Method of manufacturing a wrinkle-free fabric and a composite structure comprising a wrinkle-free fabric with an adhesive and a preform comprising a wrinkle-free fabric with an adhesive

Abstract

The present invention relates to a method of manufacturing a wrinkle-free fabric and a composite structure comprising a wrinkle-free fabric with an adhesive and a preform comprising a wrinkle-free fabric with an adhesive. The method of manufacturing the wrinkle-free fabric comprises providing a plurality of continuous fiber layers held together by stitching threads; and applying an adhesive between adjacent layers of the plurality of continuous fiber layers and on outer layers of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive is lower than the melting temperature of the stitching threads.

Description

Technical Field

[0001] This application relates to the field of composite materials, and in particular to wrinkle-free fabrics designed for use in high-performance composite structures in industries such as aerospace, automotive, and renewable energy. Background Technology

[0002] Wrinkle-free fabrics are widely used in composite material manufacturing because they can arrange continuous fibers without wrinkles, enhancing the mechanical properties of the final composite structure, such as strength and stiffness. The layers within a wrinkle-free fabric are typically secured by stitching with fine filament threads, creating a stable, wrinkle-free structure that supports efficient load transfer along the fibers and promotes resin flow during composite processing. Stitching includes, but is not limited to, various stitching styles such as chain stitch, lockstitch, or plain stitch, using threads made of one or more yarns formed by warp plying and / or twisting. The stitching thread can contain continuous or discontinuous filaments. This construction makes wrinkle-free fabrics invaluable in applications requiring lightweight and high-integrity structures.

[0003] In existing technologies, a common method for maintaining the stability of shaped, wrinkle-free fabric preforms during handling and processing is the application of tackifiers. Tackifiers provide temporary adhesion between layers to maintain the preform shape during initial processing. Tackifiers help maintain the preform's construction, particularly suitable for smaller or simpler structures. For larger or more complex structures, alternative techniques are typically explored to ensure stability over a large surface area while also allowing for efficient resin flow during resin infusion.

[0004] Therefore, those skilled in the art continue to conduct research and development in the field of wrinkle-free fabrics and composite preforms to improve the stability of preforms, enhance processing efficiency, and optimize resin infusion techniques, especially for larger or more complex structures. Summary of the Invention

[0005] A method for manufacturing wrinkle-free fabrics has been disclosed.

[0006] In one example, the disclosed method includes: providing a plurality of continuous fiber layers held together by sutures; and applying an adhesive between adjacent layers of the plurality of continuous fiber layers and on the outer layers of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive is lower than the melting temperature of the sutures.

[0007] They also unveiled wrinkle-free fabrics.

[0008] In one example, the disclosed wrinkle-free fabric comprises: a plurality of continuous fiber layers held together by seams; and an adhesive structure between adjacent layers of the plurality of continuous fiber layers and on the outer layers of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive structure is lower than the melting temperature of the seams.

[0009] A method for manufacturing composite structures was also disclosed.

[0010] In one example, the disclosed method includes: providing one or more layers of wrinkle-free fabric, each layer comprising a plurality of continuous fiber layers held together by stitches, and including an adhesive structure between adjacent layers of the plurality of continuous fiber layers and on the outer layers of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive structure is lower than the melting temperature of the stitches; arranging the one or more layers of wrinkle-free fabric to obtain a preform having a preformed shape; and heating the preform to a temperature between the activation temperature of the adhesive structure and the melting temperature of the stitches, thereby activating the adhesive structure and maintaining the preformed shape.

[0011] Preforms were also made public.

[0012] In one example, the disclosed preform comprises: one or more layers of wrinkle-free fabric, each layer comprising a plurality of continuous fiber layers held together by stitches, the one or more layers of wrinkle-free fabric arranged to form the shape of the preform; an adhesive structure for maintaining the shape of the preform, wherein the adhesive structure comprises an adhesive material and is located between adjacent layers of the plurality of continuous fiber layers and on the outer layers of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive structure is lower than the melting temperature of the stitches; and stitches within the wrinkle-free fabric define gap spaces between the plurality of continuous fiber layers that do not contain the adhesive material, providing pathways for resin impregnation.

[0013] Other examples of the disclosed wrinkle-free fabrics, preforms, and manufacturing methods will become apparent from the following detailed description, drawings, and appended claims. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of an example of a multilayer wrinkle-free fabric structure, showing a bidirectional construction of a first continuous fiber layer oriented in one direction and a second continuous fiber layer oriented in a second direction. The diagram also depicts the seams securing the inner continuous fiber layers and the adhesive structure located between adjacent fiber layers and on the outermost surface of the wrinkle-free fabric laminate. The diagram also includes optional interlayer toughening yarns located between the continuous fiber layers to enhance the impact resistance and durability of the composite structure.

[0015] Figure 2 This is a flowchart illustrating a method for manufacturing the wrinkle-free fabric described herein. The method includes the following steps: providing multiple continuous fiber layers, applying stitches to fix the fiber arrangement, and applying an adhesive structure to stabilize the wrinkle-free fabric structure.

[0016] Figure 3 The process of unfolding a wrinkle-free fabric layer and guiding it to a lamination roll, which applies adhesive yarn to both surfaces, is illustrated. The structure is then heated in an oven to activate the adhesive and stabilize the wrinkle-free fabric without affecting the seams.

[0017] Figure 4 A powder spraying method for applying adhesive is shown. Adhesive powder is sprayed onto the wrinkle-free fabric as it passes under the nozzle, followed by heating to activate the adhesive and fix it to the wrinkle-free fabric while maintaining the integrity of the seam.

[0018] Figure 5 This is a flowchart depicting the method for manufacturing composite structures using wrinkle-free fabric preforms as described in this specification.

[0019] Figure 6 This is a cross-sectional view of a preform structure consisting of multiple layers of wrinkle-free fabric located within a mold. Detailed Implementation

[0020] This description relates to a wrinkle-free fabric comprising multiple continuous fiber layers held together by seams. The structure includes an adhesive applied between adjacent continuous fiber layers to form an adhesive structure. The adhesive may also be applied to the outermost layer of the multiple continuous fiber layers. The adhesive helps maintain the shape of the fabric during preform processing by fixing the relative positions of the fiber layers or the relative positions of the wrinkle-free fabric within the preform. The activation temperature of the adhesive is set below the melting temperature of the seam material, allowing the adhesive to be activated without affecting the seams. This temperature relationship ensures that the seams do not melt, thereby maintaining open channels for resin impregnation. The combined use of seams and adhesive in the wrinkle-free fabric simultaneously supports mechanical properties and efficient processing, making the material suitable for the manufacture of composite materials that benefit from precise fiber alignment and efficient resin flow.

[0021] In some instances, the wrinkle-free fabric comprises more than two consecutive fiber layers, with an adhesive structure situated between the individual layers within the multilayer structure. By placing the adhesive between each layer, the stability and alignment of the fabric are enhanced after heating the preform, maintaining the intended positions of each fiber layer within the preform structure until resin impregnation.

[0022] Wrinkle-free fabrics are structural materials composed of continuous layers of fibers arranged without interlacing, forming a wrinkle-free structure. This construction contrasts with woven fabrics, where interlacing fibers create wrinkles, which can affect mechanical properties. The wrinkle-free arrangement of fibers in wrinkle-free fabrics enhances load transfer along the fibers, providing improved strength, stiffness, and overall mechanical properties. Wrinkle-free fabrics are ideal for composite material applications requiring high impact resistance, fatigue durability, and tensile strength. Furthermore, the open structure facilitates efficient resin flow during composite manufacturing, making these fabrics advantageous in industries requiring lightweight materials and reliable structural performance, such as aerospace, automotive, and wind energy.

[0023] Wrinkle-free fabrics can comprise multiple continuous fiber layers, each with a specific fiber orientation that contributes to the fabric's mechanical properties. Orientations include unidirectional, bidirectional, and multiaxial arrangements, each with different structural functions. In a unidirectional configuration, all fibers within a layer are arranged parallel to each other in a single direction, optimizing the fabric's high tensile strength along that axis. This arrangement is particularly effective for applications subjected to concentrated loads in one direction (such as structural beams or reinforcements). In a bidirectional configuration, fibers are oriented at two different angles (e.g., 0° and 90°) within a layer, enabling the fabric to withstand loads from two different directions. Multiaxial orientation involves fibers arranging at multiple angles (e.g., 0°, 90°, and ±45°), resulting in a more versatile fabric structure capable of handling complex loads from various directions. This arrangement distributes forces more evenly and enhances the resistance of structures made from this fabric to shear and torsional stresses. Multiaxial configurations can be used in advanced composite materials for applications where multidirectional strength and durability are critical, such as wind turbine blades, automotive components, and aerospace structures. Wrinkle-free fabrics can also be customized by continuously layering different orientations and / or different area weights per layer. Adjusting the number and orientation of layers can affect properties such as impact resistance and fatigue durability.

[0024] Wrinkle-free fabrics can be composed of a variety of fiber types, each selected based on desired properties such as strength, stiffness, heat resistance, or chemical compatibility. Fiber types include carbon fiber, known for its strength-to-weight ratio and thermal stability; cost-effective glass fiber, providing good tensile strength and moderate weight; and aramid fiber, valued for its impact resistance and energy absorption. Blended fabrics can also be used, combining different fiber types in the same layer or multiple layers to achieve a balance of properties, such as combining carbon fiber for stiffness with glass fiber for improved flexibility and elasticity. This choice of fiber composition allows wrinkle-free fabrics to be modified for specific applications, balancing performance requirements with cost and weight considerations.

[0025] In wrinkle-free fabrics, stitching is used to hold multiple consecutive fiber layers together without causing fiber misalignment, maintaining the fabric's structural integrity. The stitching not only holds the layers in place but also allows relative movement between the fibers. This feature is advantageous during the forming process because it allows wrinkle-free fabrics to be arranged into preforms with specific shapes. The freedom of fiber movement minimizes the strain applied to the fabric during forming, reducing the likelihood of fiber breakage or misalignment and ensuring that the final preform maintains the desired fiber orientation. By maintaining flexibility, the stitching simultaneously supports strength and adaptability, making wrinkle-free fabrics ideal for complex composite applications.

[0026] The seams in wrinkle-free fabrics are selected with a melt temperature higher than the adhesive activation temperature to ensure stability and prevent melting during adhesive activation. Typically, depending on specific performance requirements, the melt temperature of the seam material ranges from 120°C to above 400°C. For many applications, a range of 150°C to 300°C can be used, while for higher heat requirements, a range of 300°C to above 400°C can be employed. By selecting seam materials with melt temperatures within these ranges, the seams firmly maintain the fiber layers throughout the processing, reducing the risk of fiber misalignment or structural damage. Furthermore, by preventing melting during adhesive activation, the seams maintain an open gap, allowing for faster resin infusion in subsequent steps.

[0027] Seam materials in wrinkle-free fabrics are selected to provide stability, heat resistance, and compatibility with the composite structure. Suitable seam materials include high-melting-point polyesters, polyamides, and aramid fibers to ensure stability during adhesive activation. High-melting-point polyesters, with melting temperatures above 250°C, provide thermal stability and durability. Polyamides, with melting points ranging from 190 to 350°C, offer flexibility and elasticity during processing depending on the type of polyamide and its chemical properties, while aramid fibers, with melting points above 400°C, provide enhanced heat resistance for applications requiring higher high-temperature tolerance. Selecting seam materials within these melting temperature ranges ensures that the seam maintains structural integrity, firmly holds the fiber layers, and maintains unobstructed full-thickness pathways for resin flow during subsequent composite processing.

[0028] Stitching in wrinkle-free fabrics can be performed using textile machinery designed to join multiple fiber layers without affecting their alignment. The process involves laying out the individual fiber layers according to the desired orientation and then sewing them together with a continuous stitch path that avoids introducing tension or deformation. Automated stitching equipment is typically equipped with computer-aided design (CAD) controls, allowing for precise stitch positioning and adapting to different stitch types and patterns. Various stitch patterns are used in wrinkle-free fabrics to achieve specific mechanical properties and facilitate resin infusion during composite processing. Common patterns include plain weave stitches for lightweight support and flexibility, and chain stitches for increased strength in applications requiring higher durability. In some cases, lockstitches are also used due to their strength and stability in high-stress applications. The choice of stitch pattern can affect the fabric's flexibility and resin flow, as certain patterns create small, full-thickness channels that contribute to a more uniform distribution of the resin.

[0029] An adhesive structure is introduced into a wrinkle-free fabric to maintain the shape of the preform after the wrinkle-free fabric is arranged into its target configuration. The adhesive structure can be any permeable adhesive material located between adjacent continuous fiber layers and / or on the outermost layer of the wrinkle-free fabric. The structure is activated at a temperature below the melting point of the stitching material, bonding the fiber layers to maintain the shape and stability of the preform while creating open pathways for resin impregnation. It can be applied in various forms, such as powder, nonwoven yarn, or hybrid constructions, to provide adhesion and, in some cases, additional toughening properties.

[0030] The adhesive structure remains inactive during molding, allowing the continuous fiber layers within the wrinkle-free fabric to move relative to each other. This minimizes strain during molding and reduces the likelihood of fiber misalignment or breakage. Once the preform shape is finalized, the structure is bonded by activating the adhesive to a specific temperature, thus properly locking the shape of the preform. The adhesive structure can be located (1) between adjacent continuous fiber layers, where, upon activation, it forms an internal bond that restricts movement between the fiber layers, helping to maintain alignment and stability; and (2) on one or both outer surfaces of the fiber layer stack, where, upon activation, it helps to secure the preform by restricting movement between the wrinkle-free fabric and any adjacent material (e.g., another layer of wrinkle-free fabric). By controlling the arrangement and activation of the adhesive structure, the preform achieves stability while avoiding unnecessary strain during molding, supporting the fabric alignment, and preparing for subsequent composite manufacturing steps (e.g., resin infusion and curing).

[0031] The activation temperature of the adhesive structure is the temperature at which the adhesive material softens or melts to form a bond between adjacent fiber layers, fixing the preform shape after curing. This activation temperature is selected below the melting temperature of the suture material to ensure that the adhesive is activated without affecting the suture. Depending on the expected bonding requirements, the typical activation temperature of the adhesive material is approximately 70°C to 180°C. This selective activation stabilizes the preform structure while maintaining full-thickness channels open for resin infusion during composite processing.

[0032] The adhesive structure in wrinkle-free fabrics can be used in powder form, enabling uniform distribution between continuous fiber layers and precise control over coverage. This powdered adhesive, located between adjacent fiber layers or even on the outer layers, is activated upon heating to a specified activation temperature, bonding the layers and maintaining the preform shape. The powder form offers application flexibility, ensuring uniform adhesion on complex or shaped preforms, and allowing the adhesive to be customized to the specific bonding requirements of the composite structure.

[0033] The powder binder composition is formulated to exhibit little or no tack at room temperature, allowing for easy handling and positioning of the wrinkle-free fabric layers without prematurely bonding adjacent fiber layers together. This low-tack property ensures that the layers remain freely adjustable during assembly, enabling precise alignment before the preform shape is finalized. Suitable powder binder compositions include, but are not limited to, thermosetting materials such as epoxy resins, bismaleimides, polyesters, acrylics, and vinyl esters, and thermoplastic materials such as polyamides, polyesters, polysulfones, polyetherketones, polyurethanes, and polyimides. In some instances, it is preferred that the binder reacts with the matrix resin injected into the preform, chemically incorporating it into the polymer backbone of the matrix resin. Upon reaching its activation temperature, the powder binder softens or melts, firmly bonding the fiber layers in situ while maintaining open pathways for effective resin infusion in subsequent composite processing.

[0034] The adhesive structure can also be implemented as a nonwoven tuft located between fiber layers and optionally also on the outer layer of the fabric laminate, i.e., a thin and flexible sheet. When heated to its activation temperature, the nonwoven tuft bonds the fabric layers in situ to maintain the pre-formed shape. This tuft structure enables uniform adhesive coverage across the entire fabric and can conform to complex contours, ensuring uniform adhesion. Furthermore, the open structure of the nonwoven tuft supports resin permeability, making it suitable for composite material applications requiring both stable adhesion and resin flow.

[0035] Nonwoven tulle adhesive structures are composed of thermoplastic fibers that are activated at specific temperatures, thereby forming bonds between fiber layers without interfering with resin flow. Suitable materials for nonwoven tulle include polyamides, polyimides, polyamide-imides, polyesters, polybutadiene, polyurethanes, polypropylene, polyetherimides, polysulfones, polyethersulfones, polyphenylene sulfones, polyphenylene sulfides, polyetherketones, polyetheretherketones, polyarylamides, polyketones, polyphthalamides, polyphenylene ethers, polybutylene terephthalate, polyethylene terephthalate, and polyester-polyaryl esters (e.g., VECTRAN). TM The open structure of these tufts ensures that the resin can effectively penetrate through the adhesive layer, making these compositions suitable for applications in composite manufacturing processes that require both stable adhesion and efficient resin infusion.

[0036] Interlayer toughening yarns can also be placed between adjacent continuous fiber layers in wrinkle-free fabrics to improve impact resistance and toughness. Interlayer toughening yarns can be placed in the same interlayer space as the nonwoven yarn adhesive structure. When placed in the same interlayer space with the nonwoven yarn adhesive structure, the two yarns can work together to provide both bonding and toughening functions within a single layer. Alternatively, placing interlayer toughening yarns separately allows for independent reinforcement and toughening where additional impact resistance is required, without affecting the primary bonding locations of the adhesive structure. This arrangement provides design flexibility, enabling precise control over the structural and impact resistance properties of the composite material while maintaining open pathways for resin flow during processing.

[0037] Interlaminar toughening yarns are selected with melt temperatures higher than the activation temperatures of any adhesive to ensure their stability during adhesive activation. This stability allows the interlaminar toughening yarns to provide structural reinforcement without compromising the adhesive function of the adhesive structure. Depending on the specific thermal and mechanical property requirements of the composite material, the melt temperature of the interlaminar toughening yarns typically ranges from 120°C to 300°C. For applications requiring moderate heat resistance, a melt temperature range of 150°C to 250°C can be used, while for higher heat requirements, materials with melt temperatures exceeding 250°C are preferred. Selecting an appropriate melt temperature for the interlaminar toughening yarns ensures that they effectively perform their toughening function without interfering with the activation of the adhesive.

[0038] Interlayer toughening tufts are composed of fibers or materials specifically selected to enhance the toughness and durability of composite materials. Suitable materials include polyamides, polyimides, polyamide-imides, polyesters, polybutadiene, polyurethanes, polypropylene, polyetherimides, polysulfones, polyethersulfones, polyphenylene sulfones, polyphenylene sulfides, polyetherketones, polyetheretherketones, polyarylamides, polyketones, polyphthalamides, polyphenylene ethers, polybutylene terephthalate, polyethylene terephthalate, and polyester-polyaryl esters (e.g., VECTRAN). TM ), polyaramid (e.g., KEVLAR) TM ), polybenzoxazole (e.g., ZYLON) TM ), viscose fibers (e.g., RAYON) TM ), carbon fiber and glass fiber.

[0039] Blended yarns can be incorporated to provide both bonding and toughening functions within wrinkle-free fabrics. These blended yarns contain a combination of low-melting-point and high-melting-point components, each playing a specific role. The low-melting-point component acts as an adhesive, with an activation temperature below the melting point of the seam material, allowing it to bond adjacent fiber layers without affecting the seam. The high-melting-point component acts as an interlayer toughening yarn, enhancing impact resistance and durability; its melting temperature is above the activation range of the adhesive, thus maintaining stability during bonding. Blended yarns can be constructed by interweaving or blending low-melting-point and high-melting-point fibers in a single nonwoven structure, or by laminating individual sheets of various materials to form a multifunctional yarn. For example, a blended yarn can contain low-melting-point polyester fibers (activation range 100°C to 140°C) as an adhesive component and aramid fibers (melting temperature above 400°C) as a toughening component. The low-melting-point polyester fibers activate upon heating to bond the layers, while the aramid fibers remain intact, providing structural reinforcement. Similarly, bicomponent yarns can be manufactured by combining high-melting-point and low-melting-point variants of a single polymer species, for example, using two different polyamide variants, such as a low-melting-point copolyamide constituting one part and a different polyamide or copolyamide constituting the other part with a higher melting point, and combining them as described above. By combining these components, blended yarns enable integrated bonding and toughening within a single layer, while optimizing the structural integrity and impact resistance of the composite material. Blended yarns can be located between adjacent fiber layers or on the outer surface of the fabric laminate, providing flexibility in composite design and enhancing the performance of wrinkle-free fabrics in demanding applications.

[0040] Figure 1An example of the multilayer wrinkle-free fabric structure described herein is shown. In this example, the wrinkle-free fabric structure comprises a first continuous fiber layer (10) arranged in parallel and a second continuous fiber layer (20) also arranged in parallel. Notably, the fibers in the first layer are arranged perpendicularly to the fibers in the second layer, providing a bidirectional structure. However, those skilled in the art will understand that additional layers can be added, and other orientations of the fiber arrangement (e.g., unidirectional or multiaxial structures) can be implemented to achieve specific mechanical properties tailored to the application. Figure 1 The sutures (30) shown here are for securing the layers together; the arrangement of the sutures shown is for illustrative purposes only. Various suture patterns and techniques can be employed depending on the number of layers, the specific fiber orientation, and the type of fiber used. Those skilled in the art will fully understand this variation and can select a suitable suture pattern based on the expected performance requirements of the composite structure.

[0041] Representative adhesive structures (40) in Figure 1 Located between the first and second continuous fiber layers, this layer is designated as an adhesive tuft. This adhesive structure helps maintain the structural integrity of the wrinkle-free fabric structure by stabilizing the relative positions of the fiber layers during preform processing and subsequent finishing stages. Although the adhesive structure is designated as tuft, it should be noted that a powdered adhesive structure may also be used, depending on processing requirements and desired properties. The adhesive structure (40) may also be located on the outermost layer of the continuous fiber laminate to enhance stability during processing and finishing. The adhesive's activation temperature is below the melting temperature of the suture, allowing it to activate and firmly bond the layers without compromising the integrity of the suture.

[0042] also, Figure 1 Optional interlayer toughening yarns (50) may also be included between the continuous fiber layers. These toughening yarns are designed to improve the impact resistance and durability of the composite by providing additional reinforcement between the fiber layers. Although the interlayer toughening yarn (50) is shown herein, it should be understood that the yarn can be included in other constructions of a wrinkle-free fabric structure if enhanced toughness is required. Furthermore, Figure 1 It can contain hybrid yarns that provide both bonding and toughening functions. These hybrid yarns can contain a low-melting-point component that acts as an adhesive and a high-melting-point component that acts as an interlayer toughening yarn. This dual-function yarn can be located between adjacent fiber layers or on the outer surface of the fiber laminate, providing design flexibility and enhancing the performance of wrinkle-free fabrics in demanding applications.

[0043] Figure 2A flowchart illustrating a method 100 for manufacturing the wrinkle-free fabric described herein is provided, consistent with the steps of claim 1. Step 110 begins by providing multiple continuous fiber layers. The continuous fibers within each layer can be arranged without interlacing to maintain a wrinkle-free structure and optimize load transfer performance. The layers are sewn together using a sewing material with a melting point higher than the activation temperature of the adhesive to secure them while maintaining their orientation. Step 120 involves applying an adhesive structure between adjacent continuous fiber layers or on the outer layer of the fiber laminate, which is also a continuous fiber layer. The adhesive structure can be applied before or after the sewing and can be in powder form, as a nonwoven yarn, or as a blend of yarns with low-melting-point and high-melting-point components. Its activation temperature is set below the melting temperature of the sewing line, allowing it to activate without compromising the integrity of the sewing line. This adhesive structure stabilizes the preform while maintaining the flexibility of molding, as will be described in further detail below.

[0044] In one approach, wrinkle-free fabrics can be manufactured using any standard method known in the art. Typically, wrinkle-free fabrics are constructed by arranging multiple continuous fiber layers in a specific orientation to achieve a wrinkle-free structure. Depending on the desired mechanical properties of the final composite material, these continuous fibers can be arranged in a unidirectional, bidirectional, or multiaxial configuration. The layers are arranged in parallel, non-interlacing to avoid wrinkles and maximize load transfer along the fibers. After the fiber layers are arranged, they are secured with stitches. Various stitching patterns, such as plain stitch, chain stitch, or lockstitch, can be used depending on the number of layers, fiber orientation, and type of fiber used. The stitching is performed in a manner that minimizes fiber misalignment, thereby maintaining the structural integrity of the fabric and supporting the flexibility of forming preforms. The stitching material is typically selected for its high melting point to ensure its stability during any subsequent adhesive activation process. After stitching, the wrinkle-free fabric structure is ready for further processing or application of adhesive structures.

[0045] In some instances, an adhesive structure is applied to the outermost layer of a previously manufactured wrinkle-free fabric. The adhesive structure can be located on one or both sides of the wrinkle-free fabric to enhance preform stability during preform handling and subsequent composite processing. Various exemplary methods can be used to apply the adhesive structure. In one method, powdered adhesive is sprayed onto the outer surface of the wrinkle-free fabric, enabling controlled distribution across the fabric. Alternatively, nonwoven adhesive yarns can be laminated onto one or both outer surfaces of the wrinkle-free fabric. This lamination method provides uniform coverage and additional adhesive strength, which can be advantageous for applications requiring enhanced stability. After application of the adhesive structure, a heat treatment is performed to firmly adhere the adhesive structure to the outer layer of the wrinkle-free fabric. In this step, the wrinkle-free fabric is heated to a temperature above the adhesive activation temperature but below the melting temperature of the stitching and any optional interlayer toughening yarns. This selective heating ensures that the adhesive is activated and bonded to the fiber layers without compromising the integrity of the stitching or other structural components. By performing this heat treatment, the adhesive structure is effectively bonded to the outer layer of the wrinkle-free fabric, enhancing the fabric's stability and fixing the pre-formed shape.

[0046] Figure 3 and Figure 4 Two different methods are shown for applying adhesive to the layers of a wrinkle-free fabric structure prior to sewing, ensuring the adhesive remains inactive and flexible during preform forming. In one method, fibers are removed from a spool and spread into strips, cut to length, and then the ends of the strips are properly held in a machine tool (usually by clamping). This process is repeated for each layer except for continuous 0-degree fibers along the length of the machine tool. Figure 3 Fabric lamination is depicted, in which an adhesive in the form of nonwoven yarn is applied to the top and / or bottom surfaces of individual, continuous fiber layers as they are placed on the machine (rather than after the entire layer has been unfolded). The fiber layers with adhesive are then lightly heated to fix the adhesive to the monolayer, but not to fully activate it. This low-level heat treatment only adheres the adhesive to the individual fiber layers to facilitate handling and sewing, preventing premature bonding that would restrict drape. After all layers have been applied with adhesive and lightly adhered, they are sewn together with sutures (30), which remain aligned and do not restrict interlayer movement. After sewing, the wrinkle-free fabric structure with inactive adhesive is wound onto an output reel (90) for transport. In subsequent processing steps, after the wrinkle-free fabric has been shaped into a preform, controlled heating is applied to activate the adhesive and stabilize the preform shape.

[0047] Figure 4An alternative method using powder spraying is shown, in which adhesive is applied to individual continuous fiber layers prior to sewing. Here, the layers within the wrinkle-free fabric are unrolled from an input spool (60) and conveyed below a nozzle (92), which disperses the powdered adhesive onto one side of each layer. Applying adhesive only to one side avoids the potential problems associated with coating both sides. When the layers are assembled, the adhesive is present between them, providing sufficient bonding during subsequent processing. After powder application, the layers are passed through an oven (80), which provides a light heat sufficient to allow the adhesive powder to adhere to the fiber surface without fully activating it. Similar to the lamination method, this heat treatment merely fixes the adhesive for stacking and sewing. In some setups, adhesive application can be performed continuously, but it can also be done by preparing a unidirectional fabric with adhesive, which is then fed into a warp knitting machine to produce the wrinkle-free fabric. After the layers have been treated, they are stacked and sewn together with stitches (30), maintaining the adhesive arrangement between the layers while allowing flexibility. The complete wrinkle-free fabric structure with an inactive adhesive is then wound onto an output reel (90) for transport. Subsequently, after the wrinkle-free fabric has been shaped into a preform, the adhesive is activated by controlled heating to lock the preform shape.

[0048] In another approach, the manufacture of wrinkle-free fabrics can be modified by introducing an adhesive structure between sub-laminated layers of selected continuous fiber layers during assembly, keeping the adhesive inactive at this stage. This integration method can provide internal bonding potential within the fabric structure, enhancing post-forming stability and fiber alignment, but can reduce the flexibility or drape of the wrinkle-free fabric, which is crucial for forming complex preforms. Conventional wrinkle-free fabric manufacturing machines are not typically designed to stitch single layers together with adhesive structures between the layers; instead, they may stitch two or more sub-laminated layers together. However, stitching sub-laminated layers together with an inter-layer adhesive can make the fabric too rigid for some applications requiring high drape to fit complex preforms. To manufacture wrinkle-free fabrics, continuous fibers, such as carbon fibers, glass fibers, or aramid fibers, are selected based on the desired mechanical properties of the final composite. These fibers are prepared in continuous lengths and aligned to avoid wrinkles, supporting effective load transfer along the fibers. Depending on the desired properties of the wrinkle-free fabric, the continuous fiber layers are laid out in a specific orientation (e.g., unidirectional, bidirectional, or multiaxial). When the fiber layers are distributed onto the warp knitting machine, a powder form (uniformly distributed across each fiber layer) or a binder structure as a nonwoven yarn can be introduced between adjacent sublayer stacks. If necessary, continuous fiber laying and the binder structure are continued to achieve the desired layered structure. Various stitching patterns, such as chain stitch, lockstitch, or warp straight stitch, can be used depending on the number of layers, fiber type, and orientation. A stitching material with a high melting point is selected to ensure its stability during subsequent processing. The stitches properly secure the layers, maintaining fiber alignment and flexibility within the wrinkle-free fabric structure. After all layers and binder structures have been aligned and secured with stitches, a wrinkle-free fabric structure is obtained for shaping into the desired preform. At this stage, the binder structures remain inactive, allowing the fabric to remain flexible and move relative to each other as needed for shaping. By incorporating the binder structures at the layer level and keeping them inactive, the wrinkle-free fabric achieves a degree of internal stability while maintaining sufficient shaping adaptability, although applications requiring high drape may benefit from other constructions.

[0049] This description also includes a method for manufacturing a composite structure, comprising forming a preform using a wrinkle-free fabric layer. This method utilizes the structural advantages of combining a wrinkle-free fabric providing a continuous, wrinkle-free fiber layer held together by stitches with an adhesive structure that stabilizes the shape of the preform during processing. The steps involved in manufacturing this composite structure are described in... Figure 5 The flowchart is shown.

[0050] Figure 5A method (200) is shown, which is a process for manufacturing a composite structure using layers of wrinkle-free fabric. The method begins in step (210) by providing one or more layers of wrinkle-free fabric. Each wrinkle-free fabric layer comprises multiple continuous fiber layers arranged in a wrinkle-free configuration and held together by sutures that maintain the fiber alignment and structural integrity. An adhesive structure is also included, located between adjacent fiber layers or even on the outermost layer. The activation temperature of this adhesive structure is lower than the melting temperature of the sutures, allowing for selective activation without affecting the sutures.

[0051] After preparing the wrinkle-free fabric layers, step (220) involves arranging these layers into a preform shape suitable for composite material processing. The stitching in the wrinkle-free fabric layers provides the flexibility required to shape each layer while maintaining fiber alignment and stability. This enables the customization of precise preform designs to meet the expected structural requirements of the composite material.

[0052] In step (230), the preform is heated to a controlled temperature between the activation temperature of the adhesive structure and the melting temperature of the suture. This selective heating activates the adhesive structure, bonding the fiber layers together while maintaining the suture, which keeps open channels for resin impregnation in subsequent steps. This controlled activation stabilizes the preform, allowing it to maintain its shape throughout subsequent processing.

[0053] Following activation of the adhesive structure, step (240) involves impregnating the preform with resin to complete the composite structure. The open gap channels maintained by the sutures facilitate resin flow across the entire thickness, enabling rapid and uniform impregnation across all fiber layers. A variety of resins can be used depending on the desired mechanical properties, thermal stability, and environmental resistance of the final composite. Suitable resins include, but are not limited to, epoxy resins, polybenzoxazine, bismaleimide, polyimide, polyester resins, vinyl ester resins, mixtures of various compatible resin types (such as epoxy and benzoxazine), and phenolic resins. Epoxy resins are widely used due to their high mechanical strength and chemical resistance, making them ideal for applications requiring durability under stress. Polyester resins offer cost-effective reinforcement with good tensile properties, while vinyl ester resins provide enhanced chemical and heat resistance suitable for harsh environments. Phenolic resins can be selected for applications requiring high fire resistance and low smoke emission. The resin is applied to the preform by infusion, which can be achieved using vacuum-assisted resin transfer molding (VARTM), resin transfer molding (RTM), or other suitable impregnation techniques. During the infusion process, resin is drawn into the preform under controlled pressure, ensuring complete impregnation of fibers within each layer of the wrinkle-free fabric. Vacuum or pressure helps minimize voids within the composite structure, improving consistency and mechanical reliability. Depending on the resin's viscosity, reactivity, and flow characteristics, impregnation can be performed at ambient or elevated temperatures and should be optimized to achieve complete and uniform resin distribution throughout the preform.

[0054] After the preform is fully impregnated with resin, step (250) involves curing the resin to harden the structure and ultimately determine the mechanical properties of the composite. Curing can be performed at ambient temperature or elevated temperature, depending on the resin system. For example, depending on the specific formulation and thickness of the composite structure, epoxy resins may require curing temperatures of 80°C to 180°C, typically maintained for 30 minutes to 6 hours. Elevated temperature curing can be performed in an oven, autoclave, or using a heated press to ensure consistent heat distribution and complete polymerization of the resin. Some resins, such as room temperature curing epoxy or polyester resins, can be cured for longer periods under ambient conditions, which may be advantageous for applications requiring lower energy input or for manufacturing larger parts. In these cases, curing agents or accelerators can be added to the resin to control the curing rate and optimize the properties of the final composite. Pressure curing (especially in an autoclave or closed mold) can improve the quality of the composite by reducing porosity, increasing fiber-resin contact, and improving mechanical properties. Complete curing allows the resin to solidify, firmly bonding the layers of the preform and locking in the fiber arrangement initially established by the wrinkle-free fabric and stitching. This results in a unified, high-strength composite structure suitable for a variety of demanding applications requiring enhanced load-bearing capacity, durability, and environmental resistance. Therefore, this method provides a robust approach to manufacturing composite materials using controlled fiber alignment, resin impregnation, and curing to achieve composite structures with optimal mechanical and structural properties.

[0055] In another instance, this description relates to a preform structure used as an intermediate product in composite material manufacturing. Figure 6 An example of this preform is shown, which consists of one or more layers of wrinkle-free fabric arranged to form a stable, shape-preserving structure, and is designed to facilitate efficient resin impregnation and composite processing.

[0056] The wrinkle-free fabric layers in the preform structure can consist of multiple continuous fiber layers. These layers are held together by stitches within the wrinkle-free fabric layers, which ensure fiber alignment and maintain the wrinkle-free construction. For example... Figure 1 and Figure 2 As shown, this internal structure of each wrinkle-free fabric layer maintains optimal load transfer characteristics and mechanical properties, and the stitches secure the continuous fiber layers without affecting interlayer flexibility. Figure 6 As shown, the preform (7) consists of multiple wrinkle-free fabric layers, represented by the first layer (1) and the second layer (2), which are arranged in the desired shape within the mold (3) for processing of the composite material.

[0057] An adhesive structure is incorporated within the wrinkle-free fabric to stabilize and maintain the shape of the preform. This adhesive structure can be located between adjacent continuous fiber layers within the individual wrinkle-free fabric layers or also on the outermost layer. The adhesive is selected to have an activation temperature below the melting point of the stitching material, ensuring that it can fix the fiber layers into the desired shape without compromising the integrity of the stitch. This selective activation of the adhesive structure locks the fiber layers within the individual wrinkle-free fabric layers into the preformed shape, maintaining stability throughout the processing and resin impregnation.

[0058] The preform contains gaps between continuous fiber layers within each wrinkle-free fabric layer, and these gaps are free of adhesive material. These full-thickness open channels are crucial for resin flow during subsequent resin impregnation, enabling rapid and uniform distribution of resin throughout the fiber structure. This resin permeability helps minimize voids and supports the formation of a robust, cohesive composite structure.

[0059] In some constructions, the adhesive structure is applied in powder form, enabling controlled distribution and coverage between the fiber layers. This powder adhesive can be formulated to be nearly tackless or non-tackless at room temperature, facilitating easy handling and precise positioning of individual wrinkle-free fabric layers during preform assembly. Upon heating, the powder adhesive softens or melts, firmly bonding the fiber layers and stabilizing the preform.

[0060] Alternatively, the adhesive structure can be implemented as a nonwoven tuft (a thin and flexible sheet) that can be located between multiple consecutive fiber layers within the individual wrinkle-free fabric layers or also on the outer surface of the wrinkle-free fabric laminate. This nonwoven tuft provides uniform adhesion on the fabric surface, conforms to the complex contours within the preform, and maintains open channels for resin flow throughout the full thickness, enabling effective impregnation in subsequent stages.

[0061] For applications requiring additional impact resistance and toughness, interlayer toughening yarns can be incorporated into the preform, located between continuous fiber layers within each wrinkle-free fabric layer or between adjacent wrinkle-free fabric layers. These toughening yarns have a melting temperature higher than the adhesive activation temperature, ensuring stability during adhesive activation. The inclusion of toughening yarns enhances the preform structure, improving the durability and impact resistance of the final composite material.

[0062] In some constructions, the adhesive structure can be a hybrid yarn containing both low-melting-point and high-melting-point components. The low-melting-point component is activated at a lower temperature to bond the fiber layers within the individual wrinkle-free fabric layers, while the high-melting-point component acts as an interlayer toughening yarn, providing additional strength and elasticity. This bifunctional hybrid yarn allows preforms to effectively maintain their shape while providing increased toughness, meeting the demands of high-performance composite applications.

[0063] The preform structure integrates the advantages of wrinkle-free fabric and selectively activated adhesive structure, forming a shape-stable, resin-permeable intermediate. This design allows the preform to be customized for specific applications, for example, by incorporating powdered binders, nonwoven yarns, or mixed toughening layers. By maintaining open resin flow channels and enhancing structural stability, this preform construction supports efficient composite processing, making it suitable for applications in aerospace, automotive, wind energy, and other industries requiring high structural integrity and processing efficiency.

[0064] In summary, the described wrinkle-free fabric and preform construction provides an innovative approach to achieving precise fiber alignment, enhanced structural stability, and efficient resin impregnation in composite material manufacturing. Each wrinkle-free fabric layer comprises multiple continuous fiber layers held together by stitches, maintaining a wrinkle-free structure with optimized load transfer and mechanical integrity. This layered structure allows for a variety of fiber orientations, including unidirectional, bidirectional, and multiaxial configurations, which can be customized to suit specific application requirements and improve strength, stiffness, impact resistance, and fatigue durability.

[0065] Selectively activated adhesive structures, located between continuous fiber layers or on the outermost surface of wrinkle-free fabrics, offer advantages in stabilizing the shape of preforms during molding, handling, and processing. The activation temperature of the adhesive structure is tailored to be below the melting point of the stitching material, allowing the preform shape to be properly locked in without compromising the open channels for resin flow. This ensures the integrity of the stitches and the alignment of the fiber layers throughout processing.

[0066] Various examples of adhesive structures (including powder adhesives, nonwoven yarns, and hybrid yarns) allow for the construction of modifiable preforms. These examples support open gap spaces between fiber layers for effective resin impregnation and bonding during composite material manufacturing. Furthermore, interlayer toughening yarns or hybrid yarns with both low-melting-point and high-melting-point components provide enhanced impact resistance and durability, enabling these preforms to meet the demands of demanding applications in industries such as aerospace, automotive, and renewable energy.

[0067] The disclosed method for manufacturing composite structures further optimizes the impregnation and curing of preforms. By controlling the activation of the adhesive structure and ensuring the existence of open, full-thickness resin flow pathways, this method achieves rapid and uniform resin distribution across all fiber layers. Subsequent resin curing can be carried out at ambient or elevated temperatures, ultimately determining the mechanical properties of the composite material and producing a high-strength, cohesive structure with reduced porosity and excellent load-bearing capacity.

[0068] In some instances, the adhesive structure is formulated to be chemically reactive with the resin used to impregnate the preform. During curing, the adhesive structure interacts with the resin, chemically bonding to the matrix resin. This reactive bonding further enhances the cohesion between the fiber layers, forming a monolithic composite structure with improved mechanical integrity. By forming covalent bonds with the matrix resin, the adhesive contributes to the overall stability and durability of the final composite material. This reactive bonding allows for a more seamless integration between the adhesive and resin, reduces the likelihood of delamination, and enhances load transfer between the fiber layers in the composite structure.

[0069] The described wrinkle-free fabric preform and composite material manufacturing method represents a robust solution for high-performance composite material manufacturing. By utilizing a combination of precise fiber alignment, customizable adhesive structures, and efficient resin flow pathways, the disclosed examples enable the fabrication of composite structures with optimized mechanical and thermal properties. This versatility makes the disclosed invention applicable to a wide range of applications requiring structural integrity, impact resistance, and processing efficiency.

[0070] Although various examples of the disclosed wrinkle-free fabrics, preforms formed therefrom, and methods for manufacturing composite structures have been shown and described, those skilled in the art will understand that modifications can be made without departing from the scope and spirit of the invention. This application includes such modifications and is limited only by the scope of the claims.

Claims

1. A method for manufacturing a wrinkle-free fabric (1), comprising: Provides multiple continuous fiber layers (10, 20) held together by sutures (30); as well as An adhesive is applied between adjacent layers of the plurality of continuous fiber layers (10, 20) and on the outer layer of the plurality of continuous fiber layers (10, 20), wherein the activation temperature of the adhesive is lower than the melting temperature of the suture.

2. The method as described in claim 1, wherein, The adhesive is applied before the suture (30) is applied; preferably, the adhesive is applied to the outer layer of the plurality of continuous fiber layers (10, 20) after the suture (30) is applied.

3. The method as described in claim 1 or 2, wherein, The adhesive is in powder form; preferably, the powder has little or no tackiness at room temperature; or Wherein, the adhesive is in the form of nonwoven yarn; or Interlayer toughening yarn (50) is provided between adjacent layers of the plurality of continuous fiber layers (10, 20), wherein the melting temperature of the interlayer toughening yarn is higher than the activation temperature of the adhesive; or The step of applying the adhesive includes applying a yarn having a low-melting-point component and a high-melting-point component, wherein the low-melting-point component of the yarn acts as the adhesive and the high-melting-point component acts as an interlayer toughening yarn.

4. A wrinkle-free fabric (1), comprising: Multiple continuous fiber layers (10, 20) held together by sutures (30); and An adhesive structure (40) is provided between adjacent layers of the plurality of continuous fiber layers and on the outer layer of the plurality of continuous fiber layers, wherein, The activation temperature of the adhesive structure (40) is lower than the melting temperature of the suture.

5. The wrinkle-free fabric as described in claim 4, wherein, The adhesive structure (40) is in powder form; preferably, the powder has little or no tackiness at room temperature. Wherein, the adhesive structure (40) is in the form of a nonwoven tulle; or The wrinkle-free fabric further comprises: interlayer toughening yarn (50) between adjacent layers of the plurality of continuous fiber layers, wherein the melting temperature of the interlayer toughening yarn is higher than the activation temperature of the adhesive structure; or The adhesive structure (40) comprises a low-melting-point component and a high-melting-point component, wherein the low-melting-point component of the adhesive structure acts as the adhesive, and the high-melting-point component acts as the interlayer toughening yarn.

6. A method for manufacturing a composite structure, the method comprising: One or more layers of wrinkle-free fabric (1, 2) are provided, each layer of wrinkle-free fabric comprising a plurality of continuous fiber layers (10, 20) held together by a suture (30), and an adhesive structure (40) is included between adjacent layers of the plurality of continuous fiber layers and on the outer layer of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive structure (40) is lower than the melting temperature of the suture. Arrange one or more layers of wrinkle-free fabric to obtain a preform (7) with a preformed shape; and The preform is heated to a temperature between the activation temperature of the adhesive structure (40) and the melting temperature of the suture (30), thereby activating the adhesive structure (40) and maintaining the preform shape.

7. The method of claim 6, wherein, The adhesive structure (40) is in powder form; preferably, the powder has little or no tackiness at room temperature; or Wherein, the adhesive structure (40) is in the form of a nonwoven tulle; or Interlayer toughening yarn (50) is provided between adjacent layers of the plurality of continuous fiber layers (10, 20), wherein the melting temperature of the interlayer toughening yarn is higher than the activation temperature of the adhesive structure (40); or The adhesive structure (40) comprises a low-melting-point component and a high-melting-point component, wherein the low-melting-point component acts as the adhesive and the high-melting-point component acts as an interlayer toughening yarn; or The method further includes impregnating the preform (7) with resin, and preferably curing the resin; wherein, preferably, during the curing process of the resin, the adhesive structure reacts with the resin.

8. A preform comprising: One or more layers of wrinkle-free fabric (1, 2), each layer of wrinkle-free fabric comprising multiple continuous fiber layers (10, 20) held together by stitches (30), the one or more layers of wrinkle-free fabric arranged to form the shape of the preform (7); An adhesive structure (40) that maintains the shape of the preform, wherein, The adhesive structure comprises an adhesive material and is located between adjacent layers of the plurality of continuous fiber layers and on the outer layer of the plurality of continuous fiber layers, wherein the activation temperature of the adhesive structure (40) is lower than the melting temperature of the suture (30); and The wrinkle-free fabric (1, 2) defines gap spaces without the adhesive material between the plurality of continuous fiber layers (10, 20), providing a pathway for resin impregnation.

9. The preform as claimed in claim 8, wherein, The adhesive structure (40) is in powder form; preferably, the powder has little or no tackiness at room temperature; or The adhesive structure (40) is in the form of nonwoven yarn.

10. The preform as claimed in claim 8 or 9, further comprising: interlayer toughening yarn (50) between adjacent layers of the plurality of continuous fiber layers (10, 20), wherein, The melting temperature of the interlayer toughening yarn (50) is higher than the activation temperature of the adhesive structure (40); and / or The adhesive structure (40) comprises a low-melting-point component and a high-melting-point component, wherein the low-melting-point component acts as the adhesive and the high-melting-point component acts as the interlayer toughening yarn.

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