A method for improving interlaminar shear properties of carbon fiber preforms and carbon fiber preforms prepared thereby

Abstract

The application provides a method for improving interlayer shear performance of a carbon fiber prepreg and a carbon fiber prepreg prepared by the method, and relates to the technical field of carbon-carbon composite materials. The method comprises the following steps: sequentially performing short cutting, carding and needling on carbon fiber filaments to obtain a carbon fiber web; performing wire drawing and laying on the carbon fiber filaments to obtain a carbon fiber unidirectional cloth; cross-laminating and laying the carbon fiber web and the carbon fiber unidirectional cloth to obtain a laminated carbon fiber felt; and performing composite needling on the laminated carbon fiber felt, and simultaneously performing ultrasonic vibration treatment and airflow impact treatment on the needled area to obtain the carbon fiber prepreg. The method adjusts the ratio of single-layer needling density and overall needling density, enhances the interlayer bonding force, controls the generation of short fibers by adjusting the needling frequency, reduces the negative influence of the short fibers on the interlayer bonding force by using ultrasonic vibration and airflow impact, and thus improves the overall strength and reliability of the carbon fiber prepreg.

Description

Technical Field

[0001] This invention relates to the technical field of carbon-carbon composite materials, and more particularly to a method for improving the interlaminar shear properties of carbon fiber preforms and the carbon fiber preforms prepared therefrom. Background Technology

[0002] Carbon-carbon composites are high-performance materials composed of carbon fiber reinforced carbon matrix. Due to their high-temperature stability, high specific strength, and thermal shock resistance, they are widely used in aerospace, braking systems, and high-end industrial fields. Their preparation typically involves multiple steps, including preform preparation, carbonization, and densification. Currently, the final product exhibits delamination issues during use, which stem from problems in the preform preparation process. In the preform preparation process, single-layer carbon fiber felt is first prepared using needle-punching reinforcement technology. These needle-punched single-layer carbon fiber felts are then stacked together and needle-punched again. Due to limitations in current technology, the interlayer bonding of these stacked needle-punched preforms is weak, leading to delamination in the final product during use.

[0003] Current methods for preparing carbon fiber preforms mainly include the following steps:

[0004] (1) Single-layer needle punching: 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 needle punching: The multi-layer structure after stacking is then needle punched again. The two adjacent independent needle punching felts contribute free fibers at the same time, and they become entangled under the action of needle punching, which is used for the bonding between layers. The multi-layer independent carbon fiber needle punching felts are transformed into a whole carbon fiber needle punching felt, which is a needle punching preform.

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

[0008] (I) Insufficient free fibers at the interlayer interface result in a lack of fibers for interlayer entanglement: a) In the current process, each layer of carbon short fiber felt is needle-punched individually before multilayer composite, which results in most fibers already forming entanglement within the single layer, lacking sufficient free fibers for interlayer cross-entanglement; b) Due to the insufficient number of free fibers between layers, even if the overall needle-punching density is increased after multilayer composite, it is not possible to effectively enhance the interlayer bonding force, and delamination still easily occurs in the end.

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

[0010] (III) Limitations of simply increasing the overall needle density and needle frequency: a) Insufficient free fibers. Increasing the needle density alone has limitations. That is, only by increasing the overall needle density can the interlayer bonding force be enhanced. However, due to the lack of sufficient free fibers for entanglement, simply increasing the needle density can only act on the existing entanglement area and cannot effectively improve the interlayer bonding problem; b) Excessive needle frequency leads to too many broken fibers, which affects the interlayer bonding strength.

[0011] Therefore, in existing needle-punching processes, because the single-layer carbon fiber needle-punched felt is individually needle-punched before lamination, the degree of interlayer fiber entanglement is low, leading to a risk of interlayer delamination in the prepared carbon-carbon composite material. Furthermore, short fibers generated during needle-punching remain at the interlayer interface, potentially acting as a lubricant and further reducing interlayer bonding strength. Due to these aforementioned problems in traditional processes, insufficient interlayer entanglement easily leads to interlayer cracking or delamination during subsequent high-temperature treatment and use, affecting product quality.

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

[0013] The purpose of this invention is to provide a method for improving the interlaminar shear properties of carbon fiber preforms and the carbon fiber preforms prepared therefrom. This invention addresses the problems of insufficient interlaminar bonding and easy delamination in carbon-carbon composite preforms by optimizing the needle punching process and short fiber removal method to improve interlaminar bonding and enhance the overall mechanical properties of carbon-carbon composites. This invention primarily solves the delamination problem caused by insufficient interlaminar bonding in carbon-carbon composite preforms during the needle punching process.

[0014] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

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

[0016] Carbon fiber filaments are sequentially chopped, combed into a web, and needle-punched to obtain a carbon fiber web; carbon fiber filaments are then drawn and laid to obtain a carbon fiber unidirectional fabric.

[0017] The carbon fiber mesh and carbon fiber unidirectional fabric are cross-layered and laid to obtain the laminated carbon fiber felt.

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

[0019] Furthermore, the carbon fiber filament is polyacrylonitrile-based carbon fiber.

[0020] Furthermore, the length of the carbon fiber filaments obtained after scissor cutting is 5–20 mm.

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

[0022] Furthermore, the thickness of the carbon fiber mesh is 0.7–1.0 mm, and the basis weight of the carbon fiber mesh is 70–120 g / m². 2 .

[0023] Furthermore, the carbon fiber filament is a continuous filament that has not been chopped.

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

[0025] Furthermore, the thickness of the unidirectional carbon fiber fabric is 0.3–0.6 mm, and the basis weight of the unidirectional carbon fiber fabric is 200–400 g / m². 2 .

[0026] Furthermore, the cross-layering includes: using an alternating layering method of one carbon fiber mesh and one carbon fiber unidirectional fabric, with the carbon fiber unidirectional fabrics separated only by one carbon fiber mesh being orthogonally interlaced at 0° and 90°.

[0027] Furthermore, in the laminated carbon fiber felt, the number of layers of the carbon fiber mesh is 10 to 25, and the number of layers of the carbon fiber unidirectional fabric 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 precast structure.

[0029] Furthermore, in the stacked carbon fiber felt, the preferred layering sequence is to use carbon fiber mesh as the starting and ending layer, with the intermediate layer consisting of alternating layers of unidirectional fabric and mesh (i.e., the intermediate layer uses an alternating layering method of one carbon fiber mesh and one carbon fiber unidirectional fabric), so that both the upper and lower surfaces are flexible mesh structures, which is beneficial to the stability of the needle punching initiation and termination.

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

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

[0032] Furthermore, during the composite needle punching process of the laminated carbon fiber felt, a staged needle punching method is adopted: the frequency of the first stage needle punching is 600-800 times / min; the frequency of the second stage needle punching is 800-1200 times / min.

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

[0034] Furthermore, the acupuncture time for 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 precast body, the number of layers, and the needle density to achieve the best interlayer entanglement effect.

[0036] Furthermore, the ultrasonic vibration treatment includes: using an ultrasonic generator to emit ultrasonic waves, and converting electrical energy into mechanical energy through a transducer, and transmitting it to the area to be needled; and the ultrasonic vibration treatment is started when the needle is inserted into the stacked carbon fiber felt, continues for the period of time when the needle remains in the stacked carbon fiber felt, and ends when the needle begins to return and leaves the carbon fiber felt.

[0037] Furthermore, the frequency of the ultrasound is 20–50 kHz.

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

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

[0040] Furthermore, the airflow impact treatment includes: generating airflow using a compressor and guiding the airflow to the needled area through a nozzle; and the airflow impact treatment starts from the needle return phase, continues during the time period of the needle return process, and ends before the next needle re-insertion of the carbon fiber.

[0041] Furthermore, the working pressure of the airflow is 0.5–5.0 MPa; the velocity of the airflow is 100–500 m / s; and the jet 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 area punctured by the needle 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 properties of the carbon fiber preform as described in the first aspect.

[0044] Furthermore, the density of the carbon fiber preform is 0.38–0.52 g / cm³. 3 .

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

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

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

[0048] (1) Optimize the needle punching density ratio to improve interlayer fiber entanglement: The method described in this 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 in a free state, providing more fibers for interlayer bonding after multilayer composite, and increasing the needle punching density during multilayer composite to enhance interlayer bonding force.

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

[0050] (3) Using ultrasonic vibration + airflow impact to remove short fibers at the interface: After multi-layer composite needle punching, the method of the present invention uses ultrasonic vibration + airflow impact to effectively remove short fibers at the interlayer interface and prevent them from having a lubricating effect on the interlayer bonding force; ultrasonic vibration causes loose short fibers to detach from the fiber network structure, and airflow impact further removes these short fibers and improves the interlayer bonding force.

[0051] (4) Comprehensive optimization of needle punching process to improve interlayer bonding strength of carbon-carbon composite materials: The method described in this invention reduces the risk of delamination from the source by optimizing the needle punching density ratio, adjusting the needle punching frequency, and removing short fibers, thereby improving the interlayer bonding strength and overall mechanical properties of carbon-carbon composite materials. Attached Figure Description

[0052] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the needle punching process for the method of improving the interlaminar shear properties of carbon fiber preforms according to the present invention.

[0054] Among them, 1 is the compressor, 2 is the pressure regulating valve, 3 is the high-pressure air tank, 4 is the adjustable nozzle, 5 is the needle plate, and 6 is the ultrasonic generator. Detailed Implementation

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

[0056] It should be noted that specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many ways other than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0057] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

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

[0060] Carbon fiber filaments are sequentially chopped, combed into a web, and needle-punched to obtain a carbon fiber web; carbon fiber filaments are then drawn and laid to obtain a carbon fiber unidirectional fabric.

[0061] The carbon fiber mesh and carbon fiber unidirectional fabric are cross-layered and laid to obtain the laminated carbon fiber felt.

[0062] The laminated carbon fiber felt is needle-punched, and the needle-punched areas are simultaneously subjected to ultrasonic vibration and airflow impact treatment (e.g., Figure 1 As shown in the figure, the carbon fiber preform is obtained.

[0063] In this invention, by optimizing needle punching process parameters and introducing ultrasonic vibration and airflow impact treatment, the interlayer bonding strength of carbon-carbon composite preforms is significantly improved, and delamination is reduced. First, by adjusting the needle punching density ratio between single-layer and multi-layer composites, the effective fibers used for interlayer entanglement are rationally controlled, allowing for more complete interweaving and improving interlayer bonding strength. Second, by adjusting the needle punching frequency in single-layer and multi-layer composite needle punching, the generation of short interlayer fibers is effectively controlled, reducing the lubrication effect and interface defects that short fibers may cause during interlayer bonding. Furthermore, ultrasonic vibration and airflow impact technology are used to remove broken fibers at the interface, eliminating potential weak bonding areas and making the interlayer bonding tighter. The synergistic effect of this series of optimization measures gives carbon-carbon composites superior structural stability and mechanical properties under high temperature and high load environments, greatly enhancing their engineering application value.

[0064] As an optional implementation, in the preparation process of the carbon fiber mesh and carbon fiber unidirectional fabric, the carbon fiber filaments are polyacrylonitrile-based carbon fibers.

[0065] As an optional implementation, in the preparation process of the carbon fiber mesh, the length of the carbon fiber filaments obtained after shaving 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 this invention, the length of the carbon fiber filaments obtained after shaving can be selected according to the requirements for layup thickness and mechanical properties in subsequent steps. A single length or a mixture of lengths can be used to ensure good uniformity of the length of the shaving carbon fiber, which is beneficial to the uniform distribution and interaction of fibers during the subsequent needle punching process.

[0067] As an optional implementation, in the preparation process of the carbon fiber mesh, the needle punching density is 5-10 needles / cm. 2 For example, it could be 5 needles / cm 2 6 needles / cm 2 7 needles / cm 2 8 needles / cm 2 9 needles / cm 2 10 stitches / cm 2 wait.

[0068] In this invention, the needle-punching density range enables the chopped carbon fibers to initially form a certain network structure with preliminary integrity, while preventing excessive fiber entanglement at this stage, thus preserving enough free fibers for subsequent interlayer entanglement.

[0069] As an optional implementation, during the preparation of the carbon fiber mesh, the depth of the needle punching is 8 to 12 mm, for example, it can be 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, etc.

[0070] In this invention, the depth range of the needle insertion ensures that the needle can penetrate the fiber layer, allowing the fibers to initially interweave together.

[0071] As an optional implementation, during the preparation of the carbon fiber mesh, the frequency of the needle punching 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 this invention, the frequency range of the acupuncture is kept at a relatively low level to further reduce the generation of short fibers.

[0073] As an optional implementation, the thickness of the carbon fiber mesh is 0.7 to 1.0 mm, for example, it can be 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 implementation, the basis weight of the carbon fiber mesh is 70–120 g / m². 2 For example, it could 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 implementation, in the preparation process of the carbon fiber unidirectional fabric, the carbon fiber filaments are continuous filaments that have not been chopped.

[0076] As an optional implementation, in the preparation process of the carbon fiber unidirectional fabric, the drawing and laying process is carried out using high-precision drawing equipment (such as the Japanese Toray TMT-700 model) and laying device (such as the German Mayer AT-500).

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

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

[0079] As an optional implementation, 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 implementation, the center-to-center spacing of the filaments is 0.1 to 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 implementation, 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 implementation, the layup angle is -2 to 2°, for example, it can be -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 implementation, the thickness of the carbon fiber unidirectional fabric is 0.3 to 0.6 mm, for example, it can be 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 implementation, the basis weight of the carbon fiber unidirectional fabric is 200–400 g / m². 2 For example, it could 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 implementation, the cross-layering includes: using an alternating layering method of one carbon fiber mesh and one carbon fiber unidirectional fabric, with the carbon fiber unidirectional fabrics separated by only one carbon fiber mesh being orthogonally interlaced at 0° and 90°.

[0086] In this invention, unidirectional fabric and mesh are stacked alternately, and the unidirectional fabrics are laid in a 0° / 90° alternating manner. This stacking method can enhance the mechanical properties of the precast structure in multiple directions. During the laying process, it is necessary to ensure the accurate positioning of each layer, avoid misalignment or wrinkles, and ensure good interlayer contact.

[0087] As an optional implementation, the carbon fiber mesh in the laminated carbon fiber felt has 10 to 25 layers, for example, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25 layers, etc.

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

[0090] As an optional implementation, the preferred layering sequence of the stacked carbon fiber felt is to use a carbon fiber mesh as the starting and ending layer, with the intermediate layer consisting of alternating layers of unidirectional fabric and mesh (i.e., the intermediate layer uses an alternating layering method of one carbon fiber mesh and one carbon fiber unidirectional fabric), so that both the upper and lower surfaces are flexible mesh structures, which is beneficial to the stability of the needle punching start and end.

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

[0092] As an optional implementation, during the composite needle punching process of the laminated carbon fiber felt, the needle punching density is 20-25 needles / cm. 2 For example, it could be 20 stitches / cm 2 21 stitches / cm 2 22 stitches / cm 2 23 stitches / cm 2 24 stitches / cm 2 25 stitches / cm 2 wait.

[0093] In this invention, during the composite needle punching process of the laminated carbon fiber felt, the needle punching density needs to be based on the previous single-layer needle punching density (5-10 needles / cm). 2 Adjustments were made to increase the overall acupuncture density to 20-25 needles / cm². 2This involves adjusting the ratio of single-layer needle-punching density to the overall needle-punching density in multi-layer composites. By increasing the needle-punching density, the fibers between layers can fully interweave and entangle, thus enhancing the interlayer bonding force.

[0094] As an optional implementation, during the composite needle punching process of the laminated carbon fiber felt, the needle punching depth is 10-15mm, for example, it can be 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, etc.

[0095] In this invention, during the composite needle punching process of the stacked carbon fiber felt, the needle punching depth is preferably set to 10-15 mm to further ensure that the needle punch can penetrate deep between the fibers of each layer and promote fiber entanglement.

[0096] As an optional implementation, the composite needle punching process of the laminated carbon fiber felt is carried out in a staged needle punching manner: the frequency of the first stage needle punching is 600 to 800 times / min; the frequency of the second stage needle punching is 800 to 1200 times / min.

[0097] In this invention, the needle-punching frequency is adjusted according to different stages. Initially, the frequency is moderate, at 600-800 times / min, allowing the fibers to gradually adapt to the needle-punching action. This avoids the result of excessive fiber breakage due to high-frequency needle-punching before a stable interwoven structure is formed, leading to an increase in interfacial fiber fragmentation. As needle-punching progresses, the fibers begin to interweave, the felt structure gradually tightens, and the interaction strength between the needles and fibers increases, raising the needle-punching frequency to 800-1200 times / min. More fibers are driven by the needles, achieving a more complete and tighter entanglement based on the existing preliminary interwoven structure. This tight entanglement significantly increases the friction and interaction forces between fibers. Compared to traditional constant-frequency processes, gradient-controlled needle-punching frequency can more precisely regulate the fiber movement state, avoiding the random distribution disorder caused by excessive initial stirring, and also enhancing interlayer bonding strength in the later stages. This significantly enhances the interlayer bonding strength of the preform and effectively improves the overall mechanical properties of the preform.

[0098] As an optional implementation, the frequency of acupuncture in the first stage is 600 to 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 implementation, the frequency of acupuncture in the second stage is 800 to 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 implementation, the acupuncture time in the first stage is 20 to 30 minutes, for example, 20 minutes, 22 minutes, 24 minutes, 25 minutes, 26 minutes, 28 minutes, 30 minutes, etc.

[0101] As an optional implementation, the acupuncture time in the second stage is 20 to 30 minutes, for example, 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 precast body, the number of layers, and the needle density to achieve the best interlayer entanglement effect.

[0103] As an optional implementation, the ultrasonic vibration treatment includes: using an ultrasonic generator to emit ultrasonic waves, and converting electrical energy into mechanical energy through a transducer, and transmitting it to the area to be needled; and the ultrasonic vibration treatment is started when the needle is inserted into the stacked carbon fiber felt, continues for the period of time when the needle remains in the stacked carbon fiber felt, and ends when the needle begins to return and leaves the carbon fiber felt.

[0104] As an optional implementation, 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 implementation, the power of the ultrasonic wave is 200 to 400W, for example, it can be 200W, 220W, 240W, 260W, 280W, 300W, 320W, 340W, 360W, 380W, 400W, etc.

[0106] As an optional implementation, 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 this invention, the entire needle punching process is carried out simultaneously using an ultrasonic generator and a compressor. The ultrasonic generator produces ultrasonic waves with a frequency of 20 to 50 kHz, which are converted from electrical energy to mechanical energy by a transducer and transmitted to the needle punching area. The vibration of the ultrasonic waves acts on the carbon fiber felt, making it easier for the loose short fibers between the layers to detach 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 implementation, the airflow impact treatment includes: generating airflow using a compressor and guiding the airflow to the acupuncture area through a nozzle; and the airflow impact treatment starts from the acupuncture return phase, continues during the time period of the acupuncture process recovery, and ends before the next acupuncture re-insertion of the carbon fiber.

[0109] As an optional implementation, 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 this invention, a compressor generates a high-pressure airflow of 0.5–5.0 MPa, which is guided to the needle-punching area through a nozzle. The nozzle's position and angle are precisely adjusted to ensure that the airflow covers the entire needle-punching area, especially the interlayer interface. The high-speed airflow impacts the short fibers in the needle-punching area, generating impact momentum and shear force significantly higher than under low-pressure jet conditions, thus powerfully scouring the fiber particles. Ultrasonic vibration generates high-speed vibrational waves, reducing the adhesion between the fiber and the substrate and inducing micro-vibrations in the fiber, helping the short fibers to detach from the substrate surface. The synergistic effect of high-speed airflow and ultrasound can efficiently remove tiny particles adhering to the workpiece surface. After the short fibers are loosened by ultrasonic vibration, they are quickly blown away from the interlayer interface, achieving effective removal of the short fibers. Through this synergistic working method, short fibers generated during the needle-punching process are promptly removed, preventing their accumulation between layers and thus improving interlayer bonding strength.

[0111] As an optional implementation, the airflow velocity is 100–500 m / s, for example, it can be 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 is proportional to the square of the flow velocity, forming a high-density, focused air cone.)

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

[0113] As an optional implementation method, such as Figure 1 As shown, the present invention also provides a needle punching process system for improving the interlaminar shear properties of carbon fiber preforms. The system includes: a compressor 1, a pressure regulating valve 2, a high-pressure air tank 3, an adjustable nozzle 4, a needle plate 5, and an ultrasonic generator 6. The adjustable nozzle 4 can freely adjust the spray angle around the needle plate 5 (the area to be needled) and can be offset in the horizontal direction to cover the entire needle punching width.

[0114] As an optional implementation, 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, this angle is the tilt angle of the nozzle spray direction relative to the direction of movement of the needle (vertical direction).

[0116] As an optional implementation, the distance between the end face of the nozzle and the area of ​​needle puncture is 10 to 50 mm, for example, it can be 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, etc.

[0117] As an optional implementation, the nozzle diameter is 0.5 to 5.0 mm, for example, it can be 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 should be noted that the needle-punching process system described in this invention differs from the general contact-type needle-punching airflow micro-jet aperture (0.08–0.2 mm) and included angle (10–75°). The nozzle of this invention has a larger diameter and a continuously adjustable angle, 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 depressurized by pressure regulating valve 2, it is delivered to the adjustable nozzle 4 through pipeline. Simultaneously, ultrasonic generator 6 emits ultrasonic vibrations in the needle-punching area (needle plate 5).

[0119] In a second aspect, the present invention provides a carbon fiber preform prepared by the method for improving the interlaminar shear properties of the 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 / cm³. 3 For example, it could be 0.4 g / cm³. 3 0.42g / cm 3 0.44 g / cm 3 0.45g / cm 3 0.46 g / cm 3 0.48g / cm 3 0.5g / cm 3 wait.

[0121] As an optional implementation, the coefficient of variation (CV) 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 implementation, the interlaminar shear strength of the carbon fiber preform is 6.5 MPa or higher, 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 will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly 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 cut into short fibers of 10mm length by a chopped fiber cutter. The short carbon fiber is then carded and needle-punched by a carding machine to obtain carbon fiber mesh.

[0128] The acupuncture density of the pre-needle acupuncture machine is 6 needles / cm. 2 The needle puncture depth is 9mm, and the needle puncture frequency is set to 350 times / min; the thickness of the carbon fiber mesh is 0.9mm, and the basis weight of the carbon fiber mesh is 80g / m². 2 ;

[0129] (2) Preparation of unidirectional fabric:

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

[0131] The fiber drawing and laying process utilizes high-precision drawing equipment (Toray TMT-700 from Japan) and a laying device (Mayer AT-500 from Germany); the tension of each filament is 20 N / filament; the center-to-center spacing of the filaments is 0.2 mm; the drawing speed is 20 m / min; the layup angle is 0°; the thickness of the carbon fiber unidirectional fabric is 0.4 mm; and the basis weight of the carbon fiber unidirectional fabric is 300 g / m². 2 .

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

[0133] (3-1) A layered needle punching process is carried out using a layered method of one mesh and one unidirectional fabric, wherein the carbon fiber unidirectional fabric is laid in an alternating pattern of 0° / 90° to form an orthogonal reinforcement structure, and the resulting carbon fiber felt is obtained.

[0134] In the laminated carbon fiber felt, the carbon fiber mesh has 21 layers and the carbon fiber unidirectional fabric has 20 layers.

[0135] (3-2) The laminated carbon fiber felt is subjected to composite needle punching, and the needle punched area is subjected to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform.

[0136] The compound acupuncture was performed on a ZN-1200 acupuncture machine, with a needle density set at 25 needles / cm². 2 The needle-punching depth is 12mm; the needle-punching frequency adopts a segmented control mode: the initial stage is set to 600 times / min, the initial stage needle-punching time is 20min, and as the felt gradually tightens, in order to enhance the effect of needle-punching on the fibers, the needle-punching frequency is linearly increased to 900 times / min at a rate of 10 times / min to end the needle-punching.

[0137] The composite acupuncture treatment integrates an ultrasonic processing system and a high-pressure airflow purging device: an industrial-grade ultrasonic generator is selected; the output frequency of the ultrasonic processing 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 through a servo adjustment system; the compressor used is a screw compressor with a stable output pressure of 0.3MPa and a stable airflow velocity of 50m / s. The airflow is sprayed onto the acupuncture area through a customized L-shaped nozzle assembly. The nozzle is made of tungsten carbide alloy to resist the scouring of high-speed airflow. Its installation angle is optimized and set to a 45° tilt angle through three-dimensional simulation to ensure that the airflow coverage width reaches 80mm, and the vertical distance between the nozzle and the acupuncture area is controlled at 50mm.

[0138] The ultrasonic treatment system and the high-pressure airflow removal device are synchronized with the main shaft of the needle punching machine through a PLC control system. When the needle group descends and pierces the felt, the ultrasonic generator starts vibrating synchronously, and the duration is precisely matched with the needle dwell time (0.04~0.06s / time). During the needle return stage, the high-pressure airflow valve group opens and sprays airflow with a pulse duration of 50ms to remove loose short fibers. When the thickness of the preform reaches 12mm, the needle punching stops, and the preform is processed by the cutting machine into a finished preform of 1000mm×1000mm×12mm.

[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 cut into short fibers of 10mm length by a chopped fiber cutter. The short carbon fiber is then carded and needle-punched by a carding machine to obtain carbon fiber mesh.

[0143] The acupuncture density of the pre-needle acupuncture machine is 4 needles / cm. 2 The needle puncture depth is 8mm, and the needle puncture frequency is set to 400 times / min; the thickness of the carbon fiber mesh is 1.0mm, and the basis weight of the carbon fiber mesh is 100g / m². 2 .

[0144] (2) Preparation of unidirectional fabric:

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

[0146] The fiber drawing and laying process utilizes high-precision drawing equipment (Toray TMT-700 from Japan) and a laying device (Mayer AT-500 from Germany); the tension of each filament is 15 N / filament; the center-to-center spacing of the filaments is 0.1 mm; the drawing speed is 40 m / min; the layup angle is 0°; the thickness of the carbon fiber unidirectional fabric is 0.33 mm; and the basis weight of the carbon fiber unidirectional fabric is 300 g / m². 2 .

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

[0148] (3-1) A layered needle punching process is carried out using a layered method of one mesh and one unidirectional fabric, wherein the carbon fiber unidirectional fabric is laid in an alternating pattern of 0° / 90° to form an orthogonal reinforcement structure, and the resulting carbon fiber felt is obtained.

[0149] The stacked carbon fiber felt has a total of 41 layers, the carbon fiber mesh has 21 layers, and the carbon fiber unidirectional fabric has 20 layers.

[0150] (3-2) The laminated carbon fiber felt is subjected to composite needle punching, and the needle punched area is subjected to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform.

[0151] The compound acupuncture was performed on a ZN-1200 acupuncture machine, with a needle density set at 35 needles / cm². 2 The needle-punching depth is 13mm; the needle-punching frequency adopts a segmented control mode: the initial stage is set to 700 times / min, the initial stage needle-punching time is 30min, and as the felt gradually tightens, in order to enhance the effect of needle-punching on the fibers, the needle-punching frequency is linearly increased from 25 times / min to 1200 times / min to end the needle-punching.

[0152] The composite needle punching process integrates an ultrasonic processing system and a high-pressure airflow purging device: an industrial-grade ultrasonic generator is selected; the output frequency of the ultrasonic processing 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 using a laser vibrometer; the compressor used is a screw compressor with a stable output pressure of 0.5MPa and a stable airflow velocity of 250m / s. The airflow is sprayed onto the needle punching area through a customized L-shaped nozzle assembly. The nozzle is made of tungsten carbide alloy to resist the scouring of high-speed airflow. Its installation angle is optimized and set to a 35° tilt angle through three-dimensional simulation to ensure that the airflow coverage width reaches 60mm. The vertical distance between the nozzle and the needle punching area is controlled at 40mm to achieve high-speed stripping of short fibers.

[0153] The ultrasonic treatment system and the high-pressure airflow removal device are synchronized with the main shaft of the needle punching machine through a PLC control system. When the needle group descends and pierces the felt, the ultrasonic generator starts vibrating synchronously, and the duration is precisely matched with the needle dwell time (0.04~0.06s / time). During the needle return stage, the high-pressure airflow valve group opens and sprays airflow with a pulse duration of 50ms to remove loose short fibers. When the thickness of the preform reaches 12mm, the needle punching stops, and the preform is processed by the cutting machine into a finished preform of 1000mm×1000mm×12mm.

[0154] Example 3

[0155] This embodiment provides a carbon fiber preform, which differs from Embodiment 2 only in that, in step (1), the needle-punching density is 12 needles / cm. 2 The acupuncture depth is 7mm, the acupuncture frequency is 600 times / min, and the other steps are the same as 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 needle-punching density is 4 needles / cm. 2 The acupuncture depth is 14 mm, the acupuncture frequency is 200 times / min, and the other steps are the same as in Example 2.

[0158] Example 5

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

[0160] Example 6

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

[0162] Example 7

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

[0164] Example 8

[0165] This embodiment provides a carbon fiber preform, which differs from Embodiment 2 only in that, in step (2), the frequency of the first stage needle puncture is 1200 times / min and the needle puncture time of the first stage needle puncture is 10min; the frequency of the second stage needle puncture is 700 times / min and the needle puncture time of the first stage needle puncture is 40min; the other steps are the same as in Embodiment 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 10kHz, the power of the ultrasonic wave is 60W, and the vibration amplitude of the ultrasonic wave is 2μm; the other steps are the same as in 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 60kHz, the power of the ultrasonic wave is 120W, and the vibration amplitude of the ultrasonic wave is 20μm; the other steps are the same as in Embodiment 2.

[0170] Example 11

[0171] This embodiment provides a carbon fiber preform, which differs from Embodiment 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 area of ​​the needle punch is 5 mm; the other steps are the same as in Embodiment 2.

[0172] Example 12

[0173] This embodiment provides a carbon fiber preform, which differs from Embodiment 2 only in that, in step (3), the working pressure of the airflow is 6.0 MPa; the velocity 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 area of ​​the needle punch is 60 mm; the other steps are the same as in Embodiment 2.

[0174] Comparative Example 1

[0175] This comparative example provides a carbon fiber preform, which differs from Example 4 only in that the area to be needled is no longer subjected to ultrasonic vibration treatment and airflow impact treatment in step (3-2). All other steps and preparation conditions are the same as in Example 4. Correspondingly, after 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 cut into short fibers of 10mm length by a chopped fiber cutter. The short carbon fiber is then carded and needle-punched by a carding machine to obtain carbon fiber mesh.

[0180] The acupuncture density of the pre-needle acupuncture machine is 4 needles / cm. 2 The needle-punching depth is 14mm, and the needle-punching frequency is set to 200 times / min to ensure that the short-cut fibers are initially consolidated while retaining more free fibers; the thickness of the carbon fiber mesh is 1.0mm, and the basis weight of the carbon fiber mesh is 100g / m². 2 ;

[0181] (2) Preparation of unidirectional fabric:

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

[0183] The fiber drawing and laying process utilizes high-precision drawing equipment (Toray TMT-700 from Japan) and a laying device (Mayer AT-500 from Germany); the tension of each filament is 20 N / filament; the center-to-center spacing of the filaments is 0.2 mm; the drawing speed is 20 m / min; the layup angle is 0°; the thickness of the carbon fiber unidirectional fabric is 0.4 mm; and the basis weight of the carbon fiber unidirectional fabric is 300 g / m². 2 .

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

[0185] (3-1) A layered needle punching process is carried out using a layered method of one mesh and one unidirectional fabric, wherein the carbon fiber unidirectional fabric is laid in an alternating pattern of 0° / 90° to form an orthogonal reinforcement structure, and the resulting carbon fiber felt is obtained.

[0186] The stacked carbon fiber felt has a total of 41 layers, the carbon fiber mesh has 21 layers, and the carbon fiber unidirectional fabric has 20 layers.

[0187] (3-2) The laminated carbon fiber felt is subjected to composite needle punching, and the needle punched area is subjected to ultrasonic vibration treatment and airflow impact treatment to obtain the carbon fiber preform.

[0188] The compound acupuncture was performed on a ZN-1200 acupuncture machine, with a needle density set at 23 needles / cm². 2 The acupuncture depth was 13mm; the acupuncture frequency was set to 900 times / min and maintained for 50 minutes until the acupuncture was completed.

[0189] The composite needle punching process integrates an ultrasonic processing system and a high-pressure airflow purging device: an industrial-grade ultrasonic generator is selected; the output frequency of the ultrasonic processing 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 using a laser vibrometer; the compressor used is a screw compressor with a stable output pressure of 0.5MPa and a stable airflow velocity of 250m / s. The airflow is sprayed onto the needle punching area through a customized L-shaped nozzle assembly. The nozzle is made of tungsten carbide alloy to resist the scouring of high-speed airflow. Its installation angle is optimized and set to a 35° tilt angle through three-dimensional simulation to ensure that the airflow coverage width reaches 60mm. The vertical distance between the nozzle and the needle punching area is controlled at 40mm to achieve high-speed stripping of short fibers.

[0190] The ultrasonic treatment system and the high-pressure airflow removal device are synchronized with the main shaft of the needle punching machine through a PLC control system. When the needle group descends and pierces the felt, the ultrasonic generator starts vibrating synchronously, and the duration is precisely matched with the needle dwell time (0.04~0.06s / time). During the needle return stage, the high-pressure airflow valve group opens and sprays airflow with a pulse duration of 50ms to remove loose short fibers. When the thickness of the preform reaches 12mm, the needle punching stops, and the preform is processed by the cutting machine into a finished preform of 1000mm×1000mm×12mm.

[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 cut into short fibers of 10mm length by a chopped fiber cutter. The short carbon fiber is then carded and needle-punched by a carding machine to obtain carbon fiber mesh.

[0195] The acupuncture density of the pre-needle acupuncture machine is 4 needles / cm. 2 The needle penetration depth is 14mm, and the needle penetration frequency is set to 200 times / min; the thickness of the carbon fiber mesh is 1.0mm, and the basis weight of the carbon fiber mesh is 100g / m². 2 ;

[0196] (2) Preparation of unidirectional fabric:

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

[0198] The fiber drawing and laying process utilizes high-precision drawing equipment (Toray TMT-700 from Japan) and a laying device (Mayer AT-500 from Germany); the tension of each filament is 20 N / filament; the center-to-center spacing of the filaments is 0.2 mm; the drawing speed is 20 m / min; the layup angle is 0°; the thickness of the carbon fiber unidirectional fabric is 0.4 mm; and the basis weight of the carbon fiber unidirectional fabric is 300 g / m². 2 .

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

[0200] (3-1) A layered needle punching process is carried out using a layered method of one mesh and one unidirectional fabric, wherein the carbon fiber unidirectional fabric is laid in an alternating pattern of 0° / 90° to form an orthogonal reinforcement structure, and the resulting carbon fiber felt is obtained.

[0201] In the laminated carbon fiber felt, the carbon fiber mesh has 21 layers and the carbon fiber unidirectional fabric has 20 layers.

[0202] (3-2) The laminated carbon fiber felt is subjected to composite needle punching to obtain the carbon fiber preform;

[0203] The compound acupuncture was performed on a ZN-1200 acupuncture machine, with a needle density set at 25 needles / cm². 2 The needle-punching depth is 12mm; the needle-punching frequency adopts a segmented control mode: the initial stage is set to 600 times / min, and the initial stage needle-punching time is 20min. As the felt gradually tightens, in order to enhance the effect of needle-punching on the fibers, the needle-punching frequency is linearly increased from 10 times / min to 900 times / min until the needle-punching ends.

[0204] Comparative Example 4

[0205] This comparative example provides a carbon fiber preform, which differs from Example 4 only in that it does not adopt a segmented control mode, but only maintains a needle-punching frequency of 600 times / min for 50 minutes until the needle-punching ends. Other steps and preparation conditions are the same as in Example 4. Correspondingly, after 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 it does not adopt a segmented control mode, but only maintains a needle-punching frequency of 900 times / min for 50 minutes until the needle-punching ends. Other steps and preparation conditions are the same as in Example 4. Correspondingly, after 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 cut into short fibers of 10mm length by a chopped fiber cutter. The short carbon fiber is then carded and needle-punched by a carding machine to obtain carbon fiber mesh.

[0212] The acupuncture density of the pre-needle acupuncture machine is 4 needles / cm. 2 The needle-punching depth is 14mm, and the needle-punching frequency is set to 200 times / min to ensure that the short-cut fibers are initially consolidated while retaining more free fibers; the thickness of the carbon fiber mesh is 1.0mm, and the basis weight of the carbon fiber mesh is 100g / m². 2 ;

[0213] (2) Preparation of unidirectional fabric:

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

[0215] The fiber drawing and laying process utilizes high-precision drawing equipment (Toray TMT-700 from Japan) and a laying device (Mayer AT-500 from Germany); the tension of each filament is 20 N / filament; the center-to-center spacing of the filaments is 0.2 mm; the drawing speed is 20 m / min; the layup angle is 0°; the thickness of the carbon fiber unidirectional fabric is 0.4 mm; and the basis weight of the carbon fiber unidirectional fabric is 300 g / m². 2 .

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

[0217] A layered needle-punching process is employed, using a layup method of one layer of carbon fiber mesh and one layer of unidirectional fabric. The unidirectional carbon fiber fabric is laid up alternately at 0° / 90° to form an orthogonal reinforcement structure, resulting in a laminated carbon fiber felt. The laminated carbon fiber felt comprises a total of 41 layers: 21 layers of carbon fiber mesh and 20 layers of carbon fiber unidirectional fabric. In the composite needle-punching stage, the needle-punching density is increased to 23 needles / cm². 2The needle penetration depth was 13mm, and the needle penetration frequency was 900 times / min. Needling was stopped when the preform thickness reached 12mm. After cutting, a finished carbon fiber preform of 1000mm×1000mm×12mm was obtained.

[0218] Test case

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

[0220] Test method:

[0221] (1) Density: Where ρ represents density (g / cm³) 3 m represents the sample mass (g); L, W, and H represent the sample length, width, and thickness (cm), respectively.

[0222] The density test method is carried out in accordance with the "geometric method" specified in GB / T 1446-2005 "General Rules for Test Methods of Fiber Reinforced Plastics", which means that 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 for CV value (coefficient of variation) refers to GB / T 8170-2008 "Rules for Rounding Off Numerical Values ​​and Expression and Judgment of Limiting Values" and the general rules for statistical analysis. Statistical analysis is performed on the density data of carbon fiber preform samples taken from different regions, and the standard deviation and sample mean are calculated. Based on this, the coefficient of variation is calculated:

[0224] Coefficient of variation (CV) value: Where CV represents the coefficient of variation; S represents the standard deviation; X: sample standard density (g / cm³) 3 ):

[0225] A smaller CV value indicates higher structural uniformity and better needle-punching stability of the carbon fiber preform. This invention uses a 9-point distribution method to collect density values ​​in different regions of the sample and calculates the CV value according to the above formula, serving 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 Determination of Interlaminar Shear Strength of Polymer-Based Composites by Short Beam Method" or GB / T 3357-2014 "Test Method for Interlaminar Shear Strength of Fiber-Reinforced Plastics". The preform samples are subjected to shear failure tests 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; and h represents the specimen thickness in mm.

[0229] All of the above tests were conducted in a laboratory at a temperature of 23±2℃ 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 / cm³. 3 The coefficient of variation (CV) is below 4%, indicating good uniformity in preform thickness and fiber distribution; the interlaminar shear strength of the carbon fiber preform is above 6.5 MPa, indicating a significant improvement in interlaminar bonding strength.

[0235] A comparison of Example 1 and Comparative Example 1 shows that improving the composite acupuncture process alone, without subjecting the acupunctured area to ultrasonic vibration and airflow impact treatment, significantly reduces the average interlaminar shear strength. A comparison of Example 1 and Comparative Example 2 shows that subjecting the acupunctured area to ultrasonic vibration and airflow impact treatment but without employing the composite acupuncture process also significantly reduces the average interlaminar shear strength. A comparison of Example 1 and Comparative Example 3 shows that simply increasing the gradient acupuncture frequency without subjecting the acupunctured area to ultrasonic vibration and airflow impact treatment also significantly reduces the average interlaminar shear strength.

[0236] Meanwhile, these three test results show that, under the simultaneous action of both methods, the removal rate of particles larger than 6μm can exceed 98%. In addition, this compressed gas purging process is non-contact, with the nozzle always kept isolated from the needle-punching area, eliminating the need for mechanical contact with the fibers and needle plates, thus avoiding direct damage to the fibers caused by traditional contact purging methods.

[0237] The comparison between Example 1 and Comparative Examples 4-5 shows that when using a single needle-punching frequency for the laminated needle-punching process, the interlaminar 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 felt density uniformity reaches 7.4%, indicating that the low frequency leads to insufficient fiber entanglement. The interlaminar shear strength of the preform in Comparative Example 5 is 6.1 MPa. Broken fibers clogging the needle holes increases the needle-punching resistance by 40%, requiring frequent machine shutdowns for cleaning. The results indicate that a constant frequency process cannot simultaneously achieve fiber protection and sufficient entanglement, while the present invention, by gradient-controlling the needle-punching frequency, improves the interlaminar shear performance of the carbon fiber preform by more than 20%.

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

[0239] 1. Optimize the needle punching density ratio to enhance interlayer fiber entanglement: a) By adjusting the ratio of single-layer needle punching density to the overall needle punching density in multi-layer composites, the single-layer needle punching density is reduced, allowing some fibers to remain free, so as to provide more interlayer interwoven entangled fibers in multi-layer composites; b) By optimizing the single-layer needle punching density to form a reasonable ratio with the final overall needle punching density, the entanglement within the single layer is ensured to be stable, while retaining enough free fibers for interlayer entanglement.

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

[0241] 3. Using ultrasonic vibration + airflow impact to remove short fibers at the interface: a) Short fibers are inevitably generated during the needle punching process. Therefore, this invention further introduces ultrasonic vibration + airflow impact technology to remove short fibers on the interlayer interface after needle punching. This method can effectively reduce the residue of short fibers between layers and avoid their weakening effect on the interlayer bonding force, thereby improving the overall bonding strength.

[0242] Therefore, through the above method, the present invention can optimize the needle punching frequency, reduce the generation of short fibers, and effectively remove short fibers between layers while controlling the fiber entanglement state, thereby significantly improving the interlayer bonding force of carbon-carbon composite materials, 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, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the interlaminar shear properties of carbon fiber preforms, characterized in that, The method includes: Carbon fiber filaments are sequentially chopped, combed into a web, and needle-punched to obtain a carbon fiber web; carbon fiber filaments are then drawn and laid to obtain a carbon fiber unidirectional fabric. The carbon fiber mesh and carbon fiber unidirectional fabric are cross-layered and laid to obtain the 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 airflow impact treatment to obtain the carbon fiber preform. During the preparation of the carbon fiber mesh, the needle punching density is 5-10 needles / cm. 2 The depth of the acupuncture is 8-12 mm, and the frequency of the acupuncture is 300-500 times / min; During the composite needle punching process of the laminated carbon fiber felt, the needle punching density is 20-25 needles / cm. 2 The depth of the needle insertion is 10-15 mm; During the composite needle punching process of the laminated carbon fiber felt, a staged needle punching method is adopted: the frequency of the first stage needle punching is 600~800 times / min; the frequency of the second stage needle punching is 800~1200 times / min.

2. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The carbon fiber filaments are polyacrylonitrile-based carbon fibers.

3. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The length of the carbon fiber filaments obtained after scissor cutting is 5~20 mm.

4. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The thickness of the carbon fiber mesh is 0.7~1.0 mm, and the basis weight of the carbon fiber mesh is 70~120 g / m². 2 .

5. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The process parameters for the drawing and laying of the filaments include: the tension of a single filament is 5~50 N / filament; the center-to-center spacing of the filaments is 0.1~1.0 mm; the drawing speed is 5~50 m / min; and the layup angle is -2~2°.

6. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The thickness of the unidirectional carbon fiber fabric is 0.3~0.6 mm, and the basis weight of the unidirectional carbon fiber fabric is 200~400 g / m. 2 .

7. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The cross-layering includes: using an alternating layering method of a carbon fiber mesh and a carbon fiber unidirectional fabric, with the carbon fiber unidirectional fabrics being orthogonally interlaced at 0° and 90°.

8. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, In the laminated carbon fiber felt, the number of layers of the carbon fiber mesh is 10 to 25, and the number of layers of the carbon fiber unidirectional fabric is 10 to 25.

9. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The acupuncture time for the first stage is 20-30 minutes.

10. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The acupuncture time for the second stage is 20-30 minutes.

11. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The ultrasonic vibration treatment includes: using an ultrasonic generator to emit ultrasonic waves, and converting electrical energy into mechanical energy through a transducer, which is then transmitted to the area to be needled; and the ultrasonic vibration treatment is initiated when the needle is inserted into the stacked carbon fiber felt, continues for the period of time during which the needle remains in the stacked carbon fiber felt, and ends when the needle begins to return and leaves the carbon fiber felt.

12. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 11, characterized in that, The frequency of the ultrasound is 20~50 kHz.

13. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 11, characterized in that, The power of the ultrasonic wave is 200~400 W.

14. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 11, characterized in that, The vibration amplitude in the area punctured by the needle is 5~15 μm.

15. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 1, characterized in that, The airflow impact treatment includes: generating airflow using a compressor and guiding the airflow to the acupuncture area through a nozzle; and the airflow impact treatment starts from the acupuncture return phase, continues during the time period of the acupuncture needle's return process, and ends before the next acupuncture needle re-inserts into the carbon fiber felt.

16. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 15, characterized in that, The working pressure of the airflow is 0.5~5.0 MPa; the velocity of the airflow is 100~500 m / s; and the jet pulse duration of the airflow is 40~70 ms.

17. The method for improving the interlaminar shear properties of carbon fiber preforms according to claim 15, characterized in that, The nozzle has a diameter of 0.5 to 5.0 mm, and the distance between the end face of the nozzle and the area to be needled is 10 to 50 mm.

18. A carbon fiber preform, characterized in that, The carbon fiber preform is prepared by the method for improving the interlaminar shear properties of the carbon fiber preform as described in any one of claims 1 to 17.

19. The carbon fiber preform according to claim 18, characterized in that, The density of the carbon fiber preform is 0.38~0.52 g / cm³. 3 .

20. The carbon fiber preform according to claim 18, characterized in that, The coefficient of variation (CV) of the carbon fiber preform is less than 4%.

21. The carbon fiber preform according to claim 18, characterized in that, The interlaminar shear strength of the carbon fiber preform is above 5.5 MPa.

22. The carbon fiber preform according to claim 18, characterized in that, The interlaminar shear strength of the carbon fiber preform is above 6.5 MPa.

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