Rapid composite material repairing method based on short carbon fiber technology

Abstract

The invention relates to the technical field of composite material repair, in particular to a short carbon fiber technology-based composite material rapid repair method, which comprises the following steps of short carbon fiber pretreatment; preparing a resin matrix; preparing spraying slurry; cleaning the damaged area by laser; scanning the unmanned aerial vehicle; layering and synchronous curing; evaluating the quality of the coating; a chopped fiber spraying technology is applied to the aspect of composite material damage repair, repair time is shortened, cost is reduced, interface bonding strength and fiber orientation are optimized, and the problem that the mechanical property recovery rate of the repaired material is low due to the fact that interlayer stripping or fiber orientation mismatching is prone to occurring in a repair area is solved. And the method can be used for rapidly detecting the thickness of the bubble defect, is suitable for efficient, accurate and light-weight repair of the damage of the CFRP, and is particularly suitable for on-site rapid maintenance scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material repair, and particularly relates to a rapid repair method for composite materials based on short carbon fiber technology. Background Art

[0002] An unmanned aerial vehicle (UAV) is an unpiloted aircraft that is operated by radio remote control equipment and an on-board control device. It can complete complex aerial flight tasks and various payload tasks under unmanned conditions, so it is called an "aerial robot".

[0003] Carbon fiber composite material is a high-performance material commonly used in the design of UAVs. It is composed of carbon fiber and resin-based materials. Compared with traditional metal materials and composite materials, it has the advantages of light weight, high strength, impact resistance, high temperature resistance, etc. Through reasonable design and processing, carbon fiber composite materials can be made into the fuselage, wings, rotors, control surfaces, etc. of UAVs. The characteristics of light weight, high strength, fatigue resistance and salt spray erosion resistance of carbon fiber composite materials can greatly improve and enhance the comprehensive performance of UAVs when applied to the UAV structure.

[0004] Although carbon fiber composite materials have advantages such as high strength and corrosion resistance, during the use of aircraft, carbon fiber composite material components may be damaged in various ways, such as impact, fatigue, etc. With the continuous development of aerospace technology, the requirements for the safety, reliability and usability of aircraft are getting higher and higher. Rapidly and effectively repairing damaged carbon fiber composite material components to make their performance reach or approach the performance indicators of the original components is crucial for ensuring the normal operation and flight safety of aircraft. At present, although there are already some repair technologies for carbon fiber composite materials, there are still some problems in actual applications. For example, cleaning agents may have an adverse impact on the structure and performance of carbon fiber composite materials, the accuracy and depth of damage detection are insufficient, the performance of repair materials cannot meet the strict requirements of aerospace, and the repair process is not perfect, resulting in unstable repair quality, etc.

[0005] CN119239008A discloses a rapid repair method for aerospace carbon fiber composite materials, belonging to the technical field of carbon fiber composite material repair. In terms of cleaning, the self-developed special cleaning agent is non-damaging and efficient, and can reach the preset cleanliness when combined with a tool with a replaceable brush head, laying the foundation for repair. Advanced detection equipment can accurately measure damage with a detection accuracy of 0.1 mm and a depth of 5 mm, providing a basis for precise repair. The repair material formula is scientific and the proportion of each component is reasonable, which can ensure that the performance of the repaired component is close to that of the original component. Rigorous repair processes, such as vacuum-assisted pressure injection and autoclave curing, ensure the full curing of the material and the best performance. Surface treatment and detection ensure that the quality meets the standards. Each device of the equipment is coordinated and has an intelligent system, which can adjust parameters and automatically adjust the process. Its structure meets the special requirements of aviation, is easy to carry and operate, and meets the needs of various scenarios. However, although the above patent can ensure that the performance of the repaired component is close to that of the original component, generally speaking, when using the methods of vacuum-assisted pressure injection and autoclave curing, the forming cycle of carbon fiber composite materials in autoclaves is long, and it is necessary to return to the factory for autoclave curing, and the time range is from several hours to dozens of hours, which cannot meet the high-frequency use requirements of unmanned aerial vehicles and cannot meet the requirements of quickly and effectively repairing damaged carbon fiber composite materials.

[0006] Therefore, when repairing carbon fiber composite materials at present, traditional repair methods (such as prepreg patching method) usually require autoclave curing, which is highly dependent on equipment and it is difficult to quickly carry out repair operations on site. Moreover, problems such as interlayer delamination or fiber orientation mismatch are likely to occur in the repair area, resulting in a low recovery rate of the mechanical properties of the repaired material. For example, the tensile strength can only be restored to 70%-80% of the raw material. It is difficult to apply uniform pressure to complex surfaces (such as rotor blades), and thin-walled structures are prone to deformation due to thermal stress. When repairing complex surfaces, customized molds are required, which not only consumes time but also increases costs. For example, the repair cycle of the aircraft wing skin is often more than 24 hours. When repairing by laying carbon fiber cloth layer by layer, high-temperature curing is required, and the repaired part will gain weight significantly, with a weight gain of more than 10%. The short fiber spraying technology is currently mostly used for coating protection. In the aspect of composite material damage repair, it has not been optimized for the interfacial bonding strength and fiber orientation. Problems such as interlayer delamination or fiber orientation mismatch are likely to occur in the repair area, resulting in a low recovery rate of the mechanical properties of the repaired material, and it has not been able to quickly detect the thickness of bubble defects. When using traditional adhesives or continuous fiber patches for repair, the interfacial bonding force is weak and secondary failure is likely to occur. Although microwave-assisted curing has also been proposed currently, it has not been optimized for the lightweight and high-precision repair requirements of unmanned aerial vehicle components. Summary of the Invention

[0007] Aiming at the deficiencies of the above-mentioned existing technologies, a rapid repair method for composites based on short carbon fiber technology is provided. The short fiber spraying technology is used for the repair of composite material damage, reducing the repair time and cost. Optimization is carried out for the interfacial bonding strength and fiber orientation, solving the problem that delamination or fiber orientation mismatch is likely to occur in the repair area, resulting in a low mechanical property recovery rate of the repaired material. Moreover, the thickness of bubble defects can be quickly detected, which is applicable to the efficient, precise and lightweight repair of carbon fiber reinforced composite (CFRP) damage, especially suitable for on-site rapid repair scenarios.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is a rapid repair method for composites based on short carbon fiber technology, including the following steps:

[0009] (1) Short carbon fiber pretreatment: Select short carbon fibers with a length of 2 - 8 mm and a diameter of 5 - 12 μm, and perform oxidation treatment on the fiber surface to improve the wettability of the resin to the fiber. After treatment, the fibers are sealed and stored after drying to ensure that the environmental humidity < 30% RH to prevent moisture absorption;

[0010] (2) Resin matrix preparation: Select photocurable resin or low-temperature thermosetting resin, add 0.1% - 1% of nano-enhancer to it, mix the resin and curing agent in proportion, and after adding nano-materials, perform ultrasonic dispersion to ensure that the nano-materials are evenly dispersed without agglomeration;

[0011] (3) Spraying slurry preparation: According to the volume ratio of short carbon fiber to resin of 35% - 55%, use a stirrer to mix the two into a uniform slurry, and use a rotational viscometer to detect the slurry viscosity to make it within the target range of 500 - 2000 cP. If necessary, add a diluent for adjustment;

[0012] (4) Laser cleaning of the damaged area: Use a laser with a power of 50 - 100 W and a pulse width of 10 ns to clean the damaged area, removing the surface contamination layer and performing micro-texturing treatment on the surface at the same time;

[0013] (5) Scan the drone to obtain damage morphology data, generate an adaptive spiral spraying path, and perform curvature-optimized speed control. Spray the short carbon fiber-resin slurry in layers, and through the application of an electrostatic field of 10 ± 5% kV, make the fibers orient along the main stress direction of the matrix, with the deviation controlled within ≤ 5°;

[0014] (6) Adopt a UV-infrared composite light source, with a wavelength of 365 nm + medium-wave infrared, where the UV power density ≥ 8 W / cm 2 , and the infrared temperature can be regulated within the range of 60 - 100 °C to achieve layered synchronous curing, and the single-layer curing time ≤ 2 minutes;

[0015] (7) Evaluate the coating quality.

[0016] In the above rapid repair method of composite materials based on the chopped carbon fiber technology, in step (5), the generation of the adaptive spiral spraying path includes the following steps:

[0017] S1: Generate a continuous spiral line by gradually offsetting the polygon boundary, and the operation formula is as follows:

[0018]

[0019] Where: P is the polygon of the original damage area;

[0020] B is the unit circle (used for Minkowski difference operation);

[0021] d is the current offset distance, with an initial value of the spray gun radius r, and the iteration step Δd = r(1 - overlap), where overlap is the overlap rate;

[0022] This formula generates a spiral path by calculating the inner shrinkage offset of the polygon boundary to ensure that there is no blind area in the area covered by the spray gun. In unmanned aerial vehicle repair, the step size Δd needs to be dynamically adjusted according to the geometric characteristics of the damage area, and a typical overlap rate is 45%;

[0023] S2: Calculate the curvature to identify areas with too small turning radii, and the operation formula is as follows:

[0024] Path curvature parameterized curvature formula:

[0025] For the parameterized path r(s) = (x(s), y(s)), the curvature k is calculated as:

[0026]

[0027] Where s is the arc length parameter;

[0028] In high curvature areas, the moving speed of the spray gun needs to be reduced to avoid material accumulation while ensuring coating uniformity;

[0029] S3: Adaptive speed adjustment, and the operation formula is as follows:

[0030] The relationship between the moving speed v of the spray gun and the curvature k can be modeled as:

[0031]

[0032] Where: v max is the maximum allowable moving speed (determined by the material curing time);

[0033] α is the curvature sensitivity coefficient, with typical values of 0.3 - 0.5.

[0034] For the above-mentioned rapid composite material repair method based on short carbon fiber technology, in step (7),

[0035] To evaluate the coating thickness uniformity, the operation formula is as follows:

[0036] The thickness uniformity of the repair layer is evaluated by the coefficient of variation C v as follows:

[0037]

[0038] where and M are the average thickness mean value and the effective measurement points respectively. It is required that C v < 10% is qualified.

[0039] For the above-mentioned rapid composite material repair method based on short carbon fiber technology, in step (7),

[0040] For the thickness anomaly modeling of bubble defects, an exponential decay function is adopted:

[0041]

[0042] where:

[0043] h nominal is the normal coating thickness: 1 - 1.5 mm;

[0044] Δh is the maximum thickness deviation: 0.3 mm;

[0045] (x0,y0) is the defect center coordinate;

[0046] σ d controls the defect area radius: 1 mm.

[0047] For the above-mentioned rapid composite material repair method based on short carbon fiber technology, the diameter of the pits for micro-texture treatment is 50 - 200 μm, and the depth is 20 - 50 μm.

[0048] For the above-mentioned rapid composite material repair method based on short carbon fiber technology, in step (7), the curing temperature uniformity is monitored by an infrared thermal imager to ensure that the temperature difference ≤ 5 °C, avoiding resin degradation caused by local overheating. If bubbles or uncovered areas are detected, re-spraying is immediately carried out, and the curing time is appropriately extended. A transparent polyurethane topcoat with a spraying thickness of 50 μm is cured at 80 °C for 30 minutes to improve the weather resistance of the repaired part.

[0049] For the above-mentioned rapid composite material repair method based on short carbon fiber technology, in step (5):

[0050] Base layer: The spraying thickness is 0.3 mm, the fiber volume fraction is 55%, to enhance the edge bonding with high density. First, perform ultraviolet irradiation for 1 minute, and simultaneously heat with infrared to 80 °C to preliminarily cure and form an anchoring layer;

[0051] Intermediate layer: The thickness of each layer is 0.5 - 1 mm, the fiber volume fraction is 45%, the spraying speed is 200 mm / s, and the interlayer is slightly roughened with 600 - mesh sandpaper to enhance the interlayer bonding force;

[0052] Functional layer: The thickness is 0.2 mm, the fiber volume fraction is 35%, add 5% fluorosilane to improve the hydrophobicity, perform ultraviolet curing for 3 minutes, without using infrared, to reduce the surface roughness.

[0053] In the above - mentioned rapid repair method of composite materials based on the chopped carbon fiber technology, in step (7), the repaired surface is subjected to laser polishing treatment to make the roughness Ra < 1.0 μm, and then a hygrothermal aging test is carried out to verify the durability of the repaired part.

[0054] In the above - mentioned rapid repair method of composite materials based on the chopped carbon fiber technology, set the nozzle voltage to 5 - 15 kV, the air pressure to 0.3 - 0.8 MPa, and the distance between the spray gun and the substrate to 20 - 40 cm.

[0055] The beneficial effect of the rapid repair method of composite materials based on the chopped carbon fiber technology of the present invention is that the chopped fiber spraying technology is used for the damage repair of composite materials. There is no need for autoclave curing, reducing the dependence on equipment. When repairing complex curved surfaces, there is no need to customize molds, reducing the repair time and cost. Optimize the interfacial bonding strength and fiber orientation, solve the problem that delamination or fiber orientation mismatch is likely to occur in the repaired area, resulting in a low recovery rate of the mechanical properties of the repaired material, and is suitable for the efficient, precise and lightweight repair of carbon fiber reinforced composite (CFRP) damage, especially suitable for on - site rapid repair scenarios.

[0056] For the abnormal thickness modeling of bubble defects, use an exponential decay function: The thickness deviation decreases exponentially (not linearly) with the distance from the defect center, which is closer to the real diffusion law of bubbles - the central area has the greatest influence and weakens rapidly at the edge. The defect edge smoothly transitions to the normal thickness, avoiding misjudgment caused by artificially setting thresholds and improving the detection accuracy. There is no need for complex numerical integration or iterative calculation, directly expressing the spatial distribution of the defect thickness through an exponential function, with fast calculation speed, making the detection of abnormal thickness of bubble defects faster. Brief Description of the Drawings

[0057] Figure 1 It is the repair flow chart of the present invention;

[0058] Figure 2 It is the schematic diagram of electrostatic - assisted spraying and curing. Detailed implementation manners

[0059] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0060] As shown in the figure, a rapid repair method for composites based on short carbon fiber technology includes the following steps:

[0061] (1) Pretreatment of short carbon fibers: Select short carbon fibers (T300 or T700 grade) with a length of 2 - 8 mm and a diameter of 5 - 12 μm, and perform oxidation treatment on the fiber surface (such as air plasma treatment for 10 minutes) to improve the wettability of the resin to the fiber. After treatment, the fibers are sealed and stored after drying. They need to be dried in an 80°C oven for 2 hours to ensure that the environmental humidity < 30%RH and prevent moisture absorption; the original diameter of carbon fiber filaments is mostly 5 - 10 μm. For carbon fiber repair, raw filaments that are slightly denser than the raw material are mostly used. For example, if a damaged workpiece uses 3K carbon cloth, 6K or 12K raw filaments can be used for repair to fit the repair surface. The wettability is better and it is more suitable for complex shapes.

[0062] (2) Preparation of resin matrix: Select a photocurable resin (such as cationic epoxy resin CY179) or a low-temperature thermosetting resin (such as polyurethane PU - 401), add 0.1% - 1% of nano-enhancers (such as CNT, graphene) to it, mix the resin and the curing agent in proportion, and after adding the nano-materials, perform ultrasonic dispersion for 30 minutes to ensure that the nano-materials are evenly dispersed without agglomeration;

[0063] (3) Preparation of spraying slurry: According to the volume ratio of short carbon fibers to resin of 35% - 55%, use a stirrer to mix the two into a uniform slurry, and use a rotational viscometer to detect the viscosity of the slurry to make it within the target range of 500 - 2000 cP. If necessary, add a diluent (such as acetone) for adjustment;

[0064] (4) Laser cleaning of the damaged area: Use a laser with a power of 50 - 100 W and a pulse width of 10 ns to clean the damaged area, removing the surface contamination layer and performing micro-texturing treatment on the surface at the same time;

[0065] (5) Scan the drone to obtain damaged morphology data, generate an adaptive spiral spraying path, and perform curvature-optimized speed control. Spray the short carbon fiber-resin slurry in layers. By applying an electrostatic field of 10 ± 5% kV, make the fibers align along the main stress direction of the matrix, and control the deviation within ≤ 5°; Use a high-precision 3D scanner (accuracy ±0.05 mm, scanning rate 50 kHz) to scan the drone. High-voltage electrode: Ring electrode. Dynamically adjust the voltage according to the data of the fiber orientation sensor (high-speed camera) to ensure the consistency of fiber arrangement.

[0066] (6) Adopt an ultraviolet-infrared composite light source with a wavelength of 365 nm + mid-wave infrared, where the ultraviolet power density ≥ 8 W / cm 2 , and the infrared temperature can be adjusted within the range of 60 - 100 °C to achieve layered synchronous curing, and the single-layer curing time ≤ 2 minutes;

[0067] (7) Evaluate the coating quality.

[0068] In the said step (5), the generation of the adaptive spiral spraying path includes the following steps:

[0069] S1: Generate a continuous spiral line by gradually offsetting the polygon boundary, and the operation formula is as follows:

[0070]

[0071] Where: P is the polygon of the original damage area;

[0072] B is a unit circle (used for Minkowski difference operation);

[0073] d is the current offset distance, with an initial value of the spray gun radius r, and the iteration step size Δd = r(1 - overlap) (overlap is the overlap rate);

[0074] This formula generates a spiral path by calculating the inner shrinkage offset (Minkowski difference) of the polygon boundary, ensuring that there is no blind area in the area covered by the spray gun. In UAV repair, the step size Δd needs to be dynamically adjusted according to the geometric characteristics of the damage area, and a typical overlap rate is taken as 45%;

[0075] Carbon fiber composite materials are usually composed of unidirectional or bidirectional woven fibers. The path needs to be sprayed along the fiber direction to ensure the bonding force between the coating and the matrix. The spiral path generated by the Minkowski difference can adapt to different fiber bundle spacings through dynamic step size adjustment (Δd = r(1 - overlap)), avoiding problems such as too thick coating or fiber shielding caused by a fixed step size.

[0076] The continuous inner shrinkage characteristic of the spiral path (the offset d increases layer by layer) shortens the moving distance by about 30% - 50% compared with the traditional back-and-forth scanning path, and the efficiency is significantly improved.

[0077] After being damaged, carbon fiber components may undergo minor deformations (such as bending, delamination). The path generation algorithm needs to adapt to geometric changes in real time. By dynamically adjusting the overlap rate (such as automatically increasing the overlap to 50% in the narrow area of the damage area), the local coverage density is enhanced to compensate for the spraying deviation caused by deformation.

[0078] The path boundary generated by the unit circle offset (with B being the unit circle) always maintains a safe distance from the damaged area (initial d = r), preventing the spray gun from overly intruding into the fragile internal structure.

[0079] Dynamic step size control (Δd is linked with overlap) can flexibly adjust the single-layer spraying speed (combined with the v(k) formula in step S3), decelerate in areas with large curvature to match the leveling requirements of low-viscosity resin, and maintain efficient movement in large-area regions.

[0080] The path generated by the Minkowski difference has geometric closure. Even with small position errors, subsequent spiral loops can still cover the missed areas (benefiting from the 45% overlap rate design).

[0081] Since the spray gun needs to start and stop frequently, it is prone to wear. The smooth spiral path reduces rapid acceleration / deceleration, reduces the losses of the drive and transmission systems, and extends the mean time between failures of the equipment.

[0082] S2: Curvature calculation to identify areas with too small turning radii. The operation formula is as follows:

[0083] Path curvature parameterized curvature formula:

[0084] For the parameterized path r(s) = (x(s), y(s)), the curvature k is calculated as:

[0085]

[0086] where s is the arc length parameter;

[0087] Decelerating in high-curvature areas can prevent the resin from being thrown out by centrifugal force, and maintaining efficient movement in low-curvature areas. Therefore, in high-curvature areas, the moving speed of the spray gun needs to be reduced to avoid material accumulation and ensure the coating uniformity (reduce the orange peel effect);

[0088] By calculating the curvature in real time to identify areas with too small turning radii, trigger path replanning, and avoid resin drawing or matrix damage caused by sharp turns of the spray gun.

[0089] Carbon fiber composites usually have unidirectional or bidirectional fiber laminates. The path needs to be sprayed along the fiber direction to enhance the bonding force. Curvature calculation can identify the local curvature changes of the fiber bundles (such as the edges of reinforcement patches), and dynamically adjust the spraying angle and path spacing to ensure that the coating is consistent with the fiber orientation.

[0090] Carbon fiber components may contain honeycomb cores or fastener holes, and it is necessary to avoid the spray gun from intruding into the fragile interior. By analyzing the curvature to identify the curvature mutation points at the edges of the holes, trigger path offset correction, and maintain a safe spraying distance.

[0091] S3: Adaptive speed regulation. The operation formula is as follows:

[0092] The relationship between the spray gun movement speed v and the curvature k can be modeled as:

[0093]

[0094] where: v max is the maximum allowable movement speed (determined by the material curing time);

[0095] α is the curvature sensitivity coefficient, with typical values of 0.3 - 0.5.

[0096] There are often sharp corners, holes or complex curved surfaces at the edges of carbon fiber components. Traditional constant-speed spraying easily leads to resin accumulation (at large curvatures) or too thin coatings (at small curvatures).

[0097] The formula automatically adjusts the speed through the non-linear attenuation effect of k - the greater the curvature, the slower the speed, ensuring the uniformity of the coating thickness.

[0098] Carbon fiber composites are usually laminated along a specific direction (such as unidirectional fibers). The spraying speed needs to match the fiber orientation to avoid coating peeling. Curvature calculation can identify the local bending of fiber bundles and trigger a speed reduction to ensure a tight fit between the coating and the fibers.

[0099] Carbon fiber coatings are expensive (such as epoxy resin with a unit price of ￥500 - 2000 / kg), and overspray needs to be avoided. Coordinated control of speed and curvature can reduce resin splashing or accumulation caused by sudden stops / turns (such as a 50% sudden drop in speed at curvature mutations), and the material loss is reduced by about 15% - 20%.

[0100] During the spraying process, it is crucial to adjust the speed in real-time. The formula has a simple structure, only involving one division operation, is fast to calculate, has a very low calculation time-consuming, meets the high-frequency real-time adjustment requirements, and is suitable for real-time control systems. Ensure uniform coating coverage and avoid accumulation or splashing at turns.

[0101] In the step (7),

[0102] To evaluate the uniformity of the coating thickness, the operation formula is as follows:

[0103] The uniformity of the repair layer thickness is evaluated through the coefficient of variation C v as follows:

[0104]

[0105] where and M are the average thickness mean and the effective measurement points respectively. It is required that C v < 10% is qualified.

[0106] By weighted average of squared deviations, amplify the error contribution of local extremely thick / thin regions (such as abrupt changes in edge curvature or spraying splashes), and avoid masking key defects by traditional average metrics (such as average thickness error).

[0107] In the multi-directional braided structure of carbon fiber composites, the uneven coating thickness may exhibit anisotropic distribution along the fiber direction or perpendicular direction. This formula can be combined with a directional sampling strategy (such as calculating separately along the fiber orientation and perpendicular direction) to identify uneven defects of specific patterns. It adapts to the fiber texture characteristics of carbon fiber.

[0108] C v By weighted average of squared deviations, it is sensitive to outliers (such as local extremely thick / thin regions) and can effectively reflect the "extremely uneven" defects in the coating.

[0109] Combined with the bubble defect model and C v Evaluation can quantify the comprehensive impact of bubble clusters on the overall uniformity.

[0110] In the said step (7),

[0111] For the thickness anomaly modeling of bubble defects, use an exponential decay function:

[0112]

[0113] Where:

[0114] h nominal Is the normal coating thickness: 1 - 1.5 mm;

[0115] Δh is the maximum thickness deviation: 0.3 mm;

[0116] (x0, y0) is the defect center coordinate; locate the defect center to support the expansion of multi-defect scenarios (such as multiple bubbles overlapping).

[0117] σ d Control the defect area radius: 1 mm. Define the defect influence radius as 1 mm to quantify the expansion range of bubbles and adapt to different process conditions (such as spraying pressure, flow rate).

[0118] Using the exponential decay function, achieve the exponential decay of defect intensity with distance, perfectly simulating the "center concentration, edge weakening" characteristics of bubble defects (such as the depression formed by resin shrinkage after bubble rupture). And compared with the uniform deviation model, it can distinguish local severe defects (such as Δh = 0.3 mm in the central region) from large-area slight fluctuations (such as Δh = 0.05 mm far from the center) to avoid misjudgment. The formula only involves square operations and exponential functions, and the calculation time consumption is extremely low, meeting the real-time detection requirements.

[0119] Multi-scale adaptability:

[0120] σ d Control defect area radius: 1 mm

[0121] Small σ d (such as 0.5 mm): Detecting tiny bubbles (such as pinhole defects), suitable for high-precision repair scenarios (such as near aviation fastener holes).

[0122] Large σ d (such as 2 mm): Capturing larger bubble clusters (such as debonding areas), adapting to the requirements of rapid inspection.

[0123] Parametric modeling: h nominal = 0.5 mm: Directly related to the target thickness of the carbon fiber coating, without additional calibration. Δh = 0.3 mm: Preset the maximum allowable deviation based on material properties (such as epoxy resin shrinkage rate), adapting to different substrates. (x0, y0) is the defect center coordinate; Locate the defect center, supporting the expansion of multi-defect scenarios (such as multiple bubbles overlapping).

[0124] Closed-loop coordination with the repair process:

[0125] If h defect <h nominal - 0.1 mm, trigger the local offset correction of step S1 (spiral path generation) (such as increasing the overlap rate to 60%), and perform secondary coverage on the defect area.

[0126] Speed adjustment linkage:

[0127] Combined with the formula in step S3 Automatically reduce the spraying speed in the bubble defect area (usually accompanied by sudden curvature changes) to avoid defect expansion due to insufficient leveling.

[0128] Multi-layer coating collaborative verification:

[0129] Model the cumulative thickness deviation of multi-layer spraying (such as the thickness h of the nth layer n =h n-1 +h defect (x, y)), ensuring that the interlayer bonding force meets the standards (such as ASTM D792).

[0130] Defect root cause analysis: Identify the high-incidence defect area (such as near fiber lap joints) through the two-dimensional histogram of h defect σ d ; Statistically analyze the frequency distribution of σ d to determine whether the main cause of the defect is spraying equipment failure (large-scale defects) or material bubbles (small-scale defects).

[0131] Reduce rework costs: By real-time detecting C v (coefficient of variation) and h defectThe combined threshold triggers local re-spraying before the coating semi-cures, avoiding the high cost of grinding and repairing after curing. Analyze h defect The timing data of to predict gun jams or nozzle wear (such as persistent large-scale defects in a certain area), and replace components in advance.

[0132] For the abnormal thickness modeling of bubble defects, an exponential decay function is adopted: the thickness deviation decreases exponentially with the distance from the center of the defect (instead of linearly), which is closer to the diffusion law of real bubbles - the central area has the greatest influence and the edge weakens rapidly. The edge of the defect smoothly transitions to the normal thickness, avoiding misjudgment caused by artificially setting the threshold and improving the detection accuracy. Without complex numerical integration or iterative calculations, the spatial distribution of the defect thickness is directly expressed by an exponential function, with a fast calculation speed, making the detection of abnormal thickness of bubble defects faster.

[0133] In the step (5), an electrostatic-assisted spraying technique is adopted to spray the chopped carbon fiber-resin slurry 1 in layers. As Figure 2 shown, compressed gas is used as the power source, and a two-way gas control (carrier gas pressure 0.3 - 0.8 MPa, atomizing gas pressure 0.1 - 0.3 MPa) is adopted to send the spraying slurry into the spray gun 2, and part of the compressed gas enters the spray gun 2 after being heated by the gas heater 3, so that the chopped carbon fiber-resin slurry is better atomized, and the chopped carbon fiber-resin slurry is sprayed in layers onto the substrate 4 to form a coating 5. By applying an electrostatic field of 10 kV, the fibers are oriented along the main stress direction of the matrix, and layered synchronous curing is carried out.

[0134] The diameter of the pits in the micro-texture treatment is 50 - 200 μm, and the depth is 20 - 50 μm. The pit structure increases the contact points between the fibers and the coating, and prevents the coating from peeling off through physical embedding. In the composite material, uneven fiber directions are likely to cause local stress concentration. The micro-pits can buffer the shear force between the coating and the fibers, reducing the risk of coating cracking. The micro-channels formed by the pits utilize the capillary effect to guide the coating deep into the gaps between the fiber bundles, covering the "blind areas" that are difficult to reach by traditional spraying and reducing the porosity. The depth of the micro-pits (20 - 50 μm) can cover most of the fibers, avoiding excessive cutting of the substrate.

[0135] In the step (6), the curing temperature uniformity is monitored by an infrared thermal imager to ensure that the temperature difference ≤ 5 °C, avoiding resin degradation caused by local overheating. If bubbles or uncovered areas are detected, re-spraying is immediately carried out, and the curing time is appropriately extended. A transparent polyurethane topcoat with a spraying thickness of 50 μm is cured at 80 °C for 30 minutes to improve the weather resistance of the repaired area.

[0136] In the step (5):

[0137] Base layer: The spraying thickness is 0.3 mm, the fiber volume fraction is 55%, to enhance the edge bonding with high density. First, perform ultraviolet irradiation for 1 minute, while heating with infrared to 80 °C, and initially cure to form an anchoring layer;

[0138] Intermediate layer: The thickness of each layer is 0.5 - 1 mm, the fiber volume fraction is 45%, the spraying speed is 200 mm / s, and the surface between layers is slightly roughened with 600 - mesh sandpaper to enhance the interlayer bonding force;

[0139] Functional layer: The thickness is 0.2 mm, the fiber volume fraction is 35%, add 5% fluorosilane to improve hydrophobicity, perform ultraviolet curing for 3 minutes, without using infrared, to reduce the surface roughness.

[0140] In step (7), perform laser polishing treatment on the repaired surface to make the roughness Ra < 1.0 μm, and then conduct a damp - heat aging test (85 °C / 85% RH, 48 h) to verify the durability of the repaired part.

[0141] Set the nozzle voltage to 5 - 15 kV, the air pressure to 0.3 - 0.8 MPa, and the distance between the spray gun and the substrate to 20 - 40 cm. The nozzle is a fan - shaped nozzle, corrosion - resistant and anti - clogging.

[0142] The mechanical execution unit used in electrostatic - assisted spraying includes: Multi - axis robotic arm: Use a six - degree - of - freedom collaborative robotic arm (such as UR10e), with a load ≥ 10 kg and a repeat positioning accuracy of ±0.05 mm. End - effector: Integrate an electrostatic spray gun, a 3D scanner, and an infrared temperature sensor. Mobile chassis: Equipped with an AGV chassis (navigation accuracy ±1 cm) to achieve large - range mobile spraying.

[0143] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those of ordinary skill in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A rapid repair method for composites based on the chopped carbon fiber technology, characterized in that: It includes the following steps: (1) Short carbon fiber pretreatment: Select short carbon fibers with a length of 2-8 mm and a diameter of 5-12 μm, and oxidize the fiber surface to improve the wettability of the resin to the fiber. After treatment, the fibers are sealed and stored after drying to ensure that the environmental humidity < 30%RH to prevent moisture absorption. (2) Resin matrix preparation: Select a photocurable resin or a low-temperature thermosetting resin, add 0.1%-1% of nano-enhancer to it, mix the resin and the curing agent in proportion. After adding the nano-material, ultrasonic dispersion is carried out to ensure that the nano-material is evenly dispersed without agglomeration. (3) Spraying slurry preparation: According to the volume ratio of short carbon fiber to resin of 35%-55%, use a stirrer to mix the two into a uniform slurry, and use a rotational viscometer to detect the slurry viscosity to make it within the target range of 500-2000 cP. If necessary, add a diluent for adjustment. (4) Laser cleaning of the damaged area: Use a laser with a power of 50-100 W and a pulse width of 10 ns to clean the damaged area, removing the surface contamination layer and performing micro-texturing treatment on the surface at the same time. (5) Scan the drone to obtain damage morphology data, generate an adaptive spiral spraying path, and perform curvature-optimized speed control. Spray the short carbon fiber-resin slurry in layers. By applying an electrostatic field of 10 ± 5% kV, the fibers are oriented along the main stress direction of the matrix, and the deviation is controlled within ≤ 5°. (6) Adopt an ultraviolet-infrared composite light source with a wavelength of 365nm + mid-wave infrared, where the ultraviolet power density ≥ 8W / cm 2 , and the infrared temperature can be adjusted within the range of 60 - 100°C to achieve layered synchronous curing, and the single-layer curing time ≤ 2 minutes; (7) Evaluate the coating quality.

2. The rapid repair method of the composite material based on the chopped carbon fiber technology according to claim 1, characterized in that , in the step (5), the generation of the adaptive spiral spraying path includes the following steps: S1: Generate a continuous spiral line by gradually offsetting the polygon boundary, and the operation formula is as follows: Where: P is the polygon of the original damaged area; B is the unit circle; d is the current offset distance, with an initial value of the spray gun radius r, and the iteration step Δd = r(1 - overlap), where overlap is the overlap rate; This formula generates a spiral path by calculating the inner shrinkage offset of the polygon boundary to ensure that there is no blind area in the area covered by the spray gun. In drone repair, the step Δd needs to be dynamically adjusted according to the geometric characteristics of the damaged area, and a typical overlap rate is 45%. S2: Calculate the curvature to identify the area with too small turning radius, and the operation formula is as follows: Path curvature parameterized curvature formula: For the parameterized path r(s) = (x(s), y(s)), the curvature k is calculated as: Where s is the arc length parameter; In the high-curvature area, the moving speed of the spray gun needs to be reduced to avoid material accumulation while ensuring the coating uniformity. S3: Adaptive speed adjustment, and the operation formula is as follows: The relationship between the moving speed v of the spray gun and the curvature k can be modeled as: where: v max is the maximum allowable moving speed; α is the curvature sensitivity coefficient, and the typical value is 0.3-0.

5.

3. The rapid repair method of composite materials based on the chopped carbon fiber technology according to claim 2, characterized in that, In the step (7), to evaluate the coating thickness uniformity, the operation formula is as follows: The thickness uniformity of the repair layer is evaluated by the coefficient of variation C v Evaluation: Among them C and M are the average thickness mean value and the effective measurement points respectively, and it is required that C v Less than 10% is qualified.

4. A rapid repair method for a composite material based on a chopped carbon fiber technology according to claim 3, characterized in that In the step (7), for the thickness anomaly modeling of bubble defects, an exponential decay function is adopted: Where: h nominal For normal coating thickness: 1 - 1.5 mm; Δh is the maximum thickness deviation: 0.3 mm; (x0, y0) is the center coordinate of the defect; σ d Radius of the control defect area: 1 mm.

5. The rapid repair method for composite materials based on the chopped carbon fiber technology according to claim 4, characterized in that The diameter of the pits in the micro-texturing treatment is 50-200 μm, and the depth is 20-50 μm.

6. A rapid repair method for a composite material based on a chopped carbon fiber technology according to claim 5, characterized in that, In step (7), the curing temperature uniformity is monitored by an infrared thermal imager to ensure that the temperature difference ≤ 5°C, avoiding resin degradation caused by local overheating. If bubbles or uncovered areas are detected, re-spraying shall be carried out immediately and the curing time shall be appropriately extended. A transparent polyurethane topcoat with a spraying thickness of 50μm is cured at 80°C for 30 minutes to improve the weather resistance of the repaired part.

7. The rapid repair method of composite materials based on the chopped carbon fiber technology according to claim 6, characterized in that, In step (5): Primer layer: The spraying thickness is 0.3mm and the fiber volume fraction is 55%. To enhance the edge bonding with high density, first conduct ultraviolet irradiation for 1 minute while heating with infrared to 80°C to initially cure and form an anchoring layer. Intermediate layer: The thickness of each layer is 0.5 - 1mm, the fiber volume fraction is 45%, the spraying speed is 200mm / s, and the surface between layers is slightly roughened with 600-mesh sandpaper to enhance the interlayer bonding force. Functional layer: The thickness is 0.2mm, the fiber volume fraction is 35%, 5% fluorosilane is added to improve hydrophobicity, and ultraviolet curing is carried out for 3 minutes without using infrared to reduce the surface roughness.

8. The rapid repair method of composite materials based on the chopped carbon fiber technology according to claim 7, characterized in that In step (7), the repaired surface is subjected to laser polishing treatment to make the roughness Ra < 1.0μm, and then a damp heat aging test is carried out to verify the durability of the repaired part.

9. The rapid repair method of composite materials based on the chopped carbon fiber technology according to claim 8, characterized in that, Set the nozzle voltage to 5 - 15kV, the air pressure to 0.3 - 0.8MPa, and the distance between the spray gun and the substrate to 20 - 40cm.

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