Woven-needled preform reinforcing method capable of changing interlayer fiber pressure

Abstract

According to the woven-needled preform reinforcing method capable of changing the interlayer fiber pressure, the flexible deformation characteristic of the preform is associated with interlayer reinforcement, so that the effect of interlayer performance reinforcement is achieved, the preparation efficiency of the woven-needled preform is improved, the material processing cost is reduced, and the method is suitable for large-scale popularization and application. And meanwhile, the in-plane damage in the needling process is reduced due to the increase of the gap area, so that the stability of the overall performance of the formed preform can be ensured.

Description

Technical Field

[0001] The invention belongs to the field of three-dimensional composite material weaving, and in particular relates to a braiding-needling preform reinforcement method for changing interlayer fiber pressure. Background Art

[0002] The preparation technology of preforms is one of the core technologies of the preparation process of three-dimensional woven composite materials. The fiber preform plays the role of a reinforcement in the composite material. The stability and performance of the preform structure directly affect the performance and usage scenarios of the final composite material. As the application scenarios continue to expand, the working environment becomes more harsh. The traditional needle-punched woven carbon cloth process has been unable to meet the growing demand for equipment and materials. The key problem is that the needles penetrate into the preform during the needle-punching process, which will cause the fabric yarn to break and be damaged, destroying the original in-plane performance of the fabric. In addition, the state of the interlayer fibers implanted by needle-punching is unstable, which may lead to inefficient or even ineffective implantation, and the reinforcement effect of the preform deviates from expectations.

[0003] Currently, the effectiveness of the needling process is primarily improved through compaction by pressing plates, varying the needling depth and density, and changing the needle type. Pressing plates can reduce warping and peeling of the web between adjacent needling holes, improving the uniformity of the preform. Changing the needling parameters can alter the number and depth of embedded fibers, improving interlayer bonding. However, this can also lead to more severe damage to the woven fabric and in-plane damage. Changing the needle type can increase the number of embedded fibers, and different barb designs can improve the smoothness of the needling process, such as reducing fiber blockage and increasing needle life. However, the resulting fine needle processing increases costs, making it unsuitable for large-scale preform preparation and production.

[0004] In general, the existing needle-punching process still has shortcomings such as severe in-plane damage and unsatisfactory interlayer reinforcement. Therefore, a needle-punching preform method that reduces in-plane damage and can enhance interlayer performance is urgently needed. Summary of the Invention

[0005] Purpose of the invention: To solve the above problems, the purpose of the present 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 needling process.

[0006] To achieve the above-mentioned purpose, the technical solution of the braiding-needling preform reinforcement method for changing the interlayer fiber pressure provided by the present invention is as follows:

[0007] A braided-needle punched preform reinforcement method for changing interlayer fiber pressure comprises the following steps:

[0008] (1) increasing the braiding angle of the braided fabric layer from its initial state;

[0009] (2) cutting the nonwoven fabric into a suitable size, laminating and laying the nonwoven fabric on the deformed woven fabric layer so that the nonwoven fabric covers the needle punching area, pre-pressing the nonwoven fabric on the woven fabric layer to form a preform to be formed, and pressing a compacting device on the preform;

[0010] (3) acupuncture the pressed preform;

[0011] (4) After the needle-punched preform is removed, the braiding angle of the woven fabric layer is reduced to form a preform after the deformation is restored;

[0012] (5) Compacting the preform after recovering the deformation.

[0013] Furthermore, in step (1), the braiding angle of the braided fabric is β is the angle between the warp and weft. When the braiding angle changes, the boundary condition is to fix the edge warp yarn. At this time, the interweaving center of the warp yarn and all the weft yarns remains unchanged. The spacing between adjacent interweaving points is d, and the yarn width is w. According to the geometric relationship, the area of ​​the diamond gap is

[0014]

[0015] Build a function with sinβ as the independent variable and gap area S as the dependent variable.

[0016]

[0017] Furthermore, in step (3), the verticality of the needle direction is maintained during the insertion of the needle, and after each needling, the preform is observed to see if there is any tilting or sliding, and then the preform is adjusted so that the preform remains stable during the needling.

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

[0019] Furthermore, in step (4), the braiding angle of the woven fabric layer is deformed after needling, and an edge warp yarn is fixed so that the interweaving center of the edge warp yarn and all the weft yarns remains unchanged.

[0020] Beneficial effects:

[0021] (1) The braided-needle-punched preform reinforcement method proposed in the present invention, which changes the interlayer fiber pressure, deforms the braided fabric to achieve the effect of strengthening the interlayer performance without incurring unnecessary costs, thereby improving the preparation efficiency of the braided-needle-punched preform and reducing the cost of material processing.

[0022] (2) The braiding-needling preform reinforcement method proposed in the present invention for 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 gap area reduces the in-plane damage during the needling process, so that the preform after forming can not only ensure the stability of the overall performance, but also can undergo a certain degree of size and shape changes, and has higher designability. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0025] Figure 3 Schematic diagram of the funnel shape a nonwoven fabric exhibits when needled.

[0026] Figure 4 Graph of the void area change function of woven fabrics. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present 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 "inward" and "outward" refer to directions toward or away from the geometric center of a particular component, respectively.

[0028] The present invention discloses a braiding-needling preform reinforcement method for changing the interlayer fiber pressure, comprising the following steps:

[0029] (1) Using the variable braiding angle of the braided fabric, the pre-treatment operation of the braiding-needling process is carried out. The size relationship and gap size of the initial braided fabric are as follows: Figure 1 As shown, the interlacing point distance is d, the yarn width is w, and the braiding angle is The gap area is S2, and the braiding angle of the braided fabric is increased. At this time, the geometric dimensions are as follows: Figure 2 As shown, the braiding angle after the increase Since the number of yarns is fixed, increasing the braiding angle will increase the spacing between adjacent yarns, reducing the yarn coverage, and ultimately increasing the void area of ​​the woven fabric, thereby reducing fiber cutting and damage to the woven fabric caused by the needles during the needling process.

[0030] The principle of changing the braiding angle in this step is:

[0031] The braiding angle of a woven fabric is At this time, when the braiding angle changes, the boundary condition is to fix the edge warp yarn. At this time, the interweaving center of the warp yarn and all the weft yarns remains unchanged, the spacing between adjacent interweaving points is d, and the yarn width is w. According to the geometric relationship, the area of ​​the diamond gap is

[0032]

[0033] Build a function with sinβ as the independent variable and gap area S as the dependent variable.

[0034]

[0035] Get in When, that is, the braiding angle When the gap area S=0, the woven fabric is fully covered. So the domain of the S(sinβ) function is And in this region it is a monotonically increasing function, sinβ is in the domain of definition It is also a monotonically increasing function, so we can conclude that the gap area S increases with the braiding angle. The actual braiding angle increases with the deformation process. Changes to And β1>β2, so S1>S2, the gap area decreases.

[0036] (2) Cut the nonwoven fabric into appropriate sizes and lay them on the deformed woven fabric so that the nonwoven fabric can cover all the needle-punching areas. After smoothing and pre-pressing the nonwoven fabric, press the compacting device on the preform to be formed to ensure that the nonwoven fabric will not warp or slide relative to each other during the needle-punching process. The reason for compacting the preform is that during the needle-punching process, the fibers in the nonwoven fabric will entangle with each other. When they are hooked and implanted by the needle, they will drive the fibers in a certain area around them to move, resulting in a local funnel shape. At this time, the fibers at the edge of the funnel will warp and deform, and easily detach from the fabric bonding surface, resulting in an unsatisfactory needle-punching effect. Therefore, a compacting device is used to ensure the flatness and stability of the preform during the needle-punching process to achieve an ideal needle-punching strength.

[0037] (3) Puncture the pressed preform with certain process parameters. The specific process parameters are determined according to the actual use requirements. The verticality of the needle should be maintained when the needle is implanted. The nonwoven fabric will appear funnel-shaped when it is punctured. Figure 3 Therefore, it is necessary to observe whether the preform has any warping or sliding after each needling so as to timely adjust the stability and consistency of the preform during needling.

[0038] (4) The needle-punched preform is removed and the flatness and stability of the preform are observed. On the premise of having a certain interlayer bonding performance, the braiding angle of the woven fabric layer is reduced to the initial state.

[0039] If the number of fibers implanted between layers by each needle is n, the braiding angle is Time and When , the density of the fibers implanted inside the voids is:

[0040]

[0041] Because β1>β2, ρ1<ρ2, the fiber density increases after deformation, the fiber extrusion degree increases, the entanglement between fibers increases and the friction between them increases, and the interlayer performance of the preform is enhanced.

[0042] Therefore, as can be seen from the above formula, due to the consistency of the yarn, the distance between adjacent yarns will decrease, the gap size will become smaller, and the gap area size change function is as follows: Figure 4 At the same time, the fibers in the yarn will also bunch up. Both phenomena will squeeze the interlayer fibers that penetrate into them. Since the interlayer bonding force is generated by the mutual entanglement and mutual 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, ultimately strengthening the interlayer performance of the braided-needle-punched preform.

Claims

1. A braided-needle punched preform reinforcement method for changing interlayer fiber pressure, characterized in that: The following steps are involved: (1) increasing the braiding angle of the braided fabric layer from an initial state; (2) cutting the nonwoven fabric into a suitable size, laminating and laying the nonwoven fabric on the deformed woven fabric layer so that the nonwoven fabric can cover the needle punching area, pre-pressing the nonwoven fabric on the woven fabric layer to form a preform to be formed, and pressing a compacting device on the preform; (3) acupuncture the pressed preform; (4) After the needle-punched preform is removed, the braiding angle of the woven fabric layer is reduced to form a preform after the deformation is restored; (5) Compacting the preform after the deformation is restored.

2. The braiding-needling preform reinforcement method for changing the interlayer fiber pressure according to claim 1 is characterized in that: In step (1), the braiding angle of the braided fabric is β is the angle between the warp and the weft. When the weaving angle changes, the boundary condition is to fix the edge warp yarn. At this time, the interlacing center of the warp yarn and all the weft yarns remains unchanged, the spacing between adjacent interlacing points is d, and the yarn width w remains unchanged. According to the geometric relationship, the area of ​​the rhombus gap is obtained as Use sinβ as the independent variable and the gap area S as the dependent variable to establish a function.

3. The braiding-needling preform reinforcement method for changing the interlayer fiber pressure according to claim 1 is characterized in that: In step (3), the verticality of the needle direction is maintained during the implantation of the needle, and after each acupuncture, the preform is observed to see whether it is tilted or slipped, and then the preform is adjusted to ensure that it remains stable during the acupuncture.

4. The braiding-needling preform reinforcement method for changing the interlayer fiber pressure according to claim 1 is characterized in that: In step (4), the braiding angle of the braided fabric layer is reduced to an initial state.

5. The braiding-needling preform reinforcement method for changing the interlayer fiber pressure according to claim 1 or 4, characterized in that: In step (4), the woven fabric layer is deformed in a weaving angle after needling, and an edge warp yarn is fixed so that the interlacing center of the edge warp yarn and all the weft yarns remains unchanged.

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