Composite rapid repair method based on chopped carbon fiber technology

Abstract

The present application relates to the technical field of composite material repair, and particularly relates to a composite material rapid repair method based on chopped carbon fiber technology, comprising the following steps: chopped carbon fiber pretreatment; resin matrix preparation; spray slurry preparation; laser cleaning of the damaged area; scanning of the unmanned aerial vehicle; layered synchronous curing; evaluation of the coating quality; the chopped fiber spraying technology is used in the aspect of composite material damage repair, the repair time is reduced, the cost is reduced, the interface bonding strength and the fiber orientation are optimized, the problem that the interlayer peeling or the fiber orientation mismatching is prone to occur in the repair area, and the mechanical property recovery rate of the repaired material is low is solved, the thickness of the bubble defect can be rapidly detected, the method is suitable for efficient, accurate and lightweight repair of carbon fiber reinforced composite material (CFRP) damage, and is particularly suitable for on-site rapid repair scene.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material repair, and particularly relates to a composite material rapid repair method based on chopped carbon fiber technology. BACKGROUND

[0002] An unmanned aerial vehicle is a kind of unmanned aerial vehicle, which is operated by radio remote control equipment and on-board control device. It can complete complex aerial flight tasks and various load tasks under unmanned conditions, so it is called "air robot".

[0003] Carbon fiber composite material is a kind of high-performance material commonly used in the design of unmanned aerial vehicles. It is composed of carbon fiber and resin-based material, and compared with traditional metal materials and composite materials, it has the advantages of light weight, high strength, impact resistance, high temperature resistance, etc. Carbon fiber composite material can be made into the fuselage, wings, rotors, rudders and other parts of unmanned aerial vehicles through reasonable design and processing. The light weight, high strength, fatigue resistance and salt spray resistance of carbon fiber composite material can greatly improve and enhance the comprehensive performance of unmanned aerial vehicles.

[0004] Although carbon fiber composite material has the advantages of high strength, corrosion resistance, etc., in the use process of the aircraft, the carbon fiber composite material parts may be damaged by various damages such as impact, fatigue, etc. With the continuous development of aerospace technology, the safety, reliability and usability of the aircraft are required more and more, and the damaged carbon fiber composite material parts are quickly and effectively repaired to make their performance reach or close to the performance index of the original parts, which is very important to ensure the normal operation and flight safety of the aircraft. At present, although there are some repair technologies for carbon fiber composite materials, there are still some problems in practical application, for example, the cleaning agent may have adverse effects on the structure and performance of carbon fiber composite materials, the accuracy and depth of damage detection are not enough, the performance of the repair material cannot meet the strict requirements of aerospace, the repair process is not perfect enough to cause unstable repair quality, etc.

[0005] CN119239008A discloses a method for repairing aerospace carbon fiber composite materials, which belongs to the technical field of carbon fiber composite material repair. The case is clean, the self-developed special cleaner is non-damaging and efficient, and the tool with replaceable brush head can achieve the preset cleanliness, laying the foundation for repair. Advanced detection equipment accurately measures the damage with a detection accuracy of 0.1 mm and a depth of 5 mm, providing accurate repair basis. The repair material formula is scientific, and the proportion of each component is reasonable, which can ensure that the performance of the repaired part is close to that of the original part. Strict repair process, such as vacuum-assisted pressure injection and autoclave curing, ensures full curing and optimal performance of the material. Surface treatment and detection ensure quality standards. The devices cooperate with each other and have an intelligent system, which can adjust parameters and automatically adjust the process. The structure meets the special requirements of aviation and is easy to carry and operate, meeting the needs of various scenes. However, although the above patent can ensure that the performance of the repaired part is close to that of the original part, the use of vacuum-assisted pressure injection and autoclave curing generally requires a long cycle for carbon fiber composite material autoclave molding, and the time range from several hours to several tens of hours is different, 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 generally require autoclave curing, which has strong dependence on equipment and is difficult to carry out repair operations quickly on site. Moreover, the repair area is prone to interlaminar peeling or fiber orientation mismatch, resulting in low mechanical property recovery rate of the repaired material, for example, the tensile strength can only recover to 70%-80% of the original material. It is difficult to uniformly press the complex curved surface such as the rotor blade, and the thin-walled structure is easy to deform due to thermal stress. When repairing complex curved surfaces, custom molds are required, which not only consumes time but also increases costs. For example, the repair cycle of an aircraft wing skin is often more than 24 hours. When repairing with carbon fiber cloth layer by layer, high-temperature curing is required, and the weight of the repaired part will increase significantly, with an increase of more than 10%. The chopped fiber spraying technology is currently mainly used for coating protection, and has not been optimized for interfacial bonding strength and fiber orientation in the repair of composite material damage. The repaired area is prone to interlaminar peeling or fiber orientation mismatch, resulting in low mechanical property recovery rate of the repaired material, and the thickness of the bubble defect has not been quickly detected. When using traditional adhesives or continuous fiber patches for repair, the interfacial bonding force is weak, which can easily cause secondary failure. Although microwave-assisted curing is currently proposed, it has not been optimized for the lightweight and high-precision repair requirements of unmanned aerial vehicle parts. SUMMARY

[0007] In view of the above problems of the prior art, the short carbon fiber technology-based composite material rapid repair method is provided, the short fiber spraying technology is used in the composite material damage repair aspect, the repair time is reduced, the cost is reduced, the interface bonding strength and the fiber orientation are optimized, the problems that the interlayer peeling or the fiber orientation mismatching is prone to occur in the repair area, and the mechanical property recovery rate of the repaired material is low are solved, the thickness of the bubble defect can be quickly detected, the method is suitable for efficient, accurate and light-weight repair of carbon fiber reinforced composite material (CFRP) damage, and is especially suitable for on-site rapid repair scene.

[0008] To solve the above technical problems, the technical solution adopted by the present application is a short carbon fiber technology-based composite material rapid repair method, comprising 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, oxidize the fiber surface to improve the wettability of the resin to the fiber, and seal the treated fiber after drying to ensure that the environmental humidity is less than 30% RH to prevent moisture absorption;

[0010] (2) Resin matrix preparation: select a photocurable resin or a low-temperature thermosetting resin, add 0.1%-1% of a nano-enhancing agent to the resin, mix the resin and the curing agent in a certain proportion, and after adding the nano material, disperse it by ultrasonic to ensure uniform dispersion of the nano material without agglomeration;

[0011] (3) Preparation of spraying slurry: mix the short carbon fibers and the resin in a proportion of 35%-55% by volume using a stirrer to form a uniform slurry, detect the viscosity of the slurry using a rotary viscometer to ensure that it is within the target range of 500-2000 cP, and if necessary, add a diluent to adjust it;

[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, remove the surface contamination layer and perform micro-texturing treatment on the surface;

[0013] (5) Scan the unmanned aerial vehicle to obtain damage morphology data, generate an adaptive spiral spraying path, and perform curvature optimization and speed control, then spray the short carbon fiber-resin slurry in layers, apply a static electric field of 10±5% kV to make the fibers align along the main stress direction of the matrix, and the deviation is controlled to be ≤5°;

[0014] (6) Use a UV-IR composite light source with a wavelength of 365 nm+medium wave infrared, wherein the UV power density is ≥8 W / cm 2 , the infrared temperature can be controlled in the range of 60-100℃, the single-layer curing time is ≤2 minutes, and the single-layer curing time is ≤2 minutes;

[0015] (7) evaluate the coating quality.

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

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

[0018]

[0019] Wherein: P is the original damaged area polygon;

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

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

[0022] The formula generates a spiral path by calculating the inward offset of the polygon boundary, ensuring that the spray gun coverage area has no blind area. In unmanned aerial vehicle repair, the step Δd needs to be adjusted dynamically according to the geometric characteristics of the damaged area, and the typical overlap rate is 45%;

[0023] S2: curvature calculation identifies areas with too small turning radius, 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] High-curvature areas need to reduce the spray gun moving speed to avoid material accumulation while ensuring coating uniformity;

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

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

[0031]

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

[0033] α is the curvature sensitivity coefficient, typical value 0.3-0.5.

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

[0035] The coating thickness uniformity is evaluated, and the operation formula is as follows:

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

[0037]

[0038] Wherein And M are the average thickness mean value and effective measurement points, respectively, and C v <10% is qualified.

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

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

[0041]

[0042] Wherein:

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

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

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

[0046] σ d The defect area radius is controlled to be 1mm.

[0047] The above-mentioned composite material rapid repair method based on chopped carbon fiber technology, wherein the micro-texture processing pit diameter is 50-200μm, and the depth is 20-50μm.

[0048] The above-mentioned composite material rapid repair method based on chopped carbon fiber technology, in the step (7), the curing temperature uniformity is monitored by an infrared thermal imager, to ensure that the temperature difference is ≤5℃, to avoid local overheating leading to resin degradation, if bubbles or uncovered areas are detected, immediately spray and appropriately extend the curing time, spray a transparent polyurethane topcoat with a thickness of 50μm, and cure at 80℃ for 30 minutes, to improve the weather resistance of the repaired part.

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

[0050] Base layer: 0.3mm in thickness, 55% in fiber volume fraction, high-density edge reinforcement, 1min UV irradiation, 80℃ infrared heating, anchor layer;

[0051] Middle layer: 0.5-1mm in thickness, 45% in fiber volume fraction, 200mm / s in spraying speed, 600-mesh sandpaper for slight roughening between layers, enhanced interlayer bonding;

[0052] Functional layer: 0.2mm in thickness, 35% in fiber volume fraction, 5% fluorinated silane for hydrophobicity, 3min UV curing, no infrared, reduced surface roughness.

[0053] The above short-cut carbon fiber technology-based composite material rapid repair method, in step (7), the repaired surface is subjected to laser polishing treatment to make the roughness Ra<1.0μm, then wet heat aging test is conducted to verify the durability of the repaired part.

[0054] The above short-cut carbon fiber technology-based composite material rapid repair method, the nozzle voltage is set to 5-15kV, the air pressure is set to 0.3-0.8MPa, and the spray gun distance from the base body is set to 20-40cm.

[0055] The short-cut carbon fiber technology-based composite material rapid repair method has the advantages that the short-cut fiber spraying technology is used for composite material damage repair, no need for autoclave curing, reduced dependence on equipment, no need for customized molds when repairing complex curved surfaces, reduced repair time and cost, optimized interface bonding strength and fiber orientation, solved the problem of low mechanical property recovery rate of the repaired material due to easy interlayer peeling or fiber orientation mismatch in the repaired area, and the method is suitable for efficient, precise and lightweight repair of carbon fiber reinforced polymer (CFRP) damage, especially suitable for on-site rapid repair scenarios.

[0056] For thickness abnormal modeling of bubble defects, an exponential decay function is adopted: the thickness deviation decreases exponentially (rather than linearly) with the distance from the defect center, which is closer to the diffusion law of real bubbles, i.e., the central area has the greatest impact and the edge quickly weakens. The defect edge is smoothly transitioned to the normal thickness, avoiding false judgments caused by artificial threshold setting and improving detection accuracy. Without complex numerical integration or iterative calculation, the spatial distribution of defect thickness is directly expressed by the exponential function, which is fast in calculation, making the thickness abnormal detection of bubble defects faster. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 The figure is a repair flowchart of the present application;

[0058] Figure 2 The figure is a schematic diagram of electrostatic auxiliary spraying and curing. Detailed Implementation

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

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

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

[0062] (2) Resin matrix preparation: Select a light-curing resin (such as cationic epoxy resin CY179) or a low-temperature thermosetting resin (such as polyurethane PU-401), add 0.1%-1% of nano-reinforcing agent (such as CNT, graphene), mix the resin and curing agent in proportion, add the nanomaterial, and then disperse it by ultrasonication for 30 minutes to ensure that the nanomaterial is uniformly dispersed and there is no agglomeration.

[0063] (3) Preparation of spray slurry: Mix the short carbon fiber and resin in a volume ratio of 35%-55% using a mixer to form a uniform slurry. Use a rotational viscometer to test the viscosity of the slurry and keep it within the target range of 500-2000 cP. If necessary, add a diluent (such as acetone) to adjust the viscosity.

[0064] (4) Laser cleaning of damaged areas: A laser with a power of 50-100W and a pulse width of 10ns is used to clean the damaged areas, removing the surface contamination layer while performing microtexturing treatment on the surface.

[0065] (5) Scan the UAV to acquire damage morphology data, generate an adaptive spiral spraying path, and perform curvature optimization speed control. Spray the short-cut carbon fiber-resin slurry in layers. By applying an electrostatic field of 10±5%kV, the fibers are oriented along the main force direction of the matrix, with the deviation controlled within ≤5°. A high-precision 3D scanner (accuracy ±0.05mm, scanning rate 50kHz) is used to scan the UAV. High-voltage electrode: ring electrode. The voltage is dynamically adjusted according to the fiber orientation sensor (high-speed camera) data to ensure fiber alignment consistency.

[0066] (6) An ultraviolet-infrared composite light source is used, with a wavelength of 365nm+ mid-wave infrared, of which the ultraviolet power density is ≥8W / cm². 2 The infrared temperature can be adjusted within the range of 60-100℃ to achieve simultaneous curing of layers, and the curing time of a single layer is ≤2 minutes;

[0067] (7) Evaluate the coating quality.

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

[0069] S1: Generate a continuous spiral by progressively offsetting the polygon boundary. The operation formula is as follows:

[0070]

[0071] Where: P is the polygon of the original damaged region;

[0072] B is the unit circle (used for Minkowski difference operations);

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

[0074] This formula generates a spiral path by calculating the inward offset (Minkowski difference) of the polygon boundary, ensuring that there are no blind spots in the spray gun coverage area. In UAV repair, the step size Δd needs to be dynamically adjusted according to the geometric characteristics of the damaged area, with a typical overlap rate of 45%.

[0075] Carbon fiber composites are typically composed of unidirectional or bidirectional woven fibers, and the coating path must be sprayed along the fiber direction to ensure the adhesion between the coating and the matrix. The helical path generated by the Minkowski difference can be adapted to different fiber bundle spacings by dynamically adjusting the step size (Δd = r(1-overlap)), avoiding problems such as excessive coating thickness or fiber occlusion caused by a fixed step size.

[0076] The continuous inward shrinkage characteristic of the spiral path (layer-by-layer offset d increases) reduces the travel distance by about 30% to 50% compared with the traditional back-and-forth scanning path, resulting in a significant improvement in efficiency.

[0077] Carbon fiber components may undergo minor deformations (such as bending or delamination) after damage, requiring path generation algorithms to adapt to these geometric changes in real time. Dynamic adjustment of the overlap ratio (e.g., automatically increasing overlap to 50% in narrow damaged areas) enhances local coverage density and compensates for coating deviations caused by deformation.

[0078] The path boundary generated by the unit circle offset (B is the unit circle) always keeps a safe distance from the damage area (initial d = r), preventing the spray gun from excessively invading the fragile internal structure.

[0079] Dynamic step control (Δd linked with overlap) can flexibly adjust the single-layer spraying speed (combined with the v(k) formula in step S3) to reduce speed in areas with large curvature to match the leveling requirements of low-viscosity resin, while maintaining high efficiency in large-area areas.

[0080] The path generated by the Minkowski difference has geometric closure, so even if there is a small position error, the subsequent spiral can still cover the missed area (benefiting from the 45% overlap design).

[0081] Because the spray gun needs to be frequently started and stopped, it is easy to cause wear. The smooth spiral path reduces sudden acceleration / deceleration, reduces the loss of the drive and transmission system, and prolongs the mean time between failures of the equipment.

[0082] S2: Curvature calculation identifies areas with too small turning radius, and the operation formula is as follows:

[0083] Path curvature parameterizes the 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] High-curvature area deceleration can prevent resin from being thrown out due to centrifugal force, and low-curvature area maintains high efficiency. Therefore, high-curvature area needs to reduce the moving speed of the spray gun to avoid material accumulation and ensure coating uniformity (reduce orange peel effect);

[0088] Through curvature calculation, areas with too small turning radius are identified in real time, triggering path re-planning to avoid resin stringing or substrate damage caused by sudden turning of the spray gun.

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

[0090] Carbon fiber parts may contain honeycomb cores or fastener holes, which need to avoid the invasion of the spray gun into the fragile interior. Through curvature analysis, the curvature mutation point of the hole edge is identified, triggering path offset correction to maintain a safe spraying distance.

[0091] S3: Adaptive speed adjustment, operation formula as follows:

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

[0093]

[0094] wherein v max is the maximum allowed moving speed (determined by the material curing time);

[0095] a is a curvature sensitivity coefficient, typically 0.3-0.5.

[0096] The edges of carbon fiber parts often have sharp corners, holes or complex curved surfaces. Traditional constant speed spraying is prone to cause resin accumulation (where the curvature is large) or too thin coating (where the curvature is small).

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

[0098] Carbon fiber composites are usually laid in a specific direction (such as unidirectional fibers), and the spraying speed needs to match the fiber direction to avoid coating peeling. Curvature calculation can identify the local bending of the fiber bundle, triggering a speed reduction to ensure that the coating closely adheres to the fibers.

[0099] Carbon fiber coatings are expensive (such as epoxy resin at a price of ￥500-2000 / kg), and excessive spraying needs to be avoided. Speed and curvature coordinated control can reduce resin splashing or accumulation caused by sudden stop / sudden turn (such as a 50% speed reduction at a sudden change in curvature), reducing material loss by about 15%-20%.

[0100] During the spraying process, real-time adjustment of the speed is crucial. The formula structure is simple, involving only one division operation, and the calculation is fast with very low time consumption, meeting the high-frequency real-time adjustment requirements and being suitable for real-time control systems. Ensure uniform coating coverage and avoid accumulation or splashing at turns.

[0101] In the step (7),

[0102] Evaluate the uniformity of the coating thickness, and the operation formula is as follows:

[0103] The uniformity of the repair layer thickness is evaluated by the coefficient of variation C v Evaluation:

[0104]

[0105] wherein and M are the average thickness mean and the effective measurement points, respectively, and C v <10% is qualified.

[0106] By square deviation weighted average, amplify the error contribution of local extremely thick / thin area (such as edge curvature mutation or spraying splashing), avoid the traditional average value index (such as average thickness error) to cover up the key defects.

[0107] In the multi-directional weaving structure of carbon fiber composite material, the uneven coating thickness may present anisotropic distribution along the fiber direction or the vertical direction. This formula can identify specific pattern of uneven defects by combining directional sampling strategy (such as calculating along the fiber direction and the vertical direction respectively). Adapt to the fiber texture characteristics of carbon fiber.

[0108] C v By square deviation weighted average, sensitive to outliers (such as local extremely thick / thin area), can effectively reflect the "extreme unevenness" defects in the coating.

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

[0110] In the step (7),

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

[0112]

[0113] Where:

[0114] h nominal Normal coating thickness: 1-1.5mm;

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

[0116] (x0, y0) is the center coordinate of the defect; positioning the defect center, supporting the expansion of multiple defect scenarios (such as multiple bubble superposition).

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

[0118] Using an exponential decay function, the intensity of the defect decreases exponentially with distance, perfectly simulating the "center concentration, edge weakening" characteristics of bubble defects (such as the depression formed by the shrinkage of resin after bubble rupture). And compared with the uniform deviation model, it can distinguish between local severe defects (such as Δh = 0.3mm in the center area) and large-area slight fluctuations (such as Δh = 0.05mm far from the center), avoiding misjudgment. The formula only involves square operation and exponential function, the calculation time is extremely low, which meets the real-time detection demand.

[0119] Multi-scale adaptability:

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

[0121] Small σ d (like 0.5mm): Detect focused micro-bubbles (like pinhole defects), suitable for high-precision repair scenarios (like near the hole of an aviation fastener).

[0122] Large σ d (like 2mm): Capture larger bubble groups (like debonding areas), suitable for fast inspection needs.

[0123] Parameterized modeling: h nominal =0.5mm: Directly relate to the target thickness of the carbon fiber coating, no additional calibration needed. Δh=0.3mm: Based on material properties (like epoxy shrinkage), preset the maximum allowed deviation, suitable for different substrates. (x0,y0) is the defect center coordinate; locate the defect center, support the expansion of multiple defect scenarios (like multiple bubbles superimposed).

[0124] Collaborate with repair process closed loop:

[0125] If h defect < h nominal -0.1mm, trigger local offset correction (like increase the overlap rate to 60%) of step S1 (spiral path generation) for secondary coverage of the defect area.

[0126] Speed adjustment linkage:

[0127] Combine the formula of step S3 Automatically reduce the spraying speed in the bubble defect area (usually accompanied by curvature mutation), avoid the defect from expanding due to insufficient leveling.

[0128] Multi-coating collaborative verification:

[0129] Model the cumulative thickness deviation of multi-layer spraying (like the thickness of the nth layer h n = h n-1 + h defect (x,y)), ensure that the interlayer adhesion meets the standard (like ASTM D792).

[0130] Defect root analysis: through h defect σ d Two-dimensional histogram identifies high-risk defect areas (like near the fiber lap joint); statistics the frequency distribution of σ d , judge whether the main cause of the defect is spraying equipment failure (large-scale defects) or material bubbles (small-scale defects).

[0131] Reduce rework cost: through real-time detection of C v (variation coefficient) and h defectThe joint threshold value triggers local re-spraying before the semi-cured coating, avoiding the high cost of polishing and repairing after curing. Analyzing the time series data of h defect The timing data of h

[0132] An abnormal thickness model is established for bubble defects, using an exponential decay function: the thickness deviation decreases exponentially with the distance from the defect center (rather than linearly), which is closer to the diffusion law of real bubbles - the central area has the greatest impact, and the edge decreases rapidly. The defect edge is smoothly transitioned to normal thickness, avoiding false positives caused by artificial threshold setting and improving detection accuracy. Without complex numerical integration or iterative calculation, the spatial distribution of defect thickness is directly expressed by the exponential function, which is fast and makes the thickness anomaly detection of bubble defects faster.

[0133] In step (5), electrostatic assisted spraying technology is used to layer spray the chopped carbon fiber-resin slurry 1. As shown in Figure 2 The compressed gas is used as a power source, and a double-gas control system is used to send the spraying slurry into the spray gun 2 by controlling the pressure of the carrier gas at 0.3-0.8 MPa and the pressure of the atomizing gas at 0.1-0.3 MPa. Part of the compressed gas is heated by a gas heater 3 and then enters the spray gun 2, which makes the chopped carbon fiber-resin slurry better atomized, and the chopped carbon fiber-resin slurry is layered sprayed 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 substrate and are simultaneously cured in layers.

[0134] The micro-texture treatment has a pit diameter of 50-200 μm and a depth of 20-50 μm. The pit structure increases the contact points between the fibers and the coating, preventing the coating from peeling off by physical embedding. The uneven direction of the fibers in the composite material can easily cause local stress concentration, and the micro-pit can buffer the shear force between the coating and the fibers, reducing the risk of coating cracking. The micro-channel formed by the pit utilizes the capillary effect to guide the coating into the gap between the fiber bundles, covering the "blind area" that is difficult to reach by traditional spraying, and reducing the porosity. The depth of the micro-pit (20-50 μm) can cover most of the fibers, avoiding excessive cutting of the substrate.

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

[0136] In step (5):

[0137] Base layer: 0.3mm thickness, 55% fiber volume fraction, high density edge reinforcement, 1min UV irradiation, 80℃ infrared heating, anchor layer;

[0138] Middle layer: 0.5-1mm thickness, 45% fiber volume fraction, 200mm / s spraying speed, 600 mesh sandpaper between layers, slightly roughened to enhance interlayer adhesion;

[0139] Functional layer: 0.2mm thickness, 35% fiber volume fraction, 5% fluorinated silane added to improve hydrophobicity, 3min UV curing, no infrared, reduced surface roughness.

[0140] In step (7), the repaired surface is subjected to laser polishing to achieve a roughness Ra<1.0μm, then subjected to a wet heat aging test (85℃ / 85%RH, 48h) to verify the durability of the repaired area.

[0141] The nozzle voltage is set to 5-15kV, the gas pressure is 0.3-0.8MPa, and the gun distance from the substrate is 20-40cm. The nozzle is a fan-shaped nozzle with corrosion resistance and anti-clogging.

[0142] The mechanical execution unit for electrostatic assisted spraying includes: multi-axis robot arm: six degrees of freedom collaborative robot arm (such as UR10e), load ≥10kg, repeat positioning accuracy ±0.05mm. End effector: integrated electrostatic spraying gun, 3D scanner, infrared temperature sensor. Mobile chassis: AGV chassis (navigation accuracy ±1cm), realizes large range mobile spraying.

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

Claims

1. A method for rapid repair of composite materials based on the chopped carbon fiber technology, characterized in that: The method comprises 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, oxidize the surface of the fibers to improve the resin's wettability to the fibers, and seal the treated fibers after drying to ensure that the environmental humidity is less than 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 a nano-enhancing agent to the resin, mix the resin and the curing agent in a certain proportion, and disperse the nano-materials uniformly after adding the nano-materials by ultrasonic dispersion to prevent agglomeration; (3) Spray slurry preparation: mix the short carbon fibers and the resin in a proportion of 35%-55% by volume using a stirrer to form a uniform slurry, detect the slurry viscosity using a rotary viscometer to ensure that the slurry viscosity is within the target range of 500-2000 cP, and add a diluent as necessary 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, remove the surface contamination layer, and perform micro-texturing treatment on the surface; (5) Scan the unmanned aerial vehicle to obtain damage morphology data, generate an adaptive spiral spraying path, and perform curvature optimization and speed control, then spray the short carbon fiber-resin slurry in layers, apply a static electric field of 10±5 kV to make the fibers align along the main stress direction of the matrix, and control the deviation to be ≤5°; (6) Use a UV-IR composite light source with a wavelength of 365 nm+medium wave infrared, a UV power density of ≥8 W / cm², and an infrared temperature that can be controlled within the range of 60-100°C to achieve synchronous curing in layers, and the single-layer curing time is ≤2 minutes; (7) Evaluate the coating quality; In step (5), the generation of the adaptive spiral spraying path comprises the following steps: S1: Generate a continuous spiral line by gradually offsetting the polygon boundary, and the operation formula is as follows: ； Wherein: P is the original damaged area polygon; B is a unit circle; d is the current offset distance, initial value is the spray gun radius r, iteration step , overlap is the overlap rate; The formula generates a spiral path by calculating the inward offset of the polygon boundary, ensures that the spray gun coverage area has no blind area, and in unmanned aerial vehicle repair, the step length needs to be dynamically adjusted according to the geometric characteristics of the damage area , and the typical overlap rate is 45%. S2: Calculate the curvature to identify areas with too small turning radius, and the operation formula is as follows: Path curvature parameterization curvature formula: For a parameterized path The curvature k is calculated as: ； Wherein: s is the arc length parameter; High-curvature areas need to reduce the spraying gun moving speed to avoid material accumulation while ensuring the uniformity of the coating; S3: Adaptive speed adjustment, and the operation formula is as follows: The relationship between the spraying gun moving speed v and the curvature k can be modeled as: ； wherein: is the maximum allowed movement speed; C is the curvature sensitivity coefficient, typical value 0.3-0.5; In step (7), evaluate the coating thickness uniformity, and the operation formula is as follows: Repair layer thickness uniformity by coefficient of variation Evaluation: ； Wherein and are the average thickness mean value and the effective measurement point, respectively, with the requirement <10% is qualified; In step (7), model the thickness anomaly of the bubble defect by using an exponential decay function: ； Wherein: 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 Controlled defect zone radius: 1 mm.

2. The method of claim 1, wherein the chopped carbon fiber technology based composite rapid repair method is characterized by, The micro-texturing treatment has a pit diameter of 50-200 μm and a depth of 20-50 μm.

3. The method of claim 2, wherein the chopped carbon fiber technology based composite material rapid repair method is characterized by, In step (7), the curing temperature uniformity is monitored by an infrared thermal imager to ensure that the temperature difference is ≤5°C, avoiding local overheating that leads to resin degradation. If bubbles or uncovered areas are detected, immediately perform a supplementary spray and appropriately extend the curing time. A transparent polyurethane topcoat with a thickness of 50 μm is cured at 80°C for 30 minutes to improve the weather resistance of the repaired area.

4. The chopped carbon fiber technology based composite rapid repair method according to claim 3, characterized in that, In step (5): Base layer: The spraying thickness is 0.3 mm, the fiber volume fraction is 55%, the high-density reinforced edge is combined, 1 minute of ultraviolet irradiation is performed, and the infrared is heated to 80°C to form an anchor layer; Middle layer: The thickness of each layer is 0.5-1 mm, the fiber volume fraction is 45%, the spraying speed is 200 mm / s, 600 mesh sandpaper is used to slightly roughen the interlayer to enhance the interlayer bonding force; Functional layer: The thickness is 0.2 mm, the fiber volume fraction is 35%, 5% fluorinated silane is added to improve hydrophobicity, 3 minutes of ultraviolet curing is performed, and the infrared is not used to reduce the surface roughness.

5. The chopped carbon fiber technology based composite rapid repair method according to claim 4, characterized in that, In step (7), the repaired surface is subjected to laser polishing treatment to make the roughness Ra <1.0 μm, and then wet heat aging test is performed to verify the durability of the repaired area.

6. The chopped carbon fiber technology based composite rapid repair method according to claim 5, characterized in that, The nozzle voltage is set to 5-15 kV, the air pressure is 0.3-0.8 MPa, and the spray gun distance from the substrate is 20-40 cm.

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