Repairing method for composite material laminated plate with fiber guiding characteristic

Abstract

The invention relates to the technical field of composite material damage repair, in particular to a method for repairing a composite material laminated plate with a fiber guiding characteristic. The repairing method comprises the following steps of pneumatic grinding, patch preparation, surface treatment, cleaning, adhesive film cutting, pasting, adhesive film curing, finishing and the like. According to the method, the adaptive patch is prepared by pneumatically polishing the rectangular cut hole of the stepped surface, the adhesive film is used for curing in the middle, and the adhesive layer is combined with the matched patch, so that a fiber-guided repairing structure is realized; under the condition that the structure repairing strength is guaranteed, the area for removing healthy mother board materials is reduced to the maximum extent, the probability of local stress concentration of a repairing bonding face is reduced, the machining difficulty is lowered, and the universality of repairing design application is improved. And by setting different step lengths, the stress load of the cementing repair surface is more uniform instead of being excessively concentrated on the 0-degree laying layer, so that the repair setting is more reasonable, and the service life of the repaired structure is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material damage repair, and in particular to a composite material laminate repair method with fiber guiding characteristics. Background Art

[0002] Composite materials have been widely used in various industries due to their excellent strength-to-weight and stiffness-to-weight ratios, as well as their comprehensive performance advantages such as excellent fatigue resistance and corrosion resistance. Among the many types of composite materials, laminate structures are the most commonly used and fundamental structural form. However, the widespread use of composite laminates inevitably encounters many challenges. During service, they may suffer penetrating damage due to factors such as collisions, impacts, lightning, and corrosion, which seriously threatens the structural integrity. Therefore, composite laminates need to be repaired. Traditional patching repair methods patch the damaged area on the surface, which affects the aerodynamic shape of the laminate component. In existing traditional patching repair methods, a constant patching slope is often used, resulting in an excessively large patching area and excessive removal of material from the intact motherboard. Existing repair methods cannot customize the bonding dimensions according to the load-bearing capacity of different composite laminate layers, which easily leads to stress concentration on the bonding surface and cannot ensure the long-term service life of the repaired component. In addition, traditional patching repair methods are mainly based on bevel patching repairs. However, in the in-situ repair of composite materials during service, the implementation of bevel patching repairs is often challenging as the processing is more difficult and the use of professional equipment is limited in on-site maintenance.

[0003] In the existing traditional patching repair method, since the patching slope is constant, in order to ensure sufficient repair strength, a smaller patching slope is required, thus requiring a larger patching area. This will be affected by the special shape of the equipment to be repaired, the on-site repair environment and the interference between components during the actual repair of composite laminates, resulting in poor repair feasibility. In addition, a smaller patching slope will result in a larger amount of removal of the damaged motherboard, which may lead to premature failure of the motherboard after repair. When using patching repair to repair damage, it is necessary to lay a patch on the surface of the damaged component, which easily leads to stress concentration at the edge of the patch, and is not friendly to some components with aerodynamic requirements, and the repair rate is low. When using inclined patching repair for damage repair, high precision is required when processing the bonding surface, which may cause defects in the bonding surface, thereby reducing the bonding strength between the motherboard and the patch. The constant patching slope results in the same bonding area for different layers. Due to the different bearing capacities of different layers, uneven stress distribution on the bonding surface may occur when the structure is loaded after repair. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a composite laminate repair method with fiber-guided properties. By varying the fiber orientation of the plies, a fiber-guided configuration is created to ensure sufficient axial repair strength while minimizing the removal of the parent sheet. This fiber-guided repair structure is then combined with a matching patch through an adhesive layer. This design minimizes the removal of healthy parent sheet material while maintaining structural repair strength, reducing the probability of localized stress concentration at the repair interface.

[0005] The technical solutions adopted are:

[0006] A method for repairing composite laminates with fiber-guiding properties comprises the following steps:

[0007] (1) Pneumatic grinding: The through-damage area of ​​the composite motherboard is polished away by pneumatic grinding to form a rectangular cut hole with a stepped surface. Then, the stepped surface is polished layer by layer on both sides of the cut hole.

[0008] (2) Patch preparation: Select a composite laminate and cut it according to the size of the patch area on the motherboard to prepare the patch;

[0009] (3) Surface treatment: Sand the patched area of ​​the composite motherboard with sandpaper;

[0010] (4) Cleaning: Use organic solvent to clean the patched area of ​​the composite material motherboard;

[0011] (5) Cutting the film: According to the pneumatically polished stepped surface, cut the film to a size that matches the rectangular cut hole;

[0012] (6) Pasting: Place the adhesive film on the adhesive surface of the composite motherboard to make the adhesive film adhere to the adhesive surface. Then place the prepared patch on the adhesive film that has been pasted on the adhesive surface of the composite motherboard and make the adhesive surface of the patch and the adhesive film stick tightly together.

[0013] (7) Film curing: Use a hot patching device to cure the repaired structure;

[0014] (8) Finishing: After the film is cured, the excess resin and non-ideal process shape on the surface of the composite material and the intersection of the cured composite material motherboard and the patch are trimmed and polished.

[0015] Preferably, in step (1), a patching slope of 1:30 is selected in the steps of the motherboard 0° ply; a patching slope of 1:20 is selected in the steps of the motherboard ±45° ply; and finally a patching slope of 1:10 is selected in the 90° ply.

[0016] Preferably, in step (1), the fiber of the composite motherboard is any one of carbon fiber, glass fiber, aramid fiber, and boron fiber; the matrix of the composite motherboard is a thermoplastic resin base or a thermosetting resin base, the thermoplastic resin base is any one of polyethylene, polystyrene, polyamide, polycarbonate, and polypropylene; the thermosetting resin base is any one of epoxy, phenolic, and unsaturated polyester.

[0017] Preferably, in step (2), the patch is a composite material laminate made of the same material, thickness and layup as the original motherboard, and its size is not smaller than the size of the patched area of ​​the motherboard.

[0018] Preferably, the corresponding steps are milled layer by layer on the laminate by mechanical milling, and then the composite laminate is cut according to the size of the patched area of ​​the mother plate.

[0019] Preferably, in step (3), the processed edge is manually polished using 400-grit sandpaper.

[0020] Preferably, in step (4), the organic solvent is acetone or ethanol.

[0021] Preferably, in step (7), the cured adhesive film is LJM-170 type or GXA120 type.

[0022] Preferably, in step (7), a hot patching apparatus is used for curing and vacuum treatment, and the curing steps are: first, the repaired structure is vacuum treated, and then the temperature is uniformly increased to 120°C within 90 minutes and maintained at this state for 180 minutes. After 180 minutes, the heat preservation is released and the repaired structure is allowed to cool naturally to room temperature and the pressure is reduced to standard atmospheric pressure.

[0023] Preferably, in step (8), coarse grinding is first performed with 200-mesh sandpaper, then grinding is performed with 1000-mesh sandpaper, and finally fine grinding is performed with 2000-mesh sandpaper.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention effectively reduces the area of ​​the patching repair by adopting a patching repair design with a variable step surface, can adapt to different repair needs, and reduces the difficulty of repairing components in service, making on-site in-situ repair easier to achieve.

[0026] The present invention makes the stress load of the adhesive repair surface more uniform by setting different step lengths instead of being excessively concentrated on the 0° ply, making the repair setting more reasonable and being conducive to improving the service life of the repaired structure.

[0027] The present invention prepares an adapted patch by pneumatically grinding rectangular cut holes on the stepped surface, solidifies the patch through an adhesive film in the middle, and combines the adhesive layer with the matching patch to achieve a fiber-guided repair structure. While ensuring the strength of the structural repair, it minimizes the area of ​​removal of healthy motherboard material, reduces the probability of local stress concentration on the repair adhesive surface, reduces processing difficulty, and improves the wide application of the repair design. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of cutting holes in the damaged area;

[0029] Figure 2 This is a top view of the motherboard;

[0030] Figure 3 This is the side view of the patch;

[0031] Figure 4 is a schematic diagram of the adhesive layer;

[0032] Figure 5 Schematic diagram of the repair structure with fiber-guiding properties. DETAILED DESCRIPTION

[0033] The accompanying drawings are for illustrative purposes only; in order to make the purpose, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0034] The present invention proposes a composite laminate repair method with fiber-guiding properties, which is intended to repair a through-damaged area of ​​a composite laminate, and specifically comprises the following steps:

[0035] Step 1, pneumatic grinding. Figure 1 、 2 As shown, observe the through-damage area of ​​the composite motherboard, mark the damage area with a marker, draw a rectangular outline around the damage area based on the length and width of the through-damage area, and polish off the through-damage part by pneumatic polishing to form a rectangular cut hole. Then, perform step-by-step polishing on the different ply directions of the outer composite motherboard near the rectangular cut hole according to different patching slopes. First, polish the innermost step, and then polish outwards in sequence. During polishing, the polishing force and range should be gradually reduced to avoid excessive polishing at one time, which may cause uneven surface or mismatch with the patch. Compared with a circle, a rectangle has a smaller polishing area, so the polished shape is a rectangle. After polishing, the outer side of the cut hole is stepped. The patching configuration is symmetrical on both sides of the rectangular cut hole to ensure uniform force on the bonding surface after repair.

[0036] The ply layup of the composite motherboard is [45 / 0 / -45 / 90]s, that is, the ply layup sequence is 45° / 0° / -45° / 90° / 90° / -45° / 0° / 45°;

[0037] The patching slope is the ratio of the step height to the step bonding surface length. Its value varies depending on the ply type: ±45° plies have a patching slope of 1:20, 0° plies have a patching slope of 1:30, and 90° plies have a patching slope of 1:10. Because the fiber orientation of 0° plies aligns with the axial load direction, they can bear more load. A patching slope of 1:20 is selected for the steps of the ±45° plies of the motherboard, as these two plies have a certain deviation from the axial load direction and can only bear a limited axial load. Finally, a patching slope of 1:10 is selected for the 90° plies, as the fiber orientation of 90° plies is completely perpendicular to the axial load direction, and only the matrix can bear very small loads. Therefore, the patching slope for these plies is set to the maximum, and the polished shape is rectangular, resulting in a stepped outer surface of the cut hole after polishing.

[0038] The bonding surface is a stepped surface parallel to the plane of the laminate;

[0039] When sanding, use fine-grained sanding paper or other sanding materials to avoid scratches or unevenness on the surface caused by coarse-grained sanding paper or other sanding materials.

[0040] If the matrix of the composite motherboard is a thermoplastic resin, it should be ensured that the processing temperature does not exceed the transition temperature of the thermoplastic matrix.

[0041] Step 2, patch preparation. Figure 3 As shown, in order to ensure the repair effect and the long-term life of the repaired parts, a composite laminate with the same material, thickness and layup as the original motherboard is selected. The size will be adjusted according to the size of the motherboard patching area to ensure that the size of the composite laminate is not smaller than the size of the motherboard patching area. Specifically, according to the size of the motherboard patching area after polishing in step 1, use a marker and a ruler to draw a rectangular outline of the same size on the composite laminate, and continue to draw the corresponding outline according to the size of the cut hole on the motherboard and the size of each ply bonding surface, and use mechanical milling to cut the bonding surface outline drawn on the laminate. Mill the corresponding steps layer by layer, and the milling order is from the vicinity of the cut hole contour to both sides. Stop and observe the processing depth after each milling pass to avoid over-processing. When all the steps are milled, cut along the rectangular contour with the same size as the patched area of ​​the composite motherboard. After cutting, use 400-grit sandpaper to manually polish the processed edges to remove the burrs generated during milling. After polishing, the patch is finally obtained to ensure that the patch can be directly placed in the patched configuration after the motherboard is polished and fits accurately, without the need to use traditional prepreg paving, thereby achieving the purpose of repairing damaged composite laminates.

[0042] Step 3: Surface treatment: Use 400-grit sandpaper to manually sand the bonding surface, stepped side, cut-hole side, and patch bonding surface of the composite motherboard. Sand each surface in a random direction for 3 minutes to increase the bonding surface roughness, thereby improving the bonding strength of the adhesive to the motherboard and patch.

[0043] Step 4: Cleaning: Use a cotton swab soaked in an organic solvent (acetone or ethanol) to clean and dry the adhesive surface, step sides, cut hole sides, and adhesive surface of the composite motherboard in the patched area to remove resin debris generated when sanding the composite laminate.

[0044] Step 5: Cut the film. Figure 4 As shown, different sizes of adhesive films are cut out according to the size of the stepped adhesive surface polished in step 1. The cut adhesive film type is (LJM-170 or GXA120) medium-temperature curing adhesive film, and the size of the adhesive film is the same as the size of the motherboard adhesive surface, thereby achieving precise fitting of the adhesive film with the motherboard and the patch adhesive surface.

[0045] Step 6, paste. Figure 5 As shown, first, the prepared adhesive films of different sizes are placed on the bonding surface of the composite material mother board of the same size, so that the adhesive films of the same size are bonded to the bonding surface. Secondly, the prepared patch is placed on the adhesive film that has been pasted on the bonding surface of the composite material mother board, and the bonding surface of the patch and the adhesive film are tightly adhered to avoid incomplete repair or excess material.

[0046] Step 7: Curing the adhesive film. A thermal patching apparatus is used to cure the repaired structure. First, the repaired structure is vacuumed. Next, the temperature is uniformly raised to 120°C over 90 minutes and maintained at this temperature for 180 minutes. After 180 minutes, the heat preservation is removed and the repaired structure is allowed to naturally cool to room temperature. The pressure is then reduced to standard atmospheric pressure. During the heating phase, the adhesive slowly cures, fully filling the gaps. The heat preservation phase increases the curing degree of the adhesive film. Curing the adhesive film improves the bond strength between the film and the patch, and between the film and the motherboard.

[0047] Step 8: Finishing. After the curing process, the composite surface and the intersection of the cured composite motherboard and the patch are trimmed and polished to remove excess resin and non-ideal process shapes. This will basically conform to the pre-damage composite laminate structure and reduce the aerodynamic performance loss caused by the repair. First, use 200-grit sandpaper for rough sanding. Once the shape is basically acceptable, use 1000-grit sandpaper for general sanding. Finally, use 2000-grit sandpaper for fine sanding to complete the finishing and polishing of the laminate surface.

[0048] 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 technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for repairing composite laminates with fiber-guiding properties, characterized in that: The following steps are involved: (1) Pneumatic grinding: The through-damage area of ​​the composite motherboard is polished away by pneumatic grinding to form a rectangular cut hole with a stepped surface. Then, the stepped surface is polished layer by layer on both sides of the cut hole. (2) Patch preparation: Select a composite laminate and cut it according to the size of the patch area on the motherboard to prepare the patch; (3) Surface treatment: Sand the patched area of ​​the composite motherboard with sandpaper; (4) Cleaning: Use organic solvent to clean the patched area of ​​the composite material motherboard; (5) Cutting the film: According to the pneumatically polished stepped surface, cut the film to a size that matches the rectangular cut hole; (6) Pasting: Place the adhesive film on the adhesive surface of the composite motherboard to make the adhesive film adhere to the adhesive surface. Then place the prepared patch on the adhesive film that has been pasted on the adhesive surface of the composite motherboard and make the adhesive surface of the patch and the adhesive film stick tightly together. (7) Film curing: Use a hot patching device to cure the repaired structure; (8) Finishing: After the film is cured, the excess resin and non-ideal process shape on the surface of the composite material and the intersection of the cured composite material motherboard and the patch are trimmed and polished.

2. A method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (1), a patching slope of 1:30 is selected in the steps of the motherboard 0° ply; a patching slope of 1:20 is selected in the steps of the motherboard ±45° ply; and finally a patching slope of 1:10 is selected in the 90° ply.

3. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (1), the fiber of the composite material motherboard is any one of carbon fiber, glass fiber, aramid fiber, and boron fiber; the matrix of the composite material motherboard is a thermoplastic resin base or a thermosetting resin base, the thermoplastic resin base is any one of polyethylene, polystyrene, polyamide, polycarbonate, and polypropylene; the thermosetting resin base is any one of epoxy, phenolic, and unsaturated polyester.

4. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (2), the patch is selected from a composite material laminate having the same material, thickness and layup as the original motherboard, and its size is not smaller than the size of the motherboard patching area.

5. A method for repairing composite laminates with fiber-guiding properties according to claim 4, characterized in that: First, the corresponding steps are milled layer by layer on the laminate using mechanical milling, and then the composite laminate is cut according to the size of the patching area of ​​the motherboard.

6. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (3), the processed edge is manually polished using 400-grit sandpaper.

7. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (4), the organic solvent is acetone or ethanol.

8. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (7), the cured adhesive film is of LJM-170 type or GXA120 type.

9. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (7), a heat repair instrument is used for curing and vacuum treatment. The curing steps are as follows: first, the repair structure is vacuum treated, and then the temperature is evenly increased to 120°C within 90 minutes and maintained at this state for 180 minutes. After 180 minutes, the heat preservation is released and the repair structure is allowed to cool naturally to room temperature and the pressure is reduced to standard atmospheric pressure.

10. The method for repairing composite laminates with fiber-guiding properties according to claim 1, characterized in that: In the step (8), firstly, coarse grinding is performed with 200-mesh sandpaper, then grinding is performed with 1000-mesh sandpaper, and finally fine grinding is performed with 2000-mesh sandpaper.

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