A woven-needled preform reinforcement method that changes interlaminar fiber pressure

Abstract

The application provides a woven-needled prefabricated body reinforcing method for changing interlayer fiber pressure, links the flexible deformation characteristics of the prefabricated body with interlayer reinforcement, achieves the effect of interlayer performance reinforcement, improves the preparation efficiency of the woven-needled prefabricated body, reduces the material processing cost, simultaneously, the increase of the gap area reduces the in-plane damage in the needling process, and the formed prefabricated body can ensure the stability of the overall performance.

Description

Technical Field

[0001] This invention belongs to the field of three-dimensional composite material weaving, specifically relating to a method for reinforcing woven-needle-punched preforms by changing the interlayer fiber pressure. Background Technology

[0002] Preform fabrication technology is one of the core processes in the preparation of three-dimensional woven composite materials. The fiber preform acts as a reinforcement in the composite material, and its structural stability and performance directly affect the final composite material's performance and application scenarios. With the continuous expansion of application scenarios and increasingly harsh working environments, traditional needle-punched woven carbon cloth processes are no longer sufficient to meet the growing demands of equipment and materials. A key issue is that the needles inserted into the preform during the needle-punching process can cause breakage and damage to the fabric yarns, disrupting the fabric's original in-plane properties. Furthermore, the unstable state of the needle-implanted interlayer fibers can lead to inefficient or even ineffective implantation, resulting in a deviation of the expected reinforcement effect on the preform.

[0003] Currently, improving the effectiveness of the needle punching process mainly involves compaction with a pressure plate, changing the needle punching depth and density, and altering the needle type. Compaction with a pressure plate can reduce the lifting and peeling of the mesh at adjacent needle punches, improving the uniformity of the preform. Changing the needle punching parameters can alter the number and depth of implanted fibers, improving interlayer bonding performance, but at the same time, it causes more severe damage to the woven fabric and more severe in-plane damage. Changing the needle type can increase the number of implanted fibers, and different barb designs can improve the smoothness of the needle punching process, such as reducing fiber blockage rate and increasing needle lifespan, but the corresponding fine processing of the needles leads to increased costs and is not suitable for large-scale preform preparation and production.

[0004] Overall, existing needle punching processes still suffer from drawbacks such as severe in-plane damage and inadequate interlayer reinforcement. Therefore, there is an urgent need for a needle punching preform method that reduces in-plane damage and enhances interlayer properties. Summary of the Invention

[0005] Purpose of the invention: To solve the above problems, the purpose of this invention is to provide a braided-needle-punched preform reinforcement method that changes the interlayer fiber pressure, so as to solve the problems of severe in-plane damage and unsatisfactory interlayer reinforcement in the needle-punching process.

[0006] To achieve the above objectives, the technical solution of the braided-needle-punched preform reinforcement method for changing interlayer fiber pressure provided by the present invention is as follows:

[0007] A method for reinforcing a braided-needle-punched preform by altering interlayer fiber pressure includes the following steps:

[0008] (1) Increase the weaving angle of the woven fabric layer from the initial state;

[0009] (2) Cut the nonwoven fabric into appropriate sizes and lay it on the above-mentioned deformed woven fabric layer so that the nonwoven fabric can cover the needle-punched area. After the nonwoven fabric is pre-pressed on the woven fabric layer, a preform is formed and the compaction device is pressed on the preform.

[0010] (3) Puncture the pressed preform;

[0011] (4) After removing the needle-punched preform, the braided fabric layer is braided at a reduced angle to form a preform after restoration deformation.

[0012] (5) Compact the precast body after it has recovered its deformation.

[0013] Furthermore, in step (1), the weaving angle of the woven fabric is... β is the angle between the warp and weft yarns. When the weaving angle changes, the boundary condition is that the outermost warp yarn is fixed, and its interlacing center with all the weft yarns remains unchanged. The distance between adjacent interlacing points is d, and the yarn width is constant (w). Based on geometric relationships, the area of ​​the rhomboid gap is calculated as follows:

[0014]

[0015] A function is established with sinβ as the independent variable and the void area S as the dependent variable.

[0016]

[0017] Furthermore, in step (3), the needle is inserted while maintaining the verticality of the needle direction. After each needle insertion, the preform is adjusted to ensure that it remains stable during needle insertion after observing whether it lifts or slides.

[0018] Furthermore, in step (4), the weaving angle of the woven fabric layer is reduced to the initial state.

[0019] Furthermore, in step (4), after needle punching, the weaving angle of the woven fabric layer is deformed, and an edge warp is fixed so that the center of the interlacing of the edge warp with all the weft yarns remains unchanged.

[0020] Beneficial effects:

[0021] (1) The braided-needle-punched preform reinforcement method proposed in this invention, which modifies the braided fabric to achieve interlayer performance enhancement without incurring unnecessary costs, improves the preparation efficiency of the braided-needle-punched preform and reduces the cost of material processing.

[0022] (2) The braided-needle-punched preform reinforcement method proposed in this invention by changing the interlayer fiber pressure links the flexible deformation characteristics of the preform with the interlayer reinforcement. At the same time, the increase in the void area reduces the in-plane damage during the needle punching process, so that the formed preform can not only ensure the stability of the overall performance, but also make certain changes in size and shape, and has higher designability. Attached Figure Description

[0023] Figure 1 A schematic diagram of the geometric relationship between the warp and weft threads in the initial woven fabric.

[0024] Figure 2 A schematic diagram of the geometric relationship between the warp and weft threads of a woven fabric after deformation.

[0025] Figure 3 A schematic diagram showing the funnel shape that appears when a nonwoven fabric is needled.

[0026] Figure 4 A graph showing the change in the void area of ​​a woven fabric. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0028] This invention discloses a method for reinforcing a braided-needle-punched preform by altering interlayer fiber pressure, comprising the following steps:

[0029] (1) Utilizing the variable weaving angle of woven fabrics, pretreatment operations are performed for the weaving-needling process. The initial dimensional relationships and gap sizes of the woven fabric are as follows: Figure 1 As shown, the distance between interlacing points is d, the yarn width is w, and the weaving angle is... The void area is S2. When the weave angle of the woven fabric is increased, the geometric dimensions are as follows: Figure 2 As shown, this is the increased knitting angle. This results in a void area where S1 > S2. Since the number of yarns is fixed, increasing the weaving angle leads to a larger spacing between adjacent yarns, reducing the yarn coverage and ultimately increasing the void area of ​​the woven fabric. This reduces fiber cutting and damage to the woven fabric during the needle punching process.

[0030] The principle behind the change in the knitting angle in this step is as follows:

[0031] The weave angle of the woven fabric is When the weaving angle changes, the boundary condition is that the outermost warp yarn is fixed. At this point, the center of its interlacing with all weft yarns remains unchanged, the distance between adjacent interlacing points is d, and the yarn width is w. Based on geometric relationships, the area of ​​the rhomboid gap is calculated as follows:

[0032]

[0033] A function is established with sinβ as the independent variable and the void area S as the dependent variable.

[0034]

[0035] Get In At that time, that is, weaving corners At this time, the gap area S = 0, and the woven fabric achieves full coverage. Due to the weaving angle... Therefore, the domain of the function S(sinβ) is And within this region, it is a monotonically increasing function, sinβ in its domain. Since the internal structure is also a monotonically increasing function, we can conclude that the void area S increases with the weaving angle. As it increases, the actual weaving angle increases during the deformation process. Change to Since β1>β2, S1>S2, and the void area decreases.

[0036] (2) Cut the nonwoven fabric to an appropriate size and lay it in layers on the deformed woven fabric to cover all the needle-punched areas. After smoothing and pre-pressing the nonwoven fabric, press the compaction device onto the preform to ensure that the nonwoven fabric does not lift or slip between layers during the needle-punching process. The reason for compacting the preform is that during the needle-punching process, the fibers in the nonwoven fabric become entangled and, when hooked and inserted by the needle, will cause the surrounding fibers to move, creating a local funnel shape. At this time, the fibers at the edge of the funnel shape will lift and deform, easily detaching from the fabric bonding surface, resulting in an unsatisfactory needle-punching effect. Therefore, a compaction device is used to ensure the flatness and stability of the preform during the needle-punching process to achieve the ideal needle-punching strength.

[0037] (3) The pressed preform is needle-punched according to certain process parameters. The specific process parameters are determined according to actual usage requirements. When inserting the needle, the needle direction should be kept perpendicular. The nonwoven fabric will form a funnel shape when needle-punched, such as... Figure 3 As shown. Therefore, it is necessary to observe whether the precast body lifts or slides after each needle insertion, so as to adjust the stability and consistency of the precast body during needle insertion in a timely manner.

[0038] (4) Remove the needled preform and observe its flatness and stability. Under the premise of having a certain interlayer bonding performance, reduce the weaving angle of the woven fabric layer to the initial state.

[0039] If each needle implants n fibers between layers, and the weaving angle is... Time and At that time, the density of the fibers implanted inside the gaps were as follows:

[0040]

[0041] Because β1>β2, ρ1<ρ2. After deformation, the fiber density increases, the degree of fiber compression increases, the entanglement between fibers increases, and the friction between them increases, thus strengthening the interlayer properties of the preform.

[0042] Therefore, as shown in the above formula comparison, due to the consistency of the yarn, the spacing between adjacent yarns will decrease, the gap size will become smaller, and the function of the change in gap area is as follows: Figure 4 As shown. At the same time, the fibers in the yarn will also undergo a bundle phenomenon. Both of these phenomena will have a squeezing effect on the interlayer fibers inserted into it. Since the interlayer bonding force is generated by the mutual entanglement and friction of the fibers, the pressure between the fibers increases after squeezing, the number of entanglements increases, and the friction between the fibers also increases, which ultimately strengthens the interlayer performance of the braided-needle-punched preform.

Claims

1. A method for reinforcing a braided-needle-punched preform by altering interlayer fiber pressure, characterized in that, Includes the following steps: (1) Increase the weave angle of the woven fabric layer from the initial state; the weave angle of the woven fabric is , β The angle between the warp and weft yarns is the boundary condition when the weaving angle changes. The outermost warp yarn is fixed, and its interlacing center with all weft yarns remains unchanged. The distance between adjacent interlacing points is... d Yarn width w To keep the area constant, the area of ​​the rhomboid gap can be calculated using geometric relationships as follows: ； sin β As the independent variable, the void area S Create a function for the dependent variable. ； (2) Cut the nonwoven fabric into appropriate sizes and lay it on the above-mentioned deformed woven fabric layer so that the nonwoven fabric can cover the needle-punched area. After the nonwoven fabric is pre-pressed on the woven fabric layer, a preform is formed and the compaction device is pressed on the preform. (3) Puncture the pressed precast body with needles; (4) After removing the needle-punched preform, the braided fabric layer is woven at a reduced angle to form a restored preform. (5) Compact the precast body after it has recovered its deformation.

2. The method for reinforcing a braided-needle-punched preform by changing interlayer fiber pressure according to claim 1, characterized in that, In step (3), the needle is inserted while maintaining the verticality of the needle direction. After each needle insertion, the precast body is adjusted to ensure that it remains stable during needle insertion after observing whether it lifts or slides.

3. The method for reinforcing a braided-needle-punched preform by changing interlayer fiber pressure according to claim 1, characterized in that, In step (4), the weaving angle of the woven fabric layer is reduced to the initial state.

4. The method for reinforcing a braided-needle-punched preform by altering interlayer fiber pressure according to claim 1 or 3, characterized in that, In step (4), after needle punching, the knitting angle of the woven fabric layer is deformed, and an edge warp is fixed so that the center of the interlacing of the edge warp with all the weft yarns remains unchanged.

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