A method for repairing cracks in a glass fiber reinforced resin-based composite material and applications thereof

Abstract

The application relates to a crack repairing method and application of a glass fiber reinforced resin-based composite material. By combining a 'layered damage removal process + infiltration reinforcement process + multi-layer glass fiber reinforcement process', the glass fiber reinforced resin-based composite material surface powder layer can be removed, the secondary crack propagation path can be effectively blocked, the substrate fiber infiltration defect can be repaired and the structural mechanics consistency can be restored, the component deformation error can be precisely corrected, the mechanical strength, the bonding performance, the size precision and the weather resistance of the repaired area can be close to those of the original substrate, the high-performance compliance reuse of the defective glass fiber reinforced resin-based composite material is realized, and the material scrapping loss and the production and operation cost are significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of defect repair technology for glass fiber reinforced resin matrix composites, and particularly to a method and application for crack repair of glass fiber reinforced resin matrix composites. Background Technology

[0002] To meet the requirements of lightweighting and environmental protection, energy conservation, and emission reduction in automobiles, glass fiber reinforced resin matrix composites are now being used for the integral molding of side panels in small and medium-sized passenger vehicles via pultrusion. These components offer advantages such as high specific strength, excellent corrosion resistance, good molding consistency, and excellent dimensional stability, and are widely used in exterior components and auxiliary structural load-bearing components of buses and aircraft. However, these skins are subjected to complex environments including long-term storage, outdoor transportation, and alternating high and low temperatures, as well as wet and dry cycles. This makes them highly susceptible to a combination of damage, including surface resin aging and powdering, surface dryness and whitening, localized fiber exposure, microcrack propagation, and localized cracking. Most of these damages are localized regional failures, without fundamentally damaging the overall matrix structure and mechanical properties of the component. Directly scrapping the entire component would result in significant waste of raw materials, increased production costs, and low resource utilization.

[0003] At present, the conventional repair methods for weathering and cracking defects of pultruded skin have obvious technical shortcomings and are difficult to meet the stringent engineering requirements of high-precision bonding and assembly, long-term weather resistance and anti-aging, and consistent mechanical strength of the side composite skin of medium and small passenger car bodies and large commercial equipment. The specific technical defects are as follows: (1) Incomplete defect removal and low interface bonding reliability: Traditional repair only fills and levels the surface cracks, without completely removing the surface powdery aging layer and the internal loose dry fiber failure layer. After repair, there is a loose interlayer at the interface between the new and old materials, which is very easy to absorb moisture and delamination and interface peeling. This leads to the repaired area turning white, cracking and falling off again in a short period of time, resulting in extremely poor repair durability. (2) Lack of crack arrest mechanism and easy secondary expansion failure: Conventional repair only seals the crack ends on the surface, without carrying out stress release, grooving crack arrest and fatigue layer removal treatment at the crack root. Under the working conditions of equipment operation vibration and ambient temperature change, the crack is very easy to extend and expand from the root again, causing the overall failure of the repaired structure. (3) No secondary impregnation and reinforcement process for fibers, resulting in mismatched mechanical properties: For original defects such as insufficient resin impregnation and local dry fiber exposure left over from the molding process, traditional repair only performs surface covering treatment, which cannot achieve secondary impregnation and densification of the gaps inside the fiber bundle. The structural density, mechanical properties and interfacial bonding performance of the repaired area are significantly different from those of the original substrate, making it difficult to meet the requirements of long-term load-bearing and precision assembly of the component. (4) The weather resistance of the repair layer is inconsistent with that of the substrate: Conventional repair resin has not been designed with weather resistance modification. The repaired area has weak resistance to ultraviolet aging and oxidation and powdering, and there is a gradient difference in weather resistance with the original substrate. After long-term outdoor service, secondary quality defects such as local color difference and local preferential weathering are prone to occur, affecting the overall appearance and service life of the component.

[0004] In summary, existing technologies cannot achieve high-quality repair and compliant reuse of defective skins, resulting in a persistently high component scrap rate. There is an urgent need for targeted, refined, and high-performance repair and reinforcement solutions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method and application for crack repair of glass fiber reinforced resin matrix composites. Through multi-process composite design, it solves the problems of incomplete defect removal, easy secondary crack propagation, mismatch between mechanical properties and substrate after repair, and poor weather resistance in existing repair methods.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for repairing cracks in a glass fiber reinforced resin matrix composite material. The method for repairing cracks in a glass fiber reinforced resin matrix composite material includes the following steps: (1) Determine the repair area with the crack area of ​​the glass fiber reinforced resin matrix composite as the center, perform gradient grinding on the repair area, and then determine the crack arrest area with the crack area as the center, and perform grinding and grooving treatment on the crack arrest area. (2) Apply reinforcing resin A to the part of the repair area other than the crack-stopping area for impregnation and reinforcement; (3) Fill the crack-stopping area with reinforcing resin B and perform initial curing. After initial curing, lay short-cut fiberglass mats with the crack area as the geometric center and the area gradually increasing from bottom to top on the crack-stopping area after coating with reinforcing resin B. Reinforcing resin B is coated between each layer of short-cut fiberglass mats and on the surface of the outermost layer of short-cut fiberglass mats. After laying and curing, a fiber-reinforced area is formed. (4) The fiber-reinforced area is subjected to gradient grinding, and then the protective resin is applied to the repair area and cured to complete the crack repair of the glass fiber reinforced resin matrix composite material.

[0007] This invention addresses the complex damage issues in glass fiber reinforced resin composites by combining a layered damage removal process, an impregnation and reinforcement process, and a multi-layered glass fiber reinforcement process. These three processes work synergistically to resolve problems such as surface resin aging and powdering, surface dryness and whitening, localized fiber exposure, microcrack propagation, and localized cracking. This overcomes the shortcomings of traditional processes, which often result in incomplete removal of defects, secondary crack propagation, insufficient quality leading to mismatched mechanical properties, and poor weather resistance. Specifically, the layered damage removal process precisely removes aged and failed fibers and eliminates potential microscopic damage, laying a solid foundation for subsequent processing. The impregnation and reinforcement process penetrates and fills fiber pores, optimizing fiber interface properties and improving material density and toughness. The multi-layered glass fiber reinforcement process constructs a three-dimensional reinforcement network, comprehensively enhancing the mechanical strength and weather resistance of the substrate.

[0008] Preferably, the repair area extends radially 50-80 mm in length and width independently from the crack area, for example, it can be 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm or 80 mm.

[0009] Preferably, the crack-stopping area has a V-shaped groove structure.

[0010] Preferably, the maximum length of the V-shaped groove structure extends radially 10-20 mm from both ends of the maximum length of the crack region, for example, it can be 10 mm, 12 mm, 14 mm, 15 mm, 16 mm, 18 mm or 20 mm, etc.

[0011] Preferably, the included angle of the V-shaped groove structure is 60°~90°, for example, it can be 60°, 70°, 80° or 90°.

[0012] Preferably, the maximum width of the V-shaped groove structure is 8-15 mm, for example, it can be 8 mm, 10 mm, 12 mm, 14 mm or 15 mm.

[0013] Preferably, the ratio of the depth of the V-shaped groove structure to the thickness of the glass fiber reinforced resin matrix composite material is (0.5-0.67):1, for example, it can be 0.5:1, 0.55:1, 0.6:1, 0.65:1 or 0.67:1.

[0014] Preferably, the bottom of the V-shaped groove structure has a rounded transition structure.

[0015] Preferably, the radius of the arc transition structure is 1.5-3 mm, for example, it can be 1.5 mm, 2 mm, 2.5 mm or 3 mm, etc.

[0016] The crack repair method for glass fiber reinforced resin matrix composites provided by this invention is applicable to various defects such as microcracks (crack width < 0.1 mm, fine surface cracks, damage only to the surface resin), medium-width cracks (crack width 0.1-0.5 mm, crack depth penetrating the surface resin and extending to the fiber layer), and wide-deep composite damage (crack width > 0.5 mm, crack depth fully penetrating, wider crack, further damaging the fiber layer, accompanied by local fiber loosening or warping damage). Specifically, when the object to be repaired is a microcrack (crack width < 0.1 mm), the included angle of the V-shaped groove structure can be set to 60-70°, and the maximum width of the V-shaped groove structure can be set to 8-10 mm; when the object to be repaired is a medium-width crack (crack width 0.1-0.5 mm), the included angle of the V-shaped groove structure can be set to 70-80°, and the maximum width of the V-shaped groove structure can be set to 9-12 mm; when the object to be repaired is a wide-deep composite damage (crack width > 0.5 mm), the included angle of the V-shaped groove structure can be set to 80-90°, and the maximum width of the V-shaped groove structure can be set to 12-15 mm.

[0017] Preferably, the gradient grinding in step (1) includes grinding with a grinding medium containing coarse abrasive particles first, and then grinding with a grinding medium containing fine abrasive particles.

[0018] Preferably, the abrasive medium includes any one or a combination of at least two of sandpaper, blades, disc abrasive, or polishing wheels.

[0019] Preferably, the abrasive medium for the coarse abrasive particles is 80-120 mesh sandpaper (e.g., 80 mesh, 90 mesh, 100 mesh, 110 mesh or 120 mesh, etc.).

[0020] Preferably, the abrasive medium for the fine abrasive particles is 400-600 mesh sandpaper (e.g., 400 mesh, 450 mesh, 500 mesh, 550 mesh, or 600 mesh).

[0021] This invention employs a layered removal process. First, a coarse abrasive grinding medium is used to peel away the loose, powdery, and aged resin on the surface of the repair area. The coarse abrasive has a gentle cutting amount, avoiding excessive cutting of the intact substrate, while also providing a smooth transition at the grinding interface, preventing the formation of deep and shallow scratches on the substrate surface and preventing new stress defects. Then, a fine abrasive grinding medium is used for further grinding to quickly remove the insufficient resin wetting and loose fiber-rich middle layer failure areas in the repair area, until a non-porous, fiber-free, continuous, and dense substrate layer is exposed. Next, a crack-stopping zone is determined centered on the crack area, and further grinding is performed until the substrate is completely exposed, forming a V-shaped groove structure to eliminate the potential for stress concentration at the crack root. By constructing a layered removal process of "fine grinding removal of the surface powdery layer + removal of the loose dry fiber middle layer + crack widening and fatigue removal," all failed materials are precisely peeled off, while the dense and intact substrate is completely preserved, fundamentally solving the industry's technical problems of residual loose interlayers and easy delamination at the interface in traditional repairs.

[0022] Preferably, step (1) further includes dust removal, oil removal and pre-activation treatment of the repaired area.

[0023] Preferably, the dust removal process includes blowing with an air gun.

[0024] Preferably, the degreasing treatment includes wiping the repaired area with a cleaning agent.

[0025] Preferably, the pre-activation treatment includes placing the glass fiber reinforced resin matrix composite material at 25-35°C (e.g., 25°C, 26°C, 28°C, 30°C, 32°C, 34°C, or 35°C, etc.) and drying for 30-60 min (e.g., 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, etc.).

[0026] This invention removes water vapor adsorbed on glass fiber reinforced resin matrix composites through pre-activation treatment, activates and repairs the interface, and enhances interlayer bonding.

[0027] Preferably, the reinforcing resin A in step (2) comprises, by weight, 100 parts of matrix resin A, 1.8-2.5 parts of curing agent A, and 0.3-0.5 parts of coupling agent A.

[0028] Among them, 1.8-2.5 portions can be, for example, 1.8 portions, 1.9 portions, 2 portions, 2.1 portions, 2.2 portions, 2.3 portions, 2.4 portions, or 2.5 portions; 0.3-0.5 portions can be, for example, 0.3 portions, 0.35 portions, 0.4 portions, 0.45 portions, or 0.5 portions.

[0029] Preferably, the matrix resin A comprises bisphenol A type epoxy resin.

[0030] Preferably, the epoxy equivalent of the bisphenol A type epoxy resin is 180-220 g / eq, for example, it can be 180 g / eq, 190 g / eq, 200 g / eq, 210 g / eq or 220 g / eq, etc.

[0031] Preferably, the curing agent A comprises a modified alicyclic amine curing agent.

[0032] Preferably, the coupling agent A comprises KH-560.

[0033] Preferably, the coating amount of the reinforcing resin A is 180-240 g / m³. 2 For example, it could be 180 g / m 2 190 g / m 2 200 g / m 2 210 g / m 2 220 g / m 2 230 g / m 2 Or 240 g / m 2 wait.

[0034] This invention specifies that the coating amount of reinforcing resin A is 180-240 g / m³. 2 This coating amount ensures that the resin fully penetrates into the micropores of the fiber bundle.

[0035] Preferably, the impregnation reinforcement is performed under a slight negative pressure.

[0036] Preferably, the pressure of the micro negative pressure is -0.02 to -0.04 MPa, for example, it can be -0.02 MPa, -0.025 MPa, -0.03 MPa, -0.035 MPa or -0.04 MPa, etc.

[0037] Preferably, the impregnation and reinforcement time is 15-25 min, for example, it can be 15 min, 16 min, 18 min, 20 min, 22 min, 24 min or 25 min, etc.

[0038] This invention employs an impregnation and reinforcement process. In the repair area, excluding the crack-arresting area (i.e., the loose fiber region), reinforcing resin A is coated, and a slight negative pressure of -0.02 to -0.04 MPa is applied to allow the reinforcing resin A to fully penetrate the fiber gaps, completing the resin impregnation and filling of the loose fiber region. If the slight negative pressure is too low, the resin impregnation will be insufficient, and dry areas and air bubbles will easily remain inside the fibers, resulting in poor interfacial bonding. If the slight negative pressure is too high, the fibers will be easily dispersed, causing fiber misalignment, porosity defects, and reducing the mechanical strength of the repair.

[0039] Preferably, the reinforcing resin B in step (3) comprises, by weight, 100 parts of matrix resin B, 1.8-2.5 parts of curing agent B, and 0.3-0.5 parts of coupling agent B.

[0040] Among them, 1.8-2.5 portions can be, for example, 1.8 portions, 1.9 portions, 2 portions, 2.1 portions, 2.2 portions, 2.3 portions, 2.4 portions, or 2.5 portions; 0.3-0.5 portions can be, for example, 0.3 portions, 0.35 portions, 0.4 portions, 0.45 portions, or 0.5 portions.

[0041] Preferably, the matrix resin B comprises bisphenol A type epoxy resin.

[0042] Preferably, the epoxy equivalent of the bisphenol A type epoxy resin is 180-220 g / eq, for example, it can be 180 g / eq, 190 g / eq, 200 g / eq, 210 g / eq or 220 g / eq, etc.

[0043] Preferably, the curing agent B comprises a modified alicyclic amine curing agent.

[0044] Preferably, the coupling agent B comprises KH-560.

[0045] In this invention, coupling agent A and coupling agent B are preferably selected from penetrating silane coupling agent KH-560, one end of which can bind to the hydroxyl groups on the surface of glass fiber, and the other end can undergo a cross-linking reaction with the matrix resin, which greatly improves the wetting and bonding force between the resin and the exposed glass fiber and eliminates the risk of delamination at the fiber interface.

[0046] Preferably, the initial curing temperature is 25-35℃ (e.g., 25℃, 26℃, 28℃, 30℃, 32℃, 34℃ or 35℃, etc.), and the time is 2.5-4 h (e.g., 2.5 h, 3 h, 3.5 h or 4 h, etc.).

[0047] Preferably, step (3) further includes compaction and grinding / leveling after filling.

[0048] In this invention, the reinforcing resin B is completely filled in the crack-stopping area, and after compaction and grinding, it is ensured that there are no gaps or pinholes in the V-shaped groove structure.

[0049] Preferably, the chopped fiberglass mats in step (3) with their areas increasing from bottom to top include a first chopped fiberglass mat, a second chopped fiberglass mat, and a third chopped fiberglass mat.

[0050] Preferably, the first chopped fiberglass mat covers the cracked area.

[0051] Preferably, the second chopped fiberglass mat extends radially by 20-30 mm in length and width independently from the first chopped fiberglass mat as the center, for example, it can be 20 mm, 22 mm, 24 mm, 25 mm, 26 mm, 28 mm or 30 mm, etc.

[0052] Preferably, the third chopped fiberglass mat extends radially by 20-30 mm in length and width independently from the second chopped fiberglass mat as the center, for example, it can be 20 mm, 22 mm, 24 mm, 25 mm, 26 mm, 28 mm or 30 mm, etc.

[0053] Preferably, the thickness of the first chopped fiberglass mat, the second chopped fiberglass mat, and the third chopped fiberglass mat is independently 0.3-0.5 mm, for example, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, or 0.5 mm.

[0054] Preferably, the areal density of the first, second, and third chopped fiberglass mats is independently 280-320 g / m³. 2 For example, it could be 280 g / m 2 290 g / m 2 300 g / m 2 310 g / m 2 Or 320 g / m 2 wait.

[0055] Preferably, the amount of reinforcing resin B coated between each layer of chopped fiberglass mat and on the surface of the outermost chopped fiberglass mat is independently 120-160 g / m². 2 For example, it could be 120 g / m 2 130 g / m 2 140 g / m 2 150 g / m 2 Or 160g / m 2 wait.

[0056] The present invention specifies that the coating amount of reinforcing resin B between each layer of chopped fiberglass mat and on the surface of the outermost chopped fiberglass mat is independently 120-160 g / m². 2 This coating amount allows for a thin and even application of the adhesive, preventing issues such as air or adhesive buildup.

[0057] Preferably, the curing temperature in step (3) is 18-30℃ (e.g., 18℃, 20℃, 22℃, 24℃, 25℃, 26℃, 28℃ or 30℃, etc.), and the time is 4-6 h (e.g., 4 h, 4.5 h, 5 h, 5.5 h or 6 h, etc.).

[0058] Preferably, the surface hardness of the fiber-reinforced region formed after curing is >36, for example, it can be 38, 40, 45, 50, 55 or 60.

[0059] The surface hardness was tested in accordance with GB / T 3854-2017 "Barcol Hardness Test Method for Fiber Reinforced Plastics".

[0060] This invention employs a multi-layer glass fiber reinforcement process to form a gradual reinforcement structure with glass fiber laid layer by layer and layered impregnation and curing. This results in an integrated structure of "dense V-shaped groove filling + multi-layer glass fiber composite reinforcement + smooth interface transition," which effectively blocks the crack propagation path and significantly improves the vibration resistance and deformation fatigue resistance of the repaired area.

[0061] Preferably, the gradient grinding in step (4) includes grinding with a grinding medium containing second coarse abrasive particles, grinding with a grinding medium containing medium coarse abrasive particles, grinding with a grinding medium containing medium fine abrasive particles, and grinding with a grinding medium containing second fine abrasive particles.

[0062] Preferably, the abrasive medium includes any one or a combination of at least two of sandpaper, blades, disc abrasive, or polishing wheels.

[0063] Preferably, the abrasive medium for the second coarse abrasive particles is 80-180 mesh sandpaper, such as 80 mesh, 100 mesh, 120 mesh, 140 mesh, 150 mesh, 160 mesh or 180 mesh.

[0064] Preferably, the grinding medium for the medium-coarse abrasive particles is 200-300 mesh sandpaper, such as 200 mesh, 220 mesh, 240 mesh, 250 mesh, 260 mesh, 280 mesh or 300 mesh, etc.

[0065] Preferably, the abrasive medium for the medium and fine abrasive particles is 350-450 mesh sandpaper, such as 350 mesh, 360 mesh, 380 mesh, 400 mesh, 420 mesh, 440 mesh or 450 mesh, etc.

[0066] Preferably, the abrasive medium for the second fine abrasive particles is 550-650 mesh sandpaper, such as 550 mesh, 560 mesh, 580 mesh, 600 mesh, 620 mesh, 640 mesh or 650 mesh, etc.

[0067] This invention further performs gradient polishing on the surface after the multilayer glass fiber reinforcement process. First, a polishing medium with coarse abrasive particles is used to quickly remove protrusions, steps, and unevenness in the joints of the repair area. Then, the polishing medium with increasingly fine abrasive particles is gradually replaced to polish the texture, gradually eliminating the height difference between interlayer joints and the color difference of the texture on the board surface. Finally, the repair area is flush with the surface of the side glass fiber reinforced resin matrix composite material and the texture transition is uniform.

[0068] Preferably, the protective resin in step (4) comprises, by weight, 100 parts of matrix resin C, 1.8-2.5 parts of curing agent C, 0.2-0.4 parts of ultraviolet absorber, and 0.1-0.3 parts of antioxidant.

[0069] Among them, 1.8-2.5 portions can be, for example, 1.8 portions, 1.9 portions, 2 portions, 2.1 portions, 2.2 portions, 2.3 portions, 2.4 portions, or 2.5 portions, etc.; 0.2-0.4 portions can be, for example, 0.2 portions, 0.25 portions, 0.3 portions, 0.35 portions, or 0.4 portions, etc.; 0.1-0.3 portions can be, for example, 0.1 portions, 0.15 portions, 0.2 portions, 0.25 portions, or 0.3 portions, etc.

[0070] Preferably, the matrix resin C comprises bisphenol A type epoxy resin.

[0071] Preferably, the epoxy equivalent of the bisphenol A type epoxy resin is 180-220 g / eq, for example, it can be 180 g / eq, 190 g / eq, 200 g / eq, 210 g / eq or 220 g / eq, etc.

[0072] Preferably, the curing agent C comprises a modified alicyclic amine curing agent.

[0073] The selection of matrix resin A, matrix resin B, and matrix resin C used in this invention includes, but is not limited to, bisphenol A type epoxy resin. The matrix resin can be selected based on the choice of matrix resin in the glass fiber reinforced resin matrix composite material being repaired, or a matrix resin with excellent compatibility within the same system can be chosen to reduce the shrinkage rate of the repaired part, improve the adhesion strength with the original substrate, and ensure that it is not prone to yellowing and cracking during long-term outdoor use. The selection of curing agent A, curing agent B, and curing agent C includes, but is not limited to, modified alicyclic amine curing agents suitable for bisphenol A type epoxy resin. Alternatively, a suitable curing agent can be selected based on the choice of matrix resin A, matrix resin B, and matrix resin C to improve the curing effect and ensure the toughness and resistance to alternating thermal stress of the repaired part.

[0074] Preferably, the ultraviolet absorber includes benzotriazole ultraviolet absorbers.

[0075] Preferably, the benzotriazole UV absorber includes UV-329.

[0076] Preferably, the antioxidant includes hindered phenolic antioxidants.

[0077] Preferably, the hindered phenolic antioxidant includes antioxidant 1010.

[0078] This invention preferably employs a protective resin system composed of UV-329 and antioxidant 1010. UV-329 has an ultraviolet absorption band of 300-380 nm, which can cover the entire spectrum of outdoor ultraviolet light. It has good thermal stability, low volatility, and excellent compatibility with bisphenol A type epoxy resin. It can effectively block the photosing of resin molecules and inhibit yellowing and chalking of the board surface. Antioxidant 1010 has a high molecular weight and low migration rate, which can capture free radicals caused by thermo-oxidative aging and inhibit the oxidative degradation of resin caused by high temperature and diurnal temperature difference. When combined with UV-329, it has a synergistic effect on weather resistance and significantly extends the outdoor service life of the repair layer.

[0079] Preferably, the coating amount of the protective resin is 80-110 g / m². 2 For example, it could be 80 g / m 2 90 g / m 2 100g / m 2 Or 110 g / m 2 wait.

[0080] The present invention specifies that the coating amount of the protective resin is 80-110 g / m². 2 This process forms a protective coating with a thickness of 0.1-0.3 mm, ensuring that the coating is thin and continuous, without sagging or exposed substrate.

[0081] Preferably, the curing temperature in step (4) is 25-35℃ (e.g., 25℃, 26℃, 28℃, 30℃, 32℃, 34℃ or 35℃, etc.), and the time is 2.5-4 h (e.g., 2.5 h, 3 h, 3.5 h or 4 h, etc.).

[0082] Preferably, the protective resin, after curing, forms a resin protective layer with a thickness of 0.1-0.3 mm (e.g., 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, or 0.3 mm, etc.).

[0083] This invention employs a dual-layer gradient weather-resistant regenerative protection system. Reinforcing resins A and B have high penetration and wetting properties, ensuring interfacial bonding strength and structural integrity. The surface is coated with protective resin to construct a dense protective layer, forming a dual-layer composite structure of "high-strength adhesive reinforcement + long-lasting weather-resistant protection". The repaired area has no color difference and no localized powdering or aging, making it suitable for long-term stable service under complex outdoor working conditions.

[0084] Secondly, the present invention provides an application of the crack repair method of glass fiber reinforced resin matrix composite material as described in the first aspect in the defect repair of vehicle body side panel skin.

[0085] Compared with the prior art, the present invention has at least the following beneficial effects: This invention, by combining a "layered damage removal process + impregnation and reinforcement process + multi-layer glass fiber reinforcement process," can completely remove the powdery layer on the surface of glass fiber reinforced resin matrix composites, effectively block the secondary propagation path of cracks, repair defects in poor fiber impregnation of the substrate and restore the structural mechanical consistency, and accurately correct component deformation errors. It enables the mechanical strength, bonding performance, dimensional accuracy and weather resistance of the repaired area to approach those of the original substrate, achieving high-performance and compliant reuse of defective glass fiber reinforced resin matrix composites, and significantly reducing material scrap and production and maintenance costs. Detailed Implementation

[0086] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0087] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., used to indicate orientation or positional relationships are based solely on orientation or positional relationships and are used only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0088] The reinforcing resin A and reinforcing resin B used in the following examples and comparative examples were prepared by the following method: Mix 100 parts by weight of the matrix resin (E51, purchased from Nantong Xingchen Synthetic Materials Co., Ltd.), 2 parts by weight of the curing agent (650, purchased from Jiangsu Sanmu Group Co., Ltd.), and 0.4 parts by weight of the coupling agent (KH-560, purchased from Nanjing Shuguang Chemical Group Co., Ltd.) for later use.

[0089] The protective resins used in the following examples and comparative examples were prepared by the following method: Mix 100 parts by weight of the base resin (E51, purchased from Nantong Xingchen Synthetic Materials Co., Ltd.), 2 parts by weight of the curing agent (650, purchased from Jiangsu Sanmu Group Co., Ltd.), 0.3 parts by weight of the ultraviolet absorber (UV-329, purchased from BASF), and 0.2 parts by weight of the antioxidant (antioxidant 1010, purchased from BASF) for later use. The chopped fiberglass mats used in the following examples and comparative examples were all EMC300 purchased from Shandong Taishan Fiberglass Co., Ltd., with a thickness of 0.3-0.5 mm and a surface density of 300 g / m³. 2 .

[0090] Example 1 This embodiment provides a method for repairing cracks in a glass fiber reinforced resin matrix composite material. The method for repairing cracks in the glass fiber reinforced resin matrix composite material includes: (1) Determine the repair area centered on the cracked area (crack width is 0.1-0.5 mm) of the glass fiber reinforced resin matrix composite material (extend radially 60 mm independently in length and width centered on the cracked area), and perform gradient grinding on the repair area (first use 100-grit sandpaper to grind and peel off the loose powdery aged resin on the surface, then use 500-grit sandpaper to grind until a non-porous, non-fiber loose, continuous and dense substrate is exposed), then determine the crack arrest area centered on the cracked area, and perform grinding and grooving treatment on the crack arrest area (open a 75° V-shaped groove structure along the crack arrest area, the depth of the V-shaped groove structure is 0.6:1 to the thickness of the glass fiber reinforced resin matrix composite material, the maximum width of the V-shaped groove structure is 10 mm, and the maximum length of the V-shaped groove structure extends radially 15 mm at both ends along the maximum length of the cracked area; the bottom of the groove is ground into a circular arc transition structure with a radius of 2 mm), until the substrate is completely exposed; The repaired area was treated by blowing with an air gun, wiping with acetone to remove oil, and drying in a constant temperature environment of 30℃ for 45 minutes for pre-activation treatment. (2) Apply reinforcing resin A (coating amount is 200 g / m²) to the repaired area, excluding the crack-stopping area. 2 Apply a local pressure of -0.03 MPa and allow it to penetrate for 20 minutes to perform infiltration and reinforcement. (3) Completely fill the crack arrest area with reinforcing resin B and allow it to cure at 30°C for 3 hours. After initial curing, lay a first chopped fiberglass mat covering the crack area with the crack area as the geometric center on the crack arrest area after applying reinforcing resin B. Then apply reinforcing resin B (coating amount is 150 g / m) on the first chopped fiberglass mat. 2After the first chopped fiberglass mat is coated, a second chopped fiberglass mat is laid (the second chopped fiberglass mat extends radially by 25 mm in length and width independently from the first chopped fiberglass mat as the center), and then reinforcing resin B is coated on the second chopped fiberglass mat (coating amount is 150 g / m). 2 After coating, a third chopped fiberglass mat is laid (the third chopped fiberglass mat extends radially by 25 mm independently in length and width, with the second chopped fiberglass mat as the center), and then reinforcing resin B is coated on the third chopped fiberglass mat (coating amount is 150 g / m). 2 After coating, the fiber-reinforced area is cured at 25°C for 5 hours to form a fiber-reinforced area with a surface hardness >36. (4) First, use 120-grit sandpaper to sand the fiber-reinforced area to remove protrusions, steps, and unevenness in the joints. Then, use 240-grit, 400-grit, and 600-grit sandpaper to sand and polish the texture, gradually eliminating the height difference between layers and the color difference in the texture of the board surface. After sanding, apply protective resin to the repaired area (coating amount is 100 g / m²). 2 The resin is cured at 30°C for 3 hours to form a 0.2 mm thick protective layer, thus completing the crack repair of the glass fiber reinforced resin matrix composite.

[0091] Example 2 This embodiment provides a method for repairing cracks in a glass fiber reinforced resin matrix composite material. The method for repairing cracks in the glass fiber reinforced resin matrix composite material includes: (1) Determine the repair area centered on the cracked area (crack width < 0.1 mm) of the glass fiber reinforced resin matrix composite material (extend radially by 50 mm for length and width independently centered on the cracked area), and perform gradient grinding on the repair area (first use 80-grit sandpaper to grind and peel off the loose, powdery, aged resin on the surface, then use 400-grit sandpaper to grind until a non-porous, non-fiber loose, continuous and dense substrate is exposed), then determine the crack arrest area centered on the cracked area, and perform grinding and grooving treatment on the crack arrest area (open a 60° V-shaped groove structure along the crack arrest area, the depth of the V-shaped groove structure is 0.5:1 to the thickness of the glass fiber reinforced resin matrix composite material, the maximum width of the V-shaped groove structure is 8 mm, and the maximum length of the V-shaped groove structure extends radially by 10 mm at both ends along the maximum length of the cracked area; the bottom of the groove is ground into a circular arc transition structure with a radius of 1.5 mm), until the substrate is completely exposed; The repaired area was treated by blowing with an air gun, wiping with acetone to remove oil, and drying in a constant temperature environment of 25℃ for 30 minutes for pre-activation treatment. (2) Apply reinforcing resin A (coating amount is 180 g / m²) to the repaired area, excluding the crack-stopping area. 2Apply a local pressure of -0.02 MPa and allow it to penetrate for 15 minutes to perform infiltration and reinforcement. (3) Completely fill the crack arrest area with reinforcing resin B and allow it to cure at 35°C for 2.5 h. After initial curing, lay a first chopped fiberglass mat covering the crack area with the crack area as the geometric center on the crack arrest area after applying reinforcing resin B. Then apply reinforcing resin B (coating amount is 120 g / m) on the first chopped fiberglass mat. 2 After the first chopped fiberglass mat is coated, a second chopped fiberglass mat is laid (the second chopped fiberglass mat extends radially by 20 mm in length and width independently from the first chopped fiberglass mat as the center), and then reinforcing resin B is coated on the second chopped fiberglass mat (coating amount is 120 g / m). 2 After coating, a third chopped fiberglass mat is laid (the third chopped fiberglass mat extends radially by 20 mm independently in length and width, with the second chopped fiberglass mat as the center), and then reinforcing resin B is coated on the third chopped fiberglass mat (coating amount is 120 g / m). 2 After coating, the fiber-reinforced area is cured at 18℃ for 6 hours to form a fiber-reinforced area with a surface hardness >36. (4) First, use 80-grit sandpaper to sand the fiber-reinforced area to remove protrusions, steps, and unevenness in the joints. Then, use 200-grit, 350-grit, and 550-grit sandpaper to sand and polish the texture, gradually eliminating the height difference between layers and the color difference in the texture of the board surface. After sanding, apply protective resin to the repaired area (coating amount is 80 g / m²). 2 The resin was cured at 35°C for 2.5 h to form a 0.1 mm thick protective layer, thus completing the crack repair of the glass fiber reinforced resin matrix composite.

[0092] Example 3 This embodiment provides a method for repairing cracks in a glass fiber reinforced resin matrix composite material. The method for repairing cracks in the glass fiber reinforced resin matrix composite material includes: (1) Determine the repair area centered on the cracked area (crack width is 0.5-1 mm) of the glass fiber reinforced resin matrix composite material (extend radially 80 mm independently in length and width centered on the cracked area), and perform gradient grinding on the repair area (first use 120 grit sandpaper to grind and peel off the loose powdery aged resin on the surface, then use 600 grit sandpaper to grind until the substrate without pores, loose fibers, and continuous density is exposed), then determine the crack arrest area centered on the cracked area, and perform grinding and grooving treatment on the crack arrest area (open a 90° V-shaped groove structure along the crack arrest area, the depth of the V-shaped groove structure is 0.67:1 to the thickness of the glass fiber reinforced resin matrix composite material, the maximum width of the V-shaped groove structure is 15 mm, and the maximum length of the V-shaped groove structure extends radially 20 mm at both ends along the maximum length of the cracked area; the bottom of the groove is ground into a circular arc transition structure with a radius of 3 mm), until the substrate is completely exposed. The repaired area was treated by blowing with an air gun, wiping with acetone to remove oil, and drying in a constant temperature environment of 35℃ for 60 minutes for pre-activation treatment. (2) Apply reinforcing resin A (coating amount of 240 g / m²) to the repaired area, excluding the crack-stopping area. 2 Apply a local pressure of -0.04 MPa and allow it to penetrate for 25 minutes to perform infiltration and reinforcement. (3) Completely fill the crack arrest area with reinforcing resin B and allow it to cure at 25°C for 4 hours. After initial curing, lay a first chopped fiberglass mat covering the crack area with the crack area as the geometric center on the crack arrest area after applying reinforcing resin B. Then apply reinforcing resin B (coating amount is 160 g / m) on the first chopped fiberglass mat. 2 After the first chopped fiberglass mat is coated, a second chopped fiberglass mat is laid (the second chopped fiberglass mat extends radially for 30 mm independently in length and width, with the first chopped fiberglass mat as the center), and then reinforcing resin B is coated on the second chopped fiberglass mat (coating amount is 160 g / m). 2 After coating, a third chopped fiberglass mat is laid (the third chopped fiberglass mat extends radially for 30 mm independently from the second chopped fiberglass mat in length and width), and then reinforcing resin B is coated on the third chopped fiberglass mat (coating amount is 160 g / m). 2 After coating, the fiber-reinforced area is cured at 30℃ for 4 hours to form a fiber-reinforced area with a surface hardness >36. (4) First, use 180-grit sandpaper to sand the fiber-reinforced area to remove protrusions, steps, and unevenness in the joints. Then, use 300-grit, 450-grit, and 650-grit sandpaper to sand and polish the texture, gradually eliminating the height difference between layers and the color difference in the texture of the board surface. After sanding, apply protective resin to the repaired area (coating amount is 110 g / m). 2The resin is cured at 25°C for 2.5 hours to form a 0.3 mm thick protective layer, thus completing the crack repair of the glass fiber reinforced resin matrix composite material.

[0093] Example 4 This embodiment provides a method for repairing cracks in glass fiber reinforced resin matrix composites. The difference from Embodiment 1 is that the local pressure applied during impregnation reinforcement is adjusted to -0.02 MPa.

[0094] Example 5 This embodiment provides a method for repairing cracks in glass fiber reinforced resin matrix composites. The difference from Embodiment 1 is that the local pressure applied during impregnation reinforcement is adjusted to -0.04 MPa.

[0095] Example 6 This embodiment provides a method for repairing cracks in glass fiber reinforced resin matrix composites. The difference from Embodiment 1 is that the local pressure applied during impregnation reinforcement is adjusted to -0.01 MPa.

[0096] Example 7 This embodiment provides a method for repairing cracks in glass fiber reinforced resin matrix composites. The difference from Embodiment 1 is that the local pressure applied during impregnation reinforcement is adjusted to -0.05 MPa.

[0097] Comparative Example 1 This comparative example provides a method for repairing cracks in a glass fiber reinforced resin matrix composite material, the method comprising: (1) Determine the repair area centered on the cracked area (crack width is 0.1-0.5 mm) of the glass fiber reinforced resin matrix composite material (extend radially 60 mm independently in length and width centered on the cracked area), and perform gradient grinding on the repair area (first use 100-grit sandpaper to grind and peel off the loose powdery aged resin on the surface, then use 500-grit sandpaper to grind until a non-porous, non-fiber loose, continuous and dense substrate is exposed), then determine the crack arrest area centered on the cracked area, and perform grinding and grooving treatment on the crack arrest area (open a 75° V-shaped groove structure along the crack arrest area, the depth of the V-shaped groove structure is 0.6:1 to the thickness of the glass fiber reinforced resin matrix composite material, the maximum width of the V-shaped groove structure is 10 mm, and the maximum length of the V-shaped groove structure extends radially 15 mm at both ends along the maximum length of the cracked area; the bottom of the groove is ground into a circular arc transition structure with a radius of 2 mm), until the substrate is completely exposed; The repaired area was treated by blowing with an air gun, wiping with acetone to remove oil, and drying in a constant temperature environment of 30℃ for 45 minutes for pre-activation treatment. (2) Apply reinforcing resin A (coating amount is 200 g / m²) to the repaired area, excluding the crack-stopping area. 2 Apply a local pressure of -0.03 MPa and allow it to penetrate for 20 minutes to perform infiltration and reinforcement. (3) Completely fill the crack arrest area with reinforcing resin B and allow it to cure at 30°C for 3 hours. After initial curing, lay chopped fiberglass mat covering the crack area with the crack area as the geometric center on the crack arrest area after applying reinforcing resin B. Then apply reinforcing resin B (coating amount is 150 g / m) on the chopped fiberglass mat. 2 After coating, the fiber-reinforced area is cured at 25°C for 5 hours to form a fiber-reinforced area with a surface hardness >36. (4) First, use 120-grit sandpaper to sand the fiber-reinforced area to remove protrusions, steps, and unevenness in the joints. Then, use 240-grit, 400-grit, and 600-grit sandpaper to sand and polish the texture, gradually eliminating the height difference between layers and the color difference in the texture of the board surface. After sanding, apply protective resin to the repaired area (coating amount is 100 g / m²). 2 The resin is cured at 30°C for 3 hours to form a 0.2 mm thick protective layer, thus completing the crack repair of the glass fiber reinforced resin matrix composite.

[0098] Comparative Example 2 This comparative example provides a method for repairing cracks in a glass fiber reinforced resin matrix composite material, the method comprising: (1) Determine the repair area centered on the cracked area (crack width is 0.1-0.5 mm) of the glass fiber reinforced resin matrix composite material (extend radially 60 mm independently in length and width centered on the cracked area), and perform gradient grinding on the repair area (first use 100-grit sandpaper to grind and peel off the loose, powdery, aged resin on the surface, then use 500-grit sandpaper to grind until a non-porous, non-fiber loose, continuous and dense substrate is exposed) until the substrate is completely exposed. The repaired area was treated by blowing with an air gun, wiping with acetone to remove oil, and drying in a constant temperature environment of 30℃ for 45 minutes for pre-activation treatment. (2) The reinforcing resin B is completely filled into the crack arresting area and initially cured at 25°C for 4 hours. After initial curing, a first chopped fiberglass mat is laid on the crack arresting area after the reinforcing resin B is applied, with the crack area as the geometric center, covering the crack area. Then, the reinforcing resin B is applied on the first chopped fiberglass mat (the coating amount is 160 g / m). 2After the first chopped fiberglass mat is coated, a second chopped fiberglass mat is laid (the second chopped fiberglass mat extends radially for 30 mm independently in length and width, with the first chopped fiberglass mat as the center), and then reinforcing resin B is coated on the second chopped fiberglass mat (coating amount is 160 g / m). 2 After coating, a third chopped fiberglass mat is laid (the third chopped fiberglass mat extends radially for 30 mm independently from the second chopped fiberglass mat in length and width), and then reinforcing resin B is coated on the third chopped fiberglass mat (coating amount is 160 g / m). 2 After coating, the fiber-reinforced area is cured at 30℃ for 4 hours to form a fiber-reinforced area with a surface hardness >36. (3) First, use 120-grit sandpaper to sand the fiber-reinforced area to remove protrusions, steps, and unevenness in the joints. Then, use 240-grit, 400-grit, and 600-grit sandpaper to sand and polish the texture, gradually eliminating the height difference between layers and the color difference of the board surface texture. After sanding, apply protective resin to the repaired area (coating amount is 100 g / m). 2 The resin is cured at 30°C for 3 hours to form a 0.2 mm thick protective layer, thus completing the crack repair of the glass fiber reinforced resin matrix composite.

[0099] Test methods The following tests were performed on the glass fiber reinforced resin matrix composites after crack repair in the examples and comparative examples: (1) Repair effect: The repaired area was inspected by visual inspection combined with a 30x magnifying glass and tapping. Advantages: No delamination at the interface between the repair layer and the substrate, no internal voids, and no new micro-cracks in the repair surface and the V-groove structure filling area; Poor: Defects such as arbitrary delamination, hollow areas, and surface / internal cracks are present; (2) The mechanical strength of the repaired area is consistent with that of the original substrate: The bending strength of the original substrate and the repaired area is determined according to GB / T 1449-2005. Five samples are tested in parallel for each group of samples, and the average value is taken. Advantages: The flexural strength of the repaired area is ≥ 95% of the flexural strength of the original substrate; Good: The flexural strength of the repaired area is 85-95% of the original substrate flexural strength; Poor: The flexural strength of the repaired area is less than 85% of the flexural strength of the original substrate; (3) Weather resistance of the repaired area: Xenon lamp accelerated aging test was conducted in accordance with GB / T 16422.3; Advantages: No powdering, blistering, or cracking; Barcol hardness decrease ≤3. Good: Slight yellowing, no powdering or cracking, Barcol hardness decreased by 3-6; Poor: Significant powdering, new cracks, and a decrease in Barcol hardness >6; (4) Consistency of weather resistance between the repaired area and the original substrate: Compare the color difference and Barcol hardness difference between the repaired area and the original substrate after aging; Advantages: No visible color difference, hardness difference ≤2; Good: Slight color difference, hardness difference 2-5; Poor: Significant color difference, aging defects not present in the substrate appearing in the repaired area, and hardness difference > 5.

[0100] The test results are shown in Table 1: Table 1 The test results show that: (1) As can be seen from Examples 1 to 7, the present invention combines “layered damage removal process + impregnation and reinforcement process + multi-layer glass fiber reinforcement process” to make the mechanical strength, bonding performance, dimensional accuracy and weather resistance of the repaired area close to the original substrate, thereby realizing the high-performance and compliant reuse of defective glass fiber reinforced resin matrix composite materials and significantly reducing material scrap loss and production and maintenance costs.

[0101] (2) As can be seen from Examples 1 and 4-7, the present invention further coats the loose fiber area (excluding the crack-stopping area) with reinforcing resin A and applies a micro-negative pressure of -0.02 to -0.04 MPa to allow the reinforcing resin A to fully penetrate into the fiber gaps, thus completing the resin impregnation and filling of the loose fiber area. If the micro-negative pressure is too low, the resin impregnation will be insufficient, and dry areas and air bubbles will easily remain inside the fibers, resulting in poor interfacial bonding. If the micro-negative pressure is too high, the fibers will be easily dispersed, causing fiber misalignment, pore defects, and reducing the mechanical strength of the repaired area.

[0102] (3) As can be seen from Example 1 and Comparative Examples 1-2, the present invention adopts a multi-layer glass fiber reinforcement process to form a gradual reinforcement structure of glass fiber layer by layer and layer impregnation and curing, forming an integrated structure of "V-shaped groove structure dense filling + multi-layer glass fiber composite reinforcement + smooth interface transition", which effectively blocks the crack extension path and greatly improves the vibration resistance and deformation fatigue resistance of the repair area. If only one layer of chopped glass fiber felt is laid, the reinforcement thickness of the repair area is insufficient, the load-bearing capacity is low, and micro-cracks are easily generated inside after being stressed; the bending strength is lower than that of the original substrate, the difference in deformation due to cold and heat cycles is large, and the repair effect, mechanical consistency and weather resistance consistency are all poor. Only the surface protective resin is intact, and the short-term weather resistance and appearance are good. If the V-shaped groove structure is not opened, the stress concentration at the crack tip cannot be eliminated, the repair interface is prone to hidden cracks, and the mechanical strength of the repair area does not meet the standard. Although the surface protective coating formula is the same as that of Example 1, there are no serious appearance defects after short-term aging, but after long-term service, the aging rate of the repair area is much higher than that of the substrate, and the repair effect, mechanical consistency and weather resistance consistency are poor.

[0103] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for repairing cracks in glass fiber reinforced resin matrix composites, characterized in that, The crack repair method for the glass fiber reinforced resin matrix composite material includes the following steps: (1) Determine the repair area with the crack area of ​​the glass fiber reinforced resin matrix composite as the center, perform gradient grinding on the repair area, and then determine the crack arrest area with the crack area as the center, and perform grinding and grooving treatment on the crack arrest area. (2) Apply reinforcing resin A to the part of the repair area other than the crack-stopping area for impregnation and reinforcement; (3) Fill the crack-stopping area with reinforcing resin B and perform initial curing. After initial curing, lay short-cut fiberglass mats with the crack area as the geometric center and the area gradually increasing from bottom to top on the crack-stopping area after coating with reinforcing resin B. Reinforcing resin B is coated between each layer of short-cut fiberglass mats and on the surface of the outermost layer of short-cut fiberglass mats. After laying and curing, a fiber-reinforced area is formed. (4) The fiber-reinforced area is subjected to gradient grinding, and then the protective resin is applied to the repair area and cured to complete the crack repair of the glass fiber reinforced resin matrix composite material.

2. The crack repair method for glass fiber reinforced resin matrix composites according to claim 1, characterized in that, The repair area extends radially 50-80 mm in length and width independently, centered on the crack area. Preferably, the crack-stopping area has a V-shaped groove structure; Preferably, the maximum length of the V-shaped groove structure extends radially 10-20 mm from both ends along the maximum length of the crack region; Preferably, the included angle of the V-shaped groove structure is 60°~90°; Preferably, the maximum width of the V-shaped groove structure is 8-15 mm; Preferably, the depth of the V-shaped groove structure to the thickness of the glass fiber reinforced resin matrix composite material is (0.5-0.67):1; Preferably, the bottom of the V-shaped groove structure has a rounded transition structure; Preferably, the radius of the circular arc transition structure is 1.5-3 mm.

3. The crack repair method for glass fiber reinforced resin matrix composites according to claim 1 or 2, characterized in that, The gradient grinding in step (1) includes grinding first with a grinding medium containing coarse abrasive particles, and then grinding with a grinding medium containing fine abrasive particles. Preferably, the abrasive medium includes any one or a combination of at least two of sandpaper, blades, disc abrasive, or polishing wheels; Preferably, the abrasive medium for the first coarse abrasive particles is 80-120 mesh sandpaper; Preferably, the abrasive medium for the first fine abrasive particles is 400-600 grit sandpaper.

4. The crack repair method for glass fiber reinforced resin matrix composites according to any one of claims 1-3, characterized in that, Step (1) also includes dust removal, oil removal and pre-activation treatment of the repaired area; Preferably, the dust removal process includes blowing with an air gun; Preferably, the degreasing treatment includes wiping the repaired area with a cleaning agent; Preferably, the pre-activation treatment includes placing the glass fiber reinforced resin matrix composite material at 25-35°C and drying it for 30-60 min.

5. The crack repair method for glass fiber reinforced resin matrix composites according to any one of claims 1-4, characterized in that, The reinforcing resin A mentioned in step (2) comprises, by weight, 100 parts of matrix resin A, 1.8-2.5 parts of curing agent A, and 0.3-0.5 parts of coupling agent A; Preferably, the matrix resin A comprises bisphenol A type epoxy resin; Preferably, the epoxy equivalent of the bisphenol A type epoxy resin is 180-220 g / eq; Preferably, the curing agent A comprises a modified alicyclic amine curing agent; Preferably, the coupling agent A comprises KH-560; Preferably, the coating amount of the reinforcing resin A is 180-240 g / m³. 2 ; Preferably, the impregnation reinforcement is performed under a slight negative pressure; Preferably, the pressure of the micro-negative pressure is -0.02 to -0.04 MPa; Preferably, the impregnation and reinforcement time is 15-25 min.

6. The crack repair method for glass fiber reinforced resin matrix composites according to any one of claims 1-5, characterized in that, The reinforcing resin B mentioned in step (3) comprises, by weight, 100 parts of matrix resin B, 1.8-2.5 parts of curing agent B, and 0.3-0.5 parts of coupling agent B; Preferably, the matrix resin B comprises bisphenol A type epoxy resin; Preferably, the epoxy equivalent of the bisphenol A type epoxy resin is 180-220 g / eq; Preferably, the curing agent B comprises a modified alicyclic amine curing agent; Preferably, the coupling agent B comprises KH-560; Preferably, the initial curing temperature is 25-35℃ and the time is 2.5-4 h.

7. The crack repair method for glass fiber reinforced resin matrix composites according to any one of claims 1-6, characterized in that, The chopped fiberglass mats in step (3) whose area increases from bottom to top include a first chopped fiberglass mat, a second chopped fiberglass mat, and a third chopped fiberglass mat; Preferably, the first chopped fiberglass mat covers the cracked area; Preferably, the second chopped fiberglass mat extends radially by 20-30 mm in length and width, with the first chopped fiberglass mat as the center; Preferably, the third chopped fiberglass mat extends radially by 20-30 mm in length and width, with the second chopped fiberglass mat as the center; Preferably, the thickness of the first chopped fiberglass mat, the second chopped fiberglass mat, and the third chopped fiberglass mat is each independently 0.3-0.5 mm; Preferably, the areal density of the first, second, and third chopped fiberglass mats is independently 280-320 g / m³. 2 ; Preferably, the amount of reinforcing resin B coated between each layer of chopped fiberglass mat and on the surface of the outermost chopped fiberglass mat is independently 120-160 g / m². 2 .

8. The crack repair method for glass fiber reinforced resin matrix composites according to any one of claims 1-7, characterized in that, The curing temperature in step (3) is 18-30℃, and the time is 4-6 h; Preferably, the surface hardness of the fiber-reinforced region formed after curing is >36.

9. The crack repair method for glass fiber reinforced resin matrix composites according to any one of claims 1-8, characterized in that, Step (4) The gradient grinding includes first grinding with a grinding medium containing second coarse abrasive particles, then grinding with a grinding medium containing medium coarse abrasive particles, then grinding with a grinding medium containing medium fine abrasive particles, and then grinding with a grinding medium containing second fine abrasive particles. Preferably, the abrasive medium includes any one or a combination of at least two of sandpaper, blades, disc abrasive, or polishing wheels; Preferably, the abrasive medium for the second coarse abrasive particles is 80-180 grit sandpaper; Preferably, the grinding medium for the medium-coarse abrasive particles is 200-300 grit sandpaper; Preferably, the abrasive medium for the medium-fine abrasive particles is 350-450 mesh sandpaper; Preferably, the abrasive medium for the second fine abrasive particles is 550-650 mesh sandpaper; Preferably, the protective resin in step (4) comprises, by weight, 100 parts of matrix resin C, 1.8-2.5 parts of curing agent C, 0.2-0.4 parts of ultraviolet absorber, and 0.1-0.3 parts of antioxidant; Preferably, the matrix resin C comprises bisphenol A type epoxy resin; Preferably, the epoxy equivalent of the bisphenol A type epoxy resin is 180-220 g / eq; Preferably, the curing agent C comprises a modified alicyclic amine curing agent; Preferably, the ultraviolet absorber includes benzotriazole ultraviolet absorbers; Preferably, the antioxidant includes hindered phenolic antioxidants; Preferably, the coating amount of the protective resin is 80-110 g / m². 2 ; Preferably, the curing temperature in step (4) is 25-35℃ and the time is 2.5-4 h.

10. The application of a crack repair method for glass fiber reinforced resin matrix composite material as described in any one of claims 1-9 in the defect repair of vehicle body side panel skin.

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