Method for improving interlaminar shear performance of carbon fiber preform and carbon fiber preform prepared by method

Abstract

The invention provides a method for improving interlaminar shear performance of a carbon fiber preform and the carbon fiber preform prepared by the method, and relates to the technical field of carbon-carbon composite materials. The method comprises the following steps: sequentially chopping, carding into a net and needling carbon fiber filaments to obtain a carbon fiber net tire; performing wiredrawing laying on the carbon fiber filaments to obtain carbon fiber unidirectional cloth; the carbon fiber net tire and the carbon fiber one-way cloth are laid in a crossed and laminated mode, and a laminated carbon fiber felt is obtained; and performing composite needling on the laminated carbon fiber felt, and performing ultrasonic vibration treatment and airflow impact treatment on a needled area to obtain the carbon fiber preform. According to the method, the ratio of the single-layer needling density to the overall needling density is adjusted, and the interlayer binding force is enhanced; the production of the short fibers is controlled by adjusting the needling frequency, and the negative influence of the short fibers on the interlayer binding force is reduced by utilizing ultrasonic vibration and airflow impact, so that the overall strength and reliability of the carbon fiber preform are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon-carbon composite materials, and in particular to a method for improving the interlaminar shear performance of a carbon fiber preform and a carbon fiber preform prepared thereby. Background Art

[0002] Carbon-carbon composite material is a high-performance material composed of a carbon fiber reinforced carbon matrix. Due to its high-temperature stability, high specific strength and heat shock resistance, it is widely used in aerospace, braking systems and high-end industrial fields. Its preparation usually includes multiple steps such as preform preparation, carbonization and densification. The final product now has a delamination problem during use, and the reason is that there is a problem in the preparation of the preform. In the preform preparation process, a single layer of carbon fiber felt is first prepared through needle punching reinforcement technology, and then the needle-punched single layers of carbon fiber felt are stacked together and then needle-punched. Due to the shortcomings of the existing technology, the interlayer bonding force of the stacked needle-punched preform is weak, which leads to delamination of the final product during use.

[0003] The current method for preparing a carbon fiber preform mainly includes the following steps:

[0004] (1) Single-layer needling: Each layer of carbon short fiber felt is needle-punched separately to ensure that the single layer has a certain mechanical strength.

[0005] (2) Multi-layer stacking: Then stack multiple needle-punched carbon fiber felts.

[0006] (3) Overall needling: The stacked multi-layer structure is then subjected to overall needling. The two adjacent independent needle-punched felt layers contribute free fibers at the same time, which are entangled under the action of needling and used to combine the layers. The multiple independent carbon fiber needle-punched felt layers are transformed into an integral carbon fiber needle-punched felt, that is, a needle-punched preform.

[0007] However, this method has at least three major problems:

[0008] (I) There are too few free fibers at the interface between layers, resulting in insufficient fibers for interlayer entanglement: a) In the current process, each layer of carbon short fiber felt is needle-punched separately before multi-layer composite, which causes most of the fibers to form entanglements within the single layer, and there is a lack of sufficient free fibers for interlayer interlacing and entanglement; b) Due to the insufficient number of free fibers between layers, even if the overall needle-punching density is increased after multi-layer composite, the interlayer bonding strength cannot be effectively enhanced, and delamination is still prone to occur in the end.

[0009] (II) Broken fibers remain at the interface between layers, acting as a lubricant and affecting the bonding strength: a) During the needling process, some fibers will break to form short fibers and accumulate at the interface between layers. These short fibers not only fail to effectively enhance the bonding strength between layers, but may also further weaken the bonding strength between layers due to their lubricating effect, making the final product easy to peel along the layers during use; b) The existing process does not take this into consideration, resulting in a lack of effective means to remove short fibers, causing these short fibers to remain during the subsequent densification process, affecting the mechanical properties of the final material.

[0010] (III) Limitations of simply increasing the overall needling density and needling frequency: a) Insufficient free fibers. Increasing the needling density alone has limitations. That is, simply increasing the overall needling density can enhance the interlayer bonding strength. However, due to the lack of sufficient free fibers available for entanglement, simply increasing the needling density can only act on the existing entangled areas and cannot effectively improve the interlayer bonding problem; b) Excessively high needling frequency leads to excessive broken fibers, which affects the interlayer bonding strength.

[0011] Therefore, in the existing needling process, because the single-layer carbon fiber needled felt is individually needled before composite, the degree of entanglement between the layers is low, resulting in the risk of interlayer delamination in the prepared carbon-carbon composite material. In addition, the short fibers produced during the needling process remain at the interlayer interface, potentially acting as a lubricant and further reducing the interlayer bonding strength. It is precisely because of the above-mentioned problems in the traditional process that the interlayer entanglement is insufficient, and interlayer cracking or delamination is prone to occur during subsequent high-temperature processing and use, affecting product quality.

[0012] In view of this, the present invention is proposed. Summary of the Invention

[0013] The present invention aims to provide a method for improving the interlaminar shear performance of a carbon fiber preform and a carbon fiber preform produced thereby. This method addresses the problem of insufficient interlaminar bonding and easy delamination in carbon-carbon composite preforms by optimizing the needling process and short fiber removal method to improve interlaminar bonding and enhance the overall mechanical properties of the carbon-carbon composite material. This invention primarily addresses the delamination problem of carbon-carbon composite preforms caused by insufficient interlaminar bonding during the needling process.

[0014] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0015] In a first aspect, the present invention provides a method for improving the interlaminar shear performance of a carbon fiber preform, the method comprising:

[0016] The carbon fiber filaments are sequentially chopped, carded into a web and needle-punched to obtain a carbon fiber mesh; the carbon fiber filaments are drawn and laid to obtain a carbon fiber unidirectional fabric;

[0017] Cross-laying the carbon fiber web and the carbon fiber unidirectional fabric to obtain a laminated carbon fiber felt;

[0018] The laminated carbon fiber felt is needle-punched, and the needle-punched area is simultaneously subjected to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform.

[0019] Furthermore, the carbon fiber filaments are polyacrylonitrile-based carbon fibers.

[0020] Furthermore, the length of the carbon fiber filaments obtained after the chopped carbon fiber is 5 to 20 mm.

[0021] Furthermore, during the preparation of the carbon fiber mesh, the density of the needle punching is 5 to 10 needles / cm 2 The depth of the acupuncture is 8 to 12 mm, and the frequency of the acupuncture is 300 to 500 times / min.

[0022] Furthermore, the thickness of the carbon fiber mesh is 0.7-1.0 mm, and the weight of the carbon fiber mesh is 70-120 g / m 2 .

[0023] Furthermore, the carbon fiber filaments are unchopped continuous filaments.

[0024] Furthermore, the process parameters of the wire drawing and laying include: a tension of the monofilament of 5 to 50 N / filament; a center spacing of the filaments of 0.1 to 1.0 mm; a wire drawing speed of 5 to 50 m / min; and a laying angle of -2 to 2°.

[0025] Furthermore, the thickness of the carbon fiber unidirectional cloth is 0.3-0.6 mm, and the weight of the carbon fiber unidirectional cloth is 200-400 g / m 2 .

[0026] Furthermore, the cross-ply laying includes: adopting an alternating laying method of a carbon fiber mesh and a carbon fiber unidirectional cloth, and the carbon fiber unidirectional cloths separated by only one carbon fiber mesh are orthogonally staggered at 0° and 90°.

[0027] Furthermore, in the laminated carbon fiber felt, the number of layers of the carbon fiber web is 10 to 25, and the number of layers of the carbon fiber unidirectional cloth is 10 to 25.

[0028] It should be noted that the specific number of layers can be adjusted according to the thickness and performance requirements of the preform.

[0029] Furthermore, in the laminated carbon fiber felt, the ply order is preferably to use the carbon fiber mesh as the starting layer and the ending layer, and the middle layer is alternating unidirectional cloth and mesh (that is, the middle layer adopts an alternating plying method of a carbon fiber mesh and a carbon fiber unidirectional cloth), so that the upper and lower surfaces are both mesh structures with good flexibility, which is conducive to the stability of the start and end of needling.

[0030] Furthermore, in the laminated carbon fiber felt, the plying sequence is more preferably a 1:1 alternating ply structure of the web and the unidirectional fabric, with the total number of layers being controlled between 20 and 50 layers to form a dense orthogonal reinforcement system.

[0031] Furthermore, during the composite needling process of the laminated carbon fiber felt, the needling density is 20 to 25 needles / cm 2 The depth of the acupuncture is 10 to 15 mm.

[0032] Furthermore, during the composite needling of the laminated carbon fiber felt, the needling is performed in stages: the frequency of the needling in the first stage is 600 to 800 times / min; and the frequency of the needling in the second stage is 800 to 1200 times / min.

[0033] Furthermore, the acupuncture time of the first stage is 20 to 30 minutes.

[0034] Furthermore, the acupuncture time of the second stage is 20 to 30 minutes.

[0035] It should be noted that the specific time can be flexibly adjusted according to the thickness of the preform, the number of layers and the needling density, so as to achieve the best interlayer entanglement effect.

[0036] Furthermore, the ultrasonic vibration treatment includes: utilizing ultrasonic waves emitted by an ultrasonic generator, and converting electrical energy into mechanical energy through a transducer, and transmitting it to the acupuncture area; and the ultrasonic vibration treatment is started by the needle penetrating the carbon fiber felt after the laminate, lasts for the time period when the needle remains in the carbon fiber felt after the laminate, and ends when the acupuncture needle starts to return and leaves the carbon fiber felt.

[0037] Furthermore, the frequency of the ultrasonic wave is 20 to 50 kHz.

[0038] Furthermore, the power of the ultrasonic wave is 200-400W.

[0039] Furthermore, the vibration amplitude of the acupuncture area is 5 to 15 μm.

[0040] Furthermore, the airflow impact treatment includes: using a compressor to generate airflow, and guiding the airflow to the needling area through a nozzle; and the airflow impact treatment starts from the needling return stage, lasts during the time period of the needling process recovery, and ends before the next needling re-inserts the carbon fiber.

[0041] Furthermore, the working pressure of the airflow is 0.5-5.0 MPa; the speed of the airflow is 100-500 m / s; and the injection pulse duration of the airflow is 40-70 ms.

[0042] Furthermore, the nozzle has a diameter of 0.5 to 5.0 mm, and the distance between the end face of the nozzle and the acupuncture area is 10 to 50 mm.

[0043] In a second aspect, the present invention provides a carbon fiber preform, which is prepared by the method for improving the interlaminar shear performance of a carbon fiber preform as described in the first aspect.

[0044] Furthermore, the density of the carbon fiber preform is 0.38 to 0.52 g / cm 3 .

[0045] Furthermore, the coefficient of variation (CV) value of the carbon fiber preform is less than 4%.

[0046] Furthermore, the interlaminar shear strength of the carbon fiber preform is greater than 5.5 MPa, preferably greater than 6.5 MPa.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) Optimizing the needle punching density ratio and improving the interlayer fiber entanglement: The method of the present invention optimizes the number of free fibers used for interlayer entanglement by adjusting the ratio of the needle punching density of a single layer of carbon fiber felt to the overall needle punching density after multilayer composite. The specific method includes: reducing the needle punching density of a single layer to keep some fibers free, providing more fibers for interlayer connection after multilayer composite, and at the same time increasing the needle punching density during multilayer composite to enhance the interlayer bonding force.

[0049] (2) Optimizing the needling frequency to reduce the generation of short fibers between layers: In the method described in the present invention, a lower frequency is used in the single-layer needling stage to reduce fiber breakage and reduce the amount of short fibers generated; the frequency is increased in the multi-layer composite needling stage to enhance the degree of fiber entanglement between layers.

[0050] (3) Using ultrasonic vibration + air flow impact to remove short fibers on the interface: After multi-layer composite needling, the method described in the present invention uses ultrasonic vibration + air flow impact to effectively remove short fibers on the interface between layers to prevent them from having a lubricating effect on the interlayer bonding force; ultrasonic vibration causes loose short fibers to separate from the fiber network structure, and air flow impact further removes these short fibers to improve the interlayer bonding force.

[0051] (4) Comprehensive optimization of the needling process to improve the interlayer bonding strength of carbon-carbon composite materials: The method described in the present invention reduces the risk of delamination from the source and improves the interlayer bonding strength and overall mechanical properties of carbon-carbon composite materials by optimizing the needling density ratio, adjusting the needling frequency, and removing short fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 Schematic diagram of the needling process of the method for improving the interlaminar shear performance of a carbon fiber preform according to the present invention.

[0054] Among them, 1 is a compressor, 2 is a pressure regulating valve, 3 is a high-pressure gas storage tank, 4 is an adjustable nozzle, 5 is a needle plate, and 6 is an ultrasonic generator. DETAILED DESCRIPTION

[0055] Unless otherwise defined herein, scientific and technological terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0056] It should be noted that the following description sets forth specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art may make similar generalizations without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0057] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0059] In a first aspect, the present invention provides a method for improving the interlaminar shear performance of a carbon fiber preform, the method comprising:

[0060] The carbon fiber filaments are sequentially chopped, carded into a web and needle-punched to obtain a carbon fiber mesh; the carbon fiber filaments are drawn and laid to obtain a carbon fiber unidirectional fabric;

[0061] Cross-laying the carbon fiber web and the carbon fiber unidirectional fabric to obtain a laminated carbon fiber felt;

[0062] The laminated carbon fiber felt is needle-punched, and the needle-punched area is subjected to ultrasonic vibration treatment and air flow impact treatment (such as Figure 1 As shown), the carbon fiber preform is obtained.

[0063] In the present invention, the present invention significantly improves the interlayer bonding strength of the carbon-carbon composite material preform and reduces the occurrence of delamination by optimizing the needling process parameters and introducing ultrasonic vibration treatment and airflow impact treatment. First, by adjusting the needling density ratio of the single-layer carbon fiber needling layer and the multi-layer composite, the effective fibers used for interlayer entanglement are reasonably controlled, so that the interlayer fibers can be more fully interwoven, thereby improving the interlayer bonding strength. Secondly, by adjusting the needling frequency during single-layer needling and multi-layer composite needling, the generation of short fibers between the layers is effectively controlled, reducing the lubrication effect and interface defects that may be caused by the short fibers during interlayer bonding. Furthermore, ultrasonic vibration and airflow impact technology are used to remove broken fibers on the interface, eliminate potential weak bonding areas, and make the interlayer bonding tighter. The synergistic effect of this series of optimization measures enables carbon-carbon composite materials to have better structural stability and mechanical properties under high temperature and high load environments, greatly improving their engineering application value.

[0064] As an optional embodiment, in the process of preparing the carbon fiber web and the carbon fiber unidirectional cloth, the carbon fiber filaments are polyacrylonitrile-based carbon fibers.

[0065] As an optional embodiment, during the preparation of the carbon fiber mesh, the length of the carbon fiber filaments obtained after the short cut is 5 to 20 mm, for example, it can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, etc.

[0066] In the present invention, the length of the carbon fiber filaments obtained after chopped can be selected according to the requirements of the layer thickness and mechanical properties in the subsequent steps, and a single length or a mixture can be selected to ensure that the length of the carbon fiber after chopped is uniform, which is beneficial to the uniform distribution and interaction of the fibers during the subsequent needling process.

[0067] As an optional embodiment, during the preparation of the carbon fiber web, the density of the needle punching is 5 to 10 needles / cm 2 , for example, 5 stitches / cm 2 , 6 needles / cm 2 , 7 needles / cm 2 , 8 needles / cm 2 , 9 needles / cm 2 , 10 needles / cm 2 wait.

[0068] In the present invention, the needle punching density range can not only enable the chopped carbon fibers to initially form a certain network structure and have preliminary integrity, but also prevent excessive entanglement of too many fibers at this stage, thereby retaining sufficient free fibers for subsequent interlayer entanglement.

[0069] As an optional embodiment, during the preparation of the carbon fiber web, the needling depth is 8 to 12 mm, for example, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, etc.

[0070] In the present invention, the depth range of the needling ensures that the needling needles can penetrate the fiber layer and cause the fibers to be preliminarily interwoven.

[0071] As an optional embodiment, during the preparation of the carbon fiber mesh, the frequency of acupuncture is 300 to 500 times / min, for example, it can be 300 times / min, 320 times / min, 340 times / min, 360 times / min, 380 times / min, 400 times / min, 420 times / min, 440 times / min, 460 times / min, 480 times / min, 500 times / min, etc.

[0072] In the present invention, the frequency range of the needling is kept at a relatively low level to further reduce the generation of short fibers.

[0073] As an optional embodiment, the carbon fiber web has a thickness of 0.7 to 1.0 mm, for example, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1.0 mm, etc.

[0074] As an optional embodiment, the carbon fiber mesh has a gram weight of 70 to 120 g / m 2 , for example, it can be 70g / m 2 , 75g / m 2 , 80g / m 2 , 85g / m 2 , 90g / m 2 , 95g / m 2 , 100g / m 2 , 105g / m 2 , 110g / m 2 , 115g / m 2 , 120g / m 2 wait.

[0075] As an optional embodiment, during the preparation of the carbon fiber unidirectional cloth, the carbon fiber filaments are unchopped continuous filaments.

[0076] As an optional embodiment, during the preparation of the carbon fiber unidirectional cloth, the drawing and laying is performed by high-precision drawing equipment (such as Japan's Toray TMT-700) and a laying device (such as Germany's Mayer AT-500).

[0077] As an optional embodiment, the process parameters of the wire drawing and laying include: the tension of the monofilament is 5 to 50 N / filament; the center spacing of the filaments is 0.1 to 1.0 mm; the wire drawing speed is 5 to 50 m / min; and the laying angle is -2 to 2°.

[0078] In the present invention, the process parameters of the drawing and laying control the tension and arrangement spacing of the filaments, so that the distribution of carbon fibers in the unidirectional cloth is uniform and consistent, while ensuring that the carbon fiber filaments are closely arranged and highly parallel, providing a stable foundation for subsequent compounding with the carbon fiber mesh.

[0079] As an optional embodiment, the tension of the monofilament is 5 to 50 N / filament, for example, it can be 5 N / filament, 10 N / filament, 15 N / filament, 20 N / filament, 25 N / filament, 30 N / filament, 35 N / filament, 40 N / filament, 45 N / filament, 50 N / filament, etc., preferably 10 to 30 N / filament; the tension of the monofilament can be adjusted in real time by a magnetic powder brake, and the tension fluctuation is ≤±1%.

[0080] As an optional embodiment, the center spacing of the filaments is 0.1-1.0 mm, for example, it can be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, etc., with an accuracy of ±5 μm.

[0081] As an optional embodiment, the wire drawing speed is 5 to 50 m / min, for example, it can be 5 m / min, 10 m / min, 15 m / min, 20 m / min, 25 m / min, 30 m / min, 35 m / min, 40 m / min, 45 m / min, 50 m / min, etc.

[0082] As an optional embodiment, the ply angle is -2 to 2°, for example, -2°, -1.5°, -1°, -0.5°, 0°, 0.5°, 1°, 1.5°, 2°, etc., and can be calibrated by a visual positioning system.

[0083] As an optional embodiment, the carbon fiber unidirectional cloth has a thickness of 0.3 to 0.6 mm, for example, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, etc.

[0084] As an optional embodiment, the carbon fiber unidirectional cloth has a gram weight of 200 to 400 g / m 2 , for example, it can be 200g / m 2 , 220g / m 2 , 240g / m 2 , 250g / m 2 , 260g / m 2 , 280g / m 2 , 300g / m 2 , 320g / m 2 , 340g / m 2 , 350g / m 2 , 360g / m 2 , 380g / m 2 , 400g / m 2 wait.

[0085] As an optional embodiment, the cross-ply laying includes: using an alternating laying method of a carbon fiber mesh and a carbon fiber unidirectional cloth, and the carbon fiber unidirectional cloths separated by only one carbon fiber mesh are orthogonally staggered at 0° and 90°.

[0086] In this method, unidirectional fabrics are stacked crosswise with the web, alternating between 0° and 90°. This stacking pattern enhances the mechanical properties of the preform in multiple directions. During the placement process, each layer must be positioned accurately to avoid shifting or wrinkling, ensuring good contact between layers.

[0087] As an optional embodiment, in the laminated carbon fiber felt, the number of layers of the carbon fiber mesh is 10 to 25 layers, for example, it can be 10 layers, 12 layers, 14 layers, 15 layers, 16 layers, 18 layers, 20 layers, 22 layers, 24 layers, 25 layers, etc.

[0088] As an optional embodiment, in the laminated carbon fiber felt, the number of layers of the carbon fiber unidirectional cloth is 10 to 25 layers, for example, it can be 10 layers, 12 layers, 14 layers, 15 layers, 16 layers, 18 layers, 20 layers, 22 layers, 24 layers, 25 layers, etc.

[0089] It should be noted that the specific number of layers can be adjusted according to the thickness and performance requirements of the preform.

[0090] As an optional embodiment, in the laminated carbon fiber felt, the laying order is preferably with the carbon fiber mesh as the starting layer and the ending layer, and the middle layer is alternating unidirectional cloth and mesh (that is, the middle layer adopts an alternating laying method of a carbon fiber mesh and a carbon fiber unidirectional cloth), so that the upper and lower surfaces are both mesh structures with good flexibility, which is conducive to the stability of the start and end of needling.

[0091] As an optional embodiment, in the laminated carbon fiber felt, the plying sequence is more preferably a 1:1 alternating ply structure of the web and the unidirectional fabric, with the total number of layers controlled between 20 and 50 to form a dense orthogonal reinforcement system.

[0092] As an optional embodiment, during the composite needling of the laminated carbon fiber felt, the needling density is 20 to 25 needles / cm 2 , for example, it can be 20 needles / cm 2 , 21 needles / cm 2 , 22 needles / cm 2 , 23 needles / cm 2 , 24 needles / cm 2 , 25 needles / cm 2 wait.

[0093] In the present invention, during the composite needling of the laminated carbon fiber felt, the needling density needs to be based on the needling density of the previous single layer (5 to 10 needles / cm 2 ) to adjust the overall acupuncture density to 20-25 needles / cm 2, that is, adjusting the ratio of the single-layer needling density to the overall needling density of the multi-layer composite. By increasing the needling density, the fibers between the layers can be fully intertwined and entangled, thus enhancing the bonding strength between the layers.

[0094] As an optional embodiment, during the composite needling of the laminated carbon fiber felt, the needling depth is 10 to 15 mm, for example, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, etc.

[0095] In the present invention, during the composite needling of the laminated carbon fiber felt, the needling depth is preferably set to 10-15 mm, to further ensure that the needling needles can penetrate deep between the layers of fibers and promote fiber entanglement.

[0096] As an optional embodiment, during the composite needling of the laminated carbon fiber felt, a staged needling method is adopted: the frequency of the first stage needling is 600 to 800 times / min; the frequency of the second stage needling is 800 to 1200 times / min.

[0097] In the present invention, the needling frequency is adjusted according to the different stages. Initially, the frequency is moderate, at 600 to 800 times / min, allowing the fibers to gradually adapt to the needling action. This prevents high-frequency needling before a stable interwoven structure is formed, which can lead to significant fiber breakage and an increase in interfacial fiber fragmentation. As the needling progresses, the fibers become initially interwoven, the felt structure gradually tightens, and the interaction between the needles and fibers begins to strengthen. The needling frequency is then increased to 800 to 1200 times / min. This allows more fibers to be drawn into the felt by the needles, achieving a more complete and dense entanglement based on the existing initial interwoven structure. This dense entanglement significantly increases interfiber friction and interaction. Compared to conventional constant-frequency processes, gradient-controlled needling frequency allows for more precise control of fiber motion, avoiding initial excessive agitation that can lead to random fiber distribution and disorder, while also improving interlayer bonding through reinforcement in the later stages. This significantly enhances interlayer bonding in the preform, effectively improving the overall mechanical properties of the preform.

[0098] As an optional embodiment, the frequency of acupuncture in the first stage is 600-800 times / min, for example, it can be 600 times / min, 620 times / min, 640 times / min, 650 times / min, 660 times / min, 680 times / min, 700 times / min, 720 times / min, 740 times / min, 750 times / min, 780 times / min, 800 times / min, etc.

[0099] As an optional embodiment, the frequency of acupuncture in the second stage is 800-1200 times / min, for example, it can be 800 times / min, 820 times / min, 840 times / min, 850 times / min, 860 times / min, 880 times / min, 900 times / min, 920 times / min, 940 times / min, 950 times / min, 960 times / min, 980 times / min, 1000 times / min, 1020 times / min, 1040 times / min, 1060 times / min, 1080 times / min, 1100 times / min, 1120 times / min, 1140 times / min, 1160 times / min, 1180 times / min, 1200 times / min, etc.

[0100] As an optional embodiment, the acupuncture time of the first stage is 20 to 30 minutes, for example, it can be 20 minutes, 22 minutes, 24 minutes, 25 minutes, 26 minutes, 28 minutes, 30 minutes, etc.

[0101] As an optional embodiment, the acupuncture time of the second stage is 20 to 30 minutes, for example, it can be 20 minutes, 22 minutes, 24 minutes, 25 minutes, 26 minutes, 28 minutes, 30 minutes, etc.

[0102] It should be noted that the specific time can be flexibly adjusted according to the thickness of the preform, the number of layers and the needling density, so as to achieve the best interlayer entanglement effect.

[0103] As an optional embodiment, the ultrasonic vibration treatment includes: utilizing ultrasonic waves emitted by an ultrasonic generator, converting electrical energy into mechanical energy through a transducer, and transmitting the energy to the puncture area; and the ultrasonic vibration treatment is started by the needle puncturing the carbon fiber felt after the laminate, lasts for the time period when the needle remains in the carbon fiber felt after the laminate, and ends when the needle starts to return and leaves the carbon fiber felt.

[0104] As an optional embodiment, the frequency of the ultrasonic wave is 20 to 50 kHz, for example, it can be 20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, 45 kHz, 50 kHz, etc.

[0105] As an optional embodiment, the power of the ultrasound is 200-400W, for example, it can be 200W, 220W, 240W, 260W, 280W, 300W, 320W, 340W, 360W, 380W, 400W, etc.

[0106] As an optional embodiment, the vibration amplitude of the acupuncture area is 5 to 15 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0107] In the present invention, an ultrasonic generator and a compressor are used for processing while the whole is needling, wherein the ultrasonic generator generates ultrasonic waves with a frequency of 20 to 50 kHz, converts electrical energy into mechanical energy through a transducer, and transmits it to the needling area. The vibration of the ultrasonic wave acts on the carbon fiber felt, making it easier for the loose short fibers between the layers to break away from the fiber network structure. The vibration amplitude is controlled between 5 and 15 μm, which can effectively loosen the short fibers without damaging the overall fiber structure.

[0108] As an optional embodiment, the airflow impact treatment includes: using a compressor to generate airflow, and guiding the airflow to the needling area through a nozzle; and the airflow impact treatment is started from the needling return stage, lasts for the time period during the needling process recovery, and ends before the next needling re-inserts the carbon fiber.

[0109] As an optional embodiment, the working pressure of the airflow is 0.5 to 5.0 MPa, for example, it can be 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, 4.0 MPa, 4.5 MPa, 5.0 MPa, etc.

[0110] In the present invention, the compressor generates a high-pressure airflow with a pressure of 0.5 to 5.0 MPa, and guides the airflow to the needling area through the nozzle. The position and angle of the nozzle are precisely adjusted to ensure that the airflow can cover the entire needling area, especially the interlayer interface. The high-speed airflow impacts the short fibers in the needling area, generating impact momentum and shear force significantly higher than that under low-pressure jet conditions, thereby strongly flushing the fiber particles; the ultrasonic vibration generates high-speed vibration fluctuations, which reduces the adhesion between the fibers and the substrate and induces micro-vibration of the fibers, helping the short fibers to tear off the substrate surface. The synergistic effect of high-speed airflow and ultrasound can efficiently remove tiny particles attached to the surface of the workpiece. After the ultrasonic vibration loosens the short fibers, they are quickly blown away from the interlayer interface to achieve effective removal of the short fibers. Through this collaborative working mode, the short fibers generated during the needling process are promptly removed to avoid their accumulation between layers, thereby improving the interlayer bonding strength.

[0111] As an optional embodiment, the air flow velocity is 100-500 m / s, for example, 100 m / s, 120 m / s, 140 m / s, 150 m / s, 160 m / s, 180 m / s, 200 m / s, 220 m / s, 240 m / s, 250 m / s, 260 m / s, 280 m / s, 320 m / s, 340 m / s, 350 m / s, 360 m / s, 380 m / s, 400 m / s, 420 m / s, 440 m / s, 460 m / s, 480 m / s, 500 m / s, etc. (According to Bernoulli's equation, pressure and flow velocity are proportional to the square, forming a high-density, focused air cone.)

[0112] As an optional embodiment, the injection pulse duration of the air flow is 40 to 70 ms, for example, it can be 40ms, 42ms, 44ms, 45ms, 46ms, 48ms, 50ms, 52ms, 54ms, 56ms, 58ms, 60ms, 62ms, 64ms, 66ms, 68ms, 70ms, etc.

[0113] As an optional implementation, Figure 1 As shown, the present invention also provides a needling process system for improving the interlaminar shear performance of a carbon fiber preform, the system comprising: a compressor 1, a pressure regulating valve 2, a high-pressure gas storage tank 3, an adjustable nozzle 4, a needle plate 5, and an ultrasonic generator 6; wherein the adjustable nozzle 4 can freely adjust the spray angle around the needle plate 5 (the needling area) and make an offset adjustment in the horizontal direction to cover the entire needling width.

[0114] As an optional embodiment, the spray angle of the nozzle is 15° to 45°, for example, it can be 15°, 20°, 25°, 30°, 35°, 40°, 45°, etc.

[0115] It should be noted that the spray angle refers to the angle formed between the central axis of the nozzle and the direction perpendicular to the surface of the carbon fiber felt, that is, the angle is the inclination angle of the nozzle spray direction relative to the movement direction of the acupuncture needle (vertical direction).

[0116] As an optional embodiment, the distance between the end face of the nozzle and the needling area is 10 to 50 mm, for example, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, etc.

[0117] As an optional embodiment, the nozzle has a diameter of 0.5 to 5.0 mm, for example, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, etc.

[0118] It's important to note that the needle punching system described herein differs from conventional contact needle punching systems, which use tiny jets with a diameter (0.08-0.2mm) and angles (10-75°). The nozzles in this system feature a larger aperture and continuously adjustable angles, fully utilizing the energy of the high-pressure airflow. During operation, high-pressure air is delivered by compressor 1 and stored in high-pressure air tank 3. After being reduced in pressure by pressure regulating valve 2, it is piped to adjustable nozzle 4. Simultaneously, ultrasonic generator 6 simultaneously emits ultrasonic vibrations in the needle punching area (needle plate 5).

[0119] In a second aspect, the present invention provides a carbon fiber preform, which is prepared by the method for improving the interlaminar shear performance of a carbon fiber preform as described in the first aspect.

[0120] As an optional embodiment, the density of the carbon fiber preform is 0.4-0.5 g / cm 3 , for example, it can be 0.4g / cm 3 , 0.42g / cm 3 , 0.44g / cm 3 , 0.45g / cm 3 , 0.46g / cm 3 , 0.48g / cm 3 , 0.5g / cm 3 wait.

[0121] As an optional embodiment, the coefficient of variation CV value of the carbon fiber preform is less than 4%, for example, it can be 4%, 3.8%, 3.6%, 3.5%, 3.4%, 3.2%, 3%, 2%, 1%, etc.

[0122] As an optional embodiment, the interlaminar shear strength of the carbon fiber preform is greater than 6.5 MPa, for example, it can be 6.5 MPa, 6.6 MPa, 6.7 MPa, 6.8 MPa, 6.9 MPa, 7.0 MPa, 7.1 MPa, 7.2 MPa, 7.3 MPa, 7.4 MPa, 7.5 MPa, etc.

[0123] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0124] Example 1

[0125] This embodiment provides a carbon fiber preform, which is prepared by the following steps:

[0126] (1) Preparation of carbon fiber mesh:

[0127] The fiber raw material is 12K polyacrylonitrile-based carbon fiber (model: T300-12K). The carbon fiber filaments are chopped into 10mm long chopped fibers by a chopped machine. The chopped carbon fibers are combed and needle-punched by a carding machine to obtain a carbon fiber mesh.

[0128] Among them, the needle density of the pre-needling machine is 6 needles / cm 2 The needling depth is 9 mm, the needling frequency is set to 350 times / min; the thickness of the carbon fiber mesh is 0.9 mm, and the weight of the carbon fiber mesh is 80 g / m 2 ;

[0129] (2) Preparation of unidirectional fabric:

[0130] 12K polyacrylonitrile-based carbon fiber is used for drawing and laying to obtain carbon fiber unidirectional cloth;

[0131] The drawing and laying process is carried out by high-precision drawing equipment (Toray TMT-700, Japan) and laying device (Mayer AT-500, Germany); the tension of the monofilament is 20N / filament; the center spacing of the filament is 0.2mm; the drawing speed is 20m / min; the laying angle is 0°; the thickness of the carbon fiber unidirectional cloth is 0.4mm, and the weight of the carbon fiber unidirectional cloth is 300g / m 2 .

[0132] (3) Preparation of carbon fiber preform:

[0133] (3-1) a laminated needle punching method is used in which a web and a unidirectional fabric are laid in a 0° / 90° staggered manner to form an orthogonal reinforcement structure, thereby obtaining a laminated carbon fiber felt;

[0134] Wherein, in the laminated carbon fiber felt, the number of layers of the carbon fiber web is 21, and the number of layers of the carbon fiber unidirectional cloth is 20.

[0135] (3-2) subjecting the laminated carbon fiber felt to composite needling, and simultaneously subjecting the needling area to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform;

[0136] The composite needling was carried out on a ZN-1200 needling machine, and the composite needling density was set at 25 needles / cm. 2 The needling depth is 12 mm. The needling frequency is controlled in a segmented manner: the initial stage is set at 600 times / min, and the needling time is 20 minutes. As the felt gradually becomes tighter, in order to enhance the effect of the needle on the fiber, the needling frequency is linearly increased from 10 times / min to 900 times / min until the end of the needling.

[0137] The ultrasonic treatment system and high-pressure airflow removal device are integrated during the composite acupuncture process: an industrial-grade ultrasonic generator is used; the output frequency of the ultrasonic treatment system is stable at 40kHz, the power is 300W, and it is equipped with a PZT-8 transducer. The vibration amplitude is precisely controlled within the range of 10±2μm by a servo adjustment system; the compressor used is a screw compressor with a stable output pressure of 0.3MPa and a stable output airflow speed of 50m / s. The airflow is sprayed into the acupuncture area through a customized L-shaped nozzle assembly. The nozzle is made of tungsten carbide alloy to resist high-speed airflow erosion. Its installation angle is set to 45° through 3D simulation optimization to ensure that the airflow coverage width reaches 80mm. The vertical distance between the nozzle and the acupuncture area is controlled at 50mm.

[0138] Among them, the two sets of devices, the ultrasonic treatment system and the high-pressure airflow removal device, are synchronized with the needling machine main shaft through the PLC control system. When the needling needle group moves downward and penetrates the felt body, the ultrasonic generator starts to vibrate synchronously, and the duration is precisely matched with the needling residence time (0.04-0.06s / time); in the needling return stage, the high-pressure airflow valve group is opened, and the airflow is ejected with a pulse duration of 50ms to remove the loose short fibers; when the thickness of the preform reaches 12mm, the needling is stopped, and the preform is processed into a finished preform of 1000mm×1000mm×12mm by the cutting machine.

[0139] Example 2

[0140] This embodiment provides a carbon fiber preform, which is prepared by the following steps:

[0141] (1) Preparation of carbon fiber mesh:

[0142] The fiber raw material is 12K polyacrylonitrile-based carbon fiber (model: T300-12K). The carbon fiber filaments are chopped into 10mm long chopped fibers by a chopped machine. The chopped carbon fibers are combed and needle-punched by a carding machine to obtain a carbon fiber mesh.

[0143] Among them, the needle density of the pre-needling machine is 4 needles / cm 2 The needling depth is 8 mm, the needling frequency is set to 400 times / min; the thickness of the carbon fiber mesh is 1.0 mm, and the weight of the carbon fiber mesh is 100 g / m 2 .

[0144] (2) Preparation of unidirectional fabric:

[0145] 12K polyacrylonitrile-based carbon fiber is used for drawing and laying to obtain carbon fiber unidirectional cloth;

[0146] The drawing and laying process is carried out by high-precision drawing equipment (Toray TMT-700, Japan) and laying device (Mayer AT-500, Germany); the tension of the monofilament is 15N / filament; the center spacing of the filament is 0.1mm; the drawing speed is 40m / min; the laying angle is 0°; the thickness of the carbon fiber unidirectional cloth is 0.33mm, and the weight of the carbon fiber unidirectional cloth is 300g / m 2 .

[0147] (3) Preparation of carbon fiber preform:

[0148] (3-1) a laminated needle punching method is used in which a web and a unidirectional fabric are laid in a 0° / 90° staggered manner to form an orthogonal reinforcement structure, thereby obtaining a laminated carbon fiber felt;

[0149] The laminated carbon fiber felt has a total of 41 layers, the carbon fiber web has 21 layers, and the carbon fiber unidirectional cloth has 20 layers.

[0150] (3-2) subjecting the laminated carbon fiber felt to composite needling, and simultaneously subjecting the needling area to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform;

[0151] The composite needling was carried out on a ZN-1200 needling machine, and the composite needling density was set at 35 needles / cm. 2 The needling depth is 13mm; the needling frequency adopts a segmented control mode: the initial stage is set to 700 times / min, the initial needling time is 30min, and as the felt gradually becomes tighter, in order to enhance the effect of the needle on the fiber, the needling frequency is linearly increased from 25 times / min to 1200 times / min until the end of the needling;

[0152] The ultrasonic treatment system and high-pressure airflow removal device are integrated during the composite needling process: an industrial-grade ultrasonic generator is used; the output frequency of the ultrasonic treatment system is stable at 45kHz, the power is 300W, and it is equipped with a PZT-8 transducer. The vibration amplitude is precisely controlled at 15μm by a laser vibrometer; the compressor used is a screw compressor with a stable output pressure of 0.5MPa and a stable output airflow speed of 250m / s. It is sprayed to the needling area through a customized L-shaped nozzle assembly. The nozzle is made of tungsten carbide alloy to resist high-speed airflow erosion. Its installation angle is set to 35° through three-dimensional simulation optimization to ensure that the airflow coverage width reaches 60mm. The vertical distance between the nozzle and the needling area is controlled at 40mm to achieve high-speed stripping of short fibers.

[0153] Among them, the two sets of devices, the ultrasonic treatment system and the high-pressure airflow removal device, are synchronized with the needling machine main shaft through the PLC control system. When the needling needle group moves downward and penetrates the felt body, the ultrasonic generator starts to vibrate synchronously, and the duration is precisely matched with the needling residence time (0.04-0.06s / time); in the needling return stage, the high-pressure airflow valve group is opened, and the airflow is ejected with a pulse duration of 50ms to remove the loose short fibers; when the thickness of the preform reaches 12mm, the needling is stopped, and the preform is processed into a finished preform of 1000mm×1000mm×12mm by the cutting machine.

[0154] Example 3

[0155] This embodiment provides a carbon fiber preform, which differs from embodiment 2 only in that, in step (1), the density of the needle punching is 12 needles / cm 2 The depth of the acupuncture was 7 mm, the frequency of the acupuncture was 600 times / min, and the other steps were consistent with those in Example 2.

[0156] Example 4

[0157] This embodiment provides a carbon fiber preform, which differs from embodiment 2 only in that, in step (1), the density of the needle punching is 4 needles / cm 2 The depth of the acupuncture was 14 mm, the frequency of the acupuncture was 200 times / min, and the other steps were consistent with those in Example 2.

[0158] Example 5

[0159] This embodiment provides a carbon fiber preform, which differs from Example 2 only in that, in step (2), the process parameters of the drawing and laying include: the tension of the single filament is 5N / filament; the center spacing of the filament is 1.0mm; the drawing speed is 50m / min; and the other steps are consistent with Example 2.

[0160] Example 6

[0161] This embodiment provides a carbon fiber preform, which differs from Example 2 only in that, in step (2), the process parameters of the drawing and laying include: the tension of the single filament is 50N / filament; the center spacing of the filament is 0.1mm; the drawing speed is 5m / min; and the other steps are consistent with Example 2.

[0162] Example 7

[0163] This embodiment provides a carbon fiber preform, which differs from Example 2 only in that, in step (2), the frequency of needling in the first stage is 500 times / min, and the needling time of the first stage is 10 minutes; the frequency of needling in the second stage is 1500 times / min, and the needling time of the first stage is 40 minutes; the other steps are consistent with Example 2.

[0164] Example 8

[0165] This embodiment provides a carbon fiber preform, which differs from Example 2 only in that, in step (2), the frequency of needling in the first stage is 1200 times / min, and the needling time of the first stage is 10 minutes; the frequency of needling in the second stage is 700 times / min, and the needling time of the first stage is 40 minutes; the other steps are consistent with Example 2.

[0166] Example 9

[0167] This embodiment provides a carbon fiber preform, which differs from embodiment 2 only in that, in step (3), the frequency of the ultrasonic wave is 10 kHz, the power of the ultrasonic wave is 60 W, and the vibration amplitude of the ultrasonic wave is 2 μm; the other steps are consistent with embodiment 2.

[0168] Example 10

[0169] This embodiment provides a carbon fiber preform, which differs from embodiment 2 only in that, in step (3), the frequency of the ultrasonic wave is 60 kHz, the power of the ultrasonic wave is 120 W, and the vibration amplitude of the ultrasonic wave is 20 μm; the other steps are consistent with embodiment 2.

[0170] Example 11

[0171] This embodiment provides a carbon fiber preform, which differs from Example 2 only in that, in step (3), the working pressure of the airflow is 0.1 MPa; the speed of the airflow is 50 m / s, the diameter of the nozzle is 6.0 mm, and the distance between the end face of the nozzle and the needle-punched area is 5 mm; the other steps are consistent with Example 2.

[0172] Example 12

[0173] This embodiment provides a carbon fiber preform, which differs from Example 2 only in that, in step (3), the working pressure of the airflow is 6.0 MPa; the speed of the airflow is 600 m / s, the diameter of the nozzle is 0.1 mm, and the distance between the end face of the nozzle and the needle-punched area is 60 mm; the other steps are consistent with Example 2.

[0174] Comparative Example 1

[0175] This comparative example provides a carbon fiber preform, which differs from Example 4 only in that in step (3-2), the needle-punched area is no longer subjected to ultrasonic vibration treatment and airflow impact treatment, and the other steps and preparation conditions are the same as those in Example 4. After corresponding cutting, a carbon fiber preform with a specification of 1000mm×1000mm×12mm is obtained.

[0176] Comparative Example 2

[0177] This comparative example provides a carbon fiber preform, which is prepared by the following steps:

[0178] (1) Preparation of carbon fiber mesh:

[0179] The fiber raw material is 12K polyacrylonitrile-based carbon fiber (model: T300-12K). The carbon fiber filaments are chopped into 10mm long chopped fibers by a chopped machine. The chopped carbon fibers are combed and needle-punched by a carding machine to obtain a carbon fiber mesh.

[0180] Among them, the needle density of the pre-needling machine is 4 needles / cm 2 The needling depth is 14 mm, and the needling frequency is set to 200 times / min to ensure the initial consolidation of the chopped fibers while retaining more free fibers; the thickness of the carbon fiber mesh is 1.0 mm, and the weight of the carbon fiber mesh is 100 g / m 2 ;

[0181] (2) Preparation of unidirectional fabric:

[0182] 12K polyacrylonitrile-based carbon fiber is used for drawing and laying to obtain carbon fiber unidirectional cloth;

[0183] The drawing and laying process is carried out by high-precision drawing equipment (Toray TMT-700, Japan) and laying device (Mayer AT-500, Germany); the tension of the monofilament is 20N / filament; the center spacing of the filament is 0.2mm; the drawing speed is 20m / min; the laying angle is 0°; the thickness of the carbon fiber unidirectional cloth is 0.4mm, and the weight of the carbon fiber unidirectional cloth is 300g / m 2 .

[0184] (3) Preparation of carbon fiber preform:

[0185] (3-1) a laminated needle punching method is used in which a web and a unidirectional fabric are laid in a 0° / 90° staggered manner to form an orthogonal reinforcement structure, thereby obtaining a laminated carbon fiber felt;

[0186] The laminated carbon fiber felt has a total of 41 layers, the carbon fiber web has 21 layers, and the carbon fiber unidirectional cloth has 20 layers.

[0187] (3-2) subjecting the laminated carbon fiber felt to composite needling, and simultaneously subjecting the needling area to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform;

[0188] The composite needling was carried out on a ZN-1200 needling machine, and the composite needling density was set at 23 needles / cm. 2 The acupuncture depth was 13 mm; the acupuncture frequency was set at 900 times / min and maintained for 50 min until the end of acupuncture;

[0189] The ultrasonic treatment system and high-pressure airflow removal device are integrated during the composite needling process: an industrial-grade ultrasonic generator is used; the output frequency of the ultrasonic treatment system is stable at 45kHz, the power is 300W, and it is equipped with a PZT-8 transducer. The vibration amplitude is precisely controlled at 15μm by a laser vibrometer; the compressor used is a screw compressor with a stable output pressure of 0.5MPa and a stable output airflow speed of 250m / s. It is sprayed to the needling area through a customized L-shaped nozzle assembly. The nozzle is made of tungsten carbide alloy to resist high-speed airflow erosion. Its installation angle is set to 35° through three-dimensional simulation optimization to ensure that the airflow coverage width reaches 60mm. The vertical distance between the nozzle and the needling area is controlled at 40mm to achieve high-speed stripping of short fibers.

[0190] Among them, the two sets of devices, the ultrasonic treatment system and the high-pressure airflow removal device, are synchronized with the needling machine main shaft through the PLC control system. When the needling needle group moves downward and penetrates the felt body, the ultrasonic generator starts to vibrate synchronously, and the duration is precisely matched with the needling residence time (0.04-0.06s / time); in the needling return stage, the high-pressure airflow valve group is opened, and the airflow is ejected with a pulse duration of 50ms to remove the loose short fibers; when the thickness of the preform reaches 12mm, the needling is stopped, and the preform is processed into a finished preform of 1000mm×1000mm×12mm by the cutting machine.

[0191] Comparative Example 3

[0192] This comparative example provides a carbon fiber preform, which is prepared by the following steps:

[0193] (1) Preparation of carbon fiber mesh:

[0194] The fiber raw material is 12K polyacrylonitrile-based carbon fiber (model: T300-12K). The carbon fiber filaments are chopped into 10mm long chopped fibers by a chopped machine. The chopped carbon fibers are combed and needle-punched by a carding machine to obtain a carbon fiber mesh.

[0195] Among them, the needle density of the pre-needling machine is 4 needles / cm 2 The needling depth is 14 mm, the needling frequency is set to 200 times / min; the thickness of the carbon fiber mesh is 1.0 mm, and the weight of the carbon fiber mesh is 100 g / m 2 ;

[0196] (2) Preparation of unidirectional fabric:

[0197] 12K polyacrylonitrile-based carbon fiber is used for drawing and laying to obtain carbon fiber unidirectional cloth;

[0198] The drawing and laying process is carried out by high-precision drawing equipment (Toray TMT-700, Japan) and laying device (Mayer AT-500, Germany); the tension of the monofilament is 20N / filament; the center spacing of the filament is 0.2mm; the drawing speed is 20m / min; the laying angle is 0°; the thickness of the carbon fiber unidirectional cloth is 0.4mm, and the weight of the carbon fiber unidirectional cloth is 300g / m 2 .

[0199] (3) Preparation of carbon fiber preform:

[0200] (3-1) a laminated needle punching method is used in which a web and a unidirectional fabric are laid in a 0° / 90° staggered manner to form an orthogonal reinforcement structure, thereby obtaining a laminated carbon fiber felt;

[0201] Wherein, in the laminated carbon fiber felt, the number of layers of the carbon fiber web is 21, and the number of layers of the carbon fiber unidirectional cloth is 20.

[0202] (3-2) subjecting the laminated carbon fiber felt to composite needling to obtain the carbon fiber preform;

[0203] The composite needling was carried out on a ZN-1200 needling machine, and the composite needling density was set at 25 needles / cm. 2 The needling depth is 12 mm; the needling frequency adopts a segmented control mode: the initial stage is set to 600 times / min, the initial needling time is 20 minutes, and as the felt gradually becomes tighter, in order to enhance the effect of the needling needle on the fiber, the needling frequency is linearly increased from 10 times / min to 900 times / min until the needling ends.

[0204] Comparative Example 4

[0205] This comparative example provides a carbon fiber preform, which differs from Example 4 only in that the segmented control mode is not adopted, and the needling frequency is maintained at 600 times / min for 50 minutes until the needling is completed. The other steps and preparation conditions are the same as those in Example 4. After corresponding cutting, a carbon fiber preform with a specification of 1000mm×1000mm×12mm is obtained.

[0206] Comparative Example 5

[0207] This comparative example provides a carbon fiber preform, which differs from Example 4 only in that the segmented control mode is not adopted, and the needling frequency is maintained at 900 times / min for 50 minutes until the needling is completed. The other steps and preparation conditions are the same as those in Example 4. After corresponding cutting, a carbon fiber preform with a specification of 1000mm×1000mm×12mm is obtained.

[0208] Comparative Example 6

[0209] This comparative example provides a carbon fiber preform, which is prepared by the following steps:

[0210] (1) Preparation of carbon fiber mesh:

[0211] The fiber raw material is 12K polyacrylonitrile-based carbon fiber (model: T300-12K). The carbon fiber filaments are chopped into 10mm long chopped fibers by a chopped machine. The chopped carbon fibers are combed and needle-punched by a carding machine to obtain a carbon fiber mesh.

[0212] Among them, the needle density of the pre-needling machine is 4 needles / cm 2 The needling depth is 14 mm, and the needling frequency is set to 200 times / min to ensure the initial consolidation of the chopped fibers while retaining more free fibers; the thickness of the carbon fiber mesh is 1.0 mm, and the weight of the carbon fiber mesh is 100 g / m 2 ;

[0213] (2) Preparation of unidirectional fabric:

[0214] 12K polyacrylonitrile-based carbon fiber is used for drawing and laying to obtain carbon fiber unidirectional cloth;

[0215] The drawing and laying process is carried out by high-precision drawing equipment (Toray TMT-700, Japan) and laying device (Mayer AT-500, Germany); the tension of the monofilament is 20N / filament; the center spacing of the filament is 0.2mm; the drawing speed is 20m / min; the laying angle is 0°; the thickness of the carbon fiber unidirectional cloth is 0.4mm, and the weight of the carbon fiber unidirectional cloth is 300g / m 2 .

[0216] (3) Preparation of carbon fiber preform:

[0217] The laminated needle punching method is to use a layer of mesh and a layer of unidirectional cloth, wherein the carbon fiber unidirectional cloth is stacked at 0° / 90° to form an orthogonal reinforcement structure, thereby obtaining a laminated carbon fiber felt; wherein, the laminated carbon fiber felt has a total of 41 layers, of which the carbon fiber mesh has 21 layers and the carbon fiber unidirectional cloth has 20 layers. Composite needle punching stage: the needle punching density is increased to 23 needles / cm 2The needling depth was 13 mm and the needling frequency was 900 times / min. Needling was stopped when the preform thickness reached 12 mm. After cutting, a finished carbon fiber preform of 1000 mm × 1000 mm × 12 mm was obtained.

[0218] Test Case

[0219] Test samples: the carbon fiber preforms provided in Examples 1 to 12 and the carbon fiber preforms provided in Comparative Examples 1 to 6.

[0220] Test method:

[0221] (1) Density: Where ρ represents the density (g / cm 3 ); m represents the sample mass (g); L, W, and H represent the length, width, and thickness of the sample (cm), respectively.

[0222] The density test method is carried out in accordance with the “geometric method” specified in GB / T 1446-2005 “General principles for test methods for properties of fiber reinforced plastics”, that is, the volume is calculated by measuring the mass of the sample and its geometric dimensions, and then the density is obtained.

[0223] (2) The test method of CV value (coefficient of variation) refers to GB / T 8170-2008 "Numerical Rounding Rules and Representation and Determination of Limit Values" and the General Rules of Statistical Analysis. The density data of carbon fiber preform samples taken from different areas are statistically analyzed, and the standard deviation and sample mean are calculated. The coefficient of variation is calculated based on this:

[0224] Coefficient of variation CV value: Wherein, CV value represents the coefficient of variation; S represents the standard deviation; X: the standard density of the sample (g / cm 3 ):

[0225] The smaller the CV value, the higher the structural uniformity of the carbon fiber preform and the better the needle punching stability. The present invention uses a 9-point distribution method to obtain density values in different areas of the sample and calculates the CV value according to the above formula as an evaluation index for the preform molding quality.

[0226] (3) Interlaminar shear strength: The test method for interlaminar shear strength refers to ASTM D2344 / D2344M-21 "Standard test method for interlaminar shear strength of polymer-based composite materials by short beam method" or GB / T 3357-2014 "Test method for interlaminar shear strength of fiber-reinforced plastics". The preform sample is subjected to shear failure test using the short beam shear method. The calculation formula is as follows:

[0227]

[0228] Where τ represents the interlaminar shear strength in MPa; F represents the failure load in N; b represents the specimen width in mm; h represents the specimen thickness in mm

[0229] All the above tests were carried out in the laboratory at a temperature of 23±2°C and a humidity of 50±5%.

[0230] The specific test results are shown in Table 1 below:

[0231] Table 1

[0232]

[0233]

[0234] As shown in Table 1, the density of the carbon fiber preform of the present invention is 0.4-0.5 g / cm 3 The coefficient of variation CV value is less than 4%, which indicates that the thickness of the preform and the uniformity of fiber distribution are good; the interlaminar shear strength of the carbon fiber preform is above 6.5 MPa, which indicates that the interlaminar bonding force of the carbon fiber preform is significantly improved.

[0235] A comparison of Example 1 and Comparative Example 1 shows that even when the ultrasonic vibration and airflow impact treatments are omitted from the needled area and the composite needling process is merely improved, the average interlaminar shear strength is significantly reduced. A comparison of Example 1 and Comparative Example 2 shows that even when the ultrasonic vibration and airflow impact treatments are applied to the needled area without composite needling, the average interlaminar shear strength is also significantly reduced. A comparison of Example 1 and Comparative Example 3 shows that even when the gradient needling frequency is increased without ultrasonic vibration and airflow impact treatments, the average interlaminar shear strength is also significantly reduced.

[0236] At the same time, the three test results show that the simultaneous action of the two methods can achieve a removal rate of over 98% for particles larger than 6μm. In addition, the compressed gas cleaning process is non-contact, and the nozzle is always isolated from the needling area, eliminating the need for mechanical contact between the fiber and the needle plate, thus avoiding direct damage to the fiber caused by traditional contact cleaning.

[0237] A comparison of Example 1 and Comparative Examples 4-5 shows that the laminated needling process uses only a single needling frequency. The results show that the interlayer shear strength of the preform in Comparative Example 4 is only 5.7 MPa. Although the fiber breakage rate is controlled at 9%, the CV value of the density uniformity of the felt reaches 7.4%, indicating that the low frequency leads to insufficient fiber entanglement. The interlayer shear strength of the preform in Comparative Example 5 is 6.1 MPa. Broken fibers clog the needle holes, resulting in a 40% increase in needling resistance and requiring frequent shutdowns for cleaning. The results show that the constant frequency process cannot take into account both fiber protection and sufficient entanglement. The present invention improves the interlayer shear performance of the carbon fiber preform by more than 20% by gradient control of the needling frequency.

[0238] In summary, the present invention aims to address the issues of insufficient interlayer bonding and easy delamination in carbon-carbon composite preforms by optimizing the needling process and short fiber removal method to improve interlayer bonding and enhance the overall mechanical properties of the carbon-carbon composite. Specifically, this invention includes the following aspects:

[0239] 1. Optimize the needling density ratio to enhance interlayer fiber entanglement: a) By adjusting the ratio of the single-layer needling density to the overall needling density in multi-layer composites, the single-layer needling density is reduced, so that some fibers remain free, thereby providing more interlayer interlaced entangled fibers in multi-layer composites; b) By optimizing the single-layer needling density to form a reasonable ratio with the final overall needling density, the internal entanglement of the single layer is ensured to be stable, while retaining sufficient free fibers for interlayer entanglement.

[0240] 2. Optimize the needling frequency to reduce the generation of short fibers between layers: a) By adjusting the matching relationship between the single-layer needling frequency and the multi-layer composite needling frequency, the formation of short fibers is reduced, thereby reducing the negative impact of short fibers on the bonding strength between layers. b) During the single-layer needling stage, a lower frequency is used to reduce carbon fiber breakage, thereby reducing the amount of short fibers generated; during the multi-layer composite needling stage, the needling frequency is increased to enhance interlayer entanglement and maximize interlayer bonding strength. c) This method ensures improved interlayer bonding strength while avoiding the lubrication caused by excessive short fibers, further reducing the risk of delamination.

[0241] 3. Use ultrasonic vibration + air flow impact to remove short fibers on the interface: a) Short fibers are inevitably generated during the needling process, so the present invention further introduces ultrasonic vibration + air flow impact technology to remove short fibers on the interface between layers after needling; this method can effectively reduce the residual short fibers between layers, avoid their weakening effect on the interlayer bonding force, and thus improve the overall bonding strength.

[0242] Therefore, through the above method, the present invention can optimize the needling frequency, reduce the generation of short fibers, and effectively remove the interlayer short fibers while controlling the fiber entanglement state, thereby significantly improving the interlayer bonding strength of the carbon-carbon composite material, reducing the risk of delamination, and improving the overall mechanical properties.

[0243] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the interlaminar shear performance of a carbon fiber preform, characterized in that: The method comprises: The carbon fiber filaments are sequentially chopped, carded into a web and needle-punched to obtain a carbon fiber mesh; the carbon fiber filaments are drawn and laid to obtain a carbon fiber unidirectional fabric; Cross-laying the carbon fiber web and the carbon fiber unidirectional fabric to obtain a laminated carbon fiber felt; The laminated carbon fiber felt is subjected to composite needle punching, and the needle punched area is subjected to ultrasonic vibration treatment and air flow impact treatment to obtain the carbon fiber preform.

2. The method for improving the interlaminar shear performance of a carbon fiber preform according to claim 1, characterized in that: The carbon fiber filaments are polyacrylonitrile-based carbon fibers; Preferably, the length of the carbon fiber filaments obtained after the chopped fibers is 5 to 20 mm; Preferably, during the preparation of the carbon fiber mesh, the density of the needle punching is 5 to 10 needles / cm 2 The acupuncture depth is 8 to 12 mm, and the acupuncture frequency is 300 to 500 times / min; Preferably, the thickness of the carbon fiber mesh is 0.7-1.0 mm, and the weight of the carbon fiber mesh is 70-120 g / m 2 .

3. The method for improving the interlaminar shear performance of a carbon fiber preform according to claim 1, characterized in that: The process parameters of the wire drawing and laying include: the tension of the monofilament is 5 to 50 N / filament; the center spacing of the filaments is 0.1 to 1.0 mm; the wire drawing speed is 5 to 50 m / min; the laying angle is -2 to 2°; Preferably, the thickness of the carbon fiber unidirectional cloth is 0.3-0.6 mm, and the weight of the carbon fiber unidirectional cloth is 200-400 g / m 2 .

4. The method for improving the interlaminar shear performance of a carbon fiber preform according to claim 1, wherein: The cross-ply laying includes: using a carbon fiber web and a carbon fiber unidirectional cloth in an alternating laying mode, with the carbon fiber unidirectional cloth being orthogonally laid at 0° and 90°; Preferably, in the laminated carbon fiber felt, the number of layers of the carbon fiber web is 10 to 25, and the number of layers of the carbon fiber unidirectional cloth is 10 to 25.

5. The method for improving the interlaminar shear performance of a carbon fiber preform according to claim 1, wherein: During the composite needling of the laminated carbon fiber felt, the needling density is 20 to 25 needles / cm 2 The acupuncture depth is 10 to 15 mm; Preferably, during the composite needling of the laminated carbon fiber felt, the needling is performed in stages: the frequency of the needling in the first stage is 600 to 800 times / min; the frequency of the needling in the second stage is 800 to 1200 times / min; Preferably, the acupuncture time of the first stage is 20 to 30 minutes; Preferably, the acupuncture time of the second stage is 20 to 30 minutes.

6. The method for improving the interlaminar shear performance of a carbon fiber preform according to claim 1, wherein: The ultrasonic vibration treatment includes: utilizing ultrasonic waves emitted by an ultrasonic generator, converting electrical energy into mechanical energy through a transducer, and transmitting the ultrasonic vibration treatment to the acupuncture area; and the ultrasonic vibration treatment is initiated when the needles penetrate the laminated carbon fiber felt, continues while the needles remain in the laminated carbon fiber felt, and ends when the needles begin to return and leave the carbon fiber felt; Preferably, the frequency of the ultrasonic wave is 20 to 50 kHz; Preferably, the power of the ultrasonic wave is 200-400W; Preferably, the vibration amplitude of the punctured area is 5 to 15 μm.

7. The method for improving the interlaminar shear performance of a carbon fiber preform according to claim 1, wherein: The airflow impact treatment includes: using a compressor to generate airflow and guiding the airflow to the needling area through a nozzle; and the airflow impact treatment starts from the needling return stage, lasts during the period of the needling needles recovering, and ends before the needling needles re-enter the carbon fiber felt. Preferably, the working pressure of the airflow is 0.5-5.0 MPa; the speed of the airflow is 100-500 m / s; the injection pulse duration of the airflow is 40-70 ms; Preferably, the nozzle has a diameter of 0.5 to 5.0 mm, and the distance between the end face of the nozzle and the acupuncture area is 10 to 50 mm.

8. A carbon fiber preform, characterized in that: The carbon fiber preform is prepared by the method for improving the interlaminar shear performance of a carbon fiber preform according to any one of claims 1 to 7.

9. The carbon fiber preform according to claim 8, characterized in that: The density of the carbon fiber preform is 0.38-0.52 g / cm 3 ; Preferably, the coefficient of variation (CV) value of the carbon fiber preform is 4% or less.

10. The carbon fiber preform according to claim 8, characterized in that: The interlaminar shear strength of the carbon fiber preform is greater than 5.5 MPa, preferably greater than 6.5 MPa.

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