A z-pin reinforced composite sandwich structure and method of making the same

Abstract

The application provides a Z-pin reinforced composite sandwich structure and a preparation method thereof.The Z-pin reinforced composite sandwich structure has a structure form comprising an upper composite skin, a core material and a lower composite skin, and composite pins are implanted in the Z direction of a preformed body of the sandwich structure for Z direction reinforcement;the composite pins are made of the same material as the composite skin, and the composite pins are implanted by a high-pressure air gun; and the composite pins are carbon fiber pins or high-strength glass steel pins.The beneficial effects of the application are as follows: composite reinforcing bars perpendicular to fiber cloth are implanted, and the scheme solves the problems of different reinforcement angles, large direction difference dispersion, non-obvious effect, weakening of other direction performance and the like caused by other reinforcement schemes, especially solves the engineering problem that large products, sandwich parts and special-shaped parts are difficult to realize sewing, and eliminates the problems of defects easily generated in the X and Y directions of the in-plane fabric and the like.

Description

Technical Field

[0001] This invention belongs to the field of composite material structural components, and in particular relates to the technical field of preparation process technology for foam sandwich preforms. Background Technology

[0002] The composite material is composed of fiber-reinforced composite material + foam + fiber-reinforced composite material. The fiber-reinforced composite material can be obtained by vacuum filling and curing of fiber cloth with resin, or by hot pressing and curing of prepreg.

[0003] The Z-direction of the interlayer of composite materials is its weak point. The existing reinforcement schemes mainly include the continuous fiber stitching three-dimensional weaving scheme. This Z-direction reinforcement scheme is currently the main research reinforcement scheme in the domestic industry, and domestic and foreign scientific research institutes and universities have related research. By using continuous fibers to stitch and weave the fiber cloth or sandwich material into a whole, its Z-direction strength is enhanced.

[0004] This scheme is the most readily conceived Z-axis augmentation approach in conventional thinking, but its research progress has been greatly limited, and the results have not been ideal. The main reasons are:

[0005] 1) There are two types of suturing: manual suturing and machine suturing. Both are quite difficult, have limitations, and generate many problems.

[0006] Manual sewing: It is inefficient, and the consistency of parameters such as angle, force and depth of manual sewing is poor. At the same time, when the product is large enough, it is difficult to turn it over. Especially for sandwich parts, manual sewing is almost impossible. This type of reinforcement solution is only suitable for templates, small products, or local areas near the edge of the product.

[0007] Mechanical sewing: Mechanical sewing can solve the problems of low efficiency and instability of manual sewing. However, for irregularly shaped products, it is necessary to customize matching sewing equipment according to the size, line type and other specifications. That is, each product with a different shape needs to be customized with a corresponding sewing machine to be sewn well. Moreover, the sewing machine also needs to be adjusted and calibrated, which greatly limits its application.

[0008] 2) May cause defects

[0009] Because it is a continuous fiber stitch, it not only has fiber implantation reinforcement in the Z direction, but also inevitably turns in the X and Y directions of the fabric when it is flipped and interlaced. This will affect the state of the fiber fabric in the X and Y directions, resulting in a certain amount of unevenness, warping, and unevenness defects in the fibers in these directions. It can strengthen in the Z direction, but it will also cause certain defects and weakening in the X and Y directions. The fiber stitching layout, angle, depth, and force will all affect the final performance of the product to a certain extent. The product surface will also form a certain degree of unevenness, which will cause a series of defect problems and greatly limit its application.

[0010] 2. Three-dimensional weaving, which involves weaving fiber fabrics in three dimensions; however, the cost is too high, each type of piece needs to be designed and tested for correction, the versatility is poor, and the application is very limited.

[0011] By directly weaving fiber cloth into a three-dimensional woven fabric according to its shape, this type of fabric has high strength in the X, Y, and Z directions because it is woven into a whole.

[0012] However, its application is also quite limited, mainly in the following aspects:

[0013] 1) Low weaving efficiency and very high weaving cost

[0014] Three-dimensional weaving is expensive, especially since it involves irregular shapes. It requires designing weaving programs and using specialized equipment, and its efficiency is generally low. Weaving equipment for complex and strong irregular shapes is often not universal and may even require multiple weaving iterations and optimizations. Its cost is very high, which greatly limits its application.

[0015] 2) Weaving equipment is difficult to standardize

[0016] Traditionally, weaving equipment for irregularly shaped fabrics is difficult to generalize and requires customized weaving equipment. The high cost of equipment investment, as well as the corresponding personnel and maintenance, greatly hinders its widespread application.

[0017] 3) Changes in three-dimensional fabric properties

[0018] The Z-axis properties of three-dimensional fabrics are greatly enhanced, but the extensive fiber folding significantly affects their X and Y-axis properties.

[0019] 4) Application process is limited

[0020] On the one hand, its woven body is relatively thick, making it unsuitable for prepreg production, and autoclave and OOA processes are not appropriate; on the other hand, its weaving is a thickened fiber layer, making it unsuitable for splicing, so it needs to be woven into a whole, and it is particularly difficult to weave complex irregular-shaped products, which greatly limits its application.

[0021] The main problems with composite material structures are:

[0022] 1) Layered structure, interlayer forces are relatively low compared to in-plane strength;

[0023] 2) In order to reduce weight as much as possible, the foam density in the sandwich structure is low, and the strength is much lower than that of reinforced composite materials, resulting in a lower overall compressive strength.

[0024] Chinese Patent Publication No. CN113246585B, entitled "Perforating Needle, Yarn-Threading Needle, System, and Method for Manufacturing Foam Sandwich Preforms," ​​provides a foam sandwich preform comprising a first covering layer, a foam core material, a second covering layer, and yarn. The foam core material is located between the first and second covering layers, forming a sandwich structure. The yarn passes through the sandwich structure, connecting the first covering layer, the foam core material, and the second covering layer. It can, to a certain extent, obtain foam sandwich preforms with different fiber column contents.

[0025] Using its patented technology, a punching device and auxiliary systems such as punching needles and threading needles are developed, designed and manufactured for foam sandwich preforms. By employing a series of punching and threading processes, fiber yarns can be threaded into the sandwich preform according to the set specifications, and resin is introduced to form and cure, thus forming Z-direction fiber reinforcement in the preform for Z-direction strengthening.

[0026] It also has the following problems: 1) The pre-inserted fiber Z-Pin reinforced implanted fiber material requires the use of liquid resin introduction process to allow the resin to be immersed and cured before the reinforcement effect can be formed. Therefore, it is only suitable for liquid resin molding process.

[0027] 2) It uses a special fixed pre-installed equipment to implant fiber filaments, and can only be pre-installed in standard flat boards. When the foam board needs secondary processing or curved surface application, its application will be limited. Summary of the Invention

[0028] To address the aforementioned technical problems, this invention provides a method for embedding reinforcing prefabricated needle-like composite materials in the Z-direction during foam laying.

[0029] The technical solution of this invention is:

[0030] A Z-Pin reinforced composite sandwich structure is provided, comprising an upper composite skin, a core material, and a lower composite skin. Composite needles are implanted in the Z-direction of the preform of the sandwich structure for Z-direction reinforcement.

[0031] Furthermore, the composite material needle is made of the same material as the composite material skin, and the insertion of the composite material needle is completed by a high-pressure air gun.

[0032] Furthermore, the aforementioned composite material needles are made of carbon fiber or high-strength fiberglass.

[0033] Furthermore, the diameter of the composite material needles is 0.6 to 1.5 mm, and they are arranged in an array or crisscross pattern within the surface of the sandwich preform. The vertical spacing of the composite material needles in the X and Y directions within the surface is between 10 and 20 mm.

[0034] Furthermore, the aforementioned composite material needles can be arranged with variable density, that is, the needle spacing can be appropriately reduced in areas with high stress and appropriately increased in areas with low stress.

[0035] A method for preparing a Z-Pin reinforced composite sandwich structure includes the following steps:

[0036] S1) Prefabricated composite material needles are cut into prefabricated reinforcing needles of the design specifications using a guillotine cutter according to the required injection length;

[0037] S2) The composite sandwich structure is laid in the following order: skin fiber cloth + core material + upper surface 1-2 layers of composite fiber cloth;

[0038] S3) Place the composite material needle into the high-pressure air gun and implant the composite material needle into the sandwich preform body along the Z direction according to the Z-Pin reinforcement scheme.

[0039] S4) Upper surface fiber cloth (remaining fibers) laying step;

[0040] S5) Following the vacuum-assisted molding process, lay out the corresponding release cloth, flow medium, flow pipe, vacuum bag film, and sealing tape auxiliary materials. After the sealing and leak test is qualified, introduce the corresponding resin and cure to obtain the Z-pin reinforced composite sandwich structure.

[0041] Furthermore, the diameter of the aforementioned composite material needle is 0.6-1.5 mm.

[0042] Furthermore, the above-mentioned implantation design involves the composite material needles being arranged with a vertical distance of 10-20mm in both longitudinal and transverse directions, and arranged in a longitudinal, transverse, or staggered manner.

[0043] Furthermore, the thickness of the aforementioned cladding layer is 2mm carbon fiber + 20mm foam + 2mm carbon fiber.

[0044] The beneficial effects of this invention are as follows: by implanting composite material reinforcing ribs perpendicular to the fiber cloth, this solution solves the problems that may be caused by other reinforcement solutions, such as large dispersion of different reinforcement angles and directions, insignificant effects, and weakened performance in other directions. In particular, it solves the engineering problem of difficult to achieve the stitching of large products, sandwich parts, and irregular parts, and eliminates the problem that defects are easy to occur in the X and Y directions of the in-plane fabric.

[0045] Benefits: 1) The enhancement scheme is not affected by the size or irregular shape of the product and can be implemented well;

[0046] 2) The implementation plan is simple;

[0047] 3) After implementation, the reinforcement is only applied in the Z direction, with minimal impact on the in-plane strength in the X and Y directions;

[0048] 4) Significant enhancement benefits: with minimal impact on weight and X and Y directions, Z-direction strength and peel resistance are significantly enhanced. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of a foam sandwich preform according to the present invention;

[0050] Figure 2 Schematic diagram of Z-Pin reinforced carbon needle arrangement (vertical and horizontal arrangement);

[0051] Figure 3 Schematic diagram of Z-Pin reinforced carbon needle arrangement (staggered arrangement);

[0052] Figure 4 Pull-out shear strength test;

[0053] Figure 5 : Enhanced sample group (still connected after damage);

[0054] Figure 6 Unreinforced sample group (separated after tensile failure);

[0055] Figure 7 Compression strength test;

[0056] Figure 8 Unreinforced compression sample (with obvious compression loss);

[0057] Figure 9 : Enhanced compressed sample (no obvious signs of damage observed by the naked eye);

[0058] Wherein 1-composite material skin; 2-foam; 3-composite material needle. Implementation

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings:

[0060] like Figure 1 Z-Pin reinforcement mechanism of preforms: In the Z-direction of the composite material, needle-like reinforcing ribs of the composite material are implanted perpendicular to the skin of the composite material.

[0061] This solution solves the problems that other reinforcement solutions may cause, such as large differences in reinforcement angles and directions, insignificant effects, and weakened performance in other directions. In particular, it solves the engineering problem of difficult-to-engineer the sewing of large products, sandwich parts, and irregular parts, and eliminates the problem that defects are easy to occur in the X and Y directions of in-plane fabrics.

[0062] Implementation plan:

[0063] 1) Prefabricated carbon fiber rods / needles with a diameter of 0.6-1.5mm (hereinafter referred to as needles) are cut into prefabricated reinforcing needles of the design specifications using a guillotine cutter according to the required injection length;

[0064] 2) Fiber cloth + foam / other functional material layer + 1-2 layers of fiber cloth;

[0065] 3) Place the prepared carbon needle into a special high-pressure air gun, select the appropriate air gun according to the diameter of the carbon needle, and inject the carbon needle into the surfacing layer according to the designed implantation plan;

[0066] 4) Laying the remaining fabric layer of the surface fiber cloth;

[0067] 5) Following the vacuum-assisted molding process, lay out the corresponding vacuum bag film, sealing strips and other auxiliary materials. After the seal and leak test are qualified, introduce the corresponding resin and cure to obtain the Z-pin reinforced product.

[0068] This handheld high-pressure air gun can be a regular carpenter's nail gun, injecting one nail at a time, or it can be a self-designed and optimized air gun for continuous injection.

[0069] This handheld high-pressure air gun is a standard carpenter's nail-driving high-pressure air gun.

[0070] By selecting composite needles of different thicknesses (0.6, 1.0, and 1.5 mm) and different arrangements of the composite needles, samples were prepared using a 2 mm carbon fiber + 20 mm H80 foam + 2 mm carbon fiber layup structure. The results are shown in Table 1 below.

[0071]

[0072] Note: 1) 10*10 longitudinal and transverse arrangement: When each carbon needle is pre-placed, the longitudinal and transverse spacing is 10mm, distributed in a square grid pattern. For example, see the 100×100mm plate. Figure 2 Indication;

[0073] 2) 10*10 staggered arrangement: The vertical spacing of each carbon needle is 10mm, and the carbon needles in each adjacent row are staggered laterally. For example, see a 100×100mm plate. Figure 3 Indication.

[0074] 1) Explanation of pull-out shear strength

[0075] like Figure 5 , Figure 6As shown: Special tooling: A steel joint tooling with a bonding surface diameter of 40mm, the clamping end is clamped by the universal testing machine chuck, the bonding surface and the core sample are bonded with high-strength epoxy adhesive, the bonding force is greater than the sample strength, and the pull-out test is performed on the interface bonding strength. As can be seen from the results in the figure and the table below, after Z-Pin reinforcement of the preform, the carbon fiber composite sandwich foam product, taking #7 as an example, has a pull-out shear strength increased by 36.3% and a weight increased by 5.3%. After the test, the unreinforced sample was directly pulled into two pieces after stretching. The sample reinforced with Z-Pin, although there was some damage after the pull-out test, the Z-direction preform still connected the two parts into one, and it was not completely destroyed. That is, under the external force Z-direction pull-out failure, it still has a good ability to stop the further spread of damage. When applied to products, it can effectively stop the spread of damage under external force.

[0076] 3) Compressive strength benefits;

[0077] Preparation of carbon fiber sandwich foam composite material: 2mm carbon composite + 20mm H80 foam + 2mm carbon composite, and testing its Z-axis compressive strength, such as... Figure 7 , Figure 8 As shown in Table 2, after Z-Pin reinforcement, the compressive strength of the carbon fiber composite sandwich foam product, taking part #2 as an example, increased by about 193%, while the weight increased by only 2.2%. After testing, the unreinforced sample showed obvious local compression damage to the foam, while the Z-Pin reinforced sample showed no obvious damage after compression. That is, under a certain range of external force, the Z-Pin reinforced board with the above-mentioned dimensions not only increased the final compressive strength to 2.93 times, but also suffered less damage under higher pressure than the unreinforced board under 1 times the pressure.

[0078] Table 2 Gain Ratio Table:

[0079]

[0080] The data above shows that:

[0081] 1) After using carbon needle preforms for reinforcement, the weight of the sandwich composite material increases slightly by 0.2~5.3%, but its overall compressive strength and tensile shear strength (except for part #5) are significantly increased.

[0082] 2) After the carbon needle preforms are used for reinforcement, the carbon needles can still play a certain role in connection or support after the test failure, preventing the foam from being damaged or splitting.

[0083] 3) When carbon needle preforms are staggered, the compressive strength is slightly better than that of longitudinal and transverse distribution, and the tensile shear strength is significantly better. In particular, as can be seen from part #5, when longitudinal and transverse distribution is adopted and the distribution spacing is large, its tensile shear strength is actually reduced.

[0084] 4) When the carbon needle preforms are distributed at a spacing of 10, 15, and 20 mm, the smaller the spacing, the better the reinforcement effect. The 10 and 15 mm spacings are significantly better than the 20 mm spacing. Due to the reduction in spacing, the workload of carbon needle injection increases significantly in a square proportion. It is preferred to carry out distributed pre-implantation reinforcement at a spacing of 10-20 mm.

[0085] 5) A carbon needle preform diameter of 0.6-1.5mm can provide significant reinforcement. Carbon needles with a diameter of less than 0.6mm have low strength, are difficult to preform, and are prone to breakage during implantation. They are not recommended. If the carbon needle has a diameter of 2mm, the cross-section is too large, and the implantation process becomes significantly more difficult. The preferred carbon needle diameter is 0.6-1.5mm.

[0086] 4) Conclusion

[0087] In summary, the precast Z-Pin reinforcement scheme has a relatively simple reinforcement process, is not constrained by the structural shape of the product, and the composite panel can achieve the following benefits or changes:

[0088] a) With a small increase in weight, it can significantly increase its resistance to delamination, interfacial bonding, and compressive strength;

[0089] Taking sample #2 as an example, under the condition of a 2.2% increase in weight, the compressive strength increased by 193% and the tensile shear strength increased by 33.5%;

[0090] If only local areas with high stress are targeted for reinforcement, such as 10% of the area, the total weight increase is almost negligible (0.22%).

[0091] It is limited to local point reinforcement of carbon needles in the Z direction, and its impact on the strength of composite materials in the X and Y directions is much smaller than that of continuous stitching and three-dimensional weaving.

[0092] b) The ability to terminate local layered defects is significantly improved, effectively extending its service life in the event of sudden damage.

[0093] In the technical solution of this invention, the skin refers to composite materials reinforced with fibers such as glass fiber and carbon fiber.

[0094] The skin can be made by hot pressing and curing prepreg material, or by pre-laying and then vacuum-filling resin and curing it.

[0095] Core material: Low-density, lightweight, high-strength foam.

[0096] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments.

[0097] Within the scope of the technical concept of this invention, various simple modifications can be made to the technical solution of this invention, and all such simple modifications fall within the protection scope of this invention.

[0098] It should also be noted that the specific technical features described in the above embodiments are not contradictory.

[0099] In the case of a shield, it can be combined in any suitable way. To avoid unnecessary repetition, this invention will not describe the various possible combinations separately.

[0100] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A Z-Pin reinforced composite sandwich structure, characterized in that, Its structural form includes an upper composite material skin + core material + lower composite material skin. In the Z-direction of the preform of the sandwich structure, composite material needles are implanted for Z-direction reinforcement. The method for preparing the composite material sandwich structure includes the following steps: S1) Prefabricated composite material needles, cut into prefabricated reinforcing needles of the designed specifications using a guillotine cutter according to the required implantation length. S2) The composite sandwich structure is laid in the following order: skin fiber cloth + core material + upper surface layer 1-2 layers of composite fiber cloth. S3) The composite material needle is placed in a high-pressure air gun and implanted into the sandwich preform body along the Z direction in the Z-Pin reinforcement direction. The composite material needles are arranged in a longitudinal or cross-sectional manner in the sandwich preform body. The vertical spacing of the composite material needles in the X and Y directions in the plane is between 10 and 20 mm. The diameter of the composite material needle is 1.0 or 1.5 mm; S4) Steps for laying the remaining fiber cloth on the upper surface; S5) Vacuum-assisted molding process steps: that is, according to the vacuum-assisted molding process, the corresponding release cloth, flow medium, flow pipe, vacuum bag film, sealing tape and auxiliary materials are laid out. After the sealing and leak test is qualified, the corresponding resin is introduced and cured to obtain the Z-pin reinforced composite sandwich structure. The core material is a low-density, lightweight, high-strength foam.

2. The composite material sandwich structure as described in claim 1, characterized in that, The composite material needle is a composite material needle made of the same material as the surface skin.

3. The composite material sandwich structure as described in claim 2, characterized in that, The composite material needles are arranged with a variable density, meaning that the needle spacing can be reduced in areas of high stress and increased in areas of low stress.

4. A method for preparing a Z-Pin reinforced composite sandwich structure as described in any one of claims 1-3, characterized in that, Includes the following steps: S1) Prefabricated composite material needles are cut into prefabricated reinforcing needles of the design specifications using a guillotine according to the required implantation length; S2) The composite sandwich structure is laid in the following order: down skin fiber cloth + core material + upper surface layer 1-2 layers of composite fiber cloth; S3) The composite material needle is placed into a high-pressure air gun and implanted into the sandwich preform body along the Z-direction in the Z-Pin reinforcement direction; the composite material needle is arranged in a longitudinal or transverse or staggered manner in the sandwich preform body. S4) Steps for laying the remaining fiber cloth on the upper surface; S5) Following the vacuum-assisted molding process, lay out the corresponding release cloth, flow medium, flow pipe, vacuum bag film, and sealing tape auxiliary materials. After the sealing and leak test is qualified, introduce the corresponding resin and cure to obtain the Z-pin reinforced composite sandwich structure.

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