Carbon fiber round tube for rail transit and preparation method thereof

Abstract

The present application relates to a kind of carbon fiber round tube for rail transit and its preparation method, carbon fiber round tube for rail transit includes unidirectional carbon fiber prepreg main layer and bidirectional carbon fiber fabric prepreg layer, the bidirectional carbon fiber fabric prepreg layer is divided into inner surface layer fabric layer, outer surface layer fabric layer and intermediate interlayer fabric layer, the intermediate interlayer fabric layer is symmetrically distributed with the center position of round tube thickness direction as symmetry center.The preparation process sets segmented hot compaction and stepwise temperature rise curing, effectively improves pipe denseness and straightness, product structure stiffness is good, service life is long.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber composite materials technology, and in particular to a carbon fiber circular tube for rail transit and its preparation method. Background Technology

[0002] Carbon fiber composites possess excellent properties such as high specific strength, high specific modulus, lightweight, corrosion resistance, and fatigue resistance, and are widely used in the field of lightweight structures for high-end equipment. Currently, rail transit vehicles are gradually iterating towards higher speeds, energy efficiency, and lighter weights. The requirements for the weight, mechanical properties, dimensional accuracy, and long-term service stability of core load-bearing components such as the car body structure, undercarriage suspension, and equipment compartment supports are continuously increasing.

[0003] Currently, the support structures, car body connections, and undercarriage suspension structures of rail transit equipment mostly use metal round tubes such as steel and aluminum alloys. While these components have mature manufacturing processes and reliable foundation strength, their high material density and overall weight significantly increase vehicle traction energy consumption, making them unsuitable for the lightweight development needs of rail transit. Therefore, existing technologies are gradually replacing metal components with conventional carbon fiber round tubes. The lightweight and highly designable advantages of carbon fiber composite materials improve the weight reduction problem, making it the closest alternative solution in this field at present.

[0004] However, existing carbon fiber cylindrical tubes for rail transit still have many technical shortcomings, making them unsuitable for the complex service conditions of high-frequency vibration and alternating impact in rail transit. Firstly, their fatigue resistance is insufficient. Conventional carbon fiber cylindrical tubes have a single layup pattern, mostly simple angle layups or unidirectional layups, resulting in limited resistance to bending, torsion, and alternating loads. Long-term vibration and impact can easily lead to fatigue failure problems such as interlaminar delamination, cracking, and debonding, resulting in a short service life. Secondly, their molding accuracy and dimensional stability are poor. During the molding process of long-length carbon fiber cylindrical tubes, uneven layup distribution and unreasonable molding processes can easily lead to deformation defects such as bending, warping, and ellipticization, resulting in low product straightness and affecting assembly accuracy and structural reliability. Thirdly, their comprehensive mechanical property adaptability is weak. Conventional layup designs lack specificity and cannot simultaneously address multiple properties such as bending, torsion, and impact resistance. Under complex loads, they are prone to local instability and interlaminar failure, resulting in insufficient load-bearing safety.

[0005] In summary, existing support structures for rail transit suffer from defects such as poor molding quality of carbon fiber cylindrical tubes, uneven mechanical properties, and short fatigue life, making it difficult to simultaneously meet the requirements of lightweight, high precision, high stability, and long service life for rail transit equipment. Therefore, optimizing the structural design and molding process of carbon fiber cylindrical tubes to balance lightweight characteristics, high dimensional accuracy, excellent comprehensive mechanical properties, and long-term fatigue resistance, while adapting to the complex service conditions of rail transit, is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical issues, this invention optimizes the ply-lay symmetrical structure design and segmented hot-pressing preparation method, taking into account product lightweighting, comprehensive mechanical properties, fatigue resistance, and molding precision, thus meeting the long-term use requirements under complex working conditions in rail transit.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a carbon fiber circular tube for rail transit, comprising a unidirectional carbon fiber prepreg body layer and a bidirectional carbon fiber fabric prepreg layer, wherein the bidirectional carbon fiber fabric prepreg layer is divided into an inner surface fabric layer, an outer surface fabric layer and an intermediate interlayer fabric layer, wherein the intermediate interlayer fabric layer is symmetrically distributed with the center position in the thickness direction of the circular tube as the center of symmetry.

[0008] This invention uses unidirectional carbon fiber prepreg as the main material of carbon fiber round tube, and interweaves bidirectional carbon fiber fabric prepreg layers in the structure, symmetrically arranged with the center of the round tube thickness as the reference. The symmetrical reinforcement layer structure can uniformly transfer stress in the tube wall thickness direction, avoid local stress concentration, effectively improve the overall structural stability of the tube, enhance the resistance to vibration and alternating loads, and adapt to the long-term vibration service environment of rail transit.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0010] As a preferred technical solution of the present invention, the ratio of the number of layers of the unidirectional carbon fiber prepreg body layer to the bidirectional carbon fiber fabric prepreg layer is (9~11):1, for example, it can be 9:1, 9.8:1, 10.2:1, 10.7:1 or 11:1, and more preferably 10:1.

[0011] As a preferred technical solution of the present invention, the intermediate interlayer fabric layer is distributed at equal intervals on both the inner and outer sides with the center position of the thickness direction of the circular tube as the center of symmetry.

[0012] As a preferred technical solution of the present invention, the fiber orientation of the unidirectional carbon fiber prepreg body layer is symmetrically arranged on both the inner and outer sides with the center position of the thickness direction of the circular tube as the center of symmetry.

[0013] As a preferred technical solution of the present invention, the fiber orientation of the unidirectional carbon fiber prepreg body layer is arranged in a cyclic pattern with the center position of the tube thickness direction as the center of symmetry and the inner and outer sides in the order of 45°, 90°, -45° and 0° respectively.

[0014] The fiber orientation described in this invention is the angle between the direction of the unidirectional carbon fibers in the unidirectional carbon fiber prepreg body layer and the axial direction of the carbon fiber tube for rail transit.

[0015] This invention employs a symmetrical arrangement of unidirectional carbon fiber main layer fibers, which complements the symmetrical structure of the bidirectional fabric layer, allowing the mechanical properties in the wall thickness direction of the circular tube to complement each other and balance the axial and radial load-bearing capacity of the tube. Specifically, the 0° orientation enhances the axial load-bearing capacity, the 90° orientation improves the radial structural strength, and the ±45° orientation enhances the shear and torsional resistance. The combination of multiple angles achieves synergistic mechanical properties.

[0016] The total number of carbon fiber layers in the carbon fiber circular tube for rail transit described in this invention can be selected and optimized according to product requirements, and no further limitations are made here.

[0017] The straightness of the carbon fiber round tube for rail transit described in this invention is ≤0.2mm, more preferably ≤0.1mm, the porosity is ≤3%, more preferably ≤2%, and the deformation under 400kg load is ≤0.3mm, more preferably ≤0.15mm.

[0018] In a second aspect, the present invention provides a method for preparing carbon fiber round tubes for rail transit as described in the first aspect, including segmented lay-up, intermediate hot compaction, curing and molding, and post-treatment. Except for the last segmented lay-up, the formed lay-up blank is subjected to intermediate hot compaction after each segmented lay-up, and curing and molding and post-treatment are performed after the last segmented lay-up.

[0019] Except for the last segmented ply, the number of layers in each segmented ply of the present invention is ≤20.

[0020] As a preferred technical solution of the present invention, the intermediate hot compaction includes simultaneously heating the ply blank and applying molding pressure, and maintaining the temperature and pressure to densify the interlayer.

[0021] Preferably, the heat preservation temperature of the intermediate hot compaction is 55~65℃, for example, it can be 55℃, 58℃, 61℃, 63℃ or 65℃, etc., and the heating rate is 0.1~3℃ / min, for example, it can be 0.1℃ / min, 0.8℃ / min, 1.6℃ / min, 2.4℃ / min or 3℃ / min, etc.

[0022] Preferably, the holding pressure of the intermediate hot compaction is 0.55~0.65MPa, for example, it can be 0.55MPa, 0.58MPa, 0.61MPa, 0.63MPa or 0.65MPa, etc., and the pressurization rate is 0.01~0.1MPa / min, for example, it can be 0.01MPa / min, 0.03MPa / min, 0.05MPa / min, 0.08MPa / min or 0.1MPa / min, etc.

[0023] Preferably, the heat preservation and pressure holding time for intermediate hot compaction is 50~60 minutes, for example, it can be 50 minutes, 53 minutes, 56 minutes, 58 minutes or 60 minutes.

[0024] Preferably, the intermediate hot pressing is carried out under vacuum conditions, with a vacuum degree ≥ -0.085 MPa.

[0025] Preferably, after the heat preservation and pressure holding are completed, cooling and depressurization are carried out simultaneously to room temperature and normal pressure. The cooling rate is 0.1~3℃ / min, for example, it can be 0.1℃ / min, 0.9℃ / min, 1.7℃ / min, 2.5℃ / min or 3℃ / min, etc., and the depressurization rate is 0.01~0.1MPa / min, for example, it can be 0.01MPa / min, 0.03MPa / min, 0.05MPa / min, 0.07MPa / min or 0.1MPa / min, etc.

[0026] This invention employs segmented layering combined with intermediate hot compaction to densify the green body in layers. This process can effectively remove air bubbles inside the layers, reduce the porosity of the finished product, and avoid the problems of uneven tension and bending deformation of the green body caused by excessive single layering. It also effectively improves the interlayer bonding strength and product dimensional stability.

[0027] As a preferred technical solution of the present invention, the curing molding is a stepped temperature rise curing process.

[0028] Preferably, the stepped temperature curing includes heating from room temperature to a first temperature followed by a first heat preservation, heating to a second temperature followed by a second heat preservation, heating to a third temperature followed by a third heat preservation, and cooling back to the first temperature to complete the curing process.

[0029] As a preferred technical solution of the present invention, the first temperature is 55~65℃, for example, it can be 55℃, 58℃, 61℃, 63℃ or 65℃, etc., and the first heat preservation time is 25~35min, for example, it can be 55℃, 58℃, 61℃, 63℃ or 65℃, etc.

[0030] Preferably, the second temperature is 75~85℃, for example, it can be 75℃, 78℃, 81℃, 83℃ or 85℃, etc., and the second heat preservation time is 55~65 min, for example, it can be 55 min, 58 min, 61 min, 63 min or 65 min, etc.

[0031] Preferably, the third temperature is 115~125℃, for example, it can be 115℃, 118℃, 121℃, 123℃ or 125℃, etc., and the third heat preservation time is 85~95min, for example, it can be 85min, 88min, 91min, 93min or 95min, etc.

[0032] As a preferred technical solution of the present invention, the curing and molding is carried out under vacuum conditions, with a vacuum degree ≥ -0.085MPa.

[0033] Preferably, a molding pressure of 0.1 MPa is applied during the curing process.

[0034] As a preferred technical solution of the present invention, the heating rate of the stepped heating curing is 0.1~3℃ / min, for example, it can be 0.1℃ / min, 0.9℃ / min, 1.7℃ / min, 2.5℃ / min or 3℃ / min, etc.

[0035] This invention adopts a stepped heating and segmented heat preservation curing mode, in which the resin gradually melts, cross-links, and cures, avoiding excessive internal stress caused by one-time high-temperature curing, preventing component warping and deformation during heating and curing, improving the dimensional stability of the round tube, and ensuring uniform bonding between the fiber and the resin, thereby reducing internal defects such as localized resin enrichment and incomplete curing.

[0036] The post-processing described in this invention includes sequentially performing core removal, tape pulling, cutting, dimensional measurement, appearance inspection, weighing, polishing, and cleaning and packaging.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention adopts a composite symmetrical layup structure consisting of a unidirectional carbon fiber prepreg body layer and a bidirectional carbon fiber fabric prepreg layer, which can achieve uniform distribution of pipe wall stress, effectively ensure the straightness of pipe forming, and improve the overall mechanical strength and load performance of the pipe. (2) The present invention adopts a segmented layering combined with segmented intermediate hot compaction molding method, which can discharge the gas inside the layer layer by layer, greatly reduce the porosity of the product, and combined with the curing molding step, effectively improve the dimensional accuracy of long-sized round tubes and avoid porosity defects and bending and warping of pipes. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating the preparation method of carbon fiber cylindrical tubes for rail transit provided in some embodiments of the present invention. Detailed Implementation

[0039] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0040] Example 1 This embodiment provides a carbon fiber cylindrical tube for rail transit, comprising a total of 66 layers, including a unidirectional carbon fiber prepreg body layer and a bidirectional carbon fiber fabric prepreg layer. The unidirectional carbon fiber prepreg body layer comprises 60 layers, and the bidirectional carbon fiber fabric prepreg layer comprises 6 layers. The bidirectional carbon fiber fabric prepreg layers are distributed from the inside out at layers 1, 17, 33, 34, 50, and 66. The remaining layers are unidirectional carbon fiber prepreg body layers. The unidirectional carbon fiber prepreg body layers use C1500FR-32 / T700 unidirectional prepreg, and the bidirectional carbon fiber fabric prepreg layers use Cross 3K fabric prepreg. Both have a resin content of 32%. The fiber orientation of the unidirectional carbon fiber prepreg body layers is symmetrically arranged cyclically with the center of the tube thickness direction as the center of symmetry, extending outwards and inwards in the order of 45°, 90°, -45°, and 0°. The layer structure is shown in Table 1.

[0041] Table 1 like Figure 1 As shown, the carbon fiber cylindrical tube for rail transit is prepared using the following steps: (1) After completing 20 layers from the inside out, the material is placed in a tank for intermediate hot compaction. The vacuum degree inside the tank is -0.085MPa. The temperature is raised to 60℃ at a rate of 1.5℃ / min. Simultaneously, a molding positive pressure of 0.6MPa is applied at a rate of 0.05MPa / min. The material is kept at constant temperature and pressure for 30min. After the temperature and pressure are maintained, the material is cooled and depressurized to room temperature and atmospheric pressure simultaneously at a cooling rate of 1.5℃ / min and a depressurization rate of 0.05MPa / min. (2) After completing 21 to 40 layers of ply, perform intermediate hot compaction with the same parameters as (1); (3) After completing the layup of 41 to 66 layers, the tube is wound by a triaxial tube winding machine and then cured and formed, maintaining a vacuum of -0.08MPa and a heating rate of 1.5℃ / min. The specific curing process is as follows: the temperature is raised from room temperature to 60℃ and kept for 30min, during which 0.1MPa forming pressure is applied simultaneously; the temperature is raised to 80℃ and kept for 30min; the temperature is raised to 120℃ and kept for 90min; after all the heat preservation processes are completed, the temperature is naturally cooled to 60℃. After the curing process is completed and the tube is removed from the can, the core is removed, the tape is pulled out, the tube is cut, the dimensions are measured, the appearance is checked, the weight is weighed, the tube is polished, and the tube is cleaned and packaged to obtain the finished carbon fiber round tube for rail transit.

[0042] Example 2 This embodiment provides a carbon fiber cylindrical tube for rail transit, comprising a total of 66 layers, including a unidirectional carbon fiber prepreg body layer and a bidirectional carbon fiber fabric prepreg layer. The unidirectional carbon fiber prepreg body layer comprises 60 layers, and the bidirectional carbon fiber fabric prepreg layer comprises 6 layers. The bidirectional carbon fiber fabric prepreg layers are distributed symmetrically from the inside out at layers 1, 17, 33, 34, 50, and 66, with the center of the cylindrical tube thickness direction as the center of symmetry. The remaining layers are unidirectional carbon fiber prepreg body layers. The unidirectional carbon fiber prepreg body layers use C1500FR-32 / T700 unidirectional prepreg, and the bidirectional carbon fiber fabric prepreg layers use Cross 3K fabric prepreg, both with a resin content of 32%. The fiber orientation of the unidirectional carbon fiber prepreg body layers is symmetrically arranged in a cyclical pattern of 45°, 90°, -45°, and 0° from the center of the cylindrical tube thickness direction to both the inside and outside sides.

[0043] The carbon fiber cylindrical tube for rail transit is prepared using the following steps: (1) After completing 20 layers from the inside out, the material is placed in a tank for intermediate hot compaction. The vacuum degree inside the tank is -0.085MPa, and the temperature is raised to 55℃ at a rate of 0.1℃ / min. Simultaneously, a molding positive pressure of 0.55MPa is applied at a rate of 0.01MPa / min. The material is kept at constant temperature and pressure for 50min. After the heat preservation and pressure preservation are completed, the material is simultaneously cooled and depressurized to room temperature and atmospheric pressure at a cooling rate of 0.1℃ / min and a depressurization rate of 0.01MPa / min. (2) After completing 21 to 40 layers of ply, perform intermediate hot compaction with the same parameters as (1); (3) After completing the layup of 41 to 66 layers, the tube is wound by a triaxial tube winding machine and then cured and shaped, maintaining a vacuum of -0.08MPa and a heating rate of 0.1℃ / min. The specific curing process is as follows: the temperature is raised from room temperature to 55℃ and held for 25 minutes, during which 0.1MPa molding pressure is applied simultaneously; the temperature is raised to 75℃ and held for 55 minutes; the temperature is raised to 115℃ and held for 85 minutes; after all the heat preservation processes are completed, the temperature is naturally cooled to 55℃. After the curing process is completed and the tube is removed from the can, the core is removed, the tape is pulled out, the tube is cut, the dimensions are measured, the appearance is checked, the weight is weighed, the tube is polished, and the tube is cleaned and packaged to obtain the finished carbon fiber round tube for rail transit.

[0044] Example 3 This embodiment provides a carbon fiber cylindrical tube for rail transit, comprising a total of 66 layers, including a unidirectional carbon fiber prepreg body layer and a bidirectional carbon fiber fabric prepreg layer. The unidirectional carbon fiber prepreg body layer comprises 60 layers, and the bidirectional carbon fiber fabric prepreg layer comprises 6 layers. The bidirectional carbon fiber fabric prepreg layers are distributed symmetrically from the inside out at layers 1, 17, 33, 34, 50, and 66, with the center of the cylindrical tube thickness direction as the center of symmetry. The remaining layers are unidirectional carbon fiber prepreg body layers. The unidirectional carbon fiber prepreg body layers use C1500FR-32 / T700 unidirectional prepreg, and the bidirectional carbon fiber fabric prepreg layers use Cross 3K fabric prepreg, both with a resin content of 32%. The fiber orientation of the unidirectional carbon fiber prepreg body layers is symmetrically arranged in a cyclical pattern of 45°, 90°, -45°, and 0° from the center of the cylindrical tube thickness direction to both the inside and outside sides.

[0045] The carbon fiber cylindrical tube for rail transit is prepared using the following steps: (1) After completing 20 layers from the inside out, the product is placed in a tank for intermediate hot compaction. The vacuum degree inside the tank is -0.085MPa. The temperature is raised to 65℃ at a rate of 3℃ / min. Simultaneously, a molding positive pressure of 0.65MPa is applied at a rate of 0.1MPa / min. The product is kept at constant temperature and pressure for 60min. After the heat preservation and pressure preservation are completed, the product is simultaneously cooled and depressurized to room temperature and atmospheric pressure at a cooling rate of 3℃ / min and a depressurization rate of 0.1MPa / min. (2) After completing 21 to 40 layers of ply, perform intermediate hot compaction with the same parameters as (1); (3) After completing the layup of 41 to 66 layers, the tube is wound by a triaxial tube winding machine and then cured and shaped, maintaining a vacuum of -0.08MPa and a heating rate of 3℃ / min. The specific curing process is as follows: the temperature is raised from room temperature to 65℃ and held for 35min, during which 0.1MPa molding pressure is applied simultaneously; the temperature is raised to 85℃ and held for 65min; the temperature is raised to 125℃ and held for 95min; after all the heat preservation processes are completed, the temperature is naturally cooled to 65℃. After the curing process is completed and the tube is removed from the can, the core is removed, the tape is pulled out, the tube is cut, the dimensions are measured, the appearance is checked, the weight is weighed, the tube is polished, the tube is cleaned and packaged to obtain the finished carbon fiber round tube for rail transit.

[0046] Example 4 This embodiment provides a carbon fiber cylindrical tube for rail transit. Except for the insulation temperature of 80°C during intermediate hot compaction in the preparation method, it is the same as that in Embodiment 1.

[0047] Example 5 This embodiment provides a carbon fiber cylindrical tube for rail transit. Except for the insulation temperature of 50°C during intermediate hot compaction in the preparation method, it is the same as that in Embodiment 1.

[0048] Example 6 This embodiment provides a carbon fiber cylindrical tube for rail transit, which is the same as that in Embodiment 1 except that intermediate hot compaction is not performed in the preparation method.

[0049] Example 7 This embodiment provides a carbon fiber cylindrical tube for rail transit. Except for the curing and molding method, which involves directly heating to 120°C and holding for 180 minutes, the rest is the same as in Embodiment 1.

[0050] Example 8 This embodiment provides a carbon fiber round tube for rail transit, in which the fiber orientation of the unidirectional carbon fiber prepreg body layer is 0°, and the rest is the same as in embodiment 1.

[0051] Comparative Example 1 This comparative example provides a carbon fiber circular tube for rail transit. Except for replacing the bidirectional carbon fiber fabric prepreg layer in Example 1 with the unidirectional carbon fiber prepreg body layer, everything else is the same as in Example 1.

[0052] Test methods The finished carbon fiber round tubes for rail transit prepared in the examples and comparative examples were subjected to performance tests. Straightness was tested according to the gap method of GB / T 11336-2004, porosity was tested according to the density method of GB / T 3365-2008, and compression deformation test under 400kg load was carried out according to GB / T 5350-2005. The test results are shown in Table 2.

[0053] Test Results Table 2 The test results show that: (1) As can be seen from Examples 1 to 3, the carbon fiber tube structure provided by the present invention, combined with the process parameters of intermediate hot compaction and stepped temperature rise curing, produces products with stable straightness, porosity, and deformation under 400kg load, and exhibits excellent performance.

[0054] (2) As can be seen from Examples 1 and Examples 4-8, in Examples 4-5, when the intermediate hot compaction insulation temperature exceeds the limit range, the porosity of the pipe increases, the straightness of the axis deteriorates, and the deformation under load also increases; in Example 6, after the intermediate hot compaction process is cancelled, the gas inside the layer cannot be fully discharged, the porosity increases significantly, the axis is prone to deviation, the straightness deteriorates, the interlayer bonding strength decreases, and the deformation under load increases; in Example 7, the stepped heating curing is changed to single constant temperature curing, the resin curing reaction is uneven, the internal stress of the component increases, and the dimensional accuracy and deformation resistance decrease simultaneously; in Example 8, the multi-angle fiber orientation is changed to a single 0° orientation, the mechanical properties of the pipe in each direction are unbalanced, and the deformation under the same load increases significantly.

[0055] (3) As can be seen from Example 1 and Comparative Example 1, the present invention adopts a composite structure of unidirectional carbon fiber prepreg main layer and bidirectional carbon fiber fabric prepreg layer. Relying on the reinforcing effect of bidirectional fabric layer, it can obtain uniform stress distribution, lower porosity defects and better deformation resistance. However, when the bidirectional carbon fiber fabric prepreg layer is removed and replaced entirely with unidirectional prepreg, the toughening and interlayer reinforcement effect of the fabric layer in the wall thickness direction is lost. The overall structural consistency of the pipe deteriorates, and the straightness of the axis, internal density and load-bearing deformation resistance all decrease significantly. It is impossible to meet the dimensional accuracy and long-term load-bearing requirements under rail transit conditions.

[0056] In summary, this invention adopts a composite symmetrical layup structure combining a unidirectional carbon fiber prepreg main layer with a bidirectional carbon fiber fabric prepreg layer. By relying on the design of zonal reinforcement of the fabric layer, the stress distribution of the pipe wall and the interlayer bonding performance are optimized. The synergistic segmented intermediate hot compaction and stepped temperature rise curing effectively reduce the porosity of the pipe, improve the axial straightness and structural stiffness, and adapt to the complex service conditions of long-term vibration and heavy load of rail transit equipment.

[0057] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A carbon fiber circular tube for rail transit, characterized in that, It includes a unidirectional carbon fiber prepreg body layer and a bidirectional carbon fiber fabric prepreg layer. The bidirectional carbon fiber fabric prepreg layer is divided into an inner surface fabric layer, an outer surface fabric layer and an intermediate sandwich fabric layer. The intermediate sandwich fabric layer is symmetrically distributed with the center position of the tube thickness direction as the center of symmetry.

2. The carbon fiber circular tube for rail transit according to claim 1, characterized in that, The intermediate interlayer fabric layer is distributed at equal intervals to the inner and outer sides with the center of the tube thickness as the center of symmetry.

3. The carbon fiber circular tube for rail transit according to claim 1 or 2, characterized in that, The fiber orientation of the unidirectional carbon fiber prepreg body layer is symmetrically arranged on both the inner and outer sides with the center position of the tube thickness direction as the center of symmetry.

4. The carbon fiber circular tube for rail transit according to claim 3, characterized in that, The fiber orientation of the unidirectional carbon fiber prepreg body layer is arranged cyclically on both the inner and outer sides in the order of 45°, 90°, -45°, and 0°, with the center of the tube thickness direction as the center of symmetry.

5. A method for preparing a carbon fiber circular tube for rail transit as described in any one of claims 1 to 4, characterized in that, The process includes segmented lay-up, intermediate hot compaction, curing and shaping, and post-treatment. Except for the last segmented lay-up, the ply blank formed after each segmented lay-up is subjected to intermediate hot compaction. After the last segmented lay-up, curing and shaping and post-treatment are carried out.

6. The preparation method according to claim 5, characterized in that, The intermediate hot compaction includes simultaneously heating the plywood and applying molding pressure, and maintaining the temperature and pressure to densify the interlayers. Preferably, the intermediate hot compaction insulation temperature is 55~65℃, and the heating rate is 0.1~3℃ / min; Preferably, the holding pressure of the intermediate hot compaction is 0.55~0.65MPa, and the pressurization rate is 0.01~0.1mpa / min; Preferably, the heat preservation and pressure holding time for intermediate hot compaction is 50~60 minutes; Preferably, the intermediate hot pressing is carried out under vacuum conditions, with a vacuum degree ≥ -0.085 MPa; Preferably, after the heat preservation and pressure holding are completed, the temperature is simultaneously reduced and the pressure is released to room temperature and normal pressure, with a cooling rate of 0.1~3℃ / min and a pressure release rate of 0.01~0.1MPa / min.

7. The preparation method according to claim 5 or 6, characterized in that, The curing process is a stepped temperature increase curing method; Preferably, the stepped temperature curing includes heating from room temperature to a first temperature followed by a first heat preservation, heating to a second temperature followed by a second heat preservation, heating to a third temperature followed by a third heat preservation, and cooling back to the first temperature to complete the curing process.

8. The preparation method according to claim 7, characterized in that, The first temperature is 55~65℃, and the first heat preservation time is 25~35 min; Preferably, the second temperature is 75~85℃, and the second heat preservation time is 55~65 min; Preferably, the third temperature is 115~125℃, and the third heat preservation time is 85~95 min.

9. The preparation method according to any one of claims 5 to 8, characterized in that, The curing and molding process is carried out under vacuum conditions, with a vacuum degree ≥ -0.085 MPa; Preferably, a molding pressure of 0.1 MPa is applied during the curing process.

10. The preparation method according to claim 7, characterized in that, The heating rate for the stepped heating curing is 0.1~3℃ / min.

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