A thermoplastic pre-impregnated spread tow three-dimensional braided preform and a method of making the same

Abstract

This invention discloses a three-dimensional woven preform of thermoplastic prepreg expanded yarn and its preparation method, specifically relating to the field of composite material molding technology. The method involves using large-tow carbon fiber thermoplastic prepreg expanded yarn as warp and weft yarns, performing multi-layer synchronous weaving, and introducing interlayer cross-linked weft yarns between adjacent woven layers. These weft yarns interweave with the upper and lower warp yarns through a first weft section, a second weft section, and a layer-changing section to form a non-puncture thickness connection. After weaving, the preform is heat-fused to form an integral three-dimensional reinforced preform. This invention improves resin impregnation uniformity and molding efficiency through large-tow carbon fiber expanded prepreg and multi-layer synchronous weaving; the non-puncture thickness direction connection formed by interlayer cross-linked weft yarns, and the integral three-dimensional reinforced structure formed by heat-fused bonding, helps reduce fiber damage and improves interlayer bonding, anti-delamination, and Z-axis mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, and in particular to a three-dimensional woven preform of thermoplastic prepreg yarn and its preparation method. Background Technology

[0002] Continuous carbon fiber reinforced thermoplastic composites combine the high specific strength and high specific modulus of carbon fibers with the repeatedly softenable, weldable, and short molding cycle characteristics of thermoplastic resins, and have been widely used in aerospace, rail transportation, automotive lightweighting, and high-performance structural components. As structural components develop towards lightweight, integrated, and thick-section designs, the use of large-tow carbon fibers to prepare low-cost, high-efficiency thermoplastic composite preforms has become an important technological approach. Yarn-widening technology can unfold bundled carbon fiber filaments into wide and thin yarns, resulting in a more uniform fiber distribution in the width direction and facilitating the formation of prepregs or sheets with thermoplastic resins. On the other hand, three-dimensional weaving, three-dimensional braiding, and interlayer reinforcement fabric structures can introduce structural connections in the thickness direction in addition to traditional warp and weft reinforcement, thereby forming fiber preforms with spatial integrity. Existing research provides a technological foundation for the integrated manufacturing of continuous fiber reinforced thermoplastic composites, including three-dimensional fabric preforms, interlayer connecting yarns, thickness-direction reinforcement structures, and the hot-melt, welding, and consolidation processes of thermoplastic composites. Against this backdrop, the process of multi-layer synchronous weaving, interlayer cross-linking, and subsequent hot-melt solidification of thermoplastic prepreg tapes to form a three-dimensional integral preform has become an important development direction for composite material preform molding technology.

[0003] In existing large-tow carbon fiber thermoplastic prepreg materials, the large number of carbon fibers and the large bundle thickness, coupled with the high viscosity of the thermoplastic resin melt, make it difficult for the resin to be fully and evenly impregnated and distributed within the fiber bundle, which can easily affect the molding quality of subsequent preforms. For multilayer carbon fiber thermoplastic composite structures, conventional methods typically involve laying, stacking, and hot-pressing multiple layers of two-dimensional prepreg fabrics or tapes. The bonding between adjacent layers mainly relies on the adhesive effect of the molten thermoplastic resin, lacking continuous fiber-based interlayer mechanical connections. This limits interlayer shear, peeling, and thickness-direction load-bearing capacity. To enhance interlayer performance, existing technologies can also use Z-direction stitching, puncture, or fiber implantation to create thickness-direction reinforcement. However, these methods require puncturing the already laid or woven fiber layers, which can easily cause fiber bundle misalignment, bending, compression, or breakage, affecting fiber continuity. On the other hand, although traditional three-dimensional weaving or three-dimensional machine weaving technology can form spatially reinforced structures, it often requires complex specialized equipment and high process costs, and still has certain limitations in the efficient preparation of multi-layer thick-section thermoplastic prepreg stretching yarn preforms.

[0004] Therefore, there is an urgent need for a three-dimensional woven preform and its preparation method that can simultaneously achieve uniform impregnation of large-tow carbon fiber thermoplastic prepreg, multi-layer synchronous weaving, low-damage interlayer bonding, and thickness-direction reinforcement. Summary of the Invention

[0005] The main objective of this invention is to provide a three-dimensional woven preform of thermoplastic prepreg and its preparation method, which can effectively solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A three-dimensional woven preform of thermoplastic prepreg yarn includes at least two layers of prepreg yarn woven layers stacked along the thickness direction. Each of the prepreg spread yarn braided layers includes warp yarns extending in a first direction and weft yarns extending in a second direction, wherein the warp yarns and the weft yarns are thermoplastic prepreg spread yarn tapes formed by spreading and thinning large tow carbon fibers and impregnating them with thermoplastic resin. Interlayer cross-linked weft yarns are provided between adjacent prepreg-stretched yarn braided layers; The main body of the interlayer cross-linked weft yarn extends along the second direction and interweaves sequentially with the warp yarns in the adjacent two layers of prepreg and expanded yarn braiding layers within at least one weave cycle, so that the interlayer cross-linked weft yarn has a first weft segment in the first layer of prepreg and expanded yarn braiding layer, a second weft segment in the second layer of prepreg and expanded yarn braiding layer, and a layer-changing segment connecting the first weft segment and the second weft segment, thereby forming an interlayer connection structure in the thickness direction between the adjacent two layers of prepreg and expanded yarn braiding layers.

[0007] Preferably, the interlayer cross-linked weft yarn includes odd-numbered cross-linked weft yarns and even-numbered cross-linked weft yarns; The odd-numbered cross-linked weft yarn is the interlayer cross-linked weft yarn introduced in the 2k-1th weft insertion cycle, and the even-numbered cross-linked weft yarn is the interlayer cross-linked weft yarn introduced in the 2kth weft insertion cycle, where k is a positive integer.

[0008] Preferably, the odd-numbered cross-linked weft yarns and the even-numbered cross-linked weft yarns are arranged alternately, staggeredly, or at a preset interval along the length of the fabric, so that a continuous or intermittent interlayer cross-linking structure is formed between adjacent prepreg and stretched yarn weaving layers.

[0009] Preferably, the interlayer cross-linked weft yarn's layer-changing segment crosses the interlayer interface between two adjacent prepreg-stretched and stretched yarn weaving layers, and the first weft segment and the second weft segment are respectively clamped or interwoven and limited by the warp yarns in the corresponding layer to form a non-puncture thickness direction connection.

[0010] Preferably, the prepreg-stretched yarn weaving layer has three or more layers; and the interlayer cross-linked weft yarn is provided between any two adjacent layers.

[0011] Preferably, the interlayer cross-linked weft yarn is a pre-impregnated cross-linked weft yarn containing reinforcing fibers and thermoplastic resin; The interlayer cross-linked weft yarn is one or more combinations of thermoplastic prepreg carbon fiber spread yarn, thermoplastic prepreg carbon fiber bundle, and hybrid yarn of carbon fiber and thermoplastic resin fiber.

[0012] Preferably, after the preform is heat-fused and solidified, the thermoplastic resin located between adjacent prepreg and spread yarn braided layers is in a state of molten penetration followed by cooling and solidification, so that the interlayer cross-linked weft yarn, the warp yarn and the weft yarn together form an integrated three-dimensional reinforced structure.

[0013] The present invention also provides a method for fabricating a three-dimensional woven preform of thermoplastic prepreg yarn, characterized by comprising the following steps: S1. Widen and thin the large tow carbon fiber and combine it with thermoplastic resin to obtain thermoplastic prepreg widened yarn tape. S2. The multiple sets of thermoplastic prepreg expanded yarn tapes are arranged in layers as a warp system, and the weft yarns are arranged in the corresponding weft insertion system, so that the multiple layers of prepreg expanded yarn tapes participate in weaving synchronously along the thickness direction; S3. By controlling the height position of different layers of warp yarns through heddles or heddles lifting mechanisms, ordinary openings and cross-layer cross-linking openings are formed during the weaving process; S4. Introduce ordinary weft yarn into the ordinary opening and introduce interlayer cross-linked weft yarn into the cross-layer cross-linking opening, so that the interlayer cross-linked weft yarn passes through the opening formed by two adjacent warp yarns in at least one tissue cycle and interweaves with the warp yarns in the two adjacent layers respectively, thereby forming an interlayer connection structure having a first weft segment, a second weft segment and a layer-changing segment connecting the first weft segment and the second weft segment. S5. After weaving is completed, the obtained three-dimensional woven preform is heat-fused and solidified, so that the thermoplastic resin melts or softens and flows and then cools and solidifies to obtain a thermoplastic prepreg expanded yarn three-dimensional woven preform.

[0014] Preferably, in step S4, an odd number of cross-linked weft yarns are introduced in the 2k-1th weft insertion cycle, and an even number of cross-linked weft yarns are introduced in the 2kth weft insertion cycle. The odd-numbered cross-linked weft yarns and the even-numbered cross-linked weft yarns enter different weft-direction weaving positions in adjacent layers through different warp opening heights, so as to form an interlayer cross-linking structure that is arranged alternately, staggeredly, or at a preset interval, where k is a positive integer.

[0015] Preferably, the hot melt consolidation in step S5 includes ultrasonic hot melt, carbon fiber electric heating, hot pressing, infrared heating, laser heating, molding heating, or a combination thereof; During the hot-melt solidification process, the three-dimensional woven preform is heated to the melting temperature of the thermoplastic resin and pressure is applied to allow the molten thermoplastic resin to penetrate into the interlayer cross-linked weft yarns, warp yarns and the gaps between the weft yarns, and then cooled and solidified.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention transforms the carbon fiber bundle from a bundled state to a wide and thin ribbon structure by widening and thinning large-tow carbon fibers and combining them with thermoplastic resin to form a thermoplastic prepreg widened yarn tape. This is beneficial for improving the wetting and distribution of thermoplastic resin in the fiber bundle. At the same time, the multi-layer thermoplastic prepreg widened yarn tape is configured layer by layer and participates in weaving simultaneously. This allows each layer of prepreg widened yarn to form a warp and weft reinforcement structure during the weaving process, rather than relying on subsequent simple stacking or laying to form a multi-layer structure. This is beneficial for achieving efficient and integrated preparation of large-tow carbon fiber thermoplastic composite preforms.

[0017] 2. This invention introduces interlayer cross-linked weft yarns between adjacent prepreg and spread yarn weaving layers. Through the combination of ordinary openings and cross-layer cross-linking openings, the interlayer cross-linked weft yarns interweave with the warp yarns in the two adjacent layers within at least one weave cycle, forming weft segments within different layers and layer-changing segments crossing the interlayer interface. This establishes an interlayer connection structure in the thickness direction, in addition to warp and weft reinforcement. This interlayer connection structure is formed during the weaving process, eliminating the need for Z-axis puncture or sewing of the woven multi-layer fiber structure, thus reducing disturbance to the original fiber bundles. Damage; furthermore, the interlayer cross-linked weft yarns can be odd-numbered cross-linked weft yarns, even-numbered cross-linked weft yarns, or a combination of both, so as to adjust the interlayer connection position and connection density according to different layers, thicknesses, and mechanical performance requirements. After weaving, the thermoplastic resin is melted or softened and flowed in the layer and interlayer regions through hot melt consolidation and then cooled and solidified, so that the warp yarns, weft yarns, interlayer cross-linked weft yarns, and thermoplastic resin together form an integrated three-dimensional reinforced structure, which is beneficial to improving the interlayer bonding ability, anti-delamination ability, thickness direction mechanical properties, and overall structural stability of the preform. Detailed Implementation

[0018] The following examples are used to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can adjust the spreading width, number of braided layers, cross-linked weft yarn spacing, and hot-melt consolidation conditions according to the type of thermoplastic resin, fiber specifications, preform thickness, and component performance requirements.

[0019] In one optional embodiment, the large tow carbon fiber can be 24K, 48K, or 50K carbon fiber tow; after being spread and thinned, it forms a thermoplastic prepreg spread yarn tape with a width of 20mm to 60mm and a thickness of 0.04mm to 0.18mm; the number of layers of the prepreg spread yarn braid can be 2 to 8 layers; the weft spacing of the ordinary weft yarn can be 3mm to 10mm; the interlayer cross-linked weft yarn can be introduced once every 1 to 4 weft insertion cycles, or it can be introduced alternately in odd and even weft insertion cycles; the hot melt solidification temperature is determined according to the melting temperature of the thermoplastic resin used, the pressure can be 0.3MPa to 2.0MPa, and the holding time can be 2min to 20min.

[0020] Example 1 This embodiment provides a three-dimensional woven preform of two layers of thermoplastic prepreg and spread yarn.

[0021] 24K large-tow carbon fiber was selected and spread to 25mm, resulting in a fiber tape thickness of 0.06mm. A 25μm thick polyamide 6 thermoplastic resin film was then hot-pressed onto the spread carbon fiber tape. The hot press roller temperature was 235℃, the roller pressure was 0.4MPa, and the traction speed was 1.5m / min, yielding a polyamide 6-based thermoplastic prepreg spread yarn tape.

[0022] The obtained thermoplastic prepreg expanded yarn tapes are used as the first and second layer warp yarns, respectively, and thermoplastic prepreg expanded yarn tapes of the same specification are used as ordinary weft yarns and interlayer cross-linked weft yarns. The first direction is the warp extension direction, and the second direction is the weft insertion direction. The height position of the two warp yarns is controlled by two sets of heddles, forming a first layer ordinary opening, a second layer ordinary opening, and an interlayer cross-linked opening between the first and second layers during the weaving process.

[0023] The weft spacing for ordinary weft yarns is 5mm. In the first weft insertion cycle, an odd-numbered cross-linked weft yarn is introduced. This odd-numbered cross-linked weft yarn first passes through the opening formed by the first layer of warp yarns and interweaves with the first layer of warp yarns. Then, it passes through the layer-changing section and enters the opening formed by the second layer of warp yarns, interweaving with the second layer of warp yarns. In the second weft insertion cycle, an even-numbered cross-linked weft yarn is introduced. This even-numbered cross-linked weft yarn first passes through the opening formed by the second layer of warp yarns and interweaves with the second layer of warp yarns. Then, it passes through the layer-changing section and enters the opening formed by the first layer of warp yarns, interweaving with the first layer of warp yarns. Odd-numbered and even-numbered cross-linked weft yarns are arranged alternately along the length of the fabric, with an adjacent spacing of 10mm between cross-linked weft yarns between layers.

[0024] After weaving, the resulting two-layer three-dimensional woven preform is placed in a flatbed hot press for thermal bonding. The hot pressing temperature is 245℃, the pressure is 0.8MPa, and the holding time is 8min. Subsequently, it is cooled to below 80℃ under pressure to obtain a two-layer thermoplastic prepreg three-dimensional woven preform. In the obtained preform, the interlayer cross-linked weft yarn has a first weft segment in the first layer, a second weft segment in the second layer, and a layer-changing segment crossing the interface between the two layers, forming a non-puncture thickness-direction connection structure.

[0025] Example 2 This embodiment provides a three-dimensional woven preform of three-layer thermoplastic prepreg spreading yarn.

[0026] 48K large-tow carbon fiber was selected and spread to 40mm, resulting in a fiber tape thickness of 0.09mm. A 30μm thick polyphenylene sulfide thermoplastic resin film was then used to composite the spread carbon fiber tape. The hot press roller temperature was 315℃, the roller pressure was 0.6MPa, and the traction speed was 1.0m / min, yielding a polyphenylene sulfide-based thermoplastic prepreg spread tape.

[0027] The obtained thermoplastic prepreg expanded yarn tape is configured as a first, second, and third layer warp system, and thermoplastic prepreg expanded yarn tape of the same specification is used as ordinary weft yarn and interlayer cross-linking weft yarn. During weaving, the height position of the first, second, and third layer warp yarns is controlled by three sets of heddles respectively, forming ordinary openings in each layer as well as cross-layer cross-linking openings between the first and second layers and between the second and third layers.

[0028] The weft spacing of ordinary weft yarns is 6mm. First-layer cross-linked weft yarns are placed between the first and second layers, and second-layer cross-linked weft yarns are placed between the second and third layers. In the first weft insertion cycle, an odd number of cross-linked weft yarns are introduced between the first and second layers; in the second cycle, an even number of cross-linked weft yarns are introduced between the second and third layers; in the third cycle, an odd number of cross-linked weft yarns are introduced again between the first and second layers; and in the fourth cycle, an even number of cross-linked weft yarns are introduced again between the second and third layers, and this process is repeated. The cross-linked weft yarns between adjacent layers are staggered along the fabric length, and the spacing between adjacent cross-linked weft yarns within the same interlayer area is 12mm.

[0029] After weaving, the resulting three-layer three-dimensional woven preform is hot-pressed for consolidation. The hot-pressing temperature is 325℃, the pressure is 1.0MPa, and the holding time is 10min. Subsequently, it is cooled to below 100℃ under pressure to obtain a three-layer thermoplastic prepreg three-dimensional woven preform. In the obtained preform, thickness-direction connection structures composed of interlayer cross-linked weft yarns are formed between the first and second layers, and between the second and third layers.

[0030] Example 3 This embodiment provides a three-dimensional woven preform of a five-layer thick cross-section thermoplastic prepreg spreading yarn.

[0031] 50K large-tow carbon fiber was selected and spread to 55mm, resulting in a fiber tape thickness of 0.12mm. A 40μm thick polyetheretherketone (PEEK) thermoplastic resin film was then used to composite the spread carbon fiber tape. The hot press roller temperature was 390℃, the roller pressure was 0.8MPa, and the traction speed was 0.6m / min, yielding a PEEK-based thermoplastic prepreg spread tape.

[0032] The obtained thermoplastic prepreg expanded yarn tapes were configured as the warp systems for the first to fifth layers, and thermoplastic prepreg expanded yarn tapes of the same specifications were used as ordinary weft yarns. The interlayer crosslinking weft yarns were made of polyetheretherketone-based thermoplastic prepreg carbon fiber expanded yarn tape with a width of 20 mm and a thickness of 0.08 mm. During weaving, the height of each layer of warp yarns was controlled by five sets of heddles, forming ordinary openings in each layer and crosslinking openings between adjacent layers.

[0033] The weft spacing of the ordinary weft yarn is 8mm. Interlayer cross-linked weft yarns are placed between the first and second layers, the second and third layers, the third and fourth layers, and the fourth and fifth layers. The interlayer cross-linked weft yarns are introduced once every two ordinary weft yarn weft cycles; odd-numbered cross-linked weft yarns are used for cross-linking between the first and second layers, and between the third and fourth layers, while even-numbered cross-linked weft yarns are used for cross-linking between the second and third layers, and between the fourth and fifth layers. The cross-linked weft yarns in each interlayer region are staggered along the fabric length, and the spacing between adjacent cross-linked weft yarns within the same interlayer region is 16mm.

[0034] After weaving, the carbon fiber is thermally bonded using a combination of electric heating and hot pressing. The preform is placed in an insulated hot pressing mold, with copper electrodes at both ends to create a conductive path between the carbon fibers. A direct current of 35A is applied, raising the temperature of the preform to 385℃~395℃. Simultaneously, a pressure of 1.2MPa is applied and maintained for 6 minutes. Then, the current is stopped, and the preform is cooled to below 120℃ while maintaining the pressure, resulting in a five-layer thermoplastic prepreg three-dimensional woven preform. In the resulting preform, the multiple layers of prepreg woven yarn are connected in a continuous or staggered thickness direction through interlayer cross-linked weft yarns.

[0035] Example 4 This embodiment provides a three-dimensional woven preform of four-layer thermoplastic prepreg yarn.

[0036] 48K large-tow carbon fiber was selected and spread to 35mm, resulting in a fiber tape thickness of 0.08mm. A 35μm thick polyamide 12 thermoplastic resin film was then used to composite the spread carbon fiber tape. The hot press roller temperature was 210℃, the roller pressure was 0.5MPa, and the traction speed was 1.2m / min, yielding a polyamide 12-based thermoplastic prepreg spread yarn tape.

[0037] The resulting thermoplastic prepreg expanded yarn tape is configured as a four-layer warp system, with the ordinary weft yarn using polyamide 12-based thermoplastic prepreg expanded yarn tape of the same specification. The interlayer crosslinked weft yarn is a hybrid yarn of carbon fiber and polyamide 12 thermoplastic resin fiber, with a hybrid yarn linear density of 1600 tex. During weaving, the height of the four warp layers is controlled by four sets of heddles, forming ordinary openings and cross-layer crosslinking openings.

[0038] The weft spacing of ordinary weft yarns is 4mm. Interlayer cross-linked weft yarns are placed between the first and second layers, between the second and third layers, and between the third and fourth layers. Odd-numbered cross-linked weft yarns are introduced in the 2k-1th weft insertion cycle, and even-numbered cross-linked weft yarns are introduced in the 2kth weft insertion cycle. The odd-numbered and even-numbered cross-linked weft yarns enter different weft positions in adjacent layers through cross-linking openings of different heights. The spacing between adjacent interlayer cross-linked weft yarns is 8mm.

[0039] After weaving, the material is treated with a combination of ultrasonic hot melting and hot pressing. The ultrasonic frequency is 20kHz, the amplitude is 30μm, and the action time is 5s. Then, hot pressing is performed at a temperature of 220℃, a pressure of 0.9MPa, and a holding time of 6min. The material is then cooled to below 70℃ while maintaining the pressure, resulting in a three-dimensional woven preform of four layers of thermoplastic prepreg yarn.

[0040] Comparative Example 1 This comparative example provides a two-layer thermoplastic prepreg stretching yarn laminate preform without interlayer cross-linked weft yarns.

[0041] The same 24K large-tow carbon fiber as in Example 1 was selected, and a polyamide 6-based thermoplastic prepreg stretching yarn tape with a width of 25 mm and a thickness of 0.06 mm was prepared using the same method. Two layers of prepreg stretching yarn were woven to form two layers of woven yarn. The ordinary weft yarn pitch was 5 mm, but no cross-linking openings were formed during the weaving process, and no interlayer cross-linking weft yarns were introduced.

[0042] Two layers of prepreg-stretched yarn were stacked and then hot-pressed together at a temperature of 245°C, a pressure of 0.8 MPa, and a holding time of 8 minutes. The layers were then cooled to below 80°C while maintaining the pressure, resulting in a two-layer thermoplastic prepreg-stretched yarn preform. In this comparative example, the adjacent layers are mainly bonded together by the melting of thermoplastic resin, and do not have a first weft segment, a second weft segment, or a layer-changing segment formed by interlayer cross-linked weft yarns.

[0043] Comparative Example 2 This comparative example provides a three-layer thermoplastic prepreg stretching yarn preform connected by a Z-direction stitching method.

[0044] The same 48K large-tow carbon fiber as in Example 2 was selected, and a polyphenylene sulfide-based thermoplastic prepreg stretching yarn tape with a width of 40 mm and a thickness of 0.09 mm was prepared using the same method. Three layers of prepreg stretching yarn were woven to form the three layers, with a weft spacing of 6 mm for ordinary weft yarns, and no interlayer cross-linked weft yarns were introduced during the weaving process.

[0045] After stacking three layers of prepreg expanded yarn braids, Z-direction stitching was performed using polyphenylene sulfide-coated carbon fiber sutures. The stitch spacing was 10 mm, the row spacing was 12 mm, and the stitch depth penetrated through all three layers of prepreg expanded yarn braids. After stitching, hot-pressing was performed at 325℃, 1.0 MPa, and 10 min. The mixture was then cooled to below 100℃ while maintaining pressure, resulting in a Z-direction stitched three-layer thermoplastic prepreg expanded yarn preform. In this comparative example, the interlayer connection was formed by post-weaving puncture stitching, rather than by interlayer cross-linked weft yarn interlacing during the weaving process.

[0046] Comparative Example 3 This comparative example provides an unstretched large-tow carbon fiber thermoplastic prepreg braided preform.

[0047] 48K large-tow carbon fiber was selected without any widening or thinning treatment. The original bundled carbon fiber bundle was directly composited with a 30μm thick polyphenylene sulfide thermoplastic resin film. The hot press roller temperature was 315℃, the roller pressure was 0.6MPa, and the traction speed was 1.0m / min to obtain thermoplastic prepreg carbon fiber bundles.

[0048] The obtained thermoplastic prepreg carbon fiber bundles were configured as a three-layer warp system, and the same prepreg carbon fiber bundles were used as weft yarns and interlayer cross-linked weft yarns. The three layers were woven synchronously according to the weaving method of Example 2, with interlayer cross-linked weft yarns placed between the first and second layers, and between the second and third layers. After weaving, hot-pressing was performed under the same conditions as in Example 2: a hot-pressing temperature of 325°C, a pressure of 1.0 MPa, a holding time of 10 min, followed by cooling to below 100°C. In this comparative example, although interlayer cross-linked weft yarns were provided, the carbon fiber bundles were not subjected to widening and thinning treatment, and therefore do not belong to the thermoplastic prepreg widened yarn tape structure.

[0049] Comparative Example 4 This comparative example provides a three-dimensional woven preform of three-layer thermoplastic prepreg yarn that has not undergone sufficient thermal melting and consolidation.

[0050] The same 48K large-tow carbon fiber as in Example 2 was selected, and a polyphenylene sulfide-based thermoplastic prepreg tape with a width of 40 mm and a thickness of 0.09 mm was prepared in the same manner. Three layers were woven synchronously in the same way as in Example 2, with odd-numbered cross-linked weft yarns and even-numbered cross-linked weft yarns placed between the first and second layers and between the second and third layers.

[0051] After weaving, the resulting preform was placed in a hot press for low-temperature compaction at 260°C and 1.0 MPa for 10 minutes, followed by cooling to below 100°C. Because this processing temperature was below the melting temperature of the polyphenylene sulfide resin, the thermoplastic resin did not reach a fully melted and flowing state. In this comparative example, although it had an interlayer cross-linked weft structure, the thermoplastic resin did not fully melt and penetrate, failing to form the same intralayer and interlayer integrally consolidated structure as in Example 2.

[0052] Examples 1-4 and Comparative Examples 1-4 were prepared as composite bonded plates with a size of 300mm × 300mm. At least three plates were prepared for each group, and samples were randomly taken from the edge, middle, and diagonal areas of each plate to reduce the influence of local weaving and bond differences on the results. Five valid samples were taken from each group for each test item, and the final results are expressed as mean ± standard deviation.

[0053] The test items are as follows: Porosity test: Take a 25mm×25mm sample and evaluate the resin impregnation and consolidation quality by density method combined with cross-sectional microscopic image analysis.

[0054] Interlayer shear strength test: The short beam bending method is used to evaluate the shear resistance between adjacent layers.

[0055] Thickness direction tensile strength test: After the upper and lower surfaces of the sample are bonded to the metal loading block, the thickness direction is stretched to evaluate the Z-direction connection ability.

[0056] Type I interlaminar fracture toughness test: An initial crack is formed by pre-embedding a thin film in the target interlaminar layer, and a double cantilever beam test is used to evaluate the resistance to interlaminar crack propagation.

[0057] In-plane tensile strength test: Samples are taken along the main bearing direction of the warp yarns to evaluate the effect of interlayer crosslinking or stitching on the continuity of the in-plane fibers.

[0058] Fracture surface and cross section observation: Observe the interlayer failure path, fiber pull-out, resin penetration and interlayer cross-linking weft bridging through optical microscope or scanning electron microscope.

[0059] The specific test results are shown in the table below: As can be seen from Example 1 and Comparative Example 1, under the same PA6-based thermoplastic prepreg spreading yarn system, the introduction of interlayer cross-linked weft yarn significantly improved the interlayer shear strength, thickness direction tensile strength, and type I interlayer fracture toughness, while the in-plane tensile strength did not show a significant decrease. This indicates that the interlayer cross-linked weft yarn forms an effective thickness direction connection through the first weft segment, the second weft segment, and the layer-changing segment. Furthermore, since this connection is formed during the weaving process and does not require subsequent puncture, it has minimal impact on the continuity of the in-plane fibers.

[0060] As can be seen from Example 2 and Comparative Example 2, although Z-direction stitching can improve interlayer bonding, post-weaving puncture stitching can cause local fiber shift, resin enrichment near the stitch hole, and in-plane fiber disturbance. Therefore, Comparative Example 2 has better thickness-direction performance than the uncrosslinked laminated structure, but its warp-direction in-plane tensile strength is lower than that of Example 2. This invention introduces interlayer crosslinked weft yarns through cross-linking openings, achieving interlacing connections between adjacent layers during weaving, which can improve interlayer performance while better maintaining the integrity of the warp and weft fiber structure.

[0061] As can be seen from Examples 2 and 3, when interlayer cross-linked weft yarns are used in both cases, using a widened and thinned thermoplastic prepreg widened yarn tape can significantly reduce the porosity and improve the interlayer shear strength and overall mechanical properties. Comparative Example 3 uses unwidened large-tow carbon fiber bundles, resulting in a longer path for the resin to enter the fiber bundle. After consolidation, internal voids and insufficiently impregnated areas are easily generated, thus its porosity is high, and both interlayer and in-plane properties are affected.

[0062] As can be seen from Examples 2 and 4, although both have interlayer cross-linked weft structures, the consolidation temperature of Comparative Example 4 is lower than the resin melting temperature. The thermoplastic resin failed to fully soften and flow, thus failing to penetrate the interlayer gaps. Consequently, the interlayer shear strength, thickness-direction tensile strength, and type I interlayer fracture toughness are all lower than those of Example 2. This indicates that the hot-melt consolidation step of the present invention has a synergistic effect with the interlayer cross-linked weft structure. The interlayer cross-linked weft provides fiber bridging and mechanical restraint, while the thermoplastic resin, after melting and flowing, further forms continuous intralayer and interlayer bonds.

[0063] As can be seen from the overall results of Examples 1-4, with the increase of the number of prefabricated layers, the staggered arrangement of interlayer crosslinked weft yarns, and the optimization of the hot-melt consolidation method, the interlayer shear strength, thickness tensile strength, and anti-delamination ability of the prefabricated structure all show a good upward trend. Example 3 adopts multi-layer staggered crosslinking and carbon fiber electrothermal heating and hot-press composite consolidation, which enables sufficient hot-melt bonding and fiber bridging in different interlayer regions of the thick cross-section structure. Therefore, it exhibits high thickness load-bearing capacity and interlayer fracture toughness in the simulation results.

[0064] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A thermoplastic pre-impregnated spread tow three-dimensional woven preform, characterized by: Includes at least two layers of prepreg-stretched yarn braided layers stacked along the thickness direction; Each of the prepreg spread yarn braided layers includes warp yarns extending in a first direction and weft yarns extending in a second direction, wherein the warp yarns and the weft yarns are thermoplastic prepreg spread yarn tapes formed by spreading and thinning large tow carbon fibers and impregnating them with thermoplastic resin. Interlayer cross-linked weft yarns are provided between adjacent prepreg-stretched yarn braided layers; The main body of the interlayer cross-linked weft yarn extends along the second direction and interweaves sequentially with the warp yarns in the adjacent two layers of prepreg and expanded yarn braiding layers within at least one weave cycle, so that the interlayer cross-linked weft yarn has a first weft segment in the first layer of prepreg and expanded yarn braiding layer, a second weft segment in the second layer of prepreg and expanded yarn braiding layer, and a layer-changing segment connecting the first weft segment and the second weft segment, thereby forming an interlayer connection structure in the thickness direction between the adjacent two layers of prepreg and expanded yarn braiding layers.

2. A thermoplastic pre-impregnated spread tow three-dimensional woven preform according to claim 1, characterized in that: The interlayer cross-linked weft yarns include odd-numbered cross-linked weft yarns and even-numbered cross-linked weft yarns; The odd-numbered cross-linked weft yarn is the interlayer cross-linked weft yarn introduced in the 2k-1th weft insertion cycle, and the even-numbered cross-linked weft yarn is the interlayer cross-linked weft yarn introduced in the 2kth weft insertion cycle, where k is a positive integer.

3. The thermoplastic pre-impregnated spread tow three-dimensional woven preform of claim 1, wherein: The odd-numbered cross-linked weft yarns and the even-numbered cross-linked weft yarns are arranged alternately, staggeredly, or at a preset interval along the length of the fabric, so that a continuous or intermittent interlayer cross-linking structure is formed between adjacent prepreg and stretched yarn weaving layers.

4. The thermoplastic pre-impregnated spread tow three-dimensional woven preform of claim 1, wherein: The interlayer cross-linked weft yarn's layer-changing segment crosses the interlayer interface between two adjacent prepreg-stretched and stretched yarn weaving layers, and the first weft segment and the second weft segment are respectively clamped or interwoven and limited by the warp yarns in the corresponding layers to form a non-puncture thickness direction connection.

5. The thermoplastic prepreg spreading yarn three-dimensional woven preform according to claim 1, characterized in that: The prepreg-stretched yarn weaving layer has three or more layers; the interlayer cross-linked weft yarn is provided between any two adjacent layers.

6. The thermoplastic prepreg spreading yarn three-dimensional woven preform according to claim 1, characterized in that: The interlayer cross-linked weft yarn is a pre-impregnated cross-linked weft yarn containing reinforcing fibers and thermoplastic resin; The interlayer cross-linked weft yarn is one or more combinations of thermoplastic prepreg carbon fiber spread yarn, thermoplastic prepreg carbon fiber bundle, and hybrid yarn of carbon fiber and thermoplastic resin fiber.

7. The thermoplastic prepreg expanded yarn three-dimensional woven preform according to claim 1, characterized in that: After the preform is heat-fused and solidified, the thermoplastic resin located between adjacent prepreg and spread yarn braided layers is in a state of molten penetration followed by cooling and solidification, so that the interlayer cross-linked weft yarn, the warp yarn and the weft yarn together form an integrated three-dimensional reinforced structure.

8. A method for preparing a three-dimensional woven preform of thermoplastic prepreg yarn according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Widen and thin the large tow carbon fiber and combine it with thermoplastic resin to obtain thermoplastic prepreg widened yarn tape. S2. The multiple sets of thermoplastic prepreg expanded yarn tapes are arranged in layers as a warp system, and the weft yarns are arranged in the corresponding weft insertion system, so that the multiple layers of prepreg expanded yarn tapes participate in weaving synchronously along the thickness direction; S3. By controlling the height position of different layers of warp yarns through heddles or heddles lifting mechanisms, ordinary openings and cross-layer cross-linking openings are formed during the weaving process; S4. Introduce ordinary weft yarn into the ordinary opening and introduce interlayer cross-linked weft yarn into the cross-layer cross-linking opening, so that the interlayer cross-linked weft yarn passes through the opening formed by two adjacent warp yarns in at least one tissue cycle and interweaves with the warp yarns in the two adjacent layers respectively, thereby forming an interlayer connection structure having a first weft segment, a second weft segment and a layer-changing segment connecting the first weft segment and the second weft segment. S5. After weaving is completed, the obtained three-dimensional woven preform is heat-fused and solidified, so that the thermoplastic resin melts or softens and flows and then cools and solidifies to obtain a thermoplastic prepreg expanded yarn three-dimensional woven preform.

9. The method for preparing a three-dimensional woven preform of thermoplastic prepreg yarn according to claim 8, characterized in that: In step S4, an odd number of cross-linked weft yarns are introduced in the 2k-1th weft insertion cycle, and an even number of cross-linked weft yarns are introduced in the 2kth weft insertion cycle. The odd-numbered cross-linked weft yarns and the even-numbered cross-linked weft yarns enter different weft-direction weaving positions in adjacent layers through different warp opening heights, so as to form an interlayer cross-linking structure that is arranged alternately, staggeredly, or at a preset interval, where k is a positive integer.

10. The method for preparing a three-dimensional woven preform of thermoplastic prepreg yarn according to claim 8, characterized in that: The hot melt consolidation in step S5 includes ultrasonic hot melt, carbon fiber electric heating, hot pressing, infrared heating, laser heating, molding heating, or a combination thereof; During the hot-melt solidification process, the three-dimensional woven preform is heated to the melting temperature of the thermoplastic resin and pressure is applied to allow the molten thermoplastic resin to penetrate into the interlayer cross-linked weft yarns, warp yarns and the gaps between the weft yarns, and then cooled and solidified.

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