the sound-absorbing core material in situ within the 2.5D preformed fabric, the processing and assembly of the sound-absorbing core material are avoided, simplifying the traditional multi-step stitching composite process and shortening the manufacturing cycle.

[0012] (3) In-situ foaming of the core material ensures the continuity of the sound-absorbing core material structure. On the other hand, the structural interface eliminates weak bonding areas through the injection process, enhances the interlayer bonding strength and anti-delamination ability, and extends the service life of the component. Attached Figure Description

[0013] Figure 1 This is a schematic cross-sectional view of the Z-axis reinforced pressure-resistant sound-absorbing composite structure described in this invention.

[0014] Figure 2 This is a schematic diagram of the vertical cross-section of the Z-direction reinforced pressure-resistant sound-absorbing composite structure described in this invention.

[0015] Figure 3 This is a flow chart of the in-situ foaming process described in this invention.

[0016] Figures 1-2 The components are labeled as follows: 1-surface skin, 2-sound-absorbing core layer, 3-Z-direction reinforcing skeleton. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0018] A Z-direction reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming process includes a fiber-reinforced composite material frame and an internal sound-absorbing core layer. The fiber-reinforced composite material frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-direction reinforced skeleton. The main structure of the fiber-reinforced composite frame uses hollow 2.5D fabric as the outer surface skin. The inner hollow layer uses the same type of 2.5D fabric fibers to form a Z-direction reinforcing skeleton in the Z direction. The fiber structure and size of the Z-direction reinforcing skeleton can be adjusted according to the sound absorption and pressure resistance requirements of the actual application. The recommended values ​​are columnar fibers with a diameter of 1~9mm and a fiber spacing of 20~60mm. The Z direction is the thickness direction of the sound-absorbing core layer and the hollow 2.5D fabric. The hollow 2.5D fabric has a fiber volume content of 40% to 60%, and the surface layer thickness can be adjusted according to the needs of sound-absorbing materials in different frequency bands, with a recommended value of 2 to 100 mm; the cavity thickness is matched with the sound-absorbing core layer thickness and can be designed according to sound absorption requirements, with a recommended value of 4 to 200 mm. The sound-absorbing core layer is formed by in-situ foaming of sound-absorbing foam material in the cavity inside a 2.5D hollow fabric, achieving sound absorption performance within the designed frequency band.

[0019] Furthermore, the warp and weft yarns of the hollow 2.5D fabric described in this invention are made of glass fiber, carbon fiber or aramid fiber, and the yarn linear density is 1000~3000tex.

[0020] Furthermore, the sound-absorbing foaming material of the present invention is a polymer foaming material or an inorganic-organic hybrid foaming material, wherein the polymer foaming material is a polyurethane foaming material or a rubber foaming material, and the inorganic-organic hybrid foaming material is a ceramic microsphere / epoxy resin composite foam.

[0021] Furthermore, the present invention also provides a method for preparing the above-mentioned Z-axis reinforced pressure-resistant sound-absorbing composite structure, comprising the following steps: (1) Cut and weave 2.5D fabric into a pre-set size structure, hollow layer with a pre-set sound-absorbing core layer thickness inside, and use Z-direction traction fiber columns to connect the upper and lower fabric surfaces to form a Z-direction reinforcing skeleton to obtain a pre-formed fabric. Then, put the pre-formed fabric into a forced-air drying oven to dry and set it for later use. The drying temperature is 90~120℃, and the drying time is 1~3h; In step (1), according to the pressure resistance requirements, other Z-direction reinforcement structures are also embedded in the hollow layer of the 2.5D fabric and wrapped around the outside of the Z-direction tension fiber. The Z-direction reinforcement structure includes metal support columns or 3D printed reinforcements. The 3D printed reinforcement contains open pores with a porosity of 50-80%, which facilitates the flow of foaming adhesive. (2) The pre-formed fabric after pretreatment and drying in step (1) is laid in the mold. After the mold is closed, it fits the 2.5D fabric size and is limited to ensure that the fabric is fixed in position during the foaming process. The mold is a stainless steel male and female mold, with an injection port and an exhaust hole on each side of the mold. The mold cavity size matches the size of the preformed fabric, and the preformed fabric is embedded in the mold cavity to restrict its movement. Furthermore, the mold is provided with a limiting structure for positioning the preformed fabric. Specifically, a metal hook is inserted into the 2.5D fabric to fix it or double-sided tape is used to fix the fabric. (3) After mixing the components of the foaming material, inject it into the 2.5D hollow fabric layer in the mold through the injection port, and let the internal air out through the vent hole. After filling the cavity of the hollow 2.5D fabric, seal the injection port and the vent hole, and let the foaming material chemically foam and form itself. The foaming material mainly includes sound-absorbing foaming material and foaming agent. Specifically, the foaming material formula in the embodiment of patent CN118725238 B can be used. (4) The overall structure after foaming and molding in step (3) is injected with resin matrix using vacuum infusion process so that the fabric is completely impregnated. After the resin gels, it is placed in an oven to cure and mold. The resin matrix is ​​epoxy resin or vinyl ester resin; The vacuum level is controlled between -0.08 and -0.1 MPa.

[0022] (5) After curing and molding, demolding is performed. After demolding, the structure is trimmed to remove flash and excess material, and the composite structure described in this invention is obtained.

[0023] Example 1 This embodiment prepares an in-situ foamed Z-direction reinforced pressure-resistant sound-absorbing composite structure, including a fiber-reinforced composite material frame and an internal sound-absorbing core layer. The fiber-reinforced composite material frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-direction reinforced skeleton. Specific preparation methods include: (1) Preparation of 2.5D fabric: 2.5D orthogonal fabric of glass fiber is used. The thickness of the upper layer is 5mm, the thickness of the lower layer is 10mm, the thickness of the middle layer cavity is 35mm, and fiber yarns with a diameter of 2mm are interlaced in the Z direction between the upper and lower layers, with a spacing of 30mm to form a dot matrix structure; the obtained preformed fabric is dried and set for later use. Fiber volume content 50%, warp / weft yarn linear density 2000tex; (2) Foaming mold: Stainless steel male and female molds are used. The size of the mold after closing is consistent with the size of the 2.5D fabric to ensure that the fabric is fixed in position during the foaming process; (3) In-situ foaming: Polyether polyol (molecular weight 2000) and diphenylmethane diisocyanate (MDI) are mixed at a molar ratio of 1:1.1. Water, accounting for 5% of the mass percentage of the above foaming material, is added as a foaming agent. After stirring for 45 seconds, the mixture is injected into the hollow fabric layer in the mold. After the injection is completed, the vent and injection port are closed. The mixture is kept at 50°C for 30 minutes to foam and form. (4) Composite frame molding: After foaming is completed, epoxy resin is injected using vacuum infusion process to completely impregnate the 2.5D fabric; after the resin gels, it is placed in a 60℃ oven for curing for 12 hours. (5) Post-processing: After curing, demold and use a CNC milling machine to trim the edges and remove burrs and excess material.

[0024] Example 2 This embodiment prepares an in-situ foamed Z-direction reinforced pressure-resistant sound-absorbing composite structure, including a fiber-reinforced composite material frame and an internal sound-absorbing core layer. The fiber-reinforced composite material frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-direction reinforced skeleton. Specific preparation methods include: (1) Preparation of 2.5D fabric: 2.5D orthogonal fabric of aramid fiber is used. The thickness of the upper layer is 5mm, the thickness of the lower layer is 10mm, the thickness of the middle layer cavity is 35mm, and fiber yarns with a diameter of 4mm are interlaced in the Z direction between the upper and lower layers, with a spacing of 30mm to form a dot matrix structure; the obtained preformed fabric is dried and then set for later use. Fiber volume content 50%, warp / weft yarn linear density 2000tex; (2) Foaming mold: Stainless steel male and female molds are used. The size of the mold after closing is consistent with the size of the 2.5D fabric to ensure that the fabric is fixed in position during the foaming process; (3) In-situ foaming: Polyether polyol (molecular weight 2000) and diphenylmethane diisocyanate (MDI) are mixed at a molar ratio of 1:1.1. Water, accounting for 5% of the mass percentage of the above foaming material, is added as a foaming agent. After stirring for 45 seconds, the mixture is injected into the hollow fabric layer in the mold. After the injection is completed, the vent and injection port are closed. The mixture is kept at 50°C for 30 minutes to foam and form. (4) Composite frame molding: After foaming is completed, epoxy resin is injected using vacuum infusion process to completely impregnate the 2.5D fabric; after the resin gels, it is placed in a 60℃ oven for curing for 12 hours. (5) Post-processing: After curing, demold and use a CNC milling machine to trim the edges and remove burrs and excess material.

[0025] Example 3 This embodiment prepares an in-situ foamed Z-direction reinforced pressure-resistant sound-absorbing composite structure, including a fiber-reinforced composite material frame and an internal sound-absorbing core layer. The fiber-reinforced composite material frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-direction reinforced skeleton. Specific preparation methods include: (1) 2.5D fabric preparation: 2.5D orthogonal fabric of aramid fiber is used. The thickness of the upper layer is 5mm, the thickness of the lower layer is 10mm, the thickness of the middle layer cavity is 35mm, and fiber yarns with a diameter of 2mm are interlaced in the Z direction between the upper and lower layers, with an interval of 60mm to form a dot matrix structure. The obtained preformed fabric is dried and then set for later use. Fiber volume content 50%, warp / weft yarn linear density 2000tex; (2) Foaming mold: Stainless steel male and female molds are used. The size of the mold after closing is consistent with the size of the 2.5D fabric to ensure that the fabric is fixed in position during the foaming process; (3) In-situ foaming: Polyether polyol (molecular weight 2000) and diphenylmethane diisocyanate (MDI) are mixed at a molar ratio of 1:1.1. Water, accounting for 5% of the mass percentage of the above foaming material, is added as a foaming agent. After stirring for 45 seconds, the mixture is injected into the hollow fabric layer in the mold. After the injection is completed, the vent and injection port are closed. The mixture is kept at 50°C for 30 minutes to foam and form. (4) Composite frame molding: After foaming is completed, epoxy resin is injected using vacuum infusion process to completely impregnate the 2.5D fabric; after the resin gels, it is placed in a 60℃ oven for curing for 12 hours. (5) Post-processing: After curing, demold and use a CNC milling machine to trim the edges and remove burrs and excess material.

[0026] Example 4 This embodiment prepares an in-situ foamed Z-axis reinforced pressure-resistant sound-absorbing composite structure, including a fiber-reinforced composite material frame and an internal sound-absorbing core layer. The fiber-reinforced composite material frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-axis reinforced skeleton. The internal sound-absorbing core layer is made of open-cell polyvinyl chloride.

[0027] Specific preparation methods include: (1) Preparation of 2.5D fabric: 2.5D orthogonal fabric of glass fiber is used. The thickness of the upper layer is 5mm, the thickness of the lower layer is 10mm, the thickness of the middle layer cavity is 35mm, and fiber yarns with a diameter of 2mm are interlaced in the Z direction between the upper and lower layers, with a spacing of 30mm to form a dot matrix structure; the obtained preformed fabric is dried and set for later use. Fiber volume content 50%, warp / weft yarn linear density 2000tex; (2) Foaming mold: Stainless steel male and female molds are used. The size of the mold after closing is consistent with the size of the 2.5D fabric to ensure that the fabric is fixed in position during the foaming process; (3) In-situ foaming: Weigh 100 parts of polyvinyl chloride, 6-10 parts of azodicarbonamide, and 4-6 parts of calcium zinc heat stabilizer according to the ratio; weigh the mixture according to the mold specifications, add 60-70 parts of the miscible plasticizer azodiisobutyronitrile and 60-70 parts of the diluent dichloromethane, stir quickly until wet clumps, and then inject into the hollow fabric layer in the mold. After the injection is completed, close the vent and the injection port, and foam at 190-195℃ for 10 minutes. (4) Composite frame molding: After foaming, epoxy resin is injected using a vacuum infusion process to completely impregnate the 2.5D fabric. After the resin gels, it is placed in a 60℃ oven for curing for 12 hours; (5) Post-processing: After curing, demold and use a CNC milling machine to trim the edges and remove burrs and excess material.

[0028] Comparative Example The pressure-resistant sound-absorbing structure prepared in this comparative example uses the same materials as that used in Example 1. The difference is that the polyurethane core material is not produced by in-situ foaming. Instead, the core material is prefabricated and then embedded into the support.

[0029] The detailed steps are as follows: (1) Pre-fabrication of polyurethane core material: Mix polyether polyol (molecular weight 2000) with diphenylmethane diisocyanate (MDI) at a molar ratio of 1:1.1, add 5% water as a foaming agent, stir for 45 seconds and then inject the foaming agent into the mold. After the injection is completed, close the vent and the injection port, and keep it at 50°C for 30 minutes to foam. (2) Prefabricated fiber column: Fiber with a fiber volume content of 50% and a warp / weft yarn density of 2000tex is injected with epoxy resin and then cured and processed into a rod with a diameter of 2mm and a length of 35mm.

[0030] (3) Polyurethane core material processing: The thickness of the polyurethane core material is processed to 35mm using a processing machine tool, and then holes with a diameter of 2mm are drilled in the polyurethane core material at intervals of 30mm to form a dot matrix structure. (4) Embedded support structure: Prefabricated fiber columns matching the thickness of the core material are inserted into the holes processed in the polyurethane core material and bonded with epoxy resin to form a lattice structure support. (5) Composite surface molding: 5mm fiberglass cloth is laid on the upper surface of the polyurethane core material and 10mm fiberglass cloth is laid on the lower surface. The corresponding auxiliary materials are laid, and epoxy resin is injected using a vacuum infusion process. After the resin gels, it is placed in a 60℃ oven for curing for 12 hours. (6) Post-processing: After curing, demold and use a CNC milling machine to trim the edges and remove burrs and excess material.

[0031] The performance of the composite material structures of Examples 1, 2, and 3 was compared, and the results are shown in Table 1 below: Table 1 Performance Tests of Composite Structures in Examples 1, 2, and 3 The performance of the composite material structures of Examples 1 and 4 was compared with that of the comparative examples. The results are shown in Table 2 below: Table 2 Performance tests of composite structures in Examples 1, 4 and comparative examples From the data in Tables 1 and 2, we can find that: The structure reinforced by in-situ foaming in the Z-direction has significantly improved manufacturing efficiency and compression resistance compared to the structure without in-situ foaming, and its sound absorption performance under 4.5MPa water pressure is also significantly improved.

Claims

1. A Z-axis reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming technology, characterized in that, It includes a fiber-reinforced composite frame and an internal sound-absorbing core layer. The fiber-reinforced composite frame is a 2.5D fabric-reinforced resin matrix composite material formed by vacuum-introducing a resin matrix into a continuous structure of hollow 2.5D fabric and Z-direction reinforcing skeleton. The sound-absorbing core layer is formed by in-situ foaming of sound-absorbing foam material in the internal cavity of a 2.5D hollow fabric.

2. The Z-axis reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming technology according to claim 1, characterized in that, The main structure of the fiber-reinforced composite material frame adopts hollow 2.5D fabric, with the outside serving as the surface skin. The internal hollow layer uses the same type of 2.5D fabric fibers to form a Z-direction reinforcing skeleton in the Z direction. The fibers pulled by the Z-direction reinforcing skeleton are columnar fibers with a diameter of 1~9mm and a fiber spacing of 20~60mm to form a lattice structure. The Z direction is the thickness direction of the sound-absorbing core layer and the hollow 2.5D fabric.

3. The Z-axis reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming technology according to claim 1, characterized in that, The hollow 2.5D fabric has a fiber volume content of 40% to 60% and a surface layer thickness of 2 to 100 mm; the cavity thickness matches the sound-absorbing core layer thickness, specifically 4 to 200 mm.

4. The Z-axis reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming technology according to claim 1, characterized in that, The warp and weft yarns of the hollow 2.5D fabric are made of glass fiber, carbon fiber or aramid fiber, and the yarn linear density is 1000~3000tex.

5. A Z-axis reinforced pressure-resistant sound-absorbing composite structure based on in-situ foaming technology according to claim 1, characterized in that, The sound-absorbing foam material is a polymer foam material or an inorganic-organic hybrid foam material, wherein the polymer foam material is a polyurethane foam material or a rubber foam material, and the inorganic-organic hybrid foam material is a ceramic microsphere / epoxy resin composite foam.

6. A method for preparing the Z-axis reinforced pressure-resistant sound-absorbing composite structure according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Cut and weave 2.5D fabric into a pre-set size structure, hollow layer with a pre-set sound-absorbing core layer thickness inside, and use Z-direction traction fiber columns to connect the upper and lower fabric surfaces to form a Z-direction reinforcing skeleton to obtain a pre-formed fabric. Then, put the pre-formed fabric into a forced-air drying oven to dry and set it for later use. (2) The pre-formed fabric after pretreatment and drying in step (1) is laid in the mold. After the mold is closed, it fits the 2.5D fabric size and is limited to ensure that the fabric is fixed in position during the foaming process. (3) After mixing the components of the foaming material, inject it into the 2.5D hollow fabric layer in the mold through the injection port, and let the internal air out through the vent hole. After filling the cavity of the hollow 2.5D fabric, seal the injection port and the vent hole, and let the foaming material chemically foam and form itself. The foaming material mainly includes sound-absorbing foaming material and foaming agent; (4) The overall structure after foaming and molding in step (3) is injected with resin matrix using vacuum infusion process so that the fabric is completely impregnated. After the resin gels, it is placed in an oven to cure and mold. (5) After curing and molding, demolding is performed. After demolding, the structure is trimmed to remove flash and excess material, and the composite structure described in this invention is obtained.

7. The preparation method according to claim 6, characterized in that, The drying temperature in step (1) is 90~120℃ and the drying time is 1~3h.

8. The preparation method according to claim 6, characterized in that, In step (1), according to the pressure resistance requirements, other Z-direction reinforcement structures are also embedded in the hollow layer of the 2.5D fabric and wrapped around the outside of the Z-direction tension fiber. The Z-direction reinforcement structure includes metal support columns or 3D printed reinforcements, wherein the 3D printed reinforcement contains open pores and its porosity is 50~80%.

9. The preparation method according to claim 6, characterized in that, The mold in step (2) is a stainless steel male and female mold, with an injection port and an exhaust hole on each side of the mold; the size of the mold cavity matches the size of the preformed fabric, and the preformed fabric is embedded in the mold cavity to restrict its movement; The mold is provided with a limiting structure for positioning the preformed fabric. Preferably, a metal hook is inserted into the 2.5D fabric to fix it, or double-sided adhesive is used to fix the fabric.

10. The preparation method according to claim 6, characterized in that, The resin matrix in step (4) is epoxy resin or vinyl ester resin; The vacuum level is controlled between -0.08 and -0.1 MPa.

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