A method for repairing carbon fiber composite material

Abstract

The present invention discloses a method for repairing carbon fiber composite materials, comprising the following steps: (1) marking the damaged position on the protective layer, and using a micro-grinding device to grind the damaged carbon fiber composite material layer by layer to form an overlap area; (2) testing the grinding quality; (3) taking a piece of carbon fiber fabric of the same quality as the carbon fiber electric heating layer, applying epoxy conductive glue on the overlap area and the corresponding position on the carbon fiber fabric, laying the carbon fiber fabric, and curing the glue according to a vacuum infusion process, thereby completing the repair of the carbon fiber composite material. The present invention proposes a set of reference criteria for evaluating and identifying product quality, and at the same time proposes targeted evaluation indicators and methods for the repair effect, thereby solving the problem of repairing high-temperature electric heating formed after damage to carbon fiber composite materials, and filling the technical problem of reliable repair of carbon fiber composite materials after the electric heating performance is damaged.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber composite materials, and in particular to a homogeneous repair method for damaged thermoelectric properties of carbon fiber composite materials. Background Art

[0002] Carbon fiber composite materials not only have excellent mechanical properties, but also have the characteristics of integrated heating function and structure, high heating efficiency, fast heating rate and strong fatigue resistance. Therefore, carbon fiber composite materials are often used as electrothermal anti-icing or de-icing materials for large wind turbine blades. In the actual production or service process of carbon fiber composite electrothermal laminates of wind turbine blades, various defects or damages are inevitable, such as penetration damage, wrinkles, delamination and poor infiltration. Depending on the degree of damage, the damage will not only reduce the strength and stiffness of the carbon fiber composite electrothermal laminate, but also affect the electrothermal performance of the carbon fiber composite electrothermal laminate, which is usually manifested as abnormal resistance and the presence of high-temperature areas during heating. However, defects with less damage generally do not need to be repaired.

[0003] At present, existing repair methods often focus on repairing the appearance or mechanical properties of carbon fiber composite materials, and lack a systematic method for repairing damage to electrical and thermal properties, as well as an effective means of verifying the repair effect. Summary of the Invention

[0004] The present invention provides a method for repairing carbon fiber composite materials, which is used to solve the technical problem that the prior art lacks relevant methods and means.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A method for repairing a carbon fiber composite material, the carbon fiber composite material comprising a carbon fiber electric heating layer and a protective layer covering the surface of the carbon fiber electric heating layer, the method comprising the following steps:

[0007] (1) Marking the damaged position on the protective layer, using a micro-grinding device to grind the damaged carbon fiber composite material layer by layer, removing the protective layer around the damaged position and exposing the carbon fibers in the carbon fiber electric heating layer, the exposed carbon fiber electric heating layer area being the overlap area;

[0008] (2) testing the polishing quality of step (1) to ensure that the carbon fibers of the carbon fiber electric heating layer are exposed and have no groove defects;

[0009] (3) Take a piece of carbon fiber fabric of the same quality as the carbon fiber electric heating layer, apply epoxy conductive glue on the overlapping area and the position corresponding to the overlapping area on the carbon fiber fabric, align the position where the carbon fiber fabric is coated with epoxy conductive glue with the overlapping area, lay the carbon fiber fabric above the damaged position of the carbon fiber composite material, and then perform glue infusion and curing on the carbon fiber fabric according to the vacuum infusion process to form a new carbon fiber electric heating layer and protective layer, thereby completing the repair of the carbon fiber composite material.

[0010] As a further preference of the above technical solution, in step (1), the damaged carbon fiber composite material is polished layer by layer, and when the protective layer around the damaged position is removed and the carbon fiber electric heating layer is exposed, the damaged area is polished along the boundary in a circular ring, square ring or overall grinding manner to form an overlap area, and the width of the overlap area is 50 to 150 mm.

[0011] As a further preference of the above technical solution, in step (1), the damaged carbon fiber composite material is polished layer by layer to remove the protective layer around the damaged position and expose the carbon fiber electric heating layer. The rotation speed of the polishing device is less than or equal to 15000 rpm, the roughness of the polishing sheet is greater than or equal to 120 mesh, and the size of the polishing sheet is less than or equal to 3 inches.

[0012] As a further preferred embodiment of the above technical solution, when testing the polishing quality in step (2), the following method is adopted: fix one end probe of the resistance measuring instrument at the boundary position of the overlapping area, and move the other end probe along the horizontal and vertical directions of the overlapping area. If the resistance measuring instrument displays a resistance value during the movement of the probe, it means that the polishing quality is qualified; otherwise, continue polishing until the resistance value can be measured in the overlapping area.

[0013] As a further preference of the above technical solution, after the repair of the carbon fiber composite material is completed in step (3), the electric and thermal performance of the repaired part is tested to verify the repair effect. The testing method includes the following operations: testing the resistance change before and after the repair part; using the design power density of the carbon fiber electric heating layer as a reference to convert it into a power supply voltage U, loading it to both ends of the repaired carbon fiber composite material, keeping heating for 10 minutes, and using a thermal imager to continuously monitor the heating status. If the temperature difference in the heating area is within 10°C, the repair effect is qualified.

[0014] As a further preferred embodiment of the above technical solution, in step (3), when the carbon fiber fabric is glue-infused and cured according to the vacuum infusion process, auxiliary material laying, vacuum sealing, glue-infusion and heat curing are first carried out in sequence, and the auxiliary material can be demolded after curing; wherein, the vacuum sealing is sealed with at least two layers of vacuum bags, the vacuum pump pressure of the innermost vacuum bag is below -950Mpa; the gauge pressure of the second inner vacuum bag is below -950mbar, and the pressure drop is guaranteed to be within 20mbar when the pressure is maintained for 10 minutes.

[0015] As a further preference of the above technical solution, the heating method in the heating and curing operation is: first heat to 35°C and keep warm for 120 to 140 minutes, then heat to 50°C within 30 minutes after the insulation is completed, and keep warm for 30 minutes; then heat to 60°C within 50 minutes after the insulation is completed, and keep warm for 120 to 140 minutes.

[0016] As a further preferred embodiment of the above technical solution, the epoxy conductive adhesive in step (3) has a room temperature mixing viscosity of 12000-13000 mPa.s, a thermal conductivity of 2.5-3.0 W / (mk), and a volume resistivity of 1e -3 ~1e -4 Ω.cm, the epoxy conductive adhesive cures itself within 24 hours at room temperature.

[0017] The present invention has the following beneficial effects:

[0018] The present invention proposes targeted evaluation indicators and methods for the repair effect, which can quantitatively evaluate the reliability of the repair method, solves the problem of repairing high-temperature electric heating after damage to carbon fiber composite materials, and forms a set of practical, effective and replicable repair solutions, filling the technical difficulties in reliability repair of carbon fiber composite materials after damage to their electric heating properties.

[0019] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 This is a schematic structural diagram of a carbon fiber composite material with defects and damage according to Example 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of a specific polishing method for polishing a damaged carbon fiber composite material layer by layer according to Example 1 of the present invention;

[0023] Figure 3 Schematic diagram of the scanning trajectory for detecting the polishing quality in Example 1 of the present invention;

[0024] Figure 4 This is a schematic diagram of the operation of laying a carbon fiber fabric onto a damaged location of a carbon fiber composite material according to Example 1 of the present invention;

[0025] Figure 5 The temperature distribution diagram before and after repair is obtained by testing the electric and thermal performance after repair in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0027] Example 1:

[0028] The carbon fiber composite material repair method of this embodiment is used to repair the damage defects of the carbon fiber composite material covering the surface of the wind turbine blade. The structure of the carbon fiber composite material is as follows: Figure 1 As shown, it includes a carbon fiber electric heating layer and a glass fiber protective layer laid from the inside to the outside ( Figure 1 (1) The blade body, 2) The damage defect, 3) The carbon fiber electric heating layer, and 4) The glass fiber protective layer. The repair method specifically includes the following steps:

[0029] (1) Defect damage marking: Confirm the specific location and area of ​​the defect, and mark the staggered grinding line with a marker.

[0030] (2) Grinding treatment of damaged area: Use micro-grinding device to grind the damaged carbon fiber composite material electric heating layer layer by layer, such as Figure 2 As shown, the damaged area is arranged in a circular pattern ( Figure 2 a), square ring ( Figure 2 b) or overall wear-off ( Figure 2 c) Perform external processing to avoid secondary damage and expansion of the original damage area, polish and remove the glass fiber protective layer and expose the carbon fiber in the carbon fiber electric heating layer. The exposed carbon fiber electric heating layer area is the overlap area ( Figure 2 (⑤ in the middle is the overlapping area), the overlapping width of the overlapping area should be controlled at 50-150mm, the speed of the grinding device should be controlled at 12000rpm, the roughness of the grinding piece should be 140 mesh, and the size should be 3 inches.

[0031] (3) Confirmation of polishing quality: Figure 2 The overall grinding method shown in Figure 2 c) as an example, the quality confirmation should be carried out continuously when the carbon fiber electric heating layer is polished, and the carbon fiber in the carbon fiber electric heating layer should be ensured to be exposed and without groove defects. The following method is used: fix one end of the probe of the resistance measuring instrument (which can be used but not limited to a multimeter, micro-ohmmeter or resistance meter) at the boundary position of the overlap area (i.e., the scanning fixed point), and move the other end of the probe along the horizontal and vertical directions of the overlap area (the moving track is as follows Figure 3 As shown, the horizontal track is x, the vertical track is y, the scanning point is z, and the overlapping area is ⑤). When the probe passes through each point in the overlapping area during the movement, the resistance measuring instrument displays a resistance value, which means the polishing quality is qualified. Otherwise, continue polishing until the resistance value can be measured in the overlapping area.

[0032] (4) Homogeneous repair treatment: After the polishing quality is confirmed, the overlap area is cleaned with anhydrous alcohol or DMC cleaner. The cleaned area needs to be blown dry with a hair dryer to remove any droplets. Then, epoxy conductive glue is used to apply to the overlap area of ​​the carbon fiber composite material and the corresponding overlap area of ​​the homogeneous carbon fiber fabric. Figure 4 As shown ( Figure 4 The epoxy conductive adhesive is applied at position ⑥), and then the carbon fiber fabric is laid on the damaged position of the carbon fiber composite material. Subsequently, the auxiliary materials are laid, vacuum sealed, glued and heated for curing according to the vacuum infusion process. After curing, the auxiliary materials can be demoulded, and the repair is completed.

[0033] Among them, the epoxy conductive adhesive has a room temperature mixed viscosity of 12000mPa.s, a thermal conductivity of 2.5W / (mk), and a volume resistivity of 1e -3 Ω.cm, can be cured by itself within 24 hours at room temperature.

[0034] The vacuum seal has two layers of bag film sealing. The vacuum pump pressure requirement for one bag of vacuum is -950Mpa; the Hgbar gauge for the second bag of vacuum is -950mbar, and it is guaranteed that the pressure drop is within 20mbar when the pressure is maintained for 10 minutes.

[0035] The heating system for heat curing is as follows: keep warm at 35°C for 120 minutes, then heat from 35°C to 50°C within 30 minutes, heat at 50°C for 30 minutes, then heat from 50°C to 60°C within 50 minutes, heat at 60°C for 120 minutes, and end the heating program.

[0036] (4) Verification of repair effect: Mainly verify the electric heating performance after repair to ensure that the temperature of the repaired area is uniform after power on and heating, without abnormal high and low points. The verification process is: ① Test the resistance change before and after the repair part; the resistance change of the carbon fiber composite material before and after the repair of this embodiment is shown in Table 1 below; ② Use the design power density of the electric heating layer as a reference to convert it into a power supply voltage U, load it to both ends of the repaired electric heating layer, keep heating for 10 minutes, and use a thermal imager to continuously monitor the heating status. If the temperature difference in the heating area is within 10°C, it can be considered that the repair is qualified, otherwise it needs to be repaired again. The electric heating effect of the carbon fiber composite material before and after the repair of this embodiment is as follows Figure 5 As shown, it can be seen that the temperature distribution of the intact sample is uniform, and the highest temperature is 57.9℃ ( Figure 5 a), the temperature distribution of the repaired specimen is relatively uniform, with the highest temperature being 59.5℃ ( Figure 5 b) The temperature deviation is within 10°C.

[0037] Table 1 Resistance changes of carbon fiber composite materials before and after repair of Example 1

[0038] Sample name Intact sample resistance Repair sample resistance Resistance deviation carbon fiber composites 0.580 0.541 -6.7％

[0039] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A method for repairing a carbon fiber composite material, wherein the carbon fiber composite material comprises a carbon fiber electric heating layer and a protective layer covering the surface of the carbon fiber electric heating layer, characterized in that: The repair method comprises the following steps: (1) Mark the damaged position on the protective layer, and use a micro-grinding device to grind the damaged carbon fiber composite material layer by layer to remove the protective layer around the damaged position and expose the carbon fibers in the carbon fiber electric heating layer. The exposed carbon fiber electric heating layer area is the overlap area; (2) The polishing quality of step (1) is tested to ensure that the carbon fibers of the carbon fiber electric heating layer are exposed and there are no groove defects; when testing the polishing quality, the following method is used: fix one end probe of the resistance measuring instrument at the boundary position of the overlap area, and move the other end probe along the horizontal and vertical directions of the overlap area. If the resistance measuring instrument displays the resistance value during the movement of the probe, the polishing quality is qualified; otherwise, continue polishing until the resistance value can be measured in the overlap area; (3) Take a piece of carbon fiber fabric of the same quality as the carbon fiber electric heating layer, apply epoxy conductive glue on the overlap area and the position of the corresponding overlap area on the carbon fiber fabric, align the position where the carbon fiber fabric is applied with the epoxy conductive glue with the overlap area, lay the carbon fiber fabric above the damaged position of the carbon fiber composite material, and then perform glue curing on the carbon fiber fabric according to the vacuum infusion process to form a new carbon fiber electric heating layer and a protective layer, thus completing the repair of the carbon fiber composite material; after completing the repair of the carbon fiber composite material, test the electric heating performance after the repair to verify the repair effect. The test method includes the following operations: first, test the resistance change of the carbon fiber composite material before and after repair. If the resistance deviation range before and after repair is 0~-10%, it is qualified; if the resistance change is qualified, convert the design power density of the carbon fiber electric heating layer into a power supply voltage U as a reference, load it to both ends of the repaired carbon fiber composite material, keep heating for 10 minutes, and use a thermal imager to continuously monitor the heating state. If the temperature difference in the heating area is within 10℃, the repair effect is qualified.

2. The method for repairing carbon fiber composite materials according to claim 1, characterized in that: In step (1), the damaged carbon fiber composite material is ground layer by layer, and when the protective layer around the damaged position is removed and the carbon fiber electric heating layer is exposed, the damaged area is ground in a circular, square or overall manner along the boundary of the damaged area to form an overlap area, and the width of the overlap area is 50 to 150 mm.

3. The method for repairing carbon fiber composite materials according to claim 1, characterized in that: In step (1), the damaged carbon fiber composite material is polished layer by layer to remove the protective layer around the damaged position and expose the carbon fiber electric heating layer. The rotation speed of the polishing device is less than or equal to 15,000 rpm, the roughness of the polishing sheet is greater than or equal to 120 mesh, and the size of the polishing sheet is less than or equal to 3 inches.

4. The method for repairing a carbon fiber composite material according to any one of claims 1 to 3, characterized in that: In step (3), when the carbon fiber fabric is glued and cured according to the vacuum infusion process, auxiliary material laying, vacuum sealing, glue pouring and heating and curing are carried out in sequence, and the auxiliary material is demoulded after curing; wherein, the vacuum sealing adopts at least two layers of vacuum bag sealing.

5. The method for repairing carbon fiber composite materials according to claim 4, characterized in that: The heating method in the heating and curing operation is as follows: first heat to 35°C and keep warm for 120-140 minutes, then heat to 50°C within 30 minutes and keep warm for 30 minutes; then heat to 60°C within 50 minutes and keep warm for 120-140 minutes.

6. The method for repairing a carbon fiber composite material according to any one of claims 1 to 3, characterized in that: The epoxy conductive adhesive in step (3) has a room temperature mixed viscosity of 12000~13000mPa·s, a thermal conductivity of 2.5~3.0W / (m·k), and a volume resistivity of 1e -3 ~1e -4 Ω·cm, the epoxy conductive adhesive cures itself within 24 hours at room temperature.

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