Composite material structure for bolted connection and reinforcing method thereof

Abstract

The invention discloses a composite material structure for bolt connection and a reinforcing method of the composite material structure. The composite material structure comprises a bolt hole metal sleeve and a metal grating net, wherein the peripheral outer surface of the bolt hole metal sleeve is sleeved with the metal grating net; and an upper composite layer and a lower composite layer. According to the technical scheme provided by the invention, the metal net is laid in the material and is welded with the metal sleeve into a whole, and the bolt pressure borne by the sleeve is transferred through the metal net, so that the bearing capacity and reliability of the composite material bolt connection joint are improved.

Description

Technical Field

[0001] The present invention relates to the field of composite materials, and particularly to a composite material structure for bolt connection and an enhancement method thereof. Background Art

[0002] Composite materials, with their advantages of light weight, high strength, corrosion resistance, environmental aging resistance, and thermal stability, have been widely used in many fields such as aerospace, automotive manufacturing, and building structures, providing effective material solutions for reducing structural weight, improving energy efficiency and performance, and enhancing durability. At the same time, the connection methods of composite materials mainly include bolt connection, adhesive bonding connection, and hybrid connection. Among them, bolt connection is one of the most widely used composite material connection methods due to its high structural strength, easy maintenance and disassembly, good impact resistance, and safety and reliability. However, the transfer efficiency of bolt connection mainly depends on the strength of the material itself at the bolt hole. In practical applications, the friction of the thread on the material will also cause irreversible damage, and the tightening of the nut will also cause extrusion stress on the material.

[0003] Currently, the existing enhancement methods on the market mainly involve embedding sleeves at the bolt holes. However, the enhancement effect of this method is very limited, and its reliability still depends on the strength of the material itself in contact with the sleeve, and the strength of the material around the bolt hole cannot be fully utilized. Summary of the Invention

[0004] The present invention provides a composite material structure for bolt connection and an enhancement method thereof, laying a metal mesh into the material and welding it into one body with a metal sleeve, and transmitting the bolt pressure received by the sleeve through the metal mesh, thereby improving the bearing capacity and reliability of the composite material bolt connection joint.

[0005] According to the first aspect of the present invention, the present invention provides an enhancement method for a composite material structure for bolt connection, and the composite material structure includes: A metal sleeve for bolt hole, A metal grid mesh, sleeved on the circumferential outer surface of the metal sleeve for bolt hole; and An upper composite material layer and a lower composite material layer; Wherein, the enhancement method includes the following steps: S1, determining the circumferential shape and size of the metal sleeve for bolt hole, and punching holes in the metal grid mesh, the upper composite material layer and the lower composite material layer according to the circumferential shape and size of the metal sleeve for bolt hole, so that the metal grid mesh, the upper composite material layer and the lower composite material layer are successively provided with grid mesh installation holes, upper layer installation holes and lower layer installation holes; S2. Sheath the metal grille through the grille mounting hole on the outer circumferential surface of the metal sleeve of the bolt hole, and then weld the metal grille to the outer circumferential surface of the metal sleeve of the bolt hole. S3. Develop a laying plan for the upper composite material layer and the lower composite material layer according to the circumferential shape and size of the metal sleeve of the bolt hole and the shape and size of the metal grille. Sheath the upper composite material layer and the lower composite material layer through the upper layer mounting hole and the lower layer mounting hole on the outer circumferential surface of the metal sleeve of the bolt hole respectively, and lay the upper composite material layer and the lower composite material layer on the upper surface and the lower surface of the metal grille respectively according to the laying plan.

[0006] In addition to one or more of the above-disclosed features, or as an alternative, the laying plan is a symmetric layering.

[0007] In addition to one or more of the above-disclosed features, or as an alternative, the mesh diameter of the metal grille is 1 - 4 mm.

[0008] In addition to one or more of the above-disclosed features, or as an alternative, after welding the metal grille to the outer circumferential surface of the metal sleeve of the bolt hole, the number of welding points between the metal grille and the metal sleeve of the bolt hole is 8 - 16, and the welding points are evenly distributed in the circumferential direction of the metal sleeve of the bolt hole.

[0009] In addition to one or more of the above-disclosed features, or as an alternative, the thickness of the metal grille is equal to the wire diameter of the metal grille, and the thickness of the metal grille is 0.2 - 0.5 mm.

[0010] In addition to one or more of the above-disclosed features, or as an alternative, the size of the metal grille satisfies the following relationship: , where: is the mesh size of the metal grille; is the number of mesh holes in the length direction; is the length occupied by continuously distributed sieve holes and is the wire diameter in millimeters. From the formula, we can see that the larger the wire diameter of the metal mesh and the more mesh holes there are, the smaller the mesh size of the metal mesh is. The contact area between the metal mesh with a smaller mesh size and the composite material increases, and the interfacial bonding force is improved. The smaller pores make the metal mesh and the composite material in closer contact, so that stress can be transferred more effectively during the stretching process, avoiding delamination or slippage between the composite material and the metal mesh. When subjected to tensile loads, the mesh with a small pore size can provide a more uniform stress distribution, reduce local stress concentration, and thus reduce the risk of structural fracture. In addition, when the metal mesh size is small, the mesh is more stable and is not easy to deform or break under external force, thereby improving the durability of the structure. When the metal mesh size is small, the support effect of the mesh structure is more significant and can provide stronger tensile resistance. This is because the smaller pores reduce the deformation space of the metal mesh, thereby increasing the overall stiffness of the mesh, enabling it to more effectively share the external force applied to the composite material. Therefore, choosing a metal mesh with a larger wire diameter, a larger number of mesh holes, and a smaller metal mesh size can help improve the tensile properties of the composite material bolt connection structure, especially in terms of enhancing strength, stiffness, and durability.

[0011] In addition to one or more of the features disclosed above, or as an alternative, after the metal grille is welded to the bolt hole metal sleeve, there is at least one mesh of the metal grille within a unit radius of the bolt hole metal sleeve, and the number of meshes satisfies the following relationship: ， in, It refers to the diameter of the metal sleeve of the bolt hole; Unit The number of mesh holes in length; is the wire diameter of the metal grille; w is the mesh size. From the above formula, it can be deduced that the larger the size of the metal sleeve, the larger the metal wire diameter and the smaller the density of the metal mesh should be.

[0012] In addition to or as an alternative to one or more of the features disclosed above, the bolt hole stress of the bolt hole metal sleeve satisfies the following relationship: , in, is the cross-sectional area of ​​the metal sleeve; is the stress intensity of the metal sleeve; is the stress intensity of a single solder joint; is the total number of solder joints; is the effective area of a single solder joint; Assume that the outer diameter of the metal sleeve is , and the inner diameter is Then can be expressed as: .

[0013] It can be seen that the enhanced force-bearing situation of the bolt hole is closely related to the sleeve size and the strength of the solder joints. The size of the sleeve (such as inner diameter, outer diameter, length, etc.) directly affects the load-bearing capacity of the bolt hole. If the sleeve size is unreasonable, it will lead to uneven stress, and may even cause local stress concentration, increasing the risk of cracks or deformation. The inner diameter of the sleeve should adapt to the diameter of the bolt to ensure a tight enough fit between the bolt and the hole. At the same time, the outer diameter design should ensure that the load can be effectively distributed. The sleeve metal mesh is connected by welding, and the strength of the solder joints plays a crucial role. Insufficient strength at the welded joints may lead to fatigue failure or plastic deformation in the welding area, thus affecting the force-bearing performance of the entire structure. Therefore, the thicker the wire diameter of the metal mesh, the larger the area of the solder joints. At the same time, increasing the number of solder joints can also increase the load-bearing capacity of the welded component of the metal mesh and the sleeve.

[0014] In addition to one or more of the features disclosed above, or as an alternative, the tensile load of the metal grille mesh satisfies the following relationship: , Where: is the total strength of the metal grille mesh; is the load applied to the metal grille mesh; is the force-bearing area of the metal mesh , is the wire diameter of the metal mesh. It can be seen that the larger the wire diameter, the stronger the load-bearing capacity of the metal mesh. The strength of the metal mesh is also affected by the way the load is applied. If the load on the composite material bolt connection component is evenly distributed, the strength of the metal mesh may be manifested as the maximum load-bearing capacity of the material; if the load is concentrated on certain parts (such as point load), it may lead to local failure of the metal mesh. Therefore, by welding the metal sleeve to the metal mesh, the load can be redistributed through the circumferential metal sleeve. The situation of point load is effectively avoided, so that the load can be evenly distributed and the stress concentration phenomenon can be prevented. Furthermore, selecting a metal mesh with a larger wire diameter can improve the tensile strength and stability of the overall composite material bolt connection component.

[0015] In addition to one or more of the features disclosed above, or as an alternative, the shape of the solder joints between the metal grille mesh and the bolt hole metal sleeve is circular, and the strength of the solder joints satisfies the following relationship: The effective contact area of the solder joints

[0016] Calculate the shear strength of the solder joint

[0017] Calculate the tensile strength

[0018] Wherein: is the shear strength of the solder joint; is the shear strength of the welding material, wherein, ; is the tensile strength of the solder joint; is the tensile strength of the welding material; is the effective contact area of the solder joint.

[0019] The total strength of the solder joint usually depends on its weakest part (shear failure or tensile failure). If both failures are possible, the final solder joint strength should be the smaller value of the shear strength and the tensile strength. From the shear strength formula and the tensile strength formula, it can be seen that it is proportional to the diameter of the solder joint, and the larger the wire diameter of the wire mesh, the larger the diameter of the solder joint. Therefore, choosing a wire mesh with a larger wire diameter can improve the connection strength of the overall structure. In addition, since the tensile load is mainly transmitted through the solder joints of the metal sleeve, the more solder joints there are, the greater the connection strength between the wire mesh and the sleeve welded member.

[0020] In addition to one or more of the features disclosed above, or as an alternative, the aperture size of the upper laying layer mounting hole and the aperture size of the lower laying layer mounting hole are 96% - 98% of the outer diameter of the bolt hole metal sleeve.

[0021] In addition to one or more of the features disclosed above, or as an alternative, the length of the bolt hole metal sleeve is 96% - 99% of the total thickness of the metal grille mesh, the upper composite material laying layer and the lower composite material laying layer.

[0022] In addition to one or more of the features disclosed above, or as an alternative, the circumferential shape of the bolt hole metal sleeve is circular or regular polygon.

[0023] According to the second aspect of the present invention, the present invention provides a composite material structure for bolt connection, comprising: A bolt hole metal sleeve, A metal grille mesh, sleeved on the outer circumferential surface of the bolt hole metal sleeve; and The upper composite material ply and the lower composite material ply, and the upper composite material ply and the lower composite material ply are sleeved on the outer circumferential surface of the bolt hole metal sleeve; Wherein, the upper composite material ply and the lower composite material ply are respectively laid on the upper surface and the lower surface of the metal grid mesh.

[0024] In addition to one or more of the features disclosed above, or as an alternative, the outer edges of the upper composite material ply and the lower composite material ply are adapted to the outer edges of the metal grid mesh.

[0025] One of the technical solutions in the above technical solutions has the following advantages or beneficial effects: In this technical solution, the metal mesh is laid into the material and welded to the metal sleeve as a whole, and the bolt pressure received by the sleeve is transmitted through the metal mesh, so as to improve the bearing capacity and reliability of the composite material bolt connection joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The technical solutions and other beneficial effects of the present invention will be obvious by combining the drawings and describing the specific embodiments of the present invention in detail.

[0027] Figure 1 is a schematic structural diagram of a metal grid mesh and a bolt hole metal sleeve after welding according to an embodiment of the present invention; Figure 2 is a top view of a metal grid mesh and a bolt hole metal sleeve after welding according to an embodiment of the present invention; Figure 3 is a front view of a metal grid mesh and a bolt hole metal sleeve after welding according to an embodiment of the present invention; Figure 4 is a longitudinal sectional view of a metal grid mesh and a bolt hole metal sleeve after welding according to an embodiment of the present invention; Figure 5 is a longitudinal sectional view of a metal grid mesh, a bolt hole metal sleeve and a composite material structure after molding according to an embodiment of the present invention; Figure 6 is a schematic structural diagram of an overall component of a metal grid mesh, a bolt hole metal sleeve and a composite material structure after molding according to an embodiment of the present invention; Figure 7 is a schematic diagram of a hot pressing molding process according to an embodiment of the present invention; Figure 8 is a schematic diagram of a vacuum assisted resin injection molding (VARI) process according to an embodiment of the present invention; Figure 9 is a force diagram of a metal grid mesh and a bolt hole metal sleeve after welding according to an embodiment of the present invention; Figure 10 It is a comparison diagram of the results of a hot pressing forming process provided according to an embodiment of the present invention; Figure 11 It is a comparison diagram of the test results of a vacuum-assisted resin injection molding process provided according to an embodiment of the present invention. Specific embodiments

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts fall within the protection scope of the present invention.

[0029] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after without special explanation.

[0030] An embodiment of the present invention provides a method for strengthening a composite material structure for bolt connection. The composite material structure includes: A metal sleeve for a bolt hole; A metal grille mesh sleeved on the outer circumferential surface of the metal sleeve for the bolt hole; and An upper composite material ply and a lower composite material ply; Wherein, the strengthening method includes the following steps: S1. Determine the circumferential shape and size of the metal sleeve for the bolt hole, and punch the metal grille mesh, the upper composite material ply and the lower composite material ply according to the circumferential shape and size of the metal sleeve for the bolt hole, so that the metal grille mesh, the upper composite material ply and the lower composite material ply are successively provided with grille mesh installation holes, upper ply installation holes and lower ply installation holes; S2. Sleeve the metal grille mesh on the outer circumferential surface of the metal sleeve for the bolt hole through the grille mesh installation holes, and then weld the metal grille mesh to the outer circumferential surface of the metal sleeve for the bolt hole; S3. According to the circumferential shape and size of the bolt-hole metal sleeve and the shape and size of the metal grille, formulate the laying schemes for the upper composite material layer and the lower composite material layer. Sleeve the upper composite material layer and the lower composite material layer respectively on the outer circumferential surface of the bolt-hole metal sleeve through the upper layer installation holes and the lower layer installation holes, and lay the upper composite material layer and the lower composite material layer respectively on the upper surface and the lower surface of the metal grille according to the laying schemes.

[0031] Further, the laying scheme is a symmetric laying. Compared with other laying methods, the symmetric laying method can ensure the uniform distribution of stress in each layer of material when stressed, make full use of the composite material characteristics of the upper and lower layers of the metal mesh, and improve the overall bonding property. The structure of the symmetric laying helps to reduce the warping or deformation of the metal mesh and the fiber layer due to the difference in interlayer stress. This helps to avoid the generation of material breakage or cracks caused by stress concentration.

[0032] Further, the mesh diameter of the metal grille is 1 - 4 mm.

[0033] Further, after welding the metal grille to the outer circumferential surface of the bolt-hole metal sleeve, the number of welding points between the metal grille and the bolt-hole metal sleeve is 8 - 16, and the welding points are evenly distributed in the circumferential direction of the bolt-hole metal sleeve. It is appropriate that the mesh hole of the metal mesh is between 1 mm and 4 mm, so that the metal grille can have 8 - 16 welding points after pre-drilling in the center, and the welding points can be evenly distributed around the metal sleeve. The appropriate number of welding points and the positions of the welding points can disperse the load, reduce the stress borne by a single welding point, thereby improving the durability and stability of the overall structure, and at the same time avoiding the phenomenon of local stress concentration.

[0034] Further, the thickness of the metal grille is equal to the wire diameter of the metal grille, and the thickness of the metal grille is 0.2 - 0.5 mm. The thickness of the metal mesh should be equal to the thickness of the wire, and it is appropriate to be about between 0.2 mm and 0.5 mm. The metal mesh with a larger wire thickness can enhance the connection strength of the welding points, and then improve the strength of the overall structure. The thickness parameter should be moderate. Too thick will affect the bonding strength between the glass fiber and the metal grille during the forming process and affect the interlayer performance. Too thin will affect the strength of the welding points and cause them to be ineffective. At the same time, it should be placed at the neutral axis of the laminate to enhance the prevention of failure due to excessive tensile stress or compressive stress near the outer layer.

[0035] Further, the size of the metal grille satisfies the following relational expression: , where: is the mesh size of the metal grille; is The number of mesh holes in terms of length; is continuously distributed sieve holes and the length occupied by the wire; is the wire diameter in millimeters.

[0036] Further, after the metal grille mesh is welded to the bolt-hole metal sleeve, there is at least 1 mesh hole of the metal grille mesh within the unit radius of the bolt-hole metal sleeve, and the number of mesh holes satisfies the following relationship: ， wherein, refers to the diameter of the bolt-hole metal sleeve; is the unit number of mesh holes in terms of length; is the wire diameter of the metal grille mesh; w is the mesh size.

[0037] Further, the stress of the bolt hole of the bolt-hole metal sleeve satisfies the following relationship: , wherein, is the cross-sectional area of the metal sleeve; is the stress strength of the metal sleeve; is the stress strength of a single solder joint; is the total number of solder joints; is the effective area of a single solder joint; Assume the outer diameter size of the metal sleeve is , and the inner diameter size is Then can be expressed as: .

[0038] Further, the tensile load of the metal grille mesh satisfies the following relationship: , wherein: is the total strength of the metal grille mesh; is the load applied to the metal grille mesh; is the stress area of the metal mesh , is the wire diameter of the metal mesh.

[0039] Furthermore, the shape of the solder joint between the metal grille and the bolt-hole metal sleeve is circular, and the strength of the solder joint satisfies the following relational expression: Effective contact area of the solder joint

[0040] Calculate the shear strength of the solder joint

[0041] Calculate the tensile strength

[0042] Where: is the shear strength of the solder joint; is the shear strength of the welding material, where ; is the tensile strength of the solder joint; is the tensile strength of the welding material; is the effective contact area of the solder joint.

[0043] Furthermore, the aperture sizes of the upper ply mounting holes and the lower ply mounting holes are 96% - 98% of the outer diameter of the bolt-hole metal sleeve.

[0044] Furthermore, the length of the bolt-hole metal sleeve is 96% - 99% of the total thickness of the metal grille, the upper composite ply and the lower composite ply.

[0045] Furthermore, the circumferential shape of the bolt-hole metal sleeve is circular or regular polygon.

[0046] It is more appropriate that the shape of the metal mesh is square or diamond. Among them, the square can provide greater displacement and energy absorption capacity, thereby increasing the toughness and impact resistance of the material. It is advisable to use a square metal mesh for components under dynamic impact. The diamond metal mesh has anisotropy. The long diagonal direction of the diamond grid is consistent with the tensile direction, which can disperse the tensile stress and provide additional support and stability, thereby effectively enhancing the tensile strength in this direction. And the diamond metal mesh is more suitable for continuous static loads.

[0047] The inner diameter size of the metal sleeve for the bolt hole can be adjusted according to bolts of different diameters. The larger the inner diameter size of the metal sleeve, the thicker the metal mesh with a smaller density should be selected. For a larger-sized metal sleeve, the reason for choosing a metal mesh with a smaller density is that it can provide appropriate strength and flexibility. The smaller the density of the metal mesh, the larger the gaps between the grids, which can not only reduce the weight of the entire metal sleeve and avoid overloading the equipment or structure with an overly heavy sleeve, but also enhance flexibility. A smaller density of the metal mesh can make the stress distribution on the sleeve more uniform, reduce local stress concentration, and prevent excessive rigid deformation of the sleeve. However, the density of the metal mesh cannot be too small, otherwise it may not provide sufficient support force, resulting in the overall welded metal sleeve structure not having the necessary load-bearing capacity. Selecting a thicker metal mesh can increase the strength of the solder joints and thus enhance the strength of the bolt hole.

[0048] For a bolt hole sleeve with a larger diameter, a metal mesh with a relatively larger thickness and density should be selected, and several 45-degree fiberglass layers should be laid more. Because it can significantly enhance various properties of the material, including tensile strength, shear strength, bending performance, fatigue resistance, interlayer bonding strength, and toughness, etc., thereby enhancing the strength of the metal mesh and the welded sleeve structure, and thus improving the strength of the bolt hole.

[0049] The present invention also provides a composite material structure for bolt connection, including: A metal sleeve for the bolt hole, A metal grille mesh, sleeved on the outer circumferential surface of the metal sleeve for the bolt hole; and An upper composite material layer and a lower composite material layer, the upper composite material layer and the lower composite material layer are sleeved on the outer circumferential surface of the metal sleeve for the bolt hole; Wherein, the upper composite material layer and the lower composite material layer are respectively laid on the upper surface and the lower surface of the metal grille mesh.

[0050] Furthermore, the outer edges of the upper composite material layer and the lower composite material layer are adapted to the outer edge of the metal grille mesh. Embodiment

[0051] Taking the hot pressing forming method of fiberglass composite material as an example in this instance, the structure of an example provided by the present invention is shown in the figure, which is composed of a metal mesh 1, solder joints 2, a metal sleeve 3, and a composite material prepreg (multi-layer material) 4.

[0052] First, punch the glass fiber material prepreg 4 according to the size of the metal sleeve 2. At the same time, laser punch the center of the metal mesh 1. Place the metal ring at the center of the metal hole, and use laser welding technology to weld each exposed metal wire solder joint 2 near the metal mesh hole to the metal sleeve 3 one by one into an integral component. Ensure the strength of the solder joints and the stability of the overall structure during the welding process. Then, perform surface treatment on the punched glass fiber prepreg 4 and the metal mesh component with a sleeve. After cleaning, place the welded metal mesh component with a metal sleeve in the middle of the glass fiber prepreg 4 layup. The layup direction of the glass fiber prepreg 4 can be changed, but it should be ensured that the amount of glass fiber prepreg in the upper and lower layers is the same and the sleeve length is slightly less than the thickness of the glass fiber prepreg layup. Finally, perform molding through a hot press. Under the action of high temperature and uniform pressure, melt the resin in the prepreg and immerse it into the metal mesh holes, so that there is a strong interfacial strength between the metal mesh and the composite material after molding. Finally, it is molded into a composite material component with a metal mesh and a bolt hole sleeve welded component that can enhance the strength of the bolt hole. Conduct three groups of tensile test tests in accordance with the specification ASTM D5766. Each group includes specimens with a metal mesh and a bolt hole sleeve welded reinforcement component and non-reinforced specimens. Refer to Figure 8 The test results show that the metal mesh and bolt hole sleeve welded reinforcement component can significantly improve the stiffness at the bolt hole and the tensile strength of the specimen. The schematic diagram of its hot pressing molding process is as Figure 6 shown. Example

[0053] In this example, the vacuum assisted resin infusion (VARI) molding method of glass fiber composite materials is taken as an example. The structure of an example of the metal mesh and bolt hole sleeve welded component provided by the present invention is as Figure 1 shown, which is composed of a metal mesh 1, solder joints 2, a metal sleeve 3, and a glass fiber composite (multi-layer material) 4. And prepare the materials such as a flow guiding mesh, a demolding cloth, a tee, and a vacuum bag required during the molding process accordingly.

[0054] First, punch holes in the cut fiberglass material 4 according to the size of the metal sleeve 2. At the same time, laser punch holes in the centers of the two metal meshes 1. Place the metal ring at the center of the metal mesh holes, and use laser welding technology to weld each metal wire solder joint 2 exposed near the metal mesh holes to the metal ring sleeve 3 one by one into an integral component. Ensure the strength of the solder joints and the stability of the overall structure during the welding process. Subsequently, perform surface treatment on the punched fiberglass 4 and the metal mesh component with a sleeve. After cleaning, place the welded metal mesh component with a metal sleeve in the middle of the fiberglass material 4 layup. The layup direction of the fiberglass material 4 can be changed, but it should be ensured that the number of fiberglass materials in the upper and lower layers is the same and the sleeve length is slightly less than the layup thickness of the fiberglass material. After all materials are prepared, lay the same number of fiberglass on the upper and lower layers of the bolt hole sleeve welding reinforcement component. Place the materials on a flat rigid table in the order of wrapping the outer layer of the fiberglass with a release cloth and then wrapping the outer layer of the release cloth with a flow guide net. The size of the flow guide net is slightly smaller than that of the release cloth to facilitate demolding after curing. After laying the fiber and other materials, lay a circle of vacuum glue around them and bond the vacuum bag. Leave spaces at both ends for placing a spiral tube and a tee, and bond the tee and the flow guide tube with vacuum glue to make the entire device form a sealed vacuum state. Turn on the vacuum pump for pre-pumping. After ensuring good airtightness of the entire device, prepare a vinyl resin, a curing agent, and an accelerator in a ratio of 100:2:1, and fully stir the prepared mixed resin solution. Block one end of the vacuum tube, insert it into the mixed resin solution and then release it. The resin infiltrates the fiber continuously through the flow guide net under the action of vacuum negative pressure until the resin reaches the middle layer of the metal mesh welded bolt hole sleeve reinforcement component. After the resin is fully and evenly infiltrated, clamp the two ends of the flow guide tube with tweezers so that the fiber in the middle is filled with resin and remains in a vacuum-sealed state. Let it stand at room temperature for about 3 to 4 hours. After the resin and the curing agent have fully reacted and hardened, the entire molding process is completed. Then perform demolding treatment, and finally form a composite material component with a metal mesh and a bolt hole sleeve welding component that can enhance the strength of the bolt hole. Conduct three groups of tensile test measurements according to the standard ASTM D5766. Each group includes specimens with a metal mesh and a bolt hole sleeve welding reinforcement component and specimens without reinforcement. Refer to the test results of the vacuum-assisted resin injection molding process Figure 9 , the metal mesh and bolt hole sleeve welding reinforcement component can also significantly improve the stiffness at the bolt hole and the tensile strength of the specimen. The schematic diagram of its vacuum-assisted resin injection molding (VARI) process is as Figure 6 shown. Example

[0055] Taking the composite bolt connection structure with enhanced M6 bolt holes as an example, three different ply sequences, namely A, B, and C, are adopted in the case. Among them, Group A is [0 / 45 / -45 / 90 / 0 / metal grille mesh and sleeve welded part / 0 / 90 / -45 / 45 / 0], the ply sequence of Group B is [0 / 90 / 90 / 90 / 0 / metal grille mesh and sleeve welded component / 0 / 90 / 90 / 90 / 0], and the ply sequence of Group C is [0 / 45 / 45 / 45 / 0 / metal grille mesh and sleeve welded component / 0 / 45 / 45 / 45 / 0]. The size of the metal sleeve in the metal grille mesh and sleeve welded component is an inner diameter of 6 mm and a thickness of 1.5 mm, so that the M6 bolt can pass through freely. The size of the metal grille mesh is 8 mesh (that is, in each inch of the grid, there are 8 holes along the direction of the grid). The 8-mesh metal grille mesh can have 12 solder joints after pre-drilling at the center, and the solder joints can be evenly distributed around the metal sleeve. The appropriate number and position of solder joints can disperse the load, reduce the stress borne by a single solder joint, thereby improving the durability and stability of the overall structure, and at the same time avoiding local stress concentration. The metal wire diameter is 0.35 mm. Using a metal mesh with a larger wire diameter can enhance the connection strength of the solder joints, and further improve the strength of the overall structure. In addition, the overall thickness of the metal grille mesh is 0.35 mm, and the thickness parameter should be moderate. Too thick will affect the interlayer performance, and too thin will not play a role. It should be placed at the neutral axis of the laminate to enhance the prevention of failure due to excessive tensile or compressive stress near the outer layer. A diamond grid metal grille mesh with a short diagonal of 14 mm and a long diagonal of 25 mm for the mesh holes is used. It has anisotropy, and the long diagonal direction of the diamond grid is consistent with the tensile direction, which can disperse the tensile stress and provide additional support and stability, thereby effectively enhancing the tensile strength in this direction. The size of the finally formed specimen is 150 mm in length, 36 mm in width, and 2.5 mm in thickness. The hole diameter at the center metal sleeve is 6 mm. Two different forming processes, namely the hot press forming process and the vacuum-assisted resin forming process, are used for forming. After forming, the composite bolt connection structures with bolt holes of three different ply sequences and the unenhanced specimens are subjected to three groups of single-bolt tensile tests in accordance with the specification ASTM D5766. The results are as Figure 10, as shown in Figure 11, compared with the metal grid mesh reinforced component without bolt holes, no matter what forming method is adopted, the bolt connection composite material structure performance can be significantly improved by the metal grid mesh. And all three laying methods have obvious effects on strengthening the bolt holes. Among them, the effects of Group A and Group C are the most obvious because the glass fibers in the 45-degree direction can bear composite loads (such as tensile and shear forces existing simultaneously); in addition, the reinforcement of the glass fibers in the 45-degree direction helps to improve the interlaminar bonding strength of the laminate and reduce the failure risk caused by interlaminar delamination. 0 degrees, 90 degrees, ±45 degrees, etc., are arranged alternately to obtain better strength and stiffness. The strengthening effect of the glass fibers enhances the bonding force between each layer and the metal grid mesh, reduces the possibility of material failure when stressed between layers, and thus enhances the strength of the bolt holes.

[0056] The present invention enhances the bolt connection strength by welding the metal mesh and the sleeve into one body and embedding them in the composite material. Compared with the traditional strengthening method of only embedding the sleeve, which can only conduct force through the sleeve, the force-bearing situation of this method is as Figure 7 shown. The compressive stress applied by the bolt on one side of the ring can be converted into tensile stress on the other side of the ring through the joint action of the metal mesh and the sleeve, with higher conduction efficiency. This method is simple to operate, widely applicable to composite material fiber types and forming methods, and can be adjusted according to the actual working conditions.

[0057] As described above, only some implementation manners of the embodiments of the present invention are provided, and there is no limitation in any form to this application. The protection scope of the embodiments of the present invention is not limited thereto. Any simple modification, equivalent change and modification that can be easily thought of by those skilled in the art within the technical scope disclosed by the embodiments of the present invention should be covered within the protection scope of the embodiments of the present invention.

Claims

1. A method for enhancing a composite material structure for bolt connection, characterized in that, The composite material structure includes: A metal sleeve for bolt holes; A metal grille mesh sleeved on the circumferential outer surface of the metal sleeve for bolt holes; and An upper composite material ply and a lower composite material ply; Wherein, the strengthening method includes the following steps: S1. Determine the circumferential shape and size of the metal sleeve for bolt holes, and punch the metal grille mesh, the upper composite material ply and the lower composite material ply according to the circumferential shape and size of the metal sleeve for bolt holes, so that the metal grille mesh, the upper composite material ply and the lower composite material ply are successively provided with grille mesh installation holes, upper ply installation holes and lower ply installation holes; S2. Sleeve the metal grille mesh on the circumferential outer surface of the metal sleeve for bolt holes through the grille mesh installation holes, and then weld the metal grille mesh to the circumferential outer surface of the metal sleeve for bolt holes; S3. Develop a laying scheme for the upper composite material ply and the lower composite material ply according to the circumferential shape and size of the metal sleeve for bolt holes and the shape and size of the metal grille mesh, sleeve the upper composite material ply and the lower composite material ply on the circumferential outer surface of the metal sleeve for bolt holes respectively through the upper ply installation holes and the lower ply installation holes, and lay the upper composite material ply and the lower composite material ply on the upper surface and the lower surface of the metal grille mesh respectively according to the laying scheme.

2. The enhancement method according to claim 1, wherein The laying scheme is a symmetric ply.

3. The enhancement method according to claim 1, wherein The mesh diameter of the metal grille mesh is 1 - 4 mm.

4. The enhancement method according to claim 1, wherein After welding the metal grille mesh to the circumferential outer surface of the metal sleeve for bolt holes, the number of welding points between the metal grille mesh and the metal sleeve for bolt holes is 8 - 16, and the welding points are evenly distributed in the circumferential direction of the metal sleeve for bolt holes.

5. The enhancement method according to claim 1, wherein The thickness of the metal grille mesh is equal to the wire diameter of the metal grille mesh, and the thickness of the metal grille mesh is 0.2 - 0.5 mm.

6. The enhancement method according to claim 1, wherein The size of the metal grille mesh satisfies the following relationship: ， Wherein: is the mesh size of the metal grille; is the number of meshes in terms of length; is the length occupied by continuous sieve holes and metal wires, with the unit of millimeter for the metal wire diameter.

7. The enhancement method according to claim 6, wherein After welding the metal grille mesh to the metal sleeve for bolt holes, there is at least 1 mesh hole of the metal grille mesh within the unit radius of the metal sleeve for bolt holes, and the number of mesh holes satisfies the following relationship: ， Among them, refers to the diameter of the metal sleeve of the bolt hole; per unit number of apertures in the length; is the wire diameter of the metal grille mesh; w is the mesh size.

8. The enhancement method according to claim 1, wherein The bolt hole stress of the metal sleeve for bolt holes satisfies the following relationship: ， Among them, is the cross-sectional area of the metal sleeve; is the stress intensity of the metal sleeve; is the stress intensity of a single solder joint; is the total number of solder joints; is the effective area of a single solder joint; Assume that the outer diameter of the metal sleeve is , and the inner diameter is Then can be expressed as: 。 9. The enhancement method according to claim 1, wherein The tensile load of the metal grille mesh satisfies the following relationship: ， Wherein: is the total strength of the metal grille mesh; is the load applied to the metal grille mesh; is the stress area of the metal mesh , is the wire diameter of the metal mesh.

10. The enhancement method according to claim 1, characterized in that, The shape of the welding points between the metal grille mesh and the metal sleeve for bolt holes is circular, and the strength of the welding points satisfies the following relationship: The effective contact area of the welding points: ， Calculate the shear strength of the welding points: ， Calculate the tensile strength: ， Wherein: is the shear strength of the solder joint; is the shear strength of the welding material, where ; is the tensile strength of the solder joint; is the tensile strength of the welding material; is the effective contact area of the solder joint.

11. The enhancement method according to claim 1, wherein The aperture size of the upper ply installation holes and the aperture size of the lower ply installation holes are 96% - 98% of the outer diameter of the metal sleeve for bolt holes.

12. The enhancement method according to claim 1, wherein The length of the metal sleeve for bolt holes is 96% - 99% of the total thickness of the metal grille mesh, the upper composite material ply and the lower composite material ply.

13. The enhancement method according to claim 1, wherein The circumferential shape of the metal sleeve for bolt holes is circular or regular polygon.

14. A composite material structure for bolt connection, characterized in that, Includes: A metal sleeve for bolt holes, A metal grille mesh sleeved on the circumferential outer surface of the metal sleeve for bolt holes; And An upper composite material ply and a lower composite material ply, the upper composite material ply and the lower composite material ply are sleeved on the circumferential outer surface of the metal sleeve for bolt holes; Among them, the upper composite material ply and the lower composite material ply are respectively laid on the upper surface and the lower surface of the metal grille.

15. The composite material structure according to claim 14, characterized in that, The outer edges of the upper composite material ply and the lower composite material ply are adapted to the outer edge of the metal grille.

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