A fatigue-resistant badminton racket rod based on three-dimensional woven composite material and a manufacturing method thereof

Abstract

The application belongs to the technical field of sports equipment, and particularly relates to an anti-fatigue badminton racket rod based on three-dimensional woven composite material and a manufacturing method, which comprises a net frame, a racket rod and a handle connected in sequence, and the net frame, the racket rod and the handle are integrally formed into a continuous whole member by three-dimensional woven composite material; the three-dimensional woven composite material comprises a reinforcing body and a matrix, the reinforcing body is a carbon fiber three-dimensional woven preform, and the matrix is modified epoxy resin; the fiber volume content of the racket rod is 55%-65%, the application constructs a fiber space interlocking network through a four-way weaving structure, eliminates interlayer interfaces and splicing stress concentration in combination with an integrated forming process, and improves the anti-fatigue performance, anti-torsion stiffness and interlayer bonding strength of the racket rod; through optimization of the fiber volume content and a stepped curing process, the best balance of strength, formability and fatigue life is achieved, and the technical problems of easy delamination, poor anti-fatigue performance and low connection reliability of a traditional laminated material badminton racket rod are solved.

Description

Technical Field

[0001] This invention relates to the field of sports equipment technology, specifically to a fatigue-resistant badminton racket shaft based on three-dimensional woven composite material and its manufacturing method. Background Technology

[0002] In badminton, the racket shaft, as the core load-bearing component, must frequently withstand the combined bending and torsional loads generated by actions such as smashes and backhand drives. Its fatigue resistance and structural reliability directly affect the racket's lifespan and safety of use.

[0003] Most high-end badminton racket shafts are made of carbon fiber laminated composite materials (such as patent publication number CN108579152A), which are formed by stacking multiple layers of carbon fiber cloth. Although they have the characteristics of being lightweight and high-strength, they have inherent defects: the interlayers of the laminated structure rely solely on resin bonding and lack fiber interlocking. Under repeated torsional loads, interlayer slippage and shear damage are prone to occur, eventually leading to delamination and cracking. At the same time, traditional rackets often use a process where the frame and shaft are manufactured separately and then glued or mechanically connected (such as patent publication number CN219921982U). The connection area forms stress concentration due to structural abrupt changes, and the glue layer is prone to fatigue failure after aging.

[0004] To address the aforementioned issues, some existing technologies attempt to optimize the structure. For example, CN219921982U proposes adjusting the bending range of the shaft through a mechanical structure, but this introduces additional moving parts, increasing structural complexity and weight, and does not solve the delamination problem from the material's inherent nature. CN113664766A discloses a three-dimensional woven composite material racket frame, but it does not optimize the woven structure for the stress characteristics of the variable diameter section of the shaft, and the fiber volume content and curing process design are unreasonable, resulting in limited improvement in fatigue resistance.

[0005] Three-dimensional braided composite materials, with their interlocking fiber structure, possess excellent interlayer bonding performance and torsional stiffness, and have been applied in aerospace and other fields. However, when applied to badminton racket shafts, the following technical challenges need to be addressed: how to balance the lightweight requirements of badminton rackets with mechanical performance; how to optimize the braided structure to adapt to the complex stresses of the shaft's variable diameter section; and how to design an integrated molding process to eliminate stress concentration at the joints. This invention successfully solves the above problems through a specific four-way braided structure, optimized fiber volume content, and a stepped curing process, achieving a significant improvement in the fatigue resistance of the racket shaft. Therefore, we propose a fatigue-resistant badminton racket shaft based on three-dimensional braided composite materials and its manufacturing method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fatigue-resistant badminton racket shaft based on three-dimensional woven composite materials and its manufacturing method, thus solving the problems mentioned above.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A fatigue-resistant badminton racket shaft based on a three-dimensional woven composite material includes a net frame, a shaft, and a grip connected in sequence. The net frame, shaft, and grip are integrally formed into a continuous whole component from the three-dimensional woven composite material. The three-dimensional woven composite material includes a reinforcement and a matrix. The reinforcement is a three-dimensional woven carbon fiber preform, and the matrix is ​​a modified epoxy resin. The fiber volume content of the shaft is 55%-65%. As a further aspect of the present invention, the carbon fiber three-dimensional braided preform adopts a four-way braiding structure, which includes a knotting yarn, a weft 90° yarn, a +45° oblique yarn, and a -45° oblique yarn, wherein the +45° oblique yarn and the -45° oblique yarn are interwoven in the structure in a ±45° direction.

[0008] As a further part of the present invention, the racket shaft includes a straight tube section and a variable diameter section, wherein the braiding density of the variable diameter section is 10-15 strands / cm², the braiding density of the straight tube section is 8-12 strands / cm², and the variable diameter section forms a torsional reinforcement zone.

[0009] As a further part of the present invention, the modified epoxy resin is a bisphenol A type epoxy resin modified with an amine curing agent.

[0010] As a further part of the present invention, the outer surface of the racket shaft is provided with visual markings, which are raised stripes or color marks extending along the main bearing direction.

[0011] As a further part of the present invention, the diameter of the single filament of the three-dimensional woven carbon fiber preform is 5-7 μm.

[0012] A method for manufacturing a fatigue-resistant badminton racket shaft based on three-dimensional braided composite material includes the following steps: S1: Integrated Fiber Preform: Based on the overall structural parameters of the racket, including the frame curvature, shaft diameter, and grip connection transition angle, carbon fiber bundles are selected and woven with four-way interlacing parameters using a three-dimensional weaving device to form an integrated fiber preform that includes the frame, shaft, and grip connection. S2: Mold preparation: Place the integrated fiber preform into a special integrated mold. The transition between the mesh frame and the paddle of the mold cavity is provided with a smooth arc surface of R5-R8mm. The inner wall of the mold is coated with a release agent. S3: Vacuum-assisted resin transfer molding: Evacuate the mold to a vacuum level of ≤-0.09MPa and hold the pressure for 10-15 minutes. Slowly inject modified epoxy resin from the injection port at a pressure of 0.1-0.3MPa to ensure that the resin completely impregnates the preform. The impregnation time is 20-30 minutes. S4: Stepped curing: First, heat to 80℃ at a heating rate of 5℃ / min and hold for 2-3 hours for pre-curing; then heat to 120℃ at a heating rate of 3℃ / min, apply 0.3-0.5MPa pressure and hold for 3-4 hours to complete the full curing. S5: Post-processing: After the mold cools to room temperature of 20℃, open the mold, take out the integrated component, grind and trim the component to remove burrs and excess resin. S6: Quality Inspection: Inspect the fiber volume content, appearance defects, and mechanical properties of the components. Appearance defects include bubbles, cracks, and delamination, while mechanical properties include torsional stiffness and flexural strength.

[0013] As a further part of the present invention, in step S3, the injection temperature of the modified epoxy resin is 40-50°C.

[0014] As a further part of the present invention, in step S4, the pressure during the complete curing stage is applied by a built-in pressurizing device in the mold, and the pressure direction is perpendicular to the axis of the drumstick.

[0015] As a further step of the present invention, after step S6, a visual mark is formed on the outer surface of the racket shaft by laser engraving.

[0016] This invention provides a fatigue-resistant badminton racket shaft based on a three-dimensional woven composite material and its manufacturing method. Compared with the prior art, it has the following advantages: 1. Overcoming the defect of traditional laminated materials being prone to delamination, the four-way weaving structure adopted in this design forces cracks to bypass more fiber interlacing points when they propagate, thereby blocking the crack propagation path, forcing cracks to deflect, fork, or terminate, dispersing the damage over a larger volume area, and improving the fatigue life of the racket shaft; while the design of 55% to 65% fiber volume content takes into account the strength, rigidity, and interlayer bonding quality of the racket, further enhancing the anti-fatigue effect.

[0017] 2. High durability and safety: Traditional laminated rackets not only suffer from internal delamination and matrix cracking, which accumulate latently under long-term cyclic loads, but also experience rapid transformation from "microscopic damage" to "macroscopic fracture" (usually triggered by only 1-2 normal ball hits), easily leading to wrist sprains and elbow joint vibration injuries. The three-dimensional woven composite material of this invention, through interlocking of fibers, can significantly reduce the accumulation of such hidden damage, lower the risk of sudden fracture, and improve safety.

[0018] 3. Integrated structure and stable performance: "Integrated molding" eliminates the interlayer interface of the laminated structure and blocks the interlayer delamination path through the three-dimensional interlocking of fibers; at the same time, it avoids the stress concentration problem of splicing seams caused by the segmented molding of the racket shaft, thus improving fatigue life from the structural root. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the main structure of the present invention; Figure 2 This is a schematic diagram comparing the damage of traditional laminated materials and three-dimensional braided composite materials according to the present invention. Figure 3 This is a schematic diagram of the internal material structure of the present invention.

[0020] In the diagram: 1. Net frame; 2. Paddle; 3. Handle; 9. Bonding yarn; 10. 90° weft yarn; 11. +45° slant yarn; 12. -45° slant yarn. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1-3 This invention provides a technical solution: a fatigue-resistant badminton racket shaft based on a three-dimensional woven composite material, comprising a net frame 1, a shaft 2, and a grip 3 connected in sequence. The net frame 1, shaft 2, and grip 3 are integrally formed into a continuous whole component from the three-dimensional woven composite material. The three-dimensional woven composite material includes a reinforcement and a matrix. The reinforcement is a carbon fiber three-dimensional woven preform, and the matrix is ​​a modified epoxy resin. The fiber volume content of the shaft 2 is 55%-65%. The carbon fiber three-dimensional braided preform adopts a four-way braiding structure, which includes a knotting yarn 9, a weft 90° yarn 10, a +45° oblique yarn 11, and a -45° oblique yarn 12. The +45° oblique yarn 11 and the -45° oblique yarn 12 are interwoven in the structure in a ±45° direction.

[0023] The racket shaft 2 includes a straight tube section and a variable diameter section. The braiding density of the variable diameter section is 10-15 strands / cm², and the braiding density of the straight tube section is 8-12 strands / cm². The variable diameter section forms a torsional reinforcement zone.

[0024] The modified epoxy resin is a bisphenol A type epoxy resin modified with an amine curing agent.

[0025] The outer surface of the handle 2 is provided with visual markings, which are raised stripes or color marks extending along the main bearing direction.

[0026] The diameter of the single filament of the three-dimensional woven carbon fiber preform is 5-7 μm.

[0027] A method for manufacturing a fatigue-resistant badminton racket shaft based on three-dimensional braided composite material includes the following steps: S1: Integrated Fiber Preform: Based on the overall structural parameters of the racket, including the arc of the net frame, the diameter of the shaft, and the transition angle of the grip connection, carbon fiber bundles are selected and woven with four-way interlacing parameters using a three-dimensional weaving device to form an integrated fiber preform that includes the connection of the net frame 1, shaft 2, and grip 3. S2: Mold preparation: Place the integrated fiber preform into a special integrated mold. The transition between the mesh frame 1 and the handle 2 of the mold cavity is provided with a smooth arc surface of R5-R8mm. The inner wall of the mold is coated with a release agent. S3: Vacuum-assisted resin transfer molding: Evacuate the mold to a vacuum level of ≤-0.09MPa and hold the pressure for 10-15 minutes. Slowly inject modified epoxy resin from the injection port at a pressure of 0.1-0.3MPa to ensure that the resin completely impregnates the preform. The impregnation time is 20-30 minutes. S4: Stepped curing: First, heat to 80℃ at a heating rate of 5℃ / min and hold for 2-3 hours for pre-curing; then heat to 120℃ at a heating rate of 3℃ / min, apply 0.3-0.5MPa pressure and hold for 3-4 hours to complete the full curing. S5: Post-processing: After the mold cools to room temperature of 20℃, open the mold, take out the integrated component, grind and trim the component to remove burrs and excess resin. S6: Quality Inspection: Inspect the fiber volume content, appearance defects, and mechanical properties of the components. Appearance defects include bubbles, cracks, and delamination, while mechanical properties include torsional stiffness and flexural strength.

[0028] In step S3, the injection temperature of the modified epoxy resin is 40-50℃. In step S4, the pressure during the complete curing stage is applied by the built-in pressure device in the mold, and the pressure direction is perpendicular to the axis of the handle 2. After step S6, a visual mark is formed on the outer surface of the handle 2 by laser engraving.

[0029] like Figures 1 to 3 As shown, the mechanical response and damage suppression mechanism of the three-dimensional braided composite material racket shaft described in this invention are disclosed herein. To specifically illustrate its superior effects, the following explanation is based on typical loads borne by the racket shaft during a smash.

[0030] like Figure 2As shown, the smash action subjects the racket shaft 2 to significant torsional load, bending load, and a combination of these loads sequentially. For the initial torsional load, the three-dimensional woven prefabricated body utilizes its internal Z-axis knotted yarns 9 to create spatial constraints, effectively suppressing interlayer shear slip at the initial stage of load application and distributing torsional stress into the three-dimensional network composed of warp and weft fibers. For the main bending load, thanks to the fiber continuity from the frame 1 to the racket shaft 2 within the integrated fiber prefabricated body, bending stress is smoothly transmitted along the axis of the racket shaft 2, thus avoiding stress concentration caused by abrupt changes in cross-section and adhesive interfaces in traditional split-connection structures.

[0031] For peak conditions of combined bending and torsion loads, the four-way braided structure forms a three-dimensional interlocking network in the variable diameter section of the handle 2. This network can convert macroscopic interlaminar shear stress into tension and compression of fiber bundles. The Z-axis fibers significantly constrain the relative misalignment between layers, thereby mechanistically preventing conditions such as... Figure 2 The initiation of the conventional interlaminar cracking mode is shown in marks 5 and 6. Simultaneously, even if microcracks develop in the matrix resin under high stress, their propagation paths will be forced to deflect, bypass, or terminate at points such as the dense fiber interlacing points in the described three-dimensional interlocking network. Figure 2 Within the locally interlocked units shown (marked 7, marked 8), the material damage can be effectively controlled within a localized area through the dual function of the three-dimensional interlocking network, preventing it from evolving into a through-type delamination crack and significantly improving the damage tolerance of the handle 2.

[0032] During the vibration attenuation process after the load is removed, the three-dimensional braided structure, with its overall interconnectivity and high stiffness, can quickly dissipate residual vibration energy, causing the racket arm 2 to rapidly return to a stable shape. At this time, through the above-mentioned mechanical response and damage suppression throughout the entire process, the mechanical properties of the racket arm 2 are maintained after bearing complex loads, thereby ensuring its high fatigue life.

[0033] In contrast, such as Figure 2 As shown, traditional badminton rackets, made of two-dimensional carbon fiber laminated material and using a modular splicing process, have inherent defects under the aforementioned smash load. The laminated structure relies solely on resin bonding between layers, lacking fiber interlocking. Under torsional loads, interlayer slippage easily occurs, leading to increased interlayer shear stress and ultimately causing interlayer cracking. Furthermore, the segmented molding and splicing process creates stress concentration points at the seams, which become weak points under repeated loads, accelerating the fatigue failure of the shaft 2.

[0034] In this embodiment, the three-dimensional braided composite material employs four-way high-density interlacing weaving in the diameter-changing section of the shaft 2, forming a unique torsional reinforcement zone. This structure can more effectively distribute and transfer the load to more fibers in three-dimensional space, thereby significantly reducing the stress concentration in this critical area.

[0035] Please see Figure 3 This diagram illustrates a microscopic structural unit of the three-dimensional woven composite material described in this invention. This structure visually reveals the interlocking morphology of the carbon fiber preform in three-dimensional space, which is key to understanding the superior performance of the racket under intense movements such as "smash."

[0036] Please see Figure 3 This diagram illustrates a microscopic structural unit of the three-dimensional braided composite material described in this invention. The structure visually reveals the interlocking morphology of the carbon fiber preform in three-dimensional space.

[0037] The structural unit is composed of a multi-directional yarn system: Bonding yarn 9: runs through the entire structure along the Z-direction, effectively locking the fibers in each layer under the intense torsional moment generated by a smash, preventing interlayer slippage and delamination; Weft 90° yarn 10: laid along the weft direction, forming the main load-bearing network together with the warp yarns, directly resisting the longitudinal bending stress of the racket shaft 2 during a smash; +45° oblique yarn 11 and -45° oblique yarn 12, interwoven in the structure at ±45° angles, specifically designed to handle the complex in-plane shear and torsional forces experienced by the racket face and shaft 2 at the moment of a smash, ensuring no structural deflection occurs during power transmission. Therefore, Figure 3 The three-dimensional four-way woven structure shown provides a fundamental microstructural basis for the excellent performance of the racket shaft 2 under extreme conditions such as smashes.

[0038] In this example, epoxy resin has low shrinkage and high chemical stability, which can improve the defects inside the three-dimensional braided composite material, making the racket structure stable and improving its fatigue life compared with traditional two-dimensional layered rackets.

[0039] The core of this invention's integrated molding process lies in the combination of the characteristics of three-dimensional woven composite materials and precision manufacturing technology. First, based on the overall structural parameters of the racket, including the curvature of the frame 1, the diameter of the shaft 2, and the transition angle of the grip 3 connection, an integrated fiber preform is designed. Then, using carbon fiber as raw material, it is woven using a three-dimensional weaving device according to four-way interlacing parameters to obtain the integrated fiber preform. In this preform, carbon fiber bundles interweave and interlock in three-dimensional space, allowing the transition area between the frame 1 and the shaft 2 to be naturally connected through continuous fibers, eliminating the connection interfaces and structural breaks inherent in traditional split-jointing processes in terms of material morphology.

[0040] Subsequently, the preform is placed into a dedicated integrated mold that matches the final shape of the racket. This mold cavity contains the complete outline of the connection between the frame 1, shaft 2, and grip 3, and features a smooth arc surface of R5-R8mm at the transition between the frame 1 and shaft 2 to optimize stress distribution. Vacuum-assisted resin transfer molding is used for molding: first, the mold cavity is evacuated and held under pressure for 10 minutes. Then, epoxy resin is slowly injected through the injection port. After the resin completely impregnates the preform, a stepped temperature curing process is executed: first, pre-curing is performed at 80℃ for 2 hours, then the temperature is increased to 120℃ and held for 3 hours for complete curing. This process prevents internal stress caused by excessively rapid heating. Simultaneously, a pressure of 0.3MPa is applied using a mold pressurizing device and held for 1 hour to ensure a tight bond between the resin and the carbon fiber. Throughout the curing process, the spatial interlocking structure of the three-dimensional braided carbon fiber effectively suppressed interlayer slip, while the low shrinkage characteristics of epoxy resin reduced the generation of internal defects, ultimately resulting in an integrated component without splicing or interlayer delamination, ensuring the reliability of the structure from both material and process dimensions.

[0041] After the curing process is completed, the mold is allowed to cool to room temperature before the mold is opened and the one-piece molded "frame 1 - racket 2" component is removed. The component is then surface treated, including sanding and trimming, to remove burrs and residual resin at the parting line, making the component smooth and regular in shape, and enhancing its surface consistency and integrity.

[0042] The final racket shaft 2 is a seamless, integrated component without splices or interlayer interfaces. The inherent spatial interlocking characteristics of the three-dimensional braided structure, combined with the low shrinkage of the epoxy resin matrix, enable the racket shaft 2 (especially in the variable diameter section) to exhibit excellent resistance to interlaminar shear and fatigue performance.

[0043] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fatigue-resistant badminton racket shaft based on a three-dimensional woven composite material, comprising a net frame (1), a shaft (2), and a grip (3) connected in sequence, characterized in that: The frame (1), the racket shaft (2), and the grip (3) are integrally formed from three-dimensional woven composite material into a continuous whole component; the three-dimensional woven composite material includes a reinforcement and a matrix, the reinforcement is a carbon fiber three-dimensional woven preform, and the matrix is ​​a modified epoxy resin; the fiber volume content of the racket shaft (2) is 55%-65%.

2. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material according to claim 1, characterized in that: The carbon fiber three-dimensional braided preform adopts a four-way braiding structure, which includes a knotting yarn (9), a weft 90° yarn (10), a +45° oblique yarn (11), and a -45° oblique yarn (12), and the +45° oblique yarn (11) and the -45° oblique yarn (12) are interwoven in the structure in a ±45° direction.

3. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material according to claim 2, characterized in that: The racket shaft (2) includes a straight pipe section and a variable diameter section. The braiding density of the variable diameter section is 10-15 strands / cm², and the braiding density of the straight pipe section is 8-12 strands / cm². The variable diameter section forms a torsional reinforcement zone.

4. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material according to claim 3, characterized in that: The modified epoxy resin is a bisphenol A type epoxy resin modified with an amine curing agent.

5. A fatigue-resistant badminton racket shaft based on a three-dimensional braided composite material according to claim 4, characterized in that: The outer surface of the handle (2) is provided with visual markings, which are raised stripes or color marks extending along the main bearing direction.

6. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material according to claim 5, characterized in that: The diameter of the single filament of the three-dimensional braided carbon fiber preform is 5-7 μm.

7. A method for manufacturing a fatigue-resistant badminton racket shaft based on a three-dimensional braided composite material as described in any one of claims 1-6, characterized in that: Includes the following steps: S1: Woven integrated fiber preform: Based on the overall structural parameters of the racket, including the arc of the net frame, the diameter of the shaft and the transition angle of the grip connection, carbon fiber bundles are selected and woven with four-way interlacing parameters through a three-dimensional weaving device to form an integrated fiber preform containing the connection of the net frame (1), shaft (2) and grip (3); S2: Mold preparation: Place the integrated fiber preform into a special integrated mold. The transition between the mesh frame (1) and the handle (2) of the mold cavity is provided with a smooth arc surface of R5-R8mm. The inner wall of the mold is coated with a release agent. S3: Vacuum-assisted resin transfer molding: Evacuate the mold to a vacuum level of ≤-0.09MPa and hold the pressure for 10-15 minutes. Slowly inject modified epoxy resin from the injection port at a pressure of 0.1-0.3MPa to ensure that the resin completely impregnates the preform. The impregnation time is 20-30 minutes. S4: Stepped curing: First, heat to 80℃ at a heating rate of 5℃ / min and hold for 2-3 hours for pre-curing; then heat to 120℃ at a heating rate of 3℃ / min, apply 0.3-0.5MPa pressure and hold for 3-4 hours to complete the full curing. S5: Post-processing: After the mold cools to room temperature of 20℃, open the mold, take out the integrated component, grind and trim the component to remove burrs and excess resin. S6: Quality Inspection: Inspect the fiber volume content, appearance defects, and mechanical properties of the components. Appearance defects include bubbles, cracks, and delamination, while mechanical properties include torsional stiffness and flexural strength.

8. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material and its manufacturing method according to claim 7, characterized in that: In step S3, the injection temperature of the modified epoxy resin is 40-50℃.

9. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material and its manufacturing method according to claim 8, characterized in that: In step S4, the pressure during the fully cured stage is applied through the built-in pressurizing device in the mold, and the pressure direction is perpendicular to the axis of the stick (2).

10. The fatigue-resistant badminton racket shaft based on three-dimensional braided composite material and its manufacturing method according to claim 9, characterized in that: After step S6, a visual mark is formed on the outer surface of the racket shaft (2) by laser engraving.

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